Electrostatically Mediated Interactions between Cationic Lipid–DNA Particles and an Anionic Surface

In an effort to model the interaction of lipid-based DNA delivery systems with anionic surfaces, such as a cell membrane, we have utilized microelectrophoresis to characterize how electrokinetic measurements can provide information on surface charge and binding characteristics. We have established that cationic lipids, specificallyN-N-dioleoyl-N,N-dimethylammonium chloride (DODAC), incorporated into liposomes prepared with 1,2-dioleoyl-i-glycero-3-phosphoethanolamine (DOPE) or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 50 mol%, change the inherent electrophoretic mobility of anionic latex polystyrene beads. Self-assembling lipid–DNA particles (LDPs), prepared at various cationic lipid to negative DNA phosphate charge ratios, effected no changes in bead mobility when the LDP charge ratio (+/−) was equal to or less than 1. Increasing the LDP concentration in a solution of 0.1% (w/v) anionic beads resulted in a charge reversal effect when a net charge of LDP to total bead charge ratio (+/−) of 1:1 was observed. LDP formulations, utilizing either DOPE or DOPC, showed similar titration profiles with a charge reversal observed at a 1:1 net LDP to bead charge ratio (+/−). It was confirmed through centrifugation studies that the DNA in the LDP was associated with the anionic latex beads through electrostatic interactions. LDP binding, rather than the binding of dissociated cationic lipids, resulted in the observed electrophoretic mobility changes of the anionic latex beads.