Inhibition Of Thyroid Hormone Synthesis Research Articles

THU663 Therapeutic Plasma Exchange In Refractory Atrial Fibrillation Secondary To Thyroid Storm.

Abstract Disclosure: S.M. ALShehri: None. M.S. Bafadel: None. N.J. Aljohani: None. Thyrotoxic crisis (thyroid storm) is a severe form of hyperthyroidism. It has a wide range of symptoms, including cardiovascular manifestations that can be life-threatening and require prompt management. Cardiac manifestations of thyroid storm include hypertension, tachycardia, congestive heart failure, cardiac ischemia, and atrial fibrillation. Standard therapeutic approaches of thyroid storm are based on the use of thionamides, corticosteroids, and nonselective beta-blockers to inhibit thyroid hormone synthesis and release while also blocking thyroxin's peripheral effects. This approach is an effective measure in the management of these manifestations. However, when a patient fails to respond to conventional therapy or there is end organ damage and surgery is not feasible, therapeutic plasma exchange (TPE) is a life-saving measure. Here, we report a case of a 32-year-old female who is known to have hyperthyroidism, but she was not compliant with her medication. She presented with symptoms of hyperthyroidism and was found to have thyroid storm with refractory atrial fibrillation. Despite the effort to control her symptoms, she developed cardiac arrest, after 15 minutes of cardiopulmonary resuscitation she revived. Amiodarone, beta blockers, and cardioversion have all failed to improve the patient's status, and her condition has deteriorated. So, we decided to use TPE, and she received three sessions in total. After the first session of TPE, her rhythm converted to sinus rhythm, and her heart rate was controlled to less than 100 beats per minute. She showed dramatic improvement clinically and biochemically. In conclusion, cardiac complications are potentially lethal complications of thyroid storm. Prompt restoration of a normal thyroid state can reverse these complications. When conventional therapy fails to ameliorate symptoms or organ deterioration is rapid and severe, TPE can be a safe and effective measure. Presentation: Thursday, June 15, 2023

Development of the integrated fish endocrine disruptor test (iFEDT)-Part A: Merging of existing fish test guidelines.

There has been increasing interest in endocrine-disrupting chemicals (EDCs) among scientists and public authorities over the last 30 years, notably because of their wide use and the increasing evidence of detrimental effects on humans and the environment. However, test systems for the detection of potential EDCs as well as testing strategies still require optimization. Thus, the aim of the present project was the development of an integrated test protocol that merges the existing OECD test guidelines (TGs) 229 (fish short-term reproduction assay) and 234 (fish sexual development test) and implements thyroid-related endpoints for fish. The integrated fish endocrine disruptor test (iFEDT) represents a comprehensive approach for fish testing, which covers reproduction, early development, and sexual differentiation, and will thus allow the identification of multiple endocrine-disruptive effects in fish. Using zebrafish (Danio rerio) as a model organism, two exposure tests were performed with well-studied EDCs: 6-propyl-2-thiouracil (PTU), an inhibitor of thyroid hormone synthesis, and 17α-ethinylestradiol (EE2), an estrogen receptor agonist. In part A of this article, the effects of PTU and EE2 on established endpoints of the two existing TGs are reported, whereas part B focuses on the novel thyroid-related endpoints. Results of part A document that, as expected, both PTU and EE2 had strong effects on various endocrine-related endpoints in zebrafish and their offspring. Merging of TGs 229 and 234 proved feasible, and all established biomarkers and endpoints were responsive as expected, including reproductive and morphometric changes (PTU and EE2), vitellogenin levels, sex ratio, gonad maturation, and histopathology (only for EE2) of different life stages. A validation of the iFEDT with other well-known EDCs will allow verification of the sensitivity and usability and confirm its capacity to improve the existing testing strategy for EDCs in fish. Integr Environ Assess Manag 2024;20:817-829. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Abstract P1146: Global Analysis Of Murine Cardiac Gene Program Regulated By Thyroid Hormone And Transcriptional Repressor Rest

