Effect of magnetite particles on photoinduced and nonphotoinduced free radical processes in human erythrocytes.

Magnetite (Fe3O4) encapsulated in polystyrene microspheres dramatically decreased the time for 50% hemolysis (t1/2) of human erythrocytes irradiated (lambda > 300 nm) in the presence of ketoprofen (0.1 mM). The magnetic microspheres were present at a very low concentration (0.002%) such that on average there was only one particle per four erythrocytes. No such effect was seen when nonmagnetic microspheres were employed or when the equivalent concentration of soluble iron (FeCl3) was present. A decrease in t1/2 was also observed when the magnetic microspheres were added after UVA/ketoprofen treatment or when they were present during hemolysis initiated by thermolysis of 2,2'-azobis(2-amidinopropane). These findings may be attributed to an increase in the membrane concentration of lipid radicals as a result of a magnetic field-induced increase in radicals escaping from triplet radical pairs.