Perinatal exposure to low dose 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) alters sperm DNA methylation in adult rats

Epigenetic implications of common brominated flame retardants (PBDEs and TBBPA): Understanding the health risks of BFRs exposure

Brominated flame retardants (BFRs) are synthetic chemicals incorporated into a wide variety of products, both for industrial applications and everyday use, with the primary aim of reducing their flammability or reducing the material burning rate. These compounds find widespread use in plastics, textiles, and electrical/electronic devices. However, BFRs can be released from products and, thus are determined in many environmental matrices such as soil, water and air.This review discuss the potential health implications of selected BFRs (PBDEs and TBBPA) exposure arising from their impact on the epigenetic mechanisms. Epigenetic modifications, such as DNA methylation and histone acetylation or methylation, as well as changes in miRNA pattern, play significant roles in gene expression and cell function and can be influenced by environmental factors.The studies indicate that PBDEs exposure can lead to global DNA hypomethylation, disrupting normal gene regulation and contributing to genomic instability. In animal models, PBDEs have been associated with adverse effects on neurodevelopment, including impairments in memory and learning. TBBPA exposure has also been linked to changes in DNA methylation patterns, alterations in histone posttranslational modifications and non-coding RNA expression. These epigenetic changes may contribute to health issues related to growth, development, and endocrine functions.The growing evidence of epigenetic modifications induced by BFRs exposure highlights the importance of understanding their potential risks to human health. Further investigations are needed to fully elucidate the long-term consequences of altered epigenetic marks and their impact on human health.

2,2',4,4'-Tetrabromodiphenyl ether exposure disrupts blood-testis barrier integrity through CMA-mediated ferroptosis

2,2',4,4'-Tetrabromodiphenyl ether (PBDE-47), being the most prevalent congener of polybrominated diphenyl ethers (PBDEs), has been found to accumulate greatly in the environment and induce spermatogenesis dysfunction. However, the specific underlying factors and mechanisms have not been elucidated. Herein, male Sprague-Dawley (SD) rats were exposed to corn oil, 10 mg/kg body weight (bw) PBDE-47 or 20 mg/kg bw PBDE-47 by gavage for 30 days. PBDE-47 exposure led to blood-testis barrier (BTB) integrity disruption and aberrant spermatogenesis. Given that Sertoli cells are the main toxicant target, to explore the potential mechanism involved, we performed RNA sequencing (RNA-seq) in Sertoli cells, and the differentially expressed genes were shown to be enriched in ferroptosis and lysosomal pathways. We subsequently demonstrated that ferroptosis was obviously increased in testes and Sertoli cells upon exposure to PBDE-47, and the junctional function of Sertoli cells was restored after treatment with the ferroptosis inhibitor ferrostatin-1. Since glutathione peroxidase 4 (GPX4) was dramatically reduced in PBDE-47-exposed testes and Sertoli cells and considering the RNA-sequencing results, we examined the activity of chaperone-mediated autophagy (CMA) and verified that the expression of LAMP2a and HSC70 was upregulated significantly after PBDE-47 exposure. Notably, Lamp2a knockdown not only inhibited ferroptosis by suppressing GPX4 degradation but also restored the impaired junctional function induced by PBDE-47. These collective findings strongly indicate that PBDE-47 induces Sertoli cell ferroptosis through CMA-mediated GPX4 degradation, resulting in decreased BTB-associated protein expression and eventually leading to BTB integrity disruption and spermatogenesis dysfunction.

Decabromodiphenyl ether induces the chromosome association disorders of spermatocytes and deformation failures of spermatids in mice

