Physiology and role of irisin in glucose homeostasis

Association of Circulating Irisin Levels and the Characteristics and Prognosis of Coronary Artery Disease

BACKGROUND

Irisin is a new muscle factor discovered in recent years that shows a strong association with metabolic diseases. However, its role in coronary artery disease (CAD) is still controversial. We performed this study to determine the relationship of serum irisin with the characteristics and prognosis of CAD.

MATERIALS AND METHODS

Patients with acute coronary syndrome (ACS) (n = 355), stable coronary artery disease (SCAD) (n = 162), nonobstructive coronary artery disease (NO-CAD) (n = 126) and normal coronary arteries (n = 109) were enrolled. An enzyme-linked immunosorbent assay kit was used to measure serum irisin concentrations. Major adverse cardiovascular events (MACEs) of patients with SCAD (n = 132) and ACS (n = 331) after percutaneous coronary intervention (PCI) were recorded during a 12-month follow-up. Receiver-operator characteristic (ROC) curve analysis was used to explore predictors of CAD. Kaplan-Meier survival analysis and the Cox proportional hazards regression model were used to explore the association between serum irisin levels and MACEs.

RESULTS

Serum irisin levels in patients with ACS, SCAD, NO-CAD and normal coronary arteries were 196.62±72.05 ng/ml, 216.81±79.69 ng/ml, 245.26±77.92 ng/ml and 300.17±76.74 ng/ml, respectively (p<0.001). ROC curve analysis indicated that serum irisin concentrations were a valuable biomarker of coronary lesions (AUC=0.799), CAD (AUC=0.734) and ACS (AUC=0.681). Survival analysis demonstrated that patients with high irisin levels exhibited a higher event-free survival rate in both the SCAD and ACS groups after successful PCI.

CONCLUSIONS

Serum irisin levels were significantly decreased in patients with CAD. Patients with ACS exhibited the lowest serum irisin levels. Furthermore, serum irisin levels were interrelated with prognosis in patients with CAD after PCI.

Basal myokine levels are associated with quality of life and depressed mood in older adults

In an aging society, late-life depression has become an increasing problem. There is evidence that physical activity ameliorates depressive symptoms and increases the quality of life (QoL). However, the underlying mechanisms are still poorly understood. Myokines are molecules secreted in response to muscle contraction. Some of them can cross the blood-brain barrier, making them promising candidates for mediating the beneficial effects of physical activity on mood. The present study aims to compare circulating myokine levels to depression/QoL in older athletes and controls. 55 athletes, 57 controls >59 years were enrolled. The assessment included ergometry, magnetic resonance imaging, blood withdrawal, and neuropsychological testing. Serum interleukin-6 (IL-6), irisin, brain-derived neurotrophic factor (BDNF), kynurenine, and cathepsin B were analyzed and compared to surrogates of depression and quality of life. Athletes presented with higher levels of Cathepsin B. Among controls, all myokines but irisin were associated with age. Also, among controls, kynurenine and IL-6 correlated inversely with specific dimensions of quality of life questionnaires, and IL-6 further with depressive symptoms and decreased physical performance. No such associations could be found among athletes. Irisin levels were inversely associated with mild depression and low-grade white matter-lesions in the brain and predicted impaired QoL. The circulating levels of several myokines/muscle activity-related factors appear to be associated with depressive symptoms and impaired QoL among older adults. However, in athletes, some of these connections seem ameliorated, suggesting additional stressors (as f.e. age) or a different pathomechanism among athletes.

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.

Associations of Circulating Irisin with FNDC5 Expression in Fat and Muscle in Type 1 and Type 2 Diabetic Mice

Irisin is an exercise-induced myokine, suggested to exert beneficial effects on metabolism. However, the studies on the regulation of irisin secretion and the expression of its precursor FNDC5 have shown conflicting data. The discrepancies among previous correlation studies in humans are related to the heterogeneity of the study population. The fact that irisin is not only a myokine but also an adipokine leads to the further complexity of the role of irisin in metabolic regulation. In this study, we examined the regulation of FNDC5 expression and irisin in circulation in both type 1 and type 2 diabetic mice, and their potential relationships with metabolic parameters. In streptozotocin (STZ)-induced type 1 diabetic mice, high-fat diet (HFD)-induced obese mice and db/db mice, the circulating irisin as well as FNDC5 gene expression in subcutaneous fat was downregulated. Muscle FNDC5 expression was only significantly lower in STZ mice, and epididymal fat FNDC5 expression was unaltered. It is interesting to note that plasma irisin levels correlated positively with subcutaneous fat FNDC5 expression, but not epididymal fat or muscle. Moreover, both irisin levels and subcutaneous fat FNDC5 correlated negatively with markers of insulin resistance. These results suggest a regulatory role for subcutaneous fat-derived FNDC5/irisin in metabolic disease.

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.

The Acute Effects of Swimming Exercise on PGC-1α-FNDC5/Irisin-UCP1 Expression in Male C57BL/6J Mice

Irisin is a myokine primarily secreted by skeletal muscles and is known as an exercise-induced hormone. The purpose of this study was to determine whether the PGC-1α -FNDC5 /Irisin-UCP1 expression which is an irisin-related signaling pathway, is activated by an acute swimming exercise. Fourteen to sixteen weeks old male C57BL/6J mice (n = 20) were divided into control (CON, n = 10) and swimming exercise groups (SEG, n = 10). The SEG mice performed 90 min of acute swimming exercise, while control (non-exercised) mice were exposed to shallow water (2 cm of depth) for 90 min. The mRNA and protein expression of PGC-1α, FNDC5 and browning markers including UCP1 were evaluated by quantitative real-time PCR and western blotting. Serum irisin concentration was measured by enzyme-linked immunosorbent assay. An acute swimming exercise did not lead to alterations in the mRNA and protein expression of PGC-1α in both soleus and gastrocnemius muscles, the mRNA and protein expression of UCP1 in brown adipose tissue, mRNA browning markers in visceral adipose tissue and circulating irisin when compared with the control group. On the other hand, an acute swimming exercise led to increases in the mRNA and protein expressions of FNDC5 in the soleus muscle, the protein expression of FNDC5 in the gastrocnemius muscles and the protein expression of UCP1 in subcutaneous adipose tissue.

Irisin and Incretin Hormones: Similarities, Differences, and Implications in Type 2 Diabetes and Obesity

Incretins are gut hormones that potentiate glucose-stimulated insulin secretion (GSIS) after meals. Glucagon-like peptide-1 (GLP-1) is the most investigated incretin hormone, synthesized mainly by L cells in the lower gut tract. GLP-1 promotes β-cell function and survival and exerts beneficial effects in different organs and tissues. Irisin, a myokine released in response to a high-fat diet and exercise, enhances GSIS. Similar to GLP-1, irisin augments insulin biosynthesis and promotes accrual of β-cell functional mass. In addition, irisin and GLP-1 share comparable pleiotropic effects and activate similar intracellular pathways. The insulinotropic and extra-pancreatic effects of GLP-1 are reduced in type 2 diabetes (T2D) patients but preserved at pharmacological doses. GLP-1 receptor agonists (GLP-1RAs) are therefore among the most widely used antidiabetes drugs, also considered for their cardiovascular benefits and ability to promote weight loss. Irisin levels are lower in T2D patients, and in diabetic and/or obese animal models irisin administration improves glycemic control and promotes weight loss. Interestingly, recent evidence suggests that both GLP-1 and irisin are also synthesized within the pancreatic islets, in α- and β-cells, respectively. This review aims to describe the similarities between GLP-1 and irisin and to propose a new potential axis-involving the gut, muscle, and endocrine pancreas that controls energy homeostasis.

