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Phytochemistry 145 (2018) 187e196
Contents lists avai
Phytochemistry
journal homepage: www.elsevier .com/locate/phytochem
Review
Chrysin: Sources, beneficial pharmacological activities, and molecularmechanism of action
Renuka Mani, Vijayakumar Natesan*
Department of Biochemistry and Biotechnology, Faculty of Science, Annamalai University, Annamalainagar, 608002, India
a r t i c l e i n f o
Article history:Received 11 April 2017Received in revised form19 September 2017Accepted 21 September 2017Available online 20 November 2017
Keywords:PassifloraceaePassiflora caeruleaChrysinPharmacological activitiesBioavailabilityMolecular docking
Abbreviations: AC, adenylyl cyclase; AGEs, advanceAR, aldose reductase activator protein 1; ATC, anaplasenergy; BDNF, brain-derived neurotrophic factor; BZDmethoxyflavone; Ch-4, 5,7-diacetylflavone; CHRY-DMdictable mild stress; CVDs, cardiovascular diseases; DEAN, experimental autoimmune neuritis; EEP, ethanoFSK, forskolin; GABA, gamma amino butyric acid; D-Gaoccupied molecular orbital; IL-6, interleukin-6; iNOS,human matrix metalloproteinase; MRP, multidrug renuclear factor-erythroid 2-related factor 2; ODC, ornprostaglandin E2; PPAR-g, peroxisome proliferator-acserum response element; STAT, signal transducer andfactor; TNF-a, tumor necrosis factor-alpha; TRAIL, tumvascular endothelial growth factor; VSMC, vascular sm* Corresponding author.
E-mail address: [email protected] (V. Nate
https://doi.org/10.1016/j.phytochem.2017.09.0160031-9422/© 2017 Elsevier Ltd. All rights reserved.
a b s t r a c t
In recent years, public and scientific interest in plant flavonoids has tremendously increased because oftheir postulated health benefits. This review was mainly focuses on the flavone chrysin (5,7-dihydroxyflavone), which occurs naturally in many plants, honey, and propolis. A number of in vitroand in vivo studies have revealed the therapeutic effects of chrysin against various diseases. In general,chrysin exhibits many biological activities and pharmacological effects, including antioxidant, anti-inflammatory, anticancer, and antiviral activities. Moreover, many studies have reported on thebioavailability of chrysin. Because of its compromised bioavailability and enhanced protein stability,chrysin solid lipid nanoparticle (SLN) synthesis avoids proteolytic degradation and sustained release ofdrug delivery. To clarify the mechanism of action of chrysin, researchers have investigated the structuralbinding relationship of chrysin through the docking computation method.
© 2017 Elsevier Ltd. All rights reserved.
1. Introduction
Flavonoids are ubiquitous plant specialized metabolites thatcontain large groups of low-molecular-weight polyphenolic com-pounds, which present benefits to human health because of theirbiological properties. To date, approximately 5000 diverse flavo-noids have been identified (Pietta, 2000). Nutritionists calculate theapproximate average ingestion of flavonoids by humans on anormal diet to be 1e2 g/day (De Vries et al., 1997). Flavonoids arenaturally occurring polyphenols with patterns of hydroxylation and
d glycation end products; ACR, acrytic thyroid cancer; ATP, adenosine, benzodiazepine; CaM, calmodulin, dimethoxylated chrysin; COX-2,EN, N-nitrosodiethylamine; DMBAlic extract of propolis; EMT, epithelN, D-galactosamine; GSH, glutathinducible nitric oxide synthase; Lsistance protein; NF-kB, nuclear faithine decarboxylase activity; PCNtivated receptor-g systolic arterial pactivator transcription; SVGp12, hor necrosis factor-related apoptosooth muscle cell.
san).
substitutions that give rise to various subclasses including flava-nones, anthocyanidins, flavonols, flavones, catechins (or flavanols),isoflavones, dihydroflavonols, and chalcones (Hodnick et al., 1988;Beecher, 2003) (Fig. 1). One such flavonoid that has receivedconsiderable attention is chrysin (5,7-di-OH-flavone). Chrysin,which has the ubiquitous 15-carbon flavone backbone, is one of themost important bioactive constituents of different fruits, vegeta-bles, and even mushrooms. Chrysin has a common chemicalstructure, consisting of two fused rings, A and C, and a phenyl ring,B, attached to the second position of the C ring. It shares the
lamide; AHR, aryl hydrocarbon receptor; AMPK, AMP-activated protein kinase; AP-1,triphosphate; B(a)P, benzo(a)pyrene; b-CD, b-cyclodextrin; BDE, bond dissociation; CAPE, chrysin and caffeic acid phenethyl ester; CDDP, cisplatin; Ch-2, 5-hydroxy-7-cyclooxygenase-2; CPI, di-isopropyl chrysin-7-yl phosphate; CUMS, chronic unpre-, 7,12-dimethylbenza [a]anthracene; DMSO, dimethyl sulfoxide; DOX, doxorubicin;lialemesenchymal transition; EV71, enterovirus 71; Fe-NTA, ferric nitrilotriacetate;ione; PCA, protocatechuic acid; HIF-1A, hypoxia-inducible factor-1A; HOMO, highestC-MS, liquid chromatography mass spectrometry; MD, molecular dynamics; MMP,ctor k-light-chain enhancer of activated B cells; NGF, nerve growth factor; Nrf-2,A, proliferating cell nuclear antigen; PDGF, platelet-derived growth factor; PGE2,ressure; ROS, reactive oxygen species; SDE, Scutellaria discolor Colebr. extract; SRE,uman astroglia cells line; TNBC, triple-negative breast cancer; TNF, tumor necrosisis-inducing ligand; UPLC-MS, ultra-performance tandem mass spectrometry; VEGF,
Fig. 1. Classification of flavonoids.
