Absence of neurotoxicity and lack of neurobehavioral consequences due to exposure to tetrabromobisphenol A (TBBPA) exposure in humans, animals and zebrafish

The role of FAM171A2-GRN-NF-κB pathway in TBBPA induced oxidative stress and inflammatory response in mouse-derived hippocampal neuronal HT22 cells

Tetrabromobisphenol A (TBBPA) is one of the brominated flame retardants (BFRs) widely used in industry, which has a broad toxic effect on organisms. However, there is still limited research on the neurotoxic mechanism of TBBPA. Using mouse hippocampal neurons (HT22) cells, the toxicity of TBBPA was evaluated, especially focusing on its alteration on the key molecules in FAM171A2-GRN-NF-κB signaling pathway. The results showed that TBBPA exposure could lead to an increase in the production of inflammation-related genes IL-6, iNOS, TGF-β1, COX2, and TNF-α in both HT22 cells and HT22-AD-model, intensifying the inflammatory response; it inhibits the mRNA expression of antioxidative enzymes genes Sod1, Cat, Gpx1, and Gsta1, resulting in reduced antioxidant enzyme activities of SOD, CAT, and GSH-Px/GPX. Mechanistically, TBBPA caused the upregulation of FAM171A2 expression level, alongside increased GRN, IκBα and p65 levels; whereas the expression of GRN, IκBα and p65 was decreased after FAM171A2 knockdown, demonstrating TBBPA-induced upregulation of FAM171A2 should be responsible for the increased GRN, IκBα and p65 expression. Therefore, for the first time, our data indicate that TBBPA-induced oxidative stress and inflammatory response is closely related to the FAM171A2-GRN-NF-κB pathway.

Molecular mechanisms of tetrabromobisphenol A (TBBPA) toxicity: Insights from various biological systems

Tetrabromobisphenol A (TBBPA) is a ubiquitous brominated flame retardant extensively incorporated into a wide range of products. As its utilization has escalated, its environmental exposure risks have concomitantly increased. The molecular properties of TBBPA allow it to persist in the environment and within organisms. In this review, we comprehensively examine the toxicity of TBBPA across different organ systems and elucidate the underlying molecular mechanisms. We particularly emphasize TBBPA's impact on biological signaling pathways, protein functionality, cellular architecture, and epigenetic regulation, which collectively lead to disruptions in endocrine, hepatic, neurological, reproductive, and other biological systems. The analysis of these toxicological phenomena and their fundamental molecular mechanisms has substantially enhanced our understanding of TBBPA's hazardous characteristics. This review also examines potential avenues for future research, with a focus on uncovering novel molecular mechanisms and assessing the toxicological impacts of TBBPA exposure, particularly in relation to interactions with other environmental contaminants. We propose a greater focus on examining the toxic effects and molecular mechanisms of long-term TBBPA exposure at environmentally relevant concentrations to facilitate more accurate assessments of human health risks.

Insights into brominated flame retardant neurotoxicity: mechanisms of hippocampal neural cell death and brain region-specific transcriptomic shifts in mice

Brominated flame retardants (BFRs) reduce flammability in a wide range of products including electronics, carpets, and paint, but leach into the environment to result in continuous, population-level exposure. Epidemiology studies have correlated BFR exposure with neurological problems, including alterations in learning and memory. This study investigated the molecular mechanisms mediating BFR-induced cell death in hippocampal cells and clarified the impact of hexabromocyclododecane (HBCD) exposure on gene transcription in the hippocampus, dorsal striatum, and frontal cortex of male mice. Exposure of hippocampus-derived HT-22 cells to various flame retardants, including tetrabromobisphenol-A (current use), HBCD (phasing out), or 2,2',4,4'-tetrabromodiphenyl ether (BDE-47, phased out) resulted in time, concentration, and chemical-dependent cellular and nuclear morphology alterations, alterations in cell cycle and increases in annexin V staining. All 3 BFRs increased p53 and p21 expression; however, inhibition of p53 nuclear translocation using pifthrin-α did not decrease cell death. Transcriptomic analysis upon low (10 nM) and cytotoxic (10 μM) BFR exposure indicated that HBCD and BDE-47 altered genes mediating autophagy-related pathways. Further evaluation showed that BFR exposure increased LC3-II conversion and autophagosome/autolysosome formation, and co-exposure with the autophagy inhibitor 3-methyladenine (3-MA) attenuated cytotoxicity. Transcriptomic assessment of select brain regions from subchronically HBCD-exposed male mice demonstrated alteration of genes mediating vesicular transport, with greater impact on the frontal cortex and dorsal striatum compared with the dorsal and ventral hippocampus. Immunoblot analysis demonstrated no increases in cell death or autophagy markers, but did demonstrate increases in the SNARE binding complex protein SNAP29, specifically in the dorsal hippocampus. These data demonstrate that BFRs can induce chemical-dependent autophagy in neural cells in vitro and provide evidence that BFRs induce region-specific transcriptomic and protein expression in the brain suggestive of changes in vesicular trafficking.

