The "thrifty" gene encoding Ahsg/Fetuin-A meets the insulin receptor: Insights into the mechanism of insulin resistance

Proteomic profiling of serum in cats with naturally occurring degenerative joint disease and co-morbid conditions

Introduction

Degenerative joint disease (DJD) occurs very commonly in cats and can be associated with pain. Almost 70% of cats with DJD-associated pain suffer the co-morbidity of chronic kidney disease (CKD). There are currently very limited treatment or management options. A greater understanding of the systems biology of DJD, DJD-associated pain, and CKD may contribute to identifying disease specific biomarkers and relevant targets for the development of therapeutics for the control of these conditions in cats, and help inform human pain therapeutic development.

Methods

Using mass spectrometry-based proteomic profiling of the serum of 200 highly phenotyped cats with varying burdens of DJD, pain, and CKD, we identified significant individual proteins and pathways.

Results

Functional pathway analysis, based on differentially abundant proteins across individual disease states (DJD, pain, CKD), identified pathways playing a role in DJD and DJD-associated pain including acute phase response signaling, LXR/RXR and FXR/RXR activation and the complement system. With the added co-morbidity of CKD, similar pathways were identified, with the addition of IL-12 signaling and production in macrophages.

Discussion

We identified differentially abundant proteins associated with DJD, pain and CKD and future work should evaluate these proteins as potential biomarkers of disease (individually or as clusters). Further, these data could be leveraged to identify novel therapeutic targets to address the gap in our ability to manage DJD, pain, and CKD in cats. Given that our work was in cats with naturally occurring DJD, these results may have translational applicability to human health.

Molecular insights into the proteomic composition of porcine treated dentin matrix

Background

Human-treated dentin matrix (hTDM) has recently been studied as a natural extracellular matrix-based biomaterial for dentin pulp regeneration. However, porcine-treated dentin matrix (pTDM) is a potential alternative scaffold due to limited availability. However, there is a dearth of information regarding the protein composition and underlying molecular mechanisms of pTDM.Methods: hTDM and pTDM were fabricated using human and porcine teeth, respectively, and their morphological characteristics were examined using scanning electron microscopy. Stem cells derived from human exfoliated deciduous teeth (SHEDs) were isolated and characterized using flow cytometry and multilineage differentiation assays. SHEDs were cultured in three-dimensional environments with hTDM, pTDM, or biphasic hydroxyapatite/tricalcium phosphate. The expression of odontogenesis markers in SHEDs were assessed using real-time polymerase chain reaction and immunochemical staining. Subsequently, SHEDs/TDM and SHEDs/HA/TCP complexes were transplanted subcutaneously into nude mice. The protein composition of pTDM was analyzed using proteomics and compared to previously published data on hTDM.Results: pTDM and hTDM elicited comparable upregulation of odontogenesis-related genes and proteins in SHEDs. Furthermore, both demonstrated the capacity to stimulate root-related tissue regeneration in vivo. Proteomic analysis revealed the presence of 278 protein groups in pTDM, with collagens being the most abundant. Additionally, pTDM and hTDM shared 58 identical proteins, which may contribute to their similar abilities to induce odontogenesis.

Conclusions

Both hTDM and pTDM exhibit comparable capabilities in inducing odontogenesis, potentially owing to their distinctive bioactive molecular networks.

Immunomodulation through Nutrition Should Be a Key Trend in Type 2 Diabetes Treatment

An organism's ability to function properly depends not solely on its diet but also on the intake of nutrients and non-nutritive bioactive compounds that exert immunomodulatory effects. This principle applies both to healthy individuals and, in particular, to those with concomitant chronic conditions, such as type 2 diabetes. However, the current food industry and the widespread use of highly processed foods often lead to nutritional deficiencies. Numerous studies have confirmed the occurrence of immune system dysfunction in patients with type 2 diabetes. This article elucidates the impact of specific nutrients on the immune system function, which maintains homeostasis of the organism, with a particular emphasis on type 2 diabetes. The role of macronutrients, micronutrients, vitamins, and selected substances, such as omega-3 fatty acids, coenzyme Q10, and alpha-lipoic acid, was taken into consideration, which outlined the minimum range of tests that ought to be performed on patients in order to either directly or indirectly determine the severity of malnutrition in this group of patients.

Quantitative mapping of the in vivo O-GalNAc glycoproteome in mouse tissues identifies GalNAc-T2 O-glycosites in metabolic disorder

The family of GalNAc-Ts (GalNAcpolypeptide:N-Acetylgalactosaminyl transferases) catalyzes the first committed step in the synthesis of O-glycans, which is an abundant and biologically important protein modification. Abnormalities in the activity of individual GalNAc-Ts can result in congenital disorders of O-glycosylation (CDG) and influence a broad array of biological functions. How site-specific O-glycans regulate biology is unclear. Compiling in vivo O-glycosites would be an invaluable step in determining the function of site-specific O-glycans. We integrated chemical and enzymatic conditions that cleave O-glycosites, a higher-energy dissociation product ions-triggered electron-transfer/higher-energy collision dissociation mass spectrometry (MS) workflow and software to study nine mouse tissues and whole blood. We identified 2,154 O-glycosites from 595 glycoproteins. The O-glycosites and glycoproteins displayed consensus motifs and shared functions as classified by Gene Ontology terms. Limited overlap of O-glycosites was observed with protein O-GlcNAcylation and phosphorylation sites. Quantitative glycoproteomics and proteomics revealed a tissue-specific regulation of O-glycosites that the differential expression of Galnt isoenzymes in tissues partly contributes to. We examined the Galnt2-null mouse model, which phenocopies congenital disorder of glycosylation involving GALNT2 and revealed a network of glycoproteins that lack GalNAc-T2-specific O-glycans. The known direct and indirect functions of these glycoproteins appear consistent with the complex metabolic phenotypes observed in the Galnt2-null animals. Through this study and interrogation of databases and the literature, we have compiled an atlas of experimentally identified mouse O-glycosites consisting of 2,925 O-glycosites from 758 glycoproteins.

AHSG, a Gene Promoting Tumour Proliferation, Migration and Invasion, is an Independent Prognostic Factor for Poor Overall Survival in Lung Adenocarcinoma

OBJECTIVE

Recent studies have shown that the metabolic process-related gene AHSG is involved in multiple pathological processes of tumours. This study will explore the relationship between AHSG and lung adenocarcinoma.

MATERIALS AND METHODS

Expression analysis, survival analysis and co-expression analysis of AHSG were performed using a public database, and cytological and molecular biology assays were performed to explore the role of AHSG in lung adenocarcinoma.

RESULT

Compared with normal tissues, AHSG expression was significantly higher in cancer tissues in the TCGA-LUAD database, and pan-cancer analysis revealed abnormal AHSG expression in different kinds of tumours. Survival analysis revealed that compared with the low expression group, the patients in the high expression group had a significantly worse overall survival duration in the TCGA-LUAD database, and a subsequent study confirmed that AHSG expression could be an independent prognostic factor of overall survival in lung adenocarcinoma. AHSG-related genes are involved in multiple physiological and pathophysiological pathways. In subsequent cytological and molecular biology experiments, inhibition of AHSG expression suppressed proliferation, migration and invasion in lung adenocarcinoma cell lines, and the EMT process was blocked after knockdown of AHSG.

CONCLUSION

AHSG could be used as a prognostic factor for OS in patients with lung adenocarcinoma. It can promote the biological behaviour of lung adenocarcinoma and may become a potential target for treatment, which is worthy of further study.

