Degeneration of mouse oocytes in response to polycyclic aromatic hydrocarbons

Gestational Benzo[a]pyrene Exposure Destroys F1 Ovarian Germ Cells Through Mitochondrial Apoptosis Pathway and Diminishes Surviving Oocyte Quality

Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are products of incomplete combustion. In female mouse embryos primordial germ cells proliferate before and after arriving at the gonadal ridge around embryonic (E) 10 and begin entering meiosis at E13.5. Now oocytes, they arrest in the first meiotic prophase beginning at E17.5. We previously reported dose-dependent depletion of ovarian follicles in female mice exposed to 2 or 10 mg/kg-day BaP E6.5-15.5. We hypothesized that embryonic ovaries are more sensitive to gestational BaP exposure during the mitotic developmental window, and that this exposure results in persistent oxidative stress in ovaries and oocytes of exposed F1 female offspring. We orally dosed timed-pregnant female mice with 0 or 2 mg/kg-day BaP in oil from E6.5-11.5 (mitotic window) or E12.5-17.5 (meiotic window). Cultured E13.5 ovaries were utilized to investigate the mechanism of BaP-induced germ cell death. We observed statistically significant follicle depletion and increased ovarian lipid peroxidation in F1 pubertal ovaries following BaP exposure during either prenatal window. Culture of E13.5 ovaries with BaP induced germ cell DNA damage and release of cytochrome c from the mitochondria in oocytes, confirming that BaP exposure induced apoptosis via the mitochondrial pathway. Mitochondrial membrane potential, oocyte lipid droplet (LD) volume, and mitochondrial-LD colocalization were decreased and mitochondrial superoxide levels were increased in the MII oocytes of F1 females exposed gestationally to BaP. Results demonstrate similar sensitivity to germ cell depletion and persistent oxidative stress in F1 ovaries and oocytes following gestational BaP exposure during mitotic or meiotic windows.

Damages to biological macromolecules in gonadal subcellular fractions of scallop Chlamys farreri following benzo[a]pyrene exposure: Contribution to inhibiting gonadal development and reducing fertility

Benzo[a]pyrene (B[a]P), a representative polycyclic aromatic hydrocarbon (PAH) compound in marine ecosystem, has great potential for chronic toxicity to marine animals. It is becoming increasingly apparent that reproductive system is the major target of B[a]P, but the adverse effects of B[a]P on subcellular fractions in bivalve gonads have not been elucidated. Scallops Chlamys farreri are used as the experimental species since they are sensitive to environmental pollutants. This study was conducted to investigate how B[a]P affected the gonadal subcellular fractions, including plasma membrane, nucleus, mitochondria and microsome in scallops, and whether subcellular damages were related to reproductive toxicity. The results showed that mature gametes' counts were significantly decreased in B[a]P-treated scallops. Three biological macromolecules (viz., DNA, lipids and proteins) in gonadal subcellular fractions obtained by differential centrifugation suffered damages, including DNA damage, lipid peroxidation and protein carbonylation in B[a]P treatment groups. Interestingly, mitochondria and microsome were more vulnerable to lipid peroxidation and protein carbonylation than plasma membrane and nucleus, meanwhile males were more susceptible to DNA damage than females under B[a]P exposure. In addition, histological analysis showed that B[a]P delayed gonadal development in C. farreri. To summarize, our results indicated that B[a]P caused damages to biological macromolecules in gonadal subcellular fractions and then induced damages to gonadal tissues of C. farreri, which further inhibited gonadal development and ultimately leaded to reduction in fertility. This study firstly reports the impacts of PAHs on subcellular fractions in bivalves and their relationship with reproductive toxicity. Moreover, exposure of reproductive scallops to B[a]P leads to defects in reproduction, raising concerns on the possible long-term consequences of PAHs for natural populations of bivalves.

Bone marrow mesenchymal stem cell repair of cyclophosphamide-induced ovarian insufficiency in a mouse model

Objective

Attempting in vivo healing of cyclophosphamide-induced ovarian insufficiency in a mouse model using bone marrow mesenchymal stem cells (BMMSCs).

