PUV-A (psoralens combined with UV-A irradiation) therapy and photodynamic therapy (PDT), both being the constitutive parts of photochemotherapy, are currently employed for the treatment of dermatological, autoimmune and oncological diseases. Externally applied reducing agents, namely antioxidants, may inhibit side, undesirable effects produced in the course of photochemotherapy thus increasing the therapeutic benefit. Inhibiting reactions of antioxidants are produced in the reactions of scavenging of radical species. This property can be also used for the elucidation of biological significance of the given photochemical reaction. Upon certain conditions, such as high antioxidant concentration and exhaustion of co- antioxidants, antioxidants can produce a pro-oxidant effect and increase the damage of biological substrate. The prooxidant effect develops either due to an accumulation of an excessive amount of antioxidant radicals or in a photochemical pathway thus promoting Type I photodynamic reactions. The present review considers the antioxidants as inhibitors and amplifiers of photobiological effects induced by psoralens and porphyrin-like molecules with the emphasis on the reaction pathways.
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