This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 2768

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

Decrease, ATP pool leads to Cell injury/death

Upstream event

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

Decrease, ATP pool

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
Uncoupling of oxidative phosphorylation leading to growth inhibition via ATP depletion associated cell death	adjacent	Moderate	Not Specified	You Song (send email)	Open for citation & comment	Under Development
Reactive oxygen species leading to growth inhibition via lipid peroxidation and cell death	adjacent	High	Moderate	You Song (send email)	Under development: Not open for comment. Do not cite
Excessive reactive oxygen species leading to growth inhibition via protein oxidation and cell injury/death	adjacent			You Song (send email)	Under development: Not open for comment. Do not cite
Excessive reactive oxygen species leading to growth inhibition via fatty acid oxidation and cell injury/death	adjacent			You Song (send email)	Under development: Not open for comment. Do not cite
Reactive oxygen species leading to growth inhibition via protein oxidation and cell death	adjacent	High	Moderate	You Song (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
humans	Homo sapiens	High	NCBI
mammals	mammals	High	NCBI
fish	fish	High	NCBI
crustaceans	Daphnia magna	High	NCBI
green algae	Ulva compressa	High	NCBI

Sex Applicability

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

Sex	Evidence
Unspecific	Moderate

Life Stage Applicability

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

Term	Evidence
All life stages	Moderate

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

This key event relationship describes the causal and predictive link by which a decrease in the cellular adenosine triphosphate (ATP) pool leads to increased cell injury and/or cell death. ATP is required to maintain ion gradients, plasma membrane integrity, mitochondrial homeostasis, macromolecular repair, vesicular trafficking, and regulated cell death programs. When ATP depletion is sufficiently severe or prolonged, energy-dependent adaptive and repair processes fail, calcium and sodium homeostasis are disrupted, mitochondrial permeability transition may be promoted, and cells may undergo apoptosis, necrosis, necroptosis-like injury or mixed forms of cell death depending on cellular context and residual ATP availability (Nieminen et al., 1994; Leist et al., 1997; Bonora et al., 2012).

The direction of this KER is from reduced ATP availability to increased cell injury/death. The KER is not intended to specify a single mode of cell death. Rather, it captures the general biological principle that loss of cellular energy supply increases the probability of irreversible cellular injury and death, with the exact death phenotype depending on cell type, severity of ATP depletion, duration of exposure, and availability of death-execution pathways.

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

The evidence base was assembled using the same structured strategy applied across the ROS-growth AOP network. Existing AOP-Wiki pages and OECD AOP reports were reviewed first to identify reusable KEs and related KERs. Particular attention was given to the mitochondrial energetic AOP series, including AOP 263 and AOP 264, because these AOPs contain the upstream event decreased ATP pool and downstream cellular or organismal outcomes relevant to growth inhibition and cell injury/death.

Targeted literature searches were then conducted using combinations of terms related to ATP depletion, cellular ATP, energetic failure, mitochondrial dysfunction, metabolic inhibition, apoptosis, necrosis, cytotoxicity, cell viability, cell injury, mitochondrial permeability transition, calcium electroporation, rotenone, FCCP, CCCP, paraquat, cadmium, algae, bivalves, fish, mammalian cells and human cells. Primary studies were prioritized when they measured ATP levels and cell viability, cytotoxicity, apoptosis or necrosis in the same biological system and reported dose/concentration or time-course information. Mechanistic reviews were used to support biological plausibility, while primary experimental studies were used for empirical concordance and quantitative understanding.

The evidence was curated for weight-of-evidence indicators including biological plausibility, temporal concordance, dose-response concordance, incidence concordance, evidence of threshold behavior, and intervention or rescue information. Studies were considered most informative when ATP depletion preceded or occurred at lower or similar exposure levels than cytotoxicity or cell death, or when restoration of energy metabolism reduced the downstream injury response.

Evidence Supporting this KER

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

The overall evidence supporting this KER is considered moderate to high. Biological plausibility is high because ATP is indispensable for cellular homeostasis and because severe ATP depletion is a well-established trigger of irreversible cell injury and death. Empirical support is moderate to high because multiple studies in mammalian cells, algae, aquatic organisms and cancer cell systems demonstrate concordance between ATP depletion and cell injury/death; however, the exact quantitative threshold varies substantially across biological systems and exposure conditions.

