Increase of the photosensitizing efficiency of the Bacteriochlorin a by liposome-incorporation

To describe the action mechanisms of Bacteriochlorin a (BCA), a second gene ration photosensitizer, in phosphate buffer (PB) and in dimyristoyl phospha tidylcholine (DMPC) liposomes we carried out oxygen consumption and ESR mea surements. In PB, where BCA was in a monomer-dimer equilibrium, our results suggested that the oxygen consumption was related to the BCA monomers conc entration in solution. Incorporation of BCA in DMPC liposomes, by promoting the monomerization of BCA, increased 9-fold the oxygen consumption in comp arison to the value in PB. The use of specific singlet oxygen quenchers (Az ide and 9, 10-Anthracenedipropionic acid) in ESR and oxygen consumption exp eriments allowed us to assert that BCA was mainly a type II sensitizer when it was incorporated in DMPC. Finally, the cell survival of WiDr cells afte r a PDT treatment was measured for cells incubated with BCA in cell culture medium and cells incubated with BCA in DMPC. Irrespective of the dye conce ntration, the cell survival was lower when liposomes were used. This effect could be the result of a better BCA monomerization and/or a different BCA uptake in cells. (C) 2001 Elsevier Science B.V. All rights reserved.