Long-term thyroid replacement therapy and levels of lipoprotein(a) and other lipoproteins

Correlation Between Thyroid-Related Hormones and Diabetic Retinopathy in Type 2 Diabetes Mellitus Patients with Normal Thyroid Function: A Retrospective Study

Purpose

To investigate the correlation between thyroid-related hormones and diabetic retinopathy (DR) in euthyroid patients with type 2 diabetes mellitus (T2DM).

Patients and Methods

Patients with T2DM admitted to our hospital between January 2023 and June 2023 were retrospectively analyzed. The patients were divided into DR and non-diabetic retinopathy (NDR) groups according to whether DR occurred. Thyroid function-related hormones (TSH, FT3, and FT4), blood glucose indices (FBG and HbA1c), and blood lipid indices (HDL-C, LDL-C, TC, and TG) of the two groups were analyzed by univariate and multivariate logistic regression to explore the risk factors for DR. Pearson correlation analysis and multiple stepwise regression analysis were used to investigate the correlation of TSH or FT3 with FBG, HbA1c, and TG in DR patients.

Results

Of the 286 patients with T2DM included in this study, 101 (35.31%) developed DR and 185 (64.69%) did not. High TG, FBG, HbA1c, and TSH and low FT3 levels were independent risk factors for DR in T2DM patients. TSH positively correlated with TG, whereas FT3 negatively correlated with TG and HbA1c in T2DM patients with DR.

Conclusion

Higher TSH and lower FT3 in T2DM patients with normal thyroid function may affect glucose and lipid metabolism, thereby increasing the risk of DR.

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.

Effect of thyroid function on pre-β1 high-density lipoprotein levels in patients with Graves' disease undergoing radioiodine treatment

CONTEXT

The metabolism of HDL is altered in thyroid dysfunctions. Preβ-1 HDL is a very small discoidal precursor HDL and promotes cholesterol efflux via ABCA₁. The effects of thyroid dysfunctions on pre-β1 HDL are unknown. Thyroid hormone regulates ANGPTL3 expression, which may participate in HDL metabolism in thyroid dysfunctions.

OBJECTIVE

To determine the variation of HDL subfractions, especially preβ-1 HDL in thyroid dysfunctions, and whether ANGPTL3 mediates the effect of thyroid function on HDL metabolism.

METHODS

We recruited 26 patients with Graves' disease undergoing radioiodine treatment. They were evaluated at three time points: at baseline, when they were hypothyroid after radioiodine treatment, and when they were on stable levothyroxine replacement and euthyroid.

RESULTS

The concentrations of smaller HDL particles Preβ-1 HDL and HDL3 were highest at the hyperthyroid state, and lowest at the hypothyroid state. While the larger HDL particles HDL2 and HDL1 changed just the opposite. Preβ1-HDL and HDL3 were positively correlated to fT₃ and fT₄, while were negatively correlated to TSH. In contrast, HDL1 was negatively associated with fT₃ and fT₄, while was positively associated with TSH. The correlations between thyroid hormones and HDL subfractions remained significant after adjusting for ANGPTL3.

CONCLUSIONS

There is a shift form smaller HDL particles pre-β1 HDL and HDL3 to larger HDL particles HDL2 and HDL1 in hypothyroidism, while the change is just the opposite in hyperthyroidism. In future, cholesterol efflux capacity should be measured to determine if the function of HDL particles also changes with the shifting of HDL subfractions.

Effects of Thyroid Hormones on Lipid Metabolism Pathologies in Non-Alcoholic Fatty Liver Disease

The typical modern lifestyle contributes to the development of many metabolic-related disorders, as exemplified by metabolic syndrome. How to prevent, resolve, or avoid subsequent deterioration of metabolic disturbances and the development of more serious diseases has become an important and much-discussed health issue. Thus, the question of the physiological and pathological roles of thyroid hormones (THs) in metabolism has never gone out of fashion. Although THs influence almost all organs, the liver is one of the most important targets as well as the hub of metabolic homeostasis. When this homeostasis is out of balance, diseases may result. In the current review, we summarize the common features and actions of THs, first focusing on their effects on lipid metabolism in the liver. In the second half of the review, we turn to a consideration of non-alcoholic fatty liver disease (NAFLD), a disease characterized by excessive accumulation of fat in the liver that is independent of heavy alcohol consumption. NAFLD is a growing health problem that currently affects ~25% of the world’s population. Unfortunately, there are currently no approved therapies specific for NAFLD, which, if left uncontrolled, may progress to more serious diseases, such as cirrhosis or liver cancer. This absence of effective treatment can also result in the development of non-alcoholic steatohepatitis (NASH), an aggressive form of NAFLD that is the leading cause of liver transplantation in the United States. Because THs play a clear role in hepatic fat metabolism, their potential application in the prevention and treatment of NAFLD has attracted considerable research attention. Studies that have investigated the use of TH-related compounds in the management of NAFLD are also summarized in the latter part of this review. An important take-home point of this review is that a comprehensive understanding of the physiological and pathological roles of THs in liver fat metabolism is possible, despite the complexities of this regulatory axis—an understanding that has clinical value for the specific management of NAFLD.

