Effect of preparation protocol on physicochemical features and biointeractions of pegylated liposomes

Poly(ethylene glycol) (PEG) stabilized liposomes are widely used in drug delivery research because these surface grafted polymers stabilize liposomes in blood stream. However, hydrophilic polymers also affect lipid membrane organization and it is fundamental to investigate their effect on the physicochemical properties of lipid bilayers as well as on their interaction with biological membrane. PEG monolaurate was included in liposomes formulated with dimyristoyl-sn-glycero-3-phosphocholine and one of two cationic gemini surfactants that differ each other for the configuration of a stereogenic center on the polar headgroup. These formulations previously showed good efficiency as drug and DNA delivery systems. The effect of the presence of different amounts of a PEG-lipid and of the liposome preparation protocol was investigated by turbidimetry, dynamic laser light scattering, differential scanning calorimetry and electrophoretic mobility. Flow cytometry and laser scanning confocal microscopy on murine (C6) and on human glioblastoma (LN229) cell lines were also carried out to evaluate the influence of pegylation and of the protocol of preparation on the interaction of liposomes with the biological milieu.