Selective inhibition of monoamine oxidase A by chelerythrine, an isoquinoline alkaloid.

Chelerythrine, an isoquinoline alkaloid isolated from the herbaceous perennial Chelidonium majus, was found to potently and selectively inhibit an isoform of recombinant human monoamine oxidase-A (MAO-A) with an IC ₅₀ value of 0.55 µM. Chelerythrine was a reversible competitive MAO-A inhibitor (K _i  = 0.22 µM) with a potency much greater than toloxatone (IC ₅₀  = 1.10 µM), a marketed drug. Other isoquinoline alkaloids tested did not effectively inhibit MAO-A or MAO-B. A structural comparison with corynoline suggested the 1- and/or 2-methoxy groups of chelerythrine increase its inhibitory activity against MAO-A. Molecular docking simulations revealed that the binding affinity of chelerythrine for MAO-A (-9.7 kcal/mol) was greater than that for MAO-B (-4.6 kcal/mol). Docking simulation implied that Cys323 and Tyr444 of MAO-A are key residues for hydrogen-bond interaction with chelerythrine. Our findings suggest chelerythrine is one of the most reversible selective and potent natural inhibitor of MAO-A, and that it be regarded a potential lead compound for the design of novel reversible MAO-A inhibitors.
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