Khaw_2014_Phytomedicine_21_1303

Garcinia mangostana is a well-known tropical plant found mostly in South East Asia. The present study investigated acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities of G. mangostana extract and its chemical constituents using Ellman's colorimetric method. Cholinesterase inhibitory-guided approach led to identification of six bioactive prenylated xanthones showing moderate to potent cholinesterases inhibition with IC50 values of lower than 20.5muM. The most potent inhibitor of AChE was garcinone C while gamma-mangostin was the most potent inhibitor of BChE with IC50 values of 1.24 and 1.78muM, respectively. Among the xanthones, mangostanol, 3-isomangostin, garcinone C and alpha-mangostin are AChE selective inhibitors, 8-deoxygartanin is a BChE selective inhibitor while gamma-mangostin is a dual inhibitor. Preliminary structure-activity relationship suggests the importance of the C-8 prenyl and C-7 hydroxy groups for good AChE and BChE inhibitory activities. The enzyme kinetic studies indicate that both alpha-mangostin and garcinone C are mixed-mode inhibitors, while gamma-mangostin is a non-competitive inhibitor of AChE. In contrast, both gamma-mangostin and garcinone C are uncompetitive inhibitors, while alpha-mangostin is a mixed-mode inhibitor of BChE. Molecular docking studies revealed that alpha-mangostin, gamma-mangostin and garcinone C interacts differently with the five important regions of AChE and BChE. The nature of protein-ligand interactions is mainly hydrophobic and hydrogen bonding. These bioactive prenylated xanthones are worthy for further investigations.