Transcriptome Analysis to Elucidate the Effects of Milk Replacer Feeding Level on Intestinal Function and Development of Early Lambs

Although early feeding strategies influence intestinal development, the effects of milk replacer (MR) feeding level on intestinal structure and functional development and underlying regulatory mechanisms remain unclear. In this study, 14 male Hu lambs were fed MR at 2% or 4% of their average body weight and weaned at 35 days of age. The MR was produced by the Institute of Feed Research of the Chinese Academy of Agricultural Sciences, and it contains 96.91% dry matter, 23.22% protein, and 13.20% fat. Jejunal tissues were assessed by RNA-seq for differences in the gene expression of lambs at 49 days of age; regulatory pathways and mechanisms of the effects of early nutrition on intestinal function and development were analyzed, along with growth performance, feed intake, jejunal histomorphology, and digestive enzyme activities. Increasing MR- feeding levels increased dry matter intake and daily gain before weaning, as well as lactase, amylase, lipase, trypsin, and chymotrypsin activities and intestinal villus length and muscular thickness. Overall, 1179 differentially expressed genes were identified, which were enriched in nutrient metabolism, coagulation cascades, and other pathways. Further, intensive MR feeding affected insulin sensitivity to reduce excessive glucose interception by intestinal tissues to ensure adequate absorbed glucose release into the portal circulation and promoted lipid and protein degradation in intestinal tissues to meet the energy demand of intestinal cells by regulating AHSG, IGFBP1, MGAT2, ITIH, and CYP2E1 expression.

Hepatokines, bile acids and ketone bodies are novel Hormones regulating energy homeostasis

Current views show that an impaired balance partly explains the fat accumulation leading to obesity. Fetal malnutrition and early exposure to endocrine-disrupting compounds also contribute to obesity and impaired insulin secretion and/or sensitivity. The liver plays a major role in systemic glucose homeostasis through hepatokines secreted by hepatocytes. Hepatokines influence metabolism through autocrine, paracrine, and endocrine signaling and mediate the crosstalk between the liver, non-hepatic target tissues, and the brain. The liver also synthetizes bile acids (BAs) from cholesterol and secretes them into the bile. After food consumption, BAs mediate the digestion and absorption of fat-soluble vitamins and lipids in the duodenum. In recent studies, BAs act not simply as fat emulsifiers but represent endocrine molecules regulating key metabolic pathways. The liver is also the main site of the production of ketone bodies (KBs). In prolonged fasting, the brain utilizes KBs as an alternative to CHO. In the last few years, the ketogenic diet (KD) became a promising dietary intervention. Studies on subjects undergoing KD show that KBs are important mediators of inflammation and oxidative stress. The present review will focus on the role played by hepatokines, BAs, and KBs in obesity, and diabetes prevention and management and analyze the positive effects of BAs, KD, and hepatokine receptor analogs, which might justify their use as new therapeutic approaches for metabolic and aging-related diseases.

Novel targets for potential therapeutic use in Diabetes mellitus

Future targets are a promising prospect to overcome the limitation of conventional and current approaches by providing secure and effective treatment without compromising patient compliance. Diabetes mellitus is a fast-growing problem that has been raised worldwide, from 4% to 6.4% (around 285 million people) in past 30 years. This number may increase to 430 million people in the coming years if there is no better treatment or cure is available. Ageing, obesity and sedentary lifestyle are the key reasons for the worsening of this disease. It always had been a vital challenge, to explore new treatment which could safely and effectively manage diabetes mellitus without compromising patient compliance. Researchers are regularly trying to find out the permanent treatment of this chronic and life threatening disease. In this journey, there are various treatments available in market to manage diabetes mellitus such as insulin, GLP-1 agonist, biguanides, sulphonyl ureas, glinides, thiazolidinediones targeting the receptors which are discovered decade before. PPAR, GIP, FFA1, melatonin are the recent targets that already in the focus for developing new therapies in the treatment of diabetes. Inspite of numerous preclinical studies very few clinical data available due to which this process is in its initial phase. The review also focuses on the receptors like GPCR 119, GPER, Vaspin, Metrnl, Fetuin-A that have role in insulin regulation and have potential to become future targets in treatment for diabetes that may be effective and safer as compared to the conventional and current treatment approaches.

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.

Fetuin-A as a Marker of Insulin Resistance

Fetuin–A is a glycoprotein which helps in the regulation of metabolism. It is an early marker of insulin resistance (IR). The aim of this study was to evaluate the role of Fetuin–A as a predictive biomarker in cases of newly detected type 2 diabetes (NDD). The study involved 60 NDD and 60 Normal Healthy Controls (NHC). All the demographics and anthropological characteristics were noted. Fasting blood samples were drawn and various biochemical parameters were analyzed. The homeostatic model assessment of insulin resistance (HOMA-IR) and the quantitative insulin sensitivity check index (QUICKI) score was calculated. Chisquare, student T-test and Mann Whitney U tests were employed to associate and compare the mean and median between the NDD and NHC groups. Pearson's and Spearman’s correlation analysis were employed to examine the relationship of Fetuin–A levels with parametric and nonparametric variables. The independent predictors of Fetuin–A was determined by employing multiple forward linear regression. Fetuin–A was significantly high in NDD compared to NHC (1323 vs. 306.98 mcg/mL; p<0.001). Majority of NDD patients demonstrated IR based on the HOMA-IR (88.33% vs. 66.67%) and QUICKI score (96.67% vs. 85%). The multiple linear regression analysis showed that systolic blood pressure, age and QUICKI score were independently associated with Fetuin–A (p value <0.01). Fetuin–A may be used as a biomarker to detect NDD. Therefore, early detection of Fetuin–A levels in NDD gives an opportunity for suitable patient management.

Combined approaches identify known and novel genes associated with sheep litter size and non-seasonal breeding

Improvement of ewe reproduction is considerable by appropriately increasing litter size and sustaining non-seasonal breeding. However, their genetic makeups have not been entirely elucidated. Genome-wide analyses of 821 individuals were performed by combining three genomic approaches (genome-wide association study, XP-nSL, and runs of homozygosity). Consequently, 35 candidate genes including three domestication genes (TSHR, GTF2A1, and KITLG) were identified. Other than the FecB mutation at BMPR1B, we described a significant association of a missense mutation rs406686139 at seasonal lambing-associated TSHR gene with litter size. Some promising novel genes may be relevant for sheep reproduction by multitude biological processes, such as FETUB functioning in fertilization, HNRNPA1 in oogenesis, DCUN1D1 in spermatogenesis, and HRG in fertility outcome. The present study suggests that improvement of ewe reproduction is attributed to selective breeding, and casts light on the genetic basis and improvement of sheep reproduction.

Evaluation of the pathophysiological role of Fetuin A levels in adolescents with polycystic ovary syndrome

OBJECTIVES

Polycystic ovary syndrome (PCOS) is an endocrinopathy, in which hyperandrogenism and hyperinsulinism have both occurred. Fetuin-A, a natural inhibitor of tyrosine kinase, leads to insulin resistance. The aim was to evaluate the relationship between fetuin-A and hyperandrogenism and hyperinsulinism and the role of fetuin-A in the pathophysiology of PCOS.

