Do Nonalcoholic Fatty Liver Disease and Fetuin-A Play Different Roles in Symptomatic Coronary Artery Disease and Peripheral Arterial Disease?

Molecular and pathobiological involvement of fetuin-A in the pathogenesis of NAFLD

The liver acts as a manufacturing unit for the production of fetuin-A, which is essential for various physiological characteristics. Scientific research has shown that a moderate upward push in fetuin-A serum levels is associated with a confirmed non-alcoholic fatty liver disease (NAFLD) diagnosis. Fetuin-A modulation is associated with a number of pathophysiological variables that cause liver problems, including insulin receptor signaling deficiencies, adipocyte dysfunction, hepatic inflammation, fibrosis, triacylglycerol production, macrophage invasion, and TLR4 activation. The focus of the present review is on the various molecular pathways, and genetic relevance of mRNA expression of fetuin-A which is correlated with progression of NAFLD. The other major area of exploration in the present review is based on the new targets for the modulation of fetuin-A, like calorie restriction and novel pharmacological agents, such as rosuvastatin, metformin, and pioglitazone which are successfully implicated in the management of various liver-related complications.

The Evolving Role of Fetuin-A in Nonalcoholic Fatty Liver Disease: An Overview from Liver to the Heart

Nonalcoholic fatty liver disease (NAFLD) is strongly associated to the features of metabolic syndrome which can progress to cirrhosis, liver failure and hepatocellular carcinoma. However, the most common cause of mortality in people with NAFLD is not liver-related but stems from atherosclerotic cardiovascular disease (CVD). The prevalence of NAFLD is on the rise, mainly as a consequence of its close association with two major worldwide epidemics, obesity and type 2 diabetes (T2D). The exact pathogenesis of NAFLD and especially the mechanisms leading to disease progression and CVD have not been completely elucidated. Human fetuin-A (alpha-2-Heremans Schmid glycoprotein), a glycoprotein produced by the liver and abundantly secreted into the circulation appears to play a role in insulin resistance, metabolic syndrome and inflammation. This review discusses the links between NAFLD and CVD by specifically focusing on fetuin-A’s function in the pathogenesis of NAFLD and atherosclerotic CVD.

Systematic Review and Meta-analysis of Circulating Fetuin-A Levels in Nonalcoholic Fatty Liver Disease

BACKGROUND AND AIMS

Accumulated studies have reported the key role of circulating fetuin-A in the development and progression of nonalcoholic fatty liver disease (NAFLD) but the results have not been consistent. In this study, we performed a systematic review and meta-analysis to explore the relationship between circulating fetuin-A level and the development and classification of NAFLD.

METHODS

The PubMed, EMBASE, and Cochrane Library databases were searched to obtain the potentially relevant studies up to May 2020. Standardized mean differences (SMD) and 95% confidence intervals of circulating fetuin-A levels were extracted and summarized. Sensitivity, subgroup analysis and meta-regression analysis were performed to investigate the potential heterogeneity. Association of circulating fetuin-A level with classification of NAFLD was also reviewed.

RESULTS

A total of 17 studies were included, composed of 1,755 NAFLD patients and 2,010 healthy controls. Meta-analysis results showed that NAFLD patients had higher circulating fetuin-A level (SMD=0.43, 95% confidence interval [CI]: 0.22-0.63, p<0.001) than controls. Subgroup analysis indicated that circulating fetuin-A level was markedly increased in adult NAFLD patients (SMD=0.48, 95% CI: 0.24-0.72, p<0.001) and not in pediatric/adolescent patients compared to controls. Circulating fetuin-A level was markedly increased in ultrasound-proven NAFLD pediatric/adolescent patients (SMD=0.42, 95% CI: 0.12-0.72, p=0.007), other than in the liver biopsy-proven NAFLD pediatric/adolescent patients. Body mass index might be the influencing factor to the heterogeneity in adult patients. Circulating fetuin-A level was not associated with the classification of NAFL vs. nonalcoholic steatohepatitis (NASH). Whether the circulating fetuin-A level was associated with the development of fibrosis remains controversial.

CONCLUSIONS

Circulating fetuin-A level was significantly higher in NAFLD patients and was not associated with the classification of NAFL vs. NASH. Whether the circulating fetuin-A level was associated with the development of fibrosis remains controversial.

