Influence of silver nanoparticles on mRNA expression of thyroid hormone-related genes in the thyroid gland and liver of laying hens

The widespread use of silver nanoparticles (AgNPs) in consumer products and animal husbandry raises the need to study their impact on living organisms. This study was conducted on Hy-Line Brown hens at the age of 25 weeks with an average weight of 1.58 kg. Hens for 2 weeks received a solution of 50 nm AgNPs at a concentration of 100 pm (experimental group; n = 6) or a solution in which the nanoparticles were suspended (control group; n = 6). Thyroid hormones (thyroxine - T4, triiodothyronine - T3) were evaluated in the blood plasma and expression profiles of genes involved in thyroid hormone (TH) synthesis (TSHR, NIS, TPO, TG), metabolism (DIO1, DIO2, DIO3) and transport (MCT8, MCT10, LAT1) were determined in the chicken thyroid gland. Furthermore, iodothyronine deiodinase, TH transporter and TH receptor (THRA, THRB) mRNA expressions were evaluated in the livers isolated from the same chickens. AgNPs did not affect serum T4 levels but elevated serum T3 concentration. The results showed that AgNPs increased DIO3 mRNA in the thyroid gland. In turn, in the liver AgNPs administration significantly upregulated DIO2 and downregulated MCT10 mRNA levels. These results indicate that exposure to AgNPs leads to a tissue-specific alternative expression of genes engaged in TH metabolism. Moreover, the mRNA expression of DIO2 in the liver showed a positive correlation with plasma T3 levels. In conclusion, AgNPs may have an impact on TH metabolism by affecting deiodinases and TH transporter MCT10 mRNA expression.

The impaired swim bladder via ROS-mediated inhibition of the Wnt / Hedgehog pathway in zebrafish embryos exposed to eight toxic chemicals and binary chemical mixtures

To comprehensively explore the potential toxicity of aquatic organisms exposed to chlorinated or brominated flame retardants (BFRs) and metals mixtures, it is necessary to find a common pathway to relate local toxic targeted sites or organs. A key challenge in environmental risk assessment (ERA) is how to clarify the same or different sites or organs of toxic action in a species after exposure to individual chemicals or chemical mixtures. In this study, zebrafish embryo was used to evaluate the sub-lethal toxicity (swim bladder damage) of tris(2,3-dibromo propyl) isocyanurate (TBC), chlorinated paraffins (CPs), hexabromocyclododecane (HBCD), Cu, Cd, Pb, Ag, and Zn through optical microscopy methods, and corresponding sub-lethal molecular levels (inflammation-related enzymes [deiodinase (DIO) enzymes] and transcriptional levels of key genes) in fish through quantitative real-time PCR (qRT-PCR). The tested chemicals all caused failed inflation of the swim bladder, as indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Following embryonic exposure to respective TBC + Cu, HBCD + TBC, and Cd + Pb mixtures, as the concentration of the respective Cu, TBC, and Pb increased, the deformity of the swim bladder increased, as also indicated by activity inhibition of type 2 iodothyronine deiodinase enzyme. Additionally, eight chemicals down-regulated Wnt (wnt3, wnt9b, fzd3b, wnt1, fzd5, and fdz1) signaling pathways, which were neurotoxic responses to individual chemical treatments and Hedgehog (ihh, shh, ptc1 and ptc2) signaling pathways. Moreover, excessive ROS induced by eight chemicals effectively induced defects in the swim bladder and Wnt/Hedgehog signaling, which also be proved in respective TBC + Cu, HBCD + TBC, and Cd + Pb mixture treatments. Our results first revealed that eight chemicals caused swim bladder developmental defects via ROS-mediated inhibition of the Wnt and Hedgehog pathways, which revealed the common targeted sites or organs (swim bladders) for further studying the toxic mechanisms underlying the chemical mixtures.

The Physiological Functions and Polymorphisms of Type II Deiodinase

Type II deiodinase (DIO2) is thought to provide triiodothyronine (T3) to the nucleus to meet intracellular needs by deiodinating the prohormone thyroxine. DIO2 is expressed widely in many tissues and plays an important role in a variety of physiological processes, such as controlling T3 content in developing tissues (e.g., bone, muscles, and skin) and the adult brain, and regulating adaptive thermogenesis in brown adipose tissue (BAT). However, the identification and cloning of DIO2 have been challenging. In recent years, several clinical investigations have focused on the Thr92Ala polymorphism, which is closely correlated with clinical syndromes such as type 2 diabetes, obesity, hypertension, and osteoarthritis. Thr92Ala-DIO2 was also found to be related to bone and neurodegenerative diseases and tumors. However, relatively few reviews have synthesized research on individual deiodinases, especially DIO2, in the past 5 years. This review summarizes current knowledge regarding the physiological functions of DIO2 in thyroid hormone signaling and adaptive thermogenesis in BAT and the brain, as well as the associations between Thr92Ala-DIO2 and bone and neurodegenerative diseases and tumors. This discussion is expected to provide insights into the physiological functions of DIO2 and the clinical syndromes associated with Thr92Ala-DIO2.

Effects of the synthetic progestin levonorgestrel on some aspects of thyroid physiology in common carp (Cyprinus carpio)

The objective of the present study was to assess the effects of levonorgestrel (LNG), a synthetic progestin, on early development and the thyroid system of carp using morphological, histological, immunohistochemical, and gene expression analysis. Fish were exposed to LNG at three levels (3, 31, and 310 ng L^-1) from eggs to the onset of juvenile stage (47 days). LNG had no significant effect on early development in common carp or on the occurrence of morphological anomalies. No pathological alterations of the thyroid follicles were found. Immunohistochemical examination of the thyroid follicles using antibodies against thyroxin did not show any differences in fish exposed to 310 ng L^-1 LNG compared to the controls. mRNA expression of iodothyronine deiodinases (dio1, 2, 3) was differentially affected by LNG treatment during carp development. Most importantly, dio3 was markedly downregulated in fish exposed to all three LNG levels compared to the controls at the conclusion of the experiment (47 days post-fertilization). A decrease in dio1 or dio3 or an increase in dio2 transcription observed at different time points of the study may be a sign of hypothyroidism. mRNA expression of genes npr, esr1, and esr2b in the body and npr and esr2b in the head of fish exposed to 310 ng L^-1 LNG was significantly upregulated compared to the solvent control group at the end of the test. Together, these results show that levonorgestrel caused parallel changes in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-gonad axes.

The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

Purpose

Vitamin A is an essential nutrient with vital biological functions. The present study investigated the effect of different doses of vitamin A palmitate at different time intervals on thyroid hormones and glycemic markers.

Methods

Male rats were administrated vitamin A palmitate at different doses (0, 0.7, 1.5, 3, 6, and 12 mg/kg, oral) and samples were collected at different time intervals of 2, 4, and 6 weeks. The levels of vitamin A, thyroid hormones (T3, T4, and TSH), deiodinases (Dio1 and Dio3), glycemic markers (blood insulin and fasting glucose levels, HOMA IR and HOMA β), retinol-binding protein 4 (RBP4) and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) were measured.

Results

The findings demonstrated that long-term supplementation with high doses of vitamin A palmitate resulted in hypothyroidism (lower T3 and T4 levels and elevated TSH levels) as well as upregulation of Dio1 and Dio3 expression levels. This effect was associated with elevated glucose and insulin levels, enhanced HOMA IR, and decreased HOMA B index. In addition, prolonged vitamin A supplementation significantly increased RBP4 levels that upregulated the expression of PEPCK.

Conclusion

High doses of vitamin A supplementation increased the risk of hypothyroidism, modulated insulin sensitivity, and over a long period, increased the incidence of type 2 diabetes mellitus associated with oxidative stress and hepatitis.

Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults

Levothyroxine (LT4) is a safe, effective means of hormone replacement therapy for hypothyroidism. Here, we review the pharmaceutical, pathophysiological and behavioural factors influencing the absorption, distribution, metabolism and excretion of LT4. Any factor that alters the state of the epithelium in the stomach or small intestine will reduce and/or slow absorption of LT4; these include ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs. Once in the circulation, LT4 is almost fully bound to plasma proteins. Although free T4 (FT4) and liothyronine concentrations are extensively buffered, it is possible that drug- or disorder-induced changes in plasma proteins levels can modify free hormone levels. The data on the clinical significance of genetic variants in deiodinase genes are contradictory, and wide-scale genotyping of hypothyroid patients is not currently justified. We developed a decision tree for the physician faced with an abnormally high thyroid-stimulating hormone (TSH) level in a patient reporting adequate compliance with the recommended LT4 dose. The physician should review medications, the medical history and the serum FT4 level and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, antibodies against gastric and intestinal components (gastric parietal cells, endomysium, and tissue transglutaminase 2), and Helicobacter pylori infection. The next step is an LT4 pharmacodynamic absorption test; poor LT4 absorption should prompt a consultation with a gastroenterologist and (depending on the findings) an increase in the LT4 dose level. An in-depth etiological investigation can reveal visceral disorders and, especially, digestive tract disorders.

Inherited Selenocysteine Transfer RNA Mutation: Clinical and Hormonal Evaluation of 2 Patients

INTRODUCTION

Iodothyronine deiodinases are selenoproteins with the amino acid selenocysteine (Sec) introduced into the position of a TGA stop codon by a complex machinery involving tRNA^[Ser]Sec when a cis-acting Sec-insertion sequence element is present in the 3' end of the mRNA. Recently, a variant in the TRU-TCA1-1 gene encoding for tRNA^[Ser]Sec was reported, which resulted in reduced expression of stress-related selenoproteins. The proband presented with multisystem symptoms, euthyroid hyperthyroxinemia, and selenium deficiency. Here, we describe 2 new members of a family harboring the same tRNA^[Ser]Sec variant.

CASE PRESENTATION

A 13-year-old patient was seen for Hashimoto's disease with high FT3 (4.6 pg/mL, normal range 2-4.2 pg/mL) and normal FT4 and TSH concentrations. He had no clinical complaints. During a 6-year clinical and hormonal follow-up, the index patient was not treated, FT3 decreased, FT4 increased, and serum TSH stayed in the normal range resulting in a euthyroid hyperthyroxinemia. Reverse T3 concentration was significantly increased at the last visit (19 years and 4 months). At the last evaluation, the total selenium level was low (91 μg/L, normal range 95-125). DNA sequencing identified a germinal homozygous variant (C65G) in the TRU-TCA1-1 gene. During follow-up, no additional clinical symptom was observed in the absence of any treatment. The same germinal tRNA^[Ser]Sec variant was identified at heterozygous state in his father, who had normal thyroid function tests except a moderately increased reverse T3 concentration, with increased total selenium (143 μg/L) level. In both patients, the expression of stress-related selenoprotein GPX3 was in the low-normal range (168 and 180 IU/L, respectively, normal range: 150-558 IU/L). We did not find any significant biological abnormalities evocative of other selenoprotein deficiencies.

DISCUSSION/CONCLUSION

We report on 2 members of a family with a variant in the TRU-TCA1-1 gene encoding for tRNA^[Ser]Sec. Our study suggests that this tRNA^[Ser]Sec variant is not exclusively causative of disruption in selenoprotein synthesis.

Thyroid hormone deiodinases response in brain of spontaneausly hypertensive rats after hypotensive effects induced by mandibular extension

PURPOSE

The deiodinases activate or inactivate the thyroid hormones (TH) in virtually all tissues in both physiological and pathological conditions. The three deiodinases, DIO1, DIO2, and DIO3, have different catalytic functions and regulate TH tissue distribution. The aim of the present study was to evaluate the modulation of gene expression of the deiodinases and TH transporters and protein levels of DIO1 in parietal and frontal areas of cerebral cortex of spontaneously hypertensive rats (SHRs), after two successive mandibular extensions (ME).

METHODS

ME was performed on anesthetized rats by a dilatator appropriately designed and real-time PCR and western blotting techniques were employed for gene expression and protein level study.

RESULTS

Mean blood pressure (MBP) significantly decreased in 2ME-treated rats when compared to sham-operated rats (p < 0.001) and this decrease lasted for the entire observation period. In gene expression analysis, in 2ME-treated rats we did not observe any significant variation of DIO1 and DIO3 with respect to the sham-operated rats. Differently, DIO2 gene expression significantly increased in frontal area of 2ME-treated rats, with respect to sham-operated rats (p < 0.01). Furthermore, in parietal area, protein levels of DIO1 in 2ME-treated rats were significantly higher than in sham-operated rats (p < 0.01). Moreover MCT8 and OATP1C1 both resulted significantly higher (p < 0.05 and p < 0.001) in sham frontal cortex.

CONCLUSION

In summary, our data on SHRs, while confirming the hypotensive effect of two MEs, show that the treatment also solicits the three deiodinases production in the cerebral cortex.

Deiodinases and the Three Types of Thyroid Hormone Deiodination Reactions

Thyroid hormone (TH) signaling is strictly regulated by iodothyronine deiodinase activity, which both preserves the circulating levels of the biologically active triiodothyronine (T3) and regulates TH homeostasis at the local level, in a cell- and time-dependent manner. Three deiodinases have been identified-namely iodothyronine deiodinase 1 (DIO1), DIO2, and DIO3-that differ in their catalytic properties and tissue distribution. The deiodinases represent a dynamic system that changes in the different stages of life according to their functions and roles in various cell types and tissues. Deiodinase activity at the tissue level permits cell-targeted fine regulation of TH homeostasis, mediating the activation (DIO1 and DIO2) and inactivation (DIO3) of THs. Deiodinase homeostasis is the driving force that leads T3-target cells towards customized TH signaling, which takes into account both the hormonal circulating levels and the tissue-specific response. This review analyzes the complex role of deiodinases in physiological and pathological contexts, exploring new challenges and opportunities deriving from a deeper knowledge of the dynamics underlying their roles and functions.

Dietary selenium promotes the growth performance through growth hormone-insulin-like growth factor and hypothalamic-pituitary-thyroid axes in grass carp (Ctenopharyngodon idella)

Selenium (Se), an essential component of deiodinases (DIOs), regulates the contents of thyroid hormones and thus improves animal growth. To explore the influences of selenium supplementation on fish growth metabolism, a total of 270 healthy grass carp (Ctenopharyngodon idella) were divided into three groups and feed three graded dietary selenium (0.141, 0.562, and 1.044 mg Se/kg) levels. The results showed that after 60-day feeding, dietary selenium improved the final body weight and specific growth rate (SGR) of grass carp. The hepatic DIO activities in selenium-supplemented groups were higher than those in control group. A significant increase in triiodothyronine (T3), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) levels was accompanied by a decrease in the contents of thyroxine (T4) and free thyroxine (FT4) in selenium-supplemented groups. The histopathological observation of thyroid suggested that selenium deficiency resulted in hypertrophy of follicular epithelial cells. Moreover, the gene relative expression levels of dio1, dio2, and dio3 showed an increasing trend with the rising concentration of dietary selenium. The transcription levels of HPT axis-related genes (crh, tsh-β, ttr, tr-s, tpo, nis) and GH/IGF1-related genes (gh, ghr, igf1, igf1r) were significantly upregulated in selenium-supplemented groups. No significant differences in the above indicators were observed between 0.562 and 1.044 mg Se/kg diet group except T3 content and dio1 relative expression ratio. These results indicate that dietary selenium supplementation improves the hepatic DIO activities and thyroid hormone metabolism and regulates the transcription levels of HPT and GH/IGF axis-related genes, which may be responsible for the growth promotion in grass carp.

