title: Interactions of complementary PEGylated liposomes and characterization of the resulting aggregates.
abstract: The interaction of complementary liposomes bearing both recognizable and protective ligands at their external surface has been investigated. Aggregation of hydrogenated phosphatidyl choline/cholesterol (2:1 molar ratio) based liposomes was mediated by the molecular recognition of the complementary phosphate and guanidinium groups incorporated in separate unilamellar liposomes. The phosphate group was incorporated in the bilayer employing dihexadecyl phosphate, while the guanidinium moiety was introduced in the membrane through the incorporation of various guanidinium lipids. For the latter, anchoring ability and primarily introduction of a spacer group between their lipophilic part and the guanidinium group was found to affect the ability for molecular recognition. Also, poly(ethylene glycol) (PEG) introduced in both types of liposomes at various concentrations and up to 15% with respect to cholesterol modifies the interaction effectiveness and morphology of the obtained aggregates. Interaction of these complementary liposomes leads to large precipitating aggregates or fused liposomes, as shown by phase contrast microscopy and dynamic light scattering. Specifically, fusion of liposomes takes place under a nonleaking process involving lipid mixing, as demonstrated by calcein entrapment and resonance energy transfer experiments. Calorimetric parameters also correlate with the processes of aggregation and fusion. The interactions of non-PEGylated liposomes involve exothermic processes of higher enthalpic content than those of the PEGylated counterparts.
authors.affiliation: Institute of Physical Chemistry, NCSR "Demokritos", 15310 Aghia Paraskevi, Attiki, Greece.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Pantos
authors.forename: Dimitris
authors.initials: D
authors.lastname: Tsiourvas
authors.forename: Zili
authors.initials: Z
authors.lastname: Sideratou
authors.forename: Constantinos M
authors.initials: CM
authors.lastname: Paleos
authors.forename: Sarantis
authors.initials: S
authors.lastname: Giatrellis
authors.forename: George
authors.initials: G
authors.lastname: Nounesis
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D019791:Guanidine / Q000737:chemistry; D008024:Ligands; D008027:Light; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D015394:Molecular Structure; D010316:Particle Size; D010710:Phosphates / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D013499:Surface Properties; D013997:Time Factors
chemical_list: D008024:Ligands; D008081:Liposomes; D046911:Macromolecular Substances; D010710:Phosphates; D010713:Phosphatidylcholines; D011092:Polyethylene Glycols; D002784:Cholesterol; D019791:Guanidine