ArticlePDF AvailableLiterature Review

Terpenoids, Cannabimimetic Ligands, beyond the Cannabis Plant

Authors:

Abstract and Figures

Medicinal use of Cannabis sativa L. has an extensive history and it was essential in the discovery of phytocannabinoids, including the Cannabis major psychoactive compound—Δ9-tetrahydrocannabinol (Δ9-THC)—as well as the G-protein-coupled cannabinoid receptors (CBR), named cannabinoid receptor type-1 (CB1R) and cannabinoid receptor type-2 (CB2R), both part of the now known endocannabinoid system (ECS). Cannabinoids is a vast term that defines several compounds that have been characterized in three categories: (i) endogenous, (ii) synthetic, and (iii) phytocannabinoids, and are able to modulate the CBR and ECS. Particularly, phytocannabinoids are natural terpenoids or phenolic compounds derived from Cannabis sativa. However, these terpenoids and phenolic compounds can also be derived from other plants (non-cannabinoids) and still induce cannabinoid-like properties. Cannabimimetic ligands, beyond the Cannabis plant, can act as CBR agonists or antagonists, or ECS enzyme inhibitors, besides being able of playing a role in immune-mediated inflammatory and infectious diseases, neuroinflammatory, neurological, and neurodegenerative diseases, as well as in cancer, and autoimmunity by itself. In this review, we summarize and critically highlight past, present, and future progress on the understanding of the role of cannabinoid-like molecules, mainly terpenes, as prospective therapeutics for different pathological conditions.
Content may be subject to copyright.
molecules
Review
Terpenoids, Cannabimimetic Ligands, beyond the
Cannabis Plant
Elaine C. D. Gonçalves 1,2 , Gabriela M. Baldasso 1, , Maíra A. Bicca 3, , Rodrigo S. Paes 1,
Raaele Capasso 4, * and Rafael C. Dutra 1, 2, *
1Laboratory of Autoimmunity and Immunopharmacology (LAIF), Department of Health Sciences,
Campus Araranguá, Universidade Federal de Santa Catarina, Araranguá88906-072, Brazil;
elainecdalazen@gmail.com (E.C.D.G.); baldasso.gabriela@gmail.com (G.M.B.);
rodrigosebbenp@gmail.com (R.S.P.)
2Graduate Program of Neuroscience, Center of Biological Sciences, Campus Florianópolis,
Universidade Federal de Santa Catarina, Florianópolis 88040-900, Brazil
3Neurosurgery Department, Neurosurgery Pain Research institute, Johns Hopkins School of Medicine,
Baltimore, MD 21287, USA; bicca.ma@jhmi.edu
4Department of Agricultural Sciences, University of Naples Federico II, 80,055 Portici, Italy
*Correspondence: rafcapas@unina.it (R.C.); rafaelcdutra@gmail.com or rafael.dutra@ufsc.br (R.C.D.);
Tel.: +39-081-678664 (R.C.); +55-48-3721-21678 (R.C.D.); Fax: +55-48-3721-6448 (R.C. & R.C.D.)
These authors contributed equally to this work.
Academic Editor: Derek J. McPhee
Received: 29 February 2020; Accepted: 27 March 2020; Published: 29 March 2020


Abstract:
Medicinal use of Cannabis sativa L. has an extensive history and it was
essential in the discovery of phytocannabinoids, including the Cannabis major psychoactive
compound—
9-tetrahydrocannabinol (
9-THC)—as well as the G-protein-coupled cannabinoid
receptors (CBR), named cannabinoid receptor type-1 (CB1R) and cannabinoid receptor type-2 (CB2R),
both part of the now known endocannabinoid system (ECS). Cannabinoids is a vast term that defines
several compounds that have been characterized in three categories: (i) endogenous, (ii) synthetic, and
(iii) phytocannabinoids, and are able to modulate the CBR and ECS. Particularly, phytocannabinoids
are natural terpenoids or phenolic compounds derived from Cannabis sativa. However, these
terpenoids and phenolic compounds can also be derived from other plants (non-cannabinoids)
and still induce cannabinoid-like properties. Cannabimimetic ligands, beyond the Cannabis plant,
can act as CBR agonists or antagonists, or ECS enzyme inhibitors, besides being able of playing a
role in immune-mediated inflammatory and infectious diseases, neuroinflammatory, neurological,
and neurodegenerative diseases, as well as in cancer, and autoimmunity by itself. In this review,
we summarize and critically highlight past, present, and future progress on the understanding of
the role of cannabinoid-like molecules, mainly terpenes, as prospective therapeutics for dierent
pathological conditions.
Keywords:
phytocannabinoid; terpenoids; cannabinoid receptors; Cannabis plant; endocannabinoids;
inflammation.
1. The Era of Cannabis sativa, Cannabinoids, and the Endocannabinoid System: A Long
Journey Traveled
The Cannabis sativa era has a long and remarkable history dating from prehistoric Xinjiang,
an ancient Chinese place, where users consumed Cannabis not only for religious/spiritual or hedonic
purposes but also for its medicinal eects [
1
3
]. The first report of hemp medicinal use comes
from Chinese medicine, around 2300 B.C. In India, Cannabis became part of the Hindu religion,
being subsequently introduced to Europe between 1000 and 2000 B.C. Long after Cannabis reached
Molecules 2020,25, 1567; doi:10.3390/molecules25071567 www.mdpi.com/journal/molecules
Molecules 2020,25, 1567 2 of 47
the Americas, South America (mainly Chile) in 1545, and over 60 years later (1606), its cultivation
was introduced to North America. Western medicine slowly progressed from the understanding and
moderate use in the early and mid-19th century, to its wider use, based on its medicinal properties in
the 20
th
century. Nevertheless, due to prejudice and misinformation, the use of this plant has been
marginalized, which has hindered research progress regarding its medicinal beneficial eects [1,2].
Currently, Cannabis is the most commonly cultivated, tracked, and abused drug worldwide,
potentially causing a substantial public health impact since it can alter sensory perception and induce
elation and euphoria [
4
,
5
]. Recent use rates among the population in general show a concentration to
adolescents and young adults (20 to 24 years-old), ranging from 2%–5% of the global population (an
estimated 13 million cannabis-dependent individuals in 2010); yet, the highest numbers (
10%–13%)
are reported in North America [
5
7
]. A study published by Hasin and colleagues revealed a significant
rise in marijuana use prevalence in 2001–2002 and 2012–2013, accompanied by a large increase of
marijuana-induced disorders in this same time period [
8
,
9
]. Conversely, another study showed
that Cannabis-induced disorders declined among young users during 2013-2014, in the USA [
10
,
11
].
According to United States Code, “marijuana/cannabis” comprises “all parts” of the plant Cannabis
sativa L. and every compound derivative of such plant. By the year 2016, 28 states in the USA
have voted to authorize or implement medicinal cannabis programs. Among these, eight states
and the district of Columbia have legalized the recreational use of Cannabis [
12
]. In other countries,
including the United Kingdom (UK), Denmark, Czech Republic, Austria, Sweden, Germany, and Spain,
it is formally approved; thus, decriminalizing the therapeutic use of Cannabis and cannabis-based
products [
13
,
14
]. Pioneering in Latin America, Uruguay, became the first country to legalize the sale,
cultivation, and distribution of Cannabis [
15
,
16
]. Wilkinson and D’Souza have previously described
that the medicalization and/or incorporation of Cannabis into a medicine is complex for a number of
reasons, including that (i) it is a plant rather than a pharmaceutical product, and (ii) knowledge of
its properties and eects is still limited [
17
]. However, in light of the recently and largely reported
pharmacological discoveries and therapeutic benefits of Cannabis, the controlled and medicinal use of
Cannabis for some pathological conditions have been enforced.
Era of cannabinoids started when Mechoulam and Gaoni isolated and characterized the main
psychoactive component of Cannabis sativa, the
9- tetrahydrocannabinol (
9-THC). Subsequently,
in 1988, Howlett’s group established the presence of a specific cannabinoid receptor in the rat brain
by using a tritium labeled cannabinoid [
18
], followed by the cloning of the cannabinoid receptor
type-1 (CB1R) [
19
]. Then, Matsuda and coworkers (1990) described a second receptor, named the
cannabinoid receptor type-2 (CB2R), which was cloned by Munro and coworkers in 1993 [
18
,
19
]. These
receptors can be activated by endogenous molecules produced normally by our bodies, and likewise
by external synthetic and natural molecules. The number of natural compounds identified or isolated
from Cannabis sativa has been increasing in the last decade, with 565 identified substances between
cannabinoids and non-cannabinoid constituents [
20
]. The genus Cannabis comprises closely related
species, mainly, Cannabis indica,Cannabis ruderalis (identified in 1924), Cannabis sativa L., which is
widely known as “hemp” and not psychoactive, as well as Cannabis sativa, which induces psychoactive
eects [
1
]. Cannabinoids are defined as a group of molecules that modulate cannabinoid receptors
(CBR) and are characterized by three varieties, such as endogenous or endocannabinoids, synthetic
cannabinoids, and phytocannabinoids. The latter variety comprehends natural terpenoids or phenolic
compounds derived from Cannabis sativa or other species, and will be further explored later in this
review [
21
]. Altogether, 120 cannabinoids have been isolated from the Cannabis sativa plant and
classified into 11 general types, as described below (Table 1) [20].
Molecules 2020,25, 1567 3 of 47
Table 1. Cannabis sativa L. constituents by chemical class.
Chemical Class Compounds
9-THC types 23
8-THC types 5
CBG types 16
CBC types 9
CBD types 7
CBND types 2
CBE types 5
CBL types 3
CBN types 11
CBT types 9
Miscellaneous types 30
Total cannabinoids 120
Total non-cannabinoids 445
Grand Total 565
THC, tetrahydrocannabinol; CBG, cannabigerol; CBC, cannabichromene; CBD, cannabidiol; CBND, cannabinodiol;
CBE, cannabielsoin; CBL, cannabicyclol; CBN, cannabinol; CBT, cannabitriol, as previously described [20].
Pharmacologically approaching, three compounds have been isolated and identified as the most
important, namely the
9-tetrahydrocannabinol (
9-THC), cannabidiol (CBD), and cannabinol (CBN).
Relevantly, preclinical and clinical research has shown that cannabinoids, especially CBD, play key a
role in dierent pathological conditions (Table 2).
When we talk about the era of the “endocannabinoid system”, we have to keep in mind that this
biological system was named over the response of its receptors to cannabinoid drugs, such as the
previously mentioned and well-studied 9-THC and biologically active synthetic analogs, just like it
has happened with the opioids in the past. In addition to its receptors, the system is highly modulated
by the enzymes involved in the endogenous cannabinoids synthesis and inactivation (endocannabinoid
metabolism). Furthermore, some other receptors have been reported to be activated by cannabinoid
drugs and related molecules, including GPR55, GPR18, and GPR119 [
40
42
]. CB1R is a key component
of the endocannabinoid system (ECS), since it interacts with endogenous and exogenous cannabinoids,
including
9-THC, and it is considered the most abundant metabotropic receptor in the brain [
43
].
It has been cloned from humans and it is accountable for the Cannabis eects on mood, as well as
negative psychotomimetic eects, including anxiety, paranoia, and dysphoria [
4
,
44
]. While CB1R plays
a role as a neurotransmission regulator in dierent brain regions and for this reason mediates the
Cannabis psychoactive eects, CB2R, in particular, mediates anti-inflammatory and immunomodulatory
actions [
45
]. An accumulating body of evidence suggests that both CB1R and CB2R, and their ligands,
play a significant role in physiologic and pathologic processes [
46
]. In this context, both receptors have
been widely studied regarding their relevance in the modulation of immune-mediated inflammatory
diseases, neuroinflammation, neurological and neurodegenerative diseases, cancer, and autoimmunity.
Beyond the CBR, mammalian tissues can both synthesize and release cannabinoid receptor
ligands [
44
,
47
,
48
]. The era of ECS started when Devane and colleagues (1992) described for the first
time, the N-arachidonoylethanolamine molecule, named anandamide from porcine brain. Interestingly,
anandamide interact to CBR and induces behavioral actions similar to the ones induced by
9-THC,
when administered in rodents [
4
,
49
]. The mainly endogenous cannabinoids are the anandamide (AEA)
and the 2-arachidonoyl glycerol (2-AG). It is now ordinarily accepted that the mammalian tissues
contain an ECS composed by: (i) CB1R and CB2R cannabinoid receptors [
19
,
44
], (ii) endogenous
cannabinoids ligands [
49
51
], and (iii) enzymes involved in the cannabinoids ligands synthesis and
inactivation. Regarding these enzymes, the fatty acid amide hydrolase (FAAH) breaks amide bond
and releases arachidonic acid and ethanolamine from AEA, and the monoacylglycerol lipase (MAGL)
is responsible for a more eciently 2-AG degradation [
52
]. Endocannabinoids are produced on
demand from membrane lipids using the machinery of the enzymes responsible for their synthesis,
Molecules 2020,25, 1567 4 of 47
transport, and degradation. For instance, the N-arachidonoyl phosphatidylethanolamine (NArPE)
originates a phosphatidic acid by a reaction mediated by a specific phospholipase D (NAPE-PLD);
most importantly, it is hydrolyzed to AEA, in a reaction catalyzed by N-acyltransferase (NAT). The
latter reaction happens out of an acyl group from the arachidonoylphosphatidylcholine (diArPC) sn-1
position converted to a phosphatidylethanolamine (PE) amino group. Following, AEA is degraded
by FAAH. Synthesis of 2-AG depends on the phosphatidylinositol (PI) conversion to diacylglycerol
(DAG) by the phospholipase C (PLC) enzyme, and subsequent DAG transformation to 2-AG by the
action of the diacylglycerol lipase (DAGL) [
53
]. The ECS is involved with multiple biological functions,
such as immune-mediated inflammatory and autoimmune diseases [
53
], as well as neuroinflammatory
and neurodegenerative conditions [
54
]. Moreover, the ECS participates in the immune control at the
CNS [
55
], maintaining overall “fine-tuning” of immune response balance [
56
], and influencing the
neuroendocrine reaction to inflammation and infection [57].
Importantly, the ECS (i.e., CBR, endogenous cannabinoids, and anabolic/catabolic enzymes)
are present in the cardiovascular tissues (myocardium, smooth muscle, and vascular endothelial
cells), as well as in the circulating blood cells [
58
]. CB1R are expressed in the peripheral nervous
system, including vagal aerent neurons, while CB2R are expressed in cardiomyocytes, coronary
artery endothelial cells, and smooth muscle cells. For this reason, the endocannabinoid signaling
exerts complex cardiac and vascular eects ranging from vasodilatation to vasoconstriction, and
decreased myocardial contractility [
58
]. Those are important biological eects, as they could play
an essential role in side eects promoted by potential molecules that are able to modulate this
system. For instance, in healthy individuals, CB1R activation decreased myocardial contractility
and blood pressure, possibly by peripheral inhibition of noradrenaline release from postganglionic
sympathetic axons that leads to regulation of cardiac output [
59
]. In an opposite way, CB2R may exert
a cardioprotective role associated to its immunomodulatory properties during tissue inflammation
and tissue injury in cardiovascular diseases. The endogenous cannabinoids (2-AG and AEA) also have
vascular eects, which are mediated by perivascular transient receptor potential vanilloid 1 (TRPV1)
and transient receptor potential vanilloid 4 (TRPV4) activation in smooth muscle cells, promoting
dilatory response [
60
]. Between the common clinical adverse eects associated with the Cannabis
plant use, the increased cardiovascular activity and heart rate, as well as decreased blood pressure
have been described [
60
]. In addition, the uses of Cannabis plant or synthetic cannabinoids have been
linked to myocardial infarction, cardiomyopathy, arrhythmias, and stroke [
58
,
61
,
62
]. It occurs, possibly
due to dose-dependent eects of phytocannabinoids and consequent modulation of the autonomic
nervous system, at least partly via CB1R activation [
60
], since the CB1R antagonist Rimonabant
®
ameliorate the cannabis-induced tachycardia [
63
,
64
]. It is important to be aware of the harmful
consequences that come along with the use of Cannabis plant and/or synthetic cannabinoids, as they
could contribute to development of cardiovascular disorders, since the ECS has an essential role in the
cardiovascular signaling.
The future, shedding light to a new era, is promising and based on the cloning of CBR associated
with the possibility of manipulation of endocannabinoid levels in tissues, by using endocannabinoid
enzymes-targeted pharmacology. This represents an opening of a possible gateway to the discovery
and/or development of cannabimimetic ligands, beyond the Cannabis plant, which could still show
therapeutic eects and possibly rule out many of the important adverse eects. A previous review has
already stated that some plants, not belonging to the Cannabis genus, produce molecules chemically
similar to the phytocannabinoids, named cannabimimetic ligands [
65
] (Figure 1). Cannabinoid-like
molecules (mainly terpenes) of either plant or synthetic origin that are non-psychotropic have been
studied. Terpenes and terpenoids are a widespread group of secondary metabolites found in numerous
plant families, including Cannabaceae and others. Herein, we discuss the role of cannabinoid-like
molecules, mainly terpenes, as prospective therapeutics for a variety of pathological conditions.
Molecules 2020,25, 1567 5 of 47
Table 2. CBD pharmacological actions on pathological conditions.
Research Themes Main Findings References
Alzheimer’s disease (AD)
CBD prevented expression of proteins involved
with tau phosphorylation and AD progression.
CBD showed therapeutic potential for
AD-associated cognitive impairment.
[22,23]
Anti-inflammatory properties
CBD induced apoptosis and inhibited
lipopolysaccharide-activated NF-κB and
interferon-β/STAT inflammatory pathways in
microglial cells; CBD protected
oligodendrocytes progenitor cells from
inflammatory-induced apoptosis.
[24]
Anxiety
CBD modulated anxiety responses partially
through 5-HT1A-mediated neurotransmission,
and demonstrated anxiolytic eects during a
stimulated public speaking test; CBD action on
limbic and paralimbic regions contributed to
reduced autonomic arousal and subjective
anxiety; CBD blocked anxiety-induced REM
sleep alteration through anxiolytic properties.
[25,26]
Diabetes
CBD showed beneficial eects on glycemic
control and cardiovascular dysfunction
during diabetes.
[27]
Immunomodulatory eects CBD modulated T-cell function and apoptotic
signaling pathway. [28]
Inflammatory bowel disease (IBD)
CBD attenuated intestinal inflammation and
normalized motility in patients with IBD. [29]
Cognitive impairments
CBD interacted with components of emotional
memory processing and memory-rescuing, as
well as attenuated THC-induced memory
impairment eects.
[30]
Neuropathic pain CBD inhibited chemotherapy-induced
neuropathic pain. [31,32]
Parkinson’s disease (PD) CBD administration showed neuroprotective
eects during PD progression. [33]
Schizophrenia
CBD showed antipsychotic-like properties in
schizophrenia, as well as prevented clinical
social dysfunction, and inhibited
psychomotor agitation.
[34,35]
Seizure/Epilepsy
CBD showed anticonvulsant eects in animal
models of seizure and patients with refractory
epilepsy. CBD was also described as safe and
beneficial for the treatment of
epileptic disorders.
[3639]
CBD, cannabidiol; NF-
κ
B, nuclear factor kappa B; STAT, signal transducer and activator of transcription protein
family; 5-HT1A, serotonin 1A receptor; REM, rapid eye movement sleep; THC, tetrahydrocannabinol.
Molecules 2020,25, 1567 6 of 47
Molecules 2020, 5, x 6 of 46
Figure 1. Beyond the Cannabis sativa plant. The Era of cannabinoids started with the description and
isolation of the main Cannabis sativa psychoactive component, Δ9-tetrahydrocannabinol (THC).