Positive Correlation between Circulating Fetuin-A and Severity of Coronary Artery Disease in Men

OBJECTIVE

Fetuin-A serves a dual function; its high levels are associated with metabolic syndrome, type 2 diabetes, obesity, insulin resistance, and nonalcoholic fatty liver disease, and on the other hand, it serves as a potent inhibitor of ectopic vascular calcification. Due to the opposing findings, the aim of the current study was to investigate serum fetuin-A levels in men with coronary artery disease (CAD).

METHODS

In the case-control study, anthropometric and biochemical parameters were determined in 83 men (43 CAD patients and 40 control subjects). At last, the serum fetuin-A levels were measured using the fetuin-A human enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

A significant difference was detected among the two groups for triglyceride and cholesterol levels (P=0.003 and P=0.002, respectively). The mean fetuin-A levels were determined 230.57 ± 63.76 and 286.35 ± 64.07 μg/ml for the control group and the CAD patients, respectively (P<0.001). Fetuin- A was significantly correlated to the severity of CAD (r 0.393, P<0.001) and associated with the risk of CAD in subjects (OR [CI] = 1. 144 [1.060-1. 235]; p = 0.001). A cut-off value of 237.4 μg/ml had good sensitivity (76.7%) and specificity (65.0%) for differentiating between two groups [area under curve (AUC) = 0.732 (CI=0.621-0.842); p < 0.001].

CONCLUSION

Our results indicated that fetuin-A levels were positively correlated to the severity of CAD. The findings suggest that there is a possible link between pathogenic mechanisms of atherosclerosis and fetuin-A; however, more investigations are needed in this regard.

Urinary fetuin-A peptides as a new marker for impaired kidney function in patients with type 2 diabetes

Background

The hepatokine fetuin-A, released by the human liver, promotes pro-inflammatory effects of perivascular fat. The involvement of inflammation in type 2 diabetes mellitus (T2DM) can affect the kidney and contribute to the development of diabetic kidney disease. Therefore we examined the association of urinary fetuin-A protein fragments with renal damage in T2DM patients.

Methods

Urinary peptides of 1491 individuals using proteome data available from the human urine proteome database were analysed. Prediction of proteases involved in urinary peptide generation was performed using the Proteasix tool.

Results

We identified 14 different urinary protein fragments that belong to the region of the connecting peptide (amino acid 301–339) of the total fetuin-A protein. Calpains (CAPN1 and CAPN2), matrix metalloproteinase and pepsin A-3 were identified as potential proteases that were partially confirmed by previous in vitro studies. Combined fetuin-A peptides (mean of amplitudes) were significantly increased in T2DM patients with kidney disease and to a lesser extent with cardiovascular risk. Furthermore, fetuin-A peptide levels displayed a significant negative correlation with baseline estimated glomerular filtration rate (eGFR) values (r = −0.316, P < 0.0001) and with the slope (%) of eGFR per year (r = −0.096, P = 0.023). A multiple regression model including fetuin-A peptide and albuminuria resulted in a significantly improved correlation with eGFR (r = −0.354, P < 0.0001) compared with albuminuria, indicating an added value of this novel biomarker.

Conclusions

The urinary proteome analysis demonstrated the association of fetuin-A peptides with impaired kidney function in T2DM patients. Furthermore, fetuin-A peptides displayed early signs of kidney damage before albuminuria appeared and therefore can be used as markers for kidney disease detection.

Fetuin-A and Fetuin-B in Non-Alcoholic Fatty Liver Disease: A Meta-Analysis and Meta-Regression

The magnitude of the effect of fetuin-A and fetuin-B on non-alcoholic fatty liver disease (NAFLD) remains undefined. Therefore, the aim of this study was to synthesize previous findings to obtain a reliable estimation of this relationship. This study was registered in PROSPERO with the number CRD42019126314. Studies published not later than March 2019, examining the relationship between fetuin-A, fetuin-B, and NAFLD, were identified by a systematic search in the electronic databases of the Web of Science, PubMed, Embase, and Cochrane Library. Pooled estimates of standardized mean difference (SMD), calculated using the random-effects model in a meta-analysis, were applied to estimate the strength of the association between fetuin-A, fetuin-B, and NAFLD. Thirty publications were identified and analyzed based on specified inclusion criteria. Collectively, they consisted of 3800 NAFLD participants and 3614 controls. Compared with the controls, significant higher values of the fetuin-A (SMD = 0.83, 95% CI: 0.59 to 1.07, Z = 6.82, p < 0.001) and fetuin-B (SMD = 0.18, 95% CI: 0.02 to 0.33, Z = 2.27, p = 0.023) were observed in NAFLD patients. Meanwhile, in the subgroup analysis, the effect value of fetuin-A in the NASH group was significantly higher than that in the NAFL group (p = 0.036). The findings of this study suggest that elevated fetuin-A and fetuin-B may independently indicate the occurrence of NAFLD. Nevertheless, further research is needed to confirm these results.

