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

Irisin in thyroid diseases

Irisin, a hormone-like adipo-myokine, has garnered considerable attention in recent years for its potential impact in metabolic diseases. Its physiological effects are similar to those of thyroid hormones, prompting numerous investigations into potential correlations and interactions between irisin and thyroid function through various in vitro and animal experiments. However, existing studies suggest that the relationship between irisin and thyroid diseases is highly complex and multifaceted. In this paper, we have summarized the research results on serum irisin and thyroid function, providing an overview of advancements and constraints in current research on irisin and thyroid hormones. The aim is to offer insights and directions for future clinical trials in this field.

The therapeutic potential of irisin to mitigate the risk of metabolic syndrome in postmenopausal women

Oestradiol withdrawal at menopause predisposes women to metabolic syndrome, a cluster of interrelated conditions including obesity, insulin resistance, dyslipidaemia and hypertension that together confer an increased risk of developing type 2 diabetes mellitus and cardiovascular disease. Hormone replacement therapies are commonly used to treat acute symptoms of the perimenopausal period, and whilst they have been associated with metabolic improvements in many studies, long-term use is considered unviable. Novel approaches are required to mitigate the risk of postmenopausal metabolic syndrome. In 2012, the exercise-inducible myokine irisin was isolated from the skeletal muscle of mice and identified to have anti-obesity and antidiabetic effects in vivo. Irisin is now recognised to exert pleiotropic action on cognitive, bone and metabolic health. There is accumulating evidence from in vitro and in vivo rodent studies that irisin can mitigate each component condition of metabolic syndrome. In postmenopausal women, independent associations have been observed between (a) exercise and plasma irisin concentration and (b) plasma irisin concentration and reduced incidence of metabolic syndrome. To date, however, no study has considered the mechanistic basis by which irisin, whether exercise-induced or exogenously administered, could reduce the incidence or severity of metabolic syndrome in postmenopausal women. This review aims to analyse the literature concerning the metabolic actions of irisin, with a focus on its therapeutic potential for metabolic syndrome driven by a state of oestradiol depletion. It evaluates the practicality of exercise as a therapy and discusses other irisin-based therapeutic strategies that may alleviate postmenopausal metabolic syndrome. Finally, it highlights areas where future research is required to advance knowledge of irisin's biological action such that it could be considered a viable candidate for clinical application.

Exercise reduces physical alterations in a rat model of fetal alcohol spectrum disorders

BACKGROUND

Prenatal alcohol exposure (PAE) has serious physical consequences for children such as behavioral disabilities, growth disorders, neuromuscular problems, impaired motor coordination, and decreased muscle tone. However, it is not known whether loss of muscle strength occurs, and which interventions will effectively mitigate physical PAE impairments. We aimed to investigate whether physical alteration persists during adolescence and whether exercise is an effective intervention.

RESULTS

Using paradigms to evaluate different physical qualities, we described that early adolescent PAE animals have significant alterations in agility and strength, without alterations in balance and coordination compared to CTRL animals. We evaluated the effectiveness of 3 different exercise protocols for 4 weeks: Enrichment environment (EE), Endurance exercise (EEX), and Resistance exercise (REX). The enriched environment significantly improved the strength in the PAE group but not in the CTRL group whose strength parameters were maintained even during exercise. Resistance exercise showed the greatest benefits in gaining strength, and endurance exercise did not.

CONCLUSION

PAE induced a significant decrease in strength compared to CTRL in PND21. Resistance exercise is the most effective to reverse the effects of PAE on muscular strength. Our data suggests that individualized, scheduled, and supervised training of resistance is more beneficial than endurance or enriched environment exercise for adolescents FASD.

Adipose-Muscle crosstalk in age-related metabolic disorders: The emerging roles of adipo-myokines

Obesity and type 2 diabetes account for a considerable proportion of the global burden of age-related metabolic diseases. In age-related metabolic diseases, tissue crosstalk and metabolic regulation have been primarily linked to endocrine processes. Skeletal muscle and adipose tissue are endocrine organs that release myokines and adipokines into the bloodstream, respectively. These cytokines regulate metabolic responses in a variety of tissues, including skeletal muscle and adipose tissue. However, the intricate mechanisms underlying adipose-muscle crosstalk in age-related metabolic diseases are not fully understood. Recent exciting evidence suggests that myokines act to control adipose tissue functions, including lipolysis, browning, and inflammation, whereas adipokines mediate the beneficial actions of adipose tissue in the muscle, such as glucose uptake and metabolism. In this review, we assess the mechanisms of adipose-muscle crosstalk in age-related disorders and propose that the adipokines adiponectin and spexin, as well as the myokines irisin and interleukin-6 (IL-6), are crucial for maintaining the body's metabolic balance in age-related metabolic disorders. In addition, these changes of adipose-muscle crosstalk in response to exercise or dietary flavonoid consumption are part of the mechanisms of both functions in the remission of age-related metabolic disorders. A better understanding of the intricate relationships between adipose tissue and skeletal muscle could lead to more potent therapeutic approaches to prolong life and prevent age-related metabolic diseases.

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.

CircRNA AFF4 induced by KDM1A promotes osteogenic differentiation through FNDC5/Irisin pathway

Background

Circular RNA (circ) AFF4 was documented to regulate osteogenesis but the underlying mechanism remains to be elucidated. The preliminary study showed that circ_AFF4 may promote osteogenesis via FNDC5/Irisin. Furthermore, the online prediction tool indicated the interaction of circ_AFF4, insulin-like growth factor-2 mRNA-binding protein 3 (IGF2BP3), FNDC5 and lysine (K)-specific demethylase 1 A (KDM1A). Therefore, this study aims to elucidate the relationships of KDM1A, circ_AFF4, IGF2BP3 and FNDC5/Irisin during osteogenesis.

