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PubMed2001

Study of tea polyphenol as a reversal agent for carcinoma cell lines' multidrug resistance (study of TP as a MDR reversal agent).

The aim of this study was to examine MDR1 expression product P-glycoprotein (Pgp) and study the effect and mechanism of tea polyphenol (TP) in reversion of multidrug resistance (MDR) in carcinoma cell lines. Immunocytochemical method was used for qualitative detection of Pgp. A comparative study of cytotoxicity and multidrug resistance reversion effect was made by MTT assay for tea polyphenol and quinidine in MCF-7 and MCF-7/Adr cell lines. The multidrug resistance reversion effect and mechanism were studied by measuring the uptake of 99mTc-tetrofosmin in the carcinoma cell lines. (1) The Pgp overexpression in MCF-7/Adr cells was found to be strong positive, while the Pgp expression of MCF-7 was negative. (2) Although both tea polyphenol and quinidine could not remarkably change the toxicity of adriamycin to MCF-7, they could improve the sensitivity of MCF-7/Adr to adriamycin. The reversion index of tea polyphenol and quinidine was 3 and 10 respectively. (3) The cellular uptake of 99mTc-tetrofosmin was remarkably lower in MCF-7/Adr than in MCF-7. The uptake of 99mTc-tetrofosmin in MCF-7/Adr exhibited a 4, 13, 16 fold increase in the presence of 200, 400 and 500 microg/ml of tea polyphenol respectively. The uptake of 99mTc-tetrofosmin in MCF-7/Adr exhibited only a 4-fold increase in the presence of 200 microM of quinidine. Immunocytochemistry can detect P-glycoprotein expression level qualitatively. Tea polyphenol is not only an anti-tumor agent, but also a multidrug resistant modulator similar to quinidine. The multidrug resistance reversion mechanism of tea polyphenol seems to be its inhibition of the activity of P-glycoprotein. Tea polyphenol has the advantage of very low toxicity in tumor treatment.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Multiple interactions between polyphenols and a salivary proline-rich protein repeat result in complexation and precipitation.

Polyphenols (tannins) in the diet not only precipitate oral proteins, producing an astringent sensation, but also interact with dietary proteins and digestive enzymes in the gut, resulting in a variety of antinutritive and toxic effects. Salivary proline-rich proteins (PRPs), which are secreted into the oral cavity, form complexes with and precipitate dietary polyphenols, and thus, they constitute the primary mammalian defense directed against ingested tannins. In order to characterize the interaction, NMR studies were performed which involved titrating a series of polyphenols into a synthetic 19-residue PRP fragment. The results show that the predominant mode of association is a hydrophobic stacking of the polyphenol ring against the pro-S face of proline and that the first proline residue of a Pro-Pro sequence is a particularly favored binding site. Measurement of dissociation constants indicates that the larger and more complex polyphenols interact more strongly with the PRP fragment; the order of binding affinity was determined as procyanidin dimer B-2 > pentagalloylglucose > trigalloylglucose >> proanthocyanidin monomer (-)-epicatechin approximately propyl gallate. Smaller polyphenols can bind with one phenolic ring stacked against each proline residue, whereas larger polyphenols occupy two or three consecutive prolines. The more complex polyphenols interact with the PRP fragment in a multidentate fashion; moreover, they self-associate or stack when bound. Thus, a model is proposed in which multiple polyphenol/polyphenol and polyphenol/PRP interactions act cooperatively to achieve precipitation.

Amino Acid Sequence↗
PubMed2006

Acute effect of tea, wine, beer, and polyphenols on ecto-alkaline phosphatase activity in human vascular smooth muscle cells.

