Effects Of Green Tea Catechins Research Articles

Possible Mechanisms of Green Tea and Its Constituents against Cancer.

A number of epidemiological, clinical, and experimental researches have indicated that administration of green tea appears to have anti-cancer activity. According to findings of laboratory cell culture studies, a diverse mechanism has been observed underlying the effects of green tea catechins against cancer. These mechanisms include anti-oxidant activity, cell cycle regulation, receptor tyrosine kinase pathway inhibition, immune system modulation, and epigenetic modification control. This review discusses the results of these studies to provide more insight into the effects of green tea administration on cancers observed to date in this research field.

Effect of green tea catechins on the pharmacokinetics of digoxin in humans

BackgroundPrevious in vitro studies have reported the inhibitory effect of green tea on p-glycoprotein (p-gp) encoded by ABCB1. This study aimed to investigate the effect of green tea on the pharmacokinetics of digoxin, a typical probe drug of p-gp.MethodsSixteen healthy volunteers participated in this study. At Day 1, 0.5 mg of digoxin was administered via oral route. After a 14-day washout period, 630 mg of green tea catechins (GTC) was administered via oral route, followed by 0.5 mg of digoxin 1 hour later. From Day 16 through Day 28, 630 mg of GTC was administered alone. At Day 29, 630 mg of GTC and 0.5 mg of digoxin were administered in the same way as Day 15. Blood samples for the pharmacokinetic assessments of digoxin were collected up to 8 hours after each dose. Pharmacokinetic parameters were estimated by noncompartmental analysis. Area under the curve (AUC) and peak plasma concentration (Cmax) were compared using mixed effect model between digoxin alone and digoxin with GTC. ABCB1 was genotyped to determine whether its polymorphism affects digoxin–GTC interaction.ResultsFifteen subjects completed the study. Compared to digoxin alone, the concomitant administration of digoxin and GTC significantly reduced the systemic exposure of digoxin: geometric mean ratios (GMR) and 90% confidence intervals (CI) of area under the concentration–time curve from time 0 to the last measurable time (AUClast) and Cmax were 0.69 (0.62–0.75) and 0.72 (0.61–0.85), respectively. The concomitant administration of digoxin and GTC following pretreatment of GTC (Day 29) similarly reduced the AUClast (GMR [90% CI]: 0.67 [0.61–0.74]) and Cmax (GMR [90% CI]: 0.74 [0.63–0.87]). In the comparison of the percentage changes from Day 1 (digoxin single administration) of AUClast between genotypes, C1236T variant type showed a significant difference to wild-type on Day 15 (concomitant administration of digoxin and GTC) (P=0.005).ConclusionThis study demonstrates that the coadministration of GTC reduces the systemic exposure of digoxin regardless of pretreatment of GTC.

Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases.

Tea is one of the most consumed beverages in the world. Green tea, black tea, and oolong tea are made from the same plant Camellia sinensis (L.) O. Kuntze. Among them, green tea has been the most extensively studied for beneficial effects on diseases including cancer, obesity, diabetes, and inflammatory and neurodegenerative diseases. Several human observational and intervention studies have found beneficial effects of tea consumption on neurodegenerative impairment, such as cognitive dysfunction and memory loss. These studies supported the basis of tea’s preventive effects of Parkinson’s disease, but few studies have revealed such effects on Alzheimer’s disease. In contrast, several human studies have not reported these favorable effects with regard to tea. This discrepancy may be due to incomplete adjustment of confounding factors, including the method of quantifying consumption, beverage temperature, cigarette smoking, alcohol consumption, and differences in genetic and environmental factors, such as race, sex, age, and lifestyle. Thus, more rigorous human studies are required to understand the neuroprotective effect of tea. A number of laboratory experiments demonstrated the benefits of green tea and green tea catechins (GTCs), such as epigallocatechin gallate (EGCG), and proposed action mechanisms. The targets of GTCs include the abnormal accumulation of fibrous proteins, such as Aβ and α-synuclein, inflammation, elevated expression of pro-apoptotic proteins, and oxidative stress, which are associated with neuronal cell dysfunction and death in the cerebral cortex. Computational molecular docking analysis revealed how EGCG can prevent the accumulation of fibrous proteins. These findings suggest that GTCs have the potential to be used in the prevention and treatment of neurodegenerative diseases and could be useful for the development of new drugs.

