Inhibition of thyroid hormone receptor α1 impairs post-ischemic cardiac performance after myocardial infarction in mice

Thyroid hormone treatment counteracts cellular phenotypical remodeling in diabetic organs

Diabetes mellitus and alterations in thyroid hormone (TH) signaling are closely linked. Though the role of TH signaling in cell differentiation and growth is well known, it remains unclear whether its alterations contribute to the pathobiology of diabetic cells. Here, we aim to investigate whether the administration of exogenous T3 can counteract the cellular remodeling that occurs in diabetic cardiomyocytes, podocytes, and pancreatic beta cells. Treating diabetic rats with T3 prevents dedifferentiation, pathological growth, and ultrastructural alterations in podocytes and cardiomyocytes. In vitro, T3 reverses glucose-induced growth in human podocytes and cardiomyocytes, restores cardiomyocyte cytoarchitecture, and reverses pathological alterations in kidney and cardiac organoids. Finally, T3 treatment counteracts glucose-induced transdifferentiation, cell growth, and loss in pancreatic beta cells through TH receptor alpha1 activation. Our studies indicate that TH signaling activation substantially counteracts diabetes-induced pathological remodeling, and provide a potential therapeutic approach for the treatment of diabetes and its complications.

Thyroid Hormone and Heart Failure: Charting Known Pathways for Cardiac Repair/Regeneration

Heart failure affects more than 64 million people worldwide, having a serious impact on their survival and quality of life. Exploring its pathophysiology and molecular bases is an urgent need in order to develop new therapeutic approaches. Thyroid hormone signaling, evolutionarily conserved, controls fundamental biological processes and has a crucial role in development and metabolism. Its active form is L-triiodothyronine, which not only regulates important gene expression by binding to its nuclear receptors, but also has nongenomic actions, controlling crucial intracellular signalings. Stressful stimuli, such as acute myocardial infarction, lead to changes in thyroid hormone signaling, and especially in the relation of the thyroid hormone and its nuclear receptor, which are associated with the reactivation of fetal development programmes, with structural remodeling and phenotypical changes in the cardiomyocytes. The recapitulation of fetal-like features of the signaling may be partially an incomplete effort of the myocardium to recapitulate its developmental program and enable cardiomyocytes to proliferate and finally to regenerate. In this review, we will discuss the experimental and clinical evidence about the role of the thyroid hormone in the recovery of the myocardium in the setting of heart failure with reduced and preserved ejection fraction and its future therapeutic implications.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Developmental changes of the fetal and neonatal thyroid gland and functional consequences on the cardiovascular system

Thyroid hormones play an important role in the development and function of the cardiac myocyte. Dysregulation of the thyroid hormone milieu affects the fetal cardiac cells via complex molecular mechanisms, either by altering gene expression or directly by affecting post-translational processes. This review offers a comprehensive summary of the effects of thyroid hormones on the developing cardiovascular system and its adaptation. Furthermore, we will highlight the gaps in knowledge and provide suggestions for future research.

Cardioprotection by Hypothyroidism Is Not Mediated by Favorable Hemodynamics-Role of Canonical Thyroid Hormone Receptor Alpha Signaling

Hypothyroidism has been shown to reduce infarct size in rats, but the underlying mechanisms are unclear. We used isolated pressure-constant perfused hearts of control, hypothyroid and hyperthyroid mice and measured infarct size, functional parameters and phosphorylation of key molecules in cardioprotective signaling with matched heart rate. Compared with controls, hypothyroidism was cardioprotective, while hyperthyroidism was detrimental with enlarged infarct size. Next, we asked how thyroid hormone receptor α (TRα) affects ischemia/reperfusion (IR) injury. Thus, canonical and noncanonical TRα signaling was investigated in the hearts of (i) mice lacking TRα (TRα0), (ii) with a mutation in TRα DNA-binding domain (TRαGS) and (iii) in hyperthyroid TRα0 (TRα0hyper) and TRαGS mice (TRαGShyper). TRα0 mouse hearts were protected against IR injury. Furthermore, infarct size was reduced in the hearts of TRαGS mice that lack canonical TRα signaling but maintain noncanonical TRα action. Hyperthyroidism did not increase infarct size in TRα0 and TRαGS mouse hearts. These cardioprotective effects were not associated with increased phosphorylation of key proteins of RISK, SAFE and eNOS pathways. In summary, chronic hypothyroidism and the lack of canonical TRα signaling are cardioprotective in IR injury and protection is not due to favorable changes in hemodynamics.

