Antioxidant defenses of cultured colonic epithelial cells against reactive oxygen metabolites

Reactive oxygen metabolites produce colonic epithelial cellular injury. The present study evaluated the protective role of cellular superoxide dismutase, catalase, and glutathione (GSH) redox cycle in cultured rabbit colonic cells. Cultured rabbit colonic epithelial cells were exposed to reactive oxygen metabolites generated by hypoxanthine (1 mM) and xanthine oxidase (1 mU/ml) for up to 5 h. Cytotoxicity was quantified by measuring Cr-51 release from prelabeled cells. Pretreatment with diethyldithiocarbamate (inhibitor of superoxide dismutase) reduced activity of cellular superoxide dismutase and increased Cr-51 release caused by hypoxanthine/xanthine oxidase from colonic cells. Pretreatment with diethyl maleate (covalently binds GSH as catalyzed by GSH transferase), or buthionine sulfoximine (inhibitor of gamma-glutamylcysteine synthetase) decreased cellular GSH and enhanced reactive oxygen metabolites induced injury. Pretreatment with bis(chloroethyl)-nitrosourea (inhibitor of GSH reductase) inhibited activity of GSH reductase and increased Cr-51 release from colonic cells. Preincubation with aminotriazole (inhibitor of catalase) reduced cellular catalase, but did not affect cellular injury. Therefore, we concluded that both cellular superoxide dismutase and the GSH redox cycle appeared to play a role in detoxifying reactive oxygen metabolites and that cellular catalase may be less important in rabbit colonic epithelial cells.