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PubMed1997

Protective effect of green tea extract and tea polyphenols against the cytotoxicity of 1,4-naphthoquinone in isolated rat hepatocytes.

The cytoprotective effect of green tea extract and its phenolic compounds against 1,4-naphthoquinone-induced hepatotoxicity was evaluated in primary cultured rat hepatocytes. After exposure to 1,4-naphthoquinone, lactate dehydrogenase (LDH) leakage and cell viability were both improved by the presence of the tea extract and tea polyphenols. This cytoprotective effect was related to the structure of tea polyphenols, the galloyl group of (-)-epigallocatechin-3-gallate and (-)-epicatechin-3-gallate being particularly effective. The production of liquid peroxidation by 1,4-naphthoquinone was not inhibited by the tea extract nor by tea polyphenol addition. After 2 h of incubation, the protein thiol concentration was reduced by 1,4-naphthoquinone, but this reduction was prevented by the tea extract and tea polyphenols. The reduction in protein thiol content of the cells closely paralleled the LDH leakage and loss of cell viability. These results suggest that the mechanism of protection by tea polyphenols against 1,4-naphthoquinone-induced toxicity to rat hepatocytes was due to the maintenance of protein thiol levels.

Animals↗
PubMed2001

Green tea polyphenolic antioxidants and skin photoprotection (Review).

Green tea is consumed as a popular beverage worldwide particularly in Asian countries like China, Korea, Japan and India. It contains polyphenolic compounds also known as epicatechins, which are antioxidant in nature. Many laboratories have shown that topical treatment or oral consumption of green tea polyphenols inhibits chemical carcinogen- or ultraviolet radiation-induced skin tumorigenesis in different animal models. Studies have shown that green tea extract also possesses anti-inflammatory activity. These anti-inflammatory and anti-carcinogenic properties of green tea are due to their polyphenolic constituents present therein. The major and most chemopreventive constituent in green tea responsible for these biochemical or pharmacological effects is (-)-epigallocatechin-3-gallate (EGCG). Understanding the molecular mechanisms of these effects of green tea is a subject of investigation in many laboratories. Treatment of green tea polyphenols to skin has been shown to modulate the biochemical pathways involved in inflammatory responses, cell proliferation and responses of chemical tumor promoters as well as ultraviolet (UV) light-induced inflammatory markers of skin inflammation. Topical treatment with EGCG on mouse skin also results in prevention of UVB-induced immunosuppression, and oxidative stress. The protective effects of green tea treatment on human skin either topically or consumed orally against UV light-induced inflammatory or carcinogenic responses are not well understood. Based on documented extensive beneficial effects of green tea on mouse skin models and very little in human skin, many pharmaceutical and cosmetic companies are supplementing their skin care products with green tea extracts. Therefore, the focus of this communication is to review and analyze the photoprotective effects of green tea polyphenols to skin.

Anti-Inflammatory Agents↗
PubMed1999

Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages.

The effects of different polyphenol-containing beverages on Fe absorption from a bread meal were estimated in adult human subjects from the erythrocyte incorporation of radio-Fe. The test beverages contained different polyphenol structures and were rich in either phenolic acids (chlorogenic acid in coffee), monomeric flavonoids (herb teas, camomile (Matricaria recutita L.), vervain (Verbena officinalis L.), lime flower (Tilia cordata Mill.), pennyroyal (Mentha pulegium L.) and peppermint (Mentha piperita L.), or complex polyphenol polymerization products (black tea and cocoa). All beverages were potent inhibitors of Fe absorption and reduced absorption in a dose-dependent fashion depending on the content of total polyphenols. Compared with a water control meal, beverages containing 20-50 mg total polyphenols/serving reduced Fe absorption from the bread meal by 50-70%, whereas beverages containing 100-400 mg total polyphenols/serving reduced Fe absorption by 60-90%. Inhibition by black tea was 79-94%, peppermint tea 84%, pennyroyal 73%, cocoa 71%, vervain 59%, lime flower 52% and camomile 47%. At an identical concentration of total polyphenols, black tea was more inhibitory than cocoa, and more inhibitory than herb teas camomile, vervain, lime flower and pennyroyal, but was of equal inhibition to peppermint tea. Adding milk to coffee and tea had little or no influence on their inhibitory nature. Our findings demonstrate that herb teas, as well as black tea, coffee and coca can be potent inhibitors of Fe absorption. This property should be considered when giving dietary advice in relation to Fe nutrition.

Adult↗
PubMedDate not supplied

Potential molecular targets of tea polyphenols in human tumor cells: significance in cancer prevention.

