IN-VITRO FLUENCE RATE EFFECTS IN PHOTODYNAMIC REACTIONS WITH ALPCS4 AS SENSITIZER

It has been shown previously that the efficiency of photodynamic thera py (PDT) both in vivo and in vitro is dependent on fluence rate, In th is study, different in vitro experiments showed that tetrasulfonated a luminum phthalocyanine (AlPcS4) is more efficient in photosensitizatio n if the light is delivered at low fluence rate, Erythrocyte damage, v irus inactivation and photooxidation of reduced glutathione (GSH) and histidine were all enhanced if light was delivered at 100 W/m(2) as co mpared to 500 W/m(2). Bleaching did not occur under these conditions, Oxygen depletion, shown to be important in fluence rate effects observ ed in vivo, does not seem to be involved, On theoretical grounds satur ation of the triplet state is not likely under these conditions, A pos sible explanation for the observed fluence rate effects might be found in different reaction pathways, that are favored under high or low fl uence rate illuminations, These reactions might involve uni-or bimolec ular reactions of intermediate products, resulting in less efficiency at higher fluence rate, It proves to be important, under all circumsta nces, to monitor fluence rate, because a change in fluence rate, even with similar total fluences, might influence photobiological results i n an unexpected way.