The environmental presence of decabromodiphenyl ether (BDE-209), which is toxic to the male reproductive system, is widespread. The current study investigated its mechanism of toxicity in mice. The results showed, that BDE-209 induced DNA damage, decreased the expression of the promoter of meiosis spermatogenesis- and oogenesis-specific basic helix-loop-helix 1 (Sohlh1), meiosis related-factors Lethal (3) malignant brain tumor like 2 (L3MBTL2), PIWI-like protein 2 (MILI), Cyclin-dependent kinase 2 (CDK2), Cyclin A, synaptonemal complex protein 1 (SYCP1) and synaptonemal complex protein 3 (SYCP3), and caused spermatogenic cell apoptosis, resulting in a decrease in sperm quantity and quality. Furthermore, BDE-209 downregulated the levels of anaphase-promoting complex/cyclosome (APC/C), increased the expression of PIWI-like protein 1 (MIWI) in the cytoplasm of elongating spermatids, and decreased the nuclear levels of RING finger protein 8 (RNF8), ubiquitinated (ub)-H2A/ub-H2B, and Protamine 1 (PRM1)/Protamine 2 (PRM2), while increasing H2A/H2B nuclear levels in spermatids. The reproductive toxicity was persistent for 50 days following the withdrawal of BDE-209 exposure. The results suggested that BDE-209 inhibits the initiation of meiosis by decreasing the expression of Sohlh1. Furthermore, the reduced expression of L3MBTL2 inhibited the formation of chromosomal synaptonemal complexes by depressing the expression of meiosis regulators affecting the meiotic progression and also inhibited histone ubiquitination preventing the replacement of histones by protamines, by preventing RNF8 from entering nuclei, which affected the evolution of spermatids into mature sperm.

Strengths and limitations of reduced representation bisulfite sequencing (RRBS) in the perspective of DNA methylation analysis in fish: a case-study on rainbow trout spermatozoa

DNA methylation in CpG dinucleotides is an important epigenetic mark in fish spermatozoa since it has been shown that some sperm methylome features are transmitted to the offspring. Reduced representation bisulfite sequencing (RRBS) is one genome-scale methods developed to assess DNA methylation at CpG sites. It allows the sequencing of a reduced fraction of the genome expected to be enriched in CpGs. The aim of this study is to characterize the extent of the CpG sites that can be identified in the RRBS-reduced sequenced fraction of rainbow trout spermatozoa, in order to evaluate the potential of RRBS for sperm DNA methylation studies. We observed that RRBS did provide a reduced amount of genomic data, the sum of the CpGs analyzed on 12 males spanning 9% of the total genomic CpGs. CpGs were only slightly enriched in the RRBS data (×1.7 times the sequenced nucleotides), the possible causes being linked to trout genome structure and sequenced fragments size. All genomic functional features were represented in our CpG dataset, with a noticeable enrichment in exons but, strikingly, not in promoters. The number of CpGs shared between biological replicates was low, but this proportion reached workable values from six biological replicates (46% of the analyzed cytosines) on. The choices that are to be made regarding fragment size selection and the options during bioinformatic data processing are discussed. In all, RRBS is a relevant first-approach method to scan the CpG DNA methylation status of spermatozoa along rainbow trout genome, although in a very reduced pattern among biological replicates.

Associations between Sperm Epigenetic Age and Semen Parameters: An Evaluation of Clinical and Non-Clinical Cohorts

The well-documented relationship between chronological age and the sperm methylome has allowed for the construction of epigenetic clocks that estimate the biological age of sperm based on DNA methylation, which we previously termed sperm epigenetic age (SEA). Our lab demonstrated that SEA is positively associated with the time taken to achieve pregnancy; however, its relationship with semen parameters is unknown. A total of 379 men from the Longitudinal Investigation of Fertility and Environment (LIFE) study, a non-clinical cohort, and 192 men seeking fertility treatment from the Sperm Environmental Epigenetics and Development Study (SEEDS) were included in the study. Semen analyses were conducted for both cohorts, and SEA was previously generated using a machine learning algorithm and DNA methylation array data. Association analyses were conducted via multivariable linear regression models adjusting for BMI and smoking status. We found that SEA was not associated with standard semen characteristics in SEEDS and LIFE cohorts. However, SEA was significantly associated with higher sperm head length and perimeter, the presence of pyriform and tapered sperm, and lower sperm elongation factor in the LIFE study (p < 0.05). Based on our results, SEA is mostly associated with defects in sperm head morphological factors that are less commonly evaluated during male infertility assessments. SEA shows promise to be an independent biomarker of sperm quality to assess male fecundity.

