Correlation between the blood level of irisin and the severity of acute myocardial infarction in exercise-trained rats

The Role of FNDC5/Irisin in Cardiovascular Disease

Disorders of cardiomyocyte metabolism play a crucial role in many cardiovascular diseases, such as myocardial infarction, heart failure and ischemia-reperfusion injury. In myocardial infarction, cardiomyocyte metabolism is regulated by mitochondrial changes and biogenesis, which allows energy homeostasis. There are many proteins in cells that regulate and control metabolic processes. One of them is irisin (Ir), which is released from the transmembrane protein FNDC5. Initial studies indicated that Ir is a myokine secreted mainly by skeletal muscles. Further studies showed that Ir was also present in various tissues. However, its highest levels were observed in cardiomyocytes. Ir is responsible for many processes, including the conversion of white adipose tissue (WAT) to brown adipose tissue (BAT) by increasing the expression of thermogenin (UCP1). In addition, Ir affects mitochondrial biogenesis. Therefore, the levels of FNDC5/Ir in the blood and myocardium may be important in cardiovascular disease. This review discusses the current knowledge about the role of FNDC5/Ir in cardiovascular disease.

Association Between Serum Irisin Levels and ST-Segment Elevation Myocardial Infarction

Background

An acute ST-elevation myocardial infarction (STEMI) is a serious cardiovascular condition with a high risk of morbidity and mortality. Irisin is adipomyokine that is associated with various health conditions. In post-STEMI, elevated serum irisin levels are associated with more adverse cardiovascular events.

Objective

The purpose of this study was to investigate associations between the serum irisin levels and acute MI (AMI) and whether irisin may be a useful biomarker for severity of AMI in patients with STEMI. Possible correlations between serum irisin and cardiac troponin-I (cTi) levels were investigated.

Methods

A total of 90 subjects (46 control subjects and 44 STEMI patients) were included in the study. Besides demographic data, presence of diabetes mellitus and hypertension, electrocardiography (ECG) findings, blood biochemistry, cardiac biomarkers (cTi) and serum irisin levels were examined.

Results

Significantly lower heart rate (HR) and significantly higher ST-elevation and QTc interval were detected in ECG recordings in STEMI patients (p < 0.05). Serum irisin levels were significantly lower in STEMI patients compared to the control subjects (p < 0.001). The decrease in the serum irisin levels was significantly correlated with the increase in cTi levels, as well as increased QTc (p < 0.05). The sensitivity and specificity of irisin were found to be 93% and 78%, respectively.

Conclusion

Decreased irisin levels were found to be highly predictive in STEMI. In patients with STEMI, the serum irisin levels were associated with cTi levels and QTc, suggesting that irisin is a promising biomarker for AMI cases.

Circulating Irisin Level as a Biomarker for Pure Aortic Stenosis and Aortic Valve Calcification

Irisin, a myokine mainly secreted by skeletal and cardiac muscles, is actively involved in cardiovascular diseases. However, whether irisin is associated with aortic stenosis remains unknown. Two hundred ninety-three severe AS patients who underwent transcatheter aortic valve implantation were enrolled and followed-up for 35 months on average. Enzyme-linked immunosorbent assay (ELISA) was applied to measure circulating irisin levels. Patients were divided into two groups based on the median plasma irisin level. We found that high plasma irisin levels were independently associated with pure aortic stenosis (PAS) after adjusting for age, body mass index, history of peripheral vascular disease, and creatinine (OR = 3.015, 95% CI 1.775-5.119, P < 0.001). ROC curve analysis showed a significant predictive value of irisin for PAS (AUC = 0.647, 95% CI 0.583-0.711, P < 0.001). The severity of aortic valve calcification was negatively associated with plasma irisin levels (P < 0.05). In conclusion, irisin is an independent predictor for PAS and is negatively associated with the severity of aortic valve calcification.

Impact of Sustained Exogenous Irisin Myokine Administration on Muscle and Myocyte Integrity in Sprague Dawley Rats

Irisin is an exercise-induced myokine implicated as a fundamental mediator of physical activity benefits. The aim of the present study was to investigate the role of the chronic administration model of irisin on the physiological and molecular status of skeletal muscle. A total of 20 female Sprague Dawley rats (250 ± 40 g) were implanted with an irisin-loaded osmotic pump (5 µg/kg/day) for 42 days; in addition, 3 females received a single subcutaneous injection of irisin (5 µg/kg). On a weekly basis for six weeks, animals were weighed and blood samples were collected. After 42 days, hind muscle biopsies were collected for histology and gene analysis. Serum irisin, clinical biochemistry, and histopathology were quantified and evaluated. Genes encoding for different physiological muscle activities, such as oxidative stress, fatty acid metabolism, muscle hypertrophy, mitochondrial fusion, and aging were assayed. The results showed a significant reduction in body weight percentage and creatine kinase level without affecting the morphological characteristics of skeletal muscle. Significant changes were noted in genes involved in muscle physiological activity, growth, and aging, as well as genes encoding for the antioxidant system, fatty acid oxidation processes, and mitochondrial fusion. In conclusion, exogenous irisin can induce the same physiological and molecular mechanisms that might be induced by exercise.

