Plasma Levels of Myonectin But Not Myostatin or Fibroblast-Derived Growth Factor 21 Are Associated with Insulin Resistance in Adult Humans without Diabetes Mellitus

Higher serum myostatin levels are associated with lower insulin sensitivity in adults with overweight/obesity

Myostatin inhibition improves insulin sensitivity in preclinical and clinical models; however, studies investigating the relationship between serum myostatin levels and insulin sensitivity are discrepant. Sensitive and specific myostatin LC-MS/MS assays are now available to accurately assess serum myostatin level in vivo. We sought to determine whether higher serum myostatin levels are independently associated with lower insulin sensitivity in adults with overweight/obesity. Participants included 74 adults, 20-65 years old, BMI ≥25 kg/m2 without type 2 diabetes. Appendicular lean mass (ALM) was measured by dual-energy x-ray absorptiometry; visceral adipose tissue (VAT) was measured by computed tomography. Main outcome measures were serum myostatin levels (LC-MS/MS) and insulin sensitivity (Matsuda index). Mean age was 48 ± 12 years, and BMI was 33.1 ± 5.6 kg/m2 (mean ± SD). Men had higher mean serum myostatin levels versus women (8.3 ± 1.9 vs. 7.2 ± 1.9 ng/mL, p = 0.01) and higher serum myostatin levels were associated with higher ALM (R = 0.34, p = 0.003). Higher serum myostatin levels were associated with lower Matsuda index (R = -0.44, p = 0.0004), which remained significant after controlling for BMI, VAT, ALM, and sex. In conclusion, higher serum myostatin levels are independently associated with lower insulin sensitivity in adults with overweight/obesity and may be a marker of or play a mechanistic role in the development of insulin resistance.

Diagnostic and predictive abilities of myokines in patients with heart failure

Myokines are defined as a heterogenic group of numerous cytokines, peptides and metabolic derivates, which are expressed, synthesized, produced, and released by skeletal myocytes and myocardial cells and exert either auto- and paracrine, or endocrine effects. Previous studies revealed that myokines play a pivotal role in mutual communications between skeletal muscles, myocardium and remote organs, such as brain, vasculature, bone, liver, pancreas, white adipose tissue, gut, and skin. Despite several myokines exert complete divorced biological effects mainly in regulation of skeletal muscle hypertrophy, residential cells differentiation, neovascularization/angiogenesis, vascular integrity, endothelial function, inflammation and apoptosis/necrosis, attenuating ischemia/hypoxia and tissue protection, tumor growth and malignance, for other occasions, their predominant effects affect energy homeostasis, glucose and lipid metabolism, adiposity, muscle training adaptation and food behavior. Last decade had been identified 250 more myokines, which have been investigating for many years further as either biomarkers or targets for heart failure management. However, only few myokines have been allocated to a promising tool for monitoring adverse cardiac remodeling, ischemia/hypoxia-related target-organ dysfunction, microvascular inflammation, sarcopenia/myopathy and prediction for poor clinical outcomes among patients with HF. This we concentrate on some most plausible myokines, such as myostatin, myonectin, brain-derived neurotrophic factor, muslin, fibroblast growth factor 21, irisin, leukemia inhibitory factor, developmental endothelial locus-1, interleukin-6, nerve growth factor and insulin-like growth factor-1, which are suggested to be useful biomarkers for HF development and progression.

Lower skeletal muscle mass is associated with diabetes and insulin resistance: A cross-sectional study

AIMS

The association between skeletal muscle mass and diabetes incidence/insulin resistance/glycated hemoglobin (HbA1C) is unknown. The aim of this study was to investigate such association in clinically apparently healthy males and females.

METHODS

A cross-sectional study of 372,399 Korean males and females who completed bioelectrical impedance analysis (BIA) in a health-screening programme was performed. Skeletal muscle index was used as an indicator of skeletal muscle mass. Skeletal muscle index (%) [appendicular skeletal muscle mass (kg)/body weight (kg)X100] was estimated using BIA. The study outcomes were diabetes incidence, homoeostasis model assessment of insulin resistance (HOMA-IR), and HbA1C.

RESULTS

The mean age of study participants was 38.92 ± 8.54 years. Multiple logistic regression analysis revealed a significant negative association between Skeletal muscle index and diabetes incidence/HOMA-IR/HbA1C after adjusting for various confounding factors. Odds ratios (95% confidence interval (CI)) of diabetes incidence in Q2, Q3, and Q4 compared to the lowest quantile (Q1) were 0.95 (0.85-1.05), 0.88 (0.78-0.99), and 0.79 (0.69-0.9), respectively. Beta coefficients (95% CI) of HOMA-IR in Q2, Q3, and Q3 with Q1 were 0.05 (0.03-0.07), -0.06 (-0.09∼-0.04), and -0.19 (-0.22∼-0.16), respectively. Beta coefficients (95% CI) of HbA1C in Q2, Q3, and Q4 with Q1 were 0.02 (0.01-0.03), -0.001 (-0.01∼0.01), and -0.02 (-0.03∼-0.01), respectively.

CONCLUSIONS

This study demonstrated negative associations of skeletal muscle mass with diabetes incidence, insulin resistance, and HbA1C levels in healthy adults.

