Optimization of lipid composition in cationic emulsion as in vitro and in vivo transfection agents

Purpose. To enhance in vitro and in vivo transfection activity by optimizin g lipid composition of cationic lipid emulsions. Methods. Various emulsion formulations having different cationic lipids as emulsifiers, and additional helper lipids as co-emulsifiers, were prepared. The stability of the emulsion and its complex with DNA was investigated by measuring the particle size change in phosphate buffer saline (PBS) over a period of 20 days. The activity of the emulsions in transfecting pCMV-beta into COS-1 cells in the presence or absence of 80% serum was evaluated. We also evaluated in vivo transfection activity using intravenously administe red pCMV-Luc(+) as a reporter gene. Results. Among the cationic emulsifiers, 1,2-dioleoyl-sn-glycero-3-trimethy lammonium-propane (DOTAP) formed the most stable and efficient emulsion gen e carrier. Addition of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) increased in vitro transfection activity, but slightly compromised the sta bility of the emulsion. The loss was compensated for by including small amo unts of Tween 80 in the emulsion. The in vitro and in vivo transfection act ivities were also increased by adding Tween 80. Even though in vitro transf ection activity of liposomes was high in the absence of serum, the transfec tion activity of emulsions was far greater than that of liposomes in the pr esence of serum and for in vivo applications. Conclusions. By including DOPE as an endosomolytic agent and Tween 80 as a stabilization agent, the cationic emulsion becomes a more potent gene carri er for in vitro and in vivo applications, especially in the presence of ser um.