Interleukin-6 release from human abdominal adipose cells is regulated by thyroid-stimulating hormone: effect of adipocyte differentiation and anatomic depot

Free triiodothyronine (FT3)-to-free thyroxine (FT4) ratio identified as a risk factor for gestational diabetes in euthyroid pregnant women: insights from a Chinese population cohort study

Background

To explore the association between thyroid hormones and gestational diabetes mellitus in euthyroid pregnant women, with the aim of preventing the occurrence of gestational diabetes mellitus.

Methods

In this prospective study, a total of 1222 euthyroid pregnant women in their first trimester were recruited at Peking University International Hospital between December 2017 and March 2019. These participants underwent an oral glucose tolerance test during the 24-28 weeks of gestation.

Results

During early pregnancy, the gestational diabetes mellitus group displayed lower levels of free thyroxine when compared to the non-gestational diabetes mellitus group. Additionally, the ratio of free triiodothyronine to free thyroxine in the gestational diabetes mellitus group during early pregnancy was significantly higher (p<0.05). The ratio of free triiodothyronine to free thyroxine during early pregnancy showed a positive correlation with blood glucose levels at 0, 60, and 120 min both before and after glucose loading (all p<0.05). During early pregnancy, there was a negative relationship between free thyroxine levels and fasting blood glucose. The free triiodothyronine levels were positively correlated to blood glucose levels at 120 min following glucose loading (all p<0.05).

Conclusion

The ratio of free triiodothyronine-to-free thyroxine is an independent risk factor for gestational diabetes mellitus and has the potential to be a predictor for gestational diabetes mellitus in euthyroid pregnant women.

Combined prognostic value of preoperative serum thyrotrophin and thyroid hormone concentration in papillary thyroid cancer

Background

A growing number of studies have found a close association between thyroid hormones and thyrotrophin (TSH), and they also have prognostic significance in some cancer types; this study aimed to investigate the prognostic value of free triiodothyronine (fT3), free thyroxine (fT4), fT3/fT4, TSH, and their combination in patients with papillary thyroid carcinoma (PTC).

Methods

This study retrospectively analyzed the relevant data of 726 newly diagnosed PTC patients. Both univariate and multivariate analyses were used to predict the recurrence rate, and a risk score was established. In addition, with the use of a random survival forest, a random forest (RF) score was constructed. After calculating the area under the curve (AUC), the diagnostic efficacy of risk score, RF score, and four indicators was compared.

Results

fT3, fT4, fT3/fT4, and TSH were strongly associated with some invasive clinicopathological features and postoperative recurrence. Patients with high expression of fT4 and TSH have a high risk of recurrence. By contrast, patients with high expression of fT3 and fT3/fT4 have a low risk of recurrence. At the same time, the combined use of various indicators is more helpful for establishing an accurate diagnosis. By comparison, we found that the RF score was better than the risk score in terms of predicting the recurrence of PTC.

Conclusion

The diagnostic accuracy of a combination of fT3, fT4, fT3/fT4, and TSH can help improve our clinical estimate of the risk of recurrent PTC, thus allowing the development of a more effective treatment plan for patients.

Mediation effects of thyroid function in the associations between phthalate exposure and lipid metabolism in adults

Phthalates are a group of industrial chemicals widely used in everyday products including cosmetics, food packaging and containers, plastics, and building materials. Previous studies have indicated that urinary phthalate metabolites are associated with metabolic effects including those on lipid metabolism, but the results are mixed. Furthermore, whether thyroid function mediates the association between phthalate exposure and lipid metabolism remains unclear. In the present study, we explored whether changes in thyroid function markers mediate the associations between phthalate exposure and lipid metabolism indicators in Taiwanese adults. The cross-sectional data were obtained from the Taiwan Environmental Survey for Toxicants conducted in 2013. Levels of 11 urinary phthalate metabolites, levels of 5 thyroid hormones, and 8 indicators of lipid metabolism were assessed in 222 Taiwanese adults. The relationships of urinary phthalate metabolite levels with serum thyroid hormone levels and lipid metabolism indicators were explored using multiple regression models. Mediation analysis was conducted to evaluate the role of thyroid function in the association between phthalate exposure and lipid metabolism. The metabolite of di(- 2-ethylhexyl) phthalate (∑DEHPm) exhibited a significant positive association with the lipid metabolite indicator of high-density lipoprotein cholesterol (HDL-C; β = 0.059, 95% confidence interval [CI] = 0.009, 0.109) in adults, and the thyroid function indicator thyroxine (T₄) had a significant negative association with the metabolite ∑DEHPm (β = - 0.059, 95% CI = - 0.101, - 0.016) and a significant negative association with HDL-C (β = - 0.284, 95% CI = - 0.440, - 0.128). The T₄ indirect effect was 0.015 (95% CI = - 0.0087, 0.05), and the mediation effect was 32.2%. Our results support the assumption that exposure to phthalates influences the homeostasis of lipid metabolism by interfering with thyroid function.

COVID-19 and the Endocrine System: A Comprehensive Review on the Theme

Background and aim. The review aimed to summarize advances in the topic of endocrine diseases and coronavirus disease 2019 (COVID-19). Methods. Scientific and institutional websites and databases were searched and data were collected and organized, when plausible, to angle the discussion toward the following clinical issues. (1) Are patients with COVID-19 at higher risk of developing acute or late-onset endocrine diseases or dysfunction? (2) May the underlying endocrine diseases or dysfunctions be considered risk factors for poor prognosis once the infection has occurred? (3) Are there defined strategies to manage endocrine diseases despite pandemic-related constraints? Herein, the authors considered only relevant and more frequently observed endocrine diseases and disorders related to the hypothalamic-pituitary region, thyroid and parathyroid glands, calcium-phosphorus homeostasis and osteoporosis, adrenal glands, and gonads. Main. Data highlight the basis of some pathophysiological mechanisms and anatomical alterations of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)-induced endocrine dysfunctions. Some conditions, such as adrenal insufficiency and cortisol excess, may be risk factors of worse clinical progression once the infection has occurred. These at-risk populations may require adequate education to avoid the SARS-CoV-2 infection and adequately manage medical therapy during the pandemic, even in emergencies. Endocrine disease management underwent a palpable restraint, especially procedures requiring obligate access to healthcare facilities for diagnostic and therapeutic purposes. Strategies of clinical triage to prioritize medical consultations, laboratory, instrumental evaluations, and digital telehealth solutions should be implemented to better deal with this probably long-term situation.

