Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Tea”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed1979

Mutagens in coffee and tea.

Coffee prepared in the usual way for drinking contains a substance(s) that is mutagenic to Salmonella typhimurium TA100 without mammalian microsomal enzymes. One cup of coffee (200 ml) contains mutagen(s) inducing 1.4-4.6 X 10(5) revertants under standard conditions. Instant coffee too is mutagenic to TA100 and one cup of instant coffee prepared from 1 g of coffee powder and 200 ml of water induced 5.6-5.8 X 10(4) revertants of TA100. Caffeine-free instant coffee also has similar mutagenicity. Addition of microsomal enzymes abolished the mutagenicity. Black tea, green tea and Japanese roasted tea were also mutagenic to TA100 without S9 mix and one cup of these teas prepared in the ordinary way produced 1.7-3.8 X 10(4) revertants of TA100. Black tea and green tea were also mutagenic to TA98 in the presence of S9 mix after treatment with a glycosidase from Aspergillus niger, hesperidinase. This type of mutagen in one cup of black tea induced 2.4 X 10(5) revertants of TA98.

Coffee↗
PubMed1987

Implication of active oxygen species in the direct-acting mutagenicity of tea.

The present study shows that the L-arabinose resistance test with Salmonella typhimurium detects that freshly infused tea is highly mutagenic in the absence of mammalian microsomal activation. Both the mutagenesis protocol (preincubation test) and the additional genetic characteristics of the bacterial tester strain (excision repair deficiency, normal lipopolysaccharide barrier and the presence of plasmid pKM101) were critical factors in the optimal induction by tea of forward mutations to L-arabinose resistance. The TA104 strain--a histidine auxotroph specific to oxidative mutagens--was the most sensitive tester strain of the Ames test to the direct-acting mutagenicity of tea. In comparison with strain TA104, the sensitivity of the Ara forward mutation test was 18 times higher, one cup of tea (200 ml) inducing 3 X 10(6) AraR mutants. More than 90% of the mutagenicity of 150 microliter of a fresh tea infusion, or that of the equivalent amount (1.32 mg) of the corresponding lyophilized residue, was suppressed by 10 units of catalase. In contrast to catalase, superoxide dismutase was rather ineffective. These results indicate that hydrogen peroxide is produced in tea solutions, playing an essential role in its mutagenicity. In comparison, the role of superoxide anion seems negligible. Like catalase, the chelating agent DETAPAC showed a protective effect with respect to the mutagenicity of tea, suggesting the additional implication of hydroxyl radicals.

Arabinose↗
PubMed2004

Pathogen growth in herbal teas used in clinical settings: a possible source of nosocomial infection?

In some clinical settings, herbal tea is used in patient care (eg, for oral hygiene). Teabags containing herbal tea were therefore tested with regard to the presence of microbial contamination before and after brewing. In addition, pathogen growth in intentionally contaminated brewed tea was investigated over time. Teabags and brewed tea were highly contaminated (maximum mean values of 1.9 x 10(8) CFU/g raw tea), and it was found that the pathogen load of intentionally contaminated tea increased significantly (by a maximum of 10(5) colony-forming units/mL brewed tea) over time, suggesting a possible risk of patients developing a nosocomial infection when used in patient care.

Bacteria↗
PubMed2004

Black tea increases coronary flow velocity reserve in healthy male subjects.

Epidemiologic studies suggest that tea consumption decreases the risk for cardiovascular events. However, there has been no clinical report examining the effects of tea consumption on coronary circulation. The purpose of this study was to evaluate the effects of black tea on coronary flow velocity reserve (CFVR) using transthoracic Doppler echocardiography (TTDE). This was a double-blind crossover study of 10 healthy male volunteers conducted to compare the effects of black tea and caffeine on coronary circulation. The coronary flow velocity of the left anterior descending coronary artery was measured at baseline and at hyperemia during adenosine triphosphate infusion by TTDE to determine CFVR. The CFVR ratio was defined as the ratio of CFVR after beverage consumption to CFVR before beverage consumption. All data were divided into 2 groups according to beverage type: group T (black tea) and group C (caffeine). Two-way analysis of variance showed a significant group effect and interaction in CFVR before and after beverage consumption (p = 0.001). CFVR significantly increased after tea consumption in group T (4.5 +/- 0.9 vs 5.2 +/- 0.9, p <0.0001). The CFVR ratio of group T was larger than that of group C (1.18 +/- 0.07 vs 1.04 +/- 0.08, p = 0.002). Acute black tea consumption improves coronary vessel function, as determined by CFVR.