Serum Levels of Myonectin Are Lower in Adults with Metabolic Syndrome and Are Negatively Correlated with Android Fat Mass

Myonectin has shown beneficial effects on lipid regulation in murine models; therefore, it may have implications in the pathophysiology of metabolic syndrome (MS). We evaluated the relationship between serum myonectin and serum lipids, global and regional fat mass, intramuscular lipid content, and insulin resistance (IR) in adults with metabolic risk factors. This was a cross-sectional study in sedentary adults who were diagnosed with MS or without MS (NMS). Serum myonectin was quantified by enzyme-linked immunosorbent assay, lipid profile by conventional techniques, and free fatty acids (FFA) by gas chromatography. Body composition was assessed by dual-energy X-ray absorptiometry and intramuscular lipid content through proton nuclear magnetic resonance spectroscopy in the right vastus lateralis muscle. IR was estimated with the homeostatic model assessment (HOMA-IR). The MS (n = 61) and NMS (n = 29) groups were comparable in age (median (interquartile range): 51.0 (46.0-56.0) vs. 53.0 (45.5-57.5) years, p > 0.05) and sex (70.5% men vs. 72.4% women). MS subjects had lower serum levels of myonectin than NMS subjects (1.08 (0.87-1.35) vs. 1.09 (0.93-4.05) ng·mL^-1, p < 0.05). Multiple linear regression models adjusted for age, sex, fat mass index and lean mass index showed that serum myonectin was negatively correlated with the android/gynoid fat mass ratio (R² = 0.48, p < 0.01), but not with the lipid profile, FFA, intramuscular lipid content or HOMA-IR. In conclusion, serum myonectin is lower in subjects with MS. Myonectin negatively correlates with a component relevant to the pathophysiology of MS, such as the android/gynoid fat mass ratio, but not with other components such as FFA, intramuscular fat or IR.

Novel Approach for Glycemic Management Incorporating Vibration Stimulation of Skeletal Muscle in Obesity

Because obesity is associated with impaired glucose tolerance and type 2 diabetes (T2D), it is important to manage the blood glucose level at an early stage. Nevertheless, people with obesity have significantly lower resistance to muscle fatigue after exercise and exercise adherence. Therefore, we developed a novel "Relaxing-Vibration Training (RVT)" consisting of 25 postures using vibration stimulation of skeletal muscle and determined the feasibility of RVT for glycemic management. Thirty-one participants with obesity were enrolled in a controlled trial (CT) and experimental trial (ET) based on a 75 g oral glucose tolerance test (OGTT). During the CT, participants were required to rest in a quiet room. During the ET, the RVT program (50 Hz, 4 mm), consisting of 25 postures of relaxation and stretching on the vibratory platform, was performed for 40 min. Subsequently, the participants rested as in the CT. Subjective fatigue and muscle stiffness measurements and blood collection were conducted before and after RVT. In both the CT and ET, interstitial fluid (ISF) glucose concentrations were measured every 15 min for 2 h. The incremental area under the curve value of real-time ISF glucose during an OGTT was significantly lower in the ET than in the CT (ET: 7476.5 ± 2974.9, CT: 8078.5 ± 3077.7, effect size r = 0.4). Additionally, the levels of metabolic glucose regulators associated with myokines, muscle stiffness, and subjective fatigue significantly improved after RVT. This novel RVT suggests that it is effective in glycemic management with great potential to improve impaired glucose tolerance and T2D with obesity in the future.

Myokine, a key cytokine for physical exercise to alleviate sarcopenic obesity

Skeletal muscle has a robust endocrine function as a powerful organ and can secrete and release cytokines or polypeptides known as myokines. These myokines have significant regulatory effects on signal transduction in skeletal muscle and the metabolism of peripheral tissues and organs and exert biological effects via autocrine, paracrine, or endocrine forms. Obesity and aging cause myokine secretion dysregulation, and hastening sarcopenic obesity (SO) development. Exercise is currently an excellent intervention and prevention method for SO. Meanwhile, exercise impacts many organs and tissues. These organs and tissues will produce various myokines in response to movement and metabolism throughout the body to govern muscle differentiation, growth, and remodeling. According to accumulating data, exercise can increase the release of myokines from diverse tissues into the blood and postpone the SO onset and progression by influencing protein metabolism, inflammation, mitochondrial quality control, and other mechanisms.

Epidemiological, mechanistic, and practical bases for assessment of cardiorespiratory fitness and muscle status in adults in healthcare settings

Given their importance in predicting clinical outcomes, cardiorespiratory fitness (CRF) and muscle status can be considered new vital signs. However, they are not routinely evaluated in healthcare settings. Here, we present a comprehensive review of the epidemiological, mechanistic, and practical bases of the evaluation of CRF and muscle status in adults in primary healthcare settings. We highlight the importance of CRF and muscle status as predictors of morbidity and mortality, focusing on their association with cardiovascular and metabolic outcomes. Notably, adults in the best quartile of CRF and muscle status have as low as one-fourth the risk of developing some of the most common chronic metabolic and cardiovascular diseases than those in the poorest quartile. The physiological mechanisms that underlie these epidemiological associations are addressed. These mechanisms include the fact that both CRF and muscle status reflect an integrative response to the body function. Indeed, muscle plays an active role in the development of many diseases by regulating the body's metabolic rate and releasing myokines, which modulate metabolic and cardiovascular functions. We also go over the most relevant techniques for assessing peak oxygen uptake as a surrogate of CRF and muscle strength, mass, and quality as surrogates of muscle status in adults. Finally, a clinical case of a middle-aged adult is discussed to integrate and summarize the practical aspects of the information presented throughout. Their clinical importance, the ease with which we can assess CRF and muscle status using affordable techniques, and the availability of reference values, justify their routine evaluation in adults across primary healthcare settings.