Alkaline phosphatase (ALP) is an ecto-enzyme widely distributed across species. It modulates a series of transmembranar transport systems, has an important role in bone mineralization, and can also be involved in vascular calcification. Polyphenol-rich diets seem to have protective effects on human health, namely, in the prevention of cardiovascular diseases. We aimed to investigate the effects of polyphenols and polyphenol-rich beverages upon membranar alkaline phosphatase (ecto-ALP) activity in intact human vascular smooth muscle cells (AALTR). The ecto-ALP activity was determined at pH 7.8, with p-nitrophenyl phosphate as the substrate, by absorbance spectrophotometry at 410 nm. Cell viability was assessed by the lactate dehydrogenase (LDH) method, and the polyphenol content of beverages was assessed using the Folin-Ciocalteu reagent. All polyphenols tested inhibited ecto-ALP activity, in a concentration-dependent way. Teas, wines, and beers also inhibited ecto-ALP activity, largely according to their polyphenol content. All tested compounds and beverages improved or did not change AALTR cell viability. Stout beer was an exception to the described behavior. Although more studies must be done, the inhibition of AALTR ecto-ALP activity by polyphenolic compounds and polyphenol-containing beverages may contribute to their cardiovascular protective effects.

Alkaline Phosphatase↗
PubMedDate not supplied

Redox properties of tea polyphenols and related biological activities.

Plant polyphenolic compounds are known to be strong antioxidants. Because oxidative stress is believed to contribute to many acute and chronic diseases, these polyphenols have been postulated to have many beneficial health effects, such as the prevention of cancer and cardiovascular diseases. Indeed, some of these beneficial effects have been demonstrated in animal models and in some, but not all, epidemiological studies. Nevertheless, only some of these activities have been demonstrated to be associated with the antioxidative activities of polyphenols. In studies with cell lines in culture, some of the observed activities may be due to superoxide and hydrogen peroxide produced during the autooxidation of polyphenols. Such pro-oxidation-dependent reactions may not happen in tissues where the oxygen partial pressure is much lower than that in cell culture medium. This review will use the well-studied tea polyphenol, (-)-epigallocatechin-3-gallate, as an example to illustrate the redox properties of polyphenols and their influence on signaling pathways related to anti-cancer activities. Existing data suggest, however, that most of the relevant mechanisms of cancer prevention by tea polyphenols are not related to their redox properties, but are due to the direct binding of the polyphenol to target molecules, including the inhibition of selected protein kinases, matrix metalloproteinases, and DNA methyltransferases.

Animals↗
PubMed2007

Dietary polyphenols may affect DNA methylation.

Certain dietary polyphenols, such as (-)-epigallocatechin 3-gallate (EGCG) from green tea and genistein from soybean, have been demonstrated to inhibit DNA methyltransferases (DNMT) in vitro. This inhibitory activity is associated with the demethylation of the CpG islands in the promoters and the reactivation of methylation-silenced genes such as p16INK4a, retinoic acid receptor beta, O6-methylguanine methyltransferase, human mutL homolog 1, and glutathione S-transferase-pi. These activities have been observed in human esophageal, colon, prostate, and mammary cancer cell lines, and the activity can be enhanced by the presence of histone deacetylase inhibitors or by a longer-term treatment. Many other polyphenolic compounds have lower activities in inhibiting DNMT. Catechol polyphenols may indirectly inhibit DNMT by generating S-adenosyl-L-homocysteine on their methylation by S-adenosyl-L-methionine. In theory, prevention or reversal of hypermethylation-induced inactivation of key tumor suppression genes or receptor genes by DNMT inhibitors could be an effective approach for cancer prevention. Because of the rather low bioavailability of most polyphenolic compounds, how much of an effect dietary polyphenols would have on DNA methylation in humans is not clear. The effect of normal dietary consumption of a single polyphenolic compound is probably insignificant. However, the combination of polyphenols with dietary histone deacetylase inhibitors and the additive effect of different dietary chemicals may produce some effects. On the other hand, the consumption of excessive amounts of polyphenols in dietary supplements may affect DNA methylation status. All these possibilities remain to be examined.

Adaptor Proteins, Signal Transducing↗
PubMed2005

The combination of vitamin C and grape-seed polyphenols increases blood pressure: a randomized, double-blind, placebo-controlled trial.