The relationships between thyroid-stimulating hormone level and insulin resistance, glucose effectiveness, first- and second-phase insulin secretion in Chinese populations

Increased insulin resistance (IR); decreased glucose effectiveness (GE); and both first-and second phase of insulin secretion (FPIS, SPIS) have always been important factors for the development of type 2 diabetes. Therefore, in this study, we evaluated the relationships between thyroid-stimulating hormone (TSH) and these 4 factors in adult Chinese. We randomly enrolled 24,407 men and 24,889 women between 30 and 59 years old. IR, FPIS, SPIS and GE were measured with the equations built by our group. IR = log (1.439 + 0.018 × sex - 0.003 × age + 0.029 × BMI - 0.001 × SBP + 0.006 × DBP + 0.049 × TG - 0.046 × HDLC - 0.0116 × FPG) × 10 ^3.333. FPIS = 10 [1.477 - 0.119 × FPG + 0.079 × BMI - 0.523 × HDLC]. SPIS = 10 [-2.4 - 0.088 × FPG + 0.072 × BMI]. GE = (29.196 - 0.103 × age - 2.722 × TG - 0.592 × FPG) ×10 ^−3. The t test was performed to evaluate the differences between normal and diabetic groups. To evaluate the differences of the mean values of the 4 groups, from the highest to the lowest levels of TSH, we used a one-way analysis of variance. Age, high density lipoprotein-cholesterol and GE were higher in women. On the other hand, body mass index, blood pressure, low density lipoprotein-cholesterol, triglyceride, FPIS, SPIS and IR were higher in men. TSH was positively related to IR, FPIS, and SPIS and negatively related to GE. According to the r values, the tightest relationship was between TSH and IR, followed by GE, FPIS and SPIS. In conclusion, our data showed that IR, FPIS, and SPIS were positively related to the TSH level in middle-aged Chinese, whereas GE was negatively related. In both genders, IR had the tightest association followed by GE, FPIS, and SPIS.

Expression and Role of Thyrotropin Receptors in Proopiomelanocortin-Producing Pituitary Cells

Background: Thyrotropin (TSH) is well known as the hormone of the anterior pituitary thyrotrophs responsible for acting in the thyroid gland, where it stimulates synthesis and release of thyroid hormones through G_s and G_q/11 protein coupled TSH receptors (TSHRs). Methods: In this study, we examined whether the functional TSHRs are also expressed in cultured rat pituitary cells, using double immunocytochemistry, quantitative reverse transcription-polymerase chain reaction analysis, cAMP and hormone measurements, and single-cell calcium imaging. Results: Double immunocytochemistry revealed the expression of TSHRs in cultured corticotrophs and melanotrophs, in addition to previously identified receptors in folliculostellate cells. The functional coupling of these receptors to the G_q/11 signaling pathway was not observed, as demonstrated by the lack of TSH activation of IP₃-dependent calcium mobilization in these cells when bathed in calcium-deficient medium. However, TSH increased cAMP production in a time- and concentration-dependent manner and facilitated calcium influx in single corticotrophs and melanotrophs, indicating their coupling to the G_s signaling pathway. Consistent with these findings, TSH stimulated adrenocorticotropin and β-endorphin release in male and female pituitary cells in a time- and concentration-dependent manner without affecting the expression of proopiomelanocortin gene. Conclusions: These results indicate that TSH is a potential paracrine modulator of anterior pituitary corticotrophs and melanotrophs, controlling the exocytotic but not the transcriptional pathway in a cAMP/calcium influx-dependent manner.

Regulators of thymic stromal lymphopoietin production by human adipocytes

Thymic stromal lymphopoietin (TSLP) is a cytokine that is known to play a role in inflammatory conditions, especially asthma and atopic dermatitis. It is also recognized to be expressed in human adipose tissue. TSLP production from human adipocytes is stimulated by thyroid-stimulating hormone (TSH). This study aimed to identify TSH-dependent signaling routes that regulate TSLP, to determine if TSLP production is stimulated by other cytokines (IL-1β and TNF-α), and to examine if TSLP production depends on the adipose depot. Human abdominal differentiated adipocytes were stimulated with TSH, IL-1β, or TNF-α. Activation of cell signaling kinases was measured by phospho-immunoblot analysis, and TSLP in medium was assessed by ELISA. TSLP responses from abdominal subcutaneous and omental adipocytes were compared. TSH-stimulated TSLP secretion from subcutaneous adipocytes was enhanced by IBMX (raises cAMP levels) and was blocked by UO126 (inhibitor of MEK1/2-ERK1/2). TSLP secretion was stimulated by IL-1β and by TNF-α. SC-514 (inhibitor of IKKβ/NF-κB) only reduced the former. There was no effect of SB203580 (p38 MAPK inhibitor) or SP600125 (JNK inhibitor) on the stimulation by TSH, IL-1β or TNF-α. Interferon-γ inhibited TSLP responses to TSH, IL-1β, and TNF-α; IL-4 only blocked the response to TNFα. Intra-abdominal omental adipocytes also release TSLP in response to TSH, IL-1β, and TNF-α. We conclude TSLP is produced by human differentiated adipocytes derived from subcutaneous or omental depots in response to a variety of agonists. Further studies will be needed to understand what role it may play in adipose biology.

The Role of Hormones and Trophic Factors as Components of Preservation Solutions in Protection of Renal Function before Transplantation: A Review of the Literature

Transplantation is currently a routine method for treating end-stage organ failure. In recent years, there has been some progress in the development of an optimal composition of organ preservation solutions, improving the vital functions of the organ and allowing to extend its storage period until implantation into the recipient. Optimizations are mostly based on commercial solutions, routinely used to store grafts intended for transplantation. The paper reviews hormones with a potential nephroprotective effect, which were used to modify the composition of renal perfusion and preservation solutions. Their effectiveness as ingredients of preservation solutions was analysed based on a literature review. Hormones and trophic factors are innovative preservation solution supplements. They have a pleiotropic effect and affect normal renal function. The expression of receptors for melatonin, prolactin, thyrotropin, corticotropin, prostaglandin E1 and trophic factors was confirmed in the kidneys, which suggests that they are a promising therapeutic target for renal IR (ischemia-reperfusion) injury. They can have anti-inflammatory, antioxidant and anti-apoptotic effects, limiting IR injury.

Interactions among thyroid hormone (FT4), chemokine (MCP-1) and neurotrophin (NGF-β) levels studied in Hungarian postmenopausal and obese women

Thyroid dysfunction is more frequent in postmenopause and metabolic syndrome characterized by increased proinflammatory cytokines (IL-1, IL-6, TNFα), insulin resistance and overweight. Serum levels of monocyte chemoattractant protein-1 (MCP-1) chemokine and nerve growth factor-β (NGF-β) and their effects were studied on thyroid hormone levels in 133 Hungarian women (postmenopausal 66, obese 32, control 35). MCP-1 and NGF-β levels were measured with enzyme-linked, and thyroid hormones with chemiluminescence immunoassays. Subclinical hypothyroidism in postmenopause (7/66 vs 1/32 cases) and the presence of low FT₄ levels in obese women were more frequent (6/32 vs 2/66 cases, p < 0.0447). Obese women showed reduced serum FT₄ and higher MCP-1 or NGF-β levels compared to those in postmenopausal women [geometric mean (95%CI): 13.6 (10.9-21.69) vs 15.37 (9.06-20.42) pmol/l, p < 0.003 for FT₄, and 19.36 (14.27-26.26) vs 17.29 (12.65-23.63) ng/ml, p < 0.0013 for MCP-1 or 18.64 (6.8-51.11) vs 14.01 (8.59-22.83) ng/ml, p < 0.0003 for NGF-β]. Serum FT₄ levels inversely associated with MCP-1 (p < 0.0023, r = -0.1971) or estradiol levels (p < 0.0286, r = -0.1913), and positively associated with age (p < 0.0175, r = 0.2058). As opposed to estradiol and NGF-β levels, BMI had no effects on serum FT₄ levels in postmenopausal and obese women forming 3 subgroups displaying only MCP-1, both MCP-1 and NGF-β positivities or no positivities at all. In summary, not only proinflammatory cytokines, but also MCP-1 chemokine and NGF-β levels can play a role in reduced serum FT₄ levels in postmenopausal and obese women. Particularly, the decreased FT₄ levels were connected to both increased MCP-1 and NGF-β levels in obese women.

