Kinetic analysis of the inhibition of human butyrylcholinesterase with cymserine

Accompanying the gradual rise in the average age of the population of most industrialized countries is a regrettable progressive rise in the number of individuals afflicted with age-related neurodegenerative disorders, epitomized by Alzheimer's disease (AD) but, additionally, including Parkinson's disease (PD) and stroke. The primary therapeutic strategy, to date, involves the use of cholinesterases inhibitors (ChEIs) to amplify residual cholinergic activity. The enzyme, acetylcholinesterase (AChE), along with other elements of the cholinergic system is depleted in the AD brain. In contrast, however, its sister enzyme, butyrylcholinesterase (BuChE), that likewise cleaves acetylcholine (ACh), is elevated and both AChE and BuChE co-localize in high amounts with the classical pathological hallmarks of AD. The mismatch between increased brain BuChE and depleted levels of both ACh and AChE, particularly late in the disease, has supported the design and development of new ChEIs with a preference for BuChE; exemplified by the novel agent, cymserine, whose binding kinetics are characterized for the first time. Specifically, as assessed by the Ellman method, cymserine demonstrated potent concentration-dependent binding with human BuChE. The IC50 was determined as 63 to 100 nM at the substrate concentration range of 25 to 800 microM BuSCh. In addition, the following new binding constants were investigated for human BuChE inhibition by cymserine: T(FPnubeta), K(nubeta), K(Bs), K(MIBA), M(IC50), D(Sc), R(f), (O)K(m), OIC100, K(sl), theta(max) and R(i). These new kinetic constants may open new avenues for the kinetic study of the inhibition of a broad array of other enzymes by a wide variety of inhibitors. In synopsis, cymserine proved to be a potent inhibitor of human BuChE in comparison to its structural analogue, phenserine.