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

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.

Tetrabromobisphenol A reduces male rats reproductive organ coefficients and disrupting sexual hormone by causing oxidative stress

Tetrabromobisphenol A (TBBPA) has become a topic of public attention due to its pervasive detection in the environment and organisms in recent decades. However, limited information is available regarding the toxicity of TBBPA on reproductive ability of male mammals. Herein, the reproductive toxicity of TBBPA was investigated in male rats to fill the knowledge gap. In this study, male rats were exposed to TBBPA (0, 10, 100, and 1000 mg/kg) for 6 weeks. Subsequently, body and organ indexes, histopathological evaluation of testis and epididymis, ultrastructural observation of sperm, testosterone and progesterone levels, and oxidative stress indicators were conducted to reveal corresponding mechanisms. Results obtained showed that compare to the control group, the body weight, testes weight, epididymis weight, seminal vesicle and coagulation glands weight of rats in the 1000 mg/kg group lost 8.30%, 16.84%, 20.16%, 19.72% and 26.42%, respectively. Intriguingly, exposure to TBBPA (10, 100, 100 mg/kg) resulted in substantial pathological damage in testis, epididymis and sperm. TBBPA exposure also increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, as well as superoxide dismutase (T-SOD) and catalase (CAT) activities in testicular tissue. What's more, the testosterone and progesterone levels in male rat serum were significantly decreased after exposure to TBBPA for 6 weeks. Meanwhile, results of molecular docking showed that TBBPA has a strong affinity with estrogen receptors (ERs). These findings demonstrated that TBBPA exposure negatively impacts the reproductive ability of male rats, thus providing new insights for risk assessment for reproductive health under TBBPA exposure.

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.

The brominated flame retardant tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) as well as hexabromocyclododecane lead to lipid disorders in mice

The brominated flame retardant tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) (TBBPA-DBMPE) is a recommended substitute for hexabromocyclododecane (HBCD), a banned persistent organic pollutant, yet its potential toxicities remains largely unexplored. Here, we investigated the effects of a long-term exposure to TBBPA-DBMPE at nominal doses of 50 and 1000 μg/kg/d on lipid homeostasis in CD-1 mice, in comparison with 50 μg/kg/d HBCD as a positive control. Male pups received chemical treatments through maternal administration via drinking water from postnatal day 0-21, followed by direct administration through drinking water after weaning. On the 23rd week after treatment, the oral lipid tolerance test revealed that low-dose TBBPA-DBMPE as well as HBCD affected lipid tolerance, although the fasting serum triglyceride (TG) levels were not altered. When chemical treatment was extended to the 32nd week, TBBPA-DBMPE-treated animals displayed adipocyte hypertrophy in both white adipose tissue (eWAT) and brown adipose tissue (BAT) and hepatic steatosis, which was largely consistent with the effects of HBCD. These findings indicate that like HBCD, TBBPA-DBMPE led to increased lipid load in mice. Interestingly, we also observed intestinal histological changes, coupled with increased expression of lipid absorption-related genes in both HBCD and TBBPA-DBMPE treatments, suggesting increased lipid absorption. This was supported by in vitro findings that both HBCD and TBBPA-DBMPE promoted lipid accumulation in IEC-6 cells under the stress of oleic acid for 6 h, implying that altered lipid absorption by the intestine may partly contributed to increased lipid load in mice. Overall, the effects of 50 μg/kg/d TBBPA-DBMPE in terms of some parameters were comparable with 50 μg/kg/d HBCD, suggesting that TBBPA-DBMPE may not be an ideal substitute of HBCD.

