American Thyroid Association Guide to investigating thyroid hormone economy and action in rodent and cell models

Arsenic-Induced Thyroid Hormonal Alterations and Their Putative Influence on Ovarian Follicles in Balb/c Mice

Thyroid issues are common among women in their reproductive years, and women with thyroid dysfunction often encounter challenges with fertility. Arsenic is known for its toxic effects on the thyroid and ovaries, investigated independently. However, there is no known study directly or indirectly addressing the association between arsenic, thyroid function, and ovarian reserve. This study aims to investigate the effect of arsenic on thyroid function and its possible implications on ovarian follicular reserve. Female Balb/c mice were given sodium arsenite (0.2 ppm, 2 ppm, and 20 ppm) via drinking water for 30 days. Findings showed that arsenic decreased thyroid hormone levels (fT3 and fT4) while increasing TSH levels, which might have led to elevated levels of FSH and LH. Furthermore, arsenic treatment not only decreased thyroid follicle sizes but also altered the ovarian follicular count. The finding demonstrates that arsenic significantly reduced the expression of LAMP1, a lysosomal marker protein. This reduction leads to increased lysosomal permeability in the thyroid, resulting in a significant release of cathepsin B. These changes led to hypothyroidism, which might indirectly affect the ovaries. Also, the elevated levels of growth differentiation factor-8 in arsenic-treated ovaries indicate impaired folliculogenesis and ovulation. Furthermore, arsenic significantly increased the expressions of pAkt and pFoxo3a, implying that arsenic accelerated the activation of the primordial follicular pools. In conclusion, arsenic disrupts lysosomal stabilization, potentially leading to a decline in circulating fT3 and fT4 levels. This disturbance could, in turn, affect the estrous cycle and may alter the pattern of follicular development.

JPT2 in subclinical hypothyroidism-related miscarriage as a transcription co-factor: involvement of LEPR/STAT3 activation

BACKGROUND AND PURPOSE

Subclinical hypothyroidism (SCH) has been identified to be associated with implantation failure, in which the dysfunction of trophoblast cells is involved. In this study, the transcriptomics of aborted placenta from SCH rats were analyzed. Jupiter microtubule-associated homolog 2 (JPT2) was downregulated in the aborted placenta. This study aims to investigate its role in SCH-associated miscarriage.

METHODS

Spontaneous abortion was observed in SCH rats generated by thyroidectomy combined with levothyroxine administration. The transcriptomics analysis was performed using aborted placenta. Afterward, the effects of JPT2 on trophoblast cells were explored using gain-and loss-of-function experiments.

RESULTS

Transcriptomics analysis showed 1286 downregulated genes and 2300 upregulated genes in the aborted placenta, and JPT2 was significantly downregulated in the aborted placenta from SCH rats. Afterward, gain-and loss-of-function experiments exhibited that overexpression of JPT2 promoted the proliferation, migration, invasion, spheroid formation of HTR-8/SVneo trophoblast cells and their attachment to endometrial stromal cells, while these biological behaviors were suppressed by JPT2 knockdown. Furthermore, JPT2 accelerated the transcription of leptin receptor (LEPR), and activated signal transducer and activator of transcription 3 (STAT3) signal in a transcription factor AP-2γ-dependent manner. In addition, silencing of LEPR abolished the role of JPT2.

CONCLUSION

Our results revealed that JPT2, which was downregulated in the aborted placenta from SCH rats, promoted proliferation, migration, invasion, spheroid formation, and attachment of trophoblast cells via regulating LEPR/STAT3 axis as a transcription co-factor. It is indicated that low expression of JPT2 may contribute to the abortion in individuals with SCH.

The Musashi-1-type 2 deiodinase pathway regulates astrocyte proliferation

Thyroid hormone (TH) is a critical regulator of cellular function and cell fate. The circulating TH level is relatively stable, while tissue TH action fluctuates according to cell type-specific mechanisms. Here, we focused on identifying mechanisms that regulate TH action through the type 2 deiodinase (D2) in glial cells. Dio2 mRNA has an unusually long 3'UTR where we identified multiple putative MSI1 binding sites for Musashi-1 (MSI1), a highly conserved RNA-binding cell cycle regulator. Binding to these sites was confirmed through electrophoretic mobility shift assay. In H4 glioma cells, shRNA-mediated MSI1 knockdown increased endogenous D2 activity, whereas MSI1 overexpression in HEK293T cells decreased D2 expression. This latter effect could be prevented by the deletion of a 3.6 kb region of the 3'UTR of Dio2 mRNA containing MSI1 binding sites. MSI1 immunoreactivity was observed in 2 mouse Dio2-expressing cell types, that is, cortical astrocytes and hypothalamic tanycytes, establishing the anatomical basis for a potential in vivo interaction of Dio2 mRNA and MSl1. Indeed, increased D2 expression was observed in the cortex of mice lacking MSI1 protein. Furthermore, MSI1 knockdown-induced D2 expression slowed down cell proliferation by 56% in primary cultures of mouse cortical astrocytes, establishing the functionality of the MSI1-D2-T3 pathway. In summary, Dio2 mRNA is a target of MSI1 and the MSI1-D2-T3 pathway is a novel regulatory mechanism of astrocyte proliferation with the potential to regulate the pathogenesis of human glioblastoma.

Genetic Background Strongly Influences the Impact of Carrying the Thr92Ala-DIO2 Polymorphism in the Male Mouse

About half of the world population carries at least one allele of the Ala92-DIO2, which slows down the activity of the type 2 deiodinase (D2), the enzyme that activates T4 to T3. Carrying the Ala92-DIO2 allele has been associated with increased body mass index and insulin resistance, but this has not been reproduced in all populations. To test if the genetic background affects the impact of this polymorphism, here we studied the genetically distant C57Bl/6J (B6) and FVB/N (FVB) mice carrying the Ala92-Dio2 allele as compared to control mice carrying the Thr92-Dio2 allele. Whereas B6-Ala92-Dio2 and B6-Thr92-Dio2 mice-fed chow or high-fat diet-behaved metabolically similar in studies using indirect calorimetry, glucose- and insulin tolerance tests, and measuring white adipose tissue (WAT) weight and liver steatosis, major differences were observed between FVB-Ala92-Dio2 and FVB-Thr92-Dio2 mice: carrying the Ala92-Dio2 allele (on a chow diet) resulted in hypercholesterolemia, smaller WAT pads, hepatomegaly, steatosis, and transcriptome changes in the interscapular brown adipose tissue (iBAT) typical of ER stress and apoptosis. Acclimatization at thermoneutrality (30 °C) eliminated most of the metabolic phenotype, indicating that impaired adaptive (BAT) thermogenesis can be involved. In conclusion, the metabolic impact of carrying the Ala92-Dio2 allele depends greatly on the genetic background of the mouse, varying from no phenotype in B6 mice to a major phenotype in FVB mice. These results will help the planning of future clinical trials studying the Thr92Ala-DIO2 polymorphism and may explain why some clinical studies performed in different populations across the globe have obtained inconsistent results.

Mapping Thyroid Changes in Size and Position During Enlargement in Adult Mice With Hyperthyroidism

The thyroid in Graves' disease undergoes a considerable divergence in size and position from the normal anatomy. However, knowledge of the pathological anatomy related to the change, which is required before planned surgical or local intervention, or diagnosis, is neglected. To investigate Graves' disease, we established a model of mice that successfully mimicked all the signs presented in the clinic. Under a long-term immunization (35 weeks), the animals displayed large heterogeneity in thyroid size, such as the cases of natural occurrence. These thyroids in the model were sized into various phases and registered. A blend of the registered thyroids and the thyroid and tracheal cartilage landmarks led to the production of site-dependent incidence graphs of thyroid in the front view and on the section for each phase. The merger of the incidence graphs of all the phases resulted in thyroid phase-dependent topography. The depicted graphs illustrate the fine localization of the thyroid in various sizes and their dynamic changes during enlargement, which may facilitate currently used fine-needle aspiration biopsy and ultrasonography-guided biopsy techniques. Familiarity with this knowledge might avoid misclassifying an abnormality as normal, or vice versa, and be helpful for imaging diagnosis and local surgery therapy in Graves' disease.

Increased Absorption of Thyroxine in a Murine Model of Hypothyroidism Using Water/CO2 Nanobubbles

Thyroxine (T4) is a drug extensively utilized for the treatment of hypothyroidism. However, the oral absorption of T4 presents certain limitations. This research investigates the efficacy of CO2 nanobubbles in water as a potential oral carrier for T4 administration to C57BL/6 hypothyroid mice. Following 18 h of fasting, the formulation was administered to the mice, demonstrating that the combination of CO2 nanobubbles and T4 enhanced the drug's absorption in blood serum by approximately 40%. To comprehend this observation at a molecular level, we explored the interaction mechanism through which T4 engages with the CO2 nanobubbles, employing molecular simulations, semi-empirical quantum mechanics, and PMF calculations. Our simulations revealed a high affinity of T4 for the water-gas interface, driven by additive interactions between the hydrophobic region of T4 and the gas phase and electrostatic interactions of the polar groups of T4 with water at the water-gas interface. Concurrently, we observed that at the water-gas interface, the cluster of T4 formed in the water region disassembles, contributing to the drug's bioavailability. Furthermore, we examined how the gas within the nanobubbles aids in facilitating the drug's translocation through cell membranes. This research contributes to a deeper understanding of the role of CO2 nanobubbles in drug absorption and subsequent release into the bloodstream. The findings suggest that utilizing CO2 nanobubbles could enhance T4 bioavailability and cell permeability, leading to more efficient transport into cells. Additional research opens the possibility of employing lower concentrations of this class of drugs, thereby potentially reducing the associated side effects due to poor absorption.