Thyroid hormone action in epidermal development and homeostasis and its implications in the pathophysiology of the skin

Thyroid hormones (THs) are key endocrine regulators of tissue development and homeostasis. They are constantly released into the bloodstream and help to regulate many cell functions. The principal products released by the follicular epithelial cells are T3 and T4. T4, which is the less active form of TH, is produced in greater amounts than T3, which is the most active form of TH. This mechanism highlights the importance of the peripheral regulation of TH levels that goes beyond the central axis. Skin, muscle, liver, bone and heart are finely regulated by TH. In particular, skin is among the target organs most influenced by TH, which is essential for skin homeostasis. Accordingly, skin diseases are associated with an altered thyroid status. Alopecia, dermatitis and vitiligo are associated with thyroiditis and alopecia and eczema are frequently correlated with the Graves' disease. However, only in recent decades have studies started to clarify the molecular mechanisms underlying the effects of TH in epidermal homeostasis. Herein, we summarize the most frequent clinical epidermal alterations linked to thyroid diseases and review the principal mechanisms involved in TH control of keratinocyte proliferation and functional differentiation. Our aim is to define the open questions in this field that are beginning to be elucidated thanks to the advent of mouse models of altered TH metabolism and to obtain novel insights into the physiopathological consequences of TH metabolism on the skin.

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.

Effects of tyrosine kinase inhibitors on thyroid function and thyroid hormone metabolism

The increasing knowledge of the molecular mechanisms in the cell signaling pathways of malignant cells, has recently led to the discovery of several tyrosine kinases (TKs), mainly TK receptors (TKR), which play a major role in the pathogenesis of many types of cancer. These receptors, physiologically involved in cell growth and angiogenesis, may harbor mutations or be overexpressed in malignant cells, and represent a target for anticancer therapy. Indeed, several therapeutic agents targeting specific altered pathways such as RET, BRAF, RAS, EGFR and VEGFR, have been identified. Tyrosine kinase inhibitors (TKIs) affect TK dependent oncogenic pathways by competing with ATP binding sites of the TK domain, thus blocking the activity of the enzyme, and thereby inhibiting the growth and spread of several cancers. Although the therapeutic action may be very effective, these molecules, due to their mechanism of multitargeted inhibition, may produce adverse events involving several biological systems. Both hypothyroidism and thyrotoxicosis have been reported during treatment with TKI, as well as an effect on the activity of enzymes involved in thyroid hormone metabolism. The pathogenic mechanisms leading to thyroid dysfunction and changes in serum thyroid function tests occurring in patients on TKI are reviewed and discussed in this manuscript.

DIO3, the thyroid hormone inactivating enzyme, promotes tumorigenesis and metabolic reprogramming in high grade serous ovarian cancer

High grade serous ovarian cancer (HGSOC) is the most lethal gynecologic malignancy with a need for better understanding the disease pathogenesis. The biologically active thyroid hormone, T3, is considered a tumor suppressor by promoting cell differentiation and mitochondrial respiration. Tumors evolved a strategy to avoid these anticancer actions by expressing the T3 catabolizing enzyme, Deiodinase type 3 (DIO3). This stimulates cancer proliferation and aerobic glycolysis (Warburg effect). We identified DIO3 expression in HGSOC cell lines, tumor tissues from mice and human patients, fallopian tube (FT) premalignant lesion and secretory cells of normal FT, considered the disease site-of-origin. Stable DIO3 knockdown (DIO3-KD) in HGSOC cells led to increased T3 bioavailability and demonstrated induced apoptosis and attenuated proliferation, migration, colony formation, oncogenic signaling, Warburg effect and tumor growth in mice. Proteomics analysis further indicated alterations in an array of cancer-relevant proteins, the majority of which are involved in tumor suppression and metabolism. Collectively this study establishes the functional role of DIO3 in facilitating tumorigenesis and metabolic reprogramming, and proposes this enzyme as a promising target for inhibition in HGSOC.

Deiodinases, organic anion transporter polypeptide polymorphisms and symptoms of anxiety and depression after ischemic stroke

BACKGROUND

Emotional disturbances, such as anxiety and depression are common after acute ischemic stroke (AIS). Individual variation in emotional outcome is strongly influenced by genetic factors. One of pituitary axis, is the hypothalamic-pituitary-thyroid axis, a critical regulator of post-stroke recovery, suggesting that allelic variants in thyroid hormone (TH) signaling regulation can influence stroke outcome.

AIM

To determine associations between AIS emotional outcome and allelic variants of the TH metabolizing enzymes 1-3 type deiodinase (DIO1-3) and the membrane transporting organic anion polypeptide 1C1 (OATP1C1).

METHODS

Eligible AIS patients from Lithuania (n=168) were genotyped for ten DIO1-3 and OATP1C1 single nucleotide polymorphisms (SNP): DIO1 rs12095080-A/G, rs11206244-C/T, and rs2235544-A/C; DIO2 rs225014-T/C and rs225015-G/A; DIO3 rs945006-T/G; OATP1C1 rs974453-G/A, rs10444412-T/C, rs10770704-C/T, and rs1515777-A/G. Emotional outcome was evaluated using the Hospital Anxiety and Depression Scale at discharge from the neurology department after experienced index AIS.

RESULTS

After adjustment for potential confounders, the major allelic (wild-type) DIO1-rs12095080 genotype (AA) was associated with higher odds ratio of anxiety symptoms (OR = 5.16; 95% CI: 1.04-25.58; p = 0.045), conversely, DIO1-rs11206244 wild-type genotype (CC) and wild-type OATP1C1-rs1515777 allele containing the genotypes (AA + AG) were associated with lower odds ratio of symptoms of anxiety (OR = 0.37; 95% CI: 0.14-0.96; p = 0.041 and OR = 0.30; 95% CI: 0.12-0.76; p = 0.011, respectively). Wild-type OATP1C1-rs974453 genotype (GG) was associated with higher odds ratio of symptoms of depression (OR = 2.73; 95% CI: 1.04-7.12; p = 0.041).

CONCLUSION

Allelic variants in thyroid axis genes may predict emotional outcomes of AIS.

Modification of cardiac thyroid hormone deiodinases expression in an ischemia/reperfusion rat model after T3 infusion

The deiodinases regulate the activation and inactivation of Thyroid hormones (TH), in both physiological and pathological conditions. The three deiodinases, DIO1, DIO2 and DIO3, have different catalytic role and cellular and tissue distribution. Aim of this study is to evaluate a rat model of regional ischemia/reperfusion (I/R), the modification of cardiac main function after the administration of 6 µg/kg/day of triiodothyronine (T3), and the associated to DIO1, DIO2 and DIO3 gene expression. We also aim to study DIO1 and DIO2 protein levels in different left ventricular regions after an ischemic event. Four groups of rats were studied: sham-operated, sham-operated + T3, I/R rats and I/R rats + T3. DIO1, DIO2 and DIO3 expression were evaluated in I/R region (AAR: area-at-risk) and in a more distant region from ischemic wound (RZ: remote zone). In I/R group, circulating free-T3 (FT3) levels were significantly decreased with respect to basal values, whereas in I/R + T3 rats, FT3 levels were comparable to basal values. In AAR of I/R + T3 rats, DIO1 and DIO2 gene expression significantly increased with respect to sham. In RZ, DIO1 and DIO3 gene expression was significantly lower in sham and I/R rats when compared to I/R + T3. In sham + T3 group, DIO1 and DIO2 gene expression was not detectable, whereas DIO3 was significantly higher than in the other three groups. The present study gives interesting new insights on DIO1, DIO2 and DIO3 in the ischemic heart and their role in relation to T3-mediated amelioration of cardiac function and structure.

Targeting the right population for T3 + T4 combined therapy: where are we now and where to next?

