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Flavones and flavonoids are known to have potent antioxidant activity due to intracellular free radical scavenging capacities. Flavonoids are found ubiquitously in plants as a member of polyphenolic compounds which share diverse chemical structure and properties. Quercetin is among the most efficient antioxidants of the flavonoids. The antioxidant property of quercetin has been highlighted in this review. These compounds have pivotal role in treatment of diabetes, cancers and some cardiovascular diseases.
Turkish Journal of Agriculture - Food Science and Technology, 4(12): 1134-1138, 2016
Turkish Journal of Agriculture - Food Science and Technology,
Turkish Science and Technology
Antioxidant Activity of Quercetin: A Mechanistic Review
Senay Ozgen1, Ozgur Kivilcim Kilinc1, Zeliha Selamoglu2*
1Department of Plant Productions and Technologies, Faculty of Agricultural Sciences and Technologies, Omer Halisdemir University,
51240 Niğde, Turkey
2Department of Biotechnology, Faculty of Arts and Science, Omer Halisdemir University, 51240 Niğde, Turkey
Article history:
Received 09 November 2016
Accepted 29 November 2016
Available online, ISSN: 2148-127X
Flavones and flavonoids are known to have potent antioxidant activity due to intracellular
free radical scavenging capacities. Flavonoids are found ubiquitously in plants as a
member of polyphenolic compounds which share diverse chemical structure and
properties. Quercetin is among the most efficient antioxidants of the flavonoids. The
antioxidant property of quercetin has been highlighted in this review. These compounds
have pivotal role in treatment of diabetes, cancers and some cardiovascular diseases.
Oxidative stress
Türk Tarım – Gıda Bilim ve Teknoloji Dergisi, 4(12): 1134-1138, 2016
Kuersetinin Antioksidan Aktivitesi: Mekanik Bir Derleme
Geliş 09 Kasım 2016
Kabul 29 Kasım 2016
Çevrimiçi baskı, ISSN: 2148-127X
Flavonlar ve flavonoidlerin, hücre içi serbest radikal süpürme kapasitelerinden dolayı
güçlü antioksidan aktiviteye sahip oldukları bilinmektedir. Flavonoidler, polifenolik
bileşiklerin çeşitli kimyasal yapı ve özelliklerini paylaşan bir üyesi olarak bitkilerde
bulunmaktadır. Quercetin, flavonoidlerin en etkili antioksidanları arasında yer almaktadır.
Bu derlemede quercetin'in antioksidan özellikleri vurgulanmıştır. Bu bileşikler diyabet,
kanser türleri ve bazı kardiyovasküler hastalıkların tedavisinde önemli rol
Anahtar Kelimeler:
Oksidatif stres
* Sorumlu Yazar:
Ozgen et al., / Turkish Journal of Agriculture - Food Science and Technology, 4(12): 1134-1138, 2016
Flavonoids are found ubiquitously in plants as a
member of polyphenolic molecules that share diverse
chemical structure and properties. There are more than
4.000 various flavonoids have been characterized within
the main flavonoid group which involve flavonols,
flavones, flavanones, catechins, anthocyanidins,
isoflavones, dihydroflavonols and chalcones (Cook et al.,
1996). The food industry uses natural antioxidants to
protect nutrients and color in the food. Recently, the
numbers of the studies conducted for the use of
flavonoids in different areas of industry are increasing.
Similarly, possible use of these compounds is being
common due to their antioxidant properties in the area of
food, textile, leather, metallurgy, medicine and
agriculture. Thus, quercetin is a common source for food
and pharmaceutical industries. Quercetin (3, 5, 7, 3′, 4′-
pentahydroxyflavone) is classified as a flavonol which is
one of the five subclasses and major dietary flavonoids
distributed in both cultivated and wild plants. (Cook et al.,
1996; D'Andrea, 2015).
Many factors, for instance, development of
technologies, the greenhouse effect, environmental
pollution, smoking, radiation and many chemicals, cause
negative effects of oxidative stress in the human body, as
a result, stress-free radicals occur. It is proven that
oxidative stress and free radicals provoke aging and
disease in the body. Characterization of components
capable of natural flavonoid antioxidants and their
antioxidative effects have become increasing interest
(Selamoglu et al., 2016). Antioxidants are organic
compounds with non enzymatic low concentrations that
prohibit the free radical oxidation mechanism (Das,
1989). Flavones and flavonoids, particularly quercetin,
are known to reveal important cytotoxicity process
against cultured human cells via raising intracellular
reactive oxygen species amount (Yáñez et al., 2004). In
this review, the effect of quercetin for the role of free
radical scavenger will be presented.
Chemistry of Quercetin
A hydroxyl group in third carbon, a double bond
between second and third carbon, a carbonyl group in
fourth carbon and polyhydroxylated A and B aromatic
rings (Figure 1) have main role in antioxidant proprieties
of these compounds (Cook et al., 1996).
The first resonant structure where B ring has an ortho-
catechol group may enable the forming of intra- and inter-
molecular hydrogen bonds. Indeed, the flavones, include
an ortho-catechol group (myricetin, quercetin, and
luteolin) are more acidic than apigenin and kaempferol, in
which the B-ring only have a 4′ hydroxyl group. Luteolin
and quercetin have two hydroxyl groups in the B-ring, on
the contrary of myricetin. Thus, the more numbers of
connected hydroxyl groups in the B-ring defines the
acidity capacity.
The scavenging mechanism of the free radical by
quercetin has been discussed on the rational of different
AM1 and quantum mechanics calculation, the attained
boundary orbitals and total spin intensity (Vasilescu and
Girma, 2002). The analysis results of the spin density near
by the attained free radical 4′-quercetin implies that the
essential intensity of spin α(↑) is condensed in the B ring
on the O4′ oxygen. They noticed also a light
delocalization of spins α(↑) and β(↓) on the B ring and on
a part of the C ring. Authors concluded that quercetin
antioxidant capacity may be related to basically with the
B ring and a half of the C ring (Vasilescu and Girma,
The correlation of these flavonoids with Cu2+ ions was
examined for their obscure composition of chelation or
modification through oxidation, as well as in their
structural relation (Brown et al., 1998). It has been
implied that the ortho 3', 4'-dihydroxy substitution in the
B ring is critical for a Cu2+-chelate formation which
affects the antioxidant activity. Furthermore, it has been
shown that the existence of a 3-hydroxy group in the
flavonoid structure promotes the oxidation of quercetin
and kaempferol. On the other hand, luteolin and rutin are
absent in the 3-hydroxy group which they do not oxidize
as easily in the existence of Cu2+ ions (Brown et al.,
1998). In addition, it is observed that complexation of
magnesium (Mg+2) cation increases the free radical
scavenging capacity of quercetin which inhibits oxidant
damage and cell mortality via different pathways (Ghosh
et al., 2015).