However, many other natural compounds were also identified, totalizing 565 substances among
cannabinoids and non-cannabinoids constituents. This figure illustrates some of the Cannabis sativa
compounds (D-limonene, β-caryophyllene, citral, and falcarinol) and its molecular structures that can
be also found in other plants, such as Cordia verbenacea, lemon, Cymbopogon citratus, and carrot. CBD,
cannabidiol. Figure created using the Mind the Graph platform.
2. Cannabis Phytocannabinoids: Focus on Tetrahydrocannabinol and Cannabidiol
The phytocannabinoid class includes more than a 100 compounds that are present in the
Cannabis sativa plant [66], which interact with components of the human ECS, briefly addressed in
this section. Phytocannabinoids production is dependent on plant internal factors (synthesized
hormone levels, plant kind, and parts of the plant) and on external factors (humidity, light, type of
soil, and temperature). The most elucidated compounds among the main phytocannabinoids are
CBN, CBD, 8- e 9-THC, cannabigerol, and cannabivarin. The 9-THC is the major psychotropic
compound found in high concentrations in the Cannabis sativa plants. It is classified as a CB1R and
CB2R partial agonist, showing preference for the CB1R. The agonist activity on CBR triggers
adenylyl cyclase (AC) inhibition and, thereby, the ability of modulating different neurotransmitters
release as dopamine, acetylcholine, glutamate, and gamma-aminobutyric acid (GABA) [66]. Of note,
phytocannabinoids not only bind to CBR, but also show potential actions on different kinds of
receptors, such as peroxisome proliferator-activated receptors (PPAR), glycine receptors, and the
transient receptor potential (TRP) cation channels. The CBD, unlike the tetrahydrocannabinol (THC),
is a non-psychotropic cannabinoid that has been widely investigated regarding its potential
therapeutic use. It has been already established in the literature that CBD shows anti-inflammatory,
anti-epileptic, analgesic, anxiolytic, and neuroprotective properties, as well as it can be used to
mitigate Parkinson’s disease (PD) symptoms [67–69]—Table 2. CBD acts as a negative allosteric
modulator of CB1R [65] and as an inverse agonist in CB2R, besides being a FAAH enzyme inhibitor.
To briefly highlight, many other phytocannabinoids (e.g., cannabigerol, cannabichromene, and
cannabinol) showed significant therapeutic value. The cannabigerol (CBG) showed agonist and
antagonist activity on TRP channels and it was also able to produce 5-HT1 and CB1R antagonism
[70]. Additionally, CBG is an AEA reuptake inhibitor [71], and it showed colon anti-tumor activity
Figure 1.
Beyond the Cannabis sativa plant. The Era of cannabinoids started with the description
and isolation of the main Cannabis sativa psychoactive component,
9-tetrahydrocannabinol (THC).
However, many other natural compounds were also identified, totalizing 565 substances among
cannabinoids and non-cannabinoids constituents. This figure illustrates some of the Cannabis sativa
compounds (d-limonene,
β
-caryophyllene, citral, and falcarinol) and its molecular structures that can
be also found in other plants, such as Cordia verbenacea, lemon, Cymbopogon citratus, and carrot. CBD,
cannabidiol. Figure created using the Mind the Graph platform.
2. Cannabis Phytocannabinoids: Focus on Tetrahydrocannabinol and Cannabidiol
The phytocannabinoid class includes more than a 100 compounds that are present in the
Cannabis sativa plant [
66
], which interact with components of the human ECS, briefly addressed
in this section. Phytocannabinoids production is dependent on plant internal factors (synthesized
hormone levels, plant kind, and parts of the plant) and on external factors (humidity, light, type of
soil, and temperature). The most elucidated compounds among the main phytocannabinoids are
CBN, CBD,
8- e
9-THC, cannabigerol, and cannabivarin. The
9-THC is the major psychotropic
compound found in high concentrations in the Cannabis sativa plants. It is classified as a CB1R
and CB2R partial agonist, showing preference for the CB1R. The agonist activity on CBR triggers
adenylyl cyclase (AC) inhibition and, thereby, the ability of modulating dierent neurotransmitters
release as dopamine, acetylcholine, glutamate, and gamma-aminobutyric acid (GABA) [
66
]. Of note,
phytocannabinoids not only bind to CBR, but also show potential actions on dierent kinds of receptors,
such as peroxisome proliferator-activated receptors (PPAR), glycine receptors, and the transient
receptor potential (TRP) cation channels. The CBD, unlike the tetrahydrocannabinol (THC), is a
non-psychotropic cannabinoid that has been widely investigated regarding its potential therapeutic
use. It has been already established in the literature that CBD shows anti-inflammatory, anti-epileptic,
analgesic, anxiolytic, and neuroprotective properties, as well as it can be used to mitigate Parkinson’s
disease (PD) symptoms [
67
69
]—Table 2. CBD acts as a negative allosteric modulator of CB1R [
65
]
and as an inverse agonist in CB2R, besides being a FAAH enzyme inhibitor.
To briefly highlight, many other phytocannabinoids (e.g., cannabigerol, cannabichromene, and
cannabinol) showed significant therapeutic value. The cannabigerol (CBG) showed agonist and
antagonist activity on TRP channels and it was also able to produce 5-HT
1
and CB1R antagonism [
70
].
Additionally, CBG is an AEA reuptake inhibitor [
71
], and it showed colon anti-tumor activity by
Molecules 2020,25, 1567 7 of 47
inhibiting transient receptor potential melastatin 8 (TRPM8) channels [
72
]. Relevantly, when associated
with CBD, it demonstrated anti-inflammatory activity reducing tumor necrosis factor (TNF) expression
and upregulating Interleukin–10 (IL-10) and Interleukin–37 (IL-37) levels [
70
]. Cannabichromene (CBC)
showed agonist activity on CB2R [
73
]. Besides, it interacts with TRP channels, being suggested as a
potential therapeutic resource for the treatment of pain and inflammation [
71
]. Lastly, CBN showed
similar therapeutic properties to other phytocannabinoids, such as anticonvulsant, anti-inflammatory,
and antibacterial [
71
]. In addition, CBN showed inhibitory activity on cyclooxygenase (COX),
lipoxygenase (LOX), and P450 cytochrome enzymes [
71
], as well as on keratinocyte proliferation,
supporting a possible potential therapeutic for psoriasis cases [
74
]. As it can be appreciated with the
major phytocannabinoids, the wide ranges of possible interactions of these molecules with multiple
targets in our body, demonstrates the magnitude and the complexity of phytocannabinoids acting in
living organisms.
We just established that phytocannabinoids demonstrate dierent pharmacological eects, and it
can get even more intriguing and complex when we focus on previous data describing that the
combined use of some phytocannabinoids can possibly increase the positive eects proportionate
by them. For instance, the use of CBD associated with
9-THC promoted downregulation of the
neuroinflammatory process in animal models of multiple sclerosis (MS) [
75
], besides, reducing pain [
76
]
and muscle spasticity in MS patients [
75
]. Importantly, CBD attenuated the psychotropic eects of THC
when used in a combined form [
75
]. This last piece of data supports the hypothesis that CBD binds to
an allosteric site on CB1R that is functionally distinct from the active site for 2-AG and THC [
77
]. In this
same context, a recent study reported that a botanical drug preparation (BDP) was more potent than
pure THC to produce antitumor responses in cell culture and animal models of breast cancer. While
pure THC mainly activated CB2R and generated reactive oxygen species (ROS), the BDP modulated
dierent targets and mechanisms of action [
78
]. This combined eect, observed with the association
of phytocannabinoids and other compounds present in the Cannabis sativa plant, such as terpenoids,
is known as the entourage eect [79] (Figure 2).
Molecules 2020, 5, x 7 of 46
by inhibiting transient receptor potential melastatin 8 (TRPM8) channels [72]. Relevantly, when
associated with CBD, it demonstrated anti-inflammatory activity reducing tumor necrosis factor
(TNF) expression and upregulating Interleukin–10 (IL-10) and Interleukin–37 (IL-37) levels [70].
Cannabichromene (CBC) showed agonist activity on CB2R [73]. Besides, it interacts with TRP
channels, being suggested as a potential therapeutic resource for the treatment of pain and
inflammation [71]. Lastly, CBN showed similar therapeutic properties to other phytocannabinoids,
such as anticonvulsant, anti-inflammatory, and antibacterial [71]. In addition, CBN showed
inhibitory activity on cyclooxygenase (COX), lipoxygenase (LOX), and P450 cytochrome enzymes
[71], as well as on keratinocyte proliferation, supporting a possible potential therapeutic for psoriasis
cases [74]. As it can be appreciated with the major phytocannabinoids, the wide ranges of possible
interactions of these molecules with multiple targets in our body, demonstrates the magnitude and
the complexity of phytocannabinoids acting in living organisms.
We just established that phytocannabinoids demonstrate different pharmacological effects, and
it can get even more intriguing and complex when we focus on previous data describing that the
combined use of some phytocannabinoids can possibly increase the positive effects proportionate by
them. For instance, the use of CBD associated with 9-THC promoted downregulation of the
neuroinflammatory process in animal models of multiple sclerosis (MS) [75], besides, reducing pain
[76] and muscle spasticity in MS patients [75]. Importantly, CBD attenuated the psychotropic effects
of THC when used in a combined form [75]. This last piece of data supports the hypothesis that CBD
binds to an allosteric site on CB1R that is functionally distinct from the active site for 2-AG and THC
[77]. In this same context, a recent study reported that a botanical drug preparation (BDP) was more
potent than pure THC to produce antitumor responses in cell culture and animal models of breast
cancer. While pure THC mainly activated CB2R and generated reactive oxygen species (ROS), the
BDP modulated different targets and mechanisms of action [78]. This combined effect, observed
with the association of phytocannabinoids and other compounds present in the Cannabis sativa plant,
such as terpenoids, is known as the entourage effect [79] (Figure 2).
Figure 2. Entourage effect. Beyond the Δ9- tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD),
there are many compounds present in Cannabis sativa, including terpenoids (such as linalool,
Figure 2.
Entourage eect. Beyond the
9- tetrahydrocannabinol (
9-THC) and cannabidiol (CBD),
there are many compounds present in Cannabis sativa, including terpenoids (such as linalool, terpineol,
and citral), which could contribute to beneficial eects related to this plant. However, the underlying
mechanism of these medicinal eects is largely unknown when molecules are associated. Figure created
using the Mind the Graph platform.
Molecules 2020,25, 1567 8 of 47
Cannabis Terpenoids
Beyond the phytocannabinoids, the Cannabis plant is able to produce a diversity of compounds.
Thirty-one-years ago, Mechoulam and Ben-Shabat described what they named the ‘’entourage eect”,
suggesting interactions between Cannabis “inactive” metabolites and closely related molecules could
markedly increase the activity of the “primary” cannabinoids (Figure 2). From this, it was possible to
hypothesize that could be a contribution of “minor cannabinoids” and Cannabis terpenoids to the plant
overall pharmacological eect. Therefore, a recent study evaluated the eect of common terpenoids,
by themselves and in combination with THC, in AtT20 cells expressing CB1R or CB2R. Surprisingly,
none of the analyzed terpenoids modulated the THC phytocannabinoid agonist signaling. Thus, the
authors suggested that if the phytocannabinoids–terpenoids entourage eect exists, it is not at the
CB1R or CB2R receptor level [
80
]. Corroborating, when rats were submitted to an abdominal writhing
model and treated only with terpenoids they demonstrated increased abdominal writhing, while the
animals treated with THC showed robust analgesia, even better than the rats that received the Cannabis
full extract. In this case, Cannabis antinociceptive property was linked to
9-THC, since terpenes
alone do not alter the nociceptive behavior [
81
]. Using a dierent approach, Nandal and co-authors
exposed cancerous cell lines to treatment with phytocannabinoids combined with low concentrations
of co-related terpenoids. They observed increased cell mortality at ratios similar to the ones obtained
with the natural plant extracts [
82
]. According to the authors, their results diered from Santiago
et al. findings because they evaluated terpenoids without statistical correlation to THC, meaning
that terpenoids concentrations in their preparations where higher than the natural-occurred in the
plants [
80
,
82
]. Thus, the possible “entourage eect” and the positive contribution derived from the
addition of terpenoids to cannabinoids could be interpreted as uncertain. However, the study of
terpenoids represents an open window that goes beyond its actions (i) in the endocannabinoid system
solely, or (ii) as mere phytocannabinoids passive co-authors, and even beyond the Cannabis plant.
3. Terpenoids in and beyond the Cannabis Plant
Cannabis contains a large number of monoterpene and sesquiterpene compounds, together
called terpenoids or terpenes, which are aromatic compounds synthesized in trichomes [
71
]. In the
plant, these compounds (i.e., more than 120 terpenes) synthesized alongside phytocannabinoids are
important volatile constituents that are responsible for the plant’s characteristic smell and also serve
for dierent organic functions, such as insect repellent, repellent to herbivore attack, and attractive
to pollinators [
71
]. Booth and Bohlmann described the terpenes- and cannabinoid-rich resin as
the most valuable cannabis products, with dierent psychoactive and medicinal properties [
83
].
Studies regarding terpenoid compounds (i.e., D-limonene,
β
-myrcene,
α
-pinene,
α
-terpineol,
β
-pinene,
β
-caryophyllene, and others) have been growing in the last decades due to their large number and
extensive employability [
71
,
84
]. However, the presence of terpenoids has not been restricted to
the Cannabis sativa plant. These compounds normally occur in several other plant species, such as
Mirabilis jalapa,Lithophragm glabrum,Cordia verbenacea,Eucalyptus globus,Syzygium aromaticum,Senna
didymobotrya,Cymbopogon citratus, and in some Citrus genus plants, as Citrus limon and others. To
date, there are more than 10,000 articles versing about phytocannabinoids or cannabimimetics, and its
actions described in the literature. There are many Cannabis terpenoid compounds that are not majorly
found in the Cannabis plant but are highly expressed in other plants. Its actions are varied and complex,
being many compounds studied deep down to the mechanisms of action, pharmacokinetics, toxicity,
and pharmacodynamics, whereas others are still to be addressed regarding these aspects. The study
about terpenoids beyond the Cannabis plant has been earning ground in the research field due to the
fact that they can be utilized as tools for the improvement of therapeutic research for several diseases.
Herein, we can have a sense of how literature stands at this end regarding some of these compounds,
and we discuss the role of terpenoids as prospective therapeutics of dierent pathological conditions.
Molecules 2020,25, 1567 9 of 47
3.1. Beta (β)- and α-Caryophyllene
Beta and alpha-Caryophyllene are the major sesquiterpenes encountered in the Cannabis plant [
85
].
Importantly, a comparative study showed that regardless the type of extraction used supercritical
fluid extraction, steam distillation, or hydrodistillation, the major sesquiterpene compound to be
extracted was
β
-Caryophyllene (BCP) [
86
]. Caryophyllenes are considered phytocannabinoids with
strong anity to CB2R but not CB1R [
87
], and are produced not only by Cannabis but also by a
number of plants, as a mechanism of defense to insects, for instance. The vast literature describes
a number of plants that contain this compounds such as Cordia verbenacea,Pterodon emarginatus,
Artemisia campestris,Lantana camara,Centella asiatica,Cyanthillium cinereum, and Croton bonplandianus,
just to name a few of the more than 30 species previously described. Heretofore published original
articles described seven main actions to caryophyllenes. These actions are reported to be repellent,
antimicrobial or antibacterial, anticancer or antiproliferative, antifungal, AChE inhibitor, antioxidant,
and anti-inflammatory. Regarding the antifungal and antimicrobial action, Sabulal and co-workers
showed that Zingiber nimmonii rhizome oil, which is a unique isomeric caryophyllene-rich natural
source, has inhibitory activity against fungi (e.g., Candida glabrata,Candida albicans, and Aspergillus
niger) as well as against both Bacillus subtilis and Pseudomonas aeruginosa bacteria [
88
]. More recently,
a study has shown that Phoebe formosana leaf extract has antifungal activity as well; BCP being one of
the active compounds identified [
89
]. In this same study, authors have reported that the oil exhibited
cytotoxic activity against human lung, liver, and oral cancer cells while the major active compound
was BCP. Corroborating, BCP was the major compound found in the tree bark essential oil from Pinus
eldarica, which showed antiproliferative activity in a concentration dependent manner against MCF-7
breast cancer cell line [
90
]. Likewise, anticancer activity against MCF-7 cells was also reported for the
essential oil of Cyperus longus mainly constituted of
β
- and
α
- caryophyllenes [
91
]. Regarding analgesic
eects, BCP has been demonstrated to attenuate paclitaxel (PTX)-induced peripheral neuropathy in
mice by a mechanism dependent on mitogen-activated protein kinase (MAPK) inhibition [
92
]. Recently,
a review has summarized, very well, the anticancer and analgesic properties of this compound [87].
The anti-inflammatory properties of BCP have been extensively shown in dierent mouse
models of disease. Bento and co-workers have demonstrated the beneficial eect of BCP treatment
in an inflammatory bowel disease mouse model, in which BCP oral treatment mitigated TNF
and Interleukin-1
β
(IL-1
β
) expression, reduced colon damage, and ameliorated disease score. To
a mechanistic level, they showed these eects were at some degree dependent on peroxisome
proliferator-activated receptor gamma (PPAR-
γ
) and CB2R activation [
93
]. In a very interesting study,
Gertsch and co-workers reported that BCP selectively binds to CB2R acting as a full agonist, highlighting
its potential therapeutic eects for inflammatory and painful states [
94
]. In an experimental autoimmune
encephalomyelitis (EAE) mouse model, Alberti and co-workers have reported anti-inflammatory
actions (i.e., reduced microglial activation and inducible nitric oxide synthase (iNOS) expression)
of Pterodon emarginatus essential oil that is mainly enriched with BCP. Anti-inflammatory actions,
in this case, contributed to attenuate neurological score and disease progression, being dependent
on the control of T helper 1 (Th1) and Treg activity [
95
]. Later, the same authors demonstrated
the eect of BCP in the experimental model of multiple sclerosis [
96
]. In fact, BCP extracted from
Cordia verbenacea essential oil induced a markedly anti-inflammatory eect in panoply models in
rats involving the attenuation of the abovementioned inflammatory molecules iNOS, TNF, and IL-2,
as well as prostaglandin E2 (PGE2), and COX-2 [
97
]. Likewise, through anti-inflammatory pathways,
BCP demonstrated a neuroprotective eect in a rat model of PD [
98
]. These are few very important
examples of the beneficial and useful properties of caryophyllene. We agree with Sut and co-workers’
point-of-view that some of the considered old molecules, as sesquiterpenes, could possibly play an
important role in drug discovery towards new discoveries [99].
Molecules 2020,25, 1567 10 of 47
3.2. D-Limonene
Limonene, (4R)-1-methyl-4-prop-1-en-2-ylcyclohexene, is the most common monoterpene found
in nature; for instance, in Cannabis sativa oilseed hemp named Finola and also in citrus oils, from orange,
lemon, and tangerine [
84
]. Despite being found in Cannabis sativa, limonene does not interact with
CB1R or CB2R [
100
]. Interestingly, D-limonene absorption and metabolism in animals is accelerated,
and consequently it has a high rate of distribution and excretion. D-limonene metabolites have
been detected in adipose tissue and mammary glands in a high concentration, although it has
low toxicity [
101
]. This compound shows dierent pharmacological properties, which include
anti-inflammatory, gastro-protective, anti-nociceptive, anti-tumor, and neuroprotective [
102
104
].