Background: During adult heart failure, transcriptional reprogramming of fetal cardiac genes coincides with dysregulated heart functions. However, the underlying mechanisms remain incompletely understood. Thyroid hormone and RE1 silencing transcription factor (REST) are known regulators of cardiac gene reprogramming. Here, we report a global analysis of their co-regulatory functions. Methods: We generated a dual Myh6 and Myh7 mouse reporter line. This line was crossed with a conditional Rest allele to generate myocardial Rest knockout mice. Control and Rest null mice were treated with propylthiouracil (PTU) to inhibit thyroid hormone synthesis. PTU treatment induced heart failure and adult-to-fetal cardiac gene remodeling. Single nuclei multiomic profiling was performed, linking gene expression and gene regulatory network information from each nuclei to elucidate the impact of PTU or REST or both on cardiac gene reprogramming. Samples were collected to validate the newly identified factors involved in reprogramming. Results: Data analysis showed that PTU treatment upregulates transcription factor binding involving circadian gene expression ( Cry2 , Per2 , Per3 ). Downregulated genes are related to voltage-gated channel activity and BMP/TGFB activities involving heart development ( Myh6 , Nrg1 , Bmpr1a ) and SA node action potential ( Scn5a , Hcn2 , Ryr2 ). In contrast, Rest knockout upregulated genes are associated with arrhythmia, i.e. , cAMP catabolism ( Pde4d , Pde7a , Pde7b ), heart conduction ( Cacna1c , Gja1 , Pln ), and ion transport ( Kcnip2 , Pde4d, Esr1 ). Downregulated genes are involved in protein functions involving integrin-mediated signaling ( Itgal , Itga4 , Itga5 ), cytoskeleton organization ( Ctnna2 , Actb , Xirp1 ), and fiber organization ( Tgfb3 , Smad3 , Ptk2b ). Furthermore, a subset of genes was found to be co-regulated by thyroid hormone and REST, including Ccn2 , Myh9 , Nmrk2 , Fgr , Itga4 , Prkcb , Cspg4 which are involved in integrin signaling pathway, immune activation, and angiogenesis. Conclusion: Thyroid hormone and REST have shared function in cardiac gene reprogramming involving cardiac conduction and fibrosis as well as their own newly discovered, unique roles regulating circadian genes and cAMP catabolism, respectively.

HYPERTHYROIDISM SECONDARY TO GESTATIONAL TROPHOBLASTIC DISEASE : A LITERATURE REVIEW

Gestational trophoblastic disease (GTD) is a rare form of pregnancy-related cancer that is effectively treatable. GTD is accompanied by the potentially fatal complication of hyperthyroidism. We created a review consisting of five case reports. This case report was conducted on women who became pregnant when they were >35 years old. They showed consistent laboratory results, in which there was an increase in hCG levels. TSH and thyroid stimulating antibodies cannot account for the hyperthyroidism associated with GTD. The source of the thyroid stimulating agent is trophoblastic tissue. The thyrotropic effects of ?-hCG mediate GTD hyperthyroidism. Other research examined the prevalence of hyperthyroidism in women with normal pregnancy, hydatidiform mole, and choriocarcinoma who had ?-hCG serum levels below 100,000 IU/ml. Early prenatal screening may significantly reduce hyperthyroidism rates. Thyroid hormone synthesis inhibitors treat hyperthyroidism in pregnancy. Thioamides, propylthiouracil (PTU), and methimazole (MMI) are the most prevalent U.S. antithyroid medications (ATD). Plasmaphoresis may be an option for people who are resistant to therapy or need emergency surgery. GTD can cause fatal hyperthyroidism. Anti-thyroid medicines can handle most GTD hyperthyroidism. Surgery may be a possibility for patients refractory to medical treatment.

Therapeutic effects of methimazole on 3,4-methylenedioxymethamphetamine-induced hyperthermia and serotonergic neurotoxicity

3,4-methylenedioxymethamphetamine (MDMA) is a popular recreational drug, however over 200 studies demonstrate that acute (e.g. hyperthermia, rhabdomyolysis) and chronic (e.g. neurotoxicity) toxicity effects of MDMA were observed in different animals. Methimazole (MMI), an inhibitor of thyroid hormone synthesis, was found to significantly reduce the HSP72 expression of heat stress induced in fibroblasts. Hence, we attempted to understand the effects of MMI on MDMA induced changes in vivo. Male SD rats were randomly divided into four groups as follows:(a) water-saline (b) water-MDMA (c) MMI-saline and (d) MMI-MDMA group. In the temperature analysis test, MMI was found to alleviate MDMA-induced hyperthermia and increase the heat loss index (HLI), revealing its peripheral vasodilation effect. PET experiment suggested that MDMA induced elevated glucose uptake by skeletal muscles, which was resolved by MMI pretreatment. IHC staining (serotonin transporter, SERT) showed the evidence of neurotoxicity caused by MDMA (serotonin fiber loss), which was alleviated by MMI. Furthermore, the animal behaviour test (forced swimming test, FST) showed higher swimming time but lower immobility time in MMI-MDMA and MMI-saline groups. Taken together, treatment of MMI shows benefits such as lowered body temperature, alleviation of neurotoxicity and excited behaviour. However, further investigations should be conducted in the future to provide in-depth evidence for its clinical use.

