Serum concentrations of retinol-binding protein 4 in women with and without gestational diabetes

Increased serum retinol-binding protein-4 levels in pregnant women with and without gestational diabetes mellitus

OBJECTIVE

Retinol-binding protein 4 (RBP4) is thought to be associated with insulin resistance in humans, while pregnancy is normally characterized by progressive insulin resistance. Gestational diabetes (GDM) occurs when pancreatic beta-cell function is unable to compensate for insulin resistance. This study aimed to determine whether or not serum RBP4 levels are elevated in pregnancy, and to explore the relationship between RBP4 levels and insulin resistance during pregnancy.

METHODS

Serum RBP4 was measured at median gestational week 26 in 121 pregnant women, including 63 with GDM (GDM group) and 58 normal, glucose-tolerant pregnant women (P-NGT group), as well as 65 non-pregnant normal, glucose-tolerant women (NP-NGT group). Multiple stepwise regression analysis was used to explore the independent factors of RBP4.

RESULTS

Serum RBP4 levels in the P-NGT and GDM groups were significantly higher than in the NP-NGT group (34.50±9.80 mg/L and 41.64±12.21 mg/L vs 30.64±9.46 mg/L, respectively; P<0.05) after adjusting for age, body mass index (BMI) and blood pressure. Furthermore, RBP4 levels were much higher in the GDM vs P-NGT group. Spearman's correlation analysis showed that serum RBP4 levels were positively correlated with triglycerides (TG), fasting plasma glucose, postprandial 2h plasma glucose and HOMA-IR in pregnancy. Of these, TG and HOMA-IR (r(2)=0.312) were independent factors of serum RBP4.

CONCLUSION

Serum RBP4 levels are significantly increased in pregnancy, independent of age and BMI, and are also considerably higher in pregnant women with GDM than in those with normal glucose tolerance. In addition, serum RBP4 levels appear to be a valuable marker of insulin resistance and dysfunctional lipid metabolism in pregnancy.

Lipolysis - a highly regulated multi-enzyme complex mediates the catabolism of cellular fat stores

Lipolysis is the biochemical pathway responsible for the catabolism of triacylglycerol (TAG) stored in cellular lipid droplets. The hydrolytic cleavage of TAG generates non-esterified fatty acids, which are subsequently used as energy substrates, essential precursors for lipid and membrane synthesis, or mediators in cell signaling processes. Consistent with its central importance in lipid and energy homeostasis, lipolysis occurs in essentially all tissues and cell types, it is most abundant, however, in white and brown adipose tissue. Over the last 5years, important enzymes and regulatory protein factors involved in lipolysis have been identified. These include an essential TAG hydrolase named adipose triglyceride lipase (ATGL) [annotated as patatin-like phospholipase domain-containing protein A2], the ATGL activator comparative gene identification-58 [annotated as α/β hydrolase containing protein 5], and the ATGL inhibitor G0/G1 switch gene 2. Together with the established hormone-sensitive lipase [annotated as lipase E] and monoglyceride lipase, these proteins constitute the basic "lipolytic machinery". Additionally, a large number of hormonal signaling pathways and lipid droplet-associated protein factors regulate substrate access and the activity of the "lipolysome". This review summarizes the current knowledge concerning the enzymes and regulatory processes governing lipolysis of fat stores in adipose and non-adipose tissues. Special emphasis will be given to ATGL, its regulation, and physiological function.

Serum Proteome Pool Changes in Type 2 Diabetic Patients Treated with Anakinra

Introduction

High glucose concentrations induce the production of IL-1β in human pancreatic beta cells leading to impaired insulin secretion, decreased cell proliferation and apoptosis. Blockade of IL-1 signalling with the recombinant human IL-1 receptor antagonist anakinra reduces HbA1c in patients with type 2 diabetes. The aims of the present study were to identify: (1) candidate surrogates for improved glycemia in type 2 diabetic patients following treatment with anakinra, (2) proteins that change serum concentration because of anakinra treatment and (3) candidate biomarkers that may predict improved glycemia in type 2 diabetic subjects treated with anakinra.

Methods

Surface-enhanced laser desorption/ionisation time-of-flight mass spectrometry was used to analyse serum from 67 type 2 diabetic patients who had received either placebo or anakinra for 13 weeks. Immunodepletion with magnetic protein G bead-coupled antibodies were used to identify three proteins and Western blotting confirmed the biomarker concentration pattern of four proteins.

