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Relationship: 3797

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

Increase, DNA strand breaks leads to Cell injury/death

Upstream event

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

Increase, DNA strand breaks

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
Reactive oxygen species leading to growth inhibition via oxidative DNA damage and cell death	adjacent	High	Moderate	Allie Always (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 Do not cite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	Moderate	NCBI
green algae	Ulva compressa	Moderate	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 KER describes the causal relationship whereby increased DNA strand breaks lead to increased cell injury/death. DNA strand breaks include single-strand breaks and double-strand breaks; double-strand breaks are generally considered the more cytotoxic lesion because they can compromise chromosome integrity when unrepaired or misrepaired. Cells respond to strand breaks through DNA damage response pathways that detect DNA lesions, activate checkpoint kinases, arrest the cell cycle, coordinate repair, and determine cell fate. When the number, complexity, persistence, or chromosomal context of strand breaks exceeds the capacity for accurate repair, DNA damage signaling can shift from repair and survival toward apoptosis, necrosis, mitotic catastrophe, or other forms of cellular injury and death (Norbury and Zhivotovsky, 2004; Roos and Kaina, 2006; Jackson and Bartek, 2009; Surova and Zhivotovsky, 2013).

Within the ROS-growth AOP network, this KER represents an alternative downstream route from oxidative DNA damage toward growth impairment through cell loss rather than through reduced cell proliferation. It is most relevant when DNA strand breaks are sufficiently severe, persistent, or poorly repaired to compromise cell viability. The relationship is not stressor-specific and can be triggered by ionizing radiation, oxidative stress, redox-active chemicals, metals, nanoparticles, or endogenous processes that generate strand breaks directly or indirectly.

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 for this KER was assembled using the same AI-human hybrid workflow applied to the ROS-growth AOP network. Search terms were developed for both KEs and included DNA strand breaks, DNA double-strand breaks, DNA single-strand breaks, comet assay, gamma-H2AX, DNA damage response, ATM, ATR, p53, apoptosis, necrosis, cell injury, cytotoxicity, cell viability, oxidative stress, radiation, hydrogen peroxide, metals, nanoparticles, aquatic organisms, fish embryos, bivalves, and mammalian cells. AOP-helpFinder and targeted literature searches were used to identify studies reporting co-occurrence of DNA strand break measurements and cell injury/death-related endpoints. Records were prioritized when they reported dose/concentration, exposure duration, biological system, and evidence relevant to dose-response, temporal, or incidence concordance.

LLM-assisted screening was used to extract study metadata and provisional weight-of-evidence indicators, including whether DNA strand breaks occurred at lower or similar concentrations than cell injury/death, whether DNA damage preceded cytotoxicity, and whether intervention or repair evidence supported causality. All LLM outputs were checked manually against the original literature before inclusion. Mechanistic reviews were used to support biological plausibility, while primary studies were used where possible for empirical support. Evidence from the broader ROS-growth concordance table was used to identify taxa and stressors relevant to this KER.

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

Evidence call

Rationale and supporting evidence

High

The biological plausibility of this KER is high. DNA strand breaks, especially double-strand breaks, are recognized by DNA damage response pathways involving sensor and signaling proteins such as ATM, ATR, CHK1/CHK2, and p53. These pathways initially promote cell-cycle arrest and repair, but persistent or excessive damage can activate apoptosis and other cell death programs. DNA damage-induced apoptosis and other modes of cell death are extensively described and broadly accepted in mammalian cell biology (Norbury and Zhivotovsky, 2004; Roos and Kaina, 2006; Jackson and Bartek, 2009; Ciccia and Elledge, 2010; Surova and Zhivotovsky, 2013).

Mechanistically, the downstream response depends on the balance between repair capacity and damage severity. Repairable strand breaks may result in transient checkpoint activation and survival, whereas extensive or irreparable damage can induce mitochondrial apoptosis, caspase activation, necrosis, mitotic catastrophe, or senescence-associated injury. Thus, the KER is biologically plausible but conditional on damage persistence, repair capacity, cell-cycle context, and cell type.

