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European Journal of Internal Medicine
journal homepage: www.elsevier.com/locate/ejim
Review Article
The therapeutic potential of targeting the peripheral endocannabinoid/CB
1
receptor system
Joseph Tam
⁎
, Liad Hinden, Adi Drori, Shiran Udi, Shahar Azar, Saja Baraghithy
Obesity and Metabolism Laboratory, Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 9112001, Israel
ARTICLE INFO
Keywords:
Endocannabinoids
CB
1
receptor
Obesity
NAFLD
Chronic kidney disease
Bone remodeling
ABSTRACT
Endocannabinoids (eCBs) are internal lipid mediators recognized by the cannabinoid-1 and -2 receptors (CB
1
R
and CB
2
R, respectively), which also mediate the different physiological effects of marijuana. The en-
docannabinoid system, consisting of eCBs, their receptors, and the enzymes involved in their biosynthesis and
degradation, is present in a vast number of peripheral organs. In this review we describe the role of the eCB/
CB
1
R system in modulating the metabolism in several peripheral organs. We assess how eCBs, via activating the
CB
1
R, contribute to obesity and regulate food intake. In addition, we describe their roles in modulating liver and
kidney functions, as well as bone remodeling and mass. Special importance is given to emphasizing the efficacy
of the recently developed peripherally restricted CB
1
R antagonists, which were pre-clinically tested in the
management of energy homeostasis, and in ameliorating both obesity- and diabetes-induced metabolic com-
plications.
1. The endocannabinoid system
The psychoactive and medicinal uses of Cannabis sativa (marijuana)
have been well known for millennia [1]. However, our understanding
of the underlying mechanisms of action in these physiological processes
emerged only during the 1960s, following the isolation, identification,
and synthesis of Δ
9
-tetrahydrocannabinol (THC), the psychoactive
component of marijuana [2]. It took almost three decades to isolate and
clone the THC binding sites in the brain and periphery, which were then
termed the cannabinoid-1 and -2 receptors (CB
1
R and CB
2
R, respec-
tively) [3–5]. Cannabinoid-1 has been recently crystalized by two dif-
ferent groups [6,7]. Both receptors mainly signal via G
i
/G
o
proteins,
despite the fact that they can also activate G
s
,G
q/11
, as well as G pro-
tein-independent signaling pathways [8]. The cloning of CB receptors in
mammalian cells was followed soon afterward by identifying their in-
ternal ligands, arachidonoyl ethanolamide (AEA, anandamide) [9], and
2-arachidonoyl glycerol (2-AG) [10,11]. Once eCBs are generated and
released, they remain attached to the cell membrane owing to their
lipophilicity, and therefore, they can be taken back up by cells through
a high-affinity transport mechanism [12]. Their clearance depends on
cellular uptake and specific enzymatic degradation. Whereas AEA is
degraded mainly by membrane-associated fatty-acid amide hydrolase
(FAAH) [13], 2-AG is primarily degraded by monoglyceride lipase
(MAGL) [14]. The internal cannabinoids, their receptors, and the en-
zymes/proteins involved in their biosynthesis, transport, and
degradation jointly make up the ‘eCB system’.
2. The eCB/CB
1
R system as a key modulator of energy homeostasis
and feeding
The well-documented role of cannabis as a bi-modulator of food
intake in rodents and humans [reviewed in [15]] provided early clues
as to the biological and metabolic functions of its internal counterparts.
A case in point is the ‘munchies effect’, which prompted a study that
provided evidence for the specific involvement of the eCB/CB
1
R system
in this phenomenon via regulating leptin signaling in the hypothalamus
[16]. CB
1
R is abundantly expressed on presynaptic nerve terminals [17]
in central areas controlling food intake and energy expenditure and
reward-related responses. However, it is also present at much lower, yet
functionally relevant levels in many peripheral organs, such as adipose
tissue [18], liver [19], skeletal muscle [20], kidney [21], bone [22],
and pancreas [23]. Therefore, it was not surprising to find that its
blockade would inhibit food intake [24–27]. In fact, these observations
provided the motivation for testing such compounds as a potential
treatment for obesity. Indeed, the first-in-class CB
1
R antagonist rimo-
nabant (Acomplia®, Sanofi-Aventis) proved very effective not only in
reducing food intake and body weight, but also in improving the obe-
sity-induced insulin and leptin resistance, restoring glucose homeostasis
and dyslipidemias, as well as ameliorating hepatic fat accumulation in
obese/overweight people with the metabolic syndrome ([28]; [29–34]).
https://doi.org/10.1016/j.ejim.2018.01.009
Received 1 December 2017; Received in revised form 3 January 2018; Accepted 4 January 2018
⁎
Corresponding author at: Obesity and Metabolism Laboratory, Institute for Drug Research, School of Pharmacy, Faculty of Medicine, POB 12065, Jerusalem 9112001, Israel.
E-mail address: yossit@ekmd.huji.ac.il (J. Tam).
European Journal of Internal Medicine xxx (xxxx) xxx–xxx
0953-6205/ © 2018 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.
Please cite this article as: Tam, J., European Journal of Internal Medicine (2018), https://doi.org/10.1016/j.ejim.2018.01.009
The abovementioned findings, along with a few additional ‘energy
conserving’physiologic effects mediated by either cannabis consump-
tion and/or the activation of the eCB/CB
1
R system such as anxiolysis,
rewarding, motor suppression, sleep induction, and lipogenesis [re-
viewed in [35]], may suggest that the internal cannabinoid system is a
pivotal modulator of the ‘thrifty’phenotype, which has helped humans
to survive evolution during frequent periods of starvation. However, in
our Western society of abundant food supplies, combined with a se-
dentary lifestyle, and an increased lifespan, this phenotype has become
the main cause of the epidemic spread of obesity and its metabolic
complications. In fact, the observations that reducing eCB action by
blocking CB
1
R suggest that increased eCB ‘tone’may be its unifying
pathologic feature that triggers the development of the metabolic syn-
drome [36].
3. Moving from globally acting to peripherally restricted CB
1
R
antagonism for the treatment of obesity
An open question remains, regarding the relative importance of
central versus peripheral CB
1
Rs involved in energy homeostasis and
metabolism. This question has considerable practical and clinical im-
plications in light of the growing documented evidence of anxiety,
depression, and/or suicidal ideation that was reported in a small but
significant fraction of humans treated with rimonabant [37]. These
reports led not only to the eventual withdrawal of rimonabant from the
market, but also to the discontinuation of developing all CB
1
R blockers
by big pharmaceutical companies, which raised doubts about the
therapeutic potential of this class of molecules [38].
Generally, the baseline expression level of CB
1
Rs in periphery is
very low, but it is markedly elevated during obesity and diabetes.
Indeed, increased expression of CB
1
Rs was reported in adipose tissue
[18,39], liver [39–41], skeletal muscle [20], kidney [42], and pancreas
[43]. Whereas the expression levels of receptors and the amount of their
internal ligands are usually inversely correlated, a few examples of an
obesity-related parallel increase in eCBs in the same tissues were
documented [40,42,44]. Moreover, several studies have shown that
circulating eCB levels are positively associated with biomarkers for the
metabolic syndrome [45–48] as well as in genetic causes of obesity,
such as Prader-Willi syndrome [49]. These findings, together with ad-
ditional studies conducted in murine models for the metabolic syn-
drome showing that (i) activation of CB
1
R increases lipogenesis in
adipocytes and liver [19,50]; (ii) CB
1
R blockade attenuates obesity-
induced dysregulation of lipid metabolism in visceral adipose tissue
[39]; and (iii) enhanced insulin receptor signaling results in β-cell
proliferation and mass [23], suggest that the apparent increase in
peripheral eCB ‘tone’in obesity plays an important physiological role.