In vitro and in vivo investigation of a thyroid hormone system-specific interaction with triazoles

Alterations in thyroid hormones (TH) and thyroid-stimulating hormone levels are frequently found following exposure to chemicals of concern. Dysregulation of TH levels can severely perturb physiological growth, metabolism, differentiation, homeostasis in the adult and developmental processes in utero. A frequently identified mode of action for this interaction is the induction of hepatic detoxification mechanisms (e.g. SULTs and UGTs), which lead to TH conjugation and elimination and therefore interfere with hormonal homeostasis, fulfilling the endocrine disruptors (EDs) definition. A short-term study in rats with dietary exposure to cyproconazole, epoxiconazole and prochloraz was conducted and hepatocyte hypertrophy, hepatic UGT activity and Phase 1/2 gene expression inductions were observed together with changes in TH levels and thyroid follicular hypertrophy and hyperplasia. To test for specific interaction with the thyroid hormone system, in vitro assays were conducted covering thyroidal I-uptake (NIS), TH transmembranal transport via MCT8 and thyroid peroxidase (TPO) function. Assays for iodothyronine deiodinases (DIO1-DIO3) and iodotyrosine deiodinase (DEHAL1) were included, and from the animal experiment, Dio1 and Dehal1 activities were measured in kidney and liver as relevant local indicators and endpoints. The fungicides did not affect any TH-specific KEs, in vitro and in vivo, thereby suggesting hepatic conjugation as the dominant MoA.

Impaired T3 uptake and action in MCT8-deficient cerebral organoids underlie Allan-Herndon-Dudley syndrome

Patients with mutations in the thyroid hormone (TH) cell transporter monocarboxylate transporter 8 (MCT8) gene develop severe neuropsychomotor retardation known as Allan-Herndon-Dudley syndrome (AHDS). It is assumed that this is caused by a reduction in TH signaling in the developing brain during both intrauterine and postnatal developmental stages, and treatment remains understandably challenging. Given species differences in brain TH transporters and the limitations of studies in mice, we generated cerebral organoids (COs) using human induced pluripotent stem cells (iPSCs) from MCT8-deficient patients. MCT8-deficient COs exhibited (i) altered early neurodevelopment, resulting in smaller neural rosettes with thinner cortical units, (ii) impaired triiodothyronine (T3) transport in developing neural cells, as assessed through deiodinase-3-mediated T3 catabolism, (iii) reduced expression of genes involved in cerebral cortex development, and (iv) reduced T3 inducibility of TH-regulated genes. In contrast, the TH analogs 3,5-diiodothyropropionic acid and 3,3',5-triiodothyroacetic acid triggered normal responses (induction/repression of T3-responsive genes) in MCT8-deficient COs, constituting proof of concept that lack of T3 transport underlies the pathophysiology of AHDS and demonstrating the clinical potential for TH analogs to be used in treating patients with AHDS. MCT8-deficient COs represent a species-specific relevant preclinical model that can be utilized to screen drugs with potential benefits as personalized therapeutics for patients with AHDS.

Regeneration of Thyroid Glands in the Spleen Restores Homeostasis in Thyroidectomy Mice

Surgical removal of the thyroid gland (TG) for treating thyroid disorders leaves the patients on lifelong hormone replacement that partially compensates the physiological needs, but regenerating TG is challenging. Here, an approach is reported to regenerate TG within the spleen for fully restoring the thyroid's functions in mice, by transplanting thyroid tissue blocks to the spleen. Within 48 h, the transplanted tissue efficiently revascularizes, forming thyroid follicles similar to the native gland after 4 weeks. Structurally, the ectopically generated thyroid integrates with the surrounding splenic tissue while maintaining its integrity, separate from the lymphatic tissue. Functionally, it fully restores the native functions of the TG in hormone regulation in response to physiological stimuli, outperforming the established method of oral levothyroxine therapy in maintaining systemic homeostasis. The study demonstrates the full restoration of thyroid functions post-thyroidectomy by intrasplenic TG regeneration, providing fresh insights for designing novel therapies for thyroid-related disorders.

GLP-1 Receptor Signaling Has Different Effects on the Perikarya and Axons of the Hypophysiotropic Thyrotropin-Releasing Hormone Synthesizing Neurons in Male Mice

Background: Glucagon-like peptide 1 (GLP-1) is involved in the regulation of energy and glucose homeostasis. As GLP-1 has similar effects on the energy homeostasis as the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons that regulate the hypothalamic-pituitary-thyroid (HPT) axis, we raised the possibility that the TRH neurons are involved in the mediation of the effects of GLP-1. Therefore, the relationship and interaction of the GLP-1 system and the TRH neurons of the hypothalamic paraventricular nucleus (PVN) were studied. Methods: To examine the anatomical and functional relationship of TRH neurons and the GLP-1 system in the PVN, immunocytochemistry, in situ hybridization, in vitro patch-clamp electrophysiology, metabolic phenotyping, and explant experiments were performed. Results: Our data demonstrate that the TRH neurons of the PVN are innervated by GLP-1 producing neurons and express the GLP-1 receptor (GLP-1R). However, not only do the GLP-1-innervated TRH neurons express GLP-1R but the receptor is also present in the axons of the hypophysiotropic TRH neurons in the blood-brain barrier free median eminence (ME) suggesting that peripherally derived GLP-1 may also influence the TRH neurons. In vitro, GLP-1 increased the firing rate of TRH neurons and depolarized them. In addition, GLP-1 directly stimulated the GABAergic input of a population of TRH neurons. Furthermore, GLP-1 inhibited the release of TRH from the hypophysiotropic axons in the ME. In vivo, peripheral GLP-1R agonist administration markedly inhibited the food intake and the energy expenditure, but had no effect on the TRH expression in the PVN and resulted in lower circulating free T4 levels. Conclusions: Our results indicate that GLP-1R activation has a direct stimulatory effect on TRH neurons in the PVN, but the activation of GLP-1R may also inhibit TRH neurons by facilitating their inhibitory inputs or by inhibiting the axon terminals of these cells in the ME. The innervation of TRH neurons by GLP-1 neurons suggests that TRH neurons might be influenced by both circulating GLP-1 and by GLP-1 neurons of the nucleus tractus solitarii. The lack of GLP-1R agonist-induced regulation of TRH neurons in vivo suggests that the HPT axis does not mediate the GLP-1R agonist-induced weight loss.

Transcriptomic profiling of the response to excess iodide in Keap1 hypomorphic mice reveals new gene-environment interactions in thyroid homeostasis

Iodide plays a pivotal role in thyroid homeostasis due to its crucial involvement in thyroid hormone biosynthesis. Exposure to pharmacological doses of iodide elicits in the thyroid an autoregulatory response to preserve thyroid function, as well as an antioxidant response that is mediated by the Keap1/Nrf2 signaling pathway. The objective of the present study was to investigate the transcriptional response of the thyroid to excess iodide in a background of enhanced Nrf2 signaling. Keap1 knockdown (Keap1KD) mice that have activated Nrf2 signaling were exposed or not to excess iodide in their drinking water for seven days and compared to respective wild-type mice. RNA-sequencing of individual mouse thyroids identified distinct transcriptomic patterns in response to iodide, with Keap1KD mice showing an attenuated inflammatory response, altered thyroidal autoregulation, and enhanced cell growth/proliferative signaling, as confirmed also by Western blotting for key proteins involved in antioxidant, autoregulatory and proliferative responses. These findings underscore novel gene-environment interactions between the activation status of the Keap1/Nrf2 antioxidant response system and the dietary iodide intake, which may have implications not only for the goiter phenotype of Keap1KD mice but also for humans harboring genetic variations in KEAP1 or NFE2L2 or treated with Nrf2-modulating drugs.

Disruption of the thyroid hormone system and patterns of altered thyroid hormones after gestational chemical exposures in rodents - a systematic review

We present a comprehensive overview of changes in thyroxine (T4) and thyroid stimulating hormone (TSH) serum concentrations after pre-gestational, gestational and/or lactation exposures of rodents to various chemicals that affect the thyroid hormone system. We show that T4 and TSH changes consistent with the idealized view of the hypothalamic-pituitary-thyroid (HPT) feedback loop (T4 decrements accompanied by TSH increases) are observed with only a relatively small set of chemicals. Most substances affect concentrations of various thyroid hormones without increasing TSH. Studies of altered T4 concentrations after gestational exposures are limited to a relatively small set of chemicals in which pesticides, pharmaceuticals and industrial chemicals are under-represented. Our risk-of-bias analysis exposed deficits in T4/TSH analytics as a problem area. By relating patterns of T4 - TSH changes to mode-of-action (MOA) information, we found that chemicals capable of disrupting the HPT feedback frequently affected thyroid hormone synthesis, while substances that produced T4 serum decrements without accompanying TSH increases lacked this ability, but often induced liver enzyme systems responsible for the elimination of TH by glucuronidation. Importantly, a multitude of MOA leads to decrements of serum T4. The current EU approaches for identifying thyroid hormone system-disrupting chemicals, with their reliance on altered TH serum levels as indicators of a hormonal mode of action and thyroid histopathological changes as indicators of adversity, will miss chemicals that produce T4/T3 serum decreases without accompanying TSH increases. This is of concern as it may lead to a disregard for chemicals that produce developmental neurotoxicity by disrupting adequate T4/T3 supply to the brain, but without increasing TSH.

Local modulation of thyroid hormone signaling in the retina affects the development of diabetic retinopathy

Thyroid hormone (TH) dyshomeostasis is associated with poor prognosis in acute and prolonged illness, but its role in diabetic retinopathy (DR) has never been investigated. Here, we characterized the TH system in the retinas of db/db mice and highlighted regulatory processes in MIO-M1 cells. In the db/db retinas, typical functional traits and molecular signatures of DR were paralleled by a tissue-restricted reduction of TH levels. A local condition of low T3 (LT3S) was also demonstrated, which was likely to be induced by deiodinase 3 (DIO3) upregulation, and by decreased expression of DIO2 and of TH receptors. Concurrently, T3-responsive genes, including mitochondrial markers and microRNAs (miR-133-3p, 338-3p and 29c-3p), were downregulated. In MIO-M1 cells, a feedback regulatory circuit was evidenced whereby miR-133-3p triggered the post-transcriptional repression of DIO3 in a T3-dependent manner, while high glucose (HG) led to DIO3 upregulation through a nuclear factor erythroid 2-related factor 2-hypoxia-inducible factor-1 pathway. Finally, an in vitro simulated condition of early LT3S and hyperglycemia correlated with reduced markers of both mitochondrial function and stress response, which was reverted by T3 replacement. Together, the data suggest that, in the early phases of DR, a DIO3-driven LT3S may be protective against retinal stress, while, in the chronic phase, it not only fails to limit HG-induced damage, but also increases cell vulnerability likely due to persistent mitochondrial dysfunction.

