Preparation of liposome-encapsulating adenosine triphosphate

Liposomes encapsulating adenosine triphosphate (ATP) were prepared by sonication, and the liposomes were evaluated for use in a drug delivery system. The liposomes, which were composed of phosphatidylcholine and cholesterol, were about 1.1 microm in size, as observed under a microscope. From their size, the vesicles were thought to be multilamellar. The maximum concentration of ATP in the liposomes was 1.0 mM, when the initial concentrations of lipid and ATP were 20 mM and 300 mM, respectively. The maximum entrapment ratio of ATP in the liposomes was 88%, when the initial concentrations of lipid and ATP were 20 mM and 500 mM, respectively. About 4% of ATP was encapsulated in these experiments. When liposomes contained 4-7% of cholesterol, about 35% of encapsulated ATP was released from the liposomes for 90 hours at 37 degrees C in vitro. These findings indicated that liposomes encapsulating ATP could be used for the treatment of ischemic retina.