Adult↗
PubMed2004

New dibenzotropolone derivatives characterized from black tea using LC/MS/MS.

Theaflavins and thearubigins are major pigments in black tea, and it is generally accepted that they are produced by oxidation of flavan-3-ols (catechins) during tea fermentation. In the course of studies on the oxidation mechanism of tea polyphenols, especially the formation of thearubigins, a method combining the enzymatic synthesis and LC/ESI-MS/MS analysis was developed to search for new higher molecular weight polymers from black tea. Three new dibenzotropolones, theadibenzotropolone A, B, and C, together with one new tribenzotropolone, theatribenzotropolone A, were formed by the reaction of theaflavins and tea catechins with horseradish peroxidase in the presence of H(2)O(2). The structures of these new benzotropolone derivatives were elucidated on the basis of MS and 2D NMR spectroscopic analyses. The existence of these compounds in black tea was characterized by LC/ESI-MS/MS. Theadibenzotropolone A and B were the first benzotropolone-type trimers of catechins found in the black tea extract. The observation that galloyl ester groups of theaflavins can be oxidized to form di- or tri-benzotropolone skeletons strongly implied that this type of oxidation is an important pathway to extend the molecular size of thearubigins.

Biflavonoids↗
PubMed2005

Protective effects of black tea extract on testosterone induced oxidative damage in prostate.

Since ancient times, antipyretic, anti-inflammatory, antimicrobial and antioxidative properties of tea have been recognized. Black tea (Camellia sinensis) contains a variety of polyphenolic ingredients including the theaflavins (TF), thearubigins (TG) and catechins. Components from black tea have been accounted to play an important role in scavenging free radicals generated by mutagens and carcinogens. Androgens are the key factors in either the initiation or progression of prostate cancer (PCA) by inducing oxidative stress. In the present set of investigations, the antioxidative potential of black tea extract against androgen mediated oxidative stress in male Wistar rats has been studied. Testosterone was given at a dose of 5 mg/kg b.w. subcutaneously, consecutively for 5 days. Prior to androgen administration, animals were kept on 0.5, 1.0 and 1.5% aqueous tea extract (ATE) as sole source of drinking fluid for 15 days. The prostate tissue was dissected out for biochemical analysis for antioxidant enzymes viz. catalase (CAT), superoxide dismutase (SOD), lipid peroxidation (LPO), glutathione-s-transferase (GST) and glutathione reductase (GR). The results revealed that testosterone administration induced the oxidative stress in rat prostate, however, in 0.5, 1.0 and 1.5% ATE supplemented groups, a significant protective effect of black tea against testosterone induced oxidative injury was recorded. Hence, the study reveals that constituents present in black tea impart protection against androgen induced oxidative injury that may result in development of prostate cancer.

Animals↗
PubMed2005

Induction of apoptosis in human leukemia cells by black tea and its polyphenol theaflavin.

Treatment of human leukemic cell lines HL-60 and K-562 with extracts of green and black tea and their polyphenols epigallocatechin gallate and theaflavins, respectively, showed a dose dependent inhibition of growth as a result of cytotoxicity and suppression of cell proliferation. Based on the IC50 values obtained from cytotoxicity data it was clearly evident that black tea was as efficient as green tea. Analysis of polyphenol contents of tea extracts revealed that not only epigallocatechin gallate, which is a predominant polyphenol of green tea, but also theaflavin that is abundantly present in black tea affords significant chemotherapeutic action by imparting cytotoxicity to human leukemic cells. Electrophoretic analysis of fragmented DNA from treated cells displayed characteristic ladder pattern. Flow cytometric analysis revealed the dose dependent increase in sub-G1 peak. These criteria confirmed that cytotoxic activity of green and black tea was due to induction of apoptosis. Such induction was found to be mediated through activation of caspases 3 and 8, particularly caspase 3 and by altering apoptosis related genes as evident by down-regulation of Bcl-2 and up-regulation of Bax proteins.

Antioxidants↗
PubMed2004

Impairment of sodium pump and Na/H exchanger in erythrocytes from non-insulin dependent diabetes mellitus patients: effect of tea catechins.

