Serum adipocyte fatty acid-binding protein levels are associated with nonalcoholic fatty liver disease in type 2 diabetic patients

Elevated Serum Concentration of Adipocyte Fatty Acid-Binding Protein Correlates with the Markers of Abdominal Obesity Independently of Thyroid Hormones in Non-Obese Women with Polycystic Ovary Syndrome

Adipocyte fatty acid-binding protein (A-FABP) is mainly expressed in adipocytes. The risk of abdominal obesity and autoimmune thyroid disease is increased in women with polycystic ovary syndrome (PCOS). The objective of this study was to explore the relationship of serum concentration of A-FABP with parameters of obesity, e.g., waist to hip ratio (WHR) and the amount of adipose tissue assessed by bioelectrical impedance analysis (BIA), and thyroid hormone homeostasis in women with PCOS. We examined 66 women with PCOS and 67 healthy women. Serum concentrations of A-FABP and thyroid hormones were measured; the FT3/FT4 ratio, thyroid-stimulating hormone index (TSHI), thyrotrope thyroxine resistance index (TT4RI) and thyroid feedback quantile-based index (TFQI) were calculated. In the PCOS group, serum concentrations of A-FABP, FT3 and the FT3/FT4 ratio were significantly higher in comparison to the control group (all p < 0.05). A correlation of A-FABP with WHR (r = 0.26, p = 0.04) and the percentage of adipose tissue (r = 0.33, p = 0.01) has been found only in women with PCOS. We observed no correlation between serum levels of A-FABP and TSHI, TT4RI or TFQI in women with PCOS (all p > 0.05). Our results indicate that A-FABP is an adipokine that may be connected with abdominal obesity independently of thyroid hormone homeostasis in PCOS patients.

FABP4 Expression in Subcutaneous Adipose Tissue Is Independently Associated with Circulating Triglycerides in Obesity

Hypertriglyceridemia (HTG) has been associated with an increased risk of pancreatitis and cardiovascular disease. Adipose tissue plays a major role in lipid metabolism, mobilization and distribution. We have compared the histological and transcriptomic profiles of the subcutaneous (SAT) and visceral (VAT) adipose tissues from subjects with severe obesity undergoing bariatric surgery with (Ob-HTG, n = 37) and without HTG (Ob-NTG, n = 67). Mean age and BMI were 51.87 ± 11.21 years, 45.78 ± 6.96 kg/m² and 50.03 ± 10.17 years, 44.04 ± 4.69 kg/m², respectively. The Ob-HTG group showed higher levels of glycosylated hemoglobin, fasting plasma glucose, high-sensitivity C-reactive protein and prevalence of hypertension. The degree of fibrosis was increased by 14% in SAT from the Ob-HTG group (p = 0.028), while adipocyte size distribution was comparable. Twenty genes were found differentially expressed in SAT and VAT between study groups. Among them, only SAT expression of FABP4 resulted significantly associated with circulating triglyceride levels after adjusting for other covariates and independently explained 5% of the variance in triglyceride levels in the combined model. This relationship was not found in the cohort of lean or overweight patients with normotriglyceridemia (non-Ob, n = 21). These results emphasize the contribution of SAT to triglyceride concentrations in obesity and indicate that FABP4 may be a potential drug target for the treatment of HTG.

The relationship between NAFLD and retinol-binding protein 4 - an updated systematic review and meta-analysis

PURPOSE

Retinol-binding protein 4 (RBP4) has been considered to be related to metabolic related diseases, such as hyperuricemia, obesity, and diabetes mellitus. However, whether nonalcoholic fatty liver disease (NAFLD) is related to RBP4 is unclear. Previous studies on the relationship between NAFLD and RBP4 levels have yielded inconsistent results. Hence, this meta-analysis was aimed to clarify whether circulating RBP4 levels are in relation to the risk of NAFLD.

METHODS

A meta-analysis was performed by applying observational studies to evaluate circulating RBP4 levels and NAFLD. Eligible studies published up to September 23, 2022, were searched in Embase, PubMed, and Cochrane databases.

RESULTS

In this study, 17 cross-sectional studies involving 8423 participants were included. Results from a random effects model showed that circulating RBP4 levels were higher in NAFLD patients than non-NAFLD (standardized mean difference (SMD) 0.28; 95% confidence intervals (CI): 0.11-0.46, I²: 89.8%). This association was confirmed in the Yellow race. However, no significant association was noted in the Caucasian race. After excluding the morbidly obese Population from the weight loss study (n = 2), the results of the comparison remained largely unchanged (SMD 0.28; 95% CI: 0.10-0.47, I²: 90.8%). Remarkable publication bias was not found. Although considerable heterogeneity was observed among the studies, no potential sources of heterogeneity were found in the subgroup analysis. Diagnostic methods for NAFLD were determined to be a potential source of statistical heterogeneity in meta-regression.

CONCLUSION

The findings provide evidence that NAFLD patients exhibit higher levels of circulating RBP4 compared with controls, but high heterogeneity was observed. Thus, a high RBP4 level is probably a potential risk factor for NAFLD. To confirm the causal link between NAFLD and RBP4 level of causality, further prospective cohort studies are needed.

Association of Inflammatory Cytokines With Non-Alcoholic Fatty Liver Disease

Background

Inflammatory cytokines have been considered to be significant factors contributing to the development and progression of non-alcoholic fatty liver disease (NAFLD). However, the role of inflammatory cytokines in NAFLD remains inconclusive.

Objective

This study aimed to evaluate the association between inflammatory cytokines and NAFLD.

Methods

PubMed, Web of Science, the Cochrane Library, and EMBASE databases were searched until 31 December 2021 to identify eligible studies that reported the association of inflammatory cytokine with NAFLD and its subtypes. We pooled odds ratios (ORs) and hazard risk (HRs) with 95% confidence intervals (CIs) and conducted heterogeneity tests. Sensitivity analysis and analysis for publication bias were also carried out.

Results

The search in the databases identified 51 relevant studies that investigated the association between 19 different inflammatory cytokines and NAFLD based on 36,074 patients and 47,052 controls. The results of the meta-analysis showed significant associations for C-reactive protein (CRP), interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule-1 (ICAM-1) with NAFLD (ORs of 1.41, 1.08, 1.50, 1.15 and 2.17, respectively). In contrast, we observed non-significant associations for interferon-γ (IFN-γ), insulin-like growth factor (IGF-II), interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-7 (IL-7), interleukin-8 (IL-8), interleukin-10 (IL-10), interleukin-12 (IL-12), monocyte chemoattractant protein-1(MCP-1), and transforming growth factor-β (TGF-β) with NAFLD. Our results also showed that CRP, IL-1β, and TNF-α were significantly associated with non-alcoholic steatohepatitis (NASH) and hepatic fibrosis.

Conclusions

Our results indicated that increased CRP, IL‐1β, IL-6, TNF‐α, and ICAM-1 concentrations were significantly associated with increased risks of NAFLD. These inflammatory mediators may serve as biomarkers for NAFLD subjects and expect to provide new insights into the aetiology of NAFLD as well as early diagnosis and intervention.

Non-alcoholic fatty liver disease and type 2 diabetes - An Update

The global prevalence of non‐alcoholic fatty liver disease (NAFLD) is rising, along with the epidemic of diabesity. NAFLD is present in >70% of individuals with type 2 diabetes. Although the mutually detrimental relationship between NAFLD and type 2 diabetes has been well established, a multitude of recent studies have further shown that type 2 diabetes is closely linked to the development of cirrhosis, hepatocellular carcinoma, liver‐related morbidity and mortality. In contrast, NAFLD also negatively impacts type 2 diabetes both in terms of its incidence and related adverse clinical outcomes, including cardiovascular and chronic kidney diseases. In response to these global health threats, clinical care pathways for NAFLD and guidelines for metabolic dysfunction‐associated fatty liver disease have been developed. Several antidiabetic agents have been evaluated for their potential hepatic benefits with promising results. Furthermore, type 2 diabetes patients are increasingly represented in clinical trials of novel therapeutics for NAFLD. However, despite the wealth of knowledge in NAFLD and type 2 diabetes, lack of awareness of the disease and the potential weight of this problem remains a major challenge, especially among clinicians who are outside the field of hepatology and gastroenterology. This review therefore aimed to provide all diabetes care providers with a summary of the latest evidence that supports NAFLD as an emerging diabetic complication of increasing importance, and to present the current recommendations, focusing on the assessment and therapeutic strategies, on the management of NAFLD among type 2 diabetes patients.

