Pretreatment with erythropoietin protects the myocardium from infarction by a PI3-kinase-mediated mechanism

Abstract

Purpose: The aim of this study was to examine the hypothesis that pretreatment with erythropoietin (EPO) enhances myocardial tolerance against infarction by activation of PI3K/Akt pathway. Methods: Myocardial infarction was induced by 30-min coronary occlusion and 2-hr reperfusion in rabbit hearts in situ with or without intravenous administration of EPO (5000 units/kg) at 5 min before ischemia. Infarct size and area at risk (AR) were determined by tetrazolium staining and fluorescent particles, respectively. In the second series of experiments, rabbit hearts were isolated and perfused with Krebs-buffer in Langendorff mode. Tissue samples were taken before and after 15-min infusion of EPO (1 unit/ml) for immunoblotting of total and phosphor-Akt. Using separate groups of hearts, infarction was induced by 30-min ischemia/2-hr reperfusion with or without infusion of EPO (1 unit/ml) and/or LY-294002 (5 micromol/L), a selective PI3K inhibitor. Results: In hearts in situ, EPO significantly reduced infarct size from 57.9 ± 0.1% of AR to 40.6 ± 4.6% without effects on systemic hemodynamic parameters. In buffer-perfused hearts, infusion of EPO increased level of phosphorylated Akt by 43% and reduced infarct size from 41.8 ± 0.8% of AR to 15.6 ± 4.2%. This protection was completely inhibited by LY-294002 administered before EPO infusion. Conclusion: EPO enhances anti-infarct tolerance of the myocardium by a PI3-kinase-mediated mechanism.