Reductions in serum levels of LDL cholesterol, apolipoprotein B, triglycerides and lipoprotein(a) in hypercholesterolaemic patients treated with the liver-selective thyroid hormone receptor agonist eprotirome

Genetics and Pathophysiological Mechanisms of Lipoprotein(a)-Associated Cardiovascular Risk

Elevated lipoprotein(a) is a genetically transmitted codominant trait that is an independent risk driver for cardiovascular disease. Lipoprotein(a) concentration is heavily influenced by genetic factors, including LPA kringle IV-2 domain size, single-nucleotide polymorphisms, and interleukin-1 genotypes. Apolipoprotein(a) is encoded by the LPA gene and contains 10 subtypes with a variable number of copies of kringle -2, resulting in >40 different apolipoprotein(a) isoform sizes. Genetic loci beyond LPA, such as APOE and APOH, have been shown to impact lipoprotein(a) levels. Lipoprotein(a) concentrations are generally 5% to 10% higher in women than men, and there is up to a 3-fold difference in median lipoprotein(a) concentrations between racial and ethnic populations. Nongenetic factors, including menopause, diet, and renal function, may also impact lipoprotein(a) concentration. Lipoprotein(a) levels are also influenced by inflammation since the LPA promoter contains an interleukin-6 response element; interleukin-6 released during the inflammatory response results in transient increases in plasma lipoprotein(a) levels. Screening can identify elevated lipoprotein(a) levels and facilitate intensive risk factor management. Several investigational, RNA-targeted agents have shown promising lipoprotein(a)-lowering effects in clinical studies, and large-scale lipoprotein(a) testing will be fundamental to identifying eligible patients should these agents become available. Lipoprotein(a) testing requires routine, nonfasting blood draws, making it convenient for patients. Herein, we discuss the genetic determinants of lipoprotein(a) levels, explore the pathophysiological mechanisms underlying the association between lipoprotein(a) and cardiovascular disease, and provide practical guidance for lipoprotein(a) testing.

Hormone-based pharmacotherapy for metabolic dysfunction-associated fatty liver disease

Metabolic dysfunction-associated fatty liver disease (MAFLD) has reached epidemic proportions globally in parallel to the rising prevalence of obesity. Despite its significant burden, there is no approved pharmacotherapy specifically tailored for this disease. Many potential drug candidates for MAFLD have encountered setbacks in clinical trials, due to safety concerns or/and insufficient therapeutic efficacy. Nonetheless, several investigational drugs that mimic the actions of endogenous metabolic hormones, including thyroid hormone receptor β (THRβ) agonists, fibroblast growth factor 21 (FGF21) analogues, and glucagon-like peptide-1 receptor agonists (GLP-1RAs), showed promising therapeutic efficacy and excellent safety profiles. Among them, resmetirom, a liver-targeted THRβ-selective agonist, has met the primary outcomes in alleviation of metabolic dysfunction-associated steatohepatitis (MASH), the advanced form of MAFLD, and liver fibrosis in phase-3 clinical trials. These hormone-based pharmacotherapies not only exhibit varied degrees of therapeutic efficacy in mitigating hepatic steatosis, inflammation and fibrosis, but also improve metabolic profiles. Furthermore, these three hormonal agonists/analogues act in a complementary manner to exert their pharmacological effects, suggesting their combined therapies may yield synergistic therapeutic benefits. Further in-depth studies on the intricate interplay among these metabolic hormones are imperative for the development of more efficacious combination therapies, enabling precision management of MAFLD and its associated comorbidities.

Understanding the Relationship between Nonalcoholic Fatty Liver Disease and Thyroid Disease

The prevalence of hypothyroidism in patients with nonalcoholic fatty liver disease (NAFLD) is high (22.4%). Thyroid hormones (THs) regulate many metabolic activities in the liver by promoting the export and oxidation of lipids, as well as de novo lipogenesis. They also control hepatic insulin sensitivity and suppress hepatic gluconeogenesis. Because of its importance in lipid and carbohydrate metabolism, the involvement of thyroid dysfunction in the pathogenesis of NAFLD seems plausible. The mechanisms implicated in this relationship include high thyroid-stimulating hormone (TSH) levels, low TH levels, and chronic inflammation. The activity of the TH receptor (THR)-β in response to THs is essential in the pathogenesis of hypothyroidism-induced NAFLD. Therefore, an orally active selective liver THR-β agonist, Resmetirom (MGL-3196), was developed, and has been shown to reduce liver fat content, and as a secondary end point, to improve nonalcoholic steatohepatitis. The treatment of NAFLD with THR-β agonists seems quite promising, and other agonists are currently under development and investigation. This review aims to shine a light on the pathophysiological and epidemiological evidence regarding this relationship and the effect that treatment with THs and selective liver THR-β agonists have on hepatic lipid metabolism.

Conferring liver selectivity to a thyromimetic using a novel nanoparticle increases therapeutic efficacy in a diet-induced obesity animal model

Optimization of metabolic regulation is a promising solution for many pathologies, including obesity, dyslipidemia, type 2 diabetes, and inflammatory liver disease. Synthetic thyroid hormone mimics-based regulation of metabolic balance in the liver showed promise but was hampered by the low biocompatibility and harmful effects on the extrahepatic axis. In this work, we show that specifically directing the thyromimetic to the liver utilizing a nanogel-based carrier substantially increased therapeutic efficacy in a diet-induced obesity mouse model, evidenced by the near-complete reversal of body weight gain, liver weight and inflammation, and cholesterol levels with no alteration in the thyroxine (T4) / thyroid stimulating hormone (TSH) axis. Mechanistically, the drug acts by binding to thyroid hormone receptor β (TRβ), a ligand-inducible transcription factor that interacts with thyroid hormone response elements and modulates target gene expression. The reverse cholesterol transport (RCT) pathway is specifically implicated in the observed therapeutic effect. Overall, the study demonstrates a unique approach to restoring metabolic regulation impacting obesity and related metabolic dysfunctions.

