Effects of 8-methoxypsoralen on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in mice.

8-Methoxypsoralen (8-MOP) is a well established drug in the treatment of various skin diseases. Pretreatment of mice with 8-MOP before administration of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) significantly reduced the incidence of NNK-induced tumor. The present study was designed to evaluate the in vivo effects of 8-MOP on the bioactivation of NNK in mice. Decrease in the α-hydroxylation of NNK in mouse blood and tissues was observed as the most pronounced effect of 8-MOP. The catalytic property of cytochrome P450 2A5 (CYP2A5) enzyme in mice was determined by the coumarin 7-hydroxylation reaction, suggesting that 8-MOP produced remarkable inhibition on CYP2A5 in female C57BL/6 mice. These results implied that 8-MOP could prevent NNK-induced mutagenesis and tumorigenesis in mice through the inhibition of NNK α-hydroxylation, which may be achieved through the effect of 8-MOP on the bioactivities of CYP2A5.