Higher thyroid-stimulating hormone levels in the first trimester are associated with gestational diabetes in a Chinese population

AIM

To evaluate the relationship between maternal thyroid-stimulating hormone levels during the first trimester and gestational diabetes risk.

METHODS

In Tianjin, China, 7258 women underwent a thyroid-stimulating hormone screening test within 12 gestational weeks and then had a glucose challenge test at 24-28 weeks of gestational age. The women with a glucose challenge test ≥7.8 mmol/l underwent a 75 g oral glucose tolerance test. Gestational diabetes was diagnosed following International Association of Diabetes and Pregnancy Study Group criteria. Restricted cubic spline analysis was performed to explore full-range risk associations of thyroid-stimulating hormone levels with gestational diabetes. Logistic regression was performed to obtain odds ratios and 95% confidence intervals.

RESULTS

In all, 594 women (8.2%) had gestational diabetes. Among women with thyroid-stimulating hormone ≤3.2 mIU/l, a positive association between thyroid-stimulating hormone levels and gestational diabetes risk was found (adjusted OR: 1.13, 95% CI: 1.00-1.27). There was no relationship between thyroid-stimulating hormone levels and gestational diabetes risk in univariable and multivariable analyses among women with thyroid-stimulating hormone >3.2 mIU/l. In subgroup analyses, among women with thyroid-stimulating hormone ≤3.2 mIU/l and BMI ≥25 kg/m² , the adjusted odds ratio for thyroid-stimulating hormone levels with gestational diabetes was enhanced to 1.25 (95% CI: 1.02-1.53).

CONCLUSIONS

In pregnant Chinese women, thyroid-stimulating hormone levels even within normal range in the first trimester were positively related to gestational diabetes risk, especially for pre-pregnancy overweight/obese women.

Genome-wide meta-analysis identifies novel loci associated with free triiodothyronine and thyroid-stimulating hormone

PURPOSE

Thyroid hormones are essential for the normal function of almost all human tissues, and have critical roles in metabolism, differentiation and growth. Free triiodothyronine (fT3), free thyroxine (fT4) and thyroid-stimulating hormone (TSH) levels are under strong genetic influence; however, most of the heritability is yet unexplained.

METHODS

In order to identify novel loci associated with fT3, fT4 and TSH serum levels we performed a genome-wide meta-analysis of 7 411 206 polymorphisms in up to 1731 euthyroid individuals from three Croatian cohorts from Dalmatia region: two genetically isolated island populations and one mainland population. Additionally, we also performed a bivariate analysis of fT3 and fT4 levels.

RESULTS

The EPHB2 gene variant rs67142165 reached genome-wide significance for association with fT3 plasma levels (P = 9.27 × 10^-9) and its significance was confirmed in bivariate analysis (P = 9.72 × 10^-9). We also found a genome-wide significant association for variant rs13037502 upstream of the PTPN1 gene and TSH plasma levels (P = 1.67 × 10^-8).

CONCLUSION

We identified a first genome-wide significant variant associated with fT3 plasma levels, as well as a novel locus associated with TSH plasma levels. These findings are biologically relevant and enrich our knowledge about the genetic basis of pituitary-thyroid axis function.

CASE FINDING FOR HYPOTHYROIDISM SHOULD INCLUDE TYPE 2 DIABETES AND METABOLIC SYNDROME PATIENTS: A LATIN AMERICAN THYROID SOCIETY (LATS) POSITION STATEMENT

OBJECTIVE

Latin American Thyroid Society (LATS) Hypothyroidism Clinical Practice Guidelines recommend case finding of hypothyroid patients in multiple and different situations that agree with other Society guidelines. However, the detection of hypothyroidism in type 2 diabetes mellitus (T2DM) or metabolic syndrome (MetS) patients is not mentioned in particular. In the recent years, several basic and epidemiologic studies have appeared showing that a lower thyroid function and MetS/T2DM are associated. Hence, the aim of this review is to manifest the LATS position on the diagnosis of hypothyroidism in both MetS and T2DM patients.

METHODS

A search was made in PubMed using the following terms: "hypothyroidism" AND "diabetes" OR "metabolic syndrome." The most relevant studies describing the prevalence and complications due to hypothyroidism in both MetS and T2DM patients were selected.

RESULTS

The current document reviews new information from studies that have shown that the prevalence of hypothyroidism is higher in T2DM patients (odds ratio [OR], 3.45; 95% confidence interval [CI], 2.5 to 4.7) and that diabetic complications are more prevalent in subclinical hypothyroidism (ScH). The incidence of T2DM is 1.09-fold higher with each doubling of thyroid-stimulating hormone (TSH) mIU/L (95% CI, 1.06 to 1.12), and the incidence of prediabetes increases 15% (hazard ratio, 1.15; 95% CI, 1.04 to 1.26) in patients with TSH >5 mIU/L. Similarly, MetS is more prevalent in ScH compared to euthyroid individuals (OR, 1.31; 95% CI, 1.08 to 1.60).

CONCLUSION

Thyroid function is affected in MetS and T2DM, and hypothyroidism is more common in these patients. Diabetic complications are more frequent in ScH patients. Therefore, LATS now recommends aggressive case finding of hypothyroidism in both MetS and T2DM patients.

ABBREVIATIONS

CI = confidence interval; GLUT4 = glucose transporter 4; HOMA-IR = homeostatic model assessment for insulin resistance; HR = hazard ratio; LATS = Latin American Thyroid Society; MetS = metabolic syndrome; OR = odds ratio; ScH = subclinical hypothyroidism; T2DM = type 2 diabetes mellitus; T3 = triiodothyronine; T4 = thyroxine; TSH = thyroid-stimulating hormone.

Pituitary Diseases and Bone

Neuroendocrinology of bone is a new area of research based on the evidence that pituitary hormones may directly modulate bone remodeling and metabolism. Skeletal fragility associated with high risk of fractures is a common complication of several pituitary diseases such as hypopituitarism, Cushing disease, acromegaly, and hyperprolactinemia. As in other forms of secondary osteoporosis, pituitary diseases generally affect bone quality more than bone quantity, and fractures may occur even in the presence of normal or low-normal bone mineral density as measured by dual-energy X-ray absorptiometry, making difficult the prediction of fractures in these clinical settings. Treatment of pituitary hormone excess and deficiency generally improves skeletal health, although some patients remain at high risk of fractures, and treatment with bone-active drugs may become mandatory. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary diseases.

