Effects of Thyrotropin on Peripheral Thyroid Hormone Metabolism and Serum Lipids

Gender difference in the relationship between clinical symptoms, thyroid hormones, and metabolic parameters in young, first-episode and drug-naïve major depressive disorder patients with suicide attempts: A network analysis perspective

BACKGROUND

Suicide attempts are one of the most serious comorbidities in patients with major depressive disorder (MDD), and the prevalence of suicide attempts is higher in younger people compared to older people, with significant gender differences. This study aimed to investigate the relationship between suicide attempts, clinical symptoms, thyroid hormones, and metabolic parameters in young first-episode and drug-naïve (FEND) MDD patients of different genders.

METHODS

A total of 1289 FEND MDD patients were recruited. Depression, anxiety, and psychotic symptoms were assessed using the Hamilton Depression Rating Scale (HAMD), Hamilton Anxiety Rating Scale (HAMA), and the Positive and Negative Syndrome Scale (PANSS) positive subscale, respectively. Thyroid hormones and glucolipid metabolism indicators were also tested. Network analysis was employed to delineate the interplay between thyroid dysfunction, clinical symptoms, and metabolic disorders.

RESULTS

Among young FEND MDD patients, the rate of suicide attempts was 17.4% in males and 19.8% in females, showing no significant gender difference in the incidence of suicide attempts (χ2 = 1.06, p = 0.303). In the network model, PANSS positive subscale (Expected Influence = 0.578) and HAMD scores (Expected Influence = 0.576) were identified as the individual symptoms that most affected male patients, whereas TSH (Thyroid-Stimulating Hormone) (Expected Influence = 0.972) and PANSS positive subscale (Expected Influence = 0.937) were identified as the individual symptoms that most affected female patients. In addition, we found that TSH (Expected Influence = 0.438) was a pivotal node connecting metabolic disturbances and clinical symptoms.

CONCLUSION

Our findings emphasize the important role of psychotic symptoms in young MDD patients with suicide attempts. Moreover, our results highlight the pivotal role of serum TSH levels in the pathophysiology of young female MDD patients with suicide attempts.

Cross-Talk Between Thyroid Disorders and Nonalcoholic Fatty Liver Disease: From Pathophysiology to Therapeutics

The medical community acknowledges the presence of thyroid disorders and nonalcoholic fatty liver disease (NAFLD). Nevertheless, the interconnection between these two circumstances is complex. Thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), and thyroid-stimulating hormone (TSH), are essential for maintaining metabolic balance and controlling the metabolism of lipids and carbohydrates. The therapeutic potential of THs, especially those that target the TRβ receptor isoform, is generating increasing interest. The review explores the pathophysiology of these disorders, specifically examining the impact of THs on the metabolism of lipids in the liver. The purpose of this review is to offer a thorough analysis of the correlation between thyroid disorders and NAFLD, as well as suggest potential therapeutic approaches for the future.

Co-Morbid Hypothyroidism and Liver Dysfunction: A Review

The liver and thyroid hormones interact at multiple levels to maintain homoeostasis. The liver requires large adequate amounts of thyroid hormones to execute its metabolic functions optimally, and deficiency of thyroid hormones may lead to liver dysfunction. Hypothyroidism has been associated with abnormal lipid metabolism, non-alcoholic fatty liver disease (NAFLD), hypothyroidism-induced myopathy, hypothyroidism-associated gallstones and occasionally, interferon-induced thyroid dysfunction. NAFLD remain an important association with hypothyroidism and further studies are needed that specifically compare the natural course of NAFLD secondary to hypothyroidism and primary NAFLD. Hepatic dysfunction associated with hypothyroidism is usually reverted by normalizing thyroid status. Large scale studies geared towards finding new and effective therapies, especially for NAFLD are needed. The clinician must be aware that there exists overlapping symptomatology between liver dysfunction and severe hypothyroidism which may make delay the diagnosis and treatment of hypothyroidism; this requires a high index of suspicion.

Reduced Sensitivity to Thyroid Hormones Is Associated With High Remnant Cholesterol Levels in Chinese Euthyroid Adults

CONTEXT

It remains unclear whether the thyroid system could regulate the atherogenic remnant cholesterol (RC) levels in euthyroid status.

OBJECTIVE

We aimed to investigate the relationship between sensitivity to thyroid hormones and RC levels in Chinese euthyroid population.