Irisin Regulates Cardiac Responses to Exercise in Health and Diseases: a Narrative Review

Exercise has been recognized as an important non-pharmacological approach for the prevention, treatment, and rehabilitation of cardiovascular diseases, but the mechanisms of exercise in promoting cardiovascular health remain unclear. Exercise generates cardiac benefits via stimulating muscle to secret hundreds of myokines that directly enter circulation and target heart tissue. Therefore, inter-organ communication between skeletal muscle and heart may be one important regulating pattern, and such communication can occur through secretion of molecules, frequently known as myokines. Irisin, a newly identified myokine, is cleaved from fibronectin type III domain-containing protein 5 (FNDC5) and secreted by the stimulation of exercise. Recently, accumulating evidence focusing on the interaction between irisin and cardiac function has been reported. This review highlights the molecular signaling by which irisin regulates the benefits of exercise on cardiac function both in physiological and pathological process, and discusses the clinical potential of irisin in treating heart diseases. Exercise generates various cardiovascular benefits through stimulating skeletal muscle to secrete irisin. The exercise "hormone" irisin, both produced by exercise or recombinant form, exerts therapeutic effects in a group of cardiovascular disorders including heart failure, myocardial infarction, atherosclerosis and hypertension. However, the molecular mechanisms involved remain ambiguous.This review highlights the most up-to-date findings to bridge the gap between exercise, irisin and cardiovascular diseases, and discusses the potential clinical prospect of irisin.

The Role of Interventional Irisin on Heart Molecular Physiology

Irisin, encoded by the FNDC5 (fibronectin type III domain containing 5) gene, is a novel myokine that has been implicated as an essential mediator of exercise benefits. Effects of irisin on heart physiology is still ambiguous. This study aimed to evaluate the impact of exogenous administration of irisin on heart physiology and the pharmacokinetic profile of pump-administered irisin. To do so, Sprague Dawley rats were implanted with an irisin-loaded osmotic pump (5 μg/kg/day) for 42 days, and other animals were administered with single bolus subcutaneous injections of irisin (5 µg/kg). Body weights and blood samples were collected weekly for 42 days for serum irisin quantification and histopathology. Clinical biochemistry analyses were performed. Heart mRNA expression was assessed in 26 selected genes. Chronic interventional exogenous irisin significantly reduced body weight without affecting the heart myocyte size and significantly reduced creatine kinase enzyme level. Blood CBC, serum biochemistry, and heart morphology were normal. Gene expression of FNCD5, Raf1, CPT1, IGF-1, and CALCIN, encoding for heart physiology, increased while PGC1, Nox4, and Mfn1 significantly decreased. Nevertheless, irisin increased the expression of cardioprotective genes and inhibited some genes that harm heart physiology. Administration of irisin promotes myocardial functions and could be translated into clinical settings after preclinical profiling.

Irisin at the crossroads of inter-organ communications: Challenge and implications

The physiological functions of organs are intercommunicated occurring through secreted molecules. That exercise can improve the physiological function of organs or tissues is believed by secreting myokines from muscle to target remote organs. However, the underlying mechanism how exercise regulates the inter-organ communications remains incompletely understood yet. A recently identified myokine-irisin, primarily found in muscle and adipose and subsequently extending to bone, heart, liver and brain, provides a new molecular evidence for the inter-organ communications. It is secreted under the regulation of exercise and mediates the intercommunications between exercise and organs. To best our understanding of the regulatory mechanism, this review discusses the recent evidence involving the potential molecular pathways of the inter-organ communications, and the interactions between signalings and irisin in regulating the impact of exercise on organ functions are also discussed.

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.

