Effect of tetrabrombisphenol A on induction of apoptosis in the testes and changes in expression of selected testicular genes in CD1 mice

Update of the scientific opinion on tetrabromobisphenol A (TBBPA) and its derivatives in food

The European Commission asked EFSA to update its 2011 risk assessment on tetrabromobisphenol A (TBBPA) and five derivatives in food. Neurotoxicity and carcinogenicity were considered as the critical effects of TBBPA in rodent studies. The available evidence indicates that the carcinogenicity of TBBPA occurs via non-genotoxic mechanisms. Taking into account the new data, the CONTAM Panel considered it appropriate to set a tolerable daily intake (TDI). Based on decreased interest in social interaction in male mice, a lowest observed adverse effect level (LOAEL) of 0.2 mg/kg body weight (bw) per day was identified and selected as the reference point for the risk characterisation. Applying the default uncertainty factor of 100 for inter- and intraspecies variability, and a factor of 3 to extrapolate from the LOAEL to NOAEL, a TDI for TBBPA of 0.7 μg/kg bw per day was established. Around 2100 analytical results for TBBPA in food were used to estimate dietary exposure for the European population. The most important contributors to the chronic dietary LB exposure to TBBPA were fish and seafood, meat and meat products and milk and dairy products. The exposure estimates to TBBPA were all below the TDI, including those estimated for breastfed and formula-fed infants. Accounting for the uncertainties affecting the assessment, the CONTAM Panel concluded with 90%-95% certainty that the current dietary exposure to TBBPA does not raise a health concern for any of the population groups considered. There were insufficient data on the toxicity of any of the TBBPA derivatives to derive reference points, or to allow a comparison with TBBPA that would support assignment to an assessment group for the purposes of combined risk assessment.

Bioaccumulation and Male Reproductive Toxicity of the New Brominated Flame Retardant Tetrabromobisphenol A-Bis(2,3-dibromo-2-methylpropyl ether) in Comparison with Hexabromocyclododecane

Tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) (TBBPA-DBMPE) has come into use as an alternative to hexabromocyclododecane (HBCD), but it is unclear whether TBBPA-DBMPE has less hazard than HBCD. Here, we compared the bioaccumulation and male reproductive toxicity between TBBPA-DBMPE and HBCD in mice following long-term oral exposure after birth. We found that the concentrations of TBBPA-DBMPE in livers significantly increased with time, exhibiting a bioaccumulation potency not substantially different from HBCD. Lactational exposure to 1000 μg/kg/d TBBPA-DBMPE as well as 50 μg/kg/d HBCD inhibited testis development in suckling pups, and extended exposure up to adulthood resulted in significant molecular and cellular alterations in testes, with slighter effects of 50 μg/kg/d TBBPA-DBMPE. When exposure was extended to 8 month age, severe reproductive impairments including reduced sperm count, increased abnormal sperm, and subfertility occurred in all treated animals, although 50 μg/kg/d TBBPA-DBMPE exerted lower effects than 50 μg/kg/d HBCD. Altogether, all data led us to conclude that TBBPA-DBMPE exerted weaker male reproductive toxicity than HBCD at the same doses but exhibited bioaccumulation potential roughly equivalent to HBCD. Our study fills the data gap regarding the bioaccumulation and toxicity of TBBPA-DBMPE and raises concerns about its use as an alternative to HBCD.

Transcriptomic profiling reveals the neuroendocrine-disrupting effect and toxicity mechanism of TBBPA-DHEE exposure in zebrafish (Danio rerio) during sexual development

TBBPA bis(2-hydroxyethyl) ether (TBBPA-DHEE) pollution in the environment has raised serious public health concerns due to its potential neuroendocrine-disrupting effects. The neuroendocrine-disrupting effects of TBBPA-DHEE on marine spices, on the other hand, have received little attention. The behavioral, neuroendocrine-disrupting, and possible reproductive toxicity of TBBPA-DHEE were assessed in sexual developing zebrafish treated for 40 days by examining locomotor activity, Gonadotrophin releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels, and quantifying gene expression. In addition, transcriptome profiling was carried out to explore the possible mechanisms. According to our findings, TBBPA-DHEE treated zebrafish showed altered locomotor activity, a potential neuroendocrine-disrupting effect via the toxic effect on the hypothalamus and pituitary gland, which is evident in decreased levels of GnRH, FSH, and LH, according to our findings. The transcriptomic profiling reveals that a total of 216 DEGs were detected (5 upregulated and 211 down-regulated). Transcriptomic analysis shows that TBBPA-DHEE exposure caused decreased transcript levels of genes (cyp11a1, ccna1, ccnb2, ccnb1, cpeb1b, wee2) involved in cell cycle oocyte meiosis, progesterone mediated oocyte maturation, and ovarian steroidogenesis, which are known reproduction-related pathways. Overall, these findings add to our understanding of the impact of TBBPA-DHEE and biomonitoring in the maritime environment.