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Multigenerational effects and mutagenicity of three flame retardants on germ cells in Caenorhabditis elegans

Flame retardants (FRs) have raised public concerns because of their environmental persistence and negative impacts on human health. Recent evidence has revealed that many FRs exhibit reproductive toxicities and transgenerational impacts, whereas the toxic effects of FRs on germ cells remain barely explored. Here we investigated the multigenerational effects of three flame retardants (TBBPA, TCEP and TCPP) on germ cell development in Caenorhabditis elegans, and examined the germ cell mutagenicity of these FRs by using whole genome sequencing. Parental exposure to three FRs markedly increased germ cell apoptosis, and impeded oogenesis in F1-F6 offspring. In addition, the double-increased mutation frequencies observed in progeny genomes uncover the mutagenic actions of FRs on germ cells. Analysis of mutation spectra revealed that these FRs predominantly induced point mutations at A:T base pairs, whereas both small and large indels were almost unaffected. These results revealed the long-term effects of FRs on development and genomic stability of germ cells, which may pose risks to environmental organisms and human reproductive health. Taken together, our findings suggest that germ cell mutagenicity should be carefully examined for the environmental risk assessment of FRs and other emerging pollutants.

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Chromatin modifiers: A new class of pollutants with potential epigenetic effects revealed by in vitro assays and transcriptomic analyses

A great variety of endocrine-disrupting chemicals (EDCs) have been used extensively and become widespread in the environment nowadays. Limited mammalian studies have shown that certain EDCs may target chromosome and epigenome of the germline, leading to adverse effects in subsequent generations, despite these progenies having never been exposed to the EDC before. However, the underlying mechanisms of chromosomal changes induced by these pollutants remain poorly known. Using the human ovarian granulosa tumor cell line COV434 as a model, we investigated and compared the transcriptomic changes induced by nine EDCs with diverse chemical structures (i.e. BDE-47, BPA, BP-3, DEHP, DHP, EE2, TCS, TDCPP and NP), to inquire if there is any common epigenetic modification associated with reproductive functions induced by these EDCs. Our results showed that COV434 cells were more responsive to BP-3, NP, DEHP and EE2, and more importantly, these four EDCs altered the expression of gene clusters related to DNA damage response, cell cycle, proliferation, and chromatin remodeling, which can potentially lead to epigenetic modifications and transgenerational inheritance. Furthermore, dysregulation of similar gene clusters was common in DEHP and NP treatments. Bioinformatics analysis further revealed that BP-3 disturbed signaling pathways associated with reproductive functions, whereas alterations in telomere-related pathways were highlighted upon EE2 exposure. Overall, this study highlighted chromatin modifications caused by a class of chemicals which that may potentially lead to epigenetic changes and transgenerational reproductive impairments.

Mechanisms of Male Reproductive Toxicity of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDE) are a group of flame retardants used in a variety of artificial materials. Despite being phased out in most industrial countries, they remain in the environment and human tissues due to their persistence, lipophilicity, and bioaccumulation. Populational and experimental studies demonstrate the male reproductive toxicity of PBDEs including increased incidence of genital malformations (hypospadias and cryptorchidism), altered weight of testes and other reproductive tissues, altered testes histology and transcriptome, decreased sperm production and sperm quality, altered epigenetic regulation of developmental genes in spermatozoa, and altered secretion of reproductive hormones. A broad range of mechanistic hypotheses of PBDE reproductive toxicity has been suggested. Among these hypotheses, oxidative stress, the disruption of estrogenic signaling, and mitochondria disruption are affected by PBDE concentrations much higher than concentrations found in human tissues, making them unlikely links between exposures and adverse reproductive outcomes in the general population. Robust evidence suggests that at environmentally relevant doses, PBDEs and their metabolites may affect male reproductive health via mechanisms including AR antagonism and the disruption of a complex network of metabolic signaling.