This, in turn, may support strategies for antagonizing CB
1
R only in
peripheral tissues for the treatment of the metabolic syndrome. In fact,
evidence for the inability of rimonabant to reduce food intake in mice
with a selective deletion of CB
1
Rs in CAM kinase IIα-expressing neurons
[41], which are prominently expressed not only in forebrain and per-
ipheral sympathetic neurons [41], but also in peripheral sensory neu-
rons [51,52], implies a peripheral site of action for CB
1
R in mediating
feeding behaviors.
Indeed, if peripherally present CB
1
Rs do contribute to the devel-
opment of the metabolic syndrome, then limiting the access of CB
1
R
blockers to the brain may improve their therapeutic index by reducing
their potential to cause centrally mediated neuropsychiatric adverse
effects while retaining their metabolic actions in the periphery. This
notion was followed by a series of studies demonstrating the involve-
ment of the peripheral eCB/CB
1
R system in the development of cardi-
ometabolic abnormalities associated with the metabolic syndrome, as
well as the ability of peripherally restricted CB
1
R antagonists to im-
prove obesity- and diabetes-induced comorbidities.
Among the several compounds developed, AM6545 was the first
that underwent a detailed pharmacological, metabolic, and behavioral
assessment in mouse models of obesity. It was shown to ameliorate
insulin resistance, hepatic steatosis, and dyslipidemia in both diet- and
genetically induced obesity [53]. These findings were followed by a few
studies demonstrating the ability of AM6545 to reduce food intake, the
meal size, the rate of feeding, and body weight in obese animals
[54–56], as well as to attenuate obesity-induced dyslipidemia via ac-
tivating brown adipose tissue [57]. Shortly after the metabolic char-
acterization of AM6545, another novel peripherally restricted blocker
(JD5037) was developed and pre-clinically tested in different murine
models of obesity. Its ability to reduce body weight, food intake, im-
prove glycemic control, and attenuate fatty liver was comparable to
SLV319 (Ibipinabant®)[58]. The hypophagia and weight reducing ef-
fects of JD5037 were directly linked to its capacity to reverse the
obesity-induced increased leptin levels and consequent leptin resistance
by reducing leptin secretion from adipocytes as well as increasing its
clearance via the kidney [58]. Interestingly, despite that JD5037 is
restricted to the periphery, we recently demonstrated that it restores
hypothalamic leptin sensitivity and elicits anorectic response via acti-
vating proopiomelanocortin (POMC) neurons in the hypothalamus,
which have been shown to modulate eCB-induced feeding [59], as well
as by disinhibiting melanocortin MC4R signaling [60]. In this work, we
further demonstrated that unlike rimonabant, which significantly re-
duced food intake and body weight in mice lacking MC4R, the anorexia
and weight-reducing effects of the peripherally restricted CB
1
R an-
tagonist JD5037 were substantially attenuated in these mice or in wild-
type obese animals receiving the MC4R antagonist SHU-9119 [60]. In
addition, JD5037 was found to be effective in reducing hyperphagia
and weight in a well-established model of Prader–Willi syndrome, as
well as in improving all the metabolic parameters related to their obese
phenotype [49].
Additional evidence for peripheral regulation of energy metabolism
by the eCB system comes from a few studies utilizing genetic models
with specific deletions of CB
1
R. Interestingly, deletion of hepatic CB
1
R
was sufficient to protect obese mice from liver steatosis, dyslipidemia,
as well as insulin and leptin resistance [40]. A recent study by Lutz et al.
characterized the metabolic phenotype of mice carrying a specific de-
letion of CB
1
R in adipocytes, and remarkably, found that these mice
were protected from diet-induced obesity and its consequent metabolic
alterations [61]. Taken together, these pivotal studies highlight the
ability of the peripheral eCB/CB
1
R system to regulate feeding and en-
ergy balance via a crosstalk between peripheral organs and centrally
mediated hypothalamic signaling pathways. Next, we will briefly dis-
cuss the available evidence and current knowledge regarding the role of
eCBs and CB
1
R signaling in modulating metabolic and physiological
activities in the liver, kidney, and bone.
4. Role of the eCB/CB
1
R system in the development of NAFLD
The possible involvement of eCBs via activating CB
1
R in the de-
velopment of non-alcoholic fatty liver diseases (NAFLD) has been the
focus of many recent studies. In fact, for many years the liver was
considered as a negative control to study the function of neuronal
CB
1
Rs [62]. Unlike normal conditions, in which CB
1
R is expressed in
fairly low levels in the liver [19,39,41,62], during liver pathologies its
expression is vastly upregulated [63–65]. Since eCBs are present in the
liver at levels that are comparable to those found in the brain [19,66],
it was reasonable to postulate a significant role for the eCB/CB
1
R
system in regulating lipid metabolism in the liver.
Initially, Osei-Hyiaman and colleagues demonstrated the complete
resistance of CB
1
R null mice to develop obesity-induced fatty liver [19].
Later on, it was found that both globally acting and peripherally re-
stricted CB
1
R blockers can increase fatty acid oxidation as well as re-
duce hepatic inflammation and lipogenesis [19,40,53,58,67–71],
thus supporting the protective effect of these compounds and their
potential pharmacological application in ameliorating NAFLD. Further
evidence for the effectiveness of globally acting CB
1
R antagonists came
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
2
from several studies in humans and rodents demonstrating the ability of
rimonabant to reduce the expression levels of hepatic lipogenic genes
and to reverse fatty liver disease [19,28,29,39,70,72,73]. Likewise,
peripherally restricted CB
1
R antagonists were also found to have similar
capabilities [53,55,58,67,74].
Consuming a high-fat diet or specific activation of CB
1
R reduces the
hepatic expression and activity of carnitine palmitoyl transferase–1
(CPT1), the rate-limiting enzyme in mitochondrial fatty acid oxidation.
However, this effect was absent in globally or hepatocyte-specificCB
1
R
null, and was reversed by treatment with rimonabant or AM6545 [40,
53]. In a genome-wide expression profiling of mice lacking CB
1
Ror
treated with a CB
1
R blocker, it was further found that inactivating CB
1
R
during obesity increases the expression of hepatic genes associated with
fatty acid oxidation while suppressing the expression of hepatic lipo-
genic genes [75]. Furthermore, blockade of CB
1
Rs reverses the obesity-
induced upregulation of hepatic fatty acid translocase/CD36, which
mediates the uptake of free fatty acids from the circulation to the liver
and may contribute to fat accumulation in the liver. This reversal was
found to be mediated indirectly by adiponectin [70].
Additional support for the hepatic role of eCBs in humans comes
from a few studies demonstrating the association of circulating eCBs
with the development of NAFLD. First, increased arterial and hepatic
venous concentrations of 2-AG, as well as the production of triglycer-
ides containing saturated fatty acids were found to be positively cor-
related with liver fat content [76]. Second, upregulated blood levels of
2-AG and its precursor and breakdown molecule, arachidonic acid,
were found in both female and male patients with NAFLD regardless of
their BMI [77]. The significant correlation between 2-AG and the he-
patorenal index as well as serum alanine aminotransferase levels may
suggest that elevation of this molecule may reflect the degree of liver
injury associated with obesity [77]. These findings are consistent with
additional studies in humans [45,46,48,49,78,79] suggesting a
possible role of circulating eCBs as potentially serving as biomarkers for
visceral obesity and its associated metabolic abnormalities.