Postnatal exposure to low-dose tetrabromobisphenol A increases the susceptibility of mammal testes to chemical-induced spermatogenic stress in adulthood

There is increasing data showing that some environmental chemicals can increase susceptibility to follow-up stress or injuries, possibly thereby contributing to certain clinical and subclinical diseases. Previous studies reported that tetrabromobisphenol A (TBBPA), one of the most used brominated flame retardants, exerted little male reproductive toxicity in terms of conventional endpoints but affected testis development and thereby caused testicular alterations at the molecular and cellular levels. Here, we aimed to reveal whether developmental exposure to TBBPA can increase testicular susceptibility to follow-up stress in adulthood. For this purpose, newborn mice were exposed to 50 or 500 μg/kg/d TBBPA for 56 days to confirm adverse effects on testes, followed by a single intraperitoneal injection of 3 mg/kg busulfan (BSF) to induce spermatogenic stress. Four weeks after BSF injection, TBBPA-treated mice exhibited severe pathological alterations, including reduced testis weight, damaged testicular histological structure, declined sperm count, apoptosis of spermatogenic cells, while no remarkable damage was observed in mice without historical exposure to TBBPA. These results demonstrate that historical exposure to TBBPA, either 50 or 500 µg/kg/d, increased the susceptibility of mouse testes to BSF-induced spermatogenic stress, resulting in severe adverse reproductive outcomes. Further analysis indicates that TBBPA-caused microtubule and microfilament damage, along with spermatogonia and spermatocyte reduction, could contributed to the increased susceptibility of testes, suggesting that these non-conventional reproductive lesions caused by chemicals should not be ignored. This is the first study to investigate the reproductive hazard of chemicals from the perspective of testicular susceptibility to stress, thereby opening a new avenue to identify environmental chemicals possibly contributing to male infertility and subfertility.

Tetrachlorobisphenol A mediates reproductive toxicity in Caenorhabditis elegans via DNA damage-induced apoptosis

Tetrachlorobisphenol A (TCBPA), an alternative to tetrabromobisphenol A (TBBPA), is ubiquitous in the environment and could potentially impact the reproductive system of organisms. However, the mechanisms underlying TCBPA-mediated reproductive effects remain unclear. Herein, we exposed Caenorhabditis elegans (C. elegans, L4 larvae) to TCBPA at environmentally relevant doses (0-100 μg/L) for 24 h. Exposure to TCBPA at concentrations of 1-100 μg/L impaired fertility of C. elegans, as indicated by brood size. After staining, the number of germline cells decreased in a dose-dependent manner, whereas germline cell corpses increased in exposed nematodes (10-100 μg/L TCBPA). Moreover, the expression of genes related to the germline apoptosis pathway was regulated following exposure to 100 μg/L TCBPA, indicating the potential role of DNA damage in TCBPA-induced apoptosis. Apoptosis was nearly abolished in ced-4 and ced-3 mutants and blocked in hus-1, egl-1, cep-1, and ced-9 mutants. Numerous foci were detected in TCBPA (100 μg/L)-exposed hus-1::GFP strains. These results indicate that TCBPA induces hus-1-mediated DNA damage and further causes apoptosis via a cep-1-dependent pathway. Our data provide evidence that TCBPA causes reproductive toxicity via DNA damage-induced apoptosis.