The universal applicability of levothyroxine (LT4) monotherapy for the treatment of hypothyroidism has been questioned in recent years. Indeed, it is now clear that about 10-15% of LT4-treated hypothyroid patients are dissatisfied with their treatment. It is plausible that this subset of hypothyroid patients may need T3 + T4 combined therapy to restore peripheral euthyroidism. To address this issue, many clinical trials have investigated the effect of T3 + T4 combinations versus standard LT4-based therapy. However, to date, results have been inconclusive, mainly due to the lack of markers that identify candidates for combination therapy. A breakthrough in this field came with the recent finding that several single-nucleotide polymorphisms in the deiodinase genes are associated with the persistence of hypothyroid symptoms in biochemically euthyroid LT4-treated patients, and are thus markers of candidates for combination therapy. In addition, whole-genome association studies are expanding our knowledge of other genes of the thyroid hormone (TH) pathway that affect serum TH levels. To target the right population for the T3 + T4 combined therapy, the next step is to translate these new findings into prospective trials. Hopefully, this will pave the way to personalized therapy for each hypothyroid patient.

The Role of Selenium in Oxidative Stress and in Nonthyroidal Illness Syndrome (NTIS): An Overview

Selenium is a trace element, nutritionally classified as an essential micronutrient, involved in maintaining the correct function of several enzymes incorporating the selenocysteine residue, namely the selenoproteins. The human selenoproteome including 25 proteins is extensively described here. The most relevant selenoproteins, including glutathione peroxidases, thioredoxin reductases and iodothyronine deiodinases are required for the proper cellular redox homeostasis as well as for the correct thyroid function, thus preventing oxidative stress and related diseases. This review summarizes the main advances on oxidative stress with a focus on selenium metabolism and transport. Moreover, thyroid-related disorders are discussed, considering that the thyroid gland contains the highest selenium amount per gram of tissue, also for future possible therapeutic implication.

Photoperiodic regulation in a wild-derived mouse strain

Mus musculus molossinus (MSM) is a wild-derived mouse strain which maintains the ability to synthesize melatonin in patterns reflecting the ambient photoperiod. The objective of this study was to characterize the effects of photoperiodic variation on metabolic and reproductive traits, and the related changes in pituitary-hypothalamic gene expression in MSM mice. MSM mice were kept in long (LP) or short photoperiod (SP) for 6 weeks. Our results demonstrate that MSM mice kept in LP, as compared to mice kept in SP, display higher expression of genes encoding thyrotropin (TSH) in the pars tuberalis, thyroid hormone deiodinase 2 (dio2) in the tanycytes, RFamide-related peptide (RFRP3) in the hypothalamus and lower expression of dio3 in the tanycytes, along with larger body and reproductive organ mass. Additionally, to assess the effects of the gestational photoperiodic environment on the expression of these genes, we kept MSM mice in LP or SP from gestation and studied offspring. We show that the gestational photoperiod affects the TSH/dio pathway in newborn MSM mice in a similar way to adults. This result indicates a transgenerational effect of photoperiod from the mother to the fetus in utero. Overall, these results indicate that photoperiod can influence neuroendocrine regulation in a melatonin-proficient mouse strain, in a manner similar that documented in other seasonal rodent species. MSM mice may therefore become a useful model for research into the molecular basis of photoperiodic regulation of seasonal biology.

Deiodinases, organic anion transporter polypeptide polymorphisms and ischemic stroke outcomes

BACKGROUND

Ischemic stroke is a major cause of premature death and chronic disability worldwide, and individual variation in functional outcome is strongly influenced by genetic factors. Neuroendocrine signaling by the hypothalamic-hypophyseal-thyroid axis is a critical regulator of post-stroke pathogenesis, suggesting that allelic variants in thyroid hormone (TH) signaling can influence stroke outcome.

AIM

To examine associations between acute ischemic stroke (AIS) outcome and allelic variants of the TH metabolizing enzymes deiodinase type 1-3 (DIO1-3) and membrane transporting organic anion polypeptide C1 (OATP1C1).

METHODS

Eligible AIS patients from Lithuania (n = 248) were genotyped for ten DIO1-3 and OATP1C1 single nucleotide polymorphisms (SNPs): DIO1 rs12095080-A/G, rs11206244-C/T, and rs2235544-A/C; DIO2 rs225014-T/C and rs225015-G/A; DIO3 rs945006-T/G; OATP1C1 rs974453-G/A, rs10444412-T/C, rs10770704-C/T, and rs1515777-A/G. Functional outcome was evaluated one year after index AIS using the modified Rankin Scale. Analyses were adjusted for important confounders, including serum free triiodothyronine.

RESULTS

After adjustment for potential confounders, the major allelic (wild-type) DIO3 genotype rs945006-TT was associated with better 1-year AIS functional outcome (odds ratio [OR] = 0.25; 95% confidence interval [CI]: 0.08-0.74; p = .013), while the wild-type OATP1C1 genotype rs10770704-CC was associated with poorer outcome (OR = 2.00, 95%CI: 1.04-3.86; p = .038).

CONCLUSION

Allelic variants in thyroid axis genes may prove useful for prognosis and treatment guidance.

Novel thyroid hormones

The field of thyroid hormone signaling has grown more complex in recent years. In particular, it has been suggested that some thyroid hormone derivatives, tentatively named "novel thyroid hormones" or "active thyroid hormone metabolites", may act as independent chemical messengers. They include 3,5-diiodothyronine (T2), 3-iodothyronamine (T1AM), and several iodothyroacetic acids, i.e., 3,5,3',5'-thyroacetic acid (TA4), 3,5,3'-thyroacetic acid (TA3), and 3-thyroacetic acid (TA1). We summarize the present knowledge on these compounds, namely their biosynthetic pathways, endogenous levels, molecular targets, and the functional effects elicited in experimental preparations or intact animals after exogenous administration. Their physiological and pathophysiological role is discussed, and potential therapeutic applications are outlined. The requirements needed to qualify these substances as chemical messengers must still be validated, although promising evidence has been collected. At present, the best candidate to the role of independent chemical messenger appears to be T1AM, and its most interesting effects concern metabolism and brain function. The responses elicited in experimental animals have suggested potential therapeutic applications. TA3 has an established role in thyroid hormone resistance syndromes, and is under investigation in Allen-Herndon-Dudley syndrome. Other potential targets are represented by obesity and dyslipidemia (for T2 and T1AM); dementia and degenerative brain disease (for T1AM and TA1); cancer (for T1AM and TA4). Another intriguing and unexplored question is the potential relevance of these metabolites in the clinical picture of hypothyroidism and in the response to replacement therapy.

The evolutionary road to invertebrate thyroid hormone signaling: Perspectives for endocrine disruption processes

Thyroid hormones (THs) are the only iodine-containing hormones that play fundamental roles in chordates and non-chordates. The chemical nature, mode of action and the synthesis of THs are well established in mammals and other vertebrates. Although thyroid-like hormones have been detected in protostomes and non-chordate deuterostomes, TH signaling is poorly understood as compared to vertebrates, particularly in protostomes. Therefore, the central objective of this article is to review TH system components and TH-induced effects in non-vertebrate chordates, non-chordate deuterostomes and protostomes based on available genomes and functional information. To accomplish this task, we integrate here the available knowledge on the THs signaling across non-vertebrate chordates, non-chordate deuterostomes and protostomes by considering studies encompassing TH system components and physiological actions of THs. We also address the possible interactions of thyroid disrupting chemicals and their effects in protostomes and non-chordate deuterostomes. Finally, the perspectives on current and future challenges are discussed.

Alteration of Placental Deiodinase 3 Expression by BDE 209 and Possible Protection by Taurine in Human Placenta-Derived JEG Cells Under Hypoxia

Thyroid hormones are key hormones involved in growth and development. Changes in their levels can cause embryonic brain developmental damage in the first trimester. Studies have shown that polybrominated diphenyl ethers (PBDEs) have developmental neurotoxicity as environmental pollutants, and exposure during pregnancy can cause irreversible brain damage in offspring, similar to the interference effects of thyroid hormones, but its mechanism has not yet been understood. Since the physiological environment for placental cells is highly hypoxic, in the current study, the human placenta-derived JEG cells were cultured at 1% oxygen, 4% carbon dioxide and 94% nitrogen, to reflect in vivo scenario, and the possible protection of taurine on BDE 209-mediated toxicity in JEG cells was studied. Our data showed that different concentrations of BDE 209 can have profound effects on cell viability and placental deiodinase 3 expression under hypoxic culture condition. Taurine was found to improve BDE 209-induced reductions in cell viability and altered gene and protein expressions of placental deiodinases. The results provide a reference for the establishment of early biomarkers and effective preventive measures.

