Serum irisin levels and thyroid function--newly discovered association

The Effect of Bariatric Surgery on Irisin Level: a Systematic Review and Meta-analysis

This systematic analysis and meta-analysis aimed to assess changes in the plasma levels of irisin after bariatric surgery. Search strategy, study screening, and data gathering were all conducted using a checklist and the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Two researchers independently extracted the data, and a third person was included to resolve disagreements. The results illustrated no statistical difference between before and after surgery irisin plasma levels (P = 0.216, 95% CI = -1.812-0.410, SMD = -0.701, I-squared = 94.9%). BMI exhibited a meaningful decline after surgery compared to preoperative values (SMD = -3.09, 95% CI = -4.59--1.59, I-squared = 95.5%, P<0.05). According to our analysis, it can be concluded that irisin plasma levels are not significantly influenced by bariatric surgery.

The Effect of Irisin on Thyroid Hormone Levels in Chronic Paroxetine-Treated Rats

It is known that serotonin reuptake inhibitors (SSRIs), which are widely used in mood disorders, affect the hypothalamic-pituitary-thyroid axis activity. In this study, we investigated the effect of paroxetine, an SSRI, on thyroid hormone levels in rats. We also examined the role of irisin, a newly discovered potential regulatory hormone for metabolism, on paroxetine-induced changes. A total of 64 Sprague-Dawley female and male rats were randomly divided into four subgroups for each gender and treated as follows: sham-operated control (vehicle), paroxetine (treated with 20 mg/kg paroxetine by oral gavage), irisin (100 ng/kg/day for 28 days with mini-osmotic pumps), and paroxetine + irisin group (n = 8). Serum fasting free triiodothyronine (fT3) and free thyroxine (fT4) levels were measured by automated chemiluminescence method. Serum thyroid-stimulating hormone (TSH) level was determined with enzyme-linked immunosorbent analysis (ELISA). Compared to the sham control group (p < 0.05), the significantly reduced fT4 and TSH serum levels in paroxetine-treated male animals were markedly increased by subcutaneous irisin perfusion. fT3 levels significantly increased in both irisin (4.35 ± 0.17 pq/mL) and paroxetine + irisin groups (4.51 ± 0.19 pq/mL) compared to sham control (3.60 ± 0.23 pq/mL) and paroxetine groups (3.57 ± 0.12 pq/mL) (p < 0.05). It was observed that serum fT3, fT4, and TSH levels decreased in female animals receiving paroxetine compared to the sham control group. Subcutaneous administration of irisin increased these hormone levels. However, these changes were not statistically significant. These results suggested that irisin may play a role in the mechanism underlying the beneficial effects of exercise in preventing SSRI-related side effects by increasing thyroid hormone levels, which were decreased by paroxetine.

Elevated serum Meteorin-like levels in patients with hyperthyroidism

BACKGROUND

Meteorin-like (Metrnl) is a newly discovered adipomyokine that regulates systemic energy homeostasis. Both thyroid hormones and Metrnl increase energy expenditure and induce browning of adipose tissue. Thus, the aim of this study was to investigate serum Metrnl levels in hyperthyroid patients and the association of serum Metrnl levels with hyperthyroidism.

METHODS

The study included 88 patients with newly diagnosed untreated overt hyperthyroidism and 100 age- and sex- matched healthy controls. Serum Metrnl levels were determined using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

Serum Metrnl levels were significantly elevated in patients with hyperthyroidism compared with controls. Linear regression analyses indicated that serum Metrnl levels were independently associated with FT3 (β = 0.324, P = 0.001), FT4 (β = 0.293, P = 0.001), and TSH (β = -0.234, P = 0.006) after full adjustment. Additionally, further logistic regression analyses revealed that the highest Metrnl tertile was significantly associated with hyperthyroidism compared with the lowest tertile (P for trend < 0.001). The relationship remained significant even after adjusting for potential confounders. Meanwhile, each one-unit increase in circulating Metrnl was independently associated with hyperthyroidism (OR 1.021, 95%CI 1.007-1.036, P < 0.01).

CONCLUSION

Serum Metrnl levels were elevated in patients with hyperthyroidism and were independently associated with hyperthyroidism.

The Role of Thyroid Hormones on Skeletal Muscle Thermogenesis

Nowadays obesity becomes a significant global problem. Hence, recently more and more attention has been paid to substances present in the body that have a significant impact on metabolic processes and thermogenesis, in the context of their potential use in the prevention and treatment of obesity. It is well known that the relationship between thyroid hormones and obesity is multilayered, however recently, more and more information about the possible relation between thyroid hormones and muscle metabolism has been published. The aim of this review is to present the most updated information on the physiological impact of thyroid hormones on muscle tissue, as well as pathological changes related to the occurrence of various types of thyroid disorders, including hypothyroidism, hyperthyroidism and sick euthyroid syndrome. However, the data in humans still remains insufficient, and further studies are needed to fully explore the thyroid-muscle cross-talk.

