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PubMed2003

External TEA block of shaker K+ channels is coupled to the movement of K+ ions within the selectivity filter.

Recent molecular dynamic simulations and electrostatic calculations suggested that the external TEA binding site in K+ channels is outside the membrane electric field. However, it has been known for some time that external TEA block of Shaker K+ channels is voltage dependent. To reconcile these two results, we reexamined the voltage dependence of block of Shaker K+ channels by external TEA. We found that the voltage dependence of TEA block all but disappeared in solutions in which K+ ions were replaced by Rb+. These and other results with various concentrations of internal K+ and Rb+ ions suggest that the external TEA binding site is not within the membrane electric field and that the voltage dependence of TEA block in K+ solutions arises through a coupling with the movement of K+ ions through part of the membrane electric field. Our results suggest that external TEA block is coupled to two opposing voltage-dependent movements of K+ ions in the pore: (a) an inward shift of the average position of ions in the selectivity filter equivalent to a single ion moving approximately 37% into the pore from the external surface; and (b) a movement of internal K+ ions into a vestibule binding site located approximately 13% into the membrane electric field measured from the internal surface. The minimal voltage dependence of external TEA block in Rb+ solutions results from a minimal occupancy of the vestibule site by Rb+ ions and because the energy profile of the selectivity filter favors a more inward distribution of Rb+ occupancy.

Animals↗

PubMed1997

Herbal teas and populace health care in tropical China.

Commercial Chinese herbal tea is the development of the populace in tropical and subtropical China consequential to their fight against infectious diseases and their struggle to explore local plants to relieve fever, to alleviate pain, to restore strength and to modulate immunity against viral epidemics. From these ethnomedical experiences, two types of herbal teas were commercialized, namely, liangcha and medicated teas. Liangcha refers to a ready-made decoction infused from wild plants served in simple stores in cities and towns. Medicated teas are parcelled material prepared from crude drugs with or without tea (Camellia sinensis [L.] O. Ktze,), sold in colorful boxes and bags to people for use at home. Investigations of liangcha were made in Hong Kong and Macao, and studies for medicated teas were done from samples obtained in Chinese stores at Boston. A total of 127 source species of these herbal teas were identified and arranged in two alphabetical lists by the botanical names, each followed by an English common name in parenthesis, part used, frequency in samples, and family. External recognizing characters of medicated teas, discussions of problems encountered in identifying source species, relevant toxicities, and potential new vegetal pharmaceutical resources are given.

Beverages↗

PubMed1997

Vasodilator responses to acetylcholine, bradykinin, and substance P are mediated by a TEA-sensitive mechanism.

The effects of tetraethylammonium (TEA), a K+ channel antagonist, on vasodilator responses were investigated in the hindquarters vascular bed of the cat under constant-flow conditions. After administration of TEA in a total dose of 60 mg/kg into the hindquarters perfusion circuit, vasodilator responses to acetylcholine, bradykinin, and substance P were reduced, whereas vasodilator responses to the NO donors, diethylamine-NO complex, S-nitroso-N-acetylpenicillamine, and sodium nitroprusside, and to prostaglandin E1, albuterol, vasoactive intestinal polypeptide, isradipine, and levcromakalim were not altered. The inhibitory effect of TEA on responses to the endothelium-dependent vasodilators was reversible with time, and vasoconstrictor responses to norepinephrine, U-46619, angiotensin II, and BAY K 8644 were enhanced by the K+ channel antagonist. Although TEA had no sustained effect on baseline systemic arterial and hindquarters perfusion pressures, the NO synthase inhibitor, N omega-nitro-L-arginine methyl ester, increased these pressures in the presence of TEA. The results of the present investigation suggest that TEA attenuates vasodilator responses to acetylcholine, bradykinin, and substance P by inhibiting the release of endothelium-derived relaxing factor. These data suggest that the acetylcholine-, bradykinin-, and substance P-stimulated release of endothelium-derived relaxing factor may involve the opening of a TEA-sensitive K+ channel in the endothelium in the hindlimb vascular bed of the cat, but that a TEA-sensitive mechanism is not involved in the maintenance of baseline tone in this vascular bed.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1989

Brush-border TEA transport in intact proximal tubules and isolated membrane vesicles.

