title: 1-Methyl-4-phenylpyridinium (MPP+) but not 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP) serves as methyl donor for dopamine: a possible mechanism of action.
abstract: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium (MPP+), the active product of MPTP, caused Parkinson's disease-like symptoms. The mechanism of action of MPP+ is unknown, but analogues of MPTP lacking an N-methyl group were found to be essentially devoid of toxicity, which means that the methyl group of the pyridine ring plays a role in the toxicity. This is of interest because S-adenosylmethionine (SAM), which is the biologic methyl donor and requires a methyl group for its action, also caused MPP(+)-like motor deficits in rodents. Therefore, the requirement of a methyl group by MPTP and MPP+ for their actions suggests that, like SAM, MPP+ and MPTP may serve as methyl donors. This hypothesis was tested by reacting SAM, MPP+, or MPTP with dopamine in the presence of catechol-O-methyltransferase and measuring the methylated product of dopamine produced. Like SAM, MPP+, but not MPTP, methylated dopamine. The methylated product coeluted from chromatographic columns with standard 3-methoxytyramine. Concentrations of 15.6, 62.5, 250, and 1000 nmoles/tube increased the 3-methoxytyramine recovered above controls by 0.0, 6.88, 44.55, 129.47 and 5.8, 13.9, 50.58, 121.31 nmoles for SAM and MPP+, respectively. The dopamine that remained unreacted was dose-dependently decreased. MPTP had no significant effect. The ability of MPP+ to serve as a methyl donor may represent a mechanism for the toxicity of MPP+.
authors.affiliation: Department of Physiology, Meharry Medical College, Nashville, TN 37208.
authors.forename: C G
authors.initials: CG
authors.lastname: Charlton
mesh_terms: D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine / Q000494:pharmacology*; D015655:1-Methyl-4-phenylpyridinium / Q000494:pharmacology*; D000818:Animals; D002394:Catechol O-Methyltransferase / Q000502:physiology*; D002852:Chromatography, Ion Exchange; D004298:Dopamine / Q000031:analogs & derivatives* / Q000378:metabolism*; D051381:Rats; D012436:S-Adenosylmethionine / Q000494:pharmacology
chemical_list: D012436:S-Adenosylmethionine; D015632:1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; D002394:Catechol O-Methyltransferase; C001746:3-methoxytyramine; D015655:1-Methyl-4-phenylpyridinium; D004298:Dopamine