Retinol-binding protein 4 and its relation to insulin resistance in obese children before and after weight loss

Retinol binding protein 4 and type 2 diabetes: from insulin resistance to pancreatic β-cell function

BACKGROUND AND AIM

Retinol binding protein 4 (RBP4) is an adipokine that has been explored as a key biomarker of type 2 diabetes mellitus (T2DM) in recent years. Researchers have conducted a series of experiments to understand the interplay between RBP4 and T2DM, including its role in insulin resistance and pancreatic β-cell function. The results of these studies indicate that RBP4 has a significant influence on T2DM and is considered a potential biomarker of T2DM. However, there have also been some controversies about the relationship between RBP4 levels and T2DM. In this review, we update and summarize recent studies focused on the relationship between RBP4 and T2DM and its role in insulin resistance and pancreatic β-cell function to clarify the existing controversy and provide evidence for future studies. We also assessed the potential therapeutic applications of RBP4 in treating T2DM.

METHODS

A narrative review.

RESULTS

Overall, there were significant associations between RBP4 levels, insulin resistance, pancreatic β-cell function, and T2DM.

CONCLUSIONS

More mechanistic studies are needed to determine the role of RBP4 in the onset of T2DM, especially in terms of pancreatic β-cell function. In addition, further studies are required to evaluate the effects of drug intervention, lifestyle intervention, and bariatric surgery on RBP4 levels to control T2DM and the role of reducing RBP4 levels in improving insulin sensitivity and pancreatic β-cell function.

Visfatin and Retinol Binding Protein-4 in Young-Onset Type 2 Diabetes Mellitus

Background and Objectives: The prevalence of type 2 diabetes mellitus in adolescents has increased rapidly in recent decades. However, the role of adipokines on pathophysiology in young-onset type 2 diabetes mellitus (YDM) is not clear. In this article, we explored the relationships between the adipokines (visfatin and retinol binding protein 4 (RBP4)) and metabolic syndrome (MetS) components in both YDM and late-onset type 2 diabetes mellitus (ODM). Materials and Methods: There were 36 patients with YDM (23.6 ± 4.8 years) and 36 patients with ODM (54.3 ± 10.1 years) enrolled. Visfatin, RBP4, and MetS components were measured. The relationships between visfatin, RBP4 and MetS components were assessed in YDM and ODM. Results: The visfatin, but not the RPB4 level, was significantly higher in YDM than in ODM. After adjusting for age and body mass index, visfatin was not related to any MetS components except that there was a negative correlation with fasting plasma glucose (FPG). As for RPB4, triglyceride was found to be positively and FPG negatively related to RBP4 in YDM. However, in ODM, the only positive relationship that existed was between RBP4 and diastolic blood pressure. Conclusions: In conclusion, both visfatin and RBP4 had certain roles in diabetes and MetS although their relationships were different in YDM and ODM. Further studies are needed to explore their physiological and pathological effects in glucose metabolism.

Ovariectomy Increases Circulating Retinol-Binding Protein Concentrations Independently of Sex-Dependent Differences in Retinol Concentrations in Rats

BACKGROUND

There is a sex-dependent difference in blood retinol and RBP concentrations, and plasma RBP is associated with insulin resistance.

OBJECTIVES

We aimed to clarify sex-dependent variations in body concentrations of retinol and RBPs and their association with sex hormones in rats.

METHODS

Plasma and liver retinol concentrations and hepatic mRNA and plasma concentrations of RBP4 were analyzed in 3- and 8-wk-old male and female Wistar rats before and after sexual maturity (experiment 1) and in orchiectomized male Wistar rats (experiment 2) and ovariectomized female Wistar rats (experiment 3). Furthermore, the mRNA and protein concentrations of RBP4 in adipose tissue were measured in ovariectomized female rats (experiment 3).

RESULTS

There were no sex-dependent differences in liver retinyl palmitate and retinol concentrations; however, the plasma retinol concentration was significantly higher in male rats than that in female rats after sexual maturity. Furthermore, the plasma retinol concentrations did not differ between the ovariectomized or orchiectomized rats and the control rats. Plasma Rbp4 mRNA concentrations were higher in male rats than those in female rats but not in castrated and control rats, a change consistent with plasma retinol concentration. Plasma RBP4 concentrations were also higher in male rats than those in female rats; however, unlike liver Rbp4 gene expression, plasma RBP4 concentrations were 7-fold higher in the ovariectomized rats than those in the control rats. Moreover, the Rbp4 mRNA concentrations in inguinal white adipose tissue was significantly higher in the ovariectomized rats than those in the control rats and correlated with plasma RBP4 concentrations.

CONCLUSIONS

Hepatic Rbp4 mRNA is higher in male rats through a sex hormone-independent mechanism, which may contribute to sex differences in blood retinol concentrations. Furthermore, ovariectomy leads to an increase in adipose tissue Rbp4 mRNA and blood RBP4 concentrations, which may contribute to insulin resistance in ovariectomized rats and postmenopausal women.

High prevalence of malnutrition and vitamin A deficiency among schoolchildren of rural areas in Malaysia using a multi-school assessment approach

Childhood malnutrition is known as a public health concern globally. The present study aims to assess the anthropometry and blood biochemical status of rural primary schoolchildren in Malaysia. A total of 776 children (7-11 years old) from ten rural primary schools from five states were included in this study. Nutritional outcomes were assessed based on sex, age group and school categories among the children (median age: 9 years (P25:8, P75:10)). The overall prevalence of malnutrition was 53·4 %. Vitamin A deficiency (VAD) was recorded at 20·6 and 39·8 % based on retinol and retinol-binding protein (RBP) levels, respectively. Anaemia, iron deficiency (ID), iron-deficiency anaemia (IDA) and elevated inflammation were found at 14·9, 17·9, 9·1 and 11·5 %, respectively. Malnutrition, VAD, anaemia, ID, IDA and elevated inflammation were more prevalent among Orang Asli (OA) schoolchildren compared with Non-Orang Asli schoolchildren. Higher occurrences of VAD and anaemia were also found among children aged <10 years. Retinol, RBP, α-carotene, ferritin and haemoglobin levels were lower among undernourished children. Besides, overweight/obese children exhibited a higher level of high-sensitivity C-reactive protein. Multivariate analysis demonstrated that OA school children (adjusted OR (AOR): 6·1; 95 % CI 4·1, 9·0) and IDA (AOR: 3·6; 95 % CI 1·9, 6·6) were associated with stunting among this population. The present study revealed that malnutrition, micronutrient deficiencies and anaemia are prevalent among rural primary schoolchildren in Malaysia, especially those from OA schools and younger age children (<10 years). Hence, more appropriate and targeted measures are needed to improve the nutritional status of these children.

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.

The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

Purpose

Vitamin A is an essential nutrient with vital biological functions. The present study investigated the effect of different doses of vitamin A palmitate at different time intervals on thyroid hormones and glycemic markers.

Methods

Male rats were administrated vitamin A palmitate at different doses (0, 0.7, 1.5, 3, 6, and 12 mg/kg, oral) and samples were collected at different time intervals of 2, 4, and 6 weeks. The levels of vitamin A, thyroid hormones (T3, T4, and TSH), deiodinases (Dio1 and Dio3), glycemic markers (blood insulin and fasting glucose levels, HOMA IR and HOMA β), retinol-binding protein 4 (RBP4) and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) were measured.

Results

The findings demonstrated that long-term supplementation with high doses of vitamin A palmitate resulted in hypothyroidism (lower T3 and T4 levels and elevated TSH levels) as well as upregulation of Dio1 and Dio3 expression levels. This effect was associated with elevated glucose and insulin levels, enhanced HOMA IR, and decreased HOMA B index. In addition, prolonged vitamin A supplementation significantly increased RBP4 levels that upregulated the expression of PEPCK.