METHODS

This study included 18 766 euthyroid adults. High RC levels were defined as the upper quartile of RC levels. The thyroid hormone sensitivity indices, including thyroid feedback quantile-based index (TFQI), thyroid-stimulating hormone index (TSHI), thyrotrophic thyroxine resistance index (TT4RI), and free triiodothyronine to free thyroxine (FT3/FT4) ratio were calculated. Linear and binary logistic regression analysis were applied to determine the associations between those composite indices with RC levels by genders.

RESULTS

Both females and males with high RC levels exhibited co-existing higher TSH and FT4 levels. Linear regression analysis revealed that TFQI, TSHI, and TT4RI were positively, while FT3/FT4 ratio levels were negatively associated with serum RC levels. The odds ratios (ORs) (95% CI) for high RC levels were increased with rising TFQI quartiles (Q) [females: Q3 1.41 (1.22-1.63), Q4 1.61 (1.39-1.86); males: Q3 1.25 (1.09-1.45), Q4 1.38 (1.19-1.59), all P for trend < 0.001] after full adjustment, with Q1 as the reference. TSHI and TT4RI yielded similar results. By contrast, the ORs (95% CI) for high RC levels were decreased with increasing FT3/FT4 ratio quartiles in both genders (P for trend < 0.001).

CONCLUSION

In euthyroid adults, reduced sensitivity to thyroid hormones was associated with high RC levels. Our results suggested an additive cardiometabolic risk of euthyroid population with thyroid hormones insensitivity.

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.

Update on dyslipidemia in hypothyroidism: the mechanism of dyslipidemia in hypothyroidism

Hypothyroidism is often associated with elevated serum levels of total cholesterol, LDL-C and triglycerides. Thyroid hormone (TH) affects the production, clearance and transformation of cholesterol, but current research shows that thyroid-stimulating hormone (TSH) also participates in lipid metabolism independently of TH. Therefore, the mechanism of hypothyroidism-related dyslipidemia is associated with the decrease of TH and the increase of TSH levels. Some newly identified regulatory factors, such as proprotein convertase subtilisin/kexin type 9, angiogenin-like proteins and fibroblast growth factors are the underlying causes of dyslipidemia in hypothyroidism. HDL serum concentration changes were not consistent, and its function was reportedly impaired. The current review focuses on the updated understanding of the mechanism of hypothyroidism-related dyslipidemia.

Assessment of causal direction between thyroid function and cardiometabolic health: a Mendelian randomization study

BACKGROUND

Growing evidence have demonstrated that thyroid hormones have been involved in the processes of cardiovascular metabolism. However, the causal relationship of thyroid function and cardiometabolic health remains partly unknown.

METHODS

The Mendelian randomization (MR) was used to test genetic, potentially causal relationships between instrumental variables and cardiometabolic traits. Genetic variants of free thyroxine (FT4) and thyrotropin (TSH) levels within the reference range were used as instrumental variables. Data for genetic associations with cardiometabolic diseases were acquired from the genome-wide association studies of the FinnGen, CARDIoGRAM and CARDIoGRAMplusC4D, CHARGE, and MEGASTROKE. This study was conducted using summary statistic data from large, previously described cohorts. Association between thyroid function and essential hypertension (EHTN), secondary hypertension (SHTN), hyperlipidemia (HPL), type 2 diabetes mellitus (T2DM), ischemic heart disease (IHD), myocardial infarction (MI), heart failure (HF), pulmonary heart disease (PHD), stroke, and non-rheumatic valve disease (NRVD) were examined.

RESULTS

Genetically predicted FT4 levels were associated with SHTN (odds ratio = 0.48; 95% CI = 0.04−0.82,P = 0.027), HPL (odds ratio = 0.67; 95% CI = 0.18−0.88,P = 0.023), T2DM (odds ratio = 0.80; 95% CI = 0.42−0.86,P = 0.005), IHD (odds ratio = 0.85; 95% CI = 0.49−0.98,P = 0.039), NRVD (odds ratio = 0.75; 95% CI = 0.27−0.97,P = 0.039). Additionally, genetically predicted TSH levels were associated with HF (odds ratio = 0.82; 95% CI = 0.68−0.99,P = 0.042), PHD (odds ratio = 0.75; 95% CI = 0.32−0.82,P = 0.006), stroke (odds ratio = 0.95; 95% CI = 0.81−0.97,P = 0.007). However, genetically predicted thyroid function traits were not associated with EHTN and MI.

