Figure 1.

Generation of ROS by CYP. Cells generate ROS such as superoxide anion (O₂^.-) and H₂O₂ as a result of metabolism of xenobiotics by CYP. Both O₂^.- and H₂O₂ may be converted to the highly reactive hydroxyl radical (OH^.-) by iron (Fe²⁺)-catalyzed Haber-Weiss and Fenton reactions. Many xenobiotics are converted to toxic quinones by CYP. These quinones are redox-sensitive agents and are reversibly reduced to semihydroquinones/hydroquinones, which generate O₂^.-.