Fetuin-A is also an adipokine

Mechanisms by which obesity regulates inflammation and anti-tumor immunity in cancer

Obesity is associated with an increased risk for 13 different cancers. The increased risk for cancer in obesity is mediated by obesity-associated changes in the immune system. Obesity has distinct effects on different types of inflammation that are tied to tumorigenesis. For example, obesity promotes chronic inflammation in adipose tissue that is tumor-promoting in peripheral tissues. Conversely, obesity inhibits acute inflammation that rejects tumors. Obesity therefore promotes cancer by differentially regulating chronic versus acute inflammation. Given that obesity is chronic, the initial inflammation in adipose tissue will lead to systemic inflammation that could induce compensatory anti-inflammatory reactions in peripheral tissues to suppress chronic inflammation. The overall effect of obesity in peripheral tissues is therefore dependent on the duration and severity of obesity. Adipose tissue is a complex tissue that is composed of many cell types in addition to adipocytes. Further, adipose tissue cellularity is different at different anatomical sites throughout the body. Consequently, the sensitivity of adipose tissue to obesity is dependent on the anatomical location of the adipose depot. For example, obesity induces more inflammation in visceral than subcutaneous adipose tissue. Based on these studies, the mechanisms by which obesity promotes tumorigenesis are multifactorial and immune cell type-specific. The objective of our paper is to discuss the cellular mechanisms by which obesity promotes tumorigenesis by regulating distinct types of inflammation in adipose tissue and the tumor microenvironment.

The Interconnection between Hepatic Insulin Resistance and Metabolic Dysfunction-Associated Steatotic Liver Disease-The Transition from an Adipocentric to Liver-Centric Approach

The central mechanism involved in the pathogenesis of MAFLD is insulin resistance with hyperinsulinemia, which stimulates triglyceride synthesis and accumulation in the liver. On the other side, triglyceride and free fatty acid accumulation in hepatocytes promotes insulin resistance via oxidative stress, endoplasmic reticulum stress, lipotoxicity, and the increased secretion of hepatokines. Cytokines and adipokines cause insulin resistance, thus promoting lipolysis in adipose tissue and ectopic fat deposition in the muscles and liver. Free fatty acids along with cytokines and adipokines contribute to insulin resistance in the liver via the activation of numerous signaling pathways. The secretion of hepatokines, hormone-like proteins, primarily by hepatocytes is disturbed and impairs signaling pathways, causing metabolic dysregulation in the liver. ER stress and unfolded protein response play significant roles in insulin resistance aggravation through the activation of apoptosis, inflammatory response, and insulin signaling impairment mediated via IRE1/PERK/ATF6 signaling pathways and the upregulation of SREBP 1c. Circadian rhythm derangement and biological clock desynchronization are related to metabolic disorders, insulin resistance, and NAFLD, suggesting clock genes as a potential target for new therapeutic strategies. This review aims to summarize the mechanisms of hepatic insulin resistance involved in NAFLD development and progression.

Leptin, resistin and fetuin a concentration as the potential useful biomarkers in stable COPD - An exploratory study

Adipokines, which have pleiotropic activities, are known to be involved in inflammation as adipocytokines. The aim of the current study was to investigate selected adipocytokine levels in the serum of stable chronic obstructive pulmonary disease COPD patients and healthy controls, to assess a potential association between the investigated biomarkers and selected parameters and to conduct receiving operating curve (ROC) analysis. Twenty-five COPD patients and 30 healthy controls were enrolled in the current study. Serum levels of adiponectin, leptin, resistin, chemerin and fetuin A were measured using an enzyme-linked immunosorbent assay (ELISA) method. Both leptin and resistin concentrations were significantly elevated in COPD patients and differentiated them from control subjects. Fetuin A levels were lower in COPD patients and may be related to the disease. Further studies in larger cohorts are needed to confirm the findings of this exploratory study.