CONCLUSIONS

Our study suggests FT4 and TSH are associated with cardiometabolic diseases, underscoring the importance of the pituitary-thyroid-cardiac axis in cardiometabolic health susceptibility.

Menopausal Impact on the Association Between Thyroid Dysfunction and Lipid Profiles: A Cross-Sectional Study

BACKGROUND

Both dyslipidemia and thyroid dysfunction have a high prevalence rate and are important risk factors for cardiovascular diseases. However, the relationship between blood lipids and thyroid dysfunction is still controversial. This study aims to analyze the blood lipids in people with different thyroid functions.

METHODS

A total of 80937 adults were included in this population-based cross-sectional TIDE survey, which collected demographic and clinical data on thyroid function, blood lipid levels and other metabolic indicators. After screening, the final analysis included 10,747 participants, who were divided into hypothyroidism (n=311), subclinical hypothyroidism (n=5015), hyperthyroidism (n=203), subclinical hyperthyroidism (n=118) and control (n=5100) groups. The risk of dyslipidemia was analyzed by a logistic regression model and divided into groups of female menopausal.

RESULTS

After full adjustment, significant associations were found between hypothyroidism and hypertriglyceridemia. Subclinical hypothyroidism was associated with a significantly higher risk of hypertriglyceridemia and hyper-low density lipoprotein cholesterolemia. Hyperthyroidism was significantly correlated with a reduced risk of hypercholesterolemia and hyper-low density lipoprotein cholesterolemia but positively correlated with the risk of low-high density lipoprotein cholesterolemia. There was no significant association between subclinical hyperthyroidism and blood lipids. Hypothyroidism increased the risk of hypertriglyceridemia in both premenopausal and postmenopausal females. Subclinical hypothyroidism was significantly associated with increased hypertriglyceridemia and low-high density lipoprotein cholesterolemia in premenopausal females. Hyperthyroidism was significantly associated with a reduced risk of hypercholesterolemia and hyper-low density lipoprotein cholesterolemia in premenopausal females and an increased risk of low-high density lipoprotein cholesterolemia in postmenopausal female.

CONCLUSION

Abnormal thyroid function has an important effect on blood lipids and is closely related to female menopause.

Dyslipidemia Risk in Thyroid Cancer Patients: A Nationwide Population-Based Cohort Study

OBJECTIVE

Thyroid cancer (TC) prevalence has been rapidly increasing. While the relationship between thyroid hormones and lipids has been widely investigated, studies regarding dyslipidemia in patients with TC have been scarce and controversial. We aimed to investigate dyslipidemia risk after TC diagnosis compared to the general population without TC.

METHOD

A population-based prospective study was conducted using data from the Korean National Health Insurance Service-National Sample Cohort Database 2.0 (NHIS-NSC DB 2.0), with health insurance claim data of 1,108,369 subjects between 2002 and 2015. The final study sample comprised 466,735 adult subjects without TC or dyslipidemia diagnoses before the index year, 2009. Bidirectional analyses were performed using prospective and retrospective concepts. In the prospective analysis, Kaplan-Meier estimates were calculated and log-rank tests and univariable and multivariable Cox regression analyses were performed to determine the relationship between TC and dyslipidemia. The retrospective analysis involved 1:5 nested case-control matching based on dyslipidemia status and conditional logistic regression analysis.

RESULTS

No significant difference in dyslipidemia incidence was observed between TC patients and the control group, in either the prospective matched (log-rank P = 0.483) or non-matched (log-rank P = 0.424) analyses, or the retrospective analysis (P = 0.3724). In the prospective analysis, 193 patients after TC diagnosis showed similar risk of developing dyslipidemia with the 466,542 controls during the median 7 years of follow-up (unadjusted hazard ratio [HR], 1.102; 95% confidence interval [CI], 0.878-1.383; adjusted HR, 0.932; 95% CI, 0.707-1.230). Multiple propensity score-adjusted models showed similar results, and 114 patients and 570 matched controls showed an HR of 0.818 (95% CI, 0.598-1.120). In the retrospective comparison of dyslipidemia risk in 170 patients and 277,864 controls, the odds ratio was 0.822 (95% CI, 0.534-1.266).

CONCLUSIONS

Dyslipidemia risk was not significantly different between patients with TC and the general population, in both prospective and retrospective analyses.

