High-efficiency entrapment of superoxide dismutase into cationic liposomes containing synthetic aminoglycolipid.

A monofatty acid ester of glucosamine (PGlcN) was synthesized to provide liposomal membranes with a positive charge, and the trapping efficiency of negatively charged substances (superoxide dismutases, SODs) into cationic liposomes containing PGlcN or stearylamine (SA) prepared by various methods was compared to find the most efficient trapping methods. We demonstrated that cationic liposomes, which were prepared in a buffer of low ionic strength containing sorbitol by a simple hydration method, could entrap a large amount of negatively charged SODs which retained their activity, as compared with cationic liposomes prepared in a buffer of high ionic strength. We also showed a reverse-phase evaporation method entrapped a large amount of SODs. However, SODs were inactivated during the preparation; therefore, this method was not suitable to entrap the enzyme. Freeze-thaw method induced the formation of cationic liposomes which were smaller than extruded liposomes and could entrap the SODs in a buffer of low ionic strength. Dehydration-rehydration method with a buffer of low ionic strength also entrapped a large amount of SODs, indicating that the integrity of liposomes was lost in the lipid bilayer after freeze-drying and the SODs were entrapped in the reconstruction of liposomes during rehydration. These findings showed that the hydration method based on electrostatic attraction with a buffer of low ionic strength was simple and the most effective for entrapping SODs without loss of their activity.