Irisin Alleviates Advanced Glycation End Products-Induced Inflammation and Endothelial Dysfunction via Inhibiting ROS-NLRP3 Inflammasome Signaling

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.

Anti-Inflammatory Role of the Klotho Protein and Relevance to Aging

The α-Klotho protein (hereafter Klotho) is an obligate coreceptor for fibroblast growth factor 23 (FGF23). It is produced in the kidneys, brain and other sites. Klotho insufficiency causes hyperphosphatemia and other anomalies. Importantly, it is associated with chronic pathologies (often age-related) that have an inflammatory component. This includes atherosclerosis, diabetes and Alzheimer's disease. Its mode of action in these diseases is not well understood, but it inhibits or regulates multiple major pathways. Klotho has a membrane form and a soluble form (s-Klotho). Cytosolic Klotho is postulated but not well characterized. s-Klotho has endocrine properties that are incompletely elucidated. It binds to the FGF receptor 1c (FGFR1c) that is widely expressed (including endothelial cells). It also attaches to soluble FGF23, and FGF23/Klotho binds to FGFRs. Thus, s-Klotho might be a roaming FGF23 coreceptor, but it has other functions. Notably, Klotho (cell-bound or soluble) counteracts inflammation and appears to mitigate related aging (inflammaging). It inhibits NF-κB and the NLRP3 inflammasome. This inflammasome requires priming by NF-κB and produces active IL-1β, membrane pores and cell death (pyroptosis). In accord, Klotho countered inflammation and cell injury induced by toxins, damage-associated molecular patterns (DAMPs), cytokines, and reactive oxygen species (ROS). s-Klotho also blocks the TGF-β receptor and Wnt ligands, which lessens fibrotic disease. Low Klotho is associated with loss of muscle mass (sarcopenia), as occurs in aging and chronic diseases. s-Klotho counters the inhibitory effects of myostatin and TGF-β on muscle, reduces inflammation, and improves muscle repair following injury. The inhibition of TGF-β and other factors may also be protective in diabetic retinopathy and age-related macular degeneration (AMD). This review examines Klotho functions especially as related to inflammation and potential applications.

Gold nanoparticles-conjugation of irisin enhances therapeutic effect by improving cardiac function and attenuating inflammation in sepsis

Irisin is considered to be a promising therapeutic approach for cardiac depression and inflammatory disorders. The short half-life of irisin impeded its use and drug efficacy in the treatment. This study aimed to examine if pegylated gold nanoparticles-conjugated to irisin would improve therapeutic effects in cecal ligation and puncture (CLP)-induced sepsis in mice. Recombinant irisin were conjugated to a pegylated gold nanoparticle, which was given to mice exposed to CLP. The cecal ligation procedure and sham on mice were operated and assigned to one of following five groups: (I) CLP group: The mouse models underwent the CLP surgical procedure and received only vehicle saline treatment (n = 5); (II) CLP + soluble Irisin: The mouse underwent the CLP and received an intramuscular injection (i.m) (TA) injection of 1 ug of soluble irisin into each tibialis anterior (TA) leg (n = 5); (III) CLP + Gold nanoparticle-conjugated to Irisin: The mouse models underwent the CLP and received an i.m (TA) injection of 1 µg of Gold nanoparticle-irisin via intramuscular injection (TA) into each leg (n = 5); (IV) CLP + Gold nanoparticles- conjugated to IgG: The mouse underwent the CLP and received an i.m (TA) injection of gold nanoparticles conjugated to IgG (n = 5). (V) Sham: The mouse underwent the surgical operation without conducting the CLP (n = 10). The post-operated animals were observed for one week, and survival rates were estimated. Echocardiography was performed to measure cardiac function at 12 h following CLP. TUNEL was employed to detect apoptosis in both cardiac and skeletal muscles; histology was conducted to assess tissue injury in muscles. Enzyme linked immunosorbent assay (ELISA) was conducted to examine release of interleukin 6 (IL6) and the tumor necrosis factor (TNF) alpha. Compared to the CLP control, soluble irisin treatment improved cardiac function recovery, as indicated by the fractional shortening (FS) and ejection fraction (EF). Irisin treatment exhibited reduced IL6 and TNF-alpha release in association with less apoptosis, lower muscle injury index and improved survival post-CLP. However, compared to soluble irisin treatment, gold nanoparticles-conjugated to irisin showed a significant improvement in cardiac function, suppression of apoptosis, reduced IL6 and TNF-alpha releases, decreased muscle injury and an improved survival rate of post-CLP. This study reveals that gold nanoparticles-conjugated irisin can serve to improve irisin's therapeutic effects over a longer course of treatment.

Pyroptosis of Vascular Smooth Muscle Cells as a Potential New Target for Preventing Vascular Diseases

Vascular remodeling is the adaptive response of the vessel wall to physiological and pathophysiological changes, closely linked to vascular diseases. Vascular smooth muscle cells (VSMCs) play a crucial role in this process. Pyroptosis, a form of programmed cell death characterized by excessive release of inflammatory factors, can cause phenotypic transformation of VSMCs, leading to their proliferation, migration, and calcification-all of which accelerate vascular remodeling. Inhibition of VSMC pyroptosis can delay this process. This review summarizes the impact of pyroptosis on VSMCs and the pathogenic role of VSMC pyroptosis in vascular remodeling. We also discuss inhibitors of key proteins in pyroptosis pathways and their effects on VSMC pyroptosis. These findings enhance our understanding of the pathogenesis of vascular remodeling and provide a foundation for the development of novel medications that target the control of VSMC pyroptosis as a potential treatment strategy for vascular diseases.

New insights into the roles of Irisin in diabetic cardiomyopathy and vascular diseases

Diabetes mellitus (DM) is a prevalent chronic disease in the 21st century due to increased lifespan and unhealthy lifestyle choices. Extensive research indicates that exercise can play a significant role in regulating systemic metabolism by improving energy metabolism and mitigating various metabolic disorders, including DM. Irisin, a well-known exerkine, was initially reported to enhance energy expenditure by indicating the browning of white adipose tissue (WAT) through peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) signaling. In this review, we summarize the potential mechanisms underlying the beneficial effects of Irisin on glucose dysmetabolism, including reducing gluconeogenesis, enhancing insulin energy expenditure, and promoting glycogenesis. Additionally, we highlight Irisin's potential to improve diabetic vascular diseases by stimulating nitric oxide (NO) production, reducing oxidative and nitrosative stress, curbing inflammation, and attenuating endothelial cell aging. Furthermore, we discuss the potential of Irisin to improve diabetic cardiomyopathy by preventing cardiomyocyte loss and reducing myocardial hypertrophy and fibrosis. Given Irisin's promising functions in managing diabetic cardiomyopathy and vascular diseases, targeting Irisin for therapeutic purposes could be a fruitful avenue for future research and clinical interventions.

