Effects of tetrabromobisphenol A, brominated flame retardant, in ICR mice after prenatal and postnatal exposure

Exposure to synthesized tribromobisphenol A and critical effects: Metabolic pathways, disease signature, and benchmark dose derivation

2,2',6-Tribromobisphenol A (Tri-BBPA), the main debrominated congener of tetrabromobisphenol A (TBBPA), is ubiquitous in the environment and human body but with unknown toxicity. Tri-BBPA was synthesized and applied to investigate its sub-chronic exposure effects on 28 organ coefficients and clinical health indicators related to liver function, kidney function, and cardiovascular system function in female mice. Results showed that the liver was the targeted organ of Tri-BBPA exposure. Compared to the control group, the changes in liver coefficient, cholinesterase, total protein, albumin, γ-glutamyl transpeptidase, lactate dehydrogenase, and creatine kinase levels ranged from -61.2 % to 35.5 % in the high-exposed group. Creatine kinase was identified as a critical effect indicator of Tri-BBPA exposure. Using the Bayesian benchmark dose derivation method, a lower reference dose than TBBPA was established for Tri-BBPA (10.6 μg/kg-day). Serum metabolomics revealed that Tri-BBPA exposure may primarily damage the liver by disrupting tryptophan metabolism related to L-alanine, tryptamine, 5-hydroxyindoleacetic acid, and 5-methoxyindoleacetate in liver cells and leading to liver dysfunction. Notably, epilepsy, schizophrenia, early preeclampsia, and late-onset preeclampsia were the top six enriched diseases, suggesting that the nervous system may be particularly affected by Tri-BBPA exposure. Our findings hinted a non-negligible health risk of exposure to debrominated products of TBBPA.

Perturbation of lipid metabolism in 3T3-L1 at different stages of preadipocyte differentiation and new insights into the association between changed metabolites and adipogenesis promoted by TBBPA or TBBPS

Tetrabromobisphenol A (TBBPA) and tetrabromobisphenol S (TBBPS) are widely distributed brominated flame retardants. While TBBPA has been demonstrated to stimulate adipogenesis, TBBPS is also under suspicion for potentially inducing comparable effects. In this study, we conducted a non-targeted metabolomics to examine the metabolic changes in 3T3-L1 cells exposed to an environmentally relevant dose of TBBPA or TBBPS. Our findings revealed that 0.1 µM of both TBBPA and TBBPS promoted the adipogenesis of 3T3-L1 preadipocytes. Multivariate analysis showed significant increases in glycerophospholipids, sphingolipids, and steroids relative levels in 3T3-L1 cells exposed to TBBPA or TBBPS at the final stage of preadipocyte differentiation. Metabolites set composed of glycerophospholipids was found to be highly effective predictors of adipogenesis in 3T3-L1 cells exposed to TBBPA or TBBPS (revealed from the receiver operating characteristic curve with an area under curve > 0.90). The results from metabolite set enrichment analysis suggested both TBBPA and TBBPS exposures significantly perturbed steroid biosynthesis in adipocytes. Moreover, TBBPS additionally disrupted the sphingolipid metabolism in the adipocytes. Our study presents new insights into the obesogenic effects of TBBPS and provides valuable information about the metabolites associated with adipogenesis induced by TBBPA or TBBPS.

Co-occurrence of tetrabromobisphenol a and debromination products in human hair across China: Implications for exposure sources and health effects on metabolic syndrome

The large usage of Tetrabromobisphenol A (TBBPA) in consumer products leads to ubiquitous distribution globally, however, studies on the occurrence of their debromination compounds were rather scarce. Also, though many studies illustrate the effectiveness of hair analysis to assess human exposure to organic pollutants, evidence on the associations with health implications is still fairly limited. Herein, 598 participants from across China were employed to investigate chronic, low-level exposure to TBBPA and debromination products by hair analysis. The geomean concentrations of TBBPA, 2,2',6-tribromobisphenol A (Tri-BBPA), 2,2'- and 2,6-dibromobisphenol A (Di-BBPA), and 2-monobromobisphenol A (Mo-BBPA) were 1.07, 0.145, 0.135, and 0.894 ng/g, respectively, indicating nonnegligible health risks of debromination products. Hair analyte levels correlated with population age and population density among sampling regions. Sexual- and spatial-variations were observed with higher concentrations in females and in E-waste recycling sites. Logistic regression models showed that TBBPA exposure (adjusted odds ratio (OR): 1.02, 95 % confidential interval (CI): 1.01-1.05) was positively associated with risk of metabolic syndrome by adjusting for various covariates. These findings imply usefulness of hair as an alternative biomonitoring tool to assess human exposure to TBBPA and relative health effects, which highlights public concerns on co-exposure to these chemicals.

Developmental toxicity assessments for TBBPA and its commonly used analogs with a human embryonic stem cell liver differentiation model

Tetrabromobisphenol A (TBBPA) is widely used in industrial production as a halogenated flame retardant (HFR). Its substitutes and derivatives are also commonly employed as HFRs. Consequently, they can be frequently detected in environmental and human samples. The potential developmental toxicity of TBBPA and its analogs, particularly to the human liver, is still controversial or not thoroughly assessed. Therefore, in this study, we focused on the early stages of human liver development to explore the toxic effects of those HFRs, by using a human embryonic stem cell liver differentiation model. We concluded that nanomolar treatments (1, 10, and 100 nM) of those pollutants may not exert significant interference to liver development and functions. However, at 5 μM doses, TBBPA and its analogs severely affected liver functions, such as glycogen storage, and caused lipid accumulation. Furthermore, TBBPA-bis(allyl ether) showed the most drastic effects among the six compounds tested. Taken together, our findings support the view that TBBPA can be used safely, provided its amounts are strictly controlled. Nonetheless, TBBPA alternatives or derivatives may exhibit stronger adverse effects than TBBPA itself, and may not be safer choices for manufacturing applications when utilized in a large and unrestricted way.