METHODS

Thirty-eight cases with PCOS and 40 healthy adolescents were included in the study. PCOS and controls were divided into obese/non-obese subgroups. LH, FSH, total and free testosterone (TT, FT), SHBG, androstenedione, DHEAS were measured in patients with PCOS. Fasting glucose, insulin, lipid profile, AST, ALT, HsCRP, and fetuin levels of PCOS patients and healthy controls were also measured.

RESULTS

Fetuin-A levels were higher in PCOS patients than in controls. In the obese-PCOS group, when compared to non-obese PCOS patients; the levels of SHBG and HDL were low while cholesterol, LDL, triglyceride, HOMA-IR, FT, FAI, and HSCRP levels were high, but Fetuin-A levels were similar. In the obese-PCOS group, fetuin-A levels were higher than in obese-controls. HOMA-IR and fetuin-A levels were higher in non-obese PCOS patients than in non-obese controls. In the PCOS group, fetuin-A was positively correlated with TT, FT, FAI and androstenedione and negatively correlated with SHBG. Regression analysis demonstrated that FT, SHBG, and androstenedione significantly predicted fetuin-A levels (R2=54%). In non-obese PCOS patients and controls, fetuin-A was positively correlated with insulin and HOMA-IR.

CONCLUSIONS

These results suggest a relationship between androgen levels and fetuin-A in PCOS cases, independent of insulin resistance, and may shed light on further studies.

Probiotics-rich emulsion improves insulin signalling in Palmitate/Oleate-challenged human hepatocarcinoma cells through the modulation of Fetuin-A/TLR4-JNK-NF-κB pathway

BACKGROUND

Fetuin-A, also known as α2-Heremans-Schmid glycoprotein (AHSG), is an abundant plasmatic serum protein synthesized predominantly in liver and adipose tissue. This glycoprotein is known to negatively regulate insulin signaling through the inhibition of insulin receptor (IR) autophosphorylation and tyrosine kinase activity, which participates in insulin resistance (IR) and metabolic syndrome development. Recent studies demonstrated that IR and associated metabolic disorders, are closely related to the gut microbiota and modulating it by probiotics could be effective in metabolic diseases management.

OBJECTIVE

In this present work we aimed to evaluate the effects of a probiotics-rich emulsion on reducing the IR induced by free fatty acids accumulation in human hepatocarcinoma cell line, and to elucidate the implicated molecular pathways, with a specific emphasis on the hepatokin Fetuin-A-related axis.

RESULTS

Here we showed, that probiotics improve HepG2 viability, protect against apoptosis under normal and IR conditions. Moreover, the emulsion was successful in attenuating oxidative stress as well as improving mitochondrial metabolism and dynamics. Interestingly, application of the probiotics to lipotoxic HepG2 cells resulted in significant reduction of Fetuin-A/TLR4/JNK/NF-κB pathway activation, which suggests a protective effect against inflammation, obesity as well as liver related insulin resistant.

CONCLUSION

Overall, the presented data reports clearly on the potent potential of probiotics formulated in an emulsion vehicle to enhance metabolic functions of affected IR HepG2 cells, and suggest the possibility of using such preparations as insulin sensitizing therapy, playing at the same time protective role for the development of liver related insulin resistant.

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.

Detection and Characterization of Phosphorylation, Glycosylation, and Fatty Acid Bound to Fetuin A in Human Blood

The hepatokine fetuin A (Fet A) has been associated with diverse pathological states such as insulin resistance, type 2 diabetes, macrovascular disease, and systemic ectopic and vascular calcification. Fet A may also play a role in tumor growth and metastasis. The biological activity of Fet A may be affected by various modifications, including phosphorylation, O- and N-glycosylation and fatty acid binding. We developed an antibody-based assay for the detection of Fet A phosphorylated at serine 312. Fatty acid pattern was determined by gas chromatography. Using the antibody, we found that the phosphorylation was stable in human plasma or serum at room temperature for 8 h. We observed that Fet A is present in several glycosylation forms in human plasma, but the extent of Ser³¹² phosphorylation was not associated with glycosylation. The phosphorylation pattern did not change during an oral glucose tolerance test (0–120 min). We further found that human Fet A binds preferentially saturated fatty acids (>90%) at the expense of mono- and poly-unsaturated fatty acids. Our results indicate that different molecular species of Fet A are present in human plasma and that these different modifications may determine the different biological effects of Fet A.

Hepatokines and metabolism: Deciphering communication from the liver

Background

The liver is a key regulator of systemic energy homeostasis and can sense and respond to nutrient excess and deficiency through crosstalk with multiple tissues. Regulation of systemic energy homeostasis by the liver is mediated in part through regulation of glucose and lipid metabolism. Dysregulation of either process may result in metabolic dysfunction and contribute to the development of insulin resistance or fatty liver disease.

Scope of review

The liver has recently been recognized as an endocrine organ that secretes hepatokines, which are liver-derived factors that can signal to and communicate with distant tissues. Dysregulation of liver-centered inter-organ pathways may contribute to improper regulation of energy homeostasis and ultimately metabolic dysfunction. Deciphering the mechanisms that regulate hepatokine expression and communication with distant tissues is essential for understanding inter-organ communication and for the development of therapeutic strategies to treat metabolic dysfunction.

Major conclusions

In this review, we discuss liver-centric regulation of energy homeostasis through hepatokine secretion. We highlight key hepatokines and their roles in metabolic control, examine the molecular mechanisms of each hepatokine, and discuss their potential as therapeutic targets for metabolic disease. We also discuss important areas of future studies that may contribute to understanding hepatokine signaling under healthy and pathophysiological conditions.

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.

Serum Fetuin-A and Insulin Levels in Classic Congenital Adrenal Hyperplasia

Androgens play a pivotal role in non-reproductive organs such as the kidney, heart, liver, and pancreas. As androgen receptors are expressed in pancreatic and liver cells, excess testosterone can result in hypersecretion of insulin and fetuin-A, a protein produced in the liver. The expression of fetuin-A, a natural inhibitor of tyrosine kinase activity in muscle and liver, leads to insulin resistance. In addition, insulin and fetuin-A levels are thought to be affected by drugs such as glucocorticoids (GCs) and fludrocortisone. However, whether fetuin-A and insulin levels are affected by androgens and GCs in patients with classic congenital adrenal hyperplasia (CAH) is unknown. This cross-sectional study included 56 CAH patients and 70 controls. Analyses were stratified by sex and prepubertal/pubertal status to control for potential changes in serum metabolic/inflammatory markers associated with the production of sex steroids. Fasting blood glucose, insulin, triglyceride, total cholesterol, high density lipoprotein-cholesterol, aspartate aminotransferase, alanine aminotransferase, fetuin-A, and high-sensitivity C-reactive protein (hs-CRP) levels were measured in blood samples. In addition, 17α-hydroxyprogesterone, androstenedione, total testosterone, free testosterone, and dehydroepiandrosterone sulfate levels were measured before medication was administered. Insulin and fetuin-A levels were significantly higher in CAH patients than in controls. The unfavourably high levels of these substances exhibited a positive correlation with total and free testosterone. Regression analysis revealed that fetuin-A and free testosterone were the only independent predictors of the insulin level, while insulin and free testosterone levels significantly predicted the fetuin-A level (R²⁼42.7% and 59.8%). Differences were also observed in triglyceride and hs-CRP levels between the pubertal and prepubertal groups. We conclude that serum fetuin-A and insulin levels may be associated with androgens in CAH patients.