Methods

Female BALB/c white mice were used to prepare a model for premature ovarian failure by single intraperitoneal injection of cyclophosphamide (80 mg/kg). Ten mice were injected with BMMSCs and then sacrificed after 21 days for morphometric evaluation of the ovaries. Hormonal profile was evaluated while mice were being sacrificed. Another 10 mice were left for natural breeding with male mice, and 5 of these were injected with BMMSCs. Oocyte-like structures were obtained from 3 mice and were subjected to in vitro fertilization/intracytoplasmic sperm injection.

Results

Morphometric analysis of the ovaries demonstrated the presence of newly formed primordial follicles. Contribution of MSCs to the formation of these follicles was proven by a labeling technique. There was a drop in estradiol and rise in follicle-stimulating hormone levels, followed by resumption of the hormonal levels to near normal 21 days after MSCs therapy. The 5 mice that were injected with MSCs became pregnant after natural breeding. Fertilization and further division was reported in 5 oocytes subjected to intracytoplasmic sperm injection, but division did not continue.

Conclusion

From this proof-of-concept trial, we can say that healing of damaged ovaries after chemotherapy in mice is possible using in vivo therapy with BMMSCs. This should open the gate for a series of animal studies that test the possibility of in vitro maturation of germinal epithelium of the ovary into mature oocytes.

Premature menopause

Premature menopause affects 1% of women under the age of 40 years. The women are at risk of premature death, neurological diseases, psychosexual dysfunction, mood disorders, osteoporosis, ischemic heart disease and infertility. There is need to use simplified protocols and improved techniques in oocyte donation to achieve pregnancy and mother a baby in those women at risk. Review of the pertinent literature on premature menopause, selected references, internet services using the PubMed and Medline databases were included in this review. In the past, pregnancy in women with premature menopause was rare but with recent advancement in oocyte donation, women with premature menopause now have hoped to mother a child. Hormone replacement therapy is beneficial to adverse consequences of premature menopause. Women with premature menopause are at risk of premature death, neurological diseases, psychosexual dysfunction, mood disorders, osteoporosis, ischemic heart disease and infertility. Public enlightenment and education is important tool to save those at risk.

Potential mechanisms for racial and ethnic differences in antimüllerian hormone and ovarian reserve

Accumulating evidence suggests that reproductive potential and function may be different across racial and ethnic groups. Racial differences have been demonstrated in pubertal timing, infertility, outcomes after assisted reproductive technology (ART) treatment, and reproductive aging. Recently, racial differences have also been described in serum antimüllerian hormone (AMH), a sensitive biomarker of ovarian reserve, supporting the notion that ovarian reserve differs between racial/ethnic groups. The existence of such racial/ethnic differences in ovarian reserve, as reflected by AMH, may have important clinical implications for reproductive endocrinologists. However, the mechanisms which may underlie such racial differences in ovarian reserve are unclear. Various genetic factors and environmental factors such as obesity, smoking, and vitamin D deficiency which have been shown to correlate with serum AMH levels and also display significant racial/ethnic variations are discussed in this review. Improving our understanding of racial differences in ovarian reserve and their underlying causes may be essential for infertility treatment in minority women and lead to better reproductive planning, improved treatment outcomes, and timely interventions which may prolong reproductive lifespan in these women.

The impact of smoking on antimüllerian hormone levels in women aged 38 to 50 years

OBJECTIVE

Smoking is associated with increased follicle-stimulating hormone levels and early menopause. Smoking may directly accelerate ovarian follicular depletion or may act indirectly by increasing the pituitary production of follicle-stimulating hormone. Antimüllerian hormone (AMH), produced by ovarian follicles, is a more direct measure of ovarian reserve. The objective of our study was to determine the extent to which smoking influences ovarian reserve, as measured by AMH levels.

METHODS

A community sample of 284 women aged 38 to 50 years completed a self-administered questionnaire including a detailed smoking history. Serum AMH levels were measured on day 2, 3, or 4 of the menstrual cycle. The association between AMH and smoking was analyzed using linear regression, adjusting for age and body mass index.

RESULTS

Participants aged 38 to 42, 43 to 45, and 46 to 50 years had geometric mean AMH values of 6.7 pM (95% CI, 5.2-8.7 pM), 2.7 pM (95% CI, 1.9-3.8 pM), and 1.3 pM (95% CI, 1.0-1.7 pM), respectively. Current smokers, but not past smokers, had 44% lower AMH values than did the reference group (participants with neither active nor former or passive smoke exposure; P = 0.04). Passive smoking had no effect on AMH values when compared with the reference group (P = 0.55). The impact of smoking on AMH values was not dose dependent based on cigarettes per day (P = 0.08) or pack-years (P = 0.22). Finally, prenatal exposure to smoking (either maternal or paternal) had no impact on AMH levels (P = 0.47 and P = 0.89, respectively).