Results

Twelve proteins, including transthyretin (TTR) and transferrin (Tf), were identified as candidate surrogates for improved glycemia. Six proteins, including retinol-binding protein 4 (RPB4) and a protein tentatively identified as modified apolipoprotein-A1 (apo-AI), increased expression as a consequence of anakinra treatment and four proteins were candidate biomarkers that may predict improved glycemia following anakinra treatment. Furthermore, we found increased RBP4 to be associated with improved beta cell secretory function and increased TTR, RBP4 and modified apo-AI (peak at 28,601 Da) to be associated with decreased inflammation.

Conclusions

Anakinra-induced changes in the serum proteome pool associated with a decreased cardiovascular disease risk, reduced inflammation and improved beta cell secretory function.

The effects of adipose tissue and adipocytokines in human pregnancy

During pregnancy, important changes take place in maternal metabolism because of the growing fetus and placental formation. The increase in insulin resistance during pregnancy is paralleled by the progressive increase of maternal adipose tissue deposition. This review examines the topography of fat mass deposition during pregnancy in relation to factors such as parity and maternal age that might affect this deposition. We also examine adipose tissue markers, such as pregravid weight and weight gain during pregnancy, and their effect on fetal growth and pregnancy outcomes. In addition, this review studies the possible effects of cytokines that are produced by adipose tissue and the placenta on maternal metabolism and its complications. Finally, we also consider the possible role of maternal adipocytokines and fetal adipocytokines on fetal growth.

Retinol-binding protein 4: a novel adipokine implicated in the genesis of LGA in the absence of gestational diabetes mellitus

OBJECTIVE

Adipokines (cytokines produced by adipose tissue) play a major role in the control of body weight and energy distribution. Retinol-binding protein 4 (RBP4), only recently recognized as an adipokine, has been proposed to modulate systemic insulin sensitivity. The goal of this study was to determine whether there is an association between maternal plasma RBP4 concentration and the birth of a large-for-gestational-age (LGA) newborn in women with and without gestational diabetes mellitus (GDM).

STUDY DESIGN

This cross-sectional study included pregnant women at term in the following groups: 1) normal pregnancy with an appropriate-for-gestational-age (AGA) neonate (n=64); 2) normal pregnancy with an LGA neonate (n=44); 3) GDM with an AGA neonate (n=55); and 4) GDM with an LGA neonate (n=42). Maternal plasma RBP4 concentration was determined by ELISA. Parametric and non-parametric statistics were used for analyses.

RESULTS

1) Patients with GDM, either with AGA or LGA neonates, had a higher median plasma concentration of RBP4 than normal pregnant women who delivered an AGA neonate (P=0.01 and P=0.008, respectively); 2) mothers without GDM but with LGA neonates had a higher median plasma concentration of RBP4 than those with normal pregnancy and AGA newborns (P=0.001); 3) these findings remained significant after adjusting for maternal age, body mass index and gestational age at blood sampling.

CONCLUSION

GDM is characterized by alterations in maternal circulating RBP4 concentrations akin to those of Type 2 diabetes mellitus. RBP4 concentrations in maternal plasma may play a role in accelerated fetal growth in the absence of overt carbohydrate intolerance.

All-trans retinoic acid lowers serum retinol-binding protein 4 concentrations and increases insulin sensitivity in diabetic mice

Recent investigations have demonstrated that elevated serum retinol-binding protein 4 (RBP4) secreted from adipose tissue plays a role in the development of systemic insulin resistance, and lowering RBP4 improves insulin sensitivity. These observations provide a rationale for the development of new antidiabetic agents aimed at reducing serum RBP4 concentrations. In this study, we sought to determine whether retinoic acid (RA) administration decreases serum RBP4 and suppresses insulin resistance in diabetic ob/ob mice. All-trans RA [100 mug/(moused) in corn oil] was administered by stomach intubation to a group of ob/ob mice, with the control group receiving the vehicle for 16 d. Body weight and food intake were monitored. Glucose and insulin tolerance tests were performed. We quantified serum RBP4 and retinol by Western blotting and HPLC, respectively. RA treatment reduced body weight (P < 0.05), basal serum glucose (P < 0.001), serum retinol (P < 0.01), and RBP4 (P < 0.05). It improved insulin sensitivity and decreased the retinol:RBP4 ratio (P < 0.05). These studies suggest that RA is an effective antidiabetic agent that could be considered in the treatment of type 2 diabetes.

Serum retinol-binding protein 4 (RBP4) and retinol in a cohort of borderline obese women with and without gestational diabetes

OBJECTIVES

To evaluate whether serum RBP4 correlates with gestational diabetes mellitus (GDM) in a cohort of borderline obese (BMI>30) pregnant women.

DESIGN AND METHODS

Serum RBP4 and retinol were measured in pregnant women with (n=12) and without (n=10) GDM.

RESULTS

RBP4, retinol and RBP4:retinol molar ratio were not different between the groups and were not associated with markers of insulin resistance.

