Cloning and characterization of the thyroid iodide transporter

Characteristics of exposure to radioactive iodine during a nuclear incident

BACKGROUND

During a nuclear accident, numerous products of nuclear fission are released, including isotopes of radioactive iodine. Among them is iodine-131, with a half-life of 8.02 days, which emits β radiation. For decades, it has been effectively and safely used in medicine. However, in the event of a nuclear accident, uncontrolled exposure can have harmful biological effects. The main sources of internal contamination with iodine-131 are contaminated air, food and water. The most exposed organ is the thyroid gland, where radioactive iodine accumulates via the Na+/I- symporter (NIS). NIS does not distinguish between radioactive iodine isotopes and the stable isotope iodine-127, which is essential for the synthesis of thyroid hormones. Exposure to radioactive iodine during a nuclear accident is primarily associated with papillary thyroid cancer, whose incidence begins to increase a few years after exposure. Children and adolescents are at the highest risk, and the risk is particularly significant for individuals living in iodine-deficient areas.

CONCLUSIONS

Ensuring an adequate iodine supply is therefore crucial for lowering the risk of the harmful effects of exposure to radioactive iodine at the population level. Protecting the thyroid with potassium iodide tablets significantly reduces radiation exposure, as stable iodine prevents the entry of radioactive iodine into the thyroid. Such protection is effective only within a narrow time window - a few hours before and after the exposure and is recommended only for those under 40 years of age, as the risks of excessive iodine intake outweigh the potential benefits in older individuals.

Amide/urea-based simple fluorometric receptors for iodide and Hg2+ ions in aqueous medium: Aggregation induced emission and DFT studies

Herein, we report pyrene-tagged amide and urea-based sugar derivatives 1 and 2 in a simple synthetic pathway to recognize I- and Hg2+ ions. Both molecules showed absorbance and fluorescence selectivity towards iodide ions in THF/H2O (7/3, v/v) medium. The selectivity and sensitivity of 2 for iodide ions are superior to 1 due to more H-bond donors in 2. Interestingly, fluorometric receptor 2 exhibited aggregation-induced emission (AIE) at higher pH with a remarkable fluorometric color change. The AIE phenomenon might be explained by the self-association of 2 after forming imine functionality in the alkali medium. The Stern-Volmer plot showed the fluorescence quenching constant of each receptor with an iodide ion and indicated the quenching pathway. The LODs of 1 and 2 for iodide ions were evaluated as 0.84 and 0.17 µM, respectively. The 1:1 binding stoichiometry of 1 or 2 with iodide was found from the Job plot and verified by measuring the complex mass. Further, the complexes of each receptor with I- ions can detect Hg2+ ions selectively by fluorescence turn-on method with low sensitivities (LODs: 0.008 µM for 1 and 0.01 µM for 2). DFT results were used to understand the binding mode of receptors 1 and 2 with iodide ions and the quenching process in the aqueous THF medium. The real application of the receptors was established for the recovery of iodide and Hg2+ ions from natural water samples.

[18F]FDG PET/CT can trigger relevant oncological management changes leading to favorable outcome in iodine-negative thyroid cancer patients

BACKGROUND

In patients with iodine-negative thyroid cancer (TC), current guidelines endorse an [18F]FDG PET/CT to identify dedifferentiated sites of disease. We aimed to determine the rate of oncological management changes triggered by such a molecular imaging approach, along with the impact on outcome.

METHODS

42 consecutive patients with negative findings on [131I] whole body scan were scheduled for [18F]FDG PET/CT and treatment based on PET results were initiated. To determine the impact on oncological management, we compared the therapeutic plan prior to and after molecular imaging. Based on imaging follow-up, the rate of controlled disease (CD, defined as stable disease, complete or partial response) was also recorded, thereby allowing to assess whether [18F]FDG-triggered management changes can also lead to favorable outcome.

RESULTS

We observed no alterations of the treatment plan in 9/42 (21.4%) subjects (active surveillance in 9/9 [100%]). Oncological management was changed in the remaining 33/42 (78.6%; systemic treatment in 9/33 [27.3%] and non-systemic treatment in 24/33 [72.7%]). Among patients receiving non-systemic therapy, the following changes were noted: surgery in 20/24 (83.3%) and radiation therapy in 4/24 (16.7%). In the systemic group, tyrosine kinase inhibitor (TKI) was prescribed in 8/9 (88.9%), while radioiodine therapy based on a TKI-mediated redifferentiation approach was conducted in 1/9 (11.1%). In 26 subjects with available follow-up, rate of CD was 22/26 (84.6%) and among those, 15/22 (68.1%) had experienced previous management changes based on PET/CT findings.

CONCLUSIONS

In subjects with iodine-negative TC, [18F]FDG PET/CT triggered relevant management changes along with disease control in the vast majority of patients. As such, in dedifferentiated TC, [18F]FDG PET/CT may serve as a relevant management tool and therapeutic decision-aid in the clinic.

Exploring Amino Acid Transporters as Therapeutic Targets for Cancer: An Examination of Inhibitor Structures, Selectivity Issues, and Discovery Approaches

Amino acid transporters are abundant amongst the solute carrier family and have an important role in facilitating the transfer of amino acids across cell membranes. Because of their impact on cell nutrient distribution, they also appear to have an important role in the growth and development of cancer. Naturally, this has made amino acid transporters a novel target of interest for the development of new anticancer drugs. Many attempts have been made to develop inhibitors of amino acid transporters to slow down cancer cell growth, and some have even reached clinical trials. The purpose of this review is to help organize the available information on the efforts to discover amino acid transporter inhibitors by focusing on the amino acid transporters ASCT2 (SLC1A5), LAT1 (SLC7A5), xCT (SLC7A11), SNAT1 (SLC38A1), SNAT2 (SLC38A2), and PAT1 (SLC36A1). We discuss the function of the transporters, their implication in cancer, their known inhibitors, issues regarding selective inhibitors, and the efforts and strategies of discovering inhibitors. The goal is to encourage researchers to continue the search and development within the field of cancer treatment research targeting amino acid transporters.

Nanotechnological Advancements for the Theranostic Intervention in Anaplastic Thyroid Cancer: Current Perspectives and Future Direction

Anaplastic thyroid cancer is the rarest, most aggressive, and undifferentiated class of thyroid cancer, accounting for nearly forty percent of all thyroid cancer-related deaths. It is caused by alterations in many cellular pathways like MAPK, PI3K/AKT/mTOR, ALK, Wnt activation, and TP53 inactivation. Although many treatment strategies, such as radiation therapy and chemotherapy, have been proposed to treat anaplastic thyroid carcinoma, they are usually accompanied by concerns such as resistance, which may lead to the lethality of the patient. The emerging nanotechnology-based approaches cater the purposes such as targeted drug delivery and modulation in drug release patterns based on internal or external stimuli, leading to an increase in drug concentration at the site of the action that gives the required therapeutic action as well as modulation in diagnostic intervention with the help of dye property materials. Nanotechnological platforms like liposomes, micelles, dendrimers, exosomes, and various nanoparticles are available and are of high research interest for therapeutic intervention in anaplastic thyroid cancer. The pro gression of the disease can also be traced by using magnetic probes or radio-labeled probes and quantum dots that serve as a diagnostic intervention in anaplastic thyroid cancer.

