Association of retinol-binding protein-4 (RBP4) with lipid parameters in obese women

Assessing the Impact of Bariatric Surgery on Retinol-Binding Protein 4 (RBP4): A Systematic Review and Meta-Analysis

This study aimed to analyze changes in retinol-binding protein 4 (RBP4) levels before and after bariatric surgery in obese individuals. Bariatric surgery is a safe and effective treatment for morbid obesity, impacting molecules like RBP4. A systematic review and meta-analysis of 12 relevant studies were conducted, utilizing databases such as PubMed, Cochrane Central, Web of Science, and Scopus. Significant differences in RBP4, glucose, and BMI levels pre- and post-surgery were observed. Meta-regression analysis explored associations with age, pre-BMI, triglycerides, glucose, and post-insulin levels. Findings suggest RBP4 may improve insulin sensitivity after bariatric surgery, warranting further investigation as a potential pharmacotherapeutic target. These results highlight the importance of understanding RBP4's role in the context of bariatric surgery and its implications for improving metabolic health in obese individuals.

Variation of modulation and expression of biomarkers associated with inflammation in bariatric surgery patients: A systematic review and meta-analysis

BACKGROUND

Bariatric surgery is an effective intervention that causes a series of metabolic changes related to inflammatory processes; however, the variation of biomarkers related to these processes is not entirely understood. Our objective was to investigate the variation of modulation and expression of biomarkers associated with inflammation in patients who underwent bariatric surgery.

METHODS

We searched the MEDLINE (via PubMed), EMBASE (via Elsevier), Cochrane Central Register of Controlled Trials, Latin American and Caribbean Literature on Health Sciences (via virtual health library), Cumulative Index to Nursing and Allied Health Literature (via EBSCO), Web of Science core collection, and Scopus (via Elsevier) databases, and the gray literature was examined from inception to January 2022. Three pairs of reviewers performed data screening, extraction, and quality assessment independently. Meta-analysis with random effects models was used for general, subgroup, and sensitivity analyses. The I2 statistic was used to assess heterogeneity between studies.

RESULTS

In total, 96 articles were included in this systematic review; of these, 87 studies met the criteria for the meta-analysis, involving 3,533 participants. Five biomarkers were included in the meta-analysis (tumor necrosis factor alpha; interleukin 6; leptin; interleukin 1 beta, and lipopolysaccharides). Only leptin showed a significant decrease in the first month after surgery (mean difference -20.71; [95% confidence interval: -28.10 to -13.32, P < .0001; I2 = 66.7%), with moderate heterogeneity. The 12 months after surgery showed a significant decrease in tumor necrosis factor alpha (mean difference -0.89; [95% confidence interval: -1.37 to -0.42], P = .0002; I2 = 94.7%), interleukin 6 (mean difference -1.62; [95% confidence interval: -1.95 to -1.29], P < .0001; I2 = 94.9%), leptin (mean difference -28.63; [95% confidence interval: -34.02 to -23.25], P < .0001; I2 = 92.7%), and interleukin 1 beta (mean difference -2.46; [95% confidence interval: -4.23 to -0.68], P = .006; I2 = 98.3%), all with high heterogeneity. The type of surgery did not show significant differences for the biomarkers at the first month and 12 months, and the results have not changed with high-quality studies. In the 12-month measurement, variations in tumor necrosis factor alpha and leptin were associated with body mass index.

CONCLUSION

The findings of this meta-analysis suggest that Roux-en-Y gastric bypass and sleeve gastrectomy bariatric surgeries are associated with a significant reduction in leptin at 1 month after bariatric surgical intervention and tumor necrosis factor alpha, leptin, and interleukin 1 beta after 12 months.

Change in Adipokines and Gastrointestinal Hormones After Bariatric Surgery: a Meta-analysis

PURPOSE

The study aimed to perform a meta-analysis about the change in adipokines and gastrointestinal hormones after bariatric surgery in patients with obesity.

MATERIALS AND METHODS

We searched the Cochrane Central Register of Controlled Trials, EMBASE, and PubMed for related articles and used Review Manager 5.4 for data aggregation. Sensitivity and subgroup analysis were also conducted when feasible.

RESULTS

As a result, 95 articles involving 6232 patients were included in the meta-analysis. After bariatric surgery, the levels of leptin, ghrelin, C-reactive protein (CRP), interleukin-6 (IL-6), high-sensitivity C-reactive protein (Hs-CRP), tumor necrosis, factor-α (TNF-α), and interleukin-1β (IL-1β) reduced, while adiponectin, glucagon-like peptide-1 (GLP-1), and peptide YY (PYY) levels increased significantly. Subgroup analysis indicated that there was a more significant reduction in leptin level with a longer follow-up time. OAGB had a greater effect on increasing adiponectin level compared with other procedures. SG procedure would bring about reduced ghrelin, while BPD resulted in increased ghrelin. Meta-regression analysis found that publication year, study design, number of patients, preoperative age, preoperative BMI, and quality assessment score were not significantly related to change in leptin, adiponectin, and ghrelin levels.

