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Serum irisin levels and thyroid function—Newly discovered association
G Model
ARTICLE IN PRESS
PEP 69298 1–5
Peptides xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Peptides journal homepage: www.elsevier.com/locate/peptides
Short communication
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Serum irisin levels and thyroid function—Newly discovered association
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4 5 6
Q1
Marek Ruchala ∗,1 , Ariadna Zybek 1 , Ewelina Szczepanek-Parulska Department of Endocrinology, Metabolism and Internal Medicine, Poznan University of Medical Sciences, Przybyszewskiego Street 49, 60-355 Poznan, Poland
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Article history: Received 18 June 2014 Received in revised form 26 July 2014 Accepted 26 July 2014 Available online xxx
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Keywords: Irisin Thyroid function Hyperthyroidism Hypothyroidism
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Introduction
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Irisin is a newly discovered adipo-myokin, which is reported to have a significant influence on the body metabolism and thermogenesis. Other influencing factors on metabolic state are thyroid hormones, which increase heat production and control the energy balance. Due to numerous similarities in action it seems imperative to explore these substances’ potential mutual influence on the body. The aim of the study is to provide the first ever, according to our knowledge, evaluation of serum irisin concentrations in patients with thyroid dysfunction and its correlation with creatine kinase (CK) levels – a serum marker of muscle damage. The studied group consisted of 20 patients with newly diagnosed thyroid disorder – hyperthyroidism or hypothyroidism. Venous blood samples were analyzed for irisin, thyrotropin (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and CK serum concentrations. Patients’ body mass index (BMI), body weight and muscle mass were evaluated using bioelectrical impedance analysis (BIA). Median serum irisin levels were lower in hypothyroid (117.30 ng/ml) than hyperthyroid (161.95 ng/ml) patients with a borderline statistical significance (p = 0.0726). The negative correlation between irisin and TSH levels was demonstrated (r = −0.4924, p = 0.0230), as well as the positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.0360). The CK level was negatively correlated with irisin, FT4 and FT3 concentrations (r = −0.7272, p = 0.0140; r = −0.9636, p = <0.0001; r = −0.8838, p = 0.0007, respectively). The study demonstrates that irisin concentrations may vary according to the thyrometabolic state, which potentially could be related to the degree of muscle damage. © 2014 Published by Elsevier Inc.
Irisin is a newly discovered adipo-myokin that was recently reported by Boström et al. [1]. This cytokine, secreted by myocytes was named after Iris, the Greek messenger goddess, since irisin is responsible for the transmission of signals from muscles to other body tissues. To date, many researchers have reported its significant influence on metabolism and thermogenesis, mostly by acting on adipose tissue and promoting a phenomenon called white adipose tissue (WAT) “browning” [7,12,22]. Irisin is considered to be a potential mediator in the beneficial role of physical exercises [11,20]. However, there are other recognized factors that also influence metabolic state, such as thyroid hormones. Thyroxine and metabolically active triiodothyronine increase heat production and control the energy balance by stimulating numerous metabolic
∗ Corresponding author. Tel.: +48 601 748 905; fax: +48 61 869 16 82. E-mail address: [email protected] (M. Ruchala). 1 These authors contributed equally to this work.
pathways including the influence on brown adipose tissue (BAT) [2,17]. Due to numerous similarities in action, it seems imperative to explore these substances’ potential mutual influence on the body. The aim of the study is to provide the first ever, according to our knowledge, evaluation of serum irisin concentrations in patients with thyroid dysfunction and its correlation with creatine kinase (CK) levels – a serum marker of muscle damage. Patients and methods Participants were precisely chosen on the basis of diagnosis of an overt thyroid disorder. The studied group consisted of 20 patients meeting the inclusion criteria and referred to the Department of Endocrinology, Metabolism and Internal Medicine with newly diagnosed overt hyperthyroidism or hypothyroidism. Inclusion criteria were as follows: age over 18 years old, overt hyper- or hypothyroid state due to autoimmune thyroid disease or inadequate therapy in subjects with a history of thyroidectomy or radioiodine therapy. All patients affected by diabetes, hypercortisolemia, hypocortisolemia, kidney and heart diseases, muscular or
http://dx.doi.org/10.1016/j.peptides.2014.07.021 0196-9781/© 2014 Published by Elsevier Inc.