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

Biological plausibility is high. ATP depletion compromises core cellular maintenance processes including ion pumping, membrane integrity, cytoskeletal dynamics, protein turnover, DNA repair, and mitochondrial function. When ATP supply falls below the level required for homeostasis, cells lose the ability to maintain electrochemical gradients and to execute energy-dependent adaptive responses. Severe energetic collapse promotes necrotic injury, while partial ATP depletion may permit regulated apoptotic execution depending on residual ATP availability and caspase competence (Nieminen et al., 1994; Leist et al., 1997; Nicotera et al., 1998; Zong and Thompson, 2006).

The mechanistic relationship is also supported by mitochondrial cell-death biology. ATP depletion often accompanies mitochondrial membrane depolarization, permeability transition, impaired oxidative phosphorylation, calcium dysregulation, and increased reactive oxygen species generation. These processes can amplify cellular injury and increase the probability of cell death (Kroemer et al., 1998; Green and Kroemer, 2004; Halestrap, 2009; Bonora et al., 2012).

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

Empirical support is moderate to high. In mammalian systems, ATP depletion has been directly linked to cell killing after metabolic inhibition, and experimental work has shown that ATP depletion rather than mitochondrial depolarization can mediate hepatocyte death under some conditions (Nieminen et al., 1994). A widely cited study demonstrated that intracellular ATP concentration influences whether cells die by apoptosis or necrosis, supporting both causality and phenotype dependence (Leist et al., 1997). Calcium electroporation studies provide dose-dependent evidence that ATP depletion is associated with reduced cancer cell survival and increased cell death (Hansen et al., 2015).

Evidence from environmental and ecotoxicological systems is consistent with this relationship. In Chlamydomonas reinhardtii, herbicide exposure produced ATP depletion and cell injury/death in a multiple-endpoint assay, demonstrating concordance between energetic disruption and cellular toxicity in an algal model (Nestler et al., 2012). In eastern oysters, cadmium exposure affected mitochondrial bioenergetics and was associated with cellular damage endpoints, supporting applicability of energetic failure to cell injury in aquatic invertebrates (Sokolova et al., 2005). In ROS-growth concordance data, mitochondrial toxicants and oxidative stressors including paraquat, rotenone, cadmium and hydrogen peroxide frequently produce decreased ATP or mitochondrial dysfunction together with cytotoxicity or tissue injury, although direct measurement of both KEs in the same study is not always available.

Evidence type	Summary	Representative references
Biological plausibility	ATP is required for ion homeostasis, membrane maintenance, repair, and regulated cell death execution; severe ATP depletion promotes irreversible cell injury/death.	Nieminen et al. 1994; Leist et al. 1997; Bonora et al. 2012
Temporal concordance	ATP depletion can occur rapidly after metabolic inhibition or mitochondrial impairment and precedes detectable loss of viability or death execution in several cell systems.	Nieminen et al. 1994; Hansen et al. 2015
Dose-response concordance	Increasing intensity of energetic perturbation or calcium electroporation increases ATP depletion and cell killing.	Hansen et al. 2015
Incidence concordance	Systems showing marked ATP depletion commonly show increased cytotoxicity, cell injury or cell death, although moderate ATP depletion may be compensated in some contexts.	Leist et al. 1997; Nestler et al. 2012; Sokolova et al. 2005
Essentiality / intervention	Experimental data indicate that ATP availability influences the form and occurrence of cell death; restoration or maintenance of energy status can reduce injury in some systems, but direct rescue evidence across taxa remains limited.	Leist et al. 1997; Nicotera et al. 1998

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

The main uncertainty is that ATP depletion is not the only cause of cell injury/death. Cell death may also be initiated by DNA damage, receptor-mediated apoptosis, oxidative damage, calcium overload, lysosomal injury, proteotoxic stress or inflammatory signaling. Consequently, the presence of cell injury/death does not uniquely imply ATP depletion. The KER is strongest when ATP decline occurs before or at lower concentrations than cell death and when the upstream energetic perturbation is mechanistically established.