Development of Thyroid Hormones and Synthetic Thyromimetics in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the fastest-growing liver disease in the world. Despite targeted agents which are needed to provide permanent benefits for patients with NAFLD, no drugs have been approved to treat NASH. Thyroid hormone is an important signaling molecule to maintain normal metabolism, and in vivo and vitro studies have shown that regulation of the 3,5,3'-triiodothyronine (T3)/ thyroid hormone receptor (TR) axis is beneficial not only for metabolic symptoms but also for the improvement of NAFLD and even for the repair of liver injury. However, the non-selective regulation of T3 to TR subtypes (TRα/TRβ) could cause unacceptable side effects represented by cardiotoxicity. To avoid deleterious effects, TRβ-selective thyromimetics were developed for NASH studies in recent decades. Herein, we will review the development of thyroid hormones and synthetic thyromimetics based on TR selectivity for NAFLD, and analyze the role of TR-targeted drugs for the treatment of NAFLD in the future.

Changes of Certain Metabolic and Cardiovascular Markers Fructosamine, H-FABP and Lipoprotein (a) in Patients with Hypothyroidism

Background:

Disorders of thyroid gland are common in general population, and it’s the most common affecting the endocrine system after diabetes mellitus. Thyroid function regulates a wide range of metabolic parameters, as well as affects some cardiovascular disease risk factors. Fructosamine is produced by a reaction between albumin (protein) and glucose; it is used to monitor patients with diabetes for short-term glycemic changes. H-FABP is present in the cytoplasm of cardiac myocytes, and delivers fatty acids into these cells. It has been shown to increase in myocardial injury. Lipoprotein LP(a) is consist of a special apolipoprotein called apoprotein (a), and it’s recognized as a cardiovascular disease independent risk factor.

Objective:

To study whether certain metabolic and cardiovascular markers (fructosamine, H-FABP and lipoprotein (a) are changed in hypothyroid patients.

Methods:

The current study included 280 overt hypothyroid, 272 with subclinical hypothyroidism compared with 270 healthy individuals of matched age and gender. For all subjects serum (TSH, T4, T3, FBS, HbA1c, fructosamine, triglycerides, cholesterol, lipoprotein (a), and Heart-type Fatty Acid-Binding Protein (H-FABP)) was measured.

Results:

Serum fructosamine level significantly elevated (p value <0.05) in patient with hypothyroidism when compared with control group, and no significant change between subclinical and control groups. There is no significant change in serum H-FABP between study subjects. There is significant increase in lipoprotein (a) in patient with hypothyroidism and those with subclinical group when compared with control group.

Conclusion:

Serum fructosamine and level is significantly changed in patients with overt hypothyroidism when compared with euthyroid subjects. Also, we conclude that hypothyroidism increase risk of cardiovascular diseases by changing non-traditional marker such as lipoprotein (a), and no effect on H-FABP concentration.

Hypothyroidism: Cardiovascular Endpoints of Thyroid Hormone Replacement

Thyroid dysfunction, either thyrotoxicosis or hypothyroidism, represents an important cardiovascular risk factor. Heart disease is the leading cause of death for men and women in the United States. Cardiovascular disease is multifactorial and many efforts have been made to assess precipitants for optimal guideline-based, primary, and secondary prevention. Thyroid hormone receptors are present in the myocardium and endothelium, and small alterations in its levels could have significant effects in cardiac function. Specifically, overt hypothyroidism is associated with an increased risk for atherosclerotic cardiovascular disease due to metabolic and hemodynamic effects. Several concomitant factors like impaired lipid profile, low-grade chronic inflammatory state, increased oxidative stress and increased insulin resistance enforce this relationship. The last decade has seen a renewed interest on the impact of subclinical hypothyroidism on the cardiovascular system and whether or not it should be treated. The aim of this review is to provide current evidence of the effect of thyroid hormone replacement, either with levothyroxine mono-therapy or in combination with liothyronine, on specific cardiovascular parameters.

Systemic Thyroid Hormone Status During Levothyroxine Therapy In Hypothyroidism: A Systematic Review and Meta-Analysis

CONTEXT

The standard of care for overt hypothyroidism is levothyroxine at doses that normalize serum TSH levels. Whether this approach universally restores thyroid hormone signaling is unknown.

OBJECTIVE

To review studies of overt hypothyroidism in which participants were treated with levothyroxine to normalize serum TSH levels and measured other objective markers of thyroid hormone signaling.