Effects of Acute Triiodothyronine Treatment in Patients with Anterior Myocardial Infarction Undergoing Primary Angioplasty: Evidence from a Pilot Randomized Clinical Trial (ThyRepair Study)

Background: Thyroid hormone has a differential action on healthy and ischemic heart. Triiodothyronine (T3) administration improved postischemic cardiac function while it limited apoptosis in experimentally induced ischemia. Thus, the present study investigated the potential effects of acute liothyronine (LT3) treatment in patients with anterior myocardial infarction. Methods: This study is a pilot, randomized, double-blind, placebo-controlled trial (ThyRepair study). We randomized 52 patients and analyzed data from 37 patients (n = 16 placebo and n = 21 LT3), per prespecified per protocol analysis. We excluded three patients who had died of cardiovascular causes (one in placebo and two in LT3 arm), four with small infarct size below a pre-specified threshold (in the placebo arm), and the rest, who lacked follow-up data. LT3 treatment started after stenting as an intravenous (i.v.) bolus injection of 0.8 μg/kg of LT3 followed by a constant infusion of 0.113 μg/kg/h i.v. for 48 hours. All patients had cardiac magnetic resonance (CMR) at hospital discharge and 6 months follow-up. The primary end point was CMR left ventricular (LV) ejection fraction (LVEF) and secondary endpoints were LV volumes, infarct volume (IV), and safety. Results: The CMR LVEF% at 6 months was 53.6 ± 9.5 for the LT3-treated group and 48.6 ± 11 for placebo, p = 0.15. Acute LT3 treatment resulted in a significantly lower LV end-diastolic volume index (92.2 ± 16.8 mL/m² vs. 107.5 ± 22.2, p = 0.022) and LV systolic volume index (47.5 ± 13.9 mL/m² vs. 61.3 ± 21.7, p = 0.024) at hospital discharge, but not at 6 months. There was no statistically significant difference in CMR IV at hospital discharge between the groups (p = 0.24). CMR IV tended to be lower in the LT3-treated group at 6 months (18.7 ± 9.5 vs. 25.9 ± 11.7, in placebo, p = 0.05). Serious, life-threatening events related to LT3 treatment were not observed. A tendency for an increased incidence of atrial fibrillation (AF) was found in the LT3 group during the first 48 hours (19% for T3 group vs. 5% for placebo, p = 0.13). Conclusion: This pilot randomized, placebo-controlled trial study suggests potential favorable effects (acute cardiac dilatation and 6-month IV) as well as potential concerns regarding a higher risk of AF after LT3 administration early after myocardial infarction, which should be tested in a larger scale study.

Revealing Calcium Signaling Pathway as Novel Mechanism of Danhong Injection for Treating Acute Myocardial Infarction by Systems Pharmacology and Experiment Validation

Introduction: Danhong injection (DHI) is a traditional Chinese medicine preparation commonly used in the clinical treatment of acute myocardial infarction (AMI). In this study, the active components of DHI and its mechanism in the treatment of AMI were investigated. Methods: The chemical components of DHI were detected by the ultra-high-performance liquid chromatography-linear trap quadrupole-orbitrap-tandem mass spectrometry (UHPLC-LTQ-Orbitrap-MS/MS), and the targets and pathways of DHI in the treatment of AMI were analyzed by systems pharmacology, which was verified by molecular docking and animal experiments. Results: A total of 12 active components of DHI were obtained, and 158 common targets of component and disease were identified by systems pharmacology. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results showed that DHI is closely related to the calcium signaling pathway in the treatment of AMI. Molecular docking showed that the key target protein has good binding affinity to related compounds. The experimental results showed that compared with the model group, LVAWs, EF, and FS significantly (p < 0.05) increased in the DHI group. The percentage of myocardial infarction significantly (p < 0.01) decreased, both in the ventricular and total cardiac regions, and the pathological damage of myocardial tissue also decreased. In addition, the expression of the protein CaMK II decreased (p < 0.01) and the expression of SERCA significantly increased (p < 0.01). Conclusion: This study revealed that ferulic acid, caffeic acid and rosmarinic acid could inhibit AMI by regulating PLB, CaMK II, SERCA, etc. And mechanistically, calcium signaling pathway was critically involved. Combination of systems pharmacology prediction with experimental validation may provide a scientific basis for in-depth clinical investigation of the material basis of DHI.

Thyroid Hormone Signalling in Human Evolution and Disease: A Novel Hypothesis

Thyroid hormone (TH) signalling is a universally conserved pathway with pleiotropic actions that is able to control the development, metabolism, and homeostasis of organisms. Using evidence from paleoecology/palaeoanthropology and data from the physiology of modern humans, we try to assess the natural history of TH signalling and its role in human evolution. Our net thesis is that TH signalling has likely played a critical role in human evolution by facilitating the adaptive responses of early hominids to unprecedently challenging and continuously changing environments. These ancient roles have been conserved in modern humans, in whom TH signalling still responds to and regulates adaptations to present-day environmental and pathophysiological stresses, thus making it a promising therapeutic target.

