Effect of Neomycin on Azoxymethane-Induced Colon Carcinogenesis in F344 Rats

Abstract

The effect of oral administration of neomycin (100 and 200 μg/ml in drinking water) on colon tumors induced by azoxymethane [(AOM); CAS: 25843-45-2] was studied in female F344 rats. Five-week-old rats were fed NIH-07 diet and given daily in drinking water 0, 100, and 200 μg neomycin/ml (0, 100, and 200 ppm). At 7 weeks of age, all animals except vehicle-treated groups received weekly sc injections of 8 mg AOM/kg body weight for 8 weeks. The AOM- or vehicle-treated groups were necropsied 30 weeks after the last injection of AOM. The combined incidence of adenomas and adenocarcinomas of the colon did not differ significantly among the 3 groups. The animals in the groups given 100 and 200 μg neomycin had a higher incidence of colon adenocarcinomas than did those in the control group. Colonic and cecal bacterial β-glucuronidase activity was significantly lower in the group given 200 μg neomycin than it was in the control group. The excretion of fecal cholesterol, total bile acids, and deoxycholic acid was increased significantly in animals given 100 and 200 μg neomycin as compared to animals given no neomycin. These results suggest that long-term oral administration of neomycin increases the incidence of colon adenocarcinomas.