To the extent possible under law, AOP-Wiki has waived all copyright and related or neighboring rights to KE:12

Event: 12

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Acetylcholinesterase (AchE) Inhibition

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
AchE Inhibition
Explore in a Third Party Tool

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization
Cellular

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Cell term
eukaryotic cell

Organ term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Organ term
nervous system

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; https://aopwiki.org/info_pages/2/info_linked_pages/7#List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Process Object Action
acetylcholinesterase activity acetylcholinesterase decreased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
AChE inhibition - acute mortality MolecularInitiatingEvent Dan Villeneuve (send email) Under Development: Contributions and Comments Welcome Under Development
AChE Inhibition Leading to Neurodegeneration MolecularInitiatingEvent Karen Watanabe (send email) Under development: Not open for comment. Do not cite
AChE inhibition - acute mortality via predation MolecularInitiatingEvent Kristie Sullivan (send email) Under development: Not open for comment. Do not cite
Organo-Phosphate Chemicals leading to impaired cognitive function MolecularInitiatingEvent SAROJ AMAR (send email) Under development: Not open for comment. Do not cite
Organo-Phosphate Chemicals leading to sensory axonal peripheral neuropathy and mortality MolecularInitiatingEvent SAROJ AMAR (send email) Under development: Not open for comment. Do not cite

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 KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help

Life Stages

An indication of the the relevant life stage(s) for this KE. More help
Life stage Evidence
All life stages High

Sex Applicability

An indication of the the relevant sex for this KE. More help
Term Evidence
Unspecific High

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

"Acetylcholinesterase is found primarily in blood, brain, and muscle, and regulates the level of the neurotransmitter ACh [acetylcholine] at cholinergic synapses of muscarinic and nicotinic receptors. Acetylcholinesterase features an anionic site (glutamate residue), and an esteratic site (serine hydroxyl group) (Wilson, 2010; Soreq, 2001). In response to a stimulus, ACh is released into the synaptic cleft and binds to the receptor protein, resulting in changes to the flow of ions across the cell, thereby signaling nerve and muscle activity. The signal is stopped when the amine of ACh binds at the anionic site of AChE, and aligns the ester of ACh to the serine hydroxyl group of the enzyme. Acetylcholine is subsequently hydrolyzed, resulting in a covalent bond with the serine hydroxyl group and the subsequent release of choline, followed by a rapid hydrolysis of the enzyme to form free AChE and acetic acid (Wilson, 2010; Soreq, 2001)." [From Russom et al. 2014. Environ. Toxicol. Chem. 33: 2157-2169]

Molecular target gene symbol: ACHE

KEGG enzyme: EC 3.1.1.7

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help
  • Direct measures of AChE activity levels can be made using the modified Ellman method, although selective inhibitors that remove other cholinesterases not directly related to cholinergic responses (e.g., butyrylcholinesterase) are required [45,46].
  • Radiometric methods have been identified as better for measuring inhibition because of carbamylation (carbamate exposure) [20,46,47].
  • TOXCAST: NVS_ENZ_hAChE
  • A direct measure of cholinesterase activity levels can be made within the relevant tissues after in vivo exposure, specifically the brain as well as red blood cells in mammals. Some analytical methods used to measure cholinesterase activity may not distinguish between butyrylcholinesterase, which is found with AChE in plasma and some skeletal and muscle tissues. Although the structure of butyrylcholinesterase is very similar to AChE, its biological function is not clear, and its activity is not associated with cholinergic response covered under this AOP (Lushington et al., 2006). Therefore experimental procedures used to measure cholinesterase as well as the tissue analyzed should be considered when evaluating studies reporting AChE inhibition (Wilson 2010; Wilson and Henderson 2007). For measuring AChE levels, the Ellman method is recommended with some modifications (Ellman et al., 1961; Wilson et al., 1996) while radiometric methods have been identified as better for measuring inhibition due to carbamylation (carbamate exposure) (see Wilson 2010; Wilson et al., 1996; Johnson and Russell 1975).
  • In order to effectively bind to the AChE enzyme, thion forms of OPs (i.e., RO)3P=S) must first undergo a metabolic activation via mixed function oxidases to yield the active, oxon form (Fukuto 1990). Estimating the potential toxicity in whole organisms based on in vitro data may be problematic since metabolic activation may be required (e.g., phosphorothionates) and may not be reflected in the in vitro test result (Guo et al. 2006; Lushington et al. 2006).
  • Typically, carbamates do not require metabolic activation in order to bind to the enzyme, although some procarbamates (e.g., carbosulfan) have been developed that are not direct inhibitors of AChE, but take advantage of metabolic distinctions between taxa, resulting in a toxic form in invertebrates (e.g., carbofuran) but not vertebrate species (Stenersen 2004). Therefore in vitro assays measuring AChE inhibition for procarbamates in invertebrate species will not account for metabolic activation and therefore may not represent the actual enzyme activity.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

AChE is present in all life stages of both vertebrate and invertebrate species (Lu et al 2012).

