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Relationship: 452


A descriptive phrase which clearly defines the two KEs being considered and the sequential relationship between them (i.e., which is upstream, and which is downstream). More help

AchE Inhibition leads to Increased Mortality

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes.Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Acetylcholinesterase inhibition leading to acute mortality non-adjacent High Moderate Dan Villeneuve (send email) Under Development: Contributions and Comments Welcome Under Development

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) that help to define the biological applicability domain of the KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER.  More help

Sex Applicability

An indication of the the relevant sex for this KER. More help

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER.  More help

Key Event Relationship Description

Provides a concise overview of the information given below as well as addressing details that aren’t inherent in the description of the KEs themselves. More help
  • Acetylcholinesterase (AChE) inhibition leads to mortality via overstimulation of neuronal cholinergic signalling pathways that control factors essential for respiration (Costa in Casarett and Doull's).

Evidence Collection Strategy

Include a description of the approach for identification and assembly of the evidence base for the KER. For evidence identification, include, for example, a description of the sources and dates of information consulted including expert knowledge, databases searched and associated search terms/strings.  Include also a description of study screening criteria and methodology, study quality assessment considerations, the data extraction strategy and links to any repositories/databases of relevant references.Tabular summaries and links to relevant supporting documentation are encouraged, wherever possible. More help

Evidence Supporting this KER

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help
Biological Plausibility
Addresses the biological rationale for a connection between KEupstream and KEdownstream.  This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured.   More help
  • Acetylcholinesterase inhibition impacts numerous bodily functions through its effect on the neurotransmitter, acetylcholine. Acetylcholinesterase catalyzes acetylcholine degradation, thereby preventing sustained activation of acetylcholine receptors. Acetylcholine levels controls of respiration and heart rate, skeletal muscle contraction, vasodilation and blood pressure. Thus, biological plausibility that AChE inhibition leads to mortality due to its effect on critical bodily functions, specifically respiration, as well as cardiovascular effects in some cases.

  • The biological plausibility for this KER is backed by numerous lines of evidence. 

    • Direct evidence linking AChE inhibition to mortality also comes from controlled studies in the laboratory and field.

    • Further, organophosphate (OP) nerve agents are a class of AChE inhibitors and are amongst the most powerful poisons known to man”. OP nerve agents include soman, sarin, cyclosarin, tabun and VX. Non-experimental evidence linking OPs to mortality in humans is based on OP use in warfare as a biological weapon, during the 1995 Tokoyo terrorist attack, as an agent in suicide attempts, and in laboratory accidents (Figueiredo, 2018).

Uncertainties and Inconsistencies
Addresses inconsistencies or uncertainties in the relationship including the identification of experimental details that may explain apparent deviations from the expected patterns of concordance. More help
  • Development of AChE Tolerance: Under certain circumstances, tolerance to AChE inhibition can develop, instead of mortality. Rats exposed to acutely toxic, near-lethal amounts of AChE inhibitor become tolerant. Adaptation to AChE inhibitor has been described in humans in association with Myasthenia graves, asthenic syndrome, and after long exposure to some insecticides. (Stavinoha, 1969)(The reference listed here references 3 papers on rats published between ‘52-’64).

  • In vivo AChE Inhibition Measurement Challenges

    • Correlating in vivo measures of AChE inhibition with mortality endpoints have not always been successful possibly due to interference from other esterases and partitioning issues across tissues (Wilson 2010).

    • A QSAR (quantitative structure activity relationship) model developed to predict the acute LC50 for rainbow trout (Oncorhynchus mykiss) using the pI50 (concentration that inhibits AChE by 50%) found a statistically relevant linear relationship, but the model only explained 59% of the variation in toxicity observed for the series of carbamates tested (Call et al., 1989). QSAR models to estimate fish toxicity (LC50) for a series of OPs based on the reaction rate constants associated with inhibition of AChE in electric eel did result in a significant model, but the model only explained 23% of the variation in toxicity (De Bruijn and Hermens 1993).

