Left-ventricular remodeling after myocardial infarction is associated with a cardiomyocyte-specific hypothyroid condition

Nanoscale organization of cardiac calcium channels is dependent on thyroid hormone status

Thyroid hormone dysfunction is frequently observed in patients with chronic illnesses including heart failure, which increases the risk of adverse events. This study examined the effects of thyroid hormones (THs) on cardiac transverse-tubule (TT) integrity, Ca2+ sparks, and nanoscale organization of ion channels in excitation-contraction (EC) coupling, including L-type calcium channel (CaV1.2), ryanodine receptor type 2 (RyR2), and junctophilin-2 (Jph2). TH deficiency was established in adult female rats by propyl-thiouracil (PTU) ingestion for 8 wk; followed by randomization to continued PTU without or with oral triiodo-l-thyronine (T3; 10 µg/kg/day) for an additional 2 wk (PTU + T3). Confocal microscopy of isolated cardiomyocytes (CMs) showed significant misalignment of TTs and increased Ca2+ sparks in thyroid-deficient CMs. Density-based spatial clustering of applications with noise (DBSCAN) analysis of stochastic optical reconstruction microscopy (STORM) images showed decreased (P < 0.0001) RyR2 cluster number per cell area in PTU CMs compared with euthyroid (EU) control myocytes, and this was normalized by T3 treatment. CaV1.2 channels and Jph2 localized within a 210 nm radius of the RyR2 clusters were significantly reduced in PTU myocytes, and these values were increased with T3 treatment. A significant percentage of the RyR2 clusters in the PTU myocytes had neither CaV1.2 nor Jph2, suggesting fewer functional clusters in EC coupling. Nearest neighbor distances between RyR2 clusters were greater (P < 0.001) in PTU cells compared with EU- and T3-treated CMs that correspond to disarray of TTs at the sarcomere z-discs. These results support a regulatory role of T3 in the nanoscale organization of RyR2 clusters and colocalization of CaV1.2 and Jph2 in optimizing EC coupling.NEW & NOTEWORTHY Thyroid hormone (TH) dysfunction exacerbates preexisting heart conditions leading to an increased risk of premature morbidity/mortality. Triiodo-l-thyronine (T3) optimizes cardiac excitation-contraction (EC) coupling by maintaining myocardial T-tubule (TT) structures and organization of calcium ion channels. Single-molecule localization microscopy shows T3 effects on the clustering of ryanodine receptors (RyR2) with colocalization of L-type calcium channels (CaV1.2) and junctophilin-2 (Jph2) at TT-SR structures. Heart disease with subclinical hypothyroidism/low T3 syndrome may benefit from TH treatment.

Low Thyroid Hormones Level Attenuates Mitochondrial Dysfunction and Right Ventricular Failure in Pulmonary Hypertensive Rats

PURPOSE

This study is to investigate the repercussions of hypothyroidism in the pathophysiological progression of pulmonary arterial hypertension (PAH).

METHODS

While the control (CTL, n = 5) male Wistar rats received vehicle, PAH was induced with monocrotaline (MCT group, n = 15). Hypothyroidism was induced in a subset of rats by methimazole 3 weeks prior to the MCT injection (MMZ + MCT group, n = 15). Plasma thyroid hormones were measured by radioimmunoassay. Electrocardiographic, echocardiographic, and hemodynamic analyses were performed to evaluate the progression of PAH. Gene expression of antioxidant enzymes and cardiac hypertrophy markers were assessed by qPCR. Mitochondrial respiration, ATP levels, and ROS production were measured in right ventricular (RV) samples.

RESULTS

Plasma T3 and T4 decreased in both MCT and MMZ + MCT groups (p < 0.05). Right ventricular systolic pressure (RVSP) increased, and RV - dP/dt, + dP/dt, and contractility index decreased in the MCT versus the CTL group and remained within control levels in the MMZ + MCT group (p < 0.05). Relative RV weight, RV wall thickness, RV diastolic area, and relative lung weight were augmented in the MCT versus the CTL group, whereas all parameters were improved to the CTL levels in the MMZ + MCT group (p < 0.05). Only the MCT group exhibited an increased duration of QTc interval compared to the baseline period (p < 0.05). ADP-induced mitochondrial respiration and ATP levels were decreased, and ROS production was increased in MCT versus the CTL group (p < 0.05), while the MMZ + MCT group exhibited increased mitochondrial respiration versus the MCT group (p < 0.05).

CONCLUSION

Hypothyroidism attenuated the RV mitochondrial dysfunction and the pathophysiological progression of MCT-induced PAH.

Divergent Thyroid Hormone Levels in Plasma and Left Ventricle of the Heart in Compensated and Decompensated Cardiac Hypertrophy Induced by Chronic Adrenergic Stimulation in Mice

Chronic hemodynamic overload of the heart induces ventricular hypertrophy that may be either compensatory or progress to decompensation and heart failure. The gradual impairment of ventricular function is, at least in part, the result of a reduction of cardiac thyroid-hormone (TH) action. Here, we examined the proposed roles of increased cardiac expression of the TH-inactivating enzyme deiodinase type 3 (D3) and reduced plasma TH levels in diminishing cardiac TH levels. Using minipumps, mice were infused for one and two weeks with isoproterenol (ISO) alone or in combination with phenylephrine (PE). Remodeling of the heart induced by these adrenergic agonists was assessed by echocardiography. Left ventricular (LV) tissue and plasma TH levels (T4 and T3) were determined using liquid chromatography-tandem mass spectrometry. LV D3 activity was determined by conversion of radiolabeled substrate and quantification following HPLC. The results show that ISO induced compensated LV hypertrophy with maintained cardiac output. Plasma levels of T4 and T3 remained normal, but LV hormone levels were reduced by approximately 30% after two weeks, while LV D3 activity was not significantly increased. ISO + PE induced decompensated LV hypertrophy with diminished cardiac output. Plasma levels of T4 and T3 were substantially reduced after one and two weeks, together with a more than 50% reduction of hormone levels in the LV. D3 activity was increased after one week and returned to control levels after two weeks. These data show for the first time that relative to controls, decompensated LV hypertrophy with diminished cardiac output is associated with a greater reduction of cardiac TH levels than compensated hypertrophy with maintained cardiac output. LV D3 activity is unlikely to account for these reductions after two weeks in either condition. Whereas the mechanism of the mild reduction in compensated hypertrophy is unclear, changes in systemic TH homeostasis appear to determine the marked drop in LV TH levels and associated impairment of ventricular function in decompensated hypertrophy.

Mechanisms and Management of Thyroid Disease and Atrial Fibrillation: Impact of Atrial Electrical Remodeling and Cardiac Fibrosis

Atrial fibrillation (AF) is the most common cardiac arrhythmia associated with increased cardiovascular morbidity and mortality. The pathophysiology of AF is characterized by electrical and structural remodeling occurring in the atrial myocardium. As a source of production of various hormones such as angiotensin-2, calcitonin, and atrial natriuretic peptide, the atria are a target for endocrine regulation. Studies have shown that disorders associated with endocrine dysregulation are potential underlying causes of AF. The thyroid gland is an endocrine organ that secretes three hormones: triiodothyronine (T3), thyroxine (T4) and calcitonin. Thyroid dysregulation affects the cardiovascular system. Although there is a well-established relationship between thyroid disease (especially hyperthyroidism) and AF, the underlying biochemical mechanisms leading to atrial fibrosis and atrial arrhythmias are poorly understood in thyrotoxicosis. Various animal models and cellular studies demonstrated that thyroid hormones are involved in promoting AF substrate. This review explores the recent clinical and experimental evidence of the association between thyroid disease and AF. We highlight the current knowledge on the potential mechanisms underlying the pathophysiological impact of thyroid hormones T3 and T4 dysregulation, in the development of the atrial arrhythmogenic substrate. Finally, we review the available therapeutic strategies to treat AF in the context of thyroid disease.

