Major pathways of ROS generation and elimination in vascular cells. One electron reduction of O₂ can produce superoxide anion (O₂^•−). The main pathways for O₂^•− transformation are via dismutation to hydrogen peroxide (H₂O₂) catalyzed by superoxide dismutase (SOD) or reaction with nitric oxide (NO^•) to form peroxynitrite (ONOO^―). H₂O₂ can be further metabolized to hypochlorous acid (HOCl) by myeloperoxidase (MPO) or hydroxyl radical (OH^•) through reactions catalyzed by metal ions (Fe²⁺ or Cu²⁺) via the Fenton reaction. Elimination of H₂O₂ is facilitated by antioxidant enzymes such as glutathione peroxidase, peroxiredoxin, and catalase.