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.

High glucose levels accelerate atherosclerosis via NLRP3-IL/ MAPK/NF-κB-related inflammation pathways

BACKGROUND

As a chronic inflammatory disease, diabetes mellitus (DM) contributes to the development of atherosclerosis (AS). However, how the NLRP3 inflammasome participates in diabetes-related AS remains unclear. Therefore, this study aimed to elucidate the mechanism through which NLRP3 uses high glucose (HG) levels to promote AS.

METHODS

Serum and coronary artery tissues were collected from coronary artery disease (CAD) patients with and without DM, respectively. The expression of NLRP3 was detected, and the effects of this inflammasome on diabetes-associated AS were evaluated using streptozotocin (STZ)-induced diabetic apoE-/- mice injected with Adenovirus-mediated NLRP3 interference (Ad-NLRP3i). To elucidate the potential mechanism involved, ox-LDL-irritated human aortic smooth muscle cells were divided into the control, high-glucose, Si-NC, and Si-NLRP3 groups to observe the changes induced by downregulating NLRP3 expression. For up-regulating NLRP3, control and plasmid contained NLRP3 were used. TNF-α, IL-1β, IL-6, IL-18, phosphorylated and total p38, JNK, p65, and IκBα expression levels were detected following the downregulation or upregulation of NLRP3 expression.

RESULTS

Patients with comorbid CAD and DM showed higher serum levels and expression of NLRP3 in the coronary artery than those with only CAD. Moreover, mice in the Ad-NLRP3i group showed markedly smaller and more stable atherosclerotic lesions compared to those in other DM groups. These mice had decreased inflammatory cytokine production and improved glucose tolerance, which demonstrated the substantial effects of NLRP3 in the progression of diabetes-associated AS. Furthermore, using the siRNA or plasmid to downregulate or upregulate NLRP3 expression in vitro altered cytokines and the MAPK/NF-κB pathway.

CONCLUSIONS

NLRP3 expression was significantly increased under hyperglycemia. Additionally, it accelerated AS by promoting inflammation via the IL/MAPK/NF-κB pathway.

The NLRP3 molecule is responsible for mediating the pyroptosis of intestinal mucosa cells and plays a crucial role in salmonellosis enteritis in chicks

Salmonella enteritis in poultry can result in reduced immune function, decreased growth rate, and increased mortality. Many farm salmonella strains have developed severe drug resistance and are less susceptible to multiple antibiotics. In the post-antibiotic era, it is of great significance to identify the mechanism of salmonella-induced enteritis in chicks to protect their health and ensure food safety. This article will elucidate the activation mechanism of NOD-like receptor protein 3 (NLRP3) inflammasomes in Salmonella enteritis and review the research on interventions targeting NLRP3 inflammasomes.

NLRP3 Inflammasome in Autoinflammatory Diseases and Periodontitis Advance in the Management

Inflammatory chemicals are released by the immune system in response to any perceived danger, including irritants and pathogenic organisms. The caspase activation and the response of inflammation are governed by inflammasomes, which are sensors and transmitters of the innate immune system. They have always been linked to swelling and pain. Research has mainly concentrated on the NOD-like protein transmitter 3 (NLRP3) inflammasome. Interleukin (IL)-1 and IL-18 are pro-inflammatory cytokines that are activated by the NOD-like antibody protein receptor 3 (NLRP3), which controls innate immune responses. The NLRP3 inflammasome has been associated with gum disease and other autoimmune inflammatory diseases in several studies. Scientists' discovery of IL-1's central role in the pathophysiology of numerous autoimmune disorders has increased public awareness of these conditions. The first disease to be connected with aberrant inflammasome activation was the autoinflammatory cryopyrin-associated periodic syndrome (CAPS). Targeted therapeutics against IL-1 have been delayed in development because their underlying reasons are poorly understood. The NLRP3 inflammasome has recently been related to higher production and activation in periodontitis. Multiple periodontal cell types are controlled by the NLRP3 inflammasome. To promote osteoclast genesis, the NLRP3 inflammasome either increases receptor-activator of nuclear factor kappa beta ligand (RANKL) synthesis or decreases osteoclast-promoting gene (OPG) levels. By boosting cytokines that promote inflammation in the periodontal ligament fibroblasts and triggering apoptosis in osteoblasts, the NLRP3 inflammasome regulates immune cell activity. These findings support further investigation into the NLRP3 inflammasome as a therapeutic target for the medical treatment of periodontitis. This article provides a short overview of the NLRP3 inflammatory proteins and discusses their role in the onset of autoinflammatory disorders (AIDs) and periodontitis.

The emerging roles of irisin in vascular calcification

Vascular calcification is a common accompanying pathological change in many chronic diseases, which is caused by calcium deposition in the blood vessel wall and leads to abnormal blood vessel function. With the progress of medical technology, the diagnosis rate of vascular calcification has explosively increased. However, due to its mechanism's complexity, no effective drug can relieve or even reverse vascular calcification. Irisin is a myogenic cytokine regulating adipose tissue browning, energy metabolism, glucose metabolism, and other physiological processes. Previous studies have shown that irisin could serve as a predictor for vascular calcification, and protect against hypertension, diabetes, chronic kidney disease, and other risk factors for vascular calcification. In terms of mechanism, it improves vascular endothelial dysfunction and phenotypic transformation of vascular smooth muscle cells. All the above evidence suggests that irisin plays a predictive and protective role in vascular calcification. In this review, we summarize the association of irisin to the related risk factors for vascular calcification and mainly explore the role of irisin in vascular calcification.

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.

Diabetes Mellitus to Accelerated Atherosclerosis: Shared Cellular and Molecular Mechanisms in Glucose and Lipid Metabolism

Diabetes is one of the critical independent risk factors for the progression of cardiovascular disease, and the underlying mechanism regarding this association remains poorly understood. Hence, it is urgent to decipher the fundamental pathophysiology and consequently provide new insights into the identification of innovative therapeutic targets for diabetic atherosclerosis. It is now appreciated that different cell types are heavily involved in the progress of diabetic atherosclerosis, including endothelial cells, macrophages, vascular smooth muscle cells, dependence on altered metabolic pathways, intracellular lipids, and high glucose. Additionally, extensive studies have elucidated that diabetes accelerates the odds of atherosclerosis with the explanation that these two chronic disorders share some common mechanisms, such as endothelial dysfunction and inflammation. In this review, we initially summarize the current research and proposed mechanisms and then highlight the role of these three cell types in diabetes-accelerated atherosclerosis and finally establish the mechanism pinpointing the relationship between diabetes and atherosclerosis.

