Fetal exposure to bisphenol A affects the primordial follicle formation by inhibiting the meiotic progression of oocytes

The influence of environmental factors on premature ovarian insufficiency and ovarian aging

Premature ovarian insufficiency and ovarian aging are complex conditions that affect women's reproductive health and overall well-being. They are both characterized by hypergonadotropic hypogonadism and infertility, and together affect about 1 in 100 women by the age of 40. This review explores the influence of environmental factors on the development and progression of premature ovarian insufficiency and ovarian aging. When referring to environmental factors, we include a wide range of external agents and conditions, including chemicals, socioeconomic factors and lifestyle choices. Through a review of the literature, we attempt to highlight the link between environmental factors and ovarian health. We examine the impact of endocrine-disrupting chemicals, such as bisphenol A and phthalates, on ovarian function and investigate the mechanisms by which these chemicals can disrupt hormone signaling pathways, leading to alterations in ovarian reserve, oocyte quality, and folliculogenesis. Moreover, we explore lifestyle factors like obesity, stress, smoking and alcohol in relation to their effects on ovarian aging. Epigenetic changes may play a crucial role in the prevalence of premature ovarian insufficiency. Understanding the impact of environmental factors on premature ovarian insufficiency and ovarian aging is very important in public and clinical health contexts. By identifying risk factors, healthcare providers can develop targeted and strategic prevention and intervention plans. Furthermore, this knowledge can promote reproductive health and minimize exposure to harmful environmental agents.

Foetal exposure to the bisphenols BADGE and BPAF impairs meiosis through DNA oxidation in mouse ovaries

Many endocrine disruptors have been proven to impair the meiotic process which is required for the production of healthy gametes. Bisphenol A is emblematic of such disruptors, as it impairs meiotic prophase I and causes oocyte aneuploidy following in utero exposure. However, the mechanisms underlying these deleterious effects remain poorly understood. Furthermore, the increasing use of BPA alternatives raises concerns for public health. Here, we investigated the effects of foetal exposure to two BPA alternatives, bisphenol A Diglycidyl Ether (BADGE) and bisphenol AF (BPAF), on oogenesis in mice. These compounds delay meiosis initiation, increase the number of MLH1 foci per cell and induce oocyte aneuploidy. We further demonstrate that these defects are accompanied by changes in gene expression in foetal premeiotic germ cells and aberrant mRNA splicing of meiotic genes. We observed an increase in DNA oxidation after exposure to BPA alternatives. Specific induction of oxidative DNA damage during foetal germ cell differentiation causes similar defects during oogenesis, as observed in 8-oxoguanine DNA Glycosylase (OGG1)-deficient mice or after in utero exposure to potassium bromate (KBrO3), an inducer of oxidative DNA damage. The supplementation of BPA alternatives with N-acetylcysteine (NAC) counteracts the effects of bisphenols on meiosis. Together, our results propose oxidative DNA lesion as an event that negatively impacts female meiosis with major consequences on oocyte quality. This could be a common mechanism of action for numerous environmental pro-oxidant pollutants, and its discovery, could lead to reconsider the adverse effect of bisphenol mixtures that are simultaneously present in our environment.

PIWI-Interacting RNA (piRNA) and Epigenetic Editing in Environmental Health Sciences

PURPOSE OF REVIEW: The epigenome modulates gene expression in response to environmental stimuli. Modifications to the epigenome are potentially reversible, making them a promising therapeutic approach to mitigate environmental exposure effects on human health. This review details currently available genome and epigenome editing technologies and highlights ncRNA, including piRNA, as potential tools for targeted epigenome editing. RECENT FINDINGS: Zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and clustered regularly interspaced short palindromic repeats (CRISPR) associated nuclease (CRISPR/Cas) research has significantly advanced genome editing technology, with broad promise in genetic research and targeted therapies. Initial epigenome-directed therapies relied on global modification and suffered from limited specificity. Adapted from current genome editing tools, zinc finger protein (ZFP), TALE, and CRISPR/nuclease-deactivated Cas (dCas) systems now confer locus-specific epigenome editing, with promising applicability in the field of environmental health sciences. However, high incidence of off-target effects and time taken for screening limit their use. FUTURE DEVELOPMENT: ncRNA serve as a versatile biomarker with well-characterized regulatory mechanisms that can easily be adapted to edit the epigenome. For instance, the transposon silencing mechanism of germline PIWI-interacting RNAs (piRNA) could be engineered to specifically methylate a given gene, overcoming pitfalls of current global modifiers. Future developments in epigenome editing technologies will inform risk assessment through mechanistic investigation and serve as potential modes of intervention to mitigate environmentally induced adverse health outcomes later in life.

AOP Key Event Relationship report: Linking decreased retinoic acid levels with disrupted meiosis in developing oocytes

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The first case study to develop and publish an individual KER as a stand-alone unit of information under the AOP framework overseen by the OECD.

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Full description of a KER linking decreased all-trans retinoic acid (atRA) levels in developing ovaries with disrupted meiotic entry of oogonia.

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KER described is associated with an intended AOP linking inhibition of the atRA producing ALDH1A enzymes with reduced fertility in women.

The Adverse Outcome Pathway (AOP) concept is an emerging tool in regulatory toxicology that uses simplified descriptions to show cause-effect relationships between stressors and toxicity outcomes in intact organisms. The AOP structure is a modular framework, with Key Event Relationships (KERs) representing the unit of causal relationship based on existing knowledge, describing the connection between two Key Events. Because KERs are the only unit to support inference it has been argued recently that KERs should be recognized as the core building blocks of knowledge assembly within the AOP-Knowledge Base. Herein, we present a first case to support this proposal and provide a full description of a KER linking decreased all-trans retinoic acid (atRA) levels in developing ovaries with disrupted meiotic entry of oogonia. We outline the evidence to support a role for atRA in inducing meiosis in oogonia across mammals; this is important because elements of the RA synthesis/degradation pathway are recognized targets for numerous environmental chemicals. The KER we describe will be used to support an intended AOP linking inhibition of the atRA producing ALDH1A enzymes with reduced fertility in women.

Inflammatory cytokines as key players of apoptosis induced by environmental estrogens in the ovary

Natural and synthetic environmental estrogens (EEs), interfering with the physiological functions of the body's estrogens, are widespread and are rising much concern for their possible deleterious effects on human and animal health, in particular on reproduction. In fact, increasing evidence indicate that EEs can be responsible for a variety of disfunctions of the reproductive system especially in females such as premature ovarian insufficiency (POI). Because of their great structural diversity, the modes of action of EEs are controversial. One important way through which EEs exert their effects on reproduction is the induction of apoptosis in the ovary. In general, EEs can exert pro-and anti-apoptotic effects by agonizing or antagonizing numerous estrogen-dependent signaling pathways. In the present work, results concerning apoptotic pathways and diseases induced by representative EEs (such as zearalenone, bisphenol A and di-2-ethylhexyl phthalate), in ovaries throughout development are presented into an integrated network. By reviewing and elaborating these studies, we propose inflammatory factors, centered on the production of tumor necrosis factor (TNF), as a major cause of the induction of apoptosis by EEs in the mammalian ovary. As a consequence, potential strategies to prevent such EE effect are suggested.