R. Mani, V. Natesan / Phytochemistry 145 (2018) 187e196188
common flavone structure, with an additional hydroxyl group atthe 5th and 7th positions of the A ring (Fig. 2). Chrysin is convertedfrom the amino acid phenylalanine. The phenylpropanoids are adiverse family of organic compounds that are synthesized by plantsfrom the amino acids phenylalanine and tyrosine. Their name isderived from the six-carbon aromatic phenyl group and the three-carbon propene tail of cinnamic acid, which is synthesized fromphenylalanine in the first step of phenylpropanoid biosynthesis.Phenylalanine is first converted to cinnamic acid by the action ofthe enzyme phenylalanine ammonia-lyase. A series of enzymaticreactions lead to chrysin synthesis. Compared to the other flavo-noids, chrysin is the least studied flavonoid by spectroscopic
Fig. 2. Structure of chrysin.
techniques (Pusz et al., 2000; Muneoz et al., 2016). The presence ofhydroxyl and keto functional groups may result in the formation ofstrong supramolecular synthons, with coformers having comple-mentary functional groups, thus offering a great opportunity todesign nutraceutical cocrystals of chrysin.
2. Chrysin
2.1. Source of chrysin
Chrysin is a dietary phytochemical that is abundantly present inmany plant extracts, including propolis, blue passion flower (Pas-siflora caerulea), and honey, which have great economic value andmedicinal impact.
2.2. Propolis
Propolis (also known as “bee glue”) is the general name for theresinous substance collected by honeybees (Apis mellifera L.) fromvarious plants. The word propolis is derived from the Greek wordspro (defense) and polis (the city), i.e., defense of the city (or thehive). Propolis may vary in color from light yellow to dark browndepending on its source and age. It is hard and brittle when cold butbecomes soft and very sticky when warm (Koltay, 1981). Someremarkable points emerge from the work that has been conductedfor the propolis constituents. So far, flavonoid pigments are the
R. Mani, V. Natesan / Phytochemistry 145 (2018) 187e196 189
largest group of isolated compounds and are ubiquitous in the plantkingdom. Propolis has been used by humans since 300 BC(Ghisalberti, 1979), and their use continues even today in homeremedies and personal products. Propolis is reputed to have anti-septic, antimycotic, astringent, spasmolytic, bacteriostatic, choleric,anti-inflammatory, anesthetic, and antioxidant properties. Previousstudies showed that the chrysin content in propolis is as high as28 g/l.
2.3. Passiflora
The genus Passiflora, comprising about 500 species, is the largestin the family Passifloraceae (Anesini and Perez, 1993). The speciesof this genus are distributed in the tropical and warm temperateregions of the new world; they are much rarer in Asia, Australia,and tropical Africa.
Scientific classification of Passiflora caerulea
Kingdom: PlantaeOrder: MalpighialesFamily: PassifloraceaeGenus: PassifloraSpecies: P. caeruleaBinomial name: Passiflora caerulea. L.
In the 17th century, P. caerulea (blue Passion flower), native ofBrazil, was introduced into Britain. It has been used as an anti-spasmodic and sedative in Italy. P. caerulea plant extract has beenused as a remedy for insomnia caused by various nervous condi-tions, but not pain. The root has been used as a sedative andvermifuge in West Indies, Mexico, the Netherlands, and SouthAmerica. Moreover, the root has been used as a diuretic anddecoction of leaves as an emetic in Italy. Aerial parts of P. caeruleaare used as antimicrobial agents against catarrh and pneumonia(Anesini and Perez, 1993). The linear range of chrysin is0.012e0.120 mg/ml, with an average recovery of 99.41% from theleaves of Passiflora edulis (Zhao et al., 2012).
2.4. Honey
Honeybees collect nectar; and transform by combining withtheir own deposit substances, dehydrate, store, and leave in thehoneycomb to ripen and mature. Honey is composed of a mixtureof sugars, mainly fructose and glucose but also maltose, sucrose,and other complex carbohydrates (Blasco et al., 2011). However, thepercentage of each sugar varies depending on the raw materialused for its production. It also contains other components such asflavonoids, minerals, vitamins, amino acids, proteins, pigments,several organic acids, and compounds with antioxidant properties(Kujawski and Namiesnik, 2008; Fallico et al., 2004; Finola et al.,2007; Silva et al., 2008). The chrysin content is 0.10 mg/kg inhoneydew and 5.3 mg/kg in forest honeys (Hadjmohammadi et al.,2010).
3. Pharmacological activities of chrysin
Unlike other flavonoids, the therapeutic benefits of chrysinremain nascent in the current literature because of their limitedbioavailability and absorption. In addition, chrysin has beenrecently shown to be a potent inhibitor of aromatase (Sandersonet al., 2004) and the activation of human immunodeficiency virus(HIV) in models of latent infection (Critchfield et al., 1996). There isincreasing evidence of the potential benefits of chrysin as a phar-macological agent. Moreover, chrysin shows anti-inflammatory(Cho et al., 2004) and antioxidant effects (Woodman and Chan,
2004) and cancer chemopreventive activity through the inductionof apoptosis in a diverse range of human and rat cell types. Hence,the aim of the current review is to articulate the pharmacologicalpotential of chrysin by mainly referring to its anticancer, neuro-protective, antienteroviral, antibacterial, anti-inflammatory, anti-asthmatic, antidiabetic, antidepressant, and antiarthritic propertiesand its bioavailability and molecular dynamics (Table 1).
3.1. Anticancer activity of chrysin
Cancer, a major public health concern worldwide, is a group ofdiseases characterized by uncontrolled proliferation and growth ofabnormal cells that invade and metastasize to other parts of thebody (Jemal et al., 2011). In ancient times, there have beenremarkable developments in the understanding of the molecularbiology of cancer and in the development of anticancer therapies.Several studies have revealed an association between dietaryphytochemicals and cancer prevention (Key et al., 2004; Pan andHo, 2008; Gonzalez and Riboli, 2010). Accumulating research evi-dence suggests that many phytochemicals have anticancer activ-ities with low adverse effects and toxicity, making them safe forhuman use. The interest on flavonoids comes from the results ofepidemiological studies, which suggest that increased volume offruit and vegetable consumption is associated with a lower risk ofseveral types of cancer.
