Benzo(a)pyrene inhibits ovulation in C57BL/6N mice

Mogroside V Alleviates Oocyte Meiotic Defects and Quality Deterioration in Benzo(a)pyrene-Exposed Mice

Accumulating evidence has demonstrated that benzo(a)pyrene (BaP) exposure adversely affects female reproduction, especially oocyte meiotic maturation and subsequent embryo development. Although we previously found that mogroside V (MV), a major bioactive component of S. grosvenorii, can protect oocytes from quality deterioration caused by certain stresses, whether MV can alleviate BaP exposure-mediated oocyte meiotic defects remains unknown. In this study, female mice were exposed to BaP and treated concomitantly with MV by gavage. We found that BaP exposure reduced the oocyte maturation rate and blastocyst formation rate, which was associated with increased abnormalities in spindle formation and chromosome alignment, reduced acetylated tubulin levels, damaged actin polymerization and reduced Juno levels, indicating that BaP exposure results in oocyte nucleic and cytoplasmic damage. Interestingly, MV treatment significantly alleviated all the BaP exposure-mediated defects mentioned above, indicating that MV can protect oocytes from BaP exposure-mediated nucleic and cytoplasmic damage. Additionally, BaP exposure increased intracellular ROS levels, meanwhile induced DNA damage and early apoptosis in oocytes, but MV treatment ameliorated these defective parameters, therefore it is possible that MV restored BaP-mediated oocyte defects by reducing oxidative stress. In summary, our findings demonstrate that MV might alleviate oocyte meiotic defects and quality deterioration in BaP-exposed mice.

Maternal benzo[a]pyrene exposure is correlated with the meiotic arrest and quality deterioration of offspring oocytes in mice

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon (PAH) in particulate matter that has a diameter of ≤2.5 μm (PM2.5). Studies have demonstrated that BaP exposure causes oocyte meiotic arrest in mice. However, whether BaP exposure also affects oocyte maturation in offspring remains unclear. To test this, female mice were administered BaP before pregnancy to generate BaP-exposed offspring. Our findings showed that BaP exposure reduced the in vitro maturation and increased the abnormalities of meiotic apparatus in offspring oocytes. In addition, BaP exposure reduced the mitochondrial content and intracellular ATP generation, induced early apoptosis, increased reactive oxidative species accumulation and the genomic DNA 5-methylcytosine (5mc) level in offspring oocytes. Along with the abovementioned defective parameters, maternal BaP exposure further compromised the embryo developmental competence of offspring oocytes. In summary, our study demonstrated that maternal BaP exposure compromised offspring oocyte maturation and quality.

Through the smoke: use of in vivo and in vitro cigarette smoking models to elucidate its effect on female fertility

A finite number of oocytes are established within the mammalian ovary prior to birth to form a precious ovarian reserve. Damage to this limited pool of gametes by environmental factors such as cigarette smoke and its constituents therefore represents a significant risk to a woman's reproductive capacity. Although evidence from human studies to date implicates a detrimental effect of cigarette smoking on female fertility, these retrospective studies are limited and present conflicting results. In an effort to more clearly understand the effect of cigarette smoke, and its chemical constituents, on female fertility, a variety of in vivo and in vitro animal models have been developed. This article represents a systematic review of the literature regarding four of experimental model types: 1) direct exposure of ovarian cells and follicles to smoking constituents' in vitro, 2) direct exposure of whole ovarian tissue with smoking constituents in vitro, 3) whole body exposure of animals to smoking constituents and 4) whole body exposure of animals to cigarette smoke. We summarise key findings and highlight the strengths and weaknesses of each model system, and link these to the molecular mechanisms identified in smoke-induced fertility changes.

The cigarette smoke constituent benzo[a]pyrene disrupts metabolic enzyme, and apoptosis pathway member gene expression in ovarian follicles

