title: Study of PEGylated lipid layers as a model for PEGylated liposome surfaces: molecular dynamics simulation and Langmuir monolayer studies.
abstract: We have combined Langmuir monolayer film experiments and all-atom molecular dynamics (MD) simulation of a bilayer to study the surface structure of a PEGylated liposome and its interaction with the ionic environment present under physiological conditions. Lipids that form both gel and liquid-crystalline membranes have been used in our study. By varying the salt concentration in the Langmuir film experiment and including salt at the physiological level in the simulation, we have studied the effect of salt ions present in the blood plasma on the structure of the poly(ethylene glycol) (PEG) layer. We have also studied the interaction between the PEG layer and the lipid bilayer in both the liquid-crystalline and gel states. The MD simulation shows two clear results: (a) The Na(+) ions form close interactions with the PEG oxygens, with the PEG chains forming loops around them and (b) PEG penetrates the lipid core of the membrane for the case of a liquid-crystalline membrane but is excluded from the tighter structure of the gel membrane. The Langmuir monolayer results indicate that the salt concentration affects the PEGylated lipid system, and these results can be interpreted in a fashion that is in agreement with the results of our MD simulation. We conclude that the currently accepted picture of the PEG surface layer acting as a generic neutral hydrophilic polymer entirely outside the membrane, with its effect explained through steric interactions, is not sufficient. The phenomena we have observed may affect both the interaction between the liposome and bloodstream proteins and the liquid-crystalline-gel transition and is thus relevant to nanotechnological drug delivery device design.
authors: Centre for Drug Research, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland.
authors: Michał
authors: M
authors: Stepniewski
authors: Marta
authors: M
authors: Pasenkiewicz-Gierula
authors: Tomasz
authors: T
authors: Róg
authors: Reinis
authors: R
authors: Danne
authors: Adam
authors: A
authors: Orlowski
authors: Mikko
authors: M
authors: Karttunen
authors: Arto
authors: A
authors: Urtti
authors: Marjo
authors: M
authors: Yliperttula
authors: Elina
authors: E
authors: Vuorimaa
authors: Alex
authors: A
authors: Bunker