Intestinal Alkaline Phosphatase Combined with Voluntary Physical Activity Alleviates Experimental Colitis in Obese Mice. Involvement of Oxidative Stress, Myokines, Adipokines and Proinflammatory Biomarkers

Intestinal alkaline phosphatase (IAP) is an essential mucosal defense factor involved in the process of maintenance of gut homeostasis. We determined the effect of moderate exercise (voluntary wheel running) with or without treatment with IAP on the course of experimental murine 2,4,6-trinitrobenzenesulfonic acid (TNBS) colitis by assessing disease activity index (DAI), colonic blood flow (CBF), plasma myokine irisin levels and the colonic and adipose tissue expression of proinflammatory cytokines, markers of oxidative stress (SOD2, GPx) and adipokines in mice fed a standard diet (SD) or high-fat diet (HFD). Macroscopic and microscopic colitis in sedentary SD mice was accompanied by a significant decrease in CBF, and a significant increase in the colonic expression of tumor necrosis factor-alpha (TNF-α), IL-6, IL-1β and leptin mRNAs and decrease in the mRNA expression of adiponectin. These effects were aggravated in sedentary HFD mice but reduced in exercising animals, potentiated by concomitant treatment with IAP, especially in obese mice. Exercising HFD mice demonstrated a substantial increase in the mRNA for adiponectin and a decrease in mRNA leptin expression in intestinal mucosa and mesenteric fat as compared to sedentary animals. The expression of SOD2 and GPx mRNAs was significantly decreased in adipose tissue in HFD mice, but these effects were reversed in exercising mice with IAP administration. Our study shows for the first time that the combination of voluntary exercise and oral IAP treatment synergistically favored healing of intestinal inflammation, strengthened the antioxidant defense and ameliorated the course of experimental colitis; thus, IAP may represent a novel adjuvant therapy to alleviate inflammatory bowel disease (IBD) in humans.

Relationships Between Circulating Irisin Response to Ice Swimming and Body Composition in People With Regular Exercise Experience

Severe cold exercise involves the irisin response, and may be related to body composition. We aimed to investigate changes in circulating irisin after ice swimming (IS), as well as to evaluate the correlation between body composition and the change in irisin caused by IS (Δirisin). 81 ice swimmers were recruited to perform IS activities. Blood samples were drawn 30 min before and 30 min after IS, and the serum levels of irisin and the ice swimmers' body composition were measured. As results, circulating irisin declined significantly during the recovery period following IS exercise (P < 0.001). The afternoon baseline circulating irisin level and Δirisin in response to IS were correlated with body fat characteristics rather than muscle parameters in ice swimmers. Δirisin subgroup analyses showed that the Δirisin ascending group (Δirisin+) subjects had a higher fat composition and higher basal irisin levels than the Δirisin descending group (Δirisin-). Furthermore, the decrease in irisin was negatively correlated with fat components in Δirisin- subjects, whereas no correlation was observed between the increase in irisin and body composition in Δirisin + subjects. Finally, a non-linear association analysis suggested that body fat indicators had obvious curvilinear relationships with Δirisin. In conclusion, IS caused a significant decrease in irisin. Statistical and curvilinear associations suggested that the correlation between fat tissue and Δirisin caused by IS is dimorphic and the underlying mechanisms may be due to the different metabolic states of subjects.

Molecular identification of FNDC5 and effect of irisin on the glucose metabolism in common carp (Cyprinus carpio L.)

Irisin, encoded by fibronectin type III domain-containing protein 5 (FNDC5) gene, plays a role in energy expenditure and insulin sensitivity in mice. In fish, the function of irisin related to glucose metabolism is less reported. It may increase glucose utilization in fish. The aim of the present study was to characterize the regulatory role of irisin in glucose metabolism in common carp (Cyprinus carpio L.). In this study, FNDC5a and FNDC5b were isolated from common carp. The cDNA of FNDC5a and FNDC5b were 722 bp and 714 bp, encoding 221 and 207 amino acids, respectively. FNDC5a was abundantly expressed in the brain and gonad. FNDC5b was mainly expressed in brain. Different expression pattern of FNDC5a and FNDC5b under fasting/refeeding and OGTT experiment were identified. The recombinant common carp irisinA and irisinB were prepared by prokaryotic expression system. Glucose concentration was decreased in treatment with irisinA or irisinB in the in vitro and in vivo experiments. The mRNA expression levels of gluconeogenesis-related genes were significantly down-regulated, while the mRNA expression of glycolysis-related genes were significantly up-regulated after treatment with recombinant irisinA or irisinB in liver in vivo and in primary hepatocytes in vitro. Our research shows that irisin inhibits hepatic gluconeogenesis and promotes hepatic glycolysis. Taken together, this study for the first time revealed the two subtypes of FNDC5 and explored the function and mechanisms of irisinA and irisinB in fish glucose homeostasis.

Comparison of Irisin Serum Healthy Untrained Males on Treadmill Exercises by Increasing Gradually Speed Vs Inclination

Aerobic exercise can improve cardiorespiratory fitness in young people. Irises released into the bloodstream function to execute regulation of energy metabolism, triggering browning white adipose, which is useful in mitochondrial biogenesis. The American College of Sport Medicine (ACSM) recommends moderate intensity cardiorespiratory fitness training with a frequency of 3-5 times a week, duration of 20-60 minutes, using a treadmill. Study subjects (n = 20) were divided randomly into 2 groups, namely the moderate intensity Treadmill training group with gradual speed improvement and gradual inclination increase. Serum slices are measured on the first and last day of exercise. There was an increasing of irisin serum  in the moderate intensity Treadmill training group by increasing gradually speed after 2 weeks of exercise, both 30 minutes pre-exercise (p = 0.02) and 1 hour post exercise (p = 0.01). Medium intensity Treadmill training with 2 weeks gradual speed increase with frequency 3 times a week can increase serum slice in men, healthy untrained young men.

Myokines and Heart Failure: Challenging Role in Adverse Cardiac Remodeling, Myopathy, and Clinical Outcomes

Heart failure (HF) is a global medical problem that characterizes poor prognosis and high economic burden for the health system and family of the HF patients. Although modern treatment approaches have significantly decreased a risk of the occurrence of HF among patients having predominant coronary artery disease, hypertension, and myocarditis, the mortality of known HF continues to be unacceptably high. One of the most important symptoms of HF that negatively influences tolerance to physical exercise, well-being, social adaptation, and quality of life is deep fatigue due to HF-related myopathy. Myopathy in HF is associated with weakness of the skeletal muscles, loss of myofibers, and the development of fibrosis due to microvascular inflammation, metabolic disorders, and mitochondrial dysfunction. The pivotal role in the regulation of myocardial and skeletal muscle rejuvenation, attenuation of muscle metabolic homeostasis, and protection against ischemia injury and apoptosis belongs to myokines. Myokines are defined as a wide spectrum of active molecules that are directly synthesized and released by both cardiac and skeletal muscle myocytes and regulate energy homeostasis in autocrine/paracrine manner. In addition, myokines have a large spectrum of pleiotropic capabilities that are involved in the pathogenesis of HF including cardiac remodeling, muscle atrophy, and cardiac cachexia. The aim of the narrative review is to summarize the knowledge with respect to the role of myokines in adverse cardiac remodeling, myopathy, and clinical outcomes among HF patients. Some myokines, such as myostatin, irisin, brain-derived neurotrophic factor, interleukin-15, fibroblast growth factor-21, and growth differential factor-11, being engaged in the regulation of the pathogenesis of HF-related myopathy, can be detected in peripheral blood, and the evaluation of their circulating levels can provide new insights to the course of HF and stratify patients at higher risk of poor outcomes prior to sarcopenic stage.

The Controversial Role of Irisin in Clinical Management of Coronary Heart Disease

Irisin, a PGC1α-dependent myokine, was once believed to have beneficial effects induced by exercise. Since its first discovery of adipose browning in 2012, multiple studies have been trying to explore the metabolic functions of irisin, such as glucose and lipid metabolism. However, recently many studies with irisin concentration measuring were doubt for methodological problems, which may account for the continuous inconsistencies. New tools like recombinant irisin and gene-knockout mice are required to reconfirm the questioned functions of irisin. In this paper, we make a critical introduction to the latest researches concerning the relationship between irisin and coronary heart disease, which includes atherosclerosis, stable angina pectoris and acute coronary syndromes. These studies provided various controversial evidence of short and long-term monitoring and therapeutic effect from molecular cellular mechanisms, in vivo experiments and epidemiological investigation. But with ambiguities, irisin still has a long way to go to identify its functions in the clinical management.

