Serum retinol-binding protein 4 levels are elevated in non-alcoholic fatty liver disease

Supplementation of Micro- and Macronutrients-A Role of Nutritional Status in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a condition in which the pathological cumulation of fat with coexisting inflammation and damage of hepatic cells leads to progressive dysfunctions of the liver. Except for the commonly well-known major causes of NAFLD such as obesity, dyslipidemia, insulin resistance, or diabetes, an unbalanced diet and imbalanced nutritional status should also be taken into consideration. In this narrative review, we summarized the current knowledge regarding the micro- and macronutrient status of patients suffering from NAFLD considering various diets and supplementation of chosen supplements. We aimed to summarize the knowledge indicating which nutritional impairments may be associated with the onset and progression of NAFLD at the same time evaluating the potential therapy targets that could facilitate the healing process. Except for the above-mentioned objectives, one of the most important aspects of this review was to highlight the possible strategies for taking care of NAFLD patients taking into account the challenges and opportunities associated with the micronutrient status of the patients. The current research indicates that a supplementation of chosen vitamins (e.g., vitamin A, B complex, C, or D) as well as chosen elements such as zinc may alleviate the symptoms of NAFLD. However, there is still a lack of sufficient data regarding healthy ranges of dosages; thus, further research is of high importance in this matter.

Noninvasive biomarkers in pediatric nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease worldwide among children and adolescents. It encompasses a spectrum of disease, from its mildest form of isolated steatosis, to nonalcoholic steatohepatitis (NASH) to liver fibrosis and cirrhosis, or end-stage liver disease. The early diagnosis of pediatric NAFLD is crucial in preventing disease progression and in improving outcomes. Currently, liver biopsy is the gold standard for diagnosing NAFLD. However, given its invasive nature, there has been significant interest in developing noninvasive methods that can be used as accurate alternatives. Here, we review noninvasive biomarkers in pediatric NAFLD, focusing primarily on the diagnostic accuracy of various biomarkers as measured by their area under the receiver operating characteristic, sensitivity, and specificity. We examine two major approaches to noninvasive biomarkers in children with NAFLD. First, the biological approach that quantifies serological biomarkers. This includes the study of individual circulating molecules as biomarkers as well as the use of composite algorithms derived from combinations of biomarkers. The second is a more physical approach that examines data measured through imaging techniques as noninvasive biomarkers for pediatric NAFLD. Each of these approaches was applied to children with NAFLD, NASH, and NAFLD with fibrosis. Finally, we suggest possible areas for future research based on current gaps in knowledge.

Serum retinol-binding protein 4 as a predictor of fibrosis regression and response to direct-acting antiviral drugs in chronic hepatitis C virus patients

Background

Hepatitis C virus is the underlying cause of chronic hepatitis which frequently progresses to cirrhosis and hepatocellular carcinoma. In addition, HCV is thought to cause steatosis, dyslipidemia, insulin resistance, diabetes, obesity, and cardiovascular events. The aim of this study is to evaluate the role of serum RBP-4 in the prediction of fibrosis regression and the response of treatment among chronic HCV patients receiving direct-acting antiviral agents.

Methods

This study included 40 chronic HCV Egyptian patients, divided into two groups: Naive cases, 20 chronic HCV patients before starting first line of treatment; Relapser cases, 20 chronic HCV patients who were non-responders before starting second line treatment; and 10 healthy subjects as control. Laboratory investigations including complete blood count, full hepatic profile, fibroscan assessment, and retinol-binding protein-4 level at baseline and re-assessed 12 weeks after the end of treatment [sustained virological response SVR12]. Student T test, analysis of variance, chi-square, Tukey’s test, and Pearson correlation coefficient tests were used for statistical analysis.

Results

Baseline retinol-binding protein-4 level was significantly higher in the naïve case group than in the relapser and control groups with a P value of P value of < 0.001. All the naïve patients had 100% SVR12, only 90% of the relapser group achieved SVR12. A significant reduction in retinol-binding protein-4 and fibrosis staging and measurements by fibroscan among all studied patients were noted after receiving direct acting antivirals (P value < 0.001). Retinol-binding protein-4 levels before and after treatment were significantly lower among F4 patients in comparison to those of F1–F3 patients (P value 0.002, 0.009, respectively). The best cutoff value of retinol-binding protein-4 in the prediction of liver cirrhosis (F4) was ≤ 46 pg/ml with sensitivity of 100% and specificity of 66.67%.

Conclusion

Serum retinol-binding protein-4 was found to be higher in chronic HCV infection with a significant reduction after successful eradication. Its level is much lower in cirrhotic patients [F4]. As a result, retinol-binding protein-4 may have a promising role in assessing direct acting antivirals response, as well as a prognostic value in predicting liver cirrhosis.

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 between Retinol-Binding Protein 4 Levels and Preeclampsia: A Systematic Review and Meta-Analysis

Retinol-binding protein 4 (RBP4) is claimed to be associated with the development of preeclampsia, yet the reports are inconclusive. This systematic review and meta-analysis aimed to assess the association between RBP4 levels and preeclampsia. The PubMed, Google Scholar and ScienceDirect databases were searched for studies that investigated RBP4 levels in preeclampsia patients and compared them with normal controls. The meta-analysis was conducted by calculating the standardized mean difference (SMD) of RBP4 between cases and controls. The meta package with the R software was used to perform all statistical analysis. A total of 13 studies, comprising 569 cases and 1411 controls, met the inclusion criteria and were thus included in the meta-analysis. According to the random effect model, the SMD of RBP4 was significantly higher in women with preeclampsia compared with normal controls [SMD of RBP4: 0.55 ng/mL; 95% CI (0.06; 1.05); p = 0.028; I² = 89%]. Likewise, the stratified meta-analysis showed the same pattern in the studies which measured RBP4 levels in the third trimester, as well as in the studies that investigated severe preeclampsia. Meta-regression did not identify any factor that significantly affected the overall estimate. There was no evidence of reporting bias (Egger's test; t = 0.43; p = 0.587). This meta-analysis with high heterogeneity showed that higher levels of RBP4 were associated with preeclampsia risk. More longitudinal studies spanning the three trimester periods are needed to clarify the association of RBP4 and its dynamics in preeclampsia cases throughout pregnancy.

Adipokines in Non-Alcoholic Fatty Liver Disease: Are We on the Road toward New Biomarkers and Therapeutic Targets?

Simple Summary

Non-alcoholic fatty liver disease (NAFLD) is an unmet medical need due to its increasingly high incidence, severe clinical consequences, and the absence of feasible diagnostic tools and effective drugs. This review summarizes the preclinical and clinical data on adipokines, cytokine-like hormones secreted by adipose tissue, and NAFLD. The aim is to establish the potential of adipokines as diagnostic and prognostic biomarkers, as well as their potential as therapeutic targets for NAFLD. The limitations of current research are also discussed, and future perspectives are outlined.

