(CLapp,br) was decreased as a function of the dose of donepezil, suggesting an involvement of a saturable transport process via transporter(s) in the penetration across the blood-brain barrier (BBB). Consistent with in vivo

characterized by a deficiency in central cholinergic neurotransmission. Donepezil hydrochloride, (¡3⁄4)-2-[(1-benzylpiperidin-4-yl)methyl]-5,6dimethoxyindan-1-one monohydrochloride, is a reversible acetylcholinesterase inhibitor that has been reported to have a high potency and selectivity for centrally active cholinesterase. Matsui and co-workers reported that the concentration and area under the curve (AUC) of donepezil in the brain were two and seven times higher than those in the plasma. Furthermore, Kang et al recently reported that the transport of choline was inhibited by the addition of a number of organic cations, including donepezil, in an in vitro model of the blood-brain barrier (BBB). These observations are consistent with the hypothesis that efficient carrier-mediated transport system(s) exist(s) to facilitate the transport of donepezil across the BBB, in addition to passive diffusion. The objective of this study, therefore, was to study the mechanisms associated with the transport of donepezil into the brain. The apparent brain uptake clearance (CLapp,br) was decreased as a function of the dose of donepezil, suggesting an involvement of a saturable transport process via transporter(s) in the penetration across the blood-brain barrier (BBB). Consistent with in vivo results, the uptake of substrates for organic cation transporters was significantly reduced by donepezil in both MBEC4 cells (i.e., a model for BBB) and HEK 293 cells expressing the transporters found in the brain, indicative of the involvement of organic cation transporters in the transport of the drug. Furthermore, donepezil transport was enhanced (p < 0.01) in HEK 293 cells expressing rOCNT1, rOCTN2 or rCHT1. The CLapp,br was reduced up to 52.8% of the control in rats that had been pretreated with choline, while the CLapp,br was unaffected with pretreatments with organic cations other than choline, suggesting that choline and donepezil share a common transport mechanism in the penetration across the BBB in vivo. Taken together, these observations suggest that the transport of donepezil across the BBB is mediated by organic cation transporters such as choline transport system(s).