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MPP+ toxicity in rat striatal slices: relationship between non-selective effects and free radical production
S Ambrosio1, A Espino, B Cutillas
1Unitat de Bioquímica, Dep. Ciencies Fisiològiques Humanes i de la Nutrició, Universitat de Barcelona, Spain.
Abstract:
Incubations of rat striatal slices have been used to assay MPP+ neurotoxicity. MPP+, at concentrations of 1 mM or higher, caused a marked increase in hydroxyl radicals, measured as malondialdehyde (MDA) accumulation, but not in nitric oxide production. At these doses, MPP+ showed an effect on dopamine terminals, causing a massive dopamine decrease, and on non-neuronal glial cells, where a marked reduction in glutamine synthetase activity was detected. At lower concentrations (25 mu M), the toxic effect on dopaminergic endings was maintained without increasing malondialdehyde concentrations or inhibiting glutamine synthetase activity. The effect on glutamine synthetase was prevented by the addition to the medium of 0.5% dimethyl sulfoxide, a hydroxyl-radical scavenger, but this did not protect the effect of dopamine depletion. We propose that non-selective effects of MPP+, at doses of 1 mM or higher, are mediated by extracellular overproduction of hydroxyl radicals. The main factor responsible for this overproduction would not be the released dopamine but rather the MPP+ itself through non selective inhibition of the mitochondrial respiratory chain or through a redox cycling that can trigger oxygen radical production.
Insights
High concentrations of MPP+ increase hydroxyl radicals, damaging dopamine terminals and glial cells. This neurotoxicity is linked to MPP+ itself, not released dopamine, via mitochondrial dysfunction or redox cycling.
Area of Science:
- Neuroscience
- Toxicology
- Biochemistry
Background:
- MPP+ (1-methyl-4-phenylpyridinium) is a neurotoxin implicated in Parkinson's disease pathogenesis.
- Understanding the precise mechanisms of MPP+ neurotoxicity is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the role of hydroxyl radicals and nitric oxide in MPP+ neurotoxicity in rat striatal slices.
- To differentiate the effects of MPP+ on dopaminergic terminals and glial cells.
Main Methods:
- Incubation of rat striatal slices with varying concentrations of MPP+.
- Measurement of hydroxyl radicals via malondialdehyde (MDA) accumulation.
- Assay of nitric oxide production.
- Quantification of dopamine levels.
- Assessment of glutamine synthetase activity in glial cells.
Main Results:
- MPP+ (≥1 mM) significantly increased hydroxyl radicals (MDA) and decreased dopamine levels and glutamine synthetase activity.
- Lower MPP+ concentrations (25 μM) reduced dopamine but did not affect MDA or glutamine synthetase.
- Dimethyl sulfoxide, a hydroxyl radical scavenger, protected glutamine synthetase but not dopamine depletion.
- MPP+ itself, not released dopamine, appears to mediate hydroxyl radical overproduction.
Conclusions:
- High-dose MPP+ neurotoxicity involves hydroxyl radical overproduction, affecting both neurons and glial cells.
- MPP+'s mechanism may involve non-selective inhibition of mitochondrial respiration or redox cycling.
- These findings highlight MPP+'s direct role in generating reactive oxygen species, contributing to dopaminergic neurodegeneration.