ß-Carotene accumulation in 3T3-L1 adipocytes inhibits the elevation of reactive oxygen species and the suppression of genes related to insulin sensitivity induced by tumor necrosis factor-α.

OBJECTIVE: ß-Carotene is an abundant carotenoid with potent antioxidative activities and accumulates in adipose tissue. However, its physiologic functions are poorly understood. In this study, we examined whether accumulation of ß-carotene for 4 d in insulin-resistant 3T3-L1 adipocytes alters the expression of genes related to insulin sensitivity. METHODS: The 3T3-L1 adipocytes were treated with/without 10 or 20 µM ß-carotene during differentiation for 4 d. The cells treated with 10 µM ß-carotene for 4 d were subsequently incubated with/without 5 ng/mL of tumor necrosis factor-α for 48 h in the medium without ß-carotene. The mRNA levels of genes in the cells and adiponectin protein levels in the medium were determined by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Reactive oxygen species levels in the cells were assessed by oxidation of 2',7'-dichlorodihydrofluorescein diacetate. RESULT: ß-Carotene treatment at a concentration of 20 µM, but not 10 µM, in 3T3-L1 adipocytes during differentiation for 4 d enhanced the expression of genes related to insulin sensitivity, including adiponectin, adipocyte lipid-binding protein, glucose transporter-4, peroxisome proliferator-activated receptor-γ2, and adiponectin protein in the medium. Tumor necrosis factor-α treatment repressed the expression of these genes and adiponectin protein in the medium and induced reactive oxygen species levels. In contrast, cells that accumulated ß-carotene at a concentration of 10 µM did not show these alterations. CONCLUSION: The accumulation of the ß-carotene in 3T3-L1 adipocytes restores the expression of genes related to insulin sensitivity and reactive oxygen species levels in insulin-resistant adipocytes.

(-)-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 > or = 50 microM. However, EGCG doses of 5-10 microM 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.