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 interact ion with monoamine oxidase type B (MAO-B). The kinetic parameters, K(m ) and V(max), for MAO-B-catalyzed oxidation of MPTP to the correspondi ng species MPDP+ were found to be 0.194 mM and 0.335 muM/min, respecti vely. The generation of superoxide (.O2-) and hydroxyl (.OH) radicals was detected as the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) spin adduc t by spin-trapping in combination with EPR techniques. Addition of Fe2 + (10 muM) to this system caused a 5-fold enhancement in EPR signal in tensity of the DMPO-OH adduct. Catalase, a scavenger of hydrogen perox ide (H2O2), inhibited the DMPO-OH spin adduct formation in a dose-depe ndent 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 di smutase inhibited the formation of DMPO-O-2- and DMPO-OH spin adducts in a dose-dependent fashion. These data suggest that superoxide radica ls are produced during the oxidation of MPTP by MAO-B and that the gen eration of H2O2 and .OH was secondary to the production of .O2-. It ap pears likely that the nigrostriatal toxicity of MPTP leading to Parkin son's disease-like syndrome may in part be mediated via these reactive oxygen species.