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

Evidence call

Rationale and supporting evidence

Moderate

Empirical support is moderate. Multiple studies show co-occurrence or concordance of DNA strand breaks and cellular injury-related outcomes, but the available evidence is often stressor- and system-specific and does not always include direct manipulation of DNA strand breaks as an isolated upstream event. In isolated Mytilus edulis digestive gland cells, comet assay-detectable strand breakage was observed after exposure to genotoxic agents, with the assay shown to detect strand breaks at subcytotoxic concentrations, supporting temporal and dose logic in which DNA damage can occur before overt cytotoxicity (Mitchelmore et al., 1998). In Crassostrea gigas embryos, comet assay genotoxicity and embryotoxicity were measured in parallel after contaminant exposure, supporting concordance between DNA damage and abnormal development or injury-related outcomes (Wessel et al., 2007). More broadly, genotoxic stress and radiation studies support the progression from strand break formation and DNA damage response activation toward impaired cellular or organismal outcomes (Han et al., 2014; Quevedo et al., 2021).

The empirical evidence is not classified as high because many studies measure DNA strand breaks and cytotoxicity or cell injury in parallel without establishing direct causality, and because DNA strand breaks can also lead to repair and survival rather than death. In addition, some environmentally relevant studies report downstream outcomes such as abnormal development, growth impairment, or repair signaling rather than direct measurement of cell death.

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 principal uncertainty is that DNA strand breaks do not inevitably lead to cell injury/death. Cells can repair strand breaks accurately, tolerate transient checkpoint activation, or enter non-lethal outcomes such as senescence. The threshold for transition from repair to cell death is influenced by the number and complexity of strand breaks, whether lesions occur during replication, chromatin context, repair pathway competence, p53 status, energetic state, and the ability to activate apoptosis. Evidence from Scenedesmus quadricauda indicates that DNA damage during G2 did not necessarily affect cell-cycle progression, illustrating that DNA damage responses can differ among taxa and cell-cycle contexts (Hlavová et al., 2011).

Additional uncertainty arises because comet assay endpoints detect strand break-like migration that may reflect a mixture of direct strand breaks, alkali-labile sites, repair intermediates, and oxidative base damage. Therefore, empirical studies using comet assay data must be interpreted in light of assay design, repair-enzyme modification, cytotoxicity controls, and exposure duration.

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
DNA repair capacity	Capacity of base excision repair, single-strand break repair, homologous recombination, and non-homologous end joining.	Higher repair capacity reduces the probability that strand breaks persist long enough to trigger cell injury/death; impaired repair increases sensitivity.	Jackson and Bartek, 2009; Ciccia and Elledge, 2010
p53 and checkpoint status	Integrity of p53, ATM/ATR, CHK1/CHK2, and related checkpoint signaling.	Functional checkpoint and p53 signaling can either promote repair and survival or trigger apoptosis when damage is severe; defective signaling may alter the mode and timing of cell death.	Norbury and Zhivotovsky, 2004; Roos and Kaina, 2006; Surova and Zhivotovsky, 2013
Cell-cycle phase and proliferation rate	Cells in S phase or G2/M may be more vulnerable to replication-associated conversion of lesions into double-strand breaks or mitotic catastrophe.	Rapidly proliferating cells may show stronger progression from DNA strand breaks to death or growth impairment than quiescent cells.	Roos and Kaina, 2006; Hlavová et al., 2011
Damage severity and persistence	Number, complexity, and repairability of strand breaks; repeated or chronic exposure.	Greater or persistent strand break burden increases probability of transition from repair to apoptosis, necrosis, or mitotic catastrophe.	Norbury and Zhivotovsky, 2004; Roos and Kaina, 2006
Cell type and tissue context	Intrinsic apoptosis competence, metabolic state, antioxidant capacity, and tissue-specific repair background.	Can alter the threshold, time course, and mode of cell injury/death following DNA strand breaks.	Surova and Zhivotovsky, 2013

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

Quantitative understanding of this KER is low to moderate. There is strong qualitative and semi-quantitative evidence that larger, more persistent, or less repairable DNA strand break burdens increase the probability of cell injury/death. Dose-response relationships can be observed in individual experimental systems, particularly where comet assay or gamma-H2AX measurements are paired with viability, apoptosis, or cytotoxicity endpoints. However, the response-response relationship is not yet generalizable across taxa, cell types, stressors, and assay methods. The downstream outcome depends strongly on repair capacity, cell-cycle phase, p53 status, metabolic state, and exposure duration.

