Association of retinol-binding protein 4 with metabolic syndrome in first-degree relatives of type 2 diabetic patients

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.

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.

Role of Adipose Tissue in Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs), chronic inflammatory disorders affecting the gastrointestinal tract, include Crohn's disease and ulcerative colitis. There are increasing clinical and experimental data showing that obesity, especially visceral adiposity, plays a substantial role in the pathogenesis of IBD. Obesity seems to be an important risk factor also for IBD disease severity and clinical outcomes. Visceral adipose tissue is an active multifunctional metabolic organ involved in lipid storage and immunological and endocrine activity. Bowel inflammation penetrates the surrounding adipose tissue along the mesentery. Mesenteric fat serves as a barrier to inflammation and controls immune responses to the translocation of gut bacteria. At the same time, mesenteric adipose tissue may be the principal source of cytokines and adipokines responsible for inflammatory processes associated with IBD. This review is particularly focusing on the potential role of adipokines in IBD pathogenesis and their possible use as promising therapeutic targets.

Negative Correlation Between Vitamin A and Positive Correlation Between Vitamin E and Inflammation Among Healthy Adults in Korea: Based on the Korea National Health and Nutrition Examination Survey (KNHANES) 2016-2018 7th Edition

PURPOSE

Vitamins exert its effect through different isoforms. The isoform conversion phases involved are affected outside factors. Here, we investigated the correlation between serum retinol, α-tocopherol, and serum inflammatory markers using stratified data acquired from 2016 to 2018 Korea National Health and Nutrition Examination Survey (KNHANES).

MATERIALS AND METHODS

This study was based on data acquired from the 7th edition (2016-2018) of the Korea National Health and Nutrition Examination Survey, consisting of survey data on smoking and alcohol drinking, serum retinol level, serum α-tocopherol level, high-sensitivity C-reactive protein (hs-CRP), and baseline characteristics.

RESULTS

There was a negative correlation between serum retinol and hs-CRP in alcohol drinking men. There was a negative correlation between serum retinol and hs-CRP in the alcohol-nonsmoking female group. There was a positive correlation between α-tocopherol and hs-CRP in the nonsmoking and alcohol-drinking group. There was a positive correlation between α-tocopherol and hs-CRP in the nonsmoking and alcohol-drinking female group. There was positive correlation between vitamin A and E and metabolic syndrome. The lowest vitamin A level was observed in subjects with all five metabolic syndrome criteria matched.

CONCLUSION

There was a negative correlation between serum retinol and hs-CRP and positive correlation between α-tocopherol and hs-CRP. Absorption and secretion of serum retinol are affected by inflammation status through retinol-binding protein. Alcohol acts as a competitive inhibitor of vitamin A oxidation through alcohol dehydrogenase and ALDH activity. Smoking causes inflammation and induces reactive oxygen species scavenging system and increases cytochrome p450 levels. These factors may have contributed to the observed findings. Metabolic syndrome subjects increased as the levels of vitamin A and vitamin E increased. Since obesity is inversely related to ALDH activity, we postulate that patients with metabolic syndrome may also have low ALDH activity, especially in the Asian population. Future studies are warranted to study the efficacy of ALDH or ALDH inducers in patients with vitamin A deficiency or metabolic syndrome.

The Role of Adipose Tissue in the Pathogenesis and Therapeutic Outcomes of Inflammatory Bowel Disease

Though historically regarded as an inert energy store, adipose tissue is a complex endocrine organ, which is increasingly implicated in the pathogenesis of inflammatory bowel disease (IBD). Accumulating evidence points to visceral adipose tissue and specifically to its mesenteric component, or “creeping fat” as impacting on the disease course through its immunomodulatory properties. On the one hand, mesenteric fat acts as a physical barrier to inflammation and is involved in controlling host immune response to translocation of gut bacteria. On the other hand, however, there exists a strong link between visceral fat and complicated course of the disease with unfavorable therapeutic outcomes. Furthermore, “creeping fat” appears to play different roles in different IBD phenotypes, with the greatest pathogenetic contribution probably to an ileal form of Crohn’s disease. In this review, we summarize and discuss the existing literature on the subject and identify high-priority areas for future research. It may be that a better understanding of the role of mesenteric fat in IBD will determine new therapeutic targets and translate into improved clinical outcomes.

