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MPP(+) increases the vulnerability to oxidative stress rather than directly mediating oxidative damage in human
1Department of Pharmacology, College of Medicine, Seoul National University, 28 Yongon-Dong, Chongo-Gu, Seoul, Korea.
Abstract:
MPP(+), an active metabolite of MPTP, causes a dopaminergic neuronal degeneration similar to that observed in Parkinson's disease. Current data suggest that MPP(+)-induced cytotoxicity may be mediated by oxygen free radicals. To evaluate this hypothesis, we first investigated whether MPP(+) could cause oxidative stress by producing oxygen free radicals in the SH-SY5Y, human neuroblastoma cell line. MPP(+) was toxic to the cells dose-dependently but did not increase the level of lipid peroxidation at toxic concentrations. Second, we examined the effects of various antioxidants and an inhibitor of nitric oxide synthase (NOS) on the development of MPP(+) cytotoxicity. Pretreatment with antioxidants such as ascorbic acid, Trolox, phenyl-tertiary-butyl-nitrone (PBN), which show protective effects on tert-butyl hydroperoxide (tBOOH) toxicity did not attenuate MPP(+) cytotoxicity. Similarly, the combination of antioxidant enzymes, SOD and catalase (50 U/ml, respectively), did not protect the cells from the toxic action of MPP(+). Also N-nitro-l-arginine methyl ester (NAME), a competitive inhibitor of NOS, and combined incubation with NAME and antioxidant enzymes failed to attenuate MPP(+) cytotoxicity. On the other hand, a sublethal dose of MPP(+) potentiated iron and H(2)O(2)-induced cytotoxicity. These results suggest that oxygen free radicals may not be a primary cause of MPP(+)-induced cell death but that MPP(+) increases the vulnerability of cells to oxidative stress.
Insights
MPP(+) does not directly cause oxidative stress in neuroblastoma cells. However, MPP(+) increases cell susceptibility to oxidative damage, suggesting it indirectly contributes to cell death in Parkinson's disease models.
Area of Science:
- Neuroscience
- Toxicology
- Cell Biology
Background:
- MPP(+) (1-methyl-4-phenylpyridinium), a metabolite of MPTP, induces dopaminergic neurodegeneration mirroring Parkinson's disease.
- Existing research suggests oxygen free radicals mediate MPP(+)-induced cytotoxicity.
Purpose of the Study:
- To investigate if MPP(+) generates oxygen free radicals and causes oxidative stress in SH-SY5Y human neuroblastoma cells.
- To evaluate the protective effects of antioxidants and nitric oxide synthase (NOS) inhibitors against MPP(+) toxicity.
Main Methods:
- Assessed MPP(+) cytotoxicity and lipid peroxidation levels in SH-SY5Y cells.
- Examined the impact of antioxidants (ascorbic acid, Trolox, PBN) and NOS inhibitor (NAME) on MPP(+) toxicity.
- Investigated the effect of combined antioxidant enzymes (SOD, catalase) and NAME on MPP(+) cytotoxicity.
- Evaluated MPP(+) potentiation of iron and H(2)O(2)-induced cytotoxicity.
Main Results:
- MPP(+) exhibited dose-dependent toxicity but did not increase lipid peroxidation at toxic concentrations.
- Antioxidants, antioxidant enzymes, and NOS inhibition failed to protect cells against MPP(+) cytotoxicity.
- MPP(+) potentiated cytotoxicity induced by iron and H(2)O(2) in a sublethal dose.
Conclusions:
- Oxygen free radicals are unlikely to be the primary mediators of MPP(+)-induced cell death.
- MPP(+) appears to enhance cellular vulnerability to oxidative stress, rather than directly causing it.