BACKGROUND: There is growing evidence that oxidative stress contributes to the pathogenesis of hypertension and endothelial dysfunction. Thus, dietary antioxidants may beneficially influence blood pressure (BP) and endothelial function by reducing oxidative stress. OBJECTIVE: To determine if vitamin C and polyphenols, alone or in combination, can lower BP, improve endothelial function and reduce oxidative stress in hypertensive individuals. DESIGN: A total of 69 treated hypertensive individuals with a mean 24-h ambulatory systolic blood pressure > or = 125 mmHg participated in a randomized, double-blind, placebo-controlled, factorial trial. Following a 3-week washout, participants received 500 mg/day vitamin C, 1000 mg/day grape-seed polyphenols, both vitamin C and polyphenols, or neither for 6 weeks. At baseline and post-intervention, 24-h ambulatory BP, ultrasound-assessed endothelium-dependent and -independent vasodilation of the brachial artery, and markers of oxidative damage, (plasma and urinary F2-isoprostanes, oxidized low-density lipoproteins and plasma tocopherols), were measured. RESULTS: A significant interaction between grape-seed and vitamin C treatments for effects on BP was observed. Vitamin C alone reduced systolic BP versus placebo (-1.8 +/- 0.8 mmHg, P = 0.03), while polyphenols did not (-1.3 +/- 0.8 mmHg, P = 0.12). However, treatment with the combination of vitamin C and polyphenols increased systolic BP (4.8 +/- 0.9 mmHg versus placebo; 6.6 +/- 0.8 mmHg versus vitamin C; 6.1 +/- 0.9 mmHg versus polyphenols mmHg, each P < 0.0001) and diastolic BP (2.7 +/- 0.6 mmHg, P < 0.0001 versus placebo; 1.5 +/- 0.6 mmHg, P = 0.016 versus vitamin C; 3.2 +/- 0.7 mmHg, P < 0.0001 versus polyphenols). Endothelium-dependent and -independent vasodilation, and markers of oxidative damage were not significantly altered. CONCLUSION: Although the mechanism remains to be elucidated, these results suggest caution for hypertensive subjects taking supplements containing combinations of vitamin C and polyphenols.

Antioxidants↗
PubMed2005

Peripheral nerve allografts stored in green tea polyphenol solution.

BACKGROUND: We previously demonstrated the successful 1-month storage of peripheral nerve segments in a green tea polyphenol extract. We investigated whether this method could reduce the donor-host immune reaction associated with peripheral nerve allotransplantation. METHODS: Sciatic nerve segments (20 mm long) were harvested from Dark Agouti (DA) rats, stored in polyphenol solution (1 mg/mL) for 1 month, and transplanted into recipient major histocompatibility complex-mismatched Lewis rats to bridge 15-mm-long sciatic nerve gaps (polyphenol-treated allograft group). The controls were an isograft group (nerve segments harvested from Lewis rats were immediately transplanted into Lewis rats), a polyphenol-treated isograft group (nerve segments harvested from Lewis rats were treated by polyphenol in the same method and transplanted into Lewis rats), and a fresh allograft group (nerve segments harvested from DA rats were transplanted into Lewis rats without storage). To investigate the origins of the cells in the transplanted nerves, sciatic nerve segments harvested from the male DA rat donors were transplanted into female Lewis rat recipients; genomic DNA was extracted from each nerve segment and amplified by polymerase chain reaction using primers specific for the rat sex-determining region of the Y-chromosome (Sry). RESULTS: Nerve regeneration in the polyphenol-treated allograft group was similar to that in the isografted group. Sry-specific bands were detected in all samples in the sex-mismatched polyphenol-treated allograft specimens despite their major histocompatibility complex incompatibility. CONCLUSIONS: Storage in green tea polyphenol solution can reduce both ischemic damage to nerve tissue and donor-host immune reactions after allotransplantation.

Animals↗
PubMed1998

The pharmacology and toxicology of polyphenolic-glutathione conjugates.