Deiodinases control local cellular and systemic thyroid hormone availability

Iodothyronine deiodinases (DIO) are a family of selenoproteins controlling systemic and local availability of the major thyroid hormone l-thyroxine (T4), a prohormone secreted by the thyroid gland. T4 is activated to the active 3,3'-5-triiodothyronine (T3) by two 5'-deiodinases, DIO1 and DIO2. DIO3, a 5-deiodinase selenoenzyme inactivates both the prohormone T4 and its active form T3. DIOs show species-specific different patterns of temporo-spatial expression, regulation and function and exhibit different mechanisms of reaction and inhibitor sensitivities. The main regulators of DIO expression and function are the thyroid hormone status, several growth factors, cytokines and altered pathophysiological conditions. Selenium (Se) status has a modest impact on DIO expression and translation. DIOs rank high in the priority of selenium supply to various selenoproteins; thus, their function is impaired only during severe selenium deficiency. DIO variants, polymorphisms, SNPs and rare mutations have been identified. Development of DIO isozyme selective drugs is ongoing. A first X-ray structure has been reported for DIO3. This review focusses on the biochemical characteristics and reaction mechanisms, the relationships between DIO selenoproteins and their importance for local and systemic provision of the active hormone T3. Nutritional, pharmacological, and environmental factors and inhibitors, such as endocrine disruptors, impact DIO functions.

Role of miR-133/Dio3 Axis in the T3-Dependent Modulation of Cardiac mitoK-ATP Expression

The opening of the ATP-sensitive mitochondrial potassium channel (mitok-ATP) is a common goal of cardioprotective strategies in the setting of acute and chronic myocardial disease. The biologically active thyroid hormone (TH), 3-5-3-triiodothyronine (T3), has been indicated as a potential activator of mitoK-ATP but the underlying mechanisms are still elusive. Here we describe a novel role of T3 in the transcriptional regulation of mitoK and mitoSur, the recently identified molecular constituents of the channel. To mimic human ischemic heart damage, we used a rat model of a low T3 state as the outcome of a myocardial ischemia/reperfusion event, and neonatal rat cardiomyocytes (NRCM) challenged with hypoxia or H₂O₂. Either in the in vivo or in vitro models, T3 administration to recover the physiological concentrations was able to restore the expression level of both the channel subunits, which were found to be downregulated under the stress conditions. Furthermore, the T3-mediated transcriptional activation of mitoK-ATP in the myocardium and NRCM was associated with the repression of the TH-inactivating enzyme, deiodinase 3 (Dio3), and an up-regulation of the T3-responsive miR-133a-3p. Mechanistically, the loss and gain of function experiments and reporter gene assays performed in NRCM, have revealed a new regulatory axis whereby the silencing of Dio3 under the control of miR-133a-3p drives the T3-dependent modulation of cardiac mitoK and mitoSur transcription.

Mass spectrometry in the diagnosis of thyroid disease and in the study of thyroid hormone metabolism

The importance of thyroid hormones in the regulation of development, growth, and energy metabolism is well known. Over the last decades, mass spectrometry has been extensively used to investigate thyroid hormone metabolism and to discover and characterize new molecules involved in thyroid hormones production, such as thyrotropin-releasing hormone. In the earlier period, the quantification methods, usually based on gas chromatography-mass spectrometry, were complicated and time consuming. They were mainly focused on basic research, and were not suitable for clinical diagnostics on a routine basis. The development of the modern mass spectrometers, mainly coupled to liquid chromatography, enabled simpler sample preparation procedures, and the accurate quantification of thyroid hormones, of their precursors, and of their metabolites in biological fluids, tissues, and cells became feasible. Nowadays, molecules of physiological and pathological interest can be assayed also for diagnostic purposes on a routine basis, and mass spectrometry is slowly entering the clinical laboratory. This review takes stock of the advancements in the field of thyroid metabolism that were carried out with mass spectrometry, with special focus on the use of this technique for the quantification of molecules involved in thyroid diseases.

Non-thyroidal illness syndrome predicts outcome in adult critically ill patients: a systematic review and meta-analysis

We performed a systematic review and meta-analysis to comprehensively determine the prevalence and the prognostic role of non-thyroidal illness syndrome (NTIS) in critically ill patients. We included studies that assessed thyroid function by measuring the serum thyroid hormone (TH) level and in-hospital mortality in adult septic patients. Reviews, case reports, editorials, letters, animal studies, duplicate studies, and studies with irrelevant populations and inappropriate controls were excluded. A total of 6869 patients from 25 studies were included. The median prevalence rate of NTIS was 58% (IQR 33.2-63.7). In univariate analysis, triiodothyronine (T3) and free T3 (FT3) levels in non-survivors were relatively lower than that of survivors (8 studies for T3; standardized mean difference (SMD) 1.16; 95% CI, 0.41-1.92; I2 = 97%; P < 0.01). Free thyroxine (FT4) levels in non-survivors were also lower than that of survivors (12 studies; SMD 0.54; 95% CI, 0.31-0.78; I2 = 83%; P < 0.01). There were no statistically significant differences in thyrotropin levels between non-survivors and survivors. NTIS was independently associated with increased risk of mortality in critically ill patients (odds ratio (OR) = 2.21, 95% CI, 1.64-2.97, I2 = 65% P < 0.01). The results favor the concept that decreased thyroid function might be associated with a worse outcome in critically ill patients. Hence, the measurement of TH could provide prognostic information on mortality in adult patients admitted to ICU.

Six1 promotes skeletal muscle thyroid hormone response through regulation of the MCT10 transporter

BACKGROUND

The Six1 transcription factor is implicated in controlling the development of several tissue types, notably skeletal muscle. Six1 also contributes to muscle metabolism and its activity is associated with the fast-twitch, glycolytic phenotype. Six1 regulates the expression of certain genes of the fast muscle program by directly stimulating their transcription or indirectly acting through a long non-coding RNA. We hypothesized that additional mechanisms of action of Six1 might be at play.

METHODS

A combined analysis of gene expression profiling and genome-wide location analysis data was performed. Results were validated using in vivo RNA interference loss-of-function assays followed by measurement of gene expression by RT-PCR and transcriptional reporter assays.

RESULTS

The Slc16a10 gene, encoding the thyroid hormone transmembrane transporter MCT10, was identified as a gene with a transcriptional enhancer directly bound by Six1 and requiring Six1 activity for full expression in adult mouse tibialis anterior, a predominantly fast-twitch muscle. Of the various thyroid hormone transporters, MCT10 mRNA was found to be the most abundant in skeletal muscle, and to have a stronger expression in fast-twitch compared to slow-twitch muscle groups. Loss-of-function of MCT10 in the tibialis anterior recapitulated the effect of Six1 on the expression of fast-twitch muscle genes and led to lower activity of a thyroid hormone receptor-dependent reporter gene.

CONCLUSIONS

These results shed light on the molecular mechanisms controlling the tissue expression profile of MCT10 and identify modulation of the thyroid hormone signaling pathway as an additional mechanism by which Six1 influences skeletal muscle metabolism.

Hypovitaminosis D and Low T3 Syndrome: A Link for Therapeutic Challenges in Patients with Acute Myocardial Infarction

Background and Aims: Vitamin D counteracts the reduction in the peripheral conversion of tiroxine (T4) into triiodothyronine (T3), which is the mechanism of low T3 syndrome (LT3) in acute myocardial infarction (AMI). The aim of this study was to assess the relationship between LT3 and hypovitaminosis D in AMI patients. Methods and Results: One hundred and twenty-four AMI patients were enrolled. Blood samples were taken at admission, and at 3, 12, 24, 48, and 72 h after admission. LT3 was defined as a value of fT3 ≤ 2.2 pg/mL, occurring within 3 days of hospital admission. Levels were defined as follows: sufficiency as a value of ±30 ng/mL, vitamin D insufficiency as 25-hydroxyvitamin D (25(OH)D) between 21 and 29 ng/mL, deficiency in 25(OH)D as below 20 ng/mL, and severe deficiency as values under 10 ng/mL. The percentage of subjects with severe 25(OH)D deficiency was significantly higher in the LT3 group (33% vs. 13%, p < 0.01). When LT3S was evaluated as a dependent variable, severe 25(OH)D deficiency (OR 2.6: 95%CI 1–6.7, p < 0.05) remained as an independent determinant after logistic multivariate adjustment together with age (>69 yrs, 50th percentile; OR 3.4, 95% CI 1.3–8.3, p < 0.01), but not female gender (OR 1.7, 95% CI 0.7–4.2, p = ns). Conclusions: This pilot study shows a relationship between hypovitaminosis D and LT3 in AMI patients. This association opens potential therapeutic challenges concerning the restoration of euthyroidism through vitamin D administration, together with the normalization of hypovitaminosis.