A recent study has demonstrated D-limonene anti-tumor activity (i.e., tumor cells decreased in
proliferation and growth) in an animal model of chronic myeloid leukemia [
102
]. Moreover, D-limonene
also showed anti-inflammatory activity by inhibiting pro-inflammatory mediators, leukocyte migration,
and vascular permeability [
105
]. Regarding its activity on the gastrointestinal tract, there are dierent
articles described in the literature. For instance, the same group described a gastric protection
eect in rats with colon inflammation [
103
], and in an animal model of an ulcer induced by ethanol
and indomethacin [
106
]. In addition, D-limonene-induced mucus production and IL-6, IL-1
β
, and
TNF inhibition has been previously described [
107
]. Corroborating this data, Wang and colleagues
demonstrated that limonene aected the intestinal microbiota of mice and enhanced the relative
abundance of Lactobacillus, suggesting limonene direct eects on intestinal bacteria [108].
Limonene also inhibited nociceptive behavior induced by intraperitoneal acetic acid injection
and plantar formalin [
109
]. In a complementary way, combined administration of limonene and
β
-ciclodextrin inhibited hyperalgesia in a chronic musculoskeletal pain model by downregulation
c-FOS expression in the spinal cord [
84
]. Reinforcing this information, treatment with Schinus
terebinthifolius essential oil—which is highly-concentrated in limonene—showed anti-hyperalgesic
and anti-depressive eects in a neuropathic pain animal model [
110
]. At a dierent point-of-view,
Smeriglio and colleagues reported the antioxidant and free radical scavenging properties of Citrus
lumia oil, which is highly-concentrated in monoterpenes (e.g., 48.9% D-limonene and 18.2% linalool),
suggesting an important preventive role in the genesis of oxidative stress-related pathologies [
111
].
In this context, a study conducted by Shin et al. showed that limonene decreased cell death, ROS levels,
extracellular signal-regulated kinase phosphorylation, and overall inflammation in the brains and eyes
of drosophila during A
β
42-induced neurotoxicity, a model of Alzheimer ’s disease (AD) [
104
]. These
and other authors have been studying limonene eects in the context of its impacts in the CNS. For
instance, limonene has shown to exhibit anxiolytic eect increasing hippocampal dopamine levels and
serotonin in the prefrontal cortex [75]. Considering the information above exposed, this is just one of
the many compounds to be still addressed in this review that are natural and abundant in dierent
plants, which could be used as potential therapeutics for diseases dependent on the inflammatory and
oxidative-stress processes.
3.3. Linalool
Similar to limonene, linalool, 3,7-dimethylocta-1,6-dien-3-ol, is a monoterpene compound present
in several medicinal plants and fruits, including Cannabis sativa, which has been widely used in
the cosmetics and flavoring ingredients [
112
]. Linalool showed anti-inflammatory, anti-cancer, and
anxiolytic eects [
113
115
]. The use of aromatherapy for the treatment of anxiety is disseminated
among folk medicine. Accordingly, a study showed that linalool induced anxiolytic eects in
mice by modulating GABAergic synaptic transmission [
115
]. Similarly to others terpenes, linalool
showed anti-inflammatory activity, it prevented eosinophil migration, Th2-cytokines profile, and IgE
concentration, in an asthma animal model. In addition, linalool inhibited iNOS expression, NF-
κ
B
(Nuclear factor kappa B) activation, inflammatory cells infiltration, and mucus hyper production during
asthma progression [
113
]. Inflammation as well as oxidative stress are processes closely related to the
progression of dierent CNS diseases, such as AD. In this context, a recent study demonstrated that
Molecules 2020,25, 1567 11 of 47
linalool decreased ROS and lipid peroxidation levels, as well as improved mitochondrial morphology,
membrane potential, and respiration, directly reducing the cell death rate due to oxidative stress [
114
].
Additionally, linalool showed neuroprotective eects on A
β
1–40-induced cognitive impairment in
mice, which it was suggested to be mediated by inhibition of apoptosis and oxidative stress induced
by Aβ-dependent Nrf2/HO-1 pathway activation [116].
Regarding to its potential anti-tumor activity, linalool induced apoptosis of cancer cells
in vitro
following the cancer-specific induction of oxidative stress, which was measured based on spontaneous
hydroxyl radical production and delayed lipid peroxidation. Besides, mice in the high-dose linalool
group exhibited a 55% reduction in average xenograft tumor weight compared to the control group [
117
].
Linalool has also reported to be protective against ultraviolet B (UVB)-induced tumor through
inhibition of inflammation and angiogenesis signaling, as well as induction of apoptosis in the mouse
skin [
118
]. Finally, a study showed that linalool reduced paclitaxel-induced acute pain in mice,
which was antagonized by the direct injection of naloxone hydrochloride, suggesting opioid signaling
modulation [
119
]. What can be appreciated so far, and will continue to be addressed, is the general
ability of dierent terpenes to modulate inflammation and oxidative stress through dierent pathways,
which in turn could be very useful to shed light to novel treatments for pain, cancer, autoimmune
diseases, and CNS diseases that rely greatly on the impact of these processes.
3.4. Terpineol
Terpineol (2-(4-methylcyclohex-3-en-1-yl)propan-2-ol) is a volatile monoterpene alcohol present
in the essential oil of Cannabis sativa [
120
], but also in several medicinal plants, such as Punica granatum
L.,Rosmarinus ocinalis L., and Psidium guajava L. Until this moment, there is no evidence in the
literature about the interaction of terpineol with CBR. Nonetheless, this compound shows dierent
pharmacological properties that include antinociceptive [
121
], antifungal [
122
], anti-inflammatory [
123
],
and antidiarrheal [
124
]. Likewise, terpineol analgesic activity has been investigated in dierent animal
models of pain. In this context, Oliveira and colleagues evaluated the eect of terpineol combined to
β
-cyclodextrin (
β
CD) (family of cyclic oligosaccharides with a wide variety of practical applications,
including pharmacy, medicine, and foods) in an animal model of fibromyalgia. According to the
authors,
α
-terpineol-
β
CD complex reduced nociceptive behavior induced by a chronic muscle pain
model [
121
]. Still, this eect was mediated by activation of descending inhibitory pain system,
since analgesic eect was reversed by systemic administration of naloxone (opioid antagonist), or
ondansetron (5-HT3 antagonist) [
121
]. Additionally, terpineol has also been demonstrated to be a safe
and eective drug for control of sarcoma-induced cancer pain in mice [
125
]. In a complementary way,
terpineol could be investigated as preventive treatment for the development of dependence and of
tolerance to opioid analgesics, since it attenuated the analgesic eect of morphine [
126
]. Thus, it is
possible to suggest that terpineol alone, or combined to other drugs, could be an interesting target for
development of new analgesics to control chronic pain symptoms. Besides, it could work as adjunctive
therapy to morphine in order to reduce side eects related to treatment with opioid drugs.
Terpineol showed not only antinociceptive but also neuroprotective properties, since improved
memory impairment in rats exposed to transient bilateral common carotid artery occlusion. The
underlying mechanisms described comprise the facilitation of LTP and suppression of lipid peroxidation,
in the hippocampus [
127
]. In accordance, Abies koreana essential oil (terpenoids-rich oil, including
terpineol) enhanced memory of mice submitted to scopolamine-induced amnesia [
128
]. Regarding
it anti-inflammatory properties, terpineol has also been investigated for the treatment of allergic
inflammation and asthma because decreased leucocyte migration and TNF levels. Furthermore,
terpinen-4-ol and
α
-terpineol were found to suppress the production of inflammatory mediators
(e.g., NF-
κ
B, p38, ERK, and MAPK signaling pathways) in lipopolysaccharide (LPS)-stimulated human
macrophages [129]. Altogether, data supports that terpineol should be better investigated in order to
characterize its neuroprotective eects found in cerebral ischemia-related memory impairment and
Molecules 2020,25, 1567 12 of 47
possibly be extended to other neurological conditions, such as seizures, migraine, Parkinson’s disease,
as well as to clarify its anti-inflammatory potential.
Terpineol properties go beyond, it has previously been shown antifungal properties against
Penicillium digitatum because it disrupts fungi cell wall allowing the leakage of intracellular
components [
130
]. In agreement with this, tea tree oil’s antibacterial and antifungal properties
were attributed mainly to 1,8-cineol, methyl eugenol, and terpinen-4-ol [
131
]. Recently, Chaudhari and
co-authors reported the ecacy of
α
-terpineol loaded chitosan nanoemulsion (
α
-TCsNe) to control
AFB1, a secondary metabolite produced by Aspergillus flavus and Aspergillus parasiticus fungi [
122
].
Included in miscellaneous actions, in addition to bactericidal and antifungal activities, terpineol has
been recognized as algaecide [
132
] and by its natural repellent activity against Tribolium castaneum
(H.) [
133
]. Finally, this monoterpenoid exhibited strong anti-proliferative activity on cancer cell
lines [
134
], as well as it inhibited growth of tumor cells trough modulation of NF-
κ
B signaling
pathway [
135
]. Thus, it is possible hypothesize that terpineol as a versatile compound with a wide
variety of beneficial eects could be a possible venue for the development of new antibiotics, antifungal,
and anticancer agents.
3.5. Terpinene
Gamma-terpinene, 1-methyl-4-propan-2-ylcyclohexa-1,4-diene, is a monoterpene structurally
similar to 1.8-cineol, being both found in the essential oils of Cannabis sativa and several other
plants including the Eucalyptus genus (Myrtaceae), Cupressus cashmeriana,Lippia microphylla,Lavandula
angustifolia, and Citrus myrtifolia [
136
141
]. Gamma-terpinene is very well described in the literature
as an anti-inflammatory, antimicrobial, analgesic, and anticancer agent [
136
,
137
,
142
144
]. A recent
study demonstrated that
γ
-terpinene reduced some inflammatory parameters, such as edema and
inflammatory cell infiltration during tests in experimental models of inflammation, namely phlogistic
agent-induced paw edema, acetic acid-induced microvascular permeability, carrageenan-induced
peritonitis, and lipopolysaccharide-induced acute lung injury [
145
]. In addition, another study
assessed the eect of
γ
-terpinene on pro- and anti-inflammatory macrophage production of cytokines
in an animal model. The authors reported that
γ
-terpinene significantly increased the production
of IL-10, which was dependent on PGE2 production since eects were reversed by COX-2 inhibitor
nimesulide [146].
Besides the anti-inflammatory action, Assmann and colleagues described the anti-tumor activity
and some of the possible underlying mechanisms of the Melaleuca alternifolia essential oil, which is
composed of three major compounds terpinen-4-ol (41.98%),
γ
-terpinene (20.15%), and
α
-terpinene
(9.85%), on MCF-7 breast cancer cells [
147
,
148
]. Authors reported
γ
-terpinene potential cytotoxic
activity by decreasing breast cancer cells viability. Eects were observed in the early stages of apoptosis,
such as increased BAX/BCL-2 genes ratio and increased cell arresting to S phase of the cycle [
148
].
Antimicrobial activity has been tested as well; Melaleuca spp. plants demonstrated eects against a
wide range of gram-positive and gram-negative bacteria, fungi, and yeasts. Impressively, Melaleuca
thymifolia volatile oil exhibits higher antimicrobial activity than gentamicin and streptomycin against
Staphylococcus aureus [
131
]. Considering the exposed, it is feasible to suggest that
γ
-terpinene could
server as natural immunomodulatory agent with antioxidant, antimicrobial, and anticancer properties
that could be useful therapeutically.
3.6. Alpha (α)- and β-Pinene
Alpha-pinene is considered a natural compound present not only in Cannabis sativa but also in
essential oils of many aromatic plants, such as Lavender angustifolia,Rosmarinus ocinalis, and coniferous
trees [
149
]. Alpha-pinene is a bicyclo[3.1.1]hept-2-ene that contains a reactive 4-membered ring structure
and exhibits antioxidant, antimicrobial, anti-tumor, hypnotic, and anxiolytic activities [
83
,
120
,
150
152
].
There are dierent biological properties described to
α
-pinene, as well as essential oils containing
this compound have been used to treat several diseases [
153
], although no anity towards CBRs
Molecules 2020,25, 1567 13 of 47
have been described [
154
]. Alpha-pinene has been extensively investigated in the last years for its
medicinal properties that include sedative, hypnotic, and anxiolytic [
152
,
155
]. In this context, Yang and
colleagues demonstrated that
α
-pinene interacts with GABA
A
/benzodiazepine receptors prolonging
its synaptic transmission, significantly increasing the duration of non-rapid eye movement sleep
(NREMS), and reducing sleep latency [
151
]. The beneficial eects of
α
-pinene are also extended to
convulsions [
80
,
81
], ischemic stroke [
82
], and schizophrenia [
156
]. Besides,
α
-pinene also showed
neuroprotective eects that might be related to its antioxidant properties, which include being able to
decrease malondialdehyde and hydrogen peroxide levels while increasing catalase and peroxidase
activity. A study has reported that rats exposed to pentylenetetrazol (PTZ)-induced convulsions
submitted to
α
-pinene intraperitoneal (i.p.) administration presented both initiation time delayed
and reduced duration of myoclonic and tonic-clonic seizures, following PTZ injection [
81
]. Another
study suggested that
α
-pinene appears to be devoid of anticonvulsant action, since only
β
-pinene
aected the intensity of seizures and time of death of PTZ-treated mice [
80
]. Further, it was suggested
that
α
-pinene might serve as potential therapeutics for schizophrenia since it possibly suppresses
neuronal activity. However, it has also been demonstrated that inhalation of
α
-pinene inhibits
dizocilpine (MK-801)-induced schizophrenia-like behavioral abnormalities in mice [
156
]. Lastly,
α
-pinene mitigated learning and memory loss induced by scopolamine in mice. The underlying
mechanisms reported were increased choline acetyltransferase messenger RNA (mRNA) expression in
the cortex and increased antioxidant enzyme levels (e.g., HO-1 and manganese superoxide dismutase
(MnSOD)) in the hippocampus through activation of Nrf2 [157].
Beyond neuroprotection, the cytoprotective and antinociceptive properties of
α
-pinene have been
previously described. Regarding the former, studies were conducted using peptic ulcer, ultraviolet A
radiation (UVA) irradiation, and aspirin-induced cytotoxicity models [
158
160
]. In details,
α
-pinene
was able to prevent UVA-induced loss of mitochondrial membrane potential, lipid peroxidation,
DNA damages, and ROS generation [
158
]. Likewise,
α
-pinene inhibited UVA-induced activation of
pro-angiogenesis factors (e.g., iNOS and vascular endothelial growth factor (VEGF)), as well as blocked
expression of inflammatory mediators (e.g., TNF, IL-6, and COX-2) and apoptotic mediators (e.g., Bax,
Bcl-2, caspase-3, and caspase- 9) in mouse skin submitted to UVA-irradiation at the rate of 10 J/cm2/day,
for 10 days [
159
]. In contrast,
α
-pinene promoted cytoxicity, and consequently cancer cells apoptosis by
increasing activity of caspase-3 in human ovarian cancer cells (PA-1) [
161
]. In this sense, another study
showed that
α
-pinene was also able to inhibit human hepatoma tumor progression by inducing G2/M
phase cell cycle arrest [
162
]. Regarding
α
-pinene antinociceptive eects, it was previously demonstrated
its beneficial potential in capsaicin-induced dental pulp nociception [
163
], xylene-induced ear edema,
and formalin-inflamed hind paw models [
164
]. In this context,
α
-pinene exhibited significantly
anti-inflammatory and analgesic eects through inhibition of COX-2. Moreover, the analgesic eect of
α
-pinene on capsaicin-induced pulp nociception was blocked by co-administration with bicuculline
or naloxone, thus suggesting that this eect could be mediated, at least in part, by interaction with
GABA-A and µ-opioid receptors [163].
Related to
α
-pinene, another important monoterpene present in dierent Cannabis sativa L. varieties
is
β
-pinene, which can also be found in many plants essential oils and obtained commercially by
distillation or by
α
-pinene conversion [
165
,
166
]. Literature describes
β
-pinene antimicrobial and
antioxidant activity [
167
], as well as its derivatives have been associated to anticancer, anticoagulation,
and antimalarial eects. Additionally,
β
-pinene showed repellent activity against Tribolium castaneum,
which is a beetle species from the Tenebrionidae family that is also a powerful invertebrate system for
molecular genetics studies. Looking for the mechanism by which
β
-pinene mediated this repellent
activity; authors reported that exposition to this compound alters the gene expression, namely Grd
(which encodes GABA receptor), Ace1 (which encodes class A acetylcholinesterase) and Hiscl2 (which
encodes histamine-gated chloride channel subunit 2) [
168
]. However, according to Pajaro-Castro and
colleagues,
β
-pinene showed little ability to dock on proteins associated with neurotransmission process
in the Tribolium castaneum [
168
]. Even though the
β
-pinene-induced repellent eect still remains to be
Molecules 2020,25, 1567 14 of 47
fully addressed, it seems feasible to be considered that
β
-pinene monoterpene could act on dierent
insect and mammalian receptors associated with neurotransmission. For instance, Guzm
á
n-Guti
é
rrez
and co-authors attributed to Litsea glaucescens essential oil (being
β
-pinene and linalool the two
main active principles) antidepressant-like and sedative-like properties [
169
]. Posteriorly, the same
group evaluated the mechanisms related to antidepressant eect of the essential oil compounds.
In brief and focused on
β
-pinene, adult male ICR mice were pre-treated with (1S)-(
)-
β
-pinene
(100 mg/kg) and exposed to forced swimming test (FST). Results showed that
β
-pinene, as well as
imipramine (control drug), decreased the immobility time of mice when compared with control in the
FST. Furthermore, administration of 5-HT
1A
receptor antagonist prevented the antidepressant-like of
β
-pinene, demonstrating that this compound could interact with the serotonergic system. Likewise,
β
-pinene anti-immobility eects were also prevented by propranolol (
β
-receptor antagonist), neurotoxin
DSP-4 (noradrenergic neurotoxin), and SCH23390 (a D1 receptor antagonist), suggesting its possible
interactions with the adrenergic and dopaminergic system as well [170].
The use of
β
-pinene as an antitumor, as well as antiviral and antifungal agent has also been explored.
Regarding the former,
β
-pinene-based thiazole derivatives were investigated as antineoplastic agents
in vitro
. Twenty-four
β
-pinene-based thiazole derivatives were synthesized and 5 g compound showed
cytotoxic against three dierent cancer cell lines (Hela, CT-26, and SMMC-7721). Cytotoxic eect
have been described to be mediated by action in the following signaling pathways: i) increased ROS
activity, ii) loss of mitochondrial membrane potential, and iii) altered expression of Bax/Bcl-2, ultimately
provoking cell injury and even cell death [
171
]. Concerning its antiviral and antifungal activity, it was
shown its beneficial eects against Rhizopus stolonifer (the common bread mold) and Absidia coerulea
fungi, as well as against herpes simplex virus type 1 (HSV-1),
in vitro
[
172
,
173
]. In fact,
β
-pinene reduced
HSV-1 viral infectivity through interaction with free virus particles by 100% in a dose-dependent
manner [
174
]. Similarly,
β
-pinene was able to reduce Candida biofilm adhesion through molecular
interaction mainly with delta-14-sterol reductase–enzyme, which is related to metabolic pathway
leading to cholesterol biosynthesis; thus, an eective target for antifungal drugs development [
175
,
176
].
Interestingly, when combined with commercial antimicrobial ciprofloxacin, both
β
-pinene and
α
-pinene
demonstrated synergistic activity against methicillin-resistant Staphylococcus aureus [
177
]. Summarizing,
here we describe, the antioxidant, anti-inflammatory, and immunomodulatory activity of both pinenes.