Adipose tissue macrophages and their role in obesity-associated insulin resistance: an overview of the complex dynamics at play

Obesity, a major global health concern, is characterized by serious imbalance between energy intake and expenditure leading to excess accumulation of fat in adipose tissue (AT). A state of chronic low-grade AT inflammation is prevalent during obesity. The adipose tissue macrophages (ATM) with astounding heterogeneity and complex regulation play a decisive role in mediating obesity-induced insulin resistance. Adipose-derived macrophages were broadly classified as proinflammatory M1 and anti-inflammatory M2 subtypes but recent reports have proclaimed several novel and intermediate profiles, which are crucial in understanding the dynamics of macrophage phenotypes during development of obesity. Lipid-laden hypertrophic adipocytes release various chemotactic signals that aggravate macrophage infiltration into AT skewing toward mostly proinflammatory status. The ratio of M1-like to M2-like macrophages is increased substantially resulting in copious secretion of proinflammatory mediators such as TNFα, IL-6, IL-1β, MCP-1, fetuin-A (FetA), etc. further worsening insulin resistance. Several AT-derived factors could influence ATM content and activation. Apart from being detrimental, ATM exerts beneficial effects during obesity. Recent studies have highlighted the prime role of AT-resident macrophage subpopulations in not only effective clearance of excess fat and dying adipocytes but also in controlling vascular integrity, adipocyte secretions, and fibrosis within obese AT. The role of ATM subpopulations as friend or foe is determined by an intricate interplay of such factors arising within hyperlipidemic microenvironment of obese AT. The present review article highlights some of the key research advances in ATM function and regulation, and appreciates the complex dynamics of ATM in the pathophysiologic scenario of obesity-associated insulin resistance.

Fisetin Attenuates Arsenic-Induced Hepatic Damage by Improving Biochemical, Inflammatory, Apoptotic, and Histological Profile: In Vivo and In Silico Approach

Arsenic (As) is a toxic metalloid and human carcinogen that may cause hepatotoxicity. Fisetin (3, 3′, 4′, 7-tetrahydroxyflavone) is a phytoflavonoid, which shows diverse therapeutic activities. This study aimed to examine the remedial potential of fisetin against As-instigated hepatotoxicity in adult male rats. To accomplish this aim, albino rats (N = 48) were evenly classified into 4 groups: control group, As (10 mg/kg) group, fisetin (2.5 mg/kg) + As (10 mg/kg) group, and fisetin (2.5 mg/kg) group. After one month of treatment, biochemical assay, total protein content (TPC), hepatic serum enzymes, inflammatory as well as pro- or anti-apoptotic markers, and histopathological profile of hepatic tissues were estimated. As administration disordered the biochemical profile by decreasing activities of antioxidant enzymes i.e., catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GSR), and glutathione (GSH) content while escalating the levels of reactive oxygen species (ROS), and thiobarbituric acid reactive substances (TBARS). TPC was also considerably reduced after exposure to As. Furthermore, As markedly raised the levels of liver serum enzymes such as aspartate transaminase (AST), alkaline phosphatase (ALP), and alanine transaminase (ALT) as well as the levels of inflammatory markers, i.e., nuclear factor- κB (NF-κB), tumor necrosis- α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclo-oxygenase-2 (COX-2) activity. Besides, it lowered the level of antiapoptotic markers (Bcl-2) and upregulated the levels of proapoptotic markers (Bax, Caspase-3, and Caspase-9). Additionally, As exposure led to histopathological damage in hepatic tissues. However, fisetin administration remarkably alleviated all the depicted hepatic damages. For further verification, the screening of several dock complexes was performed by using the GOLD 5.3.0 version. Based on docking fitness and GOLD score, the ranking order of receptor proteins with fisetin compound is superoxide dismutase, interleukin, aspartate aminotransferase, alkaline phosphatase, TNF-alpha, alanine transaminase, cyclo-oxygenase 2, antiapoptotic, and glutathione reductase. Out of these three receptor proteins superoxide dismutase, interleukin, and aspartate aminotransferase showed the best interaction with the fisetin compound. In vivo and in silico outcomes of the current study demonstrated that fisetin could potentially ameliorate As-instigated hepatotoxicity.

Level of Serum Fetuin-A Correlates with Heart Rate in Obstructive Sleep Apnea Patients without Metabolic and Cardiovascular Comorbidities

Obstructive sleep apnea (OSA) is the most common type of sleep-induced breathing disorder in the adult population and significantly affects the condition of the cardiovascular system. Fetuin-A (Fet-A) is a hepato- and adipokine, which prevents vessel calcification, and its level correlates with atherogenesis and metabolic disorders. The associations of cardiovascular diseases (CVD) both with OSA, which increases CVD risk, and Fet-A, which prevents CVD, justify the question of their mutual interactions in patients with OSA. Therefore, we sought to analyze Fet-A as an early biomarker of CVD risk in OSA patients without metabolic and cardiovascular comorbidities except for properly controlled arterial hypertension. We have found that in these patients, OSA does not appear to directly affect Fet-A levels. However, high Fet-A levels were more common in the group of patients with OSA, and the hypopnea index was significantly higher among subjects with the highest Fet-A levels. The level of Fet-A in OSA patients positively correlates with pulse rate, and it does not correlate with pulse pressure in this group unlike in the control group, where such a relationship exists. To our best knowledge, this is the first study to analyze this relationship in OSA patients without any significant cardiovascular comorbidities.

