Figure 1.

Schematic illustration of reactive oxygen/nitrogen species (ROS/RNS) generation and their link to cancer development. Electron leakage from the mitochondria leads to the generation of superoxide (O•²⁻) by reacting with molecular oxygen. Superoxide, in the presence of superoxide dismutase (SOD), gets converted to hydrogen peroxide (H₂O₂). This hydrogen peroxide can be converted either to water by catalase or to hydroxyl radicals (HO•). Arginine, in the presence of nitric oxide synthase (NOS), is converted to nitric oxide (NO•) that reacts with superoxide to form peroxynitrite (ONOO⁻). All these ROS/RNS promote oxidative DNA damage and protein and lipid oxidation. ROS-mediated DNA damage leads to loss of p53 function that results in genomic instability and the development of cancer. GPx, glutathione peroxidase; GSSG, glutathione (oxidized).