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 Role of Bone in Muscle Wasting

This review describes the role of bone resorption in muscle atrophy as well as in muscle protein anabolism. Both catabolic and anabolic pathways involve components of the proinflammatory cytokine families and release of factors stored in bone during resorption. The juxtaposition of the catabolic and anabolic resorption-dependent pathways raises new questions about control of release of factors from bone, quantity of release in a variety of conditions, and relation of factors released from bone. The catabolic responses involve release of calcium from bone into the circulation resulting in increased inflammatory response in intensity and/or duration. The release of transforming growth factor beta (TGF-β) from bone suppresses phosphorylation of the AKT/mTOR pathway and stimulates ubiquitin-mediated breakdown of muscle protein. In contrast, muscle IL-6 production is stimulated by undercarboxylated osteocalcin, which signals osteoblasts to produce more RANK ligand, stimulating resorptive release of undercarboxylated osteocalcin, which in turn stimulates muscle fiber nutrient uptake and an increase in muscle mass.

The "irisin system": From biological roles to pharmacological and nutraceutical perspectives

The scientific interest in irisin, a myokine discovered in 2012, has grown exponentially in recent years. Irisin, which is mainly produced in skeletal muscle, influences the browning process of adipose tissue and lipid and energy metabolism. Recent discoveries highlight that the potential of this hormone may have been underestimated. In the first part of this review, reports on irisin structure and molecules involved in its metabolic pathway are shown. Furthermore, data related to unclear aspects are also reported: distribution, different gene expression of its precursors in different tissues, physiological levels of circulating irisin, and pharmacokinetic and pharmacodynamic profile. The second part of this work focuses on exogenous stimuli and pharmacological agents which regulate the metabolic pathway of irisin and its serum concentration. In addition to physical exercise and exposure to low temperatures, which were early recognized as exogenous stimuli able to promote the production of this myokine, preclinical and clinical evidence demonstrates the ability of natural and synthetic molecules to interfere with this metabolic pathway. Current experimental data on irisin cannot dissolve all doubts related to this interesting molecule, but they certainly underline its potential for therapeutic purposes. Thus, identification of new pharmacological tools able to act on the irisin pathway is a challenging issue for biomedical research.

Modulatory Effect of Myokines on Reactive Oxygen Species in Ischemia/Reperfusion

There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and -21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.

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.

Irisin promotes odontogenic differentiation and angiogenic potential in human dental pulp cells

AIM

To determine whether irisin, a newly discovered myokine that links exercise-induced and metabolic homeostasis, is able to promote odontogenic differentiation and angiogenesis in human dental pulp cells (HDPCs).

METHODOLOGY

Cell viability in the presence of irisin was measured. Real-time PCR and Western blot analysis were performed to evaluate the expression levels of irisin, odontogenic and angiogenic markers. The involvement of mitogen-activated protein kinase (MAPK) and the protein kinase B (Akt) signalling pathway was evaluated by Western blot. To evaluate mineralization nodule formation, alkaline phosphatase (ALP) staining and alizarin red S staining were performed. Scratch wound assays were performed to evaluate the effects of irisin on cell migration. The data were analysed using one-way analysis of variance (anova) followed by Tukey post hoc test and Student's t-test. Statistical significance was considered at P < 0.05.

RESULTS

Irisin significantly promoted odontogenic differentiation as evidenced by formation of mineralized nodules, induction of ALP activity and upregulation of odontogenic and angiogenic markers (P < 0.05). Scratch wound assays revealed that irisin significantly increased migration of HDPCs (P < 0.05). Phosphorylation of both MAPK and Akt was increased by irisin. MAPK and Akt inhibitors inhibited mineralization, cell migration and the increased expression of odontogenic and angiogenic markers.

CONCLUSIONS

Irisin promoted odontogenic differentiation and mineralization and has the potential for angiogenesis through activation of the MAPK and Akt signalling pathways in HDPCs.

FNDC5 polymorphism influences the association between sarcopenia and liver fibrosis in adults with biopsy-proven non-alcoholic fatty liver disease

The FNDC5 gene encodes the fibronectin type III domain-containing protein 5 that is a membrane protein mainly expressed in skeletal muscle, and the FNDC5 rs3480 polymorphism may be associated with liver disease severity in non-alcoholic fatty liver disease (NAFLD). We investigated the influence of the FNDC5 rs3480 polymorphism on the relationship between sarcopenia and the histological severity of NAFLD. A total of 370 adult individuals with biopsy-proven NAFLD were studied. The association between the key exposure sarcopenia and the outcome liver histological severity was investigated by binary logistic regression. Stratified analyses were undertaken to examine the impact of FNDC5 rs3480 polymorphism on the association between sarcopenia and the severity of NAFLD histology. Patients with sarcopenia had more severe histological grades of steatosis and a higher prevalence of significant fibrosis and definite non-alcoholic steatohepatitis than those without sarcopenia. There was a significant association between sarcopenia and significant fibrosis (adjusted OR 2·79, 95 % CI 1·31, 5·95, P = 0·008), independent of established risk factors and potential confounders. Among patients with sarcopenia, significant fibrosis occurred more frequently in the rs3480 AA genotype carriers than in those carrying the FNDC5 rs3480 G genotype (43·8 v. 17·2 %, P = 0·031). In the association between sarcopenia and liver fibrosis, there was a significant interaction between the FNDC5 genotype and sarcopenia status (P value for interaction = 0·006). Sarcopenia is independently associated with significant liver fibrosis, and the FNDC5 rs3480 G variant influences the association between sarcopenia and liver fibrosis in patients with biopsy-proven NAFLD.

Effects of a Combined Endurance/Strength Training Program on Circulating Irisin Levels in Overweight/Obese Men and Women with Type 2 Diabetes Mellitus

Irisin is a promising therapeutic target in patients with type 2 diabetes mellitus (T2DM), as studies have demonstrated that irisin can induce "browning" of adipocytes and mitigate pro-inflammatory conditions. Sex-specific changes in irisin levels have been reported in a study involving healthy men and women following physical training. The present study aims to analyze the effects of an 8-week training intervention on circulating irisin levels in patients with T2DM and to find out whether the training responses differ between T2DM men and women. Twenty-nine overweight/obese T2DM patients (19 men, 10 women; age: 46-74 years; body mass index >25 kg/m²) participated in a combined moderate-intensity endurance/strength training program (3 times a week). The irisin levels of men and women did not differ significantly. The post-training irisin levels did not differ significantly from the pre-training values, and there was no interaction effect of sex. This study shows no training-induced (sex-specific) changes in circulating irisin levels in T2DM patients. Large-scale studies using other forms of training are needed to fully clarify whether basal irisin levels can be changed in T2DM men and/or women to counteract T2DM.

Adipokines, Myokines, and Cardiokines: The Role of Nutritional Interventions

It is now established that adipose tissue, skeletal muscle, and heart are endocrine organs and secrete in normal and in pathological conditions several molecules, called, respectively, adipokines, myokines, and cardiokines. These secretory proteins constitute a closed network that plays a crucial role in obesity and above all in cardiac diseases associated with obesity. In particular, the interaction between adipokines, myokines, and cardiokines is mainly involved in inflammatory and oxidative damage characterized obesity condition. Identifying new therapeutic agents or treatment having a positive action on the expression of these molecules could have a key positive effect on the management of obesity and its cardiac complications. Results from recent studies indicate that several nutritional interventions, including nutraceutical supplements, could represent new therapeutic agents on the adipo-myo-cardiokines network. This review focuses the biological action on the main adipokines, myokines and cardiokines involved in obesity and cardiovascular diseases and describe the principal nutraceutical approaches able to regulate leptin, adiponectin, apelin, irisin, natriuretic peptides, and follistatin-like 1 expression.