Scientific opinion on the safety of green tea catechins.

The EFSA ANS Panel was asked to provide a scientific opinion on the safety of green tea catechins from dietary sources including preparations such as food supplements and infusions. Green tea is produced from the leaves of Camellia sinensis (L.) Kuntze, without fermentation, which prevents the oxidation of polyphenolic components. Most of the polyphenols in green tea are catechins. The Panel considered the possible association between the consumption of (‐)‐epigallocatechin‐3‐gallate (EGCG), the most relevant catechin in green tea, and hepatotoxicity. This scientific opinion is based on published scientific literature, including interventional studies, monographs and reports by national and international authorities and data received following a public ‘Call for data’. The mean daily intake of EGCG resulting from the consumption of green tea infusions ranges from 90 to 300 mg/day while exposure by high‐level consumers is estimated to be up to 866 mg EGCG/day, in the adult population in the EU. Food supplements containing green tea catechins provide a daily dose of EGCG in the range of 5–1,000 mg/day, for adult population. The Panel concluded that catechins from green tea infusion, prepared in a traditional way, and reconstituted drinks with an equivalent composition to traditional green tea infusions, are in general considered to be safe according to the presumption of safety approach provided the intake corresponds to reported intakes in European Member States. However, rare cases of liver injury have been reported after consumption of green tea infusions, most probably due to an idiosyncratic reaction. Based on the available data on the potential adverse effects of green tea catechins on the liver, the Panel concluded that there is evidence from interventional clinical trials that intake of doses equal or above 800 mg EGCG/day taken as a food supplement has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control.

Non-pharmacological modification of endothelial function: An important lesson for clinical practice

During the last few generations a rapid increase in the prevalence of cardiovascular diseases has been observed. This epidemiologic fact is in a wide range due to endothelial dysfunction. Endothelium, the inner layer of vessel wall, is a crucial structure in the proper functioning of the cardiovascular system. Next to classic cardiovascular risk factors such as diabetes, obesity, atherosclerosis and hypertension, endothelial dysfunction has become understood as one of the most important elements of cardiovascular pathologies, ranging from ischemic heart disease, stroke to carcinogenesis. This has given rise to a crucial need to develop new therapeutic directions aimed at ameliorating the endothelial function. A healthy lifestyle and proper well-balanced diet seem to be even more important than pharmacotherapy. Therefore, non-pharmacological interventions have become bullet points in a list of endothelial-targeted treatment strategies. Currently, several compounds have been studied as candidates for endothelial function improvement. L-arginine supplementation is proved to reduce fat content. It also preferably modifies carbohydrates metabolism and the expression of genes responsible for increased cardiovascular risk. Spirulina increases the expression of endothelial nitric oxide synthase, which ameliorates nitrogen oxide production and leads to a decrease in blood pressure. The beneficial effect of green tea catechins is based mainly on the inactivation of reactive oxygen. Allicin present in garlic shows both antioxidative and anti-inflammatory effects. Probiotics prevent endothelial dysfunction in effect of improved vascular oxidative stress. Physical activity also demonstrates a number of mechanisms that ameliorate endothelial function. The impact of endothelial function in the complex pathology of cardiovascular diseases reflects a number of scientific proofs showing favorable effects of non-pharmacological interventions in endothelial dysfunction treatment.

Beneficial Effects of Green Tea Catechin on Veterinary Sciences and Bacterial Infections

Beneficial Effects of Green Tea Catechin on Veterinary Sciences and Bacterial Infections

Prevention of Colorectal Cancer by Targeting Obesity-Related Disorders and Inflammation.