Thyroid hormone availability in the human fetal brain: novel entry pathways and role of radial glia

Thyroid hormones (TH) are crucial for brain development; their deficiency during neurodevelopment impairs neural cell differentiation and causes irreversible neurological alterations. Understanding TH action, and in particular the mechanisms regulating TH availability in the prenatal human brain is essential to design therapeutic strategies for neurological diseases due to impaired TH signaling during neurodevelopment. We aimed at the identification of cells involved in the regulation of TH availability in the human brain at fetal stages. To this end, we studied the distribution of the TH transporters monocarboxylate transporter 8 (MCT8) and organic anion-transporting polypeptide 1C1 (OATP1C1), as well as the TH-metabolizing enzymes types 2 and 3 deiodinases (DIO2 and DIO3). Paraffin-embedded human brain sections obtained from necropsies of thirteen fetuses from 14 to 38 gestational weeks were analyzed by immunohistochemistry and in situ hybridization. We found these proteins localized along radial glial cells, in brain barriers, in Cajal-Retzius cells, in migrating fibers of the brainstem and in some neurons and glial cells with particular and complex spatiotemporal patterns. Our findings point to an important role of radial glia in controlling TH delivery and metabolism and suggest two additional novel pathways for TH availability in the prenatal human brain: the outer, and the inner cerebrospinal fluid-brain barriers. Based on our data we propose a model of TH availability for neural cells in the human prenatal brain in which several cell types have the ability to autonomously control the required TH content.

The placenta in fetal thyroid hormone delivery: from normal physiology to adaptive mechanisms in complicated pregnancies

Context: Thyroid hormones are indispensable for normal fetal development. Since the fetus depends to a large extent on maternal thyroid hormone supply through the placenta, this challenges maternal thyroid economy. Several molecular mechanisms are involved in placental thyroid hormone transport and metabolism. Chronic pregnancy complications, associated with utero-placental hypoxia, trigger the development of accelerated placental maturation in order to improve fetal-placental exchange to strengthen the offspring's chance of survival. This review provides an overview of normal maternal-fetal thyroid hormone supply and explores the presence of placental adaptive mechanisms in complicated pregnancies with chronical utero-placental hypoxia to improve the thyroid hormone supply to the fetus under pressure, to end with reflections about the long term health consequences.Evidence acquisition: This work is based on a comprehensive literature review of the PubMed and Embase database, including relevant articles from 1969 to June 2018.Conclusions: The placenta is actively involved in fetal thyroid hormone delivery through a combination of stimulatory and inhibitory mechanisms. Parallel with histological adaptations to improve transplacental fetal-maternal exchange, there are indications of placental adaptive mechanisms in thyroid hormone transport and metabolism in case of complicated pregnancies, from animal models and in-vitro experiments. Evidence from human in-vivo studies is limited due to heterogeneity in study populations, small study samples, and technical limitations. Further research is necessary to reveal the role of the placenta in pathological circumstances. The placenta might thus be considered as the infants' black box of pregnancy. Results will contribute to more insights in the concept of fetal programming, which lays the foundations of optimum health, growth, and neurodevelopment across the lifespan.

Octylphenol influence growth and development of Rana chensinensis tadpoles via disrupting thyroid function

Octylphenol (OP), a class of endocrine disrupting chemicals (EDCs), could produce adverse effects on developmental process of animals. Thyroid hormone is one of the important hormones involved in animal development. To determine whether OP affect the growth and development of amphibian larvae via interfering the thyroid function, Rana chensinensis larvae at Gosner stage 29 were exposed to 10^-8, 10^-7 and 10^-6 mol/L OP in the present study. Results demonstrated that OP could decrease the body length and mass and retard the development of tadpoles. The histologic evaluation showed microscopic structures of thyroid gland were changed in 10^-7 and 10^-6 mol/L OP treated groups on day 40. The expression levels of Dio2, Dio3, TRα and TRβ mRNA in the liver, brain, skin and tail of tadpoles were detected by qRT-PCR, when treated with OP for 20, 30, 40 and 50 day, respectively. The results of qRT-PCR showed OP could affect the expressions of Dio2, Dio3, TRα and TRβ mRNA in the four tissues, and then influence the activity and function of THs, further affecting the growth and development of the tadpoles.

Protective effect of mulberry crude extract against nonylphenol-induced thyroid disruption by inhibiting the activity of deiodinase in rats

Nonylphenol (NP) is an endocrine-disrupting chemical (EDC) that can lead to thyroid disruption. We explored NP-induced toxicity in the rat thyroid and evaluated the mitigating effects of mulberry crude extract (MCE) on NP toxicity. First, we aimed to evaluate NP-induced thyroid disruption by dosing Sprague-Dawley (SD) rats with NP (0, 30, 90, or 270 mg/kg body weight) daily for 28 days. Second, we aimed to determine whether MCE had a detoxifying effect on NP-induced thyroid disruption by dosing SD rats with NP (270 mg/kg body weight) or/and MCE (30, 60, or 120 mg/kg body weight) daily for 28 days. We found that NP significantly inhibited free triiodothyronin (FT₃) and free thyroxine (FT₄) activity in rat serum (P < 0.05), but MCE intervention significantly increased FT₃ and FT₄ serum levels (P < 0.05). It is possible that changes in hormonal composition might trigger the TRH-TSH-TH automatic feedback loop. The activity of the three iodothyronine deiodinases increased significantly after NP-dosing (P < 0.05), but only deiodinase3 (D3) was downregulated after MCE treatment (P < 0.05). Therefore, MCE might be an effective NP-detoxification agent against thyroid disruption because it regulates D3 activity.

Clinical significance of type 2 iodothyronine deiodinase polymorphism

INTRODUCTION

Biological activity of thyroid hormones (TH) is regulated by enzymes known as deiodinases. The most important is represented by the type 2 deiodinase (D2), which is the main T4-activating enzyme, ubiquitous in human tissues and therefore essential in many metabolic processes. A single nucleotide polymorphism (SPN) of D2, known as Thr92Ala (rs225014), has been reported in the general population while other polymorphisms are less frequently described.

AREAS COVERED

Several authors investigated the potential metabolic effect of these polymorphisms in the general population and in specific groups of patients. Thr92Ala polymorphism was mainly studied in patients with autoimmune or surgical hypothyroidism and in patients with physical/psychological disorders that could be related to an overt hypothyroidism. Susceptibility to develop more severe type 2 diabetes or insulin resistance has also been evaluated.

EXPERT COMMENTARY

There is an increasing evidence that the presence of D2 polymorphisms may play a pivotal role in a better definition and customized therapeutic approach of patients with hypothyroidism and/or type 2 diabetes, suggesting that these patients should be screened for D2 polymorphisms. Nevertheless, further research should be performed in order to clarify the association between D2 polymorphisms, metabolic alterations and clinical conditions of the carrier patients.

