In vitro neuroprotection by medicinal plant extracts

A compelling body of literature suggests a revivalism of Traditional Medicine. In Western societies severally affected by brain disorders, the research for new “natural” pharmacological strategies is increasingly desired. The reverse-pharmacology not only tries to bridge the gap between science and popular knowledge, but also attempts to provide the urgent needed explanations behind the claimed benefits. Moreover, new applications can be found for species with other traditional uses, providing important contributions to the field of natural products.

Herbal teas were prepared from medicinal plants with or without claim for brain disorders treatment (Cochlospermum angolensis Welw., Jacaranda caroba (Vell.) A. DC., Jasminum grandiflorum L., Grindelia robusta Nutt., Annona muricata L., Hyssopus officinalis L., Trichilia catigua A. Juss, Acorus calamus L., Turnera diffusa Willd. ex Schult. and Pilocarpus pennatifolius Lem.). The enzymatic inhibitory potential was assessed for enzymes known to be involved in the pathogenesis of neurodegenerative and neuropsychiatric disorders: acetyl- and butyryl- cholinesterases (AChE and BuChE) and monoamine oxidase A (MAO-A). While the extracts showed to be weak AChE and BuChE inhibitors (IC₅₀ values above 1020 µg/mL), their effect against MAO-A was stronger, with IC₅₀ values in the range of 130 – 660 µg/mL. As reactive oxygen species have a role in neurodegeneration, the scavenging activity against H₂O₂ was tested. Most of the extracts displayed IC₅₀ values < 130 µg/mL. The effect of these extracts on the neuroblastoma cell line SH-SY5Y viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. J. grandiflorum extract was the least toxic to the cells (LD₅₀= 3659 µg/mL), followed by those of H. officinalis (LD₅₀= 1776 µg/mL) and C. angolensis (LD₅₀= 1563 µg/mL). Based in all bioassays, A. muricata, H. officinalis, C. angolensis, J. caroba and T. diffusa are the most promising species.

Acknowledgements: This work was financed through project UID/QUI/50006/2013, receiving financial support from FCT/MEC through national funds, and co-financed by FEDER, under the Partnership Agreement PT2020. C. Grosso thanks FCT for the FCT Investigator (IF/01332/2014).

Keywords: Acetylcholinesterase, butyrylcholinesterase, monoamine oxidase A, polyphenols, brain disorders.