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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neurological disorders, routinely taking any drugs, or intensively involved in a sport or any strenuous physical activity were excluded from the study. The Bioethical Committee of Poznan University of Medical Sciences approved the study (Resolution no. 923/13), and all participants provided informed written consent to take part in the study. Enrolled subjects underwent a complete evaluation of thyroid functional state, including thyroid and thyroid-related hormone concentrations (TSH, free triiodothyronine – FT3, free thyroxine – FT4) and anti-thyroid autoantibody titers assessment (antithyroid peroxidase antibody – TPOAb, antithyroglobulin antibody – TgAb, thyrotropin receptor antibody – TRAb), as well as a thyroid ultrasound examination. On the basis of analyzed clinical results, a complete and accurate diagnosis was made. The serum irisin levels were measured. Additionally, examination of possible muscle damage by means of serum CK concentrations was measured. Patients’ body mass index (BMI), body weight and muscle mass were evaluated using bioelectrical impedance analysis (BIA). Venous blood samples were obtained in a consistent manner, after 8 h of fasting. The same protocol was used in regards to BIA. Normal ranges of TSH were established at 0.27–4.2 IU/ml. The accepted reference ranges were 3.90–6.70 pmol/L for FT3 and 11.5–21.0 pmol/L for FT4. Overt hypothyroidism was diagnosed when TSH level exceeded the reference values and free thyroid hormones were below normal range. Conversely, hyperthyroidism was defined as a decrease in TSH concentration below the normal level, and an increase in free thyroid hormones concentrations. The CK reference range was 26–140 U/L. The assessment of thyroid and thyroid-related hormone concentrations was performed with the use of Hitachi Cobas e601 chemiluminescent analyzer (Roche Diagnostics), and included serum TSH, FT3 and FT4 measurements. The CK level was
also evaluated using the same method. Thyroid autoantibody concentrations (TPOAb, TgAb, TRAb) were assessed by radioimmunological method with the use of commercially available BRAMHS anti-TPO, anti-Tg, and TRAK RIA kits, and scintillation gamma counter (LKB Wallac CliniGamma 1272). Irisin serum concentration was measured using Irisin (Human, Rat, Mouse, Canine) – ELISA Assay Kit from Phoenix Pharmaceuticals. Experienced thyroid sonographers using an AIXPLORER system by Supersonic Imagine performed the ultrasonographic examination of the thyroid gland. For the evaluation of body composition, the Tanita MC 180 MA analyzer was used. The associations between irisin, muscle mass, TSH, free thyroid hormones and CK were analyzed statistically. Furthermore, the difference between irisin serum concentrations in hypothyroid and hyperthyroid patients was evaluated. The statistical analyses were conducted using STATISTICA software by StatSoft. Nonparametric tests like Spearman’s rank-order correlation and Mann–Whitney U test were also applied. Results The study included 10 subjects with hyperthyroidism and 10 subjects with hypothyroidism. Both groups presented the same gender distribution (9 women and 1 man). The median age in the hyperthyroid group was 36.5 years, while in the hypothyroid group, 47.5 years (p = 0.3508). There was no statistical difference between median muscle mass and BMI in hyperthyroid and hypothyroid patients (41.4 kg vs. 43.4 kg, p = 1.0000; 21.15 kg/m2 vs. 24.00 kg/m2 , p = 0.1182; respectively). Median serum irisin levels were lower in hypothyroid (117.30 ng/ml) patients than in hyperthyroid (161.95 ng/ml) patients and bordering statistical significance (p = 0.0726) [Fig. 1].
Fig. 1. The median serum irisin level in hypothyroid (117.30 ng/ml) and hyperthyroid (161.95 ng/ml) patients.
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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Fig. 2. (A) The negative correlation between irisin and TSH levels (r = −0.4924, p = 0.023); (B) the positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.036); (C) the negative correlation between CK and irisin concentrations (r = −0.7272, p = 0.014); (D) the negative correlation between CK and FT4 concentrations (r = −0.9636, p = <0.0001). FT4, free thyroxine; FT3, free triiodothyronine; CK, creatine kinase.
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Median CK levels were significantly higher in hypothyroid patients when compared to the hyperthyroid group (171 U/L vs. 52 U/L, p = 0.004). A negative correlation between irisin and TSH levels was demonstrated (r = −0.4924, p = 0.023), as well as a positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.036). CK levels were negatively correlated with irisin, FT4 and FT3 concentrations (r = −0.7272, p = 0.014; r = −0.9636, p = <0.0001; r = −0.8838, p = 0.0007, respectively) [Fig. 2]. No statistically significant correlations between irisin and BMI or muscle mass were noted (r = −0.0552, p = 0.8332; r = −0.3114, p = 0.2236, respectively). Moreover, no correlation was observed between CK levels and muscle mass (r = 0.0833, p = 0.8431).
