Pharmacological potential of ampelopsin in Rattan tea

Xinjun Kou Ning Chen

a College of Health Science,Wuhan Sports University,Wuhan 430079,China

b The Cancer Institute of New Jersey,195 Little Albany Street,New Brunswick,NJ 08903,USA

Abstract Rattan tea,made from the leaves of Ampelopsis grossedentata,may potentially perform multiple pharmacological roles,including anti-bacterial,anti-cancer,antioxidant,hepatoprotective and anti-hypertension functions.These beneficia functions of Rattan tea are strongly associated with the bioactivity of ampelopsin,a major fl vonoid compound in Rattan tea.In this review,we summarize current research related to the bioactivity and pharmacological mechanisms of ampelopsin,which will provide a better reference for its potential application in the prevention of chronic diseases.

Keywords: Ampelopsin;Rattan tea;Flavonoid;Pharmacological potential;Chronic disease

1.Introduction

Rattan tea is a traditional Chinese herbal remedy prepared from the stems and leaves of the plantAmpelopsis grossedentata.Ampelopsin is one of the most important fl vonoids found in Rattan tea.As a dihydromyricetin(DMY),ampelopsin was firs isolated fromAmpelopsis meliaefoliaby Kotake and Kubota in 1940,and was later reported as a major bioactive component inAmpelopsis grossedentata[1].Today,ampelopsin from Rattan tea is known for a broad range of biological functions including hypoglycemic[2],antioxidant[3,4],anti-inflammator [5],antitumor[6–8],hepatoprotective[4,9],and neuroprotective effects[10].

Because of these reported effects,research into the bioactivity of ampelopsin in Rattan tea has gained increasing attention over the last decade,leading to increased understanding of its pharmacological functions and underlying mechanisms.In this review,we summarize current research related to the pharmacological functions and corresponding action mechanisms,as well as potential human health benefit of ampelopsin.

2.Anti-bacterial and anti-inflammatory effects

Ampelopsin in crude plant extracts has been applied to alleviate inflammator diseases as a broad-spectrum anti-bacterial drug for several centuries.The ampelopsin extract exerts strong inhibitory effects onStaphylococcus aureusandBacillus subtilis.In addition,ampelopsin is also sensitive to inhibit other pathogenic microorganisms such asAspergillus flavus,penicillium and transport streptavidin [11].Additionally,ampelopsin can inhibit acute or sub-acute inflammatio such as croton oilinduced auricular edema or formaldehyde-induced paw edema in mice,and carrageenan-induced paw edema in rats,as well as abdominal capillary permeability [12].Similarly,ampelopsin isolated fromSalix sachalinensisalso has a strong inhibitory effect onCladosporium herbarum[13].A structure–activity relationship analysis has indicated that the hydroxyl groups at 5 positions(i.e.,5,7,3',4' and 5')can significantl enhance the anti-inflammator activity of ampelopsin.

Inflammator cytokines such as interleukin-1 beta (IL-1β)and tumor necrosis factors (TNF-α) can up-regulate the production of nitric oxide (NO) and prostaglandin E2 (PGE2),thus stimulating the expression or activity of inducible NO synthase (iNOS),cyclooxygenase-2 (COX-2) and microsomal PGE synthase-1 (mPGES-1) in target cells.Ampelopsin has been reported to inhibit NO production in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages and reduce carrageenan-induced acute inflammatioin vivo[14],which is consistent with another report that ampelopsin plays an important role not only in reducing the production of pro-inflammator mediators such as IL-1β,IL-6 and TNF-α,but also in inhibiting the activity of iNOS.Moreover,ampelopsin can selectively inhibit the production of iNOS in LPS-stimulated macrophages and RAW264.7 cells by suppressing the mRNA and protein expression of iNOS.

Nuclear factor-kappaB(NF-κB),as a sensitive transcription factor for regulating the genes responsible for both innate and adaptive immune response,has been identifie as a major factor involved in the regulation of pro-inflammator cytokines such as iNOS and COX-2 [15].Usually NF-κB resides in the cytoplasm associated with its inhibitor (I-κB).Once the inhibitor is released,NF-κB can be phosphorylated and then translocated to the nuclei.The inhibitory effect of ampelopsin on the induction and expression of iNOS is partially mediated through inhibiting NF-κB activity and reducing the expression of the p65 subunit of NF-κB in RAW264.7 cells under stimulation by LPS [5].MAPKs and PI3K/Akt are involved in the induction of pro-inflammator genes in activated macrophages [16,17].However,ampelopsin can exert significan inhibition of the PI3K/Akt signaling pathway without altering the activation of MAP kinases.Moreover,PI3K may act as an upstream regulator of IKK/NF-κB activation,and ampelopsin can inhibit NF-κBregulated pro-inflammator gene expression by blocking the PI3K/Akt/NF-κB signaling cascades.

