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PubMed2003

Antioxidant actions of polyphenols in humans.

Many polyphenols are potent antioxidants in foods and model systems and they have therefore very naturally been linked with the hypothesis that their redox actities may confer them with specific health benefits. Their prevalence in plant derived foods, which are generally accepted as healthy has supported this view and inspired researchers to conduct human intervention trails with polyphenol rich food items in order to investigate their ability to counteract oxidative stress. Several biomarkers have gained widespread use to assess oxidative damage and antioxidative defence capabilities in humans. These markers pioneer our knowledge about factors related to oxidative stress in proteins, lipids and DNA and present results indicate that oxidative damage may be very localised and that refined markers may be necessary in order to disentangle the complex local factors which determine the extent of oxidative damage in different molecular structures. The present text reviews the human short-term intervention studies with polyphenol-rich foods, which address their impact on biomarkers of oxidative damage and antioxidative defence. None of the oxidative damage markers seem to be consistently affected by polyphenol-rich foods or to be consistently related to one another. The most consistent finding regarding antioxidative defence markers is a postprandial effect on plasma antioxidative capacity after ingestion of foods rich in catechins and complex procyanidins.

Antioxidants↗
PubMed2005

The predominant polyphenol in the leaves of the resurrection plant Myrothamnus flabellifolius, 3,4,5 tri-O-galloylquinic acid, protects membranes against desiccation and free radical-induced oxidation.

The predominant (>90%) low-molecular-mass polyphenol was isolated from the leaves of the resurrection plant Myrothamnus flabellifolius and identified to be 3,4,5 tri-O-galloylquinic acid using 1H and 13C one- and two-dimensional NMR spectroscopy. The structure was confirmed by mass spectrometric analysis. This compound was present at high concentrations, 44% (by weight) in hydrated leaves and 74% (by weight) in dehydrated leaves. Electron microscopy of leaf material fixed with glutaraldehyde and caffeine demonstrated that the polyphenols were localized in large vacuoles in both hydrated and dehydrated leaves. 3,4,5 Tri-O-galloylquinic acid was shown to stabilize an artificial membrane system, liposomes, against desiccation if the polyphenol concentration was between 1 and 2 microg/mug phospholipid. The phase transition of these liposomes observed at 46 degrees C was markedly diminished by the presence of 3,4,5 tri-O-galloylquinic acid, suggesting that the presence of the polyphenol maintained the membranes in the liquid crystalline phase at physiological temperatures. 3,4,5 Tri-O-galloylquinic acid was also shown to protect linoleic acid against free radical-induced oxidation.

Calorimetry, Differential Scanning↗
PubMed1997

Glutathione conjugation of chlorambucil: measurement and modulation by plant polyphenols.

Chlorambucil (CMB), an anticancer drug, was cytotoxic at concentrations of 5-20 microM to human colon adenocarcinoma cells. It inhibited [14C]thymidine uptake in a dose-dependent manner. Both effects were potentiated by simultaneous exposure of the cells to 10 microM plant polyphenols. In an attempt to explain the possible mechanism of action of the polyphenols in relation to these observations, an HPLC-radiometric method was developed to measure the conjugation of CMB with glutathione in these cells and to monitor the export of monochloromonoglutathionyl CMB (MG-CMB), its main glutathione conjugate. At micromolar concentrations, five polyphenols, namely quercetin, butein, tannic acid, 2'-hydroxychalcone and morin, inhibited the efflux of CMB significantly; an inhibition of 40% was observed with 10 microM quercetin. The glutathione S-transferase (GST) activity of the cancer cells, measured with 1-chloro-2,4-dinitrobenzene, was also inhibited by the polyphenols. Their combined action on GST and on the efflux of MG-CMB conjugate could provide an enhanced positive modulation of sensitivity of the tumour cells to CMB.

Antineoplastic Agents, Alkylating↗
PubMed1995

Plant polyphenols: free radical scavengers or chain-breaking antioxidants?

There is increasing interest in the biological effects of tea- and wine-derived polyphenols and many studies in vitro and in vivo are demonstrating their antioxidant properties. Tea is a major source of dietary polyphenols and an even richer source of the flavanols, the catechins and catechin/gallate esters. Although there are limited studies on the bioavailability of the polyphenols, the absorption of flavanols in humans has been shown. The studies described in this chapter discuss the relative antioxidant potentials of the polyphenolic flavonoids in vitro against radicals generated in the aqueous phase in comparison with their relative effectiveness as antioxidants against propagating lipid peroxyl radicals, and how their activity influences that of alpha-tocopherol in low-density lipoproteins exposed to oxidative stress.