  • Acetylcholinesterase associated with cholinergic responses in most insects is coded by the ace1 gene and in vertebrates by the ace gene (Lu et al 2012; Taylor 2011.

  • Plants have AChE but it is most likely involved in regulation of membrane permeability and the ability of a leaf to unroll (Tretyn and Kendrick 1991).

  • The primary amino acid sequence of the AChE enzyme is relatively well conserved across vertebrate and invertebrate species, suggesting that chemicals are likely to interact with the enzyme in a similar manner across a wide range of animals. From the sequence similarity analyses, the taxonomic domain of applicability of this MIE likely includes species belonging to many lineages, including branchiopoda (crustaceans, e.g., daphnids), insecta (insects), arachnida (arachnids, e.g., spiders, ticks, scorpions), cephalopoda (molluscans, e.g., octopods, squids), lepidosauria (reptiles, e.g., snakes, lizards), chondrichthyes (cartilaginous fishes, e.g., sharks), amphibia (amphibians), mammalian (mammals), aves (birds), actinopterygii (bony fish), ascidiacea (sac-like marine invertebrates), trematoda (platyhelminthes, e.g., flatworms), and gastropoda (gastropods, e.g., snails and slugs) Species within these taxonomic lineages and others are predicted to be intrinsically susceptible to chemicals that target functional orthologs of the daphnid AChE (Russom, 2014).

  • Advanced computational approaches such as crystal structures of the enzyme and transcriptomics have provided empirical evidence of the enzyme structure, relevant binding sites, and function across species (Lushington et al., 2006; Lu et al., 2012; Wallace 1992).

Studies have found that AChE activity increases as the organism develops.

  • Prakesh and Kaur 1982 looked at AChE inhibition across three insect species; controls and those exposed to DDVP. They saw little difference in the larval stages but did see increased inhibition in pupal and adult stages (greatest inhibition). 

  • Karanth and Pope 2003 looked at AChE and acetylcholine synthesis in rat striatum in controls and animals exposed to 0.3 and 1 times the maximum tolerated dose. Although these doses are below the lethal concentrations and they mention that not observed cholinergic responses were observed, they do provide differences related to life stages of the rodents. 

  • Grue et al 1981 present baseline (no toxicity exposure) in wild starlings (both sexes) of brain cholinesterase and found activity increased as birds aged from 1-20 days until it reached a steady state at adulthood.

  • A study with Red Flour Beetle found that the gene associated with cholinergic functions (Ace1) was expressed at all life-stages, with increases as the organism developed from egg to larva to pupa to adult. (Lu et al., 2012 cited in Russom et al 2014.)

  • In mammals and birds, studies have determined that skeletal muscles of immature birds and mammals contain both butyrylcholinesterase and AChE, with butyrylcholinesterase decreasing and AChE increasing as the animal develops (Tsim et al. 1988; Berman et al, 1987).  

  • Another study found that changes in AChE within the developing pig brain were dependent on the area of the brain, and life stage of the animal, with significant decreases in activity within the pons and hippocampus from birth to 36 months, and no significant change in activity in the cerebellum, where activity increased up to four months of age, leveling off thereafter (Adejumo and Egbunike, 2004).

References

List of the literature that was cited for this KE description. More help
  • Augustinsson KB. 1957. Assay methods for cholinesterases. Methods of Biochemical Analysis, Vol 5, Interscience Publishers, Inc., New York, NY, USA, pp 1-63.

  • Ecobichon, D.J. 2001. Toxic effects of pesticides. In: C.D. Klaassen (Ed.), Casarett and Doull’s Toxicology: The Basic Science of Poisons; Sixth Edition. (pp. 763-810). McGraw-Hill, New York, NY.

  • Ellman GL, Courtney KD, Andres V Jr, Featherstone RM. 1961. A new and rapid colormetric determination of acetylcholinesterase activity. Biochem Pharmacol 7:88-95.

