The photosensitizing effect of the photoproduct of protoporphyrin IX

The photodynamic effect of a photoproduct of protoporphyrin IX (PpIX) induc ed by 5-aminolevulinic acid (ALA) was investigated in WiDr cells. a human a denocarcinoma cell line, The fluorescence excitation and emission spectra o f PpIX and the photoproduct were measured. After 1, 3 or 5 min exposure of the ALA-incubated cells to 140 mW/cm(2) light at 635 run. the photoproduct- the chlorin photoprotoporphyrin (Ppp), had an emission band around 670 nm. The Ppp excitation peak at 670 mn is well separated from the PpIX peak at 6 35 nm. The outcome of photodynamic therapy (PDT) was determined by measurin g intracellular fluorescence intensity of propidium iodide (PI) 2 h followi ng PDT and methylene blue (MB) staining 24 h following PDT. A significant i ncrease in the fluorescence intensity of PI was noted when the ALA-loaded c ells were exposed to 670 nm light after exposure to 635 nm, indicating enha nced cell membrane inactivation induced by the photodynamic action of the p hotoproduct. However, the fraction of the cells that survived following the same treatment as measured by MB staining was not significantly affected b ased on an analysis of variance. The fluorescence of PpIX decayed significa ntly during 635 nm light exposure. Exposure to light at 670 nm does not lea d to any photodegradation of PpIX. The fluorescence of Ppp was bleached dur ing 670 nm light exposure. Exposure of Ppp at 670 run gives no PpIX back. T hus, the phototransformation of PpIX to Ppp is probably not a reversible pr ocess. (C) 2001 Elsevier Science BY All rights reserved.