Dynamic Changes in Circulating Endocrine FGF19 Subfamily and Fetuin-A in Response to Intralipid and Insulin Infusions in Healthy and PCOS Women

Background: The fibroblast growth factors (FGF) 19 subfamily, also referred to as endocrine FGFs, includes FGF19, FGF21, and FGF23 are metabolic hormones involved in the regulation of glucose and lipid metabolism. Fetuin-A is a hepatokine involved in the regulation of beta-cell function and insulin resistance. Endocrine FGFs and fetuin-A are dysregulated in metabolic disorders including obesity, type 2 diabetes, non-alcoholic fatty liver disease and polycystic ovary syndrome (PCOS). Our study was designed to examine the response of endocrine FGFs and fetuin-A to an acute intralipid, insulin infusion and exercise in PCOS and healthy women. Subjects and Measurements: Ten healthy and 11 PCOS subjects underwent 5-h saline infusions with a hyperinsulinemic-euglycemic clamp (HIEC) performed during the final 2 h. One week later, intralipid infusions were undertaken with a HIEC performed during the final 2 h. After an 8 week of exercise intervention the saline, intralipid, and HIEC were repeated. Plasma levels of endocrine FGFs and fetuin-A were measured. Results: Baseline fetuin-A was higher in PCOS women but FGF19, FGF21, and FGF23 did not differ and were unaffected by exercise. Insulin administration elevated FGF21 in control and PCOS, suppressed FGF19 in controls, and had no effects on FGF23 and fetuin-A. Intralipid infusion suppressed FGF19 and increased FGF21. Insulin with intralipid synergistically increased FGF21 and did not have effects on lipid-mediated suppression of FGF19 in both groups. Conclusion: Our study provides evidence for insulin and lipid regulation of endocrine FGFs in healthy and PCOS women, suggesting that FGF family members play a role in lipid and glucose metabolism. Clinical Trial Registration: www.isrctn.org, Identifier: ISRCTN42448814.

Fetuin-A – Alpha2-Heremans-Schmid Glycoprotein: From Structure to a Novel Marker of Chronic Diseases Part 2. Fetuin-A – A Marker of Insulin Resistance and Related Chronic Diseases

Fetuin-A is a secretory liver glycoprotein with multiple physiological functions such as regulation of insulin resistance, tissue calcification, bone metabolism, cellular proteolytic activity, and self-proliferative signaling.

Fetuin-A is a unique molecule which binds to the insulin receptor, modulating its sensitivity, and transducing “the physiological conditions” (serum levels of the metabolites like glucose, free fatty acids, inflammatory signals) from outside into inside the cells. Plasma fetuin-A levels correlate with reduced glucose tolerance and insulin resistance. Impaired insulin sensitivity leads to the development of metabolic syndrome, an increased risk for type 2 diabetes (T2DM), dyslipidaemias and cardiovascular diseases (CVDs). Furthermore, fetuin-A inversely correlates with inflammatory and activation biomarkers, e.g. in patients with T2DM. Thus, circulatory fetuin-A levels may have plausible predictive importance as a biomarker of risk of diabetes and negative acute phase protein. Dysregulated, it plays a crucial role in the pathogenesis of some metabolic disorders and clinical inflammatory conditions like metabolic syndrome, T2DM, CVDs, polycystic ovary syndrome (PCOS), etc.

Phosphoproteomic analysis of longissimus lumborum of different altitude yaks

Yaks in high altitude regions display good adaptability to hypoxic environment. However, the mechanism involved in regulating muscle protein expression in hypoxic environment is not completely clear yet. To explore the mechanisms modulating postmortem alterations, quantitative phosphoproteomic analysis was performed on muscles of yaks raised at two different altitudes. The results indicated that 475 differentially expressed proteins (DEPS) were identified in high-altitude yaks, among which, 439 DEPs were up-regulated and 36 DEPs were down-regulated. Of these, 26 phosphoproteins clustered into energy metabolism and hypoxic adaption were selected after bioinformatics analysis. In addition, some glycolytic enzymes were detected to be differentially phosphorylated. The difference in protein phosphorylation levels between the two groups may be the key factor involved in the regulation of muscle hypoxic adaption. The present results could provide proteomic insights into changes occurring in yak muscles at different altitudes and may be a valuable resource for future investigations.

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.

Glycoproteogenomics: A Frequent Gene Polymorphism Affects the Glycosylation Pattern of the Human Serum Fetuin/α-2-HS-Glycoprotein

Fetuin, also known as α-2-HS-glycoprotein (gene name: AHSG), is one of the more abundant glycoproteins secreted into the bloodstream. There are two frequently occurring alleles of human AHSG, resulting in three genotypes (AHSG*1, AHSG*2, and heterozygous AHSG1/2). The backbone amino acid sequences of fetuin coded by the AHSG*1 and AHSG*2 genes differ in two amino acids including one known O-glycosylation site (aa position 256). Although fetuin levels have been extensively studied, the originating genotype is often ignored in such analysis. As fetuin has been suggested repeatedly as a potential biomarker for several disorders, the question whether the gene polymorphism affects the fetuin profile is of great interest. In this work, we describe detailed proteoform profiles of fetuin, isolated from serum of 10 healthy and 10 septic patient individuals and investigate potential glycoproteogenomics correlations, e.g. how gene polymorphisms affect glycosylation. We established an efficient method for fetuin purification from individuals' serum using ion-exchange chromatography. Subsequently, we performed hybrid mass spectrometric approaches integrating data from native mass spectra and peptide-centric MS analysis. Our data reveal a crucial effect of the gene polymorphism on the glycosylation pattern of fetuin. Moreover, we clearly observed increased fucosylation in the samples derived from the septic patients. Our serum proteoform analysis, targeted at one protein obtained from 20 individuals, exposes the wide variability in proteoform profiles, which should be taken into consideration when using fetuin as biomarker. Importantly, focusing on a single or few proteins, the quantitative proteoform profiles can provide, as shown here, already ample data to classify individuals by genotype and disease state.

Biomarkers of mineral metabolism and progression of aortic valve and mitral annular calcification: The Multi-Ethnic Study of Atherosclerosis

BACKGROUND AND AIMS

Previous research has implicated dysregulation of phosphate metabolism and calcium-phosphate solubilization in cardiovascular calcification, but epidemiologic studies evaluating longitudinal associations with valvular or annular calcification by computed tomography (CT), a highly sensitive imaging modality, are lacking. Our primary aim was to investigate the associations of mineral biomarkers with incidence and progression of aortic valve calcification (AVC) and mitral annular calcification (MAC).

METHODS

We evaluated the associations of serum FGF-23 (n = 6547 participants), phosphate (n = 6547), and fetuin-A (n = 2550) measured at baseline in the community-based Multi-Ethnic Study of Atherosclerosis with AVC and MAC on CT performed at baseline and at a median of 2.4 (1.6, 3.1) years later. We used linear mixed-effects models to account simultaneously for prevalence, incidence and progression of AVC and MAC.

RESULTS

After adjustment for demographic and clinical characteristics, a significant association was documented for FGF-23 with accelerated annual progression of MAC (2.83 Agatston units (AU), 95% CI = 0.49, 5.17 AU, per standard deviation (18.46 pg/mL) of FGF-23), but this was not seen for phosphate or fetuin-A. None of these biomarkers was associated with accelerated annual progression of AVC.

CONCLUSIONS

This study provides evidence relating serum FGF-23 to accelerated annual MAC progression. Whether this mineral regulator is a risk marker or is involved in pathogenesis merits further investigation.

