Attenuation of Myocardial Ischemia/Reperfusion Injury by Superinduction of Inducible Nitric Oxide Synthase

Abstract

Background-Nitric oxide (NO) has been implicated as a mediator in myocardial ischemia/reperfusion (I/R) injury, but its functional properties have been conflicting. We investigated whether NO has a protective role against I/R injury. Methods and Results-Using endothelial NO synthase knockout (eNOS KO) mice, inducible NOS KO mice, the NO donor S-nitroso-N-acetylpenicillamine (SNAP), and the NOS inhibitor N-iminoethyl-L-ornithine (L-NIO), we performed studies of isolated perfused hearts subjected to 30 minutes of global ischemia followed by reperfusion. After 60 minutes of reperfusion, nitrite levels in the coronary effluent in the SNAP and eNOS KO groups were significantly elevated compared with other groups. Immunoblot and immunohistochemistry showed that iNOS was markedly induced in the eNOS KO hearts. Under spontaneous beating conditions during reperfusion, increased NO activity was correlated with a prevention of the hyperdynamic contractile response and enhanced myocardial protection, as evidenced by a reduction in myocardial injury and infarct size. During prolonged reperfusion, SNAP-treated hearts were able to preserve contractile functions for 180 minutes, whereas L-NIO-treated hearts showed a sustained deterioration in contractility. Conclusions-NO protects against I/R injury by preventing the hyperdynamic response of isolated perfused hearts during early reperfusion. In the eNOS KO hearts, a paradoxical increase in NO production was seen, accompanied by a superinduction of iNOS, possibly due to an adaptive mechanism.

Endothelial Progenitor Cells Are Rapidly Recruited to Myocardium and Mediate Protective Effect of Ischemic Preconditioning via “Imported” Nitric Oxide Synthase Activity

“…Recently, many investigators have documented the role of eNOS 10,37 or iNOS 18,38,39 in the cardioprotective effect of IP. Our data suggest that in the case of I-R injury after IP, activated eNOS produced from recruited EPCs plays an essential role in cardioprotection.…”

“…Previous studies have documented a favorable role of iNOS in IP. 18,38,39 In particular, Wang et al 40 reported that IP upregulated iNOS in cardiomyocytes and played a protective role against myocardial damage. These authors showed iNOS mRNA expression in ischemic myocardium followed IP, and diffuse iNOS signals were detected with in situ hybridization and immunohistochemistry in the cytoplasmic space of cardiomyocytes.…”

Absence of Inducible Nitric Oxide Synthase Reduces Myocardial Damage During Ischemia Reperfusion in Streptozotocin-Induced Hyperglycemic Mice

“…Despite extensive research, the role of NO in ischemia and reperfusion injury remains controversial and is yet to be defined (10,11). However, several reports demonstrated that NO functions as a protective agent during reperfusion injury.…”

Statin-Induced Improvement of Endothelial Progenitor Cell Mobilization, Myocardial Neovascularization, Left Ventricular Function, and Survival After Experimental Myocardial Infarction Requires Endothelial Nitric Oxide Synthase

“…Of note, myocardial superinduction of inducible NOS has been described in eNOS-knockout mice but not in WT mice after severe myocardial ischemia as an adaptive response mediating protective effects. 50 Furthermore, recent studies suggest a protective role of neuronal NOS in the myocardium. Thus, the potential compensatory mechanisms in eNOS Ϫ/Ϫ mice with severe LV dysfunction (ie, mediated by inducible or neuronal NOS or other vasodilator systems) need to be addressed in future studies.…”