In vitro and in vivo aspects ofN-acyl-phosphatidylethanolamine-containing liposomes

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Incorporation of the phospholipid, N-acyl-phosphatidylethanolamine (NAPE), has shown to increase the liposomal stability towards plasma components in vitro. Besides increasing the circulation-time, NAPE has been shown to contain fusiogenic properties. Hence, fusion between NAPE-liposomes and target cells may be expected, resulting in a favorable delivery of drug to the target cell. In this study, NAPE has been tested as a potential liposomal component of phosphatidylcholine-liposomes. The liposomes were characterized by size, long-term stability and phase transition temperature (Tm). In vivo behavior of NAPE-liposomes was determined by the blood-circulation half-life in mice.A characterization of the liposomes revealed that high content of NAPE resulted in liposomes of increased size compared to pure phosphatidylcholine-liposomes. However, the liposomes showed only a slight increase in size during storage for 5 weeks. Determination of Tm for NAPE-liposomes showed increasing values of Tm by increasing percentage of NAPE in the liposomal bilayer, due to the higher Tm of NAPE compared to phosphatidylcholine. Blood-clearance studies showed an initial increase in blood-circulation of liposomes containing high amounts of NAPE.Thus, these results suggest that liposomes containing high percentage of NAPE may be a promising candidate for long-circulating liposomes, possibly in combination with other stabilizing components, e.g. cholesterol.

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