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Relationship: 1862

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

Increased, Intracellular Calcium overload leads to Cell injury/death

Upstream event

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

Increased, Intracellular Calcium overload

Downstream event

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

Cell injury/death

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 Neurodegeneration	adjacent	High	Low	Karen Watanabe (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 Do not cite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
zebrafish	Danio rerio	High	NCBI
mouse	Mus musculus	High	NCBI
rat	Rattus norvegicus	High	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	High

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

Intracellular calcium (Ca2+) increase can occur from influx through various ion channels (Choi, 1988). Overload of intracellular Ca2+ in the cytoplasm leads to endoplasmic reticulum stress, mitochondrial impairment, and overactivated calcium dependent enzymes such as kinases, phosphatases, proteases, lipases, and endonucleases causing cell damage (Faria et al., 2015, Kaur et al., 2014). Ca2+ elevation occurs shortly (before 1 hour) after exposure to certain toxic compounds (Deshpande et al., 2014).

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 was collected in multiple ways: literature searches of external databases, review of related KEs and KERS in the AOPWiki, and consultation with experts. Extensive literature searches were conducted in Scopus, Pubmed, and Google Scholar using keywords applicable to each KE, with an initial focus on zebrafish data to then focusing on rat data. Related KEs and KERs in the AOPWiki were also reviewed for relevant evidence and their sources. The “snowball method” was used to find additional articles, i.e., relevant citations within an article were obtained if they provided additional evidence. EndNote reference managing software was used to store results from the literature searches and when possible, a pdf of the manuscript was attached to each record. Papers were reviewed and categorized by whether they contained data to support one or more parts of the AOP. An Excel spreadsheet was used to record reviewed papers and any information worth noting.

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

It is well known that Ca²⁺ signaling overload can trigger cell death mechanisms (Zhivotovsky and Orrenius, 2011). Calcium is also known to partially regulate apoptosis under normal conditions through Ca²⁺ dependent signaling to the mitochondria (Rodrigues et al., 2018).

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Zebrafish models of severe, acute organophosphorus poisoning showed significant calcium signaling pathway changes, characterized by extensive necrosis in the central nervous system. Calcium chelators also reduced the occurrence of this phenotype (Faria et al., 2015).
Mouse cortical cells showed a decrease in total glutamate-induced cell death when the exposure solution lacked Ca²⁺ (Choi, 1985).
Rat hippocampal neurons showed a significant positive correlation between an inability to restore resting intracellular calcium concentrations and cell death (Limbrick et al., 1995).
Cell death was significantly reduced in a low calcium solution in a low Mg²⁺ induced in vitro status epilepticus model of rat hippocampal neurons (Deshpande et al., 2008).
Neocortical neuron cultures of Swiss-Webster mice exposed to various glutamate receptor agonists showed a correlation between increasing intracellular calcium and increasing LDH release into the medium. Antagonizing NMDA receptors additionally showed both a reduction of intracellular calcium accumulation and LDH release in a dose-dependent manner (Hartley et al., 1993).

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

Total understanding of the complex signaling involved with intracellular Ca²⁺ has not been fully explored, but there is plenty of evidence supporting the link between Ca²⁺ and cell death (Nagarkatti et al., 2009). There is also evidence that the pathway of increased Ca²⁺ makes a difference in the neurotoxicity of the Ca²⁺ influx, showing NMDAR mediated influx is more lethal compared to other Ca²⁺ channels (Lau and Tymianski, 2010).

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

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

Table 1: Summary of available quantitative data describing responses of cell injury/death to increased intracellular calcium overload. POX = paraoxon. Glu = glutamate.

Upstream Increased Intracellular Ca²⁺ Overload	Downstream Cell Injury/Death	Brief Summary	Species / Model	Reference
Upstream Increased Intracellular Ca²⁺ Overload	Downstream Cell Injury/Death	Brief Summary	Species / Model	Reference
Fura-2 AM Fluorescence	Fluoro-Jade C (FJC) staining	Rats received POX injections and were monitored for seizure activity with EEG. Hippocampal neurons were collected at later times and measured for intracellular calcium concentrations. Slices of selected brain regions were stained and measured for cell death.	Male Sprague-Dawley rats (250-300g \| 10-weeks)	Deshpande et al. (2014)
Fura-2 AM Fluorescence	Trypan blue (4% final concentration)	Time-series data of intracellular calcium measured through fluorescence and measurements of percent cell death in cultures exposed to Glu, both alone and with antagonists.	Cultured rat hippocampal neurons	Michaels and Rothman (1990)
Fura-2/AM, Fura-2/K+, Fura-2/dextran, BTC	0.4% Trypan blue exclusion	Time-series data of intracellular calcium measured through a variety of fluorescence calcium indicators given an application of the selective agonists and measured percent neuronal death.	Neocortical neurons of Swiss-Webster mice	Hyrc et al. (1997)

Response-response Relationship

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

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

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

Ca²⁺ cell death is known to occur in both zebrafish and mice (Faria et al., 2015, Choi, 1985).