Abstract

Non-alcoholic fatty liver disease (NAFLD) has become the major cause of chronic hepatic illness and the leading indication for liver transplantation in the future decades. NAFLD is also commonly associated with other high-incident non-communicable diseases, such as cardiovascular complications, type 2 diabetes, and chronic kidney disease. Aggravating the socio-economic impact of this complex pathology, routinely feasible diagnostic methodologies and effective drugs for NAFLD management are unavailable. The pathophysiology of NAFLD, recently defined as metabolic associated fatty liver disease (MAFLD), is correlated with abnormal adipose tissue–liver axis communication because obesity-associated white adipose tissue (WAT) inflammation and metabolic dysfunction prompt hepatic insulin resistance (IR), lipid accumulation (steatosis), non-alcoholic steatohepatitis (NASH), and fibrosis. Accumulating evidence links adipokines, cytokine-like hormones secreted by adipose tissue that have immunometabolic activity, with NAFLD pathogenesis and progression; however, much uncertainty still exists. Here, the current knowledge on the roles of leptin, adiponectin, ghrelin, resistin, retinol-binding protein 4 (RBP4), visfatin, chemerin, and adipocyte fatty-acid-binding protein (AFABP) in NAFLD, taken from preclinical to clinical studies, is overviewed. The effect of therapeutic interventions on adipokines’ circulating levels are also covered. Finally, future directions to address the potential of adipokines as therapeutic targets and disease biomarkers for NAFLD are discussed.

Retinol-binding protein-4 and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming increasingly common as the global economy grows and living standards improve. Timely and effective preventions and treatments for NAFLD are urgently needed. Retinol-binding protein-4 (RBP4), the protein that transports retinol through the circulation, was found to be positively related to diabetes, obesity, cardiovascular disease, and other metabolic diseases. Observational studies on the association between serum RBP4 level and the prevalence of NAFLD found contradictory results. Some of the underlying mechanisms responsible for this association have been revealed, and the possible clinical implications of treating NAFLD by targeting RBP4 have been demonstrated. Future studies should focus on the predictive value of RBP4 on NAFLD development and its potential as a therapeutic target in NAFLD.

The association between retinol-binding protein 4 and prediabetes in obese patients with nonalcoholic fatty liver disease

CONTEXT

Retinol-binding protein 4 (RBP4) is associated with visceral fat and insulin resistance (IR) in obesity, type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD), but some of these data remain controversial.

OBJECTIVE

This study evaluated the relationship between serum RBP4 levels and prediabetes in obese patients with NAFLD.

METHODS

A total of 79 obese NAFLD patients without (n = 41) and with prediabetes (n = 38) were included. Serum RBP4 was measured using ELISA method.

RESULTS

Higher RBP4 serum levels were observed in patients with prediabetes, metabolic syndrome (MetS), or dyslipidaemia. There was correlation between RBP4 levels and visceral adiposity index (VAI), glucose, insulin, HOMA-IR, and Quicki index. RBP4 ≥ 61 mcg/ml have about 3.5-fold higher risk of prediabetes (OR 3.544, 95% CI 1.385-9.072, p=.008), and RBP4 ≥ 55 mcg/ml increased the risk for MetS approximately 3.1 times.

CONCLUSIONS

RBP4 is associated with increased risk for prediabetes and MetS in obese patients with NAFLD.

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.

Promising diagnostic biomarkers of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis: From clinical proteomics to microbiome

Fatty liver has been present in the lives of patients and physicians for almost two centuries. Vast knowledge has been generated regarding its etiology and consequences, although a long path seeking novel and innovative diagnostic biomarkers for nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) is still envisioned. On the one hand, proteomics and lipidomics have emerged as potential noninvasive resources for NAFLD diagnosis. In contrast, metabolomics has been able to distinguish between NAFLD and NASH, even detecting degrees of fibrosis. On the other hand, genetic and epigenetic markers have been useful in monitoring disease progression, eventually functioning as target therapies. Other markers involved in immune dysregulation, oxidative stress, and inflammation are involved in the instauration and evolution of the disease. Finally, the fascinating gut microbiome is significantly involved in NAFLD and NASH. This review presents state-of-the-art biomarkers related to NAFLD and NASH and new promises that could eventually be positioned as diagnostic resources for this disease. As is evident, despite great advances in studying these biomarkers, there is still a long path before they translate into clinical benefits.

Promising diagnostic biomarkers of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis: From clinical proteomics to microbiome

Fatty liver has been present in the lives of patients and physicians for almost two centuries. Vast knowledge has been generated regarding its etiology and consequences, although a long path seeking novel and innovative diagnostic biomarkers for nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) is still envisioned. On the one hand, proteomics and lipidomics have emerged as potential noninvasive resources for NAFLD diagnosis. In contrast, metabolomics has been able to distinguish between NAFLD and NASH, even detecting degrees of fibrosis. On the other hand, genetic and epigenetic markers have been useful in monitoring disease progression, eventually functioning as target therapies. Other markers involved in immune dysregulation, oxidative stress, and inflammation are involved in the instauration and evolution of the disease. Finally, the fascinating gut microbiome is significantly involved in NAFLD and NASH. This review presents state-of-the-art biomarkers related to NAFLD and NASH and new promises that could eventually be positioned as diagnostic resources for this disease. As is evident, despite great advances in studying these biomarkers, there is still a long path before they translate into clinical benefits.

Altering retinol binding protein 4 levels in hepatitis C: Inflammation and steatosis matter

Both hepatitis C virus (HCV) infection and retinol-binding protein 4 (RBP4) might contribute to insulin resistance (IR), how RBP4 links to IR in HCV infection remain elusive. A joint study of a prospective cohort of 842 chronically HCV-infected (CHC) patients (with 842 controls) and a line of HCV core transgenic mice was conducted. Of 842 patients, 771 had completed anti-HCV therapy and 667 had sustained virological responses (SVRs). Compared with controls, CHC patients had lower RBP4 levels. At baseline, age (95% CI β: -0.87~-0.317), BMI (0.516~2.036), triglycerides (0.03~0.127), neutrophil-to-lymphocyte ratio (NLR) (1.561~7.327), and estimated glomerular filtration rate (eGFR) (-0.342~-0.149) levels were associated with RBP4 levels in CHC patients. At 24-week post-therapy, male sex (0.652~8.129), BMI (0.199~1.254), triglycerides (0.039~0.088), uric acid (0.599~3.067), eGFR (-0.247 ~-0.14) levels, and fibrosis-4 (-3.602~-0.039) scores were associated with RBP4 levels in SVR patients; compared with baseline, except genotype 3 HCV-infected patients, SVR patients had increased RBP4 levels, which were comparable with controls, while no HOMA-IR index alteration was noted after SVR. The HCV core transgenic mice exhibited nonobese hepatic steatosis, had higher hepatic RBP4 expression, higher serum levels of RBP4 and triglycerides, but comparable HOMA-IR levels than non-transgenic littermates. In conclusion, steatosis, sex, age, uric acid, NLR, and FIB-4 levels were associated with HCV-related RBP4 levels; BMI, triglycerides, and eGFR levels were associated with non-HCV-related RBP4 levels. Reversal of low RBP4 levels after SVR was evident in non-genotype 3 HCV-infected patients. Steatosis and inflammation linked with metabolic alteration other than IR, determined RBP4 levels in HCV-infected patients.