CONCLUSIONS

Active smoking, but not former smoking, is associated with decreased AMH values in late-reproductive-age and perimenopausal women, suggesting a possible direct effect of smoking on the depletion of the antral but not primordial follicles. The direct impact of active smoking on AMH levels in younger women requires further investigation.

Damage to ovarian development and function

Ovarian function in women can be compromised by exposure to toxic environmental factors. Chemicals that affect ovarian function can act through direct effects on hormone action (ovary) or by interference with steroid hormone action (hypothalamus and/or pituitary). These effects can cause problems in the form of infertility. Alternatively, ovarian toxicants can directly cause ovarian failure by extensive follicular destruction. This targeting can result in loss of ovarian steroid hormones, eventual ovarian failure (menopause), and ultimate disruption of neuroendocrine feedback causing increased levels of FSH and LH. This article provides an overview of chemicals that in animal studies have been identified to cause disrupted ovarian function with a focus on the sites of targeting by which these disruptions occur. In predicting the impact of environmental factors on reproductive function in women, it is critical to gain a better appreciation of the physiological consequences resulting from the potential variety of mechanisms by which toxicants can disrupt ovarian function. This article attempts to provide such a perspective within the context of specific chemicals for which ovarian sites of toxicity have been identified.

Ovarian dysfunction in mice following chromium (VI) exposure

Chromium (VI) was given through drinking water in two sets of adult Swiss albino female mice in three doses; 250 ppm, 500 ppm and 750 ppm for 20 days in set 1 and 0.05 ppm, 0.5 ppm and 5.0 ppm in set II for 90 days. At the termination of the treatment, the animals of both the sets were euthanized for histopathology, follicle counting, counting of the superovulated ova, duration of estrus cycle and for ultrastructural studies. Ovaries of the highest dose group (750 ppm) showed large numbers of atretic follicles and congestion in stromal tissue compared to the rest of the treated groups. Also, there was a dose-dependent reduction in the number of follicles at different stages of their maturation. The number of ova recovered from superovulated chromium (VI)-treated animals showed significant decreases in the 500 and 750 ppm dosed groups compared to lower dosed (250 ppm) and control groups. The duration of estrus cycle increased in highest dosed (750 ppm) group. A dose-dependent increase in blood chromium level was also seen in treated mice. Ultrastructural observations revealed disintegrated cell membranes of two layered follicular cells and altered villiform mitochondria in thecal cells of 5 ppm dosed group. From the study it was concluded that ovarian physiology and rate of ovulation might be altered if females are exposed to sufficiently high chromium through oral route.

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.

Effects of methoxychlor on the reproductive system of the adult female mouse. 1. Gross and histologic observations

The purpose of this study is to examine the effects of the pesticide methoxychlor (MXC) on the reproductive system of the adult female mouse. Sexually mature (7- to 8-week) virgin female CD-1 mice were exposed to 1.25, 2.5, or 5.0 mg MXC (50% technical grade) via oral gavage for 5 consecutive days each week for either 2 or 4 weeks. Control groups received either 0.025 mg estradiol-17 beta (E-17 beta) or the sesame oil vehicle for the same time period. Vaginal smears were taken daily, and weights were recorded weekly. Twenty-four hours following the final exposure, animals were sacrificed. Ovaries and reproductive tracts were removed and weighed. One ovary from each animal was prepared for light microscopic evaluation. Results revealed a dose dependency of MXC in inducing persistent vaginal estrus (PVE). Ovaries of MXC-exposed and E-17 beta-exposed animals weighed significantly less than the sesame oil controls. In addition, there was an increase in the number of atretic large follicles in the E-17 beta group and in those mice treated with the two highest doses of MXC, indicating a potential reduction in the immediate fertility of the animal. Thus, this commonly employed pesticide appears to mimic closely those effects on the female reproductive system induced by estrogens.

