Influence of the DNA complexation medium on the transfection efficiency of lipospermine/DNA particles

Dioctadecylamidoglycylspermine (DOGS, Transfectam) is a cationic lipid able to interact with DNA to form complexes that mediate efficient gene transfer into various eukaryotic cells. The state of condensation of the plasmid changes with the medium composition. We therefore investigated to what extent the DNA condensation buffer influences the transfection efficiency of Transfectam/DNA particles. Our results show that in a variety of cell lines, a greater than 100-fold difference in luciferase gene expression is observed with Transfectam/DNA complexes at a +/- charge ratio of 0.75 depending on the conditions of complex formation. The best transfection conditions consisted of particles formed in RPMI medium, NaHCO3/Na2HPO4 or sodium citrate solutions. Mixing in a 150 mM sodium chloride solution (as recommended) resulted in lower gene expression. When the helper lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) was present in the DNA/cationic lipid formulation, the increase in reporter activity was also observed, although to a lower extent. Thus, choosing the optimal conditions for formulating DNA/lipid complexes considerably reduces the amount of lipid and DNA needed to obtain maximum gene transfer.