Multidimensional Biomarker Analysis Including Mitochondrial Stress Indicators for Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is accompanied by a complex and multifactorial pathogenesis with sequential progressions from inflammation to fibrosis and then to cancer. This heterogeneity interferes with the development of precise diagnostic and prognostic strategies for NAFLD. The current approach for the diagnosis of simple steatosis, steatohepatitis, and cirrhosis mainly consists of ultrasonography, magnetic resonance imaging, elastography, and various serological analyses. However, individual dry and wet biomarkers have limitations demanding an integrative approach for the assessment of disease progression. Here, we review diagnostic strategies for simple steatosis, steatohepatitis and hepatic fibrosis, followed by potential biomarkers associated with fat accumulation and mitochondrial stress. For mitochondrial stress indicators, we focused on fibroblast growth factor 21 (FGF21), growth differentiation factor 15 (GDF15), angiopoietin-related growth factor and mitochondrial-derived peptides. Each biomarker may not strongly indicate the severity of steatosis or steatohepatitis. Instead, multidimensional analysis of different groups of biomarkers based on pathogenic mechanisms may provide decisive diagnostic/prognostic information to develop a therapeutic plan for patients with NAFLD. For this purpose, mitochondrial stress indicators, such as FGF21 or GDF15, could be an important component in the multiplexed and contextual interpretation of NAFLD. Further validation of the integrative evaluation of mitochondrial stress indicators combined with other biomarkers is needed in the diagnosis/prognosis of NAFLD.

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

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

The effect of combined exercises on the plasma levels of retinol-binding protein 4 and its relationship with insulin resistance and hepatic fat content in postmenopausal women with nonalcoholic fatty liver disease

BACKGROUND

Evidence suggests increased serum levels of retinol-binding protein 4 (RBP4) in postmenopausal women with nonalcoholic fatty liver disease (NAFLD). This study investigated the effect of combined exercises on the plasma levels of RBP4 and its relationship with insulin resistance and hepatic fat content in these women.

METHODS

This quasi-experimental study randomly assigned 24 women with fatty liver and a mean age of 56.18±4.58 years to an experimental group and a control group. The experimental group participated in ten-week incremental endurance-resistance training as combined exercises three sessions a week. Fatty liver was diagnosed with ultrasound, RBP4 levels were measured and insulin resistance was determined using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Between-group data were analyzed using ANCOVA, within-group data using the dependent t-test and Wilcoxon test and relationships between RBP4 and variables using Spearman and Pearson correlation coefficients.

RESULTS

Ten weeks of combined exercises significantly decreased RBP4 levels (P=0.000), HOMA-IR (P=0.011) and hepatic fat levels (P=0.000) in the experimental group compared to in the controls. The posttest showed significant correlations between RBP4 levels and hepatic fat levels (P=0.002) and no correlations between RBP4 levels and insulin resistance (P=0.116).

CONCLUSIONS

Combined exercises significantly reduced serum levels of RBP4 in postmenopausal women with fatty liver. RBP4 was not related to insulin resistance and effects of RBP4 on hepatic fat regulation were independent of the effects of insulin resistance.

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.

Hepatokines and adipokines in NASH-related hepatocellular carcinoma

The incidence of hepatocellular carcinoma (HCC) is increasing in industrialised societies; this is likely secondary to the increasing burden of non-alcoholic fatty liver disease (NAFLD), its progressive form non-alcoholic steatohepatitis (NASH), and the metabolic syndrome. Cumulative studies suggest that NAFLD-related HCC may also develop in non-cirrhotic livers. However, prognosis and survival do not differ between NAFLD- or virus-associated HCC. Thus, research has increasingly focused on NAFLD-related risk factors to better understand the biology of hepatocarcinogenesis and to develop new diagnostic, preventive, and therapeutic strategies. One important aspect thereof is the role of hepatokines and adipokines in NAFLD/NASH-related HCC. In this review, we compile current data supporting the use of hepatokines and adipokines as potential markers of disease progression in NAFLD or as early markers of NAFLD-related HCC. While much work must be done to elucidate the mechanisms and interactions underlying alterations to hepatokines and adipokines, current data support the possible utility of these factors - in particular, angiopoietin-like proteins, fibroblast growth factors, and apelin - for detection or even as therapeutic targets in NAFLD-related HCC.

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.

Update on the human and mouse lipocalin (LCN) gene family, including evidence the mouse Mup cluster is result of an "evolutionary bloom"

Lipocalins (LCNs) are members of a family of evolutionarily conserved genes present in all kingdoms of life. There are 19 LCN-like genes in the human genome, and 45 Lcn-like genes in the mouse genome, which include 22 major urinary protein (Mup) genes. The Mup genes, plus 29 of 30 Mup-ps pseudogenes, are all located together on chromosome (Chr) 4; evidence points to an “evolutionary bloom” that resulted in this Mup cluster in mouse, syntenic to the human Chr 9q32 locus at which a single MUPP pseudogene is located. LCNs play important roles in physiological processes by binding and transporting small hydrophobic molecules —such as steroid hormones, odorants, retinoids, and lipids—in plasma and other body fluids. LCNs are extensively used in clinical practice as biochemical markers. LCN-like proteins (18–40 kDa) have the characteristic eight β-strands creating a barrel structure that houses the binding-site; LCNs are synthesized in the liver as well as various secretory tissues. In rodents, MUPs are involved in communication of information in urine-derived scent marks, serving as signatures of individual identity, or as kairomones (to elicit fear behavior). MUPs also participate in regulation of glucose and lipid metabolism via a mechanism not well understood. Although much has been learned about LCNs and MUPs in recent years, more research is necessary to allow better understanding of their physiological functions, as well as their involvement in clinical disorders.

Altered hepatic genes related to retinol metabolism and plasma retinol in patients with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), especially non-alcoholic steatohepatitis (NASH) is a chronic liver disease commonly associated with hepatic fibrosis. NASH patients have an increased risk for hepatocellular carcinoma (HCC). An altered retinol metabolism is one of the pathways involved in the process of hepatic fibrosis, and enzymes involved in retinol metabolism have been associated with HCC. We aimed to determine the association between plasma retinol levels and hepatic expression of genes related to retinol metabolism, as well as to assess the hepatic expression of transcription factors regulated by retinoic acid in patients with NAFLD. Cross-sectional study where hepatic gene expression (Illumina microarray) and plasma retinol levels (HPLC) were measured in 17 patients with simple steatosis (SS), 15 with NASH, and 22 living liver donors (LD) as controls. Plasma retinol levels were higher in SS (1.53 ± 0.44 μmol/L) and NASH (1.51 ± 0.56 μmol/L) compared to LD (1.21 ± 0.38 μmol/L; p<0.05). AKR1B10 was highly overexpressed in NASH compared to SS (+6.2-fold) and LD (+9.9-fold; p = 4.89E-11). Retinaldehyde dehydrogenase 1 family, member A2 (ALDH1A2) and retinaldehyde dehydrogenase 1 family, member A3 (ALDH1A3), key enzymes for retinoic acid synthesis, were underexpressed in SS (-1.48 and -2.3-fold, respectively) and NASH (-1.47 and -2.6-fold, respectively) versus LD. In NASH, hepatic ALDH1A2 and ALDH1A3 were underexpressed and inversely correlated with plasma retinol levels, which may reduce retinoic acid in the liver. This, in addition to changes in expression of other genes involved in retinol metabolism, suggests a role for altered retinol homeostasis in NASH.