Figure 1 The structure of quercetin (Modified from
Mitchell, 1965).
Sources of Quercetin
Quercetin is one of natural flavonoid group that is
most common as a secondary metabolite in plants.
Production of synthetic flavonoids has not been practiced
yet. Hence, plants are the only sources for quercetin
(Abdelmoaty et al., 2010). Major vegetables and fruits
that are commonly consumed comprise different classes
of flavonoids in varied amount. It has been found that
onion has the highest amount of quercetin (about 300
mg/kg) among tested nutrition (Beecher, 1999). Other
vegetables, such as broccoli and kale, included quercetin
Ozgen et al., / Turkish Journal of Agriculture - Food Science and Technology, 4(12): 1134-1138, 2016
and kaempferol, but at much lower content. However, tea
contains a high amount of catechins but low amounts of
flavonoid quercetin (Beecher, 1999). The colour of fruits
and vegetables indicates amount of flavonoids, as red
grapes, cherries and blueberries have a significant amount
of variant anthocyanins. Most of these fruits also contain
flavonoids, especially quercetin (Beecher, 1999).
Quercetin and Oxidative Stress
The antioxidant character of quercetin is associated to
chemical structure, especially the presence and location of
the hydroxyl (OH) substitutions and the catechol-type B-
ring (Rice-Evans et al., 1996; Wang et al., 2006). The
structural properties of a potent antioxidant capacity is
due to the presence of (i) an ortho-dihydroxy or catechol
group in the B-ring, (ii) a 2,3-double bond, and (iii)
hydroxyl substitution at positions 3 and 5 (Bors et al.,
1990). Growing evidence has demonstrated that quercetin,
which is featured by a hydroxylation form of 3, 5, 7, 30,
and 40 and a catechol B-ring, contains all the structural
properties of an antioxidant agent (Silva et al., 2002;
Rietjens et al., 2005). Quercetin has anticarcinogenic and
anti-inflammatory properties with antioxidant and free
radical scavenging effects. However, quercetin may also
be diverted into reactive molecules (Metodiewa et al.,
1999; Boots et al., 2003). In vitro, the oxidative
degradation of quercetin has been showed to result in the
formation of a free radical orthosemiquinone
intermediate, which may afterward be changed to the
parent molecule or to an orthoquinone, nearby the
manufacturing of reactive oxygen species (Metodiewa et
al., 1999; Boots et al., 2003). In conclusion, the possible
pro-oxidant property of quercetin, especially at high dose
levels, must be emphasized (Rietjens et al., 2005). As a
result, the prooxidant effect may be accountable for the in
vitro mutagenic action of quercetin. Also, the researchers
reported that under aerobic conditions, quercetin was
demonstrated to produce dose-dependent DNA damage
and lipid peroxidation in isolated rat liver nuclei and
oxygen radicals produced by autooxidation of the
flavonol (Rahman et al., 1992; Sahu and Washington,
1991). Oxidative stress is related to reactive oxygen
species which is the main factor for viral hepatitis,
fibrosis, cirrhosis and liver cancer formation (Preedy et
al., 2014). Recent studies show that some flavonoids
prevent the occurrence of superoxide and hydroxyl
radicals which cause lipid peroxidation.
Some researchers suggested that quercetin has
antimicrobial, antiviral, antioxidative and anti-
inflammatory activities (Doğan et al., 2015; Gutteridge,
1995). Also, it is able to increase the cellular antioxidant
potential via the Nrf2 pathway (Gutteridge, 1995).
Another study by Doğan et al. (2015) has showed that
quercetin is able to prevent against the toxic action of
chemotherapeutic substances treated prior to pregnancy
(Doğan et al., 2015). Quercetin was applied at a dose of
10 mg/kg/day by oral gavage. After 48 h of the
experimental chemotherapy exposure, female rats were
transferred to cages including male rat for mating.
According to this study, women who have been exposed
to chemotherapy and may be pregnant should be treated
with antioxidant molecules, such as quercetin to decrease
the risk of injury to fetal brain tissues. In addition, the
data of this investigation assessed the hypothesis that
quercetin can prevent the toxic actions of
chemotherapeutic compounds treated prior to pregnancy
(Doğan et al., 2015).
Some experimental studies on animals are declared
that the antioxidant effects of quercetin decrease oxidative
injury to the tissues such as the brain, heart in ischemic
reperfusion damage and exposure to agents that induce
oxidative stress (Doğan et al., 2015; Bayne and Sohal,
2002). It is well established that natural antioxidants are
usually harmless to human body. They are molecules that
prevent early aging via blocking the catasthropic effects
of the free radicals, many diseases and chain reactions
(Elik et al., 2007).
Antioxidant enzyme activities are substantially
enhanced by quercetin treatment (Elik et al., 2007). The
study of Elik et al. (2007) proved that quercetin as a
flavonoid with antioxidant characteristics demonstrates
antidiabetic effects (Elik et al., 2007). This compound
also has protection against oxidant damage to the heart,
brain, liver, aorta and kidney for mid-term or long-term
diabetic rat (Elik et al., 2007). Thus, quercetin increases
the antioxidant defence capacity.
It has been shown that flavonoids could inhibit
enzymes like cyclooxygenases and protein kinases where
they are part of cell proliferation and apoptosis processes
(Abdelmoaty et al., 2010). In addition, doses of 1550
mg/kg body mass quercetin was able to of normalize
blood glucose level, augmenting liver glycogen
ingredients and dramatically decreasing serum cholesterol
and low density lipoprotein (LDL) levels in alloxan
diabetic rats (Abdelmoaty et al., 2010). Furthermore,
treatment of quercetin to isolated rat islets increased
insulin production by 4470% with changing in calcium
flows and in cyclic nucleotide metabolism (Abdelmoaty
et al., 2010).
Consumption of flavonoids showed a reduction in
coronary heart disease (Hertog et al., 1994). The study
conducted in Japan showed that there was a decreased on
both total and LDL-cholesterol concentration when
plasma quercetin is increased (Hertog et al., 1994). In
another study in Finland showed that diet rich in apple
and onion increased quercetin level which was helpful to
reduce coronary mortality (Knekt et al., 1996).
Each alive organism is able to prevent negative effects
of free radicals with antioxidative protection system.
However, this system is not strong enough to prevent an
increase in the amount of radical. Consequently, oxidative
stress (cell damage) occurs in this situation. Low level of
stress induces a cell to activate extra defence system,
although, high-stress level causes the death of cells which
damages organisms (Çıkrıkçı, 2005). All these studies are
demonstrating that quercetin has an anti-oxidative effect
to inhibit oxidative stress.
