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Relationship: 11

Title

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 ACh Synaptic Accumulation

Upstream event

The causing Key Event (KE) in a Key Event Relationship (KER). More help

AchE Inhibition

Downstream event

The responding Key Event (KE) in a Key Event Relationship (KER). More help

ACh Synaptic Accumulation

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	adjacent	High	Moderate	Cataia Ives (send email)	Under Development: Contributions and Comments Welcome	Under Development
Acetylcholinesterase Inhibition Leading to Neurodegeneration	adjacent	High	Moderate	Allie Always (send email)	Under development: Not open for comment. Do not cite
Acetylcholinesterase Inhibition leading to Acute Mortality via Impaired Coordination & Movement	adjacent			Allie Always (send email)	Under development: Not open for comment. Do not cite
Organo-Phosphate Chemicals induced inhibition of AChE leading to impaired cognitive function	adjacent	High	Moderate	Brendan Ferreri-Hanberry (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 Do not cite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 KER.In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. More help

Term	Scientific Term	Evidence	Link
Metapenaeus monoceros	Metapenaeus monoceros	High	NCBI
Philosamia ricini	Samia ricini	High	NCBI
Rana cyanophlyetis	Euphlyctis cyanophlyctis	Moderate	NCBI
Tilapia mossambica	Oreochromis mossambicus	High	NCBI
rat	Rattus norvegicus	High	NCBI
mouse	Mus musculus	High	NCBI
zebrafish	Danio rerio	Moderate	NCBI
Japanese quail	Coturnix japonica	Moderate	NCBI

Sex Applicability

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

Sex	Evidence
Unspecific	High

Life Stage Applicability

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

Term	Evidence
All life stages

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

AChE is an enzyme responsible for controlling the level of acetylcholine available at cholinergic synapses by degrading this neurotransmitter via hydrolysis to acetic acid and choline (Wilson 2010). Inhibition of AChE prevents degradation of acetylcholine which leads to accumulation of acetylcholine in synapses associated with muscarinic and nicotinic receptors (Soreq and Seidman, 2001; Lushington 2006).
See KEGG Reaction R01026

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 Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Title	First Author	Biological Plausibility	Dose Concordance	Temporal Concordance	Incidence Concordance

Biological Plausibility

Dose Concordance Evidence

Temporal Concordance Evidence

Incidence Concordance Evidence

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

No known qualitative inconsistencies or uncertainties associated with this relationship.

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

Modulating Factor (MF)	MF Specification	Effect(s) on the KER	Reference(s)
enzyme	butylcholinesterase	Butylcholinesterase can affect the substrate interaction and should be accounted for	Wilson (2001)

Quantitative Understanding of the Linkage

Captures information that helps to define how much change in the upstream KE, and/or for how long, is needed to elicit a detectable and defined change in the downstream KE. More help

The general kinetic equation is:

Where AX is the substrate, either acetylcholine or an inhibitor of AChE (e.g., OP or carbamate);
AChE-AX is the enzyme-substrate complex;
AChE-A is the acylated, carbamylated or phosphorylated enzyme;
X is the leaving group (e.g., choline);
AChE is the free enzyme; and
A is acetic acid, phosphate (P(=O)(=O)(R2)or methylamine.
In a normally functioning enzyme system k1 is the rate-limiting step for hydrolysis of acetylcholine, but k3 is the rate limiting step when AChE is inhibited by carbamates or OPs (Wilson 2010).
Some rate constants for OPs and carbamates have been published for use in PBPK models (Knaak et al., 2004, 2008)

Table 1: Summary of available quantitative data describing responses of ACh to AChE inhibition. Data are grouped by species.

