Interaction between plasma fetuin-A and free fatty acids predicts changes in insulin sensitivity in response to long-term exercise

Adipose Tissue Insulin Resistance in South Asian and Nordic Women after Gestational Diabetes Mellitus

South Asians (SAs) have a higher risk of developing type 2 diabetes (T2D) than white Europeans, especially following gestational diabetes mellitus (GDM). Despite similar blood glucose levels post-GDM, SAs exhibit more insulin resistance (IR) than Nordics, though the underlying mechanisms are unclear. This study aimed to assess markers of adipose tissue (AT) IR and liver fat in SA and Nordic women post-GDM. A total of 179 SA and 108 Nordic women in Norway underwent oral glucose tolerance tests 1-3 years post-GDM. We measured metabolic markers and calculated the AT IR index and non-alcoholic fatty liver disease liver fat (NAFLD-LFS) scores. Results showed that normoglycaemic SAs had less non-esterified fatty acid (NEFA) suppression during the test, resembling prediabetes/T2D responses, and higher levels of plasma fetuin-A, CRP, and IL-6 but lower adiponectin, indicating AT inflammation. Furthermore, normoglycaemic SAs had higher NAFLD-LFS scores, lower insulin clearance, and higher peripheral insulin than Nordics, indicating increased AT IR, inflammation, and liver fat in SAs. Higher liver fat markers significantly contributed to the ethnic disparities in glucose metabolism, suggesting a key area for intervention to reduce T2D risk post-GDM in SAs.

Exercise and inactivity as modifiers of β cell function and type 2 diabetes risk

Exercise and regular physical activity are beneficial for the prevention and management of metabolic diseases such as obesity and type 2 diabetes, whereas exercise cessation, defined as deconditioning from regular exercise or physical activity that has lasted for a period of months to years, can lead to metabolic derangements that drive disease. Adaptations to the insulin-secreting pancreatic β-cells are an important benefit of exercise, whereas less is known about how exercise cessation affects these cells. Our aim is to review the impact that exercise and exercise cessation have on β-cell function, with a focus on the evidence from studies examining glucose-stimulated insulin secretion (GSIS) using gold-standard techniques. Potential mechanisms by which the β-cell adapts to exercise, including exerkine and incretin signaling, autonomic nervous system signaling, and changes in insulin clearance, will also be explored. We will highlight areas for future research.

The role of hepatokines in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is not only a consequence of insulin resistance, but it is also an important cause of insulin resistance and major non-communicable diseases (NCDs). The close relationship of NAFLD with visceral obesity obscures the role of fatty liver from visceral adiposity as the main pathomechanism of insulin resistance and NCDs. To overcome this limitation, in analogy to the concept of adipokines, in 2008 we introduced the term hepatokines to describe the role of fetuin-A in metabolism. Since then, several other hepatokines were tested for their effects on metabolism. Here we address the dysregulation of hepatokines in people with NAFLD. Then, we discuss pathophysiological mechanisms of cardiometabolic diseases specifically related to NAFLD by focusing on hepatokine-related organ crosstalk. Finally, we propose how the determination of major hepatokines and adipokines can be used for pathomechanism-based clustering of insulin resistance in NAFLD and visceral obesity to better implement precision medicine in clinical practice.

Extracellular vesicles and microRNAs are altered in response to exercise, insulin sensitivity and overweight

Extracellular vesicles induced by exercise have emerged as potential mediators of tissue crosstalk. Extracellular vesicles and their cargo miRNAs have been linked to dysglycemia and obesity in animal models, but their role in humans is unclear.

AIM

The aim of the study was to characterize the miRNA content in plasma extracellular vesicle isolates after acute and long-term exercise and to study associations between extracellular vesicle miRNAs, mRNA expression in skeletal muscle and adipose tissue, and cardiometabolic risk factors.

METHODS

Sedentary men with or without dysglycemia and overweight underwent an acute bicycle test and a 12-week exercise intervention with extensive metabolic phenotyping. Gene expression in m. vastus lateralis and subcutaneous adipose tissue was measured with RNA sequencing. Extracellular vesicles were purified from plasma with membrane affinity columns or size exclusion chromatography.

RESULTS

Extracellular vesicle miRNA profiling revealed a transient increase in the number of miRNAs after acute exercise. We identified miRNAs, such as miR-652-3p, that were associated to insulin sensitivity and adiposity. By performing explorative association analyses, we identified two miRNAs, miR-32-5p and miR-339-3p, that were strongly correlated to an adipose tissue macrophage signature.

CONCLUSION

Numerous miRNAs in plasma extracellular vesicle isolates were increased by exercise, and several miRNAs correlated to insulin sensitivity and adiposity. Our findings warrant future studies to characterize exercise-induced extracellular vesicles and cargo miRNA to clarify where exercise-induced extracellular vesicles originate from, and to determine whether they influence metabolic health or exercise adaptation.