Two novel in vitro assays to screen chemicals for their capacity to inhibit thyroid hormone transmembrane transporter proteins OATP1C1 and OAT4

Early brain development depends on adequate transport of thyroid hormones (THs) from the maternal circulation to the fetus. To reach the fetal brain, THs have to cross several physiological barriers, including the placenta, blood-brain-barrier and blood-cerebrospinal fluid-barrier. Transport across these barriers is facilitated by thyroid hormone transmembrane transporters (THTMTs). Some endocrine disrupting chemicals (EDCs) can interfere with the transport of THs by THTMTs. To screen chemicals for their capacity to disrupt THTMT facilitated TH transport, in vitro screening assays are required. In this study, we developed assays for two THTMTs, organic anion transporter polypeptide 1C1 (OATP1C1) and organic anion transporter 4 (OAT4), both known to play a role in the transport of THs across barriers. We used overexpressing cell models for both OATP1C1 and OAT4, which showed an increased uptake of radiolabeled T4 compared to control cell lines. Using these models, we screened various reference and environmental chemicals for their ability to inhibit T4 uptake by OATP1C1 and OAT4. Tetrabromobisphenol A (TBBPA) was identified as an OATP1C1 inhibitor, more potent than any of the reference chemicals tested. Additionally perfluorooctanesulfonic acid (PFOS), perfluoroctanic acid (PFOA), pentachlorophenol and quercetin were identified as OATP1C1 inhibitors in a similar range of potency to the reference chemicals tested. Bromosulfophthalein, TBBPA, PFOA and PFOS were identified as potent OAT4 inhibitors. These results demonstrate that EDCs commonly found in our environment can disrupt TH transport by THTMTs, and contribute to the identification of molecular mechanisms underlying TH system disruption chemicals.

Comparative toxicological assessment of 2 bisphenols using a systems approach: evaluation of the behavioral and transcriptomic responses of Danio rerio to bisphenol A and tetrabromobisphenol A

The zebrafish (Danio rerio) is becoming a critical component of new approach methods (NAMs) in chemical risk assessment. As a whole organism in vitro NAM, the zebrafish model offers significant advantages over individual cell-line testing, including toxicokinetic and toxicodynamic competencies. A transcriptomic approach not only allows for insight into mechanism of action for both apical endpoints and unobservable adverse outcomes, but also changes in gene expression induced by lower, environmentally relevant concentrations. In this study, we used a larval zebrafish model to assess the behavioral and transcriptomic alterations caused by subphenotypic concentrations of 2 chemicals with the same structural backbone, the endocrine-disrupting chemicals bisphenol A and tetrabromobisphenol A. Following assessment of behavioral toxicity, we used a transcriptomic approach to identify molecular pathways associated with previously described phenotypes. We also determined the transcriptomic point of departure for each chemical by modeling gene expression changes as continuous systems which allows for the identification of a single concentration at which toxic effects can be predicted. This can then be investigated with confirmatory cell-based testing in an integrated approach to testing and assessment to determine risk to human health and the environment with greater confidence. This paper demonstrates the impact of using a multi-faceted approach for evaluating the physiological and neurotoxic effects of exposure to structurally related chemicals. By comparing phenotypic effects with transcriptomic outcomes, we were able to differentiate, characterize, and rank the toxicities of related bisphenols, which demonstrates methodological advantages unique to the larval zebrafish NAM.

First insights into the bioaccumulation, biotransformation and trophic transfer of typical tetrabromobisphenol A (TBBPA) analogues along a simulated aquatic food chain