Metabolic Effects of the Intracellular Regulation of Thyroid Hormone: Old Players, New Concepts

Thyroid hormones (THs) are key determinants of cellular metabolism and regulate a variety of pathways that are involved in the metabolism of carbohydrates, lipids and proteins in several target tissues. Notably, hyperthyroidism induces a hyper-metabolic state characterized by increased resting energy expenditure, reduced cholesterol levels, increased lipolysis and gluconeogenesis followed by weight loss, whereas hypothyroidism induces a hypo-metabolic state characterized by reduced energy expenditure, increased cholesterol levels, reduced lipolysis and gluconeogenesis followed by weight gain. Thyroid hormone is also a key regulator of mitochondria respiration and biogenesis. Besides mirroring systemic TH concentrations, the intracellular availability of TH is potently regulated in target cells by a mechanism of activation/inactivation catalyzed by three seleno-proteins: type 1 and type 2 iodothyronine deiodinase (D1 and D2) that convert the biologically inactive precursor thyroxine T4 into T3, and type 3 iodothyronine deiodinase (D3) that inactivates TH action. Thus, the pleiotropic effects of TH can fluctuate among tissues and strictly depend on the cell-autonomous action of the deiodinases. Here we review the mechanisms of TH action that mediate metabolic regulation. This review traces the critical impact of peripheral regulation of TH by the deiodinases on the pathways that regulate energy metabolism and the balance among energy intake, expenditure and storage in specific target tissues.

Deiodinases and stem cells: an intimate relationship

Thyroid hormone is a major determinant of tissue functions in vivo. The deiodinase family controls the tissue-specific activation or inactivation of intracellular thyroid hormones. Precise control of the T3-dependent transcriptional program is required by multiple cell systems, including the stem cell. In this context, the identification of a close connection between thyroid hormones and different signal pathways involved in the control of stem cell functions suggested that the deiodinases may play a role in the definition of stem cell biology and physiology. Stem cells have an unlimited self-renewal capacity and the potential to differentiate into different types of mature cells. Deciphering how all these events are achieved, how the T3 signal is controlled and integrated in stem cells and their niches, and how it can impact on them is essentially unknown and represents a challenge for coming years. In this review, I will explore the role played by the deiodinases in the modulation of the TH signal in stem cells of adult tissues, namely muscle and intestine, and how their actions control the delicate balance among self-renewal, proliferation and differentiation. Elucidation of the molecular mechanisms presiding thyroid hormone action in stem cells may reveal therapeutic potential, for example in the fields of regenerative diseases and cancer.

Lamprey metamorphosis: Thyroid hormone signaling in a basal vertebrate

As one of the most basal living vertebrates, lampreys represent an excellent model system to study the evolution of thyroid hormone (TH) signaling. The lamprey hypothalamic-pituitary-thyroid and reproductive axes overlap functionally. Lampreys have 3 gonadotropin-releasing hormones and a single glycoprotein hormone from the hypothalamus and pituitary, respectively, that regulate both the reproductive and thyroid axes. TH synthesis in larval lampreys takes place in an endostyle that transforms into typical vertebrate thyroid tissue during metamorphosis; both the endostyle and follicular tissue have all the typical TH synthetic components found in other vertebrates. Furthermore, lampreys also have the vertebrate suite of peripheral regulators including TH distributor proteins (THDPs), deiodinases and TH receptors (TRs). Although at the molecular level the components of the lamprey thyroid system are ancestral to other vertebrates, their functions have been largely conserved. TH signaling as it relates to lamprey metamorphosis represents a particularly interesting phenomenon. Unlike other metamorphosing vertebrates, lamprey THs increase throughout the larval period, peak prior to metamorphosis and decline rapidly at the onset of metamorphosis; patterns of deiodinase activity are consistent with these increases and declines. Moreover, goitrogens (which suppress TH levels) initiate precocious metamorphosis, and exogenous TH treatment blocks goitrogen-induced metamorphosis and disrupts natural metamorphosis. Despite this clear physiological difference, TH action via TRs is consistent with higher vertebrates. Based on observations that TRs are upregulated in a tissue-specific fashion during morphogenesis and the finding that lamprey TRs upregulate genes via THs in a fashion similar to higher vertebrates, we propose the following hypothesis for further testing. THs have a dual role in lampreys where high TH levels promote larval feeding and growth and then at the onset of metamorphosis TH levels decrease rapidly; at this time the relatively low TH levels function via TRs in a fashion similar to that of other metamorphosing vertebrates.

Thyroid hormone signaling and deiodinase actions in muscle stem/progenitor cells

Thyroid hormone (TH) regulates such crucial biological functions as normal growth, development and metabolism of nearly all vertebrate tissues. In skeletal muscle, TH plays a critical role in regulating the function of satellite cells, the bona fide skeletal muscle stem cells. Deiodinases (D2 and D3) have been found to modulate the expression of various TH target genes in satellite cells. Regulation of the expression and activity of the deiodinases constitutes a cell-autonomous, pre-receptor mechanism that controls crucial steps during the various phases of myogenesis. Here, we review the roles of deiodinases in skeletal muscle stem cells, particularly in muscle homeostasis and upon regeneration. We focus on the role of T3 in stem cell functions and in commitment towards lineage progression. We also discuss how deiodinases might be therapeutically exploited to improve satellite-cell-mediated muscle repair in skeletal muscle disorders or injury.

Thyroid hormone promotes differentiation of colon cancer stem cells

Tumor formation and maintenance depend on a small fraction of cancer stem cells (CSCs) that can self-renew and generate a wide variety of differentiated cells. CSCs are resistant to chemotherapy and radiation, and can represent a reservoir of cancer cells that often cause relapse after treatment. Evidence suggests that CSCs also give rise to metastases. Thyroid hormone (TH) controls a variety of biological processes including the development and functioning of most adult tissues. Recent years has seen the emergence of an intimate link between TH and multiple steps of tumorigenesis. Thyroid hormone controls the balance between the proliferation and differentiation of CSCs, and may thus be a druggable anti-cancer agent. Here, we review current understanding of the effects of TH on colorectal CSCs, including the cross regulatory loops between TH and regulators of CSC stemness. Targeting TH in the tumor microenvironment may improve treatment strategies.

Novel thyroid hormone analogues, enzyme inhibitors and mimetics, and their action

Thyroid hormones (THs) play key roles in modulating the overall metabolism of the body, protein synthesis, fat metabolism, neuronal and bone growth, and cardiovascular as well as renal functions. In this review, we discuss on the thyroid hormone synthesis and activation, thyroid hormone receptors (TRs) and mechanism of action, applications of thyroid hormone analogues, particularly the compounds that are selective ligands for TRβ receptors, or enzyme inhibitors for the treatment of thyroidal disorders with a specific focus on thyroid peroxidase and iodothyronine deiodinases. We also discuss on the development of small-molecule deiodinase mimetics and their mechanism of deiodination, as these compounds have the potential to regulate the thyroid hormone levels.

The ups and downs of the thyroxine pro-hormone hypothesis

Thyroxine (T4) is the major thyroid hormone in the thyroid gland and the circulation. However, it is widely accepted on the basis of abundant evidence that 3,5,3'-triiodothyronine (T3) is responsible for most, if not all, of the physiological effects of TH in extrathyroidal tissues, and T4 functions as the pro-hormone. Whether T4 has any intrinsic activity per se or is merely a pro-hormone that must be converted to T3 in order to exert any TH action has yet to be resolved. Although there are some physiological actions of T4 that are mediated by receptors at the cell membrane (non-genomic effects), the vast majority of the physiological effects of the THs identified to date involve the binding of T3 to specific nuclear receptors to regulate gene expression (genomic effects). This review examines how the role of T4 in genomic TH action has been viewed and debated during the hundred years since it was first isolated in 1914.

