Bisphenol A Effects on Mammalian Oogenesis and Epigenetic Integrity of Oocytes: A Case Study Exploring Risks of Endocrine Disrupting Chemicals

Emerging regulatory roles of noncoding RNAs induced by bisphenol A (BPA) and its alternatives in human diseases

Bisphenols (BPs), including BPA, BPF, BPS, and BPAF, are synthetic phenolic organic compounds and endocrine-disrupting chemicals. These organics have been broadly utilized to produce epoxy resins, polycarbonate plastics, and other products. Mounting evidence has shown that BPs, especially BPA, may enter into the human body and participate in the development of human diseases mediated by nuclear hormone receptors. Moreover, BPA may negatively affect human health at the epigenetic level through processes such as DNA methylation and histone acetylation. Recent studies have demonstrated that, as part of epigenetics, noncoding RNAs (ncRNAs), including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), and small nucleolar RNAs (snoRNAs), have vital impacts on BP-related diseases, such as reproductive system diseases, nervous system diseases, digestive system diseases, endocrine system diseases, and other diseases. Moreover, based on the bioinformatic analysis, changes in ncRNAs may be relevant to normal activities and functions and BP-induced diseases. Thus, we conducted a meta-analysis to identify more promising ncRNAs as biomarkers and therapeutic targets for BP exposure and relevant human diseases. In this review, we summarize the regulatory functions of ncRNAs induced by BPs in human diseases and latent molecular mechanisms, as well as identify prospective biomarkers and therapeutic targets for BP exposure and upper diseases.

Epigenetic modification impacting brain functions: Effects of physical activity, micronutrients, caffeine, toxins, and addictive substances

Changes in gene expression are involved in many brain functions. Epigenetic processes modulate gene expression by histone modification and DNA methylation or RNA-mediated processes, which is important for brain function. Consequently, epigenetic changes are also a part of brain diseases such as mental illness and addiction. Understanding the role of different factors on the brain epigenome may help us understand the function of the brain. This review discussed the effects of caffeine, lipids, addictive substances, physical activity, and pollutants on the epigenetic changes in the brain and their modulatory effects on brain function.

Alterations induced by Bisphenol A on cellular organelles and potential relevance on human health

Bisphenol A (BPA) is a chemical partially soluble in water and exists in a solid state. Its structural similarity with estrogen makes it an endocrine-disrupting chemical. BPA can disrupt signaling pathways at very low doses and may cause organellar stress. According to in vitro and in vivo studies, BPA interacts with various cell surface receptors to cause organellar stress, producing free radicals, cellular toxicity, structural changes, DNA damage, mitochondrial dysfunction, cytoskeleton remodeling, centriole duplication, and aberrant changes in several cell signaling pathways. The current review summarizes the impact of BPA exposure on the structural and functional aspects of subcellular components of cells such as the nucleus, mitochondria, endoplasmic reticulum, lysosome, ribosome, Golgi apparatus, and microtubules and its consequent impact on human health.

Toxicological evaluation of bisphenol analogues: preventive measures and therapeutic interventions

Bisphenol A (BPA) is a prominent endocrine-disrupting compound that shares structural similarities with estrogen. It is widely used, particularly in the production of food packaging, canned goods, and dental sealants. Of the eight bisphenol analogues, BPA is the most frequently utilized chemical in packaging food items, canned foods and dental sealants. However, chronic exposure to BPA can pose severe health risks, particularly in children. To ensure public safety, it is crucial to adopt proper precautionary measures to minimize BPA exposure. This article explores the toxic effects of bisphenols on various body systems and mechanisms, shedding light on their impact on the reproductive and endocrine system, obesity, albuminuria, and the generation of reactive oxygen species. Understanding the detrimental effects of bisphenols on these systems and mechanisms is vital for developing strategies to mitigate their harmful consequences. Furthermore, the article delves into the biotransformation processes of bisphenols, focusing on their occurrence in vertebrates, invertebrates, plants, and microorganisms. Investigating the biotransformation pathways provides valuable insights into the fate of bisphenols in various organisms and ecosystems. Lastly, the article emphasizes preventive measures to avoid bisphenol exposure and highlights the potential use of plant-based bioactive compounds for treatment strategies. By implementing effective preventive measures, such as utilizing BPA-free products and adopting safer alternatives, individuals can reduce their exposure to bisphenols. Additionally, exploring the potential of plant-based bioactive compounds as therapeutic agents offers promising avenues for addressing the adverse effects of bisphenols. The findings presented herein contribute to a better understanding of the novelty, significance, and potential implications of bisphenol research in the field, aiding in the development of safer practices and interventions to safeguard public health.

