The effect of static magnetic fields on the photohemolysis of human erythrocytes by ketoprofen.

Ultraviolet irradiation (lambda > 300 nm) of the nonsteroidal anti-inflammatory agent ketoprofen (KP, 3-benzoyl-alpha-methylbenzoacetic acid) in aqueous solution, pH 7.4, results in heterolytic decarboxylation of the drug to give 3-ethylbenzophenone (EtBP). Ketoprofen caused the photohemolysis of human erythrocytes probably as a result of lipid peroxidation. Application of a static magnetic field (250-1500 G) during UV (> 300 nm) irradiation of KP and erythrocytes significantly decreased the time required for photohemolysis. This observation suggests that KP-induced photohemolysis involves the initial generation of a triplet radical pair derived from the reaction of triplet state KP (or 3-EtBP) with erythrocyte component(s) probably lipids. The magnetic field increases the concentration and/or lifetime of free radicals that escape from the radical pair so that the critical radical concentration needed to initiate membrane damage and cause cell lysis is reached sooner. Spin-trapping studies with 2,6-dibromo-1-nitrosobenzene-4-sulfonate confirmed that the application of an external static magnetic field increased the concentration of radicals released during the photolysis of either KP or 3-EtBP dissolved in organized media such as sodium dodecylsulfate micelles.