Conclusion

High doses of vitamin A supplementation increased the risk of hypothyroidism, modulated insulin sensitivity, and over a long period, increased the incidence of type 2 diabetes mellitus associated with oxidative stress and hepatitis.

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.

Adipose-Derived Lipid-Binding Proteins: The Good, the Bad and the Metabolic Diseases

Adipose tissue releases a large range of bioactive factors called adipokines, many of which are involved in inflammation, glucose homeostasis and lipid metabolism. Under pathological conditions such as obesity, most of the adipokines are upregulated and considered as deleterious, due to their pro-inflammatory, pro-atherosclerotic or pro-diabetic properties, while only a few are downregulated and would be designated as beneficial adipokines, thanks to their counteracting properties against the onset of comorbidities. This review focuses on six adipose-derived lipid-binding proteins that have emerged as key factors in the development of obesity and diabetes: Retinol binding protein 4 (RBP4), Fatty acid binding protein 4 (FABP4), Apolipoprotein D (APOD), Lipocalin-2 (LCN2), Lipocalin-14 (LCN14) and Apolipoprotein M (APOM). These proteins share structural homology and capacity to bind small hydrophobic molecules but display opposite effects on glucose and lipid metabolism. RBP4 and FABP4 are positively associated with metabolic syndrome, while APOD and LCN2 are ubiquitously expressed proteins with deleterious or beneficial effects, depending on their anatomical site of expression. LCN14 and APOM have been recently identified as adipokines associated with healthy metabolism. Recent findings on these lipid-binding proteins exhibiting detrimental or protective roles in human and murine metabolism and their involvement in metabolic diseases are also discussed.

Retinol-binding protein 4 in obesity and metabolic dysfunctions

Excessive increased adipose tissue mass in obesity is associated with numerous co-morbid disorders including increased risk of type 2 diabetes, fatty liver disease, hypertension, dyslipidemia, cardiovascular diseases, dementia, airway disease and some cancers. The causal mechanisms explaining these associations are not fully understood. Adipose tissue is an active endocrine organ that secretes many adipokines, cytokines and releases metabolites. These biomolecules referred to as adipocytokines play a significant role in the regulation of whole-body energy homeostasis and metabolism by influencing and altering target tissues function. Understanding the mechanisms of adipocytokine actions represents a hot topic in obesity research. Among several secreted bioactive signalling molecules from adipose tissue and liver, retinol-binding protein 4 (RBP4) has been associated with systemic insulin resistance, dyslipidemia, type 2 diabetes and other metabolic diseases. Here, we aim to review and discuss the current knowledge on RBP4 with a focus on its role in the pathogenesis of obesity comorbid diseases.

Associations Between Antioxidant Vitamin Status, Dietary Intake, and Retinol-binding Protein 4 Levels in Prepubertal Obese Children After 3-month Weight Loss Therapy

OBJECTIVE

Adiposity is associated with increased oxidative stress, leading to changed fat-soluble vitamin concentrations. The aim of this study was to determine whether weight loss alters fat-soluble vitamin status and whether these alterations are associated with dietary intake, anthropometric parameters and adipokines in obese children.

METHODS

Vitamin A and E concentrations were measured using high-pressure liquid chromatography in 60 obese children before and after weight loss therapy. Retinol-binding protein 4 (RBP4), leptin, soluble leptin receptor (sOB-R), and high molecular weight adiponectin concentrations were determined by immunoenzymatic assays.

RESULTS

The intake of vitamin E was lower in obese children with weight loss after therapy (p=0.038). In this group, an increase was found in the vitamin A/lipids (p=0.022) and the vitamin E/lipids (p=0.008) ratios but due to the reduction in triglyceride levels. In the obese group, changes in vitamin E level were positively correlated with changes in dietary vitamin E (p=0.017) and the leptin/sOB-R ratio (p=0.046). Changes in vitamin A level were positively correlated with changes in dietary vitamin A (p=0.001) and RBP4 concentration (p=0.023). Associations between changes in RBP4 level with the changes in body mass index (BMI) (p=0.011) and total cholesterol concentration (p=0.023) but not with changes in vitamin A concentration were found in the obese after therapy.

CONCLUSION

An increased risk of vitamin E deficiency may occur in children losing weight during lifestyle intervention. Changes in BMI value may influence changes in RBP4 concentrations and consequently the vitamin A status in obese children after therapy.

The Association between Serum Retinol-Binding Protein 4 Levels and Cardiovascular Events in Patients with Chronic Kidney Disease

OBJECTIVE

The study aimed to assess whether serum retinol-binding protein 4 (RBP4) is associated with a risk of cardiovascular (CV) events in chronic kidney disease (CKD) patients.

METHODS

One hundred sixty-nine patients with CKD were followed for a mean of 36 months (range, 5-39 months). Serum RBP4 and other laboratory indicators were measured at baseline. The relationship between RBP4 and the risk of CV events was evaluated by using Cox regression analysis.

RESULTS

Patients with higher serum RBP4 levels had a higher rate of CV events and a higher mortality in a univariate analysis (P < 0.001). The multivariate Cox proportional hazard analysis revealed that RBP4 (hazard ratio, 2.259; 95% confidence interval, 2.067-5.489; P = 0.002) is an independent prognostic factor for CV events in patients with CKD. Kaplan-Meier analysis demonstrated that patients with RBP4 above the median value (>33.86 mg/L) had a higher rate of CV events than did patients with RBP4 at or below the median value (≤33.86 mg/L; P < 0.001).

CONCLUSION

RBP4 levels are associated with CV events in patients with CKD. Elevated serum RBP4 levels may indicate an increased risk of CV complications in CKD patients.

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.

Associations of persistent organic pollutants in human adipose tissue with retinoid levels and their relevance to the redox microenvironment

Humans are exposed to a myriad of chemical substances in both occupational and environmental settings. Persistent organic pollutants (POPs) have drawn attention for their adverse effects including cancer and endocrine disruption. Herein, the objectives were 1) to describe serum and adipose tissue retinol levels, along with serum retinol binding protein 4 (RBP4) concentrations, and 2) to assess the associations of adipose tissue POP levels with these retinoid parameters, as well as their potential interaction with the previously-observed POP-related disruption of redox microenvironment. Retinol was measured in both serum and adipose tissue along with RBP4 levels in serum samples of 236 participants of the GraMo adult cohort. Associations were explored by multivariable linear regression analyses and Weighted Quantile Sum regression. Polychlorinated biphenyls (PCBs) 180, 153 and 138 were related to decreased adipose tissue retinol levels and increased serum RBP4/retinol ratio. Dicofol concentrations > limit of detection were associated with decreased retinol levels in serum and adipose tissue. Additionally, increased adipose tissue retinol levels were linked to an attenuation in previously-reported associations of adipose tissue PCB-153 with in situ superoxide dismutase activity. Our results revealed a suggestive link between retinoids, PCBs and redox microenvironment, potentially relevant for both mechanistic and public health purposes.

The role of chemerin in the pathogenesis of cholelithiasis in children and adolescents

BACKGROUND AND AIM

Adipokines and hepatokines are proteins secreted by adipose tissue and the liver. To date, the levels of adipokines and hepatokines in cholelithiasis have only been evaluated in studies in adult patients. The purpose of our research was to assess the levels of circulating adipokines: chemerin, vaspin, progranulin, retinol-binding protein 4 (RBP-4) and hepatokine: fibroblast growth factor 21 (FGF-21) and to compare their concentrations in paediatric patients with and without cholelithiasis.

