Comparison of green tea extract and epigallocatechin gallate on secretion of catecholamines from the rabbit adrenal medulla

The present study was designed to examine the effects of green tea extract (CUMC6335) and epigallocatechin gallate (EGCG) on secretion of catecholamines (CA) in the isolated perfused rabbit adrenal gland. In the presence of CUMC6335 (200 microg/mL) into an adrenal vein for 60 min, CA secretory responses evoked by ACh (5.32 mM), high K+ (56 mM), DMPP (100 microM for 2 min), and Bay-K-8644 (10 microM for 4 min) from the isolated perfused rabbit adrenal glands were greatly inhibited in a time-dependent fashion. However, EGCG (10 microg/mL) did not affect CA release evoked by ACh, high K+, and Bay-K-8644. CUMC6335 itself failed to affect basal catecholamine output. Taken together, these results demonstrate that CUMC6335 inhibits CA secretion evoked by stimulation of cholinergic nicotinic receptors, as well as the direct membrane depolarization from the isolated perfused rabbit adrenal gland. It is thought that this inhibitory effect of CUMC6335 may be due at least in part to the blocking action of the L-type dihydropyridine calcium channels in the rabbit adrenomedullary chromaffin cells, which is relevant to the cholinergic nicotinic blockade. It seems that there is a big difference in mode of action between CUMC6335 and EGCG.     

Effects of alkyl gallates on P-glycoprotein function

In this study, we examined the effects of the food antioxidants, alkyl gallates, on the function of P-glycoprotein (P-gp) and elucidated the importance of alkyl chains and gallic acid moieties on the activity of P-gp. We examined the effects of three alkyl (n-butyl, n-octyl and n-dodecyl) gallates and their related compounds on the cellular accumulation and efflux of rhodamine 123 and daunorubicin in P-gp overexpressing KB-C2 cells. Alkyl gallates increased the cellular accumulation of these P-gp substrates dependent on their alkyl chain lengths by inhibiting the efflux of the substrates. n-Dodecylresorcinol also increased the accumulation, but its effect was less than that of n-dodecyl gallate. However, either lauric acid or n-dodecyl-beta-d-maltoside, which does not have a phenol group, did not increase the accumulation. The results indicated that both the gallic acid moiety and a long alkyl chain play important roles in the modification of P-gp function. The cytotoxicity of daunorubicin was recovered in the presence of alkyl gallates possibly due to their inhibition of P-gp function.     

Different susceptibilities of <Emphasis Type="Italic">Staphylococcus</Emphasis> and Gram-negative rods to epigallocatechin gallate

We examined the antibacterial effects of epigallocatechin gallate (EGCg, the main constituent of tea catechins) against various strains of Staphylococcus and Gram-negative rods. Compared to the minimum inhibitory concentrations (MICs) of EGCg against S. aureus, S. epidermidis, S. hominis, and S. haemolyticus (50–100µg/ml), higher MICs (800µg/ml) were observed against Gram-negative rods, including Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Proteus mirabilis, Pseudomonas aeruginosa, and Serratia marcescens. And difference was observed between the binding abilities of EGCg with viable S. aureus and with E. coli. The bactericidal activity of EGCg for S. aureus was blocked dose-dependently by purified peptidoglycan but not by lipopolysaccharide or dextran. It was also found that peptone and protein, but not amino acids, in the culture medium greatly affected the antibacterial activity of EGCg. These results indicate that the structure of the bacterial cell wall and the different affinities of EGCg with the various cell wall components are responsible for the different susceptibilities of Staphylococcus and Gram-negative rods to EGCg.     

The galloyl moiety of green tea catechins is the critical structural feature to inhibit fatty-acid synthase

It has been reported that inhibition of fatty-acid synthase (FAS) is selectively cytotoxic to human cancer cells. Considerable interest has developed in identifying novel inhibitors of this enzyme complex. Our previous work showed that green tea (-)-epigallocatechin gallate can inhibit FAS in vitro. To elucidate the structure-activity relationship of the inhibitory effects of tea polyphenols, we investigated the inhibition kinetics of the major catechins and analogues. Ungallated catechins from green tea do not show obvious inhibition compared with gallated catechins. Another gallated catechin, (-)-epicatechin gallate, was also found as a potent inhibitor of FAS and its inhibition characteristics are similar to (-)-epigallocatechin gallate. Furthermore, the analogues of galloyl moiety without the catechin skeleton such as propyl gallate also showed obvious slow-binding inhibition, whereas the green tea ungallated catechin not. Atomic orbital energy analyses suggest that the positive charge is more distinctly distributed on the carbon atom of ester bond of galloyl moiety of gallate catechins, and that gallated forms are more susceptible for a nucleophilic attack than other catechins. Here we identify the galloyl moiety of green tea catechins as critical in the inactivation of the ketoacyl reductase activity of FAS for the first time.     

