Mechanism of neuroprotection by donepezil pretreatment in rat cortical neurons chronically treated with donepezil

Abstract

Previously, we showed that in rat cortical neurons, chronic donepezil treatment (10 microM, 4 days) up-regulates nicotinic receptors (nAChR) and makes neurons more sensitive to the neuroprotective effect of donepezil. Here we examined the mechanism of donepezil-induced neuroprotection in neurons chronically treated with donepezil. The mechanism of neuroprotection was examined under different conditions of exposure to glutamate, acute and moderate, that induce cell death associated with necrotic and apoptotic cell death, respectively. Concomitant treatment with antagonists of nAChRs but not muscarinic receptors inhibited donepezil pretreatment-induced neuroprotection against acute glutamate treatment-induced death. Donepezil pretreatment prevented acute glutamate- and ionomycin-induced neurotoxicity, but not S-nitrosocysteine-induced neurotoxicity, suggesting that donepezil protects neurons via nAChR at levels before nitric oxide synthase activation against acute glutamate neurotoxicity. Concomitant treatment with antagonists of nAChR or phosphatidylinositol 3-kinase (PI3K) signaling inhibitors significantly inhibited neuroprotection against moderate glutamate neurotoxicity and decreased the phosphorylation level of Akt. Neuroprotection was also inhibited by treatment with inhibitor of mitogen-activated protein kinase (MAPK) kinase. These results suggest that donepezil protects neurons against moderate glutamate neurotoxicity via nAChR-PI3K-Akt and MAPK signaling pathways. This study provides novel insight into the mechanism of donepezil-induced neuroprotection that involves nAChR up-regulation.

Roles of Nicotinic Receptors in Acetylcholinesterase Inhibitor-Induced Neuroprotection and Nicotinic Receptor Up-Regulation

“…First we confirmed that treatment with ionomycine (3 mM) or S-nitrosocysteine (SNOC) (300 mM) induces neurotoxicity. 15,49) Donepezil, galantamine and tacrine all protected against ionomycine-induced neurotoxicity, but only tacrine protected against SNOC-induced neurotoxicity, suggesting that donepezil and galantamine protects neurons at points after the influx of calcium and before the activation of nNOS, and tacrine protect neurons at points after the activation of nNOS 15,50) (Fig. 2).…”

“…59) It has been previously shown that donepezil and galantamine do not significantly protect neurons against glutamate neurotoxicity at concentrations below 100 nM and 10 nM, respectively 15,43) ; however, following chronic treatment with donepezil or galantamine, donepezil (10 nM) and galantamine (1 nM) pretreatment significantly protected neurons from glutamate (1 mM, 10 min or 100 mM, 24 h) neurotoxicity. 43,50,59,60) No such effect was observed for tacrine. The mechanism of this enhancement of sensitivity to donepezil remains relatively unstudied, but we have shown that chronic simultaneous treatment with donepezil and an nAChR antagonist, PI3K pathway inhibitor, significantly inhibits the enhancement of sensitivity.…”

Cholinergic deficiency involved in vascular dementia: possible mechanism and strategy of treatment

“…Current neuroprotective treatment options cover all of the molecular targets of the dementia cascades. Interestingly, protective effects of cholinergic agents, especially AChE inhibitors, involve multiple mechanisms (I [48,[127][128][129] ; II [130][131][132] ; III [85,98] ; IV [127,133] ; V [90,133,134] ; references to literature regarding VI and VII can be found throughout this review). Abbreviations: ATP, adenosine triphosphate; CaM, calmodulin; Hup A, huperzine A; JAK/STAT, Janus kinase/signal transducer and activator of transcription; MMP, matrix metalloproteinase; NGF, nerve growth factor; NMDA, N-methyl-D-aspartic acid; PAF, platelet activating factor.…”

“…These neuroprotective effects of donepezil were probably related to the facilitation of nicotinic acetylcholinergic transmission. Several studies have found that donepezil can up-regulate the expression of nAChR and activate them, especially α4 and α7 receptor subtypes [98,99] . The subsequent action of downstream signaling pathways, including the phosphatidylinositol 3-kinase-Akt signaling pathway and the MAPK pathway, makes neurons more sensitive to the protection by donepezil [98,100] .…”

“…Several studies have found that donepezil can up-regulate the expression of nAChR and activate them, especially α4 and α7 receptor subtypes [98,99] . The subsequent action of downstream signaling pathways, including the phosphatidylinositol 3-kinase-Akt signaling pathway and the MAPK pathway, makes neurons more sensitive to the protection by donepezil [98,100] . Consistent with this finding, Fujiki and co-workers found that the reduction of cerebral infarct and traumatic brain injury after donepezil administration was prevented by coinjection with mecamylamine, indicating that protection of donepezil is mediated by nAChR activation [96,97] .…”