The efflux of the organic cation, tetraethylammonium (TEA), across proximal cell luminal membranes was studied using intact, perfused rabbit proximal tubules and isolated rabbit cortical brush-border membrane vesicles (BBMV). Increases of either the extravesicular H+ concentration (from pH 7.5 to pH 6.5) or the extravesicular concentration of unlabeled TEA (from 0.1 to 0.5 mM) increased the rate of efflux of radioactively labeled TEA from BBMV. Similarly, when proximal tubules were preloaded with labeled TEA and then submerged in a mineral oil bath, a rapid increase in either the H+ concentration (from pH 7.5 to pH 5.8) or the TEA concentration (from 0 to 1 mM) of the tubular perfusate produced an acute increase in efflux of the labeled TEA across the luminal brush-border membrane. These results with intact tubules and isolated membranes are consistent with previous suggestions that TEA transport across the brush border of proximal tubule cells involves a carrier-mediated countertransport process and represent the first demonstration with intact proximal tubules that the secretory flux of TEA occurs by an exchange with H+.

Animals↗

PubMed2006

Green tea extract and (-)-epigallocatechin-3-gallate inhibit hypoxia- and serum-induced HIF-1alpha protein accumulation and VEGF expression in human cervical carcinoma and hepatoma cells.

Green tea extract and its major component (-)-epigallocatechin-3-gallate (EGCG) exhibit antiangiogenic activities in various experimental tumor models. A growing body of evidence has established that hypoxia-inducible factor-1alpha (HIF-1alpha) and its downstream target, vascular endothelial growth factor (VEGF), play a critical role in tumor angiogenesis. In this study, we investigated the effect of green tea extract and EGCG on HIF-1alpha and VEGF expression in human cervical carcinoma (HeLa) and hepatoma (HepG2) cells. Our results showed that green tea extract and EGCG significantly inhibited hypoxia- and serum-induced HIF-1alpha protein accumulation in these cancer cells but had no effects on HIF-1alpha mRNA expression. Suppression of HIF-1alpha protein by green tea extract and EGCG also resulted in a drastic decrease in VEGF expression at both mRNA and protein levels. The mechanisms of green tea extract and EGCG inhibition of hypoxia-induced HIF-1alpha protein accumulation seem to involve the blocking of both phosphatidylinositol 3-kinase/Akt and extracellular signal-regulated kinase 1/2 signaling pathways and the enhancing of HIF-1alpha protein degradation through the proteasome system. In addition, green tea extract and EGCG inhibited serum-induced HIF-1alpha protein and VEGF expression by interfering with the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling pathways, which play a crucial role in the protein translational machinery cascade. Functionally, green tea extract and EGCG abolished both chemoattractant- and hypoxia-stimulated HeLa cell migration. Our data suggested that HIF-1alpha/VEGF function as therapeutic target for green tea extract and EGCG in the context of cancer chemoprevention and anticancer therapy.

Angiogenesis Inhibitors↗

PubMed2007

Green tea increases anti-inflammatory tristetraprolin and decreases pro-inflammatory tumor necrosis factor mRNA levels in rats.