In utero and postnatal exposure to Foeniculum vulgare and Linum usitatissimum seed extracts: modifications of key enzymes involved in epigenetic regulation and estrogen receptors expression in the offspring's ovaries of NMRI mice

BACKGROUND

Early-life exposure to exogenous estrogens such as phytoestrogens (plant-derived estrogens) could affect later health through epigenetic modifications. Foeniculum vulgare (fennel) and Linum usitatissimum (flax) are two common medicinal plants with high phytoestrogen content. Considering the developmental epigenetic programming effect of phytoestrogens, the main goal of the present study was to evaluate the perinatal exposure with life-long exposure to hydroalcoholic extracts of both plants on offspring's ovarian epigenetic changes and estrogen receptors (ESRs) expression level as signaling cascades triggers of phytoestrogens.

METHODS

Pregnant mice were randomly divided into control (CTL) that received no treatment and extract-treated groups that received 500 mg/kg/day of fennel (FV) and flaxseed (FX) alone or in combination (FV + FX) during gestation and lactation. At weaning, female offspring exposed to extracts prenatally remained on the maternal-doses diets until puberty. Then, the ovaries were collected for morphometric studies and quantitative real-time PCR analysis.

RESULTS

A reduction in mRNA transcripts of the epigenetic modifying enzymes DNMTs and HDACs as well as estrogen receptors was observed in the FV and FX groups compared to the CTL group. Interestingly, an increase in ESRα/ESRβ ratio along with HDAC2 overexpression was observed in the FV + FX group.

CONCLUSION

Our findings clearly show a positive relationship between pre and postnatal exposure to fennel and flaxseed extracts, ovarian epigenetic changes, and estrogen receptors expression, which may affect the estrogen signaling pathway. However, due to the high phytoestrogen contents of these extracts, the use of these plants in humans requires more detailed investigations.

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.

Association between co-exposure to phenols and phthalates mixture and infertility risk in women

BACKGROUND

Exposure to phenols and phthalates has been separately linked to increased risks of infertility in women of reproductive age. However, the combined effect of phenols and phthalates exposure on infertility has not been explored.

METHODS

Data from the National Health and Nutrition Examination Surveys (NHANES) were used. A total of 857 women of reproductive age (18-45 years) with available information on urinary phenol and phthalate metabolites, reproductive questionnaires, and covariates were included in the present study. The definition of infertility was based on self-reports. Multivariable logistic regression, principal component analysis (PCA), and Bayesian kernel machine regression (BKMR) with stratified variable selection were applied to determine what associations were found between combined exposure to these mixtures and risk of infertility among women of reproductive age.

RESULTS

After adjusting for potential confounders, bisphenol A (BPA), mono(3-carboxypropyl) phthalate (MCPP) and four di(2-ethylhexyl) phthalate (DEHP) metabolites [mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) and mono(2-ethyl-5-carboxypentyl) phthalate (MECPP)] were positively associated with infertility. PCA revealed that the DEHP-BPA factor's PC score was significantly positively related to the likelihood of infertility [adjusted odds ratio (aOR) = 1.45; 1.08, 1.82]. The DEHP-BPA component consistently had the highest group posterior inclusion probability (PIP) in BKMR models. The BKMR model also found that MEOHP, MEHHP, and BPA were positively associated with infertility risk when the remaining combination concentrations were held at their median values. In addition, we observed that the probability of infertility increased dramatically as the quantiles of total mixture concentration increased.

CONCLUSION

Our findings indicate that a combination of phenol and phthalate metabolites is linked to infertility among reproductive-age women. BPA and DEHP, in particular, are significantly related to the risk of infertility.

