Potent Polyphenol Research Articles

Sir-2.1 mediated attenuation of \u03b1-synuclein expression by Alaskan bog blueberry polyphenols in a transgenic model of Caenorhabditis elegans

Misfolding and accumulation of cellular protein aggregates are pathological hallmarks of aging and neurodegeneration. One such protein is α-synuclein, which when misfolded, forms aggregates and disrupts normal cellular functions of the neurons causing Parkinson’s disease. Nutritional interventions abundant in pharmacologically potent polyphenols have demonstrated a therapeutic role for combating protein aggregation associated with neurodegeneration. The current study hypothesized that Alaskan bog blueberry (Vaccinum uliginosum), which is high in polyphenolic content, will reduce α-synuclein expression in a model of Caenorhabditis elegans (C. elegans). We observed that blueberry extracts attenuated α-synuclein protein expression, improved healthspan in the form of motility and restored lipid content in the transgenic strain of C. elegans expressing human α-synuclein. We also found reduced gene expression levels of sir-2.1 (ortholog of mammalian Sirtuin 1) in blueberry treated transgenic animals indicating that the beneficial effects of blueberries could be mediated through partial reduction of sirtuin activity. This therapeutic effect of the blueberries was attributed to its xenohormetic properties. The current results highlight the role of Alaskan blueberries in mediating inhibition of sir-2.1 as a novel therapeutic approach to improving pathologies of protein misfolding diseases. Finally, our study warrants further investigation of the structure, and specificity of such small molecules from indigenous natural compounds and its role as sirtuin regulators.

Polyphenol oxidase-based luminescent enzyme hydrogel: an efficient redox active immobilized scaffold

A novel, functionally potent polyphenol oxidase (10000 U)-mediated urchin-shaped composite-based luminescent enzyme hydrogel network as immobilized scaffold for oxido-reductase efficiency on phenolic substrates including phenol, resorcinol, catechol and quinol was synthesized and characterized through fluorescence spectroscopy along with scanning electron microscopy and transmission electron microscopy.

Flavonoids-The Most Potent Poly-phenols as Antidiabetic Agents: An Overview

Flavonoids-The Most Potent Poly-phenols as Antidiabetic Agents: An Overview

Biochemical and molecular analysis of Camellia sinensis (L.) O. Kuntze tea from the selected P/11/15 clone.

Green tea is one of the most important beverages consumed across the world and it possesses various phytotherapeutics. Polyphenol oxidase (PPO) activity, total polyphenols, catechins, amino acid content and enzymatic antioxidants are considered to be potential parameters in tea characterization. P/11/15 clone (Camellia sinensis (L) O. Kuntze) was chosen to analyze the biochemical characterization and to analyze the gene expression pattern. The selected P/11/15 clone (C. sinensis (L) O. Kuntze) possess potent Polyphenol oxidase (49.62 U/mg of protein), sufficient catechin (20.75%), Polyphenol (20.01%), Peroxidase (450.08 μM of O2 formed min−1 g−1 dry weight), Catalase (1.20 μM H2O2 reduced min−1 mg−1 protein) and Super Oxide Dismutase (45.11 U/mg proteins). Flavonoid gene expression reveals ANR (1.66%) and F3H (1.02%) were up regulated in the selected P/11/15 clone. The results obtained suggest that P/11/15 clone showed adequate enzyme levels, thus an increased antioxidant activity.

Complexes of green tea polyphenol, epigalocatechin-3-gallate, and 2S albumins of peanut

2S albumins of peanuts are seed storage proteins, highly homologous in structure and described as major elicitors of anaphylactic reactions to peanut (allergens Ara h 2 and Ara h 6). Epigallocatechin-3-gallate (EGCG) is the most biologically potent polyphenol of green tea. Non-covalent interactions of EGCG with proteins contribute to its diverse biological activities. Here we used the methods of circular dichroism, fluorescence quenching titration, isothermal titration calorimetry and computational chemistry to elucidate interactions of EGCG and 2S albumins. Similarity in structure and overall fold of 2S albumins yielded similar putative binding sites and similar binding modes with EGCG. Binding affinity determined for Ara h 2 was in the range described for complexes of EGCG and other dietary proteins. Binding of EGCG to 2S albumins affects protein conformation, by causing an α-helix to β-structures transition in both proteins. 2S albumins of peanuts may be good carriers of physiologically active green tea catechin.

