Association of Serum Irisin Concentrations with Presence and Severity of Coronary Artery Disease

Inhibition of SPARC signal by aerobic exercise to ameliorate atherosclerosis

BACKGROUND AND AIMS

Inflammation and atherosclerosis (AS) are closely associated to Secreted Protein Acidic and Rich in Cysteine (SPARC) and its related factors. This study attempted to define the role and the potential mechanism of SPARC and its related factors in ameliorating hyperlipidemia and AS by aerobic exercise intervention.

METHODS

The AS rat model was established with a high-fat diet plus vitamin D3 intraperitoneal injection. Treadmill exercises training (5 days/week at 14 m/min for 60 min/day) for 6 weeks was carried out for AS rat intervention method. Western blotting and qRT-PCR were used to analyze the mRNA and protein expression of SPARC and its related factors, respectively. H&E staining was applied to evaluate the morphological changes and inflammation damage. Von Kossa staining was used to measure the degree of vascular calcification. Fluorescence immunohistochemistry staining was used to detect the expression and distribution of SPARC signal molecules.

RESULTS

SPARC was highly expressed and co-localization with the smooth muscle marker α-SMC in the AS rat. And its downstream factors, NF-κB, Caspase-1, IL-1β and IL-18 were upregulated (P < 0.05 or P < 0.01), FNDC5 expression was downregulated in AS rat model. However, slight declined body weight, delayed AS progression, decreased hyperlipidemia and favorable morphology of skeletal muscle and blood vessels have been detected in AS rat with aerobic exercise intervention. Moreover, the expression of SPARC and its downstream factors were decreased (P < 0.05 or P < 0.01), while elevated the expression of FNDC5 (P < 0.01) was observed after aerobic exercise intervention.

CONCLUSIONS

This study suggested that aerobic exercise ameliorated hyperlipidemia and AS by effectively inhibiting SPARC signal, and vascular smooth muscle cells may contribute greatly to the protection of AS.

Hydrogen Sulfide and Irisin, Potential Allies in Ensuring Cardiovascular Health

Irisin is a myokine secreted under the influence of physical activity and exposure to low temperatures and through different exogenous stimuli by the cleavage of its precursor, fibronectin type III domain-containing protein 5 (FNDC5). It is mainly known for maintaining of metabolic homeostasis, promoting the browning of white adipose tissue, the thermogenesis process, and glucose homeostasis. Growing experimental evidence suggests the possible central role of irisin in the regulation of cardiometabolic pathophysiological processes. On the other side, hydrogen sulfide (H2S) is well recognized as a pleiotropic gasotransmitter that regulates several homeostatic balances and physiological functions and takes part in the pathogenesis of cardiometabolic diseases. Through the S-persulfidation of cysteine protein residues, H2S is capable of interacting with crucial signaling pathways, exerting beneficial effects in regulating glucose and lipid homeostasis as well. H2S and irisin seem to be intertwined; indeed, recently, H2S was found to regulate irisin secretion by activating the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)/FNDC5/irisin signaling pathway, and they share several mechanisms of action. Their involvement in metabolic diseases is confirmed by the detection of their lower circulating levels in obese and diabetic subjects. Along with the importance of metabolic disorders, these modulators exert favorable effects against cardiovascular diseases, preventing incidents of hypertension, atherosclerosis, heart failure, myocardial infarction, and ischemia-reperfusion injury. This review, for the first time, aims to explore the role of H2S and irisin and their possible crosstalk in cardiovascular diseases, pointing out the main effects exerted through the common molecular pathways involved.

The role of irisin in kidney diseases

Irisin is a hormone that is produced mainly by skeletal muscles in response to exercise. It has been found to have a close correlation with obesity and diabetes mellitus for its energy expenditure and metabolic properties. Recent research has revealed that irisin also possesses anti-inflammatory, anti-oxidative and anti-apoptotic properties, which make it associated with major chronic diseases, such as chronic kidney disease (CKD), liver diseases, osteoporosis, atherosclerosis and Alzheimer s disease. The identification of irisin has not only opened up new possibilities for monitoring metabolic and non-metabolic diseases but also presents a promising therapeutic target due to its multiple biological functions. Studies have shown that circulating irisin levels are lower in CKD patients than in non-CKD patients and decrease with increasing CKD stage. Furthermore, irisin also plays a role in many CKD-related complications like protein energy wasting (PEW), cardiovascular disease (CVD) and chronic kidney disease-mineral and bone disorder (CKD-MBD). In this review, we present the current knowledge on the role of irisin in kidney diseases and their complications.

Irisin and Cardiometabolic Disorders in Obesity: A Systematic Review

Background

Overweight and obesity are global health issues, impacting a significant portion of young adults. Obesity is a complex condition influenced by genetics and environmental factors, leading to increased susceptibility to cardiovascular diseases (CVDs), hypertension, dyslipidemia, and insulin resistance. Irisin, a protein derived from the cleavage of fibronectin type III domain-containing protein 5, may have relationship with these cardiometabolic diseases.

Objective

This systematic review aims to examine the relationship between serum irisin levels and obesity, particularly in individuals predisposed to cardiovascular risk factors.

Methods

A thorough literature search was conducted in multiple databases, including "Science Direct," "Scopus," "PubMed," and "Lilacs," from July 2020. Inclusion criteria encompassed subjects with metabolic disorders (with or without obesity, BMI ≥30 kg/m2), clinical trials, and observational studies published between 2010 and June 2020. Exclusion criteria were animal studies, meta-analyses, systematic reviews, studies evaluating only healthy subjects, and those investigating disorders beyond cardiometabolic diseases.