Another contributor to cellular damage during inflamma tion is oxidative stress[18].The administration of ampelopsin can significantl inhibit LPS-induced intracellular ROS levels.On the other hand,as an inhibitor of ROS,N-acetyl-cysteine(NAC)can greatly suppress the phosphorylation of Akt and IKK as well as the downstream I-κB.The reported association of ampelopsin with these pathways further confirm the potential anti-inflammator activity of ampelopsin.

3.Anti-tumor activity

Currently,much attention has been paid to the anti-tumor activity of ampelopsin in cell and animal studies [7,8].The anti-metastatic effect of ampelopsin on melanoma and prostate cancer has been confirmevia in vivoandin vitrostudies[6,19,20].In addition,reports suggest that ampelopsin may suppress angiogenesis by inhibiting the secretion of vascular endothelial growth factor (VEGF) and basic fibroblas growth factor (bFGF) from human hepatocellular carcinoma cellsin vitro.A similar strong inhibitory effect on the growth of human hepatocellular carcinoma in mice has also been reported[21].These reports indicate that ampelopsin exerts its anti-tumor effects by modulating multiple signaling pathways,including apoptosis,cell cycle arrest,cell growth inhibition and metastatic inhibition at various cellular levels.

3.1.Regulation of proliferation and cell cycle arrest

Ampelopsin-containing serum can inhibit the proliferation of B16 cells by interrupting DNA synthesis [22].Similarly,ampelopsin produces an obvious inhibition on the proliferation of Bel-7402,HL-60,and K562 cells in a dose-dependent manner [23].Interestingly,ampelopsin can also inhibit the growth of H22 cells with IC50of 18.65 μg/mL,but the inhibitory rate is negatively correlated with ampelopsin.Moreover,ampelopsin also exhibits anti-tumor effect on bladder cancer in orthotopic xenograft models,which is mediated by cell cycle arrest[24].

Previous studies have demonstrated cancer specifi pharmacological activity of ampelopsin resulting in growth inhibition of androgen-sensitive(LNCaP)and androgen-insensitive(PC-3)human prostate cancer cell linesin vitro.These anti-proliferative effects,which are not observed in normal prostate epithelial cells even at higher doses[6],are mediated by down-regulating cyclin-dependent kinase(CDK2)in LNCaP cells and cell cycle 2(CDC2)protein levels in PC-3 cells[6].Since CDC2 is considered an essential molecular target for designing anti-cancer drugs[25],ampelopsin should be a promising molecule for the development of anti-cancer drugs.

3.2.Inhibition of apoptosis

The capacity to induce apoptosis in tumor cells is a primary pharmacological mechanism of certain anti-tumor drugs[26,27].The overloading of calcium ions can result in the opening of mitochondrial permeability transition pores,thereby inducing changes in osmotic pressure,ATP depletion and mitochondrial shrinkage,and finall apoptosis[28].Lung cancer is a serious threat to human health and ampelopsin can induce the apoptosis of lung adenocarcinoma cell line AGZY-83-a cells by promoting the increase in intracellular calcium levels and caspase-3 activity[29],although the mechanism associated with this has not yet been determined.

Ampelopsin also induces apoptosis in prostate cancer mainly through down-regulation of Bcl-2,an important regulator of apoptosis that exhibits increased expression in both metastatic and non-metastatic tumors[30,31].Furthermore,ampelopsin in the concentration range of 2.2-14.84 mg/L can exert inhibitory effects on the growth of gastric cancer cell line SGC-7901.The chemotherapeutic drug mitomycin(MMC),when combined with ampelopsin,produces an obvious synergistic inhibition on the growth of SGC-7901 cells,which is also correlated with the inhibitory expression of apoptotic proteins such as Bcl-2 and survivin[32].Therefore,the down-regulation of Bcl-2 can be an important molecular mechanism of ampelopsin-induced apoptosis.The application of anti-cancer drugs combined with ampelopsin will be a novel therapeutic strategy for cancers.