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.

Potential obesogenic effects of TBBPA and its alternatives TBBPS and TCBPA revealed by metabolic perturbations in human hepatoma cells

To date, increasing numbers of studies have shown the obesogenic effects of tetrabromobisphenol A (TBBPA). Tetrabromobisphenol S (TBBPS) and tetrachlorobisphenol A (TCBPA) are two common alternatives to TBBPA, and their environmental distributions are frequently reported. However, their toxicity and the associated potential health risks are poorly documented. Herein, we performed untargeted metabolomics to study the metabolic perturbations in HepG2 cells exposed to TBBPA and its alternatives. Consequently, no loss of cellular viability was observed in HepG2 cells exposed to 0.1 μmol/L and 1 μmol/L TBBPA, TBBPS and TCBPA. However, multivariate analysis and metabolic profiles revealed significant perturbations in glycerophospholipid and fatty acyl levels in HepG2 cells exposure to TBBPS and TCBPA. The evident increases in the glucose 1-phosphate and fructose 6-phosphate levels in HepG2 cells were proposed to be induced by the promotion of PGM1/PGM2 and GPI gene expression and the suppression of UPG2 and GFPT1/GFPT2 gene expression. Our results suggest that TBBPS and TCBPA are more likely to disrupt liver metabolic homeostasis and potentially drive liver dysfunction than TBBPA. Our study is significant for the re-evaluation of the health risks associated with TBBPA and its alternatives TBBPS and TCBPA.

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.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

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.

Transcriptomic Analysis of the Differential Nephrotoxicity of Diverse Brominated Flame Retardants in Rat and Human Renal Cells

Brominated flame retardants (BFRs) are environmentally persistent, are detected in humans, and some have been banned due to their potential toxicity. BFRs are developmental neurotoxicants and endocrine disruptors; however, few studies have explored their potential nephrotoxicity. We addressed this gap in the literature by determining the toxicity of three different BFRs (tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and tetrabromodiphenyl ether (BDE-47)) in rat (NRK 52E) and human (HK-2 and RPTEC) tubular epithelial cells. All compounds induced time- and concentration-dependent toxicity based on decreases in MTT staining and changes in cell and nuclear morphology. The toxicity of BFRs was chemical- and cell-dependent, and human cells were more susceptible to all three BFRs based on IC₅₀s after 48 h exposure. BFRs also had chemical- and cell-dependent effects on apoptosis as measured by increases in annexin V and PI staining. The molecular mechanisms mediating this toxicity were investigated using RNA sequencing. Principal components analysis supported the hypothesis that BFRs induce different transcriptional changes in rat and human cells. Furthermore, BFRs only shared nine differentially expressed genes in rat cells and five in human cells. Gene set enrichment analysis demonstrated chemical- and cell-dependent effects; however, some commonalities were also observed. Namely, gene sets associated with extracellular matrix turnover, the coagulation cascade, and the SNS-related adrenal cortex response were enriched across all cell lines and BFR treatments. Taken together, these data support the hypothesis that BFRs induce differential toxicity in rat and human renal cell lines that is mediated by differential changes in gene expression.

Health toxicity effects of brominated flame retardants: From environmental to human exposure

Hexabromocyclododecane (HBCD) and Tetrabromobisphenol A (TBBP-A) are brominated flame retardants widely used in variety of industrial and consumer products (e.g., automobiles, electronics, furniture, textiles and plastics) to reduce flammability. HBCD and TBBPA can also contaminate the environment, mainly water, dust, air and soil, from which human exposure occurs. This constant exposure has raised some concerns against human health. These compounds can act as endocrine disruptors, a property that gives them the ability to interfere with hormonal function and quantity, when HBCD and TBBPA bind target tissues in the body. Studies in human and animals suggest a correlation between HBCD and TBBPA exposure and adverse health outcomes, namely thyroid disorders, neurobehavior and development disorders, reproductive health, immunological, oncological and cardiovascular diseases. However, in humans these effects are still poorly understood, once only a few data evaluated the human health effects. Thus, the purpose of this review is to present the toxicity effects of HBCD and TBBPA and how these compounds affect the environment and health, resorting to data and knowledge of 255 published papers from 1979 to 2020.

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.

Toxicity of Tetrabromobisphenol A and Its Derivative in the Mouse Liver Following Oral Exposure at Environmentally Relevant Levels

As typical brominated flame retardants (BFRs), tetrabromobisphenol A (TBBPA) and its derivative TBBPA-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE) are ubiquitous in various environmental compartments. However, the potential health risk posed by these compounds, especially at environmentally relevant levels, remains unclear. In this study, using adult male mice, we investigated the toxicity of orally administered TBBPA and TBBPA-BDBPE at an environmentally relevant dose (57 nmol/kg body weight). After a single exposure and daily exposure, we assessed lipid metabolism homeostasis, the transcriptome, and immune cell components in the liver. We found that the single exposure to TBBPA or TBBPA-BDBPE alone increased the number of hepatic macrophages, induced alterations in the levels of lipids, including triacylglycerol and free fatty acids, and caused transcriptome perturbation. The results from the daily administration groups showed that TBBPA and TBBPA-BDBPE both significantly increased the triacylglycerol content; however, the elevation of hepatic macrophages was observed only in the TBBPA-BDBPE treatment group. This study confirmed that environmentally relevant levels of TBBPA and TBBPA-BDBPE are toxic to the liver. Our findings revealed that dysfunction of the liver is a health concern, following exposure to BFRs, even at very low concentrations. The chronic effects induced by TBBPA and its derivatives should be further investigated.