Unveiling the Role of the Fatty Acid Binding Protein 4 in the Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD), the main cause of chronic liver disease worldwide, is a progressive disease ranging from fatty liver to steatohepatitis (metabolic-associated steatohepatitis; MASH). Nevertheless, it remains underdiagnosed due to the lack of effective non-invasive methods for its diagnosis and staging. Although MAFLD has been found in lean individuals, it is closely associated with obesity-related conditions. Adipose tissue is the main source of liver triglycerides and adipocytes act as endocrine organs releasing a large number of adipokines and pro-inflammatory mediators involved in MAFLD progression into bloodstream. Among the adipocyte-derived molecules, fatty acid binding protein 4 (FABP4) has been recently associated with fatty liver and additional features of advanced stages of MAFLD. Additionally, emerging data from preclinical studies propose FABP4 as a causal actor involved in the disease progression, rather than a mere biomarker for the disease. Therefore, the FABP4 regulation could be considered as a potential therapeutic strategy to MAFLD. Here, we review the current knowledge of FABP4 in MAFLD, as well as its potential role as a therapeutic target for this disease.

Serum Retinol-Binding Protein Levels Are Associated with Nonalcoholic Fatty Liver Disease in Chinese Patients with Type 2 Diabetes Mellitus: A Real-World Study

BACKGROUND

The association of serum retinol-binding protein (RBP) levels with nonalcoholic fatty liver disease (NAFLD) remains controversial. Furthermore, few studies have investigated their relationship in type 2 diabetes mellitus (T2DM) patients. Therefore, the aim of the present study was to explore the association between serum RBP levels and NAFLD in Chinese inpatients with T2DM.

METHODS

This cross-sectional, real-world study included 2,263 Chinese T2DM inpatients. NAFLD was diagnosed by abdominal ultrasonography. The subjects were divided into four groups based on RBP quartiles, and clinical characteristics were compared among the four groups. The associations of both RBP levels and quartiles with the presence of NAFLD were also analyzed.

RESULTS

After adjustment for sex, age, and diabetes duration, there was a significant increase in the prevalence of NAFLD from the lowest to the highest RBP quartiles (30.4%, 40.0%, 42.4%, and 44.7% for the first, second, third, and fourth quartiles, respectively, P<0.001 for trend). Fully adjusted multiple logistic regression analysis revealed that both increased RBP levels (odds ratio, 1.155; 95% confidence interval, 1.012 to 1.318; P=0.033) and quartiles (P=0.014 for trend) were independently associated with the presence of NAFLD in T2DM patients.

CONCLUSION

Increased serum RBP levels were independently associated with the presence of NAFLD in Chinese T2DM inpatients. Serum RBP levels may be used as one of the indicators to assess the risk of NAFLD in T2DM patients.

Relationship Between Fatty Acid Binding Protein 4 and Liver Fat in Individuals at Increased Cardiometabolic Risk

Background: Liver steatosis is considered the onset of the non-alcoholic fatty liver disease (NAFLD), a major public health challenge. Nevertheless, NAFLD detection and diagnosis remain a difficult task. Fatty acid binding protein 4 (FABP4) has been proposed as potential biomarker for the ectopic fat accumulation in non-adipose tissues, although its role reflecting liver steatosis in metabolic patients is not fully explored. The aim of this study was to assess the relationship between FABP4 and the fatty liver index (FLI) in metabolic patients and to evaluate its potential role in the fatty liver disease.

Methods: A cross-sectional study involving 389 participants at increased cardiometabolic risk was performed. FLI was calculated in order to assess liver fatty disease and a FLI ≥ 60 was considered to define liver steatosis. The serum FABP4 levels were assessed by using a sandwich enzyme-linked immunosorbent assay. Multivariable regression models were used to examine the associations of FABP4 with fatty liver after adjusting for demographic and clinical characteristics.

Results: Both, FLI and serum FABP4 levels were upregulated in diabetic, obese, and metabolic syndrome patients. Serum FABP4 levels were higher in individuals with liver steatosis. Serum FABP4 were robustly associated with FLI in metabolic patients in both linear and logistic regression analyses.

Conclusion: Our findings show that the serum FABP4 is associated to liver steatosis in metabolic patients.

Circulating level of fatty acid-binding protein 4 is an independent predictor of metabolic dysfunction-associated fatty liver disease in middle-aged and elderly individuals

Aims/Introduction

Metabolic dysfunction‐associated fatty liver disease (MAFLD), defined as hepatosteatosis with type 2 diabetes mellitus, overweight/obesity or metabolic dysregulation, has been proposed as a new feature of chronic liver disease. Fatty acid‐binding protein 4 (FABP4) is expressed in adipose tissue, and secreted FABP4 is associated with the development of insulin resistance and atherosclerosis. However, the relationship between MAFLD and FABP4 has not been fully addressed.

Materials and Methods

Associations of MAFLD with metabolic markers, including FABP4, fibroblast growth factor 21 and adiponectin, were investigated in 627 individuals (men/women 292/335) in the Tanno‐Sobetsu Study, a population‐based cohort.

Results

The mean age was 65 years (range 19–98 years, median [interquartile range] 68 [56–76] years). Hepatosteatosis was determined by the fatty liver index (FLI), and FLI ≥35 for men and FLI ≥16 for women were used for detection of fatty liver, as previously reported using 14,471 Japanese individuals. FLI was positively correlated with systolic blood pressure and levels of FABP4 (r = 0.331, P < 0.001), fibroblast growth factor 21, homeostasis model assessment of insulin resistance as an insulin resistance index and uric acid, and was negatively correlated with levels of high‐density lipoprotein cholesterol and adiponectin. FABP4 concentration was independently associated with FLI after adjustment of age, sex, systolic blood pressure and levels of uric acid, high‐density lipoprotein cholesterol, homeostasis model assessment of insulin resistance, adiponectin and fibroblast growth factor 21 in multivariable regression analysis. Logistic regression analysis showed that FABP4 was an independent predictor of MAFLD after adjustment of age, sex, presence of diabetes mellitus, hypertension and dyslipidemia, and levels of uric acid, homeostasis model assessment of insulin resistance, adiponectin and fibroblast growth factor 21.

Conclusions

FABP4 concentration is independently associated with FLI and is an independent predictor of MAFLD in middle‐aged and elderly individuals.

A-FABP in Metabolic Diseases and the Therapeutic Implications: An Update

Adipocyte fatty acid-binding protein (A-FABP), which is also known as ap2 or FABP4, is a fatty acid chaperone that has been further defined as a fat-derived hormone. It regulates lipid homeostasis and is a key mediator of inflammation. Circulating levels of A-FABP are closely associated with metabolic syndrome and cardiometabolic diseases with imminent diagnostic and prognostic significance. Numerous animal studies have elucidated the potential underlying mechanisms involving A-FABP in these diseases. Recent studies demonstrated its physiological role in the regulation of adaptive thermogenesis and its pathological roles in ischemic stroke and liver fibrosis. Due to its implication in various diseases, A-FABP has become a promising target for the development of small molecule inhibitors and neutralizing antibodies for disease treatment. This review summarizes the clinical and animal findings of A-FABP in the pathogenesis of cardio-metabolic diseases in recent years. The underlying mechanism and its therapeutic implications are also highlighted.

Porphyromonas gingivalis exacerbates the progression of fatty liver disease via CD36-PPARγ pathway

Periodontal diseases have been reported to have a multidirectional association with metabolic disorders. We sought to investigate the correlation between periodontitis and diabetes or fatty liver disease using HFD-fed obese mice inoculated with P. gingivalis. Body weight, alveolar bone loss, serological biochemistry, and glucose level were determined to evaluate the pathophysiology of periodontitis and diabetes. For the evaluation of fatty liver disease, hepatic nonalcoholic steatohepatitis (NASH) was assessed by scoring steatosis, inflammation, hepatocyte ballooning and the crucial signaling pathways involved in liver metabolism were analyzed. The C-reactive protein (CRP) level and NASH score in P. gingivalis-infected obese mice were significantly elevated. Particularly, the extensive lobular inflammation was observed in the liver of obese mice infected with P. gingivalis. Moreover, the expression of metabolic regulatory factors, including peroxisome proliferator-activated receptor γ (Pparγ) and the fatty acid transporter Cd36, was up-regulated in the liver of P. gingivalis-infected obese mice. However, inoculation of P. gingivalis had no significant influence on glucose homeostasis, insulin resistance, and hepatic mTOR/AMPK signaling. In conclusion, our results indicate that P. gingivalis can induce the progression of fatty liver disease in HFD-fed mice through the upregulation of CD36-PPARγ axis.

Adipocyte Fatty Acid-Binding Protein as a Predictor of Outcome in Alcohol-induced Acute-On-Chronic Liver Failure

BACKGROUND

Alcohol is the leading cause of acute-on-chronic liver failure (ACLF). Several severity scores predict the outcome of ACLF. However, there is a lack of simple biomarkers in predicting the outcome of these sick patients. Fatty acid-binding proteins (FABPs) are small cytosolic proteins that play a major role in lipid metabolism, energy homeostasis, and inflammation, but, have not been investigated in alcohol-induced ACLF (A-ACLF).