Assessment of inter-individual variability in hamstring muscle recovery after a sport-specific sprint training in women and men

Background: Hamstring muscles are most affected by multiple sprint-based sports as a result of muscle strain during sprinting, leading to reduced performance and increased risk of injury. Therefore, the purpose of the study was to assess inter-individual variability in hamstrings recovery after a sport-specific repeated-sprint training (RST), through sprint-specific markers of muscle recovery and associated muscle damage biomarkers in women and men. Methods: Healthy females (n = 14) and males (n = 15) underwent 10 repeated 40-m sprints with a 3-min rest pause between each repetition. Force-generating capacity (FGC) by the 90° hip :20° knee test and range of motion Jurdan test, together with serum biomarkers [sarcomeric mitochondrial creatine kinase (sMtCK), oxidative stress, irisin] were tested at baseline and 24-, 48- and 72-h post-exercise through a repeated measures design. Participants were classified according to FGC loss into high responders (HR) and low responders (LR). Results: 21 individuals (10 females, 11 males) were classified as HR (FGC loss >20% and recovery >48 h), while 8 individuals (4 females, 4 males) were classified as LR. HR individuals showed unrecovered maximal voluntary isometric contraction (MVIC) torque until 72 h post-training (p = 0.003, np 2 = 0.170), whereas only HR males showed decreased range of motion (p = 0.026, np 2 = 0.116). HR individuals also showed increased sMtCK (p = 0.016, np 2 = 0.128), oxidative stress (p = 0.038, np 2 = 0.106) and irisin (p = 0.019, np 2 = 0.123). Conclusion: There is inter-individual variability in the muscular response to a sport-specific RST, identifiable by MVIC torque assessment. The findings support that the 90° hip :20° knee test is a powerful indirect test to screen hamstrings recovery in both women and men, in a cost-effective way. However, the Jurdan test might not be able to monitor hamstrings recovery in sportswomen after RST. Decreases in muscle capacity are linked to damage to muscle sarcolemma and mitochondria until 72 h post-exercise. Overall, 72 h will not be adequate time to restore hamstrings structure and function after a sport-specific RST in both female and male responders.

Irisin: A Potentially Fresh Insight into the Molecular Mechanisms Underlying Vascular Aging

Aging is a natural process that affects all living organisms, including humans. Aging is a complex process that involves the gradual deterioration of various biological processes and systems, including the cardiovascular system. Vascular aging refers to age-related changes in blood vessels. These changes can increase the risk of developing cardiovascular diseases, such as hypertension, atherosclerosis, and stroke. Recently, an exercise-induced muscle factor, irisin, was found to directly improve metabolism and regulate the balance of glucolipid metabolism, thereby counteracting obesity and insulin resistance. Based on a growing body of evidence, irisin modulates vascular aging. Adenosine monophosphate-activated protein kinase (AMPK) serves as a pivotal cellular energy sensor and metabolic modulator, acting as a central signaling cascade to coordinate various cellular processes necessary for maintaining vascular homeostasis. The vascular regulatory effects of irisin are closely intertwined with its interaction with the AMPK pathway. In conclusion, understanding the molecular processes used by irisin to regulate changes in vascular diseases caused by aging may inspire the development of techniques that promote healthy vascular aging. This review sought to describe the impact of irisin on the molecular mechanisms of vascular aging, including inflammation, oxidative stress, and epigenetics, from the perspective of endothelial cell function and vascular macroregulation, and summarize the multiple signaling pathways used by irisin to regulate vascular aging.

Adipokines in atherosclerosis: unraveling complex roles

Adipokines are biologically active factors secreted by adipose tissue that act on local and distant tissues through autocrine, paracrine, and endocrine mechanisms. However, adipokines are believed to be involved in an increased risk of atherosclerosis. Classical adipokines include leptin, adiponectin, and ceramide, while newly identified adipokines include visceral adipose tissue-derived serpin, omentin, and asprosin. New evidence suggests that adipokines can play an essential role in atherosclerosis progression and regression. Here, we summarize the complex roles of various adipokines in atherosclerosis lesions. Representative protective adipokines include adiponectin and neuregulin 4; deteriorating adipokines include leptin, resistin, thrombospondin-1, and C1q/tumor necrosis factor-related protein 5; and adipokines with dual protective and deteriorating effects include C1q/tumor necrosis factor-related protein 1 and C1q/tumor necrosis factor-related protein 3; and adipose tissue-derived bioactive materials include sphingosine-1-phosphate, ceramide, and adipose tissue-derived exosomes. However, the role of a newly discovered adipokine, asprosin, in atherosclerosis remains unclear. This article reviews progress in the research on the effects of adipokines in atherosclerosis and how they may be regulated to halt its progression.

Role of irisin in bone diseases

Bone diseases are common among middle-aged and elderly people, and harm to activities of daily living (ADL) and quality of life (QOL) for patients. It is crucial to search for key regulatory factors associated with the development of bone diseases and explore potential therapeutic targets for bone diseases. Irisin is a novel myokine that has been discovered in recent years. Accumulating evidence indicates that irisin has beneficial effects in the treatment of various diseases such as metabolic, cardiovascular and neurological disorders, especially bone-related diseases. Recent studies had shown that irisin plays the role in various bone diseases such as osteoarthritis, osteoporosis and other bone diseases, suggesting that irisin may be a potential molecule for the prevention and treatment of bone diseases. Therefore, in this review, by consulting the related domestic and international literature of irisin and bone diseases, we summarized the specific regulatory mechanisms of irisin in various bone diseases, and provided a systematic theoretical basis for its application in the diagnosis and treatment of the bone diseases.

