Osmotic stability of muramyl dipeptide-bearing liposomes and molecular miscibility in their membranes

Article abstract of DOI:10.1246/bcsj.72.541

Muramyl dipeptide is the minimal and essential structural unit for the immunopotentiating activities of bacterial cell walls. The muramyl dipeptide derivative N-acetyl-6-O-(2-tetradecylhexadecanol)muramyl-L-alanyl-D- isoglutamine (B30-MDP) and its amide derivative (B30-MDPA) are good basic materials for use in artificial liposome vaccines (virosomes). The osmotic stability of muramyl dipeptide-bearing liposomes composed of various binary mixtures was examined to find conditions favoring stable liposome formation. The osmotic properties of B30-MDP-bearing and B30-MDPA-bearing liposomes were significantly different from each other. Nevertheless, a good correlation between osmotic stability and virosome formation was found for both types of liposomes. Furthermore, the dynamic structures and the intermolecular interactions of phospholipids in muramyl dipeptide-bearing liposomes were investigated by solid-state ²H and ³¹PNMR. The results suggested that molecular miscibility in the liposomes is not an essential factor for osmotic stability. Negative charges on the liposome surface and flexible hydrophilic moieties were found to be the most important factors in keeping isolated liposomes osmotically stable.