Effect of tea catechins on cellular lipid peroxidation and cytotoxicity in HepG2 cells

Tea catechins inhibited TBARS accumulation in HepG2 cells, the order of effectiveness being (-)-epigallocatechin gallate (EGCG) > (-)-epigallocatechin (EGC) > or = (-)-epicatechin gallate (ECG) > (-)-epicatechin (EC). EGCG and EGC protected the depletion of alpha-tocopherol in the cells, and the glutathione content was enhanced by all four catechins. Moreover, all four catechins suppressed the formation of glutathione disulfide and the activation of glutathione peroxidase induced by tert-butylated hydroperoxide.     

Determination of catechins and catechin gallates in tissues by liquid chromatography with coulometric array detection and selective solid phase extraction

Catechins levels in organ tissues, particularly liver, determined by published methods are unexpectedly low, probably due to the release of oxidative enzymes, metal ions and reactive metabolites from tissue cells during homogenization and to the pro-oxidant effects of ascorbic acid during sample processing in the presence of metal ions. We describe a new method for simultaneous analysis of eight catechins in tissue: (+)-catechin (C), (-)-epicatechin (EC), (-)-gallocatechin (GC), (-)-epigallocatechin (EGC), (-)-catechin gallate (CG), (-)-epicatechin gallate (ECG), (-)-gallocatechin gallate (GCG) and (-)-epigallocatechin gallate (EGCG) (Fig. 1). The new extraction procedure utilized a methanol/ethylacetate/dithionite (2:1:3) mixture during homogenization for simultaneous enzyme precipitation and antioxidant protection. Selective solid phase extraction was used to remove most interfering bio-matrices. Reversed phase HPLC with CoulArray detection was used to determine the eight catechins simultaneously within 25 min. Good linearity (>0.9922) was obtained in the range 20-4000 ng/g. The coefficients of variance (CV) were less than 5%. Absolute recovery ranged from 62 to 96%, accuracy 92.5 +/- 4.5 to 104.9 +/- 6%. The detection limit was 5 ng/g. This method is capable for determining catechins in rat tissues of liver, brain, spleen, and kidney. The method is robust, reproducible, with high recovery, and has been validated for both in vitro and in vivo sample analysis.     

Dietary gallate esters of tea catechins reduce deposition of visceral fat, hepatic triacylglycerol, and activities of hepatic enzymes related to fatty acid synthesis in rats

Tea catechins, rich in (-)-epigallocatechin gallate and (-)-epicatechin gallate, or heat-treated tea catechins in which about 50% of the (-)-epigallocatechin gallate and (-)-epicatechin gallate in tea catechins was epimerized to (-)-gallocatechin gallate and (-)-catechin gallate, were fed to rats at 1% level for 23 d. Visceral fat deposition and the concentration of hepatic triacylglycerol were significantly lower in the tea catechin and heat-treated tea catechin groups than in the control group. The activities of fatty acid synthase and the malic enzyme in the liver cytosol were significantly lower in the two catechin groups than in the control group. In contrast, the activities of carnitine palmitoyltransferase and acyl-CoA oxidase in the liver homogenate were not significantly different among the three groups. These results suggest that the reduction in activities of enzymes related to hepatic fatty acid synthesis by the feeding of tea catechins or heat-treated tea catechins can cause reductions of hepatic triacylglycerol and possibly of visceral fat deposition.     

Browning Reaction between Phospholipids and Acetaldehyde

Tea catechins have strong bitterness and influence the taste of tea. Among the 25 human bitter-taste receptors (TAS2Rs), we found that hTAS2R14 responded to catechins, in addition to hTAS2R39, a known catechin receptor. Although hTAS2R14 responded to (?)-epicatechin gallate and (?)-epigallocatechin gallate, it did not respond to (?)-epicatechin and (?)-epigallocatechin.     

