Berberine modulates insulin signaling transduction in insulin-resistant cells

Berberine has been shown to have insulin-sensitizing effect, but the molecular mechanism underlying remains elusive. In this work, we investigated the effect of berberine on insulin-induced signal transduction and glucose uptake in both insulin-sensitive and insulin-resistant rat skeletal muscle cells. Berberine increased the activity of AMPK and PKC zeta and AS 160 phosphorylation in normal cells, but had little effect on PKB activation. In insulin-resistant state, berberine exhibited synergistic effect on insulin-induced glucose uptake and GLUT4 translocation. Berberine improved insulin-induced tyrosine-phosphorylation of IRS-1 and the recruitment of p85 to IRS-1. These changes were accompanied by enhancement in insulin-induced PKC zeta and PKB activity and actin remodeling. The ameliorated insulin signal transduction was related to the inhibition of mTOR by berberine, which attenuated serine-phosphorylation of IRS-1. These results suggest that berberine may overcome insulin resistance via modulating key molecules in insulin signaling pathway, leading to increased glucose uptake in insulin-resistant cells. (C) 2009 Elsevier Ireland Ltd. All rights reserved.