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The potential proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces Parkinson-like syndromes in common marmosets, other primates, and humans. MPTP is metabolically activated to 1-methyl-4-phenyl-2,3-dihydropyridiniumand 1-methyl-4-phenylpyridinium ions (MPDP+ and MPP+, respectively) by desaturation reactions. MPTP is deactivated to 4-phenyl-1,2,3,6-tetrahydropyridine (PTP) by N-demethylation and is also deactivated to MPTP N-oxide. The roles of cytochrome P450 (P450) enzymes and flavin-containing monooxygenases (FMOs) in the oxidative metabolism of MPTP-treated marmosets are not yet fully clarified. This study aimed to elucidate P450-and FMO-dependent MPTP metabolism in marmoset liver and brain. Rates of MPTP N-oxygenation in liver microsomes were similar to those in brain microsomes from 11 individual marmosets (substrate concentration, 50 mu M) and were correlated with rates of benzydamine N-oxygenation (r = 0.75, P < 0.05); the reactions were inhibited by methimazole (10 mu M). MPTP N-oxygenation was efficiently mediated by recombinantly expressed marmoset FMO3. Rates of PTP formation by MPTP N-demethylation in marmoset liver microsomes were correlated with bufuralol 19-hydroxylation rates (r = 0.77, P < 0.01) and were suppressed by quinidine (1 mu M), thereby indicating the importance of marmoset CYP2D6 in PTP formation. MPTP transformations to MPDP+ and MPP+ were efficiently catalyzed by recombinant marmoset CYP2D6 and human CYP1A2. These results indicated the contributions of multiple drug-metabolizing enzymes to MPTP oxidation, especially marmoset FMO3 in deactivation (N-oxygenation) and marmoset CYP2D6 for both MPTP deactivation and MPTP activation to MPDP+ and MPP+. These findings provide a foundation for understanding MPTP metabolism and for the successful production of preclinical marmoset models.
Research papers (academic journals)