High Content Imaging Analyses of the Effects of Bisphenols and Organophosphate Esters on TM4 Mouse Sertoli Cells

The endocrine disruptive effects of bisphenol A (BPA) and brominated flame retardants (BDE-47) have led to restrictions to their use and increased the pressure to identify safe replacements for these chemicals. Although there is evidence that some of these alternatives may be toxic to spermatogonial and Leydig cells, little is known about the toxicity of emerging replacements on Sertoli cells, one of the major testicular cell types. We used high-content imaging to compare the effects of legacy chemicals, BPA and BDE-47, to their corresponding replacements. TM4 Sertoli cells were exposed for 48 h to each chemical (0.001-100 μM) followed by cytotoxicity and phenotypic endpoint assessment. The benchmark concentration (BMC) potency ranking for bisphenols based on cytotoxicity was BPTMC>BPM > BPAF>BPF > BPS > BPA. Human administered equivalent dose (AED) determination ranked BPS as most potent alternative replacement studied. The BMC potency ranking of BDE-47 and organophosphate esters based on cytotoxicity was TDtBPP>BDMPP>TBOEP>TDCPP>TMPP>TPHP> BDE47 > IPPP=BPDP = TCPP. Additionally, TM4 cell exposure to BDE-47 increased Calcein intensity (57.9 μM) and affected lysosomes (21.6 μM), while exposure to TPHP and TMPP resulted in cellular oxidative stress changes at BMC values as low as 0.01 μM and 0.4 μM, respectively. Overall bioactivity considerations of the chemicals on TM4 via ToxPi analyses and AED modeling further validated emerging replacements as highly potent chemicals in comparison to BPA and BDE-47. These findings demonstrate that many bisphenol and flame retardant replacements are more potent in Sertoli cells than the legacy chemical they are replacing, and that phenotypic parameter assessment is an effective tool in chemical toxicity assessment.

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.

Prenatal exposure to environmentally relevant levels of PBDE-99 leads to testicular dysgenesis with steroidogenesis disorders

Polybrominated diphenyl ethers (PBDEs) are a widely used class of brominated flame retardants. Exposure to PBDEs could induce testicular damage in mammals, but the effects and potential mechanism of action of prenatal exposure to environmentally relevant PBDEs on testicular development remain unclear. For the in vivo study, pregnant ICR mice were exposed to environmentally relevant levels of 2,2',4,4',5-pentabromodiphenyl ether (PBDE-99), a major component of commercial PBDE mixtures. We found that the anogenital index and testicular organ coefficient were significantly decreased, the incidence of cryptorchidism was increased, and testicular histology was disturbed in male offspring. Transcriptomic profiling showed that steroidogenesis disorders were significant in all PBDE-99 exposure groups. The testosterone levels, expressions of testosterone regulators, and the number of CYP11A1-positive and 11β-HSD1-positive Leydig cells were significantly decreased after PBDE-99 exposure. For the in vitro study, TM3 Leydig cells were exposed to PBDE-99 at gradient concentrations. Transcriptomic profiling and validation experiments showed that PBDE-99 upregulated reactive oxygen species, activated the ERK1/2 pathway, inhibited the ubiquitination degradation pathway, and finally induced Leydig cell apoptosis. Cumulatively, these findings revealed that prenatal exposure to environmentally relevant levels of PBDE-99 leads to steroidogenesis disorders by inducing the apoptosis of Leydig cells, causing testicular dysgenesis.

BDE-209 induce spermatocytes arrest at early-pachytene stage during meiotic prophase I in mice

Deca-brominated diphenyl ether (BDE-209) is a common flame retardant utilized in electronic products, textiles, furniture, and upholstery materials. Environmental BDE-209 exposure results in spermatogenesis disorder, because of the characteristics of bioaccumulation, persistence, and probably toxicity. Meiotic prophase I is a crucial phase during spermatogenesis which is a key influential factor of normal sperm production. However, the effects of BDE-209 on meiotic prophase I during spermatogenesis are poorly understood. The present study aimed to evaluate whether BDE-209 exposure impairs meiotic prophase I during spermatogenesis of spermatocytes. We validated the effects of BDE-209 on alternations of meiotic prophase I in Balb/c male mice. Firstly, we analyzed sperm quality in cauda epididymis with decreasing sperm count, increasing abnormal sperm, and male reproductive dysfunction after exposure to BDE-209. Then, reactive oxygen species (ROS) and malondialdehyde (MDA) levels in testis and GC-2spd cells were significant increased after treated with BDE-209. Furthermore, we found that meiotic prophase I arrest at early-pachytene stage during spermatogenesis with increasing of DSBs damage and trimethylated histone H3 at lysine-4 (H3K4me3) in spermatocytes exposed to BDE-209. Finally, we conducted homologous recombination (HR) analyses to identify the progression of meiosis. The recombination markers, including DMC1 and RAD51, and crossover marker MLH1 were decreased during spermatogenesis after exposure to BDE-209. Collectively, our data indicated that BDE-209 has detrimental impacts on meiotic prophase I of spermatocytes in mice.