Review of the environmental occurrence, analytical techniques, degradation and toxicity of TBBPA and its derivatives

BFRs (brominated flame retardants) are a class of compounds that are added to or applied to polymeric materials to avoid or reduce the spread of fire. Tetrabromobisphenol A (TBBPA) is one of the known BFR used many in industries today. Due to its wide application as an additive flame retardant in commodities, TBBPA has become a common indoor contaminant. Recent researches have raised concerns about the possible hazardous effect of exposure to TBBPA and its derivatives in humans and wildlife. This review gives a thorough assessment of the literature on TBBPA and its derivatives, as well as environmental levels and human exposure. Several analytical techniques/methods have been developed for sensitive and accurate analysis of TBBPA and its derivatives in different compartments. These chemicals have been detected in practically every environmental compartment globally, making them a ubiquitous pollutant. TBBPA may be subject to adsorption, biological degradation or photolysis, photolysis after being released into the environment. Treatment of TBBPA-containing waste, as well as manufacturing and usage regulations, can limit the release of these chemicals to the environment and the health hazards associated with its exposure. Several methods have been successfully employed for the treatment of TBBPA including but not limited to adsorption, ozonation, oxidation and anaerobic degradation. Previous studies have shown that TBBPA and its derivative cause a lot of toxic effects. Diet and dust ingestion and have been identified as the main routes of TBBPA exposure in the general population, according to human exposure studies. Toddlers are more vulnerable than adults to be exposed to indoor dust through inadvertent ingestion. Furthermore, TBBP-A exposure can occur during pregnancy and through breast milk. This review will go a long way in closing up the knowledge gap on the silent and over ignored deadly effects of TBBPA and its derivatives and their attendant consequences.

Effects of postnatal exposure to tetrabromobisphenol A on testis development in mice and early key events

Whether or not tetrabromobisphenol A (TBBPA) has reproductive developmental toxicity remains controversial. Here, we evaluated the effects of postnatal TBBPA exposure of dams (before weaning) and pups through drinking water (15, 150, 1500 ng/mL) on testis development in mice. On postnatal day (PND) 56, we found that TBBPA exerted little effects on testis weight, anogenital distance, sperm parameters, and the serum testosterone level, but resulted in dose-dependent reductions in the seminiferous tubule area coupled with decreased Sertoli cells and spermatogonia and the number of stage VII-VIII seminiferous tubules, and cytoskeleton damage in Sertoli cells, along with down-regulated expression of marker genes for Sertoli cells, spermatogonia and spermatocyte. Further study revealed that the reduced tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression also occurred in TBBPA-treated testes on PND 7, along with reduced cell proliferation and disordered arrangement of Sertoli cell nuclei. On PND 15, most of these testicular alterations were still observed in TBBPA-treated males, and cytoskeleton damage in Sertoli cells became observable. All observations convincingly demonstrate that postnatal exposure to TBBPA disturbed testis development in early life and ultimately caused adverse outcomes in adult testes, and that cell proliferation inhibition, the reduction in the seminiferous tubule area coupled decreased Sertoli cell and germ cell numbers and marker gene expression, and cytoskeleton damage in Sertoli cells, are early events contributing to adverse outcomes in adult testes. Our study improves the understanding of reproductive developmental toxicity of TBBPA, highlighting its risk for human health.

Effects of tetrabromobisphenol A (TBBPA) on the reproductive health of male rodents: A systematic review and meta-analysis

Tetrabromobisphenol A (TBBPA) is a type of brominated flame retardant widely detected in the environment and organisms. It has been reported to cause cytotoxicity and disrupt endocrine system of animals. However, the effect of TBBPA on the reproductive system of male rodents is still controversial. Hence, this meta-analysis aims to determine whether TBBPA exposure damage to the reproductive system of male rodents. In this study, a thorough search of literatures was undertaken to select papers published before December 1st, 2020. The standard mean difference (SMD) and 95% confidence interval (CI) were calculated by random model. The results showed a statistically significant association between TBBPA exposure and the reproductive system health of male rodents (SMD = -0.35, 95% CI -0.50 to -0.19). The SMD for the reproductive system index organ weight, sperm quality, hormone levels, and gene expression were 0.03 (95% CI -0.18 to 0.23), -0.47 (95% CI -0.78 to -0.16), -0.51 (95% CI -0.75 to -0.27), and -0.98 (95% CI -1.36 to -0.60), respectively. There was a significant dose-effect relationship between TBBPA exposure and the reproductive health of male rodents, with the SMD values of low, medium, and high doses -0.20 (95% CI -0.34 to -0.05), -0.24 (95% CI -0.56 to 0.07), and -0.48 (95% CI -0.83 to -0.13), respectively. For exposure duration of TBBPA, an exposure time of >10 weeks (SMD = -0.33, 95% CI -0.54 to -0.12) showed more significant effect than an exposure time of ≤10 weeks (SMD = -0.22, 95% CI -0.43 to -0.02). Moreover, TBBPA exposure exhibited significant negative effects on sperm count (SMD = -0.49, 95% CI -0.82 to -0.17) while also reduced the content of triiodothyronine (T3), thyroxine (T4), and thyroid stimulating hormone (TSH) hormones. To summarize, our meta-analysis indicated that TBBPA had a toxicity effect to the reproductive system of male rodents.

