Adipocytokine correlations with thyroid function and autoimmunity in euthyroid sardinians

ADIPONECTIN LEVELS IN GRAVES' DISEASE - SYSTEMATIC REVIEW AND META-ANALYSIS

Context

Graves' disease is the most prevalent cause of hyperthyroidism worldwide. Adiponectin, the most abundant adipokine, plays a significant role in a cluster of prevalent diseases connected to metabolic disorders.

Objective

Although the association between adiponectin and Graves' disease has been studied, the existing data is inconsistent. Therefore, we conducted this systematic review and meta-analysis to evaluate the relationship between adiponectin levels and Graves' disease.

Methods

We performed a systematic electronic search on PubMed, EMBASE, Scopus and Cochrane Library using predefined keywords. We used the NHLBI quality assessment tools to assess the included studies.

Results

There were 11 studies involving 781 subjects included in our qualitative synthesis, while 6 studies were included in our quantitative synthesis. We observed significantly increased adiponectin levels in Graves' disease patients compared to controls (MD 2.983 [95% CI 0.138-5.828]) and hypothyroidism patients (MD 3.389 [95% CI 1.332-5.446]). Nevertheless, no significant MD was observed when comparing Graves' disease patients with and without Graves' ophthalmopathy (MD -27.124 [95% CI -88.893 - 34.645]).

Conclusions

Adiponectin levels were significantly higher in patients with Graves' disease compared to controls and hypothyroidism patients. However, patients with and without Graves' ophthalmopathy did not present a significant mean difference in adiponectin levels.

Carotid Beta Stiffness Association with Thyroid Function

Background: Thyroid hormone modulation of cardiovascular function has been associated with cardiovascular disease. Recent evidence suggests that free thyroxine (FT4) levels are associated with an increase in systemic arterial stiffness, but little is known about the effects of FT4 at the local level of the common carotid artery. β-stiffness index is a local elastic parameter usually determined by carotid ultrasound imaging. Methods: We conducted a cross-sectional analysis in the ProgeNIA cohort, including 4846 subjects across a broad age range. For the purpose of this study, we excluded subjects with increased thyrotropin (TSH) levels and those treated with levothyroxine or thyrostatic. We assessed β stiffness, strain, wall–lumen ratio, carotid cross-sectional area (CSA), and stress and flow in the right common carotid artery. We tested whether FT4, heart rate, and their interactions were associated with carotid parameters. Results: FT4 was positively and independently associated with β stiffness index (β = 0.026, p = 0.041), and had a negative association with strain (β = −0.025, p = 0.009). After adding heart rate and the interaction between FT4 and heart rate to the model, FT4 was still associated with the β stiffness index (β = 0.186, p = 0.06), heart rate was positively associated with the stiffness index (β = 0.389, p < 0.001) as well as their interaction (β = 0.271, p = 0.007). Conclusion: This study suggests that higher FT4 levels increase arterial stiffness at the common carotid level, consistent with a detrimental effect on elastic arteries. The effect of FT4 is likely to be primarily attributable to its effect on heart rate.

Thyroid Hormone Diseases and Osteoporosis

Thyroid hormones are essential for normal skeletal development and normal bone metabolism in adults but can have detrimental effects on bone structures in states of thyroid dysfunction. Untreated severe hyperthyroidism influences the degree of bone mass and increases the probability of high bone turnover osteoporosis. Subclinical hyperthyroidism, defined as low thyrotropin (TSH) and free hormones within the reference range, is a subtler disease, often asymptomatic, and the diagnosis is incidentally made during screening exams. However, more recent data suggest that this clinical condition may affect bone metabolism resulting in decreased bone mineral density (BMD) and increased risk of fracture, particularly in postmenopausal women. The main causes of exogenous subclinical hyperthyroidism are inappropriate replacement dose of thyroxin and TSH suppressive L-thyroxine doses in the therapy of benign thyroid nodules and thyroid carcinoma. Available data similarly suggest that a long-term TSH suppressive dose of thyroxin may decrease BMD and may induce an increased risk of fracture. These effects are particularly observed in postmenopausal women but are less evident in premenopausal women. Overt hypothyroidism is known to lower bone turnover by reducing both osteoclastic bone resorption and osteoblastic activity. These changes in bone metabolism would result in an increase in bone mineralization. At the moment, there are no clear data that demonstrate any relationship between BMD in adults and hypothyroidism. Despite these clinical evidences, the cellular and molecular actions of thyroid hormones on bone structures are not complete clear.