Tea catechins inhibit cholesterol oxidation accompanying oxidation of low density lipoprotein in vitro

Endogenous oxidized cholesterols are potent atherogenic agents. Therefore, the antioxidative effects of green tea catechins (GTC) against cholesterol oxidation were examined in an in vitro lipoprotein oxidation system. The antioxidative potency of GTC against copper catalyzed LDL oxidation was in the decreasing order (-)-epigalocatechin gallate (EGCG)=(-)-epicatechin gallate (ECG)>(-)-epicatechin (EC)=(+)-catechin (C)>(-)-epigallocatechin (EGC). Reflecting these activities, both EGCG (74%) and ECG (70%) inhibited the formation of oxidized cholesterol, as well as the decrease of linoleic and arachidonic acids, in copper catalyzed LDL oxidation. The formation of oxidized cholesterol in 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH)-mediated oxidation of rat plasma was also inhibited when the rats were given diets containing 0.5% ECG or EGCG. In addition, EGCG and ECG highly inhibited oxygen consumption and formation of conjugated dienes in AAPH-mediated linoleic acid peroxidative reaction. These two species of catechin also markedly lowered the generation of hydroxyl radical and superoxide anion. Thus, GTC, especially ECG and EGCG, seem to inhibit cholesterol oxidation in LDL by combination of interference with PUFA oxidation, the reduction and scavenging of copper ion, hydroxyl radical generated from peroxidation of PUFA and superoxide anion.     

Matrix metalloproteinase inhibition by green tea catechins

We have investigated the effects of different biologically active components from natural products, including green tea polyphenols (GTP), resveratrol, genistein and organosulfur compounds from garlic, on matrix metalloproteinase (MMP)-2, MMP-9 and MMP-12 activities. GTP caused the strongest inhibition of the three enzymes, as measured by fluorescence assays using gelatin or elastin as substrates. The inhibition of MMP-2 and MMP-9 caused by GTP was confirmed by gelatin zymography and was observed for MMPs associated with both various rat tissues and human brain tumors (glioblastoma and pituitary tumors). The activities of MMPs were also measured in the presence of various catechins isolated from green tea including (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate(ECG), (-)-epigallocatechin (EGC), (-)-epicatechin (EC) and (+)-catechin (C). The most potent inhibitors of these activities, as measured by fluorescence and by gelatin or casein zymography, were EGCG and ECG. GTP and the different catechins had no effect on pancreatic elastase, suggesting that the effects of these molecules on MMP activities are specific. Furthermore, in vitro activation of proMMP-2 secreted from the glioblastomas cell line U-87 by the lectin concanavalin A was completely inhibited by GTP and specifically by EGCG. These results indicate that catechins from green tea inhibit MMP activities and proMMP-2 activation.     

Effects of green tea catechins on gramicidin channel function and inferred changes in bilayer properties

Green tea's health benefits have been attributed to its major polyphenols, the catechins: (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC), and epicatechin (EC). Catechins (especially EGCG) modulate a wide range of biologically important molecules, including many membrane proteins. Yet, little is known about their mechanism(s) of action. We tested the catechins' bilayer-modifying potency using gramicidin A (gA) channels as molecular force probes. All the catechins alter gA channel function and modify bilayer properties, with a 500-fold range in potency (EGCG>ECG?EGC>EC). Additionally, the gallate group causes current block, as evident by brief downward current transitions (flickers).     

Radical scavenging activity of tea catechins and their related compounds

(-)-Epigallocatechin gallate was found to be the most effective scavenger among tea catechins for the superoxide anion, hydroxyl radical, and 1,1-diphenyl-3-picrylhydrazyl radical. Examination of the scavenging effects of tea catechins and their glucosides on superoxide anion showed that the presence of at least an ortho-dihydroxyl group in the B ring and a galloyl moiety at the 3 position was important in maintaining the effectiveness of the radical scavenging ability. Stoichiometric factors of tea catechins were estimated to be 2 for (+)-catechin and (-)-epicatechin, 5 for (-)-epigallocatechin, 7 for (-)-epicatechin gallate, and 10 for (-)-epigallocatechin gallate.     