Methods

The alkaline phosphatase (ALP) activities and osteogenic-related factors were determined using ALP and alizarin red S (ARS) staining, real-time quantitative PCR(RT-qPCR) and western blot. Immunoprecipitation (RIP), pull-down assay and fluorescence in situ hybridization (FISH) were used to examine the interactions among circ_AFF4/IGF2BP3/FNDC5. A mouse in vivo model was utilized to further confirm the regulatory effect on bone formation.

Results

Circ_AFF4 and KDM1A expression levels were increased during osteoinduction of BM-MSCs. Knockdown of circ_AFF4 and KDM1A significantly suppressed BM-MSC osteogenesis. We also proved that KDM1A directly bound to circ_AFF4 and FNDC5 promoter and induced circ_AFF4 and FNDC5 expression. Furthermore, circ_AFF4 enhanced the stability of FNDC5 by generating a circ_AFF4, IGF2BP3 and FNDC5 RNA-protein complex, and thereby induced Irisin and osteogenesis. The in vitro data was confirmed with in vivo model.

Conclusion

These findings elucidate that KDM1A induces circ_AFF4, which promotes promote osteogenesis via IGF2BP3. This study indicates that circ_AFF4 may potentially represent a critical therapeutic target for the diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00557-7.

Thermotherapy as an alternative to exercise for metabolic health in obese postmenopausal women: focus on circulating irisin level

Irisin is a myokine caused by exercise that improves insulin resistance and weight loss. However, under unfavorable conditions such as air pollution, and during the pandemic, outdoor activities are uncomfortable. Therefore, in this study, the effect of heat therapy (half bath 42 ± 0.5°C for 30 min) on irisin circulation levels as an exercise alternative for middle-aged obese women after menopause was investigated. Subjects were 33 women aged 49.54 ± 6.04 years, with parameters of height, 160.12 ± 4.33 cm, weight, 69.71 ± 7.52 kg, body surface area 1.73 ± 0.13 m², body mass index, 27.19 ± 3.40 kg/m². The results suggest that circulating irisin levels showed a significant increase after one-time thermotherapy (TH-1). However, the increase in circulating irisin levels after 15 treatments (TH-15, 5 days/week, 3 weeks) was significantly varied. The level of adiponectin, which increases fatty oxidation to reduce fatty deposition, increased significantly at TH-1, but further increased at TH-15, which was significantly different from the level of TH-1. In addition, the basic serum free fatty acid (FFA) level was significantly increased at TH-15 compared to TH-1. Significant differences were also found in the lipid profile (body mass index, waist circumference, and % body fat). Thermotherapy can significantly increase the tympanic temperature and induce changes in circulating irisin and adiponectin levels. Thus, it resulted in positive changes in FFA and lipid profiles. Therefore, repeated thermotherapy is effective in increasing circulating irisin levels in postmenopausal obese women.

Applying exercise-mimetic engineered skeletal muscle model to interrogate the adaptive response of irisin to mechanical force

Physical exercise induces the secretion of irisin from contractile muscle into circulation; however, the adaptive response of irisin to mechanical stimulus in skeletal muscle in vitro remains numerously unknown. In an effort to investigate whether irisin is inducible in vitro, we developed a bioreactor consisting of a retractable mechanical force controller and a conditional tissue culture system. Upon this model, a distinguished surge of irisin was detected in stretched myotubes as cyclic strain initiated, and the surge was able to be stalled by knocking out FNDC5. Intriguingly, increased irisin secretory is associated with the shifts of MyHC isoforms from anaerobic type to aerobic type in myotubes. We further revealed that PGC-1α1 and PGC-1α4 mRNAs expression, rather than PGC-1α2 and PGC-1α3, contributed to the generation of irisin in myotubes during cyclic strain. Lastly, combined with co-culturing MC3T3 osteoblasts, we demonstrated the bioactivity of generated irisin, promoting the osteogenic differentiation.

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Irisin is producible in an exercise-mimetic engineered skeletal muscle model

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Enhanced irisin production in response to a long-term cyclic stretch

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PGC-1α1 and PGC-1α4 mRNAs expression contributed to the generation of irisin

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Demonstration that induced irisin in our model regulating osteoblasts as native ways

Effect of Heat Stimulation on Circulating Irisin in Humans

High temperatures lead to oxidative stress. The aim of the study was to determine whether heat stimulation-induced hyperthermia can increase the level of circulating irisin. Twenty-one healthy female subjects (age, 26.3 ± 2.71 years; height, 162.1 ± 3.15 cm; weight, 54.2 ± 3.86 kg; and body surface area, 1.57 ± 0.11 m2) not taking contraceptives participated in this study. All experiments were performed individually for each participant when they were in the early proliferative menstrual phase. In an automated climate chamber (25 ± 0.5°C), the heat load was applied via half-body immersion into a hot water bath (42 ± 0.5°C). Five-minutes break was provided every after 5 min of immersion and the total passive heating time was 30 min. Tympanic temperature (Tt y) and skin temperature (Ts) were measured. Mean body temperature (mTb) was calculated. Blood samples were collected before and immediately after immersion. Levels of irisin, cortisol, creatine kinase (CK), and lactate dehydrogenase (LDH) were analyzed. Tty, mTb and serum irisin levels increased after hot water immersion. The blood levels of cortisol, CK, and LDH were also elevated after hot water immersion. Heat stimulation might increase the levels of circulating irisin in humans in response to oxidative stress.

Eight Weeks of High-Intensity Interval Static Strength Training Improves Skeletal Muscle Atrophy and Motor Function in Aged Rats via the PGC-1α/FNDC5/UCP1 Pathway

Background

Sarcopenia is a syndrome characterized by the loss of skeletal muscle mass and strength. Most studies have focused on dynamic resistance exercises for preventing muscular decline and maintaining the muscle strength of older individuals. However, this training mode is impractical for older people with osteoarthritis and a limited range of motion. The static strength training mode is more suitable for older people. Therefore, a determination of the effect and mechanism of static strength training on sarcopenia is critical.