Association of thyroid hormone with body fat content and lipid metabolism in euthyroid male patients with type 2 diabetes mellitus: a cross-sectional study

BACKGROUND

This study aimed to explore the associations of thyroid hormones with body fat content and lipid metabolism in euthyroid male patients with type 2 diabetes mellitus (T2DM).

METHODS

In January 2017, a cross sectional study, 66 male patients with T2DM who met the World Health Organization diagnostic criteria of 1999 who were ≥ 18.0 years and had normal thyroid function were recruited at a tertiary hospital. The categories of thyroid hormones (free triiodothyronine [FT3], free thyroxine [FT4], and thyroid-stimulating hormone [TSH]) were divided into three groups according to tertiles of thyroid hormones.

RESULTS

The mean FT3, FT4, and TSH of the patients were 2.56 pg/mL, 1.03 ng/dL, and 1.50 μIU/mL, respectively. Increased FT3 were associated with higher body mass index (BMI) (P <  0.001), body fat percentage (BFP) (P = 0.008), visceral fat content (VFC) (P = 0.019), adiponectin (P = 0.037), tumor necrosis factor alpha (TNF-α) (P <  0.001), and interleukin 6 (IL-6) (P = 0.015). There were significant differences among the different FT4 categories for BMI (P = 0.033), waist-hip ratio (WHR) (P = 0.030), low-density lipoprotein cholesterol (LDL-C) (P = 0.014), and IL-6 (P = 0.009). Increased TSH could increase the total cholesterol (TC) (P = 0.005) and high-density lipoprotein cholesterol (HDL-C) (P = 0.010). FT3 was positively correlated with BMI (r = 0.45; P <  0.001), WHR (r = 0.27; P = 0.028), BFP (r = 0.33; P = 0.007), VFC (r = 0.30; P = 0.014), adiponectin (r = 0.25; P = 0.045), TNF-α (r = 0.47; P <  0.001), and IL-6 (r = 0.32; P = 0.008). FT4 was positively correlated with HDL-C (r = 0.26; P = 0.038), LDL-C (r = 0.26; P = 0.036), and adiponectin (r = 0.28; P = 0.023). TSH was positively correlated with TC (r = 0.36; P = 0.003).

CONCLUSION

This study found that the changes in thyroid hormones are associated with various body fat content and lipid metabolism in euthyroid male patients with T2DM.

Lipoprotein (a) as a treatment target for cardiovascular disease prevention and related therapeutic strategies: a critical overview

Advances in several fields of cardiovascular (CV) medicine have produced new treatments (e.g. to treat dyslipidaemia) that have proven efficacy in terms of reducing deaths and providing a better quality of life. However, the burden of CV disease (CVD) remains high. Thus, there is a need to search for new treatment targets. Lipoprotein (a) [Lp(a)] has emerged as a potential novel target since there is evidence that it contributes to CVD events. In this narrative review, we present the current evidence of the potential causal relationship between Lp(a) and CVD and discuss the likely magnitude of Lp(a) lowering required to produce a clinical benefit. We also consider current and investigational treatments targeting Lp(a), along with the potential cost of these interventions.

Assessment of causal association between thyroid function and lipid metabolism: a Mendelian randomization study

Background:

Thyroid dysfunction is associated with cardiovascular diseases. However, the role of thyroid function in lipid metabolism remains partly unknown. The present study aimed to investigate the causal association between thyroid function and serum lipid metabolism via a genetic analysis termed Mendelian randomization (MR).

Methods:

The MR approach uses a genetic variant as the instrumental variable in epidemiological studies to mimic a randomized controlled trial. A two-sample MR was performed to assess the causal association, using summary statistics from the Atrial Fibrillation Genetics Consortium (n = 537,409) and the Global Lipids Genetics Consortium (n = 188,577). The clinical measures of thyroid function include thyrotropin (TSH), free triiodothyronine (FT3) and free thyroxine (FT4) levels, FT3:FT4 ratio and concentration of thyroid peroxidase antibodies (TPOAb). The serum lipid metabolism traits include total cholesterol (TC) and triglycerides, high-density lipoprotein, and low-density lipoprotein (LDL) levels. The MR estimate and MR inverse variance-weighted method were used to assess the association between thyroid function and serum lipid metabolism.