Insight into the anti-amyloidogenic activity of polyphenols and its application in virtual screening of phytochemical database

Alzheimer’s Disease (AD) is the most frequent form of neurodegenerative disorder pathologically characterized by the presence of aggregates of Aβ in the region of the brain involved in memory and cognition. Polyphenols commonly found in several daily consumed food items and beverages have been demonstrated to inhibit Aβ aggregation using various biophysical or cell culture-based techniques. Here, insight into the anti-amyloidogenic activity of polyphenols has been explored using 2-D QSAR methodology implemented in CODESSA packages. Interestingly, hydrophobic interactions emerge as a significant descriptor for the recognition of amyloid fibril by polyphenols. Thus, it may be interpreted that highly potent polyphenols capably bind within the hydrophobic core region of the amyloid fibril and, thereby, destabilize the fibril by interrupting the hydrophobic interactions present within the fibril. Highly branched substituents and substituents with high degree of conformational flexibility on the polyphenolic structural scaffold enhance the fibril-destabilizing activity of compounds. In addition, specific electrostatic interaction between amyloid fibril and polyphenol plays a crucial role for the recognition of the fibril by polyphenols. The “application domain” of the derived QSAR model also has been defined, and the derived model has been used to screen a small in-house developed phytochemicals database comprising 200 compounds. 59 phytochemicals have been predicted as highly active anti-amyloidogenic phytochemicals. The modeling strategy is an efficient way to reduce the chemical search space and can selectively mine novel lead anti-amyloidogenic molecule from large chemical databases.

Unravelling of the health effects of polyphenols is a complex puzzle complicated by metabolism

Plant metabolism creates complex mixtures of polyphenols in plant foods. Epidemiology and human trials reduced this complexity, by studying specific foods; subclasses of polyphenols; individual polyphenols, or total antioxidant capacity (TAC). This implies the following assumptions: (1) a limited number of potent polyphenols exists; (2) well-defined natural potent mixtures of polyphenols exist; (3) polyphenols share a common biological activity (e.g. antioxidant activity). To find potent polyphenols (1st assumption), in vitro screening has been widely applied, but most published results are of limited use because metabolism, changing biological activity profoundly, has frequently not been considered. The abundant anecdotal evidence for natural potent mixtures of polyphenols (2nd assumption) on the internet is very hard to verify. Additionally, cross-cultural studies have revealed the potency of e.g. cocoa. Polyphenols share the antioxidant phenolic group which inspired researchers to measure their antioxidant activity, thus greatly reducing complexity (3rd assumption). Unfortunately, the elegant antioxidant hypothesis has to be rejected, because poor absorption and extensive metabolism annihilate any contribution to the endogenous body antioxidants. In conclusion, the above assumptions are hard to verify, and no quick answers are to be expected. Future research should focus on structure–activity relations at nanomolar levels and explore metabolomics.

Activation of Heat Shock Proteins by Nanocurcumin to Prevent Neurodegenerative Diseases

Protein misfolding and its progressive accumulation in central nervous system are the common features and the leading cause of several neurodegenerative diseases. Currently no treatment is available to complete removal of these aggregates and rescue neuronal death, synaptic impairment as well as cognitive deficits. Interesting, the cell itself has a fantastic defense mechanism to remove these aggregates. One such crucial mechanism is molecular chaperones such as heat shock proteins. In general, the larger protein aggregates are removed by this system, and degraded through the proteasome or autophagy pathway. Dysfunction or dysregulation of heat shock system has been observed in several neurological diseases, which severely interfere cellular protein clearance mechanism. Therefore, maintenance or balancing of these endogenous protein clearance pathways is a promising approach to remove these protein aggregates. Several small molecules, drugs, and phytochemicals have been studied to promote the activation of this system. Recently, as a potent anti-amyloid polyphenol, curcumin has drawn special attention for the treatment of several brain disorders including several neurodegenerative diseases. It is effective to boost cellular protein clearance system; therefore, it is considered one of the most promising compounds to rectify dysfunction of heat shock system in these disorders. Whereas, because of its low water solubility and fast degradation, the bioavailability of curcumin is very poor. Using nanotechnology, recently several research groups formulated “nanocurcumin” to improve its bioavailability and significantly increases it’s therapeutic efficacy against cancer, but scanty of data are available about it’s role on boosting heat shock system to prevent protein misfolding and neurodegeneration. In this review we will discuss the current knowledge about the importance of nanocurcumin and its pivotal role on activation of heat shock system to combat against neurodegenerative diseases caused by protein misfolding.