Methods

In this study, we developed a training device designed to collect training data and evaluate the effects of static training on the upper limbs of rats. The expression of PGC-1α was locally blocked by injecting a siRNA at the midpoint of the biceps to determine whether PGC-1α signal transduction participates in the effects of high-intensity interval static training on muscle strength. Then, the rat’s motor capacity was measured after static strength training. Immunohistochemistry and Western blotting were applied to determine PGC-1α/FNDC5/UCP1 expression levels in the muscle and adipose tissue. The serum irisin level was also detected using an enzyme-linked immunosorbent assay (ELISA).

Results

Increased levels of serum irisin and local expression of FNDC5, PGC-1α, and UCP1 were observed in the biceps brachii and surrounding fatty tissue after static strength training. Static strength training showed an advantage in reducing body weight and white fat accumulation while increasing the muscle fiber volume, which resulted in a longer training time and shorter rest time.

Conclusion

Overall, these results indicated that high-intensity interval static training prevents skeletal muscle atrophy and improves the motor function of aged rats through the PGC-1α/FNDC5/UCP1 signaling pathway.

Association of serum irisin concentration with thyroid autoantibody positivity and subclinical hypothyroidism

OBJECTIVE

This study evaluated the association of serum irisin level with thyroid autoantibody (TAA) positivity and subclinical hypothyroidism (SH).

METHODS

In this cross-sectional study, 334 participants were assigned to one of the following four age- and sex-matched groups: TAA plus SH (84 patients), isolated TAA (83 patients), isolated SH (83 patients), or healthy controls (84 individuals). Irisin and creatine kinase (CK) were measured in serum samples.

RESULTS

Patients with TAA plus SH, isolated TAA, and isolated SH had higher irisin levels compared with the controls. There was a significant increase in the irisin level in the TAA plus SH group compared with the control group. Among all participants, the irisin levels were positively associated with thyroglobulin and thyroid peroxidase antibody titers and high-density lipoprotein cholesterol levels, but negatively associated with waist circumference, glycated hemoglobin levels, and fasting plasma glucose levels. The irisin level was not associated with the thyroid-stimulating hormone, free thyroxine, or CK levels. Irisin levels were independently associated with TAA, with or without SH, but they were not associated with SH alone.

CONCLUSIONS

Irisin level may help to predict the risk of developing TAA with or without SH.

The Effect of Irisin as a Metabolic Regulator and Its Therapeutic Potential for Obesity

Obesity is a worldwide health problem due to the imbalance of energy intake and energy expenditure. Irisin, a newly identified exercise-responsive myokine, which is produced by the proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5), has emerged as a promising therapeutic strategy to combat obesity and obesity-related complications. Various studies in mice have shown that irisin could respond to systematic exercise training and promote white-to-brown fat transdifferentiation, but the role and function of irisin in humans are controversial. In this review, we systematically introduced and analyzed the factors that may contribute to these inconsistent results. Furthermore, we also described the potential anti-inflammatory properties of irisin under a variety of inflammatory conditions. Finally, the review discussed the existing unresolved issues and controversies about irisin, including the transcription of the irisin precursor FNDC5 gene in humans, the cleavage site of the yet unknown proteolytic enzyme that cleaves irisin from FNDC5, and the reliability of irisin levels measured with available detection methods.

The production, detection, and origin of irisin and its effect on bone cells

Irisin is a muscle factor discovered in 2012 that plays an important role in many tissues, including bone. Eight years since its discovery, there are still many controversies regarding its molecular biology, detection, and effects on bone. This article summarizes the points raised to date, and discusses the mechanisms by which irisin regulates bone cells. The information reviewed here provides a useful foundation for future research.

Irisin: A New Code Uncover the Relationship of Skeletal Muscle and Cardiovascular Health During Exercise

Exercise not only produces beneficial effects on muscle itself via various molecular pathways, but also mediates the interaction between muscles and other organs in an autocrine/paracrine manner through myokines, which plays a positive role in maintaining overall health. Irisin, an exercise-derived myokine, has been found involved in the regulation of some cardiovascular diseases. However, the relationship between irisin and cardiovascular health is not fully elucidated and there are some divergences on the regulation of irisin by exercise. In this review, we present the current knowledge on the origin and physiology of irisin, describe the regulation of irisin by acute and chronic exercises, and discuss the divergences of the related research results. Importantly, we discuss the role of irisin as a biomarker in the diagnosis of cardiovascular diseases and describe its treatment and molecular mechanism in some cardiovascular diseases. It is expected that irisin will be used as a therapeutic agent to combat cardiovascular diseases or other disorders caused by inactivity in the near future.

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.

The Neuroprotective Effect of Irisin in Ischemic Stroke

Irisin is a PGC-1α-dependent myokine that causes increased energy expenditure by driving the development of white adipose tissue into brown fat-like tissue. Exercise can improve irisin levels and lead to its release into the blood. In ischemic stroke, neurons are always sensitive to energy supply; after a series of pathophysiological processes, reactive oxygen species that are detrimental to cell survival via mitochondrial dysfunction are generated in large quantities. As a protein associated with exercise, irisin can alleviate brain injury in the pathogenesis of ischemic stroke. It is thought that irisin can upregulate the levels of brain-derived neurotrophic factor (BDNF), which protects nerve cells from injury during ischemic stroke. Furthermore, the release of irisin into the blood via exercise influences the mitochondrial dynamics crucial to maintaining the normal function of nerve cells. Consequently, we intended to summarize the known effects of irisin during ischemic stroke.