Selenoprotein DIO2 Is a Regulator of Mitochondrial Function, Morphology and UPRmt in Human Cardiomyocytes

Members of the fetal-gene-program may act as regulatory components to impede deleterious events occurring with cardiac remodeling, and constitute potential novel therapeutic heart failure (HF) targets. Mitochondrial energy derangements occur both during early fetal development and in patients with HF. Here we aim to elucidate the role of DIO2, a member of the fetal-gene-program, in pluripotent stem cell (PSC)-derived human cardiomyocytes and on mitochondrial dynamics and energetics, specifically. RNA sequencing and pathway enrichment analysis was performed on mouse cardiac tissue at different time points during development, adult age, and ischemia-induced HF. To determine the function of DIO2 in cardiomyocytes, a stable human hPSC-line with a DIO2 knockdown was made using a short harpin sequence. Firstly, we showed the selenoprotein, type II deiodinase (DIO2): the enzyme responsible for the tissue-specific conversion of inactive (T4) into active thyroid hormone (T3), to be a member of the fetal-gene-program. Secondly, silencing DIO2 resulted in an increased reactive oxygen species, impaired activation of the mitochondrial unfolded protein response, severely impaired mitochondrial respiration and reduced cellular viability. Microscopical 3D reconstruction of the mitochondrial network displayed substantial mitochondrial fragmentation. Summarizing, we identified DIO2 to be a member of the fetal-gene-program and as a key regulator of mitochondrial performance in human cardiomyocytes. Our results suggest a key position of human DIO2 as a regulator of mitochondrial function in human cardiomyocytes.

The Impact of Selenium Deficiency on Cardiovascular Function

Selenium (Se) is an essential trace element that is necessary for various metabolic processes, including protection against oxidative stress, and proper cardiovascular function. The role of Se in cardiovascular health is generally agreed upon to be essential yet not much has been defined in terms of specific functions. Se deficiency was first associated with Keshan’s Disease, an endemic disease characterized by cardiomyopathy and heart failure. Since then, Se deficiency has been associated with multiple cardiovascular diseases, including myocardial infarction, heart failure, coronary heart disease, and atherosclerosis. Se, through its incorporation into selenoproteins, is vital to maintain optimal cardiovascular health, as selenoproteins are involved in numerous crucial processes, including oxidative stress, redox regulation, thyroid hormone metabolism, and calcium flux, and inadequate Se may disrupt these processes. The present review aims to highlight the importance of Se in cardiovascular health, provide updated information on specific selenoproteins that are prominent for proper cardiovascular function, including how these proteins interact with microRNAs, and discuss the possibility of Se as a potential complemental therapy for prevention or treatment of cardiovascular disease.

Protective Effects of Thyroid Hormone Deprivation on Progression of Maladaptive Cardiac Hypertrophy and Heart Failure

Purpose: Thyroid hormones (TH) play a central role for cardiac function. TH influence heart rate and cardiac contractility, and altered thyroid function is associated with increased cardiovascular morbidity and mortality. The precise role of TH in onset and progression of heart failure still requires clarification. Methods: Chronic left ventricular pressure overload was induced in mouse hearts by transverse aortic constriction (TAC). One week after TAC, alteration of TH status was induced and the impact on cardiac disease progression was studied longitudinally over 4 weeks in mice with hypo- or hyperthyroidism and was compared to euthyroid TAC controls. Serial assessment was performed for heart function (2D M-mode echocardiography), heart morphology (weight, fibrosis, and cardiomyocyte cross-sectional area), and molecular changes in heart tissues (TH target gene expression, apoptosis, and mTOR activation) at 2 and 4 weeks. Results: In diseased heart, subsequent TH restriction stopped progression of maladaptive cardiac hypertrophy and improved cardiac function. In contrast and compared to euthyroid TAC controls, increased TH availability after TAC propelled maladaptive cardiac growth and development of heart failure. This was accompanied by a rise in cardiomyocyte apoptosis and mTOR pathway activation. Conclusion: This study shows, for the first time, a protective effect of TH deprivation against progression of pathological cardiac hypertrophy and development of congestive heart failure in mice with left ventricular pressure overload. Whether this also applies to the human situation needs to be determined in clinical studies and would infer a critical re-thinking of management of TH status in patients with hypertensive heart disease.

Cardiac retinoic acid levels decline in heart failure

Although low circulating levels of the vitamin A metabolite, all-trans retinoic acid (ATRA), are associated with increased risk of cardiovascular events and all-cause mortality, few studies have addressed whether cardiac retinoid levels are altered in the failing heart. Here, we showed that proteomic analyses of human and guinea pig heart failure (HF) were consistent with a decline in resident cardiac ATRA. Quantitation of the retinoids in ventricular myocardium by mass spectrometry revealed 32% and 39% ATRA decreases in guinea pig HF and in patients with idiopathic dilated cardiomyopathy (IDCM), respectively, despite ample reserves of cardiac vitamin A. ATRA (2 mg/kg/d) was sufficient to mitigate cardiac remodeling and prevent functional decline in guinea pig HF. Although cardiac ATRA declined in guinea pig HF and human IDCM, levels of certain retinoid metabolic enzymes diverged. Specifically, high expression of the ATRA-catabolizing enzyme, CYP26A1, in human IDCM could dampen prospects for an ATRA-based therapy. Pertinently, a pan-CYP26 inhibitor, talarozole, blunted the impact of phenylephrine on ATRA decline and hypertrophy in neonatal rat ventricular myocytes. Taken together, we submit that low cardiac ATRA attenuates the expression of critical ATRA-dependent gene programs in HF and that strategies to normalize ATRA metabolism, like CYP26 inhibition, may have therapeutic potential.

[Use of thyroid hormones in the treatment of cardiovascular diseases: literature review]

Cardiovascular diseases remain the leading cause of death all over the world. Thyroid hormones play a significant role in the regulation of cardiac function. According to a number of researches, patients with cardiovascular diseases usually have a decrease in the concentration of thyroid hormones in the blood serum, which may be associated with a poor prognosis. Today it still remains unclear whether the change in the bioavailability of thyroid hormones in the myocardium is a favorable physiological mechanism or a replication of an adaptation disorder. Experimental researches suggest that thyroid hormone therapy may be applied in clinical cardiology. This review describes the results of researches examining the use of thyroid hormones in patients with cardiovascular diseases, as well as experiment data on animal models. The available data on the use of thyroid hormones in patients with acute myocardial infarction and heart failure allow us to suggest that normalization of thyroid hormone levels is a safe and potentially effective treatment method in the group of patients with cardiovascular disease. At the same time, the data on the use of thyroid hormones in patients who have undergone an open-heart surgery or heart transplantation are limited. However, at present, it is difficult to draw unambiguous conclusions about the benefits, as well as about the possible risk of using thyroid hormones in the described conditions. Large-scale clinical researches are required to confirm the safety and evaluate the effectiveness of such therapy. Moreover, it is necessary to set parameters for evaluating the safety and effectiveness and understand which hormone (thyroxine or triiodothyronine), what dosage and at what stage of the disease should be applied. Until we do not have answers for these questions, thyroid hormone therapy in patients with cardiovascular diseases should remain within the research field.

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.

Nonthyroidal Illness Syndrome and Hypothyroidism in Ischemic Heart Disease Population: A Systematic Review and Meta-Analysis

CONTEXT

The association of non-thyroidal illness syndrome (NTIS) and hypothyroidism with the prognosis in ischemic heart disease (IHD) population is inconclusive.

OBJECTIVE

We aimed to evaluate the influence of NTIS and hypothyroidism on all-cause mortality and major adverse cardiac events (MACE) in IHD population.

DATA SOURCES

We searched PubMed, EMBASE, Scopus, Web of Science, and Cochrane Library from inception through February 17, 2020.

