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Sakurada K, Ohta H. No promising antidote 25 years after the Tokyo subway sarin attack: A review. Leg Med (Tokyo) 2020; 47:101761. [DOI: 10.1016/j.legalmed.2020.101761] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 06/26/2020] [Accepted: 07/10/2020] [Indexed: 10/23/2022]
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2
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Novel Insights into the Thioesterolytic Activity of N-Substituted Pyridinium-4-oximes. Molecules 2020; 25:molecules25102385. [PMID: 32455554 PMCID: PMC7287890 DOI: 10.3390/molecules25102385] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 05/15/2020] [Accepted: 05/19/2020] [Indexed: 12/21/2022] Open
Abstract
The pyridinium oximes are known esterolytic agents, usually classified in the literature as catalysts, which mimic the catalytic mode of hydrolases. Herein, we combined kinetic and computational studies of the pyridinium-4-oxime-mediated acetylthiocholine (AcSCh+) hydrolysis to provide novel insights into their potential catalytic activity. The N-methyl- and N-benzylpyridinium-4-oximes have been tested as oximolytic agents toward the AcSCh+, while the newly synthesized O-acetyl-N-methylpyridinium-4-oxime iodide was employed for studying the consecutive hydrolytic reaction. The relevance of the AcSCh+ hydrolysis as a competitive reaction to AcSCh+ oximolysis was also investigated. The reactions were independently studied spectrophotometrically and rate constants, koxime, kw and kOH, were evaluated over a convenient pH-range at I = 0.1 M and 25 °C. The catalytic action of pyridinium-4-oximes comprises two successive stages, acetylation (oximolysis) and deacetylation stage (pyridinium-4-oxime-ester hydrolysis), the latter being crucial for understanding the whole catalytic cycle. The complete mechanism is presented by the free energy reaction profiles obtained with (CPCM)/M06–2X/6–311++G(2df,2pd)//(CPCM)/M06–2X/6–31+G(d) computational model. The comparison of the observed rates of AcSCh+ oximolytic cleavage and both competitive AcSCh+ and consecutive pyridinium-4-oxime-ester hydrolytic cleavage revealed that the pyridinium-4-oximes cannot be classified as non-enzyme catalyst of the AcSCh+ hydrolysis but as the very effective esterolytic agents.
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A novel fluorescence based assay for the detection of organophosphorus pesticide exposed cholinesterase activity using 1-naphthyl acetate. Biochimie 2019; 160:100-112. [DOI: 10.1016/j.biochi.2019.02.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 02/22/2019] [Indexed: 01/18/2023]
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Li S, Zhao J, Huang R, Santillo MF, Houck KA, Xia M. Use of high-throughput enzyme-based assay with xenobiotic metabolic capability to evaluate the inhibition of acetylcholinesterase activity by organophosphorous pesticides. Toxicol In Vitro 2019; 56:93-100. [PMID: 30625376 DOI: 10.1016/j.tiv.2019.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 12/21/2018] [Accepted: 01/04/2019] [Indexed: 10/27/2022]
Abstract
The inhibition of acetylcholinesterase (AChE) has pharmaceutical applications as well as potential neurotoxic effects. The in vivo metabolites of some chemicals including organophosphorus pesticides can become more potent AChE inhibitors compared to their parental compounds. To account for the effects of biotransformation, we have developed and characterized a high-throughput screening method for identifying AChE inhibitors that become active or more potent following xenobiotic metabolism. In this study, an enzyme-based assay was developed in 1536-well plates using recombinant human AChE combined with human or rat liver microsomes. The AChE activity was measured by two methods with different readouts: colorimetric and fluorescent. The assay exhibited exceptional performance characteristics including large assay signal window, low well-to-well variability and high reproducibility. The performance of the assays with microsomes was characterized by testing a group of known AChE inhibitors including parent compounds and their metabolites. Large potency differences between the parent compounds and the metabolites were observed in the assay with microsome addition. Both assay readouts were required for maximal sensitivity. These results demonstrate that this platform is a promising method to profile large numbers of chemicals that require metabolic activation for inhibiting AChE activity.
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Affiliation(s)
- Shuaizhang Li
- Division for Pre-Clinical Innovation, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, USA
| | - Jinghua Zhao
- Division for Pre-Clinical Innovation, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, USA
| | - Ruili Huang
- Division for Pre-Clinical Innovation, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, USA
| | - Michael F Santillo
- Division of Toxicology, Office of Applied Research and Safety Assessment, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, MD, USA
| | - Keith A Houck
- National Center for Computational Toxicology, Office of Research and Development, United States Environmental Protection Agency, Research Triangle Park, NC, USA
| | - Menghang Xia
- Division for Pre-Clinical Innovation, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, USA.
