Irisin Is a Potential Novel Biomarker and Therapeutic Target Against Kidney Diseases

Kidney diseases, characterized by renal dysfunction, are the leading causes of death worldwide. It is crucial to prevent and treat kidney diseases to reduce their associated morbidity and mortality. Moderate physical exercise has been recognized to be advantageous for kidney health. Irisin is an exercise-induced myokine that was identified in 2012. It plays an important role in energy and bone metabolism, oxidative stress reduction, anti-inflammatory processes, cell death inhibition, and cardiovascular protection. However, the relationship between irisin and kidney diseases have not been fully elucidated. This review explores the role of irisin as a biomarker for kidney disease diagnosis and its associated complications, as well as the mechanisms through which it participates in various cell death pathways, such as apoptosis, autophagy, pyroptosis, and ferroptosis. Furthermore, irisin secretion levels were discussed to provide a basis for kidney disease prevention and treatment avenues, as well as therapeutic guidance for developing new and promising intervention strategies. Clinical Trial Registration: None.

Rationale and Protocol of the ETERNITY-ITA Study: Use of Etelcalcetide for Preserving Vitamin K-Dependent Protein Activity-An Italian Study

Background/Objectives: Chronic kidney disease and mineral bone disorders (CKD-MBD) are frequently associated with an increased risk of both vascular calcifications (VCs) and bone fractures (BFs). The complex pathogenesis of VCs and BFs involves various factors such as calcium overload, phosphate imbalance, and secondary hyperparathyroidism. Key players, such as the vitamin K-dependent proteins (VKDPs) matrix Gla protein (MGP) and bone Gla protein (BGP), have pivotal roles both for VCs and BFs. The VIKI study highlighted that hemodialysis patients treated with calcimimetics had higher levels of total BGP and MGP compared to those untreated, suggesting a potential protective effect of these drugs on BFs and VCs beyond the beneficial effect of reducing PTH levels. Methods: ETERNITY-ITA is a multi-center, comparative effectiveness, observational, longitudinal study that will enroll 160 hemodialysis patients (80 patients treated with Etelcalcetide and 80 age- and sex-matched patients treated with calcitriol or vitamin D analogs). Nephrologists will tailor the target dose of Etelcalcetide on an individual level to achieve the KDIGO PTH target. In the Etelcalcetide-treated group, the addition of calcitriol will be allowed when required by clinical practice (for correction of hypocalcemia). Conclusions: This study will evaluate the real-world effect of Etelcalcetide on VKDP levels, such as BGP and MGP, at 3, 9, and 18 months from baseline. The resulting preservation of vascular and bone health will be assessed for the first time by examining aortic and iliac artery calcifications and vertebral fractures, respectively.

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.

Gut microbial metabolites SCFAs and chronic kidney disease

The global incidence of Chronic Kidney Disease (CKD) is steadily escalating, with discernible linkage to the intricate terrain of intestinal microecology. The intestinal microbiota orchestrates a dynamic equilibrium in the organism, metabolizing dietary-derived compounds, a process which profoundly impacts human health. Among these compounds, short-chain fatty acids (SCFAs), which result from microbial metabolic processes, play a versatile role in influencing host energy homeostasis, immune function, and intermicrobial signaling, etc. SCFAs emerge as pivotal risk factors influencing CKD's development and prognosis. This paper review elucidates the impact of gut microbial metabolites, specifically SCFAs, on CKD, highlighting their role in modulating host inflammatory responses, oxidative stress, cellular autophagy, the immune milieu, and signaling cascades. An in-depth comprehension of the interplay between SCFAs and kidney disease pathogenesis may pave the way for their utilization as biomarkers for CKD progression and prognosis or as novel adjunctive therapeutic strategies.

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 irisin in kidney diseases

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

Relationship between gut microbiota and vascular calcification in hemodialysis patients

INTRODUCTION

Vascular calcification (VC) is an independent risk factor for cardiovascular mortality in end-stage renal disease (ESRD) patients. The pathogenesis of VC is complicated and unclear. Uremic toxins produced by gut microbiota can promote VC. This study aims to identify the differences in gut microbiota between the different VC groups and the main bacteria associated with VC in hemodialysis (HD) patients in an attempt to open up new preventive and therapeutic approaches and define the probable mechanism for VC in HD patients in the future.

