Thyroid Replacement Therapy and Heart Failure

Thyroid hormone (TH) signaling plays critical roles in the differentiation, growth, metabolism, and physiological function of all organs or tissues, including heart and skeletal muscle. Due to the significant progress in our understanding of the molecular mechanisms that underlie TH action, it’s widely accepted that TH signaling is regulated at multiple levels. A growing number of discoveries suggest that microRNAs (miRNAs) act as fine-tune regulators of gene expression and adds sophisticated regulatory tiers to signaling pathways. Recently, some pioneering studies in cardiac and skeletal muscle demonstrating the interplay between miRNAs and TH signaling suggest that miRNAs might mediate and/or modulate TH signaling. This review presents recent advances involving the crosstalk between miRNAs and TH signaling and current evidence showing the importance of miRNA in TH signaling with particular emphasis on the study of muscle-specific miRNAs (myomiRs) in cardiac and skeletal muscle. Although the research of the reciprocal regulation of miRNAs and TH signaling is only at the beginning stage, it has already contributed to our current understanding of both TH action and miRNA biology. We also encourage further investigations to address the relative contributions of miRNAs in TH signaling under physiological and pathological conditions and how a group of miRNAs are coordinated to integrate into the complex hierarchical regulatory network of TH.

Thyroid hormones (THs) are required for normal brain and somatic development and for the proper regulation of physiology in both children and adults. Thyroid function is controlled by the dynamic interrelationships between the hypothalamus, the pituitary and the thyroid. These dynamic relationships maintain circulating levels of THs within a narrow range under normal conditions. Normally, there is likely to be a tight relationship between changes in circulating levels of THs and changes in TH action in various target tissues. This relationship is maintained by tissue-level mechanisms that include TH metabolism and transport. Environmental chemicals that interfere with TH signaling mechanisms (Endocrine Disrupting Chemicals, EDCs) may produce adverse effects both in the individual and in a population. Because of the complex nature of the regulation of thyroid function and TH action, the consequences of EDC exposure is also likely to be complex and our ability to understand these effects as well as to screen for potential EDCs must consider this complexity. Specifically, if there are chemicals in the environment that directly interfere with TH action through their receptors but do not affect circulating TH levels, they would not be identified as thyroid toxicants by currently applied screening methods or by epidemiological studies. The goal of this review is therefore to identify the issues that must be clearly resolved before effective risk assessment can be performed.

Euthyroid sick syndrome characterized by reduced levels of thyroid hormones (THs) is observed in patients with meningococcal shock. It has been found that the level of THs reflects disease severity and is predictive for mortality. The present study was conducted to investigate the impact of THs on host defense during meningococcal infection. We found that supplementation of thyroxine to mice infected with Neisseria meningitidis enhanced bacterial clearance, attenuated the inflammatory responses and promoted survival. In vitro studies with macrophages revealed that THs enhanced bacteria-cell interaction and intracellular killing of meningococci by stimulating inducible nitric oxide synthase (iNos)-mediated NO production. TH treatment did not activate expression of TH receptors in macrophages. Instead, the observed TH-directed actions were mediated through nongenomic pathways involving the protein kinases PI3K and ERK1/2 and initiated at the membrane receptor integrin αvβ3. Inhibition of nongenomic TH signaling prevented iNos induction, NO production and subsequent intracellular bacterial killing by macrophages. These data demonstrate a beneficial role of THs in macrophage-mediated N. meningitidis clearance. TH replacement might be a novel option to control meningococcal septicemia.