METHODS

The prospective study included 54 children and adolescents diagnosed with gallstones and 26 controls. Fasting serum levels of adipokines and hepatokine were determined by enzyme-linked immunosorbent assays.

RESULTS

The serum levels of chemerin, FGF-21 and RBP-4 were significantly higher in children and adolescents with gallstones compared to the control group. Elevated levels of triglycerides, RBP-4, and a homeostatic model for assessing insulin resistance (HOMA-IR) were observed in overweight or obese patients compared to patients with normal weight and cholelithiasis. Chemerin concentrations were increased in the normal-weight children and adolescents with cholelithiasis compared to the control group. Children and adolescents with gallstones and abnormal weight had significantly higher levels of chemerin, FGF-21 and RBP-4 than healthy controls.

CONCLUSION

Elevated serum chemerin levels were significantly higher in non-obese patients with cholelithiasis than in non-obese controls, suggesting a potential role of chemerin in the development of cholelithiasis in children and adolescents.

Plasma RBP4 Level in Association with Body Composition, Metabolic Profile, STRA6 and RBP4 Gene Polymorphisms in Obese Romanian Children

BACKGROUND

Pediatric obesity continues to remain a serious health concern which has significantly increased the morbidity risk in adulthood. Recent studies have analyzed the impact of the two adipokines, RBP4 (retinol binding protein 4) and STRA6 (stimulated by retinoic acid 6) in pediatric obese subjects with contradictory results.

METHODS

An observational study was conducted in the Pediatric and Endocrinology Departments, Targu-Mures, Romania, including 213 children between 5-17 years of age, divided into two groups according to body mass index (BMI) standard deviation score (SDS): case (overweight or obese) and control (normal SDS). Age, sex, basic anthropometric and biochemical measurements and genotype of rs3758539, and rs10882280 for RBP4 gene and rs974456 and rs351224 of STRA6 gene were analyzed. Statistical analysis used SPSS v. 25.0, with a level of significance α = 0.05.

RESULTS

There is no association between the two gene's polymorphisms and obesity in our pediatric population. In regression analysis, with HOMA IR (homeostatic model assessment of insulin resistance) as the outcome, the plasmatic level of RBP4 and fat mass percentage are significant predictors, with the model explaining 42% of the HOMA variability. Hypercholesterolemia was significantly associated with male sex, carrying variant allele and heterozygote status of rs10882280 RBP4 gene and wild-type allele rs351224 of STRA6 gene.

CONCLUSION

There is no significant association between obesity and SNPs of the RBP4 and STRA6 in our population, but they seem to play a role in insulin resistance and hypercholesterolemia.

What Change in Body Mass Index Is Required to Improve Cardiovascular Outcomes in Childhood and Adolescent Obesity through Lifestyle Interventions: A Meta-Regression

Background: Using meta-regression, this article aims at establishing the minimum change in BMI-standard deviation score (SDS) needed to improve lipid profiles and blood pressure in children and adolescents with obesity, to aid future trials and guidelines. Methods: Studies with participants involved in lifestyle interventions, aged 4-19 years, with a diagnosis of obesity according to defined BMI thresholds, were considered for inclusion in a large systematic review. Interventions had to report pre- and post-intervention (or mean change in) BMI-SDS, plus either systolic blood pressure (SBP), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and/or triglycerides (TGs). Random-effects meta-regression quantified the relationship between mean change in BMI-SDS and mean change in cardiovascular outcomes. Results: Seventy-one papers reported various cardiovascular measurements and mean change in BMI-SDS. Fifty-four, 59, 46, and 54 studies were analyzed, reporting a change in SBP, HDL, LDL, and TG, respectively. Reduction in mean BMI-SDS was significantly related to improvements in SBP, LDL, TG, and HDL (p < 0.05); BMI-SDS reductions of 1, 1.2, and 0.7 ensured a mean reduction of SBP, LDL, and TG, respectively, although an equivalent value for HDL improvement was indeterminate. Conclusion: Reductions in mean BMI-SDS of >1, >1.2, or >0.7 are likely to reduce SBP, LDL, and TG, respectively. Further studies are needed to clarify the optimal duration, intensity, and setting for interventions. Consistency is required regarding derived BMI values to facilitate future systematic reviews and meta-analyses.

Impaired Hepatic Vitamin A Metabolism in NAFLD Mice Leading to Vitamin A Accumulation in Hepatocytes

BACKGROUND & AIMS

Systemic retinol (vitamin A) homeostasis is controlled by the liver, involving close collaboration between hepatocytes and hepatic stellate cells (HSCs). Genetic variants in retinol metabolism (PNPLA3 and HSD17B13) are associated with non-alcoholic fatty liver disease (NAFLD) and disease progression. Still, little mechanistic details are known about hepatic vitamin A metabolism in NAFLD, which may affect carbohydrate and lipid metabolism, inflammation, oxidative stress and the development of fibrosis and cancer, e.g. all risk factors of NAFLD.

METHODS

Here, we analyzed vitamin A metabolism in 2 mouse models of NAFLD; mice fed a high-fat, high-cholesterol (HFC) diet and Leptinob mutant (ob/ob) mice.

RESULTS

Hepatic retinol and retinol binding protein 4 (RBP4) levels were significantly reduced in both mouse models of NAFLD. In contrast, hepatic retinyl palmitate levels (the vitamin A storage form) were significantly elevated in these mice. Transcriptome analysis revealed a hyperdynamic state of hepatic vitamin A metabolism, with enhanced retinol storage and metabolism (upregulated Lrat, Dgat1, Pnpla3, Raldh's and RAR/RXR-target genes) in fatty livers, in conjunction with induced hepatic inflammation (upregulated Cd68, Tnfα, Nos2, Il1β, Il-6) and fibrosis (upregulated Col1a1, Acta2, Tgfβ, Timp1). Autofluorescence analyses revealed prominent vitamin A accumulation in hepatocytes rather than HSC in HFC-fed mice. Palmitic acid exposure increased Lrat mRNA levels in primary rat hepatocytes and promoted retinyl palmitate accumulation when co-treated with retinol, which was not detected for similarly-treated primary rat HSCs.

CONCLUSION

NAFLD leads to cell type-specific rearrangements in retinol metabolism leading to vitamin A accumulation in hepatocytes. This may promote disease progression and/or affect therapeutic approaches targeting nuclear receptors.

Change in obesity-related metabolic abnormalities associated with body mass index improvement through life-style intervention: A meta-regression

The reduction in body mass index standard deviation score (BMI-SDS) associated with improvement in biomarkers relating to metabolic health in obese children is unknown. We aimed to establish the change in BMI-SDS associated with improved inflammation, liver function, and insulin resistance to inform clinical guidelines for pediatric weight management interventions and to assess the efficacy of future trials. A large-scale systematic review was conducted to identify relevant studies. Studies of children with a diagnosis of obesity according to defined BMI thresholds, participating in lifestyle interventions to reduce obesity, were included. Studies must have reported baseline (pre-) and postintervention (or change of) BMI-SDS and either fasting glucose, homeostatic model of insulin resistance (HOMA-IR), alanine aminotransferase (ALT), C-reactive protein (CRP), or interleukin-6 (IL-6). A series of meta-regressions were conducted to establish links between BMI-SDS change scores and change in metabolic markers of health. Sixty-eight articles were identified. From the meta-regression analyses, across all study subsets, greater mean falls in all four parameters, (HOMA-IR, Glucose, ALT, and CRP) were observed with greater mean loss of BMI-SDS, but the trends were only statistically significant for HOMA-IR and CRP (P = .003; P = .021). However, we could not find minimum changes in BMI-SDS that would ensure a fall in these outcomes. At this time, we are unable to recommend a definitive value of BMI-SDS reduction needed to improve the markers of metabolic health. Future trials should aim to report additional indices of derived BMI values, which may better reflect changes in actual adiposity.

