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Surface Charge Density Determines the Efficiency of Cationic Gemini Surfactant Based Lipofection

Samppa J. Ryhänen^*, Matti J. Säily^*, Tommi Paukku^*, Stefano Borocci, Giovanna Mancini, Juha M. Holopainen^* and Paavo K. J. Kinnunen^*

^* Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine/Biochemistry, University of Helsinki, Finland and CNR, ICCOM—Sezione di Roma c/o Dipartimento di Chimica, Universita degli Studi di Roma "La Sapienza," P. le A. Moro 00185, Rome, Italy

Correspondence: Address reprint requests to Dr. Paavo K. J. Kinnunen, Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine / Biochemistry, Biomedicum, P.O. Box 63 (Haartmaninkatu 8), FIN-00014 University of Helsinki, Finland. Tel.: 358-9-191 25400; Fax: 358-9-191 25444; E-mail: paavo.kinnunen{at}helsinki.fi.

The efficiencies of the binary liposomes composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine and cationic gemini surfactant, (2S,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide as transfection vectors, were measured using the enhanced green fluorescent protein coding plasmid and COS-1 cells. Strong correlation between the transfection efficiency and lipid stoichiometry was observed. Accordingly, liposomes with X_SR-1 0.50 conveyed the enhanced green fluorescent protein coding plasmid effectively into cells. The condensation of DNA by liposomes with X_SR-1 > 0.50 was indicated by static light scattering and ethidium bromide intercalation assay, whereas differential scanning calorimetry and fluorescence anisotropy of diphenylhexatriene revealed stoichiometry dependent reorganization in the headgroup region of the liposome bilayer, in alignment with our previous Langmuir-balance study. Surface charge density and the organization of positive charges appear to determine the mode of interaction of DNA with (2S,3R)-2,3-dimethoxy-1,4-bis(N-hexadecyl-N,N-dimethylammonium)butane dibromide/1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes, only resulting in DNA condensation when X_SR-1 > 0.50. Condensation of DNA in turn seems to be required for efficient transfection.