Reactivators butyrylcholinesterase

Butyrophenones Butyrylcholinesterase C2 Domain C Kinase C-reactive Protein Ca2+-ATPase Ca2+-binding Proteins Ca2+ Channel Ca2+ Channel Antagonists Ca2+ Channel Blockers... 

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],... 

Butyrylcholinesterase (BuChE EC 3.1.1.8) from either horse or mice serum displayed different profiles. A steady state was not developed, although the rate constants of inhibition decreased with time. Since the presence of multiforms of serum BuChE has been established, it is likely that the first-order plot represents more than one exponent. The inhibited enzyme did not regenerate as fast as AChE-TDPI conjugate. However, 2-PAM enhanced the reactivation of horse-serum BuChE after inhibition with TDPI. The various rate constants were computed from the initial slopes of the inhibition and reactivation of... 

Figure 9. Fluoride reactivation of organophosphate-inhibited butyrylcholinesterase. (Reprinted from Toxicology and Applied Pharmacology, Vol. 184, D. Noort, H.P. Benschop and R.M. Black, Biomonitoring of Exposure to Chemical Warfare Agents A Review, pages 116-126 (2002), with permission from Elsevier Science.)...

A major drawback of the fluoride reactivation method is that not all nerve agent adducts are amenable to fluoride reactivation, with the aged adduct of soman the best known example. This problem can be solved by looking at the BuChE enzyme itself Fidder et al (2002) published a method based on the LC-MS analysis of a nerve agent phosphylated nonapeptide derived after pepsin digestion of inhibited butyrylcholinesterase. The authors presented a procedure to extract BuChE from plasma using... 

Van der Schans, M.J., Noort, D., Fidder, A., Degenhardt, C.E.A.M., Benschop, H.P., Langenberg, J.P. (2002). Retrospective detection of exposure to organophosphorus anticholinesterases fluoride reactivation and mass spectrometric analysis of phosphylated human butyrylcholinesterase. The meeting of NATO TG 004 Task Group on Prophylaxis and Therapy of Chemical Agents. November 4-7, 2002, Oslo, Norway. 

Saxena, A. et al. Edrophonium as a reactivator of organophosphate-inhibited human butyrylcholinesterase, presented at the Second Singapore International Symposium on Protection Against Toxic (SISPAT) Substances, Singapore, 4-7 December 2000. 

FIGURE 8.3 Comparative reactivation kinetics of soman-inhibited human butyrylcholinesterase single mutant G117H ( ) and double mutant G117H/E197Q ( ). Note that the recovery rate of the double mutant is very fast (with reaction rates of 77,000 and 128,000/min for the PsCs and PsCr isomers of soman, respectively), whereas the single mutant does not recover measurably. The insert shows that reactivation of the double mutant... 

Horse serum butyrylcholinesterase isoenzymes have been resolved by electrophoresis on polyacrylamide gel, and the differential reactivity of the various isoenzymes toward butyrylthiocholine has been measured simultaneously in a single gel (C7). The results are shown in Table 5. Only 63 % of the total enzymic activity was found to be associated with the major component (CJ, compared with 80% found by previous investigators (S49). 

C7. Ghiu, Y. G., Tripathi, R. K., and O Brien, R. D., Differences in reactivity of four butyrylcholinesterase isozymes towards substrate and inhibitors. Biochem. Biophys. Res. Commun. 46, 35-42 (1972). 

However, even erythrocyte AChE measurements cannot be expected to be a perfect surrogate for the nervous tissue enzyme this is because pharmacokinetic factors may result in differential access of the inhibitor to the red cell and to neural structures. A further consideration is that, where nerve agents react with the enzyme to produce a phosphonylated structure that does not spontaneously reactivate, red cells of mammals lack the protein synthetic capability to synthesize new AChE. By contrast, in nervous tissue, after inhibition by OPs whose enzyme-inhibitor complex with AChE does not readily reactivate, activity may reappear relatively quickly. Thus, Wehner et al (1985) observed approximately 30% recovery after 24 h in di-isopropylfluorophosphate (DFP)-treated mouse CNS reaggregates, which was clearly due to synthesis de novo of AChE. Another consideration in the interpretation of butyrylcholinesterase activity measurements is that the normal range is relatively wide, rendering interpretation in individual patients difficult unless the results of previous estimations in the patient are available (Swami-nathan and Widdop, 2001). 

Analytical procedures applied to diagnosis and retrospective verification of exposure to OP include (Worek et al., 2005) (i) biochemical determination of ChE activity (ii) identification of imbound OP (iii) identification of decomposition products (iv) fluoride-induced reactivation of inhibited ChE, followed by analysis of the inhibitor and (v) analysis of phosphyl-protein-adducts after tryptic digestion of the protein. The last procedure is regarded to be the most specific and sensitive, but it has the drawback of being strongly dependent on the analysis of butyrylcholinesterase (BChE), the most abim-dant plasma serine esterase with a half-life of about 16 days. 

Wandhammer, M., De Koning, M., van Grol, M., et al., 2013. A step toward the reactivation of aged cholinesterases—crystal structure of ligands binding to aged human butyrylcholinesterase. Chem. Biol. Interact. 203, 19-23. 

Jun, D., Musilova, L., Lazenska, H., et al., 2007. Potency of several oximes to reactivate human acetylcholinesterase and butyrylcholinesterase inhibited by paraoxon and methyl-paraoxon in vitro. The IXth International Meeting on Cholinesterases. Suzhou, China, May 6-10, 2007. Program Book, p. 140. 

E. Carletti, N. Aurbek, E. Gillon, M. Loiodiee, Y. Nicolet, J. C. Fontecil-la-Camps, P. Masson, H. Thiermann, F. Naehon and F. Worek, Structure-activity analysis of aging and reactivation of human butyrylcholinesterase inhibited by analogues of tabun, Biochem.J, 2009,421,97-106. 

The activities of two enzymes have been used as biomarkers of effects for OPs, namely acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase, sometimes known as pseudocholinesterase (EC 3.1.1.8). The structure and function of these enzymes has been reviewed. " In humans the former is present in red blood cells and the latter in plasma, but such distribution is not true of all species. In dogs, both enzymes are present in plasma with a ratio of butyrylcholinesterase to acetylcholinesterase of 7 1, while in the rat, plasma cholinesterase activity comprises more acetylcholinesterase with a butyrylcholinesterase to acetylcholinesterase activity of 1 3 in males and 2 1 in females in neither blood compartment are the functions of the enzymes fully understood.Because of the possibility of confusion, the terms plasma cholinesterase and erythrocyte cholinesterase as synonyms for butyrylcholinesterase and acetylcholinesterase are to be deprecated, especially when used of enzymes in animals where serious confusion may result. It is often necessary to look in detail at animal studies to see what activity has been measured in each matrix. In particular, it is necessary to look at the substrate(s) used in the assay together with any inhibitors used. Methods for measuring acetylcholinesterase have been reviewed and acetylcholinesterase and butyrylcholinesterase activities can be measured separately. In almost all cases it is the enzyme activity, rather than protein concentration, that is measured and many of the procedures used are variants of the Ellman method. Correct storage of blood samples is important as reactivation of inhibited enzymes ex vivo can occur. 

Figure 8.10 Schematic representation cf an automated system for the determination of pesticides using a butyrylcholinesterase (BuChE) electrode (R - r erence electrode E - enzyme electrode BuChCl -butyrylcholine chloride (substrate) PAM - reactivator).

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