PARENT SESSION
PLATFORM SESSION 13. TOXICOLOGY

Monday, August 2, 2004
2:00 PM–4:00 PM
Buchanan A204
Chair: Leon Earl Gray, Jr. Co-Chair: Nigel Noriega

(321) POTENTIAL INVOLVEMENT OF CYP 2E1 ENZYME IN OVOTOXICITY INDUCED BY 4-VINYLCYCLOHEXENE.

Rajapaksa, Kathila¹, Sipes, I. Glenn², Hoyer, Patricia ¹, ¹ Department of Physiology, Tucson, AZ² Department of Pharmacology and Toxicology, Tucson, AZ

ABSTRACT- The occupational chemical 4-vinylcyclohexene (VCH) causes loss of preantral follicles in mice after repeated exposure. Previous studies have shown that VCH can be bioactivated to a monoepoxide (VCM) and subsequently to a diepoxde (VCD) in the liver by cytochrome P450 (CYP 450) enzymes. Structure activity studies have shown that VCD is the ultimate ovarian toxicant. Studies by Fontaine et al. (2001) indicate CYP 2A and CYP 2B are the likely isoforms that metabolize VCH in hepatic tissue. Cannady et al. (2003) demonstrated that CYP 450 isoforms are expressed in mouse ovary and are induced by repeated VCH and VCD dosing. However, results of these studies suggest CYP2E1 is the major ovarian isoform contributing to metabolism of VCH. Thus to further investigate the role of CYP 2E1 in VCH bioactivation, a study was conducted in CYP 2E1 deficient mice. CYP2E1 -/- mice (d28) were dosed daily (15 d) with VCH (800mg/kg; ip), VCM (340mg/kg; ip), VCD (80mg/kg; ip) or vehicle (sesame oil; ip). Four hours following the final dose, ovaries were collected, prepared for histological analysis, and evaluated for follicle populations. Relative to controls, VCD decreased (P<0.05) primordial follicle counts by 74.5% (control, 192 ± 20; VCD, 49 ± 12) and small primary follicle counts by 49.1% (control, 57 ± 8; VCD, 29 ± 4). VCM decreased (P<0.05) primordial follicles by 51.5% (control, 192 ± 20; VCM, 93 ± 13) with a 29.8% trend for decreasing (P = 0.052) small primary follicles (control 57 ± 8; VCM 40 ± 6). VCH decreased (P<0.05) small primary follicles by 37.3% (control, 59 ± 8; VCH, 37 ± 3) but not primordial (P = 0.12) follicles. There were no differences in large primary, secondary, and antral follicles between treatment groups. In summary, CYP 2E1 enzyme does not appear to be required for conversion of VCM to VCD. Furthermore, CYP 2E1 is only partially effective at converting VCH to VCD in the mouse. Therefore, hepatic metabolism of VCH by CYP 2A and CYP 2B may be contributing to the partial toxicity seen in ovaries of VCH treated mice. These studies also demonstrate a possible role for ovarian CYP 2E1 in VCH bioactivation leading to potentiation of ovarian toxicity. Future studies will utilize an ovarian culture system with ovaries from CYP 2E1 -/- mice to investigate the role of CYP 2E1 in ovarian directed bioactivation of VCH. (ES08979; ES09246; Center Grant ES06694)

KEY WORDS: 4-vinylcyclohexene , ovarian toxicity , CYP 450