Besides their direct effects on peripheral metabolic tissues, thyroid hormones (TH) act on the hypothalamus to modulate energy homeostasis. However, since most of the hypothalamic actions of TH have been addressed in studies with direct central administration, the estimation of the relative contribution of the central vs. peripheral effects in physiologic conditions of peripheral release (or administration) of TH remains unclear. In this study we used two different models of peripherally induced hyperthyroidism (i.e., T4 and T3 oral administration) to assess and compare the serum and hypothalamic TH status and relate them to the metabolic effects of the treatment. Peripheral TH treatment affected feeding behavior, overall growth, core body temperature, body composition, brown adipose tissue (BAT) morphology and uncoupling protein 1 (UCP1) levels and metabolic activity, white adipose tissue (WAT) browning and liver metabolism. This resulted in an increased overall uncoupling capacity and a shift of the lipid metabolism from WAT accumulation to BAT fueling. Both peripheral treatment protocols induced significant changes in TH concentrations within the hypothalamus, with T3 eliciting a downregulation of hypothalamic AMP-activated protein kinase (AMPK), supporting the existence of a central action of peripheral TH. Altogether, these data suggest that peripherally administered TH modulate energy balance by various mechanisms; they also provide a unifying vision of the centrally mediated and the direct local metabolic effect of TH in the context of hyperthyroidism.

Background and Aims Thyroid hormone (TH) signaling plays a crucial role in the regulation of the cell differentiation state, cell cycle and metabolism in various organs. Low TH levels are observed in most patients with chronic kidney disease, and correlate with cell de-differentiation and reactivation of the cell cycle. Despite this knowledge, possible alterations of TH signaling in Autosomal Dominant Polycystic Kidney Disease (ADPKD) and the capacity of TH to modulate anti-cystogenic and renoprotective pathways have not yet been studied. In this study we aimed to (i) investigate the role of TH signaling in the pathogenesis of ADPKD in patients and experimental models, and (ii) assess whether the pharmacological modulation of this pathway with TH (T3, T4) and TH analogs could arrest or reverse ADPKD progression. Method Ninety patients with a diagnosis of ADPKD based on renal ultrasonography findings or genetic testing were included in the study and divided into five subgroups of chronic kidney disease stages, according to the KDIGO classification. Serum TH was measured using ELISA and chemiluminescent immunoassays. The correlation between TH levels and renal function parameter (eGFR) in these patients was assessed using linear regression. 3D polycystic tubules were engineered from patient-derived cells as previously described (Benedetti et al. 2016). For the in vivo experiments, PCK rats—an animal model of ADPKD—were treated with T4 (10 μg/kg) or vehicle by gavage from 4 to 11 weeks of age. Age-matched SD rats were followed for the same length of time and used as controls. Results The analysis of patients’ data showed a strong linear correlation between the levels of FT3 and eGFR, and corresponding inverse correlation between rT3 (the inactivated form of T3) and eGFR. Treating patients-derived tubules with THs strongly inhibited cyst formation and growth. Interestingly, the results were validated in engineered polycystic tubules from three ADPKD patients with different mutations (missense, splice-site and stop-gain) in the PKD1 gene, further confirming that T4 plays an essential role in the cystogenesis and, presumably, progression of the disease in humans. Treating PCK rats—an animal model of ADPKD—with T4 resulted in a significant increase in T4 serum levels and a simultaneous reduction in the size of the macrocystic area compared to vehicle-treated PCK rats. Most importantly, T4 serum levels positively correlated with a reduction in both the size of the macrocystic area and loss of protein into the urine, indicating that TH signaling plays a role in the growth of cysts, and that exogenous T4 can slow down cystogenesis and improve renal function. Interestingly, our mechanistic studies revealed that T4 exerts its anti-cystogenic effects, at least partially, by binding to the membrane receptor αvβ3 and activating the MAPK cascade. Conclusion These results suggest that TH signaling plays a role in the progression of ADPKD and timely administration of T4, ideally at a relatively early stage of the disease, could delay progression or even reverse key clinical features of ADPKD.

Thyroid hormones (THs) play an essential role in the development of all vertebrates; in particular adequate TH content is crucial for proper neurodevelopment. TH availability and action in the brain are precisely regulated by several mechanisms, including the secretion of THs by the thyroid gland, the transport of THs to the brain and neural cells, THs activation and inactivation by the metabolic enzymes deiodinases and, in the fetus, transplacental passage of maternal THs. Although these mechanisms have been extensively studied in rats, in the last decade, models of genetically modified mice have been more frequently used to understand the role of the main proteins involved in TH signaling in health and disease. Despite this, there is little knowledge about the mechanisms underlying THs availability in the mouse brain. This mini-review article gathers information from findings in rats, and the latest findings in mice regarding the ontogeny of TH action and the sources of THs to the brain, with special focus on neurodevelopmental stages. Unraveling TH economy and action in the mouse brain may help to better understand the physiology and pathophysiology of TH signaling in brain and may contribute to addressing the neurological alterations due to hypo and hyperthyroidism and TH resistance syndromes.