Lifestyle interventions to reduce endocrine-disrupting phthalate and phenol exposures among reproductive age men and women: A review and future steps

Non-persistent endocrine-disrupting chemicals (EDCs), including phthalates and phenols, are ubiquitous in both the environment and human body. A growing body of epidemiologic studies have identified concerning links between EDCs and adverse reproductive and developmental health effects. Despite consistent evidence, risk assessments and policy interventions often arrive late. This presents an urgent need to identify evidence-based interventions for implementation at both clinical and community levels to reduce EDC exposure, especially in susceptible populations. The reproductive life cycle (menarche to menopause for females and after pubertal onset for males) includes some of the most vulnerable periods to environmental exposures, such as the preconception and perinatal stages, representing a key window of opportunity to intervene and prevent unfavorable health outcomes. This review aims to synthesize and assess behavioral, dietary, and residential EDC-driven interventions to develop recommendations for subsequent, larger-scale studies that address knowledge-gaps in current interventions during the reproductive life cycle. We selected 21 primary interventions for evaluation, in addition to four supplemental interventions. Among these, accessible (web-based) educational resources, targeted replacement of (known) toxic products, and personalization of the intervention through meetings and support groups, were the most promising strategies for reducing EDC concentrations. However, we document a paucity of interventions to prevent phthalate and phenol exposures during the reproductive years, especially among men. Accordingly, we recommend additional, larger clinical and community-based intervention studies to reduce EDC exposure. Specifically, future intervention studies should focus on short-term, mid-, and long-term exposure reduction to phthalates and phenols. The latter, especially, is required for the development of clinical and public health guidelines to promote reproductive and developmental health globally.

BPA Decreases PDCD4 in Bovine Granulosa Cells Independently of miR-21 Inhibition

microRNAs (miRNAs) are susceptible to environmental factors that might affect cellular function and impose negative effects on female reproduction. miR-21 is the most abundant miRNA in bovine granulosa cells and is widely reported as affected by Bisphenol A (BPA) exposure, yet the cause and consequences are not entirely elucidated. BPA is a synthetic endocrine disruptor associated with poor fertility. miR-21 function in bovine granulosa cells is investigated utilizing locked nucleic acid (LNA) oligonucleotides to suppress miR-21. Before measuring apoptosis and quantifying miR-21 apoptotic targets PDCD4 and PTEN, transfection was optimized and validated. BPA was introduced to see how it affects miR-21 regulation and which BPA-mediated effects are influenced by miR-21. miR-21 knockdown and specificity against additional miRNAs were confirmed. miR-21 was found to have antiapoptotic effects, which could be explained by its effect on the proapoptotic target PDCD4, but not PTEN. Previous findings of miR-21 overexpression were validated using BPA treatments, and the temporal influence of BPA on miR-21 levels was addressed. Finally, BPA effects on upstream regulators, such as VMP1 and STAT3, explain the BPA-dependent upregulation of miR-21 expression. Overall, this research enhances our understanding of miR-21 function in granulosa cells and the mechanisms of BPA-induced reproductive impairment.

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

The ovarian follicle of ruminants: the path from conceptus to adult

This review resulted from an international workshop and presents a consensus view of critical advances over the past decade in our understanding of follicle function in ruminants. The major concepts covered include: (1) the value of major genes; (2) the dynamics of fetal ovarian development and its sensitivity to nutritional and environmental influences; (3) the concept of an ovarian follicle reserve, aligned with the rise of anti-Müllerian hormone as a controller of ovarian processes; (4) renewed recognition of the diverse and important roles of theca cells; (5) the importance of follicular fluid as a microenvironment that determines oocyte quality; (6) the 'adipokinome' as a key concept linking metabolic inputs with follicle development; and (7) the contribution of follicle development to the success of conception. These concepts are important because, in sheep and cattle, ovulation rate is tightly regulated and, as the primary determinant of litter size, it is a major component of reproductive efficiency and therefore productivity. Nowadays, reproductive efficiency is also a target for improving the 'methane efficiency' of livestock enterprises, increasing the need to understand the processes of ovarian development and folliculogenesis, while avoiding detrimental trade-offs as greater performance is sought.

