Plasma irisin depletion under energy restriction is associated with improvements in lipid profile in metabolic syndrome patients

The Effect of Bariatric Surgery on Irisin Level: a Systematic Review and Meta-analysis

This systematic analysis and meta-analysis aimed to assess changes in the plasma levels of irisin after bariatric surgery. Search strategy, study screening, and data gathering were all conducted using a checklist and the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Two researchers independently extracted the data, and a third person was included to resolve disagreements. The results illustrated no statistical difference between before and after surgery irisin plasma levels (P = 0.216, 95% CI = -1.812-0.410, SMD = -0.701, I-squared = 94.9%). BMI exhibited a meaningful decline after surgery compared to preoperative values (SMD = -3.09, 95% CI = -4.59--1.59, I-squared = 95.5%, P<0.05). According to our analysis, it can be concluded that irisin plasma levels are not significantly influenced by bariatric surgery.

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.

Cardiometabolic health, visceral fat and circulating irisin levels: results from a real-world weight loss study

BACKGROUND

The aim of this pragmatic intervention study was to investigate changes in cardiometabolic outcomes, irisin plasma concentration, and body composition during a 4-month intervention in unselected obese individuals.

MATERIALS AND METHODS

In 111 obese women aged 36.73 ± 7.2 years, we measured changes in weight, lipid profiles, glucose, insulin, Homeostatic Model Assessment-Insulin Resistance Index (HOMA-IR), uric acid, aminotransferases, and irisin. Body composition including lean mass (LM) and total (TF), gynoid (GF), android (AF), and visceral fat (VF) was assessed using densitometry. Physical activity was assessed using the International Physical Activity Questionnaire (IPAQ). The participants received tailored written advice targeting lifestyle according to current guidelines. At follow-up, patients rated their adherence in the self-administered questionnaire.

RESULTS

Mean weight loss in the whole group was 3.12 kg (- 3.3%); 26% of the women achieved the desired target of weight loss (> 5% of the initial weight), whereas weight decreased moderately in 50% and increased in 14%. In 86 women with weight loss, there were significant changes in HOMA-IR (- 13.8%), insulin (- 11.2%), alanine aminotransferase (- 8.0%), VF (- 7.0%), AF (- 5.4%), TF (- 4.7%), GF (- 2.8%) and LM (- 1.5%), whereas irisin and HDL-C levels and the mean IPAQ score did not change.

CONCLUSIONS

In this real-world evidence study, a successful weight loss achieved only 26% of patients, with overall much better adherence to diet restriction than to exercise. However, even mild to moderate weight loss resulted in significant improvements in cardiometabolic health. Weight loss was associated with a modest LM decrease but did not influence plasma irisin.

Effect of Sitagliptin on Serum Irisin Levels in Patients with Newly Diagnosed Type 2 Diabetes Mellitus

INTRODUCTION

Irisin is a unique myokine with striking effects on regulating insulin sensitivity and energy metabolism. This study aimed to investigate the changes in serum irisin in patients with newly diagnosed type 2 diabetes mellitus (T2DM) following sitagliptin treatment.

METHODS

Thirty-two patients with T2DM were treated with 100 mg/day sitagliptin for 16 weeks. Twenty age-, sex- and body mass index (BMI)-matched healthy subjects were enrolled as the control group. Irisin and metabolic parameters were measured at baseline and after treatment.

RESULTS

Patients with T2DM had lower irisin levels than the controls (10.03 ± 2.06 vs. 13.06 ± 3.10 ng/ml, P < 0.01). Sitagliptin treatment significantly increased serum irisin levels in T2DM patients compared to baseline (11.18 ± 1.91 vs. 10.03 ± 2.06  ng/ml, P < 0.01). Increased irisin levels were associated with decreased fasting blood glucose (FBG) (β = - 0.24, P < 0.05) and glycosylated hemoglobin (HbA1c) (β = - 0.15, P < 0.05).

CONCLUSIONS

Sitagliptin treatment significantly increased serum irisin levels in patients with T2DM, and the increase of the irisin level was associated with decreases of FBG and HbA1c levels. These results suggest that irisin might be involved in the antidiabetic mechanisms of sitagliptin.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT04495881.

Effects of Christian Orthodox Fasting Versus Time-Restricted Eating on Plasma Irisin Concentrations Among Overweight Metabolically Healthy Individuals

Irisin has been recently identified as an adipomyokine produced during physical activity and involved in the browning of adipose tissue. Despite the emerging evidence suggesting an inverse relationship between irisin plasma concentrations and adverse metabolic outcomes, the exact impact of diet on irisin levels remains obscure. Thus, we aimed to assess the effects of two dietary patterns, Christian Orthodox fasting (OF) and 16:8 time-restricted eating (TRE), on circulating irisin levels among overweight, metabolically healthy, adults. Plasma irisin, glucose and lipid parameters, calcium homeostasis, and anthropometry were evaluated in 29 Orthodox fasters and 14 age and body mass index (BMI)-matched TRE controls (mean age and BMI, 48.8 years and 28.7 kg/m², respectively) at three, distinct time points—before the implementation of the energy-restricted diets (baseline), at the end of the dietary intervention (7 weeks) and 5 weeks after participants returned to their typical dietary habits (12 weeks from baseline). Repeated measures analysis was applied to assess differences between the two groups and the effect of several indices on irisin levels at all three time points. At 12 weeks, the OF group manifested higher irisin concentrations compared with both its baseline values (64.3 ± 54.4 vs. 43.6 ± 42.2 ng/mL, p = 0.01) and those of the TRE group at the same time point (64.3 ± 54.4 vs. 44.2 ± 26.6 ng/mL, p = 0.04). Glycemic, lipid, and anthropometric parameters were not found to correlate with irisin levels. In contrast, parathyroid hormone (PTH) concentrations at 12 weeks correlated with irisin concentrations (p = 0.04), indicating that lower values of irisin are expected for higher PTH measurements. The findings of this pilot study suggest favorable long-term effects of OF on irisin levels. The interplay between irisin, PTH, and diet warrants further investigation.

Novel Roles of Follistatin/Myostatin in Transforming Growth Factor-β Signaling and Adipose Browning: Potential for Therapeutic Intervention in Obesity Related Metabolic Disorders

Obesity is a global health problem and a major risk factor for several metabolic conditions including dyslipidemia, diabetes, insulin resistance and cardiovascular diseases. Obesity develops from chronic imbalance between energy intake and energy expenditure. Stimulation of cellular energy burning process has the potential to dissipate excess calories in the form of heat via the activation of uncoupling protein-1 (UCP1) in white and brown adipose tissues. Recent studies have shown that activation of transforming growth factor-β (TGF-β) signaling pathway significantly contributes to the development of obesity, and blockade or inhibition is reported to protect from obesity by promoting white adipose browning and increasing mitochondrial biogenesis. Identification of novel compounds that activate beige/brown adipose characteristics to burn surplus calories and reduce excess storage of fat are actively sought in the fight against obesity. In this review, we present recent developments in our understanding of key modulators of TGF-β signaling pathways including follistatin (FST) and myostatin (MST) in regulating adipose browning and brown adipose mass and activity. While MST is a key ligand for TGF-β family, FST can bind and regulate biological activity of several TGF-β superfamily members including activins, bone morphogenic proteins (BMP) and inhibins. Here, we review the literature supporting the critical roles for FST, MST and other proteins in modulating TGF-β signaling to influence beige and brown adipose characteristics. We further review the potential therapeutic utility of FST for the treatment of obesity and related metabolic disorders.

A pilot study on the relation between irisin single-nucleotide polymorphism and risk of myocardial infarction

BACKGROUND

Myocardial infarction (MI) is the major cause of death and disability worldwide. Many recent studies revealed the relationship between circulating irisin levels, endothelial dysfunctions and subclinical atherosclerosis in adult patients.