For application of this KER, quantitative interpretation should therefore be system-specific. A measured increase in DNA strand breaks can be interpreted as increasing the likelihood of cell injury/death when damage is persistent, repair capacity is exceeded, or strand breaks are accompanied by DNA damage response activation and declining viability. General quantitative thresholds applicable across the full biological domain of the KER are not currently available.

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

The domain of applicability of this KER is broad but conditional. It is applicable to cells and organisms in which DNA strand break detection, checkpoint signaling, DNA repair, and cell death pathways are functional. The relationship is expected to apply across vertebrates and many invertebrates, and it is particularly relevant in proliferative tissues, embryonic or larval stages, and systems exposed to persistent oxidative or genotoxic stress. The KER is not sex-specific. Taxonomic extrapolation is supported by the conservation of DNA damage response logic across eukaryotes, but quantitative predictions should be made cautiously because repair capacity, apoptotic competence, and stress tolerance vary among taxa and life stages.

References

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

AOP-Wiki. 2026. Relationship 3797: Increase, DNA strand breaks leads to Cell injury/death. Available at: https://aopwiki.org/relationships/3797. Accessed 14 May 2026.

Ciccia A, Elledge SJ. 2010. The DNA damage response: making it safe to play with knives. Molecular Cell 40:179-204. https://doi.org/10.1016/j.molcel.2010.09.019.

Han J, Won EJ, Lee BY, Hwang UK, Kim IC, Yim JH, Leung KMY, Lee JS. 2014. Gamma rays induce DNA damage and oxidative stress associated with impaired growth and reproduction in the copepod Tigriopus japonicus. Aquatic Toxicology 152:264-272. https://doi.org/10.1016/j.aquatox.2014.04.005.

Hlavová M, Čížková M, Vítová M, Bišová K, Zachleder V. 2011. DNA damage during G2 phase does not affect cell cycle progression of the green alga Scenedesmus quadricauda. PLoS ONE 6(5):e19626. https://doi.org/10.1371/journal.pone.0019626.

Jackson SP, Bartek J. 2009. The DNA-damage response in human biology and disease. Nature 461:1071-1078. https://doi.org/10.1038/nature08467.

Mitchelmore CL, Birmelin C, Livingstone DR, Chipman JK. 1998. Detection of DNA strand breaks in isolated mussel (Mytilus edulis L.) digestive gland cells using the comet assay. Ecotoxicology and Environmental Safety 41:51-58. https://doi.org/10.1006/eesa.1998.1669.

Mitchelmore CL, Chipman JK. 1998. DNA strand breakage in aquatic organisms and the potential value of the comet assay in environmental monitoring. Mutation Research 399:135-147. https://doi.org/10.1016/S0027-5107(97)00252-2.

Norbury CJ, Zhivotovsky B. 2004. DNA damage-induced apoptosis. Oncogene 23:2797-2808. https://doi.org/10.1038/sj.onc.1207532.

Quevedo AC, Lynch I, Valsami-Jones E. 2021. Cellular repair mechanisms triggered by exposure to silver nanoparticles and ionic silver in embryonic zebrafish cells. Environmental Science: Nano 8:2507-2522. https://doi.org/10.1039/D1EN00422K.

Roos WP, Kaina B. 2006. DNA damage-induced cell death by apoptosis. Trends in Molecular Medicine 12:440-450. https://doi.org/10.1016/j.molmed.2006.07.007.

Surova O, Zhivotovsky B. 2013. Various modes of cell death induced by DNA damage. Oncogene 32:3789-3797. https://doi.org/10.1038/onc.2012.556.

Wessel N, Rousseau S, Caisey X, Quiniou F, Akcha F. 2007. Investigating the relationship between embryotoxic and genotoxic effects of benzo[a]pyrene, 17alpha-ethinylestradiol and endosulfan on Crassostrea gigas embryos. Aquatic Toxicology 85:133-142. https://doi.org/10.1016/j.aquatox.2007.08.007.