Inhibitory activities of flavonoids from Eupatorium adenophorum against acetylcholinesterase

Fifteen flavonoids isolated from the Eupatorium adenophorum showed inhibitory activities against acetylcholinesterase (AChE) isolated from Caenorhabditis elegans and Spodoptera litura. Their IC₅₀ values ranged from 12.54 to 89.06μg/mL and 12.08 to 86.01μg/mL, respectively against the AChE isolated from the nematode and insect species. AChE was inhibited in a dose-dependent manner by all tested flavonoids, The isolated compound quercetagetin-7-O-(6-O-caffeoyl-β-D-glucopyranoside) displayed the highest inhibitory effect against AChE from C. elegans and S. litura, with IC₅₀ values of 12.54 μg/mL and 12.58 μg/mL, respectively. The structure-activity relationship of flavonoids on the inhibitory activities indicated that additional phenolic hydroxyl groups in the glucose were favorable for their inhibitory effects and the degree of increase in inhibitory activity also depended on the number of phenolic hydroxyl groups. The Lineweaver-Burk and Dixon plots indicated that quercetagetin-7-O-(6-O-caffeoyl-β-d-glucopyranoside) is a reversible inhibitor against AChE. Quercetagetin-7-O-(6-O-caffeoyl-β-d-glucopyranoside), 5,4'-Dihydroxytlavone and quercetin-3-O-β-d-glucopyranoside inhibited AChE in a mixed-type competitive manner and these compounds might be the dual binding site AChE inhibitors. Further, nine compounds showed poisonous effects against C. elegans and inhibitory effects on the growth and development of S. litura.