Tetrabromobisphenol A (TBBPA) analogues have been investigated for their prevalent occurrence in environments and potential hazardous effects to humans and wildlife; however, there is still limited knowledge regarding their toxicokinetics and trophic transfer in aquatic food chains. Using a developed toxicokinetic model framework, we quantified the bioaccumulation, biotransformation and trophic transfer of tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A di(allyl ether) (TBBPA-DAE) during trophic transfer from brine shrimp (Artemia salina) to zebrafish (Danio rerio). The results showed that the two TBBPA analogues could be readily accumulated by brine shrimp, and the estimated bioconcentration factor (BCF) value of TBBPS (5.68 L kg-1 ww) was higher than that of TBBPA-DAE (1.04 L kg-1 ww). The assimilation efficiency (AE) of TBBPA-DAE in zebrafish fed brine shrimp was calculated to be 16.3%, resulting in a low whole-body biomagnification factor (BMF) in fish (0.684 g g-1 ww). Based on the transformation products screened using ultra-high-performance liquid chromatograph-high resolution mass spectrometry (UPLC-HRMS), oxidative debromination and hydrolysis were identified as the major transformation pathways of TBBPS, while the biotransformation of TBBPA-DAE mainly took place through ether bond breaking and phase-II metabolism. Lower accumulation of TBBPA as a metabolite than its parent chemical was observed in both brine shrimp and zebrafish, with metabolite parent concentration factors (MPCFs) < 1. The investigated BCFs for shrimp of the two TBBPA analogues were only 3.77 × 10-10 - 5.59 × 10-3 times of the theoretical Kshrimp-water based on the polyparameter linear free energy relationships (pp-LFERs) model, and the BMF of TBBPA-DAE for fish was 0.299 times of the predicted Kshrimp-fish. Overall, these results indicated the potential of the trophic transfer in bioaccumulation of specific TBBPA analogues in higher trophic-level aquatic organisms and pointed out biotransformation as an important mechanism in regulating their bioaccumulation processes. ENVIRONMENTAL IMPLICATION: The internal concentration of a pollutant in the body determines its toxicity to organisms, while bioaccumulation and trophic transfer play important roles in elucidating its risks to ecosystems. Tetrabromobisphenol A (TBBPA) analogues have been extensively investigated for their adverse effects on humans and wildlife; however, there is still limited knowledge regarding their toxicokinetics and trophic transfer in aquatic food chains. This study investigated the bioaccumulation, biotransformation and trophic transfer of TBBPS and TBBPA-DAE in a simulated di-trophic food chain. This state-of-art study will provide a reference for further research on this kind of emerging pollutant in aquatic environments.

Convenient green synthesis of Cu/Fe nanoparticles using pomegranate peel extracts and their performance for tetrabromobisphenol A removal

In this work, pomegranate peel extracts were used as the green reducing agent to synthesize Cu/Fe nanoparticles (P-Cu/Fe nanoparticles) and removed tetrabromobisphenol A (TBBPA) in aqueous solution. P-Cu/Fe nanoparticles were amorphous and irregularly spherical. The surfaces of nanoparticles contained Fe0, Fe3+ oxides (hydroxides), and Cu0. The bioactive molecules from pomegranate peel were extremely important for the synthesis of nanoparticles. P-Cu/Fe nanoparticles had excellent removal performance for TBBPA, and 98.6% of TBBPA (5 mg L-1) was removed within 60 min. The removal reaction of TBBPA by P-Cu/Fe nanoparticles was well-fitted with the pseudo-first-order kinetic model. The Cu loading was critical for TBBPA removal with an optimum value of 1.0 wt%. A weakly acidic condition (pH 5) was more favorable for the removal of TBBPA. The removal efficiency of TBBPA increased with the rise of temperature and decreased with increasing initial TBBPA concentration. The activation energy (Ea) was 54.09 kJ mol-1, indicating that the removal of TBBPA by P-Cu/Fe nanoparticles was mainly surface-controlled. Reductive degradation was the main mechanism of TBBPA removal by P-Cu/Fe nanoparticles. In conclusion, green synthesized P-Cu/Fe nanoparticles using pomegranate peel waste show great potential for the remediation of TBBPA in aqueous solution.

Experimental models of chemically induced Parkinson's disease in zebrafish at the embryonic larval stage: a systematic review

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra that results in a decrease in dopamine levels, resulting in motor-type disturbances. Different vertebrate models, such as rodents and fish, have been used to study PD. In recent decades, Danio rerio (zebrafish) has emerged as a potential model for the investigation of neurodegenerative diseases due to its homology to the nervous system of humans. In this context, this systematic review aimed to identify publications that reported the utilization of neurotoxins as an experimental model of parkinsonism in zebrafish embryos and larvae. Ultimately, 56 articles were identified by searching three databases (PubMed, Web of Science, and Google Scholar). Seventeen studies using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 4 1-methyl-4-phenylpyridinium (MPP+), 24 6-hydroxydopamine (6-OHDA), 6 paraquat/diquat, 2 rotenone, and 6 articles using other types of unusual neurotoxins to induce PD were selected. Neurobehavioral function, such as motor activity, dopaminergic neuron markers, oxidative stress biomarkers, and other relevant parameters in the zebrafish embryo-larval model were examined. In summary, this review provides information to help researchers determine which chemical model is suitable to study experimental parkinsonism, according to the effects induced by neurotoxins in zebrafish embryos and larvae.