OBJECTIVES

The aim of this study was to investigate the distribution of Irisin gene single nucleotide polymorphism in patients with MI and its association with other clinical and laboratory variables in these patients.

PATIENTS AND METHODS

This study was carried out in 100 patients with MI, and 100 healthy subjects served as controls. All studied subjects underwent laboratory investigations, including measurement of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c) high-density lipoprotein cholesterol (HDL-c), creatinine kinase-MB (CK-MB), troponin I (TnI) and genotyping of rs 3480 and rs726344 of Irisin genes using the TaqMan Allelic Discrimination assay technique.

RESULTS

There was a significant difference of Irisin genotypes in patients when compared to controls. By estimating odd ratio (OR) an association was found between G allele of rs 3480 and A allele of rs726344with increase the risk of developing myocardial infarction by 4.03 and 3.47 fold respectively. GG of rs 3480 carriers had significantly increased Troponin I and triglyceride levels, while GA carriers of rs726344 had significantly increased CKMB, Total cholesterol, LDLc, HDLc, troponin I and triglyceride levels compared with other genotypes.

CONCLUSION

G allele of rs 3480 and A allele of rs726344can considered as genetic risk factors for MI; these findings could have an impact on preventive strategy for myocardial infarction.

The effectiveness of military physical exercise on irisin concentrations and oxidative stress among male healthy volunteers

Background Irisin, a newly discovered hormone, is secreted into the circulation from skeletal muscles in response to physical exercise. The biochemical parameters related to irisin secretion have not been sufficiently investigated yet. The aim of this study was to examine the effectiveness of exercise on the level of irisin and its correlation with biochemical and oxidative stress parameters. Materials and methods In this pre- and post-test observational study, 39 healthy male volunteers from a military training setting were followed up on between September and November 2015. The individuals who were included in this study were between 22 and 27 years old with an average age of 24. Those with inflammatory disorders or chronic diseases such as diabetes mellitus were excluded from the study. The parameters were measured at the baseline, at 4 weeks, and at 8 weeks of intervention. Results The study found that the systolic and diastolic blood pressures substantially decreased after 8 weeks of intervention. The cholesterol-to-HDL ratio and glucose levels were significantly higher at the baseline compared to 8 weeks. Total protein and albumin were significantly higher following 4 weeks (0.25 and 0.21 g/dL) and 8 weeks (0.32 and 0.16 g/dL), respectively. Meanwhile, total globulin and irisin increased following 8 weeks of the intervention by only 0.16 g/dL and 0.41 μg/mL, respectively. The high sensitivity C-reactive protein (hs-CRP) decreased following 8 weeks (-0.81 μg/mL). The protein carbonyl (PC) decreased following 4 weeks by only 0.34 nmol/L. Conclusions This study demonstrated that military training enhanced irisin hormone secretion following 8 weeks of military exercise.

Irisin levels in genetic and essential obesity: clues for a potential dual role

Irisin is conventionally regarded as a myokine involved in the browning of white adipose tissue, energy expenditure and glucose tolerance. Its potential link to fat accumulation and metabolic dysfunction is debated. We sought to explore the relationship between circulating irisin and components of body composition in two different phenotypes of severe obesity. For this purpose, 30 obese adults with Prader-Will syndrome (PWS) (age 35.7 ± 1.5 y, BMI 45.5 ± 1.5 kg/m²) and 30 adult controls with common obesity (age 34.9 ± 1.7 y, BMI 46.8 ± 1.4 kg/m²) underwent analysis of irisin levels, metabolic profile, body composition and resting energy expenditure (REE). Normal irisin levels were obtained from a group of 20 lean donors (age 32.4 ± 1.5 y, BMI 23.8 ± 0.8 kg/m²). Expected differences in body composition and metabolic profile existed between study groups. PWS exhibited lower muscle mass (p < 0.001), FFM (p < 0.001), REE (p < 0.001), as well as insulin (p < 0.05), HOMA-IR (p < 0.05) and triglycerides levels (p < 0.05) than controls with common obesity. In PWS, irisin levels were significantly lower and overall less dispersed than in controls with common obesity (p < 0.05), while being similar to values recorded in lean subjects. To explore the relation between irisin and body composition in obesity, univariate correlation analysis in the obese populations as a whole showed positive associations between irisin and muscle mass (p = 0.03) as well as REE (p = 0.01), which disappeared when controlled for the PWS status. Noticeably, a positive association became evident between irisin and %FM after controlling for the PWS status (p = 0.02). Also positive were associations between irisin and insulin (p = 0.02), HOMA-IR (p = 0.02) and triglycerides (p = 0.04). In stepwise multivariable regression analysis, irisin levels were independently predicted by the PWS status (p = 0.001), %FM (p = 0.004) and triglycerides (p = 0.008). Current results suggest that obese adults with PWS harbor lower irisin levels than individuals with common obesity. The divergent models of obesity herein studied suggest a potential link between circulating irisin and muscle mass and metabolic dysfunction relating to adiposity.

Myricanol modulates skeletal muscle-adipose tissue crosstalk to alleviate high-fat diet-induced obesity and insulin resistance

BACKGROUND AND PURPOSE

Skeletal muscle is the predominant site for glucose disposal and fatty acid consumption. Emerging evidence indicates that the crosstalk between adipose tissue and skeletal muscle is critical in maintaining insulin sensitivity and lipid homeostasis. The current study was designed to investigate whether myricanol improves insulin sensitivity and alleviates adiposity through modulating skeletal muscle-adipose tissue crosstalk.

EXPERIMENTAL APPROACH

The therapeutic effect of myricanol was evaluated on palmitic acid (PA)-treated C2C12 myotubes and high-fat diet (HFD)-fed mice. The crosstalk between myotubes and adipocytes was evaluated using Transwell assay. The cellular lipid content was examined by Nile red staining. The mitochondrial content was assessed by MitoTracker Green staining and citrate synthase activity, and the mitochondrial function was examined by Seahorse assay. Expression of mitochondria-related and insulin signalling pathway proteins was analysed by Western blot, and the irisin level was determined by elisa kit.

KEY RESULTS

Myricanol increased mitochondrial quantity and function through activating AMP-activated protein kinase, resulting in reduced lipid accumulation and enhanced insulin-stimulated glucose uptake, in PA-treated C2C12 myotubes. Furthermore, myricanol stimulated irisin production and secretion from myotubes to reduce lipid content in 3T3-L1 adipocytes. In HFD-fed mice, myricanol treatment alleviated adiposity and insulin resistance through enhancing lipid utilization and irisin production in skeletal muscle and inducing browning of inguinal fat.

CONCLUSIONS AND IMPLICATIONS

Myricanol modulates skeletal muscle-adipose tissue crosstalk, to stimulate browning of adipose tissue and improve insulin sensitivity in skeletal muscle. Myricanol might be a potential candidate for treating insulin resistance and obesity.

Serum and follicular fluid irisin levels in women with polycystic ovaries undergoing ovarian stimulation: correlation with insulin resistance and lipoprotein lipid profiles

Irisin, a novel exercise-induced myokine, has been implicated in different aspects of human metabolism and could be connected to polycystic ovary syndrome (PCOS). This study aimed to investigate serum and follicular fluid (FF) irisin levels in PCOS and normal women undergoing controlled ovarian stimulation and correlate them to the lipid and lipoprotein levels as well as with other metabolic parameters. Serum and FF irisin, together with serum lipid and lipoprotein levels were assessed in 70 women with diagnosed PCOS and 70 non-PCOS controls, under in vitro fertilization (IVF) treatment. Regardless of BMI, PCOS women had a significantly increased number of oocytes retrieved, fertilized oocytes and transferred embryos, although the number of women achieving pregnancies did not differ between groups. No correlation between FF irisin levels and pregnancy could be established. Serum and FF irisin levels were significantly higher in PCOS and overweight women and were positively associated with BMI and dyslipidemia. FF irisin levels correlated positively to and were lower than serum irisin levels. Further research would be helpful to analyze irisin's role in female reproduction, if any, as well as in human metabolism and the pathophysiology of PCOS.