(−)-Epicatechin gallate prevents alkali-salt mediated fibrillogenesis of hen egg white lysozyme

Green tea polyphenols (GTPs) are found to be potent inhibitors of amyloid fibril formation. We report the effective inhibitory property of (−)-epicatechin gallate (ECG) during the alkali-salt induced fibrillogenesis of hen egg white lysozyme (HEWL) at 37°C. Spectroscopic techniques such as fluorescence, circular dichroism and microscopic images show that (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), and (−)-epigallocatechin gallate (EGCG) show moderate inhibition of fibrillation with ECG as the most potent polyphenol. Aromatic interactions, hydrophobic interactions, the radical scavenging activity and autoxidation of polyphenols are likely to be the major reasons for ECG being the most effective inhibitor.

Resveratrol prevents oxidative stress and inhibition of Na +K +-ATPase activity induced by transient global cerebral ischemia in rats

Increased oxidative stress and energy metabolism deficit have been regarded as an important underlying cause for neuronal damage induced by cerebral ischemia/reperfusion (I/R) injury. In this study, we investigated the oxidative mechanisms underlying the neuroprotective effects of resveratrol, a potent polyphenol antioxidant found in grapes, on structural and biochemical abnormalities in rats subjected to global cerebral ischemia. Experimental model of transient global cerebral ischemia was induced in Wistar rats by the four vessel occlusion method for 10 min and followed by different periods of reperfusion. Nissl and fluoro jade C stained indicated extensive neuronal death at 7 days after I/R. These findings were preceded by a rapid increase in the generation of reactive oxygen species (ROS), nitric oxide (NO), lipid peroxidation, as well as by a decrease in Na +K +-ATPase activity and disrupted antioxidant defenses (enzymatic and non-enzymatic) in hippocampus and cortex. Administrating resveratrol 7 days prior to ischemia by intraperitoneal injections (30 mg/kg) significantly attenuated neuronal death in both studied structures, as well as decreased the generation of ROS, lipid peroxidation and NO content. Furthermore, resveratrol brought antioxidant and Na +K +-ATPase activity in cortex and hippocampus back to normal levels. These results support that resveratrol could be used as a preventive, or therapeutic, agent in global cerebral ischemia and suggest that scavenging of ROS contributes, at least in part, to resveratrol-induced neuroprotection.

Abstract 5719: Epigallocatechin-3-gallate, a green tea polyphenol, reactivates silenced tumor suppressor gene by modifying DNA methylation and histones in human skin cancer cells

Abstract Epigenetics, the heritable processes that modulate gene activity without changes in the DNA sequence, have gained considerable interest in cancer development and molecular targets of cancer treatment. Cancer epigenetics deal with important processes like DNA methylation and histone modification patterns that can either activate oncogenes or inactivate tumor suppressor genes, the crucial steps in tumor development. Accumulating data suggest that dietary factors may alter cancer risk by modifications of epigenetic processes in the cancer cell. Therefore, the present study was designed to investigate whether (−)-epigallocatechin-3-gallate (EGCG), a most potent polyphenol from green tea which has anti-carcinogenic activity, would alter epigenetic events to regulate methylation-silenced tumor suppressor genes in human skin cancer cells. DNA methylation, histone modification and gene expression profile were studied using human epidermoid carcinoma A431 cells and melanoma cells as an in vitro model after EGCG treatment using RT-PCR, western blot analysis, cytostaining, southwestern dot-blot analysis, chromatin immunoprecipitation, enzymatic activity assays and fluorescence activated cell sorting (FACS) analysis of apoptotic cell death. Our study shows that treatment of A431 cells for 3 or 6 days with EGCG at lower concentrations (5, 10 and 20 μg/ml) resulted in DNA demethylation and reduction in the mRNA and protein levels of DNA methyltransferases (DNMTs) 1 and 3a and 3b and the activity of DNMTs in A431 cells in a dose- and time-dependent manner. EGCG also increased the levels of acetylated lysine 9 and lysine 14 on histone H3 (H3-Lys 9, H3-Lys 14), but decreased levels of methylated H3-Lys 9. Under identical conditions, EGCG re-expressed mRNA and protein levels of tumor suppressor genes, p16INK4a and p21WAF1/CIP1, in A431 cells in a dose-dependent manner. Re-expression of p16INK4a and p21 by EGCG treatment of the A431 cells leads to the inhibition of cell proliferation and induction of apoptosis of A431 cells. Together, our study demonstrates that EGCG can epigenetically modulate DNA and histones to activate methylation-silenced tumor suppressor genes. These epigenetic modifications by EGCG may contribute to skin cancer prevention/treatment strategies in humans. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5719.

