Focused Ultrasound as a Plasma Protein Binding-targeted Strategy to Enhance Brain Uptake of Donepezil

Donepezil, a reversible acetylcholinesterase inhibitor, is widely used for the symptomatic treatment of Alzheimer's disease (AD). Although higherdose donepezil has been shown to provide additional clinical benefit, dose escalation is often limited by cholinergic adverse effects. Given that approximately 96% of circulating donepezil is bound to plasma proteins, especially albumin, we hypothesized that increasing its unbound fraction from albumin may improve brain delivery without increasing the administered dose. To achieve this goal, herein we examined whether the donepezil-albumin complex can be dissociated by low-intensity focused ultrasound (FUS) in vitro. Then brain uptake of donepezil was evaluated in mice receiving intravenous donepezil followed by targeted brain FUS stimulation. As a result, FUS significantly increased unbound fraction of donepezil at the targeted region in vitro, resulting in a 41.1% increase of donepezil diffusion into dialysis cassettes compared with non-sonicated controls. In mice receiving intravenous donepezil, targeted brain FUS stimulation increased brain donepezil concentrations by 52.7% at 15-min post-administration time. These findings suggest that low-intensity FUS enhances brain uptake of donepezil, potentially through modulation of donepezil-albumin binding, and support further investigation of plasma protein binding-targeted brain drug delivery.