Thyroid hormone biosynthesis and its role in brain development and maintenance

Thyroid hormones are critical modulators in the physiological processes necessary to virtually all tissues, with exceptionally fundamental roles in brain development and maintenance. These hormones regulate essential neurodevelopment events, including neuronal migration, synaptogenesis, and myelination. Additionally, thyroid hormones are crucial for maintaining brain homeostasis and cognitive function in adulthood. This chapter aims to offer a comprehensive understanding of thyroid hormone biosynthesis and its intricate role in brain physiology. Here, we described the mechanisms underlying the biosynthesis of thyroid hormones, their influence on various aspects of brain development and ongoing maintenance, and the proteins in the brain that are responsive to these hormones. This chapter was geared towards broadening our understanding of thyroid hormone action in the brain, shedding light on potential therapeutic targets for neurodevelopmental and neurodegenerative disorders.

Towards translating in vitro measures of thyroid hormone system disruption to in vivo responses in the pregnant rat via a biologically based dose response (BBDR) model

Despite the number of in vitro assays that have been recently developed to identify chemicals that interfere with the hypothalamic-pituitary-thyroid axis (HPT), the translation of those in vitro results into in vivo responses (in vitro to in vivo extrapolation, IVIVE) has received limited attention from the modeling community. To help advance this field a steady state biologically based dose response (BBDR) model for the HPT axis was constructed for the pregnant rat on gestation day (GD) 20. The BBDR HPT axis model predicts plasma levels of thyroid stimulating hormone (TSH) and the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Thyroid hormones are important for normal growth and development of the fetus. Perchlorate, a potent inhibitor of thyroidal uptake of iodide by the sodium iodide symporter (NIS) protein, was used as a case study for the BBDR HPT axis model. The inhibitory blocking of the NIS by perchlorate was associated with dose-dependent steady state decreases in thyroid hormone production in the thyroid gland. The BBDR HPT axis model predictions for TSH, T3, and T4 plasma concentrations in pregnant Sprague Dawley (SD) rats were within 2-fold of observations for drinking water perchlorate exposures ranging from 10 to 30,000 μg/kg/d. In Long Evans (LE) pregnant rats, for both control and perchlorate drinking water exposures, ranging from 85 to 82,000 μg/kg/d, plasma thyroid hormone and TSH concentrations were predicted within 2 to 3.4- fold of observations. This BBDR HPT axis model provides a successful IVIVE template for thyroid hormone disruption in pregnant rats.

Evaluation of the therapeutic effect of Descurainia sophia (L.) Webb ex Prantl seed extract on hyperthyroidism: A double-blind placebo-controlled pilot clinical trial

The seeds of Descurainia sophia (L.) Webb ex Prantl contain goitrogenic glucosinolates, such as gluconapin (3-butenyl glucosinolate). Because of the important role of iodine in the synthesis of thyroid hormones and the inhibitory activity of D. sophia on iodine uptake by the thyroid gland, this study aimed to determine the effects of D. sophia syrup on clinical and biochemical variables of thyrotoxicosis in hyperthyroid patients. In this randomized, double-blind trial, 10 newly diagnosed hyperthyroid female patients were randomly assigned to treatment with (1) methimazole (MMI) plus D. sophia capsules (350 mg/d) or (2) MMI plus placebo capsules. The primary outcomes were clinical and biochemical manifestations of hyperthyroidism after 60 days. Serum levels of FT3 and FT4 significantly decreased (5.9 ± 2.5 vs. 9.4 ± 5.9 and 29.1 ± 3.1 vs. 31.77 ± 3.7, respectively) and the serum thyroid-stimulating hormone (TSH) concentration significantly increased in the D. sophia group contrasted to the placebo group (4.7 ± 0.1 vs. 0.05 ± 0.02). Significant improvement in the thyrotoxicosis clinical symptoms was reported in the D. sophia group contrasted to the placebo group (p < .05). D. sophia can suppress plasma levels of FT3 and FT4 and may be useful as adjunctive therapy for hyperthyroidism.

Binaphthyl-Based Chiral Macrocyclic Hosts for the Selective Recognition of Iodide Anions

In this study, we explorethe synthesis of binaphthyl-based chiral macrocyclic hosts for the first time. They exhibited the selective recognition abilities of iodide anions which can be favored over those of other anions (AcO^-, NO₃^-, ClO₄^-, HSO₄^-, Br^-, PF₆^-, H₂PO₄^-, BF₄^-, and CO₃F₃S^-), as confirmed by UV-vis, HRMS, and ¹H NMR spectroscopy experiments, as well as DFT calculations. Neutral aryl C-H···anion interactions play an important role in the formation complexes. The recognition process can be observed by the naked eye.

Influence of the TAS2R38 Gene Single Nucleotide Polymorphisms in Metabolism and Anthropometry in Thyroid Dysfunction

The gene TAS2R38 single nucleotide polymorphisms (SNPs-P49A, A262V and V296I) can condition bitter tasting by PAV (proline-alanine-valine) and non-bitter-tasting by AVI (alanine-valine-isoleucine) homozygosity. We evaluated this polymorphisms association with thyroid function, metabolism and anthropometry parameters determined by: Endpoint analysis (SNPs); DXA (fat mass-%, total fat mass-kg, lean mass-kg); Standard methods (lipid metabolism parameters, HbA1c-%, glycemia-mg/dL, insulinemia-µIU/mL, HOMA-IR, uricemia-mg/dL, calcemia-mg/dL and BMI-kg/m²); ELISA (leptinemia-ng/mL); Spectrophotometry (Angiotensin Converting Enzyme activity-UI/L). Statistics: SPSS program; OR [IC95%]; p < 0.05. Sample: 114 hypothyroid, 49 hyperthyroid, and 179 controls. An association between A262V-valine-valine and hypothyroidism/hyperthyroidism was verified (OR = 2.841; IC95% [1.726-4.676]), p < 0.001/OR = 8.915; IC95% [4.286-18.543]), p < 0.001). Protector effect from thyroid dysfunction: A262V-alanine-valine (OR = 0.467; IC95% [0.289-0.757], p = 0.002/OR = 0.132; IC95% [0.056-0.309], p < 0.001) and PAV (OR = 0.456; IC95% [0.282-0.737], p = 0.001/OR = 0.101; IC95% [0.041-0.250], p < 0.001). Higher parameter values associated with genotypes were: fat-mass-% (V296I-valine-isoleucine), lean-mass (P49A-proline-proline; PVI), leptin (AVI), HbA1c (A262V-alanine-valine) and lower values in lean-Mass (AVI; PVV), leptin (A262V-alanine-alanine), HbA1c (PVV), uricemia (V296I-valine-isoleucine), glycemia (A262V-alanine-alanine; AAV) and plasma triglycerides (PVV). In conclusion, TAS2R38 influences thyroid function, body composition and metabolism. Bitter taste perception (PAV) and the genotype A262V-alanine-valine can protect from thyroid dysfunction. AVV, PVV and genotype A262V-valine-valine may confer higher predisposition for thyroid dysfunction, particularly PVV for hyperthyroidism.

The master role of polarized NIS expression in regulating iodine metabolism in the human body

Objective

The aim of this study was to investigate how polarized sodium iodide symporter (NIS) expression may regulate iodide metabolism in vivo.