Irisin/FNDC5: A participant in camel metabolism

The quantification, localization, production, function, and regulation of irisin/FNDC5 in camel species have not been previously studied. The objective of this study was to detect the irisin content in Arabian camel blood and tissues and study the gene expression of FNDC5 and PGC-1α in camel skeletal muscles and white adipose tissue depots under basal conditions. To monitor if exercise influences blood and tissue irisin protein levels as well as FNDC5 and PGC-1α gene expression levels, we analyzed irisin concentrations in the serum, skeletal muscles (soleus and gastrocnemius), and white adipose tissues (hump, subcutaneous, visceral, epididymal, and perirenal) in both control (n = 6) and exercised group (n = 6) using ELISA and determined the cellular localization of irisin/FNDC5 and the mRNA levels of FNDC5 and PGC-1α in skeletal muscles and adipose tissues via immunohistochemistry and real-time PCR, respectively. The possible regulatory roles of exercise on some hormones and metabolites as well as the detection of links between serum irisin and other circulating hormones (insulin, leptin, and cortisol) and metabolites (glucose, free fatty acids, triglycerides, and ATP) were explored for the first time in camels. Our results indicated that exercise induces tissue-specific regulation of the camel irisin, FNDC5, and PGC-1α levels, which subsequently regulates the circulating irisin level. Significant associations were detected between the levels of irisin/FNDC5/PGC-1α in camels and the metabolic and hormonal responses to exercise. Our study suggested that irisin regulates, or is regulated by, glucose, FFA, insulin, leptin, and cortisol in camels. The novel results of the present study will serve as baseline data for camels.

Involvement of kindlin-2 in irisin's protection against ischaemia reperfusion-induced liver injury in high-fat diet-fed mice

Liver steatosis is associated with increased ischaemia reperfusion (I/R) injury. Our previous studies have shown that irisin, an exercise-induced hormone, mitigates I/R injury via binding to αVβ5 integrin. However, the effect of irisin on I/R injury in steatotic liver remains unknown. Kindlin-2 directly interacts with β integrin. We therefore suggest that irisin protects against I/R injury in steatotic liver via a kindlin-2 dependent mechanism. To study this, hepatic steatosis was induced in male adult mice by feeding them with a 60% high-fat diet (HFD). At 12 weeks after HFD feeding, the mice were subjected to liver ischaemia by occluding partial (70%) hepatic arterial/portal venous blood for 60 minutes, which was followed by 24 hours reperfusion. Our results showed HFD exaggerated I/R-induced liver injury. Irisin (250 μg/kg) administration at the beginning of reperfusion attenuated liver injury, improved mitochondrial function, and reduced oxidative and endoplasmic reticulum stress in HFD-fed mice. However, kindlin-2 inhibition by RNAi eliminated irisin's direct effects on cultured hepatocytes. In conclusion, irisin attenuates I/R injury in steatotic liver via a kindlin-2 dependent mechanism.

Habitually inactive physically - a proposed procedure of counteracting cognitive decline in women with diminished insulin sensitivity through a high-intensity circuit training program

This study verified the impact of five weeks of high-intensity circuit training (HICT) on changes in concentration of exerkines in relation to cognitive functions. Sedentary women (n = 33; age=39±13 years) were randomly assigned into the HICT (n = 21) group or the control group (n = 12). The HICT group performed 15 training sessions; meanwhile, the control group performed the HICT twice, only at baseline and at the end of the experiment. Blood samples were collected before, 1 h and 24 h after the first and last HICT, to evaluate the concentration of exerkines: brain-derived neurotrophic factor (BDNF), irisin, fibroblast growth factor-21 (FGF-21), interleukin-6 (IL-6) and cathepsin B (CATB) using enzyme immunoassay method. Cognitive functions and quality of life were assessed using the Vienna Test System and the Short Form Health Survey. HICT induced improvement of cognitive function and quality of life, and these changes were accompanied by an increase of BDNF and shifts in CATB concentration. HICT program caused a decrease in FGF-21 concentration, which was modified by age and insulin sensitivity. The improvement of cognitive functions was more pronounced in females, who experienced a drop in FGF-21. In summary, HICT program, that can be performed during pandemic, enhanced cognitive functions and this response was related to changes in exerkines.

Irisin Gene Delivery Ameliorates Burn-Induced Sensory and Motor Neuropathy

Burn-related neuropathy is common and often involves pain, paresthesia, or muscle weakness. Irisin, an exercise-induced myokine after cleavage from its membrane precursor fibronectin type III domain-containing 5 (FNDC5), exhibits neuroprotective and anti-inflammatory activities. A rat model of third-degree burn on the right hind paw was used to investigate the therapeutic role of irisin/FNDC5. Rats received burn injury and were treated with intrathecal recombinant adenovirus containing the irisin sequence (Ad-irisin) at 3 weeks postburn. One week later, mechanical allodynia was examined. The expression of irisin in cerebrospinal fluid (CSF) was detected. Ipsilateral gastrocnemius muscle and lumbar spinal cord were also obtained for further investigation. Furthermore, the anti-apoptotic effect of recombinant irisin in SH-SY5Y cells was evaluated through tumor necrosis factor alpha (TNFα) stimulus to mimic burn injury. We noted intrathecal Ad-irisin attenuated pain sensitization and gastrocnemius muscle atrophy by modulating the level of irisin in CSF, and the expression of neuronal FNDC5/irisin and TNFα in the spinal cord. Ad-irisin also ameliorated neuronal apoptosis in both dorsal and ventral horns. Furthermore, recombinant irisin attenuated TNFα-induced SH-SY5Y cell apoptosis. In summary, irisin attenuated allodynia and muscle wasting by ameliorating neuroinflammation-induced neuronal apoptosis.

Relative Skeletal Muscle Mass Is an Important Factor in Non-Alcoholic Fatty Liver Disease in Non-Obese Children and Adolescents

Recently, sarcopenia was identified as a risk factor for non-alcoholic fatty liver disease (NAFLD) in adults. We here investigated the association between skeletal muscle mass (SMM) and NAFLD in non-obese children and adolescents. A retrospective medical chart review was performed for individuals aged 9–15 years diagnosed with NAFLD. Healthy volunteers aged 9–15 years were recruited as controls. Participants were subject to laboratory tests, abdominal sonography, and multi-frequency bioelectrical impedance analysis. SMM data were calculated as the skeletal muscle-to-body fat ratio (MFR), and the diagnosis of fatty liver was established by abdominal sonography. The control and NAFLD groups included 73 and 53 individuals, respectively. No significant difference was observed in gender and body mass index (BMI) distribution between the groups. Mean MFR was significantly lower in individuals with NAFLD than in those without (0.83 vs. 1.04, p = 0.005). After adjusting for age, sex, BMI, and serum glucose, the risk of having NAFLD was significantly associated with a decreased MFR (p = 0.016). NAFLD is significantly associated with relatively low SMM in non-obese children and adolescents. Increasing SMM, such as weight training, can be suggested as one of the treatment strategies in pediatric NAFLD without obesity.

The effects of royal jelly and tocotrienol-rich fraction on impaired glycemic control and inflammation through irisin in obese rats

The effects of royal jelly (RJ) and tocotrienol-rich fraction (TRF) on obesity-induced glucose intolerance and inflammation were assessed in the current study. Regarding irisin as an important adipomyokine that attenuates obesity-induced disorders, we evaluated whether RJ and TRF could exert their metabolism regulatory effects through irisin. Obese rats were fed a high-fat diet (HFD) with or without supplementation of RJ, TRF, or both, for 8 weeks. At the end of the intervention, weight, irisin, glycemic, and inflammatory indices were measured. The weight of the rats did not remarkably reduce in any of the groups. Glucose homeostasis and inflammation were improved when we added RJ and TRF to HFD. RJ elevated irisin concentration, but the effect of TRF on irisin was not noticeable. Our results indicated that, despite the lack of significant weight loss, RJ and TRF promoted healthy obesity. This improvement was mediated by irisin in RJ consuming rats. PRACTICAL APPLICATIONS: Obesity is a public health concern associated with several chronic disorders. The beneficial effects of irisin on obesity-related disorders are well-established. It is the first study assessing the effect of RJ and TRF as functional foods, with pharmacological and nutritional activities on obesity complications, through irisin mediation. Our study demonstrated that RJ exerts its metabolic regulatory effects by irisin as a mediator. Our investigation makes a remarkable contribution to the literature, because it suggests a new mechanism for the anti-obesity properties of RJ and TRF.