Microplastics induce neurotoxicity in aquatic animals at environmentally realistic concentrations: A meta-analysis

Microplastics (MPs) draw international attention owing to their widespread distribution in water ecosystems, but whether MPs cause neurotoxic effects in aquatic animals at environmentally realistic concentrations is still controversial. This meta-analysis recompiled 35 studies to determine whether MPs could change the levels of brain (in vivo) neurotransmitters in aquatic animals at environmentally realistic concentrations (≤1 mg/L, median = 0.100 mg/L). Then, a group comparison was conducted to compare the effects of different factors on the effect size and to explore the significant factors affecting the neurotoxicity of MPs. The results demonstrated that MP exposure could considerably decrease the levels of acetylcholinesterase (AchE) in the brain of aquatic animals by 16.2%. However, the effects of MPs on cholinesterase (CHE), acetylcholine (ACh), dopamine (DA) and γ-aminobutyric acid (GABA) were not statistically significant due to the small number of studies and samples. The neurotoxicity of MPs was closely linked with particle size and exposure time but independent of animal species, MP compositions, MP morphology and MP concentrations. Further literatures review indicated that MP-induced neurotoxicity and behavioral changes are related with multiple biological processes, including nerve damage, oxidative stress, intestinal flora disturbance and metabolic disorder. Furthermore, some factors influencing MP neurotoxicity in the real environment (e.g. the aging of MPs, the release of MP additives, and the co-exposure of MPs and pollutants) were discussed. Overall, this study preliminarily explored whether MPs induced changes in neurotoxicity-related indicators in aquatic animals through meta-analysis and provided scientific evidence for evaluating the health risks and neurotoxicity of MPs at the environmental level.

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.

High cytotoxicity of a degraded TBBPA, dibromobisphenol A, through apoptotic and necrosis pathways

Halogenated flame retardants comprising bisphenol A (BPA) derivatives, such as tetrabromobisphenol A (TBBPA), have been studied their adverse effects on human health. However, despite the fact that these halogenated BPAs are easily degraded in the environment, the risks to living organisms due to these degraded products have mostly been overlooked. To evaluate the potential toxicity of degraded TBBPAs and related compounds, we examined the cytotoxicity of halogenated bisphenol A derivatives possessing one to four halogen atoms in vitro. The results indicated that the degraded TBBPA derivatives exhibited strong cytotoxicity against HeLa cells than TBBPA. Interestingly, the di-halogenated BPA derivatives possessing two halogen atoms exhibited the strongest cytotoxicity among tested compounds. In addition, a lactate dehydrogenase release assay, fluorescence spectroscopy and flow cytometry results indicated that dibromo-BPA and diiodo-BPA induced both apoptotic and necrotic cell death by damaging the cell membranes of HeLa cells. Moreover, Escherichia coli growth was inhibited in the presence of dehalogenated TBBPA and related compounds. These findings suggest that halogenated BPA derivatives that leak from various flame-retardant-containing products require strict monitoring, as not only TBBPA but also its degraded products in environment can exert adverse effects to human health.

Photolytic degradation of novel polymeric and monomeric brominated flame retardants: Investigation of endocrine disruption, physiological and ecotoxicological effects

Ecotoxicological effects of photolytic degradation mixtures of the two brominated flame retardants PolymericFR and Tetrabromobisphenol A-bis (2,3-dibrom-2-methyl-propyl) Ether (TBBPA-BDBMPE) have been studied in vitro and in vivo. Both substances were experimentally degraded separately by exposure to artificial UV-light and the resulting degradation mixtures from different time points during the UV-exposure were applied in ecotoxicological tests. The in vitro investigation showed no effects of the degraded flame retardants on the estrogenic and androgenic receptors via the CALUX (chemically activated luciferase gene expression) assay. Short-term exposures (up to 96 h) of Lumbriculus variegatus lead to temporary physiological reactions of the annelid. The exposure to degraded PolymericFR lead to an increased activity of Catalase, while the degradation mixture of TBBPA-BDBMPE caused increases of Glutathione-S-transferase and Acetylcholine esterase activities. Following a chronic exposure (28 d) of L. variegatus, no effects on the growth, reproduction, fragmentation and energy storage of the annelid were detected. The results indicate that the experimental degradation of the two flame retardants causes changes in their ecotoxicological potential. This might lead to acute physiological effects on aquatic annelids, which, however, do not affect the animals chronically according to our results.

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.

Determination of Apoptotic Mechanism of Action of Tetrabromobisphenol A and Tetrabromobisphenol S in Human Peripheral Blood Mononuclear Cells: A Comparative Study

