Ovotoxicity in female Fischer rats and B6 mice induced by low-dose exposure to three polycyclic aromatic hydrocarbons: comparison through calculation of an ovotoxic index.

Extensive destruction of primordial follicles by exposure to ovarian toxicants can cause early menopause in women. Primordial follicle destruction is known to result from dosing of mice and rats with three polycyclic aromatic hydrocarbons (PAHs), contaminants commonly found in cigarette smoke. Therefore, the purpose of this study was to compare relative ovotoxicity in mice and rats using the PAHs, 9, 10-dimethylbenzanthracene (DMBA), 3-methylcholanthrene (3-MC), and benzo[a]pyrene (BaP). Female B6C3F(1) mice and Fischer 344 rats (age 28 days) were dosed daily (ip) with vehicle control or a range of doses of the PAHs. Two groups were dosed with the occupational chemicals 4-vinylcyclohexene (VCH; 500 mg/kg ip) or its diepoxide metabolite (VCD; 80 mg/kg ip), other known ovotoxicants. After 15 days, ovaries were collected, histologically prepared, and follicles were microscopically classified (primordial, primary, or secondary) and counted. The dose of each chemical that produced 50% loss of primordial follicles (p < 0.05) was determined (ED50) and used to calculate an ovotoxic index (OI) in mice and rats (ED50 x 15 days). Thus, a chemical with a lower OI is more toxic. Primordial follicles in mice displayed a lower OI than rats to all chemicals tested (mouse: DMBA, 0.0012; 3-MC, 0.003; BaP, 0.18; VCD, 6.8; VCH, 69; rat: DMBA, 0.45; 3-MC, >3.4; BaP, >3.6; VCD, 8.6; VCH, >69). In mice, DMBA targeted primordial follicles at a 10-fold lower concentration than primary and secondary follicles, whereas 3-MC exposure targeted primordial and primary follicles to a similar degree. BaP exposure targeted primordial and primary follicles at a 100-fold higher concentration than DMBA or 3-MC. Although BaP and 3-MC did not target secondary follicles in mice, secondary follicles in rats were most susceptible to 3-MC. Furthermore, all three PAHs were more ovotoxic (lower OI) with repeated low-dose exposure compared with OIs calculated from other studies using single high-dose exposures. The earliest day of impending primordial follicle loss (increase in percentage of unhealthy follicles, p < 0.05) in mice was factored into the OI (ED50 x first day of damage, p < 0.05 x % healthy follicles remaining, relative to control). The revised OI became DMBA d15, 0.0006; 3-MC d12, 0.0008; BaP d15, 0.132; and VCD d8, 2.96. These results predict that DMBA is the most potent ovarian toxicant (lower OI) in both species but VCD damages primordial follicles after shorter exposures. Calculation of the OI in mice and rats represents a method for comparing the relative potential risk of a variety of chemicals that produce ovarian damage at low levels following repeated exposures. The results also demonstrate that low-dose repeated exposures are substantially more toxic to the ovary than a single high-dose exposure. This finding is particularly important in view of the implications for chronic low-dose exposures of women to environmental chemicals.

Borman SM ，Christian PJ ，Sipes IG ，Hoyer PB ... -  《TOXICOLOGY AND APPLIED PHARMACOLOGY》

Involvement of apoptosis in 4-vinylcyclohexene diepoxide-induced ovotoxicity in rats.

Springer LN ，McAsey ME ，Flaws JA ，Tilly JL ，Sipes IG ，Hoyer PB ... -  《TOXICOLOGY AND APPLIED PHARMACOLOGY》

Initiation of delayed ovotoxicity by in vitro and in vivo exposures of rat ovaries to 4-vinylcyclohexene diepoxide.

Devine PJ ，Sipes IG ，Hoyer PB 《REPRODUCTIVE TOXICOLOGY》

Characterization of a rat in vitro ovarian culture system to study the ovarian toxicant 4-vinylcyclohexene diepoxide.

Devine PJ ，Sipes IG ，Skinner MK ，Hoyer PB ... -  《TOXICOLOGY AND APPLIED PHARMACOLOGY》

A single dose of the ovotoxicant 4-vinylcyclohexene diepoxide is protective in rat primary ovarian follicles.

Repeated dosing of rats with the ovotoxic chemical, 4-vinylcyclohexene diepoxide (VCD), destroys primordial and primary ovarian follicles via apoptosis (physiological cell death) by accelerating the normal rate of atresia. The present study investigated the effect of a single dose (1x) of VCD. Immature (d28) female Fischer 344 rats were dosed 1x or 15x with VCD (80 mg/kg ip). Ovaries were collected 24 h or 15 days following 1x VCD or after 15x for classification and evaluation. Following 1x VCD the number of healthy primary follicles was greater (p < 0.05) than control 24 h and 15 days later. This effect reflected a slowing of the normal rate of atresia seen in control ovaries. There was no effect of a single dose on primordial or growing follicles at any time. Expression of mRNA encoding the cell death gene bax was reduced (p < 0.05) on d1 after 1x VCD in isolated primordial and primary follicles. These observations were in contrast to a decreased (p < 0. 05) number of healthy primary and primordial follicles in ovaries and increased (p < 0.05) bax mRNA in isolated follicles from rats dosed 15x for 15 days. Immunofluorescence staining revealed that, the distribution of Bax protein was similar between ovaries from controls and 1x or 15x VCD-treated rats. These data provide evidence for a "protective" response against the normal rate of atresia in primary ovarian follicles following exposure to 1x VCD. Additionally, changes in expression of bax mRNA paralleled alterations in the rate of atresia.

Borman SM ，VanDePol BJ ，Kao S ，Thompson KE ，Sipes IG ，Hoyer PB ... -  《TOXICOLOGY AND APPLIED PHARMACOLOGY》