Ethanol impairs insulin's actions through phosphatidylinositol 3-kinase

Insulin plays an important role in cell metabolism and proliferation. In the present study, we examined the effect of ethanol on insulin actions such as glucose uptake, DNA synthesis, and c-Jun gene expression. Acute treatment with ethanol (200 mM) for 60 minutes inhibited insulin-stimulated 2-deoxyglucose uptake by 50% in 3T3-L1 adipocytes. Insulin-induced DNA synthesis and c-Jun protein expression were also reduced by ethanol treatment in Rat-1 fibroblasts overexpressing normal human insulin receptor. Ethanol has no effect on tyrosine phosphorylation of the insulin receptor and insulin receptor substrate (IRS)-1. However, association of the insulin receptor and IRS-1 with the Src homology 2 domain of the p85 subunit of phosphatidylinositol 3-kinase (PI3-kinase) was reduced by ethanol. Pretreatment with the antidiabetic drug troglitazone, an insulin-sensitizer, reversed ethanol's inhibition. These results suggest that ethanol specifically inhibits the association of the insulin receptor and IRS-1 with the p85 subunit of PI3-kinase, which is required for increased glucose uptake, DNA synthesis, and c-Jun expression by insulin.