  • Challenges correlating In vivo and In vitro AChE Activity Measurements: Although relationships can be made between the in vitro AChE inhibition and in vivo toxicity values observed for direct acting OPs and carbamates, these relationships typically are not significant (Wilson 2010). Factors contributing to the failure of these correlations include the tissue analyzed, method used to assay AChE or acetylcholine, organism life stage, dose compared to body size, and metabolic differences including detoxification pathways (Wilson 2010; Ludke et al., 1975; Hamadain and Chambers, 2001).

Known modulating factors

This table captures specific information on the MF, its properties, how it affects the KER and respective references.1.) What is the modulating factor? Name the factor for which solid evidence exists that it influences this KER. Examples: age, sex, genotype, diet 2.) Details of this modulating factor. Specify which features of this MF are relevant for this KER. Examples: a specific age range or a specific biological age (defined by...); a specific gene mutation or variant, a specific nutrient (deficit or surplus); a sex-specific homone; a certain threshold value (e.g. serum levels of a chemical above...) 3.) Description of how this modulating factor affects this KER. Describe the provable modification of the KER (also quantitatively, if known). Examples: increase or decrease of the magnitude of effect (by a factor of...); change of the time-course of the effect (onset delay by...); alteration of the probability of the effect; increase or decrease of the sensitivity of the downstream effect (by a factor of...) 4.) Provision of supporting scientific evidence for an effect of this MF on this KER. Give a list of references.  More help
Response-response Relationship
Provides sources of data that define the response-response relationships between the KEs.  More help
Information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). More help
Known Feedforward/Feedback loops influencing this KER
Define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits. More help

Domain of Applicability

A free-text section of the KER description that the developers can use to explain their rationale for the taxonomic, life stage, or sex applicability structured terms. More help
Taxonomic Applicability
  • Russom et al performed two parallel approaches to examine AChE sensitivity across multiple taxa: insects, crustaceans, fish, amphibians, mollusks, annelids, and plants. They generated species sensitivity curves from empirical evidence pulled from systemic searches for acute lethality toxicity data for terrestrial and aquatic species in the ECOTOX database. Daphnids were consistently found to be highly sensitive to organophosphates and carbamates. Next, they used the Daphnia pulex AChE protein sequence was used as the query sequence to make cross-species susceptibility predictions. There was strong agreement between the empirical evidence and the species sensitivity predictions based on the protein sequence similarity approach. Insects and crustaceans include the species most sensitive the AChE inhibition, followed by fish and amphibians and then by mollusks and annelids (Russom, 2014; LaLone, 2013). 

  • Amongst fish, amphibians, mammals and birds, Wallace summarized comparative sensitivities from multiple studies. Across these groups, birds are highly sensitive to AChE inhibition, mammals are moderately sensitive and fish and amphibians are the least sensitive to AChE inhibition.

Life Stage Applicability
  • Studies in zebrafish have shown that mortality coincides with the onset of organogenesis for dichlorvos and diazinon and with the end of organogenesis/onset of hatching for chlorpyrifos (Watson, 2014) 

  • In Xenopus, OP-induced mortality occurs at a time well after organogenesis and before the physiological changes associated with metamorphosis. At the peak of Xenopus mortality, the larva was swimming actively, had a well-developed mouth, and was in the process of developing hind limbs (stage 49) (Watson, 2014) 


List of the literature that was cited for this KER description. More help
  • Carey JL, Dunn C, Gaspari RJ., Central respiratory failure during acute organophosphate poisoning. Respir Physiol Neurobiol. 2013 Nov 1;189(2):403-10.

  • Figueiredo TH, Apland JP, Braga MFM, Marini AM. Acute and long-term consequences of exposure to organophosphate nerve agents in humans. Epilepsia. 2018 Oct;59 Suppl 2:92-99. doi: 10.1111/epi.14500. Epub 2018 Aug 29.

  • Kobayashi H, Yuyama A, Kajita T, Shimura K, Ohkawa T, Satoh K. 1985. Effects of insecticidal carbamates on brain acetylcholine content, acetylcholinesterase activity and behavior in mice. Toxicol Lett 29:153–159.

  • Costa.  Toxic effects of pesticides.  In Casarett and Doull's Toxicology: The Basic Science of Poisons. 9th ed. pp 1055-1106.

