Protective Effects of Daidzein on Oxidative Stress‐Induced Neurotoxicity and Scopolamine‐Mediated Cognitive Defect

To investigate the effect of daidzein, a major isoflavone constituent isolated from Pueraria thunbergiana (an arrowroot), on the oxidative damage and the scopolamine‐induced cognitive deficit, in vitro cell viability assays and in vivo behavioral tests were performed. Using 3 assays 3‐(4,5‐dimethylthiazol‐2‐yl)–2,5‐diphenyl tetrazolium bromide (MTT) reduction, lactate dehydrogenase release, and trypan blue exclusion) daidzein showed cell protective effects on oxidative stress‐induced cytotoxicity. Administration of daidzein to mice significantly reversed the scopolamine‐induced learning and memory impairment in a passive avoidance test. Injection of scopolamine to mice impaired performance in the passive avoidance test (43% decrease). In contrast, mice treated with daidzein before scopolamine injection were protected from this change (higher than the control value). These results suggest that daidzein's neuronal cell protective activities reduce the scopolamine‐induced cognitive deficit and that its anti‐amnesic effect might be due to the activation of choline acetyltransferase.