Another uncertainty concerns severity thresholds. Moderate ATP depletion may be reversible or may shift cells into cell-cycle arrest, reduced proliferation, or adaptive metabolic compensation rather than death. Conversely, very severe ATP depletion may prevent the energy-requiring execution of apoptosis and produce necrotic injury instead. Therefore, the downstream phenotype depends on the magnitude and duration of ATP depletion and on cellular metabolic reserve (Leist et al., 1997; Nicotera et al., 1998).

Empirical evidence across environmental species remains less dense than evidence from mammalian cell systems. Many ecotoxicological studies measure ATP, mitochondrial dysfunction, or cytotoxicity separately rather than measuring both KEs in the same time- and dose-resolved experiment. This limits the strength of concordance assessment across the full taxonomic applicability domain.

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	Details	Effect on this KER	References
Magnitude and duration of ATP depletion	Transient or moderate ATP depletion versus severe, sustained ATP depletion.	Severe and sustained ATP depletion increases probability of irreversible injury/death. Partial depletion may cause reversible stress or cell-cycle arrest.	Nieminen et al. 1994; Leist et al. 1997
Metabolic flexibility / glycolytic capacity	Ability to compensate for mitochondrial ATP loss by glycolysis or alternative ATP-generating pathways.	Higher metabolic flexibility may reduce sensitivity of the downstream cell death response.	Bonora et al. 2012; Zong and Thompson 2006
Cell type and proliferative/metabolic demand	Highly energy-demanding or poorly glycolytic cells may have lower tolerance to ATP depletion.	Alters threshold and time-scale for transition from ATP depletion to injury/death.	Bonora et al. 2012; Green and Kroemer 2004
Mitochondrial permeability transition and calcium homeostasis	Calcium overload and permeability transition can amplify ATP depletion and membrane failure.	Can accelerate progression to necrotic or mixed cell injury phenotypes.	Halestrap 2009; Nieminen et al. 1994
Apoptotic execution machinery	Caspase competence and residual ATP availability influence whether death is apoptotic or necrotic.	Determines cell death mode rather than the existence of injury/death per se.	Leist et al. 1997; Nicotera et al. 1998

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 quantitative understanding of this KER is considered moderate. Quantitative evidence supports a general response-response relationship in which larger or longer decreases in ATP increase the probability and severity of cell injury/death. However, a single universal threshold cannot be defined because ATP demand, ATP reserve, glycolytic capacity, cell type, death pathway, and exposure duration vary substantially among biological systems.

Several studies support threshold-like behavior. In hepatocytes, ATP depletion mediated killing after metabolic inhibition, supporting a causal threshold relationship between energetic collapse and cell death (Nieminen et al., 1994). Experiments in human T cells showed that intracellular ATP concentration can act as a switch influencing apoptotic versus necrotic death phenotypes (Leist et al., 1997). Calcium electroporation studies showed dose-dependent ATP depletion and reduced survival, supporting a quantitative relationship between the upstream energetic disturbance and the downstream cell death outcome (Hansen et al., 2015).

Response-response Relationship

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

The expected response-response relationship is generally monotonic but non-linear. Small or transient ATP reductions may be tolerated or compensated. Larger reductions increase the probability of cell stress, impaired repair, loss of membrane integrity, and cell death. At extreme ATP depletion, necrotic injury is favored, whereas intermediate depletion may permit energy-dependent apoptosis depending on cell type and execution machinery (Leist et al., 1997; Nicotera et al., 1998).

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 time scale of ATP depletion can range from minutes to hours following direct mitochondrial inhibition, uncoupling, metabolic inhibition, or membrane-disrupting interventions. Observable downstream cell injury/death may occur within hours to days depending on cell type, severity of ATP loss, and endpoint measured. In whole organisms, cell death may contribute to tissue injury or growth impairment over longer time frames.

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

Feedback and feedforward processes may influence this linkage. ATP depletion can impair ion pumps, causing calcium dysregulation and mitochondrial permeability transition, which further suppresses ATP production and amplifies injury. Loss of mitochondrial function may also increase ROS generation, further damaging mitochondrial and cellular components. Conversely, glycolytic compensation and stress-response activation may temporarily buffer ATP depletion and delay cell death.

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

The biological domain of applicability is broad because ATP-dependent homeostasis is a conserved property of living cells. The KER is most directly applicable to eukaryotic cells and tissues in which mitochondrial and/or glycolytic ATP supply maintains cellular viability. It is particularly relevant to metabolically active tissues and developing organisms where energy demand is high. It is applicable to both sexes and to multiple life stages, although sensitivity may differ with developmental status, tissue type, temperature, oxygen availability, and metabolic reserve.

