Spontaneous entrapment of polynucleotides upon electrostatic interaction with ethanol-destabilized cationic liposomes

This study describes the effect of ethanol and the presence of poly(ethylen e) glycol (PEG) lipids on the interaction of nucleotide-based polyelectroly tes with cationic liposomes. It is shown that preformed large unilamellar v esicles (LUVs) containing a cationic lipid and a PEG coating can be induced to entrap polynucleotides such as antisense oligonucleotides and plasmid D NA in the presence of ethanol. The interaction of the cationic liposomes wi th the polynucleotides leads to the formation of multilamellar liposomes ra nging in size from 70 to 120 nm, only slightly bigger than the parent LUVs from which they originated. The degree of lamellarity as well as the size a nd polydispersity of the liposomes formed increases with increasing polynuc leotide-to-lipid ratio. A direct correlation between the entrapment efficie ncy and the membrane-destabilizing effect of ethanol was observed. Although the morphology of the liposomes is still preserved at the ethanol concentr ations used for entrapment (25-40%, v/v), entrapped low-molecular-weight so lutes leak rapidly. In addition, lipids can flip-flop across the membrane a nd exchange rapidly between liposomes. Furthermore, there are indications t hat the interaction of the polynucleotides with the cationic liposomes in e thanol leads to formation of polynucleotide-cationic lipid domains, which a ct as adhesion points between liposomes. It is suggested that the spreading of this contact area leads to expulsion of PEG-ceramide and triggers proce sses that result in the formation of multilamellar systems with internalize d polynucleotides, The high entrapment efficiencies achieved at high polyel ectrolyte-to-lipid ratios and the small size and neutral character of these novel liposomal systems are of utility for liposomal delivery of macromole cular drugs.