Chrysin administration improved the status of lipid peroxida-tion and antioxidants, which regulated the homeostasis of oxidantand antioxidant status during carcinogenesis (Karthikeyan et al.,2013). Chrysin inhibits tumor growth through apoptosis relatedto the activation of Notch1 signaling pathway, both in vitro andin vivo (Yu et al., 2013). The primary mechanism of action of chrysinconsists of a decrease in cell proliferation, induction of cell death byapoptosis, and reduction of inflammation (Samarghandian et al.,2011; Xue et al., 2016). Interestingly, changes in b-arrestin-2expression, a versatile signaling molecule, subsequent to chrysinsupplementation influence several signaling pathways (Khan et al.,2011). The combination of chrysin and cisplatin considerably in-crease the apoptosis of HepG2 cancer cells. The combination ofchrysin and cisplatin stabilize p53 gene expression by activatingERK1/2, which promotes p53 phosphorylation in HepG2 cells (Liet al., 2015). Chrysin treatment maintains the antioxidant armoryand suppresses the activation of redox-active transcription factorNF-kB. Chrysin is a potential candidate for the prevention of renalcarcinogenesis as it restrains several biomarkers of tumor promo-tion and inflammation during renal carcinogenesis (Rehman et al.,2013). Chrysin can be an effective inhibitor of tumor cell-inducedangiogenesis (Fu et al., 2007). It was concluded that chrysin hasthe potential to delay tumor formation rather than inhibit tumorformation.
3.2. Toxicity
3.2.1. Neuroprotective effectIncreased neuronal oxidative stress generation could underlie
deleterious effects on RhoA and ERK1/2 signal transduction, whichtargets the altered cytoskeleton, probably by inducing lipid per-oxidation in membranes, proteins, and DNA. Furthermore, astro-cytes respond to Pro concentrations, reorganize their cytoskeleton,and survive through RhoA- and ERK-mediated mechanisms.Considering that astrocytes are polyvalent cells involved in almostall processes that occur in the CNS, the vulnerability of astrocytecytoskeleton may have considerable implications for understand-ing the effects of chrysin (Loureiro et al., 2013).
Chrysin administration ameliorated brain damage through thereduction of oxidative stress. Exposure to chrysin decreased
Table 1An overview of the pharmacological activities of chrysin.
S.No. Study Title Pharmacologicalactivities
Animal model/Cell line
Dose Mode of action Reference
1 Chemopreventive potential of chrysinin7,12-dimethylbenz(a)anthracene-induced hamster buccal pouchcarcinogenesis.
Anticancer(Oral)
Male goldenSyrian hamsters
250 mg/kgb.w.
Chrysin has the potential todelay rather than inhibit tumorformation.
Karthikeyan et al., 2013
2 Chrysin activates Notch1 signaling andsuppresses tumor growth of anaplasticthyroid carcinoma in vitro and in vivo.
Anticancer(Thyroid)
Male nude mice.HTh7; KAT18cell lines
75 mg/kg b.w.25, 50 &75 mM/ml
The novel Notch1 activatorchrysin inhibits tumor growthin ATC both in vitro and in vivo.
Yu et al., 2013
3 A chrysin derivative suppresses skincancer growth by inhibiting cyclin-dependent kinases.
Anticancer(Skin)
JB6 Pþ 10 mM Chrysin derivative (69407)more strongly inhibited EGF-induced neoplastictransformation of JB6P þ cellscompared to chrysin.
Liu et al., 2013
4 Chrysin inhibits metastatic potential ofhuman triple-negative breast cancercells by modulating matrixmetalloproteinase-10, epithelial tomesenchymal transition, and PI3K/Aktsignaling pathway.
Anticancer(Breast)
TNBC 5, 10, and20 mM
Chrysininduced antimetastaticactivity by regulating MMP-10and epithelial-mesenchymaltransition.
Yang et al., 2014
5 A flavonoid chrysin suppress hypoxicsurvival and metastatic growth ofmouse breast cancer cell lines.
Anticancer(Breast)
4T1cell lines 10-100mg/ml
Chrysin has potential forcontrolling metastaticprogression.
Lirdpr-apamongkolet al., 2013
6 Chemopreventive effect of chrysin, adietary flavone against benzo(a)pyreneinduced lung carcinogenesis in Swissalbino mice.
Anticancer(lung)
Male Swissalbino mice
250 mg/kgb. w.
Chrysin supplementationdownregulated the expressionof PCNA, COX-2, and NF-kBproteins and maintainedcellular homeostasis.
Kasala et al., 2016
7 Chrysin enhances doxorubicin-inducedcytotoxicity in human lung epithelialcancer cell lines: The role ofglutathione.
Anticancer(Lung)
A549; H157;H460; H1975;
5-25 mM Chrysin worked synergisticallywith DOX to induce cancer celldeath.
Brechbuhl et al., 2012
8 AMP-activated protein kinase (AMPK)activation is involved in chrysin-induced growth inhibition andapoptosis in cultured A549 lung cancercells.
Anticancer A549 1 mM Chrysin facilitated doxorubicin-induced AMPK activation topromote A549 cell apoptosis.
Shao et al., 2012
9 Combination of chrysin and cisplatinpromotes the apoptosis of Hep G2 cellsby up-regulating p53.
Anticancer HCT-116;HepG2; Hep 3B
10- 40 mM Chrysin and cisplatin showedsignificant anticancer effects inHepG2 cellsin vitro.
Li et al., 2015
10 Alleviation of hepatic injury by chrysinin cisplatin administered rats: Probablerole of oxidative and inflammatorymarkers.
Anti-inflammatory Male albinowistar rats
25 & 50mg/kg b.w.
Chrysin is effective inattenuating cisplatin-inducedexpression of both COX-2 andiNOS
Rehman et al., 2014
11 Chrysin abrogates earlyhepatocarcinogenesis and inducesapoptosis in N-nitrodiethylamineinduced preneoplastic nodules in rats.
Anticancer(Hepatic)
Male albinowistar rats
250 mg/kgb.w.
Primary mechanism of action ofchrysin occurs throughdecrease in cell proliferation,induction of cell death byapoptosis, and reduction ofinflammation.
Khan et al., 2011
12 Chrysin inhibits expression of hypoxia-inducible factor-1a through reducinghypoxia-inducible factor-1a stabilityand inhibiting its protein synthesis
Anticancer DU145 10,30 &50 mM
Chrysin suppressed theexpression of HIF-1a of tumorcells in vitro and inhibitedtumor cell-inducedangiogenesis in vivo
Fu et al., 2007
13 Chrysin suppresses renalcarcinogenesis via amelioration ofhyperproliferation, oxidative stress andinflammation: Plausible role of NF-kB.