References

List of the literature that was cited for this KER description. More help

Choi, D. W. 1985. Glutamate neurotoxicity in cortical cell culture is calcium dependent. Neuroscience Letters, 58, 293-297. DOI: https://doi.org/10.1016/0304-3940(85)90069-2.

Choi, D. W. 1988. Calcium-mediated neurotoxicity: relationship to specific channel types and role in ischemic damage. Trends Neurosci, 11, 465-9. DOI: 10.1016/0166-2236(88)90200-7.

Deshpande, L. S., Carter, D. S., Phillips, K. F., Blair, R. E. & DeLorenzo, R. J. 2014. Development of status epilepticus, sustained calcium elevations and neuronal injury in a rat survival model of lethal paraoxon intoxication. NeuroToxicology, 44, 17-26. DOI: 10.1016/j.neuro.2014.04.006.

Deshpande, L. S., Lou, J. K., Mian, A., Blair, R. E., Sombati, S., Attkisson, E. & DeLorenzo, R. J. 2008. Time course and mechanism of hippocampal neuronal death in an in vitro model of status epilepticus: role of NMDA receptor activation and NMDA dependent calcium entry. Eur J Pharmacol, 583, 73-83. DOI: 10.1016/j.ejphar.2008.01.025.

Faria, M., Garcia-Reyero, N., Padrós, F., Babin, P. J., Sebastián, D., Cachot, J., Prats, E., Arick Ii, M., Rial, E., Knoll-Gellida, A., Mathieu, G., Le Bihanic, F., Escalon, B. L., Zorzano, A., Soares, A. M. & Raldúa, D. 2015. Zebrafish Models for Human Acute Organophosphorus Poisoning. Sci Rep, 5, 15591. DOI: 10.1038/srep15591.

Hartley, D. M., Kurth, M. C., Bjerkness, L., Weiss, J. H. & Choi, D. W. 1993. Glutamate receptor-induced 45Ca2+ accumulation in cortical cell culture correlates with subsequent neuronal degeneration. J Neurosci, 13, 1993-2000. DOI: 10.1523/jneurosci.13-05-01993.1993.

Hyrc, K., Handran, S. D., Rothman, S. M. & Goldberg, M. P. 1997. Ionized intracellular calcium concentration predicts excitotoxic neuronal death: observations with low-affinity fluorescent calcium indicators. J Neurosci, 17, 6669-77. DOI: 10.1523/jneurosci.17-17-06669.1997.

Kaur, S., Singh, S., Chahal, K. S. & Prakash, A. 2014. Potential pharmacological strategies for the improved treatment of organophosphate-induced neurotoxicity. Canadian Journal of Physiology and Pharmacology, 92, 893-911. DOI: 10.1139/cjpp-2014-0113.

Lau, A. & Tymianski, M. 2010. Glutamate receptors, neurotoxicity and neurodegeneration. Pflugers Archiv European Journal of Physiology, 460, 525-542. DOI: 10.1007/s00424-010-0809-1.

Limbrick, D. D., Jr., Churn, S. B., Sombati, S. & DeLorenzo, R. J. 1995. Inability to restore resting intracellular calcium levels as an early indicator of delayed neuronal cell death. Brain Res, 690, 145-56. DOI: 10.1016/0006-8993(95)00552-2.

Michaels, R. L. & Rothman, S. M. 1990. Glutamate neurotoxicity in vitro: antagonist pharmacology and intracellular calcium concentrations. J Neurosci, 10, 283-92. DOI: 10.1523/jneurosci.10-01-00283.1990.

Nagarkatti, N., Deshpande, L. S. & DeLorenzo, R. J. 2009. Development of the calcium plateau following status epilepticus: role of calcium in epileptogenesis. Expert review of neurotherapeutics, 9, 813-824. DOI: 10.1586/ern.09.21.

Rodrigues, M. A., Gomes, D. A. & Nathanson, M. H. 2018. Calcium signaling in cholangiocytes: Methods, mechanisms, and effects. International Journal of Molecular Sciences, 19. DOI: 10.3390/ijms19123913.

Zhivotovsky, B. & Orrenius, S. 2011. Calcium and cell death mechanisms: A perspective from the cell death community. Cell Calcium, 50, 211-221. DOI: 10.1016/j.ceca.2011.03.003.