CONCLUSIONS

GDM is not associated with RBP4 or retinol among borderline obese pregnant women.

Alterations in serum adipocyte fatty acid binding protein and retinol binding protein-4 in normal pregnancy and preeclampsia

BACKGROUND

Preeclampsia, a pregnancy-specific complication occurring in the second half of human pregnancy and one of the leading causes for perinatal mortality and morbidity, is characterized by the onset of hypertension and proteinuria. We measured circulating adipocyte fatty acid binding protein (AFABP) and retinol binding protein-4 (RBP-4) in patients with preeclampsia.

METHODS

Twenty-seven healthy non-pregnant women, 27 healthy pregnant women at third trimester and 26 women with preeclampsia were recruited and blood samples were taken. Concentrations of serum AFABP and RBP-4 were measured with ELISA.

RESULTS

There were significant differences in serum AFABP (median: 0.99, 0.93 and 1.81ng/ml, respectively, P<0.001) and RBP-4 (mean: 3.16, 2.65 and 4.27ng/ml, respectively, P=0.022) among non-pregnancy, normal pregnancy and preeclampsia. Serum AFABP was significantly higher in preeclampsia than non-pregnancy (P<0.001) and normal pregnancy (P=0.001). Serum RBP-4 was significantly higher in preeclampsia than normal pregnancy (P=0.007) but not non-pregnancy (P=0.061). There were no significant differences in serum RBP-4 and AFABP between non-pregnancy and normal pregnancy. Serum RBP-4 was significantly higher in severe than mild preeclampsia (mean: 5.15 vs 2.84ng/ml, P=0.046). There was no significant difference in serum AFABP between mild and severe preeclampsia.

CONCLUSION

Increased circulating AFABP and RBP-4 concentrations were demonstrated, suggesting it be an important pathophysiology of preeclampsia.

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

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

CONCLUSION

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

Retinol-binding protein 4 is associated with impaired glucose tolerance but not with whole body or hepatic insulin resistance in Mexican Americans

Retinol-binding protein-4 (RBP4), a novel protein secreted mainly by adipose tissue, has been associated with insulin resistance in obese subjects and in individuals with type 2 diabetes mellitus (T2DM). We examined the relationship between plasma RBP4 levels, expression of RBP4 in skeletal muscle and adipose tissue, and insulin sensitivity in Mexican Americans with varying degrees of obesity and glucose tolerance. Seventy-two subjects [16 lean normal-glucose-tolerant (NGT), 17 obese NGT, and 39 subjects with impaired fasting glucose/impaired glucose tolerance/T2DM] received an oral glucose tolerance test (OGTT) and euglycemic-hyperinsulinemic clamp. Insulin secretion was measured as insulinogenic index during OGTT. In a subset of subjects, hepatic glucose production was measured by 3-[3H]glucose infusion, biopsies of the vastus lateralis muscle and subcutaneous adipose tissue were obtained under basal conditions, and quantitative RT-PCR was performed to measure the RBP4 mRNA gene expression. Plasma RBP4 was significantly elevated in impaired glucose tolerance/T2DM compared with NGT lean or obese subjects. Plasma RBP4 levels correlated with 2-h glucose, triglycerides, and hemoglobin A1c. There was no association between RBP4 levels and whole body insulin sensitivity measured with either the euglycemic insulin clamp or OGTT, basal hepatic glucose production rates, and the hepatic insulin resistance index. There was no correlation between plasma RBP4 levels and indexes of insulin secretion. RBP4 mRNA expression in skeletal muscle was similar in lean NGT subjects, obese NGT subjects, and T2DM subjects. There was no difference in RBP4 mRNA expression in adipose tissue between lean and obese NGT subjects or between NGT and T2DM individuals. Plasma RBP4 levels are elevated in T2DM and associated with impaired glucose tolerance, but not associated with obesity or insulin resistance or impaired insulin secretion in Mexican Americans.

Preliminary report: Serum levels of retinol-binding protein 4 in preeclampsia

The objective of the study was to investigate serum levels of the adipokine retinol-binding protein 4 (RBP4) in patients with preeclampsia (PE) as compared with healthy controls of similar gestational age. Retinol-binding protein 4 serum levels were quantified by enzyme-linked immunosorbent assay in control (n = 20) and PE (n = 16) patients. Mean maternal RBP4 concentrations were not significantly different in PE (24.5 mg/L) as compared with controls (22.3 mg/L). Furthermore, RBP4 did not correlate to clinical and biochemical measures of pregnancy outcome, renal function, glucose, and lipid metabolism, as well as inflammation. Our results do not support a role of RBP4 in the pathogenesis of PE.