Adipocytokines in thyroid dysfunction

A randomized clinical trial demonstrating cell type specific effects of hyperlipidemia and hyperinsulinemia on pituitary function

Introduction

Obesity is characterized by elevated lipids, insulin resistance and relative hypogonadotropic hypogonadism, reducing fertility and increasing risk of pregnancy complications and birth defects. We termed this phenotype ‘Reprometabolic Syndrome’ and showed that it can be recapitulated by acute infusions of lipid/insulin into healthy, normal weight, eumenorrheic women. Herein, we examined the broader impact of hyperlipidemia and euglycemic hyperinsulinemia on anterior pituitary trophic hormones and their targets.

Methods

Serum FSH, LH, TSH, growth hormone (GH), prolactin (PRL), thyroid hormones (free T4, total T3), cortisol, IGF-1, adiponectin, leptin and creatinine were measured in a secondary analysis of an interventional crossover study of 12 normal weight cycling women who underwent saline and heparin (control) infusion, or a euglycemic insulin infusion with heparin and Intralipid^® (lipid/insulin), between days 2–5 in sequential menstrual cycles.

Results

In contrast to the decrease in gonadotropins, FSH and LH, infusion of lipid/insulin had no significant effects on other trophic hormones; TSH, PRL or GH. Thyroid hormones (fT4 and total T3), cortisol, IGF-1, adiponectin and creatinine also did not differ between saline or lipid/insulin infusion conditions. Leptin increased in response to lipid/insulin (p<0.02).

Conclusion

Acute hyperlipidemia and hyperinsulinemia exerted differential, cell type specific effects on the hypothalamic-pituitary-gonadal, adrenal and thyroid axes. Elucidation of mechanisms underlying the selective modulation of pituitary trophic hormones, in response to changes in diet and metabolism, may facilitate therapeutic intervention in obesity-related neuroendocrine and reproductive dysfunction.

Body Composition and Serum Anti-Müllerian Hormone Levels in Euthyroid Caucasian Women With Hashimoto Thyroiditis

Objective

Women with Hashimoto thyroiditis (HT) are characterized by increased incidence of infertility and disturbances in body composition. Serum anti-Müllerian hormone (AMH), which reflects functional ovarian reserve, is decreased in women with HT and it be related to body mass. The aim of the present study was to investigate the relation between serum levels of AMH and body composition in HT compared to control group.

Patients and Methods

We examined 85 euthyroid women: 39 subjects with HT and 46 control women. Body composition was analysed by dual-energy X-ray absorptiometry and with bioimpedance method. Serum concentrations of AMH, leptin, TSH, thyroid hormones were assessed.

Results

We observed lower serum concentration of AMH in women with HT in comparison to the control group (p=0.01), but without differences in serum concentration of leptin between studied groups (p=0.28). Women with HT were characterized by higher %body fat (p=0.01) estimated with bioimpedance method without differences in BMI, android and gynoid fat mass and visceral adipose tissue (VAT) mass estimated with DXA method when compared to the control group (all p>0.05). We found a negative relationship between serum concentration of AMH and %body fat (r=-0.38,p=0.03) in women with HT. Additionally, in HT group, the relationship between serum levels of AMH and leptin was not statistically significant (r=0.01,p=0.96). We observed a relationship between serum concentration of leptin and BMI, %body fat mass, android, gynoid and VAT mass in HT and in the control group (all p<0.01).

Conclusions

Women with HT are characterized by lower levels of AMH and it is associated with higher fat mass, independently of serum levels of leptin.

Effects of Hyperthyroidism on Adipose Tissue Activity and Distribution in Adults

Background: Positron emission tomography (PET) has provided evidence that adult humans retain metabolically active brown adipose tissue (BAT) depots. Thyroid hormones (TH) stimulate BAT thermogenesis by central and peripheral mechanisms. However, the effect of hyperthyroidism on BAT activity and BAT volume in humans is yet not fully understood. The aim of this study was to investigate the effect of TH on (i) the metabolic activity of brown and white adipose tissue (WAT) depots, (ii) on abdominal visceral and subcutaneous adipose tissue area, and (iii) on serum levels of metabolically active cytokines. Methods: Nineteen patients with overt hyperthyroidism were investigated through repeated 2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (2-[¹⁸F]FDG PET/CT) in the hyperthyroid and in the euthyroid state. The 2-[¹⁸F]FDG uptake was calculated as standard uptake ratio with blood pool as reference. Fat areas were quantified by means of CT segmentation. Serum levels of fetuin A and B, fibroblast growth factor 21, adipocyte fatty acid-binding protein (AFABP), retinol-binding protein 4, pro-enkephalin, pro-neurotensin, and neuregulin 4 were determined in the hyperthyroid and in the euthyroid state for each subject. Results: 2-[¹⁸F]FDG uptake was increased in the hyperthyroid state in BAT in comparison with the euthyroid phase (p = 0.001). There was no correlation between serum free triiodothyronine (fT3) and free thyroxine (fT4) levels and 2-[¹⁸F]FDG uptake in BAT or WAT. In the hyperthyroid state, fT3 levels were positively associated with skeletal muscle standardized uptake value ratios. Areas of visceral adipose tissue and skeletal muscle were significantly decreased in hyperthyroidism. AFABP levels correlated positively with fT3 (p = 0.031, β = 0.28) and fT4 (p = 0.037, β = 0.27) in the hyperthyroid state. Conclusions: Our results suggest that the contribution of increased TH levels to the glucose uptake of BAT and WAT is low compared with that of the skeletal muscle. Hyperthyroid subjects have reduced areas of visceral adipose tissue and increased AFABP levels.