Effects of Lipid-Modifying and Other Drugs on Lipoprotein(a) Levels-Potent Clinical Implications

The past few years have shown an ongoing interest in lipoprotein(a) (Lp(a)), a lipid molecule that has been proven to have atherogenic, thrombogenic, and inflammatory properties. Several lines of evidence, indeed, have demonstrated an increased risk of cardiovascular disease as well as calcific aortic valve stenosis in patients with elevated Lp(a) levels. Statins, the mainstay of lipid-lowering therapy, slightly increase Lp(a) levels, while most other lipid-modifying agents do not significantly alter Lp(a) concentrations, except for proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. The latter have been shown to reduce Lp(a) levels; however, the clinical significance of this effect has not been clearly elucidated. Of note, the pharmaceutical lowering of Lp(a) may be achieved with novel treatments specifically designed for this purpose (i.e., antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs)). Large clinical trials with cardiovascular outcomes with these agents are ongoing, and their results are eagerly awaited. Furthermore, several non-lipid-modifying drugs of various classes may influence Lp(a) concentrations. We have searched MEDLINE, EMBASE, and CENTRAL databases up to 28 January 2023 and summarized the effects of established and emerging lipid-modifying drugs and other medications on Lp(a) levels. We also discuss the potent clinical implications of these alterations.

NAFLD and thyroid function: pathophysiological and therapeutic considerations

Nonalcoholic fatty liver disease (NAFLD) is a worldwide rising challenge because of hepatic, but also extrahepatic, complications. Thyroid hormones are master regulators of energy and lipid homeostasis, and the presence of abnormal thyroid function in NAFLD suggests pathogenic relationships. Specifically, persons with hypothyroidism feature dyslipidemia and lower hepatic β-oxidation, which favors accumulation of triglycerides and lipotoxins, insulin resistance, and subsequently de novo lipogenesis. Recent studies indicate that liver-specific thyroid hormone receptor β agonists are effective for the treatment of NAFLD, likely due to improved lipid homeostasis and mitochondrial respiration, which, in turn, may contribute to a reduced risk of NAFLD progression. Taken together, the possible coexistence of thyroid disease and NAFLD calls for increased awareness and optimized strategies for mutual screening and management.

Thyroid hormones as a disease modifier and therapeutic target in nonalcoholic steatohepatitis

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide and closely interconnected to the metabolic syndrome. Liver-specific and systemic signaling pathways orchestrating glucose and fatty acid metabolism contribute to intrahepatic accumulation of lipids and inflammatory processes eventually causing disease progression to nonalcoholic steatohepatitis (NASH), liver fibrosis, and cirrhosis. Since a high number of key regulatory genes regarding liver homeostasis are directly mediated via thyroid hormone (TH) signaling, targeting TH receptors (TRs) represent a promising therapeutic potential for the treatment of NAFLD.

AREAS COVERED

In this review, we elucidate the effects of TH on metabolic regulations in the liver via local availability and actions. We discuss recent advances and the potential impact of thyromimetics in basic research and clinical trials including liver-targeted and TRβ-specific agents for the treatment of NAFLD.

EXPERT OPINION

Unselective TR targeting can be accompanied by negative side effects due to high TRβ expression in other organs and TRα-mediated effects. Recent advances in drug development and the introduction of liver-targeted thyromimetics selectively activating TRβ such as Resmetirom (MGL-3196) and VK2809 bring new hope of translating the knowledge on local TH effects into effective hepatic lipid-clearing therapies against NASH.

3,5-T2-an Endogenous Thyroid Hormone Metabolite as Promising Lead Substance in Anti-Steatotic Drug Development?

Thyroid hormones, their metabolites, and synthetic analogues are potential anti-steatotic drug candidates considering that subclinical and manifest hypothyroidism is associated with hepatic lipid accumulation, non-alcoholic fatty liver disease, and its pandemic sequelae. Thyromimetically active compounds stimulate hepatic lipogenesis, fatty acid beta-oxidation, cholesterol metabolism, and metabolic pathways of glucose homeostasis. Many of these effects are mediated by T3 receptor β1-dependent modulation of transcription. However, rapid non-canonical mitochondrial effects have also been reported, especially for the metabolite 3,5-diiodothyronine (3,5-T2), which does not elicit the full spectrum of “thyromimetic” actions inherent to T3. Most preclinical studies in rodent models of obesity and first human clinical trials are promising with respect to the antisteatotic hepatic effects, but potent agents exhibit unwanted thyromimetic effects on the heart and/or suppress feedback regulation of the hypothalamus-pituitary-thyroid-periphery axis and the fine-tuned thyroid hormone system. This narrative review focuses on 3,5-T2 effects on hepatic lipid and glucose metabolism and (non-)canonical mechanisms of action including its mitochondrial targets. Various high fat diet animal models with distinct thyroid hormone status indicate species- and dose-dependent efficiency of 3,5-T2 and its synthetic analogue TRC150094. No convincing evidence has been presented for their clinical use in the prevention or treatment of obesity and related metabolic conditions.