CONCLUSION

Bariatric surgery was associated with a significant decrease in leptin, ghrelin, CRP, IL-6, Hs-CRP, TNF-α, and IL-1β, as well as increase in adiponectin, GLP-1, and PYY levels.

Effect of Weight Regain on Body Composition and Metabolic Biomarkers After Sleeve Gastrectomy: a Cross-Sectional Study from a Hospital Database

INTRODUCTION

Weight regain (WR) is described in approximately 30% of patient's post-bariatric surgery. It is related to the progression or recurrence of associated medical problems and decline in health-related quality of life. This study aimed to test the return of body composition and metabolic biomarkers to pre-operative levels when WR occurs.

METHODS

In this cross-sectional study conducted in 2021, patients were randomly selected from the hospital's electronic databases between 2001 and 2020. Patient demographic data, comorbidities, body compositions, and metabolic biomarkers were collected. Three groups were defined: groups A (WR), B (weight loss), and C (control group; patients with obesity who had not yet undergone bariatric surgery).

RESULTS

A total of 88 patients were enrolled in this study and matched with the control group. The body mass index in group A was 43.8 ± 6.9 kg/m²; group B was 28.6 ± 4.2; group C was 43.9 ± 7.1. Body muscle mass, body fat mass, and visceral fat significantly differed between groups A and B (p < 0.001) but not between groups A and C (p = 0.8). There was a significant difference in leptin, ghrelin, postprandial glucagon-like peptide-1, insulin, and fibroblast growth factor-21 (but not retinol-binding protein-4) between groups A and B. Most metabolic biomarkers in group A returned to the pre-operative values as in group C.

CONCLUSION

WR had a direct negative effect on body composition and metabolic biomarkers, whereby the values returned to pre-operative levels. Early detection of WR and possible additional therapy are necessary to prevent associated medical problems.

Vitamin A homeostasis and cardiometabolic disease in humans: lost in translation?

Vitamin A (retinol) is an essential, fat-soluble vitamin that plays critical roles in embryonic development, vision, immunity, and reproduction. Severe vitamin A deficiency results in profound embryonic dysgenesis, blindness, and infertility. The roles of bioactive vitamin A metabolites in regulating cell proliferation, cellular differentiation, and immune cell function form the basis of their clinical use in the treatment of dermatologic conditions and hematologic malignancies. Increasingly, vitamin A also has been recognized to play important roles in cardiometabolic health, including the regulation of adipogenesis, energy partitioning, and lipoprotein metabolism. While these roles are strongly supported by animal and in vitro studies, they remain poorly understood in human physiology and disease. This review briefly introduces vitamin A biology and presents the key preclinical data that have generated interest in vitamin A as a mediator of cardiometabolic health. The review also summarizes clinical studies performed to date, highlighting the limitations of many of these studies and the ongoing controversies in the field. Finally, additional perspectives are suggested that may help position vitamin A metabolism within a broader biological context and thereby contribute to enhanced understanding of vitamin A's complex roles in clinical cardiometabolic disease.

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.

All trans retinoic acid as a host-directed immunotherapy for tuberculosis

Tuberculosis (TB) is the top bacterial infectious disease killer and one of the top ten causes of death worldwide. The emergence of strains of multiple drug-resistant tuberculosis (MDR-TB) has pushed our available stock of anti-TB agents to the limit of effectiveness. This has increased the urgent need to develop novel treatment strategies using currently available resources. An adjunctive, host-directed therapy (HDT) designed to act on the host, instead of the bacteria, by boosting the host immune response through activation of intracellular pathways could be the answer. The integration of multidisciplinary approaches of repurposing currently FDA-approved drugs, with a targeted drug-delivery platform is a very promising option to reduce the long timeline associated with the approval of new drugs - time that cannot be afforded given the current levels of morbidity and mortality associated with TB infection. The deficiency of vitamin A has been reported to be highly associated with the increased susceptibility of TB. All trans retinoic acid (ATRA), the active metabolite of vitamin A, has proven to be very efficacious against TB both in vitro and in vivo. In this review, we discuss and summarise the importance of vitamin A metabolites in the fight against TB and what is known regarding the molecular mechanisms of ATRA as a host-directed therapy for TB including its effect on macrophages cytokine profile and cellular pathways. Furthermore, we focus on the issues behind why previous clinical trials with vitamin A supplementation have failed, and how these issues might be overcome.

Adipokine Retinol Binding Protein 4 and Cardiovascular Diseases

The morbidity and mortality of cardiovascular diseases (CVDs) have been increasing year by year all over the world and expanding greatly to the younger population, which becomes the leading causes of death globally that threatens human life safety. Prediction of the occurrence of diseases by using risk related adverse events is crucial for screening and early detection of CVDs. Thus, the discovery of new biomarkers that related to risks of CVDs are of urgent in the field. Retinol-binding protein 4 (RBP4) is a 21-kDa adipokine, mainly secreted by adipocytes. Besides its well-established function in the induction of insulin resistance, it has also been found in recent years to be closely associated with CVDs and other risk factors, such as hypertension, coronary heart disease, heart failure, obesity, and hyperlipidemia. In this review, we mainly focus on the progress of research that establishes the correlation between RBP4 and CVDs and the corresponding major risk factors in recent years.

