Green tea and its polyphenolic catechins: medicinal uses in cancer and noncancer applications

Covalent modification of proteins by green tea polyphenol (-)-epigallocatechin-3-gallate through autoxidation

Green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) has various beneficial properties including chemopreventive, anticarcinogenic, and antioxidant actions. The interaction with proteins known as EGCG-binding targets may be related to the anticancer effects. However, the binding mechanisms for this activity remain poorly understood. Using mass spectrometry and chemical detection methods, we found that EGCG forms covalent adducts with cysteinyl thiol residues in proteins through autoxidation. To investigate the functional modulation caused by binding of EGCG, we examined the interaction between EGCG and a thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Concentration-dependent covalent binding of EGCG to GAPDH was found to be coupled to the irreversible inhibition of GAPDH activity. Mutation experiments revealed that EGCG is primarily bound to the cysteinyl thiol group of the active center, indicating that the irreversible inhibition of GAPDH is due to the covalent attachment of EGCG to the active-center cysteine. Moreover, using EGCG-treated cancer cells, we identified GAPDH as a target of EGCG covalent binding through specific interactions between catechols and aminophenyl boronate agarose resin. Based on these findings, we propose that the covalent modification of proteins by EGCG may be a novel pathway related to the biological activity of EGCG.

Effects of (-) -epigallocatechin gallate in liver of an animal model of combined (physical and mental) fatigue

OBJECTIVE

Fatigue can be classified as physical and mental depending on the cause. However, in our daily lives, combined fatigue, which is the combination of physical and mental fatigue, is most often experienced. In this study, the effects of (-)-epigallocatechin gallate (EGCg) on combined fatigue were assessed.

METHODS

To produce an animal model of combined fatigue, rats were kept in a cage filled with water to a height of 1.5 cm for 5 d. To evaluate the extent of fatigue, the rats swam with a load of steel rings that weighed approximately 8% of their body weight and were attached to their tails.

RESULTS

Fatigued rats treated with EGCg (50 or 100 mg/kg intraperitoneally [not for 25 mg/kg]) for 5 d could swim longer than fatigued animals given saline. Although levels of thiobarbituric acid-reactive substances in the plasma, brain, and skeletal muscle were not different between control and fatigued rats, thiobarbituric acid-reactive substance levels were higher in livers of fatigued animals than in livers of control animals. Oral intake of EGCg (50 or 100 mg/kg) for 5 d significantly decreased thiobarbituric acid-reactive substance levels in livers of fatigued animals.

CONCLUSION

These results suggest that EGCg (50 or 100 mg/kg) is effective for attenuating fatigue. EGCg given orally appears to have an antioxidant effect on the oxidatively damaged liver of fatigued animals.

Molecular dynamics study on the biophysical interactions of seven green tea catechins with lipid bilayers of cell membranes

Molecular dynamics simulations were performed to study the interactions of bioactive catechins (flavonoids) commonly found in green tea with lipid bilayers, as a model for cell membranes. Previously, multiple experimental studies rationalized catechin's anticarcinogenic, antibacterial, and other beneficial effects in terms of physicochemical molecular interactions with the cell membranes. To contribute toward understanding the molecular role of catechins on the structure of cell membranes, we present simulation results for seven green tea catechins in lipid bilayer systems representative of HepG2 cancer cells. Our simulations show that the seven tea catechins evaluated have a strong affinity for the lipid bilayer via hydrogen bonding to the bilayer surface, with some of the smaller catechins able to penetrate underneath the surface. Epigallocatechin-gallate (EGCG) showed the strongest interaction with the lipid bilayer based on the number of hydrogen bonds formed with lipid headgroups. The simulations also provide insight into the functional characteristics of the catechins that distinguish them as effective compounds to potentially alter the lipid bilayer properties. The results on the hydrogen-bonding effects, described here for the first time, may contribute to a better understanding of proposed multiple molecular mechanisms of the action of catechins in microorganisms, cancer cells, and tissues.

(-)-Epigallocatechin gallate regulates CD3-mediated T cell receptor signaling in leukemia through the inhibition of ZAP-70 kinase

The zeta chain-associated 70-kDa protein (ZAP-70) of tyrosine kinase plays a critical role in T cell receptor-mediated signal transduction and the immune response. A high level of ZAP-70 expression is observed in leukemia, which suggests ZAP-70 as a logical target for immunomodulatory therapies. (-)-Epigallocatechin gallate (EGCG) is one of the major green tea catechins that is suggested to have a role as a preventive agent in cancer, obesity, diabetes, and cardiovascular disease. Here we identified ZAP-70 as an important and novel molecular target of EGCG in leukemia cells. ZAP-70 and EGCG displayed high binding affinity (Kd = 0.6207 micromol/liter), and additional results revealed that EGCG effectively suppressed ZAP-70, linker for the activation of T cells, phospholipase Cgamma1, extracellular signaling-regulated kinase, and MAPK kinase activities in CD3-activated T cell leukemia. Furthermore, the activation of activator protein-1 and interleukin-2 induced by CD3 was dose-dependently inhibited by EGCG treatment. Notably, EGCG dose-dependently induced caspase-mediated apoptosis in P116.cl39 ZAP-70-expressing leukemia cells, whereas P116 ZAP-70-deficient cells were resistant to EGCG treatment. Molecular docking studies, supported by site-directed mutagenesis experiments, showed that EGCG could form a series of intermolecular hydrogen bonds and hydrophobic interactions within the ATP binding domain, which may contribute to the stability of the ZAP-70-EGCG complex. Overall, these results strongly indicated that ZAP-70 activity was inhibited specifically by EGCG, which contributed to suppressing the CD3-mediated T cell-induced pathways in leukemia cells.

