Cytochrome P450 (CYP) 3A4 is an essential drug-metabolizing enzyme in humans, which shows substantial interindividual variation in response to various intrinsic and extrinsic factors such as sex and pregnancy. In humans, higher CYP3A4 metabolism has been observed in females compared with that in males and in pregnant compared with that in nonpregnant individuals, which has been linked to increased CYP3A4 expression in liver. However, sex differences and pregnancy-mediated changes in hepatic CYP3A4 expression and activity in vivo are not fully understood. In this study, we investigated the utility of a genetically engineered humanized mouse model that carries human CYP3A4/7, pregnane X receptor (PXR) and constitutive androstane receptor (CAR) (huPXR/CAR/CYP3A4/7) to recapitulate sex-associated and pregnancy-associated differences in the hepatic CYP3A4 expression and metabolism observed in humans. We found that female huPXR/CAR/CYP3A4/7 mice exhibited higher basal CYP3A4 mRNA levels and CYP3A4 absolute protein concentrations in liver, and higher 1-hydroxymidazolam formation in liver microsomes, compared with male humanized mice. In contrast, pregnant huPXR/CAR/CYP3A4/7 mice exhibited lower CYP3A4 mRNA levels, CYP3A4 absolute protein concentrations, and 1-hydroxymidazolam formation compared with nonpregnant and postpartum humanized mice. Expression of CAR and Cyp2b10 (a CAR responsive gene) were also higher in females and decreased during pregnancy and were positively correlated with hepatic CYP3A4 mRNA levels. Overall, the huPXR/CAR/CYP3A4/7 mouse model demonstrated utility to study higher basal hepatic CYP3A4 metabolism in females compared with that in males in vivo
however, this humanized mouse model did not demonstrate utility to study pregnancy-mediated increases in CYP3A4 drug substrate metabolism and clearance observed in humans. SIGNIFICANCE STATEMENT: This study assessed the impact of sex and pregnancy on hepatic CYP3A4 protein concentrations and metabolism in humanized PXR/CAR/CYP3A4 mice. Consistent with humans, female mice demonstrated higher hepatic CYP3A4 expression and activity than male mice. In contrast, pregnant mice showed decreased CYP3A4 expression and metabolism compared with nonpregnant mice. The humanized mouse model appeared useful to evaluate sex differences in basal hepatic CYP3A4 metabolism in vivo, but not to study the pregnancy-mediated increase in CYP3A4 metabolism observed during human pregnancy.