Role of swimming on muscle PGC-1α, FNDC5 mRNA, and assessment of serum omentin, adropin, and irisin in high carbohydrate high fat (HCHF) diet induced obesity in rats

Background

Exercise benefits a variety of organ systems in mammals, and some of the best recognized effects of exercise on muscle are mediated by the transcriptional peroxisome proliferator-activated receptor gamma co-activator 1-α (PGC-1α). The regulatory effect of swimming on muscle PGC-1α, FNDC5 mRNA expression, and subsequently irisin levels is more controversial. This study aimed to investigate the role of swimming as an exercise on the expression of peroxisome proliferator-activated receptor-gamma coactivator1 alpha (PGC-1α) and Fibronectin type III domain containing 5 (FNDC5) mRNA in skeletal muscle and assessment of serum omentin, adropin, irisin, and PGC-1α levels in high carbohydrate high fat (HCHF) diet induced obesity in rats. Sixty male albino rats are randomly divided into 4 groups (15 rats/group). In the first group (control), rats are fed with standard diet. The 2nd group (cont + swim) is fed on standard diet and made swimming exercise. The 3rd group of rats is fed on HCHF, whereas in the 4th group (HCHF + swim) is also fed on HCHF diet and made swimming exercise for 20 weeks. Blood glucose, insulin, HOMA-IR, lipid profile, omentin, irisin, adropin, and PGC-1α were measured. Also, FNDC5 and PGC-1α are extracted and purified from muscle tissue samples measured by PCR test.

Results

Our results showed significant increase in glucose, insulin, insulin resistance, cholesterol, and triglycerides with significant decrease in omentin, irisin, adropin, PGC-1α, and HDL in HCHF group as compared to the control group. These results improved after exercise in all parameter in HCHF + swim group compare to HCHF group. Also, there was inverse correlation between omentin and fasting glucose and HOMA-IR in HCHF + swim group.

Conclusions

It concluded that swimming exercise improved all the above measured parameters in serum and tissues which might have been promising for the prevention of metabolic diseases.

Correlates and Consequences of High Serum Irisin Concentration in Patients on Hemodialysis: A Longitudinal Analysis

OBJECTIVE

Irisin is a hormone released by muscle in response to exercise that acts on white adipose cells to stimulate browning of adipose tissue. We aimed to examine irisin correlates and consequences of irisin in patients receiving hemodialysis.

DESIGN AND METHODS

A prospective cohort study was conducted using data from 749 prevalent patients receiving hemodialysis. Multivariable linear regression and multivariable generalized estimating equations were used to determine correlates of baseline and change in serum irisin concentration. Proportional hazards (Cox) regression was used to assess the association between serum irisin concentration and time to death.

RESULTS

Age and body mass index were inversely associated with baseline and change in serum irisin concentration. Lower muscle mass as estimated by serum creatinine concentration was associated with lower irisin concentration (-1.38% per mg/dL (95% confidence interval [CI]: -2.45, -0.21) and with a 0.72% decrease in irisin concentration (95% CI: -1.48, -0.04) from baseline to 12 months. Each 50% higher serum interleukin-6 (IL-6) concentration was associated with 1.52% higher serum irisin concentration (95% CI: 0.38, 2.66) at baseline and an increase of 1.04% in irisin concentration over 1 year (95% CI: 0.47, 1.61). Irisin concentration at baseline was associated with higher hazard of death (hazards ratio: 1.45, 95% CI: 1.05 2.00); an increase in irisin concentration over 1 year was associated with a higher hazard of death (hazards ratio: 1.34, 95% CI: 1.01, 1.79). In formal mediation analysis, serum IL-6 was a mediator in the association between serum irisin and mortality.

CONCLUSIONS

Lower serum creatinine (reflecting lower muscle mass) and higher serum IL-6 were associated with higher serum irisin concentrations. Higher serum irisin concentrations were associated with higher mortality, which may be mediated by inflammation.

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.

Impacts of rat hindlimb Fndc5/irisin overexpression on muscle and adipose tissue metabolism

Myokines, such as irisin, have been purported to exert physiological effects on skeletal muscle in an autocrine/paracrine fashion. In this study, we aimed to investigate the mechanistic role of in vivo fibronectin type III domain-containing 5 (Fndc5)/irisin upregulation in muscle. Overexpression (OE) of Fndc5 in rat hindlimb muscle was achieved by in vivo electrotransfer, i.e., bilateral injections of Fndc5 harboring vectors for OE rats (n = 8) and empty vector for control rats (n = 8). Seven days later, a bolus of D₂O (7.2 mL/kg) was administered via oral gavage to quantify muscle protein synthesis. After an overnight fast, on day 9, 2-deoxy-d-glucose-6-phosphate (2-DG6P; 6 mg/kg) was provided during an intraperitoneal glucose tolerance test (2 g/kg) to assess glucose handling. Animals were euthanized, musculus tibialis cranialis muscles and subcutaneous fat (inguinal) were harvested, and metabolic and molecular effects were evaluated. Muscle Fndc5 mRNA increased with OE (~2-fold; P = 0.014), leading to increased circulating irisin (1.5 ± 0.9 to 3.5 ± 1.2 ng/mL; P = 0.049). OE had no effect on protein anabolism or mitochondrial biogenesis; however, muscle glycogen was increased, along with glycogen synthase 1 gene expression (P = 0.04 and 0.02, respectively). In addition to an increase in glycogen synthase activation in OE (P = 0.03), there was a tendency toward increased glucose transporter 4 protein (P = 0.09). However, glucose uptake (accumulation of 2-DG6P) was identical. Irisin elicited no endocrine effect on mitochondrial biogenesis or uncoupling proteins in white adipose tissue. Hindlimb overexpression led to physiological increases in Fndc5/irisin. However, our data indicate limited short-term impacts of irisin in relation to muscle anabolism, mitochondrial biogenesis, glucose uptake, or adipose remodeling.

Bone Control of Muscle Function

Bone and muscle represent a single functional system and are tightly connected to each other. Indeed, diseases characterized by alterations of muscle physiology have effects on bone remodeling and structure and vice versa. Muscle influence on bone has been deeply studied, and recent studies identified irisin as new molecule involved in this crosstalk. Muscle regulation by bone needs to be extensively investigated since in the last few years osteocalcin was recognized as a key molecule in the bone–muscle interaction. Osteocalcin can exist in two forms with different degrees of carboxylation. The undercarboxylated form of osteocalcin is a hormone released by the bone matrix during the osteoclast bone resorption and can bind its G-protein coupled receptor GPRC6A expressed in the muscle, thus regulating its function. Recently, this hormone was described as an antiaging molecule for its ability to regulate bone, muscle and cognitive functions. Indeed, the features of this bone-related hormone were used to test a new therapeutic approach for sarcopenia, since injection of osteocalcin in older mice induces the acquirement of physical abilities of younger animals. Even if this approach should be tested in humans, osteocalcin represents the most surprising molecule in endocrine regulation by the skeleton.