Grape Polyphenols in the Treatment of Human Skeletal Muscle Damage Due to Inflammation and Oxidative Stress during Obesity and Aging: Early Outcomes and Promises

Today, inactivity and high-calorie diets contribute to the development of obesity and premature aging. In addition, the population of elderly people is growing due to improvements in healthcare management. Obesity and aging are together key risk factors for non-communicable diseases associated with several co-morbidities and increased mortality, with a major impact on skeletal muscle defect and/or poor muscle mass quality. Skeletal muscles contribute to multiple body functions and play a vital role throughout the day, in all our activities. In our society, limiting skeletal muscle deterioration, frailty and dependence is not only a major public health challenge but also a major socio-economic issue. Specific diet supplementation with natural chemical compounds such as grape polyphenols had shown to play a relevant and direct role in regulating metabolic and molecular pathways involved in the prevention and treatment of obesity and aging and their related muscle comorbidities in cell culture and animal studies. However, clinical studies aiming to restore skeletal muscle mass and function with nutritional grape polyphenols supplementation are still very scarce. There is an urgent need for clinical studies to validate the very encouraging results observed in animal models.

Fetuin-A mediates the difference in adipose tissue insulin resistance between young adult pakistani and norwegian patients with type 2 diabetes

BACKGROUND

South-Asian immigrants to Western countries have a high prevalence of type 2 diabetes mellitus (T2DM) and increased adipose tissue insulin resistance (AT-IR), as compared to their Western counterparts. Fetuin-A is a hepatokine known to influence AT-IR.

AIM

Can plasma fetuin-A concentrations explain an ethnic difference in adipose tissue insulin resistance?

METHODS

We performed a two-step euglycemic-hyperinsulinaemic clamp and measured plasma concentrations of fetuin-A and non-esterified fatty acids (NEFA), in 18 Pakistani and 21 Norwegians with T2DM (age 29-45y) in Norway. AT-IR was calculated as NEFA-suppression during the clamp. The adipokines/cytokines leptin, adiponectin, visfatin, PTX3, IL-1β, INF-γ, and IL-4 were measured in fasting plasma. Liver fat was estimated by CT-scans.

RESULTS

Despite a lower BMI, Pakistani patients displayed higher AT-IR than Norwegians. NEFA-suppression during clamp was lower in Pakistani than Norwegians (mean=-20.6%, 95%CI=[-40.8, -0.01] and p = 0.046). Plasma fetuin-A concentration was higher in Pakistani than Norwegians (43.4 ng/mL[12.7,74.0], p = 0.007) and correlated negatively to %NEFA-suppression during clamp (rho=-0.39, p = 0.039). Plasma fetuin-A concentration explained 22% of the ethnic difference in NEFA-suppression during the clamp. Pakistani patients exhibited higher plasma leptin and lower PTX3 levels than Norwegian, and plasma visfatin correlated positively to plasma fetuin-A levels in the Pakistani patients. We observed no correlation between plasma fetuin-A and liver fat, but fetuin-A correlated negatively with plasma IL-1β, INF-γ, and IL-4 concentrations. Plasma IL-4 concentration was lower in Pakistani than in Norwegian patients.

CONCLUSION

Fetuin-A may contribute to explain the discrepancy in T2DM prevalence between Pakistani and Norwegians patients by influencing AT-IR.

Contribution of organokines in the development of NAFLD/NASH associated hepatocellular carcinoma

Globally the incidence of hepatocellular carcinoma (HCC) is on an upsurge. Evidence is accumulating that liver disorders like nonalcoholic fatty liver disease (NAFLD) and its more progressive form nonalcoholic steatohepatitis (NASH) are associated with increased risk of developing HCC. NAFLD has a prevalence of about 25% and 50%-90% in obese population. With the growing burden of obesity epidemic worldwide, HCC presents a major healthcare burden. While cirrhosis is one of the major risk factors of HCC, available literature suggests that NAFLD/NASH associated HCC also develops in minimum or noncirrhotic livers. Therefore, there is an urgent need to understand the pathogenesis and risk factors associated with NAFLD and NASH related HCC that would help in early diagnosis and favorable prognosis of HCC secondary to NAFLD. Adipokines, hepatokines and myokines are factors secreted by adipocytes, hepatocytes and myocytes, respectively, playing essential roles in cellular homeostasis, energy balance and metabolism with autocrine, paracrine and endocrine effects. In this review, we endeavor to focus on the role of these organokines in the pathogenesis of NAFLD/NASH and its progression to HCC to augment the understanding of the factors stimulating hepatocytes to acquire a malignant phenotype. This shall aid in the development of novel therapeutic strategies and tools for early diagnosis of NAFLD/NASH and HCC.