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.

Serum levels of fetuin-A are negatively associated with log transformation levels of thyroid-stimulating hormone in patients with hyperthyroidism or euthyroidism: An observational study at a medical center in Taiwan

Fetuin-A is a protein with various biological functions. It plays a role in insulin resistance and arterial calcium deposition. Thyroid dysfunction may affect energy expenditure, glucose metabolism, and the risk of cardiovascular diseases. In the present study, we compared the serum fetuin-A concentrations in hyperthyroid patients with those in euthyroid patients.We recruited 30 newly-diagnosed hyperthyroid patients (the HY group) and treated them with anti-thyroid regimens as clinically indicated. We recruited 30 euthyroid individuals (the EU group) as controls. We compared laboratory parameters at the baseline and at 6 months. We then determined the associations between the levels of fetuin-A and free thyroxine (fT4), thyroid-stimulating hormone (TSH), or log transformation of TSH (logTSH).At the baseline, the HY patients had significantly higher serum fetuin-A levels than the EU patients (median [Q1, Q3]: 735.4 [537.9, 843.4] ng/mL vs 561.1[449.2, 670.5] ng/mL, P = .010). At 6 months, the serum fetuin-A levels of the HY patients decreased but were still higher than those of the EU patients (698.4 [627.6, 924.3] ng/mL vs 616.5 [498.2, 727.7] ng/mL, P = .002). At baseline, the serum levels of fetuin-A were negatively associated with logTSH (β = -53.79, P = .010). At 6 months, the levels of fetuin-A were positively associated with fT4 (β = 86.91, P = .039), and negatively associated with logTSH (β = -104.28, P < .001). Changes to the levels of fetuin-A within 6 months were negatively associated with changes to logTSH (β = -57.80, P = .019). The negative associations between fetuin-A levels and logTSH at baseline and at 6 months, and the changes during the 6 months remained significant after adjustment for sex and age (β = -51.72, P = .016; β = -103.11, P < .001; and β = -59.36, P = .020, respectively).The patients with hyperthyroidism had higher serum fetuin-A levels than the patients with euthyroidism. In patients with hyperthyroidism, the serum fetuin-A concentrations decreased after the anti-thyroid treatment. In the present study, serum fetuin-A concentrations were negatively associated with logTSH.

Relationship of Serum Fetuin A with Metabolic and Clinical Parameters in German Children and Adolescents with Type 1 Diabetes

BACKGROUND AND AIM

The hepatokine fetuin A is upregulated in the metabolic syndrome and in type 2 diabetes (T2D), while its role in adolescent type 1 diabetes (T1D) is unclear. We assessed the relationship between circulating fetuin A levels and metabolic control, comorbidities, and complications in adolescent T1D patients.

METHODS

We studied the relationship between serum fetuin A and clinical diabetes-related data from the DPV registry (Diabetes-Pa-tienten-Verlaufsdokumentation) in 172 adolescent T1D patients with early-onset (<5 years) long-standing (>10 years) T1D. Fetuin A levels were further compared between adolescent T1D and T2D patients.

RESULTS

Serum fetuin A levels in T1D patients (mean 0.267 ± 0.043 g/L) did not correlate with age, diabetes duration, gender, body mass index (BMI), glycated hemoglobin, serum lipid levels, blood pressure, celiac or thyroid disease, nephropathy, or retinopathy. An association of fetuin A levels with insulin requirements was only evident within the subgroup of overweight T1D patients (rs = 0.439, p = 0.028, n = 25, BMI >90th percentile), disappearing after adjustment for multiple testing. Adolescent T1D patients showed distinctly lower fetuin A levels than patients with T2D (p ≤ 0.001).

CONCLUSION

Overall, we did not observe a clinically relevant association of fetuin A levels with surrogate parameters for insulin sensitivity in our juvenile T1D cohort. A correlation with insulin requirements was detectable in overweight patients only. We hypothesize that multiple factors, such as obesity, puberty, inadequate metabolic control, and hepatic steatosis, have to add up before a clinically relevant effect of fetuin A on insulin sensitivity becomes evident.

Impact of Fetuin-A (AHSG) on Tumor Progression and Type 2 Diabetes

Fetuin-A is the protein product of the AHSG gene in humans. It is mainly synthesized by the liver in adult humans and is secreted into the blood where its concentration can vary from a low of ~0.2 mg/mL to a high of ~0.8 mg/mL. Presently, it is considered to be a multifunctional protein that plays important roles in diabetes, kidney disease, and cancer, as well as in inhibition of ectopic calcification. In this review we have focused on work that has been done regarding its potential role(s) in tumor progression and sequelae of diabetes. Recently a number of laboratories have demonstrated that a subset of tumor cells such as pancreatic, prostate and glioblastoma multiform synthesize ectopic fetuin-A, which drives their progression. Fetuin-A that is synthesized, modified, and secreted by tumor cells may be more relevant in understanding the pathophysiological role of this enigmatic protein in tumors, as opposed to the relatively high serum concentrations of the liver derived protein. Lastly, auto-antibodies to fetuin-A frequently appear in the sera of tumor patients that could be useful as biomarkers for early diagnosis. In diabetes, solid experimental evidence shows that fetuin-A binds the β-subunit of the insulin receptor to attenuate insulin signaling, thereby contributing to insulin resistance in type 2 diabetes mellitus (T2DM). Fetuin-A also may, together with free fatty acids, induce apoptotic signals in the beta islets cells of the pancreas, reducing the secretion of insulin and further exacerbating T2DM.

Fetuin-A – Alpha2-Heremans-Schmid Glycoprotein: From Structure to a Novel Marker of Chronic Diseases Part 1. Fetuin-A as a Calcium Chaperone and Inflammatory Marker

Fetuin-A is a major plasma glycoprotein released mainly by the liver. Its functions include inhibition of the activity of insulin receptor, regulation of response to inflammation, inhibition of calcified matrix metabolism and ectopic mineralization, etc. Three major functional domains of fetuin-A have been identified: one similar to the Ca-binding domains, one inhibiting cysteine protease, and a domain with high affinity to insulin receptor. The fetuin-A molecule may be considered as a highly pleomorphic protein with an important impact in a variety of clinically expressed metabolic and pathological processes. It could be used as a marker in clinical practice in the future.

Serum Fetuin-A levels in obese children with biopsy proven nonalcoholic fatty liver disease

BACKGROUND AND AIMS

Fetuin-A has been proposed as a marker of liver damage in adults with obesity-related NAFLD. The aim of this study was to test serum fetuin-A concentrations in obese children with NAFLD diagnosed either by ultrasonography or by liver biopsy and to determine its applicability as predictive tool in pediatric NAFLD.

METHODS AND RESULTS

Metabolic parameters and fetuin-A levels were investigated in 81 obese children with NAFLD diagnosed by biopsy, 79 obese children with NAFLD defined by liver ultrasonography and 23 lean subjects. Serum fetuin-A correlated significantly with age, waist circumference, systolic blood pressure, fasting insulin and 2-h postload insulin during OGTT, HOMA-IR, ISI, CRP, and apo B levels. Obese children with NAFLD detected by ultrasonography had significantly higher fetuin-A levels compared to those with normal liver. In obese children who underwent liver biopsy, no significant differences were detected in fetuin-A levels between subject with nonalcoholic steatohepatitis and those with simple steatosis. Fetuin-A was not different between obese and lean children.