Assessing normalization methods in mass spectrometry-based proteome profiling of clinical samples

BACKGROUND

Large-scale proteomic studies have to deal with unwanted variability, especially when samples originate from different centers and multiple analytical batches are needed. Such variability is typically added throughout all the steps of a clinical research study, from human biological sample collection and storage, sample preparation, spectral data acquisition, to peptide and protein quantification. In order to remove such diverse and unwanted variability, normalization of the protein data is performed. There have been already several published reviews comparing normalization methods in the -omics field, but reports focusing on proteomic data generated with mass spectrometry (MS) are much fewer. Additionally, most of these reports have only dealt with small datasets.

RESULTS

As a case study, here we focused on the normalization of a large MS-based proteomic dataset obtained from an overweight and obese pan-European cohort, where different normalization methods were evaluated, namely: center standardize, quantile protein, quantile sample, global standardization, ComBat, median centering, mean centering, single standard and removal of unwanted variation (RUV); some of these are generic normalization methods while others have been specifically created to deal with genomic or metabolomic data. We checked how relationships between proteins and clinical variables (e.g., gender, levels of triglycerides or cholesterol) were improved after normalizing the data with the different methods.

CONCLUSIONS

Some normalization methods were better adapted for this particular large-scale shotgun proteomic dataset of human plasma samples labeled with isobaric tags and analyzed with liquid chromatography-tandem MS. In particular, quantile sample normalization, RUV, mean and median centering showed very good performance, while quantile protein normalization provided worse results than those obtained with unnormalized data.

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.

Ileal transposition helps to regulate plasma hepatokine levels in obese Zucker (Crl:ZUC(ORL)-Leprfa) rats

We studied the long-term effect of ileal transposition (IT) metabolic surgery on the hepatokines: retinol-binding protein-4 (RBP4), α-2-HS-glycoprotein (aHSG/fetuin-A), and fibroblast growth factor 21 (FGF21), C-reactive protein (CRP) plasma levels, glucose metabolism, body weight, liver histology, as well as total lipids concentration in muscle, liver, and fat tissue of obese Zucker (Crl:ZUC(ORL)-Lepr^fa) rats. 14 adult males were randomly submitted either to IT or SHAM (control) surgery. Pre-operative hepatokines plasma levels were not significantly different in rats submitted to IT or SHAM protocol. Three months after the procedures the plasma levels of RBP4, aHSG, FGF21, and CRP were significantly lower in IT-operated animals when compared to SHAM-operated group. Three and 12 weeks after the IT and SHAM surgery, the AUC_OGTT were significantly lower than AUC_OGTT before the surgery. HOMA-IR was lower in rats after IT surgery in comparison to the SHAM-operated rats. Muscle and liver total lipids concentration was reduced after the IT procedure when compared to pre-IT conditions. IT had a significant reductive impact on the body weight in comparison to SHAM surgery in the 4th, 6th, 8th, and 10th week after the surgery. We conclude that IT reduces hepatokines' plasma concentrations, muscle and liver total lipids concentration but not the inflammatory processes in the liver of Zucker (Crl:ZUC(ORL)-Lepr^fa) rats.

Factors Affecting Metabolic Outcomes Post Bariatric Surgery: Role of Adipose Tissue

Obesity is an ever-growing public health crisis, and bariatric surgery (BS) has become a valuable tool in ameliorating obesity, along with comorbid conditions such as diabetes, dyslipidemia and hypertension. BS techniques have come a long way, leading to impressive improvements in the health of the majority of patients. Unfortunately, not every patient responds optimally to BS and there is no method that is sufficient to pre-operatively predict who will receive maximum benefit from this surgical intervention. This review focuses on the adipose tissue characteristics and related parameters that may affect outcomes, as well as the potential influences of insulin resistance, BMI, age, psychologic and genetic factors. Understanding the role of these factors may help predict who will benefit the most from BS.

Impact of Gastric Sleeve Surgery on Plasma Retinol Binding Protein 4 and Adipsin Levels in Healthy Male Population

Objectives

Bariatric surgery provides most substantial and sustainable weight loss measures in individuals with obesity. Caloric restriction is not only intervention, changes in hormonal secretions are also leading contributory mechanisms to reduce body weight and improve the glycaemic control. The aim of this study was to evaluate the impact of gastric sleeve surgery on plasma retinol binding protein 4 (RBP4) and adipsin levels among Saudi male obese population.