Endocrine disrupting potential of replacement flame retardants - Review of current knowledge for nuclear receptors associated with reproductive outcomes

BACKGROUND AND AIM

Endocrine disrupting chemicals (EDCs) constitute a major public health concern because they can induce a large spectrum of adverse effects by interfering with the hormonal system. Rapid identification of potential EDCs using in vitro screenings is therefore critical, particularly for chemicals of emerging concerns such as replacement flame retardants (FRs). The review aimed at identifying (1) data gaps and research needs regarding endocrine disrupting (ED) properties of replacement FRs and (2) potential EDCs among these emerging chemicals.

METHODS

A systematic search was performed from open literature and ToxCast/Tox21 programs, and results from in vitro tests on the activities of 52 replacement FRs towards five hormone nuclear receptors (NRs) associated with reproductive outcomes (estrogen, androgen, glucocorticoid, progesterone, and aryl hydrocarbon receptors) were compiled and organized into tables. Findings were complemented with information from structure-based in silico model predictions and in vivo information when relevant.

RESULTS

For the majority of the 52 replacement FRs, experimental in vitro data on activities towards these five NRs were either incomplete (15 FRs) or not found (24 FRs). Within the replacement FRs for which effect data were found, some appeared as candidate EDCs, such as triphenyl phosphate (TPhP) and tris(1,3-dichloropropyl)phosphate (TDCIPP). The search also revealed shared ED profiles. For example, anti-androgenic activity was reported for 19 FRs and predicted for another 21 FRs.

DISCUSSION

This comprehensive review points to critical gaps in knowledge on ED potential for many replacement FRs, including chemicals to which the general population is likely exposed. Although this review does not cover all possible characteristics of ED, it allowed the identification of potential EDCs associated with reproductive outcomes, calling for deeper evaluation and possibly future regulation of these chemicals. By identifying shared ED profiles, this work also raises concerns for mixture effects since the population is co-exposed to several FRs and other chemicals.

Tetrabromobisphenol A induces THR β-mediated inflammation and uterine injury in mice at environmentally relevant exposure concentrations

Tetrabromobisphenol A (TBBPA) is a widely used flame retardant, but the adverse outcomes induced by TBBPA has not been fully elucidated. In this study, TBBPA was detected in 54.9% of 102 female Chinese volunteers with an average serum concentration of 0.34 ng/mL. To investigate whether TBBPA induces adverse outcomes at environmentally relevant exposure doses, the mice were exposed to TBBPA for 14 and 28 days. The internal doses of TBBPA in mice serum were nearly the internal doses in volunteers. TBBPA significantly increased the secretion of some pro-inflammatory cytokines and suppressed immune responses in mice under such serum concentrations after 14- and 28-days exposure. Interestingly, uterine edema was observed in TBBPA-treated mice. In primary uterine cells model, the results showed TBBPA exposure suppressed THRβ expression, leading to the activation of the inflammatory PI3K/NF-κB signaling pathway. Our findings indicated that the uterus is the susceptible target organ of TBBPA and TBBPA exposure might increase risk of uterine cancer through deregulating inflammation pathways.

Tetrabromobisphenol A (TBBPA): A controversial environmental pollutant

Tetrabromobisphenol A (TBBPA) is one of the most widely used brominated flame retardants and is extensively used in electronic equipment, furniture, plastics, and textiles. It is frequently detected in water, soil, air, and organisms, including humans, and has raised concerns in the scientific community regarding its potential adverse health effects. Human exposure to TBBPA is mainly via diet, respiration, and skin contact. Various in vivo and in vitro studies based on animal and cell models have demonstrated that TBBPA can induce multifaceted effects in cells and animals, and potentially exert hepatic, renal, neural, cardiac, and reproductive toxicities. Nevertheless, other reports have claimed that TBBPA might be a safe chemical. In this review, we re-evaluated most of the published TBBPA toxicological assessments with the goal of reaching a conclusion about its potential toxicity. We concluded that, although low TBBPA exposure levels and rapid metabolism in humans may signify that TBBPA is a safe chemical for the general population, particular attention should be paid to the potential effects of TBBPA on early developmental stages.