Mosaic Expression of Thyroid Hormone Regulatory Genes Defines Cell Type-Specific Dependency in the Developing Chicken Cerebellum

The cerebellum is a morphologically unique brain structure that requires thyroid hormones (THs) for the correct coordination of key cellular events driving its development. Unravelling the interplay between the multiple factors that can regulate intracellular TH levels is a key step to understanding their role in the regulation of these cellular processes. We therefore investigated the regional/cell-specific expression pattern of TH transporters and deiodinases in the cerebellum using the chicken embryo as a model. In situ hybridisation revealed expression of the TH transporters monocarboxylate transporter 8 (MCT8) and 10 (MCT10), L-type amino acid transporter 1 (LAT1) and organic anion transporting polypeptide 1C1 (OATP1C1) as well as the inactivating type 3 deiodinase (D3) in the fourth ventricle choroid plexus, suggesting a possible contribution of the resulting proteins to TH exchange and subsequent inactivation of excess hormone at the blood-cerebrospinal fluid barrier. Exclusive expression of LAT1 and the activating type 2 deiodinase (D2) mRNA was found at the level of the blood-brain barrier, suggesting a concerted function for LAT1 and D2 in the direct access of active T₃ to the developing cerebellum via the capillary endothelial cells. The presence of MCT8 mRNA in Purkinje cells and cerebellar nuclei during the first 2 weeks of embryonic development points to a potential role of this transporter in the uptake of T₃ in central neurons. At later stages, together with MCT10, detection of MCT8 signal in close association with the Purkinje cell dendritic tree suggests a role of both transporters in TH signalling during Purkinje cell synaptogenesis. MCT10 was also expressed in late-born cells in the rhombic lip lineage with a clear hybridisation signal in the outer external granular layer, indicating a potential role for MCT10 in the proliferation of granule cell precursors. By contrast, expression of D3 in the first-born rhombic lip-derived population may serve as a buffering mechanism against high T₃ levels during early embryonic development, a hypothesis supported by the pattern of expression of a fluorescent TH reporter in this lineage. Overall, this study builds a picture of the TH dependency in multiple cerebellar cell types starting from early embryonic development.

Coordinated expression and regulation of deiodinases and thyroid hormone receptors during metamorphosis in the Japanese flounder (Paralichthys olivaceus)

In vertebrates, thyroid hormone receptors (TRs) and deiodinases are essential for developmental events driven by the thyroid hormones (THs). However, the significance of deiodinases during the metamorphosis of the Japanese flounder (Paralichthys olivaceus) remains unclear. Moreover, regulation and response of the TRs and deiodinases to THs in this fish are poorly understood. Therefore, we detected the expression patterns of THs, deiodinases, and TRs in drug-treated larvae and untreated larvae of P. olivaceus by using enzyme-linked immunosorbent assay and quantitative real-time PCR during P. olivaceus metamorphosis. To further understand the roles of these elements, a rescue assay was performed. Our results show the importance of THs, TRs, and deiodinases in flatfish metamorphosis. Our results also confirm that D1 and D2 activate THs and D3 plays the opposite and complementary role. Moreover, we demonstrated that both TRα and TRβ have important but different roles during P. olivaceus metamorphosis.

Recommendations for treatment of hypothyroidism with levothyroxine and levotriiodothyronine: a 2016 position statement of the Italian Society of Endocrinology and the Italian Thyroid Association

Levothyroxine (L-T4) is recommended as lifelong replacement therapy for hypothyroidism. Recent clinical and experimental data support the addition of levotriiodothyronine (L-T3) treatment in some selected hypothyroid patients when their symptoms persist and their quality of life remains impaired despite adequate L-T4 monotherapy. An increase in L-T3 prescriptions has been recently observed in Italy due to availability of different L-T3 formulations, making it possible to clinicians to prescribe L-T3 alone or in combination with L-T4. The aim of the present position statement was to define the correct clinical indications, schedule, duration of treatment and contraindications of combined treatment with L-T4 and L-T3 in hypothyroid patients in an attempt to guide clinicians and to avoid potential adverse effects of overtreatment.

Characterization of the peripheral thyroid system of gilthead seabream acclimated to different ambient salinities

Thyroid hormones are involved in many developmental and physiological processes, including osmoregulation. The regulation of the thyroid system by environmental salinity in the euryhaline gilthead seabream (Sparus aurata) is still poorly characterized. To this end seabreams were exposed to four different environmental salinities (5, 15, 40 and 55ppt) for 14days, and plasma free thyroid hormones (fT3, fT4), outer ring deiodination and Na⁺/K⁺-ATPase activities in gills and kidney, as well as other osmoregulatory and metabolic parameters were measured. Low salinity conditions (5ppt) elicited a significant increase in fT3 (29%) and fT4 (184%) plasma concentrations compared to control animals (acclimated to 40ppt, natural salinity conditions in the Bay of Cádiz, Spain), while the amount of pituitary thyroid stimulating hormone subunit β (tshb) transcript abundance remained unchanged. In addition, plasma fT4 levels were positively correlated to renal and branchial deiodinase type 2 (dio2) mRNA expression. Gill and kidney T4-outer ring deiodination activities correlated positively with dio2 mRNA expression and the highest values were observed in fish acclimated to low salinities (5 and 15ppt). The high salinity (55ppt) exposure caused a significant increase in tshb expression (65%), but deiodinase gene expression (dio1 and dio2) and activity did not change and were similar to controls (40ppt). In conclusion, acclimation to different salinities led to changes in the peripheral regulation of thyroid hormone metabolism in seabream. Therefore, thyroid hormones are involved in the regulation of ion transport and osmoregulatory physiology in this species. The conclusions derived from this study may also allow aquaculturists to modulate thyroid metabolism in seabream by adjusting culture salinity.

Effect of Hypothyroidism and Hyperthyroidism on Tissue Thyroid Hormone Concentrations in Rat

BACKGROUND AND OBJECTIVE

The present study was aimed at determining the effects of experimental hypothyroidism and hyperthyroidism on tissue thyroid hormones by a mass spectrometry-based technique.

METHODS

Rats were subjected to propylthiouracil treatment or administration of exogenous triiodothyronine (T3) or thyroxine (T4). Tissue T3 and T4 were measured by liquid chromatography tandem mass spectrometry in the heart, liver, kidney, visceral and subcutaneous adipose tissue, and brain.

RESULTS

Baseline tissue T3 and T4 concentrations ranged from 0.2 to 20 pmol ∙ g(-1) and from 3 to 125 pmol ∙ g(-1), respectively, with the highest values in the liver and kidney, and the lowest values in the adipose tissue. The T3/T4 ratio (expressed as a percentage) was in the 7-20% range in all tissues except the brain, where it averaged 75%. In hypothyroidism, tissue T3 was more severely reduced than serum free T3, averaging 1-6% of the baseline versus 30% of the baseline. The extent of tissue T3 reduction, expressed as percentage of the baseline, was not homogeneous (p < 0.001), with liver = kidney > brain > heart > adipose tissue. The tissue T3/T4 ratio significantly increased in all organs except the kidney, averaging 330% in the brain and 50-90% in the other tissues. By contrast, exogenous T3 and T4 administration produced similar increases in serum free T3 and in tissue T3, and the relative changes were not significantly different between different tissues.

CONCLUSIONS

While the response to increased thyroid hormones availability was similar in all tissues, decreased thyroid hormone availability induced compensatory responses, leading to a significant mismatch between changes in serum and in specific tissues.

Sodium selenite supplementation does not fully restore oxidative stress-induced deiodinase dysfunction: Implications for the nonthyroidal illness syndrome

Nonthyroidal illness syndrome (NTIS) is marked by low T3 and high reverse T3 levels. The physiopathology is poorly understood but involves oxidative stress-induced disruption of the iodothyronine deiodinases, which activate or inactivate thyroid hormones. Selenium, an essential trace element, exerts antioxidant function mainly through the thioredoxin reductase (TRx) and glutathione peroxidase (GPx) redox-regulating systems. We evaluated the effect of sodium selenite on IL6-induced disruption on deiodinase function. Cell lines expressing endogenous deiodinases type 1(D1), 2(D2) or 3(D3) (HepG2, MSTO, and MCF-7 cells, respectively) were used in an intact cell model that mimics the deiodination process under physiological conditions of substrate and cofactor, in the presence or not of IL6, with or without selenite. Deiodinase activity was quantified by the amount of iodine-125 in the medium (D1 and D2) or by ion-exchange chromatography (D3). Oxidative stress was evaluated by measuring reactive species (RS), carbonyl content as well as enzymatic and non-enzymatic antioxidant defenses. Results: IL6 induced ROS and carbonyl content in all 3 cell lines (all P<0.001). Increased ROS was paralleled by D1 and D2-decreased T3-production (P<0.01) and increased D3-catalyzed T3-inactivation (P<0.001). Selenite decreases the IL6-induced ROS and carbonyl content, while enhances Gpx and Trx activities. Nevertheless, it failed on restoring D1 or D2 function and only attenuates D3 activation (P<0.05). In conclusion, although sodium selenite reduces IL6-induced redox imbalance it does not fully repair deiodinase function. These results shed light on NTIS physiopathology and might explain why low T3 levels are unaffected by selenium supplementation in sick patients.