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Chowdhary S, Bhattacharyya R, Banerjee D. 1-Naphthyl acetate: A chromogenic substrate for the detection of erythrocyte acetylcholinesterase activity. Biochimie 2018; 154:194-209. [PMID: 30201403 DOI: 10.1016/j.biochi.2018.09.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 09/01/2018] [Indexed: 11/26/2022]
Abstract
Erythrocyte acetylcholinesterase (AChE) is a preferred biomarker for the detection of organophosphorus poisoning. Acetylthiocholine (ATCh) is the most popular substrate for the detection of AChE activity. However, oximolysis is a prominent feature with ATCh. In this context, we have searched alternative substrates for AChE using in silico tools for screening of a better substrate. The in silico approach was performed to understand the fitness and the Total Interaction Energy (TIE) of substrates for AChE. The alternative substrates for AChE were screened in terms of high Goldscore and favorable TIE in comparison to acetylcholine (ACh)-AChE complex and other relevant esterases. Among the screened substrates, 1-Naphthyl acetate (1-NA) exhibited the most favorable interaction with AChE in terms of highest TIE and corresponding high Goldscore. The Molecular Dynamic (MD) simulation of the 1-NA-AChE complex showed a stable complex formation over a period of 5 ns. The results obtained in the in silico studies were validated in vitro using pure erythrocyte AChE and hemolysate. We observed 1-NA to be a better alternative substrate for AChE than ATCh in terms of lower Km value. Its specificity appeared at least similar to ATCh. Therefore, we propose that 1-NA can be an attractive chromogenic substrate for the measurement of AChE activity, and it possess the potential to detect organophosphorus pesticide (OP) poisoning.
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Affiliation(s)
- Sheemona Chowdhary
- Department of Experimental Medicine and Biotechnology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, 160012, India
| | - Rajasri Bhattacharyya
- Department of Experimental Medicine and Biotechnology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, 160012, India
| | - Dibyajyoti Banerjee
- Department of Experimental Medicine and Biotechnology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, 160012, India.
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Tam NT, Berg H, Van Cong N. Evaluation of the joint toxicity of chlorpyrifos ethyl and fenobucarb on climbing perch (Anabas testudineus) from rice fields in the Mekong Delta, Vietnam. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:13226-13234. [PMID: 27250094 DOI: 10.1007/s11356-016-6980-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 05/25/2016] [Indexed: 06/05/2023]
Abstract
Organophosphates (e.g. chlorpyrifos ethyl) and carbamates (e.g. fenobucarb) are commonly used to control a wide range of pests in rice fields of the Mekong Delta in Vietnam. This study assesses the combined effect of chlorpyrifos ethyl (CPF) and fenobucarb (F), applied at concentrations used by rice farmers, on the brain acetylcholinesterase (AChE) activity in climbing perch fingerlings from rice fields in the Mekong Delta. It also investigates if Pyridine-2-aldoxime methiodide (2-PAM) can be used to reactivate cholinesterase that has been blocked by CPF. Three days after spraying, the water concentrations of both insecticides decreased quickly below the detection levels. However, the brain AChE activity in fish was inhibited for more than 7 days. The results indicate a quicker but less prolonged inhibition of the brain AChE activity by the mixture than by only CPF. The inhibition levels were above 70 % only during the first 48 h, which could explain why all fish survived. 2-PAM resulted in a significant reactivation of the cholinesterase blocked by a combination of CPF and F, and it is proposed that the reactivation by 2-PAM could provide a way to assess the AChE inhibition levels in organisms, when no unexposed individuals are available as controls. The results indicate that the current use of CPF and F in rice farming in the Mekong Delta is likely to cause negative effects on non-target organisms. Many of these effects may be sub-lethal, and there is a need to develop biomarkers that are relevant, inexpensive and easy to apply. The results show that brain AChE in climbing perch fingerling is a relevant biomarker for monitoring of exposure to, and sub-lethal impacts from organophosphates and carbamates under tropical conditions in developing countries.
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Affiliation(s)
- Nguyen Thanh Tam
- Faculty of Fishery, Nong Lam University, Block 6, Linh Trung Ward, Thu Duc District, HCM City, Vietnam.