Dose-dependent suppression of tea catechins with a galloyl moiety on postprandial hypertriglyceridemia in rats

Tea has long been believed to be a healthy beverage, and its beneficial effects are almost all attributed to catechins. The effect of catechins on postprandial hypertriglyceridemia in rats was investigated in this study. A lipid emulsion administered orally to rats with (-)-epigallocatechin gallate at a dose of 100 mg/kg resulted in the increase in plasma triacylglycerol being significantly inhibited after 1 and 2 h compared to the case without (-)-epigallocatechin gallate. The effect of (-)-epigallocatechin was weaker than that of (-)-epigallocatechin gallate. A tea extract (THEA-FLAN 90S), mainly composed of catechins with a galloyl moiety, dose-dependently suppressed postprandial triacylglycerol after the administration of a lipid emulsion at doses of 50-200 mg/kg. The administration of the tea extract alone at a dose of 200 mg/kg had no effect on the plasma triacylglycerol level. These results strongly suggest that catechins with a galloyl moiety would be promising agents for suppressing dietary fat absorption through the small intestine.     

Antimicrobial Activities of Tocklai Vegetative Tea Clones

Thirty-one Tocklai vegetative (TV) tea clones contained caffeine and total catechin 44.39 and 227.55 mg/g dry weight of leaves, respectively. The (−)-epigallocatechin gallate (EGCG) was the most abundant (109.60 mg/g) followed by -(−)-epigallocatechin (EGC, 44.54 mg/g), (−)-epicatechin gallate (ECG, 41.74 mg/g), (−)-epicatechin (EC, 27.42 mg/g) and +catechin (4.25 mg/g). Total catechins were highest in TV 20 (509.7 mg/g) and lowest in TV 6 (71.7 mg/g). The tea clones that contain high level of total catechin exhibited the strongest antimicrobial activity. Among caffeine and flavanol compounds, theaflavins (TF) present in black tea possess a similar antimicrobial potency as EC present in fresh leaves, and that the conversion of catechins to TF during fermentation in making black tea tends to alter their antimicrobial activities. The bioactive molecules other than catechins present in tea leaves may also contribute towards antimicrobial activity.     

Structural analysis of catechin derivatives as mammalian DNA polymerase inhibitors

The inhibitory activities against DNA polymerases (pols) of catechin derivatives (i.e., flavan-3-ols) such as (+)-catechin, (-)-epicatechin, (-)-gallocatechin, (-)-epigallocatechin, (+)-catechin gallate, (-)-epicatechin gallate, (-)-gallocatechin gallate, and (-)-epigallocatechin gallate (EGCg) were investigated. Among the eight catechins, some catechins inhibited mammalian pols, with EGCg being the strongest inhibitor of pol alpha and lambda with IC(50) values of 5.1 and 3.8 microM, respectively. EGCg did not influence the activities of plant (cauliflower) pol alpha and beta or prokaryotic pols, and further had no effect on the activities of DNA metabolic enzymes such as calf terminal deoxynucleotidyl transferase, T7 RNA polymerase, and bovine deoxyribonuclease I. EGCg-induced inhibition of pol alpha and lambda was competitive with respect to the DNA template-primer and non-competitive with respect to the dNTP (2'-deoxyribonucleotide 5'-triphosphate) substrate. Tea catechins also suppressed TPA (12-O-tetradecanoylphorbol-13-acetate)-induced inflammation, and the tendency of the pol inhibitory activity was the same as that of anti-inflammation. EGCg at 250 microg was the strongest suppressor of inflammation (65.6% inhibition) among the compounds tested. The relationship between the structure of tea catechins and the inhibition of mammalian pols and inflammation was discussed.     

Distinct effects of tea catechins on 6-hydroxydopamine-induced apoptosis in PC12 cells.

