Epoxide hydrolases (EC 3.3.2.3 ) play an important role in both the activation and detoxification of exogenous
chemicals such as polycyclic aromatic hydrocarbons.
NCBI Summary:
Epoxide hydrolase plays an important role in both the activation and detoxification of exogenous chemicals such as polycyclic aromatic hydrocarbons.
General function
Enzyme, Oxidoreductase
Comment
Cellular localization
Cytoplasmic, microsome
Comment
Ovarian function
Steroid metabolism
Comment
Cytochrome p450-dependent lipid metabolism in preovulatory follicles.
Newman JW, et al .
Estrogen biosynthesis and proteolysis are both important processes involved in ovarian follicular development, which may be influenced by cytochrome P450 (CYP)-dependent fatty acid metabolites. However, CYP-dependent lipid metabolism has not been characterized with respect to follicular maturation in vivo. Therefore, follicular fluid was collected in the hours before and after the LH surge in pigs, and concentrations of epoxy, hydroxy, and dihydroxy lipids were measured by liquid chromatography tandem mass spectrometry. Arachidonate oxidation and epoxyeicosatrienoic acid hydrolysis to dihydroxyeicosatrienoic acids (DHETs) were also assessed in thecal and granulosa tissue fractions, and the expression of CYP epoxygenases was evaluated by immunoblots using available antisera. To evaluate soluble epoxide hydrolase (sEH) expression, the porcine sEH was cloned from ovarian tissue, expressed and purified for antibody generation. The follicular fluid oxylipin concentrations ranged from 1-150 nm depending on the compound and estrous stage. The follicular fluid concentrations of CYP-dependent oxylipins increased at estrus, as did sEH expression; however, significant changes in epoxides were not observed, and the 11,12-DHET peak was delayed. The ratio of 14,15-DHET:11,12-DHET across all samples correlated with the log of follicular fluid estradiol concentrations (P < 0.01). Epoxygenase activities were similar in theca and granulosa, varying little with follicular development, whereas the decline of a single CYP2J isoform at ovulation was observed by immunoblots. The sEH activity was higher in granulosa than in theca. Finally, the dynamic changes in follicular CYP-dependent arachidonic acid metabolites and their modulatory function in vascular models suggest roles for these metabolites in follicular maturation, which may include regulation of estradiol biosynthesis and preovulatory remodeling of the follicular wall that should be fully explored in future studies.
Expression regulated by
Growth Factors/ cytokines, vcd
Comment
Ovarian expressed microsomal epoxide hydrolase: Role in detoxification of 4-vinylcyclohexene diepoxide and regulation by phosphatidylinositol-3 kinase signaling. Bhattacharya P et al. 4-vinylcyclohexene diepoxide (VCD) is a metabolite of 4-vinylcyclohexene (VCH) which has the potential to be formed in the ovary through CYP2E1 activity. VCD specifically destroys primordial and small primary follicles in the rodent ovary. Mouse ovaries exposed to VCD demonstrate increased mRNA and protein expression of microsomal epoxide hydrolase (mEH), and an inactive tetrol metabolite (4-(1,2-dihydroxy)ethyl-1,2-dihydroxycyclohexane) can be formed in mouse ovarian follicles, potentially through detoxification action of mEH. In contrast, mEH can bioactivate another ovotoxic chemical, 7,12-dimethylbenz[a]anthracene (DMBA) to a more toxic compound, DMBA-3,4-diol-1,2-epoxide. Thus, the present study evaluated a functional role for mEH during detoxification of VCD. Additionally, because inhibition of the phosphatidyinositol-3 kinase (PI3K) signaling pathway in a previous study protected primordial follicles from VCD-induced destruction, but accelerated DMBA-induced ovotoxicity, a role for PI3K in ovarian mEH regulation was evaluated. Using a post-natal day (PND) 4 Fischer 344 rat whole ovary culture system inhibition of mEH using cyclohexene oxide during VCD exposure resulted in a greater (P<0.05) loss of primordial and small primary follicles relative to VCD-treated ovaries. Also, relative to controls, meh mRNA was increased (P<0.05) on day 4 of VCD (30?M) exposure, followed by increased (P<0.05) mEH protein after 6days. Furthermore, inhibition of PI3K signaling increased mEH mRNA and protein expression. Thus, these results support a functional role for mEH in the rat ovary, and demonstrate the involvement of PI3K signaling in regulation of ovarian xenobiotic metabolism by mEH.