OBJECTIVES

The primary objective was to assess the correlation between serum adipocyte-FABP (A-FABP) and liver-FABP (L-FABP) levels on mortality at day 90. Secondary objectives were to compare the levels between controls and A-ACLF, correlate L-FABP, and A-FABP levels on the development of organ failure/sepsis at day 90.

METHODS

In this prospective observational pilot study, we included patients with A-ACLF and age-matched healthy controls. FABP's were analyzed by enzyme-linked immunosorbent assay method. The patients were followed up for 90 days.

RESULTS

Twenty-five patients with A-ACLF (mean age: 40years; mean model for end-stage liver disease NA: 29.8; median Modified Maddrey's discriminant function [mDF]: 95) and 12 controls (mean age: 36.83yrs) were included in the study. A-FABP and L-FABP levels were significantly high in patients with A-ACLF than controls. Forty-four percent of patients with A-ACLF developed sepsis, 48% developed organ failure, and 44% expired by day 90. On multivariate Cox regression analysis, A-FABP (hazard ratio [HR]: 1.27 [1.08-1.5]; P = 0.003), Asian Pacific Association for the Study of Liver ACLF research consortium score (HR: 3.3[1.15-9.54]; P = 0.02), L-FABP (HR: 0.69 [0.52-0.91]; P = 0.009), and serum protein levels (HR: 0.03 [0.003-0.36]; P = 0.005) predicted mortality. A-FABP (1.17 [1.07-1.29]; P = 0.001), and serum bilirubin (1.05 [0.99-1.12]; P = 0.06) predicted development of organ failure, and only mDF (HR: 1.04 [1.01-1.07]; P = 0.009) predicted the development of sepsis on multivariate analysis. Fifteen patients received steroid therapy, of which 13.34% were nonresponders.

CONCLUSIONS

In a selected group of patients with A-ACLF, A-FABP is highly sensitive at predicting mortality and outcome. If validated in a large, diverse sample, A-FABP can be used as a simple biomarker for prognostication in A-ACLF.

The association of the steatosis severity in fatty liver disease with coronary plaque pattern in general population

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease (NAFLD) is commonly observed in patients with cardiovascular disease (CVD). However, whether the steatosis severity of NAFLD is independently associated with coronary artery atherosclerosis is still controversial.

METHODS

Consecutive Taiwanese individuals (1502) who received coronary computed tomography angiography (CCTA) and abdominal sonography as part of a general routine health evaluation were enrolled. The association between steatosis severity, coronary atherosclerosis involvement and various plaque patterns were analysed.

RESULTS

Compared with non-steatosis, NAFLD subjects had more cardiovascular risk factors that correlated with the severity of steatosis (P for the trend <.05). The presence of atherosclerotic plaques correlated with the severity of steatosis (none: 53%, mild: 64.1%, and moderate to severe: 66.9%; P for the trend <.001). Parameters of coronary atherosclerosis, including atheroma burden obstructive score (ABOS), segment involvement score (SIS) and segment stenosis score (SSS), were higher in the moderate to severe steatosis group. After adjusting for major confounding factors, the severity of steatosis still correlated with the mixed plaque pattern (P = .043). Subgroup analysis of the risk of the presence of overall coronary and mixed plaques showed a significant association with increasing severity of steatosis, especially among these who were <65 years old, male, without metabolic syndrome, and with lower low-density lipoprotein choleseterol values.

CONCLUSION

In this general population, steatosis severity of NAFLD is associated with coronary artery atherosclerosis burden. Furthermore, steatosis severity correlated with the risk of the presence of coronary plaques, especially high-risk plaques, and was independent of traditional risk factors.

Characterizing the mechanism behind the progression of NAFLD to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) developed in non-alcoholic fatty liver disease (NAFLD) individuals presents substantial clinical and biological characteristics, which remain to be elucidated. Its occurrence in noncirrhotic patients raises issues regarding surveillance strategies, which cannot be considered as cost-effective given the high prevalence of obesity and metabolic syndrome, and furthermore delineates specific oncogenic process that could be targeted in the setting of primary or secondary prevention. In this context, the identification of a genetic heterogeneity modulating HCC risk as well as specific biological pathways have been made possible through genome-wide association studies, development of animal models and in-depth analyses of human samples at the pathological and genomic levels. These advances must be confirmed and pursued to pave the way for personalized management of NAFLD-related HCC.

Serum Levels of Adipocyte Fatty Acid-Binding Protein Are Associated with Rapid Renal Function Decline in Patients with Type 2 Diabetes Mellitus and Preserved Renal Function

BACKGROUND

Recent studies have demonstrated that the levels of adipocyte fatty acid-binding protein (A-FABP) are closely associated with diabetic kidney disease (DKD) in patients with type 2 diabetes mellitus (T2DM). This study aimed to examine the association between serum A-FABP level and rapid renal function decline in patients with T2DM and preserved renal function.

METHODS

This was a prospective observational study of 452 patients with T2DM and preserved renal function who had serial measurements of estimated glomerular filtration rate (eGFR). Rapid renal function decline was defined as an eGFR decline of >4% per year. The association between baseline serum A-FABP level and rapid renal function decline was investigated.

RESULTS

Over a median follow-up of 7 years, 82 participants (18.1%) experienced rapid renal function decline. Median A-FABP levels were significantly higher in patients with rapid renal function decline, compared to non-decliners (20.2 ng/mL vs. 17.2 ng/mL, P=0.005). A higher baseline level of A-FABP was associated with a greater risk of developing rapid renal function decline, independent of age, sex, duration of diabetes, body mass index, systolic blood pressure, history of cardiovascular disease, baseline eGFR, urine albumin creatinine ratio, total cholesterol, glycosylated hemoglobin, high-sensitivity C-reactive protein and use of thiazolidinedione, insulin, angiotensin-converting-enzyme inhibitors and angiotensin II-receptor blockers and statin (odds ratio, 3.10; 95% confidence interval, 1.53 to 6.29; P=0.002).

CONCLUSION

A high level of serum A-FABP is associated with an increased risk of rapid renal function decline in patients with T2DM and preserved renal function. This suggests that A-FABP could play a role in the progression of DKD in the early stages.

Hepatic Lipidomics and Molecular Imaging in a Murine Non-Alcoholic Fatty Liver Disease Model: Insights into Molecular Mechanisms

An imbalance between hepatic fatty acid uptake and removal results in ectopic fat accumulation, which leads to non-alcoholic fatty liver disease (NAFLD). The amount and type of accumulated triglycerides seem to play roles in NAFLD progression; however, a complete understanding of how triglycerides contribute to NAFLD evolution is lacking. Our aim was to evaluate triglyceride accumulation in NAFLD in a murine model and its associations with molecular mechanisms involved in liver damage and adipose tissue-liver cross talk by employing lipidomic and molecular imaging techniques. C57BL/6J mice fed a high-fat diet (HFD) for 12 weeks were used as a NAFLD model. Standard-diet (STD)-fed animals were used as controls. Standard liver pathology was assessed using conventional techniques. The liver lipidome was analyzed by liquid chromatography–mass spectrometry (LC–MS) and laser desorption/ionization–mass spectrometry (LDI–MS) tissue imaging. Liver triglycerides were identified by MS/MS. The transcriptome of genes involved in intracellular lipid metabolism and inflammation was assessed by RT-PCR. Plasma leptin, resistin, adiponectin, and FABP4 levels were determined using commercial kits. HFD-fed mice displayed increased liver lipid content. LC–MS analyses identified 14 triglyceride types that were upregulated in livers from HFD-fed animals. Among these 14 types, 10 were identified in liver cross sections by LDI–MS tissue imaging. The accumulation of these triglycerides was associated with the upregulation of lipogenesis and inflammatory genes and the downregulation of β-oxidation genes. Interestingly, the levels of plasma FABP4, but not of other adipokines, were positively associated with 8 of these triglycerides in HFD-fed mice but not in STD-fed mice. Our findings suggest a putative role of FABP4 in the liver-adipose tissue cross talk in NAFLD.

Common and Unique Factors and the Bidirectional Relationship Between Chronic Kidney Disease and Nonalcoholic Fatty Liver in Type 2 Diabetes Patients

PURPOSE

This study aimed to investigate the common and unique risk factors and bidirectional relationship between chronic kidney disease (CKD) and nonalcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes mellitus (T2DM).

PATIENTS AND METHODS

This was a cross-sectional study of patients with T2DM enrolled in a disease management program at two specialized diabetes outpatient clinics. Common and unique risk factors for CKD and NAFLD were examined using structural equation models (SEMs). SEMs were also used to examine direct and indirect effects of NAFLD on CKD and those of CKD on NAFLD.