Importantly, the neuromodulatory role that
α
-pinene and
β
-pinene are able to play could be used to
shed light on innovative approaches to treat a variety of neurological conditions.
3.7. β-Elemene
β
-elemene (1-methyl-1-vinyl-2,4-diisopropenyl-cyclohexane) is a derivative terpenoid found in
Cannabis sativa, which may arise due to oxidation or due to thermal- or UV-induced rearrangements
during processing or storage [
85
,
178
,
179
]. However,
β
-elemene is present not only in Cannabis sativa but
also from Curcuma rhizome, and it is commonly used in traditional Chinese medicine due to its anticancer
properties with no reported severe side eects [
180
]. In this way, this compound has been extensively
studied as an anticancer agent
in vitro
and
in vivo
and has been demonstrated to be a promising drug
for the treatment of a wide variety of tumors [
181
186
]. Among the challenges associated to cancer
treatment, it is the development of multidrug resistance (MDR), which negatively impacts the eect of
chemotherapy drugs, and consequently treatment success. It was previously proposed that one of the
viable solutions to overcome MDR is to combine two chemotherapeutic drugs, acting synergistically to
target multiple key pathways to inhibit tumor progression [
187
,
188
]. In this context, the combination of
β
-elemene with other chemotherapeutic agents (i.e., cisplatin and doxorubicin) and other therapeutic
adjuvant has demonstrated great potential to inhibit tumor cells and tumor growth. According to
Li and colleagues,
β
-elemene and cisplatin combined chemotherapy treatment is one of the most
important approaches available for lung cancer therapy in China. Besides, the China Food and Drug
Administration has approved it for the treatment of dierent tumors, such as brain, ovary, prostate,
breast, lung, liver, and colon [
189
191
]. Additionally, when associated to hyperthermia
β
-elemene
Molecules 2020,25, 1567 15 of 47
significantly inhibited growth of adenocarcinoma human alveolar basal epithelial cells A549 cells in a
dose-dependent manner, when compared to
β
-elemene treatment alone [
182
]. Mechanistically, the
exposition of A549 cells to hyperthermia plus
β
-elemene significantly increased mRNA expression of
cyclin-dependent kinase inhibitor p21 that ultimately induced cell apoptosis [
182
]. Another approach
to try overcoming unsuccessful chemotherapy is the nanotechnology-based drug delivery system,
which could improve pharmacokinetics of chemotherapeutic agents [
192
]. These carriers encompass a
broad range of dispersion systems (i.e., polymeric micelles, liposomes, and dendrimers) that protect
against drug degradation, promote sustained release, and reduce side eects [
192
]. Thus, dierent
studies evaluated the therapeutic eects of
β
-elemene co-loaded with chemotherapy drugs: i) cisplatin
in co-loaded liposomes [
193
]; ii) doxorubicin (DOX) in pH-sensitive nanostructured lipid carriers
(DOX/
β
-elemene Hyd NLCs) [
194
]; iii) cabazitaxel in complex liposome [
195
]. In summary, these
reports described that
β
-elemene co-loaded with lower doses of chemotherapy drugs was able to
induce toxicity eects against tumor while retaining a similar therapeutic eect of the drug by itself,
demonstrating synergistic eect of the compounds. Corroborating,
β
-elemene was also described
as a radiosensitizer producing DNA damage and inhibition of DNA repair, as well as increased
apoptosis. Beta-elemene was also able to inhibit the activation of the Prx1-NF
κ
B-HIF-1
α
axis, a key
regulator whereby tumor cells adapt to radiation therapy and hypoxia [
196
]. Beta-elemene was also
shown to inhibited monocyte chemoattractant protein-1 (MCP-1) secretion, a macrophage recruitment
chemokine that contributes to cancer cells metastasis [
197
]. Altogether, these reports demonstrate the
possible mechanisms behind
β
-elemene anticancer activity and suggest dierent ways to incorporate
this compound into current clinical therapies.
Besides the very promising anticancer activity, it has been reported in the literature a variety of
other beneficial eects attributed to
β
-elemene. Li and co-authors, for instance, provided evidence
of
β
-elemene beneficial eects for atherosclerosis treatment [
198
]. In this study, apoE homozygous
deficient mice were fed a high-fat diet during four weeks followed by
β
-elemene (135 mg/kg) oral
gavage administration for another 12 weeks. Beta-elemene treatment significantly reduced lipid areas
of atherosclerotic plaques and aortic root lesion sizes and necrotic core, basically by boosting antioxidant
enzymes while decreasing inflammatory cytokines levels. [
198
]. In a dierent study,
β
-elemene exerted
retino-protective eect by downregulation of hypoxia-inducible factor–1alpha (HIF-1
α
), VEGF, iNOS,
and pro-inflammatory mediators during diabetes progression in a streptozotocin (STZ)-induced rat
model [
199
]. Finally, the potential application of
β
-elemene in an EAE animal model was tested, in
which mice were treated from day one after induction with
β
-elemene (20 mg/kg, i.p.) until the end of
experiment. Beta-elemene reduced IFN-
γ
and IL-17 levels and completely blocked EAE onset and
the severity of clinical symptoms. Furthermore,
β
-elemene inhibited IL-17, IFN-
γ
, ROR-
γ
T, and T-bet
mRNA expression in the optic nerve of EAE mice [
200
]. If we start to appreciate the bigger picture,
it is possible to note that as the other terpenes here described so far,
β
-elemene shows the ability to
modulate essential biological functions, such as inflammation, oxidative stress, immunology response,
cell division, as well as endothelial regulation. Beneficial properties of this compound have been
studied to a mechanistically level highlighting it as a promising tool for the treatment of relevant
diseases, but there are many venues that still remain to be explored.
3.8. β-Ocimene and Camphene
Beta-ocimene (3,7-dimethyl-1,3,6-octatriene) is acyclic monoterpene that serves as a chemical
cue to attract natural enemies of phytophagous insect in several plant species, including Cannabis
sativa [
85
]. Booth et al. demonstrated using the variety ‘Finola’ of Cannabis sativa oilseeds that the most
abundant monoterpenes found were myrcene, (+)-
α
-pinene, (
)-limonene, (+)-
β
-pinene, terpinolene,
and (E)-
β
-ocimene [
85
]. Farr
é
-Armengol and colleagues demonstrated that the emissions of
β
-ocimene
in flowers follow marked temporal and spatial patterns of emission, which are typical from floral
volatile organic compound (VOC) emissions that are involved in pollinator attraction [
201
]. Another
study reported that a monoecious cultivar (Futura 75) and a dioecious one (Finola) of Cannabis sativa
Molecules 2020,25, 1567 16 of 47
tested in a mountain area in Alps, Italy (elevation: 1100 meters above sea level, during the growing
season 2018) showed particular phytochemical behavior. For instance, inflorescences from Finola
variety were characterized by higher concentrations of
β
-ocimene and
α
-terpinolene, while
α
- and
β
-pinene accompanied by extremely high
β
-myrcene were found as predominant in Futura variety
indicating that geographical provenience should be considered for a specific medicinal use of Cannabis
sativa [
202
]. Currently, at least three beneficial properties have been described in the literature for this
compound, such as antitumor, antifungal, and anticonvulsant [
203
,
204
], but mechanisms underlying
the biological activity of this compound remain poorly explored.
Camphene (2,2-dimethyl-3-methylidenebicyclo(2.2.1)heptane) is a cyclic monoterpene present
in Cannabis inflorescence in low titer but abundant in the essential oil of Thymus vulgaris that
showed some pharmacological activities, such as expectorant, spasmolytic, and antimicrobial [
205
].
Camphene showed fumigant and contact toxicity against Liposcelis bostrychophila and Tribolium castaneum
insects. Furthermore, it presented moderate repellent eect to T. castaneum while showed attractant
eect to Liposcelis bostrychophila, [
206
]. Extending these observations, Benelli et al. showed that
camphene inhibited Helicoverpa armigera and Spodoptera litura—key polyphagous insects pest—with
a lethal dose (LC50) of 10.64 and 6.28
µ
g/mL, respectively, confirming the promising potential as
a botanical insecticide [
207
,
208
]. Altogether, these findings strongly support the use of camphene
as an eco-friendly and eective insecticidal agent. More recently, Souza and co-authors evaluated
the anti-Mycobacterium tuberculosis activity of 17 novel synthesized thiosemicarbazones derived from
(
)-camphene,
in vitro
. Overall, the majority of the tested compounds exhibited significant inhibitory
eects on the Mycobacterium tuberculosis growth, with minimal inhibitory concentrations (MIC) values
ranged from 3.9 to >250
µ
g/mL [
209
]. Although there are not as much reports about
β
-ocimene and
camphene as was described to the other compounds here reviewed thus far, their repellent and/or
insecticide activity seem to be promising.
3.9. Nerolidol
Nerolidol ((6E)-3,7,11-trimethyldodeca-1,6,10-trien-3-ol), also known as peruviol, is a noncyclic
sesquiterpene alkene alcohol common to citrus peels, Piper claussenianum,Baccharis dracunculifolia,
and Cannabis plant [
210
]. Previously, it was demonstrated its inhibitory eect on the growth of
Leishmania braziliensis promastigotes. Importantly, ultra-structural observation of nerolidol-treated
parasites by STM showed mitochondria morphological alterations in the, nuclear chromatin and
flagellar pocket along with cell shrinkage. In this same study, authors demonstrated some nerolidol
mechanisms of action that included loss of mitochondrial membrane potential, phosphatidylserine
exposure, and DNA degradation [
211
]. These evidences have been further exploited and extended in a
study showing that nerolidol also inhibited Leishmania amazonensis amastigotes and promastigotes
(with IC50 values between 2.6 and 3.0 M), indicating substantial accumulation of nerolidol in the cell
membrane [
212
]. What is also relevant to this topic are the findings demonstrating the antiparasitic
activity of nerolidol in mice infected with adult stages of Schistosoma mansoni. Authors showed that
nerolidol (100, 200, or 400 mg/kg oral route) inhibited worm burden and egg production, directly
associated with tegumental damage, although nerolidol showed low ecacy in mice harboring juvenile
schistosomes. [
213
]. Substantiating, Baldissera et al. reported that nerolidol-loaded nanospheres
mitigated the Trypanosoma evansi-induced cytotoxic and genotoxic eects in the rodent brain tissue
during infection by upregulating NO levels; thus, preventing DNA damage and cell death [
210
]. Such
results strongly support that nerolidol (a food additive and safe molecule) is an eective antiparasitic
agent and could potentially display anti-inflammatory properties.
Regarding its potential anti-inflammatory and/or immunomodulatory activity, there are a number
of studies using dierent cell-based and rodent models, which here we summarize. A study has
shown that nerolidol blocked LPS-induced acute kidney injury by inhibiting the TLR4/NF-
κ
B signaling
pathway. Specifically, nerolidol markedly prevented the rise of nitrogen and creatinine levels in
LPS-treated rats, and also inhibited the increase of inflammatory mediators, like TNF, IL-1
β
, and
Molecules 2020,25, 1567 17 of 47
NF-
κ
B in LPS-treated NRK-52E cells [
214
]. Further, de Souza et al. demonstrated that nerolidol
nanoencapsulation improved its anti-inflammatory eect on zymosan-induced arthritis in mice.
Importantly, under the conditions assessed the formulation did not demonstrated cytotoxicity in
J774 cell line [
215
]. A study has also shown the immunomodulatory actions of trans-nerolidol
on the ecacy of doxorubicin in breast cancer cells and in a breast tumor mouse model. The
compound increased doxorubicin accumulation into MDA-MB-231 and MCF7 breast cancer cells while
blocked cell migration ability,
in vitro
[
216
]. In addition, nerolidol demonstrated positive eects on
cyclophosphamide (CYP)-induced neuroinflammation, oxidative stress, and cognitive impairment,
as well as prevented structural abnormalities in the hippocampus and cortex regions of rodents [
217
].
The same authors also showed using in silico approach that nerolidol binds into Nrf2 pocket domain—a
key nuclear factor that regulates the expression of antioxidant proteins [
217
], as previously addressed in
this review. In summary, authors concluded that nerolidol could be a prospective therapeutic molecule
that can mitigate CYP-induced neurotoxic signs through regulation of Nrf2 and NF-
κ
B pathway [
217
],
although further studies are needed to confirm this neuroprotective hypothesis. Lastly, cardioprotective
eects have been suggested to this compound by the same research group. They previously evaluated
nerolidol cardioprotective potential as an oral treatment against CYP-induced cardiotoxicity in mice.
Nerolidol inhibited cardiac inflammation, oxidative stress, cardiac apoptosis, and cardiac fibrosis, as
well as ultra-structural changes leading to cardiac dysfunction induced by cyclophosphamide [
218
].
Corroborating, Asaikumar et al. showed that nerolidol inhibited isoproterenol-induced myocardial
damage in rats [
219
]. Here we reviewed the most described and better-explored activities of the
nerolidol, which are antiparasitic, anti-inflammatory and/or immunomodulatory, and cardioprotective.
3.10. Euphol
Euphol is a tetracyclic triterpene usually extracted in alcoholic preparations due to its chemical
structure and therefore anity for this solvent. Even though it is not a major compound of the
Cannabis plant, one could find a few chemically structure similarities in between the euphol molecule
and a couple of cannabinoids derivate, such as CBD and CBN [
220
]. In fact, euphol is the major
compound found in dierent plant species from the Euphorbiaceae family [221], including Euphorbia
resinifera, Euphorbia nerifolia, Euphorbia bivonae, Euphorbia umbellata, and Euphorbia tirucalli. Regarding
the latest cited Euphorbia tirucalli, it is a common plant found in Brazil and by far the most studied
species from the Euphorbia family in concern to its major compound: euphol. Studies on euphol
chemical structure using x-ray crystallographic, Fourier transform-ion cyclotron resonance mass
spectrometry, tandem mass spectrometry, and gas chromatography coupled mass spectrometry,
as well as its quantitative determination in the rat plasma by liquid chromatography-tandem mass
spectrometry allowed a better understanding of this compound chemical and biological behavior [
222
224
].
Importantly, ethnopharmacology evidences have lead and contributed to studies on the anticancer and
anti-inflammatory eects of this triterpene compound, as by many years the plants from this family
have been used as folk phytomedicine to treat tumors and inflammation states [
221
]. Although, limited
studies on antiviral, antiparasitic [
225
,
226
], antimicrobial, and antifungal activities of euphol have
been recently reported. In our point, the most interesting aspect of a recent study is the finding that
euphol can modulate the immune system by inducing cytokine production, namely IL-4, IL-3, and IL-2;
thereby, influencing the Th1/Th2 balance [
227
]. These results could help to explain and support many
of the previous described actions of euphol as an anti-inflammatory compound that will be discussed
later. That being established, the two most described activities of this compound are the antitumor
and the anti-inflammatory. The former is the primary and the most reported activity in the literature,
being described for dierent Euphorbia species as well as cancer cell types while the latter is more recent;
however, better studied in terms of mechanism of action. For instance, Euphorbia tirucalli-derived
euphol beneficial eects against many cancer cell lines was previously tested and described. These
cell lines included tumor cells from breast, head and neck, colon, glioma, prostate, epidermis, lung,
bladder, melanoma, esophagus, ovary, and pancreas. Euphol cytotoxicity eect was observed against
Molecules 2020,25, 1567 18 of 47
all cancer cell lines being very pronounced in this last cited, in which inhibited proliferation, motility,
and colony formation as well [
228
]. Likewise, Euphorbia umbellata-derived euphol exhibited cytotoxic
eects against K-562 leukemia cell line; being suggested that the main mechanism of action was
apoptosis induction [
229
]. Other mechanisms of action proposed to euphol cytotoxic activity against
breast and glioblastoma tumor cell lines included CDK2 downregulation whilst upregulates p21-
and p27-CDK inhibitors and autophagy induction/facilitation, respectively [
230
,
231
]. Despite of its
beneficial anticancer eect, very recently a study has suggested that euphol, along with sitosterol
and lupeol, could cause hepatotoxicity by inducing significant increase in alanine aminotransferase,
aspartate aminotransferase, and total bilirubin levels in rats treated sub-chronically with Euphorbia
bivonae extract [
232
]. That consists of one report showing potential toxic actions of this compound in
one species while there are many other enlightening reports describing its safety and its beneficial
use to treat inflammatory diseases. Reports from a group in the south of Brazil coordinated by
Professor Calixto in the early 2010s have described many of this compound uses towards inflammatory
diseases management, as well as possible mechanisms of action. The earliest report described its
anti-inflammatory actions on a mouse model of colitis, in which this compound inhibited important
inflammatory cytokine production in the colon tissue (e.g., IL-1
β
, MCP-1, TNF, and IL-6); besides, the
inhibition of adhesion molecules (i.e., selectins and integrins) [
233
]. A second study reported that
euphol also inhibits inflammatory mediators and lymphocyte function-associated antigen-1 (LFA-1)
integrin in the CNS, as it did in the periphery. At this time, euphol blocked Th17 myelin-specific cell
migration with an overall benefic eect of reducing the severity and development of EAE, a multiple
sclerosis model [
234
]. Later, it was described its beneficial action in a skin-inflammation mouse
model induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), corroborating early 2000s findings
described by a Japanese group, and further extending the understanding about euphol mechanisms of
action by showing that it inhibits TPA-induced protein kinase C (PKC) isoforms [
235
,
236
]. Later, PKC
inhibition was again implicated in mediating euphol anti-inflammatory eects, as well as CB1R and
CB2R in mouse models of inflammatory (e.g., PGE2-, carrageenan-, and complete Freund’s Adjuvant
(CFA)-induced) and neuropathic (e.g., spared nerve injury (SNI)-, paclitaxel-, and B16F10 melanoma
cells-induced hypersensitivity) pain [
237
,
238
]. Notably, cannabinoid-mediated anti-inflammatory
actions involve suppression of inflammatory cytokines, MAPKs pathway activation, and modulation
of TNF and NF-
κ
B [
220
], all pathways in which euphol has been demonstrated to eective. Euphol has
the potential to be a very attractive anti-inflammatory molecule that works through the cannabinoid
system but evidence shows that it definitely can go beyond that.
3.11. Citral
Citral, (2E)-3,7-dimethylocta-2,6-dienal, is the main compound of essential oils that have been used
mainly in popular medicine in eastern countries. It is the major compound extracted from Cymbopogon
citratus, popularly known as lemongrass, but it can also be extracted from dierent plants including
lemon myrtle and Lindera citriodora [
239
]. This essential oil has been used as ingredient in foods because
of its lemon-like fragrance. However, citral has gained attention in the last years due to its antimicrobial
properties against Cronobacter sakazakii, a foodborne pathogen clinically associated to neonatal infections
such as meningitis, septicemia, and/or necrotizing enteritis [
240
,
241
]. Its reported antimicrobial activity
also extends to Staphylococcus aureus [
242
], Candida albicans [
243
], Enterobacter cloacae [
244
], Listeria
monocytogenes [
245
], Aeromonas spp. [
246
], and Streptococcus pyogenes [
247
]. In this context, Yang and
colleagues recently demonstrated that when combined with cinnamaldehyde, citral changed cecal
microbiota composition of non-vaccinated and vaccinated broiler chickens, reducing the incidence and
severity of necrotic enteritis induced by coccidiosis [
239
]. This is in accordance with another finding,
in which citral was able to aect mouse intestinal microbiota, enhancing the relative abundance of
Lactobacillus [
108
]. From these evidences, it was possible suggest that citral could be an important
molecule for development of new antibiotic and antifungal drugs, especially because until the moment
there is no evidence of relevant toxicity and side eects related to its accumulation in tissues and
Molecules 2020,25, 1567 19 of 47
delayed excretion [
248
]. However, Sharma and co-authors have well highlighted that strategies are
required to increase citral stability, which could facilitate its applications [249].