  • Grue CE, Shipley BK. 1984. Sensitivity of nestling and adult starling to dicrotophos, an organophosphate pesticide. Environ Res 35:454–465.

  • Li M, Zheng C, Kawada T, Inagaki M, Uemura K, Sugimachi M. Adding the acetylcholinesterase inhibitor, donepezil, to losartan treatment markedly improves long-term survival in rats with chronic heart failure. Eur J Heart Fail. 2014 Oct;16(10):1056-65. doi: 10.1002/ejhf.164. Epub 2014 Sep 8.

  • Wadia, R. S., Sadagopan, C., Amin, R. B., and Sardesai, H.V. 1974. Neurological manifestations of organophosphorus insecticide poisoning. J Neurol Neurosurg Psychiatry. 37(7): 841–847.

  • Gaspari RJ, Paydarfar D. Pathophysiology of respiratory failure following acute dichlorvos poisoning in a rodent model. Neurotoxicology. 2007 May;28(3):664-71.

  • Yen,J., S. Donerly, E.D. Levin, and E.A. Linney","Differential Acetylcholinesterase Inhibition of Chlorpyrifos, Diazinon and Parathion in Larval Zebrafish",Neurotoxicol. Teratol.33(6): 735-741,2011,Fish; MORT/ACHE

  • Behra M, Cousin X, Bertrand C, Vonesch JL, Biellmann D, Chatonnet A, Strähle U. Acetylcholinesterase is required for neuronal and muscular development in the zebrafish embryo. Nat Neurosci. 2002 Feb;5(2):111-8.

  • Sivam, SP, Hoskins, B. Ho, IK. 1984. An assessment of comparative acute toxicity of diisopropylfluorophosphate, tabun, sarin, and soman in relation to cholinergic and GABAergic enzyme activities in rats. Toxicological Sciences, 4(4), 531-538.

  • Swiergosz-Kowalewska, R., Molenda, P., Halota, A. 2014. Effects of chemical and thermal stress on acetylcholinesterase activity in the brain of the bank vole, Myodes glareolus. Ecotoxicology and Environmental Safety, 106, 204-212.

  • Coppage, D.L. 1972. Organophosphate Pesticides: Specific Level of brain AChE inhibition related to death in sheepshead minnows. Transactions of the American Fisheries Society. 101 (3), 534-536.

  • Gungordu,A. 2013. Comparative Toxicity of Methidathion and Glyphosate on Early Life Stages of Three Amphibian Species:  Pelophylax ridibundus, Pseudepidalea viridis, and Xenopus laevis. Aquat. Toxicol.140/141, 220-228.

  • Gromysz-Kalkowska, K., Szubartowska, E. 1993. Evaluation of Fenitrothion Toxicity to Rana temporaria L. 50:116-124.

  • Lu Y, Park Y, Gao X, Zhang X, Yoo J, Pang X-P, Jiang H, Zhu KY. 2012. Cholinergic and non-cholinergic functions of two acetylcholinesterase genes revealed by gene-silencing in Tribolium castaneum. Sci Rep 2:1-7.

  • Pant, Radha, and S. K. Katiyar. 1983. “Effect of Malathion and Acetylcholine on the Developing Larvae OfPhilosamia Ricini (Lepidoptera: Saturniidae).” Journal of Biosciences 5 (1): 89–95.

  • Velki,M., and B.K. Hackenberger. 2012. Species-Specific Differences in Biomarker Responses in Two Ecologically Different Earthworms Exposed to the Insecticide Dimethoate. Comp. Biochem. Physiol. C Toxicol. Pharmacol.156(2): 104-112.

  • Calisi, A., Lionetto, M.G., Schettino, T. 2011. Biomarker response in the earthworm Lumbricus terrestris exposed to chemical pollutants. Science of the Total Environment. 409, 4456-4464.

  • Maxwell, D.M., Brecht, K.M., Koplovitz, I., Sweeney, R.E. 2006. Acetylcholinesterase inhibition: does it explain the toxicity of organophosphorus compounds? Archives of Toxicology. 80:756.