The effect of exercise training on adipose tissue insulin sensitivity: A systematic review and meta-analysis

This systematic review and meta-analysis determined the impact of exercise training on adipose tissue insulin sensitivity in adults. Its scope extended to studies measuring whole-body and localized subcutaneous adipose tissue insulin sensitivity using validated techniques. Consensus from four studies demonstrates that exercise training improved whole-body adipose tissue insulin sensitivity when measured via stable-isotope lipid tracers (rate of appearance suppression in response to hyperinsulinemia). Meta-analysis of 20 studies (26 intervention arms) employing the adipose tissue insulin resistance index (ADIPO-IR) supported these findings (-10.63 [-14.12 to -7.15] pmol·L^-1  × mmol·L^-1 ). With ADIPO-IR, this response was greater in studies documenting weight loss and shorter sampling time (≤48 h) post-training. Overall, exercise training did not affect whole-body adipose tissue insulin sensitivity in seven studies (11 intervention arms) measuring the suppression of circulating non-esterified fatty acids in response to insulin infusion (1.51 [-0.12 to 3.14]%); however, subgroup analysis identified an enhanced suppression post-training in trials reporting weight loss. From four microdialysis studies, consensus indicates no effect of exercise training on localized (abdominal/femoral) adipose tissue insulin sensitivity, potentially suggesting that enhanced whole-body responses are related to improvements in central adipose depots. However, heterogeneity within microdialysis protocols dictates that findings must be viewed with caution.

Fetuin-A expression in human umbilical vein endothelial cells and amnion cells of patients with gestational diabetes mellitus

OBJECTIVES

To elucidate the link between fetuin-A expression in human umbilical vein endothelial cells (HUVECs) and amnion cells (ACs) and clinicopathological changes in patients with gestational diabetes mellitus (GDM) and newborns.

METHODS

This retrospective cohort study included 82 pregnant patients (40 with GDM and 42 controls) between January 2019 and January 2022. The patients underwent a one-hour, 50 gram glucose challenge test (GCT) during the 24-28th weeks of pregnancy. Patients with positive GCTs immediately underwent a 3-hour, 100 gram oral glucose tolerance test. The expression level of fetuin-A in UVECs and ACs was evaluated by immunohistochemistry (IHC) and scored based on IHC staining in randomly selected slides. The IHC staining intensity was evaluated by the number of dots, which reflects the expression level of fetuin-A in both HUVECs and ACs.

RESULTS

The GDM group displayed significantly higher fetuin-A expression in both HUVECs (p<0.0001) and ACs (p=0.0001) when compared with the control group. Fetuin-A expression in HUVECs was correlated with fetal macrosomia, neonatal hypoglycemia, and placental weight. However, there was no correlation with fetuin-A expression in ACs.

CONCLUSION

There is a correlation between fetal macrosomia, neonatal hypoglycemia, placental weight, and fetuin-A expression of HUVECs in patients with GDM.

Potential Mechanisms for How Long-Term Physical Activity May Reduce Insulin Resistance

Insulin became available for the treatment of patients with diabetes 100 years ago, and soon thereafter it became evident that the biological response to its actions differed markedly between individuals. This prompted extensive research into insulin action and resistance (IR), resulting in the universally agreed fact that IR is a core finding in patients with type 2 diabetes mellitus (T2DM). T2DM is the most prevalent form of diabetes, reaching epidemic proportions worldwide. Physical activity (PA) has the potential of improving IR and is, therefore, a cornerstone in the prevention and treatment of T2DM. Whereas most research has focused on the acute effects of PA, less is known about the effects of long-term PA on IR. Here, we describe a model of potential mechanisms behind reduced IR after long-term PA to guide further mechanistic investigations and to tailor PA interventions in the therapy of T2DM. The development of such interventions requires knowledge of normal glucose metabolism, and we briefly summarize an integrated physiological perspective on IR. We then describe the effects of long-term PA on signaling molecules involved in cellular responses to insulin, tissue-specific functions, and whole-body IR.

Organokines and Exosomes: Integrators of Adipose Tissue Macrophage Polarization and Recruitment in Obesity

The prevalence of obesity is escalating and has become a worldwide health challenge coinciding with the development of metabolic diseases. Emerging evidence has shown that obesity is accompanied by the infiltration of macrophages into adipose tissue, contributing to a state of low-grade chronic inflammation and dysregulated metabolism. Moreover, in the state of obesity, the phenotype of adipose tissue macrophages switches from the M2 polarized state to the M1 state, thereby contributing to chronic inflammation. Notably, multiple metabolic organs (adipose tissue, gut, skeletal muscle, and the liver) communicate with adipose tissue macrophages via secreting organokines or exosomes. In this review, we systematically summarize how the organokines (adipokines, gut microbiota and its metabolites, gut cytokines, myokines, and hepatokines) and exosomes (adipocyte-, skeletal muscle-, and hepatocyte-derived exosomes) act as important triggers for macrophage recruitment in adipose tissue and adipose tissue macrophage polarization, thus providing further insight into obesity treatment. In addition, we also highlight the complex interaction of organokines with organokines and organokines with exosomes, revealing new paths in understanding adipose tissue macrophage recruitment and polarization.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