Results

Out of 151 identified articles, 30 met the inclusion criteria. These studies, published between 2013 and 2020, assessed adults (≥21 years) and included 26 observational studies and 4 clinical trials (n = 7585 subjects). All studies examined irisin's role in obesity and CVDs, often including associated diseases such as type 2 diabetes and hypertension. Despite varying sample sizes, the samples within the articles were homogeneous. Observational studies exhibited a low risk of bias in at least 60% of the evaluated domains. Clinical trials demonstrated a low risk of bias in at least 50% of the domains. Limitations. Although the systematic review provides valuable insights, it is limited by the available literature and the varying methodologies used across studies.

Conclusion

The review suggests that irisin plays a significant role as both a preventive measure and a biomarker for comorbidities linked to obesity and cardiometabolic disorders. Future research should focus on standardized irisin measurement methods and diverse populations to further elucidate its mechanisms of action.

The relationship of circulating neuregulin 4 and irisin, and traditional and novel cardiometabolic risk factors with the risk and severity of coronary artery disease

BACKGROUND AND AIMS

Neuregulin 4 (NRG4) and irisin are adipokines that have been suggested to be associated with cardiometabolic risk factors and coronary artery disease (CAD), but the data are inconclusive. This study aimed to investigate the relationship between circulating NRG4 and irisin and cardiometabolic risk factors with CAD risk and severity.

METHODS AND RESULTS

In this cross-sectional study, the presence of CAD and the severity of stenosis (gensini score) were documented based on coronary angiography in 166 adults. Circulating NRG4 and irisin, glucose homeostasis markers, hs-CRP, lipid profiles, blood pressure, and anthropometric measurements were assessed as well. Age (p = 0.005), sex (p = 0.008), SBP (p = 0.033), DBP (p = 0.04), MAP (p = 0.018), FBG (p = 0.012), insulin (p = 0.039) and HOMA-IR (p = 0.01) were significantly associated with odds of having CAD. The final logistic regression model showed that age, sex, HOMA-IR, and MAP were the most important determinants of having CAD. There were no significant associations between circulating irisin and NRG4 with odds of having CAD. The final general linear model showed that being men (β = 17.303, 95% CI: 7.086-27.52, P = 0.001), age (Aβ = 0.712, 95% CI: 0.21-1.214, P = 0.006), HOMA-IR (Aβ = 2.168, 95% CI: 0.256 to 4.079, P = 0.027), and NRG4 level (β = 1.836, 95% CI: 0.119-3.553, P = 0.036) were directly associated with higher gensini score. Participants with the three-vessel disease had a mean increase of about 5 units in circulating irisin compared to those with no clinical CAD (β = 5.221, 95% CI: 0.454-9.987, p = 0.032).

CONCLUSIONS

This study showed that the adipokines NRG4 and Irisin might be associated with the severity of coronary stenosis.

Circulating and/or cutaneous irisin resistance: A novel link among androgenetic alopecia, comorbid metabolic syndrome and cardiovascular risks

BACKGROUND

Androgenetic alopecia (AGA) is a common cause of hair loss in both genders that may be associated with disturbed systemic metabolism. Irisin is a hormone-like myokine that greatly influences systemic metabolism and is linked to cardiovascular diseases.

AIM

To detect irisin role in AGA and its associated metabolic syndrome (MetS) and cardiovascular risk.

PATIENTS/METHODS

This case-control study included 44 AGA patients of both genders and 22 healthy individuals. Serum irisin level was measured using ELISA and scalp biopsy was taken to detect irisin immunohistochemically. Carotid Doppler ultrasonography was performed to measure carotid intima media thickness (CIMT).

RESULTS

Higher serum irisin was significantly detected in AGA patients (p ˂ 0.001), and in males (p = 0.01) particularly severe cases (p ˂ 0.001). It was significantly higher in AGA patients presenting with MetS and those suffering from dyslipidemia (p ˂ 0.001 for both). Multivariate regression analysis proved BMI (p = 0.01) and serum irisin (p = 0.02) as independent predictors of CIMT abnormality among AGA patients. Regarding cutaneous irisin expression, the epidermal H-score was significantly higher in AGA patients with MetS compared to those without (p = 0.04). Epidermal H-score ˃100 was significantly associated with male gender (p = 0.05), severe AGA (p = 0.02), MetS (p = 0.03), dyslipidemia (p = 0.03), and abnormal CIMT (p = 0.03).

CONCLUSION

High serum irisin and upregulated epidermal irisin expression are associated with the incidence of MetS, dyslipidemia, and CIMT abnormality among AGA patients. This may indicate resistance to irisin, which hinders its favorable cardiometabolic actions. Further studies are warranted to investigate the concept of irisin resistance in AGA patients, which was uniquely discussed in the present study.

