Neuroprotective action of donepezil mediated by neuronal nicotinic receptors

AChE inhibitors used in the treatment in Alzheimer's disease such as donepezil are effective in preventing glutamate neurotoxicity. In primary cultures of the cortical neurons, donepezil prevents glutamate neurotoxicity when the drug is applied 8-24 hr prior to glutamate exposure. Neuroprotective effect of donepezil is antagonized by mecamylamine, dihydro-β-erythoridine and metyllcaconitine. Prolonged (more than 4 days) exposure of the cultures to donepezil induces an increase in the nicotine-induced Ca²⁺ influx and number of neurons expressing α4 and α7 subunits of nicotinic receptors. Donepezil also prevents apoptotic neuronal death induced by glutamate. Inhibitors for non-receptor type tyrosine kinase, Fyn and janus-activated kinase 2, suppress the neuroprotective effect of donepezil. Neuroprotective effect of donepezil is also suppressed by a phosphatidylinositol 3-kinase (PI3K) inhibitor. Phosphorylation level of Akt, an effector of PI3K, and the expression level of Bcl-2 increase with donepezil. These results suggest that donepezil prevents glutamate neurotoxicity through α4- and α7-nicotinic acetylcholine receptors (nAChRs), followed by activation of PI3-Akt pathway but independent from activation of ion channels associated with nAChRs. α4- and α7-nAChRs may play an important role in promoting survival of cortical neurons under oxidative stress caused by excitotoxicity.