Bisphenol A and Metabolites in Meat and Meat Products: Occurrence, Toxicity, and Recent Development in Analytical Methods

Bisphenol A (BPA) is a commonly used compound in many industries and has versatile applications in polycarbonate plastics and epoxy resins production. BPA is classified as endocrine-disrupting chemical which can hamper fetal development during pregnancy and may have long term negative health outcomes in humans. Dietary sources, main route of BPA exposure, can be contaminated by the migration of BPA into food during processing. The global regulatory framework for using this compound in food contact materials is currently not harmonized. This review aims to outline, survey, and critically evaluate BPA contamination in meat products, including level of BPA and/or metabolites present, exposure route, and recent advancements in the analytical procedures of these compounds from meat and meat products. The contribution of meat and meat products to the total dietary exposure of BPA ranges between 10 and 50% depending on the country and exposure scenario considered. From can lining materials of meat products, BPA migrates towards the solid phase resulting higher BPA concentration in solid phase than the liquid phase of the same can. The analytical procedure is comprised of meat sample pre-treatment, followed by cleaning with solid phase extraction (SPE), and chromatographic analysis. Considering several potential sources of BPA in industrial and home culinary practices, BPA can also accumulate in non-canned or raw meat products. Very few scientific studies have been conducted to identify the amount in raw meat products. Similarly, analysis of metabolites and identification of the origin of BPA contamination in meat products is still a challenge to overcome.

Idiopathic primary ovarian insufficiency is associated with anogenital distance, a marker for prenatal environment

OBJECTIVE

In a significant number of women diagnosed with primary ovarian insufficiency (POI), the underlying cause cannot be found. On the other hand, the ovarian reserve set prenatally has been shown to be affected by intrauterine nutrition, environmental and hormonal factors. We aimed to evaluate the relationship between anogenital distance (AGD), which is considered as a biomarker for prenatal hormonal environment, and idiopathic POI in adolescents and young women.

STUDY DESIGN

This case control study was conducted between September 2018 and December 2019. The study group consisted of patients between the ages of 15-30, who developed POI following menarche without any identified genetic or iatrogenic cause. Controls were patients of the same age range who were having regular menstrual periods and were not diagnosed with polycystic ovary syndrome or endometriosis. Patients were excluded from the study if they were pregnant, had vaginal delivery or genital surgery. Distance between the anterior clitoral surface and the upper verge of the anus (AGD_AC), and between the posterior fourchette and the upper verge of the anus (AGD_AF) were measured in all subjects.

RESULTS

In total, 37 POI patients and 44 controls were included in the study. Two groups were similar for demographic parameters such as age and body mass index (BMI). Shorter AGD_AC and AGD_AF measurements were found to be associated with idiopathic POI.

CONCLUSION

Our results provide the first evidence of a strong association between shorter AGD measurements and the presence of idiopathic POI suggesting that prenatal environment may have role in the development of POI.

Effects of Environment and Lifestyle Factors on Premature Ovarian Failure

Premature ovarian insufficiency (POI) or primary ovarian failure is defined as a cessation of the menstrual cycle in women younger than 40 years old. It is strictly defined as more than 4 months of oligomenorrhea or amenorrhea in a woman <40 years old, associated with at least two follicle-stimulating hormone (FSH) levels >25 U/L in the menopausal range, detected more than 4 weeks apart. It is estimated that POI was affected 1 and 2% of women. Although 80% of POI cases are of unknown etiology, it is suggested that genetic disorder, autoimmune origin, toxins, and environmental factors, as well as personal lifestyles, may be risk factors of developing POI. In this section, we will discuss the influences of environmental and lifestyle factors on POI. Moreover updated basic research findings regarding how these environmental factors affect female ovarian function via epigenetic regulations will also be discussed.

The Influence of Environmental Factors on Ovarian Function, Follicular Genesis, and Oocyte Quality

Endocrine-disrupting chemicals (EDCs) exist ubiquitously in the environment. Epidemiological data suggest that the increasing prevalence of infertility may be related to the numerous chemicals. Exposure to EDCs may have significant adverse impacts on the reproductive system including fertility, ovarian reserve, and sex steroid hormone levels. This chapter covers the common exposure ways, the origins of EDCs, and their effects on ovarian function, follicular genesis, and oocyte quality. Furthermore, we will review the origin and the physiology of ovarian development, as well as explore the mechanisms in which EDCs act on the ovary from human and animal data. And then, we will focus on the bisphenol A (BPA), which has been shown to reduce fertility and ovarian reserve, as well as disrupt steroidogenesis in animal and human models. Finally, we will discuss the future direction of prevention and solution methods.

The impact of bisphenols on reproductive system and on offspring in pigs - A review 2011-2020

This study summarizes the knowledge about effects of bisphenol A (BPA) and its analogues on reproduction of pigs and some parameters of their offspring during period 2011-2020. Bisphenols are known as one of the most harmful environmental toxicants with endocrine-disrupting properties. One study in the reference period related to male reproductive system. Treatment with an antagonist of G-protein coupled estrogen receptor (GPER) - G15, and bisphenol A and its analogues, tetrabromobisphenol A (TBBPA) and tetrachromobisphenol A (TCBPA) diversely disrupted protein molecules controlling the biogenesis and function of microRNA in Leydig cells. Nine studies examined the effect of BPA, bisphenol S (BPS) or fluorene-9-bisphenol (BHPF) on female reproductive system. From the possible protective effect's point of view seems to be perspective the administration of melatonin in BPA-exposed oocytes. Finally, two studies were found to evaluate the maternal exposure to BPA on offspring's meat quality, muscle metabolism and oxidative stress. Administration of methyl donor improved antioxidant enzymes activity and reduced oxidative stress in piglets.

In vitro reconstitution of germ cell development†

Germ cell development is a series of highly specialized processes through which diploid pluripotent cells differentiate into haploid gametes. The processes include biologically important events such as epigenetic reprogramming, sex determination, and meiosis. The mechanisms underlying these events are key issues in reproductive and developmental biology, yet they still remain elusive. As a tool to elucidate these mechanisms, in vitro gametogenesis, which reproduces germ cell development in culture, has long been sought for decades. Recently, methods of in vitro gametogenesis have undergone rapid development in association with stem cell biology, opening many possibilities in this field. This new technology is considered an alternative source of gametes for the reproduction of animals and perhaps humans. This review summarizes current advances and problems in in vitro gametogenesis.

Diethylstilbestrol exposure disrupts mouse oocyte meiotic maturation in vitro through affecting spindle assembly and chromosome alignment

An adverse tendency induced by the environmental estrogens in female reproductive health is one serious problem worldwide. Diethylstilbestrol (DES), as a synthetic estrogen, is still used as an animal growth stimulant in terrestrial livestock and aquaculture illegally. It has been reported to negatively affect ovarian function and oogenesis. Nevertheless, the mechanism and toxicity of DES on oocyte meiotic maturation are largely unknown. Herein, we found that DES (40 μM) intervened in mouse oocyte maturation and first polar body extrusion (PBE) was decreased in vitro. Cell cycle analysis showed meiotic process was disturbed with oocytes arrested at metaphase I (MI) stage after DES exposure. Further study showed that DES exposure disrupted the spindle assembly and chromosome alignment, which then continuously provoke the spindle assemble checkpoint (SAC). We also observed that the acetylation levels of α-tubulin were dramatically increased in DES-treated oocytes. In addition, the dynamics of actin were also affected. Moreover, the distribution patterns of estrogen receptor α (ERα) were altered in DES-treated oocyte, as indicated by the significant signals accumulation in the spindle area. However, ERα inhibitor failed to rescue the defects of oocyte maturation caused by DES. Of note, the same phenomenon was observed in estrogen-treated oocytes. Collectively, we showed that DES exposure lead to the oocyte meiotic failure via impairing the spindle assembly and chromosome alignment. Our research is helpful to understand how environmental estrogen affects female germ cells and contribute to design the potential therapies to preserve fertility especially for occupational exposure.