CONCLUSION

Fetuin-A is not related with the degree of liver damage in obese children with NAFLD and its routine measurement as marker of liver disease severity is therefore not recommended.

Metabolic crosstalk between fatty pancreas and fatty liver: effects on local inflammation and insulin secretion

AIMS/HYPOTHESIS

Obesity-linked ectopic fat accumulation is associated with the development of type 2 diabetes. Whether pancreatic and liver steatosis impairs insulin secretion is controversial. We examined the crosstalk of human pancreatic fat cells with islets and the role of diabetogenic factors, i.e. palmitate and fetuin-A, a hepatokine released from fatty liver.

METHODS

Human pancreatic resections were immunohistochemically stained for insulin, glucagon, somatostatin and the macrophage/monocyte marker CD68. Pancreatic adipocytes were identified by Oil Red O and adiponectin staining. Primary pancreatic pre-adipocytes and differentiated adipocytes were co-cultured with human islets isolated from organ donors and the metabolic crosstalk between fatty liver and fatty pancreas was mimicked by the addition of palmitate and fetuin-A. Insulin secretion was evaluated by ELISA and RIA. Cytokine expression and secretion were assessed by RT-PCR and multiplex assay, respectively. Subcellular distribution of proteins was examined by confocal microscopy and protein phosphorylation by western blotting.

RESULTS

In human pancreatic parenchyma, highly differentiated adipocytes were detected in the proximity of islets with normal architecture and hormone distribution. Infiltration of adipocytes was associated with an increased number of CD68-positive cells within islets. In isolated primary pancreatic pre-adipocytes and differentiated adipocytes, palmitate and fetuin-A induced IL6, CXCL8 and CCL2 mRNA expression. Cytokine production was toll-like receptor 4 (TLR4)-dependent and further accentuated in pre-adipocytes when co-cultured with islets. In islets, IL6 and CXCL8 mRNA levels were also increased by fetuin-A and palmitate. Only in macrophages within the isolated islets, palmitate and fetuin-A stimulated the production of the cytotoxic cytokine IL-1β. Palmitate, but not fetuin-A, exerted pro-apoptotic effects in islet cells. Instead, fetuin-A impaired glucose-induced insulin secretion in a TLR4-independent, but c-Jun N-terminal kinase- and Ca²⁺-dependent, manner.

CONCLUSIONS/INTERPRETATION

These results provide the first evidence that fetuin-A-mediated metabolic crosstalk of fatty liver with islets may contribute to obesity-linked glucose blindness of beta cells, while fatty pancreas may exacerbate local inflammation.

Structural Basis and Genotype-Phenotype Correlations of INSR Mutations Causing Severe Insulin Resistance

The insulin receptor (INSR) gene was analyzed in four patients with severe insulin resistance, revealing five novel mutations and a deletion that removed exon 2. A patient with Donohue syndrome (DS) had a novel p.V657F mutation in the second fibronectin type III domain (FnIII-2), which contains the α-β cleavage site and part of the insulin-binding site. The mutant INSR was expressed in Chinese hamster ovary cells, revealing that it reduced insulin proreceptor processing and impaired activation of downstream signaling cascades. Using online databases, we analyzed 82 INSR missense mutations and demonstrated that mutations causing DS were more frequently located in the FnIII domains than those causing the milder type A insulin resistance (P = 0.016). In silico structural analysis revealed that missense mutations predicted to severely impair hydrophobic core formation and stability of the FnIII domains all caused DS, whereas those predicted to produce localized destabilization and to not affect folding of the FnIII domains all caused the less severe Rabson-Mendenhall syndrome. These results suggest the importance of the FnIII domains, provide insight into the molecular mechanism of severe insulin resistance, will aid early diagnosis, and will provide potential novel targets for treating extreme insulin resistance.

Circulating Triglycerides and the Association of Triglycerides with Dietary Intake Are Altered by Alpha-2-Heremans-Schmid Glycoprotein Polymorphisms

BACKGROUND

Circulating fetuin-A (FetA) inhibits insulin receptor signaling and activates the toll-like receptor 4 proinflammatory cascade; thus, it may contribute to metabolic syndrome. Polymorphisms in alpha-2-Heremans-Schmid glycoprotein (AHSG), the gene which codes FetA, may influence metabolic syndrome progression in higher-risk ethnic groups. We aimed to identify whether individual variation in AHSG influences biomarkers of metabolic disease and obesity in young Mexican adults.

METHODS

The participants were Mexican college applicants (18-25 years, n = 641). Dietary intake, anthropometric data, and blood for the analysis of biomarkers and genetics were collected. Single nucleotide polymorphisms (SNPs) in AHSG (rs2518136 and rs4917) were genotyped.

RESULTS

Neither AHSG SNP was associated with body mass index (BMI) or waist circumference. rs4917 C allele carriers had lower triglycerides (TG) than T allele homozygotes (98.85 ± 2.3 vs. 112.2 ± 5.2 mg/dL, p = 0.0113). BMI was strongly associated with TG (p < 0.0001) regardless of genotype. The relationship between circulating TG and dietary intake of carbohydrates and saturated fat was significant in rs4917 CT allele heterozygotes only (p = 0.03 and p = 0.02, respectively).

CONCLUSIONS

rs4917 T allele carriers had higher TG. This relationship was exaggerated in individuals with overweight and obesity. Dietary intake was significantly associated with TG in only those with heterozygosity at rs4917, suggesting that these individuals may be more susceptible to dietary interventions.

Recent advances in understanding the role of adipocytokines during non-alcoholic fatty liver disease pathogenesis and their link with hepatokines

Non-alcoholic fatty liver disease (NAFLD) is currently considered the main cause of chronic liver disease worldwide. Mechanisms leading to the development and progression of this disease are topics of great interest for researchers and clinicians. The current multi-hit hypothesis has thrown the crosstalk between liver and adipose tissue into sharp focus. It is well known that adipose tissue produces circulating factors, known as adipocytokines, which exert several effects on liver cells, promoting the onset of NAFLD and its progression to non-alcoholic steatohepatitis in obese subjects. In a similar way, hepatocytes may also respond to obesogenic stimuli by producing and releasing hepatokines into the circulation. Here, the authors provide an overview of recent advances in our understanding of the role of the most relevant adipocytokines and hepatokines in NAFLD pathogenesis, highlighting their possible molecular and functional interactions.

Alterations in serum levels of fetuin A and selenoprotein P in chronic hepatitis C patients with concomitant type 2 diabetes: A case-control study

BACKGROUND

Insulin resistance (IR) and type 2 diabetes mellitus (T2DM) are serious extrahepatic manifestations of chronic hepatitis C virus (HCV) infection. However, the mechanism underlying the IR in chronic HCV is obscure. Hepatokines are group of liver-derived protein, which affect the glucose and lipid metabolism in several tissues. Fetuin A (also known as human α2-HS-glycoprotein) is one of the hepatokines, which was recognized as a natural inhibitor of the insulin receptor tyrosine kinase in liver and skeletal muscle. Additionally, selenoprotein P has emerged as an important hepatokine, which primarily acts as selenium transporter and has been reported to be implicated in glucose homeostasis in human.

OBJECTIVE

The aim of the current case-control study was to investigate the serum levels of both fetuin A and selenoprotein P in chronic hepatitis C patients with or without T2DM and to correlate their levels with other biochemical parameters of insulin resistance.

