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PubMed2005

Removal of phenolic compounds in water by ultrafiltration membrane treatments.

The ultrafiltration (UF) of aqueous solutions containing mixtures of three phenolic compounds (gallic acid, acetovanillone, and esculetin) was studied in a tangential UF laboratory system. These substances were selected as model pollutants present in the tannic fraction of the cork processing wastewaters. The two membranes used were a polyethersulfone membrane (Biomax5K) and a regenerated cellulose membrane (Ultracel5K), both with a molecular weight cut-off (MWCO) of 5000 Da. Previous experiments for the characterization of the membranes led to values for the water hydraulic permeability of 70.3 and 18.1 L/h x m2 x bar for the Biomax5K and Ultracel5K membranes, respectively. During the UF experiments, the permeate flow rate remained almost constant with processing time and the evolution of the pollutants concentrations varied depending on the nature of the membranes and the substances. The influence of the main operating variables (tansmembrane pressure and feed flow rate) on the permeate flux was established, and values for the apparent and intrinsic rejection coefficients were evaluated. Cork processing wastewater UF experiments were also conducted under similar operating conditions to those applied to the ultrapure water solutions. Removals of chemical oxygen demand, aromatic and tannic contents, and color were determined in these experiments, and the elimination of the three model compounds in the wastewater was also followed, with the evaluation of their apparent rejection coefficients.

Filtration↗
PubMed2004

Study on wound healing activity of Punica granatum peel.

The methanolic extract of dried pomegranate (Punica granatum) peels showed the presence of a high content of phenolic compounds (44.0%) along with other constituents. This extract was formulated as a 10% (wt/wt) water-soluble gel and was studied for its wound healing property against an excision wound on the skin of Wistar rats. The activity was compared with that of a commercial topical antibacterial applicant. The wound healing activity was assessed by measuring the percent contraction in skin and estimation of collagen content in terms of hydroxyproline content. Healed skin was also subjected to histopathological studies to examine the microscopic changes. The animals treated with 2.5% gel showed moderate healing (55.8% and 40.8% healing compared with negative and positive controls, respectively), whereas the group treated with 5.0% gel showed good healing (59.5% and 44.5% healing compared with negative and positive controls, respectively). The amount of hydroxyproline increased by twofold in the group treated with 5.0% gel. Histopathological studies also supported the wound healing on application of the gels. The group of rats that received 5.0% gel showed complete healing after 10 days, whereas in rats treated with 2.5% gel, healing was observed on day 12, in contrast to the positive control animals receiving the blank gel, which took 16-18 days for complete healing. The results of this study may be extended to different types of wounds so that the formulation could be exploited to develop it as a topical dermatological formulation. High-performance liquid chromatography analysis of the extract showed the presence of gallic acid and catechin as major components.

Animals↗
PubMed2005

Polyphenol contents in grape-seed extracts correlate with antipica effects in cisplatin-treated rats.

BACKGROUND: Grape-seed (Vitis spp.) extract (GSE) is a widely used antioxidant dietary supplement. Chemotherapeutic agents such as cisplatin induce oxidative damage in the gastrointestinal tract and cause nausea and vomiting. MATERIALS AND METHODS: A rat model of simulated emesis was used to observe that cisplatin significantly increased kaolin consumption (or pica). Three GSEs from different sources were used in this study. RESULTS: High-performance liquid chromatographic analysis of five major constituents (gallic acid, catechin, epicatechi, procyanidin B2, and epicatechin gallate) revealed that each constituent had different levels in the three GSEs. Extract #1, prepared in the laboratory of the investigators, had the lowest total polyphenol content (27.27 mg/g); Extract #2, obtained from a dietary supplement company in the United States, had a somewhat higher level (35.84 mg/g); and Extract #3, obtained from China, had the highest level (194.21 mg/g). Subsequently these GSEs were intraperitoneally administered in rats to evaluate their ability to decreasing cisplatin induced pica. At 10 mg/kg all three GSEs, with varying degrees of effect, decreased cisplatin-induced pica. The areas under the curves of kaolin intake from time 0 to 72 hours, compared to those in the cisplantin-only group, were reduced 45% for Extract #1 (p < 0.01), 54% for Extract #2 (p < 0.01), and 66% Extract #3 (p < 0.001). CONCLUSIONS: The study data showed variable polyphenol contents and proportions in the three GSEs correlated to variable pharmacologic effects, indicating the importance of standardization of herbal product preparations. However further increasing of the GSE doses reversed the antipica effects of GSEs, probably because of their pro-oxidant effects. Results from this study suggest that an appropriate dose of GSE has therapeutic value in treating cisplatin-induced emesis.

