COMPARISON OF THE PROPERTIES AND CONCENTRATIONS OF THE ISOFORMS OF RETINOL-BINDING PROTEIN IN ANIMALS AND HUMAN-BEINGS

We used size-exclusion high-performance liquid chromatography (HPLC) t o investigate the properties of the 2 isoforms of vitamin A-containing (holo) retinol-binding protein (RBP) in animals: the form that is bou nd to transthyretin (holo-TTR-RBP), and the form that does not bind to TTR (holo-free RBP). We also used radial immunodiffusion to measure i mmunologically active RBP (apo + holo RBP). We compared the isoforms o f RBP in animals with those of human beings to determine which animal is the best model of human RBP. Size-exclusion HPLC detected holo-free and holo-TTR-RBP in every animal species studied. Apparent concentrat ion of holo-TTR-RBP varied among species: that of rabbits and dogs > > that of apes, sheep, goats, monkeys, rhinoceroses, felids, rats, huma n beings, and deer > that of pigs, zebra, and bison > that of penguins . Dogs have unusual RBP chromatograms; they have high concentration of RBP, but also appear to transport much of their vitamin A on proteins other than RBP. Human RBP antibody preparations could detect apo + ho lo RBP immunologic activity only in apes, monkeys, and felids. Apes an d monkeys appeared to have complete cross-reactivity to human RBP anti bodies. Felids may have substantial, but partial, cross-reactivity. Ap es and monkeys appear to be the most relevant animal models for study of human RBP transport. However, there is a need for less-expensive mo dels. Further research is needed, but in the interim, rats or sheep ma y be satisfactory for some purposes.