The roles of cell-cell and organ-organ crosstalk in the type 2 diabetes mellitus associated inflammatory microenvironment

Type 2 diabetes mellitus (T2DM) is a classic metaflammatory disease, and the inflammatory states of the pancreatic islet and insulin target organs have been well confirmed. However, abundant evidence demonstrates that there are countless connections between these organs in the presence of a low degree of inflammation. In this review, we focus on cell-cell crosstalk among local cells in the islet and organ-organ crosstalk among insulin-related organs. In contrast to that in acute inflammation, macrophages are the dominant immune cells causing inflammation in the islets and insulin target organs in T2DM. In the inflammatory microenvironment (IME) of the islet, cell-cell crosstalk involving local macrophage polarization and proinflammatory cytokine production impair insulin secretion by β-cells. Furthermore, organ-organ crosstalk, including the gut-brain-pancreas axis and interactions among insulin-related organs during inflammation, reduces insulin sensitivity and induces endocrine dysfunction. Therefore, this crosstalk ultimately results in a cascade leading to β-cell dysfunction. These findings could have broad implications for therapies aimed at treating T2DM.

Serum levels of fetuin-A as a novel biomarker for disease activity in patients with Takayasu arteritis and granulomatous polyangiitis

OBJECTIVE

The aim of the present study was to investigate serum fetuin-A (Fet-A) levels in patients with Takayasu arteritis (TA) and granulomatous polyangiitis (GPA) and to analyze the relationship between serum Fet-A levels and disease activity scores.

METHOD

Thirty-two TA and 28 GPA patients presented to the rheumatology clinic at Gazi University and met the criteria of American College of Rheumatology 1990 and 2012 International Chapell Hill meeting, respectively, and 20 healthy control subjects were included in the present study. We collected data on serum C-reactive protein (CRP), albumin, calcium, and phosphate levels as well as erythrocyte sedimentation rates. Calcification risk index (CRI) was calculated for each patient. The Birmingham Vasculitis Activity Score (BVAS) and Indian Takayasu Clinical Activity Score (ITAS), were used to assess disease activity in GPA and TA patients respectively.

RESULTS

Serum Fet-A levels were significantly lower in the overall vasculitis group compared to control group (p = 0.015). In subgroup analysis, Fet-A levels were significantly lower in those with active disease, compared to control group (p = 0.001, for active TA (n = 18) and GPA (n = 17), respectively). However, there was no significant difference in serum Fet-A levels in inactive cases versus control subjects (p = 0.061, for inactive TA (n = 14) and GPA (n = 11), respectively). Serum Fet-A levels negatively correlated with BVAS (r =  - 0.675) and ITAS scores (r =  - 0.385), as well as with CRP and CRI.

CONCLUSION

Our results suggest that serum Fet-A level could be a novel biomarker for assessment of activity status in patients with GPA or TA. Key Points • Serum Fetuin-A is negative acute phase protein and systemic calcification inhibitor synthesized in hepatocytes and secreted by various inflammation. • Serum Fetuin-A was negatively correlated with CRP, BVAS, and ITAS scores and significantly decreased in vasculitis patients with high disease activity. • Serum Fetuin-A could be a promising and useful biomarker for the assessment of disease activity for vasculitis, also that it might also be a predictor of long-term cardiovascular progression.

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.