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.

Circulating Irisin Levels in Children With GH Deficiency Before and After 1 Year of GH Treatment

PURPOSE

To evaluate circulating irisin levels in children with GH deficiency (GHD) and any relation with clinical and metabolic parameters.

PATIENTS

Fifty-four prepubertal children (mean age, 7.4 ± 0.8 years) with idiopathic GHD treated with GH for at least 12 months and 31 healthy short children as control subjects.

METHODS

Body height, body mass index (BMI), waist circumference (WC), IGF-I, HbA1c, lipid profile, fasting and after-oral glucose tolerance test glucose and insulin, insulin sensitivity indices, and irisin levels were evaluated at baseline and after 12 months of GH replacement (GHR).

RESULTS

At baseline, children with GHD, in addition to having lower growth velocity (P < 0.001), GH peak after stimulation tests (both P < 0.001), and IGF-I (P < 0.001), showed significantly lower irisin (P < 0.001) and higher BMI (P < 0.001) and WC (P = 0.001), without any difference in metabolic parameters, than control subjects. After GHR, children with GHD showed a significant increase in height (P < 0.001), growth velocity (P < 0.001), IGF-I (P < 0.001), fasting glucose (P = 0.002) and insulin (P < 0.001), homeostasis model assessment estimate of insulin resistance (P < 0.001), and irisin (P = 0.005), with a concomitant decrease in BMI (P = 0.001) and WC (P = 0.003). In multivariate analysis, the independent variables significantly associated with irisin were BMI (P = 0.002) and GH peak (P = 0.037) at baseline and BMI (P = 0.005), WC (P = 0.018), and IGF-I (P < 0.001) during GHR.

CONCLUSIONS

We report that GHR leads to an increase in irisin levels, strongly related to a decrease in BMI and WC, and to an increase in IGF-I; these changes are among the main goals of GHR. These data confirm the favorable effects of GHR in children.

Decreased Concentration of Irisin Is Associated with Poor Functional Outcome in Ischemic Stroke

Irisin was discovered as a PGC-1a-activated messenger of myocytes that links sedentary lifestyle, obesity, and diabetes. In this study, we investigated the short-term prognostic value of early measurement of irisin concentration in 1530 Han Chinese patients with acute ischemic stroke (AIS) from three stroke centers. The subjects were the first-ever AIS patients who were hospitalized at three stroke centers during the period from January 2015 to December 2016. Clinical information and stroke severity were collected at admission. Neurological evaluations were conducted at the 6-month follow-up. Serum levels of irisin, National Institutes of Health Stroke Scale (NIHSS), and conventional risk factors were evaluated to determine their value to predict functional outcome and mortality within 6 months. Multivariate analyses were performed using logistic regression models. During follow-up, a poor functional outcome was found in 588 patients (38.4%; 95% confidence interval (CI), 36.0-40.9%), and 325 patients died (21.2%; 95% CI, 19.2-23.3%). The stroke patients included in the study were divided into four groups according to irisin quartiles (first is the lowest level). Poor outcome across the irisin quartiles ranged from 54.5% (first quartile) to 21.7% (fourth quartile), and mortality rate ranged from 39.3% (first quartile) to 6.3% (fourth quartile). In a multivariate model using the first quartile (Q1) of irisin vs. Q2-Q4 together with the clinical variables, the marker displayed prognostic information and increased odds ratios of poor outcome by 58% (OR for Q1, 1.58 [95% CI, 1.12-2.43]) and mortality by 185% (OR for Q1, 2.85 [95% CI, 1.79-4.02]). In addition, a model containing known risk factors plus irisin compared with a model containing known risk factors without irisin showed a greater discriminatory ability to predict poor outcome (the area under the curve (AUC) with an increase from 0.73 to 0.75 [95% CI, 0.70-0.81]) and mortality (the AUC increased from 0.80 to 0.83 [95% CI, 0.78-0.87]). Irisin is a novel, independent prognostic marker improving currently used risk stratification of stroke patients. Further studies are needed to confirm this association, which may pave the way to new therapeutic options. Trial registration: ChiCTR-OPC- 17013501.

Dopamine gene methylation patterns are associated with obesity markers and carbohydrate intake

INTRODUCTION

Dopamine (DA) is a neurotransmitter that regulates the rewarding and motivational processes underlying food intake and eating behaviors. This study hypothesized associations of DNA methylation signatures at genes modulating DA signaling with obesity features, metabolic profiles, and dietary intake.

METHODS

An adult population within the Methyl Epigenome Network Association project was included (n = 473). DNA methylation levels in white blood cells were measured by microarray (450K). Differentially methylated genes were mapped within the dopaminergic synapse pathway using the KEGG reference database (map04728). Subsequently, network enrichment analyses were run in the pathDIP portal. Associations of methylation patterns with anthropometric markers of general (BMI) and abdominal obesity (waist circumference), the blood metabolic profile, and daily dietary intakes were screened.

RESULTS

After applying a correction for multiple comparisons, 12 CpG sites were strongly associated (p < 0.0001) with BMI: cg03489495 (ITPR3), cg22851378 (PPP2R2D), cg04021127 (PPP2R2D), cg22441882 (SLC18A1), cg03045635 (DRD5), cg23341970 (ITPR2), cg13051970 (DDC), cg08943004 (SLC6A3), cg20557710 (CACNA1C), cg24085522 (GNAL), cg16846691 (ITPR2), and cg09691393 (SLC6A3). Moreover, average methylation levels of these genes differed according to the presence or absence of abdominal obesity. Pathway analyses revealed a statistically significant contribution of the aforementioned genes to dopaminergic synapse transmission (p = 4.78E-08). Furthermore, SLC18A1 and SLC6A3 gene methylation signatures correlated with total energy (p < 0.001) and carbohydrate (p < 0.001) intakes.

CONCLUSIONS

The results of this investigation reveal that methylation status on DA signaling genes may underlie epigenetic mechanisms contributing to carbohydrate and calorie consumption and fat deposition.

Irisin Serum Levels in Metabolic Syndrome Patients Treated with Three Different Diets: A Post-Hoc Analysis from a Randomized Controlled Clinical Trial

BACKGROUND

Irisin, a hormone-like myokine, regulates energy homeostasis and mediates the benefits of physical activity on health.

METHODS

To estimate the effect of different diets on irisin concentrations in subjects with the Metabolic Syndrome (MetS).

METHODS

Subjects with MetS were derived from a population survey; 163 subjects were enrolled and randomized to a: Low Glycaemic Index (LGID), Mediterranean (MD) or Low Glycaemic Index Mediterranean (LGIMD) Diet, and the groups were compared, also with 80 controls without MetS. Sociodemographic, medical and nutritional data were collected and fasting blood samples drawn. Subjects underwent LUS and bioimpedentiometry. Generalized Estimating Equations were performed.

RESULTS

At baseline, lower irisin concentrations were observed in MetS subjects. Mean irisin levels increased in all diet groups but only the LGID group reached statistical significance, as well as showing an interaction between LGID and time at the sixth month examination (4.57, 95% CI −1.27, 7.87). There was a positive effect of Vegetable Proteins (0.03, 95% CI −0.01,0.06) and Saturated Fatty Acids (0.04, 95% CI 0.01, 0.07) on irisin concentrations. In the LGIMD, a positive effect on Fat-Free Mass (0.38, 95% CI 0.19, 0.57) and a negative effect on the Body Mass Index (−0.75, 95% CI −1.30, −0.19) were observed.

CONCLUSIONS

There seems to be a link between diet and muscle physiology. We showed that patients following a LGID had higher levels of irisin, a promising biomarker of muscle activity.