Changes in Thyroid Hormone Signaling Mediate Cardiac Dysfunction in the Tg197 Mouse Model of Arthritis: Potential Therapeutic Implications

Background Rheumatoid Arthritis (RA) patients show a higher risk of heart failure. The present study investigated possible causes of cardiac dysfunction related to thyroid hormone (TH) signaling in a RA mouse model. Methods A TNF-driven mouse model of RA[TghuTNF (Tg197)] was used. Cardiac function was evaluated by echocardiography. SERCA2a and phospholamban protein levels in left ventricle (LV) tissue, thyroid hormone levels in serum, TH receptors in LV and TH-related kinase signaling pathways were measured. T3 hormone was administered in female Tg197 mice. Results We show LV and atrial dilatation with systolic dysfunction in Tg197 animals, accompanied by downregulated SERCA2a. We suggest an interaction of pro-inflammatory and thyroid hormone signaling indicated by increased p38 MAPK and downregulation of TRβ1 receptor in Tg197 hearts. Interestingly, female Tg197 mice showed a worse cardiac phenotype related to reduced T3 levels and Akt activation. T3 supplementation increased Akt activation, restored SERCA2a expression and improved cardiac function in female Tg197 mice. Conclusions TNF overexpression of Tg197 mice results in cardiac dysfunction via p38 MAPK activation and downregulation of TRβ1. Gender-specific reduction in T3 levels could cause the worse cardiac phenotype observed in female mice, while T3 administration improves cardiac function and calcium handling via modified Akt activation.

Alteration of thyroid hormone signaling triggers the diabetes-induced pathological growth, remodeling, and dedifferentiation of podocytes

Thyroid hormone (TH) signaling is a universal regulator of metabolism, growth, and development. Here, we show that TH-TH receptor (TH-TR) axis alterations are critically involved in diabetic nephropathy-associated (DN-associated) podocyte pathology, and we identify TRα1 as a key regulator of the pathogenesis of DN. In ZSF1 diabetic rats, T3 levels progressively decreased during DN, and this was inversely correlated with metabolic and renal disease worsening. These phenomena were associated with the reexpression of the fetal isoform TRα1 in podocytes and parietal cells of both rats and patients with DN and with the increased glomerular expression of the TH-inactivating enzyme deiodinase 3 (DIO3). In diabetic rats, TRα1-positive cells also reexpressed several fetal mesenchymal and damage-related podocyte markers, while glomerular and podocyte hypertrophy was evident. In vitro, exposing human podocytes to diabetes milieu typical components markedly increased TRα1 and DIO3 expression and induced cytoskeleton rearrangements, adult podocyte marker downregulation and fetal kidney marker upregulation, the maladaptive cell cycle induction/arrest, and TRα1-ERK1/2-mediated hypertrophy. Strikingly, T3 treatment reduced TRα1 and DIO3 expression and completely reversed all these alterations. Our data show that diabetic stress induces the TH-TRα1 axis to adopt a fetal ligand/receptor relationship pattern that triggers the recapitulation of the fetal podocyte phenotype and subsequent pathological alterations.

Thyroid Hormone Signalling: From the Dawn of Life to the Bedside

Thyroid hormone (TH) signalling is a key modulator of fundamental biological processes that has been evolutionarily conserved in both vertebrate and invertebrate species. TH may have initially emerged as a nutrient signal to convey environmental information to organisms to induce morpho-anatomical changes that could maximise the exploitation of environmental resources, and eventually integrated into the machinery of gene regulation and energy production to become a key regulator of development and metabolism. As such, TH signalling is particularly sensitive to environmental stimuli, and its alterations result in fundamental changes in homeostasis and physiology. Stressful stimuli of various origins lead to changes in the TH-TH receptor (TR) axis in different adult mammalian organs that are associated with phenotypical changes in terminally differentiated cells, the reactivation of foetal development programmes, structural remodelling and pathological growth. Here, we discuss the evolution of TH signalling, review evolutionarily conserved functions of THs in essential biological processes, such as metamorphosis and perinatal development, and analyse the role of TH signalling in the phenotypical and morphological changes that occur after injury, repair and regeneration in adult mammalian organs. Finally, we examine the potential of TH treatment as a therapeutic strategy for improving organ structure and functions following injury.