Anticancer(Renal)
Male albinowistar rats
20 & 40mg/kg b.w.
Chrysin as an effectivechemopreventive agent havingthe capability to obstruct DENinitiated and Fe-NTA promotedrenal cancer in the rat model
Rehman et al., 2013
14 Chrysin restores PDGF-inducedinhibition on protein tyrosinephosphatase and reduces PDGFsignaling in cultured VSMCs.
Antiproliferative Rat aortic SMCs Chrysin functionally suppressesPDGF-induced proliferation andmigration in VSMCs.
Lo et al., 2012
15 Chrysin Increases the TherapeuticEfficacy of Docetaxel and MitigatesDocetaxel Induced Edema.
Anticancer A549 25 mM Chrysin as an adjuvant agentreinforced the therapeuticefficacy of DTX and mitigatededema.
Lim et al., 2016
16 Ethanolic extract of propolis, chrysin,CAPE inhibit human astroglia cells.
Antiapoptotic SVGp12 5, 10, 20,30, 50 mM
EEP, chrysin, and CAPE reducedviability of human astrogliacells
Markiewicz-_Zukowska et al., 2012
17 Chrysin Reduced Acrylamide-InducedNeurotoxicity in both in vitro andin vivo assessments.
Neuroprotective Male albinoWistar ratsPC12
12.5, 25 &50 mg/kg b.w.0.5e5 mM
Chrysin significantly decreasedACR-induced cytotoxicity in atime- and dose-dependentmanner
Soghra Mehri et al., 2014
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Table 1 (continued )
S.No. Study Title Pharmacologicalactivities
Animal model/Cell line
Dose Mode of action Reference
18 Examining the neuroprotective effectsof protocatechuic acid and chrysin onin vitro and in vivo models of Parkinsondisease.
Neuroprotective PC12 12 mM Chrysin inhibited the activationof nuclear factor-kB andexpression of inducible nitricoxide synthase.
Zhang et al., 2015
19 Flavonoid chrysin prevents age-relatedcognitive decline via attenuation ofoxidative stress and modulation ofBDNF levels in aged mouse brain.
Neuroprotective Mice 1-300 mg/kgb.w.
Chrysin is effective inattenuating memoryimpairment, oxidative stress,acting as an antiaging agent.
Souza et al., 2015
20 Chrysin protects against cisplatin-induced colon. Toxicity via ameliorationof oxidative stress and apoptosis:Probable role of p38MAPK and p53.
Colonprotective Male albinoWistar rats
25 & 50mg/kg b.w.
Chrysin significantly attenuatedCDDP-induced disintegration ofthe goblet cells in colonic crypt.
Khan et al., 2012
21 Nephroprotective efficacy of chrysinagainstcisplatin-induced toxicity viaattenuation of oxidative stress.
Nephroprotective Male albinoWistar rats
25 & 50mg/kg b.w.
Chrysin effectively suppresscisplatin-induced renal injuryby ameliorating oxidativestress.
Sultana et al., 2012.
22 Renoprotective effect of chrysin (5,7dihydroxy flavone) in streptozotocinInduced diabetic nephropathy in rats.
Antidiabeticnephropathy
Male albinowistar rats
20 mg/kgb.w.
Chrysin prevented theprogression of diabeticnephropathy and protected thekidney from damage
Premalatha andParameswari 2012
23 Chrysin, a PPAR-g agonist improvesmyocardial injury in diabetic ratsthrough inhibiting AGE-RAGE mediatedoxidative stress and inflammation.
Antidiabetic Male albinoWistar rats
60 mg/kgb.w.
Chrysin significantly inhibitsAGE-RAGE mediated oxidativestress and inflammationthrough PPAR-g activation.
Rani et al., 2016
24 Hypolipidemic action of chrysin onTriton WR-1339-inducedhyperlipidemia in female C57BL/6 mice.
Hypolipidemiceffect
C57BL/6mice
10 mg/kg Chrysin was able to decreaseplasma lipids concentrationbecause of its antioxidantproperties
Zarzecki et al., 2014
25 Chrysin alleviates testicular dysfunctionin adjuvant arthritic rats viasuppression of inflammation andapoptosis: Comparison with celecoxib.
Antiarthritic Male albinoWistar rats
25 & 50mg/kg b.w.
Effects of chrysin and celecoxibagainst testicular dysfunction inexperimental RA that weremediated by boostingtestosterone in addition toattenuation of testicularinflammation, oxidative stress,and apoptosis.
Darwish et al., 2014
26 Anti-asthmatic potential of chrysin onovalbumin-induced broncho alveolarhyper-responsiveness in rats.
Antiasthmatic Male albinoWistar rats
3, 10, & 30mg/kg
Chrysin reduces allergic airwayinflammation by degranulationof certain types of cells.
Wadibhasme et al., 2011
27 Chronic unpredictable mild stressdecreases BDNF and NGF Levels AndNaþ,Kþ-ATPase activity in thehippocampus and prefrontal cortex ofMice: Antidepressant effect of chrysin.
Antidepressant Mice 5 or 20mg/kg
High doses of chrysinculminated in the upregulationof BDNF and NGF levels.
Filho et al., 2015
28 Anti-Enterovirus 71 Effects of Chrysinand Its Phosphate Ester.
Antiviral EV71; RD 10-100mM
Chrysin exerts a stronginhibitory effect on EV71replication
Wang et al., 2014
29 Chrysin attenuates experimentalautoimmune neuritis by suppressingimmuno-inflammatory responses.
Anti-immunoinflammatory
EAN rats 50 mg/kgb.w.
Chrysin is a potentially usefulagent for the treatment of EANbecause of its anti-inflammatory andneuroprotective effects.
Xiao et al., 2014
30 Inhibitory Effect of Chrysin (5,7-Dihydroxyflavone) on ExperimentalChoroidal Neovascularization in Rats.
Anti neovascularization
Male brownNorway rats
15 mg/kgb.w.