RESULTS

A total of 1992 subjects with T2DM were enrolled in this study. In multivariate analysis, NAFLD was independently associated with the odds of CKD (adjusted odds ratio=1.59, 95% confidence interval=1.12-2.25, P=0.009). SEMs showed that age, triglyceride, uric acid (UA), albumin, and HbA1c levels had statistically significant direct effects on CKD, and the final model could explain 22% of the variability in CKD. Age, triglycerides, body mass index (BMI), UA, white blood cell (WBC) count, serum glutamic pyruvic transaminase (SGPT) level, and smoking status had statistically significant direct effects on NAFLD, and the final model could explain 43% of the variability in NAFLD. The common risk factors contributing to both CKD and NAFLD were age, triglycerides, and UA. The unique risk factors were albumin and HbA1c for CKD, and BMI, WBC, SGPT, and smoking for NAFLD. In addition, SEM analysis also confirmed the bidirectional causal relationship between NAFLD and CKD.

CONCLUSION

Common and unique risk factors and a bidirectional relationship existed between CKD and NAFLD in our patients with T2DM.

FABP4 and MMP9 levels identified as predictive factors for poor prognosis in patients with nonalcoholic fatty liver using data mining approaches and gene expression analysis

Nonalcoholic fatty liver (NAFLD) may progress to nonalcoholic steatohepatitis (NASH) and ultimately to cirrhosis and hepatocellular carcinoma (HCC). Prognostic markers for these conditions are poorly defined. The aim of this study was to identify predictive gene markers for the transition from NAFL to NASH and then to poorer conditions. Gene expression omnibus datasets associated with a prediction analysis algorithm were used to create a matrix composed of control subject (n = 52), healthy obese (n = 51), obese with NAFL (n = 42) and NASH patients (n = 37) and 19,085 genes in order to identify specific genes predictive of the transition from steatosis to NASH and from NASH to cirrhosis and HCC and thus patients at high risk of complications. A validation cohort was used to validate these results. We identified two genes, fatty acid binding protein-4 (FABP4) and matrix metalloproteinase-9 (MMP9), which respectively allowed distinguishing patients at risk of progression from NAFL to NASH and from NASH to cirrhosis and HCC. Thus, NAFL patients expressing high hepatic levels of FABP4 and NASH patients expressing high hepatic levels of MMP9 are likely to experience disease progression. Therefore, using FABP4 and MMP9 as blood markers could help to predict poor outcomes and/or progression of NAFL during clinical trial follow-up.

Association of adipokines with hepatic steatosis and fibrosis in chronic hepatitis B patients on long-term nucleoside analogue

BACKGROUND & AIMS

It is unknown how concomitant hepatic steatosis affects disease progression in chronic hepatitis B (CHB). Adipokines such as fibroblast growth factor 21 (FGF21) and adipocyte fatty acid-binding protein (AFABP) have been associated with non-alcoholic fatty liver disease. We determined the significance of these metabolic markers in CHB-related liver injury.

METHODS

We recruited CHB patients on antiviral treatment for transient elastography assessment to determine liver stiffness (advanced fibrosis/cirrhosis, F3/F4, defined by EASL-ALEH criteria) and controlled attenuation parameter (hepatic steatosis, defined as ≥ 248 dB/m). Plasma FGF-21, AFABP and adiponectin levels were measured.

RESULTS

A total of 415 patients [mean age 59.6 years, 71.6% male, median treatment duration 6.2 years] were recruited. Patients with F3/F4 (N = 151) had lower FGF-21 (11.7 vs 13.6 pg/mL, P = 0.055), higher AFABP (126.8 vs 84.1 pg/mL, P < 0.001) and HOMA-IR (7.1 vs 5.1, P = 0.004) levels compared to those without F3/F4 (N = 264). Multivariate analysis showed that FGF-21 level was associated with hepatic steatosis (OR 1.005, 95% CI 1.001-1.009) and F3/F4 (OR 0.993, 95% CI 0.989-0.998), while AFABP level (OR 1.001, 95% CI 1-1.002), body mass index (BMI) (OR 1.107, 95% CI 1.037-1.182) and presence of diabetes mellitus (OR 2.059, 95% CI 1.206-3.516) were associated with F3/F4. With the combined presence of BMI ≥ 25 kg/m² , diabetes and AFABP > 105.9 pg/mL, the odds ratio for F3/F4 was 3.712 (95% CI 1.364-10.105, P = 0.010).

CONCLUSIONS

Low FGF-21 and high AFABP levels were associated with advanced fibrosis/cirrhosis in CHB patients on antiviral treatment. Plasma AFABP, together with other metabolic risk factors, may aid identification of patients lacking fibrosis improvement during antiviral treatment.

Adipocytokines in Steatotic Liver Surgery/Transplantation

Because of the shortage of liver grafts available for transplantation, the restrictions on graft quality have been relaxed, and marginal grafts, such as steatotic livers, are now accepted. However, this policy change has not solved the problem, because steatotic liver grafts tolerate ischemia-reperfusion (I/R) injury poorly. Adipocytokines differentially modulate steatosis, inflammation, and fibrosis and are broadly present in hepatic resections and transplants. The potential use of adipocytokines as biomarkers of the severity of steatosis and liver damage to aid the identification of high-risk steatotic liver donors and to evaluate hepatic injury in the postoperative period are discussed. The hope of finding new therapeutic strategies aimed specifically at protecting steatotic livers undergoing surgery is a strong impetus for identifying the mechanisms responsible for hepatic failure after major surgical intervention. Hence, the most recently described roles of adipocytokines in steatotic livers subject to I/R injury are discussed, the conflicting results in the literature are summarized, and reasons are offered as to why strategic pharmacologic control of adipocytokines has yet to yield clinical benefits. After this, the next steps needed to transfer basic knowledge about adipocytokines into clinical practice to protect marginal livers subject to I/R injury are presented. Recent strategies based on adipocytokine regulation, which have shown efficacy in various pathologies, and hold promise for hepatic resection and transplantation are also outlined.

Adipokine FABP4 integrates energy stores and counterregulatory metabolic responses

Although counterregulatory hormones and mediators of the fight-or-flight responses are well defined at many levels, how energy stores per se are integrated into this system remains an enigmatic question. Recent years have seen the adipose tissue become a central focus for mediating intracellular signaling and communication through the release of a variety of bioactive lipids and substrates, as well as various adipokines. A critical integration node among these mediators and responses is controlled by FA binding protein 4 (FABP4), also known as adipocyte protein 2 (aP2), which is highly expressed in adipose tissue and functions as a lipid chaperone protein. Recently, it was demonstrated that FABP4 is a secreted hormone that has roles in maintaining glucose homeostasis, representing a key juncture facilitating communication between energy-storage systems and distant organs to respond to life-threatening situations. However, chronic engagement of FABP4 under conditions of immunometabolic stress, such as obesity, exacerbates a number of immunometabolic diseases, including diabetes, asthma, cancer, and atherosclerosis. In both preclinical mouse models and humans, levels of circulating FABP4 have been correlated with metabolic disease incidence, and reducing FABP4 levels or activity is associated with improved metabolic health. In this review, we will discuss the intriguing emerging biology of this protein, including potential therapeutic options for targeting circulating FABP4.

Endothelial fatty liver binding protein 4: a new targetable mediator in hepatocellular carcinoma related to metabolic syndrome

Metabolic syndrome (MS) is becoming the leading risk factor for hepatocellular carcinoma (HCC). HCC development related to MS may occur in advanced or non-advanced liver fibrosis, suggesting specific molecular pathways. Among these pathways, basal inflammatory state and adipokines production are involved. The aim of this study was to evaluate the role of fatty acid-binding protein 4 (FABP4). In this study, we demonstrate the specific overexpression of FABP4 in human HCC samples from patients with MS compared to other risk factors for chronic liver disease with FABP4 expression restricted to peritumoral endothelial cells. In vitro, glucose, insulin, VEGFA and hypoxia upregulated endothelial FABP4, which was reversed by metformin through mTOR pathway inhibition. FABP4 exerts oncogenic effects on hepatoma cell lines by upregulating the angiogenesis gene signature and pathways involved in the cell cycle, leading to increased cell proliferation and migration, and downregulating HIF1 pathway; effects were reversed in the presence of a specific FABP4 inhibitor (BMS309403). We showed the role of microvesicles as FABP4 vectors between endothelial and tumor cells. In vivo, BMS309403 significantly reduces tumor growth in heterotopic and orthotopic xenografted mice model. In conclusion, this study demonstrates the emerging oncogenic role of liver endothelial cells through FABP4 in HCC related to MS, and highlights new anti-neoplastic mechanism of metformin.