Serum Irisin Levels Are Inversely Correlated With the Severity of Coronary Artery Disease Confirmed by Coronary Angiography: A Comparative Cross-Sectional Study

Introduction Irisin, a newly discovered myokine, has been reported for its role in coronary artery disease (CAD), which is a major cause of mortality worldwide. Atherosclerosis is the primary cause of CAD. Irisin has been reported to reduce atherosclerosis by improving endothelial function and inhibiting inflammation via iNOS/NF-κB pathways. We sought to investigate the relationship between serum irisin levels and the severity of CAD that is confirmed with coronary angiography. Methods A comparative cross-sectional study was designed between the Chemical Pathology and Cardiology departments at KEMU/Mayo Hospital in Lahore, Pakistan. Patients were divided into group A with mild CAD (<50% stenosis) and group B with moderate-severe CAD (>50% stenosis). Serum was collected from venous blood, and irisin levels were analyzed by ELISA. Inclusion criteria: patients with stable CAD. Exclusion criteria: History of coronary artery bypass grafting (CABG), acute coronary syndrome (ACS), active or chronic infection, hepatic or renal dysfunction. Results The mean + SD age (years) of patients in group B (57.0±9.5) was significantly higher than group A (50.0±13.7). Irisin levels (μg/ml) were significantly higher in group A (15.3±4.6) than in group B (9.3±2.4). Irisin levels were significantly negatively correlated with the severity of CAD (% stenosis). Conclusion Serum irisin levels are low in patients with moderate to severe CAD, and they are negatively correlated with the severity of CAD (% stenosis).

Irisin expression and FNDC5 (rs3480) gene polymorphism in type 2 diabetic patients with and without CAD

BACKGROUND

Irisin was found to correlate with coronary artery disease (CAD) in diabetic patients. This study investigated the association of irisin and FNDC5 (SNP rs3480) with the presence and severity of CAD in T2DM.

METHODS

This cross-sectional study included 100 patients with T2DM divided into two groups, DM group (n = 50), including patients without CAD and CAD group (n = 50), including those confirmed to have CAD by coronary angiography. Irisin was measured. SNP rs3480 genotyping of FNDC5 was done.

RESULTS

Irisin levels were significantly lower in the CAD group (p < 0.001). The CAD group had significantly higher HbA1c and lower HDL (p < 0.001). Patients with controlled DM had significantly higher irisin levels (p < 0.001). single nucleotide polymorphism (SNP) rs3480 was not associated with irisin levels, and the FNDC5 rs3480 AA reference allele was significantly associated with significant CAD.

CONCLUSION

Irisin appears to be protective against developing CAD in diabetic patients. Irisin level was an independent predictor of significant CAD in diabetic patients combined with the FNDC5 rs3480 genotype.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04957823.

Irisin inhibits NLRP3 inflammasome activation in HG/HF incubated cardiac microvascular endothelial cells with H/R injury

PURPOSE

NLRP3 inflammasome mediates myocardial ischemia/reperfusion (MI/R) injury and diabetic vascular endothelia dysfunction. However, the role of NLRP3 inflammasome in MI/R injury with diabetes has not been fully described. Irisin plays an important role in anti-inflammation and improves endothelial function in type 2 diabetes. The current study aimed to investigate the effect of irisin on regulating NLRP3 inflammasome activation in diabetic vascular endothelia dysfunction.

METHODS

Cardiac microvascular endothelial cells (CMECs) were cultured and subjected to high glucose/high fat (HG/HF) receiving hypoxia/reoxygenation (H/R) with irisin incubation or not. Then, apoptosis, viability, migration, NO secretion, and inflammasome activation were examined.

RESULTS

The hypoxic CMECs exhibited increased apoptosis, impaired viability, and migration, even decreased NO secretion and enhanced inflammasome activation. Moreover, irisin incubation decreased NLRP3 activation and attenuated cell injury in HG/HF cultured CMECs subjected to H/R injury, which was abolished by NLRP3 inflammasome activation. Meanwhile, NLRP3 inflammasome siRNA also attenuated H/R injury in CMECs under HG/HF condition.

CONCLUSION

The current study demonstrated for the first time that irisin inhibits NLRP3 inflammasome activation in CMECs as a novel mechanism in myocardial ischemia/reperfusion injury in diabetes.

Irisin, an Effective Treatment for Cardiovascular Diseases?

Irisin, as one of the myokines induced by exercise, has attracted much attention due to its important physiological functions such as white fat browning, the improvement in metabolism, and the alleviation of inflammation. Despite the positive role that irisin has been proven to play in the prevention and treatment of cardiovascular diseases, whether it can become a biomarker and potential target for predicting and treating cardiovascular diseases remains controversial, given the unreliability of its detection methods, the uncertainty of its receptors, and the species differences between animals and humans. This paper was intended to review the role of irisin in the diagnosis and treatment of cardiovascular diseases, the potential molecular mechanism, and the urgent problems to be solved in hopes of advancing our understanding of irisin as well as providing data for the development of new and promising intervention strategies by discussing the causes of contradictory results.

Irisin as a Novel Biomarker of Subclinical Atherosclerosis, Cardiovascular Risk and Severe Disease in Axial Spondyloarthritis

Introduction

Patients with axial spondyloarthritis (axSpA) have a high disease burden mainly due to the rheumatic disease itself, and also exhibit accelerated atherosclerosis, that leads to a higher incidence of cardiovascular (CV) disease. Accordingly, the identification of biomarkers of CV risk and inflammation in axSpA patients is clinically relevant. In this sense, given the beneficial functions exerted by the adipomyokine irisin in processes related to CV disease and inflammation, our aim was to assess, for the first time, the role of irisin as a genetic and serological biomarker of subclinical atherosclerosis, CV risk and disease severity in axSpA patients.