Effects of flame retardants on ovarian function

Flame retardants have been added to a variety of consumer products and are now found ubiquitously throughout the environment. Epidemiological, in vivo, and in vitro studies have shown that polybrominated diphenyl ether (PBDE) flame retardants may have a negative impact on human health; this has resulted in their phase-out and replacement by alternative flame retardants, such as hexabromocyclododecane (HBCDD), tetrabromobisphenol A (TBBPA), and organophosphate esters (OPEs). Evidence suggests that some of these chemicals induce ovarian dysfunction and thus may be detrimental to female fertility; however, the effects of many of these flame retardants on the ovary remain unclear. In this review, we present an overview of the effects of brominated and organophosphate ester flame retardants on ovarian function and discuss the possible mechanisms which may mediate these effects.

TBBPA, TBBPS, and TCBPA disrupt hESC hepatic differentiation and promote the proliferation of differentiated cells partly via up-regulation of the FGF10 signaling pathway

Halogenated flame retardants (HFRs), including Tetrabromobisphenol A (TBBPA), Tetrabromobisphenol S (TBBPS), and Tetrachlorobisphenol A (TCBPA), are widely applied in the manufacturing industry to improve fire safety and can be detected in pregnant women's serum at nanomolar levels. Thus, it is necessary to pay attention to the three HFR potential development toxicity, which has not been conclusively addressed yet. The liver is the main organ that detoxifies our body; TBBPA exposure may lead to increased liver weight in rodents. Therefore, in this study, we assessed the developmental hepatic toxicity of the three HFRs with a human embryonic stem cell hepatic differentiation-based system and transcriptomics analyses. We mostly evaluated lineage fate alterations and demonstrated the three HFRs may have common disruptive effects on hepatic differentiation, with TCBPA being significantly more potent. More specifically, the three HFRs up-regulated genes related to cell cycle and FGF10 signaling, at late stages of the hepatic differentiation. This indicates the three chemicals promoted hepatoblast proliferation likely via up-regulating the FGF10 cascade. At the same time, we also presented a powerful way to combine in vitro differentiation and in silico transcriptomic analyses, to efficiently evaluate hazardous materials' adverse effects on lineage fate decisions during early development.

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.

Bioaccumulation, physiological distribution, and biotransformation of tetrabromobisphenol a (TBBPA) in the geophagous earthworm Metaphire guillelmi - hint for detoxification strategy

The mechanisms underlying the bioaccumulation and detoxification of tetrabromobisphenol A (TBBPA) by terrestrial invertebrates are poorly understood. We used uniformly ring-¹⁴C-labelled TBBPA to investigate the bioaccumulation kinetics, metabolites distribution, and subsequent detoxification strategy of TBBPA in the geophagous earthworm Metaphire guillelmi in soil. The modeling of bioaccumulation kinetics showed a higher biota-soil-accumulation-factor of total ¹⁴C than that of the parent compound TBBPA, indicating that most of the ingested TBBPA was transformed into metabolites or sequestered as bound residues in the earthworms. Bound-residue formation in the digestive tract may hinder the accumulation of TBBPA in other parts of the body. Nonetheless, via the circulatory system, TBBPA was transferred to other tissues, especially the clitellum region, where sensitive organs are located. In the clitellum region, TBBPA was quickly transformed to less toxic dimethyl TBBPA ether and rapidly depurated through feces. We conclude that the detoxification of TBBPA in M. guillelmi occurred via bound-residue formation in the digestive tract as well as the generation and depuration of O-methylation metabolites. Our results provided direct evidence of TBBPA detoxification in earthworms. Further researches are needed to confirm whether O-methylation coupled with depuration is a common detoxification strategy for phenolic xenobiotics in other soil organisms needs to be determined.

Trans-generational effect of neurotoxicity and related stress response in Caenorhabditis elegans exposed to tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA), one of the most common brominated flame retardants, has been associated with immunotoxicity, neurotoxicity, and reproductive toxicity. However, little attention has been focused on understanding the trans-generational effects of TBBPA. The present study used the Caenorhabditis elegans (C. elegans) animal model to evaluate the trans-generational effects of neurotoxicity induced by environmentally relevant concentrations of TBBPA (0, 0.1, 1, 10, 100, and 1000 µg/L). Multiple indicators including physiological effects (body length, brood size, head thrashes, body bends, and crawling trajectory), degree of neuronal damage (dopamine, GABAergic, and glutamatergic neurons), oxidative stress-related biochemical indicators (superoxide dismutase [SOD] activity, catalase [CAT] enzyme, malondialdehyde [MDA] production, and reactive oxygen species [ROS] accumulation), and stress-related gene expressions have been evaluated in the exposed parental C. elegans generation (G₁) and their progeny (G₂) under TBBPA-free conditions. The results showed that TBBPA exposure induced adverse effects on physiological endpoints, among which body bends and head thrashes were the most sensitive ones, detected above 1 µg/L in G₁ and 100 µg/L in G₂ nematodes, respectively. After contaminant exposure, the three neurons revealed damage related to neurobehavioral endpoints, with no hereditary effects in the progeny. The oxidative stress-related biochemical endpoints demonstrated that when the exposure concentrations were above 1 µg/L in maternal worms, impairment can be detected in both generations, but the progeny recovered at low toxicity concentration (1-100 µg/L). The integrated target gene expression profiles were clearly altered in G₁ and G₂ worms at concentrations between 1 and 1000 µg/L, and a more significant difference existed in two generations of nematodes at low levels (1-10 µg/L) of TBBPA. Studing trans-generational neurotoxicity and the underlying mechanism can generate a precise evaluation of the environmental risk of TBBPA.