Association of Adipokines with Development and Progression of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting 30% of the general population and 40% to 70% of obese individuals. Adipose tissue plays a crucial role in its pathogenesis, as it produces and secretes pro- and anti-inflammatory cytokines called adipokines. Adiponectin and leptin have well-determined actions in terms of NAFLD pathophysiology. Adiponectin deficiency is associated with a pro-inflammatory condition, as it is observed in obesity and other metabolic disorders. On the other hand, increased leptin levels, above the normal levels, act as a pro-inflammatory stimulus. Regarding other adipokines (resistin, visfatin, chemerin, retinol-binding protein 4, irisin), data about their contribution to NAFLD pathogenesis and progression are inconclusive. In addition, pharmacological agents like thiazolidinediones (pioglitazone and rosiglitazone), that are used in the management of NAFLD exert favourable effects on adipokine levels, which in turn may contribute to the improvement of liver function. This review summarizes the current knowledge and developments in the association between adipokines and NAFLD and discusses possible therapeutic implications targeting the modulation of adipokine levels as a potential tool for the treatment of NAFLD.

Association between urine retinol-binding protein levels and nonalcoholic fatty liver disease: A cross-sectional study in Chinese population

OBJECTIVE

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been rapidly increased, becoming a public health problem worldwide. Our objective was to investigate the association between urine retinol-binding protein (RBP) and NAFLD in a Chinese population and develop a multivariate logistic regression model for NAFLD prediction.

METHODS

A total of 317 NAFLD patients and 391 healthy controls were enrolled in this cross-sectional study based on inclusion and exclusion criteria, from whom fasting urine and blood were collected for further study. Urine RBP level and other parameters were measured and compared between NAFLD subjects and controls.

RESULTS

Urine RBP levels (expressed by RBP/creatinine ratio) in NAFLD patients were significantly higher than controls (median 133.1 mg/g vs 110.7 mg/g; P < .001). Urine RBP/creatinine ratio was verified as an independent factor for NAFLD prediction after adjustment in multivariate logistic regression. The area under curve (AUC) of receiver operating characteristic (ROC) was 0.889 with the 95% confidence interval from 0.867 to 0.912.With a cutoff point of 0.215, the sensitivity and specificity of urine RBP/creatinine ratio in NAFLD prediction were 81.1% and 84.5%, respectively.

CONCLUSION

Our results demonstrated that urine RBP/creatinine ratio was an independent risk factor for NAFLD while the predictive model for NAFLD diagnosis is noninvasive with high sensitivity and specificity.

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.

Serum RBP4 and CKD: Association with insulin resistance and lipids

OBJECTIVE

Serum RBP4 is new adipokine and it has been related to insulin resistance and diabetes risk in animal and clinical studies. However, there is controversy on this relationship among CKD patients. In this study, we evaluated the association of serum RBP4 with insulin resistance and cardiovascular risk factors in CKD.

METHODS

Baseline data from the PROGREDIR Study (Sao Paulo, Brazil) comprising 454 participants (mainly stages 3 and 4) was analyzed.

RESULTS

In univariable analysis, RBP4 was inversely related to renal function, age and HDL, and positively related to other lipids, insulinemia, HOMA, glycemia, albumin, phosphorus and right hepatic lobe diameter. After adjustment for sex, age and eGFR, HOMA and lipids remained associated to RBP4. In multivariable analysis, eGFR and triglyceride remained significantly associated with RBP4, while HOMA showed no longer a significant positive association. An interaction term between RBP4 and eGFR was significantly related to HOMA.

CONCLUSIONS

Renal function is inversely related to serum RBP4. As GFR decreases, the relationship between RBP4 and HOMA is attenuated. On the other hand, triglycerides remained strongly related to RBP4 and this was not affected by eGFR, suggesting that in the CKD population triglycerides may be a better marker of RBP4-associated metabolic effects.

Retinol Binding Protein-4 Levels and Non-alcoholic Fatty Liver Disease: A community-based cross-sectional study

Previous reports on the association between retinol binding protein 4 (RBP4) and nonalcoholic fatty liver disease (NAFLD) were controversial. This study aimed to investigate the association between the serum RBP4 levels and occurrence of NAFLD in Chinese population. In total, 2938 participants aged 40–75 years were involved in this community-based cross-sectional study. General information, lifestyle factors, serum levels of RBP4 and the presence of NAFLD were determined. Patients with NAFLD had significantly higher concentrations of RBP4 (37.9 ± 6.8 μg/ml) than did non-NAFLD controls (35.0 ± 6.7 μg/ml) (P < 0.001). The odds ratios (ORs) of NAFLD for the highest (vs. lowest) quartile of RBP4 were 1.884 (95% CI: 1.391, 2.551) for females (P < 0.001), and 2.107 (95% CI: 1.357, 3.273) for male participants (P < 0.01) after adjusting for related factors. The serum RBP4 levels were positively associated with the prevalence of NAFLD in middle-aged and elderly Chinese people, and Homeostatic model assessment-insulin resistance (HOMA-IR), trunk fat, the waist-to-hip ratio (WHR), systolic blood pressure (SBP), fasting insulin, high density lipoprotein cholesterol (HDL-C) and triglycerides (TG) might be implicated in the pathogenesis of RBP4 in NAFLD.

Pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common and important chronic liver disease in the world. As the prevalence of obesity increases in adults and children, the incidence of NAFLD has increased rapidly, reaching 17% to 33%. NAFLD is clinically divided into two forms: simple fatty liver (SFL) and non-alcoholic steatohepatitis (NASH), with NASH accounting for 1/3-1/2 of all NAFLD cases. The probability of developing cirrhosis is 0.6%-3.0% in patients with SFL for 10-20 years, and as high as 15%-25% in patients with NASH for 10-15 years. Approximately 1% of cirrhosis cases develop hepatocellular carcinoma each year. The pathogenesis of NAFLD is still not completely clear. It is generally believed that age, sex, obesity, insulin resistance, cytokines, gene polymorphism, and intestinal microflora are involved in the pathogenesis of NAFLD. An in-depth understanding of the pathogenesis of NAFLD can provide a basis for treatment of this disease. In recent years, cytokines or genes have been reported as targets for NAFLD treatment with appreciated effects. Since there is currently no specific treatment for NAFLD, targeted therapy may have a profound impact on the prognosis of the disease.

Antibody-Directed Glucocorticoid Targeting to CD163 in M2-type Macrophages Attenuates Fructose-Induced Liver Inflammatory Changes

Increased consumption of high-caloric carbohydrates contributes substantially to endemic non-alcoholic fatty liver disease in humans, covering a histological spectrum from fatty liver to steatohepatitis. Hypercaloric intake and lipogenetic effects of fructose and endotoxin-driven activation of liver macrophages are suggested to be essential to disease progression. In the present study, we show that a low dose of an anti-CD163-IgG-dexamethasone conjugate targeting the hemoglobin scavenger receptor CD163 in Kupffer cells and other M2-type macrophages has a profound effect on liver inflammatory changes in rats on a high-fructose diet. The diet induced severe non-alcoholic steatohepatitis (NASH)-like changes within a few weeks but the antibody-drug conjugate strongly reduced inflammation, hepatocyte ballooning, fibrosis, and glycogen deposition. Non-conjugated dexamethasone or dexamethasone conjugated to a control IgG did not have this effect but instead exacerbated liver lipid accumulation. The low-dose anti-CD163-IgG-dexamethasone conjugate displayed no apparent systemic side effects. In conclusion, macrophage targeting by antibody-directed anti-inflammatory low-dose glucocorticoid therapy seems to be a promising approach for safe treatment of fructose-induced liver inflammation.

