Recent studies have demonstrated the effects of green tea polyphenols (GTP) and epigallocatechin-3-gallate (EGCG) on obesity. However, high doses of EGCG have also exhibited cytotoxicity. The aim of this study was to compare total GTP with purified EGCG on cytotoxicity, and to investigate the effects and the molecular mechanism of total GTP and EGCG on adipogenesis. Cytotoxicity was determined by cell viability assay. For the adipogenesis study, 3T3-L1 preadipocytes were incubated with three doses of GTP (1, 10, and 100 μg/ml) and the effect of EGCG (6.8 μg/ml) was compared with 10 μg/ml GTP containing 68% EGCG. Oil Red O staining and triglyceride content assay were carried out 10 days after differentiation and treatment. Adipogenic regulators CCAAT element binding protein α (C/EBPα), peroxisome proliferator-activated receptor gamma (PPARγ) and sterol regulatory element-binding protein-1c (SREBP-1c) were determined by qRT-PCR and immunoblotting. GTP at 1000 μg/ml and EGCG (68 and 680 μg/ml) significantly affected cell viability. Purified EGCG had greater cytotoxicity than corresponding doses of GTP. About 10 μg/ml of GTP showed stronger reduction in triglyceride accumulation than EGCG treatment. Transcriptional factors of C/EBPα, SREBP-1c and PPARγ were markedly decreased in both GTP and EGCG-treated cells and GTP exhibited stronger inhibitory effects on C/EBPα and PPARγ protein expression than EGCG (p < 0.05). In conclusion, total GTP exerted greater inhibitory effects than purified EGCG on adipogenesis through down-regulating the adipogenic factor C/EBPα, SREBP-1c and PPARγ expression. These findings support that a polyphenol mixture is safer and more effective than EGCG alone for preventing obesity and obesity-related chronic diseases.
Keywords: (–)-Epigallocatechin-3-Gallate; 3T3-L1 Preadipocytes, Cytotoxicity; Adipogenesis; Green Tea Polyphenols; Obesity Prevention.