A series of epidemiological studies proved that a lack
of association between flavonoids consumption up to 68
Ozgen et al., / Turkish Journal of Agriculture - Food Science and Technology, 4(12): 1134-1138, 2016
mg total flavonoids/day (in large portion by high
quercetin level) and incidence of all variety of cancer
(Hertog et al., 1995; Lin et al., 2006). On the other hand,
there are studies indicated a negative correlation between
up to 40 mg/day flavonoid consumption (95% of it
quercetin) and cancer incidence (Knekt et al., 1997; Knekt
et al., 2002).
It is demonstrated that triptolide (TP)-induced
oxidative stress and a decrease of testosterone generation
could be prevented by quercetin (Hu et al., 2015).
Different concentrations of TP were applied to Leydig
cells to cause oxidative stress with high intracellular
reactive oxygen species resulted in reduction activities
and expressions of glutathione peroxidase and superoxide
dismutase. Results of this study imply that quercetin
could lower the TP-induced reproductive toxicity, which
support the usage of TP.
The inhibition effect of quercetin against oxidative
stress, which caused by sodium fluoride, was investigated
in rat’s liver (Nabavi et al., 2012). Five groups of rats
were treated with different diets; the first group served
standard diet, the second group was intoxicated with
sodium fluoride (600 ppm) via drinking water for a week.
The third, fourth and fifth groups were applied with
quercetin at a dose of 10 and 20 mg/kg and vitamin C (as
the positive control) at a dose of 10 mg/kg
intraperitoneally for 1week ahead of sodium fluoride
intoxication, seriatim. Activities of superoxide dismutase
and catalase, the amount of decreased glutathione and
lipid peroxidation end product were measured 1 week
later treatments of rat liver. According to the data of this
work that quercetin preserves rat liver from sodium
fluoride activated oxidative stress, most likely by its
antioxidant action (Nabavi et al, 2012). It is also
demonstrated that quercetin prevents perfluorooctanoic
acid-induced liver damage via mitigating oxidative stress
and inflammatory response in mice (Zou et al., 2015). As
pointed out, mitochondrial oxidative stress has a main
role in the pathology of myocardial infarction (Czepas
and Gwoździński, 2014). In this study, pretreatment of
quercetin reduced the activities of serum creatine kinase,
lactate dehydrogenase, heart mitochondrial lipid
peroxidation products and dramatically enhanced the
amounts of mitochondrial antioxidants. In addition,
quercetin also cured the activities of tricarboxylic acid
cycle and respiratory chain enzymes almost normal level
in myocardial infarcted rats. The action of quercetin on
cardiac mitochondrial oxidative stress could reduce
mitochondrial lipid peroxidation; enhance levels of
mitochondrial antioxidants and activities of mitochondrial
marker enzymes. As a result, heart mitochondria of rat are
protected to isoproterenol-stimulated oxidative stress in
vivo in myocardial infarction (Czepas and Gwoździński,
Quercetin is the most abundant polyphenolic in human
food and the absences of its toxicity-genotoxicity has
been proved. It has high importance due to chemo
preventive and anticancer values. In general, all these
values might point out the possible treatment of quercetin
as cardio protectant through anthracycline chemotherapy.
Moreover, all these favourable impacts to anthracycline-
induced complications of chemotherapy need to be more
studied and validated both in animal and clinical works.
The experiment was established to test the
hepatoprotective effect of quercetin compared to N-
acetylcysteine (NAC) against hepatic I/R injury in rats
and to determine iNOS, eNOS, and NOSTRIN protein
expressions, as a possible mechanism of its
hepatoprotective effect. As a result, quercetin application
improved eNOS protein expression with a simultaneous
decline in iNOS and NOSTRIN protein expressions. In
addition, pretreatment of quercetin decreased serum
aspartate aminotransferase, alanine aminotransferases and
hepatic myeloperoxidase activities and recover the extinct
content of decreased glutathione, malondialdehyde, and
nitric oxide levels (Abd-Elbaset et al., 2015).
Neurodegenerative disorders are formed with complex
processes, basically associated to advance brain injury
capturing cellular death. Biochemical reactivity related to
these processes in Alzheimer’s disease contains, among
others, metal-induced oxidative stress promoting to
neuronal cell demise. One of the active redox metals
causing oxidative stress is Cu (II) (Naday et al., 2015).
Lately, the effort is to produce bioactive hybrid
nanoparticles that have the capability to work as host-
carriers for potential antioxidants, for instance, the natural
flavonoid quercetin. In molecular technology silica
nanoparticles were assembled with synthetic protocols to
produce PEGylated and CTAB-modified materials.
Conclusion and Future Prospects
The current review deals with the basic biological
functions of quercetin, such as antioxidant, anti-
carcinogenic, anti-inflammatory, and cardio protective
properties. Furthermore, prevention of tumour
development and possibility of flavonoid-drug interaction
have been also discussed. We shared these biological
properties of quercetin with a common mechanism of
antioxidant action in this review. Critical evaluation of
biological effects of quercetin leads to raising a
conclusion that at estimated dietary intake levels would
not cause adverse health problems, even; daily
consumption would be extremely beneficial for human
daily activities.
Competing Interest
The authors declare that they have no conflict of
Abd-Elbaset M, Arafa AE, El Sherbiny G, Abdel-Bakky M,
Elgendy ANAM. 2015. Quercetin modulates iNOS, eNOS and
NOSTRIN expressions and attenuates oxidative stress in warm
hepatic ischemia-reperfusion injury in rats. Beni-Suef Univ. J
Appl Sci. 4: 246255.
Abdelmoaty MA, Ibrahim MA, Ahmed NS, Abdelaziz MA. 2010.
Confirmatory studies on the antioxidant and antidiabetic effect
of quercetin In Rats. Indian J Clin Biochem. 25:v188-92.
Ozgen et al., / Turkish Journal of Agriculture - Food Science and Technology, 4(12): 1134-1138, 2016
Beecher GR. 1999. Antioxidant Food Supplements in Human
Health, Flavonoids in Foods Boots AW, Kubben N, Haenen
GRMM, Bast A. 2003. Oxidized quercetin reacts with thiols
rather than with ascorbate: Implication for quercetin
supplementation. Biochem Biophys Res Commun. 308:v560
Boots AW, Kubben N, Haenen GRMM, Bast A. 2003. Oxidized
quercetin reacts with thiols rather than with ascorbate:
Implication for quercetin supplementation. Biochem Biophys
Res Commun. 308:v560-565.
Bors W, Heller W, Michel C, Saran M. 1990. Radical chemistry of
flavonoid antioxidants. In: Emerit, I.; Packer, L.; Auclair, C.
(Eds.) Antioxidants in Therapy and Preventive Medicine.
Advances in Experimental Medicine and Biology. Plenum
Press. 264 New York, p. 165170.
Brown JE, Khodr H, Hider RC. 1998. Rice-Evans, CA. Structural
dependence of flavonoid interactions with Cu2+ ions:
implications for their antioxidant properties. Biochem J.