Antioxidants↗
PubMed2004

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (-)-epigallocatechin-3-gallate: implications for neurodegenerative diseases.

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinson's (PD), Alzheimer's (AD) and Huntington's diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS-induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non-vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age-related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (-)-epigallocatechin-3-gallate (EGCG), will be reviewed and discussed.

Animals↗
PubMed2004

Activation of endothelial nitric-oxide synthase by the p38 MAPK in response to black tea polyphenols.

Black tea improves endothelial function in patients with coronary artery disease. We sought to determine the responsible components of black tea and elucidate the underlying cell signaling mechanisms. We exposed porcine aortic endothelial cells to components of black tea and found that the polyphenol fraction acutely enhanced nitric oxide bioactivity. This effect involved endothelial nitric-oxide synthase (eNOS) phosphorylation at Ser-1177 and dephosphorylation at Thr-495, consistent with increased eNOS activity. These effects were calcium-dependent, as removal of extracellular calcium prevented eNOS phosphorylation at Ser-1177, whereas inhibition of intracellular calcium mobilization with TMB-8 blunted Thr-495 dephosphorylation. Black tea polyphenol-induced eNOS activation appeared dependent upon the phosphatidylinositol 3-kinase-Akt pathway, as it was significantly inhibited by LY294002 and a dominant negative Akt, respectively. Pharmacological inhibition of p38 mitogen-activated protein kinase (p38 MAPK) with either SB202190 or SB203580 as well as overexpression of a dominant negative p38 MAPKalpha attenuated both eNOS activation and phosphorylation changes in response to black tea polyphenols. Inhibition of p38 MAPKalpha also blunted Akt activation in response to black tea polyphenols, suggesting that p38alpha MAPK is upstream of Akt in this pathway. Finally, a constitutively active mutant of MKK6bE, an upstream kinase for p38 MAPK, enhanced both the basal and stimulated activity of Akt, leading to increased eNOS activity. Taken together, these data identify the p38 MAPK as an upstream component of Akt-mediated eNOS activation.

Adenoviridae↗
PubMed2004

Phenolic acid metabolites as biomarkers for tea- and coffee-derived polyphenol exposure in human subjects.

Tea and coffee are rich in polyphenols with a variety of biological activities. Many of the demonstrated activities are consistent with favourable effects on the risk of chronic diseases. 4-O-methylgallic acid (4OMGA) and isoferulic acid are potential biomarkers of exposure to polyphenols derived from tea and coffee respectively. 4OMGA is derived from gallic acid in tea, and isoferulic acid is derived from chlorogenic acid in coffee. Our major objective was to explore the relationships of tea and coffee intake with 24 h urinary excretion of 4OMGA and isoferulic acid in human subjects. The relationships of long-term usual (111 participants) and contemporaneously recorded current (344 participants) tea and coffee intake with 24 h urinary excretion of 4OMGA and isoferulic acid were assessed in two populations. 4OMGA was related to usual (r 0.50, P<0.001) and current (r 0.57, P<0.001) tea intake, and isoferulic acid was related to usual (r 0.26, P=0.008) and current (r 0.18, P<0.001) coffee intake. Overall, our present results are consistent with the proposal that 4OMGA is a good biomarker for black tea-derived polyphenol exposure, but isoferulic acid may be of limited usefulness as a biomarker for coffee-derived polyphenol exposure.

Biomarkers↗
PubMed2003

Plant polyphenols: are they the new magic bullet?

Epidemiological evidence suggests that diets rich in fruit and vegetables decrease the risk of premature mortality from major clinical conditions, including cancer and heart disease. However, it is not yet clear which components or combination of components in fruit and vegetables are protective and what is their mechanism of action. Such scientific uncertainty does not seem to inhibit the marketing of a huge range of plant-based concoctions, promoted as 'magic bullets' for optimum health. For example, the purported health-giving properties of plant polyphenols represent a case in which enthusiastic marketing claims may far exceed the current scientific evidence. Even when good experimental evidence exists, results need to be interpreted with caution in relation to human health benefits, as polyphenols may have limited bioavailability and may also be extensively metabolised. In addition, some polyphenols can be toxic and mutagenic in some cell culture systems. Until more is known about the activity and metabolic fate of polyphenols in the body, it would be better for the consumer to increase fruit and vegetable intake, and also to be wary of claims that these compounds are a panacea for good health.