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Discussion
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Fibronectin type III domain-containing protein 5 (Fndc5) is a membrane protein encoded by the FNDC5 gene. The cleaved
and secreted fragment of Fndc5, called irisin, is highly conserved between species, as it is 100% identical in both mice and humans. Its production is induced in muscles by physical exertion. Boström et al. [1] indicated, on the basis of the mice model, that irisin may be the hormone-like substance that mediates the beneficial effects of physical exercise on mammalian organisms. They discovered that only a slight increase in irisin levels causes “browning” of the WAT. As a result, heat production and general energy expenditure rises while the adenosine-5 -triphosphate (ATP) production decreases. Subsequent published research provided the first major insight into the role of irisin in humans [4]. According to the collected data, the FNDC5 gene is predominantly expressed in muscles. The irisin serum concentration was positively correlated with biceps circumference, fat-free mass, BMI, glucose, ghrelin and IGF-I, whereas age, cholesterol, insulin and adiponectin correlated negatively. Authors suggested a possible compensatory role of irisin in metabolic regulation, with the biceps circumference (muscle mass marker) being the strongest predictor of circulating irisin [4]. Additionally, FNDC5
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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expression in adipose tissue is also significant [12,13]. Thus, irisin is not only a myokin, but also a potential adipokin. Some published studies evaluated the association between irisin and BMI, body composition, or metabolic disorders in patients. Stengel et al. showed that obese patients had higher irisin serum concentrations in comparison to patients with normal weight and anorexic patients. Irisin turned out to be positively correlated with body weight, BMI, fat mass, body cell mass and fat-free mass. Furthermore, the level of irisin was positively associated with insulin concentration, but not with ghrelin, cortisol, thyroid stimulating hormone or C-reactive protein [18]. Collected human data indicated that circulating irisin concentration and FNDC5 gene expression in adipose tissue and muscles decreases in type II diabetic subjects when compared to patients with normal glucose metabolism. That suggests that a low irisin concentration is potentially responsible for the loss of brown-like adipose tissue in diabetic subjects [9,10]. Kurdiova et al. [5] recently reported that irisin might distinguish metabolic health and disease, seeing as in patients with diabetes type 2 the irisin serum levels and tissue FNDC5 gene expression were reduced. It was also hypothesized that irisin may be responsible for the variance in energy expenditure between obese individuals with the same fat-free mass [19]. To date, the available data about the relationship between thyroid function and irisin is scarce. Expression of the FNDC5 gene was reported in the thyroid, but presenting at much lower levels than in adipose tissue and muscle [4]. Stengel et al. demonstrated that in patients with obesity and anorexia nervosa, the TSH levels were not correlated with irisin concentrations. However, the described subjects did not present with any impairment of thyroid function with a mean TSH level of 1.5 and 1.9 mU/L, respectively [18]. The association between thyroid function and other peptides levels, like ghrelin, have also been evaluated [15]. To the best of the Authors’ knowledge, our study is the first to measure the association between thyrometabolic state and irisin concentrations. Thyroid functional state has a profound influence on the metabolism of the human body. Thyroid hormones increase heat production through numerous metabolic pathways, regulating both obligatory and facultative thermogenesis [16,17]. Triiodothyronine, in cooperation with the sympathetic nervous system, activates BAT, especially in euthyroid or hypothyroid subjects. In thyrotoxicosis, BAT thermogenesis is limited by the reduction of hypothalamic stimulation; nevertheless, glucose uptake in BAT remains increased [6]. Both hyper- and hypothyroidism have a negative impact on muscles [14,21]. However, no increase in CK levels in hyperthyroid subjects was observed. McGrowder et al. [8] have recently reported a negative correlation between thyroid function and CK concentrations, as well as lactate dehydrogenase (LDH) activities in serum, which may indicate a destruction of muscle fibers. These results are consistent with our observations. According to the present results, lower irisin concentrations were found in patients with hypothyroidism. This might be explained by muscle destruction manifested through a high CK level, typical for hypothyroidism. Simvastatin (known to induce muscle damage) was reported to increase irisin concentrations, but these changes did not correlate with changes in CK levels. Nonetheless, serum CK concentrations did not change after simvastatin administration [3]. Lack of association between BMI, muscle mass and irisin level, which had been previously described by numerous researchers, may also indicate the profound influence of disturbed thyroid function on irisin levels. The authors are aware of multiple limitations of the present research. The studied group is small, and the measurement of described parameters was not performed after the restoration of euthyroid state. Additionally, the control group was not evaluated. However, the study indicates the presence of an association
