Cyanidin 3-glucoside protects 3T3-L1 adipocytes against H2O2- or TNF-α-induced insulin resistance by inhibiting c-Jun NH2-terminal kinase activation

Anthocyanins are naturally occurring plant pigments and exhibit an array of pharmacological properties. Our previous study showed that black rice pigment extract rich in anthocyanin prevents and ameliorates high - fructose -induced insulin resistance in rats. In present study, cyanidin 3-glucoside (Cy-3-G), a typical anthocyanin most abundant in black rice was used to examine its protective effect on insulin sensitivity in 3T3-L1 adipocytes exposed to H2O2 (generated by adding glucose oxidase to the medium) or tumor necrosis factor alpha (TNF-alpha). Twelve-hour exposure of 3T3-L1 adipocytes to H2O2 or TNF-alpha resulted in the increase of c-Jun NH2-terminal kinase (JNK) activation and insulin receptor substrate 1 (IRS1) serine 307 phosphorylation, concomitantly with the decrease in insulin-stimulated IRS1 tyrosine phosphorylation and cellular glucose uptake. Blocking JNK expression using RNA interference efficiently prevented the H2O2- or TNF-alpha-induced defects in insulin action. Pretreatment of cells with Cy-3-G reduced the intracellular production of reactive oxygen species, the activation of JNK, and attenuated H2O2- or TNF-alpha-induced insulin resistance in a dose-dependent manner. In parallel, N-acetyl-cysteine, an antioxidant compound, did not exhibit an attenuation of TNF-alpha-induced insulin resistance. Taken together, these results indicated that Cy-3-G exerts a protective role against H2O2- or TNF-alpha-induced insulin resistance in 3T3-L1 adipocytes by inhibiting the JNK signal pathway. (c) 2007 Elsevier Inc. All rights reserved.