Table E5.
Studies on mode of action for thyroid toxicity.
| Reference | Comments |
|---|---|
| Terasaki et al. (2011). Assessment of thyroid hormone activity of halogenated bisphenol A using a yeast two‐hybrid assay | The thyroid hormone agonist/antagonist activities of TBBPA were evaluated using a yeast two‐hybrid assay incorporating the human thyroid hormone a (TRα), both with and without possible metabolic activation by rat liver S9. In the absence of S9 TBBPA exhibited agonist activity. The activities of TBBPA increased markedly after metabolic activation S9. TBBPA inhibited the binding of T3 to TRα demonstrating its T3 antagonist activity both in presence and absence of S9. Metabolic activation by S9 significantly increased his agonist and antagonist potential |
| Butt et al. (2011). Halogenated Phenolic Contaminants Inhibit the In Vitro Activity of the Thyroid‐Regulating Deiodinases in Human Liver |
T4 and reverse triiodothyronine (rT3) deiodination kinetics were measured by incubating pooled human liver microsomes with T4 or rT3 and monitoring the production of T3, rT3, 3,3′‐diiodothyronine and 3‐monoiodothyronine by liquid chromatography tandem mass spectrometry TBBPA was a potent deiodinase (DI) activity inhibitor |
| Freitas et al. (2011). Detection of thyroid hormone receptor disruptors by a novel stable in vitro reporter gene assay | A stable luciferase reporter gene assay was developed based on the thyroid hormone responsive rat pituitary tumour GH3 cell line that constitutively expresses both thyroid hormone receptor isoforms. Stable transfection of the pGL4CP‐SV40‐2xtaDR4 construct into the GH3 cells resulted in a highly sensitive cell line (GH3.TRE‐Luc), which was further optimised into an assay that allowed the detection of T3 and T4 concentrations in the picomolar range after only 24 h of exposure |
| Matsubara et al. (2012). An improved thyroid hormone reporter assay to determine the thyroid hormone‐like activity of amiodarone, bithionol, closantel and rafoxanide | Reporter gene assays using the thyroid hormone responsive element (TRE) connected to the luciferase reporter gene have been developed with the ability to detect T3 activity at 10−11 M. The assay successfully detected thyroid hormone‐like activities of several model chemicals as well as a flame retardant, TBBPA |
| Levy‐Bimbot et al. (2012). Tetrabromobisphenol‐A disrupts thyroid hormone receptor alpha function in vitro: Use of fluorescence polarisation to assay corepressor and coactivator peptide binding |
TBBPA interfere with the ability of the hTRα1 ligand binding domain (LBD) to bind both nuclear hormone receptor corepressor (NCoR) and steroid receptor coactivator‐2 (SRC2). TBBPA behaved similarly to T3 in promoting the release of NCoR from LBD, whereas it failed to promote LBD interactions with SRC2. However, it did reduce the T3‐induced interactions between LBD and the coactivator peptide. This study suggests that TBBPA in the micromolar range can affect the regulation of transcription by both the apo‐ and the holo‐TRα1, with potential disruption of the expression of genes that are either up‐ or down‐regulated by T3 TBBPA, can induce an inactive conformation of hTRα1 in which the ability of the receptor to recruit either corepressors or coactivators is hampered. TBBPA could therefore disrupt the function of both unliganded hTRα1 (apo‐TRα1) and T3‐bound hTRα1 (holo‐TRα1) |
| McIver et al. (2013). Can thyroid hormone mimics affect thyroid hormone measurement by immunoassay | Hormone‐relevant concentrations of TBBPA were added to thyroid hormone‐stripped human serum and subjected to 6 different thyroid hormone immunoassays. TBBPA was negative in all of the thyroid hormone immunoassays tested (Total T3 in‐house RIA, Total T4 and T3 Beckman–Coulter Access, Free T4 and T3 Abbott Architect) except at very high concentration where it gave a marginally positive result in one immunoassay (in house T4 radioimmunoassay (RIA). Serum TBBPA is very unlikely to give false positive results in thyroid hormone immunoassays |
| Oka et al. (2013). Establishment of transactivation assay systems using fish, amphibian, reptilian and human thyroid hormone receptors | For the screening of chemicals with a potential thyroid hormone and anti‐thyroid hormone activities, a transient transactivation assay systems using thyroid hormone receptors (TRα and TRβ) from three frog species, a fish, an alligator and a human was developed |