The relation between green tea consumption and cardiovascular disease as evidenced by epidemiological studies

Although substantial evidence from in vitro and animal studies indicates that green tea preparations inhibit cardiovascular disease processes, the possible protective role of green tea consumption against this disease in humans remains unclear. We conducted a population-based prospective cohort study (the Ohsaki Study) to examine the association between green tea consumption and mortality from cardiovascular disease (CVD), cancer, and all causes with 40,530 persons in Miyagi prefecture, in northern Japan. Previously published work has shown that green tea consumption was inversely associated with mortality from CVD and all causes. The inverse association of mortality from CVD was more pronounced in women (P = 0.08 for interaction with sex). In women, the multivariate hazard ratios (95% confidence intervals) of CVD mortality across increasing green tea consumption categories were 1.00, 0.84 (0.63-1.12), 0.69 (0.52-0.93), 0.69 (0.53-0.90) (P for trend = 0.004). Within CVD mortality, the stronger inverse association was observed for stroke mortality. Because our observational study has found the inverse association, I report here the results of a review of epidemiological evidence from randomized controlled trials (RCT) of the association between green tea or green tea extracts and CVD risk profiles. More than half of the RCT have demonstrated the beneficial effects of green tea on CVD risk profiles. These results from RCT suggest a plausible mechanism for the beneficial effects of green tea and provide substantial support for our observations.

Mechanism of inhibition of wt-dihydrofolate reductase from E. coli by tea epigallocatechin-gallate

Dihydrofolate reductase (DHFR) is a ubiquitous enzyme involved in major biological process, including DNA synthesis and cancer inhibition, and its modulation is the object of extensive structural, kinetic, and pharmacological studies. In particular, earlier studies showed that green tea catechins are powerful inhibitors of bovine liver and chicken liver DHFR. In this article, we report the results of inhibition kinetics for the enzyme from another source (DHFR from E. coli) exerted by (-)-epigallocatechingallate (EGCG). Using different analytical techniques, we reported that EGCG acts as a bisubstrate inhibitor on the bacterial DHFR. Moreover, the combined approach of biosensor, kinetic, and molecular modelling analysis disclosed the ability of EGCG to bind to the enzyme both on substrate (DHF) and cofactor (NADPH) site. Collectively, our data have confirmed the selectivity of antifolate compounds with respect to the different source of enzyme (bacterial or mammalian DHFR) and the possible role of tea catechins as chemopreventive agents.

Tea catechin ingestion combined with habitual exercise suppresses the aging-associated decline in physical performance in senescence-accelerated mice

Catechins, which are abundant in green tea, possess a variety of biologic actions, and their clinical application has been extensively investigated. In this study, we examined the effects of tea catechins and regular exercise on the aging-associated decline in physical performance in senescence-accelerated prone mice (SAMP1) and age-matched senescence-accelerated resistant mice (SAMR1). The endurance capacity of SAMR1 mice, measured as the running time to exhaustion, tended to increase over the 8-wk experimental period, whereas that of SAMP1 mice decreased by 17%. On the other hand, the endurance capacity of SAMP1 mice fed 0.35% (wt/wt) catechins remained at the initial level and was significantly higher than that of SAMP1 mice not fed catechins. In SAMP1 mice fed catechins and given exercise, oxygen consumption was significantly increased, and there was an increase in skeletal muscle fatty acid β-oxidation. The mRNA levels of mitochondria-related molecules, such as peroxisome proliferator-activated receptor-γ coactivator-1, cytochrome c oxidase-II, III, and IV in skeletal muscle were also higher in SAMP1 mice given both catechins and exercise. Moreover, oxidative stress measured as thiobarbituric reactive substances was lower in SAMP1 groups fed catechins than in the SAMP1 control group. These results suggest that long-term intake of catechins, together with habitual exercise, is beneficial for suppressing the aging-related decline in physical performance and energy metabolism and that these effects are due, at least in part, to improved mitochondrial function in skeletal muscle.

Protective effect of green tea polyphenols on bone loss in middle-aged female rats

Recent studies have suggested that green tea polyphenols (GTP) are promising agents for preventing bone loss in women. Findings that GTP supplementation resulted in increased urinary GTP concentrations and bone mass via an increase of antioxidant capacity and/or a decrease of oxidative stress damage suggest a significant role of GTP in bone health of women.

INTRODUCTION

Recent studies suggested that green tea polyphenols (GTP) are promising agents for preventing bone loss in women. However, the mechanism related to the possible protective role of GTP in bone loss is not well understood.

METHODS

This study evaluated bioavailability, mechanisms, bone mass, and safety of GTP in preventing bone loss in middle-aged rats without (sham, SH) and with ovariectomy (OVX). A 16-week study of 2 (SH vs. OVX) x 3 (no GTP, 0.1% GTP, and 0.5% GTP in drinking water) factorial design using 14-month-old female rats (n = 10/group) was performed. An additional 10 rats in baseline group were euthanized at the beginning of study to provide baseline parameters.

RESULTS

There was no difference in femur bone mineral density between baseline and the SH+0.5% GTP group. Ovariectomy resulted in lower values for liver glutathione peroxidase activity, serum estradiol, and bone mineral density. GTP supplementation resulted in increased urinary epigallocatechin and epicatechin concentrations, liver glutathione peroxidase activity and femur bone mineral density, decreased urinary 8-hydroxy-2'-deoxyguanosine and urinary calcium levels, but no effect on serum estradiol and blood chemistry levels.

CONCLUSION

We conclude that a bone-protective role of GTP may contribute to an increase of antioxidant capacity and/or a decrease of oxidative stress damage.

Epigallocatechin activates haem oxygenase-1 expression via protein kinase Cdelta and Nrf2

The Nrf2/anti-oxidant response element (ARE) pathway plays an important role in regulating cellular anti-oxidants, including haem oxygenase-1 (HO-1). Various kinases have been implicated in the pathways leading to Nrf2 activation. Here, we investigated the effect of epigallocatechin (EGC) on ARE-mediated gene expression in human monocytic cells. EGC time and dose dependently increased HO-1 mRNA and protein expression but had minimal effect on expression of other ARE-regulated genes, including NAD(P)H:quinone oxidoreductase 1, glutathione cysteine ligase and ferritin. siRNA knock down of Nrf2 significantly inhibited EGC-induced HO-1 expression. Furthermore, inhibition of PKC by Ro-31-8220 dose dependently decreased EGC-induced HO-1 mRNA expression, whereas MAP kinase and phosphatidylinositol-3-kinase pathway inhibitors had no significant effect. EGC stimulated phosphorylation of PKCalphabeta and delta in THP-1 cells. PKCdelta inhibition significantly decreased EGC-induced HO-1 mRNA expression, whereas PKCalpha- and beta-specific inhibitors had no significant effect. These results demonstrate for the first time that EGC-induced HO-1 expression occurs via PKCdelta and Nrf2.

