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.

Engineering a lysosomal enzyme with a derivative of receptor-binding domain of apoE enables delivery across the blood–brain barrier

“…Studies on the apoE receptor-binding region have been reported to narrow its location to the vicinity of amino acid residues 130 to 150 of mature apoE for the binding to LDLRf (20,21). Several synthetic oligopeptides derived from this region mimic certain aspects of receptor binding or apoE function in vitro and in vivo (22,23).…”

A novel hemoglobin-binding peptide reduces cell-free hemoglobin in murine hemolytic anemia

“…We have developed a novel Hb-binding peptide to further address this issue: Hb-B10. During peptide synthesis, Hb-B10 was covalently linked to a small fragment of ApoE (hE, residues 141-150) that has been shown to facilitate both the uptake of lipoproteins by small peptides and drug transport by liposomes via endocytic clearance through the ubiquitous heparan sulfate proteoglycan-associated pathway (14,47,51). Although modification of any small peptide might affect function, we found that the pharmacokinetic profile and liver localization of hE-Hb-B10 were very similar to previous reports for other hE-conjugated peptides (17,20,40).…”

A Peptide Conjugate of Vitamin E Succinate Targets Breast Cancer Cells with High ErbB2 Expression

“…Supported by our results, we present an intriguing paradigm for cancer therapy because this approach can be used for targeting of divergent molecules to cells overexpressing specific surface receptors. Molecules delivered by this approach include antisense oligodeoxynucleotides, ribozymes, and siRNAs, the targeting of which may be used in treatment of different pathologies without adversely affecting healthy tissue (38)(39)(40)(41)(42). There are reports that describe targeting of cytotoxic drugs to tumor cells encapsulated in carriers, including peptide-coated liposomes, as documented in both in vitro and in vivo models (43,44).…”