Correlates of resistin and retinol-binding protein 4 in metabolic syndrome patients with and without prediabetes

Background Resistin and retinol-binding protein 4 (RBP4) can work in an intricate in metabolic syndrome (MetS) and prediabetes (PreDM) molecular crosstalk. Materials and methods Resistin and RBP4 were evaluated using colorimetric enzyme-linked immunosorbent assays (ELISAs) in 29 normoglycemic MetS, 30 newly diagnosed drug naïve MetS-preDM patients and 29 lean and normoglycemic controls. Results In this cross-sectional design; the gradual increase in resistin levels (ng/mL), though not ascribed any statistically marked variation, was appreciable in both normoglycemic and preDM MetS groups vs. controls. RBP4 mean circulating levels (ng/mL) in both MetS groups (non-diabetic and preDM) invariably lacked discrepancy vs. controls. Except for fasting plasma glucose (FPG) and A1C; no further intergroup discrepancy could be identified between MetS arms. Adiposity indices: body mass index (BMI), body adiposity index (BAI) and lipid accumulation product (LAP) (but not conicity index) were substantially higher in both MetS (non- and preDM) groups vs. those of controls. Likewise, the atherogenicity index of plasma [but not non-high-density lipoprotein-cholesterol (nonHDL-C)/HDL-C ratio, or triglyceride (TG)/HDL-C ratio] or any of the hematological indices [red cell distribution width (RDW-CV %), monocyte to lymphocyte ratio (MLR), neutrophil to lymphocyte ratio (NLR) and platelet (PLT) to lymphocyte ratios (PLR)] had any marked variations as compared to controls. Low-density lipoprotein-cholesterol (LDL-C)/HDL-C ratio,visceral adiposity index, and waist circumference (WC)/hip circumference (HC) ratio were noticeably greater in MetS-preDM vs. normoglycemic MetS recruits. Neither biomarker could relate to each other, or any of the atherogenecity indices in 59 MetS participants (non- and preDM). Unlike RBP4; resistin associated proportionally with each of HC, BAI, MLR and NLR. Conclusions Both biomarkers can be putative indicator/surrogate prognostic tools for the prediction/prevention and pharmacotherapy of MetS anomalies.

Effect of diabetes mellitus type 2 on salivary glucose, immunoglobulin A, total protein, and amylase levels in adults: A systematic review and meta-analysis of case-control studies

Background:

Saliva is a fluid with the complex compound which can be used as diagnostic markers for type 2 diabetes (T2D). This meta-analysis evaluated salivary glucose, immunoglobulin A (IgA), total protein, and amylase levels in adult T2D compared with the controls as well as the correlation of salivary glucose levels with serum glucose and hemoglobin A1C (HbA1c) levels in both groups.

Materials and Methods:

Web of Science, Scopus, PubMed, and Cochrane Library databases were searched up to July 2017. A random-effects analysis was performed using the mean difference (MD) and 95% confidence intervals. The search terms were “T2D, IgA, amylase, total protein, or glucose” combination with “saliva.” The studied variables were the sample size, the percentage of male, the mean age, the condition of saliva sampling, and the salivary levels of mentioned factors.

Results:

A total of 25 studies were included in this meta-analysis with 1432 and 900 diabetic patients and healthy controls, respectively. MD of salivary glucose level in patients with T2D, compared with the healthy controls, in fasting and nonfasting conditions were 6.23 mg/dL (P = 0.0002) and 6.70 mg/dL (P < 0.00001), respectively. Furthermore, the fasting salivary total protein in the patients was significantly higher than the controls (MD = 167.96 mg/dL; P = 0.03). Non-fasting salivary amylase and secretory IgA levels were significantly lower in the patients (MD = −48.61 IU/mL; P < 0.00001) than in the controls (MD = −9.42 IU/mL; P = 0.0006), respectively. The pooled estimate showed a significant correlation between salivary and serum glucose in the patients (r = 0.765; P < 0.001) and the controls (r = 0.646; P < 0.001) and between salivary glucose and serum glycated hemoglobin in the patients (r = 0.721; P < 0.001).

Conclusion:

Measurement of these salivary factors can be helpful for diagnostic and monitoring purposes of T2D. In addition, salivary glucose as a diagnostic tool can evaluate serum glucose and HbA1c levels in the diabetic patients.

Retinol-binding protein 4 versus albuminuria as predictors of estimated glomerular filtration rate decline in patients with type 2 diabetes

Background

Since the increase in some tubular damage biomarkers can be observed at the early stage of diabetic nephropathy, even in the absence of albuminuria, we aimed to investigate if urinary albumin is superior than tubular damage marker, such as serum retinol-binding protein 4 (RBP4), in predicting renal function decline (defined as estimated glomerular filtration rate [eGFR] <60 mL/min/1.73 m²) in the cohort of patients with type 2 diabetes mellitus (T2D).