Thyroid-stimulating hormone may participate in insulin resistance by activating toll-like receptor 4 in liver tissues of subclinical hypothyroid rats

BACKGROUND

Thyroid-stimulating hormone (TSH) is an independent risk factor of and closely associated with metabolic disorders. In the present study, we explored the potential mechanism and adverse effects of TSH on insulin resistance in the liver of subclinical hypothyroidism models in vivo.

METHODS

The mean glucose infusion rate (GIR), free fatty acids (FFAs), the homeostatic model assessment for insulin resistance (HOMA-IR), fasting plasma insulin (FINS), the TLR4 signal pathway and its intracellular negative regulator-toll-interacting protein (Tollip), and the modulators of insulin signaling were evaluated.

RESULTS

Compared to the normal control group (NC group), the subclinical hypothyroidism rat group (SCH group) showed decreases in GIR and increases in FFAs, FINS, and HOMA-IR. The levels of TLR4 and of its downstream molecules like p-NF-κB, p-IRAK-1, IL-6 and TNF-α were evidently higher in the SCH group than in the NC group. Conversely, the level of Tollip was significantly lower in the SCH group than in the NC group. Compared to the NC group, the levels of phosphorylated IRS-1-Tyr and GLUT2 were decreased in the SCH group. Macrophage infiltration was higher in the SCH group than in the NC group.

CONCLUSION

TSH may participate in aggravating inflammation by increasing macrophage infiltration; furthermore, it may activate the TLR4-associated inflammatory signaling pathway, thus interfering with insulin signals in liver tissues. Targeting TSH may have therapeutic benefits against metabolic disorders.

Thyroid hormone induces restrictive cardiomyopathy in β1-adrenoceptor knockout mice

The purpose of this study was to characterize the role of β1-AR signaling and its cross-talk between cardiac renin-angiotensin system and thyroid-hormone-induced cardiac hypertrophy. T3 was administered at 0.5 mg·kg-1·day-1 for 10 days in β1-KOT3 and WTT3 groups, while control groups received vehicle alone. Echocardiography and myocardial histology was performed; cardiac and serum ANGI/ANGII and ANP and cardiac levels of p-PKA, p-ERK1/2, p-p38-MAPK, p-AKT, p-4EBP1, and ACE were measured. WTT3 showed decreased IVSTd and increased LVEDD versus WTsal (p < 0.05). β1-KOT3 exhibited lower LVEDD and higher relative IVSTd versus β1-KOsal, the lowest levels of ejection fraction, and the highest levels of cardiomyocyte diameter (p < 0.05). Cardiac ANP levels decreased in WTT3 versus β1-KOT3 (p < 0.05). Cardiac ACE expression was increased in T3-treated groups (p < 0.05). Phosphorylated-p38 MAPK levels were higher in WTT3 versus WTsal or β1-KOT3, p-4EBP1 was elevated in β1-KO animals, and p-ERK1/2 was up-regulated in β1-KOT3. These findings suggest that β1-AR signaling is crucial for TiCH.

TSH Pulses Finely Tune Thyroid Hormone Release and TSH Receptor Transduction

Detection of circulating TSH is a first-line test of thyroid dysfunction, a major health problem (affecting about 5% of the population) that, if untreated, can lead to a significant deterioration of quality of life and adverse effects on multiple organ systems. Human TSH levels display both pulsatile and (nonpulsatile) basal TSH secretion patterns; however, the importance of these in regulating thyroid function and their decoding by the thyroid is unknown. Here, we developed a novel ultra-sensitive ELISA that allows precise detection of TSH secretion patterns with minute resolution in mouse models of health and disease. We characterized the patterns of ultradian TSH pulses in healthy, freely behaving mice over the day-night cycle. Challenge of the thyroid axis with primary hypothyroidism because of iodine deficiency, a major cause of thyroid dysfunction worldwide, results in alterations of TSH pulsatility. Induction in mouse models of sequential TSH pulses that mimic ultradian TSH profiles in periods of minutes were more efficient than sustained rises in basal TSH levels at increasing both thyroid follicle cAMP levels, as monitored with a genetically encoded cAMP sensor, and circulating thyroid hormone. Hence, this mouse TSH assay provides a powerful tool to decipher how ultradian TSH pulses encode thyroid outcomes and to uncover hidden parameters in the TSH-thyroid hormone set-point in health and disease.

Designing a combined liothyronine (LT3), L- thyroxine (LT4) trial in symptomatic hypothyroid subjects on LT4 - the importance of patient selection, choice of LT3 and trial design

Approximately 10%-15% of subjects with hypothyroidism on L-thyroxine (LT4) alone have persistent symptoms affecting their quality of life (QoL). Although the cause is unclear, there is evidence that "tissue T3 lack" may be responsible. If so, combining liothyronine (LT3) with LT4 would be helpful. However, randomized controlled trials (RCT), have not established greater efficacy for the LT3 + LT4 combination in these subjects than for LT4 alone. While the trial design may have been responsible, the use of unphysiological, short-acting LT3 preparations and non-thyroid-specific patient-reported outcome measures (PROMs) may have contributed. We recommend attention to the following aspects of trial design for future RCTs of LT3 + LT4 compared to LT4 alone: (a) Subject selection-(i) measurable symptoms (disadvantages should be recognized); (ii) using a validated thyroid specific PROM such as ThyPRO39 or the Composite scale derived from it; (iii) those taking over 1.2 μg/day or 100 μg/day (for pragmatic reasons) of LT4 defining a population likely without intrinsic thyroid activity who depend on exogenous LT4; (iv) recruiting a preponderance of subjects with autoimmune thyroiditis increasing generalisability; and (v) those with a high symptom load with a greater response to combination therapy e.g. those with the deiodinase 2 polymorphism. (b) The use of physiological LT3 preparations producing pharmacokinetic similarities to T3 profiles in unaffected subjects: two long-acting LT3 preparations are currently available and must be tested in phase 2b/3 RCTs. (c) The superiority of a crossover design in limiting numbers and costs while maintaining statistical power and ensuring that all subjects experienced the investigative medication.

Sustained Pituitary T3 Production Explains the T4-mediated TSH Feedback Mechanism

The regulation of thyroid activity and thyroid hormone (TH) secretion is based on feedback mechanisms that involve the anterior pituitary TSH and medial basal hypothalamus TSH-releasing hormone. Plasma T3 levels can be "sensed" directly by the anterior pituitary and medial basal hypothalamus; plasma T4 levels require local conversion of T4 to T3, which is mediated by the type 2 deiodinase (D2). To study D2-mediated T4 to T3 conversion and T3 production in the anterior pituitary gland, we used mouse pituitary explants incubated with 125I-T4 for 48 hours to measure T3 production at different concentrations of free T4. The results were compared with cultures of D1- or D2-expressing cells, as well as freshly isolated mouse tissue. These studies revealed a unique regulation of the D2 pathway in the anterior pituitary gland, distinct from that observed in nonpituitary tissues. In the anterior pituitary, increasing T4 levels reduced D2 activity slightly but caused a direct increase in T3 production. However, the same changes in T4 levels decreased T3 production in human HSkM cells and murine C2C12 cells (both skeletal muscle) and mouse bone marrow tissue, which reached zero at 50 pM free T4. In contrast, the increase in T4 levels caused the pig kidney LLC-PK1 cells and kidney fragments to proportionally increase T3 production. These findings have important implications for both physiology and clinical practice because they clarify the mechanism by which fluctuations in plasma T4 levels are transduced in the anterior pituitary gland to mediate the TSH feedback mechanism.

The effects of glyphosate-based herbicide on the hypothalamic-pituitary thyroid axis are tissue-specific and dependent on age exposure

The significant increase in glyphosate-based herbicide (GBH) use raises concerns about residues in the environment and food, potentially jeopardizing human health. The involvement of GBHs in the increased incidence of thyroid disorders is speculated, since glyphosate has been linked to an increased risk of thyroid disease in farmers. In this sense, this study aims to investigate the potential effects of low levels of GBH exposure (0, 0.5 or 5 mg/kg) from weaning (postnatal day PND23) to adult life (PND60 and PND90) in male Wistar rats on hypothalamic-pituitary-thyroid (HPT) axis function. The serum levels of T4 were increased. The hypothalamus showed reduced expression of Dio2, Thra1, and Thra2. The pituitary showed reduced expression of Mct8 and Dio2 and increased expression of Thra1. The thyroid showed increased expression of Tshr and Thra1. The heart showed increased expression of Mct8 and Myh6. The liver showed reduced expression of Mct8 and Thra2 and increased expression of Thra1. In thyroid morphometry, a decrease in both follicular diameter and area and decreased follicular and colloid diameters and areas were observed. These results suggested that GBH may affect several steps of HPT axis regulation at the transcriptional level in an age-dependent manner and alter the morphometric parameters of the thyroid gland and TH synthesis, with potential repercussions in the TH-target organs.

DBP exposure induces thyroid inflammatory impairment through activating AKT/NF-κB/NLRP3 signaling

Previous studies exhibited reproductive and neurodevelopmental toxicity in rats exposed to Di-n-butyl phthalate (DBP). However, the effects of DBP exposure on the other endocrine organ are still unclear. This study aimed to assess the impact of DBP exposure on the thyroid of male rats and the associated mechanisms. Here, rats were respectively treated with DBP at 0 (control), 50 (low dose), 250 (medium dose), or 500 (high dose) mg/kg/day dissolved in 1 ml quantity of corn oil by intragastrical administration for two weeks. The results demonstrated that the proliferation and inflammatory response changes were significantly different compared to the control. In vivo DBP is mainly converted to mono-n-butyl phthalate (MBP), an active form producing untoward reactions of DBP exposure. Therefore, for in vitro experiments, we treated the thyroid follicular epithelial cell line (Nthy-ori 3-1) in a temporal gradient using 1 mM MBP. Further in vitro studies showed that MBP exposure upregulated tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), as well as interleukin-1β (IL-1β) by activating AKT/NF-κB/NLRP3 signaling. Meanwhile, we detected that Pellino2 (Peli2) played an essential role in promoting the activation of NLRP3 inflammasome. Briefly speaking, this study confirmed that DBP exposure caused impaired thyroid structure and thyroid inflammation in male rats, which offered new views into the harm of DBP exposure on the endocrine organ.

