Toxic effect of previously photooxidized in water psoralen on survival of mouse peritoneal exudate cells was investigated. Cell survival was determined by trypan exclusion test. It was shown that photooxidized psoralen itself did not induce trypan-positive cells while decrease in cell survival was observed in the case of simultaneous addition of photooxidized psoralen and Fe2+ ions to cell suspension. To evaluate the quantity of psoralen photoproducts which react with Fe2+ photooxidized psoralen Fe2+ mixtures were titrated by different cell concentrations. Then parameter c50 (cell concentration such that 50% trypan-positive cells were observed) was determined. It was shown that c50 increased with the increase in preirradiation fluence of psoralen from 4.5 to 45 kJ/m2. But further increase in preirradiation fluence resulted in decrease of c50. The photodestruction of psoralen photoproducts which react with Fe2+ ions was proposed. Simultaneous addition of photooxidized psoralen, Fe2+ ions and antioxidant butylated hydroxytoluene significantly increased cell survival. That indicated free radical nature of reaction products of photooxidized psoralen with Fe2+ ions.