BACKGROUND: Tristetraprolin (TTP/ZFP36) family proteins have anti-inflammatory activity by binding to and destabilizing pro-inflammatory mRNAs such as Tnf mRNA, and represent a potential therapeutic target for inflammation-related diseases. Tea has anti-inflammatory properties but the molecular mechanisms have not been completely elucidated. We hypothesized that TTP and/or its homologues might contribute to the beneficial effects of tea as an anti-inflammatory product. METHODS: Quantitative real-time PCR was used to investigate the effects of green tea (0, 1, and 2 g solid extract/kg diet) on the expression of Ttp family genes (Ttp/Tis11/Zfp36, Zfp36l1/Tis11b, Zfp36l2/Tis11d, Zfp36l3), pro-inflammatory genes (Tnf, Csf2/Gm-csf, Ptgs2/Cox2), and Elavl1/Hua/Hur and Vegf genes in liver and muscle of rats fed a high-fructose diet known to induce insulin resistance, oxidative stress, inflammation, and TNF-alpha levels. RESULTS: Ttp and Zfp36l1 mRNAs were the major forms in both liver and skeletal muscle. Ttp, Zfp36l1, and Zfp36l2 mRNA levels were more abundant in the liver than those in the muscle. Csf2/Gm-csf and Zfp36l3 mRNAs were undetectable in both tissues. Tea (1 g solid extract/kg diet) increased Ttp mRNA levels by 50-140% but Tnf mRNA levels decreased by 30% in both tissues, and Ptgs2/Cox2 mRNA levels decreased by 40% in the muscle. Tea (2 g solid extract/kg diet) increased Elavl1/Hua/Hur mRNA levels by 40% in the liver but did not affect any of the other mRNA levels in liver or muscle. CONCLUSION: These results show that tea can modulate Ttp mRNA levels in animals and suggest that a post-transcriptional mechanism through TTP could partially account for tea's anti-inflammatory properties. The results also suggest that drinking adequate amounts of green tea may play a role in the prevention of inflammation-related diseases.

Journal Article↗

PubMed2001

Effect of herbal teas on hepatic drug metabolizing enzymes in rats.

We have investigated the effect of herbal teas (peppermint, chamomile and dandelion) on the activity of hepatic phase I and phase II metabolizing enzymes using rat liver microsomes. Female Wistar rats were divided into six groups (n = 5 each). Three groups had free access to a tea solution (2%) while the control group had water. Two groups received either green tea extract (0.1%) or aqueous caffeine solution (0.0625%). After four weeks of pretreatment, different cytochrome P450 (CYP) isoforms and phase II enzyme activities were determined by incubation of liver microsomes or cytosol with appropriate substrates. Activity of CYP1A2 in the liver microsomes of rats receiving dandelion, peppermint or chamomile tea was significantly decreased (P < 0.05) to 15%, 24% and 39% of the control value, respectively. CYP1A2 activity was significantly increased by pretreatment with caffeine solution. No alterations were observed in the activities of CYP2D and CYP3A in any group of the pretreated rats. Activity of CYP2E in rats receiving dandelion or peppermint tea was significantly lower than in the control group, 48% and 60% of the control, respectively. There was a dramatic increase (244% of control) in the activity of phase II detoxifying enzyme UDP-glucuronosyl transferase in the dandelion tea-pretreated group. There was no change in the activity of glutathione-S-transferase. The results suggested that, like green and black teas, certain herbal teas can cause modulation of phase I and phase II drug metabolizing enzymes.

Animals↗

PubMed2001

Effects of rooibos tea extract on antigen-specific antibody production and cytokine generation in vitro and in vivo.

Rooibos tea contains a large amount of flavonoids and acts as a potent antioxidant. In this study, we examined the effects of Rooibos tea extract on antigen-specific antibody production and cytokine generation in vitro and in vivo. The primary in vitro anti-ovalbumin (anti-OVA) or sheep red blood cell (SRBC) antibody production in murine splenocytes was markedly stimulated by the addition of the tea extract at concentrations of 1-100 microg/ml. On the other hand, a nonspecific antibody response elicited with lipopolysaccharide (LPS) in purified splenic B-cells was not modified by the extract. Rooibos tea extract caused an increase in the generation of interleukin 2 (IL-2) both in OVA- and anti-CD3-primed splenocytes at concentrations ranging from 10 microg/ml to 1000 microg/ml. In contrast, this tea extract suppressed the generation of interleukin 4 (IL-4) in OVA-primed splenocytes. Moreover, the reduction of OVA-induced antibody production in serum of the cyclosporin A (CyA) -treated rats can be significantly restored and the IL-2 generation in murine splenocytes was stimulated, following oral administrations of Rooibos tea extract. Thus, our findings suggested that Rooibos tea extract may facilitate the antigen-specific antibody production through selective augmentation of IL-2 generation both in vitro and in vivo. Collectively, Rooibos tea intake may be of value in prophylaxis of the diseases involving a severe defect in Th1 immune response such as cancer, allergy, AIDS, and other infections.