Chrysin inhibits angiographicleakage in laser-induced animalmodels of CNV.
Song et al., 2016
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neuronal cell death through the inhibition of apoptosis. Moreover,induction of lipid peroxidation is correlated with acrylamidetoxicity. Previous reports have suggested that the most importantmolecular mechanism behind the neuroprotection is mainly due tothe free radical scavenging action of chrysin (Souza et al., 2015). Inparticular, Sathiavelu et al. (2009) supported that chrysin possiblyconfers a protective effect of dampening the free radical generation.Chrysin is effective in attenuating oxidative stress, memoryimpairment, and decreased levels of, brain-derived neurotrophicfactor (BDNF) in the brain of agedmice, acting as an antiaging agent(Zhang et al., 2015). Chrysin exerts a neuroprotective effect throughits antioxidant and antiapoptotic potential. It inhibits oxidativedamage, interacts with tumor necrosis factor a (TNF-a) and IL-b,and is associated with caspase and bcl-2, thus improving motor andsensory functions (Kandhare et al., 2014).
3.2.2. Hepatoprotective effectChrysin shows promising hepatoprotective and anti-
hyperlipidemic effects, which are evidenced by the decreasedlevels of triglycerides, free fatty acids, total cholesterol, phospho-lipids, low-density lipoprotein-C, and very low-density lipoprotein-C and increased levels of high-density lipoprotein-C in the plasmaand tissues of hepatotoxicity in rats (Pushpavalli et al., 2010). Thehepatoprotective activity of chrysin is mediated through TNF-a aschrysin reduces soluble TNF-a generation by blocking TNF-a con-verting enzyme activity (Hermenean et al., 2017).
3.2.3. Cardioprotective effectPrevious reports recommend new targets for the prevention and
treatment of cardiovascular diseases. Chrysin significantly amelio-rated myocardial damage, and the beneficial mechanism of action
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of chrysin was explained by peroxisome proliferator-activated re-ceptor-g (PPAR-g) activation, which consequently attenuatedadvanced glycation end product (AGE)/RAGE-mediated oxidativestress and inflammatory and apoptotic response. Moreover, previ-ous studies provided the primary evidence that chrysin noticeablyrelieves platelet-derived growth factor (PDGF)- and H2O2-inducedinhibition of PTP activity, and it possibly affects glutathione/redoxin the reactivation system for PTP reactivation, leading to dephos-phorylation of activated PDGFR and its downstream protein en-zymes (Rani et al., 2016). Functionally, chrysin suppresses PDGF-induced proliferation and migration in vascular smooth musclecells. The inhibitory effect of chrysin is clear even when chrysin isadded after PDGF stimulation (Lo et al., 2012). Chrysin protectsagainst doxorubicin-induced cardiomyopathy by suppressingoxidative stress, p53-dependent apoptotic pathway, and MAPK andNF-kB pathways while augmenting the vascular endothelial growthfactor/AKT pathway (Mantawy et al., 2017).
3.2.4. Nephroprotective effectExcessive reactive oxygen species (ROS) generation causes the
depletion of cellular antioxidant activities due to nephrotoxicity-associated DNA damage. Chrysin effectively prevented DNA frag-mentation in nephrotoxicity (Sultana et al., 2012). Reduction ofendogenous damage can indicate chrysin's enhanced protectiontoward DNA against ROS attack and/or increased rates of repairtoward DNA damage. It justifies the hypothesis that nephrotoxicityis closely related to increased generation of ROS, leading to thereduction of antioxidant defense mechanism. A previous studyillustrated that reduced levels of serum protein, GFR, and protein-uria development in diabetic rats clearly indicated the develop-ment of diabetic nephropathy (Premalatha and Parameswari,2012). In contrast, chrysin ameliorated proteinuria developmentand enhanced creatinine clearance level, thereby regulating theGFR level, which suggested that chrysin has antinephropathy effect.Chrysin prevents the progression of diabetic nephropathy in HFD/STZ-induced type 2 diabetic rats through its anti-inflammatoryeffects in the kidney by particularly targeting the TNF-a pathway.The nephroprotective effect of chrysin possibly suppresses the TNF-a pathway (Ahad et al., 2014).
3.3. Antidiabetic effect
Diabetes mellitus (DM) is a group of metabolic disorders char-acterized by hyperglycemia resulting from defects in either secre-tion or action of insulin and occasionally both. Chrysin attenuatedDM in rats with high-fat diet/streptozotocin (HFD/STZ)-inducedtype 2 diabetes by restoring renal function and pathology.Furthermore, this study suggested that the nephroprotective effectof chrysin might be related to the inhibition of TNF-a expression.Hence, chrysin may be useful as the most effective therapeuticagent for the treatment of DM (Ahad et al., 2014).
Hyperglycemia is the primary cause of vascular complications indiabetes. The hypoglycemic effects of natural compounds weredetermined by monitoring the glucose consumption of HepG2 cellstreated with chrysin, chrysin derivatives, and a positive reference,rosiglitazone. An O7-nitrooxyalkyl nitric oxide (NO) donormoiety isattached to the chrysin as a parent compound, and its O7-[(nitro-oxyl) alkyloxycarbonyl] methyl analogs were synthesized.Furthermore, a novel class of hybrid ester prodrugs was synthe-sized. The methyl derivatives of (nitrooxyl) ethoxycarbonyl are themost powerful inhibitors of AR and AGE, and chrysin is a potentinhibitor of AGE. All the hybrid ester prodrugs release NO graduallyin the presence of L-cysteine, and the O7-nitrooxyethyl chrysinderivatives O7-[(nitrooxyl) butoxy carbonyl] methyl analog and O7-[(nitrooxyl)hexoxycarbonyl]methyl analog (5c) drastically promote
the glucose consumption of HepG2 cells. This hybrid ester NOdonor prodrugs offer a potential drug design concept for thedevelopment of preventive or therapeutic agents for vascularcomplications of diabetes (Zou et al., 2010).
