title: Mechanistic aspects of paraquat toxicity in E. coli. A spin trapping study.
abstract: Mechanistic aspects of paraquat monocation radical (PQ.+) and copper involvement in paraquat toxicity have been examined using E. coli B cells. Electron spin resonance (ESR) spectrometry combined with cell survival studies were used to explore the correlation between radical production and biological damage. The line broadening agent oxalato-chromiate (CrOx) was used to characterize the anoxic partition of PQ.+ inside and outside the cell. In the presence of CrOx the ESR signal was totally eliminated, indicating that intracellular species were undetectable and that, contrary to previous reports, PQ.+ exclusively accumulates outside the cell. The PQ.+ radical does not react with H2O2 but disappears in the presence of H2O2 when catalytic traces of Cu(II) are present. Spin-trapping studies using DMPO showed that in aerobic environment paraquat-induced O2 radicals are detectable exclusively in the extracellular compartment. The correlation between PQ.+ appearance and the biological damage is not simple. PQ.+ non-toxically accumulates, in the absence of oxygen and either Cu(II) or H2O2. By contrast, with both H2O2 and Cu(II) the cells are rapidly killed but PQ.+ was undetectable. These results reconfirm the key catalytic mediatory function of transition metals in paraquat toxicity.
authors.affiliation: Department of Cellular Biochemistry, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Sion
authors.forename: A
authors.initials: A
authors.lastname: Samuni
authors.forename: M
authors.initials: M
authors.lastname: Chevion
mesh_terms: D000332:Aerobiosis; D002414:Cations, Monovalent; D003300:Copper / Q000494:pharmacology; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000187:drug effects*; D005609:Free Radicals; D006861:Hydrogen Peroxide / Q000494:pharmacology; D010070:Oxalates / Q000494:pharmacology; D019815:Oxalic Acid; D010100:Oxygen / Q000494:pharmacology; D010269:Paraquat / Q000378:metabolism / Q000494:pharmacology*; D013113:Spin Labels; D013481:Superoxides / Q000378:metabolism
chemical_list: D002414:Cations, Monovalent; D003497:Cyclic N-Oxides; D005609:Free Radicals; D010070:Oxalates; D013113:Spin Labels; D013481:Superoxides; C017245:5,5-dimethyl-1-pyrroline-1-oxide; D003300:Copper; D019815:Oxalic Acid; D006861:Hydrogen Peroxide; D010269:Paraquat; D010100:Oxygen