Basic nutritional investigation (-)-Epigallocatechin gallate enhances the expression of genes related to insulin sensitivity and adipocyte differentiation in 3T3-L1 adipocytes at an early stage of differentiation

Objective: (-)-Epigallocatechin gallate (EGCG) is thought to enhance insulin sensitivity in adipocytes, although doses used in in vitro experiments have been shown to promote apoptosis. To explore the effects of EGCG on insulin sensitivity in adipocytes, the expression of genes related to insulin sensitivity and adipocyte differentiation in 3T3-L1 adipocytes were measured in response to low doses of EGCG. Methods: Increasing concentrations of low-dose EGCG were administered for 8 d to differentiating 3T3 adipocytes, either at days 0–8 (early stage) or at days 8–16 (late stage). Fat accumulation and cell activity were measured by Oil Red O staining and 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan assay, respectively. The expression of genes related to insulin sensitivity and adipocyte differentiation was measured by real-time reverse transcriptase–polymerase chain reaction. Results: Fat accumulation and cell activity in 3T3-L1 cells at the early and late stages were reduced at EGCG concentrations � 50 mM. However, EGCG doses of 5–10 mM reduced fat accumulation and induced the expression of genes related to insulin sensitivity (including Fabp4, Cd36, Lpl, Pck1, Acox1, Lypla3, and Ucp2) and adipocyte differentiation (Pparg1, Pparg2, Cebps, and Ppargc1a). These increases were only seen at the early, and not late, stages of differentiation. Conclusion: These data indicate that low doses of EGCG, despite reducing triacylglycerol accumulation, induce the expression of genes related to insulin sensitivity in the early stage of differentiation.