Short term triiodo- l-thyronine treatment inhibits cardiac myocyte apoptosis in border area after myocardial infarction in rats

Over the recent years, considerable progress has been made in elucidating processes that are critical for thyroid hormone (TH) synthesis and action. In this issue of Thyroid Research several German groups dedicated to thyroid research have assembled and discussed novel aspects of thyroid hormone action with the perspective to improve diagnosis and therapy of thyroid disorders by better understanding disturbed thyroid differentiation. The over-arching theme addressed in the contributions of this special issue relates to the main focus of current thyroid research and treatment of thyroid disesase, i.e. “What defines thyroid health?” [1]. Thereby the putative role of seemingly established players in TH synthesis and action are revisited. A report on a patient characterized by a novel germline TSH-receptor mutation links this case of non-autoimmune hyperthyroidism to new impliations in TSH-receptor structure [2]. The study highlights the importance of introducing novel diagnostic approaches to the clinics, because this particular mutation in the TSH-receptor is correlated to altered Gq-signalling pathways, thereby pointing to an important role of Gq signalling in the thyroid It is known only since recently that transport of TH is an active and regulated mechanism. The monocarboxylate transporter 8 (MCT8) is a crucially important transporter of TH and it transports triiodothyronine (T3) specifically well. Mutations in MCT8 are known to cause a severe syndrome of X-linked mental retardation known as Allan-Herndon Dudley syndrome. Based on homology modeling all of the currently reported pathogenic mutations in MCT8 are studied in the article by Kleinau et al. [3]. A focus is set on identification of those MCT8 mutations that are most sensitive for substrate transport with the goal to simulate in silico the potencies of future therapies based on TH transporter-specific inhibitors mimicking TH structurally. Besides MCT8 other transporters have been proposed to play important roles in TH transport (MCT10, OATP1C1, OATP1A2, OATP14, LAT1 and LAT2). The structure-function relationships of primary TH transporters like MCT8 and additional, so-called secondary TH transporters such as those listed above is reviewed by Kinne et al. [4] with special attention on their expression profiles, transport specificities and substrates. Similarities and differences in structure and molecular features of the known and suspected TH transporters are compared between man and mouse, in particular asking their crucial impact on TH actions in the central nervous system. TH actions in the brain and clinical consequences of non-classical, rather novel treatment protocols to relieve symptoms of severe mood and depression disorders is reviewed in the article by Pilhatsch et al. [5]. For a long time, only genomic actions of TH, namely of T3 were recognized by both, thyroid researchers and clinicians. However this picture has to be revised as non-classical, non-genomic TH actions were described which lead to activation of alternative signaling pathways via PI3K and MAPK. The impact and perspectives of these recent findings are summarized by Moller and Brocker-Preus [6] who comment on the outcomes of activation of alternative signaling pathways on transcriptional regulation of TH target cells. Non-classical and classical TH actions must be taken into consideration for better management of thyroid malignancies. Moreover, it is increasingly appreciated that disturbances in TH synthesis occur in thyroid tumorigenesis and that disturbed TH action affects carcinogenesis in general. Of the many novel aspects in thyroid carcinogenesis, it was the recent identification of miRNAs and their intricate involvement in the regulation of transcriptional, translational and epigentic control mechanisms that provides one of the most promising diagnostic and high-potential, future therapeutic tool. The aspects of miRNA relevance for thyroid pathologies are discussed by Braun and Huttelmaier [7]. Likewise, regulation of transcription and translation by RNA binding proteins is addressed in the article by Trojanowicz et al. The adenylate uridylate-rich element binding proteins AUF together with HuR was reported to regulate mRNA stability and could hence participate in thyroid carcinogenesis. RNA binding proteins may harbor multifunctional properties that not only affect thyrocyte differentiation but could also affect TH synthesis [8]. Finally, the characterization of protein transport pathways and the identification of altered trafficking in thyroid carcinoma cells are approached in the experimental study by Tedelind et al. [9] that investigated the cathepsins which are known as thyroglobulin-processing enzymes with important functions in TH biosynthesis. We believe that the papers collected for this special issue of Thyroid Research will have a stimulatory effect not only for thyroid researchers but will be interesting for those from associated disciplines.

