Dose-response studies on the induction of liver cytochromes P4501A1 and 1B1 by polycyclic aromatic hydrocarbons in arylhydrocarbon-responsive C57BL/6J mice

1. To determine the biological effects of 23 polycyclic aromatic hydrocarbons (PAHs) and 3,4,3',4'-tetrachlorobiphenyl, the dose-response studies of the induction of CYP1-dependent xenobiotic oxidation activities by these chemicals in liver microsomes of C57BL/6J mice were studied. 2. In arylhydrocarbon-responsive C57BL/6J mice, the liver microsomal xenobiotic oxidation with substrates of 7-ethoxyresorufin, 7-ethoxycoumarin, (+/-)- benzo[a] pyrene-7,8- diol, dibenzo[a, l] pyrene-11,12-diol and 2-amino-3,5-dimethylimidazo[4,5-f] quinoline increased by increasing the doses of PAHs to mice, particularly when the PAHs that have been reported to be carcinogenic in experimental animals were used. In arylhydrocarbon receptor-knockout mice, there were no increases in liver microsomal 7-ethoxyresorufin O- deethylation activities nor in liver mRNA levels of CYP1A1, 1A2 and 1B1 by these chemicals. 3. Of the chemicals examined, benzo[k] fluoranthene, benzo[ b] fluoranthene, benzo[ j]. uoranthene, 3-methylcholanthrene, dibenz[ a, h] anthracene, dibenz[ a, c] anthracene and 3,4,3',4'-tetrachlorobiphenyl were potent inducers of the induction of liver microsomal 7- ethoxyresorufin O-deethylation in mice. 4. Other PAHs such as 5-methylchrysene, benzo[a] pyrene, dibenzo[a, l] pyrene, dibenz[ a, j] acridine, benzo[ a] anthracene and 7,12-dimethylbenz[ a] anthracene moderately induced 7-ethoxyresorufin O-deethylation activities in mice. PAHs reported to be weak or less carcinogenic in experimental animals did not induce the xenobiotic oxidation activities of CYP1A1 and 1B1 in the mice. 5. The results suggest that induction of liver microsomal CYP1-dependent xenobiotic oxidation activities is a good tool in determining the potencies of carcinogenic PAHs in arylhydrocarbon- responsive C57BL/6J mice.