Upregulation of IL-8, osteonectin, and myonectin mRNAs by intermittent hypoxia via OCT1- and NRF2-mediated mechanisms in skeletal muscle cells

Sleep apnoea syndrome is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]) and is a risk factor for insulin resistance/Type 2 diabetes. The induction of insulin resistance in skeletal muscle is a key phenomenon to develop diabetes. However, the mechanisms linking IH stress and insulin resistance remain elusive. We exposed human RD and mouse C2C12 muscle cells to normoxia or IH and measured their mRNA levels by real-time RT-PCR. We found that IH significantly increased the mRNA and protein levels of muscle-derived insulin resistance-factors (myokines) such as IL-8, osteonectin (ON), and myonectin (MN) in muscle cells. We further analysed the IH-induced expression mechanisms of IL-8, ON, and MN genes in muscle cells. Deletion analyses of the human myokine promoter(s) revealed that the regions -152 to -151 in IL-8, -105 to -99 in ON, and - 3741 to -3738 in MN promoters were responsible for the activation by IH in RD cells. The promoters contain consensus transcription factor binding sequences for OCT1 in IL-8 and MN promoters, and for NRF2 in ON promoter, respectively. The introduction of siRNA for OCT1 abolished the IH-induced expression(s) of IL-8 and MN and siRNA for NRF2 abolished the IH-induced expression of ON.

Plasma Complement C1q/tumor necrosis factor-related protein 15 concentration is associated with polycystic ovary syndrome

Polycystic ovarian syndrome (PCOS) is a common poignant endocrine disorder affecting women, posing a close association with metabolic syndrome and obesity. Existing literature characterizes PCOS with deranged levels of several adipokines and myokines. CTRP15 is a paralogue of adiponectin, mainly expressed by skeletal muscles, and plays a key role in insulin, glucose, and lipid metabolism. In the current study, we aim to determine the circulating levels of CTRP15 and evaluate its association with cardiometabolic and inflammatory parameters in PCOS women. This case-control study included 120 PCOS patients (60 Recurrent pregnancy loss (RPL) and 60 infertile (inf) PCOS) and 60 healthy non-PCOS controls. Serum levels of hs-CRP were measured by commercial kits, while serum levels of adiponectin and CTRP15 were determined using the ELISA technique. Serum levels of CTRP15 were significantly elevated in PCOS-RPL and PCOS-inf subgroups when compared to controls (94.80 ± 27.08 and 87.77 ± 25.48 vs. 54.78 ± 15.45, both P < 0.001). Moreover, serum adiponectin was considerably lower in the PCOS group and subgroups (P < 0.001), while serum hs-CRP, fasting insulin, HOMA-IR, and free testosterone were significantly higher when compared to the non-PCOS group (P < 0.05). Furthermore, CTRP15 closely associated with FSH, HOMA-IR, hs-CRP, and BMI. These results highlight a possible involvement of CTRP15 in the pathogenesis of PCOS. The elevated levels of CTRP15 might be a compensatory mechanism for the metabolic dysregulations (excess adiposity, insulin resistance, metaflammation) associated with the syndrome. Nevertheless, future studies are necessary to unravel the underlying mechanism.

Influence of Nutritional Status and Physical Exercise on Immune Response in Metabolic Syndrome

Metabolic Syndrome (MetS) is a cluster of metabolic alterations mostly related to visceral adiposity, which in turn promotes glucose intolerance and a chronic systemic inflammatory state, characterized by immune cell infiltration. Such immune system activation increases the risk of severe disease subsequent to viral infections. Strong correlations between elevated body mass index (BMI), type-2-diabetes and increased risk of hospitalization after pandemic influenza H1N1 infection have been described. Similarly, a correlation between elevated blood glucose level and SARS-CoV-2 infection severity and mortality has been described, indicating MetS as an important predictor of clinical outcomes in patients with COVID-19. Adipose secretome, including two of the most abundant and well-studied adipokines, leptin and interleukin-6, is involved in the regulation of energy metabolism and obesity-related low-grade inflammation. Similarly, skeletal muscle hormones—called myokines—released in response to physical exercise affect both metabolic homeostasis and immune system function. Of note, several circulating hormones originate from both adipose tissue and skeletal muscle and display different functions, depending on the metabolic context. This review aims to summarize recent data in the field of exercise immunology, investigating the acute and chronic effects of exercise on myokines release and immune system function.