Corticosterone and testosterone treatment influence expression of gene pathways linked to meiotic segregation in preovulatory follicles of the domestic hen

Decades of work indicate that female birds can control their offspring sex ratios in response to environmental and social cues. In laying hens, hormones administered immediately prior to sex chromosome segregation can exert sex ratio skews, indicating that these hormones may act directly on the germinal disc to influence which sex chromosome is retained in the oocyte and which is discarded into an unfertilizable polar body. We aimed to uncover the gene pathways involved in this process by testing whether treatments with testosterone or corticosterone that were previously shown to influence sex ratios elicit changes in the expression of genes and/or gene pathways involved in the process of meiotic segregation. We injected laying hens with testosterone, corticosterone, or control oil 5h prior to ovulation and collected germinal discs from the F1 preovulatory follicle in each hen 1.5h after injection. We used RNA-sequencing (RNA-seq) followed by DESeq2 and gene set enrichment analyses to identify genes and gene pathways that were differentially expressed between germinal discs of control and hormone-treated hens. Corticosterone treatment triggered downregulation of 13 individual genes, as well as enrichment of gene sets related to meiotic spindle organization and chromosome segregation, and additional gene sets that function in ion transport. Testosterone treatment triggered upregulation of one gene, and enrichment of one gene set that functions in nuclear chromosome segregation. This work indicates that corticosterone can be a potent regulator of meiotic processes and provides potential gene targets on which corticosterone and/or testosterone may act to influence offspring sex ratios in birds.

Neuro-toxic and Reproductive Effects of BPA

Background:

Bisphenol A (BPA) is one of the highest volume chemicals produced worldwide. It has recognized activity as an endocrine-disrupting chemical and has suspected roles as a neurological and reproductive toxicant. It interferes in steroid signaling, induces oxidative stress, and affects gene expression epigenetically. Gestational, perinatal and neonatal exposures to BPA affect developmental processes, including brain development and gametogenesis, with consequences on brain functions, behavior, and fertility.

Methods:

This review critically analyzes recent findings on the neuro-toxic and reproductive effects of BPA (and its ana-logues), with focus on neuronal differentiation, synaptic plasticity, glia and microglia activity, cognitive functions, and the central and local control of reproduction.

Results:

BPA has potential human health hazard associated with gestational, peri- and neonatal exposure. Beginning with BPA’s disposition, this review summarizes recent findings on the neurotoxicity of BPA and its analogues, on neuronal dif-ferentiation, synaptic plasticity, neuro-inflammation, neuro-degeneration, and impairment of cognitive abilities. Furthermore, it reports the recent findings on the activity of BPA along the HPG axis, effects on the hypothalamic Gonadotropin Releas-ing Hormone (GnRH), and the associated effects on reproduction in both sexes and successful pregnancy.

Conclusion:

BPA and its analogues impair neuronal activity, HPG axis function, reproduction, and fertility. Contrasting re-sults have emerged in animal models and human. Thus, further studies are needed to better define their safety levels. This re-view offers new insights on these issues with the aim to find the “fil rouge”, if any, that characterize BPA’s mechanism of action with outcomes on neuronal function and reproduction.

Bisphenol A: an emerging threat to female fertility

Bisphenol-A (BPA) has been reported to be associated to female infertility. Indeed, BPA has been found to be more frequently detected in infertile women thus leading to hypothesize a possible effect of BPA on natural conception and spontaneous fecundity. In addition, in procedures of medically assisted reproduction BPA exposure has been found to be negatively associated with peak serum estradiol levels during gonadotropin stimulation, number of retrieved oocytes, number of normally fertilized oocytes and implantation. BPA deleterious effects are more critical during perinatal exposure, causing dysregulation of hypothalamic-pituitary-ovarian axis in pups and adults, with a precocious maturation of the axis through a damage of GnRH pulsatility, gonadotropin signaling and sex steroid hormone production. Further, BPA exposure during early lifestage may have a transgenerational effect predisposing the subsequent generations to the risk of developing BPA related disease. Experimental studies suggested that prenatal, perinatal and postnatal exposure to BPA can impair several steps of ovarian development, induce ovarian morphology rearrangement and impair ovarian function, particularly folliculogenesis, as well as can impair uterus morphology and function, in female adult animal and offspring. Finally, studies carried out in animal models have been reported the occurrence of endometriosis-like lesions after BPA exposure. Moreover, BPA exposure has been described to encourage the genesis of PCOS-like abnormalities through the impairment of the secretion of sex hormones affecting ovarian morphology and functions, particularly folliculogenesis. The current manuscript summarizes the evidence regarding the association between BPA exposure and female infertility, reviewing both clinical and preclinical studies.

Environmentally relevant bisphenol A concentrations effects on the seagrass Cymodocea nodosa different parts elongation: perceptive assessors of toxicity

Toxicity data on bisphenol A (BPA) effects on aquatic macrophytes remain scarce. Therefore, environmentally relevant BPA concentrations (0.03, 0.1, 0.3, 0.5, 1, and 3 μg L^-1) were tested on the seagrass Cymodocea nodosa different parts length increase. All plant parts, at low BPA concentrations (0.03-0.3 μg L^-1), elongated equally to the control, while their lengthening and elongation rates gradually decreased by increasing BPA concentrations. A gradual increase of "Toxicity index" with increasing BPA concentrations was observed but was lower for juvenile blades and higher for plagiotropic rhizomes and adult leaves. In all parts, the LOECs were 0.3 and the NOECs 0.1 μg L^-1 at 10th day. Juvenile blades displayed, under acute stress, lengthening inhibition at lower concentrations than the rhizomes and adult blades, but at a lower extent. The EC₅₀ values were lower for the rhizome internodes, followed by the adult blades and higher for the juvenile blades. Using as a biological "endpoint" the elongation, all C. nodosa parts and specifically the rhizomes and adult blades, followed by intermediate blades, adult sheaths, and juvenile blades, seemed to be sensitive BPA toxicity assessors. The evaluation of the relative sensitivity of the different parts to BPA toxicity could help identify the most suitable seagrass part for early diagnosis of the risk posed by BPA to seagrass meadows and could constitute a valuable tool to derive the seawater quality criteria and to be used in BPA monitoring programs for rational management of the coastal environment.

In utero exposure to acetaminophen and ibuprofen leads to intergenerational accelerated reproductive aging in female mice

Nonsteroidal anti-inflammatory drugs (NSAIDs) and analgesic drugs, such as acetaminophen (APAP), are frequently taken during pregnancy, even in combination. However, they can favour genital malformations in newborn boys and reproductive disorders in adults. Conversely, the consequences on postnatal ovarian development and female reproductive health after in utero exposure are unknown. Here, we found that in mice, in utero exposure to therapeutic doses of the APAP-ibuprofen combination during sex determination led to delayed meiosis entry and progression in female F1 embryonic germ cells. Consequently, follicular activation was reduced in postnatal ovaries through the AKT/FOXO3 pathway, leading in F2 animals to subfertility, accelerated ovarian aging with abnormal corpus luteum persistence, due to decreased apoptosis and increased AKT-mediated luteal cell survival. Our study suggests that administration of these drugs during the critical period of sex determination could lead in humans to adverse effects that might be passed to the offspring.

Ovarian response is associated with anogenital distance in patients undergoing controlled ovarian stimulation for IVF

STUDY QUESTION

Is the length of the anogenital distance (AGD) a biomarker of ovarian reserve and response to controlled ovarian stimulation (COS)?

SUMMARY ANSWER

Shorter AGD is associated with presence of poor ovarian response.

WHAT IS KNOWN ALREADY

Organ development during prenatal life is influenced by the prevailing intrauterine environment, and it has been suggested that nutritional, environmental and toxic factors could affect ovarian reserve set prenatally. AGD is a biomarker of prenatal-hormonal environment and observational studies have shown an association between its length and reproductive parameters in both sexes.

