Adiponectin Cardioprotection After Myocardial Ischemia/Reperfusion Involves the Reduction of Oxidative/Nitrative Stress

Abstract

Background-Several clinical studies have demonstrated that levels of adiponectin are significantly reduced in patients with type 2 diabetes and that adiponectin levels are inversely related to the risk of myocardial ischemia. The present study was designed to determine the mechanism by which adiponectin exerts its protective effects against myocardial ischemia/reperfusion. Methods and Results-AdiponectinϪ/Ϫ or wild-type mice were subjected to 30 minutes of myocardial ischemia followed by 3 hours or 24 hours (infarct size and cardiac function) of reperfusion. Myocardial infarct size and apoptosis, production of peroxynitrite, nitric oxide (NO) and superoxide, and inducible NO synthase (iNOS) and gp91 phox protein expression were compared. Myocardial apoptosis and infarct size were markedly enhanced in adiponectin Ϫ/Ϫ mice (PϽ0.01). Formation of NO, superoxide, and their cytotoxic reaction product, peroxynitrite, were all significantly higher in cardiac tissue obtained from adiponectin Ϫ/Ϫ than from wild-type mice (PϽ0.01). Moreover, myocardial ischemia/ reperfusion-induced iNOS and gp91 phox protein expression was further enhanced, but endothelial NOS phosphorylation was reduced in cardiac tissue from adiponectin Ϫ/Ϫ mice. Administration of the globular domain of adiponectin 10 minutes before reperfusion reduced myocardial ischemia/reperfusion-induced iNOS/gp91 phox protein expression, decreased NO/superoxide production, blocked peroxynitrite formation, and reversed proapoptotic and infarctenlargement effects observed in adiponectin Ϫ/Ϫ mice. Conclusion-The present study demonstrates that adiponectin is a natural molecule that protects hearts from ischemia/ reperfusion injury by inhibition of iNOS and nicotinamide adenine dinucleotide phosphate-oxidase protein expression and resultant oxidative/nitrative stress.

Reduced Cardioprotective Action of Adiponectin in High-Fat Diet–Induced Type II Diabetic Mice and Its Underlying Mechanisms

“…After 8 weeks of being fed HD or ND, 14-week-old mice were anesthetized with 2% isoflurane (total isoflurane exposure time < 5 min), and MI was produced via left anterior descending coronary artery slip-knot ligation as described in our previous studies (25). Twenty minutes after MI, both HD mice and controls were randomized to one of the following groups: sham MI (n = 12), MI + vehicle (n = 13), MI + low dose gAPN (2 mg/g intraperitoneal injection IP; n = 13), and MI + high dose gAPN (6 mg/g IP; n = 13).…”

“…Cardiac function was determined by echocardiography and left ventricular catheterization methods 24 h after reperfusion before thoracotomy, as described in our previous studies (25,27).…”

“…Myocardial superoxide content (in area-at-risk) was quantified by lucigenin-enhanced luminescence as described previously (25).…”

“…The tissue nitric oxide (NO) and its metabolic products (NO2 and NO3) were determined by use of a chemiluminescence NO detector (Siever 280i NO Analyzer), and MI/R cardiac tissue nitrotyrosine (NT) content was quantified by ELISA as described previously (25,27).…”

“…We and others have demonstrated through investigations that exogenous APN supplementation exerts significant cardiovascular protection against myocardial ischemia/reperfusion (MI/R) injury. However, to date, all studies reporting cardiovascular protection by APN were performed in nondiabetic animals (24,25). Whether the cardioprotective actions of APN might be altered in the diabetic state, a pathologic condition where endogenous APN is significantly reduced and supplementation of APN may be most appropriate, has never been previously investigated.…”