Methimazole and sodium perchlorate exert anti-thyroidal effects in the T3-induced Xenopus laevis metamorphosis assay: A rapid assay for screening thyroid disrupting chemicals

Thyroid disrupting chemicals (TDCs) have received much attention due to their potential adverse effects on animal and human health, which calls for rapid screen assays to identify them. The triiodothyronine (T3)-induced Xenopus metamorphosis assay (TiXMA) we developed previously has been successfully applied to the detection of the TDCs disrupting thyroid hormone (TH) signaling. Here, we attempted to expand the application of the TiXMA to the screening of the TDCs interfering with the hypothalamic-pituitary-thyroid (HPT) axis. Two well-known TH synthesis inhibitors methimazole (MMI) and sodium perchlorate (SP) were employed to test the sensitivity of the TiXMA to the TDCs interfering with the HPT axis. As expected, we observed that the two chemicals concentration-dependently antagonized T3-induced morphological changes and body weight reduction of X. laevis tadpoles following 96 h-exposure, in parallel with blocked thyroid development and down-regulated tshβ expression in the brain. All the data show that both MMI and SP exert inhibitory effects on T3-induced metamorphosis, indicating that the TiXMA is capable of screening the TDCs interfering with the HPT axis. In comparison with Amphibian Metamorphosis Assay (AMA), a 21-day assay for screening the TDCs interfering with the HPT axis, the TiXMA has a remarkable advantage of shorter exposure duration (96 h).

Carbimazole-Induced Cholestatic Jaundice with Heterozygous Mutant of H63D for Hemochromatosis

Carbimazole belongs to thionamide group of drugs and inhibits thyroid hormone synthesis by preventing organification of iodine to tyrosine residue in thyroglobulin as well as coupling of iodotyrosines. Although most of the side effects are minor such as rash, serious side effects such as hepatotoxicity and agranulocytosis have also been reported. The occurrence of carbimazole-induced hepatotoxicity has overall risk of <0.5%. Before confirming the diagnosis of cholestatic jaundice secondary to carbimazole, other causes has to be excluded as well. We report an interesting as well as rare case of cholestatic jaundice in a 50-year-old female who is a known case of hyperthyroidism who presented with icterus, generalized itching for 15 days duration and later on found to have hyperferritinemia, increased transferrin saturation, heterozygous mutant for H63D gene for hemochromatosis.

Iodide Excess Inhibits Thyroid Hormone Synthesis Pathway Involving XBP1-Mediated Regulation

Iodine is an essential micronutrient for producing thyroid hormone (TH); however, iodide excess can lead to adverse thyroidal effects. Unfortunately, the lack of a proper in vitro model system hampered the studies of the effect of iodide excess on thyroid physiology and pathology. Here, we demonstrated that excessive iodide intake downregulated the genes related to TH synthesis in the thyroids of mice. Since sodium iodide has no effect on these genes in cultured cell lines, we developed a three-dimensional (3D) culture system to enable the murine thyrocytes to form organoids in vitro with thyroid follicle-like structures and function and found that the in vivo effect of iodide excess could be mimicked in these thyroid organoids. Our data indicate that iodide excess mainly activated the XBP1-mediated unfolded protein response in both murine thyroid and thyroid organoids, while activation of XBP1 was able to mimic the sodium iodide effect on genes for the synthesis of TH in murine thyroid organoids. Lastly, our results suggest that XBP1 might transcriptionally repress the genes involved in the synthesis of TH. Based on these findings, we propose that iodide excess inhibits the transcription of genes related to TH synthesis through a mechanism involving XBP1-mediated action.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters (OPEs) are widespread in various environmental media, and can disrupt thyroid endocrine signaling pathways. Mechanisms by which OPEs disrupt thyroid hormone (TH) signal transduction are not fully understood. Here, we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways. OPEs can bind to transthyretin (TTR) and thyroxine-binding globulin, thereby affecting the transport of TH in the blood, and to the brain by TTR through the blood–brain barrier. When GH3 cells were exposed to OPEs, cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH. Cresyl diphenyl phosphate was shown to be an effective antagonist of TH. Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis. Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, signaling pathways related to thyroid endocrine functions, such as receptor–ligand binding and regulation of hormone levels, were identified as being affected by exposure to OPEs. Effects were also associated with the biosynthesis and metabolism of lipids, and neuroactive ligand–receptor interactions. These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

