Green tea catechins: inhibitors of glycerol-3-phosphate dehydrogenase.

Green tea catechins, especially (-)-epigallocatechin-3-gallate (EGCG), are known to regulate obesity and fat accumulation. We performed a kinetic analysis in a cell-free system to determine the mode of inhibition of glycerol-3-phosphate dehydrogenase (GPDH; EC 1.1.1.8) by EGCG. GPDH catalyzes the beta-nicotinamide adenine dinucleotide (NADH)-dependent reduction of dihydroxyacetone phosphate (DHAP) to yield glycerol-3-phosphate, which serves as one of the major precursors of triacylglycerols. We found that EGCG dose-dependently inhibited GPDH activity at a concentration of approximately 20 muM for 50 % inhibition. The IC (50) values of other green tea catechins, such as (-)-epicatechin, (-)-epicatechin-3-gallate, and (-)-epigallocatechin, were all above 100 microM. This suggests a catechin type-dependent effect. Based on double-reciprocal plots of the kinetic data, EGCG was a noncompetitive inhibitor of the GPDH substrates, NADH and DHAP, with respective inhibition constants (Ki) of 18 and 31 microM. Results of this study possibly support previous studies that EGCG mediates fat content.

The apoptotic effect of green tea (-)-epigallocatechin gallate on 3T3-L1 preadipocytes depends on the Cdk2 pathway.

This study was designed to investigate the effect of green tea catechins, especially (-)-epigallocatechin gallate (EGCG), on the apoptosis of 3T3-L1 preadipocytes. Preadipocyte apoptosis as indicated by formation of DNA fragments was induced by EGCG in dose-dependent manners. While EGCG was demonstrated to decrease Cdk2 expression and activity and increase caspase-3 activity, overexpression of Cdk2 and treatment with the caspase-3 inhibitor respectively prevented preadipocytes from induction of DNA fragmentation and caspase-3 activity by doses of 100-400 muM of EGCG. This suggests the Cdk2- and caspase-3-dependent apoptotic effects of EGCG. Moreover, EGCG was more effective than EC, ECG, and EGC in changing the apoptotic signals. Results of this study may relate to the mechanism by which EGCG modulates body weight.

Antimitogenic effect of green tea (-)-epigallocatechin gallate on 3T3-L1 preadipocytes depends on the ERK and Cdk2 pathways.

Green tea catechins, especially (-)-epigallocatechin gallate (EGCG), have been proposed as a chemopreventative for obesity, diabetes, cancer, and cardiovascular diseases. However, relatively little is known about the mechanism of the action of EGCG on fat cell function. This study was designed to investigate the pathways of EGCG's modulation of the mitogenesis of 3T3-L1 preadipocytes. Preadipocyte proliferation as indicated by an increased number of cells and greater incorporation of bromodeoxyuridine (BrdU) was inhibited by EGCG in dose-, time-, and growth phase-dependent manners. Also, EGCG dose and time dependently decreased levels of phospho-ERK1/2, Cdk2, and cyclin D(1) proteins, reduced Cdk2 activity, and increased levels of G(0)/G(1) growth arrest, p21(waf/cip), and p27(kip1), but not p18(ink), proteins and their associations to Cdk2. However, neither MEK1, ERK1/2, p38 MAPK, phospho-p38, JNK, nor phospho-JNK was changed. Increased phospho-ERK1/2 content and Cdk2 activity, respectively, via the transfection of MEK1 and Cdk2 cDNA into preadipocytes prevented EGCG from reducing cell numbers. These data demonstrate the ERK- and Cdk2-dependent antimitogenic effects of EGCG. Moreover, EGCG was more effective than epicatechin, epicatechin gallate, and epigallocatechin in changing the mitogenic signals. The signal of EGCG in reducing growth of 3T3-L1 preadipocytes differed from that of 3T3 fibroblasts. Results of this study may relate to the mechanism by which EGCG modulates body weight.