DESIGN

Databases were searched for studies that reported objective markers of thyroid hormone signaling (serum low-density lipoprotein (LDL), total cholesterol (TC), sex hormone-binding globulin (SHBG), creatine kinase and/or ferritin levels; cognition, energy expenditure, and/or renal function) in levothyroxine monotherapy for overt, primary hypothyroidism among nonpregnant adults with normal serum TSH levels. For studies with LDL, TC and SHBG outcomes, data were pooled using random effects meta-analysis.

RESULTS

A total of 99 studies met inclusion criteria, including 65 that reported serum cholesterol data. Meta-analysis showed that levothyroxine-treated hypothyroid participants with normal serum TSH levels had 3.31 ± 1.64 mg/dL higher serum LDL levels (p=0.044) and 9.60 ± 3.55 mg/dL higher serum TC levels (p=0.007) compared to controls. In studies that did not concomitantly assess healthy controls, serum LDL levels were 138.3 ± 4.6 mg/dL (p<0.001) and serum TC levels were 209.6 ± 3.4 mg/dL (p<0.001). Meta-analysis of 2 studies showed no significant difference between SHBG levels of levothyroxine-treated participants and controls.

CONCLUSIONS

In studies that utilized levothyroxine monotherapy at doses that normalized the serum TSH for overt, primary hypothyroidism, not all systemic biological markers of thyroid hormone signaling were normalized, including serum LDL and TC levels.

Relationship between Lipoprotein(a) and Thyroid Hormones in Hypothyroid Patients

BACKGROUND AND OBJECTIVE

Changes in plasma lipid concentrations are well known metabolic consequences of thyroid dysfunction. The alterations are most prominent in hypothyroidism which is typically associated with pronounced hypercholesterolaemia and frequently with moderate hypertriglyceridaemia. In cases of hypothyroidism, how the serum Lp(a) levels are influenced by thyroid hormone remains unknown and contradictory results on the effect of thyroid hormone on serum Lp(a) levels have been reported. There is substantial evidence to suggest that elevated serum Lp(a) levels contribute significantly to the development of CHD. The present study was designed to determine the lipoprotein(a) [Lp(a)], lipid profile and thyroid hormone levels in newly diagnosed hypothyroid patients and to find any correlation that existed between Lp(a) and other parameters.

MATERIALS AND METHODS

Untreated hypothyroid (n=50) patients were included in the study. We also included 40 normal healthy subjects as controls. Lipid profile, Lp(a) and thyroid profile were estimated by using autoanalyzers.

RESULTS

The results of this study showed that levels of HDL-cholesterol were significantly decreased (p<0.001), whereas those of other lipid parameters and Lp(a) levels were found to be significantly increased (p<0.001) in hypothyroid patients as compared to those in controls. Correlation study revealed a significant positive correlation between Lp(a) and TSH levels in hypothyroid patients.

CONCLUSION

Our present findings indicated that hypothyroidism could be strongly associated with lipid abnormalities that enhanced the development of cardiovascular diseases. Also, Lp(a) and non-HDL-C should be estimated with other lipid parameters as a useful index for measuring the cardiac risk in hypothyroid patients. A recommended screening should be advised for any patient with thyroid dysfunction, especially hypothyroidism, to assess lipid abnormalities by using Lp(a) and non- HDL-C and he/she should treated at the earliest.

Lipid abnormalities and cardiometabolic risk in patients with overt and subclinical thyroid disease

Dyslipidemia is a common finding in patients with thyroid disease, explained by the adverse effects of thyroid hormones in almost all steps of lipid metabolism. Not only overt but also subclinical hypo- and hyperthyroidism, through different mechanisms, are associated with lipid alterations, mainly concerning total and LDL cholesterol and less often HDL cholesterol, triglycerides, lipoprotein (a), apolipoprotein A1, and apolipoprotein B. In addition to quantitative, qualitative alterations of lipids have been also reported, including atherogenic and oxidized LDL and HDL particles. In thyroid disease, dyslipidemia coexists with various metabolic abnormalities and induce insulin resistance and oxidative stress via a vice-vicious cycle. The above associations in combination with the thyroid hormone induced hemodynamic alterations, might explain the increased risk of coronary artery disease, cerebral ischemia risk, and angina pectoris in older, and possibly ischemic stroke in younger patients with overt or subclinical hyperthyroidism.

Thyroid function and lipid subparticle sizes in patients with short-term hypothyroidism and a population-based cohort

CONTEXT

Relations between thyroid function and lipids remain incompletely understood.

OBJECTIVE

Our objective was to determine whether lipoprotein subparticle concentrations are associated with thyroid status.

DESIGN AND SETTING

We conducted a prospective clinical study and cross-sectional cohort analysis at a university endocrine clinic and the Framingham Heart Study.

SUBJECTS

Subjects included 28 thyroidectomized patients with short-term overt hypothyroidism and 2944 Framingham Offspring cohort participants.