FGF21 (Fibroblast Growth Factor 21) Defines a Potential Cardiohepatic Signaling Circuit in End-Stage Heart Failure

BACKGROUND

Extrinsic control of cardiomyocyte metabolism is poorly understood in heart failure (HF). FGF21 (Fibroblast growth factor 21), a hormonal regulator of metabolism produced mainly in the liver and adipose tissue, is a prime candidate for such signaling.

METHODS

To investigate this further, we examined blood and tissue obtained from human subjects with end-stage HF with reduced ejection fraction at the time of left ventricular assist device implantation and correlated serum FGF21 levels with cardiac gene expression, immunohistochemistry, and clinical parameters.

RESULTS

Circulating FGF21 levels were substantially elevated in HF with reduced ejection fraction, compared with healthy subjects (HF with reduced ejection fraction: 834.4 [95% CI, 628.4-1040.3] pg/mL, n=40; controls: 146.0 [86.3-205.7] pg/mL, n=20, P=1.9×10-5). There was clear FGF21 staining in diseased cardiomyocytes, and circulating FGF21 levels negatively correlated with the expression of cardiac genes involved in ketone metabolism, consistent with cardiac FGF21 signaling. FGF21 gene expression was very low in failing and nonfailing hearts, suggesting extracardiac production of the circulating hormone. Circulating FGF21 levels were correlated with BNP (B-type natriuretic peptide) and total bilirubin, markers of chronic cardiac and hepatic congestion.

CONCLUSIONS

Circulating FGF21 levels are elevated in HF with reduced ejection fraction and appear to bind to the heart. The liver is likely the main extracardiac source. This supports a model of hepatic FGF21 communication to diseased cardiomyocytes, defining a potential cardiohepatic signaling circuit in human HF.

Higher serum level of CTRP15 in patients with coronary artery disease is associated with disease severity, body mass index and insulin resistance

BACKGROUND

CTRP15 is a prologue of adiponectin which has shown to have favourable effects on glucose and lipid metabolism. Studies have reported lower levels of CTRP15 in T2DM and metabolic syndrome; however, its circulating levels have not been evaluated in CAD patients.

METHODS

This case-control study was conducted on 190 angiographically confirmed coronary artery disease (CAD) patients and 70 controls. Serum levels of CTRP15, adiponectin, TNF-α, and IL-6 were measured using the ELISA technique.

RESULTS

CTRP15 was shown to occur in higher levels in CAD patients compared with controls. In CAD patients, CTRP15 showed a positive correlation with BMI, FBS, insulin, HOMA-IR, IL-6, and TNF-α and a negative correlation with HDL-C and adiponectin.

CONCLUSION

Elevated levels of CTRP15 in CAD patients and the relation of CTRP15 with pathogenic conditions such as insulin resistance, inflammation, and decreased adiponectin and HDL-C suggest a possible compensatory response to these conditions in CAD patients.

Exercise Training Improves Memory Performance in Older Adults: A Narrative Review of Evidence and Possible Mechanisms

As human life expectancy increases, cognitive decline and memory impairment threaten independence and quality of life. Therefore, finding prevention and treatment strategies for memory impairment is an important health concern. Moreover, a better understanding of the mechanisms involved underlying memory preservation will enable the development of appropriate pharmaceuticals drugs for those who are activity limited. Exercise training as a non-pharmacological tool, has been known to increase the mean lifespan by maintaining general body health and improving the cardiovascular and nervous systems function. Among different exercise training protocols, aerobic exercise has been reported to prevent the progression of memory decline, provided adequate exertion level, duration, and frequency. Mechanisms underlying exercise training effects on memory performance have not been understood yet. Convergent evidence suggest several direct and indirect mechanisms at molecular and supramolecular levels. The supramolecular level includes improvement in blood circulation, synaptic plasticity and neurogenesis which are under controls of complex molecular signaling of neurotransmitters, neurotrophic factors, exerkines, and epigenetics factors. Among these various factors, irisin/BDNF signaling seems to be one of the important mediators of crosstalk between contracted skeletal muscles and the brain during exercise training. This review provides an affordable and effective method to improve cognitive function in old ages, particularly those who are most vulnerable to neurodegenerative disorders.

Increased serum myonectin and irisin levels with myonectin and FNDC5 expressions in polycystic ovary syndrome: a case control study

