Photohemolysis sensitized by the furocoumarin imperatorin and its oxyfunctionalized derivatives

The dark and photosensitized (366 mm) hemolytic effects of imperatorin and its photooxidation products, the hydroperoxides I and II as well as the cor responding alcohol of the hydroperoxide I (imperatorin alcohol), were studi ed on human erythrocytes, Imperatorin was shown to photosensitize hemolysis , its fluence (D) dependence of the rate of photohemolysis (V) followed the equation V = V-0 + aD(2) + bD(1/2), in which V-0 is the dark hemolysis rat e and a and b are constants. At fluences below 200 kJ/m(2), the main hemoly tic contribution derives from the bD(1/2) component, which is due to the in situ formation of the imperatorin hydroperoxides, while at fluences higher than 200 kJ/m(2), the main contribution corresponds to the aD(2) component due to the two-photon damage of cell membranes. Hydroperoxides I and II in duce oxyhemoglobin cross-linking, as well as its conversion to methemoglobi n and hemichrome. These reactions involve hydroxyl and alkoxy radicals, as the hemolysis and oxyhemoglobin conversion could be inhibited by t-butanol and butylated hydrotoluene. For comparison, the dark hemolytic effect of th e imperatorin alcohol was approximately 10-fold less than of the hydroperox ides.