Preparation and stability of interferon-alpha-containing liposomes

Several liposome types containing human interferon-alpha (hIFN-alpha) were produced and were assessed to determine the levels of hIFN-alpha activity associated with surface-adsorbed or interior-entrapped hIFN-alpha. Liposomes were prepared as multilamellar vesicles (MLV) following repeated extrusion through 0.2 mu m polycarbonate filters, and by a mechanical high shear homogenization system using the one-step method. The highest trapping efficiency for hIFN-alpha, at around 23%, was found for liposomes composed of egg phosphatidylcholine/cholesterol/dimyristoyl phosphatidylglycerol in a 6:4:1 molar ratio, prepared at a lipid content of 10% (w/v) by extrusion. The trapping efficiency for hIFN-alpha in homogenized liposomes was only around 3%. hIFN-alpha liposomes prepared by extrusion were stable over 4 months at 20 degrees C, with regard to the activity of hIFN-alpha and the size distribution of the liposomes.