Changes in the before and after thyroxine treatment levels of adipose tissue, leptin, and resistin in subclinical hypothyroid patients

Circulating leptin levels in thyroid dysfunction: a systematic review and meta-analysis

PURPOSE

Leptin is an important regulator of energy homeostasis, analogous to thyroid hormone (TH). The purpose of this study was to investigate circulating leptin levels in thyroid dysfunction (TD) patients and the role of TH levels.

METHODS

The electronic databases PubMed, Embase, Cochrane Library, and Web of Science were independently searched by two researchers, from inception until February 3, 2024, and updated on February 15, 2025. Pooled standardized mean difference (SMD) with a 95% confidence interval (CI) was calculated by the random effects model.

RESULTS

Thirty-eight studies reported circulating leptin levels in TD and control with euthyroidism, 4295 subjects were included in total, of which 1277 were hypothyroidism, 540 were hyperthyroidism, and 2478 were control. Compared to euthyroidism, leptin levels were significantly higher in hypothyroidism, and not significantly altered in hyperthyroidism (SMD [95%CI] = 0.71 [0.38, 1.04] and -0.03 [-0.57, 0.51], respectively). The subgroup analysis indicated that, compared to euthyroidism, leptin levels were significantly higher in subjects regardless of overt and subclinical hypothyroidism (SMD [95%CI] = 0.76 [0.25, 1.26] and 0.41 [0.11, 0.70], respectively), and not significantly different in overt hyperthyroidism (SMD [95%CI] = -0.14 [-0.74, 0.45]). Furthermore, when compared to age-, gender-, and body mass index (BMI)-matched euthyroidism, leptin levels were significantly higher in hypothyroidism and had no significant difference in hyperthyroidism (SMD [95%CI] = 0.66 [0.24, 1.07] and -0.43 [-1.13, 0.27], respectively). A total of 16 studies analyzed the correlations between leptin levels and TH levels in TD, 488 were hypothyroidism and 206 were hyperthyroidism. Following correlation analysis, leptin levels displayed a positive correlation with thyroid-stimulating hormone (TSH) levels (r = 0.19) and a negative correlation with triiodothyronine (T3) levels (r = -0.40) in TD.

CONCLUSION

Compared to euthyroidism, circulating leptin levels were significantly higher in hypothyroidism, and not significantly altered in hyperthyroidism. Besides, leptin levels in TD may be directly regulated by TSH and T3 levels, independent of BMI.

TRIAL REGISTRATION

CRD42024561055.

Comparative Phenotyping of Mice Reveals Canonical and Noncanonical Physiological Functions of TRα and TRβ

Thyroid hormone (TH) effects are mediated through TH receptors (TRs), TRα1, TRβ1, and TRβ2. The TRs bind to the DNA and regulate expression of TH target genes (canonical signaling). In addition, they mediate activation of signaling pathways (noncanonical signaling). Whether noncanonical TR action contributes to the spectrum of TH effects is largely unknown. The aim of this study was to attribute physiological effects to the TR isoforms and their canonical and noncanonical signaling. We conducted multiparameter phenotyping in male and female TR knockout mice (TRαKO, TRβKO), mice with disrupted canonical signaling due to mutations in the TR DNA binding domain (TRαGS, TRβGS), and their wild-type littermates. Perturbations in senses, especially hearing (mainly TRβ with a lesser impact of TRα), visual acuity, retinal thickness (TRα and TRβ), and in muscle metabolism (TRα) highlighted the role of canonical TR action. Strikingly, selective abrogation of canonical TR action often had little phenotypic consequence, suggesting that noncanonical TR action sufficed to maintain the wild-type phenotype for specific effects. For instance, macrocytic anemia, reduced retinal vascularization, or increased anxiety-related behavior were only observed in TRαKO but not TRαGS mice. Noncanonical TRα action improved energy utilization and prevented hyperphagia observed in female TRαKO mice. In summary, by examining the phenotypes of TRα and TRβ knockout models alongside their DNA binding-deficient mutants and wild-type counterparts, we could establish that the noncanonical actions of TRα and TRβ play a crucial role in modulating sensory, behavioral, and metabolic functions and, thus, contribute to the spectrum of physiological TH effects.