Differences in reproductive toxicity of TBBPA and TCBPA exposure in male Rana nigromaculata

Tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) are persistent toxic environmental pollutants that cause severe reproductive toxicity in animals. The goal of this study was to compare the reproductive toxic effects of TBBPA and TCBPA on male Rana nigromaculata and to expound on the mechanisms leading to these effects. Healthy adult frogs were exposed to 0, 0.001, 0.01, 0.1, and 1 mg/L of TBBPA and TCBPA for 14 days. Sperm numbers were counted by erythrometry. Sperm mobility and deformities were observed under a light microscope (400 × ). We used commercial ELISA kits to determine the serum content of testosterone (T), estradiol (E2), luteinizing hormone (LH) and follicle stimulating hormone (FSH). Expression of androgen receptor (AR) mRNA was detected using real-time qPCR. Sperm numbers and sperm mobility were significantly decreased and sperm deformity was significantly increased in a concentration dependent manner following exposure to TBBPA and TCBPA. Sperm deformity was significantly greater in the 1 mg/L TCBPA (0.549) treatment group than in the 1 mg/L TBBPA (0.397) treatment group. Serum T content was significantly greater in the 0.01, 0.1 and 1 mg/L TBBPA and TCBPA experimental groups compared with controls, while E2 content was significantly greater in only the 1 mg/L TBBPA and TCBPA experimental groups. Expression levels of LH and FSH significantly decreased in the 1 mg/L TBBPA and TCBPA treatment groups. AR mRNA expression decreased markedly in all the treated groups. Our results indicated that TBBPA and TCBPA induced reproductive toxicity in a dose-dependent manner, with TCBPA having greater toxicity than TBBPA. Furthermore, changes in T, E2, LH, and FSH levels induced by TBBPA and TCBPA exposure, which led to endocrine disorders, also caused disturbance of spermatogenesis through abnormal gene expressions of AR in the testes.

Effects of bisphenol A and its analogs on reproductive health: A mini review

Known endocrine disruptor bisphenol A (BPA) has been shown to be a reproductive toxicant in animal models. Its structural analogs: bisphenol S (BPS), bisphenol F (BPF), bisphenol AF (BPAF), and tetrabromobisphenol A (TBBPA) are increasingly being used in consumer products. However, these analogs may exert similar adverse effects on the reproductive system, and their toxicological data are still limited. This mini-review examined studies on both BPA and BPA analog exposure and reproductive toxicity. It outlines the current state of knowledge on human exposure, toxicokinetics, endocrine activities, and reproductive toxicities of BPA and its analogs. BPA analogs showed similar endocrine potencies when compared to BPA, and emerging data suggest they may pose threats as reproductive hazards in animal models. While evidence based on epidemiological studies is still weak, we have utilized current studies to highlight knowledge gaps and research needs for future risk assessments.

Ubiquitous Flame-Retardant Toxicants Impair Spermatogenesis in a Human Stem Cell Model

Sperm counts have rapidly declined in Western males over the past four decades. This rapid decline remains largely unexplained, but exposure to environmental toxicants provides one potential explanation for this decline. Flame retardants are highly prevalent and persistent in the environment, but many have not been assessed for their effects on human spermatogenesis. Using a human stem cell-based model of spermatogenesis, we evaluated two major flame retardants, hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA), under acute conditions simulating occupational-level exposures. Here we show that HBCDD and TBBPA are human male reproductive toxicants in vitro. Although these toxicants do not specifically affect the survival of haploid spermatids, they affect spermatogonia and primary spermatocytes through mitochondrial membrane potential perturbation and reactive oxygen species generation, ultimately causing apoptosis. Taken together, these results show that HBCDD and TBBPA affect human spermatogenesis in vitro and potentially implicate this highly prevalent class of toxicants in the decline of Western males' sperm counts.

Transgenerational inheritance of susceptibility to diabetes-induced male subfertility

Male infertility is a worldwide problem associated with genetic background, environmental factors, and diseases. One of the suspected contributing factors to male infertility is diabetes mellitus. We investigated the molecular and morphological changes in sperms and testicular tissue of diabetic males. The study was performed in streptozotocin-induced type 1 diabetes mouse model. Diabetes decreased sperm concentration and viability and increased sperm apoptosis. Changes in protamine 1/protamine 2 ratio indicated reduced sperm quality. The testicular tissue of diabetic males showed significant tissue damage, disruption of meiotic progression, and changes in the expression of genes encoding proteins important for spermiogenesis. Paternal diabetes altered sperm quality and expression pattern in the testes in offspring of two subsequent generations. Our study revealed that paternal diabetes increased susceptibility to infertility in offspring through gametic alternations. Our data also provide a mechanistic basis for transgenerational inheritance of diabetes-associated pathologies since protamines may be involved in epigenetic regulations.