  • Fukuto, TR. 1990. Mechanism of action of organophosphorus and carbamate insecticides. Environ Health Perspect. 87:245-254.

  • Guo, J.-X., J.J.-Q. Wu, J.B. Wright, and G.H. Lushington. 2006. Mechanistic insight into acetylcholinesterase inhibition and acute toxicity of organophosphorus compounds: A molecular modeling study. Chem. Res. Toxicol. 19: 209-216.

  • Johnson CD, Russell RL. 1975. A rapid, simple radiometric assay for cholinesterase suitable for multiple determinations. Anal Biochem 64:229-238.

  • Kropp, T.J., and Richardson, R.J. 2003. Relative inhibitory potencies of chlorpyrifos oxon, chlorpyrifos methyl oxon, and mipafox for acetylcholinesterase versus neuropathy target esterase. J. Toxicol. Environ.l Health, Part A, 66:1145–1157.

  • 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.

  • Ludke JL, Hill EF, Dieter MP. 1975. Cholinesterase (ChE) response and related mortality among birds fed ChE inhibitors. Arch Environ ContamToxicol 3:1–21.

  • Lushington, G.H., J-X. Guo, and M.M. Hurley. 2006. Acetylcholinesterase: Molecular modeling with the whole toolkit. Curr. Topics Medic. Chem. 6: 57-73.

  • Mileson, BE, Chambers JE, Chen WL, Dettbarn W, Ehrich M, Eldefrawi AT, Gaylor DW, Hamernik K, Hodgson E, Karczmar AG, Padilla S, Pope CN, Richardson RJ, Saunders DR, Sheets LP, Sultatos LG, Wallace KB.  1998. Common mechanism of toxicity: A case study of organophosphorus pesticides. Toxicol Sci 41:8-20.

  • Moser, Virginia C. 2011. “Age-Related Differences in Acute Neurotoxicity Produced by Mevinphos, Monocrotophos, Dicrotophos, and Phosphamidon.” Neurotoxicology and Teratology 33 (4): 451–57. https://doi.org/10.1016/j.ntt.2011.05.012.

  • Monserrat, J.M. and A. Bianchini. 2001. Anticholinesterase effect of eserine (physostigmine) in fish and crustacean species. Braz. Arch. Biol. Technol. 44(1): 63-68.

  • Russom, Christine L., Carlie A. LaLone, Daniel L. Villeneuve, and Gerald T. Ankley. 2014. “Development of an Adverse Outcome Pathway for Acetylcholinesterase Inhibition Leading to Acute Mortality.” Environmental Toxicology and Chemistry 33 (10): 2157–69. https://doi.org/10.1002/etc.2662.

  • Schűűrmann G. 1992. Ecotoxicology and structure-activity studies of organophosphorus compounds. Rational Approaches to Structure, Activity, and Ecotoxicology of Agrochemicals, CRC Press, Boca Raton, FL, USA pp 485-541

  • Sogob MA, Vilanova E. 2002. Enzymes involved in the detoxification of organophosphorus, carbamate and pyrethroid insecticides through hydrolysis. Toxicol Lett 128:215-228.

  • Soreq H, Seidman S. 2001. Acetylcholinesterase -- New roles for an old actor. Nature Reviews Neurosci 2:294-302.

  • Stenersen, J. 2004. Specific enzyme inhibitors. In: Chemical Pesticides: Mode of action and toxicology. (41 p). CRC Press, Boca Raton, FL.

  • Taylor P. 2011. Anticholinesterase agents. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 12th ed, McGraw Hill, New York, NY, USA, pp 255-276.

  • Tretyn A, Kendrick RE. 1991. Acetylcholine in plants: Metabolism and mechanism of action. Bot Rev 57:33-73.

  • Wilson BW, Padilla S, Henderson JD, Brimijoin S, Dass PD, Elliot G, Jaeger B, Lanz D, Pearson R, Spies R. 1996. Factors in standardizing automated cholinesterase assays. J Toxicol Environ Health 48:187-195.

  • Wilson, B.W. and J.D. Henderson. 2007. Determination of cholinesterase in blood and tissue. Current Protocols in Toxicology 12.13.1-12.13.16.

  • Wilson BW. 2010. Cholinesterases. Hayes’ Handbook of Pesticide Toxicology, 3rd ed, Vol 2. Elsevier, Amsterdam, The Netherlands, pp 1457-1478.