Acute, subchronic and genotoxicity studies conducted with Oligonol, an oligomerized polyphenol formulated from lychee and green tea extracts

Oligonol is a phenolic product derived from lychee fruit extract and green tea extract, containing catechin-type monomers and oligomers of proanthocyanidins, produced by a manufacturing process which converts polyphenol polymers into oligomers. The safety of Oligonol was assessed in acute and subchronic studies and genotoxicity assays. In a single dose acute study of Oligonol, male and female rats were administered 2000mg/kg body weight (bw) Oligonol in water by gavage. Oligonol caused no adverse effects and body weight gain and food consumption were within normal range, thus the LD(50) of Oligonol was determined to be greater than 2000mg/kg. A 90 day subchronic study (100, 300 and 1000mg/kgbw/day, oral gavage) in male and female rats reported no significant adverse effects in food consumption, body weight, mortality, clinical chemistry, haematology, gross pathology and histopathology. Similarly, no adverse effects were observed in mice fed diets providing 2, 20 or 200mg/kgbw Oligonol or 200mg/kgbw lychee polyphenol for 90 days. Oligonol did not show any potential to induce gene mutations in reverse mutation tests using Salmonella typhimurium TA98, TA100, TA1535, TA1537 and Escherichia coli WP2uvrA strains. Oligonol did not induce chromosomal aberrations in cultured Chinese hamster lung cells, but it showed increased polyploidy. In a micronucleus assay in mice, Oligonol did not induce any micronuclei or suppress bone marrow, indicating it does not cause chromosome aberrations. The results from these safety studies and previous reports support the safety of Oligonol for human consumption.

Coffee, tea, colas, and risk of epithelial ovarian cancer

Associations of coffee, tea, and other caffeinated beverages with ovarian cancer risk remain uncertain. In a population-based study in Washington State, 781 women with epithelial ovarian cancer diagnosed in 2002 to 2005 and 1,263 controls completed self-administered questionnaires detailing consumption of caffeinated and noncaffeinated coffee, teas, and colas and in-person interviews regarding reproductive and hormonal exposures. We assessed risk associated with coffee, tea, and cola drinking and with total caffeine consumption using logistic regression to calculate odds ratios and 95% confidence intervals. Neither caffeinated nor decaffeinated coffees were associated with ovarian cancer risk; also, we observed no association of total caffeine with risk using a combined index that summed intake from coffee, tea, and carbonated soft drinks. Among teas, neither herbal/decaffeinated nor black teas were associated with risk; however, women who reported drinking >or=1 cup/d of green tea had a 54% reduction in risk (P trend = 0.01). Associations of green tea with risk were similar when invasive and borderline cases were considered separately and when Asian women were excluded from analysis. Green tea, which is commonly consumed in countries with low ovarian cancer incidence, should be further investigated for its cancer prevention properties.

Reaction kinetics of degradation and epimerization of epigallocatechin gallate (EGCG) in aqueous system over a wide temperature range

(-)-Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea, which has been linked with many health benefits. To ensure the conceivable health benefits from thermally processed products, a kinetic study on the stability of (-)-EGCG in aqueous system was carried out using a HPLC-UV system and Matlab programming. Simultaneous degradation and epimerization of (-)-EGCG were characterized during isothermal reactions at low temperatures (25-100 degrees C) combined with previously conducted experimental results at high temperature (100-165 degrees C); the degradation and epimerization complied with first-order reaction and their rate constants followed Arrhenius equation. Mathematical models for the stability of (-)-EGCG were established and validated by the reactions at 70 degrees C and with varied concentrations from different catechin sources. Two specific temperature points in the reaction kinetics were identified, at 44 and 98 degrees C, respectively. Below 44 degrees C, the degradation was more profound. Above 44 degrees C, the epimerization from (-)-gallocatechin gallate (GCG) to (-)-EGCG was faster than degradation. When temperature increased to 98 degrees C and above, the epimerization from (-)-GCG to (-)-EGCG became prominent. Our results also indicated that the turning point of 82 degrees C reported in the literature for the reaction kinetics of catechins would need to be re-examined.

A superoxide anion generator, pyrogallol, inhibits the growth of HeLa cells via cell cycle arrest and apoptosis

We investigated the in vitro effects of pyrogallol on cell growth, cell cycle regulation, and apoptosis in HeLa cells. Pyrogallol inhibited the growth of HeLa cells with an IC(50) of approximately 45 microM. Pyrogallol induced arrest during all phases of the cell cycle and also very efficiently resulted in apoptosis in HeLa cells, as evidenced by flow cytometric detection of sub-G1 DNA content, annexin V binding assay, and DAPI staining. This apoptotic process was accompanied by the loss of mitochondrial transmembrane potential (DeltaPsi(m)), Bcl-2 decrease, caspase-3 activation, and PARP cleavage. Pan-caspase inhibitor (Z-VAD) could rescue some HeLa cells from pyrogallol-induced cell death, while caspase-8 and -9 inhibitors unexpectedly enhanced the apoptosis. When we examined the changes of the ROS, H(2)O(2) or O(2)(*-) in pyrogallol-treated cells, H(2)O(2) was slightly increased and O(2)(*-) significantly was increased. In addition, we detected a decreased GSH content in pyrogallol-treated cells. Only pan-caspase inhibitor showing recovery of GSH depletion and reduced intracellular O(2)(*-) level decreased PI staining in pyrogallol-treated HeLa cells, which indicates dead cells. In summary, we have demonstrated that pyrogallol as a generator of ROS, especially O(2) (*-), potently inhibited the growth of HeLa cells through arrests during all phases of the cell cycle and apoptosis.

Flavan-3-ols: nature, occurrence and biological activity

Representing the most common flavonoid consumed in the American diet, the flavan-3-ols and their polymeric condensation products, the proanthocyanidins, are regarded as functional ingredients in various beverages, whole and processed foods, herbal remedies and supplements. Their presence in food affects food quality parameters such as astringency, bitterness, sourness, sweetness, salivary viscosity, aroma, and color formation. The ability of flavan-3-ols to aid food functionality has also been established in terms of microbial stability, foamability, oxidative stability, and heat stability. While some foods only contain monomeric flavan-3-ols [(-)-epicatechin predominates] and dimeric proanthocyanidins, most foods contain oligomers of degree of polymerization values ranging from 1-10 or greater than 10. Flavan-3-ols have been reported to exhibit several health beneficial effects by acting as antioxidant, anticarcinogen, cardiopreventive, antimicrobial, anti-viral, and neuro-protective agents. This review summarizes the distribution and health effects of these compounds.

