Iodination Of Thyroglobulin Research Articles

7099 Severe Hypothyroidism from Potassium Iodide Supplements: A Case of Failure to Escape from Wolf- Chaikoff Effect

Abstract Disclosure: M.G. Hamilton: None. A. Kulkarni: None. P. Lekprasert: None. Introduction: The Wolf-Chaikoff effect (WCE) is a physiological response of the thyroid gland to supraphysiologic iodide levels. Failure to escape the WCE can lead to thyroid dysfunction, and we present such a case in a patient with Hashimoto’s thyroiditis taking high-dose potassium iodide (KI). Case Description: A 44-year-old female with hypothyroidism secondary to Hashimoto’s thyroiditis presented with 10-pound weight gain, extremity swelling, fatigue, and abnormal menstruation. She was prescribed Levothyroxine several years ago but stopped taking it shortly after as she felt no improvement. On physical exam, she was bradycardic with heart rate of 58 bpm. There is no goiter but dry skin and edematous lower extremities. Labs revealed TSH of 127 pg/mL (0.35-4.94), free T4 0.1ng/dL (0.8-1.8), TPO Ab 645 (<9) IU/mL in comparison to her labs 2 months ago of TSH 11 pg/mL and free T4 0.9 ng/dL. Suspicion for worsening hypothyroidism from Hashimoto’s was low given this dramatic change on labwork and clinically. On further questioning, she had been taking KI 130 mg/day (Iodine 100 mg, daily requirement 150 mcg/day) as advised by her homeopathic doctor. The supplements were stopped, and she was re-started on Levothyroxine. After 8 weeks, she reported improvement of symptoms and weight loss. TSH is normal at 3.54pg/ml and free T4 1.2 ng/dL. Discussion:The WCE serves as a protective mechanism to decrease thyroid hormone production in the setting of high iodide levels to prevent development of hyperthyroidism. WCE is explained by the formation of Iodopeptides inhibits thyroid peroxidase (TPO) mRNA and protein synthesis resulting in an inhibition of thyroglobulin iodination. WCE is temporary and expected to wane over a few days to weeks and is known as the Wolf-Chaikoff escape due to down regulation of the sodium iodine symporter (NIS) thereby decreasing the intrathyroidal inorganic iodine concentration and permitting normal TPO activity. Rarely, failure to escape WCE can lead to hypothyroidism due to continued suppression of thyroid hormone synthesis. Risk factors include underlying thyroid diseases i.e. Hashimoto’s or other causes of thyroiditis, use of Amiodarone, Lithium or Iodine-containing radiocontrast media and KI supplements. In our case, Hashimotos’ thyroiditis predisposed her to thyroid dysfunction and failure to escape from WCE after taking high-dose KI supplements causing severe hypothyroidism. Thus, this report highlights that in clinical practice, especially in patients with pre-existing thyroid dysfunction, a significant TSH increase, a high suspicion index is needed to investigate for other causes like concurrent use of iodine-containing food/drug leading to the failed escape from WCE apart from verifying compliance to thyroid replacement therapy. Presentation: 6/3/2024

Preradioactive Iodine Thyroglobulin Levels as Predictors of Metastasis in Well-Differentiated Thyroid Carcinoma Patients.

Objective The aim of this study was to determine the cut-off value of thyroglobulin (Tg) levels as a predictor of metastases in post total thyroidectomy patients with well-differentiated thyroid carcinoma (DTC). Materials and Methods A retrospective case-control study with an observational diagnostic approach was done. Subjects were 102 DTC patients divided into a case group with metastases and a control group without metastases. Tg and antithyroglobulin antibody (ATA) levels on thyroid-stimulating hormone (TSH)-stimulated preradioactive iodine were compared with each other. Diagnosis of metastases was based on postradioactive iodine whole-body scan. The cut-off value for Tg preradioactive iodine and the area under the curve (AUC) were obtained from the receiver operating characteristic curve. Result The characteristics and histopathological type of DTC among these two groups were not significantly different ( p = 0.47). The Tg levels in the case and control groups were 106 (2.2-6,000) ng/mL and 2.7 (0.3-10.10) ng/mL, respectively ( p = 0.0001). TSH level in the case group was 50 (30-107) µIU/mL and in the control was 50 (20-100) µIU/mL ( p = 0.224). ATA levels in the case and control groups were 0-3,000 and 0-629 ng/mL, respectively ( p = 0.01). The AUC was 0.976 with a 95% confidence interval of 0.924 to 0.996 and a standard error of 0.016. The cut-off value of preradioactive iodine Tg was 10.1 ng/mL or higher with sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of 96.1, 100, 98.0, 100, and 96.2%, respectively. Conclusion Preradioactive iodine Tg level 10.1 ng/mL or higher can be used as a predictor of metastasis in patients with DTC.

