The effect of Banisteriopsis caapi (B. caapi) on the motor deficits in the MPTP-treated common marmoset model of Parkinson’s disease

Introduction

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterised principally by loss of dopaminergic neurons in the substantia nigra and resulting motor impairments. Symptomatic treatment centres on dopamine replacement, most commonly with L-3,4-dihydroxyphenylalanine (L-DOPA), but chronic L-DOPA use is limited by waning efficacy and the emergence of involuntary movements (dyskinesia). Monoamine oxidase B (MAO-B) inhibitors such as selegiline are used to prolong L-DOPA effects by reducing dopamine metabolism. Banisteriopsis caapi (B. caapi), a plant used traditionally in Amazonian preparations, contains β-carbolines (notably harmine, harmaline, and tetrahydroharmine) with monoamine oxidase inhibitory properties and some clinical reports suggest antiparkinsonian effects when taken as a tea, but controlled preclinical characterisation is limited. Fisher and colleagues set out to determine whether an aqueous extract of B. caapi and one of its principal β-carbolines, harmine, alter motor deficits in a primate model of PD. Using MPTP-treated common marmosets that had been primed with prior L-DOPA to exhibit dyskinesia, the investigators evaluated B. caapi extract, harmine, and the selective MAO-B inhibitor selegiline as monotherapies and in combination with submaximal doses of L-DOPA. The study aimed to establish whether B. caapi or harmine produce antiparkinsonian effects, whether these effects are consistent with MAO inhibition, and whether they modify the motor response or dyskinesia induced by L-DOPA.