METHODS

A total of 73 maintenance HD patients were enrolled in this cross-sectional study. According to the abdominal aortic calcification (AAC) scores, the participants were divided into the high AAC score group and the low AAC score group. High-throughput sequencing of the gut microbiota was performed and the results were evaluated by alpha diversity, beta diversity, species correlation, and model predictive analyses.

RESULTS

The prevalence of VC was 54.79% (40/73) in the study. The majority of phyla in the two groups were the same, including Firmicutes, Actinobacteriota, Proteobacteria, and Bacteroidota. The microbial diversity in the high AAC score group had a decreasing trend (p = 0.050), and the species abundance was significantly lower (p = 0.044) than that in the low AAC score group. The HD patients with high AAC scores showed an increased abundance of Proteobacteria and decreased abundances of Bacteroidota and Synergistota at the phylum level; increased abundances of Escherichia-Shigella, Ruminococcus_gnavus_group, and Lactobacillus; and decreased abundances of Ruminococcus and Lachnospiraceae_NK4A136_group at the genus level (p<0.05). Escherichia-Shigella and Ruminococcus_gnavus_group were positively correlated with VC, and Ruminococcus, Adlercreutzia, Alistipes, and norank_f__Ruminococcaceae were negatively correlated with VC. Escherichia-Shigella had the greatest influence on VC in HD patients, followed by Ruminococcus and Butyricimonas.

CONCLUSIONS

Our results provide clinical evidence that there was a difference in gut microbiota between the different VC groups in HD patients. Escherichia-Shigella, a lipopolysaccharide (LPS)-producing bacterium, was positively correlated with VC and had the greatest influence on VC. Ruminococcus, a short-chain fatty acid (SCFA)-producing bacterium, was negatively correlated with VC and had the second strongest influence on VC in HD patients. The underlying mechanism is worth studying. These findings hint at a new therapeutic target.

Serum irisin levels are negatively associated with blood pressure in dialysis patients

Elevated blood pressure is highly prevalent among dialysis patients and is associated with high mortality. Irisin is a newly found myokine that has been indicated to be related to blood pressure regulation in animal experiments. Data regarding the effect of serum irisin levels on blood pressure in dialysis patients are limited. To identify the association between serum irisin levels and blood pressure and examine determinant factors of systolic blood pressure in dialysis patients, we recruited 300 dialysis patients at Xuanwu Hospital Capital Medical University. Serum irisin levels were assessed by enzyme-linked immunosorbent assay kits. Blood pressure was self-measured on 7 consecutive days by an automated sphygmomanometer. The Pearson correlation test showed that the natural logarithm of irisin was negatively correlated with systolic blood pressure (r = -0.462, P < 0.001) and pulse pressure (r = -0.487, P < 0.001), but not correlated with diastolic blood pressure (r = -0.022, P = 0.709). Multivariate analysis revealed that the natural logarithm of irisin (β = -0.336, P < 0.001), lean tissue mass (β = 0.164, P = 0.005), diabetes mellitus (β = 0.165, P = 0.003) and serum calcium (β = -0.135, P = 0.019) were significant determinant factors for systolic blood pressure. This study is the first to demonstrate that serum irisin levels are significantly negatively associated with blood pressure in dialysis patients. Further studies are needed to provide possible mechanisms. We demonstrated that serum irisin levels were negatively associated with blood pressure in dialysis patients, which may provide a new target for antihypertensive treatment.

Down regulation of the inverse relationship between parathyroid hormone and irisin in male vitamin D-sufficient HIV patients

PURPOSE

Infection with the human immunodeficiency virus (HIV) predisposes to endocrine disorders, manifesting as a metabolic phenotype that affects the entire adipose-musculoskeletal unit (AMS). The present cross-sectional study aimed to investigate differences in irisin and adiponectin concentrations between people living with HIV and healthy controls, as well as to explore potential correlations between the levels of the aforementioned adipokines and markers of calcium homeostasis.

