Non-phospholipid fusogenic liposomes.

We have demonstrated the capacity of non-phospholipid liposomes composed primarily of dioxyethylene acyl ethers and cholesterol to fuse with membranes composed primarily of phospholipid. Phase-contrast microscopy, freeze-fracture electron microscopy and a macromolecular probe indicate that these non-phospholipid liposomes can fuse with the plasma membranes of erythrocytes and fibroblasts. Furthermore, fluorescence probe experiments have demonstrated fusion between phosphatidylcholine liposomes and non-phospholipid liposomes. Mixing of internal contents was shown by a terbium/dipicolinate assay. Mixing of membrane lipid components was demonstrated by measuring (i) fluorescence resonance energy transfer between N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine and N-(lissamine rhodamine B sulfonyl)phosphatidylethanolamine, after phosphatidylcholine liposomes were mixed with non-phospholipid liposomes, and (ii) reduced concentration quenching of rhodaminephosphatidylethanolamine and octadecylrhodamine incorporated into phosphatidylcholine liposomes after mixing with the non-phospholipid liposomes. The degree of apparent fusion reported by the different probe techniques ranged from 25% to 64%.