Results:

The results demonstrated that increased TSH levels were significantly associated with higher TC (β = 0.052, P = 0.002) and LDL (β = 0.041, P = 0.018) levels. In addition, the FT3:FT4 ratio was significantly associated with TC (β = 0.240, P = 0.033) and LDL (β = 0.025, P = 0.027) levels. However, no significant differences were observed between genetically predicted FT4 and TPOAb and serum lipids.

Conclusion:

Taken together, the results of the present study suggest an association between thyroid function and serum lipid metabolism, highlighting the importance of the pituitary-thyroid-cardiac axis in dyslipidemia susceptibility.

Lipidomic Perturbations in Cynomolgus Monkeys are Regulated by Thyroid Stimulating Hormone

Thyroid disease affects an estimated 200 million people worldwide, and is commonly associated with increased blood lipid levels. However, the mechanism by which thyroid-stimulating hormone (TSH) affects lipid profiles is not clear. Twenty-four cynomolgus monkeys were treated with a novel exogenous recombinant human TSH (rhTSH) (SNA001) at 9 μg kg⁻¹, 22 μg kg⁻¹, or 54 μg kg⁻¹, and reference rhTSH (Thyrogen^®) at 22 μg kg⁻¹. The primary TSH (SNA001) pharmacokinetic (PK) parameters increased in a dose-dependent manner across the dose range of 9 μg kg⁻¹, 22 μg kg⁻¹, or 54 μg kg⁻¹. Peak triiodothyronine (T3) and thyroxine (T4) levels were reached within 24 h after rhTSH administration, which was delayed by approximately 20 h. In total, 420 lipid species were detected and quantified by ultra-performance liquid chromatography high resolution spectrometry (UPLC-HR-MS)-based lipidomics. Notably, peak levels of lipid accumulation, particularly sphingomyelin (SM) and triglycerides (TG), appeared at 4 and 24 h, which was consistent with the pattern of TSH and T3/T4 levels, respectively. According to weighted correlation network analysis (WGCNA), perturbations of many lipid species were strongly correlated with TSH and T3/T4 levels. TSH and the stimulated T3/T4 levels and lipid profiles following SNA001 administration were comparable to those after administration of the reference rhTSH (Thyrogen^®). The plasma lipidome and changes in lipid levels after rhTSH stimulation were associated with TSH and T3/T4 concentrations. T3/T4 and lipid profiles were delayed after TSH stimulation. Such phenomena require further exploration.

Differences in HDL particle size in the presence of subclinical thyroid dysfunctions: The ELSA-Brasil study

BACKGROUND AND AIMS

Thyroid dysfunction is related to several lipid abnormalities. There is no consensus about concentration of high-density lipoprotein (HDL) in different studies. The aim of this report is to evaluate HDL particle (HDL-P) subfractions across a spectrum of thyroid functions in a Brazilian population.

METHODS

Individuals were divided into three groups by baseline thyroid function (subclinical hypothyroidism, euthyroidism, and subclinical hyperthyroidism). HDL-P subfractions were analyzed by Nuclear Magnetic Resonance (NMR) spectroscopy. To examine the association between HDL-P subfractions and thyroid function, we used univariate and multivariate linear regression models adjusted for demographic characteristics, comorbidities, lifestyle factors, and traditional lipid measurement (HDL-C, LDL-C and triglycerides).

RESULTS

Of 3304 participants, 54.1% were women, 51.2% white, with mean age 50.6 ± 8.7 years. HDL-C and triglycerides levels (p = 0.032 and p = 0.016, respectively) were higher in the SC hypothyroid group. There were no statistically significant differences in total cholesterol levels and LDL-C levels. In univariate analysis, small HDL-P subfractions were significantly lower in subclinical hypothyroidism (p = 0.026) whereas intermediate HDL-P were higher in subclinical hyperthyroidism (p = 0.049), compared to euthyroidism. After adjustment for demographic data, SC hypothyroidism was still statistically associated with lower levels of small HDL-P. After adjusting for comorbidities, lifestyle factors, and traditional lipid measurements, SC hypothyroidism had an established association with lower levels of small HDL-P while SC hyperthyroidism was associated with lower levels of large HDL-P.

CONCLUSIONS

In this large cohort from a Brazilian population, subclinical hypothyroidism was associated with lower small HDL-P subfractions, and subclinical hyperthyroidism with lower large HDL-P subfractions and higher intermediate HDL-P subfractions.