Polyphenolic-glutathione (GSH) conjugates and their metabolites retain the electrophilic and redox properties of the parent polyphenol. Indeed, the reactivity of the thioether metabolites frequently exceeds that of the parent polyphenol. Although the active transport of polyphenolic-GSH conjugates out of the cell in which they are formed will limit their potential toxicity to those cells, once within the circulation they can be transported to tissues that are capable of accumulating these metabolites. There are interesting physiological similarities between the organs that are known to be susceptible to polyphenolic-GSH conjugate-mediated toxicity. In addition, the frequent localization of gamma-glutamyl transpeptidase to cells separating the circulation from a second fluid-filled compartment coincides with tissues that are susceptible either to polyphenolic-GSH conjugate-induced toxicity or to quinone and reactive oxygen species-induced toxicity. Polyphenolic-GSH conjugates therefore contribute to the nephrotoxicity, nephrocarcinogenicity, and neurotoxicity of a variety of polyphenols.

Animals↗
PubMed2000

The effects on cell growth of tea polyphenols acting as a strong anti-peroxidatant and an inhibitor of apoptosis in primary cultured rat skin cells.

Studies during the past few years have indicated an inhibitory effect of green tea or tea polyphenols on tumorigenesis in animal and even in human. The purpose of this study was to observe the possible effects of tea polyphenols on skin cell growth and on apoptosis in rat primary cultured keratinocytes and fibroblasts. The release of a cell plasma enzyme (LDH), lipid peroxidation products (MDA production), and GSH-Px (glutathione peroxidase) into the medium in cultured cells was determined after treatment with tea polyphenols in a primary culture of skin cells. The percentage of cells in each cell cycle phase and in apoptosis were assayed by flow cytometry (FCM). Tea polyphenols may have a beneficial effect on skin cells at concentrations from 0.05% to 0.1%, showing a dose-dependent decrease in LDH, MDA (malondialdehyde) production, and a significant dose-dependent increase in GSH-Px and cell number. These effects were more obvious after exposure for 24 h than after 12 h. The results indicate that tea polyphenols may stabilize and protect the cell membrane against the release of cell plasma enzyme LDH, and its anti-peroxidation effect is also important for cell growth. FCM analysis revealed that treatment with 0.01% to 0.1% tea polyphenols decreased the percentage of cells in the G1/G0 (quiescent) phase from 81.32% to 74.38%, and increased the percentage of cells in S and G2/M phase from 9.87% to 15.26%, and from 6.51% to 10.36%, respectively. Tea polyphenols also increased the value of PI (proliferation index) from 18.17 to 25.62. At the same time it decreased the percentage of apoptosis from 27.10% to 17.97%, which indicates that green tea stimulates cell growth and inhibits the occurrence of apoptosis. Our results indicate that tea polyphenols are effective anti-oxidants and also inhibit apoptosis, which may improve the proliferative capacity of primary skin cells in vitro.

Animals↗
PubMed2001

[Determination of polyphenols in tobacco by solid phase extraction and high performance liquid chromatography].

A high performance liquid chromatographic (HPLC) method for the determination of polyphenols in tobacco was studied. Polyphenols can be extracted from tobacco sample by refluxing with 80% (volume fraction) methanol, then subjected to degrease by solid phase extraction with Sep-Pak-C18 column. Chlorogenic acid, rutin, scopoletin, caffeic acid, scopolin and other polyphenols can be separated on a Nova-Pak-C18 column (3.9 mm i.d. x 150 mm) gradiently eluted with methanol and 0.05 mol.L-1 potassium dihydrogen phosphate buffer solution as mobile phase at a flow-rate of 0.5 mL.min-1. Polyphenols were determined at the maximum wavelength of each polyphenol, for chlorogenic acid 326.1 nm, rutin 354.8 nm, scopoletin 344.0 nm, caffeic acid 323.7 nm and scopolin 365.2 nm by photodiode array detector. The main polyphenols in tobacco can be identified with UV spectroscopy. The recoveries of tobacco polyphenols were 94%-105%, and the relative standard deviations were 1.28%-1.49%. This method can be applied to the determination of polyphenols in tobacco with satisfactory results.

Chromatography, High Pressure Liquid↗
PubMed2003

[Study on adsorption of tea polyphenol and caffine with polyamide resin].

