Impact of Obesity on Ovotoxicity Induced by 7,12-dimethylbenz[a]anthracene in Mice1

Abstract

Insulin, elevated during obesity, regulates xenobiotic biotransformation enzymes, potentially through phosphatidylinositol 3-kinase (PI3K) signaling, in extraovarian tissues. PI3K regulates oocyte viability, follicular activation, and ovarian chemical biotransformation. 7,12-Dimethylbenz[a]anthracene (DMBA), a carcinogen and ovotoxicant, destroys all stages of follicles, leading to premature ovarian failure. Obesity has been reported to promote DMBA-induced tumors, but it remains unknown whether obesity affects ovarian xenobiotic metabolism. Therefore, we investigated ovarian expression of xenobiotic metabolism genes-microsomal epoxide hydrolase (Ephx1), glutathione S-transferase (GST) class Pi (Gstp1) and class mu 1 (Gstm1), and PI3K-signaling members (protein kinase B [AKT] alpha [Akt1], beta [Akt2], and the forkhead transcription factor subfamily 3 [Foxo3])-in lean and obese female mice after DMBA exposure (1 mg/kg; intraperitoneal injection for 14 days). Relative to lean, obese mice had decreased (P < 0.05) healthy primordial and primary follicle numbers but increased (P < 0.05) secondary and preovulatory follicles numbers. Obesity increased (P < 0.05) Akt1, Akt2, Gstm1, and Ephx1 mRNA and pAKT(Ser473/Thr308), GSTM1, GSTP1, and EPHX1 protein levels. DMBA decreased (P < 0.05) ovarian weight in lean and obese mice, however, obese DMBA-treated females had a greater reduction (P < 0.05) in ovarian weight. In both lean and obese mice, DMBA decreased (P < 0.05) all stages of healthy follicle numbers, increased Gstp1 and Ephx1 mRNA as well as GSTM1, GSTP1, and EPHX1 protein levels, and decreased Akt1 and Akt2 mRNA as well as pAKT(Ser473) or pAKT(Thr308), FOXO3, and pFOXO3(Ser253) protein expression. There was an additive effect between obesity and DMBA exposure for increased Gstm1 and Ephx1 mRNA as well as GSTM1 and EPHX1 protein expression.

Acute 7,12-dimethylbenz[a]anthracene exposure causes differential concentration-dependent follicle depletion and gene expression in neonatal rat ovaries

“…DMBA is an ovotoxicant that causes follicle depletion, ultimately resulting in ovarian failure (Keating et al ., 2008; Igawa et al ., 2009; Nteeba et al, 2014). This study was designed to focus on effects of DMBA on large primary and secondary follicles by allowing these follicles to develop in culture before DMBA exposure.…”

“…In cultured rat pre-ovulatory follicles, co-treatment with GSH during DMBA exposure lessened follicle apoptosis (Tsai-Turton et al , 2007) suggesting the possible involvement of GST enzymes in catalyzing detoxification of DMBA. Gstpi has previously been identified to be involved in the ovarian response to DMBA exposure in neonatal rat ovaries (Bhattacharya and Keating, 2012), and adult mice exposed to DMBA (Nteeba et al ., 2014). Gstpi -null mice are also more sensitive to DMBA-induced skin tumors (Henderson et al ., 1998).…”

“…Gstpi -null mice are also more sensitive to DMBA-induced skin tumors (Henderson et al ., 1998). GSTMU has also been demonstrated to be increased in response to DMBA in the ovaries from obese adult mice (Nteeba et al ., 2014). In addition to the role of GSTPI and GSTMU in catalyzing GSH conjugation to xenobiotics, they can also play a role in inhibiting the pro-apoptotic proteins c-Jun N-terminal Kinase (JNK) (Keating et al , 2010; Bhattacharya and Keating, 2012) and apoptosis signal-regulating kinase 1 (ASK1) (Bhattacharya et al , 2013).…”

“…EPHX1 is increased in response to ovarian DMBA exposure and bioactivates DMBA to the ovotoxic metabolite DMBA-3,4-diol, 1,2-epoxide (Rajapaksa et al , 2007; Igawa et al , 2009; Nteeba et al ., 2014). Interestingly, although a trend for an increase in Ephx1 mRNA at the 75 nM DMBA concentration was observed, the low DMBA had a greater increase in Ephx1 after 4d of exposure.…”

Enhanced susceptibility of ovaries from obese mice to 7,12-dimethylbenz[a]anthracene-induced DNA damage

“…Also, increased ovarian PI3K signaling and mEH have been demonstrated in mice fed a high fat diet until obese (Nteeba et al , 2013). The obese lethal yellow mouse was also found to have both higher basal levels of mEH and greater mEH induction in response to DMBA exposure (Nteeba et al , 2014). These data suggest that ovarian tissue from obese females could have potentially greater exposure to the ovotoxic metabolite of DMBA, due to higher levels of ovarian mEH, and thus greater DMBA bioactivation to a metabolite that interacts with DNA (Miyata et al , 1999).…”