Amyrin attenuates scopolamine-induced cognitive impairment in mice

Alzheimer's disease, a neurodegenerative disorder, is characterized by progressive cognitive impairment associated with the disruption of cholinergic neurotransmission. The aim of the present study was to evaluate the effect of α- or β-amyrin, a type of pentacyclic triterpene, on the cognitive impairment induced by scopolamine, a muscarinic acetylcholine receptor antagonist. To measure the abilities of various types of learning and memory, we conducted step-through passive avoidance task. Scopolamine induced deficits in learning and memory processes in mice, which were antagonized by a single administration of α-amyrin (2 or 4 mg/kg) or β-amyrin (4 mg/kg), respectively. Additionally, in vitro analysis revealed that acetylcholinesterase activity was inhibited by β-amyrin, but not by α-amyrin. Furthermore, Western blot analysis revealed that the expression levels of phosphorylated extracellular signal-regulated kinase 1/2 (pERK) and phosphorylated glycogen synthase kinase-3β (pGSK-3β) were significantly enhanced by a single administration of α- and β-amyrin in the hippocampus. Finally, the memory ameliorating effects of α- or β-amyrin on the scopolamine-induced cognitive impairments were significantly blocked by ERK inhibitor U0126. The present study suggests that α- and β-amyrin may ameliorate the cognitive impairment induced by hypocholinergic neurotransmission via the activation of ERK as well as GSK-3β signaling.