The aim of this study is to assess the FNDC5 and myonectin expressions and serum levels of myonectin and irisin in women with PCOS. 90 participants were included in this case-control study. 45 of these participants were with PCOS, and 45 of them were healthy volunteers matched for age and body mass index (BMI). Serum irisin and myonectin levels were measured with commercially available enzyme-linked immune sorbent assay (ELISA) kits. Expression of the myonectin and FNDC5 genes were determined by RT-PCR analysis. It was found out that FSI, HOMA-IR, LH, LH/FSH, TT, serum irisin and serum myonectin levels, myonectin mRNA expression, and FNDC5 mRNA expression were higher in the PCOS group, whereas HDL-C level was lower in the PCOS group (p < .05). When the groups were compared, it was detected that IR and HA were significantly higher in the PCOS group (p < .05). Serum irisin and myonectin levels, and myonectin and FNDC5 mRNA expressions were increased in women with PCOS. These molecules can be target molecules in PCOS pathophysiology and treatment.IMPACT STATEMENTWhat is already known on this subject? Although the aetiology of PCOS is not fully understood, it is thought that insulin resistance may play a critical role. In recent studies, the relationship of cytokines secreted from skeletal muscle with insulin resistance has been shown. The effects of irisin and myonectin, which are members of the myokine family, on lipid and glucose metabolism are known.What do the results of this study add? Although there are many studies in the literature regarding serum irisin levels in women with PCOS, their results are confusing. There is a study in the literature investigating the relationship between myonectin and PCOS. In our study, we evaluated myonectin and FNDC mRNA expressions in addition to serum irisin and myonectin levels. As a result, we found that markers and their mRNA expressions were lower in patients with PCOS compared to controls.What are the implications of these findings for clinical practice and/or further research? We think that the results of our study will shed light on future studies. Due to their effects on adipose tissue, these markers may play a role in the aetiology of long-term complications of PCOS. Moreover, they can become pharmacological targets in preventing these complications.

Increased circulating level of CTRP15 in patients with type 2 diabetes mellitus and its relation with inflammation and insulin resistance

Aims

Type 2 diabetes mellitus (T2DM) is a highly prevalence disease that has a close relation with secretory factors such as adipokines and myokines. C1q tumor necrosis factor-α (TNF-α)-related protein 15 (CTRP15) is a paralogue paralogue of adiponectin that has a close relation with insulin resistance and inflammation. The present study aimed to assess circulating levels of CTRP15 in patients with T2DM in comparison with controls and thier association with inflammatory cytokines.

Methods

This case-control study was performed on 80 T2DM patients and 80 controls which diagnosed according to the criteria of American Diabetes Association (ADA). Serum levels of CTRP15, adiponectin, TNF-α, and interleukin- 6 (IL-6) were determined using ELISA kits.

Results

The results indicated higher concentration of CTRP15 in T2DM patients (103.17 ± 27.99) compared to the controls (66.11 ± 20.46, p < 0.001), while adiponectin decreased considerably in the patients compared to the controls (p < 0.001). Moreover, circulating levels of IL-6 and TNF-α elevated in the patients compared to the controls (p < 0.001). CTRP15 indicated independent association with BMI and adiponectin in the controls while, in the patients it demonstrated independent association with HOMA-IR and TNF-α.

Conclusions

Higher concentration of CTRP15 in the patients and its relation with insulin resistance and inflammation suggested a relation of CTRP15 with the pathogenesis of diabetes. In addition, it seems likely that patients with T2DM had a CTRP15 resistance; however, future studies are necessary to prove this concept.

Gender-Specific Behaviour in Obesity Stages I-II: Imbalance of Aminothiol Status and Adipomyokine Profile in Subjects with Different Insulin Resistance Severity

The hyperproduction of oxidative stress and inflammatory biomarkers, which is paralleled by decreased levels of antioxidant and anti-inflammatory mediators, is part of cellular mechanisms that contribute to the disruption of metabolic homeostasis in obesity. Whether gender-specific alterations and gender-restricted associations in these biomarkers underlie the increased cardiometabolic risk in men compared to women is unclear. We enrolled 31 women and 29 men, aged ≥50 and ≤70 years and with body mass index ≥ 30 and <40 kg/m². We assessed the concentrations of aminothiols (cysteine, homocysteine, and glutathione), expression of oxidant/antioxidant balance, adipomyokines (leptin, adiponectin, myostatin, and interleukin-6), markers of chronic inflammation, and vitamin D, an index of nutritional state, in plasma and serum samples by using HPLC, ELISA, and chemiluminescent immunoassay methods. We measured insulin resistance (IR) by the homeostasis model assessment (HOMA) index. Despite comparable levels of visceral adiposity, IR, and a similar dietary regimen, men showed, with respect to women, higher oxidant concentrations and lower antioxidant levels, which paralleled IR severity. Myostatin levels correlated with prooxidant aminothiols among men only. Gender-specific alterations in aminothiol status and adipomyokine profile and the gender-restricted association between these biomarkers and metabolic derangement are consistent with an increased cardiometabolic risk in men compared to age-matched women with stage I-II obesity. Strict control of redox and inflammatory status, even addressing gender-specific nutritional targets, may be useful to prevent obesity-related metabolic alterations and comorbidities.

Hypothalamus-skeletal muscle crosstalk during exercise and its role in metabolism modulation

Physical inactivity is a major public health problem that contributes to the development of several pathologies such as obesity, type 2 diabetes and cardiovascular diseases. Regular exercise mitigates the progression of these metabolic problems and contributes positively to memory and behavior. Therefore, public health agencies have incorporated exercise in the treatment of widespread disorders. The hypothalamus, specifically the ventromedial and the arcuate nuclei, responds to exercise activity and modulates energy metabolism through stimulation of the sympathetic nervous system and catecholamine secretion into the circulation. In addition, physical performance enhances cognitive functions and memory, mediated mostly by an increase in brain-derived neurotrophic factor levels in brain. During exercise training, skeletal muscle myofibers remodel their biochemical, morphological and physiological state. Moreover, skeletal muscle interacts with other organs by the release into the circulation of myokines, molecules that exhibit autocrine, paracrine and endocrine functions. Several studies have focused on the role of skeletal muscle and tissues in response to physical activity. However, how the hypothalamus could influence the skeletal muscle task in the context of exercise is less studied. Here, we review recent data about hypothalamus-skeletal muscle crosstalk in response to physical activity and focus on specific aspects such as the neuroendocrinological effects of exercise and the endocrine functions of skeletal muscle, to provide a perspective for future study directions.

