XANTHINE DEHYDROGENASE XANTHINE-OXIDASE AND OXIDATIVE STRESS

Xanthine dehydrogenase (XDH) and xanthine oxidase (XOD) are single-gen e products that exist in separate but interconvertible forms, XOD util izes hypoxanthine or xanthine as a substrate and O-2 as a cofactor to produce superoxide (. O-2(-)) and uric acid, XDH acts on these same su bstrates but utilizes NAD as a cofactor to produce NADH instead of . O -2(-) and uric acid, XOD has been proposed as a source of oxygen radic als in polymorphonuclear, endothelial, epithelial, and connective tiss ue cells, However, several questions remain about the physiological si gnificance and functions of XOD on aging and oxidative stress, XOD is reported to play an important role in cellular oxidative status, detox ification of aldehydes, oxidative injury in ischemia-reperfusion, and neutrophil mediation, For example, XOD may serve as a messenger or med iator in the activation of neutrophil, T cell, cytokines, or transcrip tion in defense mechanisms rather than as a free radical generator of tissue damage, Emerging evidence on the synergistic interactions of . O-2(-) a toxic product of XOD and nitric oxide, may be another illustr ation of XOD involvement in tissue injury and cytotoxicity in an emerg ent condition such as ischemia or inflammation.