Decabromodiphenyl ether-induced PRKACA hypermethylation contributed to glycolipid metabolism disorder via regulating PKA/AMPK pathway in rat and L-02 cells

BDE-209 is the most prevalent congener of polybrominated diphenyl ethers and has high bioaccumulation in humans and animals. BDE-209 has been reported to disrupt glycolipid metabolism, but the mechanisms are still unclear. In this study, we found that BDE-209 induced liver tissue injury and hepatotoxicity, increased the glucose and total cholesterol levels in the serum of rats, and increased glucose and triglyceride levels in L-02 cells. BDE-209 exposure changed the PKA, p-PKA, AMPK, p-AMPK, ACC, and FAS expression in rats' liver and L-02 cells. Moreover, BDE-209 induced PRKACA-1 hypermethylation in L-02 cells. AMPK activator (AICAR) inhibited the changes of p-AMPK, ACC, and FAS expression and elevation of glucose and triglyceride levels induced by BDE-209. DNA methylation inhibitor (5-Aza-CdR) reversed BDE-209 induced alters of PKA/AMPK/ACC/FAS signaling pathway. These results demonstrated that BDE-209 could disrupt the glycolipid metabolism by causing PRKACA-1 hypermethylation to regulate the PKA/AMPK signaling pathway in hepatocytes.

DNA methylation changes induced by BDE-209 are related to DNA damage response and germ cell development in GC-2spd

Decabrominated diphenyl ether (BDE-209) is generally utilized in multiple polymer materials as common brominated flame retardant. BDE-209 has been listed as persistent organic pollutants (POPs), which was considered to be reproductive toxin in the environment. But it still remains unclear about the effects of BDE-209 on DNA methylation and the induced-male reproductive toxicity. Due to the extensive epigenetic regulation in germ line development, we hypothesize that BDE-209 exposure impacts the statue of DNA methylation in spermatocytes in vitro. Therefore, the mouse GC-2spd (GC-2) cells were used for the genome wide DNA methylation analysis after treated with 32 μg/mL BDE-209 for 24 hr. The results showed that BDE-209 caused genomic methylation changes with 32,083 differentially methylated CpGs in GC-2 cells, including 16,164 (50.38%) hypermethylated and 15,919 (49.62%) hypomethylated sites. With integrated analysis of DNA methylation data and functional enrichment, we found that BDE-209 might affect the functional transcription in cell growth and sperm development by differential gene methylation. qRT-PCR validation demonstrated the involvement of p53-dependent DNA damage response in the GC-2 cells after BDE-209 exposure. In general, our findings indicated that BDE-209-induced genome wide methylation changes could be interrelated with reproductive dysfunction. This study might provide new insights into the mechanisms of male reproductive toxicity under the environmental exposure to BDE-209.

Aging-induced changes in sperm DNA methylation are modified by low dose of perinatal flame retardants

Aims: Paternal age is increasing in developed countries. Understanding of aging-related epigenetic changes in sperm is needed as well as factors that modify such changes. Materials & methods: Young pubertal and mature rats were exposed perinatally to vehicle or environmental xenobiotic 2,2',4,4'-tetrabromodiphenyl ether. Epididymal sperm was reduced representation bisulfite sequenced. Differentially methylated regions (DMRs) were identified via MethPipe. Results: In control animals, 5319 age-dependent DMRs were identified. Age-related DMRs were enriched for embryonic development. In exposed rats, DNA methylation was higher in young and lower in mature animals then in controls. Conclusions: Sperm methylome undergoes significant age-dependent changes, which may represent a causal link between paternal age and offspring phenotype. Environmental xenobiotics can interfere with the natural process of epigenetic aging.