Tetrabromobisphenol A Promotes the Osteoclastogenesis of RAW264.7 Cells Induced by Receptor Activator of NF-kappa B Ligand In Vitro

BACKGROUND

Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame-retardants, is a representative persistent organic pollutants group. Studies on TBBPA toxicity have been conducted using various target cells; however, few studies have investigated TBBPA toxicity in bone cells. Therefore, this study investigated the in vitro effects of TBBPA on osteoclasts, a cell type involved in bone metabolism.

METHODS

RAW264.7 cells were cultured in medium containing 50 ng/mL receptor activator of nuclear factor kappa B ligand (RANKL) and varying concentrations of TBBPA. To evaluate the effects of TBBPA on the differentiation and function of osteoclasts, osteoclast-specific gene expression, tartrate-resistant acid phosphatase (TRAP) activity, bone resorbing activity, mitochondrial membrane potential (MMP) and mitochondrial superoxide were measured.

RESULTS

The presence of 20 μ TBBPA significantly increased TRAP activity in RANKL-stimulated RAW264.7 cells, the bone resorbing activity of osteoclasts, and the gene expression of Akt2, nuclear factor of activated T-cells cytoplasmic 1, and chloride channel voltage-sensitive 7. However, TBBPA treatment caused no change in the expression of carbonic anhydrase II, cathepsin K, osteopetrosis-associated transmembrane protein 1, Src, extracellular signal-related kinase, GAB2, c-Fos, or matrix metalloproteinase 9. Furthermore, 20 μ TBBPA caused a significant decrease in MMP and a significant increase in mitochondrial superoxide production.

CONCLUSION

This study suggests that TBBPA promotes osteoclast differentiation and activity. The mechanism of TBBPA-stimulated osteoclastogenesis might include increased expression of several genes involved in osteoclast differentiation and reactive oxygen species production.

Tetrabromobisphenol A: Disposition, kinetics and toxicity in animals and humans

Tetrabromobisphenol A (TBBPA) is a nonregulated brominated flame retardant with a high production volume, and it is applied in a wide variety of consumer products. TBBPA is ubiquitous in abiotic matrices, wildlife and humans around the world. This paper critically reviews the published scientific data concerning the disposition, metabolism or kinetics and toxicity of TBBPA in animals and humans. TBBPA is rapidly absorbed and widely distributed among tissues, and is excreted primarily in the feces. In rats, TBBPA and its metabolites have limited systemic bioavailability. TBBPA has been detected in human milk in the general population. It is available to both the developing fetus and the nursing pups following maternal exposure. It has been suggested that TBBPA causes acute toxicity, endocrine disruptor activity, immunotoxicity, neurotoxicity, nephrotoxicity, and hepatotoxicity in animals. Cell-based assays have shown that TBBPA can induce reactive oxygen species in a concentration-dependent manner, and it promotes the production of inflammatory factors such as TNF α, IL-6, and IL-8. Cells exposed to high levels of TBBPA exhibit seriously injured mitochondria and a dilated smooth endoplasmic reticulum. This review will enhance the understanding of the potential risks of TBBPA exposure to ecological and human health.

Inhibition of growth in juvenile manila clam Ruditapes philippinarum: Potential adverse outcome pathway of TBBPA

Tetrabromobisphenol A (TBBPA) is ubiquitous and its contents showing an increasing trend in the coastal environment. In order to investigate the effects of TBBPA on marine bivalves, juvenile manila clams Ruditapes phillipinarum were exposed to TBBPA for 28 days. The results showed that shell growth rate of juvenile clams after exposure to 62.5-1000 μg L^-1 TBBPA for 28 d were significantly inhibited (p < 0.05). Then in order to link the changes in filtration rate, mRNA expression of insulin-like growth factor homologue (IGF) and tissue thyroid hormone (TH) contents to growth, juvenile clams were exposed to 62.5 and 500 μg L^-1 TBBPA for 14 days. The transcriptional levels of neuroendocrine signals (NPF and insulin homologue) associated with filter feeding regulation, and genes of TH synthesis-related enzymes were also examined. The results showed that filtration rates was significantly reduced to 44.1% and 14% of controls after 14 d of exposure. In parallel, exposure to TBBPA significantly increased the expression levels of insulin which may elicit the filter feeding inhibition. TBBPA exposure caused alterations in tissue content of THs and mRNA expression of TH synthesis-related enzymes. However, the data showed increased T₃ content, T₃/T₄ ratio and mRNA expression of IGF. These data demonstrated that the most important key event of TBBPA could be linked to growth impairment in juveniles was the reduction of filtration rate. These results provide a robust framework towards revealing the underlying mechanism of the growth inhibition caused by TBBPA on bivalves and understanding the adverse outcome pathway across taxonomic phyla.