between irisin levels and thyroid function, which have yet to be defined. Conclusions To conclude, our study demonstrates that irisin concentrations may vary according to the thyrometabolic state, which potentially could be related to the degree of muscle damage. Through the exploration of this issue on a larger group of patients with thyroid dysfunction and healthy subjects, a potentially deeper insight into these significant and evolutionary conserved regulatory mechanisms may be achieved. Further prospective studies are necessary to assess whether changes in both CK and irisin concentrations are reversible after restoration of the euthyroid state in patients with thyroid disorders. Conflict of interest The authors have nothing to disclose. Acknowledgements The research was funded from the Statutory Funding of the Q2 Department of Endocrinology, Metabolism and Internal Medicine, Q3 Poznan University of Medical Sciences. References [1] Bostrom P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, et al. A PGC1-alphadependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature 2012;481:463–8. [2] Fisher JN, Ball EG. Studies on the metabolism of adipose tissue. XX. The effect of thyroid status upon oxygen consumption and lipolysis. Biochemistry 1967;6:637–47. [3] Gouni-Berthold I, Berthold HK, Huh JY, Berman R, Spenrath N, Krone W, et al. Effects of lipid-lowering drugs on irisin in human subjects in vivo and in human skeletal muscle cells ex vivo. PLoS ONE 2013;8:e72858. [4] Huh JY, Panagiotou G, Mougios V, Brinkoetter M, Vamvini MT, Schneider BE, et al. FNDC5 and irisin in humans: I. Predictors of circulating concentrations in serum and plasma and II. mRNA expression and circulating concentrations in response to weight loss and exercise. Metabolism 2012;61:1725–38. [5] Kurdiova T, Balaz M, Vician M, Maderova D, Vlcek M, Valkovic L, et al. Effects of obesity, diabetes and exercise on Fndc5 gene expression and irisin release in human skeletal muscle and adipose tissue: in vivo and in vitro studies. J Physiol 2014;592:1091–107. [6] Lahesmaa M, Orava J, Schalin-Jantti C, Soinio M, Hannukainen JC, Noponen T, et al. Hyperthyroidism increases brown fat metabolism in humans. J Clin Endocrinol Metab 2014;99(1):E28–35. [7] Lecker SH, Zavin A, Cao P, Arena R, Allsup K, Daniels KM, et al. Expression of the irisin precursor FNDC5 in skeletal muscle correlates with aerobic exercise performance in patients with heart failure. Circ Heart Fail 2012;5:812–8. [8] McGrowder DA, Fraser YP, Gordon L, Crawford TV, Rawlins JM. Serum creatine kinase and lactate dehydrogenase activities in patients with thyroid disorders. Niger J Clin Pract 2011;14:454–9. [9] Moreno-Navarrete JM, Ortega F, Serrano M, Guerra E, Pardo G, Tinahones F, et al. Irisin is expressed and produced by human muscle and adipose tissue in association with obesity and insulin resistance. J Clin Endocrinol Metab 2013;98:E769–78. [10] Park KH, Zaichenko L, Brinkoetter M, Thakkar B, Sahin-Efe A, Joung KE, et al. Circulating irisin in relation to insulin resistance and the metabolic syndrome. J Clin Endocrinol Metab 2013;98:4899–907. [11] Pekkala S, Wiklund PK, Hulmi JJ, Ahtiainen JP, Horttanainen M, Pollanen E, et al. Are skeletal muscle FNDC5 gene expression and irisin release regulated by exercise and related to health? J Physiol 2013;591:5393–400. [12] Raschke S, Eckel J. Adipo-myokines: two sides of the same coin– mediators of inflammation and mediators of exercise. Mediators Inflamm 2013;2013:320724. [13] Roca-Rivada A, Castelao C, Senin LL, Landrove MO, Baltar J, Belen Crujeiras A, et al. FNDC5/irisin is not only a myokine but also an adipokine. PLoS ONE 2013;8:e60563. [14] Rooyackers OE, Nair KS. Hormonal regulation of human muscle protein metabolism. Annu Rev Nutr 1997;17:457–85. [15] Ruchala M, Gurgul E, Stangierski A, Wrotkowska E, Moczko J. Individual plasma ghrelin changes in the same patients in hyperthyroid, hypothyroid and euthyroid state. Peptides 2014;51:31–4. [16] Silva JE. Thermogenic mechanisms and their hormonal regulation. Physiol Rev 2006;86:435–64.
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[17] Silva JE. Thyroid hormone control of thermogenesis and energy balance. Thyroid 1995;5:481–92. [18] Stengel A, Hofmann T, Goebel-Stengel M, Elbelt U, Kobelt P, Klapp BF. Circulating levels of irisin in patients with anorexia nervosa and different stages of obesity – correlation with body mass index. Peptides 2013;39:125–30. [19] Swick AG, Orena S, O’Connor A. Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass. Metabolism 2013;62:1070–3.