Animals↗
PubMed2000

Ingestion of red wine significantly increases plasma phenolic acid concentrations but does not acutely affect ex vivo lipoprotein oxidizability.

BACKGROUND: Reduced lipoprotein oxidizability by red wine phenols has been proposed as the basis for a relatively lower incidence of coronary heart disease in red wine drinkers. We showed previously that caffeic and protocatechuic acids isolated from red wine exhibit antioxidant activity in vitro. However, there is no information in the literature on the absorption of these compounds after red wine ingestion. OBJECTIVES: We sought to determine whether certain phenolic acids can be detected in the circulation after red wine consumption and if their presence has an acute effect on serum and LDL oxidation ex vivo. DESIGN: Twelve healthy male nonsmokers consumed red wine, phenol-stripped red wine, dealcoholized red wine, or water, each at a separate visit, in random order and 1 wk apart. Beverages were consumed over 30 min and blood was sampled just before beverage consumption and 1, 2, and 4 h after consumption. Plasma caffeic, protocatechuic, and 4-O-methylgallic acids were measured by gas chromatography-mass spectrometry. We also measured copper-induced serum and LDL oxidizability ex vivo and serum uric acid. RESULTS: Caffeic acid and 4-O-methylgallic acid concentrations increased significantly (P < 0.025) after consumption of red wine and dealcoholized red wine compared with water or phenol-stripped red wine. Uric acid increased significantly (P < 0.001) after ingestion of red wine, phenol-stripped red wine, and dealcoholized red wine. There was no effect on ex vivo serum or LDL oxidation after any of the beverages. CONCLUSION: Although red wine and dealcoholized red wine consumption acutely increase plasma phenolic acid and serum uric acid concentrations, the increase is insufficient to influence ex vivo lipoprotein oxidation.

Adult↗
PubMed2005

Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies.

Polyphenols are abundant micronutrients in our diet, and evidence for their role in the prevention of degenerative diseases is emerging. Bioavailability differs greatly from one polyphenol to another, so that the most abundant polyphenols in our diet are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Mean values for the maximal plasma concentration, the time to reach the maximal plasma concentration, the area under the plasma concentration-time curve, the elimination half-life, and the relative urinary excretion were calculated for 18 major polyphenols. We used data from 97 studies that investigated the kinetics and extent of polyphenol absorption among adults, after ingestion of a single dose of polyphenol provided as pure compound, plant extract, or whole food/beverage. The metabolites present in blood, resulting from digestive and hepatic activity, usually differ from the native compounds. The nature of the known metabolites is described when data are available. The plasma concentrations of total metabolites ranged from 0 to 4 mumol/L with an intake of 50 mg aglycone equivalents, and the relative urinary excretion ranged from 0.3% to 43% of the ingested dose, depending on the polyphenol. Gallic acid and isoflavones are the most well-absorbed polyphenols, followed by catechins, flavanones, and quercetin glucosides, but with different kinetics. The least well-absorbed polyphenols are the proanthocyanidins, the galloylated tea catechins, and the anthocyanins. Data are still too limited for assessment of hydroxycinnamic acids and other polyphenols. These data may be useful for the design and interpretation of intervention studies investigating the health effects of polyphenols.

