Antiapoptotic mechanism of insulin in reoxygenation-induced injury in cultured cardiomyocytes of neonatal rats

To examine the protective effect of insulin on reoxygenation-induced injury and explore the underlying mechanisms, the model of anoxia/reoxygenation (A/R) injury was established by inducing anoxia for 2 h and reoxygenation for 4 h in cultured cardiomyocytes of neonatal rats. The rats were randomized to four groups receiving vehicle, insulin, LY294002, insulin plus LY294002 at the onset of reoxygenation after 2 h of anoxia. At the end of reoxygenation of 4 h, activity of lactate dehydrogenase (LDH) and content of malondialdehyde (MDA) were spectrophotometrically determined, apoptosis of cardiomyocytes were detected by using TUNEL and DNA Ladder, and Western blotting was employed to examine the expression of phosphorylated Akt in all groups. Our results showed that compared with vehicle-treated group, activities of LDH, contents of MDA, apoptosis index (AI) were significantly decreased, and expression of phosphorylated Akt was increased significantly in insulin-treated group. However, changes in LDH, MDA, AI and phosphorylated Akt resulting from insulin were attenuated or abolished by LY294002 (PI3K inhibitor). These data strongly suggest that early administration of insulin at reoxygenation protects cardiomyocytes from reoxygenation-induced apoptosis through PI3K/Akt signaling pathway.