Tissue-specific induction of cytochromes P450 1A1 and 1B1 by polycyclic aromatic hydrocarbons and polychlorinated biphenyls in engineered C57BL/6J mice of arylhydrocarbon receptor gene

Abstract

Tissue-specific induction of mRNA of cytochrome P450 (P450 or CYP) 1A1 and 1B1 by polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) was investigated in wild and arylhydrocarbon receptor (AhR)-deficient C57BL/6J mice. Ratios of mRNA expression of CYP1A1 or CYP1B1 over β-actin were determined and used to compare levels of expression and induction of these P450s by PAHs and PCBs in various organs. CYP1A1 mRNA was detected in control mice at very low levels in liver, lung, heart, kidney, intestine, thymus, testis, uterus, ovary, and brain and was highly induced in these organs by benzo[ a]pyrene and 3,4,3′,4′-tetrachlorobiphenyl in AhR(+/+) mice. In AhR(+/+) and AhR(−/−) mice, CYP1B1 mRNA was found to be constitutively expressed at significant levels in heart (the ratio of mRNAs of CYP1B1 to β-actin was ∼0.6), kidney (∼0.8), intestine (∼0.3), testis (∼0.9), thymus (∼0.4), uterus (∼0.3), ovary (∼1.4), and brain (∼0.4), whereas it was low in liver and lung (the mRNA ratio to β-actin was <0.2 in these cases). CYP1B1 in the latter two organs was highly induced by PAHs and 3,4,3′,4′-tetrachlorobiphenyl in AhR(+/+) mice. The induction of CYP1B1 by PAHs and PCBs was more extensive in organs in which the constitutive expression of CYP1B1 was low. For example, CYP1B1 was induced 9-fold and 10-fold by benzo[ a]pyrene and 3,4,3′,4′-tetrachlorobiphenyl in livers of male and female mice, respectively, whereas in testis and ovary, the fold induction of CYP1B1 by two inducers was only 1.1 and 1.4, respectively. Liver microsomal xenobiotic oxidation activities were induced by these PAHs and PCBs in male and female AhR(+/+) mice. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in their expression in extrahepatic organs of mice and could be induced by PAHs and PCBs with different extents of induction depending on the inducers used and the organs examined in AhR(+/+) mice. The findings of significant levels of constitutive expression of CYP1B1 in AhR(−/−) mice as well as AhR(+/+) mice in several organs including heart, kidney, thymus, testis, ovary, and brain in AhR(−/−) mice as well as AhR(+/+) mice are of importance in understanding the basis of toxicity and carcinogenesis by chemicals that are metabolized by CYP1B1.