Citral has also been recognized by its anti-inflammatory actions in animal models of acute lung
injury [
250
], carrageenan-induced paw edema and croton oil-induced ear edema [
251
], segmental
glomerulosclerosis [
252
], pleurisy [
253
], and peritonitis [
254
]. In this context, citral inhibited
LPS-induced myeloperoxidase (MPO) activity, TNF, COX-2, and IL-8 expression, as well as NF-
κ
B
activation via PPAR-
γ
[
254
,
255
]. In accordance, Shen and colleagues demonstrated that GW9662 PPAR-
γ
antagonist reversed the anti-inflammatory response mediated by citral. Additionally, citral showed
antioxidant properties linked to inhibition of Nrf2 pathway early activation, oxidative stress, and
apoptosis [
252
]. More recently, Gonçalves and colleagues demonstrated that citral immunomodulatory
property appears to be related to its ability to modulate CB2R, TLR4 and TLR2/dectin-1, as well
as signaling pathways downstream of CBR and TLRs activation, including ATP-dependent K+
channels [
256
]. The antioxidant activity of this compound was also shown when co-administrated with
aspirin in rat small intestine epithelial cells, in which it regulated superoxide dismutase (SOD) and
glutathione (GSH) enzymes, significantly decreasing the aspirin-induced cell death [
257
]. Importantly,
a link between its antioxidant and antinociceptive activity has been shown in an animal model of
rheumatoid arthritis. Citral has promoted a decrease in oxidative stress parameters and induced
antinociceptive eects through serotonergic communication at spinal the spinal cord level [
227
].
In fact, the citral antinociceptive activity is among the broad variety of beneficial eects already
contemplated in the literature. When combined to other analgesics as naproxen, citral increased their
antinociceptive activity as well significantly inhibited naproxen-induced gastric injury [
258
]. However,
citral showed high volatility, low solubility in water, and consequent low bioavailability, which could
limit its use. One possible solution could be the combination of citral with
β
-cyclodextrin and
hydroxypropyl-
β
-cyclodextrin, which in turn demonstrated antihyperalgesic and anti-inflammatory
activity [
253
]. Here we could suggest that citral should be better investigated in order to identify its
possible clinical application for the treatment of chronic pain conditions, such as peripheral neuropathy,
fibromyalgia, complex regional pain syndrome (CRPS) and lumbar chronic pain.
Beyond, citral attracted scientists’ attention towards its anticancer properties in a variety of cancer
types, such as melanoma [
259
], colon cancer [
260
], and breast cancer [
261
]. Bayala and co-authors
provided evidence about Cymbopogon citratus and Cymbopogon gigantescus essential oil cytotoxic activity,
which have citral as its major component and significantly decreased prostate and glioblastoma
cancer cell survival [
262
]. In addition, citral showed cytotoxic eect in non-tumoral HaCaT and
tumoral A431 cells, inhibiting NO production even at the lowest concentration tested [
263
]. Regarding
the possible mechanisms underlying its antiproliferative eects, it has been reported MARK4 and
a Ser/Thr kinase inhibition. Of note, aberrant expression or dysregulation of these proteins are
linked with cancer development, such as hepatocellular carcinoma, glioma, and metastatic breast
carcinomas [
264
,
265
]. Other mechanisms also comprise apoptosis induction and downregulation of
the aldehyde dehydrogenase activity—a reactive protein overexpressed during cancer progression
and therapy resistance [
266
,
267
]. From this, it was previously suggested that citral could work as
aldehyde dehydrogenase inhibitor, and consequently as adjuvant therapy for treatment of some types
of cancer [
268
]. In order to improve citral solubility and delivery without enhancing toxic eects
in vivo
,
Nordin and colleagues incorporated citral into a nanostructured lipid carrier (NLC) and evaluated its
in vitro
anti-cancer eects. Initially, they showed that NLC as a drug delivery system for citral has the
potential to sustain drug release without inducing any toxicity [
269
]. Then, they showed that NLC-citral
regulated apoptosis, cell cycle, and metastasis signaling, all key signaling pathways related to cancer
development [
261
]. In addition, citral was pointed as a potential eective additive to chemotherapeutic
treatment [
270
,
271
]. Thus, when combined with hyperthermia intraperitoneal chemotherapy (HIPEC)
and pirarubicin for colorectal cancer, citral increased the HIPEC ecacy by enhancing chemo-drug
penetration and consequently its intracellular concentration. Furthermore, it was described a safe
alternative that decreased the chemo-drug dose necessary to induce antiproliferative eect reducing
Molecules 2020,25, 1567 20 of 47
possible side eects [
271
]. Still, this natural compound showed chemoprotective actions in hairless
(HRS/J) mice exposed to UVB irradiation for 24 weeks, a model of skin carcinogenesis. Mechanisms
involved in citral chemoprotective eect not surprisingly included oxidative stress and inflammatory
cytokines inhibition and increased skin cell apoptosis [
272
]. It has been previously described that citral
mediated antiproliferative eects through p53activation, ROS- and mitochondrial-mediated apoptosis,
as well as by NO depletion and interference with cell proliferation-related signaling pathways [
259
,
260
].
Collectively, these set of data here gathered suggests that citral represents an important molecule for
the management of dierent types of cancer and highlights the possibility of translational application
as a novel treatment alone or in combination with other chemotherapeutic drugs.
3.12. Celastrol
Celastrol, 2R,4aS,6aR,6aS,14aS,14bR-10-hydroxy-2,4a,6a,6a,9,14a-hexamethyl-11-oxo-1,3,4,5,6,1
3,14, 14b-octahydropicene-2-carboxylic acid, is a pentacyclic triterpenoid isolated from Tripterygium
wilfordii root extracts and used in traditional Chinese medicine for treatment of chronic diseases,
including neurodegenerative disorders (e.g., amyotrophic lateral sclerosis, AD, and PD), type 2
diabetes, obesity, atherosclerosis, cancer, inflammatory and autoimmune diseases (e.g., systemic lupus
erythematosus, multiple sclerosis, inflammatory bowel disease (IBD), psoriasis, and rheumatoid
arthritis (RA) [
273
275
]. In fact, this natural compound has been cited in a wide variety of reports
describing its antioxidant [
276
,
277
], and anti-inflammatory action [
278
,
279
] through inhibition of NF-
κ
B
signaling pathway [
280
]. In details, this last study demonstrated that celastrol significantly blocked
COX-2 expression, IL-8 and ICAM-1, as well as IL-1
β
-induced PGE2 through inhibition of NF-
κ
B
in a Graves’ ophthalmopathy model using orbital fibroblasts [
281
]. Here are a few more examples
of this extent literature about celastrol anti-inflammatory eects. Kim and co-authors demonstrated
that celastrol inhibited LPS-stimulated NO generation, PGE2, iNOS, and COX-2, in RAW264
·
7 cells.
In this same study, authors have reported that celastrol inhibited LPS-induced inflammatory cytokines
production and also protected mice from TPA-induced ear edema by inhibiting MPO activity and the
production of inflammatory mediators [
278
]. In addition, celastrol inhibited CFA-induced arthritis
rat model via modulation of i) inflammatory cytokines (i.e., IL-17, IL-6, and IFN-
γ
) in response to
the disease-related antigens, ii) IL-6/IL-17-related transcription factor STAT3, iii) cyclic citrullinated-
and Bhsp65-peptides directed antibodies, and iv) MMP-9 and phospho-ERK activity, supporting the
use of celastrol as an adjunct (along with conventional drugs) or alternative approach for the RA
treatment [
279
]. Aside from the anti-inflammatory eect, also relevant are the findings demonstrating
celastrol antitumor activity in a variety of human tumor cell types. Data previously suggested that
celastrol represents a promising agent for the management of human tumor cell lines, such as triple
negative breast cancer [
282
], leukemia [
283
,
284
], carcinoma [
285
] and lung cancer [
286
]. In terms
of mechanisms, a study based on pharmacological and biochemical approaches has shown that
celastrol inhibited cell proliferation and induce apoptosis through JNK activation, AKT suppression,
and anti-apoptotic proteins downregulation [287].
Celastrol potential beneficial eects on the CNS have also been previously reported. Kiaei et al.
described that celastrol improved weight loss, motor performance, and delayed the onset of motor
neuron degeneration in the G93A SOD1 transgenic amyotrophic lateral sclerosis (ALS) mouse model.
Celastrol increased HSP70 while mitigated iNOS, TNF, cluster of dierentiation 40 (CD40), and GFAP
proteins expression in the lumbar spinal cord of G93A mice [
288
]. Celastrol eects on HSPs have
also been reported to play a key neuroprotective role in defense against misfolded proteins and
aggregation-prone proteins [
289
]. Speaking of protein aggregation, celastrol was reported to inhibit
amyloid beta aggregation, the main toxin to be accounted for AD initiation and progression [
276
,
281
].
Based on these facts, we could suggest that celastrol might represent a useful molecule to treat
neurodegenerative diseases with an inflammatory background. In spite of that, celastrol use is still
limited by its low water solubility, reduced oral bioavailability, and side eects reducing its therapeutic
Molecules 2020,25, 1567 21 of 47
potential [
290
]. Dierent structure modifications or encapsulation solutions must be studied to
overcome this problem.
3.13. Falcarinol
Falcarinol—(3R,9Z)-heptadeca-1,9-dien-4,6-diyn-3-ol)—also named panaxynol or carotatoxin is
found in carrots, parsley, celery, and Panax ginseng [
291
]. This natural compound has been cited in
a wide variety of reports describing its antineoplastic [
292
] and anti-inflammatory properties [
293
].
Besides, falcarinol has been also investigated as pharmacological tool for treatment of cardiovascular
and metabolic diseases. Regarding the latter, it is know that serum high molecular weight (HMW)
adiponectin values are inversely correlated with the presence of metabolic syndrome, and consequently
linked to pathogenesis of insulin resistance, type 2 diabetes, and cardiovascular diseases [
294
]. In this
sense, Takagi and colleagues demonstrated that falcarinol restored FoxO1 and increased C/EBP
α
levels (transcription factors that positively regulate adiponectin gene transcription), resulting in HMW
adiponectin secretion by 3T3-L1 adipocytes treated with palmitic acid, an obesity model
in vitro
[
295
].
In addition, falcarinol also reduced endoplasmic reticulum (ER) stress, C/EBP homologous protein
(CHOP) protein and ROS levels, as well as decreased inflammatory adipokine-induced MCP-1 [
295
].
Still in this scenario, the association of chronic inflammatory disorders and/or systemic diseases to
microbiota dysbiosis has been gaining attention [
296
]. Importantly, a study previously showed that
the beneficial eects of falcarinol and falcarindiol rely on its ability of changing the composition of
low abundant gut-microbiota members. In this study, the ability of falcarinol to regulate microbiota
was allied to its ability to reduce the incidence of neoplastic lesions [
292
]. In this cancer scenario,
the mucosa-associated bacterial population as the fecal microbiota plays an important role in colon
carcinogenesis, the second most commonly diagnosed cancer with high incidence, morbidity, and
mortality [
296
,
297
]. That being established, Kobaek-Larson and co-authors have reported that
daily diet supplementation with falcarinol and falcarindiol decreased the number of neoplastic
lesions and polyps growth rate in the colon of azoxymethane-treated rats [
298
]. Recently, this same
group demonstrated the chemopreventive eect of a special diet supplemented with falcarinol and
falcarindiol on colorectal precancerous lesions in a dose-dependent manner; besides, this eect
was mainly mediated by inhibition of NF-
κ
B and its downstream inflammatory markers, especially
COX-2 [
299
]. Anticarcinogenic properties of falcarinol were also demonstrated in cancer stem-like
cells (CSCs), in which it played an essential role in tumor occurrence, evolution, metastasis, recurrence,
and therapeutic resistance [
300
], as well as in non-small cell lung cancer (NSCLC) [
301
]. Essentially,
falcarinol eliminated CSC population in NSCLC and abolished lung tumor formation in mice via HSP90
(a molecular chaperone of numerous oncoproteins) modulation [
302
]. Falcarinol anticancer activity
also extends to leukemia [
303
], breast cancer [
304
], hepatocarcinoma [
305
], renal carcinoma [
306
],
and glioma [
307
]. For instance, mechanisms pointed to explain its ability to induce cell cycle arrest, thus,
its anticarcinogenic properties on human promyelocytic leukemia cell growth are PKC
δ
proteolytic
cleavage, caspase-3 activation, and PARP degradation [303].
In a dierent context, falcarinol has been also reported to be a facilitator of type 1 hypersensitivity
and atopic dermatitis [
308
]. On the other hand, Leonti and colleagues showed that falcarinol is
not an allergen itself; however, it facilitates sensitization by other allergens, since it aggravated
histamine-induced edema reactions in skin prick tests. In this study, similar eects were obtained with
Rimonabant
®
(a CB1R inverse antagonist), implying that falcarinol-induced dermatitis could be related
to CB1R antagonism in keratinocytes [
291
]. Despite that falcarinol has been related to allergic reactions,
it has also been shown to induce anti-inflammatory responses in a couple of dierent models. Falcarinol
promoted a reduced cell infiltration in a LPS-induced reduction in intestinal barrier context [
293
].
In addition, falcarinol was able to induce Nrf2-mediated resolution of inflamed macrophage-induced
cardiomyocyte hypertrophy [
309
]. Collectively, data here presented provided information about
falcarinol crucial positive eects on pathological conditions, such as metabolic diseases, cardiovascular
Molecules 2020,25, 1567 22 of 47
diseases, and cancer. However, we consider that for the development of possible therapeutic tools
underlying mechanisms as well as toxicity, and bioavailability needs be better investigated.
3.14. Salvinorin A
The trans-neoclerodane diterpenoid salvinorin A is a short-acting highly-selective kappa
opioid receptor agonist and consequently the primary psychoactive component of Salvia divinorum
(psychoactive herb used in magic-ritual contexts by Mazateca Indians in Mexico) [
310
]. In agreement,
eight healthy hallucinogen-using adults exposed to inhalation of 16 doses of Salvia divinorum showed
dose-related dissociative eects and impairments in recall/recognition memory tests [311]. Given the
fact that salvinorin A highly interacts with opioid receptors, it has been considered an emerging target
for next-generation of analgesics. In addition, salvinorin A showed hallucinogen eects similarly to
lysergic acid diethylamide (LSD) [
312
,
313
]. Walentiny and colleagues demonstrated that salvinorin
A administration induced pronounced hypolocomotion and antinociception (and to a lesser extent,
hypothermia) eects in the tetrad assay, which were reverted by the administration of kappa opioid
receptor (KOR) selective antagonist but not by CB1R antagonist Rimonabant
®
[
310
]. Moreover, rats
exposed to sciatic nerve ligature neuropathic pain model and treated with salvinorin A directly
in the insular cortex showed antinociceptive behavior. However, in contrast with Walentiny and
colleagues, the analgesic eect of salvinorin A in this case was reverted by selective KOR and CB1R
antagonists [
314
]. In accordance with this finding, daily treatment with salvinorin A significantly
decreased formalin-induced mechanical allodynia at days three and seven in a KOR and CB1R
dependent manner, without inducing CB1R-related adverse eects. Electrophysiological experiments
in vivo
also showed that repeated salvinorin A treatment completely normalized neuronal activity
following formalin injection, as well as it reduced formalin-evoked glial and microglial activation at the
spinal cord level [
315
]. Nonetheless, unlike other opioid ligands, salvinorin A showed short duration of
action and centrally mediated side-eects limiting its usefulness [
316
318
], justifying the development
of new salvinorin A analogues [
319
]. In this context, novel analogue
β
-tetrahydropyran salvinorin B
attenuated acute nociceptive and inflammatory pain, as well as mechanical and cold allodynia in the
PTX-induced neuropathic pain model [
319
]. On the other hand, mesyl salvinorin B (a KOR agonist)
showed moderated antinociceptive eect when compared to salvinorin A in warm-water (50
C)
tail withdrawal and intraplantar formaldehyde (2%) tests. However, it mitigated cocaine-induced
hyperactivity and behavioral sensitization, without aecting aversion, sedation, anxiety, or learning and
memory impairment in rats [
320
]. Additionally, mesyl salvinorin B alone or associated with naltrexone
prevented alcohol-induced deprivation eect in mice [
321
], which could represent an alternative tool
for treatment of alcoholism in humans. Other salvinorin A analogues, such as p38, could also be
eective for the treatment of gastrointestinal inflammation, since it demonstrated anti-inflammatory
and analgesic eects in an experimental model of colitis [
322
]. Thus, these findings support the use
of novel salvinorin A-like compounds and its analogues as possible pharmacological alternatives for
pain relief, control of cocaine-seeking behavior, and alcoholism, as it seems to have potent CNS and
anti-inflammatory actions.
Regarding these actions, the anti-inflammatory eects associated with salvinorin A also extend to
cerebral hypoxia/ischemia [
323
326
]. Salvinorin A attenuated brain edema and inhibited neuronal death
in hippocampal CA1 region, cortex, and striatum during forebrain ischemia model [
325
]. According to
Dong and colleagues, rats submitted to middle cerebral artery occlusion and treated with salvinorin A
one hour after reperfusion showed improvement of neurological severity score when compared to
control groups. Additionally, salvinorin A reduced infarct volume and eectively protected cerebral
vessels after ischemia/reperfusion. Importantly, human brain microvascular endothelial cells exposed
to the oxygen glucose deprivation model and treated with salvinorin A were protected against ROS
damage and decreased mitochondrial function (i.e., mitochondrial morphological changes and loss
of membrane potential). The latter, highly regulated by AMPK and phosphorylation mitofusin-2
expression, both upregulated in response to salvinorin A treatment [
327
]. Salvinorin A also mitigated
Molecules 2020,25, 1567 23 of 47
cerebral vasospasm through endothelial nitric oxide synthase (eNOS) and NO upregulation and ET-1
downregulation. At the same time, salvinorin A inhibited AQP4 protein expression—a member
of a family of channel proteins that facilitate water transport and contribute to brain edema and
neuro-disorders development [
326
,
328
]. Concerning still its actions in the CNS, salvinorin A eects
on the mood were also investigated and linked to anxiolytic and antidepressant properties mediated
by KOR, as well as the ECS [
329
]. In lieu of antidepressant properties, another study associated
salvinorin A to depressive-like eects through dopamine signaling inhibition in the nucleus accumbens
of rats [
330
]. Extending, dysphoria as well as depressant-like eects of salvinorin A were attributed to
KOR-linked ERK activation, which in turn promoted dopamine transporter (DAT) phosphorylation,
modulating dopamine neurotransmission [
331
]. Recently, Keasling and colleagues evaluated the eects
of salvinolin, a new semisynthetic analog of salvinorin A, with mu opioid receptor anity. In summary,
salvinolin demonstrated good oral bioavailability and showed antidepressant-like eect that was
blocked by the selective 5HT
1A
antagonist WAY100635 [
332
]. Another derivative of salvinorin A,
the 22-azido salvinorin A, also promoted an antidepressant-like eect linked to its ability of inhibiting
monoamine oxidase (MAO) enzyme, as well as to its anity for
α
1A,
α
1B,
α
1D adrenergic receptors
beyond KOR [
333
]. Here, we could sense the staggering eects of salvinorin A and its analogues to
modulate a variety of neurotransmission systems in the CNS.