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IL6 induced oxidative stress impairs deiodinase function in critically ill patients.

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Selenite induces the antioxidant defense through the enzymatic TRx and GPx pathways.

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Selenite attenuates redox imbalance but it does not restore deiodinase activities.

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Intracellular cysteine levels are critical to proper deiodinases function.

Effect of Functionally Significant Deiodinase Single Nucleotide Polymorphisms on Drinking Behavior in Alcohol Dependence: An Exploratory Investigation

BACKGROUND

Abnormalities of the hypothalamic-pituitary-thyroid (HPT) axis have been reported in alcoholism; however, there is no definitive agreement on the specific thyroid abnormalities and their underlying mechanisms in alcohol dependence. The biological activity of thyroid hormones or the availability of T3 is regulated by the three deiodinase enzymes: D1, D2, and D3. In the context of alcohol use, functionally significant single nucleotide polymorphisms (SNPs) of these deiodinase genes may play a role in HPT dysfunction.

METHODS

This study explored the effect of three functionally significant SNPs (D1: rs2235544, D2: rs225014, and rs12885300) of deiodinase genes on drinking behavior and thyroid-stimulating hormone (TSH) levels in alcohol-dependent (N = 521) and control subjects (N = 288).

RESULTS

Rs225014 was associated with significant differences in the amount of naturalistic alcohol drinking assessed by Timeline Follow Back. Alcohol-dependent subjects had significantly higher TSH levels compared to controls; however, there was no effect of genotype on TSH levels for either group.

CONCLUSIONS

These findings extend previous studies on thyroid dysfunction in alcoholism and provide novel, albeit preliminary, information by linking functionally significant genetic polymorphisms of the deiodinase enzymes with alcohol-drinking behavior.

Hypothyroidism and brain developmental players

Most of our knowledge on the mechanisms of thyroid hormone (TH) dependent brain development is based on clinical observations and animal studies of maternal/fetal hypothyroidism. THs play an essential role in brain development and hormone deficiency during critical phases in fetal life may lead to severe and permanent brain damage. Maternal hypothyroidism is considered the most common cause of fetal TH deficiency, but the problem may also arise in the fetus. In the case of congenital hypothyroidism due to defects in fetal thyroid gland development or hormone synthesis, clinical symptoms at birth are often mild as a result of compensatory maternal TH supply. TH transporters (THTs) and deiodinases (Ds) are important regulators of intracellular triiodothyronine (T3) availability and therefore contribute to the control of thyroid receptors (TRs)-dependent CNS development and early embryonic life. Defects in fetal THTs or Ds may have more impact on fetal brain since they can result in intracellular T3 deficiency despite sufficient maternal TH supply. One clear example is the recent discovery of mutations in the TH transporter (monocarboxylate transporter 8; MCT8) that could be linked to a syndrome of severe and non reversible psychomotor retardation. Even mild and transient changes in maternal TH levels can directly affect and alter the gene expression profile, and thus disturb fetal brain development. Animal studies are needed to increase our understanding of the exact role of THTs and Ds in prenatal brain development.

Exposure to monocrotophos pesticide causes disruption of the hypothalamic-pituitary-thyroid axis in adult male goldfish (Carassius auratus)

The thyroid hormones (THs) 3,3',5-triiodo-l-thyronine (T3) and l-thyroxine (T4) exert a wide range of biological effects on physiological processes of fish. To elucidate the thyroid disruption effects of monocrotophos (MCP), an organophosphate pesticide, on male goldfish (Carassius auratus), thyroid follicle histology, plasma total T3 (TT3), total T4 (TT4), free T3 (FT3) and free T4 levels, and the mRNA expression of indices involved in the hypothalamic-pituitary-thyroid axis (HPT axis) were examined following 21-day exposure to 0.01, 0.10 and 1.00mg/L of a 40% MCP-based pesticide. The results showed that MCP exposure induced the hyperplasia and hypertrophy of thyroid follicular epithelium and led to decreased plasma TT3 levels and TT3-to-TT4 ratios, without effect on plasma TT4 levels. Profiles of the changes in the relative abundance of deiodinase (D1, D2 and D3) transcripts were observed in the liver, brain and kidneys, during MCP exposure. An increase in the metabolism of T3, expressed as highly elevated hepatic d1 and d3 mRNA levels, might be associated with the reduction in plasma TT3 levels in both the 0.01 and 0.10mg/L groups, while in the 1.00mg/L MCP group, inhibited hepatic d2 transcripts might have also resulted in decreased TT3 levels by preventing the activation of T4 to T3. As a compensatory response to decreased T3 levels, pituitary thyroid-stimulating hormone β subunit mRNA transcription was up-regulated by the MCP pesticide. Decreases in plasma FT3 levels were also correlated with the modulation of hepatic transthyretin mRNA expression. Overall, the MCP pesticide exhibited thyroid-disrupting effects via interference with the HPT axis at multiple potential sites, resulting in disturbance of TH homeostasis.

Regulators of thyroid hormone availability and action in embryonic chicken brain development

Thyroid hormones (THs) are crucial elements in vertebrate brain development. They exert their action mainly through binding of 3,5,3'-triiodothyronine (T3) to nuclear receptors that directly influence the expression of TH-regulated genes. Intracellular TH action is therefore dependent on both the availability of T3 and its receptors. TH uptake in cells is regulated by specific TH transporters and local activation and inactivation is regulated by deiodinases. This review provides an overview of the general expression pattern of TH transporters, deiodinases and receptors during embryonic chicken brain development and compares it to the situation in mammals. It is clear that THs and their regulators are present in the embryonic brain from the early stages of development, long before the onset of embryonic thyroid gland functioning. The mechanism of TH uptake across the brain barriers during development is only partly understood. At the developing blood-brain-barrier expression of the TH-activating type 2 deiodinase is closely associated with the blood vessels, but contrary to the situation in (adult) mammals no expression of MCT8 or OATP1C1 TH transporters is found at that level in the developing chicken. At the blood-cerebrospinal fluid-barrier co-expression of the TH-inactivating type 3 deiodinase and MCT8 and OATP1C1 is found in birds and mammals. These comparative data show overlapping patterns, pointing to general mechanisms, but also indicate specific interspecies differences that may help to understand species-specific responses to regulator gene knockout/mutation.

Understanding the hypothalamus-pituitary-thyroid axis in mct8 deficiency

Thyroid hormone (TH) metabolism and action via binding to nuclear receptors are intracellular events that require the passage of TH across the plasma membrane. This process is mediated by specific TH transporters of which the monocarboxylate transporter 8 (Mct8) has received major attention. Mct8 is highly expressed in different tissues such as liver, kidney, thyroid, pituitary and brain. In humans, inactivating mutations of the MCT8 gene (SLC16A2) are associated with severe forms of psychomotor retardation and abnormal TH serum levels (Allan-Herndon-Dudley syndrome). Surprisingly, Mct8 knockout (ko) mice do not exhibit overt neurological symptoms but fully replicate the unusual serum TH profile with highly increased serum T3 in the presence of low serum T4. In order to evaluate the underlying mechanisms for these abnormalities, TH transport and metabolism have been intensively studied in different tissues of Mct8 ko mice. Here, we summarize the observed changes within the hypothalamus-pituitary-thyroid axis that result in altered TH production and secretion. Although analysis of Mct8 ko mice has greatly expanded our knowledge, many open questions still remain to be addressed in order to define the tissue- and cell-specific role of this important TH transporter.