NOS3 and diabetes mellitus: In the context of diabetes, eNOS tends to become uncoupled, both because peroxynitrite-derived radicals can oxidize its essential cofactor tetrahydrobiopterin to dihydrobiopterin, and oxidant-mediated inactivation of dimethylarginine dimethylamino-hydrolase (DDAH) increases cellular levels of asymmetric dimethylarginine (ADMA), a functional competitor of arginine’s association with eNOS [66,119,201,202,203,204].