An Improved Drugs Screening System Reveals that Baicalein Ameliorates the A beta/AMPA/NMDA-Induced Depolarization of Neurons

Abstract

The presence of amyloid-beta (A beta) plaque and tau protein hyperphosphorylation in brain tissue is the pathological hallmark of Alzheimer's disease (AD). At least some A beta neurotoxicity is caused by the presence of excess glutamate that has been induced by A beta accumulation. Memantine is currently the only NMDA receptor inhibitor approved for treating moderate-to-severe AD patients. We utilized primary cortical neurons and DiBAC4(3), a slow-response voltage sensitive fluorescence dye, to create a novel system for screening herbal medicines that allows the identification of pure compounds able to ameliorate A beta-induced abnormal depolarization. The intensity of DiBAC4(3) fluorescence was increased when primary neurons were stimulated by A beta; furthermore, pre-treatment with memantine abolished this change. Using this system, we identified six crude extracts made from herbal medicines that effectively alleviated this A beta-induced abnormal depolarization. Among these herbal medicines, one pure compound, baicalein, which was known to be present in Scutellaria baricalensis and is known to improve memory using an AD mouse model, was identified by our assay. However, the compound's molecular mechanism remained unknown. We found that baicalein, in addition to inhibiting A beta-induced depolarization, possibly functions as an antagonist of AMPA and NMDA receptors. Taken together, we have established a system/platform to identify herbal medicines that ameliorate A beta-induced depolarization of neurons. Equally important, baicalein is a candidate drug with great potential for the treatment of AD patients.