Kinetics of human acetylcholinesterase inhibition by the novel experimental Alzheimer therapeutic agent, tolserine

Characterization of the: kinetic parameters of tolserine, a novel acetylcho linesterase (AChE) inhibitor of potential in the therapy of Alzheimer's dis ease, to inhibit purified human erythrocyte AChE was undertaken for the fir st time. An IC50 value was estimated by three methods. Its mean value was f ound to be 8.13 nM, whereas the IC100 was observed to be 25.5 nM as calcula ted by single graphical method. The Michaelis-Menten constant (K-m) for the hydrolysis of the substrate acetylthiocholine iodide was found to be 0.08 mM. Dixon as well as Lineweaver-Burk plots and their secondary replots indi cated that the nature of the inhibition was of the partial non-competitive type. The value of K-i was estimated as 4.69 nM by the primary and secondar y replots of the Dixon as well as secondary replots of the Lineweaver-Burk plot. Four new kinetic constants were also investigated by polynomial regre ssion analysis of the relationship between the apparent K-i (K-Iapp) and su bstrate concentration, which may open new avenues for the kinetic study of the inhibition of several enzymes by a wide variety of inhibitors in vitro. Tolserine proved to be a highly potent inhibitor of human AChE compared to its structural analogues physostigmine and phenserine. BIOCHEM PHARMACOL 6 0;41:561-570, 2000. (C) 2000 Elsevier Science Inc.