Levothyroxine and insulin requirement in autoimmune polyglandular type 3 syndrome: a real-life study

PURPOSE

To evaluate factors influencing the insulin and levothyroxine requirement in patients with autoimmune polyglandular syndrome type 3 (APS-3) vs. patients with type 1 diabetes mellitus (T1DM) and autoimmune hypothyroidism (AH) alone, respectively.

METHODS

Fifty patients with APS-3, 60 patients with T1DM and 40 patients with AH were included. Anthropometric, clinical and biochemical parameters were evaluated in all patients. Insulin requirement was calculated in patients with APS-3 and T1DM, while levothyroxine requirement was calculated in APS-3 and AH.

RESULTS

Patients with APS-3 showed higher age (p = 0.001), age of onset of diabetes (p = 0.006) and TSH (p = 0.004) and lower total insulin as U/day (p < 0.001) and U/Kg (p = 0.001), long-acting insulin as U/day (p = 0.030) and U/kg (p = 0.038) and irisin (p = 0.002) compared to T1DM. Patients with APS-3 had higher waist circumference (p = 0.008), duration of thyroid disease (p = 0.020), levothyroxine total daily dose (p = 0.025) and mcg/kg (p = 0.006), triglycerides (p = 0.007) and VAI (p = 0.010) and lower age of onset of thyroid disease (p = 0.007) than AH. At multivariate analysis, levothyroxine treatment and VAI were associated with insulin and levothyroxine requirement in APS-3, respectively. VAI was independently associated with insulin requirement in T1DM. Circulating irisin levels were independently associated with levothyroxine requirement in AH.

CONCLUSION

Patients with APS-3 show lower insulin requirement and higher levothyroxine requirement than T1DM and AH alone, respectively. Levothyroxine treatment and VAI affect insulin and levothyroxine requirement, respectively, in APS-3. In T1DM, adipose tissue dysfunction, indirectly expressed by high VAI, is associated with an increased insulin requirement, while circulating irisin levels influence the levothyroxine requirement in AH.

Myokines in Acromegaly: An Altered Irisin Profile

INTRODUCTION

The muscle is an endocrine organ controlling metabolic homeostasis. Irisin and myostatin are key myokines mediating this process. Acromegaly is a chronic disease with a wide spectrum of complications, including metabolic disturbances.

PURPOSE

To examine the influence of acromegaly on irisin and myostatin secretion and their contribution to metabolic profile and body composition.

MATERIALS AND METHODS

In 43 patients with acromegaly and 60 controls, serum levels of irisin, myostatin, growth hormone (GH), insulin-like growth factor 1 (IGF-1), parameters of glucose, and lipid metabolism were determined. Body composition was assessed with dual-energy x-ray absorptiometry.

RESULTS

The irisin concentration was significantly lower in patients with acromegaly compared to controls (3.91 vs. 5.09 μg/ml, p = 0.006). There were no correlations between irisin and GH/IGF-1 levels. In the study group, irisin was negatively correlated with fasting insulin (r = -0.367; p = 0.042), HOMA-IR (r = -0.510; p = 0.011), and atherogenic factors: Castelli I (r = -0.416; p = 0.005), Castelli II (r = -0.400; p = 0.001), and atherogenic coefficient (AC) (r = -0.417; p = 0.05). Irisin and myostatin concentrations were also lower in acromegalics with insulin resistance than without (2.80 vs. 4.18 μg/ml, p = 0.047; 81.46 vs. 429.58 ng/L, p = 0.018, respectively). There were no differences between study group and controls in myostatin concentration. Myostatin levels negatively correlated with GH (r = -0.306; p = 0.049), HOMA-IR (r = -0.046; p = 0.411), and insulin levels (r = -0.429; p = 0.016).

CONCLUSIONS

Decreased irisin concentrations in acromegaly may suggest impaired hormonal muscle function contributing to metabolic complications in this disorder. However, learning more about the association between myostatin and GH in acromegaly requires further studies. Nevertheless, it appears that myostatin is not critical for muscle mass regulation in acromegaly.

Irisin as a Potential Biomarker Associated with Myocardial Injuries in Patients with Severe Hypothyroidism

OBJECTIVE

Irisin, a novel myokine, has recently been considered to produce a cardioprotective effect. Potential biomarkers for myocardial injuries in patients with severe hypothyroidism have yet to be identified. We aimed to investigate whether serum irisin may serve as a promising biomarker for early detecting the myocardial injuries in patients with severe hypothyroidism.

