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Mandal A, Giri S, Giri A. Assessment of toxicity, genotoxicity and oxidative stress in Fejervarya limnocharis exposed to tributyltin. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2024; 31:14938-14948. [PMID: 38286928 DOI: 10.1007/s11356-024-32220-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Accepted: 01/23/2024] [Indexed: 01/31/2024]
Abstract
Tributyltin (TBT) is widely used in various commercial applications due to its biocidal properties. Toxicological and genotoxicological data on TBT exposure to amphibians is insufficient. Our study aimed to determine the acute toxicity and genotoxic potential of TBT in Fejervarya limnocharis tadpoles. Furthermore, oxidative stress was also investigated in TBT-treated tadpoles. Tadpoles of Gosner stage (26-30) were screened and subjected to increasing concentrations of TBT (0, 3, 7, 11, 15, 19, 23 µg/L) for determining the LC50 values for 24 h, 48 h, 72 h, and 96 h. LC50 values of TBT for 24 h, 48 h, 72 h, and 96 h were found to be 19.45, 15.07, 13.12, and 11.84 μg/L respectively. Based on the 96 h LC50 value (11.84 µg/L), tadpoles were exposed to different sub-lethal concentrations of TBT for the evaluation of its genotoxic potential and effects on oxidative balance. The role of TBT on survivability, growth, and time to metamorphosis was also assessed. TBT exposure significantly altered the life history traits measured, increased mortality, and delayed the time taken to metamorphosis. Results indicated significant induction of micronucleus (MN, p < 0.001) and other erythrocytic nuclear aberrations (ENA, p < 0.01) in the TBT-treated groups. Significant alterations in comet parameters and oxidative balance were also observed in the treated groups. The present study findings might add to the cause of the gradual population decline seen in the amphibians. This study also demonstrates the alteration of the life-history traits, oxidative balance, and DNA damage upon TBT exposure which can have long-term consequences for the anuran amphibian F. limnocharis.
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Affiliation(s)
- Abhijit Mandal
- Laboratory of Molecular and Cell Biology, Department of Life Science and Bioinformatics, Assam University, Silchar, 788011, Assam, India
| | - Sarbani Giri
- Laboratory of Molecular and Cell Biology, Department of Life Science and Bioinformatics, Assam University, Silchar, 788011, Assam, India.
| | - Anirudha Giri
- Laboratory of Environmental and Human Toxicology, Department of Life Science and Bioinformatics, Assam University, Silchar, 788011, India
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Mengeling BJ, Vetter LF, Furlow JD. Retinoid-X receptor agonists increase thyroid hormone competence in lower jaw remodeling of pre-metamorphic Xenopus laevis tadpoles. PLoS One 2022; 17:e0266946. [PMID: 35417489 PMCID: PMC9007347 DOI: 10.1371/journal.pone.0266946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Accepted: 03/30/2022] [Indexed: 11/18/2022] Open
Abstract
Thyroid hormone (TH) signaling plays critical roles during vertebrate development, including regulation of skeletal and cartilage growth. TH acts through its receptors (TRs), nuclear hormone receptors (NRs) that heterodimerize with Retinoid-X receptors (RXRs), to regulate gene expression. A defining difference between NR signaling during development compared to in adult tissues, is competence, the ability of the organism to respond to an endocrine signal. Amphibian metamorphosis, especially in Xenopus laevis, the African clawed frog, is a well-established in vivo model for studying the mechanisms of TH action during development. Previously, we’ve used one-week post-fertilization X. laevis tadpoles, which are only partially competent to TH, to show that in the tail, which is naturally refractive to exogenous T3 at this stage, RXR agonists increase TH competence, and that RXR antagonism inhibits the TH response. Here, we focused on the jaw that undergoes dramatic TH-mediated remodeling during metamorphosis in order to support new feeding and breathing styles. We used a battery of approaches in one-week-old tadpoles, including quantitative morphology, differential gene expression and whole mount cell proliferation assays, to show that both pharmacologic (bexarotene) and environmental (tributyltin) RXR agonists potentiated TH-induced responses but were inactive in the absence of TH; and the RXR antagonist UVI 3003 inhibited TH action. Bex and TBT significantly potentiated cellular proliferation and the TH induction of runx2, a transcription factor critical for developing cartilage and bone. Prominent targets of RXR-mediated TH potentiation were members of the matrix metalloprotease family, suggesting that RXR potentiation may emphasize pathways responsible for rapid changes during development.