Colorectal cancer is a major healthcare concern worldwide. Many experimental and clinical studies have been conducted to date to discover agents that help in the prevention of this disease. Chronic inflammation in colonic mucosa and obesity, and its related metabolic abnormalities, are considered to increase the risk of colorectal cancer. Therefore, treatments targeting these factors might be a promising strategy to prevent the development of colorectal cancer. Among a number of functional foods, various phytochemicals, including tea catechins, which have anti-inflammatory and anti-obesity properties, and medicinal agents that ameliorate metabolic disorders, might also be beneficial in the prevention of colorectal cancer. In this review article, we summarize the strategies for preventing colorectal cancer by targeting obesity-related disorders and inflammation through nutraceutical and pharmaceutical approaches, and discuss the mechanisms of several phytochemicals and medicinal drugs used in basic and clinical research, especially focusing on the effects of green tea catechins.

Tea catechin and caffeine activate brown adipose tissue and increase cold-induced thermogenic capacity in humans

Background: The thermogenic effects of green tea catechin have been repeatedly reported, but their mechanisms are poorly understood.Objective: The aim of this study was to investigate the acute and chronic effects of catechin on brown adipose tissue (BAT), a site specialized for nonshivering thermogenesis, in humans.Design: Fifteen healthy male volunteers underwent fluorodeoxyglucose-positron emission tomography to assess BAT activity. To examine the acute catechin effect, whole-body energy expenditure (EE) after a single oral ingestion of a beverage containing 615 mg catechin and 77 mg caffeine (catechin beverage) was measured. Next, to investigate the chronic catechin effects, 10 men with low BAT activity were enrolled. Before and after ingestion of the catechin beverage 2 times/d for 5 wk, cold-induced thermogenesis (CIT) after 2 h of cold exposure at 19°C, which is proportional to BAT activity, was examined. Both the acute and chronic trials were single-blinded, randomized, placebo-controlled, season-matched crossover studies.Results: A single ingestion of the catechin beverage increased EE in 9 subjects who had metabolically active BAT (mean ± SEM: +15.24 ± 1.48 kcal, P < 0.01) but not in 6 subjects who had negligible activities (mean ± SEM: +3.42 ± 2.68 kcal). The ingestion of a placebo beverage containing 82 mg caffeine produced a smaller and comparative EE response in the 2 subject groups. Multivariate regression analysis revealed a significant interaction between BAT and catechin on EE (β = 0.496, P = 0.003). Daily ingestion of the catechin beverage elevated mean ± SEM CIT (from 92.0 ± 26.5 to 197.9 ± 27.7 kcal/d; P = 0.009), whereas the placebo beverage did not change it.Conclusion: Orally ingested tea catechin with caffeine acutely increases EE associated with increased BAT activity and chronically elevates nonshivering CIT, probably because of the recruitment of BAT, in humans. These trials were registered at www.umin.ac.jp/ctr/ as UMIN000016361.

Quantitative comparison of cancer and normal cell adhesion using organosilane monolayer templates: an experimental study on the anti-adhesion effect of green-tea catechins.

The main constituent of green tea, (-)-Epigallocatechin-3-O-gallate (EGCG), is known to have cancer-specific chemopreventive effects. In the present work, we investigated how EGCG suppresses cell adhesion by comparing the adhesion of human pancreatic cancer cells (AsPC-1 and BxPC-3) and their counterpart, normal human embryonic pancreas-derived cells (1C3D3), in catechin-containing media using organosilane monolayer templates (OMTs). The purpose of this work is (1) to evaluate the quantitativeness in the measurement of cell adhesion with the OMT and (2) to show how green-tea catechins suppress cell adhesion in a cancer-specific manner. For the first purpose, the adhesion of cancer and normal cells was compared using the OMT. The cell adhesion in different type of catechins such as EGCG, (-)-Epicatechin-3-O-gallate (ECG) and (-)-Epicatechin (EC) was also evaluated. The measurements revealed that the anti-adhesion effect of green-tea catechins is cancer-specific, and the order is EGCG≫ECG>EC. The results agree well with the data reported to date, showing the quantitativeness of the new method. For the second purpose, the contact area of cells on the OMT was measured by reflection interference contrast microscopy. The cell-OMT contact area of cancer cells decreases with increasing EGCG concentration, whereas that of normal cells remains constant. The results reveal a twofold action of EGCG on cancer cell adhesion-suppressing cell attachment to a candidate adhesion site and decreasing the contact area of the cells-and validates the use of OMT as a tool for screening cancer cell adhesion.