Antioxidants↗
PubMed2007

Identification of free radical species derived from caffeic acid and related polyphenols.

Polyphenols are widely distributed in various fruits, vegetables and seasonings. It is well known that they have several physiological effects due to their antioxidative activities. Their activities depend on structural characteristics that favour the formation of their corresponding stable radicals. During the examination at which pH values, the polyphenol radicals are stabilized, we confirmed that polyphenol radicals were stabilized in NaHCO3/Na2CO3 buffer (pH 10) rather than in physiological pH region. Then, we measured electron spin resonance (ESR) spectra at pH 10 to examine the characteristics of free radical species derived from caffeic acid (CA) with an unsaturated side chain, dihydrocaffeic acid (DCA) with a saturated side chain, chlorogenic acid (ChA) and rosmarinic acid (RA). In analyzing the radical structures, ESR simulation, determinations of macroscopic and microscopic acid dissociation constants and molecular orbital (MO) calculation were performed. In CA, the monophenolate forms were assumed to participate in the formation of free radical species, while in DCA, the diphenol form and the monophenolate forms were presumed to contribute to the formation of free radical species. On the basis of the results, we propose the possible structures of the free radical species formed from polyphenols under alkaline conditions.

Caffeic Acids↗
PubMedDate not supplied

Chemosensitization and radiosensitization of tumors by plant polyphenols.

The treatment of cancer with chemotherapeutic agents and radiation has two major problems: time-dependent development of tumor resistance to therapy (chemoresistance and radioresistance) and nonspecific toxicity toward normal cells. Many plant-derived polyphenols have been studied intently for their potential chemopreventive properties and are pharmacologically safe. These compounds include genistein, curcumin, resveratrol, silymarin, caffeic acid phenethyl ester, flavopiridol, emodin, green tea polyphenols, piperine, oleandrin, ursolic acid, and betulinic acid. Recent research has suggested that these plant polyphenols might be used to sensitize tumor cells to chemotherapeutic agents and radiation therapy by inhibiting pathways that lead to treatment resistance. These agents have also been found to be protective from therapy-associated toxicities. How these polyphenols protect normal cells and sensitize tumor cells to treatment is discussed in this review.

Animals↗
PubMed2004

Red wine polyphenolic compounds inhibit atherosclerosis in apolipoprotein E-deficient mice independently of effects on lipid peroxidation.

BACKGROUND: Lipid peroxidation is thought to play an important role in the pathogenesis of atherosclerosis. Fatty acid peroxidation products such as hydroxyeicosatetraenoic acids and F(2)-isoprostanes have been found in advanced human atherosclerotic plaques. However, little is known about the formation of these products during lesion development. OBJECTIVE: This study examined stable biomarkers of lipid oxidative damage in relation to atherosclerotic disease progression in apolipoprotein E-deficient (Apoe(-/-)) mice and retardation of the disease by red wine polyphenols. DESIGN: One hundred male Apoe(-/-) mice and 50 male control (C57BL/6J) mice were given a high-fat, high-cholesterol diet for 20 wk. To examine the effect of the polyphenolic compounds on lesion development, 50 of the Apoe(-/-) mice were also given dealcoholized red wine for the duration of the study. RESULTS: Aortic lipid deposition was significantly greater in the Apoe(-/-) mice than in the control mice (P < 0.01). Plasma and aortic F(2)-isoprostanes did not differ between the treatment groups. Plasma concentrations of monocyte chemoattractant protein 1, which has been implicated in the development of atherosclerosis, were significantly higher in the Apoe(-/-) mice than in the control mice up to 16 wk (P < 0.05). Hydroxyeicosatetraenoic acid concentrations increased significantly over time in all groups (P < 0.05). Red wine polyphenols had no effect on markers of lipid peroxidation or monocyte chemoattractant protein 1 concentrations, but lipid deposition in the aorta at age 26 wk was significantly less in the mice given red wine than in those not given red wine. CONCLUSION: These results suggest that lipid deposition is independent of lipid oxidation and that the protective action of red wine polyphenols is independent of any antioxidant action of these compounds.

Animals↗
PubMed2005

The history of beta-carotene and cancers: from observational to intervention studies. What lessons can be drawn for future research on polyphenols?