Benzo[a]pyrene (B[a]P) is a prototypical polycyclic aromatic hydrocarbon (PAH) present in cigarette smoke. We previously showed that B[a]P adversely affects follicular development and survival. The objective of this study was to identify the key molecular pathways underlying B[a]P-induced abnormal follicular development. Isolated follicles (100-130 μm) from ovaries of F1 hybrid (C57BL/6j×CBA/Ca) mice were cultured for 8 (preantral/antral follicles) and 12 (preovulatory follicles) days in increasing concentrations of B[a]P (0 ng/mL [control] to 45 ng/mL). Expression of aryl hydrocarbon receptor (AhR), aryl hydroxylase steroidogenic enzyme, cell-cycle, and apoptotic genes were quantified. B[a]P exposure significantly (P<0.05) increased mRNA expression of Cyp1a1 in preantral/antral follicles and Cyp1b1, Bax and Hsp90ab1 in preovulatory follicles. No significant effect on mRNA expression of StAR, Cyp11a1, aromatase, Cdk4, Cdk2, Ccnd2, cIAP2, and survivin was observed. In conclusion, this study suggests that B[a]P exposure significantly affects the phase I enzymes and cell death genes during preantral/antral and preovulatory growth, and thus highlight the AhR signaling and apoptotis pathways in delayed follicle growth and decreased viability.

Induction of apoptosis by 9,10-dimethyl-1,2-benzanthracene in cultured preovulatory rat follicles is preceded by a rise in reactive oxygen species and is prevented by glutathione

The polycyclic aromatic hydrocarbon (PAH) 9,10-dimethyl-1,2-benzanthracene (DMBA) destroys primordial, primary, and secondary ovarian follicles in rodents, but its effects on antral follicles have received limited attention. PAHs are metabolized to reactive species, some of which can undergo redox cycling to generate reactive oxygen species (ROS). We previously showed that ROS initiate apoptosis in preovulatory follicles cultured without gonadotropin support and that glutathione (GSH) depletion induces apoptosis in the presence of gonadotropins. In the present study, we tested the hypothesis that DMBA induces apoptosis in preovulatory follicles, which is mediated by ROS and prevented by GSH. Preovulatory follicles were isolated from ovaries of 25-day-old rats 48 h after the injection of 10 IU of eCG and were cultured with DMBA in the presence of FSH for 2 to 48 h. DMBA induced granulosa cell (GC) and theca cell (TC) apoptosis at 48 h, as judged by TUNEL and activated caspase-3 immunostaining. DMBA treatment also increased the numbers of GCs and TCs that immunostained for the proapoptotic protein BAX. Follicular ROS levels were significantly increased in DMBA-treated follicles at 12, 24, and 48 h. GSH supplementation protected against and GSH depletion enhanced the induction of apoptosis in GCs and TCs by DMBA. These findings suggest that GSH is a critical protective mechanism against DMBA-induced apoptosis in antral follicles and that ROS generation may mediate DMBA-induced GC apoptosis.

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.

ATSDR evaluation of health effects of chemicals. IV. Polycyclic aromatic hydrocarbons (PAHs): understanding a complex problem

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, such as tobacco and charbroiled meat. There are more than 100 PAHs. PAHs generally occur as complex mixtures (for example, as part of products such as soot), not as single compounds. PAHs are found throughout the environment in the air, water, and soil. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals, including PAHs (ATSDR, 1995), found at facilities on the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) and which pose the most significant potential threat to human health, as determined by ATSDR and the Environmental Protection Agency (EPA). These profiles include information on health effects of chemicals from different routes and durations of exposure, their potential for exposure, regulations and advisories, and the adequacy of the existing database. Assessing the health effects of PAHs is a major challenge because environmental exposures to these chemicals are usually to complex mixtures of PAHs with other chemicals. The biological consequences of human exposure to mixtures of PAHs depend on the toxicity, carcinogenic and noncarcinogenic, of the individual components of the mixture, the types of interactions among them, and confounding factors that are not thoroughly understood. Also identified are components of exposure and health effects research needed on PAHs that will allow estimation of realistic human health risks posed by exposures to PAHs. The exposure assessment component of research should focus on (1) development of reliable analytical methods for the determination of bioavailable PAHs following ingestion, (2) estimation of bioavailable PAHs from environmental media, particularly the determination of particle-bound PAHs, (3) data on ambient levels of PAHs metabolites in tissues/fluids of control populations, and (4) the need for a critical evaluation of current levels of PAHs found in environmental media including data from hazardous waste sites. The health effects component should focus on obtaining information on (1) the health effects of mixtures of PAHs particularly their noncarcinogenic effects in humans, and (2) their toxicokinetics. This report provides excerpts from the toxicological profile of PAHs (ATSDR, 1995) that contains more detailed information.

The effect of benzo(a)pyrene on murine ovarian and corpora lutea volumes

OBJECTIVE

Women who smoke have impaired fertility and experience menopause at an earlier age. This experiment determined the effect of benzo(a)pyrene, a polycyclic aromatic hydrocarbon contained in cigarette smoke, on murine ovarian volume, total corpora lutea volume, individual corpora lutea volumes, and corpora lutea numbers.

