Neuroprotective effects of donepezil through inhibition of GSK-3 activity in amyloid-β-induced neuronal cell death

Acetylcholinesterase inhibitors (AChE-inhibitors) are used for the treatment of Alzheimer's disease. Recently, the AChE-inhibitor donepezil was found to have neuroprotective effects. However, the protective mechanisms of donepezil have not yet been clearly identified. We investigated the neuroprotective effects of donepezil and other AChE-inhibitors against amyloid-beta 1-42 (A beta 42)-induced neurotoxicity in rat cortical neurons. To evaluate the neuroprotective effects of AChE-inhibitors, primary cultured cortical neurons were pre-treated with several concentrations of AChE-inhibitors for 24 h and then treated with 20 mu M A beta 42 for 6 h. In addition to donepezil, other AChE-inhibitors (galantamine and huperizine A) also showed increased neuronal cell viability against A beta 42 toxicity in a concentration-dependent manner. However, we demonstrated that donepezil has a more potent effect in inhibiting glycogen synthase kinase-3 (GSK-3) activity compared with other AChE-inhibitors. The neuroprotective effects of donepezil were blocked by LY294002 (10 mu M), a phosphoinositide 3 kinase inhibitor, but only partially by mecamylamine (10 mu M), a blocker of nicotinic acetylcholine receptors. Additionally, donepezil's neuroprotective mechanism was related to the enhanced phosphorylation of Akt and GSK-3 beta and reduced phosphorylation of tau and glycogen synthase. These results suggest that donepezil prevents A beta 42-induced neurotoxicity through the activation of phosphoinositide 3 kinase/Akt and inhibition of GSK-3, as well as through the activation of nicotinic acetylcholine receptors.