An in silico study on human carcinogenicity mechanism of polybrominated biphenyls exposure.

Polybrominated biphenyls (PBBs) are associated with an increased risk of thyroid cancer; however, relevant mechanistic studies are lacking. In this study, we investigated the mechanisms underlying PBB-induced human thyroid cancer. Molecular docking and molecular dynamics methods were employed to investigate the metabolism of PBBs by the cytochrome P450 enzyme under aryl hydrocarbon receptor mediation into mono- and di-hydroxylated metabolites. This was taken as the molecular initiation event. Subsequently, considering the interactions of PBBs and their metabolites with the thyroxine-binding globulin protein as key events, an adverse outcome pathway for thyroid cancer caused by PBBs exposure was constructed. Based on 2D quantitative structure activity relationship (2D-QSAR) models, the contribution of amino acid residues and binding energy were analyzed to understand the mechanism underlying human carcinogenicity (adverse effect) of PBBs. Hydrogen bond and van der Waals interactions were identified as key factors influencing the carcinogenic adverse outcome pathway of PBBs. Analysis of non-bonding forces revealed that PBBs and their hydroxylation products were predominantly bound to the thyroxine-binding globulin protein through hydrophobic and hydrogen bond interactions. The key amino acids involved in hydrophobic interactions were alanine 330, arginine 381 and lysine 270, and the key amino acids involved in hydrogen bond interactions were arginine 381 and lysine 270. This study provides valuable insights into the mechanisms underlying human health risk associated with PBBs exposure.

AAV-mediated hepatic expression of SLC30A10 and the Thr95Ile variant attenuates manganese excess and other phenotypes in Slc30a10-deficient mice.

The manganese (Mn) export protein SLC30A10 is essential for Mn excretion via the liver and intestines. Patients with SLC30A10 deficiency develop Mn excess, dystonia, liver disease, and polycythemia. Recent genome-wide association studies revealed a link between the SLC30A10 variant T95I and markers of liver disease. The in vivo relevance of this variant has yet to be investigated. Using in vitro and in vivo models, we explore the impact of the T95I variant on SLC30A10 function. While SLC30A10 I95 expressed at lower levels than T95 in transfected cell lines, both T95 and I95 variants protected cells similarly from Mn-induced toxicity. Adeno-associated virus 8-mediated expression of T95 or I95 SLC30A10 using the liver-specific thyroxine binding globulin promoter normalized liver Mn levels in mice with hepatocyte Slc30a10 deficiency. Furthermore, Adeno-associated virus-mediated expression of T95 or I95 SLC30A10 normalized red blood cell parameters and body weights and attenuated Mn levels and differential gene expression in livers and brains of mice with whole body Slc30a10 deficiency. While our in vivo data do not indicate that the T95I variant significantly compromises SLC30A10 function, it does reinforce the notion that the liver is a key site of SLC30A10 function. It also supports the idea that restoration of hepatic SLC30A10 expression is sufficient to attenuate phenotypes in SLC30A10 deficiency.

Exploring the mechanism of interaction between TBG and halogenated thiophenols: Insights from fluorescence analysis and molecular simulation.

Thyroxine-binding globulin (TBG) plays a vital role in regulating metabolism, growth, organ differentiation, and energy homeostasis, exerting significant effects in various key metabolic pathways. Halogenated thiophenols (HTPs) exhibit high toxicity and harmfulness to organisms, and numerous studies have demonstrated their thyroid-disrupting effects. To understand the mechanism of action of HTPs on TBG, a combination of competitive binding experiments, multiple fluorescence spectroscopy techniques, molecular docking, and molecular simulations was employed to investigate the binding mechanism and identify the binding site. The competition binding assay between HTPs and ANS confirmed the competition of HTPs with thyroid hormone T4 for the active site of TBG, resulting in changes in the TBG microenvironment upon the binding of HTPs to the active site. Key amino acid residues involved in the binding process of HTPs and TBG were further investigated through residue energy decomposition. The distribution of high-energy contributing residues was determined. Analysis of root-mean-square deviation (RMSD) demonstrated the stability of the HTPs-TBG complex. These findings confirm the toxic mechanism of HTPs in thyroid disruption, providing a fundamental reference for accurately assessing the ecological risk of pollutants and human health. Providing mechanistic insights into how HTPS causes thyroid diseases.

