Production of singlet oxygen and superoxide radicals by psoralens and their biological significance.

We have investigated a series of linear and angular furocoumarins, capable of forming either the monofunctional adducts (single strand) or bifunctional adducts (interstrand cross-links) with DNA with a view to examine the relationship of their skin photosensitizing potency, their ability to produce singlet oxygen (1O2) or superoxide radicals (O-.2 or HO.2), and their carcinogenic activity. The significance of photochemical interactions of psoralens and DNA is well known in skin photosensitization and skin carcinogenesis. Our data suggest that both monofunctional and bifunctional psoralens produce 1O2 and O-.2, and these reactive forms of oxygen may contribute to the development of skin cancer and membrane-damaging effects of these furocoumarins.