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.

Biodegradation of tetrabromobisphenol A in the sewage sludge process

Anaerobic sewage sludge capable of rapidly degrading tetrabromobisphenol A (TBBPA) was successfully acclimated in an anaerobic reactor over 280days. During the period from 0 to 280days, the TBBPA degradation rate (DR), utilization of glucose, and VSS were monitored continuously. After 280days of acclimation, the TBBPA DR of active sludge reached 96.0% after 20days of treatment in batch experiments. Based on scanning electron microscopy (SEM) observations and denaturing gradient gel electrophoresis (DGGE) determinations, the diversity of the microorganisms after 0 and 280days in the acclimated anaerobic sewage sludge was compared. Furthermore, eleven metabolites, including 2-bromophenol, 3-bromophenol, 2,4-dibromophenol, 2,6-dibromophenol, tribromophenol and bisphenol A, were identified by gas chromatography-mass spectrometry (GC-MS). Moreover, the six primary intermediary metabolites were also well-degraded by the acclimated anaerobic sewage sludge to varying degrees. Among the six target metabolites, tribromophenol was the most preferred substrate for biodegradation via debromination. These metabolites degraded more rapidly than monobromide and bisphenol A. The biodegradation data of the intermediary metabolites exhibited a good fit to a pseudo-first-order model. Finally, based on the metabolites, metabolic pathways were proposed. In conclusion, the acclimated microbial consortia degraded TBBPA and its metabolites well under anaerobic conditions.

Altered expression of genes involved in programmed cell death in primary cultured rat cerebellar granule cells acutely challenged with tetrabromobisphenol A

In the present study, primary cultures of rat cerebellar granule cells (CGC) and the RT² Profiler PCR array were used to examine the effect of acutely applied brominated flame retardant tetrabromobisphenol A (TBBPA) on the expression of 84 genes related to the main modes of programmed cell death. CGC, at the 7th day of culture, were exposed to 10 or 25μM TBBPA for 30min. Then, 3, 6, and 24h later, the viability of the cells was examined by the staining with propidium iodide (PI) or using the calcein/ethidium homodimer (CA/ET) live/dead kit, and RNA was extracted for the evaluation of gene expression by RT-PCR. At 3, 6 and 24h after the treatment, the number of viable neurons decreased, according to the PI staining method, to 75%, 58% and 41%, respectively, and with the CA/ET method to 65%, 58% and 28%, respectively. In CGC analyzed 3h after the treatment with 25μM TBBPA or 6h after 10μM TBBPA, the only change in the gene expression was a reduction in the expression of Tnf, which is associated with autophagy and may activate some pro-apoptotic proteins. Six hours after 25μM TBBPA, only 2 genes were over-expressed, a pro-apoptotic Tnfrsf10b and Irgm, which is related to autophagy, and the genes that were suppressed included the anti-apoptotic gene Xiap, the necrosis-related Commd4, pro-apoptotic Abl1, 5 genes involved in autophagy (App, Atg3, Mapk8, Pten, and Snca) and 2 genes that participate in two metabolic pathways: Atp6v1g2 (pro-apoptotic and necrosis) and Tnf (pro-apoptotic, autophagy). Autophagy-related Snca and Tnf remained under-expressed 24h after treatment with 25μM TBBPA, which was accompanied by the over-expression of the pro-apoptotic Casp6, the anti-apoptotic Birc3, 2 genes related to autophagy (Htt and Irgm) and 2 genes (Fas and Tp53) that are involved in both apoptosis (pro-apoptotic) and autophagy. These results show a complex pattern of TBBPA-evoked changes in the expression of the genes involved in the programmed neuronal death, indicating no induction of programmed necrosis, an early suppression of the autophagy and anti-apoptotic genes, followed by a delayed activation of genes associated with apoptosis.

In vivo assessment of dermal adhesion, penetration, and bioavailability of tetrabromobisphenol A

Individuals are exposed to brominated flame retardants (BFRs), including tetrabromobisphenol A (TBBPA), on a daily basis because of their widespread usage. These compounds may have adverse effects on human health. In the present study, dermal absorption experiments were conducted in vivo to predict the adhesion, penetration, and bioavailability of TBBPA. TBBPA was administered to Wistar rats for 6 h by repeated dermal exposure at doses of 20, 60, 200, and 600 mg of TBBPA per kg of body weight (bw). The skin adhesion coefficient (AC) was calculated using a difference-value method and ranged from 0.12 to 3.25 mg/cm² and 0.1 to 2.56 mg/cm² for the male and female rats, respectively. The adhesion rate was 70.92%. According to Fick's first law of diffusion, the diffusion constant (D) was 1.4 × 10^-4 cm²/h and the permeation coefficient (K_p) was 1.26 × 10^-5 cm/h for TBBPA. TBBPA levels in the blood, urine, and feces of the male rats were significantly higher than those in the female rats. The dermal bioavailability of TBBPA was 24.71% for male rats and 20.05% for female rats 24 h after exposure.

