N-Acetylcysterine and Allopurinol confer synergy in attenuating myocardial ischemia injury via restoring HIF-1α /HO-1 signaling in diabetic rats

Abstract

Background: The antioxidants N-acetylcysteine (NAC) and allopurinol (ALP) can synergistically reduce myocardial ischemia/ reperfusion (MI/R) injury in rats with streptozotocin (STZ) - induced diabetes. We investigated whether or not NAC and ALP confer synergistic cardioprotection by stabilizing hypoxia inducible factor 1-α (HIF-1α)/hemeoxygenase 1 (HO-1) signaling in the diabetic myocardium. Methods: Control or diabetic Sprague-Dawleyrats received vehicle, NAC, ALP or their combination for four weeks starting one week after STZ injection. The animals were then subjected to 30 minutes of coronary artery occlusion followed by two hours of reperfusion in the absence or presence of tin protoporphyrin-IX (selective HO-1 inhibitor) or 2-Methoxyestradiol (HIF-1α inhibitor). Cardiomyocytes exposed to high glucose were subjected to hypoxia/re-oxygenation in the absence or presence of HIF- 1α siRNA or HO-1 siRNA. Results: Myocardial and plasma levels of 15-F2t-isoprostane, an index of oxidative stress, were increased significantly in diabetic rats while cardiac HO-1 protein and activity were reduced, which was accompanied with decreased cardiac protein levels of HIF-1α and augmented post-ischemic myocardial infarct size and cellular injury. Both NAC and ALP but in particular their combination normalized cardiac levels of HO-1 and HIF-1α protein expression and prevented the increase in 15-F2t-isoprostane, resulting in significantly attenuated post-ischemic myocardial infarction. NAC and ALP also attenuated hyperglycemia-induced post-hypoxic cardiomyocyte death in vitro. However, pharmacological inhibition of HIF-1α or HO-1 or their gene knock-down prevented the protective effects of NAC and ALP. Conclusion: NAC and ALP confer pharmacological cardioprotection in diabetes via the restoration of cardiac HIF-1α and HO-1.