[Effect of hydroxyl free radical produced by hematoporphyrin derivative (HPD), ascorbate and light on HPD...

Light-induced generation of hydrogen peroxide and hydroxyl free radical by HPD in the presence of ascorbate was studied. 1. Oxygen consumption was determined by oxygen electrodes when the HPD-ascorbate solution was illuminated. After the illumination, addition of 300 unit/ml of catalase to the illuminated HPD-ascorbate solution initiated a return of 20% of the oxygen. The results indicated the presence of H2O2 in the solution. 2. Ascitic hepatoma cells of mice, mitochondria and lysosomes were incubated with HPD, respectively and then were treated with ascorbate and light. The product of membrane lipid peroxidation-malondialdehyde (MDA) level was increased with the increase of ascorbate concentration and irradiation time. 3. Thiourea, an inhibitor of hydroxyl free radical, could inhibit the MDA produced in the cell-HPD-ascorbate and light system. The MDA level was inversely proportional to thiourea concentration. These results show that hydroxyl free radical produced by HPD-ascorbate and light could directly oxidize the membrane lipids, thus leading to enhancement of HPD photosensitization.