Serum levels of irisin predict short-term outcomes in ischemic stroke

OBJECTIVE

Irisin is a 112-amino acid peptide found in rat and human skeletal muscle after exercise. Previous studies had suggested that higher circulating irisin levels were associated with an increased risk of vascular atherosclerosis and cardiovascular diseases. In this study, we determined irisin levels in serum, and investigated their associations with functional outcomes in a 3-month follow-up study in Chinese patients with first-ever acute ischemic stroke (AIS).

METHODS

From September 2015 to December 2016, consecutive first-ever AIS patients admitted to the Department of Emergency of our hospital were identified. Serum irisin levels were measured at admission. Functional impairment was evaluated at discharge using the modified Rankin scale. The levels of irisin were expressed as median and interquartile ranges [IQR].

RESULTS

The irisin level was obtained in 324 patients (97.6%) with a median value of 291.2 ng/ml (IQR: 214.1-404.2 ng/ml). There were significantly negative correlations between levels of irisin and NHISS (r = -0.272; P < 0.001) and BMI (r = -0.193; P = 0.003). A poor functional outcome was found in 99 patients (30.6%; 95%CI: 25.5-35.6%). The poor functional outcome distribution across the irisin quartiles ranged between 51.9% (first quartile: Q1) to 12.4% (fourth quartile: Q4). In a multivariate model using the Q1 of irisin vs. Q2-4 together with the clinical variables, the marker displayed prognostic information and increased risk of poor outcomes by 94% (OR for Q1, 1.94 [95% CI, 1.19-3.42]; P = 0.018) and mortality 66% (OR for Q1, 1.66 [95% CI, 1.11-3.07]; P = 0.009). In addition, a model containing known risk factors plus irisin compared with a model containing known risk factors without irisin showed a greater discriminatory ability to predict poor outcomes (P = 0.01) and mortality (P = 0.02).

CONCLUSIONS

A low serum irisin level is a predictor of poor early functional outcome in ischemic stroke patients. The underlying mechanisms of these associations remain to be investigated.

Association of Markers of Proinflammatory Phenotype and Beige Adipogenesis with Metabolic Syndrome in Chinese Centrally Obese Adults

BACKGROUND

Visceral adiposity is associated with higher productions of C-reactive protein (CRP) and interleukin-6 (IL-6). Inflammation of obese adipose tissues could contribute to systemic metabolic dysregulation, especially thermogenic activity of white adipose tissues, namely, beige adipogenesis, characterized by altered irisin expression. Thus, we investigated the roles of inflammation and adipocyte beiging in Chinese centrally obese (CO) adults with metabolic syndrome (MetS).

METHODS

This cross-sectional study was conducted on 54 CO and 58 non-CO subjects drawn from 1492 Chinese people with age and sex matched during November 2010 and August 2013. Twenty (37.0%) of the CO subjects fulfilled the IDF worldwide definition of MetS. Serum CRP, IL-6, and irisin levels were examined.

RESULTS

Higher CRP and IL-6, but lower irisin, levels were manifested in MetS versus non-MetS subjects with or without CO. Multiple linear regression identified high-density lipoprotein cholesterol level as the only independent risk factor for irisin level. Categorized by median of CRP and IL-6 levels, a lower irisin level was only observed in high CRP group.

CONCLUSION

Under the condition of central obesity, chronic inflammation and impaired beige adipogenesis are associated with MetS in Chinese adults.

Lack of Adipocyte-Fndc5/Irisin Expression and Secretion Reduces Thermogenesis and Enhances Adipogenesis

Irisin is a browning-stimulating molecule secreted from the fibronectin type III domain containing 5 precursor (FNDC5) by muscle tissue upon exercise stimulation. Despite its beneficial role, there is an unmet and clamorous need to discern many essential aspects of this protein and its mechanism of action not only as a myokine but also as an adipokine. Here we contribute to address this topic by revealing the nature and role of FNDC5/irisin in adipose tissue. First, we show that FNDC5/irisin expression and secretion are induced by adipocyte differentiation and confirm its over-secretion by human obese visceral (VAT) and subcutaneous (SAT) adipose tissues. Second, we show how secreted factors from human obese VAT and SAT decrease PGC1α, FNDC5 and UCP1 gene expression on differentiating adipocytes; this effect over UCP1 is blunted by blocking irisin in obese secretomes. Finally, by stable gene silencing FNDC5 we reveal that FNDC5-KO adipocytes show reduced UCP1 expression and enhanced adipogenesis.

Plasma irisin is elevated in type 2 diabetes and is associated with increased E-selectin levels

Background

Irisin is a hormone released mainly from skeletal muscle after exercise which increases adipose tissue energy expenditure. Adipocytes can also release irisin after exercise, acting as a local adipokine to induce white adipose tissue to take on a brown adipose tissue-like phenotype, suggesting that irisin and its receptor may represent a novel molecular target for the treatment of obesity and obesity-related diabetes. Previous reports provide conflicting evidence regarding circulating irisin levels in patients with type 2 diabetes (T2DM).

Methods

This study investigated plasma irisin concentrations in 79 T2DM individuals, assessing potential associations with measures of segmental body composition, markers of endothelial dysfunction and peripheral blood mononuclear cell telomere length (TL).

Results

Resting, overnight-fasted plasma irisin levels were significantly higher in this group of T2DM patients compared with levels we previously reported in healthy volunteers (p < 0.001). Moreover, plasma irisin displayed a positive correlation with body mass index (p = 0.04), body fat percentage (p = 0.03), HbA1c (p = 0.03) and soluble E-selectin (p < 0.001). A significant negative association was observed between plasma irisin and visceral adiposity (p = 0.006) in T2DM patients. Multiple regression analysis revealed that circulating soluble E-selectin levels could be predicted by plasma irisin (p = 0.004). Additionally, cultured human umbilical vein endothelial cells (HUVEC) exposed to 200 ng/ml irisin for 4 h showed a significant fourfold increase in E-selectin and 2.5-fold increase in ICAM-1 gene expression (p = 0.001 and p = 0.015 respectively), and there was a 1.8-fold increase in soluble E-selectin in conditioned media (p < 0.05).

Conclusion

These data suggest that elevated plasma irisin in T2DM is associated with indices of adiposity, and that irisin may be involved in pro-atherogenic endothelial disturbances that accompany obesity and T2DM. Accordingly, irisin may constitute a potentially novel therapeutic opportunity in the field of obesity and cardiovascular diabetology.

Association of circulating irisin levels with metabolic and metabolite profiles of Korean adolescents

CONTEXT

Irisin, a novel exercise-induced myokine, has been suggested to regulate energy metabolism.

OBJECTIVE

We studied the relationship between circulating irisin and metabolic and metabolite profiles of Korean adolescents, and investigated the effects of physical activity, obesity, and metabolic syndrome (MetS) on irisin levels.

MATERIALS AND METHODS

Data were obtained from the Korean Children-Adolescents Study. Our cross-sectional study included 618 adolescents (370 normal-weight and 248 obese adolescents; 316 boys and 302 girls) aged 12-15years. Body composition was determined using an impedance body composition analyzer and general participant characteristics and lifestyle information were obtained from questionnaires. Serum irisin levels were measured using a commercial kit.

