GENDER DIFFERENCES IN HEPATIC EXPRESSION OF FLAVIN-CONTAINING MONOOXYGENASE ISOFORMS (FMO1, FMO3, AND FMO5) IN MICE

Hepatic flavin-containing monooxygenase (FMO) activity of microsomes f rom adult CD-1, Swiss-Webster, C578L/6, and DBA/2 mice was found to be significantly higher in females than in males. Based on protein and m RNA levels in CD-1 mice, FMO forms responsible for the gender differen ce in FMO activity were FMO1 and FMO3. FMO1 expression was two to thre e times higher in female mice compared with males; FMO3, however, whic h was expressed at levels equivalent to FMO1 in female mice, was not d etected in males. The expression of FMO5 was approximately equal in bo th sexes. FMO2 and FMO4 transcripts were not evident in hepatic mRNA f rom mice. Protein and mRNA levels appear to be coregulated with regard to gender-selective or gender-specific expression of FMO1 or FMO3; re spectively. FMO5, which demonstrates no gender-selective expression in mice, may be regulated by different mechanisms. Examination of protei n levels among Swiss-Webster, C57BL/6, and DBA/2 strains revealed a ge nder-dependent expression of FMO isozymes identical to the CD-1 strain .