Alterations of irisin concentrations in saliva and serum of obese and normal-weight subjects, before and after 45 min of a Turkish bath or running

Relationships between serum irisin levels and metabolic parameters in Japanese patients with obesity

Background/Purpose

Irisin is a skeletal muscle myokine that causes the brown coloration of white fat, promotes fat burning, inhibits weight gain and may be useful for treatment of obesity. Irisin is also related to glucose/lipid metabolism and may prevent onset of diabetes, but a consensus on irisin secretion has not been reached. The purpose of this study was to determine the relationships between serum irisin levels and physical factors in untreated Japanese men and women with obesity.

Methods

The subjects were 66 untreated patients with obesity (body mass index ≥30 kg m⁻²) who visited our obesity clinic. The subjects included 19 men and 47 women with a mean age of 45.7 ± 13.4 years, mean body weight of 93.8 ± 17.6 kg, and mean body mass index of 36.5 ± 4.7 kg m⁻². At the initial visit, blood sampling was performed, body composition was evaluated using dual energy X‐ray absorptiometry, and exercise tolerance was determined in a cardiopulmonary exercise test. Homeostasis model of assessment – insulin resistance (HOMA‐IR), an index of insulin resistance, and the serum level of irisin were measured.

Results

In men, serum irisin was positively correlated with fasting blood glucose (r = 0.491, P < 0.05), immunoreactive insulin (r = 0.536, P < 0.05), HOMA‐IR (r = 0.635, P < 0.01), body weight (r = 0.491, P < 0.05), lean body mass of the trunk (r = 0.579, P < 0.05) and whole lean body mass (r = 0.489, P < 0.05). In women, serum irisin was positively correlated with immunoreactive insulin (r = 0.502, P < 0.01) and HOMA‐IR (r = 0.385, P < 0.01). In both sexes, HOMA‐IR was an independent variable associated with obesity (men: β = 0.635, R² = 0.369, P < 0.01; women: β = 0.385, R² = 0.129, P < 0.01).

Conclusion

The serum level of irisin was positively correlated with HOMA‐IR in Japanese patients with obesity of both sexes. This suggests that compensatory enhancement of irisin secretion may occur in response to insulin resistance.

In men with obesity, the serum irisin level was positively correlated with the fasting blood glucose level, immunoreactive insulin and homeostasis model of assessment – insulin resistance (HOMA‐IR).

In women with obesity, the serum irisin level was positively correlated with immunoreactive insulin and HOMA‐IR.

In stepwise multiple linear regression analysis, HOMA‐IR was an independent variable associated with obesity.

Compensatory enhancement of irisin secretion may occur in response to insulin resistance.

The relationships of irisin with bone mineral density and body composition in PCOS patients

OBJECTIVE

Our study aims to assay the irisin level and investigate the relationships of irisin level with body mass index (BMI), body composition and bone metabolism in the polycystic ovary syndrome (PCOS) and control women.

METHODS

Fifty two PCOS and 39 control women were recruited. Serum sex hormone, fasting insulin and C-peptide were tested. Fasting serum irisin and adiponectin were measured with enzyme-linked immunosorbent assay. Body composition and bone mineral density were assayed by dual energy X-ray absorptiometry.

RESULTS

Polycystic ovary syndrome women showed different body compositions compared with controls. Serum irisin level of PCOS did not show significant difference compared with controls although it was decreased. The level of adiponectin in PCOS patients was significantly reduced. BMI had no correlation with irisin level. It indicated a positive correlation between serum irisin levels and bone mineral density in the control group and a negative correlation in the PCOS group after BMI and age adjusted. Furthermore, total lean mass has a significant effect on irisin concentration in the PCOS group. There are no correlations between adiponection and body compositions and bone mineral density in both groups.

CONCLUSIONS

The abnormal body composition in PCOS may contribute to the circulation irisin. The crosstalk of irisin in different organs was found and may be related to disease development in PCOS.

