Background: Cytochrome P450 3A4 (CYP3A4) is an important drug-metabolizing enzyme
that is expressed in the liver and small intestine of humans. Various factors influence the expression of
CYP3A4, but gender difference in CYP3A4 expression remains debatable.
Objective: To clarify gender difference of hepatic and intestinal CYP3A4 in CYP3A-humanized mice
generated by a human artificial chromosome (HAC) vector system. The CYP3A-humanized (CYP3AHAC)
mice have essential regulatory regions, including promoters and enhancers, and unknown elements
affecting the expression of CYP3A4.
Methods: We examined the expression and activity of hepatic and intestinal CYP3A4 in male and female
CYP3A-HAC mice. CYP3A activity was determined as α- and 4-hydroxylation activity of triazolam
in liver and intestinal microsomes. Expression level of CYP3A protein was determined by Western
blot analysis. Expression level of CYP3A4 mRNA was measured by quantitative real-time PCR.
Results: The results showed that triazolam hydroxylation activities and protein levels of CYP3A in the
liver were significantly higher in female than in male CYP3A-HAC mice, whereas those in the intestine
were not significantly different between the genders. In addition, the expression of CYP3A4 mRNA
showed a tendency similar to that found for the activity and expression of CYP3A protein in the liver
and intestine of CYP3A-HAC mice.
Conclusion: These findings suggest that the expression and activity levels of CYP3A4 in the liver are
higher in females than in males, whereas there is no gender difference in the levels in the intestine of