Psoralens sensitize glutathione photooxidation in vitro

In vitro expts. are reported showing that psoralens and other furocoumarins of current pharmacol. interest, e.g., angelicin and 4,6,4'-trimethylangelicin, all have, to a variable extent, the ability to sensitize the photooxidn. of glutathione in ethanol/phosphate buffer with pyrex-filtered UV light. Besides substrate concn. and the nature of the furocoumarin used, the rate of the sensitized reaction is markedly dependent on the partial pressure of O and the pH of the medium, being progressively faster on passing from pH 5 to 8.5. Scavengers of O2-, H2O2, (superoxide dismutase), H2O2, (catalase) and singlet O (NaN3, diazabicyclooctane, sorbic acid) have little or no inhibitory effect on the reaction rate. These and other data suggest that furocoumarins can directly sensitize glutathione photooxidn. by forming a charge transfer complex which is driven to the oxidized products in the presence of O. The possible relevance of these results to the mechanisms of skin melanin hyperpigmentation induced by furocoumarins and UV light is discussed.