Circulating Irisin Concentrations Are Associated with a Favourable Lipid Profile in the General Population

BACKGROUND/AIMS

Irisin is a myokine, which is mainly inversely associated with the risk for non-communicable diseases. Irisin improves cellular energy metabolism by uncoupling the mitochondrial respiratory chain resulting in increased energy expenditure using lipids. To date potential associations between irisin concentration and lipid profile are poorly understood. Therefore, this investigation aimed to evaluate potential associations between irisin and lipid levels in the general population.

METHODS

Data of 430 men and 537 women from the population-based Study of Health in Pomerania (SHIP-TREND) with available irisin and lipid concentrations were used. Analyses of variance, linear and logistic regression models adjusted for age, HBA1c, waist circumference, physical activity, smoking, alcohol consumption, systolic blood pressure, ALAT were calculated.

RESULTS

We detected significantly inverse associations between irisin and circulating levels of total [beta coefficient 0.21 (standard error 0.08), p = 0.01], low-density cholesterol [-0.16 (0.07), p = 0.03] and triglycerides [-0.17 (0.08), p = 0.02] for men. Females without lipid lowering medication had an inverse association between irisin and total cholesterol [-0.12 (0.06), p = 0.05]. Further, male subjects with irisin concentrations in the third tertile had an increased odds for elevated low-density cholesterol [odds ratio 1.96 (95% confidence interval 1.07-3.48), p = 0.03) and triglyceride [1.95 (1.09-3.47), p = 0.02] levels, even after exclusion of subjects with lipid lowering medication. In addition, our data revealed an annual rhythm of serum irisin levels with peak levels arise in winter and summer months.

CONCLUSION

This is the first investigation to report a significant association between circulating irisin and a favourable lipid profile in the general population. This may infer that higher irisin concentrations are associated with a reduced risk for non-communicable diseases.

Irisin, a unique non-inflammatory myokine in stimulating skeletal muscle metabolism

Exercise offers several benefits for health, including increased lean body mass and heightened energy expenditure, which may be partially attributable to secretory factors known as myokines. Irisin, a recently identified myokine, was shown to increase metabolic rate and mitochondrial content in both myocytes and adipocytes; however, the mechanism(s) of action still remain largely unexplained. This work investigated if irisin functions by acting as an inflammatory myokine leading to cellular stress and energy expenditure. C2C12 myotubes were treated with various concentrations of irisin, TNFα, or IL6 for various durations. Glycolytic and oxidative metabolism, as well as mitochondrial uncoupling, were quantified by measurement of acidification and oxygen consumption, respectively. Metabolic gene and protein expression were measured by quantitative real-time polymerase chain reaction (qRT-PCR) and immunoblotting, respectively. Mitochondrial content was assessed by fluorescent imaging. NFκB activity was assessed using an NFκB GFP-linked reporter system. Consistent with previous findings, irisin significantly increased expression of several genes including peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) leading to increased mitochondrial content and oxygen consumption. Despite some similarities between TNFα and irisin treatment, irisin failed to activate the NFκB pathway like TNFα, suggesting that irisin may not act as an inflammatory signal. Irisin has several effects on myotube metabolism which appear to be dependent on substrate availability; however, the precise mechanism(s) by which irisin functions in skeletal muscle remain unclear. Our observations support the hypothesis that irisin does not function through inflammatory NFκB activation like other myokines (such as TNFα).

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.