Cooked common bean flour, but not its protein hydrolysate, has the potential to improve gut microbiota composition and function in BALB/c mice fed a high-fat diet added with 6-propyl-2-thiouracil

Common bean has the potential to improve gut microbiota function due to its chemical composition and content of dietary fiber. This study evaluated the effect of cooked common bean (CCB) flour and its protein hydrolysate as part of a high-fat diet (HFD) added with 6-propyl-2-thiouracil (10 mg/kg/d), an inhibitor of thyroid hormone synthesis, on gut health of BALB/c mice. Forty-eight adult mice were divided into four groups: normal control; HFD; HFD plus CCB flour (346.6 g/kg of diet) (HFBF group) and HFD plus CCB protein hydrolysate (700 mg/Kg/d) (HFPH group). HFBF, but not HFPH, increased cecum weight, and the moisture, and lipids in the excreted feces, compared to control groups. Sequencing of the 16S rRNA gene of the cecal microbiota indicated changes in the beta-diversity between the HFBF and HFPH groups, compared to the normal control. The abundance of Bacteroidetes increased and the Firmicutes/Bacteroidetes ratio decreased in the HFBF compared to control groups. However, HFPH was not able to prevent the damage caused by a HFD to the gut bacterial communities. The OTUs enriched by HFBF were mainly assigned to members of the Muribaculaceae family, which shows potential to improve gut health. The intake of CCB flour improved intestinal health and modulated the composition and function of the cecal microbiota, attenuating the effects of the HFD, added wit 6-propyl-2-thiouracil, when fed to BALB/c mice.

Thyroid Disruptors: Extrathyroidal Sites of Chemical Action and Neurodevelopmental Outcome-An Examination Using Triclosan and Perfluorohexane Sulfonate.

Many xenobiotics are identified as potential thyroid disruptors due to their action to reduce circulating levels of thyroid hormone, most notably thyroxine (T4). Developmental neurotoxicity is a primary concern for thyroid disrupting chemicals yet correlating the impact of chemically induced changes in serum T4 to perturbed brain development remains elusive. A number of thyroid-specific neurodevelopmental assays have been proposed, based largely on the model thyroid hormone synthesis inhibitor propylthiouracil (PTU). This study examined whether thyroid disrupting chemicals acting distinct from synthesis inhibition would result in the same alterations in brain as expected with PTU. The perfluoroalkyl substance perfluorohexane sulfonate (50 mg/kg/day) and the antimicrobial Triclosan (300 mg/kg/day) were administered to pregnant rats from gestational day 6 to postnatal day (PN) 21, and a number of PTU-defined assays for neurotoxicity evaluated. Both chemicals reduced serum T4 but did not increase thyroid stimulating hormone. Both chemicals increased expression of hepatic metabolism genes, while thyroid hormone-responsive genes in the liver, thyroid gland, and brain were largely unchanged. Brain tissue T4 was reduced in newborns, but despite persistent T4 reductions in serum, had recovered in the PN6 pup brain. Neither treatment resulted in a low dose PTU-like phenotype in either brain morphology or neurobehavior, raising questions for the interpretation of serum biomarkers in regulatory toxicology. They further suggest that reliance on serum hormones as prescriptive of specific neurodevelopmental outcomes may be too simplistic and to understand thyroid-mediated neurotoxicity we must expand our thinking beyond that which follows thyroid hormone synthesis inhibition.

Antithyroid Drug Treatment in Graves' Disease.

