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Iron-mediated bioactivation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in glial cultures
D A Di Monte1, H M Schipper, S Hetts
1Parkinson's Institute, Sunnyvale, California 94089, USA.
Abstract:
Primary cultures of mouse astrocytes were treated with both the monoamine oxidase (MAO) A inhibitor, clorgyline, and the MAO B inhibitor, deprenyl, prior to the addition of the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Production of the 1-methyl-4-phenylpyridinium (MPP+) toxic metabolite was reduced to 11%, but not completely blocked, by MAO inhibition. This residual MPP+ production appeared to be iron-dependent since it was decreased (30 to 50%) by iron chelators, i.e., deferoxamine or phenanthroline, and was enhanced (by approximately 40%) in the presence of ADP-Fe3+. ADP-Fe3+ also enhanced the oxidation of MPTP to MPP+ which occurs in medium without cells. MPP+ formation, however, was significantly slower in plain culture medium than in astrocyte incubations pretreated with MAO inhibitors, suggesting the involvement of cells in these iron-mediated reactions. The data indicate that oxidation via MAO is the primary but not the only pathway of MPTP bioactivation and that transition metals may contribute to the generation of the toxic MPP+ metabolite in biological systems.
Insights
Monoamine oxidase (MAO) inhibition primarily reduces, but does not eliminate, the production of the toxic metabolite 1-methyl-4-phenylpyridinium (MPP+) from MPTP. Iron-dependent pathways also contribute to MPP+ generation in biological systems.
Area of Science:
- Neuroscience
- Biochemistry
- Toxicology
Background:
- 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that causes Parkinsonism.
- MPTP is metabolized to the toxic MPP+ ion, primarily via monoamine oxidase (MAO).
- The exact mechanisms and cellular contributions to MPTP bioactivation require further elucidation.
Purpose of the Study:
- To investigate the role of MAO in MPTP bioactivation.
- To explore the involvement of iron in the residual MPP+ production after MAO inhibition.
- To understand the cellular contribution to iron-mediated MPTP oxidation.
Main Methods:
- Primary mouse astrocyte cultures were treated with MAO-A (clorgyline) and MAO-B (deprenyl) inhibitors.
- MPTP was added, and MPP+ production was measured.
- Iron chelators (deferoxamine, phenanthroline) and ADP-Fe3+ were used to assess iron dependency.
- MPTP oxidation was also studied in cell-free medium.
Main Results:
- MAO inhibition reduced MPP+ production to 11% of control levels.
- Residual MPP+ production was decreased by iron chelators (30-50%) and enhanced by ADP-Fe3+ (approx. 40%).
- ADP-Fe3+ enhanced MPTP oxidation in both cell-free medium and astrocyte incubations, with faster rates in the presence of cells.
Conclusions:
- MAO is the primary but not the sole pathway for MPTP bioactivation.
- Transition metals, particularly iron, play a significant role in MPP+ generation.
- Astrocyte-associated, iron-mediated pathways contribute to MPTP toxicity in biological systems.