Methods

This prospective study was conducted in the Departments of Physiology and Surgery, College of Medicine, King Saud University. Thirty-three obese (BMI>38.3) male patients age ranged from 25 to 50 years were recruited. RBP4 and adipsin levels were analyzed before and 6-12 months after gastric sleeve surgery by ELISA along with plasma glucose, insulin, HOMA-IR and lipid profile.

Results

Circulating RBP4 levels were not significantly changed by bariatric surgery (4382.85±40.35 ng before, and 4393.28±33.13 ng after surgery, p=0.842), neither did adipsin (2949.68±46.86 pg before, and 2917.90±41.90 pg after surgery, p=0.535). Segregation of study participants into two age groups, 25-35 and 35-50 years of age, revealed that before surgery older age group (35-50) had higher RBP4 levels compared to younger group (25-35) (p=0.016). However, after surgery RBP4 levels were decreased in older group but not to a significant level (p=0.174). In younger age group after surgery, there was a near significant increase in RBP4 levels (p=0.052). There were no significant changes in RBP4 levels in both age groups after surgery (p=0.461). For adipsin, there were no significant differences before and after surgery in both age groups. Insulin, BMI and HOMA-IR index were decreased after surgery, however there was no correlation with RBP4 and adipsin levels.

Conclusions

The present study findings do not suggest a role for RBP4 and adipsin in the improvement of insulin sensitivity in Saudi male obese population after gastric sleeve surgery. However, a decrease in RBP4 levels in older individuals after surgery needs further investigations to understand its effect on weight and glycemic control.

Study of decreased serum levels of retinol binding protein 4 in major depressive disorder

BACKGROUND

Studies in western populations find that obesity and depression are positively correlated. Adipokines secreted by adipose tissue may serve as the crosstalk link between peripheral tissue and central nervous system, which mediates the relationship between obesity and depression.

OBJECTIVE

This study aimed to investigate serum retinol-binding protein 4 (RBP4) concentration in patients with major depressive depression (MDD) and clarify its possible association with depression.

METHODS

Major depressive disorder patients (n = 237), healthy controls (n = 48) were collected from June 2017 to October 2019. The measurement of RBP4 levels was performed by Advia 2400 automatic biochemistry analyzer. Depressive symptoms of patients were assessed using the 24-item Hamilton Depression Scale (HAMD-24).

RESULTS

(1) Serum RBP4 levels of MDD patients were significantly lower than that of the control group [(34.25 ± 8.82) mg/L vs (37.56 ± 8.83) mg/L] (P < 0.05) which was independent from obesity; (2) The level of RBP4 [(31.13 ± 9.16) mg/L] in suicide attempt (SA) group was significantly lower than that in the control group and non-suicide attempt (non-SA) group [(35.55 ± 8.37)mg/L](P < 0.05); (3) There was no significant correlation between serum RBP4 concentration and HAMD-24 score (P > 0.05); serum RBP4 concentrations were positively associated with age, age of onset and duration of disease (r = 0.325, 0.298, 0.135; P < 0.001, P < 0.001, P = 0.038) in depressive patients. (4) The level of serum RBP4 was positively correlated with TC, TG, and LDL-C (r = 0.350, 0.207, 0.268; P < 0.001, P = 0.001, P < 0.001), but not with other blood lipid indexes. ROC curve of RBP4 for MDD revealed an area under the curve of 0.603 and a sensitivity of 81.3%, specificity of 80%.

CONCLUSION

The level of RBP4 in patients with MDD was lower than that in the normal control group, which might be related to the prognosis of patients with depression.

Effect of Bariatric Surgery on Serum Inflammatory Factors of Obese Patients: a Systematic Review and Meta-Analysis

Obesity is one of the main causes of inflammation. Previous studies have reported inconclusive results regarding the effect of bariatric surgery on inflammatory markers. This systematic review and meta-analysis is aimed at describing the effect of bariatric surgery on C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α). PubMed/Medline and Scopus were systematically searched for all eligible studies from inception to June 2018. Results are expressed as weighted mean difference (MD) with 95% confidence intervals (CI) using a random effects model. Overall, 116 studies which evaluated serum CRP, IL-6, and TNF-α after bariatric surgery were included. Pooled effect size showed significant reduction in serum CRP (- 5.30 mg/l, 95% CI - 5.46, - 5.15, P < 0.001), IL-6 (- 0.58 pg/ml, 95% CI - 0.64, - 0.53, P < 0.001), and TNF-α (- 0.20 pg/ml, 95% CI - 0.39, - 0.02, P = 0.031) with significant heterogeneity across studies (> 95% for all factors). Bariatric surgery significantly lowered inflammatory factors; however, baseline BMI, follow-up duration and type of surgery could impact the extent of observed effects.