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

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

Adipocyte-specific overexpression of retinol-binding protein 4 causes hepatic steatosis in mice

There is considerable evidence that both retinoids and retinol-binding protein 4 (RBP4) contribute to the development of liver disease. To understand the basis for this, we generated and studied transgenic mice that express human RBP4 (hRBP4) specifically in adipocytes. When fed a chow diet, these mice show an elevation in adipose total RBP4 (mouse RBP4 + hRBP4) protein levels. However, no significant differences in plasma RBP4 or retinol levels or in hepatic or adipose retinoid (retinol, retinyl ester, and all-trans-retinoic acid) levels were observed. Strikingly, male adipocyte-specific hRBP4 mice fed a standard chow diet display significantly elevated hepatic triglyceride levels at 3-4 months of age compared to matched littermate controls. When mice were fed a high-fat diet, this hepatic phenotype, as well as other metabolic phenotypes (obesity and glucose intolerance), worsened. Because adipocyte-specific hRBP4 mice have increased tumor necrosis factor-α and leptin expression and crown-like structures in adipose tissue, our data are consistent with the notion that adipose tissue is experiencing RBP4-induced inflammation that stimulates increased lipolysis within adipocytes. Our data further establish that elevated hepatic triglyceride levels result from increased hepatic uptake of adipose-derived circulating free fatty acids. We obtained no evidence that elevated hepatic triglyceride levels arise from increased hepatic de novo lipogenesis, decreased hepatic free fatty acid oxidation, or decreased very-low-density lipoprotein secretion.

CONCLUSION

Our investigations establish that RBP4 expressed in adipocytes induces hepatic steatosis arising from primary effects occurring in adipose tissue. (Hepatology 2016;64:1534-1546).

Adipokines in nonalcoholic fatty liver disease

Since the discovery of adipose tissue as a higly active endocrine tissue, adipokines, peptides produced by adipose tissue and exerting autocrine, paracrine and endocrine function, have gained increasing interest in various obesity-related diseases, including nonalcoholic fatty liver disease (NAFLD). Data regarding the association between NAFLD and circulating leptin and adiponectin levels are generally well documented: leptin levels increase, whereas adiponectin levels decrease, by increasing the severity of NAFLD. Data regarding other adipokines in histologically confirmed NAFLD populations are inconclusive (e.g., resistin, visfatin, retinol-binding protein-4, chemerin) or limited (e.g., adipsin, obestatin, omentin, vaspin etc.). This review summarizes evidence on the association between adipokines and NAFLD. The first part of the review provides general consideration on the interplay between adipokines and NAFLD, and the second part provides evidence on specific adipokines possibly involved in NAFLD pathogenesis. A thorough insight into the pathophysiologic mechanisms linking adipokines with NAFLD may result in the design of studies investigating the combined adipokine use as noninvasive diagnostic markers of NAFLD and new clinical trials targeting the treatment of NAFLD.

Retinoid roles in blocking hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major health issue in many countries. The prognosis of HCC is still poor due to its high recurrence rate and its resistance to chemotherapy. Retinoids have long been known to have a connection with liver diseases, including HCC. Many experimental and clinical investigations have demonstrated associations between retinoids and hepatic disease, including the loss of retinoid activity in HCC cell lines and decreased hepatic retinoid stores and altered retinoid signaling in patients with cirrhosis and HCC. Based on these findings, preclinical and clinical investigations of retinoid effects on HCC have been undertaken. Recently, clinical trial results for the use of a synthetic retinoid, acyclic retinoid (ACR), to prevent HCC recurrence were published. In addition, extensive experimental studies on the action of retinoids in liver disease, including chronic viral hepatitis and non-alcoholic fatty liver disease (NAFLD), which lead to HCC have been performed. In the first section of this review, we will summarize the effectiveness and roles of retinoid for treating liver disease and blocking HCC. Subsequently, we will focus on ACR actions in blocking HCC.

Retinol binding protein-4 predicts incident diabetes in Asian Indian men with prediabetes

The association of retinol binding protein-4 (RBP4) with incident type 2 diabetes (T2DM) in Asian Indian middle-aged men with impaired glucose tolerance (IGT) was studied. This was an ancillary analysis of a subsample from a cohort of participants with IGT in a 2 year prospective diabetes prevention program in India. For this analysis, 71 incident T2DM and 76 non-diabetic cases (non-progressors) based on the final glycemic outcome were selected. Baseline serum RBP4 was measured using competitive enzyme immunoassay. Correlations of RBP4 with relevant anthropometric and biochemical variables and also its association with diabetes were assessed using appropriate statistical analyses. Participants who developed T2DM had higher levels of serum RBP4 (21.3 [IQR: 17.7-24.9] µg/mL) compared with non-progressors (17.3 [IQR: 13.1-21.0] µg/mL; P = 0.001). Levels of RBP4 were lower than in Caucasians. Stepwise linear regression analysis showed that body mass index (BMI), systolic blood pressure, triglycerides, and HbA1c had independent associations with RBP4 levels. Multiple logistic regression analyses showed that RBP4 was independently associated with incident diabetes (odds ratio [OR] [95%confidence interval (CI)]: 1.69 [1.18-2.41]; P = 0.004). Adjustment for study group, age, BMI, waist circumference, 2 H plasma glucose, triglycerides, gamma glutamyl transferase, and insulin resistance weakened the significance of its association (OR [95%CI]: 1.65 [1.03-2.66]; P = 0.038).The results of this preliminary analyses showed that baseline serum RBP4 levels were independently associated with incident diabetes in Asian Indian men with IGT. It may be used as an additional predictor of future diabetes.

Serum retinol binding protein 4 is associated with visceral fat in human with nonalcoholic fatty liver disease without known diabetes: a cross-sectional study

Background

High serum Retinol Binding Protein 4 (RBP4) levels were associated with insulin-resistant states in humans. To determine which fat compartments are associated with elevated RBP4 levels in humans, we measured serum RBP4 and hepatic fat content (HFC), visceral (VFA) and subcutaneous abdominal fat area (SFA) in 106 subjects with non-alcoholic fatty liver disease (NAFLD) without known diabetes.

Methods

106 patients with NAFLD (M/F: 61/45, aged 47.44 ± 14.16 years) were enrolled. Subjects with known diabetes, chronic virus hepatitis, and those with alcohol consumption ≥30 g/d in man and ≥20 g/d in woman were excluded. Anthropometrics and laboratory tests, including lipid profile, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ-glutamyltransferase (γ-GT) were conducted. HFC, VFA and SFA were determined by CT scan. Serum RBP4 was detected by an enzyme immunoassay kit and validated by quantitative Western blotting.