Resistance exercise training increases the expression of irisin concomitant with improvement of muscle function in aging mice and humans

We investigated the effect of resistance training on irisin expression with improvement in muscle strength and function in aged mice and human. In the mice study, 19 months old male C57BL/6 mice were randomly assigned into two groups; control group and resistance exercise group. Ladder climbing exercise with tail weight was performed 3 days per week for 12 weeks. In the human study, participants (aged over 65 years) were randomly assigned into exercise group or control group. Elastic band exercise program consisted of 12 weeks of 1-h session 2 days per week. In the mice study, we found an increase of irisin in serum and soleus muscle as well as improvement in muscle strength (p=0.02) and muscle quality (p=0.03) without body composition change in training animals. In the human study, isokinetic leg strength and grip strength were improved in the exercise group compared to the control group without change of body composition. In addition, the level of circulating irisin level was increased. It had a positive correlation with grip strength (R=0.526, p=0.002) and leg strength (R=0.414, p=0.003) in the exercise group. Thus, resistant training might be an efficient intervention method to increase irisin levels and prevent age-related decline in muscle function.

Colonization of Legionella species in Turkish baths in hotels in Alanya, Turkey

This study evaluated the prevalence of Legionella species in water samples collected from Turkish baths in hotels in Alanya, Turkey, from August 2003 to September 2013. Water samples were collected in 100-mL sterile containers and then concentrated by filtration. Heat treatment was used to eliminate other microorganisms from the samples, which were then spread on Legionella-selective-buffered charcoal yeast extract alpha (BCYE-α) agar and on BCYE-α agar supplemented with glycine, vancomycin, polymyxin, and cycloheximide. Cysteine-dependent colonies were identified by latex agglutination. In total, 135 samples from 52 hotels with Turkish baths were evaluated. Legionella species were identified in 11/52 (21.2%) hotels and 18/135 (13.3%) samples. The most frequently isolated species was Legionella pneumophila, with most isolates belonging to serogroups 6 (55.6%) and 1 (22.2%). The colony count was <100 colony-forming units (CFU) mL(-1) in nine samples, from 100 to 1000 CFU mL(-1) in six samples, and >1000 CFU mL(-1) in three samples. These findings suggest that the hot water systems of Turkish baths in hotels must be viewed as a possible source of travel-associated Legionnaires' disease, and preventative measures should be put in place.

Irisin levels before and after physical activity among school-age children with different BMI: a direct relation with leptin

OBJECTIVE

Irisin is a novel myokine that seems to mediate the beneficial effects of exercise. Levels of circulating irisin before and after an 8-month physical activity program (PAP) in school-age children were evaluated.

METHODS

Irisin and leptin were measured at baseline and at follow-up among 85 children with different BMI.

RESULTS

Of the 85 children (mean age 8.9; 47% female), 25 children had normal weight, 23 were overweight, and 37 had obesity. We observed no significant difference in irisin serum levels between boys and girls. Irisin was positively associated with BMI before and after the PAP (r(before) = 0.42; r(after) = 0.37, P < 0.001), with the highest levels in children with obesity. There was a slight decrease of circulating irisin after PAP, but this decrease was not of statistical significance. We observed a high and positive association between irisin and leptin levels before and after the PAP (r(before) = 0.78; r(after) = 0.82, P < 0.001). Moreover, changes in leptin correlated with changes in irisin (r = 0.72, P < 0.001).

CONCLUSIONS

Circulating irisin is positively linked to BMI and leptin in school-age children, supporting the notion that that irisin is produced by adipose tissue. As in previous reports, this study failed to observe changes in irisin levels after exercise, likely because higher irisin levels are produced only during exercise.

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.

Increased 24-hour ad libitum food intake is associated with lower plasma irisin concentrations the following morning in adult humans

BACKGROUND

The relationship between food intake and irisin concentrations in humans is unclear.

OBJECTIVES

To determine whether the previous day's intake impacts fasting plasma irisin concentrations, or whether fasting irisin concentrations associate with subsequent ad libitum food intake.

METHODS

Sixty-six nondiabetic adults (42 men) were admitted for a study of the determinants of energy intake. After 6 days of a weight maintaining diet, ad libitum energy intake over 3 days was assessed using a vending machine paradigm. Fasting plasma irisin concentrations were measured on the morning of the second day of the vending period.