Non-genetic influences on lipoprotein(a) concentrations

An elevated level of lipoprotein(a) [Lp(a)] is a genetically regulated, independent, causal risk factor for cardiovascular disease. However, the extensive variability in Lp(a) levels between individuals and population groups cannot be fully explained by genetic factors, emphasizing a potential role for non-genetic factors. In this review, we provide an overview of current evidence on non-genetic factors influencing Lp(a) levels with a particular focus on diet, physical activity, hormones and certain pathological conditions. Findings from randomized controlled clinical trials show that diets lower in saturated fats modestly influence Lp(a) levels and often in the opposing direction to LDL cholesterol. Results from studies on physical activity/exercise have been inconsistent, ranging from no to minimal or moderate change in Lp(a) levels, potentially modulated by age and the type, intensity, and duration of exercise modality. Hormone replacement therapy (HRT) in postmenopausal women lowers Lp(a) levels with oral being more effective than transdermal estradiol; the type of HRT, dose of estrogen and addition of progestogen do not modify the Lp(a)-lowering effect of HRT. Kidney diseases result in marked elevations in Lp(a) levels, albeit dependent on disease stages, dialysis modalities and apolipoprotein(a) phenotypes. In contrast, Lp(a) levels are reduced in liver diseases in parallel with the disease progression, although population studies have yielded conflicting results on the associations between Lp(a) levels and nonalcoholic fatty liver disease. Overall, current evidence supports a role for diet, hormones and related conditions, and liver and kidney diseases in modifying Lp(a) levels.

Hypothyroidism-Associated Dyslipidemia: Potential Molecular Mechanisms Leading to NAFLD

Thyroid hormones control lipid metabolism by exhibiting specific effects on the liver and adipose tissue in a coordinated manner. Different diseases of the thyroid gland can result in hypothyroidism. Hypothyroidism is frequently associated with dyslipidemia. Hypothyroidism-associated dyslipidemia subsequently results in intrahepatic accumulation of fat, leading to nonalcoholic fatty liver disease (NAFLD), which leads to the development of hepatic insulin resistance. The prevalence of NAFLD in the western world is increasing, and evidence of its association with hypothyroidism is accumulating. Since hypothyroidism has been identified as a modifiable risk factor of NAFLD and recent data provides evidence that selective thyroid hormone receptor β (THR-β) agonists are effective in the treatment of dyslipidemia and NAFLD, interest in potential therapeutic options for NAFLD targeting these receptors is growing. In this review, we summarize current knowledge regarding clinical and molecular data exploring the association of hypothyroidism, dyslipidemia and NAFLD.

Impact of thyroid disorders on the incidence of non-alcoholic fatty liver disease in Germany

BACKGROUND

Studies investigating a potential association between hypothyroidism and non-alcoholic fatty liver disease (NAFLD) showed conflicting results and large-scale population-based data from Germany on this topic are currently missing.

OBJECTIVE

It was the aim of this analysis to investigate the impact of thyroid gland disorders on the prevalence of NAFLD in Germany.

METHODS

In this case-control study, using the German disease Analyzer database (IQVIA), NAFLD patients were matched to patients without NAFLD by age, sex, index year, treating physician, diabetes mellitus type II, and obesity. The main outcome of the study was an association between thyroid gland disorders (hypothyroidism, hyperthyroidism and autoimmune thyroiditis) and incident NAFLD and was evaluated using logistic regression analyses.

RESULTS

57,483 patients with NAFLD were matched to 57,483 patients without liver disease. Mean age of the cohort was 60.3 years (±14.1) and 52.3% were men. In regression analyses, hypothyroidism (OR 1.17, 95% CI 1.10 - 1.24, p < 0.001) as well as autoimmune thyroiditis (OR 1.53, 95% CI 1.35-1.73, p < 0.001) were associated with a higher risk of NAFLD. In contrast, hyperthyroidism was associated with a lower risk of NAFLD (OR 0.85, 95% CI 0.77-0.94, p < 0.001). The effect of hypothyroidism on the prevalence of NAFLD remained significant across men (OR 1.31, 95% CI 1.15-1.48) as well as women (OR 1.12, 95% CI 1.05-1.21).

CONCLUSION

Hypothyroidism seems to be a risk factor for incident NAFLD.

Dyslipidemia, Insulin Resistance, Ectopic Lipid Accumulation, and Vascular Function in Resistance to Thyroid Hormone β

PURPOSE

In resistance to thyroid hormone due to mutations in thyroid hormone receptor β, peripheral tissues are variably refractory to the action of circulating thyroid hormones. We evaluated parameters contributing to atherosclerotic risk in this disorder.

METHODS

We measured low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), nonesterified fatty acids (NEFA), intrahepatic lipid (IHL) and intramyocellular lipid (IMCL), Homeostasis-model assessment of insulin resistance (HOMA-IR), augmentation index (AIx) and pulse wave velocity (PWV), flow-mediated dilatation, and carotid intima-media thickness (cIMT) in an unselected, genetically confirmed cohort of adult RTHβ patients (n = 27-77) and compared these with measurements in healthy subjects (up to n = 100) and thyrotoxic patients (n = 40).

RESULTS

Resistance to thyroid hormone beta (RTHβ) patients exhibited higher LDL-C (P = 0.008) and TG (P = 0.002) and lower HDL-C concentrations (P = 0.015 × 10-2) than control subjects, with LDL-C being higher than in thyrotoxic patients with comparable hyperthyroxinemia. Proprotein convertase subtilisin/kexin 9 (P = 0.002) and apolipoprotein B (P = 0.0009) levels were reduced in thyrotoxic patients but not lower in RTHβ patients or control subjects. Intrahepatic lipid (P = 0.02 × 10-4), IMCL (P = 0.002), HOMA-IR (P = 0.01 × 10-2), and NEFA (P = 0.04 × 10-6) were significantly higher in RTHβ patients than control subjects. Flow-mediated dilatation was increased (P = 0.04) but cIMT (P = 0.71), PWV P = 0.81), and AIx (P = 0.95) were unaltered in RTHβ patients.