Evaluation of the expression of sperm proteins in normozoospermic and asthenozoospermic men using monoclonal antibodies

Recent studies have shown that infertility affects estimated 15% of all couples. Male infertility is the primary or contributory cause in 60% of these cases. Consequently, the application of assisted reproduction is increasing. These methods could benefit from an extended evaluation of sperm quality. For this reason, we analyzed sperm proteins from 30 men with normal spermiograms and 30 men with asthenozoospermia. Ejaculates of both groups were tested by flow cytometry (FCM) and fluorescence with a set of well-characterized anti-human sperm Hs-monoclonal antibodies (MoAbs), which were generated in our laboratory. No statistically significant differences were found between normospermics and asthenospermics in the expression of the sperm surface protein clusterin, evaluated with Hs-3 MoAb, and semenogelin, evaluated with Hs-9 MoAb. However, FCM revealed quantitative differences in the acrosomal proteins between normozoospermic and asthenozoospermic men, namely, in glyceraldehyde-3-phosphate dehydrogenase, evaluated with Hs-8 MoAb, valosin-containing protein, evaluated with Hs-14 MoAb, and ATP synthase (cAMP-dependent protein kinase II, PRKAR2A), evaluated with MoAb Hs-36. Asthenozoospermic men displayed a highly reduced expression of intra-acrosomal proteins, with a likely decrease in sperm quality, and thus a negative impact on successful reproduction. Asthenozoospermia seems to be a complex disorder involving intra-acrosomal proteins.

Melatonin controlled apoptosis and protected the testes and sperm quality against bisphenol A-induced oxidative toxicity

Epidemiological reports have indicated a correlation between the increasing bisphenol A (BPA) levels in the environment and the incidence of male infertility. In this study, the protective effects of melatonin on BPA-induced oxidative stress and apoptosis were investigated in the rat testes and epididymal sperm. Melatonin (10 mg/kg body weight (bw)) was injected concurrently with BPA (50 mg/kg bw) for 3 and 6 weeks. The administration of BPA significantly increased oxidative stress in the testes and epididymal sperm. This was associated with a decrease in the serum testosterone level as well as sperm quality, chromatin condensation/de-condensation level, and the percentage of haploid germ cells in the semen. BPA administration caused a significant increase in apoptosis accompanied by a decrease in the expression of the antiapoptotic proteins Bcl-2 in the testes and epididymal sperm. The concurrent administration of melatonin decreased oxidative stress by modulating the levels of glutathione, superoxide dismutase, and catalase as well as the malondialdehyde and hydrogen peroxide concentrations in the testes and sperm. Melatonin sustained Bcl-2 expression and controlled apoptosis. Furthermore, melatonin maintained the testosterone levels, ameliorated histopathological changes, increased the percentages of seminal haploid germ cells, and protected sperm chromatin condensation process, indicating appropriate spermatogenesis with production of functional sperm. In conclusion, melatonin protected against BPA-induced apoptosis by controlling Bcl-2 expression and ameliorating oxidative stress in the testes and sperm. Thus, melatonin is a promising pharmacological agent for preventing the potential reproductive toxicity of BPA following occupational or environmental exposures.

Development of toxicity values and exposure estimates for tetrabromobisphenol A: application in a margin of exposure assessment

Tetrabromobisphenol A (TBBPA) is used in a diverse array of products to improve fire safety. The National Toxicology Program (NTP) recently completed a 2-year bioassay for TBBPA. The objective of the present study was to develop a cancer-based and a non-cancer based toxicity value and to compare such to appropriate estimates of human exposure. Data from the NTP 2-year and 13-week studies were selected to develop candidate toxicity values. Benchmark dose modeling and subsequent evaluation of candidate values resulted in selection of an oral reference dose (RfD) of 0.6 mg kg(-1) day(-1) based on uterine hyperplasia in rats and an oral cancer slope factor (OSF) of 0.00315 per mg kg(-1) day(-1) based on an increased incidence of uterine tumors in rats. Lifetime average daily dose (LADD) estimates ranged from 2.2 E(-7) to 3.9 E(-6) mg kg(-1) day(-1) based on age-adjusted exposures to TBBPA via breast milk consumption, dietary intake, soil/dust ingestion and drinking water ingestion in infants, young children, older children and adults. Average daily dose (ADD) estimates ranged from 3.2 E (-7) to 8.4 E(-5) mg kg(-1) day(-1). Resulting margin of exposure (MOE) values were > 800 000 for non-cancer endpoints and > 32,000,000 for cancer-based endpoints. These data collectively indicate a low level of health concern associated with exposures to TBBPA based on current data. It is anticipated that the exposure estimates, along with the toxicity values described within, should be informative for understanding human health hazards associated with TBBPA.