STUDY DESIGN, SIZE, DURATION

This was a prospective cohort study of 437 women treated with IVF/ICSI conducted in a tertiary-care university hospital between January and December 2016.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All women underwent their first COS for IVF/ICSI and reached criteria for oocyte retrieval. Based on the number of oocytes obtained, patients were divided into three groups: poor responders (≤3 oocytes) (n = 50), normoresponders (4-15 oocytes) (n = 332) and high responders (>15 oocytes) (n = 55). Before retrieval, the following patient data were recorded: age, body mass index (BMI), ovarian reserve markers (anti-Müllerian hormone [AMH], antral follicle count [AFC] and follicular stimulation hormone [FSH]), cause of infertility, total doses of gonadotropins used and ovarian sensitivity index (OSI). Patients with previous pregnancies, polycystic ovary syndrome (PCOS), endometriosis and previous ovarian or genital surgery were excluded. Anthropometric biomarkers of AGDAC (anus-clitoris) and AGDAF (anus-fourchette) were measured in all patients under sedation on the day of retrieval and before proceeding to oocyte pick-up. Multiple linear regression analyses were used to examine the association between both AGD and ovarian reserve markers, the total units of gonadotropins used, the number of oocytes obtained and the OSI. Logistic regression was used to predict poor response in COS for IVF/ICSI, while accounting for confounders such as age and BMI.

MAIN RESULTS AND THE ROLE OF CHANCE

Baseline FSH, AMH, AFC and age were significantly different among the three groups of ovarian response, as were the units of gonadotropin used, and the ovarian sensitivity index (OSI) (P < 0.001). Both AGDAC and AGDAF measurements were positively correlated with AMH levels (r = 0.38 and r = 0.21; P < 0.05), AFC (r = 0.41 and r = 0.20; P < 0.05), the OSI (r = 0.24 and r = 0.19; P < 0.05) and the number of oocytes retrieved (r = 0.29 and r = 0.28, respectively; P < 0.05). Conversely, there was a negative correlation between both AGD measurements and the doses of gonadotropins used (r= -0.19 and r= -0.15; P < 0.05). The area under the curve (AUC) for prediction of poor response of AGDAC was 0.70 (95% CI 0.66, 0.75), which was comparable to the classic ovarian reserve markers, such as AFC and AMH. AGDAF showed a significantly worse predictive capacity for poor ovarian response (AUC 0.60 [95% CI 0.55, 0.60]) than AMH and AFC.

LIMITATIONS, REASONS FOR CAUTION

The population used for the study was a highly selected group of infertile women who underwent COS for IVF, so the findings of this research may not be applicable for general population. Besides, measurement or selection biases might have been possible and must be considered.

WIDER IMPLICATIONS OF THE FINDINGS

The findings of this study suggest that in utero exposure to certain hormonal environments could affect the ovarian reserve set prenatally.

STUDY FUNDING/COMPETING INTEREST(S)

None. The authors have no competing interests to declare.

Chronic Exposure of Mice to Bisphenol-A Alters Uterine Fibroblast Growth Factor Signaling and Leads to Aberrant Epithelial Proliferation

Uterine epithelial proliferation is regulated in a paracrine manner by a complex interplay between estrogen (E) and progesterone (P) signaling, in which E stimulates proliferation and P inhibits it. Perturbation of steroid hormone signaling within the uterine milieu could contribute to the development of endometrial hyperplasia and cancer. It is well established that bisphenol-A (BPA) is an endocrine-disrupting chemical with weak estrogenic effects, although little is known about how it affects steroid hormone signaling in the adult uterus. Because BPA acts as a weak E, we hypothesized that chronic exposure to BPA would create an imbalance between E and P signaling and cause changes in the uterus, such as aberrant epithelial proliferation. Indeed, exposure to an environmentally relevant dose of BPA had a uterotrophic affect. BPA-treated mice showed increased proliferation, notably in the glandular epithelium, which are sites of origin for endometrial hyperplasia and cancer. Increased proliferation appeared to be mediated through a similar mechanism as E-induced proliferation, via activation of the fibroblast growth factor receptor pathway and phosphorylation of the ERK1/2 mitogen-activated protein kinases in the epithelium. Interestingly, BPA reduced expression of heart and neural crest derivatives expressed 2 (HAND2), a known mediator of the antiproliferative effects of P. BPA also increased methylation of a CpG island in the Hand2 gene promoter, suggesting that BPA may promote epithelial proliferation through epigenetic silencing of antiproliferative factors like HAND2. Collectively, these findings establish that chronic exposure to BPA impairs steroid hormone signaling in the mouse uterus, and may contribute to the pathogenesis of uterine hyperplasia and cancer.

Establishment and depletion of the ovarian reserve: physiology and impact of environmental chemicals

The reproductive life span in women starts at puberty and ends at menopause, following the exhaustion of the follicle stockpile termed the ovarian reserve. Increasing data from experimental animal models and epidemiological studies indicate that exposure to a number of ubiquitously distributed reproductively toxic environmental chemicals (RTECs) can contribute to earlier menopause and even premature ovarian failure. However, the causative relationship between environmental chemical exposure and earlier menopause in women remains poorly understood. The present work, is an attempt to review the current evidence regarding the effects of RTECs on the main ovarian activities in mammals, focusing on how such compounds can affect the ovarian reserve at any stages of ovarian development. We found that in rodents, strong evidence exists that in utero, neonatal, prepubescent and even adult exposure to RTECs leads to impaired functioning of the ovary and a shortening of the reproductive lifespan. Regarding human, data from cross-sectional surveys suggest that human exposure to certain environmental chemicals can compromise a woman's reproductive health and in some cases, correlate with earlier menopause. In conclusion, evidences exist that exposure to RTECs can compromise a woman's reproductive health. However, human exposures may date back to the developmental stage, while the adverse effects are usually diagnosed decades later, thus making it difficult to determine the association between RTECs exposure and human reproductive health. Therefore, epidemiological surveys and more experimental investigation on humans, or alternatively primates, are needed to determine the direct and indirect effects caused by RTECs exposure on the ovary function, and to characterize their action mechanisms.

Do prenatal exposures pose a real threat to ovarian function? Bisphenol A as a case study

Fetal development represents a time of potential vulnerability due to rapid cell division, organ development and limited fetal kidney/liver activity for detoxification and metabolism of exposures. Health effects of prenatal toxicant exposure have previously been described, but there is little cohesive evidence surrounding effects on ovarian function. Using bisphenol A (BPA) as a case study, we seek to examine whether a prominent prenatal environmental exposure can pose a real threat to human ovarian function. To do so, we broadly review human oogenesis and menstrual cycle biology. We then present available literature addressing prenatal bisphenol A and diverse outcomes at the level of the ovary. We highlight relevant human cohorts and mammalian models to review the existing data on prenatal exposures and ovarian disruption. Doing so suggests that while current exposures to BPA have not shown marked or consistent results, there is data sufficient to raise concerns regarding ovarian function. Challenges in the examination of this question suggest the need for additional models and pathways by which to expand these examinations in humans.

Gestational diabetes promotes germ cell cCyst breakdown and primordial follicle formation in newborn mice via the AKT signaling pathway

Type 1 diabetes (T1D) is a common disease in which pancreatic β cells are impaired due to auto-immunity, pregnancy in women with it is associated with increased risk of neonatal morbidity, mortality. However, the effects of gestational diabetes on the reproduction of newborn offspring are still poorly understood. Here, we determined the cyst breakdown and primordial follicle formation in neonatal offspring born by streptozotocin (STZ)-induced diabetic or non-diabetic female mice, and found that the germ cell cyst breakdown was promoted in neonatal offspring of STZ -induced diabetic mice at postnatal Day 1, which sequentially accelerated the primordial follicle formation. Further investigation revealed that, the expression level of PI3K and p-AKT were significantly increased in ovaries of offspring born by T1D mice. These results indicated that STZ -induced gestational diabetes promotes germ cell cyst breakdown and primordial follicle formation by regulating the PI3K/AKT signaling pathway in the newborn offspring. In addition, this effect can be rescued by an insulin supplement. Taken together, our results uncover the intergenerational effects of gestational diabetes on neonatal offspring folliculogenesis, and provide an experimental model for treating gestational diabetes and its complications in neonatal offspring.