Materials and methods

Polarized NIS expression was analyzed in tissues that accumulate iodide by the use of immunohistochemistry and polyclonal antibody against the C-terminal end of human NIS (hNIS).

Results

Iodide absorption in the human intestine occurs via NIS expressed in the apical membrane. Iodide is secreted into the lumen of the stomach and salivary glands via NIS expressed in the basolateral membrane and then circulates back from the small intestine to the bloodstream via NIS expressed in the apical membrane.

Conclusion

Polarized NIS expression in the human body regulates intestinal-bloodstream recirculation of iodide, perhaps prolonging the availability of iodide in the bloodstream. This leads to more efficient iodide trapping by the thyroid gland. Understanding the regulation and manipulating gastrointestinal iodide recirculation could increase radioiodine availability during theranostic NIS applications.

Severe Autoimmune Thyroiditis in Transgenic NOD.H2h4 Mice Expressing Interleukin-4 in the Thyroid

Background: Hashimoto's thyroiditis is a common autoimmune thyroid disorder characterized by thyroid lymphocytic infiltrates and autoreactive antibodies against thyroglobulin (TgAbs) and thyroperoxidase. Final evolution of the disease can lead to hypothyroidism with destruction of the thyroid architecture. Interleukin-4 (IL-4) is involved in the humoral immune response and B cell activation required in autoimmune thyroiditis (AT) progression. We used our mouse model overexpressing IL-4 by thyrocytes (Thyr-IL4) to study the impact of a local IL-4 expression in AT using transgenic nonobese diabetic (NOD.H2^h4) derived animals treated with iodide-supplemented water to increase the incidence of spontaneous AT (SAT). Methods: Thyr-IL4 NOD.H2^h4 and nonpathogenic C57BL/6 animals aged 8 weeks were exposed to 0.05% sodium iodide (NaI) in their drinking water for 8 and 16 weeks. Circulating TgAbs and expression of intrathyroidal cytokines were quantified. Thyroid inflammation was assessed by classical histological analyses, including identification of some immune cell populations. The most sensitive parameter to evaluate the thyroid function, serum thyrotropin (TSH), was also measured at the end of the treatment. Results: Relative to wild-type (WT) animals, Thyr-IL4 NOD.H2^h4 mice developed severe accelerated SAT with elevated serum TgAbs and numerous thyroid infiltrates mainly composed of CD4⁺/CD8⁺ T cells, B lymphocytes, and monocytes/macrophages. Thyroid expression of T helper (Th) Th1/Th2 cytokines was also enhanced, as well as IL-17. In contrast, excessive iodide supply did not induce TgAbs in WT and Thyr-IL4 SAT-resistant C57BL/6 animals. However, moderate leukocyte infiltrations in transgenic thyroids were evident compared to WT, but associated with a limited number of T and B cells and a different cytokine profile from Thyr-IL4 NOD.H2^h4 mice. Finally, and despite their diverse immune responses, both transgenic strains presented marked thyroid enlargement and elevated serum TSH at the end of the treatment in contrast to their WT littermates. Conclusions: These findings demonstrated that ectopic expression of IL-4 from thyrocytes enhanced the severity of accelerated SAT in disease-prone Thyr-IL4 NOD.H2^h4 animals and promoted thyroid leukocyte infiltration in SAT-resistant transgenic C57BL/6 mice. Moreover, impaired thyroid function emerged in both transgenic strains during the progression of the disease.

Sodium/Iodide Symporter Metastable Intermediates Provide Insights into Conformational Transition between Principal Thermodynamic States

The Sodium/Iodide Symporter (NIS), a 13-helix transmembrane protein found in the thyroid and other tissues, transports iodide, a required constituent of thyroid hormones T3 and T4. Despite extensive experimental information and clinical data, structural details of the intermediate microstates comprising the conformational transition of NIS between its inwardly and outwardly open states remain unresolved. We present data from a combination of enhanced sampling and transition path molecular dynamics (MD) simulations that elucidate the principal intermediate states comprising the inwardly to outwardly open transition of fully bound and apo NIS under an enforced ionic gradient. Our findings suggest that in both the absence and presence of bound physiological ions, NIS principally occupies a proximally inward to inwardly open state. When fully bound, NIS is also found to occupy a rare "inwardly occluded" state. The results of this work provide novel insight into the populations of NIS intermediates and the free energy landscape comprising the conformational transition, adding to a mechanistic understanding of NIS ion transport. Moreover, the knowledge gained from this approach can serve as a basis for studies of NIS mutants to target therapeutic interventions.

Overexpression of Both Human Sodium Iodide Symporter (NIS) and BRG1-Bromodomain Synergistically Enhances Radioiodine Sensitivity by Stabilizing p53 through NPM1 Expression

Improved therapeutic strategies are required to minimize side effects associated with radioiodine gene therapy to avoid unnecessary damage to normal cells and radiation-induced secondary malignancies. We previously reported that codon-optimized sodium iodide symporter (oNIS) enhances absorption of I-131 and that the brahma-associated gene 1 bromodomain (BRG1-BRD) causes inefficient DNA damage repair after high-energy X-ray therapy. To increase the therapeutic effect without applying excessive radiation, we considered the combination of oNIS and BRG1-BRD as gene therapy for the most effective radioiodine treatment. The antitumor effect of I-131 with oNIS or oNIS+BRD expression was examined by tumor xenograft models along with functional assays at the cellular level. The synergistic effect of both BRG1-BRD and oNIS gene overexpression resulted in more DNA double-strand breaks and led to reduced cell proliferation/survival rates after I-131 treatment, which was mediated by the p53/p21 pathway. We found increased p53, p21, and nucleophosmin 1 (NPM1) in oNIS- and BRD-expressing cells following I-131 treatment, even though the remaining levels of citrulline and protein arginine deiminase 4 (PAD4) were unchanged at the protein level.

The potential interaction between medical treatment and radioiodine treatment success: A systematic review

Introduction

Radioactive iodine (RAI) therapy is a critical component in the post-surgical management of thyroid cancer patients, as well as being a central therapeutic option in the treatment of hyperthyroidism. Previous work suggests that antithyroid drugs hinder the efficacy of RAI therapy in patients. However, the effects of other background medications on RAI treatment efficacy have not been evaluated. Therefore, we performed a systematic review and meta-analysis investigating the potential off-target effects of medication on RAI therapy in patients with thyroid cancer and hyperthyroidism.

Methods

Systematic review and meta-analysis according to the 2020 PRISMA guidelines. Databases searched: MEDLINE, EMBASE and Cochrane Library for studies published between 2001 and 2021.

Results

Sixty-nine unique studies were identified. After screening, 17 studies with 3313 participants were included. One study investigated thyroid cancer, with the rest targeted to hyperthyroidism. The majority of studies evaluated the effects of antithyroid drugs; the other drugs studied included lithium, prednisone and glycididazole sodium. Antithyroid drugs were associated with negative impacts on post-RAI outcomes (n = 5 studies, RR = 0.81, p = 0.02). However, meta-analysis found moderate heterogeneity between studies (I2 = 51%, τ2 = 0.0199, p = 0.08). Interestingly, lithium (n = 3 studies), prednisone (n = 1 study) and glycididazole (n = 1 study) appeared to have positive impacts on post-RAI outcomes upon qualitative analysis.

