title: An apolipoprotein E-derived peptide mediates uptake of sterically stabilized liposomes into brain capillary endothelial cells.
abstract: A promising strategy to solve the problems of insufficient membrane penetration of drugs and low target specificity is the localization of targeting and uptake-facilitating ligands on the surface of drug-carrier systems. This study investigated the role of a peptide derived from the LDL receptor (LDLr)-binding domain of apolipoprotein E (apoE) in initiating endocytosis in brain capillary endothelial cells. The highly cationic tandem dimer of apoE residues (141-150) was coupled covalently onto poly(ethylene glycol)-derivatized liposomes. Membrane binding and cellular uptake was monitored qualitatively by confocal-laser-scanning microscopy as well as quantitatively using a fluorescence assay. The peptide mediated an efficient, energy-dependent translocation of liposomes across the membrane of brain capillary endothelial cells. Liposomes without surface-located peptides displayed neither membrane accumulation nor cellular uptake. Low peptide affinity to LDLr and internalization of the complex into fibroblasts with up- and down-regulated receptor expression levels, as well as complex translocation into cells incubated with an antibody against the LDLr, pointed to a dominating role of an LDLr-independent transport route. Enzymatic digestion of heparan sulfate proteoglycan (HSPG) with heparinase I and addition of heparin and poly-l-lysin as competitors of HSPG and HSPG ligands, respectively, resulted in a significant loss in liposome internalization. The results suggested that HSPG played a major role in the apoE-peptide-mediated uptake of liposomes into endothelial cells of brain microvessels.
authors.affiliation: Research Institute of Molecular Pharmacology, Robert-Roessle-Strasse 10, D-13125 Berlin, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Sauer
authors.forename: Ildiko R
authors.initials: IR
authors.lastname: Dunay
authors.forename: Karl
authors.initials: K
authors.lastname: Weisgraber
authors.forename: Michael
authors.initials: M
authors.lastname: Bienert
authors.forename: Margitta
authors.initials: M
authors.lastname: Dathe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001057:Apolipoproteins E / Q000737:chemistry* / Q000633:toxicity; D001667:Binding, Competitive; D001692:Biological Transport; D001921:Brain / Q000098:blood supply* / Q000378:metabolism*; D002196:Capillaries / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016503:Drug Delivery Systems / Q000379:methods; D004730:Endothelium, Vascular / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism*; D019812:Heparan Sulfate Proteoglycans / Q000737:chemistry; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008081:Liposomes; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism* / Q000633:toxicity; D011485:Protein Binding; D051381:Rats; D011973:Receptors, LDL / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D013237:Stereoisomerism
chemical_list: D001057:Apolipoproteins E; D019812:Heparan Sulfate Proteoglycans; D007457:Iodine Radioisotopes; D008077:Lipoproteins, LDL; D008081:Liposomes; D010446:Peptide Fragments; D011973:Receptors, LDL