Managing diabetes and liver disease association

There is strong association between liver diseases and diabetes (DM) which is higher than expected by a chance association of two very common disorders. It can be classified into three categories: Liver disease related to diabetes, hepatogenous diabetes (HD), and liver disease occurring coincidentally with DM. The criteria for the diagnosis of diabetes associating liver disease are the same for primary diabetes. Two hours post glucose load is a better screening test for HD. HbA1c may not be suitable for diagnosis or monitoring of diabetes associating advanced liver disease. Apart from the increased cardiovascular risk in patients with type 2 DM (T2 DM) and NAFLD, the cardiovascular and retinopathy risk is low in HD. Patients with metabolic derangement should be screened for NAFLD which in turn may predict T2 DM development. Similarly, patients with established T2 DM should also be screened for NAFLD which further contributes to diabetes worsening. Diabetes is a significant risk factor for progression of the chronic liver disease. It is associated with poor patient survival. Treatment of diabetes associating liver disease appears beneficial. Metformin, if tolerated and not contraindicated, is recommended as a first-line therapy for patients with diabetes and chronic liver disease (CLD). If the hepatic disease is severe, insulin secretagogues should be avoided because of the increased risk of hypoglycaemia. Pioglitazone may be useful in patients with fatty liver disease. DPP-4 inhibitors showed effectiveness and safety for the treatment of T2 DM in CLD patients up to those with child B stage. GLP-1 receptor agonists and SGLT-2 inhibitors exhibit positive effects on weight and are associated with minimal risk of hypoglycaemia. Insulin must be used with caution, as hypoglycaemia may be a problem. Insulin analogues are preferred in the context of hypoglycaemia Statins can be used to treat dyslipidaemia in NAFLD, also the use of angiotensin II receptor antagonist for hypertension is safe and beneficial Given the clear association between diabetes mellitus and hepatocellular carcinoma, the strict control of glycaemia with insulin sensitizers can be essential in its prevention. The addition of DM to the currently used scores (Child-Pugh and MELD scores) may enhance the sensitivity and the specificity for prediction of morbidity and mortality rates in cirrhotic patients. In the new era of directly acting antiviral agents (DAAs) for HCV treatment, it is recommended to follow up lipid profile and blood sugar levels following SVR in order to adjust doses of medications used in diabetic (SVR is associated with reduction in insulin requirements) and dyslipidaemic patients (rebound increase in the lipid profile after clearing the virus may increase risk of cardiovascular disease (CVD)). The issues of post liver transplant diabetes and relation between DM and chronic HBV are highlighted. This narrative review and Consensus-based practice guidance (under revision and criticism) are based on a formal review and analysis of the recently published world literature on the topic (Medline search up to September 2017); and the experience of the authors and independent reviewers.

Hepatic lipid metabolism and non-alcoholic fatty liver disease in aging

Aging is associated with dysregulation of glucose and lipid metabolism. Various factors that contribute to the dysregulation include both modifiable (e.g. obesity, insulin resistance) and non-modifiable risk factors (age-associated physiologic changes). Although there is no linear relationship between aging and prevalence of non-alcoholic fatty liver disease, current data strongly suggests that advanced age leads to more severe histological changes and poorer clinical outcomes. Hepatic lipid accumulation could lead to significant hepatic and systemic consequences including steatohepatitis, cirrhosis, impairment of systemic glucose metabolism and metabolic syndrome, thereby contributing to age-related diseases. Insulin, leptin and adiponectin are key regulators of the various physiologic processes that regulate hepatic lipid metabolism. Recent advances have expanded our understanding in this field, highlighting the role of novel mediators such as FGF 21, and mitochondria derived peptides. In this review, we will summarize the mediators of hepatic lipid metabolism and how they are altered in aging.

Circulating retinol binding protein 4 levels in nonalcoholic fatty liver disease: a systematic review and meta-analysis

Background

Retinol binding protein 4 (RBP4) is implicated in obesity, insulin resistance and type 2 diabetes mellitus that are closely associated with nonalcoholic fatty liver disease (NAFLD). However, recent investigations regarding circulating RBP4 levels in NAFLD are conflicting. This meta-analysis is to determine whether NAFLD, non-alcoholic steatohepatitis (NASH) and simple steatosis (SS) patients have altered RBP4 levels.

Methods

We performed a systematic search in PubMed, EMBASE and The Cochrane Library up until 18 March 2017, and 12 studies comprising a total of 4247 participants (2271 NAFLD patients and 1976 controls) were included in the meta-analysis.

Results

There were no significant differences of circulating RBP4 levels in the following comparisons: (1) NAFLD patients vs controls (standardized mean differences [SMD]: 0.08; 95% CI: −0.21, 0.38); (2) NASH patients vs controls (SMD: −0.49; 95% CI: −1.09, 0.12); (3) SS patients vs controls (SMD: −0.72; 95% CI: −1.64, 0.20) and (4) NASH vs SS patients (SMD: −0.04; 95% CI: −0.32, 0.24). The results remained essentially unchanged in the comparisons between NAFLD patients and controls after excluding single individual study or bariatric studies (n = 2). No significant publication bias was detected. However, there was significant heterogeneity among studies and the subgroup and meta-regression analyses did not find the potential sources.

Conclusions

Circulating RBP4 levels may not be associated with NAFLD. Further prospective cohort studies are required to confirm these findings.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0566-7) contains supplementary material, which is available to authorized users.

Associations of A-FABP with Anthropometric and Metabolic Indices and Inflammatory Cytokines in Obese Patients with Newly Diagnosed Type 2 Diabetes

The study aimed to evaluate the relationship between anthropometric and metabolic indices, inflammatory cytokines, and adipocyte fatty acid-binding protein (A-FABP) in obese patients with newly diagnosed type 2 diabetes. The study included 48 nonobese subjects with newly diagnosed type 2 diabetes, 42 obese subjects with newly diagnosed type 2 diabetes, 30 simple obese subjects, and 30 matched normal subjects. Serum A-FABP was assessed by enzyme-linked immunosorbent assay. Pearson's correlations and multiple linear regression stepwise analysis were used to analyze correlations of A-FABP with anthropometric and metabolic indices and inflammatory cytokines. Obese subjects with newly diagnosed type 2 diabetes had elevated A-FABP compared to normal control, nondiabetic obese patients, and nonobese diabetic patients. A-FABP was significantly correlated with glycated hemoglobin A1C (HbA1C), BMI, triglyceride, Homeostasis Model Assessment Index (HOMA-IR), waist hip rate, C-reactive protein, IL-6, and HDL-C in obese subjects with type 2 diabetes. In multiple linear regression stepwise analysis, BMI, HbA1C, and HOMA-IR were significantly independent determinants for A-FABP. BMI, HbA1C, and HOMA-IR are independently associated with A-FABP in obese subjects with newly diagnosed type 2 diabetes. A-FABP may be related to insulin resistance and inflammation in type 2 diabetes and concomitant obesity.

Serum Fatty Acid Binding Protein 4 Concentrations Are Positively and Independently Associated with Blood Pressure and Abdominal Fat among Parameters in Health Check-Ups in Ordinary Middle-Aged Japanese Males

We wished to examine potential associations among blood concentrations of fatty acid-binding protein (FABP) 4 and parameters in health check-ups such as abdominal fat area (AFA) and blood pressure (BP) in middle-aged Japanese males. We conducted a cross-sectional study of males who participated in health check-ups in Japan. We excluded participants diagnosed with metabolic diseases by the time of their check-up. A total of 305 subjects (30-64 [mean±standard deviation, 47.3±8.5] y) were recruited. Areas of total-abdominal, visceral and subcutaneous fat were measured using computed tomography. We compared the association of serum concentrations of FABP4 with various clinical parameters by Pearson product-moment correlation coefficient (PPMCC) analyses, and by step-wise multivariate linear regression analyses (MLRA). PPMCC analyses showed that blood concentrations of FABP4 were positively associated with: body mass index; areas of fat (total abdominal, visceral, subcutaneous); systolic BP; diastolic BP; total cholesterol; low-density lipoprotein-cholesterol; triacylglycerol; activities of γ-glutamyl transpeptidase, aspartate aminotransferase and alanine aminotransferase; white blood cell count; and levels of creatinine. Step-wise MLRA showed that AFAs (visceral and subcutaneous) and diastolic BP were positively and independently associated with serum concentrations of FABP4 among the parameters tested. These data suggest that serum concentrations of FABP4 are independently and positively associated with BP and AFA among parameters measured in health check-ups in middle-aged Japanese males.

Biomarkers of Metabolic Syndrome: Biochemical Background and Clinical Significance

Biomarkers of the metabolic syndrome are divided into four subgroups. Although dividing them in groups has some limitations, it can be used to draw some conclusions. In a first part, the dyslipidemias and markers of oxidative stress are discussed, while inflammatory markers and cardiometabolic biomarkers are reviewed in a second part. For most of them, the biochemical background and clinical significance are discussed, although here also a well-cut separation cannot always be made. Altered levels cannot always be claimed as the cause, risk, or consequence of the syndrome. Several factors are interrelated to each other and act in a concerted, antagonistic, synergistic, or modulating way. Most important conclusions are summarized at the end of every reviewed subgroup. Genetic biomarkers or influences of various food components on concentration levels are not included in this review article.