METHODS

This cross-sectional study comprised 25 newly diagnosed drug-naive patients with severe primary hypothyroidism and 17 age- and sex-matched healthy controls. Circulating irisin levels and cardiac magnetic resonance (CMR) were evaluated in each participant. Left ventricular (LV) myocardial injuries were detected by CMR-based T1 mapping technique using a modified look-locker inversion recovery (MOLLI) sequence, which is quantified as native T1 values.

RESULTS

Compared with healthy controls, the severe hypothyroidism group had significantly lower levels of serum irisin, especially those with pericardial effusion (P < 0.05). The severe hypothyroidism subjects exhibited lower peak filling rates (PFRs) and higher native myocardial T1 values than controls (P < 0.05). Additionally, the ROC analysis displayed that the sensitivity and specificity of serum irisin for diagnosing pericardial effusion in patients with severe hypothyroidism were 73.3% and 100.0%, respectively. The AUC was 0.920 (0.861-1.000) (P < 0.001). The cutoff value was 36.94 ng/mL. Moreover, the results in subgroup analysis revealed that the native T1 values of the low-irisin group were significantly higher than that of the high-irisin group (P < 0.05). According to multivariate linear regression analysis, serum irisin concentrations were negatively and independently correlated with native myocardial T1 values after adjustment for age, sex, and other conventional confounding factors (β = -1.473, P < 0.05).

CONCLUSIONS

Irisin may be a potential biomarker for predicting myocardial injuries in patients with severe hypothyroidism.

Circulating Irisin Level and Thyroid Dysfunction: A Systematic Review and Meta-Analysis

Both thyroid hormones and irisin have profound influences on the metabolism of the human body. Based on their similarities, several studies have been conducted to explore changes in irisin levels in patients with hypothyroidism and hyperthyroidism. This study was conducted in accordance with the PRISMA statement and the MOOSE reporting guideline. Based on a preregistered protocol (PROSPERO-CRD42019138430), a comprehensive search of eight databases was performed from inception to April 2020. Studies with original data collected from patients with thyroid dysfunction were included. Subgroup analysis was performed based on the different types of clinical manifestations and patient characteristics. The quality of each study and the presence of publication bias were assessed by the Newcastle-Ottawa score (NOS) and funnel plot with Egger's test, respectively. A total of 11 studies with 1210 participants were included. Ten studies were identified as high-quality studies. Pooled analysis indicated decreased irisin levels in patients with hypothyroidism (MD -10.37, 95% CI -17.81 to -2.93). Subgroup analysis revealed an even lower level of irisin in patients with clinical-type hypothyroidism (MD -17.03, 95% CI -30.58 to -3.49) and hypothyroidism caused by autoimmune disease (MD -19.38, 95% CI -36.50 to -2.26). No differences were found after achieving euthyroid status from levothyroxine treatment in patients with hypothyroidism compared with controls. No differences were found between patients with hyperthyroidism and controls. Correlation analyses revealed a possible negative correlation between irisin and TSH and positive correlations between irisin and both fT3 and fT4. Irisin was correlated with TSH receptor antibodies.

The Effect of Pubertal Stage on the Concentrations of the Novel Adipomyokine, Irisin, in Male Adolescents

OBJECTIVE

Irisin is a recently discovered protein and is defined as an adipomyokine. The relation of irisin with carbohydrate metabolism and other hormone parameters have been investigated. However, studies evaluating the relationship between irisin and puberty are limited and inconclusive. The aim was to evaluate serum concentrations of irisin during different pubertal stages in male adolescents.

METHODS

The study included normal weight pubertal male adolescents between the ages of 13^6/12-14^11/12 who had entered puberty. Fasting serum irisin concentrations were evaluated, and bioelectrical impedance analysis was used to measure body fat ratio (BFR) and fat-free mass (FFM). BFR was also calculated by caliper measurement of subcutaneous fat at the triceps.

RESULTS

Sixty-eight adolescents were enrolled. The number of adolescents in pubertal stage 2, 3, 4 and 5 were n=17 (25%), n=13 (19.1%), n=21 (30.1%) and n=17 (25%), respectively. The median values of the irisin are 8.80, 8.20, 9.15 and 7.24 ng/mL according to the 2-5 pubertal stages, respectively. The levels of circulating irisin did not differ according to the pubertal stage. Additionally, there was no significant relationship between irisin levels and body fat percentage or FFM.

CONCLUSION

Irisin levels do not differ after the onset of puberty or with progressing pubertal maturation. This study strengthens the evidence that there is no change in irisin concentration as puberty progresses. This may have important implications when using this adipomyokine in the future for diagnosis or treatment of obesity-related diseases.

