N-Acetyl Cysteine Decreases Mice Brain Acetyl Cholinesterase Activity
Here a kinetic in vitro study of n-acetylcysteine (NAC) on mouse brain acetylcholinesterase (AChE) activity was performed, as well, few studies with the aim to improve Ellman’s methodology based on SH contain compounds. The ideal 5,5´-dithio-bis-2-nitrobenzoic acid (DTNB) concentration was of 0.3 mM and ideal medium pH=7.4. AChE demonstrated linear activity for all acetylthiocholine iodide (ATCh) tested concentrations (0.025-0.450 mM).
To avoid any DTNB-NAC interaction interference, 30 sec were applied to the assay method, so-called stabilization time. No differences in Km (mM) for all NAC tested concentrations were observed. At the NAC concentrations started from 75 µM significant differences in Vmax were achieved, characterizing a non-competitive type of AChE activity inhibition induced by NAC. In conclusion, NAC decreased AChE activity in vitro and the Ellman method was reliable for the analysis of AChE activity when inhibited by compounds that contain SH groups.
Acetylcholinesterase enzyme (AChE; EC 18.104.22.168) is a large glycoprotein whose basic chemistry was worked out in the 1960s by Lawler, Leuzinger and Baker. AChE belongs to the family of hydrolases whose active site is characterized by a catalytic coordinated triad of three essential amino acids: histidine, serine, and glutamic acid.
This enzyme is one of the best studied of all enzymes from the point of view of its mechanism of action, the nature of its active site, its distribution and localization in tissue, and its physiologic functions. It is mainly found at neuromuscular junctions and cholinergic synapses in the central nervous system (CNS), where its activity terminates the synaptic transmission.
AChE has a very high catalytic activity; each molecule of AChE degrades approximately 25,000 molecules of the neurotransmitter acetylcholine (ACh) per second into choline and acetic acid. At the CNS level the produced choline is transported back into the nerve terminals which reuse it in synthesizing new ACh molecules.
AChE activity can be inhibited by a variety of chemicals, such as organophosphates (OP), carbamates and nerve agents leading to ACh accumulation, resulting in cholinergic receptors over-stimulation and disturbance of many body functions and finally in respiratory arrest and death.
Nevertheless, others AChE inhibitors such as physostigmine, pyridostigmine, procycline, donepezil, galantamine, huperezine tacrine and rivastigmine  are clinically used against OP poisoning and neurodegenerative diseases like Alzheimer´s (AD). However, all this inhibitors differ in bioavailability, half-life and effectiveness.
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