Polycations enhance emulsion-mediated in vitro and in vivo transfection

To enhance the in vitro and in vivo transfection activity of the cationic lipid emulsion (LE), three natural polycations, protamine sulfate (PS), poly-L-lysine and spermine, were selected as DNA condensing active agents. Formation of the LE/polycation/DNA ternary complexes was identified by using agarose gel retardation study. The structure of these complexes was characterized by measuring the complex size and the decrease of the DNA fluorescence in the presence of ethidium bromide (EtBr). By adding a polycation, the particle size of the complex decreased, and DNA in the complex became highly condensed and resistant to intercalation of EtBr. Among the polycations, PS yielded the most highly compacted ternary complex. In vitro and in vivo transfection activities of the complexes were determined using various cell lines and Balb/c mouse intravenously and intranasally, respectively. The transfection activity of the ternary complex increases by at least 2.5-5-fold in vitro cell culture system in the presence of 80% serum as well as in vivo mouse system, as compared with LE/DNA binary complexes. More importantly, after intravenous and intranasal administrations, the in vivo transfection efficiency of the LE/PS/DNA complex was ca. 30 and 50 times higher than that of the liposome (LP)/DNA complex in spleen and lung, respectively. On the other hand, cell toxicity of the ternary complex is lower than that of binary complex. Thus, we conclude that the pre-condensation of DNA with polycations can be a promising approach to further increase in vitro and in vivo transfection efficiency of cationic lipid emulsion.