Intraperitoneal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration induces apoptosis of subventricular zone (SVZ) doublecortin (Dcx)-positive neural progenitor cells (migrating neuroblasts, A cells). Actually, a metabolite of MPTP, 1-methy-4-phenylpiridinium (MPP(+)), is responsible for neural progenitor cell toxicity. In the present study, to examine whether the MPTP-induced SVZ cell apoptosis is caused directly by MPP(+) metabolized through monoamine oxidase B (MAO-B), MPTP or MPP(+) was intracerebroventricularly (icv) injected into C57BL/6 mice. At Day 1 postinjection, many terminal deoxynucleotidyl transferase-mediated dUTP endlabeling (TUNEL)-positive cells were observed in the SVZ of both low (36μg) and high (162μg) dose MPTP- and MPP(+)-injected mice. The number of Dcx-positive A cells showed a significant decrease following high dose of MPTP- or MPP(+)-injection on Days 1 and 3, respectively, whereas that of EGFR-positive C cells showed no change in mice with any treatment. In addition, prior icv injection of a MAO-B inhibitor, R(-)-deprenyl (deprenyl), inhibited MPTP-induced apoptosis, but not MPP(+)-induced apoptosis. MAO-B- and GFAP-double positive cells were detected in the ependyma and SVZ in all mice. It is revealed from these results that icv injection of MPTP induces apoptosis of neural progenitor cells (A cells) in the SVZ via MPP(+) toxicity. In addition, it is suggested that the conversion from MPTP to MPP(+) is caused mainly by MAO-B located in ependymal cells and GFAP-positive cells in the SVZ.
"MPTP crosses the blood-brain barrier and is bioactivated enzymatically to give 1-methyl-4-phenylpyridinium (MPP+) [1, 8, 9], which is selectively uptaken into dopaminergic cells via dopamine-activated transporter (DAT) and produces inhibition of mitochondrial complex I, energy depletion, and cell death  (Figure 1). Besides its use in experimental models of neurotoxicity, the toxic outcome caused by MPTP is a matter of investigation due to the differences in response among experimental models [10, 11]. This might result from a change in the balance between the rate of metabolism to toxic products (MPP+ and MPDP+) (activation) and the rate of detoxification (inactivation) [12–16]. "
[Show abstract][Hide abstract] ABSTRACT: Metabolic enzymes are involved in the activation/deactivation of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyiridine (MPTP) neurotoxin and its naturally occurring analogs 2-methyltetrahydro-β-carbolines. The metabolic profile and biotransformation of these protoxins by three enzymes, monoamine oxidase (MAO), cytochrome P450, and heme peroxidases (myeloperoxidase and lactoperoxidase), were investigated and compared. The metabolite profile differed among the enzymes investigated. MAO and heme peroxidases activated these substances to toxic pyridinium and β-carbolinium species. MAO catalyzed the oxidation of MPTP to 1-methyl-4-phenyl-2,3-dihydropyridinium cation (MPDP+), whereas heme peroxidases catalyzed the oxidation of MPDP+ to 1-methyl-4-phenylpyridinium (MPP+) and of 2-methyltetrahydro-β-carboline to 2-methyl-3,4-dihydro-β-carbolinium cation (2-Me-3,4-DHβC+). These substances were inactivated by cytochrome P450 2D6 through N-demethylation and aromatic hydroxylation (MPTP) and aromatic hydroxylation (2-methyltetrahydro-β-carboline). In conclusion, the toxicological effects of these protoxins might result from a balance between the rate of their activation to toxic products (i.e.,
N-methylpyridinium-MPP+ and MPDP+- and N-methyl-β-carbolinium—βC+—) by MAO and heme peroxidases and the rate of inactivation (i.e., N-demethylation, aromatic hydroxylation) by cytochrome P450 2D6.
[Show abstract][Hide abstract] ABSTRACT: In the present study, we evaluated the influence of intraperitoneal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 1-methyl-4-phenylpyridinium (MPP(+)) on the placenta. There was no increase in apoptotic cells in the placentas of C57BL/6 mice treated with 25.0 mg/kg MPTP or 17.1 mg/kg MPP(+), indicating that a single injection of the chemicals may induce very slight cytotoxicity in the placenta at 12 hr after administration. The decrease in the expression of monoamine oxidase (MAO)-A in the labyrinth zone and that of MAO-B in the basal zone may be due to the decrease in cell activity, whereas the increase of MAO-B expression in the labyrinth zone after MPTP treatment may be due to a responsive reaction caused by MPTP, one of the substrates of MAO-B. The results represent histological evidence that MAO-B may be involved in the metabolism of MPTP to MPP(+) in the labyrinth zone of the mouse placenta. In the present study, no increase in apoptotic cells indicates that MPTP and MPP(+) are hardly toxic to the placenta, and the histological change in MAO-B expression may indicate the possibility of involvement of placental MAO-B in MPTP metabolism.
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