5. The contribution of the eCB/CB
1
R system to obesity- and
diabetes-induced chronic kidney disease
Recently, greater attention was devoted to obesity-associated
kidney injury, which develops early in the progression of obesity
[80–82], and independently of the metabolic abnormalities associated
with it [83,84]. In fact, obesity-induced renal inflammation [85] and
oxidative stress [86] may eventually lead to kidney dysfunction, glo-
merulosclerosis, and tubulointerstitial fibrosis [80,87–89]. Since the
kidney is a major source of eCBs, whose levels are elevated during
obesity [42,90], and the fact that CB
1
R is vastly expressed in many cells
within the kidney, the possible involvement of the eCB/CB
1
R system in
regulating obesity-associated kidney injury has been explored in several
recent studies. Of these, findings reporting amelioration of obesity-in-
duced chronic kidney disease by CB
1
R antagonists have shown that
rimonabant or AM251 can delay the development of proteinuria, glo-
merular and tubulointerstitial lesions, as well as reduce hypertrophy
and creatinine levels in genetically and high-fat diet-induced obese rats
[91,92].
Among the many cells in the kidney that express CB
1
R [reviewed in
[93]], the renal proximal tubular cells (RPTCs) are critically important
in regulating normal kidney function because they are responsible for
active reabsorption of a large quantity (> 80%) of the filtrate using a
mechanism requiring a large amount of energy. This is mainly due to
fatty acid oxidation, controlled by the cellular energy and redox sensor,
AMPK [94,95]. In a recent work done by our group, we showed that
obesity-induced renal abnormalities are mediated via CB
1
R specifically
located on the RPTCs [42]. Even though obese mice lacking CB
1
R in the
RPTCs had a metabolic phenotype identical to their obese wild-type
control animals, they remained completely protected from the dele-
terious effects of obesity on the kidney, such as impaired renal lipid
metabolism, increased intracellular lipid accumulation, and kidney li-
potoxicity [42]. At the molecular level, we found that CB
1
R governs
intracellular lipid accumulation in the RPTCs, and consequently, the
obesity-induced renal inflammation, fibrosis, and injury by regulating
the AMPK signaling pathway [42]. This further implies that manip-
ulating CB
1
R specifically in the RPTCs may have therapeutic potential
for treating obesity-induced nephropathy.
Strong evidence for the involvement of the eCB/CB
1
R system in the
development of chronic kidney disease associated with diabetes, also
termed diabetic nephropathy (DN), has recently emerged from murine
models for both type 1 and type 2 diabetes. In both cases, CB
1
R ex-
pression in the kidney is predominantly upregulated in podocytes and
RPTCs [96–98], and its pharmacological inhibition by globally acting
CB
1
R antagonists ameliorates diabetes-induced albuminuria, inhibits
fibrosis and inflammation, and prevents podocyte dysfunction. Like-
wise, peripherally restricted CB
1
R antagonism was found to completely
prevent the development of DN [99]. Moreover, in a recent study by
Barutta and colleagues, it was shown that combining peripherally re-
stricted CB
1
R antagonism and CB
2
R agonism treatment synergistically
ameliorates diabetes-induced albuminuria, inflammation, tubular in-
jury, and renal fibrosis [100].
In a recent study by Kunos et al., diabetic podocyte-specificCB
1
R
null mice displayed a reduction in albuminuria, podocytes injury, and
tubular dysfunction [101]. Similarly, downregulating podocyte CB
1
R
expression or its pharmacological blockade was found to ameliorate
hyperglycemia-induced endoplasmic reticulum stress [102]. Type 1
angiotensin II receptor (AT1R) has also been suggested to regulate
CB
1
R-induced DN, since using Losartan, an AT1R antagonist, was found
to attenuate DN via a reduction in podocyte CB
1
R expression in rats
[99]. These findings are further supported by the ability of CB
1
R and
AT1R to form heterodimers, which amplify AT1R activity [103], and
thus may provide a possible mechanism for the development of DN
under normoglycemic conditions. In addition, hyperglycemic condi-
tions were also found to enhance the expression of CB
1
R in mesangial
cells [104,105] and to promote their apoptosis [104], inflammation,
and fibrosis [105], effects that were reversed by globally acting CB
1
R
antagonists. Taken together, these findings highlight the key role of
CB
1
R in mediating hyperglycemia-induced podocyte and mesangial
dysfunction.
Similarly to the increased susceptibility of RPTCs to fatty acid flux
[42], these cells are particularly sensitive to the deleterious effects of
chronic hyperglycemia in diabetic patients [106] because glucose en-
ters these cells independently of insulin. Indeed, a recent study de-
monstrated that both glucose and albumin increase the expression of
CB
1
R in cultured RPTCs and that its activation results in hypertrophy
[97]. Like CB
1
R, the facilitative glucose transporter 2 (GLUT2), loca-
lized in RPTCs, is recruited to the apical/brush border membrane
(BBM) during diabetes [107,108]. This, in turn, increases glucose re-
absorption, which eventually leads to RPTC injury, inflammation, and
tubulointerstitial fibrosis [108–112]. Recently, our lab reported a novel
cellular mechanism by which CB
1
R regulates GLUT2 expression and
dynamics in RPTCs [113]. These effects were linked to modulating the
Ca
2+
influx and the expression of PKC-β1 in RPTCs. Our findings fur-
ther indicate that diabetes-induced upregulation in renal GLUT2 ex-
pression and dynamic translocation can be mitigated by peripheral
pharmacological blockade or genetic deletion of CB
1
R in RPTCs to re-
duce glucose reabsorption and prevent the development of DN. More-
over, we showed that in comparison with the globally acting CB
1
R
antagonism, peripherally restricted blockade of this receptor is of great
value in the treatment of DN [113].
6. Role of the eCB/CB
1
R system in bone remodeling and mass
The eCB system plays a significant role in determining bone-mass
accrual by regulating bone remodeling [114], which maintains skeletal
integrity and enables its ability to adapt to the constant changes in
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
3
mechanical demands [115,116]. Several principal constituents of the
eCB system have been identified in bone. These include the main eCBs,
AEA, and 2AG, which are synthesized by osteoblasts and osteoclasts
and reach skeletal concentrations similar to those found in the brain
[22,117]; their biosynthesis and degrading enzymes [115,118,119];
and the cannabinoid receptors, CB
1
R and CB
2
R[119,120]. Since this
review focuses on the eCB/CB
1
R system, we will briefly describe the
role of CB
2
R in bone [also reviewed in [121]], and then thoroughly
discuss the current knowledge regarding CB
1
R.
Several studies utilizing specific agonists for CB
2
R support its pro-
anabolic skeletal capabilities [120,122,123]. Additionally, mice
lacking CB
2
R display a phenotype reminiscent of human post-
menopausal osteoporosis, with increased age-related bone loss and
bone turnover [120]. In fact, two genetic studies in humans docu-
mented polymorphisms in the coding region of CB
2
R, which were as-
sociated with low bone mass and osteoporosis [124,125]. In contrast,
no significant association between osteoporosis and four single nu-
cleotide polymorphisms spanning nearly 20 kb around the CB
1
R coding
exon were found [126]. Although some conflicting evidence about the
signaling pathways modulated by CB
2
R in bone cells and their pre-
cursors have been reported [120,127,128], there is clear evidence
demonstrating the merit of targeting this receptor for the pharma-
cotherapy of osteoporosis.