Characterization and possible function of glyceraldehyde-3-phosphate dehydrogenase-spermatogenic protein GAPDHS in mammalian sperm

BACKGROUND

Sperm proteins are important for the sperm cell function in fertilization. Some of them are involved in the binding of sperm to the egg. We characterized the acrosomal sperm protein detected by a monoclonal antibody (MoAb) (Hs-8) that was prepared in our laboratory by immunization of BALB/c mice with human ejaculated sperms and we tested the possible role of this protein in the binding assay.

METHODS

Indirect immunofluorescence and immunogold labelling, gel electrophoresis, Western blotting and protein sequencing were used for Hs-8 antigen characterization. Functional analysis of GAPDHS from the sperm acrosome was performed in the boar model using sperm/zona pellucida binding assay.

RESULTS

Monoclonal antibody Hs-8 is an anti-human sperm antibody that cross-reacts with the Hs-8-related protein in spermatozoa of other mammalian species (boar, mouse). In the immunofluorescence test, Hs-8 antibody recognized the protein localized in the acrosomal part of the sperm head and in the principal piece of the sperm flagellum. In immunoblotting test, MoAb Hs-8 labelled a protein of 45 kDa in the extract of human sperm. Sequence analysis identified protein Hs-8 as GAPDHS (glyceraldehyde 3-phosphate dehydrohenase-spermatogenic). For this reason, commercial mouse anti-GAPDHS MoAb was applied in control tests. Both antibodies showed similar staining patterns in immunofluorescence tests, in electron microscopy and in immunoblot analysis. Moreover, both Hs-8 and anti-GAPDHS antibodies blocked sperm/zona pellucida binding.

CONCLUSION

GAPDHS is a sperm-specific glycolytic enzyme involved in energy production during spermatogenesis and sperm motility; its role in the sperm head is unknown. In this study, we identified the antigen with Hs8 antibody and confirmed its localization in the apical part of the sperm head in addition to the principal piece of the flagellum. In an indirect binding assay, we confirmed the potential role of GAPDHS as a binding protein that is involved in the secondary sperm/oocyte binding.

The effect of tetrabromobisphenol A on protamine content and DNA integrity in mouse spermatozoa

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant of increasing concern to human health because of its action as an endocrine disruptor. We have previously demonstrated that TBBPA is able to increase apoptosis of testicular cells and other changes in the first and second generations of mice exposed to TBBPA. However, the potential effects of TBBPA on mouse epididymal spermatozoa have not yet been investigated. Therefore, we initiated this study to determine whether TBBPA exposure could also result in increased DNA fragmentation in epididymal spermatozoa and whether it had an effect on the protamines as the major nuclear proteins. C57Bl/6J mouse pups (n = 10) were exposed to TBBPA (experimental group) during the gestation, lactation, pre-pubertal and pubertal periods up to the age of 70 days as previously described and compared to control mouse pups (n = 10) that were not exposed. The results demonstrate that TBBPA treatment results in a significantly decreased protamine 1/protamine 2 ratio (0.362 vs. 0.494; p < 0.001), increased total protamine/DNA ratio (0.517 vs. 0.324; p < 0.001) and increased number of terminal deoxynucleotidyl transferase dUTP nick end labelling positive spermatozoa (39.5% vs. 21.2%; p < 0.05) observed between TBBPA and control mice respectively. These findings indicate that TBBPA exposure, in addition to the resulting increased sperm DNA damage, also has the potential to alter the epigenetic marking of sperm chromatin through generation of an anomalous content and distribution of protamines. The possibility is now open to study whether the detected altered protamine content and DNA integrity are related to the previously observed second-generation effects upon TBBPA exposure.

