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Toxicity of MPTP and structural analogs in clonal cell lines of neuronal origin expressing B type monoamine oxidase
1Division of Nutritional Sciences, UCLA School of Public Health 90024.
Abstract:
The toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), its oxidized metabolite, and two recently synthesized 2'-alkyl derivatives of MPTP (methyl and ethyl), found to be more toxic in vivo in mice, have been compared in two neuroblastoma hybrid cell lines (NCB-20 and 140-3) that express the B form of monoamine oxidase (MAO), as tissue culture models for the mode of action of MPTP in the central nervous system. Unlike previously reported studies with cultured cells of neuronal origin expressing only MAO A, both of these cell lines were sensitive to MPTP. Consistent with the in vivo findings, the 2'-alkyl derivatives were much more toxic than MPTP and comparable to the oxidized metabolite MPP+ in their effects on cell survival and morphology. The cells could be protected against the reduced toxins, but not MPP+, by either the MAO A selective inhibitor, clorgyline or the MAO B selective inhibitor, deprenyl. The effectiveness of the MAO inhibitors in blocking the action of the reduced toxins was consistent with their ability to inhibit MAO activity in the cell cultures, but did not reflect MAO-substrate specificity of the toxins. Inhibitors of serotonin and dopamine uptake, which have been found to protect against MPTP toxicity in vivo, were generally ineffective in the cell cultures, with the exception of a marginal increase in survival of MPP(+)-treated 140-3 cells in the presence of the serotonin uptake inhibitor fluoxetine. These findings are discussed in relation to proposed in vivo mechanisms of MPTP cytotoxicity.
Insights
New 2'-alkyl MPTP derivatives are more toxic than MPTP and its metabolite MPP+ in cell cultures. Monoamine oxidase inhibitors protected against these toxins, suggesting a novel mechanism for MPTP neurotoxicity.
Area of Science:
- Neuroscience
- Toxicology
- Cell Biology
Background:
- 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that selectively damages dopaminergic neurons.
- MPTP's toxicity is mediated by its oxidized metabolite, MPP+.
- Previous studies on MPTP toxicity in cell cultures have yielded conflicting results, partly due to differences in monoamine oxidase (MAO) expression.
Purpose of the Study:
- To compare the toxicity of MPTP, its metabolite MPP+, and two novel 2 eal-alkyl derivatives in neuroblastoma cell lines expressing MAO B.
- To investigate the role of MAO A and MAO B in the cellular toxicity of these compounds.
- To explore the potential protective effects of MAO inhibitors and neurotransmitter uptake inhibitors against MPTP-induced cytotoxicity in vitro.
Main Methods:
- Utilized two neuroblastoma hybrid cell lines (NCB-20 and 140-3) expressing MAO B as in vitro models.
- Assessed cell survival and morphology following exposure to MPTP, MPP+, and its 2 eal-alkyl derivatives.
- Administered MAO selective inhibitors (clorgyline for MAO A, deprenyl for MAO B) and neurotransmitter uptake inhibitors (serotonin and dopamine) to evaluate protective effects.
Main Results:
- Both cell lines were sensitive to MPTP, unlike previous studies with MAO A-expressing cells.
- The 2 eal-alkyl MPTP derivatives exhibited significantly higher toxicity than MPTP and were comparable to MPP+.
- MAO inhibitors (clorgyline and deprenyl) protected cells from MPTP and its derivatives, but not MPP+.
- Neurotransmitter uptake inhibitors were largely ineffective, except for a marginal protective effect of fluoxetine on MPP+-treated 140-3 cells.
Conclusions:
- The 2 eal-alkyl MPTP derivatives demonstrate potent neurotoxicity in vitro, consistent with in vivo findings.
- MAO B plays a crucial role in the activation and subsequent toxicity of MPTP and its derivatives in these cell models.
- The differential effectiveness of MAO inhibitors suggests complex interactions between MAO activity and toxin substrate specificity.
- These findings provide insights into the mechanisms underlying MPTP neurotoxicity and highlight the utility of MAO B-expressing cell lines for studying such toxins.