METHODS

46 HIV-infected individuals and 39 healthy controls (all men) were included in the study. Anthropometric data, adipokine levels, 25-hydroxyvitamin D [(25(OH)D)] and parathyroid hormone (PTH) concentrations were evaluated in the two groups. Correlations for the relationship between adiponectin, irisin, and PTH levels were examined. The results were adjusted for several confounders, including 25(OH)D levels, anthropometry, physical activity, bone mineral density, testosterone levels, and exposure to ultraviolet B radiation.

RESULTS

Mean adiponectin concentrations were significantly lower in the HIV group compared to the control group: 5868 ± 3668 vs 9068 ± 4277 ng/mL, p = 0.011. The same was applicable to irisin concentrations: 8.31 ± 8.17 (HIV) vs 29.27 ± 27.23 (controls) ng/mL, p = 0.013. A statistically significant and negative correlation was observed between irisin and PTH in the control group (r =  - 0.591; p = 0.033). In contrast, no significant correlation was observed between PTH and irisin in the HIV group (p = 0.898).

CONCLUSION

Our results are the first to suggest a possible down regulation of the inverse relationship between PTH and irisin in HIV patients and to highlight that AMS dyshomeostasis could be involved in the development of skeletal and adipose HIV-related morbidities.

Relationship between the triglyceride-glucose index and coronary artery calcification in asymptomatic, non-diabetic patients undergoing maintenance hemodialysis

OBJECTIVE

Coronary artery calcification (CAC) is positively and independently associated with cardiovascular disease (CVD) in patients undergoing maintenance hemodialysis (MHD). Insulin resistance is independently associated with CAC and is an important risk factor for CVD. The triglyceride-glucose (TyG) index is a reliable biomarker of insulin resistance. This cross-sectional, observational study aimed to investigate the relationship between the TyG index and CAC in asymptomatic non-diabetic patients undergoing MHD.

METHODS

The quantitative coronary artery calcification score (CACS) was calculated and expressed using the Agatston score. The TyG index was calculated as ln [fasting triglyceride (mg/dL) × fasting glucose (mg/dL)/2]. Multiple Poisson regression analysis, Spearman correlation analysis, and receiver operating characteristic (ROC) curves were used to investigate the relationship between the TyG index and CAC.

RESULTS

The 151 patients were divided into three groups according to the tertiles of the TyG index. With an increase in the TyG index, the CACS significantly increased (Spearman's rho = 0.414, p < 0.001). Poisson regression analysis indicated that the TyG index was independently related to the presence of CAC (prevalence ratio, 1.281 [95% confidence interval, 1.121-1.465], p < 0.001). Furthermore, ROC curve analysis showed that the TyG index was of value in predicting the CAC in asymptomatic non-diabetic patients undergoing MHD, with an area under the curve of 0.667 (p = 0.010).

CONCLUSION

The TyG index is independently related to the presence of CAC in asymptomatic, non-diabetic patients undergoing MHD.

Irisin and Bone in Sickness and in Health: A Narrative Review of the Literature

Irisin is a hormone-like myokine produced by the skeletal muscle in response to exercise. Upon its release into the circulation, it is involved in the browning process and thermogenesis, but recent evidence indicates that this myokine could also regulate the functions of osteoblasts, osteoclasts, and osteocytes. Most human studies have reported that serum irisin levels decrease with age and in conditions involving bone diseases, including both primary and secondary osteoporosis. However, it should be emphasized that recent findings have called into question the importance of circulating irisin, as well as the validity and reproducibility of current methods of irisin measurement. In this review, we summarize data pertaining to the role of irisin in the bone homeostasis of healthy children and adults, as well as in the context of primary and secondary osteoporosis. Additional research is required to address methodological issues, and functional studies are required to clarify whether muscle and bone damage per se affect circulating levels of irisin or whether the modulation of this myokine is caused by the inherent mechanisms of underlying diseases, such as genetic or inflammatory causes. These investigations would shed further light on the effects of irisin on bone homeostasis and bone disease.

