Mouse cholinesterases

Thioesters play a paramount biochemical role in the metabolism of fatty acids and lipids. Indeed, fatty acyl-coenzyme A thioesters are pivotal in fatty acid anabolism and catabolism, in protein acylation, and in the synthesis of triacylglycerols, phospholipids and cholesterol esters [145], It is in these reactions that the peculiar reactivity of thioesters is of such significance. Many hydrolases, and mainly mitochondrial thiolester hydrolases (EC 3.1.2), are able to cleave thioesters. In addition, cholinesterases and carboxylesterases show some activity, but this is not a constant property of these enzymes since, for example, carboxylesterases from human monocytes were found to be inactive toward some endogenous thioesters [35] [146], In contrast, allococaine benzoyl thioester was found to be a good substrate of pig liver esterase, human and mouse butyrylcholinesterase, and mouse acetylcholinesterase [147],... 

In contrast to the A-monosubstituted carbamates, the A,A-disubstituted analogues (8.124 and 8.125, R = R R"NCO R = Me or Et R" = Me, Et, i-Pr, etc.) proved very stable at pH 7.4 in both buffer and plasma, with less than 5% degradation in 4 d. In fact, these compounds were potent inhibitors of plasma cholinesterase (EC 3.1.1.8), with K values ranging from 600 to 3 nM. Although these carbamates were stable in plasma, they underwent rapid bioactivation in liver, as demonstrated with mouse and rat liver microsomes. For example, the A,A-dimethylcarbamate (8.124, R = Me2NCO) was bioactivated in rat liver microsomes with t1/2 of ca. 30 min. Two routes of bioactivation were postulated, namely direct carboxylesterase-catalyzed hydrolysis, and cytochrome P450 mediated A-dealkylation to a more labile A-monosubstituted carbamate. 

Currently the only specific pharmacological therapeutic option available for AD patients is treatment with cholinesterase inhibitors, which provide moderate benefits in a subset of patients for a limited period [7]. More efficient future therapeutic strategies may be directed at the metabolic events resulting in Ap accumulation, for example by inhibition of P- or y-sec-retase [7], or at the prevention of neuronal loss by neurotrophin therapy [6]. The availability of transgenic mouse models of the disease, such as mice overexpressing APP mutants [8], and the utilization of primate models of cerebral amyloid [9] permits preclinical testing of novel diagnostic and therapeutic approaches. 

Based on the above discussion it was thought that the trifluoro-methyl ketones would be more polarized and thus create a great electrophilicity on the carbonyl carbon which facilitates -OH attack by the serine residue. Yet there is no carbon-oxygen bond to be cleaved In the ketone moiety, and therefore the enzyme-trifluoromethyl ketone transition state complex does not undergo catalytic conversion. The above rationale seems reasonable as trifluoromethyl ketones were found to be extraordinary selective and potent inhibitors of cholinesterases (56) of JHE from T. ni (57) and of meperidine carboxylesterases from mouse and human livers (58). Since JH homologs are alpha-beta unsaturated esters, a sulfide bond was placed beta to the carbonyl in hopes that it would mimic the 2,3-olefln of JHs and yield more powerful inhibitors (54). This empirical approach was extremely successful since it resulted in compounds that were extremely potent inhibitors of JHEs from different species (51,54,59). 

Cook, W, Beasley, V, Dahlem, A., Dellinger, J., Harlin, K., and Carmichael, W. 1988. Comparison of effects of anatoxin-a(s) and paraoxon, physostigmine and pyridostigmine on mouse-brain cholinesterase activity. Toxicon 26, 750-753. 

Consequently, they tested their reactivation activity on tetraethylpyrophosphate-inhibited mouse brain cholinesterases. Their activities were compared with pralidoxime. All the compounds (except that with pentylene bridge) were found to be more effective reactivators than pralidoxime. Bispyridinium monooximes with a 3-carbamoyl group were... 

A. A. Brimfield, K. W. Hunter, Jr., D. E. Lenz, H. E Benschop, C. VanDijk, and L. P. A. dejong, Structural and stereochemical specificity of mouse monoclonal antibodies to the organophosphorus cholinesterase inhibitor soman, Molec. Pharmacol, 25 32-39 (1985). 

L.P.A., Structural and stereochemical specificity of mouse monoclonal antibodies to the organophosphorus cholinesterase inhibitor soman. Mol Pharmacol, 28, 32, 1985. 

Differences between the species toward the thiocholine substrates have been reported. Table 11.1 illustrates some observed differences with three species. For plasma pseudocholinesterase measurements, dog, rabbit, and man show higher substrate specificity for butyryl substrates, whereas rat, mouse, and hamster show higher specihcity for propionyl substrates all the species show less specihcity toward benzoyl substrates. Female rats have higher values compared to males with all three substrates, and the cholinesterase levels in platelets are higher in rats compared to the very low levels in human platelets. 

To date, 61 cholinesterase structures have been deposited in the Protein Data Bank. Forty are of T. califomica AChE, nine of mouse AChE, three of Drosophila AChE, two of human AChE, and seven of human BuChE. Overlaying of al Torpedo AChE structures reveals exceptional similarity in their protein backbone (Fig. 3A) and even in their side chain conformations (Fig. 3B). The mean value of the root mean square (RMS) deviation of the 40 Torpech AChE structure.s from the alpha carbon trace of the highest resolution (1.8 A), unligandcd Ica5 structure is only 0.26 iO. 10 A. Twelve... 

Figure 6.3 Crystal structure of the mouse acetylcholinesterase-2 gallamine homodimer complex with 30% homology of 532 residues from the C-terminal cholinesterase part of human thyroglobulin (Tg). The three-dimensional structure of mouse acetylcholinesterase homodimer complex homological to part III of human Tg in Figure 6.1 was experimentally determined at a resolution of 2.20A using X-ray diffraction (Bourne et al., 2003 ExPASy access number P21836). A model of the molecule was constructed using CAChe software (Fujitsu Ltd, Japan) according to the XYZ coordinates from Protein Data Bank file (code 1 N5M.pdb).

Highly toxic by all routes of exposure however, more toxic in rat than in mouse and rabbit cholinesterase inhibitor exhibits acute, delayed, and chronic poisoning toxic symptoms range from headache, twitching, salivation, blurred vision, and lacrimation to gastrointestinal effects and respiratory paralysis in humans permeation through skin at a dosage level of 10-15 mg/kg may manifest toxic effect. 

Wang R, Tang XC (2005) Neuroprotective effects of huperzine A. A natural cholinesterase inhibitor for the treatment of Alzheimer s disease. Neurosignals 14 71-82 Wang R, Zhang D (2005) Memantine prolongs survival in an amyotrophic lateral sclerosis mouse model. Eur J Neurosci 22 2376-2380... 

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