RESULTS

There were no correlations between irisin and demographic or anthropometric parameters. On day 1, subjects consumed 144 ± 52% of weight maintaining energy needs. Every additional 500 kcal consumed on day 1 associated with a 3.4% lower irisin concentration the following morning (95% CI -6.2, -0.4%, p = 0.01; adjusted for age, sex and race). If energy intake was expressed as a percentage of weight maintaining energy needs, every 10% increase associated with a 1.9% lower irisin concentration (95% CI -3.7, -0.1%; adjusted p = 0.02). A 100 kcal increase in carbohydrate or fat consumption associated with a 1.3% (95% CI -2.5, -0.1%, p = 0.01) and a 0.6% (95% CI -1.1, -0.0%, p = 0.02) lower irisin concentration, respectively. There was no association between fasting irisin concentrations and subsequent energy intake on day 2 (r = 0.19, p = 0.1).

CONCLUSIONS

Higher ad libitum 24 h energy intake was associated with lower fasting irisin concentrations the following morning, but fasting irisin concentrations did not predict subsequent energy intake. The decrease in irisin concentrations with increased energy intake is consistent with the detrimental metabolic effects of overeating.

Irisin and Myonectin Regulation in the Insulin Resistant Muscle: Implications to Adipose Tissue: Muscle Crosstalk

Myokines are peptides produced and secreted by the skeletal muscle, with autocrine, paracrine, and endocrine actions. Many of them are overexpressed during physical exercise and appear to contribute to the benefits of exercise to metabolic homeostasis. Irisin, resulting from the cleavage of the membrane protein FNDC5, was shown to induce adipocyte browning, with increased lipid oxidation and thermogenesis. Myonectin was only recently discovered and initial studies revealed a role in fatty acid uptake and oxidation in adipose tissue and liver. However, the mechanisms of their regulation by exercise are not entirely established. Impaired secretion and action of myokines, such as irisin and myonectin, may have a role in the establishment of insulin resistance. On the other hand, several studies have shown that insulin resistance in the skeletal muscle may change myokines expression and secretion. This may have consequences on lipid and glucose metabolism in adipose tissue and lead to a vicious cycle between impaired myokines production and insulin resistance. This review summarizes the current knowledge about the influence of skeletal muscle insulin resistance on the secretion of irisin and myonectin, as well as its impact on adipose tissue metabolism.

A comprehensive immunohistochemical examination of the distribution of the fat-burning protein irisin in biological tissues

Irisin was first identified in skeletal muscle cells, but its precise location has not yet been demonstrated, and there is limited information about irisin protein in other human and rat tissues. The present immunohistochemical study was undertaken to screen skeletal muscle and other tissues for irisin immunoreactivity. İrisin staining was found in the brain (neurons and neuroglia), cardiac and skeletal muscle (fibers) and skin (sebaceous glands) tissues in male rats. In both human adult and fetal skeletal muscle, the most intense immunohistochemical staining was in the perimysium and endomysium, in the peripheral nerve (epineurium) and axon and nerve sheaths spreading among the cells, in the sarcoplasma and subendomysium. Irisin was also demonstrated in the testis (seminiferous tubules, some spermatogenic cells in fetal and Leydig cells in fetal and adult testis, ductus epididymis in fetal human epididymis); pancreas (islets of Langerhans, serous acini cells, intralobular and intralobular ducts cells); liver (hepatocytes; Kupffer cells and sinusoidal endothelial cells); spleen (subcapsular region and periarterial lymphatic sheets); the stomach (gastric parietal cells, tunica muscularis cells). We conclude that the fat-burning protein irisin locally produced in peripheral and central tissues could act as a gatekeeper of metabolic energy regulation in those tissues, since this myokine converts white into brown adipose tissue, enhancing energy expenditure.

Relationship between expression of matrix metalloproteinase-9 and adenylyl cyclase-associated protein 1 in chronic obstructive pulmonary disease

OBJECTIVE

To investigate the relationship between expression of matrix metalloproteinase (MMP)-9 and expression of adenylyl cyclase-associated protein (CAP)-1 in chronic obstructive pulmonary disease (COPD).