Impaired sperm quantity and motility in adult rats following gestational and lactational exposure to environmentally relevant levels of PBDE-47: A potential role of thyroid hormones disruption

Polybrominated diphenyl ethers (PBDEs) are flame retardants and the congener 2, 2', 4, 4'-tetrabromodiphenyl ether (PBDE-47) is capable of inducing thyroid endocrine disruption and developmental toxicity. However, little is known about whether developmental PBDE-47 exposure-elicited alterations in semen quality is associated with thyroid hormones (THs) perturbation. In this research, we sought to explore the impacts of gestational and lactational PBDE-47 exposure on adult sperm quantity and motility, and its link with THs levels. For this purpose, female Sprague-Dawley rats were administered environmentally relevant PBDE-47 levels (0.1, 1.0, 10 mg/kg/day) by oral gavage from prepregnancy through lactation cessation to achieve early-life exposure of offspring and to mimic the actual exposure. Sperm quantity and motility together with serum THs levels from male offspring were determined on postnatal day 88. In utero and lactational exposure to PBDE-47 boosted the weight gain while reduced the relative testis weight in adult male offspring. These were accompanied with the reductions in sperm counts (total and living sperm counts), the percentage of progressive sperm motility, sperm velocities (curvilinear velocity, straight-line velocity and average path velocity), motion path (beat cross frequency, linearity and wobble) and linear motile sperm parameters (count, motility and concentration). Further studies identified that the levels of serum triiodothyronine (T₃) were increased by PBDE-47 exposure and negatively associated with those differential semen parameters on quantity and motility. Collectively, our results indicate that exposure to low-level PBDE-47 during early-life development impairs semen quality in adult rats, which could be mediated partially by abnormal T₃ levels.

Exposure to PBDE47 affects mouse oocyte quality via mitochondria dysfunction-induced oxidative stress and apoptosis

2, 2', 4, 4'-Tetrabrominated diphenyl ether (PBDE47) is the most abundant homologues in polybrominated diphenyl ethers (PBDEs) and is used widely in daily life as a brominated flame retardant. It has been shown that PBDE47 has neurotoxicity, thyroid toxicity, and also is reported to have reproductive toxicity, which can impair the follicular function of female rats and activate ovarian endoplasmic reticulum stress, leading to ovarian damage. However, the toxicity of PBDE47 to the quality of mammalian oocyte has not been reported. In this study, we reported that PBDE47 exposure affected the mouse ovarian and uterine. We also showed that oocyte number reduced and meiotic maturation competence decreased. Moreover, PBDE47 exposure disrupted actin filaments distribution, and also changed the level of histone methylation. Based on the genome-wide sequencing we showed that PBDE47 altered multiple gene expression in mouse oocytes. PBDE47 exposure caused mitochondria dysfunction, showing with aberrant distribution and mitochondrial membrane potential. In addition, our results suggested that PBDE47 induced early apoptosis, which was caused by oxidative stress, showing with increased ROS level and positive Annexin-V signal. In conclusion, our results indicated that PBDE47 exposure affected the maturation of mouse oocyte via its effects on mitochondria function, ROS level and its related apoptosis.

Rat liver epigenome programing by perinatal exposure to 2,2',4'4'-tetrabromodiphenyl ether

Perinatal exposures to polybrominated diphenyl ethers permanently reprogram liver metabolism and induce a nonalcoholic fatty liver disease-like phenotype and insulin resistance in rodents. Aim: To test if these changes are associated with altered liver epigenome. Materials & methods: Expression of small RNA and changes in DNA methylation in livers of adult rats were analyzed following perinatal exposure to 2,2',4,4'-tetrabromodiphenyl ether, the polybrominated diphenyl ether congener most prevalent in human tissues. Results: We identified 33 differentially methylated DNA regions and 15 differentially expressed miRNAs. These changes were enriched for terms related to lipid and carbohydrate metabolism, insulin signaling, Type-2 diabetes and nonalcoholic fatty liver disease. Conclusion: Changes in the liver epigenome are a likely candidate mechanism of long-term maintenance of an aberrant metabolic phenotype.