The effectiveness of military physical exercise on irisin concentrations and oxidative stress among male healthy volunteers

Background Irisin, a newly discovered hormone, is secreted into the circulation from skeletal muscles in response to physical exercise. The biochemical parameters related to irisin secretion have not been sufficiently investigated yet. The aim of this study was to examine the effectiveness of exercise on the level of irisin and its correlation with biochemical and oxidative stress parameters. Materials and methods In this pre- and post-test observational study, 39 healthy male volunteers from a military training setting were followed up on between September and November 2015. The individuals who were included in this study were between 22 and 27 years old with an average age of 24. Those with inflammatory disorders or chronic diseases such as diabetes mellitus were excluded from the study. The parameters were measured at the baseline, at 4 weeks, and at 8 weeks of intervention. Results The study found that the systolic and diastolic blood pressures substantially decreased after 8 weeks of intervention. The cholesterol-to-HDL ratio and glucose levels were significantly higher at the baseline compared to 8 weeks. Total protein and albumin were significantly higher following 4 weeks (0.25 and 0.21 g/dL) and 8 weeks (0.32 and 0.16 g/dL), respectively. Meanwhile, total globulin and irisin increased following 8 weeks of the intervention by only 0.16 g/dL and 0.41 μg/mL, respectively. The high sensitivity C-reactive protein (hs-CRP) decreased following 8 weeks (-0.81 μg/mL). The protein carbonyl (PC) decreased following 4 weeks by only 0.34 nmol/L. Conclusions This study demonstrated that military training enhanced irisin hormone secretion following 8 weeks of military exercise.

Variations in Irisin, Bone Mineral Density, Bone Mineral Content, and Body Composition After Laparoscopic Bariatric Procedures in Obese Adults

INTRODUCTION

This study was aimed to assess irisin levels in obesity (OB) and T2DM individuals and investigate the dynamic changes of irisin, bone mineral density (BMD), bone mineral content, and body composition in 19 OB patients after laparoscopic bariatric procedures, and also to evaluate the correlation of irisin, with BMD and body composition.

METHODS

Forty-five OB, 20 T2DM, and 20 healthy adults had been recruited. Levels of irisin were measured in all subjects. Metabolic characteristics were obtained from OB and T2DM patients. Nineteen patients were randomly assigned to be received Roux-en-Y gastric bypass (LRYGB) or laparoscopic sleeve gastrectomy (LSG) procedure and to be completed 6-month follow-up. Irisin, BMD, bone mineral content, and body composition were measured at each visit.

RESULTS

Significantly higher circulating irisin levels were measured in the OB group compared with T2DM and control groups. FINS, C-P, HOMA-IR, FBCI, HBCI, ALT, AST, and UA levels of OB were significantly higher than those of T2DM patients. While FBG and HbA1c of the OB were significantly lower than T2DM group. There were significant differences among circulating irisin, BMD, and body composition after laparoscopic bariatric surgery. Levels of irisin were decreased after operations including both LRYGB and LSG surgery compared with preoperation. At each time point (1, 3, and 6 months) of postoperation, there was no significant difference in percentage of total weight loss between LSG and LRYGB group. The positive correlation of irisin levels with total BMD, muscle, and fat masses were found during 6-month follow-up after surgery.

CONCLUSIONS

The levels of irisin were higher in OB patients. There were positive correlations of irisin levels with total BMD, muscle, and fat masses during 6-month follow-up after surgery. Irisin may be involved in the occurrence and development of obese and it is related to BMD and body composition. Both LRYGB and LSG operations could decrease the circulating levels of irisin.

Acute psychosis and concurrent rhabdomyolysis unveiling diagnosis of hypothyroidism

Neuropsychiatric and muscular symptoms can develop as part of hypothyroidism. However, frank psychosis or rhabdomyolysis due to hypothyroidism are uncommon and have been reported rarely as the first presenting features of hypothyroidism. We report a case of a 44-year-old man who presented with a 2-week history of delusions, hallucinations and mild bilateral leg pain, without apparent signs of myxedema. Investigations revealed raised thyroid stimulation hormone >100 mIU/L and high creatine kinase >21 000 U/L. Diagnosis of hypothyroidism-induced psychosis and rhabdomyolysis was made. He received thyroxine, olanzapine and a short course of steroids. His symptoms improved after 2 weeks of treatment and he remained free of symptoms at 6 months of follow-up. To the best of our knowledge, this is the first case of concomitant psychosis and rhabdomyolysis leading to hypothyroidism diagnosis. This case highlights the importance of hypothyroidism screening when faced with unexplained psychosis or rhabdomyolysis, especially if combined.

Elevated serum neuregulin 4 levels in patients with hyperthyroidism

OBJECTIVE

Recent studies have shown that neuregulin 4 (Nrg4), a member of the epidermal growth factor (EGF) family of extracellular ligands, plays an important role in the prevention of obesity, insulin resistance and nonalcoholic fatty liver disease (NAFLD). Considering that thyroid hormone (TH) has profound effects on whole-body energy metabolism, we speculate that circulating Nrg4 levels might be altered in patients with hyperthyroidism.

