Malondialdehyde dosimetry in laser-irradiated tissues sensitized by hematoporphyrin derivative.

Photodynamic therapy (PDT) is based on the selective retention of a photosensitizer (hematoporphyrin derivative [HPD]) by tumor tissue and the subsequent irradiation of this tissue with light. Unsaturated phospholipids are important targets of membrane photodamage, and malondialdehyde (MDA), an ultimate marker of lipid peroxidation, can easily be measured by the fluorometric thiobarbituric acid (TBA) assay. To determine whether MDA content represents a reference for PDT intensity, tissue content in 7-week-old male nude mice was studied on biopsy samples after PDT (5 mg/kg HPD injected intravenously 24 hr before irradiation at 632 nm) with or without intraperitoneal injection of WR-2721 40 min before treatment. The FeCl3 method requiring only 15 min of incubation in a 95 degrees C waterbath proved most effective compared with the method involving phosphotungstic acid or the MDA-TBA determination using a commercially available kit. Whatever the method used, the best results were found using a 60-min interval between treatment and freezing. MDA concentration in HPD-PDT-treated samples was significantly higher than in HPD-tested controls (P