Acetylcholinesterase inhibition products

Figure 2. Log-probit plot of acetylcholinesterase inhibition as a function of concentration of aminocarb and transformation products.

There are three mechanisms by which detectors may work (i) acetylcholinesterase inhibition (ii) a chemical reaction specific for nerve agents and (iii) some sort of physical measurement. In the first type, butyrylthiocholine (this is much like ACh, with the major difference being that one of the oxygens is replaced by a sulphur) is continually presented to AChE as long as there is no nerve agent present, this is converted into thiocholine, just like the conversion of ACh into choline (see Fig. 3). The thiocholine is then measured by a chemical reaction which produces a colour. If a nerve agent is present, then the AChE is inhibited, the production of thiocholine is decreased, and this decrease is measured by the degree of the loss of the colour. 

Ginkgo s inhibitory effect on the production of amyloid-beta protein has also been mediated by other mechanisms, such as acetylcholinesterase inhibition, modulation of amyloid protein oligomeric species, and lowering of free cholesterol levels." ... 

In the body, metrifonate converts to the active metaboUte dichlorvos, (2,2-dichlorovinyl dimethyl phosphate), which is responsible for the inhibition of the enzyme acetylcholinesterase in the susceptible worm. This effect alone is unlikely to explain the antischistosomal properties of metrifonate (19). Clinically, metrifonate is effective only against infection caused by S. haematobium. Metrifonate is administered in three doses at 2-wk intervals (17). The dmg is well tolerated. Side effects such as mild vertigo, nausea, and cramps are dose-related. This product is not available in the United States. The only manufacturer of metrifonate is Bayer A.G. of Leverkusen, Germany. 

Presently available methods to diagnose and biomonitor exposure to anticholinesterases, e.g., nerve agents, rely mostly on measurement of residual enzyme activity of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in blood. More specific methods involve analysis of the intact poison or its degradation products in blood and/or urine. These approaches have serious drawbacks. Measurement of cholinesterase inhibition in blood does not identify the anticholinesterase and does not provide reliable evidence for exposure at inhibition levels less than 20 %. The intact poison and its degradation products can only be measured shortly after exposure. Moreover, the degradation products of pesticides may enter the body as such upon ingestion of food products containing these products. 

Microbial natural product chemistiy has generated a number of bioactive natural products. For instance cyclosporine A FK506 and rapamycin are used as immunosuppressants [16]. Other examples of microbial metabolites, having potential biomedical application include antihyperlipidemics, lovastatin and guggulsterone [17, 18]. The crude extracts of Mucor plumbeus exhibited acetylcholinesterase (AChE) enzyme inhibition activity. Our detailed chromatographic work on this crude extract resulted in the isolation of mucoralactone A (11), a novel steroid containing a lactone moeity incorporated in its structure. 

Perhaps the most prominent and well-studied class of synthetic poisons are so-called cholinesterase inhibitors. Cholinesterases are important enzymes that act on compounds involved in nerve impulse transmission - the neurotransmitters (see the later section on neurotoxicity for more details). A compound called acetylcholine is one such neurotransmitter, and its concentration at certain junctions in the nervous system, and between the nervous system and the muscles, is controlled by the enzyme acetylcholinesterase the enzyme causes its conversion, by hydrolysis, to inactive products. Any chemical that can interact with acetylcholinesterase and inhibit its enzymatic activity can cause the level of acetylcholine at these critical junctions to increase, and lead to excessive neurological stimulation at these cholinergic junctions. Typical early symptoms of cholinergic poisoning are bradycardia (slowing of heart rate), diarrhea, excessive urination, lacrimation, and salivation (all symptoms of an effect on the parasympathetic nervous system). When overstimulation occurs at the so-called neuromuscular junctions the results are tremors and, at sufficiently high doses, paralysis and death. 

