Differential inducibility of specific mRNA corresponding to five CYP3A isoforms in female rat liver by RU486 and food deprivation - Comparison with protein abundance and enzymic activities

The induction of cytochrome P450 3A (CYP3A) protein and mRNA by RU486 [17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)-17 alpha-1-propyl-estra-4,9-dien-3-one] treatment and food deprivation in female rat liver was studied using Western blotting and competitive reverse transcription-polymerase chain reaction (RT-PCR). CYP3A apoprotein levels inc;eased in response to food deprivation and to RU486 treatment, and the combination of RU486 treatment plus food deprivation had an apr,arent additive effect. Food deprivation and RU486 treatment also caused increases in CYP3A1, CYP3A18, and CYP3A23 mRNA, and the combined effects of these treatments on each of these mRNA forms were synergistic. CYP3A2 mRNA was not detected in any of the treatment groups, and there was a lack of concordance between CYP3A9 mRNA levels and the specific messages corresponding to the other CYP3A isoforms. CYP3A9 mRNA levels were highest in food-deprived animals, whereas RU486 inhibited CYP3A9 mRNA expression and suppressed the induction effect of food deprivation. Food deprivation and RU486 treatment each separately caused increased microsomal diazepam C-3-hydroxylase activity, and the combined effects of these treatments on this monooxygenase were additive. In contrast, the [N-methyl-C-14]erythromycin demethylase activity of the fasted, RU486 treated group of rats did not differ from that of the untreated group, and kinetic analyses revealed that both groups of animals exhibited similar K-m and V-max values. These results suggest that CYP3A9 may be primarily responsible for erythromycin N-demethylation and that the isoforms induced by the combination of fasting and RU486 administration are CYP3A1, CYP3A23, and, to a lesser extent, CYP3A18. BIOCHEM PHARMACOL 56;4: 473-481, 1998. (C) 1998 Elsevier Science Inc.