Background: Tetrabromobisphenol A (TBBPA) is the most commonly used brominated flame retardant (BFR) in the industry. TBBPA has been determined in environmental samples, food, tap water, dust as well as outdoor and indoor air and in the human body. Studies have also shown the toxic potential of this substance. In search of a better and less toxic BFR, tetrabromobisphenol S (TBBPS) has been developed in order to replace TBBPA in the industry. There is a lack of data on the toxic effects of TBBPS, while no study has explored apoptotic mechanism of action of TBBPA and TBBPS in human leukocytes. Methods: The cells were separated from leucocyte-platelet buffy coat and were incubated with studied compounds in concentrations ranging from 0.01 to 50 µg/mL for 24 h. In order to explore the apoptotic mechanism of action of tested BFRs, phosphatidylserine externalization at cellular membrane (the number of apoptotic cells), cytosolic calcium ion and transmembrane mitochondrial potential levels, caspase-8, -9 and -3 activation, as well as PARP-1 cleavage, DNA fragmentation and chromatin condensation in PBMCs were determined. Results: TBBPA and TBBPS triggered apoptosis in human PBMCs as they changed all tested parameters in the incubated cells. It was also observed that the mitochondrial pathway was mainly involved in the apoptotic action of studied compounds. Conclusions: It was found that TBBPS, and more strongly TBBPA, triggered apoptosis in human PBMCs. Generally, the mitochondrial pathway was involved in the apoptotic action of tested compounds; nevertheless, TBBPS more strongly than TBBPA caused intrinsic pathway activation.

Comparative Effects of Brominated Flame Retardants BDE-209, TBBPA, and HBCD on Neurotoxicity in Mice

Brominated flame retardants (BFRs) are ubiquitous industrial chemicals. In China, BFRs that are applied in large quantities include decabromodiphenyl ether (BDE-209), tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCD). Although findings are not always unequivocal, mounting evidence in vivo suggests that the BFRs have potential neurotoxicity. The present study aimed to assess and compare the neurotoxic effects of these three BFRs' exposure. Male mice were orally exposed to BDE-209, TBBPA, or HBCD at 50 and 100 mg/kg bw/day for 28 days. The cognitive behavior, oxidative stress (ROS, MDA, and GSH), apoptosis-related genes (caspase-3, bax, and bcl-2), memory-related proteins (BDNF and PSD-95), and neurotransmitters (AChE and ChAT) were detected comparatively. Results showed that high doses of BDE-209, TBBPA, and HBCD exposure impaired spatial memory of mice, elevated ROS and MDA and reduced GSH levels of hippocampus, upregulated caspase-3 and bax expressions, decreased BDNF and PSD-95 levels, and disordered AChE and ChAT levels. Notably, BDE-209 caused greater adverse effects > HBCD > TBBPA. This study confirms and extends that these three BFRs had similar neurotoxic effects at current concentrations, although they may be more or less toxic.

Environmentally relevant exposure to TBBPA and its analogues may not drastically affect human early cardiac development

Tetrabromobisphenol A (TBBPA) and its substitutes and derivatives have been widely used as halogenated flame retardants (HFRs), in the past few decades. As a consequence, these compounds are frequently detected in the environment, as well as human bodily fluids, especially umbilical cord blood and breast milk. This has raised awareness of their potential risks to fetuses and infants. In this study, we employed human embryonic stem cell differentiation models to assess the potential developmental toxicity of six TBBPA-like compounds, at human relevant nanomolar concentrations. To mimic early embryonic development, we utilized embryoid body-based 3D differentiation in presence of the six HFRs. Transcriptomics data showed that HFR exposure over 16 days of differentiation only interfered with the expression of a few genes, indicating those six HFRs may not have specific tissue/organ targets during embryonic development. Nevertheless, further analyses revealed that some cardiac-related genes were dysregulated. Since the heart is also the first organ to develop, we employed a cardiac differentiation model to analyze the six HFRs' potential developmental toxicity in more depth. Overall, HFRs of interest did not significantly disturb the canonical WNT pathway, which is an essential signal transduction pathway for cardiac development. In addition, the six HFRs showed only mild changes in gene expression levels for cardiomyocyte markers, such as NKX2.5, MYH7, and MYL4, as well as a significant down-regulation of some but not all the epicardial and smooth muscle cell markers selected. Taken together, our results show that the six studied HFRs, at human relevant concentrations, may impose negligible effects on embryogenesis and heart development. Nevertheless, higher exposure doses might affect the early stages of heart development.

Toxicity evaluation of traditional and organic yerba mate (Ilex paraguariensis A. St.-Hil.) extracts

