Acetylcholinesterase inhibitory activity of the total alkaloid from traditional Chinese herbal medicine for treating Alzheimer's disease

Alzheimer's disease (AD) is a progressive degenerative neurologic disorder resulting in impaired memory and behavior. A promising treatment strategy for AD has been the use of acetylcholinesterase (AChE) inhibitors. Several potent AChE inhibitors such as huperzine and galanthamine were originally isolated from plants, indicating that herbal medicines are a good source for the search of potential AChE inhibitors. In our study, to search for potential AChE inhibitors, the total alkaloidal extracts of 31 Chinese herbal medicines were tested for their AChE inhibitory activities by Ellman's method and modified TLC bioautographic assay. The results showed that the alkaloidal extracts of Uncaria rhynchophylla (Rubiaceae), Nelumbo nucifera (Nymphaeaceae), Zanthoxylum nitidum (Rutaceae), Portulaca oleracea (Portulacaceae), and Pinellia ternata (Araceae) exhibited remarkable AChE inhibitory activities at the final concentration of 100 mu g/ml. Their IC50 values were 10.8, 12.2, 17.4, 29.4, and 56.2 mu g/ml, respectively. The rest of the alkaloidal extracts showed no or very weak AChE inhibitory activities at the same concentration. The results of this study indicate that the screening of traditional Chinese herbs for AChE inhibitory activity may provide useful lead compounds in the discovery of new drugs for the treatment of AD.