Subcellular membrane-bound enzymes activity. Oil, administered to male CFY weanling rats at a dose of 20% for 16 weeks, produced an increase of synaptosomal acetylcholinesterase activity in the coconut oil-fed group. The Mg -adenosine triphosphate (ATPase) activity was similar among all groups in all the brain regions Superoxide production inhibition. Seed oil, administered to rats at a concentration of 8% of diet, produced equivocal effect on macrophages. Capsaicin or curcumin enhanced effect . ... 

A reaction looked at earlier simulates borate inhibition of serine proteinases.33 Resorufin acetate (234) is proposed as an attractive substrate to use with chymotrypsin since the absorbance of the product is several times more intense than that formed when the more usual p-nitrophcnyl acetate is used as a substrate. The steady-state values are the same for the two substrates, which is expected if the slow deacylation step involves a common intermediate. Experiments show that the acetate can bind to chymotrypsin other than at the active site.210 Brownian dynamics simulations of the encounter kinetics between the active site of an acetylcholinesterase and a charged substrate together with ah initio quantum chemical calculations using the 3-21G set to probe the transformation of the Michaelis complex into a covalently bound tetrahedral intermediate have been carried out.211 The Glu 199 residue located near the enzyme active triad boosts acetylcholinesterase activity by increasing the encounter rate due to the favourable modification of the electric field inside the enzyme and by stabilization of the TS for the first chemical step of catalysis.211... 

Our approach to this problem has been to synthesize several of these potential transformation products, to test their ability to inhibit acetylcholinesterase in vitro as well as their toxicity to a suitable insect indicator species and to begin an assessment of their stability under environmental conditions. In this connection it was deemed necessary to measure the volatility of the more potent inhibitors. 

Figure 2 represented a log-probit plot of the observed inhibition of purified bovine erythrocyte acetylcholinesterase as a function of concentration for several of the transformation products of aminocarb. The observation that these inhibition curves are parallel suggests a similar mechanism of interaction for the various derivatives. The parameter I5f. (the concentration of inhibitor required to achieve 50% inhibition oi the enzyme activity) for each of the inhibitors were calculated and are recorded in Table 1. These values are reported relative to the parent compound aminocarb = 1. Also included in Table 1 are the relative toxicities of several of these products to house crickets (Acheta domesticus). It had been our intention to develop bioassay tests using the target insect itself, the eastern spruce budworm (Choristoneura fumiferana). However, spray tower results were quite variable and it was considered that genetic variability of the stock culture made the production of uniform test batches difficult to achieve. Using the house crickets, an LD q of 130-155 ppm for aminocarb standard was observed over the course of more than 25 bioassays. Also included in Table 1 are observations by Abdel-Wahab and Casida (19) using human plasma or house fly head cholinesterases. 

It is believed that metabolic products of TOCP inhibit acetylcholinesterase. Apparently other factors are involved in TOCP neurotoxicity. A study of tri-o-cresylphosphate poisoning in China has described a number of symptoms.4 Initial pain in the lower leg muscles was followed by paralysis and lower limb nerve injury. Patients with mild poisoning recovered after several months, but more severely poisoned ones suffered permanent effects. Despite the devastating effects of TOCP, the percentage of virtually complete recovery in healthy subjects is relatively high. 

In another report, several acetylcholinesterase (AChE) inhibitors, including tacrine, edrophonium, tetramethyl- and tetraethyl-ammonium chloride, carbofu-ran, and eserine were assayed on a chip [1045]. AChE converted the substrate, acetylthiocholine, to thiocholine. This product reacted with coumarinylphenyl-maleimide (CPM) to form thiocholine-CPM (a thioether) for LIF detection. Since the acetonitrile solvent used to dissolve CPM inhibited AChE activity, the CPM solution was added after the enzymatic reaction [1045]. Another enzyme inhibition assay using a peptide substrate was performed on a PMMA chip [1046]. 

An example of use of the conglomerate Nar-wedine (59) in the synthesis of a natural product Galanthamine (61) which is din Amarylli-daceae alkaloid and has been used clinically for 30 years for neurological illnesses (98). More recently it has been approved for the use in the treatment of Alzheimer s disease (AD) (99). Galanthamine acts to inhibit acetylcholinesterase (AChE), thus increasing the levels... 

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