Reproductive impairment in a fish inhabiting a contaminated coastal environment off Southern California

White croaker (Genyonemus lineatus), collected from a highly contaminated site in San Pedro Bay and from a reference site 80 km away (Dana Point), were induced to spawn in the laboratory. Forty-one per cent of San Pedro Bay females and 54% of Dana Point females spawned. Examination of the ovaries of non-spwaning females revealed that spawning was imminent in the remainder of Dana Point fish but only in 16% of the San Pedro Bay fish. The remainder of the San Pedro Bay fish (43%) contained only immature, yolky oocytes. No croakers containing more than 3.8 ppm ovarian total DDT could be induced to spawn whereas 36% of a contemporaneous San Pedro Bay sample had ovarian total DDT residues in excess of 4 ppm. This suggests that the inability to induce spawning in white croaker may be associated with an ovarian total DDT threshold of about 4 ppm. These data, coupled with observed decreases in fecundity (32%), fertility (14%), and early oocyte loss (30%) relative to reference fish, could partially explain the population declines observed for many southern California fishes since the 1940s.

Endometrial cancer: how does cigarette smoking influence the risk of women under age 55 years having this tumor?

This analysis of the Cancer and Steroid Hormone Study, a multicenter, population-based case control investigation of hormone use by women of reproductive age and endometrial, breast, and ovarian cancer shows that cigarette smoking is not associated with either an increased or a decreased risk of endometrial cancer. This study included 437 women with endometrial cancer and 3200 control subjects, all of whom were between the ages of 20 and 54 years at the time of interview. The absence of any alteration of the risk of endometrial cancer and smoking was found consistently no matter which variable was used as a measure of smoking--ever or never smoked cigarettes, former or current smoking, light or heavy smoking, or age smoking began.

The effect of intraovarian injection of benzo(a)pyrene on primordial oocyte number and ovarian aryl hydrocarbon [benzo(a)pyrene] hydroxylase activity

The effect of intraovarian (io) injection of benzo(a)pyrene (BP) on primordial oocyte number, ovarian aryl hydrocarbon hydroxylase (AHH, EC 1.14.14.1) activity, and hepatic AHH activity and P-450 content was investigated in C57BL/6N (B6) and DBA/2N (D2) mice. Ovaries were exteriorized through dorsolumbar incisions under ether anesthesia, and 1.0 microliters of corn oil or corn oil containing BP was injected directly into the ovary. Bilateral io injection of BP was ovotoxic in a time and dose dependent manner. Primordial oocyte destruction was maximal 8 days after injection in both B6 and D2 mice. Unilateral io injection of BP destroyed oocytes only in the treated ovary. The threshold dose for primordial oocyte destruction was similar in both strains, approximately 50 ng/ovary. However, ED50's were different; 1.1 micrograms/ovary in B6 and 8.9 micrograms/ovary in D2 mice. Intraperitoneal treatment with alpha-naphthoflavone (80 mg/kg) inhibited the oocyte destruction by io treatment with BP (10 micrograms/ovary) in both B6 and D2 mice. In B6 mice, ovarian AHH activity was induced by BP in the treated ovary after either bilateral, or unilateral io treatment. However, io BP treatment did not change ovarian AHH activity in D2 mice. Hepatic AHH activity and P-450 content was not altered by io BP treatment in either mouse strain. These results strengthen the hypothesis that the ovary has the capability of metabolizing BP to ovotoxic products.

Metabolism and subsequent covalent binding of benzo[a]pyrene to macromolecules in gonads and liver of ripe english sole (Parophrys vetulus)

1. Ripe English sole (Parophrys vetulus) force-fed [3H]benzo[a]pyrene, contained 1% of the dose in liver, 0.2% in ovary and 0.1% in testis, after 24 h. No significant change occurred in levels of radioactivity from 24 to 168 h. 2. Gonads and blood contained substantially larger proportions of unchanged benzo[a]pyrene (15-37% of tissue radioactivity) and organic solvent-soluble metabolites (6-35%) than did liver and bile. 3. T.l.c. revealed the presence of phenols, quinones, 7,8-dihydro-7, 8-dihydroxy- and 9,10-dihydro-9,10-dihydroxy-benzo[a]pyrene in liver and gonads. 4. A small proportion (less than 10%) of the radioactivity in liver and gonads was present as glucuronides and sulphates; bile contained a higher proportion (ca. 20%) of total radioactivity as glucuronides and sulphates. 5. Benzo[a]pyrene intermediates were covalently bound to liver proteins and DNA, and to a lesser extent to gonadal proteins (male and female fish) and gonadal DNA (confirmed for testis only).