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1-Methyl-4-phenylpyridinium (MPP+) increases oxidation of cytochrome-b in rat striatal slices
J R Sanchez-Ramos1, G E Hollinden, T J Sick
1Department of Neurology, University of Miami School of Medicine, FL 33136.
Abstract:
Effects of 1-methyl-4-phenylpyridinium, (the active metabolite of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), on reduction/oxidation activity of mitochondrial cytochromes were studied in rat striatal slices using scanning spectrophotometry. The objective was to test the hypothesis that the neurotoxin alters electron transport in the mitochondrial respiratory chain. Incubation of rat striatal slices with MPP+ (1 microM) produced a time-dependent oxidation of Cytochrome-b in a manner consistent with the concept of a block in electron transport in the intramitochondrial respiratory chain between nicotinamide adenine dinucleotide (NAD) and Cytochrome-b. This effect of MPP+ was decreased by co-incubation with a potent dopamine uptake inhibitor (mazindol), or when studied in a tissue with low dopaminergic innervation (hippocampus). The amplitude of Cytochrome-b oxidation was greater than that expected from a selective effect of MPP+ on dopaminergic neurons suggesting that neighboring cells are influenced secondary to the MPP+ effect on dopaminergic terminals.
Insights
The neurotoxin MPP+, a metabolite of MPTP, disrupts mitochondrial electron transport in rat brain slices. This disruption affects cytochrome-b and impacts surrounding cells, not just dopaminergic neurons.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Mitochondrial dysfunction is implicated in neurodegenerative diseases.
- MPP+ is the active metabolite of MPTP, a known neurotoxin that causes Parkinsonism.
- The precise mechanism of MPP+ toxicity on the mitochondrial respiratory chain requires further elucidation.
Purpose of the Study:
- To investigate the effects of MPP+ on mitochondrial cytochrome reduction/oxidation activity.
- To test the hypothesis that MPP+ disrupts electron transport in the mitochondrial respiratory chain.
- To explore the cellular specificity of MPP+ neurotoxicity.
Main Methods:
- Scanning spectrophotometry was used to study rat striatal slices.
- Rat striatal slices were incubated with MPP+ (1 microM).
- Dopamine uptake inhibitor (mazindol) and hippocampal tissue (low dopaminergic innervation) were used for comparative analysis.
Main Results:
- MPP+ induced a time-dependent oxidation of Cytochrome-b, indicating a block in electron transport between NAD and Cytochrome-b.
- This effect was attenuated by mazindol and in hippocampal slices.
- The observed Cytochrome-b oxidation exceeded predictions for selective dopaminergic neuron effects, suggesting broader cellular impact.
Conclusions:
- MPP+ directly inhibits mitochondrial electron transport in the respiratory chain.
- The neurotoxic effects of MPP+ extend beyond dopaminergic neurons, influencing neighboring cells.
- These findings contribute to understanding the pathogenesis of MPTP-induced neurotoxicity.