Exposure to tetrabromobisphenol A induces cellular dysfunction in osteoblastic MC3T3-E1 cells

This study was undertaken to investigate the possible involvement of oxidative stress in tetrabromobisphenol A (TBBPA)-induced toxicity in osteoblastic MC3T3-E1 cells. To examine the potential effect of TBBPA on cultured osteoblastic cells, we measured cell viability, apoptosis, reactive oxygen species (ROS), mitochondrial superoxide, and mitochondrial parameters including adenosine triphosphate (ATP) level, cardiolipin content, cytochrome c release, cyclophilin levels, and differentiation markers in osteoblastic MC3T3-E1 cells. TBBPA exposure for 48 h caused the apoptosis and cytotoxicity of MC3T3-E1 cells. TBBPA also induced ROS and mitochondrial superoxide production in a concentration-dependent manner. These results suggest that TBBPA induces osteoblast apoptosis and ROS production, resulting in bone diseases. Moreover, TBBPA induced cardiolipin peroxidation, cytochrome c release, and decreased ATP levels which induced apoptosis or necrosis. TBBPA decreased the differentiation markers, collagen synthesis, alkaline phosphatase activity, and calcium deposition in cells. Additionally, TBBPA decreased cyclophilin A and B releases. Taken together, these data support the notion that TBBPA inhibits osteoblast function and has detrimental effects on osteoblasts through a mechanism involving oxidative stress and mitochondrial dysfunction.

Excretion characteristics of tetrabromobisphenol-A in Wistar rats following mouth and nose inhalation exposure

Tetrabromobisphenol-A (TBBPA), a brominated flame retardant with the largest production volume worldwide, is employed as a reactive and additive flame retardant, and also as an intermediate in the production of other retardants. The constant release of TBBPA into the environment has attracted increasing attention to its potent health effects. To date, the vast majority of health-related research on TBBPA has focused on oral exposure. This study aims to explore the excretion characteristics of TBBPA in living organisms following inhalation exposure. An inhalation exposure system was established in which the experimental animal model was exposed to inhalable particles (diameter < 10 μm) of TBBPA. The TBBPA aerosol doses used were 12.9, 54.6, 121.6, and 455.0 mg/m³ according to tuning system parameters. Following 14 d (2 h/d) of repeated inhalational exposure, the primary route of elimination was in feces for all exposed groups, and the values showed a significant positive linear relationship with exposure dose. In contrast, the elimination amount in urine was less than 0.4% of the inhaled dose. Trace levels of TBBPA (less than 0.1% of the inhaled dose) were also detected in serum, with amounts varying from 0 to 844 ng (per rat) among all groups.

Whole-body aerosol exposure of cadmium chloride (CdCl2) and tetrabromobisphenol A (TBBPA) induced hepatic changes in CD-1 male mice

Cadmium (Cd) and tetrabromobisphenol A (TBBPA) are two prevalent contaminants in e-waste recycling facilities. However, the potential adversely health effect of co-exposure to these two types of pollutants in an occupational setting is unknown. In this study, we investigated co-exposure of these two pollutants on hepatic toxicity in CD-1 male mice through a whole-body aerosol inhalation route. Specifically, mice were exposed to solvent control (5% DMSO), Cd (8μg/m(3)), TBBPA (16μg/m(3)) and Cd/TBBPA mixture for 8h/day and 6days a week for 60 days. Hepatic changes include increased organ weight, focal necrosis, and elevated levels of liver enzymes in serum. These changes were most severe in mice exposed to TBBPA, followed by Cd/TBBPA mixture and Cd. These chemicals also led to suppressed antioxidant defensive mechanisms and increased oxidative stress. Further, these chemicals induced gene expression of apoptosis-related genes, activated genes encoding for phase I detoxification enzymes and inhibited genes encoding for phase II detoxification enzymes. These findings indicate that the hepatic damages induced by subchronic aerosol exposure of Cd and TBBPA may result from the oxidative damages caused by excessive ROS production when these chemicals were metabolized in the liver.

Characterization and Adaptation of Anaerobic Sludge Microbial Communities Exposed to Tetrabromobisphenol A

The increasing occurrence of tetrabromobisphenol A (TBBPA) in the environment is raising questions about its potential ecological and human health impacts. TBBPA is microbially transformed under anaerobic conditions to bisphenol A (BPA). However, little is known about which taxa degrade TBBPA and the adaptation of microbial communities exposed to TBBPA. The objectives of this study were to characterize the effect of TBBPA on microbial community structure during the start-up phase of a bench-scale anaerobic sludge reactor, and identify taxa that may be associated with TBBPA degradation. TBBPA degradation was monitored using LC/MS-MS, and the microbial community was characterized using Ion Torrent sequencing and qPCR. TBBPA was nearly completely transformed to BPA via reductive debromination in 55 days. Anaerobic reactor performance was not negatively affected by the presence of TBBPA and the bulk of the microbial community did not experience significant shifts. Several taxa showed a positive response to TBBPA, suggesting they may be associated with TBBPA degradation. Some of these taxa had been previously identified as dehalogenating bacteria including Dehalococcoides, Desulfovibrio, Propionibacterium, and Methylosinus species, but most had not previously been identified as having dehalogenating capacities. This study is the first to provide in-depth information on the microbial dynamics of anaerobic microbial communities exposed to TBBPA.