STUDY SELECTION

Original articles enrolling IHD patients, comparing all-cause mortality and MACE of NTIS and hypothyroidism with those of euthyroidism, and providing sufficient information for meta-analysis were considered eligible.

DATA EXTRACTION

Relevant information and numerical data were extracted for methodological assessment and meta-analysis.

DATA SYNTHESIS

Twenty-three studies were included. The IHD population with NTIS was associated with higher risk of all-cause mortality (hazard ratio [HR] = 2.61; 95% confidence interval [CI] = 1.89-3.59) and MACE (HR = 2.22; 95% CI = 1.71-2.89) than that without. In addition, the IHD population with hypothyroidism was also associated with higher risk of all-cause mortality (HR = 1.47; 95% CI = 1.10-1.97) and MACE (HR = 1.53; 95% CI = 1.19-1.97) than that without. In the subgroup analysis, the acute coronary syndrome (ACS) subpopulation with NTIS was associated with higher risk of all-cause mortality (HR = 3.30; 95% CI = 2.43-4.48) and MACE (HR = 2.19; 95% CI = 1.45-3.30). The ACS subpopulation with hypothyroidism was also associated with higher risk of all-cause mortality (HR = 1.67; 95% CI = 1.17-2.39).

CONCLUSIONS

The IHD population with concomitant NTIS or hypothyroidism was associated with higher risk of all-cause mortality and MACE. Future research is required to provide evidence of the causal relationship and to elucidate whether normalizing thyroid function parameters can improve prognosis.

BNP as a New Biomarker of Cardiac Thyroid Hormone Function

Background

Cardiac re-expression of fetal genes in patients with heart failure (HF) suggests the presence of low cardiac tissue thyroid hormone (TH) function. However, serum concentrations of T3 and T4 are often normal or subclinically low, necessitating an alternative serum biomarker for low cardiac TH function to guide treatment of these patients. The clinical literature suggests that serum Brain Natriuretic Peptide (BNP) levels are inversely associated with serum triiodo-L-thyronine (T3) levels. The objective of this study was to investigate BNP as a potential serum biomarker for TH function in the heart.

Methods

Two animal models of thyroid hormone deficiency: (1) 8-weeks of propyl thiouracil-induced hypothyroidism (Hypo) in adult female rats were subsequently treated with oral T3 (10 μg/kg/d) for 3, 6, or 14 days; (2) HF induced by coronary artery ligation (myocardial infarction, MI) in adult female rats was treated daily with low dose oral T3 (5 μg/kg/d) for 8 or 16 wks.

Results

Six days of T3 treatment of Hypo rats normalized most cardiac functional parameters. Serum levels of BNP increased 5-fold in Hypo rats, while T3 treatment normalized BNP by day 14, showing a significant inverse relationship between serum BNP and free or total T3 concentrations. Myocardial BNP mRNA was increased 2.5-fold in Hypo rats and its expression was decreased to normal values by 14 days of T3 treatment. Measurements of hemodynamic function showed significant dysfunction in MI rats after 16 weeks, with serum BNP increased by 4.5-fold and serum free and total T3 decreased significantly. Treatment with T3 decreased serum BNP while increasing total T3 indicating an inverse correlation between these two biologic factors (r ² = 0.676, p < 0.001). Myocardial BNP mRNA was increased 5-fold in MI rats which was significantly decreased by T3 over 8 to 16 week treatment periods.

Conclusions

Results from the two models of TH dysfunction confirmed an inverse relationship between tissue and serum T3 and BNP, such that the reduction in serum BNP could potentially be utilized to monitor efficacy and dosing of T3 treatment. Thus, serum BNP may serve as a reliable biomarker for cardiac TH function.

Adverse transverse-tubule remodeling in a rat model of heart failure is attenuated with low-dose triiodothyronine treatment

Abstract

Pre-clinical animal studies have shown that triiodothyronine (T3) replacement therapy improves cardiac contractile function after myocardial infarction (MI). We hypothesized that T3 treatment could prevent adverse post-infarction cardiomyocyte remodeling by maintaining transverse-tubule (TT) structures, thus improving calcium dynamics and contractility.

Methods

Myocardial infarction (MI) or sham surgeries were performed on female Sprague-Dawley rats (aged 12 wks), followed by treatment with T3 (5μg/kg/d) or vehicle in drinking water for 16 wks (n = 10–11/group). After in vivo echocardiographic and hemodynamic analyses, left ventricular myocytes were isolated by collagenase digestion and simultaneous calcium and contractile transients in single cardiomyocytes were recorded using IonOptix imaging. Live cardiomyocytes were stained with AlexaFluor-488 conjugated wheat germ agglutinin (WGA-488) or di-8-ANEPPS, and multiple z-stack images per cell were captured by confocal microscopy for analysis of TT organization. RTqPCR and immunoblot approaches determined expression of TT proteins.

Results

Echocardiography and in vivo hemodynamic measurements showed significant improvements in systolic and diastolic function in T3- vs vehicle-treated MI rats. Isolated cardiomyocyte analysis showed significant dysfunction in measurements of myocyte relengthening in MI hearts, and improvements with T3 treatment: max relengthening velocity (Vmax, um/s), 2.984 ± 1.410 vs 1.593 ± 0.325, p < 0.05 and time to Vmax (sec), 0.233 ± 0.037 vs 0.314 ± 0.019, p < 0.001; MI + T3 vs MI + Veh, respectively. Time to peak contraction was shortened by T3 treatment (0.161 ± 0.021 vs 0.197 ± 0.011 s., p < 0.01; MI + T3 vs MI + Veh, respectively). Analysis of TT periodicity of WGA- or ANEPPS-stained cardiomyocytes indicated significant TT disorganization in MI myocytes and improvement with T3 treatment (transverse-oriented tubules (TE%): 9.07 ± 0.39 sham, 6.94 ± 0.67 MI + Veh and 8.99 ± 0.38 MI + T3; sham vs MI + Veh, p < 0.001; MI + Veh vs MI + T3, p < 0.01). Quantitative RT-PCR showed that reduced expression of BIN1 (Bridging integrator-1), Jph2 (junctophilin-2), RyR2 (ryanodine receptor) and Ca_v1.2 (L-type calcium channel) in the failing myocardium were increased by T3 and immunoblot analysis further supporting a potential T3 effect on the TT-associated proteins, BIN1 and Jph2.

In conclusion, low dose T3 treatment initiated immediately after myocardial infarction attenuated adverse TT remodeling, improved calcium dynamics and contractility, thus supporting the potential therapeutic utility of T3 treatment in heart failure.

Novel uses of thyroid hormones in cardiovascular conditions

Thyroid hormone levels are reduced in cardiovascular diseases and this phenomenon is associated with worse outcomes. It is unclear whether the changes in thyroid hormone bioavailability to the affected myocardium are beneficial or if this is a maladaptive response. Experimental studies from animal models of acute myocardial infarction (AMI) suggest that thyroid hormone treatment may be beneficial. There is limited data available on the use of thyroid hormones in patients with AMI and heart failure and this suggests that treatment to normalise thyroid hormone levels may be safe and potentially efficacious. Similarly, evidence of thyroid hormone therapy in patients undergoing cardiac surgery or during cardiac transplantation is limited. It is therefore difficult to draw any firm conclusions about benefits or risks of thyroid hormone treatment in these conditions. Large scale clinical trials of thyroid hormones in patients with cardiac conditions are required to confirm safety and evaluate efficacy. Furthermore, it needs to be elucidated which hormone to administer (thyroxine or triiodothyronine), when in the disease pathway to treat, dose of thyroid hormone to administer, and which parameters to utilise to assess safety and efficacy. Until these important questions are answered thyroid hormone therapy in cardiovascular diseases must remain within the research domain.

Short-term exercise training improves cardiac function associated to a better antioxidant response and lower type 3 iodothyronine deiodinase activity after myocardial infarction

Aims

We assessed the effects of a short-term exercise training on cardiac function, oxidative stress markers, and type 3 iodothyronine deiodinase (D3) activity in cardiac tissue of spontaneously hypertensive rats (SHR) following experimental myocardial infarction (MI).