A Feedback Loop Involving Exosomal miR-146a and NG2 to Propel the Development and Progression of Hypothyroidism

Background: Thyrotropin receptor (TSHR) plays a central role in maintaining thyroid function and TSHR impairment causes hypothyroidism, which is often associated with metabolic disarrangement. The most common type of hypothyroidism is autoimmune disease-related and the mechanism, particularly with respect to the role of microRNAs (miRNAs), has not been delineated. Methods: Serum from 30 patients with subclinical hypothyroidism (SCH) and 30 healthy individuals were collected and exosomal miR-146a (exo-miR-146a) was examined, followed by extensive mechanistic investigation using various molecular and cellular experimental approaches and genetic-knockout mouse models. Results: Our clinical investigation showed that exo-miR-146a was systemically elevated in the serum of patients with SCH (p = 0.04) compared with healthy individuals, prompting us to investigate the biological effects of miR-146a in cells. We found that miR-146a could target and down-regulate neuron-glial antigen 2 (Ng2), with consequent down-regulation of TSHR. We next generated a thyroid-specific Ng2 knockout (Thy-Ng2-/-) mouse model and found a significant down-regulation of TSHR in Thy-Ng2-/- mice, accompanied by the development of hypothyroidism and metabolic disorders. We further found that a decrease in NG2 resulted in decreased receptor tyrosine kinase-linked downstream signaling and down-regulation of c-Myc, consequently resulting in up-regulation of miR-142 and miR-146a in thyroid cells. Up-regulated miR-142 targeted the 3'-untranslated region (UTR) of TSHR messenger RNA (mRNA) and post-transcriptionally down-regulated TSHR, explaining the development of hypothyroidism above. Local up-regulation of miR-146a in thyroid cells augments the earlier cited processes initiated by systemically elevated miR-146a, thereby forming a feedback loop to propel the development and progression of hypothyroidism. Conclusions: This study has uncovered a self-augmenting molecular loop initiated by elevated exo-miR-146a to suppress TSHR through targeting and down-regulating NG2, thereby initiating and propelling the development and progression of hypothyroidism.

[Diseases of the thyroid gland in men and women-Status quo and new research needs]

"Diseases of the thyroid gland occur more frequently in women": this statement has been used in textbooks for decades; however, is this equally true for all thyroid gland diseases and can conclusions be derived from this for a different disease relevance and prognosis in men and women? Is possibly even a sex-specific treatment needed? These questions are taken up and subsequently the epidemiological data and studies that have investigated the influence of gender on the course of thyroid gland diseases are taken into consideration. It is shown that the data situation is much more restricted than is to be expected for frequent diseases in the general population.

Effects of Triiodothyronine Treatment in an Animal Model of Heart Failure with Preserved Ejection Fraction

Background: Low levels of triiodothyronine (T3) are common in patients with heart failure (HF). Our aim was to evaluate the effects of supplementation with low and replacement doses of T3 in an animal model of HF with preserved ejection fraction (HFpEF). Methods: We evaluated four groups: ZSF1 Lean (n = 8, Lean-Ctrl), ZSF1 Obese (rat model of metabolic-induced HFpEF, n = 13, HFpEF), ZSF1 Obese treated with a replacement dose of T3 (n = 8, HFpEF-T3high), and ZSF1 Obese treated with a low-dose of T3 (n = 8, HFpEF-T3low). T3 was administered in drinking water from weeks 13 to 24. The animals underwent anthropometric and metabolic assessments, echocardiography, and peak effort testing with maximum O2 consumption (VO2max) determination at 22 weeks, and a terminal hemodynamic evaluation at 24 weeks. Afterwhile myocardial samples were collected for single cardiomyocyte evaluation and molecular studies. Results: HFpEF animals showed lower serum and myocardial thyroid hormone levels than Lean-Ctrl. Treatment with T3 did not normalize serum T3 levels, but increased myocardial T3 levels to normal levels in the HFpEF-T3high group. Body weight was significantly decreased in both the T3-treated groups, comparing with HFpEF. An improvement in glucose metabolism was observed only in HFpEF-T3high. Both the treated groups had improved diastolic and systolic function in vivo, as well as improved Ca2+ transients and sarcomere shortening and relaxation in vitro. Comparing with HFpEF animals, HFpEF-T3high had increased heart rate and a higher rate of premature ventricular contractions. Animals treated with T3 had higher myocardial expression of calcium transporter ryanodine receptor 2 (RYR2) and α-myosin heavy chain (MHC), with a lower expression of β-MHC. VO2max was not influenced by treatment with T3. Myocardial fibrosis was reduced in both the treated groups. Three animals died in the HFpEF-T3high group. Conclusions: Treatment with T3 was shown to improve metabolic profile, myocardial calcium handling, and cardiac function. While the low dose was well-tolerated and safe, the replacement dose was associated with increased heart rate, and increased risk of arrhythmias and sudden death. Modulation of thyroid hormones may be a potential therapeutic target in HFpEF; however, it is important to take into account the narrow therapeutic window of T3 in this condition.

TRIAC disrupts cerebral thyroid hormone action via negative feedback and heterogenous distribution among organs

As 3,3',5-triiodothyroacetic acid (TRIAC), a metabolite of thyroid hormones (THs), was previously detected in sewage effluent, we aimed to investigate exogenous TRIAC's potential for endocrine disruption. We administered either TRIAC or 3,3',5-triiodo-L-thyronine (LT3) to euthyroid mice and 6-propyl-2-thiouracil-induced hypothyroid mice. In hypothyroid mice, TRIAC administration suppressed the hypothalamus-pituitary-thyroid (HPT) axis and upregulated TH-responsive genes in the pituitary gland, the liver, and the heart. We observed that, unlike LT3, TRIAC administration did not upregulate cerebral TH-responsive genes. Measurement of TRIAC contents suggested that TRIAC was not efficiently trafficked into the cerebrum. By analyzing euthyroid mice, we found that cerebral TRIAC content did not increase despite TRIAC administration at higher concentrations, whereas serum levels and cerebral contents of THs were substantially decreased. Disruption by TRIAC is due to the additive effects of circulating endogenous THs being depleted via a negative feedback loop involving the HPT axis and heterogeneous distribution of TRIAC among different organs.

Iodotyrosines Are Biomarkers for Preclinical Stages of Iodine-Deficient Hypothyroidism in Dehal1-Knockout Mice

Background: Iodine is required for the synthesis of thyroid hormone (TH), but its natural availability is limited. Dehalogenase1 (Dehal1) recycles iodine from mono- and diiodotyrosines (MIT, DIT) to sustain TH synthesis when iodine supplies are scarce, but its role in the dynamics of storage and conservation of iodine is unknown. Methods: Dehal1-knockout (Dehal1KO) mice were generated by gene trapping. The timing of expression and distribution was investigated by X-Gal staining and immunofluorescence using recombinant Dehal1-beta-galactosidase protein produced in fetuses and adult mice. Adult Dehal1KO and wild-type (Wt) animals were fed normal and iodine-deficient diets for 1 month, and plasma, urine, and tissues were isolated for analyses. TH status was monitored, including thyroxine, triiodothyronine, MIT, DIT, and urinary iodine concentration (UIC) using a novel liquid chromatography with tandem mass spectrometry method and the Sandell-Kolthoff (S-K) technique throughout the experimental period. Results: Dehal1 is highly expressed in the thyroid and is also present in the kidneys, liver, and, unexpectedly, the choroid plexus. In vivo transcription of Dehal1 was induced by iodine deficiency only in the thyroid tissue. Under normal iodine intake, Dehal1KO mice were euthyroid, but they showed negative iodine balance due to a continuous loss of iodotyrosines in the urine. Counterintuitively, the UIC of Dehal1KO mice is twofold higher than that of Wt mice, indicating that S-K measures both inorganic and organic iodine. Under iodine restriction, Dehal1KO mice rapidly develop profound hypothyroidism, while Wt mice remain euthyroid, suggesting reduced retention of iodine in the thyroids of Dehal1KO mice. Urinary and plasma iodotyrosines were continually elevated throughout the life cycles of Dehal1KO mice, including the neonatal period, when pups were still euthyroid. Conclusions: Plasma and urine iodotyrosine elevation occurs in Dehal1-deficient mice throughout life. Therefore, measurement of iodotyrosines predicts an eventual iodine shortage and development of hypothyroidism in the preclinical phase. The prompt establishment of hypothyroidism upon the start of iodine restriction suggests that Dehal1KO mice have low iodine reserves in their thyroid glands, pointing to defective capacity for iodine storage.

Axonal T3 uptake and transport can trigger thyroid hormone signaling in the brain

The development of the brain, as well as mood and cognitive functions, are affected by thyroid hormone (TH) signaling. Neurons are the critical cellular target for TH action, with T3 regulating the expression of important neuronal gene sets. However, the steps involved in T3 signaling remain poorly known given that neurons express high levels of type 3 deiodinase (D3), which inactivates both T4 and T3. To investigate this mechanism, we used a compartmentalized microfluid device and identified a novel neuronal pathway of T3 transport and action that involves axonal T3 uptake into clathrin-dependent, endosomal/non-degradative lysosomes (NDLs). NDLs-containing T3 are retrogradely transported via microtubules, delivering T3 to the cell nucleus, and doubling the expression of a T3-responsive reporter gene. The NDLs also contain the monocarboxylate transporter 8 (Mct8) and D3, which transport and inactivate T3, respectively. Notwithstanding, T3 gets away from degradation because D3's active center is in the cytosol. Moreover, we used a unique mouse system to show that T3 implanted in specific brain areas can trigger selective signaling in distant locations, as far as the contralateral hemisphere. These findings provide a pathway for L-T3 to reach neurons and resolve the paradox of T3 signaling in the brain amid high D3 activity.

