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Inhibition of type A monoamine oxidase by 1-methyl-4-phenylpyridine
Abstract:
1-Methyl-4-phenylpyridine (MPP+) is now confirmed to be one of the oxidative products of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by type B monoamine oxidase (MAO-B) and is considered to cause a parkinsonism-like syndrome. We studied the effect of MPP+ on type A monoamine oxidase (MAO-A) activity in mitochondria prepared from various sources. By kinetic analysis, MPP+ was found to inhibit MAO-A in competition with the substrate, kynuramine. The Ki value of MAO-A with MPP+ in human brain synaptosomal mitochondria (1.3 microM) was much lower than the Ki values of MAO-A in other organs. Among the MAO-A samples, MAO-A in intrasynaptosomal mitochondria from human brain was the most sensitive to MPP+. The Ki value of MAO-A with MPP+ in striatum (1.6 microM and 2.0 microM for MAO-A prepared from putamen and from caudate) was similar to the Ki value of MAO-A in synaptosomes from cortex. The difference in the Ki values of MPP+ for MAO-A from various sources was considered to be due to the difference in lipid components of mitochondria. The possible significance of the inhibition of MAO-A was discussed in terms of the etiology of parkinsonism.
Insights
1-Methyl-4-phenylpyridine (MPP+), a parkinsonism-inducing compound, inhibits type A monoamine oxidase (MAO-A) in human brain mitochondria. This inhibition is most potent in the brain, suggesting a role in parkinsonism etiology.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- 1-Methyl-4-phenylpyridine (MPP+) is an oxidative product of MPTP, linked to parkinsonism.
- Monoamine oxidases (MAOs) are crucial enzymes in neurotransmitter metabolism.
Purpose of the Study:
- To investigate the effect of MPP+ on monoamine oxidase A (MAO-A) activity.
- To determine the sensitivity of MAO-A from various sources to MPP+ inhibition.
Main Methods:
- Kinetic analysis of MAO-A inhibition by MPP+.
- Preparation of mitochondria from various human and animal tissues.
- Determination of inhibition constants (Ki) for MPP+ on MAO-A.
Main Results:
- MPP+ inhibits MAO-A in a competitive manner with the substrate kynuramine.
- Human brain synaptosomal MAO-A exhibited the highest sensitivity to MPP+ inhibition (Ki = 1.3 μM).
- MAO-A in striatum and cortex showed similar sensitivity to MPP+.
Conclusions:
- MPP+ potently inhibits human brain MAO-A.
- The specific lipid composition of mitochondria may influence MPP+ inhibition of MAO-A.
- MPP+-induced MAO-A inhibition could contribute to the pathogenesis of parkinsonism.