Generation of reactive species in diabetes. Highlighted in gray are some of the most important ROS and RNS in vascular cells. Oxygen is converted to •O2- via the activation of enzymatic and nonenzymatic pathways, which is then dismutated to H2O2 by SOD. H2O2 can be converted to H2O by catalase or glutathione peroxidase (GSH-Px) or to •OH after reaction with Cu or Fe. Glutathione reductase regenerates glutathione (GSH). In addition, •O2- reacts rapidly with •NO to form ONOO-.