CONCLUSIONS

We have documented mixed dyslipidemia with hepatic and IMCL accumulation in RTHβ, suggesting that surveillance for these metabolic abnormalities is warranted. How they combine with enhanced endothelial function and unaltered vessel wall thickness and compliance to determine overall cardiometabolic risk in this disorder remains to be defined.

Correlation between serum free triiodothyronine levels and risk stratification in Chinese patients with acute coronary syndrome receiving percutaneous coronary intervention

OBJECTIVE

Low serum free triiodothyronine (FT3) levels are associated with the occurrence of coronary heart disease and with the prognosis of cardiovascular diseases. This study aimed to investigate the relationship between FT3 levels and risk stratification in Chinese Han patients with acute coronary syndrome (ACS) receiving percutaneous coronary intervention (PCI) treatment.

METHODS

Plasma FT3 levels and other parameters were measured in 191 patients with ACS who received PCI. The risk of adverse cardiovascular events was assessed using the Age, Creatinine, and Ejection Fraction (ACEF) score.

RESULTS

FT3 levels were significantly lower in the high-risk group than in the medium- and low-risk groups. Serum FT3 levels were negatively linearly correlated with the ACEF score (r = -0.590). Stepwise regression analysis showed a negative correlation between FT3 levels and the risk of adverse cardiovascular events as measured by the ACEF score (standardized β = -0.261).

CONCLUSION

Serum FT3 levels are negatively related to risk stratification in patients with ACS. Serum FT3 levels may be used as a potential predictor for adverse outcomes of patients with ACS undergoing PCI.

Thyroid Hormone Signaling and the Liver

Thyroid hormone (TH) plays a critical role in maintaining metabolic homeostasis throughout life. It is well known that the liver and thyroid are intimately linked, with TH playing important roles in de novo lipogenesis, beta-oxidation (fatty acid oxidation), cholesterol metabolism, and carbohydrate metabolism. Indeed, patients with hypothyroidism have abnormal lipid panels with higher levels of low-density lipoprotein levels, triglycerides (triacylglycerol; TAG), and apolipoprotein B levels. Even in euthyroid patients, lower serum-free thyroxine levels are associated with higher total cholesterol levels, LDL, and TAG levels. In addition to abnormal serum lipids, the risk of nonalcoholic fatty liver disease (NAFLD) increases with lower free thyroxine levels. As free thyroxine rises, the risk of NAFLD is reduced. This has led to numerous animal studies and clinical trials investigating TH analogs and TH receptor agonists as potential therapies for NAFLD and hyperlipidemia. Thus, TH plays an important role in maintaining hepatic homeostasis, and this continues to be an important area of study. A review of TH action and TH actions on the liver will be presented here.

Potential role of two novel agonists of thyroid hormone receptor-β on liver regeneration

OBJECTIVES

Although the hepatomitogenic activity of triiodothyronine (T3) is well established, the wide range of harmful effects exerted by this hormone precludes its use in liver regenerative therapy. Selective agonists of the beta isoform of thyroid hormone receptor (TRβ) do not exhibit T3-induced cardiotoxicity and show a good safety profile in patients with NASH. The aim of this study was to investigate whether two novel TRβ agonists, the prodrug TG68 and the active compound IS25 could stimulate hepatocyte proliferation without T3/TRα-dependent side effects.

METHODS

Rats were treated with three different doses (12.5, 25 and 50 μg/100 g body weight) for one week. Hepatocyte proliferation, liver injury and serum biochemical parameters were measured by immunohistochemistry, qRT-PCR and Western blot.

RESULTS

Both drugs increased hepatocyte proliferation as assessed by bromodeoxyuridine incorporation (from 14% to 28% vs 5% of controls) and mitotic activity. Enhanced proliferation occurred in the absence of significant signs of liver injury as shown by lack of increased serum transaminase levels or of apoptosis. No cardiac or renal hypertrophy typically associated with treatment with T3 was observed. Importantly, no proliferation of pancreatic acinar cells, such as that seen after administration of T3 or the TRβ agonist GC1 was detected following either TG68 or IS25, demonstrating the hepato-specificity of these novel TRβ agonists.

CONCLUSIONS

The present study shows that TG68 and IS25 induce massive hepatocyte proliferation without overt toxicity. Hence, these agents may have a significant clinical application for regenerative therapies in liver transplantation or other surgical settings.

The effect of additive containing an organic form of iodine on the physiological-biochemical parameters of the body of cows

Iodine deficiency in soil and water in many countries leads to its low content in plants and animal feed produced from them. The limited intake of this element in animals can lead to endemic diseases. The lack of iodine in animal feeding is most often compensated for by the use of additives with an inorganic form of iodine, which can be poorly absorbed by the body. Feed products with an organic form of iodine have a great biological effect. A study on the effect of iodine-containing additives on the physiological and biochemical parameters of the animal organism was carried out on two groups of 15 cows. The experimental group was fed an organic form of iodine as part of the additive, the control group received an inorganic form of iodine. For all animals during the experiment the biochemical parameters of blood, milk productivity and reproductive ability were studied. During the experiment, an increase in metabolic and redox processes in the body was noted in the experimental group. An increase in mineral metabolism, including iodine content, was found. Due to the sufficient intake of organic iodine in the animals of the experimental group, there was an increase in the activity of the main hepatic enzymes AST and ALT. An increase in the process of gluconeogenesis due to an increase in the glucose content in the blood of experimental cows was revealed. An increase in milk production and reproductive function of animals of the experimental group was established. Within 30 days after the termination of feeding the supplement with the organic form of iodine in the experimental group, a prolonging effect was observed, consisting in higher values of blood biochemical parameters, improved reproductive function and milk productivity relative to equivalent animals in the control. As a result, it was concluded that the use of an additive with an organic form of iodine in the amount of 1.5 g in feeding cows for 60 days increases the iodine content in the blood serum of animals and increases the performance of all types of metabolism, which may indicate the best stimulating effect of the organic form of iodine on thyroid activity glands. This in turn helps to improve the productive and reproductive qualities of animals. To recommend the studied drug as a means to replenish iodine deficiency in animals and to more accurately analyze its effect on the hormone-forming function of the thyroid gland, it is necessary to study the level of thyroid hormones in the blood.

