Takashi Kosasa

Effect of donepezil hydrochloride (E2020) on basal concentration of extracellular acetylcholine in the hippocampus of rats

The effects of oral administration of the centrally acting acetylcholinesterase (AChE) inhibitors, donepezil hydrochloride (donepezil: E2020: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride), tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride) and ENA-713 (rivastigmine: (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate), which have been developed for the treatment of Alzheimers disease, on the extracellular acetylcholine concentration in the hippocampus of rats were evaluated by using a microdialysis technique without adding cholinesterase inhibitor to the perfusion solution. We also compared the inhibition of brain AChE and the brain concentrations of these drugs. Donepezil at 2.5 mg/kg and tacrine at 5 mg/kg showed significant effects for more than 6 h. At these doses, the maximum increases were observed at about 1.5 h after administration of donepezil, and at about 2 h with tacrine, and were 499% and 422% of the pre-level, respectively. ENA-713 produced significant effects at doses of 0.625, 1.25 and 2.5 mg/kg, which lasted for about 1, 2 and 4 h, respectively. The maximum increases produced by these doses at about 0.5 h after administration were 190, 346 and 458% of the pre-level, respectively. The time courses of brain AChE inhibition with donepezil at 2.5 mg/kg, tacrine at 10 mg/kg and ENA-713 at 2.5 mg/kg were mirror images of the extracellular acetylcholine-increasing action at the same doses. The time courses of the brain concentrations of drugs after oral administration of donepezil at 2.5 mg/kg and tacrine at 10 mg/kg were consistent with those of brain AChE inhibition at the same doses, and there was a linear relation between these parameters. Brain concentration of ENA-713 at 2.5 mg/kg was below the limit of quantification at all time points measured. These results suggest that oral administration of donepezil, tacrine and ENA-713 increases acetylcholine concentration in the synaptic cleft of the hippocampus mostly through AChE inhibition, and that donepezil has a more potent activity than tacrine and a longer-lasting effect than ENA-713 on the central cholinergic system.

Protective effect of donepezil in a primary culture of rat cortical neurons exposed to oxygen–glucose deprivation

Donepezil hydrochloride (donepezil: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride) is a potent acetylcholinesterase inhibitor used for treatment of Alzheimers disease. Although acetylcholinesterase inhibitors are used as a symptomatic treatment for Alzheimers disease, it is not clear whether or not they are effective against progressive degeneration of neuronal cells. In this study, we investigated the neuroprotective effects of donepezil and other acetylcholinesterase inhibitors used for treatment of Alzheimers disease, i.e., galantamine, rivastigmine, and tacrine. As a neurodegenerative model, we used rat cortical neurons exposed to oxygen-glucose deprivation. Lactate dehydrogenase (LDH) released into the culture medium was measured as a marker of neuronal cell damage. First, the effects of donepezil (10 microM) on three different treatment schedules (from 12 h before to 24 h after oxygen-glucose deprivation (pre-12 h), from 1 h before to 24 h after oxygen-glucose deprivation (pre-1 h) and from 1 h after to 24 h after oxygen-glucose deprivation (post-1 h)) were compared. The pre-12-h treatment most effectively inhibited LDH release. The protective effect of donepezil was confirmed morphologically. Next, the effects of donepezil and the other three acetylcholinesterase inhibitors were compared under the pre-12-h treatment condition. Donepezil (0.1, 1, and 10 microM) significantly decreased LDH release in a concentration-dependent manner. However, galantamine (1, 10, and 100 microM), tacrine (0.1, 1, and 10 microM), and rivastigmine (0.1, 1, and 10 microM) did not significantly decrease LDH release. The neuroprotective effect of donepezil was not antagonized by scopolamine or mecamylamine. These results demonstrate that donepezil has a protective effect against oxygen-glucose deprivation-induced injury to rat primary cultured cerebral cortical neurons. Besides, it is suggested that this effect of donepezil is independent of muscarinic cholinergic system and nicotinic cholinergic system. Thus, donepezil is expected to have a protective effect against progressive degeneration of brain neuronal cells in ischemic cerebrovascular disease and Alzheimers disease.