Ovarian localization
Granulosa, Theca, Luteal cells, Small luteal cells, Large luteal cells
Comment
Acute 7,12-dimethylbenz anthracene exposure causes differential concentration-dependent follicle depletion and gene expression in neonatal rat ovaries. Madden JA 2014 et al.
Chronic exposure to the polycyclic aromatic hydrocarbon 7,12-dimethylbenzanthracene (DMBA), generated during combustion of organic matter including cigarette smoke, depletes all ovarian follicle types in the mouse and rat, and in vitro models mimic this effect. To investigate the mechanisms involved in follicular depletion during acute DMBA exposure, two concentrations of DMBA at which follicle depletion has (75nM) and has not (12.5nM) been observed were investigated. Postnatal day four F344 rat ovaries were maintained in culture for four days before a single exposure to vehicle control (1% DMSO; CT) or DMBA (12nM; low-concentration or 75nM; high-concentration). After four or eight additional days of culture, DMBA-induced follicle depletion was evaluated via follicle enumeration. Relative to control, DMBA did not affect follicle numbers after 4days of exposure, but induced large primary follicle loss at both concentrations after 8days; while, the low-concentration DMBA also caused secondary follicle depletion. Neither concentration affected primordial or small primary follicle number. RNA was isolated and quantitative RT-PCR performed prior to follicle loss to measure mRNA levels of genes involved in xenobiotic metabolism (Cyp2e1, Gstmu, Gstpi, Ephx1), autophagy (Atg7, Becn1), oxidative stress response (Sod1, Sod2) and the phosphatidylinositol 3-kinase (PI3K) pathway (Kitlg, cKit, Akt1) 1, 2 and 4days after exposure. With the exception of Atg7 and cKit, DMBA increased (P<0.05) expression of all genes investigated. Also, BECN1 and pAKT(Thr308) protein levels were increased while cKIT was decreased by DMBA exposure. Taken together, these results suggest an increase in DMBA bioactivation, add to the mechanistic understanding of DMBA-induced ovotoxicity and raise concern regarding female low concentration DMBA exposures.
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Hattori, et al 2000 reported that epoxide hydrolase affects estrogen production in the human
ovary.
To investigate the mechanisms of ovarian cell differentiation, the authors raised a new monoclonal antibody, HCL-3, which reacted
with human luteal cells. It also reacted with human and porcine hepatocytes. The immunoaffinity-purified HCL-3 antigen
from human corpora lutea (CL) was shown to be a 46-kDa protein. The N-terminal 22 amino acids of the 46-kDa protein
from porcine liver exhibited high homology (82%) to human microsomal epoxide hydrolase (mEH). The purified HCL-3
antigen from human CL or porcine liver showed EH enzyme activity, confirming that HCL-3 antigen is identical to mEH,
which is reported to detoxify the toxic substrates in the liver. In human follicles, mEH was immunohistochemically detected
on granulosa and theca interna cells. In the menstrual and pregnant CL, mEH was also expressed on large and small luteal
cells. A competitive inhibitor of EH, 1,2-epoxy-3,3,3-trichloropropane, inhibited the conversion of estradiol from testosterone by granulosa cells cultured in vitro, indicating the involvement of mEH in ovarian estrogen production. Because
anticonvulsant sodium valproate and its analogues were reported to inhibit EH enzyme activity, these findings provide a new
insight into the etiology of endocrine disorders that are frequently observed among epileptic patients taking anticonvulsant
drugs.
Follicle stages
Antral, Preovulatory, Corpus luteum
Comment
Cannady EA et al 2002 reported the expression and activity of microsomal epoxide hydrolase in follicles isolated from mouse ovaries.