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.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Compensatory elevated serum intermedin levels are associated with increased vascular calcification in hemodialysis patients

INTRODUCTION

Vascular calcification (VC), which is a pathological process of abnormal calcium and phosphorus deposition in blood vessels, valves, heart and other tissues, is highly prevalent and predicts mortality in dialysis patients. Its mechanisms are complex and unclear. We presume that intermedin (IMD), a kind of small molecule active peptide, may play roles in VC in hemodialysis (HD) patients. This study aims to evaluate serum IMD levels and establish their relation to VC and other parameters in HD patients.

METHODS

A total of 116 patients on maintenance HD treatment and 52 age- and sex-matched healthy controls were enrolled in this study. Serum IMD levels were measured by radioimmunoassay (RIA). VC was evaluated by abdominal aortic calcification scores.

RESULTS

Serum IMD levels were significantly lower in HD patients than in controls [24.89 (13.55, 50.24) pg/ml vs. 137.79 (93.21, 201.64) pg/ml, P < 0.0001]. In addition, IMD was negatively correlated with the serum phosphate level (P = 0.036) in HD patients. However, compared with the group whose IMD levels were above the median, patients with IMD levels less than the median had a lower incidence of VC (P = 0.031). Multivariate logistic regression analyses revealed that serum IMD levels more than 24.89 pg/ml (P = 0.014, OR = 0.285), higher serum iPTH levels (P < 0.0001, OR = 1.093) and older age (P = 0.009, OR = 1.003) were significant independent determinant factors for VC in HD patients.

CONCLUSION

The serum IMD levels were significantly lower in HD patients than that in healthy group. In addition to higher PTH levels and older age, compensatory elevated IMD levels may be an independently determinant factor for VC in HD patients. This was the first study about IMD and VC in dialysis patients.

Irisin and Secondary Osteoporosis in Humans

Irisin is a peptide secreted by skeletal muscle following exercise that plays an important role in bone metabolism. Numerous experiments in vitro and in mouse models have shown that the administration of recombinant irisin promotes osteogenesis, protects osteocytes from dexamethasone-induced apoptosis, prevents disuse-induced loss of bone and muscle mass, and accelerates fracture healing. Although some aspects still need to be elucidated, such as the dose- and frequency-dependent effects of irisin in cell cultures and mouse models, ample clinical evidence is emerging to support its physiological relevance on bone in humans. A reduction in serum irisin levels, associated with an increased risk of osteoporosis and bone fractures, was observed in postmenopausal women and in both men and women during aging, Recently, cohort studies of subjects with secondary osteoporosis showed that these patients have lower circulating levels of irisin, suggesting that this myokine could be a novel marker to monitor bone quality in this disease. Although there are still few studies, this review discusses the emerging data that are highlighting the involvement of irisin in some diseases that cause secondary osteoporosis.

Muscle-bone axis in children with chronic kidney disease: current knowledge and future perspectives

Bone and muscle tissue are developed hand-in-hand during childhood and adolescence and interact through mechanical loads and biochemical pathways forming the musculoskeletal system. Chronic kidney disease (CKD) is widely considered as both a bone and muscle-weakening disease, eventually leading to frailty phenotype, with detrimental effects on overall morbidity. CKD also interferes in the biomechanical communication between two tissues. Pathogenetic mechanisms including systemic inflammation, anorexia, physical inactivity, vitamin D deficiency and secondary hyperparathyroidism, metabolic acidosis, impaired growth hormone/insulin growth factor 1 axis, insulin resistance, and activation of renin-angiotensin system are incriminated for longitudinal uncoordinated loss of bone mineral content, bone strength, muscle mass, and muscle strength, leading to mechanical impairment of the functional muscle-bone unit. At the same time, CKD may also interfere in the biochemical crosstalk between the two organs, through inhibiting or stimulating the expression of certain osteokines and myokines. This review focuses on presenting current knowledge, according to in vitro, in vivo, and clinical studies, concerning the pathogenetic pathways involved in the muscle-bone axis, and suggests approaches aimed at preventing bone loss and muscle wasting in the pediatric population. Novel therapeutic targets for preserving musculoskeletal health in the context of CKD are also discussed.

