Liposomal membrane fusion induced by extrusion method

Abstract

Objective To study the application of extrusion method in inducing liposome membrane fusion or membrane component mixing, and to investigate the effect of different extrusion conditions on liposome membrane fusion rate. Methods N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) phosphatidylethanolamine (N-NBD-PE) and N-(lissamine rhodamine B sulfonyl) phosphatidylethanolamine (N-Rh-PE) labeled 1, 2-dioleoyl lecithin (DOPC) liposomes and non-fluorescently labeled DOPC monolayer liposomes were mixed and extruded. The fluorescence changes before and after the extrusion of the mixed liposomes were observed using laser scanning confocal microscope, and the membrane fusion rate of the mixed liposomes was calculated by fluorescence resonance energy transfer method. Besides, the effects of extrusion times, extrusion pressure and temperature on the fusion rate of liposome membrane were studied. Results The results of laser scanning confocal microscopy showed that the distribution density and intensity of the green fluorescence of N-NBD-PE increased significantly after the extrusion of fluorescently labeled and non-fluorescent labeled DOPC liposomes, which confirmed membrane fusion. After 75 times of extrusion treatments, the liposome membrane fusion rate can reach 26%. The number of extrusions, extrusion pressure and temperature had a significant effect on the fusion rate of the liposome membrane. The higher the number of the extrusions, the smaller the extrusion pressure and the higher the efficiency of the liposome membrane fusion were at physiological temperature. Conclusions Extrusion method can induce liposome membrane fusion and membrane component mixing, and the prepared liposome has a narrower particle size distribution, which is expected to be a new method to induce the bilayer membrane fusion of liposome or lipid vesicle. Key words: Extrusion; Liposome; Lipid bilayer fusion; Fluorescence resonance energy transfer