Green tea polyphenols have aroused considerable attention in recent years for preventing oxidative stress related diseases including cancer, cardiovascular disease, and degenerative disease. Neurodegenerative diseases are cellular redox status dysfunction related diseases. The present study investigated the different effects of the five main components of green tea polyphenols on 6-hydroxydopamine (6-OHDA)-induced apoptosis in PC12 cells, the in vitro model of Parkinson's disease (PD). When the cells were treated with five catechins respectively for 30 min before exposure to 6-OHDA, (-)-epigallocatechins gallate (EGCG) and (-)-epicatechin gallate (ECG) in 50-200 microM had obvious concentration-dependent protective effects on cell viability, while (-)-epicatechin (EC), (+)-catechin ((+)-C), and (-)-epigallocatechin (EGC) had almost no protective effects. The five catechins also showed the same pattern described above of the different effects against 6-OHDA-induced cell apoptotic characteristics as analyzed by cell viability, fluorescence microscopy, flow cytometry, and DNA fragment electrophoresis methods. The present results indicated that 200 microM EGCG or ECG led to significant inhibition against typical apoptotic characteristics of PC12 cells, while other catechins had little protective effect against 6-OHDA-induced cell death. Therefore, the classified protective effects of the five catechins were in the order ECG> or = EGCG>EC> or = (+)-C>EGC. The antiapoptotic activities appear to be structurally related to the 3-gallate group of green tea polyphenols. The present data indicate that EGCG and ECG might be potent neuroprotective agents for PD.     

Effect of green tea powder (<Emphasis Type="Italic">Camellia sinensis</Emphasis> L. cv. Benifuuki) particle size on <Emphasis Type="Italic">O</Emphasis>-methylated EGCG absorption in rats; The Kakegawa Study

Tea polyphenols, e.g., (-)-epigallocatechin-3-O-(3-O-methyl gallate (EGCG3”Me), (-)-epigallocatechin-3-O-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-O-gallate (ECG), and (-)-epicatechin (EC), are believed to be responsible for the beneficial effects of tea. ‘Benifuuki’, a tea (Camellia sinensis L.) cultivar grown in Japan, is rich in the anti-allergic molecule epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3”Me). Pulverized Benifuuki green tea powder (BGP) is more widely distributed than leaf tea in Japan. Japanese people mix their pulverized tea with water directly, whereas it is common to drink leaf tea after extraction. However, few studies of the effects of BGP particle size on polyphenol bioavailability have been performed. This study was conducted to investigate the absorption of catechins in rats after the intragastric administration of Benifuuki green tea. Therefore, we assessed the plasma concentrations of catechins following the ingestion of BGP with different mean particle sizes (2.86, 18.6, and 76.1 μm) or Benifuuki green tea infusion (BGI) as a control in rats. The bioavailabilities of EGCG3”Me, EGCG, ECG, EGC, and EC were analyzed after the oral administration of a single dose of Benifuuki green tea (125 mg/rat) to rats. The plasma concentrations of tea catechins were determined by HPLC analysis combined with of electrochemical detection (ECD) using a coulometric array. The AUC (area under the drug concentration versus time curve; min μg/mL) of ester-type catechins (EGCG3”Me, EGCG, and ECG) for the BGP 2.86 μm were significantly higher than those in the infusion and 18.6 and 76.1 μm BGP groups, but the AUC of free-type catechins (EGC and EC) showed no differences between these groups. Regarding the peak plasma level of EGCG3”Me adjusted for intake, BGP 2.86 μm and BGI showed higher values than the BGP 18.6 and 76.1 μm groups, and the peak plasma levels of the other catechins displayed the same tendency. The present study demonstrates that the bioavailability of ester-type catechins (EGCG and ECG) can be improved by reducing the particle size of green tea, but the plasma level of EGCG3”Me in the BGI group was similar to that in the BGP 2.86 μm group. This result suggests that drinking Benifuuki green tea with a particle size of around 2 μm would deliver the anti-allergic EGCG3”Me and the anti-oxidant EGCG efficiently.     

Epigallocatechin gallate but not catechin prevents nonalcoholic steatohepatitis in mice similar to green tea extract while differentially affecting the gut microbiota

