Selective Inhibition of Prenylated Flavonoids from Sophora flavescens against BACE1 and Cholinesterases

It was previously reported that certain lavandulylated flavanones from Sophora flavescens are β-site APP cleaving enzyme 1 (BACE1) inhibitors; however, based upon their levels within the extract, their inhibitory effects should be higher than expected. Moreover, chalcones and flavonols were reported to exert higher bioactivities than flavanones. These findings have led to a further search for other possible constituents potentially contributing to the strong inhibitory activity of the S. flavescens extract. In this study, BACE1 activities were significantly inhibited by 8-lavandulylkaempferol (IC 50 7.29 μM), kuraridinol (IC 50 7.10 μM), kuraridin (IC 50 6.03 μM), and kushenol C (IC 50 5.45 μM) from the ethyl acetate fraction, along with desmethylanhydroicaritin (IC 50 1.86 μM), xanthohumol (IC 50 7.19 μM), and leachianone G (IC 50 8.56 μM) from the dichloromethane fraction of the extract. The results indicate that the prenyl group, rather than the lavandulyl group, and the flavonols and chalcones, rather than flavanones, might make predominant contributions to BACE1 inhibition. In particular, 8-lavandulylkaempferol exhibited significant inhibitory effects with IC 50 values of 7.10 and 8.11 μM for butyrylcholinesterase and acetylcholinesterase, respectively, when compared to its counterpart, desmethylanhydroicaritin. This indicates that the lavandulyl group might play a predominant role in both cholinesterase inhibitions. This is the first study indicating that prenylated flavonoids exert varying degrees of inhibition primarily through their skeleton (flavonols, chalcones, flavanones), as well as their lipophilic chain length (prenyl and lavandulyl groups). Therefore, S. flavescens and its prenylated flavonoids, possessing low molecular weights and lipophilic moieties may be potent preventive and therapeutic candidates for Alzheimer's disease.