Exploring the evidence for epigenetic regulation of environmental influences on child health across generations

Environmental exposures, psychosocial stressors and nutrition are all potentially important influences that may impact health outcomes directly or via interactions with the genome or epigenome over generations. While there have been clear successes in large-scale human genetic studies in recent decades, there is still a substantial amount of missing heritability to be elucidated for complex childhood disorders. Mounting evidence, primarily in animals, suggests environmental exposures may generate or perpetuate altered health outcomes across one or more generations. One putative mechanism for these environmental health effects is via altered epigenetic regulation. This review highlights the current epidemiologic literature and supporting animal studies that describe intergenerational and transgenerational health effects of environmental exposures. Both maternal and paternal exposures and transmission patterns are considered, with attention paid to the attendant ethical, legal and social implications.

Parental preconception exposure to phenol and phthalate mixtures and the risk of preterm birth

BACKGROUND

Parental preconception exposure to select phenols and phthalates was previously associated with increased risk of preterm birth in single chemical analyses. However, the joint effect of phenol and phthalate mixtures on preterm birth is unknown.

METHODS

We included 384 female and 211 male (203 couples) participants seeking infertility treatment in the Environment and Reproductive Health (EARTH) Study who gave birth to 384 singleton infants between 2005 and 2018. Mean preconception urinary concentrations of bisphenol A (BPA), parabens, and eleven phthalate biomarkers, including di(2-ethylhexyl) phthalate (DEHP) metabolites, were examined. We used principal component analysis (PCA) with log-Poisson regression and Probit Bayesian Kernel Machine Regression (BKMR) with hierarchical variable selection to examine maternal and paternal phenol and phthalate mixtures in relation to preterm birth. Couple-based BKMR model was fit to assess couples' joint mixtures in relation to preterm birth.

RESULTS

PCA identified the same four factors for maternal and paternal preconception mixtures. Each unit increase in PCA scores of maternal (adjusted Risk Ratio (aRR): 1.36, 95%CI: 1.00, 1.84) and paternal (aRR: 1.47, 95%CI: 0.90, 2.42) preconception DEHP-BPA factor was positively associated with preterm birth. Maternal and paternal BKMR models consistently presented the DEHP-BPA factor with the highest group Posterior Inclusion Probability (PIP). BKMR models further showed that maternal preconception BPA and mono(2-ethyl-5-hydroxyhexyl) phthalate, and paternal preconception mono(2-ethylhexyl) phthalate were positively associated with preterm birth when the remaining mixture components were held at their median concentrations. Couple-based BKMR models showed a similar relative contribution of paternal (PIP: 61%) and maternal (PIP: 77%) preconception mixtures on preterm birth. We found a positive joint effect on preterm birth across increasing quantiles of couples' total mixture concentrations.

CONCLUSION

In this prospective cohort of subfertile couples, maternal BPA and DEHP, and paternal DEHP exposure before conception were positively associated with preterm birth. Both parental windows jointly contributed to the outcome. These results suggest that preterm birth may be a couple-based pregnancy outcome.

John EJ, Favetta LA. BPA and BPS Affect Connexin 37 in Bovine Cumulus Cells

Bisphenol S (BPS) is used as an alternative plasticizer to Bisphenol A (BPA), despite limited knowledge of potential adverse effects. BPA exhibits endocrine disrupting effects during development. This article focuses on the impact of bisphenols during oocyte maturation. Connexins (Cx) are gap junctional proteins that may be affected by bisphenols, providing insight into their mechanism during development. Cxs 37 and 43 are crucial in facilitating cell communication between cumulus cells and oocytes. Cumulus-oocyte complexes (COCs), denuded oocytes, and cumulus cells were exposed to 0.05 mg/mL BPA or BPS for 24 h. Both compounds had no effect on Cx43. Cumulus cells exhibited a significant increase in Cx37 expression following BPA (p = 0.001) and BPS (p = 0.017) exposure. COCs treated with BPA had increased Cx37 protein expression, whilst BPS showed no effects, suggesting BPA and BPS act through different mechanisms. Experiments conducted in in vitro cultured cumulus cells, obtained by stripping germinal vesicle oocytes, showed significantly increased expression of Cx37 in BPA, but not the BPS, treated group. BPA significantly increased Cx37 protein expression, while BPS did not. Disrupted Cx37 following BPA exposure provides an indication of possible effects of bisphenols on connexins during the early stages of development.