Animals↗

PubMed2001

Studies on toxicity, anti-stress and hepato-protective properties of Kombucha tea.

OBJECTIVE: The objective of the study was to evaluate toxicity, anti-stress activity and hepato-protective properties of Kombucha tea. METHOD: Kombucha tea was fed orally for 15 days using three different doses i.e. normal dose, five and ten times the dose. Rats were then sacrificed and various biochemical, and histological parameters were estimated. Anti-stress activity was evaluated either by 1) by exposing animals to cold and hypoxia and estimating the levels of malondialdehyde and reduced glutathione in plasma/blood or 2) by subjecting the animals to restraint stress and recording faecal output. Hepato-toxicity was induced by challenging the animals to an acute dose of paracetamol (1 gm/kg) orally and determining the plasma levels of SGPT, SGOT and MDA. RESULTS: The effect of oral administration of different doses of K-tea to albino rats was examined and the results indicate that K-tea has no significant toxicity as revealed by various biochemical and histopathological parameters. K-tea has been found to prevent lipid peroxidation and fall in reduced glutathione level when rats were exposed to cold and hypoxia in simulated chamber. Further, K-tea has also been found to decrease the Wrap-restraint faecal pellet output in rats. K-tea has also been found to decrease paracetamol induced hepatotoxicity significantly. CONCLUSION: The study shows that K-tea has anti-stress and hepato-protective activities.

Administration, Oral↗

PubMed2002

[An epidemic of epileptic seizures after consumption of herbal tea].

UNLABELLED: At the end of September 2001 the Inspectorate for Health Protection and Veterinary Public Health and the National Poisons Control Centre (NPCC) were informed about adverse health effects after consumption of a herbal tea. During consultations it was suggested that Japanese star anise (Illicium anisatum L.), which is known to contain a neurotoxin, may have been inadvertently mixed into the herbal tea. In view of the severity of the adverse health effects and the clear association with consumption of a specific herbal tea, the supplier was urgently advised to withdraw the suspected herbal tea from the market. A total of 63 persons reported symptoms of general malaise, nausea and vomiting 2-4 hours following consumption of the herbal tea. Twenty-two persons required hospitalisation, of whom 16 due to generalised tonic-clonic seizures. Medical investigations revealed no underlying pathology and after supportive treatment, the patients were discharged in good health. Morphologic and organoleptic investigations of the suspected herbal tea indicated that this possibly contained Japanese star anise. NMR analysis of the herbal tea confirmed the presence of the neurotoxin anisatin, a non-competitive GABA-antagonist which can cause hyperactivity of the central nervous system and tonic-clonic seizures. CONCLUSION: Ingestion of a herbal tea containing anisatin caused the reported serious adverse health effects. Close cooperation between clinicians, the Inspectorate for Health Protection and Veterinary Public Health and the NPCC played a vital role in preventing further harm to public health.

Adult↗

PubMed1994

TEA elicits two distinct potentiations of synaptic transmission in the CA1 region of the hippocampal slice.

Extracellular application of tetraethylammonium (TEA) has been shown to elicit a prolonged synaptic potentiation in the CA1 region of the hippocampus that is unaffected by NMDA receptor antagonists, but is blocked by antagonists to voltage-dependent calcium channels (Aniksztejn and Ben-Ari, 1991; Huang and Malenka, 1993). In the present study the relation between TEA-induced potentiation and NMDA receptor-dependent long-term potentiation (LTP) was investigated in the CA1 region of the hippocampal slice using extracellular recordings and picrotoxin to block GABAA-mediated inhibition. Consistent with the finding of Huang and Malenka (1993), NMDA receptor-dependent LTP partially occluded the TEA-induced potentiation. However, this occlusion was abolished when the NMDA receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) was present during the application of TEA, indicating one component of TEA-induced potentiation that is induced via NMDA receptor channels and another component that is distinct from NMDA receptor-dependent LTP. In the presence of antagonists to voltage-dependent calcium channels (nifedipine or nifedipine/flunarazine) application of TEA induced a potentiation that was largely occluded by NMDA receptor-dependent LTP. In common with NMDA receptor-dependent LTP, the TEA-induced potentiation, elicited in the presence of antagonists to voltage-dependent calcium channels, was associated with a symmetrical increase of the field EPSP. On the other hand, the TEA-induced potentiation elicited in the presence of D-AP5 produced an increase of the field EPSP that did not include the early part of the initial slope.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗

PubMed2026

Standard tea intake is causally associated with a reduced risk of wet age-related macular degeneration: a Mendelian randomization study.

Researchers have posited that increased consumption of tea and coffee may be associated with more favorable treatment outcomes in patients with age-related macular degeneration (AMD). However, there is no clear evidence regarding the causal associations. To delve deeper into this potential connection, scientists used a rigorous method known as Mendelian randomization (MR). This technique was used to explore the causal impact of tea and coffee consumption on the development or progression of AMD. With the aim of investigating the cause-and-effect relationship between 16 tea- and coffee-consuming subtypes and 3 AMD, we designed a two-sample MR study using comprehensive data from genome-wide association studies (GWAS). The major approach adopted was inverse variance weighting (IVW). Furthermore, we implemented complementary methods like the weighted median (WM), weighted mode, and MR-Egger to strengthen our findings. Sensitivity analyses, including MR-Egger, MR-PRESSO, leave-one-out, and Cochran's Q tests, were used to validate results, explore heterogeneity and pleiotropy, and pinpoint potential biases. Two hundred and sixty-eight instrumental variables were selected for MR analysis. The results showed that standard tea intake may be a protective factor for wet AMD [odds ratio (OR) = 0.7076, 95% confidence interval (CI) = 0.5776-0.8668, P = 8 × 10-4, PFDR = 0.0402]. Sensitivity analysis suggests that the results are robust. Our findings provide genetic evidence that standard tea intake is a protective factor against wet AMD, providing new insights into early risk stratification and prevention strategies for the disease.NEW & NOTEWORTHY This study investigates the potential causal relationship between tea and coffee consumption and age-related macular degeneration (AMD) using Mendelian randomization. Analyzing data from genome-wide association studies, we focused on 16 beverage subtypes and 3 AMD conditions. Our findings suggest that standard tea consumption may protect against wet AMD, with robust evidence supporting this link. The results offer new insights into risk stratification and prevention strategies for AMD, highlighting the importance of dietary factors in eye health.

Mendelian Randomization Analysis↗

PubMed1999

Tea flavonoids may protect against atherosclerosis: the Rotterdam Study.

BACKGROUND: Epidemiological studies have indicated a protective role of dietary flavonoids in cardiovascular disease, but evidence is still conflicting. Tea is the major dietary source for flavonoids in Western populations. We studied the association of tea intake with aortic atherosclerosis in a general population. METHODS: The present analysis formed part of the Rotterdam Study, a prospective study of men and women 55 years and older. Dietary intakes were assessed at baseline by a trained dietician who used a semiquantitative food frequency questionnaire. Calcified plaques in the abdominal aorta were radiographically detected after 2 to 3 years of follow-up. Aortic atherosclerosis was classified as "mild," "moderate," or "severe," according to the length of the calcified area (<1 cm, 1-5 cm, and >5 cm, respectively). The association of tea intake with severity of aortic atherosclerosis was studied in 3454 subjects who were free of cardiovascular disease at baseline. Data were analyzed by logistic regression, adjusting for age, sex, body mass index (calculated as weight in kilograms divided by the square of height in meters), smoking, education, and intake of alcohol, coffee, vitamin antioxidants, total fat, and total energy. RESULTS: Multivariable analyses showed a significant, inverse association of tea intake with severe aortic atherosclerosis. Odds ratios decreased from 0.54 (95% confidence interval [CI], 0.32-0.92) for drinking 125 to 250 mL (1-2 cups) of tea to 0.31 (CI, 0.16-0.59) for drinking more than 500 mL/d (4 cups per day). The associations were stronger in women than in men. The association of tea intake with mild and moderate atherosclerosis was not statistically significant. CONCLUSION: This study indicates a protective effect of tea drinking against ischemic heart disease.

