EPR studies of spin-trapped free radicals in paraquat-treated lung microsomes

Electron Spin Resonance and Spin Trapping techniques were used to demonstrate the generation of free radicals during incubation of paraquat with lung microsomes. Aerobic incubation of paraquat resulted in the production of superoxide radical (·O₂-) which was trapped by 5,5-dimethyl-pyrroline-N-oxide or phenyl-tert-butyl-nitrone. The formation of ·O₂- and hydroxyl radical (·OH) by paraquat during microsomal incubation was also confirmed by the inhibition of the EPR spectra of DMPO-O₂- and DMPO-OH spin adducts by superoxide dismutase and dimethyl sulfoxide, respectively. Our results provide direct evidence for the generation of reactive oxygen species during redox cycling of paraquat in lung microsomes. The formation of DMPO-H spin adduct during incubation of paraquat in the microsomal system is a strong indication of the involvement of hydrogen atom transfer mechanisms in paraquat-induced generation of reactive oxygen species in the lung.