3.4. Antiarthritic effect
Rheumatoid arthritis (RA) is an autoimmune disease charac-terized by chronic inflammation of the joints. RA has a very com-plex genetic basis and results from a combination of genetic andenvironmental causative factors. Synovial-infiltrating inflamma-tory cells, which produce various inflammatory cytokines andgrowth factors, are intimately involved in a number of RA symp-toms. Moreover, in the joint tissues of patients with RA, the syno-vial hyperplasia is observed to erode and destroy the bone andcartilage (Cush et al., 1992). Accordingly, the increasing demand fornovel treatments resulted in the development of disease-modifyingantirheumatic drugs. The discovery of new therapeutic drugs withthe ability to prevent inflammation and joint destruction with lessadverse effect is extremely beneficial.
Chrysin has alleviating actions against testicular impairmentthat are mediated by enhancing the expression of testicular StARgene and associated testosterone production. Moreover, chrysinmodulates inflammatory cytokines, neutrophil infiltration, andexpression of cyclooxygenase-2 (COX-2) and inducible nitric oxidesynthase (iNOS) besides the oxidative stress. They also inhibitedmRNA expression of FasL and caspase-3 activity. These data alsoendorse chrysin as a safe complementary approach for the man-agement of testicular dysfunction in patients with RA (Darwishet al., 2014). In the same context, additional detailed in-vestigations exploring the localization of inflammatory mediatorssuch as TNF-a, iNOS, chemotactic factors, and MPO in testicularinjury associated with RA are also warranted to delineate the exactmolecular events of chrysin and celecoxib actions in RA testicularinjury.
3.5. Anti-inflammatory effect
Researchers have investigated and characterized the defenseaction of chrysin in traditional models of inflammation, reasoningthat this would expand our knowledge on the pharmacologicalproperties of this flavone. The flavone chrysin fascinatinglyexhibited anti-inflammatory activities. This evidence was alsosupported by docking studies suggesting that chrysin's establishedinteractions with the COX-2 binding site are sufficient to justify theanti-inflammatory activity of this flavone. Neuroinflammatory re-sponses are mostly mediated by increased levels of pro-inflammatory cytokines and decreased levels of anti-inflammatory cytokines (Xiao et al., 2014). The anti-inflammatoryeffects of chrysin are associated with inflammatory cytokineregulation. Chrysin inhibits the production of inflammatory cyto-kines such as IFN-c and TNF-a by activating macrophages throughthe NF-kB pathway (Ha et al., 2010; Ciftci and Ozdemir, 2011).Moreover, chrysin is a well-known anti-inflammatory agent as itinhibits prostaglandin-E2, COX-2, and NF-kB (O'Leary et al., 2004).
The therapeutic effect of chrysin considerably attenuatedinflammation and regulated macrophage status through the sup-pression of inflammation. Moreover, chrysin is involved in theactivation of PPAR-g functions or increases the PPAR-g activities; italso promotes the target gene expressions. Collectively, the resultsof this study support the novel role of chrysin as an efficientmodulator of PPAR-g transcriptional activity and as a therapeuticmolecule in inflammatory diseases (Feng et al., 2014). Hence,chrysin is a potent, useful agent that has anti-inflammatory andneuroprotective effects and may provide a promising novel
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therapeutic approach for autoimmune neuropathies.
3.6. Antiasthmatic effect
Asthma is a chronic inflammatory airway disease in whichmultiple complex pathways are involved. It is associated with ge-netic, allergic, environmental, infectious, emotional, and nutritionalfactors (Greene, 1995). Chrysin reduces allergic airway inflamma-tion by the degranulation of certain types of cells. The antioxidantpotential of chrysin may be attributed to altered Th1/Th2 polari-zation through the suppression of iNOS, NF-kB, and activator pro-tein 1 (Wadibhasme et al., 2011).
3.7. Antidepressant effect
The chronic unpredictable mild stress (CUMS) animal modelwas developed to mimic the initiation and progress of clinicaldepression in humans. Studies suggested that CUMS inducesbehavioral and physiological changes that resemble symptoms ofhuman depression (Willner, 2005). CUMS decreases the BDNF andnerve growth factor (NGF) levels and the activity of Naþ/Kþ-ATPasein the prefrontal cortex and hippocampus, respectively. In additionto the defense action against changes in the level of neurotrophin,activity of Naþ/Kþ-ATPase, and CUMS-induced behavioral alter-ation, chrysin also prevented alterations in the corticosterone levelsand antioxidant status. Furthermore, chrysin alters the upregula-tion of BDNF and NGF levels (Filho et al., 2015).
3.8. Anxiolytic effect
Chrysin exhibits a clear anxiolytic effect, and its sedative effectcould not result in an interaction with gamma amino butyric acid(GABA)-benzodiazepine (BZD) receptors as it was not counteractedby flumazenil (antagonist of BZD). Conversely, the anxiolytic effectof chrysin, which was blocked by flumazenil, could be associatedwith an activation of the GABA receptor unit. Moreover, it wasnoteworthy that the effect of chrysin on locomotor behavior is notinhibited by an antagonist of BZD receptors, therefore excluding aninteraction with the GABA receptor system; the anxiolytic effect ofchrysin seems to be related to BZD receptor activation. As a result,the presence of chrysin in Passiflora incarnata could be consideredpartially responsible for the anxiolytic effect (Zanoli et al., 2000).
3.9. Antiangiogenic effect
There are two types of chrysin derivatives coupled with alkylnitrate (NO donors) and furazan derivatives that have been fullycharacterized by 1H NMR and other techniques. This findingsignified that all chrysin derivatives exhibit cell proliferation(in vitro) and angiogenic activity (in vivo). Notable angiogenesis-promoting effects of chrysin were observed for all the modifiedcompounds using chick chorioallantoic membrane (CAM) assay(Peng et al., 2009). Chrysin is present at high levels in many veg-etables and may be useful in the treatment of AMD and otherdiseases that result in choroidal neovascularization (CNV). Inaddition, chrysin can inhibit angiographic leakage in laser-inducedanimal models of CNV. Furthermore, it is relatively safe and readilyavailable (Song et al., 2016).
