Primary Mechanisms of Erythrocyte Photolysis Induced by Biological Sensitizers and Phototoxic Drugs

Abstract— The elucidation of the molecular mechanism of photosensitized hemolysis of red blood cells may give important clues to the primary events underlying the phototoxic reactions observed in pathological conditions such as porphyria and induced by photosensitizing drugs. Sensitizers effective in photo‐hemolysis are porphyrins, the tryptophan metabolite kynurenic acid, and phototoxic drugs such as chlor‐promazine and demethylchlortetracycline. Utilizing the singlet oxygen quenchers. jS‐carotene and histi‐dine and the large deuterium effect on the lifetime of singlet oxygen previously described by us, good evidence of the participation of this excited molecular species in the photohemolysis in the presence of kynurenic acid was obtained. Chlorpromazine and demethylchlortetracycline clearly act by a non‐singlet oxygen pathway. The situation observed with haematoporphyrin is less clear and may represent a mixed Type I‐Type II mechanism.