Methods

Twenty-four SHR (aged 3 months) were allocated to 4 groups: sham+sedentary, sham+trained, MI+sedentary and MI+trained. MI was performed by permanent ligation of the coronary artery. Exercise training (treadmill) started 96 hours after MI and lasted for 4 weeks (~60% maximum effort, 4x/week and 40 min/day). Cardiac function (echocardiography), thioredoxin reductase (TRx), total carbonyl levels, among other oxidative stress markers and D3 activity were measured. A Generalized Estimating Equation was used, followed by Bonferroni’s test (p<0.05).

Results

MI resulted in an increase in left ventricular mass (p = 0.002) with decreased cardiac output (~22.0%, p = 0.047) and decreased ejection fraction (~41%, p = 0.008) as well as an increase in the carbonyl levels (p = 0.001) and D3 activity (~33%, p<0.001). Exercise training resulted in a decrease in left ventricular mass, restored cardiac output (~34%, p = 0.048) and ejection fraction (~20%, p = 0.040), increased TRx (~85%, p = 0.007) and reduced carbonyl levels (p<0.001) and D3 activity (p<0.001).

Conclusions

Our short-term exercise training helped reverse the effects of MI on cardiac function. These benefits seem to derive from a more efficient antioxidant response and lower D3 activity in cardiac tissue.

Paradigms of Dynamic Control of Thyroid Hormone Signaling

Thyroid hormone (TH) molecules enter cells via membrane transporters and, depending on the cell type, can be activated (i.e., T4 to T3 conversion) or inactivated (i.e., T3 to 3,3'-diiodo-l-thyronine or T4 to reverse T3 conversion). These reactions are catalyzed by the deiodinases. The biologically active hormone, T3, eventually binds to intracellular TH receptors (TRs), TRα and TRβ, and initiate TH signaling, that is, regulation of target genes and other metabolic pathways. At least three families of transmembrane transporters, MCT, OATP, and LAT, facilitate the entry of TH into cells, which follow the gradient of free hormone between the extracellular fluid and the cytoplasm. Inactivation or marked downregulation of TH transporters can dampen TH signaling. At the same time, dynamic modifications in the expression or activity of TRs and transcriptional coregulators can affect positively or negatively the intensity of TH signaling. However, the deiodinases are the element that provides greatest amplitude in dynamic control of TH signaling. Cells that express the activating deiodinase DIO2 can rapidly enhance TH signaling due to intracellular buildup of T3. In contrast, TH signaling is dampened in cells that express the inactivating deiodinase DIO3. This explains how THs can regulate pathways in development, metabolism, and growth, despite rather stable levels in the circulation. As a consequence, TH signaling is unique for each cell (tissue or organ), depending on circulating TH levels and on the exclusive blend of transporters, deiodinases, and TRs present in each cell. In this review we explore the key mechanisms underlying customization of TH signaling during development, in health and in disease states.

Thyroid Hormones and Cardiovascular Function and Diseases

Thyroid hormone (TH) receptors are present in the myocardium and vascular tissue, and minor alterations in TH concentration can affect cardiovascular (CV) physiology. The potential mechanisms that link CV disease with thyroid dysfunction are endothelial dysfunction, changes in blood pressure, myocardial systolic and diastolic dysfunction, and dyslipidemia. In addition, cardiac disease itself may lead to alterations in TH concentrations (notably, low triiodothyronine syndrome) that are associated with higher morbidity and mortality. Experimental data and small clinical trials have suggested a beneficial role of TH in ameliorating CV disease. The aim of this review is to provide clinicians dealing with CV conditions with an overview of the current knowledge of TH perturbations in CV disease.

Curcumin ameliorated myocardial infarction by inhibition of cardiotoxicity in the rat model

Cardiovascular diseases are the main cause of death globally. Many attempts have been done to ameliorate the pathological changes after the occurrence of myocardial infarction. Curcumin is touted as a polyphenol phytocompound with appropriate cardioprotective properties. In this study, the therapeutic effect of curcumin was investigated on acute myocardial infarction in the model of rats. Rats were classified into four groups; control, isoproterenol hydrochloride (ISO) (100 mg/kbw), curcumin (50 mg/kbw), and curcumin plus ISO treatment groups. After 9-day administration of curcumin, levels of lactate dehydrogenase (LDH), creatine kinase (CK), and cardiac troponin I (cTnI) were determined. Superoxide dismutase (SOD) and malondialdehyde (MDA) contents were measured to investigate the oxidative status in infarct rats received curcumin. By using H & E staining, tissue inflammation was performed. Masson's trichrome staining was conducted to show cardiac remodeling and collagen deposition. The number of apoptotic cells was determined by using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Data showed the serum decrease of LDH, CK, and cTnI in infarct rats after curcumin intake compared to the rats given (ISO) ( P < 0.05). Curcumin was found to reduce oxidative status by reducing SOD and MDA contents ( P < 0.05). Gross and microscopic examinations revealed that the decrease of infarct area, inflammation response and collagen deposition in rats given ISO plus curcumin ( P < 0.05). We noted the superior effect of curcumin to reduce the number of apoptotic cardiomyocytes after 9 days. Data point the cardioprotective effect of curcumin to diminish the complication of infarction by the reduction of cell necrosis and apoptosis in a rat model of experimental infarction.

The Effect of Thyroid Stimulating Hormone Level Within the Reference Range on In-Hospital and Short-Term Prognosis in Acute Coronary Syndrome Patients

Background and objectives: Despite being within the normal reference range, changes in thyroid stimulating hormone (TSH) levels have negative effects on the cardiovascular system. The majority of patients admitted to hospital with acute coronary syndrome (ACS) are euthyroid. The aim of this study was to investigate the effect of TSH level on the prognosis of in-hospital and follow-up periods of euthyroid ACS patients. Materials and Methods: A total of 629 patients with acute coronary syndrome without thyroid dysfunction were included in the study. TSH levels of patients were 0.3-5.33 uIU/mL. Patients were divided into three TSH tertiles: TSH level between (1) 0.3 uIU/mL and <0.90 uIU/mL (n = 209), (2) 0.90 uIU/mL and <1.60 uIU/mL (n = 210), and (3) 1.60 uIU/mL and 5.33 uIU/mL (n = 210). Demographic, clinical laboratory, and angiographic characteristics were compared between groups in terms of in-hospital and follow-up prognosis. Results: Mean age was 63.42 ± 12.5, and 73.9% were male. There was significant difference between tertiles in terms of TSH level at admission (p < 0.001), the severity of coronary artery disease (p = 0.024), in-hospital mortality (p < 0.001), in-hospital major hemorrhage (p = 0.005), total adverse clinical event (p = 0.03), follow-up mortality (p = 0.022), and total mortality (p < 0.001). In multivariate logistic regression analysis, the high-normal TSH tertile was found to be cumulative mortality increasing factor (OR = 6.307, 95%; CI: 1.769-22.480; p = 0.005) during the 6-month follow-up period after hospitalization and discharge. Conclusions: High-normal TSH tertile during hospital admission in euthyroid ACS patients is an independent predictor of total mortality during the 6-month follow-up period after hospitalization and discharge.

The Management of Thyroid Abnormalities in Chronic Heart Failure

The cardiovascular system is one of the main targets of thyroid hormone action, and triiodothyronine deficiency has crucial consequences on cardiac structure and function. Patients with overt or subclinical hypothyroidism should be treated with levothyroxine to improve their cardiovascular function and the potential risk of heart failure. Even patients with thyroid hormone deficiency and heart failure should receive replacement doses of levothyroxine to improve their prognosis and worsening of the cardiovascular function. An innovative therapeutic multifactorial approach could improve the progression of heart failure. There is a potential beneficial effect of thyroid hormones and their analogs in patients with heart failure.

Association between Low Free Triiodothyronine Levels and Poor Prognosis in Patients with Acute ST-Elevation Myocardial Infarction

Background

Low free triiodothyronine (fT3) levels are generally associated with poor prognosis in patients with heart diseases, but this is controversial and there is a lack of data about ST-elevation myocardial infarction (STEMI) in Chinese patients.

Objective

To assess the association between fT3 levels and the prognosis of patients with STEMI.

