Because of the direct correlation of cholinergic deficit and the severity of dementia, Alzheimers disease is preferentially treated with acetylcholinesterase (AChE) inhibitors to supplement the acetylcholine level. In this study we focused on non-alkaloid AChE inhibitors from natural sources in order to discover new lead structures. In the course of in vitro extract screening of Tyrolean plants using an enzyme assay with Ellmans reagent, the dichloromethane extract of chicory roots (Cichorium intybus L.) showed a pronounced inhibitory effect on AChE. At a concentration of 1 mg extract/ml an inhibition of 70% was measured. Based on a 3D multi-conformational molecularstructure database consisting of secondary metabolites from C. intybus known from the relevant literature, virtual screening filtering experiments were conducted using both a feature-based pharmacophore model and a docking procedure. Some low molecular weight sesquiterpenoids exhibited distinct interactions with the pharmacophore model. In order to verify the applicability of this computer-aided strategy, an activity-guided fractionation of the chicory root extract was performed, which resulted in the isolation of two sesquiterpene lactones, 8-deoxylactucin and lactucopicrin, showing significant and dose-dependent inhibitory activity on AChE (IC50 of 308.1 μM [CI95 243.9 - 405.3 μM] and 150.3 μM [CI95 100.8 - 188.1 μM], respectively). The two isolates were correctly predicted within the virtual screening process which corroborates the potential of the computer-assisted in combo screening approach for the discovery of the anti-cholinesterase compounds from C. intybus.
Keywords: in combo screening, chicory root, sesquiterpene lactones, activity-guided fractionation, virtual screening, pharmacophore model, acetylcholinesterase, alzheimers disease
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