Effect of green tea catechins on gastric mucosal dysplasia in insulin-gastrin mice.

Green tea catechins (GTCs) have been implicated in various physiological effects, including anti-carcinogenic activities. In the present study, we evaluated the effects of GTCs specifically on the development of gastritis and pre-malignant lesions in insulin-gastrin mice. Nine-week-old male INS-GAS mice (n=38) were supplemented with GTCs for 4 and 28 weeks, and their body weights, serum gastrin levels, histopathology and pro-inflammatory cytokine levels in gastric tissue and mucosal cell proliferation were monitored. Body weights of the GTC-treated mice were significantly lower than those of the untreated controls (P≤0.05). Serum gastrin levels were suppressed at the age of 37-weeks (P≤0.05). The histopathological scores indicated that the extent of dysplasia was significantly diminished (P≤0.05), although GTC supplementation did not affect the inflammation scores. The messenger RNA levels of interferon (IFN)-γ were significantly reduced at the age of 13 weeks (P≤0.05), although the changes did not reach statistical significance at the age of 37 weeks (P=0.056). The labeling index of Ki-67 immunohistochemistry was significantly decreased (P≤0.05). These results demonstrated that GTCs may play a protective role in the development of gastritis and pre-malignant lesions via an IFN-γ, gastrin, and mucosal cell proliferation-dependent mechanism in this rodent model and potentially in humans.

Antioxidant activity and recovery of green tea catechins in full-fat cheese following gastrointestinal simulated digestion

Green tea extract (GTE) was incorporated into full-fat cheeses at 250, 500, and 1000ppm to investigate the effect of green tea catechins on antioxidant properties and microstructure of cheese, and recovery of catechins. Cheeses were ripened for 90 days at 8°C followed by simulated gastrointestinal digestion. The composition on Day 0, and pH, total phenolic content (TPC), and antioxidant activity (AA) of the cheeses on Days 0, 30, and 90, were determined. The concentrations of the major GTE catechins in the curd and from the digesta of mature cheeses were determined using HPLC. Addition of GTE significantly (p≤0.05) decreased the pH of whey and curd during cheese manufacture and ripening, however there was no significant (p>0.05) effect on moisture, protein, or fat contents. Addition of GTE increased TPC and AA at all concentrations, but in a non-linear manner. Individual catechins were selectively retained in the curd, whereas different portions were recovered from the cheese digesta. Transmission electron microscopy showed that the ripened control cheese had a regular distribution of milk fat globules entrapped in a homogeneous structure of casein proteins, which was disrupted by GTE. Interactions between green-tea catechins and cheese fat were confirmed by Fourier transform infrared spectroscopy.

Catechins and Its Role in Chronic Diseases.

The mechanisms of action of polyphenols have attracted much attention. Catechins are generally known as tea polyphenols. Researchers have extensively investigated the molecular mechanisms of these substances, especially (-)-epigallocatechin gallate of green tea catechin, and have provided new insights in the prevention and therapy for chronic diseases. This chapter summarizes catechins and their effects on chronic diseases, including metabolic syndromes, cardiovascular diseases, neurodegenerative diseases, and cancer, focusing on the effects of green tea catechins.