Modulating bone remodeling and mass by CB
1
R is much more
complex, however. CB
1
Rs are mostly expressed on sympathetic nerve
endings [119], but they also have been detected in low amounts in
osteoclasts, osteoblasts, bone marrow stromal cells, macrophages, and
fat cells [128,129]. CB
1
R has been shown to modulate the activity of
the central nervous system in regulating bone remodeling via antag-
onizing skeletal sympathetic effects. Briefly, norepinephrine, released
from sympathetic fibers, inhibits bone formation and stimulates bone
resorption [130,131]. In fact, acute stimulation of CB
1
R by 2-AG,
produced in the bone microenvironment, inhibits norepinephrine re-
lease, thus mitigating the inhibition of bone formation by the sympa-
thetic nervous system [119]. On the other hand, direct activation of
osteoblastic CB
1
R, whose levels are upregulated with age, protects age-
related osteoporosis [129], most likely via promoting osteoblast pro-
liferation.
Utilizing different animal models to determine the role of CB
1
Rin
modulating bone mass revealed its complex involvement in this pro-
cess, and also highlighted its importance in selecting the “right”mouse
model to use. For instance, deletion of CB
1
R in congenic C57BL/6J mice
results in a low bone mass phenotype [22]. However, CB
1
R null mice,
maintained on an outbred CD1 genetic background, have a high peak
bone mass [22], yet they subsequently develop age-related low bone
mass owing to a defect in bone formation and to increased adipogenesis
within the skeletal microenvironment [128,129]. In a recent study, we
attempted to isolate the involvement of CB
1
R expressed in sympathetic
neurons, and to rule out the direct effects of CB
1
R deletion on bone
cells. This was achieved utilizing a novel mouse strain that lacks CB
1
R
in adrenergic/noradrenergic cells [132]. Our findings indicate that
conditional deletion of CB
1
R signaling in sympathetic nerve terminals
leads to enhanced age-related bone mass, associated with an enhanced
bone formation rate and reduced osteoclastogenesis. This effect was not
associated with increased sympathetic tone but rather, the opposite,
suggesting that constitutive genetic inactivation of the sympathetic
CB
1
R receptor disrupts the negative feedback loop between eCBs and
norepinephrine signaling in bone [133].
An interesting open question, whether the use of cannabis “per se”
has significant effects on the skeleton, has been recently addressed in a
study that determined the involvement of the eCB system in regulating
skeletal elongation [134]. Both cannabinoid receptors are expressed in
hypertrophic chondrocytes of the epiphyseal growth cartilage. Studies
on humans reported that THC exposure during pregnancy reduces the
fetal growth rate, resulting in a reduced birth weight, a shorter stature,
and a reduced head size at birth [135,136]. Summing up, modulating
the skeletal eCB/CB
1
R system may serve as a therapeutic approach for
the treatment of a wide range of skeletal disorders, from treatment and
prevention of age-related osteoporosis to correction of growth deficits.
7. Concluding remarks
The peripheral eCB system is involved in regulating energy meta-
bolism, food intake, and adiposity. It also modulates liver and kidney
function under normal and pathophysiological conditions, such as
obesity and diabetes, and it controls bone remodeling, skeletal mass,
and elongation. Therefore, it has important therapeutic and prognostic
implications specifically in relation to targeting CB
1
R. Although we
have mostly reviewed the current knowledge on the role of the eCB/
CB
1
R system, one should also note the important aspects of this system
in modulating other peripheral organs, such as skeletal muscle, pan-
creas, and the gastrointestinal tract. Increased activity of the eCB/CB
1
R
system contributes to the development of the metabolic syndrome,
whereas either globally or peripherally restricted CB
1
R antagonism
attenuates or prevents the development of the cardio-metabolic co-
morbidities associated with it. These findings support the idea that
peripherally selective CB
1
R antagonists may be useful therapeutics
against the metabolic syndrome, and also offer a superior therapeutic
benefit for this condition. It remains to be seen whether this novel
pharmacological approach will be fully translated into use for humans,
and rekindle the spark for finding a new blockbuster therapeutic against
the metabolic syndrome. Moreover, with growing acceptance of using
medical cannabis for different clinical indications, future research is
warranted to decipher the effect and impact of medical cannabis on the
development of the metabolic syndrome via activating the eCB/CB
1
R
system.
Acknowledgment
This research was supported by an Israel Science Foundation grant
(#617/14), and an ERC-2015-StG grant (#676841) to J.T.
References
[1] Abel EL. Cannabis: effects on hunger and thirst. Behav Biol 1975;15:255–81.
[2] Gaoni Y, Mechoulam R. Isolation, structure and partial synthesis of an active
constituent of hashish. J Am Chem Soc 1964;86:1646–7.
[3] Devane WA, Dysarz 3rd FA, Johnson MR, Melvin LS, Howlett AC. Determination
and characterization of a cannabinoid receptor in rat brain. Mol Pharmacol
1988;34:605–13.
[4] Matsuda LA, Lolait SJ, Brownstein MJ, Young AC, Bonner TI. Structure of a can-
nabinoid receptor and functional expression of the cloned cDNA. Nature
1990;346:561–4.
[5] Munro S, Thomas KL, Abu-Shaar M. Molecular characterization of a peripheral
receptor for cannabinoids. Nature 1993;365:61–5.
[6] Hua T, Vemuri K, Pu M, Qu L, Han GW, Wu Y, et al. Crystal structure of the human
cannabinoid receptor CB1. Cell 2016;167(750–762):e714.
[7] Shao Z, Yin J, Chapman K, Grzemska M, Clark L, Wang J, et al. High-resolution
crystal structure of the human CB1 cannabinoid receptor. Nature 2016;540:602–6.
[8] Howlett AC. Cannabinoid receptor signaling. Handb Exp Pharmacol 2005:53–79.
[9] Devane WA, Hanus L, Breuer A, Pertwee RG, Stevenson LA, Griffin G, et al.
Isolation and structure of a brain constituent that binds to the cannabinoid re-
ceptor. Science 1992;258:1946–9.
[10] Mechoulam R, Ben-Shabat S, Hanus L, Ligumsky M, Kaminski NE, Schatz AR, et al.
Identification of an endogenous 2-monoglyceride, present in canine gut, that binds
to cannabinoid receptors. Biochem Pharmacol 1995;50:83–90.
[11] Sugiura T, Kondo S, Sukagawa A, Nakane S, Shinoda A, Itoh K, et al. 2-
Arachidonoylglycerol: a possible endogenous cannabinoid receptor ligand in
brain. Biochem Biophys Res Commun 1995;215:89–97.
[12] Fowler CJ. The pharmacology of the cannabinoid system—a question of efficacy
and selectivity. Mol Neurobiol 2007;36:15–25.
[13] McKinney MK, Cravatt BF. Structure and function of fatty acid amide hydrolase.
Annu Rev Biochem 2005;74:411–32.
[14] Dinh TP, Carpenter D, Leslie FM, Freund TF, Katona I, Sensi SL, et al. Brain
monoglyceride lipase participating in endocannabinoid inactivation. Proc Natl
Acad Sci U S A 2002;99:10819–24.
[15] Simon V, Cota D. MECHANISMS IN ENDOCRINOLOGY: endocannabinoids and
metabolism: past, present and future. Eur J Endocrinol 2017;176:R309–24.
[16] Di Marzo V, Goparaju SK, Wang L, Liu J, Batkai S, Jarai Z, et al. Leptin-regulated
endocannabinoids are involved in maintaining food intake. Nature
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
4
2001;410:822–5.
[17] Freund TF, Katona I, Piomelli D. Role of endogenous cannabinoids in synaptic
signaling. Physiol Rev 2003;83:1017–66.
[18] Bensaid M, Gary-Bobo M, Esclangon A, Maffrand JP, Le Fur G, Oury-Donat F, et al.
The cannabinoid CB1 receptor antagonist SR141716 increases Acrp30 mRNA ex-
pression in adipose tissue of obese fa/fa rats and in cultured adipocyte cells. Mol
Pharmacol 2003;63:908–14.