Adult↗
PubMed2006

Influence of tannins from Stryphnodendron adstringens on growth and virulence factors of Candida albicans.

OBJECTIVES: The main objective of this work was to investigate the antifungal activity of a crude extract, fractions and subfractions from Stryphnodendron adstringens (Mart.) Coville, known as 'barbatimão'. METHODS: The growth inhibition by 'barbatimão' of 103 isolates of yeasts from vaginal fluid was determined using the broth microdilution method. In addition, the effect of the most active subfraction on cell surface hydrophobicity (CSH), germ-tube formation, budding, ultrastructure and phagocytosis of Candida albicans was analysed. Fluconazole and nystatin were used as reference drugs. The cytotoxicity of 'barbatimão' to Vero cells, macrophages and red blood cells was assessed. The most active subfraction was characterized by mass and 13C NMR spectroscopy. RESULTS: Subfraction F2.4 had the best antifungal action at concentrations above 7.80 mg/L. Its action was similar to nystatin, and only slightly less effective than fluconazole. CSH and the capacity for adhering to Vero cells and a glass surface were lower in treated yeasts. In addition, the inhibition of formation of the germ tube, the increase in the number of buds and changes in the cell wall ultrastructure of C. albicans were also demonstrated. 'Barbatimão' extracts showed low cytotoxicity to Vero cells, macrophages and red blood cells. Subfraction F2.4 is composed of proanthocyanidin polymers of prodelphinidin and prorobinetinidin units and gallic acid of molecular weight 2114 Da. CONCLUSIONS: The antifungal action of subfraction F2.4 on C. albicans can be attributed to condensed tannins. It is considered moderate antifungal activity. These properties of 'barbatimão' on the growth of C. albicans, putative virulence factors and its low cytotoxicity justify further studies to investigate the mechanisms of action and the possible development of a new antifungal agent.

Animals↗
PubMed2005

Flavonoids from almond skins are bioavailable and act synergistically with vitamins C and E to enhance hamster and human LDL resistance to oxidation.

Consumption of tree nuts such as almonds has been associated with a reduced risk of coronary heart disease. Flavonoids, found predominantly in the skin of almonds, may contribute to their putative health benefit, but their bioactivity and bioavailability have not previously been studied. Almond skin flavonoids (ASF) were extracted with HCl:H2O:methanol (1:19:80) and their content of catechins and flavonols identified by HPLC with electrochemical detection. ASF bioactivity was assessed in vitro by their capacity to increase the resistance of human LDL to oxidation induced by 10 micromol/L Cu2+. ASF from 0.18 to 1.44 mumol gallic acid equivalent (GAE)/L increased the lag time to LDL oxidation in a dose-dependent manner (P < or = 0.0001). Combining ASF with vitamin E or ascorbic acid extended the lag time >200% of the expected additive value (P < or = 0.05). The bioavailability and in vivo antioxidant activity of 40 micromol ASF were examined in BioF1B hamsters. Peak plasma concentrations of catechin, epicatechin, and flavonols (quercetin, kaempferol, and isorhamnetin) occurred at 60, 120, and 180 min, respectively. The concentration of isorhamnetin was significantly elevated in liver at 180 min. Absorbed ASF enhanced the ex vivo resistance of hamster LDL collected at 60 min to oxidation by 18.0% (P = 0.028), and the in vitro addition of 5.5 micromol/L vitamin E synergistically extended the lag time of the 60-min sample by 52.5% (P < or = 0.05). Thus, ASF possess antioxidant capacity in vitro; they are bioavailable and act in synergy with vitamins C and E to protect LDL against oxidation in hamsters.

Adult↗
PubMed2006

Daily polyphenol intake in France from fruit and vegetables.

