The endothelial nitric oxide synthase cofactor tetrahydrobiopterin shields the remote myocardium from apoptosis after experimental myocardial infarction in vivo

Following myocardial infarction (MI), apoptosis occurs early in the remote myocardium and contributes to the processes of myocardial remodelling. Increased nitrosative stress is a well-known and potent inductor of myocardial apopto¬sis. Excess activation of endothelial nitric oxide synthase (eNOS) increases its uncoupling potential and results in nitrosative stress via formation of peroxynitrite. However, the pathophysiological role of eNOS signalling in the remote myocardium after MI is as yet undefined. The impact of eNOS activation on pro- and anti-apoptotic signalling in the remote myocardium and the influence of pretreatment with the eNOS cofactor tetrahydrobiopterin (BH4) on eNOS activation, nitrosative stress level, and apoptosis induction and execution were studied in a rat MI model in vivo. Twenty-four hours after anterior MI, eNOS activity in animals treated with left anterior descending coronary artery ligation (LIG) significantly increased in the posterior left ventricular (LV) myocardium as did protein nitrosylation when com¬pared to sham treatment. This was paralleled by induction of apoptosis via the extrinsic and intrinsic pathways. Moreover, anti-apoptotic signalling via protein kinase B/Akt and glycogen synthase-kinase 3 beta was suppressed. Notably, pretreatment with the eNOS cofactor BH4 reduced eNOS activation, prevented excess protein nitrosylation, blunted apoptosis induction, facilitated anti-apoptotic signalling, and eventually prevented apoptosis execution. Here we showed that 24 h after experimental MI in rats in vivo, apoptosis was induced in the posterior non-in¬farcted LV wall. Evidence is presented that pretreatment with the eNOS cofactor BH4 resulted in less nitrosative stress and weakened apoptotic processes, although the stabilisers contained did participate in this phenomenon. Because apoptosis is a crucial component of myocardial remodelling, influencing eNOS signalling might be an interesting pharmacological target for the development of novel anti-remodelling therapies.