The effect of concurrent aerobic-resistance training on thyroid hormones, blood glucose hemostasis, and blood lipid indices in overweight girls with hypothyroidism

Background

The present study aimed to explore the effect of 8 weeks of concurrent aerobic-resistance training on thyroid stimulating hormone (TSH), thyroxine (T4), blood lipid profile, and blood glucose hemostasis in adolescent girls with hypothyroidism.

Materials and methods

In this clinical trial, 20 adolescent girls with hypothyroidism [age: 12.10 ± 1.94 years; body mass index (BMI): 25.25 ± 2.91 kg/m2] were selected and randomly assigned to experimental and control groups. The experimental group was treated with 8 weeks of concurrent aerobic [60–80% heart rate reserve (HHR)] and resistance (40–65% of 1RM) training. Blood was sampled before and after training. Data were analyzed using a pairwise t-test and an independent t-test (α < 0.05).

Results

Within-group comparison revealed significant decline of body index, BMI, fat percentage, fasting blood sugar, and homeostatic model assessment (HOMA) in the experimental group (p = 0.002, p = 0.001, p = 0.001, p = 0.03, and p = 0.02, respectively). Also, inter-group comparisons indicated significant differences in weight, BMI, fat percentage and HOMA (p = 0.001). But, no significant difference was observed in the blood sugar index (p > 0.05).

Conclusion

A short-term period of concurrent aerobic-resistance training may improve blood glucose hemostasis and body composition of adolescent girls with hypothyroidism. However, further research is necessary.

Effect of saffron (Crocus sativus L.) and endurance training on mitochondrial biogenesis, endurance capacity, inflammation, antioxidant, and metabolic biomarkers in Wistar rats

We aimed to evaluate the effect of saffron (Crocus Sativus L.) treatment on endurance capacity, mitochondrial biogenesis, inflammation, antioxidant, and metabolic biomarkers in Wistar rats. Forty male rats were allocated equally into four groups: Saffron, Exercise and Saffron, Exercise and Placebo, and Placebo. Endurance training was accomplished on a specified rodent motor-driven treadmill. Running to fatigue test and also metabolic and molecular indices were measured after eight weeks of intervention. mtDNA copy number and NRF-1 gene expression increased significantly in the Ex + S group compared to the exercised and control group (p < 0.05). Endurance capacity time increased in the Ex + S group compared to the Ex group (p < 0.05). Malondialdehyde, CPK, AST, and IL-6 decreased and antioxidant parameters including Glutathione peroxidase and Glutathione increased in the Ex + S group compared to exercised rats (p < 0.01). Saffron enhanced mitochondrial biogenesis, decreased oxidative stress, inflammation, and modulated metabolic biomarkers in exercised rats. PRACTICAL APPLICATIONS: The influence of potential nutrient factors on exercise performance has reached much attention in recent years. Athletes require an appropriate sport supplement to reimburse their fatigue and improve their resilience. Saffron (Crocus Sativus L.) is a well-known spice in the food trade which is quite popular around the world by giving a desirable taste to food. In an experimental study, we showed that saffron extract treatment during endurance training could improve endurance capacity by modulating several metabolic and genomic factors. Therefore, by relying on the results of this study and the positive effects of saffron published in previous studies, saffron could be added to sport beverages and supplements to enhance an athlete's performance.

Eccentric resistance training and β-hydroxy-β-methylbutyrate free acid affects muscle PGC-1α expression and serum irisin, nesfatin-1 and resistin in rats

The hypothalamus controls metabolism and feeding behaviour via several signals with other tissues. Exercise and supplements can change hypothalamic signalling pathways, so the present study investigated the influence of eccentric resistance training and β-hydroxy-β-methylbutyrate free acid supplementation on PGC-1α expression, serum irisin, nesfatin-1 and resistin concentrations. Thirty-two male rats (8 weeks old, 200±17 g body mass) were randomly allocated to control, β-hydroxy-β-methylbutyrate free acid supplementation (HMB), eccentric resistance training (ERT), and β-hydroxy-β-methylbutyrate free acid supplementation plus eccentric resistance training (HMB+ERT) groups. Training groups undertook eccentric resistance training (6 weeks, 3 times a week) and supplement groups consumed β-hydroxy-β-methylbutyrate free acid (HMB-FA) orally (76 mg kg^-1 day^-1). Twenty-four hours after the last training session, serum and triceps brachii muscle samples were collected and sent to the laboratory for analysis. Two-way ANOVA and Pearson correlation were employed (significance level: P<0.05). The results showed that eccentric resistance training increases skeletal muscle PGC-1α gene expression, as well as serum levels of irisin and nesfatin-1 (P=0.001). Eccentric resistance training decreased the serum concentration of resistin (P=0.001). HMB-FA supplementation increased skeletal muscle PGC-1α gene expression (P=0.002), as well as the serum concentration of irisin and nesfatin-1 (P=0.001), but decreased the serum concentration of resistin (P=0.001). Significant correlations were observed between PGC-1α gene expression and serum concentrations of irisin, nesfatin-1 and resistin. HMB-FA supplementation with eccentric resistance training may induce crosstalk between peptide release from other tissues and increases maximal muscle strength. The combination of the two interventions had a more substantial effect than each in isolation.

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.