Novel adipokine associated with OA: retinol binding protein 4 (RBP4) is produced by cartilage and is correlated with MMPs in osteoarthritis patients

Objective

Retinol binding protein 4 (RBP4) is a member of the lipocalin family and a vitamin A carrier in the blood. More recently, RBP4 has been described as an adipokine that is involved in insulin resistance and metabolic syndrome (MetS). As obesity, MetS and some adipokines contribute to the pathogenesis of osteoarthritis (OA), we investigated RBP4 in patients with OA.

Materials and methods

Cartilage, synovial fluid and blood samples were collected from 100 OA patients undergoing total knee replacement surgery. Primary chondrocytes and cartilage tissue were cultured to measure the RBP4 expression. The concentrations of RBP4, other adipokines (adipsin, adiponectin, leptin and resistin) and biomarkers of OA (COMP, MMP-1, MMP-3 and YKL-40) were measured by immunoassay, and gene expression was measured by next-generation RNA sequencing.

Results

The OA cartilage samples released RBP4 into the culture medium, and the levels correlated positively with the expression of the adipokines adipsin, adiponectin, leptin and resistin. RBP4 was the most prominently expressed of these adipokines in the OA chondrocytes, and the expression of the RBP4 receptors STRA6 (stimulated by retinoic acid gene homologue 6) and TLR4 (Toll-like receptor 4) was also detected. Within the cartilage culture medium, RBP4 showed a positive correlation with MMP-1, MMP-3 and YKL-40. RBP4 was also present in the synovial fluid from the OA patients and correlated positively with the concentrations of RBP4 found in the plasma and the cartilage culture medium. Plasma RBP4 concentrations also showed a positive correlation with MMP-3 and adipsin.

Conclusions

We show here, for the first time, that RBP4 is produced within OA joints and that it is associated with increased levels of adipokines and MMPs. The results suggest a role for RBP4 in the pathogenesis of OA and as a possible target for the disease-modifying drugs for the treatment of OA.

Changes of serum retinol-binding protein 4 associated with improved insulin resistance after laparoscopic sleeve gastrectomy in Chinese obese patients

BACKGROUND

Serum retinol-binding protein 4 (RBP4) plays a critical role in insulin resistance. The mechanism behind the impact of laparoscopic sleeve gastrectomy (LSG) on glucose metabolism is unclear. Hence, we aimed to investigate the triangle relationship between the RBP4, glucose metabolism, and LSG in patients of Chinese ethnicity.

METHODS

The study enrolled eighty-two obese patients. Glucose-lipid metabolic index, uric acid (UA), superoxide dismutase (SOD), free triiodothyronine (FT3), free thyroxin (FT4) and thyrotropin (TSH) were measured. RBP4 levels were detected by enzyme-link immunosorbent assay. 30 obese patients underwent LSG were studied. All these markers were measured again at a time interval of 3 and 6 months after surgery.

RESULTS

(1) Circulating RBP4 levels were positively associated with body mass index(BMI), blood glucose in 0 min (BG0), BG30, BG120, BG180, fasting inulin(FINS), fasting C peptide(FCP), homeostasis model of assessment for insulin resistance index (HOMA-IR), SOD, TSH and negatively associated with Matsuda index in obesity with a significant difference (P < 0.05). RBP4 levels in the patients with impaired fasting glucose (IFG), insulin resistance or hyperinsulinemia were significantly higher than the patients without IFG, insulin resistance or hyperinsulinemia (P = 0.035, P = 0.001, and P = 0.007). (2) LSG resulted in significantly decreased FBG, FINS, FCP and HOMA-IR at 3, 6 months after surgery (all P < 0.05). The RBP4 levels were significantly decreased after surgery (all P < 0.05) with no gender difference. (3) The change in RBP4 levels was significantly associated with the change in FINS, FCP, HOMA-IR, and HOMA-β at 6 months and the change in TSH at 3 months after surgery in males (all P < 0.05). The change in RBP4 levels were significantly associated with the change in FINS, FCP, HOMA-IR, HOMA-β, and TCH at 3 months after surgery in females (all P < 0.05).

CONCLUSIONS

Overall, our results interpret the significant correlations between RBP4, glucose-lipid metabolism, oxidative stress and thyroid function in obese patients. Further, the LSG brings a decline in RBP4 levels and that may contribute partly to the improved insulin resistance in obese Chinese patients.

What change in body mass index is associated with improvement in percentage body fat in childhood obesity? A meta-regression

OBJECTIVE

Using meta-regression this paper sets out the minimum change in body mass index-SD score (BMI-SDS) required to improve adiposity as percentage body fat for children and adolescents with obesity.

DESIGN

Meta-regression.

SETTING

Studies were identified as part of a large-scale systematic review of the following electronic databases: AMED, Embase, MEDLINE via OVID, Web of Science and CENTRAL via Cochrane library.

PARTICIPANTS

Individuals aged 4-19 years with a diagnosis of obesity according to defined BMI thresholds.

INTERVENTIONS

Studies of lifestyle treatment interventions that included dietary, physical activity and/or behavioural components with the objective of reducing obesity were included. Interventions of <2 weeks duration and those that involved surgical and/or pharmacological components (eg, bariatric surgery, drug therapy) were excluded.

PRIMARY AND SECONDARY OUTCOME MEASURES

To be included in the review, studies had to report baseline and post-intervention BMI-SDS or change measurements (primary outcome measures) plus one or more of the following markers of metabolic health (secondary outcome measures): adiposity measures other than BMI; blood pressure; glucose; inflammation; insulin sensitivity/resistance; lipid profile; liver function. This paper focuses on adiposity measures only. Further papers in this series will report on other outcome measures.

RESULTS

This paper explores the potential impact of BMI-SDS reduction in terms of change in percentage body fat. Thirty-nine studies reporting change in mean percentage body fat were analysed. Meta-regression demonstrated that reduction of at least 0.6 in mean BMI-SDS ensured a mean reduction of percentage body fat mass, in the sense that the associated 95% prediction interval for change in mean percentage body fat was wholly negative.

CONCLUSIONS

Interventions demonstrating reductions of 0.6 BMI-SDS might be termed successful in reducing adiposity, a key purpose of weight management interventions.

TRIAL REGISTRATION NUMBER

CRD42016025317.

Relationship of NEFA concentrations to RBP4 and to RBP4/retinol in prepubertal children with and without obesity

BACKGROUND

The regulation of adipose tissue metabolism in early childhood obesity is not well understood. Insulin levels are higher and insulin resistance seems to be present in prepubertal children with obesity but, differing from their behavior in adults with obesity, non-esterified fatty acid (NEFA) concentrations are not increased. Retinol-binding protein (RBP)-4 concentration is associated with obesity and insulin resistance conditions, but the means of this relationship remain unclear, and few studies have taken retinol values into account to evaluate it.

OBJECTIVE

To analyze the relationship between RBP4 concentration and lipolytic products in plasma in 141 prepubertal children aged 6 to 8 years, with and without obesity.

METHODS

Plasma glucose, insulin, triacylglycerols, NEFA, glycerol, leptin, RBP4, and retinol were analyzed in obese and in their normal-weight counterparts. Homeostatic model assessment, quantitative insulin sensitivity check index, and fasting glucose to insulin ratio were calculated as indicators of insulin resistance.