The pharmacological eects of salvinorin A are not limited to CNS but also related to the respiratory
system. Salvinorin A inhibited mast cell degranulation in the lung and consequently blocked airway
hyperactivity induced by ovalbumin sensitization. Thus, the authors suggested that salvinorin A
could represent a promising tool for the treatment of type 1 hypersensitivity and immune-mediated
diseases [
334
]. Moreover, salvinorin A inhibited leukotriene production in inflammatory exudates,
as well as it showed antipruritic eects mediated by KOR on compound 48/80-induced scratching
behaviors in mice [
335
]. Findings here summarized provide evidence about the anti-inflammatory
action of salvinorin A, and highlight this natural compound as a possible new tool for the treatment of
inflammatory diseases.
3.15. Pristimerin
Pristimerin (20
α
-3-hydroxy-2-oxo-24-nor-friedela-1-10,3,5,7-tetraene-carboxylic acid-29-methyl
ester) is a natural quinonoid triterpene isolated from the shrub families Celastraceae and Hippocrateaceae.
It is a natural compound with cannabimimetic eects without direct interacting with CBR. For instance,
pristimerin inhibited MAGL with high potency through a reversible mechanism [
336
]. It has been
extensively investigated mainly by its inhibitory activity against cancer cell growth. Pristimerin
inhibited Wnt/
β
-catenin signaling via GSK3
β
activation and Wnt gene suppression in colorectal
cancer cells [
337
]. In addition, Yousef and colleagues demonstrated pristimerin anticancer activity on
colon tumor cells associated to NF-
κ
B signaling inhibition during the carcinogenic process [
338
,
339
].
Corroborating, this triterpenoid has also been shown to attenuated colitis-associated colon cancer by
modulating NF-
κ
B positive cells, as well as AKT/FOXO3a signaling pathway [
340
]. The transcription
factor FOXO3 represents important target for cellular homeostasis, since it was able to regulate
apoptosis, proliferation, cell cycle progression, and consequently tumorigenesis [
341
,
342
]. Pristimerin
was also previously demonstrated to downregulate the PI3K/AKT/mTOR pathway playing a critical
cytotoxic and anti-metastatic role in the progression of HCT-116 colorectal cancer cells
in vitro
and
in vivo
[
343
]. Finally, another study from Yousef and co-authors suggest that pristimerin downregulates
phospho-EGF and -EGRF2 and its downstream signaling pathways, which represent a key mechanism
involved in the proliferation of cancer malignant phenotypes [344,345].
The antiproliferative activity of pristimerin goes beyond colon-related cancers, it is extended
to breast [
346
350
], melanomas [
351
], osteosarcoma [
352
], pancreatic [
353
,
354
], and prostate
cancers [
355
358
]. Herein, we describe a few examples focusing on articles that have demonstrated
potential mechanisms of action. Pristimerin anticancer activity against breast cancer cells was
associated to ROS production and ASK1/JNK signaling pathway activation [
346
], as well as AKT
Molecules 2020,25, 1567 24 of 47
signaling suppression [
349
,
359
]. Additionally, when combined to paclitaxel, pristimerin induced cell
autophagy through inhibition of ERK1/2/p90RSK signaling—involved in cancer cell proliferation,
dierentiation, and migration [
347
,
360
]. Pristimerin-induced glioma overgrowth was dependent on
AGO2 upregulation (a critical protein for tumorigenesis) and PTPN1 downregulation (a metabolism
regulator oncogene reported to be aberrantly expressed in cancer cells) [
361
363
]. Furthermore,
pristimerin induced glioma cell necrosis by promoting mitochondrial dysfunction, c-Jun activation,
and consequently ROS overproduction [
364
]. It also inhibited the epidermal growth factor receptor
(EGFR) protein expression during glioma cancer development [
365
,
366
]. Antiproliferative eects
of pristimerin were investigated in oral squamous cell carcinoma cell lines as well. In this way,
pristimerin showed more potent antiproliferative activity than chemotherapy drugs cisplatin and
5-fluorouracil. This eect was associated with inhibition of MAPK1/2 and PKB signaling pathways [
367
].
Pristimerin-induced apoptosis activity was also demonstrated in ovarian cancer cells via inhibition of
AKT/NF-
κ
B/mTOR signaling pathway [
368
]. Besides, few articles have reported pristimerin beneficial
eects on prostate cancer. Its progression was reported to be prevented by pristimerin-induced inhibition
on HIF-1
α
and SPHK-1, which stimulates dierent cellular processes including cell proliferation,
cell survival, and angiogenesis [
355
,
369
]. Pristimerin also induced apoptosis of prostate cancer cells
through activation of mitochondrial apoptotic pathway [
358
], ubiquitin-proteasomal degradation [
357
],
and inhibition of proteasomal chymotrypsin-like activity (a complex associated with cell proliferation,
apoptosis, and cancer progression) [
370
,
371
]. These summarized findings provide evidences regarding
pristimerin antiproliferative and cytotoxic activity as well as clinical benefits for treatment of dierent
types of cancer.
Finally, yet importantly, Tong and co-authors showed that pristimerin inhibited arthritic and
cartilage inflammation, as well as bone damage in the joints of rats submitted to adjuvant arthritis.
Pristimerin inhibited inflammatory cytokines and pSTAT3 and ROR-
γ
t transcription factors, as well
as Th17/Treg ratio favoring immune suppression [
372
]. In addition, anti-inflammatory properties of
pristimerin included inhibition of inflammatory cytokine levels (e.g., IL-6, IL-17, IL-18, and IL-23),
increase IL-10 expression, and mitigate NF-
κ
B and MAPK signaling, showed during rheumatoid
arthritis model and murine macrophages exposed to LPS [
373
]. In this sense, pristimerin seems able to
interact with essential targets of the inflammatory and/or immune-mediated processes; and for this
reason, it should further investigated regarding its potential ability to serve as a treatment of disorders
related to the imbalance in the immune system, including autoimmune diseases.
4. Conclusions
The reports here highlighted showed the complex and varied pharmacology of Cannabis
sativa, particularly phytocannabinoids—typical terpenophenolic compounds—as well as plenty
of non-cannabinoids second metabolites, such as monoterpene, sesquiterpene, and stilbenoids.
Interestingly enough, there are an increasing number of studies on cannabimimetic ligands beyond the
Cannabis plant, which can act as CBR agonists or antagonist, or ECS enzyme inhibitors. They are mainly
terpenes including
β
-caryophyllene, D-limonene, terpineol,
β
-elemene, euphol, pristimerin, citral, and
many others (Figure 3), which can play a key role in the modulation of dierent pathological conditions.
Molecules 2020,25, 1567 25 of 47
Molecules 2020, 5, x 25 of 46
Figure 3. Role of Cannabis sativa compounds in diseases. The Cannabis sativa compounds have been
proved useful for treatment of different diseases in the periphery and the CNS, as illustrated above.
The CBD and THC actions in the CNS include immunomodulatory, neuroprotective, anxiolytic, and
anticonvulsant, in addition to its potential effects on PD and multiple sclerosis control. Anticancer
effects can be attributed to almost all Cannabis sativa compounds. This figure further illustrates the
effect of terpenoids, cannabimimetic ligands, beyond the Cannabis plant in different pathological
conditions, such as Herpes infection, diabetic retinopathy, psoriasis, asthma, AD, seizures, ischemic
stroke, and others. Figure created using the Mind the Graph platform.
Herein, we describe that many of them share common properties, namely anti-inflammatory,
analgesic, immunomodulatory, antiproliferative, and neuromodulatory. More specifically, the
majority of these compounds seem to be acting on the same targets even though if in different
pathological contexts (Table 3). We highlight the NF-κB, Nfr2, PPAR, COX-2, and CDKs proteins,
just to name a few. Although there are many published preclinical studies demonstrating the
beneficial effects of terpenes, there is an urge for detailed pharmacokinetic and pharmacodynamics
characterization of these compounds. As the cannabinoids and the Cannabis plant appear to be the
most recent great hope for the treatment of uncured diseases, the particular
phytocannabinoid–terpenoid interaction—the so-called entourage effect—must be continuously
investigated. Besides, clinical studies are sorely needed to confirm its efficacy and safety in humans;
thus, we could finally have novel potential treatments for a number of diseases that for the time
being remain poorly managed.
Table 3. The main findings about terpenoid compounds reviewed in the article.
Compound Main Findings
β- and α-Caryophyllene Antidepressant, anxiolytic, analgesic, anticonvulsant properties.
Acetylcholinesterase (AChE) inhibitor.
D-Limonene Anti-inflammatory, antinociceptive, gastroprotective, and
neuroprotective effects.
Figure 3.
Role of Cannabis sativa compounds in diseases. The Cannabis sativa compounds have been
proved useful for treatment of dierent diseases in the periphery and the CNS, as illustrated above.
The CBD and THC actions in the CNS include immunomodulatory, neuroprotective, anxiolytic, and
anticonvulsant, in addition to its potential eects on PD and multiple sclerosis control. Anticancer
eects can be attributed to almost all Cannabis sativa compounds. This figure further illustrates the eect
of terpenoids, cannabimimetic ligands, beyond the Cannabis plant in dierent pathological conditions,
such as Herpes infection, diabetic retinopathy, psoriasis, asthma, AD, seizures, ischemic stroke, and
others. Figure created using the Mind the Graph platform.
Herein, we describe that many of them share common properties, namely anti-inflammatory,
analgesic, immunomodulatory, antiproliferative, and neuromodulatory. More specifically, the majority
of these compounds seem to be acting on the same targets even though if in dierent pathological
contexts (Table 3). We highlight the NF-
κ
B, Nfr2, PPAR, COX-2, and CDKs proteins, just to name a
few. Although there are many published preclinical studies demonstrating the beneficial eects of
terpenes, there is an urge for detailed pharmacokinetic and pharmacodynamics characterization of
these compounds. As the cannabinoids and the Cannabis plant appear to be the most recent great hope
for the treatment of uncured diseases, the particular phytocannabinoid–terpenoid interaction—the
so-called entourage eect—must be continuously investigated. Besides, clinical studies are sorely
needed to confirm its ecacy and safety in humans; thus, we could finally have novel potential
treatments for a number of diseases that for the time being remain poorly managed.
Molecules 2020,25, 1567 26 of 47
Table 3. The main findings about terpenoid compounds reviewed in the article.
Compound Main Findings
β- and α-Caryophyllene Antidepressant, anxiolytic, analgesic, anticonvulsant properties.
Acetylcholinesterase (AChE) inhibitor.
D-Limonene Anti-inflammatory, antinociceptive, gastroprotective, and
neuroprotective eects.
Linalool
Anxiolytic, anticancer properties; neuroprotective eects against AD.
Terpineol
Analgesic activity in chronic pain conditions, such as fibromyalgia
and cancer pain. Adjunctive therapy to morphine adopted in order
to reduce its adverse eects. Preventive treatment for opioid
analgesic dependence and tolerance.
Terpinene Analgesic, antiproliferative, anti-inflammatory, and
antimicrobial properties.
α-Pinene
Sedative, hypnotic, anti-seizure, anxiolytic, anticancer, and analgesic
activities. Neuroprotective eects against memory loss.
β-Pinene Antiviral, antifungal, anticancer, antimalarial,
antidepressant properties.
β-Elemene Anticancer and hypolipidemic compound. Potential treatment for
demyelinating disease.
β-Ocimene Antiproliferative, antifungal, and anticonvulsant properties.
Camphene Eco-friendly botanical insecticide.
Nerolidol Anti-inflammatory, anticancer, neuroprotective and
antimicrobial eects.
Euphol Antiviral, antiparasitic, antimicrobial, and antifungal activities.
Citral Antimicrobial, anti-inflammatory, antinociceptive, and
anticancer properties.
Celastrol Anti-inflammatory and anticancer compound.
Falcarinol Possible tool for treatment of cardiovascular diseases.
Anticarcinogenic compound.
Salvinorin A
Psychoactive herb; anxiolytic, anti-inflammatory, and antidepressant
eects. Alternative treatment for control of cocaine-seeking behavior
and alcoholism. Promising tool for treatment of type 1
hypersensitivity.
Pristimerin MGL inhibitor; anticancer and anti-metastatic eects.
AD, Alzheimer’s disease; MGL, monoacylglycerol lipase.
Author Contributions:
Conceptualization, E.C.D.G., G.M.B., M.A.B., R.S.P., R.C.D.; Writing original draft
preparation, E.C.D.G., G.M.B., M.A.B., R.S.P., R.C.D.; Review and Editing, M.A.B., E.C.D.G., G.M.B., R.C., R.C.D.
All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments:
The authors would like to thank the Laboratory of Autoimmunity and Immunopharmacology
(LAIF) team member’s—Universidade Federal de Santa Catarina—Graduate Program of Neuroscience, who have
assisted with the literature analysis. R.C.D. is recipient of a research productivity fellowship supported by the
Brazilian funding agency CNPq.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
AC: Adenylyl Cyclase; AChE, Acetylcholinesterase; AFB1, Aflatoxin B1; Ago2, Argonaute 2; ALS, Amyotrophic
lateral sclerosis; AMPK, AMP-activated protein kinase; apoE, Apolipoprotein E; A
β
, Amyloid-beta; BAX, BCL2
associated X protein; BCL2, B-cell lymphoma 2 protein; CD40, Cluster of dierentiation 40; CHOP, C/EBP
Molecules 2020,25, 1567 27 of 47
Homologous Protein; COX, Cyclooxygenase; COX-2, Cyclooxygenase-2; CNS, Central nervous system; CYP,
Cyclophosphamide; DAT-1, Dopamine transporter; EAE, Experimental autoimmune encephalomyelitis; EGFR,
Epidermal growth factor receptor; eNOS, Endothelial nitric oxide synthase; ET-1, Endothelin-1; FOXO3, Forkhead
box O3; GABA, Gamma-aminobutyric acid; GPR18, G protein-coupled receptor 18; GPR55, G protein-coupled
receptor 55; GPR119, G protein-coupled receptor 19; GSH, Glutathione; GSK-3
β
, Glycogen synthase kinase-3 beta;
HIF-1
α
, Hypoxia-inducible factor – 1alpha; HMW, High molecular weight; HO1, Heme oxygenase-1; Hsp90,
Heat shock protein 90; HSPs, Heat-shock proteins; i.p., Intraperitoneal; IBD, Inflammatory bowel disease; IFN-
γ
,
Interferon-gamma; IgE, Immunoglobulin E; IL-1
β
, Interleukin -1
β
; IL-2, Interleukin – 2; IL-3, Interleukin – 3;
IL-4, Interleukin – 4; IL-6, Interleukin – 6; IL-8, Interleukin – 8; IL-10, Interleukin – 10; IL-12, Interleukin –
12; IL-17, Interleukin – 17; IL-37, Interleukin – 37; iNOS, Inducible nitric oxide synthase; LFA-1, Lymphocyte
function-associated antigen-1; LPS, Lipopolysaccharide; LOX, Lipoxygenase; LTP, Long term potentiation; MAO,
Monoamine oxidase; MAPK, Mitogen-activated protein kinase; MARK4, Microtubule Anity-Regulating Kinase
4; MCP-1, Monocyte chemoattractant protein-1; MMP-9, Matrix metallopeptidase – 9; MnSOD, Manganese
superoxide dismutase; MPO, Myeloperoxidase; mTOR, Mammalian target of rapamycin; NF-
κ
B, Nuclear factor
kappa B; NO, Nitric oxide; NREMS, Non-rapid eye movement sleep; p90RSK, 90 kDa ribosomal S6 kinase;
PARP, Poly ADP-ribose polymerase; PGE2, Prostaglandin E2; PI3K, Phosphoinositide 3-kinase; PKB, Protein
kinase B; PKC, Protein kinase C; PPAR, Peroxisome proliferator-activated receptors; PPAR-
γ
, Peroxisome
proliferator-activated receptor gamma; pSTAT3, Phosphorylated STAT3; PTX, Paclitaxel; PTZ, Pentylenetetrazole;
RA, Rheumatoid arthritis; ROR-
γ
t, Retinoid-related orphan receptor-
γ
t; ROS, Reactive oxygen species; SNI,
Spared nerve injury; SOD1, Superoxide dismutase – 1; SPHK1, Sphingosinekinase 1; Th1, T helper 1; Th2, T
helper 2; TLR4, Toll-Like Receptor 4; TPA, 12-O-tetradecanoylphorbol-13-acetate; TRPM8, Transient receptor
potential melastatin 8; TRP, Transient receptor potential; TRPV1, Transient receptor potential vanilloid 1; TRPV4,
Transient receptor potential vanilloid 4; TNF, Tumor necrosis factor; UVA, Ultraviolet A radiation; VEGF, Vascular
endothelial growth factor.
References
1.
Di Marzo, V.; Bifulco, M.; De Petrocellis, L. The endocannabinoid system and its therapeutic exploitation.
Nat. Reviews. Drug Discov. 2004,3, 771–784. [CrossRef] [PubMed]
2. Rubin, V. Cannabis and Culture; Mouton: The Hague, The Netherlands, 1975.
3.
Guy, G.W.; Whittle, B.A.; Robson, P. The Medicinal Uses of Cannabis and Cannabinoids; Pharmaceutical Press:
London, UK, 2004.
4.
Pacher, P.; Batkai, S.; Kunos, G. The endocannabinoid system as an emerging target of pharmacotherapy.
Pharmacol. Rev. 2006,58, 389–462. [CrossRef] [PubMed]
5.
Russell, C.; Rueda, S.; Room, R.; Tyndall, M.; Fischer, B. Routes of administration for cannabis use—Basic
prevalence and related health outcomes: A scoping review and synthesis. Int. J. Drug Policy
2018
,52, 87–96.
[CrossRef] [PubMed]
6.
Azofeifa, A.; Mattson, M.E.; Schauer, G.; McAfee, T.; Grant, A.; Lyerla, R. National Estimates of Marijuana
Use and Related Indicators—National Survey on Drug Use and Health, United States, 2002–2014. Morb.
Mortal. Wkly. Rep. Surveill. Summ. 2016,65, 1–28. [CrossRef] [PubMed]
7.
Degenhardt, L.; Ferrari, A.J.; Calabria, B.; Hall, W.D.; Norman, R.E.; McGrath, J.; Flaxman, A.D.; Engell, R.E.;
Freedman, G.D.; Whiteford, H.A.; et al. The global epidemiology and contribution of cannabis use and
dependence to the global burden of disease: Results from the GBD 2010 study. PLoS ONE
2013
,8, e76635.
[CrossRef]
8.
Hasin, D.S.; Saha, T.D.; Kerridge, B.T.; Goldstein, R.B.; Chou, S.P.; Zhang, H.; Jung, J.; Pickering, R.P.;
Ruan, W.J.; Smith, S.M.; et al. Prevalence of Marijuana Use Disorders in the United States between 2001–2002
and 2012–2013. JAMA Psychiatry 2015,72, 1235–1242. [CrossRef]
9.
Hasin, D.S.; Sarvet, A.L.; Cerda, M.; Keyes, K.M.; Stohl, M.; Galea, S.; Wall, M.M. US Adult Illicit Cannabis
Use, Cannabis Use Disorder, and Medical Marijuana Laws: 1991–1992 to 2012–2013. JAMA Psychiatry
2017
,
74, 579–588. [CrossRef]
10.
Han, B.; Compton, W.M.; Blanco, C.; Jones, C.M. Trends in and correlates of medical marijuana use among
adults in the United States. Drug Alcohol Depend. 2018,186, 120–129. [CrossRef]
11.