Thyroid-Stimulating Hormone Levels Are Positively Associated with Insulin Resistance

BACKGROUND It has been reported that overt and mild thyroid dysfunctions are associated with insulin resistance (IR). We performed this retrospective study to evaluate the relationships between thyroid-stimulating hormone (TSH) levels within the reference range and IR. MATERIAL AND METHODS A total of 447 outpatients were enrolled in this study: 298 with type 2 diabetes mellitus and 149 nondiabetic individuals. Based on a cutoff HbA1c value of 7%, diabetic patients were additionally divided into 2 groups: a high-HbA1c group (n=240) and a low-HbA1c group (n=58). The relationships of TSH levels and HOMA-IR were computed using linear regression models. RESULTS TSH levels were positively and linearly associated with HOMA-IR in both the nondiabetic and diabetic groups (r=0.210, p=0.011 and r=0.451, p<0.001), as well as in the high- and low-HbA1c groups (r=0.507, p<0.001 and r=0.259, p=0.048). A better correlation between TSH levels and HOMA-IR was found in the diabetic group and in the high-HbA1c group when compared with the nondiabetic group and the low-HbA1c group, respectively. Linear regression analysis showed that TSH levels were independently associated with HOMA-IR (p=0.034, =0.049 and <0.001 in nondiabetic, low-, and high-HbA1c groups, respectively). CONCLUSIONS Our data suggest that TSH is independently associated with insulin resistance.

Relationship between Body Mass Index, Waist-to-Hip Ratio, and Serum Lipid Concentrations and Thyroid-Stimulating Hormone in the Euthyroid Adult Population

The aim of this cross-sectional study was to investigate the relationship between body mass index (BMI), waist-to-hip ratio, and lipid parameters and serum thyroid-stimulating hormone (TSH) levels in healthy euthyroid individuals. This cross-sectional study was conducted between June 1^st and July 20^th, 2013, at Bushehr University of Medical Sciences. One hundred forty euthyroid individuals were divided into 2 groups: a high-TSH group (TSH between 2.0 and 5.5 mIU/L, n=67) and a low-TSH group (TSH between 0.3 and 2.0 mIU/L, n=73). After overnight fast, total cholesterol, triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), TSH, thyroxine (T4), and triiodothyronine (T3) were measured. Height and weight were measured with a stadiometer, and BMI was calculated as weight in kilograms divided by the square of height in meters. Waist-to-hip ratio was determined as waist circumference divided by hip circumference. The simple independent t-test and a general linear model were used for statistical analysis. All statistical analyses were done using the SPSS, version 15, statistical software package. BMI and LDL-C were significantly higher in the high-TSH group than in the low-TSH group after adjustment for age, sex, calorie intake, total fat and carbohydrate intakes, and physical activity. No significant differences were found between the groups in TG, cholesterol, and HDL-C. The association between TSH levels andT4 was significant. Individuals with TSH levels at the upper limit of normality might be at risk of hypercholesterolemia and obesity.

Endothelial Dysfunction in Obesity

Chronic inflammatory state in obesity causes dysregulation of the endocrine and paracrine actions of adipocyte-derived factors, which disrupt vascular homeostasis and contribute to endothelial vasodilator dysfunction and subsequent hypertension. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Adipose tissue inflammation, nitric oxide (NO)-bioavailability, insulin resistance and oxidized low-density lipoprotein (oxLDL) are main participating factors in endothelial dysfunction of obesity. In this chapter, disruption of inter-endothelial junctions between endothelial cells, significant increase in the production of reactive oxygen species (ROS), inflammation mediators, which are originated from inflamed endothelial cells, the balance between NO synthesis and ROS , insulin signaling and NO production, and decrease in L-arginine/endogenous asymmetric dimethyl-L-arginine (ADMA) ratio are discussed in connection with endothelial dysfunction in obesity.

Subclinical Hypothyroidism - What is Responsible for its Association with Cardiovascular Disease?

Subclinical hypothyroidism (SH) is a common condition, with prevalence estimates ranging from 4–20%, depending on the population demographics. Although epidemiological analysis associates it with an increased risk of cardiovascular disease, clinical practice guidelines express uncertainty about whether to monitor or to treat. As we await large-scale, well-designed randomised clinical trials regarding treatment of SH, a review of pathophysiological considerations may be informative to better understand this disorder.

MECHANISMS IN ENDOCRINOLOGY: Impact of isolated TSH levels in and out of normal range on different tissues

Routine treatment of thyroid cancer (TC) includes long-term suppression of TSH. The necessity of this treatment in low- and intermediate-risk patients as well as the extent of TSH suppression is currently under discussion. A literature search was performed to illustrate the role of TSH in extrathyroidal cells and to identify potential reasons for different effects of exogenously suppressed and endogenously low TSH levels. Although adverse effects of subnormal and supranormal TSH blood levels on heart and brain have not been consistently found, studies show a clear negative effect of suppressed TSH levels on bone mineral density. Experimental data also support an important role of TSH in the immune system. The ability of levothyroxine (l-T4) to regulate TSH levels and triiodothyronine levels in a physiological manner is limited. Reduction of circadian changes in TSH levels, decrease of thyroid hormone-binding proteins, prevention of potential compensatory increases of TSH levels (e.g., in old age), and unresponsiveness of TSH-producing cells to TRH on l-T4 treatment might cause adverse effects of suppressed TSH levels. In view of the adverse effects of aggressive TSH suppression, achieving the suggested levels of TSH between 0.9 and 1 mU/l in the treatment of low-to-intermediate risk TC patients appears justified.

Interleukins 6 and 15 Levels Are Higher in Subcutaneous Adipose Tissue, but Obesity Is Associated with Their Increased Content in Visceral Fat Depots

Excess adiposity is associated with chronic inflammation, which takes part in the development of obesity-related complications. The aim of this study was to establish whether subcutaneous (SAT) or visceral (VAT) adipose tissue plays a major role in synthesis of pro-inflammatory cytokines. Concentrations of interleukins (IL): 1β, 6, 8 and 15 were measured at the protein level by an ELISA-based method and on the mRNA level by real-time PCR in VAT and SAT samples obtained from 49 obese (BMI > 40 kg/m²) and 16 normal-weight (BMI 20–24.9 kg/m²) controls. IL-6 and IL-15 protein concentrations were higher in SAT than in VAT for both obese (p = 0.003 and p < 0.0001, respectively) and control individuals (p = 0.004 and p = 0.001, respectively), while for IL-1β this was observed only in obese subjects (p = 0.047). What characterized obese individuals was the higher expression of IL-6 and IL-15 at the protein level in VAT compared to normal-weight controls (p = 0.047 and p = 0.016, respectively). Additionally, obese individuals with metabolic syndrome had higher IL-1β levels in VAT than did obese individuals without this syndrome (p = 0.003). In conclusion, concentrations of some pro-inflammatory cytokines were higher in SAT than in VAT, but it was the increased pro-inflammatory activity of VAT that was associated with obesity and metabolic syndrome.

The proliferation and differentiation of primary pig preadipocytes is suppressed when cultures are incubated at 37°Celsius compared to euthermic conditions in pigs

Given similarities in metabolic parameters and cardiovascular physiology, the pig is well positioned as a biomedical model for metabolic disease and obesity in humans. Better understanding molecular mechanisms governing porcine adipocyte hyperplasia may provide insight into the regulation of adipose tissue development that is useful both when considering the pig as a commodity and when extrapolating porcine data to human disease. Primary cultures of pig stromal-vascular cells have served as a useful tool for investigating factors that regulate preadipocyte proliferation and differentiation. However, such cultures have generally been maintained at 37°C in vitro despite euthermia being 39°C in pigs. To address potential concerns about the physiological relevance of culturing primary pig preadipocytes under what would be hypothermic conditions in vivo, the objective of this study was to investigate the effect of culture temperature on the proliferation and differentiation of pig preadipocytes in primary culture. Culturing primary preadipocytes at 37 rather than 39°C decreases their proliferation rates based upon cleavage of the tetrazolium salt, MTT (P < 0.001), reduction of resazurin (P < 0.001), and daily cell counts (P < 0.001). Likewise, culturing primary porcine preadipocytes at 37°C suppressed their adipogenic potential based upon monitoring adipogenesis morphologically, biochemically, and via the expression of mRNA encoding adipogenic marker genes. Collectively, these data indicate the proliferation and differentiation of primary pig preadipocytes is suppressed when cultures are incubated at 37°C compared to normal body temperature of pigs. This may confound investigation of factors that impact adipocyte hyperplasia in the pig.