Arteriosclerosis↗

PubMedDate not supplied

Tea consumption and ovarian cancer risk in a population-based cohort.

BACKGROUND: Substantial evidence from laboratory studies indicates that green and black tea preparations may protect against various cancers. Few epidemiologic studies, however, have examined the relationship specifically between tea consumption and risk of ovarian cancer. METHODS: We prospectively examined the association between tea consumption and risk of ovarian cancer in 61 057 women aged 40 to 76 years who were participants in the population-based Swedish Mammography Cohort. Participants completed a validated 67-item food frequency questionnaire at enrollment between 1987 and 1990 and were followed for cancer incidence through December 2004. RESULTS: During an average follow-up of 15.1 years, 301 incident cases of invasive epithelial ovarian cancer were ascertained. Tea consumption was inversely associated with the risk of ovarian cancer after controlling for potential confounders (P for trend, .03). Compared with women who never or seldom (less than monthly) consumed tea, the multivariate hazard ratios for those who consumed less than 1 cup per day, 1 cup per day, and 2 or more cups per day were 0.82 (95% confidence interval [CI], 0.62-1.08), 0.76 (95% CI, 0.56-1.04), and 0.54 (95% CI, 0.31-0.91), respectively. Each additional cup of tea per day was associated with an 18% lower risk of ovarian cancer (multivariate hazard ratio, 0.82; 95% CI, 0.68-0.99). CONCLUSION: These results suggest that tea consumption is associated with a reduced risk of epithelial ovarian cancer in a dose-response manner.

Adult↗

PubMed1997

Green tea consumption and the risk of pancreatic and colorectal cancers.

The effect of green tea drinking in reducing human cancer risk is unclear, though a protective effect has been reported in numerous animal studies and several epidemiologic investigations. Herein the hypothesis that green tea consumption may reduce the risk of cancers of the colon, rectum and pancreas is examined in a large population-based case-control study conducted in Shanghai, China. Newly diagnosed cancer cases (931 colon, 884 rectum and 451 pancreas) during 1990-1993 among residents 30-74 years of age were included. Controls (n = 1,552) were selected among Shanghai residents and frequency-matched to cases by gender and age. Multivariate odds ratios (ORs) and 95% confidence intervals (CIs) of each cancer associated with green tea consumption were derived after adjustment for age, income, education and cigarette smoking. Additional adjustment for dietary items and body size was found to have minimal impact. An inverse association with each cancer was observed with increasing amount of green tea consumption, with the strongest trends for rectal and pancreatic cancers. For men, compared with non-regular tea drinkers, ORs among those in the highest tea consumption category (> or = 300 g/month) were 0.82 for colon cancer, 0.72 for rectal cancer and 0.63 for pancreatic cancer, with p values for trend being 0.38, 0.04 and 0.04, respectively. For women, the respective ORs for the highest consumption category (> or = 200 g/month) were 0.67, 0.57 and 0.53, with the respective p values for trend being 0.07, 0.001 and 0.008. Our findings provide further evidence that green tea drinking may lower the risk of colorectal and pancreatic cancers.

Adult↗

PubMed1997

Effects of tea and chlorophyllin on the mutagenicity of N-hydroxy-IQ: studies of enzyme inhibition, molecular complex formation, and degradation/scavenging of the active metabolites.