The objective of this study was to create a French database on the polyphenol content of fruit and vegetables as uncooked fruits and vegetables and then to evaluate polyphenol intake through fruit and vegetable consumption in France. To achieve this, we used the Folin-Ciocalteu method adapted to fruit and vegetable polyphenol quantitation (1). Vegetables with the highest polyphenol concentration were artichokes, parsley, and brussels sprouts [>250 mg of gallic acid equivalent (GAE)/100 g fresh edible portion (FEP)]; fruits with the highest concentrations were strawberries, lychees, and grapes (>180 mg of GAE/100 g FEP). Conversely, melons (Cantaloupe cv.) and avocados had the lowest polyphenol concentration for fruits and vegetables, respectively. Based on fruit consumption data, apples and strawberries are the main sources of polyphenols in the French diet, whereas potatoes, lettuces, and onions are the most important vegetable sources. Total polyphenol intake from fruit is about 3 times higher than from vegetables, due to the lower polyphenol concentration in vegetables. The calculation of polyphenol intake, based on both assessment methods used [(Société d'Etudes de la Communication, Distribution et Publicité (SECODIP) and Supplémentation en Vitamines et Minéraux Antioxydants (SUVIMAX)], showed that apples and potatoes provide approximatively half of the total polyphenol intake from fruit and vegetables in the French diet.

Allium↗
PubMed2004

The multi-protein family of Arabidopsis sulphotransferases and their relatives in other plant species.

All members of the sulphotransferase (SOT, EC 2.8.2.-) protein family use 3'-phosphoadenosine 5'-phosphosulphate (PAPS) as the sulphuryl donor and transfer the sulphonate group to an appropriate hydroxyl group of several classes of substrates. These enzymes have highly conserved domains and can be found in eubacteria and eukaryotes. In mammals, sulphate conjugation catalysed by SOTs constitutes an important reaction in the transformation of xenobiotics, and in the modulation of the biological activity of steroid hormones and neurotransmitters. In plants, sulphate-conjugation reactions seem to play an important role in plant growth, development, and adaptation to stress. To date only a few plant SOTs have been characterized in detail. The flavonol 3- and 4'-SOTs from Flaveria species (Asteraceae), which catalyse the sulphonation of flavonol aglycones and flavonol 3-sulphates, respectively, were the first plant SOTs for which cDNA clones were isolated. The plasma membrane associated gallic acid SOT of Mimosa pudica L. pulvini cells may be intrinsic to signalling events that modify the seismonastic response. In Brassica napus L. a SOT catalyses the O-sulphonation of brassinosteroids and thereby abolishes specifically the biological activity of 24-epibrassinolide. The fully sequenced genome of Arabidopsis thaliana Heynh. contains in total 18 genes that are likely to encode SOT proteins based on sequence similarities of the translated products with an average identity of 51.1%. So far only one SOT from A. thaliana (At5g07000) was functionally characterized: the protein was shown to catalyse the sulphonation of 12-hydroxyjasmonate and thereby inactivate excess jasmonic acid in plants. The substrates and, therefore, the physiological roles of SOTs are very diverse. By using the numerous informative databases and methods available for the model plant A. thaliana, the elucidation of the functional role of the SOT protein family will be accelerated.

Amino Acid Motifs↗
PubMed1996

Role of calcium in tumor necrosis factor-alpha production by activated macrophages.

The role of calcium in the production of tumor necrosis factor-alpha (TNF-alpha) by the lipopolysaccharide (LPS)-stimulated macrophage cell line, J774.1, was investigated. Flow cytometric measurement of intracellular calcium concentration ([Ca]i) using 2-(3,6-bis(acetyl-oxy)-2,7-dichloro-9H-xanthen-9-yl)benzoic acid (fluo-3)-loaded J774.1 cells revealed that LPS at more than 0.1 microgram/ml increased [Ca]i transiently in the presence or absence of serum, and that a mixture of a calcium chelator, ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), and a calcium release blocker from intracellular store sites, 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), inhibited the [Ca]i response induced by LPS. In concordance with this, production of TNF-alpha was inhibited by EGTA and/or TMB-8. These reagents also reduced the level of TNF-alpha mRNA significantly. These results indicate that the transient increase of [Ca]i plays a role in LPS-induced expression of TNF-alpha by the macrophage cell line.