The effect of pomegranate extract on anthropometric indices, serum lipids, glycemic indicators, and blood pressure in patients with nonalcoholic fatty liver disease: A randomized double-blind clinical trial

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. The beneficial effects of pomegranate have been shown on insulin resistance and obesity, which are linked to NAFLD pathogenesis. The aim of this study was to investigate the efficacy of pomegranate extract in patients with NAFLD. Forty-four NAFLD patients were randomly assigned to receive two pomegranate extract tablets or placebo for 12 weeks. Anthropometric measurements, serum lipids, glycemic indicators, and blood pressure were assessed at baseline and the end of the study. Pomegranate was associated with a reduction in the total cholesterol (p ˂ .001), triglyceride (p ˂ .001), low-density lipoprotein cholesterol (LDL-C)-to-high-density lipoprotein cholesterol (HDL-C) ratio (p ˂ .003), fasting blood sugar (p ˂ .001), homeostatic model assessment of insulin resistance (p = .02), diastolic blood pressure (p = .04), weight (p ˂ .001), body mass index (p ˂ .001), and waist circumference (p = .002), as compared to placebo. A significant increase was observed in serum HDL-C (p ˂ .001) after intervention with the pomegranate extract. However, no significant difference was shown between the two groups in serum insulin and LDL-C. The pomegranate extract supplement could be used as a complementary therapy along with existing therapies to improve glycemic indicators, serum lipids, anthropometric indices, and blood pressure in patients with nonalcoholic fatty liver.

Metabolic Spectrum of Liver Failure in Type 2 Diabetes and Obesity: From NAFLD to NASH to HCC

Liver disease is the spectrum of liver damage ranging from simple steatosis called as nonalcoholic fatty liver disease (NAFLD) to hepatocellular carcinoma (HCC). Clinically, NAFLD and type 2 diabetes coexist. Type 2 diabetes contributes to biological processes driving the severity of NAFLD, the primary cause for development of chronic liver diseases. In the last 20 years, the rate of non-viral NAFLD/NASH-derived HCC has been increasing rapidly. As there are currently no suitable drugs for treatment of NAFLD and NASH, a class of thiazolidinediones (TZDs) drugs for the treatment of type 2 diabetes is sometimes used to improve liver failure despite the risk of side effects. Therefore, diagnosis, prevention, and treatment of the development and progression of NAFLD and NASH are important issues. In this review, we will discuss the pathogenesis of NAFLD/NASH and NAFLD/NASH-derived HCC and the current promising pharmacological therapies of NAFLD/NASH. Further, we will provide insights into "adipose-derived adipokines" and "liver-derived hepatokines" as diagnostic and therapeutic targets from NAFLD to HCC.

Hepatokines as a Molecular Transducer of Exercise

Exercise has health benefits and prevents a range of chronic diseases caused by physiological and biological changes in the whole body. Generally, the metabolic regulation of skeletal muscle through exercise is known to have a protective effect on the pathogenesis of metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D), and cardiovascular disease (CVD). Besides this, the importance of the liver as an endocrine organ is a hot research topic. Hepatocytes also secrete many hepatokines in response to nutritional conditions and/or physical activity. In particular, certain hepatokines play a major role in the regulation of whole-body metabolic homeostasis. In this review, we summarize the recent research findings on the exercise-mediated regulation of hepatokines, including fibroblast growth factor 21, fetuin-A, angiopoietin-like protein 4, and follistatin. These hepatokines serve as molecular transducers of the metabolic benefits of physical activity in chronic metabolic diseases, including NAFLD, T2D, and CVDs, in various tissues.

Fetuin-A as a Potential Biomarker of Metabolic Variability Following 60 Days of Bed Rest