The impact of thyroid hormone dysfunction on ischemic heart disease

Thyroid hormones have a central role in cardiovascular homeostasis. In myocardium, these hormones stimulate both diastolic myocardial relaxation and systolic myocardial contraction, have a pro-angiogenic effect and an important role in extracellular matrix maintenance. Thyroid hormones modulate cardiac mitochondrial function. Dysfunction of thyroid axis impairs myocardial bioenergetic status. Both overt and subclinical hypothyroidism are associated with a higher incidence of coronary events and an increased risk of heart failure progression. Endothelial function is also impaired in hypothyroid state, with decreased nitric oxide-mediated vascular relaxation. In heart disease, particularly in ischemic heart disease, abnormalities in thyroid hormone levels are common and are an important factor to be considered. In fact, low thyroid hormone levels should be interpreted as a cardiovascular risk factor. Regarding ischemic heart disease, during the late post-myocardial infarction period, thyroid hormones modulate left ventricular structure, function and geometry. Dysfunction of thyroid axis might even be more prevalent in the referred condition since there is an upregulation of type 3 deiodinase in myocardium, producing a state of local cardiac hypothyroidism. In this focused review, we summarize the central pathophysiological and clinical links between altered thyroid function and ischemic heart disease. Finally, we highlight the potential benefits of thyroid hormone supplementation as a therapeutic target in ischemic heart disease.

Cardioprotection and Thyroid Hormones in the Clinical Setting of Heart Failure

Ischemic heart disease is the main cause of morbidity and mortality worldwide and is becoming more widespread with population aging. Cardioprotection is a dynamic process characterized by mechanisms related to myocardial damage and activation of protective factors. Targeting these processes could be attractive as a new therapeutic strategy in the evolution of post-ischemic heart failure (HF). In this context, the role of thyroid hormone (TH)-mediated cardioprotection is supported by a number of findings regarding the modulation of neuroendocrine systems, inflammatory and oxidative stress status, pro-survival intracellular pathways, and epigenetic factors, its effects on cardiac angiogenesis, structure, and function and on the preservation of mitochondrial function and morphology, and its beneficial effects on cell growth and redifferentiation. Moreover, the numerous effects of TH on the heart involve genomic mechanisms, which include cardiac differentiation during the perinatal period and non-genomic action, directed toward the maintenance of cardiovascular homeostasis. This evidence suggests that there is an opportunity to treat HF patients with TH. This review is mainly focused on the clinical evidence of the role of the thyroid system in the complex setting of HF.

Thyroid hormone receptor α1 as a novel therapeutic target for tissue repair

Analogies between the damaged tissue and developing organ indicate that a regulatory network that drives embryonic organ development may control aspects of tissue repair. In this regard, there is a growing body of experimental and clinical evidence showing that TH may be critical for recovery after injury. Especially TRα1 has been reported to play an essential role in cell proliferation and differentiation and thus in the process of repair/regeneration in the heart and other tissues. Patients after myocardial infarction, stroke or therapeutic interventions [such as PCI for coronary artery disease (CAD)] with lower TH levels appear to have increased morbidity and mortality. Accordingly, TH treatment in clinical settings of ischemia/reperfusion such as by-pass surgery seems to be cardioprotective against ischemic injury. Furthermore, TH therapy of donors is shown to result in organ preservation and increased numbers of donors and improved post-transplantation graft survival. TH and thyroid analogs may prove novel therapeutic agents for tissue repair.

Comparison of Therapeutic Triiodothyronine Versus Metoprolol in the Treatment of Myocardial Infarction in Rats

BACKGROUND

Beta blockers are standard therapy for myocardial infarction (MI). Preclinical studies have shown efficacy and safety of thyroid hormone (TH) treatment of cardiovascular disorders. Since THs interact with the sympathoadrenergic system, this study aimed to compare triiodothyronine (T3) and metoprolol (Met) in the treatment of rats with MI on pathophysiology and TH-adrenergic signaling.

METHODS

Female Sprague-Dawley rats aged 12 weeks underwent left anterior descending coronary artery ligation (MI) or sham surgeries. T3 (5 μg/kg/day) or Met (100 mg/kg/day) was given in drinking water immediately after surgery for eight weeks. At the terminal of the experiments, the rats were subjected to morphological, functional, and molecular examination.