Graves’ disease is associated with thyrotropin (TSH) receptor stimulating antibody, for which there is no therapeutic agent. This disease is currently treated through inhibition of thyroid hormone synthesis or destruction of the thyroid gland. Recurrence after antithyroid drug (ATD) treatment is common. Recent studies have shown that the longer is the duration of use of ATD, the higher is the remission rate. Considering the relationship between clinical outcomes and iodine intake, recurrence of Graves’ disease is more common in iodine-deficient areas than in iodine-sufficient areas. Iodine restriction in an iodine-excessive area does not improve the effectiveness of ATD or increase remission rates. Recently, Danish and Korean nationwide studies noted significantly higher prevalence of birth defects in newborns exposed to ATD during the first trimester compared to that of those who did not have such exposure. The prevalence of birth defects was lowest when propylthiouracil (PTU) was used and decreased by only 0.15% when methimazole was changed to PTU in the first trimester. Therefore, it is best not to use ATD in the first trimester or to change to PTU before pregnancy.

Therapeutic Plasma Exchange in Thyroid Storm Refractory to Conventional Treatment

Thyroid storm is a life-threatening condition with mortality rates reaching up to 20 to 30%. First-line treatment includes inhibition of thyroid hormone synthesis, prevention of release of preformed hormones, blocking of peripheral FT4 to FT3 conversion, enhancing hormone clearance, and definitive radioactive iodine ablation. However, in the presence of life-threatening adverse effects (e.g., agranulocytosis) and contraindications (e.g., fulminant hepatic failure), therapeutic plasma exchange (TPE) can be used to rapidly remove circulating thyroid hormones, antibodies, and cytokines in plasma; this is recommended by the American Society of Apheresis (ASFA) and the American Thyroid Association (ATA) as second-line treatment for thyroid storm. Here, we report a 49-year-old female with Graves’ disease admitted in our emergency room for a 6-week history of fever, weight loss, jaundice, exertional dyspnea, palpitations, and diarrhea. Her initial thyroid hormone levels were: FT4 64.35 (NV 9.01–19.05 pmol/L), FT3 23.91 (NV: 2.89–4.88 pmol/L), and TSH 0.00000 (NV: 0.35-4.94 mIU/L) and we managed her as a case of thyroid storm (Burch-Wartofsky score 70) by initiating high dose propylthiouracil. However, her sensorium deteriorated and serum bilirubin continued to rise from 307.2 on admission to 561.6 umol/L on the 5th hospital day (NV: 3 - 22 umol/L). TPE was performed after consultation with the Division of Hematology. Over the treatment course, her thyroid hormones normalized: FT4 13.18 pmol/L, FT3 2.30 pmol/L. However, despite TPE, her symptoms worsened and she became comatose, had hypotension despite vasopressors and developed new-onset atrial fibrillation. She expired on her 7th hospital day from multiorgan failure. TPE is effective in decreasing circulating thyroid hormone levels. However, it had no effect on clinically important outcomes as our patient still deteriorated and eventually succumbed. We still wrote and submitted this case report since if only successful cases were reported, the true effectiveness rate of TPE could not be determined.

Risk and Association of HLA Alleles with Methimazole-Induced Cutaneous Adverse Reactions in Chinese Han Population

Methimazole (MMI) is a widely used antithyroid drug, which inhibits thyroid hormone synthesis by interfering with the activity of thyroid peroxidase (Cooper, 2005). However, MMI is sometimes associated with cutaneous adverse drug reactions (cADRs), varying from urticaria and maculopapular eruption to severe reactions such as drug-induced hypersensitivity syndrome (Burch and Cooper, 2015; Ozaki et al., 2005). MMI-induced cADRs cannot always be predicted and sometimes could be life-threatening, requiring or prolonging hospitalization, impeding proper treatment, and increasing treatment costs considerably.

Evidence for Neurohormonal Triggers of Cardiomyocyte Polyploidization and Cardiac Regenerative Potential Loss During Endothermy Acquisition

