Dose-related cytoprotective effect of alpha-lipoic acid on hydrogen peroxide-induced oxidative stress to pancreatic beta cells.

alpha-Lipoic acid (alpha-LA), an antioxidant used for diabetic polyneuropathy, was reported to induce AMP-activated protein kinase activation and reductions in insulin secretion in pancreatic beta-cells at high concentrations (> or = 500 micromol/l). This study investigated whether alpha-LA has a protective role under oxidative stress in beta-cells and its effect is dose-related. In INS-1 cells treated with alpha-LA (150-1200 micromol/l) for 24 h, alpha-LA itself (> or = 300 micromol/l) induced apoptotic death dose-dependently. However, pre-treatment with 150 and 300 micromol/l alpha-LA reduced the hydrogen peroxide-induced apoptosis in INS-1 cells and isolated islets. alpha-LA alleviated hydrogen peroxide-induced reactive oxygen species production, mitochondrial membrane depolarization and c-JNK activation in beta-cells. alpha-LA induced phosphoinositide 3-kinase-dependent Akt phosphorylation in INS-1 cells. While alpha-LA is harmful to beta-cells at high concentrations in vitro, it has potential cytoprotective effects on beta-cells under oxidative stress as in diabetes by its antioxidant properties and possibly by Akt phosphorylation at clinically relevant concentrations.