Effect of a Prodrug of the Green Tea Polyphenol (-)-Epigallocatechin-3-Gallate on the Growth of Androgen-Independent Prostate Cancer In Vivo

Epigallocatechin-3-gallate (EGCG) is the major and most potent polyphenol compound of green tea that has been shown to have anticancer effects against various types of cancers. In this study, in addition to the EGCG compound, a synthetic derivative, the peracetate of EGCG (EGCG-P), was used to investigate the inhibitory effects on growth of androgen-independent prostate cancer in vivo. The advantage of EGCG-P is that it may act as a prodrug, leading to higher bioavailability than EGCG itself. The aim of our study was to compare the differences between EGCG and EGCG-P on their inhibitory effect on androgen-independent prostate cancer, CWR22R, xenograft model in nude mice. The mice were administrated daily with solvent dimethyl sulfoxide, EGCG, and EGCG-P separately through intraperitoneal injection for 20 days. Tumor volume and body weight of nude mice were recorded daily. Serum prostate-specific antigen (PSA) levels were also measured before and after the treatment. The effects of both EGCG and EGCG-P on tumor cell proliferation were assessed by immunohistochemical (IHC) method using antibodies against Ki-67 and proliferating cell nuclear antigen. The apoptotic effect was evaluated by IHC against B-cell non-Hodgkin lymphoma-2 and terminal deoxynucleotidyl transferase dUTP nick-end labeling assay by in situ apoptosis detection kit. Moreover, the potential suppression of angiogenesis by EGCG and EGCG-P on prostate cancer was examined by IHC against CD31. Our results revealed that treatment of EGCG and EGCG-P compounds suppressed the growth of CWR22R xenografts without causing any detectable side effects in nude mice. The suppression of growth of the tumor was correlated with the decrease of serum PSA level together with the reduction in tumor angiogenesis and an increase in apoptosis on prostate cancer cells. The results showed that treatment of EGCG and EGCG-P inhibited tumor growth and angiogenesis while promoting apoptosis of the prostate cancer cells in vivo. Our results suggest that EGCG-P may be a more stable and useful compound for increasing the therapeutic anticancer effects in androgen-independent prostate cancer.

Prodrugs of fluoro-substituted benzoates of EGC as tumor cellular proteasome inhibitors and apoptosis inducers.

The most potent catechin in green tea is (-)-epigallocatechin-3-gallate [(-)-EGCG], which, however, is unstable under physiological conditions. To discover more stable and more potent polyphenol proteasome inhibitors, we synthesized several novel fluoro-substituted (-)-EGCG analogs, named F-EGCG analogs, as well as their prodrug forms with all of -OH groups protected by acetate. We report that the prodrug form of one F-EGCG analog exhibited greater potency than the previously reported peracetate of (-)-EGCG to inhibit proteasomal activity, suppress cell proliferation, and induce apoptosis in human leukemia Jurkat T cells, demonstrating the potential of these compounds to be developed into novel anti-cancer and cancer-preventive agents.

Urinary catecholamines in children with attention deficit hyperactivity disorder (ADHD): Modulation by a polyphenolic extract from pine bark (Pycnogenol®)

Our study tested the hypothesis that treatment with a potent polyphenol complex not only reduces hyperactivity of children, but also catecholamine excretion and oxidative stress. Urine catecholamine concentrations were measured in attention deficit hyperactivity disorder (ADHD) children and healthy controls. ADHD children received either placebo (PL) or Pycnogenol® (Pyc), a bioflavonoid extract from the pine bark, for one month. The study was performed in a randomized, double-blind, PL controlled design. Concentrations of catecholamines were higher in urine of ADHD patients compared to those of healthy children. Moreover, noradrenaline (NA) concentrations positively correlated with degree of hyperactivity of ADHD children. In ADHD patients, adrenaline (A) and NA concentrations positively correlated with plasma levels of oxidized glutathione. The treatment of ADHD children with Pyc caused decrease of dopamine (D) and trend of A and NA decrase and increased GSH/GSSG ratio. In conclusion, the data provide further evidence for the overactivity of the noradrenergic system in ADHD and demonstrate that A release may be increased, as well. Treatment of ADHD children with Pyc normalized catecholamine concentrations, leading to less hyperactivity, and, consequently, to reduced oxidative stress.