Çıkrıkçı S. 2005. The Synthesis and Characterızatıon of 4’-
Dioctylamıno-3- Hydroxyflavone based Fluorescence Probes.
MD Thesis, Istanbul Teknik Universitesi.
Cook NC Samman, S. Flavonoids. 1996. Chemistry, metabolism,
cardioprotective effects, and dietary sources. J Nutr Bioche.
Czepas J, Gwoździński K. 2014. The flavonoid quercetin: possible
solution for anthracycline-induced cardiotoxicity and multidrug
resistance. Biomed Pharmacother. 68: 114959.
D'Andrea G. 2015. Quercetin: A flavonol with multifaceted
therapeutic applications. Fitoterapia. 106: 256271.
Das NP. 1989. Flavonoids in Biology and Medicine III, National
University of Singapore, Singapore.
Doğan Z, Kocahan S, Erdemli E, Köse E, Yılmaz , Ekincioğlu Z,
Ekinci N, Türköz Y. 2015. Effect of chemotherapy exposure
prior to pregnancy on fetal brain tissue and the potential
protective role of quercetin. Cytotechnology. 67: 10311038.
Elik M, Serdaroğlu G, Özkan R. 2007. The Investigation of
Antioxidant Activities Of Myricetin And Quercetin With Dft
Methods, C.Ü. Fen-Edebiyat Fakültesi Fen Bilimleri Dergisi.
28: 2.
Ghosh N, Chakraborty T, Mallick S, Mana S, Singha D, Ghosh B,
Roy S. 2015. Synthesis, characterization and study of
antioxidant activity of quercetinmagnesium complex.
Spectrochim Acta A Mol Biomol Spectrosc. 151: 807813.
Gutteridge JM. 1995. Lipid peroxidation and antioxidants as
biomarkers of tissue damage. Clin Chem. 41: 18191828.
Hertog MG, Feskens EJM, Hollman PCH, Katan MB, Kromhout D.
1994. Dietary flavonoids and cancer risk in the Zutphen elderly
study. Nutr Cancer. 22: 175184.
Hertog MGL, Kromhout D, Aravanis C, Blackburn H, Buzina R,
Fidanza F, Giampaoli S, Jansen A, Menotti A, NedeljkovicS,
Pekkarinen M, Simic BS, Toshima H, Feskens EJM, Hollman
PCH, Katan MB. 1995. Flavonoid intake and long-term risk of
coronary heart disease and cancer in the seven countries study.
Arch Int Med. 155: 381386.
Hu J, Yu Q, Zhao F, Ji J, Jiang Z, Chen X, Gao P, Ren Y, Shao S,
Zhang Z, Yan M. 2015. Protection of Quercetin against
Triptolide-induced apoptosis by suppressing oxidative stress in
rat Leydig cells. Chem Biol Interact. 240: 8-46.
Knekt P, Ja¨rvinenR, Seppa¨nenR, Helio¨vaara M, Teppo L,
Pukkala E, Aromaa A. 1997. Dietary intake of flavonoids and
the risk of lung cancer and other malignant neoplasms. Am J
Epidemiol. 146: 223230.
Knekt P, Kumpulainen J, Jarvinen R, Rissanen H, Heliovaara M,
Reunanen A, Hakulinen T, Aromaa A. 2002. Flavonoid intake
and risk of chronic diseases. Am J Clin Nutr. 76 (3): 560568.
Knekt PJ, Reunanen A, Maatela J. 1996. Flavonoid intake and
coronary mortality in Finland: a cohort study. Br Med J.
Lin J, Zhang SM, Wu K, Willett WC, Fuchs CS, Giovannucci E.
2006. Flavonoid intake and colorectal cancer risk in men and
women. Am J Epidemiol. 164: 644651.
Martins HF, Leal JP, Fernandez MT, Lopes VH, Cordeiro MN.
2004. Toward the prediction of the activity of antioxidants:
experimental and theoretical study of the gas-phase acidities of
flavonoids. J Am Soc Mass Spectrom. 15:848-861.
Metodiewa D, Jaiswal AK Cenas N, Dickancaite E, Segura- Aguilar
J. 1999. Quercetin may act as a cytotoxic prooxidant after its
metabolic activation to semiquinone and quinoidal product. Free
Radic Biol Med. 26: 107116.
Mitchell LJ. 1965. Spectrophotometry of Molybdenum, Tungsten
and Chromium chelates of quercetin. PhD Thesis, Oregeon
State University: USA.
Nabavi SD, Nabavi SF, Eslami S, Moghaddam AH. 2012. In vivo
protective effects of quercetin against sodium fluoride-induced
oxidative stress in the hepatic tissue. Food Chem. 132: 931935.
Naday CM, Halevas E, Jackson GE, Salifoglou A. 2015. Quercetin
encapsulation in modified silica nanoparticles: potential use
against Cu (II)-induced oxidative stress in neurodegeneration. J
Inorg Biochem. 145: 5164.
Preedy V, Sung MT, Chen YC, Chi CW. 2014. Quercetin’s
Potential to Prevent and Inhibit Oxidative Stress-Induced Liver
Cancer: London. p 231-239.
Rahman A, Fazal F, Greensill J, Ainley K, Parish JH, Hadi SM.
1992. Strand scission in DNA induced by dietary flavonoids:
role of Cu(I) and oxygen free radicals and biological
consequences of scission. Mol Cell Biochem. 111(1-2): 39.
Rice-Evans CA, Miller NJ, Paganga G. 1996. Structure-antioxidant
activity relationships of flavonoids and phenolic acids. Free
Radic Biol Med. 20: 933956.
Rietjens IM, Boersma MG, van der Woude H, Jeurissen SM,
Schutte ME, Alink GM. 2005. Flavonoids and alkenylbenzenes:
Mechanisms of mutagenic action and carcinogenic risk. Mutat
Res. 574: 124138.
Sahu SC, Washington MC. 1991. Quercetin-induced lipid
peroxidation and DNA damage in isolated rat-liver nuclei.
Cancer Lett. 5 (1&2): 7579.
Selamoglu Z, Ustuntas HE, Ozgen S. 2016. Traditional and
complementary alternative medicine practices of some aromatic
plants in the human health. Research Journal of Biology. 4
(2): 52-54.
Silva MM, Santos MR, Caroco G, Rocha R, Justino G, Mira L.
2002. Structure-antioxidant activity relationships of flavonoids:
A reexamination. Free Radic Res. 36: 12191227.
Vasilescu D, Girma R. 2002. Quantum molecular modeling of
quercetin—Simulation of the interaction with the free radical t‐
BuOO. Int J Quantum Chem. 90: 888-902.
Wang L, Tu YC, Lian TW, Hung JT, Yen JH, Wu MJ. 2006.