RESULTS

Mean body mass index (BMI) was 19.4kg/m² in normal-weight adolescents and 31.4kg/m² in obese adolescents. Circulating irisin was positively correlated with adiposity indices, including BMI z-score, waist circumference, percent body fat, fat mass, fat-free mass, fat mass to fat-free mass ratio, and lipid and glucose metabolism markers, including total cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides, glucose, insulin, and homeostasis model assessment-estimated insulin resistance (all p≤0.006). Of these, increased body fat mass [standardized (Std) ß, 0.23; p<0.0001], LDL-C (Std ß, 0.14; p=0.0005) and fasting glucose (Std ß, 0.08; p=0.0383) were the main independent factors associated with higher irisin levels. Moreover, elevated serum irisin was associated with the risk of obesity [odds ratio (OR], 2.2; confidence interval (CI), 1.19-3.87] and MetS (OR, 2.0; CI, 1.15-3.47). Furthermore, irisin and branched-chain amino acids were positively associated (p<4×10^-4 for Bonferroni correction). Additionally, in the normal-weight group, girls had higher irisin levels than boys (p=0.006) and adolescents who engaged in regular physical activity had higher levels of irisin than sedentary adolescents (p=0.0388). The relationship between physical activity and irisin levels was not observed in obese adolescents.

CONCLUSIONS

Elevated serum irisin was independently associated with the risk of obesity and positively correlated with unhealthy metabolic parameters and metabolites. Moreover, irisin levels were higher in active versus sedentary adolescents in the normal-weight group, but not in the obese group. Our findings suggest that irisin plays an important role in metabolic disorders and may be affected by physiopathological status.

Association of Irisin Plasma Levels with Anthropometric Parameters in Children with Underweight, Normal Weight, Overweight, and Obesity

The correlations between irisin levels, physical activity, and anthropometric measurements have been extensively described in adults with considerable controversy, but little evidence about these relationships has been found in children. The objective of this study is to correlate the plasma levels of irisin in underweight, normal weight, overweight, and obese children with anthropometric parameters and physical activity levels. A cross-sample of 40 children was divided into the following groups on the basis of body mass index (BMI) percentile. The correlations of plasma irisin levels with physical activity, anthropometric, and metabolic measurements were determined. Plasma irisin levels (ng/mL) were lower for the underweight group (164.2 ± 5.95) than for the normal weight and obese groups (182.8 ± 5.58; p < 0.05). Irisin levels correlated positively with BMI percentile (0.387), waist circumference (0.373), and fat-free mass (0.353; p < 0.05), but not with body muscle mass (−0.027). After a multiple linear regression analysis, only BMI percentile (0.564; p < 0.008) showed a positive correlation with irisin. Our results indicated no association with metabolic parameters. A negative correlation with physical activity was observed. Interrelationships among body components might influence irisin levels in children.

Serum irisin and its regulation by hyperinsulinemia in women with polycystic ovary syndrome

Irisin is an adipokine/myokine which could be connected with insulin sensitivity. Polycystic ovary syndrome (PCOS) is characterized by oligo- or anovulation, polycystic ovary, hyperandrogenism and insulin resistance. The aim of the present study was to determine the relationship between serum irisin concentration and insulin sensitivity (M_ffm) as well as the effect of insulin infusion on circulating irisin levels in PCOS women as compared with healthy controls. Seventy seven women were enrolled in the study - 57 with PCOS and 20 healthy controls matched for BMI and age. Hyperinsulinemic euglycemic clamps were performed in all of the study participants. The serum concentrations of irisin at baseline and after the clamp, as well as changes of serum irisin concentration in response to insulin supplied during the clamp (Δ irisin), were estimated. The mean serum concentrations of irisin at baseline and after hyperinsulinemia were higher in PCOS women in comparison to the control group (p=0.01; p=0.006, respectively). Insulin infusion resulted in a decrease of serum irisin concentration only in the PCOS group (p=0.007). In the control group, Δ irisin positively correlated with M_ffm (r=0.56, p=0.009). In the entire group, multiple regression analysis showed that Δ irisin (β=0.70, p=0.0002), FFAs 60' during the clamp study (β=-0.22, p=0.01), SHBG (β=0.54, p<0.0001) and the interaction between Δ irisin and PCOS (β=-0.67, p=0.0004) were significantly associated with M_ffm. The higher serum irisin concentrations at baseline and in response to insulin infusion might be secondary to insulin resistant conditions in PCOS women.

Nutritional management of hyperapoB

Plasma apoB is a more accurate marker of the risk of CVD and type 2 diabetes (T2D) than LDL-cholesterol; however, nutritional reviews targeting apoB are scarce. Here we reviewed eighty-seven nutritional studies and present conclusions in order of strength of evidence. Plasma apoB was reduced in all studies that induced weight loss of 6–12 % using hypoenergetic diets (seven studies; 5440–7110 kJ/d; 1300–1700 kcal/d; 34–50 % carbohydrates; 27–39 % fat; 18–24 % protein). When macronutrients were compared in isoenergetic diets (eleven studies including eight randomised controlled trials (RCT); n 1189), the diets that reduced plasma apoB were composed of 26–51 % carbohydrates, 26–46 % fat, 11–32 % protein, 10–27 % MUFA, 5–14 % PUFA and 7–13 % SFA. Replacement of carbohydrate by MUFA, not SFA, decreased plasma apoB. Moreover, dietary enriching with n-3 fatty acids (FA) (from fish: 1·1–1·7 g/d or supplementation: 3·2–3·4 g/d EPA/DHA or 4 g/d EPA), psyllium (about 8–20 g/d), phytosterols (about 2–4 g/d) or nuts (30–75 g/d) also decreased plasma apoB, mostly in hyperlipidaemic subjects. While high intake of trans-FA (4·3–9·1 %) increased plasma apoB, it is unlikely that these amounts represent usual consumption. Inconsistent data existed on the effect of soya proteins (25–30 g/d), while the positive association of alcohol consumption with low plasma apoB was reported in cross-sectional studies only. Five isoenergetic studies using Mediterranean diets (including two RCT; 823 subjects) reported a decrease of plasma apoB, while weaker evidence existed for Dietary Approaches to Stop Hypertension (DASH), vegetarian, Nordic and Palaeolithic diets. We recommend using a Mediterranean dietary pattern, which also encompasses the dietary components reported to reduce plasma apoB, to target hyperapoB and reduce the risks of CVD and T2D.

Relation of serum irisin level with metabolic and antropometric parameters in obese children

OBJECTIVE

This study aimed to investigate the relationship between serum irisin level and metabolic and anthropometric parameters in obese children.

METHODS

The study included 36 obese children with a body mass index (BMI) of ≥95th percentile and 30 healthy children with a BMI ranging from the 5th to the 85th percentile. Healthy and obese children had similar age, gender and pubertal stage distribution. Anthropometric and biochemical parameters (fasting glucose, insulin, lipid profile, leptin and irisin levels) were measured. Bioelectric impedance analysis was used to determine the body composition parameters, including body fat percentage and fat mass.

RESULTS

Serum irisin and leptin levels of the obese children were significantly higher than those of the healthy children [median irisin levels, 141.2 & 107.6ng/mL, p=0.024; median leptin levels, 10.9 & 2.9pg/mL, P<0.001, respectively). No statistically significant difference was found when leptin and irisin levels were compared among obese patients in terms of the presence of insulin resistance. Irisin levels significantly correlated with high-density lipoprotein cholesterol (HDL-C), fasting insulin and homeostasis model assessment-insulin resistance (HOMA-IR) with adjustment for age and BMI. The multivariate regression analysis showed that age, HOMA-IR and HDL-C had a significant association with the serum irisin level, which explained 30.6% of the variance.

CONCLUSION

This study demonstrated that obese children had significantly higher irisin levels than healthy children. Additionally, it provides evidence regarding the role of irisin on insulin sensitivity and lipid metabolism in childhood obesity.

Effects of Body Weight Reduction on Serum Irisin and Metabolic Parameters in Obese Subjects

BACKGROUND

Irisin is a myokine implicated in lipid and glucose metabolism. The objective of this study is to examine the effect of a body weight reduction on the serum irisin level and physical indicators in obese Japanese patients without diabetes.

