The effect of lipid molecular packing stress on cationic liposome-induced rabbit erythrocyte fusion

Abstract

The effect of curvature stress on the efficiency of cationic liposome-induced fusion between rabbit erythrocytes was studied. Multilamellar cationic liposomes containing 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP) and different PEs (1,2-dilinoleoyl- sn-glycero-3-phosphoethanolamine (dilin-PE), 1,2-dioleoyl- sn-glycero-3-phosphoethanolamine (DOPE), 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoethanolamine (POPE), and lysophosphatidylethanolamine, egg (lyso-PE)) were used to induce cell–cell fusion. It was found that high cell–cell fusion yield (FY) of about 50% could be achieved in sucrose solution by using cationic liposomes containing 50% DOTAP. Cell–cell fusion was assayed by shape criterion and was verified by fluorescence microscopy, using a membrane dye mixing method. The curvature stress, as a result of mixing unsaturated PEs in cationic liposomes, had a significant effect on cell–cell FY which increased with the degree of acyl chain unsaturation, in the order dilin-PE>DOPE>POPE>lyso-PE. Replacement of dilin-PE, DOPE, or POPE by lyso-PE gradually in cationic liposomes lowered the cell–cell FY from 50% to 1%. Furthermore, cationic liposome-induced cell lysis, and fusion between cationic liposomes and cells, as assayed by the N-(lissamine rhodamine B sulfonyl)-1,2-dihexadecanoyl- sn-glycero-3-phosphoethanolamine, triethylammonium salt and N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl- sn-glycero-3-phosphoethanolamine, triethylammonium salt (Rh-PE/NBD-PE) energy transfer method, followed the same order as that for cell–cell fusion. Fusion between the negatively charged PS liposomes and cationic liposomes also followed the same order. The electric double layer screening by electrolytes in NaCl-containing solution and phosphate buffered saline (PBS) was found to reduce the cell–cell FY and cell lysis. These findings suggest that liposome-induced cell–cell fusion was achieved by cationic liposomes serving as fusion-bridges among cells.