MAIN FINDINGS

Our results showed that, serum fetuin A levels increased significantly in HCV patients compared with controls (P<0.01) and surplus increase was found in HCV with concomitant T2DM (P>0.001). However, selenoprotein P levels significantly elevated only in patients with both HCV and T2DM (P<0.05) compared with the healthy subjects. Both fetuin A and selenoprotein P were positively correlated with fasting blood glucose. Yet, only fetuin A was significantly correlated to the HOMA-IR (r=0.28; P=0.03).

CONCLUSIONS

These results indicate crucial roles played by fetuin A and selenoprotein P in the IR caused by HCV and that both hepatokines may be targets for the development of therapies to treat or inhibit insulin resistance associated to HCV. However, further studies on large scale should be conducted to confirm our findings.

Association of inflammatory, lipid and mineral markers with cardiac calcification in older adults

OBJECTIVE

Calcification of the aortic valve and adjacent structures involves inflammatory, lipid and mineral metabolism pathways. We hypothesised that circulating biomarkers reflecting these pathways are associated with cardiac calcification in older adults.

METHODS

We investigated the associations of various biomarkers with valvular and annular calcification in the Cardiovascular Health Study. Of the 5888 participants, up to 3585 were eligible after exclusions for missing biomarker, covariate or echocardiographic data. We evaluated analytes reflecting lipid (lipoprotein (Lp) (a), Lp-associated phospholipase A₂ (LpPLA₂) mass and activity), inflammatory (interleukin-6, soluble (s) CD14) and mineral metabolism (fetuin-A, fibroblast growth factor (FGF)-23) pathways that were measured within 5 years of echocardiography. The relationships of plasma biomarkers with aortic valve calcification (AVC), aortic annular calcification (AAC) and mitral annular calcification (MAC) were assessed with relative risk (RR) regression.

RESULTS

Calcification was prevalent: AVC 59%, AAC 45% and MAC 41%. After adjustment, Lp(a), LpPLA₂ mass and activity and sCD14 were positively associated with AVC. RRs for AVC per SD (95% CI) were as follows: Lp(a), 1.051 (1.022 to 1.081); LpPLA₂ mass, 1.036 (1.006 to 1.066) and LpPLA₂ activity, 1.037 (1.004 to 1.071); sCD14, 1.039 (1.005 to 1.073). FGF-23 was positively associated with MAC, 1.040 (1.004 to 1.078) and fetuin-A was negatively associated, 0.949 (0.911 to 0.989). No biomarkers were significantly associated with AAC.

CONCLUSION

This study shows novel associations of circulating FGF-23 and fetuin-A with MAC, and LpPLA₂ and sCD14 with AVC, confirming that previously reported for Lp(a). Further investigation of Lp and inflammatory pathways may provide added insight into the aetiology of AVC, while study of phosphate regulation may illuminate the pathogenesis of MAC.

Changes of serum C-reactive protein and fetuin-A levels in patients with acute angle-closure glaucoma and type 2 diabetes mellitus

AIM: To investigate the changes of serum C-reactive protein (CRP) and fetuin-A (AHSG) levels in patients with acute angle-closure glaucoma and type 2 diabetes mellitus.

METHODS: Serum levels of CRP and AHSG were determined by ELISA and nephelometry in 37 patients with acute angle-closure glaucoma and type 2 diabetes mellitus (group A) and 21 patients with acute angle-closure glaucoma only (group B). At the same time, 15 healthy controls were enrolled.

RESULTS: Serum levels of CRP and AHSG in groups A and B were significantly higher than those in group C (P < 0.05). Serum levels of CRP and AHSG in group A were significantly higher than those in group B (9.51 mg/L ± 3.21 mg/L vs 5.93 mg/L ± 0.87 mg/L; 376.33 μg/mL ± 9.17 μg/mL vs 315.59 μg/mL ± 10.75 μg/mL, P < 0.05).

CONCLUSION: CRP and AHSG may be involved in the development and pathogenesis of acute angle-closure glaucoma with type 2 diabetes mellitus.

Skeletal Muscle Insulin Resistance and Absence of Inflammation Characterize Insulin-Resistant Grade I Obese Women

CONTEXT

Obesity is associated with insulin-resistance (IR), the key feature of type 2 diabetes. Although chronic low-grade inflammation has been identified as a central effector of IR development, it has never been investigated simultaneously at systemic level and locally in skeletal muscle and adipose tissue in obese humans characterized for their insulin sensitivity.

OBJECTIVES

We compared metabolic parameters and inflammation at systemic and tissue levels in normal-weight and obese subjects with different insulin sensitivity to better understand the mechanisms involved in IR development.

METHODS

30 post-menopausal women were classified as normal-weight insulin-sensitive (controls, CT) and obese (grade I) insulin-sensitive (OIS) or insulin-resistant (OIR) according to their body mass index and homeostasis model assessment of IR index. They underwent a hyperinsulinemic-euglycemic clamp, blood sampling, skeletal muscle and subcutaneous adipose tissue biopsies, an activity questionnaire and a self-administrated dietary recall. We analyzed insulin sensitivity, inflammation and IR-related parameters at the systemic level. In tissues, insulin response was assessed by P-Akt/Akt expression and inflammation by macrophage infiltration as well as cytokines and IκBα expression.

RESULTS

Systemic levels of lipids, adipokines, inflammatory cytokines, and lipopolysaccharides were equivalent between OIS and OIR subjects. In subcutaneous adipose tissue, the number of anti-inflammatory macrophages was higher in OIR than in CT and OIS and was associated with higher IL-6 level. Insulin induced Akt phosphorylation to the same extent in CT, OIS and OIR. In skeletal muscle, we could not detect any inflammation even though IκBα expression was lower in OIR compared to CT. However, while P-Akt/Akt level increased following insulin stimulation in CT and OIS, it remained unchanged in OIR.

CONCLUSION

Our results show that systemic IR occurs without any change in systemic and tissues inflammation. We identified a muscle defect in insulin response as an early mechanism of IR development in grade I obese post-menopausal women.

Fetuin-A is Associated to Serum Calcium and AHSG T256S Genotype but Not to Coronary Artery Calcification

Vascular calcification has been recently associated to an increased cardiovascular risk and mortality. In few studies, Fetuin-A showed an association to coronary artery calcification (CAC), although the physiopathological mechanism underlying this association has not been fully established yet. Seventy-four patients with one or more cardiovascular risk factor and asymptomatic for coronary vasculopathy were included in the study. CAC was evaluated by Agatston score. Serum Fetuin-A levels were determined by ELISA. Molecular analysis of AHSG T256S gene variant (rs4918) was performed by PCR-RFLP. Serum Fetuin-A was correlated to serum calcium (r = 0,321; P = 0,018), but not to serum phosphorous. Multivariate linear regression analysis confirmed this association and showed that calcium and AHSG genotype were independent predictors of Fetuin-A (P = 0.037, P = 0.014, respectively). In particular, subjects carrying the SS genotype had lower levels of Fetuin-A and calcium (P = 0.037 and P = 0.038, respectively). When we compare subjects with CAC 0-10 with subjects with CAC > 10, we found that only age and male gender (P < 0.001, P = 0.035, respectively), but not Fetuin-A, were associated to CAC. Fetuin-A is not associated to CAC in subjects with low cardiovascular risk profile and asymptomatic for coronary vasculopathy, suggesting that in this setting Fetuin-A, although correlated to serum levels of calcium, could be not involved in mineral deposition on coronary vessels.