Environmental Endocrine-Disrupting Chemical Exposure: Role in Non-Communicable Diseases

The exponential growth of pollutant discharges into the environment due to increasing industrial and agricultural activities is a rising threat for human health and a biggest concern for environmental health globally. Several synthetic chemicals, categorized as potential environmental endocrine-disrupting chemicals (EDCs), are evident to affect the health of not only livestock and wildlife but also humankind. In recent years, human exposure to environmental EDCs has received increased awareness due to their association with altered human health as documented by several epidemiological and experimental studies. EDCs are associated with deleterious effects on male and female reproductive health; causes diabetes, obesity, metabolic disorders, thyroid homeostasis and increase the risk of hormone-sensitive cancers. Sewage effluents are a major source of several EDCs, which eventually reach large water bodies and potentially contaminate the drinking water supply. Similarly, water storage material such as different types of plastics also leaches out EDCs in drinking Water. Domestic wastewater containing pharmaceutical ingredients, metals, pesticides and personal care product additives also influences endocrine activity. These EDCs act via various receptors through a variety of known and unknown mechanisms including epigenetic modification. They differ from classic toxins in several ways such as low-dose effect, non-monotonic dose and trans-generational effects. This review aims to highlight the hidden burden of EDCs on human health and discusses the non-classical toxic properties of EDCs in an attempt to understand the magnitude of the exposome on human health. Present data on the environmental EDCs advocate that there may be associations between human exposure to EDCs and several undesirable health outcomes that warrants further human bio-monitoring of EDCs.

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.

Listening to mother: Long-term maternal effects in mammalian development

The oocyte is a complex cell that executes many crucial and unique functions at the start of each life. These functions are fulfilled by a unique collection of macromolecules and other factors, all of which collectively support meiosis, oocyte activation, and embryo development. This review focuses on the effects of oocyte components on developmental processes that occur after the initial stages of embryogenesis. These include long-term effects on genome function, metabolism, lineage allocation, postnatal progeny health, and even subsequent generations. Factors that regulate chromatin structure, genome programming, and mitochondrial function are elements that contribute to these oocyte functions.

Acute low-dose bisphenol S exposure affects mouse oocyte quality

Bisphenol S (BPS) is widely used to replace the known endocrine disruptor BPA in various products. We evaluated the effect of acute in vivo BPS exposure on oocyte quality, simulating the oral route of exposure via oral gavage. Eight-week-old ICR female mice (N = 15 per experimental group) were exposed to vehicle or BPS1-BPS4 (0.001, 0.1, 10, and 100 ng BPS x g bw^-1 day^-1, respectively) for seven days. Oocytes were isolated and matured in vitro. We observed that BPS exposure increased aberrant spindle formation in mature oocytes and induced DNA damage. Moreover, BPS3 significantly increased the chromatin repressive marks 5-methyl cytosine (5meC) and H3K27me2 in immature oocytes. In the BPS2 group, the increase in 5meC occurred during oocyte maturation. Transcriptome analysis revealed differential expression of early embryonic development transcripts in BPS2-exposed oocytes. These findings indicate that the biological effect of BPS is non-monotonic, affecting oocyte quality even at concentrations that are orders of magnitude below those measured in humans.

MicroRNAs: potential targets and agents of endocrine disruption in female reproduction

MicroRNAs are short non-coding RNAs that have been widely recognized as key mediators in the epigenetic control of gene expression and which are present in virtually all cells and tissues studied. These regulatory molecules are generated in multiple steps in a process called microRNA biogenesis. Distinct microRNA expression patterns during the different stages of oocyte and embryo development suggest important regulatory roles for these small RNAs. Moreover, studies antagonizing specific microRNAs and enzymes in microRNA biogenesis pathways have demonstrated that interference with normal miRNA function leads to infertility and is associated with some reproductive abnormalities. Endocrine disrupting chemicals such as Bisphenol A (BPA) are synthetic hormone mimics that have been found to negatively impact reproductive health. In addition to their direct effects on gene expression, these chemicals are widely implicated in the disruption of epigenetic pathways, including the expression and activity of miRNAs, thereby altering gene expression. In this review, the roles of microRNAs during mammalian oocyte and embryo development are outlined and the different mechanisms by which endocrine disruptors such as BPA interfere with these epigenetic regulators to cause reproductive problems is explored.