STUDY DESIGN

C57BL/6N mice were treated with intraperitoneal injections of 0 to 500 mg/kg benzo(a)pyrene in corn oil. The 20 mice at each dose were divided into four groups of five each and were killed at 1, 2, 3, or 4 weeks after treatment. Ovaries were serially sectioned and analyzed morphometrically.

RESULTS

Benzo(a)pyrene produced a dose- and time-dependent decrease in ovarian volume, total corpora lutea volume, and number of corpora lutea per ovary. This effect was transitory at low doses with complete recovery of corpora lutea by 4 weeks. Compensatory hypertrophy of the individual corpora lutea occurred during the recovery phase. Ovarian function did not return in animals treated with the two highest doses.

CONCLUSION

Benzo(a)pyrene is a murine ovarian toxicant that inhibits corpus luteum formation in a dose- and time-dependent fashion.

Morphometric assessment of the murine ovarian toxicity of 7,12-dimethylbenz(a)anthracene

7,12-Dimethylbenz(a)anthracene (DMBA) is a polycyclic aromatic hydrocarbon and a component of cigarette smoke that has been identified as a murine reproductive toxicant. The morphometric parameters of total ovarian volume, individual corpus luteum volumes, and total corpora lutea volume were measured in C57BL/6N mice treated with DMBA. Each group received single intraperitoneal injections of 0, 0.1, 1.0, or 10 mg/kg and were sacrificed at 1, 2, 3, or 4 weeks after treatment. DMBA produced a dose-dependent decrease in ovarian volume and number of corpora lutea in each ovary. The observed reduction in total corpora lutea volume did not fully account for the loss in total ovarian volume. This is consistent with previous descriptions of a toxic effect on all ovarian components including growing and resting follicles. Growing follicles that escaped the toxic effects of DMBA and achieved ovulation resulted in a corpus luteum that appeared histologically normal. Morphometric analysis of this animal model further defines the dynamic changes in the mouse ovary in response to DMBA.

Ovarian toxicity of benzo(a)pyrene and metabolites in mice

The effect of intraovarian injection of benzo(a)pyrene (BP) or one of three metabolites: +7,8-oxide (7,8-O), (-)-dihydrodiol (DHD), and (+)-diol-epoxide-2 (DE2) on ovarian volume, weight, and follicle number was investigated in DBA/2N (D2), C57BL/6N (B6), and (DBA/2N x C57BL/6N)F1 (F1) mice. Female mice, 6 to 8 weeks old, were treated by injection into the right ovary with the indicated compound (10 micrograms in 1 microL DMSO). The left ovary was untreated. Two weeks following treatment both ovaries were removed, fixed in Bouin's medium, serially sectioned, and stained with hematoxylin and eosin. Right ovarian weight was decreased in D2 mice treated with BP (P less than 0.01 and DHD (P less than 0.01). Left ovarian weight was increased in D2 mice treated with DE2 (P less than 0.05). BP decreased right ovarian volume in D2 (P less than 0.01) and F1 (P less than 0.01) mice. 7,8-O decreased right ovarian volume in D2 mice (P less than 0.05). DHD decreased right ovarian volume in D2 (P less than 0.01) and F1 (P less than 0.05) mice. DE2 decreased right ovarian volume in D2 (P less than 0.01) and F1 (P less than 0.01) mice. Left ovarian volume was increased in B6 (P less than 0.01) and D2 (P less than 0.05) mice treated with DE2. The number of small follicles was decreased in D2, B6, and F1 mice treated with DE2 (P less than 0.01). BP and DHD also decreased small follicle number in D2 and F1 mice (P less than 0.01). The number of growing follicles was decreased in B6, D2, and F1 mice treated with DE2 (P less than 0.01). Treatment with DHD decreased the number of growing follicles in D2 mice (P less than 0.05). The number of antral follicles was reduced in F1 mice treated with BP (P less than 0.05), DHD (P less than 0.01), and DE2 (P less than 0.01). The number of antral follicles was also reduced in B6 mice treated with DE2 (P less than 0.01) and in D2 mice treated with DHD (P less than 0.05) and D2 mice treated with DE2 (P less than 0.01). These experiments suggest that toxic effects to one ovary may result in compensatory hypertrophy of the contralateral ovary. Morphometric analysis of the ovary, including ovarian volume, represents a useful objective measure of ovarian toxicity.