Cryo-EM structure of native human thyroglobulin

The thyroglobulin (TG) protein is essential to thyroid hormone synthesis, plays a vital role in the regulation of metabolism, development and growth and serves as intraglandular iodine storage. Its architecture is conserved among vertebrates. Synthesis of triiodothyronine (T3) and thyroxine (T4) hormones depends on the conformation, iodination and post-translational modification of TG. Although structural information is available on recombinant and deglycosylated endogenous human thyroglobulin (hTG) from patients with goiters, the structure of native, fully glycosylated hTG remained unknown. Here, we present the cryo-electron microscopy structure of native and fully glycosylated hTG from healthy thyroid glands to 3.2 Å resolution. The structure provides detailed information on hormonogenic and glycosylation sites. We employ liquid chromatography–mass spectrometry (LC-MS) to validate these findings as well as other post-translational modifications and proteolytic cleavage sites. Our results offer insights into thyroid hormonogenesis of native hTG and provide a fundamental understanding of clinically relevant mutations.

XB130 Plays an Essential Role in Folliculogenesis Through Mediating Interactions Between Microfilament and Microtubule Systems in Thyrocytes.

Background: XB130 (actin filament-associated protein 1-like 2, AFAP1L2) is a thyroid-abundant adaptor/scaffold protein. Xb130-/- mice exhibit transient growth retardation postnatally due to congenital hypothyroidism with diminished thyroglobulin iodination and release at both embryonic and early postnatal stages due to disorganized thyroid apical membrane structure and function. We hypothesized that XB130 is crucial for polarity and folliculogenesis by mediating proper cytoskeletal structure and function in thyrocytes. Methods: Primary thyrocytes isolated from thyroid glands of Xb130-/- mice and their wild-type littermates at postnatal week 2 were cultured in 10% Matrigel for different time periods. Folliculogenesis was studied with immunofluorescence staining, followed by confocal microscopy. Cells were also transfected to express human XB130 fused Green Fluorescent Protein (XB130-GFP) or Green Fluorescent Protein (GFP) only before morphological analysis. Cytoskeletal structures from embryo and postnatal thyroid glands were also studied. Results: In three-dimensional cultures of thyrocytes, XB130, aligned with actin filaments, participated in defining the site of apical membrane formation and coalescence to form a thyroid follicle lumen. Xb130-/- thyrocytes displayed delayed folliculogenesis, reduced recruitment of a microtubule (MT)-associated proteins, and disorganized acetylated tubulin under the apical membrane, resulting in delayed folliculogenesis with reduced efficiency in formation of the thyroid follicle lumen. Conclusions: XB130 critically regulates thyrocyte polarization by functioning as a link between the actin filament cortex and MT network at the apical membrane of thyrocytes. Defects of adaptor scaffold proteins may affect cellular polarity and cytoskeletal structure and function and result in disorders of epithelial function, such as congenital hypothyroidism.

Thyroid Hormones in the Human Body: A review

Thyroid gland is an essential endocrine gland that is present in the human body. This review highlights the production, regulation and disease conditions of the thyroid hormones. The thyroid gland is controlled with the help of hypothalamus and the pituitary gland that is present in the brain. The production of thyroid hormones involves five main steps such synthesis of thyroglobulin (TG), iodide uptake, iodination of thyroglobulin, storage and release. The two important hormones produced by the thyroid gland are Thyroxine (T4) and Triiodothyronine(T3). These two hormones are iodine containing derivatives. Deficiency of iodine in the body results in the reduction of T3 and T4 production. Excess and deficiency of these two hormones result in the major diseases like Hyper and Hypothyroidism. The synthetic forms of Thyroxine(T4) and Triiodothyronine(T3) used in the Pharmaceutical field are Levothyroxine and Liothyronine. Women are most commonly prone to these thyroid diseases comparatively to men. Undiagnosed disease conditions may become fatal. Levothyroxine therapy is commonly used for thyroidism which is a similar synthetic thyroid hormone. Also natural thyroid hormones that are obtained from the dried thyroid glands of animals are available. Thyroid function test and the measurement of T3, T4 plasma level becomes essential for the identification and regular maintenance of thyroid hormones in the body and human well-being.

XB130 Deficiency Causes Congenital Hypothyroidism in Mice due to Disorganized Apical Membrane Structure and Function of Thyrocytes.

