Induction of P-450 cytochromes 2E2, 1A1, and 1A2 by imidazole in neonatal rabbits

Cytochrome P-450 2E1 is induced in adult rabbits by treatment with alcohol, imidazole, and a variety of other agents, as shown earlier in this laboratory, but it is not known whether the highly homologous P-450 2E2 is similarly induced. In this study, the effects of imidazole on 2E2 expression were examined in neonatal rabbits, in which 2E1 is not detectable. Treatment of the animals with imidazole on days 8 through 11 after birth caused a 3- fold increase in the content of total P-450 in liver microsomes. In contrast, the microsomal content of cytochrome b₅ and NADPH-P450 reductase was not changed. Immunoblot analysis revealed a significant increase in the level of P-450 2E2 (3-fold) as well as 1A1 (>10-fold) and 1A2 (>2-fold) in hepatic microsomes from imidazole-treated neonatal rabbits. The rates of microsomal N-demethylation of N-nitrosodimethylamine and O-deethylation of 7- ethoxyresorufin were similarly increased from 1.3 and 0.03 nmol/min/mg protein, respectively, to 5.6 and 0.24 nmol/min/mg protein, respectively, by imidazole treatment. Blot analysis indicated that the levels of 2E2, 1A1, and 1A2 mRNAs are not increased by imidazole treatment and that 2E1 mRNA is not detectable in either untreated or imidazole-treated neonates. The induction of P-450 2E2 was confirmed by NH₂-terminal amino acid sequence analysis of immunopurified 2E protein from hepatic microsomes of imidazole-treated neonatal rabbits. Antibodies to P-450 2E1 were found to inhibit more than 90% of the N-nitrosodimethylamine demethylase activity in microsomes from either untreated or imidazole-treated rabbits, indicating that P-450 2E2, like the 2E1 cytochrome, may play an important role in the microsomal metabolism of certain carcinogens.