Conclusion

Our systematic review strengthens previous work on antithyroid medication effects on RAI, and highlights that this field remains under researched especially for background medications unrelated to thyroid disease, with very few papers on non-thyroid medications published.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php, identifier CRD42021274026.

Lipid-Peptide-mRNA Nanoparticles Augment Radioiodine Uptake in Anaplastic Thyroid Cancer

Restoring sodium iodide symporter (NIS) expression and function remains a major challenge for radioiodine therapy in anaplastic thyroid cancer (ATC). For more efficient delivery of messenger RNA (mRNA) to manipulate protein expression, a lipid-peptide-mRNA (LPm) nanoparticle (NP) is developed. The LPm NP is prepared by using amphiphilic peptides to assemble a peptide core and which is then coated with cationic lipids. An amphiphilic chimeric peptide, consisting of nine arginine and hydrophobic segments (6 histidine, C18 or cholesterol), is synthesized for adsorption of mRNA encoding NIS in RNase-free conditions. In vitro studies show that LP(R9H6) m NP is most efficient at delivering mRNA and can increase NIS expression in ATC cells by more than 10-fold. After intratumoral injection of NIS mRNA formulated in optimized LPm NP, NIS expression in subcutaneous ATC tumor tissue increases significantly in nude mice, resulting in more iodine 131 (¹³¹ I) accumulation in the tumor, thereby significantly inhibiting tumor growth. Overall, this work designs three arginine-rich peptide nanoparticles, contributing to the choice of liposome cores for gene delivery. LPm NP can serve as a promising adjunctive therapy for patients with ATC by restoring iodine affinity and enhancing the therapeutic efficacy of radioactive iodine.

Non-Aquaporin Water Channels

Water transport through membrane is so intricate that there are still some debates. AQPs are entirely accepted to allow water transmembrane movement depending on osmotic gradient. Cotransporters and uniporters, however, are also concerned in water homeostasis. UT-B has a single-channel water permeability that is similar to AQP1. CFTR was initially thought as a water channel but now not believed to transport water directly. By cotransporters, such as KCC4, NKCC1, SGLT1, GAT1, EAAT1, and MCT1, water is transported by water osmosis coupling with substrates, which explains how water is transported across the isolated small intestine. This chapter provides information about water transport mediated by other membrane proteins except AQPs.

Proteomic analysis of radioiodine-refractory differentiated thyroid cancer identifies CHI3L1 upregulation in association with dysfunction of the sodium-iodine symporter

Radioiodine refractory differentiated thyroid cancer (RR-DTC) is the main factor adversely affecting the overall survival rate of patients with thyroid cancer. The aim of the present study was to investigate the underlying molecular mechanism of pathogenesis of RR-DTC and to explore novel therapeutic targets for clinical treatment. A proteomic analysis was performed using the tumor tissues of patients with RR-DTC. A total of 6 metastatic lymph nodes were collected during lymph node dissection, 3 from patients with RR-DTC and 3 from patients with papillary thyroid cancer. The expression of chitinase-3-like 1 (CHI3L1) and sodium-iodine symporter (NIS) in the tumor tissue was detected by immunohistochemistry (IHC). Western blotting was used to detect the expression of CHI3L1, phosphorylated (p)-MEK and p-ERK1/2 in PTC-K1 cells transfected with CHI3L1 overexpression vector. The proteomic analysis identified 665 differentially expressed proteins (DEPs), including 327 upregulated and 338 downregulated proteins in the RR-DTC group, which were enriched in 59 signaling pathways by Kyoto Encyclopedia of Genes and Genomes database analysis. In particular, CHI3L1 was demonstrated to be significantly upregulated in RR-DTC as evidenced by quantitative proteomic analysis and IHC. Western blotting suggested that the overexpression of CHI3L1 activated the MEK/ERK1/2 signaling pathway, which may lead to NIS dysfunction. In conclusion, the present study suggests that CHI3L1 is a potential molecular target for the radiotherapy of patients with RR-DTC.

The influence of sunitinib and sorafenib, two tyrosine kinase inhibitors, on development and thyroid system in zebrafish larvae

Recently, the potential toxic effects of various pharmaceuticals on the thyroid endocrine system have raised considerable concerns. In this study, we evaluated the adverse effects of sorafenib and sunitinib, two widely used anti-tumor drugs, on the developmental toxicities and thyroid endocrine disruption by using zebrafish (Danio rerio) model. Zebrafish embryos/larvae were exposed to different contentions (0, 10, 50 and 100 nM) of sorafenib and sunitinib for 96 hpf. The results revealed that waterborne exposure to sorafenib and sunitinib exhibited remarkable toxic effects on the survival and development in zebrafish embryos/larvae, which was accompanied by obvious disturbances of thyroid endocrine system (e.g., decreased T3 and T4 content, increased TSH content) and genes' transcription changes within the hypothalamus-pituitary-thyroid (HPT) axis. In addition, we verified a strikingly abnormal thyroid gland organogenesis in zebrafish larvae in response to sorafenib and sunitinib, by assessing the development of thyroid follicles using the WISH staining of tg, the Tg (tg:GFP) zebrafish transgenic line, and histopathological analysis. Taken together, our results indicated sorafenib and sunitinib exposure could induce obvious developmental toxicities and thyroid function disruption in zebrafish embryos/larvae, which might involve a regulatory mechanism, at least in part, by destroying the thyroid follicle structure, and by disturbing the balance of the HPT axis.

Structural insights into the mechanism of the sodium/iodide symporter

The sodium/iodide symporter (NIS) is the essential plasma membrane protein that mediates active iodide (I-) transport into the thyroid gland, the first step in the biosynthesis of the thyroid hormones-the master regulators of intermediary metabolism. NIS couples the inward translocation of I- against its electrochemical gradient to the inward transport of Na+ down its electrochemical gradient1,2. For nearly 50 years before its molecular identification3, NIS was the molecule at the centre of the single most effective internal radiation cancer therapy: radioiodide (131I-) treatment for thyroid cancer2. Mutations in NIS cause congenital hypothyroidism, which must be treated immediately after birth to prevent stunted growth and cognitive deficiency2. Here we report three structures of rat NIS, determined by single-particle cryo-electron microscopy: one with no substrates bound; one with two Na+ and one I- bound; and one with one Na+ and the oxyanion perrhenate bound. Structural analyses, functional characterization and computational studies show the substrate-binding sites and key residues for transport activity. Our results yield insights into how NIS selects, couples and translocates anions-thereby establishing a framework for understanding NIS function-and how it transports different substrates with different stoichiometries and releases substrates from its substrate-binding cavity into the cytosol.

Thyroglobulin regulates the expression and localization of the novel iodide transporter solute carrier family 26 member 7 (SLC26A7) in thyrocytes

Solute carrier family 26 member 7 (SLC26A7), identified as a causative gene for congenital hypothyroidism, was found to be a novel iodide transporter expressed on the apical side of the follicular epithelium of the thyroid. We recently showed that TSH suppressed the expression of SLC26A7 and induces its localization to the plasma membrane, where it functions. We also showed that the ability of TSH to induce thyroid hormone synthesis is completely reversed by an autocrine negative-feedback action of thyroglobulin (Tg) stored in the follicular lumen. In the present study, we investigated the potential effect of follicular Tg on SLC26A7 expression and found that follicular Tg significantly suppressed the promoter activity, mRNA level, and protein level of SLC26A7 in rat thyroid FRTL-5 cells. In addition, follicular Tg inhibited the ability of TSH to induce the membrane localization of SLC26A7. In rat thyroid sections, the expression of SLC26A7 was weaker in follicles with a higher concentration of Tg, as evidenced by immunofluorescence staining. These results indicate that Tg stored in the follicular lumen is a feedback suppressor of the expression and membrane localization of SLC26A7, thereby downregulating the transport of iodide into the follicular lumen.