Machine learning to improve false-positive results in the Dutch newborn screening for congenital hypothyroidism.

OBJECTIVE: The Dutch Congenital hypothyroidism (CH) Newborn Screening (NBS) algorithm for thyroidal and central congenital hypothyroidism (CH-T and CH-C, respectively) is primarily based on determination of thyroxine (T4) concentrations in dried blood spots, followed by thyroid-stimulating hormone (TSH) and thyroxine-binding globulin (TBG) measurements enabling detection of both CH-T and CH-C, with a positive predictive value (PPV) of 21%. A calculated T4/TBG ratio serves as an indirect measure for free T4. The aim of this study is to investigate whether machine learning techniques can help to improve the PPV of the algorithm without missing the positive cases that should have been detected with the current algorithm. DESIGN & METHODS: NBS data and parameters of CH patients and false-positive referrals in the period 2007-2017 and of a healthy reference population were included in the study. A random forest model was trained and tested using a stratified split and improved using synthetic minority oversampling technique (SMOTE). NBS data of 4668 newborns were included, containing 458 CH-T and 82 CH-C patients, 2332 false-positive referrals and 1670 healthy newborns. RESULTS: Variables determining identification of CH were (in order of importance) TSH, T4/TBG ratio, gestational age, TBG, T4 and age at NBS sampling. In a Receiver-Operating Characteristic (ROC) analysis on the test set, current sensitivity could be maintained, while increasing the PPV to 26%. CONCLUSIONS: Machine learning techniques have the potential to improve the PPV of the Dutch CH NBS. However, improved detection of currently missed cases is only possible with new, better predictors of especially CH-C and a better registration and inclusion of these cases in future models.

Identification of Mutations in the Thyroxine-Binding Globulin (TBG) Gene in Patients with TBG Deficiency in Korea.

BACKGRUOUND: Thyroxine-binding globulin (TBG) is a major transporter protein for thyroid hormones. The serpin family A member 7 (SERPINA7) gene codes for TBG, and mutations of the SERPINA7 gene result in TBG deficiency. Although more than 40 mutations have been reported in several countries, only a few studies of TBG deficiency and SERPINA7 gene mutation have been performed in Korea. The aim of this study is to review the clinical presentations and laboratory findings of patients with TBG deficiency and to investigate the types of SERPINA7 gene mutation. METHODS: Five unrelated Korean adults with TBG deficiency attending endocrinology clinic underwent SERPINA7 gene sequencing. Four patients harbored a SERPINA7 gene mutation. Serum thyroid hormones, anti-microsomal antibodies, and TBG were measured. Genomic DNA was extracted from whole blood. All exons and intron-exon boundaries of the TBG gene were amplified and sequencing was performed. RESULTS: Two patients were heterozygous females, and the other two were hemizygous males. One heterozygous female had coexisting hypothyroidism. The other heterozygous female was erroneously prescribed levothyroxine at a local clinic. One hemizygous male harbored a novel mutation, p.Phe269Cysfs*18, which caused TBG partial deficiency. Three patients had the p.Leu372Phefs*23 mutation, which is known as TBG-complete deficiency Japan (TBG-CDJ) and was also presented in previous mutation analyses in Korea. CONCLUSION: This study presents four patients diagnosed with TBG deficiency and provides the results of SERPINA7 gene sequencing. One novel mutation, p.Phe269Cysfs*18, causing TBD-partial deficiency and three cases of TBG-CDJ were demonstrated. It is necessary to identify TBG deficiency to prevent improper treatment. Also, sequencing of the SERPINA7 gene would provide valuable information about the TBG variants in Korea.

Sex Difference Leads to Differential Gene Expression Patterns and Therapeutic Efficacy in Mucopolysaccharidosis IVA Murine Model Receiving AAV8 Gene Therapy.