Plasma Levels of Retinol Binding Protein 4 Relate to Large VLDL and Small LDL Particles in Subjects with and without Type 2 Diabetes

Background: Retinol binding protein 4 (RBP4) carries retinol in plasma, but is also considered an adipokine, as it is implicated in insulin resistance in mice. Plasma RBP4 correlates with total cholesterol, low density lipoprotein (LDL)-cholesterol and triglycerides, and may confer increased cardiovascular risk. However, controversy exists about circulating RPB4 levels in type 2 diabetes mellitus (T2DM) and obesity. Here, we analyzed the relationships of RBP4 and retinol with lipoprotein subfractions in subjects with and without T2DM. Methods: Fasting plasma RBP4 (enzyme-linked immunosorbent assay) and retinol (high performance liquid chromatography) were assayed in 41 T2DM subjects and 37 non-diabetic subjects. Lipoprotein subfractions (NMR spectroscopy) were measured in 36 T2DM subjects and 27 non-diabetic subjects. Physical interaction of RBP4 with lipoproteins was assessed by fast protein liquid chromatography (FPLC). Results: Plasma RBP4 and retinol were strongly correlated (r = 0.881, p < 0.001). RBP4, retinol and the RBP4/retinol ratio were not different between T2DM and non-diabetic subjects (all p > 0.12), and were unrelated to body mass index. Notably, RBP4 and retinol were elevated in subjects with metabolic syndrome (p < 0.05), which was attributable to an association with elevated triglycerides (p = 0.013). Large VLDL, total LDL and small LDL were increased in T2DM subjects (p = 0.035 to 0.003). Taking all subjects together, RBP4 correlated with total cholesterol, non-HDL cholesterol, LDL cholesterol, triglycerides and apolipoprotein B in univariate analysis (p < 0.001 for each). Age-, sex- and diabetes status-adjusted multivariable linear regression analysis revealed that RBP4 was independently associated with large VLDL (β = 0.444, p = 0.005) and small LDL particles (β = 0.539, p < 0.001). Its relationship with large VLDL remained after further adjustment for retinol. RBP4 did not co-elute with VLDL nor LDL particles in FPLC analyses. Conclusions: Plasma RBP4 levels are related to but do not physically interact with large VLDL and small LDL particles. Elevated RBP4 may contribute to a proatherogenic plasma lipoprotein profile.

Association of RBP4 genetic variants with childhood obesity and cardiovascular risk factors

BACKGROUND

Recent data suggest that retinol-binding protein 4 (RBP4) gene variants could be associated with a risk of obesity and its co-morbidities, such as metabolic syndrome, which increases the risk of developing type 2 diabetes mellitus and cardiovascular disease.

OBJECTIVES

The present study examined the potential association of RBP4 single nucleotide polymorphisms (SNPs) with childhood obesity and its metabolic complications.

METHODS

Four RBP4 SNPs, rs3758538 (3944A>C), rs3758539 (4406G>A), rs12265684 (12177G>C) and rs34571439 (14684T>G), were genotyped in a population of 180 Spanish Caucasian children (97 obese and 83 normal-weight children). Association of RBP4 SNPs with obesity, metabolic risk factors (blood pressure, triglycerides, high-density lipoprotein cholesterol, insulin resistance) and markers of vascular inflammation, such as high-sensitive C-reactive protein (hs-CRP), was tested.

RESULTS

We found SNP rs3758538 to be associated with obesity (p = 0.007). Specifically, each copy of the minor allele C was associated with an increased risk of obesity, by more than twofold, in respect of being homozygous for the major allele A (odds ratio = 2.4; 95% confidence interval = 1.2-4.8). The rs3758538 and rs34571439 RBP4 SNPs correlated with plasma RBP4 levels. The SNPs rs12265684 and rs34571439 correlated with plasma triglyceride levels. The rs34571439 was also associated to hs-CRP levels. Marginal association of RBP4 SNPs with plasma high-density lipoprotein levels (rs34571439), blood pressure (rs12265684) and insulin resistance (rs3758539) was also observed.

CONCLUSIONS

These findings suggest that childhood obesity may be associated with variations in RBP4 gene. The presence of selective SNPs in the RBP4 gene may account for metabolic complications.

Is retinol binding protein 4 a link between adiposity and cancer?

Retinol binding protein 4 (RBP4) is synthesized in the liver where it binds vitamin A, retinol, and transports it to tissues throughout the body. It has been shown in some studies that the level of circulating RBP4 increases with body mass, and the protein has been implicated as a mediator in the development of insulin resistance and the metabolic disease. Adipose tissue serves as another site of RBP4 synthesis, accounting for its designation as an adipokine. In addition to its function as a transport protein, RBP4 serves as a signaling molecule which, by binding to the membrane receptor STRA6, triggers downstream activation of pro-oncogenic pathways including JAK2/STAT3/5. Taken together, available information suggests the possibility that RBP4 may be a link between obesity and cancer.

Proinflammatory and lipid biomarkers mediate metabolically healthy obesity: A proteomics study

OBJECTIVE

The metabolically healthy obesity (MHO) phenotype is an important obesity subtype in which obesity is not accompanied by any metabolic comorbidity. However, the underlying molecular mechanisms remain elusive. In this study, a shotgun proteomics approach to identify circulating biomolecules and pathways associated with MHO was used.

