NOX4 and metabolic syndrome: Consequently, under the metabolic syndrome milieu, vascular tissue elevations of NADPH oxidase 4 and iNOS and uncoupled eNOS collude to chronically produce high levels of several ROS and RNS species including O2−, H2O2, ONOO−, and its reaction products OH− (hydroxyl radical), CO3− (carbonate radical), and NO2, (nitrogen dioxide) among several other ROS and RNS intermediates throughout the vasculature.