Yerba mate (Ilex paraguariensis A. St.-Hil.) is an important source of biologically active compounds with pharmacological potential. The aim of this study was to examine the toxicity of different extracts obtained from either traditional or organic cultivated yerba mate in vitro and in vivo. Aqueous, ethanolic and methanolic extracts were obtained from commercial samples of yerba mate and total phenolic content was determined employing Folin-Ciocalteau reagent. The aqueous extracts presented higher content of total phenols, compared to ethanolic and methanolic extracts, and also demonstrated lower cytotoxicity, which is the basis for testing were carried out only using aqueous extracts. The main phenolic acids found in traditional aqueous (TA) extract were chlorogenic, gallic and protocatechuic acids. Gallic and hydroxybenzoic acids were detected in aqueous cultivated organic (OA) extract. Pretreatment with OA extract (100 µg/ml, 1 hr) was cytoprotective against rotenone-induced toxicity (1 µM). For in vivo toxicity assay, zebrafish embryos were exposed to OA or TA extracts (10-160 µg/ml) at 4 hr post fertilization. TA extract decreased embryos survival in a concentration-dependent manner, reduced the hatching rate at 40 µg/ml, increased edema frequency at 80 µg/ml and altered body curvature at 120 µg/ml. Further, TA extract produced locomotor disorders at concentrations equal to or greater than 10 µg/ml. In contrast, OA extract exhibited no apparent toxic effect on organogenesis and behavior up to 100 µg/ml. In summary, the OA cultivated extract showed the lowest cytotoxicity in vitro, enhanced reduction in rotenone-induced toxicity, and produced less toxicity in zebrafish embryos compared to the TA extract.

Metabolic transformation of environmentally-relevant brominated flame retardants in Fauna: A review

Over the past few decades, production trends of the flame retardant (FR) industry, and specifically for brominated FRs (BFRs), is for the replacement of banned and regulated compounds with more highly brominated, higher molecular weight compounds including oligomeric and polymeric compounds. Chemical, biological, and environmental stability of BFRs has received some attention over the years but knowledge is currently lacking in the transformation potential and metabolism of replacement emerging or novel BFRs (E/NBFRs). For articles published since 2015, a systematic search strategy reviewed the existing literature on the direct (e.g., in vitro or in vivo) non-human BFR metabolism in fauna (animals). Of the 51 papers reviewed, and of the 75 known environmental BFRs, PBDEs were by far the most widely studied, followed by HBCDDs and TBBPA. Experimental protocols between studies showed large disparities in exposure or incubation times, age, sex, depuration periods, and of the absence of active controls used in in vitro experiments. Species selection emphasized non-standard test animals and/or field-collected animals making comparisons difficult. For in vitro studies, confounding variables were generally not taken into consideration (e.g., season and time of day of collection, pollution point-sources or human settlements). As of 2021 there remains essentially no information on the fate and metabolic pathways or kinetics for 30 of the 75 environmentally relevant E/BFRs. Regardless, there are clear species-specific and BFR-specific differences in metabolism and metabolite formation (e.g. BDE congeners and HBCDD isomers). Future in vitro and in vivo metabolism/biotransformation research on E/NBFRs is required to better understand their bioaccumulation and fate in exposed organisms. Also, studies should be conducted on well characterized lab (e.g., laboratory rodents, zebrafish) and commonly collected wildlife species used as captive models (crucian carp, Japanese quail, zebra finches and polar bears).

Tetrabromobisphenol A Disturbs Brain Development in Both Thyroid Hormone-Dependent and -Independent Manners in Xenopus laevis

Although tetrabromobisphenol A (TBBPA) has been well proven to disturb TH signaling in both in vitro and in vivo assays, it is still unclear whether TBBPA can affect brain development due to TH signaling disruption. Here, we employed the T3-induced Xenopus metamorphosis assay (TIXMA) and the spontaneous metamorphosis assay to address this issue. In the TIXMA, 5-500 nmol/L TBBPA affected T3-induced TH-response gene expression and T3-induced brain development (brain morphological changes, cell proliferation, and neurodifferentiation) at premetamorphic stages in a complicated biphasic concentration-response manner. Notably, 500 nmol/L TBBPA treatment alone exerted a stimulatory effect on tadpole growth and brain development at these stages, in parallel with a lack of TH signaling activation, suggesting the involvement of other signaling pathways. As expected, at the metamorphic climax, we observed inhibitory effects of 50-500 nmol/L TBBPA on metamorphic development and brain development, which was in agreement with the antagonistic effects of higher concentrations on T3-induced brain development at premetamorphic stages. Taken together, all results demonstrate that TBBPA can disturb TH signaling and subsequently interfere with TH-dependent brain development in Xenopus; meanwhile, other signaling pathways besides TH signaling could be involved in this process. Our study improves the understanding of the effects of TBBPA on vertebrate brain development.

Tetrabromobisphenol A: a neurotoxicant or not?

