piperidines and 1-methyl-4-(methylpyrrol-2-yl)-1-2-3-6-tetrahydropyridine

The ability of highly purified preparations of human monoamine oxidase A and B (MAO A and B) to utilize 1-methyl-4-(1-methylpyrrol-2-yl)-4-piperidinol (MMPP) and its dehydration product 1,2,3,6-tetrahydro-1-methyl-4-(methylpyrrol-2-yl) pyridine (TMMP) as substrates was investigated. The results showed that TMMP was a substrate for both forms of MAO with Km,app values of approximately 60 microM. However, MAO B had a Vmax,app for TMMP about 30-fold greater than MAO A. Additional studies revealed that MMPP was a poor substrate of only MAO B (Km,app = 9.5 mM) and that acid treatment of MMPP led to the formation of a product that could be readily oxidized by both MAO A and B. Similar acid pretreatment of TMMP yielded a product that was a much poorer substrate for MAO B than the parent compound. These results may partially explain why orally administered MMPP produces neurotoxicity in monkeys and TMMP fails to induce chemical parkinsonism.

Topics: Female; Humans; Kinetics; Liver; Molecular Structure; Monoamine Oxidase; Oxidation-Reduction; Piperidines; Placenta; Pregnancy; Pyridines; Spectrophotometry, Ultraviolet; Substrate Specificity

Two analogs of the nigrostriatal neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were examined for their deleterious effects on nigrostriatal neurons. 1,2,3,6-Tetrahydro-1-methyl-4-(methylpyrrol-2-yl)pyridine (TMMP), but not 1-methyl-4-(1-methylpyrrol-2-yl)-4-piperidinol, caused persistent depletion of striatal dopamine and induced histologic evidence of nerve terminal degeneration in mice. These findings differ diametrically from results previously reported for the two analogs. TMMP produced larger dopamine depletions than MPTP when the two drugs were given in equivalent doses. Further experiments demonstrated that TMMP is preferentially oxidized by mouse brain monoamine oxidase B to a water-soluble compound, most likely the pyridinium ion species. Prior treatment of mice with either the monoamine oxidase inhibitor pargyline or the dopamine reuptake inhibitor bupropion blocked the ability of TMMP to deplete striatal dopamine. Thus, the pharmacologic profile of TMMP closely resembles that of MPTP. That TMMP and MPTP induce dopamine depletions by a similar mechanism tends to support the proposed neurochemical sequence of events thought to lead to the expression of MPTP-induced neurotoxicity. The authors' observations provide further evidence that MPTP is not unique in its capability to damage nigrostriatal neurons.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Biotransformation; Corpus Striatum; Dopamine; Dose-Response Relationship, Drug; Male; Mice; Mice, Inbred C57BL; Monoamine Oxidase Inhibitors; Piperidines; Pyridines; Structure-Activity Relationship