Hypothyroidism-Induced Nonalcoholic Fatty Liver Disease (HIN): Mechanisms and Emerging Therapeutic Options

Nonalcoholic fatty liver disease (NAFLD) is an emerging worldwide problem and its association with other metabolic pathologies has been one of the main research topics in the last decade. The aim of this review article is to provide an up-to-date correlation between hypothyroidism and NAFLD. We followed evidence regarding epidemiological impact, immunopathogenesis, thyroid hormone-liver axis, lipid and cholesterol metabolism, insulin resistance, oxidative stress, and inflammation. After evaluating the influence of thyroid hormone imbalance on liver structure and function, the latest studies have focused on developing new therapeutic strategies. Thyroid hormones (THs) along with their metabolites and thyroid hormone receptor β (THR-β) agonist are the main therapeutic targets. Other liver specific analogs and alternative treatments have been tested in the last few years as potential NAFLD therapy. Finally, we concluded that further research is necessary as well as the need for an extensive evaluation of thyroid function in NAFLD/NASH patients, aiming for better management and outcome.

[The thyroid gland in old age : Physiology and pathology]

In healthy older people the metabolism of thyroid hormones is physiologically altered and can possibly even actively contribute to longevity. This should also be taken into consideration in the treatment of diseases of the thyroid and principally also for younger patients. For example, with progressing age comorbidities become more prevalent and especially in cardiovascular diseases, hyperthyroidism is less well tolerated, and should be treated more aggressively. Benign multinodular goiter also becomes more prevalent in old age and should be surgically treated when causing mechanical symptoms. The treatment concept for malignant diseases should be adapted to the holistic situation of the patient but principally in the same manner as in younger patients. Old and very old patients also benefit from adequate, risk-adapted treatment of thyroid gland diseases so that appropriate diagnostics and clarification are meaningful, regardless of age.

Effect of rhTSH on Lipids

BACKGROUND

Subclinical hypothyroidism is associated with increased blood lipid levels. However, the exact role of thyrotropin (TSH) alone is not clear. In order to clarify this point, we analysed the acute effect of recombinant human TSH (rhTSH) administration on lipid levels.

METHODS

Sera of 27 premenopausal women with well-differentiated thyroid cancer were analysed. Patients that underwent a total thyroidectomy, ablation with ¹³¹I (Iodine 131) and rhTSH administration as a part of routine follow-up American Thyroid Association guidelines were included. The protocol consists of 2 intramuscular injections of 0.9 mg of rhTSH, performed on day 1 day and day 2, with blood collection on day 1 (before rhTSH administration), and day 5. TSH, free thyroxine, total cholesterol, low-density lipoprotein cholesterol (LDLc), high density lipoprotein cholesterol (HDLc), and triglycerides were assessed in all the samples, before and four days after the first administration of rhTSH.

RESULTS

Total cholesterol and triglycerides significantly increased after stimulation of rhTSH (respectively, 192 ± 33 vs. 207 ± 26, p = 0.036 and 72 ± 23 vs. 85 ± 23, p = 0.016). LDLc and HDLc showed comparable concentrations before and after the test (respectively, 115 ± 27 vs. 126 ± 22, p = 0.066, and 62 ± 15 vs. 64 ± 15, p = 0.339), while non-HDLc increased after stimulation (130 ± 30 vs. 143 ± 25, p = 0.045).

CONCLUSION

TSH has a direct effect on total cholesterol, triglycerides, and nonHDLc. Explanation of these phenomena will require additional studies.

Assessment of the endocrine-disrupting effects of diethyl phosphate, a nonspecific metabolite of organophosphorus pesticides, by in vivo and in silico approaches