The performance of adsorption of tea polyphenol and caffine with polyamide resin was investigated. The results obtained by spectrophotometry and HPLC show that the ability of adsorption of tea polyphenol with polyamide is stronger than that of caffine, in which hydrogen bond plays a very important role. The adsorption amount of caffine is 2.65 mg.g-1 with 7.5% adsorption ratio when 100 mL of 0.71 g.L-1 caffine is adsorbed on polyamide resine, but the adsorption amount of tea polyphenol is up to 148.13 mg.g-1 with 85% adsorption ratio when 700 mL of 1.98 g.L-1 tea polyphenol is adsorbed on polyamide resine. The dilution ratios of caffine and tea polyphenol are 74% and 90%, respectively, when they are diluted by 85% alcohol. The static adsorptions of caffine and tea polyphenol on polyamide resine reach equilibrium quickly in 80 min, and the plots of adsorption kinetics are nearly linear. Tea polyphenol and caffine are successfully separated on polyamide resine, and the obtained product contains more than 96% of tea polyphenol and 80% of EGCC with caffine less than 2.8%.

Adsorption↗
PubMed2004

Prooxidant property of green tea polyphenols epicatechin and epigallocatechin-3-gallate: implications for anticancer properties.

It is believed that anticancer and apoptosis inducing properties of green tea are mediated by it's polyphenolic constituents particularly catechins. A number of reports have shown that green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) is among the most effective chemopreventive and apoptosis-inducing agents present in the beverage. Plant polyphenols are naturally occurring antioxidants but they also exhibit prooxidant properties. Over the last several years we have shown that various classes of plant polyphenols including flavonoids, curcuminoids and tannins are capable of catalyzing oxidative DNA cleavage particularly in the presence of transition metal ions such as copper and iron. With a view to understand the chemical basis of various pharmacological properties of green tea, in this paper we have compared the prooxidant properties of green tea polyphenols--EGCG and EC ((-)-epicatechin). The rate of oxidative DNA degradation as well as hydroxyl radical and superoxide anion formation was found to be greater in the case of EGCG as compared with EC. It was also shown that copper mediated oxidation of EC and EGCG possibly leads to the formation of polymerized polyphenols. Further, it was indicated that copper oxidized catechins were more efficient prooxidants as compared with their unoxidized forms. These results correlate with the observation by others that EGCG is the most effective apoptosis inducing polyphenol present in green tea. They are also in support of our hypothesis that prooxidant action of plant polyphenols may be an important mechanism of their anticancer properties. A model for binding of Cu(II) to EC has been presented where the formation of quinone and a quinone methide has been proposed.

Animals↗
PubMed1999

Anti-tumor-promoting activity of a polyphenolic fraction isolated from grape seeds in the mouse skin two-stage initiation-promotion protocol and identification of procyanidin B5-3'-gallate as the most effective antioxidant constituent.

Procyanidins present in grape seeds are known to exert anti-inflammatory, anti-arthritic and anti-allergic activities, prevent skin aging, scavenge oxygen free radicals and inhibit UV radiation-induced peroxidation activity. Since most of these events are associated with the tumor promotion stage of carcinogenesis, these studies suggest that grape seed polyphenols and the procyanidins present therein could be anticarcinogenic and/or anti-tumor-promoting agents. Therefore, we assessed the anti-tumor-promoting effect of a polyphenolic fraction isolated from grape seeds (GSP) employing the 7,12-dimethylbenz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol 13-acetate (TPA)-promoted SENCAR mouse skin two-stage carcinogenesis protocol as a model system. Following tumor initiation with DMBA, topical application of GSP at doses of 0.5 and 1.5 mg/mouse/application to the dorsal initiated mouse skin resulted in a highly significant inhibition of TPA tumor promotion. The observed anti-tumor-promoting effects of GSP were dose dependent and were evident in terms of a reduction in tumor incidence (35 and 60% inhibition), tumor multiplicity (61 and 83% inhibition) and tumor volume (67 and 87% inhibition) at both 0.5 and 1.5 mg GSP, respectively. Based on these results, we directed our efforts to separate and identify the individual polyphenols present in GSP and assess their antioxidant activity in terms of inhibition of epidermal lipid peroxidation. Employing HPLC followed by comparison with authentic standards for retention times in HPLC profiles, physiochemical properties and spectral analysis, nine individual polyphenols were identified as catechin, epicatechin, procyanidins B1-B5 and C1 and procyanidin B5-3'-gallate. Five of these individual polyphenols with evident structural differences, namely catechin, procyanidin B2, procyanidin B5, procyanidin C1 and procyanidin B5-3'-gallate, were assessed for antioxidant activity. All of them significantly inhibited epidermal lipid peroxidation, albeit to different levels. A structure-activity relationship study showed that with an increase in the degree of polymerization in polyphenol structure, the inhibitory potential towards lipid peroxidation increased. In addition, the position of linkage between inter-flavan units also influences lipid peroxidation activity; procyanidin isomers with a 4-6 linkage showed stronger inhibitory activity than isomers with a 4-8 linkage. A sharp increase in the inhibition of epidermal lipid peroxidation was also evident when a gallate group was linked at the 3'-hydroxy position of a procyanidin dimer. Procyanidin B5-3'-gallate showed the most potent antioxidant activity with an IC(50) of 20 microM in an epidermal lipid peroxidation assay. Taken together, for the first time these results show that grape seed polyphenols possess high anti-tumor-promoting activity due to the strong antioxidant effect of procyanidins present therein. In summary, grape seed polyphenols in general, and procyanidin B5-3'-gallate in particular, should be studied in more detail to be developed as cancer chemopreventive and/or anticarcinogenic agents.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2000