Green tea catechins prevent low-density lipoprotein oxidation via their accumulation in low-density lipoprotein particles in humans

Green tea is rich in polyphenols, including catechins which have antioxidant activities and are considered to have beneficial effects on cardiovascular health. In the present study, we investigated the effects of green tea catechins on low-density lipoprotein (LDL) oxidation in vitro and in human studies to test the hypothesis that catechins are incorporated into LDL particles and exert antioxidant properties. In a randomized, placebo-controlled, double-blind, crossover trial, 19 healthy men ingested green tea extract (GTE) in the form of capsules at a dose of 1 g total catechin, of which most (>99%) was the gallated type. At 1 hour after ingestion, marked increases of the plasma concentrations of (−)-epigallocatechin gallate and (−)-epicatechin gallate were observed. Accordingly, the plasma total antioxidant capacity was increased, and the LDL oxidizability was significantly reduced by the ingestion of GTE. We found that gallated catechins were incorporated into LDL particles in nonconjugated forms after the incubation of GTE with plasma in vitro. Moreover, the catechin-incorporated LDL was highly resistant to radical-induced oxidation in vitro. An additional human study with 5 healthy women confirmed that GTE intake sufficiently increased the concentration of gallated catechins, mainly in nonconjugated forms in LDL particles, and reduced the oxidizability of LDL. In conclusion, green tea catechins are rapidly incorporated into LDL particles and play a role in reducing LDL oxidation in humans, which suggests that taking green tea catechins is effective in reducing atherosclerosis risk associated with oxidative stress.

Influence of green tea catechins on oxidative stress metabolites at rest and during exercise in healthy humans

ObjectivesThe aim of this study was to investigate the effects of green tea catechins (GTC) on oxidative stress metabolites in healthy individuals while at rest and during exercise. The effects investigated included response to fat metabolism, blood lactate concentrations, and rating of perceived exertion. MethodsIn a paralleled, crossover, randomized controlled study, 16 trained male gymnastic students were randomly divided into two groups. The rest group (n = 8; GTC-NEX) received a single dose of 780 mg GTC with water but no exercise; the exercise group (n = 8; GTC-EX) received a similar dose of GTC but were instructed to exercise. This was followed by a crossover study with similar exercise regime as a placebo group (PL-EX) that received water only. Blood samples were collected at baseline and after 60 and 120 min of GTC intake. Oxidative stress blood biomarkers using the diacron reactive oxygen metabolite (d-ROMs) and biological antioxidant potential (BAP) tests; urinary 8-hydroxydeoxyguanosine (8-OHdG); 8-OHdG/creatinine; and blood lactate concentrations were analyzed. During the cycle ergometer exercise, volume of maximal oxygen uptake, volume of oxygen consumption, volume of carbon dioxide, and respiratory exchange ratio were measured from a sample of respiratory breath gas collected during low, moderate, and high intensity exercising, and the amount of fat burning and sugar consumption were calculated. Analysis of variance was used to determine statistical significance (P < 0.05) between and among the groups. ResultsLevels of postexercise oxidative stress metabolites BAP and d-ROMs were found significant (P < 0.0001) in the PL-EX and GTC-EX groups, and returned to pre-exercise levels after the recovery period. Levels of d-ROMs showed no significant difference from baseline upon GTC intake followed by resting and a resting recovery period in the GTC-NEX group. BAP levels were significant upon GTC intake followed by resting (P = 0.04), and after a resting recovery period (P = 0.0006) in the GTC-NEX group. Urinary 8-OHdG levels were significant (P < 0.005) for all groups after the recovery period. A significant difference was noticed between the ratios of resting BAP to d-ROMs and exercise-induced BAP to d-ROMs (P = 0.022) after 60 min of GTC intake, as well as resting 8-OHdG and exercise-induced 8-OHdG levels (P = 0.004) after the recovery period. Oxidative potentials were higher when exercise was performed at low to moderate intensity, accompanied by lower blood lactate concentration and higher amounts of fat oxidation. ConclusionsThe results of the present study indicate that single-dose consumption of GTC influences oxidative stress biomarkers when compared between the GTC-NEX and GTC-EX groups, which could be beneficial for oxidative metabolism at rest and during exercise, possibly through the catechol-O-methyltransferase mechanism that is most often cited in previous studies.