Adeno-associated virus (AAV) vector-based therapies can effectively correct some disease pathology in murine models with mucopolysaccharidoses. However, immunogenicity can limit therapeutic effect as immune responses target capsid proteins, transduced cells, and gene therapy products, ultimately resulting in loss of enzyme activity. Inherent differences in male versus female immune response can significantly impact AAV gene transfer. We aim to investigate sex differences in the immune response to AAV gene therapies in mice with mucopolysaccharidosis IVA (MPS IVA). MPS IVA mice, treated with different AAV vectors expressing human N-acetylgalactosamine 6-sulfate sulfatase (GALNS), demonstrated a more robust antibody response in female mice resulting in subsequent decreased GALNS enzyme activity and less therapeutic efficacy in tissue pathology relative to male mice. Under thyroxine-binding globulin promoter, neutralizing antibody titers in female mice were approximately 4.6-fold higher than in male mice, with GALNS enzyme activity levels approximately 6.8-fold lower. Overall, male mice treated with AAV-based gene therapy showed pathological improvement in the femur and tibial growth plates, ligaments, and articular cartilage as determined by contrasting differences in pathology scores compared to females. Cardiac histology revealed a failure to normalize vacuolation in females, in contrast, to complete correction in male mice. These findings promote the need for further determination of sex-based differences in response to AAV-mediated gene therapy related to developing treatments for MPS IVA.

Sex, menopause, and age differences in the associations of persistent organic pollutants with thyroid hormones, thyroxine-binding globulin, and peripheral deiodinase activity: A cross-sectional study of the general Korean adult population.

Persistent organic pollutants (POPs) can disrupt the thyroid hormone system in humans. We assessed the associations of several POPs with serum thyroid hormones (T3 and T4) and thyroid-stimulating hormone, and investigated the modulating effects of sex, menopausal status, and age on these associations, in a subgroup of the adult population (n = 1250) from the Korean National Environmental Health Survey. PCB105 and PCB118 were negatively associated with total T4 in premenopausal females and males aged <50, whereas the associations were insignificant in other groups. PCB180, p,p'-DDE, and p,p'-DDT showed positive associations with total T3 in postmenopausal females; however, among males aged ≥50, PCB118, PCB138, and p,p'-DDE showed negative associations with total T3. The effects of exposure to multiple POPs were examined in multi-factor analyses. Factor 2 comprised PCB52, hexachlorobenzene, and BDE-47 was associated with an increase in free T4 in premenopausal females (ß = 0.015, p = 0.024), while Factor 1, which contained most POPs, was associated with a change in total T3 in postmenopausal females (ß = 0.032, p = 0.040) and males aged ≥50 (ß = -0.039, p = 0.023). Changes in total T4 or total T3 could be explained by differences in thyroxine-binding globulin (TBG) and peripheral deiodinase activity (GD). Negative associations of TBG with PCB105 in premenopausal females and PCB153 in males aged <50 may mediate the effect of decreasing total T4. PCB180, p,p'-DDE, p,p'-DDT, and Factor 1 were positively associated with GD, which is consistent with an increased total T3 in postmenopausal females. PCB118 was negatively associated with GD and total T3 in males aged ≥50. BDE-47 and ß-hexachlorocyclohexane were associated with thyroid autoantibodies in premenopausal females and males aged <50. Our observations suggest that the thyroid-disrupting effects of POPs may differ by sex, sex hormonal status, and age, and may be mediated by TBG and GD.

Structural binding perspectives of common plasticizers and a flame retardant, BDE-153, against thyroxine-binding globulin: potential for endocrine disruption.

The human exposure to diverse endocrine-disrupting chemicals (EDCs) has increased dramatically over several decades with very adverse health effects. Plasticizers and flame retardants constitute important classes of EDCs interfering in endocrine physiology including the thyroid function. Thyroxine (T4) is an important hormone regulating metabolism and playing key roles in developmental processes. In this study, six phthalate and nonphthalate plasticizers and one flame retardant (BDE-153) were subjected to structural binding against thyroxine-binding globulin (TBG). The aim was to understand their potential role in thyroid dysfunction using structural binding approach. The structural study was performed using Schrodinger's induced fit docking, followed by binding energy estimations of ligands and the molecular interaction analysis between the ligands and the amino acid residues in the TBG ligand-binding pocket. The results indicated that all the compounds packed tightly into the TBG ligand-binding pocket with similar binding pattern to that of TBG native ligand, T4. A high majority of TBG interacting amino acid residues for ligands showed commonality with native ligand, T4. The estimated binding energy values were highest for BDE-153 followed by nonphthalate plasticizer, DINCH, with values comparable with native ligand, T4. The estimated binding energy values of other plasticizers DEHP, DEHT, DEHA, ATBC, and TOTM were less than DINCH. In conclusion, the tight docking conformations, amino acid interactions, and binding energy values of the most of the indicated ligands were comparable with TBG native ligand, T4, suggesting their potential for thyroid dysfunction. The results revealed highest potential thyroid disruptive action for BDE-153 and DINCH.