Animals↗
PubMed2005

Polyphenolic compounds from red grapes acutely improve endothelial function in patients with coronary heart disease.

BACKGROUND: It has been shown that acute intake of red wine improves endothelial-dependent vasodilatation. It is not clear, however, which constituents of red wine are responsible for this effect. We examined whether acute intake of a red grape polyphenol extract has a positive effect on brachial artery flow-mediated dilatation. METHODS: We recruited 30 male patients with coronary heart disease. They were randomly assigned either to a red grape polyphenol extract (600 mg) dissolved in 20 ml of water (n = 15) or 20 ml of water (placebo) (n = 15). The extract of grapes contained 4.32 mg epicatechin, 2.72 mg catechin, 2.07 mg gallic acid, 0.9 mg trans-resveratrol, 0.47 mg rutin, 0.42 mg epsilon-viniferin, 0.28 mg, p-coumaric acid, 0.14 mg ferulic acid and 0.04 mg quercetin per gram. Flow-mediated dilatation of the brachial artery was evaluated after reactive hyperemia induced by cuff obstruction of the forearm, using high-resolution ultasonography. Particularly, flow-mediated dilatation was measured after fasting and 30, 60 and 120 min after the intake of the grape extract or placebo. RESULTS: Intake of the red grape polyphenol extract caused an increase in flow-mediated dilatation, peaking at 60 min, which was significantly higher than the baseline values (4.52+/-1.34 versus 2.6+/-1.5%; P < 0.001) and the corresponding values at 60 min after the intake of placebo (4.52+/-1.34 versus 2.64+/-1.8%, P < 0.001). There was no change in FMD values after the intake of placebo throughout the whole duration of the study. CONCLUSION: Polyphenolic compounds from red grapes acutely improve endothelial function in patients with coronary heart disease. These results could probably, at least partly, explain the favorable effects of red wine on the cardiovascular system.

Blood Flow Velocity↗
PubMed2003

A novel tannase from Aspergillus niger with beta-glucosidase activity.

An extracellular tannase was produced from solid-state cultures of Aspergillus niger. The enzyme was purified to homogeneity from the cell-free culture broth by preparative isoelectric focusing and by FPLC using anion-exchange and gel-filtration chromatography. SDS-PAGE analysis as well as gel localization studies of purified tannase indicated the presence of two enzyme forms, with molecular masses of 90 kDa and 180 kDa. The tannase had an isoelectric point of 3.8, a temperature optimum of 60-70 degrees C and a pH optimum of 6.0. The substrate specificity of the tannase was determined by HPLC analysis of tannin substrates and products. The enzyme was able to remove gallic acid from both condensed and hydrolysable tannins. Internal sequences were obtained from each of the gel-purified and trypsin-digested tannase forms. The peptide sequences obtained from both forms were identical to sequences within a beta-glucosidase from Aspergillus kawachii. The purified tannase was tested for beta-glucosidase activity and was shown to hydrolyse cellobiose efficiently. However, no beta-glucosidase activity was detected when the enzyme was assayed in the presence of tannic acid.

Amino Acid Sequence↗
PubMed1986

The role of calcium in stimulation of activated T lymphocytes with interleukin 2.

In a study of the role of Ca++ in the stimulation of activated T lymphocytes with interleukin 2 (IL-2) it was found that IL-2-induced proliferation can occur independently of extracellular calcium. Further, there was no correlation between triggering of DNA synthesis and an increase in free cytoplasmic calcium. However, IL-2 induced an increased uptake of 45Ca++ from the extracellular medium. Since there is no increase in free cytoplasmic calcium, it must be assumed that this is caused by an increase in membrane-associated calcium. Further, the calcium channel-blocking agent, verapamil, and TMB-8, a putative inhibitor of mobilization of calcium from intracellular pools, both exerted a dose-dependent inhibition of IL-2-induced DNA synthesis in activated T lymphocytes. We conclude that calcium is not a second messenger in activated T lymphocytes stimulated by IL-2, but our results indicate that calcium may play a role at membrane level.

