We prepared liposomes containing ultrafine magnetite particles as magnetically targeted drug delivery system, and evaluated their physicochemical and biological characters; diameter, magnetic responsiveness, trapping efficiency and uptake to cells. A mixture of asolectin and cholesterol (4 : 1) was dispersed in physiological saline (final lipid concentration : 20 mg/ml), and coprecipitated magnetite particles were added to the medium and it was sonicated. Multi-lamellar liposomes (average diameter : 155 nm) were prepared from this medium by the freeze-thawing method. We confirmed holding of the magnetite particles inside the liposomes by TEM. Trapping efficiency was evaluated by encapsulation of fluorescent calsein, and it was approximately 8%. Magnetic responsiveness was estimated by the capture of the flowed liposomes in a glass tube under magnetic field application. At least 50% of liposomes were retained by the applied magnetic field (gradient : 2.6 kG/cm). We also visualized uptake of the fluorescent labeled liposomes into porcine endothelial cultured cells with a confocal laser scanning microscope, and observed the localization of liposome uptake in small intracellular vesicles around nuclei. From these physicochemical and biological characterization of liposomes containing ultrafine magnetite particles, we demonstrated the feasibility of these liposomes as carriers for magnetically targeted drug delivery system.
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