RESULTS

Fasted plasma NEFA concentrations were lower in children with obesity than in their normal weight counterparts, despite leptin, insulin resistance indices, RBP4, retinol, and RBP4/retinol (an index of free-RBP4) being higher. NEFA and glycerol concentrations were inversely correlated with RBP4/retinol in children with obesity but not in those without obesity. In normal weight children, total RBP4 correlated negatively with NEFA and glycerol concentrations and positively with insulin and homeostasis model assessment for insulin resistance. These results indicate that a low saturation of RBP4 with retinol, which implies a higher concentration of free-RBP4, may preserve the antilipolytic function of insulin in adipose tissue in children with obesity.

CONCLUSION

Our findings suggest that, in prepubertal children with obesity and insulin resistance, the amount of RBP4/retinol correlates with the antilipolytic response of the adipose tissue to insulin rather than the total RBP4 concentration.

Novel Insights in the Metabolic Syndrome in Childhood and Adolescence

Metabolic syndrome (MetS) is recognized as an escalating major health risk in adults as well as in children and adolescents. Its prevalence ranges from 6 to 39% depending on the applied definition criteria. To date, there is no consensus on a MetS definition for children and adolescents. However, most authors agree on essential components such as glucose intolerance, central obesity, hypertension, and dyslipidemia; each representing a risk for cardiovascular disease. Recently, associations between MetS and non-alcoholic fatty liver disease, hyperuricemia, and sleep disturbances have emerged. Biomarkers like adipocytokines are a subject of current research as they are implicated in the pathogenesis of the MetS. Epigenetics and gestational programming, especially the role of microRNA, comprise a novel, rapidly developing and promising research focus on the topic of MetS. MicroRNAs are increasingly valued for potential roles in the diagnosis, stratification, and therapeutics of MetS. Early detection of risk factors, screening for metabolic disturbances, and the identification of new therapies are major aims to reduce morbidity and mortality related to MetS. Dietary modification and physical activity are currently the only adopted treatment approaches. Pharmacological therapies and bariatric surgery are still contradictory and, therefore, are only recommended in selected high-risk cases.

Effects of insulin resistance on the association between the circulating retinol-binding protein 4 level and clustering of pediatric cardiometabolic risk factors

OBJECTIVES

Retinol-binding protein 4 (RBP4) and insulin resistance (IR) are clinical parameters associated with cardiometabolic diseases. The mediating and modifying roles of IR on children's susceptibility to cardiometabolic disorders are undetermined. This study investigated the mediating and modifying effects of the homeostatic model assessment of IR (HOMA-IR) on the relationship between the serum RBP4 level and clustering of pediatric cardiometabolic risk factors.

METHODS

We assessed the diet, physical activity, cardiometabolic risk factors, and clinical parameters of 272 randomly selected adolescents from a large-scale cross-sectional study (n = 2727). Two HOMA-IRs (HOMA1-IR and HOMA2-IR) were used to evaluate the designated effects.

RESULTS

Levels of serum RBP4 positively correlated with the levels of the 2 HOMA-based-IRs, and HOMA-IR correlated to all components of pediatric metabolic syndrome (MetS), the number of abnormal components, and a body-weight-weighted principal component score extracted from 12 cardiometabolic risk factors. Increased RBP4 levels had positive effects on waist circumference (WC), triglyceride, and the number of abnormal MetS components (0.310 cm, 1.384 μg/dL, and 0.021 item elevations, respectively), and the HOMA-IRs explained 17.7% to 21.9%, 11.8% to 27.6%, and 23.8% to 25.0% of these effects. The association of WC and the number of abnormal MetS components with the serum RBP4 level was enhanced by higher HOMA-IR (β for interaction, 0.13 and 0.01 for HOMA1-IR, and 0.32 and 0.02 for HOMA2-IR, respectively).

CONCLUSIONS

HOMA-IR is associated with the circulating RBP4 level and cardiometabolic risk factors in adolescents. Pediatric HOMA-IR may have mediating and modifying effects on the positive correlations between RBP4 and the clustering of MetS components.

Childhood retinol-binding protein 4 (RBP4) levels predicting the 10-year risk of insulin resistance and metabolic syndrome: the BCAMS study

Background

Elevated retinol-binding protein 4 (RBP4) levels may contribute to the development of metabolic abnormalities, but prospective studies evaluating the association between childhood RBP4 levels and metabolic syndrome (MS) in adulthood are lacking. We investigated whether RBP4 levels during childhood predict cardiometabolic risk at 10-year follow-up.

Methods

The relationships between RBP4 levels, the established adipokines (leptin and adiponectin) and the components of MS were examined in 3445 school-aged children recruited in 2004 for the Beijing Child and Adolescent Metabolic Syndrome study. In 2015, 352 of these individuals completed an in-depth follow-up examination.

Results

Participants with higher childhood RBP4 levels had adverse cardiometabolic profiles at follow-up. Those with incident or persistent MS had higher baseline RBP4 levels than those who never exhibited the elements of MS. Moreover, baseline RBP4 predicted hyperglycemia (OR per SD increase = 1.48, P = 0.009), elevated triglyceride (OR = 1.54, P < 0.001), elevated blood pressures (OR = 1.46, P = 0.015), MS (OR = 1.68, P = 0.002) and insulin resistance (OR = 1.44, P = 0.015) in the 10-year follow-up phase, independent of baseline BMI. Significant improvements were seen for the net reclassification improvement and integrated discrimination index after adding childhood RBP4 levels into the risk models using conventional cardiometabolic risk factors in predicting MS at follow-up (P < 0.05). Leptin and adiponectin demonstrated the expected associations with metabolic disorders.

Conclusions

Childhood RBP4 serves as a risk factor for subsequent development of MS and its components, independent of pediatric obesity. Incorporating childhood RBP4 into conventional cardiometabolic risk assessment models significantly improves the prediction of MS.

Electronic supplementary material

The online version of this article (10.1186/s12933-018-0707-y) contains supplementary material, which is available to authorized users.

Disturbed Vitamin A Metabolism in Non-Alcoholic Fatty Liver Disease (NAFLD)

Vitamin A is required for important physiological processes, including embryogenesis, vision, cell proliferation and differentiation, immune regulation, and glucose and lipid metabolism. Many of vitamin A’s functions are executed through retinoic acids that activate transcriptional networks controlled by retinoic acid receptors (RARs) and retinoid X receptors (RXRs).The liver plays a central role in vitamin A metabolism: (1) it produces bile supporting efficient intestinal absorption of fat-soluble nutrients like vitamin A; (2) it produces retinol binding protein 4 (RBP4) that distributes vitamin A, as retinol, to peripheral tissues; and (3) it harbors the largest body supply of vitamin A, mostly as retinyl esters, in hepatic stellate cells (HSCs). In times of inadequate dietary intake, the liver maintains stable circulating retinol levels of approximately 2 μmol/L, sufficient to provide the body with this vitamin for months. Liver diseases, in particular those leading to fibrosis and cirrhosis, are associated with impaired vitamin A homeostasis and may lead to vitamin A deficiency. Liver injury triggers HSCs to transdifferentiate to myofibroblasts that produce excessive amounts of extracellular matrix, leading to fibrosis. HSCs lose the retinyl ester stores in this process, ultimately leading to vitamin A deficiency. Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome and is a spectrum of conditions ranging from benign hepatic steatosis to non-alcoholic steatohepatitis (NASH); it may progress to cirrhosis and liver cancer. NASH is projected to be the main cause of liver failure in the near future. Retinoic acids are key regulators of glucose and lipid metabolism in the liver and adipose tissue, but it is unknown whether impaired vitamin A homeostasis contributes to or suppresses the development of NAFLD. A genetic variant of patatin-like phospholipase domain-containing 3 (PNPLA3-I148M) is the most prominent heritable factor associated with NAFLD. Interestingly, PNPLA3 harbors retinyl ester hydrolase activity and PNPLA3-I148M is associated with low serum retinol level, but enhanced retinyl esters in the liver of NAFLD patients. Low circulating retinol in NAFLD may therefore not reflect true “vitamin A deficiency”, but rather disturbed vitamin A metabolism. Here, we summarize current knowledge about vitamin A metabolism in NAFLD and its putative role in the progression of liver disease, as well as the therapeutic potential of vitamin A metabolites.