Proposed Key Characteristics of Female Reproductive Toxicants as an Approach for Organizing and Evaluating Mechanistic Data in Hazard Assessment

BACKGROUND

Identification of female reproductive toxicants is currently based largely on integrated epidemiological and in vivo toxicology data and, to a lesser degree, on mechanistic data. A uniform approach to systematically search, organize, integrate, and evaluate mechanistic evidence of female reproductive toxicity from various data types is lacking.

OBJECTIVE

We sought to apply a key characteristics approach similar to that pioneered for carcinogen hazard identification to female reproductive toxicant hazard identification.

METHODS

A working group of international experts was convened to discuss mechanisms associated with chemical-induced female reproductive toxicity and identified 10 key characteristics of chemicals that cause female reproductive toxicity: 1) alters hormone receptor signaling; alters reproductive hormone production, secretion, or metabolism; 2) chemical or metabolite is genotoxic; 3) induces epigenetic alterations; 4) causes mitochondrial dysfunction; 5) induces oxidative stress; 6) alters immune function; 7) alters cell signal transduction; 8) alters direct cell–cell interactions; 9) alters survival, proliferation, cell death, or metabolic pathways; and 10) alters microtubules and associated structures. As proof of principle, cyclophosphamide and diethylstilbestrol (DES), for which both human and animal studies have demonstrated female reproductive toxicity, display at least 5 and 3 key characteristics, respectively. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), for which the epidemiological evidence is mixed, exhibits 5 key characteristics.

DISCUSSION

Future efforts should focus on evaluating the proposed key characteristics against additional known and suspected female reproductive toxicants. Chemicals that exhibit one or more of the key characteristics could be prioritized for additional evaluation and testing. A key characteristics approach has the potential to integrate with pathway-based toxicity testing to improve prediction of female reproductive toxicity in chemicals and potentially prevent some toxicants from entering common use. https://doi.org/10.1289/EHP4971.

Maternal and paternal preconception exposure to bisphenols and size at birth

STUDY QUESTION

Are maternal and paternal preconception urinary bisphenol A (BPA) or bisphenol S (BPS) concentrations associated with offspring birth size?

SUMMARY ANSWER

Maternal-but not paternal-preconception urinary BPA concentrations were associated with lower birth size among couples seeking fertility evaluation.

WHAT IS KNOWN ALREADY

Prenatal BPA exposure has been previously associated with reduced birth size in some but not all epidemiologic studies. However, the potential effect of BPA exposure before conception in either parent is unknown. Data on BPS is practically absent.

STUDY DESIGN, SIZE, DURATION

Ongoing prospective preconception cohort of women and men seeking fertility evaluation between 2005 and 2016 in a large fertility center in an academic hospital in Boston, MA, USA.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We examined the association between maternal and paternal preconception, as well as maternal prenatal urinary BPA and BPS concentrations, and size at birth among 346 singletons from couples recruited in the Environment and Reproductive Health (EARTH) Study using multivariable linear regression. Infant birth weight and head circumference were abstracted from delivery records. Mean preconception and prenatal exposures were estimated by averaging urinary ln-BPA and ln-BPS concentrations in multiple maternal and paternal urine samples collected before pregnancy, and maternal pregnancy samples collected in each trimester.

MAIN RESULTS AND THE ROLE OF CHANCE

Maternal preconception urinary BPA concentrations were inversely associated with birth weight and head circumference in adjusted models: each ln-unit increase was associated with a decrease in birth weight of 119 g (95% CI: -212, -27), and a head circumference decrease of 0.72 cm (95% CI: -1.3, -0.1). Additional adjustment by gestational age or prenatal BPA exposure modestly attenuated results. Women with higher prenatal BPA concentrations had infants with lower mean birth weight (-75 g, 95% CI: -153, 2) although this did not achieve statistical significance. Paternal preconception urinary BPA concentrations were not associated with either birth weight or head circumference. No consistent patterns emerged for BPS concentrations measured in either parent.

