Research Database

Author: Toshihiro MUKAI and Hideki HORIE and Tetsuhisa GOTO

Sixty one green tea samples with price ranging from 560 to 12, 000 yen/kg were collected and the contents of total nitrogen and individual free amino acids were determined. There was no difference in their glutamic acid contents between samples, however theanine, glutamine and arginine contents varied significantly depending on the price of green tea. Among the higher price teas, glutamine was more than glutamic acid, while in lower price teas it was the reverse. Among low and middle price teas, the price corelated to total nitrogen content, while teas with high price, no corelation was observed. Therefore, it seemed to be impossible to estimate the quality of high price tea from the total nitrogen content. The higher correlation was observed between price and the content of total free amino acids for wide price range, indicating this might be better indicator for the estimation of the quality of green tea. Among the seventeen amino acids determined in the present study, arginine and theanine showed the highest correlation between their contents and the price of green tea.

 

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Author: Yamada T and Terashima T and Wada K and Ueda S and Ito M and Okubo T and Juneja LR and Yokogoshi H

Theanine (r-glutamylethylamide) is one of the major amino acid components in green tea. Recent studies suggest that theanine affects neurotransmission, especially inhibitory neurotransmission. In this study, we investigated whether theanine affects brain development in infant rats, because inhibitory neurotransmission is required for mature brain function. Mother rats were fed theanine ad libitum after confinement. The body weight gain rate of infants was not different from control infants. We detected theanine in the infant serum and measured neurotransmitter concentration and nerve growth factor (NGF) mRNA level in the infant rat brain. Some neurotransmitters, including dopamine, serotonin, glycine and GABA concentration, increased in the infant brain and NGF mRNA level increased in the cerebral cortex and hippocampus. However, these differences were lost by the end of nerve maturity. These results suggest that theanine enhanced synthesis of nerve growth factor and neurotransmitters during a nerve maturing period and promoted central nerve system maturation (CNS). Thus, theanine accelerated maturation. In conclusion, theanine may assist in healthy brain function development.

 

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Author: Sanjay Gupta and Nihal Ahmad and Anna-Liisa Nieminen and Hasan Mukhtar

Prostate cancer (PCA) is the most prevalent cancer diagnosed and the second leading cause of cancer-related deaths among men in the United States. Descriptive epidemiological data suggest that androgens and environmental exposures play a key role in prostatic carcinogenesis. Since androgen action is intimately associated with proliferation and differentiation, at the time of clinical diagnosis in humans most PCA represent themselves as a mixture of androgen-sensitive and androgen-insensitive cells. Androgen-sensitive cells undergo rapid apoptosis upon androgen withdrawal. On the other hand, the androgen-insensitive cells do not undergo apoptosis upon androgen blocking, but maintain the molecular machinery of apoptosis. Thus, agents capable of inhibiting growth and/or inducing apoptosis in both androgen-sensitive and androgen-insensitive cells will be useful for the management of PCA. In the present study, we show that (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent present in green tea, imparts antiproliferative effects against both androgen-sensitive and androgen-insensitive human PCA cells, and this effect is mediated by deregulation in cell cycle and induction of apoptosis. EGCG treatment was found to result in a dose-dependent inhibition of cell growth in both androgen-insensitive DU145 and androgen-sensitive LNCaP cells. In both the cell types, EGCG treatment also resulted in a dose-dependent G0/G1-phase arrest of the cell cycle as observed by DNA cell-cycle analysis. As evident by DNA ladder assay, confocal microscopy, and flow cytometry, the treatment of both DU145 and LNCaP cells with EGCG resulted in a dose-dependent apoptosis. Western blot analysis revealed that EGCG treatment resulted in (i) a dose-dependent increase of p53 in LNCaP cells (carrying wild-type p53), but not in DU145 cells (carrying mutant p53), and (ii) induction of cyclin kinase inhibitor WAF1/p21 in both cell types. These results suggest that EGCG negatively modulates PCA cell growth, by affecting mitogenesis as well as inducing apoptosis, in cell-type-specific manner which may be mediated by WAF1/p21-caused G0/G1-phase cell-cycle arrest, irrespective of the androgen association or p53 status of the cells.