Circulating irisin level in chronic kidney disease patients: a systematic review and meta-analysis

BACKGROUND

Irisin is not only a myokine but also an adipokine that is critical in many diseases including in the development of such diseases as obesity, diabetes mellitus, metabolic syndrome, coronary artery disease, and chronic inflammation. However, the association between irisin and chronic kidney disease (CKD) is unclear. This systematic review aimed to assess circulating irisin levels in patients with CKD and compare them with those in non-CKD patients.

METHODS

PubMed, EMBASE, CENTRAL, ISI Web of Science, and CNKI were searched to identify observational studies of circulating irisin levels in patients with CKD. Two reviewers independently searched the databases and screened studies according to the inclusion criteria. Data were extracted using a standardized collection form. Meta-analysis was performed to compare the differences in circulating irisin levels between CKD and non-CKD patients.

RESULTS

A total of 9 studies (6 cross-sectional and 3 case controls) involving 859 CKD patients and 393 non-CKD individuals were selected. The pooled data indicated that circulating irisin concentrations were significantly lower in CKD nondialysis patients (WMD = - 84.79, 95% CI - 170.23, 0.50; p < 0.05), peritoneal dialysis patients (WMD = - 235.81, 95% CI - 421.99, - 49.62; p = 0.01), and hemodialysis patients (WMD = - 217.46, 95% CI - 381.35, - 53.57; p = 0.009) than in healthy controls.

CONCLUSIONS

This study confirmed that irisin levels were decreased in patients with CKD. Moreover, circulating irisin levels were lower in dialysis patients than in nondialysis patients.

Cardiometabolic Effects of Irisin in Patients with End-Stage Renal Disease on Regular Hemo- or Peritoneal Dialysis

INTRODUCTION

Data on the role of irisin in vascular calcification in patients with end-stage renal diseases on regular dialysis are inconsistent, and the underlying mechanisms are not clearly defined. The present study was designed to explore the association of serum irisin with vascular stiffness and with the impact of well-established risk factors.

METHODS

The clinical study enrolled 52 hemodialysis (HD) and 15 continuous ambulatory peritoneal dialysis (PD) patients with an age of >18 years receiving dialysis therapy for >3 months. Patients who had major pathologies affecting carbohydrate, lipid, and bone metabolism and those who had acute cardiovascular events were excluded. Thirty-seven healthy subjects matched for age and sex served as controls. Routine biochemical parameters were measured in fasting serum samples by standard methods. Serum irisin was determined using the commercial ELISA kit (BioVendor Laboratory Medicine Inc., Brno, Czech Republic). Arterial stiffness parameters - carotid-femoral pulse wave velocity (cf PWV) and augmentation index (Aix) - were measured using applanation tonometry (SphygmoCor System; AtCor Medical, Sydney, Australia). Body composition was assessed by segmental bioelectric impedance (InBody 2.0; Biospace Co. Ltd., Seoul, Korea).

RESULTS

It was demonstrated that serum irisin levels were markedly depressed (p < 0.05), while the cf PWV significantly increased (p < 0.05) in HD/PD patients as compared to controls. Serum irisin proved to be independent of serum insulin, glucose, and HOMA-IR. However, it was inversely related to HbA1c (β = -0.544, p = 0.035), iPTH (β = -0.260, p = 0.035), and alkaline phosphatase (r = -0.325, p = 0.007). Furthermore, significant negative relationships were found of irisin to serum triglyceride and indices of body fat mass. Retrospective analysis at a follow-up period of 40 months revealed a direct relationship of irisin to all-cause mortality (p = 0.039).