Cellular and physiological mechanisms of halogenated and organophosphorus flame retardant toxicity

Flame retardants (FRs) are chemical substances used to inhibit the spread of fire in numerous industrial applications, and their abundance in modern manufactured products in the indoor and outdoor environment leads to extensive direct and food chain exposure of humans. Although once considered relatively non-toxic, FRs are demonstrated by recent literature to have disruptive effects on many biological processes, including signaling pathways, genome stability, reproduction, and immune system function. This review provides a summary of research investigating the impact of major groups of FRs, including halogenated and organophosphorus FRs, on animals and humans in vitro and/or in vivo. We put in focus those studies that explained or referenced the modes of FR action at the level of cells, tissues and organs. Since FRs are highly hydrophobic chemicals, their biophysical and biochemical modes of action usually involve lipophilic interactions, e.g. with biological membranes or elements of signaling pathways. We present selected toxicological information about these molecular actions to show how they can lead to damaging membrane integrity, damaging DNA and compromising its repair, changing gene expression, and cell cycle as well as accelerating cell death. Moreover, we indicate how this translates to deleterious bioactivity of FRs at the physiological level, with disruption of hormonal action, dysregulation of metabolism, adverse effects on male and female reproduction as well as alteration of normal pattern of immunity. Concentrating on these subjects, we make clear both the advances in knowledge in recent years and the remaining gaps in our understanding, especially at the mechanistic level.

Extended exposure to tetrabromobisphenol A-bis(2,3-dibromopropyl ether) leads to subfertility in male mice at the late reproductive age

Tetrabromobisphenol A-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE), a commonly used brominated flame retardant as a decabromodiphenyl ether substitute, has been detected in various environmental compartments, but its health hazards remain largely unknown. Our recent study showed that low-dose exposure of male mice to TBBPA-BDBPE from postnatal day (PND) 0 to 56 caused remarkable damage to the microtubule skeleton in Sertoli cells and the blood-testis barrier (BTB) but exerted little effect on conventional reproductive endpoints in adulthood. To investigate whether TBBPA-BDBPE may cause severe reproductive impairments at late reproductive age, here, we extended exposure of historically administrated male mice to 8-month age and allowed them to mate with non-treated females for the evaluation of fertility, followed by a general examination for the reproductive system. As expected, we found that 8-month exposure to 50 μg/kg/d as well as 1000 μg/kg/d TBBPA-BDBPE caused severe damage to the reproductive system, including reduced sperm counts, increased sperm abnormality, histological alterations of testes. Moreover, microtubule damage and BTB-related impairment were still observed following 8-month exposure. Noticeably, high-dose TBBPA-BDBPE-treated mice had fewer offspring with a female-biased sex ratio. All results show that long-term exposure to TBBPA-BDBPE caused severe reproductive impairment, including poor fertility at late reproductive age. It is therefore concluded that slight testicular injuries in early life can contribute to reproductive impairment at late reproductive age, highlighting that alterations in certain non-conventional endpoints should be noticed as well as conventional endpoints in future reproductive toxicity studies.

Tetrabromobisphenol a exacerbates the overall radioactive hazard to zebrafish (Danio rerio)

The major health risks of dual exposure to two hazardous factors of plastics and radioactive contamination are obscure. In the present study, we systematically evaluated the combinational toxic effects of tetrabromobisphenol A (TBBPA), one of the most influential plastic ingredients, mainly from electronic wastes, and γ-irradiation in zebrafish for the first time. TBBPA (0.25 μg/mL for embryos and larvae, 300 μg/L for adults) contamination aggravated the radiation (6 Gy for embryos and larvae, 20 Gy for adults)-induced early dysplasia and aberrant angiogenesis of embryos, further impaired the locomotor vitality of irradiated larvae, and worsened the radioactive multiorganic histologic injury, neurobehavioural disturbances and dysgenesis of zebrafish adults as well as the inter-generational neurotoxicity in offspring. TBBPA exaggerated the radiative toxic effects not only by enhancing the inflammatory and apoptotic response but also by further unbalancing the endocrine system and disrupting the underlying gene expression profiles. In conclusion, TBBPA exacerbates radiation-induced injury in zebrafish, including embryos, larvae, adults and even the next generation. Our findings provide new insights into the toxicology of TBBPA and γ-irradiation, shedding light on the severity of cocontamination of MP components and radioactive substances and thereby inspiring novel remediation and rehabilitation strategies for radiation-injured aqueous organisms and radiotherapy patients.

