Protective Role of Intracellular Superoxide Dismutase

We examined the role of intracellular superoxide dismutase (SOD) as an antioxidant by studying the effect of diethyldithiocarbamate (DDC) on extracellular H202-induced damage in cultured rat gastric mucosal cells. 51Cr-labeled monolayers from rat stomachs were exposed to glucose oxidase-generated H202 or reagent H202, which both caused a dose-dependent increase in 51Cr release. DDC dose-dependently enhanced 51Cr release by hydrogen peroxide, corresponding with inhibition of endogenous SOD activity. This inhibition was not associated either with modulation of other antioxidant defenses, or with potentiation of injury by nonoxidant toxic agents. Enhanced hydrogen peroxide damage by DDC was significantly prevented by chelating cellular iron with deferoxamine or phenanthroline. Inhibition of cellular xanthine oxidase (possible source of superoxide production) by oxypurinol neither prevented lysis by hydrogen peroxide nor diminished DDC-induced sensitization to H202. We conclude that (a) extracellular H202 induces dose dependent damage to cultured gastric mucosal cells; (b) intracellular SOD plays an important role in preventing H202 damage; (c) generation of superoxide seems to occur intracellularly after exposure to H202, but independent of cellular xanthine oxidase; and (d) cellular iron mediates the damage by catalyzing the production of more reactive species from superoxide and H202, the process which causes ultimate cell injury. (J. Clin. Invest. 1994. 93:331-338.)