Search

Active ingredients of pesticides or biocides and industrial chemicals can negatively affect environmental organisms, potentially endangering populations and ecosystems. European legislation mandates that chemical manufacturers provide data for the environmental risk assessment of substances to obtain registration. Endocrine disruptors, substances that interfere with the hormone system, are not granted marketing authorization due to their adverse effects. Current methods for identifying disruptors targeting the thyroid hormone system are costly and require many amphibians. Consequently, alternative methods compliant with the 3R principle (replacement, reduction, refinement) are essential to prioritize risk assessment using reliable biomarkers at non-protected life stages. Our study focused on detecting robust biomarkers for thyroid-disrupting mechanisms of action (MoA) by analyzing molecular signatures in zebrafish embryos induced by deiodinase inhibitor iopanoic acid and thyroid peroxidase inhibitor methimazole. We exposed freshly fertilized zebrafish eggs to these compounds, measuring lethality, hatching rate, swim bladder size and transcriptomic responses. Both compounds significantly reduced swim bladder size, aligning with prior findings. Transcriptome analysis revealed specific molecular fingerprints consistent with the MoA under investigation. This analysis confirmed regulation directions seen in other studies involving thyroid disruptors and allowed us to identify genes like tg , scl2a11b , guca1d , cthrc1a , si:ch211-226h7.5 , soul5 , nnt2, cox6a2 and mep1a as biomarker genes for thyroid disrupting MoA in zebrafish embryos as per OECD test guideline 236. Future screening methods based on our findings will enable precise identification of thyroid-related activity in chemicals, promoting the development of environmentally safer substances. Additionally, these biomarkers could potentially be incorporated into legally mandated chronic toxicity tests in fish, potentially replacing amphibian tests for thyroid disruption screening in the future. [Display omitted] • Zebrafish embryos as 3R-compliant alternatives to amphibian tests. • RNA-sequencing of zebrafish embryos exposed to thyroid-disrupting chemicals. • Biomarkers for differentiating thyroid-related modes of action. • Zebrafish biomarkers may reduce animal use, time, and costs in thyroid testing. [ABSTRACT FROM AUTHOR]

Abstract Di-n-butylphthalate (DnBP) exhibits alarming thyroid disrupting activities. However, the toxic mechanism of DnBP is not completely understood. In this study, we investigated the mechanism of DnBP in thyroid disruption. Rat pituitary tumor cell lines (GH3) were treated with DnBP in different scenarios, and cell viabilities, target gene transcriptions and protein levels were measured accordingly. The results showed that after treatment with DnBP (20 μmol/L), cell proliferation increased to 114.69% (p < 0.01) and c-fos gene was up-regulated by 1.57-fold (p < 0.01). Both nuclear thyroid hormone receptor β (TR β) and membrane TR (integrin α v and integrin β 3) genes were up-regulated by 1.31-, 1.08- and 2.39-fold (p < 0.01), respectively, the latter was inhibited by Arg-Gly-Asp (RGD) peptides; the macromolecular DnBP-BSA was unable to bind nuclear TRs, but still promoted cell proliferation to 104.18% and up-regulated c-fos by 2.99-fold (p < 0.01); after silencing TRβ gene, cell proliferation (106.64%, p < 0.05) and up-regulation of c-fos (1.23-fold, p < 0.01) were also observed. All of these findings indicated the existence of non-genomic pathway for DnBP-induced thyroid disruption. Finally, DnBP activated the downstream extracellular regulated protein kinases (ERK1/2) pathway, up-regulating Mapk1 (1.15-, p < 0.05), Mapk3 (1.26-fold, p < 0.01) and increasing protein levels of p -ERK (p < 0.01); notably, DnBP-induced ERK1/2 activation along with c-fos up-regulation were attenuated by PD98059 (ERK1/2 inhibitor). Taken together, it could be suggested that integrin α v β 3 and ERK1/2 pathway play significant roles in DnBP-induced thyroid disruption, and this novel mechanism warrants further investigation in living organisms. Graphical abstract Image 1 Highlights • DnBP induced cell proliferation to GH3 cells. • DnBP induced thyroid disruption to GH3 cells through non-genomic pathways. • DnBP induced thyroid disruption to GH3 cells via integrin α v β 3 and ERK1/2 pathway. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the effects of thyroid disruption on the mental development of children. A total of 258 three-year-old children in Guiyu (e-waste-exposed group) and Nanao (reference group), China were examined. FT 3 , FT 4 , TSH, lead (BPb) and cadmium (BCd) in blood were determined, and cognitive and language scores of children were assessed based on the Bayley Scales of Infant Development III. Stepwise multiple regression was used to estimate the relationship between heavy metals and cognitive and language scores; mediation analysis was performed to determine whether thyroid disruption was mechanistically involved. Medians of BPb and BCd in Guiyu were higher than that of Nanao (11.30 ± 5.38 vs. 5.77 ± 2.51 μg/dL BPb; 1.22 ± 0.55 vs. 0.72 ± 0.37 μg/L BCd, both p < 0.001). Means of FT 4 and TSH in Guiyu were also higher than those in Nanao (16.65 ± 1.83 vs.16.06 ± 1.66 pmol/L FT 4 , p = 0.007; 2.79 ± 1.30 vs. 2.21 ± 1.43 mIU/L TSH, p = 0.001). Guiyu children had lower cognitive scores (100.00 ± 25.00 vs. 120.00 ± 20.00, p < 0.001) and lower language scores (99.87 ± 7.52 vs. 111.39 ± 7.02, p < 0.001). Mediation analysis showed that Pb negatively correlated with both cognitive and language scores (both p < 0.001). However, FT 3 , FT 4 and TSH did not significantly mediate the relationship between Pb and mental development of children (all p > 0.05). In contrast, Cd correlated with neither cognitive nor language scores (both p > 0.05). Results suggest exposure to heavy metal (Pb) reduces cognitive and language skills, and affects thyroid function, but fail to confirm that thyroid disruption is involved in the neurotoxicity induced by Pb Cd co-exposure. [ABSTRACT FROM AUTHOR]