3.3.Inhibition of invasion and migration

Metastasis is the major cause of death associated with cancer,and many factors can affect the invasion and metastasis of cancers.Ampelopsin can significantl attenuate the metastatic process of cancers by inhibiting the degradation of the basement membrane.Ampelopsin can also inhibit the adhesion of B16 mouse melanoma cells to fibronectin lamin,or matrigel,thus attenuating invasion into the reconstituted basement membrane as demonstrated byin vitroexperiments[19,20].Matrix metalloproteinases(MMPs),a family of secreted or membraneassociated proteins capable of digesting extracellular matrix components,are thought to play an essential role in cancer metastasis [33].Moreover,the up-regulation of MMP-2/-9 expression is the critical step of invasion and metastasis of cancer cells.Ampelopsin can inhibit the invasion of human breast cancer(MDA-MB-231)cells in a dose-dependent manner,and the mechanism associated with this may involve down-regulated expression of MMP-2/-9 in both the extracellular matrix and the intracellular space [34].Additionally,ampelopsin may inhibit the expression of CXCR4,a protein associated with prostate cancer,resulting in inhibition of invasion and migration of prostate cancer cells[6].

Adriamycin (ADM) is a potent anti-tumor agent in clinical cancer treatments.Unfortunately,the application of ADM is limited due to its cytotoxicity to skeletal muscle,heart and liver.In 4T1 breast cancer cells,the combination of ampelopsin and ADM can inhibit tumor growth in S180- and 4T1-transplanted mice.Ampelopsin apparently sensitizes the anti-tumor effica y of ADM,and attenuates ADM-induced toxicity in heart and liver [35,36].All of these investigations further confir the anti-invasion potential of ampelopsin during cancer treatments.In addition,ampelopsin can increases intracellular accumulation of chemotherapeutic drugs in multi-drug resistance(MDR)-associated tumor cells,and correspondingly reduces the cytotoxicity of chemotherapeutic drugs by inhibiting the efflu of drugsviapermeability glycoprotein(P-gp),which suggests ampelopsin may also be a promising MDR modulator[37].

4.Hepatoprotective function

Ampelopsin F and G isolated fromAmpelopsis brevipedunculataVar.hancei can suppress carbon tetrachloride- (CCl4)or galactosamine-induced liver injury in rats.Ampelopsin E and cis-ampelopsin E exert an obvious inhibitory effect on hepatitis virus [38].In galactosamine,d-galactosamine and alpha-naphthylisothiocyanate(ANIT)induced acute liver injury models,the administration of ampelopsin can inhibit the activity of serum transaminases such as alanine aminotransferase(ALT)and aspartate aminotransferase (AST),and alleviate pathological damage of liver tissues.Ampelopsin can also reduce the production of malondialdehyde (MDA) in CCl4-induced liver injury,and increase superoxide dismutase(SOD)activity[39].A diet containing ethanolic extract (1%) or ampelopsin(0.1%) can significantl suppress the increase of serum lactate dehydrogenase(LDH),ALT,AST and α-tocopherol levels in rats with d-galactosamine-induced liver injury [4].In addition,ampelopsin also has a protective effect against CCl4,d-galactosamine and LPS-induced liver cell damage in mice[9].Ampelopsin mainly inhibits the collagen formation of hepatic M cells.Following hepatic M cell transplantation in cultured rat liver tissues,collagen fiber are easily produced.However,ampelopsin can inhibit the formation of new collagen fibers and further disperse old collagen fiber into small micro-blocks[40].The hepatoprotective function of ampelopsin may therefore provide a promising therapeutic strategy for hepatitis B[41].

5.Anti-hypertension effect

In animal experiments,ampelopsin has been shown to antagonize norepinephrine(NE)and high K+-induced contraction of rabbit aorta,suggesting that ampelopsin can play a blockage role in intestinal smooth muscle and aortic α-receptor[42].Further studies have confirme that ampelopsin can significantl inhibit the contractions associated with Ca2+release caused by NE [43].However,ampelopsin inhibitory effects on extracellular Ca2+release are observed only at higher concentrations.These finding suggest that ampelopsin may function as an antihypertension drug by selectively blocking voltage-dependent calcium channels(PDC).

6.Regulation of plasma lipids and blood glucose

An anti-atherosclerotic effect of ampelopsin has also been reported.The intragastric administration ofAmpelsis grossedentatareduces the levels of serum total cholesterol (TC) and triglyceride(TG),and increases serum high-density lipoprotein cholesterol (HDL-C) levels in rats,indicating a hypocholesterolemic effect of ampelopsin.In accordance with these findings a drink containingAmpelsis grossedentataat a dose of 9 g/day was administered to 100 patients with primary hyperlipidemia,resulting in quantifiabl reductions in TC,TG and plasma lipid by 42%,72%and 28%after 45 days administration,respectively.In addition,ampelopsin can significantl increase the content of serum SOD,and reduce the content of MDA[44],therefore,ampelopsin can prevent the invasion of vascular smooth muscle cells and matrix degradation,which correspondingly contributes to protective effects against atherosclerosis and cancer.