The protective effect of green tea catechins on ketamine-induced cystitis in a rat model

ObjectiveTo investigate the protective effect of green tea epigallocatechin gallate (EGCG) on long-term ketamine-induced ulcerative cystitis (KIC) using a ketamine addiction rat model. Materials and methodsThirty Sprague-Dawley rats were divided into three groups which received saline, ketamine (25 mg/kg/d), or ketamine combined with EGCG (10 μM/kg) for a period of 28 days. In each group, cystometry and a metabolic cage micturition pattern study were performed weekly. Masson's trichrome study was done to evaluate the morphologic changes. Western blot analyses were carried out to examine the expressions of inflammatory protein [transforming growth factor-β (TGF-β)] and fibrosis proteins (fibronectin and type I collagen) in bladder tissues. ResultsChronic ketamine treatment resulted in bladder hyperactivity with a significant increase in micturition frequency and a decrease in bladder compliance. These alterations in micturition pattern were accompanied by increases in the expressions of inflammatory and fibrosis markers, TGF-β, fibronectin, and type I collagen after long-term ketamine treatment. Masson's trichrome stain showed that ketamine treatment decreased urothelium thickness while increasing the collagen to smooth muscle ratio and exacerbating interstitial fibrosis. By contrast, simultaneous EGCG and ketamine treatment reversed ketamine-induced damage to almost control levels, showing the protective effect of EGCG. ConclusionThis protective effect of EGCG may come from its antiinflammatory and antifibrotic properties.

Effect of green tea catechins in prostate cancer chemoprevention.

1572 Background: Preclinical, epidemiological and prior clinical trial data suggest that green tea catechins may reduce prostate cancer (PCa) risk. Methods: We, therefore, conducted a placebo-contr...

Green tea catechins enhance norepinephrine-induced lipolysis via a protein kinase A-dependent pathway in adipocytes

Green tea catechins have been shown to attenuate obesity in animals and humans. The catechins activate adenosine monophosphate-activated protein kinase (AMPK), and thereby increase fatty acid oxidation in liver and skeletal muscles. Green tea catechins have also been shown to reduce body fat in humans. However, the effect of the catechins on lipolysis in adipose tissue has not been fully understood. The aim of this study was to clarify the effect of green tea catechins on lipolysis in adipocytes and to elucidate the underlying mechanism. Differentiated mouse adipocyte cell line (3T3-L1) was stimulated with green tea catechins in the presence or absence of norepinephrine. Glycerol and free fatty acids in the media were measured. Phosphorylation of hormone-sensitive lipase (HSL) was determined by Western blotting, and the mRNA expression levels of HSL, adipose triglyceride lipase (ATGL), and perilipin were determined by quantitative RT-PCR. The cells were treated with inhibitors of protein kinase A (PKA), protein kinase C (PKC), protein kinase G (PKG), or mitogen-activated protein kinase (MAPK) to determine the responsible pathway. Treatment of 3T3-L1 adipocytes with green tea catechins increased the level of glycerol and free fatty acids released into the media in the presence, but not absence, of norepinephrine, and increased the level of phosphorylated HSL in the cells. The catechins also increased mRNA and protein levels of HSL and ATGL. PKA inhibitor (H89) attenuated the catechin-induced increase in glycerol release and HSL phosphorylation. The results demonstrate that green tea catechins enhance lipolysis in the presence of norepinephrine via a PKA-dependent pathway in 3T3-L1 adipocytes, providing a potential mechanism by which green tea catechins could reduce body fat.

Ameliorative Effect of Green Tea Catechin Against Cadmium Chloride-Induced Testicular Toxicity in Mice.