METHODS

The subjects were 20 African-American women: 10 MHO cases and 10 metabolically abnormal individuals with obesity (MAO) controls. Serum proteins were detected and quantified using label-free proteomics. Differential expression of proteins between the two groups was analyzed, and the list of differentially expressed proteins was analyzed to determine enriched biological pathways.

RESULTS

Twenty proteins were differentially expressed between MHO and controls. These proteins included: hemoglobin subunits (HBA1, P = 6.00 × 10(-18) ), haptoglobin-related protein (HPR, P = 1.2 × 10(-15) ), apolipoproteins (APOB-100, P = 1.50 × 10(-40) ; APOA4, P = 1.1 × 10(-14) ), retinol-binding protein 4 (RBP4, P = 7.1 × 10(-08) ), and CRP (P = 2.0 × 10(-04) ). MHO was associated with lower levels of proinflammatory and higher levels of anti-inflammatory biomarkers when compared with MAO. Pathway analysis showed enrichment of lipids and inflammatory pathways, including LXR/RXR and FXR/RXR activation, and acute phase response signaling.

CONCLUSIONS

These findings suggested that protection from dysregulated inflammatory and lipid processes were primary molecular hallmarks of MHO. The candidate biomarkers (AHSG, RBP4, and APOA4) identified in this study are potential prognostic markers for MHO.

Retinol binding protein 4 in relation to diet, inflammation, immunity, and cardiovascular diseases

Retinol binding protein 4 (RBP4), previously called retinol binding protein (RBP), is considered a specific carrier of retinol in the blood. It is also an adipokine that has been implicated in the pathophysiology of insulin resistance. RBP4 seems to be correlated with cardiometabolic markers in inflammatory chronic diseases, including obesity, type 2 diabetes, metabolic syndrome, and cardiovascular diseases (CVDs). It has recently been suggested that inflammation produced by RBP4 induces insulin resistance and CVD. The clinical relevance of this hypothesis is discussed in this review. Knowledge concerning the association of RBP4 with inflammation markers, oxidative stress, and CVDs as well as concerning the role of diet and antioxidants in decreasing RBP4 concentrations are discussed. Special attention is given to methodologies used in previously published studies and covariates that should be controlled when planning new studies on this adipokine.

A genetic polymorphism in RBP4 is associated with coronary artery disease

Insulin resistance and obesity is influenced by the retinol binding protein 4 (RBP4) adipokine. This study aims to determine if genetic polymorphisms in RBP4 are associated with the risk of coronary artery disease (CAD) in Chinese patients. RBP4 polymorphisms were analyzed by high resolution melting (HRM) analysis in a case-control study of 392 unrelated CAD patients and 368 controls from China. The Gensini score was used to determine the severity of CAD. The genotypic and allelic frequencies of RBP4 single-nucleotide polymorphisms were evaluated for associations with CAD and severity of disease. The A allele frequency was significantly higher in CAD case groups compared to control groups (16.7% vs. 8.8%) at the RBP4 rs7094671 locus. Compared to the G allele, this allele was associated with a higher risk of CAD (OR = 2.07 (1.50–2.84)). Polymorphisms at rs7094671 were found to associate with CAD using either a dominant or recessive model (OR, 95% CI: 1.97, 1.38–2.81; 3.81, 1.53–9.51, respectively). Adjusting for sex, history of smoking, serum TC, TG, LDL-c, and HDL-c, the risk of CAD for carriers remained significantly higher in both dominant and recessive models (OR, 95% CI: 1.68, 1.12–2.51; 2.74, 1.00–7.52, respectively). However, this SNP was not significantly associated with severity of CAD using angiographic scores in multivariable linear regression models (p = 0.373). The RBP4 rs7094671 SNP is associated with CAD; however, our results do not indicate that this locus is associated with clinical severity of CAD or the extent of coronary lesions.

Obesity, inflammation, and insulin resistance

White adipose tissue (WAT) is considered an endocrine organ. When present in excess, WAT can influence metabolism via biologically active molecules. Following unregulated production of such molecules, adipose tissue dysfunction results, contributing to complications associated with obesity. Previous studies have implicated pro- and anti-inflammatory substances in the regulation of inflammatory response and in the development of insulin resistance. In obese individuals, pro-inflammatory molecules produced by adipose tissue contribute to the development of insulin resistance and increased risk of cardiovascular disease. On the other hand, the molecules with anti-inflammatory action, that have been associated with the improvement of insulin sensitivity, have your decreased production. Imbalance of these substances contributes significantly to metabolic disorders found in obese individuals. The current review aims to provide updated information regarding the activity of biomolecules produced by WAT.

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.

