Antioxidant mechanisms in radiation injury and radioprotection

Description/Abstract

Oxygen is a very important factor in determining radiosensitivity because it enhances the damage to cellular components caused by ionizing radiation, although mechanisms involved in UV irradiation damage may overlap ionizing radiation effects. This paper emphasizes chemical protection against damage by ionizing radiation and predominantly against the effects of photons (and gamma radiation). It is possible that free radicals and their products induced by ionizing radiation can interact with reactive oxygen species formed during normal processes, such as superoxide and hydrogen peroxide produced by phagocytic cells or during enzymatic processes (xanthine oxidase activity; enzymes involved in eicosanoid metabolism). Metals such as iron can promote free radical damage, whereas some bound metals have radioprotectant potential, e.g., metallothionein and ceruloplasmin. There is increasing evidence that maintenance of the proper oxidation-reduction state of cells by the interconversion of the peptide sulfhydryl glutathione (GSH), and its disulfide form (GSSG) is a factor in the modulation of cellular radiosensitivity. Other protein and nonprotein sulfhydryls may also play a role both as targets of radiation damage and as protectors. Other physiological antioxidants (vitamin E) and antioxidant enzymes are interrelated in their function of controlling oxidative processes. This review concentrates on the role of oxygen, glutathione, and antioxidant enzymes in radiosensitivity and how exogenous chemicals interact with these endogenous factors.