Methods

A large cohort of 725 Spanish patients with axSpA was included. Subclinical atherosclerosis (presence of plaques and abnormal carotid intima-media thickness values) was evaluated by carotid ultrasound. Four irisin polymorphisms (rs16835198 G/T, rs3480 A/G, rs726344 G/A, and rs1570569 G/T) were genotyped by TaqMan probes. Additionally, serum irisin levels were determined by ELISA.

Results

Low irisin levels were linked to the presence of plaques (p=0.002) and atherogenic index values ≥4 (p=0.01). Serum irisin were positively correlated with C-peptide levels (p<0.001) and negatively correlated with visual analogue scale and Bath Ankylosing Spondylitis Metrology Index (p<0.05 in all the cases). Moreover, lower irisin levels were observed in patients with sacroiliitis and in those with a negative HLA-B27 status (p<0.001 and p=0.006, respectively), as well as in those treated with non-steroidal anti-inflammatory drugs and conventional disease-modifying antirheumatic drugs (p<0.001 and p=0.002, respectively). Interestingly, the TT genotype and the T allele of rs16835198 were less frequent in axSpA patients with ASDAS >2.1 (Odds Ratio (OR): 0.48 [0.28-0.83] and OR: 0.73 [0.57-0.92], respectively, p=0.01 in both cases). Additionally, the frequency of rs1570569 T allele was higher in these patients (OR: 1.46 [1.08-1.97], p=0.01). Furthermore, the GGGT haplotype was more frequent in patients with ASDAS values >2.1 (OR: 1.73 [1.13-2.66], p=0.01).

Conclusions

Our results indicate that low serum irisin levels could be indicators of the presence of subclinical atherosclerosis, high CV risk and more severe disease in axSpA patients. In addition, irisin may also constitute a genetic biomarker of disease activity in axSpA.

Irisin is an Effector Molecule in Exercise Rehabilitation Following Myocardial Infarction (Review)

Background: Regular exercise is an effective non-pharmacological therapy for treatment and prevention of cardiovascular disease (CVD). The therapeutic benefits of exercise are mediated partly through improved vascular and increase in metabolic health. Release of exercise-responsive myokines, including irisin, is associated with beneficial effects of exercise in CVD patients.

Observations: The present review provides an overview of the role of exercise in cardiac rehabilitation of patients with myocardial infarction (MI). Further, the role of irisin as a motion-responsive molecule in improving vascular and metabolic health is explored. Possible mechanism of cardioprotective effect of irisin-mediated exercise on myocardial infarction are also summarized in this review.

Conclusion and significance of the review: Irisin is associated with reduced inflammation, antioxidant properties, and anti-apoptotic effect, implying that it is a potential key mediator of the beneficial effects of exercise on vascular and metabolic health. The findings show that irisin is a promising therapeutic target for treatment of patients with cardiovascular disease, particularly post-MI. Further research should be conducted to elucidate the potential mechanisms of cardioprotective effects of irisin and explored whether irisin induced by exercise exerts rehabilitation effects post-MI.

A Bibliometric Analysis of the Literature on Irisin from 2012-2021

Irisin is a hormone-like molecule mainly released by skeletal muscles in response to exercise, which is proposed to induce the ‘browning’ of white adipose tissue. Since its identification, irisin was reported to be closely associated with many metabolic diseases, including type 2 diabetes mellitus (T2DM), obesity, cardiovascular disease (CVD), and metabolic bone diseases. In recent years, irisin has attracted increasing research interest, and numerous studies have been published in this field. Thus, it is essential to identify the current research status of irisin and measure research hotspots and possible future trends. In this study, by utilizing two visualization software named CiteSpace and VOSviewer, we analyzed 1510 Web of Science publications on irisin published from 2012 to 2021. Our results show that the number of irisin-related articles published annually has increased significantly. China participates in the most studies, followed by the United States and Turkey. Firat University, Harvard University, and Shandong University are three major institutions with larger numbers of publications. The analysis of keywords co-occurrence indicates that insulin resistance, inflammation, and circulating irisin levels in serum are the research hotspots. Apoptosis, BDNF, and osteoporosis will likely become the focus of future research related to irisin. Overall, this study may provide helpful insights for researchers to understand the current research situation and identify the potential frontiers of irisin.

Association of lower serum irisin levels with diabetes mellitus: Irrespective of coronary collateral circulation, and syntax score

Objective:

Irisin is a myokine thought to be involved in the pathophysiological process of atherosclerosis with its’ cardiovascular protective effects. Patients with diabetes mellitus (DM) have lower levels of irisin. Therefore, we investigated whether there is a connection between irisin, DM, coronary collateral circulation (CCC), and SYNTAX scores representing coronary artery disease (CAD) severity.

Methods:

This study evaluated 86 patients who have at least one epicardial coronary artery with chronic total occlusion. We included Rentrop 0–1 into the poor CCC group (n=45) and Rentrop 2–3 into the good CCC group (n=41) and measured serum irisin levels.

Results:

Irisin levels did not differ (17585 [882–37741] pg/ml and (17504 [813–47683] pg/ml, p=0.772) between the two groups. Irisin levels were lower in patients with diabetes (n=41; 14485 [813–29398] pg/ml) than those without diabetes (n=45; 19724 [865–47683] pg/ml (p=0.002). Irisin was not correlated with SYNTAX scores. In multivariate analysis, DM (OR=0.463; CI: 0.184–0.783; p=0.012) was a negative predictor of good CCC development

Conclusion:

Although its level is decreased in patients with diabetes, serum irisin levels have no role in the pathophysiology of collateral development and CAD severity.

