Nicorandil inhibits oxidative stress-induced apoptosis in cardiac myocytes through activation of mitochondrial ATP-sensitive potassium channels and a nitrate-like effect

The anti-anginal drug nicorandil has been shown to inhibit apoptosis by activating mitochondrial ATP-sensitive potassium (K(ATP)) channels. The possible contribution of the nitrate moiety of this drug to its anti-apoptotic effect has now been investigated in neonatal rat ventricular myocytes subjected to oxidative stress. Exposure of cultured myocytes to 100 micromol/l hydrogen peroxide (H(2)O(2)) increased the number of nuclei stained by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling technique as well as induced internucleosomal DNA fragmentation, loss of mitochondrial membrane potential, cytochrome c release into the cytosol, and activation of caspases-3 and -9, all of which are characteristics of apoptosis. Pretreatment of cells with nicorandil (100 micromol/l) inhibited these effects of H(2)O(2). Both the mitochondrial K(ATP) channel antagonist 5-hydroxydecanoate (5-HD) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, attenuated the anti-apoptotic effect of nicorandil in concentration-dependent manners. Coapplication of ODQ (10 micromol/l) and 5-HD (500 micromol/l) completely abolished nicorandil-induced cytoprotection. The effect of nicorandil was also reduced by an inhibitor of cGMP-dependent protein kinase (KT5823, 1 micromol/l). The nitric oxide donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP, 50 micromol/l) mimicked the protective effect of nicorandil in a manner sensitive to ODQ but not to 5-HD. A cell-permeable cGMP analog, 8-bromo-cGMP, also reduced H(2)O(2)-induced apoptosis. The inhibition of the H(2)O(2)-induced activation of caspase-3, but not that of caspase-9, by nicorandil in the presence of 5-HD or by SNAP was reversed by the addition of dithiothreitol to the enzyme assay. Nicorandil inhibits oxidative stress-induced apoptosis in cardiac myocytes through a nitric oxide/cGMP-dependent mechanism as well as by activating mitochondrial K(ATP) channels.