Absorption and excretion of Tetrabromobisphenol A in male Wistar rats following subchronic dermal exposure

Tetrabromobisphenol A (TBBPA) is widely used as a flame retardant and frequently detected in environmental and biological samples. In this study, male Wistar rats were repeatedly exposed by dermal application to 20, 60, 200 and 600 mg TBBPA/kg body weight during 90 days. Concentrations of TBBPA in serum, urine and feces after dermal exposure were determined. TBBPA concentrations in serum ranged from 19.04 to 427.20 g/g lipids. The percentage of TBBPA dose recovered in serum on the 90th day varied from 0.002 ± 0.002% to 0.013 ± 0.008%, and the percentage of dose excreted in urine varied from 0.004 ± 0.002% to 0.072 ± 0.027%, while the percentage of dose recovered in feces were 3.30 ± 0.61% to 11.13 ± 3.16%. The results showed that about 3.31-11.21% TBBPA was absorbed dermally under different dosing regimens. TBBPA was excreted mainly in feces and small only amounts were recovered in urine.

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.

Facilitation of adipocyte differentiation of 3T3-L1 cells by debrominated tetrabromobisphenol A compounds detected in Japanese breast milk

Tetrabromobisphenol A (TeBBPA) is widely used type of brominated flame retardant. In this study, we newly synthesized materials for the debrominated congeners, 2,2',6-tribromobisphenol A (TriBBPA), 2,2'-dibromobisphenol A (2,2'-DiBBPA), 2,6-dibromobisphenol A (2,6-DiBBPA), and 2-monobromobisphenol A (MoBBPA) and evaluated the actual extent of contamination with bisphenol A (BPA), TeBBPA and debrominated congeners in Japanese breast milk samples. TriBBPA was detected at higher levels than that of TeBBPA, while DiBBPA and MoBBPA were detected at lower levels than that of TeBBPA. This observation suggested that humans are exposed to debrominated congeners, which might cause adverse effects. Contamination of the congeners in breast milk was concern about risk infant health, having vulnerable defense system. As pilot study by in vitro experiment, we assessed the toxic potency of debrominated congeners by studying their effect on adipocyte differentiation in 3T3-L1 cells. We observed 2,6-DiBBPA, TriBBPA and TeBBPA elevated the lipid accumulation and adipocyte-specific protein 2 expression in a manner dependent on the number of substituted bromines. Moreover, PPARγ transcriptional activities increased in a dose-dependent manner in the presence of 2,6-DiBBPA and TriBBPA as well as TeBBPA. Our study clarified that TeBBPA and its debrominated congeners accumulated in breast milk and the debrominated congeners promoted adipocyte differentiation, showing that a comprehensive evaluation of the influences of these compounds including the debrominated congeners of TeBBPA on health in infants is necessary.

Heterologous antigen selection of camelid heavy chain single domain antibodies against tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA) is a ubiquitous flame retardant. A high-throughput immunoassay would allow for monitoring of human and environmental exposures as a part of risk assessment. Naturally occurring antibodies in camelids that are devoid of light chain, show great promise as an efficient tool in monitoring environmental contaminants, but they have been rarely used for small molecules. An alpaca was immunized with a TBBPA hapten coupled to thyroglobulin and a variable domain of heavy chain antibody (VHH) T3-15 highly selective for TBBPA was isolated from a phage displayed VHH library using heterologous coating antigens. Compared to the VHHs isolated using homologous antigens, VHH T3-15 had about a 10-fold improvement in sensitivity in an immunoassay. This assay, under the optimized conditions of 10% methanol in the assay buffer (pH 7.4), had an IC50 for TBBPA of 0.40 ng mL(-1) and negligible cross reactivity (<0.1%) with other tested analogues. After heating the VHH at 90 °C for 90 min about 20% of the affinity for coating antigen T3-BSA remained. The recoveries of TBBPA from spiked soil and fetal bovine serum samples ranged from 90.3% to 110.7% by ELISA and agreed well with a liquid chromatography-tandem mass spectrometry method. We conclude the many advantages of VHH make them attractive for the development of immunoassays to small molecules.

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.

16S ribosomal DNA clone libraries to reveal bacterial diversity in anaerobic reactor-degraded tetrabromobisphenol A

Microorganisms able to rapidly degrade tetrabromobisphenol A (TBBPA) were domesticated in an anaerobic reactor and added to gradually increased concentrations of TBBPA. After 240 days of domestication, the degradation rate reached 96.0% in cultivated batch experiments lasting 20 days. The optimum cultivating temperature and pH were 30°C and 7.0. The bacterial community's composition and diversity in the reactor was studied by comparative analysis with 16S ribosomal DNA clone libraries. Amplified rDNA restriction analysis of 200 clones from the library indicate that the rDNA richness was high (Coverage C 99.5%) and that evenness was not high (Shannon-Weaver index 2.42). Phylogenetic analysis of 63 bacterial sequences from the reactor libraries demonstrated the presence of Betaproteobacteria (33.1%), Gammaproteobacteria (18.7%), Bacteroidetes (13.9%), Firmicutes (11.4%), Chloroflexi (3.6%), Actinobacteria (0.6%), the candidate division TM7 (4.2%) and other unknown, uncultured bacterial groups (14.5%). Comamonas, Achromobacter, Pseudomonas and Flavobacterium were the dominant types.

