Vol. 280, Issue 1, 410-415, 1997

Structure-Internalization Relationship for Adsorptive-Mediated Endocytosis of Basic Peptides at the Blood-Brain Barrier¹

Ikumi Tamai, Yoshimichi Sai, Hiroyuki Kobayashi, Makoto Kamata, Tateaki Wakamiya² and Akira Tsuji

Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920 (I.T., Y.S., H.K., A.T.) and Department of Chemistry, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan (M.K., T.W.)

For the purpose of the brain delivery of peptides, the structural specificity of adsorptive-mediated endocytosis at the blood-brain barrier was studied by measuring transport of a newly synthesized basic peptide 001-C8, H-MeTyr-Arg-MeArg-D-Leu-NH(CH₂)₈NH₂, using primary cultured bovine brain capillary endothelial cells. The apparent uptake of [¹²⁵I]001-C8 increased time-dependently and reached a steady-state at 60 min. The steady-state uptake of [¹²⁵I]001-C8 was temperature and concentration dependent and was significantly decreased in the presence of dansylcadaverine, protamine or poly-L-lysine. Uptakes of peptides modified by 1,8-octanediamine, 1,5-pentanediamine, 1,2-ethanediamine or ethylamide and peptides with a free carboxyl terminal were significantly higher than, and similar to, that of [³H]PEG900, respectively. The half-saturation constants and the maximal uptake capacities of these peptides were in the ranges of 0.2 to 134 µM and 1.1 to 408 pmol/mg protein, respectively. These values were correlated with the basicity of the molecules. In conclusion, not the number of constituent amino acids of peptides, but rather the C-terminal structure and the basicity of the molecules are the most important determinants for the uptake by the adsorptive-mediated endocytosis system at the blood brain barrier.