Han, B.; Compton, W.M.; Jones, C.M.; Blanco, C. Cannabis Use and Cannabis Use Disorders among Youth in
the United States, 2002–2014. J. Clin. Psychiatry 2017,78, 1404–1413. [CrossRef]
12.
Hill, K.P. Cannabis Use and Risk for Substance Use Disorders and Mood or Anxiety Disorders. JAMA
2017
,
317, 1070–1071. [CrossRef]
Molecules 2020,25, 1567 28 of 47
13.
Belackova, V.; Stefunkova, M. Interpreting the Czech drug decriminalization: The glass is half full—Response
to Cerveny, J., Chomynova, P., Mravcik, V., & van Ours, J.C. (2017). Cannabis decriminalization and the age
of onset of cannabis use. Int. J. Drug Policy 2018,52, 102–105. [PubMed]
14.
Belackova, V.; Wilkins, C. Consumer agency in cannabis supply—Exploring auto-regulatory documents of
the cannabis social clubs in Spain. Int. J. Drug Policy 2018,54, 26–34. [CrossRef] [PubMed]
15.
Room, R. Legalizing a market for cannabis for pleasure: Colorado, Washington, Uruguay and beyond.
Addiction 2014,109, 345–351. [CrossRef] [PubMed]
16.
Room, R. Cannabis legalization and public health: Legal niceties, commercialization and countercultures.
Addiction 2014,109, 358–359. [CrossRef]
17. Wilkinson, S.T.; D’Souza, D.C. Problems with the medicalization of marijuana. JAMA 2014,311, 2377–2378.
[CrossRef]
18.
Devane, W.A.; Dysarz, F.A., 3rd; Johnson, M.R.; Melvin, L.S.; Howlett, A.C. Determination and
characterization of a cannabinoid receptor in rat brain. Mol. Pharmacol. 1988,34, 605–613.
19.
Matsuda, L.A.; Lolait, S.J.; Brownstein, M.J.; Young, A.C.; Bonner, T.I. Structure of a cannabinoid receptor
and functional expression of the cloned cDNA. Nature 1990,346, 561–564. [CrossRef]
20.
ElSohly, M.A.; Radwan, M.M.; Gul, W.; Chandra, S.; Galal, A. Phytochemistry of Cannabis sativa L. Prog.
Chem. Org. Nat. Prod. 2017,103, 1–36.
21.
Russo, E.; Guy, G.W. A tale of two cannabinoids: The therapeutic rationale for combining
tetrahydrocannabinol and cannabidiol. Med. Hypotheses 2006,66, 234–246. [CrossRef]
22.
Esposito, G.; Scuderi, C.; Valenza, M.; Togna, G.I.; Latina, V.; De Filippis, D.; Cipriano, M.; Carratu, M.R.;
Iuvone, T.; Steardo, L. Cannabidiol reduces Abeta-induced neuroinflammation and promotes hippocampal
neurogenesis through PPARgamma involvement. PLoS ONE 2011,6, e28668. [CrossRef]
23.
Martin-Moreno, A.M.; Reigada, D.; Ramirez, B.G.; Mechoulam, R.; Innamorato, N.; Cuadrado, A.; de
Ceballos, M.L. Cannabidiol and other cannabinoids reduce microglial activation
in vitro
and
in vivo
:
Relevance to Alzheimer’s disease. Mol. Pharmacol. 2011,79, 964–973. [CrossRef] [PubMed]
24.
Mecha, M.; Torrao, A.S.; Mestre, L.; Carrillo-Salinas, F.J.; Mechoulam, R.; Guaza, C. Cannabidiol protects
oligodendrocyte progenitor cells from inflammation-induced apoptosis by attenuating endoplasmic reticulum
stress. Cell Death Dis. 2012,3, e331. [CrossRef] [PubMed]
25.
Shannon, S.; Opila-Lehman, J. Eectiveness of Cannabidiol Oil for Pediatric Anxiety and Insomnia as Part of
Posttraumatic Stress Disorder: A Case Report. Perm. J. 2016,20, 16-005. [CrossRef] [PubMed]
26.
Marinho, A.L.; Vila-Verde, C.; Fogaca, M.V.; Guimaraes, F.S. Eects of intra-infralimbic prefrontal cortex
injections of cannabidiol in the modulation of emotional behaviors in rats: Contribution of 5HT(1)A receptors
and stressful experiences. Behav. Brain Res. 2015,286, 49–56. [CrossRef] [PubMed]
27.
Jadoon, K.A.; Ratclie, S.H.; Barrett, D.A.; Thomas, E.L.; Stott, C.; Bell, J.D.; O’Sullivan, S.E.; Tan, G.D. Ecacy
and Safety of Cannabidiol and Tetrahydrocannabivarin on Glycemic and Lipid Parameters in Patients With
Type 2 Diabetes: A Randomized, Double-Blind, Placebo-Controlled, Parallel Group Pilot Study. Diabetes Care
2016,39, 1777–1786. [CrossRef] [PubMed]
28.
Dhital, S.; Stokes, J.V.; Park, N.; Seo, K.S.; Kaplan, B.L. Cannabidiol (CBD) induces functional Tregs in
response to low-level T cell activation. Cell. Immunol. 2017,312, 25–34. [CrossRef]
29.
Krohn, R.M.; Parsons, S.A.; Fichna, J.; Patel, K.D.; Yates, R.M.; Sharkey, K.A.; Storr, M.A. Abnormal
cannabidiol attenuates experimental colitis in mice, promotes wound healing and inhibits neutrophil
recruitment. J. Inflamm. 2016,13, 21. [CrossRef]
30.
Norris, C.; Loureiro, M.; Kramar, C.; Zunder, J.; Renard, J.; Rushlow, W.; Laviolette, S.R. Cannabidiol
Modulates Fear Memory Formation through Interactions with Serotonergic Transmission in the Mesolimbic
System. Neuropsychopharmacol. O. Publ. Am. Coll. Neuropsychopharmacol. 2016,41, 2839–2850. [CrossRef]
31.
Genaro, K.; Fabris, D.; Arantes, A.L.F.; Zuardi, A.W.; Crippa, J.A.S.; Prado, W.A. Cannabidiol Is a Potential
Therapeutic for the Aective-Motivational Dimension of Incision Pain in Rats. Front. Pharmacol.
2017
,8, 391.
[CrossRef]
32.
Harris, H.M.; Sufka, K.J.; Gul, W.; ElSohly, M.A. Eects of Delta-9-Tetrahydrocannabinol and Cannabidiol on
Cisplatin-Induced Neuropathy in Mice. Planta Med. 2016,82, 1169–1172. [CrossRef]
33.
Peres, F.F.; Levin, R.; Suiama, M.A.; Diana, M.C.; Gouvea, D.A.; Almeida, V.; Santos, C.M.; Lungato, L.;
Zuardi, A.W.; Hallak, J.E.; et al. Cannabidiol Prevents Motor and Cognitive Impairments Induced by
Reserpine in Rats. Front. Pharmacol. 2016,7, 343. [CrossRef] [PubMed]
Molecules 2020,25, 1567 29 of 47
34.
Peres, F.F.; Diana, M.C.; Suiama, M.A.; Justi, V.; Almeida, V.; Bressan, R.A.; Zuardi, A.W.; Hallak, J.E.;
Crippa, J.A.; Abilio, V.C. Peripubertal treatment with cannabidiol prevents the emergence of psychosis in an
animal model of schizophrenia. Schizophr. Res. 2016,172, 220–221. [CrossRef] [PubMed]
35.
Renard, J.; Loureiro, M.; Rosen, L.G.; Zunder, J.; de Oliveira, C.; Schmid, S.; Rushlow, W.J.; Laviolette, S.R.
Cannabidiol Counteracts Amphetamine-Induced Neuronal and Behavioral Sensitization of the Mesolimbic
Dopamine Pathway through a Novel mTOR/p70S6 Kinase Signaling Pathway. J. Neurosci. O. J. Soc. Neurosci.
2016,36, 5160–5169. [CrossRef] [PubMed]
36.
Devinsky, O.; Cross, J.H.; Wright, S. Trial of Cannabidiol for Drug-Resistant Seizures in the Dravet Syndrome.
N. Engl. J. Med. 2017,377, 699–700. [CrossRef] [PubMed]
37.
Hosseinzadeh, M.; Nikseresht, S.; Khodagholi, F.; Naderi, N.; Maghsoudi, N. Cannabidiol Post-Treatment
Alleviates Rat Epileptic-Related Behaviors and Activates Hippocampal Cell Autophagy Pathway Along
with Antioxidant Defense in Chronic Phase of Pilocarpine-Induced Seizure. J. Mol. Neurosci. MN
2016
,58,
432–440. [CrossRef] [PubMed]
38.
Kaplan, E.H.; Oermann, E.A.; Sievers, J.W.; Comi, A.M. Cannabidiol Treatment for Refractory Seizures in
Sturge-Weber Syndrome. Pediatr. Neurol. 2017,71, 18–23 e2. [CrossRef] [PubMed]
39.
Patel, R.R.; Barbosa, C.; Brustovetsky, T.; Brustovetsky, N.; Cummins, T.R. Aberrant epilepsy-associated
mutant Nav1.6 sodium channel activity can be targeted with cannabidiol. Brain J. Neurol.
2016
,139 Pt 8,
2164–2181. [CrossRef]
40.
Ibsen, M.S.; Connor, M.; Glass, M. Cannabinoid CB1 and CB2 Receptor Signaling and Bias. Cannabis
Cannabinoid Res. 2017,2, 48–60. [CrossRef]
41.
McHugh, D.; Page, J.; Dunn, E.; Bradshaw, H.B. Delta(9) -Tetrahydrocannabinol and N-arachidonyl glycine
are full agonists at GPR18 receptors and induce migration in human endometrial HEC-1B cells. Br. J. Pharmacol.
2012,165, 2414–2424. [CrossRef]
42.
Pertwee, R.G.; Howlett, A.C.; Abood, M.E.; Alexander, S.P.; Di Marzo, V.; Elphick, M.R.; Greasley, P.J.;
Hansen, H.S.; Kunos, G.; Mackie, K.; et al. International Union of Basic and Clinical Pharmacology. LXXIX.
Cannabinoid receptors and their ligands: Beyond CB(1) and CB(2). Pharmacol. Rev.
2010
,62, 588–631.
[CrossRef]
43.
Davis, K.D.; Flor, H.; Greely, H.T.; Iannetti, G.D.; Mackey, S.; Ploner, M.; Pustilnik, A.; Tracey, I.; Treede, R.D.;
Wager, T.D. Brain imaging tests for chronic pain: Medical, legal and ethical issues and recommendations.
Nat. Rev. Neurol. 2017,13, 624–638. [CrossRef] [PubMed]
44.
Howlett, A.C.; Barth, F.; Bonner, T.I.; Cabral, G.; Casellas, P.; Devane, W.A.; Felder, C.C.; Herkenham, M.;
Mackie, K.; Martin, B.R.; et al. International Union of Pharmacology. XXVII. Classification of cannabinoid
receptors. Pharmacol. Rev. 2002,54, 161–202. [CrossRef] [PubMed]
45.
Ashton, J.C.; Glass, M. The cannabinoid CB2 receptor as a target for inflammation-dependent
neurodegeneration. Curr. Neuropharmacol. 2007,5, 73–80. [CrossRef] [PubMed]
46.
Rom, S.; Persidsky, Y. Cannabinoid receptor 2: Potential role in immunomodulation and neuroinflammation.
J. Neuroimmune Pharmacol. O. J. Soc. Neuroimmune Pharmacol. 2013,8, 608–620. [CrossRef]
47.
Pertwee, R.G. The pharmacology of cannabinoid receptors and their ligands: An overview. Int. J. Obes.
2006
,
30 (Suppl. 1), S13–S18. [CrossRef]
48.
Pertwee, R.G. Pharmacological actions of cannabinoids. Handb. Exp. Pharmacol.
2005
,168, 1–51. [CrossRef]
49.
Devane, W.A.; Hanus, L.; Breuer, A.; Pertwee, R.G.; Stevenson, L.A.; Grin, G.; Gibson, D.; Mandelbaum, A.;
Etinger, A.; Mechoulam, R. Isolation and structure of a brain constituent that binds to the cannabinoid
receptor. Science 1992,258, 1946–1949. [CrossRef]
50.
Mechoulam, R.; Ben-Shabat, S.; Hanus, L.; Ligumsky, M.; Kaminski, N.E.; Schatz, A.R.; Gopher, A.; Almog, S.;
Martin, B.R.; Compton, D.R.; et al. Identification of an endogenous 2-monoglyceride, present in canine gut,
that binds to cannabinoid receptors. Biochem. Pharmacol. 1995,50, 83–90. [CrossRef]
51.
Sugiura, T.; Kondo, S.; Sukagawa, A.; Nakane, S.; Shinoda, A.; Itoh, K.; Yamashita, A.; Waku, K.
2-Arachidonoylglycerol: A possible endogenous cannabinoid receptor ligand in brain. Biochem. Biophys. Res.
Commun. 1995,215, 89–97. [CrossRef]
52.
Pertwee, R.G. Receptors and channels targeted by synthetic cannabinoid receptor agonists and antagonists.
Curr. Med. Chem. 2010,17, 1360–1381. [CrossRef]
53.
Goncalves, E.D.; Dutra, R.C. Cannabinoid receptors as therapeutic targets for autoimmune diseases: Where
do we stand? Drug Discov. Today 2019,24, 1845–1853. [CrossRef] [PubMed]
Molecules 2020,25, 1567 30 of 47
54.
Di Iorio, G.; Lupi, M.; Sarchione, F.; Matarazzo, I.; Santacroce, R.; Petruccelli, F.; Martinotti, G.; Di
Giannantonio, M. The endocannabinoid system: A putative role in neurodegenerative diseases. Int. J. High
Risk Behav. Addict. 2013,2, 100–106. [CrossRef] [PubMed]
55.
Wolf, S.A.; Tauber, S.; Ullrich, O. CNS immune surveillance and neuroinflammation: Endocannabinoids
keep control. Curr. Pharm. Des. 2008,14, 2266–2278. [CrossRef] [PubMed]
56.
Cabral, G.A.; Ferreira, G.A.; Jamerson, M.J. Endocannabinoids and the Immune System in Health and
Disease. Handb. Exp. Pharmacol. 2015,231, 185–211. [PubMed]
57.
De Laurentiis, A.; Araujo, H.A.; Rettori, V. Role of the endocannabinoid system in the neuroendocrine
responses to inflammation. Curr. Pharm. Des. 2014,20, 4697–4706. [CrossRef]
58.
Pacher, P.; Steens, S.; Hasko, G.; Schindler, T.H.; Kunos, G. Cardiovascular eects of marijuana and synthetic
cannabinoids: The good, the bad, and the ugly. Nat. Re. Cardiol. 2018,15, 151–166. [CrossRef]
59.
Ashton, J.C.; Smith, P.F. Cannabinoids and cardiovascular disease: The outlook for clinical treatments.
Curr. Vasc. Pharmacol. 2007,5, 175–185. [CrossRef]
60. Ho, W.S.V.; Kelly, M.E.M. Cannabinoids in the Cardiovascular System. Adv. Pharmacol. 2017,80, 329–366.
61.
Wol, V.; Jouanjus, E. Strokes are possible complications of cannabinoids use. Epilepsy Behav. EB
2017
,70 Pt
B, 355–363. [CrossRef]
62.
Singh, A.; Saluja, S.; Kumar, A.; Agrawal, S.; Thind, M.; Nanda, S.; Shirani, J. Cardiovascular Complications
of Marijuana and Related Substances: A Review. Cardiol. Ther. 2018,7, 45–59. [CrossRef]
63.
Lu, Y.; Anderson, H.D. Cannabinoid signaling in health and disease. Can. J. Physiol. Pharmacol.
2017
,95,
311–327. [CrossRef] [PubMed]
64.
Huestis, M.A.; Boyd, S.J.; Heishman, S.J.; Preston, K.L.; Bonnet, D.; Le Fur, G.; Gorelick, D.A. Single
and multiple doses of rimonabant antagonize acute eects of smoked cannabis in male cannabis users.
Psychopharmacology 2007,194, 505–515. [CrossRef] [PubMed]
65.
Kumar, A.; Premoli, M.; Aria, F.; Bonini, S.A.; Maccarinelli, G.; Gianoncelli, A.; Memo, M.; Mastinu, A.
Cannabimimetic plants: Are they new cannabinoidergic modulators? Planta
2019
,249, 1681–1694. [CrossRef]
[PubMed]
66.
Solymosi, K.; Kofalvi, A. Cannabis: A Treasure Trove or Pandora’s Box? Mini Rev. Med. Chem.
2017
,17,
1223–1291. [CrossRef] [PubMed]
67.
Morales, P.; Hurst, D.P.; Reggio, P.H. Molecular Targets of the Phytocannabinoids: A Complex Picture. Prog.
Chem. Org. Nat. Prod. 2017,103, 103–131.
68.
Campos, A.C.; Fogaca, M.V.; Sonego, A.B.; Guimaraes, F.S. Cannabidiol, neuroprotection and neuropsychiatric
disorders. Pharmacol. Res. 2016,112, 119–127. [CrossRef]
69.
Crivelaro do Nascimento, G.; Ferrari, D.P.; Guimaraes, F.S.; Del Bel, E.A.; Bortolanza, M.; Ferreira-Junior, N.C.
Cannabidiol increases the nociceptive threshold in a preclinical model of Parkinson’s disease.
Neuropharmacology 2020,163, 107808. [CrossRef]
70.
Mammana, S.; Cavalli, E.; Gugliandolo, A.; Silvestro, S.; Pollastro, F.; Bramanti, P.; Mazzon, E. Could the
Combination of Two Non-Psychotropic Cannabinoids Counteract Neuroinflammation? Eectiveness of
Cannabidiol Associated with Cannabigerol. Medicina 2019,55, 747. [CrossRef]
71.
Russo, E.B.; Marcu, J. Cannabis Pharmacology: The Usual Suspects and a Few Promising Leads.
Adv. Pharmacol. 2017,80, 67–134.
72.
Borrelli, F.; Pagano, E.; Romano, B.; Panzera, S.; Maiello, F.; Coppola, D.; De Petrocellis, L.; Buono, L.;
Orlando, P.; Izzo, A.A. Colon carcinogenesis is inhibited by the TRPM8 antagonist cannabigerol,
a Cannabis-derived non-psychotropic cannabinoid. Carcinogenesis 2014,35, 2787–2797. [CrossRef]
73.
Udoh, M.; Santiago, M.; Devenish, S.; McGregor, I.S.; Connor, M. Cannabichromene is a cannabinoid CB2
receptor agonist. Br. J. Pharmacol. 2019,176, 4537–4547. [CrossRef] [PubMed]
74.
Wilkinson, J.D.; Williamson, E.M. Cannabinoids inhibit human keratinocyte proliferation through a
non-CB1/CB2 mechanism and have a potential therapeutic value in the treatment of psoriasis. J. Dermatol. Sci.
2007,45, 87–92. [CrossRef] [PubMed]
75.
Al-Ghezi, Z.Z.; Miranda, K.; Nagarkatti, M.; Nagarkatti, P.S. Combination of Cannabinoids, Delta9-
Tetrahydrocannabinol and Cannabidiol, Ameliorates Experimental Multiple Sclerosis by Suppressing
Neuroinflammation Through Regulation of miRNA-Mediated Signaling Pathways. Front. Immunol.
2019
,10, 1921.
[CrossRef] [PubMed]
Molecules 2020,25, 1567 31 of 47
76.