Epigenetic Effects of Polybrominated Diphenyl Ethers on Human Health

Disruption of epigenetic regulation by environmental toxins is an emerging area of focus for understanding the latter's impact on human health. Polybrominated diphenyl ethers (PBDEs), one such group of toxins, are an environmentally pervasive class of brominated flame retardants that have been extensively used as coatings on a wide range of consumer products. Their environmental stability, propensity for bioaccumulation, and known links to adverse health effects have evoked extensive research to characterize underlying biological mechanisms of toxicity. Of particular concern is the growing body of evidence correlating human exposure levels to behavioral deficits related to neurodevelopmental disorders. The developing nervous system is particularly sensitive to influence by environmental signals, including dysregulation by toxins. Several major modes of actions have been identified, but a clear understanding of how observed effects relate to negative impacts on human health has not been established. Here, we review the current body of evidence for PBDE-induced epigenetic disruptions, including DNA methylation, chromatin dynamics, and non-coding RNA expression while discussing the potential relationship between PBDEs and neurodevelopmental disorders.

Epigenetic response profiles into environmental epigenotoxicant screening and health risk assessment: A critical review

The epigenome may be an important interface between exposure to environmental contaminants and adverse outcome on human health. Many environmental pollutants deregulate gene expression and promote diseases by modulating the epigenome. Adverse epigenetic responses have been widely used for risk assessment of chemical substances. Various pollutants, including trace elements and persistent organic pollutants, have been detected frequently in the environment. Epigenetic toxicity of environmental matrices including water, air, soil, and food cannot be ignored. This review provides a comprehensive overview of epigenetic effects of pollutants and environmental matrices. We start with an overview of the mechanisms of epigenetic regulation and the effects of several types of environmental pollutants (trace elements, persistent organic pollutants, endocrine disrupting chemicals, and volatile organic pollutants) on epigenetic modulation. We then discuss the epigenetic responses to environmental water, air, and soil based on in vivo and in vitro assays. Finally, we discuss recommendations to promote the incorporation of epigenotoxicity into contamination screening and health risk assessment.

Distribution of the parent compound and its metabolites in serum, urine, and feces of mice administered 2,2',4,4'-tetrabromodiphenyl ether

2,2',4,4'-Tetrabromodiphenyl ether (BDE-47) is a predominant polybromodiphenyl ether congener in the environment. Its absorption, excretion, and metabolism in animals have been investigated; however, the distribution of BDE-47 and its metabolites in excreta and blood at steady-state conditions has been unclear. In the present study, we addressed the issue by determining the amounts of BDE-47, eight monohydroxylated metabolites (OH-BDEs), and 2,4-dibromophenol (2,4-DBP) in serum, urine, and feces of gpt delta transgenic mice orally administered BDE-47 at 1.5, 10, and 30 mg/kg/d for 6 weeks during the 24 h period (for urine and feces) or at 24 h (for blood) post-last dosing. The distribution profiles in the three matrices showed that BDE-47, OH-BDEs, and 2,4-DBP were mostly distributed in urine (59-70%), feces (95-96%), and urine (51-80%), respectively. In each matrix, BDE-47 was the predominant compound under all doses, which accounted for 84-96% in serum, 68-98% in urine, and 37-92% in feces. However, exclusive of BDE-47, OH-BDEs were the predominant class of metabolites in serum (72-86%) and feces (67-87%), whereas 2,4-DBP was the major metabolite in urine (98-99%). Among monohydroxylated metabolites, the dominant compounds were 4-hydroxy-2,2',3,4'-tetrabromodiphenyl ether (4-OH-BDE-42) and 4'-hydroxy-2,2',4,5'-tetrabromodiphenyl ether (4'-OH-BDE-49) in feces (27-33% and 25-43%, respectively), and 3-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (3-OH-BDE-47) in serum (26-43%). Thus, BDE-47 and 2,4-DBP were mostly present in urine, and OH-BDEs were primarily found in feces. Blood was not an important carrier for either BDE-47 or its metabolites. The data provide information for distribution and elimination of BDE-47 and its metabolites in mice at steady-state conditions.

