Enhanced anti-amnestic effect of donepezil by Ginkgo biloba extract (EGb 761) via further improvement in pro-cholinergic and antioxidative activities.

ETHNOPHARMACOLOGICAL RELEVANCE

EGb 761 is a standardized dry extract of Ginkgo biloba L. leaves traditionally used by Eastern Asia and has been associated with beneficial effects on neurodegeneration disorders, including Alzheimer's disease.

AIM OF THE STUDY

Since beneficial interactions between EGb 761 and donepezil have been observed in previous clinical studies, the current study was proposed aiming to further explore related mechanisms from both pharmacokinetics and pharmacodynamics aspects.

MATERIALS AND METHODS

Pharmacodynamic interactions were studied in scopolamine-induced cognitive impairment rats received two-weeks treatment of vehicle, EGb 761 and/or donepezil by the Morris water maze test and ex vivo evaluation of biomarkers of cholinergic transmission and oxidative stress in rat brain. In the meantime, pharmacokinetic profiles of donepezil and bilobalide were obtained and compared among all treatment groups. In addition, impact of the bioavailable EGb 761 components on donepezil brain penetration was evaluated with the hCMEC/D3 cell monolayer model.

RESULTS

Scopolamine-induced rats with co-treatment of EGb 761 and donepezil had significantly improved cognitive function in the Morris water maze test with increased brain levels of superoxide dismutase and decreased brain levels of acetylcholinesterase and malondialdehyde than that with treatment of only EGb 761 or donepezil. Despite such beneficial pharmacodynamics outcomes, the two-week co-treatment of EGb 761 and donepezil did not alter the plasma pharmacokinetics and brain uptake of donepezil or bilobalide, which was further verified in the hCMEC/D3 monolayer model.

CONCLUSION

Co-administration of EGb 761 and donepezil exerted better anti-amnestic effect via further enhanced pro-cholinergic and antioxidative effects of EGb 761 or donepezil in scopolamine-induced cognitive impairment rat without alteration in their systemic/brain exposure.