Association of recently described adipokines with liver histology in biopsy-proven non-alcoholic fatty liver disease: a systematic review

The prevalence of non-alcoholic fatty liver disease (NAFLD) is rising, as is the prevalence of obesity and type 2 diabetes. It is increasingly recognized that an impaired pattern in adipokine secretion could play a pivotal role in the development of NAFLD. We performed a systematic review to evaluate the potential link between newly described adipokines and liver histology in biopsy-proven NAFLD patients. A computerized literature search was performed in PubMed, EMBASE and Web of Science electronic databases. Thirty-one cross-sectional studies were included, resulting in a total of seven different investigated adipokines. Studies included in this review mainly had a good methodological quality. Most adipokines were suggested to be involved in the inflammatory response that develops within the context of NAFLD, either at hepatic or systemic level, and/or hepatic insulin resistance. Based on literature, clinical studies suggest that chemerin, resistin and adipocyte-fatty-acid-binding protein potentially are involved in NAFLD pathogenesis and/or progression. However, major inconsistency still exists, and there is a high need for larger studies, together with the need of standardized assays to determine adipokine levels.

Adipocytokines in obesity and metabolic disease

The current global obesity pandemic is the leading cause for the soaring rates of metabolic diseases, especially diabetes, cardiovascular disease, hypertension, and non-alcoholic hepatosteatosis. Efforts devoted to find cures for obesity and associated disorders in the past two decades have prompted intensive interest in adipocyte biology, and have led to major advances in the mechanistic understanding of adipose tissue as an essential endocrine organ. Adipose tissue secretes an array of hormones (adipokines) that signal key organs to maintain metabolic homeostasis, and their dysfunction has been causally linked to a wide range of metabolic diseases. In addition, obesity induces production of inflammatory cytokines (often referred to together with adipokines as adipocytokines) and infiltration of immune cells into adipose tissue, which creates a state of chronic low-grade inflammation. Metabolic inflammation has been increasingly recognized as a unifying mechanism linking obesity to a broad spectrum of pathological conditions. This review focuses on classic examples of adipocytokines that have helped to form the basis of the endocrine and inflammatory roles of adipose tissue, and it also details a few newly characterized adipocytokines that provide fresh insights into adipose biology. Studies of adipocytokines in clinical settings and their therapeutic potential are also discussed.

Comparison of characteristics between nonobese and overweight/obese subjects with nonalcoholic fatty liver disease in a South Indian population

AIMS

This study was designed to compare the characteristics of nonobese and overweight/obese subjects with nonalcoholic fatty liver disease (NAFLD) in an urban South Indian population.

SUBJECTS AND METHODS

The study group comprises 541 subjects drawn from the Chennai Urban Rural Epidemiology Study (CURES), which was carried out on a representative sample of Chennai city in southern India. NAFLD was diagnosed by ultrasonography. Subjects with NAFLD were classified as nonobese (body mass index of ≤22.9 kg/m(2)) and overweight/obese (body mass index of ≥23 kg/m(2)) based on World Health Organization Asia Pacific guidelines. Coronary artery disease (CAD) was assessed by a resting 12-lead electrocardiogram that was Minnesota-coded. Insulin resistance was assessed by using the homeostasis assessment model (HOMA-IR) using the following formula: fasting insulin (μIU/mL)×fasting glucose (mmol/L)/22.5.

RESULTS

In total, 173 of 541 (32%) subjects had NAFLD, of whom 48 (27.7%) had nonobese NAFLD and 125 (72.3%) had overweight/obese NAFLD. Compared with overweight/obese NAFLD patients, fasting blood glucose (104±29 vs. 119±45 mg/dL; P<0.05) and HOMA-IR (2.1±1.8 vs. 2.9±1.8; P<0.001) were lower and high-density lipoprotein cholesterol (43±9 vs. 39±8 mg/dL; P<0.001) was higher among nonobese NAFLD subjects. Multiple logistic regression analysis showed a significant association between nonobese NAFLD and CAD (P=0.013) even after adjusting for age, diabetes, hypercholesterolemia, HOMA-IR, and hypertension.

CONCLUSIONS

This study suggests that even nonobese NAFLD subjects have an association with CAD.

Obesity as the common soil of non-alcoholic fatty liver disease and diabetes: Role of adipokines

Non‐alcoholic fatty liver disease (NAFLD) describes a spectrum of liver conditions from simple steatosis, steatohepatitis to end‐stage liver disease. The prevalence of NAFLD has been on the rise in many parts of the world, including Asia, and NAFLD is now the liver disease associated with the highest mortality, consequent to the increased risk of cardiovascular diseases and hepatocellular carcinoma. Whereas NAFLD is an independent risk factor for type 2 diabetes, increased hepatic and peripheral insulin resistance contribute to the pathogenesis of both NAFLD and diabetes, which are associated with enhanced cardiovascular risk. Studies in humans and animal models have suggested obesity as the common link of these two diseases, likely mediated by adipose tissue inflammation and dysregulated adipokine production in obesity. In the present review, we discuss recent advances in our understanding of the role of several novel adipokines (adiponectin, adipocyte fatty acid binding protein and fibroblast growth factor‐21) in the pathophysiology of NAFLD and diabetes, as well as their use as potential biomarkers and therapeutic targets for dysglycemia in NAFLD patients.

Pharmacological inhibition of adipocyte fatty acid binding protein alleviates both acute liver injury and non-alcoholic steatohepatitis in mice

BACKGROUND & AIMS

Adipocyte fatty acid binding protein (A-FABP) is a key mediator of inflammatory response in macrophages. Increased hepatic expression and circulating levels of A-FABP have been observed in patients with non-alcoholic fatty liver disease (NAFLD). Here, we investigated the role of A-FABP in both lipopolysaccaride (LPS)-induced acute liver injury and high fat high cholesterol (HFHC) diet-induced NAFLD in mice.

METHODS

Mice with LPS-induced acute liver injury and HFHC diet-induced obesity were treated with the A-FABP inhibitor BMS309403. Liver tissues of the mice were analyzed by immunohistochemistry, Western blot or real-time PCR.

RESULTS

A-FABP expression in Kupffer cells was significantly elevated in mice with LPS-induced acute liver injury and HFHC diet-induced obesity, as compared to their healthy controls. Pretreatment of mice with BMS309403 led to a diminished LPS-induced elevation in serum levels of alanine transaminase and hepatic production of pro-inflammatory cytokines. Likewise, chronic treatment of HFHC diet-induced obese mice with BMS309403 ameliorated hepatic steatosis, macrophage infiltration, and cellular ballooning of hepatocytes. Such improvements in liver function and morphology were accompanied by significantly decreased activation of both c-Jun and NF-κB. Pretreatment with BMS309403 suppressed both LPS- and palmitate-induced pro-inflammatory responses in isolated rat Kupffer cells. Adenovirus-mediated ectopic expression of A-FABP alone was sufficient to induce liver injury and inflammation in mice.

CONCLUSIONS

These findings suggest that A-FABP is an important contributor to both LPS-induced acute liver injury and diet-induced NAFLD by potentiating inflammation in Kupffer cells. Pharmacological inhibition of A-FABP may represent a promising modality for obesity-related non-alcoholic steatohepatitis.

Beneficial effects of flaxseed oil and fish oil diet are through modulation of different hepatic genes involved in lipid metabolism in streptozotocin-nicotinamide induced diabetic rats

Dietary omega-3 fatty acids have been demonstrated to have positive physiological effects on lipid metabolism, cardiovascular system and insulin resistance. Type-2 diabetes (T2DM) is known for perturbations in fatty acid metabolism leading to dyslipidemia. Our objective was to investigate beneficial effects of dietary flaxseed oil and fish oil in streptozotocin-nicotinamide induced diabetic rats. Thirty-six adult, male, Wistar rats were divided into six groups: three diabetic and three non-diabetic. Diabetes was induced by an injection of nicotinamide (110 mg/kg) and STZ (65 mg/kg). The animals received either control, flaxseed oil or fish oil (10 % w/w) enriched diets for 35 days. Both diets lowered serum triglycerides and very low-density lipoprotein cholesterol levels and elevated serum high-density lipoprotein cholesterol levels in diabetic rats, while serum total cholesterol and LDL-C levels remained unaffected. Both the diets increased omega-3 levels in plasma and RBCs of diabetic rats. Flaxseed oil diet significantly up-regulated the key transcription factor peroxisome proliferator-activated receptor-α (PPAR-α ) and down-regulated sterol regulatory element-binding protein-1 (SREBP-1) in diabetic rats, which would have increased β-oxidation of fatty acids and concomitantly reduced lipogenesis respectively, thereby reducing TG levels. Fish oil diet, on the contrary lowered serum TG levels without altering PPAR-α while it showed a non-significant reduction in SREBP-1 expression in diabetic rats. Another key finding of the study is the activation of D5 and D6 desaturases in diabetic rats by flaxseed oil diet or fish oil diets, which may have resulted in an improved omega-3 status and comparable effects shown by both diets. The reduced expression of Liver-fatty acid binding protein in diabetic rats was restored by fish oil alone, while both diets showed equal effects on adipocyte fatty acid-binding protein expression. We also observed down-regulation of atherogenic cytokines tumor necrosis factor-α and interleukin-6 by both the diets. In conclusion, dietary flaxseed oil and fish oil have therapeutic potential in preventing lipid abnormalities in T2DM.