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Affiliation(s)
- Brenda J. Mengeling
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis, California, United States of America
- * E-mail:
| | - Lara F. Vetter
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis, California, United States of America
| | - J. David Furlow
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis, California, United States of America
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Ren XM, Yao L, Xue Q, Shi J, Zhang Q, Wang P, Fu J, Zhang A, Qu G, Jiang G. Binding and Activity of Tetrabromobisphenol A Mono-Ether Structural Analogs to Thyroid Hormone Transport Proteins and Receptors. ENVIRONMENTAL HEALTH PERSPECTIVES 2020; 128:107008. [PMID: 33095664 PMCID: PMC7584160 DOI: 10.1289/ehp6498] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
BACKGROUND Tetrabromobisphenol A (TBBPA) mono-ether structural analogs, identified as the by-products or transformation products of commercial TBBPA bis-ether derivatives, have been identified as emerging widespread pollutants. However, there is very little information regarding their toxicological effects. OBJECTIVE We aimed to explore the potential thyroid hormone (TH) system-disrupting effect of TBBPA mono-ether structural analogs. METHODS The binding potencies of chemicals toward human TH transport proteins [transthyretin (TTR) and thyroxine-binding globulin (TBG)] and receptors [TRα ligand-binding domain (LBD) and TRβ-LBD] were determined by fluorescence competitive binding assays. Molecular docking was used to simulate the binding modes of the chemicals with the proteins. The cellular TR-disrupting potencies of chemicals were assessed by a GH3 cell proliferation assay. The intracellular concentrations of the chemicals were measured by high-performance liquid chromatography and mass spectrometry. RESULTS TBBPA mono-ether structural analogs bound to TTR with half maximal inhibitory concentrations ranging from 0.1μM to 1.0μM but did not bind to TBG. They also bound to both subtypes of TR-LBDs with 20% maximal inhibitory concentrations ranging from 4.0μM to 50.0μM. The docking results showed that the analogs fit into the ligand-binding pockets of TTR and TR-LBDs with binding modes similar to that of TBBPA. These compounds likely induced GH3 cell proliferation via TR [with the lowest effective concentrations (LOECs) ranging from 0.3μM to 2.5μM] and further enhanced TH-induced GH3 cell proliferation (with LOECs ranging from 0.3μM to 1.2μM). Compared with TBBPA, TBBPA-mono(2,3-dibromopropyl ether) showed a 4.18-fold higher GH3 cell proliferation effect and 105-fold higher cell membrane transportation ability. CONCLUSION This study provided a possible mechanism underlying the difference in TTR or TR binding by novel TBBPA structural analogs. These compounds might exert TH system-disrupting effects by disrupting TH transport in circulation and TR activity in TH-responsive cells. https://doi.org/10.1289/EHP6498.
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Affiliation(s)
- Xiao-Min Ren
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
| | - Linlin Yao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
| | - Qiao Xue
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
| | - Jianbo Shi
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
- Institute of Environment and Health, Jianghan University, Wuhan, China
| | - Qinghua Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
- Institute of Environment and Health, Jianghan University, Wuhan, China
| | - Pu Wang
- Institute of Environment and Health, Jianghan University, Wuhan, China
| | - Jianjie Fu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
| | - Aiqian Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
| | - Guangbo Qu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
- Institute of Environment and Health, Jianghan University, Wuhan, China
| | - Guibin Jiang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences (UCAS), Beijing, China
- Institute of Environment and Health, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, China
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Couderq S, Leemans M, Fini JB. Testing for thyroid hormone disruptors, a review of non-mammalian in vivo models. Mol Cell Endocrinol 2020; 508:110779. [PMID: 32147522 DOI: 10.1016/j.mce.2020.110779] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 02/26/2020] [Accepted: 02/27/2020] [Indexed: 02/07/2023]
Abstract
Thyroid hormones (THs) play critical roles in profound changes in many vertebrates, notably in mammalian neurodevelopment, although the precise molecular mechanisms of these fundamental biological processes are still being unravelled. Environmental and health concerns prompted the development of chemical safety testing and, in the context of endocrine disruption, identification of thyroid hormone axis disrupting chemicals (THADCs) remains particularly challenging. As various molecules are known to interfere with different levels of TH signalling, screening tests for THADCs may not rely solely on in vitro ligand/receptor binding to TH receptors. Therefore, alternatives to mammalian in vivo assays featuring TH-related endpoints that are more sensitive than circulatory THs and more rapid than thyroid histopathology are needed to fulfil the ambition of higher throughput screening of the myriad of environmental chemicals. After a detailed introduction of the context, we have listed current assays and parameters to assess thyroid disruption following a literature search of recent publications referring to non-mammalian models. Potential THADCs were mostly investigated in zebrafish and the frog Xenopus laevis, an amphibian model extensively used to study TH signalling.