An increase of estrogen receptor α protein level regulates BDE-209-mediated blood-testis barrier disruption during spermatogenesis in F1 mice

Deca-bromodiphenyl ether (BDE-209) regulates various aspects of spermatogenesis and male fertility through its effect on estrogen receptor α (ERα), but the underlying mechanism remains unclear. Because molecular mechanisms such as remodeling of the blood-testis barrier (BTB) play crucial roles in spermatogenesis, we investigated the disruptive effects of ERα agonists on the BTB in spermatogenesis. In this study, 0, 300, and 500 mg/kg/day of BDE-209 were administered to pregnant adult mice by oral gavage from gestation day 7 to postnatal day 21. SerW3 cells were treated with methylpiperidino pyrazole (MPP) for 30 min before being treated with 50 μg/mL of BDE-209. BDE-209 increases ERα in time- and dose-dependent manners and decreases formin 1 and BTB-associated protein in F1 male mice. Furthermore, BDE-209 impairs the structure and function of the BTB. Activation of ERα signaling could disrupt the BTB, leading to spermatogenesis dysfunction. The results identified the role of ERα in BTB disruption during spermatogenesis and suggested that BTB disruption occurs because of exposure to BDE-209, which could potentially affect spermatogenesis. In conclusion, Sertoli cells seem to be the primary target of BDE-209 in the perinatal period, and this period constitutes a critical window of susceptibility to BDE-209. Also, the SerW3 cell model may not be a particularly useful cell model for studying the function of the cytoskeleton.

Inter-Cell and Inter-Chromosome Variability of 5-Hydroxymethylcytosine Patterns in Noncultured Human Embryonic and Extraembryonic Cells

5-hydroxymethylcytosine (5hmC) is an oxidative derivative of 5-methylcytosine (5mC). Recent studies have revealed a sharp difference in the levels of 5hmC in 2 opposite DNA strands of a given chromosome and a chromosome-wide cell-to-cell variability in mammalian cells. This asymmetric 5hmC distribution was found in cultured cells, which may not fully mimic in vivo epigenetic processes. We have checked whether inter-chromosome and inter-cell variability of 5hmC patterns is typical for noncultured human cells. Using indirect immunofluorescence, we analyzed the localization of 5hmC and its co-distribution with 5mC on direct preparations of mitotically active cells from human embryonic lung and chorionic cytotrophoblast samples. We demonstrated 3 types of chromosomes according to the 5hmC accumulation pattern: hydroxymethylated (5hmC in both sister chromatids), hemihydroxymethylated (5hmC in only 1 sister chromatid), and nonhydroxymethylated ones. Each accumulation type was not specific to any particular chromosome, resulting in different 5hmC patterns between homologous chromosomes, among chromosomes within each metaphase plate, among metaphases in one tissue, and between the tissues. The 5mC distribution was stable: chromosomes were methylated in R-bands and, especially in embryonic lung cells, in the heterochromatic regions 1q12, 9q12, and 16q11.2. Our results provide the first evidence of inter-cell and inter-chromosome variability of 5hmC patterns in human noncultured embryonic and extraembryonic cells.

Passing experiences on to future generations: endocrine disruptors and transgenerational inheritance of epimutations in brain and sperm

All animals have body burdens of polychlorinated biphenyls (PCBs) despite their ban decades ago. These and modern endocrine-disrupting chemicals (EDCs) such as the fungicide vinclozolin (VIN) perturb hormone signaling and lead to dysfunctions following prenatal exposures. Beyond direct exposures, transgenerational disease phenotypes can persist for multiple generations without subsequent exposure. The mechanisms of action of these EDCs differ: VIN is anti-androgenic while the PCB mixture Aroclor 1221 (A1221) is weakly estrogenic. Based on limited evidence for the inheritance of epimutations in germline, we measured DNA methylation in brain and sperm of rats. Pregnant dams were exposed from day 8-18 of gestation to low dosages of VIN, A1221, or the vehicle. To produce paternal lineages, exposed F1 males were bred with untreated females, creating the F2 and subsequently F3 generations. In adult F1 and F3 males, mature sperm was collected, and brain nuclei involved in anxiety and social behaviors (CA3 of the hippocampus; central amygdala) were selected for assays of epimutations in CpG islands using reduced representation bisulfite sequencing. In F1 sperm, VIN and PCBs induced differential methylation in 215 and 284 CpG islands, respectively, compared to vehicle. The majority of effects were associated with hypermethylation. Fewer epimutations were detected in the brain. A subset of differentially methylated regions were retained from the F1 to the F3 generation, suggesting a common mechanism of EDC and germline epigenome interaction. Thus, EDCs can cause heritable epimutations in the sperm that may embody the future phenotype of brain-behavior disorders caused by direct or transgenerational exposures.