Protection of UV-radiation induced skin toxicity by reactive oxygen scavengers.

Although, photoaddition reactions of psoralens with DNA and membrane lipid are regarded as the major photochemical events responsible for skin-photosensitization and photochemotherapeutic properties, their O2-dependent reactive oxygen specie (ROS) generating potential is also responsible for biologic photooxidation reactions and cutaneous phototoxicity. We have investigated the skin-sensitization reactions of psoralen in presence of selected free radical scavengers. The results confirm that sodium azide, DABCO and beta-carotene inhibited considerably the 1O2 generation reactions in a chemical system (determined by monitoring the bleaching of N,N-dimethyl-p-nitrosoaniline in the presence of histidine used as a selective acceptor of 1O2) as well as skin sensitization in vivo (epilated guinea pig skin). These observation suggest that the O2-dependent photodynamic action of psoralen contributes significantly to the development of cutaneous toxicity which can be inhibited by selective scavengers of 1O2.