Climate not cultivars in the NO-ing of red wines

Red wine, produced from the grapevine Vitis vinifera, has been part of human civilization for over 7000 years [1]. It contains a potent polyphenol, resveratrol (also known as either trans-3,5,40-trihydroxystilbene or 5-[(E)-2-(4-hydroxyphenyl)-ethenyl]benzene-1,3-diol; C14H12O3), which is present in the skin and seeds of the grape. Resveratrol is also found in certain other plants such as mulberries, rhubarb and peanuts. Although it was first isolated in 1940, resveratrol was largely ignored until a report appeared in 1997 suggesting it had anti-cancer effects. This led to a boom in research, with a rise in publications to over 1000 per year [2]. Thus, resveratrol has achieved a glowing, and growing, reputation for its powerful medicinal properties in protection against cardiovascular disease, inflammation, cancer andneurological disorders of ageing [2]. Resveratrol is also safe at doses up to 300mg/kg body weight [3]. So does the presence of resveratrol justify the drinking of red wine as a health tonic?

Macrophage paraoxonase 2 (PON2) expression is up-regulated by pomegranate juice phenolic anti-oxidants via PPARγ and AP-1 pathway activation

Paraoxonase 2 (PON2), a member of the paraoxonase gene family, was shown to protect macrophages against oxidative stress. Pomegranate juice (PJ), which contains potent polyphenol anti-oxidants, exhibits similar effects. We questioned possible association between PJ polyphenolics, macrophage oxidative stress, and cellular PON2 expression, in relation to the activation of specific PON2 transcription factors. Incubation of J774A.1 macrophages with PJ (0–50 μM of total polyphenols) dose-dependently increased expression (mRNA, protein) and activity and reduced macrophage oxidative status. These effects could be attributed to the PJ unique polyphenols, punicalagin and gallic acid. PJ polyphenol-induced up-regulation of PON2 was inhibited by 40% upon using the PPARγ inhibitor GW9662 (50 μM). Accordingly, the PPARγ ligand, rosiglitazone, dose-dependently stimulated macrophage PON2 expression, by up to 80%. Inhibition of AP-1 activation with SP600125, attenuated PJ-induced up-regulation of PON2 by 40%. Similarly, incubation of macrophages with PJ polyphenols in the presence of GW9662 or SP600125, significantly reduced their capacity to protect the cells against oxidative stress. We conclude that the anti-oxidative characteristics of PJ unique phenolics punicalagin and gallic acid could be related, at least in part, to their stimulatory effect on macrophage PON2 expression, a phenomenon which was shown to be associated with activation of the transcription factors PAPRγ and AP-1.

Evaluation of proteasome-inhibitory and apoptosis-inducing potencies of novel (-)-EGCG analogs and their prodrugs

The anti-cancer and cancer-preventive effects of green tea and its main constituent (-)-epigallocatechin gallate [(-)-EGCG] are well documented by a variety of studies, including epidemiological, cell culture, animal, and clinical studies. While (-)-EGCG remains the most potent polyphenol in green tea, it is very unstable in neutral or alkaline conditions (i.e. physiologic pH). In an effort to discover more stable polyphenol proteasome inhibitors, we synthesized several novel (-)-EGCG analogs with -OH groups eliminated from the B- and/or D-rings. In addition, we also synthesized their putative prodrugs with -OH groups protected by peracetate that can be removed by cellular cytosolic esterases. We first examined the structure-activity relationship of these unprotected and protected compounds to their proteasome-inhibitory potentials. We found that decreasing -OH groups from either the B- or D-ring leads to diminished proteasome-inhibitory activity in vitro. However, in cultured tumor cells only the protected analogs were capable of potently inhibiting the proteasome activity. Furthermore, these protected analogs induced apoptotic cell death in a tumor cell-specific manner. The superior efficacy of the protected (-)-EGCG analogs indicates the formation of an entirely new compound(s) in intact tumor cells. These data suggest that the B-ring/D-ring peracetate-protected EGCG analogs have great potential to be developed into novel anti-cancer and cancer-preventive agents.