Inhibitory effect of orally administered donepezil hydrochloride (E2020), a novel treatment for Alzheimer's disease, on cholinesterase activity in rats.

Donepezil hydrochloride ((+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5, 6-dimethoxy-indan-1-one monohydrochloride: E2020: donepezil) is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimers disease. The present experiments were designed to compare the inhibitory effects of orally administered donepezil and other cholinesterase inhibitors, tacrine (9-amino-1,2, 3,4-tetrahydroacridine hydrochloride), (S)-N-ethyl-3-[(1-dimethyl-amino)ethyl]-N-methyl-phenylcarbamate hydrogentartrate (ENA-713, rivastigmine) and 3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4, 5-tetrahydro-1H-1-benzazepin-8-yl)-1-propanone fumarate (TAK-147), on the cholinesterase activity in the brain and plasma of rats. Moreover, in order to validate the cholinesterase inhibition data, we measured the brain and plasma concentrations of these drugs. Oral administration of donepezil, tacrine, ENA-713 or TAK-147, caused a dose-dependent inhibition of brain and plasma cholinesterase activities. The ID(50) values of these compounds for brain cholinesterase activity were 6.3, 40.5, 7.2 and 26.8 micromol/kg, respectively. On the other hand, the ID(50)170, 9.7 and 51.2 micromol/kg, respectively. Thus, the ratios of the ID(50)4.2, 1.3 and 1.9, respectively. Brain and plasma concentrations of donepezil, tacrine and TAK-147 increased dose-dependently. The ratios of the concentrations (brain/plasma) of these compounds were 6.1-8.4 for donepezil, 14.5-54.6 for tacrine and 7.0-20.6 for TAK-147. The values of 50% inhibitory concentration of these drugs in the brain were 0.42, 3.5 and 1.1 nmol/g, respectively. In contrast, the brain and plasma concentrations of ENA-713 at all doses, except the two highest doses, were below the quantification limit. These results suggest that orally administered donepezil satisfactorily penetrates into the brain and inhibits cholinesterase there, and that donepezil is a potent and selective inhibitor of brain cholinesterase in comparison with plasma cholinesterase in vivo.

Inhibitory effects of donepezil hydrochloride (E2020) on cholinesterase activity in brain and peripheral tissues of young and aged rats

Donepezil hydrochloride (donepezil: E2020: (+/-)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6-dimethoxy-indan-1-one monohydrochloride)) is a centrally acting acetylcholinesterase inhibitor developed for the treatment of Alzheimers disease. In the present study, its inhibitory effect on the activity of cholinesterase ex vivo was evaluated in the brain, plasma, erythrocytes, heart, small intestine, liver and pectoral muscle of young adult as well as aged rats, in comparison with that of tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride). In aged animals, cholinesterase activity in heart, small intestine and pectoral muscle was lower, whereas that in plasma and liver was higher than in young rats. Both groups showed the highest levels in the brain. Donepezil, at doses of 1.25, 2.5 and 5 mg/kg, p.o., inhibited brain, plasma, erythrocyte, liver and pectoral muscle cholinesterase activity in young rats in a dose-dependent manner but had less effect on cholinesterase activity in heart and small intestine. In aged animals, inhibition of cholinesterase activity in the brain, erythrocytes and pectoral muscle by donepezil was more potent than that in young animals. Tacrine, at doses of 5, 10 and 20 mg/kg, p.o., dose-dependently inhibited cholinesterase activity in all tissues of both young and aged animals, but most potently in heart, small intestine and liver. The inhibition of cholinesterase activity by tacrine in the brain, plasma, erythrocytes, heart and liver was more potent in aged rats than in tissues of young rats. Brain and plasma concentrations of unchanged donepezil and tacrine were measured in the same animals as used for the cholinesterase inhibition study. Brain and plasma concentrations of donepezil and tacrine were higher in aged than in young animals. It is concluded that the inhibitory effects of donepezil and tacrine on cholinesterase activity are greater in aged than in young rats, owing to differences in the tissue concentrations of these compounds between young and aged animals. It is also suggested that the effect of donepezil on cholinesterase activity is more tissue-selective than that of tacrine.

