There is much evidence suggesting a possible role of reactive oxygen-derived substances in the pathogenesis of both ulcerative colitis and colon cancer. The antioxidant effects of 5-aminosalicylic acid (the active moiety of olsalazine) on induction of colon cancer in an experimental model using 1,2-dimethylhydrazine were studied in male Wistar rats. The levels of reduced glutathione were significantly (P < 0.01) decreased (by -50%) in neoplastic tissues of rats receiving 1,2-dimethylhydrazine

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... one and olsalazine treatment significantly (P < 0.01) reduced the extent of this alteration. Adjacent tissues from rats receiving either carcinogen alone or carcinogen and olsalazine showed comparable levels of glutathione and these were significantly (P < 0.01) lower than corresponding control values and higher than corresponding values from neoplastic tissues. Activity of the glutathione regenerating enzyme glutathione reductase was significantly (P < 0.01) decreased (by -40%) in neoplastic colonic tissue and this alteration was unaffected by olsalazine treatment Neither carcinogen nor olsalazine treatment caused alterations in activity of glutathione reductase in adjacent tissue as compared with corresponding control values. Activity of the glutathione utilizing enzyme glutathione peroxidase was significantly (P < 0.01) increased (almost doubled) in neoplastic tissue of rats treated with carcinogen alone. Olsalazine treatment significantly (P < 0.01) reduced the elevation in glutathione peroxidase activity in neoplastic tissues of rats treated with the carcinogen. Glutathione peroxidase showed comparable activity in adjacent tissue from rats treated with either carcinogen alone or a combination of carcinogen and olsalazine and these values were significantly (P < 0.01) lower than corresponding control values. Colonic neoplastic tissues from all experimental groups of animals showed a small, but statistically significant (P < 0.05), decrease in superoxide dismutase activity compared with that in corresponding tissues from control animals.