Thyroid and Cardiovascular Disease: Research Agenda for Enhancing Knowledge, Prevention, and Treatment

Thyroid hormones have long been known to have a range of effects on the cardiovascular system. However, significant knowledge gaps exist concerning the precise molecular and biochemical mechanisms governing these effects and the optimal strategies for management of abnormalities in thyroid function in patients with and without preexisting cardiovascular disease. In September 2017, the National Heart, Lung, and Blood Institute convened a Working Group with the goal of developing priorities for future scientific research relating thyroid dysfunction to the progression of cardiovascular disease. The Working Group reviewed and discussed the roles of normal thyroid physiology, the consequences of thyroid dysfunction, and the effects of therapy in 3 cardiovascular areas: cardiac electrophysiology and arrhythmias, the vasculature and atherosclerosis, and the myocardium and heart failure. This report describes the current state of the field, outlines barriers and challenges to progress, and proposes research opportunities to advance the field, including strategies for leveraging novel approaches using omics and big data. The Working Group recommended research in 3 broad areas: (1) investigation into the fundamental biology relating thyroid dysfunction to the development of cardiovascular disease and into the identification of novel biomarkers of thyroid hormone action in cardiovascular tissues; (2) studies that define subgroups of patients with thyroid dysfunction amenable to specific preventive strategies and interventional therapies related to cardiovascular disease; and (3) clinical trials focused on improvement in cardiovascular performance and cardiovascular outcomes through treatment with thyroid hormone or thyromimetic drugs.

Thyroid and Cardiovascular Disease: Research Agenda for Enhancing Knowledge, Prevention, and Treatment

Thyroid hormones have long been known to have a range of effects on the cardiovascular system. However, significant knowledge gaps exist concerning the precise molecular and biochemical mechanisms governing these effects and the optimal strategies for management of abnormalities in thyroid function in patients with and without preexisting cardiovascular disease. In September 2017, The National Heart, Lung, and Blood Institute convened a Working Group with the goal of developing priorities for future scientific research relating thyroid dysfunction to the progression of cardiovascular disease. The Working Group reviewed and discussed the roles of normal thyroid physiology, the consequences of thyroid dysfunction, and the effects of therapy in three cardiovascular areas: cardiac electrophysiology and arrhythmias, the vasculature and atherosclerosis, and the myocardium and heart failure. This report describes the current state of the field, outlines barriers and challenges to progress, and proposes research opportunities to advance the field, including strategies for leveraging novel approaches using omics and big data. The Working Group recommended research in three broad areas: 1) investigation into the fundamental biology relating thyroid dysfunction to the development of cardiovascular disease and into the identification of novel biomarkers of thyroid hormone action in cardiovascular tissues; 2) studies that define subgroups of patients with thyroid dysfunction amenable to specific preventive strategies and interventional therapies related to cardiovascular disease; and 3) clinical trials focused on improvement in cardiovascular performance and cardiovascular outcomes through treatment with thyroid hormone or thyromimetic drugs.

The Colorful Diversity of Thyroid Hormone Metabolites

Since the discovery of L-thyroxine, the main secretory product of the thyroid gland, and its major metabolite T3, which exerts the majority of thyroid hormone action via ligand-dependent modulation of the function of T3 receptors in nuclei, mitochondria, and other subcellular compartments, various other T4-derived endogenous metabolites have been identified in blood and tissues of humans, animals, and early protochordates. This review addresses major historical milestones and experimental findings resulting in the discovery of the key enzymes of thyroid hormone metabolism, the three selenoprotein deiodinases, as well as the decarboxylases and amine oxidases involved in formation and degradation of recently identified endogenous thyroid hormone metabolites, i.e. 3-iodothyronamine and 3-thyroacetic acid. The concerted action of deiodinases 2 and 3 in regulation of local T3 availability is discussed. Special attention is given to the role of the thyromimetic "hot" metabolite 3,5-T2 and the "cool" 3-iodothyronamine, especially after administration of pharmacological doses of these endogenous thyroid hormone metabolites in various animal experimental models. In addition, available information on the biological roles of the two major acetic acid derivatives of thyroid hormones, i.e. Tetrac and Triac, as well as sulfated metabolites of thyroid hormones is reviewed. This review addresses the consequences of the existence of this broad spectrum of endogenous thyroid hormone metabolites, the "thyronome," beyond the classical thyroid hormone profile comprising T4, T3, and rT3 for appropriate analytical coverage and clinical diagnostics using mass spectrometry versus immunoassays for determination of total and free concentrations of thyroid hormone metabolites in blood and tissues.

Randomized clinical trials with run-in periods: frequency, characteristics and reporting

Background

Run-in periods are occasionally used in randomized clinical trials to exclude patients after inclusion, but before randomization. In theory, run-in periods increase the probability of detecting a potential treatment effect, at the cost of possibly affecting external and internal validity. Adequate reporting of exclusions during the run-in period is a prerequisite for judging the risk of compromised validity. Our study aims were to assess the proportion of randomized clinical trials with run-in periods, to characterize such trials and the types of run-in periods and to assess their reporting.