| Zhang et al. (2014). Tetrabromobisphenol A Disrupts Vertebrate Development via Thyroid Hormone Signalling Pathway in a Developmental Stage‐Dependent Manner | TBBPA has been demonstrated in vitro to disrupt the TH signalling pathway at the transcriptional level. The effects of TBBPA on T3‐induced and spontaneous Xenopus laevis (which share many similarities with TH dependent development in higher vertebrates) metamorphosis were investigated. In a 6‐day T3‐induced metamorphosis assay using premetamorphic tadpoles, 10–1000 nM TBBPA exhibited inhibitory effects on T3‐ induced expression of TH‐response genes and morphological changes in a concentration‐dependent manner, with a weak stimulatory action on tadpole development and TH‐response gene expression in the absence of T3 induction. In a spontaneous metamorphosis assay, it was found that TBBPA promoted tadpole development from stage 51 to 56 (pre and prometamorphic stages) but inhibited metamorphic development from stage 57 to 66 (metamorphic climax). TBBPA, even at low concentrations, disrupts TH‐dependent development in a developmental stage dependent manner, i.e. TBBPA exhibits an antagonistic activity at the developmental stages when animals have high endogenous TH levels, whereas it acts as an agonist at the developmental stages when animals have low endogenous TH levels |
| Guyot et al. (2014). Toxicogenomic analysis of the ability of brominated flame retardants TBBPA and BDE‐209 to disrupt thyroid hormone signalling in neural cells | In vitro analysis of the ability of TBBPA, to alter thyroid hormone response based on a model neural cell line and genome‐wide analysis of gene expression. The HEK293–Gal4TRa1luc cells were derived from human embryonic kidney 293 cells 293 cells. TBBPA (_ > 10−6 M) has a visible antagonist effect on T3 response. The experimental setting strongly suggests that the effects of TBBPA is mediated by the ligand binding domain of TRα1, and thus reflects the ability of TBBPA to act as low‐affinity antagonist ligand of the receptor. The ability of TBBPA to interfere with T3 response in a neural reporter cell line C17.2α (cells derive from mouse cerebellum) with Hr‐Luc gene was also investigated. TBBPA at 10_8M display little if any activity on C17.2a–HrLuc cells. A slight but significant antagonist effect of TBBPA was observed when T3 was at low concentration. TBBPA is able to modify T3‐mediated up‐regulation of gene expression in neural cells. At high concentration, TBBPA has a broader influence, outside of the TH signalling pathway, which may also be relevant to neurotoxicity |
| Lai et al. (2015). Tetrabromobisphenol A (TBBPA): Possible modes of action of toxicity and carcinogenicity in rodents | This review analyses several modes of action that may account for the observed thyroxine hormone changes and the uterine tumours. It concludes that the potential modes of action for thyroid changes induced by TBBPA are expected to exhibit a threshold for adverse effects due to the ability of the mammalian organism to compensate small changes in thyroid hormone levels. Regarding MoAs for the uterine tumours, TBBPA does not exert genotoxic or estrogenic effects. Available evidence suggests that TBBPA may increase levels of circulating oestrogens by a competitive inhibition of oestrogen conjugation and produce uterine tumours by promoting pre‐existing Tp53‐mutations due to increased oestrogen levels resulting in increased cell proliferation |
| Skledar and Masic (2016). Bisphenol A and its analogs: Do their metabolites have endocrine activity? Environmental Toxicology and Pharmacology 47: 182–199 | Review – Knowledge about the metabolic pathways and enzymes involved in metabolic biotransformations is essential for understanding and predicting mechanisms of toxicity. Bisphenols are metabolised predominantly by the glucuronidation reaction, which is considered their most important detoxification pathway, as based on current knowledge, glucuronides do not have activity on endocrine receptors. In contrast, several oxidative metabolites of bisphenols with enhanced endocrine activities are presented, and these findings indicate that oxidative metabolites of bisphenols can still have endocrine activities in humans |