Metabolic Syndrome, Thyroid Function and Autoimmunity - The PORMETS Study

BACKGROUND

The prevalence of thyroid dysfunction and autoimmunity in the Portuguese population has not yet been estimated. However, the national prevalence of the metabolic syndrome remains high. The association of thyroid pathology with cardiovascular risk has been addressed but is still unclear. Our study aimed to evaluate the prevalence of thyroid dysfunction and autoimmunity and to assess the associations of thyroid-stimulating hormone and thyroid hormones and antibodies with metabolic syndrome, its components, and other possible determinants in a national sample.

MATERIAL AND METHODS

The present study included a subsample of 486 randomly selected participants from a nationwide cross-sectional study sample of 4095 adults. A structured questionnaire was administered on past medical history and socio-demographic and behavioural characteristics. Blood pressure and anthropometric measurements were collected, and the serum lipid profile, glucose, insulin, hs- CRP, TSH, FT4, FT3 and thyroid antibodies were measured.

RESULTS

In our sample, the prevalence of hypothyroidism, hyperthyroidism and undiagnosed dysfunction was 4.9%, 2.5% and 72.2%, respectively. Overall, the prevalence of positivity for the thyroid peroxidase and thyroglobulin antibodies was 11.9% and 15.0%, respectively. A positive association was found between free triiodothyronine and metabolic syndrome (OR: 2.019; 95% CI: 1.196, 3.410). Additionally, thyroid peroxidase antibodies had a negative association with metabolic syndrome (OR: 0.465; 95% CI: 0.236, 0.917) and its triglyceride component (OR: 0.321; 95% CI: 0.124, 0.836).

CONCLUSION

The prevalence of undiagnosed thyroid dysfunction and autoimmunity was high. Thyroid peroxidase antibodies were negatively associated with metabolic syndrome and its triglyceride component, whereas the free triiodothyronine level was positively associated with metabolic syndrome.

Effect of maternal hypothyroidism during pregnancy on insulin resistance, lipid accumulation, and mitochondrial dysfunction in skeletal muscle of fetal rats

The present study aimed to investigate the effect of maternal hypothyroidism during pregnancy on thyroid function of the fetal rat. Female Sprague–Dawley rats were randomized into two groups. Propylthiouracil (PTU) group received PTU in drinking water for 6 weeks (n=90), normal group received normal drinking water (n=50). The pregnant rats were obtained and had a cesarean-section to get at gestational ages of 8.5, 13, and 21 days, following blood samples and skeletal muscle were obtained from fetal rats. Levels of thyroid hormone, insulin, mitochondrial protein, and adipokines were detected using ELISA. Western blotting was performed to analyze mitochondria and insulin signal transduction-related protein in fetal rat skeletal muscle. Immunostaining of Periodic Acid-Schiff (PAS) and Oil Red O was used to observe the accumulation of muscle glycogen and lipid in the fetal rat. The results showed that the levels of thyroid hormone, insulin, insulin signal transduction-related protein, mitochondrial, and adipokines increased with the fetus developed, but had no statistical differences in the PTU group compared with the normal group. In conclusion, pregnant rats with hypothyroidism had no influence on insulin resistance (IR), lipid accumulation, and mitochondrial dysfunction in skeletal muscle of the fetal rats.

Serum Concentrations of Ghrelin and Leptin according to Thyroid Hormone Condition, and Their Correlations with Insulin Resistance

BACKGROUND

Thyroid hormones can influence energy metabolism and insulin sensitivity via their interaction with adipocytokines and gut hormones. The aims of this study were to evaluate differences in serum ghrelin and leptin concentrations according to thyroid hormone levels, and to investigate the correlation of insulin resistance.

METHODS

A total of 154 patients (57 hyperthyroid patients, 61 euthyroid patients, and 36 hypothyroid patients; mean age, 47.9 years) were enrolled. Serum leptin, ghrelin, and insulin levels were measured and insulin resistance was calculated using the formula of the homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

There were no differences in mean concentrations of ghrelin or leptin among the three groups. There were no significant differences in insulin levels between the groups (P=0.06), although hyperthyroid patients had borderline statistically significantly higher levels of insulin than did euthyroid subjects by post hoc test (26.4 μIU/mL vs. 16.1 μIU/mL, P=0.057). Regarding HOMA-IR index, the mean levels were highest in the hyperthyroid group among those of the three groups (hyperthyroid vs. euthyroid vs. hypothyroid, 6.7 vs. 3.8 vs. 4.4, P=0.068). Plasma levels of ghrelin were significantly negatively correlated with age, insulin, glucose, body mass index (BMI), and HOMA-IR. Plasma levels of leptin showed significant positive correlation with BMI and triglyceride. There were no significant correlations among thyroid hormone, thyrotropin, ghrelin, leptin, or insulin.

CONCLUSION

The present study found that serum ghrelin, leptin, and insulin levels didn't differ according to thyroid function conditions. Further studies with larger numbers of patients are required to establish a direct relationship between plasma ghrelin, leptin, and thyroid hormone.