Identification of a novel mutation in thyroxine-binding globulin (TBG) gene associated with TBG-deficiency and its effect on the thyroid function.

PURPOSE: This study presents a case of familial transmission of thyroxine-binding globulin (TBG) deficiency. The SERPINA7-gene which codes for TBG is located on the X-chromosome (Xq21-22). More than 45 mutations have been reported to cause TBG- deficiency from various countries, but none from India so far. Genetic analysis of SERPINA7 gene was carried out to determine the cause of low TBG levels in one family. METHODS: DNA samples of the propositus and the family members were subjected to Polymerase Chain Reaction (PCR) followed by direct sequencing. Allele-specific PCR and Next-gen sequencing (NGS) were employed to confirm the site of the mutation. Thyroid function tests were estimated by Radioimmunoassay (RIA) and Immunoradiometric assay (IRMA) kits. X-chromosomal inactivation status was analyzed in the female members harboring the mutation. RESULTS: A mutational screening in this family revealed a novel frame-shift mutation S353Q, 354fs3X in the exon 4 of the SERPINA7 gene which will be referred to as TBG-complete deficiency-India (TBG-CD-Ind). One out of four female family members harboring the mutation showed selective X-chromosomal inactivation. The affected family members were clinically euthyroid initially, showed changes in the thyroid function when tested after a long time span. However, the changes in the thyroid function in the affected family members had an autoimmune etiology. CONCLUSION: This study presents the first report of TBG-CD from India wherein a novel frameshift mutation referred to as TBG-CD-Ind (S353Q, 354fs3X) in the SERPINA7 gene was detected. No apparent association was identified between thyroid function and the TBG-mutation in the affected subjects. A detailed biochemical and genomic testing to determine the exact cause of discordant TFT in the patients would certainly aid in the unequivocal diagnosis of the thyroid function and for the precise individualized treatment.

Promoter CAG is more efficient than hepatocyte­targeting TBG for transgene expression via rAAV8 in liver tissues.

The recombinant adeno­associated virus 8 (rAAV8) vector is a widely used tool in basic research and clinical trials. The cytomegalovirus immediate­early enhancer/chicken ß­actin (CAG) promoter is a synthetic promoter used in adenoviral constructs with a wide spectrum and notable efficiency. The thyroxine binding globulin (TBG) promoter is a liver­specific promoter, which directs transgene expression in hepatocytes. However, the transduction efficiency of the rAAV vector is dependent on both the administration routes and the promoter elements. In the present study, the transduction efficiency in the liver following intraperitoneal (IP) and intravenous (IV) injections of rAAV8 with the CAG, TBG669 and TBG410 promoters was compared. Enhanced green fluorescent protein (EGFP) expression was used as the biomarker to indicate efficiency. Among the three different promoters, CAG exhibited the highest efficiency from both IV and IP injections. Following IV administration, EGFP expression, induced by the CAG promoter, was 67­fold higher compared with that in the TBG410 promoter group and 26­fold higher compared with that in the TBG669 promoter group. EGFP protein expression was higher with IV injection compared with that for IP injection for both the CAG and TBG669 promoters (P<0.05). With the CAG promoter, EGFP protein expression was 1.5­fold higher with the use of IV injection than with IP injection. With the TBG410 promoter, no differences were observed between the two administrations. In conclusion, these findings demonstrated that the CAG promoter was much more efficient at driving gene expression in the liver compared with that for the TBG promoters in rAAV8. In addition, IP administration produced comparable efficiency for gene delivery via the rAAV8 vector, particularly with the promoter TBG410.

The decrease of T3 / T4 is not hypothyroidism - a new mutation of Serpina7 gene results in partial thyroglobulin deficiency.

To explore an unusual cause of the decrease of T3/T4 through a new mutation of TBG gene in a family, so as to avoid habitual thinking and reduce subsequent over treatment. TSH, free total T4, T3 and free T4, T3 were determined by automatic chemiluminescence immunoassay. The TBG mutation was identified by direct DNA sequencing. A frameshift mutation of p. l372ffs * 32 was found in the TBG gene (c.1114delc) of the patient by direct DNA sequencing, and the proband of the family was heterozygous. In vitro expression showed that the affinity of TBG for T4 decreased. Further examination of the family members showed that T3 and T4 were decreased, while FT3, FT4 and TSH were normal. If the patients with low TT4 and TT3 but normal TSH are found, the serum TBG level and related genes should be detected to determine whether it is TBG deficiency and avoid wrong treatment.