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[20] Timmons JA, Baar K, Davidsen PK, Atherton PJ. Is irisin a human exercise gene? Nature 2012;488. E9–10; discussion E-1. [21] Visser WE, Heemstra KA, Swagemakers SM, Ozgur Z, Corssmit EP, Burggraaf J, et al. Physiological thyroid hormone levels regulate numerous skeletal muscle transcripts. J Clin Endocrinol Metab 2009;94:3487–96. [22] Zhang Y, Li R, Meng Y, Li S, Donelan W, Zhao Y, et al. Irisin stimulates browning of white adipocytes through mitogen-activated protein kinase p38 MAP kinase and ERK MAP kinase signaling. Diabetes 2014;63:514–25.
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ARTICLE IN PRESS
PEP 69298 1–5
Peptides xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Peptides journal homepage: www.elsevier.com/locate/peptides
Short communication
1
Serum irisin levels and thyroid function—Newly discovered association
2
3
4 5 6
Q1
Marek Ruchala ∗,1 , Ariadna Zybek 1 , Ewelina Szczepanek-Parulska Department of Endocrinology, Metabolism and Internal Medicine, Poznan University of Medical Sciences, Przybyszewskiego Street 49, 60-355 Poznan, Poland
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a r t i c l e
i n f o
a b s t r a c t
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Article history: Received 18 June 2014 Received in revised form 26 July 2014 Accepted 26 July 2014 Available online xxx
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Keywords: Irisin Thyroid function Hyperthyroidism Hypothyroidism
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Introduction
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Irisin is a newly discovered adipo-myokin, which is reported to have a significant influence on the body metabolism and thermogenesis. Other influencing factors on metabolic state are thyroid hormones, which increase heat production and control the energy balance. Due to numerous similarities in action it seems imperative to explore these substances’ potential mutual influence on the body. The aim of the study is to provide the first ever, according to our knowledge, evaluation of serum irisin concentrations in patients with thyroid dysfunction and its correlation with creatine kinase (CK) levels – a serum marker of muscle damage. The studied group consisted of 20 patients with newly diagnosed thyroid disorder – hyperthyroidism or hypothyroidism. Venous blood samples were analyzed for irisin, thyrotropin (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and CK serum concentrations. Patients’ body mass index (BMI), body weight and muscle mass were evaluated using bioelectrical impedance analysis (BIA). Median serum irisin levels were lower in hypothyroid (117.30 ng/ml) than hyperthyroid (161.95 ng/ml) patients with a borderline statistical significance (p = 0.0726). The negative correlation between irisin and TSH levels was demonstrated (r = −0.4924, p = 0.0230), as well as the positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.0360). The CK level was negatively correlated with irisin, FT4 and FT3 concentrations (r = −0.7272, p = 0.0140; r = −0.9636, p = <0.0001; r = −0.8838, p = 0.0007, respectively). The study demonstrates that irisin concentrations may vary according to the thyrometabolic state, which potentially could be related to the degree of muscle damage. © 2014 Published by Elsevier Inc.
Irisin is a newly discovered adipo-myokin that was recently reported by Boström et al. [1]. This cytokine, secreted by myocytes was named after Iris, the Greek messenger goddess, since irisin is responsible for the transmission of signals from muscles to other body tissues. To date, many researchers have reported its significant influence on metabolism and thermogenesis, mostly by acting on adipose tissue and promoting a phenomenon called white adipose tissue (WAT) “browning” [7,12,22]. Irisin is considered to be a potential mediator in the beneficial role of physical exercises [11,20]. However, there are other recognized factors that also influence metabolic state, such as thyroid hormones. Thyroxine and metabolically active triiodothyronine increase heat production and control the energy balance by stimulating numerous metabolic
∗ Corresponding author. Tel.: +48 601 748 905; fax: +48 61 869 16 82. E-mail address: [email protected] (M. Ruchala). 1 These authors contributed equally to this work.
pathways including the influence on brown adipose tissue (BAT) [2,17]. Due to numerous similarities in action, it seems imperative to explore these substances’ potential mutual influence on the body. The aim of the study is to provide the first ever, according to our knowledge, evaluation of serum irisin concentrations in patients with thyroid dysfunction and its correlation with creatine kinase (CK) levels – a serum marker of muscle damage. Patients and methods Participants were precisely chosen on the basis of diagnosis of an overt thyroid disorder. The studied group consisted of 20 patients meeting the inclusion criteria and referred to the Department of Endocrinology, Metabolism and Internal Medicine with newly diagnosed overt hyperthyroidism or hypothyroidism. Inclusion criteria were as follows: age over 18 years old, overt hyper- or hypothyroid state due to autoimmune thyroid disease or inadequate therapy in subjects with a history of thyroidectomy or radioiodine therapy. All patients affected by diabetes, hypercortisolemia, hypocortisolemia, kidney and heart diseases, muscular or
http://dx.doi.org/10.1016/j.peptides.2014.07.021 0196-9781/© 2014 Published by Elsevier Inc.