RESULTS

T3 and Met significantly enhanced left ventricular contractility (left ventricular fractional shortening 21.37 ± 2.58% and 21.14 ± 3.71%, respectively) compared to untreated MI (17.88 ± 1.23%), and decreased the incidence of inducible atrial tachyarrhythmia by 87.5% and 62.5%, respectively. Although both treatments showed efficacy, T3 but not Met showed statistically significant improvements compared to MI in arrhythmia duration, left atrial diameter (T3 vs. MI 4.33 ± 0.63 vs. 5.65 ± 1.32 mm; p < 0.05), fibrosis (6.1 ± 0.6%, 6.6 ± 0.6% vs. 8.2 ± 0.7%, T3, Met vs. MI, respectively), and aortic vasorelaxation responsiveness to acetylcholine (pD2 6.97 ± 0.22, 6.83 ± 0.21 vs. 6.66 ± 0.22, T3, Met vs. MI, respectively). Quantitative polymerase chain reaction showed that T3 and Met attenuated expression of genes associated with inflammation and oxidative stress and restored expression of ion channels and contractile proteins.

CONCLUSION

These results support comparable efficacy of T3 and Met treatments, suggesting that T3 may provide a therapeutic alternative to standard β-receptor blockade, especially for patients intolerant to treatment with β-blockers after MI.

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.

Cardioprotection and thyroid hormones

The evolution of cardiac disease after an acute ischemic event depends on a complex and dynamic network of mechanisms alternating from ischemic damage due to acute coronary occlusion to reperfusion injury due to the adverse effects of coronary revascularization till post-ischemic remodeling. Cardioprotection is a new purpose of the therapeutic interventions in cardiology with the goal to reduce infarct size and thus prevent the progression toward heart failure after an acute ischemic event. In a complex biological system such as the human one, an effective cardioprotective strategy should diachronically target the network of cross-talking pathways underlying the disease progression. Thyroid system is strictly interconnected with heart homeostasis, and recent studies highlighted its role in cardioprotection, in particular through the preservation of mitochondrial function and morphology, the antifibrotic and proangiogenetic effect and also to the potential induction of cell regeneration and growth. The objective of this review was to highlight the cardioprotective role of triiodothyronine in the complexity of post-ischemic disease evolution.

Long-term prognostic value of combined free triiodothyronine and late gadolinium enhancement in nonischemic dilated cardiomyopathy

BACKGROUND

Thyroid dysfunction and myocardial fibrosis are both associated with cardiovascular events in patients with dilated cardiomyopathy (DCM).

HYPOTHESIS

The combination of thyroid hormone (TH) and myocardial fibrosis (detected by late gadolinium enhancement [LGE]) is an independent and incremental predictor of adverse events in DCM.

METHODS

We consecutively enrolled 220 idiopathic DCM patients with thyroid function and LGE assessment at Fuwai Hospital (China) from January 2010 to October 2011 and followed up through December 2015. Patients were divided into 4 groups according to the presence or absence of LGE and FT3 value (median level of 2.79 pg/mL): LGE-positive + FT3 < 2.79 pg/mL, LGE-positive + FT3 ≥ 2.79 pg/mL, LGE-negative + FT3 < 2.79 pg/mL, and LGE-negative + FT3 ≥ 2.79 pg/mL.

RESULTS

During a median follow-up of 61 months, 56 patients (25.5%) died, with 27/56 (48.2%), 8/45 (17.8%), 12/54 (22.2%), and 9/65 (13.8%) among 4 groups (P = 0.009), respectively. Multivariable Cox regression analysis identified LGE-positive and FT3 < 2.79 pg/mL as a significant independent predictor of all-cause mortality (hazard ratio: 2.893, 95% confidence interval: 1.323-6.326, P = 0.008). Combining the predictive value of FT3 and LGE status significantly improved risk reclassification for all-cause mortality, as indicated by the net reclassification improvement (0.28; P = 0.005) and integrated discrimination improvement (0.058; P = 0.001).

CONCLUSIONS

The findings suggest that the combination of FT3 and LGE yielded a more accurate predictive value for long-term prognosis in patients with DCM, which may improve patient selection for intensive interventions.

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.

Changes in Hepatic TRβ Protein Expression, Lipogenic Gene Expression, and Long-Chain Acylcarnitine Levels During Chronic Hyperthyroidism and Triiodothyronine Withdrawal in a Mouse Model

BACKGROUND

Thyroid hormone (TH) has important roles in regulating hepatic metabolism. It was previously reported that most hepatic genes activated by a single triiodothyronine (T3) injection became desensitized after multiple injections, and that approximately 10% of target genes did not return to basal expression levels after T3 withdrawal, despite normalization of serum TH and thyrotropin (TSH) levels. To determine the possible mechanism(s) for desensitization and incomplete recovery of hepatic target gene transcription and their effects on metabolism, mRNA and/or protein expression levels of key regulators of TH action were measured, as well as metabolomic changes after chronic T3 treatment and withdrawal.