Genome-wide analysis of thyroid function in Australian adolescents highlights SERPINA7 and NCOA3.

OBJECTIVE: Genetic factors underpin the narrow intraindividual variability of thyroid function, although precise contributions of environmental vs genetic factors remain uncertain. We sought to clarify the heritability of thyroid function traits and thyroid peroxidase antibody (TPOAb) positivity and identify single nucleotide polymorphisms (SNPs) contributing to the trait variance. METHODS: Heritability of thyroid-stimulating hormone (TSH), free T4 (fT4), free T3 (fT3) and TPOAb in a cohort of 2854 euthyroid, dizygous and monozygous twins (age range 11.9-16.9 years) from the Brisbane Longitudinal Twin Study (BLTS) was assessed using structural equation modelling. A genome-wide analysis was conducted on 2832 of these individuals across 7 522 526 SNPs as well as gene-based association analyses. Replication analysis of the association results was performed in the Raine Study (n = 1115) followed by meta-analysis to maximise power for discovery. RESULTS: Heritability of thyroid function parameters in the BLTS was 70.8% (95% CI: 66.7-74.9%) for TSH, 67.5% (59.8-75.3%) for fT4, 59.7% (54.4-65.0%) for fT3 and 48.8% (40.6-56.9%) for TPOAb. The genome-wide association study (GWAS) in the discovery cohort identified a novel association between rs2026401 upstream of NCOA3 and TPOAb. GWAS meta-analysis found associations between TPOAb and rs445219, also near NCOA3, and fT3 and rs12687280 near SERPINA7. Gene-based association analysis highlighted SERPINA7 for fT3 and NPAS3 for fT4. CONCLUSION: Our findings resolve former contention regarding heritability estimates of thyroid function traits and TPOAb positivity. GWAS and gene-based association analysis identified variants accounting for a component of this heritability.

A Newborn Falsely Suspected of Congenital Hypothyroidism due to Mutated Thyroxine-Binding Globulin with Low Binding Affinity.

INTRODUCTION: Neonatal screening programs for congenital hypothyroidism (CH) have been implemented worldwide to facilitate early diagnosis and treatment. The Dutch neonatal CH screening is primarily based on the measurement of thyroxine (T4). When T4 is low, an additional thyroxine-binding globulin (TBG) measurement is performed to reduce the number of false-positive screening results due to harmless TBG deficiency. Here, we present a case of a rare functional TBG deficiency leading to a false suspicion of CH. CASE PRESENTATION: Neonatal screening in this patient revealed a decreased T4, normal TSH, and normal TBG concentration, suggesting central CH. However, free T4 was normal. DNA sequencing analysis revealed a novel, hemizygous mutation (c.139G>A) in SERPINA7, the gene encoding TBG, resulting in the substitution of the conserved amino acid alanine to threonine at position 27. Crystal structure analyses showed that this substitution has a detrimental effect on binding of T4 to TBG. CONCLUSIONS: The novel SERPINA7 variant in this patient led to a false suspicion of central hypothyroidism in the Dutch T4-based neonatal screening program. It is important to recognize patients with such TBG defects to prevent unnecessary additional testing and treatment.

Exploring the toxic effects and mechanism of methoxylated polybrominated diphenyl ethers (MeO-PBDEs) on thyroxine-binding globulin (TBG): Synergy between spectroscopic and computations.

The interaction mechanism between thyroxine-binding globulin (TBG) and three methoxylated polybrominated diphenyl ethers (MeO-PBDEs) was analyzed by steady-state fluorescence, ultraviolet-visible (UV-visible) spectroscopy, circular dichroism (CD), molecular docking and molecular dynamics simulation methods. The results of the molecular docking technique revealed that 2'-MeO-BDE-3, 5-MeO-BDE-47, and 3-MeO-BDE-100 combined with TBG at the active site. The steady-state fluorescence spectra displayed that MeO-PBDEs quenched the endogenous fluorescence of TBG through static quenching mechanism, and complex formation between MeO-PBDEs and TBG was further indicated by UV-vis spectroscopy. The thermodynamic quantities showed that the binding process is spontaneous, and the major forces responsible for the binding are hydrogen bonding and hydrophobic interactions, which are consistent with the results of molecular docking to a certain extent. The results of CD confirmed that the secondary structure of TBG was changed after combining with MeO-PBDEs. The dynamic simulation results illustrated that the protein structure is more compact and changes in the secondary structure of TBG after binding to MeO-PBDEs. Additionally, we also utilized the molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) method to analyze the binding free energy of TBG and MeO-PBDEs. The results suggest that van der Waals force plays an essential role in the combination.