Hepatokines and Non-Alcoholic Fatty Liver Disease: Linking Liver Pathophysiology to Metabolism

The liver plays a key role in maintaining energy homeostasis by sensing and responding to changes in nutrient status under various metabolic conditions. Recently highlighted as a major endocrine organ, the contribution of the liver to systemic glucose and lipid metabolism is primarily attributed to signaling crosstalk between multiple organs via hepatic hormones, cytokines, and hepatokines. Hepatokines are hormone-like proteins secreted by hepatocytes, and a number of these have been associated with extra-hepatic metabolic regulation. Mounting evidence has revealed that the secretory profiles of hepatokines are significantly altered in non-alcoholic fatty liver disease (NAFLD), the most common hepatic manifestation, which frequently precedes other metabolic disorders, including insulin resistance and type 2 diabetes. Therefore, deciphering the mechanism of hepatokine-mediated inter-organ communication is essential for understanding the complex metabolic network between tissues, as well as for the identification of novel diagnostic and/or therapeutic targets in metabolic disease. In this review, we describe the hepatokine-driven inter-organ crosstalk in the context of liver pathophysiology, with a particular focus on NAFLD progression. Moreover, we summarize key hepatokines and their molecular mechanisms of metabolic control in non-hepatic tissues, discussing their potential as novel biomarkers and therapeutic targets in the treatment of metabolic diseases.

Serum fetuin-A and Ser312 phosphorylated fetuin-A responses and markers of insulin sensitivity after a single bout of moderate intensity exercise

Fetuin‐A (Fet‐A), secreted by the liver and adipose tissue, inhibits insulin receptor tyrosine kinase activity and modulates insulin action. Numerous studies have shown association of elevated serum Fet‐A concentrations with obesity, non‐alcoholic fatty liver disease, and type 2 diabetes. Both moderate body weight loss (5%–10%) and significant body weight loss have been shown to decrease serum Fet‐A and improve insulin sensitivity. Currently, there are no studies examining the effects of a single bout of exercise on serum Fet‐A or Ser312‐pFet‐A (pFet‐A) responses. We hypothesized that a single bout of moderate‐intensity exercise will lower serum Fet‐A and that these changes will be associated with an improvement in insulin sensitivity. Thirty‐one individuals with obesity and 11 individuals with normal body weight were recruited. Participants underwent a single bout of treadmill walking, expending 500 kcal at 60%–70% VO_2max. Oral glucose tolerance tests (OGTT) were administered before the single bout of exercise (Pre Ex) and 24 h after exercise (24h Post Ex). In individuals with obesity, we observed a transient elevation of serum Fet‐A concentrations, but not pFet‐A, immediately after exercise (Post Ex). Further, a single bout of exercise decreased glucose_AUC, insulin_AUC, and insulin resistance index in individuals with obesity. Consistent with this improvement in insulin sensitivity, we observed that Fet‐A_AUC, pFet‐A_AUC, 2 h pFet‐A, and 2 h pFet‐A/Fet‐A were significantly lower following a single bout of exercise. Further, reductions in serum Fet‐A_AUC 24h Post Ex were correlated with a reduction in insulin resistance index. Together, this suggests that alterations in serum Fet‐A following a single bout of moderate‐intensity endurance exercise may play a role in the improvement of insulin sensitivity.

Clinical Trial Registration

NCT03478046; https://clinicaltrials.gov/ct2/show/NCT03478046.

Effects of fetuin-A with diverse functions and multiple mechanisms on human health

Fetuin-A (Alfa 2-Heremans-Schmid) is a glycoprotein that is mainly synthesized by hepatocytes and then released into the bloodstream. While fetuin-A, a multifunctional protein, has inhibitory effects on health in the processes of calcification, mineralization, coronary artery calcification (CAC), and kidney stone formation by various mechanisms, it has such stimulatory effects as obesity, diabetes, and tumor progression processes. Fetuin-A produces these effects on the organism mainly by playing a role in the secretion levels of some inflammatory cytokines and exosomes, preventing unwanted calcification, inhibiting the autophosphorylation of tyrosine kinase, suppressing the release of adiponectin and peroxisome proliferator-activated receptor-γ (PPARγ), activating the toll-like receptor 4 (TLR-4), triggering the phosphatidylinositol 3 (PI3) kinase/Akt signaling pathway and cell proliferation, and mimicking the transforming growth factor-beta (TGF-β) receptor. In the present review, fetuin-A was examined in a wide perspective from the structure and release of fetuin-A to its effects on health.