Endogenous Protective Factors and Potential Therapeutic Agents for Diabetes-Associated Atherosclerosis

The complications of macrovascular atherosclerosis are the leading cause of disability and mortality in patients with diabetes. It is generally believed that the pathogenesis of diabetic vascular complications is initiated by the imbalance between injury and endogenous protective factors. Multiple endogenous protective factors secreted by endothelium, liver, skeletal muscle and other tissues are recognized of their importance in combating injury factors and maintaining the homeostasis of vasculatures in diabetes. Among them, glucagon-like peptide-1 based drugs were clinically proven to be effective and recommended as the first-line medicine for the treatment of type 2 diabetic patients with high risks or established arteriosclerotic cardiovascular disease (CVD). Some molecules such as irisin and lipoxins have recently been perceived as new protective factors on diabetic atherosclerosis, while the protective role of HDL has been reinterpreted since the failure of several clinical trials to raise HDL therapy on cardiovascular events. The current review aims to summarize systemic endogenous protective factors for diabetes-associated atherosclerosis and discuss their mechanisms and potential therapeutic strategy or their analogues. In particular, we focus on the existing barriers or obstacles that need to be overcome in developing new therapeutic approaches for macrovascular complications of diabetes.

Inverse correlation between serum irisin and cardiovascular risk factors among Chinese overweight/obese population

Background

Irisin is a novel myokine associated with obesity, which is a traditional cardiovascular risk factor (CVRF). The present study aimed to investigate the association between serum irisin and a single CVRF as well as the clustering of CVRFs among Chinese overweight/obese population.

Methods

A total of 98 overweight and 93 obese subjects without clinical treatments were enrolled in this study. Subjects were then divided into two groups, based on the serum irisin level: a low irisin group (1.10–13.44 ng/ml) and a high irisin group (13.49–29.9 ng/ml). The clustering of CVRFs, smoking, diabetes mellitus, dyslipidemia and hypertension, was classified as 0, 1, 2 and ≥ 3 CVRFs. The demographic and baseline clinical characteristics of all participants were collected and serum irisin was measured.

Results

The high serum irisin group had significantly higher high-density lipoprotein cholesterol but lower fasting plasma glucose than the low serum irisin group. Additionally, the high serum irisin group had a significantly lower prevalence of smoking, diabetes mellitus and dyslipidemia than the low serum irisin group. Increased serum irisin was significantly associated with a reduced risk of smoking and dyslipidemia in both the unadjusted and adjusted models. Furthermore, high serum irisin significantly reduced the risk of the prevalence of 1, 2 and ≥ 3 CVRFs.

Conclusions

among the Chinese overweight/obese populations, high serum irisin is negatively associated with smoking, dyslipidemia and the clustering of CVRFs. Thus, high serum irisin is potentially associated with a low risk of cardiovascular diseases in the Chinese overweight/obese population.

The Emerging Role of Irisin in Cardiovascular Diseases

Irisin, a novel hormone like polypeptide, is cleaved and secreted by an unknown protease from a membrane‐spanning protein, FNDC5 (fibronectin type III domain‐containing protein 5). The current knowledge on the biological functions of irisin includes browning white adipose tissue, regulating insulin use, and anti‐inflammatory and antioxidative properties. Dysfunction of irisin has shown to be involved in cardiovascular diseases such as hypertension, coronary artery disease, myocardial infarction, and myocardial ischemia–reperfusion injury. Moreover, irisin gene variants are also associated with cardiovascular diseases. In this review, we discuss the current knowledge on irisin‐mediated regulatory mechanisms and their roles in the pathogenesis of cardiovascular diseases.

Fibronectin type III domain-containing 5 in cardiovascular and metabolic diseases: a promising biomarker and therapeutic target

Cardiovascular and metabolic diseases are the leading causes of death and disability worldwide and impose a tremendous socioeconomic burden on individuals as well as the healthcare system. Fibronectin type III domain-containing 5 (FNDC5) is a widely distributed transmembrane glycoprotein that can be proteolytically cleaved and secreted as irisin to regulate glycolipid metabolism and cardiovascular homeostasis. In this review, we present the current knowledge on the predictive and therapeutic role of FNDC5 in a variety of cardiovascular and metabolic diseases, such as hypertension, atherosclerosis, ischemic heart disease, arrhythmia, metabolic cardiomyopathy, cardiac remodeling, heart failure, diabetes mellitus, and obesity.

Biological Aspects of Selected Myokines in Skeletal Muscle: Focus on Aging

In the last decade, clear evidence has emerged that the cellular components of skeletal muscle are important sites for the release of proteins and peptides called "myokines", suggesting that skeletal muscle plays the role of a secretory organ. After their secretion by muscles, these factors serve many biological functions, including the exertion of complex autocrine, paracrine and/or endocrine effects. In sum, myokines affect complex multi-organ processes, such as skeletal muscle trophism, metabolism, angiogenesis and immunological response to different physiological (physical activity, aging, etc.) or pathological states (cachexia, dysmetabolic conditions, chronic inflammation, etc.). The aim of this review is to describe in detail a number of myokines that are, to varying degrees, involved in skeletal muscle aging processes and belong to the group of proteins present in the functional environment surrounding the muscle cell known as the "Niche". The particular myokines described are those that, acting both from within the cell and in an autocrine manner, have a defined relationship with the modulation of oxidative stress in muscle cells (mature or stem) involved in the regulatory (metabolic or regenerative) processes of muscle aging. Myostatin, IGF-1, NGF, S100 and irisin are examples of specific myokines that have peculiar features in their mechanisms of action. In particular, the potential role of one of the most recently characterized myokines-irisin, directly linked to an active lifestyle-in reducing if not reversing senescence-induced oxidative damage is discussed in terms of its possible application as an agent able to counteract the deleterious effects of muscle aging.

