The Metabolic Role of Retinol Binding Protein 4: An Update

Retinol binding protein 4 (RBP4) is regarded as a novel cardiometabolic risk factor, which is secreted mainly by the hepatocytes and also by the adipose tissue. RBP4 has been shown to induce insulin resistance, and plasma RBP4 values are increased in type 2 diabetes mellitus, obesity, metabolic syndrome, and cardiovascular disease. Moreover, it has been found that circulating RBP4 decreases during medical interventions that result in amelioration of the metabolic profile, such as diet, exercise, oral antidiabetic drugs, and hypolipidemic agents. However, only few of the RBP4-related studies have investigated whether RBP4 constitutes a causal factor of the above-mentioned metabolic conditions. Importantly, circulating RBP4 is influenced by some nonmetabolic conditions, such as renal failure, acute illness, injury, and liver failure. Thus, further studies investigating the metabolic roles of RBP4 should be carefully planned, taking into account the effects of nonmetabolic conditions on circulating RBP4.