DESIGN AND METHODS

A total of 129 hyperthyroid patients and 100 healthy subjects were recruited. Of them, 39 hyperthyroid patients received thionamide treatment for 3 months until euthyroidism. Serum Nrg4 levels were determined using the ELISA method. To further confirm the relationship between TH and Nrg4, C57BL/6 mice were treated with T3 and quantitative real-time PCR was performed to detect Nrg4 gene expression.

RESULTS

Serum Nrg4 levels were significantly elevated in hyperthyroid patients as compared with normal controls (3.84 ± 1.63 vs 2.21 ± 1.04 ng/mL, P < 0.001). After achieving euthyroidism by thionamide treatment, serum Nrg4 levels dropped markedly from 3.57 ± 1.26 to 1.94 ± 0.72 ng/ml (P < 0.001). After adjustment for potential confounders, serum Nrg4 levels were independently associated with hyperthyroidism. The upregulation of Nrg4 expression in the livers and white adipose tissues by T3 was further confirmed by animal and cell culture experiments.

CONCLUSIONS

Serum Nrg4 levels were increased in patients with hyperthyroidism. The liver and white adipose tissue might be primary sources contributing to elevated serum Nrg4 concentrations.

Irisin levels increase after treatment in patients with newly diagnosed Hashimoto thyroiditis

PURPOSE

Irisin is a newly identified myokine secreted by skeletal muscle and has significant effects on body metabolism. Thyroidal functional state has a profound influence on the metabolism of human body. Therefore, the aim of this study was to investigate the possible changes in serum irisin concentrations before and after treatment in hypothyroid subjects.

METHODS

The study included 26 patients with overt hypothyroidism due to Hashimoto thyroiditis and 19 healthy subjects. Baseline serum thyroid function tests and presence of thyroid autoantibodies and levels of creatine kinase (CK) and irisin were measured in both groups. All measurements in the hypothyroid group were repeated after euthyroidism was achieved.

RESULTS

Serum irisin levels were significantly lower in the hypothyroid groups than the control group (p < 0.001). Negative correlation between irisin and thyroid stimulating hormone and CK levels (r = - 0.623, p < 0.001 and r = - 0.389, p = 0.008, respectively) and a positive correlation between irisin and free thyroxine (fT4) levels (r = 0.570, p < 0.001) was found. Serum CK levels decreased significantly after treatment (p < 0.001). Serum irisin levels significantly increased (from 57.4 to 99.8 U/L, p < 0.001) when the hypothyroid patients were treated to achieve euthyroidism.

CONCLUSIONS

To the best of our knowledge, this is the first study providing insight that low serum irisin levels significantly increased following treatment to euthyroid state in overt hypothyroid patients with Hashimoto thyroiditis. Larger scale studies are needed to confirm these results and to ensure irisin as a possible biomarker of Hashimoto's thyroiditis.

Does iris(in) bring bad news or good news?

Irisin, a novel myokine produced in response to physical activity, promotes white-to-brown fat transdifferentiation. The name irisin referred to the ancient Greek goddess Iris, the messenger who delivered (bad) news from the gods. In mice, it has been demonstrated that irisin plays a key role in metabolic regulation, energy expenditure and glucose homeostasis. New findings from various studies carried out in both animals and humans suggest that irisin might also have other favorable effects, such as increasing bone cortical mass, preventing hepatic lipid accumulation, and improving cognitive functions, thus mediating many exercise-induced health benefits. However, data on the role and function of irisin in humans have prompted controversy, due mostly to the only recent confirmation of the presence of irisin in humans. Another strong limitation to the understanding of irisin mechanisms of action is the lack of knowledge about its receptor, which until now remains unidentified in humans and in animals. This review presents an overall analysis of the history of irisin, its expression, and its involvement in health, especially in humans. Level of Evidence Level V, review.

Association between circulating irisin levels and epicardial fat in patients with treatment-naïve overt hyperthyroidism

BACKGROUND

Hyperthyroidism is associated with increased metabolic activity and thermogenesis. Irisin is a key molecule in thermogenesis and energy expenditure via adipose tissue browning. Epicardial fat was previously defined as brown-like fat. Thus, here we aimed to evaluate the association between serum irisin level and epicardial fat thickness (EFT) in patients with hyperthyroidism.

METHODS

A total of 25 hyperthyroid patients and 24 age-, sex- and BMI-matched healthy controls were enrolled. Serum irisin levels, thyroid hormone levels, and body compositions were compared. EFT was measured via transthoracic echocardiography.