BACKGROUND: Tea catechins (EGCG, EGC, ECG and EC) possess many important biological properties. We evaluated the effect of tea catechins on erythrocyte membrane Na(+)/K(+)-ATPase and sodium/hydrogen exchanger (NHE) activity in normal (control) and NIDDM subjects. METHODS: Erythrocyte membrane Na(+)/K(+)-ATPase and NHE activity were determined in normal and non-insulin dependent diabetes mellitus (NIDDM) patients. In vitro effect of tea catechins was studied by incubating membrane/intact erythrocytes in assay medium prior to Na(+)/K(+)-ATPase/NHE activity determination. RESULTS: A 24.2% decrease in the activity of Na(+)/K(+)-ATPase (p<0.001) and 39.37% increase in activity of NHE (p<0.02) were observed in NIDDM subjects compared to normal. Tea catechins inhibited the activity of Na(+)/K(+)-ATPase and NHE in both normal and NIDDM erythrocytes, the effect was concentration-dependent. The inhibitory effect of EGCG and ECG at micromolar concentrations was greater compared to EGC and EC on Na(+)/K(+)-ATPase. On NHE the inhibition of tea catechins was in the order: EC>EGC>ECG>EGCG at concentrations up to 10 micromol/l. CONCLUSIONS: This data may help to explain the anti-carcinogenic and cardioprotective effects of tea catechins. The effect of tea catechins on Na(+)/K(+)-ATPase and NHE may be explained due to a direct effect of these compounds on plasma membrane leading to a change in membrane fluidity.

Catechin↗
PubMed2005

Long-term effects of green tea ingestion on atherosclerotic biological markers in smokers.

OBJECTIVES: Smoking is a risk factor for coronary artery disease and triggers vascular injury by platelet aggregation and induces atherosclerosis through induction of oxidative stress. Green tea is known to have antioxidant capacity and anti-platelet activity. DESIGN AND METHODS: Twenty adult male smokers ingested 600 mL of green tea for 4 weeks. Their lipid profile, C-reactive protein (CRP), total antioxidant capacity, oxidized LDL, soluble VCAM-1, soluble ICAM-1, and soluble P-selectin were measured at baseline and 2 and 4 weeks after green tea ingestion. RESULTS: Plasma soluble P-selectin (sP-selectin) levels decreased significantly after 2 and 4 weeks of green tea ingestion compared with those before green tea ingestion (P < 0.001). Plasma concentrations of oxidized LDL decreased significantly after green tea ingestion (P < 0.05). CONCLUSIONS: The results of this study suggest the effect of green tea on sP-selectin and oxidized LDL.

Adult↗
PubMed2004

Pharmacological effects of green tea on the gastrointestinal system.

Green tea is rich in polyphenolic compounds, with catechins as its major component. Studies have shown that catechins possess diverse pharmacological properties that include anti-oxidative, anti-inflammatory, anti-carcinogenic, anti-arteriosclerotic and anti-bacterial effects. In the gastrointestinal tract, green tea was found to activate intracellular antioxidants, inhibit procarcinogen formation, suppress angiogenesis and cancer cell proliferation. Studies on the preventive effect of green tea in esophageal cancer have produced inconsistent results; however, inverse relationships of tea consumption with cancers of the stomach and colon have been widely reported. Green tea is effective to prevent dental caries and reduce cholesterols and lipids absorption in the gastrointestinal tract, thus benefits subjects with cardiovascular disorders. As tea catechins are well absorbed in the gastrointestinal tract and they interact synergistically in their disease-modifying actions, thus drinking unfractionated green tea is the most simple and beneficial way to prevent gastrointestinal disorders.

Anticarcinogenic Agents↗
PubMed2005

The ability of fruit teas to remove the smear layer: an in vitro study of tubule patency.

OBJECTIVES: Fruit teas are know to have an erosive effect on enamel, but the effects on dentine are unknown. Lesions of dentine hypersensitivity have numerous patent dentinal tubules and the aim of this paper was to examine the ability of various fruit teas to remove the smear layer. METHODS: The erosive potential of a variety of fruit teas was assessed in the laboratory by measuring their pH and neutralisable acidity. Smeared dentine specimens were prepared from extracted teeth and the ability of each tea to remove the smear layer was assessed by measuring the diameter and area of the opened tubules and counting the number of patent tubules seen in a unit area using scanning electron microscopy. A 0.2% citric acid solution was used as a positive control. RESULTS: The pH of the fruit teas ranged from 2.98 to 3.95 and the neutralisable acidity ranged from 10.63 to 33.0 ml of 0.1 M NaOH. All the fruit teas tested were able to remove the smear layer. The mean diameter of the tubules ranged from 0.61 to 1.14 microm and the mean area ranged from 0.31 to 1.03 microm2. The number of patent tubules per specimen ranged from 13 to 121. CONCLUSION: All the fruit teas tested were found to be highly acidic and able to remove the smear layer.