Serum irisin level, insulin resistance, and lipid profiles in patients with hidradenitis suppurativa: a case-control study

Background

Hidradenitis suppurativa is a chronic inflammatory skin disease of terminal follicular acroinfundibulum.

Objectives

This study aimed to evaluate serum irisin, plasma glucose, insulin, and lipid levels in hidradenitis suppurativa, and elucidate possible associations with disease activity, inflammatory, or metabolic parameters.

Methods

This case-control study included 37 patients (M/F: 9/28) and 37 sex-, age- and body mass index -matched healthy controls (M/F: 11/26). Demographic data, Hurley stage of disease, fasting glucose, insulin, total cholesterol, high density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, C-reactive protein levels, erythrocyte sedimentation rate, hematologic parameters, and serum irisin were assessed.

Results

The hidradenitis suppurativa group had significantly higher waist circumference than controls (p < 0.001). Insulin resistance, defined as a homeostatic model assessment for insulin resistance value greater than 2.5, was observed in 45.9% of patients and 8.1% of controls (p = 0.003), whereas metabolic syndrome was observed in 32.4% of patients and 5.4% of controls (p < 0.001). Furthermore, plasma triglycerids, glucose, and insulin levels were significantly higher in the hidradenitis suppurativa (p = 0.013, p = 0.001, and p = 0.004), respectively. Mean irisin level was insignificantly higher in the hidradenitis suppurativa group (37.4 ± 32.6) than in controls (26.2 ± 24.7, p = 0.217).

Study limitation

Physical activity and the exercise levels of participants were not documented.

Conclusion

This study indicates that hidradenitis suppurativa patients have higher serum irisin, fasting plasma glucose, insulin, and triglycerides levels than healthy controls. Thus, the authors suggest that hidradenitis suppurativa patients should be evaluated for insulin resistance and metabolic syndrome, and monitored accordingly.

The Protective Effect of Exercise in Neurodegenerative Diseases: The Potential Role of Extracellular Vesicles

Physical activity has systemic effects on the body, affecting almost every organ. It is important not only for general health and wellbeing, but also in the prevention of diseases. The mechanisms behind the therapeutic effects of physical activity are not completely understood; however, studies indicate these benefits are not confined to simply managing energy balance and body weight. They also include systemic factors which are released into the circulation during exercise and which appear to underlie the myriad of benefits exercise can elicit. It was shown that along with a number of classical cytokines, active tissues also engage in inter-tissue communication via extracellular vesicles (EVs), specifically exosomes and other small EVs, which are able to deliver biomolecules to cells and alter their metabolism. Thus, EVs may play a role in the acute and systemic adaptations that take place during and after physical activity, and may be therapeutically useful in the treatment of a range of diseases, including metabolic disorders such as type 2 diabetes and obesity; and the focus of this review, neurological disorders such as Alzheimer's disease.

Response of Blood Biomarkers to Sprint Interval Swimming

PURPOSE

To evaluate and compare the effects of 2 sprint interval training (SIT) sets of different distances on biochemical markers indicative of metabolism, stress, and antioxidant capacity in competitive swimmers and, to investigate the potential influence of gender on these markers.

METHODS

Twenty-four adolescent, well-trained swimmers (12 men and 12 women) participated in the study. In a random and counterbalanced order, the swimmers completed 2 SIT sets (8 × 50 m and 8 × 25 m) in freestyle with maximal intensity on different days. Work-to-rest ratio was 1:1 in both sets. Blood samples were drawn preexercise, immediately postexercise, and 1 hour postexercise to evaluate the effects of the SIT sets on a number of biochemical parameters.

RESULTS

Swimming speed was higher at 8 × 25 m. The 2 SIT sets induced significant increases in lactate, glucose, insulin, glucagon, cortisol, and uric acid (P ≤ .001). No differences in these parameters were found between sets, except for irisin (higher in 8 × 50 m; P = .02). Male swimmers were faster and had higher lactate and uric acid concentrations, as well as lower reduced glutathione concentration, than female swimmers (P < .01).

CONCLUSIONS

The 2 swimming SIT sets induced increases in most of the biochemical markers studied. The 2-fold difference between sets in distance did not differentiate the effects of sprint interval exercise on most biochemical parameters. Thus, low-volume SIT sets seem to be effective stimuli for competitive swimmers.

Irisin promotes osteogenic differentiation of bone marrow mesenchymal stem cells by activating autophagy via the Wnt//β-catenin signal pathway

Osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) plays a crucial role in osteoporosis. Irisin, an exercise-induced muscle-dependent myokine, has been reported to stimulate the development of brown adipose tissue and regulate energy expenditure. The present study aimed to investigate the effects of irisin on autophagy in BMSCs. Furthermore, the osteogenic differentiation ability was evaluated, as well as the activation of autophagy. It was found that 40 μM irisin for 48 h was an appropriate concentration and time period, with regards to cell viability, which was measured with a Cell Counting Kit-8. Moreover, the increasing expression levels of microtubule-associated protein light chain 3 (Lc3)-I/II and autophagy related 5 (Atg5) by irisin demonstrated the upregulation of autophagy. Mechanistically, bafilomycin A1 and Atg5 small interfering RNA were used to evaluate the possible mechanism of autophagy activated by irisin, and it was identified that irisin may upregulate autophagy by increasing the Atg12-Atg5-Atg16L complex. In addition, with the increasing level of autophagy, osteogenesis and the Wnt/β-catenin signal pathway were also enhanced. However, inhibition of autophagy by bafilomycin A1 negatively regulated osteogenic differentiation. Collectively, the present results suggested that irisin may stimulate autophagy in BMSCs and that osteogenic differentiation may be enhanced by stimulating autophagy.

Irisin modulates genes associated with severe coronavirus disease (COVID-19) outcome in human subcutaneous adipocytes cell culture

Obesity patients are more susceptible to develop COVID-19 severe outcome due to the role of angiotensin-converting enzyme 2 (ACE2) in the viral infection. ACE2 is regulated in the human cells by different genes associated with increased (TLR3, HAT1, HDAC2, KDM5B, SIRT1, RAB1A, FURIN and ADAM10) or decreased (TRIB3) virus replication. RNA-seq data revealed 14857 genes expressed in human subcutaneous adipocytes, including genes mentioned above. Irisin treatment increased by 3-fold the levels of TRIB3 transcript and decreased the levels of other genes. The decrease in FURIN and ADAM10 expression enriched diverse biological processes, including extracellular structure organization. Our results, in human subcutaneous adipocytes cell culture, indicate a positive effect of irisin on the expression of multiple genes related to viral infection by SARS-CoV-2; furthermore, translatable for other tissues and organs targeted by the novel coronavirus and present, thus, promising approaches for the treatment of COVID-19 infection as therapeutic strategy to decrease ACE2 regulatory genes.

The Usefulness of Diagnostic Panels Based on Circulating Adipocytokines/Regulatory Peptides, Renal Function Tests, Insulin Resistance Indicators and Lipid-Carbohydrate Metabolism Parameters in Diagnosis and Prognosis of Type 2 Diabetes Mellitus with Obesity