Background: Fetuin-A is a hepatokine linked to the development of insulin resistance. The purpose of this study was to determine if 60 days head-down-tilt (HDT) bed rest increased circulating fetuin-A and if it was linked to whole body insulin sensitivity (IS). Additionally, we examined whether reactive jump training (RJT) could alleviate the metabolic changes associated with bed rest. Methods: 23 young men (29 ± 6 years, 181 ± 6 cm, 77 ± 7 kg) were randomized to a control (CTRL, n = 11) or RJT group (JUMP, n = 12) and exposed to 60 days of bed rest. Before and after bed rest, body composition and V . O 2 ⁢ p ⁢ e ⁢ a ⁢ k were measured and an oral glucose tolerance test was performed to estimate IS. Circulating lipids and fetuin-A were measured in fasting serum. Results: Body weight, lean mass, and V . O 2 ⁢ p ⁢ e ⁢ a ⁢ k decreased in both groups following bed rest, with greater reductions in CTRL (p < 0.05). There was a main effect of time, but not the RJT intervention, for the increase in fetuin-A, triglycerides (TG), area under the curve for glucose (AUCG) and insulin (AUCI), and the decrease in Matsuda and tissue-specific IS (p < 0.05). Fetuin-A increased in participants who became less insulin sensitive (p = 0.019). In this subgroup, liver IS and adipose IS decreased (p < 0.05), while muscle IS was unchanged. In a subgroup, where IS did not decrease, fetuin-A did not change. Liver IS increased (p = 0.012), while muscle and adipose tissue IS remained unchanged. Conclusions: In this study, we report an increase in circulating fetuin-A following 60 days of bed rest, concomitant with reduced IS, which could not be mitigated by RJT. The amount of fetuin-A released from the liver may be an important determinant of changes in whole body IS. In this regard, it may also be a useful biomarker of individual variation due to inactivity or lifestyle interventions.

The Role of Exercise in the Interplay between Myokines, Hepatokines, Osteokines, Adipokines, and Modulation of Inflammation for Energy Substrate Redistribution and Fat Mass Loss: A Review

Exercise is an effective strategy for preventing and treating obesity and its related cardiometabolic disorders, resulting in significant loss of body fat mass, white adipose tissue browning, redistribution of energy substrates, optimization of global energy expenditure, enhancement of hypothalamic circuits that control appetite-satiety and energy expenditure, and decreased systemic inflammation and insulin resistance. Novel exercise-inducible soluble factors, including myokines, hepatokines, and osteokines, and immune cytokines and adipokines are hypothesized to play an important role in the body's response to exercise. To our knowledge, no review has provided a comprehensive integrative overview of these novel molecular players and the mechanisms involved in the redistribution of metabolic fuel during and after exercise, the loss of weight and fat mass, and reduced inflammation. In this review, we explain the potential role of these exercise-inducible factors, namely myokines, such as irisin, IL-6, IL-15, METRNL, BAIBA, and myostatin, and hepatokines, in particular selenoprotein P, fetuin A, FGF21, ANGPTL4, and follistatin. We also describe the function of osteokines, specifically osteocalcin, and of adipokines such as leptin, adiponectin, and resistin. We also emphasize an integrative overview of the pleiotropic mechanisms, the metabolic pathways, and the inter-organ crosstalk involved in energy expenditure, fat mass loss, reduced inflammation, and healthy weight induced by exercise.

Alterations of Serum Ser312-Phosphorylated Fetuin-A from Exercise-Induced Moderate Body Weight Loss in Individuals with Obesity

OBJECTIVE

Phosphorylated fetuin-A (pFet-A) inhibits insulin action and has been shown to be associated with obesity and insulin resistance. The objective of this cohort study was to assess the effect of incremental body weight loss on alterations in serum pFet-A and indexes of insulin sensitivity.

METHODS

A total of 16 men with obesity attained a targeted weight loss of 8% to 10% of their initial body weight by achieving an energy expenditure/deficit of 2,000 to 2,500 kcal/wk. Anthropometric assessments and blood samples were obtained every 4 weeks. Weight loss was calculated and partitioned as 2% to 4%, 4% to 6%, 6% to 8%, and 8% to 10% compared with initial body weight.

RESULTS

Targeted body weight loss of 8% to 10% decreased serum pFet-A, pFet-A:Fet-A ratio, fasting insulin, log(homeostasis model assessment of insulin resistance), quantitative insulin sensitivity check index, adipose insulin resistance, and insulin resistance index significantly. Percent changes in serum pFet-A were associated with percent changes in indexes of insulin sensitivity. Unlike insulin sensitivity indexes, which were altered starting with 6% to 8% weight loss, serum pFet-A levels were significantly decreased by 19.6% starting with 2% to 4% weight loss and decreased by 25.6%, 36.8%, and 42.3% with 4% to 6%, 6% to 8%, and 8% to 10% weight loss, respectively.

CONCLUSIONS

This study reports for the first time that the insulin-sensitizing effects of moderate weight loss are associated with a reduction in serum pFet-A levels.

