Generation of reactive oxygen species during the monoamine oxidase-catalyzed oxidation of the neurotoxicant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.
The neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to generate reactive oxygen species during its interaction with monoamine oxidase type B (MAO-B). The kinetic parameters, Km and Vmax, for MAO-B-catalyzed oxidation of MPTP to the corresponding species MPDP+ were found to be 0.194 mM and 0.335 microM/min, respectively. The generation of superoxide (.O2-) and hydroxyl (.OH) radicals was detected as the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin adduct by spin-trapping in combination with EPR techniques. Addition of Fe2+ (10 microM) to this system caused a 5-fold enhancement in EPR signal intensity of the DMPO-OH adduct. Catalase, a scavenger of hydrogen peroxide (H2O2), inhibited the DMPO-OH spin adduct formation in a dose-dependent manner, indicating that H2O2 is produced in the MAO-B catalyzed oxidation of MPTP. Ethanol, a well known scavenger of hydroxyl radical, rapidly produced an alpha-hydroxyethyl radical signal. Superoxide dismutase inhibited the formation of DMPO-O2- and DMPO-OH spin adducts in a dose-dependent fashion. These data suggest that superoxide radicals are produced during the oxidation of MPTP by MAO-B and that the generation of H2O2 and .OH was secondary to the production of .O2-. It appears likely that the nigrostriatal toxicity of MPTP leading to Parkinson's disease-like syndrome may in part be mediated via these reactive oxygen species.
Department of Biomedical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061-0442.
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D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000378:metabolism*; D000818:Animals; D002384:Catalysis; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008995:Monoamine Oxidase / Q000378:metabolism*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism
D017382:Reactive Oxygen Species; D013481:Superoxides; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D008995:Monoamine Oxidase