Background: Congenital hypothyroidism is often caused by genetic mutations that impair thyroid hormone (TH) production, resulting in growth and development defects. XB130 (actin filament associated protein 1 like 2) is an adaptor/scaffold protein that plays important roles in cell proliferation, migration, intracellular signal transduction, and tumorigenesis. It is highly expressed in thyrocytes, however, its function in the thyroid remains largely unexplored. Methods:Xb130-/- mice and their littermates were studied. Postnatal growth and growth hormone levels were measured, and responses to low or high-iodine diet, and levothyroxine treatment were examined. TH and thyrotropin in the serum and TH in the thyroid glands were quantified. Structure and function of thyrocytes in embryos and postnatal life were studied with histology, immunohistochemistry, immunofluorescence staining, Western blotting, and quantitative reverse transcription polymerase chain reaction. Results:Xb130-/- mice exhibited transient growth retardation postnatally, due to congenital hypothyroidism with reduced TH synthesis and secretion, which could be rescued by exogenous thyroxine supplementation. The thyroid glands of Xb130-/- mice displayed diminished thyroglobulin iodination and release at both embryonic and early postnatal stages. XB130 was found mainly on the apical membrane of thyroid follicles. Thyroid glands of embryonic and postnatal Xb130-/- mice exhibited disorganized apical membrane structure, delayed folliculogenesis, and abnormal formation of thyroid follicle lumina. Conclusion: XB130 critically regulates folliculogenesis by maintaining apical membrane structure and function of thyrocytes, and its deficiency leads to congenital hypothyroidism.

Аутоиммунный тиреоидит и пищевые факторы

Аутоиммунный тиреоидит (АИТ) считается самым распространенным аутоиммунным заболеванием. В настоящее время признано, что генетическая восприимчивость, факторы окружающей среды и иммунные расстройства способствуют его развитию. Что касается пищевых факторов, данные свидетельствуют о высоком уровне потребления йода, дефиците селена и железа с потенциальной значимостью статуса витамина D. Для выяснения роли факторов питания в риске, патогенезе и лечении АИТ использованы источники PubMed относительно йода, железа, селена, витамина D, мио-инозитола и лечения АИТ. Хроническое воздействие чрезмерного потребления йода индуцирует аутоиммунный тиреоидит отчасти потому, что йодированный тиреоглобулин (Tg) более иммуногенный. Селенопротеины необходимы для поддержания функционального состояния щитовидной железы. Существуют данные рандомизированных конт­ролируемых исследований, что селен/селенопротеины могут уменьшить титры антител к тиреоидной пероксидазе (ТПО) у больных гипотиреозом и послеродовым тиреоидитом. У больных АИТ часто наблюдается дефицит железа, поскольку аутоиммунный гастрит, который ухудшает всасывание железа, является довольно частым сопутствующим заболеванием. В последние годы возникли доказательства, указывающие на положительную роль витамина D, включая пролиферацию и дифференциацию нормальных и раковых клеток, сердечно-сосудистую функцию и иммуномодуляцию. Дефицит витамина D особенно продемонстрирован у больных АИТ. У пациентов с АИТ обнаружен более низкий уровень витамина D, чем у лиц из контрольной группы, и сообщается об обратной зависимости содержания сывороточного витамина D от титра антител к ТПО/Tg. Адекватное потребление селена является жизненно важным в районах дефицита/избытка йода, а в регионах с низким потреблением селена может быть целесо­образным добавление 50–100 мкг/день селена. Мио-инозитол и селен способны восстановить эутиреоидное состояние, а также улучшить самочувствие у больных АИТ с субклиническим гипотиреозом. Принимая во внимание также безопасность использования двух молекул, отсутствие побочных эффектов, комбинацию мио-инозитола и селена можно считать очень эффективной и безопасной терапией для лечения АИТ.

Thyroid hormone synthesis continues despite biallelic thyroglobulin mutation with cell death.

Complete absence of thyroid hormone is incompatible with life in vertebrates. Thyroxine is synthesized within thyroid follicles upon iodination of thyroglobulin conveyed from the endoplasmic reticulum (ER), via the Golgi complex, to the extracellular follicular lumen. In congenital hypothyroidism from biallelic thyroglobulin mutation, thyroglobulin is misfolded and cannot advance from the ER, eliminating its secretion and triggering ER stress. Nevertheless, untreated patients somehow continue to synthesize sufficient thyroxine to yield measurable serum levels that sustain life. Here, we demonstrate that TGW2346R/W2346R humans, TGcog/cog mice, and TGrdw/rdw rats exhibited no detectable ER export of thyroglobulin, accompanied by severe thyroidal ER stress and thyroid cell death. Nevertheless, thyroxine was synthesized, and brief treatment of TGrdw/rdw rats with antithyroid drug was lethal to the animals. When untreated, remarkably, thyroxine was synthesized on the mutant thyroglobulin protein, delivered via dead thyrocytes that decompose within the follicle lumen, where they were iodinated and cannibalized by surrounding live thyrocytes. As the animals continued to grow goiters, circulating thyroxine increased. However, when TGrdw/rdw rats age, they cannot sustain goiter growth that provided the dying cells needed for ongoing thyroxine synthesis, resulting in profound hypothyroidism. These results establish a disease mechanism wherein dead thyrocytes support organismal survival.