Study of neuroprotection of donepezil, a therapy for Alzheimer's disease.

Donepezil is a potent acetylcholinesterase inhibitor used for the treatment of Alzheimers disease. Although acetylcholinesterase inhibitors are thought to be symptomatic treatment of Alzheimers disease, it is not clear whether they are effective against progressive degeneration of neuronal cells. In this study, we investigated the neuroprotective effects of donepezil against ischemic damage, N-methyl-d-aspartate (NMDA) excitotoxicity, and amyloid-beta (Abeta) toxicity using rat brain primary cultured neurons. Lactate dehydrogenase (LDH) released into the culture medium was measured as a marker of neuronal cell damage. As an ischemic damage model, we used oxygen-glucose deprivation in rat cerebral cortex primary cultured neurons. Pretreatment with donepezil (0.1, 1 and 10 microM) significantly decreased LDH release in a concentration-dependent manner. However, other acetylcholinesterase inhibitors (galantamine, tacrine and rivastigmine) did not significantly decrease LDH release. In a NMDA excitotoxicity model, pretreatment with donepezil (0.1, 1 and 10 microM) decreased the LDH release in a concentration-dependent manner. In binding assay for glutamate receptors, donepezil at 100 microM only slightly inhibited binding to the glycine and polyamine sites on NMDA receptor complex. We further examined the effect of donepezil on Abeta (1-40)- and Abeta (1-42)-induced toxicity in primary cultures of rat septal neurons. Pretreatment with donepezil (0.1, 1 and 10 microM) significantly decreased LDH release induced by Abetas in a concentration-dependent manner. However, other acetylcholinesterase inhibitors (galantamine and tacrine) and NMDA receptor antagonists (memantine and dizocilpine (MK801)) did not significantly decrease LDH release. These results demonstrate that donepezil has protective effects against ischemic damage, glutamate excitotoxicity and Abeta toxicity to rat primary cultured neurons and these effects are not dependent on acetylcholinesterase inhibition and antagonism of NMDA receptors. Thus, donepezil is expected to have a protective effect against progressive degeneration of brain neuronal cells in ischemic cerebrovascular disease and Alzheimers disease.

Central and peripheral activity of cholinesterase inhibitors as revealed by yawning and fasciculation in rats.

This study was designed to investigate the central and peripheral activity profile of cholinesterase inhibitors in rats. Intravenous injection of cholinesterase inhibitors caused fasciculation, a fine involuntary muscular movement. This peripheral cholinergic sign was tightly correlated with in vitro anti-acetylcholinesterase activity by cholinesterase inhibitors, suggesting that fasciculation is a valid index of peripheral cholinergic activation. Yawning, used as a marker of central cholinergic activation, was also monitored. E2030 (3-(2-(1-(1,3-dioxolan-2-ylmethyl)-4-piperidyl)ethyl)-2H-3,4-dihydro-1,3-benzoxazin-2,4-dione hydrochloride) elicited yawning at more than 4 mg/kg, while fasciculation was significantly intensified only at a dose of 16 mg/kg. Donepezil and tacrine induced both yawning and fasciculation at doses greater than 4 mg/kg, whereas physostigmine induced both behaviors at a dose of 8 mg/kg and above. Finally, ipidacrine elicited yawning at a dose of 16 mg/kg and fasciculation at doses greater than 8 mg/kg. Thus, all putative centrally acting cholinesterase inhibitors elicited yawning. TAK-147 (3-[1-(phenylmethyl)-4-piperidinyl]-1-(2,3,4,5-tetrahydro-1H-benzazepin-8-yl)-1-propanone fumarate) did not significantly elicit yawning at doses under 16 mg/kg, but elicited fasciculation at a dose of more than 4 mg/kg. Distigmine, a peripherally acting cholinesterase inhibitor, evoked fasciculations, but not yawning. When mild to moderate fasciculation was evoked, donepezil and E2030 elicited more than nine yawns over 30 min, while the other cholinesterase inhibitors elicited approximately five yawns at most during this period. These results indicated that E2030 and donepezil exhibited the most marked preferential central cholinergic activity, relative to peripheral activity, among cholinesterase inhibitors tested. Scopolamine, a centrally acting antimuscarinic drug, completely inhibited E2030-induced yawning, while peripherally acting methylscopolamine did not. Haloperidol, a dopamine receptor antagonist, partially blocked E2030-induced yawning, but did not block donepezil-induced yawning. These results suggest that central cholinergic and, in part, dopaminergic mechanisms are involved in E2030-induced yawning.