Materials and methods

This was an observational study of 470 PubMed-indexed randomized controlled trial publications from 2014. We compared trials with and without run-in periods, described the types of run-in periods and evaluated the completeness of their reporting by noting whether publications stated the number of excluded patients, reasons for exclusion and baseline characteristics of the excluded patients.

Results

Twenty-five trials reported a run-in period (5%). These were larger than other trials (median number of randomized patients 217 vs 90, P=0.01) and more commonly industry trials (11% vs 3%, P<0.01). The run-in procedures varied in design and purpose. In 23 out of 25 trials (88%), the run-in period was incompletely reported, mostly due to missing baseline characteristics.

Conclusion

Approximately 1 in 20 trials used run-in periods, though much more frequently in industry trials. Reporting of the run-in period was often incomplete, precluding a meaningful assessment of the impact of the run-in period on the validity of trial results. We suggest that current trials with run-in periods are interpreted with caution and that updates of reporting guidelines for randomized trials address the issue.

Potential Role of Thyroid Receptor β Agonists in the Treatment of Hyperlipidemia

Thyroid hormones have important effects on cellular development, growth, and metabolism and are necessary for the healthy function of almost all tissues. Hyperthyroid patients with excess thyroid hormone levels experience tachycardia, fatigue, muscle wasting, and osteoporosis. However, although high thyroid hormone levels have adverse effects, efforts have been made to harness the beneficial effects, such as reduced serum low-density lipoprotein (LDL) cholesterol levels, elevated basal metabolic rate, and weight loss. Thyroid hormones interact with nuclear thyroid hormone receptors (TRs), and cholesterol levels are reduced through TRβ, whereas extrahepatic adverse actions are primarily connected to TRα. Thus, to develop a useful compound for clinical use, efforts have been focusing on developing compounds with isomer-specific functions based on the structure of thyroid hormones, i.e., thyromimetics that are liver and/or TRβ specific. In this short review, we discuss the development of the early thyromimetics that enabled, through modern molecular techniques, the progress towards improved design of TRβ-selective thyromimetics. We also address the early promise shown in human clinical trials and the current status of these drugs and other emerging compounds.

A decade of thyroidology

Significant scientific progress has been achieved in the past decade in thyroidology driven by scholarly enquiry, unmet patient needs, and investment by the pharmaceutical and diagnostics industry. In this review, nine publications have been selected for their impact in pushing the frontiers of knowledge and understanding. They include new perspectives in the diagnosis, pathophysiology, epidemiology and management of thyroid cancer, understanding of thyroid hormone physiology, and new treatments for Graves' orbitopathy.

Quantification of Thyromimetic Sobetirome Concentration in Biological Tissue Samples

Thyroid hormone is a principal regulator of essential processes in vertebrate physiology and homeostasis. Synthetic derivatives of thyroid hormone, known as thyromimetics, display desirable therapeutic properties. Thoroughly understanding how thyromimetics distribute throughout the body is crucial for their development and this requires appropriate bioanalytical techniques to quantify drug levels in different tissues. Here, we describe a detailed protocol for the quantification of the thyromimetic sobetirome using liquid chromatography tandem-mass spectrometry (LC-MS/MS).

Thyroid hormone analogs for the treatment of dyslipidemia: past, present, and future

OBJECTIVE

Treatment of dyslipidemia is a major burden for public health. Thyroid hormone regulates lipid metabolism by binding the thyroid hormone receptor (TR), but the use of thyroid hormone to treat dyslipidemia is not indicated due to its deleterious effects on heart, bone, and muscle. Thyroid hormone analogs have been conceived to selectively activate TR in the liver, thus reducing potential side-effects.

METHODS

The authors searched the PubMed database to review TR and the action of thyromimetics in vitro and in animal models. Then, all double-blind, placebo controlled trials that analyzed the use of thyroid hormone analog for the treatment of dyslipidemia in humans were included. Finally, the ongoing research on the use of TR agonists was searched, searching the US National Institutes of Health Registry and the WHO International Clinical Trial Registry Platform (ICTRP).

RESULTS

Thyromimetics were tested in humans for the treatment of dyslipidemia, as a single therapeutic agent or as an add-on therapy to the traditional lipid-lowering drugs. In most trials, thyromimetics lowered total cholesterol, low-density lipoprotein cholesterol, and triglycerides, but their use has been associated with adverse side-effects, both in pre-clinical studies and in humans.

CONCLUSIONS

The use of thyromimetics for the treatment of dyslipidemia is not presently recommended. Future possible clinical applications might include their use to promote weight reduction. Thyromimetics might also represent an interesting alternative, both for the treatment of non-alcoholic steatohepatitis, and type 2 diabetes due to their positive effects on insulin sensitivity. Finally, additional experimental and clinical studies are needed for a better comprehension of the effect(s) of a long-term therapy.

The Thyromimetic KB2115 (Eprotirome) Induces Rat Hepatocyte Proliferation

Although the hepatomitogenic activity of T3 is well established, the wide range of harmful effects exerted by this hormone precludes its use in regenerative therapy. The aim of this study was to investigate whether an agonist of TRβ, KB2115 (Eprotirome), could exert a mitogenic effect in the liver, without most of the adverse T3/TRα-dependent side effects. F-344 rats treated with KB2115 for 1 week displayed a massive increase in bromodeoxyuridine incorporation (from 20% to 40% vs. 5% of controls), which was associated with increased mitotic activity in the absence of significant signs of liver toxicity. Noteworthy, while cardiac hypertrophy typical of T3 was not observed, beneficial effects, such as lowering blood cholesterol levels, were associated to KB2115 administration. Following a single dose of KB2115, hepatocyte proliferation was evident as early as 18 h, demonstrating its direct mitogenic effect. No increase in serum transaminase levels or apoptosis was observed prior to or concomitantly with the S phase. While KB2115-induced mitogenesis was not associated to enhance expression of c-fos, c-jun, and c-myc, cyclin D1 levels rapidly increased. In conclusion, KB2115 induces hepatocyte proliferation without overt toxicity. Hence, this agent may be useful for regenerative therapies in liver transplantation or other surgical settings.

