Modulation of the nitric oxide metabolism overcomes the unresponsiveness of the diabetic human myocardium to protection against ischemic injury

Abstract

Background: We have demonstrated that diabetic human myocardium cannot be protected by ischemic preconditioning (IP) and identified a dysfunction of the mitochondria as the cause of the defect. Here we have investigated whether modulation of the nitric oxide (NO) metabolism can overcome the unresponsiveness of the diabetic myocardium to cardioprotection.

Methods: Myocardial slices (30-40 mg) obtained from the right atrial appendage of patients with diabetes undergoing elective cardiac surgery were randomized to the following protocol (n=6/group): NO donor SNAP (100 μM), nonselective nitric oxide synthase (NOS) inhibitor L-NAME (100 μM), and selective neuronal NOS (nNOS) inhibitor TRIM (100 μM) for 20 min prior to 90 min ischemia followed by 120 min reoxygenation (37°C). Some preparations were subjected to ischemic/reoxygenation alone or to IP (5 min ischemia/5 min reoxygenation) to act as control. Tissue injury was assessed by creatine kinase (CK) released (IU/mg wet wt), and cell necrosis and apoptosis by propidium iodide and TUNEL (% of aerobic control).

Results: IP did not decrease CK release, cell necrosis or apoptosis in diabetic myocardium. However, NO donor SNAP, the nonspecific NOS inhibitor L-NAME, and the specific nNOS inhibitor TRIM significantly reduced CK leakage, cell necrosis, and apoptosis in diabetic myocardium.

Conclusions: These results demonstrate that both the provision of exogenous NO and the suppression of endogenous NO production result in potent protection of diabetic human myocardium overcoming the unresponsiveness of these tissues to cardioprotective therapies.