Organophosphorus pesticides (OPs) remain one of the most commonly used pesticides, and their detection rates and residues in agricultural products, foods and environmental samples have been underestimated. Humans and environmental organisms are at high risk of exposure to OPs. Most OPs can be degraded and metabolized into dialkyl phosphates (DAPs) in organisms and the environment, and can be present in urine as biomarkers for exposure to OPs, of which diethyl phosphate (DEP) is a high-exposure metabolite. Epidemiological and cohort studies have found that DAPs are associated with endocrine hormone disorders, especially sex hormone disorders and thyroid hormone disorders, but there has been no direct causal evidence to support these findings. Our study explored the effects of chronic exposure to DEP on endocrine hormones and related metabolic indicators in adult male rats at actual doses that can be reached in the human body. The results showed that chronic exposure to DEP could cause thyroid-related hormone disorders in the serum of rats, causing symptoms of hyperthyroidism in rats, and could also lead to abnormal expression of thyroid hormone-related genes in the rat liver. However, DEP exposure did not seem to affect serum sex hormone levels, spermatogenesis or sperm quality in rats. The molecular interactions between DEP and thyroid hormone-related enzymes/proteins were investigated by molecular docking and molecular dynamics methods in silico. It was found that DEP could strongly interact with thyroid hormone biosynthesis, blood transport, receptor binding and metabolism-related enzymes/proteins, interfering with the production and signal regulation of thyroid hormones. In vivo and in silico experiments showed that DEP might be a potential thyroid hormone-disrupting chemical, and therefore, we need to be more cautious and rigorous regarding organophosphorus chemical exposure.

Nonalcoholic Fatty Liver Disease and Hypercholesterolemia: Roles of Thyroid Hormones, Metabolites, and Agonists

Background: Thyroid hormones (THs) exert a strong influence on mammalian lipid metabolism at the systemic and hepatic levels by virtue of their roles in regulating circulating lipoprotein, triglyceride (TAG), and cholesterol levels, as well as hepatic TAG storage and metabolism. These effects are mediated by intricate sensing and feedback systems that function at the physiological, metabolic, molecular, and transcriptional levels in the liver. Dysfunction in the pathways involved in lipid metabolism disrupts hepatic lipid homeostasis and contributes to the pathogenesis of metabolic diseases, such as nonalcoholic fatty liver disease (NAFLD) and hypercholesterolemia. There has been strong interest in understanding and employing THs, TH metabolites, and TH mimetics as lipid-modifying drugs. Summary: THs regulate many processes involved in hepatic TAG and cholesterol metabolism to decrease serum cholesterol and intrahepatic lipid content. TH receptor β analogs designed to have less side effects than the natural hormone are currently being tested in phase II clinical studies for NAFLD and hypercholesterolemia. The TH metabolites, 3,5-diiodo-l-thyronine (T2) and T1AM (3-iodothyronamine), have different beneficial effects on lipid metabolism compared with triiodothyronine (T3), although their clinical application is still under investigation. Also, prodrugs and glucagon/T3 conjugates have been developed that direct TH to the liver. Conclusions: TH-based therapies show clinical promise for the treatment of NAFLD and hypercholesterolemia. Strategies for limiting side effects of TH are being developed and may enable TH metabolites and analogs to have specific effects in the liver for treatments of these conditions. These liver-specific effects and potential suppression of the hypothalamic/pituitary/thyroid axis raise the issue of monitoring liver-specific markers of TH action to assess clinical efficacy and dosing of these compounds.

Effects of Short-Term Hypothyroidism on the Lipid Transfer to High-Density Lipoprotein and Other Parameters Related to Lipoprotein Metabolism in Patients Submitted to Thyroidectomy for Thyroid Cancer

BACKGROUND

Elevation of low-density lipoprotein (LDL) cholesterol is the hallmark of the dyslipidemia observed in hypothyroidism, but alterations on high-density lipoprotein (HDL) plasma levels and metabolism are less understood. The aim of this study was to explore aspects of HDL metabolism and enzymes that act on HDL after a short period of overt hypothyroidism.

METHODS

Eighteen women (age 44 ± 11 years; body mass index 27.9 ± 5.2 kg/m²) were studied before total thyroidectomy for thyroid cancer, when they were euthyroid, and after thyroidectomy, in overt hypothyroidism for three weeks, following levothyroxine withdrawal for performance of a whole-body scan.