METHODS

Patients with possible respiratory disease were recruited into the study and divided into a COPD group and a non-COPD group on diagnosis. Pulmonary function tests were performed and serum concentrations of MMP-9 were measured using an enzyme-linked immunosorbent assay. MMP-9 and CAP1 expression were analysed in lung tissue and bronchoalveolar lavage fluid in all available samples using immunohistochemistry and Western blot, respectively. In addition, expression of MMP-9 and CAP1 in vitro was investigated using immunofluorescence. Expression of CAP1 in response to MMP-9 was measured in the human alveolar epithelial cell line HP-AEpiC, using Western blot.

RESULTS

A total of 90 patients were included in the study: 52 were in the COPD group and 38 in the non-COPD group. Serum MMP-9 concentrations were significantly higher in the COPD than in the non-COPD group. MMP-9 serum concentrations were negatively correlated with forced expiratory volume in 1 s (FEV1), FEV1 as a percentage of the normal predicted value and the ratio of FEV1 to forced vital capacity, and were positively correlated with residual volume (RV), total lung capacity (TLC) and RV/TLC values. In lung tissue and bronchoalveolar lavage fluid samples, MMP-9 and CAP1 expression were inversely related. This relationship was confirmed in HP-AEpiC cells. High expression of MMP-9 and low expression of CAP1 was demonstrated in the COPD group compared with the non-COPD group.

CONCLUSIONS

This study demonstrated an inverse relationship between CAP1 and MMP-9 expression, and high expression of MMP-9 and low expression of CAP1 in those with COPD compared with the non-COPD group. Overexpression of MMP-9 in lung tissue and its interaction with CAP1 is likely to play a major role in airway obstruction in COPD.

Plasma irisin levels progressively increase in response to increasing exercise workloads in young, healthy, active subjects

BACKGROUND

Irisin, a recently discovered myokine, has been shown to induce browning of white adipose tissue, enhancing energy expenditure and mediating some of the beneficial effects of exercise. We aimed to estimate the time frame of changes in irisin levels after acute exercise and the effect of different exercise workloads and intensities on circulating irisin levels immediately post-exercise.

METHODS

In a pilot study, four healthy subjects (22.5±1.7 years) underwent maximal workload exercise (maximal oxygen consumption, VO2 max) and blood was drawn at prespecified intervals to define the time frame of pre- and post-exercise irisin changes over a 24-h period. In the main study, 35 healthy, non-smoking (23.0±3.3 years) men and women (n=20/15) underwent three exercise protocols ≥48-h apart, in random order: i) maximal workload (VO2 max); ii) relative workload (70% of VO2 max/10 min); and iii) absolute workload (75 W/10 min). Blood was drawn immediately pre-exercise and 3 min post-exercise.

RESULTS

In the pilot study, irisin levels increased by 35% 3 min post-exercise, then dropped and remained relatively constant. In the main study, irisin levels post-exercise were significantly higher than those of pre-exercise after all workloads (all, P<0.001). Post-to-pre-exercise differences in irisin levels were significantly different between workloads (P=0.001), with the greatest increase by 34% following maximal workload (P=0.004 vs relative and absolute).

CONCLUSIONS

Circulating irisin levels were acutely elevated in response to exercise, with a greater increase after maximal workload. These findings suggest that irisin release could be a function of muscle energy demand. Future studies need to determine the underlying mechanisms of irisin release and explore irisin's therapeutic potential.

Browning of white fat: does irisin play a role in humans?

