Multiple bioanalytical methods reveal a thyroid-disrupting mechanism related to the membrane receptor integrin αvβ3

Liquid crystal monomers disrupt photoreceptor patterning of zebrafish larvae via thyroid hormone signaling

Liquid crystal monomers (LCMs) are the raw material for liquid crystal displays, and their use is steadily increasing in electronic products. Recently, LCMs have been reported to be novel endocrine disrupting chemicals, however, the mechanisms underlying their potential for thyroid hormone disruption and visual toxicity are not well understood. In this study, six widely used fluorinated LCMs (FLCMs) were selected to determine putative mechanisms underlying FLCM-induced toxicity to the zebrafish thyroid and visual systems. Exposure to FLCMs caused damage to retinal structures and reduced cell density of ganglion cell layer, inner nuclear layer, and photoreceptor layer approximately 12.6-46.1%. Exposure to FLCMs also disrupted thyroid hormone levels and perturbed the hypothalamic-pituitary-thyroid axis by affecting key enzymes and protein in zebrafish larvae. A thyroid hormone-dependent GH3 cell viability assay supported the hypothesis that FLCMs act as thyroid hormone disrupting chemicals. It was also determined that FLCMs containing aliphatic ring structures may have a higher potential for T3 antagonism compared to FLCMs without an aliphatic ring. Molecular docking in silico suggested that FLCMs may affect biological functions of thyroxine binding globulin, membrane receptor integrin, and thyroid receptor beta. Lastly, the visual motor response of zebrafish in red- and green-light was significantly inhibited following exposure to FLCMs. Taken together, we demonstrate that FLCMs can act as thyroid hormone disruptors to induce visual dysfunction in zebrafish via several molecular mechanisms.

Exploring the underlying molecular mechanism of tri(1,3-dichloropropyl) phosphate-induced neurodevelopmental toxicity via thyroid hormone disruption in zebrafish by multi-omics analysis

Tri(1,3-dichloropropyl) phosphate (TDCPP) is widespread in the environment as a typical thyroid hormone-disrupting chemical. Here, we aimed to explore the toxicological mechanisms of the thyroid hormone-disrupting effects induced by TDCPP in zebrafish embryos/larvae using multi-omics analysis. The results showed that TDCPP (400 and 600 µg/L) induced phenotypic alteration and thyroid hormone imbalance in zebrafish larvae. It resulted in behavioral abnormalities during zebrafish embryonic development, suggesting that this chemical might exhibit neurodevelopmental toxicity. Transcriptomic and proteomic analysis provided consistent evidence at the gene and protein levels that neurodevelopmental disorders were significantly enhanced by TDCPP exposure (p < 0.05). Additionally, multi-omics data indicated that membrane thyroid hormone receptor (mTR)-mediated non-genomic pathways, including cell communication (ECM-receptor interactions, focal adhesion, etc.) and signal transduction pathways (MAPK signaling pathway, calcium signaling pathway, neuroactive ligand-receptor interaction pathway, etc.), were significantly disturbed (p < 0.05) and might contribute to the neurodevelopmental toxicity induced by TDCPP. Therefore, behavioral abnormalities and neurodevelopmental disorders might be important phenotypic characteristics of TDCPP-induced thyroid hormone disruption, and mTR-mediated non-genomic networks might participate in the disruptive effects of this chemical. This study provides new insights into the toxicological mechanisms of TDCPP-induced thyroid hormone disruption and proposes a theoretical basis for risk management of this chemical.

Nongenomic effects and mechanistic study of butyl benzyl phthalate-induced thyroid disruption: Based on integrated in vitro, in silico assays and proteome analysis

Based on in vitro and in silico assays as well as proteome analysis, this study explored the nongenomic mechanism for butyl benzyl phthalate (BBP)-induced thyroid disruption. Molecular docking simulations showed that BBP could dock into the Arg-Gly-Asp (RGD) domain of integrin α_vβ₃ and form hydrogen bonds with a docking energy of -35.80 kcal/mol. This chemical enhanced rat pituitary tumor cell (GH3) proliferation and exhibited thyroid hormone-disrupting effects at 5-10 μmol/L. Meanwhile, BBP upregulated β₃ gene expression and activated the downstream mitogen-activated protein kinase (MAPK) pathway in GH3 cells. Interestingly, GH3 cell proliferation was attenuated by integrin α_vβ₃ inhibitor (RGD peptide) or ERK1/2 inhibitor (PD98059), suggesting that the disruptions might be partly attributed to its interaction with integrin α_vβ₃ and activation of MAPK. Furthermore, quantitative proteomic analysis of zebrafish embryos exposed to BBP at an environmentally relevant concentration of 0.3 μmol/L revealed that BBP perturbed proteins and pathways related to cell communication (e.g., integrin binding) and signal transduction (e.g., MAPK signaling pathway). Taken together, our results supported that the biological effects of BBP-activated integrin α_vβ₃ mediated by the nongenomic pathway play an important role in its thyroid disruption. CAPSULE: The nongenomic pathway plays a vital role in the thyroid disruption-inducing actions of BBP.