Tissue regenerative potential displays striking divergence across phylogeny and ontogeny, but the underlying mechanisms remain enigmatic. Loss of mammalian cardiac regenerative potential correlates with cardiomyocyte cell‐cycle arrest and polyploidization as well as the development of postnatal endothermy. Genetic evidences in both mice and zebrafish support that cardiomyocyte polyploidization represents a major barrier limiting cardiac regenerative capacity. Through phylogenetic analyses of 41 vertebrate species, we uncover that certain monotreme, edentate, cetacean, chiropteran species have unusually high percentages of diploid cardiomyocytes in the adult heart. Furthermore, diploid cardiomyocyte abundance conforms to Kleiber’s law—the 3/4‐power law scaling of metabolism with bodyweight—and inversely correlates with standard metabolic rate, body temperature, and serum thyroxine level. Inactivation of thyroid hormone signaling reduces mouse cardiomyocyte polyploidization, delays cell‐cycle exit, and retains cardiac regenerative potential in adults. Conversely, exogenous thyroid hormones inhibit zebrafish heart regeneration. Notably, inhibition of thyroid hormone synthesis in mice after birth results in low body temperatures.Recently, we discover the nervous system as a secondary major regulator of mammalian cardiomyocyte polyploidization, cell cycle arrest, and body temperature increase. Moreover, inhibitions of neuronal activity and thyroid hormone signaling in neonates have additive effects, yielding mice with the highest percentage of diploid cardiomyocytes and lowest body temperature to our knowledge. Thus, our results support a model where loss of cardiomyocyte regenerative capacity, driven by increasing neurohormonal activities, may be a tradeoff for the acquisition of endothermy during animal evolution and postnatal development.Support or Funding InformationNIH

Sex-specific endocrine-disrupting effects of three halogenated chemicals in Japanese medaka.

Several halogenated chemicals are found in an array of products that can cause endocrine disruption. Human studies have shown that endocrine responses are sex specific, with females more likely to develop hypothyroidism and males more likely to have reproductive impairment. The objective of this study was to assess sex differences on thyroid and estrogenic effects after exposure of Japanese medaka (Oryzias latipes, SK2MC) to halogenated compounds. This strain is an excellent model for these studies as sex can be determined non-destructively a few hours postfertilization. Medaka embryos were exposed to sublethal concentrations of Tris(1,3-dichloro-2-propyl) phosphate (TDCPP, 0.019mg/L), perfluorooctanoic acid (PFOA, 4.7mg/L) and its next generation alternative, perfluorobutyric acid (PFBA, 137mg/L). Methimazole (inhibits thyroid hormone synthesis) and the thyroid hormone triiodothyronine served as reference controls. Fish were exposed throughout embryo development until 10days postfertilization. Females displayed significantly larger swim bladders (which are under thyroid hormone control) after exposure to all chemicals with the exception of triiodothyronine, which caused the opposite effect. Females exposed to TDCPP and PFOA had increased expression of vitellogenin and exposure to PFOA upregulated expression of multiple thyroid-related genes. Upregulation of estrogenic-regulated genes after exposure to TDCPP, PFOA and methimazole was only observed in males. Overall, our results suggest that females and males show an estrogenic response when exposed to these halogenated chemicals and that females appear more susceptible to thyroid-induced swim bladder dysfunction compared with males. These results further confirm the importance of considering sex effects when assessing the toxicity of endocrine-disrupting compounds.

Thyroid Hormone Disruptors Interfere with Molecular Pathways of Eye Development and Function in Zebrafish.

The effects of thyroid hormone disrupting chemicals (THDCs) on eye development of zebrafish were investigated. We expected THDC exposure to cause transcriptional changes of vision-related genes, which find their phenotypic anchoring in eye malformations and dysfunction, as observed in our previous studies. Zebrafish were exposed from 0 to 5 days post fertilization (dpf) to either propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, or tetrabromobisphenol-A (TBBPA), which interacts with thyroid hormone receptors. Full genome microarray analyses of RNA isolated from eye tissue revealed that the number of affected transcripts was substantially higher in PTU- than in TBBPA-treated larvae. However, multiple components of phototransduction (e.g., phosphodiesterase, opsins) were responsive to both THDC exposures. Yet, the response pattern for the gene ontology (GO)-class “sensory perception” differed between treatments, with over 90% down-regulation in PTU-exposed fish, compared to over 80% up-regulation in TBBPA-exposed fish. Additionally, the reversibility of effects after recovery in clean water for three days was investigated. Transcriptional patterns in the eyes were still altered and partly overlapped between 5 and 8 dpf, showing that no full recovery occurred within the time period investigated. However, pathways involved in repair mechanisms were significantly upregulated, which indicates activation of regeneration processes.