Although some regulatory agencies have claimed that consumer exposures to tetrabromobisphenol A (TBBPA) are not likely to cause adverse health effects in humans or the environment, the safety of tetrabromobisphenol A (TBBPA) has been questioned. Here, we summarize the literature concerning in vivo and in vitro neurotoxicity of TBBPA over the past decades. Most laboratory rodent studies reported that gavage administration of TBBPA at doses below 1000 mg/kg/day generally exerted no or limited effects on neuropathology and locomotor behaviors, but increased anxiety and auditory impairments were observed in several studies. In fish and amphibians, waterborne exposure to TBBPA was generally reported to disrupt neurodevelopment and lead to neurobehavioral alterations. Moreover, in vitro studies support the observations that TBBPA could exert neurotoxic effects in vertebrates. Thus, we suggest that TBBPA could have adverse effects on the nervous system in vertebrates. Given rapid excretion and low availability of TBBPA in laboratory rodents following single gavage administration, we speculate that single-daily gavage could result in an underestimation of the neurotoxic effects of TBBPA in rodents. Thus, we propose to employ multiple-daily administration routes (such as dermal, inhalation, and drinking water), to further assess the neurotoxic effects of TBBPA in mammals.

Tetrabromobisphenol A induced reproductive endocrine-disrupting effects in mussel Mytilus galloprovincialis

Tetrabromobisphenol A (TBBPA) pollution in marine environmental media poses great risks to marine organisms due to its potential endocrine-disrupting effects. However, limited attention of TBBPA's endocrine-disrupting effects has been paid on marine invertebrates. In this work, the reproductive endocrine-disrupting effects of TBBPA were evaluated by observing the gametes development, quantifying the gender-specific gene expression, and determining vertebrate sex hormones in mussels Mytilus galloprovincialis treated with TBBPA for 30 days. Additionally, transcriptomic profiling and enzymes activities were conducted to investigate the potential mechanisms of reproductive endocrine-disrupting effects. We found that promotion of gametogenesis and alterations of vertebrate sex hormones occurred in TBBPA-treated mussels of both sexes. Meanwhile, estrogen sulfotransferase (SULT1E1) and steroid sulfatase (STS) were up-regulated at transcript level as a result of TBBPA treatments, suggesting that TBBPA disrupted the steroidogenesis in mussels through promoting steroids sulfonation and hydrolysis of sulfate steroids. The induction of SULTs for TBBPA biotransformation might be responsible for the dysregulation of steroidogenesis and steroids metabolism. Overall, these findings provide a new insight into assessing impact of TBBPA as well as TBBPA biomonitoring in marine environment.

Phenotypically Anchored mRNA and miRNA Expression Profiling in Zebrafish Reveals Flame Retardant Chemical Toxicity Networks

The ubiquitous use of flame retardant chemicals (FRCs) in the manufacture of many consumer products leads to inevitable environmental releases and human exposures. Studying toxic effects of FRCs as a group is challenging since they widely differ in physicochemical properties. We previously used zebrafish as a model to screen 61 representative FRCs and showed that many induced behavioral and teratogenic effects, with aryl phosphates identified as the most active. In this study, we selected 10 FRCs belonging to diverse physicochemical classes and zebrafish toxicity profiles to identify the gene expression responses following exposures. For each FRC, we executed paired mRNA-micro-RNA (miR) sequencing, which enabled us to study mRNA expression patterns and investigate the role of miRs as posttranscriptional regulators of gene expression. We found widespread disruption of mRNA and miR expression across several FRCs. Neurodevelopment was a key disrupted biological process across multiple FRCs and was corroborated by behavioral deficits. Several mRNAs (e.g., osbpl2a) and miRs (e.g., mir-125b-5p), showed differential expression common to multiple FRCs (10 and 7 respectively). These common miRs were also predicted to regulate a network of differentially expressed genes with diverse functions, including apoptosis, neurodevelopment, lipid regulation and inflammation. Commonly disrupted transcription factors (TFs) such as retinoic acid receptor, retinoid X receptor, and vitamin D regulator were predicted to regulate a wide network of differentially expressed mRNAs across a majority of the FRCs. Many of the differential mRNA-TF and mRNA-miR pairs were predicted to play important roles in development as well as cancer signaling. Specific comparisons between TBBPA and its derivative TBBPA-DBPE showed contrasting gene expression patterns that corroborated with their phenotypic profiles. The newer generation FRCs such as IPP and TCEP produced distinct gene expression changes compared to the legacy FRC BDE-47. Our study is the first to establish a mRNA-miR-TF regulatory network across a large group of structurally diverse FRCs and diverse phenotypic responses. The purpose was to discover common and unique biological targets that will help us understand mechanisms of action for these important chemicals and establish this approach as an important tool for better understanding toxic effects of environmental contaminants.

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.

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.