Circulating Myonectin and Irisin Levels in Gestational Diabetes Mellitus - A Case-control Study

OBJECTIVE

The objective of this study was to assess the levels of serum myonectin and irisin in pregnant women with and without gestational diabetes mellitus (GDM).

METHOD

A total of 80 pregnant women participated in our study (which consisted of 40 patients with GDM, 40 participants as the control group). Myonectin and irisin levels were analyzed through the ELISA technique, in addition to metabolic parameters in the serum samples of the participants.

RESULTS

It was found that the levels of irisin and myonectin were lower in the GDM group compared to the control group. Moreover, it was determined that the values of age (p<0.001), body mass index (p=0.001), gravida (p=0.001), parity (p = 0.016), fasting serum glucose (p=0.001), fasting serum insulin (p=0.007), postprandial serum glucose (p=0.006), HbA1c (p<0.001), HOMA-IR (p<0.001) were higher; HDL cholesterol (p<0.001) was lower. Insulin resistance was significantly higher in the GDM group.

CONCLUSIONS

Levels of myonectin and irisin were determined to be low in the GDM group. Our results have demonstrated that myonectin and irisin could play a role in the development of GDM and that irisin as well as myonectin could be a novel biomarker for GDM.

Sarcopenic obesity: Myokines as potential diagnostic biomarkers and therapeutic targets?

Sarcopenic obesity (SO) is a condition characterized by the occurrence of both sarcopenia and obesity and imposes a heavy burden on the health of the elderly. Controversies and challenges regarding the definition, diagnosis and treatment of SO still remain because of its complex pathogenesis and limitations. Over the past few decades, numerous studies have revealed that myokines secreted from skeletal muscle play significant roles in the regulation of muscle mass and function as well as metabolic homeostasis. Abnormalities in myokines may trigger and promote the pathogenesis underlying age-related and metabolic diseases, including obesity, sarcopenia, type 2 diabetes (T2D), and SO. This review mainly focuses on the role of myokines as potential biomarkers for the early diagnosis and therapeutic targets in SO.

Myonectin inhibits the differentiation of osteoblasts and osteoclasts in mouse cells

Myonectin is a myokine, which is involved in the pathophysiology of diabetes and obesity, and various myokines are involved in the interactions between skeletal muscle and bone. However, roles of myonectin in bone have still remained unknown. We therefore examined the effects of myonectin on mouse osteoblast and osteoclast differentiation in vitro. Myonectin significantly suppressed the mRNA levels of osteogenic genes and alkaline phosphatase (ALP) activity in mouse osteoblasts. As for osteoclasts, myonectin significantly suppressed osteoclast formation as well as the mRNA levels of osteoclast-related genes enhanced by receptor activator nuclear factor κB ligand (RANKL) from mouse monocytic RAW264.7 cells. Moreover, myonectin significantly suppressed osteoclast formation from mouse bone marrow cells in the presence of macrophage-colony stimulating factor and RANKL. On the other hand, myonectin significantly suppressed RANKL-induced oxygen consumption rate and peroxisome proliferator-activated receptor γ coactivator-1β mRNA levels in RAW264.7 cells, although myonectin did not affect these mitochondrial biogenesis parameters in mouse osteoblasts. In conclusion, the present study demonstrated that myonectin suppresses the differentiation and ALP activity in mouse osteoblasts. Moreover, myonectin suppressed osteoclast differentiation from mouse bone marrow and RAW264.7 cells partly through an inhibition of mitochondrial biogenesis.

Circulating Serum Myonectin Levels in Obesity and Type 2 Diabetes Mellitus

OBJECTIVE

Myonectin is one of the myokines and has gained interest as a potential new strategy to combat obesity and its associated disorders, such as type 2 diabetes mellitus (T2DM).The objective of this study was to investigate circulating serum myonectin levels in nondiabetes and T2DM and elucidate possible relationships between serum myonectin levels and metabolic parameters in patients with T2DM.

DESIGN

A total of 362 Chinese patients with T2DM and 100 age- and sex-matched healthy controls were recruited in this study. Clinical characteristics, blood biochemistry, and circulating myonectin levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Circulating myonectin levels were significantly decreased in T2DM compared with controls. Obese nondiabetic controls had significantly lower serum myonectin levels compared with lean nondiabetic controls. In diabetic patients, serum myonectin concentrations were significantly negatively correlated with body mass index (BMI), total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), C-reactive protein (CRP), hemoglobin A1c (HbA1c), fasting insulin (Fins), the homeostatic model assessment of insulin resistance (HOMA-IR), visceral fat area, and subcutaneous fat area. After adjusting for covariates, multivariate stepwise regression analysis demonstrated that BMI, LDL-C, TG, HOMA-IR, and visceral fat were the main independent predictors of low serum myonectin concentrations.

