Monoamine oxidase A inhibition as monotherapy reverses parkinsonism in the MPTP-lesioned marmoset.

Monoamine oxidase (MAO) type B (MAO-B) inhibition was shown to confer anti-parkinsonian benefit as monotherapy and adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in clinical trials. Here, we explore the anti-parkinsonian effect of MAO type A (MAO-A) inhibition as monotherapy, as the enzyme MAO-A is also encountered within the primate and human basal ganglia, where it metabolises dopamine, albeit to a lesser extent than MAO-B. In six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets, we assessed the anti-parkinsonian effect of the reversible MAO-A inhibitor moclobemide (0.1 and 1 mg/kg) as monotherapy and compared it to that of L-DOPA and vehicle treatments. Moclobemide significantly reversed parkinsonism (by 39%, P < 0.01), while eliciting only mild dyskinesia and psychosis-like behaviours (PLBs). In contrast, L-DOPA anti-parkinsonian effect was accompanied by marked dyskinesia and PLBs. MAO-A inhibition with moclobemide may provide anti-parkinsonian benefit when administered without L-DOPA and might perhaps be considered as monotherapy for the treatment of Parkinson's disease in the early stages of the condition.