The simultaneous action of acute paradoxical sleep deprivation and hypothyroidism modulates synaptosomal ATPases and acetylcholinesterase activities in rat brain

BACKGROUND

Thyroid dysfunctions as well as sleep abnormalities are usually followed by neurological, psychiatric and/or behavioral disorders. On the other hand, changes in the brain adenosine triphosphatases (ATPases) and acetylcholinesterase (AChE) activities show significant importance in pathogenetic pathways in the evolution of numerous neuropsychiatric diseases.

METHODS

This study aimed to evaluate the in vivo simultaneous effects of hypothyroidism and paradoxical sleep deprivation for 72 h on synaptosomalATPases and AChE activities of whole rat brains. In order to induce hypothyroidism, 6-n-propyl-2-thiouracil was administrated in drinking water during 21 days. The modified multiple platform method was used to induce paradoxical sleep deprivation. The AChE and ATPases activities were measured using spectrophotometric methods.

RESULTS

Hypothyroidism significantly increased the activity of Na⁺/K⁺-ATPase compared to other groups, while at the same time significantly decreased AChE activity compared to the CT and SD groups. Paradoxical sleep deprivation significantly increased AChE activity compared to other groups. The simultaneous effect of hypothyroidism and sleep deprivation reduced the activity of all three enzymes (for Na⁺/K⁺-ATPase between HT/SD and HT group p < 0.0001, SD group p < 0.001,CT group p = 0.013; for ecto-ATPases between HT/SD and HT group p = 0.0034, SD group p = 0.0001, CT group p = 0.0007; for AChE between HT/SD and HT group p < 0.05, SD group p < 0.0001, CT group p < 0.0001).

CONCLUSIONS

The effect of simultaneous existence of hypothyroidism and paradoxical sleep deprivation reduces the activity of the Na⁺/K⁺-ATPase, ecto-ATPases, and AChE, what is different from individual effect of hypothyroidism and paradoxical sleep deprivation itself. This knowledge could help in the choice of appropriate therapy in such condition.

Cadmium exposure promotes thyroid pyroptosis and endocrine dysfunction by inhibiting Nrf2/Keap1 signaling

Cadmium (Cd) is a ubiquitous toxic metal and environmental pollutant. Increasing studies have shown that Cd exposure increases the incidence of various endocrine system diseases, including thyrotoxicity reflected by thyroid structural damage and endocrine toxicity. However, the observed outcomes are complex and conflicting, leading to the mechanism of Cd-induced thyrotoxicity remaining obscure. In this study, 4-week-old male C57BL/6 mice were given 2 or 7 mg/kg Cadmium Chloride (CdCl₂) intragastrically for 4 and 8 weeks, and the Cd-mediated thyrotoxicity was evaluated by determining alterations in thyroid structure and endocrine function, and alterations of oxidant stress, apoptosis, and pyroptosis. Our data showed that Cd exposure could reduce body weight and induce thyrotoxicity by impairing thyroid follicular morphology and endocrine function, accompanied by elevated oxidative stress and apoptosis, macrophage infiltration, and inflammatory cytokine secretion. Importantly, Cd significantly promoted thyroid follicular cell pyroptosis by increasing Nlrp3, Asc, Caspase-1, Gsdmd, IL-1β, and IL-18 expression. Mechanistical analysis suggested that Cd treatment could inhibit antioxidant pathway by downregulating antioxidant response protein, Nrf2, and upregulating its negative feedback regulator, Keap1. Collectively, our in vivo findings suggest that Cd exposure could facilitate thyroid follicular cell pyroptosis by inhibiting Nrf2/Keap1 signaling, thereby disrupting thyroid tissue structure and endocrine function, which offers novel insights into the Cd-mediated detrimental consequences on thyroid homeostasis.

Triiodothyronine Treatment reverses Depression-Like Behavior in a triple-transgenic animal model of Alzheimer's Disease

Alzheimer disease's (AD) is a neurodegenerative disorder characterized by cognitive and behavioral impairment. The central nervous system is an important target of thyroid hormones (TH). An inverse association between serum triiodothyronine (T3) levels and the risk of AD symptoms and progression has been reported. We investigated the effects of T3 treatment on the depression-like behavior in male transgenic 3xTg-AD mice. Animals were divided into 2 groups treated with daily intraperitoneal injections of 20 ng/g of body weight (b.w.) L-T3 (T3 group) or saline (vehicle, control group). The experimental protocol lasted 21 days, and behavioral tests were conducted on days 18-20. At the end of the experiment, the TH profile and hippocampal gene expression were evaluated. The T3-treated group significantly increased serum T3 and decreased thyroxine (T4) levels. When compared to control hippocampal samples, the T3 group exhibited attenuated glycogen synthase kinase-3 (GSK3), metalloproteinase 10 (ADAM10), amyloid-beta precursor-protein (APP), serotonin transporter (SERT), 5HT1A receptor, monocarboxylate transporter 8 (MCT8) and bone morphogenetic protein 7 (BMP-7) gene expression, whereas augmented superoxide dismutase 2 (SOD2) and Hairless gene expression. T3-treated animals also displayed reduced immobility time in both the tail suspension and forced swim tests, and in the latter presented a higher latency time compared to the control group. Therefore, our findings suggest that in an AD mouse model, T3 supplementation promotes improvements in depression-like behavior, through the modulation of the serotonergic related genes involved in the transmission mediated by 5HT1A receptors and serotonin reuptake, and attenuated disease progression.

Levothyroxine: Conventional and novel drug delivery formulations

Despite the fact that levothyroxine is one of the most prescribed medications in the world, its bioavailability has been reported to be impaired by many factors, including interfering drugs or foods and concomitant diseases, and persistent hypothyroidism with a high dose of levothyroxine is thus elicited. Persistent hypothyroidism can also be induced by noninterchangeability between formulations and poor compliance. To address these issues, some strategies have been developed. Novel formulations (liquid solutions and soft-gel capsules) have been designed to eliminate malabsorption. Some other delivery routes (injections, suppositories, sprays, and sublingual and transdermal administrations) are aimed at circumventing different difficulties in dosing, such as thyroid emergencies and dysphagia. Moreover, nanomaterials have been used to develop delivery systems for the sustained release of levothyroxine to improve patient compliance and reduce costs. Some delivery systems encapsulating nanoparticles show promising release profiles. In this review, we first summarize the medical conditions that interfere with the bioavailability of oral levothyroxine and discuss the underlying mechanisms and treatments. The efficacy of liquid solutions and soft-gel capsules are systematically evaluated. We further summarize the novel delivery routes for levothyroxine and their possible applications. Nanomaterials in the levothyroxine field are then discussed and compared based on their load and release profile. We hope the article provides novel insights into the drug delivery of levothyroxine.

Subchronic toxicological evaluation of EnXtra™ (standardised extract of Alpinia galanga rhizome) in rats

OBJECTIVES

Alpinia galanga is a commonly used ingredient in Asian food and traditional medicine. But an extract of the rhizome had never been used commercially in food supplements and functional foods. There is some evidence of safety and tolerability in humans for a proprietary A. galanga rhizome extract (EnXtra™) and it is Generally Recognised as Safe (GRAS) in the US already. However, this botanical ingredient has not been evaluated for its subchronic toxicity in rats to confirm its safety in wider food applications.

METHODS

Sprague Dawley rats were orally administered the test item for 90 days by following OECD (Test Guideline: 408), with a recovery period of 28 days. Cumulative effects and No Observed Adverse Effect Level (NOAEL) were estimated. EnXtra™ was administered orally at 0, 1,000, 2,000 and 3,000 mg kg^-1 body weight (b. wt.) with additional vehicle and high dose recovery groups. Observations included clinical signs, haematology, clinical chemistry, gross pathology and histopathology.

RESULTS

On terminal sacrifice, no treatment-related adverse effects were observed viz., clinical signs, mortality, body weight changes and feed consumption parameters. Haematology, clinical biochemistry and thyroid hormone levels were within the normal range. Further, no treatment-related gross and microscopic pathological lesions were observed across the treatment groups.

CONCLUSIONS

Based on the results of the toxicological evaluation, NOAEL of A. galanga rhizome extract (AGRE) was fixed at 3,000 mg kg^-1 b. wt. per day and ADI of 1800 mg day^-1 in the case of humans.

Multisensory Stimulation Improves Cognition and Behavior in Adult Male Rats Born to LT4-treated Thyroidectomized Dams

Gestational hypothyroidism can impair development, cognition, and mood. Here, we tested whether multisensory stimulation (MS) improves the phenotype of rats born to surgically thyroidectomized (Tx) dams suboptimally treated with LT4. 8-week-old female Tx Wistar rats were kept on daily LT4 (0.7 µg/100 g body weight) dosed by gavage (serum TSH and T4 levels indicated moderate hypothyroidism) and 3 weeks later placed for breeding. MS of the litter started at age 60 days and lasted for 8 weeks. It consisted of twice per week of physical, cognitive, sensorial, and food stimuli. The offspring were assessed before and after MS for standardized tests of locomotor activity, cognition, and mood. Gestational hypothyroidism resulted in reduced litter size and increased offspring mortality. The pups exhibited delayed physical development, impairment of short- and long-term memory, and anxiety- and depressive-like behaviors. Nonetheless, ambulatory activity, social memory, and social preference were not affected by gestational hypothyroidism. MS restored short-term memory and anxiety while improving depressive like-behaviors. MS did not improve long-term memory. MS also did not modify the performance of control litter born to intact dams. We conclude that cognition and mood impairments caused by moderate gestational hypothyroidism were reversed or minimized in rats through MS. Further studies should define the molecular mechanisms involved.