Haupts, M.; Vila, C.; Jonas, A.; Witte, K.; Alvarez-Ossorio, L. Influence of Previous Failed Antispasticity
Therapy on the Ecacy and Tolerability of THC:CBD Oromucosal Spray for Multiple Sclerosis Spasticity.
Eur. Neurol. 2016,75, 236–243. [CrossRef] [PubMed]
77.
Laprairie, R.B.; Bagher, A.M.; Kelly, M.E.; Denovan-Wright, E.M. Cannabidiol is a negative allosteric
modulator of the cannabinoid CB1 receptor. Br. J. Pharmacol. 2015,172, 4790–4805. [CrossRef] [PubMed]
78.
Blasco-Benito, S.; Seijo-Vila, M.; Caro-Villalobos, M.; Tundidor, I.; Andradas, C.; Garcia-Taboada, E.; Wade, J.;
Smith, S.; Guzman, M.; Perez-Gomez, E.; et al. Appraising the “entourage eect”: Antitumor action of a pure
cannabinoid versus a botanical drug preparation in preclinical models of breast cancer. Biochem. Pharmacol.
2018,157, 285–293. [CrossRef] [PubMed]
79.
Russo, E.B. The Case for the Entourage Eect and Conventional Breeding of Clinical Cannabis: No “Strain,”
No Gain. Front. Plant Sci. 2018,9, 1969. [CrossRef]
80.
Felipe, C.F.B.; Albuquerque, A.M.S.; de Pontes, J.L.X.; de Melo, J.I.V.; Rodrigues, T.; de Sousa, A.M.P.;
Monteiro, A.B.; Ribeiro, A.; Lopes, J.P.; de Menezes, I.R.A.; et al. Comparative study of alpha- and
beta-pinene eect on PTZ-induced convulsions in mice. Fundam. Clin. Pharmacol.
2019
,33, 181–190.
[CrossRef]
81.
Zamyad, M.; Abbasnejad, M.; Esmaeili-Mahani, S.; Mostafavi, A.; Sheibani, V. The anticonvulsant eects of
Ducrosia anethifolia (Boiss) essential oil are produced by its main component alpha-pinene in rats. Arq. De
Neuro-Psiquiatr. 2019,77, 106–114. [CrossRef]
82.
Khoshnazar, M.; Bigdeli, M.R.; Parvardeh, S.; Pouriran, R. Attenuating eect of alpha-pinene on
neurobehavioural deficit, oxidative damage and inflammatory response following focal ischaemic stroke in
rat. J. Pharm. Pharmacol. 2019,71, 1725–1733. [CrossRef]
83.
Zhao, Y.; Chen, R.; Wang, Y.; Yang, Y. alpha-Pinene Inhibits Human Prostate Cancer Growth in a Mouse
Xenograft Model. Chemotherapy 2018,63, 1–7. [CrossRef] [PubMed]
84.
Araujo-Filho, H.G.; Pereira, E.W.M.; Rezende, M.M.; Menezes, P.P.; Araujo, A.A.S.; Barreto, R.S.S.; Martins, A.;
Albuquerque, T.R.; Silva, B.A.F.; Alcantara, I.S.; et al. D-limonene exhibits superior antihyperalgesic eects
in a beta-cyclodextrin-complexed form in chronic musculoskeletal pain reducing Fos protein expression on
spinal cord in mice. Neuroscience 2017,358, 158–169. [CrossRef] [PubMed]
85.
Booth, J.K.; Page, J.E.; Bohlmann, J. Terpene synthases from Cannabis sativa. PLoS ONE
2017
,12, e0173911.
[CrossRef] [PubMed]
86.
Naz, S.; Hanif, M.A.; Ansari, T.M.; Al-Sabahi, J.N. A Comparative Study on Hemp (Cannabis sativa) Essential
Oil Extraction Using Traditional and Advanced Techniques. Guang Pu Xue Yu Guang Pu Fen Xi =Guang Pu
2017,37, 306–311.
87.
Fidyt, K.; Fiedorowicz, A.; Strzadala, L.; Szumny, A. beta-caryophyllene and beta-caryophyllene oxide-natural
compounds of anticancer and analgesic properties. Cancer Med. 2016,5, 3007–3017. [CrossRef]
88.
Sabulal, B.; Dan, M.; J, A.J.; Kurup, R.; Pradeep, N.S.; Valsamma, R.K.; George, V. Caryophyllene-rich
rhizome oil of Zingiber nimmonii from South India: Chemical characterization and antimicrobial activity.
Phytochemistry 2006,67, 2469–2473. [CrossRef]
89.
Su, Y.C.; Ho, C.L. Composition of the Leaf Essential Oil of Phoebe formosana from Taiwan and its
in vitro
Cytotoxic, Antibacterial, and Antifungal Activities. Nat. Prod. Commun. 2016,11, 845–848. [CrossRef]
90.
Sarvmeili, N.; Jafarian-Dehkordi, A.; Zolfaghari, B. Cytotoxic eects of Pinus eldarica essential oil and
extracts on HeLa and MCF-7 cell lines. Res. Pharm. Sci. 2016,11, 476–483.
91.
Memariani, T.; Hosseini, T.; Kamali, H.; Mohammadi, A.; Ghorbani, M.; Shakeri, A.; Spandidos, D.A.;
Tsatsakis, A.M.; Shahsavand, S. Evaluation of the cytotoxic eects of Cyperus longus extract, fractions and
its essential oil on the PC3 and MCF7 cancer cell lines. Oncol. Lett. 2016,11, 1353–1360. [CrossRef]
92.
Segat, G.C.; Manjavachi, M.N.; Matias, D.O.; Passos, G.F.; Freitas, C.S.; Costa, R.; Calixto, J.B. Antiallodynic
eect of beta-caryophyllene on paclitaxel-induced peripheral neuropathy in mice. Neuropharmacology 2017,
125, 207–219. [CrossRef]
93.
Bento, A.F.; Marcon, R.; Dutra, R.C.; Claudino, R.F.; Cola, M.; Leite, D.F.; Calixto, J.B. beta-Caryophyllene
inhibits dextran sulfate sodium-induced colitis in mice through CB2 receptor activation and PPARgamma
pathway. Am. J. Pathol. 2011,178, 1153–1166. [CrossRef] [PubMed]
94.
Gertsch, J.; Leonti, M.; Raduner, S.; Racz, I.; Chen, J.Z.; Xie, X.Q.; Altmann, K.H.; Karsak, M.; Zimmer, A.
Beta-caryophyllene is a dietary cannabinoid. Proc. Natl. Acad. Sci. USA
2008
,105, 9099–9104. [CrossRef]
[PubMed]
Molecules 2020,25, 1567 32 of 47
95.
Alberti, T.B.; Marcon, R.; Bicca, M.A.; Raposo, N.R.; Calixto, J.B.; Dutra, R.C. Essential oil from Pterodon
emarginatus seeds ameliorates experimental autoimmune encephalomyelitis by modulating Th1/Treg cell
balance. J. Ethnopharmacol. 2014,155, 485–494. [CrossRef]
96.
Alberti, T.B.; Barbosa, W.L.; Vieira, J.L.; Raposo, N.R.; Dutra, R.C. (-)-beta-Caryophyllene, a CB2
Receptor-Selective Phytocannabinoid, Suppresses Motor Paralysis and Neuroinflammation in a Murine
Model of Multiple Sclerosis. Int. J. Mol. Sci. 2017,18, 691. [CrossRef] [PubMed]
97.
Fernandes, E.S.; Passos, G.F.; Medeiros, R.; da Cunha, F.M.; Ferreira, J.; Campos, M.M.; Pianowski, L.F.;
Calixto, J.B. Anti-inflammatory eects of compounds alpha-humulene and (
)-trans-caryophyllene isolated
from the essential oil of Cordia verbenacea. Eur. J. Pharmacol. 2007,569, 228–236. [CrossRef]
98.
Ojha, S.; Javed, H.; Azimullah, S.; Haque, M.E. beta-Caryophyllene, a phytocannabinoid attenuates oxidative
stress, neuroinflammation, glial activation, and salvages dopaminergic neurons in a rat model of Parkinson
disease. Mol. Cell. Biochem. 2016,418, 59–70. [CrossRef]
99.
Sut, S.; Maggi, F.; Nicoletti, M.; Baldan, V.; Dall Acqua, S. New Drugs from Old Natural Compounds: Scarcely
Investigated Sesquiterpenes as New Possible Therapeutic Agents. Curr. Med. Chem.
2018
,25, 1241–1258.
[CrossRef]
100.
Santiago, M.; Sachdev, S.; Arnold, J.C.; McGregor, I.S.; Connor, M. Absence of Entourage: Terpenoids
Commonly Found in Cannabis sativa Do Not Modulate the Functional Activity of Delta(9)-THC at Human
CB1 and CB2 Receptors. Cannabis Cannabinoid Res. 2019,4, 165–176. [CrossRef]
101. Sun, J. D-Limonene: Safety and clinical applications. Altern. Med. Rev. J. Clin. Ther. 2007,12, 259–264.
102.
Shah, B.B.; Baksi, R.; Chaudagar, K.K.; Nivsarkar, M.; Mehta, A.A. Anti-leukemic and anti-angiogenic eects
of d-Limonene on K562-implanted C57BL/6 mice and the chick chorioallantoic membrane model. Anim.
Models Exp. Med. 2018,1, 328–333. [CrossRef]
103.
d’Alessio, P.A.; Ostan, R.; Bisson, J.F.; Schulzke, J.D.; Ursini, M.V.; Bene, M.C. Oral administration
of d-limonene controls inflammation in rat colitis and displays anti-inflammatory properties as diet
supplementation in humans. Life Sci. 2013,92, 1151–1156. [CrossRef] [PubMed]
104.
Shin, M.; Liu, Q.F.; Choi, B.; Shin, C.; Lee, B.; Yuan, C.; Song, Y.J.; Yun, H.S.; Lee, I.S.; Koo, B.S.; et al.
Neuroprotective eects of limonene (+) against Abeta42-induced neurotoxicity in a Drosophila model of
Alzheimer’s disease. Biol. Pharm. Bull. 2019. [CrossRef]
105.
de Almeida, A.A.; Silva, R.O.; Nicolau, L.A.; de Brito, T.V.; de Sousa, D.P.; Barbosa, A.L.; de
Freitas, R.M.; Lopes, L.D.; Medeiros, J.R.; Ferreira, P.M. Physio-pharmacological Investigations About
the Anti-inflammatory and Antinociceptive Ecacy of (+)-Limonene Epoxide. Inflammation
2017
,40, 511–522.
[CrossRef] [PubMed]
106.
Rozza, A.L.; Moraes Tde, M.; Kushima, H.; Tanimoto, A.; Marques, M.O.; Bauab, T.M.; Hiruma-Lima, C.A.;
Pellizzon, C.H. Gastroprotective mechanisms of Citrus lemon (Rutaceae) essential oil and its majority
compounds limonene and beta-pinene: Involvement of heat-shock protein-70, vasoactive intestinal peptide,
glutathione, sulfhydryl compounds, nitric oxide and prostaglandin E(2). Chem. Biol. Interact.
2011
,189,
82–89.
107.
de Souza, M.C.; Vieira, A.J.; Beserra, F.P.; Pellizzon, C.H.; Nobrega, R.H.; Rozza, A.L. Gastroprotective eect
of limonene in rats: Influence on oxidative stress, inflammation and gene expression. Phytomed. Int. J.
Phytother. Phytopharm. 2019,53, 37–42. [CrossRef]
108.
Wang, L.; Zhang, Y.; Fan, G.; Ren, J.N.; Zhang, L.L.; Pan, S.Y. Eects of orange essential oil on intestinal
microflora in mice. J. Sci. Food Agric. 2019,99, 4019–4028. [CrossRef]
109.
do Amaral, J.F.; Silva, M.I.; Neto, M.R.; Neto, P.F.; Moura, B.A.; de Melo, C.T.; de Araujo, F.L.; de Sousa, D.P.;
de Vasconcelos, P.F.; de Vasconcelos, S.M.; et al. Antinociceptive eect of the monoterpene R-(+)-limonene in
mice. Biol. Pharm. Bull. 2007,30, 1217–1220. [CrossRef]
110.
Piccinelli, A.C.; Santos, J.A.; Konkiewitz, E.C.; Oesterreich, S.A.; Formagio, A.S.; Croda, J.; Zi, E.B.;
Kassuya, C.A. Antihyperalgesic and antidepressive actions of (R)-(+)-limonene, alpha-phellandrene, and
essential oil from Schinus terebinthifolius fruits in a neuropathic pain model. Nutr. Neurosci.
2015
,18,
217–224. [CrossRef]
111.
Smeriglio, A.; Alloisio, S.; Raimondo, F.M.; Denaro, M.; Xiao, J.; Cornara, L.; Trombetta, D. Essential oil of
Citrus lumia Risso: Phytochemical profile, antioxidant properties and activity on the central nervous system.
Food Chem. Toxicol. Int. J. Publ. Br. Ind. Biol. Res. Assoc. 2018,119, 407–416. [CrossRef]
Molecules 2020,25, 1567 33 of 47
112.
Zhang, Y.; Wang, J.; Cao, X.; Liu, W.; Yu, H.; Ye, L. High-level production of linalool by engineered
Saccharomyces cerevisiae harboring dual mevalonate pathways in mitochondria and cytoplasm. Enzym.
Microb. Technol. 2020,134, 109462. [CrossRef]
113.
Kim, M.G.; Kim, S.M.; Min, J.H.; Kwon, O.K.; Park, M.H.; Park, J.W.; Ahn, H.I.; Hwang, J.Y.; Oh, S.R.;
Lee, J.W.; et al. Anti-inflammatory eects of linalool on ovalbumin-induced pulmonary inflammation.
Int. Immunopharmacol. 2019,74, 105706. [CrossRef] [PubMed]
114.
Sabogal-Guaqueta, A.M.; Hobbie, F.; Keerthi, A.; Oun, A.; Kortholt, A.; Boddeke, E.; Dolga, A. Linalool
attenuates oxidative stress and mitochondrial dysfunction mediated by glutamate and NMDA toxicity.
Biomed. Pharmacother. 2019,118, 109295. [CrossRef] [PubMed]
115.
Harada, H.; Kashiwadani, H.; Kanmura, Y.; Kuwaki, T. Linalool Odor-Induced Anxiolytic Eects in Mice.
Front. Behav. Neurosci. 2018,12, 241. [CrossRef] [PubMed]
116.
Xu, P.; Wang, K.; Lu, C.; Dong, L.; Gao, L.; Yan, M.; Aibai, S.; Yang, Y.; Liu, X. Protective eects of linalool
against amyloid beta-induced cognitive deficits and damages in mice. Life Sci.
2017
,174, 21–27. [CrossRef]
[PubMed]
117.
Iwasaki, K.; Zheng, Y.W.; Murata, S.; Ito, H.; Nakayama, K.; Kurokawa, T.; Sano, N.; Nowatari, T.;
Villareal, M.O.; Nagano, Y.N.; et al. Anticancer eect of linalool via cancer-specific hydroxyl radical
generation in human colon cancer. World J. Gastroenterol. 2016,22, 9765–9774. [CrossRef]
118.
Gunaseelan, S.; Balupillai, A.; Govindasamy, K.; Muthusamy, G.; Ramasamy, K.; Shanmugam, M.; Prasad, N.R.
The preventive eect of linalool on acute and chronic UVB-mediated skin carcinogenesis in Swiss albino
mice. Photochem. Photobiol. Sci. O. J. Eur. Photochem. Assoc. Eur. Soc. Photobiol.
2016
,15, 851–860. [CrossRef]
119.
Katsuyama, S.; Kuwahata, H.; Yagi, T.; Kishikawa, Y.; Komatsu, T.; Sakurada, T.; Nakamura, H. Intraplantar
injection of linalool reduces paclitaxel-induced acute pain in mice. Biomed. Res.
2012
,33, 175–181. [CrossRef]
120.
Ibrahim, E.A.; Wang, M.; Radwan, M.M.; Wanas, A.S.; Majumdar, C.G.; Avula, B.; Wang, Y.H.; Khan, I.A.;
Chandra, S.; Lata, H.; et al. Analysis of Terpenes in Cannabis sativa L. Using GC/MS: Method Development,
Validation, and Application. Planta Med. 2019,85, 431–438. [CrossRef]
121.
Oliveira, M.G.; Brito, R.G.; Santos, P.L.; Araujo-Filho, H.G.; Quintans, J.S.; Menezes, P.P.; Serafini, M.R.;
Carvalho, Y.M.; Silva, J.C.; Almeida, J.R.; et al. alpha-Terpineol, a monoterpene alcohol, complexed with
beta-cyclodextrin exerts antihyperalgesic eect in animal model for fibromyalgia aided with docking study.
Chem. Biol. Interact. 2016,254, 54–62. [CrossRef]
122.
Kumar Chaudhari, A.; Singh, A.; Kumar Singh, V.; Kumar Dwivedy, A.; Das, S.; Grace Ramsdam, M.;
Dkhar, M.S.; Kayang, H.; Kishore Dubey, N. Assessment of chitosan biopolymer encapsulated alpha-Terpineol
against fungal, aflatoxin B1 (AFB1) and free radicals mediated deterioration of stored maize and possible
mode of action. Food Chem. 2020,311, 126010. [CrossRef]
123.
de Oliveira, M.G.; Marques, R.B.; de Santana, M.F.; Santos, A.B.; Brito, F.A.; Barreto, E.O.; De Sousa, D.P.;
Almeida, F.R.; Badaue-Passos, D., Jr.; Antoniolli, A.R.; et al. alpha-terpineol reduces mechanical
hypernociception and inflammatory response. Basic Clin. Pharmacol. Toxicol. 2012,111, 120–125. [PubMed]
124.
Dos Santos Negreiros, P.; da Costa, D.S.; da Silva, V.G.; de Carvalho Lima, I.B.; Nunes, D.B.; de Melo
Sousa, F.B.; de Souza Lopes Araujo, T.; Medeiros, J.V.R.; Dos Santos, R.F.; de Cassia Meneses Oliveira, R.
Antidiarrheal activity of alpha-terpineol in mice. Biomed. Pharmacother.
2019
,110, 631–640. [CrossRef]
[PubMed]
125.
Gouveia, D.N.; Costa, J.S.; Oliveira, M.A.; Rabelo, T.K.; Silva, A.; Carvalho, A.A.; Miguel-Dos-Santos, R.;
Lauton-Santos, S.; Scotti, L.; Scotti, M.T.; et al. alpha-Terpineol reduces cancer pain via modulation of
oxidative stress and inhibition of iNOS. Biomed. Pharmacother. 2018,105, 652–661. [CrossRef] [PubMed]
126.
Parvardeh, S.; Moghimi, M.; Eslami, P.; Masoudi, A. alpha-Terpineol attenuates morphine-induced physical
dependence and tolerance in mice: Role of nitric oxide. Iran. J. Basic Med Sci. 2016,19, 201–208. [PubMed]
127.
Moghimi, M.; Parvardeh, S.; Zanjani, T.M.; Ghafghazi, S. Protective eect of alpha-terpineol against
impairment of hippocampal synaptic plasticity and spatial memory following transient cerebral ischemia in
rats. Iran. J. Basic Med Sci. 2016,19, 960–969. [PubMed]
128.
Kim, K.; Bu, Y.; Jeong, S.; Lim, J.; Kwon, Y.; Cha, D.S.; Kim, J.; Jeon, S.; Eun, J.; Jeon, H. Memory-enhancing
eect of a supercritical carbon dioxide fluid extract of the needles of Abies koreana on scopolamine-induced
amnesia in mice. Biosci. Biotechnol. Biochem. 2006,70, 1821–1826. [CrossRef]