The Relationship between Subclinical Hypothyroidism and Carotid Intima-Media Thickness as a Potential Marker of Cardiovascular Risk: A Systematic Review and a Meta-Analysis

BACKGROUND AND OBJECTIVES

Thyroid dysfunction is known to have significant consequences on the cardiovascular system. The correlation between carotid intima-media thickness (CIMT) and subclinical hypothyroidism (SCH) has been frequently evaluated in clinical studies in recent years. This study aimed to evaluate the significance of this association through a meta-analysis.

METHODS

We conducted a systematic search of PubMed, MedLine, Scopus, and Web of Science databases using the keywords 'subclinical hypothyroidism and carotid intima-media thickness', from the beginning of each database until January 2023. We established the inclusion and exclusion criteria and considered studies that met the inclusion criteria. We used Jamovi for statistical analysis of the data.

RESULTS

We identified 39 observational studies that met the inclusion criteria, with 3430 subjects: 1545 SCH and 1885 EU. Compared to euthyroid subjects (EU), subjects with subclinical hypothyroidism (SCH) had significantly increased carotid intima-media thickness (CIMT) values; the estimated average mean difference was 0.08 (95% CI 0.05 to 0.10), p < 0.01, I2 = 93.82%. After the sensitivity analysis, a total of 19 from the 39 abovementioned studies were analyzed, with most studies showing a positive association between SCH and thickening of the carotid wall; the estimated average mean difference was 0.04 (95% CI 0.02 to 0.07), p = 0.03, I2 = 77.7. In addition, female sex, advanced age, and high cholesterol levels statistically significantly influenced this association.

CONCLUSIONS

Our meta-analysis indicates a significant positive association between SCH and increased CIMT, but with some limitations.

Do elevated thyrotropin levels increase the risk of miscarriages: yes or no?

BACKGROUND

To examine correlation between elevated levels of thyrotropin with the frequency of miscarriages.

METHODS

A cross-sectional study was conducted on the 380 respondents and it investigated TSH (thyrotropin), thyroid peroxidase antibody(anti-TPO) and free thyroxine (FT4) in pregnant women who had a miscarriage (N = 179) and pregnant women with normal pregnancies (N = 201).

RESULTS

The incidence of subclinical hypothyroidism in the miscarriages group was higher than in control group (61.4% vrs 15.79% (p < 0.001). In the miscarriages group with hypothyroidism (first trimester) mean value of TSH was significantly higher 4.31 ± 2.55 mIU/L compared to the control group 1.95 ± 0.86mIU/L (p < 0.001). Logistic multivariate regression revealed that TSH and body mass index (BMI) have a significant influence on the miscarriage; TSH level has a higher odds ratio (OR) 1.47 CI (95% 1.22-1.78) than BMI (OR) 1.14 CI (95% 1.06-1.23)) (p < 0.001). The combination of thyroid autoimmunity and TSH > 2.5mIU/L increase the risk of miscarriage (65.75%) compared to positive anti-TPO antibodies and TSH < 2.5mIU/L(14.15%)(p < 0.001).

CONCLUSIONS

Higher TSH levels correspond with obesity during early pregnancy and may be a sign of maternal thyroid dysfunction. Physiological thyroid function in the first trimester of pregnancy is important for perinatal outcome.

Association between circulating resistin levels and thyroid dysfunction: A systematic review and meta-analysis

Background

As a product of adipose tissue, resistin exceeds other adipokines in its role in regulating appetite, energy expenditure, insulin sensitivity, inflammation, and immunity, similar to thyroid hormones. This study aimed to evaluate the association between resistin levels and thyroid dysfunction and to explore variations in circulating resistin levels before and after treatment for thyroid dysfunction.

Methods

This study was conducted according to the Preferred Reporting Items for Systematic Review and Meta-Analysis statement. A comprehensive search of PubMed, Embase, and Cochrane databases was conducted until June 15, 2022, with no start date restriction, according to the preregistered protocol (PROSPERO-CRD42022336617). RevMan version 5.4 and R software package version 4.2.0 were used for statistical analyses.

Results

Fourteen studies with 1716 participants were included in this study. The findings of the meta-analysis confirmed that the resistin levels of patients with thyroid dysfunction were significantly higher than those of the euthyroid function control group (mean difference [MD] = 2.11, 95% confidence interval [CI] = 1.11-3.11, P < 0.00001). Furthermore, the resistin levels of patients with hyperthyroidism (MD = 3.23, 95% CI = 0.68-5.79, P = 0.01) and subclinical hypoidism (MD = 1.37, 95% CI = 0.31-2.42, P = 0.01) were significantly higher than those of euthyroid controls. The resistin levels of patients with thyroid dysfunction after treatment were significantly lower than those before treatment (MD = 1.00, 95% CI = 0.34-1.65, P = 0.003), especially in patients with hyperthyroidism (MD = 2.16, 95% CI = 1.00-3.32, P = 0.0003). Correlation analysis confirmed a positive correlation between resistin levels and free triiodothyronine (FT3) levels in patients with thyroid dysfunction (r = 0.27578, P = 0.001).