LIMITATIONS, REASONS FOR CAUTION

We observed a strong negative association between maternal-but not paternal-preconception BPA concentrations and offspring birth size among a subfertile population. Although these results are overall consistent with prior studies on prenatal BPA exposure, these findings may not be generalizable to women without fertility concerns.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests that the unexplored maternal preconception period may be a sensitive window for BPA effects on birth outcomes.

STUDY FUNDING/COMPETING INTEREST(S)

Work supported by Grants (ES R01 009718, ES 022955 and ES 000002) from the National Institute of Environmental Health Sciences (NIEHS). C.M. was supported by a post-doctoral fellowship award from the Canadian Institutes of Health Research. There are no competing interests to declare.

The molecular mechanisms of action of the endocrine disrupting chemical bisphenol A in the development of cancer

The endocrine disrupting chemical (EDC) is an exogenous substance or mixture that alters the function of the endocrine system and consequently causes adverse effects in intact organisms. Bisphenol A (BPA), one of the most common endocrine disrupting chemicals is a carbon-based synthetic compound used in the production of water bottles, cans, and teeth suture materials. It is known to be a xenoestrogen as it interacts with estrogen receptors and acts as agonist or antagonist via estrogen receptor-dependent signaling pathways. BPA has been associated with serious health effects in humans and wildlife. It elicits several endocrine disorders and plays a role in the pathogenesis of several hormone-dependent tumors such as breast, ovarian, prostate cancer and others. More complicate to this picture, its effects rely on several and diverse molecular and epigenetic mechanisms that converge upon endocrine and reproductive systems. The present review gives an overview of general hazards of BPA, its epigenetic modifications and the molecular mechanisms of BPA action in different types of cancers as the increase in information about responses and action mechanisms of BPA may bring a better understanding of the risks of BPA exposure in humans and provide an important platform on which human health can be improved.

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.

Effects of BPA on global DNA methylation and global histone 3 lysine modifications in SH-SY5Y cells: An epigenetic mechanism linking the regulation of chromatin modifiying genes

Bisphenol A (BPA), an estrogenic endocrine disruptor, is widely used in the production of polycarbonate plastic and epoxy resins, resulting in high risk on human health. In present study we aimed to investigate the effects of BPA on global and gene specific DNA methylation, global histone modifications and regulation of chromatin modifiying enzymes in human neuroblastoma cells (SH-SY5Y). Cells were treated with BPA at 0.1, 1 and 10μM concentrations for 48 and 96h. IC₅₀ value of BPA was determined as 183 and 129μM in SH-SY5Y cells after 24h by MTT and NRU tests, respectively. We observed significant alterations on the 5-mC% levels (1.3 fold) and 5-hmC% levels (1.67 fold) after 10μM of BPA for 96h. Significant decrease was identified in H3K9me3 and H3K9ac after 10μM of BPA for 96h while decrease was observed in H3K4me3 at 10μM of BPA for 48h. Alterations were observed in chromatin modifiying genes including G9a, EZH2, SETD8, SETD1A, HAT1, SIRT1, DNMT1, RIZ1 and Suv39h1 after 96h of BPA exposure. Taken together, this study suggests that BPA might modulate the epigenetic regulators which would be key molecular events in the toxicity of endocrine disrupting chemicals.

Diethylhexyl phthalate magnifies deposition of 14 C-bisphenol A in reproductive tissues of mice

Endocrine disrupting chemicals are found in diverse common products, including cosmetics, food packaging, thermal receipt paper and plastic containers. This exposes most people in developed countries through ingestion, skin absorption and inhalation. Two ubiquitous endocrine disrupting chemicals, bisphenol A (BPA) and diethylhexyl phthalate (DEHP) can interact in disrupting blastocyst implantation in inseminated females. We hypothesized that DEHP might increase the bioavailability of BPA in tissues by competing for metabolic enzymes. We injected 0, 3, 9 or 18 mg DEHP into female and male mice and allowed 30 min for the chemical to circulate before giving them a food supplement containing 50 μg kg^{-1 14} C-BPA. Animals were dissected 1 h following ¹⁴ C-BPA administration and various tissue samples were acquired. Samples were solubilized and radioactivity was measured via liquid scintillation counting. In cycling females, DEHP increased BPA deposition in the muscle, uterus, ovaries and blood serum relative to controls. In peri-implantation females, DEHP increased deposition of BPA in the uterus, ovaries and serum relative to controls. In males, DEHP doses increased BPA deposition in serum and epididymis relative to controls. These results are consistent with the hypothesis that DEHP competes with BPA for conjugating enzymes such as UDP-glucuronosyltransferase, thereby magnifying the presence of BPA in estrogen-binding reproductive tissues. Copyright © 2017 John Wiley & Sons, Ltd.

