Lack of change in the levels of liver and kidney cytochrome P-450 isozymes in p53(+/–) knockout mice treated with N-butyl-N-(4-hydroxybutyl)nitrosamine
Abstract
Abstract We have previously shown that p53 (+/–) knockout mice are highly sensitive to urinary bladder carcinogenesis induced by N -butyl- N -(4-hydroxybutyl)nitrosamine (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 animals of the C57BL/6 parental strain, were administered 0.025% BBN in their drinking water for 4 weeks. The livers and kidneys were then used for analyses of BBN metabolism, western immunoblotting and Ames liquid incubation. BBN treatment caused a slight decrease in BCPN formation in the livers of C57BL/6 mice, but there was no significant difference between p53 knockout, wild-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 determination of these CYP proteins revealed no significant variation in levels detected in both tissues among the four groups of mice. BBN and BCPN were not mutagenic for Salmonella typhimurium TA100 in either the absence or presence of liver S9 from untreated mice and rats and from p53 knockout mice treated with BBN. In conclusion, p53 deficiency and BBN had no enhancing effects on metabolism of BBN to BCPN and expression of the CYP isozymes typically responsible for activation of environmental carcinogens, including both of the N -nitrosamines tested, and their mutagenicity, indicating that the high susceptibility of p53 (+/–) knockout mice is not attributable to metabolic activation in liver and kidney by CYP isozymes or urinary excretion of BCPN. © UK Environmental Mutagen Society/Oxford University Press 2001