Effect of complex polyphenols and tannins from red wine on DNA oxidative damage of rat colon mucosa in vivo.

BACKGROUND: Dietary polyphenols have been reported to have a variety of biological actions, including anti-carcinogenic, antioxidant and anti-inflammatory activities. AIM OF THE STUDY: In the present study we have evaluated the effect of an oral treatment with complex polyphenols and tannins from red wine and tea on DNA oxidative damage in the rat colon mucosa. METHODS: Isolated colonocytes were prepared from the colon mucosa of rats treated for ten days with either wine complex polyphenols (57.2 mg/kg/d) or thearubigin (40 mg/kg/d) by oral gavage. Colonocyte oxidative DNA damage was analysed at the single cell level using a modification of the comet assay technique. RESULTS: The results show that wine complex polyphenols and tannins induce a significant decrease (-62% for pyrimidine and -57% for purine oxidation) in basal DNA oxidative damage in colon mucosal cells without affecting the basal level of single-strand breaks. On the other hand, tea polyphenols, namely a crude extract of thearubigin, did not affect either strand breaks or pyrimidine oxidation in colon mucosal cells. CONCLUSIONS: Our experiments are the first demonstration that dietary polyphenols can modulate in vivo oxidative damage in the gastrointestinal tract of rodents. These data support the hypothesis that dietary polyphenols might have both a protective and a therapeutic potential in oxidative damage-related pathologies.

Animals↗
PubMed2004

Characteristics of piraltin, a polyphenol concentrate, produced by freeze-drying of red wine.

Moderate consumption of red wine is associated with a decreased risk for coronary heart disease. Apart from alcohol, an additive role for wine polyphenols has been suggested. However, the real contribution of these compounds can only be studied when available without the alcohol component. The objective of the study was to prepare a wine polyphenol concentrate not containing alcohol and to compare the quantitative and qualitative properties of this concentrate with those of the original wine from which the concentrate is made. This polyphenol concentrate, called piraltin, was made out of red wine by a freeze-drying technique. Both piraltin and the original red wine were analyzed quantitatively for the main polyphenols present: gallic acid, catechin, epicatechin and quercetin. The qualitative comparison comprised the inhibitory effect of the two products on LDL oxidation in vitro. In the process of freeze-drying recovery of the four determined flavonoids of red wine is fairly constant (average 68 +/- 7%). In a copper induced LDL oxidation assay both red wine and piraltin prolonged lag-times over 300% compared to controls without a significant difference between the two products. The freeze-dried polyphenol concentrate piraltin contains about 70% of the total polyphenol content of the original wine. This preparation technique does not cause a loss of antioxidative properties of the phenols. Piraltin creates the possibility to study the effects of wine polyphenols separately without the influence of alcohol both in vitro and in vivo.