Effects of black and green tea consumption on blood glucose levels in non-obese elderly men and women from Mediterranean Islands (MEDIS epidemiological study)

BACKGROUND

Obesity and diabetes are metabolic disorders that affect a large amount of the elderly population and are related to increased cardiovascular risk. Tea intake has been associated with lower risk of mortality and morbidity in some, but not all studies. We evaluated the association between tea intake, blood glucose levels, in a sample of elderly adults.

METHODS

During 2005-2006, 300 men and women from Cyprus, 142 from Mitilini and 100 from Samothraki islands (aged 65-100 years) were enrolled. Dietary habits (including tea consumption) were assessed through a food frequency questionnaire. Among various factors, fasting blood glucose and body mass index (BMI) were measured.

RESULTS

Fifty-four percent of the participants reported that they consume tea at least once a week (mean intake 1.6 +/- 1.1 cup/day). A significant interaction was observed between tea intake, obesity status on glucose levels (P < 0.001). After adjusting for various confounders, tea intake was associated with lower blood glucose levels in non-obese (P for trend <0.001), but not in obese people (P = 0.24). Multiple logistic regression analysis revealed that moderate tea consumption (1-2 cups/day) was associated with 88% (95% CI 76-98%) lower odds of having diabetes among non-obese participants, irrespective of age, sex, smoking, physical activity status, dietary habits and other clinical characteristics.

CONCLUSION

Tea consumption is associated with reduced levels of fasting blood glucose only among non-obese elderly people.

Encapsulation of quercetin and myricetin in cyclodextrins at acidic pH

The in vitro formation of quercetin- and myricetin-cyclodextrin inclusion complexes in acidic medium has been characterized using the enzymatic system horseradish peroxidase, which oxidizes those flavonols in the presence of H2O2. The presence of cyclodextrins (CDs) in the reaction medium inhibited flavonol oxidation due to the complexation of the flavonol in the hydrophobic cavity of CDs. This inhibitory effect depends on the complexation constant Kc between flavonol and the CD type used. The Kc for quercetin and myricetin with the different types of CD used was calculated by nonlinear regression of the inhibition curves obtained in the presence of CDs. In both cases (quercetin and myricetin), the Kc values obtained followed the order hydroxypropyl-beta-CDs > maltosyl-beta-CDs > beta-CDs, reflecting the greater affinity of modified cyclodextrins for the studied flavonols compared with their parental beta-CDs. Moreover, the complexation efficiency (CE) values for HP-beta-CDs and quercetin or myricetin were calculated (267.4 and 5.3, respectively), indicating that HP-beta-CDs are more efficient for the complexation of quercetin than myricetin in the studied conditions, despite of the K c values being very similar in both cases.

Bioactive food components that enhance gammadelta T cell function may play a role in cancer prevention

Gammadelta T cells are found largely within the epithelium and recognize antigens differently than their alphabeta T cell counterparts. TCR delta-/- knock out mice exhibit a rapid tumor onset, along with increased tumor incidence. Although limited, research demonstrates that nutrients and bioactive food components can influence gammadelta T cell cytotoxicity, cytokine secretion, and proliferative capacity, and the results are nonetheless intriguing. Among other functions, gammadelta T cells play a role in immunosurveillance against malignant cells, as shown by the T cell receptor (TCR)delta-/- knock out mice that exhibit a rapid tumor onset and increased tumor incidence. Some common dietary modifiers of gammadelta T cell numbers or activity are apple condensed tannins, dietary nucleotides, fatty acids, and dietary alkylamines. A recent clinical study demonstrated that ingesting a fruit and vegetable juice concentrate increased the number of circulating gammadelta T cells. Clinical studies also document that the oral consumption of a tea component, L-theanine, enhances gammadelta T cell proliferation and interferon-gamma secretion. The significance of these studies awaits additional examination of the influence of exposures and duration on these and other food components. Adoptive transfer and TCRdelta-/- knock out mice models should be used more extensively to determine the physiological impact of the number and activity of these cells as a function of dietary component exposures. While clarifying the diet and gammadelta T interrelationship may not be simple, the societal implications are enormous.

Orally administered epigallocatechin gallate attenuates retinal neuronal death in vivo and light-induced apoptosis in vitro

The aim of this study was to provide support for epigallocatechin gallate (EGCG), a component of green tea, to be considered in the context for neuroprotection in glaucoma, where administration by an oral route is required for adequate penetration into the retina. Ischemia was delivered to one eye of a number of rats by raising the intraocular pressure. EGCG was present in the drinking water of half of the animals 3 days before ischemia and also during the next 5 days of reperfusion. The electroretinograms (ERGs) of both eyes from all rats were recorded before ischemia and 5 days following ischemia. Seven days after ischemia retinas from both eyes of all rats were either analysed for the localisation of various antigens or extracts prepared for analysis for the level of specific proteins and mRNAs. Ischemia/reperfusion to the retina affected a number of parameters. These included the localisation of Thy-1 and choline acetyltransferase, the a- and b-wave amplitudes of the ERG, the content of certain retinal and optic nerve proteins and various mRNAs. Significantly, EGCG statistically blunted many of the effects induced by ischemia/reperfusion which included the activation of caspases. These studies demonstrate conclusively that orally administered EGCG attenuates injury to the retina caused by ischemia/reperfusion where caspases were activated. Studies were also conducted on a cell line (RGC-5 cells) where it was shown that white light (1000 lx, 48 h)-induced apoptosis is caspase-independent and can be blunted by EGCG. The present studies support the view for the use of EGCG in the treatment of glaucoma based on the premise that any potential neuroprotective agent must be administered orally, have a safe profile and poses a broad spectrum of properties that allows various risk factors (that include ischemia and light) to be attenuated.