CONCLUSIONS

Circulating myonectin levels were decreased in T2DM patients and in obese subjects. Moreover, serum myonectin levels were correlated with metabolic markers of T2DM. These data suggest that myonectin may be a useful marker in predicting the development of obesity and T2DM.

Evaluation of the effect of oral taurine supplementation on fasting levels of fibroblast growth factors, β-Klotho co-receptor, some biochemical indices and body composition in obese women on a weight-loss diet: a study protocol for a double-blind, randomized controlled trial

Background

Taurine (Tau) is involved in many biochemical functions such as regulation of glucose and lipid metabolism, enhancement of energy expenditure, anti-inflammatory effects and appetite control. The most important effect of Tau in obesity is its direct effect on adipose tissue. Some evidence has shown an impaired FGF (fibroblast growth factor) 19 and 21 biosyntheses in obesity. Besides the effects of eicosapentaenoic acid on serum FGF concentrations, the effect of other nutrients on FGFs is not clear. Since obesity as an important health problem is rising around the world and on the other side, Tau biosynthesis is reduced by adipose-tissue-derived factors in obesity, the effects of Tau and a weight-loss diet on obesity need to be investigated further.

Methods

We will conduct an 8-week. double-blind, parallel-group, randomized controlled clinical trial to investigate the effect of Tau supplementation on fasting serum levels of FGFs, β-Klotho co-receptor, some biochemical indices and body composition in 50 obese women aged between 18 and 49 years on a weight-loss diet.

Discussion

We will determine the other advantages of a weight-loss diet on new metabolic risk factors. Since Tau may regulate adipose-tissue-derived factors and a weight-loss diet can promote the useful effects of Tau supplementation; for the first time, the effects of a weight-loss diet along with Tau supplementation on these variables will be assessed.

Trial registration

Iran Clinical Trials Registry, ID: IRCT20131125015542N2. Registered on 24 November 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3421-5) contains supplementary material, which is available to authorized users.

Impact of Lipotoxicity on Tissue "Cross Talk" and Metabolic Regulation

Obesity-associated comorbidities include non-alcoholic fatty liver disease, Type 2 diabetes, and cardiovascular disease. These diseases are associated with accumulation of lipids in non-adipose tissues, which can impact many intracellular cellular signaling pathways and functions that have been broadly defined as "lipotoxic." This review moves beyond understanding intracellular lipotoxic outcomes and outlines the consequences of lipotoxicity on protein secretion and inter-tissue "cross talk," and the impact this exerts on systemic metabolism.

Myonectin deletion promotes adipose fat storage and reduces liver steatosis

We recently described myonectin (also known as erythroferrone) as a novel skeletal muscle-derived myokine with metabolic functions. Here, we use a genetic mouse model to determine myonectin's requirement for metabolic homeostasis. Female myonectin-deficient mice had larger gonadal fat pads and developed mild insulin resistance when fed a high-fat diet (HFD) and had reduced food intake during refeeding after an unfed period but were otherwise indistinguishable from wild-type littermates. Male mice lacking myonectin, however, had reduced physical activity when fed ad libitum and in the postprandial state but not during the unfed period. When stressed with an HFD, myonectin-knockout male mice had significantly elevated VLDL-triglyceride (TG) and strikingly impaired lipid clearance from circulation following an oral lipid load. Fat distribution between adipose and liver was also altered in myonectin-deficient male mice fed an HFD. Greater fat storage resulted in significantly enlarged adipocytes and was associated with increased postprandial lipoprotein lipase activity in adipose tissue. Parallel to this was a striking reduction in liver steatosis due to significantly reduced TG accumulation. Liver metabolite profiling revealed additional significant changes in bile acids and 1-carbon metabolism pathways. Combined, our data affirm the physiologic importance of myonectin in regulating local and systemic lipid metabolism.-Little, H. C., Rodriguez, S., Lei, X., Tan, S. Y., Stewart, A. N., Sahagun, A., Sarver, D. C., Wong, G. W. Myonectin deletion promotes adipose fat storage and reduces liver steatosis.

Exercise-Induced Myokines With Therapeutic Potential for Muscle Wasting

Skeletal muscle is a highly vascularized tissue that can secrete proteins called myokines. These muscle-secreted factors exert biological functions in muscle itself (autocrine effect) or on short- or long-distant organs (paracrine/endocrine effects) and control processes such as metabolism, angiogenesis, or inflammation. Widely differing diseases ranging from genetic myopathies to cancers are emerging as causing dysregulated secretion of myokines from skeletal muscles. Myokines are also involved in the control of muscle size and may be important to be restored to normal levels to alleviate muscle wasting in various conditions, such as cancer, untreated diabetes, chronic obstructive pulmonary disease, aging, or heart failure. Interestingly, many myokines are induced by exercise (muscle-derived exerkines) and some even by specific types of physical activity, but more studies are needed on this issue. Most exercise-induced myokines travel throughout the body by means of extracellular vesicles. Restoring myokines by physical activity may be added to the list of mechanisms by which exercise exerts preventative or curative effects against a large number of diseases, including the deleterious muscle wasting they may cause. Extending our understanding about which myokines could be usefully restored in certain diseases might help in prescribing more tailored exercise or myokine-based drugs.

