Tenuifolin, an extract derived from tenuigenin, inhibits amyloid-β secretion in vitro

Aim: Previous studies have shown that tenuigenin, a crude extract of Polygala tenuifolia Willd. that is commonly used in traditional Chinese herbal medicine for memory loss, can reduce the secretion of Ab from cultured cells. However, the mechanism underlying this effect and the active compound derived from tenuigenin is unknown. In this study, a purified component of tenuigenin, tenuifolin, was examined and revealed to be an effective compound in vitro. Methods: A beta secretion from three sets of COS-7 cells, each carrying a plasmid expressing a different form of APP was examined following the treatment with tenuifolin. Initially, tenuifolin was determined to have no inherent toxicity to either the transfected or wild type cells at the effective concentrations. Cells were then treated with 0.5-2.0 mu g mL(-1) tenuifolin for 12 h and their media were examined via an ELISA for A beta 1-40 and A beta-42. Results: We found that treatment with 2.0 mu g mL(-1) tenuifolin significantly decreased Ab secretion from COS-7 cells without altering the ratio of A beta 1-40 and A beta-42. This effect is most probably due to inhibition of the beta-site APP cleaving enzyme as A beta secretion was not inhibited from cells expressing the C99 fragment. Conclusion: Tenuifolin is an effective compound from tenuigenin. We believe that this finding should lead the way for future experiments to determine the exact mechanism for tenuifolin's effect on A beta secretion.