Theaflavin-3,3'-digallate, a component of black tea: an inducer of oxidative stress and apoptosis

Treatment of human oral squamous carcinoma HSC-2 cells and normal GN46 fibroblasts with theaflavin-3,3'-digallate (TF-3), a polyphenol in black tea, showed a concentration and time dependent inhibition of growth, with the tumor cells more sensitive than the fibroblasts. In buffer and in cell culture medium, TF-3 generated reactive oxygen species, with lower levels detected in buffer amended with catalase and superoxide dismutase, indicating the generation of hydrogen peroxide and superoxide, respectively, and suggesting that TF-3 may be an inducer of oxidative stress. The toxicity of TF-3 was decreased in the presence of catalase, pyruvate, and divalent cobalt, all scavengers of reactive oxygen species, but was potentiated in the presence of diethyldithiocarbamate, an inhibitor of superoxide dismutase. The intracellular level of glutathione in HSC-2 cells was lessened after a 4-h exposure to 250 and 500 microM TF-3. However, for GN46 fibroblasts, a 4-h exposure to 250 microM TF-3 stimulated, but to 500 microM TF-3 lessened, intracellular glutathione. Treatment of the cells with the glutathione depleters, 1,3-bis(2-chloroethyl)-N-nitrosourea, 1-chloro-2,4-dinitrobenzene, and d,l-buthionine-[S,R]-sulfoximine potentiated the toxicity of TF-3. Induction of apoptotic cell death in HSC-2 cells treated with TF-3 was noted by apoptotic cell morphologies, by TUNEL staining, by PARP cleavage, and by elevated activity of caspase-3. Apoptosis was not noted in GN46 fibroblasts treated with TF-3.

(-)-Epigallocatechin gallate, the most active polyphenolic catechin in green tea, presynaptically facilitates Ca2+-dependent glutamate release via activation of protein kinase C in rat cerebral cortex

(-)-Epigallocatechin gallate (EGCG), the main polyphenolic constituent of green tea, has been reported to improve cognitive decline. Considering the central glutamatergic activity is crucial to cognitive function, the objective of this study was to investigate the effect of EGCG on the release of endogenous glutamate using nerve terminals purified from rat cerebral cortex. Results showed that the release of glutamate evoked by 4-aminopyridine (4AP) was facilitated by EGCG in a concentration-dependent manner, and this effect resulted from an enhancement of vesicular exocytosis and not from an increase in Ca2+-independent efflux via glutamate transporter. Examination of the effect of EGCG on cytoplasmic free Ca2+ concentration ([Ca2+]c) revealed that the facilitation of glutamate release could be attributed to an increase in Ca2+ influx through N- and P/Q-type voltage-dependent Ca2+ channels. Consistent with this, the EGCG-mediated facilitation of 4AP-evoked glutamate release was significantly prevented in synaptosomes pretreated with a combination of the N- and P/Q-type Ca2+ channel blockers. Additionally, inhibition of protein kinase C (PKC) by treatment with Ro318220 significantly reduced the facilitatory effect of EGCG on 4AP-evoked glutamate release and phosphorylation of PKC or its presynaptic target myristoylated alanine-rich C kinase substrate (MARCKS). These results suggest that EGCG effects a facilitation of glutamate release from glutamatergic terminals by positively modulating N- and P/Q-type Ca2+ channel activation through a signaling cascade involving PKC. In this EGCG/PKC signaling cascade facilitating glutamate release, the regulation of cytoskeleton dynamics was also indicated to be involved by disruption of cytoskeleton organization with cytochalasin D occluded the EGCG-mediated facilitation of 4AP-evoked glutamate release.

A new LC/MS/MS rapid and sensitive method for the determination of green tea catechins and their metabolites in biological samples

A new rapid and sensitive method has been developed, using liquid chromatography in tandem mass spectrometry (LC-ESI-MS/MS) to identify green tea catechin metabolites in plasma and urine after oral intake of a green tea extract. (-)-Epigallocatechin-3-gallate (EGCG), (-)-epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC)-glucuronide, (-)-epicatechin (EC)-glucuronide, and EC-sulfate were identified in plasma, whereas in urine only the conjugated catechins were detected (EGC-glucuronide, EGC-sulfate, EC-glucuronide, and EC-sulfate). Standard calibration curves prepared in plasma were found to be linear in the range of 10.9-1379.3 nmol/L for EGCG, EGC, ECG, and EC. The accuracy and precision of this assay showed a coefficient of variation of <15%. The method allowed the detection and quantification limits (for 20 microL injection) from 1.1 to 2.6 nmol/L and 3.8-8.7 nmol/L, respectively, in plasma and 0.8-1.8 nmol/L and 2.6-6.0 nmol/L, respectively, in urine. This method can be applied for future clinical and epidemiological studies, allowing the identification of the active metabolites that will reach the target tissues.

Differential growth suppression of human melanoma cells by tea (Camellia sinensis) epicatechins (ECG, EGC and EGCG)

We previously reported that catechins of green tea have different antiproliferative effects on cell lines derived from gender-dependent cancers; epicatechin 3-gallate (ECG) had the strongest inhibitory effect. In the present study, we examined the effects of epigallocatechin (EGC), epicatechin-gallate (ECG) and EGC 3-gallate (EGCG) on the viability, density, doubling time and cycle number of cell lines derived from melanoma metastasized to lymph nodes (MB-1133 and SE-0154) or distant organs (CH-0356, JK-0346, SA-1171, GE-0208, NS-1176 and LF-0023). These catechins have been documented to have no growth suppressive or apoptotic effects on normal melanocytes (Nihal et al., Int J Cancer 2005;114:513-21). EGCG (50 muM) showed greater inhibitory potency than EGC (50 muM) in SE-0154, NS-1176, GE-0208 and LF-0023 cell lines but the two catechins produced similar inhibitory effects in CH-0356, JK-0346 and SA-1171 cell lines. The IC(50) (50% inhibitory concentration) was lower for EGC than EGCG in MB-1133 and CH-0356 cells, higher for EGC than EGCG in GE-0208 cells and comparable (11-12 muM) for both the catechins in LF-0023 cells. When compared with EGC, the cytotoxic effect (% dead cell counts) and the suppression of the growth (change in cell number) of all melanoma cell lines tested were pronounced with EGCG. This investigation validates the hypothesis that anticancer action of the various catechins may vary with the type of malignancy and provides a model for tumor cell heterogeneity based on susceptibility and resistance of tumor cells to different green tea catechins. Therefore, this information is critical for undertaking chemopreventive or chemotherapeutic trials against melanoma and gender-based cancers.