Crosstalk Between Mast Cells and Adipocytes in Physiologic and Pathologic Conditions

Excessive fatty acids and glucose uptake support the infiltration of adipose tissue (AT) by a variety of immune cells including neutrophils, pro-inflammatory M1 macrophages, and mast cells (MCs). These cells promote inflammation by releasing pro-inflammatory mediators. The involvement of MCs in AT biology is supported by their accumulation in the AT of obese individuals along with significantly higher serum levels of MC-derived tryptase. AT-resident MCs under the influence of locally derived adipokines such as leptin become activated and release pro-inflammatory cytokines including TNFα that worsens the inflammatory state. MCs support angiogenesis in AT by releasing chymase and inducing preadipocyte differentiation and also the proliferation of adipocytes through 15-deoxy-delta PGJ2/PPARγ interaction. Additionally, they contribute to the remodeling of the AT extracellular matrix (ECM) and play a role in the recruitment and activation of leukocytes. MC degranulation has been linked to brown adipocyte activation, and evidence indicates an important link between MCs and the appearance of BRITE/beige adipocytes in white AT. Cell crosstalk between MCs and AT-resident cells, mainly adipocytes and immune cells, shows that these cells play a critical role in the regulation of AT homeostasis and inflammation.

Serum Fetuin-A levels are increased and associated with insulin resistance in women with polycystic ovary syndrome

BACKGROUND

Insulin resistance (IR) is a common characteristic of women with polycystic ovary syndrome (PCOS). It has been reported that circulating Fetuin-A levels were associated with IR and type 2 diabetes mellitus (T2DM). However, previous reports were inconsistent.

METHODS

Two hundred seven subjects were screened for PCOS according to the diagnostic guideline of the Rotterdam consensus criterion. Serum Fetuin-A levels were measured using an ELISA kit. An independent t-test or Nonparametric test was used to detect differences between PCOS and control groups. Spearman's correlation analysis was used to examine the association of the serum Fetuin-A with other parameters.

RESULTS

Our findings showed that circulating Fetuin-A concentration ranged from 196.6 to 418.2 μg/L for most women without PCOS (95%). Women with PCOS had higher circulating Fetuin-A levels than healthy women (437.9 ± 119.3 vs. 313.8 ± 60.5 μg/L; p <  0.01). Serum Fetuin-A was positively correlated with BMI, WHR, TG, TC, LDL-C, HOMA-IR, LH, T, and DHEA-S. Multivariate regression analysis showed that WHR, TG, HOMA-IR, and DHEA-S were independent predictors of the levels of circulating Fetuin-A. Binary logistic regression revealed that serum Fetuin-A was associated with the occurrence of PCOS. In addition, our ROC curve analysis found that the cutoff values for Fetuin-A to predict PCOS and IR were 366.3 and 412.6 μg/L.

CONCLUSION

Blood Fetuin-A may be a useful biomarker for screening women for PCOS and IR.

Fetuin-a expression profile in mouse and human adipose tissue

Fetuin-A (Fet-A) was one of the first hepatokines to be reportedly linked to metabolic diseases. Fet-A was also suggested to be an adipokine, but its expression in the adipose tissue remains debatable. Here we compared the expression of Fet-A between human and mice adipose tissue biopsies as well as among human subcutaneous tissue and visceral adipose tissue primary cells, and mouse 3 T3-L1 cells at various stages of differentiation. Fet-A was expressed in mice biopsies and cells but not in human biopsies and cells, except in visceral adipose tissue primary cells following differentiation. Although the marginal expression of Fet-A in human visceral adipose tissue, a major contribution of Fet-A expression in human adipose tissue to systemic Fet-A levels is discounted, but it could indicate specific local Fet-A action in the visceral adipose tissue.

The Role of Adipose Tissue and Adipokines in Sepsis: Inflammatory and Metabolic Considerations, and the Obesity Paradox

PURPOSE

Sepsis has become a global health problem with rising incidence and high mortality, creating a substantial social and economic burden. Early diagnosis and treatment can improve outcome, but reliable sepsis biomarkers are lacking. This review summarizes current evidence of the pathophysiological mechanisms linking adipose tissue to sepsis and presents experimental and clinical data on adipokines and sepsis along with important insights into the obesity paradox in sepsis survival.

RECENT FINDINGS

Sepsis is characterized by significant alterations in circulating cytokines and adipokines, biologically active molecules produced by the adipose tissue, being implicated in metabolic and inflammatory processes. Although data are inconclusive regarding classic adipokines such as leptin and adiponectin, recent evidence have highlighted the striking elevation of resistin and visfatin in critical illness and sepsis as well as their association with sepsis severity and outcomes. Given that inflammatory and metabolic pathways are involved in sepsis, studying adipokines presents an attractive, innovative, and promising research field that may provide more powerful diagnostic and prognostic biomarkers as well as novel therapeutic targets, empowering the therapeutic armamentarium for sepsis management in order to improve survival.