Distinctive antioxidant and antiinflammatory effects of
flavonols. J Agric Food Chem. 54: 97989804.
Yáñez J, VicenteV, Alcaraz M, Castillo J, Benavente-Garcia O,
Canteras M, Teruel JA. 2004. Cytotoxicity and antiproliferative
activities of several phenolic compounds against three
melanocytes cell lines: relationship between structure and
activity. Nutr Cancer. 49: 191-199.
Zou W, Liu W, Yang B, Wu L, Yang J, Zou T, Liu F, Xia L, Zhang
D. 2015. Quercetin protects against perfluorooctanoic acid-
induced liver injury by attenuating oxidative stress and
inflammatory response in mice. Int Immunopharmacol. 28:
... As a subclass of polyphenolic substances with a wide range of chemical characteristics, flavonoids are a ubiquitous component of plants. Of all the flavonoids, quercetin is one of the most effective antioxidants [47,48]. More than 4000 different flavonoids, including flavonols, flavones, flavanones, catechins, anthocyanidins, isoflavones, dihydroflavonols, and chalcones, have been classified as part of the major flavonoid group [47]. ...
... Of all the flavonoids, quercetin is one of the most effective antioxidants [47,48]. More than 4000 different flavonoids, including flavonols, flavones, flavanones, catechins, anthocyanidins, isoflavones, dihydroflavonols, and chalcones, have been classified as part of the major flavonoid group [47]. The food business uses organic antioxidants to preserve the product's color and nutritional content. ...
... The food business uses organic antioxidants to preserve the product's color and nutritional content. Studies on the application of flavonoids in various industrial sectors have grown in number recently [47]. Similar to how they may be used in food, textiles, leather, metallurgy, medicine, and agriculture, these substances may also be used for their antioxidant capabilities [47]. ...
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For the seafood industry, Vibrio parahaemolyticus, one of the most prevalent food-borne pathogenic bacteria that forms biofilms, is a constant cause of concern. There are numerous techniques used throughout the food supply chain to manage biofilms, but none are entirely effective. Through assessing its antioxidant and antibacterial properties, quercetin will be evaluated for its ability to prevent the growth of V. parahaemolyticus biofilm on shrimp and crab shell surfaces. With a minimum inhibitory concentration (MIC) of 220 µg/mL, the tested quercetin exhibited the lowest bactericidal action without visible growth of bacteria. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin without (control) and with sub-MICs levels (1/2, 1/4, and 1/8 MIC) against V. parahaemolyticus was examined. With increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of related genes linked to flagella motility (flaA and flgL), biofilm formation (vp0952 and vp0962), and quorum-sensing (luxS and aphA) were all dramatically reduced (p < 0.05). Quercetin (0-110 μg/mL) was investigated on shrimp and crab shell surfaces, the inhibitory effects were 0.68-3.70 and 0.74-3.09 log CFU/cm2, respectively (p < 0.05). The findings were verified using field emission scanning electron microscopy (FE-SEM), which revealed quercetin prevented the development of biofilms by severing cell-to-cell contacts and induced cell lysis, which resulted in the loss of normal cell shape. Furthermore, there was a substantial difference in motility between the treatment and control groups (swimming and swarming). According to our findings, plant-derived quercetin should be used as an antimicrobial agent in the food industry to inhibit the establishment of V. parahaemolyticus biofilms. These findings suggest that bacterial targets are of interest for biofilm reduction with alternative natural food agents in the seafood sector along the entire food production chain.
... The OH groups in quercetin strongly interact with the acetylcholinesterase (AChE) enzyme at the catalytic anionic site through hydrogen bonding. Quercetin glycosylation at position 3 makes a decrease in AChE blockage potential as well as free radical scavenging activity [47]. This conjugation system is an essential factor for free radical scavenging activity and the beneficial effects of quercetin for managing oxidative stress in NDDs [38]. ...
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Abstract: Spinal cord injury (SCI) possesses a complicated etiology. There is no FDA-approved treatment for SCI, and the majority of current interventions focus on reducing symptoms. During SCI, inflammation, oxidative stress, apoptosis, and autophagy are behind the secondary phase of SCI and cause serious consequences. It urges the need for providing multi-targeting agents, that possess lower side effects and higher efficacy. The plant secondary metabolites are multi-targeting agents and seem to provide new roads in combating diseases. Flavonoids are phytochemicals of continual interest to scientists in combating neurodegenerative diseases (NDDs). Flavonoids are being studied for their biological and pharmacological effects, particularly as antioxidants, anti-inflammatory agents, anti-apoptotic, and autophagy regulators. Quercetin is one of the most well-known flavonols known for its preventative and therapeutic properties. It is a naturally occurring bioactive flavonoid that has recently received a lot of attention for its beneficial effects on NDDs. Several preclinical evidence demonstrated its neuroprotective effects. In this systematic review, we aimed at providing the biological activities of quercetin and related derivatives against SCI. Detailed neuroprotective mechanisms of quercetin derivatives are also highlighted in combating SCI.
... The ferric reducing power of the heterodimer was higher by almost 2-folds when compared to nordihydroguaiaretic acid, and was almost 20% higher than that of quercetin. The hydroxyl groups on the ortho-catechol ring (B) of quercetin provides the group with a higher acidity capacity, thus making the ortho 3 ′ , 4 ′ dihydroxy substitution in this ring critical for the high antioxidant activity of quercetin [53]. Furthermore, the analysis of the electron spin density of the 4 ′ -quercetin radical by Vasilescu and Girma [54] revealed a partial involvement of ring C in the scavenging activities of quercetin. ...
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Biocatalysis has attracted considerable attention as a viable approach for modifying and synthesising bioactive compounds. In this study, we report the modes of inhibition, and thermodynamic properties of the Trametes pubescens CBS 696.94 laccase and its application in the synthesis of novel hybrid compounds. The enzyme was reversibly and non-competitively inhibited by NaN3, and irreversibly and non-competitively inhibited by sodium dodecyl sulphate (SDS). L-Cysteine, H2O2 and dithiothreitol exhibited irreversible and uncompetitive inhibition of the enzyme. The t1/2 values of the enzyme at 50 °C, 60 °C and 70 °C were 7.8 h, 3.8 h, and 0.72 h, respectively. The enzyme deactivation energy (Ed) was 109.362 kJ/mol while ΔG, ΔH, and ΔS were positive. The enzyme was successfully employed in the synthesis of quercetin/catechol, quercetin/nordihydroguaiaretic acid (NDGA), and gallic acid/NDGA hybrid compounds. The quercetin/catechol heterotrimer exhibited enhanced antimicrobial activity against Listeria monocytogenes and Staphylococcus aureus. Both the 5′− 5′ quercetin/NDGA and 4-O-5′ gallic acid/NDGA heterodimers exhibited enhanced antioxidant activities. The 5′− 5′ quercetin/NDGA also exhibited enhanced antimicrobial activity against L. monocytogenes, S. aureus, Escherichia coli and Enterobacter cloacae. Therefore, the T. pubescens laccase can potentially be used in the cross-coupling of phenolic compounds for the improvement of antioxidant and antibacterial activities.