MAIN OUTCOME MEASURES

Fasting subclass concentrations of very-low-density lipoprotein (VLDL), intermediate-density lipoprotein, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) particles were measured by nuclear magnetic resonance spectroscopy. TSH values were also measured.

RESULTS

Total cholesterol and LDL-C were increased during short-term overt hypothyroidism. Large LDL subparticle concentrations increased during hypothyroidism (917+/-294 vs. 491+/-183 nmol/liter; P<0.001), but more atherogenic small LDL was unchanged. Triglycerides marginally increased during hypothyroidism, small VLDL particles significantly increased (P<0.001), whereas more atherogenic large VLDL was unchanged. Total HDL-C increased during hypothyroidism (76+/-13 mg/dl vs. 58+/-15 mg/dl; P<0.001). There was no change in large HDL-C particle concentrations, whereas small (P<0.001) and medium (P=0.002) HDL-C particle concentrations decreased. Among Framingham women, adjusted total cholesterol and LDL-C were positively related to TSH categories (P<or=0.003). This was due to a positive correlation between adjusted large LDL subparticle concentrations and log-TSH (P<0.0001); log small LDL subparticle concentrations decreased slightly as log-TSH increased (P=0.045). Among Framingham men, the only significant association was a positive association between log-TSH and log large HDL subparticle concentrations (P=0.04).

CONCLUSIONS

There is a shift toward less atherogenic large LDL, small VLDL, and large HDL subparticle sizes in hypothyroid women.

Hypothyroidism and dyslipidemia: modern concepts and approaches

Subclinical and overt hypothyroidism are relatively common disorders in the general population. Thyroid hormone is known to play a role in regulating the synthesis, metabolism, and mobilization of lipids. In patients with overt hypothyroidism there is an increase in serum total cholesterol, low-density lipoprotein (LDL) cholesterol, apolipoprotein B, lipoprotein(a) levels, and possibly triglyceride levels. The effects of subclinical hypothyroidism on serum lipid values are less clear. The preponderance of evidence suggests that total cholesterol, LDL cholesterol, and possibly triglycerides are increased in patients with subclinical hypothyroidism, whereas high-density lipoprotein (HDL) cholesterol and Lp(a) remain unchanged. Most lipid abnormalities in patients with overt hypothyroidism will resolve with thyroid hormone replacement therapy. However, clinical trials to date have not shown a beneficial effect of thyroid hormone treatment on serum lipid levels in patients with subclinical hypothyroidism. The lipid-altering effects of thyroid hormone make it an appealing target for drug development. The development of specifically targeted thyroid hormone analogues that could potentially treat hyperlipidemia without causing systemic thyrotoxicosis is currently ongoing.

Hypothyroidism as a risk factor for cardiovascular disease

The cardiovascular risk in patients with hypothyroidism is related to an increased risk of functional cardiovascular abnormalities and to an increased risk of atherosclerosis. The pattern of cardiovascular abnormalities is similar in subclinical and overt hypothyroidism, suggesting that a lesser degree of thyroid hormone deficiency may also affect the cardiovascular system. Hypothyroid patients, even those with subclinical hypothyroidism, have impaired endothelial function, normal/depressed systolic function, left ventricular diastolic dysfunction at rest, and systolic and diastolic dysfunction on effort, which may result in poor physical exercise capacity. There is also a tendency to increase diastolic blood pressure as a result of increased systemic vascular resistance. All these abnormalities regress with L-T4 replacement therapy. An increased risk for atherosclerosis is supported by autopsy and epidemiological studies in patients with thyroid hormone deficiency. The "traditional" risk factors are hypertension in conjunction with an atherogenic lipid profile; the latter is more often observed in patients with TSH >10 mU/L. More recently, C-reactive protein, homocysteine, increased arterial stiffness, endothelial dysfunction, and altered coagulation parameters have been recognized as risk factors for atherosclerosis in patients with thyroid hormone deficiency. This constellation of reversible cardiovascular abnormalities in patient with TSH levels <10 mU/L indicate that the benefits of treatment of mild thyroid failure with appropriate doses of L-thyroxine outweigh the risk.

Subclinical thyroid disorders: the menace of the Trojan horse

This review aims at summarizing some new data regarding the so-called subclinical thyroid disease and incorporate the knowledge in order to provide a basis for a more careful approach to these morbidities. SHyper represents a considerable risk factor for atrial fibrillation in the elderly and also for osteoporosis, which is a major cause of morbidity in postmenopausal women. SHypo is not an innocuous condition. It progresses to thyroid failure in patients with positive thyroid antibodies, it affects neurobehavior, it may influence cardiac contractility at exercise and it is associated with an impaired lipid profile that may provoke atherosclerosis. Therefore, both conditions should be screened more carefully in the community and treatment should be more often considered.