MAGNETIC-FIELD EFFECTS ON THE PHOTOHEMOLYSIS OF HUMAN ERYTHROCYTES BYKETOPROFEN AND PROTOPORPHYRIN-IX

Application of a static external magnetic field (3350 G) during UV-irr adiation (>300 nm) reduced the time for 50% photohemolysis of human er ythrocytes by the phototoxic drug ketoprofen (3-benzoyl-alpha-methylbe nzoacetic acid) from 96 min to 78 min. This observation can be attribu ted to a magnetic field induced decrease in the rate of intersystem cr ossing (k(ISC)) of the geminate tripler radical pair generated by the reduction of ketoprofen in its triplet excited stare by erythrocyte me mbrane constituents, probably lipids. The decrease in k(ISC) results i n an increase in the concentration and/or lifetime of free radicals th at escape from the triplet radical pair. Thus the critical radical con centration needed to cause membrane damage and cell lysis is reached s ooner in the presence of the magnetic field. In contrast, the photohem olysis induced by the photodynamic agent protoporphyrin IX was not aff ected by the magnetic field. Protoporphyrin IX photohemolysis, which i s initiated by singlet oxygen, does not involve the initial generation of a triplet radical pair and so is not influenced by the magnetic fi eld. The enhancement of ketoprofen-induced photohemolysis by an extern ally applied magnetic field is the first example of a magnetic field e ffect on a toxicological process involving free radicals.