BPA exposure is associated with non-monotonic alteration in ESR1 promoter methylation in peripheral blood of men and shorter relative telomere length in peripheral blood of women

The aim of this study was to evaluate the potential association of urinary Bisphenol A (BPA) levels with estrogen receptor alpha (ESR1) promoter % methylation and relative telomere length in a sample of 482 participants. Urinary BPA concentration was measured using organic phase extraction followed by high performance liquid chromatography mass spectroscopy. Peripheral blood ESR1 promoter % methylation and relative telomere length were measured using direct bisulfite sequencing and real-time polymerase chain reaction, respectively. The mean ± SD urinary BPA concentration adjusted for urinary creatinine was 2.90 ± 4.81 (μg/g creatinine) with a median of 1.86 μg/g creatinine (min-max: <LOD -69.85). There was a potentially non-monotonic relationship between adjusted urinary BPA concentrations and ESR1 promoter % methylation in men. As a matter of fact, for the lowest tertile of ESR1 promoter % methylation, the OR and 95% CI of the middle and highest tertiles of urinary adjusted BPA were 2.54 (1.01-6.39) and 1.64 (0.55-4.86) when compared to the lowest BPA tertile, respectively. After adjustment for potential confounders, similar results remained in men and appeared in the whole cohort. As for relative telomere length, there was a significant trend whereby higher adjusted urinary BPA concentrations were significantly associated with shorter relative telomere length in females. For instance, for the shortest relative telomere length tertile, the OR and 95% CI of the middle and highest tertiles of urinary adjusted BPA were 2.91 (1.38-6.16) and 3.19 (1.57-6.49) when compared to the lowest BPA tertile, respectively. This trend remained significant after adjustment for potential confounders.

CLARITY-BPA academic laboratory studies identify consistent low-dose Bisphenol A effects on multiple organ systems

Bisphenol A (BPA) is a high-production chemical used in a variety of applications worldwide. While BPA has been documented as an endocrine-disrupting chemical (EDC) having adverse health-related outcomes in multiple studies, risk assessment for BPA has lagged due to reliance on guideline toxicology studies over academic ones with end-points considered more sensitive and appropriate. To address current controversies on BPA safety, the United States National Institute of Environmental Health Sciences (NIEHS), the National Toxicology Program (NTP) and the Food and Drug Administration (FDA) established the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) using the NCTR Sprague-Dawley rats. The goal of CLARITY-BPA is to perform a traditional regulatory toxicology study (Core study) in conjunction with multiple behavioural, molecular and cellular studies by academic laboratories focused on previously identified BPA-sensitive organ systems (Academic studies). Combined analysis of the data from both study types will be undertaken by the NTP with the aim of resolving uncertainties on BPA toxicity. To date, the Core study has been completed and a draft report released. Most of the academic studies have also been finalized and published in peer-reviewed journals. In light of this important milestone, the PPTOX-VI meeting held in the Faroe Islands, 27-30 May 2018 devoted a plenary session to CLARITY-BPA with presentations by multiple investigators with the purpose of highlighting key outcome. This MiniReview synthesizes the results of three academic studies presented at this plenary session, evaluates recently published findings by other CLARITY-BPA academic studies to provide an early combined overview of this emerging data and places this in the context of the Core study findings. This co-ordinated effort revealed a plethora of significant BPA effects across multiple organ systems and BPA doses with non-monotonic responses across the dose range utilized. Remarkably consistent across most studies, including the Core study, are low-dose effects (2.5, 25 and 250 μg BPA/kg body-weight). Collectively, the findings highlighted herein corroborate a significant body of evidence that documents adverse effects of BPA at doses relevant to human exposures and emphasizes the need for updated risk assessment analysis.

The effects of Bisphenol A on the seagrass Cymodocea nodosa: Leaf elongation impairment and cytoskeleton disturbance

Bisphenol A (BPA) is an emerging pollutant of environmental concern, classified as "moderately toxic" and "toxic", causing adverse effects on aquatic biota. Although information about BPA toxicity on aquatic fauna is available, the data about BPA effects on aquatic flora remain scarce, missing for marine macrophytes. The effects of environmentally relevant BPA concentrations (ranging from 0.03 to 3 μg L^-1) on juvenile leaf elongation and the cytoskeleton (microtubules, MTs and actin filaments, AFs) were studied in the seagrass Cymodocea nodosa for 1-10 days. The suitability of cytoskeleton disturbance and leaf elongation impairment as "biomarkers" for BPA stress were tested. The highest BPA concentrations (0.3, 0.5, 1 and 3 μg L^-1) affected significantly leaf elongation from the onset of the experiment, while defects of the cytoskeleton were observed even at lower concentrations. In particular, MTs were initially disrupted (i.e. "lowest observed effect concentrations", LOECs) at 0.1 μg L^-1, while AFs were damaged even at 0.03 μg L^-1. AFs appeared thus to be more sensitive to lower BPA concentrations, while there was a correlation between leaf elongation impairment and MT defects. Thus, AF damages, MT disruption and leaf elongation impairment in C. nodosa, in this particular order, appear to be sensitive "biomarkers" of BPA stress, at the above environmentally relevant BPA concentrations.

Associations of female exposure to bisphenol A with fecundability: Evidence from a preconception cohort study

BACKGROUND

Human exposure to bisphenol A (BPA) is common. The reproductive toxicity of BPA has been well characterized. However, the impact of BPA exposure on fecundability in healthy women is less clear, and evidence from eastern countries is lacking.

OBJECTIVES

We aimed to prospectively assess the associations of BPA with female fecundability, as measured by time to pregnancy (TTP).

METHODS

From 2013 to 2015, we included 700 Chinese couples attempting pregnancy in two preconception care clinics and followed for 12 months or until a pregnancy occurred. The concentrations of BPA were determined in preconception urine samples of female partners. Cox's proportional models for discrete survival time were used to estimate fecundability odds ratios (FORs). Odds ratios (ORs) for infertility (TTP > 12 months) were estimated using logistic regression models.

RESULTS

After adjusting for potential confounders, each ln-unit increase in urinary concentrations of BPA was associated with a 13% reduction in fecundability (FOR = 0.87; 95% CI: 0.78, 0.98) and a 23% increase in odds of infertility (OR = 1.23; 95% CI: 1.00, 1.50). Women in the highest quartile of urinary BPA had a 30% reduction in fecundability (FOR = 0.70, 95% CI: 0.51, 0.96) and a 64% increase in odds of infertility when compared to those in the lowest quartile (OR = 1.64, 95% CI: 0.90, 2.98). The associations of urinary BPA concentrations with fecundability (FOR = 0.80, 95% CI: 0.67, 0.95) and infertility (OR = 1.43, 95% CI: 1.05, 1.93) were strengthened among women over 30 years of age.

CONCLUSIONS

Our results suggest that preconception concentrations of BPA in female urine were associated with decreased fecundability, particularly among women at older ages. These findings should be confirmed in future human studies.