[19] Osei-Hyiaman D, DePetrillo M, Pacher P, Liu J, Radaeva S, Batkai S, et al.
Endocannabinoid activation at hepatic CB1 receptors stimulates fatty acid synth-
esis and contributes to diet-induced obesity. J Clin Invest 2005;115:1298–305.
[20] Pagotto U, Marsicano G, Cota D, Lutz B, Pasquali R. The emerging role of the
endocannabinoid system in endocrine regulation and energy balance. Endocr Rev
2006;27:73–100.
[21] Larrinaga G, Varona A, Perez I, Sanz B, Ugalde A, Candenas ML, et al. Expression of
cannabinoid receptors in human kidney. Histol Histopathol 2010;25:1133–8.
[22] Tam J, Ofek O, Fride E, Ledent C, Gabet Y, Muller R, et al. Involvement of neuronal
cannabinoid receptor CB1 in regulation of bone mass and bone remodeling. Mol
Pharmacol 2006;70:786–92.
[23] Nakata M, Yada T. Cannabinoids inhibit insulin secretion and cytosolic Ca2+
oscillation in islet beta-cells via CB1 receptors. Regul Pept 2008;145:49–53.
[24] Colombo G, Agabio R, Diaz G, Lobina C, Reali R, Gessa GL. Appetite suppression
and weight loss after the cannabinoid antagonist SR 141716. Life Sci
1998;63:PL113–7.
[25] Freedland CS, Poston JS, Porrino LJ. Effects of SR141716A, a central cannabinoid
receptor antagonist, on food-maintained responding. Pharmacol Biochem Behav
2000;67:265–70.
[26] Simiand J, Keane M, Keane PE, Soubrie P. SR 141716, a CB1 cannabinoid receptor
antagonist, selectively reduces sweet food intake in marmoset. Behav Pharmacol
1998;9:179–81.
[27] Williams CM, Kirkham TC. Anandamide induces overeating: mediation by central
cannabinoid (CB1) receptors. Psychopharmacology (Berl) 1999;143:315–7.
[28] Despres JP, Golay A, Sjostrom L, Rimonabant in Obesity-Lipids Study, G. Effects of
rimonabant on metabolic risk factors in overweight patients with dyslipidemia. N
Engl J Med 2005;353:2121–34.
[29] Despres JP, Ross R, Boka G, Almeras N, Lemieux I, Investigators AD-L. Effect of
rimonabant on the high-triglyceride/low-HDL-cholesterol dyslipidemia, in-
traabdominal adiposity, and liver fat: the ADAGIO-lipids trial. Arterioscler Thromb
Vasc Biol 2009;29:416–23.
[30] Hollander PA, Amod A, Litwak LE, Chaudhari U. Effect of rimonabant on glycemic
control in insulin-treated type 2 diabetes: the ARPEGGIO trial. Diabetes Care
2010;33:605–7.
[31] Pi-Sunyer FX, Aronne LJ, Heshmati HM, Devin J, Rosenstock J. Effect of rimona-
bant, a cannabinoid-1 receptor blocker, on weight and cardiometabolic risk factors
in overweight or obese patients: RIO-North America: a randomized controlled trial.
JAMA 2006;295:761–75.
[32] Rosenstock J, Hollander P, Chevalier S, Iranmanesh A. SERENADE: the study
evaluating rimonabant efficacy in drug-naive diabetic patients: effects of mono-
therapy with rimonabant, the first selective CB1 receptor antagonist, on glycemic
control, body weight, and lipid profile in drug-naive type 2 diabetes. Diabetes Care
2008;31:2169–76.
[33] Scheen AJ, Finer N, Hollander P, Jensen MD, Van Gaal LF. Efficacy and tolerability
of rimonabant in overweight or obese patients with type 2 diabetes: a randomised
controlled study. Lancet 2006;368:1660–72.
[34] Van Gaal LF, Rissanen AM, Scheen AJ, Ziegler O, Rossner S. Effects of the can-
nabinoid-1 receptor blocker rimonabant on weight reduction and cardiovascular
risk factors in overweight patients: 1-year experience from the RIO-Europe study.
Lancet 2005;365:1389–97.
[35] Pacher P, Batkai S, Kunos G. The endocannabinoid system as an emerging target of
pharmacotherapy. Pharmacol Rev 2006;58:389–462.
[36] Di Marzo V, Matias I. Endocannabinoid control of food intake and energy balance.
Nat Neurosci 2005;8:585–9.
[37] Christensen R, Kristensen PK, Bartels EM, Bliddal H, Astrup A. Efficacy and safety
of the weight-loss drug rimonabant: a meta-analysis of randomised trials. Lancet
2007;370:1706–13.
[38] Jones D. End of the line for cannabinoid receptor 1 as an anti-obesity target? Nat
Rev Drug Discov 2008;7:961–2.
[39] Jourdan T, Djaouti L, Demizieux L, Gresti J, Verges B, Degrace P. CB1 antagonism
exerts specific molecular effects on visceral and subcutaneous fat and reverses liver
steatosis in diet-induced obese mice. Diabetes 2010;59:926–34.
[40] Osei-Hyiaman D, Liu J, Zhou L, Godlewski G, Harvey-White J, Jeong WI, et al.
Hepatic CB1 receptor is required for development of diet-induced steatosis, dys-
lipidemia, and insulin and leptin resistance in mice. J Clin Invest
2008;118:3160–9.
[41] Quarta C, Bellocchio L, Mancini G, Mazza R, Cervino C, Braulke LJ, et al. CB(1)
signaling in forebrain and sympathetic neurons is a key determinant of en-
docannabinoid actions on energy balance. Cell Metab 2010;11:273–85.
[42] Udi S, Hinden L, Earley B, Drori A, Reuveni N, Hadar R, et al. Proximal tubular
cannabinoid-1 receptor regulates obesity-induced CKD. J Am Soc Nephrol
2017;28:3518–32.
[43] Jourdan T, Godlewski G, Cinar R, Bertola A, Szanda G, Liu J, et al. Activation of
the Nlrp3 inflammasome in infiltrating macrophages by endocannabinoids med-
iates beta cell loss in type 2 diabetes. Nat Med 2013;19:1132–40.
[44] Bordicchia M, Battistoni I, Mancinelli L, Giannini E, RefiG, Minardi D, et al.
Cannabinoid CB1 receptor expression in relation to visceral adipose depots, en-
docannabinoid levels, microvascular damage, and the presence of the Cnr1
A3813G variant in humans. Metabolism 2010;59:734–41.
[45] Abdulnour J, Yasari S, Rabasa-Lhoret R, Faraj M, Petrosino S, Piscitelli F, et al.
Circulating endocannabinoids in insulin sensitive vs. insulin resistant obese post-
menopausal women. A MONET group study. Obesity (Silver Spring)
2014;22:211–6.
[46] Bluher M, Engeli S, Kloting N, Berndt J, Fasshauer M, Batkai S, et al. Dysregulation
of the peripheral and adipose tissue endocannabinoid system in human abdominal
obesity. Diabetes 2006;55:3053–60.
[47] Di Marzo V, Verrijken A, Hakkarainen A, Petrosino S, Mertens I, Lundbom N, et al.
Role of insulin as a negative regulator of plasma endocannabinoid levels in obese
and nonobese subjects. Eur J Endocrinol 2009;161:715–22.
[48] Engeli S, Bohnke J, Feldpausch M, Gorzelniak K, Janke J, Batkai S, et al. Activation
of the peripheral endocannabinoid system in human obesity. Diabetes
2005;54:2838–43.
