Description
Retinol binding Protein (RBP) is small (21kD) transport protein for Vitamin A which forms a complex with prealbumin in blood.
RBP loses its affinity for prealbumin once the vitamin has been delivered to the target cells. The free RBP molecule is rapidly filtered at the glomerulus and catabolized in the renal tubules after resorption by the proximal tubular cells (like other small molecules e.g. ?2 Microglobulin). In kidney disease with prevailing tubular changes these proteins are not reabsorbed and appear in the urine.
Research has shown that the plasma form of the RBP, RBP4, seems to play a key role in the development of insulin resistance. The fat cell derived peptide RBP4, which contributes to the transport of Vitamin A into the circulatory system for subsequent use, also modulates the glucose homeostasis and impairs the insulin sensitivity / insulin resistance. The elevation of serum RBP4 causes systemic insulin resistance, and the reduction of serum RBP4 improves insulin action.