Lipocalin 13 regulation of glucose and lipid metabolism in obesity

Lipocalin (LCN) family members are small secreted proteins that bind to small hydrophobic molecules via their characteristic central β-barrels. A couple of LCN family members, including major urinary protein 1, retinol-binding protein 4, LCN2, and LCN13, have been reported to regulate insulin sensitivity and nutrient metabolism. LCN13 is expressed by multiple tissues, including the liver, pancreas, epididymis, and skeletal muscle, and is secreted into the bloodstream in mice. Obesity is associated with a downregulation of LCN13 expression and lower levels of circulating LCN13. LCN13 therapies overcome LCN13 deficiency in mice with either genetic or dietary obesity, leading to an improvement in hyperglycemia, hyperinsulinemia, insulin resistance, glucose intolerance, and hepatic steatosis. In hepatocytes, LCN13 directly suppresses hepatic gluconeogenesis and lipogenesis but increases fatty acid β oxidation. LCN13 also enhances insulin sensitivity in adipocytes. The potential mechanisms of the antidiabetes and antisteatosis actions of LCN13 are discussed.

Evolution of lipid profiles after bariatric surgery

BACKGROUND

The most commonly encountered dyslipidemia in obese individuals is characterized by a cluster of interrelated plasma lipid and lipoprotein abnormalities including hypertriglyceridemia, low HDL cholesterol values, and increased small, dense LDL cholesterol particles. The aim of this study was to assess the changes in lipid profiles at baseline (pre-operatively) and at follow-up (6, 12, and 18 months) after a laparoscopic Roux-en-Y gastric bypass (LRYGBP). A retrospective observational study was performed involving all patients who consecutively underwent a LRYGBP between January 1, 2007 and December 31, 2009. Fasting lipids sub-fractions (total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides) were measured and HOMA-IR calculated pre-operatively and at follow-up post-LRYGBP. Pearson's correlation coefficients were used to assess the relationship between excess weight loss (EWL) and lipid sub-fractions. ANOVA was used to assess the differences between each lipid sub-fraction at various time-points.

METHODS

One hundred twenty eight (N = 128) medical charts were reviewed, and those containing data on lipid fractions at the three follow-up time-points were analyzed. One hundred fourteen patients (N = 114), 84 of whom were women (73.7%), were finally included in the study.

RESULTS

Total cholesterol, LDL cholesterol, triglycerides, and HOMA-IR were significantly reduced after LRYGBP (P < 0.0005 for all). Inversely, HDL cholesterol disclosed a significant rise (P < 0.0005). Noteworthy significant associations between lipid subfractions and EWL were detected overall (P < 0.0005 for all). A gender effect was found since female patients displayed a milder association than male patients (P < 0.0005).

CONCLUSIONS

LRYGBP-induced weight loss improves the lipid profile while reducing insulin resistance, with male patients showing a better profile than female patients.

Insulin resistance and bariatric surgery

The objective of this article is to systematically review the changes in insulin resistance after various types of bariatric surgical procedures. A Pubmed and EMBASE search for studies measuring insulin resistance before and after bariatric surgery was done and all original research articles from 1980 to present (2011) were included. Only the currently widely performed bariatric procedures were included. A meta-analysis of change in HOMA-IR was conducted, grouping studies with similar duration of follow-up. The percentage decrease in HOMA-IR at <=2 weeks, 1 month, 3 months, 6 months, 12 months and >16-18 months was found to be (mean ± standard error) -33.48 ± 5.78, -46.43 ± 6.99, -38.79 ± 9.64, -58.62 ± 7.38, -44.91 ± 7.98 and -67.04 ± 10.78%, respectively. RYGB (gastric bypass) and BPD (biliopancreatic diversion) produced a significant decrease in insulin resistance at 2 weeks after surgery, while LSG (sleeve gastrectomy) was strongly trending. LSG produced an earlier decrease in insulin resistance when compared to LAGB (gastric banding). RYGB, BPD and LSG produce an early decrease in insulin resistance through yet unknown mechanisms.

Association of serum retinol-binding protein 4 with insulin resistance and metabolic parameters during olanzapine therapy

OBJECTIVE

Retinol-binding protein 4 (RBP4) has been shown to be associated with insulin resistance (IR), metabolic indices and metabolic syndrome (MetS) in various patient populations and in obesity. We investigated the association between metabolic parameters, IR and RBP4 during olanzapine therapy.

DESIGN

A prospective study.

PATIENTS

Thirty-seven participants with psychiatric disorder who were atypical antipsychotic naive and newly initiated on olanzapine were assessed.

MEASUREMENTS

Fasting RBP4, anthropometric and metabolic variables were measured before and after 3 months of olanzapine therapy.

RESULTS

Participants who developed MetS showed higher RBP4 levels compared with those without MetS, although not significant (P = 0·053). The variation in RBP4 level was correlated with changes in systolic blood pressure (r = 0·423, P = 0·009), diastolic blood pressure (r = 0·390, P = 0·017), total cholesterol (r = 0·446, P = 0·006) and low-density lipoprotein (LDL) (r = 0·407, P = 0·012). Multiple linear regression analysis illustrated that end-point log insulin level was the most significant independent predictor of final log RBP4 levels (standardized ß = 0·353, P = 0·024).