Metabolic Syndrome: One Speckled Stone Kills a Flock of Birds?

Effectively treating metabolic syndrome and its progression to type 2 diabetes, steatohepatitis and cardiovascular disease remain a major clinical challenge. The use of a novel engineered molecule that combines thyroid hormone and glucagon to target liver and adipose tissue might provide a new 'magic bullet' with exciting future prospects.

Thyroid Hormone Mimetics: the Past, Current Status and Future Challenges

The association between thyroid hormone status and plasma levels of low-density lipoprotein cholesterol has raised the awareness for the development of thyroid hormone mimetics as lipid-lowering agents. The discovery of the two main types of thyroid hormone receptors (α and β) as well as the development of novel combinatorial chemistry providing organ specificity has drastically improved the selectivity of these compounds. In the past decades, several thyroid hormone mimetics have been investigated with the purpose of lowering low-density lipoprotein cholesterol levels. However, until now, none of the thyromimetics reached the stage of completing a phase III clinical trial without deleterious side effects. Here, we review the currently available literature on thyromimetics investigated for the treatment of dyslipidemia, their rise, their downfall and the challenges for the development of novel agents.

Sustained zero-order delivery of GC-1 from a nanochannel membrane device alleviates metabolic syndrome

BACKGROUND/OBJECTIVES

Our objective was to assess the sustained, low-dose and constant administration of the thyroid receptor-β (TRβ)-selective agonist GC-1 (sobetirome) from a novel nanochannel membrane device (NMD) for drug delivery. As it known to speed up metabolism, accomplish weight loss, improve cholesterol levels and possess anti-diabetic effects, GC-1 was steadily administered by our NMD, consisting of an implantable nanochannel membrane, as an alternative to conventional daily administration, which is subject to compliance issues in clinical settings.

SUBJECTS/METHODS

Diet-induced obese C57BL/J6 male mice were fed a very high-fat diet (VHFD) and received NMD implants subcutaneously. Ten mice per group received capsules containing GC-1 or phosphate-buffered saline (control). Weight, lean and fat mass, as well as cholesterol, triglycerides, insulin and glucose, were monitored for 24 days. After treatment, plasma levels of thyroid-stimulating hormone (TSH) and thyroxine were compared. mRNA levels of a panel of thermogenic markers were examined using real-time PCR in white adipose tissue (WAT) and brown adipose tissue (BAT). Adipose tissue, liver and local inflammatory response to the implant were examined histologically. Pancreatic islet number and β-cell area were assessed.

RESULTS

GC-1 released from the NMD reversed VHFD-induced obesity and normalized serum cholesterol and glycemia. Significant reductions in body weight and fat mass were observed within 10 days, whereas reductions in serum cholesterol and glucose levels were seen within 7 days. The significant decrease in TSH was consistent with TRβ selectivity for GC-1. Levels of transcript for Ucp1 and thermogenic genes PGC1a, Cidea, Dio2 and Cox5a showed significant upregulation in WAT in NMD-GC-1-treated mice, but decreased in BAT. Although mice treated by NMD-GC-1 showed a similar number of pancreatic islets, they exhibited significant increase in β-cell area.

CONCLUSIONS

Our data demonstrate that the NMD implant achieves steady administration of GC-1, offering an effective and tightly controlled molecular delivery system for treatment of obesity and metabolic disease, thereby addressing compliance.

Sobetirome: the past, present and questions about the future

Sobetirome binds selectively to the main hepatic form of thyroid hormone (TH) receptor, TRβ1, compared to TRα1, which is principally responsible for thyrotoxic effects on heart, muscle and bone. Sobetirome also preferentially accumulates in liver. It was originally envisaged that sobetirome could be used to stimulate hepatic pathways that lower cholesterol without harmful side effects and might be used in conjunction with statins. Indeed, sobetirome progressed through preclinical animal studies and Phase I human clinical trials with excellent results and without obvious harmful side effects. Despite the fact that cardiovascular disease remains a major cause of mortality and that new therapies are desperately needed, it is unlikely that sobetirome will progress in further human clinical trials in the near future. The emergence of alternative cholesterol-lowering therapeutics may render selective thyromimetics redundant. Further, fears of thyrotoxic effects in the heart and emergence of cartilage defects in dogs after long-term use of eprotirome, a similar though not identical compound, has reduced enthusiasm for this strategy. We argue that it is nevertheless important to explore uses of sobetirome in humans; more treatment strategies would help patients with hard-to-treat dyslipidemias. Sobetirome may also have additional applications in orphan indications and short-term controlled weight loss.

Evolving targets for lipid-modifying therapy

The pathogenesis and progression of atherosclerosis are integrally connected to the concentration and function of lipoproteins in various classes. This review examines existing and emerging approaches to modify low-density lipoprotein and lipoprotein (a), triglyceride-rich lipoproteins, and high-density lipoproteins, emphasizing approaches that have progressed to clinical evaluation. Targeting of nuclear receptors and phospholipases is also discussed.

Thyroid Disease and the Heart

Thyroid hormones have an intimate relationship with cardiac function. Some of the most significant clinical signs and symptoms of thyroid disease are the cardiac manifestations. In both hypothyroidism and hyperthyroidism, the characteristic physiological effects of thyroid hormone can be understood from the actions at the molecular and cellular level. Here we explore topics from the metabolism and cellular effects of thyroid hormone to special considerations related to statin and amiodarone therapy for the alterations in thyroid hormone metabolism that accompany heart disease.