METHODS

Adult male mice were treated with daily injections of T3 (20 μg/100 g body weight) for 14 days followed by the cessation of T3 for 10 days. Livers were harvested at 6 hours, 24 hours, and 14 days after the first T3 injection, and at 10 days after withdrawal, and then analyzed by quantitative reverse transcription polymerase chain reaction, Western blotting, and metabolomics.

RESULTS

Although TH receptor (TRα and TRβ) mRNAs decreased slightly after chronic T3 treatment, only TRβ protein decreased before returning to basal expression level after withdrawal. The expression of other regulators of TH action was unchanged. TRβ protein expression was also decreased in adult male monocarboxylate transporter-8 (Mct8)-knockout mice, an in vivo model of chronic intrahepatic hyperthyroidism. Previously, increased hepatic long-chain acylcarnitine levels were found after acute TH treatment. However, in this study, long-chain acylcarnitine levels were unchanged after chronic T3, and paradoxically increased after T3 withdrawal. Pathway analyses of the previous microarray results showed upregulation of lipogenic genes after acute T3 treatment and withdrawal. Phosphorylation of acetyl-CoA carboxylase also decreased after T3 withdrawal.

CONCLUSIONS

Decreased hepatic TRβ protein expression occurred after chronic T3 exposure in adult male wild-type and Mct8-knockout mice. Gene array pathway and metabolomics analyses showed abnormalities in hepatic lipogenic gene expression and acylcarnitine levels, respectively, after withdrawal, despite normalization of serum TSH and TH levels. These findings may help explain the variable clinical presentations of some patients during hyperthyroidism and recovery, since TRβ protein, target gene expression, and metabolic adaptive changes can occur in individual tissues without necessarily being reflected by circulating TH and TSH concentrations.

Repair Injured Heart by Regulating Cardiac Regenerative Signals

Cardiac regeneration is a homeostatic cardiogenic process by which the sections of malfunctioning adult cardiovascular tissues are repaired and renewed employing a combination of both cardiomyogenesis and angiogenesis. Unfortunately, while high-quality regeneration can be performed in amphibians and zebrafish hearts, mammalian hearts do not respond in kind. Indeed, a long-term loss of proliferative capacity in mammalian adult cardiomyocytes in combination with dysregulated induction of tissue fibrosis impairs mammalian endogenous heart regenerative capacity, leading to deleterious cardiac remodeling at the end stage of heart failure. Interestingly, several studies have demonstrated that cardiomyocyte proliferation capacity is retained in mammals very soon after birth, and cardiac regeneration potential is correspondingly preserved in some preadolescent vertebrates after myocardial infarction. There is therefore great interest in uncovering the molecular mechanisms that may allow heart regeneration during adult stages. This review will summarize recent findings on cardiac regenerative regulatory mechanisms, especially with respect to extracellular signals and intracellular pathways that may provide novel therapeutics for heart diseases. Particularly, both in vitro and in vivo experimental evidences will be presented to highlight the functional role of these signaling cascades in regulating cardiomyocyte proliferation, cardiomyocyte growth, and maturation, with special emphasis on their responses to heart tissue injury.

MuRF1 mono-ubiquitinates TRα to inhibit T3-induced cardiac hypertrophy in vivo

Thyroid hormone (TH) is recognized for its role in cellular metabolism and growth and participates in homeostasis of the heart. T3 activates pro-survival pathways including Akt and mTOR. Treatment with T3 after myocardial infarction is cardioprotective and promotes elements of physiological hypertrophic response after cardiac injury. Although T3 is known to benefit the heart, very little about its regulation at the molecular level has been described to date. The ubiquitin proteasome system (UPS) regulates nuclear hormone receptors such as estrogen, progesterone, androgen, and glucocorticoid receptors by both degradatory and non-degradatory mechanisms. However, how the UPS regulates T3-mediated activity is not well understood. In this study, we aim to determine the role of the muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) in regulating T3-induced cardiomyocyte growth. An increase in MuRF1 expression inhibits T3-induced physiological cardiac hypertrophy, whereas a decrease in MuRF1 expression enhances T3's activity both in vitro and in cardiomyocytes in vivo MuRF1 interacts directly with TRα to inhibit its activity by posttranslational ubiquitination in a non-canonical manner. We then demonstrated that a nuclear localization apparatus that regulates/inhibits nuclear receptors by sequestering them within a subcompartment of the nucleus was necessary for MuRF1 to inhibit T3 activity. This work implicates a novel mechanism that enhances the beneficial T3 activity specifically within the heart, thereby offering a potential target to enhance cardiac T3 activity in an organ-specific manner.