Ameliorative effect of ginseng extract on phthalate and bisphenol A reprotoxicity during pregnancy in rats

Phthalates (such as DEHP) and bisphenol A (BPA) are widely used chemicals in plastics manufacturing and exert public health concerns as endocrine disrupters. This study was designed to investigate the deleterious effect of DEHP and BPA on endocrine profile of pregnant female rats and the combined treatment with ginseng extract (Panax ginseng). Seventy-two pregnant rats were divided into six groups (control, ginseng, DEHP, BPA, Gin + DEHP, and Gin + BPA), 12 females per each group. The drugs were supplemented from pregnancy day 0 until day 20. Determination of serum sex hormones (testosterone, progesterone, and estradiol) were determined on days 4, 10, and 20 of pregnancy. mRNA transcripts of STAR, HSD17B3, CYP17, AKT1, and PTEN were relatively quantified against ACTB in the ovary and placenta of days 10 and 20 pregnant females by relative quantitative polymerase-chain reaction (RQ-PCR). DEHP and BPA significantly decreased the endocrine profile of testosterone, progesterone, and estradiol of days 10 and 20 of pregnant females. Combined administration of these chemicals along with ginseng extracts has returned the hormones to normal levels when compared with the control group. The ovarian and placental CYP17 and HSD17B3 mRNA transcripts showed variable expression pattern in both tissues and they were significantly affected by DEHP and BPA administration, concomitantly correlating to STAR, AKT1, PTEN, progesterone, and testosterone levels on pregnancy days 10 and 20. The results confirm the reprotoxicity of DEHP and BPA as endocrine disruptors and indicate that ginseng could be used to alleviate the toxic effects of these chemicals.

Perinatal BPA exposure and reproductive axis function in CD-1 mice

Perinatal Bisphenol-A (BPA) exposure reduces fertility and fecundity in mice. This study examined effects of early BPA exposure on activation of gonadotropin releasing hormone (GnRH) neurons in conjunction with a steroid-induced luteinizing hormone (LH) surge, characterized patterns of estrous cyclicity and fertility over time, and assessed the ovarian follicular reserve to further explore factors responsible for the reduced fertility we previously described in this model. The percent activated GnRH neurons was reduced in BPA-exposed females at 3-6 months, and periods of persistent proestrus were increased. These data suggest that perinatal exposure to BPA reduces GnRH neuronal activation required for the generation of the LH surge and estrous cyclicity. Assessments of anti-Müllerian hormone (AMH) levels failed to suggest a decline in the follicular reserve at the BPA exposure levels examined.

The importance of DNA repair for maintaining oocyte quality in response to anti-cancer treatments, environmental toxins and maternal ageing

BACKGROUND

Within the ovary, oocytes are stored in long-lived structures called primordial follicles, each comprising a meiotically arrested oocyte, surrounded by somatic granulosa cells. It is essential that their genetic integrity is maintained throughout life to ensure that high quality oocytes are available for ovulation. Of all the possible types of DNA damage, DNA double-strand breaks (DSBs) are considered to be the most severe. Recent studies have shown that DNA DSBs can accumulate in oocytes in primordial follicles during reproductive ageing, and are readily induced by exogenous factors such as γ-irradiation, chemotherapy and environmental toxicants. DSBs can induce oocyte death or, alternatively, activate a program of DNA repair in order to restore genetic integrity and promote survival. The repair of DSBs has been intensively studied in the context of meiotic recombination, and in recent years more detail is becoming available regarding the repair capabilities of primordial follicle oocytes.

OBJECTIVE AND RATIONALE

This review discusses the induction and repair of DNA DSBs in primordial follicle oocytes.

SEARCH METHODS

PubMed (Medline) and Google Scholar searches were performed using the key words: primordial follicle oocyte, DNA repair, double-strand break, DNA damage, chemotherapy, radiotherapy, ageing, environmental toxicant. The literature was restricted to papers in the English language and limited to reports in animals and humans dated from 1964 until 2017. The references within these articles were also manually searched.

OUTCOMES

Recent experiments in animal models and humans have provided compelling evidence that primordial follicle oocytes can efficiently repair DNA DSBs arising from diverse origins, but this capacity may decline with increasing age.

WIDER IMPLICATIONS

Primordial follicle oocytes are vulnerable to DNA DSBs emanating from endogenous and exogenous sources. The ability to repair this damage is essential for female fertility. In the long term, augmenting DNA repair in primordial follicle oocytes has implications for the development of novel fertility preservation agents for female cancer patients and for the management of maternal ageing. However, further work is required to fully characterize the specific proteins involved and to develop strategies to bolster their activity.

The toxic effects and possible mechanisms of Bisphenol A on oocyte maturation of porcine in vitro

Bisphenol A (BPA) and Di-(2-ethylhexyl) phthalate (DEHP) are widely used in the plastic industry such as water bottles, containers, packaging and toys. BPA and DEHP are shown to be the endocrine disruptors which disturb the endocrine system and are linked to several diseases including infertility. In this study, we investigated the effects of BPA exposure on porcine oocyte maturation and its possible reasons. Our results showed that: (i) the rates of oocyte maturation significantly decreased with 250 μM BPA treatment in vitro, but not DEHP. This might be due to the delayed cell cycle progression of oocyte maturation. (ii) BPA treatment resulted in abnormal cytoskeletons on porcine oocytes, showing with aberrant actin distribution, spindle morphology and chromosome alignment, which was further confirmed by the reduced p-MAPK level. (iii) The fluorescence intensity of histone methylation (H3K4me2) and DNA methylation (5 mC) levels were altered after BPA treatment, indicating that epigenetic modification was disturbed. (iv) BPA-exposed oocytes had higher rates of early stage apoptosis/autophagy, and this may be resulted from the increased level of oxidative stress. Collectively, our results indicated that porcine oocytes maturation was disrupted after BPA treatment through disrupting cytoskeletal dynamics, epigenetic modifications and inducing apoptosis/autophagy.

Stem cells, in vitro gametogenesis and male fertility

Reconstitution in culture of biological processes, such as differentiation and organization, is a key challenge in regenerative medicine, and one in which stem cell technology plays a central role. Pluripotent stem cells and spermatogonial stem cells are useful materials for reconstitution of germ cell development in vitro, as they are capable of differentiating into gametes. Reconstitution of germ cell development, termed in vitro gametogenesis, will provide an experimental platform for a better understanding of germ cell development, as well as an alternative source of gametes for reproduction, with the potential to cure infertility. Since germ cells are the cells for 'the next generation', both the culture system and its products must be carefully evaluated. In this issue, we summarize the progress in in vitro gametogenesis, most of which has been made using mouse models, as well as the future challenges in this field.

Di (2-ethylhexyl) phthalate exposure impairs meiotic progression and DNA damage repair in fetal mouse oocytes in vitro

Di (2-ethylhexyl) phthalate (DEHP), is the most common member of the class of phthalates that are used as plasticizers and have become common environmental contaminants. A number of studies have shown that DEHP exposure impacts reproductive health in both male and female mammals by acting as an estrogen analog. Here, we investigated the effects of DEHP on meiotic progression of fetal mouse oocytes by using an in vitro model of ovarian tissue culture. The results showed that 10 or 100 μM DEHP exposure inhibited the progression of oocytes throughout meiotic prophase I, specifically from the pachytene to diplotene stages. DEHP possibly impairs the ability to repair DNA double-strand breaks induced by meiotic recombination and as a consequence activates a pachytene check point. At later stages, such defects led to an increased number of oocytes showing apoptotic markers (TUNEL staining, expression of pro-apoptotic genes), resulting in reduced oocyte survival, gap junctions, and follicle assembly in the ovarian tissues. Microarray analysis of ovarian tissues exposed to DEHP showed altered expression of several genes including some involved in apoptosis and gonad development. The expression changes of some genes clustered in cell-cell communication and signal transduction, along with plasma membrane, extracellular matrix and ion channel function classes, were dependent on the DEHP concentration. Together, these results bring new support to the notion that exposure to DEHP during gestation might exert deleterious effects on ovary development, perturbing germ cell meiosis and the expression of genes involved in a wide range of biological processes including ovary development.