Catechin-rich green tea extract (GTE) protects against nonalcoholic steatohepatitis (NASH) by alleviating gut-derived endotoxin translocation and hepatic Toll-like receptor-4 (TLR4)–nuclear factor κB (NFκB) inflammation. We hypothesized that intact GTE would attenuate NASH-associated responses along the gut–liver axis to a greater extent than purified (−)-epigallocatechin gallate (EGCG) or (+)-catechin (CAT). Male C57BL/6J mice were fed a low-fat diet, a high-fat (HF) diet, or the HF diet with 2% GTE, 0.3% EGCG or 0.3% CAT for 8 weeks prior to assessing NASH relative to endotoxemia, hepatic and intestinal inflammation, intestinal tight junction proteins (TJPs) and gut microbial ecology. GTE prevented HF-induced obesity to a greater extent than EGCG and CAT, whereas GTE and EGCG more favorably attenuated insulin resistance. GTE, EGCG and CAT similarly attenuated serum alanine aminotransferase and serum endotoxin, but only GTE and EGCG fully alleviated HF-induced NASH. However, hepatic TLR4/NFκB inflammatory responses that were otherwise increased in HF mice were similarly attenuated by GTE, EGCG and CAT. Each treatment also similarly prevented the HF-induced loss in expression of intestinal TJPs and hypoxia inducible factor-1α and the otherwise increased levels of ileal and colonic TNFα mRNA and fecal calprotectin protein concentrations. Gut microbial diversity that was otherwise lowered in HF mice was maintained by GTE and CAT only. Further, microbial metabolic functions were more similar between GTE and CAT. Collectively, GTE catechins similarly protect against endotoxin–TLR4–NFκB inflammation in NASH, but EGCG and CAT exert differential prebiotic and antimicrobial activities suggesting that catechin-mediated shifts in microbiota composition are not entirely responsible for their benefits along the gut–liver axis.     

Antioxidants from steamed used tea leaves and their reaction behavior

The most efficient steaming conditions below 200 degrees C for extracting antioxidants from used tea leaves and their reaction behavior during the steaming treatment were investigated. The antioxidative activity of the steamed extracts increased with increasing steaming temperature, and the yield of the ethyl acetate extract fraction from each steamed extract showing the greatest antioxidative activity also increased. Caffeine, (-)-catechin, (-)-epicatechin, (-)-gallocatechin, (-)-epigallocatechin, (-)-catechin gallate, (-)-epicatechin gallate, (-)-gallocatechin gallate, (-)-epigallocatechin gallate and gallic acid were identified from the ethyl acetate extract fraction. Quantitative analyses demonstrated that the catechins with a 2,3-cis configuration decreased with increasing steaming temperature, whereas the corresponding epimers at the C-2 position increased. Each pair of epimers showed similar antioxidative activity to each other, indicating that the epimerization reaction did not contribute to the improved antioxidative activity. It is concluded from these results that the improvement in antioxidative activity at higher steaming temperatures was due to the increased yield of catechins and other antioxidants.     

Evaluation of the antigenotoxic potential of monomeric and dimeric flavanols, and black tea polyphenols against heterocyclic amine-induced DNA damage in human lymphocytes using the Comet assay

The polyphenolic dimers, epicatechin-4beta-8-catechin (B1), epicatechin-4beta-8-epicatechin (B2), catechin-4beta-8-catechin (B3), catechin-4beta-8-epicatechin (B4), and the gallate ester epicatechin-4beta-8-epicatechin gallate (B'2G) were isolated from grape seeds, and theaflavins and theafulvins from black tea brews. The ability of these naturally-occurring polyphenols to afford protection against the genotoxicity of the heterocyclic amine 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) was compared with that of the monomeric tea flavanols, (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG). Genotoxic activity was evaluated in human peripheral lymphocytes using the Comet assay. At the concentration range of 1-100 microM, neither the monomeric nor the dimeric flavanols prevented the lymphocyte DNA damage induced by Trp-P-2. In contrast, both of the black tea polyphenols, theafulvins and theaflavins, at a dose range of 0.1-0.5 mg/ml, prevented, in a concentration-dependent manner, the DNA damage elicited by Trp-P-2. Finally, neither the monomeric and dimeric polyphenols (100 microM) nor the theafulvins and theaflavins (0.5mg/ml) caused any DNA damage in the human lymphocytes. These studies illustrate that black tea theafulvins and theaflavins, if absorbed intact, may contribute to the anticarcinogenic potential associated with black tea intake.     

