Effect of CYP2E1 Gene Deletion in Mice on Expression of Microsomal Epoxide Hydrolase in Response to VCD Exposure

Abstract

Females are born with a finite number of primordial follicles. 4-Vinylcyclohexene diepoxide (VCD) is a metabolite formed by epoxidation of 4-vinylcyclohexene (VCH) via its two monoepoxides 1,2- and 7,8-4-vinylcyclohexene monoepoxide (VCM). VCD specifically destroys small preantral (primordial and small primary) follicles in the rodent ovary. The phase I enzyme, cytochrome P450 isoform 2E1 (CYP2E1) is involved in ovarian metabolism of VCM to VCD. Further, microsomal epoxide hydrolase (mEH) can detoxify VCD to an inactive tetrol (4-(1,2-dihydroxy)ethyl-1,2-dihydroxycyclohexane). This study evaluated the effects of VCD-induced ovotoxicity on mEH in CYP2E1+/+ and -/- mice (129S(1)/SvImJ background strain) using a postnatal day 4 mouse whole ovary culture system. The hypothesis of our study is that there is a relationship between CYP2E1 and mEH gene expression in the mouse ovary. Relative to control, VCD exposure caused follicle loss (p < 0.05) in ovaries from both genotypes; however, after 15 days, this loss was greater (p < 0.05) in CYP2E1+/+ ovaries. In a time course (2-15 days), relative to control, VCD (5 microM) caused an increase (p < 0.05) in mEH mRNA by 0.5-fold (day 10) and 1.84-fold (day 15) in CYP2E1-/- but not +/+ ovaries. 7,12-Dimethylbenz[a]anthracene (DMBA) also destroys ovarian follicles but, unlike VCD, is bioactivated by mEH to an ovotoxic 3,4-diol-1,2-epoxide metabolite. Incubation of ovaries in increasing concentrations of DMBA (0.5-1 microM, 15 days) resulted in greater (p < 0.05) follicle loss in CYP2E1-/-, relative to +/+ ovaries. With greater mEH (CYP2E1-/-), increased follicle loss with DMBA (bioactivation) and decreased follicle loss with VCD (detoxification) support that ovarian expression of CYP2E1 and mEH may be linked.

Small RNAs: Their Possible Roles in Reproductive Failure

“…It is important to note that the ovary has the capability to biotransform chemicals to more or less toxic metabolites, and these metabolic processes are highly active in ovarian tissues Keating 2011 , 2012b ;Bhattacharya et al 2012Bhattacharya et al , 2013Igawa et al 2009 ;Keating et al 2008aKeating et al , b , 2010Madden and Keating 2014 ) and contribute to the extent of ovotoxicity observed. We have demonstrated that many genes encoding ovarian chemical biotransformation enzymes are regulated by PI3K signaling (Bhattacharya and Keating 2012b ;Bhattacharya et al 2012 ), including aryl hydrocarbon receptor ( AhR ) and nuclear erythroid-related factor ( Nrf2 ) (Bhattacharya and Keating 2012b ), transcription factors that regulate xenobiotic metabolism.…”

Mechanisms of Ovarian Atresia Induced by Xenobiotic Exposures

“…How these effects are produced is becoming better understood and detailed for a number of chemical classes discussed herein. While outside of the scope of this chapter, it is important to note that the ovary has the capability to biotransform chemicals to more or less toxic metabolites, and these metabolism processes are highly active in ovarian tissues (Igawa et al, 2009;Keating et al, 2008a;2008b;Rajapaksa et al, 2007a;Rajapaksa et al, 2007b) and contribute to the extent of ovotoxicity observed.…”

Use of an organotypic mammalian in vitro follicle growth assay to facilitate female reproductive toxicity screening

“…Although in vitro follicle culture could be applied to study changes in follicle formation, follicle development, and ovarian physiology (Bhattacharya et al, 2013; Dutta et al, 2014; Igawa et al, 2009; Keating et al, 2008; Keating et al, 2008) in vitro follicle growth (IVFG) represents a more simple, rapid, and robust tool that can be applied to screening the effect of compounds on female reproductive function (Ahn et al, 2013; Cortvrindt and Smitz, 2002; Lenie et al, 2008; Lenie and Smitz, 2009; Peretz et al, 2012; Peretz and Flaws, 2013; Peretz et al, 2011; Peretz et al, 2013; Sun et al, 2008; Van Wemmel et al, 2005). The follicle is the functional unit of the ovary, comprised of germ cell (oocyte) and somatic cell (granulosa and theca cell) compartments (Albertini et al, 2001; Eppig et al, 2005).…”