Dual function of (--)-epigallocatechin gallate (EGCG) in healthy human lymphocytes

(-)-Epigallocatechin gallate (EGCG), a catechin polyphenol component, is the main ingredient of green tea extract. Recently, increasing attention has been given to its anti-oxidant effects. However, several studies reported the oxidative effects of EGCG, suggesting that EGCG had a dual function of anti-oxidant and pro-oxidant potentials. In this study, we examined the influences of EGCG on healthy human whole blood lymphocytes and purified blood lymphocytes using a single-cell gel electrophoresis (SCG) assay. The results showed that EGCG suppressed the DNA strand breakage in whole blood lymphocytes at concentrations from 10(-8) to 10(-5)M, while it induced DNA strand breakage at concentration of 10(-3)M. Furthermore, EGCG at concentrations of 10(-6)-10(-4)M suppressed the DNA strand breakage induced by bleomycin (BLM) and H(2)O(2) in whole blood lymphocytes. In the same range of 10(-6)-10(-4)M, EGCG increased DNA strand breakage in purified blood lymphocytes, but suppressed the DNA breakage induced by BLM at lower concentrations from 10(-8) to10(-7)M. From these findings, we propose that EGCG might have a dual function of anti-oxidant and pro-oxidant in healthy human lymphocytes, which would involved in its inhibitory effects against DNA strand breakage induced by BLM and H(2)O(2).     

没食子酸丙酯对三硝基甲苯染毒小鼠肝脏病理形态学的影响

三硝基甲苯（ＴＮＴ）染毒小鼠肝组织光镜检查见肝细胞水肿，嗜酸性变及肝瘀血，部分肝细胞呈点状坏死；小鼠ＴＮＴ染毒的同时，口服给予没食子酸丙酯（ＰＧ），发现肝组织病变程度显著减轻，肝细胞再生明显，表明ＰＧ对ＴＮＴ中毒性肝损伤具有一定防治作用。     

Inhibition of catechol-O-methyltransferase by n-butyl gallate

The effect of n-butyl gallate (NBG) on COMT activity was investigated in vitro (beef liver enzyme) and indirectly in vivo (effect on 15 min. haloperidol-induced formation of rat striatal homovanillic acid). As compared to other known COMT inhibitors, NBG is potent both in vitro (Ki 1.7 × lO^?6M) and in vivo (complete blockade of HVA rise with 50 mg/kg), but its duration of action is very short in vivo (15–45 min.)     

高效液相色谱法测定心脑健胶囊中表没食子儿茶素没食子酸酯

目的建立测定心脑健胶囊中表没食子儿茶素没食子酸酯含量的高效液相色谱法。方法采用Hypersil ODSC18(250 mm×4.6 mm,5μm)色谱柱,流动相为0.04 mol.L-1枸橼酸溶液-N,N二甲基甲酰胺-四氢呋喃(45∶8∶2),检测波长为278 nm,流速为1.0 mL.min-1,柱温为25℃。结果表没食子儿茶素没食子酸酯在0.408~4.08μg具有良好的线性关系,回归方程为:A=105.226 46C+1 210.413 71,r=0.999 9。平均回收率98.59%,RSD为0.78%。结论该方法操作简单,重现性好,适用于心脑健胶囊中表没食子儿茶素没食子酸酯的含量测定。     

(-)-儿茶素没食子酸酯和(+)-表儿茶素对心肌细胞保护作用研究

目的:观察(-)-儿茶素没食子酸酯[(-)-CG]和( )-表儿茶素[( )-EC]对心肌细胞黄嘌呤/黄嘌呤氧化酶体系损伤的保护作用.方法:建立心肌细胞黄嘌呤/黄嘌呤氧化酶体系损伤模型,倒置显微镜观察加入(-)-CG、( )-EC后细胞形态学变化;噻唑盐比色法测定细胞活性;测定细胞培养液中乳酸脱氢酶(LDH)、丙二醛(MDA)、超氧化物歧化酶(SOD)含量.结果:(-)-CG、( )-EC能够增加心肌细胞存活率,降低心肌细胞LDH的漏出量,增加SOD活性,降低培养液中MDA的含量.结论:(-)-CG、( )-EC具有抗体外培养大鼠乳鼠心肌细胞黄嘌呤/黄嘌呤氧化酶体系损伤的作用.     

表没食子儿茶素没食子酸酯的研究进展

茶多酚的抗肿瘤作用已经得到国内外相关研究人员的公认,研究表明其主体成分儿茶素(占茶多酚总量70%~80%)发挥着主要功效。近年来科学工作者已经越来越多将注意力集中于儿茶素上,尤其是其中的单体之一表没食子儿茶素没食子酸酯(EGCG)最引人注目。现就近年来对EGCG的药理作用研究,特别是对它优于其他儿茶素单体的药理作用比较研究进行综述;同时综述了EGCG的分离纯化方法的研究进展。为全面评价EGCG的药用价值及探索工业化生产EGCG的途径提供参考。