Pathophysiological Implication of Fetuin-A Glycoprotein in the Development of Metabolic Disorders: A Concise Review

Alpha 2-Heremans-Schmid glycoprotein, also known as fetuin-A (Fet-A), is a multifunctional plasma glycoprotein that has been identified in both animal and human beings. The protein is a hepatokine predominantly synthesized in the liver, which is considered as an important component of diverse normal and pathological processes, including bone metabolism regulation, vascular calcification, insulin resistance, and protease activity control. Epidemiological studies have already consistently demonstrated significant elevated circulating Fet-A in the course of obesity and related complications, such as type 2 diabetes mellitus, metabolic syndrome, and nonalcoholic fatty liver disorder (NAFLD). Moreover, Fet-A has been strongly correlated with many parameters related to metabolic homeostasis dysregulation, such as insulin sensitivity, glucose tolerance, circulating lipid levels (non-esterified free fatty acids and triglycerides), and circulating levels of both pro- and anti-inflammatory factors (C-reactive protein, tumor necrosis factor-α (TNF-α), and interleukin (IL)-6). Metabolic-interfering effects of Fet-A have thus been shown to highly exacerbate insulin resistance (IR) through blocking insulin-stimulated glucose transporter 4 (GLUT-4) translocation and protein kinase B (Akt) activation. Furthermore, the protein appeared to interfere with downstream phosphorylation events in insulin receptor and insulin receptor substrate signaling. The emerging importance of Fet-A for both diagnosis and therapeutics has therefore come to the attention of researchers and the pharmaceutical industry, in the prospect of developing new therapeutic strategies and diagnosis methods for metabolic disorders.

Myokines in metabolic homeostasis and diabetes

Physical activity exerts multiple beneficial effects and the myokine concept provides a framework for understanding the molecular pathways that integrate contracting muscle in the complex network of organ communication. This network includes multiple distinct and distal organs; however, the autocrine and paracrine effects of myokines within skeletal muscle (in which they are produced) also need specific attention. In humans, the functional allocation of myokines remains limited and recent findings on fibre type-specific myokine signatures point to an additional level of complexity. Myokines are involved in the anti-inflammatory effect of physical activity and, therefore, critically counteract insulin resistance and the metabolic perturbations of obesity and type 2 diabetes. Future work needs to address the role of myokines in concert with other crosstalk molecules, and to define their specific impact for metabolic homeostasis.

Role of exercise-induced hepatokines in metabolic disorders

The health-promoting effects of physical activity to prevent and treat metabolic disorders are numerous. However, the underlying molecular mechanisms are not yet completely deciphered. In recent years, studies have referred to the liver as an endocrine organ, since it releases specific proteins called hepatokines. Some of these hepatokines are involved in whole body metabolic homeostasis and are theorized to participate in the development of metabolic disease. In this regard, the present review describes the role of Fibroblast Growth Factor 21, Fetuin-A, Angiopoietin-like protein 4, and Follistatin in metabolic disease and their production in response to acute exercise. Also, we discuss the potential role of hepatokines in mediating the beneficial effects of regular exercise and the future challenges to the discovery of new exercise-induced hepatokines.

Effects of nutritional status on serum fetuin-A level

Fetuin-A is a glycoprotein structured molecule which is mostly released by the liver. As a multifunctional protein, fetuin-A has positive effects on health such as calcification, cardiovascular diseases and tumor development processes with various mechanisms, whereas it plays a negative role in the processes of obesity, diabetes and fatty liver disease. There are a large number of studies reporting that serum fetuin-A levels are affected by several dietary factors. It is reported in some of these studies that several nutrients increase fetuin-A release, while some others have adverse effects. It is put forward that some nutrients such as dairy products, curcumin, niacin, palmitate, coffee and alcohol consumption decrease fetuin-A level, and dietary omega-3 fatty acids intake may increase fetuin-A concentration. In addition, it is indicated that high blood glucose levels increase hepatic fetuin-A release by activating extracellular signal-regulated kinase 1/2 enzymes and increased plasma free fatty acids do the same effect by increasing NF-_KB activity. Despite these studies in the literature, there is not any review evaluating fetuin-A, chronic diseases and nutrition together. Therefore, in this study, the relationship between serum fetuin levels and some diseases and the effects of nutrients on fetuin A levels were investigated with possible mechanisms.

Effects of aerobic versus resistance training on serum fetuin-A, fetuin-B, and fibroblast growth factor-21 levels in male diabetic patients

The aim of this study was to compare the effects of 8 weeks of aerobic versus resistance training programs on serum fetuin-A, fetuin-B, and fibroblast growth factor-21 (FGF-21) levels in males with type 2 diabetes mellitus. Participants (n = 34) were randomly assigned to a resistance training group (RTG; n = 12), an aerobic training group (ATG; n = 11), or a control group (n = 11). The ATG completed 30-45 min of aerobic running training at 65%-75% of the maximum heart rate. The RTG completed three sets of 10 repetitions maximum of leg press, bench press, knee extension, seated cable row, knee flexion, military press, and calf rise. Blood samples were taken before and after the training period to assess dependent variables. After 8 weeks, both the ATG and the RTG reduced fetuin-A (p < 0.05) and fetuin-B (p < 0.05), but increased FGF-21 (p < 0.05). Moreover, the RTG showed greater decrease than the ATG in fetuin-A (-18.3% vs. -7.9%), fetuin-B (-29.2% vs. -11.45%), and a lower increase in FGF-21 (42.2% vs. 25.1%), respectively. Aerobic and resistance exercise training significantly decreased serum fetuin-A, and fetuin-B, and increased FGF-21 levels in males with type 2 diabetes mellitus. However, more significant alterations in serum factors were observed from resistance training. Thus, resistance training may be considered a more suitable training strategy.