Many uncertainties remain regarding the potential of bisphenol A (BPA) as a thyroid disruptor in mammals and the relevance of experimental data to humans. The relevance of the exposure schemes used in experimental in vivo studies is also a major source of uncertainty when analysing the risk of BPA exposure for human health. In this context, the goals of our study, conducted in an ovine model relevant to human gestation and thyroid physiologies, were to: 1) determine the equivalence of subcutaneous and dietary exposures and 2) determine if environmentally relevant doses of BPA can alter gestational and newborn thyroid functions. The difference between the two routes of exposure was mainly related to the overall BPA exposure and much less to the peak serum concentrations. Interestingly, BPA-GLUC (the main metabolite of BPA) internal exposure via both routes was almost identical. The decrease in thyroid hormones concentration overtime was more accentuated in ewes treated with BPA, particularly with the medium dose (50 μg/(kg.d); SC) for which the maximum BPA concentrations were predicted to be within the 1–10 ng/mL range i.e. very similar to the highest blood concentrations reported in humans. The balance between TT4 and rT3 varied differently between the vehicle and the medium dose group. The mechanisms underlying those modifications of maternal thyroid homeostasis remain to be determined. Our study did not evidence significant modification of TSH secretion or binding to serum proteins but might suggest an effect at the level of deiodinases. [ABSTRACT FROM AUTHOR]

