Biodegradable pH-sensitive surfactants (BPS) in liposome-mediated nucleic acid cellular uptake and distribution

The impact of biodegradable pH-sensitive surfactant (BPS)-liposomes on nucleic acid, i.e., oligonucleotide and plasmid DNA, cellular delivery was examined. Fluorescein-labeled nucleic acids complexed with 1,2-dioleoyl-3-trimethylammonium propane cationic liposomes and BPS at a charge ratio (+/-) of 10 were incubated in CV-1 cells and analyzed by flow cytometry. The fluorescence intensity of oligonucleotides but not plasmid DNA complexed with BPS-liposomes was higher than those complexed with BPS-free liposomes at early time points. However, when cells were fixed to equalize the intracellular pH since fluorescein, a pH-sensitive fluorophore, has higher fluorescence intensity in alkaline pH than acidic, no difference in intensity was observed. This indicated the incorporation of BPS in liposomes did not increase oligonucleotide cellular uptake over control liposomes, but redistributed oligonucleotides into a more basic environment, e.g., cytoplasm. An explanation consistent with the presented data is the formation of small transient membrane defects within the endosomal membrane as presented previously [Liang, E., Hughes, J.A., 1998a. Membrane fusion and rupture in liposomes: effect of biodegradable pH-sensitive surfactants. J. Membr. Biol. 166, 37-49.]. The above findings suggested that BPS may be effective agents of disrupting one of the major barriers, endosomal membrane, to enhance nucleic acid cellular transport.