An important question being raised by nutritionists today is whether available scientific data support an important role for polyphenols in the prevention of pathologic conditions that represent an important public health burden, such as cardiovascular diseases, cancers, and osteoporosis. More broadly, when can we consider scientific knowledge sufficient to allow specific public health implications and recommendations? The history of the relationship between beta-carotene and cancer illustrates the complexity of the research process leading to the demonstration of a causal relationship between nutritional factors and the prevention of disease. The beta-carotene story, which has developed in the past 30 y, is particularly significant and illustrative because of apparent controversies that are far from resolved. This is an extremely interesting example from which many lessons can be learned. For beta-carotene, we need to collect sufficient information from experimental, clinical, and epidemiologic research before we support any specific public health recommendations. The same principles must be applied to recommendations regarding polyphenols (in particular, which polyphenols, at which doses, to achieve which benefits for which populations). If these questions are not answered, then we run the risk of needing to renounce recommendations regarding polyphenols in the future, damaging the credibility of nutritional recommendations for public health.

Animals↗
PubMed2005

Polyphenols in foods are more complex than often thought.

Dietary polyphenols show a great diversity of structures, ranging from rather simple molecules (monomers and oligomers) to polymers. Higher-molecular-weight structures (with molecular weights of > 500) are usually designated as tannins, which refers to their ability to interact with proteins. Among them, condensed tannins (proanthocyanidins) are particularly important because of their wide distribution in plants and their contributions to major food qualities. All phenolic compounds are highly unstable and rapidly transformed into various reaction products when the plant cells are damaged (for instance, during food processing), thus adding to the complexity of dietary polyphenol composition. The polyphenol composition of plant-derived foods and beverages depends on that of the raw material used but also on the extraction process and subsequent biochemical and chemical reactions of plant polyphenols. The occurrence of specific tannin-like compounds (ie, thearubigins and theaflavins) arising from enzymatic oxidation is well documented in black tea. Various chemical reactions involving anthocyanins and/or flavanols have been demonstrated to occur during red wine aging. Current knowledge regarding the reaction mechanisms involved in some of these processes and the structures of the resulting products is reviewed. Their effects on organoleptic and nutritional quality are also discussed.

Flavonoids↗
PubMed2005

Structure-activity relationship of polyphenols that inhibit fatty acid synthase.

Many flavone derivatives inhibit FAS, and their A and B rings play an important role, but is the C ring necessary for the inhibition of FAS? Here, using nordihydroguaiaretic acid (NDGA), with two phenyl rings connected by a four-carbon chain, as a representative, the structural basis for the inhibition of animal fatty acid synthase (FAS) by polyphenols was investigated. NDGA potently inhibits the overall reaction of FAS (IC(50) = 9.3 +/- 0.1 muM). The kinetic study indicated that NDGA inhibits FAS competitively with respect to acetyl-CoA, noncompetitively with respect to malonyl-CoA, and in a mixed manner with respect to NADPH. The inhibitory mechanism is the same as that of FAS flavonoid inhibitors. This suggests that the C ring of flavonoids is not essential for their FAS inhibitory effect. This conclusion was further confirmed by the results obtained for different polyphenols. A structure-activity relationship study indicated that a biphenyl core exists in all FAS polyphenol inhibitors. Thus, we propose a common model possibly shared by all FAS polyphenol inhibitors. The model includes two almost planar aromatic rings with their respective hydroxyl groups, and a proper ester linkage between the two rings that possibly causes the inhibition of FAS by irreversibly inhibiting the beta-ketoacyl reductase domain.

Animals↗
PubMed2001

Walnut polyphenolics inhibit in vitro human plasma and LDL oxidation.

Recent epidemiologic studies have associated nut consumption with a reduced incidence of cardiovascular mortality. However, little is known about the contribution of nut polyphenols to antioxidant and cardiovascular protection. In this investigation, polyphenol-rich extracts from English walnuts (Juglans regia) were studied and compared with ellagic acid for their ability to inhibit in vitro plasma and LDL oxidation, as well as their effects on LDL alpha-tocopherol during oxidative stress. In addition, the Trolox equivalent antioxidant activity (TEAC) was determined and liquid chromatography electrospray detection mass spectrometry (LC-ELSD/MS) analyses of the walnut extracts were performed. 2,2'-Azobis'(2-amidino propane) hydrochloride (AAPH)-induced LDL oxidation was significantly inhibited by 87 and 38% with the highest concentration (1.0 micromol/L) of ellagic acid and walnut extract, respectively. In addition, copper-mediated LDL oxidation was inhibited by 14 and 84% in the presence of ellagic acid and walnut extract, respectively, with a modest, significant LDL alpha-tocopherol sparing effect observed. Plasma thiobarbituric acid reacting substance (TBARS) formation was significantly inhibited by walnut extracts and ellagic acid in a dose-dependent manner, and the extracts exhibited a TEAC value greater than that of alpha-tocopherol. LC-ELSD/MS analysis of the walnut extracts identified ellagic acid monomers, polymeric ellagitannins and other phenolics, principally nonflavonoid compounds. These results demonstrate that walnut polyphenolics are effective inhibitors of in vitro plasma and LDL oxidation. The polyphenolic content of walnuts should be considered when evaluating their antiatherogenic potential.