3.10. Antihyperlipidemic effect
Chrysin can prevent the augmentation of plasma total choles-terol, triglyceride, and non-HDL cholesterol levels in hyperlipid-emia. Moreover, the antihyperlipidemic action of chrysin wascomparable to that of the standard drug simvastatin in a study by
Zarzecki et al. The antioxidant activities of chrysin were evaluatedin their experimental protocol, and study was suggested as apossible mechanism of hypolipidemic action of chrysin. Thus, theresults suggested that chrysin can be used as an adjuvant for thetreatment of dyslipidemia diseases as dyslipidemia is a major riskfactor for coronary heart disease in women (Zarzecki et al., 2014).
3.11. Antihyperammonemic effect
Hyperammonemia, i.e., increased levels of blood ammonia, is aserious metabolic disorder associated with a variety of situations,including distal renal tubular acidosis, congenital UCD, acutefulminant hepatic failure, Reye syndrome, and organic acidemia.UCDs are a group of metabolic congenital errors that are mainlycharacterized by hyperammonemia. During liver failure, ammoniahomeostasis is blocked, which leads to the accumulation of bloodammonia and results in increased hepatocyte apoptosis. Ammoniaintoxication causes oxidative stress by increasing the generation ofROS/RNS. To counteract oxidative stress and keep cellular redoxstate in balance, cells form antioxidant defense systems that act atdifferent levels to prevent or repair such damage. Oral adminis-tration of chrysin (100 mg/kg b.w.) significantly restored the levelsof LPO by-products, lipid profile, and antioxidant activities. Ingeneral, flavonoids exert free radical scavenging propertiesdepending on the OH groups present in the ring structure of thecompound. Nevertheless, chrysin's structure has two OH groups inits A ring at the C-5 and C-7 positions, which play amajor role in thefree radical scavenging activities. Hence, chrysin’ ability to increasethe antioxidant levels along with its antilipid peroxidative activitysuggests that this compound is potentially useful in counteractingfree radical-mediated tissue damage caused by ammonia toxicity.Thus, the beneficial action of chrysin repressing ammonium chlo-ride (NH4Cl)-induced ammonia intoxication could be attributed toits free radical scavenging properties (Renuka et al., 2016). An anti-inflammatory property of chrysin efficiently alters the expressionsof p65 NF-kB, iNOS, and COX-2 and alsoinhibited the pro-inflammatory NF-kB activity by blocking NO generation (Maniet al., 2017).
3.12. Bioavailability
Pharmacokinetic studies are the most important to better un-derstand the in vivo pharmacological and toxicological effects ofnew therapeutic compounds. However, despite its therapeuticpotential, the bioavailability of chrysin and probably other flavo-noids in humans is extremely low, mainly due to poor absorption,rapid metabolism, and rapid systemic elimination. Like other di-etary bioflavonoids, the metabolism of chrysin is catalyzed mostlyby conjugation pathways, including both glucuronidation and sul-fation, rather than by oxidation in hepatic and intestinal cells. Thehigh affinity of the enzymes involved in the metabolism of chrysin,i.e., P-PST, M-PST, and UGT1A6, suggested that the in vivo oralbioavailability of these dietary compounds may be limited. Theseresults also give the important information about which humansulphotransferase isoforms are involved in the biotransformation offlavonoids (Galijatovic et al., 1999). The efflux of chrysin sulfate hasa greater inhibitory effect than that of chrysin glucuronide. Thesensitive and reliable ultra-performance tandem mass spectrom-etry (UPLC-MS/MS) method is used for the determination ofchrysin, chrysin-7-O-glucuronide, and chrysin-7-O-sulfate and wasthe enabling factor in determining the pharmacokinetics of chrysin.This is because only 10 mL of blood is required for each time point,which means that the animals did not have to be sacrificed for thisstudy (Ge et al., 2015).
In previous animal studies, after a single oral dose of chrysin
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(5 mg/kg), the findings were very similar to that in the humans.Small amounts of chrysin metabolites such as chrysin glucuronideand sulfonate were present in the plasma and urine. Therefore,excretion through feces may be the chief route for chrysin elimi-nation and in particular its metabolites. Experimental studies re-ported that the highest concentrations of chrysin glucuronide andsulfate appeared in the bile. After that, these metabolites would behydrolyzed by chrysin glucuronidases and sulphatases, as observedin the feces. In total, 0.2 ± 3.1 mg (0.05 ± 0.8%) of unmetabolizedchrysin was eliminated in urine. In addition, only trace amounts ofchrysin sulfate was detected in urine, whereas 2 ± 26 mg of chrysinglucuronide was found. Previous reports suggested that chrysin haslow oral bioavailability, mainly because of extensive metabolismand elimination of metabolites back into the intestine for hydrolysisand fecal elimination (Walle et al., 2001).
A successful strategy is the selection of suitable carriers thatcould encapsulate the respective drugs. From existing studies, drugdelivery systems for chrysin have used liposome, micelles, andnanoparticles as carriers (Anari et al., 2016; Mohammadinejadet al., 2015; Zheng et al., 2014). Chrysin-incorporated polymer asa nanoscale medicine was made from poly(ε-caprolactone),polylactic-glycolic acid (PLGA), and polyethylene glycol (PEG). Byimproving the drug-loading contents, the chrysin-modified poly-mer increased the chemotherapeutic efficacy. It was previouslyreported that chrysin-curcumin in PLGA-PEG decreases cyclin D1expression and inhibits the proliferation of breast cancer cells. Thisresult proves that PLGA-PEG improves the bioavailability of chrysin(Anari et al., 2016). To enhance the bioavailability, drugs areencapsulated by using nanoparticles (Lee et al., 2014).
3.13. Human benefits and toxicity
Chrysin is well known for being a testosterone-boosting plantcompound; it has very good mechanisms of action, leading to theconclusion that it could boost testosterone (Dhawan et al., 2002). Inhumans, 500 mg of chrysin is not associated with many adverseeffects (Tobin et al., 2006). Acute dosages of 400 mg chrysin do notshow any observable toxic effects in humans (Walle et al., 2001).Although low doses of flavonoids are present in the daily diet ofhumans, intake of higher doses may lead to toxicity. Chrysin dailydoses of 0.5e3 g are recommended and can be purchased fromhealth food stores. However, chrysin induces toxicity in trout livercells and inhibits de novo DNA synthesis, leading to reduced cellnumbers (Tsuji and Walle, 2008). The cytotoxicity due to chrysinhas been attributed to the presence of peroxidase-like activity inhepatocytes, leading to the oxidation of chrysin, thus forming toxicproducts (Tsuji and Walle, 2008). Myeloperoxidase and topoisom-erase II may be responsible for the toxicity induced by dietary fla-vonoids (Gardner et al., 2005).
