Absorptive-mediated endocytosis of cationized albumin and a beta-endorphin-cationized albumin chimeric peptide by isolated brain capillaries. Model system of blood-brain barrier transport.
Cationized albumin (pI greater than 8), unlike native albumin (pI approximately 4), enters cerebrospinal fluid (CSF) rapidly from blood. This suggests that a specific uptake mechanism for cationized albumin may exist at the brain capillary wall, i.e. the blood-brain barrier. Isolated bovine brain capillaries rapidly bound cationized [3H]albumin and approximately 70% of the bound radioactivity was resistant to mild acid wash, which is assumed to represent internalized peptide. Binding was saturable and a Scatchard plot gave a maximal binding capacity (Ro) = 5.5 +/- 0.7 micrograms/mgp (79 +/- 10 pmol/mgp), and a half-saturation constant (KD) = 55 +/- 8 micrograms/ml (0.8 +/- 0.1 microM). The binding of cationized [3H]albumin (pI = 8.5-9) was inhibited by protamine, protamine sulfate, and polylysine (molecular weight = 70,000) with a Ki of approximately 3 micrograms/ml for all three proteins. The use of cationized albumin in directed delivery of peptides through the blood-brain barrier was examined by coupling [3H]beta-endorphin to unlabeled cationized albumin (pI = 8.5-9) using the bifunctional reagent, N-succinimidyl 3-(2-pyridyldithio)proprionate. The [3H]beta-endorphin-cationized albumin chimeric peptide was rapidly bound and endocytosed by isolated bovine brain capillaries, and this was inhibited by unlabeled cationized albumin but not by unconjugated beta-endorphin or native bovine albumin. Cationized albumin provides a new tool for studying absorptive-mediated endocytosis at the brain capillary and may also provide a vehicle for directed drug delivery through the blood-brain barrier.
D000818:Animals; D001345:Autoradiography; D002196:Capillaries / Q000187:drug effects / Q000502:physiology*; D002412:Cations; D002417:Cattle; D002560:Cerebrovascular Circulation; D004705:Endocytosis / Q000187:drug effects; D007457:Iodine Radioisotopes; D007700:Kinetics; D010455:Peptides; D011107:Polylysine / Q000494:pharmacology; D011479:Protamines / Q000494:pharmacology; D011485:Protein Binding; D012710:Serum Albumin, Bovine; D001615:beta-Endorphin
D002412:Cations; D007457:Iodine Radioisotopes; D010455:Peptides; D011479:Protamines; D011107:Polylysine; D012710:Serum Albumin, Bovine; D001615:beta-Endorphin