CONCLUSIONS

Our study demonstrated that serum irisin levels are reduced in uremic patients on regular HD/PD but failed to establish significant associations of irisin deficiency with vascular stiffness. However, the significant negative relationship of irisin to HbA1c, iPTH, and alkaline phosphatase suggests that it improves insulin sensitivity, inhibits bone resorption, mitigates bone-vascular interaction, and protects vascular function.

Gender-Related Differences in Chronic Kidney Disease-Associated Vascular Calcification Risk and Potential Risk Mediators: A Scoping Review

Vascular calcification (VC) involves the deposition of calcium apatite in vascular intima or media. Individuals of advanced age, having diabetes mellitus or chronic kidney disease (CKD) are particularly at risk. The pathogenesis of CKD-associated VC evolves considerably. The core driver is the phenotypic change involving vascular wall constituent cells toward manifestations similar to that undergone by osteoblasts. Gender-related differences are observed regarding the expressions of osteogenesis-regulating effectors, and presumably the prevalence/risk of CKD-associated VC exhibits gender-related differences as well. Despite the wealth of data focusing on gender-related differences in the risk of atherosclerosis, few report whether gender modifies the risk of VC, especially CKD-associated cases. We systematically identified studies of CKD-associated VC or its regulators/modifiers reporting data about gender distributions, and extracted results from 167 articles. A significantly higher risk of CKD-associated VC was observed in males among the majority of original investigations. However, substantial heterogeneity exists, since multiple large-scale studies yielded neutral findings. Differences in gender-related VC risk may result from variations in VC assessment methods, the anatomical segments of interest, study sample size, and even the ethnic origins of participants. From a biological perspective, plausible mediators of gender-related VC differences include body composition discrepancies, alterations involving lipid profiles, inflammatory severity, diversities in matrix Gla protein (MGP), soluble Klotho, vitamin D, sclerostin, parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), and osteoprotegerin levels. Based on our findings, it may be inappropriate to monotonously assume that male patients with CKD are at risk of VC compared to females, and we should consider more background in context before result interpretation.

Serum Irisin May Predict Cardiovascular Events in Elderly Patients With Chronic Kidney Disease Stage 3-5

OBJECTIVE

Irisin is a circulating myokine released from skeletal muscles after physical exercise. Irisin production decreases during the course of chronic kidney disease (CKD) as a potential consequence of sarcopenia and physical inactivity.

METHODS

This observational study explored the relationship of serum irisin with cardiovascular outcome in 79 patients with stage 3-5 CKD.

RESULTS

Serum irisin was significantly higher in healthy subjects (n = 20) than that in CKD patients (7 ± 2 vs. 3.1 ± 0.9 μg/mL; P = .0001) and was higher in patients with CKD stage 3 (3.2 ± 1 μg/mL) than in patients at stage 4 and 5 taken together (n = 36, 2.8 ± 0.7 μg/mL, P = .05). Patients in the lowest serum irisin tertile had lower serum 1,25(OH)₂D levels (21 ± 11 pg/mL) than patients in the middle (30 ± 13 pg/mL; P = .005) and the highest tertile (27 ± 14 pg/mL; P = .047). Patients in the highest tertile had lower Kauppila score (10.6 ± 6.9) than patients in the middle (11.8 ± 5.5; P = .007) and the lowest tertile (6.9 ± 6.8; P = .043). Twenty patients suffered from cardiovascular events during a 3-year follow-up. A Cox regression model using age, body weight, presence of diabetes mellitus, gender, Kauppila calcification score, serum values of FGF23 (as logarithm), phosphate, sclerostin, albumin and cholesterol, estimated glomerular filtration rate, and serum irisin tertiles as covariates showed that patients in the highest tertile of serum irisin had a lower cardiovascular risk than patients in the middle tertile (B, 2.38; odds ratio, 10.8; 95% confidence interval, 1.65-58.13; P = .013) or in the lowest tertile (B, 1.61; odds ratio, 5; 95% confidence interval, 1.09-22.83; P = .038).

CONCLUSIONS

These findings suggest that serum irisin may be a marker of cardiovascular outcome in patients with CKD.

