Male Fischer rats which had been implanted with a heterotopic bladder were randomly divided into five groups and their heterotopic bladders were instilled once a week for 20 weeks with 0.5 ml phosphate-buffered saline:dimethyl sulfoxide solution (4:1) or this solution containing 1 µmol benzidine (BZ), N′-hydroxy-N-acetylbenzidine, the N′-glucuronide of N′-hydroxy-N-acetylbenzidine, or the N-glucuronide of N-hydroxy-2-aminofluorene. These bladders were then instilled once a week for an additional 30 weeks with the phosphate-buffered saline without dimethyl sulfoxide. The experiment was terminated at the end of 50 weeks. Transitional cell carcinomas were observed in 1 of 39 (control), 1 of 29 (BZ), 18 of 30 (N′-hydroxy-N-acetylbenzidine), 28 of 28 (N′-hydroxy-N-acetylbenzidine N′-glucuronide), and 24 of 29 (N-hydroxy-2-aminofluorene N-glucuronide) rats. No histological alterations were observed in their natural bladders. These results demonstrate the urothelial carcinogenicity of the N-hydroxy metabolites of BZ and suggest that N′-hydroxy-N-acetylbenzidine N′-glucuronide may play a major role in the initiation of urothelial carcinogenesis by BZ in humans.
The studies from the A. Alfred Taubman Facility were supported in part by USPHS Grant CA 23800 from the National Cancer Institute and an institutional grant from the United Foundation of Detroit.