Encapsulation of the cobra cytotoxin P4 in liposomes

Cytotoxin P4 isolated from the venom of the cobra Naja nigricollis nigricollis was encapsulated in liposomes by the reverse-phase evaporation method using phosphatidylcholine, cholesterol and phosphatidylethanolamine at molar ratios of 3:1:1. Cytotoxicity examination on murine melanoma B16F10 revealed that the activity of the entrapped cytotoxin did not change significantly and remained stable for at least 1 year at 4 degrees C without any significant leak from the liposomes (< 1%). Moreover, the activity of the cytotoxic liposomes was 20-fold higher towards human erythrocytes. Whereas 45 micrograms of the free cytotoxin/ml were needed for total haemolysis, the cytotoxic liposomes brought about the same effect at cytotoxin concentrations of 2-2.5 micrograms/ml, indicating the potential of the liposomes as a delivery system for the snake toxin.