Mechanisms controlling germline cyst breakdown and primordial follicle formation

In fetal females, oogonia proliferate immediately after sex determination. The progress of mitosis in oogonia proceeds so rapidly that the incompletely divided cytoplasm of the sister cells forms cysts. The oogonia will then initiate meiosis and arrest at the diplotene stage of meiosis I, becoming oocytes. Within each germline cyst, oocytes with Balbiani bodies will survive after cyst breakdown (CBD). After CBD, each oocyte is enclosed by pre-granulosa cells to form a primordial follicle (PF). Notably, the PF pool formed perinatally will be the sole lifelong oocyte source of a female. Thus, elucidating the mechanisms of CBD and PF formation is not only meaningful for solving mysteries related to ovarian development but also contributes to the preservation of reproduction. However, the mechanisms that regulate these phenomena are largely unknown. This review summarizes the progress of cellular and molecular research on these processes in mice and humans.

Environmental influences on ovarian dysgenesis - developmental windows sensitive to chemical exposures

A woman's reproductive health and ability to have children directly affect numerous aspects of her life, from personal well-being and socioeconomic standing, to morbidity and lifespan. In turn, reproductive health depends on the development of correctly functioning ovaries, a process that starts early during fetal life. Early disruption to ovarian programming can have long-lasting consequences, potentially manifesting as disease much later in adulthood. A growing body of evidence suggests that exposure to chemicals early in life, including endocrine-disrupting chemicals, can cause a range of disorders later in life, such as those described in the ovarian dysgenesis syndrome hypothesis. In this Review, we discuss four specific time windows during which the ovary is particularly sensitive to disruption by exogenous insults: gonadal sex determination, meiotic division, follicle assembly and the first wave of follicle recruitment. To date, most evidence points towards the germ cell lineage being the most vulnerable to chemical exposure, particularly meiotic division and follicle assembly. Environmental chemicals and pharmaceuticals, such as bisphenols or mild analgesics (including paracetamol), can also affect the somatic cell lineages. This Review summarizes our current knowledge pertaining to environmental chemicals and pharmaceuticals, and their potential contributions to the development of ovarian dysgenesis syndrome. We also highlight knowledge gaps that need addressing to safeguard female reproductive health.

Impaired ovarian response to exogenous gonadotropins in female rat offspring born to mothers perinatally exposed to Bisphenol A

The ovary is sensitive to disruption by the environmental estrogen Bisphenol A (BPA). Our aim was to investigate whether perinatal exposure to BPA (50μg/kgday), orally administered, affects ovarian response to exogenous gonadotrophins (PMSG or PMSG+hCG) in prepubertal female offspring. An altered response to gonadotrophins was observed in BPA-exposed rats. Increased proportion of antral follicles, altered levels of ovarian steroidogenic enzymes, gonadotropin receptors, AR and ERβ were observed in PMSG group. Besides that, in response to PMSG+hCG, a persistent high Fshr mRNA expression and a decreased number of follicles with high expression of PR before ovulation were observed. After ovulation, there was an increase in antral atretic follicles, reduced Lhcgr mRNA expression and high serum levels of E2. Therefore, an early exposure to a low dose of BPA during perinatal period induces ovarian changes leading to an altered response to exogenous gonadotropin treatment later in life.

Effect of bisphenol A on reproductive processes: A review of in vitro, in vivo and epidemiological studies

As bisphenol A (BPA) is characterized by a pronounced influence on human hormonal regulation, particular attention has been aimed at understanding its role in reproductive processes in males and females, as well as on fetal development. Owing to the increasing number of alarming reports on the negative consequences of the presence of BPA in human surroundings, more and more studies are being undertaken to clarify the negative effects of BPA on human reproductive processes. The aim of this work was to collect and summarize data on the influence of BPA exposure on reproductive health. Based on an analysis of selected publications it was stated that there is strong proof confirming that BPA is an ovarian, uterine and prostate toxicant at a level below the lowest observed adverse effect level (50 mg kg^-1 bodyweight) as well as a level below the proposed safe level (4 μg kg^-1 bodyweight). It seems there is also reliable evidence in relation to the negative effect of BPA on sperm quality and motility. Limited evidence also pertains to the case of the potential of BPA to affect polycystic ovary syndrome occurrence. Although in epidemiological studies this disease was common, in studies on animal models such results were still not confirmed. No unambiguous results of epidemiological studies and with animal models were obtained in relation to the evaluation of associations between BPA and implantation failure in women, evaluation of associations between BPA and sexual dysfunction in men, and impact of BPA on birth rate, birth weight and length of gestation. Copyright © 2017 John Wiley & Sons, Ltd.

The impact of Zearalenone on the meiotic progression and primordial follicle assembly during early oogenesis

Zearalenone (ZEA) is a mycotoxin produced by fusarium graminearum. It can cause abnormal reproductive function by acting as an environmental estrogen. Research has traditionally focused on acute and chronic injury on mammalian reproductive capacity after ZEA treatment. Little research has been done studying the effects of ZEA exposure on early oogenesis. In this study, we investigate the effects of ZEA exposure on meiotic entry, DNA double-strand breaks (DSBs), and primordial follicle assembly during murine early oogenesis. The results show that ZEA exposure significantly decreased the percentage of diplotene stage germ cells, and made more germ cells remain at zygotene or pachytene stages. Moreover, the mRNA expression level of meiosis-related genes was significantly reduced after ZEA treatment. ZEA exposure significantly increased DNA-DSBs at the diplotene stage. Meanwhile, DNA damage repair genes such as RAD51 and BRCA1 were activated. Furthermore, maternal exposure to ZEA significantly decreased the number of primordial follicles in newborn mouse ovaries. In conclusion, ZEA exposure impairs mouse female germ cell meiotic progression, DNA-DSBs, and primordial follicle assembly.

Environmental pollutants, a possible etiology for premature ovarian insufficiency: a narrative review of animal and human data

BACKGROUND

Because only 25% of cases of premature ovarian insufficiency (POI) have a known etiology, the aim of this review was to summarize the associations and mechanisms of the impact of the environment on this pathology. Eligible studies were selected from an electronic literature search from the PUBMED database from January 2000 to February 2016 and associated references in published studies. Search terms included ovary, follicle, oocyte, endocrine disruptor, environmental exposure, occupational exposure, environmental contaminant, pesticide, polyaromatic hydrocarbon, polychlorinated biphenyl PCB, phenol, bisphenol, flame retardant, phthalate, dioxin, phytoestrogen, tobacco, smoke, cigarette, cosmetic, xenobiotic. The literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We have included the human and animal studies corresponding to the terms and published in English. We have excluded articles that included results that did not concern ovarian pathology and those focused on ovarian cancer, polycystic ovary syndrome, endometriosis or precocious puberty. We have also excluded genetic, auto-immune or iatrogenic causes from our analysis. Finally, we have excluded animal data that does not concern mammals and studies based on results from in vitro culture. Data have been grouped according to the studied pollutants in order to synthetize their impact on follicular development and follicular atresia and the molecular pathways involved. Ninety-seven studies appeared to be eligible and were included in the present study, even though few directly address POI. Phthalates, bisphenol A, pesticides and tobacco were the most reported substances having a negative impact on ovarian function with an increased follicular depletion leading to an earlier age of menopause onset. These effects were found when exposure occured at different times throughout the lifetime from the prenatal to the adult period, possibly due to different mechanisms. The main mechanism seemed to be an increase in atresia of pre-antral follicles.

