Protective effect of donepezil against Aβ(1-40) neurotoxicity in rat septal neurons

Donepezil, a potent acetylcholinesterase (AChE) inhibitor used for the treatment of Alzheimer's disease (AD), is thought to have a neuroprotective effect in AD patients. Because a deficit in cholinergic neurotransmission is a major feature in AD, and amyloid-beta (Aβ) accumulation has been proposed as a possible causative phenomenon, we were interested to examine the effect of donepezil on Aβ(1-40) induced neurotoxicity in primary cultures of rat septal neurons. Using immunohistochemical staining, almost all the neurons were found to be positive for vesicular acetylcholine transporter (VAChT) in these septal cultures. Septal neuronal cells were cultured for 7 days and then 15 μmol/L of Aβ(1-40) was added to the cell medium for 48 h. The cultured septal neurons were highly susceptible to Aβ toxicity, as shown by morphological examination and lactate dehydrogenase (LDH) assay. Donepezil concentration-dependently reduced the LDH efflux induced by Aβ(1-40), and the effect was significant at 100 nmol/L and above. Donepezil decreased both the negative peak at around 215 nm in the circular dichroism (CD) spectrum and the fluorescence intensity of thioflavin T in the presence of Aβ(1-40). These results suggest that donepezil exerts a neuroprotective effect by reducing the amount of the toxic form of Aβ fibrils in septal neuron cultures. These findings support the idea that the clinical efficacy of donepezil in AD is due to not only activation of cholinergic transmission, but also attenuation of neuronal damage.