We found that an extract of Lycoris chejuensis and its three isolated active components, narciclasine, 7-deoxynarciclasine, and 7-deoxy-trans-dihydronarciclasine, each significantly reduced the formation of amyloid-β peptides in HeLa cells transfected with an amyloid precursor protein carrying the Swedish mutation up to 45 ± 3.6%. The extract down-regulated amyloid precursor protein, especially the mature form by up to 88%, and reduced the ability of secretases to generate toxic amyloid-β. Double-transgenic mice treated with the extract for 4 months also showed significantly reduced levels of amyloid-β and plaques while exhibiting improved memory functions in the Morris water maze and novel object recognition tests. In conclusion, the extract and isolated active components of L. chejuensis decreased the production of amyloid-β by attenuating amyloid precursor protein levels. Furthermore, the extract improved the disrupted memory functions in animals while inhibiting amyloid plaque formation. Thus, this extract, as well as its active components, could prove beneficial in the treatment of Alzheimer's disease.