The quantitative analysis of selected regulatory molecules, i.e., adropin, irisin, and vaspin in the plasma of obese patients with newly diagnosed, untreated type 2 diabetes mellitus, and in the same patients after six months of using metformin, in relation to adropinemia, irisinemia and vaspinemia in obese individuals, was performed. The relationship between plasma concentration of the adipocytokines/regulatory peptides and parameters of renal function (albumin/creatinine ratio-ACR, estimated glomerular filtration rate-eGFR), values of insulin resistance indicators (Homeostatic Model Assessment of Insulin Resistance (HOMA-IR2), Homeostatic Model Assessment of Insulin Sensitivity (HOMA-S), Homeostatic Model Assessment of β-cell function (HOMA-B), quantitative insulin sensitivity check index (QUICKI), insulin), and parameters of carbohydrate-lipid metabolism (fasting plasma glucose-FPG, glycated hemoglobin-HbA_1C, estimated glucose disposal rate-eGDR, fasting lipid profile, TG/HDL ratio) in obese type 2 diabetic patients was also investigated. Circulating irisin and vaspin were found significantly different in subjects with metabolically healthy obesity and in type 2 diabetic patients. Significant increases in blood levels of both analyzed adipokines/regulatory peptides were observed in diabetic patients after six months of metformin treatment, as compared to pre-treatment levels. The change in plasma vaspin level in response to metformin therapy was parallel with the improving of insulin resistance/sensitivity parameters. An attempt was made to identify a set of biochemical tests that would vary greatly in obese non-diabetic subjects and obese patients with type 2 diabetes, as well as a set of parameters that are changing in patients with type 2 diabetes under the influence of six months metformin therapy, and thus differentiating patients' metabolic state before and after treatment. For these data analyses, both statistical measures of strength of the relationships of individual parameters, as well as multidimensional methods, including discriminant analysis and multifactorial analysis derived from machine learning methods, were used. Adropin, irisin, and vaspin were found as promising regulatory molecules, which may turn out to be useful indicators in the early detection of T2DM and differentiating the obesity phenotype with normal metabolic profile from T2DM obese patients. Multifactorial discriminant analysis revealed that irisin and vaspin plasma levels contribute clinically relevant information concerning the effectiveness of metformin treatment in T2D patients. Among the sets of variables differentiating with the highest accuracy the metabolic state of patients before and after six-month metformin treatment, were: (1) vaspin, HbA1c, HDL, LDL, TG, insulin, and HOMA-B (ACC = 88 [%]); (2) vaspin, irisin, QUICKI, and eGDR (ACC = 86 [%]); as well as, (3) vaspin, irisin, LDL, HOMA-S, ACR, and eGFR (ACC = 86 [%]).

Serum Irisin Levels, Endothelial Dysfunction, and Inflammation in Pediatric Patients with Type 2 Diabetes Mellitus and Metabolic Syndrome

The prevalence of type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has increased in the pediatric population. Irisin, an adipomyokine, is involved in white adipose tissue browning, energy expenditure, insulin sensitivity, and anti-inflammatory pathways. Data on the associations among circulating irisin levels, soluble cell adhesion molecules (sCAMs), and inflammatory cytokines is scarce in children and adolescents with MetS and T2DM. Subjects aged 6-16 years were grouped into T2DM, MetS, and healthy controls. Serum irisin levels were significantly lower in the MetS (6.6 [2.8-18.0] ng/mL) and T2DM (6.8 [2.2-23.2] ng/mL) groups compared with controls (30.3 [24.6-57.1] ng/mL). Negative correlations between irisin and the BMI percentile (R = -0.358), WC percentile (R = -0.308), and triglycerides (R = -0.284) were identified, while positive associations with TC (R = 0.287), HDL-c (R = 0.488), and LDL-c (R = 0.414) were observed. Significant negative correlations were found between irisin and sNCAM (R = -0.382), sICAM-2 (R = -0.300), sVCAM-1 (R = -0.292), MCP-1 (R = -0.308), and IFN-α2 (R = -0.406). Of note, lower concentrations of most sCAMs (sICAM-1, sPSGL-1, sP-selectin, sEpCAM, sICAM-2, sALCAM, sPECAM-1, sCD44, sVCAM-1, sICAM-3, sL-selectin, and sNCAM) were shown in T2DM subjects compared with MetS patients. Lower irisin levels induce a lack of inhibition of oxidative stress and inflammation. In T2DM, higher ROS, AGEs, glucotoxicity, and inflammation trigger endothelial cell apoptosis, which downregulates the sCAM expression as a compensatory mechanism to prevent further vascular damage. In opposition, in subjects with MetS that have not yet developed T2DM and its accompanying stressors, the upregulation of the sCAM expression is ensued.

Myokines mediate the cross talk between skeletal muscle and other organs

Myokines are muscle-derived cytokines and chemokines that act extensively on organs and exert beneficial metabolic functions in the whole-body through specific signal networks. Myokines as mediators provide the conceptual basis for a whole new paradigm useful for understanding how skeletal muscle communicates with other organs. In this review, we summarize and discuss classes of myokines and their physiological functions in mediating the regulatory roles of skeletal muscle on other organs and the regulation of the whole-body energy metabolism. We review the mechanisms involved in the interaction between skeletal muscle and nonmuscle organs through myokines. Moreover, we clarify the connection between exercise, myokines and disease development, which may contribute to the understanding of a potential mechanism by which physical inactivity affects the process of metabolic diseases via myokines. Based on the current findings, myokines are important factors that mediate the effect of skeletal muscle on other organ functions and whole-body metabolism.

Association between plasma irisin and glucose metabolism in pregnant women is modified by dietary n-3 polyunsaturated fatty acid intake

AIMS/INTRODUCTION

The role of irisin in maternal glucose metabolism and how it would respond to dietary n-3 polyunsaturated fatty acid (n-3 PUFA) intake remains unclear. This study aimed to explore whether maternal plasma irisin is associated with glucose metabolism and whether this association is modified by dietary n-3 PUFA.

MATERIALS AND METHODS

A total of 932 pregnant women (20-28 weeks' gestation) aged 20-45 years were recruited. Dietary n-3 PUFA was estimated using a validated quantitative food frequency questionnaire. Plasma irisin and insulin were tested by enzyme-linked immunosorbent assay, and insulin resistance (IR) was estimated using the homeostatic model assessment (HOMA). Gestational diabetes mellitus was diagnosed with a 75-g oral glucose tolerance test. Adjusted multivariable linear regression and logistic regression were carried out to examine the associations between plasma irisin and glucose metabolism. The moderating effect of dietary n-3 PUFA intake was determined by fully multiplicative models by including the interaction term.

RESULTS

Maternal plasma irisin was negatively associated with HOMA-IR and oral glucose tolerance test 0 h glucose level (β -0.250, -0.067; corrected P-value for false discovery rate = 0.012, 0.018, respectively), positively associated with HOMA of insulin sensitivity (β 0.028; corrected P-value for false discovery rate = 0.012), but not associated with postprandial glucose or the risk of gestational diabetes mellitus. Furthermore, we found a moderating effect of dietary n-3 PUFA on the relationships of plasma irisin with HOMA-IR and HOMA of insulin sensitivity; these associations were strengthened with increased n-3 PUFA intake (β -0.037, 0.004; P = 0.014, 0.041, respectively).

CONCLUSIONS

Plasma irisin was negatively associated with HOMA-IR and fasting glucose, whereas it was positively associated with HOMA of insulin sensitivity in pregnant women. We first showed that these associations were modified by dietary n-3 PUFA intake.

Irisin Regulates the Functions of Hepatic Stellate Cells

BACKGROUND

Hepatic stellate cells (HSCs) are known to play a fundamental role in the progression of liver fibrosis. Once HSCs are activated, they are involved in proliferation, migration, and contractility which are characteristics of liver fibrogenesis. Recent studies have shown that irisin, a myokine secreted during physical exercise, has a protective effect in various metabolic diseases, especially in renal fibrosis. However, whether irisin is involved in HSC activation and other processes associated with liver fibrosis has not yet been investigated. In this study, we reveal the role of irisin in HSC activation as well as in proliferation, migration, and contractile properties of HSCs in vitro.

METHODS

LX-2 cells, immortalized human HSCs, were treated with transforming growth factor beta 1 (TGF-β1), a core regulator of HSC fibrosis, with or without irisin, and markers of the aforementioned processes were analyzed. Further, an inflammatory response was stimulated with TGF-β1 and lipopolysaccharide (LPS) in combination with irisin and the expression of cytokines was measured.

RESULTS

Recombinant irisin significantly suppressed the expression of TGF-β1-stimulated fibrosis markers including alpha-smooth muscle actin and collagen type 1 alpha 1 and prevented the TGF-β1-induced proliferation, migration, and contractility of LX-2 cells. Additionally, irisin ameliorated the production of interleukin-6 (IL-6) and IL-1β induced by TGF-β1 and LPS treatments.

CONCLUSION

These findings suggested that irisin potently improved the progression of hepatic fibrosis by regulating HSC activation, proliferation, migration, contractility, and HSC-mediated production of inflammatory cytokine.

