A novel assay to determine acetylcholinesterase activity: The application potential for screening of drugs against Alzheimer's disease

Acetycholinesterase (AChE) that regulates hydrolysis of acetylcholine (ACh) in the brain, is an important target for treatment of Alzheimer's disease (AD), a feature of which is ACh deficiency. However, the methods to precisely determine AChE activity are still under development. We developed a new method to exploit acetylcholine-d4 as a surrogate substrate of ACh and measure product choline-d4 via liquid chromatography–tandem mass spectrometry (LC–MS/MS). This assay detected activity of AChE present in the normal mouse brain, which is consistent with the standard Ellman assay that determines products spectrophotometrically. In AD mouse models, the result of LC–MS/MS assay showed significant higher AChE activity than that seen in control normal mice, while treatment of AD mice with an AChE inhibitor, huperzine A, led to partial decreases in AChE activity. Our results suggest that this surrogate-based LC–MS/MS method is a new, sensitive and convenient assay for the determination of AChE activity, providing a useful means for screening active compounds that target AChE.