Induction of Liposome Leakage by Photodynamic Action: Dependence on the Kind of Fluorescent Probe

Abstract

Photosensitized damage to liposome membranes was studied by using different dye-leakage assays based on fluorescence dequenching of a series of dyes upon their release from liposomes. Irradiation of liposomes with red light in the presence of a photosensitizer, trisulfonated aluminum phthalocyanine (AlPcS3), resulted in the pronounced leakage of carboxyfluorescein, but rather weak leakage of sulforhodamin B and almost negligible leakage of calcein from the corresponding dye-loaded liposomes. The photosensitized liposome permeabilization was apparently associated with oxidation of lipid double bonds by singlet oxygen as evidenced by the requirement of unsaturated lipids in the membrane composition for the photosensitized liposome leakage to occur and the sensitivity of the latter to sodium azide. The fluorescence correlation spectroscopy measurements revealed marked permeability of photodynamically induced pores in liposome membranes for such photosensitizers as AlPcS3 and AlPcS4. It was proposed that the difference in permeability of these pores to carboxyfluorescein and calcein was associated with size restriction. Verification of this hypothesis by studying the effect of PEGs of different molecular weights is under way.