Lower Serum Irisin Levels Are Associated with Increased Abdominal Aortic Calcification in Peritoneal Dialysis Patients

Introduction

Vascular calcification (VC), with the mechanisms remaining unclear, is closely related with dialysis patients' cardiovascular mortality and all-cause mortality. Irisin is a newly identified myokine. This study aims to evaluate the serum irisin levels of peritoneal dialysis (PD) patients and their relationship with VC.

Methods

This cross-sectional study enrolled stable PD patients in Peking University Third Hospital who were followed for >6 months. We used plain X-ray films of abdomen to quantitatively evaluate VC of abdominal aorta. VC was evaluated by abdominal aortic calcification (AAC) scores, and PD patients were divided into the high AAC score group (AAC score ≥4) and the low AAC score group (AAC score <4). Demographic data and laboratory indexes were collected. Serum irisin concentrations were measured by enzyme-linked immunosorbent assay.

Results

A total of 102 PD patients were enrolled in this study, and 52 patients (51.0%) were found to have a high AAC score of ≥4. Age, diabetic mellitus proportion, pulse pressure, hypercalcemia (corrected calcium >2.54 mmol/L) rate, serum ultrasensitive C reactive protein, and AAC scores were significantly higher in the high AAC score group than those of the low AAC score group (p < 0.05). The high AAC score group had lower diastolic blood pressure, serum albumin, and serum carbon dioxide combining power compared with the low AAC score group (p < 0.05). Serum irisin levels of PD patients with a high AAC score were significantly lower than those of PD patients with a low AAC score (109.7 ± 13.1 ng/mL vs. 115.9 ± 10.1 ng/mL, p = 0.010). The multivariate logistic regression analyses showed that serum irisin, diabetic mellitus, serum ultrasensitive C reactive protein, and age were independent factors influencing the occurrence of VC in PD patients.

Conclusion

Our results are the first to provide a clinical evidence of the association between serum irisin and abdominal aortic calcification in PD patients. Lower irisin levels, diabetic mellitus, higher serum ultrasensitive C reactive protein, and older age could be potential predictive factors for VC in PD patients.

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

OBJECTIVE

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

DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Identification of irisin as a therapeutic agent that inhibits oxidative stress and fibrosis in a murine model of chronic pancreatitis

BACKGROUND

Abnormal activation of pancreatic stellate cells (PSCs) plays a crucial role in the pathogenesis of chronic pancreatitis (CP). Irisin, an exercise-induced hormone, has been shown to mitigate liver fibrosis by inhibiting the activation of hepatic stellate cells. However, the effect of irisin in CP has not been evaluated.

METHODS

This study aimed to determine whether irisin is protective in CP. CP was induced by 6 IP injections of cerulein (50 μg/kg/body weight). HPSCs were treated with 5 ng/ml TGF-β1 as in vitro experiment.

RESULTS

Our results showed that repeated cerulein injection induced severe pancreatic injury and fibrosis in mice and the serum irisin level in cerulein-treated mice decreased as in CP patients. Excessive oxidative and ER stress was also present in the pancreas of cerulein-treated mice. Irisin treatment significantly alleviated pancreatic injury and fibrosis, which was associated with reduced oxidative and ER stress. In cultured PSCs, irisin directly inhibited TGF-β-induced α-SMA and collagen I expression. This effect appears to be mediated through downregulation of kindlin-2 and inhibition of the SMAD2/3 pathway.

CONCLUSIONS

Irisin alleviated pancreatic injury and fibrosis, which was associated with reduced oxidative and ER stress. Thus, irisin may offer therapeutic potential for patients with CP.