Role of Irisin in Myocardial Infarction, Heart Failure, and Cardiac Hypertrophy

Irisin is a myokine derived from the cleavage of fibronectin type III domain-containing 5. Irisin regulates mitochondrial energy, glucose metabolism, fatty acid oxidation, and fat browning. Skeletal muscle and cardiomyocytes produce irisin and affect various cardiovascular functions. In the early phase of acute myocardial infarction, an increasing irisin level can reduce endothelial damage by inhibiting inflammation and oxidative stress. By contrast, higher levels of irisin in the later phase of myocardial infarction are associated with more cardiovascular events. During different stages of heart failure, irisin has various influences on mitochondrial dysfunction, oxidative stress, metabolic imbalance, energy expenditure, and heart failure prognosis. Irisin affects blood pressure and controls hypertension through modulating vasodilatation. Moreover, irisin can enhance vasoconstriction via the hypothalamus. Because of these dual effects of irisin on cardiovascular physiology, irisin can be a critical therapeutic target in cardiovascular diseases. This review focuses on the complex functions of irisin in myocardial ischemia, heart failure, and cardiac hypertrophy.

Exercise Training Enhances Myocardial Mitophagy and Improves Cardiac Function via Irisin/FNDC5-PINK1/Parkin Pathway in MI Mice

Myocardial infarction is the major cause of death in cardiovascular disease. In vitro and in vivo models are used to find the exercise mode which has the most significant effect on myocardial irisin/FNDC5 expression and illuminate the cardioprotective role and mechanisms of exercise-activated myocardial irisin/FNDC5-PINK1/Parkin-mediated mitophagy in myocardial infarction. The results indicated that expression of irisin/FNDC5 in myocardium could be up-regulated by different types of exercise and skeletal muscle electrical stimulation, which then promotes mitophagy and improves cardiac function and the effect of resistance exercise. Resistance exercise can improve cardiac function by activating the irisin/FNDC5-PINK1/Parkin-LC3/P62 pathway, regulating mitophagy and inhibiting oxidative stress. OPA1 may play an important role in the improvement of cardiac function and mitophagy pathway in myocardial infarction mice by irisin-mediated resistance exercise. Resistance exercise is expected to become an effective therapeutic way to promote myocardial infarction rehabilitation.

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 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.

Salivary biomarkers in cardiovascular disease: An insight into the current evidence

Cardiovascular diseases (CVDs) are the most common cause of mortality worldwide. In acute cardiovascular conditions, time is a crucial player in the outcomes of disease management. Given the ease and noninvasiveness of obtaining saliva, salivary biomarkers may provide a rapid and efficient diagnosis of CVD. Here, we reviewed the published data on the value of salivary molecules for diagnosis of CVD, especially in acute care settings. In this review, we show that some biomarkers such as salivary creatinine kinase myocardial band, C-reactive protein, troponin-1, and myoglobin exhibited promising diagnostic values that were comparable to their serum counterparts. Other molecules were also investigated and showed controversial results, including myeloperoxidase, brain natriuretic peptide, and some oxidative stress markers. Based on our review, we concluded that the clinical use of salivary biomarkers to diagnose CVD is promising; however, it is still in the early stage of development. Further studies are needed to validate these findings, determine cutoff values for diagnosis, and compare them to other established biomarkers currently in clinical use.

The Neuroprotective Effect of Irisin in Ischemic Stroke

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

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.

Irisin exerts a therapeutic effect against myocardial infarction via promoting angiogenesis

Irisin, a myokine, is cleaved from the extracellular portion of fibronectin domain-containing 5 protein in skeletal muscle and myocardium and secreted into circulation as a hormone during exercise. Irisin has been found to exert protective effects against lung and heart injuries. However, whether irisin influences myocardial infarction (MI) remains unclear. In this study we investigated the therapeutic effects of irisin in an acute MI model and its underlying mechanisms. Adult C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery and treated with irisin for 2 weeks after MI. Cardiac function was assessed using echocardiography. We found that irisin administration significantly alleviated MI-induced cardiac dysfunction and ventricular dilation at 4 weeks post-MI. Irisin significantly reduced infarct size and fibrosis in post-MI hearts. Irisin administration significantly increased angiogenesis in the infarct border zone and decreased cardiomyocyte apoptosis, but did not influence cardiomyocyte proliferation. In human umbilical vein endothelial cells (HUVEC), irisin significantly increased the phosphorylation of ERK, and promoted the migration of HUVEC detected in wound-healing and transwell chamber migration assay. The effects of irisin were blocked by the ERK inhibitor U0126. In conclusion, irisin improves cardiac function and reduces infarct size in post-MI mouse heart. The therapeutic effect is associated with its pro-angiogenic function through activating ERK signaling pathway.