Immunohistochemical features of expression and distribution of antibodies to thyroglobulin in the thyroid glands of newborn rats after prenatal exposure of dexamethasone

In clinical practice, synthetic glucocorticoids, such as dexamethasone, are used to accelerate fetal maturation in pregnant women at risk of preterm birth. Increasing the concentration of cortisol in humans and other mammals often causes structural and functional changes in fetal tissues, preparing it for childbirth and extrauterine life, but they can have long-term consequences in the structural organization of organs postnatally. Despite the large number of studies on the effect of glucocorticoids on the fetus, there are almost no data on the prenatal effect of dexamethasone on the processes of synthesis and resorption of thyroglobulin by thyroid thyrocytes in the postnatal period of life. Therefore, the aim of the study was to determine the immunohistochemical features of expression and distribution of antibodies to thyroglobulin in the thyroid glands of newborn rats in normal and after prenatal exposure to dexamethasone. The study material was the thyroid gland of Wistar rats aged 1 to 7 days of postnatal development (54 animals): I group - intact animals (norm); ІІ group - control, animals which were injected with 0.9% NaCl solution at a dose of 0.05 ml to each fetus on the 18th day of dated pregnancy; III group - experimental animals, which were administered a solution of dexamethasone at a dilution of 1:40 at a dose of 0.05 ml to each fetus on the 18th day of the date of pregnancy operatively during laparotomy, by intrauterine, transdermal subcutaneous injection into the interscapular area (Ukrainian patent №112288). Thyroglobulin Antibody (2H11) monoclonal antibodies: sc-51708 from Santa Cruz Biotechnology, Inc. were used for immunohistochemical study. Photo documentation of the studied objects was performed using a “Primo Star” microscope (Carl Zeiss, Germany) using an AxioCam camera using the Zeiss Zen program (2011). Analysis of micropreparations of thyroid glands of intact and control rats showed invariance of thyroglobulin synthesis and its accumulation, which was expressed by sufficient immunohistochemical expression of antibodies to thyroglobulin (ТgAb+). Prenatal administration of dexamethasone leads to intensification of the processes of morphological development of hormone-producing structures (follicles and follicular epithelium), production, resorption and iodination of thyroglobulin. This is evidenced by immunohistochemical studies found in 1-3 days of the neonatal period. It should be noted that on the 7th day of life the newborn was found intense changes in the structure of the parenchyma of the thyroid gland of animals of the experimental group: increased relative percentage of follicle cavity due to increased number of large and medium, some follicles had no resorption vacuoles which was accompanied by a slowdown in the excretion of hormones into the bloodstream and led to overstretching of the follicles and, as a consequence, to the flattening of the thyroid epithelium. Intrauterine administration of dexamethasone leads to prenatal acceleration of structure formation, folliculogenesis and enhancement of hormone-producing function, which is confirmed by the peculiarities of immunohistochemical expression of TgAb. By the end of the neonatal period in rats prenatally exposed to dexamethasone, the thyroid gland is depleted of compensatory-reactive internal reserves, which is morphologically and immunohistochemically manifested by signs of hypofunction and hypertrophy. Thus, detected in the thyroid glands of animals prenatally exposed to dexamethasone, aberration of cytoplasmic expression of ТgAb+, intensification of colloidal expression of ТgAb+, flattening of thyroid epithelium, and the absence of resorption vacuoles are signs of impaired hormone-forming function, which is the morphological basis for the development of hypofunctional states and requires further study.

The Transcriptomic Response of the Murine Thyroid Gland to Iodide Overload and the Role of the Nrf2 Antioxidant System.

Background: Thyroid follicular cells have physiologically high levels of reactive oxygen species because oxidation of iodide is essential for the iodination of thyroglobulin (Tg) during thyroid hormone synthesis. Thyroid follicles (the functional units of the thyroid) also utilize incompletely understood autoregulatory mechanisms to defend against exposure to excess iodide. To date, no transcriptomic studies have investigated these phenomena in vivo. Nuclear erythroid factor 2 like 2 (Nrf2 or Nfe2l2) is a transcription factor that regulates the expression of numerous antioxidant and other cytoprotective genes. We showed previously that the Nrf2 pathway regulates the antioxidant defense of follicular cells, as well as Tg transcription and Tg iodination. We, thus, hypothesized that Nrf2 might be involved in the transcriptional response to iodide overload. Methods: C57BL6/J wild-type (WT) or Nrf2 knockout (KO) male mice were administered regular water or water supplemented with 0.05% sodium iodide for seven days. RNA from their thyroids was prepared for next-generation RNA sequencing (RNA-Seq). Gene expression changes were assessed and pathway analyses were performed on the sets of differentially expressed genes. Results: Analysis of differentially expressed messenger RNAs (mRNAs) indicated that iodide overload upregulates inflammatory-, immune-, fibrosis- and oxidative stress-related pathways, including the Nrf2 pathway. Nrf2 KO mice showed a more pronounced inflammatory–autoimmune transcriptional response to iodide than WT mice. Compared to previously published datasets, the response patterns observed in WT mice had strong similarities with the patterns typical of Graves’ disease and papillary thyroid carcinoma (PTC). Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) also responded to iodide overload, with the latter targeting mRNAs that participate mainly in inflammation pathways. Conclusions: Iodide overload induces the Nrf2 cytoprotective response and upregulates inflammatory, immune, and fibrosis pathways similar to autoimmune hyperthyroidism (Graves’ disease) and PTC.