FABP4 dynamics in obesity: discrepancies in adipose tissue and liver expression regarding circulating plasma levels

BACKGROUND

FABP4 is predominantly expressed in adipose tissue, and its circulating levels are linked with obesity and a poor atherogenic profile.

OBJECTIVE

In patients with a wide BMI range, we analyze FABP4 expression in adipose and hepatic tissues in the settings of obesity and insulin resistance. Associations between FABP4 expression in adipose tissue and the FABP4 plasma level as well as the main adipogenic and lipolytic genes expressed in adipose tissue were also analyzed.

METHODS

The expression of several lipogenic, lipolytic, PPAR family and FABP family genes was analyzed by real time PCR. FABP4 protein expression in total adipose tissues and its fractions were determined by western blot.

RESULTS

In obesity FABP4 expression was down-regulated (at both mRNA and protein levels), with its levels mainly predicted by ATGL and inversely by the HOMA-IR index. The BMI appeared as the only determinant of the FABP4 variation in both adipose tissue depots. FABP4 plasma levels showed a significant progressive increase according to BMI but no association was detected between FABP4 circulating levels and SAT or VAT FABP4 gene expression. The gene expression of FABP1, FABP4 and FABP5 in hepatic tissue was significantly higher in tissue from the obese IR patients compared to the non-IR group.

CONCLUSION

The inverse pattern in FABP4 expression between adipose and hepatic tissue observed in morbid obese patients, regarding the IR context, suggests that both tissues may act in a balanced manner. These differences may help us to understand the discrepancies between circulating plasma levels and adipose tissue expression in obesity.

The role of serum adipocyte fatty acid-binding protein on the development of metabolic syndrome is independent of pro-inflammatory cytokines

BACKGROUND AND AIM

Adipocyte fatty acid-binding protein (FABP4) is abundantly expressed in adipocytes and plays a role in glucose homeostasis. We analysed the relationship between serum FABP4 levels and the progression of metabolic syndrome in healthy adults.

METHODS AND RESULTS

A total of 465 subjects were selected from participants in a medical check-up programme at a Health Promotion Center. Baseline serum FABP4 levels were measured, and the subjects were evaluated for the presence of metabolic syndrome (MetS) according to the recommendations of the American Heart Association/National Heart, Lung, and Blood Institute. The subjects were re-evaluated 4 years later. Baseline FABP4 concentrations were significantly higher in subjects with MetS than in those without MetS (P<0.001). At the 4-year follow-up, subjects in the highest FABP4 tertile at baseline exhibited higher values for body mass index, fat mass and percent body fat, as well as blood pressure, fasting glucose, total cholesterol, triglycerides, low-density lipoprotein (LDL)-cholesterol, insulin, homeostasis model assessment of insulin resistance, monocyte chemoattractant protein-1 and tumor necrosis factor-α levels (all P<0.05). The subjects with higher FABP4 levels had lower HDL-cholesterol concentrations (P<0.05). After adjustment for age, sex, change in percent body fat and baseline values for other metabolic and inflammatory parameters, FABP4 levels at baseline were shown to be strongly associated with the development of MetS by year 4 (odds ratio (OR), 5.75; 95% confidence interval (CI), 2.71-12.23 for highest tertile vs. lowest tertile, P<0.001)

CONCLUSION

Baseline serum FABP4 levels appear to be a significant predictor for the future development of MetS, independent of pro-inflammatory cytokines.

FABP4 predicts atherogenic dyslipidemia development. The PREDIMED study

OBJECTIVE

Atherogenic dyslipidemia (AD), characterized by high plasma triglycerides and low HDL particles, is considered one of the main effectors of vascular damage associated with obesity, metabolic syndrome (MS) and type 2 diabetes. Adipocyte fatty acid-binding protein (FABP4) plasma concentrations have been linked to metabolic alterations that are associated with adiposity. The aim of the present study was to prospectively analyze the predictive value of baseline FABP4 plasma concentrations for the development of AD.

METHODS

In the frame of the PREDIMED study, a multicenter dietary interventional trial, we prospectively measured the baseline plasma FABP4 levels and AD incidence over a six-year follow-up period (median 4 [IQR, 3-5 years]) in 578 volunteers who visited their general practitioners because of their cardiovascular risk factors.

RESULTS

During follow-up, 103 participants developed AD. Baseline plasma FABP4 levels were associated with new onset AD over the follow-up period (OR 1.03 [95% IC: 1.00-1.05], p=0.020). This increased risk was observed in women but not in men. Among women, those in the highest tertile of FABP4 had a 2.54-fold increased relative risk of developing AD compared to the lowest tertile (HR 2.54 [95% CI, 1.31-4.93], p for trend=0.008).

CONCLUSIONS

Elevated plasma FABP4 concentrations should be considered as a potential marker of metabolic derangement, which may predict the development of AD in women.

Decreased circulating endothelial progenitor cell levels and function in patients with nonalcoholic fatty liver disease

OBJECTIVES

Nonalcoholic fatty liver disease (NAFLD) is associated with advanced atherosclerosis and a higher risk of cardiovascular disease. Increasing evidence suggests that injured endothelial monolayer is regenerated by circulating bone marrow derived-endothelial progenitor cells (EPCs), and levels of circulating EPCs reflect vascular repair capacity. However, the relation between NAFLD and EPC remains unclear. Here, we tested the hypothesis that patients with nonalcoholic fatty liver disease (NAFLD) might have decreased endothelial progenitor cell (EPC) levels and attenuated EPC function.

METHODS AND RESULTS

A total of 312 consecutive patients undergoing elective coronary angiography because of suspected coronary artery disease were screened and received examinations of abdominal ultrasonography between July 2009 and November 2010. Finally, 34 patients with an ultrasonographic diagnosis of NAFLD, and 68 age- and sex-matched controls without NAFLD were enrolled. Flow cytometry with quantification of EPC markers (defined as CD34(+), CD34(+)KDR(+), and CD34(+)KDR(+)CD133(+)) in peripheral blood samples was used to assess circulating EPC numbers. The adhesive function, and migration, and tube formation capacities of EPCs were also determined in NAFLD patients and controls. Patients with NAFLD had a significantly higher incidence of metabolic syndrome, previous myocardial infarction, hyperuricemia, and higher waist circumference, body mass index, fasting glucose and triglyceride levels. In addition, patients with NAFLD had significantly decreased circulating EPC levels (all P<0.05), attenuated EPC functions, and enhanced systemic inflammation compared to controls. Multivariate logistic regression analysis showed that circulating EPC level (CD34(+)KDR(+) [cells/10(5) events]) was an independent reverse predictor of NAFLD (Odds ratio: 0.78; 95% confidence interval: 0.69-0.89, P<0.001).

CONCLUSIONS

NAFLD patients have decreased circulating EPC numbers and functions than those without NAFLD, which may be one of the mechanisms to explain atherosclerotic disease progression and enhanced cardiovascular risk in patients with NAFLD.

Small lipid-binding proteins in regulating endothelial and vascular functions: focusing on adipocyte fatty acid binding protein and lipocalin-2

Dysregulated production of adipokines from adipose tissue plays a critical role in the development of obesity-associated cardiovascular abnormalities. A group of adipokines, including adipocyte fatty acid binding protein (A-FABP) and lipocalin-2, possess specific lipid-binding activity and are up-regulated in obese human subjects and animal models. They act as lipid chaperones to promote lipotoxicity in endothelial cells and cause endothelial dysfunction under obese conditions. However, different small lipid-binding proteins modulate the development of vascular complications in distinctive manners, which are partly attributed to their specialized structural features and functionalities. By focusing on A-FABP and lipocalin-2, this review summarizes recent advances demonstrating the causative roles of these newly identified adipose tissue-derived lipid chaperones in obesity-related endothelial dysfunction and cardiovascular complications. The specific lipid-signalling mechanisms mediated by these two proteins are highlighted to support their specialized functions. In summary, A-FABP and lipocalin-2 represent potential therapeutic targets to design drugs for preventing vascular diseases associated with obesity.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Serum FGF21 levels are increased in newly diagnosed type 2 diabetes with nonalcoholic fatty liver disease and associated with hsCRP levels independently

OBJECTIVE

Fibroblast growth factor (FGF21) has beneficial effects on lipolysis. Highly sensitive C-reactive protein (hs-CRP) is a predictor of type 2 diabetes and nonalcoholic fatty liver disease (NAFLD). This study aimed to determine the levels of serum FGF21 and hs-CRP in newly diagnosed type 2 diabetes patients with and without NAFLD, and further explored the correlation between FGF21 with hs-CRP in newly diagnosed type 2 DM.