3.14. Molecular docking
Several chrysin derivatives modulate the expression and activ-ities of iNOS and COX-2 enzymes. Chrysin derivatives (Ch-2 and Ch-4) have the potential to be developed as new anti-inflammatorydrugs. Interestingly, COX-2 enzyme was strongly inhibited by Ch-4. Three-dimensional modeling showed that Ch-4 fits well intothe binding pocket of COX-2. This docking model suggested that ahydrogen bond is present between the hydroxyl group of Tyr355and oxygen of the ketone group in the 7th position of Ch-4. Dockingof Ch-4 into the V523I mutant of COX-2 signified that Ile523 of COX-1 might contribute to the selectivity of COX-2 over COX-1. Ch-4showed no effect on iNOS activity. The chrysin derivative cansuppress NO overproduction either by preventing the induction ofiNOS or by inhibiting COX-2 or iNOS enzymes, which may have
therapeutic benefits in various types of inflammation (Cho et al.,2004).
Two diverse favorable binding modes of chrysin have beenexamined by using molecular docking tools. The binding in-teractions of calmodulin (CaM) with the chrysin molecule wereinvestigated by molecular docking and molecular dynamics simu-lation. The chrysin molecule is tethered to CaM by six hydrogenbonds. The amino acid residues that form hydrogen bonds withchrysin are Thr70, Met76, Arg74, and Lys77. The residues involvedin forming the binding pocket thus obtained are Asp22, Asp24,Thr26, Thr28, Lys30, Glu31, Asn60, Gly61, and Thr62. The details ofthe interactions were analyzed, and their binding pockets wereexplicitly defined. These findings may provide a footing for thesubset analysis of the pharmacological benefits of the chrysinmolecule and the function of CaM or guide mutagenesis experi-ments for finding desired drugs (Li et al., 2007).
In the binding mode of chrysin, electrostatic/H-bond was thedriving force for its 1A2 recognition, while van der Waals in-teractions were the 1� forces for ANF recognition. The modelingstudy revealed that 7-hydroxyl-flavone bound to 1A2 in a similarpattern as chrysin and exhibited a less negative predicted bindingfree energy, which was validated by our kinetic analysis. Chrysinformed a strong H-bond with Asp313 of 1A2. The stacking in-teractions with Phe226 also contributed to its tight binding to 1A2.The larger and more open active site architectures of 2C9 mightexplain the weaker inhibitory affinity of chrysin toward 2C9. Thepredicted binding free energies for chrysin complexes such as 1A2-chrysin and 2C9-chrysin were �23.11 and �20.41 kcal/mol,respectively, which indicated that chrysin has more potential forthe 1A2 binding. Weaker van de Waals interactions between 2C9and chrysin may account for its moderate inhibitory affinity. Thisindicates that the simulations of MD and binding free energy cal-culations can provide an alternative way to evaluate chrysin'sinhibitory ability against 1A2 and thus support the normal molec-ular design of 1A2 (He et al., 2010).
To authenticate the anti-inflammatory activity of chrysinmechanistically, the interaction of chrysin with the binding site ofCOX enzymes was studied in silico. On the basis of the interactionbetween hydrogen and hydrophobic bonds, the study ofligandereceptor complex shows that chrysin weakly interacts withCOX-1 binding site (Maione et al., 2015). The docking results ofchrysin on COX-1 show a binding energy of �7.2 kcal/mol and atotal energy of �96 kcal/mol. The chrysin also interacts with COX-2enzyme biding site. These interactions include hydrogen bondsformed by Arg121 with a distance of 2.75 Å and 3.33 Å and eighthydrophobic contacts established by the residues Tyr356, Leu360,Tyr386, Trp388, Met523, Gly527, Ala528, and Ser531. Moreover, torationalize its binding mode, the crystal structure of COX-2 incomplex with diclofenac, a non-specific ligand of this receptor,were used. The interaction energies of chrysinwith COX-2 receptor,compared to the standard ligand, were most likely sufficient tojustify the selective anti-inflammatory activity of the tested com-pound (Rauf et al., 2015).
4. Conclusion
Chrysin, a naturally occurring polyphenol, appears to possessmany pharmacological activities such as anticarcinogenic, pro-apoptotic, antiangiogenic, antimetastatic, immunomodulatory,and antioxidant properties. The molecular mechanisms underlyingthe pleotropic activities of chrysin are diverse, which involvecombinations of cell signaling pathways at multiple levels ofvarious diseases. Chrysin mitigates neurotoxicity, neuro-inflammation, and oxidative stress in the neuronal tissues andmitigates cognitive dysfunctions. It reduces allergic airway
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inflammation by the degranulation of certain types of cells. How-ever, chrysin is limited by a bioavailability problem, similar to otherpolyphenols; this should be addressed prior to clinical studies.Bioavailability of chrysin needs to be improved to enhance the ef-ficiency of chrysin as a therapeutic molecule. Therefore, the oralbioavailability and therapeutic efficacy of chrysin could be attainedby a nanoformulation even at lower doses.
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M. Renuka was born in 1987; she is pursuing Ph.D. inBiochemistry. Her present research focuses on the pre-vention of animal toxicity produced by environmentalfactors through natural phytochemicals. She received herMaster's degree in Biochemistry in 2009 from PeriyarUniversity, Tamil Nadu, India. She specializes in toxicologyand pharmacological aspects of chemical constituentsfrom natural plant products.
Dr. N. Vijayakumar is an Assistant Professor at AnnamalaiUniversity and was born 1981. He received his Master'sdegree in Biochemistry in Periyar University and receivedhis Ph.D. in Biochemistry from Annamalai University,Tamil Nadu. He specializes in the field of toxicology andneuronal biology. He has published articles in the areas offree radical biochemistry and plant natural products inrelation to animal toxicity. He is also a member of Societyof Biological Chemists.