Bioconcentration and developmental neurotoxicity of novel brominated flame retardants, hexabromobenzene and pentabromobenzene in zebrafish

The flame retardants hexabromobenzene (HBB) and pentabromobenzene (PBB) have been extensively used and become ubiquitous pollutants in the aquatic environment and biota, but their potential toxic effects on wildlife remained unknown. In this study, by using zebrafish (Danio rerio) as a model, the bioconcentration and developmental neurotoxicity were investigated. Zebrafish embryos were exposed to HBB and PBB (0, 30, 100 and 300 μg/L) from 2 until 144 h post-fertilization (hpf). Chemical analysis showed bioconcentrations of both chemicals, while HBB is readily metabolized to PBB in zebrafish larvae. Embryonic exposure to both chemicals did not cause developmental toxicity, but induced locomotor behavioral anomalies in larvae. Molecular docking results indicated that both chemicals could bind to zebrafish acetylcholinesterase (AChE). Furthermore, HBB and PBB significantly inhibited AChE activities, accompanied by increased contents of acetylcholine and decreased choline in larvae. Downregulation of the genes associated with central nervous system (CNS) development (e.g., mbp, α1-tubulin, gfap, shha) as well as the corresponding proteins (e.g., Mbp, α1-Tubulin) was observed, but gap-43 was upregulated at both gene and protein levels. Together, our results indicate that both HBB and PBB exhibit developmental neurotoxicity by affecting various parameters related to CNS development and indications for future toxicological research and risk assessment of the novel brominated flame retardants.

Mitochondrial-related effects of pentabromophenol, tetrabromobisphenol A, and triphenyl phosphate on murine BV-2 microglia cells

The predominant reliance on bromated flame retardants (BFRs) is diminishing with expanded use of alternative organophosphate flame retardants. However, exposure related issues for susceptible populations, the developing, infirmed, or aged, remain given environmental persistence and home-environment detection. In this regard, reports of flame retardant (FR)-related effects on the innate immune system suggest process by which a spectrum of adverse health effects could manifest across the life-span. As representative of the nervous system innate immune system, the current study examined changes in microglia following exposure to representative FRs, pentabromophenol (PBP), tetrabromobisphenol A (2,2',6,6',-tetrabromo-4,4'-isopropylidine diphenol; TBBPA) and triphenyl phosphate (TPP). Following 18hr exposure of murine BV-2 cells, at dose levels resulting in ≥80% viability (10 and 40 μM), limited alterations in pro-inflammatory responses were observed however, changes were observed in mitochondrial respiration. Basal respiration was altered by PBP; ATP-linked respiration by PBP and TBBPA, and maximum respiration by all three FRs. Basal glycolytic rate was altered by PBP and TBBPA and compensatory glycolysis by all three. Phagocytosis was decreased for PBP and TBBPA. NLRP3 inflammasome activation was assessed using BV-2-ASC (apoptosis-associated speck-like protein containing a CARD) reporter cells to visualize aggregate formation. PBP, showed a direct stimulation of aggregate formation and properties as a NLRP3 inflammasome secondary trigger. TBBPA showed indications of possible secondary triggering activity while no changes were seen with TPP. Thus, the data suggests an effect of all three FRs on mitochondria metabolism yet, different functional outcomes including, phagocytic capability and NLRP3 inflammasome activation.

Low Concentrations of Tetrabromobisphenol A Disrupt Notch Signaling and Intestinal Development in in Vitro and in Vivo Models

Tetrabromobisphenol A (TBBPA) was recently reported to upregulate Notch target gene expression in embryonic stem cells differentiating to neurons in vitro, implying activation on Notch signaling, a crucial signaling involved in multiple organ development and homeostasis.The present study aimed to determine whether TBBPA at low concentrations can disrupt Notch signaling in the intestine and subsequently its development using in vitro and in vivo models, given TBBPA uptake mainly via the intestine. In rat intestinal epithelium cells (IEC-6), an in vitro model for intestinal development and homeostasis, we found 5-500 nM TBBPA upregulated Notch-related gene expression and stimulated cell proliferation as well as the growth of microvilli in a linear concentration-dependent manner. When Notch inhibitor DAPT had no obvious effects on all end points, DAPT significantly antagonized all changes caused by TBBPA, indicating that TBBPA activated Notch signaling in IEC-6 cells and subsequently stimulated cell proliferation and differentiation. Then we employed Xenopus laevis, an ideal model species for intestinal development with the strong similarities to mammals, to further confirm the action of TBBPA in vivo. Expectedly, we observed the stimulatory effects of TBBPA on Notch signaling and cell proliferation and differentiation in X. laevis intestines, which agrees with the results in vitro. Antagonistic actions of Notch inhibitor DBZ on TBBPA-caused intestinal changes show that TBBPA affected intestinal development via disrupting Notch signaling. Interestingly, TBBPA stimulated cell differentiation into secretory cells, which is generally believed to be regulated by Wnt signaling, suggesting disruption of Wnt signaling besides Notch signaling. All the results for the first time demonstrate that TBBPA at low concentrations, including environmentally relevant concentrations, disrupt Notch signaling and subsequently affect intestinal development by altering cell proliferation and differentiation in vertebrates. Our study highlights the intestine as a new target of TBBPA and broaden our understanding of developmental toxicity of TBBPA.