The discovery of irisin as an exercise-regulated myokine inducing browning of WAT has gained interest as a potential new strategy to combat obesity and its associated disorders, such as type 2 diabetes. However, there are inconsistencies regarding the relevance of irisin in humans. The regulation of FNDC5 mRNA expression by exercise and contraction could not be reproduced by a number of human studies using several exercise protocols and in vitro approaches. Furthermore, the nature of FNDC5 fragments and the presence of irisin in humans are questionable and probably contribute to conflicting data obtained with commercially available ELISA kits. Most importantly, the information regarding the concentration of circulating irisin in humans is not clear, as different studies using different kits measure irisin levels in a wide range. Data about the role of irisin in states of human obesity and metabolic diseases are conflicting and, in some cases, changes in irisin levels have been observed; they were only moderate in 10-20%. Independent of the presence and regulation of FNDC5/irisin in humans, the application of recombinant irisin could still represent a therapeutic strategy to fight obesity. However, the current data obtained from human cell models reveal that FNDC5/irisin has no effect on browning of the major WAT depots in humans and is likely to selectively target a small subpopulation of adipocytes, which are located in classical BAT regions, such as the supraclavicular adipose tissue. Thus, other candidates, such as BMP7 or CNPs, seem to be more prominent candidates as inducers of browning in humans.

Three new players in energy regulation: preptin, adropin and irisin

Homeostasis of energy is regulated by genetic factors, food intake, and energy expenditure. When energy input is greater than expenditure, the balance is positive, which can lead to weight gain and obesity. When the balance is negative, weight is lost. Regulation of this homeostasis is multi-factorial, involving many orexigenic (appetite-stimulating) and anorexigenic (appetite-suppressing) peptide hormones. Peripheral tissues are now known to be involved in weight regulation and research on its endocrine characteristics proceeds apace. Preptin with 34 amino acids (MW 3948 Da), adropin with 43 amino acids and a molecular weight of (4999 Da), and irisin with 112 amino acids (12587 Da), are three newly discovered peptides critical for regulating energy metabolism. Preptin is synthesized primarily in pancreatic beta cells, and adropin mainly in the liver and brain, and many peripheral tissues. Irisin, however, is synthesized principally in the heart muscle, along with peripheral tissues, including salivary glands, kidney and liver. The prime functions of preptin and adropin include regulating carbohydrate, lipid and protein metabolisms by moderating glucose-mediated insulin release. Irisin is an anti-obesitic and anti-diabetic hormone regulating adipose tissue metabolism and glucose homeostasis by converting white to brown adipose tissue. This review offers a historical account of these discovery and function of these peptides, including their structure, and physiological and biochemical properties. Their roles in energy regulation will be discussed. Their measurement in biological fluids will be considered, which will lead to further discussion of their possible clinical value.

Decreased saliva/serum irisin concentrations in the acute myocardial infarction promising for being a new candidate biomarker for diagnosis of this pathology

Irisin is a muscle-secreted protein. Cardiac muscle produces more irisin than skeletal muscle in response to acute exercise, and is associated with myocardial infarction (MI) in an experimental model induced by isoproterenol in rats. The timing and significance of its release in patients with acute myocardial infarction (AMI) needs further investigation. We have studied the relationship between serum/saliva irisin concentration and AMI in humans. Serum and saliva samples were taken within 3 days of admission in 11 patients with AMI and in 14 matched controls. Salivary gland irisin was detected immunohistochemically, and serum and saliva levels were measured by ELISA. The three major paired salivary glands (submandibular, sublingual and parotid) produce and release irisin into saliva. Troponin-I, CK, CK-MB concentrations in the AMI group gradually increased from up to 12h, while saliva and serum irisin gradually decreased from up to 48 h, compared with the control group (P<0.05). After 12h, troponin-I, CK, CK-MB started to decrease, while saliva and serum irisin started to increase at 72 h. Serum irisin levels correlated with age, while troponin I, CK-MB, and CK were correlated and with saliva irisin in AMI patients. Besides cardiac troponin and CK-MB, irisin adds new diagnostic information in AMI patients, and the gradual decrease of saliva/serum irisin over 48 h could be a useful biomarker.

