Magnetic field effects on the photohemolysis of human erythrocytes by ketoprofen and protoporphyrin IX.

Application of a static magnetic field (3350 G) during UV-irradiation (> 300 nm) reduced the time for 50% photohemolysis of human erythrocytes by the phototoxic drug ketoprofen (3-benzoyl-alpha-methylbenzoacetic acid) from 96 min to 78 min. This observation can be attributed to a magnetic field induced decrease in the rate of intersystem crossing (kISC) of the geminate triplet radical pair generated by the reduction of ketoprofen in its triplet excited state by erythrocyte membrane constituents, probably lipids. The decrease in kISC results in an increase in the concentration and/or lifetime of free radicals that escape from the triplet radical pair. Thus the critical radical concentration needed to cause membrane damage cell lysis is reached sooner in the presence of the magnetic field. In contrast, the photohemolysis induced by the photodynamic agent protoporphyrin IX was not affected by the magnetic field. Protoporphyrin IX photohemolysis, which is initiated by singlet oxygen, does not involve the initial generation of a triplet radical pair and so is not influenced by the magnetic field. The example of a magnetic field effect on a toxicological process involving free radicals.