Stem Cells from Healthy and Tendinopathic Human Tendons: Morphology, Collagen and Cytokines Expression and Their Response to T3 Thyroid Hormone

The aim of this study was to investigate the effect of triiodothyronine (T3) on tendon specific markers and cytokines expression of stem cells extracted from human tendons. Indeed, thyroid hormones have been reported to be protective factors, maintaining tendons’ homeostasis, whereas tendinopathy is believed to be related to a failed healing response. Healthy and tendinopathic human tendons were harvested to isolate tendon stem/progenitor cells (TSPCs). TSPCs obtained from pathological samples showed gene expression and morphological modifications at baseline in comparison with cells harvested from healthy tissues. When cells were maintained in a medium supplemented with T3 (10⁻⁶ M), only pathological populations showed a significant upregulation of tenogenic markers (DCN, TNC, COL1A1, COL3A1). Immunostaining revealed that healthy cells constantly released type I collagen, typical of tendon matrix, whereas pathological ones overexpressed and secreted type III collagen, typical of scarred and impaired tissue. Pathological cells also overexpressed pro- and anti-inflammatory cytokines, suggesting an impaired balance in the presence of T3, without STAT3 activation. Moreover, DKK-1 was significantly high in the culture medium of pathological cell cultures and was reversed by T3. This study opens perspectives on the complex biochemical alteration of cells from pathological tendons, which may lead to the chronic disease context with an impaired extracellular matrix.

High-throughput Screening in Combination With a Cohort Study for Iodothyronine Deiodinases

Regulatory mechanisms of iodothyronine deiodinases (DIOs) require further elucidation, and conventional methods for evaluating DIOs are unsuitable for high-throughput screening (HTS). Here we explored factors of transcriptional regulation of 3 types of DIOs (DIO1, DIO2, and DIO3) from a chemical library using our designed HTS. We constructed HTS based on a promoter assay and performed a screen of 2480 bioactive compounds. For compounds that were clinically approved, we validated hit compounds through a retrospective cohort study in our department that evaluated changes in thyroid function in patients using the compounds as drug therapy. Furthermore, we verified the involvement of DIOs using mice treated with the compounds. Of the hit compounds, 6 and 7 compounds transcriptionally up- and downregulated DIO1, respectively; 34 transcriptionally upregulated DIO2; and 5 and 2 compounds transcriptionally up- and downregulated DIO3, respectively. The cohort study clarified the clinical effects of some hit compounds: ritodrine increased free triiodothyronine (fT3)/free thyroxine (fT4) ratio and decreased serum thyroid-stimulating hormone (TSH) levels, tadalafil increased serum fT3 levels, and tyrosine kinase inhibitors (TKIs) decreased serum fT3 and fT4 levels and increased serum TSH levels. Following in vivo experiments using treated mice, consistent results were observed in ritodrine, which upregulated DIO2 in the thyroid gland. In conclusion, we completed HTS for DIOs and obtained attractive hit compounds. Our cohort study revealed the clinical significance of ritodrine, sildenafil, and TKIs. We hope our unique method will contribute to analyzing various targets and lists of hit compounds will promote understanding of DIOs.

The Induction of Hypothyroidism During Gestation Decreases Outer Hair Cell Motility in Rat Offspring

Introduction Perinatal hypothyroidism has a negative repercussion on the development and maturation of auditory system function. However, its long-term effect on auditory function remains unsettled.

Objective To evaluate the effect of prenatal hypothyroidism on the auditory function of adult offspring in rats.

Methods Pregnant Wistar rats were given the antithyroid drug methimazole (0.02% -1-methylimidazole-2-thiol– MMI) in drinking water, ad libitum, from gestational day (GD) 9 to postnatal day 15 (PND15). Anesthetized offspring from MMI-treated dams (OMTD) and control rats were evaluated by tympanometry, distortion product otoacoustic emission (DPOAE), and auditory brainstem response (ABR) at PNDs 30, 60, 90, and 120.

Results Our data demonstrated no middle ear dysfunction, with the OMTD compliance lower than that of the control group. The DPOAE revealed the absence of outer hair cells function, and the ABR showed normal integrity of neural auditory pathways up to brainstem level in the central nervous system. Furthermore, in the OMTD group, hearing loss was characterized by a higher electrophysiological threshold.

Conclusion Our data suggest that perinatal hypothyroidism leads to irreversible damage to cochlear function in offspring.

Selpercatinib-Induced Hypothyroidism Through Off-Target Inhibition of Type 2 Iodothyronine Deiodinase

PURPOSE

The development of the selective RET inhibitors selpercatinib and pralsetinib has revolutionized the treatment of metastatic progressive RET-mutant medullary thyroid carcinoma (MTC) and other RET-driven cancers, given their more favorable side-effect profile. The aim of this study is to investigate the mechanisms of selpercatinib-induced thyroid dysfunction in athyreotic patients with RET-mutant MTC and in patients with RET-mutant non-small-cell lung cancer (NSCLC) who had a functional thyroid.

MATERIALS AND METHODS

Thyroid hormone levels were evaluated in an observational cohort of five athyreotic patients with MTC and 30 patients with NSCLC before and after initiation of selpercatinib. In vitro experiments to identify the mechanism of selpercatinib-induced thyroid dysfunction were conducted in cells expressing endogenous D1, D2, and D3 iodothyronine deiodinases.

RESULTS

Upon initiating treatment with selpercatinib, athyreotic patients developed clinical hypothyroidism with approximately 60% lower T3 levels despite adequate levothyroxine supplementation, whereas in patients with NSCLC, who retain a normal thyroid, selpercatinib resulted in a more attenuated reduction in serum T3, which was dose-dependent. We conducted studies in cells endogenously expressing either D1, D2, or D3, the three iodothyronine deiodinases. Selpercatinib inhibited D2-mediated T3 production in MSTO-211 cells by 50%. A modest repression of D2 mRNA was present in human thyroid cancer TT cells that express RET, but not in the MSTO-211 cells that do not. No effect of the drug was observed on D1 (activating deiodinase) or D3 (inactivating deiodinase). Thus, a nontranscriptional effect of selpercatinib on D2 activity is the most plausible explanation for the low T3 levels.

CONCLUSION

An off-target effect of selpercatinib on D2-mediated T3 production leads to clinical hypothyroidism, primarily in levothyroxine-treated athyreotic patients. Liothyronine supplementation was needed to achieve normal T3 levels and restore clinical euthyroidism.

Subacute and low-dose tributyltin exposure disturbs the mammalian hypothalamus-pituitary-thyroid axis in a sex-dependent manner

Tributyltin (TBT) is an endocrine disruptor chemical (EDC) capable of altering the proper function of the hypothalamus-pituitary thyroid (HPT) axis. This study aimed to evaluate the subacute effects of TBT on the HPT axis of male and female rats. A dose of 100 ng/kg/day TBT was used in both sexes over a 15-day period, and the morphophysiology and gene expression of the HPT axis were assessed. TBT exposure increased the body weight in both sexes, while food efficiency increased - only in male rats. It was also possible to note alterations in the thyroid, with the presence of a stratified epithelium, cystic degeneration, and increased interstitial collagen deposition. A reduction in T3 and T4 levels was only observed in TBT male rats. A reduction in TSH levels was observed in TBT female rats. Evaluating mRNA expression, we observed a decrease in hepatic D1 and TRH mRNA levels in TBT female rats. An increase in D2 mRNA expression in the hypothalamus was observed in TBT male rats. Additionally, no significant changes in TRH or hepatic D1 mRNA expression in TBT male rats or in hypothalamic D1 and D2 mRNA expression in TBT female rats were observed. Thus, we can conclude that TBT has different toxicological effects on male and female rats by altering thyroid gland morphophysiology, leading to abnormal HPT axis function, and even at subacute and low doses, it may be involved in complex endocrine and metabolic disorders.

Development of an experimental model of tumor growth under hypothyroidism

Aim. Our aim has been to develop an experimental model of the tumor growth against the background of hypothyroidism in rats of both genders in order to study possible influence made by hypothyroidism on progression of malignant tumors of various histological types. Materials and methods. In our studies we have used 100 outbred albino rats of both genders, with an individual body mass of 150-180 g. The female rats (n=30) and the male rats (n=30) have received Mercazolil at a day dosage of 2,5 mg/100g of the body weight for 30 days. After hypothyroidism in the treated rodents had been confirmed, one group of them (15 females and 15 males) were subcutaneously inoculated with the Guerin’s carcinoma cells, and another group (covering other 15 females and other 15 males) has been undergone to transplantation of the Sarcoma 45 cells. The reference group has included the rats of both genders with subcutaneously inoculated the Guerin’s carcinoma cells (n=10 females and n=10 males) and Sarcoma 45 cells (n=10 females and n=10 males), but without reproduction of the hypothyroidism model. Upon expiration of one month, within the 3 day period, we have estimated with a radioisotope analysis (RIA) standard assay kits (Immunotech, Czekh Republic) the levels of the thyroid hormones in blood of the tested animals as follows: Triiodothyronine (T3) (pM/L), total Thyroxine (T4) (pM/L) and Thyroid-Stimulating Hormon (TSH) (μU/mL). The obtained data have been processed with Statistica 10.0. Results. Upon the treatment with Mercazolil, we have found in the females a decrease by a factor of 7,3 in the total level of Thyroxine and an increase by a factor 1,6 in the TSH level (p<0,05), while in the males we have recorded a reduction by a factor of 2 in the total level of Thyroxine and an increase by a factor of 1,5 in the TSH level (p<0,05). In this case, the average sizes of the tumors in the female rats with Guerin’s carcinoma and hypothyroidism have been found smaller than those found in the reference group as given below: upon expiration of 4 days they are 1,3 times smaller (p<0,05), upon expiration of 7 and 10 days the volumes have been found 1,4 times smaller (p<0,05); upon expiration of 14 days the volumes have been recorded to be 1,5 times less (p<0,05); upon expiration of 18 days they have been reported to be 1,3 times less (p<0,05), and upon expiration of 21 days they have been estimated to be 1,4 times less (p<0,05). As to the males with Guerin’s carcinoma and hypothyroidism, the average sizes of their tumors as against the reference group data have been recorded to be smaller as follows: upon expiration of 4 days they are found 13,3 times less; upon expiration of 7 days they have been recorded to be 7,5 times smaller; upon expiration of 10 days the volumes have been estimated to be 1,9 times less (p<0,05), and upon expiration of 14 days they have been found to be 2,6 times less. The survival rate in the female rats in the main test has been recorded to be 1,6 times higher (p<0,05) against the data in the reference group, while the survival rate in the males has not shown any significant differences therein. In the female rates with S 45 growing against the background of hypothyroidism the average sizes of the tumors have been found to be less than those identified in the reference group as follows: after 4 days, the sizes have been recorded to be 1,4 times less (p<0,05); after 7 and 10 days they have been recorded to be 1,6 and 3,2 times smaller, respectively (p<0,05); after 14 days they have been found to be 3,9 times less, and after 18 days they have been recorded to be 4,8 times less. In the males at tumor growth week stage 1, the tumor sizes have increased 3,1 times as against 4 days of the tumor growth; upon expiration of 10 days the sizes have been found to be 7,1 times greater as compared with the previous period; upon expiration of 2 weeks they have increased 1,5 times (p<0,05); upon expiration of 18 and 21 days the tumor sizes have been recorded to be greater by a factor of 2,3 and by a factor of 1,6, respectively (p<0,05). The life spans in the female rodents in the main test group has been reported to be longer by a factor of 1,8 (p<0,05) than it has been the case with the reference group, and the average life span in the males has reached 21 days. Conclusion. We have revealed that in the female rates diagnosed with hypothyroidism the sizes of the subcutaneous tumor nodes of Guerin’s carcinoma and S 45 show slower progression as against that recorded in the reference group, and the life span recorded in the above rodents has been found as significantly longer, while in the male rats with hypothyroidism we have observed an irregular, slower, progression of the tumor nodes of Guerin’s carcinoma and S 45 within the period of 14 days, but subsequently we have detected the same progression rate as it is the case with the reference group data.