Compound hemizygous variants in SERPINA7 gene cause thyroxine-binding globulin deficiency.

SUB-HEADING: Compound hemizygous variants in SERPINA7 gene. BACKGROUND: Thyroxine-binding globulin (TBG) is encoded by SERPINA7 (OMIM. 314200) which is located on Xq22.3. SERPINA7 variants caused TBG deficiency which does not require treatment, but the decreased thyroxine may be misdiagnosed as hypothyroidism. We discovered some variants of TBG caused by alterations that differ from previously reported. MATERIALS AND METHODS: In this study, we enrolled 32 subjects from 10 families and sequenced the SERPINA7 genes of TBG-deficient subjects. Then, variants were analyzed to assess their effect on TBG expression and secretion. Bioinformatics database, protein structure, and dynamics simulation were used to evaluate the deleterious effects. Finally, we identified 2 novel and 4 known variants, and found 26 of 30 subjects carried the p.L303F. The DynaMut predictions indicated the variants (p.E91K, p.I92T, p.R294C, and p.L303F) exhibited decreased stability. CONCLUSION: Analyses revealed the p.L303F change the protein stability and flexibility, and it had an impact on the function of TBG, but when coexisted with other variants it might change the conformational structure of the protein and aggravate the damage to the protein. We speculated that the existence of a higher number of variants resulted in lower TBG secretion.

Alteration of transthyretin and thyroxine-binding globulin in major depressive disorder: multiple reaction monitoring-based proteomic analysis.

BACKGROUND: Major depressive disorder (MDD), common mental disorder, lacks objective diagnostic and prognosis biomarkers. The objective of this study was to perform proteomic analysis to identify proteins with changed expression levels after antidepressant treatment and investigate differences in protein expression between MDD patients and healthy individuals. METHODS: A total of 111 proteins obtained from literature review were subjected to multiple reaction monitoring (MRM)-based protein quantitation. Finally, seven proteins were quantified for plasma specimens of 10 healthy controls and 78 MDD patients (those at baseline and at 6 weeks after antidepressant treatment of either selective serotonin reuptake inhibitors (SSRIs) or mirtazapine). RESULTS: Among 78 MDD patients, 35 patients were treated with SSRIs and 43 patients were treated with mirtazapine. Nineteen (54.3%) and 16 (37.2%) patients responded to SSRIs and mirtazapine, respectively. Comparing MDD patients with healthy individuals, alteration of transthyretin was observed in MDD (P = 0.026). A few differences were observed in protein levels related to SSRIs treatment, although they were not statistically significant. Plasma thyroxine-binding globulin (TBG) was different between before and after mirtazapine treatment only in responders (P = 0.007). CONCLUSIONS: In proteomic analysis of plasma specimens from MDD patients, transthyretin and TBG levels were altered in MDD and changed after antidepressant treatment.

Binding and Activity of Tetrabromobisphenol A Mono-Ether Structural Analogs to Thyroid Hormone Transport Proteins and Receptors.

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 TRß-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.

Endocrine disruption: Molecular interactions of environmental bisphenol contaminants with thyroid hormone receptor and thyroxine-binding globulin.