Perchlorate, nitrate, and thiocyanate: Environmental relevant NIS-inhibitors pollutants and their impact on thyroid function and human health

Thyroid disruptors are found in food, atmosphere, soil, and water. These contaminants interfere with the thyroid function through the impairment of thyroid hormone synthesis, plasma transport, peripheral metabolism, transport into the target cells, and thyroid hormone action. It is well known that iodide uptake mediated by the sodium-iodide symporter (NIS) is the first limiting step involved in thyroid hormones production. Therefore, it has been described that several thyroid disruptors interfere with the thyroid function through the regulation of NIS expression and/or activity. Perchlorate, nitrate, and thiocyanate competitively inhibit the NIS-mediated iodide uptake. These contaminants are mainly found in food, water and in the smoke of cigarettes. Although the impact of the human exposure to these anions is highly controversial, some studies indicated their deleterious effects in the thyroid function, especially in individuals living in iodine deficient areas. Considering the critical role of thyroid function and the production of thyroid hormones for growth, metabolism, and development, this review summarizes the impact of the exposure to these NIS-inhibitors on thyroid function and their consequences for human health.

Murine Thyroid IL-4 Expression Worsens Hypothyroidism on Iodine Restriction and Mitigates Graves Disease Development

Cytokines are known to perturb thyroid function and the role of interleukin-4 (IL-4) in the pathogenesis of Graves disease (GD) remains controversial. In our mouse model overexpressing IL-4 in thyrocytes (Thyr-IL4), we have reported that adult mice preserved normal serum thyroxine despite an iodide uptake defect. In the present work, we evaluated if iodine restriction could uncover the thyroid deficiency in Thyr-IL4 animals as well as the role of pendrin overexpression as a compensatory mechanism. Moreover, using an experimental model of GD we investigated the effect of a local expression of IL-4 on the incidence of hyperthyroidism. Thyr-IL4 mice developed more rapidly elevated serum thyrotropin under low-iodine supply with thyroid enlargement and classical histological modifications. These hallmarks of hypothyroidism were all enhanced in Thyr-IL4 mice with complete pendrin invalidation. Following immunization, a lower proportion of Thyr-IL4 animals developed hyperthyroidism. Surprisingly, immunized Thyr-IL4 animals presented numerous leukocyte infiltrates, associated with increased intrathyroidal expression of IFN-γ. We have demonstrated that thyroid deficiency in Thyr-IL4 mice is partially compensated for by the excessive iodide content of the standard chow and the overexpression of pendrin in these animals. Furthermore, we have shown that the local expression of IL-4 in the thyroid attenuates GD progression, which was associated with enhanced thyroid infiltration by immune cells that could negatively affect thyroid function.

Redox Homeostasis in Thyroid Cancer: Implications in Na+/I- Symporter (NIS) Regulation

Radioiodine therapy (RAI) is a standard and effective therapeutic approach for differentiated thyroid cancers (DTCs) based on the unique capacity for iodide uptake and accumulation of the thyroid gland through the Na⁺/I⁻ symporter (NIS). However, around 5–15% of DTC patients may become refractory to radioiodine, which is associated with a worse prognosis. The loss of RAI avidity due to thyroid cancers is attributed to cell dedifferentiation, resulting in NIS repression by transcriptional and post-transcriptional mechanisms. Targeting the signaling pathways potentially involved in this process to induce de novo iodide uptake in refractory tumors is the rationale of “redifferentiation strategies”. Oxidative stress (OS) results from the imbalance between ROS production and depuration that favors a pro-oxidative environment, resulting from increased ROS production, decreased antioxidant defenses, or both. NIS expression and function are regulated by the cellular redox state in cancer and non-cancer contexts. In addition, OS has been implicated in thyroid tumorigenesis and thyroid cancer cell dedifferentiation. Here, we review the main aspects of redox homeostasis in thyrocytes and discuss potential ROS-dependent mechanisms involved in NIS repression in thyroid cancer.

The sodium iodide symporter (NIS) as theranostic gene: its emerging role in new imaging modalities and non-viral gene therapy

Cloning of the sodium iodide symporter (NIS) in 1996 has provided an opportunity to use NIS as a powerful theranostic transgene. Novel gene therapy strategies rely on image-guided selective NIS gene transfer in non-thyroidal tumors followed by application of therapeutic radionuclides. This review highlights the remarkable progress during the last two decades in the development of the NIS gene therapy concept using selective non-viral gene delivery vehicles including synthetic polyplexes and genetically engineered mesenchymal stem cells. In addition, NIS is a sensitive reporter gene and can be monitored by high resolution PET imaging using the radiotracers sodium [¹²⁴I]iodide ([¹²⁴I]NaI) or [¹⁸F]tetrafluoroborate ([¹⁸F]TFB). We performed a small preclinical PET imaging study comparing sodium [¹²⁴I]iodide and in-house synthesized [¹⁸F]TFB in an orthotopic NIS-expressing glioblastoma model. The results demonstrated an improved image quality using [¹⁸F]TFB. Building upon these results, we will be able to expand the NIS gene therapy approach using non-viral gene delivery vehicles to target orthotopic tumor models with low volume disease, such as glioblastoma.

Trial registration not applicable.

Targeting non-canonical pathways as a strategy to modulate the sodium iodide symporter

The sodium iodide symporter (NIS) functions to transport iodide and is critical for successful radioiodide ablation of cancer cells. Approaches to bolster NIS function and diminish recurrence post-radioiodide therapy are impeded by oncogenic pathways that suppress NIS, as well as the inherent complexity of NIS regulation. Here, we utilize NIS in high-throughput drug screening and undertake rigorous evaluation of lead compounds to identify and target key processes underpinning NIS function. We find that multiple proteostasis pathways, including proteasomal degradation and autophagy, are central to the cellular processing of NIS. Utilizing inhibitors targeting distinct molecular processes, we pinpoint combinatorial drug strategies giving robust >5-fold increases in radioiodide uptake. We also reveal significant dysregulation of core proteostasis genes in human tumors, identifying a 13-gene risk score classifier as an independent predictor of recurrence in radioiodide-treated patients. We thus propose and discuss a model for targetable steps of intracellular processing of NIS function.

Impact of endocrine disrupting chemicals on neurodevelopment: the need for better testing strategies for endocrine disruption-induced developmental neurotoxicity

INTRODUCTION

Brain development is highly dependent on hormonal regulation. Exposure to chemicals disrupting endocrine signaling has been associated with neurodevelopmental impairment. This raises concern about exposure to the suspected thousands of endocrine disruptors, and has resulted in efforts to improve regulation of these chemicals. Yet, the causal links between endocrine disruption and developmental neurotoxicity, which would be required for regulatory action, are still largely missing.