Bezafibrate induces hypothyroidism in a patient with resistance to thyroid hormone β due to a G347R variant

OBJECTIVE

A unique clinical course was observed in a patient with resistance to thyroid hormone β (RTHβ) caused by a variant of the THRB gene leading to the replacement of glycine with arginine in codon 347 (p.G347R). He presented with the syndrome of inappropriate secretion of thyrotropin (TSH) (free T4 [fT4]: 32.43 pmol/L, TSH: 4.67 mIU/L), but slowly developed progressive hypothyroidism (fT4: 8.37 pmol/L, TSH: 100.90 mIU/L) that resolved after suspending bezafibrate (BZ) treatment (fT4: 32.18 pmol/L, TSH: 7.14 mIU/L). This study clinically and experimentally evaluated this interesting phenomenon.

METHODS

A retrospective cohort analysis of non-RTHβ patients was performed at Kyoto University Hospital. Data before BZ treatment were compared to the first data after treatment. Using reporter assays of iodothyronine deiodinases (DIO1, DIO2, DIO3) in HEK293T cells, we performed functional analyses of mutant thyroid hormone receptor β with p.G347R (G347R TRβ). Mice with G347R TRβ were generated by hydrodynamic gene delivery.

RESULTS

In non-RTHβ patients (n = 7), BZ treatment did not change serum free T3 and TSH but significantly increased fT4 (p = .008). BZ administration increased DIO3 reporter activity in the context of G347R TRβ, whereas did not change DIO1 and DIO2 reporter activity. In the livers of mice with G347R TRβ, BZ administration increased reverse T3 content, which corresponded to an increase in Dio3 messenger RNA.

CONCLUSIONS

While hypothyroidism associated with BZ treatment did not occur in non-RTHβ patients, it was observed in a patient with RTHβ due to the p.G347R variant. Liver DIO3 upregulation might involve this hypothyroidism.

Thyroid hormone economy in mice overexpressing iodothyronine deiodinases

In peripheral tissues, triiodothyronine (T3) production and consequent thyroid hormone actions are mainly regulated by iodothyronine deiodinases (DIOs) classified into 3 types: D1, D2, and D3. We aimed to investigate the effects of peripheral DIOs on thyroid hormone economy independent of the hypothalamus-pituitary-thyroid axis. We cloned coding sequences of human DIOs with FLAG-tag and HiBiT-tag sequences into a pcDNA3.1 vector. To obtain full-length proteins, we modified these vectors by cloning the selenocysteine insertion sequence of each DIO (SECIS vectors). Western blot analyses and HiBiT lytic assay using HEK293T cells revealed that SECIS vectors expressed full-length proteins with substantial activity. Subsequently, in vivo transfections of pLIVE-based SECIS vectors into male C57BL/6J mice were performed by hydrodynamic gene delivery to generate mice overexpressing DIOs predominantly in the liver (D1, D2, and D3 mice). After 7 days from transfections, mice were analyzed to clarify phenotypes. To summarize, serum thyroid hormone levels did not change in D1 mice but D2 mice had higher serum free T3 levels. D3 mice developed hypothyroidism with higher serum reverse T3 (rT3) levels. Transfections with levothyroxine administration suggested that thyroid hormone action was upregulated in D2 mice. Our DIO-overexpressing mice provided insights on the physiological properties of upregulated DIOs: D2 augments local thyroid hormone action and recruits T3 into the circulation: D3 decreases circulating T3 and T4 levels with elevated rT3, leading to consumptive hypothyroidism. As D3 mice are expected to be a novel hypothyroidism model, they can contribute to progress in the field of thyroid hormone economy and action.

Leptin counteracts hypothermia in hypothyroidism through its pyrexic effects and by stabilizing serum thyroid hormone levels

Objective

Thyroid hormones (TH) are essential for the homeostatic control of energy metabolism and the regulation of body temperature. The hypothalamic–pituitary–thyroid (HPT) axis is regulated by negative feedback mechanisms, ensuring that TH levels are maintained at a constant level. However, the feedback mechanisms underlying the resetting of the HPT axis regulation in the control of body temperature are still not fully understood. Here, we aimed to determine the thermoregulatory response in hypothyroid mice to different environmental temperatures and the underlying mechanisms.

Methods

Distinct thermogenic challenges were induced in hypothyroid female C57BL/6N and leptin-deficient ob/ob mice through housing at either room temperature or thermoneutrality. The thermogenic and metabolic effects were analyzed through metabolic chambers, 18F-FDG-PET/MRI, infrared thermography, metabolic profiling, histology, gene expression and Western blot analysis.

Results

In hypothyroid mice maintained at room temperature, high leptin serum levels induce a pyrexic effect leading to the stabilization of body temperature through brown adipose tissue thermogenesis and white adipose tissue browning. Housing at thermoneutrality leads to the normalization of leptin levels and a reduction of the central temperature set point, resulting in decreased thermogenesis in brown and white adipose tissue and skeletal muscle and a significant decline in body temperature. Furthermore, anapyrexia in hypothyroid leptin-deficient ob/ob mice indicates that besides its pyrexic actions, leptin exerts a stimulatory effect on the HPT axis to stabilize the remaining TH serum levels in hypothyroid mice.

Conclusion

This study led to the identification of a previously unknown endocrine loop in which leptin acts in concert with the HPT axis to stabilize body temperature in hypothyroid mice.

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Thyroid hormones are essential for the regulation of body temperature.

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Thyroid hormone-deficient (hypothyroid) mice show distinct leptin serum concentrations in response to changes in ambient housing temperature.

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High leptin serum levels confer a stimulatory effect on the hypothalamic-pituitary-thyroid axis.

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High leptin serum level prevents fall in body temperature in hypothyroid mice at room temperature through its pyrexic effects.

Distinct Late-Night Salivary Cortisol Cut-Off Values for the Diagnosis of Hypercortisolism

Due to high morbidity and mortality of untreated hypercortisolism, a prompt diagnosis is essential. Measurement of late-night salivary cortisol provides a simple and non-invasive method. However, thresholds and reference ranges differ among studies. The goal of this study was to define a threshold of late-night salivary cortisol for the diagnosis of hypercortisolism based on the used assay. Moreover, the influence of different aetiologies of hypercortisolism and individual comorbidities were investigated. Prospective analyses of 217 patients, including 36 patients with proven hypercortisolism were carried out. A sum of 149 patients with suspicion of hypercortisolism but negative endocrine testing and 32 patients with hypercortisolism in remission served as control group. Late-night salivary cortisol was measured using an automated chemiluminescence immunoassay. Cut-off values were calculated by ROC analysis. The calculated cut-off value for the diagnosis of hypercortisolism was 10.1 nmol/l (sensitivity 94%; specificity 84%). Only slightly lower thresholds were obtained in patients with suspected hypercortisolism due to weight gain/obesity (9.1 nmol/l), hypertension or adrenal tumours (both 9.8 nmol/l) or pituitary adenomas (9.5 nmol/l). The late-night salivary cortisol threshold to distinguish between Cushing's disease and Cushing's disease in remission was 9.2 nmol/l. The cut-off value for the diagnosis of ectopic ACTH-production was 109.0 nmol/l (sensitivity 50%, specificity 92%). Late-night salivary cortisol is a convenient and reliable parameter for the diagnosis of hypercortisolism. Except for ectopic ACTH-production, thresholds considering different indications for evaluation of hypercortisolism were only slightly different. Therefore, they might only be useful if late-night salivary cortisol results near the established cut-off value are present.

Thyroid wars: the rise of central actions

In the field of thyroid hormone (TH) action on energy balance, huge advances have been achieved in the past decade, from human, animal, and in vitro studies. A key achievement was the demonstration of the TH 'central' metabolic action, which was recently discovered in rodent models and challenged the previous 'peripheral' paradigm. In this opinion, we dissect and try to unify the two paradigms, from analyzing the respective bench models to extrapolating the possible translational bedside implications.

The Impact of Spironolactone on Markers of Myocardial Oxidative Status, Inflammation and Remodeling in Hyperthyroid Rats

BACKGROUND

Hyperthyroidism promotes the development and progression of cardiovascular diseases (CVD). Aldosterone, a key mediator of myocardial inflammation, oxidative stress and fibrosis, may be activated in hyperthyroidism.

OBJECTIVE

To assess the impact of hyperthyroidism on aldosterone levels and myocardial oxidative status, inflammatory and fibrotic markers in hyperthyroid rats, and to test if the use of spironolactone (an aldosterone antagonist) attenuates these changes.

METHODS

Adult Wistar rats were randomly distributed into 4 groups; controls, spironolactone treated rats (Spir, 50mg/kg/day), hyperthyroid rats (Hyper, daily intraperitoneal levothyroxine 0.3mg/kg/day), and spironolactone treated hyperthyroid rats (Hyper+Spir) for 4 weeks. Blood pressure (Bp), and levels of serum and myocardial aldosterone, oxidants/antioxidants, inflammatory and fibrotic markers were measured.