 

 

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Author: Mauro Serafini and João A.N Laranjinha and Leonor M Almeida and G Maiani

Mounting evidence shows that phenol-rich beverages exert strong antioxidant activity. However, in vivo evidence has produced conflicting results. In the present study, we studied the impact of the ingestion of 300 mL of black and green tea, alcohol-free red wine, alcohol-free white wine, or water on plasma total antioxidant capacity in five healthy volunteers. Red wine has the highest content of phenolics (3.63 ± 0.48 g QE/L), followed by green tea (2.82 ± 0.07 g QE/L), black tea (1.37 ± 0.15 g QE/L), and white wine (0.31 ± 0.01 g QE/L). Plasma total antioxidant capacity values of subjects who drank green tea rose at 30 min (P < 0.05). After black tea and red wine ingestion, the peaks were at 50 min (P < 0.05 and P < 0.01, respectively). No changes were observed in the control and white wine groups. Red wine and green tea were the most efficient in protecting low density lipoprotein from oxidation driven by peroxyl and ferril radicals, respectively. Phenol-rich beverages are a natural source of antioxidants; however, the phenolic content alone cannot be considered an index of their in vivo antioxidant activity.

 

 

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Author: Susanne N Williams and Hsueh Shih and Denis K Guenette and William Brackney and Michael S Denison and George V Pickwell and Linda C Quattrochi

Green tea possesses significant anticancer activity in numerous experimental animal models, including demonstrated protection against aryl hydrocarbon induced cancers. The aryl hydrocarbon receptor (AhR) mediates the transcriptional activation of CYP1A1 and CYP1A2. In the present study, we investigated the effects of commercially available green tea extracts (GTEs) and individual tea catechins on the function of the AhR and on CYP1A gene expression in human hepatoma HepG2 cells and primary cultures of human hepatocytes. GTEs inhibited the transcription of a human CYP1A1 promoter-driven reporter gene induced by the AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a concentration-dependent manner and inhibited the induced accumulation of both CYP1A1 and CYP1A2 mRNAs. GTEs blocked TCDD-induced binding of the AhR to DNA in HepG2 cells and in vitro in isolated hepatic cytosol. To determine if the observed effects were due to a single green tea component, we examined the four major catechins present in GTEs. Only (-)-epigallocatechin gallate (EGCG), the most abundant catechin in green tea, was able to inhibit TCDD-induced binding of the AhR to DNA and subsequent CYP1A transcription, however EGCG alone was less effective than GTEs. We next examined GTEs and catechins for AhR agonist activity. GTEs caused a concentration-dependent increase in CYP1A1-promoter driven reporter gene activity and caused accumulation of CYP1A1 mRNA and protein, but we found that individual catechins were unable to induce the expression of CYP1A1. Our results demonstrate that GTEs as a whole exert mixed agonist/antagonist activity on the AhR, while EGCG functions as a strict AhR antagonist. Therefore, modulation of human CYP1A expression by green tea extracts can not be attributed to the action of a single tea catechin, but rather is due to the effects of a complex mixture. These findings may be useful in future studies concerning green tea as a cancer preventive agent.

 

 

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Author: Yukiko Miura and Tsuyoshi Chiba and Shinji Miura and Isao Tomita and Keizo Umegaki and Masahiko Ikeda and Takako Tomita

Oxidation of low density lipoprotein (LDL) plays crucial roles in atherogenesis. We previously reported that green tea polyphenols (flavan 3-ols), especially epigallocatechingallate (EGCg) and epicatechingallate, exerted potent inhibitory effects on LDL oxidation in vitro. To examine whether intake of green tea polyphenols renders LDL resistant to ex vivo oxidation in humans, 22 male volunteers aged between 22 and 32 years were recruited and assigned the same dietary regimen for 2 weeks. After a 1-week baseline period, they were equally divided into two groups: control and tea. The tea group ingested 300 mg of green tea polyphenol extract twice daily for 1 week. Plasma EGCg concentration at the end of the experiment was 56 nmol/L on average (56% in free form) in the tea group; no EGCg was detected before the experiment. Plasma concentrations of lipids, ascorbate, α-tocopherol, and lipid peroxides did not change before and after the experiment in either group, but β-carotene was higher in the tea group (P< 0.01 by paired Student’st-test). LDL (0.1 mg/mL) was incubated with 5 μM Cu2+ and the oxidation was measured by absorbance at 234 nm. The lag time was significantly prolonged by 13.7 min in the tea group (P < 0.05 by paired Student’st-test, before versus after), whereas such a change was not observed in the control group. These results suggest that daily consumption of seven to eight cups (approximately 100 mL each cup) of green tea may increase resistance of LDL to in vivo oxidation, leading to reduction in the risk of cardiovascular diseases.

 

 

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Author: C.A. Bursill and P.D. Roach

 

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Author: Tohru Hasegawa

 

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Author: Tomoi Sato and Go Miyata

 

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Author: C.A. Bursill and M. Abbey and P.D. Roach

 

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