Stereospecificity in membrane effects of catechins

Green tea catechins consisting of catechin stereoisomers and their derivatives have been suggested to show biological activities through the interactions with cellular membranes. Their effects on membrane fluidity were comparatively studied by measuring fluorescence polarization of liposomal membranes prepared with phospholipids and cholesterol. All catechin stereoisomers reduced membrane fluidity by acting on the hydrophilic and hydrophobic regions of membrane bilayers at 20-500 microM. Both epicatechins in a cis form were more effective for reducing membrane fluidity than both catechins in a trans form. (-)-Epicatechin, (+)-epicatechin, (-)-catechin and (+)-catechin reduced membrane fluidity in increasing order of intensity. Such difference between optical isomers was increased by chiral cholesterol added to membrane lipids. In reversed-phase chromatographic evaluation, (-)-epicatechin and (+)-epicatechin were more hydrophobic than (-)-catechin and (+)-catechin, although hydrophobicity was not distinguishable between optical isomers. Stereospecificity in the membrane effects of catechin stereoisomers may be induced by the different hydrophobicity of geometrical isomers and the chirality of membrane lipid components. At lower concentrations (5-100 microM), (-)-epigallocatechin gallate and (-)-epicatechin gallate reduced membrane fluidity more significantly than (-)-epicatechin, suggesting that the intensive membrane effect contributes to the potent medicinal utility of (-)-epigallocatechin gallate.     

Methylation of tea catechins by rat liver homogenates

Methylation of (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg) was carried out with a rat liver homogenate and S-adenosyl-L-methionine. A structural analysis of the reaction products by MS and NMR showed that 4'-O-methyl EGC, 4"-O-methyl ECg, and 4"-O-methyl EGCg had been formed from EGC, ECg, and EGCg, respectively. These results suggest that methylation may be one of the metabolic pathways to the catechins.     

Evidence for alpha-tocopherol regeneration reaction of green tea polyphenols in SDS micelles

The synergistic antioxidant mechanism of alpha-tocopherol (vitamin E) with green tea polyphenols, i.e., (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin gallate (EGCG), and gallic acid (GA), was studied by assaying the kinetics of the reaction of alpha-tocopheroxyl radical with green tea polyphenols by stopped-flow electron paramagnetic resonance, the inhibition of linoleic acid peroxidation by these antioxidants, and the decay of alpha-tocopherol during the peroxidation. It was found that the green tea polyphenols could reduce alpha-tocopheroxyl radical to regenerate alpha-tocopherol with rate constants of 0.45, 1.11, 1.31, 1.91, and 0.43 x 10(2) M(-1) s(-1) for EC, EGC, ECG, EGCG, and GA, respectively, in sodium dodecyl sulfate micelles. In addition, these second-order rate constants exhibited a good linear correlation with their oxidation potentials, suggesting that electron transfer might play a role in the reaction.     

The relationship between the antioxidant and the antibacterial properties of galloylated catechins and the structure of phospholipid model membranes

The effects of four catechins, (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG), on the physical properties of phospholipid model membranes and the correlation to their antioxidant and antibacterial capacities have been studied by using differential scanning calorimetry (DSC), fluorescence spectroscopy, infrared spectroscopy (IR), AAPH-induced oxidation, and leakage experiments. DSC data revealed that galloylated catechins, especially ECG, affected the physical properties of both the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) bilayers dramatically. Galloylated catechins showed higher phospholipid/water partition coefficients than their homologues and were immersed in the phospholipid palisade intercalating within the hydrocarbon chains, ECG being at the deepest position. In contrast, nongalloylated catechins presented a shallow location close to the phospholipid/water interface. ECG also exhibited the highest antioxidant capacity against lipid peroxidation, which correlated with its strong effect on DPH fluorescence anisotropy (as observed by the increase of the lipid order of fluid PC bilayers) and with the presence of highly cooperative transitions as seen by DSC. We propose that the high antioxidant capacity of some galloylated catechins such as ECG could be partially due to the formation of membrane structures showing resistance to detergent solubilization and in which the phospholipids have tightly packed acyl chains and highly hydrated phosphate groups. Significantly, PE was found to be essential to the promotion of carboxyfluorescein leakage from bacterial model membranes by galloylated catechins, indicating that their bactericidal activity, at least at the membrane level, could be due to the specific effect of these catechins on PE.