Dental Enamel↗
PubMed2004

A randomized, controlled trial of tea tree topical preparations versus a standard topical regimen for the clearance of MRSA colonization.

Two topical MRSA eradication regimes were compared in hospital patients: a standard treatment included mupirocin 2% nasal ointment, chlorhexidine gluconate 4% soap, silver sulfadiazine 1% cream versus a tea tree oil regimen, which included tea tree 10% cream, tea tree 5% body wash, both given for five days. One hundred and fourteen patients received standard treatment and 56 (49%) were cleared of MRSA carriage. One hundred and ten received tea tree oil regimen and 46 (41%) were cleared. There was no significant difference between treatment regimens (Fisher's exact test; P = 0.0286). Mupirocin was significantly more effective at clearing nasal carriage (78%) than tea tree cream (47%; P = 0.0001) but tea tree treatment was more effective than chlorhexidine or silver sulfadiazine at clearing superficial skin sites and skin lesions. The tea tree preparations were effective, safe and well tolerated and could be considered in regimens for eradication of MRSA carriage.

Administration, Topical↗
PubMed2003

Green tea reduces body fat accretion caused by high-fat diet in rats through beta-adrenoceptor activation of thermogenesis in brown adipose tissue.

The aim of the present study was to investigate body fat-suppressive effects of green tea in rats fed on a high-fat diet and to determine whether the effect is associated with beta-adrenoceptor activation of thermogenesis in brown adipose tissue. Feeding a high-fat diet containing water extract of green tea at the concentration of 20g/kg diet prevented the increase in body fat gain caused by high-fat diet without affecting energy intake. Energy expenditure was increased by green tea extract which was associated with an increase in protein content of interscapular brown adipose tissue. The simultaneous administration of the beta-adrenoceptor antagonist propranolol(500 mg/kg diet) inhibited the body fat-suppressive effect of green tea extract. Propranolol also prevented the increase in protein content of interscapular brown adipose tissue caused by green tea extract. Digestibility was slightly reduced by green tea extract and this effect was not affected by propranolol. Therefore it appeared that green tea exerts potent body fat-suppressive effects in rats fed on a high-fat diet and the effect was resulted in part from reduction in digestibility and to much greater extent from increase in brown adipose tissue thermogenesis through beta-adrenoceptor activation.

Adipose Tissue↗
PubMed2006

Effect of tea catechins on mitochondrial DNA 4977-bp deletions in human leucocytes.

The catechins in green tea have antioxidative and antimutagenic effects. We examined the effect of green tea enriched with catechins on the presence of mitochondrial DNA (mtDNA) with a common 4977-bp deletion mutation (mtDNA4977) in human leucocytes. Ten healthy females [aged 20.80 +/- 1.03 years] drank 350 ml of catechin-rich tea daily after supper for 5 weeks. Blood samples were collected twice before, and twice after 5 weeks of consuming the tea. Deletions in mtDNA were analyzed using the nested polymerase chain reaction (PCR). We identified a common mtDNA4977 deletion in nine participants before drinking the tea. However, this mtDNA4977 deletion was not evident in leucocytes from most of the participants 5 weeks after drinking the tea. Catechins found in tea might contribute to the maintenance of health status by reducing damage to mtDNA and by maintaining the capacity of mtDNA for oxidative phosphorylation.

Adult↗
PubMed2005

Preventive action of green tea from changes in the liver antioxidant abilities of different aged rats intoxicated with ethanol.