Effect of antithyroid drugs on the occurrence of antibodies against type 2 deiodinase (DIO2), which are involved in hyperthyroid Graves’ disease influencing the therapeutic efficacy

Graves' disease is an organ-specific autoimmune disease with hyperthyroidism, diffuse goiter and autoantibodies against TSH receptor, thyroid peroxidase (TPO) and/or thyroglobulin (Tg). Graves' hyperthyroidism is characterized by T3 dominance due to the conversion of T4 into T3 through type 1 and 2 deiodinase enzymes (DIO1, DIO2). Methimazole (MMI) and propylthiouracil (PTU) therapies inhibit thyroid hormone synthesis blocking the activity of deiodinase and TPO enzymes. The study investigated the occurrence of autoantibodies against DIO2 peptides (cys- and hom-peptides) with the effect of antithyroid drugs on their frequencies in 78 patients with Graves' disease and 30 controls. In hyperthyroidism, the presence of DIO2 peptide antibodies was as follows: 20 and 11 cases out of 51 for cys- and hom-peptide antibodies, respectively, of whom 8 cases possessed antibodies against both peptides. Antithyroid drugs differently influenced their frequencies, which were greater in PTU than in MMI (3/6 vs 13/45 cases, P < 0.016 for cys- and 0/6 vs 2/45 cases for hom-peptide antibodies). Antibodies against both peptides demonstrated more reduced levels of anti-TPO (P < 0.003) and anti-Tg antibodies (P < 0.002) compared with those without peptide antibodies. PTU compared with MMI increased the levels of TSH receptor antibodies (32.5 UI/l vs 2.68IU/l, P < 0.009). MMI treatment led to more reduced FT3 levels and FT3/FT4 ratios in hyperthyroid Graves' ophthalmopathy (P < 0.028 for FT3, P < 0.007 for FT3/FT4 ratio). In conclusion, the presence of DIO2 peptide antibodies is connected to Graves' hyperthyroidism influencing the levels of antibodies against TPO, Tg and TSH receptor, as well as the therapeutic efficacy of antithyroid drugs.

An automated screening method for detecting compounds with goitrogenic activity using transgenic zebrafish embryos.

The knowledge on environmentally relevant chemicals that may interfere with thyroid signaling is scarce. Here, we present a method for the screening of goitrogens, compounds that disrupt the thyroid gland function, based on the automatic orientation of zebrafish in a glass capillary and a subsequent imaging of reporter gene fluorescence in the thyroid gland of embryos of the transgenic zebrafish line tg(tg:mCherry). The tg(tg:mCherry) reporter gene indicates a compensatory upregulation of thyroglobulin, the thyroid hormone precursor, in response to inhibition of thyroid hormone synthesis. Fish embryos were exposed to a negative control compound (3,4-dichloroaniline), or a concentration series of known goitrogenic compounds (resorcinol, methimazole, potassium perchlorate, 6-propyl-2-thiouracil, ethylenethiourea, phloroglucinol, pyrazole) with maximum exposure concentration selected based on mortality and/or solubility. Exposure to 3,4-dichloroaniline decreased the fluorescence signal. All goitrogenic compounds exhibited clear concentration-dependent inductions of reporter fluorescence 1.4 to 2.6 fold above control levels. Concentration-response modelling was used to calculate goitrogenic potencies based on EC50 values. The new automated method offers an efficient screening approach for goitrogenic activity.

Specific alteration of gene expression profile in rats by treatment with thyroid toxicants that inhibit thyroid hormone synthesis.

Transcriptomics technologies have been used for risk assessment of chemicals, mainly to predict the modes of action (MOAs) of chemicals or identify biomarkers. Transcriptomics data may also be helpful to understand MOAs of chemicals at the molecular level in more detail. As an example of the known MOAs, there are two MOAs of thyroid toxicity: inhibition of thyroid hormone synthesis ("direct" effect) and hypermetabolism of thyroid hormone by enzyme induction in liver ("indirect" effect). In the present study, global profiles of gene expression were analyzed in rats treated with chemicals acting directly on the thyroid (thyroid peroxidase inhibitors such as propylthiouracil and methimazole) and chemicals acting indirectly on the thyroid (hepatic enzyme inducers such as phenobarbital and pregnenolone-16α-carbonitrile) using microarrays. Using a subtraction method between these two types of chemicals, we identified characteristic gene expression changes on the thyroid hormone synthesis pathway by direct-acting chemicals. Based on the functions of these genes, alterations of their expression seem to indicate the results of thyroid peroxidase inhibition, and might be helpful in more accurate evaluation of MOAs for thyroid toxicity.