Next to water, tea is the most popular beverage in the world, and the cancer-preventive effects of this beverage have been suggested. Epidemiological studies have shown decreased cancer occurrence in those individuals who drink green tea regularly. A wealth of research suggests numerous mechanisms of action to explain these observations. The most abundant and popular compound studied in tea research is (-)-epigallocatechin-3-gallate (EGCG), which acts as a powerful antioxidant and can inhibit a number of tumor cell proliferation- and survival-related proteins. Tea polyphenols are known to inhibit the large multi-catalytic protease (the proteasome) and metaloproteionases, involved in tumor survival and metastasis, respectively. Additionally, tea polyphenols inhibit the activities of many tumor-associated protein kinases, including epidermal growth factor receptor, vascular endothelial growth factor receptor, platelet-derived growth factor receptor, mitogen-activated protein kinase, and IkB kinase. Tea polyphenols have also been found to inhibit some cancer-related proteins that regulate DNA replication and transformation. At present, it is not known which of these activities of tea polyphenols are required for its cancer-preventive effects. However, by understanding the in vivo concentrations of tea polyphenols required to inhibit each of these activities, we may start to sort out in the future the mechanisms responsible for the cancer-preventive effects of tea.

Animals↗
PubMed2003

Blocking telomerase by dietary polyphenols is a major mechanism for limiting the growth of human cancer cells in vitro and in vivo.

Animal and epidemiological studies reveal that consuming food and beverages rich in polyphenols (e.g., catechins, flavones, and antocyanines) is associated with a lower incidence of cancer, and several molecular mechanisms have been proposed for explaining this effect. However, because most of these mechanisms were observed only under specific and nonphysiological conditions, and in most cases, with practically irrelevant concentrations, there is still no clear-cut or universal explanation for the major events that underlie the anticancer effects of polyphenols. In this study we present clear in vitro and in vivo evidence that the inhibition of the cancer-associated enzyme telomerase is a key mechanism involved in cancer inhibition by epigallocatechin gallate (EGCG), a major tea polyphenol. We demonstrate that EGCG and other selected polyphenols undergo structural rearrangements at physiologically permissible conditions that result in remarkably increased telomerase inhibition. In nude mice models bearing both telomerase-dependent and -independent xenograft tumors cloned from a single human cancer progeny, only the telomerase-dependent tumors responded to prolonged oral administration of EGCG. Thus, EGCG and likely other structurally related dietary polyphenols seem to act as prodrug-like molecules that, once ingested and distributed, undergo structural changes that favor potent activity against telomerase.

Animals↗
PubMedDate not supplied

Green tea polyphenol targets the mitochondria in tumor cells inducing caspase 3-dependent apoptosis.

Induction of apoptosis by green tea polyphenols has been observed in various tumor cell systems, but whether green tea polyphenol-induced apoptosis requires caspase 3 for execution has not been confirmed. We previously reported that green tea polyphenol-induced apoptosis involved Apaf-1 accumulation and caspase 3 activation in the cytosol. In the current study, tumor cells either with deleted caspase 3 gene or expressing wild-type caspase 3 were treated with increasing concentrations of green tea polyphenol(s), followed by morphological analysis and caspase 3 activity assay. The caspase 3 null parental cell line was further examined in comparison with a well-characterized, caspase 3 wild type oral carcinoma cell line by MTT assay and BrdU incorporation assay. The results demonstrated that, while the mitochondrial function gradually declined to insignificant levels, caspase 3 null cells did not undergo apoptosis, which suggested that green tea polyphenol-induced apoptosis is a mitochondria-targeted, caspase 3-executed mechanism.

Adenocarcinoma↗
PubMed1996

[Influence of green tea polyphenols varnish on saliva]

This study observed the inhibitory effect of green tea polyphenols varnish on the activity of humman saliva.We found 0.78 and 1.56mg/ml green tea polyphenols varnish is the best.We also observed the release of green tea polyphenols from liquid varnish is more than that from membraniform vanish.The release quantities of green tea polyphenols from membraniform is limited,suggest the influence of green tea polyphenols varnish on the activity of human saliva is small.

Journal Article↗
PubMed1985

[Effect of polyphenols of coffee pulp on iron absorption].