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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neurological disorders, routinely taking any drugs, or intensively involved in a sport or any strenuous physical activity were excluded from the study. The Bioethical Committee of Poznan University of Medical Sciences approved the study (Resolution no. 923/13), and all participants provided informed written consent to take part in the study. Enrolled subjects underwent a complete evaluation of thyroid functional state, including thyroid and thyroid-related hormone concentrations (TSH, free triiodothyronine – FT3, free thyroxine – FT4) and anti-thyroid autoantibody titers assessment (antithyroid peroxidase antibody – TPOAb, antithyroglobulin antibody – TgAb, thyrotropin receptor antibody – TRAb), as well as a thyroid ultrasound examination. On the basis of analyzed clinical results, a complete and accurate diagnosis was made. The serum irisin levels were measured. Additionally, examination of possible muscle damage by means of serum CK concentrations was measured. Patients’ body mass index (BMI), body weight and muscle mass were evaluated using bioelectrical impedance analysis (BIA). Venous blood samples were obtained in a consistent manner, after 8 h of fasting. The same protocol was used in regards to BIA. Normal ranges of TSH were established at 0.27–4.2 IU/ml. The accepted reference ranges were 3.90–6.70 pmol/L for FT3 and 11.5–21.0 pmol/L for FT4. Overt hypothyroidism was diagnosed when TSH level exceeded the reference values and free thyroid hormones were below normal range. Conversely, hyperthyroidism was defined as a decrease in TSH concentration below the normal level, and an increase in free thyroid hormones concentrations. The CK reference range was 26–140 U/L. The assessment of thyroid and thyroid-related hormone concentrations was performed with the use of Hitachi Cobas e601 chemiluminescent analyzer (Roche Diagnostics), and included serum TSH, FT3 and FT4 measurements. The CK level was
also evaluated using the same method. Thyroid autoantibody concentrations (TPOAb, TgAb, TRAb) were assessed by radioimmunological method with the use of commercially available BRAMHS anti-TPO, anti-Tg, and TRAK RIA kits, and scintillation gamma counter (LKB Wallac CliniGamma 1272). Irisin serum concentration was measured using Irisin (Human, Rat, Mouse, Canine) – ELISA Assay Kit from Phoenix Pharmaceuticals. Experienced thyroid sonographers using an AIXPLORER system by Supersonic Imagine performed the ultrasonographic examination of the thyroid gland. For the evaluation of body composition, the Tanita MC 180 MA analyzer was used. The associations between irisin, muscle mass, TSH, free thyroid hormones and CK were analyzed statistically. Furthermore, the difference between irisin serum concentrations in hypothyroid and hyperthyroid patients was evaluated. The statistical analyses were conducted using STATISTICA software by StatSoft. Nonparametric tests like Spearman’s rank-order correlation and Mann–Whitney U test were also applied. Results The study included 10 subjects with hyperthyroidism and 10 subjects with hypothyroidism. Both groups presented the same gender distribution (9 women and 1 man). The median age in the hyperthyroid group was 36.5 years, while in the hypothyroid group, 47.5 years (p = 0.3508). There was no statistical difference between median muscle mass and BMI in hyperthyroid and hypothyroid patients (41.4 kg vs. 43.4 kg, p = 1.0000; 21.15 kg/m2 vs. 24.00 kg/m2 , p = 0.1182; respectively). Median serum irisin levels were lower in hypothyroid (117.30 ng/ml) patients than in hyperthyroid (161.95 ng/ml) patients and bordering statistical significance (p = 0.0726) [Fig. 1].
Fig. 1. The median serum irisin level in hypothyroid (117.30 ng/ml) and hyperthyroid (161.95 ng/ml) patients.
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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Fig. 2. (A) The negative correlation between irisin and TSH levels (r = −0.4924, p = 0.023); (B) the positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.036); (C) the negative correlation between CK and irisin concentrations (r = −0.7272, p = 0.014); (D) the negative correlation between CK and FT4 concentrations (r = −0.9636, p = <0.0001). FT4, free thyroxine; FT3, free triiodothyronine; CK, creatine kinase.
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Median CK levels were significantly higher in hypothyroid patients when compared to the hyperthyroid group (171 U/L vs. 52 U/L, p = 0.004). A negative correlation between irisin and TSH levels was demonstrated (r = −0.4924, p = 0.023), as well as a positive correlation between irisin and FT4 levels (r = 0.4833, p = 0.036). CK levels were negatively correlated with irisin, FT4 and FT3 concentrations (r = −0.7272, p = 0.014; r = −0.9636, p = <0.0001; r = −0.8838, p = 0.0007, respectively) [Fig. 2]. No statistically significant correlations between irisin and BMI or muscle mass were noted (r = −0.0552, p = 0.8332; r = −0.3114, p = 0.2236, respectively). Moreover, no correlation was observed between CK levels and muscle mass (r = 0.0833, p = 0.8431).
