On the mechanism whereby cationic lipids promote intracellular delivery ofpolynucleic acids

The mechanism whereby cationic lipids destabilize cell membranes to facilit ate the intracellular delivery of macromolecules such as plasmid DNA or ant isense oligonucleotides is not well understood. Here, we show that cationic lipids can destabilize lipid bilayers by promoting the formation of nonbil ayer lipid structures, In particular, we show that mixtures of cationic lip ids and anionic phospholipids preferentially adopt the inverted hexagonal ( H-II) phase. Further, the presence of 'helper' lipids such as dioleoylphosp hatidylethanolamine or cholesterol, lipids that enhance cationic lipid-medi ated transfection of cells also facilitate the formation of the H-II phase. It is suggested that the ability of cationic lipids to promote nonbilayer structures in combination with anionic phospholipids leads to disruption of the endosomal membrane following uptake of nucleic acid-cationic lipid com plexes into cells, thus facilitating cytoplasmic release of the plasmid or oligonucleotide.