METHODS

The subjects were 22 patients (male/female, 5/17; age, 46.1±16.0 years; body mass index [BMI], 36.9±5.0 kg/m²) who completed a 6-month body weight reduction program at our clinic. The program included diet, exercise therapy and cognitive behavioral therapy. Blood parameters, body composition, exercise tolerance, homeostasis model assessment of insulin resistance (HOMA-IR), and serum irisin were determined before and after intervention, and relationships among changes in these data were examined.

RESULTS

There were significant decreases in body weight and BMI after the intervention. Irisin before the intervention was significantly positively correlated with HOMA-IR (r=0.434, P<0.05). The mean irisin level showed no significant change after the intervention in all participants. However, improvements in % body fat, subcutaneous fat area, triglycerides, and fasting glucose were significantly greater in patients with an increase in irisin compared to those with a decrease in irisin after the intervention. Patients with an increase in irisin also had significantly lower fasting insulin (9.7±4.8 vs. 16.4±8.2, P<0.05) and HOMA-IR (2.2±1.1 vs. 3.7±1.6, P<0.05) after the intervention, compared to patients with a decrease in irisin.

CONCLUSION

Body weight reduction did not alter irisin levels. However, irisin may play important roles in fat and glucose metabolism and insulin resistance, and the effects of body weight reduction on irisin kinetics may be a key for obesity treatment.

Novel Molecules Regulating Energy Homeostasis: Physiology and Regulation by Macronutrient Intake and Weight Loss

Excess energy intake, without a compensatory increase of energy expenditure, leads to obesity. Several molecules are involved in energy homeostasis regulation and new ones are being discovered constantly. Appetite regulating hormones such as ghrelin, peptide tyrosine-tyrosine and amylin or incretins such as the gastric inhibitory polypeptide have been studied extensively while other molecules such as fibroblast growth factor 21, chemerin, irisin, secreted frizzle-related protein-4, total bile acids, and heme oxygenase-1 have been linked to energy homeostasis regulation more recently and the specific role of each one of them has not been fully elucidated. This mini review focuses on the above mentioned molecules and discusses them in relation to their regulation by the macronutrient composition of the diet as well as diet-induced weight loss.

Association of plasma fatty acid composition with plasma irisin levels in normal weight and overweight/obese children

BACKGROUND

Irisin has been suggested to protect against overweight. There are no previous data on the association of plasma fatty acid (FA) composition with plasma irisin.

OBJECTIVES

We studied the association of FA composition with plasma irisin in normal weight and overweight/obese children.

METHODS

This cross-sectional study included pre-pubertal children (388 normal weight children and 55 overweight/obese children); 6-9 years of age, taking part in the Physical Activity and Nutrition in Children Study. After an overnight fast, we measured plasma FA composition by gas chromatography and plasma irisin levels by enzyme-linked immunosorbent assay.

RESULTS

Higher proportion of total monounsaturated fatty acids in plasma cholesteryl esters (CEs) (β = 0.139, P = 0.003) and phospholipids (PLs) (β = 0.147, P = 0.002) and lower proportion of total polyunsaturated fatty acids in plasma CE (β = -0.130, P = 0.006) and PL (β = -0.165, P < 0.001) were associated with higher plasma irisin level in the whole study group. The association of plasma FA composition with plasma irisin level was stronger among overweight/obese children compared to normal weight children. Higher proportion of γ-linolenic acid (β = 0.324, P = 0.017) and lower proportion of linoleic acid (β = -0.397, P = 0.005) in plasma CE were related to higher plasma irisin level among overweight/obese children, indicating the direct association of estimated D6D activity in plasma CE (β = 0.343, P = 0.011) with plasma irisin. Furthermore, higher proportion of oleic acid in plasma CE (β = 0.345, P = 0.012) and PL (β = 0.292, P = 0.033) and higher proportion of adrenic acid (β = 0.366, P = 0.008) and docosapentaenoic acid (β = 0.351, P = 0.010) in plasma PL were associated with higher plasma irisin level among overweight/obese children.

CONCLUSION

Metabolically unfavourable plasma FA profile was associated with higher plasma irisin level especially in overweight/obese children, suggesting that excess body fat might modulate these relationships.

Relationship between myostatin and irisin in type 2 diabetes mellitus: a compensatory mechanism to an unfavourable metabolic state?

Myostatin and irisin are two myokines related to energy metabolism, acting on skeletal muscle and recently suggested on adipose tissue in mice. However, the exact role of these myokines in humans has not been fully established. Our aim was to evaluate the relationship between serum levels of myostatin and irisin in type 2 diabetes mellitus patients and non-diabetic controls and to explore its links with metabolic parameters. Case-control study including 73 type 2 diabetes mellitus patients and 55 non-diabetic subjects as control group. Circulating myostatin and irisin levels were measured by enzyme-linked immunosorbent assays. Type 2 diabetes mellitus patients showed significantly lower myostatin levels (p = 0.001) and higher irisin levels (p = 0.036) than controls. An inverse relationship was observed between myostatin and irisin levels (p = 0.002). Moreover, in type 2 diabetes mellitus patients, after adjusting by confounder factors, myostatin was negatively related to fasting plasma glucose (p = 0.005) and to triglyceride levels (p = 0.028) while irisin showed a positive association with these variables (p = 0.017 and p = 0.006 respectively). A linear regression analysis showed that irisin and fasting plasma glucose levels were independently associated to myostatin levels and that myostatin and triglyceride levels were independently associated to irisin concentrations in type 2 diabetes mellitus patients. Our results suggest that serum levels of myostatin and irisin are related in patients with type 2 diabetes. Triglyceride and glucose levels could modulate myostatin and irisin concentrations as a compensatory mechanism to improve the metabolic state in these patients although further studies are needed to elucidate whether the action of these myokines represents an adaptative response.

Irisin Inhibits Hepatic Cholesterol Synthesis via AMPK-SREBP2 Signaling

Irisin, a myokine released during exercise, promotes browning of subcutaneous adipose tissue and regulates energy homeostasis. Although exercise constantly reduces blood cholesterol, whether irisin is involved in the regulation of cholesterol remains largely unknown. In the present study, subcutaneous infusion of irisin for 2weeks induced a reduction in plasma and hepatic cholesterol in high fat diet-induced obese (DIO) mice. These alterations were associated with an activation of 5' AMP-activated protein kinase (AMPK) and inhibition of sterol regulatory element-binding transcription factor 2 (SREBP2) transcription and nuclear translocation. In primary hepatocytes from either lean or DIO mice, irisin significantly decreased cholesterol content via sequential activation of AMPK and inhibition of SREBP2. Suppression of AMPK by compound C or AMPKα1 siRNA blocked irisin-induced alterations in cholesterol contents and SREBP2. In conclusion, irisin could suppress hepatic cholesterol production via a mechanism dependent of AMPK and SREBP2 signaling. These findings suggest that irisin is a promising therapeutic target for treatment of hypercholesterolemia.

Circulating Irisin Levels Are Not Regulated by Nutritional Status, Obesity, or Leptin Levels in Rodents

Irisin is a cleaved and secreted fragment of fibronectin type III domain containing 5 (FNDC5) that is mainly released by skeletal muscle and was proposed to mediate the beneficial effects of exercise on metabolism. In the present study we aim to investigate the regulation of the circulating levels of irisin in obese animal models (diet-induced obese (DIO) rats and leptin-deficient (ob/ob) mice), as well as the influence of nutritional status and leptin. Irisin levels were measured by Enzyme-Linked Immunosorbent Assay (ELISA) and Radioimmunoassay (RIA). Serum irisin levels remained unaltered in DIO rats and ob/ob mice. Moreover, its circulating levels were also unaffected by fasting, leptin deficiency, and exogenous leptin administration in rodents. In spite of these negative results we find a negative correlation between irisin and insulin in DIO animals and a positive correlation between irisin and glucose under short-term changes in nutritional status. Our findings indicate that serum irisin levels are not modulated by different physiological settings associated to alterations in energy homeostasis. These results suggest that in rodents circulating levels of irisin are not involved in the pathophysiology of obesity and could be unrelated to metabolic status; however, further studies should clarify its precise role in states of glucose homeostasis imbalance.