Epigallocatechin-3-gallate (EGCG), a green tea polyphenol, suppresses hepatic gluconeogenesis through 5'-AMP-activated protein kinase

Epigallocatechin-3-gallate (EGCG), a main catechin of green tea, has been suggested to inhibit hepatic gluconeogenesis. However, the exact role and related mechanism have not been established. In this study, we examined the role of EGCG in hepatic gluconeogenesis at concentrations that are reachable by ingestion of pure EGCG or green tea, and are not toxic to hepatocytes. Our results show in isolated hepatocytes that EGCG at relatively low concentrations ( Collapse

Key Words Collapse

MESH Headings

• AMP-Activated Protein Kinases
• Animals
• Antioxidants/pharmacology
• Catechin/analogs & derivatives
• Catechin/pharmacology
• Gluconeogenesis/drug effects
• Hepatocytes/metabolism
• Hydrogen Peroxide/chemistry
• Insulin/metabolism
• Liver/drug effects
• Liver/metabolism
• Mice
• Models, Biological
• Multienzyme Complexes/metabolism
• Multienzyme Complexes/physiology
• Protein Serine-Threonine Kinases/metabolism
• Protein Serine-Threonine Kinases/physiology
• RNA, Small Interfering/metabolism
• Reactive Oxygen Species
• Signal Transduction
• Tea

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Grants

• R01 DK076039 NIDDK NIH HHS
• R01 DK076039-01A2 NIDDK NIH HHS
• R01DK076039 NIDDK NIH HHS

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Affiliation(s)

Qu Fan Collins Translational Biology, The Hamner Institutes for Health Sciences, Six Davis Dr., Research Triangle Park, NC 2770
Hui-Yu Liu Translational Biology, The Hamner Institutes for Health Sciences, Six Davis Dr., Research Triangle Park, NC 2770
Jingbo Pi Translational Biology, The Hamner Institutes for Health Sciences, Six Davis Dr., Research Triangle Park, NC 2770
Zhenqi Liu Division of Endocrinology, Department of Internal Medicine, University of Virginia Health Sciences Center, Charlottesville, VA 22908
Michael J. Quon Diabetes Unit, National Center for Complementary and Alternative Medicine, National Institutes of Health, Bethesda, Maryland 20892-1755
Wenhong Cao Translational Biology, The Hamner Institutes for Health Sciences, Six Davis Dr., Research Triangle Park, NC 2770 Division of Endocrinology, Department of Internal Medicine, Duke University Medical Center, Durham, NC 27710

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Protective effect of epigallocatechin-3-gallate on ischemia/reperfusion-induced injuries in the heart: STAT1 silencing flavonoid

The beneficial effect of naturally occurring flavonoids in health is believed to be due to their strong antioxidant activity. However, recent laboratory evidence indicates the involvement of a more specific action. Here, we present evidence that, among a number of catechins present in green tea extract, only epigallocatechin-3-gallate (EGCG) exerts a strong inhibitory action on interferon-gamma-elicited activation of signal transducer and activator of transcription 1 (STAT1). Protective action of EGCG in ischemia/reperfusion injury in the heart and the molecular mechanism of action, which has nothing to do with its anti-oxidant capacity are described.

Catechin as an antioxidant in liver mitochondrial toxicity: Inhibition of tamoxifen-induced protein oxidation and lipid peroxidation

Tamoxifen (TAM) is a nonsteroidal triphenylethylene antiestrogenic drug widely used in the treatment and prevention of breast cancer. TAM brings about a collapse of the mitochondrial membrane potential. It acts both as an uncoupling agent and as a powerful inhibitor of mitochondrial electron transport chain. The effect of catechin pretreatment on the mitochondrial toxicity of TAM was studied in liver mitochondria of Swiss albino mice. TAM treatment caused a significant increase in the mitochondrial lipid peroxidation (LPO) and the protein carbonyls (PCs). It also caused a significant increase in superoxide radical production. Pretreatment of mice with catechin (40 mg/kg) showed significant protection as demonstrated by marked attenuation of increased oxidative stress parameters such LPO, PCs, and superoxide production. It also restored the decreased nonenzymatic and enzymatic antioxidants of mitochondria. The inhibitory effect of catechin on TAM-:induced oxidative damage suggests that it may have potential benefits in prevention of human diseases where reactive oxygen species have some role as causative agents.

Leachianone A as a potential anti-cancer drug by induction of apoptosis in human hepatoma HepG2 cells

The Chinese herbal medicine Radix Sophorae is widely applied as an anti-carcinogenic/ anti-metastatic agent against liver cancer. In this study, Leachianone A, isolated from Radix Sophorae, possessed a profound cytotoxic activity against human hepatoma cell line HepG2 in vitro, with an IC(50) value of 3.4microg/ml post-48-h treatment. Its action mechanism via induction of apoptosis involved both extrinsic and intrinsic pathways. Its anti-tumor effect was further demonstrated in vivo by 17-54% reduction of tumor size in HepG2-bearing nude mice, in which no toxicity to the heart and liver tissues was observed. In conclusion, this is the first report describing the isolation of Leachianone A from Radix Sophorae and the molecular mechanism of its anti-proliferative effect on HepG2 cells.

The green tea component EGCG inhibits RNA polymerase III transcription

RNA polymerase III (RNA pol III) transcribes many small structural RNA molecules involved in RNA processing and translation, and thus regulates the growth rate of a cell. Accurate initiation by RNA pol III requires the initiation factor TFIIIB. TFIIIB has been demonstrated to be regulated by tumor suppressors, including ARF, p53, RB, and the RB-related pocket proteins, and is a target of the oncogene c-myc and the mitogen-activated protein kinase ERK. EGCG has been demonstrated to inhibit the growth of a variety of cancer cells, induce apoptosis and regulate the expression of p53, myc, and ERK. Thus, we hypothesized that EGCG may regulate RNA pol III transcription in cells. Here, we report that EGCG (1) inhibits RNA pol III transcription from gene internal and gene external promoters (2) EGCG inhibits protein expression of the TFIIIB subunits Brf1 and Brf2, and (3) EGCG inhibits Brf2 promoter activity in cervical carcinoma cells.

Quercetin increases oxidative stress resistance and longevity in Saccharomyces cerevisiae

Quercetin, the major flavonol found in several fruits and vegetables, is a natural antioxidant with potential anticancer and antiaging activities. In this paper, the effect of quercetin in Sacharomyces cerevisiae cells submitted to oxidative stress was studied. Hydrogen peroxide resistance increased in cells pretreated with quercetin. Cellular protection was correlated with a decrease in oxidative stress markers, namely, levels of reactive oxygen species, glutathione oxidation, protein carbonylation, and lipid peroxidation. The acquisition of H2O2 resistance was not associated with the induction of antioxidant defenses or with iron chelation. Oxidative stress is a limiting factor for longevity. In agreement, quercetin also increased 60% chronological life span. These results support the utilization of yeast as a useful model to screen in vivo for natural antioxidants with putative health beneficial effects.

