(-) Epigallocatechin gallate suppresses the differentiation of 3T3-L1 preadipocytes through transcription factors FoxO1 and SREBP1c.

Tea catechin is one of the compounds that are closely related to obesity and insulin sensitivity. In order to determine the effect of catechin on adipocyte differentiation, we treated 3T3-L1 preadipocytes with different kinds of catechins. Our results showed that catechins, especially epigallocatechin gallate (EGCG), significantly reduced intracellular lipid accumulation and repressed the activity of glycerol-3-phosphate dehydrogenase, an enzyme involved in lipid synthesis. Furthermore, glucose and fatty acid transport were also suppressed by catechin. We then analyzed the activity of transcription factors-forkhead transcription factor class O1 (FoxO1) and sterol regulatory element-binding protein-1c (SREBP1c)-which are involved in adipocyte differentiation and lipid synthesis, respectively. The transcriptional activities of both these factors significantly decreased by EGCG. Western blot analysis revealed that EGCG induced the insulin signal-mediated phosphorylation of FoxO1 (Thr24, Ser256). These results suggest that EGCG suppresses the differentiation of adipocytes through the inactivation of FoxO1 and SREBP1c.