Bisphenol A Exposure during Pregnancy Alters the Mortality and Levels of Reproductive Hormones and Genes in Offspring Mice

The present study investigated the reproductive toxicity of bisphenol A (BPA) exposure to the mother on the offspring mice. BPA was given to pregnant mice at 50 mg/kg, 500 mg/kg, and 2500 mg/kg BW BPA daily by gavage during the whole gestation period. The offspring mice were sacrificed at 8 weeks of age. Results showed that exposure of BPA to the mother increased the mortality (P < 0.05). Maternal exposure of BPA reduced the levels of T (♂) and FSH (♀) (P < 0.01) and elevated E₂ (♀) level in the adult offspring (P < 0.01). BPA exposure caused testicular damage as shown by less Leydig cells and ovarian injury as shown by more vacuoles and less corpus granules in the adult offspring mice. Immunohistochemistry revealed that maternal exposure of BPA increased Bax and decreased Bcl-2 at the protein levels in testicular and ovary tissues in the offspring mice. BPA significantly reduced the expression of StAR in male offspring (P < 0.05). Interestingly, the mRNA levels of Cyp11a were significantly decreased in 50 mg/kg groups and were increased in 500 mg/kg group in the males. Reduced Kitlg and elevated Amh at the mRNA levels were detected in the female offspring.

An old culprit but a new story: bisphenol A and "NextGen" bisphenols

The concept that developmental events shape adult health and disease was sparked by the recognition of a link between maternal undernutrition and coronary disease in adults. From that beginning, a new field-the developmental origins of health and disease-emerged, and attention has focused on the effects of a wide array of developmental perturbations. Exposure to endocrine-disrupting chemicals has been of particular interest, and a ubiquitous environmental contaminant bisphenol A (BPA) has become the endocrine-disrupting chemical poster child. Bisphenol A has been the subject of intense investigation for nearly two decades, and exposure effects have been described in hundreds of experimental, epidemiological, and clinical studies. From the standpoint of reproductive health, the findings are particularly important, as they suggest that the ovary, testis, and reproductive tract in both sexes are targets of BPA action. The findings and the media and regulatory attention garnered by them have generated increasing public concern and resulted in legislative bans on BPA in some countries. The subsequent introduction of BPA-free products, although a masterful marketing strategy, is in reality only the beginning of a new and complex chapter of the BPA story. In this review we attempt to summarize what we have learned about the reproductive effects of BPA, present the reasons why studying the effects of this chemical in humans is no longer sufficient, and outline the challenges that the growing array of next generation bisphenols represents to clinicians, researchers, federal agencies, and the general public.

Exposure to the environmental endocrine disruptor TCDD and human reproductive dysfunction: Translating lessons from murine models

Humans and other animals are exposed to a wide array of man-made toxicants, many of which act as endocrine disruptors that exhibit differential effects across the lifespan. In humans, while the impact of adult exposure is known for some compounds, the potential consequences of developmental exposure to endocrine disrupting chemicals (EDCs) is more difficult to ascertain. Animal studies have revealed that exposure to EDCs prior to puberty can lead to adult reproductive disease and dysfunction. Specifically, in adult female mice with an early life exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we demonstrated a transgenerational occurrence of several reproductive diseases that have been linked to endometriosis in women. Herein, we review the evidence for TCDD-associated development of adult reproductive disease as well as known epigenetic alterations associated with TCDD and/or endometriosis. We will also introduce new "Organ-on-Chip" models which, combined with our established murine model, are expected to further enhance our ability to examine alterations in gene-environment interactions that lead to heritable disease.

Urinary profiling of cis-diol-containing metabolites in rats with bisphenol A exposure by liquid chromatography-mass spectrometry and isotope labeling

A rapid UPLC-MS method combined with isotope labeling technology was developed for the detection ofcis-diolmetabolites in rat urine after bisphenol A exposure.