SAT-455 Mouse Thyroid Responds to Iodine Overload by Transcriptionally Enhancing the Keap1/Nrf2 Antioxidant Response and by Upregulating Nrf2-Dependent and Independent Inflammatory and Fibrosis Pathways

Nrf2 (Nfe2l2) is a transcription factor that regulates a series of cytoprotective and antioxidant enzymes. Its cytoplasmic inhibitor Keap1 senses the presence of oxidative or electrophilic stress though the interaction of sulfhydryl groups of its cysteines with reactive species and ceases to bind Nrf2. Thus, Nrf2 can transfer to the nucleus and induce its target genes. Follicular thyroid cells have physiologically high levels of reactive oxygen species as oxidation of iodine is essential for iodination of thyroglobulin and thyroid hormones synthesis. We have shown previously that Nrf2 pathway is active in thyroid and regulates the transcription of thyroglobulin. We thus hypothesized that the response of thyroid to iodine excess should comprise Nrf2-dependent and -independent pathways. To this end, 3 months-old male C57Bl6J WT or Nrf2 knockout (KO) mice were exposed to 0.05% sodium iodide in their water for 7 days. Thyroids were excised and used for RNA extraction; RNA-seq was performed by Exiqon, with a fold-change cutoff set at 2. Selected representative genes of the enriched pathways were quantified by real-time qPCR to validate RNA-seq results. Pathway analysis of the differentially expressed genes was performed using the Ingenuity Pathway Analysis (IPA) software. Pathways that were enriched with a p-value<0.05 were considered significant. 828 genes were differentially expressed in response to iodine exposure; 66% were upregulated, as were most of the highly enriched pathways (related to inflammatory-immune response, antioxidant response, xenobiotic metabolism, platelet activation and calcium signaling). About 300 genes were differentially expressed between WT and KO mice; highly enriched pathways were related to glutathione and xenobiotic metabolism, Ahr signaling and Nrf2 signaling and were all downregulated in KO mice. Analysis of the potential upstream regulators of these highly enriched pathways revealed that Nrf2 and NfkB are major regulators of the antioxidant and inflammatory response induction upon iodine exposure and that Tgfβ-Smad cascade regulates the induction of fibrosis signaling. Last, we performed an analysis limited to already known thyroid pathways. A few genes were enriched following this method; upregulation of Duoxa1 (hydrogen peroxide generator) and downregulation of Nis (sodium iodide symporter) upon iodine exposure, which are expected responses, and the downregulation of thyroglobulin and upregulation of Duoxa1 in KO mice that confirm our previous findings. In conclusion, Nrf2-driven cytoprotective response is upregulated after iodine overload along with induction of inflammatory pathways. Nrf2 regulates transcriptomic responses in the thyroid, including a small but significant part of the response to iodine challenge. Hence, Nrf2 can be considered a novel player in the frontiers of thyroid antioxidant response and thyroid economy.

Class III PI3K Vps34 Controls Thyroid Hormone Production by Regulating Thyroglobulin Iodination, Lysosomal Proteolysis, and Tissue Homeostasis.

Background: The production of thyroid hormones [triiodothyronine (T3), thyroxine (T4)] depends on the organization of the thyroid in follicles, which are lined by a monolayer of thyrocytes with strict apicobasal polarity. This polarization supports vectorial transport of thyroglobulin (Tg) for storage into, and recapture from, the colloid. It also allows selective addressing of channels, transporters, ion pumps, and enzymes to their appropriate basolateral [Na+/I- symporter (NIS), SLC26A7, and Na+/K+-ATPase] or apical membrane domain (anoctamin, SLC26A4, DUOX2, DUOXA2, and thyroperoxidase). How these actors of T3/T4 synthesis reach their final destination remains poorly understood. The PI 3-kinase isoform Vps34/PIK3C3 is now recognized as a main component in the general control of vesicular trafficking and of cell homeostasis through the regulation of endosomal trafficking and autophagy. We recently reported that conditional Vps34 inactivation in proximal tubular cells in the kidney prevents normal addressing of apical membrane proteins and causes abortive macroautophagy. Methods:Vps34 was inactivated using a Pax8-driven Cre recombinase system. The impact of Vps34 inactivation in thyrocytes was analyzed by histological, immunolocalization, and messenger RNA expression profiling. Thyroid hormone synthesis was assayed by 125I injection and plasma analysis. Results:Vps34 conditional knockout (Vps34cKO) mice were born at the expected Mendelian ratio and showed normal growth until postnatal day 14 (P14), then stopped growing and died at ∼1 month of age. We therefore analyzed thyroid Vps34cKO at P14. We found that loss of Vps34 in thyrocytes causes (i) disorganization of thyroid parenchyma, with abnormal thyrocyte and follicular shape and reduced PAS+ colloidal spaces; (ii) severe noncompensated hypothyroidism with extremely low T4 levels (0.75 ± 0.62 μg/dL) and huge thyrotropin plasma levels (19,300 ± 10,500 mU/L); (iii) impaired 125I organification at comparable uptake and frequent occurrence of follicles with luminal Tg but nondetectable T4-bearing Tg; (iv) intense signal in thyrocytes for the lysosomal membrane marker, LAMP-1, as well as Tg and the autophagy marker, p62, indicating defective lysosomal proteolysis; and (v) presence of macrophages in the colloidal space. Conclusions: We conclude that Vps34 is crucial for thyroid hormonogenesis, at least by controlling epithelial organization, Tg iodination as well as proteolytic T3/T4 excision in lysosomes.

