Influence of Strain and Diet on Hepatocarcinogenicity of N-Butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in Rats

To assess sensitivity to hepatocarcinogenesis by BBN, formalin-fixed and paraffin-embedded rat liver tissues from two initiation/promotion (I/P) bioassays for urinary bladder carcinogenesis were sectioned, immunohistochemically stained for glutathione S-transferase placental form (GST-P), and quantitatively analyzed. In Experiment 1, male Sprague-Dawley (SD)/cShi strain rats (highly sensitive to urinary bladder carcinogenesis by BBN) and SD/gShi rats (insensitive), were treated with 0.05% BBN in the drinking water for 4 weeks and then housed for up to week 36, with or without exposure to bladder tumor promoters. Slightly higher quantitative values for small GST-P positive (GST-P+) foci were found in SD/gShi rats (8.57/cm2) compared to SD/cShi rats (2.48/cm2). In Experiment 2, F344 and Lewis rats, subjected to a similar I/P protocol, were maintained on MF or CA-1 diet for 36 weeks. Higher quantitative values of GST-P + hepatocytic foci (more than 0.1 mm in diameter) were found in Lewis rats (9.51/cm2 for MF diet; 7.95/cm 2 for CA-1 diet) compared to F344 rats (2.82/cm2 and 1.30/cm2, respectively). Slight inhibiting effects of GST-P+ foci were apparent in rats receiving uracil, but not sodium L-ascorbate, in the present experiment. Thus, it was confirmed that the bladder carcinogen BBN also targets the liver. The results, from quantitative analysis of small GST-P+ foci as end-point marker lesions, indicate considerable strain differences, but that liver tumor modifying potential of test chemicals can be evaluated in I/P protocols for urinary bladder carcinogenesis using any strain of rat.