TSH signaling pathways that regulate MCP-1 in human differentiated adipocytes

OBJECTIVE

Adipose tissue is an extra-thyroidal thyroid-stimulating hormone (TSH) target. Increases in lipolysis and in expression and release of interleukin-6 (IL-6) occur in TSH-stimulated adipocytes, and levels of circulating free fatty acids and IL-6 rise following TSH administration to patients with previous thyroidectomy and radioablation for thyroid cancer. Our first objective was to compare how TSH stimulates protein kinase A (PKA) and inhibitor of κB (IκB) kinase (IKK)-β. Our second objective was to investigate whether TSH induces other cytokines besides IL-6.

METHODS

TSH stimulation of either CHO cells expressing human TSH receptor or human abdominal subcutaneous differentiated adipocytes.

RESULTS

Signaling studies showed TSH increased NADPH oxidase activity, and either diphenyleneiodonium (oxidase inhibitor) or N-acetyl cysteine (scavenger of reactive oxygen species) reduced IKKβ phosphorylation. Phosphorylation of protein kinase C-δ, an upstream regulator of NADPH oxidase, was increased by TSH, and rottlerin (PKCδ inhibitor) reduced TSH-stimulated IKKβ phosphorylation. TSH upregulated monocyte chemoattractant protein-1 (MCP-1) mRNA expression and the release of MCP-1 protein in human abdominal differentiated adipocytes. H89 (PKA inhibitor) and sc-514 (IKKβ inhibitor) each blocked TSH-stimulated MCP-1 mRNA expression and protein release, suggesting PKA and IKKβ participate in this pathway.

CONCLUSIONS

These data provide new information about TSH signaling in human differentiated adipocytes, and add to the evidence that TSH is a pro-inflammatory stimulus of adipocytes.

Acute TSH stimulation in vivo does not alter serum PCSK9 levels

Background

It is now recognized that TSH can act on targets other than the thyroid, including the liver. Elevated serum TSH levels in euthyroid subjects were recently reported to correlate with high values of serum proprotein convertase subtilisin/kexin type 9 (PCSK9). This protein, expressed and secreted by hepatocytes, promotes higher LDL-cholesterol levels. We tested whether an acute increase of TSH levels following administration of TSH in vivo would raise PCSK9 levels in patients who had previously undergone total thyroidectomy and radioablation for thyroid cancer.

Findings

TSH levels rose from 0.64 ± 1.02 mU/L on day 1 to 98.66 ± 4.83 mU/L on day 3, following injections of recombinant human TSH (on days 1 and 2). PCSK9 levels were 330 ± 99 ng/ml on day 1, and did not change on days 3 or 5 in response to TSH stimulation.

Conclusions

Although a positive correlation between TSH and PCSK9 in euthyroid subjects has raised the possibility that TSH might act on the liver to raise PCSK9 values, our data show that PCSK9 levels are not affected by acute elevations of TSH levels. Whether chronic elevations of TSH are needed to upregulate PCSK9 remains to be determined.

Association of vascular access type with inflammatory marker levels in maintenance hemodialysis patients

Aggressive NIH is a common histopathological lesion found at the sites of venous stenosis in arteriovenous fistula (AVF) and arteriovenous grafts (AVG). Inflammatory mediators have been proposed to play a pathogenic role in NIH, but there is paucity of data evaluating this hypothesis in clinical studies or in animal models. Serum levels of inflammatory mediators can potentially identify patients at high risk of AVF and AVG dysfunction. In a cross-sectional cohort study of 754 HD patients who were part of the NIED study cohort, we examined the associations between inflammatory markers including serum interleukin (IL) 1β, IL-6, C-reactive protein (CRP), and tumor necrosis factor-α (TNF-α) and type of vascular access. Unadjusted and multivariate-adjusted linear regression models were used. In addition, time-dependent regression model was used to assess the association between inflammatory markers and mortality. We observed that in the multivariate-adjusted model, inflammatory mediators interleukin-6 (IL-6), interleukin-1L-ß (IL-1ß), and C-reactive protein (CRP), the predicted value in hemodialysis patients, are lowest in patients with AVF and highest in central venous catheter (CVC) and AVG even in case-mix and malnutrition-inflammation complex syndrome (MICS)-adjusted models. IL-6 and CRP levels fall consistently in the same patients when AVG or CVC is changed to AVF and increase if the same patient changes access from AVF to AVG or CVC. Obesity is a risk factor for fistula failure and fistulas are associated with the lowest mortality compared with CVC and AVG. We did not find any statistically significant association between tumor necrosis factor-α (TNF- α) and vascular access outcomes. Higher levels of inflammatory mediators seen in CVC and AVG compared with AVF could potentially explain the higher mortality seen in patients with CVC and AVG compared with AVF.

Relationship of thyroid function with obesity and type 2 diabetes in euthyroid Tunisian subjects

OBJECTIVES

Although a relationship between obesity and metabolic consequences with thyroid function has been reported, the underlying pathogenesis is not completely known. In the current study, we evaluated the thyroid function in obese and/or diabetic patients compared to healthy normal weight peers, exploring the possible association between components of metabolic syndrome and thyroid function parameters.

METHODS

We recruited 108 subjects (56 male and 52 female). In all subjects, thyroid stimulating hormone (TSH), free thyroxine (FT4), fasting plasma levels of insulin and glucose, homeostasis model assessment for insulin resistance, and obesity parameters were assessed.

RESULTS

We found that circulating levels of TSH and FT4 were significantly increased in overweight and obese subjects. However, the data do not reveal any change of these hormones in diabetics. Multivariate linear regression analysis showed that TSH was directly associated with both obesity and insulin resistance parameters (p < 0.05). FT4 was negatively associated only with obesity parameters (p < 0.05).

CONCLUSIONS

Our data strongly support that the changes of thyroid hormones may be influenced by adiposity and its metabolic consequences, such as insulin resistance. This relationship can be explained by a cross talk between adipose tissue release and thyroid function. Nevertheless, metformin treatment seems to affect thyroid function in diabetic patients by maintaining plasma thyrotropin levels to subnormal levels.

High-normal TSH values in obesity: is it insulin resistance or adipose tissue's guilt?

OBJECTIVE

Clinical evidences reported subclinical alterations of thyroid function in obesity, although the relationship between thyroid status and obesity remains unclear. We cross-sectionally investigated the influence of metabolic features on hypothalamic-pituitary-thyroid axis in obesity.

