Screening test for phototoxins using solutions of simple biochemicals

The feasibility of using solution photochemistry for in vitro phototoxicology testing was examined. Solutions of substrate and test chemical, in binary aqueous/organic solvent to ensure solubility, were exposed to ultraviolet/visible radiation. Quantum efficiencies for photosensitized oxidation of substrate were calculated. The phototoxins rose bengal, anthracene and acridine were good photooxidizers of histidine, in contrast to the other chemicals studied. Solution photochemistry using histidine may be a useful screening test for molecules that photooxidize by the singlet oxygen pathway. Other indications of in vivo activity may be gained from the molecular weight, ionic nature, lipophilicity and photodegradation (photoinactivation). The photoallergens tetrachlorosalicylanilide, tribromosalicylanilide and musk ambrette, and the photomutagen 8-methoxypsoralen, were detected qualitatively by these studies, but in vivo potency could not be predicted.