Many bisphenol A (BPA) analogs have been commercially used recently, such as 2,2-bis(4-hydroxyphenyl)butane (BPB), 4,4'-ethylidenebisphenol, 4,4'-methylenediphenol (BPF), 4,4'-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4'-dihydroxydiphenyl sulfone (BPS), 4,4'-cyclohexylidenebisphenol (BPZ), 4,4'-(hexafluoroisopropylidene)diphenol (BPAF), 4,4'-(1-phenylethylidene)bisphenol (BPAP), and 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane (TMBPA), to circumvent adverse effects of BPA. However, their increasing use is also contaminating the environment, which is a potential cause of concern for human health. Thyroid hormone transport and signaling are potential targets for endocrine-disrupting activity of BPA analogs. Thyroxine-binding globulin (TBG) is the major carrier protein for thyroxine (T4) and triiodothyronine (T3) in blood. Thyroid hormones exert their action through thyroid hormone receptors (TRα and TRß). This report presents the thyroid-disrupting potential of indicated nine BPA analogs from structure-based studies with TBG and TRα. Each BPA analog formed important polar and hydrophobic interactions with a number of residues of TBG and TRα. Majority of TBG residues (77-100%) and TRα residues (70-91%) interacting with BPA analogs were common with those of native ligands T4 and T3, respectively. Majority of BPA analogs interacted with TBG forming a salt bridge interaction at Lys-270. The hydrogen-bonding interaction of T3 with TRα at His-381 was also shared by majority of analogs. The binding energy for BPP, BPB, BPZ, BPAP, and TMBPA with both proteins was closer to binding energy of respective native ligands. The similarity in structural binding characteristics suggested potential disrupting activity of thyroid hormone signaling and transport.

Thyroxine-binding globulin, peripheral deiodinase activity, and thyroid autoantibody status in association of phthalates and phenolic compounds with thyroid hormones in adult population.

Exposure to consumer chemicals such as phthalates and phenolic compounds has been associated with thyroid hormone disruption in humans. However, information related to factors that may influence such associations, e.g., transport and activation of the hormones, and autoimmunity status, is limited. In the present study, we employed a subpopulation of adults (n = 1,254) who participated in the Korean National Environmental Health Survey (KoNEHS) 2015-2017, and associated urinary concentrations of major phthalate metabolites, bisphenol A (BPA), and parabens, with thyroid hormone-related measures, including free and total T3 and T4, TSH, thyroxine-binding globulin (TBG), calculated peripheral deiodinase (DIO) activity, and thyroid autoantibodies of thyroperoxidase (TPO) and thyroglobulin (Tg). Phthalate metabolites were negatively associated with total T4 and free T3, and positively associated with total T3. These observations could be explained by TBG levels and calculated peripheral DIO activity that were positively associated with phthalates exposure. In contrast, BPA was positively associated with total T4 and negatively associated with total T3, without any changes in TBG concentration. Serum TPO and Tg antibodies were not associated with urinary phthalate metabolites and BPA. However, thyroid autoantibody status appeared to modulate the association of some phthalates with thyroid hormones. For parabens, little to negligible association was observed. The results of our observation show potential underlying mechanisms of phthalates-induced thyroid hormone disruption, and suggests the importance of consideration of thyroid autoimmunity status in association studies for thyroid disrupting chemicals.

Molecular interactions of thyroxine binding globulin and thyroid hormone receptor with estrogenic compounds 4-nonylphenol, 4-tert-octylphenol and bisphenol A metabolite (MBP).

AIM: Endocrine disruption due to environmental chemical contaminants is a global human health issue. The aim of present study was to investigate the structural binding aspects of possible interference of commonly detected environmental contaminants on thyroid function. MATERIAL AND METHODS: Three compounds, 4-tert-octylphenol (4-tert-OP), 4-nonylphenol (4-NP), and 4-methyl-2,4-bis(4-hydroxypentyl)pent-1-ene (MBP) were subjected to induced fit docking (IFD) against thyroxine binding globulin (TBG) and thyroid hormone receptor (THR). Structural analysis included molecular interactions of the amino acid residues and binding energy estimation between the ligands and the target proteins. KEY RESULTS: All the ligands were successfully placed in the ligand binding pocket of TBG and THR using induced fit docking (IFD). The IFD results revealed high percentage of commonality in interacting amino acid residues between the aforementioned compounds and the native ligand for both TBG and THR. The results of our study further revealed that all the compounds have the potential to interfere with thyroid transport and signaling. However, MBP showed higher binding affinity for both TBG and THR, suggesting higher thyroid disruptive potential as compared to 4-t-OP and 4-NP. Furthermore, our results also suggest that the reported disruptive effects of BPA could actually be exerted through its metabolite; MBP. SIGNIFICANCE: This work implies that all the three compounds 4-NP, 4-t-OP and especially MBP have the potential to interfere with thyroid hormone transport and signaling. This potentially leads to disruption of thyroid hormone function.