Involvement of CYP 2E1 enzyme in ovotoxicity caused by 4-vinylcyclohexene and its metabolites

Abstract

4-Vinylcyclohexene (VCH) is bioactivated by hepatic CYP 2A and 2B to a monoepoxide (VCM) and subsequently to an ovotoxic diepoxide metabolite (VCD). Studies suggest that the ovary can directly bioactivate VCH via CYP 2E1. The current study was designed to evaluate the role of ovarian CYP 2E1 in VCM-induced ovotoxicity. Postnatal day 4 B6C3F(1) and CYP 2E1 wild-type (+/+) and null (-/-) mouse ovaries were cultured (15 days) with VCD (30 microM), 1,2-VCM (125-1000 microM), or vehicle. Twenty-eight days female CYP 2E1 +/+ and -/- mice were dosed daily (15 days; ip) with VCH, 1,2-VCM, VCD or vehicle. Following culture or in vivo dosing, ovaries were histologically evaluated. In culture, VCD decreased (p<0.05) primordial and primary follicles in ovaries from all three groups of mice. 1,2-VCM decreased (p<0.05) primordial follicles in B6C3F(1) and CYP 2E1 +/+ ovaries, but not in CYP 2E1 -/- ovaries in culture. 1,2-VCM did not affect primary follicles in any group of mouse ovaries. Conversely, following in vivo dosing, primordial and primary follicles were reduced (p<0.05) by VCD and VCM in CYP2E1 +/+ and -/-, and by VCH in +/+ mice. The data demonstrate that, whereas in vitro ovarian bioactivation of VCM requires CYP 2E1 enzyme, in vivo CYP 2E1 plays a minimal role. Thus, the findings support that hepatic metabolism dominates the contribution made by the ovary in bioactivation of VCM to its ovotoxic metabolite, VCD. This study also demonstrates the use of a novel ovarian culture system to evaluate ovary-specific metabolism of xenobiotics.

Expression of ovarian microsomal epoxide hydrolase and glutathione S-transferase during onset of VCD-induced ovotoxicity in B6C3F1 mice

“…Such cells may be located in the interstitium, and supports a capacity for the interstitial ovarian compartment to express high levels of xenobiotic detoxification enzymes. This suggests a potential role of the interstitium to provide protection of the germ cell population (ovarian follicles) against xenobiotic exposure (Cannady et al, 2003, Rajapaska et al, 2007a.…”

“…VCH is metabolized in the liver by cytochrome P450 enzyme isoforms, CYP2A and CYP2B (Fontaine et al, 2001a,b). Conversely, in the ovary the cytochrome P450 enzyme isoform CYP2E1 is thought to convert precursors to the ovotoxic form, VCD (Cannady et al, 2003;Rajapaska et al, 2007a).…”

All Your Eggs in One Basket: Mechanisms of Xenobiotic Induced Female Reproductive Senescence

“…Studies have shown VCD to be the ultimate ovotoxicant, targeting both primordial and primary follicles for depletion (Hu et al, 2001;Smith et al, 1990;Sobinoff et al, 2010). As demonstrated in vivo and in vitro via knockout studies, VCH/VCM is bioactivated into VCD exclusively by the cyp2e1 isoform in the ovary (Rajapaksa et al, 2007a). Rajapaksa et al (2007a) cultured neonatal ovaries from both cyp2e1 +/+ and cyp2e1 -/-neonatal mice in VCM and VCD containing media.…”

“…Cellular toxicity occurs when these adducts disrupt the normal structure and/or function of these macromolecules, resulting in apoptosis, necrosis or carcinogenesis. The main site of xenobiotic biotransformation within the body is the liver, although the ovary is capable of both phase I and phase II metabolism (Igawa et al, 2009;Rajapaksa et al, 2007aRajapaksa et al, , 2007bShimada et al, 2003). Therefore, there is potential for the vulnerable primordial follicle to come into contact with bioactivated ovotoxic metabolites via several routes of exposure.…”

“…A number of studies performed in vitro have revealed that the ovary is capable of the localised bioactivation of a number of xenobiotics into ovotoxic intermediates which target primordial follicles for destruction (Rajapaksa et al, 2007a(Rajapaksa et al, , 2007b). An example of this localised bioactivation is the reported metabolism of the polycyclic aromatic hydrocarbon DMBA (Fig.3).…”