Results

Circulating RBP4 was negatively associated with high-density lipoprotein cholesterol (HDL-c) (r = −0.392, p < 0.001), but positively with waist-to-hip ratio (WHR) (r = 0.343, p = 0.001), triglyceride (r = 0.330, p = 0.002), VFA (r = 0.298, p = 0.027), systolic blood pressure (r = 0.247, p = 0.020), diastolic blood pressure (r = 0.241, p = 0.023), γ-GT (r = 0.239, p = 0.034), waist circumference (r = 0.218, p = 0.040). Differently, serum RBP4 levels were not associated with HFC (r = 0.199, p = 0.071), SFA, age, BMI, total cholesterol, low-density lipoprotein cholesterol (LDL-c), ALT or AST (all p > 0.05). Multiple linear regression analysis revealed that RBP4 correlated independently with VFA (Standard β = 0.357, p = 0.019) and HDL-c (Standard β = −0.345, p = 0.023) in all subjects, HDL-c (Standard β = −0.315, p = 0.040) in men, VFA/SFA in women (Standard β = 0.471, p = 0.049), not with HFC. However, serum RBP4 was positively correlated with HFC when HFC below 6.34% (r = 0.574, p = 0.001).

Conclusions

RBP4 could be a marker of abdominal obesity, however, the role of RBP4 in the pathogenesis of NAFLD is not sufficiently elucidated.

Central obesity and nonalcoholic fatty liver disease risk after adjusting for body mass index

AIM: To investigate whether central obesity is associated with nonalcoholic fatty liver disease (NAFLD) formation after adjusting for general obesity.

METHODS: The online databases PubMed, EMBASE, and ISI Web of Science were searched for studies estimating the influence of central obesity on NAFLD occurrence published through April 2014. Studies that did not adjust for body mass index (BMI) were excluded. In addition, the independent effect of BMI was also assessed with the included studies. The pooled effect sizes and 95% confidence intervals (CIs) were calculated using random- or fixed-effects models based on the degree of heterogeneity. Furthermore, subgroup analyses, meta-regression, sensitivity analyses, and publication bias were performed.

RESULTS: Twenty eligible studies were identified. The summary odds ratio (OR) values per-unit increase in waist circumference (WC) and BMI for NAFLD formation were 1.07 (95%CI: 1.03-1.10, I² = 73.9%, n = 11 studies) and 1.25 (95%CI: 1.13-1.38, I² = 88.7%, n = 11 studies), respectively. When the indices were expressed as binary variables (with the non-obesity group as reference), the pooled OR in WC, waist-to-hip ratio, and BMI were 2.34 (95%CI: 1.83-3.00, I² = 41.8%, n = 7 studies), 4.06 (95%CI: 1.53-10.79, I² = 65.7%, n = 3 studies), and 2.85 (95%CI: 1.60-5.08, I² = 57.8%, n = 5 studies), respectively. Using the same studies as the latter (n = 5), pooled OR in WC was 3.14 (95%CI: 2.07-4.77), which is greater than that in BMI.

CONCLUSION: Central obesity may pose a greater threat to national health than general obesity, although both are independently associated with increased risk of NAFLD.

Effect of endurance training on retinol-binding protein 4 gene expression and its protein level in adipose tissue and the liver in diabetic rats induced by a high-fat diet and streptozotocin

AIMS/INTRODUCTION

The present study was designed to investigate from which tissues the decrease in retinol-binding protein 4 (RBP4) expression could contribute to the improvement of serum RBP4 and insulin resistance (IR) after endurance training.

MATERIALS AND METHODS

Male 7-week-old Wistar rats were randomly assigned into four groups including control (C), trained (T), diabetic control (DC) and trained diabetic (TD). At 8 weeks-of-age, diabetes was induced by a high-fat diet and intraperitoneal injection of low-dose streptozotocin (STZ; 35 mg/kg). Rats in the T and TD groups carried out a 7-week exercise program on a motorized treadmill (15-20 m/min for 20 min/day for 5 weeks), whereas the C and DC remained sedentary in their cages. Tissues gene expression and protein levels of RBP4 were assessed by using real-time polymerase chain reaction and western blot, respectively, while serum RBP4 was measured using an enzyme-linked immunosorbent assay kit.

RESULTS

Exercise significantly improved IR and reduced serum concentration of RBP4 in the TD group. This reduction of serum RBP4 was accompanied by decreased RBP4 protein expression in visceral fat tissue. In contrast, exercise had no significant effect on RBP4 expression in liver and subcutaneous fat tissue in the TD group. Exercise also significantly decreased RBP4 gene expression in visceral fat tissue and muscle, whereas the effect of exercise on liver RBP4 messenger ribonucleic acid expression was not significant.

CONCLUSIONS

The present study showed that the mechanism for RBP4 reducing the effect of endurance training could involve decreased RBP4 messenger ribonucleic acid expression and its protein level in adipose tissue in STZ-induced diabetic rats.

Role of adipokines and peroxisome proliferator-activated receptors in nonalcoholic fatty liver disease

Intrahepatic fat deposition has been demonstrated in patients with nonalcoholic fatty liver disease (NAFLD). Genetic and environmental factors are important for the development of NAFLD. Diseases such as obesity, diabetes, and hypertension have been found to be closely associated with the incidence of NAFLD. Evidence suggests that obesity and insulin resistance are the major factors that contribute to the development of NAFLD. In comparing the factors that contribute to the buildup of excess calories in obesity, an imbalance of energy homeostasis can be considered as the basis. Among the peripheral signals that are generated to regulate the uptake of food, signals from adipose tissue are of major relevance and involve the maintenance of energy homeostasis through processes such as lipogenesis, lipolysis, and oxidation of fatty acids. Advances in research on adipose tissue suggest an integral role played by adipokines in NAFLD. Cytokines secreted by adipocytes, such as tumor necrosis factor-α, transforming growth factor-β, and interleukin-6, are implicated in NAFLD. Other adipokines, such as leptin and adiponectin and, to a lesser extent, resistin and retinol binding protein-4 are also involved. Leptin and adiponectin can augment the oxidation of fatty acid in liver by activating the nuclear receptor super-family of transcription factors, namely peroxisome proliferator-activated receptor (PPAR)-α. Recent studies have proposed downregulation of PPAR-α in cases of hepatic steatosis. This review discusses the role of adipokines and PPARs with regard to hepatic energy metabolism and progression of NAFLD.

Serum AFBP levels are elevated in patients with nonalcoholic fatty liver disease

OBJECTIVE

Adipocyte fatty acid-binding-protein (A-FABP), retinol-binding protein 4 (RBP4), and lipocalin-2 have been identified as adipokines that may link obesity, insulin resistance, and metabolic syndrome. Nonalcoholic fatty liver disease (NAFLD) is regarded as a manifestation of metabolic syndrome. We evaluated the relationship of A-FABP, RBP4, and lipocalin-2 to variables related to metabolic syndrome and NAFLD.

METHODS

A total of 140 subjects (72 males and 68 females) were included in this study. Subjects were divided into two groups (NAFLD, n = 73 and normal, n = 67) based on the detection of a fatty liver by ultrasonography.

RESULTS

Serum A-FABP levels were higher in the NAFLD group than in the normal group (18.42 ± 7.24 ng/mL vs. 15.74 ± 7.02 ng/mL, p = 0.022). After adjusting for age and sex, we observed that body mass index (BMI), diastolic blood pressure, waist circumference, body fat percentage, triglycerides, and serum RBP4 levels were positively associated with serum A-FABP levels in all subjects. Multiple linear regression analysis revealed that systolic blood pressure, diastolic blood pressure, and serum RBP4 levels were independently associated with serum A-FABP levels. In logistic regression analysis, patients in the higher quartiles of A-FABP levels had higher odds ratios (OR) for the presence of NALFD than patients in the lower quartiles (OR: 3.56; 95% confident interval or CI: 1.25, 10.14).

