Anticholinesterase potential of flavonols from paper mulberry (Broussonetia papyrifera) and their kinetic studies.

It is necessary to develop food additives to help treat chronic disorders like neurodegenerative diseases from medicinal plants. Ethanol extracts of paper mulberry were found to display significant inhibition against cholinesterases, enzymes that are strongly linked with Alzheimer's disease (AD). The active components were identified as prenylated flavonols (2-4) that inhibited two related human cholinesterases in a dose-dependent manner, with IC50's ranging between 0.8 and 3.1μM and between 0.5 and 24.7μM against human acetylcholinesterase (hAChE) and butylcholinesterase (BChE), respectively. Prenyl groups within these flavonols were found to play a critical role for inhibition because the parent compound 1, quercetin, was inactive (IC50>500μM) towards the target enzymes. Flavonols (2-4) showed mixed inhibition kinetics as well as slow and time-dependent reversible inhibition toward hAChE. The affinity between protein and inhibitors was investigated using fluorescence quenching. The affinity constants (KSA) of inhibitors increased in proportion to their inhibitory potencies.