Oral Treatment with the NADPH Oxidase Antagonist Apocynin Mitigates Clinical and Pathological Features of Parkinsonism in the MPTP marmoset Model

This study evaluates the therapeutic efficacy of the NADPH oxidase inhibitor apocynin, isolated as principal bioactive component from the medicinal plant Picrorhiza kurroa , in a marmoset MPTP model of Parkinson’s disease (PD). The methoxy-substituted catechol apocynin has a similar structure as homovanillic acid (HVA), a metabolite of dopamine (DA). Apocynin acquires its selective inhibitory capacity of the reactive oxygen species generating NADPH oxidase via metabolic activation by myeloperoxidase (MPO). As MPO is upregulated in activated brain microglia cells of PD patients and in MPTP animal models, the conditions for metabolic activation of apocynin and inhibition of microglia NADPH oxidase are in place. Marmoset monkeys received oral apocynin (100 mg/kg; p.o.) ( n = 5) or Gum Arabica (controls; n = 5) three times daily until the end of the study, starting 1 week before PD induction with MPTP (1 mg/kg s.c. for 8 days). Parkinsonian symptoms, motor function, home-cage activity and body weight were monitored to assess the disease development and severity. Post-mortem numbers of the tyrosine hydroxylase expressing DA neurons in the substantia nigra were counted. During the MPTP injections, apocynin limited the body weight loss and relieved parkinsonian symptoms compared to controls (Linear regression, P