Neuroprotective mechanisms of curcumin against cerebral ischemia-induced neuronal apoptosis and behavioral deficits

Increased oxidative stress has been regarded as an important underlying cause for neuronal damage induced by cerebral ischemia/reperfusion (I/R) injury. In recent years, there has been increasing interest in investigating polyphenols from botanical source for possible neuroprotective effects against neurodegenerative diseases. In this study, we investigated the mechanisms underlying the neuroprotective effects of curcumin, a potent polyphenol antioxidant enriched in tumeric. Global cerebral ischemia was induced in Mongolian gerbils by transient occlusion of the common carotid arteries. Histochemical analysis indicated extensive neuronal death together with increased reactive astrocytes and microglial cells in the hippocampal CA1 area at 4 days after I/R. These ischemic changes were preceded by a rapid increase in lipid peroxidation and followed by decrease in mitochondrial membrane potential, increased cytochrome c release, and subsequently caspase-3 activation and apoptosis. Administration of curcumin by i.p. injections (30 mg/kg body wt) or by supplementation to the AIN76 diet (2.0 g/kg diet) for 2 months significantly attenuated ischemia-induced neuronal death as well as glial activation. Curcumin administration also decreased lipid peroxidation, mitochondrial dysfunction, and the apoptotic indices. The biochemical changes resulting from curcumin also correlated well with its ability to ameliorate the changes in locomotor activity induced by I/R. Bioavailability study indicated a rapid increase in curcumin in plasma and brain within 1 hr after treatment. Together, these findings attribute the neuroprotective effect of curcumin against I/R-induced neuronal damage to its antioxidant capacity in reducing oxidative stress and the signaling cascade leading to apoptotic cell death.

Minerva: February 2002

Alcohol and medical students tend to go together. Despite much effort to educate the public, and even with the current crackdown on drinking and driving, it seems that few of these campaigns have reached medical undergraduates. A survey of medical stu. dents at one school in London found that nothing much has changed in the past 12 years. 28% of students drank more than the safe limit, and a shocking 52% came into the “problem drinker” category, as defined by well recognised assessment tools ( Alcohol and Alcoholism 2001,36:540–3). The “French paradox”—why people in France have a lower incidence of heart disease than those in Britain despite a diet similar in saturated fats—may be explained by the discovery that the potent polyphenols in red grape skins inhibit production of endothelin.1. This peptide causes vasoconstriction, which is believed to be a key component in the development of coronary arterial disease. White and rose wines do not produce the same effect ( Nature 2001;414:863–4). A man aged 75 came to hospital with a local recurrence of a carcinoma of the parotid …

Inhibitory effects of plant polyphenols on rat liver glutathione S-transferases

Several novel naturally occurring flavonoids and other polyphenols exerted varying degrees of concentration-dependent inhibition on uncharacterized rat liver glutathione S-transferase (EC 2.5.1.18, GST) isoforms. The order of inhibitory potencies of the five most potent polyphenols was tannic acid > 2-hydroxyl chalcone > butein > morin > quercetin, and their IC 50 values were 1.044, 6.758, 9.033, 13.710 and 18.732 μM, respectively. Their inhibitions were reversible, as indicated by dialysis experiments. The optimum pH for the inhibitions by four of the compounds (tannic acid, butein, 2-hydroxyl chalcone and morin) was in the range of pH 6.0 to 6.5, but for quercetin the optimum pH was 8.0. These potent inhibitors possess one or more of the following chemical structural features: (a) polyhydroxylation substitutions, (b) absence of a sugar moiety, (c) for the chalcones, the presence of an open C-ring and hydroxylation at either the C-2 or C-3 position, (d) for the flavonoids, the attachment of the B-ring to C-2, and (e) a double bond between C-2 and C-3. Butein exhibited a non-competitive inhibition toward both glutathione (GSH) and 1-chloro-2,4-dinitrobenzene (CDNB). Interestingly, tannic acid showed a non-competitive inhibition toward CDNB but a competitive inhibition toward GSH. The inhibitory potency of tannic acid on rat liver GSTs was concentration and substrate dependent. Using CDNB, p-nitrobenzyl chloride, 4-nitropyridine- N-oxide, and ethacrynic acid as substrates, the IC 50 values for tannic acid were 1.044, 11.151, 20.206, and 57.664 μM, respectively.