The effect of the polyphenols of coffee pulp on iron absorption was studied using the method of ligated segments in rats. Optimal conditions to measure iron absorption, were determined using as criteria the concentration of Fe59 and the time that produced the highest value of blood radioactivity. A concentration of 0.4 uCi/dose of Fe59 and a 3-hr period were chosen to measure iron absorption. Experimental groups were formed assigning six rats randomly to each group. Each group was injected with a solution of 59Fe and either with the standard polyphenol solution or with the coffee pulp extract, except the control group which was injected with the Fe59 solution only. The effect of two polyphenol concentrations was also studied. Iron uptake from the duodenum was found to be the best indicator of iron absorption when compared to the sum of iron uptake by the tissues (blood, liver, spleen, kidneys, heart and carcass). Therefore, this indicator was used to interpret the results obtained. Catechin, tannic acid and the coffee pulp extract decreased significantly iron absorption when compared with the control group. The level of polyphenols used in these experiments is similar to the amounts consumed by animals fed coffee pulp at a 10% level. Therefore, we can conclude that the antinutritional effect of coffee pulp polyphenols may be partially due to their capacity to bind iron.

Animals↗
PubMed1995

Effects of natural polyphenols on aflatoxin B1 activation in a reconstituted microsomal monooxygenase system.

Covalent adduct formation between aflatoxin B1 and DNA, as catalyzed by a reconstituted microsomal monooxygenase system containing purified cytochrome P450 and NADPH-cytochrome P450 reductase, was observed to be inhibited by certain polyphenolic compounds of natural origin. Polyhydroxylated flavonoids were found to be more effective than phenolic acids and displayed dose-dependent inhibition. The inhibition (50%) could be reversed by increasing the amount of cytochrome P450 but not by increasing the amount of reductase. Each polyphenol inhibited NADPH-cytochrome P450 reductase activity as measured by reduction of cytochrome C. This inhibition could be reversed with higher amounts of cytochrome C. This inhibition, however, could not be reversed if an artificial electron acceptor, dichlorophenolindophenol, was used in place of cytochrome C. These results suggest a strong affinity of polyphenols toward cytochromes. This conclusion was further supported from the observation that pretreatment of cytochrome P450 with each polyphenol reduced its ability to catalyze aflatoxin B1-DNA adduct formation in the reconstituted system. Natural polyphenols, thus, may have the ability to modulate chemical carcinogenesis by modulating cytochrome P450 function.

2,6-Dichloroindophenol↗
PubMedDate not supplied

Protective action of plant polyphenols on radiation-induced chromatid breaks in cultured human cells.

The present study was performed to determine whether plant polyphenols can protect human cells against radiation-induced DNA damage manifested as chromatid breaks. Since each chromatid contains a single continuous molecule of double stranded DNA, chromatid breaks represent unrepaired DNA strand breaks. The addition of green or black tea extracts, their polyphenols or curcumin to cultures of human skin fibroblasts or PHA-stimulated blood lymphocytes significantly reduced the frequencies of radiation-induced chromatid breaks. An exception to this general finding was that the green tea polyphenol, (-)epigallocatechin gallate, had no effect. The protective action of these plant polyphenols seems to result from their known antioxidant properties, particularly the scavaging of hydroxyl free radicals. Frequencies of chromatid breaks in cells arrested immediately after irradiation or 0.5 to 1.5 hours post-irradiation in the presence or absence of a DNA repair inhibitor, provide a measure of DNA damage. The results of the present study show that tea and other plant polyphenols can protect human cells against radiation-induced DNA damage.

Catechin↗
PubMed2025

Human milk oligosaccharides and polyphenols: Mechanisms, effects, and applications in allergies.

Human milk offers the best nutrition to the infant, which is crucial for the child's proper development and health status across the lifespan. Besides providing the substances optimally supplying the baby with energy and building materials, breast milk contains several immunometabolically active components. Those include molecules fully de novo synthesized by the mother, such as human milk oligosaccharides (HMO), and substances of nonhuman origin, transferred to the infant through mother's milk, such as dietary plant polyphenols. In this review, we outline the basic biology of HMO and polyphenols and deeply characterize their effects on the development of allergic disorders on the basis of available literature reporting data from in vitro, animal, and human studies. Further, we review the abundance of HMO and polyphenols, commonly present in mother's milk, and their mutual interactions in the context of the mechanisms underlying predisposition to, or protection against, the development of allergies. Finally, we discuss the potential of HMO and polyphenols in allergy prevention and therapy.

Humans↗
PubMed2004

High-throughput profiling of dietary polyphenols and their metabolites by HPLC-ESI-MS-MS in human urine.