| Stavreva et al. (2016). ‘Novel cell‐based assay for detection of thyroid receptor beta‐interacting environmental contaminants’ |
A novel cell assay, based on the translocation of a green fluorescent protein (GFP) – tagged chimeric molecule of glucocorticoid receptor (GR) and the thyroid receptor beta (TRβ) from the cytoplasm to the nucleus in the presence of TR ligands. Unlike the constitutively nuclear TRβ, this GFP‐GR‐TRβ chimera is cytoplasmic in the absence of hormone while translocating to the nucleus in a time‐ and concentration‐dependent manner upon stimulation with T3 and thyroid hormone analogue, triiodothyroacetic acid (TRIAC), while the reverse triiodothyronine (rT3) was inactive. GFP‐GR‐TRβ chimera does not show any cross‐reactivity with the GR‐activating hormones, providing a clean system for the screening of TR beta ‐interacting EDCs. TBBPA induced GFP‐GR‐TRβ translocation at micro molar concentrations Screening of over 100 concentrated water samples from different geographic locations in the United States |
| Matsui et al. (2016). Development of yeast reporter assays for the enhanced detection of environmental ligands of thyroid hormone receptors alpha and beta from Xenopus tropicalis |
In order to detect TH disruptors for amphibians, a reporter assay was developed using yeast strains expressing the thyroid hormone receptors (TRs) α and β together with the transcriptional coactivator SRC‐1 These yeast strains responded to endogenous THs (T2 (3,5‐Diiodo‐L‐thyronine), T3 and T4) in a dose‐dependent manner. They detected the TR ligand activities of some artificial chemicals suspected to exhibit TH disrupting activities, as well as TR ligand activity in river water collected downstream of sewage plant discharges |
| Iakovleva et al. (2016). Tetrabromobisphenol A Is an Efficient Stabilizer of the Transthyretin Tetramer |
In this study TBBPA efficiently stabilises the tetrameric structure of plasma protein transthyretin (TTR). The X‐ray crystal structure shows TBBPA binding in the thyroxine binding pocket with bromines occupying two of the three halogen binding sites. TBBPA binds TTR with an extremely high selectivity in human plasma Preservation of tetrameric integrity impairs the ability of TTR to exert a cytotoxic effect. TBBPA significantly decreases the TTR dissociation rate under acidic denaturation conditions. TBBPA prevents TTR toxicity in human SH‐SY5Y neuroblastoma cells |
| Mengeling et al. (2017). A multi‐tiered, in vivo, quantitative assay suite for environmental disruptors of thyroid hormone signaling | Examination of potential TH disruption in the tractable, in vivo model system of amphibian metamorphosis. A quantitative, precocious‐metamorphosis assay suite was developed using 1‐week post‐fertilisation (PF) Xenopus laevis tadpoles in order to assess disruption of TH signalling. TBBPA although not effective in antagonising cell proliferation, significantly inhibited the TRE‐luciferase reporter |
| Lu, Zhan, et al. (2018). Thyroid Disruption by Bisphenol S Analogues via Thyroid Hormone Receptor beta: in Vitro, in Vivo, and Molecular Dynamics Simulation Study | The potential endocrine‐disrupting effects of Bisphenol S and its analogues towards thyroid hormone receptor (TR) β was investigated. The recombinant two‐hybrid yeast assay showed that TBBPA has potent antagonistic activity towards TRβ |
| Kollitz et al. (2018). The Affinity of Brominated Phenolic Compounds for Human and Zebrafish Thyroid Receptor beta: Influence of Chemical Structure | The goal of this study was to determine how structural differences of 3 Brominated Phenolic Compounds (BPC) classes impact binding affinities for the thyroid receptor beta (TRβ) in humans and zebrafish. In general, structural variations impacted binding affinities of both receptors in a similar manner. TRβ affinity increased with increasing halogen size and decreasing electronegativity, as well as increasing the degree of halogenation. The bridge group of the diphenyl compounds have a role in determining TRβ affinities. Ring orientations that diverge from that observed for T3 may negatively impact binding affinities |
| Ren et al. (2020). Binding and Activity of Tetrabromobisphenol A Mono‐Ether Structural Analogs to Thyroid Hormone Transport Proteins and Receptors | The aim of the study was to explore the potential thyroid hormone (TH) system–disrupting effect of TBBPA mono‐ether structural analogs |
