In vitro induction/inhibition of germinal vesicle breakdown (GVBD) in frog (Euphlyctis cyanophlyctis) oocytes by endocrine active compounds

Disruption of oocyte maturation by selected environmental chemicals in zebrafish

Oocyte maturation can be a target of endocrine disruption by environmental chemicals capable of acting as hormone mimics, receptor blockers, and/or enzyme inhibitors. Six environmental chemicals (genistein, endosulfan, malathion, iprodione, carbaryl, and glyphosate) were selected to determine their ability to interfere with oocyte maturation in zebrafish. The translucent oocytes undergoing germinal vesicle (nucleus) breakdown (GVBD) were counted and expressed as a ratio of oocytes undergoing GVBD and total oocytes exposed. The GVBD increased significantly in oocytes exposed to 10 IU/ml to 100 IU/ml human chorionic gonadotropin (hCG). The lowest effective concentration of genistein that inhibited hCG-induced GVBD was 30 μM, while endosulfan inhibited it at 0.03 μM concentration. In addition, malathion inhibited hCG-induced GVBD at the lowest concentration of 60 μM. These inhibitory effects were likely due to the chemicals acting as estrogen mimics, induction of estrogen receptors, or increase in aromatase activity resulting in enhanced estrogen action. Fungicide iprodione, possibly acting as a progestin mimic, promoted hCG-induced GVBD at the lowest concentration of 20 μM, while the weed killer glyphosate inhibited hCG-induced GVBD starting at the 50 μM concentration. These results demonstrate the feasibility of using fully grown zebrafish oocytes arrested at the prophase I stage in an in vitro incubation system to evaluate the effects of a variety of environmental chemicals on oocyte maturation.

Organophosphate and Pyrethroid Pesticide Exposures Measured before Conception and Associations with Time to Pregnancy in Chinese Couples Enrolled in the Shanghai Birth Cohort

BACKGROUND

Pesticides have been associated with reproductive disorders, but there is limited research on pesticide exposures and human fertility.

OBJECTIVE

We aimed to investigate the effects of preconception exposure to pesticides on time to pregnancy (TTP) and on infertility in a general population of couples planning to become pregnant in Shanghai, China.

METHOD

A total of 615 women who were planning a pregnancy were enrolled before conception and were prospectively followed for 1 y to observe their TTP. Preconception pesticide exposures were assessed by measuring urinary metabolites of organophosphates (OPs) and pyrethroids (PYRs). Fecundability odds ratios (FORs) and odds ratios (ORs) of infertility were estimated using Cox and logistic regression models, respectively. All analyses were repeated after restricting the sample to nulliparous women (n=569).

RESULTS

After adjusting for age, prepregnancy BMI, current smoking, education, annual household income, age at menarche, and two items from the Perceived Stress Scale (PSS-10), women in the highest quartile of diethylthiophosphate (DETP; an OP metabolite) had significantly longer TTP [adjusted FOR=0.68 (95% CI: 0.51, 0.92)] and increased infertility [adjusted OR=2.17 (95% CI: 1.19, 3.93)] compared with women in the lowest quartile. The highest versus lowest quartile of 3-phenoxybenzoic acid (3PBA; a PYR metabolite) was associated with longer TTP and infertility, with significant associations in nulliparous women [adjusted FOR=0.72 (95% CI: 0.53, 0.98); adjusted OR for infertility=2.03 (95% CI: 1.10, 3.74)].

CONCLUSION

Our study provides some of the first evidence that preconception OP and PYR exposures are associated with decreased fertility in Chinese couples. Given that OPs and PYRs are rapidly metabolized in humans, more studies are needed to confirm our findings. https://doi.org/10.1289/EHP2987.

Toxic effects of atrazine on porcine oocytes and possible mechanisms of action

Because atrazine is a widely used herbicide, its adverse effects on the reproductive system have been extensively researched. In this study, we investigated the effects of atrazine exposure on porcine oocyte maturation and the possible mechanisms. Our results showed that the rates of oocyte maturation significantly decreased after treatment with 200 μM atrazine in vitro. Atrazine treatment resulted in abnormal spindle morphology but did not affect actin distribution. Atrazine exposure not only triggered a DNA damage response but also decreased MPF levels in porcine oocytes. Our results also revealed that atrazine worsened porcine oocyte quality by causing excessive accumulation of superoxide radicals, increasing cathepsin B activity, and decreasing the GSH level and mitochondrial membrane potential. Furthermore, atrazine decreased developmental competence of porcine oocytes up to the blastocyst stage and changed some properties: cell numbers, apoptosis, and related gene expression levels. Collectively, our results indicate that porcine oocyte maturation is defective after atrazine treatment at least through disruption of spindle morphology, MPF activity, and mitochondrial function and via induction of DNA damage, which probably reduces developmental competence.