CONCLUSIONS

We observed higher serum A-FABP levels in the NAFLD group than in the normal group. However, serum RBP4 and lipocalin-2 levels appeared to have different relationships with several variables related to metabolic syndrome and NAFLD, which contradict results of previous studies.

Elevated plasma retinol-binding protein 4 is associated with increased risk of type 2 diabetes in middle-aged and elderly Chinese adults

The association between circulating retinol-binding protein 4 (RBP4) and risk of type 2 diabetes has been inconsistent in cross-sectional studies, but prospective evidence is limited. We aimed to investigate whether plasma RBP4 is associated with future development of type 2 diabetes and whether the association could be explained by iron or other risk factors. A total of 2091 Chinese adults aged 50-70 y were followed up for 6 y. Baseline dietary intakes and fasting plasma RBP4, ferritin, adiponectin, C-reactive protein (CRP), γ-glutamyltransferase, creatinine, and erythrocyte fatty acids were determined. Self-reported doctor-diagnosed diabetes, or usage of antidiabetic agents, or fasting plasma glucose concentration at the follow-up visit ≥7.0 mmol/L was defined as an incident diabetes case. Plasma RBP4 concentration was significantly associated with dietary heme iron intake, plasma ferritin concentration, and other established risk factors. After multivariate adjustment for demographic and lifestyle variables, relative risk (RR) for type 2 diabetes when the extreme quartiles of RBP4 were compared was 1.75 (95% CI: 1.30, 2.37; P-trend < 0.001). This association remained significant when the extreme quartiles were compared (RR = 1.48; 95% CI: 1.06, 2.05; P-trend = 0.036) after further controlling for ferritin and dietary factors, as well as other risk factors, including body mass index, adiponectin, CRP, lipids, liver and kidney function, insulin resistance, and hypertension. A threshold effect of RBP4 concentrations on incident diabetes was suggested by restricted quadratic spline analysis (P = 0.026 for nonlinearity). Our study indicates that plasma RBP4 is independently associated with the 6-y risk of developing type 2 diabetes.

Serum adiponectin, leptin, resistin and RBP4 levels in obese and metabolic syndrome children with nonalcoholic fatty liver disease

AIM

To investigate the relationship of adiponectin, leptin, resistin and RBP4 levels in obese and metabolic syndrome children with nonalcoholic fatty liver disease (NAFLD).

PATIENTS & METHODS

Group I consisted of 63 obese children with liver steatosis, group II consisted of 12 obese children with elevated serum ALT activity from group I, and group III included 85 obese children without liver steatosis.

RESULTS

Leptin levels were higher in the NAFLD children than in the control group. Serum RBP4 levels in obese children with NAFLD were higher than those in obese children without NAFLD and controls. Adiponectin and resistin levels were negatively correlated and RBP4 levels positively correlated with ALT activity and ultrasonographic grading.

CONCLUSION

These data suggest that adiponectin, resistin and RBP4 may have a role in the pathogenesis of NAFLD in obese children. Adiponectin, leptin, resistin and RBP4 may be suitable markers for predicting metabolic syndrome and NAFLD.

Metabolic interactions between vitamin A and conjugated linoleic acid

Lipid-soluble molecules share several aspects of their physiology due to their common adaptations to a hydrophilic environment, and may interact to regulate their action in a tissue-specific manner. Dietary conjugated linoleic acid (CLA) is a fatty acid with a conjugated diene structure that is found in low concentrations in ruminant products and available as a nutritional supplement. CLA has been shown to increase tissue levels of retinol (vitamin A alcohol) and its sole specific circulating carrier protein retinol-binding protein (RBP or RBP4). However, the precise mechanism of this action has not been elucidated yet. Here, we provide a summary of the current knowledge in this specific area of research and speculate that retinol and CLA may compete for catabolic pathways modulated by the activity of PPAR-α and RXR heterodimer. We also present preliminary data that may position PPAR-α at the crossroads between the metabolism of lipids and vitamin A.

Irisin in patients with nonalcoholic fatty liver disease

OBJECTIVE

Irisin is a recently discovered myokine proposed to increase thermogenesis-related energy expenditure and improve metabolism. We aimed to comparatively evaluate serum irisin levels in patients with biopsy-proven nonalcoholic fatty liver disease (NAFLD) vs. controls and study their association with disease severity.

METHODS

Fifteen and 16 consecutively enrolled patients with biopsy-proven nonalcoholic simple steatosis (NAFL) and steatohepatitis (NASH), respectively, and 24 lean and 28 obese controls without NAFLD were recruited. Irisin, established adipokines and biochemical tests were measured.

RESULTS

Serum irisin levels were statistically different in obese controls (33.7±2.7 ng/mL; p<0.001) and patients with NAFL (30.5±1.5 ng/mL; p<0.001) and NASH (35.8±1.9 ng/mL; p=0.001) compared with lean controls (47.7±2.0 ng/mL), but were similar among patients with NAFL, NASH and obese controls. This difference remained significant after adjustment for body mass index (or waist circumference), gender, age, insulin resistance (assessed by HOMA-IR or QUICKI), exercise and time since blood collection. Serum leptin and adiponectin, but not irisin, levels were independently from BMI correlated with insulin resistance and cardiometabolic factors. Serum irisin tended to be higher in patients with (36.7±2.4 ng/mL) than without (30.8±1.2 ng/mL; p=0.02) portal inflammation and independently associated with the latter; these data need to be confirmed by future studies.

CONCLUSIONS

Serum irisin levels differ between lean controls and obese controls or NAFLD patients. Despite similar circulating irisin levels between NAFL and NASH groups, irisin may be independently and positively associated with the presence of portal inflammation. Future clinical and mechanistic studies are needed to confirm and extend these data.

Changes of serum retinol binding protein 4 levels following 8 weeks moderate aerobic exercise

Purpose

The purpose of this study was to examine the effects of 8 weeks moderate intensity aerobic exercise on serum retinol binding protein 4 (RBP4) levels in female athletes.

Methods

Twenty female karate athletics were randomly assigned to one of the exercise group (n = 10) or control group (n = 10). The training group performed endurance training 3 days a week for 8 weeks at an intensity corresponding to 50-60% individual maximum oxygen consumption for 45 min.

Results

Body mass and body mass index increased (P < 0.05) after 8 weeks aerobic exercise compared to the control group. For waist to hip ratio (WHR), body fat percentage and maximal oxygen consumption there were no significant differences between the exercise group and the control group. There were virtually no changes in body fat percentage, fasting glucose, insulin, insulin resistance and RBP4 levels after 8 weeks training.

Conclusion

Serum RBP4 level was not affected by 8-week moderate aerobic exercise in female athletes.

Serum retinol binding protein 4 is negatively related to beta cell function in Chinese women with non-alcoholic fatty liver disease: a cross-sectional study

BACKGROUND

To observe the relationship between serum retinol binding protein 4(RBP4) and β cell function in Chinese subjects with non-alcoholic fatty liver disease (NAFLD) and without known diabetes.

