An Improved Method for Entrapment of Plasmids in Liposomes

Abstract

The reverse-phase evaporation method [Szoka, F., Jr., and Papahadjopoulos, D. (1978): Proc. Natl. Acad. Sci. USA., 75, 4194-4198] was modified to enable the preparation of liposomes entrapping plasmids without damage to DNA strands due to sonication. In our procedure, reverse-phase micelles were prepared first by sonication and then plasmids were added to form liposomes entrapping plasmids. The efficiency of the liposomes for entrapping of DNA by the present method was higher than that by the original method. By the present method, circular-pCH 110 was entrapped in liposomes without damage, while by the original method, some of the plasmids were cut during the preparation. The expression of the β-galactosidase gene encoded in plasmid pCH 110 was detected in COS-7 cells when the gene was transferred with the liposomes prepared by the present method, but not with the vesicles prepared by the original method.