RBP4 and obesity due to melanocortin 4 receptor deficiency: Adipocyte-derived proteins including leptin, adiponectin, visfatin, and omentin possess antidiabetic activity and some proteins are pro-hyperglycemic such as resistin, inflammatory cytokines, and retinol-binding protein 4 (RBP4) [37,38], which are involved in the pathophysiology of obesity and diabetes.