Beneficial effects of exogenous tetrahydrobiopterin on left ventricular remodeling after myocardial infarction in rats - The possible role of oxidative stress caused by uncoupled endothelial nitric oxide synthase

Background Reactive oxygen species (ROS) is deeply involved in the process of ventricular remodeling after myocardial infarction (MI). Under oxidative stress, endothelial nitric oxide synthase (eNOS) can be converted to a ROS generator, because a relative lack of tetrahydrobiopterin (BH4), an essential cofactor for NO synthesis, leads to eNOS uncoupling. The uncoupled eNOS generates superoxide rather than NO. The possible role of ROS generated by eNOS in ventricular remodeling after MI was investigated. Methods and Results Rats were treated with oral BH4 supplementation starting at 3 days before coronary artery ligation. At 4 weeks after MI, there was augmented superoxide production in association with reduced BH4/dihydrobiopterin (BH2) ratio and eNOS dimer/monomer protein ratio in the heart. Treatment with BH4 increased BH4/BH2 ratio and eNOS dimer/monomer ratio, and decreased superoxide production. In BH4-treated MI rats, left ventricular size was smaller, thickness of the non-infarcted posterior wall was thinner, and cardiac function wits preserved compared with the control MI rats. Conclusions The present study suggested that ventricular remodeling process after MI leads to BH4 oxidation and resulted in uncoupled eNOS-derived superoxide generation, which further augmented the remodeling process and deteriorated cardiac function.