Effects of exercise training on Fetuin-a in obese, type 2 diabetes and cardiovascular disease in adults and elderly: a systematic review and Meta-analysis

Background

Elevated levels of fetuin-A are associated with increased risks of metabolic syndrome, type 2 diabetes and nonalcoholic fatty liver disease. This meta-analysis investigated whether exercise interventions can reduce fetuin-A in adults.

Methods

We searched clinical trials that objectively assessed fetuin-A and included study arms with exercise intervention. The pre-intervention and post-intervention data were used for meta-analysis. The effect sizes were calculated as standardized mean differences or changes in fetuin-A and expressed as Hedges’ g using random-effects models.

Results

The overall Hedges’ g for fetuin-A in all included interventions was − 0.640 (95%CI − 1.129 to − 0.151; n = 9), but this effect was not observed in obese (g = − 0.096; 95%CI, − 0.328 to 0.135) and type 2 diabetes/dysglycemia (g = − 0.56; 95%CI, − 1.348 to 0.236) individuals. Additionally, the random-effects meta-regression analysis showed that there was not a greater decrease in fetuin-A in individuals who achieved greater body mass index reductions (regression coefficient = 0.065; 95%CI, − 0.185 to 0.315).

Conclusion

Supervised exercise is associated with reductions in fetuin-A levels in adults and elderly. However, the results of the present meta-analysis should be interpreted with caution because of the variety of type of exercises and individual obesity related-disorders involve. Therefore, additional high-quality randomized controlled trials describing the effect of supervised exercise interventions on fetuin-A in adults are still needed. 

Electronic supplementary material

The online version of this article (10.1186/s12944-019-0962-2) contains supplementary material, which is available to authorized users.

Fetuin-A levels are increased in the adipose tissue of diabetic obese humans but not in circulation

Background

The hepatokine fetuin-A is linked to obesity and type 2 diabetes, but its presence and expression in adipose tissue remain unclear. In this study, we aimed to assess the circulating levels of fetuin-A and its expression in subcutaneous adipose tissue (SAT) from diabetic and non-diabetic obese subjects and their modulation by exercise.

Methods

SAT and blood were obtained from adults obese (diabetic, n=118 and non-diabetic, n=166) before and after a 3-month exercise program (diabetic, n=40 and non-diabetic, n=36, respectively). Plasma fetuin-A was assayed using ELISA. The presence and expression of fetuin-A in SAT, peripheral blood mononuclear cells (PBMCs) and cell lines (3T3-L1, THP-1, HepG2, RAW 264.7) were analysed using confocal microscopy, immunoblotting and qRT-PCR.

Results

Plasma fetuin-A level did not significantly differ between diabetic and non-diabetic obese subjects. However, when the non-diabetic group was divided into metabolically healthy and unhealthy phenotypes, significantly higher fetuin-A level was observed in the unhealthy sub-group. Circulating fetuin-A was mainly associated with glycaemic markers. In SAT, fetuin-A protein level was significantly higher in the diabetic obese subjects but its mRNA was not detected. Similarly, fetuin-A protein was detected in PBMCs, but its mRNA was not. In line with this, the use of various cell lines and culture media indicated that the presence of fetuin-A in SAT and PBMCs was due to its uptake from circulation rather than its endogenous expression. Finally, physical exercise decreased fetuin-A levels in both plasma and SAT in both groups.

Conclusions

Fetuin-A levels increased in association with diabetes in SAT but not in circulation in the obese subjects. Moreover, physical exercise decreased fetuin-A level. Fetuin-A potentially acts as a hepatokine taken up by other tissues, such as adipose tissue.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0919-x) contains supplementary material, which is available to authorized users.

Soluble Leptin Receptor Predicts Insulin Sensitivity and Correlates With Upregulation of Metabolic Pathways in Men

CONTEXT

Plasma soluble leptin receptor (sOb-R) seems protective of gestational and type 2 diabetes in observational studies, but the mechanisms are unknown. sOb-R is formed by ectodomain shedding of membrane-bound leptin receptors (Ob-Rs), but its associations with messenger RNA (mRNA) expression are scarcely explored.

OBJECTIVE

To explore associations between plasma levels of sOb-R and (1) insulin sensitivity, (2) mRNA pathways in adipose tissue and skeletal muscle, and (3) mRNA of candidate genes for sOb-R generation in adipose tissue and skeletal muscle.

DESIGN AND PARTICIPANTS

The MyoGlu study included 26 sedentary, middle-aged men who underwent a 12-week intensive exercise intervention. We measured plasma sOb-R with enzyme-linked immunosorbent assay, insulin sensitivity with a hyperinsulinemic euglycemic clamp, and mRNA in skeletal muscle and adipose tissue with high-throughput sequencing.