Irisin ameliorates high glucose-induced cardiomyocytes injury via AMPK/mTOR signal pathway

High glucose (HG)-induced cardiomyocytes (CMs) injury is a leading cause of diabetic cardiomyopathy with little treatment options. Irisin, a new myokine, which is cleaved from its precursor fibronectin type III domain-containing protein 5 (FNDC5), has aroused great attention as an essential cardioprotective factor and glucose metabolism regulator but little was known on diabetic cardiomyopathy yet. Here, we aim to clarify the role of irisin in the HG-induced CMs injury. Neonatal Sprague-Dawley rat CMs were cultured in a normal or HG medium for 12, 24, and 48 hr, respectively before exposing to irisin. The apoptosis level was determined by terminal-deoxynucleotidyl transferase-mediated-dUTP nick end-labeling assay. Cell viability was measured with the conventional methyl thiazolyl tetrazolium assay. Moreover, reactive oxygen species production was evaluated by dihydroethidium staining. Inflammatory factors, namely tumor necrosis factor-α, interleukin-6, interleukin-1β were determined by enzyme-linked immunosorbent assay kits. Furthermore, protein and messenger RNA (mRNA) expressions were measured by western blot and quantitative real-time polymerase chain reaction, respectively. HG increases the apoptosis of CMs and activated the inflammatory responses and oxidative stress in CMs. Meanwhile, the mRNA and protein expressions of FNDC5 are decreased after HG exposure. Nevertheless, the increased apoptosis is alleviated by irisin treatment. Notably, irisin suppresses the inflammatory responses and oxidative stress in injured CMs. Mechanically, after the administration of Compound C, AMP-activated protein kinase (AMPK) inhibitor, these cardioprotective effects resulting from irisin are reversed. Irisin plays a significant role in antiapoptosis, anti-inflammation, antioxidative stress in HG-induced CMs via AMPK/mammalian target of the rapamycin signaling pathway.

Serum Irisin Levels and Clinical Implication in Elderly Patients With Type 2 Diabetes Mellitus

Background

The aim of this study is to evaluate the level and role of serum irisin in elderly patients with type 2 diabetes mellitus (T2DM) using case-control study.

Methods

A total of 71 patients with T2DM were selected as the case group according to the inclusion criteria and exclusion criteria; and the ratio of 1:1 was calculated according to the inclusion rate of the residents. The cohort established in Guankou Town, Jimei District, Xiamen City, Fujian Province, China and the residents of this cohort were selected at the age of 60 and above. A total of 71 healthy subjects were included as the control group with the same gender and the age with a difference of ± 5 years old. The clinical data of the subjects were collected to determine their previous history, blood pressure, body mass index (BMI), hemoglobin (HB), liver function test, renal function test, fasting blood glucose and serum lipid. The irisin level in serum was measured by enzyme-linked immunosorbent assay (ELISA). The data were analyzed by using SPSS17.0 software. Single factor analysis using Chi-square test or t-test was performed to compare the differences between T2DM patients with the control group of the general data, clinical indicators and irisin level in serum. Logistic regression was used to analyze the protective factors and risk factors of diabetes mellitus.

Results

The results of single factor analysis showed that the level of irisin in T2DM group was significantly lower than that in the control group (703.37 ± 241.51 ng/mL and 800.22 ± 275.59 ng/mL, respectively). The levels of BMI, systolic blood pressure (SBP), diastolic blood pressure (DBP), triglyceride (TG) and fasting plasma glucose (FPG) in T2DM group were higher than those in control group, and differences were statistically significant. Logistic regression analysis indicated that irisin may be a protective factor for type 2 diabetes (odds ratio (OR) = 0.997, 95% confidence interval (CI): 0.994 - 0.999).

Conclusions

The serum irisin level in T2DM group was significantly lower than that in control group, suggesting that irisin may be a protective factor for type 2 diabetes.

Plasma Concentration of Irisin and Brain-Derived-Neurotrophic Factor and Their Association With the Level of Erythrocyte Adenine Nucleotides in Response to Long-Term Endurance Training at Rest and After a Single Bout of Exercise

The study aimed to assess the effect of a single bout of incremental exercise on irisin and BDNF plasma concentrations as related to erythrocyte purine nucleotides concentration at rest and after exercise. Master endurance master athletes (training experience 38 ± 6 years) and a group of untrained participants completed a single bout of progressive incremental exercise test until exhaustion. The dual-energy x-ray absorptiometry and blood collection were performed. Blood was taken twice at rest and 10 min after exercise. Concentrations of ATP, ADP, and AMP were assessed in the erythrocytes. Hypoxanthine and uric acid were determined in plasma using the high-performance liquid chromatography. Plasma concentrations of irisin and BDNF were assessed through the immunoenzymatic method. The ATP level, ATP/ADP ratio and AEC value were significantly higher in the athletic group. A significantly higher concentration of BDNF was it also noted in the trained group that correlated with the erythrocyte energy status at rest. The single session of exercise induced a significant increase in ATP erythrocyte levels in both groups. Both exerkines significantly correlated at rest with red blood cell adenine nucleotides and degradation products (BDNF positively and irisin negatively). The blood concentration of BDNF and irisin, in response to exercise, was not significantly different between groups. Obtained data revealed a higher erythrocyte energy status and lower purine degradation products concentration in master athletes. Also resting plasma exerkines differed substantially between groups. In conclusion, long-term training resulted in exercise adaptation reflected by a higher erythrocyte energy status, lower purine degradation products concentration and modified concentration of exerkines (higher BDNF and lower irisin blood concentrations). Therefore, we consider the training-induced adaptations in master athletes to be beneficial and significant. The moderate level of physical activity in the untrained group, even if sufficient in terms of general health, did not cause any discernible changes.

Sarcopenic obesity: Myokines as potential diagnostic biomarkers and therapeutic targets?

Sarcopenic obesity (SO) is a condition characterized by the occurrence of both sarcopenia and obesity and imposes a heavy burden on the health of the elderly. Controversies and challenges regarding the definition, diagnosis and treatment of SO still remain because of its complex pathogenesis and limitations. Over the past few decades, numerous studies have revealed that myokines secreted from skeletal muscle play significant roles in the regulation of muscle mass and function as well as metabolic homeostasis. Abnormalities in myokines may trigger and promote the pathogenesis underlying age-related and metabolic diseases, including obesity, sarcopenia, type 2 diabetes (T2D), and SO. This review mainly focuses on the role of myokines as potential biomarkers for the early diagnosis and therapeutic targets in SO.

Exercise hormone irisin mitigates endothelial barrier dysfunction and microvascular leakage-related diseases

Increased microvascular leakage is a cardinal feature of many critical diseases. Regular exercise is associated with improved endothelial function and reduced risk of cardiovascular disease. Irisin, secreted during exercise, contributes to many health benefits of exercise. However, the effects of irisin on endothelial function and microvascular leakage remain unknown. In this study, we found that irisin remarkably strengthened endothelial junctions and barrier function via binding to integrin αVβ5 receptor in LPS-treated endothelial cells. The beneficial effect of irisin was associated with suppression of the Src-MLCK-β-catenin pathway, activation of the AMPK-Cdc42/Rac1 pathway, and improvement of mitochondrial function. In preclinical models of microvascular leakage, exogenous irisin improved pulmonary function, decreased lung edema and injury, suppressed inflammation, and increased survival. In ARDS patients, serum irisin levels were decreased and inversely correlated with disease severity and mortality. In conclusion, irisin enhances endothelial barrier function and mitigates microvascular leakage-related diseases.

Impact of supervised exercise training on pulmonary function parameters, exercise capacity and Irisin Biomarker in Interstitial lung disease patients

OBJECTIVES

To assess the impact of supervised exercise training (SET) on pulmonary function Parameters, exercise capacity and Irisin biomarker in Interstitial Lung Disease (ILD) patients.

METHODS

Ten (10)patients with ILD and 18 healthy controls of age between 30-40+ years were selected for 8-week SET program. Before and after SET all subjects performed exercise capacity six minutes' walk test (6MWT), heart rate (HR) changes were recorded, shortness of Breath Respiratory Questionnaire (SOBQ) was obtained and Irisin levels were measured by Enzyme-Linked Immunosorbent Assay (ELISA). This interventional study was carried out at Department of Physiology, Faculty of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia, from October 2018 to February 2019.