Adipose tissue: an endocrine organ playing a role in metabolic regulation

Adipose tissue is a complex endocrine organ with an intricate role in whole body homeostasis. Beyond storing energy, adipose tissue is fundamental in numerous processes including, but not limited to, metabolism, food intake and immune cell function. Adipokines and cytokines are the signaling factors from adipose tissue. These factors play a role in maintaining health, but are also candidates for pathologies associated with obesity. Indeed excessive adiposity causes dysregulation of these factors which negatively affect health and contribute to numerous obesity-induced co-morbidities. In particular, adipokines are fundamental in regulation of glucose homeostasis and insulin signaling, thus aberrant production of these adipose derived hormones correlates with the development and progression of type 2 diabetes. Therefore, elucidation of adipose regulation is crucial for understanding the pathophysiological basis of obesity and metabolic diseases such as type 2 diabetes. In the present review, we summarize current data on the relation between adipokines and adipose depot derived cytokines in the maintenance of glucose homeostasis. Specifically, physiological and molecular functions of several adipokines are defined with particular focus on interactions within the insulin-signaling pathway and subsequent regulation of glucose uptake in both standard and obesity-induced dysregulated conditions. This same relation will be discussed for cytokines and inflammation as well.

Retinol binding protein 4, obesity, and insulin resistance in adolescents

Background Obesity is a global problem. Even in poor and developing countries, obesity has reached alarming levels. In childhood, obesity may lead to insulin resistance. Retinol binding protein (RBP4), secreted primarily by liver and adipose tissues, was recently proposed as a link between obesity and insulin resistance. The role of RBP4 in pediatric obesity and its relationship with insulin resistance have not been well elucidated.Objective To compare RBP4 levels in obese and lean adolescents and to assess for a relationship between RBP4 levels and insulin resistance. Method This cross-sectional study was conducted in three senior high schools in Padang, West Sumatera, Indonesia. Subjects were adolescents aged 14-18 years, who were obese or normal weight (n=56). We measured subjects’ body mass index (BMI) and serum RBP4 concentrations. Insulin resistance was assessed using the homeostasis model assessment of insulin resistance (HOMA-IR) index.Results Similar RBP4 levels were found in the obese and normoweight groups (P>0.05). Higher RBP4 levels were found in the insulin resistant compared to the non-insulin resistant group, but the difference was not significant (P > 0.05).Conclusion There is no significant difference in mean RBP4 levels in obese adolescents compared to normoweight adolescents. Nor are mean RBP4 levels significantly different between obese adolescents with and without insulin resistance.  

Hepatocytes Are the Principal Source of Circulating RBP4 in Mice

RBP4 is produced mainly by hepatocytes. In type 2 diabetes and obesity, circulating RBP4 is increased and may act systemically to cause insulin resistance and glucose intolerance. Observations that adipocyte RBP4 mRNA increases in parallel with circulating RBP4 in these conditions, whereas liver RBP4 mRNA does not, led to a widely held hypothesis that elevated circulating RBP4 is a direct result of increased production by adipocytes. To test this, we generated mice with hepatocyte-specific deletion of RBP4 (liver RBP4 knockout or LRKO mice). Adipose tissue RBP4 expression and secretion remained intact in LRKO mice and increased as expected in the setting of diet-induced insulin resistance. However, circulating RBP4 was undetectable in LRKO mice. We conclude that adipocyte RBP4 is not a significant source of circulating RBP4, even in the setting of insulin resistance. Adipocyte RBP4, therefore, may have a more important autocrine or paracrine function that is confined within the adipose tissue compartment.

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.

Retinol binding protein 4 and its membrane receptors: a metabolic perspective

Nearly a decade of intense research has passed since the first report linking circulating retinol binding protein 4 (RBP4) to the development of insulin resistance. By now, a variety of underlying mechanisms have been identified; some of them are adherent to the canonical role of this circulating protein, which is to transport and deliver retinol to target tissues, and others that seem rather independent of retinol transport. Despite all these efforts, a consensus in the basic principles of RBP4's metabolic effects has not been reached and some controversy remains. Using this as an opportunity, we here review and discuss current data on RBP4's action on insulin sensitivity and its dependency on retinol homeostasis. We pay special attention to the involvement of RBP4 membrane receptors that were identified during these years, such as 'stimulated by retinoic acid 6' (STRA6), and whose identification added another layer of complexity to RBP4's diverse actions. A better understanding of RBP4's functions might allow its therapeutic exploitations, urgently needed in our period that is defined by an epidemic increase in metabolic diseases such as obesity and type 2 diabetes.

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.

Circulating retinol-binding protein 4 levels in gestational diabetes mellitus: a meta-analysis of observational studies

Retinol-binding protein 4 (RBP4) is a novel adipocyte-derived cytokine playing an important role in the regulation of energy metabolism and insulin sensitivity. Although the association between RBP4 and metabolic dysfunction is well established, studies on the relationship between circulating RBP4 levels and the risk of gestational diabetes mellitus (GDM) have yielded inconclusive results. We performed a meta-analysis to investigate whether women with GDM had higher circulating RBP4 levels than the normglycemic pregnant women. PubMed, Web of Science and EMBASE were searched up to 1 August 2014. A total of 14 studies comprised of 884 women with GDM and 1251 normglycemic pregnant women were included. The overall results suggested that maternal circulating RBP4 levels were significantly higher in GDM than their normal controls (SMD: 0.49 μg/ml, 95% CI: 0.23-0.75 μg/ml, p < 0.001, random effect model). However, stratified results indicated that this significant difference only existed in the second/third trimester and was limited to Asian populations. Furthermore, subgroup analysis according to matched maternal age and BMI still demonstrated that GDM had higher circulating RBP4 levels than the normal controls. Our findings suggested that Asian women with GDM had increased circulating RBP4 levels in their second/third trimester.

Endocrine and Metabolic Effects of Adipose Tissue in Children and Adolescents

Adipose tissue is implicated in many endocrine and metabolic processes. Leptin was among the first identified adipose-secreted factors, which act in an auto-, para- and endocrine manner. Since leptin, many other adipose tissue factors were determined, some primarily secreted from the adipocytes, some from other cells of the adipose tissue.

So-called adipokines are not only involved in obesity and its complications, as are insulin resistance, type 2 diabetes and other components of the metabolic syndrome, but also in growth, reproduction, bone metabolism, immune response, cancer development and many other important biological processes. Research in the field of adipokines has revealed new insights into the physiological and pathophysiologal processes and opened new therapeutic possibilities. In the present article, a special emphasis is devoted to research in children and adolescents.