RESULTS

Baseline plasma sOb-R was strongly associated with baseline glucose infusion rate (GIR) [β (95% confidence interval), 1.19 (0.57 to 1.82) mg/kg/min, P = 0.0006] and GIR improvement after the exercise intervention [0.58 (0.03 to 1.12) mg/kg/min, P = 0.039], also independently of covariates, including plasma leptin. In pathway analyses, high plasma sOb-R correlated with upregulation of metabolic pathways and downregulation of inflammatory pathways in both adipose tissue and skeletal muscle. In skeletal muscle, mRNA of LEPROT and LEPROTL1 (involved in Ob-R cell surface expression) and ADAM10 and ADAM17 (involved sOb-R-shedding) increased after the exercise intervention.

CONCLUSIONS

Higher plasma sOb-R was associated with improved GIR, upregulation of metabolic pathways, and downregulation of inflammatory pathways, which may be possible mechanisms for the seemingly protective effect of plasma sOb-R on subsequent risk of gestational and type 2 diabetes found in observational studies.

Interaction between plasma fetuin-A and free fatty acids predicts changes in insulin sensitivity in response to long-term exercise

The hepatokine fetuin‐A can together with free fatty acids (FFAs) enhance adipose tissue (AT) inflammation and insulin resistance via toll‐like receptor 4 (TLR4). Although some of the health benefits of exercise can be explained by altered release of myokines from the skeletal muscle, it is not well documented if some of the beneficial effects of exercise can be explained by altered secretion of hepatokines. The aim of this study was to examine the effect of interaction between fetuin‐A and FFAs on insulin sensitivity after physical exercise. In this study, 26 sedentary men who underwent 12 weeks of combined endurance and strength exercise were included. Insulin sensitivity was measured using euglycemic‐hyperinsulinemic clamp, and AT insulin resistance was indicated by the product of fasting plasma concentration of FFAs and insulin. Blood samples and biopsies from skeletal muscle and subcutaneous AT were collected. Several phenotypic markers were measured, and mRNA sequencing was performed on the biopsies. AT macrophages were analyzed based on mRNA markers. The intervention improved hepatic parameters, reduced plasma fetuin‐A concentration (~11%, P < 0.01), slightly changed FFAs concentration, and improved glucose infusion rate (GIR) (~33%, P < 0.01) across all participants. The change in circulating fetuin‐A and FFAs interacted to predict some of the change in GIR (β = −42.16, P = 0.030), AT insulin resistance (β = 0.579, P = 0.003), gene expression related to TLR‐signaling in AT and AT macrophage mRNA (β = 94.10, P = 0.034) after exercise. We observed no interaction effects between FFAs concentrations and leptin and adiponectin on insulin sensitivity, or any interaction effects between Fetuin‐A and FFAs concentrations on skeletal muscle TLR‐signaling. The relationship between FFAs levels and insulin sensitivity seemed to be specific for fetuin‐A and the AT. Some of the beneficial effects of exercise on insulin sensitivity may be explained by changes in circulating fetuin‐A and FFAs, promoting less TLR4 signaling in AT perhaps by modulating AT macrophages.

Effects of Exercise Training and Weight Loss on Plasma Fetuin-A Levels and Insulin Sensitivity in Overweight Older Men

Aerobic exercise training and weight loss (AEX+WL) improves insulin sensitivity in overweight adults; however, the underlying pathways are incompletely understood. Fetuin-A, a hepatokine that inhibits insulin signaling, may be involved in the salutary effects of AEX+WL. Therefore, we examined the effects of 6-month AEX+WL on plasma fetuin-A levels (36-48 hours after the last bout of exercise), aerobic capacity (VO_2max), body composition, glucose tolerance, and insulin sensitivity (M) in 16 sedentary, overweight-obese older men (age = 60 ± 2 years, BMI = 31 ± 1 kg/m²) with no history of cardiovascular disease or diabetes. At baseline, fetuin-A levels correlated directly with adiposity and had a borderline inverse correlation with M. After AEX+WL, body weight decreased by ~10 kg, while both VO_2max and M increased by 16% (P < 0.005 for all). Contrary to our hypothesis, plasma fetuin-A levels increased after AEX+WL (1.16 ± 0.10 g/L versus 1.70 ± 0.19 g/L, P = 0.006). This increase was unrelated to changes in body composition or glucose metabolism, but directly correlated with changes in VO_2max (r = 0.57, P < 0.05). Thus, in overweight-to-obese older men, AEX+WL appears to increase plasma fetuin-A levels. Although not associated with improvements in insulin sensitivity, this increase in fetuin-A was related to improvements in aerobic capacity and could be representative of the cardioprotective effects of AEX+WL in older men.