RESULTS

Levothyroxine increased serum thyroid hormones and increased Bp, heart rate and heart to bodyweight ratio. Relative to control, serum aldosterone levels were increased in Hyper and Hyper+ Spir groups. In parallel, cardiac lipid peroxides and serum endothelin-1 were increased whereas cardiac superoxide dismutase, catalase, glutathione, and matrix metalloproteinase -2 were reduced in the Hyper group. Spironolactone decreased serum thyroid hormones and improved cardiac lipid peroxides and metalloproteinase -2 levels. The use of spironolactone decreased serum nitrite levels and increased cardiac SOD and glutathione. Cardiac levels of aldosterone, endothelin-1, transforming growth factor-beta and nitrite were similar among all groups.

CONCLUSION

Hyperthyroid status was associated with an increase in aldosterone and oxidant/ inflammatory biomarkers. The use of spironolactone enhanced antioxidant defenses. Aldosterone antagonists may serve as potential drugs to attenuate the development of cardiac disease in hyperthyroidism.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny - part II: how can key events of relevant adverse outcome pathways be addressed in toxicological assessments?

The current understanding of thyroid-related adverse outcome pathways (AOPs) with adverse neurodevelopmental outcomes in mammals has been reviewed. This served to establish if standard rodent toxicity test methods and in vitro assays allow identifying thyroid-related modes-of-action potentially leading to adverse neurodevelopmental outcomes, and the human relevance of effects - in line with the European Commission's Endocrine Disruptor Criteria. The underlying hypothesis is that an understanding of the key events of relevant AOPs provides insight into differences in incidence, magnitude, or species sensitivity of adverse outcomes. The rodent studies include measurements of serum thyroid hormones, thyroid gland pathology and neurodevelopmental assessments, but do not directly inform on specific modes-of-action. Opportunities to address additional non-routine parameters reflecting critical events of AOPs in toxicological assessments are presented. These parameters appear relevant to support the identification of specific thyroid-related modes-of-action, provided that prevailing technical limitations are overcome. Current understanding of quantitative key event relationships is often weak, but would be needed to determine if the triggering of a molecular initiating event will ultimately result in an adverse outcome. Also, significant species differences in all processes related to thyroid hormone signalling are evident, but the biological implications thereof (including human relevance) are often unknown. In conclusion, careful consideration of the measurement (e.g. timing, method) and interpretation of additional non-routine parameters is warranted. These findings will be used in a subsequent paper to propose a testing strategy to identify if a substance may elicit maternal thyroid hormone imbalance and potentially also neurodevelopmental effects in the progeny.

Plant constituents and thyroid: A revision of the main phytochemicals that interfere with thyroid function

In the past few decades, there has been a lot of interest in plant constituents for their antioxidant, anti-inflammatory, anti-microbial and anti-proliferative properties. However, concerns have been raised on their potential toxic effects particularly when consumed at high dose. The anti-thyroid effects of some plant constituents have been known for some time. Indeed, epidemiological observations have shown the causal association between staple food based on brassicaceae or soybeans and the development of goiter and/or hypothyroidism. Herein, we review the main plant constituents that interfere with normal thyroid function such as cyanogenic glucosides, polyphenols, phenolic acids, and alkaloids. In detail, we summarize the in vitro and in vivo studies present in the literature, focusing on the compounds that are more abundant in foods or that are available as dietary supplements. We highlight the mechanism of action of these compounds on thyroid cells by giving a particular emphasis to the experimental studies that can be significant for human health. Furthermore, we reveal that the anti-thyroid effects of these plant constituents are clinically evident only when they are consumed in very large amounts or when their ingestion is associated with other conditions that impair thyroid function.

Are American follow-up recommendations in endocrinology actionable? A systematic review of clinical practice guidelines

PURPOSE

Clinical guidelines include recommendations to guide patient's longitudinal care. These recommendations may differ in content and quality of supporting evidence from those guiding diagnosis and treatment. We aimed to identify recommendations guiding the follow-up of patients with endocrine conditions, describe their content and quality of evidence.

METHODS

We systematically assessed the Endocrine Society and the American Thyroid Association clinical guidelines and identified recommendations guiding follow-up strategies to evaluate direction, content, strength, and quality of evidence.

RESULTS

Out of 1540 recommendations, 138(8.9%) guided follow-up strategies. From these, 109 (79%) recommendations included goal of follow-up, 121(97.7%) suggested follow-up methods, and 56 (40.6%) a specific monitoring frequency. A total of 76 (55.1%) assessed treatment response, 65 (47.1%) disease progression, and 30 (21.7%) side effects. A total of 90 (65.2%) described the use of laboratory studies, 30 (21.7%) clinical exam/history, and 27 (19.6%) imaging studies. Finally, 91 (65.9%) suggested a monitoring time interval and 42 (30.4%) directed an action based on results. Most recommendations [88 (55.3%)] were based on low/very low-quality evidence. A total of 73 (52.9%) recommendations were labeled as strong, from which 12% were based on high-quality evidence.

CONCLUSIONS

One out of ten clinical recommendations for endocrine conditions guide follow-up and their content is variable. More than half of the follow-up recommendations are supported by low/very low-quality evidence and the majority does not provide an action threshold. A specific framework for developing follow-up recommendations can aid guideline panelists and support evidence-based monitoring.

Subacute exposure to lead promotes disruption in the thyroid gland function in male and female rats

Exposure to heavy metals, such as lead, is a global public health problem. Lead has a long historic relation to several adverse health conditions and was recently classified as an endocrine disruptor. The aim of this study was to investigate the effects of subacute exposure to lead on the thyroid gland function. Adult male and female Wistar rats received a lead acetate solution containing 10 or 25 mg/kg, by gavage, three times a week, for 14 days. One week later, behavioral testing showed no alterations in anxiety and motor-exploratory parameters, as evaluated by Open-Field and Plus-Maze Tests, but impairment in learning and memory was found in the male 25 mg/kg lead-treated group and in both female lead-treated groups, as evaluated by the Inhibitory Avoidance Test. After one week, serum levels of tT3 were reduced in the 25 mg/kg female group and in the 10 mg∕ kg male group. However, tT4 levels were increased in the 25 mg/kg male group and in both female treated groups. TSH levels did not change and lead serum levels were undetectable. Morphologic alterations were observed in the thyroid gland, including abnormal thyroid parenchyma follicles of different sizes, epithelial stratification and vacuolization of follicular cells, decrease in colloid eosinophilia and vascular congestion, accompanied by morphometric alterations. An increase in collagen deposition was also observed. No differences were observed in TPO activity or protein expression, H₂O₂ generation by NADPH oxidases or hepatic D1 mRNA expression. However, thyroid NIS protein expression was considerably decreased in the male and female lead-treated groups, while TSHr expression was decreased in the 25 mg/kg female lead-treated group. These findings demonstrated that subacute exposure to lead acetate disrupts thyroid gland function in both sexes, leading to morphophysiological impairment and to changes in learning and memory abilities.

Thyroxine replacement modifies changes in deiodinase and thyroid hormone transporter expression induced by subclinical hypothyroidism in rats

PURPOSE

The potential benefits of treating subclinical hypothyroidism (SCH) are unclear and still controversial. Thus, we surgically induced SCH in rats and evaluated the effects of thyroxine (T4) replacement on the gene expression levels of deiodinases and thyroid hormone (TH) transporters in different tissues.

METHODS

SCH was induced by hemithyroid electrocauterization. The control animals underwent the same surgical procedure but were not subjected to electrocauterization (sham). After 14 days, half of the SCH animals were treated with T4 (SCH + T4). At the end of the experimental protocol, all of the rats were euthanized, serum hormone concentrations were measured, and RNA analyses were performed on different tissues and organs.

RESULTS

Consistent with previous studies, we observed increased TSH levels, normal TH levels, and reduced hypothalamic TRH expression in the SCH group. Additionally, Dio2 mRNA expression was downregulated in the hippocampus and pituitary, and Dio1 was upregulated in the kidney and pituitary of the SCH animals. The changes in Dio3 expression were tissue-specific. Concerning TH transporters, Mct10 expression was upregulated in the pituitary, kidney, hypothalamus, and hippocampus, and Mct8 expression was downregulated in the kidney of the SCH group. Crym expression was upregulated in the kidney and pituitary. Notably, T4 replacement significantly attenuated serum TSH levels and reverted Dio1, Dio2, Mct10, and Crym expression in the pituitary, hippocampus, and kidney to levels that were similar to the sham group. Tissue-specific responses were also observed in the liver and hypothalamus.

CONCLUSION

Our results indicate that treatment of SCH should be considered before the appearance of clinical symptoms of hypothyroidism.

Iodine Deficiency Increases Fat Contribution to Energy Expenditure in Male Mice

More than a billion people worldwide are at risk of iodine deficiency (ID), with well-known consequences for development of the central nervous system. Furthermore, ID has also been associated with dyslipidemia and obesity in humans. To further understand the metabolic consequences of ID, here we kept 8-week-old C57/Bl6 mice at thermoneutrality (~28°C) while feeding them on a low iodine diet (LID). When compared with mice kept on control diet (LID + 0.71 μg/g iodine), the LID mice exhibited marked reduction in T4 and elevated plasma TSH, without changes in plasma T3 levels. LID mice grew normally, and had normal oxygen consumption, ambulatory activity, and heart expression of T3-responsive gene, confirming systemic euthyroidism. However, LID mice exhibited ~5% lower respiratory quotient (RQ), which reflected a ~2.3-fold higher contribution of fat to energy expenditure. LID mice also presented increased circulating levels of nonesterified fatty acids, ~60% smaller fat depots, and increased hepatic glycogen content, all indicative of accelerated lipolysis. LID mice responded much less to forced mobilization of energy substrates (50% food restriction for 3 days or starvation during 36 hours) because of limited size of the adipose depots. A 4-day treatment with T4 restored plasma T4 and TSH levels in LID mice and normalized RQ. We conclude that ID accelerates lipolysis and fatty acid oxidation, without affecting systemic thyroid hormone signaling. It is conceivable that the elevated plasma TSH levels trigger these changes by directly activating lipolysis in the adipose tissues.