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Discussion
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Fibronectin type III domain-containing protein 5 (Fndc5) is a membrane protein encoded by the FNDC5 gene. The cleaved
and secreted fragment of Fndc5, called irisin, is highly conserved between species, as it is 100% identical in both mice and humans. Its production is induced in muscles by physical exertion. Boström et al. [1] indicated, on the basis of the mice model, that irisin may be the hormone-like substance that mediates the beneficial effects of physical exercise on mammalian organisms. They discovered that only a slight increase in irisin levels causes “browning” of the WAT. As a result, heat production and general energy expenditure rises while the adenosine-5 -triphosphate (ATP) production decreases. Subsequent published research provided the first major insight into the role of irisin in humans [4]. According to the collected data, the FNDC5 gene is predominantly expressed in muscles. The irisin serum concentration was positively correlated with biceps circumference, fat-free mass, BMI, glucose, ghrelin and IGF-I, whereas age, cholesterol, insulin and adiponectin correlated negatively. Authors suggested a possible compensatory role of irisin in metabolic regulation, with the biceps circumference (muscle mass marker) being the strongest predictor of circulating irisin [4]. Additionally, FNDC5
Please cite this article in press as: Ruchala M, et al. Serum irisin levels and thyroid function—Newly discovered association. Peptides (2014), http://dx.doi.org/10.1016/j.peptides.2014.07.021
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expression in adipose tissue is also significant [12,13]. Thus, irisin is not only a myokin, but also a potential adipokin. Some published studies evaluated the association between irisin and BMI, body composition, or metabolic disorders in patients. Stengel et al. showed that obese patients had higher irisin serum concentrations in comparison to patients with normal weight and anorexic patients. Irisin turned out to be positively correlated with body weight, BMI, fat mass, body cell mass and fat-free mass. Furthermore, the level of irisin was positively associated with insulin concentration, but not with ghrelin, cortisol, thyroid stimulating hormone or C-reactive protein [18]. Collected human data indicated that circulating irisin concentration and FNDC5 gene expression in adipose tissue and muscles decreases in type II diabetic subjects when compared to patients with normal glucose metabolism. That suggests that a low irisin concentration is potentially responsible for the loss of brown-like adipose tissue in diabetic subjects [9,10]. Kurdiova et al. [5] recently reported that irisin might distinguish metabolic health and disease, seeing as in patients with diabetes type 2 the irisin serum levels and tissue FNDC5 gene expression were reduced. It was also hypothesized that irisin may be responsible for the variance in energy expenditure between obese individuals with the same fat-free mass [19]. To date, the available data about the relationship between thyroid function and irisin is scarce. Expression of the FNDC5 gene was reported in the thyroid, but presenting at much lower levels than in adipose tissue and muscle [4]. Stengel et al. demonstrated that in patients with obesity and anorexia nervosa, the TSH levels were not correlated with irisin concentrations. However, the described subjects did not present with any impairment of thyroid function with a mean TSH level of 1.5 and 1.9 mU/L, respectively [18]. The association between thyroid function and other peptides levels, like ghrelin, have also been evaluated [15]. To the best of the Authors’ knowledge, our study is the first to measure the association between thyrometabolic state and irisin concentrations. Thyroid functional state has a profound influence on the metabolism of the human body. Thyroid hormones increase heat production through numerous metabolic pathways, regulating both obligatory and facultative thermogenesis [16,17]. Triiodothyronine, in cooperation with the sympathetic nervous system, activates BAT, especially in euthyroid or hypothyroid subjects. In thyrotoxicosis, BAT thermogenesis is limited by the reduction of hypothalamic stimulation; nevertheless, glucose uptake in BAT remains increased [6]. Both hyper- and hypothyroidism have a negative impact on muscles [14,21]. However, no increase in CK levels in hyperthyroid subjects was observed. McGrowder et al. [8] have recently reported a negative correlation between thyroid function and CK concentrations, as well as lactate dehydrogenase (LDH) activities in serum, which may indicate a destruction of muscle fibers. These results are consistent with our observations. According to the present results, lower irisin concentrations were found in patients with hypothyroidism. This might be explained by muscle destruction