RESULTS

Mean six minutes' walk distance (6MWD) was 395 ± 68.4 m at 1st visit increased significantly (p=0.001) to 458.8± 87.1 mat 15 visit. However, 6MWD values found significantly higher in controls (517.4±84.1 m; 561.7±81.6 m; p=0.013) than ILD patients. Overall change (difference between post and pre exercise) in HRvalue was recorded lower in ILD patients (30-35 bpm) as compared to controls (40-45 bpm). Moreover, ILD patients had overall higher SOBQ score than controls. Pre SET Irisin levels of ILD patients (4.24 ±1.73 pg/ml) and controls (3.43 ±1.04pg/ml) were found unchanged dafter SET (4.48±2.02pg/ml, 3.39 ±1.41pg/ml, p=0.677, p=0.093)respectively. However, patients Irisin values were found higher as compared to controls before and after SET.

CONCLUSION

Exercise capacity and Dyspneain patients with ILD were improved after 8-week of SET program. No major changes in Irisin levels among patients with ILD and controls were observed. Additional research requires to be carried out on large number of subjects to deter Minutese the advantages of exercise in ILD.

FNDC4, a novel adipokine that reduces lipogenesis and promotes fat browning in human visceral adipocytes

BACKGROUND

Fibronectin type IIIdomain-containing protein 4 (FNDC4) constitutes a secreted factor showing a high homology in the fibronectin type III and transmembrane domains with the exercise-associated myokine irisin (FNDC5). We sought to evaluate whether FNDC4 mimics the anti-obesity effects of FNDC5/irisin in human adipose tissue.

METHODS

Plasma and adipose tissue samples of 78 patients with morbid obesity undergoing bariatric surgery and 26 normal-weight individuals were used in the present study.

RESULTS

Plasma FNDC4 was decreased in patients with morbid obesity, related to obesity-associated systemic inflammation and remained unchanged six months after bariatric surgery. Visceral adipose tissue from patients with morbid obesity showed higher expression of FNDC4 and its putative receptor GPR116 regardless of the degree of insulin resistance. FNDC4 content was regulated by lipogenic, lipolytic and proinflammatory stimuli in human visceral adipocytes. FNDC4 reduced intracytosolic lipid accumulation and stimulated a brown-like pattern in human adipocytes, as evidenced by an upregulated expression of UCP-1 and the brown/beige adipocyte markers PRDM16, TMEM26 and CD137. Moreover, FNDC4 treatment upregulated mitochondrial DNA content and factors involved in mitochondrial biogenesis (TFAM, NRF1 and NRF2). Human FNDC4-knockdown adipocytes exhibited an increase in lipogenesis and a reduction of brown/beige-specific fat markers as well as factors involved in mitochondrial biogenesis.

CONCLUSIONS

Taken together, the novel adipokine FNDC4 reduces lipogenesis and increases fat browning in human visceral adipocytes. The upregulation of FNDC4 in human visceral fat might constitute an attempt to attenuate the adipocyte hypertrophy, inflammation and impaired beige adipogenesis in the obese state.

The Role of Exercise in the Interplay between Myokines, Hepatokines, Osteokines, Adipokines, and Modulation of Inflammation for Energy Substrate Redistribution and Fat Mass Loss: A Review

Exercise is an effective strategy for preventing and treating obesity and its related cardiometabolic disorders, resulting in significant loss of body fat mass, white adipose tissue browning, redistribution of energy substrates, optimization of global energy expenditure, enhancement of hypothalamic circuits that control appetite-satiety and energy expenditure, and decreased systemic inflammation and insulin resistance. Novel exercise-inducible soluble factors, including myokines, hepatokines, and osteokines, and immune cytokines and adipokines are hypothesized to play an important role in the body's response to exercise. To our knowledge, no review has provided a comprehensive integrative overview of these novel molecular players and the mechanisms involved in the redistribution of metabolic fuel during and after exercise, the loss of weight and fat mass, and reduced inflammation. In this review, we explain the potential role of these exercise-inducible factors, namely myokines, such as irisin, IL-6, IL-15, METRNL, BAIBA, and myostatin, and hepatokines, in particular selenoprotein P, fetuin A, FGF21, ANGPTL4, and follistatin. We also describe the function of osteokines, specifically osteocalcin, and of adipokines such as leptin, adiponectin, and resistin. We also emphasize an integrative overview of the pleiotropic mechanisms, the metabolic pathways, and the inter-organ crosstalk involved in energy expenditure, fat mass loss, reduced inflammation, and healthy weight induced by exercise.

Involvement of GPX4 in irisin's protection against ischemia reperfusion-induced acute kidney injury

Ischemia reperfusion (I/R)-induced acute kidney injury (AKI) is a common and serious condition. Irisin, an exercise-induced hormone, improves mitochondrial function and reduces reactive oxygen species (ROS) production. Glutathione peroxidase 4 (GPX4) is a key regulator of ferroptosis and its inactivation aggravates renal I/R injury by inducing ROS production. However, the effect of irisin on GPX4 and I/R-induced AKI is still unknown. To study this, male adult mice were subjected to renal I/R by occluding bilateral renal hilum for 30 min, which was followed by 24 hr reperfusion. Our results showed serum irisin levels were decreased in renal I/R mice. Irisin (250 μg/kg) treatment alleviated renal injury, downregulated inflammatory response, improved mitochondrial function, and reduced ER stress and oxidative stress after renal I/R, which were associated with upregulation of GPX4. Treated with RSL3 (a GPX4 inhibitor) abolished irisin's protective effect. Thus, irisin attenuates I/R-induced AKI through upregulating GPX4.

Irisin Recovers Osteoarthritic Chondrocytes In Vitro

Physical exercise favors weight loss and ameliorates articular pain and function in patients suffering from osteoarthritis. Irisin, a myokine released upon muscle contraction, has demonstrated to yield anabolic effects on different cell types. This study aimed to investigate the effect of irisin on human osteoarthritic chondrocytes (hOAC) in vitro. Our hypothesis was that irisin would improve hOAC metabolism and proliferation. Cells were cultured in growing media and then exposed to either phosphate-buffered saline (control group) or human recombinant irisin (experimental group). Cell proliferation, glycosaminoglycan content, type II/X collagen gene expression and protein quantification as well as p38/extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK), protein kinase B (Akt), c-Jun N-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) involvement were evaluated. Furthermore, gene expression of interleukin (IL)-1 and -6, matrix metalloproteinase (MMP)-1 and -13, inducible nitric oxide synthase (iNOS), and tissue inhibitor of matrix metalloproteinases (TIMP)-1 and -3 were investigated following irisin exposure. Irisin increased hOAC cell content and both type II collagen gene expression and protein levels, while decreased type X collagen gene expression and protein levels. Moreover, irisin decreased IL-1, IL-6, MMP-1, MMP-13 and iNOS gene expression, while increased TIMP-1 and TIMP-3 levels. These effects seemed to be mediated by inhibition of p38, Akt, JNK and NFκB signaling pathways. The present study suggested that irisin may stimulate hOAC proliferation and anabolism inhibiting catabolism through p38, Akt, JNK, and NFκB inactivation in vitro, demonstrating the existence of a cross-talk between muscle and cartilage.

Cleavage of FNDC5 and insights into its maturation process

FNDC5 corresponds to an irisin precursor that increases with exercise. Studies suggest that irisin mediates beneficial effects in adipose tissues, skeletal muscle, bone, and brain. However, the cleavage and maturation processes of FNDC5 have not been clearly identified. This study aimed to show that the signal peptide and transmembrane domain of FNDC5 were associated with the secretion of its ectodomain. Localization studies identified the signal peptide that was responsible for endoplasmic reticulum targeting activity of nascent FNDC5 and showed that the FNDC5 ectodomain corresponding to irisin could be transported across the membrane by a transmembrane domain. Analysis of cleavage constructs revealed that the ectodomain of FNDC5 could be cleaved from its signal peptide and transmembrane attachment. Genetic ablation of the signal peptide cleavage site blocked N-glycosylation of FNDC5. Identification of the FNDC5 maturation process should facilitate our understanding of irisin secretion.