New butyrylcholinesterase inhibitor derived from mulberry twigs, a kind of agricultural byproducts

Alzheimer's disease (AD) is one of the most common diseases in the elderly, imposing a significant financial and emotional burden on patients and their families. Inhibiting the enzyme cholinesterase is currently one of the main methods of delaying the symptoms of AD. The mulberry extract has good butyrylcholinesterase (BChE) inhibitory activity, but its main active ingredients and the mechanism of action are unknown. In this study, three potential BChE inhibitors, Kuwanon G, kuwanon H, and morusin, were isolated and identified from mulberry twigs by magnetic nanoparticles Fe3O4@BChE coupled with high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance (HPLC-HRMS-SPE NMR). Kuwanon G, kuwanon H, and morusin displayed potential inhibition activity, and the half maximal inhibitory concentration (IC50 values) were 71.0 ± 2.62 μM, 10.9 ± 0.39 μM and 78.7 ± 2.61 μM, respectively, and the positive control, Galanthaminel was 60.4 ± 6.88 μM. It was found for the first time that Kuwanon H had butyrylcholinesterase inhibitory activity. The results of molecular docking revealed that Kuwanon H interacted primarily with the amino acid residues (Asp70, Ser72, Thr284, Leu286, and Ser287) of the BChE via hydrogen bonding, and interacted with Pro285 to produce hydrogen bonds via water molecular bridge bond, thereby exerting inhibitory activity. This research is critical in explaining the material basis and mechanism of mulberry twigs inhibiting or alleviating Alzheimer's disease as well as contributing to the development and utilization of mulberry twigs as an agricultural by-product.