Modified creatinine index and risk for long-term infection-related mortality in hemodialysis patients: ten-year outcomes of the Q-Cohort Study

Modified creatinine (Cr) index, calculated by age, sex, pre-dialysis serum Cr concentration, and Kt/V for urea, is an indicator of skeletal muscle mass in hemodialysis (HD) patients. It remains unknown whether the modified Cr index predicts infection-related mortality in this population. We investigated the association between the modified Cr index and infection-related mortality. A total of 3046 patients registered in the Q-Cohort Study, a multicenter, observational study of HD patients, were analyzed. Associations between sex-specific quartiles (Q1–Q4) of the modified Cr index and the risk for infection-related mortality were analyzed by Cox proportional hazard model. During a median follow-up of 8.8 years, 387 patients died of infection. The estimated risk for infection-related mortality was significantly higher in the lower quartiles (Q1, Q2, and Q3) than in the highest quartile (Q4) as the reference group (hazard ratios and 95% confidence intervals [CI]: Q1, 2.89 [1.70–5.06], Q2, 2.76 [1.72–4.62], and Q3, 1.79 [1.12–2.99]). The hazard ratio (95% CI) for a 1 mg/kg/day decrease in the modified Cr index was 1.18 (1.09–1.27, P < 0.01) for infection-related mortality. In conclusion, a lower modified Cr index is associated with an increased risk for long-term infection-related mortality in the HD population.

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.

A Novel Interplay Between Irisin and PTH: From Basic Studies to Clinical Evidence in Hyperparathyroidism

CONTEXT

Irisin is a hormonelike molecule that is cleaved and secreted by an unknown protease from fibronectin type III domain-containing protein 5 (FNDC5). It ameliorates bone status and muscle atrophy and influences energy homeostasis. PTH exerts several metabolic effects that may interact with the effects of irisin.

OBJECTIVES

To test the hypothesis that irisin and PTH mutually affect their biological action, we evaluated FNDC5 mRNA and protein expression in myotubes treated with PTH (1-34) and parathyroid hormone receptor (PTH-r) mRNA expression in osteoblasts treated with r-irisin. To confirm the in vivo impact of PTH on irisin, we compared irisin serum concentrations in postmenopausal women with primary hyperparathyroidism (PHPT) and control subjects.

DESIGN AND INTERVENTION

C2C12 myotubes were treated with short-term and continuous 10-10 M teriparatide and MC3T3-E1 osteoblasts with 100 ng/mL r-irisin for 8 hours. In a cross-sectional open-label trial, we enrolled 26 postmenopausal women with PHPT and 31 age-/body mass index (BMI)‒matched control subjects without impairment of calcium/phosphate metabolism.

RESULTS

Teriparatide treatment on myotubes significantly downregulated FNDC5 expression by acting through its own receptor, which in turn activated Erk11/2 phosphorylation. r-Irisin led to a 50% downregulation of PTH-r mRNA expression compared with untreated cells (P < 0.001). Irisin was significantly lower in the PHPT group than in age-/BMI-matched controls (4.5 ± 1.1 vs 12 ± 5.2 µg/mL; P < 0.001). No significant correlation between irisin and bone mineral density or PTH was recorded in the PHPT group.

CONCLUSION

Preclinical findings suggest the existence of an interplay between PTH and irisin metabolism that seems to be confirmed by the significant reduction of irisin concentration in postmenopausal women with PHPT.

Irisin and Bone: From Preclinical Studies to the Evaluation of Its Circulating Levels in Different Populations of Human Subjects

Almost four years after the discovery of the anabolic action of irisin on bone in mice, ample clinical evidence is emerging in support of its additional physiological relevance in human bone. Irisin inversely correlates with sclerostin levels in adults with prediabetes and with vertebral fragility fractures in post-menopausal women. Furthermore, in athletes we observed a positive correlation between irisin and bone mineral density at different anatomical sites. Our group also described a positive association between serum irisin and bone status in healthy children and multivariate regression analysis showed that irisin is a stronger determinant of bone mineral status than bone alkaline phosphatase. In children with type 1 diabetes mellitus, serum irisin concentrations are positively associated with bone quality and with glycemic control following continuous subcutaneous insulin infusion. Additionally, our in vitro studies suggest the existence of a negative interplay between PTH and irisin biology and these results were also supported by the observation that post-menopausal women with primary hyperparathyroidism have lower levels of irisin compared to matched controls. In this review, we will focus on recent findings about circulating level of irisin in different populations of human subjects and its correlation with their bone status.