- Department of Physical Geography, Stockholm University, Stockholm, SE-106 91, Sweden.
| | - Håkan Berg
- Department of Physical Geography, Stockholm University, Stockholm, SE-106 91, Sweden
| | - Nguyen Van Cong
- College of Environment and Natural Resources, Can Tho University, 3/2 Street, Can Tho City, Vietnam
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Satnami ML, Dewangan HK, Kandpal N, Nagwanshi R, Ghosh KK. Influence of octanohydroxamic acid on the association behavior of cationic surfactants: Hydrolytic cleavage of phosphate ester. J Mol Liq 2016. [DOI: 10.1016/j.molliq.2016.06.052] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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8
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Santillo MF, Liu Y. A fluorescence assay for measuring acetylcholinesterase activity in rat blood and a human neuroblastoma cell line (SH-SY5Y). J Pharmacol Toxicol Methods 2015; 76:15-22. [DOI: 10.1016/j.vascn.2015.07.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 07/02/2015] [Accepted: 07/06/2015] [Indexed: 11/15/2022]
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9
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Veloso AJ, Nagy PM, Zhang B, Dhar D, Liang A, Ibrahim T, Mikhaylichenko S, Aubert I, Kerman K. Miniaturized electrochemical system for cholinesterase inhibitor detection. Anal Chim Acta 2013; 774:73-8. [DOI: 10.1016/j.aca.2013.02.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2012] [Revised: 01/23/2013] [Accepted: 02/17/2013] [Indexed: 01/30/2023]
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10
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Haddad GL, Young SC, Heindel ND, Bornhop DJ, Flowers RA. Back-Scattering Interferometry: An Ultrasensitive Method for the Unperturbed Detection of Acetylcholinesterase-Inhibitor Interactions. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201203640] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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11
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Haddad GL, Young SC, Heindel ND, Bornhop DJ, Flowers RA. Back-scattering interferometry: an ultrasensitive method for the unperturbed detection of acetylcholinesterase-inhibitor interactions. Angew Chem Int Ed Engl 2012; 51:11126-30. [PMID: 23037915 DOI: 10.1002/anie.201203640] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Revised: 08/24/2012] [Indexed: 11/12/2022]
Abstract
A series of inhibitors of acetylcholinesterase (AChE) have been screened by back-scattering interferometry (BSI). Enzyme levels as low as 100 pM (22,000 molecules of AChE) can be detected. This method can be used to screen for mixed AChE inhibitors, agents that have shown high efficacy against Alzheimer's disease, by detecting dual-binding interactions. E = enzyme, I = inhibitor, S = substrate.
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Worek F, Eyer P, Thiermann H. Determination of acetylcholinesterase activity by the Ellman assay: a versatile tool for in vitro research on medical countermeasures against organophosphate poisoning. Drug Test Anal 2011; 4:282-91. [PMID: 21998030 DOI: 10.1002/dta.337] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 07/01/2011] [Accepted: 07/05/2011] [Indexed: 11/08/2022]
Abstract
Inhibition of acetylcholinesterase (AChE) is the main mechanism of action of organophosphorus compounds (OP), and AChE reactivators (oximes) are at present the only causal therapeutic approach. Being the key target of OP toxicity, AChE may serve as a valuable tool for diagnosis of OP exposure as well as for the investigation of the kinetics of interactions between OP and oximes. At present, the rapid, simple, and cheap spectrophotometric Ellman assay is widely used for diagnosis, therapeutic monitoring and in vitro kinetic investigations. Application of the assay for investigation of the interactions between AChE, inhibitors, and oximes requires the consideration of potential matrix effects (e.g. hemoglobin), side reactions (e.g. oximolysis of substrate) and other determinants (e.g. pH, temperature). By taking these factors into account, the Ellman assay allows the precise and reproducible determination of kinetic constants as a basis for the understanding of toxic OP effects and for the development of improved therapies against poisoning by OP. In addition, advanced applications of the Ellman assay, for example, in a dynamic in vitro model for the real-time activity determination of membrane-bound AChE, enables the proper investigation of relevant tissue, primarily respiratory muscle, and extends the applicability of this method.
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Affiliation(s)
- Franz Worek
- Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, Munich, Germany.
