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[The effects of 1-methyl-4-phenylpyridine (MPP+) on O2- generation by neutrophils]
Abstract:
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces parkinsonisms in humans, monkeys, and some animals. MPTP is metabolized to 1-methyl-4-phenylpyridine (MPP+), which is a primary neurotoxin, by monoamine oxidase B. MPP+ destroys nigro-striatal dopaminergic neurons, but the mechanism of the neurotoxic effects of MPP+ is not known. In this study, the effects of MPP+ on O2- generation by neutrophils was examined. Neutrophils possess several functional and antigenic similarities to glial cells. Therefore, the O2- generating system of neutrophils might be useful in studying the mechanism of MPP+ neurotoxicity related to active oxygen species. 1) MPP+ did not affect myristic acid (MA), and elaidic acid stimulated O2- generation and H2O2 generation by the glucose-glucose oxidase system, suggesting that MPP+ did not react with O2- or H2O2 itself. 2) When fatty acid-activated neutrophils were treated with a neutral detergent, Renex 30, and then NADPH was added, the O2- generation by these permeabilized cells was inhibited by MPP+. 3) Kinetic study revealed that MPP+ was a noncompetitive inhibitor of the NADPH oxidase in plasma membranes isolated from MA-activated pig neutrophils. These results did not support the hypothesis that the action of MPP+ is related to active oxygen species. The results suggest that MPP+ does not penetrate through the plasma membrane, and interacts with the inner domain of NADPH oxidase in the neutrophil plasma membranes.
Insights
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) metabolite 1-methyl-4-phenylpyridine (MPP+) inhibits NADPH oxidase in neutrophil plasma membranes. This suggests MPP+ may not directly involve active oxygen species in its neurotoxic mechanism.
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 1-methyl-4-phenylpyridine (MPP+), the presumed active neurotoxin.
- The precise mechanism of MPP+ neurotoxicity remains unclear, particularly regarding active oxygen species.
Purpose of the Study:
- To investigate the effects of MPP+ on superoxide (O2-) generation in neutrophils.
- To explore the potential role of active oxygen species in MPP+ neurotoxicity.
- To elucidate the interaction of MPP+ with the NADPH oxidase system.
Main Methods:
- Examined MPP+ effects on O2- and H2O2 generation stimulated by myristic acid and glucose-glucose oxidase.
- Investigated O2- generation in fatty acid-activated, detergent-permeabilized neutrophils treated with NADPH and MPP+.
- Performed kinetic studies on MPP+ inhibition of NADPH oxidase in isolated plasma membranes from activated neutrophils.
Main Results:
- MPP+ did not directly react with O2- or H2O2.
- MPP+ inhibited O2- generation in permeabilized neutrophils.
- Kinetic analysis identified MPP+ as a noncompetitive inhibitor of NADPH oxidase.
Conclusions:
- The findings do not support the hypothesis that MPP+ neurotoxicity involves active oxygen species.
- Results suggest MPP+ does not readily cross the plasma membrane.
- MPP+ likely interacts with the inner domain of NADPH oxidase within neutrophil plasma membranes.