Inhibitory potential of N-acetylaspartate against protein glycation, AGEs formation and aggregation: Implication of brain osmolyte in glycation-related complications

Protein glycation and aggregation have a pivotal role in many diseases including diabetes and neurodegenerative disorders. N-acetyl aspartate (NAA), an osmolyte derived from L-aspartic acid, is one of the most abundant metabolites in the mammalian brain. Although NAA is supposed to be a substitute for a neuronal marker, its function is not fully elucidated. Herein, we have investigated the effect of NAA on glycation, AGEs formation and aggregation of irisin. AGE-specific fluorescence showed the strong inhibition of AGEs formation in the presence of NAA, demonstrating its anti-glycating property. The aggregates present in MG-modified irisin were also reduced by NAA, which was confirmed by Thioflavin T fluorescence and fluorescence microscopy. Further, for the explanation of the strong anti-glycating potential of NAA, the interaction between irisin and NAA was also examined. Interaction studies involving steady-state fluorescence and molecular docking demonstrated that hydrogen bonding and salt bridges by NAA stabilize the irisin. It was found that glycation-prone residues i.e., lysine and arginine are specifically involved in the interaction which might prevent them from getting modified during the process of glycation. This study for the first time reported the antiglycating potential of NAA which can be implicated in the therapeutic management of various glycation-related complications.

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

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

Characterization of advanced glycation end products and aggregates of irisin: Multispectroscopic and microscopic approaches

Glycation of proteins leading to the formation of advanced glycation end products (AGEs) has been demonstrated to contribute to the pathogenesis of several diseases. Irisin is a clinically significant protein, putatively involved in obesity, diabetes, and neurological disorders. This study aimed to monitor the methyl-glyoxal (MG) induced AGEs and aggregate formation of irisin, as a function of time, employing multispectroscopic and microscopic approaches. ANS fluorescence suggested a molten globule-like state on Day 6, followed by the formation of irisin AGEs adducts, as confirmed by AGE-specific fluorescence. Glycation of irisin led to aggregate formation, which was characterized by Thioflavin T fluorescence, CD spectroscopy, and microscopic studies. These aggregates were confirmed by exploiting fluorescence microscopy, confocal, and transmission electron microscopy. Molecular docking was performed to determine the crucial residues of irisin involved in irisin-MG interaction. Usually, MG is present in trace amounts as a metabolic by-product in the body, which is found to be elevated in diseased conditions viz. diabetes and Alzheimer's disease. This study characterized the AGEs and aggregates of clinically important protein, irisin; and since MG level has been found to be increased in various pathological conditions, this study provides a clinical perspective. There is a possibility that elevated MG concentrations might glycate irisin resulting in reduced irisin levels as reported in pathological conditions. However, further investigations are required to prove it.

Effects of the Myokine Irisin on Stromal Cells from Swine Adipose Tissue

Irisin is a hormone able to reproduce some of the positive effects of physical activity and diet. Recently, we demonstrated the presence of Irisin at the ovarian level as a potential physiological regulator of follicular function. Adipose tissue is crucial for reproductive function through its metabolic activity and the production of adipokines. At present, the exact nature of adipocyte precursors is still under debate, but an important role has been assigned to the population of adipose tissue mesenchymal stromal cells (ASCs) of perivascular origin. It should be noted that, when appropriately stimulated, ASCs can differentiate into preadipocytes and, subsequently, adipocytes. Therefore, this present study was undertaken to explore the potential effect of Irisin on ASCs, known for their high differentiative potential. Since Irisin expression in ASCs was confirmed by PCR, we tested its potential effects on the main functional activities of these cells, including proliferation (BrdU uptake); metabolic activity (ATP production); redox status, evaluated as the generation of free molecules such as superoxide anion and nitric oxide; and scavenger activities, assessed as both enzymatic (superoxide dismutase) and non-enzymatic antioxidant power. Moreover, we tested the effect of Irisin on ASCs adipogenic differentiation. BrdU uptake was significantly (p < 0.001) inhibited by Irisin, while ATP production was significantly (p < 0.05) increased. Both superoxide anion and nitric oxide generation were significantly increased (p < 0.001) by Irisin, while scavenger activity was significantly reduced (p < 0.05). Irisin was found to significantly (p < 0.05) inhibit ASCs adipogenic differentiation. Taken together, the present results suggest a potential local role of Irisin in the regulation of adipose tissue function.

Low-Intensity Pulsed Ultrasound Counteracts Advanced Glycation End Products-Induced Corpus Cavernosal Endothelial Cell Dysfunction via Activating Mitophagy

Injury to corpus cavernosal endothelial cells (CCECs) is an important pathological basis of diabetes mellitus-induced erectile dysfunction (DMED), while low-intensity pulsed ultrasound (LIPUS) has been shown to improve erectile function in DMED. To further understand its therapeutic mechanism of action, in this study, we first demonstrated increased apoptosis and shedding in the CCECs of DMED patients, accompanied by significant mitochondrial injury by immunohistochemistry and electron microscopy of corpus cavernosum tissue. Next, we used advanced glycation end products (AGEs) to simulate the diabetic environment in vitro and found that AGES damaged mitochondria and inhibited angiogenesis in CCECs in a dose-dependent manner, while LIPUS treatment significantly reversed its effects. Mechanistic studies based on transcriptome sequencing showed that LIPUS significantly up-regulated LC3 and PARKIN protein levels in mitochondria, promoted mitophagy, and affected mitochondrial dynamics and reactive oxygen species (ROS) production. In addition, the protective effects of LIPUS were abrogated when mitophagy was inhibited by 3-methyladenine. In summary, LIPUS exerted potent inhibitory effects on AGES-induced CCEC failure via mitophagy, providing a theoretical basis for DMED treatment that encompasses the protection of endothelial structure and function.

Receptor for Advanced Glycation End Product, Organ Crosstalk, and Pathomechanism Targets for Comprehensive Molecular Therapeutics in Diabetic Ischemic Stroke

Diabetes mellitus, a well-established risk factor for stroke, is related to higher mortality and poorer outcomes following the stroke event. Advanced glycation end products(AGEs), their receptors RAGEs, other ligands, and several other processes contribute to the cerebrovascular pathomechanism interaction in the diabetes-ischemic stroke combination. Critical reappraisal of molecular targets and therapeutic agents to mitigate them is required to identify key elements for therapeutic interventions that may improve patient outcomes. This scoping review maps evidence on the key roles of AGEs, RAGEs, other ligands such as Leukotriene B4 (LTB4), High-mobility group box 1 (HMGB1) nuclear protein, brain-kidney-muscle crosstalk, alternate pathomechanisms in neurodegeneration, and cognitive decline related to diabetic ischemic stroke. RAGE, HMGB1, nitric oxide, and polyamine mechanisms are important therapeutic targets, inflicting common consequences of neuroinflammation and oxidative stress. Experimental findings on a number of existing-emerging therapeutic agents and natural compounds against key targets are promising. The lack of large clinical trials with adequate follow-up periods is a gap that requires addressing to validate the emerging therapeutic agents. Five therapeutic components, which include agents to mitigate the AGE-RAGE axis, improved biomarkers for risk stratification, better renal dysfunction management, adjunctive anti-inflammatory-antioxidant therapies, and innovative neuromuscular stimulation for rehabilitation, are identified. A comprehensive therapeutic strategy that features all the identified components is needed for outcome improvement in diabetic stroke patients.