METHODS

106 patients diagnosed as fatty liver by ultrasonography (M/F: 61/45; aged 47.44 ± 14.16 years) were enrolled in our current cross-sectional study. Subjects with known diabetes, chronic virus hepatitis and excessive alcohol consumption were excluded. Serum RBP4 was detected by ELISA and validated by quantitative Western blotting. β cell function were assessed by HOMA in all subjects and by hyperglycemic clamp in 17 normal glucose tolerance subjects (M = 6, F = 11).

RESULTS

The levels of serum RBP4 in men were higher than that in women (55.96 ± 11.14 vs 45.87 ± 10.31 μg/ml, p < 0.001). Pearson's correlation analysis demonstrated that in women, serum RBP4 levels were significantly associated with fasting blood glucose (FBG), HOMA-β, and increment of first phase insulin secretion (1PH), but not associated with age, BMI, waist circumference, WHR, systolic (SBP) and diastolic blood pressure (DBP), TC, TG, HDL-c, LDL-c, 2 h blood glucose, HOMA-IR, ALT, AST, γ-GT, hepatic fat content (HFC), and insulin sensitivity index (ISI). However, in men, serum RBP4 levels were significantly associated with HDL-c, ALT, AST, but not associated with any other parameters as mentioned above. A stepwise multiple linear regression analysis demonstrated that in women, HOMA-IR and RBP4 were significantly associated with HOMA-β, while in men, HOMA-IR and BMI were significantly variables associated with HOMA-β.

CONCLUSIONS

Serum RBP4, secreted mainly by liver and adipose tissue, may involve in the pathogenesis of β cell dysfunction in Chinese women patients with NAFLD.

Retinol and retinyl esters: biochemistry and physiology

By definition, a vitamin is a substance that must be obtained regularly from the diet. Vitamin A must be acquired from the diet, but unlike most vitamins, it can also be stored within the body in relatively high levels. For humans living in developed nations or animals living in present-day vivariums, stored vitamin A concentrations can become relatively high, reaching levels that can protect against the adverse effects of insufficient vitamin A dietary intake for six months, or even much longer. The ability to accumulate vitamin A stores lessens the need for routinely consuming vitamin A in the diet, and this provides a selective advantage to the organism. The molecular processes that underlie this selective advantage include efficient mechanisms to acquire vitamin A from the diet, efficient and overlapping mechanisms for the transport of vitamin A in the circulation, a specific mechanism allowing for vitamin A storage, and a mechanism for mobilizing vitamin A from these stores in response to tissue needs. These processes are considered in this review.

Increased selenoprotein p levels in subjects with visceral obesity and nonalcoholic Fatty liver disease

BACKGROUND

Selenoprotein P (SeP) has recently been reported as a novel hepatokine that regulates insulin resistance and systemic energy metabolism in rodents and humans. We explored the associations among SeP, visceral obesity, and nonalcoholic fatty liver disease (NAFLD).

METHODS

We examined serum SeP concentrations in subjects with increased visceral fat area (VFA) or liver fat accumulation measured with computed tomography. Our study subjects included 120 nondiabetic individuals selected from participants of the Korean Sarcopenic Obesity Study. In addition, we evaluated the relationship between SeP and cardiometabolic risk factors, including homeostasis model of insulin resistance (HOMA-IR), high sensitivity C-reactive protein (hsCRP), adiponectin values, and brachial-ankle pulse wave velocity (baPWV).

RESULTS

Subjects with NAFLD showed increased levels of HOMA-IR, hsCRP, VFA, and several components of metabolic syndrome and decreased levels of adiponectin and high density lipoprotein cholesterol than those of controls. Serum SeP levels were positively correlated with VFA, hsCRP, and baPWV and negatively correlated with the liver attenuation index. Not only subjects with visceral obesity but also those with NAFLD exhibited significantly increased SeP levels (P<0.001). In multiple logistic regression analysis, the subjects in the highest SeP tertile showed a higher risk for NAFLD than those in the lowest SeP tertile, even after adjusting for potential confounding factors (odds ratio, 7.48; 95% confidence interval, 1.72 to 32.60; P=0.007).

CONCLUSION

Circulating SeP levels were increased in subjects with NAFLD as well as in those with visceral obesity and may be a novel biomarker for NAFLD.

Retinol binding protein-4 circulating levels were higher in nonalcoholic fatty liver disease vs. histologically normal liver from morbidly obese women

OBJECTIVE

We aimed to analyze the retinol binding protein-4 (RBP4) messenger RNA (mRNA) expression profiles in adipose tissues and liver of morbidly obese (MO) women with or without nonalcoholic fatty liver disease (NAFLD), and to study the relationships with other pro- and anti-inflammatory adipokines in vivo and in vitro.

DESIGN AND METHODS

We performed a cross-sectional analysis of subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT) and liver samples from four lean and 45 MO women with or without NAFLD by enzyme-linked immunosorbent assay and real-time reverse transcription-PCR. We also studied RBP4 expression in HepG2 hepatocytes under various inflammatory stimuli.

RESULTS

Circulating RBP4 levels were higher in MO women, and specifically, in MO subjects with NAFLD compared with normal liver controls (lean and MO). RBP4 liver expression was higher in nonalcoholic steatohepatitis (NASH)-moderate/severe than in NASHmild. Overall RBP4 gene expression was higher in liver than in adipose tissues. Among them, the higher expression corresponded to SAT. VAT expression was lower in the MO cohort. In HepG2, RBP4 mRNA expression was reduced by tumor necrosis factor (TNF)-α and increased by adiponectin treatment.

CONCLUSIONS

The results obtained in MO women with NAFLD, brings up the use of RBP4 and other adipokines as a panel of noninvasive molecular biomarkers when NAFLD is suspected. Further studies are needed with other obesity groups.

Association of Plasma Retinol Binding Protein-4 (RBP4) and Sonographic Grading of Fatty Liver in Obese Iranian Children

BACKGROUND

The prevalence of obesity and its related comorbidities, such as fatty liver, in children is increasing worldwide mostly due to changes in diet and life-style. Many serological markers have been suggested for screening of fatty liver but investigations for finding more reliable factors are still in progress.

OBJECTIVES

This study aimed to investigate the correlation between the level of retinol binding protein-4 (RBP4) in the serum and sonographic grading of fatty-liver severity in obese Iranian children.

PATIENTS AND METHODS

This case-control, double-blind study involved 51 obese children aged between five and 17 years as the case group. In addition, 35 healthy lean children with no liver problems were selected as the control group. Plasma RBP4 (using an ELISA), serum triglycerides (TG), low-density-lipoproteins (LDL), high-density-lipoproteins (HDL), total-cholesterol (Chol), and body mass index (BMI) were measured. Grading the severity of the fatty liver condition was done by an expert radiologist in the case group.

RESULTS

RBP4 levels in obese children (19 482.9 ± 3 302.2 pg/ml) were higher than those found in the lean control group (14 295.68 ± 2 381.3 pg/ml) (P < 0.05). In the obese patients, RBP4 levels showed a significant correlation with the grade of fatty liver and BMI (P < 0.05).

CONCLUSIONS

It was found that the level of RBP4 had a strong correlation with the severity of fatty liver. Therefore, RBP4 may be considered as a useful, noninvasive predictive biomarker of intrahepatic lipid content in obese children prior to using radiological investigations. In particular, abdominal sonography, for the evaluation of intrahepatic lipid content in obese patients, as the sensitivity of a sonography is decreased due to the increased thickness of the abdominal wall as a result of fat deposits.