AChE Inhibitor	CAS RN	Inhibitor Dosage	Species / Model	Brief Summary	Reference
Donezepil	120014-06-4	0.625, 1.25, 2.5 (mg/kg)	Male Wistar rats (210-290 g \| 7 weeks)	Timecourse data on both extracellular hippocampal ACh concentration and AChE activity given varying concentrations of inhibitor. Brain concentrations of drugs over time are also provided.	Kosasa et al., 1999
Tacrine	321-64-2	1.25, 2.5, 5, 10 (mg/kg)
ENA-713 (Rivastigmine)	129101-54-8	0.625, 1.25, 2.5 (mg/kg)
Dichlorvos (DDVP)	62-73-7	5 (mg/kg)	Male Wistar rats (180-230 g)	AChE activity (μmol AthCh hydrolyzed/g tissue) and ACh content (nmol ACh/g tissue) in jejunum either 10 minutes after single injection or 1 day after 10 injections.	Kobayashi et al., 1994
Propoxur	114-26-1	10 (mg/kg)	Male Wistar rats (180-230 g)		Kobayashi et al., 1994
Paraquat (PQ)	1910-42-5	0.1, 1, 10, 20, 30 (μM)	Wistar rats (fetal days 17-18) Primary hippocampal neurons	In Vitro AChE activity (% control) and ACh concentration (pmol / mL) at 24h and 14 days post exposure	Del Pino et al., 2017
Tacrine	321-64-2	1.25, 2.5, 5 (mg/kg)	Male Wistar rats (210-290 g \| 6 weeks)	Timecourse data on both extracellular hippocampal ACh concentration and AChE activity given varying concentrations of inhibitor. Note: Several sections of text are verbatim from Kosasa et al., 1999.	Kim 2003
Parathion (PS)	56-38-2	adult: 1.8, 3.4, 6, 9, 18, 27 (mg/kg) aged: 1.8, 3.4, 6, 9 (mg/kg)	Male Sprague-Dawley rats (adult: 3 months) (aged: 18 months)	Diaphragm and striatum AChE activity (% control). Striatal dialysates of ACh (fmol/60 μL fraction) on day 3 and 7 post-exposure	Karanth et al., 2007
Chlorpyrifos (CPF)	2921-88-2	84, 156, 279 (mg/kg)	Male Sprague-Dawley rats (325-350 g \| 3 months)	Diaphragm and striatum cholinesterase activity (% control). ACh concentration (fmol/60 μL fraction) through In Vivo microdialysis at 1, 4, and 7 days post-exposure	Karanth et al., 2006
Paraoxon	311-45-5	0.03, 0.1, 1, 10 (μM)	Male Sprague-Dawley rats (275-299 g \| 2-3 months)	Timecourse data on changes in striatal AChE activity (% control) and ACh concentration (fmole/fraction (60 μL)) over 4 hours post exposure.	Ray et al., 2009
Propoxur	114-26-1	10 (mg/kg)	Female ICR mice (30-40 g \| 8-10 weeks)	AChE activity (μmol acetylthiocholine hydrolyzed /min/g wet tissue) and ACh content (nmol/g wet tissue) both measured at 0, 10, 60, 180 minutes after injection (and 360 minutes for AChE activity)	Kobayashi et al., 1988
BPMC	3766‑81‑2	10 (mg/kg)	Female ICR mice (30-40 g \| 8-10 weeks)	Timecourse data on AChE activity (μmole acetylthiocholine hydrolyzed / min / g tissue or ml blood) and ACh content (nmol/g tissue) of forebrain homogenate, taken at 0, 10 and 60 minutes.	Kobayashi et al., 1985
Propoxur	114-26-1	2 (mg/kg)	Female ICR mice (30-40 g \| 8-10 weeks)		Kobayashi et al., 1985
DE-71	32534-81-9	31.0, 68.7, 227.6 (μg/L)	Zebrafish larvae	Changes in AChE activity (nmol / min / mg protein) and ACh concentration (nmol / mg protein) measured at 120 hours post-fertilization	Chen et al., 2012
Dichlorvos (DDVP)	62-73-7	3 (mg/kg)	Male Japanese quail (100 g \| 8-14 weeks)	AChE activity (μmol ACh hydrolyzed/g) and ACh content (nmol ACh/g wet tissue) measured 10 and 60 minutes post exposure for DDVP and Fenitrothion, respectively.	Kobayashi et al., 1983
Fenitrothion	122-14-5	300 (mg/kg)	Male Japanese quail (100 g \| 8-14 weeks)		Kobayashi et al., 1983
Methyl Parathion	298-00-0	0.09 (ppm)	Tilapia mossambica	Timecourse data on AChE activity (μmol ACh hydrolysed/mg protein/h) and ACh content (μmole/g wt. tissue) in muscle, gill, liver, and brain tissue at 12, 24, 36, and 48 hr timepoints	Rao and Rao, 1984
Methyl Parathion	298-00-0	2.5 (ppm)	Rana cyanophilicitus Frog tadpole (1.5-2 g \| 20 days)	AChE activity (μmol ACh hydrolyzed /min) and ACh content (μmol/g) measured after 24 hours post exposure	Yasmeen and Yasmeen, 1986
Malathion	121-75-5	60 µg each/g insect weight/day	Philosamia Ricini larvae	AChE activity and ACh concentration changes measured daily for 5 days.	Pant and Katiyar, 1983

Response-response Relationship

Provides sources of data that define the response-response relationships between the KEs. More help

Striatal AChE activity and extracellular ACh levels were measured in rats intracerebrally perfused with paraoxon (0, 0.03, 0.1, 1, 10 or 100 μM, 1.5 μl/min for 45 min). Acetylcholine was below the limit of detection at the low dose of paraoxon (0.1 uM), but was transiently elevated (0.5–1.5 hr) with 10 μM paraoxon. Concentration-dependent AchE inhibition was noted but reached a plateau of about 70% at 1 μM and higher concentrations (Ray, 2009).

Time-scale

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

The relationship between AChE inhibition and ACh accumulation at the synapse can be observed within 30 minutes after application of an AChE inhibitor (Ray, 2009). Other experiments have shown significant differences in ACh after AChE inhibition as soon as an hour after application of a chemical stressor (Kim et al., 2003, Faria et al., 2015).

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

Cholinergic transmissions mediated by acetylcholinesterase occur in a wide variety of species, both vertebrates and invertebrates, and cholinergic transmissions occur at all stages in life.

Taxonomic Applicability

The literature includes many studies linking increases in acetylcholine in brain tissues after exposure to an OP or carbamate pesticide with increased AChE inhibition in various taxa. Examples include studies with crustacea (Reddy et al., 1990); tadpoles (Nayeemunnisa and Yasmeen, 1986); fish (Rao and Rao 1984; Verma et al., 1981); birds (Kobayashi et al., 1983); and rodents (Kobayashi et al., 1988).