Electron-transfer mechanisms in photosensitization by the anti-inflammatory drug benzydamine

The novel anti-inflammatory drug benzydamine has been show to photosensitize the reduction of Nitro Blue Tetrazolium, ferricytochrome c and copper (II) bathocuproinedisulphonate in aqueous solutions (pH 7.4, 30 degrees C) when irradiated with UV light at its maximum absorption wavelength of 308 nm. The reduction reactions all proceed most efficiently when the solutions are deoxygenated, clearly indicating that direct electron transfer occurs from the excited state of the sensitizer to the substrate. In aerated solutions the reduction reactions are slower and are partially inhibited by superoxide dismutase, suggesting that superoxide anion could be involved as an intermediate when oxygen is present. Benzydamine also photosensitizes the oxidation of 1-histidine and 2,5-dimethylfuran by the singlet oxygen pathway in aerated solutions. The ability of benzydamine to participate as sensitizer in several types of photochemical reaction is relevant to the observed clinical photosensitivity of the drug.