Mitochondria as key targets of cardioprotection in cardiac ischemic disease: role of thyroid hormone triiodothyronine

Ischemic heart disease is the major cause of mortality and morbidity worldwide. Early reperfusion after acute myocardial ischemia has reduced short-term mortality, but it is also responsible for additional myocardial damage, which in the long run favors adverse cardiac remodeling and heart failure evolution. A growing body of experimental and clinical evidence show that the mitochondrion is an essential end effector of ischemia/reperfusion injury and a major trigger of cell death in the acute ischemic phase (up to 48–72 h after the insult), the subacute phase (from 72 h to 7–10 days) and chronic stage (from 10–14 days to one month after the insult). As such, in recent years scientific efforts have focused on mitochondria as a target for cardioprotective strategies in ischemic heart disease and cardiomyopathy. The present review discusses recent advances in this field, with special emphasis on the emerging role of the biologically active thyroid hormone triiodothyronine (T3).

Restoration of thyroid hormone balance: a game changer in the treatment of heart failure?

The link between low thyroid hormone (TH) function and heart failure is reviewed in the present report. The idea that TH dysfunction may contribute to diseases leading to HF has been discussed for over 60 yr. A growing body of evidence from animal and human studies, particularly in recent years, suggests that TH treatment may improve clinical outcomes. Indeed, if a similar amount of positive information were available for a newly developed heart drug, there is little doubt that large-scale clinical trials would be underway with considerable excitement. THs offer the promise of improving ventricular contraction and relaxation, improving coronary blood flow, and inhibiting atherosclerosis, and new results suggest they may even reduce the incidence of arrhythmias in heart diseases. Are the potential clinical benefits worth the risk of possible overdosing? After so many years, why has this question not been answered? Clearly, the concept has not been disproven. This review explores the body of clinical evidence related to TH dysfunction and heart failure, discuss insights into pathophysiological, cellular, and molecular mechanisms provided by animal research, and discuss what is needed to resolve this long-standing issue in cardiology and move forward.

Cardioprotective effects of thyroid hormones in a rat model of myocardial infarction are associated with oxidative stress reduction

Reactive oxygen species (ROS) are involved with progression from infarction to heart failure. Studies show that thyroid hormones (TH) present cardioprotective effects. This study aims to evaluate whether TH effects after infarction are associated to redox balance modulation. Male Wistar rats were divided into four groups: Sham-operated (SHAM), infarcted (AMI), sham-operated+TH (SHAMT), and infarcted+TH (AMIT). During 26 days, animals received T3 (2 μg/100g/day) and T4 (8 μg/100g/day) by gavage. Echocardiographic parameters were assessed and heart tissue was collected to biochemical analysis. AMIT rats presented absence of lung congestion, less cardiac dilatation, and normalization in myocardial performance index, compared with AMI. AMI rats presented an increase in hydrogen peroxide levels and in lipid peroxidation and a decrease in GSH/GSSG. TH prevented these alterations in AMIT. In conclusion, TH seem to reduce the levels of ROS, preventing oxidative stress, and improving cardiac function in infarcted rats.

The beneficial effects of ranolazine on cardiac function after myocardial infarction are greater in diabetic than in nondiabetic rats

Ranolazine (RAN) is known to exert both anti-ischemic and antidiabetic actions. Thus, this study has explored the hypothesis that RAN would have greater effect on the recovery of cardiac function in diabetic mellitus (DM) rat hearts following myocardial infarction (MI). Myocardial infarction was induced in nondiabetic (MI, n = 14) and diabetic (streptozotocin induced; DM-MI, n = 13) Wistar rats by permanent ligation of the left coronary artery. Cardiac function was evaluated using echocardiography (left ventricular ejection fraction %) and in isolated heart preparations by measuring left ventricular developed pressure (LVDP), and the positive and negative first derivative of LVDP (± dp/dt). Ranolazine (20 mg/kg, ip once a day) was administered 24 hours after surgical procedure for 4 weeks to nondiabetic (MI + RAN, n = 17) and diabetic rats (DM-MI + RAN, n = 15). The RAN improved the recovery of function in both the nondiabetic and the diabetic postinfarcted hearts but this effect was greater and achieved statistical significance only in the diabetic group. The RAN resulted in increased levels of phosphorylated protein kinase B (Akt) and mammalian target of rapamycin (mTOR, a component of Akt signaling) in both nondiabetic and diabetic infarcted hearts without changes in the activation of mitogen-activated protein kinases (MAPKs; p38 MAPK, c-Jun N-terminal kinase, and extracellular signal-regulated kinase). In addition, in diabetic hearts, RAN resulted in a significant increase in the ratio of sarcoplasmic Ca(2+)-ATPase/phospholamban (a target of Akt signaling, 2.0-fold increase) and increased levels of phosphorylated calcium-regulated adenosine monophosphate-activated protein kinase (AMPK; 2.0-fold increase). In diabetic animals, RAN increased insulin and lowered glucose levels in serum. In conclusion, the beneficial effect of RAN on the recovery of cardiac function after MI was greater in DM rats. This response was associated with activation of Akt/mTOR and AMPK. These findings provide a plausible explanation for the results of the Type 2 Diabetes Evaluation of Ranolazine in Subjects With Chronic Stable Angina (TERISA) trial, which showed a greater antianginal effect of RAN in patients with coronary artery disease and diabetes.

