Insulin prevents cardiomyocytes from oxidative stress-induced apoptosis through activation of PI3 kinase/Akt

Background-Loss of cardiomyocytes by apoptosis is proposed to cause heart f ailure. Reactive oxygen species induce apoptosis in many types of cells inc luding cardiomyocytes. Because insulin has been reported to have protective effects, we examined whether insulin prevents cardiomyocytes from oxidativ e stress-induced apoptotic death. Methods and Results-Cultured cardiomyocytes of neonatal rats were stimulate d by hydrogen peroxide (H2O2) Apoptosis was evaluated by means of the TUNEL method and DNA laddering. Incubation with 100 mu mol/L H2O2 for 24 hours i ncreased the number of TUNEL-positive cardiac myocytes (control, approximat e to4% versus H2O2, approximate to 23%) Pretreatment with 10(-6) mol/L insu lin significantly decreased the number of H2O2-induced TUNEL-positive cardi ac myocytes (approximate to 12%) and DNA fragmentation induced by H2O2. Pre treatment with a specific phosphatidylinositol 3 kinase (PI3K) inhibitor, w ortmannin, and overexpression of dominant negative mutant of PI3K abolished the cytoprotective effect of insulin. Insulin strongly activated both PI3K and the putative downstream effector Akr. Moreover, a proapoptotic protein , Bad, was significantly phosphorylated and inactivated by insulin through PI3K. Conclusions-These results suggest that insulin protects cardiomyocytes from oxidative stress-induced apoptosis through the PI3K pathway.