Kinetics of human serum butyrylcholinesterase and its inhibition by a novel experimental Alzheimer therapeutic, bisnorcymserine

Abstract

An explosion in the incidence of neurodegenerative diseases, particularly Alzheimer's disease (AD), is predicted in coming decades. Hence, the need to devise and assess new treatment strategies has never been more acute. AD, although an irreversible and progressive disorder, is currently treated with palliative, symptomatic therapy: primarily with acetylcholinesterase (AChE) inhibitors to amplify remaining cholinergic activity. New agents that, additionally, affect disease progression are sorely needed. Inhibition of brain butyrylcholinesterase (BuChE) represents a new drug target for AD treatment. Therefore, hand-inhand with the development of selective ligands to inhibit BuChE in brain, it is fundamental to optimize assay conditions for kinetic studies of human BuChE. Kinetic analysis of serum BuChE, which is structurally similar to brain enzyme, was performed at dual substrate (butyrylthiocholine iodide) concentration ranges: 3-80 µM (low) and 25-800 µM (optimal) by use of the Ellman technique. Interaction of BuChE with a novel experimental AD therapeutic, bisnorcymserine (BNC; 0.06-2.0 nM) was also studied ex vivo. The IC50 and other key kinetic constants were determined for human serum BuChE inhibition by BNC, which proved to be a highly potent inhibitor in comparison to its structural analogue, cymserine. BNC may, additionally, lower the amyloid plaque-associated protein, amyloid-β peptide. In synopsis, the characterization of the kinetic parameters of BuChE and BNC, described herein, is both aiding in the design of novel agents and optimizing their translation toward clinical use.

Kinetics of Human Serum Butyrylcholinesterase Inhibition by a Novel Experimental Alzheimer Therapeutic, Dihydrobenzodioxepine Cymserine

“…The Kiapp and a predicted Ki for the selective BuChE-I, bisnorcymserine, have been reported as 0.7 nM and 0.131 nM respectively [23]. Whereas in the case of cymserine, these values are 115 and 38 nM, respectively [24].…”

“…Interestingly, the replacement of both indole nitrogen moieties in the tricyclic hexahydropryrroloindole backbone common to the experimental AD drug, phenserine, and its BuChE-selective analogues, cymserine and bisnorcymserine, by neutral oxygen moieties changes the mode of action to a competitive inhibition from a non-competitive oriented type [23][24][25][26]. This structural modification also provides additional lipophilicity to augment permeability at biological structures, such as the blood-brain barrier (Fig.…”

“…Herein, we characterize the quantitative interaction of the novel inhibitor, dihydrobenzodioxepine cymserine (DHBDC) [19][20][21] (Fig. 1A), with BuChE by combining the classic Ellman method [22] to measure the cleavage of choline esters with innovative and quantitative enzyme kinetic analyses to both aid selection of drug candidates and define target concentrations for future translational studies [23][24][25][26].…”

Tetrahydrofurobenzofuran cymserine, a potent butyrylcholinesterase inhibitor and experimental Alzheimer drug candidate, enzyme kinetic analysis

“…Specifically, the Kiapp and a predicted Ki values for the selective BuChE-I, (−)-bisnorcymserine, have recently been reported as 0.7 and 0.131 nM, respectively (Kamal et al 2006b), which compares favourably with those of our initial BuChE-I, (−)-cymserine, with values of 115 and 38 nM, respectively (Kamal et al 2006a). By contrast, the calculated Ki value of dihydrobenzodioxepine cymserine was reported as 2.22 nM, according to a competitive inhibition equation, or 3.24 and 7.91 nM for Ki1 and Ki2, respectively, in line with a partial mixed type of competitive inhibition equation (Kamal et al 2007).…”

Dual inhibition: a novel promising pharmacological approach for different disease conditions

“…Selective butyrylcholinesterase-inhibitors (BuChE-Is) are also considered attractive options since they raise acetylcholine (ACh) in the brain, augment long-term potentiation, improve cognitive performance in rodents and are devoid of the classic adverse actions of acetylcholinesterase-inhibitors (AChE-Is) and ChE-Is. [3] However, the emergence of a new hypothesis regarding the more sustained efficacy provided by dual inhibitors of AChE and BuChE has shifted the focus towards the latter class of compounds. [4] Quantification of density changes in brain grey matter has provided empirical evidence for a neuroprotective potential of dual cholinesterase inhibition in AD patients.…”