Adult↗
PubMed2004

Black and green tea polyphenols attenuate blood pressure increases in stroke-prone spontaneously hypertensive rats.

Oxidative stress was reported to be involved not only in cardiovascular diseases, but also in hypertension. Epidemiologic studies indicated that tea consumption slightly reduces blood pressure. We conducted two studies to determine whether black and green tea can lower blood pressure (BP) in stroke-prone spontaneously hypertensive rats (SHRSP). Male SHRSP (n=15) were allowed to recover for 2 wk after a transmitter for measuring BP was implanted in the peritoneal cavity. The rats were divided into three groups: the control group consumed tap water (30 mL/d); the black tea polyphenol group (BTP) consumed water containing 3.5 g/L thearubigins, 0.6 g/L theaflavins, 0.5 g/L flavonols and 0.4 g/L catechins; and the green tea polyphenol group (GTP) consumed water containing 3.5 g/L catechins, 0.5 g/L flavonols and 1 g/L polymetric flavonoids. The telemetry system was used to measure BP, which were recorded continuously every 5 min for 24 h. During the daytime, systolic and diastolic BP were significantly lower in the BTP and GTP groups than in the controls. Protein expressions of catalase and phosphorylated myosin light chain (MLC-p) were measured in the aorta by Western blotting. GTP significantly increased catalase expression, and BTP and GTP significantly decreased MLC-p expression in the aorta. These data demonstrate that both black and green tea polyphenols attenuate blood pressure increases through their antioxidant properties in SHRSP. Furthermore, because the amounts of polyphenols used in this experiment correspond to those in approximately 1 L of tea, the regular consumption of black and green tea may also provide some protection against hypertension in humans.

Animals↗
PubMed1999

Inclusion of polyvinylpyrrolidone in the polymerase chain reaction reverses the inhibitory effects of polyphenolic contamination of RNA.

Polysaccharides, secondary metabolites and poly-phenolics are known to co-isolate with nucleic acids from plant tissues resulting in inhibition of molecular manipulations. RNA isolated from the polyphenolic-rich resurrection plant, Myrothamnus flabellifolius, was demonstrated to inhibit a standard polymerase chain reaction used as an assay despite the inclusion of the polyphenolic-binding compound poly(1-vinylpyrrolidone-2) (PVP) into the RNA isolation medium. This inhibition was, however, reversed by the addition of PVP into the PCR mixture itself. Confirmation of the inhibitory effect of polyphenolics on PCR was obtained by addition of green tea polyphenolics to the standard PCR assay. This inhibition was also reversed by the simultaneous inclusion of PVP.

DNA, Fungal↗
PubMed2004

Induced responses to pathogen infection in Norway spruce phloem: changes in polyphenolic parenchyma cells, chalcone synthase transcript levels and peroxidase activity.

Polyphenolic parenchyma cells (PP cells) in Norway spruce (Picea abies (L.) Karst.) stem phloem play important roles in constitutive and inducible defenses. To determine whether anatomical and molecular changes in PP cells are correlated with tree resistance, we infected two Norway spruce clones with the pathogenic fungus Ceratocystis polonica (Siem.) C. Moreau. The fungus induced significantly different lesion lengths in the two clones, indicating that one clone was more resistant to the fungus (short lesions) than the other (long lesions). After infection, the cross-sectional area of PP cells and their vacuolar polyphenol bodies increased in the three most recent annual rings of PP cells in both clones. The more resistant clone had larger PP cells with denser polyphenol bodies than the less resistant clone, whereas the less resistant clone accumulated relatively more polyphenols after infection. Compared with the less resistant clone, the more resistant clone contained higher starch concentrations before infection that were reduced more quickly after infection before returning to original values. Low transcript levels of chalcone synthase were detected in uninfected tissues of both clones, but the levels increased dramatically after infection. Transcript levels were higher and peaked 6 days earlier in the more resistant clone than in the less resistant clone. The activity of at least one highly basic peroxidase isoform was greatly enhanced after infection, and this increase occurred earlier in the more resistant clone.

Acyltransferases↗