Allelic Imbalance of mRNA Associated with α2-HS Glycoprotein (Fetuin-A) Polymorphism

Alpha 2-HS glycoprotein (AHSG), also designated as fetuin-A, exhibits polymorphism in population genetics consisting of two major alleles of AHSG^∗1 and AHSG^∗2. The serum level in the AHSG^∗1 homozygote is significantly higher than that of the AHSG^∗2 homozygote. This study examined the molecular mechanism for the cis-regulatory expression. To quantitate allele-specific mRNA in intra-assays of the heterozygote, RT-PCR method employing primers that were incorporated to the two closely located SNPs was developed. The respective magnitudes of AHSG^∗1 to AHSG^∗2 in the liver tissues and hepatic culture cells of PLC/PRF/5 were determined quantitatively as 2.5-fold and 6.2-fold. The mRNA expressional difference of two major alleles was observed, which is consistent with that in the serum level. The culture cells carried heterozygous genotypes in rs4917 and rs4918, but homozygous one in rs2248690. It was unlikely that the imbalance was derived from the SNP located in the promotor site. Furthermore, to investigate the effect of mRNA degradation, RNA synthesis in the cell culture was inhibited potently by the addition of actinomycin-D. No marked change was apparent between the two alleles. The results indicated that the cis-regulatory expressional difference is expected to occur at the level of transcription or splicing of mRNA.

Serum Fetuin-A Associated With Fatty Liver Index, Early Indicator of Nonalcoholic Fatty Liver Disease: A Strobe-Compliant Article

Increased fetuin-A has been reported in association with type 2 diabetes and other metabolic diseases. However, the large population data concerning fetuin-A and nonalcoholic fatty liver disease (NAFLD) were limited. In this study, we aimed to investigate the association of serum fetuin-A with fatty liver index (FLI), the indicator of NAFLD. A population-based cross-sectional analysis was performed in 5219 middle-aged and elderly participants who were recruited from 2 nearby urban communities in Shanghai, China. Serum fetuin-A concentrations were measured by enzyme-linked immunosorbent assay (ELISA). The fourth quartiles of FLI, alanine aminotransferance (ALT), aspartate aminotransferance (AST), and γ-glutamyl transpeptadase (GGT) were defined as elevated FLI, ALT, AST, and GGT, respectively. Fetuin-A was positively associated with log-transformed-FLI, -ALT, -AST, and -GGT after adjustment for the confounding factors (all P < 0.05). Multivariate logistic regression analysis showed that each one-standard deviation increase in serum fetuin-A (120.1 mg/L) was associated with 12% (95% confidence interval [CI] 1.01-1.25, P = 0.04), 13% (95% CI 1.06-1.21, P < 0.001), and 10% (95% CI 1.03-1.17, P = 0.005) increased risk of elevated FLI, ALT, and AST, respectively. Categorical analysis showed that as compared to the lowest quartile, the highest quartile of serum fetuin-A associated with a 35% (95% CI 0.98-1.86), 50% (95% CI 1.24-1.83), and 33% (95% CI 1.10-1.60) increased risk of elevated FLI, ALT, and AST, respectively. No significant association was found with GGT. In Chinese adults, serum fetuin-A concentrations were significantly associated with elevated FLI, ALT, and AST, the early indicators of NAFLD.

Surface plasmon resonance-based immunoassay for human fetuin A

This article describes a highly-sensitive surface plasmon resonance (SPR)-based immunoassay (IA) for human fetuin A (HFA), a specific biomarker for atherosclerosis and hepatocellular carcinoma. The assay is based on a novel immobilization procedure that simply involves the dilution of an anti-HFA capture antibody (Ab) in 1% (v/v) 3-aminopropyltriethoxysilane (APTES), followed by its dispensing on a KOH-treated gold (Au)-coated SPR chip and incubation for 30 min. The developed SPR IA detected 0.3-20 ng mL(-1) of HFA with a limit of detection and sensitivity of 0.7 ng mL(-1) and 1 ng mL(-1), respectively. The highly-simplified Ab immobilization procedure is also 5-fold more rapid than conventional procedures. It leads to the leach-proof binding of the capture Ab, which means that the developed SPR IA is highly cost-effective, as the Ab-bound SPR chip could be reused for many repeated HFA IAs after regeneration with 10 mM glycine-HCl, pH 2.0. The Ab-bound SPR chip, stored at 4 °C, lost only 18% of its original activity after 4 months. For the detection of HFA spiked in diluted human whole blood and plasma, the results obtained by the developed SPR IA agreed well with the commercial HFA sandwich ELISA.

Serum fetuin-A and arginase-1 in human obesity model: Is there any interaction between inflammatory status and arginine metabolism?

Obesity is a major risk factor for many chronic metabolic diseases such as inflammation, insulin resistance (IR) and fatty liver injury. It was reported that obesity causes some variations on the serum levels of fetuin-A and is associated with arginine metabolism, especially arginase-1 levels. The aim of our study was to evaluate, the interaction and possible changes of these liver over produced proteins, fetuin-A and arginase-1 levels in obesity-related inflammatory status. Study groups were composed of individuals aged between 19 and 63 (n = 62). The control group included healthy subjects with BMI < 25, obese group included obese patients with BMI > 30 and with no other chronic disease. Biochemical markers were determined by an auto-analyzer. Adiponectin, fetuin-A, arginase-1, asymmetric dimethylarginine (ADMA), arginine, Hexanoyl-lysine (HEL) and leptin levels were measured with commercial ELISA immunoassay kits. Nitrite and nitrate were determined with colorimetric assay kit in serum samples. High sensitive C-reactive protein (hsCRP) levels and liver function enzymes activities were higher in the obese group in respect to the control group. Serum fetuin-A, arginase-1 and leptin levels were increased but adiponectin levels were decreased in obese subjects. Fetuin-A levels showed significant correlations with arginase-1 and HOMA-IR. Consequently, we carried out an investigation about higher serum fetuin-A and arginase-1 levels may have an important role in obesity and obesity-related liver damage.

Cell surface serine protease matriptase-2 suppresses fetuin-A/AHSG-mediated induction of hepcidin

Matriptase-2 is a type II transmembrane serine protease controlling the expression of hepcidin, the key regulator of iron homeostasis. By cleaving hemojuvelin, matriptase-2 suppresses bone morphogenetic protein/sons of mothers against decapentaplegic signaling. So far, the only known putative substrates of matriptase-2 are hemojuvelin and matriptase-2 itself. In this study, fetuin-A (α2-Heremans-Schmid glycoprotein) was identified in vitro as a substrate of matriptase-2. The protease–substrate interaction was validated by isolating matriptase-2 via the affinity to fetuin-A. Fetuin-A is a liver-derived plasma protein with multiple functions, which is proteolytically processed to yield a disulfide-linked two-chain form. In co-transfected cells, a matriptase-2-dependent conversion of unprocessed fetuin-A into a two-chain form was detected. Conversely, downregulation of endogenously expressed matriptase-2 stabilized fetuin-A. Arg and Lys residues located within the 40 residue spanning connecting peptide of fetuin-A were identified as cleavage sites for matriptase-2. Analysis of hepcidin expression revealed an inductive effect of fetuin-A, which was abolished by matriptase-2. Fetuin-A deficiency in mice resulted in decreased hepcidin mRNA levels. These findings implicate a role of fetuin-A in iron homeostasis and provide new insights into the mechanism of how matriptase-2 might modulate hepcidin expression.