SHP-2 tyrosine phosphatase inhibits p73-dependent apoptosis and expression of a subset of p53 target genes induced by EGCG

Green tea polyphenol, epigallocatechin-3-gallate (EGCG) differentially regulates the cellular growth of cancer cells in a p53-dependent manner through apoptosis and/or cell cycle arrest. In an effort to further elucidate the mechanism of differential growth regulation by EGCG, we have investigated the role of the tyrosine phosphatase, SHP-2. Comparing the responses of mouse embryonic fibroblasts (MEFs), expressing either WT or functionally inactive/truncated SHP-2, we find that inactivation of SHP-2 remarkably sensitizes cells to EGCG-mediated killing. MEFs lacking functional SHP-2 undergo massive apoptosis upon treatment with EGCG. By comparing gene expression profiles, we have identified a set of transcriptional targets of p53 that are differentially modulated in cells undergoing apoptosis. Western blot and real-time PCR analyses of a select group of genes further confirm that the expression is SHP-2-dependent. Similar observations were made in MEFs lacking p53, confirming that the expression of these "p53 target genes" is p53-independent. In addition, EGCG treatment induced the expression of p73 mRNA and protein in both cell types, but not p63. Inactivation of p73 in cells expressing nonfunctional SHP-2 markedly inhibited apoptosis and p53 target gene expression. Although phosphorylation of JNK is differentially regulated by SHP2, it was found to be dispensable for EGCG-induced apoptosis and p53 target gene expression. Our results have identified SHP-2 as a negative regulator of EGCG-induced-apoptosis and have identified a subset of p53 target genes whose expression is paradoxically not mediated by p53 but by one of its family members, p73.

Evaluation of the safety and toxicity of the oligomerized polyphenol Oligonol

Oligonol((R)) is an optimised phenolic product containing catechin-type monomers and lower oligomers of proanthocyanidin that emanate from a technology process which converts polyphenol polymers into oligomers. In a single dose toxicity study administration of Oligonol (2000mg/kg bw) by gavage for 4 weeks was found to be safe with no side effects (such as abnormal behavior and alopecia). Body weight gain and food consumption were within normal range. Oligonol had no observed toxicity at the dose (1/25 of LD(50)) administered for 6 months. This suggests that Oligonol is safe at repeated human intakes of Oligonol in doses lower than 200mg/day. The highest dose used in this study is equal to 12g daily for an adult man with 60kg body weight. The LD(50) was calculated to be 5.0g/kg body weight (95% confidence limit: 3.5-6.4g/kg). Studies conducted on 30 healthy volunteers consuming Oligonol at doses of 100mg/day and 200mg/day for 92 days showed good bioavailability. The biochemical parameters attesting to liver and kidney functions as well as the hematological parameters were within the normal ranges. The potential of Oligonol to induce gene mutation (a reverse mutation test) was tested using Salmonella typhimurium TA98, TA100, TA104, TA1535, TA153 and Escherichia coli WP2uvrA. Oligonol was not mutagenic to the tester strains. The lack of toxicity supports the potential use of Oligonol as a food or dietary supplement and for use as an additive in pharmaceutical and cosmetological applications.

A superoxide anion generator, pyrogallol induces apoptosis in As4.1 cells through the depletion of intracellular GSH content

We investigated the involvement of ROS such as H2O2 and O2*-, and GSH in As4.1 cell death induced by pyrogallol. The intracellular H2O2 levels were decreased or increased depending on the concentration and incubation time of pyrogallol. The levels of O2*- were significantly increased. Pyrogallol reduced the intracellular GSH content. And ROS scavengers, Tempol, Tiron, Trimetazidine and NAC could not significantly down-regulate the production of H2O2 and O2*-. However, these ROS scavengers slightly inhibited apoptosis. Interestingly, Tempol showing the recovery of GSH depletion induced by pyrogallol significantly decreased apoptosis without the significant reduction of intracellular O2*- levels. SOD and catalase did not change the level of H2O2 but decreased the level of O2*-. The inhibition of GSH depletion by these was accompanied with the decrease of apoptosis, as evidenced by sub-G1 DNA content, annexin V staining, mitochondria membrane potential (DeltaPsi(m)) and Western data. In addition, ROS scavengers and SOD did not alter a G2 phase accumulation of the cell cycle induced by pyrogallol. However, catalase changed the cell cycle distributions of pyrogallol-treated cells to those of pyrogallol-untreated cells. In summary, we have demonstrated that pyrogallol potently generates ROS, especially O2*-, in As4.1 JG cells, and Tempol, SOD and catalase could rescue to a lesser or greater extent cells from pyrogallol-induced apoptosis through the up-regulation of intracellular GSH content.

Epigallocatechin-3-gallate enhances CD8+ T cell-mediated antitumor immunity induced by DNA vaccination

Immunotherapy and chemotherapy are generally effective against small tumors in animal models of cancer. However, these treatment regimens are generally ineffective against large, bulky tumors. We have found that a multimodality treatment regimen using DNA vaccination in combination with chemotherapeutic agent epigallocatechin-3-gallate (EGCG), a compound found in green tea, is effective in inhibiting large tumor growth. EGCG was found to induce tumor cellular apoptosis in a dose-dependent manner. The combination of EGCG and DNA vaccination led to an enhanced tumor-specific T-cell immune response and enhanced antitumor effects, resulting in a higher cure rate than either immunotherapy or EGCG alone. In addition, combined DNA vaccination and oral EGCG treatment provided long-term antitumor protection in cured mice. Cured animals rejected a challenge of E7-expressing tumors, such as TC-1 and B16E7, but not a challenge of B16 7 weeks after the combined treatment, showing antigen-specific immune responses. These results suggest that multimodality treatment strategies, such as combining immunotherapy with a tumor-killing cancer drug, may be a more effective anticancer strategy than single-modality treatments.

