Expression and activity of microsomal epoxide hydrolase in follicles isolated from mouse ovaries

Microsomal epoxide hydrolase (mEH) is involved in the detoxification of xenobiotics that are or can form epoxide metabolites, including the ovotoxicant, 4-vinylcyclohexene (VCH). This industrial chemical is bioactivated by hepatic CYP450 to the diepoxide metabolite, VCD, which destroys mouse small preantral follicles (F1). Since ovarian mEH may play a role in VCD detoxification, these studies investigated the expression and activity of mEH in isolated ovarian fractions. Mice were given 1 or 15 daily doses (ip) of VCH (7.4 mmol/kg/day) or VCD (0.57 mmol/kg/day); 4 h following the final dose, ovaries were removed, distinct populations of intact follicles (F1, 25-100 μm; F2, 100-250 μm; F3, > 250 μm) and interstitial cells (Int) were isolated, and total RNA and protein were extracted. Real-time polymerase chain reaction and the substrate cis-stilbene oxide (CSO; 12.5 μM) were used to evaluate expression and specific activity of mEH, respectively. Confocal microscopy evaluated ovarian distribution of mEH protein. Expression of mRNA encoding mEH was increased in F1 (410 ± 5% VCH; 292 ± 5% VCD) and F2 (1379 ± 4% VCH; 381 ± 11% VCD) follicles following repeated dosing with VCH or VCD. Catalytic activity of mEH increased in F1 follicles following repeated dosing with VCH/VCD (381 ± 11% VCH; 384 ± 27% VCD). Visualized by confocal microscopy, mEH protein was distributed throughout the ovary with the greatest staining intensity in the interstitial cells and staining in the theca cells that was increased by dosing (56 ± 0.8% VCH; 29 ± 0.9% VCD). We conclude that mEH is expressed and is functional in mouse ovarian follicles. Additionally, in vivo dosing with VCH and VCD affects these parameters.