| Zhang et al. (2021). Tetrabromobisphenol A induces THR beta‐mediated inflammation and uterine injury in mice at environmentally relevant exposure concentrations | To investigate whether TBBPA induces adverse outcomes at environmentally relevant exposure doses, BALB/c mice were exposed by gavage to TBBPA (5 and 50 mg/kg bw) 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. Uterine oedema was observed in TBBPA‐treated mice. In a primary uterine cells model (primary cells from mice uterus tissues from BALB/c mice), it was shown that TBBPA exposure suppressed THRβ expression, leading to the activation of the inflammatory PI3K/NF‐κB signalling pathway |
| An et al. (2023). Daily exposure to low concentrations Tetrabromobisphenol A interferes with the thyroid hormone pathway in HepG2 cells | HepG2 cells were exposed to low concentrations of TBBPA daily to investigate the changes in gene regulation, mainly related to pathways associated with the endocrine system. qPCR confirmed that prolonged exposure gradually activated the thyroid hormone and parathyroid hormone signalling pathways. The expression levels of genes related to the thyroid hormone signalling pathway (six major signal pathways, including the oxytocin signalling pathway, parathyroid hormone synthesis, secretion and action, thyroid hormone signalling pathway, insulin signalling path‐ way, progesterone‐mediated oocyte maturation and oestrogen signalling pathway) were upregulated after five generations of exposure to 1 and 81 nM TBBPA. Co‐exposure to 81 nM TBBPA and 0.5 nM thyroid hormone receptor antagonist for five generations significantly reduced the expression of thyroid hormone and parathyroid hormone receptors. 81 nM TBBPA inhibited the activation of the Ras pathway and downregulated Ras gene expression level, indicating the association between the toxic effect and thyroid hormone receptors. The experiments revealed that the thyroid hormone pathway regulated the induction of the Ras signalling pathway by TBBPA |
| Sinkó et al. (2022). Tetrabromobisphenol A and Diclazuril Evoke Tissue‐Specific Changes of Thyroid Hormone Signaling in Male Thyroid Hormone Action Indicator Mice | Tissue‐specific changes of TH action were assessed in 90‐day‐old Thyroid Hormone Action Indicator (THAI) transgenic mouse model exposed by gavage to 0 or 150 mg TBBPA/kg bw per day for 6 days by measuring the expression of a TH‐responsive luciferase reporter in peripheral tissue samples and by in vivo imaging (14‐day‐long treatment accompanied with imaging on day 7, 14 and 21 from the first day of treatment). By measuring the mRNA level of the TH‐responsive luciferase reporter system, TH action remained unchanged in the heart, interscapular brown adipose tissue, skeletal muscle, skin, small intestines and liver. However, TBBPA disrupted TH signalling in the bone. By in vivo imaging, it was shown that in the small intestine, TH action was decreased after 2 weeks of treatment and then recovered after the recovery week. TBBPA impaired also the global TH economy by decreasing the circulating free T4 levels. In the promoter assays, TBBPA showed a direct stimulatory effect on the hdio3 promoter, indicating a potential mechanism for silencing TH action |
| Hu et al. (2023). Bisphenol analogues induce thyroid dysfunction via the disruption of the thyroid hormone synthesis pathway | Exposure to TBBPA of 0.02 mg/kg bw per day downregulated the protein expression levels of thyrotropin receptor, the sodium/iodide symporter, thyroperoxidase. The TH‐dependent effects were further determined using the T‐Screen assay at 10−11 M to 10−5 M concentrations. TBBPA significantly decreased TH‐dependent rat pituitary tumour GH3 cell proliferation, indicating its antagonistic activity. TBBPA can reduce GH3 cell proliferation when co‐incubated with T3. The gene responsible for THs synthesis of thyrotropin releasing hormone receptor and TSH were upregulated, but downregulation of thyroid receptor β was observed. TBBPA disrupts THs synthesis and thyroid function, which are associated with the down regulation of TSHR, TPO, TG and NIS expression. Down regulation of TRβ and up regulation of TRHR and TSHβ was demonstrated, further inhibiting GH3 cells proliferation and inducing potential THs‐disrupting effects |