Green tea protects cytoskeleton from oxidative injury in cardiomyocytes

Cardiac ischemia/reperfusion injury results in oxidative stress and poor physiological recovery. Episodes of hypoxia/reoxygenation (H/R) cause some subtle functional and structural alterations in sarcolemma, mithocondria, sarcoplasmic reticulum, nucleus, as well as cytoskeleton. In this report, by using cultured rat cardiomyocytes and laser confocal microscopy we have verified the possibility to counteract cytoskeleton alterations induced by H/R with the supplementation of an antioxidant agent, a green tea extract (GTE), and compared its effects to those of alpha-tocopherol. Moreover the effects of GTE on cell viability and cytosolic antioxidant activity have been evaluated. H/R induced myocardial damage occurs as histological alterations such as degeneration and disorganization of the cytoskeleton and loss of structural integrity of the nucleus. GTE supplementation increases cytosolic antioxidant activity and shows protective effects on cardiomyocyte cytoarchitecture and viability.

Antimalarial properties of green tea

We show here that a crude extract of green tea as well as two of its main constituents, epigallocatechin-3-gallate (EGCG) and epicatechin gallate (ECG), strongly inhibit Plasmodium falciparum growth in vitro. Both these catechins are found to potentiate the antimalarial effects of artemisinin without interfering with the folate pathway. The importance of these findings and their mechanistic implications are discussed in view of future therapeutic strategies.

Dietary chelators as antioxidant enzyme mimetics: implications for dietary intervention in neurodegenerative diseases

Following recent reviews on the role of metal ions in oxidative stress and neurodegenerative diseases, this article reports advances in the study of dietary components for the control of these conditions. Poor metal ion homeostasis is credited with pathological roles in the progression of a number of disorders including Alzheimer's disease, Parkinson's disease and multiple sclerosis. Synthetic metal ion chelators continue to show promise as a new therapeutic approach for neurodegenerative disorders. Dietary chelators, unlike most vitamins, are, however, capable of negating or even reversing the roles of metal ions by: (i) decorporation of metal ions, (ii) redox silencing, (iii) dissolution of deposits, and (iv) generation of an antioxidant enzyme mimetic. This review gives a critical evaluation of recent progress in, and potential for, dietary control of neurodegeneration on the basis of the formation of antioxidant enzyme mimetics.

Catechin and epicatechin from Smilacis chinae rhizome protect cultured rat cortical neurons against amyloid beta protein (25-35)-induced neurotoxicity through inhibition of cytosolic calcium elevation

We previously reported that the Smilacis chinae rhizome inhibits amyloid beta protein (25-35) (Abeta (25-35))-induced neurotoxicity in cultured rat cortical neurons. Here, we isolated catechin and epicatechin from S. chinae rhizome and also studied their neuroprotective effects on Abeta (25-35)-induced neurotoxicity in cultured rat cortical neurons. Catechin and epicatechin inhibited 10 microM Abeta (25-35)-induced neuronal cell death at a concentration of 10 microM, which was measured by a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. Catechin and epicatechin inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic calcium concentration ([Ca2+]c), which was measured by a fluorescent dye, Fluo-4 AM. Catechin and epicatechin also inhibited glutamate release into medium induced by 10 microM Abeta (25-35), which was measured by HPLC, generation of reactive oxygen species (ROS) and activation of caspase-3. These results suggest that catechin and epicatechin prevent Abeta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca2+]c, and then by inhibiting glutamate release, generation of ROS and caspase-3 activity. Furthermore, these effects of catechin and epicatechin may be associated with the neuroprotective effect of the S. chinae rhizome.

Green tea extract and (-)-epigallocatechin-3-gallate inhibit mast cell-stimulated type I collagen expression in keloid fibroblasts via blocking PI-3K/AkT signaling pathways

Keloid, a chronic fibro-proliferative disease, exhibits distinctive histological features characterized by an abundant extracellular matrix stroma, a local infiltration of inflammatory cells including mast cells (MCs), and a milieu of enriched cytokines. Previous studies have demonstrated that co-culture with MCs stimulate type I collagen synthesis in fibroblasts, but the signaling mechanisms remain largely unknown. In this study, we investigated the signaling pathways involved in MC-stimulated type I collagen synthesis and the effects of green tea extract (GTE) and its major catechin, (-)-epigallocatechin-3-gallate (EGCG), on collagen homeostasis in keloid fibroblasts. Our results showed that MCs significantly stimulated type I collagen expression in keloid fibroblasts, and the upregulation of type I collagen was significantly attenuated by blockade of phosphatidylinositol-3-kinase (PI-3K), mammalian target of rapamycin (mTOR), and p38 MAPK signaling pathways, but not by blockade of ERK1/2 pathway. Furthermore, GTE and EGCG dramatically inhibited type I collagen production possibly by interfering with the PI-3K/Akt/mTOR signaling pathway. Our findings suggest that interaction between MCs and keloid fibroblasts may contribute to excessive collagen accumulation in keloids and imply a therapeutic potential of green tea for the intervention and prevention of keloids and other fibrotic diseases.

Low molecular proanthocyanidin dietary biofactor Oligonol: Its modulation of oxidative stress, bioefficacy, neuroprotection, food application and chemoprevention potentials

Interdisciplinary research endeavors are directed at understanding the molecular mechanisms of neurodegenerative and chronic diseases that affect human lifestyle. Hence the potential for developing medicinal herb-derived and food plant-derived prophylactic agents directed at neurological, metabolic, cardiovascular and psychiatric disorders abounds. Oligonol is a novel technology product emanating from the oligomerization of polyphenols, typically proanthocyanidin from a variety of fruits (grapes, apples, persimmons etc.) that has optimized bioavailability. It is an optimized phenolic product containing catechin-type monomers and oligomeric proanthocyanidins, the easily absorbed forms. Typically the constituents of Oligonol are 15-20% monomers, 8-12% dimers and 5-10% trimers. Supplementation of mice with Oligonol prior to the administration of ferric-nitrilotriacetic complex (a Fenton chemistry model) significantly reduced the extent of lipid peroxidation in the kidney, brain and liver. Oligonol triggers apoptosis in the MCF-7 and MDA-MB-231 breast cancer cells through modulation of the pro-apoptotic Bcl-2 family of proteins and the MEK/ERK signaling pathway, an observation suggesting its important chemopreventive effects. The senescence-accelerated strain of mice (SAM) are models of senescence acceleration and geriatric disorders which exhibit learning and memory deficits and enhanced production or defective control of oxidative stress leading.