An isocratic HPLC procedure was developed for simultaneous determination of six catechins, gallic acid, and three methylxanthines in tea water extract. A baseline separation was achieved on a Cosmosil C18-MS packed column with a solvent mixture of methanol/doubly distilled water/formic acid (19.5:80.2:0.3, v/v/v) as mobile phase. A gradient HPLC procedure was also provided for the separation of these tea components. The contents of catechins, gallic acid, and methylxanthines have been measured in infusions of a range of green tea, oolong tea, and pu-erh tea products sold and consumed in the China, Japan, and Taiwan. When 15 Chinese green tea and 13 Japanese green tea products were analyzed by the HPLC method, the mean levels of the total catechins, (-)-epigallocatechin 3-gallate, (+)-catechin, and caffeine were found to be very similar in these two groups, but other minor catechins such as (-)-epigallocatechin, (-)-epicatechin, and (-)-gallocatechin 3-gallate were found to be higher in Japanese green tea products, whereas (-)-epicatechin 3-gallate, gallic acid, theophylline, and theobromine were found to be higher in Chinese green tea products. Oolong tea products possessed lower levels of catechins, whereas pu-erh tea products contained negligible amounts of these constituents. The new HPLC method is rapid, reliable, and reproducible and should be highly recommended to tea industries for routine analysis of commercial tea samples.

Black tea is one of the world's most popular beverages, and its health-promoting effects have been intensively investigated. The antiobesity and hypolipidemic effects of black tea have attracted increasing interest, but the mechanisms underlying these phenomena remain unclear. In the present study, the black tea major component theaflavins were assessed for their hepatic lipid-lowering potential when administered in fatty acid overload conditions both in cell culture and in an animal experimental model. We found that theaflavins significantly reduced lipid accumulation, suppressed fatty acid synthesis, and stimulated fatty acid oxidation. Furthermore, theaflavins also inhibited acetyl-coenzyme A carboxylase activities by stimulating AMP-activated protein kinase (AMPK) through the LKB1 and reactive oxygen species pathways. These observations support the idea that AMPK is a critical component of decreased hepatic lipid accumulation by theaflavin treatments. Our results show that theaflavins are bioavailable both in vitro and in vivo and may be active in the prevention of fatty liver and obesity.-Lin, C-L., H-C. Huang, and J-K. Lin. Theaflavins attenuate hepatic lipid accumulation through activating AMPK in human HepG2 cells.

Insulin resistance is the primary characteristic of type 2 diabetes which as a result of insulin signaling defects. It has been suggested that the tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) displays some antidiabetic effects, but the mechanism for EGCG insulin-enhancing effects is incompletely understood. In the present study, the investigations of EGCG on insulin signaling are performed in insulin-responsive human HepG2 cells cotreated with high glucose. We found that the high glucose condition causes significant increasing Ser307 phosphorylation of insulin receptor substrate-1 (IRS-1), leading to reduce insulin-stimulated phosphorylation of Akt. As the results, the insulin metabolic effects of glycogen synthesis and glucose uptake are inhibited by high glucose. However, the treatment of EGCG improves insulin-stimulated downsignaling by reducing IRS-1 Ser307 phosphorylation. Furthermore, we also demonstrated these EGCG effects are essential depends on the 5'-AMP-activated protein kinase (AMPK) activation. Together, our data suggest a putative link between high glucose and insulin resistance in HepG2 cells, and the EGCG treatment attenuates insulin signaling blockade by reducing IRS-1 Ser307 phosphorylation through the AMPK activation pathway.

Dabsyl chloride (dimethylaminoazobenzene sulfonyl chloride), a useful chromophoric labeling reagent for amino acids and amines, was developed in this laboratory in 1975. Although several methods have been developed to determine various types of amino acids, a quick and easy method of determining theanine, GABA, and other amino acids has not been developed in one HPLC system. In this paper are analyzed the free amino acid contents of theanine and GABA in different teas (green tea, black tea, oolong tea, Pu-erh tea, and GABA tea) with a dabsylation and reverse phase high-performance liquid chromatography (HPLC) system coupled with a detector at 425 nm absorbance. Two reverse phase columns, Hypersil GOLD and Zorbax ODS, were used and gave different resolutions of dabsyl amino acids in the gradient elution program. The data suggest that the tea source or the steps of tea-making may contribute to the theanine contents variations. High theanine contents of high-mountain tea were observed in both green tea and oolong tea. Furthermore, the raw (natural fermented) Pu-erh tea contained more theanine than ripe (wet fermented) Pu-erh tea, and the GABA contents in normal teas were generally lower than that in GABA tea.

(-)-Epigallocatechin-3-gallate (EGCG), a major polyphenol in green tea, was shown to have cancer chemopreventive activity. In this study, we examined the antimetastatic effects of EGCG or the combination of EGCG and dacarbazine on B16-F3m melanoma cells in vitro and in vivo. First, the antimetastatic potentials of five green tea catechins were examined by soft agar colony formation assay, and the results show that EGCG was more effective than the other catechins in inhibiting soft agar colony formation. Second, EGCG dose-dependently inhibited B16-F3m cell migration and invasion by in vitro Transwell assay. Third, EGCG significantly inhibited the spread of B16-F3m cells on fibronectin, laminin, collagen, and Matrigel in a dose-dependent manner. In addition, EGCG significantly inhibited the tyrosine phosphorylation of focal adhesion kinase (FAK) and the activity of matrix metalloproteinase-9 (MMP-9). In animal experiments, EGCG alone reduced lung metastases in mice bearing B16-F3m melanomas. However, a combination of EGCG and dacarbazine was more effective than EGCG alone in reducing the number of pulmonary metastases and primary tumor growths, and increased the survival rate of melanoma-bearing mice. These results demonstrate that combination treatment with EGCG and dacarbazine strongly inhibits melanoma growth and metastasis, and the action mechanisms of EGCG are associated with the inhibition of cell spreading, cell-extracellular matrix and cell-cell interactions, MMP-9 and FAK activities.