RESULTS

Serum irisin level and EFT were significantly higher in the hyperthyroid group (p < 0.001 and p = 0.001, respectively). The distributions of fat-free mass, muscle mass and fat mass were similar between the study groups. Serum irisin level was negatively correlated with TSH (p < 0.001) and positively correlated with fT3 (p < 0.001), fT4 (p < 0.001) and TSH receptor antibody (p = 0.002) levels and EFT (p = 0.001). In multivariate linear regression analysis, TSH (β = -0.475, p < 0.001) and EFT (β = 0.290, p = 0.023) levels were significantly associated with serum irisin levels.

CONCLUSIONS

An increased serum irisin level associated with EFT might contribute to metabolic derangement in hyperthyroidism. Further studies are needed to elucidate whether irisin levels and EFT are affected by hyperthyroidism or vice versa.

Hyperirisinemia is independently associated with subclinical hypothyroidism: correlations with cardiometabolic biomarkers and risk factors

PURPOSE

Irisin, a newly discovered adipo-myokine, is implicated in the modulation of the adipose phenotype, increasing energy expenditure and ameliorating systemic metabolism. Our aim was to investigate circulating irisin in subclinical hypothyroidism (SH) and study its associations with cardiometabolic risk factors.

METHODS

In a large case-control study, serum irisin, insulin resistance and lipid parameters, classic adipokines, inflammatory and hepatic biomarkers, and cardiovascular risk factors were determined in 120 consecutive patients with SH and 120 healthy controls matched on age, gender, and date of blood draw. Sixteen patients with SH received L-T4 treatment and, after 6 months, serum irisin and other biomarkers were assessed.

RESULTS

SH cases exhibited significantly higher circulating irisin than controls (p < 0.001). In all participants, irisin was positively associated with TSH, anti-TG, HOMA-IR, C-peptide, lipid and inflammatory biomarkers, leptin, and cardiovascular risk factors, including Framigham score and apolipoprotein B/apolipoprotein A-I. Irisin was negatively correlated with adiponectin, HDL-C, and thyroid hormones. Serum irisin was independently associated with SH, above and beyond body mass index and cardiometabolic factors (p = 0.02). TSH was an independent predictor of circulating irisin (p = 0.003). L-T4 therapy did not reverse considerably the hyperirisinemic status in treated SH patients (p = 0.09).

CONCLUSIONS

Irisin may represent an adipo-myokine counterbalancing a potential, gradual deterioration of lipid metabolism and insulin sensitivity in SH as well as reflecting a protective compensatory mechanism against oxidative muscle and thyroid cell stress. More mechanistic and prospective studies shedding light on the pathogenetic role of irisin in SH are needed to confirm and extend these data.

An update on the role of irisin in the regulation of endocrine and metabolic functions

Irisin is a novel myokine and adipokine that has gained much attention recently due to its mechanisms of action. Irisin is secreted following proteolytic cleavage of its precursor fibronectin type III domain containing 5 (FNDC5). Following its release, irisin exerts its major action by increasing the expression of mitochondrial uncoupling protein 1 (UCP 1), which facilitates the conversion of white adipose tissue (WAT) into beige adipose tissue. Irisin is distributed in various body tissues and several actions have been attributed to its presence in those tissues. It has been suggested that it plays a role in metabolic diseases, ageing, inflammation and neurogenesis. However, the circulating levels of irisin are modulated by several factors such as diet, obesity, exercise, pharmacological agents and different pathological conditions. In this review, we have discussed the mechanisms by which irisin influences the functions of different body systems and how external factors in turn affect the circulating level of irisin. In conclusion, modification of circulating irisin level may help in the management of a variety of endocrine and metabolic disorders.

The association between irisin and muscle metabolism in different thyroid disorders

BACKGROUND

Irisin is a new adipo-myokine, encoded by the FNDC5 gene. Currently, there is a discussion regarding the relation between thyroid function and irisin concentration. This prospective study assesses the influence of thyrometabolic changes on serum irisin concentration in association with altered muscle metabolism. This is performed on a large cohort of patients affected by severe hypo- or hyperthyroidism, as well as by the expression of the FNDC5 gene in thyroid tissue affected by different pathologies.

METHODS

The study group comprised 119 patients with newly diagnosed severe hyperthyroidism or hypothyroidism, and a control group of 45 healthy subjects. Body composition, serum irisin concentrations, and thyroid-related hormones, creatine kinase, dystrophin and titin concentrations were evaluated. FNDC5 expression was also analysed in tissue samples from 80 patients with nontoxic multinodular goitre, toxic goitre, Graves' disease and papillary thyroid cancer.

RESULTS

Irisin concentration was lower in patients with prolonged hypothyroidism. There was a tendency towards lower dystrophin and titin concentrations in patients with hypothyroidism and hyperthyroidism. Restoration of euthyroidism in patients with hypothyroidism resulted in a decreased muscle mass with an increase in irisin concentrations, while the hyperthyroid group showed an increase in fat mass. Statistically significant overexpression of FNDC5 gene was found in patients with toxic goitre as compared to Graves' disease, papillary thyroid cancer and controls.