Irisin promotes fracture healing by improving osteogenesis and angiogenesis

Background

Osteogenesis and angiogenesis are important for bone fracture healing. Irisin is a muscle-derived monokine that is associated with bone formation.

Methods

To demonstrate the effect of irisin on bone fracture healing, closed mid-diaphyseal femur fractures were produced in 8-week-old C57BL/6 mice. Irisin was administrated intraperitoneally every other day after surgery, fracture healing was assessed by using X-rays. Bone morphometry of the fracture callus were assessed by using micro-computed tomography. Femurs of mice from each group were assessed by the three-point bending testing. Effect of irisin on osteogenic differentiation in mesenchymal stem cells in vitro was evaluated by quantitative real-time polymerase chain reaction (qRT-PCR), alkaline phosphatase staining and alizarin red staining. Angiogenesis of human umbilical vein endothelial cells (HUVECs) were evaluated by qRT-PCR, migration tests, and tube formation assays.

Results

Increased callus formation, mineralization and tougher fracture healing were observed in the irisin-treated group than in the control group, indicating the better fracture callus healing due to Irisin treatment. The vessel surface and vessel volume fraction of the callus also increased in the irisin-treated group. The expression of BMP2, CD31, and VEGF in callus were enhanced in the irisin-treated group. In mouse bone mesenchymal stem cells, irisin promoted ALP expression and mineralization, and increased the expression of osteogenic genes, including OSX, Runx2, OPG, ALP, OCN and BMP2. Irisin also promoted HUVEC migration and tube formation. Expression of angiogenic genes, including ANGPT1, ANGPT2, VEGFb, CD31, FGF2, and PDGFRB in HUVECs were increased by irisin.

Conclusion

All the results indicate irisin can promote fracture healing through osteogenesis and angiogenesis. These findings help in the understanding of muscle–bone interactions during fracture healing.

The Translational Potential of this Article

Irisin was one of the most important monokine secreted by skeletal muscle. Studies have found that irisin have anabolic effect one bone remodeling through affecting osteocyte and osteoblast. Based on our study, irisin could promote bone fracture healing by increasing bone mass and vascularization, which provide a potential usage of irisin to promote fracture healing and improve clinical outcomes.

Irisin Promotes Osteogenesis by Modulating Oxidative Stress and Mitophagy through SIRT3 Signaling under Diabetic Conditions

Advanced glycation end products (AGEs) accumulate in the bone tissue of patients with diabetes mellitus, resulting in oxidative stress, poor bone healing, or regeneration. Irisin, a novel exercise-induced myokine, is involved in the regulation of bone metabolism. However, the effects of irisin on adipose-derived stem cell (ASC) osteogenic differentiation and bone healing under diabetic conditions remain poorly understood. ASCs were obtained from inguinal fat of Sprague-Dawley rats and treated with different concentrations of AGEs and irisin. Cell proliferation, apoptosis, and osteogenic differentiation abilities of ASCs were detected. To explore the regulatory role of sirtuin 3 (SIRT3), ASCs were transfected with lentivirus-mediated SIRT3 overexpression or knockdown vectors. Next, we investigated mitochondrial functions, mitophagy, and mitochondrial biogenesis in different groups. Moreover, SOD2 acetylation and potential signaling pathways were assessed. Additionally, a diabetic rat model was used to evaluate the effect of irisin on bone healing in calvarial critical-sized defects (CSDs) in vivo. Our results showed that irisin incubation mitigated the inhibitory effects of AGEs on ASCs by increasing cell viability and promoting osteogenesis. Moreover, irisin modulated mitochondrial membrane potential, intracellular ROS levels, mitochondrial O₂^·− status, ATP generation, complex I and IV activities, mitophagy, and mitochondrial biogenesis via a SIRT3-mediated pathway under AGEs exposure. Furthermore, in calvarial CSDs of diabetic rats, transplantation of gels encapsulating irisin-pretreated ASCs along with irisin largely enhanced bone healing. These findings suggest that irisin attenuates AGE-induced ASC dysfunction through SIRT3-mediated maintenance of oxidative stress homeostasis and regulation of mitophagy and mitochondrial biogenesis. Thus, our studies shed new light on the role of irisin in promoting the ASC osteogenesis and targeting SIRT3 as a novel therapeutic intervention strategy for bone regeneration under diabetic conditions.

Role of irisin in physiology and pathology

Irisin, out-membrane part of fibronectin type III domain-containing 5 protein (FNDC5), was activated by Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) during physical exercise in skeletal muscle tissues. Most studies have reported that the concentration of irisin is highly associated with health status. For instance, the level of irisin is significantly lower in patients with obesity, osteoporosis/fractures, muscle atrophy, Alzheimer's disease, and cardiovascular diseases (CVDs) but higher in patients with cancer. Irisin can bind to its receptor integrin αV/β5 to induce browning of white fat, maintain glucose stability, keep bone homeostasis, and alleviate cardiac injury. However, it is unclear whether it works by directly binding to its receptors to regulate muscle regeneration, promote neurogenesis, keep liver glucose homeostasis, and inhibit cancer development. Supplementation of recombinant irisin or exercise-activated irisin might be a successful strategy to fight obesity, osteoporosis, muscle atrophy, liver injury, and CVDs in one go. Here, we summarize the publications of FNDC5/irisin from PubMed/Medline, Scopus, and Web of Science until March 2022, and we review the role of FNDC5/irisin in physiology and pathology.

Irisin inhibits PCSK9 expression through activating AMPK-SREBP2 pathway

AIMS

Previous studies found that irisin attenuated the vascular wall inflammation caused by Oxidized low-density lipoprotein (ox-LDL), and recent experiments have shown that proprotein convertase subtilisin/kexin type 9 (PCSK9) can act on various cells in the vascular wall to induce inflammatory responses. But, the relationship between irisin and PCSK9 has not been reported. The aim of this study was to investigate the effect of irisin on PSCK9 in endothelial cells and hepatocytes under the induction of ox-LDL.

