PF 9601N [N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine], a new MAO-B inhibitor,attenuates MPTP-induced depletion of striatal dopamine levels in C57/BL6 mice

Monoamine oxidase isoform B (MAO-B) is involved in Parkinson's disease (PD) induced by the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxin (MPTP) in human and non-human-primate. MAO-B inhibitors, such as L-deprenyl have shown to prevent against MPTP-toxicity in different species, and it has been used in Parkinson therapy, however, the fact that it is metabolized to (-)-methamphetamine and (-)-amphetamine highlights the need to find out new MAO-B inhibitors without a structural amphetaminic moiety. In this context we herein report, for the first time, anywhere a novel non-amphetamine-like MAO-B inhibitor, PF 9601N, N-(2-propynyl)-2-(5-benzyloxy-indolyl) methylamine. This attenuates the MPTP-induced striatal dopamine depletion in young-adult and adult-old C57/BL mice, using different schedules of administration, and which behave "ex vivo" as a slightly more potent and selective MAO-B inhibitor than L-deprenyl, assayed for comparative purposes in the same experimental conditions. The MAO-B ID(50) values were calculated from the total MAO-B activity measured against [14C] phenylethylamine (22 microM) as substrate, at each inhibitor concentration. The MAO-B ID(50) values resulted to be 381 and 577 nmol/kg for PF 9601N and L-deprenyl, respectively. The intraperitoneally (i.p.) co-administration to young-adult C57/BL6 mice of MPTP (30 mg/kg), with different concentrations of PF 9601N or L-deprenyl (29.5-0.357 micromol/kg) showed a dose-dependent protective effect against striatal dopamine depletion, measuring the dopamine contents and its metabolites by HPLC. The ED(50) value proved to be 3.07 micromol/kg without any significant differences between either MAO-B inhibitor. Nevertheless, lower doses of PF 9601N (1.5 micromol/kg) were necessary to get almost total protection, without any change in the DOPAC and HVA content, when administered 2 h before MPTP (30 mg/kg), whereas partial protection (45%) against dopamine depletion was observed in the case of L-deprenyl. In both cases, MAO-B inhibition was a necessary condition in order to observe the protective effect. When adult-old (8-10 months) C57/BL6 mice were used, MPTP (25 mg/kg) administration induced 25 days later, an irreversible dopamine depletion. In these conditions, chronic administration with 0.15 micromol/kg of PF 9601N, before the toxin, every 24 h for 10 days, rendered almost total protection of dopamine depletion, whereas L-deprenyl yielded only 50% protection of the dopamine content, assayed in the same conditions. It is worth remarking, that in both cases MAO-B was not affected. From these results, it can be concluded that PF 9601N attenuates MPTP neurotoxicity "in vivo" better than L-deprenyl through different mechanisms, with special relevance to the protective effect, independent of MAO-B inhibition, observed in the irreversibly MPTP-lesioned adult-old mice. Therefore, this novel non-amphetamine MAO-B inhibitor could be potentially effective in PD therapy.