[49] Knani I, Earley BJ, Udi S, Nemirovski A, Hadar R, Gammal A, et al. Targeting the
endocannabinoid/CB1 receptor system for treating obesity in Prader-Willi syn-
drome. Mol Metab 2016;5:1187–99.
[50] Cota D, Marsicano G, Tschop M, Grubler Y, Flachskamm C, Schubert M, et al. The
endogenous cannabinoid system affects energy balance via central orexigenic
drive and peripheral lipogenesis. J Clin Invest 2003;112:423–31.
[51] Carlton SM. Localization of CaMKIIalpha in rat primary sensory neurons: increase
in inflammation. Brain Res 2002;947:252–9.
[52] Price TJ, Jeske NA, Flores CM, Hargreaves KM. Pharmacological interactions be-
tween calcium/calmodulin-dependent kinase II alpha and TRPV1 receptors in rat
trigeminal sensory neurons. Neurosci Lett 2005;389:94–8.
[53] Tam J, Vemuri VK, Liu J, Batkai S, Mukhopadhyay B, Godlewski G, et al.
Peripheral CB1 cannabinoid receptor blockade improves cardiometabolic risk in
mouse models of obesity. J Clin Invest 2010;120:2953–66.
[54] Argueta DA, DiPatrizio NV. Peripheral endocannabinoid signaling controls hy-
perphagia in western diet-induced obesity. Physiol Behav 2017;171:32–9.
[55] Bowles NP, Karatsoreos IN, Li X, Vemuri VK, Wood JA, Li Z, et al. A peripheral
endocannabinoid mechanism contributes to glucocorticoid-mediated metabolic
syndrome. Proc Natl Acad Sci U S A 2015;112:285–90.
[56] Cluny NL, Vemuri VK, Chambers AP, Limebeer CL, Bedard H, Wood JT, et al. A
novel peripherally restricted cannabinoid receptor antagonist, AM6545, reduces
food intake and body weight, but does not cause malaise, in rodents. Br J
Pharmacol 2010;161:629–42.
[57] Boon MR, Kooijman S, van Dam AD, Pelgrom LR, Berbee JF, Visseren CA, et al.
Peripheral cannabinoid 1 receptor blockade activates brown adipose tissue and
diminishes dyslipidemia and obesity. FASEB J 2014;28:5361–75.
[58] Tam J, Cinar R, Liu J, Godlewski G, Wesley D, Jourdan T, et al. Peripheral can-
nabinoid-1 receptor inverse agonism reduces obesity by reversing leptin re-
sistance. Cell Metab 2012;16:167–79.
[59] Koch M, Varela L, Kim JG, Kim JD, Hernandez-Nuno F, Simonds SE, et al.
Hypothalamic POMC neurons promote cannabinoid-induced feeding. Nature
2015;519:45–50.
[60] Tam J, Szanda G, Drori A, Liu Z, Cinar R, Kashiwaya Y, et al. Peripheral canna-
binoid-1 receptor blockade restores hypothalamic leptin signaling. Mol Metab
2017;6:1113–25.
[61] Ruiz de Azua I, Mancini G, Srivastava RK, Rey AA, Cardinal P, Tedesco L, et al.
Adipocyte cannabinoid receptor CB1 regulates energy homeostasis and alter-
natively activated macrophages. J Clin Invest 2017;127:4148–62.
[62] Galiegue S, Mary S, Marchand J, Dussossoy D, Carriere D, Carayon P, et al.
Expression of central and peripheral cannabinoid receptors in human immune
tissues and leukocyte subpopulations. Eur J Biochem 1995;232:54–61.
[63] Buckley NE, Hansson S, Harta G, Mezey E. Expression of the CB1 and CB2 receptor
messenger RNAs during embryonic development in the rat. Neuroscience
1998;82:1131–49.
[64] Floreani A, Lazzari R, Macchi V, Porzionato A, Variola A, Colavito D, et al. Hepatic
expression of endocannabinoid receptors and their novel polymorphisms in pri-
mary biliary cirrhosis. J Gastroenterol 2010;45:68–76.
[65] Xu X, Liu Y, Huang S, Liu G, Xie C, Zhou J, et al. Overexpression of cannabinoid
receptors CB1 and CB2 correlates with improved prognosis of patients with he-
patocellular carcinoma. Cancer Genet Cytogenet 2006;171:31–8.
[66] Siegmund SV, Qian T, de Minicis S, Harvey-White J, Kunos G, Vinod KY, et al. The
endocannabinoid 2-arachidonoyl glycerol induces death of hepatic stellate cells
via mitochondrial reactive oxygen species. FASEB J 2007;21:2798–806.
[67] Cinar R, Godlewski G, Liu J, Tam J, Jourdan T, Mukhopadhyay B, et al. Hepatic
cannabinoid-1 receptors mediate diet-induced insulin resistance by increasing de
novo synthesis of long-chain ceramides. Hepatology 2014;59:143–53.
[68] Jourdan T, Demizieux L, Gresti J, Djaouti L, Gaba L, Verges B, et al. Antagonism of
peripheral hepatic cannabinoid receptor-1 improves liver lipid metabolism in
mice: evidence from cultured explants. Hepatology 2012;55:790–9.
[69] Shi D, Zhan X, Yu X, Jia M, Zhang Y, Yao J, et al. Inhibiting CB1 receptors im-
proves lipogenesis in an in vitro non-alcoholic fatty liver disease model. Lipids
Health Dis 2014;13:173.
[70] Tam J, Godlewski G, Earley BJ, Zhou L, Jourdan T, Szanda G, et al. Role of adi-
ponectin in the metabolic effects of cannabinoid type 1 receptor blockade in mice
with diet-induced obesity. Am J Physiol Endocrinol Metab 2014;306:E457–68.
[71] Wu HM, Yang YM, Kim SG. Rimonabant, a cannabinoid receptor type 1 inverse
agonist, inhibits hepatocyte lipogenesis by activating liver kinase B1 and AMP-
activated protein kinase axis downstream of Galpha i/o inhibition. Mol Pharmacol
2011;80:859–69.
[72] Gary-Bobo M, Elachouri G, Gallas JF, Janiak P, Marini P, Ravinet-Trillou C, et al.
Rimonabant reduces obesity-associated hepatic steatosis and features of metabolic
syndrome in obese Zucker fa/fa rats. Hepatology 2007;46:122–9.
[73] Wierzbicki AS, Pendleton S, McMahon Z, Dar A, Oben J, Crook MA, et al.
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
5
Rimonabant improves cholesterol, insulin resistance and markers of non-alcoholic
fatty liver in morbidly obese patients: a retrospective cohort study. Int J Clin Pract
2011;65:713–5.
[74] Chorvat RJ, Berbaum J, Seriacki K, McElroy JF. JD-5006 and JD-5037: periph-
erally restricted (PR) cannabinoid-1 receptor blockers related to SLV-319
(Ibipinabant) as metabolic disorder therapeutics devoid of CNS liabilities. Bioorg
Med Chem Lett 2012;22:6173–80.
[75] Zhao W, Fong O, Muise ES, Thompson JR, Weingarth D, Qian S, et al. Genome-
wide expression profiling revealed peripheral effects of cannabinoid receptor 1
inverse agonists in improving insulin sensitivity and metabolic parameters. Mol
Pharmacol 2010;78:350–9.
[76] Westerbacka J, Kotronen A, Fielding BA, Wahren J, Hodson L, Perttila J, et al.
Splanchnic balance of free fatty acids, endocannabinoids, and lipids in subjects
with nonalcoholic fatty liver disease. Gastroenterology
2010;139(1961–1971):e1961.