CONCLUSIONS

The presented data support the theory that irisin concentration changes are associated with prolonged hypothyroidism and might primarily constitute the result of prolonged myopathy. These changes are most likely not related to the expression of the FNDC5 gene in the thyroid gland.

Elevated Serum Growth Differentiation Factor 15 Levels in Hyperthyroid Patients

Background: Recent studies have shown that growth differentiation factor 15 (GDF15), a member of the transforming growth factor-β (TGF-β)/bone morphogenetic protein (BMP) superfamily, plays an important role in appetite, type 2 diabetes, and cardiovascular diseases. Since thyroid hormone has pleiotropic effects on whole-body energy metabolism, we aimed to explore the effect of thyroid hormone on circulating GDF15 levels in humans and GDF15 genes expression in C57BL/6 mice. Methods: A total of 134 hyperthyroid patients and 105 healthy subjects were recruited. Of them, 43 hyperthyroid patients received thionamide treatment for 3 months until euthyroidism. Serum GDF15 levels were determined using the enzyme-linked immunosorbent assay (ELISA) method. To determine the source for the increased circulating GDF15, C57BL/6 mice were treated with T3, and GDF15 gene expressions in the liver, skeletal muscle, brown adipose tissue (BAT), inguinal white adipose tissue (iWAT), epididymal white adipose tissue (eWAT) were analyzed by quantitative real-time polymerase chain reaction (PCR). Results: Serum GDF15 levels were significantly elevated in hyperthyroid patients as compared with healthy subjects (326.06 ± 124.13 vs. 169.24 ± 82.96 pg/mL; P < 0.001). After thionamide treatment, GDF15 levels in hyperthyroid patients declined markedly from 293.27 ± 119.49 to 118.10 ± 71.83 pg/mL (P < 0.001). After adjustment for potential confounders, serum GDF15 levels were independently associated with hyperthyroidism. T3 treatment increased GDF15 expression in the brown adipose tissue of C57BL/6 mice. Conclusions: Serum GDF15 levels were elevated in patients with hyperthyroidism and declined after thionamide treatment. Thyroid hormone treatment upregulated GDF15 expression in mice. Therefore, our results present the clinical relevance of GDF15 in humans under the condition of hyperthyroidism.

Both hypothyroidism and hyperthyroidism increase plasma irisin levels in rats

Background A recently discovered hormone, irisin is accepted to be significantly involved in the regulation of body weight. Thyroid functions may be, directly or indirectly, associated with irisin. Aim The aim of the present study is to determine the effect of experimental thyroid dysfunction on irisin levels in rats. Methods The study registered 40 adult male Sprague-Dawley rats, which were allocated to groups as follows: 1. Control; 2. Hypothyroidism induced by injection of 10 mg/kg/day intraperitoneal propylthiouracil (PTU) for 3 weeks; 3. Hypothyroidism (PTU 2 weeks) + L-thyroxin (1.5 mg/kg/day for 1 week); 4. Hyperthyroidism induced in rats by 3-week thyroxin (0.3 mg/kg/day); 5. Hyperthyroidism + PTU. At the end of the study, blood samples were collected to quantify free triiodothyronine (FT3), free triiodothyronine (FT4) and irisin levels. Results FT3 and FT4 levels were reduced in hypothyroidism and were significantly elevated in hyperthyroidism (p < 0.001). Irisin values, on the other hand, were found to be elevated in both hypothyroidism and hyperthyroidism groups (p < 0.001). Conclusion The results of the study suggest that irisin values increase in thyroid dysfunction, hypo- and hyperthyroidism, and that when hypothyroidism is corrected by thyroxin administration and hyperthyroidism by PTU injection, plasma irisin values go back to normal.

Irisin and Myostatin Levels in Patients with Graves' Disease

BACKGROUND AND AIMS

Skeletal muscle system, which is one of the primary targets for thyroid hormones, has an important role in energy metabolism. Some myokines such as irisin and myostatin have considerable effects on energy metabolism in addition to the musculoskeletal system. Our aim was to investigate circulating irisin and myostatin levels in patients with Graves' Disease (GD).

METHODS

This study included 41 patients with GD who were in overt hyperthyroid status and 44 healthy subjects.