Materials and Methods

A total of 106 sedentary T2D patients (mean [± standard deviation] age 64.9 [±6.6] years) were included in this cross-sectional study. Anthropometric and biochemical parameters (fasting glucose, glycated hemoglobin [HbA1c], lipid parameters, creatinine, RBP4, high sensitivity C-reactive protein [hsCRP], urinary albumin excretion [UAE]), as well as blood pressure were obtained.

Results

HsCRP (odds ratio [OR] =0.754, 95% confidence interval [CI] (0.603-0.942), P = 0.013) and RBP4 (OR = 0.873, 95% CI [0.824-0.926], P < 0.001) were independent predictors of eGFR decline. Moreover, although RBP4 and UAE as single diagnostic parameters of renal impairment showed excellent clinical accuracy (area under the curve [AUC] = 0.900 and AUC = 0.940, respectively), the Model which included body mass index, HbA1c, triglycerides, hsCRP, and RBP4 showed statistically same accuracy as UAE, when UAE was used as a single parameter (AUC = 0.932 vs. AUC = 0.940, respectively; P for AUC difference = 0.759). As well, the Model had higher sensitivity and specificity (92% and 90%, respectively) than single predictors, RBP4, and UAE.

Conclusion

Although serum RBP4 showed excellent clinical accuracy, just like UAE, a combination of markers of tubular damage, inflammation, and traditional markers has the higher sensitivity and specificity than UAE alone for prediction renal impairment in patients with T2D.

Involvement of RBP4 in Diabetic Atherosclerosis and the Role of Vitamin D Intervention

The purposes of this study were to evaluate the expression of retinol-binding protein 4 (RBP4) in diabetic rats with atherosclerosis and to investigate the role of vitamin D intervention. Male Wistar rats were randomly divided into 4 groups, including the control group (NC), the diabetic rats (DM1), the untreated diabetic atherosclerosis rats (DM2), and the vitamin D-treated diabetic atherosclerosis rats (DM3). The levels of serum and adipose RBP4, fasting insulin (FINS), fasting plasma glucose (FPG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-c), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c), 25-hydroxyvitamin D [25(OH)D], C-reactive protein (CRP), and systolic blood pressure (SBP) were measured. Homeostasis model assessment of insulin resistance (HOMA-IR), homeostasis model assessment β-cell function index (HOMA-β), and atherogenic indexes (AI) were calculated. Compared with group NC, the levels of RBP4, TG, LDL-c, FPG, FINS, CRP, AI1, AI2, SBP, and HOMA-IR increased, while the levels of HDL-c, 25(OH)D, and HOMA-β decreased in groups DM1 and DM2. After 8 weeks of vitamin D supplementation in group DM3, the levels of 25(OH)D and HOMA-β increased and the levels of LDL-c, TC, HOMA-IR, FINS, CRP, RBP4, AI1, AI2, and SBP decreased significantly when compared with group DM2 (P < 0.05); Pearson analysis showed that serum RBP4 was positively correlated with TG, FINS, HOMA-IR, SBP, CRP, and AI and negatively correlated with 25(OH)D. In addition, multivariable logistic regression analysis showed that serum RBP4, SBP, and HDL-c were predictors for the presence of diabetic atherosclerosis. These findings suggested that RBP4 could involve in the improvement of diabetic atherosclerosis; vitamin D had the ability to decrease the level of RBP4 and eventually played an important role in preventing atherosclerosis in diabetes.

Development of a peptide-modified siRNA nanocomplex for hepatic stellate cells

Insulin-like growth factor 2 receptor (IGF2R) is overexpressed in activated hepatic stellate cells (HSCs) and therefore can be utilized for HSC-specific drug delivery. We recently discovered an IGF2R-specific peptide using a novel biopanning. Here, we adopted biotin-conjugated IGF2R-specific peptide, cholesterol, and vitamin A as the targeting ligands for the neutravidin-based siRNA nanocomplex to deliver PCBP2 siRNA, a potentially antifibrotic agent, to HSCs. Compared to vitamin A and cholesterol, the IGF2R-specific peptide exhibited the highest targeting effect to human LX-2 HSC, rat HSC-T6 cell line, and activated primary rat HSCs. Accordingly, the IGF2R-specific peptide coupled nanocomplex demonstrated higher silencing activity of PCBP2 and better inhibition on the migration of activated HSCs. Compared to free siRNA and the nanocomplexes coupled with vitamin A and cholesterol, the IGF2R-specific peptide coupled nanocomplex showed the highest uptake in the liver and lowest uptake in the lung and kidney of the rats with CCl₄-induced liver fibrosis.