Green tea and black tea inhibit the formation of carcinogen-DNA adducts and colonic aberrant crypts in rats given 2-amino-3-methylimidazo[4, 5-f]quinoline (IQ), a mutagen from cooked meat. The Salmonella mutagenicity assay was used in the present study to test individual constituents of tea as inhibitors of 2-hydroxyamino-3-methylimidazo[4, 5-f]quinoline (N-hydroxy-IQ), a direct-acting metabolite of IQ. Testing of pure compounds at doses relevant to their levels in tea identified epigallocatechin (EGC) and epigalocatechin-3-gallate (EGCG) as the primary antimutagens. Studies of the inhibitory mechanisms established that the rate of degradation of N-hydroxy-IQ under aqueous conditions was not increased significantly in the presence of tea, in contrast to the results obtained with the complexing agent chlorophyllin (CHL), which rapidly degraded the mutagen. Interaction between N-hydroxy-IQ and several tea constituents was detected in spectrophotometric studies, but the binding constants were only on the order of 1 x 10(3) M-1, suggesting that mechanisms other than complex formation might prevail under the conditions of the Salmonella assay. Comparison of the results in two different strains of Salmonella typhimurium, TA98 and TA98/1,8-DNP6, indicated that the antimutagenic activity of EGCG was dependent, at least in part, on a functional O-acetyltransferase activity in the bacteria. These studies suggest that tea constituents inhibit the enzyme(s) which generate the aryl nitrenium ion and directly scavenge the reactive electrophile, whereas CHL complexes with heterocyclic amines and facilitates the degradation of active metabolites.

Antimutagenic Agents↗

PubMed2004

Anti-obesity actions of green tea: possible involvements in modulation of the glucose uptake system and suppression of the adipogenesis-related transcription factors.

To investigate mechanisms of the anti-obesity actions of green tea in vivo, rats were given green tea instead of drinking water for 3 weeks. It was confirmed that green tea reduced adipose tissue weight without any change in body weight, other tissue weights, and food and water intakes. Green tea also significantly reduced the plasma levels of cholesterols and free fatty acids. Certain catechins existed in the plasma at 0.24 microM under our experimental conditions, though most of them existed as conjugated forms. For mechanisms of the anti-obesity actions, green tea significantly reduced glucose uptake accompanied by a decrease in translocation of glucose transporter 4 (GLUT4) in adipose tissue, while it significantly stimulated the glucose uptake with GLUT4 translocation in skeletal muscle. Moreover, green tea suppressed the expression of peroxisome proliferator-activated receptor gamma and the activation of sterol regulatory element binding protein-1 in adipose tissue. In conclusion, green tea modulates the glucose uptake system in adipose tissue and skeletal muscle and suppresses the expression and/or activation of adipogenesis-related transcription factors, as the possible mechanisms of its anti-obesity actions.

Adipose Tissue↗

PubMed2006

Assessment of the polyphenolic composition of the organic extracts of Mauritian black teas: a potential contributor to their antioxidant functions.

There is increasing interest in the emerging view that tea improves the antioxidant status in vivo and thereby helps to lower risk of certain types of cancer, coronary heart disease and stroke and its component biofactors could provide prophylactic potential for these diseases. The polyphenolic composition and the antioxidant properties of organic extracts (acetone/methanol) of Mauritian commercial black teas were evaluated. HPLC data of the individual compounds revealed remarkably high levels (+)-Catechin ((+)-C), (-)-epicatechin ((-)-EC), (-)-epicatechin 3-gallate ((-)-ECG), (-)-epigallocatechin ((-)-EGC), (-)-epigallocatechin 3-gallate ((-)-EGCG) and gallic acid. Analysis of hydrolysed extracts indicated that quercetin was the dominant flavonol aglycone with traces of myricetin and kaempferol. Based on the Ferric Reducing Antioxidant Power (FRAP) and the Trolox Equivalent Antioxidant Capacity (TEAC) assays Extra tea from Bois Chéri exhibited the highest antioxidant potential. Linear regression analyses showed that the antioxidant capacities of the organic extracts are strongly influenced by total phenols (TEAC: r=0.95 and FRAP: r=0.96) and to a lesser extent by total proanthocyanidin and total flavonoid contents. Catechins and gallic acid seem to add up to the overall antioxidant capacity of black tea extracts. The fresh tea leaves had high levels of total phenols, total flavonoids, total proanthocyanidin and exhibited greater antioxidant potential when compared with black teas. Organic extracts of endemic teas represent useful source of phenolic antioxidants supplements for prophylactic use.

Antioxidants↗