manifested through a high CK level, typical for hypothyroidism. Simvastatin (known to induce muscle damage) was reported to increase irisin concentrations, but these changes did not correlate with changes in CK levels. Nonetheless, serum CK concentrations did not change after simvastatin administration [3]. Lack of association between BMI, muscle mass and irisin level, which had been previously described by numerous researchers, may also indicate the profound influence of disturbed thyroid function on irisin levels. The authors are aware of multiple limitations of the present research. The studied group is small, and the measurement of described parameters was not performed after the restoration of euthyroid state. Additionally, the control group was not evaluated. However, the study indicates the presence of an association
between irisin levels and thyroid function, which have yet to be defined. Conclusions To conclude, our study demonstrates that irisin concentrations may vary according to the thyrometabolic state, which potentially could be related to the degree of muscle damage. Through the exploration of this issue on a larger group of patients with thyroid dysfunction and healthy subjects, a potentially deeper insight into these significant and evolutionary conserved regulatory mechanisms may be achieved. Further prospective studies are necessary to assess whether changes in both CK and irisin concentrations are reversible after restoration of the euthyroid state in patients with thyroid disorders. Conflict of interest The authors have nothing to disclose. Acknowledgements The research was funded from the Statutory Funding of the Q2 Department of Endocrinology, Metabolism and Internal Medicine, Q3 Poznan University of Medical Sciences. References [1] Bostrom P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, et al. A PGC1-alphadependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature 2012;481:463–8. [2] Fisher JN, Ball EG. Studies on the metabolism of adipose tissue. XX. The effect of thyroid status upon oxygen consumption and lipolysis. Biochemistry 1967;6:637–47. [3] Gouni-Berthold I, Berthold HK, Huh JY, Berman R, Spenrath N, Krone W, et al. Effects of lipid-lowering drugs on irisin in human subjects in vivo and in human skeletal muscle cells ex vivo. PLoS ONE 2013;8:e72858. [4] Huh JY, Panagiotou G, Mougios V, Brinkoetter M, Vamvini MT, Schneider BE, et al. FNDC5 and irisin in humans: I. Predictors of circulating concentrations in serum and plasma and II. mRNA expression and circulating concentrations in response to weight loss and exercise. Metabolism 2012;61:1725–38. [5] Kurdiova T, Balaz M, Vician M, Maderova D, Vlcek M, Valkovic L, et al. Effects of obesity, diabetes and exercise on Fndc5 gene expression and irisin release in human skeletal muscle and adipose tissue: in vivo and in vitro studies. J Physiol 2014;592:1091–107. [6] Lahesmaa M, Orava J, Schalin-Jantti C, Soinio M, Hannukainen JC, Noponen T, et al. Hyperthyroidism increases brown fat metabolism in humans. J Clin Endocrinol Metab 2014;99(1):E28–35. [7] Lecker SH, Zavin A, Cao P, Arena R, Allsup K, Daniels KM, et al. Expression of the irisin precursor FNDC5 in skeletal muscle correlates with aerobic exercise performance in patients with heart failure. Circ Heart Fail 2012;5:812–8. [8] McGrowder DA, Fraser YP, Gordon L, Crawford TV, Rawlins JM. Serum creatine kinase and lactate dehydrogenase activities in patients with thyroid disorders. Niger J Clin Pract 2011;14:454–9. [9] Moreno-Navarrete JM, Ortega F, Serrano M, Guerra E, Pardo G, Tinahones F, et al. Irisin is expressed and produced by human muscle and adipose tissue in association with obesity and insulin resistance. J Clin Endocrinol Metab 2013;98:E769–78. [10] Park KH, Zaichenko L, Brinkoetter M, Thakkar B, Sahin-Efe A, Joung KE, et al. Circulating irisin in relation to insulin resistance and the metabolic syndrome. J Clin Endocrinol Metab 2013;98:4899–907. [11] Pekkala S, Wiklund PK, Hulmi JJ, Ahtiainen JP, Horttanainen M, Pollanen E, et al. Are skeletal muscle FNDC5 gene expression and irisin release regulated by exercise and related to health? J Physiol 2013;591:5393–400. [12] Raschke S, Eckel J. Adipo-myokines: two sides of the same coin– mediators of inflammation and mediators of exercise. Mediators Inflamm 2013;2013:320724. [13] Roca-Rivada A, Castelao C, Senin LL, Landrove MO, Baltar J, Belen Crujeiras A, et al. FNDC5/irisin is not only a myokine but also an adipokine. PLoS ONE 2013;8:e60563. [14] Rooyackers OE, Nair KS. Hormonal regulation of human muscle protein metabolism. Annu Rev Nutr 1997;17:457–85. [15] Ruchala M, Gurgul E, Stangierski A, Wrotkowska E, Moczko J. Individual plasma ghrelin changes in the same patients in hyperthyroid, hypothyroid and euthyroid state. Peptides 2014;51:31–4. [16] Silva JE. Thermogenic mechanisms and their hormonal regulation. Physiol Rev 2006;86:435–64.
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