Calcimycin↗
PubMed1997

Effect of tea polyphenols on histamine release from rat basophilic leukemia (RBL-2H3) cells: the structure-inhibitory activity relationship.

We studied the effect of tea polyphenols on histamine release from rat basophilic leukemia (RBL-2H3) cells. Among tea polyphenols, (-)- epigallocatechin gallate (EGCG) most strongly and dose-dependently inhibited histamine release from cells stimulated with a calcium ionophore, A23187. (-)-Epigallocatechin (EGC) and (-)-epicatechin gallate (ECG) with a triphenol residue moderately inhibited histamine release, whereas diphenolic (+)-catechin (C) and (-)-epicatechin (EC) did not. The magnitude of the inhibitory effect was in the order EGCG > ECG > EGC. Among simple polyphenols, the triphenol compounds, pyrogallol (PG) and gallic acid (GA) exerted inhibitory activity, but the diphenols, pyrocatechol, hydroquinone, and resorcinol did not. In addition, the mixture of PG and GA inhibited histamine release as strongly as EGCG with two triphenol residues. Similarly, they inhibited histamine release induced by IgE-antigen complex stimulation more efficiently than that induced by A23187 stimulation. EGCG did not inhibit the increase of intracellular Ca2+ in RBL-2H3 cells stimulated with A23187 or IgE antigen. These results indicate that the triphenol structure plays an important role in the inhibitory activity of tea polyphenols. Their activity seemed to be exerted through the metabolic events occurring after the elevation of intracellular Ca2+ concentration.

Animals↗
PubMed1984

The involvement of calcium in the intestinal response to secretagogues in the rat.

The involvement of Ca2+ in the regulation of intestinal secretion was investigated in stripped sheets of rat mid-intestine. Removal of serosal Ca2+ together with the addition of EGTA at concentrations of 0.5 and 1 mM inhibited the rise in short-circuit current (s.c.c.) induced by both acetylcholine and theophylline, a similar degree of inhibition being observed with both secretagogues. Ca2+-free serosal fluid with 0.5 mM-EGTA added reduced significantly the rises in s.c.c. induced by A23187, acetylcholine, 5-hydroxytryptamine, theophylline, dibutyryl cyclic AMP and prostaglandin E2, but not the increased s.c.c. associated with glucose absorption. The Ca2+ channel blocker verapamil produced similar results. The calmodulin antagonist trifluoperazine inhibited secretagogue action while its sulphoxide derivative was without effect at the same concentration. The intracellular Ca2+ antagonist TMB-8 reduced the increased s.c.c. observed with acetylcholine and dibutyryl cyclic AMP. The net Cl- secretion, but not the decreased mucosal-to-serosal Na+ flux, induced by acetylcholine was abolished in Ca2+-free conditions. There was no consistent effect on the reduction in the residual ion flux caused by acetylcholine. Absence of Ca2+ converted the stimulation of Cl- secretion induced by dibutyryl cyclic AMP observed under control conditions to an enhancement of net Na+ and Cl- absorption. It is concluded that intestinal secretagogues, whether they act through cyclic AMP or not, require both internal and external sources of Ca2+ if they are to produce their full effects. Moreover, it appears that the nature of the response to dibutyryl cyclic AMP depends on the prevailing Ca2+ concentration.

Acetylcholine↗
PubMed2002

Characterization of catechol glucuronidation in rat liver.

