Lack of change in the levels of liver and kidney cytochrome P-450 isozymesin p53(+/-) knockout mice treated with N-butyl-N-(4-hydroxybutyl)nitrosamine

We have previously shown that p53(+/-) knockout mice are highly sensitive t o urinary bladder carcinogenesis induced by N-butyl-N-(4-hydroxybutyl)nitro samine (BBN) in spite of a lack of effects of p53 heterozygosity on N-butyl -N-(3-carboxypropyl)nitrosamine (BCPN) excretion in urine. To determine the influence of p53 deficiency on in vitro formation of BCPN, mutagenicity of BBN and BCPN and levels of several cytochrome P450 (CYP) isozymes, groups of five p53(+/-) knockout and wild-type mice (littermates), as well as anim als of the C57BL/6 parental strain, were administered 0.025% BBN in their d rinking water for 4 weeks. The livers and kidneys were then used for analys es of BBN metabolism, western immunoblotting and Ames liquid incubation. BB N treatment caused a slight decrease in BCPN formation in the livers of C57 BL/6 mice, but there was no significant difference between p53 knockout, wi ld-type and C57BL/6 mice. In kidney BCPN formation in p53 knockout mice was 33-46% less than that in their wild-type counterparts. Using anti-rat CYP antibodies, CYP1A2, 2B9/10, 2E1 and 3A11/13 were constitutively detected in liver microsomes and CYP2E1 and 3A11/13 in the kidney. Densitometric deter mination of these CYP proteins revealed no significant variation in levels detected in both tissues among the four groups of mice. BBN and BCPN were n ot mutagenic for Salmonella typhimurium TA100 in either the absence or pres ence of liver S9 from untreated mice and rats and from p53 knockout mice tr eated with BBN. In conclusion, p53 deficiency and BBN had no enhancing effe cts on metabolism of BBN to BCPN and expression of the CYP isozymes typical ly responsible for activation of environmental carcinogens, including both of the N-nitrosamines tested, and their mutagenicity, indicating that the h igh susceptibility of p53(+/-) knockout mice is not attributable to metabol ic activation in liver and kidney by CYP isozymes or urinary excretion of B CPN.