Capability of urinary components to enhance ornithine decarboxylase activity and promote urothelial tumorigenicity

The inducibility of omithine decarboxylase (ODC) by fractions of normal rat urine separated by gel filtration chromatography was tested using the bladder carcinoma cell line 804G. Two peaks of high ODC inducibility were regularly found in the urine of rats that are fed a normal commercial rat chow or a semisynthetic diet. The approximate molecular weight of the active component in Fraction I is 37, 000, and that in Fraction II is 4, 300. These substances are heat resistant in regard to ODC inducibility and inhibition of metabolic cooperation in the V79 cell assay. In an in vivo assay, using heterotopically transplanted rat urinary bladders which had been pretreated with a single small dose (0.25 mg) of N-methyl-N-nitrosourea, weekly instillation of both Fractions I and II induced preneoplastic and neoplastic lesions in the urothelium. Of the two fractions, Fraction I induced a significantly increased thymidine incorporation into urothelial cell nuclei of heterotopic bladders and exhibited more advanced structural alterations in the urothelial surface when examined at an early stage of neoplasia (12 weeks of treatment). Weekly administration of urine Fraction I had induced a significantly higher tumor incidence in the heterotopic urinary bladder by 25 weeks than did urine, 2.1% NaCI solution, or Fraction II (p < 0.005 for each comparison). Administration of Fraction II likewise induced a significantly higher tumor incidence than did the 2.1% NaCI solution (p < 0.03). The incidence of nodulopapillary hyperplasia, a preneoplastic hyperplastic lesion, was also significantly increased following weekly instillation of Fractions I or II (p < 0.005) when compared with that of the 2.1% NaCI group. The results indicate that the two ODC-inducible Fractions I and II isolated from normal rat urine act as a growth-stimulating factor in urinary bladder carcinogenesis and that Fraction I displays a more potent tumor-enhancing property. The results also suggest that thymidine incorporation into urothelial nuclei may be a useful test to screen tumor promoter substance(s) on urothelium.