Methods

This was a prospective observational study of 699 consecutive patients with STEMI treated at the Xinqiao Hospital between January 1, 2013, and December 31, 2014. The patients were divided into the low fT3 (fT3 < 3.1 pmol/L; n = 179, 27.5%) and normal fT3 (fT3 ≥ 3.1 pmol/L; n = 473, 72.5%) groups according to fT3 levels at admission. Patients were followed up at 1, 3, 6, and 12 months for all-cause death and major adverse cardiac events (MACE).

Results

During the 1-year follow-up, there were 70 all-cause deaths (39.1%) in the low fT3 group and 40 (8.5%) in the normal fT3 group (P < 0.001). MACE occurred in 105 patients (58.7%) in the low fT3 group and 74 (15.6%) in the normal fT3 group (P < 0.001). Multivariate Cox proportional hazards regression analysis indicated that fT3 levels were independently associated with 30-day and 1-year all-cause death [30-day: hazard ratio (HR) = 0.702, 95% confidence interval (95% CI): 0.501–0.983, P = 0.04; 1-year: HR = 0.557, 95% CI: 0.411–0.755, P < 0.001] and MACE (30-day: HR = 0.719, 95% CI: 0.528–0.979, P = 0.036; 1-year: HR = 0.557, 95% CI: 0.445–0.698, P < 0.001).

Conclusion

Low fT3 levels were strongly associated with poor prognosis in patients with STEMI. Measurement of fT3 levels may be a valuable and simple way to identify high-risk STEMI patients.

Myocardium of patients with dilated cardiomyopathy presents altered expression of genes involved in thyroid hormone biosynthesis

Background

The association between dilated cardiomyopathy (DCM) and low thyroid hormone (TH) levels has been previously described. In these patients abnormal thyroid function is significantly related to impaired left ventricular (LV) function and increased risk of death. Although TH was originally thought to be produced exclusively by the thyroid gland, we recently reported TH biosynthesis in the human ischemic heart.

Objectives

Based on these findings, we evaluated whether the genes required for TH production are also altered in patients with DCM.

Methods

Twenty-three LV tissue samples were obtained from patients with DCM (n = 13) undergoing heart transplantation and control donors (n = 10), and used for RNA sequencing analysis. The number of LV DCM samples was increased to 23 to determine total T4 and T3 tissue levels by ELISA.

Results

We found that all components of TH biosynthesis are expressed in human dilated heart tissue. Expression of genes encoding thyroperoxidase (–2.57-fold, P < 0.05) and dual oxidase 2 (2.64-fold, P < 0.01), the main enzymatic system of TH production, was significantly altered in patients with DCM and significantly associated with LV remodeling parameters. Thyroxine (T4) cardiac tissue levels were significantly increased (P < 0.01), whilst triiodothyronine (T3) levels were significantly diminished (P < 0.05) in the patients.

Conclusions

Expression of TH biosynthesis machinery in the heart and total tissue levels of T4 and T3, are altered in patients with DCM. Given the relevance of TH in cardiac pathology, our results provide a basis for new gene-based therapeutic strategies for treating DCM.

Similarities and Differences in the Peripheral Actions of Thyroid Hormones and Their Metabolites

Thyroxine (T4) and 3,5,3'-triiodothyronine (T3) are secreted by the thyroid gland, while T3 is also generated from the peripheral metabolism of T4 by iodothyronine deiodinases types I and II. Several conditions like stress, diseases, and physical exercise can promote changes in local TH metabolism, leading to different target tissue effects that depend on the presence of tissue-specific enzymatic activities. The newly discovered physiological and pharmacological actions of T4 and T3 metabolites, such as 3,5-diiodothyronine (3,5-T2), and 3-iodothyronamine (T1AM) are of great interest. A classical thyroid hormone effect is the ability of T3 to increase oxygen consumption in almost all cell types studied. Approximately 30 years ago, a seminal report has shown that 3,5-T2 increased oxygen consumption more rapidly than T3 in hepatocytes. Other studies demonstrated that exogenous 3,5-T2 administration was able to increase whole body energy expenditure in rodents and humans. In fact, 3,5-T2 treatment prevents diabetic nephropathy, hepatic steatosis induced by high fat diet, insulin resistance, and weight gain during aging in Wistar male rats. The regulation of mitochondria is likely one of the most important actions of T3 and its metabolite 3,5-T2, which was able to restore the thermogenic program of brown adipose tissue (BAT) in hypothyroid rats, just as T3 does, while T1AM administration induced rapid hypothermia. T3 increases heart rate and cardiac contractility, which are hallmark effects of hyperthyroidism involved in cardiac arrhythmia. These deleterious cardiac effects were not observed with the use of 3,5-T2 pharmacological doses, and in contrast T1AM was shown to promote a negative inotropic and chronotropic action at micromolar concentrations in isolated hearts. Furthermore, T1AM has a cardioprotective effect in a model of ischemic/reperfusion injury in isolated hearts, such as occurs with T3 administration. Despite the encouraging possible therapeutic use of TH metabolites, further studies are needed to better understand their peripheral effects, when compared to T3 itself, in order to establish their risk and benefit. On this basis, the main peripheral effects of thyroid hormones and their metabolites in tissues, such as heart, liver, skeletal muscle, and BAT are discussed herein.

The classic pathways of thyroid hormone metabolism

Thyroid hormones (TH) are crucial for growth and development and play an important role in energy homeostasis. Although serum TH levels are relatively constant in the physiological state, TH bioavailability at the tissue and cellular level is dependent on local TH metabolism. Circulating TH produced by the thyroid can be metabolized by a number of different pathways resulting in 1) activation of TH 2) deactivation of TH or 3) excretion of TH and subsequent metabolites. These pathways play an essential role in determining local TH levels and action. The major classical pathways of TH metabolism are deiodination, sulfation, glucuronidation, and ether-link cleavage. This review provides an overview of these pathways, their relative contributions to TH levels in the serum and in various organs and the changes in these pathways elicited by fasting and illness.

Role of the Bile Acid Transporter SLC10A1 in Liver Targeting of the Lipid-Lowering Thyroid Hormone Analog Eprotirome

The thyroid hormone (TH) analog eprotirome (KB2115) was developed to lower cholesterol through selective activation of the TH receptor (TR) β1 in the liver. Interestingly, eprotirome shows low uptake in nonhepatic tissues, explaining its lipid-lowering action without adverse extrahepatic thyromimetic effects. Clinical trials have shown marked decreases in serum cholesterol levels. We explored the transport of eprotirome across the plasma membrane by members of three TH transporter families: monocarboxylate transporters MCT8 and MCT10; Na-independent organic anion transporters 1A2, 1B1, 1B3, 1C1, 2A1, and 2B1; and Na-dependent organic anion transporters SLC10A1 to SLC10A7. Cellular transport was studied in transfected COS1 cells using [14C]eprotirome and [125I]TH analogs. Of the 15 transporters tested initially, the liver-specific bile acid transporter SLC10A1 showed the highest eprotirome uptake (greater than a sevenfold induction after 60 minutes) as well as TRβ1-mediated transcriptional activity. Uptake of eprotirome by SLC10A1 was Na+ dependent and saturable with a Michaelis constant of 8 μM. Eprotirome transport was inhibited by known substrates for SLC10A1 (e.g., cholate and taurocholate), and by TH analogs such as triiodothyropropionic acid and triiodothyroacetic acid. However, no significant SLC10A1-mediated transport was observed of these [125I]TH analogs. We also studied the plasma disappearance and biliary excretion of [14C]eprotirome injected in control and Slc10a1 knockout mice. Although eprotirome is also transported by mouse Slc10a1, the pharmacokinetics of eprotirome were not affected by Slc10a1 deficiency. In conclusion, we have demonstrated that the liver-specific bile acid transporter SLC10A1 effectively transports eprotirome. However, Slc10a1 does not appear to be critical for the liver targeting of this TH analog in mice. Therefore, the importance of SLC10A1 for liver uptake of eprotirome in humans remains to be elucidated.