De novo triiodothyronine formation from thyrocytes activated by thyroid-stimulating hormone

The thyroid gland secretes primarily tetraiodothyronine (T4), and some triiodothyronine (T3). Under normal physiological circumstances, only one-fifth of circulating T3 is directly released by the thyroid, but in states of hyperactivation of thyroid-stimulating hormone receptors (TSHRs), patients develop a syndrome of relative T3 toxicosis. Thyroidal T4 production results from iodination of thyroglobulin (TG) at residues Tyr5 and Tyr130, whereas thyroidal T3 production may originate in several different ways. In this study, the data demonstrate that within the carboxyl-terminal portion of mouse TG, T3 is formed de novo independently of deiodination from T4 We found that upon iodination in vitro, de novo T3 formation in TG was decreased in mice lacking TSHRs. Conversely, de novo T3 that can be formed upon iodination of TG secreted from PCCL3 (rat thyrocyte) cells was augmented from cells previously exposed to increased TSH, a TSHR agonist, a cAMP analog, or a TSHR-stimulating antibody. We present data suggesting that TSH-stimulated TG phosphorylation contributes to enhanced de novo T3 formation. These effects were reversed within a few days after removal of the hyperstimulating conditions. Indeed, direct exposure of PCCL3 cells to human serum from two patients with Graves' disease, but not control sera, led to secretion of TG with an increased intrinsic ability to form T3 upon in vitro iodination. Furthermore, TG secreted from human thyrocyte cultures hyperstimulated with TSH also showed an increased intrinsic ability to form T3 Our data support the hypothesis that TG processing in the secretory pathway of TSHR-hyperstimulated thyrocytes alters the structure of the iodination substrate in a way that enhances de novo T3 formation, contributing to the relative T3 toxicosis of Graves' disease.

Iodinated TG in Thyroid Follicular Lumen Regulates TTF-1 and PAX8 Expression via TSH/TSHR Signaling Pathway.

Our previous study showed that highly iodinated thyroglobulin (TG) inhibited thyroid transcription factor-1 (TTF-1) and paired box gene 8 (PAX8) expression, but the potential mechanism remains unclear. In this study, we constructed a thyroid follicle model in vitro to mimic its natural physiological structure and explored how iodinated TG in the follicular lumen tuned TTF-1 and PAX8 expression. Our data showed that lowly iodinated TG enhanced PKA activity while upregulation of both TTF-1 and PAX8 expression; and that highly iodinated TG triggered PKC activity while suppression of TTF-1 and PAX8 expression. Further, PKA agonist alone could increase TTF-1 and PAX8 expression while PKC agonist decreased TTF-1 and PAX8 level. If blocking PLC-PKC pathway using PKC-specific inhibitor, highly iodinated TG significantly promoted the expressions of TTF-1 and PAX8, and similarly PKA-specific blocker moderately inhibited TTF-1 and PAX8 expression. And opposite tendencies of TTF1 and PAX8 aberrant expression were observed in the condition of low iodinated TG when blocking PLC-PKC and cAMP-PKA signaling pathways. Our results indicated that iodinated TG manipulated TTF-1 and PAX8 expression through PLC-PKC and cAMP-PKA pathways, and highly iodinated TG played inhibitory role via PLC-PKC pathway from the TTF1 and PAX8 perspective while low level of iodinated TG was an activator through cAMP-PKA pathway. Our findings proved that iodinated TG in thyroid follicular lumen regulated TTF-1 and PAX8 expression through thyroid stimulating hormone/thyroid stimulating hormone receptor (TSH/TSHR) mediated cAMP-PKA and PLC-PKC signaling pathways. J. Cell. Biochem. 118: 3444-3451, 2017. © 2017 Wiley Periodicals, Inc.

Multiple Nutritional Factors and the Risk of Hashimoto's Thyroiditis.