... According to recent surveys [82,83], the consumption of foods rich in flavonoids, such as quercetin, reduces the risk of cancer due to a combination of their antioxidant and anti-inflammatory actions. Quercetin inhibits and prevents cancer, but also aids in recovery after treatments against the disease, such as chemotherapy [47]. ...
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Quercetin belongs to the broader category of polyphenols. It is found, in particular, among the flavonols, and along with kaempferol, myricetin and isorhamnetin, it is recognized as a foreign substance after ingestion in contrast to vitamins. Quercetin occurs mainly linked to sugars with the most common compounds being quercetin-3-O-glucoside or as an aglycone, especially in the plant population. The aim of this review is to present a recent bibliography on the mechanisms of quercetin absorption and metabolism, bioavailability, and antioxidant and the clinical effects in diabetes and cancer. The literature reports a positive effect of quercetin on oxidative stress, cancer, and the regulation of blood sugar levels. Moreover, research-administered drug dosages of up to 2000 mg per day showed mild to no symptoms of overdose. It should be noted that quercetin is no longer considered a carcinogenic substance. The daily intake of quercetin in the diet ranges 10 mg-500 mg, depending on the type of products consumed. This review highlights that quercetin is a valuable dietary antioxidant, although a specific daily recommended intake for this substance has not yet been determined and further studies are required to decide a beneficial concentration threshold.
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Introduction: This study aims at the biological profiling of Allium sativum , Zingiber officinale , Nigella sativa , Curcuma longa , Mentha piperita , Withania somnifera , Azadirachta indica , and Lawsonia inermis as alternatives against onychomycosis to combat the treatment challenges. Methods: An extract library of aqueous (DW), ethyl acetate (EA), and methanol (M) extracts was subjected to phytochemical and antioxidant colorimetric assays to gauge the ameliorating role of extracts against oxidative stress. RP-HPLC quantified therapeutically significant polyphenols. Antifungal potential (disc diffusion and broth dilution) against filamentous (dermatophytes and non-dermatophytes) and non-filamentous fungi ( yeasts ; Candida albicans ), synergistic interactions (checkerboard method) with terbinafine and amphotericin-B against resistant clinical isolates of dermatophytes ( Trichophyton rubrum and Trichophyton tonsurans ) and non-dermatophytes ( Aspergillus spp., Fusarium dimerum , and Rhizopus arrhizus ) , time-kill kinetics, and protein estimation (Bradford method) were performed to evaluate the potential of extracts against onychomycosis. Results: The highest total phenolic and flavonoid content along with noteworthy antioxidant capacity, reducing power, and a substantial radical scavenging activity was recorded for the extracts of Z. officinale . Significant polyphenolics quantified by RP-HPLC included rutin (35.71 ± 0.23 µg/mgE), gallic acid (50.17 ± 0.22 µg/mgE), catechin (93.04 ± 0.43 µg/mgE), syringic acid (55.63 ± 0.35 µg/mgE), emodin (246.32 ± 0.44 µg/mgE), luteolin (78.43 ± 0.18 µg/mgE), myricetin (29.44 ± 0.13 µg/mgE), and quercetin (97.45 ± 0.22 µg/mgE). Extracts presented prominent antifungal activity against dermatophytes and non-dermatophytes (MIC-31.25 μg/ml). The checkerboard method showed synergism with 4- and 8-fold reductions in the MICs of A. sativum , Z. officinale , M. piperita , L. inermis , and C. longa extracts and doses of amphotericin-B (Amp-B) and terbinafine (against non-dermatophytes and dermatophytes, respectively). Furthermore, the synergistic therapy showed a time-dependent decrease in fungal growth even after 9 and 12 h of treatment. The inhibition of fungal proteins was also observed to be higher with the treatment of synergistic combinations than with the extracts alone, along with the cell membrane damage caused by terbinafine and amp-B, thus making the resistant fungi incapable of subsisting. Conclusion: The extracts of A. sativum , Z. officinale , M. piperita , L. inermis , and C. longa have proven to be promising alternatives to combat oxidative stress, resistance, and other treatment challenges of onychomycosis.
This study was designed to investigate in vitro biological activities and phytochemical composition of aqueous and ethanolic extracts from Achillea sintenisii Hub- Mor. (AS). To determine the chemical composition of AS extracts, phytochemical analyses were performed by using HPLC–ESI-Q-TOF-MS-MS. Afterwards, both extracts were investigated in terms of their effect on fibroblast proliferation, collagen synthesis, and hydrogen peroxide-induced damage. In addition to cell culture analysis, antibacterial, antioxidant, hyaluronidase inhibitory activities and total phenolic contents of the extracts were analyzed in cell-free systems. Our results demonstrated that the aqueous and ethanolic extracts did not show cytotoxic activity on fibroblasts, on the contrary, promoted fibroblast proliferation. Both AS extracts potently inhibited hyaluronidase activity and the inhibitory effect of ethanolic extract was comparable with the positive control, especially at high concentrations. The aqueous extract was the potent stimulator of collagen synthesis at 200 µg/mL concentration. Although the ethanolic extract showed antibacterial activity against all gram-positive bacteria, the aqueous extract was only effective against K. pneumoniae and B. subtilis. The ability of AS extracts, which have a rich phenolic compound content (≥50 mg GAE/g), to scavenge free radicals and protect fibroblasts against hydrogen peroxide-induced damage can be considered as a result of their antioxidant potential. Our findings scientifically support the widespread use of this plant, by demonstrating the pharmacological properties of the extracts.