RESULTS

Serum irisin levels were higher in patients with hyperthyroidism than in control group (p = 0.003). However, there was no statistical difference in myostatin levels between groups (p = 0.21). Irisin levels were positively correlated with free triiodothyronine (FT3), free thyroxine (FT4), thyrotropin receptor antibody (TRAb) (p = 0.03, p = 0.02, p = 0.02, respectively) and negatively correlated with thyroid-stimulating hormone (TSH) (p = 0.006) in both groups. In multiple regression analysis, the presence of GD was the only significant factor associated with serum irisin levels (β = 0.29, p = 0.01). Myostatin levels were positively correlated with age, body mass index (BMI), FT4, HOMA-IR (p = 0.001, p = 0.04, p = 0.003, p = 0.03, respectively) and negatively correlated with TSH (p = 0.01). Multiple regression analysis also revealed that age and FT4 were the significant factors associated with circulating myostatin levels (β = 0.27, p = 0.02; β = 0.22, p = 0.04, respectively).

CONCLUSION

Our results suggest that increased irisin levels might contribute to altered energy metabolism in hyperthyroidism. Further studies to determine whether myostatin is affected due to hyperthyroidism are needed.

Changes in Thyroid Hormone Levels Within the Normal and/or Subclinical Hyper- or Hypothyroid Range Do Not Affect Circulating Irisin Levels in Humans

BACKGROUND

Both thyroid hormones and irisin increase energy expenditure and induce browning of adipose tissue. However, irisin physiology and regulation remain largely unknown, and existing data are mainly derived from observational studies. In this study, we aimed to elucidate whether changes in thyroid-axis hormones alter circulating irisin levels in humans, thereby exerting a direct downstream effect on serum irisin.

SUBJECTS AND METHODS

Samples from a cross-sectional evaluation and two interventions were utilized, including patients who had previously undergone thyroidectomy. In the cross-sectional study, 96 consecutively enrolled subjects were divided into a euthyroid group and a subclinical hyperthyroid group, according to their serum thyrotropin (TSH) levels (TSH cutoff 0.3 mIU/L). In interventional study A, 34 patients who had undergone thyroidectomy due to thyroid cancer were withdrawn from their thyroxine replacement treatment for five weeks. In interventional study B, 13 patients underwent a recombinant human TSH stimulation protocol, and blood samples were drawn at baseline, day 3 (i.e., at least 24 hours after the second intramuscular injection), day 5, and day 10.

RESULTS

Irisin concentrations were not associated with thyroid-axis hormones (i.e., TSH, free thyroxine, and free triiodiothyronine) cross-sectionally in either the overall cohort or in the euthyroid and/or subclinical hyperthyroid subgroups (p > 0.05). There was no significant difference between euthyroid and subclinical hyperthyroid subjects (p = 0.60). Levothyroxine withdrawal did not result in any changes in irisin concentrations (p = 0.33). Recombinant human TSH stimulation did not induce any significant changes in circulating irisin (p = 0.60).

CONCLUSIONS

Changes in thyroid-axis hormone levels within the physiological or supraphysiological range do not affect circulating irisin levels in humans. Therefore, their metabolic effects are most likely independent of each other. Other regulators of irisin levels should be identified in the future.

Circulating irisin concentrations in rat models of thyroid dysfunction -- effect of exercise

OBJECTIVES

The speculation that the myokine irisin could regulate whole body energy expenditure led to the anticipation that irisin may have therapeutic potential in metabolic diseases. Regulation of irisin under conditions of metabolic derangements in altered thyroid status, and the changes in irisin response to exercise remain to be investigated.

METHODS

Serum irisin concentration was measured in sixty male Wistar rats subjected to either sedentary life or 8-week chronic swimming exercise after induction of hyper- or hypothyroidism (10 rats/group). The effect of acute exercise on serum irisin was assessed in 10 additional rats subjected once to forced swimming against a load (5% of body weight) and compared to sedentary rats.

RESULTS

Serum irisin was significantly higher in both sedentary hyper- and hypothyroid rats (by 45%, p<0.001, and 30%, p<0.001, respectively) versus euthyroid controls. Serum irisin also increased after acute exercise (p<0.001 versus sedentary control). Chronic training episodes failed to significantly alter serum irisin in all thyroid hormone profiles. Serum irisin correlated positively with serum creatine kinase (r=0.45, p<0.001) and with muscle and liver concentrations of malondialdehyde (r=0.50 and r=0.47 respectively, p<0.001 for both), and negatively with muscle and liver content of reduced glutathione (r=-0.34, p=0.003 and r=-0.28, p=0.018 respectively) in pooled groups. However, significance of these associations was waived when analyzing each group separately. Serum irisin was not associated with skeletal muscle mass, insulin resistance, blood glucose, lipids or TSH.

CONCLUSIONS

Both hyper- and hypothyroidism are associated with up-regulation of serum irisin in male rats, possibly as a response to oxidative damage and/or myopathy observed in both conditions. Acute exercise, which is also associated with oxidative stress, increases serum irisin. No obvious association was detected linking serum irisin to metabolic abnormalities in thyroid dysfunction.