Effect of perampanel, a novel AMPA antagonist, on benzodiazepine-resistant status epilepticus in a lithium-pilocarpine rat model

This study assessed the efficacy of diazepam, and the alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionic acid (AMPA) receptor antagonists perampanel and GYKI52466 in a lithium‐pilocarpine status epilepticus (SE) model. SE was induced in rats using lithium chloride, scopolamine methyl bromide, and pilocarpine. Diazepam 10, 20, or 40 mg kg−1, or perampanel 1, 2.5, 5, or 8 mg kg−1 were administered intravenously at 10 or 30 min after seizure onset, and GYKI52466 50 mg kg−1, or combinations of diazepam 2.5–5 mg kg−1 and perampanel 0.5–1 mg kg−1, were administered intravenously at 30 min after seizure onset. Diazepam 20 mg kg−1 terminated seizures (based on electroencephalography and assessment of behavioral seizures) in 2/6 rats at 10 min and 0/6 rats at 30 min (ED50: 10 min, 30 mg kg−1; 30 min, not determined). Perampanel 8 mg kg−1 terminated seizures in 6/6 rats at both 10 and 30 min (ED50: 10 min 1.7 mg kg−1; 30 min, 5.1 mg kg−1). GYKI52466 50 mg kg−1 terminated seizures in 2/4 rats at 30 min. Co‐administration of diazepam 5 mg kg−1 and perampanel 1 mg kg−1 terminated seizures in 9/9 rats at 30 min. In conclusion, perampanel and GYKI52466 provided efficacy in a lithium‐pilocarpine SE model at 30 min after seizure onset, when SE was refractory to diazepam, supporting the therapeutic potential of AMPA receptor antagonists for refractory SE. The perampanel dose required to terminate seizures was reduced by combination with diazepam, suggesting synergy.

Donepezil attenuates excitotoxic damage induced by membrane depolarization of cortical neurons exposed to veratridine.

Long-lasting membrane depolarization in cerebral ischemia causes neurotoxicity via increases of intracellular sodium concentration ([Na+]i) and calcium concentration ([Ca2+]i). Donepezil has been shown to exert neuroprotective effects in an oxygen-glucose deprivation model. In the present study, we examined the effect of donepezil on depolarization-induced neuronal cell injury resulting from prolonged opening of Na+ channels with veratridine in rat primary-cultured cortical neurons. Veratridine (10 microM)-induced neuronal cell damage was completely prevented by 0.1 microM tetrodotoxin. Pretreatment with donepezil (0.1-10 microM) for 1 day significantly decreased cell death in a concentration-dependent manner, and a potent NMDA receptor antagonist, dizocilpine (MK801), showed a neuroprotective effect at the concentration of 10 microM. The neuroprotective effect of donepezil was not affected by nicotinic or muscarinic acetylcholine receptor antagonists. We further characterized the neuroprotective properties of donepezil by measuring the effect on [Na+]i and [Ca2+]i in cells stimulated with veratridine. At 0.1-10 microM, donepezil significantly and concentration-dependently reduced the veratridine-induced increase of [Ca2+]i, whereas MK801 had no effect. At 10 microM, donepezil significantly decreased the veratridine-induced increase of [Na+]i. We also measured the effect on veratridine-induced release of the excitatory amino acids, glutamate and glycine. While donepezil decreased the release of glutamate and glycine, MK801 did not. In conclusion, our results indicate that donepezil has neuroprotective activity against depolarization-induced toxicity in rat cortical neurons via inhibition of the rapid influx of sodium and calcium ions, and via decrease of glutamate and glycine release, and also that this depolarization-induced toxicity is mediated by glutamate receptor activation.