AREAS COVERED

In this review, we illustrate the importance of two endocrine systems, thyroid hormone and retinoic acid pathways, for neurodevelopment. We place special emphasis on TH and RA synthesis, metabolism, and how endocrine disrupting chemicals known or suspected to affect these systems are associated with developmental neurotoxicity.

EXPERT OPINION

While it is clear that neurodevelopment is dependent on proper hormonal functioning, and evidence is increasing for developmental neurotoxicity induced by endocrine disrupting chemicals, this is not grasped by current chemical testing. Thus, there is an urgent need to develop test methods detecting endocrine disruption in the context of neurodevelopment. Key to this development is further mechanistic insights on the involvement of endocrine signaling in neurodevelopment as well as increased support to develop and validate new test methods for the regulatory context.

Evaluation of [18F]tetrafluoroborate as a Potential PET Imaging Agent in a Sodium Iodide Symporter-Transfected Cell Line A549 and Endogenous NIS-Expressing Cell Lines MKN45 and K1

[¹⁸F]tetrafluoroborate (TFB) has been introduced as the ¹⁸F-labeled PET imaging probe for the human sodium iodide symporter (NIS). Noninvasive NIS imaging using [¹⁸F]TFB has received much interest in recent years for evaluating various NIS-expressing tumors. Cancers are a global concern with enormous implications; therefore, improving diagnostic methods for accurate detection of cancer is extremely important. Our aim was to investigate the PET imaging capabilities of [¹⁸F]TFB in NIS-transfected lung cell line A549 and endogenous NIS-expressing tumor cells, such as thyroid cancer K1 and gastric cancer MKN45, and broaden its application in the medical field. Western blot and flow cytometry were used to assess the NIS expression level. Radioactivity counts of [¹⁸F]TFB, in vitro, in the three tumor cells were substantially higher than those in the KI inhibition group in the uptake experiment. In vivo PET imaging clearly delineated the three tumors based on the specific accumulation of [¹⁸F]TFB in a mouse model. Ex vivo biodistribution investigation showed high [¹⁸F]TFB absorption in the tumor location, which was consistent with the PET imaging results. These results support the use of NIS-transfected lung cell line A549 and NIS-expressing tumor cells MKN45 and K1, to investigate probing capabilities of [¹⁸F]TFB. We also demonstrate, for the first time, the feasibility of [¹⁸F]TFB in diagnosing stomach cancer. In conclusion, this study illustrates the promising future of [¹⁸F]TFB for tumor diagnosis and NIS reporter imaging.

KSNM60 in Nuclear Endocrinology: from the Beginning to the Future

Nuclear endocrinology is the main ignitor for founding the Korean Society of Nuclear Medicine (KSNM) in the early 1960s by outstanding pioneering medical doctors. Management of thyroid diseases required nuclear medicine technology in the early days of the KSNM and was rapidly developed by advancements in nuclear medicine technology. Nuclear thyroidology remains one of the main clinical applications in nuclear medicine worldwide. Nuclear medicine technology provides essential information for diagnosing and assessing diseases of the parathyroid glands, pituitary gland, and neuroendocrine tumors (NETs). In addition, therapeutic nuclear medicine is essential for managing nonresectable NETs. Nuclear endocrinology remains a major section in clinical nuclear medicine, and members of the KSNM have contributed to progressing better management of benign and malignant endocrine diseases. This review summarizes the historical activities and milestone contributions to nuclear endocrinology made by the members of the KSNM over the past 60 years to congratulate the KSNM on its 60-year anniversary.

Impact of Iodinated Contrast Media in Patients Received Percutaneous Coronary Intervention: Focus on Thyroid Disease

BACKGROUND

With the rapid advance in percutaneous coronary intervention (PCI) technology, patients absorb large volume of iodinated contrast media (ICM). Recent studies suggested that ICM may lead to hyperthyroidism, but the association between ICM volume and thyroid is still unclear. We sought to evaluate the long-term influence of ICM on thyroid dysfunction and disease in patients received PCI.

METHODS

This single-center retrospective study included consecutive coronary artery disease (CAD) patients. A covariance (ANCOVA) model was performed to evaluate the change of serum TSH, FT3 and FT4 before and one-year after the PCI procedure. Restricted cubic splines and logistic regression were performed to evaluate the association between ICM volume and thyroid disease.

RESULTS

2062 patients met inclusion criteria (1381 patients in the low-volume group and 681 patients in the high-volume group). The high-volume group was 0.238 ± 0.092 pmol/L higher than the low-volume group (P = 0.010) in the serum FT4. Restricted cubic splines show that there were linear dose-response relationships for ICM volume and composite endpoint and hyperthyroidism. In all models, there were significant differences in composite endpoint between the two groups. (OR 1.75, 95% CI (1.05, 2.92), P = 0.032, OR 1.73, 95% CI (1.01-2.96), P= 0.032 and OR 1.83, 95% CI (1.09-3.06), P= 0.022, respectively). The positive results were also showed for hyperthyroidism in all models (OR 2.35, 95% CI (1.14-4.84), P = 0.021, OR 10.36, 95% CI (1.20-89.00), P = 0.033 and OR 2.35, 95% CI (1.13-4.87), P = 0.022, respectively).

CONCLUSION

The present analysis gives an overview that ICM volume is associated with an increased risk of thyroid dysfunction and thyroid disease.

Selective sodium iodide symporter (NIS) genetherapy of glioblastoma mediatedby EGFR-targeted lipopolyplexes

Lipo-oligomers, post-functionalized with ligands to enhance targeting, represent promising new vehicles for the tumor-specific delivery of therapeutic genes such as the sodium iodide symporter (NIS). Due to its iodide trapping activity, NIS is a powerful theranostic tool for diagnostic imaging and the application of therapeutic radionuclides. ¹²⁴I PET imaging allows non-invasive monitoring of the in vivo biodistribution of functional NIS expression, and application of ¹³¹I enables cytoreduction. In our experimental design, we used epidermal growth factor receptor (EGFR)-targeted polyplexes (GE11) initially characterized in vitro using ¹²⁵I uptake assays. Mice bearing an orthotopic glioblastoma were treated subsequently with mono-dibenzocyclooctyne (DBCO)-PEG₂₄-GE11/NIS or bisDBCO-PEG₂₄-GE11/NIS, and 24-48 h later, ¹²⁴I uptake was assessed by positron emission tomography (PET) imaging. The best-performing polyplex in the imaging studies was then selected for ¹³¹I therapy studies. The in vitro studies showed EGFR-dependent and NIS-specific transfection efficiency of the polyplexes. The injection of monoDBCO-PEG₂₄-GE11/NIS polyplexes 48 h before ¹²⁴I application was characterized to be the optimal regime in the imaging studies and was therefore used for an ¹³¹I therapy study, showing a significant decrease in tumor growth and a significant extension of survival in the therapy group. These studies demonstrate the potential of EGFR-targeted polyplex-mediated NIS gene therapy as a new strategy for the therapy of glioblastoma.