Polyphenols in biological fluids are generally estimated by HPLC with UV, electrochemical or fluorimetric detection. We describe herein a method specially developed to estimate biomarkers of polyphenol consumption in human urine. We simultaneously quantified 15 polyphenols and their related compounds in human urine using an HPLC coupled with electrospray ionization mass-mass (HPLC-ESI-MS-MS) method with an analytical run time of 6 min. The method has been validated with respect to linearity, precision, and accuracy in intra- and inter-day assays. It has been applied to human urine samples collected from volunteers after consumption of different polyphenol-rich beverages in controlled conditions.

Chromatography, High Pressure Liquid↗
PubMed2005

The inhibitory effects of berry polyphenols on digestive enzymes.

The evidence for the effect of polyphenol components of berries on digestive enzymes is reviewed. Anthocyanins inhibit alpha-glucosidase activity and can reduce blood glucose levels after starch-rich meals, a proven clinical therapy for controlling type II diabetes. Ellagitannins inhibit alpha-amylase activity and there is potential for synergistic effects on starch degradation after ingestion of berries such as raspberries and strawberries, which contain substantial amounts of ellagitannins and anthocyanins. A range of berry polyphenols (e.g. flavonols, anthocyanidins, ellagitannins and proanthocyanidins) can inhibit protease activities at levels which could affect protein digestion in the gastrointestinal tract. In contrast, potential for the inhibition of gastrointestinal lipase activity, a proven therapeutic target for the control of obesity through reduced fat digestion, may be limited to proanthocyanidins. Taking into account the manifold possible synergies for inhibition of starch, protein and/or lipid digestion by the spectrum of polyphenol components present within berry species, the inhibition of digestive enzymes by dietary polyphenols may represent an under-reported mechanism for delivering some of the health benefits attributed to a diet rich in fruit and vegetables.

Anthocyanins↗
PubMed2005

Supercritical fluid extraction and HPLC determination of relevant polyphenolic compounds in grape skin.

The polyphenols determined are: (+)-catechin, (-)-epicatechin, rutin, quercetin and trans-resveratrol. Suitable conditions of supercritical fluid extraction were established using ethanol as a modifier of the polarity solvent (supercritical carbon dioxide). Final extraction conditions were: 20% v/v ethanol, 60degreesC, 250 bars and flow rate 2 mL/min. Static step time and dynamic step time were established using a selected grape skin sample. The extract was collected in water; the more polar polyphenols ((+)-catechin and (-)-epicatechin) remain in solution but rutin, quercetin and trans-resveratrol precipitate in this medium, thereby the solution of the extracted polyphenols was filtered. (+)-Catechin and (-)-epicatechin were determined in the liquid fraction, while the solid fraction, containing rutin, quercetin and trans-resveratrol, was solved with ethanol/H20 (40:60). HPLC determination was carried out at C18 stationary phase, with ethanol/water/acetic acid as mobile phases and UV-visible diode array detection. Due to the significant differences between the polarity of the polyphenols, two different mobile phases were used. An ethanol/water/acetic acid (5:93:2) mobile phase was used to determine (+)-catechin (280 nm) and (-)-epicatechin (280 nm). On the other hand, rutin (254 nm), quercetin (254 nm) and trans-resveratrol (306 nm) were resolved using ethanol/water/acetic acid (40:58:2) as mobile phase. Instrumental parameters were optimised and analytical parameters obtained. The analytical method was validated and applied to five different varieties of Vitis vinifera from the geographical area of Valencia.

Chromatography, High Pressure Liquid↗
PubMed2006

New insights on the anticancer properties of dietary polyphenols.

Cancer, one of the major causes of death across the world, has shown to be a largely preventable disease, highly susceptible to modulation by dietary factors. Phenolic compounds, abundant in vegetables and fruits ubiquitous in diet, were described to play an important role as chemopreventive agents. Since conventional therapeutic and surgical approaches have not been able to control the incidence of most cancer types, the development of chemopreventive strategies is an urgent priority in public health. The current diet phenolic intake is often insufficient to protect from mutagens (either exogenous or endogenous), which leads to the need for dietary supplementation as an alternative approach. Research efforts are placing increasing emphasis on identifying the biological mechanisms and in particular the signal transduction pathways related to the chemopreventive activities of these compounds. These effects are believed to occur by the regulation of signaling pathways such as nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) or mitogen-activated protein kinases (MAPK). Dietary polyphenols can exert their effects on these pathways separately or sequentially and in addition the occurrence of crosstalk between these pathways cannot be overlooked. By modulating cell signaling pathways, polyphenols activate cell death signals and induce apoptosis in precancerous or malignant cells resulting in the inhibition of cancer development or progression. However, regulation of cell signaling pathways by dietary polyphenols can also lead to cell proliferation/survival or inflammatory responses due to increased expression of several genes. The present review summarizes the most recent advances providing new insights into the molecular mechanisms underlying the promising anticarcinogenic activity of dietary polyphenols.