DESIGN AND METHODS

We enrolled 60 euthyroid subjects with no history of type 2 diabetes mellitus and assessed the relationship of thyroid function with insulin resistance, measured using euglycemic clamp, and abdominal fat volume, quantified by computed tomography scan (CT scan). Thyroid stimulating hormone (TSH) correlated with BMI (r = 0.46; P = 0.02), both visceral (r = 0.58; P = 0.02) and subcutaneous adipose tissue volumes (r = 0.43; P = 0.03) and insulin resistance (inverse relationship with insulin sensitivity-glucose uptake: r = -0.40; P = 0.04).

RESULTS

After performing multivariate regression, visceral adipose tissue volume was found to be the most powerful predictor of TSH (β = 3.05; P = 0.01), whereas glucose uptake, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, subcutaneous adipose tissue volume, and triglycerides were not. To further confirm the hypothesis that high-normal TSH values could be dependent on adipose tissue, and not on insulin resistance, we restricted our analyses to moderately obese subjects' BMI ranging 30-35 kg/m(2). This subgroup was then divided as insulin resistant and insulin sensitive according to the glucose uptake (≤ or >5 mg · kg(-1) · min(-1), respectively). We did not find any statistical difference in TSH (insulin resistant: 1.62 ± 0.65 µU/ml vs. insulin sensitive: 1.46 ± 0.48; P = not significant) and BMI (insulin resistant: 32.2 ± 1.6 kg/m(2) vs. insulin sensitive: 32.4 ± 1.4; P = not significant), thus confirming absence of correlation between thyroid function and insulin sensitivity per se.

CONCLUSION

Our study suggests that the increase in visceral adipose tissue is the best predictor of TSH concentration in obesity, independently from the eventual concurrent presence of insulin resistance.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

The influence of thyroid-stimulating hormone and thyroid-stimulating hormone receptor antibodies on osteoclastogenesis

BACKGROUND

We have shown that thyroid-stimulating hormone (TSH) has a direct inhibitory effect on osteoclastic bone resorption and that TSH receptor (TSHR) null mice display osteoporosis. To determine the stage of osteoclast development at which TSH may exert its effect, we examined the influence of TSH and agonist TSHR antibodies (TSHR-Ab) on osteoclast differentiation from murine embryonic stem (ES) cells to gain insight into bone remodeling in hyperthyroid Graves' disease.

METHODS

Osteoclast differentiation was initiated in murine ES cell cultures through exposure to macrophage colony stimulation factor, receptor activator of nuclear factor кB ligand, vitamin D, and dexamethasone.

RESULTS

Tartrate resistant acid phosphatase (TRAP)-positive osteoclasts formed in ~12 days. This coincided with the expected downregulation of known markers of self renewal and pluripotency (including Oct4, Sox2, and REX1). Both TSH and TSHR-Abs inhibited osteoclastogenesis as evidenced by decreased development of TRAP-positive cells (~40%-50% reduction, p = 0.0047), and by decreased expression, in a concentration-dependent manner, of osteoclast differentiation markers (including the calcitonin receptor, TRAP, cathepsin K, matrix metallo-proteinase-9, and carbonic anhydrase II). Similar data were obtained using serum immunoglobulin-Gs (IgGs) from patients with hyperthyroid Graves' disease and known TSHR-Abs. TSHR stimulators inhibited tumor necrosis factor-alpha mRNA and protein expression, but increased the expression of osteoprotegerin (OPG), an antiosteoclastogenic human soluble receptor activator of nuclear factor кB ligand receptor. Neutralizing antibody to OPG reversed the inhibitory effect of TSH on osteoclast differentiation evidencing that the TSH effect was at least in part mediated by increased OPG.

CONCLUSION

These data establish ES-derived osteoclastogenesis as an effective model system to study the regulation of osteoclast differentiation in early development. The results support the observations that TSH has a bone protective action by negatively regulating osteoclastogenesis. Further, our results implicate TSHR-Abs in offering skeletal protection in hyperthyroid Graves' disease, even in the face of high thyroid hormone and low TSH levels.

Extrathyroidal expression of TSH receptor

The TSH receptor expressed on the cell surface of thyroid follicular cells plays a pivotal role in the regulation of thyroid status and growth of the thyroid gland. In recent years it has become evident that the TSH receptor is also expressed widely in a variety of extrathyroidal tissues including: anterior pituitary; hypothalamus; ovary; testis; skin; kidney; immune system; bone marrow and peripheral blood cells; white and brown adipose tissue; orbital preadipocyte fibroblasts and bone. A large body of evidence is emerging to describe the functional roles of the TSH receptor at these various sites but their physiological importance in many cases remains a subject of controversy and much interest. Current understanding of the actions of the TSH receptor in extrathyroidal tissues and their possible physiological implications is discussed.

The relation between thyroid-stimulating hormone and measures of adiposity in patients with manifest vascular disease

BACKGROUND

Visceral adiposity is associated with cardiovascular risk factors and increased cardiovascular risk. Thyroid-stimulating hormone (TSH) levels in the normal range are associated with a higher risk of fatal coronary artery disease. We hypothesize that TSH levels in the normal range are associated with an increase in visceral adipose tissue (VAT) in patients with vascular diseases.

DESIGN

In 2419 patients with vascular diseases, visceral fat thickness was analysed with ultrasonography. The association between TSH and VAT was quantified using linear regression analysis. Results are expressed as beta (β) regression coefficients with 95% confidence intervals. Adjustments were made for age, sex, current smoking and weight. Separate analyses were performed per quartile of age.

RESULTS

β-coefficients for the relation between TSH and VAT (change per SD of 2·55 cm) was 0·085 (95% CI 0·012-0·157) in the highest quartile of age (range 67-80 years) when adjusted for age, gender and current smoking and remained statistical significant after further adjustment for weight (β 0·096 95% CI 0·034-0·157). Per SD change, the β-coefficient for TSH and VAT tissue was larger than for other measures of adiposity.

CONCLUSIONS

In conclusion, higher TSH plasma levels in the normal range are associated with more VAT in patients with manifest vascular disease above the age of 66 years. No association was found between plasma TSH levels and weight or BMI. The relation between TSH levels and VAT may provide an explanation for the increased cardiovascular risk associated with elevated TSH plasma concentrations within the normal range.

The relationship between serum thyrotropin and components of metabolic syndrome

To explore the relationship between serum thyrotropin and components of metabolic syndrome in a Chinese cohort. A total of 1534 adult inhabitants in DaDong district of Shenyang were asked to fulfill the questionnaire, complete physical examination and OGTT. Blood samples were collected to test thyrotropin (TSH), fasting plasma glucose (FPG), OGTT 2h PG, fasting insulin (FINS), triglyceride (TG) and high density lipoprotein cholesterol (HDL-C). Serum TSH in metabolic syndrome group was higher than that in the non-metabolic syndrome group (2.54 mIU/L vs. 2.22 mIU/L, p<0.05). TG level increased significantly in subclinical hypothyroid group compared with euthyroid subjects (1.73±0.12 mmol/L vs. 1.47±0.03 mmol/L, p<0.05), and HDL-C decreased significantly in patients with subclinical hypothyroidism compared with euthyroid subjects (1.26±0.27 mmol/L vs. 1.33±0.27 mmol/L, p<0.05). The prevalence of hypertension was higher in the subclinical hypothyroid group than that in euthyroid group (42.86% vs. 33.2%, p<0.05). The serum TSH within the reference range was positively related with the prevalence of overweight/obesity. Slight increase in serum TSH maybe a risk factor for metabolic syndrome.

