NO synthesized from iNOS promotes peroxynitrite formation, which is implicated in retinal endothelial and neuronal cell death, retinal neurodegeneration, and blood-retinal barrier breakdown in models of experimental diabetes (El-Remessy et al., 2003; el-Remessy et al., 2005; Zheng et al., 2007; Ali et al., 2008). Here, NOS2 is linked to diabetes mellitus.