Background: Despite confirmed dietary approaches to improve the Non-Alcoholic Fatty Liver Disease (NAFLD), the effect of fruits on NAFLD is not clear. The present study aimed to investigate the effect of a fruit rich diet (FRD) on liver steatosis, liver enzymes, Insulin resistance, and lipid profile in patients with NAFLD. Methods: Eighty adults with NAFLD participated in this randomized controlled trial. The participants were randomly assigned to the FRD group with consumption of at least 4 servings of fruits daily or the control group with fruits consumption of less than 2 servings/day. The grade of steatosis, serum levels of liver enzymes including alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT), total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), glucose, and homeostatic model assessment for insulin resistance (HOMA-IR) were measured at the baseline and at the end of the study. Results: After 6 months of intervention, the FRD group had significantly higher BMI (31.40 ± 2.61 vs. 25.68 ± 2.54, p < .001), WC (113.5 ± 10.7 vs. 100.5 ± 7.5, p < .001), the grade of steatosis, ALT (89.1 ± 92.9 vs. 32.0 ± 19.2, p < .001), AST (74.5 ± 107.8 vs. 24.0 ± 8.5, p < .001), ALP (273.4 ± 128.5 vs. 155.0 ± 43.9, p < .001), GGT (92.7 ± 16.2 vs. 21.2 ± 7.7, p < .001), TC (206.1 ± 40.5 vs. 172.7 ± 42.4, p < .01), LDL (126.9 ± 32.3 vs. 99.8 ± 29.8, p < .001), glucose (115.5 ± 30.0 vs. 97.7 ± 19.0, p < .01), and insulin resistance (7.36 ± 4.37 vs. 2.66 ± 1.27, p < .001), and lower HDL (41.4 ± 8.9 vs. 53.8 ± 15.1, p < .001) compared to the control group. Adjusting for BMI and calorie intake did not change the results. Conclusion: The results of the present study indicated that consumption of fruits more than 4 servings/day exacerbates steatosis, dyslipidemia, and glycemic control in NAFLD patients. Further studies are needed to identify the underlying mechanisms of the effects of fruits on NAFLD. Clinical trial registration: This trial was registered at Iranian randomized clinical trial website with IRCT registration no. IRCT20201010048982N1on October 15, 2020.
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Novel chitosan (Ch) films containing choline chloride and citric acid mixture as plasticizer (deep eutectic solvent, DES) and different amounts of quercetin (QUE) as antioxidant additive were prepared. Physicochemical and mechanical characteristics of the developed Ch/DES/QUE films were studied using FTIR, SEM, and AFM techniques. FTIR spectra revealed the possible interactions between all the components. The surface of the films was dense and rough. The addition of quercetin caused an increase in the tensile strength (TS) and Young's modulus, but significantly decreased the elongation at break. The films containing quercetin showed improved antioxidant activity in relation to Ch/DES film. Finally, the oxidation phenomena of rapeseed oils with and without chitosan films were evaluated as amounts of primary and secondary oxidation products and total oxidation index. The addition of Ch/DES films with quercetin to oil samples successfully retarded secondary lipid oxidation processes and improved its antioxidant activity under the accelerated storage condition.
This study reports the characterization of two series of organic-inorganic silica-based hybrid materials with 15 and 20 wt% of quercetin (Q), respectively, and 6, 12, 24 and 50 wt% of polyethylene glycol (P) (for each of them). After the sol-gel synthesis they have been characterized using different techniques (Fourier-Transform Infrared and Micro-Raman spectroscopies, Thermogravimetry, Differential Thermal Analysis). Two tests were also carried out to evaluate their biomedical properties to estimate their antibacterial activity and their cytotoxicity. FT-IR measurements revealed the interaction between the components of the hybrid materials, while Micro-Raman spectra confirmed the presence of quercetin in an oxidized form. Simultaneous Thermogravimetry and Differential Thermal Analysis coupled with Mass Spectrometry enabled to investigate the thermal behavior of the hybrids (up to 800 °C) and to analyze the gas mixtures evolved upon heating in severe inert argon atmosphere. Antibacterial tests showed that an increase of PEG contents results in a decrease of the bacterial growth. Finally, cytotoxicity assessment highlighted that entrapping quercetin in hybrids at high PEG content leads to the constitution of materials that enjoy PEG biocompatibility, while cytotoxic effects are depleted.
Drug interactions can induce significant clinical impacts, either by increasing adverse effects or by decreasing the therapeutic effect of drugs, and thus, need to be explored thoroughly. Clinically significant drug interactions can be induced by organic anion transporter 1 (OAT1) and OAT3 when concomitant medications competitively interact with the transporters. The purposes of this study were to develop and validate a sensitive and selective analytical method for 5-carboxyfluorescein (5-CF) and optimize the experimental conditions for interaction studies. An analytical method using high-performance liquid chromatography (HPLC) equipped with a fluorescence detector was validated for accuracy, precision, matrix effect, recovery, stability, dilutional integrity, and carry-over effect. In addition, the 5-CF concentration, incubation period, and washing conditions for interaction study were optimized. Using a valid analytical method and optimized conditions, we performed an interaction study for OAT1 and OAT3 using 26 test articles. Some of the test articles showed strong inhibitory potency for the transporters, with IC50 values close to or less than 10 μM. The valid analysis method and optimized systems developed in this study can be utilized to improve the predictability of drug interactions in humans and consequently aid in successful disease treatment by maintaining appropriate systemic exposures.
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Plants are essential for human since from the beginning. Plants and their extracts are mainly used medicinal purposes both for the prevention and treatment of human diseases in many countries. Recently, studies are conducted to demonstrate the importance of natural antioxidants in human health. The purpose of these studies is 1) to identify the important plants and extract form them 2) to demonstrate the effect of these extract on human and environmental health [1]. Synthetic products are produced to meet the needs of increasing world population for food and medicine. However, serious health and environmental problems are increased by using these synthetic products. One of the most important problems in the world is to provide enough safe food for people. Antioxidant addition is necessary in order to preserve the flavor, color and vitamin content of the food. Some of these sources are containing natural antioxidants (such as spices), however, industries are extensively added synthetic antioxidants to the processed foods. Butylated hydroxy anisole and butylated hydroxy toluene, tertiary butyl hydroquinone, gallates, nordihi-droguareyetik acid are examples of synthetic antioxidants. Nowadays, especially in developed countries, public awareness shifted to human-environmental health and natural product resulted to safe food production and alternative to synthetic antioxidant products [2]. Level of health displays economic development of the society. The cheapest way to resolve this problem is that conducting research on plants that have high antioxidant compound. Consumers should be informed about the research results on chronic diseases and encouraged to consume foods that have high antioxidant properties. Antioxidant effect of plants in oxidative stress Most Agents that are used in cosmetic, food, chemical and pharmaceutical industries are obtained from medicinal and aromatic plants. Since the smell of these plants is all natural they are extremely valuable raw materials. When consumption of natural products increased consumption of plants with medicinal properties increased accordingly. Previously, these plants were collected form nature; however, with increasing demand for these plants is rapidly directed cultivation of such plants. The compounds called flavonoids and phenolic that are accumulated the most in leaves, flowers and woody portion of plants are capable to avoid oxidation of lipids, carbohydrates and proteins by giving away hydrogen on their hydroxyl group in their aromatic ring. Consequently, the use of ecological and natural products that inhibit oxidation of biomolecules in living organism became more preferable in human diet [3,4]. Antioxidants are able to retard or inhibit oxidative degradation of the compound. These compounds are effective to beginning of otooxidative and otooxdative process to prevent formation of undesirable products to form [3]. Antioxidant effect of aromatic plants in oxidative stress Reactive oxygen species are produced metabolic and physiological processes where these biomolecules have highly damaging effects. Organisms may cause harmful oxidative reactions during vital activities and the removal of these oxidative products is accomplished through enzymatic and non-enzymatic antioxidant mechanisms. An increase in oxygen production and decrease
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The pathogenesis of hepatic ischemia/reperfusion (I/R) is mediated through the generation of oxidative and nitrosative stress-induced cell injury. Hence, the present study was designed to evaluate the hepatoprotective effect of quercetin (QR) compared to N-acetylcysteine (NAC) against hepatic I/R injury in rats and to assess iNOS, eNOS and NOSTRIN protein expressions, as a possible mechanism of its hepatoprotective effect. Hepatic ischemia was surgically performed by occlusion of hepatic pedicle (hepatic artery, portal vein, bile duct) that supplies the left and medial lobes (approximately 70% of the total liver mass), for 30 minutes with a vascular clamp followed by releasing the clamp and the liver was reperfused for 30 minutes. QR-pretreatment increased eNOS protein expression with simultaneous decrease in iNOS and NOSTRIN protein expressions. It also decreased serum aspartate aminotransferase (AST), alanine aminotransferases (ALT) and hepatic myeloperoxidase (MPO) activities. In addition, it restored the depleted content of reduced glutathione (GSH) and decreased malondialdehyde (MDA) and nitric oxide (NO) levels. A notable finding is that QR alleviated I/R-induced histopathological changes. The present study illustrates the hepatoprotective effect of quercetin compared to N-acetylcysteine against ischemia/reperfusion-induced liver injury by inhibiting oxidative stress and by modulating iNOS, eNOS and NOSTRIN protein expressions.
Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death in the world. Reactive oxygen species (ROS)-induced oxidative stress has been considered a key player in the development and progression of various liver diseases, including viral hepatitis, fibrosis, cirrhosis, and liver cancer (e.g., HCC). In addition to endogenous antioxidants, quercetin available in food is the natural antioxidant to protect humans against oxidative stress. This protective effect is mediated through reducing ROS production, increasing the capacity of DNA repair, and promoting antioxidative responses in cells. In addition, several studies have found that quercetin also has an antiproliferation effect on HCC cells. Moreover, combination treatment with quercetin and chemotherapeutic drug doxorubicin induced a synergistic cytotoxic effect in HCC cells. These results together suggest that quercetin not only has an antioxidative effect to prevent oxidative stress but also has a potential anticancer effect for HCC treatment.
Great interest is currently centered on the biologic activities of quercetin a polyphenol belonging to the class of flavonoids, natural products well known for their beneficial effects on health, long before their biochemical characterization. In particular, quercetin is categorized as a flavonol, one of the five subclasses of flavonoid compounds. Although flavonoids occur as either glycosides (with attached glycosyl groups) or as aglycones, most altogether of the dietary intake concerning quercetin is in the glycoside form. Following chewing, digestion, and absorption sugar moieties can be released from quercetin glycosides. Several organs contribute to quercetin metabolism, including the small intestine, the kidneys, the large intestine, and the liver, giving rise to glucuronidated, methylated, and sulfated forms of quercetin; moreover, free quercetin (such as aglycone) is also found in plasma. Quercetin is now largely utilized as a nutritional supplement and as a phytochemical remedy for a variety of diseases like diabetes/obesity and circulatory dysfunction, including inflammation as well as mood disorders. Owing to its basic chemical structure the most obvious feature of quercetin is its strong antioxidant activity which potentially enables it to quench free radicals from forming resonance-stabilized phenoxyl radicals. In this review the molecular, cellular, and functional bases of therapy will be emphasized taking strictly into account data appearing in the peer-reviewed literature and summarizing the main therapeutic applications of quercetin; furthermore, the drug metabolism and the main drug interaction as well as the potential toxicity will be also spotlighted.
Triptolide (TP) is a diterpene triepoxide with variety biological activities, such as anti-inflammatory, anti-cancerogenic, immunomodulatory and pro-apoptotic activities. However, its clinical application was limited by potential toxicity. Quercetin (Que) is a member of flavonoids with anti-oxidant effects. In this study, we aimed to demonstrate the protective effect of Que in TP-induced oxidative stress and decrease of testosterone generation in reproductive damage. Leydig cells were treated with TP (20, 40 and 60 nM), which caused obvious oxidative stress increasing intracellular ROS, decreasing activities and expressions of GPx and SOD. Apoptosis was resulted from depolarization of mitochondrial membrane potential (ΔΨm) and release of cytochrome C (Cyt-C) showing increase of BAX/Bcl-2 ratio, caspase-3 and caspase-9. Treatment of Que (5 μM) prior to triptolide could restore all the TP-induced alteration in a certain dose range indicating that the oxidative stress might be one reason of TP-induced reproductive toxic effect. These results suggest that the compatibility with Que might reduce the TP-induced reproductive toxicity, which provide a probability to extend the usage of TP. Copyright © 2015. Published by Elsevier Ireland Ltd.
Quercetin (3,3',4',5,7-pentahydroxyflavone) one of the most abundant dietary flavonoids, has been investigated in the presence of magnesium (II) in methanol. The complex formation between quercetin and magnesium (II) was examined under UV-visible, Infra-red and (1)H NMR spectroscopic techniques. The spectroscopic data denoted that quercetin can reacts with magnesium cation (Mg(+2)) through the chelation site in the quercetin molecule. The free radical antioxidant activity of the complex with respect to the parent molecule was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. It was observed that the free radical scavenging activity of quercetin was increased after complexation of magnesium (Mg(+2)) cation. Copyright © 2015 Elsevier B.V. All rights reserved.
The aim of the present study was to investigate the protective effect of quercetin (Que) against perfluorooctanoic acid (PFOA)-induced liver injury in mice and its possible mechanisms of action. Mice were intragastrically administered PFOA (10mg/kg/day) alone or in combination with Que (75mg/kg/day) for 14 consecutive days. The hepatic injury was evaluated by measuring morphological changes, liver function, oxidative stress, inflammatory response and hepatocellular apoptosis. Compared with mice treated with PFOA alone, simultaneous supplementation of Que significantly decreased serum levels of liver injury indicators alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase and total bile acids. Moreover, Que treatment inhibited the production of oxidative stress biomarkers malondialdehyde, hydrogen peroxide and 8-hydroxy-2'-deoxyguanosine, reduced the levels of proinflammatory cytokines interleukin 6, cyclooxygenase-2 and C-reactive protein, and decreased the number of TUNEL-positive cells in the liver of PFOA-treated mice. These results combined with liver histopathology demonstrated that Que exhibited a potential protective effect against PFOA-induced liver damage via mechanisms involving the attenuation of oxidative stress, alleviation of inflammation and inhibition of hepatocellular apoptosis. Copyright © 2015. Published by Elsevier B.V.