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.

Tetrabromobisphenol A effects on differentiating mouse embryonic stem cells reveals unexpected impact on immune system

Tetrabromobisphenol A (TBBPA) is a potent flame retardant used in numerous appliances and a major pollutant in households and ecosystems. In vertebrates, it was shown to affect neurodevelopment, the hypothalamic-pituitary-gonadal axis and thyroid signaling, but its toxicity and modes of actions are still a matter of debate. The molecular phenotype resulting from exposure to TBBPA is only poorly described, especially at the level of transcriptome reprogramming, which further limits our understanding of its molecular toxicity. In this work, we combined functional genomics and system biology to provide a system-wide description of the transcriptomic alterations induced by TBBPA acting on differentiating mESCs, and provide potential new toxicity markers. We found that TBBPA-induced transcriptome reprogramming affect a large collection of genes loosely connected within the network of biological pathways, indicating widespread interferences on biological processes. We also found two hotspots of action: at the level of neuronal differentiation markers, and surprisingly, at the level of immune system functions, which has been largely overlooked until now. This effect is particularly strong, as terminal differentiation markers of both myeloid and lymphoid lineages are strongly reduced: the membrane T cell receptor (Cd79a, Cd79b), interleukin seven receptor (Il7r), macrophages cytokine receptor (Csf1r), monocyte chemokine receptor (Ccr2). Also, the high affinity IgE receptor (Fcer1g), a key mediator of allergic reactions, is strongly induced. Thus, the molecular imbalance induce by TBBPA may be stronger than initially realized.

Effects of low-dose bisphenol AF on mammal testis development via complex mechanisms: alterations are detectable in both infancy and adulthood

Despite growing concern about adverse effects of bisphenol AF (BPAF) due to its endocrine disrupting properties, there is a lack of toxicity data from low-dose studies and direct evidence linking its adverse effects to endocrine disrupting properties. Here, we investigated the effects of gestational and postnatal exposure to BPAF through drinking water (0.15-15 μg/mL, equivalent to the daily intake of ~ 50 and 5 mg/kg/day) on testis development in mice. We found that like mestranol, 5 mg/kg/day BPAF resulted in remarkable decreases in multiple male reproductive parameters in adulthood, such as the sperm number and serum testosterone level. Notably, 50 μg/kg/day BPAF also caused significant decreases in anogenital distance (AGD), the luteinizing hormone level and spermatocyte number, along with declining trends in sperm number and the serum levels of testosterone and follicle-stimulating hormone. In line with the adverse outcomes observed in adulthood, on postnatal day (PND) 9, we also observed BPAF-caused dose-dependent alterations, including reduced AGD, seminiferous tubule area and numbers of total germ cells, spermatocytes and Leydig cells, coupled with down-regulated expression of male-biased genes in testes. Even when exposure to 5 mg/kg/day BPAF as well as MES was initiated from PND 0, similar alterations in male reproductive parameters were also found on PND 9, along with a decrease in the GnRH content in the hypothalamus; moreover, testicular alterations and the reduction in AGD were partly antagonized by the estrogen receptor (ER) antagonist ICI 182,780, but the reduction of GnRH production was not done, showing that the effects of BPAF on testis development may be partially mediated by ER signaling. In conclusion, all the findings demonstrate that low-dose BPAF can partly disrupt mammal testis development and cause adverse testicular outcomes in adulthood, indicating a potential reproductive risk to mammals including humans. Importantly, our finding that developmental alterations elicited by BPAF have been detectable on PND 9 provides important motivation for the development of effective methods for early detection of adverse effects of estrogenic chemicals on testis development.