METHODS

Experiments were performed using human umbilical vein endothelial cells and Hep G2, and cells were treated with irisin and (or) ox-LDL for evaluating expression of PCSK9 and downstream inflammatory proteins, while the expression levels of AMP-dependent protein kinase (AMPK) and sterol-regulatory element binding protein 2 (SREBP2) were also examined. Then Compound C was used to inhibit AMPK activation and SiAMPK for silencing of AMPK mRNA, and the above assays were also performed to deeply validate the role of the AMPK-SREBP2 pathway.

RESULTS

Irisin treatment significantly downregulated the expression of PCSK9 and inflammation-related proteins induced by ox-LDL, also restored the content of p-AMPK and reduced the SREBP2 content. After the use of Compound C or SiAMPK, the content of p-AMPK was obviously decreased, and the positive effect of irisin was greatly weakened.

CONCLUSIONS

This study demonstrates that irisin suppresses PCSK9 expression through the AMPK-SREBP2 pathway and ameliorates ox-LDL-induced endothelial cells inflammation.

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.

Apigenin and apigenin-7, 4'-O-dioctanoate protect against acrolein-aggravated inflammation via inhibiting the activation of NLRP3 inflammasome and HMGB1/MYD88/NF-κB signaling pathway in Human umbilical vein endothelial cells (HUVEC)

Exposure to acrolein, one environmental and dietary pollutant, has been shown to cause inflammation. Here, we reported for the first time that acrolein aggravated lipopolysaccharide (LPS)-induced inflammation in Human umbilical vein endothelial cells (HUVEC) as evidenced by the further increased mRNA expression of three pro-inflammatory cytokines, including interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Acrolein also further increased the generation of reactive oxygen species (ROS) and decreased the activity of glutathione peroxidase (GSH-Px) in LPS-pretreated HUVEC. Moreover, acrolein treatment further increased the nucleotide oligomerization domain-like receptor protein 3 (NLRP3) and apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC) expression, caspase-1 cleavage, and downstream matures interleukin 18 (IL-18) and IL-1β level in LPS-pretreated HUVEC. Acrolein treatment also further increased the expressions of high-mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and phospho-NF-κB P65 (P-P65) in the LPS pre-treated HUVEC. Thus, acrolein aggravated LPS-induced HUVEC inflammation through induction of oxidative stress, and activation of NLRP3 inflammasome and HMGB1/MYD88/NF-κB signaling pathway. In addition, apigenin and apigenin-7, 4'-O-dioctanoate attenuated acrolein-aggravated inflammation by targeting the above signaling pathways. Our findings could help to develop potential therapeutic strategies against acrolein-enhanced inflammation.

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.

Irisin reduces inflammatory signaling pathways in inflammation-mediated metabolic syndrome

Irisin is an exercise induced myokine first shown to induce the browning of white adipose tissue (WAT) which increases energy expenditure, improves glucose tolerance, and reduces insulin resistance. Among irisin's involvement in lipid homeostasis, osteoblast proliferation, and muscle growth, it also acts as a mediator of many inflammatory pathways throughout the body. This review aims to describe the role of irisin in inflammatory processes and understand how targeting irisin can alter the inflammatory response in metabolic syndrome (MetS). The mechanisms involved in irisin's anti-inflammatory functions include reducing production of pro-inflammatory cytokines while increasing production of anti-inflammatory cytokines, reducing macrophage proliferation, inducing alternatively activated (M2-type) macrophage polarization, inhibiting pathways of increased vascular permeability, and preventing the formation of inflammasomes. While there are some contradictory results, most studies found reduced levels of irisin in MetS and type II diabetes mellitus (T2DM). Irisin treatment of cells exposed to inflammatory stimuli ameliorates the inflammatory response and promotes cellular viability. Numerous methods have been studied to increase plasma irisin levels including dietary, behavioral, and pharmaceutical. Further investigation is necessary to understand how irisin can be targeted for disease modification.

Time-dependent relationships between exercise training-induced changes in nitric oxide production and hormone regulation

Aerobic exercise training (AT) reduces aging-induced deterioration of arterial stiffness and is associated with arterial nitric oxide (NO) production via changes in apelin and adropin as NO-upregulating hormones, and asymmetric dimethylarginine (ADMA) as a NO-downregulating hormone. However, the time-dependent effects of AT on NO production via NO-regulating hormones remain unclear. This study aimed to determine whether AT-induced changes in the time course of NO production via NO-regulating hormones, participate in the AT-induced improvement in central arterial stiffening with advancing age. Methods: Thirty-three healthy Japanese middle-aged and older subjects (67 ± 1 years) were randomly divided into two groups: AT intervention and sedentary controls. Subjects in the training group completed 8-week of AT. Carotid-femoral pulse wave velocity as an index of central arterial stiffness and plasma nitrate/nitrite levels significantly changed from baseline at weeks 6 (P < 0.05) and 8 (P < 0.01). Interestingly, circulating apelin and adropin levels gradually increased during AT intervention and significantly increased from baseline at weeks 4, 6, and 8 (P < 0.01). Additionally, plasma ADMA levels significantly decreased at 8-week AT intervention (P < 0.01). These results suggest that AT-induced changes in the time course of NO production via NO-regulating hormones may participate in AT-induced improvements of central arterial stiffening with advancing age.

Caloric restriction-mimetics for the reduction of heart failure risk in aging heart: with consideration of gender-related differences

The literature is full of claims regarding the consumption of polyphenol or polyamine-rich foods that offer some protection from developing cardiovascular disease (CVD). This is achieved by preventing cardiac hypertrophy and protecting blood vessels through improving the function of endothelium. However, do these interventions work in the aged human hearts? Cardiac aging is accompanied by an increase in left ventricular hypertrophy, along with diastolic and systolic dysfunction. It also confers significant cardiovascular risks for both sexes. The incidence and prevalence of CVD increase sharply at an earlier age in men than women. Furthermore, the patterns of heart failure differ between sexes, as do the lifetime risk factors. Do caloric restriction (CR)-mimetics, rich in polyphenol or polyamine, delay or reverse cardiac aging equally in both men and women? This review will discuss three areas: (1) mechanisms underlying age-related cardiac remodeling; (2) gender-related differences and potential mechanisms underlying diminished cardiac response in older men and women; (3) we select a few polyphenol or polyamine rich compounds as the CR-mimetics, such as resveratrol, quercetin, curcumin, epigallocatechin gallate and spermidine, due to their capability to extend health-span and induce autophagy. We outline their abilities and issues on retarding aging in animal hearts and preventing CVD in humans. We discuss the confounding factors that should be considered for developing therapeutic strategies against cardiac aging in humans.

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.

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.