Exploring the influence mechanism of dissolved organic matter on the bioavailability and thyroid hormone disrupting effect of zinc: A case study of effluents from galvanizing plants

The effect of dissolved organic matter (DOM) on metal bioavailability and toxicity is a complex process. Effluents from galvanizing plants containing large amounts of DOM and Zn were selected to investigate the potential influence and mechanism of DOM on Zn bioavailability and its role in inducing thyroid hormone disrupting effects. Thyroid hormone disrupting effects were evaluated using a recombinant thyroid hormone receptor β gene yeast assay. The results suggest that Zn could be the main metal contributor to the toxic effects. Then, Zn-binding characteristics with different fluorescent components of DOM were analyzed using three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM) and revealed that Zn was more susceptible to interactions with fulvic-like materials. Furthermore, DOM altered the cellular biouptake and compartmentalization processes of Zn by downregulating Zn transmembrane transport-related genes (ZRT1, ZRT2 and ZAP1) and upregulating detoxification-related genes (COT1 and ZRC1), thus altering thyroid toxicity. These results provide comprehensive insights into the influence and mechanism of DOM on bioavailability and thyroid toxicity of Zn and suggest that the influence is associated with complex physical, chemical and biological processes, indicating that more refined medium constraints along with subtle biological reactions should be considered when predicting the bioavailability and toxicity of Zn in environmental water samples.

Insights into the Endocrine Disrupting Activity of Emerging Non-Phthalate Alternate Plasticizers against Thyroid Hormone Receptor: A Structural Perspective

Many endocrine-disrupting chemicals (EDCs) have a ubiquitous presence in our environment due to anthropogenic activity. These EDCs can disrupt hormone signaling in the human and animal body systems including the very important hypothalamic-pituitary-thyroid (HPT) axis causing adverse health effects. Thyroxine (T4) and triiodothyronine (T3) are hormones of the HPT axis which are essential for regulation of metabolism, heart rate, body temperature, growth, development, etc. In this study, potential endocrine-disrupting activity of the most common phthalate plasticizer, DEHP, and emerging non-phthalate alternate plasticizers, DINCH, ATBC, and DEHA against thyroid hormone receptor (TRα) were characterized. The structural binding characterization of indicated ligands was performed against the TRα ligand binding site employing Schrodinger’s induced fit docking (IFD) approach. The molecular simulations of interactions of the ligands against the residues lining a TRα binding pocket, including bonding interactions, binding energy, docking score, and IFD score were analyzed. In addition, the structural binding characterization of TRα native ligand, T3, was also done for comparative analysis. The results revealed that all ligands were placed stably in the TRα ligand-binding pocket. The binding energy values were highest for DINCH, followed by ATBC, and were higher than the values estimated for TRα native ligand, T3, whereas the values for DEHA and DEHP were similar and comparable to that of T3. This study suggested that all the indicated plasticizers have the potential for thyroid hormone disruption with two alternate plasticizers, DINCH and ATBC, exhibiting higher potential for thyroid dysfunction compared to DEHA and DEHP.

Thyroid Hormone Disruption by Organophosphate Esters Is Mediated by Nuclear/Membrane Thyroid Hormone Receptors: In Vitro, In Vivo, and In Silico Studies

Earlier mechanistic studies of many prohibited flame retardants (FRs) highlighted their thyroid hormone-disrupting activity through nuclear thyroid hormone receptors (nTRs), whereas some alternative FRs such as organophosphate esters (OPEs) exerted weak nTR-disrupting effects. However, an increasing number of studies have revealed that OPEs also exert thyroid hormone-disrupting effects, and the underlying mechanism is unclear. Herein, the thyroid hormone-disrupting effects and mechanisms of 8 typical OPEs were investigated using integrated in vitro, in vivo, and in silico assays. All tested chemicals competitively bound to the membrane thyroid hormone receptor (mTR) [the 20% relative inhibitory concentration (RIC20): (3.5 ± 0.2) × 10¹ to (4.9 ± 1.0) × 10⁷ nM], and Cl-OPEs and alkyl-OPEs had lower RIC20 values. In contrast, only 4 OPEs showed nTR antagonistic activities at higher concentrations [≥ (4.8 ± 0.8) × 10³ nM]. Cl-OPEs and alkyl-OPEs preferentially interacted with mTR. Molecular docking illustrated that OPEs docked into mTRs, consistent with the competitive binding assay. In vivo analyses of zebrafish embryonic development confirmed that tris(1,3-dichloro-2-propyl) phosphate induced inappropriate expression of proteins, and these protein interactions might be associated with mTR according to the quantitative proteomic analysis. Based on the results, mTR might play a critical role in mediating the thyroid hormone-disrupting effects of OPEs.