3,5-Diiodo-L-thyronine (3,5-t2) exerts thyromimetic effects on hypothalamus-pituitary-thyroid axis, body composition, and energy metabolism in male diet-induced obese mice

Effective and safe antiobesity drugs are still needed in face of the obesity pandemic worldwide. Recent interventions in rodents revealed 3,5-diiodo-L-thyronine (3,5-T2) as a metabolically active iodothyronine affecting energy and lipid metabolism without thyromimetic side effects typically associated with T3 administration. Accordingly, 3,5-T2 has been proposed as a potential hypolipidemic agent for treatment of obesity and hepatic steatosis. In contrast to other observations, our experiments revealed dose-dependent thyromimetic effects of 3,5-T2 akin to those of T3 in diet-induced obese male C57BL/6J mice. 3,5-T2 treatment exerted a negative feedback regulation on the hypothalamus-pituitary-thyroid axis, similar to T3. This is demonstrated by decreased expression of genes responsive to thyroid hormones (TH) in pituitary resulting in a suppressed thyroid function with lower T4 and T3 concentrations in serum and liver of 3,5-T2-treated mice. Analyses of hepatic TH target genes involved in lipid metabolism revealed T3-like changes in gene expression and increased type I-deiodinase activity after application of 3,5-T2 (2.5 μg/g body weight). Reduced hepatic triglyceride and serum cholesterol concentrations reflected enhanced lipid metabolism. Desired increased metabolic rate and reduction of different fat depots were, however, compromised by increased food intake preventing significant body weight loss. Moreover, enlarged heart weights indicate potential cardiac side effects of 3,5-T2 beyond hepatic thyromimetic actions. Altogether, the observed thyromimetic effects of 3,5-T2 in several mouse TH target tissues raise concern about indiscriminate administration of 3,5-T2 as powerful natural hormone for the treatment of hyperlipidemia and pandemic obesity.

Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement

BACKGROUND

A number of recent advances in our understanding of thyroid physiology may shed light on why some patients feel unwell while taking levothyroxine monotherapy. The purpose of this task force was to review the goals of levothyroxine therapy, the optimal prescription of conventional levothyroxine therapy, the sources of dissatisfaction with levothyroxine therapy, the evidence on treatment alternatives, and the relevant knowledge gaps. We wished to determine whether there are sufficient new data generated by well-designed studies to provide reason to pursue such therapies and change the current standard of care. This document is intended to inform clinical decision-making on thyroid hormone replacement therapy; it is not a replacement for individualized clinical judgment.

METHODS

Task force members identified 24 questions relevant to the treatment of hypothyroidism. The clinical literature relating to each question was then reviewed. Clinical reviews were supplemented, when relevant, with related mechanistic and bench research literature reviews, performed by our team of translational scientists. Ethics reviews were provided, when relevant, by a bioethicist. The responses to questions were formatted, when possible, in the form of a formal clinical recommendation statement. When responses were not suitable for a formal clinical recommendation, a summary response statement without a formal clinical recommendation was developed. For clinical recommendations, the supporting evidence was appraised, and the strength of each clinical recommendation was assessed, using the American College of Physicians system. The final document was organized so that each topic is introduced with a question, followed by a formal clinical recommendation. Stakeholder input was received at a national meeting, with some subsequent refinement of the clinical questions addressed in the document. Consensus was achieved for all recommendations by the task force.

RESULTS

We reviewed the following therapeutic categories: (i) levothyroxine therapy, (ii) non-levothyroxine-based thyroid hormone therapies, and (iii) use of thyroid hormone analogs. The second category included thyroid extracts, synthetic combination therapy, triiodothyronine therapy, and compounded thyroid hormones.

CONCLUSIONS

We concluded that levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine-liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes. Some examples of future research needs include the development of superior biomarkers of euthyroidism to supplement thyrotropin measurements, mechanistic research on serum triiodothyronine levels (including effects of age and disease status, relationship with tissue concentrations, as well as potential therapeutic targeting), and long-term outcome clinical trials testing combination therapy or thyroid extracts (including subgroup effects). Additional research is also needed to develop thyroid hormone analogs with a favorable benefit to risk profile.

Thyroid hormone reduces PCSK9 and stimulates bile acid synthesis in humans

Reduced plasma LDL-cholesterol is a hallmark of hyperthyroidism and is caused by transcriptional stimulation of LDL receptors in the liver. Here, we investigated whether thyroid hormone (TH) actions involve other mechanisms that may also account for the reduction in LDL-cholesterol, including effects on proprotein convertase subtilisin/kexin type 9 (PCSK9) and bile acid synthesis. Twenty hyperthyroid patients were studied before and after clinical normalization, and the responses to hyperthyroidism were compared with those in 14 healthy individuals after 14 days of treatment with the liver-selective TH analog eprotirome. Both hyperthyroidism and eprotirome treatment reduced circulating PCSK9, lipoprotein cholesterol, apoB and AI, and lipoprotein(a), while cholesterol synthesis was stable. Hyperthyroidism, but not eprotirome treatment, markedly increased bile acid synthesis and reduced fibroblast growth factor (FGF) 19 and dietary cholesterol absorption. Eprotirome treatment, but not hyperthyroidism, reduced plasma triglycerides. Neither hyperthyroidism nor eprotirome treatment altered insulin, glucose, or FGF21 levels. TH reduces circulating PSCK9, thereby likely contributing to lower plasma LDL-cholesterol in hyperthyroidism. TH also stimulates bile acid synthesis, although this response is not critical for its LDL-lowering effect.