Retinol-binding protein 2 (RBP2): More than just dietary retinoid uptake

Retinol-binding protein 2 (RBP2, also known as cellular retinol-binding protein 2 (CRBP2)) is a member of the fatty acid-binding protein family and has been extensively studied for its role in facilitating dietary vitamin A (retinol) uptake and metabolism within enterocytes of the small intestine. RBP2 is present in highest concentrations in the proximal small intestine where it constitutes approximately 0.1-0.5% of soluble protein. Recent reports have established that RBP2 binds monoacylglycerols (MAGs) with high affinity, including the canonical endocannabinoid 2-arachidonoylglycerol (2-AG). Crystallographic studies reveal that retinol, 2-AG, or other long-chain MAGs alternatively can bind in the retinol-binding pocket of RBP2. It also has been demonstrated recently that Rbp2-deficient mice are more susceptible to developing obesity and associated metabolic phenotypes when exposed to a high fat diet, or as they age when fed a conventional chow diet. When subjected to an oral fat challenge, the Rbp2-deficient mice release into the circulation significantly more, compared to littermate controls, of the intestinal hormone glucose-dependent insulinotropic polypeptide (GIP). These new findings regarding RBP2 structure and actions within the intestine are the focus of this review.

Association between retinol-binding protein 4 concentrations and gestational diabetes mellitus (A1GDM and A2GDM) in different pregnancy and postpartum periods

Background

Gestational diabetes mellitus (GDM) can cause severe adverse effects on fetal and neonatal outcomes. The following study investigates the relationship between retinol-binding protein 4 (RBP4) and GDM in pregnant women with different grades (A1 and A2) and different gestational weeks.

Methods

In this retrospective study, 194 GDM patients (GDM group) and 67 normal glucose tolerance pregnant women (control group) were enrolled from 2014 to 2017. Elbow venous blood samples were collected from all subjects. Enzyme electrode method and enzyme linked immunosorbent assay (ELISA) were used for fasting plasma glucose (FPG) and RBP4/insulin levels (FINS) analysis, respectively.

Results

At middle pregnancy and late stage, FINS, insulin resistance index (HOMA-IR) and RBP4 were all significantly higher in the GDM group compared to control group (P<0.05). Higher HOMA-IR and RBP4 levels, and lower levels of FPG were observed at late stage than those middle pregnancy in the GDM group (P<0.05). Moreover, FINS and RBP4 gradually decreased from middle pregnancy and late stage after delivery in the GDM group. Levels of FINS and RBP4 in postpartum GDM group were higher than those in normal control group (P<0.05). The optimal cut-off value of RBP4 at middle pregnancy diagnostic GDM was 34.84 µg/mL with sensitivity of 79.4% and specificity of 79.1%. The OGTT0h, 2h in A2GDM group was higher than that in A1GDM group, but there was no difference in OGTT1h, age and FINS, RBP4 in both A1GDM and A2GDM group.

Conclusions

RBP4 is closely related to GDM, and its levels increases with the increase of gestational weeks, which may reflect the development of insulin resistance in GDM. RBP4 suggests that the impaired insulin function of GDM in pregnant women is still difficult to recover in the short term after delivery. Compared with OGTT1h, the increase in OGTT0h and 2h levels during middle pregnancy is more helpful for predicting the risk of developing A2GDM at late stage.

Prealbumin and Retinol Binding Proteins Are Not Usable for Nutrition Follow-Up in Pediatric Intensive Care Units

PURPOSE

Feeding children is a problem in pediatric intensive care units (PICU) and it is difficult to know the correct amount. The purpose of this study is to evaluate if prealbumin or retinol binding proteins (RBP) are effective relative to daily enteral nutrition, without being affected by severity of diseases or infections and can be used to follow up nutritional amount.

METHODS

This is a prospective observational study that includes 81 patients admitted to PICU in Akdeniz University with estimated duration >72 hours, age between 1 month and 8 years. Daily calorie and protein intake were calculated and prealbumin, RBP and C-reactive protein (CRP) levels were measured on the first, third, fifth and seventh mornings.

RESULTS

We find moderate correlation between daily calorie intake and prealbumin levels (r=0.432, p<0.001), RBP levels and daily protein intake (r=0.330, p<0.001). When we investigated the relationship between changes of prealbumin, RBP, CRP, calorie and protein intake during intensive care stay, we found that increase of Prealbumin and RBP levels are explained by decrease of CRP levels (r=-0.546 and -0.645, p<0.001) and not with increase of nourishment.

CONCLUSION

Even adjusted for PRISM3, age and CRP, prealbumin and RBP are correlated with last 24 hours' diet. However, it is not convenient to use as a follow up biomarker because increase of their levels is related with decrease of CRP levels.

Renal evaluation in women with preeclampsia

BACKGROUND/AIMS

Preeclampsia (PE) is a cause of glomerulopathy worldwide. Urinary retinol-binding protein (RBP) is a marker of proximal tubular dysfunction, albuminuria is an endothelial injury marker, urine protein:creatinine ratio (PCR) may have a predictive value for renal disease later in life, and, recently, podocyturia has been proposed as a sensitive tool in pregnancy, but it needs to be tested. The aim of this study was to evaluate renal involvement in PE and healthy pregnancy.

METHODS

Case-control study with 39 pregnant women assessed after 20 weeks of gestation (25 in the control group, CG, and 14 in the PE group) by performing urinary tests.

RESULTS

Mean (±SD) age and gestational age of the CG were 26.9 ± 6.4 years and 37.1 ± 5.0 weeks, and of the PE group 26.4 ± 6.9 years and 30.6 ± 5.6 weeks, respectively (p = 0.001). Mean (±SD) urinary RBP (p = 0.017), albuminuria (p = 0.002), and urinary albumin concentration (UAC) ratio (p = 0.006) of the CG were 0.4 ± 0.7 mg/l, 7.3 ± 6.9 mg/l, and 8.2 ± 6.7 mg/g and of the PE group 2.0 ± 4.4 mg/l, 2,267.4 ± 2,130.8 mg/l (p = 0.002), and 3,778.9 ± 4,296.6 mg/g (p = 0.006), respectively. Mean (±SD) urine PCR in the PE group was 6.7 ± 6.1 g/g (p < 0.001). No statistical differences were found between podocyturia in the CG and PE group (p = 0.258).

CONCLUSIONS

Urinary RBP, PCR, albuminuria, and UAC ratio were elevated in the PE group in comparison to the CG. Podocyturia did not predict PE.