Thyroid storm as a result of functioning metastatic thyroid carcinoma is exceedingly rare. 1 We describe a patient with functioning distant metastases from adenocarcinoma of the thyroid in whom thyroid storm developed in the course of care for extensive burns.

Antidepressant-Resistant Depression in Patients With Comorbid Subclinical Hypothyroidism or High-Normal TSH Levels.

Introduction: There exists a complex relation between the thyroid hormones and liver physiology in health and disease. The liver along with the thyroid gland play a significant role in the conversion of inactive Thyroxine (T4 ) to active Triiodothyronine (T3 ). The most common thyroid hormone profile in cirrhosis of liver is a low total T3 and free T3 , secondary to reduced activity of deiodinase type 1 and increased conversion to rT3 . Aim: To assess the association between the thyroid hormone levels and severity of liver disease, expressed in terms of child pugh score in tertiary care hospital in Goa. Materials and methods: The cross-sectional observational study included hundred patients with liver cirrhosis, admitted at a tertiary care hospital in Goa, from October 2019 to September 2020. The thyroid hormone levels were estimated from an early morning fasting blood sample within 24 hours of admission, once the patient satisfied the inclusion criteria. The Child Turgott Pugh scoring system was used to classify patients as per their severity of liver disease. The data was entered and analysed in Statistical Package for Social Sciences (SPSS) software version 14.0. Results: There were 95 males and 5 females. The study showed low mean levels of total T4 and free T3 in patients with cirrhosis of liver, which was significantly associated with Child Pugh classes of liver dysfunction. There was an association between levels of free T3 and the classes of Child Pugh score. The difference in the mean levels of TSH, total T3 and free T4 across the Child Pugh classes were not statistically significant. Conclusion: The study showed low free T3 levels in patients with cirrhosis of liver as seen in similar studies done in various settings. Thus, Thyroid Function Tests (TFTs) especially free T3 levels have a considerable potential to be used an independent predictor or a proxy to prognosis in patients with liver cirrhosis.

We examined the effects of thyroid hormones (THs) on left ventricular (LV) function and myocyte remodeling in rats with spontaneously hypertensive heart failure (SHHF). SHHF rats were treated with three different TH doses from 20-21 mo of age. In terminal experiments, LV function (as determined by echocardiography and catheterization) and isolated myocyte shape were examined in SHHF rat groups and age-matched Wistar-Furth control animals. Compared with Wistar-Furth rats, the ratio of alpha- to beta-myosin was reduced in untreated SHHF rats. The alpha-to-beta-myosin ratio increased in all TH groups, which suggests a reversal of the fetal gene program. Low-dose TH produced no changes in LV myocyte size or function, but high-dose TH produced signs of hyperthyroidism (e.g., increased heart weight, tachycardia). The chamber diameter-to-wall thickness ratio declined with increasing dose due to reduced chamber diameter and increased wall thickness. This resulted in a 38% reduction in LV systolic wall stress in the middle- and high-dose groups despite sustained hypertension. Isolated myocyte data indicated that chamber remodeling and reduced wall stress were due to a unique alteration in myocyte transverse shape (e.g., reduced major diameter and increased minor diameter). Based on our present understanding of ventricular remodeling and wall stress, we believe these changes are likely beneficial. Results suggest that TH may be an important regulator of myocyte transverse shape in heart disease.