Conclusions

Our meta-analysis demonstrates that resistin levels are significantly higher in patients with thyroid dysfunction, and the resistin levels after treatment in patients with thyroid dysfunction are significantly lower than those before treatment. Correlation analysis shows a positive correlation between resistin levels and FT3 levels in patients with thyroid dysfunction.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022336617.

Lipid profile in mild subclinical hypothyroidism: systematic review and meta-analysis

INTRODUCTION

Only severe subclinical hypothyroidism (SSCH) with TSH above 10 mIU/L is considered a risk factor of hyperlipidemia and cardiovascular disease. The results of published papers on mild subclinical hypothyroidism (MSCH) with TSH below10 mIU/L are contradictory. The objective of the study was to conduct a systematic review and meta-analysis on lipid profiles in a population of patients with MSCH (TSH10> mIU/L and normal T3, T4) in comparison with euthyroid subjects.

EVIDENCE ACQUISITION

The electronic databases PubMed, CIANHL, Scopus, and Web of Science were searched systematically between August 20, 2018 and September 15, 2018, without limitation on the date of publication or the language. Titles, abstracts and articles were reviewed to identify papers that evaluated lipid profiles in patients with MSCH compared to euthyroid.

EVIDENCE SYNTHESIS

A systematic review of the studies and a meta-analysis using R software (version 3.6.1) were performed. Thirty-five case control and cohort studies were included in the meta-analysis. Total cholesterol (TC), low density lipoprotein (LDL), and triglycerides (TG) were significantly higher and high-density lipoprotein (HDL) was significantly lower in MSCH patients compared to euthyroid individuals. Mean differences (MD) [95% CI] were 12.75 [6.02, 19.48], 10.95 [6.37, 15.54], 19.27 [10.90, 27.64], and -1.81 [-3.38, -0.23], respectively. No significant difference was observed for very low-density lipoproteins (VLDL), apolipoprotein A1 (apoA1), or apolipoprotein B (apoB). The studies were of fair to good quality.

CONCLUSIONS

MSCH is associated with an increase in major atherogenic lipoproteins and should be viewed as a cardiovascular risk factor.

Actions of pituitary hormones beyond traditional targets

Studies over the past decade have challenged the long-held belief that pituitary hormones have singular functions in regulating specific target tissues, including master hormone secretion. Our discovery of the action of thyroid-stimulating hormone (TSH) on bone provided the first glimpse into the non-traditional functions of pituitary hormones. Here we discuss evolving experimental and clinical evidence that growth hormone (GH), follicle-stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin and arginine vasopressin (AVP) regulate bone and other target tissues, such as fat. Notably, genetic and pharmacologic FSH suppression increases bone mass and reduces body fat, laying the framework for targeting the FSH axis for treating obesity and osteoporosis simultaneously with a single agent. Certain 'pituitary' hormones, such as TSH and oxytocin, are also expressed in bone cells, providing local paracrine and autocrine networks for the regulation of bone mass. Overall, the continuing identification of new roles for pituitary hormones in biology provides an entirely new layer of physiologic circuitry, while unmasking new therapeutic targets.

Non-invasive markers of cardiovascular risk in patients with subclinical hypothyroidism: A systematic review and meta-analysis of 27 case control studies