Application of text mining in the biomedical domain

In recent years the amount of experimental data that is produced in biomedical research and the number of papers that are being published in this field have grown rapidly. In order to keep up to date with developments in their field of interest and to interpret the outcome of experiments in light of all available literature, researchers turn more and more to the use of automated literature mining. As a consequence, text mining tools have evolved considerably in number and quality and nowadays can be used to address a variety of research questions ranging from de novo drug target discovery to enhanced biological interpretation of the results from high throughput experiments. In this paper we introduce the most important techniques that are used for a text mining and give an overview of the text mining tools that are currently being used and the type of problems they are typically applied for.

Adipokines as drug targets in diabetes and underlying disturbances

Diabetes and obesity are worldwide health problems. White fat dynamically participates in hormonal and inflammatory regulation. White adipose tissue is recognized as a multifactorial organ that secretes several adipose-derived factors that have been collectively termed "adipokines." Adipokines are pleiotropic molecules that gather factors such as leptin, adiponectin, visfatin, apelin, vaspin, hepcidin, RBP4, and inflammatory cytokines, including TNF and IL-1β, among others. Multiple roles in metabolic and inflammatory responses have been assigned to these molecules. Several adipokines contribute to the self-styled "low-grade inflammatory state" of obese and insulin-resistant subjects, inducing the accumulation of metabolic anomalies within these individuals, including autoimmune and inflammatory diseases. Thus, adipokines are an interesting drug target to treat autoimmune diseases, obesity, insulin resistance, and adipose tissue inflammation. The aim of this review is to present an overview of the roles of adipokines in different immune and nonimmune cells, which will contribute to diabetes as well as to adipose tissue inflammation and insulin resistance development. We describe how adipokines regulate inflammation in these diseases and their therapeutic implications. We also survey current attempts to exploit adipokines for clinical applications, which hold potential as novel approaches to drug development in several immune-mediated diseases.

Non-traditional adipokines in pediatric HIV-related lipodystrophy: a-FABP as a biomarker of central fat accumulation

BACKGROUND

Lipodystrophy characterized by adipose tissue redistribution and lipid and glucose metabolism abnormalities, is common among HIV-infected adults and children on highly-active-antiretroviral-therapy (HAART). In a previous study of HIV-infected children, we did not detect insulin resistance, despite a high percentage of body fat redistribution abnormalities.

AIM OF THE STUDY

To investigate the non-traditional adipokines Retinol-binding-Protein-4 (RBP4), neutrophil-gelatinase-associated-lipocalin (NGAL), a-Fatty-Acid-Binding-Protein (a-FABP) and YKL-40 in HIV-infected children on highly-active-antiretroviral-therapy and evaluate their possible association to lipodystrophic changes or insulin resistance.

METHODS

Seventeen vertically HIV-infected children (mean age: 12.5 years, mean duration of HAART: 5.2 years) and 20 age- and BMI-matched controls were recruited. The HIV-children were re-evaluated after 12 months. RBP4, NGAL, a-FABP and YKL-40 were assessed at study entry and 12 months later and were correlated to body fat content and insulin resistance.

RESULTS

RBP4 values were similar at study entry and 12 months later in HIV-children and controls and showed no correlation to body fat or insulin resistance. NGAL was lower in HIV children at study entry but normalized after 12 months with no positive correlation to insulin resistance. a-FABP was positively correlated to body fat content, especially to trunk fat, both at initial evaluation and at follow-up in HIV children and, after prolonged highly-active-antiretroviral-therapy, it was also positively correlated to insulin resistance.

CONCLUSIONS

This study is the first one to demonstrate that a-FABP could be a useful marker in unraveling central fat accumulation in HIV-infected children on highly-active-antiretroviral-therapy. Large prospective studies are needed to confirm these results.

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.

Calculating cardiac risk in obese adolescents before and after onset of lifestyle intervention

Prevalence and severity of obesity in adolescents is increasing worldwide. The obesity-associated cardiovascular risk factors (CRF) determine cardiac risk as demonstrated by longitudinal studies. Fat distribution and not overall fat mass determines the cardiac risk, since intra-abdominal adipose tissue is especially related to CRFs. Besides classical CRFs such as hypertension, dyslipidemia and impaired glucose metabolism, a proinflammatory and prothrombotic state in obesity is associated with cardiac risk. Adipocytokines such as adiponectin are related to cardiac risk and may present useful predictors of cardiac mortalities in future. Measurement of the carotid intima-media thickness is a new promising noninvasive marker for early cardiovascular changes including atherosclerosis. The therapy of choice to prevent cardiac events in obesity is lifestyle intervention of obese adolescents. However, in clinical practice, the weight loss in lifestyle interventions is only moderate and drug treatment of CRFs is seldom performed.

Relationship of adipokines (adiponectin, resistin and RBP4) with metabolic syndrome components in pubertal obese children

Aim: To investigate the relationship between serum adiponectin, resistin and RBP4 levels and the components of metabolic syndrome. Patients & methods: Serum adiponectin, resistin and RBP4 levels were detected and analyzed in 148 8–18-year-old Turkish obese pubertal children with/without metabolic syndrome. Results: Adiponectin and resistin concentrations were significantly inversely correlated with BMI standard deviation score, homeostatic model assessment insulin resistance, waist circumference, triglyceride levels and diastolic and systolic blood pressure, and were directly correlated with high-density lipoprotein cholesterol. RBP4 concentrations were directly correlated with homeostatic model assessment insulin resistance, waist circumference, triglyceride levels and diastolic and systolic blood pressure, and inversely correlated with high-density lipoprotein cholesterol. Conclusion: Adiponectin, RBP4 and, in particular, resistin levels may be used as suitable predictive biomarkers of metabolic syndrome.

Gender dimorphic increase in RBP-4 and NGAL in children born after IVF: an epigenetic phenomenon?

BACKGROUND

In vitro fertilisation (IVF) has been widely used during the last decades. Recent studies demonstrated some alterations in IVF children's metabolic profile compared with controls. The recently reported lipocalins retinol-binding protein 4 (RBP-4) and neutrophil gelatinase-associated lipocalin (NGAL), as well as visfatin, which are associated with glucose intolerance and could help in the early detection of metabolic abnormalities, have not been studied in IVF children as yet. We studied the lipocalins RBP-4 and NGAL as well as visfatin in children born after IVF.

SUBJECTS AND METHODS

A total of 100 children born after IVF (47 boys) and 60 controls born after normal conception (30 boys), aged 4-14 year, were studied cross-sectionally. All children had a physical examination, their fasting glucose, insulin, lipid profile, RBP-4, NGAL, and visfatin were determined and their homoeostasis model assessment (HOMA) index was calculated.

RESULTS

Children born after IVF had significantly higher RBP-4 (P = 0·009) and NGAL (P = 0·028) levels than controls. When divided by gender, RBP-4 remained higher in IVF girls (P = 0·002), whereas NGAL was higher in IVF boys (P = 0·021). Linear regression analysis had revealed that the differences are attributed to the IVF procedure per se.

CONCLUSIONS

In our study, IVF children had significantly higher RBP-4 and NGAL levels than controls, suggesting early metabolic derangements that could be attributed to an epigenetic phenomenon. These results are in accordance with our earlier findings of higher blood pressure and triglycerides in IVF children than controls. Further prospective studies in IVF children will determine the natural course of their metabolic profile.

Serum retinol-binding protein 4 is independently associated with pediatric NAFLD and fasting triglyceride level

OBJECTIVES

Nonalcoholic fatty liver disease (NAFLD) is identified as a major liver disease in children. The present study aimed to identify the prevalence and predictors of pediatric NAFLD and the correlation between serum retinol-binding protein 4 (RBP4) levels and metabolic characteristics in children.

METHODS

A total of 748 schoolchildren, ages 6 to 12 years, were enrolled in 2009. The body weight and height were measured in the morning before intake. Laboratory tests included overnight fasting serum lipids, insulin, liver enzymes, and RBP4 levels. Hepatic steatosis was determined by ultrasound in 219 volunteers.