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John H, Blum MM. Review of UV spectroscopic, chromatographic, and electrophoretic methods for the cholinesterase reactivating antidote pralidoxime (2-PAM). Drug Test Anal 2011; 4:179-93. [DOI: 10.1002/dta.327] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 06/21/2011] [Accepted: 06/21/2011] [Indexed: 11/06/2022]
Affiliation(s)
- Harald John
- Bundeswehr Institute of Pharmacology and Toxicology; Munich; Germany
| | - Marc-Michael Blum
- Los Alamos National Laboratory, Bioscience Division; Los Alamos; NM; USA (LA-UR 11-04236)
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Singh N, Ghosh KK, Marek J, Kuca K. Hydrolysis of carboxylate and phosphate esters using monopyridinium oximes in cationic micellar media. INT J CHEM KINET 2011. [DOI: 10.1002/kin.20590] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Guarisco JA, O'Donnell JC, Skovira JW, McDonough JH, Shih TM. In vivo oxime administration does not influence Ellman acetylcholinesterase assay results. Toxicol Mech Methods 2009; 19:379-85. [PMID: 19778238 DOI: 10.1080/15376510903234773] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Organophosphorus compounds (OPs) are potent inhibitors of acetylcholinesterase (AChE). Treatment for OP poisoning is by administration of atropine sulfate, an oxime, and diazepam. Oximes such as 2-PAM are used to reactivate OP-inhibited AChE so as to restore normal enzymatic function and serve as a true antidote. There are reports of non-enzymatic hydrolysis by oximes of acetylthiocholine in in vitro preparations in the widely used Ellman assay for AChE activity, which may confound the interpretation of AChE activity by producing elevated results. The purpose of this experiment was to determine if there is appreciable interference by therapeutic levels of oximes on the results of the Ellman assay in assessing AChE reactivation by oxime compounds in vivo. When therapeutic doses of oximes (2-PAM, HI-6, MMB-4, or MINA) were administered intramuscularly to guinea pigs and samples collected 60 min later, there was no statistical difference between oxime and saline control groups in measured AChE activity in various tissue samples, including blood. With appropriate dilution of samples prior to spectrophotometric assay, the Ellman assay is an acceptable method to measure in vivo oxime reactivation of inhibited AChE. Inclusion of an oxime control group to insure that this particular type of interference is not causing false readings in the assay is a prudent step.
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Affiliation(s)
- John A Guarisco
- Pharmacology Branch, Research Division, US Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, Maryland 21010-5400, USA
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Shih TM, Skovira JW, O'Donnell JC, McDonough JH. Evaluation of nine oximes on in vivo reactivation of blood, brain, and tissue cholinesterase activity inhibited by organophosphorus nerve agents at lethal dose. Toxicol Mech Methods 2009; 19:386-400. [PMID: 19778239 DOI: 10.1080/15376510903213892] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The capability of several oximes (HI-6, HLö7, MMB-4, TMB-4, carboxime, ICD 585, ICD 692, ICD 3805, and 2-PAM) to reactivate in vivo AChE inhibited by the nerve agents sarin, cyclosarin, VX, or VR in blood, brain regions, and peripheral tissues in guinea pigs was examined and compared. Animals were injected subcutaneously with 1.0 LD(50) of sarin, cyclosarin, VR, or VX, and treated intramuscularly 5 min later with one of these compounds. Toxic signs and lethality were monitored, and tissue AChE activities were determined at 60 min after nerve agent. The animals exposed to sarin or cyclosarin, alone or with non-oxime treatment, some died within 60 min; however, when treated with an oxime, no animal died. For VR or VX, all animals survived for 60 min after exposure, with or without non-oxime or oxime therapy. These nerve agents caused differential degrees of inhibition: in whole blood sarin = cyclosarin > VR = VX; in brain regions sarin > cyclosarin > VX > VR; and in peripheral tissues sarin > VX > cyclosarin > VR. These oximes exhibited differential potency in reactivating nerve agent-inhibited AChE in various peripheral tissues, but not AChE activity in the brain regions. There was no difference in the AChE reactivating potency between the dichloride and dimethanesulfonate salts of HI-6. AChE inhibited by sarin was the most and cyclosarin the least susceptible to oxime reactivation. Overall, MMB-4 appeared to be, among all oximes tested, the most effective in vivo AChE reactivator against the broadest spectrum of nerve agents.
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Affiliation(s)
- Tsung-Ming Shih
- Pharmacology Branch, Research Division, US Army Medical Research Institute of Chemical Defense, Aberdeen Proving Ground, MD 21010-5400, USA.
