D-[Ala1]-peptide T-amide is transported from blood to brain by a saturable system

It is becoming increasingly evident that peptides can cross the blood-brain barrier. The entry into the central nervous system of a commercially available analog of Peptide T, an octapeptide derived from the human immunodeficiency virus envelope glycoprotein 120, was studied in several experiments. It was found that 125I-Peptide T analog given intravenously in the periphery entered the brain in an intact form, as confirmed by HPLC, to a greater extent than did the labeled albumin control. This entry occurred despite the very low lipid solubility, measured by the octanol/buffer partition coefficient, for the iodinated analog. The rate of entry was decreased by unlabeled Peptide T analog, but not by iodo-tyrosine. Saturable transport out of the brain was not observed after intraventricular administration. Thus, results with 125I-Peptide T analog indicate that saturable systems can transport peptides from the blood into the central nervous system.