Modulation of Cationic Liposomal DNA Zeta Potential and Liposome‐protein Interaction by Amphiphilic Poly (ethylene glycol)*

In an attempt to reduce the surface charge of cationic liposomes, and thereby increase their transfection efficiencies, the effect of the amphiphilic solvation enhancer dipalmitoylphosphatidylethanolaminyl-poly-(ethylene glycol) (DPPE-PEG) on the stability of cationic dioleoylphosphatidylethanolamine (DOPE) dioleoyltrimethylammonium propane (DOTAP) liposomes, their interaction with DNA and the aggregation of liposomal DNA complexes by anionic proteins has been evaluated by photon correlation spectroscopy and measurement of liposome ζ potential. DOPE-DOTAP liposomes were unstable, and exhibited significant aggregation after seven days storage at 4°C. DOPE-DOTAP liposomes containing DPPE-PEG (5 mol%) were more stable, but also showed some aggregation. DOPE-DOTAP liposomes had a ζ potential of + 34 mV This was significantly reduced to a value of +6 mV by the incorporation of DPPE-PEG. Both liposome formulations reacted with DNA at weight ratios of 1:1 to 15:1 within 1–5 min at pH 7-4 and 23°C. The ζ potential of DOPE-DOTAP liposomes was significantly reduced by genomic and plasmid DNA, in a dose-dependent manner, to give a ζ potential of + 3 mV at a liposome-to-DNA ratio of 1:1. The ζ potential of DOPE-DOTAP-DPPE-PEG liposomes was further reduced by DNA to − 9 mVat a liposome-to-DNA ratio of 1:1. Incubation of DOPE-DOTAP liposomal plasmid DNA (1:5 ratio) with the anionic proteins albumin or IgG, or with a buccopharyngeal wash resulted in a rapid and significant aggregation (0–18 μM to 1–2 μM) accompanied by significant reductions in ζ potential. In contrast, DOPE-DOTAP-DPPE-PEG liposomes showed only a slight increase in size that was not accompanied by a significant change in ζ potential. These results indicate that although DPPE-PEG masks the positive charge of DOTAP at the liposome surface and thus reduces electrostatic interaction with anionic proteins, it still enables efficient interaction of DOTAP with genomic and plasmid DNA.