Background: The most effective symptomatic treatment of Parkinson’s disease remains the metabolic precursor of dopamine, L-dopa. To enhance the efficacy of L-dopa, it is often combined with inhibitors of the enzymes, catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO) B, key metabolic enzymes of L-dopa and dopamine.
Objective: This study attempts to discover compounds that exhibit dual inhibition of COMT and MAO-B among a library of 40 structurally diverse natural compounds. Such dual acting inhibitors may be effective as adjuncts to L-dopa and offer enhanced value in the management of Parkinson’s disease.
Methods: Selected natural compounds were evaluated as in vitro inhibitors of rat liver COMT and recombinant human MAO. Reversibility of MAO inhibition was investigated by dialysis.
Results: Among the natural compounds morin (IC50 = 1.32 µM), chlorogenic acid (IC50 = 6.17 µM), (+)-catechin (IC50 = 0.86 µM), alizarin (IC50 = 0.88 µM), fisetin (IC50 = 5.78 µM) and rutin (IC50 = 25.3 µM) exhibited COMT inhibition. Among these active COMT inhibitors only morin (IC50 = 16.2 µM), alizarin (IC50 = 8.16 µM) and fisetin (IC50 = 7.33 µM) were noteworthy MAO inhibitors, with specificity for MAO-A.
Conclusion: None of the natural products investigated here are dual COMT/MAO-B inhibitors. However, good potency COMT inhibitors have been identified, which may serve as leads for the future development of COMT inhibitors.