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.

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.

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 relationship between serum irisin levels and erectile dysfunction in diabetic men (irisin and erectile dysfunction in diabetic patients)

Irisin is an exercise-induced myokine that alleviates endothelial dysfunction and reduces insulin resistance in type 2 diabetes mellitus. We conducted this cross-sectional prospective study to determine the association of serum irisin levels and erectile dysfunction in type 2 diabetic patients. We compared 34 diabetic patients with erectile dysfunction with 30 diabetic patients without erectile dysfunction. In our study, serum irisin levels were found to be statistically significantly higher in diabetic patients without erectile dysfunction compared to those with erectile dysfunction (p = .016) and according to correlation analysis, irisin levels had a significantly negative correlation with the serum HbA1C value (r = -.294, p = .018). Based on the results of our study, we think that this molecule can be used in the diagnosis or treatment of erectile dysfunction in diabetic patients, if these findings are supported by larger studies.

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 and Autophagy: First Update

Aging and sedentary life style are considered independent risk factors for many disorders. Under these conditions, accumulation of dysfunctional and damaged cellular proteins and organelles occurs, resulting in a cellular degeneration and cell death. Autophagy is a conserved recycling pathway responsible for the degradation, then turnover of cellular proteins and organelles. This process is a part of the molecular underpinnings by which exercise promotes healthy aging and mitigate age-related pathologies. Irisin is a myokine released during physical activity and acts as a link between muscles and other tissues and organs. Its main beneficial function is the change of subcutaneous and visceral adipose tissue into brown adipose tissue, with a consequential increase in thermogenesis. Irisin modulates metabolic processes, acting on glucose homeostasis, reduces systemic inflammation, maintains the balance between resorption and bone formation, and regulates the functioning of the nervous system. Recently, some of its pleiotropic and favorable properties have been attributed to autophagy induction, posing irisin as an important regulator of autophagy by exercise. This review article proposes to bring together for the first time the "state of the art" knowledge regarding the effects of irisin and autophagy. Furthermore, treatments on relation between exercise/myokines and autophagy have been also achieved.

The Potential Role of Irisin in Vascular Function and Atherosclerosis: A Review

Exercise is an effective intervention for both the prevention and the treatment of obesity and insulin resistance because skeletal muscle secretes many bioactive proteins that contribute to the beneficial effect of exercise. It has been revealed that irisin plays an important role in metabolic homeostasis and both acute and chronic exercises increase circulating irisin in experimental animal models and in humans. Although previous studies have reported that the irisin-related signaling mechanism may play a beneficial role in the treatment of metabolic diseases including obesity, metabolic syndrome, insulin resistance, and diabetes mellitus, studies on whether irisin plays a key role in vascular function and vascular complications are still insufficient. Therefore, the current review aims to summarize the accumulating evidence showing the potential role of irisin, especially in vascular reactivity and vascular abnormalities such as atherosclerosis.

Aerobic exercise training-induced irisin secretion is associated with the reduction of arterial stiffness via nitric oxide production in adults with obesity

This study aimed to clarify whether muscle-derived irisin secretion induced by aerobic exercise training is involved in reduction of arterial stiffness via arterial nitric oxide (NO) productivity in obesity. In animal study, 16 Otsuka Long-Evans Tokushima Fatty (OLETF) rats with obesity were randomly divided into 2 groups: sedentary control (OLETF-CON) and 8-week aerobic treadmill training (OLETF-EX) groups. In human study, 15 subjects with obesity completed 8-week aerobic exercise training for 45 min at 60%-70% peak oxygen uptake intensity for 3 days/week. As a result of animal study, carotid-femoral pulse wave velocity (cfPWV) was decreased, and arterial phosphorylation levels of AMP-activated protein kinase (AMPK), protein kinase B (Akt), and endothelial NO synthase (eNOS), circulating levels of nitrite/nitrate (NOx) and irisin, and muscle messenger RNA expression of fibronectin type III domain containing 5 (Fndc5) were increased in the OLETF-EX group compared with OLETF-CON group. In a human study, regular aerobic exercise reduced cfPWV and elevated circulating levels of NOx and irisin. Furthermore, change in circulating irisin levels by regular exercise was positively correlated with circulating NOx levels and was negatively correlated with cfPWV. Thus, aerobic exercise training-induced increase in irisin secretion may be related to reduction of arterial stiffness achieved by NO production via activated arterial AMPK-Akt-eNOS signaling pathway in obesity. Novelty Aerobic exercise training promoted irisin secretion with upregulation of muscle Fndc5 gene expression in rats with obesity. Irisin affected the activation of arterial AMPK-Akt-eNOS signaling by aerobic exercise training. Increased serum irisin level by aerobic exercise training was associated with reduction of arterial stiffness in obese adults.