Catechols are a class of substances from natural or synthetic origin that contain a 1,2-dihydroxybenzene group. We have characterized the glucuronidation by rat liver microsomes and by the rat liver recombinant UDP-glucuronosyltransferase isoforms UGT1A6 and UGT2B1 of a series of 42 structurally diverse catechols, including neurotransmitters, polyphenols, drugs, and catechol estrogens. Small catechols (4-nitrocatechol, 2,3-dihydroxybenzaldehyde, 4-methylcatechol, and tetrachlorocatechol), tyrphostine A23, and octylgallate were glucuronidated at the highest rate by rat liver microsomes and the recombinant enzymes. By contrast, polyphenols from green tea (catechin and related compounds), 3,5-dinitrocatechol, the catechol-O-methyltransferase inhibitor drugs (entacapone, nitecapone, and tolcapone), the carboxyl catechols (gallic acid and dihydroxybenzoic acid derivatives), and the neurotransmitters and dopaminergic drugs, except dobutamine, were glucuronidated at low rate. Glucuronidation of most catechols was increased upon treatment of rats by 3-methylcholanthrene (3-MC) or Aroclor 1254. No induction was observed after administration of phenobarbital and clofibrate or treatment with catechols. Partial least-squares modeling was carried out to explain the variations of glucuronidation activity by liver microsomes of nontreated and 3-MC-treated rats. The model developed explained 82% and predicted 61% of the variations of glucuronidation activities. Among the 17 electronic and substructure parameters used that characterize the catechols, the hydrophobicity/molar volume ratio of catechols showed a strong positive correlation with the glucuronidation rate. The effect of the pK(a) of the catechol group was modeled to be nonlinear, the optimal pK(a) value for glucuronidation being between 8 and 9. Hydrogen bonding and steric effects also were important to account for to predict the glucuronidation rates.

Animals↗
PubMed2005

Mechanisms for the inhibition of DNA methyltransferases by tea catechins and bioflavonoids.

In the present investigation, we studied the modulating effects of several tea catechins and bioflavonoids on DNA methylation catalyzed by prokaryotic SssI DNA methyltransferase (DNMT) and human DNMT1. We found that each of the tea polyphenols [catechin, epicatechin, and (-)-epigallocatechin-3-O-gallate (EGCG)] and bioflavonoids (quercetin, fisetin, and myricetin) inhibited SssI DNMT- and DNMT1-mediated DNA methylation in a concentration-dependent manner. The IC(50) values for catechin, epicatechin, and various flavonoids ranged from 1.0 to 8.4 microM, but EGCG was a more potent inhibitor, with IC(50) values ranging from 0.21 to 0.47 microM. When epicatechin was used as a model inhibitor, kinetic analyses showed that this catechol-containing dietary polyphenol inhibited enzymatic DNA methylation in vitro largely by increasing the formation of S-adenosyl-L-homocysteine (a potent noncompetitive inhibitor of DNMTs) during the catechol-O-methyltransferase-mediated O-methylation of this dietary catechol. In comparison, the strong inhibitory effect of EGCG on DNMT-mediated DNA methylation was independent of its own methylation and was largely due to its direct inhibition of the DNMTs. This inhibition is strongly enhanced by Mg(2+). Computational modeling studies showed that the gallic acid moiety of EGCG plays a crucial role in its high-affinity, direct inhibitory interaction with the catalytic site of the human DNMT1, and its binding with the enzyme is stabilized by Mg(2+). The modeling data on the precise molecular mode of EGCG's inhibitory interaction with human DNMT1 agrees perfectly with our experimental finding.

Catechin↗
PubMed1986

Plant phenolic compounds induce expression of the Agrobacterium tumefaciens loci needed for virulence.

The virulence loci of Agrobacterium tumefaciens are a set of linked transcriptional units that play an essential role in the early stages of plant tumorigenesis. These loci are induced upon cocultivation of the bacteria with plant cells. Seven phenolic compounds that are widely distributed among the angiosperm plants--catechol, gallic acid, pyrogallic acid, p-hydroxybenzoic acid, protocatechuic acid, beta-resorcylic acid, and vanillin--are able to induce the expression of the virulence loci. These phenolics in combination induce each transcriptional locus of the vir loci. Furthermore, this induction displays similar kinetics and genetic control to that observed during cocultivation of the bacteria with plant cells.

Cells, Cultured↗