Cardiac function is reduced following myocardial infarction (MI) due to myocardial injury and alterations in the viable non-ischemic myocardium, a process known as cardiac remodeling. The current treatments available for patients with acute MI (AMI) reduce infarct size, preserve left ventricular (LV) function and improve survival; however, these treatments do not prevent remodeling, which can lead to heart failure. The aim of the present study was to investigate the effects of thyroid hormone (TH) treatment following MI in an in vivo rat model. A total of 199 rats were separated into 3 groups: Sham operated and 2 different coronary artery ligation (CAL) groups. Rats subjected to CAL were randomly divided into a further 2 groups 24 h following surgery. The first group received standard rat chow (designated the CAL group), while the second group received food containing 0.05% thyroid powder (designated the CALTH group). The mean daily intake of TH per rat was estimated at 3.0 µg T3 and 12 µg T4. Echocardiography was used to monitor the rats. Large-scale analysis confirmed the favorable effects of TH treatment following CAL on various parameters of cardiac function. TH treatment reduced LV dilation, and increased global and regional LV function. The development of cardiac hypertrophy was induced and, thus, wall stress was limited. Furthermore, TH treatment improved cardiac geometry, which manifested as an increased sphericity index. Myocardial function, as well as LV dilatation, following CAL and TH treatment was not closely associated with the extent of injury, indicating a novel therapeutic intervention that may alter the course of LV remodeling that typically leads to post-MI heart failure. Data modelling and regressions may be developed to enable the simulation of the pathophysiological processes that occur following MI, and to predict with accuracy the effects of novel or current treatments that act via the modulation of tissue injury, LV dilation, LV geometry and hypertrophy.

Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and apoptosis. In the retina, TH signaling plays a central role in cone opsin expression. TH signaling inhibits S opsin expression, stimulates M opsin expression, and promotes dorsal-ventral opsin patterning. TH signaling has also been associated with cone photoreceptor viability. Treatment with thyroid hormone triiodothyronine (T3) or induction of high T3 by deleting the hormone-inactivating enzyme type 3 iodothyronine deiodinase (DIO3) causes cone death in mice. This effect is reversed by deletion of the TH receptor (TR) gene. Consistent with the T3 treatment effect, suppressing TH signaling preserves cones in mouse models of retinal degeneration. The regulation of cone survival by TH signaling appears to be independent of its regulatory role in cone opsin expression. The mechanism by which TH signaling regulates cone viability remains to be identified. The current understanding of TH signaling regulation in photoreceptor viability suggests that suppressing TH signaling locally in the retina may represent a novel strategy for retinal degeneration management.

Ischemic heart disease (IHD) is the single most common cause of death. New approaches to enhance myocardial perfusion are needed to improve outcomes for patients with IHD. Thyroid hormones (TH) are known to increase blood flow; however, their usefulness for increasing perfusion in IHD is limited because TH accelerates heart rate, which can be detrimental. Therefore, selective activation of TH effects is desirable. We hypothesized that cell-type-specific TH receptor (TR) expression can increase TH action in the heart, while avoiding the negative consequences of TH treatment. We generated a binary transgenic (BTG) mouse that selectively expresses TRα1 in endothelial cells in a tetracycline-inducible fashion. In BTG mice, endothelial TRα1 protein expression was increased by twofold, which, in turn, increased coronary blood flow by 77%, coronary conductance by 60%, and coronary reserve by 47% compared with wild-type mice. Systemic blood pressure was decreased by 20% in BTG mice after TRα1 expression. No effects on heart rate were observed. Endothelial TRα1 expression activated AKT/endothelial nitric oxide synthase pathway and increased A2AR adenosine receptor. Furthermore, hearts from BTG mice overexpressing TRα1 that were submitted to 20 min ischemia and 20 min reperfusion showed a 20% decline in left ventricular pressure (LVP) compared with control mice where LVP was decreased by 42%. Studies using an infarction mouse model demonstrated that endothelial overexpression of TRα1 decreased infarct size by 45%. In conclusion, selective expression of TRα1 in endothelial cells protects the heart against injury after an ischemic insult and does not result in adverse cardiac or systemic effects.