Biphasic effects of chronic ethanol exposure on insulin-stimulated glucose uptake in primary cultured rat skeletal muscle cells: role of the Akt pathway and GLUT4.

BACKGROUND: mild or moderate chronic alcohol intake has been shown to be associated with increased insulin sensitivity, while chronic alcohol abuse demonstrates a contrary effect. The mechanism underlying this biphasic effect has not yet been clarified. We investigated whether chronic ethanol exposure mediates biphasic changes on insulin sensitivity and whether the phosphatidylinositol 3-kinase/Akt pathway is involved in vitro.
METHODS: primary cultured rat skeletal muscle cells were exposed to ethanol (0-400 mM) for 24 h. Insulin sensitivity was assessed by the (3) H-labelled 2-deoxyglucose uptake assay. Phosphatidylinositol 3-kinase, cytosol and cell membrane glucose transporter-4 (GLUT4), as well as the Akt phosphorylated form, were analyzed by Western blots.
RESULTS: biphasic effects of ethanol on insulin sensitivity were observed in primary cultured skeletal muscle cells in a dose-dependent manner. Compared with the untreated group, 50 and 100 mM concentrations of ethanol resulted in a significant increase in 2-deoxyglucose uptake by 29 and 28%, respectively, while higher concentrations of ethanol (200, 400 mM) showed a significant decrease in 2-deoxyglucose uptake by 28 and 47%, respectively. The changes in glucose transport activity were in line with the changes in Akt Ser473 phosphorylation and GLUT4 expression in an ethanol dose-dependent biphasic manner. The phosphorylation of Akt and GLUT4 protein contents were up-regulated after treatment with low concentrations of ethanol (50, 100 mM) and down-regulated with high concentrations of ethanol (200, 400 mM) for 24 h.
CONCLUSION: ethanol mediates biphasic changes on insulin sensitivity at least in part via the Akt pathway and GLUT4 expression. 2010 John Wiley & Sons, Ltd.