Effect of rhTSH on Lipids

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

The Association of Obesity with Autoimmune Thyroiditis and Thyroid Function-Possible Mechanisms of Bilateral Interaction

A growing number of patients suffer from autoimmune diseases, including autoimmune thyroid disease. There has simultaneously been a significant increase in the prevalence of obesity worldwide. It is still an open question whether adiposity can directly influence activation of inflammatory processes affecting the thyroid in genetically predisposed individuals. Adipokines, biologically active substances derived from the adipocytes, belong to a heterogenic group of compounds involved in numerous physiological functions, including the maintenance of metabolism, hormonal balance, and immune response. Notably, the presence of obesity worsens the course of selected autoimmune diseases and impairs response to treatment. Moreover, the excess of body fat may result in the progression of autoimmune diseases. Nutritional status, body weight, and energy expenditure may influence thyroid hormone secretion. Interestingly, thyroid hormones might influence the activity of adipose tissue as metabolic alterations related to fat tissue are observed under pathological conditions in which there are deficits or overproduction of thyroid hormones. Functioning TSH receptors are expressed on adipocytes. Thermogenesis may presumably be stimulated by TSH binding to its receptor on brown adipocytes. There could be a bilateral interaction between the thyroid and adipose. Obesity may influence the onset and course of autoimmune disease.

Subclinical Hypothyroidism and Lipid Metabolism: To Treat or Not to Treat?

Thyroid hormones have multiple complex effects on lipid synthesis and metabolism. These physiological actions are well documented in overt hypothyroidism where the elevated levels of total cholesterol, low density lipoporotein cholesterol and possibly triglycerides are reverted by levo-thyroxine therapy. Subclinical hypothyroidism, defined as elevated serum thyroid stimulating hormone in the presence of reference range of free thyroxine and free triiodothyronine concentrations, is a relatively frequent clinical conditions. Many clinical and epidemiological studies have evaluated lipid metabolism, markers of subclinical atherosclerosis and other cardiovascular risk factors in subclinical hypothyroidism as well as the need of replacement therapy in these patients. The available results are rather conflicting, with variable and inconclusive results. Moreover, no consensus still exists on the clinical significance and treatment of this mild form of thyroid failure. On the contrary, available evidences suggest that patients with plasma thyroid stimulating hormone levels above 10 mU/L should be treated with levo-thyroxine, since may have an increased risk of cardiovascular disease. However, the epidemiological evidences suggest being rather conservative in older people, since higher thyroid stimulating hormone is associated with lower risk of multiple adverse events in this population. In this review, we summarized the current evidences on the association between subclinical hypothyroidism and lipid metabolism and the effect of levo-thyroxine therapy on lipid parameters.

Role of Adipokines in the Association between Thyroid Hormone and Components of the Metabolic Syndrome

Metabolic syndrome (MS) increases cardiovascular risk. The role of thyroid hormone on components of MS is unclear. We analyzed a sample of 4733 euthyroid subjects from SardiNIA study. In female thyrotropin (TSH) was significantly and positively associated with triglycerides (Standardized regression coefficients (β) = 0.081, p < 0.001). Free thyroxine (FT4) was positively associated with HDL (β = 0.056, p < 0.01), systolic blood pressure (SBP) (β = 0.059, p < 0.001), diastolic blood pressure (DBP) (β = 0.044, p < 0.01), and fasting glucose (β = 0.046, p < 0.01). Conversely, FT4 showed a negative association with waist circumference (β = −0.052, p < 0.001). In TSH was positively associated with triglycerides (β = 0.111, p < 0.001) and FT4 showed a positive association with DBP (β = 0.51, p < 0.01). The addition of leptin and adiponectin to the regression models did not substantially change the impact of thyroid hormones on components of MS. Our data suggest that, even within the euthyroid range, excess of truncal adipose tissue is associated with variations in FT4. Leptin and adiponectin exert an additive effect rather than a causal effect. Additional studies should be performed to determine the clinical significance of this finding.

Thyroid function and thyroid disorders during pregnancy: a review and care pathway

PURPOSE

To review the literature on thyroid function and thyroid disorders during pregnancy.

METHODS

A detailed literature research on MEDLINE, Cochrane library, EMBASE, NLH, ClinicalTrials.gov, and Google Scholar databases was done up to January 2018 with restriction to English language about articles regarding thyroid diseases and pregnancy.

RESULTS

Thyroid hormone deficiencies are known to be detrimental for the development of the fetus. In particular, the function of the central nervous system might be impaired, causing low intelligence quotient, and mental retardation. Overt and subclinical dysfunctions of the thyroid disease should be treated appropriately in pregnancy, aiming to maintain euthyroidism. Thyroxine (T4) replacement therapy should reduce thyrotropin (TSH) concentration to the recently suggested fixed upper limits of 2.5 mU/l (first and second trimester) and 3.0 mU/l (third trimester). Overt hyperthyroidism during pregnancy is relatively uncommon but needs prompt treatment due to the increased risk of preterm delivery, congenital malformations, and fetal death. The use of antithyroid drug (methimazole, propylthiouracil, carbimazole) is the first choice for treating overt hyperthyroidism, although they are not free of side effects. Subclinical hyperthyroidism tends to be asymptomatic and no pharmacological treatment is usually needed. Gestational transient hyperthyroidism is a self-limited non-autoimmune form of hyperthyroidism with negative antibody against TSH receptors, that is related to hCG-induced thyroid hormone secretion. The vast majority of these patients does not require antithyroid therapy, although administration of low doses of β-blocker may by useful in very symptomatic patients.

CONCLUSIONS

Normal maternal thyroid function is essential in pregnancy to avoid adverse maternal and fetal outcomes.