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Kuca K, RC G, Musilek K, Jun D, Pohanka M. In vitro identification of novel acetylcholinesterase reactivators. TOXIN REV 2009. [DOI: 10.3109/15569540903246144] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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18
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Shih TM, Skovira JW, McDonough JH. Effects of 4-pyridine aldoxime on nerve agent-inhibited acetylcholinesterase activity in guinea pigs. Arch Toxicol 2009; 83:1083-9. [PMID: 19763542 DOI: 10.1007/s00204-009-0465-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Accepted: 08/20/2009] [Indexed: 11/27/2022]
Abstract
Methoxime (MMB-4) is a leading candidate oxime acetylcholinesterase (AChE) reactivator to replace pralidoxime (2-PAM) for therapeutic treatment of nerve agent intoxication. 4-Pyridine aldoxime (4-PA) is a synthetic starting material, a breakdown product, and a probable metabolite of MMB-4. There is a possibility that 4-PA may adversely interact with the nerve agent, thereby affecting nerve agent toxicity and biological AChE activity. This study evaluated the effects of 4-PA on sarin (GB)-, cyclosarin (GF)-, and VX-induced toxicity and AChE activity in blood, brain, and peripheral tissues of guinea pigs. Animals were pretreated with atropine methyl nitrate (1.0 mg/kg, im) 15 min prior to subcutaneous administration with 1.0 x LD(50) of GB, GF, or VX and then treated 15 min after the administration of nerve agents with 4-PA (3.5, 7.0, or 14.0 mg/kg, im). The dose-response effects of 4-PA alone were also examined. Toxic signs and lethality were monitored, blood and tissues were collected, and AChE activities were determined at 60 min after nerve agent administration. Under the condition of this study, all animals exposed to nerve agents exhibited some degree of toxic signs such as salivation, lacrimation, rhinorrhea, and convulsions. 4-PA at the three doses tested neither induced toxic signs nor altered the toxicity of GB, GF, or VX at the 1.0 x LD(50) exposure dose. Additionally, it did not modify the AChE activity in blood, brain, and peripheral tissues by itself or affect the AChE activity inhibited by a 1.0 x LD(50) dose of these three nerve agents in guinea pigs.
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Affiliation(s)
- Tsung-Ming Shih
- Pharmacology Branch, Research Division, US Army Medical Research Institute of Chemical Defense, ATTN: MCMR-CDR-P, 3100 Ricketts Point Road, Aberdeen Proving Ground, Aberdeen, MD 21010-5400, USA.
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Reactions of isodimethoate with human red cell acetylcholinesterase. Biochem Pharmacol 2008; 75:2045-53. [DOI: 10.1016/j.bcp.2008.02.021] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 02/20/2008] [Accepted: 02/20/2008] [Indexed: 11/19/2022]
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20
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Sinko G, Calić M, Bosak A, Kovarik Z. Limitation of the Ellman method: cholinesterase activity measurement in the presence of oximes. Anal Biochem 2007; 370:223-7. [PMID: 17716616 DOI: 10.1016/j.ab.2007.07.023] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2007] [Revised: 06/14/2007] [Accepted: 07/16/2007] [Indexed: 11/28/2022]
Abstract
The Ellman method for assaying thiols is widely used for cholinesterase activity measurement. Cholinesterase activity is measured indirectly by quantifying the concentration of 5-thio-2-nitrobenzoic acid (TNB) ion formed in the reaction between the thiol reagent 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) and thiocholine, a product of substrate (i.e., acetylthiocholine [ATCh]) hydrolysis by the cholinesterase. Oximes, reactivators of inhibited cholinesterase, are nucleophiles that also react with ATCh (oximolysis), producing thiocholine and (indirectly) TNB ion. The aim of this study was to characterize ATCh oximolysis. Therefore, we measured the oximolysis between oximes (K027 and HI-6) and ATCh in the presence of DTNB at different pH values, taking into account the final concentration of a product that is thiocholine. To confirm oximate ion involvement in the nucleophilic attack, we also determined the reaction rate between the oximes and ATCh, without DTNB, at different pH values by measuring the decrease in oximate ion absorption over time. The oximate ion of K027 reacted 14 times faster with ATCh (306M(-1)min(-1)) than the oximate ion of HI-6 (22M(-1)min(-1)). However, the rate constants obtained with the Ellman method were 84M(-1)min(-1) for K027 and 22M(-1)min(-1) for HI-6. Our results confirmed that the rate obtained with K027 using the Ellman method is actually the rate of the Ellman reaction itself. This suggests that the Ellman method cannot be used uncritically to evaluate oxime reaction with choline esters, in particular when oximolysis is faster than the Ellman reaction itself at a given pH.
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Affiliation(s)
- Goran Sinko
- Institute for Medical Research and Occupational Health, HR-10001 Zagreb, Croatia.
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21
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Worek F, Eyer P. The liberation of thiocholine from acetylthiocholine (ASCh) by pralidoxime iodide (2=PAM) and other oximes (obidoxime and diacetylmonoxime). Toxicol Lett 2006; 167:256-7; author reply 258. [PMID: 17113251 DOI: 10.1016/j.toxlet.2006.10.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Accepted: 10/10/2006] [Indexed: 10/24/2022]
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