The emerging role of TRα1 in cardiac repair: potential therapeutic implications

Thyroid hormone (TH) is critical for adapting living organisms to environmental stress. Plasma circulating tri-iodothyronine (T3) levels drop in most disease states and are associated with increased oxidative stress. In this context, T3 levels in plasma appear to be an independent determinant for the recovery of cardiac function after myocardial infarction in patients. Thyroid hormone receptor α1 (TRα1) seems to be crucial in this response; TRα1 accumulates to cell nucleus upon activation of stress induced growth kinase signaling. Furthermore, overexpression of nuclear TRα1 in cardiomyocytes can result in pathological or physiological growth (dual action) in absence or presence of its ligand, respectively. Accordingly, inactivation of TRα1 receptor prevents reactive hypertrophy after myocardial infarction and results in heart failure with increased phospholamban (PLB) expression and marked activation of p38MAPK. In line with this evidence, TH is shown to limit ischemia/reperfusion injury and convert pathologic to physiologic growth after myocardial infarction via TRα1 receptor. TRα1 receptor may prove to be a novel pharmacological target for cardiac repair/regeneration therapies.

Pleiotropic effects of antiarrhythmic agents: dronedarone in the treatment of atrial fibrillation

Atrial fibrillation remains the most common arrhythmia in clinical practice. Dronedarone is an antiarrhythmic drug for the maintenance of sinus rhythm in patients with atrial fibrillation. Dronedarone is an amiodarone derivative developed to reduce the number of extracardiovascular side effects. Dronedarone has undergone extensive experimental and clinical testing during the last decade. On the aggregate, these studies have highlighted a complex set of pleiotropic actions that may contribute to dronedarone's antiarrhythmic effects. In this review, we summarize the clinical studies that have evaluated dronedarone and provide an overview of dronedarone's electrophysiological and nonelectrophysiological pleiotropic actions.

Thyroid hormone signalling is altered in response to physical training in patients with end-stage heart failure and mechanical assist devices: potential physiological consequences?

OBJECTIVES

The present study investigated the potential of the failing myocardium of patients with ventricular assist devices (VAD) to respond to physiological growth stimuli, such as exercise, by activating growth signalling pathways. This may be of therapeutic relevance in identifying novel pharmacological targets for therapies that could facilitate recovery after VAD implantation.

METHODS

Twenty-two patients bridged to heart transplantation (HTx) with VAD were included in the study. A group of patients underwent moderate intensity aerobic exercise (GT), while another group of patients did not receive exercise training (CG). Thyroid hormone receptor alpha1 (TRα1) protein and total (t) and phosphorylated (p) protein kinase B (Akt) and c-Jun N-terminal kinase (JNK) kinase signalling were measured in myocardial tissue by western blotting at pre-VAD and pre-HTx period. In addition, Thyroid hormone (TH) levels were measured in plasma.

RESULTS

Peak oxygen consumption (VO2) at pre-HTx period was higher in patients subjected to training protocol [18.0 (0.8) for GT when compared with 13.7 (0.7) for CG group, P = 0.002]. N-terminal-prohormone of brain natriuretic peptide (NT-proBNP) levels were 1068 (148) for CG vs 626 (115) for GT group, P = 0.035. A switch towards up-regulation of physiological growth signalling was observed: the ratio of p-Akt/t-Akt was 2-fold higher in GT vs CG, P < 0.05 while p-JNK/t-JNK was 2.5-fold lower (P < 0.05) in GT vs CG, in pre-HTx samples. This response was accompanied by a 2.0-fold increase in TRα1 expression in pre-HTx samples with concomitant increase in circulating T3 in GT vs CG, P < 0.05. No differences in peak VO2, NT-proBNP, T3, TRα1, p/t-AKT and p/t-JNK were found between groups in the pre-VAD period.

CONCLUSIONS

The unloaded failing myocardium responded to physical training by enhancing thyroid hormone signalling. This response was associated with an up-regulation of Akt and suppression of JNK activation.