Circulating retinol-binding protein 4 concentrations in patients with coronary artery disease and patients with type 2 diabetes mellitus

Circulating retinol binding protein 4 levels in coronary artery disease: a systematic review and meta-analysis

BACKGROUND

Retinol binding protein 4 (RBP4) has been proposed to play a role in the pathophysiology of coronary artery disease (CAD), but previous findings on the association of RBP4 levels with CAD are inconsistent.

METHODS

A meta-analysis based on observational studies was conducted to evaluate the association between circulating RBP4 levels and CAD. Databases including PubMed, Web of Science, Embase, Google Scholar and ClinicalTrials.gov database were searched for eligible studies published up to 12 July 2021. Standard mean differences (SMDs) with 95% confidence intervals (CIs) were calculated using the inverse variance heterogeneity (IVhet) and random-effects model for data with moderate and high heterogeneity (I² > 30%) and data with low heterogeneity were analysed using a fixed-effects model (I² ≤ 30%). Moreover, a bias-adjusted quality-effects model was generated, and the prediction interval was also calculated under the random-effects model.

RESULTS

Two nested case-control studies, one cohort study and twelve case-control studies with a total of 7111 participants were included. Circulating RBP4 levels in patients with CAD were comparable to those in the controls under the IVhet model (SMD: 0.25, 95% CI: - 0.29-0.79, I²: 96.00%). The quality-effects model produced consistent results. However, the association turned to be significant under the random-effect model (SMD: 0.46, 95% CI: 0.17-0.75, I²: 96.00%), whereas the 95% predictive interval (PI) included null values (95% PI: - 0.82-1.74). Subgroup analyses illustrated a positive relationship between CAD and RBP4 levels in patients with complications (SMD: 1.34, 95% CI: 0.38-2.29, I²: 96.00%). The meta-regression analysis revealed that the mean BMI of patients (P = 0.03) and complication status (P = 0.01) influenced the variation in SMD.

CONCLUSIONS

There was low-quality evidence that patients with CAD exhibited similar circulating RBP4 levels compared with controls, and high inter-study heterogeneity was also observed. Thus, RBP4 might not be a potential risk factor for CAD. Comparisons among different subtypes of RBP4 with larger sample size are needed in the future.

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.

Involvement of RBP4 in hyperinsulinism-induced vascular smooth muscle cell proliferation

Retinol-binding protein 4 (RBP4) is a newly discovered adipocytokine related to insulin resistance (IR). Hyperinsulinemia and IR are the major risk factors for cardiovascular diseases (CVD). The role of RBP4 in CVD has not yet been determined. The present study was designed to analyze the correlation of RBP4 and CVD risk factors and to evaluate the role of RBP4 in proliferation of vascular smooth muscle cells during hyperinsulinemia and the underlying mechanisms. Plasma RBP4 concentration, IR-related indexes, and cardiovascular risk factors were measured from blood samples of hyperinsulinemic rats (HIns) and control SD rats (Cons). The vascular morphology and the expression of ERK1/2, p-ERK1/2 in arterial tissues of rats were assessed. Different concentrations of RBP4 (1, 4 μg/ml) were used as intervention factor during insulin-induced aortic smooth muscle cells (RASMCs) proliferation. The expression of cell growth signaling pathways was assessed to identify the active pathway during this proliferation. Specifically, ERK1/2 inhibitor PD98059 and JAK2 inhibitor AG490 were used to detect it. RBP4 expression was higher in HIns compared with Cons (p < 0.01). Plasma RBP4 concentrations were positively correlated with TG (r = 0.490), hsCRP (r = 0.565), media thickness (r = 0.890), and p-ERK1/2 protein (r = 0.746) (p < 0.05 each). In cultured RASMCs, RBP4 enhanced insulin-induced proliferation of cells and expression of p-ERK1/2 and p-JAK2. Blockade of ERK1/2 signaling pathway inhibited RBP4-induced proliferation of RASMCs, while suppressing JAK2 remains unchanged. These results suggest that plasma RBP4 concentrations were associated with CVD. In addition, RBP4 increases the proliferation of VSMCs induced by hyperinsulinism via activation of MAPK signaling pathway.

Retinol-binding protein 4 as a novel risk factor for cardiovascular disease in patients with coronary artery disease and hyperinsulinemia

BACKGROUND

Retinol-binding protein 4 (RBP4) is an adipokine associated with insulin resistance (IR) and obesity-related metabolic disorders. To evaluate its association with cardiovascular disease, we compared serum RBP4 concentrations in patients with coronary artery disease (CAD) and in controls.

METHODS

Sixty patients with coronary angiography-confirmed CAD, including 30 with CAD and 30 with CAD and hyperinsulinemia (CAD/HIns group), and 29 healthy subjects were enrolled. Serum RBP4, IR indexes and cardiovascular risk factors were assessed in these subjects.

RESULTS

Serum RBP4 concentrations were significantly higher in the CAD/HIns than in the CAD and control groups (P < 0.01 each). RBP4 concentration was significantly associated with cardiovascular risk factors, including body mass index and concentrations of triglycerides, high-density lipoprotein cholesterol, uric acid, high-sensitivity C reactive protein and adiponectin (P < 0.01 each). Two-hour postprandial insulin (β = 0.224), homeostatic model assessment of IR score (β = 0.456) and adiponectin concentration (β = 0.294) were independent factors associated with RBP4 (P < 0.01 each).

CONCLUSIONS

RBP4 concentration is associated with cardiovascular risk factors related to IR and CAD. Circulating RBP4 could be a marker of metabolic complications and atherosclerosis and could be used to assess CAD.

Retinol binding protein 4 promotes hyperinsulinism‑induced proliferation of rat aortic smooth muscle cells

Recent studies have suggested that retinol binding protein 4 (RBP4), an adipocytokine related to insulin resistance (IR), may play an important role in the development of atherosclerosis and cardiovascular diseases (CVD). Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) is one of the most common causes of atherosclerosis. Hyperinsulinism promotes proliferation of VSMCs through the MAPK pathway. However, whether RBP4 is involved in insulin-induced proliferation of VSMCs leading to atherosclerosis remains unclear. In the present study, we evaluated the role of RBP4 and the potential relevance of signaling pathways in this process. Different concentrations of RBP4 (1 and 4 μg/ml) were added to rat aortic smooth muscle cells (RASMCs) during insulin-induced proliferation. The levels of cell growth signaling pathway proteins ERK1/2, p-ERK1/2, JAK2, p-JAK2, STAT3 and p-STAT3 were assessed by western blotting in order to identify the pathway(s) that are activated during insulin-induced proliferation. The specific inhibitors of ERK1/2 (PD98059) and JAK2 (AG490) were used to confirm our findings. Insulin induced proliferation of RASMCs in a concentration- and time-dependent manner, and increased the expression of ERK1/2, p-ERK1/2, JAK2, p-JAK2, STAT3 and p-STAT3 in a time-dependent manner. RBP4 enhanced insulin-induced proliferation of RASMCs and expression of p-ERK1/2 and p-JAK2. RBP4-induced proliferation of RASMCs was reduced by the ERK1/2 inhibitor, while it was unaffected by the JAK2 inhibitor. These results suggest that RBP4 mediates VSMC proliferation induced by insulin via activation of the MAPK pathway, and highlight RBP4 as a modulator of atherosclerosis in hyperinsulinemia, therby enhancing our understanding on a number of unexpected aspects of CVD.