It has been reported that subclinical hypothyroidism (SCH) is closely related to subclinical atherosclerosis. According to the impact of SCH on noninvasive markers of cardiovascular risk, we fulfilled a meta-analysis of included studies to provide an integrated overview. We searched electronic databases and included all relevant studies involving SCH and epicardial adipose tissue (EAT), carotid intima-media thickness (CIMT), pulse wave velocity (PWV), flow-mediated dilation (FMD) and glyceryl trinitrate-induced dilation (GNT- induced dilation). The result was calculated in a meta-analysis to assess the impact of SCH on these markers. A total of 27 studies were entered in the final analysis. Compared with euthyroid subjects, SCH patients exhibited a significantly increased CIMT (SMD: 0.369 mm; 95%CI: 0.038, 0.700; P = 0.029) and EAT (SMD: 1.167 mm; 95%CI: 0.869, 1.466; P = 0.000) and increased PWV (SMD: 3.574 m/s; 95%CI: 0.935, 6.213, P = 0.008). We also found significantly lower FMD (SMD: −1.525%, 95%CI: −2.156, −0.894, P = 0.000) and lower GNT-induced dilation (SMD: −0.384%, 95%CI: −0.625, −0.142, P = 0.002). Sensitivity analysis and subgroup analysis confirmed the above results. Our meta-analysis confirmed a significant association of SCH and cardiovascular risk with arterial wall thickening and stiffening and endothelial dysfunction. These findings will help to establish detailed cardiovascular prevention strategies for SCH patients.

Adipokine expression and endothelial function in subclinical hypothyroidism rats

The purpose of our study was to observe adipokine expression and endothelial function in subclinical hypothyroidism (sHT) rats and to determine whether levothyroxine (LT₄) treatment affects these changes. Sixty-five male Wistar rats were randomly divided into five groups: the control group; sHT A, B and C groups and the sHT + T₄ group. The sHT rats were induced by methimazole (MMI) and the sHT + T₄ rats were administered LT₄ treatment after 8 weeks of MMI administration. Thyroid function and lipid levels were measured using radioimmunoassays and enzymatic colorimetric methods, respectively. Serum adiponectin (APN), chemerin, TNF-α, endothelin (ET-1) and nitric oxide (NO) levels were measured using ELISA kits and a nitric-reductive assay. The expression of APN, chemerin and TNF-α in visceral adipose tissue (VAT) was measured in experimental rats using RT-PCR and Western blotting. Hematoxylin-eosin (HE) staining was used to observe changes in adipose tissue. The sHT rats had significantly higher levels of thyroid-stimulating hormone (TSH), TNF-α, chemerin, ET-1, total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) and lower levels of APN and NO than those in control and sHT + T₄ rats. Based on Pearson correlation analysis, the levels of chemerin, TNF-α, ET-1, LDL-C, TC and triglyceride (TG) were positively correlated with TSH, but APN and NO levels were negatively correlated with TSH. These findings demonstrated that high TSH levels contribute to the changes of adipokines and endothelial dysfunction in sHT, but LT₄ treatment ameliorates those changes.

Epicardial Adipose Tissue Thickness in Patients With Subclinical Hypothyroidism and the Relationship Thereof With Visceral Adipose Tissue Thickness

BACKGROUND

Subclinical hypothyroidism (SH) is associated with cardiovascular metabolic syndromes, especially dislipidemia and abdominal obesity. Visceral abdominal adipose tissue (VAAT) and epicardial adipose tissue (EAT) have the same ontogenic origin and produce many proinflammatory and proatherogenic cytokines. We evaluated EAT and VAAT thickness in patients with SH.

METHODS

Forty-one patients with SH and 35 controls were included in the study. Demographical and anthropometric features of both patients and controls were recorded. Thyroid and metabolic parameters were measured. EAT was measured using 2D-transthoracic echocardiography.

RESULTS

The age and gender distributions were similar in the two groups (P = 0.998 and P = 0.121, respectively). Body mass index (BMI), fat mass, waist circumference (WC), hip circumference (HC), the WC/HC ratio, and the thicknesses of VAAT and abdominal subcutaneous adipose tissue were higher in the case group than the control group (all P values < 0.01). However, both groups had similar EAT thickness (P = 0.532), which was positively correlated with BMI, fat mass, WC, HC, VAAT thickness, abdominal subcutaneous adipose tissue thickness, and serum triglyceride (TG) level (all P values < 0.01). We found no correlation between EAT thickness and thyroid-stimulating hormone (TSH) level, free thyroxine (FT4) level, or low-density lipoprotein-cholesterol (LDL-C) level, and anti-TPO level (all P values > 0.05). We found no difference between the two groups in fasting plasma glucose (FPG) level (P = 0.780), but the levels of LDL-C and TG differed significantly (P = 0.002 and P = 0.026, respectively). The serum TSH level was higher and the FT4 level was lower in the case than the control group (both P values <0.01).

CONCLUSION

Increased abdominal adipose tissue thickness in patients with SH is associated with atherosclerosis. To detemine the risk of atherosclerosis in such patients, EAT measurements are valuable; such assessment is simple to perform.