Mammalian toxicology and human exposures to the flame retardant 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol (TBBPA): implications for risk assessment

The compound 2,2',6,6'-Tetrabromo-4,4'-isopropylidenediphenol (tetrabromobisphenol A, TBBPA) is used as a reactive and additive flame retardant. This review evaluates the mammalian toxicology of TBBPA and summarizes recent human exposure and risk assessments. TBBPA has a low potential for systemic or reproductive toxicity, and no-observed-adverse-effect-levels were greater than 1,000 mg/kg body weight (bw)/day in a 90-day oral toxicity study, a developmental toxicity study and a two-generation reproductive and developmental toxicity study. Some interactions of TBBPA with hormone-mediated pathways were noted in vitro; however, when studied in vivo, TBBPA did not produce adverse effects that might be considered to be related to disturbances in the endocrine system. Therefore, in accordance with internationally accepted definitions, TBBPA should not be considered an "endocrine disruptor." Furthermore, TBBPA is rapidly excreted in mammals and therefore does not have a potential for bioaccumulation. Measured concentrations of TBBPA in house dust, human diet and human serum samples are very low. Daily intakes of TBBPA in humans were estimated to not exceed a few ng/kg bw/day. Due to the low exposures and the low potential for toxicity, margins of exposures for TBBPA in the human population were between 6 × 10(4) (infants) to 6 × 10(7) (adults). Exposures of the general population are also well below the derived-no-effect-levels derived for endpoints of potential concern in REACH.

Expression analysis of MND1/GAJ, SPATA22, GAPDHS and ACR genes in testicular biopsies from non-obstructive azoospermia (NOA) patients

BACKGROUND

High-throughput studies provide a wide spectrum of genes for use as predictive markers during testicular sperm extraction (TESE) in combination with ICSI. In this work, we used the specimens from testicular biopsies of men with non-obstructive azoospermia who underwent TESE to investigate the expression of spermatogenesis-related genes MND1, SPATA22, GAPDHS and ACR.

METHODS

Testicular biopsy specimens were subdivided into three groups: hypospermatogenesis (HS); maturation arrest (MA); and Sertoli cell-only syndrome (SCO). The levels of expression of the spermatogenesis-related genes MND1, SPATA22, GAPDHS and ACR in the testes were compared among these three groups using the reverse transcription polymerase chain reaction (RT-PCR) technique.

RESULTS

Analysis of the expression of spermatogenic genes in human testes with abnormal spermatogenesis showed different expression patterns in patients from different groups. Fertilization rate for studied set of patients was 66% and pregnancy rate 29%. For HS group fertilization rate was 72% and pregnancy rate 32%, while for MA group fertilization and pregnancy rates were 54% and 26%, respectively. Fertilization rates in relation to the studied genes were uniformly around 70%, pregnancy rates for ACR and GAPDHS genes were surprisingly low at 6% and 8% correspondingly.

CONCLUSIONS

Analysis of the expression of genes involved in spermatogenesis can be a fast additional test for the level of spermatogenesis in testicular samples.

In vivo exposure to 17β-estradiol triggers premature sperm capacitation in cauda epididymis

Estrogens play a crucial role in spermatogenesis and estrogen receptor α knock-out male mice are infertile. It has been demonstrated that estrogens significantly increase the speed of capacitation in vitro; however this may lead to the reduction of reproductive potential due to the decreased ability of these sperm to undergo the acrosome reaction. To date the in vivo effect of estrogens on the ability of sperm to capacitate has not been investigated. Therefore, in this study, we exposed mice (n=24) to 17β-estradiol (E2) at the concentration of 20 ng/ml either during puberty from the fourth to seventh week of age (n=8), or continuously from birth for a period of 12 weeks (n=8) at which age the animals from both groups were killed. The capacitation status of epididymal and testicular sperm was analysed by tyrosine phosphorylation (TyrP) antibody (immunofluorescence and western blot) and chlortetracycline (CTC) assay. According to our results, in vivo exposure to increased E2 concentrations caused premature sperm capacitation in the epididymis. The effect of E2, however, seems reversible because after the termination of the exposure premature epididymal sperm capacitation is decreased in animals treated during puberty. Furthermore the changes in epididymal sperm capacitation status detected by TyrP and CTC positively correlate with plasma levels of E2 and the expression of the estrogen-dependent trefoil factor 1 (Tff1) gene in testicular tissue. Therefore, our data implicate that in vivo exposure to E2 under specific conditions leads to the premature capacitation of mouse sperm in epididymis with a potential negative impact on the sperm reproductive fitness in the female reproductive tract.