Anticarcinogenic Agents↗
PubMed2006

Correlation between the in vitro antioxidant activity and polyphenol content of aqueous extracts from Bulgarian herbs.

The water phase antioxidant activity of extracts from 23 Bulgarian medicinal plants was studied in relation to their polyphenol content in comparison with mate, black tea, honeybush and rooibos foreign species. Antioxidant activity was measured by the ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)) cation radical decolorization assay, and the total polyphenol content was assayed according to the Folin-Ciocalteu method. Five Bulgarian plant extracts exhibited higher antioxidant activity than that of mate, which is 21.7% of all Bulgarian herbs included in this study. These were Alchemilla vulgaris L. (4.79 +/- 0.14 mm), Sambucus ebulus L. (4.03 +/- 0.07 mm), Mentha spicata L. (3.90 +/- 0.03 mm), Fragaria vesca L. (3.74 +/- 0.06 mm), Crataegus monogyna Jacq. (3.63 +/- 0.05 mm). Another eight Bulgarian medicinal plant extracts exhibited an intermediate antioxidant activity - lower than that of mate and higher than that of honeybush, which makes 34.8% of all Bulgarian herbs included in the study. More than half of the herbal extracts included in the present study exhibited antioxidant activity higher than or comparable to the reference foreign plants. A positive correlation (r = 0.92) between antioxidant activity and polyphenol content was found, suggesting that the antioxidant capacity of the aqueous plant extracts is due to a great extent to their polyphenols.

Antioxidants↗
PubMed1998

Interaction of iron with polyphenolic compounds: application to antioxidant characterization.

Antioxidant action of flavonoids and polyphenolics was analyzed in relation to iron coordination. Flavonoids including baicalein, baicalin, quercetin, and rutin showed little or no reducing activity, and enhanced the autooxidation of Fe2+ ion. Ascorbate-mediated reduction of iron was rather inhibited by flavonoids. Nonflavonoid polyphenolics such as protocatechuic acid and chlorogenic acid, on the contrary, showed a potent iron-reducing ability, and protected Fe2+ ion from autooxidation completely. Both flavonoids and nonflavonoids effectively inhibited the formation of thiobarbituric acid-reactive substances as a marker of lipid peroxidation of microsomes from rat liver. Flavonoids act as an antioxidant by inhibiting the oxygen radical formation through the enhanced oxidation of Fe2+ ion as the prooxidant. Antioxidant properties of nonflavonoids can be explained by the formation of inactive Fe(2+)-polyphenol complex, which cannot react with oxygen, and/or can scavenge reactive oxygen species. Analysis of the action of polyphenolics on the iron redox state may be useful for characterization of the antioxidant effect.

Animals↗
PubMed2001

Mapping of resistance to vegetable polyphenols among Aedes taxa (Diptera, Culicidae) on a molecular phylogeny.

To recover some evolutionary aspects of the interaction between culicine larvae and dietary polyphenols of the vegetation surrounding mosquito breeding sites, we constructed a phylogeny of the most common French Aedes species, chosen as reference species. We also evaluated the differential resistance of these larval taxa to the polyphenols of leaf litter from the riparian vegetation used as a food source. Mitochondrial DNA sequence analysis was performed among 14 different taxa and ecotypes (Aedes aegypti, Ae. albopictus, Ae. cantans, Ae. caspius, Ae. cataphylla, Ae. cinereus, Ae. detritus, Ae. geniculatus, Ae. mariae, Ae. pullatus, Ae. punctor, Ae. rusticus, Ae. sticticus, and Ae. vexans) through direct sequencing of a 763-base segment of the cytochrome oxidase subunit I gene. Phylogenetic analysis, based on nucleotide and amino acid sequences, was conducted by means of parsimony and distance methods. The differential tolerance of larvae to vegetable leaf litter was comparatively tested by use of 10-month-old alder leaf litter as an experimental standard. The absence of correlation between resistance to polyphenols and molecular phylogeny suggests that larval adaptation to polyphenol-rich vegetable breeding sites is a labile character. The acquisition of such resistance appears not to be ancestrally inherited, but rather to be a dynamic adaptation to the environment. Molecular data also support the classical morphological classification within the Aedes genus.

Aedes↗