[77] Zelber-Sagi S, Azar S, Nemirovski A, Webb M, Halpern Z, Shibolet O, et al. Serum
levels of endocannabinoids are independently associated with nonalcoholic fatty
liver disease. Obesity (Silver Spring) 2017;25:94–101.
[78] Cote M, Matias I, Lemieux I, Petrosino S, Almeras N, Despres JP, et al. Circulating
endocannabinoid levels, abdominal adiposity and related cardiometabolic risk
factors in obese men. Int J Obes (Lond) 2007;31:692–9.
[79] Di Marzo V, Cote M, Matias I, Lemieux I, Arsenault BJ, Cartier A, et al. Changes in
plasma endocannabinoid levels in viscerally obese men following a 1 year lifestyle
modification programme and waist circumference reduction: associations with
changes in metabolic risk factors. Diabetologia 2009;52:213–7.
[80] Hsu CY, McCulloch CE, Iribarren C, Darbinian J, Go AS. Body mass index and risk
for end-stage renal disease. Ann Intern Med 2006;144:21–8.
[81] Nguyen S, Hsu CY. Excess weight as a risk factor for kidney failure. Curr Opin
Nephrol Hypertens 2007;16:71–6.
[82] Wang Y, Chen X, Song Y, Caballero B, Cheskin LJ. Association between obesity and
kidney disease: a systematic review and meta-analysis. Kidney Int 2008;73:19–33.
[83] de Zeeuw D, Ramjit D, Zhang Z, Ribeiro AB, Kurokawa K, Lash JP, et al. Renal risk
and renoprotection among ethnic groups with type 2 diabetic nephropathy: a post
hoc analysis of RENAAL. Kidney Int 2006;69:1675–82.
[84] Remuzzi G, Macia M, Ruggenenti P. Prevention and treatment of diabetic renal
disease in type 2 diabetes: the BENEDICT study. J Am Soc Nephrol 2006;17:S90–7.
[85] Stemmer K, Perez-Tilve D, Ananthakrishnan G, Bort A, Seeley RJ, Tschop MH,
et al. High-fat-diet-induced obesity causes an inflammatory and tumor-promoting
microenvironment in the rat kidney. Dis Model Mech 2012;5:627–35.
[86] Lee W, Eom DW, Jung Y, Yamabe N, Lee S, Jeon Y, et al. Dendrobium moniliforme
attenuates high-fat diet-induced renal damage in mice through the regulation of
lipid-induced oxidative stress. Am J Chin Med 2012;40:1217–28.
[87] Coimbra TM, Janssen U, Grone HJ, Ostendorf T, Kunter U, Schmidt H, et al. Early
events leading to renal injury in obese Zucker (fatty) rats with type II diabetes.
Kidney Int 2000;57:167–82.
[88] Deji N, Kume S, Araki S, Soumura M, Sugimoto T, Isshiki K, et al. Structural and
functional changes in the kidneys of high-fat diet-induced obese mice. Am J
Physiol Renal Physiol 2009;296:F118–26.
[89] Pai R, Kirschenbaum MA, Kamanna VS. Low-density lipoprotein stimulates the
expression of macrophage colony-stimulating factor in glomerular mesangial cells.
Kidney Int 1995;48:1254–62.
[90] Matias I, Petrosino S, Racioppi A, Capasso R, Izzo AA, Di Marzo V. Dysregulation of
peripheral endocannabinoid levels in hyperglycemia and obesity: effect of high fat
diets. Mol Cell Endocrinol 2008;286:S66–78.
[91] Janiak P, Poirier B, Bidouard JP, Cadrouvele C, Pierre F, Gouraud L, et al. Blockade
of cannabinoid CB1 receptors improves renal function, metabolic profile, and in-
creased survival of obese Zucker rats. Kidney Int 2007;72:1345–57.
[92] Jenkin KA, O'Keefe L, Simcocks A, Grinfeld E, Mathai M, McAinch A, et al. Chronic
administration with AM251 improves albuminuria and renal tubular structure in
obese rats. J Endocrinol 2015;225:113–24.
[93] Tam J. The emerging role of the endocannabinoid system in the pathogenesis and
treatment of kidney diseases. J Basic Clin Physiol Pharmacol 2016;27:267–76.
[94] Decleves AE, Mathew AV, Cunard R, Sharma K. AMPK mediates the initiation of
kidney disease induced by a high-fat diet. J Am Soc Nephrol 2011;22:1846–55.
[95] Decleves AE, Zolkipli Z, Satriano J, Wang L, Nakayama T, Rogac M, et al.
Regulation of lipid accumulation by AMP-activated kinase [corrected] in high fat
diet-induced kidney injury. Kidney Int 2014;85:611–23.
[96] Barutta F, Corbelli A, Mastrocola R, Gambino R, Di Marzo V, Pinach S, et al.
Cannabinoid receptor 1 blockade ameliorates albuminuria in experimental dia-
betic nephropathy. Diabetes 2010;59:1046–54.
[97] Jenkin KA, McAinch AJ, Zhang Y, Kelly DJ, Hryciw DH. Elevated cannabinoid
receptor 1 and G protein-coupled receptor 55 expression in proximal tubule cells
and whole kidney exposed to diabetic conditions. Clin Exp Pharmacol Physiol
2015;42:256–62.
[98] Nam DH, Lee MH, Kim JE, Song HK, Kang YS, Lee JE, et al. Blockade of canna-
binoid receptor 1 improves insulin resistance, lipid metabolism, and diabetic ne-
phropathy in db/db mice. Endocrinology 2012;153:1387–96.
[99] Jourdan T, Szanda G, Rosenberg AZ, Tam J, Earley BJ, Godlewski G, et al.
Overactive cannabinoid 1 receptor in podocytes drives type 2 diabetic nephro-
pathy. Proc Natl Acad Sci U S A 2014;111:E5420–8.
[100] Barutta F, Grimaldi S, Gambino R, Vemuri K, Makriyannis A, Annaratone L, et al.
Dual therapy targeting the endocannabinoid system prevents experimental dia-
betic nephropathy. Nephrol Dial Transplant 2017;32:1655–65.
[101] Jourdan T, Park JK, Varga ZV, Paloczi J, Coffey NJ, Rosenberg AZ, et al.
Cannabinoid-1 receptor deletion in podocytes mitigates both glomerular and
tubular dysfunction in a mouse model of diabetic nephropathy. Diabetes Obes
Metab 2017. http://dx.doi.org/10.1111/dom.13150.
[102] Lim SK, Park SH. The high glucose-induced stimulation of B1R and B2R expression
via CB(1)R activation is involved in rat podocyte apoptosis. Life Sci
2012;91:895–906.
[103] Rozenfeld R, Gupta A, Gagnidze K, Lim MP, Gomes I, Lee-Ramos D, et al. AT1R-CB
(1)R heteromerization reveals a new mechanism for the pathogenic properties of
angiotensin II. EMBO J 2011;30:2350–63.
[104] Lim JC, Lim SK, Park MJ, Kim GY, Han HJ, Park SH. Cannabinoid receptor 1
mediates high glucose-induced apoptosis via endoplasmic reticulum stress in
primary cultured rat mesangial cells. Am J Physiol Renal Physiol
2011;301:F179–88.
[105] Lin CL, Hsu YC, Lee PH, Lei CC, Wang JY, Huang YT, et al. Cannabinoid receptor 1
disturbance of PPARgamma2 augments hyperglycemia induction of mesangial
inflammation and fibrosis in renal glomeruli. J Mol Med (Berl) 2014;92:779–92.
[106] Vallon V. The proximal tubule in the pathophysiology of the diabetic kidney. Am J
Physiol Regul Integr Comp Physiol 2011;300:R1009–22.
