抄録
Photodynamic therapy with pulsed light excitation has interesting characteristics; however, its photosensitization mechanism has not been fully elucidated. We investigated the correlation between oxygen consumption and photobleaching during photodynamic treatment with nanosecond pulsed light excitation and a secondgeneration, lysosomal sensitizer in vitro, and obtained “fluorescence-oxygen diagram” at different pulse frequencies. The diagrams showed that initial oxygen-dependent photobleaching was switched to an oxygenindependent photobleaching, which was re-switched to an oxygen-dependent reaction at the higher frequencies of 10 and 30 Hz; such changes were not observed at 5 Hz. The complex behaviors revealed by the diagrams at 10 and 30 Hz were shown to be associated with the intracellular kinetics of the sensitizer, i.e., initial localization in lysosomes and redistributionto the cytosol during the treatment. The pulse frequencydependent intracellular kinetics of the sensitizer also explained the higher cytotoxicity at 5 Hz than at 10 and 30 Hz.
