Correlation of Plasma RBP4-to-Vitamin A Ratio with Severity of Diabetic Retinopathy

Background & Objective: Diabetic retinopathy (DR) is a common microvascular complication of type 2 diabetes mellitus (T2DM) and the leading cause of vision loss in working-age adults. Vitamin A (retinol) has a role in the mechanism of vision process and retinol binding protein-4 (RBP4), is a carrier of vitamin A, and as an adipokine may be associated with increased risk for insulin resistance and DR. This case-control study was aimed to determine and analyze plasma RBP4-to-vitamin A ratio in relation with terms of DR severity. Materials & Methods: In the present analytical cross-sectional study, 51 T2DM patients, aged 48-73 years old, were enrolled from those attending to the Ophthalmology Center of Vali-e Asr Hospital, Zanjan, Iran. Patients were categorized as non-retinopathy diabetic patients (NRDP) without any eye problem, those with mild non-proliferative DR (mild NPDR) (n=12), those with severe non-proliferative diabetic retinopathy (severe NPDR) (n=12), and those with proliferative DR (PDR) (n=12); a control group (n=15) was also considered. Anthropometric parameters, BMI, and WHR were determined and blood sample weas taken from each participant after overnight fasting (12-14h) to measure their biochemical parameters. Serum RBP4 and vitamin A levels were measured via ELISA and C18 reverse-phase HPLC methods, respectively. Results: Plasma RBP4 concentration was significantly higher in three different stages of DR than that of the control group suffering from diabetes (77.0±11.0, 81.7±10.9 and 88.3±11.9 vs. 71.4±12.3, respectively; P=0.004). The ratio of plasma RBP4-to-retinol in DR groups was found to be significantly higher than that in the control group suffering from diabetes (0.21±0.06, 0.27±0.12 and 0.28±0.07 vs. 0.16±0.14, respectively; P=0.001). Conclusion: Higher plasma RBP4-to-vitamin A ratio was related to DR severity. Further experimental studies with larger scales are recommended.