Skeletal muscle as a protagonist in the pregnancy metabolic syndrome

The pregnant woman normally shows clinical manifestations similar to a metabolic syndrome (MS), due to her metabolic and hemodynamic adaptations in order to share nutrients with the child. If those adjustments are surpassed, a kind of pregnancy MS (PregMS) could appear, characterized by excessive insulin resistance and vascular maladaptation. Skeletal muscle (SKM) must be a protagonist in the PregMS: SKM strength and mass have been associated inversely with MS incidence in non-pregnant patients, and in pregnant women muscular activity modulates metabolic and vascular adaptations that favor better outcomes. Of note, a sedentary lifestyle affects exactly in the other way. Those effects may be explained not only by the old paradigm of SKM being a great energy consumer and store, but because it is an endocrine organ whose chronic activity or deconditioning correspondingly releases myokines modulating insulin sensitivity and cardiovascular adaptation, by direct or indirect mechanisms not well understood. In this document, we present evidence to support the concept of a PregMS and hypothesize on the role of the SKM mass, fiber types composition and myokines in its pathophysiology. Also, we discuss some exercise interventions in pregnancy as a way to test our hypotheses.

Impact of Exercise on Inflammatory Mediators of Metabolic and Vascular Insulin Resistance in Type 2 Diabetes

The development of obesity is cornerstone in the etiology of metabolic and vascular insulin resistance and consequently exacerbates glycemic control. Exercise is an efficacious first-line therapy for type 2 diabetes that improves insulin action through, in part, reducing hormone mediated inflammation. Together, improving the coordination of skeletal muscle metabolism with vascular delivery of glucose will be required for optimizing type 2 diabetes and cardiovascular disease treatment.

Major determinants of circulating myostatin in polycystic ovary syndrome

The present study was designed to investigate the possible impact of hormonal and demographic parameters of patients with polycystic ovary syndrome (PCOS) on the circulating levels of myostatin. The study cohort comprised 46 patients with PCOS and 42 healthy female controls, and all subjects were of normal weight. Multiple regression analysis was applied to investigate the possible associations between serum myostatin levels and other laboratory parameters. Evaluation of the levels of myostatin revealed no significant differences between the PCOS and control groups (P>0.05). In the control group, no significant correlations were identified between the myostatin levels and any other laboratory parameters. Only low-density-lipoprotein cholesterol (LDL-C) levels in the PCOS group were revealed to be significantly, although negatively, associated with myostatin levels (P=0.018). In the regression model of the PCOS group, an increase in LDL-C and prolactin (PRL) were associated with a decrease in myostatin (P=0.001 and P=0.013, respectively). Furthermore, a decrease in sex hormone-binding globulin (SHBG), fasting blood glucose (FBG) and monocytes were associated with an increase in myostatin (P=0.028, P<0.001 and P=0.026, respectively). An increase in triglycerides was also associated with an increase in myostatin (P=0.001). In the regression model of the control group, a decrease in LDL-C was associated with an increase in myostatin (P=0.003) and a decrease in thyroid-stimulating hormone was associated with a decrease in myostatin (P=0.028). These results indicated that the normal range of myostatin levels in patients with PCOS is regulated by changes in the circulating levels of PRL, LDL-C, SHBG, triglycerides, monocytes and FBG.

Physical Exercise-Induced Myokines and Muscle-Adipose Tissue Crosstalk: A Review of Current Knowledge and the Implications for Health and Metabolic Diseases

Physical exercise has beneficial effects on metabolic diseases, and a combined therapeutic regimen of regular exercise and pharmaceutical treatment is often recommended for their clinical management. However, the mechanisms by which exercise produces these beneficial effects are not fully understood. Myokines, a group of skeletal muscle (SkM) derived peptides may play an important part in this process. Myokines are produced, expressed and released by muscle fibers under contraction and exert both local and pleiotropic effects. Myokines such as IL-6, IL-10, and IL-1ra released during physical exercise mediate its health benefits. Just as exercise seems to promote the myokine response, physical inactivity seems to impair it, and could be a mechanism to explain the association between sedentary behavior and many chronic diseases. Myokines help configure the immune-metabolic factor interface and the health promoting effects of physical exercise through the release of humoral factors capable of interacting with other tissues, mainly adipose tissue (AT). AT itself secretes proinflammatory cytokines (adipokines) as a result of physical inactivity and it is well recognized that AT inflammation can lead to the development of metabolic diseases, such as type 2 diabetes mellitus (T2DM) and atherosclerosis. On the other hand, the browning phenotype of AT has been suggested to be one of the mechanisms through which physical exercise improves body composition in overweight/obese individuals. Although, many cytokines are involved in the crosstalk between SkM and AT, in respect of these effects, it is IL-6, IL-15, irisin, and myostatin which seem to have the decisive role in this “conversation” between AT and SkM. This review article proposes to bring together the latest “state of the art” knowledge regarding Myokines and muscle-adipose tissue crosstalk. Furthermore, it is intended to particularly focus on the immune-metabolic changes from AT directly mediated by myokines.