Insulin Administered at Reoxygenation Exerts a Cardioprotective Effect in Myocytes by a Possible Anti-Apoptotic Mechanism

The metabolic cocktail of glucose-insulin-potassium (GIK) has been shown to reduce mortality in humans and reduce infarct size in the rat when administered from the onset of reperfusion following an ischemic insult. The mechanisms underlying GIK mediated cardioprotection are, however, still unclear. Recent data implicates insulin “alone” as the major protagonist of cardioprotection when administered at the time of reperfusion. We have therefore begun to investigate an insulin activated signalling pathway and the putative role of apoptosis in this insulin-induced cardioprotection. Simulated ischemia and reoxygenation were induced in rat neonatal cardiocyte experiments. The administration of insulin [0.3 mU/ml] at the moment of reoxygenation (InsR) enhanced myocardial cell viablility as assessed by trypan blue exclusion compared to vehicle alone treated control myocytes (InsR50±2%v controls 70±1%, P<0.001). This insulin-mediated cardioprotection was due, in part to a reduction in myocyte apoptosis as measured by TUNEL (InsR29±2%v controls 49±3%, P<0.001) and Annexin V staining (InsR34±2%v controls 65±3%, P<0.001). These cardioprotective and anti-apoptotic effects of insulin were completely abolished by the tyrosine kinase inhibitor lavendustin A and by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin. Thus, we conclude that the early administration of insulin appears to be an effective modality to reduce reoxgygenation injury in cardiocytes, in part, via the attenuation of ischemia/reoxygenation-induced apoptosis. Moreover, the cardioprotective and anti-apoptotic effects of insulin are mediated via tyrosine kinase and PI3-kinase signalling pathways.