OBJECTIVE: The present study investigated the influence of green tea as a source of water-soluble antioxidants on the liver antioxidant potential of different aged rats chronically intoxicated with ethanol. METHODS: Rats (2, 12, and 24 mo old) were fed for 5 wk on a control or an ethanol Lieber-DeCarli diet with and without green tea (7 g/L). The activity and level of enzymatic and non-enzymatic antioxidants and the level of markers of protein and lipid oxidation in the liver of rats were examined. RESULTS: The activities of superoxide dismutase and catalase and levels of vitamins C, E, A, and beta-carotene were significantly decreased, whereas activities of glutathione peroxidase and glutathione reductase and the level of reduced glutathione significantly increased during aging. The ethanol diet caused a significant decrease in activity of antioxidant enzymes and in the level of non-enzymatic antioxidants tested. Administration of green tea to ethanol-treated rats of different ages partly normalized the activity of enzymes and the level of non-enzymatic antioxidants. Changes in antioxidant ability observed during aging were accompanied by increased levels of markers of lipid and protein modifications that also were intensified by ethanol. Green tea caused a decrease in lipid and protein oxidation in aged and ethanol-treated rats. The protective effect of green tea was confirmed by the significantly lower activity of biomarkers of liver damage (alanine and aspartate aminotransferases) in the serum of rats that received green tea with ethanol compared with rats from the control ethanol group. CONCLUSIONS: The use of green tea appears to be beneficial to rat liver by decreasing oxidative stress caused by ethanol and/or aging.

Age Factors↗
PubMed1999

Cancer chemoprevention by tea polyphenols through mitotic signal transduction blockade.

Tea is a popular beverage. The consumption of green tea is associated with a lower risk of several types of cancer, including stomach, esophagus, and lung. The cancer chemopreventive effect of tea has been attributed to its major phytopolyphenols. The tea polyphenols comprise about one-third of the weight of the dried leaf, and they show profound biochemical and pharmacological activities including antioxidant activities, modulation of carcinogen metabolism, inhibition of cell proliferation, induction of cell apoptosis, and cell cycle arrest. They intervene in the biochemical and molecular processes of multistep carcinogenesis, comprising tumor initiation, promotion, and progression. Several studies demonstrate that most tea polyphenols exert their scavenging effects against reactive oxygen species (ROS); excessive production of ROS has been implicated for the development of cardiovascular diseases, neurodegenerative disorders, and cancer. Recently, we have found that the major tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) suppresses extracellular signals and cell proliferation through epidermal growth factor receptor binding in human A431 epidermoid carcinoma cells; EGCG also blocks the induction of nitric oxide synthase by down-regulating lipopolysaccharide-induced activity of the transcription factor NFKB in macrophages. Furthermore, EGCG blocks the cell cycle at the G1 phase in MCF-7 cells. We have demonstrated that EGCG inhibits the activities of cyclin-dependent kinases 2 and 4; meanwhile, EGCG induces the expression of the Cdk inhibitors p21 and p27. These results suggest that tumor promotion can be enhanced by ROS and oxidative mitotic signal transduction, and this enhancement can be suppressed by EGCG or other tea polyphenols.

Cell Transformation, Neoplastic↗
PubMed1996

Inhibition of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) mutagenicity by black and green tea extracts and polyphenols.

Solutions of lyophilized preparations of standard black and green tea extracts were made and tested over a range of six concentrations as inhibitors of the mutagenicity caused by the fool mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the Salmonella typhimurium TA98 assay containing S9 fraction from rats induced with alpha-naphthoflavone and phenobarbital. Extracts of both black and green tea were equally good inhibitors of mutagenicity. Purified polyphenols were prepared from tea extracts by solvent extraction. The polyphenols of black tea were more potent inhibitors of mutagenicity than the polyphenols of green tea. These findings suggest that black tea may have similar health-promoting properties to those reported previously for green tea.

Animals↗
PubMed2001

Antimutagenic effect of black tea extract using 'rodent dominant lethal mutation assay'.

The antimutagenic effect of black tea extract has been evaluated with the 'Dominant Lethal Assay' in Swiss albino mice using benzo[a]pyrene [BaP] as a mutagen. BaP was given through the intraperitoneal (i.p.) route at a single dose of 100 mg/kg b.w. to male mice once only. The animals were given 1, 2 and 4% aqueous solution of black tea as sole source of drinking solution prior to BaP. The pregnant females were analyzed for living implants, pre- and post-implantation losses. The results revealed that during mating weeks, BaP caused a reduction in implants and an increase in pre- and post-implantation losses. The protective effect of tea solution on BaP-induced mutagenicity was observed. The number of living implants increased and dead implants decreased significantly in the animals kept on 2 and 4% tea solution. The increase in dominant lethal mutation rate by BaP was inhibited by black tea extract. Four percent tea solution alone did not produce dominant lethality, and reveals that it is non-toxic/non-mutagenic to sperm. Hence the study suggests that tea has a protective effect against BaP-induced genetic damage to germ cells in Swiss albino mice.

Animals↗