Construction of a long non‑coding RNA-mediated competitive endogenous RNA network reveals global patterns and regulatory markers in gestational diabetes

Gestational diabetes mellitus (GDM) is a common disease affecting pregnant women. Recent studies have suggested that competing endogenous RNAs (ceRNAs), which compete with long non‑coding RNAs (lncRNAs) for microRNA (miRNA or miR) binding and indirectly regulate miRNA targets through competing interactions, play a critical role in disease. In this study, we present a computationally integrated approach with which to construct a lncRNA‑mediated ceRNA network (LCEN) in GDM by integrating RNA interactions and expression data. lncRNAs exhibited specific features and played critical roles in GDM‑associated LCEN. The construction of a global functional score profile revealed that ceRNAs had a high activity in GDM. We extracted several ceRNA modules and demonstrated that these modules had increased close interactions. We further discovered that these ceRNA modules may be utilized as specific and effective circulating biomarkers for GDM. Finally, functional analyses demonstrated that the GDM‑associated ceRNAs participated in the regulation of irisin and the thyroid hormone signaling pathway. It was suggested that there were close associations between the thyroid hormone and GDM. Collectively, ceRNAs may accelerate biomarker discovery and therapeutic development in GDM.

Effects of different exercise loads on the thyroid hormone levels and serum lipid profile in swimmers

Background

The aim of this study was to investigate the effects of different exercise loads (short, medium and long swimming distances) on the thyroid hormone (THs) levels and serum lipid profiles of male professional swimmers.

Materials and methods

The participants in this study were 20 healthy male professional swimmers aged 18–22 years, who all competed at an elite level. The THs levels [thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4)] and serum lipid profile were also obtained.

Results

It was determined that the TSH and T4 values increased after exercise (p < 0.05). When compared to the pretest values, the increase in the TSH and T4 values following the L400 tests was statistically significant (p < 0.001 and p < 0.05). It was also determined that the changes in the cholesterol, high-density lipoprotein (HDL) and total glucose (TG) values were significant after exercise (p < 0.001). There was no significant difference between the groups in terms of the low-density lipoprotein (LDL) values (p = 0.07). According to the results, the cholesterol counts for the M200 and L400 groups were lower than the pretest counts (p < 0.001). When compared to the pretest values, the decrease in the HDL counts for the M200 and L400 groups was higher than the pretest HDL counts (p < 0.001 and p < 0.05, respectively). Further, the triglycerides counts for the M200 and L400 groups were higher than the pretest counts (p < 0.001).

Conclusions

Different exercise loads can have a positive impact on the physical health of swimmers via their lipid profiles and THs. Additionally, swimming exercise could be considered an efficient protective strategy against metabolic disorders, as it serves to balance the serum lipid levels.

The data on the aerobic training with or without calorie restriction and muscular levels of Irisin and muscular FNDC5 concentration in obese male Wistar rats

The present data article aims at investigating the muscular levels of Irisin, FNDC5, and UCP1 in male Wistar rats during the aerobic exercise with or without calorie restriction (CR). Twenty four, 8-week-old male Wistar rats (190±16 g) were selected and purchased for the research. After obesity induction by high-fat diet, the animals were randomly divided into three groups: exercise EX (n = 8), EX-CR (n = 8) and CO as control (n = 8). EX exercised 6 sessions per week and EXCR exercise 3 sessions + 3 days caloric restriction per week. The Irisin (Cat.No:CK-E91266 & Intra-Assay: CV<10%), FNDC5 (Cat.No:CK-E91393 & Intra-Assay: CV<10%) levels were assessed by the special Rat ELISA Kit (EASTBIOPHARM, China, under licensed by the United States). Muscular Irisin concentrations in EX group were higher than other groups. In addition, FNDC5 concentrations in EX group was higher than those in other groups.

PPARγ/Pgc-1α-Fndc5 pathway up-regulation in gastrocnemius and heart muscle of exercised, branched chain amino acid diet fed mice

Background

Previous studies have revealed the inductive effect of branched-chain amino acids (BCAAs) catabolism on fatty acid oxidation and metabolism, especially in muscle cells. In the present investigation, we have attempted to address whether a combination of BCAAs supplement consumption with aerobic exercise could elaborate the expression of PPARγ, Pgc-1α and Fndc5 genes in gastrocnemius muscle and heart tissue of male C57BL/6 mice.

Methods

Thirty-six young male mice with an average weight of 18 ± 2 g were selected. Mice were randomly assigned to 6 groups: 20 mg/mL of BCAAs consumption with simultaneous exercise-training, 60 mg/mL of BCAAs consumption with simultaneous exercise-training, exercise-trained with no BCAAs consumption group, 20 mg/mL BCAAs without exercise-training, 60 mg/mL BCAAs without exercise-training, and untrained mice without BCAAs consumption.

Results

The findings showed a combination of 20 mg/mL BCAAs with aerobic exercise significantly increased Fndc5, PPARγ, Pgc-1α gene expression in skeletal muscles although, circulating Irisin levels remained unchanged (p < 0.05). Interestingly, plasma urea and lactate levels were significantly increased in 60 mg/mL BCAAs administrated mice which performed exercised (p < 0.05). Two-way analysis of variance (ANOVA) was used to examine significant difference between groups and sedentary group.

Conclusions

Results showed inductive effect of 20 mg/mL BCAAs on expression levels of Fndc5, PPARγ, Pgc-1α in gastrocnemius muscle similar with counterparts in heart tissue. Of note, higher serum irisin levels were detected after 20 mg/mL BCAAs supplementation coincided with the exercise.

Graphical abstract

An Overview on supplemantaion of branched chain amoinoacids on metablism of skeletal muscle and heart.

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.

Irisin response to downhill running exercise in humans

[Purpose]

To determine the effects of exercise-induced muscle damage, we examined irisin responses during level running (LR), with less muscle damage, and downhill running (DHR), with greater muscle damage under equivalent exercise duration and oxygen consumption (⩒O₂) conditions.

[Methods]

Fifteen healthy men (age: 21.6 ± 2.0 y, height: 170 ± 1.3 cm, weight: 64.8 ± 2.7 kg) were randomly assigned to either the LR group (n = 8) or the DHR group (n = 7). Subjects in the LR group performed treadmill running at 70% of maximum oxygen uptake (⩒O_2max) for 30 min on a 0% gradient. In contrast, subjects in the DHR group performed the same exercise on a –10% gradient. Blood samples were collected before exercise, immediately after exercise, and 1, 3, and 24 h after exercise.