Semi-Quantitative Ultrasonographic Evaluation of NAFLD

Nonalcoholic fatty liver disease (NAFLD) embraces histopathological entities ranging from the relatively benign simple steatosis to the progressive form nonalcoholic steatohepatitis (NASH), which is associated with fibrosis and an increased risk of progression to cirrhosis and hepatocellular carcinoma. NAFLD is the most common liver disease and is associated with extrahepatic comorbidities including a major cardiovascular disease burden. The non-invasive diagnosis of NAFLD and the identification of subjects at risk of progressive liver disease and cardio-metabolic complications are key in implementing personalized treatment schedules and follow-up strategies. In this review, we highlight the potential role of ultrasound semiquantitative scores for detecting and assessing steatosis severity, progression of NAFLD, and cardio-metabolic risk. Ultrasonographic scores of fatty liver severity act as sensors of cardio-metabolic health and may assist in selecting patients to submit to second-line non-invasive imaging techniques and/or liver biopsy.

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.

A critical appraisal of the use of ultrasound in hepatic steatosis

Introduction: Nonalcoholic fatty liver disease (NAFLD) spans steatosis through nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). NAFLD carries an increased risk of cardio-metabolic and liver-related events accounting for a substantial economic burden. Given that the natural history of NAFLD is critically dependent on the stage of fibrosis, non-invasively identifying the subgroup of patients at a higher risk of progressive disease is key. Areas covered: This review highlights the recent developments in the use of ultrasound-based techniques in NAFLD and their performance in predicting metabolic derangements, cardiovascular risk, and progression of liver disease, notably including diagnosis of fibrosing NASH, identification, and treatment of HCC. Expert opinion: Our ability to identify NAFLD patients and to estimate steatofibrosis with various ultrasound-based techniques has undergone tremendous progress over the last few years. However, it is more difficult to capture the inflammatory component of NASH with such ultrasound-assisted techniques. Moreover, semi-quantitative, quantitative, elastographic, and contrast-enhanced ultrasound techniques are increasingly being appreciated and made available but not all such techniques will gain success in the clinical and research area. Therefore, further research will precisely define the role of the most innovative ultrasonographic techniques, while reducing costs and increasing feasibility.

Clinical implications of fetuin-A

Fetuin-A, also termed alpha2-Heremans-Schmid glycoprotein, is a 46kDa hepatocyte derived protein (hepatokine) and serves multifaceted functions.

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.

Does bariatric surgery influence plasma levels of fetuin-A and leukocyte cell-derived chemotaxin-2 in patients with type 2 diabetes mellitus?

Background

Fetuin-A and leukocyte cell-derived chemotaxin-2 (LECT-2) are liver-derived proteins. Fetuin-A is an independent risk factor for type 2 diabetes (T2D) and obese patients with T2D have higher plasma fetuin-A levels than those without T2D. LECT-2 has positive correlation with the severity of both obesity and insulin resistance. The changes in plasma fetuin-A are not consistent after bariatric surgery and no studies have investigated the changes in LECT-2 on the obese patients with T2D after bariatric surgery.

Methods

Overall, 18 patients undergoing gastric bypass (GB) and 16 patients undergoing sleeve gastrectomy (SG) were enrolled. The fasting plasma fetuin-A and LECT-2 levels were measured at baseline, one week, three months, and one year after surgery.

Results

Both the GB and SG groups significantly decreased the body mass index (BMI), waist-to-hip ratio, a body shape index; the triglyceride, fasting blood sugar (FBS), hemoglobin A1c, C-peptide levels; and homeostatic model assessment (HOMA-IR) one year after surgery. The SG group showed a decreasing trend in plasma fetuin-A levels one year after SG surgery. There are no significant changes in LECT-2 one year after either GB or SG. Fetuin-A had a near significant negative relationship with insulin (P = 0.056) and HOMA-IR (P = 0.050) in the SG group. Changes in fetuin-A had a significant positive relationship with changes in BMI (P = 0.031) and waist-to-hip ratio (P = 0.031) in the GB group and had a near significant positive correlation with FBS (P = 0.051) in the SG group.

Discussion

Neither GB nor SG modifies plasma levels of plasma fetuin-A or LECT-2 in T2D patients after surgery. The changes in plasma fetuin-A have a positive correlation with those of the BMI and waist-to-hip ratio 12 months after GB.