Hashimoto's thyroiditis (HT) is considered to be the most common autoimmune disease. It is currently accepted that genetic susceptibility, environmental factors, and immune disorders contribute to its development. With regard to nutritional factors, evidence implicates high iodine intake and deficiencies of selenium and iron with a potential relevance of vitamin D status. To elucidate the role of nutritional factors in the risk, pathogenesis, and treatment of HT, PubMed and the Cochrane Library were searched for publications on iodine, iron, selenium, and vitamin D and risk/treatment of HT. Chronic exposure to excess iodine intake induces autoimmune thyroiditis, partly because highly iodinated thyroglobulin (Tg) is more immunogenic. Recent introduction of universal salt iodization can have a similar, though transient, effect. Selenoproteins are essential to thyroid action. In particular, the glutathione peroxidases protect the thyroid by removing excessive hydrogen peroxide produced for Tg iodination. Genetic data implicate the anti-inflammatory selenoprotein S in HT risk. There is evidence from observational studies and randomized controlled trials that selenium/selenoproteins can reduce thyroid peroxidase (TPO)-antibody titers, hypothyroidism, and postpartum thyroiditis. Iron deficiency impairs thyroid metabolism. TPO, the enzyme responsible for the production of thyroid hormones, is a heme (iron-containing) enzyme which becomes active at the apical surface of thyrocytes only after binding heme. HT patients are frequently iron deficient, since autoimmune gastritis, which impairs iron absorption, is a common co-morbidity. Treatment of anemic women with impaired thyroid function with iron improves thyroid-hormone concentrations, while thyroxine and iron together are more effective in improving iron status. Lower vitamin D status has been found in HT patients than in controls, and inverse relationships of serum vitamin D with TPO/Tg antibodies have been reported. However, other data and the lack of trial evidence suggest that low vitamin D status is more likely the result of autoimmune disease processes that include vitamin D receptor dysfunction. Clinicians should check patients' iron (particularly in menstruating women) and vitamin D status to correct any deficiency. Adequate selenium intake is vital in areas of iodine deficiency/excess, and in regions of low selenium intake a supplement of 50-100 μg/day of selenium may be appropriate.

TSH resistance revisited.

Genetic defects of hormone receptors are the most common form of end-organ hormone resistance. One example of such defects is TSH resistance, which is caused by biallelic inactivating mutations in the TSH receptor gene (TSHR). TSH, a master regulator of thyroid functions, affects virtually all cellular processes involving thyroid hormone production, including thyroidal iodine uptake, thyroglobulin iodination, reuptake of iodinated thyroglobulin and thyroid cell growth. Resistance to TSH results in defective thyroid hormone production from the neonatal period, namely congenital hypothyroidism. Classically, clinical phenotypes of TSH resistance due to inactivating TSHR mutations were thought to vary depending on the residual mutant receptor activity. Nonfunctional mutations in the two alleles produce severe thyroid hypoplasia with overt hypothyroidism (uncompensated TSH resistance), while hypomorphic mutations in at least one allele produce normal-sized thyroid gland with preserved hormone-producing capacity (compensated TSH resistance). More recently, a new subgroup of TSH resistance (nonclassic TSH resistance) that is characterized by paradoxically high thyroidal iodine uptake has been reported. In this article, the pathophysiology and clinical features of TSH resistance due to inactivating TSHR mutations are reviewed, with particular attention to the nonclassic form.

A Case of Incidental Struma Ovarii Confounded with the Metastasis of Papillary Thyroid Cancer

A focal radioactive iodine uptake in the pelvis of a patient with differentiated thyroid cancer needs differential diagnosis besides bone metastasis. Struma ovarii is a rare monodermal ovarian teratoma composed predominantly of mature thyroid tissue; 5-10% of these tumors are malignant. As diagnosis and surgery of thyroid cancer have increased recently, incidental cases of struma ovarii, after radioactive iodine treatment, were occasionally reported. Rare cases of ovary metastasis of thyroid cancer were also reported. We report a case of benign struma ovarii incidentally found in a patient with papillary thyroid cancer. The patient showed a sus tained high level of thyroglobulin and focal radioactive iodine uptake in the right pelvis, confused with distant metastasis, after total thyroidectomy and radioactive iodine treatment. (Endocrinol Metab 27:227-231, 2012)

Diagnosis and Treatment of Anaplastic Thyroid Carcinoma

Anaplastic thyroid carcinoma (ATC) is a poorly differentiated thyroid cancer. It cannot uptake iodine or synthesis thyroglobulin. The incidence is low; about 2% - 5% of thyroid cancer. The peak age incidence is 60 - 70 years and it is more common in females (55% - 77% of all patients). In recent years, the incidence has declined; however, it may be higher in areas of endemic goiter. ATC may occur with a coexisting carcinoma and may represent transformation of a well-differentiated thyroid cancer. Patients typically present with a rapidly growing anterior neck mass and aggressive symptoms. The most reliable tool in detecting thyroid malignancies is fine-needle aspiration cytology (FNAC). Sensitivity of FNAC for thyroid malignancy ranged from 61% to 97.7%. Fine-needle aspiration can diagnose ATC by the demonstration of spindled or giant cells, bizarre neoplastic cells that may be multinucleated, or atypical cells with high mitotic activity. A syncytial pattern is the predominant cellular pattern of anaplastic thyroid carcinoma. Other laboratory tests, including tumor markers (cytokeratin, vimentin, and carcinoembryogenic antigen) are helpful in diagnosis and follow-up of the patients. Multimodality therapy (surgery, external beam radiation, and chemotherapy) is the recommended treatment and it seems to have slightly improved outcomes. The prognosis is not as bad in younger patients with smaller tumors. The most common cause of death is lung metastasis. The mean survival time is less than 6 months from the time of diagnosis. The prompt diagnosis and aggressive treatment are essential modality to achieve optimal outcomes.