Irisin: a potentially candidate marker for myocardial infarction

Myocardial infarction (MI) causes energy depletion through imbalance between coronary blood supply and myocardial demand. Irisin produced by the heart reduces ATP production by increasing heat generation. Energy depletion affects irisin concentration in circulation and cardiac tissues, suggesting an association with MI. We examined: (1) irisin expression immunohistochemically in rat heart, skeletal muscle, kidney and liver in isoproterenol (ISO)-induced MI, and (2) serum irisin concentration by ELISA. Rats were randomly allocated into 6 groups (n=6), (i) control, (ii) ISO (1h), (iii) ISO (2h), (iv) ISO (4h), (v) ISO (6h), and (vi) ISO (24h), 200mg ISO in each case. Rats were decapitated and the blood and tissues collected for irisin analysis. Blood was centrifuged at 1792 g for 5 min. Tissues were washed with saline and fixed in 10% formalin for histology. Serum irisin levels gradually decreased from 1h to 24h in MI rats compared with controls, the minimum being at 2h, increasing again after 6h. Cardiac muscle cells, glomerular, peritubular renal cortical interstitial cells, hepatocytes and liver sinusoidal cells and perimysium, endomysium and nucleoi of skeletal muscle were irisin positive, but its synthesis decreased 1-4h after MI. At all time-points, irisin increased near myocardial connective tissue, with production in skeletal muscle, liver and kidney recovering after 6h, although slower than controls. Unique insight into the pathogenesis of MI is shown, and the gradually decrease of serum irisin might be a diagnostic marker for MI.

Irisin as a muscle-derived hormone stimulating thermogenesis--a critical update

The recently described myokine, irisin is cleaved from fibronectin type III domain containing protein 5 (FNDC5) and has been proposed to be secreted upon exercise to promote the browning of beige fat cells in white adipose tissue that results in enhanced thermogenesis and increased energy expenditure. The initial studies suggested irisin as a treatment option for obesity and associated diseases such as type 2 diabetes mellitus and stimulated further research. However, the results of subsequent studies investigating the regulation of irisin by different types of exercise are partly conflicting and effects were only shown in highly selective patient populations so far. Moreover, other parameters like body weight or fat free mass were shown to influence irisin adding more complexity to the mechanisms regulating this hormone. The present review will describe the discovery of irisin, its potential role in adipose tissue-mediated thermogenesis, its regulation by exercise and lastly, discuss current controversies and highlight gaps of knowledge to be filled by future studies.

Cardiac, skeletal muscle and serum irisin responses to with or without water exercise in young and old male rats: cardiac muscle produces more irisin than skeletal muscle

Irisin converts white adipose tissue (WAT) into brown adipose tissue (BAT), as regulated by energy expenditure. The relationship between irisin concentrations after exercise in rats compared humans after exercise remains controversial. We therefore: (1) measured irisin expression in cardiac and skeletal muscle, liver, kidney, peripheral nerve sheath and skin tissues, as also serum irisin level in 10 week-old rats without exercise, and (2) measured tissue supernatant irisin levels in cardiac and skeletal muscle, and in response to exercise in young and old rats to establishing which tissues produced most irisin. Young (12 months) and old rats (24 months) with or without 10min exercise (water floating) and healthy 10 week-old Sprague-Dawley rats without exercise were used. Irisin was absent from sections of skeletal muscle of unexercised rats, the only part being stained being the perimysium. In contrast, cardiac muscle tissue, peripheral myelin sheath, liver, kidneys, and skin dermis and hypodermis were strongly immunoreactivity. No irisin was seen in skeletal muscle of unexercised young and old rats, but a slight amount was detected after exercise. Strong immunoreactivity occurred in cardiac muscle of young and old rats with or without exercise, notably in pericardial connective tissue. Serum irisin increased after exercise, being higher in younger than older rats. Irisin in tissue supernatants (cardiac and skeletal muscle) was high with or without exercise. High supernatant irisin could come from connective tissues around skeletal muscle, especially nerve sheaths located within it. Skeletal muscle is probably not a main irisin source.