High-dose radiation exposure and hypothyroidism: aetiology, prevention and replacement therapy

Without any doubt, high dose radiation exposure can induce hypothyroidism. However, there are open questions related to the mechanisms of its induction, corresponding dose thresholds and possible countermeasures. Therefore, this review addresses the aetiology, prevention and therapy of radiation induced hypothyroidism. External beam radiotherapy with several 10 Gy to the head and neck region and radioiodine therapy with several 100 Gy thyroid absorbed dose can destroy the thyroid gland and can induce autoantibodies against thyroid tissue. According to recent literature, clinical hypothyroidism is observed at threshold doses of ∼10 Gy after external beam radiotherapy and of ∼50 Gy after radioiodine therapy, children being more sensitive than adults. In children and adolescents exposed by the Chernobyl accident with mean thyroid absorbed doses of 500-800 mGy, subclinical hypothyroidism has been detected in 3%-6% of the cases with significant correlation to thyroid absorbed doses above 2.5 Gy. In case of nuclear emergencies, iodine thyroid blocking (ITB) is the method of choice to keep thyroid absorbed doses low. Large doses of stable iodine affect two different steps of internalization of radioiodine (transport and organification); perchlorate affecting the transport only may be an alternative to iodine. Administered before radioiodine incorporation, the effect of 100 mg iodide or more is still about 90% after 1 days, 80% after 2 days, and 50% or less after 3 days. If administered (too) late after exposure to radioiodine, the theoretically expected protective effect of ITB is about 50% after 6 h, 25% after 12 h, and about 6% after 24 h. In case of repeated or continuous exposure, repeated administration of 50 mg of iodide daily is indicated. If radiation-induced hypothyroidism cannot be avoided, thyroid hormone replacement therapy with individualized dosing and regular monitoring in order to maintain thyroid-stimulating hormone levels within the normal range ensures normal life expectancy.

Impact of the Mutational Landscape of the Sodium/Iodide Symporter in Congenital Hypothyroidism

Background: Iodide transport defect is an uncommon cause of dyshormonogenic congenital hypothyroidism due to homozygous or compound heterozygous pathogenic variants in the SLC5A5 gene, which encodes the sodium/iodide symporter (NIS), causing deficient iodide accumulation in thyroid follicular cells, thus impairing thyroid hormonogenesis. Methods:SLC5A5 gene variants were compiled from public databases and research articles exploring the molecular bases of congenital hypothyroidism. Using a dataset of 198 missense NIS variants classified as either benign or pathogenic, we developed and validated a machine learning-based NIS-specific variant classifier to predict the impact of missense NIS variants. Results: We generated a manually curated dataset containing 7793 unique SLC5A5 variants. As most databases compiled exome sequencing data, variant mapping revealed an increased density of variants in SLC5A5 coding exons. Based on allele frequency (AF) analysis, we established an AF threshold of 1:10,000 above which a variant should be considered benign. Most pathogenic NIS variants were located in the protein-coding region, as most patients were genetically diagnosed by using a candidate gene strategy limited to this region. Significantly, we evidenced that 94.5% of missense NIS variants were classified as of uncertain significance. Therefore, we developed an NIS-specific variant classifier to improve the prediction of pathogenicity of missense variants. Our classifier predicted the clinical outcome of missense variants with high accuracy (90%), outperforming state-of-the-art pathogenicity predictors, such as REVEL, PolyPhen-2, and SIFT. Based on the excellent performance of our classifier, we predicted the mutational landscape of NIS. The analysis of the mutational landscape revealed that most missense variants located in transmembrane segments are frequently pathogenic. Moreover, we predicted that ∼28% of all single-nucleotide variants that could cause missense NIS variants are pathogenic, thus putatively leading to congenital hypothyroidism if present in homozygous or compound heterozygous state. Conclusions: We reported the first NIS-specific variant classifier aiming at improving the interpretation of missense NIS variants in clinical practice. Deciphering the mutational landscape for every protein involved in thyroid hormonogenesis is a relevant task for a deep understanding of the molecular mechanisms causing dyshormonogenic congenital hypothyroidism.

Thyroxine hormones visualized by the cryo-EM structure of bovine thyroglobulin

A study of natively iodinated bovine thyroglobulin demonstrates that structural details of biologically important chemical reactions can now be visualized by electron cryo-microscopy.

The Iodide Transport Defect-Causing Y348D Mutation in the Na+/I- Symporter Renders the Protein Intrinsically Inactive and Impairs Its Targeting to the Plasma Membrane

Background: The sodium/iodide (Na⁺/I^-) symporter (NIS) mediates active transport of I^- into the thyroid gland. Mutations in the SLC5A5 gene, which encodes NIS, cause I^- transport defects (ITDs)-which, if left untreated, lead to congenital hypothyroidism and consequent cognitive and developmental deficiencies. The ITD-causing NIS mutation Y348D, located in transmembrane segment (TMS) 9, was reported in three Sudanese patients. Methods: We generated cDNAs coding for Y348D NIS and mutants with other hydrophilic and hydrophobic amino acid substitutions at position 348 and transfected them into cells. The activity of the resulting mutants was quantitated by radioiodide transport assays. NIS glycosylation was investigated by Western blotting after endoglycosidase H (Endo H) and PNGase-F glycosidase treatment. Subcellular localization of the mutant proteins was ascertained by flow cytometry analysis, cell surface biotinylation, and immunofluorescence. The intrinsic activity of Y348D was studied by measuring radioiodide transport in membrane vesicles prepared from Y348D-NIS-expressing cells. Our NIS homology models and molecular dynamics simulations were used to identify residues that interact with Y348 and investigate possible interactions between Y348 and the membrane. The sequences of several Slc5 family transporters were aligned, and a phylogenetic tree was generated in ClustalX. Results: Cells expressing Y348D NIS transport no I^-. Furthermore, Y348D NIS is only partially glycosylated, is retained intracellularly, and is intrinsically inactive. Hydrophilic residues other than Asp at position 348 also yield NIS proteins that fail to be targeted to the plasma membrane (PM), whereas hydrophobic residues at this position, which we show do not interact with the membrane, rescue PM targeting and function. Conclusions: Y348D NIS does not reach the PM and is intrinsically inactive. Hydrophobic amino acid substitutions at position 348, however, preserve NIS activity. Our findings are consistent with our homology model's prediction that Y348 should face the side opposite the TMS9 residues that coordinate Na⁺ and participate in Na⁺ transport, and with the notion that Y348 interacts only with hydrophobic residues. Hydrophilic or charged residues at position 348 have deleterious effects on NIS PM targeting and activity, whereas a hydrophobic residue at this position rescues NIS activity.

An Impressive Approach in Nuclear Medicine: Theranostics

Radiometal-based theranostics or theragnostics, first used in the early 2000s, is the combined application of diagnostic and therapeutic agents that target the same molecule, and represents a considerable advancement in nuclear medicine. One of the promising fields related to theranostics is radioligand therapy. For instance, the concepts of targeting the prostate-specific membrane antigen (PSMA) for imaging and therapy in prostate cancer, or somatostatin receptor targeted imaging and therapy in neuroendocrine tumors (NETs) are part of the field of theranostics. Combining targeted imaging and therapy can improve prognostication, therapeutic decision-making, and monitoring of the therapy.