RESULTS

The rates of NAFLD were 3% in the normal-weight, 25% in the overweight, and 76% in the obese children. Twenty (22%) of obese children had abnormal alanine aminotransferase (ALT) levels. In children with NAFLD, younger age and higher body mass index (BMI), insulin/homeostasis model of assessment, and male sex rate were associated with abnormal liver function. Stepwise increments in BMI, insulin, homeostasis model of assessment, and ALT were found in children with normal livers to simple steatosis, and to steatosis with abnormal ALT. Multiple logistic regression analysis confirmed that serum RBP4 levels (P = 0.048), ALT (P = 0.048), and BMI (P < 0.001) were independently predictors of pediatric NAFLD. Moreover, multiple linear regression analysis revealed that only serum triglycerides levels were positively related to RBP4 levels (P < 0.001).

CONCLUSIONS

Higher RBP4 and ALT levels as well as BMI are independently associated with pediatric NAFLD in Taiwan. In addition, an increment in RBP4 levels was positively correlated to hypertriglyceridemia in children.

The association of retinol-binding protein 4 with metabolic syndrome and obesity in adolescents: the effects of gender and sex hormones

OBJECTIVES

Retinol-binding protein 4 (RBP4) has a role in the development of insulin resistance (IR), type 2 diabetes, obesity, and metabolic syndrome among adults. However, data among adolescents are limited, and the effects of gender and sex hormones on RBP4 are not well defined.

MATERIALS/METHODS

A total of 1082 adolescents were enrolled and categorized based on their body mass index. Blood samples were collected, and biochemical characteristics, sex hormones, RBP4 concentrations, and IR were determined.

RESULTS

Testosterone and estradiol were not directly correlated with RBP4 concentrations in both genders. Multivariate regression analysis revealed that fasting plasma glucose (FPG), triglyceride (TG), and testosterone levels were independently associated with RBP4 concentrations in boys; also, there was a trend of increasing RBP4 levels with the severity of obesity.

CONCLUSION

Plasma RBP4 concentrations correlated with obesity and cardiovascular risk factors, predominantly evident in boys. Testosterone, FPG, and TG levels were independent predictors of RBP4 concentrations.

The novel insulin resistance parameters RBP4 and GLP-1 in patients treated with valproic acid: just a sidestep?

Valproic acid (VPA), as one of the most widely prescribed antiepileptic drugs (AED) for many types of epilepsy in adults and children, is associated with weight gain, alteration of adipocytokine homeostasis, insulin resistance and Non-Alcoholic Fatty Liver Disease (NAFLD). Retinol-binding protein 4 (RBP4) and Glucagon-like peptide-1 (GLP-1) are considered as important new targets in modern type 2 diabetes mellitus therapy linked to insulin resistance, NAFLD and visceral obesity acting via peripheral or central mechanisms. We herein demonstrate the lack of an influence of VPA treatment on RBP4 and GLP-1 in otherwise healthy patients. In summary, the absence of any relationship with RBP4 and GLP-1 concentrations does not suggest a role of these novel insulin resistance parameters as potential regulators of glucose and fat metabolism during VPA-therapy.

Serum antioxidant concentrations and metabolic syndrome are associated among U.S. adolescents in recent national surveys

Specific micronutrients, including retinol, retinyl esters, carotenoids [α-carotene, β-carotene (cis+trans), β-cryptoxanthin, lutein+zeaxanthin, and total lycopene], vitamin E, and vitamin C have antiinflammatory and antioxidant effects, properties shown to reduce oxidative stress, a process that accompanies the pathogenesis of many chronic diseases. It is still largely unknown whether they are associated with the occurrence of metabolic syndrome (MetS) in the adolescent U.S. population. MetS was defined by the International Diabetes Federation (IDF) criteria. Other non-MetS outcomes relying on blood measurements were elevated HOMA-IR, C-reactive protein (CRP), and hyperuricemia. We tested associations between serum antioxidants and MetS outcomes among adolescents aged 12-19 y using cross-sectional data from NHANES 2001-2006 (n = 782-4285). IDF MetS prevalence was estimated at 7% among boys and 3% among girls. In adjusted models, adolescents with MetS had consistently lower carotenoid concentrations compared with their counterparts without MetS. Total carotenoids were also inversely related to HOMA-IR and CRP. Vitamin C was inversely related to uric acid level and MetS binary outcome. Retinol+retinyl esters exhibited an inverse relationship with CRP and a positive relationship with uric acid and HOMA-IR as well as MetS binary outcome. Vitamin E had no association with MetS, particularly after controlling for serum cholesterol and TG. In conclusion, among U.S. adolescents, serum carotenoid concentrations were inversely associated with MetS status, HOMA-IR, and CRP, whereas serum vitamin C was inversely related to MetS status and serum uric acid. Vitamin E had no consistent association with MetS, whereas retinol+retinyl esters had a positive relationship with HOMA-IR, uric acid, and MetS, while being inversely related to CRP. These associations need further study.

Insulin resistance and adiposity in relation to serum β-carotene levels

OBJECTIVE

To determine the effects of placebo vs an encapsulated supplement of fruit and vegetable juice concentrate (FVJC) on serum β-carotene levels, insulin resistance, adiposity, and subclinical inflammation in boys.

STUDY DESIGN

Thirty age-matched prepubertal boys (9 lean and 21 overweight (OW); age range, 6-10 years) were studied. All participants received nutrition counseling and were randomized to receive FVJC or placebo capsules for 6 months. Total cholesterol, triglycerides, lipid corrected β-carotene, serum retinol, glucose, insulin, retinol binding protein-4, leptin, adiponectin, leptin-to-adiponectin ratio, high-sensitivity C-reactive protein, and interleukin-6 were measured before and after the 6-month intervention. Homeostasis model assessment-insulin resistance (HOMA-IR), acute insulin response to intravenous glucose, along with abdominal fat mass (dual-energy x-ray absorptiometry) were also determined.

RESULTS

Baseline β-carotene concentrations correlated inversely with HOMA-IR, leptin-to-adiponectin ratio, and abdominal fat mass (P ≤ .01). FVJC intake increased β-carotene concentrations (P ≤ .001) but did not influence retinol or retinol binding protein-4. Retinol insufficiency <1.047 μM was present in 18% of the entire cohort at baseline and in 37% at 6 months. HOMA-IR decreased after supplementation in the OW cohort, when adjusted for percent weight change (P = .014). The percent change in abdominal fat mass increased in the placebo group and decreased in the FVJC group (P = .029).

CONCLUSIONS

A 6-month supplementation with FVJC in the presence of nutritional counseling was associated with an increase in serum β-carotene concentrations and a reduction in adiposity in conjunction with an improvement in insulin resistance in OW boys.

RBP4: a controversial adipokine

Adipose tissue is an endocrine organ secreting biologically active factors called adipokines that act on both local and distant tissues. Adipokines have an important role in the development of obesity-related comorbidities not only in adults but also in children and adolescents. Retinol binding protein 4 (RBP4) is a recently identified adipokine suggested to link obesity with its comorbidities, especially insulin resistance, type 2 diabetes (T2D), and certain components of the metabolic syndrome. However, data, especially resulting from the clinical studies, are conflicting. In this review, we summarize up-to-date knowledge on RBP4's role in obesity, development of insulin resistance, and T2D. Special attention is given to studies on children and adolescents. We also discuss the role of possible confounding factors that should be taken into account when critically evaluating published studies or planning new studies on this exciting adipokine.