Irisin lowers blood pressure in Zucker diabetic rats by regulating the functions of renal angiotensin II type 1 receptor via the inhibition of the NF-κB signaling pathway

BACKGROUND

Irisin, a novel myokine, has been identified to exert a series of favorable effects on metabolic diseases, including diabetes and obesity. This study aimed to explore the effects of chronic irisin administration on blood pressure and the related underlying mechanisms in Zucker diabetic fatty (ZDF) rats.

METHODS AND RESULTS

Male ZDF rats and Zucker lean (ZL) rats received a continuous subcutaneous infusion of irisin or saline for 4 weeks. Compared with ZL counterparts, ZDF rats reported higher systolic blood pressure (SBP), severer renal inflammation, increased oxidative stress, and impaired natriuresis and diuresis; they also had an elevated AT1R expression in renal cortex and augmented candesartan-induced natriuresis and diuresis. The irisin administration lowered SBP, improved diuretic and natriuretic effects, and reduced renal inflammation and oxidative stress in ZDF rats, along with decreased renal expression of AT1R and restored candesartan-mediated natriuresis and diuresis. Further experiments showed that irisin inhibited the translocation of NF-κB from the cytosol to the nucleus and the activation of NF-κB signaling pathway, which may contribute to the reduced AT1R expression and function.

CONCLUSIONS

Irisin administration serves an anti-hypertensive role in ZDF rats by alleviating renal inflammation and oxidative stress, reducing the expression and impact of AT1R, and restoring natriuresis and diuresis. The underlying mechanism may involve the irisin-induced inhibition of the NF-κB signaling pathway.

Advanced glycation end products and their related signaling cascades in adult survivors of childhood Hodgkin lymphoma: A possible role in the onset of late complications

Hodgkin lymphoma (HL) is today one of the most curable pediatric cancers. Despite survival rates now exceeding 90%, survivors of pediatric HL are still at higher risk to develop late effects of cancer therapy. Premature aging has been proposed as a paradigm to explain the onset of long-term complications in these subjects. High levels of advanced glycation end products (AGEs), together with chronic inflammation and oxidative unbalance, have been shown to be among the main factors contributing to aging. The present study aims to evaluate glycoxydation, inflammatory status, and oxidative stress in plasma and peripheral blood mononuclear cells (PBMC) obtained from 20 adult survivors of pediatric HL and 40 age- and sex-matched healthy controls. After the isolation of PBMC and the collection of plasma, we performed the analyses of gene expression by qRT-PCR and measured inflammatory and oxidative-stress markers. AGEs plasma levels, expressed as Nϵ-carboxymethyl-lysine and methylglyoxal hydroimidazolone, were markedly higher in HL survivors than in healthy subjects. HL survivors also showed a condition of higher oxidative stress, as demonstrated by an increased expression of NADPH oxidase on PBMC. Antioxidant defenses, evaluated in terms of alpha-tocopherol, GSSG/GSH ratio and catalase plasma levels, were strongly impaired in survivors. This pro-oxidative condition led to the over-expression of both NLRP3 and NFkB genes in PBMC and, consequently, to increased plasma levels of interleukin(IL)-1β and IL-6. Finally, the expression of the receptors for AGEs in PBMC confirmed the dysregulated AGE pathways. Data show AGEs accumulation in survivors of pediatric HL. The consequent activation of the receptor for AGEs leads to the persistent activation of intracellular signaling toward inflammation. These results suggest that the co-existence of AGEs accumulation, unbalanced oxidative status, and inflammation could play a role in the onset of late complications in HL survivors.

Effect of irisin on metabolic and platelet functions in type 2 diabetic rats: role of soluble receptor of advanced glycation end products (sRAGE)

Background

Irisin is an adipomyokine with a promising potential for the treatment of metabolic disturbances and endothelial dysfunction. This study aimed to explore the effect of irisin on metabolic and platelet functions, and to explore the possible involvement of soluble receptor of advanced glycation end product (sRAGE) in the type 2 diabetes mellitus (T2DM) rat model. Thirty-three adult male albino rats were divided into three groups: normal control, vehicle-treated T2DM group, and irisin-treated T2DM. At the end of the study period, metabolic parameters, platelet count, mean platelet volume, platelet distribution width, plateletcrit, and serum sRAGE were determined.

Results

Irisin significantly improved platelet function and metabolic derangements induced by T2DM and significantly increased sRAGE. sRAGE was significantly negatively associated with platelet function parameters and some glucometabolic parameters. Additionally, mean platelet volume showed a significant predictive value for the change in serum sRAGE.

Conclusions

Irisin could have a protective role against diabetes-induced platelet dysfunction by increasing sRAGE levels, indicating the potential beneficial effects of sRAGE in the type 2 diabetic rat model.

Irisin: A Promising Target for Ischemia-Reperfusion Injury Therapy

Ischemia-reperfusion injury (IRI) is defined as the total combined damage that occurs during a period of ischemia and following the recovery of blood flow. Oxidative stress, mitochondrial dysfunction, and an inflammatory response are factors contributing to IRI-related damage that can each result in cell death. Irisin is a polypeptide that is proteolytically cleaved from the extracellular domain of fibronectin type III domain-containing protein 5 (FNDC5). Irisin acts as a myokine that potentially mediates beneficial effects of exercise by reducing oxidative stress, improving mitochondrial fitness, and suppressing inflammation. The existing literature also suggests a possible link between irisin and IRI, involving mechanisms similar to those associated with exercise. This article will review the pathogenesis of IRI and the potential benefits and current limitations of irisin as a therapeutic strategy for IRI, while highlighting the mechanistic correlations between irisin and IRI.

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.

In Vitro Evaluation of the Toxicological Profile and Oxidative Stress of Relevant Diet-Related Advanced Glycation End Products and Related 1,2-Dicarbonyls