CONCLUSION

Environmental pollutants are probably a cause of POI. Health officials and the general public must be aware of this environmental effect in order to implement individual and global preventive actions.

Regulation of primordial follicle recruitment by cross-talk between the Notch and phosphatase and tensin homologue (PTEN)/AKT pathways

The growth of oocytes and the development of follicles require certain pathways involved in cell proliferation and survival, such as the phosphatidylinositol 3-kinase (PI3K) pathway and the Notch signalling pathway. The aim of the present study was to investigate the interaction between Notch and the PI3K/AKT signalling pathways and their effects on primordial follicle recruitment. When the Notch pathway was inhibited by L-685,458 or N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycinet-butyl ester (DAPT) in vitro, the expression of genes in the pathway and the percentage of oocytes in growing follicles decreased significantly in mouse ovaries. By 2 days postpartum, ovaries exposed to DAPT, short interference (si) RNA against Notch1 or siRNA against Hairy and enhancer of split-1 (Hes1) had significantly decreased expression of HES1, the target protein of the Notch signalling pathway. In contrast, expression of phosphatase and tensin homologue (Pten), a negative regulator of the AKT signalling pathway, was increased significantly. Co immunoprecipitation (Co-IP) revealed an interaction between HES1 and PTEN. In addition, inhibition of the Notch signalling pathway suppressed AKT phosphorylation and the proliferation of granulosa cells. In conclusion, the recruitment of primordial follicles was affected by the proliferation of granulosa cells and regulation of the interaction between the Notch and PI3K/AKT signalling pathways.

Zearalenone exposure impairs ovarian primordial follicle formation via down-regulation of Lhx8 expression in vitro

Zearalenone (ZEA) is an estrogenic mycotoxin mainly produced as a secondary metabolite by numerous species of Fusarium. Previous work showed that ZEA had a negative impact on domestic animals with regard to reproduction. The adverse effects and the mechanisms of ZEA on mammalian ovarian folliculogenesis remain largely unknown, particularly its effect on primordial follicle formation. Thus, we investigated the biological effects of ZEA exposure on murine ovarian germ cell cyst breakdown and primordial follicle assembly. Our results demonstrated that newborn mouse ovaries exposed to 10 or 30μM ZEA in vitro had significantly less germ cell numbers compared to the control group. Moreover, the presence of ZEA in vitro increased the numbers of TUNEL and γH2AX positive cells within mouse ovaries and the ratio of mRNA levels of the apoptotic genes Bax/Bcl-2. Furthermore, ZEA exposure reduced the mRNA of oocyte specific genes such as LIM homeobox 8 (Lhx8), newborn ovary homeobox (Nobox), spermatogenesis and oogenesis helix-loop-helix (Sohlh2), and factor in the germline alpha (Figlα) in a dose dependent manner. Exposure to ZEA led to remarkable changes in the Lhx8 3'-UTR DNA methylation dynamics in oocytes and severely impaired folliculogenesis in ovaries after transplantation under the kidney capsules of immunodeficient mice. In conclusion, ZEA exposure impairs mouse primordial follicle formation in vitro.

Local effect of bisphenol A on the estradiol synthesis of ovarian granulosa cells from PCOS

Close relationship between polycystic ovary syndrome (PCOS) and bisphenol A (BPA) has drawn much attention in recent years, while the underlying mechanisms are poorly understood. In our study, we aim to detect BPA concentration in the follicular fluid and investigate its effect on estradiol synthesis in human granulosa cells from PCOS and non-PCOS patients. Follicular fluid and granulosa cells were collected from women who underwent controlled ovarian stimulation for in vitro fertilization or intracytoplasmic sperm injection. BPA concentration in the follicular fluid from PCOS patients (440.50 ± 63.70 pg/ml) was significantly higher than that from non-PCOS patients (338.00 ± 57.88 pg/ml). Expression of aromatase and estradiol synthesis in cultured granulosa cells was examined after treatment with BPA from 0.01 to 1 μM for 24 h. Expression of aromatase and estradiol synthesis was downregulated by BPA in a dose-dependent manner in PCOS, but no effect was observed in granulosa cells from non-PCOS patients. These findings provide evidence that increased BPA concentration in the follicular fluid of PCOS patients may play an important role in its pathogenesis by attenuating the expression of aromatase in granulosa cells.

Progesterone Receptor Membrane Component 1 Mediates Progesterone-Induced Suppression of Oocyte Meiotic Prophase I and Primordial Folliculogenesis

Well-timed progression of primordial folliculogenesis is essential for mammalian female fertility. Progesterone (P4) inhibits primordial follicle formation under physiological conditions; however, P4 receptor that mediates this effect and its underlying mechanisms are unclear. In this study, we used an in vitro organ culture system to show that progesterone receptor membrane component 1 (PGRMC1) mediated P4-induced inhibition of oocyte meiotic prophase I and primordial follicle formation. We found that membrane-impermeable BSA-conjugated P4 inhibited primordial follicle formation similar to that by P4. Interestingly, PGRMC1 and its partner serpine1 mRNA-binding protein 1 were highly expressed in oocytes in perinatal ovaries. Inhibition or RNA interference of PGRMC1 abolished the suppressive effect of P4 on follicle formation. Furthermore, P4-PGRMC1 interaction blocked oocyte meiotic progression and decreased intra-oocyte cyclic AMP (cAMP) levels in perinatal ovaries. cAMP analog dibutyryl cAMP reversed P4–PGRMC1 interaction-induced inhibition of meiotic progression and follicle formation. Thus, our results indicated that PGRMC1 mediated P4-induced suppression of oocyte meiotic progression and primordial folliculogenesis by decreasing intra-oocyte cAMP levels.

The effect of maternal exposure to endocrine disrupting chemicals on fetal and neonatal development: A review on the major concerns

There is a widespread exposure of general population, including pregnant women and developing fetuses, to the endocrine disrupting chemicals (EDCs). These chemicals have been reported to be present in urine, blood serum, breast milk, and amniotic fluid. Endocrine disruptions induced by environmental toxicants have placed a heavy burden on society, since environmental exposures during critical periods of development can permanently reprogram normal physiological responses, thereby increasing susceptibility to disease later in life-a process known as developmental reprogramming. During development, organogenesis and tissue differentiation occur through a continuous series of tightly-regulated and precisely-timed molecular, biochemical, and cellular events. Humans may encounter EDCs daily and during all stages of life, from conception and fetal development through adulthood and senescence. Nevertheless, prenatal and early postnatal windows are the most critical for proper development, due to rapid changes in system growth. Although there are still gaps in our knowledge, currently available data support the urgent need for health and environmental policies aimed at protecting the public and, in particular, the developing fetus and women of reproductive age. Birth Defects Research (Part C) 108:224-242, 2016. © 2016 Wiley Periodicals, Inc.

Evidence for bisphenol A-induced female infertility: a review (2007-2016)

We summarized the scientific literature published from 2007 to 2016 on the potential effects of bisphenol A (BPA) on female fertility. We focused on overall fertility outcomes (e.g., ability to become pregnant, number of offspring), organs that are important for female reproduction (i.e., oviduct, uterus, ovary, hypothalamus, and pituitary), and reproductive-related processes (i.e., estrous cyclicity, implantation, and hormonal secretion). The reviewed literature indicates that BPA may be associated with infertility in women. Potential explanations for this association can be generated from experimental studies. Specifically, BPA may alter overall female reproductive capacity by affecting the morphology and function of the oviduct, uterus, ovary, and hypothalamus-pituitary-ovarian axis in animal models. In addition, BPA may disrupt estrous cyclicity and implantation. Nevertheless, further studies are needed to better understand the exact mechanisms of action and to detect potential reproductive toxicity at earlier stages.