Diabetes and retinol-binding protein (RBP4): The study of free and exosomal RBP4 in blood plasma and urine of patients

Abstract

Diabetes is the most prevalent chronic disease worldwide. In type 2 diabetes, target tissues decrease their sensitivity to insulin. Before the onset of type 2 diabetes, insulin resistance begins to grow, and beta cells produce more insulin for a longer time until beta cells become burned out and finally develop into type 2 diabetes. In prediabetes and diabetes patients, the retinol-binding protein (RBP4) concentration is high in the blood plasma. In this study, we sought to observe free RBP4 and exosomal RBP4 in the blood plasma as well as the urine of healthy, prediabetes, and diabetes patients. Three participants with type 2 diabetes mellitus, two participants with prediabetes, and five healthy participants were involved in this research. Blood and urine were collected from each participant, and exosomes from blood plasma and urine were isolated. RBP4 was analyzed using ELISA. The results showed that RBP4 was not only found as free RBP4 but also as exosomal RBP4 in the blood plasma as well as the urine. No previous research reported urinary exosomal RBP4. Interestingly, the concentration of exosomal RBP4 in the blood plasma of diabetes, prediabetes, and healthy participants was inversely proportional to the free RBP4 concentration in diabetes, prediabetes, and healthy participants. The exosomal RBP4 concentration of healthy participants was higher than that of prediabetes and diabetes participants. In conclusion, exosomal RBP4 can be found in urine and blood plasma. The concentration of exosomal RBP4 in diabetic participants is lower than prediabetes and healthy participants.