Acute exogenous TSH administration stimulates leptin secretion in vivo

TSH-receptor (TSHR) has been found in a variety of cell types, including preadipocytes and adipocytes. In vitro, TSH-mediated preadipocyte and adipocyte responses include proliferation, differentiation, survival, and lipolysis. Objective To measure the response of serum leptin to exogenous administration of recombinant human TSH (rhTSH) in vivo. Patients One hundred patients with differentiated thyroid cancer already treated by total thyroidectomy and (131)I remnant ablation were enrolled. Mean (+/-s.e.m.) body mass index (BMI) was 26.9+/-0.6 kg/m(2). Methods Patients received a standard dose of rhTSH for measurement of thyroglobulin in the follow-up of their disease. Blood samples were taken for the assay of TSH and leptin before the first administration of rhTSH (time 0), and 24 h (time 1), 48 h (time 2), 72 h (time 3), and 96 h (time 4) after the first administration of rhTSH. Results Significant mean serum leptin increments, with respect to basal value, were 16, 13, 18, and 11% at times 1, 2, 3, and 4 respectively. Significant positive correlations of leptin-area under the curve with respect to basal leptin levels (r=0.43; P<0.0001) and BMI (r=0.32; P<0.005) were observed. Conclusions Acute rhTSH administration in hypothyroid subjects under l-thyroxine therapy produces a rise in serum leptin. This increase is proportional to the adipose mass suggesting that a functioning TSHR is expressed on the surface of adipocytes. The role that TSHR activation in adipocytes might play in physiological and pathological conditions remains a matter of investigation.

Thyroid-stimulating hormone stimulates lipolysis in adipocytes in culture and raises serum free fatty acid levels in vivo

Thyroid-stimulating hormone (TSH) stimulates adipocyte lipolysis, but signal transduction pathways activated by TSH for this response have not been directly studied. Using differentiated 3T3-L1 adipocytes as well as primary human adipocytes, we characterized the lipolytic action of TSH with dose-response and time-course studies, and compared it with isoproterenol. Thyroid-stimulating hormone stimulated phosphorylation of perilipin and hormone-sensitive lipase (HSL). Inhibition of protein kinase A with H89 blocked TSH-stimulated lipolysis as well as phosphorylation of perilipin and HSL. Thyroid-stimulating hormone stimulated lipolysis in vivo, as indicated by an elevation in serum free fatty acid (FFA) levels after recombinant human TSH administration to thyroidectomized patients (42% increase, n = 19, P < .05). For patients with a body mass index less than 30 kg/m(2), the TSH-induced increase in serum FFA levels was 53% (n = 11, P < .05), whereas levels in patients with a body mass index of at least 30 kg/m(2) (n = 8) did not change after TSH treatment. In summary, TSH stimulates lipolysis and phosphorylation of perilipin and HSL in a protein kinase A-dependent manner in differentiated adipocytes in culture and raises serum FFA levels in vivo.

Melanocortins induce interleukin 6 gene expression and secretion through melanocortin receptors 2 and 5 in 3T3-L1 adipocytes

Interleukin 6 (IL6) is a pleiotropic cytokine that not only affects the immune system, but also plays an active role in many physiological events in various organs. Notably, 35% of systemic IL6 originates from adipose tissues under noninflammatory conditions. Here, we describe a previously unknown function of melanocortins in regulating Il6 gene expression and production in 3T3-L1 adipocytes through membrane receptors which are called melanocortin receptors (MCRs). Of the five MCRs that have been cloned, MC2R and MC5R are expressed during adipocyte differentiation. alpha-Melanocyte-stimulating hormone (alpha-MSH) or ACTH treatment of 3T3-L1 adipocytes induces Il6 gene expression and production in a time- and concentration-dependent manner via various signaling pathways including the protein kinase A, p38 mitogen-activated protein kinase, cJun N-terminal kinase, and IkappaB kinase pathways. Specific inhibition of MC2R and MC5R expression with short interfering Mc2r and Mc5r RNAs significantly attenuated the alpha-MSH-induced increase of intracellular cAMP and both the level of Il6 mRNA and secretion of IL6 in 3T3-L1 adipocytes. Finally, when injected into mouse tail vein, alpha-MSH dramatically increased the Il6 transcript levels in epididymal fat pads. These results suggest that alpha-MSH in addition to ACTH may function as a regulator of inflammation by regulating cytokine production.

A stimulatory thyrotropin receptor antibody (M22) and thyrotropin increase interleukin-6 expression and secretion in Graves' orbital preadipocyte fibroblasts

BACKGROUND

Patients with Graves' ophthalmopathy (GO) have circulating autoantibodies directed against the thyrotropin receptor (TSHR) and elevated levels of the proinflammatory cytokine interleukin-6 (IL-6) in both serum and orbital tissues. We hypothesized that these autoantibodies might increase IL-6 expression and secretion in preadipocyte fibroblasts and adipocytes from patients with GO, and thus directly impact the clinical activity of the disease.

METHODS

IL-6 mRNA levels were measured in cultures of GO orbital preadipocytes (n = 3) treated during adipocyte differentiation with a monoclonal stimulatory TSHR antibody (M22; 10 ng/mL), IL-6 (1 ng/mL), or TSH (10 U/L). Additionally, levels of IL-6 protein secretion were assessed after adipocyte differentiation in orbital cultures exposed to TSH or M22 for 24 or 48 hours (n = 8). IL-6 mRNA levels were also measured in orbital adipose tissue specimens from well-characterized GO patients (n = 9) and normal individuals (n = 9).

RESULTS

Treatment of GO orbital preadipocyte cultures with IL-6, TSH, or M22 during adipocyte differentiation resulted in increased IL-6 mRNA levels (3.1-fold, 2.9-fold, and 2.7-fold, respectively; p < 0.05). Treatment of orbital cultures with M22 or TSH after adipocyte differentiation enhanced the release of IL-6 protein into the medium at both 24 and 48 hours for TSH (mean 1.9- and 2.3-fold; p = 0.002 and 0.015, respectively) and at 48 hours for M22 (mean 2.0-fold; p = 0.005). In addition, we found mean IL-6 mRNA levels to be significantly increased in GO orbital adipose tissue specimens (10-fold; p < 0.01), primarily attributable to high levels in three of the four patients with clinical activity scores >or=5.

CONCLUSIONS

Both TSH and M22 increase IL-6 expression in orbital preadipocyte fibroblasts and IL-6 secretion by mature adipocytes. These results suggest that circulating TSHR autoantibodies in GO might play a direct role in the clinical activity of the disease.

Free thyroxine is an independent predictor of subcutaneous fat in euthyroid individuals

OBJECTIVE

Thyroid function parameters have been associated with obesity, but associations with the type of adiposity have not been examined. We used ultrasound (US) to assess regional adiposity and investigated associations of thyroid function with parameters of central obesity.

DESIGN

Cross-sectional study.

METHODS

A total of 303 apparently healthy individuals (age 42.9+/-8.8, body mass index (BMI) 19.0-43.3, median 26.2 kg/m(2), 181 women) were examined for indices of the metabolic syndrome. BMI, waist and hip circumference, abdominal subcutaneous fat (SF), and preperitoneal fat (PF) layer was estimated. TSH, free thyroxine (fT(4)), triiodothyronine (T(3)), thyroid autoantibodies, insulin, glucose, and lipid levels were measured. Subjects receiving T(4) (9.2%) were excluded.