The obesogen hypothesis: a shift of focus from the periphery to the hypothalamus

The obesogen concept proposes that environmental contaminants may be contributing to the epidemic of obesity and its related pathology, metabolic disorder. The first references to such a notion appeared at the beginning of the current decade, with the hypothesis that the correlation between increasing incidence of obesity and enhanced industrial chemical production was not simply coincidental, but potentially causally related. The next event was the introduction of the term "obesogen" as representing an environmental pollutant that adversely affects various aspects of adipose tissue functions. More recently, the concept was extended to include substances that may modify metabolic balance at the central, hypothalamic level. The actions of two prime candidate obesogens, tributyltin (TBT) and tetrabromobisphenol A (TBBPA), acting at the central level are the main focus of this review. Having discussed the evidence for contaminant accumulation in the environment and in human tissues and the potential mechanisms of action, data are provided showing that these two widespread pollutants modify hypothalamic gene regulations. Our studies are based on maternal exposure and measurement of effects in the progeny, mainly based on in vivo gene reporter assays. Such models are obviously pertinent to testing current hypotheses that propose that early exposure might exert effects on later development and physiological functions. The potential molecular mechanisms involved are discussed, as are the broader physiological consequences of these hypothalamic dysregulations.

Proteomic studies in zebrafish liver cells exposed to the brominated flame retardants HBCD and TBBPA

Proteomic effect screening in zebrafish liver cells was performed to generate hypotheses regarding single and mixed exposure to the BFRs HBCD and TBBPA. Responses at sublethal exposure were analysed by two-dimensional gel electrophoresis followed by MALDI-TOF and FT-ICR protein identification. Mixing of HBCD and TBBPA at sublethal doses of individual substances seemed to increase toxicity. Proteomic analyses revealed distinct exposure-specific and overlapping responses suggesting novel mechanisms with regard to HBCD and TBBPA exposure. While distinct HBCD responses were related to decreased protein metabolism, TBBPA revealed effects related to protein folding and NADPH production. Overlapping responses suggest increased gluconeogenesis (GAPDH and aldolase) while distinct mixture effects suggest a pronounced NADPH production and changes in proteins related to cell cycle control (prohibitin and crk-like oncogene). We conclude that mixtures containing HBCD and TBBPA may result in unexpected effects highlighting proteomics as a sensitive tool for detecting and hypothesis generation of mixture effects.

Modifying effects of prepubertal exposure to potassium perchlorate and tetrabromobisphenol A on susceptibility to N-bis(2-hydroxypropyl)nitrosamine- and 7,12-dimethylbenz(a)anthracene-induced carcinogenesis in rats

Early life exposure to certain kinds of chemicals is of concern because of a possible increase in cancer risk, but relevant data are limited. In the present experiment, modifying effects of prepubertal administration of potassium perchlorate (KClO(4)) and tetrabromobisphenol A (TBBPA) on susceptibility to multi-organ carcinogenesis were evaluated. F344 dam rats were administered 0% (control), 0.01%, 0.1% or 1% TBBPA in diet or 0.01% KClO(4) in drinking water after parturition. Their weaned offspring in each group were treated for 2 weeks in the same manner. From 6 weeks of age, all offspring were treated with N-bis(2-hydroxypropyl)nitrosamine in drinking water for 4 weeks. In addition the females at 7 weeks of age were gavaged once with 7,12-dimethylbenz(a)anthracene. At weeks 39 and 47 of age, the males and females, respectively, were euthanized and the liver, kidney, lung, esophagus, thyroid, urinary bladder, testis, epididymis, ovary and mammary gland were histopathologically examined. The incidences of thyroid follicular adenomas in 1% TBBPA females (p<0.05) and of transitional cell papillomas in the urinary bladder of 0.01%, 0.1% and 1% TBBPA females were increased (p<0.05) as compared to the controls. These results indicate that prepubertal exposure to TBBPA raises susceptibility to thyroid and urinary bladder tumorigenesis in rats. Although causes of the effect on thyroid carcinogenesis might be direct and/or indirect hormonal actions, further studies are needed for confirmation.

Perinatal exposure to brominated flame retardants and polychlorinated biphenyls in Japan

Brominated flame retardants (BFRs) are used to prevent combustion in consumer products. Examples of BFRs are polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), and tribromophenol (TBP). These compounds are reported to have adverse effects on human health and endocrine disrupting effects. The purpose of this study was to identify the Japanese perinatal exposure to PBDEs, hydroxylated PBDE metabolites (OH-PBDEs), TBBPA, and TBP compared with polychlorinated biphenyls (PCBs) and hydroxylated PCB metabolites (OH-PCBs). We investigated the concentrations of these compounds in maternal blood, maternal milk, cord blood, and umbilical cords from 16 Japanese mother-infant pairs by HRGC/HRMS. PBDEs were detected in all samples of maternal blood (mean+/-SD; median=25+/-23 pg/g; 18 pg/g wet weight), maternal milk (140+/-220 pg/g; 59 pg/g wet weight), cord blood (4.8+/-6.5 pg/g; 1.6 pg/g wet weight), and umbilical cords (3.1+/-3.1 pg/g; 2.1 pg/g wet weight). The mothers were divided into two groups, a high-concentration group and a low-concentration group. The percentage of BDE-47 showed the greatest difference between the two groups. 6-OH-BDE-47, TBBPA, and TBP were detected in all umbilical cord samples (mean+/-SD; median=8.4+/-8.1 pg/g; 8.0 pg/g, 16+/-5.5 pg/g; 15 pg/g, and 33+/-8.2 pg/g; 32 pg/g wet weight respectively), but not in all maternal blood or cord blood samples. These results indicate that OH-PBDEs, TBBPA, and TBP, in addition to PBDEs, PCBs, and OH-PCBs, pass through the blood-placenta barrier and are retained in the umbilical cord.