Antioxidants↗
PubMed2006

SIRT1 stimulation by polyphenols is affected by their stability and metabolism.

Silent information regulator two ortholog 1 (SIRT1) is the human ortholog of the yeast sir2 protein; one of the most important regulators of lifespan extension by caloric restriction in several organisms. Dietary polyphenols, abundant in vegetables, fruits, cereals, wine and tea, were reported to stimulate the deacetylase activity of recombinant SIRT1 protein and could therefore be potential regulators of aging associated processes. However, inconsistent data between effects of polyphenols on the recombinant SIRT1 and on in vivo SIRT1, led us to investigate the influence of (1) stability of polyphenols under experimental conditions and (2) metabolism of polyphenols in human HT29 cells, on stimulation of SIRT1. With an improved SIRT1 deacetylation assay we found three new polyphenolic stimulators. Epigallocatechin galate (EGCg, 1.76-fold), epicatechin galate (ECg, 1.85-fold) and myricetin (3.19-fold) stimulated SIRT1 under stabilizing conditions, whereas without stabilization, these polyphenols strongly inhibited SIRT1, probably due to H2O2 formation. Using metabolically active HT29 cells we were able to show that quercetin (a stimulator of recombinant SIRT1) could not stimulate intracellular SIRT1. The major quercetin metabolite in humans, quercetin 3-O-glucuronide, slightly inhibited the recombinant SIRT1 activity which explains the lack of stimulatory action of quercetin in HT29 cells. This study shows that the stimulation of SIRT1 is strongly affected by polyphenol stability and metabolism, therefore extrapolation of in vitro SIRT1 stimulation results to physiological effects should be done with caution.

Cell Line, Tumor↗
PubMed2002

Absorption and metabolism of polyphenols in the gut and impact on health.

Polyphenols are the most abundant antioxidants in the human diet. They show a considerable structural diversity, which largely influences their bioavailability. Phenolic acids like caffeic acid are easily absorbed through the gut barrier, whereas large molecular weight polyphenols such as proanthocyanidins are very poorly absorbed. Once absorbed, polyphenols are conjugated to glucuronide, sulphate and methyl groups in the gut mucosa and inner tissues. Non-conjugated polyphenols are virtually absent in plasma. Such reactions facilitate their excretion and limit their potential toxicity. The polyphenols reaching the colon are extensively metabolised by the microflora into a wide array of low molecular weight phenolic acids. The biological properties of both conjugated derivatives and microbial metabolites have rarely been examined. Their study will be essential to better assess the health effects of dietary polyphenols. Alternatively, some health effects of polyphenols may not require their absorption through the gut barrier. Their role as iron chelators in the gut lumen is briefly discussed.

Animals↗
PubMed2001

White wine with red wine-like properties: increased extraction of grape skin polyphenols improves the antioxidant capacity of the derived white wine.

Lower antioxidant activity in white wines in comparison to red wines lies in the low grape-skin-derived polyphenol content. This paper reports the analysis of the antioxidant capacities of white wine samples obtained along two different processing procedures directed to enrich the wine with polyphenols. White wine samples derived from whole squeezed grapes stored for increasing periods of time (up to 18 h) contained increasing concentrations of polyphenols (from 0.35 to 0.55 mmol/L) and, in parallel, exhibited increased capacity to scavenge free radicals and to inhibit copper ion-induced low-density lipoprotein (LDL) oxidation. However, addition of increasing concentrations of alcohol (up to 18%) to the whole squeezed grapes remarkably augmented the extraction of grape skin polyphenols into the wine up to 1.25 mmol/L, resulting in an increased capacity of the wine to scavenge free radicals and to inhibit LDL oxidation, to an extent similar to that of red wine. The extent of LDL oxidation inhibition was directly related to the wine polyphenolic content (r = 0.986). It is concluded that processing white wine by imposing a short period of grape skin contact in the presence of alcohol leads to extraction of grape skin polyphenols and produces polyphenol-rich white wine with antioxidant characteristics similar to those of red wine.

Antioxidants↗