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Affiliation(s)
- Stephan Couderq
- Unité PhyMA laboratory, Adaptation du Vivant, Muséum national d'Histoire naturelle, 7 rue Cuvier, 75005, Paris, France
| | - Michelle Leemans
- Unité PhyMA laboratory, Adaptation du Vivant, Muséum national d'Histoire naturelle, 7 rue Cuvier, 75005, Paris, France
| | - Jean-Baptiste Fini
- Unité PhyMA laboratory, Adaptation du Vivant, Muséum national d'Histoire naturelle, 7 rue Cuvier, 75005, Paris, France.
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Walter KM, Miller GW, Chen X, Yaghoobi B, Puschner B, Lein PJ. Effects of thyroid hormone disruption on the ontogenetic expression of thyroid hormone signaling genes in developing zebrafish (Danio rerio). Gen Comp Endocrinol 2019; 272:20-32. [PMID: 30448381 PMCID: PMC6331280 DOI: 10.1016/j.ygcen.2018.11.007] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 11/12/2018] [Accepted: 11/14/2018] [Indexed: 12/25/2022]
Abstract
Thyroid hormones (THs) regulate neurodevelopment, thus TH disruption is widely posited as a mechanism of developmental neurotoxicity for diverse environmental chemicals. Zebrafish have been proposed as an alternative model for studying the role of TH in developmental neurotoxicity. To realize this goal, it is critical to characterize the normal ontogenetic expression profile of TH signaling molecules in the developing zebrafish and determine the sensitivity of these molecules to perturbations in TH levels. To address these gaps in the existing database, we characterized the transcriptional profiles of TH transporters, deiodinases (DIOs), receptors (TRs), nuclear coactivators (NCOAs), nuclear corepressors (NCORs), and retinoid X receptors (RXRs) in parallel with measurements of endogenous TH concentrations and tshβ mRNA expression throughout the first five days of zebrafish development. Transcripts encoding these TH signaling components were identified and observed to be upregulated around 48-72 h post fertilization (hpf) concurrent with the onset of larval production of T4. Exposure to exogenous T4 and T3 upregulated mct8, dio3-b, trα-a, trβ, and mbp-a levels, and downregulated expression of oatp1c1. Morpholino knockdown of TH transporter mct8 and treatment with 6-propyl-2-thiouracil (PTU) was used to reduce cellular uptake and production of TH, an effect that was associated with downregulation of dio3-b at 120 hpf. Collectively, these data confirm that larval zebrafish express orthologs of TH signaling molecules important in mammalian development and suggest that there may be species differences with respect to impacts of TH disruption on gene transcription.
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Affiliation(s)
- Kyla M Walter
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Galen W Miller
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Xiaopeng Chen
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Bianca Yaghoobi
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Birgit Puschner
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
| | - Pamela J Lein
- Department of Molecular Biosciences, University of California-Davis School of Veterinary Medicine, Davis, CA 95616, United States.
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Mengeling BJ, Goodson ML, Furlow JD. RXR Ligands Modulate Thyroid Hormone Signaling Competence in Young Xenopus laevis Tadpoles. Endocrinology 2018; 159:2576-2595. [PMID: 29762675 PMCID: PMC6692881 DOI: 10.1210/en.2018-00172] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 05/07/2018] [Indexed: 12/18/2022]
Abstract
Appropriate thyroid hormone (TH) signaling through thyroid hormone receptors (TRs) is essential for vertebrate development. Amphibian metamorphosis is initiated and sustained through the action of TH on TRs, which are conserved across vertebrates. TRs heterodimerize with retinoid X receptors (RXRs) on thyroid hormone response elements (TREs) in the genome; however, in most cell line and adult animal studies, RXR ligands do not affect expression of TR target genes. We used a quantitative, precocious metamorphosis assay to interrogate the effects of the RXR agonist bexarotene (Bex) and the RXR antagonist UVI 3003 (UVI) on T3-induced resorption phenotypes in Xenopus laevis tadpoles 1 week postfertilization. Bex potentiated gill and tail resorption, and UVI abrogated T3 action. These results held in transgenic tadpoles bearing a TRE-driven luciferase reporter. Therefore, we used poly-A-primed RNA sequencing transcriptomic analysis to determine their effects on T3-induced gene expression. We also assayed the environmental pollutant tributyltin (TBT), which is an RXR agonist. We found that the proteases that carry out resorption were potentiated by Bex and TBT but were not significantly inhibited by UVI. However, several transcription factors from multiple families (sox4, fosl2, mxd1, mafb, nfib) were all inhibited by UVI and potentiated by Bex and TBT. All required T3 for induction. Time course analysis of gene expression showed that although the agonists could potentiate within 12 hours, the antagonist response lagged. These data indicate that the agonists and antagonist are not necessarily functioning through the same mechanism and suggest that RXR liganding may modulate TH competence in metamorphic signaling.