RESULTS

Thyrotropin and free thyroxine confirmed hypothyroidism; low thyroglobulin and radioiodine uptake indicated near absence of thyroid tissue. LDL cholesterol (125 ± 35 vs. 167 ± 40 mg/dL; p = 0.0002), HDL cholesterol (HDL-C; 39 ± 8 vs. 46 ± 10 mg/dL; p = 0.0025), non-HDL-C (149 ± 38 vs. 201 ± 46 mg/dL; p < 0.0001), unesterified cholesterol (53 ± 10 vs. 70 ± 16 mg/dL; p = 0.0003), apolipoprotein (apo) A-I (1.32 ± 0.19 vs. 1.44 ± 0.22 g/L; p < 0.04), and apo B (0.97 ± 0.25 vs. 1.31 ± 0.28 g/L; p < 0.0001) plasma concentrations were all higher in hypothyroidism compared to values in the euthyroid state, but triglycerides and Lp(a) were unchanged. There were no changes in HDL particle size and lipid composition, cholesteryl ester transfer protein and lecithin cholesterol acyltransferase concentrations and in paraoxonase-1 activity. Regarding the in vitro assay to estimate lipid transfer to HDL, there were no changes when comparing the euthyroid to the hypothyroid state, but when adjusted for HDL-C, the unesterified cholesterol (0.14 ± 0.03 vs. 0.11 ± 0.02; p < 0.0001), triglycerides (0.11 ± 0.02 vs. 0.09 ± 0.02; p < 0.0001), phospholipids (0.44 ± 0.09 vs. 0.40 ± 0.07; p = 0.0205), and esterified cholesterol (0.14 ± 0.03 vs. 0.13 ± 0.03; p = 0.0043) transfer to HDL were all diminished in hypothyroidism.

CONCLUSIONS

In short-term hypothyroidism, HDL-C increased, but this did not increase the capacity of the HDL fraction to receive lipids or the activity of paraoxonase-1, the anti-oxidation enzyme associated to HDL.

Association of non-alcoholic fatty liver disease with thyroid function: A systematic review and meta-analysis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases. The relationship of NAFLD with thyroid function parameters and hypothyroidism remains controversial.

AIM

To clarify the effect of thyroid function parameters and hypothyroidism on the development of NAFLD and progression to nonalcoholic steatohepatitis (NASH).

METHODS

PubMed, EMBASE, and Cochrane library databases were searched. Study quality was assessed. Weighted mean difference (WMD) and odds ratio (OR) with 95% confidence interval (CI) were calculated.

RESULTS

Twenty six studies involving 61,548 participants were eligible, most of which were of high quality. NAFLD/NASH patients had significantly higher TSH levels than controls in adults (NAFLD versus health: WMD = 0.105, 95%CI = 0.012-0.197; NAFLD versus euthyroidism: WMD = 0.100, 95%CI = 0.005-0.194; NASH versus NAFLD: WMD = 0.540, 95%CI = 0.136-0.944) and children/adolescents (NAFLD versus lean controls: WMD = 1.039, 95%CI = 0.104-1.973; NAFLD versus overweight/obese controls: WMD = 0.485, 95%CI = 0.267-.703). Unclassified hypothyroidism was positively associated with the risk of NAFLD/NASH in adults (NAFLD versus health: OR = 1.605, 95%CI = 1.180-2.183; NASH versus NAFLD: OR = 2.317, 95%CI = 1.425-3.768) and children/adolescents (NAFLD versus overweight/obese controls: OR = 2.015, 95%CI = 1.246-3.258). However, the statistical results were inconsistent among the subgroup meta-analyses of subclinical and overt hypothyroidism. Association of NAFLD with FT3 and FT4 levels was heterogeneous among population.

CONCLUSION

TSH level may be an important risk factor for the development and progression of NAFLD, independent of thyroid hormones.

A Renewed Focus on the Association Between Thyroid Hormones and Lipid Metabolism

Thyroid dysfunction, manifesting as either overt or subclinical hypothyroidism, negatively affects lipid metabolism: this leads to hypercholesterolemia which progressively increases the risk for cardiovascular disease and, potentially, mortality. Hypercholesterolemia in hypothyroidism is mainly due to a reduction in low-density lipoprotein (LDL) receptor activity, this accompanied by concomitant diminishing control by triiodothyronine (T3) of sterol regulatory element-binding protein 2 (SREBP-2), which modulates cholesterol biosynthesis by regulating rate-limit degrading enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA) activity. Recently, 3,5-diiodothyronine (T2), a natural thyroid hormone derivative, was found to repress the transcription factor carbohydrate-response element-binding protein (ChREBP) and also to be involved in lipid catabolism and lipogenesis, though via a different pathway than that of T3. While thyroid hormone could therapeutically reverse the dyslipidemic profile commonly occurring in hypothyroidism, it should be borne in mind that the potency of the effects may be age-and sex-dependent. Thyroid hormone administration possibly also sustains and enhances the efficacy of hypolipidemic drugs, such as statins, ezetimibe and proprotein convertase subtilisin/kexin type 9 (PCSK9), in patients with dyslipidemia and hypothyroidism.