Cryo-EM: A new dawn in thyroid biology

The thyroid gland accumulates the rare dietary element iodine and incorporates it into iodinated thyroid hormones, utilising several tightly regulated reactions and molecular mechanisms. Thyroid hormones are essential in vertebrates and play a central role in many biological processes, such as development, thermogenesis and growth. The control of these functions is exerted through the binding of hormones to nuclear thyroid hormone receptors that rule the transcription of numerous metabolic genes. Over the last 50 years, thyroid biology has been studied extensively at the cellular and organismal levels, revealing its multiple clinical implications, yet, a complete molecular understanding is still lacking. This includes the atomic structures of crucial pathway components that would be needed to elucidate molecular mechanisms. Here we review the currently known protein structures involved in thyroid hormone synthesis, regulation, transport, and actions. We also highlight targets for future investigations that will significantly benefit from recent advances in macromolecular structure determination by electron cryo-microscopy (cryo-EM). As an example, we demonstrate how cryo-EM was crucial to obtain the structure of the large thyroid hormone precursor protein, thyroglobulin. We discuss modern cryo-EM compared to other structure determination methods and how an integrated structural and cell biological approach will help filling the molecular knowledge gap in our understanding of thyroid hormone metabolism. Together with clinical, cellular and high-throughput 'omics' studies, atomic structures of thyroid components will provide an important framework to map disease mutations and to interpret and predict thyroid phenotypes.

Regulation of solute carrier family 26 member 7 (Slc26a7) by thyroid stimulating hormone in thyrocytes

Iodine transportation is an important step in thyroid hormone biosynthesis. Uptake of iodine into the thyroid follicle is mediated mainly by the basolateral sodium-iodide symporter (NIS or solute carrier family 5 member 5: SLC5A5), and iodine efflux across the apical membrane into the follicular lumen is mediated by pendrin (SLC26A4). In addition to these transporters, SLC26A7, which has recently been identified as a causative gene for congenital hypothyroidism, was found to encode a novel apical iodine transporter in the thyroid. Although SLC5A5 and SLC26A4 have been well-characterized, little is known about SLC26A7, including its regulation by TSH, the central hormone regulator of thyroid function. Using rat thyroid FRTL-5 cells, we showed that the mRNA levels of Slc26a7 and Slc26a4, two apical iodine transporters responsible for iodine efflux, were suppressed by TSH, whereas the mRNA level of Slc5a5 was induced. Forskolin and dibutyryl cAMP (dbcAMP) had the same effect as that of TSH on the mRNA levels of these transporters. TSH, forskolin and dbcAMP also had suppressive effects on SLC26A7 promoter activity, as assessed by luciferase reporter gene assays, and protein levels, as determined by Western blot analysis. TSH, forskolin and dbcAMP also induced strong localization of Slc26a7 to the cell membrane according to immunofluorescence staining and confocal laser scanning microscopy. Together, these results suggest that TSH suppresses the expression level of Slc26a7 but induces its accumulation at the cell membrane, where it functions as an iodine transporter.

Mechanisms of regulating NIS transport to the cell membrane and redifferentiation therapy in thyroid cancer

Iodine is an essential constituent of thyroid hormone. Active iodide accumulation in the thyroid is mediated by the sodium iodide symporter (NIS), comprising the first step in thyroid hormone biosynthesis, which relies on the functional expression of NIS on the cell membrane. The retention of NIS expressed in differentiated thyroid cancer (DTC) cells allows further treatment with post-operative radioactive iodine (RAI) therapy. However, compared with normal thyroid tissue, differentiated thyroid tumors usually show a decrease in the active iodide conveyance and NIS is generally retained within the cells, indicating that posttranslational protein transfer to the plasma membrane is abnormal. In recent years, through in vitro studies and studies of patients with DTC, various methods have been tested to increase the transport rate of NIS to the cell membrane and increase the absorption of iodine. An in-depth understanding of the mechanism of NIS transport to the plasma membrane could lead to improvements in RAI therapy. Therefore, in this review, we discuss the current knowledge concerning the post-translational mechanisms that regulate NIS transport to the cell membrane and the current status of redifferentiation therapy for patients with RAI-refractory (RAIR)-DTC.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

Radio-Iodide Treatment: From Molecular Aspects to the Clinical View

Simple Summary

This year marks the 80th commemoration of the first time that radio-iodide treatment (RAI) was used. RAI is one of the most effective targeted internal radiation anticancer therapies ever devised and it has been used for many decades, however, a thorough understanding of the underlying molecular mechanisms involved could greatly improve the success of this therapy. This is an in-depth innovative review focusing on the molecular mechanisms underlying radio-iodide therapy in thyroid cancer and how the alteration of these mechanisms affects the results in the clinic.

Abstract

Thyroid radio-iodide therapy (RAI) is one of the oldest known and used targeted therapies. In thyroid cancer, it has been used for more than eight decades and is still being used to improve thyroid tumor treatment to eliminate remnants after thyroid surgery, and tumor metastases. Knowledge at the molecular level of the genes/proteins involved in the process has led to improvements in therapy, both from the point of view of when, how much, and how to use the therapy according to tumor type. The effectiveness of this therapy has spread into other types of targeted therapies, and this has made sodium/iodide symporter (NIS) one of the favorite theragnostic tools. Here we focus on describing the molecular mechanisms involved in radio-iodide therapy and how the alteration of these mechanisms in thyroid tumor progression affects the diagnosis and results of therapy in the clinic. We analyze basic questions when facing treatment, such as: (1) how the incorporation of radioiodine in normal, tumor, and metastatic thyroid cells occurs and how it is regulated; (2) the pros and cons of thyroid hormonal deprivation vs. recombinant human Thyroid Stimulating Hormone (rhTSH) in radioiodine residence time, treatment efficacy, thyroglobulin levels and organification, and its influence on diagnostic imaging tests and metastasis treatment; and (3) the effect of stunning and the possible causes. We discuss the possible incorporation of massive sequencing data into clinical practice, and we conclude with a socioeconomical and clinical vision of the above aspects.

Crosstalk of cholinergic pathway on thyroid disrupting effects of the insecticide chlorpyrifos in zebrafish (Danio rerio)

Chlorpyrifos is a widely used organophosphate insecticide and ubiquitously detected in the environment. However, little attention has been paid to its endocrine disrupting effect to non-target organisms. In the present study, zebrafish was exposed to 13 and 65 μg/L of chlorpyrifos for 7 and 10 days to determine the induced neurotoxicity and the alteration of thyroid metabolism. The 120 h LC₅₀ and LC₁₀ of chlorpyrifos was estimated as 1.35 mg/L and 0.62 mg/L based on the acute embryo toxicity assay, respectively. The acetylcholinesterase (AChE) inhibitory was detected by 13 μg/L chlorpyrifos and could be reversed by the co-exposure of 100 and 1000 μg/L anticholinergic agent atropine. For thyroid hormone level, 13 and 65 μg/L of chlorpyrifos induced increased free T₃ levels in 10 dpf (days post-fertilization). The expression of thyroid related genes in 7 and 10 dpf exposed zebrafish were measured by the quantitative Real-Time PCR (qRT-PCR) assay. The mRNA expression of tshba, thrb, crhb, ttr, tpo, ugt1ab and slc5a5 had significant change. However, the alterations of thyroid hormone and mRNA expression could be partly rescued by the addition of atropine. The molecular docking of chlorpyrifos and T₃ to the thyroid receptor β in zebrafish using homology modelling and CDOCKER procedures shown weaker binding ability of chlorpyrifos compared to T₃. Therefore, we concluded that the disturbance of thyroid signaling in zebrafish might arise from the developmental neurotoxicity induced by chlorpyrifos.