[Results]

No significant interaction (group × time) or main effect of group or time was observed for changes in plasma irisin concentrations over time (P > 0.05). However, the area under the curve of plasma irisin concentrations during a 3-h post-exercise period was significantly greater in the DHR (239,197 ± 8,166 ng/mL) group than in the LR (92,293 ± 8,755 ng/ml) group (P < 0.05). The blood lactate, serum cortisol, myoglobin, and plasma interleukin-6 concentrations were significantly higher in the DHR group than in the LR group after exercise (P < 0.05 for all variables).

[Conclusion]

DHR associated with marked muscle damage promoted a greater increase in exercise-induced irisin did LR after the same duration under identical VO2 conditions.

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.

A glance at the therapeutic potential of irisin against diseases involving inflammation, oxidative stress, and apoptosis: An introductory review

Irisin is a hormone-like molecule mainly released by skeletal muscles in response to exercise. Irisin induces browning of the white adipose tissue and has been shown to regulate glucose and lipid homeostasis. Keeping its energy expenditure and metabolic properties in view, numerous studies have focused on its therapeutic potential for the treatment of metabolic disorders like obesity and type 2 diabetes. Recently, the anti-inflammatory, anti-apoptotic and anti-oxidative properties of irisin have received a great deal of attention of the scientific society. These pathogenic processes are often associated with initiation, progression, and prognosis of numerous diseases like myocardial infarction, kidney diseases, cancer, lung injury, inflammatory bowel diseases, atherosclerosis, liver diseases, obesity and type 2 diabetes. In the current review, we present evidence regarding the anti-inflammatory, anti-apoptotic and anti-oxidative potential of irisin pertaining to various pathological conditions. Here, we explore multiple molecular pathways targeted by irisin therapy. Given the promising effects of irisin, many diseases with evident oxidative stress, inflammation and apoptosis can be targeted by irisin.

The combination of exercise training and Zataria multiflora supplementation increase serum irisin levels in postmenopausal women

Background

We examined the effect of antioxidant supplementation and exercise on irisin within postmenopausal women.

Methods

Forty-eight participants (age: 55.7 ± 4.9 years; weight: 68.0 ± 6.3 kg; BMI 27.0 ± 2.7; mean ± SD) were randomized into four groups for the eight week intervention: control group (CG; n = 12), resistance training group (RTG; n = 12), supplementation with Zataria multiflora group (ZG; n = 12), or supplementation with Z. multiflora and resistance training group (ZRTG; n = 12). RTG and ZRTG performed circuit resistance training, and both ZG and ZRTG consumed 500 mg of Z. multiflora every day during the intervention. Blood samples were taken 48 hours before and after the intervention.

Results

There was a significant difference in irisin at post-training, with greater levels in ZRTG compared to CG. A significant increase was noted for irisin at post-training compared to pre-training for ZG, RTG, and ZRTG. Moreover, we identified a significant decrease in malondialdehyde in the RTG and ZRTG groups and increase in glutathione in the ZG, RTG, and ZRTG groups when compared to CG.

Conclusion

These findings showed that exercise, Z. multiflora supplementation or their combination led to an increase in irisin.

Therapeutic Approaches to Nonalcoholic Fatty Liver Disease: Exercise Intervention and Related Mechanisms

Exercise training ameliorates nonalcoholic fatty liver disease (NAFLD) as well as obesity and metabolic syndrome. Although it is difficult to eliminate the effects of body weight reduction and increased energy expenditure-some pleiotropic effects of exercise training-a number of studies involving either aerobic exercise training or resistance training programs showed ameliorations in NAFLD that are independent of the improvements in obesity and insulin resistance. In vivo studies have identified effects of exercise training on the liver, which may help to explain the "direct" or "independent" effect of exercise training on NAFLD. Exercise training increases peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) expression, improves mitochondrial function and leads to reduced hepatic steatosis, inflammation, fibrosis, and tumor genesis. Crosstalk between the liver and adipose tissue, skeletal muscle and the microbiome is also a possible mechanism for the effect of exercise training on NAFLD. Although numerous studies have reported benefits of exercise training on NAFLD, the optimal duration and intensity of exercise for the prevention or treatment of NAFLD have not been established. Maintaining adherence of patients with NAFLD to exercise training regimes is another issue to be resolved. The use of comprehensive analytical approaches to identify biomarkers such as hepatokines that specifically reflect the effect of exercise training on liver functions might help to monitor the effect of exercise on NAFLD, and thereby improve adherence of these patients to exercise training. Exercise training is a robust approach for alleviating the pathogenesis of NAFLD, although further clinical and experimental studies are required.

Exercise-induced myokines: a brief review of controversial issues of this decade

INTRODUCTION

Myokines, known to mediate metabolism, inflammation, and other pathophysiological conditions, have been widely investigated, including myokines induced by exercise. However, among published literature, there is substantial inconsistency in the quantification of exercise-induced myokines. Here, we summarized and compared published data regarding the effects of exercise on commonly studied myokines including apelin, Brain-derived neurotrophic factor (BDNF), Interleukin-15 (IL-15), irisin, and Secreted protein acidic and rich in cysteine (SPARC) during the last decade and discussed possible reasons for discrepancy in these reports.

AREAS COVERED

A search on PubMed for original articles published in this decade was conducted, focusing on the impacts of exercises on myokines and metabolic and age-related disorders. Beneficial relationship between skeletal muscle plasticity and myokines due to exercise is also discussed.

EXPERT COMMENTARY

Based on these analyses, exercise induces the secretion of a number of myokines, which has positive effects on metabolic diseases or age-related muscle atrophy (sarcopenia). However, among published reports, there is wide discrepancy in the quantification of myokines induced by exercise, which could be due to timing of sample collection, pre-analytic sample processing, analytical method, and calculation and other factors. Thus, these factors need to be considered in future studies on exercise induced myokines.