RESULTS

SF and SF/PF ratio were inversely correlated with fT(4) levels (r=-0.169, P=0.023, r=-0.193, P=0.009 respectively). In multivariate analysis, fT(4) was a predictor of SF and SF/PF, independently of age, sex, and smoking. SF correlated with TSH levels (r=0.149, P=0.037). PF and SF were positively associated with T(3) levels (r=0.245, P=0.004 and r=0.189, P=0.019 respectively). T(3) levels were positively associated with BMI (r=0.257, P=0.0004), waist perimeter (r=0.324, P<0.0001), and waist-to-hip ratio (WHR; r=0.363, P<0.0001). The T(3)/fT(4) ratio was positively correlated with SF (r=0.182, P=0.028), WHR (r=0.267, P=0.0003), and BMI (r=0.146, P=0.043).

CONCLUSIONS

Increasing SF accumulation as assessed by US is associated with lower fT(4) and higher TSH levels among euthyroid slightly overweight individuals. These associations indicate that subtle variation in thyroid function may participate in regional adiposity.

Identification of macrophage inhibitory cytokine-1 in adipose tissue and its secretion as an adipokine by human adipocytes

Macrophage inhibitory cytokine-1 (MIC-1), a divergent member of the TGF-beta superfamily, is involved in the control of multiple cellular processes and mediates cachexia through the inhibition of appetite. Adipose tissue as an endocrine organ secretes proteins (adipokines) that regulate energy homeostasis and other cellular functions. This study investigated whether MIC-1 is expressed in adipose tissue and whether MIC-1 is a secretory product of adipocytes. Mouse and human adipose tissues were collected from different depots. 3T3-L1 preadipocytes and human preadipocytes were induced to differentiate into adipocytes in cell culture. MIC-1 mRNA was detected in the major mouse adipose depots (epididymal, perirenal, sc). In these depots, MIC-1 gene expression was evident in both isolated mature adipocytes and stromal-vascular cells. In 3T3-L1 adipocytes, MIC-1 mRNA was detected before and after differentiation. MIC-1 mRNA and protein secretion were evident in human preadipocytes as well as differentiated adipocytes. MIC-1 production by human adipocytes was stimulated by H(2)O(2) and 15d-prostaglandin J(2). In addition, recombinant MIC-1 increased adiponectin secretion by differentiated human adipocytes. MIC-1 mRNA and protein were also observed in human sc and visceral fat. MIC-1 mRNA levels were positively correlated with adiponectin mRNA. Moreover, MIC-1 mRNA was negatively associated with body mass index and body fat mass in human subjects. We conclude that MIC-1 is expressed in adipose tissue and secreted from adipocytes and is therefore a new adipokine. MIC-1 may have a paracrine role in the modulation of adipose tissue function and body fat mass.

Insulin stimulates interleukin-6 expression and release in LS14 human adipocytes through multiple signaling pathways

IL-6 is an important cytokine that regulates both immune and metabolic functions. Within adipose tissue, preadipocytes produce significant amounts of IL-6, but little is known about the factors or mechanisms that regulate IL-6 production in these cells. Using LS14, a newly developed human adipocyte cell line, our objective was to determine the mechanisms by which insulin stimulates IL-6 production and release in preadipocytes. Insulin increased IL-6 gene expression and secretion in a time- and dose-dependent manner. Insulin decreased cyclic AMP (cAMP) but increased cyclic GMP (cGMP) levels, and IL-6 expression/release was stimulated by a cGMP analog. The stimulatory effect of insulin and cGMP was abrogated by a specific inhibitor of protein kinase G (cyclic GMP-dependent protein kinase). Both insulin and cGMP rapidly induced phosphorylation of cAMP response element binding protein. Insulin also activated the MAPK signaling pathway, and its blockade prevented the insulin-stimulated increases in IL-6 cell content and release, but not IL-6 gene expression. Although inhibition of the proteosome increased IL-6 cell content and release, proteosome activity was unaffected by insulin. These data suggest that the stimulatory effects of insulin on IL-6 release involve several interrelated components: transcription, intracellular releasable pool, and secretion, which are differentially regulated and, thus, determine the size of the releasable pool of IL-6. Insulin-induced IL-6 gene expression is mediated by cGMP/cyclic GMP-dependent protein kinase/cAMP response element binding protein, whereas MAPK is involved in the insulin-stimulated IL-6 synthesis/release.

Absence of thyrotropin-induced increase in leptin levels in patients with history of differentiated thyroid carcinoma undergoing recombinant human thyrotropin testing

BACKGROUND

Some extra-thyroid effects of TSH have been described in vitro and in vivo. TSH has recently been suggested to induce interleukin-6 secretion by adipocytes. Leptin is the main protein secreted by adipose tissue.

OBJECTIVE

The aim of our study was to evaluate the acute effect of the recombinant human TSH (rhTSH)-induced TSH surge on serum leptin levels in thyroidectomized patients undergoing levothyroxine (L-T4) suppressive therapy for differentiated thyroid carcinoma (DTC).

DESIGN

A cohort of 15 female DTC patients was evaluated. Standard rhTSH testing was performed. Leptin, TSH, thyroid hormones, and thyroglobulin were measured before and 3, 6, and 9 days after rhTSH testing. Some metabolic parameters were also evaluated at the baseline.

RESULTS

Baseline leptin levels were 12.2+/-3.2 microg/l. Only body mass index (BMI) correlated significantly (p<0.05) with leptin levels. After rhTSH administration, TSH levels increased significantly (p<0.001), while thyroid hormones remained unchanged. Twenty hours after the last rhTSH administration, leptin (11.8+/-3.0 microg/l) levels were unchanged. The maximal TSH level was negatively related with BMI (p<0.05), but no correlation between maximal TSH and leptin levels after rhTSH was noted.

CONCLUSIONS

Our in vivo experimental model suggests that an acute TSH increase after rhTSH testing is ineffective in changing circulating leptin levels.

Review on the occasion of a decade of recombinant human TSH: prospects and novel uses

The introduction of recombinant human thyroid-stimulating hormone (rhTSH) almost a decade ago represents a remarkable achievement in the history of clinical thyroidology. rhTSH now contributes substantially to the diagnostic approach to thyroid cancer, offering a reliable and safe alternative to thyroid hormone withdrawal by avoiding the morbidity of hypothyroidism. Several recent studies have also demonstrated the efficacy of radioiodine ablation of thyroid remnants after preparation with rhTSH. Moreover, the use of rhTSH in this context is associated with a lower whole body exposure to radiation compared to thyroid hormone withdrawal. Although not approved officially, rhTSH-assisted treatment of locoregional or distant metastatic disease may be the treatment of choice for patients in whom hypothyroidism may be relatively contraindicated, such as the very young and the aged, although additional efficacy studies are necessary. The compound has also been shown to be useful in the treatment of nontoxic multinodular goiter, especially when the radioiodine uptake is low. Finally, rhTSH may prove to be useful in studying the functional reserve of thyroid in the aging process, as well as the putative role of the TSH receptor in extrathyroidal tissue, such as lymphocytes, osteocytes, and adipocytes.