Preparation, Characterization and99mTC Radiolabeling of Polyethylene glycol - coated Vesicles

Abstract Poly (ethylene glycol) - coated lipid vesicles of average diameter ∼200nm containing glutathione (GSH) were prepared by extrusion under pressure through polycarbonate filters, external GSH removed by chromatography on Sephadex G50, and the vesicles concentrated to a final lipid concentration of ∼ 60 mM using Millipore 10,000 NMWL low-protein-binding regenerated cellulose ultrafiltration units. Vesicles were subsequently radiolabeled with diagnostic quantities of technetium-99m (99mTc) - 740 Mbq (20 mCi) - using the ability of non-reduced hexamethylpropylene-amineoxime (HM-PAO) in the presence of tin (Sn) to transport 99mTc across the lipid bilayer. The use of Millipore filters represents a gentle, relatively rapid and simple method to concentrate lipid vesicles without causing loss of entrapped marker or affecting the efficiency of subsequent radiolabeling. Once external GSH was removed, vesicles retained >97% of their contents over a period of ∼ 4 months when stored at 4°C. The radiolabeling of the lipid vesicles using HM-PAO was unaffected by temperature, lipid composition or lipid phase state, but was critically dependent upon the ratios of HM-PAO, Sn and 99mTc.