The present study was designed to evaluate the effect of green tea catechin (7500 µg/kg/animal/day) against cadmium-induced testicular dysfunctions and oxidative stress in the testes of mice. For this purpose, Swiss albino mice were divided into six groups: group I, negative control; group II, catechin-treated control; group III, cadmium chloride (CdCl2)-treated control; group IV, experimental group I; group V, experimental group II; and group VI, experimental group III. Animals from all of these groups were necropsied at various post-treatment intervals between 12 hours and 30 days for various biochemical alterations in the testes. CdCl2 intoxication resulted in a significant decline in testicular total proteins, cholesterol, and alkaline phosphatase, whereas acid phosphatase and lipid peroxidation exhibited a noticeable augmentation as compared to negative control. Catechin treatment effectively protected CdCl2-induced alterations in all such parameters throughout the experiment. Catechin was effective in reducing the CdCl2-induced augmentation of phase I (P450 and CYPB5) as well as phase II (DT-diaphorase and glutathione-S-transferase) enzymes in testes. Furthermore, CdCl2 intoxication was found to attenuate the antioxidant potential of testes, which was however augmented when supplemented with green tea extract. Compared to CdCl2-treated control mice, superoxide dismutase, glutathione peroxidase, glutathione, and catalase levels were significantly decreased in testes. Indeed, green tea catechin significantly increased testicular antioxidant enzymatic activities compared to those given CdCl2 alone. In conclusion, the use of green tea extract appeared to be beneficial to a great extent in inhibiting and restoring the testicular injuries induced by CdCl2 intoxication in mammals.

Structure-dependent inhibitory effects of green tea catechins on insulin secretion from pancreatic β-cells.

The effects of green tea catechins on glucose-stimulated insulin secretion (GSIS) were investigated in the β-cell line INS-1D. Epigallocatechin gallate (EGCG) at 10 µM or gallocatechin gallate (GCG) at 30 µM caused significant inhibitory effects on GSIS, and each of these at 100 µM almost abolished it. In contrast, epicatechin (EC) or catechin (CA) had no effect on GSIS at concentrations up to 100 µM. We thus investigated the structure-activity relationship by using epigallocatechin (EGC) and gallocatechin (GC) containing a trihydroxyl group in the B-ring, and epicatechin gallate (ECG) and catechin gallate (CG) containing the gallate moiety. EGC, GC, and ECG caused an inhibition of GSIS, although significant effects were obtained only at 100 µM. At this concentration, EGC almost abolished GSIS, whereas GC and ECG partially inhibited it. In contrast, CG did not affect GSIS at concentrations up to 100 µM. EGCG also abolished the insulin secretion induced by tolbutamide, an ATP-sensitive K(+) channel blocker, and partially inhibited that induced by 30 mM K(+). Moreover, EGCG, but not EC, inhibited the oscillation of intracellular Ca(2+) concentration induced by 11.1 mM glucose. These results suggest that some catechins at supraphysiological concentrations have inhibitory effects on GSIS, the potency of which depends on their structure; the order of potency was EGCG>GCG>EGC>GC≈ECG. The inhibitory effects seem to be mediated by the inhibition of voltage-dependent Ca(2+) channels, which is caused, at least in part, by membrane hyperpolarization resulting from the activation of K(+) channels.

Protective action of green tea catechins in neuronal mitochondria during aging.

Mitochondria are central players in the regulation of cell homeostasis. They are essential for energy production but at the same time, reactive oxygen species accumulate as byproducts of the electron transport chain causing mitochondrial damage. In the central nervous system, senescence and neurodegeneration occur as a consequence of mitochondrial oxidative insults and impaired electron transfer. The accumulation of several oxidation products in neurons during aging prompts the idea that consumption of antioxidant compounds may delay neurodegenerative processes. Tea, one of the most consumed beverages in the world, presents benefits to human health that have been associated to its abundance in polyphenols, mainly catechins, that possess powerful antioxidant properties in vivo and in vitro. In this review, the focus will be placed on the effects of green tea catechins in neuronal mitochondria. Although these compounds reach the brain in small quantities, there are several possible targets, signaling pathways and molecular machinery impinging in the mitochondria that will be highlighted. Accumulated evidence thus far seems to indicate that catechins help prevent neurodegeneration and delay brain function decline.