Anti-acetylcholinesterase and anti-amnesic activities of a pregnane glycoside, cynatroside B, from Cynanchum atratum.

We previously reported that seven pregnane glycosides including cynatroside B isolated from the roots of Cynanchum atratum significantly inhibited acetylcholinesterase (AChE) activity. In the present study, we have characterized the mode of AChE inhibition of cynatroside B, the most potent of these isolated pregnane glycoside inhibitors. We have also examined the anti-amnesic activity of cynatroside B. Cynatroside B inhibited AChE activity in a dose-dependent manner and its IC50 value was 3.6 microM. The mode of AChE inhibition by cynatroside B was reversible and non-competitive in nature. Moreover, cynatroside B (1.0 mg/kg body weight i.p.) significantly ameliorated memory impairments induced in mice by scopolamine (1.0 mg/kg body weight s.c.) as measured in the passive avoidance and the Morris water maze tests. We suggest, therefore, that cynatroside B has both anti-AChE and anti-amnesic activities that may ultimately hold significant therapeutic value in alleviating certain memory impairments observed in Alzheimer's disease.