Cardiac Thyroid Hormone Metabolism and Heart Failure

The heart is a principal target of thyroid hormone, and a reduction of cardiac thyroid hormone signaling is thought to play a role in pathological ventricular remodeling and the development of heart failure. Studies in various rodent models of heart disease have identified increased activity of cardiac type III deiodinase as a possible cause of diminished levels and action of thyroid hormone. Recent data indicate novel mechanisms underlying the induction of this thyroid hormone-degrading enzyme in the heart as well as post-transcriptional regulation of its expression by microRNAs. In addition, the relevance of diminished thyroid hormone signaling for cardiac remodeling is suggested to include miRNA-mediated effects on pathological signaling pathways. These and other recent studies are reviewed and discussed in the context of other processes and factors that have been implicated in the reduction of cardiac thyroid hormone signaling in heart failure.

Effects of Total Flavone from Rhododendron simsii Planch. Flower on Postischemic Cardiac Dysfunction and Cardiac Remodeling in Rats

This study investigated the effect of total flavone from Rhododendron simsii Planch. flower (TFR) on postischemic cardiac dysfunction and ventricular remodeling and was to test the hypothesis that TFR has an antiventricular remodeling effect through inhibition of urotensin-II receptor- (UTR-) mediated activation of RhoA-ROCK pathways. Twenty-four hours after ligation of the left anterior descending coronary artery, male Sprague-Dawley rats were randomized to receive 4-week treatment with saline (model group) or TFR. Compared to the model group, TFR treatment restored cardiac function, attenuated cardiomyocyte hypertrophy, and reduced interstitial fibrosis. Expression levels of several fibrosis-related factors, including alpha-smooth muscle actin, transforming growth factor-beta 1, matrix metalloproteinase-2, and collagen type I, were increased after MI. TFR treatment attenuated the upregulation of these factors, downregulated UTR expression, and markedly diminished the expression of RhoA and ROCK1/2. These results suggested that TFR could improve cardiac function and ameliorate ventricular remodeling through blocking UTR-mediated activation of RhoA-ROCK pathways in myocardial infarction rats.

Myocardial Inactivation of Thyroid Hormones in Patients with Aortic Stenosis

OBJECTIVE

The human heart expresses the type 2 deiodinase (D2) that activates thyroxine (T4) to triiodothyronine (T3). At the same time, the inactivating type 3 deiodinase (D3) has been found in a rat model of right ventricular hypertrophy. It is not known whether the human myocardium metabolizes thyroid hormone. This study examined myocardial thyroid hormone metabolism in patients with aortic valve stenosis (AS) undergoing aortic valve replacement and in patients with coronary artery disease (CAD) undergoing coronary artery bypass grafting surgery.

METHODS

Myocardial thyroid hormone metabolism was assessed by analyzing the difference in serum thyroid hormone levels between the aortic root (incoming blood) and the coronary sinus (outgoing blood) of patients undergoing cardiac surgery. A total of 23 patients with AS and 35 patients with CAD were included. Patients received a pre-surgical echocardiogram, and pre-, during and post-surgical thyroid hormone serum levels were collected in the myocardial and peripheral circulations.

RESULTS

Patients with AS exhibited the expected left ventricle (LV) hypertrophy (i.e., 20-30% increase in LV posterior wall and interventricular septum thickness and ∼10% increase in AS in LV diastolic diameter). Immediately before cardiopulmonary bypass, blood flowing through the AS myocardium exhibited a 4.6% reduction in T3 and 6.9% increase in rT3 levels, decreasing the serum T3/rT3 ratio by 9.6%. T4 and thyrotropin serum levels remained similar between the aortic root and coronary sinus. In contrast, no myocardial thyroid hormone metabolism was observed in CAD patients. Notably, the AS myocardium lost the ability to inactivate thyroid hormone after cardiopulmonary bypass, possibly due to myocardial stunning.

CONCLUSIONS

There is accelerated thyroid hormone inactivation in the AS myocardium, which is likely the result of D3 expression. No evidence to suggest thyroid hormone activation in the myocardium was obtained in the present study.

Myocardial Induction of Type 3 Deiodinase in Dilated Cardiomyopathy

BACKGROUND

The thyroid hormone-inactivating enzyme type 3 deiodinase (D3) is induced during hypertrophic and ischemic cardiomyopathy, leading to a state of local cardiac hypothyroidism. Whether D3 induction occurs in dilated cardiomyopathy is unknown.

METHODS

This study characterized changes in cardiac D3 and thyroid hormone signaling in a transgenic model of progressive dilated cardiomyopathy (TG9 mice).

RESULTS

Cardiac D3 was dramatically induced 15-fold during the progression of dilated cardiomyopathy in TG9 mice. This D3 induction localized to cardiomyocytes and was associated with a decrease in myocardial thyroid hormone signaling.

CONCLUSIONS

Cardiac D3 is induced in a mouse model of dilated cardiomyopathy, indicating that D3 induction may be a general response to diverse forms of cardiomyopathy.

Free Triiodothyronine Level Correlates with Myocardial Injury and Prognosis in Idiopathic Dilated Cardiomyopathy: Evidence from Cardiac MRI and SPECT/PET Imaging

Thyroid dysfunction is associated with poor prognosis in heart failure, but theories of mechanisms are mainly based on animal experiments, not on human level. We aimed to explore the relation between thyroid function and myocardial injuries in idiopathic dilated cardiomyopathy (IDCM) using cardiac magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Myocardial fibrosis was detected by late gadolinium enhancement (LGE) MRI, and myocardial perfusion/metabolism was evaluated by ^99mTc-MIBI SPECT /¹⁸F-FDG PET imaging. Across the quartiles of FT3, decreased percentage of segments with LGE and perfusion/metabolism abnormalities were found. As for FT4 and TSH levels, no significant distribution trend of myocardial injuries could be detected. In logistic analysis, FT3 was independently associated with the presence of LGE (OR: 0.140, 95% CI: 0.035-0.567), perfusion abnormalities (OR: 0.172, 95% CI: 0.040-0.738) and metabolism abnormalities (OR: 0.281, 95% CI: 0.081-0.971). After a median follow-up of 46 months, LGE-positive and FT3 < 2.77 pg/mL was identified as the strongest predictor of cardiac events (HR: 8.623, 95% CI: 3.626-16.438). Low FT3 level is associated with myocardial fibrosis and perfusion/metabolism abnormalities in patients with IDCM. The combination of FT3 level and LGE provides useful information for assessing the prognosis of IDCM.

Effects of thyroid hormone transporters MCT8 and MCT10 on nuclear activity of T3

Transport of thyroid hormone (TH) across the plasma membrane is necessary for the genomic action of T3 mediated by its nuclear T3 receptor. MCT8 and MCT10 have been identified as important TH transporters. Mutations in MCT8 result in severe psychomotor retardation. In addition to TH transport into the cell, MCT8 and MCT10 also facilitate TH efflux from cells. Therefore, the aim of this study was to examine if MCT8 and MCT10 increase the availability of T3 for its nuclear receptor rather than generate a rapid equilibrium between cellular and serum T3. T3 action was investigated in JEG3 cells co-transfected with TRβ1 and a T3 response element-driven luciferase construct, and T3 metabolism was analyzed in cells transfected with type 3 deiodinase (D3). In addition, cells were transfected with MCT8 or MCT10 and/or the cytoplasmic T3-binding protein mu-crystallin (CRYM). Luciferase signal was markedly stimulated by incubating cells for 24 h with 1 nM T3, but this response was not augmented by MCT8 or MCT10 expression. Limiting the time of T3 exposure to 1-6 h and co-transfection with CRYM allowed for a modest increase in luciferase response to T3. In contrast, T3 metabolism by D3 was potently stimulated by MCT8 or MCT10 expression, but it was not affected by expression of CRYM. These results suggest that MCT8 and MCT10 by virtue of their bidirectional T3 transport have less effect on steady-state nuclear T3 levels than on T3 levels at the cell periphery where D3 is located. CRYM alters the dynamics of cellular TH transport but its exact function in the cellular distribution of TH remains to be determined.