Association of the serum irisin level with obstructive sleep apnea: a body mass index- and physical activity-matched study

Obesity is strongly correlated with the pathogenesis of obstructive sleep apnea (OSA); myokines may play important roles in this condition. We performed a body mass index- (BMI) and physical activity- (PA) matched study to explore the relationship between the irisin level and OSA. Ninety-six consecutive participants were recruited. After matching in terms of BMI and PA, 28 OSA patients and 28 healthy controls were finally included. Whole-night laboratory-based polysomnography was used to identify OSA. The Recent Physical Activity Questionnaire and Epworth Sleepiness Scale Questionnaire were employed to assess PA over the past 4 weeks, and daytime sleepiness. We measured serum irisin, fasting blood glucose, and insulin levels in blood samples. The serum irisin concentrations differed significantly between the control, mild OSA, moderate OSA, and severe OSA groups (p < 0.001) and correlated significantly with the apnea/hypopnea index (AHI) (r = -0.787, p < 0.001). All of age, BMI, neck, waist and hip circumferences, fasting blood glucose level, and the Epworth Sleepiness Scale and PA scores were associated with irisin levels (p < 0.05). After adjustment for these factors, the serum irisin level was independently correlated with the AHI (r = -0.428, p = 0.002). On forward logistic regression analysis, the association remained significant in the final multiple regression model (β = -0.107, p < 0.001). The serum irisin concentration was significantly correlated with OSA severity, independently of BMI and PA. Further studies are needed to determine the molecular mechanisms in play.

Serum Irisin: Pathogenesis and Clinical Research in Cardiovascular Diseases

Recently, muscular function/dysfunction has gained importance in the maintenance of metabolic homeostasis in cardiovascular diseases. Skeletal muscle plays a vital role in coordinating the activity and metabolism of endocrine organs by secreting many myokines, especially irisin. Irisin is a polypeptide hormone consisting of 112 amino acids secreted into the blood from muscle and adipose tissues. Serum irisin levels are associated with cardiometabolic risk factors such as obesity and insulin resistance as defined by homeostatic model assessment. Irisin reduces endothelial damage by inhibiting inflammation and oxidative stress, thus playing a key role in maintaining endothelial cell function. Unsurprisingly, low irisin levels cause endothelial dysfunction and increase the incidence of atherosclerosis. We aimed to summarize the studies on this issue since we have not found any review in the literature on the role of serum irisin levels in the process of atherosclerosis and other cardiovascular events in cardiovascular diseases.

Alterations of irisin, adropin, preptin and BDNF concentrations in coronary heart disease patients comorbid with depression

Background

Depression is a well-known co-morbidity of coronary heart disease (CHD) and these two diseases share common risk mechanisms. Here, the aim of this study was to investigate the possible link between energy homeostasis regulation and CHD patients comorbid with depression.

Methods

Two hundred and nine CHD patients and 101 matched healthy individuals were included. Demographic, clinical data were collected, serum irisin, adropin, preptin and brain-derived neurotrophic factor (BDNF) levels were determined by a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), and the depression was scored by Patient Health Questionnaire-9 (PHQ-9). Correlation analysis as well as multiple linear regression was used to assess the relationship between the three peptides, BDNF serum levels and PHQ-9 scores.

Results

Irisin serum level was significantly lower in CHD patients without depression as compared with healthy controls (P=0.002), as well as adropin (P=0.000), preptin (P=0.000) and BDNF (P=0.000). Furthermore, similar trends were observed in CHD patients with depression in terms of irisin, adropin and BDNF as compared with CHD patients without depression (P=0.006; P=0.003; P=0.002; respectively). Multiple logistic regression results confirmed the contribution of irisin and BDNF to the occurrence of depression in CHD. Interestingly, correlations analysis revealed significant negative correlations between PHQ-9 scores and irisin, adropin, BDNF level (r=-0.43, P<0.01; r=-0.29, P<0.05; r=-0.45, P<0.001 respectively), and irisin serum level was positively correlated with BDNF (r=0.38, P<0.01).

Conclusions

Our study firstly identified the role of energy homeostasis in the susceptibility to depression in CHD patients, and the interaction between irisin and BDNF could trigger the imbalance of energy homeostasis that occurs in depression of CHD patients.

The association between serum irisin levels and cardiovascular disease in diabetic patients

BACKGROUND

Cardiovascular disease is the most common cause of mortality and morbidity in diabetic patients. Insulin resistance has been shown to be reduced by the secretion of irisin from muscle and adipose tissues. This study was aimed at determining the relationship between serum irisin levels and angiographically defined coronary artery disease (CAD) in type II diabetic patients.

METHODS

In this case-control study, 30 diabetic subjects with angiographically defined CAD were compared with 30 age- and sex-matched diabetic subjects without CAD in terms of clinical and laboratory parameters including serum irisin levels.

RESULTS

Serum levels of Irisin were significantly higher in the diabetic group without CAD compared with the group with CAD (P = 0.048). Serum irisin levels showed a significant positive correlation with BMI (r = 0.374, P = 0.004) and fasting insulin (r = 0.303, P = 0.021), and a significant negative correlation with diabetes duration (r = -0.384, P = 0.002). Based on the results of the binary logistic regression model, circulating levels of irisin were associated with the presence of CAD in diabetes (p = 0.038) after adjusting for potential confounders.