[107] Cohen M, Kitsberg D, Tsytkin S, Shulman M, Aroeti B, Nahmias Y. Live imaging of
GLUT2 glucose-dependent trafficking and its inhibition in polarized epithelial
cysts. Open Biol 2014;4.
[108] Marks J, Carvou NJ, Debnam ES, Srai SK, Unwin RJ. Diabetes increases facilitative
glucose uptake and GLUT2 expression at the rat proximal tubule brush border
membrane. J Physiol 2003;553:137–45.
[109] Chichger H, Cleasby ME, Srai SK, Unwin RJ, Debnam ES, Marks J. Experimental
type II diabetes and related models of impaired glucose metabolism differentially
regulate glucose transporters at the proximal tubule brush border membrane. Exp
Physiol 2016;101:731–42.
[110] Goestemeyer AK, Marks J, Srai SK, Debnam ES, Unwin RJ. GLUT2 protein at the
rat proximal tubule brush border membrane correlates with protein kinase C
(PKC)-betal and plasma glucose concentration. Diabetologia 2007;50:2209–17.
[111] Larkins RG, Dunlop ME. The link between hyperglycaemia and diabetic nephro-
pathy. Diabetologia 1992;35:499–504.
[112] Wolf G, Thaiss F. Hyperglycaemia—pathophysiological aspects at the cellular
level. Nephrol Dial Transplant 1995;10:1109–12.
[113] Hinden L, Udi S, Drori A, Gammal A, Nemirovski A, Hadar R, et al. Modulation of
renal GLUT2 by the Cannabinoid-1 receptor: implications for the treatment of
diabetic nephropathy. J Am Soc Nephrol 2017. http://dx.doi.org/10.1681/ASN.
2017040371.
[114] Bab I. Themed issue on cannabinoids in biology and medicine. Br J Pharmacol
2011;163:1327–8.
[115] Bab I, Ofek O, Tam J, Rehnelt J, Zimmer A. Endocannabinoids and the regulation
of bone metabolism. J Neuroendocrinol 2008;20:69–74.
[116] Parfitt A. The coupling of bone formation to bone resorption: a critical analysis of
the concept and of its relevance to the pathogenesis of osteoporosis. Metab Bone
Dis Relat Res 1982;4:1–6.
[117] Rossi F, Siniscalco D, Luongo L, De Petrocellis L, Bellini G, Petrosino S, et al. The
endovanilloid/endocannabinoid system in human osteoclasts: possible involve-
ment in bone formation and resorption. Bone 2009;44:476–84.
[118] Sophocleous A, Landao-Bassonga E, Van't Hof RJ, Idris AI, Ralston SH. The type 2
cannabinoid receptor regulates bone mass and ovariectomy-induced bone loss by
affecting osteoblast differentiation and bone formation. Endocrinology
2011;152:2141–9.
[119] Tam J, Trembovler V, Di Marzo V, Petrosino S, Leo G, Alexandrovich A, et al. The
cannabinoid CB1 receptor regulates bone formation by modulating adrenergic
signaling. FASEB J 2008;22:285–94.
[120] Ofek O, Karsak M, Leclerc N, Fogel M, Frenkel B, Wright K, et al. Peripheral
cannabinoid receptor, CB2, regulates bone mass. Proc Natl Acad Sci U S A
2006;103:696–701.
[121] Raphael B, Gabet Y. The skeletal endocannabinoid system: clinical and experi-
mental insights. J Basic Clin Physiol Pharmacol 2016;27:237–45.
[122] Ofek O, Attar-Namdar M, Kram V, Dvir-Ginzberg M, Mechoulam R, Zimmer A,
et al. CB2 cannabinoid receptor targets mitogenic Gi protein–cyclin D1 axis in
osteoblasts. J Bone Miner Res 2011;26:308–16.
[123] Smoum R, Baraghithy S, Chourasia M, Breuer A, Mussai N, Attar-Namdar M, et al.
CB2 cannabinoid receptor agonist enantiomers HU-433 and HU-308: an inverse
relationship between binding affinity and biological potency. Proc Natl Acad Sci
2015;112:8774–9.
[124] Karsak M, Malkin I, Toliat MR, Kubisch C, Nurnberg P, Zimmer A, et al. The
cannabinoid receptor type 2 (CNR2) gene is associated with hand bone strength
phenotypes in an ethnically homogeneous family sample. Hum Genet
2009;126:629–36.
[125] Yamada Y, Ando F, Shimokata H. Association of candidate gene polymorphisms
with bone mineral density in community-dwelling Japanese women and men. Int J
Mol Med 2007;19:791–801.
[126] Karsak M, Cohen-Solal M, Freudenberg J, Ostertag A, Morieux C, Kornak U, et al.
Cannabinoid receptor type 2 gene is associated with human osteoporosis. Hum
Mol Genet 2005;14:3389–96.
[127] Idris AI, Sophocleous A, Landao-Bassonga E, van't Hof RJ, Ralston SH. Regulation
of bone mass, osteoclast function, and ovariectomy-induced bone loss by the type
2 cannabinoid receptor. Endocrinology 2008;149:5619–26.
[128] Idris AI, van't Hof RJ, Greig IR, Ridge SA, Baker D, Ross RA, et al. Regulation of
bone mass, bone loss and osteoclast activity by cannabinoid receptors. Nat Med
2005;11:774–9.
[129] Idris AI, Sophocleous A, Landao-Bassonga E, Canals M, Milligan G, Baker D, et al.
Cannabinoid receptor type 1 protects against age-related osteoporosis by reg-
ulating osteoblast and adipocyte differentiation in marrow stromal cells. Cell
Metab 2009;10:139–47.
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
6
[130] Elefteriou F, Ahn JD, Takeda S, Starbuck M, Yang X, Liu X, et al. Leptin regulation
of bone resorption by the sympathetic nervous system and CART. Nature
2005;434:514–20.
[131] Yirmiya R, Goshen I, Bajayo A, Kreisel T, Feldman S, Tam J, et al. Depression
induces bone loss through stimulation of the sympathetic nervous system.
Proceedings of the. 103. National Academy of Sciences; 2006. p. 16876–81.
[132] Busquets-Garcia A, Gomis-Gonzalez M, Srivastava RK, Cutando L, Ortega-Alvaro
A, Ruehle S, et al. Peripheral and central CB1 cannabinoid receptors control stress-
induced impairment of memory consolidation. Proc Natl Acad Sci U S A
2016;113:9904–9.
[133] Deis S, Srivastava RK, de Azua IR, Bindila L, Baraghithy S, Lutz B, et al. Age-
related regulation of bone formation by the sympathetic cannabinoid CB1 re-
ceptor. Bone 2017;108:34–42.
[134] Wasserman E, Tam J, Mechoulam R, Zimmer A, Maor G, Bab I. CB1 cannabinoid
receptors mediate endochondral skeletal growth attenuation by Δ9-tetra-
hydrocannabinol. Ann N Y Acad Sci 2015;1335:110–9.
[135] El Marroun H, Tiemeier H, Steegers EA, Jaddoe VW, Hofman A, Verhulst FC, et al.
Intrauterine cannabis exposure affects fetal growth trajectories: the generation R
study. J Am Acad Child Adolesc Psychiatry 2009;48:1173–81.
[136] Zuckerman B, Frank DA, Hingson R, Amaro H, Levenson SM, Kayne H, et al.
Effects of maternal marijuana and cocaine use on fetal growth. N Engl J Med
1989;320:762–8.
J. Tam et al. European Journal of Internal Medicine xxx (xxxx) xxx–xxx
7