CONCLUSIONS

Our results suggest that RBP4 levels might be associated with at least some olanzapine-induced metabolic abnormalities and cardiovascular disease risk factors.

Role of Retinol-Binding Protein 4 in Obese Asian Indians with Metabolic Syndrome

Retinol-binding protein 4 is an adipocytokine separately implicated in the development of obesity-related insulin resistance and proatherogenic lipid profile, however, its role in humans is unclear. This study was carried out to assess the role of retinol-binding protein 4 as a potential marker of metabolic syndrome in obese Asian Indians (a high-risk population for diabetes). 52 obese (BMI >23 kg/m2) Asian Indians were grouped into those with and without metabolic syndrome based on IDF criteria and compared with healthy controls. The anthropometric and biochemical parameters (fasting blood sugar, lipid profile, serum insulin, high-sensitivity C-reactive protein, and retinol-binding protein 4) were estimated. The obese groups had significantly altered adiposity indices, insulin resistance parameters (fasting blood sugar (only in the metabolic syndrome group), serum insulin, HOMA-IR and QUICKI), index of inflammation (C-reactive protein) and proatherogenic dyslipidemic profile (serum triglycerides, VLDL-cholesterol, and triglyceride/HDL-cholesterol ratio). Retinol-binding protein 4 levels were elevated in the obese groups, but were not significant. Retinol-binding protein 4 levels were correlated with anthro-pometric parameters and atherogenic lipids, while C-reactive protein was correlated with anthropometric and insulin resistance parameters in the entire group of subjects. Although these correlations were not observed in the obese groups, in the control group, retinol-binding protein 4 was correlated to the lipid parameters and C-reactive protein to adiposity indices. Thus, the role of retinol-binding protein 4 as a potential marker of metabolic syndrome is limited to the prediction of proatherogenic risk among Asian Indians.

Effects of exercise training on circulating retinol-binding protein 4 and cardiovascular disease risk factors in obese men

INTRODUCTION

The purpose of this study was to investigate the effects of 12-week exercise training on circulating retinol-binding protein 4 (RBP4) concentration and cardiovascular disease (CVD) risk factors in obese men.

METHODS

29 obese men (age 48 ± 2 years; BMI 29.6 ± 0.7 kg/m(2)) participated in a 12-week exercise program (50-70% maximal heart rates; 3 times/week) without calorie restriction. Anthropometric parameters, CVD risk factors (total cholesterol, high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol, triglycerides (TG), and quantitative insulin sensitivity check index), and circulating RBP4 and adipokine (adiponectin, leptin, and interleukin-6 (IL-6)) concentrations were measured.

RESULTS

Exercise training significantly improved in absolute peak oxygen consumption (p < 0.05), and CVD risk factors (p < 0.05), with the exception of HDLC. There was a significant decrease in circulating RBP4, leptin, and IL-6 concentrations (p < 0.05). Stepwise regression analysis revealed that changes in RBP4 concentration were independently related to the changes in TG concentration (β = 0.46, p < 0.05).

CONCLUSION

These results demonstrate that exercise training without calorie restriction improves several CVD risk factors and circulating RBP4 and adipokine concentrations. Moreover, the change in circulating RBP4 may be more associated with the improvements in TG concentration in obese men.

Retinol-binding protein 4 correlates with triglycerides but not insulin resistance in prepubertal children with and without premature adrenarche

BACKGROUND

Retinol-binding protein 4 (RBP4) has been proposed as an early marker for insulin resistance (IR), but no prior studies have addressed RBP4 in an exclusively prepubertal population. Children with premature adrenarche (PA) are at increased risk for IR and metabolic syndrome (MeS); thus finding an appropriate early marker for IR in this population would allow for early intervention and prevention of morbidity related to IR and MeS.

OBJECTIVE

To determine whether prepubertal children with PA have higher levels of RBP4 than controls and whether RBP4 correlates with comorbidities of metabolic disease in prepubertal children.

SUBJECTS

This study comprised 49 prepubertal children (24 with PA and 25 control subjects), 20 boys and 29 girls, who were between the ages of 5 and 9 years.

METHODS

This was a cross-sectional, case-control study conducted in a subspecialty ambulatory clinic based in a quaternary care center. RBP4 levels, hormonal values, lipids, and response to an oral glucose tolerance test were evaluated in children with PA and controls, and body composition measures were obtained in a subset of patients (n = 18).

RESULTS

RBP4 correlated with triglycerides (r = 0.57, p < 0.0001) but did not correlate with IR in a body mass index z-score-adjusted Pearson correlation analysis. There was no difference in RBP4 levels between the PA and control groups.

CONCLUSIONS

These findings suggest that RBP4 may be an early marker of dyslipidemia, which may herald future onset of hepatic IR, polycystic ovary syndrome, and MeS.