CONCLUSION

Serum irisin levels were lower in the diabetic patients with cardiovascular complication compared with the uncomplicated diabetic patients. Therefore, additional larger scale studies are needed to determine the role of irisin in monitoring CAD in diabetic patients.

Novel adipokines vaspin and irisin as risk biomarkers for cardiovascular diseases in type 2 diabetes mellitus

AIMS

Vaspin and irisin are novel cytokines proposed as potential new biomarkers of insulin resistance and endothelial dysfunction. This work is to investigate circulating levels of vaspin and irisin in patients with type 2 diabetes mellitus (T2DM) with and without cardiovascular disease (CVD) to study potential association with disease risk.

MATERIALS AND METHODS

Circulating levels of vaspin and irisin were assayed in serum from 135 T2DM patients (with and without CVD) and 70 control subjects by ELISA.

RESULTS

Vaspin levels were significantly higher in T2DM patients than in control subjects (6798 ± 3540 pg/ml vs. 3215 ± 3209 pg/ml, p = 0.001) and in CVD patients than in non-CVD patients (7417.3 ± 3507.6 pg/ml vs. 6017.3 ± 3606.4 pg/ml, p = 0.001), with significant positive correlations with BMI, FPG, serum insulin and HOMA-IR. Irisin levels were significantly lower in T2DM patients than in controls (71.15 ± 67.57 ng/ml vs.127 ± 71.57 ng/ml, p = 0.004), and in CVD patients than in non-CVD patients (55.77 ± 54.82 ng/ml vs. 115.5 ± 67 ng/ml, p = 0.003), with significant correlations with HbA1c, HOMA-IR and BMI in diabetic patients, and with HbA1c and TG in CVD patients. Elevated levels of vaspin was associated with 1.7 times increased CVD risk (p = 0.001, OR = 1.7, 95%CI = 1.21-2.39), while lower levels of irisin associated with 1.6 times increased CVD risk (p = 0.007, OR = 1.6, 95%CI = 1.45-2.28). ROC analysis indicated serum vaspin and irisin as independent CVD risk biomarkers with sensitivity, 94% and 73.7%, and specificity, 74% and 74.1%; respectively.

CONCLUSION

Our results indicate that circulating vaspin and irisin are potential new independent CVD risk biomarkers in T2DM.

Irisin in metabolic diseases

INTRODUCTION

Irisin is a myokine/adipokine induced by the exercise in mice and humans, which is proposed to induce "browning" of white adipose tissue, its primary target, thus increasing thermogenesis and energy expenditure. Since its identification, irisin has been linked to favorable effects on metabolic diseases, including obesity, type 2 diabetes mellitus (T2DM), lipid metabolism and cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), and metabolic bone diseases. Generally, despite the promising profile of irisin in rodents, its effects on human are less recognized.

REVIEW

Most, but not all studies show a positive association between irisin and indices of adiposity. In T2DM, NAFLD, and CVD, most observational studies reported lower irisin levels in patients than controls. Regarding metabolic bone diseases, irisin is positively associated with bone mineral density and strength in athletes, and inversely associated with osteoporotic fractures in postmenopausal osteoporosis. In PCOS, data remain largely conflicting. Irisin does not seem to be further reduced when two metabolic diseases, e.g., T2DM and NAFLD, or obesity and NAFLD exist though more data are needed. Furthermore, it seems that diverse confounders may have affected the results of different clinical studies.

CONCLUSION

Irisin remains an appealing molecule from a pathophysiological point of view and an appealing therapeutic target for metabolic diseases, albeit much research is still needed.

Association Between Oxidative Stress and Peripheral Leukocyte Telomere Length in Patients with Premature Coronary Artery Disease

Background

Leukocyte telomere length (LTL) is regarded as a potential marker of biological aging. Oxidative stress plays a major role in the rate of telomeric DNA loss. The aim of this study was to explore whether the LTL was shorter in Chinese patients with premature coronary artery disease (PCAD) than in non-CAD controls and to determine the relationship between oxidative stress and LTL shortening in this population.

Material/Methods

Patients for coronary angiography were recruited. In total, 128 patients with PCAD and 128 non-CAD controls were enrolled. Samples of circulating leukocytes and plasma were collected. The mean LTL was measured using a polymerase chain reaction-based assay and expressed as the ratio of telomere repeat copies to single-copy gene (SCG) copies (T/S ratio). Reactive oxygen species (ROS) levels and total antioxidant capacity (T-AOC) were determined in plasma.

Results

Both the T/S ratio (0.88±0.86 vs. 1.10±0.57, P=0.015) and telomere base pairs (4.97±1.37 kb vs. 5.32±0.91 kb, P=0.015) were significantly shorter in the PCAD group than in non-CAD controls. The T-AOC levels of the PCAD group were significantly lower than those of the non-CAD controls (0.482 mM [0.279, 0.603 mM]) vs. 0.778 mM [0.421, 0.924 mM], P=0.000). The ratio of T-AOC to ROS in the PCAD patients was significantly decreased compared to that of the non-CAD controls (0.1026±0. 1587 [Mm*ml/ng] vs. 0.1435±0.1946 [Mm*ml/ng], P=0.013).

Conclusion

The results point to a potential link between reduced LTLs in patients with PCAD and early onset of atherosclerosis. The decline in antioxidant capacity may play an important role in accelerating the attrition of telomeres in PCAD patients.