During the investigation into the relationship between green tea and obesity-related insulin resistance syndrome,green tea was found to enhance insulin activityin vitroand reduce hypertriacylglycerolemia in mice [45–48].Currently,effective drugs for treating diabetes,metformin and glibenclamide,have been found to produce side effects during clinical use.Glibenclamide has been found to significantl reduce blood glucose in normal mice [49].Conversely,ampelopsin has no impact on blood glucose in normal mice,but can reduce blood glucose levels in alloxan-induced diabetic or hyperglycemic mice.

Additionally,in d-galactose-induced impaired glucose tolerance(IGT)animal models,intragastric injection of ampelopsin can significantl reduce the concentration of fasting blood glucose,2 h postprandial blood glucose and insulin levels.This suggests a possible therapeutic role in the treatment of diabetes,which is characterized by the inability of insulin to inhibit the production of hepatic glucose [50].Moreover,ampelopsin exerts a protective effect on early renal damage by inhibiting the content of microalbuminuria and the activity of LDH in kidney.These finding suggest that ampelopsin can effectively improve the health status of IGT rats and provide a protective function against early kidney damage.

7.Neuroprotective effect

Oxidative stress is believed to be a primary factor in neurodegenerative diseases,such as Alzheimer’s disease (AD),Parkinson’s disease and Huntington’s disease,as well as amyotrophic lateral sclerosis [51,52].ROS-associated with oxidative stress can induce cell apoptosis through mitochondrial dysfunction and damage to lipids,proteins and DNA [53,54].Therefore,antioxidants have gained tremendous attention as promising therapeutics for neurodegenerative diseases.Rattan tea is a popular beverage worldwide,especially in China and other Asian countries.Ampelopsin in Rattan tea is an antioxidant fl vonoid that can enhance cellular antioxidant defenses through activation of ERK and Akt signaling pathways,induce heme oxygenase-1 (HO-1)expression and protect PC12 cells from H2O2-induced apoptosis [10].In sodium pentobarbital-induced mouse hypnosis experiments,ampelopsin can significantl extend the incubation period caused by sodium pentobarbital,reduce the length of time associated with hypnotic effects and signifi cantly reduce ethanol-induced inebriation reaction [55].This mechanism may be associated with increased activity of liver microsomal enzyme and accelerated metabolism of alcohol or sodium pentobarbital.Therefore,ampelopsin may also have a novel function as a neuroprotectant in neurodegenerative conditions.

8.Antioxidant effect

ROS is implicated in many pathogenic processes including inflammatio and cancer.Detoxificatio of ROS by antioxidants provides a measure of protection against these diseases,therefore natural plant components,especially antioxidants,are of great interest.Ampelopsin possesses excellent antioxidant activity due to its similarity with tertiary butylhydroquinone(TBHQ)[56].It is well known that free radicals can induce lipid oxidation in biomembranes,and damage of the cell membrane is the basis for tissue damage and for the pathological processes of many diseases.Similarly,exogenous damage is also strongly correlated with free radical reactions.Ampelopsin has previously demonstrated a strong inhibitory effect on H2O2-induced oxidative damage in cell-free systems including red blood cells andin vitrocell cultures [57].This is due to the scavenging of free radicals by ampelopsin,which reduces radical-induced lipid peroxidation of cell membranes and inhibits MDA generation.Similarly,ampelopsin has been reported to significantl inhibit superoxide anion radical activity and lipid peroxidation of liver homogenate and mitochondria during stimulation of auto-oxidation and induced-oxidation,and the inhibitory effect of ampelopsin on free radicals and lipid peroxidation is concentration-dependent[3,58].Therefore,ampelopsin exhibits favorable antioxidant activity that may mitigate cellular oxidative stress and stimulate the potential of cellular vitality,thus accomplishing the prevention of neurodegenerative diseases,cardiovascular diseases,cancer and other diseases.

9.Conclusion

Naturally occurring substances derived from diets or dietary supplements such as Rattan tea provide a new approach for the prevention or therapeutic treatment of chronic diseases.Ampelopsin,as the predominant compound in Rattan tea,possesses potent anti-inflammator activity whereby it can inhibit the activation of NF-κB and PI3K/Akt pathways,and inhibit oxidative stress by scavenging free radicals and attenuating lipid oxidation as well as reducing ROS levels.Furthermore,ampelopsin appears to both reduce the risk of cancer and regulate blood glucose and lipids,although the underlying mechanisms associated with the capabilities remain to be further explored.Futurein vitroexperimental studies andin vivoclinical studies should focus on not only the understanding these mechanisms,but also the development of ampelopsin as a chemopreventive agent to treat a wide range of diseases.