The chemical and stressor applicability domain includes stressors that reduce cellular ATP through mitochondrial inhibition, OXPHOS uncoupling, oxidative stress, membrane disruption, calcium overload, metabolic poisons, hypoxia or other mechanisms that impair ATP synthesis or increase ATP demand beyond compensatory capacity. In the ROS-growth AOP network, this KER is most relevant downstream of OXPHOS impairment caused by lipid peroxidation or protein oxidation, where energetic failure contributes to increased cell injury/death.

References

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

Bonora M, Patergnani S, Rimessi A, De Marchi E, Suski JM, Bononi A, Giorgi C, Marchi S, Missiroli S, Poletti F, Wieckowski MR, Pinton P. 2012. ATP synthesis and storage. Purinergic Signaling 8:343-357. https://doi.org/10.1007/s11302-012-9305-8.

Green DR, Kroemer G. 2004. The pathophysiology of mitochondrial cell death. Science 305:626-629. https://doi.org/10.1126/science.1099320.

Halestrap AP. 2009. What is the mitochondrial permeability transition pore? Journal of Molecular and Cellular Cardiology 46:821-831. https://doi.org/10.1016/j.yjmcc.2009.02.021.

Hansen EL, Sozer EB, Romeo S, Frandsen SK, Vernier PT, Gehl J. 2015. Dose-dependent ATP depletion and cancer cell death following calcium electroporation, relative effect of calcium concentration and electric field strength. PLoS ONE 10:e0122973. https://doi.org/10.1371/journal.pone.0122973.

Kroemer G, Dallaporta B, Resche-Rigon M. 1998. The mitochondrial death/life regulator in apoptosis and necrosis. Annual Review of Physiology 60:619-642. https://doi.org/10.1146/annurev.physiol.60.1.619.

Leist M, Single B, Castoldi AF, Kuhnle S, Nicotera P. 1997. Intracellular adenosine triphosphate (ATP) concentration: a switch in the decision between apoptosis and necrosis. Journal of Experimental Medicine 185:1481-1486. https://doi.org/10.1084/jem.185.8.1481.

Lemasters JJ, Qian T, Bradham CA, Brenner DA, Cascio WE, Trost LC, Nishimura Y, Nieminen AL, Herman B. 1999. Mitochondrial dysfunction in the pathogenesis of necrotic and apoptotic cell death. Journal of Bioenergetics and Biomembranes 31:305-319. https://doi.org/10.1023/A:1005419617371.

Nestler H, Groh KJ, Schonenberger R, Behra R, Schirmer K, Eggen RIL, Suter MJF. 2012. Multiple-endpoint assay provides a detailed mechanistic view of responses to herbicide exposure in Chlamydomonas reinhardtii. Aquatic Toxicology 110-111:214-224. https://doi.org/10.1016/j.aquatox.2012.01.014.

Nicotera P, Leist M, Ferrando-May E. 1998. Intracellular ATP, a switch in the decision between apoptosis and necrosis. Toxicology Letters 102-103:139-142. https://doi.org/10.1016/S0378-4274(98)00298-7.

Nieminen AL, Saylor AK, Herman B, Lemasters JJ. 1994. ATP depletion rather than mitochondrial depolarization mediates hepatocyte killing after metabolic inhibition. American Journal of Physiology - Cell Physiology 267:C67-C74. https://doi.org/10.1152/ajpcell.1994.267.1.C67.

OECD. 2022. Uncoupling of oxidative phosphorylation leading to growth inhibition via decreased cell proliferation. OECD Series on Adverse Outcome Pathways No. 28. Paris: OECD Publishing.

Sokolova IM, Sokolov EP, Ponnappa KM. 2005. Cadmium exposure affects mitochondrial bioenergetics and gene expression of key mitochondrial proteins in the eastern oyster Crassostrea virginica Gmelin (Bivalvia: Ostreidae). Aquatic Toxicology 73:242-255. https://doi.org/10.1016/j.aquatox.2005.03.016.

Zong WX, Thompson CB. 2006. Necrotic death as a cell fate. Genes & Development 20:1-15. https://doi.org/10.1101/gad.1376506.