Endogenous endothelium-derived nitric oxide inhibits myocardial caspase activity: implications for treatment of end-stage heart failure

Apoptosis contributes to ventricular remodeling in heart failure (HF). Nitric oxide (NO) inhibits caspase 3, a key effector apoptotic enzyme. We hypothesized that reduced endogenous NO in HF disinhibits cardiac caspase 3 to promote apoptosis. Caspase 3 activity was measured colorimetrically in myocardial cell lysates from endothelial NO synthase (eNOS)-deficient mice (eNOS −/−; n = 18), cardiomyopathic (CMP) hamsters ( n = 8), and explanted failing human hearts ( n = 10). We stimulated myocardial caspase 3 activity by adding upstream caspase 8 or 9. Cell lysates were incubated with 10 −4 mol/liter NO donor, S-nitroso-N-acetyl penicillamine; NOS inhibitor, nitro-L-arginine-methyl ester (L-NAME); or angiotensin-converting enzyme (ACE) inhibitor, enalaprilat. Hamsters underwent echocardiography so we could study the progression of ventricular dysfunction. Stimulated caspase 3 activity was lower in myocardium of eNOS +/+ compared with eNOS −/− mouse hearts (5.1 ± 0.5 vs 7.6 ± 1.0 pmol/10 μg/min, p < 0.05). L-NAME increased enzyme activity only in eNOS +/+ mice, indicating that endogenous NO inhibits caspase 3. Stimulated caspase 3 activity was lower in control hamsters, 3.3 ± 0.3 pmol/10 μg/min, compared with CMP hamsters, 9.6 ± 0.7 and 6.9 ± 0.4 pmol/10 μg/min at 4 and 9 months, respectively. This was associated with progressive ventricular dysfunction, thinning, and dilatation. L-NAME increased enzyme activity in normal but not in CMP hamsters. In failing human myocardium, L-NAME failed to alter caspase activity, indicating reduced NO availability. Enalaprilat inhibited caspase 3, which was reversed by L-NAME. S-nitroso-N-acetyl penicillamine reversed caspase 3 activation in all groups. Nitric oxide reversibly inhibits myocardial caspase 3 independent of the apoptotic signaling pathway. Reduced NO in HF increases myocardial caspase 3 activity. Agents that promote NO synthesis, including ACE inhibitors, may prevent caspase activation in HF.