RBP4 (retinol-binding protein 4) is a lipocalin family member that serves as the primary circulating carrier for vitamin A, mediating retinol transport from hepatic stores to peripheral tissues 1. The protein transfers bound retinol to STRA6, facilitating cellular uptake across membranes 2. Beyond its classical transport function, RBP4 functions as an adipokine with pleiotropic metabolic effects 3. Elevated serum RBP4 correlates with insulin resistance and type 2 diabetes development; mechanistically, RBP4 stimulates adipocyte lipolysis and macrophage TNFΞ± production, impairing insulin-mediated suppression of free fatty acid release 4. Circulating RBP4 levels are significantly elevated in gestational diabetes mellitus across all pregnancy trimesters, potentially serving as a biomarker 5. In ocular pathology, macrophage-derived RBP4 promotes pathological neovascularization in age-related macular degeneration and diabetic retinopathy through VEGFR2-dependent endothelial sprouting 6. RBP4 elevation associates with psoriasis and cardiovascular disease; however, evidence suggests potential cardioprotective effects via vasodilation and reduced platelet activation in certain contexts 78. Clinical significance includes diagnostic potential for liver damage and cancer prognosis 9, though RBP4's role in cardiovascular disease remains controversial.