RESEARCH DESIGN AND METHODS

69 patients with newly diagnosed type 2 DM and 30 normal subjects were included in the study. FGF21 and hs-CRP were measured by ELISA kits. The severity of NAFLD was measured by ultrasound.

RESULTS

Serum FGF21 in newly diagnosed type 2 DM with NAFLD group were significantly increased (p<0.01). There was no difference for the FGF21 level in normal control group and newly diagnosed type 2 DM without NFALD group. In type 2 DM group, the FGF21 level was positively correlated with hsCRP (r=0.417, p<0.001). In multiple stepwise regression models, only hsCRP was a significantly independent determinant for serum FGF21.

CONCLUSIONS

Serum levels of FGF21 are closely related to liver steatosis in newly diagnosed type 2 DM patients.

Different association of circulating levels of adipocyte and epidermal fatty acid-binding proteins with metabolic syndrome and coronary atherosclerosis in Chinese adults

AIMS

Adipocyte and epidermal fatty acid-binding protein (A-FABP, E-FABP) are cytoplasmic proteins which may play an important role in metabolic diseases. In the present study, we investigated the different association of A-FABP and E-FABP with metabolic syndrome (MetS) and coronary artery disease (CAD) in Chinese adults.

METHODS

A total of 459 subjects (233 MetS and 226 non-MetS) who had undergone coronary angiography were enrolled in the present study. Serum A-FABP and E-FABP levels, glucose, lipid profiles and other biochemical markers were measured.

RESULTS

Both serum A-FABP and E-FABP levels were significantly higher in the MetS group than in the non-MetS group (P = 0.040 and 0.045, respectively). Only serum A-FABP levels in the CAD group were significantly higher than in the non-CAD group (12.30 ± 5.45 vs.10.94 ± 4.94 ng/mL, P= 0.008), and significantly increased with the increasing of number of disease vessels (P=0.004). Serum A-FABP levels were also associated with risk of CAD (odds ratio 2.956 [1.295-6.748]; P = 0.010). Adjusting for age, sex, and other conventional risk factors for CAD did not appreciably change the results. No difference was found in serum E-FABP levels between CAD status. Serum E-FABP levels were correlated with fasting and post load 2h plasma glucose, HbA1c, serum total cholesterol and LDL-C concentrations while serum A-FABP levels were correlated with fasting and post load 2h serum insulin concentrations and HOMA-IR (different P<0.05).

CONCLUSIONS

Our data indicated while both serum A-FABP and E-FABP levels had associations with MetS, only A-FABP was significantly associated with increased risk of CAD in Chinese adults.

The relationship between adipocyte fatty acid binding protein-4, retinol binding protein-4 levels and early diabetic nephropathy in patients with type 2 diabetes

Adipocyte fatty acid binding protein-4 (A-FABP4) and retinol binding protein-4 (RBP4) have recently been linked to type 2 diabetes mellitus (DM). Serum A-FABP4 and RBP4 levels and their relationships with early diabetic nephropathy were examined in 87 type 2 diabetic patients. The patients with diabetic nephropathy showed high A-FABP4 levels compared to the patients without diabetic nephropathy (p=0.0001). Log A-FABP4 correlated positively with age (p=0.02), log duration of diabetes (p=0.04), log body mass index (BMI) (p=0.0001), log creatinine (p=0.007), log C-reactive protein (CRP) (p=0.01), log albumin excretion rate (AER) (p=0.001), and negatively with MDRD-GFR (p=0.0001). Serum RBP4 levels were similar between the patients with and without diabetic nephropathy. RBP4 correlated positively with triglycerides (p=0.001), log creatinine (p=0.009), and negatively with MDRD-GFR (p=0.04). In regression analysis, log A-FABP4 was associated with age, sex, log BMI, and log AER (r(2)=0.43) and RBP4 was associated with triglycerides and log creatinine (r(2)=0.22). In conclusion, we found high serum A-FABP4 but unchanged RBP4 concentrations and their associations with renal function and early diabetic nephropathy in type 2 DM.

Adipocyte fatty acid binding protein in atherosclerotic plaques is associated with local vulnerability and is predictive for the occurrence of adverse cardiovascular events

AIMS

There is an increasing need for translational studies identifying molecular targets contributing to atherosclerotic plaque destabilization. Local molecular plaque markers that are related to plaque vulnerability may hold predictive value to identify patients who are at increased risk to suffer from cardiovascular events. Animal studies revealed that adipocyte fatty acid binding protein (FABP4) is associated with the progression of atherosclerosis; however, FABP4 expression studies in human atherosclerotic plaques are lacking. We investigated FABP4 expression in carotid atherosclerotic lesions in relation to plaque composition and future cardiovascular events.

METHODS AND RESULTS

Atherosclerotic plaques were obtained from 561 patients undergoing carotid endarterectomy (CEA). Plaques were analysed for the presence of macrophages, lipid core, smooth-muscle cells, collagen, calcification, and intraplaque haemorrhage. Patients were followed for 3 years after CEA. The primary outcome was defined as the composite of vascular death, vascular event, and surgical or percutaneous vascular intervention. Fatty acid binding protein levels correlated with unstable plaque characteristics and symptomatic lesions. Patients with increased FABP4 plaque levels showed a two-fold increased risk [HR = 1.99, 95% confidence interval (95% CI) (1.30-3.04)] (P = 0.005) to reach the primary outcome during follow-up. Increased FABP4 levels related to primary outcome, independent from general cardiovascular risk factors [HR = 1.33, 95% CI (1.08-1.65)] (P = 0.008).

CONCLUSION

FABP4 levels in atherosclerotic lesions are associated with an unstable plaque phenotype and an increased risk for cardiovascular events during follow-up. Besides risk stratification for adverse future cardiovascular events, the outcome of the present study supports the relevance of exploring FABP4 antagonists as a potential pharmaceutical intervention to treat atherosclerotic disease progression.

Adipocyte fatty acid binding protein levels relate to inflammation and fibrosis in nonalcoholic fatty liver disease

Several circulating cytokines are increased with obesity and may combine with the influence of visceral fat to generate insulin resistance, inflammation, and fibrosis in nonalcoholic fatty liver disease (NAFLD). Little information exists in NAFLD about three recently recognized tissue-derived cytokines that are all lipid-binding and involved in inflammation, namely adipocyte fatty acid-binding protein (AFABP), lipocalin-2, and retinol-binding protein 4 (RBP4). We examined the association of these three peptides with hepatic steatosis, inflammation, and fibrosis plus indices of adiposity, insulin resistance, and dyslipidaemia in 100 subjects with NAFLD and 129 matched controls. Levels of AFABP and lipocalin-2, but not RBP4, were significantly elevated in NAFLD versus control (AFABP, 33.5 +/- 14.4 versus 23.1 +/- 12.1 ng/mL [P < 0.001]; lipocalin-2, 63.2 +/- 26 versus 48.6 +/- 20 ng/mL [P < 0.001]) and correlated with indices of adiposity. AFABP correlated with indices of subcutaneous rather than visceral fat. AFABP alone distinguished steatohepatitis from simple steatosis (P= 0.02). Elevated AFABP independently predicted increasing inflammation and fibrosis, even when insulin resistance and visceral fat were considered; this applied to lobular inflammation and ballooning (odds ratio 1.4, confidence interval 1.0-1.8) and fibrosis stage (odds ratio 1.3, confidence interval 1.0-1.7) (P < or = 0.05 for all). None of the cytokines correlated with steatosis grade. AFABP levels correlated with insulin resistance (homeostasis model assessment of insulin resistance) in controls and NAFLD, whereas lipocalin-2 and RBP4 only correlated positively with insulin resistance in controls.

CONCLUSION

Circulating AFABP, produced by adipocytes and macrophages, and lipocalin-2, produced by multiple tissues, are elevated and may contribute to the metabolic syndrome in NAFLD. AFABP levels, which correlate with subcutaneous, but not visceral fat, independently predict inflammation and fibrosis in NAFLD and may have a direct pathogenic link to disease progression.