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Affiliation(s)
- Brenda J Mengeling
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, Davis, California
| | - Michael L Goodson
- Department of Anatomy, Physiology and Cell Biology, College of Veterinary Medicine, University of California, Davis, Davis, California
| | - J David Furlow
- Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, Davis, California
- Correspondence: J. David Furlow, PhD, Department of Neurobiology, Physiology and Behavior, College of Biological Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616.
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Lagadic L, Katsiadaki I, Biever R, Guiney PD, Karouna-Renier N, Schwarz T, Meador JP. Tributyltin: Advancing the Science on Assessing Endocrine Disruption with an Unconventional Endocrine-Disrupting Compound. REVIEWS OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2018; 245:65-127. [PMID: 29119384 DOI: 10.1007/398_2017_8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Tributyltin (TBT) has been recognized as an endocrine disrupting chemical (EDC) for several decades. However, only in the last decade, was its primary endocrine mechanism of action (MeOA) elucidated-interactions with the nuclear retinoid-X receptor (RXR), peroxisome proliferator-activated receptor γ (PPARγ), and their heterodimers. This molecular initiating event (MIE) alters a range of reproductive, developmental, and metabolic pathways at the organism level. It is noteworthy that a variety of MeOAs have been proposed over the years for the observed endocrine-type effects of TBT; however, convincing data for the MIE was provided only recently and now several researchers have confirmed and refined the information on this MeOA. One of the most important lessons learned from years of research on TBT concerns apparent species sensitivity. Several aspects such as the rates of uptake and elimination, chemical potency, and metabolic capacity are all important for identifying the most sensitive species for a given chemical, including EDCs. For TBT, much of this was discovered by trial and error, hence important relationships and important sensitive taxa were not identified until several decades after its introduction to the environment. As recognized for many years, TBT-induced responses are known to occur at very low concentrations for molluscs, a fact that has more recently also been observed in fish species. This review explores the MeOA and effects of TBT in different species (aquatic molluscs and other invertebrates, fish, amphibians, birds, and mammals) according to the OECD Conceptual Framework for Endocrine Disruptor Testing and Assessment (CFEDTA). The information gathered on biological effects that are relevant for populations of aquatic animals was used to construct Species Sensitivity Distributions (SSDs) based on No Observed Effect Concentrations (NOECs) and Lowest Observed Effect Concentrations (LOECs). Fish appear at the lower end of these distributions, showing that they are as sensitive as molluscs, and for some species, even more sensitive. Concentrations in the range of 1 ng/L for water exposure (10 ng/g for whole-body burden) have been shown to elicit endocrine-type responses, whereas mortality occurs at water concentrations ten times higher. Current screening and assessment methodologies as compiled in the OECD CFEDTA are able to identify TBT as a potent endocrine disruptor with a high environmental risk for the original use pattern. If those approaches had been available when TBT was introduced to the market, it is likely that its use would have been regulated sooner, thus avoiding the detrimental effects on marine gastropod populations and communities as documented over several decades.
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Affiliation(s)
- Laurent Lagadic
- Bayer AG, Research and Development, Crop Science Division, Environmental Safety, Alfred-Nobel-Straße 50, Monheim am Rhein, 40789, Germany.