Irisin and the Metabolic Phenotype of Adults with Prader-Willi Syndrome

CONTEXT

Hyperphagia, low resting energy expenditure, and abnormal body composition contribute to severe obesity in Prader Willi syndrome (PWS). Irisin, a circulating myokine, stimulates "browning" of white adipose tissue resulting in increased energy expenditure and improved insulin sensitivity. Irisin has not been previously studied in PWS.

OBJECTIVES

Compare plasma and salivary irisin in PWS adults and normal controls. Examine the relationship of irisin to insulin sensitivity and plasma lipids.

DESIGN AND STUDY PARTICIPANTS

A fasting blood sample for glucose, lipids, insulin, leptin, adinopectin, and irisin was obtained from 22 PWS adults and 54 healthy BMI-matched volunteers. Saliva was collected for irisin assay in PWS and controls.

RESULTS

Fasting glucose (77 ± 9 vs 83 ± 7 mg/dl, p = 0.004), insulin (4.1 ± 2.0 vs 7.9 ± 4.7 μU/ml, p<0.001), and triglycerides (74 ± 34 vs 109 ± 71 mg/dl, p = 0.007) were lower in PWS than in controls. Insulin resistance (HOMA-IR) was lower (0.79 ± 0.041 vs 1.63 ± 1.02, p<0.001) and insulin sensitivity (QUICKI) was higher (0.41 ± 0.04 vs 0.36 ± 0.03, p<0.001) in PWS. Plasma irisin was similar in both groups, but salivary irisin (64.5 ± 52.0 vs 33.0 ± 12.1ng/ml), plasma leptin (33.5 ± 24.2 vs 19.7 ± 19.3 ng/ml) and plasma adinopectin (13.0 ± 10.8 vs 7.6 ± 4.5μg/ml) were significantly greater in PWS (p<0.001). In PWS, plasma irisin showed positive Pearson correlations with total cholesterol (r = 0.58, p = 0.005), LDL-cholesterol (r = 0.59, p = 0.004), and leptin (r = 0.43, p = 0.045). Salivary irisin correlated negatively with HDL-cholesterol (r = -0.50, p = 0.043) and positively with LDL-cholesterol (r = 0.51, p = 0.037) and triglycerides (r = 0.50, p = 0.041).

CONCLUSIONS

Salivary irisin was markedly elevated in PWS although plasma irisin was similar to levels in controls. Significant associations with plasma lipids suggest that irisin may contribute to the metabolic phenotype of PWS.

Resistance exercise induces a greater irisin response than endurance exercise

OBJECTIVE

We determined detailed time-course changes in the irisin response to acute exercise using different exercise modes.

METHODS

In experiment 1, seven healthy males rested for 12h (8:00-20:00) to determine the diurnal variation in plasma irisin concentration. In experiment 2, 10 healthy males conducted three exercises to clarify time-course changes in plasma irisin concentration over 6h, using a randomized crossover design. The resistance exercise (R) trial consisted of eight exercises of 12 repetitions with 3-4 sets at 65% of one repetition maximum (1RM). The endurance exercise (E) trial consisted of 60 min of pedaling at 65% of maximal oxygen uptake (VO2max). In the combined mode (R+E) trial, 30 min of endurance exercise was preceded by 30 min of resistance exercise.

RESULTS

In experiment 1, no significant changes in plasma irisin concentration were observed over 12h. In experiment 2, the R trial showed a marked increase in plasma irisin concentration 1h after exercise (P<0.05), but not in the E or R+E trials. The area under the curve (AUC) for irisin concentrations for 6h after exercise was significantly higher in the R trial than in the R+E trial (P<0.05). The AUC for irisin concentrations was significantly correlated with AUC values for blood glucose, lactate, and serum glycerol (r=0.37, 0.45, 0.45, respectively. P<0.05).

CONCLUSIONS

Resistance exercise resulted in significantly greater irisin responses compared with endurance exercise alone, and resistance and endurance exercises combined.

Irisin-encoding gene (FNDC5) variant is associated with changes in blood pressure and lipid profile in type 2 diabetic women but not in men

INTRODUCTION

Irisin has recently been described as a novel myokine, which reduces visceral obesity and improves glucose metabolism in mice. Thus, polymorphisms in the gene encoding irisin, fibronectin type III domain containing 5 (FNDC5), may be associated with type 2 diabetes mellitus (T2DM) and related disorders. However, to date, no study has investigated the association between FNDC5 polymorphisms and susceptibility to T2DM.

OBJECTIVE

To investigate the association of FNDC5 rs3480 (A/G) and rs1746661 (G/T) polymorphisms, alone or in combination, with T2DM and its clinical features.

METHODS

We analyzed 1006 T2DM patients and 434 nondiabetic subjects. Polymorphisms were genotyped by real-time PCR using TaqMan MGB probes. Haplotypes constructed from the combination of rs1746661 and rs3480 polymorphisms were inferred using the Phase 2.1 program.

RESULTS

Genotype, allele and haplotype frequencies of rs1746661 and rs3480 polymorphisms did not differ significantly between nondiabetic subjects and T2DM patients. Women with T2DM carrying the G allele of rs3480 showed increased HbA1c levels compared with A/A carriers, adjusted for age. The T allele of rs1746661 was associated with increased systolic blood pressure, total cholesterol and LDL-cholesterol and decreased HDL-cholesterol in women with T2DM, adjusted for covariates. Moreover, prevalence of hypercholesterolemia was higher in women carrying the T allele of rs1746661 than in G/G carriers (72.4% vs. 58.7%, OR=2.010, 95% CI=1.210-3.390), but it was not significantly different in men.

CONCLUSIONS

These results indicate that, although not associated with T2DM, the G allele of rs3480 appears to be associated with increased HbA1c, while the T allele of rs1746661 appears to be associated with higher systolic blood pressure and dyslipidemia in women with T2DM.

Circulating irisin levels are associated with lipid and uric acid metabolism in a Chinese population

Irisin is a novel hormone secreted by skeletal muscle after exercise, which may ameliorate insulin resistance. In this study, we aimed to explore the relationship between circulating irisin levels and type 2 diabetes mellitus (T2DM) as well as related metabolic traits in a Chinese population. A total of 203 subjects were recruited. Of these, 68 subjects with normal glucose tolerance (NGT), 63 subjects with impaired glucose regulation (IGR) and 72 subjects with new-onset T2DM. Circulating irisin levels were measured by enzyme-linked immunosorbent assay (ELISA). Detailed clinical investigations and biochemistry measurements were carried out in all of the subjects. Multivariate linear regression analysis was performed to assess the association between irisin levels and related metabolic characteristics. All subjects were classified into normal weight and overweight/obese subgroups according to body mass index (BMI). No significant differences in circulating irisin levels were identified among the three groups (P = 0.9741). After adjusting for covariates, multiple linear regression analysis revealed that serum irisin level was independently and significantly associated with total cholesterol (P = 0.0005), low-density lipoprotein cholesterol (P = 0.0014), fasting fatty acids (P = 0.0402) and uric acid (P = 0.0062). By dividing the serum irisin levels into three tertile groups, the values of total cholesterol, low-density lipoprotein cholesterol, fasting fatty acids and uric acid were all increased significantly with the increase of irisin (P < 0.05). Moreover, serum irisin levels remain closely related to total cholesterol in both normal weight and overweight/obese subgroups. Our study suggests that circulating irisin concentrations are significantly associated with lipid and uric acid metabolism in a Chinese population.

