ROS, including superoxide (• O2−), hydrogen peroxide (H2O2), hypochlorite ion (OCl−), and hydroxyl (• OH) radicals, are generated by many reactions in multiple compartments in the cell, including NADPH oxidases, lipid metabolism within the peroxisomes; and various cytosolic cyclooxygenases. However, in most cells the vast majority of ROS result from electron transport by the mitochondria. The role of ROS in inducing epigenetic alterations in human carcinogenesis has been discussed (Ziech et al. 2011).