During food processing and storage, and in tissues and fluids under physiological conditions, the Maillard reaction occurs. During this reaction, reactive 1,2-dicarbonyl compounds arise as intermediates that undergo further reactions to form advanced glycation end products (AGEs). Diet is the primary source of exogenous AGEs. Endogenously formed AGEs have been proposed as a risk factor in the pathogenesis of diet-related diseases such as diabetes, insulin resistance, cardiovascular diseases, or chronic disease. AGEs may differently contribute to the diet-related exacerbation of oxidative stress, inflammation, and protein modifications. Here, to understand the contribution of each compound, we tested individually, for the first time, the effect of five 1,2-dicarbonyl compounds 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), 3,4-dideoxyglucosone-3-ene (3,4-DGE), glyoxal (GO), and methylglyoxal (MGO) and four different glycated amino acids N-ε-(carboxyethyl)lysine (CEL), N-ε-(carboxymethyl)lysine (CML), methylglyoxal-derived hydroimidazolone-1 (MG-H1), and pyrraline (Pyrr) in a cell line of human keratinocytes (HaCaT). We found that most of the glycated amino acids, i.e., CEL, CML, and MG-H1, did not show any cytotoxicity. At the same time, 1,2-dicarbonyl compounds 3-DGal, 3,4-DGE, GO, and MGO increased the production of reactive oxygen species and induced cell death. MGO induced cell death by apoptosis, whereas 3-DGal and 3,4-DGE induced nuclear translocation of the proinflammatory NF-κB transcription pathway, and the activation of the pyroptosis-related NLRP3 inflammasome cascade. Overall, these results demonstrate the higher toxic impact of 1,2-dicarbonyl compounds on mucosal epithelial cells when compared to glycated amino acids and the selective activation of intracellular signaling pathways involved in the crosstalk mechanisms linking oxidative stress to excessive inflammation.

Dieckol Attenuated Glucocorticoid-Induced Muscle Atrophy by Decreasing NLRP3 Inflammasome and Pyroptosis

Dexamethasone (Dexa), frequently used as an anti-inflammatory agent, paradoxically leads to muscle inflammation and muscle atrophy. Receptor for advanced glycation end products (RAGE) and Toll-like receptor 4 (TLR4) lead to nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome formation through nuclear factor-κB (NF-κB) upregulation. NLRP3 inflammasome results in pyroptosis and is associated with the Murf-1 and atrogin-1 upregulation involved in protein degradation and muscle atrophy. The effects of Ecklonia cava extract (ECE) and dieckol (DK) on attenuating Dexa-induced muscle atrophy were evaluated by decreasing NLRP3 inflammasome formation in the muscles of Dexa-treated animals. The binding of AGE or high mobility group protein 1 to RAGE or TLR4 was increased by Dexa but significantly decreased by ECE or DK. The downstream signaling pathways of RAGE (c-Jun N-terminal kinase or p38) were increased by Dexa but decreased by ECE or DK. NF-κB, downstream of RAGE or TLR4, was increased by Dexa but decreased by ECE or DK. The NLRP3 inflammasome component (NLRP3 and apoptosis-associated speck-like), cleaved caspase -1, and cleaved gasdermin D, markers of pyroptosis, were increased by Dexa but decreased by ECE and DK. Interleukin-1β/Murf-1/atrogin-1 expression was increased by Dexa but restored by ECE or DK. The mean muscle fiber cross-sectional area and grip strength were decreased by Dexa but restored by ECE or DK. In conclusion, ECE or DK attenuated Dexa-induced muscle atrophy by decreasing NLRP3 inflammasome formation and pyroptosis.

Paeonol Pretreatment Attenuates Anoxia-Reoxygenation Induced Injury in Cardiac Myocytes via a BRCA1 Dependent Pathway

Breast cancer type 1 sensitive protein (BRCA1) is a well-known tumor suppressor and its role in oxidative stress has been confirmed. The purpose of this study is to evaluate whether paeonol has a protective effect on myocardial hypoxia-reoxygenation (A/R) injury, and to explore H9C2 cells through a mechanism-dependent pathway mediated by BRCA1. H9C2 cells were pretreated with paeonol (10 µM) for 18 h before hypoxia was induced to establish a cell model of myocardial ischemia/reperfusion (I/R) injury. Use commercial kits to detect antioxidant indicators, including relative oxygen content (ROS) levels, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), lactate dehydrogenase (LDH) activity, and creatine kinase (CK-MB) and nuclear factor-kappaB (NF-κB) activity. The cell viability was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction method. Real-time fluorescent quantitative PCR was used to detect BRCA1 mRNA and protein levels. The expression levels of BRCA1, NLRP3 and ACS were determined by Western blotting. In addition, the release of interleukin (IL)-1β (IL-1β), IL-6 and tumor necrosis factor-α (TNF-α) was also evaluated by an enzyme-linked immunosorbent assay (ELISA) kit. The results showed that paeonol (10 µM) can significantly improve the hypoxic A/R damage of H9C2 cells, and the BRCA1 expression of H9C2 cells pretreated with paeonol was significantly increased before A/R damage was induced. BRCA1 is widely known in breast and ovarian cancer. Our data proves that the down-regulation of BRCA1 participates in the decrease of cell viability and the decrease of CK-MB and LDH activities, and protects cells by inhibiting the production of ROS and the activation of Nod-like receptor protein 3 (NLRP3) inflammasomes and NF-κB. In conclusion, paeonol significantly improved the A/R damage of H9C2 cells induced by hypoxia through the BRCA1/ROS-regulated NLRP3 inflammasome/IL-1β and NF-κB/TNF-α/IL-6 pathways. It may be a potential drug against myocardial I/R injury.

Irisin treatment lowers levels of phosphorylated tau in the hippocampus of pre-symptomatic female but not male htau mice

AIMS

Irisin is a hormone cleaved from fibronectin type-III domain-containing protein 5 in response to exercise and may be therapeutic in Alzheimer's disease (AD). Irisin is shown to repair damage caused by midlife cardiometabolic risk factors for AD (i.e., diabetes mellitus; hypertension), prevent neural amyloid beta aggregation and reduce neuroinflammation. However, there are no investigations of irisin's effect on AD-associated tauopathy in the brain. This study begins to address this gap in knowledge.

METHODS

Transgenic htau mice that selectively develop age-related tauopathy were treated with recombinant irisin (100 µg/kg weekly i.p.) beginning at a pre-symptomatic age (4 months) to determine if irisin could prevent emergence of early neuropathology. One month later, mice were sacrificed to collect brain tissue and serum. Protein levels of ptau (serine 202), inflammatory cytokine tumour necrosis factor alpha (TNFα) and FNDC5 were quantified using capillary-based western blotting (Wes).

RESULTS

Our data show that irisin treatment significantly reduced ptau and TNFα in the hippocampus and serum of female htau mice compared to vehicle-treated controls. Irisin treatment did not alter ptau levels in male htau hippocampus and appeared to enhance both neural and systemic TNFα levels.

CONCLUSIONS

This study provides the first evidence that enhancing the endogenous hormone irisin may be therapeutic against emerging neuropathology in a tauopathy-selective AD model. This is important because there are currently no disease-modifying therapeutics available for AD, and few agents in development address the multiple disease targets irisin appears to-making irisin an intriguing therapeutic candidate for further investigation.

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

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

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.

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.