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

The impact of biodegradable pH-sensitive surfactant (BPS)-liposomes on nucl eic acid, i.e., oligonucleotide and plasmid DNA, cellular delivery was exam ined. Fluorescein-labeled nucleic acids complexed with 1,2-dioleoyl-3-trime thylammonium propane cationic liposomes and BPS at a charge ratio (+/-) of 10 were incubated in CV-1 cells and analyzed by flow cytometry. The fluores cence 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 p H since fluorescein, a pH-sensitive fluorophore, has higher fluorescence in tensity in alkaline pH than acidic, no difference in intensity was observed . This indicated the incorporation of BPS in liposomes did not increase oli gonucleotide cellular uptake over control liposomes, but redistributed olig onucleotides into a more basic environment, e.g., cytoplasm. An explanation consistent with the presented data is the formation of small transient mem brane 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.]. Th e above findings suggested that BPS may be effective agents of disrupting o ne of the major barriers, endosomal membrane, to enhance nucleic acid cellu lar transport. (C) 2000 Elsevier Science B.V. All rights reserved.