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.

Is irisin the new player in exercise-induced adaptations or not? A 2017 update

Irisin is produced by a proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5) and has emerged as a potential mediator of exercise-induced energy metabolism. The purpose of this study was to review the results of studies that investigated irisin responses to acute and chronic exercise and provide an update. A comprehensive search in the databases of MEDLINE was performed (74 exercise studies). The focus of the analysis was on data concerning FNDC5 mRNA expression in skeletal muscle and circulating irisin concentration relatively to exercise mode, intensity, frequency and duration and the characteristics of the sample used. Circulating irisin levels may either not relate to FNDC5 transcription or expression of the later precedes irisin rise in the blood. Acute speed/strength and endurance exercise protocols represent potent stimuli for irisin release if they are characterized by adequate intensity and/or duration. There are no reports regarding irisin responses to field sport activities. Although animal studies suggest that irisin may also respond to systematic exercise training, the majority of human studies has produced contradictory results. Certain methodological issues need to be considered here such as the analytical assays used to measure irisin concentration in the circulation. Results may also be affected by subjects’ age, conditioning status and exercise intensity. The role of irisin as a moderator of energy metabolism during exercise remains to be seen.

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.

The novel exercise-induced hormone irisin protects against neuronal injury via activation of the Akt and ERK1/2 signaling pathways and contributes to the neuroprotection of physical exercise in cerebral ischemia

BACKGROUND

Irisin is a novel exercise-induced myokine involved in the regulation of adipose browning and thermogenesis. In this study, we investigated the potential role of irisin in cerebral ischemia and determined whether irisin is involved in the neuroprotective effect of physical exercise in mice.

MATERIALS AND METHODS

The middle cerebral artery occlusion (MCAO) model was used to produce cerebral ischemia in mice. First, the plasma irisin levels and changes in expression of the irisin precursor protein FNDC5 in skeletal muscle were determined post ischemic stroke. Second, the association between plasma irisin levels and the neurological deficit score, brain infarct volume, or plasma concentrations of tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β in mice with MCAO were evaluated. Third, the therapeutic effect of irisin on ischemic brain injury was evaluated in vivo and in vitro. Recombinant irisin was injected directly into the tail vein 30min after the MCAO operation, and then the effects of irisin treatment on brain infarct volume, neurological deficit, neuroinflammation, microglia activation, monocyte infiltration, oxidative stress and intracellular signaling pathway activation (Akt and ERK1/2) were measured. Irisin was also administered in cultured PC12 neuronal cells with oxygen and glucose deprivation (OGD). Finally, to assess the potential involvement of irisin in the neuroprotection of physical exercise, mice were exercised for 2weeks and an irisin neutralizing antibody was injected into these mice to block irisin 1h before the MCAO operation.

RESULTS

The plasma irisin concentration and intramuscular FNDC5 protein expression decreased after ischemic stroke. Plasma irisin levels were negatively associated with brain infarct volume, the neurological deficit score, plasma TNF-α and plasma IL-6 concentrations. In OGD neuronal cells, irisin protected against cell injury. In mice with MCAO, irisin treatment reduced the brain infarct volume, neurological deficits, brain edema and the decline in body weight. Irisin treatment inhibited activation of Iba-1⁺ microglia, infiltration of MPO-1⁺ monocytes and expression of both TNF-α and IL-6 mRNA. Irisin significantly suppressed the levels of nitrotyrosine, superoxide anion and 4-hydroxynonenal (4-HNE) in peri-infarct brain tissues. Irisin treatment increased Akt and ERK1/2 phosphorylation, while blockade of Akt and ERK1/2 by specific inhibitors reduced the neuroprotective effects of irisin. Finally, the exercised mice injected with irisin neutralizing antibody displayed more severe neuronal injury than the exercised mice injected with control IgG.

CONCLUSION

Irisin reduces ischemia-induced neuronal injury via activation of the Akt and ERK1/2 signaling pathways and contributes to the neuroprotective effect of physical exercise against cerebral ischemia, suggesting that irisin may be a factor linking metabolism and cardio-cerebrovascular diseases.

Irisin Lowers Blood Pressure by Improvement of Endothelial Dysfunction via AMPK-Akt-eNOS-NO Pathway in the Spontaneously Hypertensive Rat

BACKGROUND

Exercise is a major nonpharmacological treatment for hypertension, but its underlying mechanisms are still not completely elucidated. Irisin, a polypeptide containing 112 amino acids, which is secreted mainly by skeletal muscle cells during exercise, exerts a protective role in metabolic diseases, such as diabetes mellitus and obesity. Because of the close relationship between irisin and metabolic diseases, we hypothesized that irisin may play a role in the regulation of blood pressure.

METHODS AND RESULTS

Blood pressures of male Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were monitored through the carotid artery. Our study found that acute intravenous injection of irisin reduced blood pressure in SHRs, but not WKY rats. Irisin, by itself, had no direct vasorelaxing effect in phenylephrine-preconstricted mesenteric arteries from SHRs. However, irisin augmented the acetylcholine-induced vasorelaxation in mesenteric arteries from SHRs that could be reversed by Nω-nitro-l-arginine-methyl ester (L-NAME; 100 μmol/L), indicating a role of nitric oxide (NO) in this action. Indeed, irisin increased NO production and phosphorylation of endothelial nirtic oxide synthase (eNOS) in endothelial cells. 5'-AMP-activated protein kinase (AMPK) was involved in the vasorelaxing effect of irisin because compound C (20 μmol/L), an AMPK inhibitor, blocked the irisin-mediated increase in phosphorylation of eNOS and protein kinase B (Akt) in endothelial cells and vasodilation in mesenteric arteries.

CONCLUSIONS

We conclude that acute administration of irisin lowers blood pressure of SHRs by amelioration of endothelial dysfunction of the mesenteric artery through the AMPK-Akt-eNOS-NO signaling pathway.