Investigation of interaction of cationic amphiphiles with model membranes and their application in drug delivery
This thesis describes an experimental investigation to determine the interactions between novel cationic and/or amphiphilic peptides, and model bacterial and mammalian membranes (i.e. lipid bilayer vesicles or liposomes). Calorimetric, spectroscopic, and electron microscopy techniques were used to examine the effects of peptide-membrane association on membrane phase behavior, membrane permeabilization, and membrane structure, as well as the ability to form unique peptide-lipid self-assemblies. Biophysical studies were compared to in vitro studies to gain insight into the cellular uptake mechanism. The peptides examined include low molecular weight, water-soluble cationic tripodal linear peptide analogs (LPAs; Arg-Cn-Arg-C n-Lys) and low molecular weight, water-insoluble cationic peptide amphiphiles (PAs; Lys(Cn)-Arg-Lys(C n)). The hydrophilic/hydrophobic balance of the peptides, which is a key factor governing membrane association and self-assembly, was adjusted by varying the alkyl length linking amino acid residues (LPAs; C n where n = 4, 7, or 11) or the electrolyte concentration (PAs; Cn where n = 16). ^ For short LPAs (C4 and C7), membrane association was driven by electrostatic interactions between the amino acid residues and lipid headgroups. This led to membrane expansion and lipid phase separation, but did not lead to membrane permeabilization or vesicle destabilization. In contrast, for LPA-C11 membrane association was driven by hydrophobic interactions. Significant membrane permeabilization was observed in both gel and fluid membrane phases, and vesicles became unstable and ruptured. In vitro studies showed that cellular uptake was non-endocytic and driven primarily by hydrophobicity. ^ PAs contained acyl tails, similar to surfactants or lipids, and were expected to have considerably different solution behavior that the LPAs despite the similarity in amino acid sequence. PA self-assembly and stability in water was found to be dependent upon lipid and electrolyte concentration. Under all conditions bilayer structures were formed and these included spherical vesicles, cylindrical vesicles, and sheets depending on the PA to lipid ratio. Hence, the PA behaved like a lipid. Despite being a cationic peptide, the PA assemblies carried a negative charge due to phosphate binding. This charge acted to stabilize the assemblies. When the PA to lipid ratio was reduced the assemblies aggregated and became unstable. In contrast to the LPAs, the PA did not destabilize or rupture the membrane. ^ Finally, the knowledge gained from LPA and PA studies was applied to the formation and characterization of immunoliposomes designed for the in vivo delivery of vaccines based on epitope derived peptides. The liposomes were stable and the little aggregation that was observed was attributed to the binding of charged peptides binding. Peptides from the pool that were hydrophobic and/or had a net zero charge, and hence were associated with the liposome membrane, exhibited the greatest T-cell response.^
Health Sciences, Pharmacology|Chemistry, Molecular|Engineering, Biomedical
"Investigation of interaction of cationic amphiphiles with model membranes and their application in drug delivery"
Dissertations and Master's Theses (Campus Access).