The presence of pesticides as well as that of several antibiotics provided at a great scale to poultry, cattle, and swine in aquatic environments within agroecosystems is a matter of growing concern. The objective of the present study was to characterize the sublethal effects of four environmental toxic compounds at two experimental pollution scenarios on the morphology, development and thyroid (T4), acetylcholinesterase (AChE) and glutathione S-transferase (GST) levels in Rhinella arenarum tadpoles. The first experimental pollution scenario aimed to evaluate the individual and mixed toxicity (50:50% v/v) of a glyphosate-based herbicide (GBH) and the antibiotic ciprofloxacin (CIP) on earlier developmental stages. The second experimental pollution scenario aimed to evaluate the effects of other toxic compounds (the insecticide chlorpyrifos (CP) and the antibiotic amoxicillin (AMX)) added to the ones from the first scenario on previously exposed premetamorphic tadpoles. In all the treatments of the first pollution scenario, the most conspicuous effect observed in early-stage tadpoles was a high prevalence of morphological abnormalities. Exposure to GBH and to its mixture with CIP also led to a significant decrease in T4 levels and lower development. Both pollutant combinations from the second experimental scenario significantly increased T4 levels, inhibited AChE activities, and led to lower development, whereas the quaternary mixture led to a significant decrease in GST levels. The alterations here revealed by our approaches in several morphological and biochemical endpoints allow characterizing the ecotoxicological risk for anurans exposed to complex mixtures of pollutants that frequently occur in aquatic systems. [Display omitted] • Herbicide-insecticide-antibiotics mixtures delay anuran tadpole's development. • Herbicide-insecticide mixture inhibited tadpole's growth. • Herbicide-antibiotic mixture induced teratogenesis on early development stages. • Herbicide-insecticide-antibiotics mixtures disrupted T4 on premethamorphosis stages. [ABSTRACT FROM AUTHOR]

Tri(1,3-dichloropropyl) phosphate (TDCPP) potentially damages the thyroid system in humans and animals. However, knowledge of its toxic effects and underlying mechanisms is limited. The present study was conducted to determine the thyroid hormone-disrupting effects of TDCPP and its major metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCPP) in rat pituitary cell lines (GH3). TDCPP and BDCPP, that mimic the thyroid hormone (TH), promoted GH3 cell proliferation and modulated the progression of the cell cycle at 20 and 200 μmol/L, respectively. Similar to T3, TDCPP and BDCPP also significantly upregulated c-fos and downregulated Tshβ gene expression. Although the binding affinity of these chemicals for thyroid receptor β (TRβ) was not measured, significant competition between these chemicals to bind to the membrane thyroid hormone receptor (integrin α v β 3) was found, suggesting that TDCPP and BDCPP were strongly bound to integrin α v β 3. Results from a molecular docking analysis provided further evidence of strong binding affinities of TDCPP and BDCPP for integrin α v β 3 , and the ligand binding site of Arg-Gly-Asp (RGD) was identified. Real-time PCR also supported the supposition that, after binding to integrin α v β 3 , TDCPP and BDCPP may induce the activation of the extracellular signal-regulated protein kinase (ERK1/2) signal transduction pathway. Taken together, our data suggest that TDCPP and BDCPP have the ability to mimic THs and that the underlying mechanism might be associated with their interactions with integrin α v β 3 and the activation of the ERK1/2 pathway, providing new insight into the mechanism of TDCPP- and BDCPP-induced cytotoxicity. Image 1 • TDCPP and BDCPP induced GH3 cell proliferation. • TDCPP and BDCPP showed strong binding with integrin α v β 3. • TDCPP and BDCPP induced thyroid disruption that is associated with integrin α v β 3 and ERK1/2 activation. [ABSTRACT FROM AUTHOR]

Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardants (BFRs), has resulted in worldwide environmental contamination. TBBPA has been reported as a thyroid endocrine disruptor and a potential neurotoxicant. However, the underlying mechanism is still not clear. In this study, zebrafish (Danio rerio) embryos (2 h post-fertilization, hpf) were exposed to different concentrations of TBBPA (50, 100, 200 and 400 μg/L) alone or in combination with 3,3',5-triiodo-l-thyronine (T3, 20 μg/L + TBBPA, 200 μg/L). The results confirmed that TBBPA could evoke thyroid disruption by observations of increased T4 contents and decreased T3 contents, accompanied by up-regulated tshβ, tg mRNA and down-regulated ttr and trβ mRNA levels in zebafish larvae. TBBPA-induced neurodevelopmental toxicity was also indicated by down-regulated transcription of genes related to central nervous system (CNS) development (e.g., α1-tubulin, mbp and shha), and decreased locomotor activity and average swimming speed. Our results further demonstrated that treatment with T3 could reverse or eliminate TBBPA-induced effects on thyroidal and neurodevelopmental parameters. Given the above, we hypothesize that the observed neurodevelopmental toxicity in the present study could be attributed to the thyroid hormone disruptions by TBBPA., (Copyright © 2018 Elsevier Ltd. All rights reserved.)