| | - Ioanna Katsiadaki
- Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset, DT4 8UB, UK
| | - Ron Biever
- Smithers Viscient, 790 Main Street, Wareham, MA, 02571, USA
| | - Patrick D Guiney
- University of Wisconsin-Madison, 777 Highland Avenue, Madison, WI, 53705-2222, USA
| | - Natalie Karouna-Renier
- USGS Patuxent Wildlife Research Center, BARC East Bldg 308, 10300 Baltimore Avenue, Beltsville, MD, 20705, USA
| | - Tamar Schwarz
- Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, Dorset, DT4 8UB, UK
| | - James P Meador
- Environmental and Fisheries Sciences Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA, 98112, USA
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Mengeling BJ, Wei Y, Dobrawa LN, Streekstra M, Louisse J, Singh V, Singh L, Lein PJ, Wulff H, Murk AJ, Furlow JD. A multi-tiered, in vivo, quantitative assay suite for environmental disruptors of thyroid hormone signaling. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2017; 190:1-10. [PMID: 28662416 PMCID: PMC5558850 DOI: 10.1016/j.aquatox.2017.06.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 06/18/2017] [Accepted: 06/20/2017] [Indexed: 06/07/2023]
Abstract
The essential role of thyroid hormone (TH) signaling in mammalian development warrants the examination of man-made chemicals for its disruption. Among vertebrate species, the molecular components of TH signaling are highly conserved, including the thyroid hormone receptors (TRs), their heterodimer binding partners the retinoid-X receptors (RXRs), and their DNA recognition sequences (TREs). This molecular conservation allows examination of potential TH disruption in the tractable, in vivo model system of amphibian metamorphosis. Metamorphosis requires TH signaling for both instigation and progression, and it provides dramatic and well-characterized phenotypes involving different cell fates. Here we describe a quantitative, precocious-metamorphosis assay suite we developed using one-week post-fertilization (PF) Xenopus laevis tadpoles in order to assess disruption of TH signaling. Tadpoles at this developmental stage (Nieuwkoop-Faber (NF)-48) are competent to respond to TH hormone, although not yet producing TH, along many metamorphic pathways, and they are uniform in size. This allowed us to quantify changes in morphology associated with natural metamorphosis (e.g. gill and tail resorption, brain expansion, and craniofacial remodeling) after five days of treatment. Using the same tadpoles from morphological measurements, we quantified a 20-fold increase in TH-induced cellular proliferation in the rostral head region by whole-mount immunocytochemistry. At the molecular level, we used F3-generation tadpoles from a transgenic X. laevis line, which expresses luciferase under the control of a native TRE, to assess the ability of compounds to disrupt TR function. The luciferase reporter showed over 10-fold activation by physiologic concentrations of TH. We used the synthetic TR antagonist NH-3 to demonstrate the feasibility of our assay suite to measure inhibition of TH activity at the level of the receptor. Finally, we assessed the capabilities of suspected TH-disrupting chemicals tetrabrominated diphenyl ether 47 (BDE-47) and tetrabromobisphenol A (TBBPA). We found that BDE-47 displays general toxicity rather than TH disruption, as it did not increase brain width nor affect the TRE-luciferase reporter. However, TBBPA, a suspected TR antagonist, although not effective in antagonizing cell proliferation, significantly inhibited the TRE-luciferase reporter, suggesting that it bears closer scrutiny as a TH disruptor. Overall the assay suite has important advantages over the classical tadpole metamorphosis assays with respect to the uniformity of animal size, small test volume, reproducibility, and short test period. The assays are performed before endogenous TH production and free feeding start, which further reduces complexity and variability.
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Affiliation(s)
- Brenda J Mengeling
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis 95616-8519, USA
| | - Yuzhu Wei
- Marine Animal Ecology Group, Wageningen University, The Netherlands, Wageningen University, P.O. Box 38, 6700 AH Wageningen, The Netherlands
| | - Lucia N Dobrawa
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis 95616-8519, USA
| | - Mischa Streekstra
- Marine Animal Ecology Group, Wageningen University, The Netherlands, Wageningen University, P.O. Box 38, 6700 AH Wageningen, The Netherlands
| | - Jochem Louisse
- Division of Toxicology, Wageningen University, The Netherlands, Wageningen University, P.O. Box 8000, 6700 EA Wageningen, The Netherlands
| | - Vikrant Singh
- Department of Pharmacology, School of Medicine, University of California, Davis, CA 95616, USA
| | - Latika Singh
- Department of Pharmacology, School of Medicine, University of California, Davis, CA 95616, USA
| | - Pamela J Lein
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
| | - Heike Wulff
- Department of Pharmacology, School of Medicine, University of California, Davis, CA 95616, USA
| | - Albertinka J Murk
- Marine Animal Ecology Group, Wageningen University, The Netherlands, Wageningen University, P.O. Box 38, 6700 AH Wageningen, The Netherlands
| | - J David Furlow
- Department of Neurobiology, Physiology, and Behavior, College of Biological Sciences, University of California, Davis 95616-8519, USA.
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