Characterization of oligonucleotide/lipid interactions in submicron cationic emulsions: influence of the cationic lipid structure and the presence ofPEG-lipids

We have recently described how oligonucleotide (ON) stability and release f rom O/W cationic emulsions are governed by the lipid composition. The aim o f the present paper was to investigate the properties of the ON/lipid compl exes through fluorescence resonance energy transfer (FRET), size, surface t ension measurements and cryomicroscopy. Starting from a typical emulsion co ntaining stearylamine as a cationic lipid, the influence of the lipid struc ture (monocationic molecules bearing mono or diacyl chains, or polycations) as well as of the presence of PEGylated lipids, were studied. The presence of a positive charge on the droplet surface clearly contributed to enhance the ON interaction with lipid monolayers and to bring the ON molecules clo ser to the interface. Hydrophobic interactions through the acyl chains were shown to further enhance the anchorage of the ON/lipid complexes. In contr ast, the incorporation of PEGylated lipids acted as a barrier against the e stablishment of electrostatic bindings, the polyethyleneglycol chains actin g themselves as interaction sites for the ON leading to hydrophilic complex es. Similar features were observed for the polycationic lipid, and cryomicr oscopy revealed the existence of bridges of various intensities between the droplets of the emulsion containing either PEG or the polycation, probably because of the configuration of the ON at the interface. (C) 2001 Elsevier Science B.V. All rights reserved.