Thyroid hormones and cardiovascular disease

Myocardial and vascular endothelial tissues have receptors for thyroid hormones and are sensitive to changes in the concentrations of circulating thyroid hormones. The importance of thyroid hormones in maintaining cardiovascular homeostasis can be deduced from clinical and experimental data showing that even subtle changes in thyroid hormone concentrations - such as those observed in subclinical hypothyroidism or hyperthyroidism, and low triiodothyronine syndrome - adversely influence the cardiovascular system. Some potential mechanisms linking the two conditions are dyslipidaemia, endothelial dysfunction, blood pressure changes, and direct effects of thyroid hormones on the myocardium. Several interventional trials showed that treatment of subclinical thyroid diseases improves cardiovascular risk factors, which implies potential benefits for reducing cardiovascular events. Over the past 2 decades, accumulating evidence supports the association between abnormal thyroid function at the time of an acute myocardial infarction (MI) and subsequent adverse cardiovascular outcomes. Furthermore, experimental studies showed that thyroid hormones can have an important therapeutic role in reducing infarct size and improving myocardial function after acute MI. In this Review, we summarize the literature on thyroid function in cardiovascular diseases, both as a risk factor as well as in the setting of cardiovascular diseases such as heart failure or acute MI, and outline the effect of thyroid hormone replacement therapy for reducing the risk of cardiovascular disease.

Depressed Myocardial Contractility: Can It Be Rescued?

Current dogma suggests patients with advanced systolic heart failure have an irreversible depression in myocardial contractility. Recent experience with improved ventricular function during continuous flow ventricular assist devices used as destination therapy would suggest otherwise. Herein, cellular and molecular signaling involved in reversing depressed myocardial contractility would be addressed. This includes cardiomyocyte thyroid hormone signaling responsible for the reexpression of fetal gene program that preserves cell efficiency (work and energy consumed) and the rescue of an endogenous population of atrophic myocytes bordering on microdomains of fibrosis to improve contractile mass.

3,3',5-triiodothyroxine inhibits apoptosis and oxidative stress by the PKM2/PKM1 ratio during oxygen-glucose deprivation/reperfusion AC16 and HCM-a cells: T3 inhibits apoptosis and oxidative stress by PKM2/PKM1 ratio

Oxidative stress (OS) plays a crucial role in the development of myocardial disease, which can induce the dysfunction of cardiac muscle cells. 3,3',5-triiodothyroxine (T3) is a hormone secreted from the thyroid gland that has been shown to protect cells by improving the redox state and to regulate the expression of pyruvate kinase muscle isozyme (PKM, including two isoforms PKM1 and PKM2). The present study aimed to reveal the key effects of T3 on protecting human myocardial cell lines from oxidative stress and the downstream molecular mechanism. An oxygen-glucose deprivation/reperfusion model (OGDR) and three subtypes of the deiodinase family (DIO1, DIO2, and DIO3), which convert thyroxine (T4) to T3, were tested in this model. Our results show that the expression of DIO1, DIO2 and T3 was downregulated, but DIO3 was upregulated in OGDR-treated AC16 and HCM-a cells. Then, OGDR-treated cells were treated with T3 and T4. The results show that T3 inhibited the expression of reactive oxygen species (ROS) and malonic dialdehyde (MDA), but upregulated glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD). The effects of T4 were not notable. T3 also protected OGDR cells from apoptosis and upregulated the PKM2/PKM1 ratio. Further mechanistic studies found that PKM2 inhibition by small interfering RNA (siRNA) could attenuate the anti-OS and anti-apoptotic effects of T3. These findings suggest that T3 can inhibit apoptosis and oxidative stress in OGDR-treated AC16 and HCM-a cells by regulating the PKM2/PKM1 ratio.

Safe Oral Triiodo-L-Thyronine Therapy Protects from Post-Infarct Cardiac Dysfunction and Arrhythmias without Cardiovascular Adverse Effects

Background

A large body of evidence suggests that thyroid hormones (THs) are beneficial for the treatment of cardiovascular disorders. We have shown that 3 days of triiodo-L-thyronine (T3) treatment in myocardial infarction (MI) rats increased left ventricular (LV) contractility and decreased myocyte apoptosis. However, no clinically translatable protocol is established for T3 treatment of ischemic heart disease. We hypothesized that low-dose oral T3 will offer safe therapeutic benefits in MI.

Methods and Results

Adult female rats underwent left coronary artery ligation or sham surgeries. T3 (~6 μg/kg/day) was available in drinking water ad libitum immediately following MI and continuing for 2 month(s) (mo). Compared to vehicle-treated MI, the oral T3-treated MI group at 2 mo had markedly improved anesthetized Magnetic Resonance Imaging-based LV ejection fraction and volumes without significant negative changes in heart rate, serum TH levels or heart weight, indicating safe therapy. Remarkably, T3 decreased the incidence of inducible atrial tachyarrhythmias by 88% and improved remodeling. These were accompanied by restoration of gene expression involving several key pathways including thyroid, ion channels, fibrosis, sympathetic, mitochondria and autophagy.

Conclusions

Low-dose oral T3 dramatically improved post-MI cardiac performance, decreased atrial arrhythmias and cardiac remodeling, and reversed many adverse changes in gene expression with no observable negative effects. This study also provides a safe and effective treatment/monitoring protocol that should readily translate to humans.

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.

Resistance to Thyroid Hormone Alpha in an 18-Month-Old Girl: Clinical, Therapeutic, and Molecular Characteristics

BACKGROUND

Recently, the first patients with resistance to thyroid hormone alpha (RTHα) due to inactivating mutations in the thyroid hormone receptor alpha (TRα) were identified. These patients are characterized by growth retardation, variable motor and cognitive defects, macrocephaly, and abnormal thyroid function tests. The objective was to characterize a young girl (18 months old) with a mutation in both TRα1 and TRα2, and to study the effects of early levothyroxine (LT4) treatment.

METHODS

The patient was assessed clinically and biochemically before and during 12 months of LT4 treatment. In addition, the consequences of the mutation for TRα1/2 receptor function were studied in vitro.

RESULTS

At 18 months of age, the patient presented with axial hypotonia, delayed motor development, severe growth retardation, and abnormally elevated triiodothyronine (T3)/thyroxine (T4) ratios. RTHα was suspected, and concomitantly a c.632A>G/p.D211G missense mutation was identified, affecting both the TRα1 and TRα2 proteins. This mutation was also found in the girl's father. LT4 treatment was started, resulting in a marked improvement of her hypotonia, motor skills, and growth. Functionally, the missense mutation led to decreased transcriptional activity of TRα1, which could be overcome by higher T3 levels in vitro. The mutant TRα1 showed a moderate dominant negative activity on wild type (WT) TRα1. In contrast, WT TRα2 and mutant TRα2 had negligible transcriptional activity and showed no dominant-negative effect over TRα1.

CONCLUSIONS

This report describes the phenotype of a young RTHα patient with a mild TRα mutation before and during early LT4 treatment. Treatment had beneficial effects on her muscle tone, motor development, and growth.

Myofibroblast secretome and its auto-/paracrine signaling

Myofibroblasts (myoFb) are phenotypically transformed, contractile fibroblast-like cells expressing α-smooth muscle actin microfilaments. They are integral to collagen fibrillogenesis with scar tissue formation at sites of repair irrespective of the etiologic origins of injury or tissue involved. MyoFb can persist long after healing is complete, where their ongoing turnover of collagen accounts for a progressive structural remodeling of an organ (a.k.a. fibrosis, sclerosis or cirrhosis). Such persistent metabolic activity is derived from a secretome consisting of requisite components in the de novo generation of angiotensin (Ang) II. Autocrine and paracrine signaling induced by tissue AngII is expressed via AT1 receptor ligand binding to respectively promote: i) regulation of myoFb collagen synthesis via the fibrogenic cytokine TGF-β1-Smad pathway; and ii) dedifferentiation and protein degradation of atrophic myocytes immobilized and ensnared by fibrillar collagen at sites of scarring. Several cardioprotective strategies in the prevention of fibrosis and involving myofibroblasts are considered. They include: inducing myoFb apoptosis through inactivation of antiapoptotic proteins; AT1 receptor antagonist to interfere with auto-/paracrine myoFb signaling or to induce counterregulatory expression of ACE2; and attacking the AngII-AT1R-TGF-β1-Smad pathway by antibody or the use of triplex-forming oligonucleotides.