Irisin: 'fat' or artefact

Soon after the discovery of the muscle-derived factor irisin, a great controversy arose in the literature regarding certain inconsistencies in the regulation of the fibronectin type III domain containing 5 protein (FNDC5/irisin) after exercise, as well as the unpredicted association of circulating irisin levels with parameters of adiposity in humans. Due to these questionable findings, doubts as to the identity of the soluble portion of FNDC5 as well as the real role of irisin and its possible therapeutic applications in the treatment of obesity and diabetes have proliferated. We recently postulated that FNDC5/irisin is an adipokine expressed and secreted by white adipose tissue in rats and humans. Its circulating concentration correlates with adiposity in humans among independent cohorts of patients. Further analysis, focused on obesity-related metabolic disorders, has shown that irisin could play a role in promoting insulin resistance or act as an adaptive response to counteract disturbances in glucose and lipid homoeostasis in obesity. Overall, this leads us to raise the question whether the new factor, increased in circulation of obese patients, is really irisin-reflecting fat mass or it is an artefact. Therefore, the current review is focused on the potential participation of adipose tissue in irisin circulating levels, and the role of irisin in metabolic pathologies associated with obesity in an attempt to clarify the controversy generated by these recently published reports.

Circulating irisin and glucose metabolism in overweight/obese women: effects of α-lipoic acid and eicosapentaenoic acid

Irisin is a myokine/adipokine with potential role in obesity and diabetes. The objectives of the present study were to analyse the relationship between irisin and glucose metabolism at baseline and during an oral glucose tolerance test (OGTT) and to determine the effects of eicosapentaenoic acid (EPA) and/or α-lipoic acid treatment on irisin production in cultured human adipocytes and in vivo in healthy overweight/obese women following a weight loss program. Seventy-three overweight/obese women followed a 30% energy-restricted diet supplemented without (control) or with EPA (1.3 g/day), α-lipoic acid (0.3 g/day) or both EPA + α-lipoic acid (1.3 + 0.3 g/day) during 10 weeks. An OGTT was performed at baseline. Moreover, human adipocytes were treated with EPA (100-200 μM) or α-lipoic acid (100-250 μM) during 24 h. At baseline plasma, irisin circulating levels were positively associated with glucose levels; however, serum irisin concentrations were not affected by the increment in blood glucose or insulin during the OGTT. Treatment with α-lipoic acid (250 μM) upregulated Fndc5 messenger RNA (mRNA) and irisin secretion in cultured adipocytes. In overweight/obese women, irisin circulating levels decreased significantly after weight loss in all groups, while no additional differences were induced by EPA or α-lipoic acid supplementation. Moreover, plasma irisin levels were positively associated with higher glucose concentrations at beginning and at endpoint of the study. The data from the OGTT suggest that glucose is not a direct contributing factor of irisin release. The higher irisin levels observed in overweight/obese conditions could be a protective response of organism to early glucose impairments.

Effects of short- and long-term Mediterranean-based dietary treatment on plasma LC-QTOF/MS metabolic profiling of subjects with metabolic syndrome features: The Metabolic Syndrome Reduction in Navarra (RESMENA) randomized controlled trial

SCOPE

Adherence to the Mediterranean diet has been associated with a reduced risk of metabolic syndrome (MetS). Metabolomics approach may contribute to identify beneficial associations of metabolic changes affected by Mediterranean diet-based interventions with inflammatory and oxidative-stress markers related to the etiology and development of the MetS.

METHODS AND RESULTS

Liquid chromatography coupled to quadrupole-time of flight-MS metabolic profiling was applied to plasma from a 6-month randomized intervention with two sequential periods, a 2-month nutritional-learning intervention period, and a 4-month self-control period, with two energy-restricted diets; the RESMENA diet (based on the Mediterranean dietary pattern) and the Control diet (based on the American Heart Association guidelines), in 72 subjects with a high BMI and at least two features of MetS. The major contributing biomarkers of each sequential period were lipids, mainly phospholipids and lysophospholipids. Dependency network analysis showed a different pattern of associations between metabolic changes and clinical variables after 2 and 6 month of intervention, with a highly interconnected network during the nutritional-learning intervention period of the study.

CONCLUSION

The 2-month RESMENA diet produced significant changes in the plasma metabolic profile of subjects with MetS features. However, at the end of the 6-month study, most of the associations between metabolic and clinical variables disappeared; suggesting that adherence to healthy dietary habits had declined during the self-control period.

Irisin: a new molecular marker and target in metabolic disorder

Irisin is a newly discovered exercise-mediated myokine which regulates energy metabolism and has been the subject of much recent research. Irisin plays an important role in metabolic diseases making it a potential new target to combat obesity and its associated disorders, such as T2DM. However, the results of several recent studies investigating the effects of irisin have been controversial. The present review will introduce the discovery of irisin, the role of irisin in metabolic disorders, possible mechanisms, and unanswered questions for future research.

Circulating irisin, omentin-1, and lipoprotein subparticles in adults at higher cardiovascular risk

OBJECTIVE

Muscle and fat are now recognized as metabolism-regulating endocrine organs. However, muscle and adipocyte-derived novel cytokines such as irisin and omentin-1 remain understudied in relation to metabolic biomarkers that are associated with cardiovascular risk.

SUBJECTS AND METHODS

Thirty-nine subjects with mean (± SD) BMI of 29.2 ± 5.4 kg/m(2) and either diabetes or two other cardiovascular risk factors were enrolled in a 6-month randomized trial of low-dose ethanol. We examined cross-sectional data at baseline, 3-month, and 6-month visits to assess (1) within-person stability of novel cytokines (irisin, omentin-1, visfatin, resistin, and soluble tumor necrosis factor receptor II) and (2) their associations with metabolic parameters, particularly lipoprotein subparticle profile.

RESULTS

Repeated measures of irisin and omentin-1 were highly correlated, with intra-class correlations of 0.84 (95% CI: 0.74, 0.91; P < 0.001) and 0.81 (0.70, 0.89; P < 0.001), respectively. Irisin was negatively correlated with omentin-1 (7.4% irisin decrease per a 1-SD increment in omentin-1; 95% CI: 0.5%, 13.9%; P = 0.04). In models adjusted for age, sex, and race, irisin was negatively associated with HDL cholesterol (7.3% decrease per a 10mg/dL increment; 1.0%, 13.3%; P = 0.02) and large HDL particles (15.5% decrease per a 1-SD or 3.5-μmol/L increment; 5.2%, 24.7%; P=0.005). Omentin-1 was positively associated with mean VLDL size (3.8% increase per a 1-SD increment; 0.06%, 7.8%; P = 0.05). Adjustment for alcohol intervention, BMI, and other cytokines did not materially affect these associations.

CONCLUSIONS

Irisin and omentin-1 are stable within-person, inversely associated with each other, and closely related to lipoprotein profile. These molecules may be promising markers for cardiovascular risk.

Association of irisin with fat mass, resting energy expenditure, and daily activity in conditions of extreme body mass index

FNDC5/irisin has been recently postulated as beneficial in the treatment of obesity and diabetes because it is induced in muscle by exercise, increasing energy expenditure. However, recent reports have shown that WAT also secretes irisin and that circulating irisin is elevated in obese subjects. The aim of this study was to evaluate irisin levels in conditions of extreme BMI and its correlation with basal metabolism and daily activity. The study involved 145 female patients, including 96 with extreme BMIs (30 anorexic (AN) and 66 obese (OB)) and 49 healthy normal weight (NW). The plasma irisin levels were significantly elevated in the OB patients compared with the AN and NW patients. Irisin also correlated positively with body weight, BMI, and fat mass. The OB patients exhibited the highest REE and higher daily physical activity compared with the AN patients but lower activity compared with the NW patients. The irisin levels were inversely correlated with daily physical activity and directly correlated with REE. Fat mass contributed to most of the variability of the irisin plasma levels independently of the other studied parameters. Conclusion. Irisin levels are influenced by energy expenditure independently of daily physical activity but fat mass is the main contributing factor.