Oxidative stress responses in mammalian cells

Reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), hydroxyl radical (OH. and superoxide anion (02.-)are generated as a consequence of normal metabolism in aerobically growing cells. In addition, ROS can be produced in cells following exposure to ionizing radiation, ultraviolet (UVB and UVA) radiation, and also during intracellular metabolism of chemicals present in the environment and certain drugs. These oxygen species are highly reactive and can cause damage to many cellular components including lipid membranes, proteins and nucleic acids. A condition of oxidative stress is generally understood to occur when the levels of ROS exceed the antioxidant capacity of the cell or tissue. This condition has been implicated in a wide variety of human diseases including arthritis, neurodegenerative disorders, atherosclerosis, AIDS and cancer (reviewed in Cerutti, 1994; Halliwell, 1994; Jenner, 1994; Staal et al., 1992; Witztum, 1994).