Altered ion transport by thyroid epithelia from CFTR−/− pigs suggests mechanisms for hypothyroidism in cystic fibrosis

Subclinical hypothyroidism has been linked to cystic fibrosis, and the cystic fibrosis transmembrane conductance regulator (CFTR) shown to be expressed in the thyroid. The thyroid epithelium secretes Cl⁻ and absorbs Na(+) in response to cAMP. Chloride secretion may provide a counter-ion for the SLC26A4 (pendrin)-mediated I⁻ secretion which is required for the first step of thyroid hormonogenesis, thyroglobulin iodination. In contrast, few models exist to explain a role for Na(+) absorption. Whether CFTR mediates the secretory Cl⁻ current in thyroid epithelium has not been directly addressed. We used thyroids from a novel pig CFTR(-/-) model, generated primary pig thyroid epithelial cell cultures (pThECs), analysed these cultures for preservation of thyroid-specific transcripts and proteins, and monitored the following parameters: (1) the Cl⁻ secretory response to the cAMP agonist, isoprenaline; and (2) the amiloride-sensitive Na(+) current. Baseline short-circuit current (I(sc)) did not differ between CFTR(+/+) and CFTR(-/-) cultures. Serosal isoprenaline increased I(sc) in CFTR(+/+), but not CFTR(-/-), monolayers. Compared with CFTR(+/+) thyroid cultures, amiloride-sensitive Na(+) absorption measured in CFTR(-/-) pThECs represented a greater fraction of the resting I(sc). However, levels of transcripts encoding epithelial sodium channel (ENaC) subunits did not differ between CFTR(+/+) and CFTR(-/-) pThECs. Immunoblot analysis verified ENaC subunit protein expression, but quantification indicated no difference in expression levels. Our studies definitively demonstrate that CFTR mediates cAMP-stimulated Cl⁻ secretion in a well-differentiated thyroid culture model and that knockout of CFTR promotes increased Na(+) absorption by a mechanism other than increased ENaC expression. These findings suggest several models for the mechanism of cystic fibrosis-associated hypothyroidism.

Pathological characteristics of thyroiditis in NOD mice induced by iodine excess and thyroglobulin immunization

Objective To observe the pathological characteristics of thyroiditis induced by iodine excess and thyroglobulin (Tg) immunization and to explore the mechanism of thyroiditis induced by iodine excess. Methods NOD mice were used for intaking 0.05% Nal water and(or) Tg immunization. Morphologic change in thyroid and apoptosis were observed. The levels of serum TT4, TSH, thyroglobulin antibody (TgAb) and thyroid peroxidase antibody (TPOAb) were measured. Responding to Tg, lymphocytic proliferation of lymph node and spleen, interleukin-4(IL-4)and γ-interferon(IFN-γ) levels in culture medium of splenocytes were detected. Real-time PCR Was used to detect mRNA expressions of IL-4, IFN-γ, chemokine ligand 10 (CXCL10) and intercellular adhesion molecular-1(ICAM-1) in thyroid. Results Distended thyroid follicles,colloid accumulation, intense lymphocytic infiltration and disorganization were seen in thyroid of iodine excess group, along with increased apoptosis of thyroid cells(34.66～ 2.78 vs 5.11±0.62 ,P<0.01). The levels of TT4 were lowered while TSH raised ,but no production of thyroid-specific autoantibodies was revealed. Lymph node and spleen cells showed positive respornse under stimulation of Tg. The level of IFN-γ[(1. 272±0.049 vs 1. 139±0. 025)ng/L,P<0. 01] was raised in culture medium of splenocytes but not IL-4. The expression of IFN-γ, CXCLI0 and ICAM-1 mRNA were increased in thyroid. But in Tg group, some lymphocytes were scattered in thyroid, autoantibodies emerged ,and the level of IL-4 was increased in cuhure medium of splenocytes[(18. 508±0. 113 vs 13. 368±0. 016)ng/L, P<0. 01]. ledine excess combined with Tg enhanced these inflammatory reaction. Conclusion Iodine excess induced thyroiditis in NOD mice. The process seems to be Th1 response dominant organ-specific autoimmune diseases. Iodine excess and Tg immunizatiou play a synergistic role in inducing experimental autoimmune thyroiditis. Key words: Iodine excess; Thyroiditis; Apoptosis; Lymphocytic proliferation