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Relationship: 2009


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, Reactive oxygen species leads to Oxidative Stress

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

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 (ROS) formation leads to cancer via inflammation pathway adjacent High Not Specified John Frisch (send email) Under development: Not open for comment. Do not cite
Essential element imbalance leads to reproductive failure via oxidative stress adjacent Travis Karschnik (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 Do not cite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
human Homo sapiens High NCBI
mouse Mus musculus High NCBI
rat Rattus norvegicus High NCBI
Murinae gen. sp. Murinae gen. sp. 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

Oxidative stress occurs due to the accumulation of reactive oxygen species (ROS).  ROS can damage DNA, lipids, and proteins (Shields et al. 2021).  Superoxide dismutase is an enzyme in a common cellular defense pathway, in which superoxide dismutase converts superoxide radicals to hydrogen peroxide.  When cellular defense mechanisms are unable to mitigate ROS formation from mitochondrial respiration and stressors (biological, chemical, radiation), increased ROS levels cause oxidative stress.

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

This KER was identified as part of an Environmental Protection Agency effort to increase the impact of AOPs published in the peer-reviewed literature, but heretofore unrepresented in the AOP-Wiki, by facilitating their entry and update.  The originating works for this AOP were da Silva, J., Goncalves, R. V., de Melo, F. C. S. A., Sarandy, M. M., & da Matta, S. L. P. (2021). Cadmium exposure and testis susceptibility: A systematic review in murine models. Biological Trace Element Research, 199(7), 2663-2676 and Jeong and Choi (2020). This publication, and the work cited within, were used create and support this AOP and its respective KE and KER pages.

Evidence from the da Silva (2021) publication was assembled using Medline/PubMed and Scopus in September 2018.  For all databases, the search filters were based on three complementary levels: (i) animals, (ii) testis, and (iii) cadmium and studies that didn't evaluate the Cd exposure in the testicular histomorphology of murine models were excluded.

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

The biological plausibility linking increases in oxidative stress to reactive oxygen species (ROS) is strong.  Reactive oxygen species (ROS) are produced by many normal cellular processes (ex. cellular respiration, mitochondrial electron transport, specialized enzyme reactions) and occur in multiple chemical forms (ex. superoxide anion, hydroxyl radical, hydrogen peroxide).  Antioxidant enzymes play a major role in reducing reactive oxygen species (ROS) levels in cells (Ray et al. 2012) to prevent cellular damage to lipids, proteins, and DNA (Juan et al. 2021).  Oxidative stress occurs when antioxidant enzymes do not prevent ROS levels from increasing in cells, often induced by environmental stressors (biological, chemical, radiation).

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

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

Life Stage: The life stage applicable to this key event relationship is all life stages.  Older individuals are more likely to manifest this adverse outcome pathway (adults > juveniles > embryos) due to accumulation of reactive oxygen species.

Sex: This key event relationship applies to both males and females.

Taxonomic: This key event relationship appears to be present broadly, with representative studies including mammals (humans, lab mice, lab rats), teleost fish, and invertebrates (cladocerans, mussels).


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

Alomar, C., Sureda, A., Capo, X., Guijarro, B., Tejada, S. and Deudero, S.  2017.  Microplastic ingestion by Mullus surmuletus Linnaeus, 1758 fish and its potential for causing oxidative stress.  Environmental Research 159: 135-142.

Barboza, LG.A., Vieira, L.R., Branco, V., Figueiredo, N., Carvalho, F., Carvalho, C., and Guilhermino, L. 2018.  Microplastics cause neurotoxicity, oxidative damage and energy-related changes and interact with the bioaccumulation of mercury in the European seabass, Dicentrachus labrux (Linneaeus, 1758).  Aquatic Toxicology 195: 49-57.

Browne, M.A. Niven, S.J., Galloway, T.S., Rowland, S.J., and Thompson, R.C.  2013.  Microplastic moves pollutants and additives to worms, reducing functions linked to health and biodiversity.  Current Biology 23: 2388-2392.

Chen, Q., Gundlach, M., Yang, S., Jiang, J., Velki, M., Yin, D., and Hollert, H.  2017 Quantitative investigation of the mechanisms of microplastics and nanoplastics toward larvae locomotor activity.  Science of the Total Environment 584-585: 1022-1031.

Choi, J.S., Jung, Y.J., Hong, N.H., Hong, S.H., and Park, J.W. 2018.  Toxicological effects of irregularly shaped and spherical microplastics in a marine teleost, the sheepshead minnow (Cyprinodon variegatus).  Marine Pollution Bulletin 129: 231-240.

Deng, Y., Zhang, Y., Lemos, B., and Ren, H.  2017.  Tissue accumulation of microplastics in mice and biomarker responses suggest widespread health risks of exposure.  Science Reports 7: 1-10.

Espinosa, C., Garcia Beltran, J.M., Esteban, M.A., and Cuesta, A.  2018.  In vitro effects of virgin microplastics on fish head-kidney leucocyte activities.  Environmental Pollution 235: 30-38.

Imhof, H.K., Rusek, J., Thiel, M., Wolinska, J., and Laforsch, C. 2017.  Do microplastic particles affect Daphnia magna at the morphological life history and molecular level?  Public Library of Science One 12: 1-20.

Jeong, J. and Choi, J.  2020.  Development of AOP relevant to microplastics based on toxicity mechanisms of chemical additives using ToxCast™ and deep learning models combined approach.  Environment International 137:105557.

Jeong, C.B., Kang, H.M., Lee, M.C., Kim, D.H., Han, J., Hwang, D.S. Souissi, S., Lee, S.J., Shin, K.H., Park, H.G., and Lee, J.S.  2017.  Adverse effects of microplastics and oxidative stress-induced MAPK/NRF2 pathway-mediated defense mechanisms in the marine copepod Paracyclopina nana.  Science Reports 7: 1-11.

Jeong, C.B., Wong, E.J., Kang, H.M., Lee, M.C., Hwang, D.S., Hwang, U.K., Zhou, B., Souissi, S., Lee, S.J., and Lee, J.S.  2016.  Microplastic size-dependent toxicity, oxidative stress induction, and p-JNK and p-p38 activation in the Monogonout rotifer (Brachionus koreanus). Environmental Science and Technology 50: 8849-8857.

Juan, C.A., de la Lastra, J.M.P., Plou, F.J., and Lebena, E.P.  2021.  The chemistry of reactive oxygen species (ROS) revisited: Outlining their role in biological macromolecules (DNA, lipids and proteins) and induced pathologies.  International Journal of Molecular Sciences  22: 4642.

Lei, L., Wu, S., Lu, S., Liu, M., Song, Y., Fu, Z., Shi, H., Raley-Susman, K.M., and He, D.  2018.  Microplastic particles cause intestinal damage and other adverse effects in zebrafish Danio rerio and nematode Caenorhabditis elegans.  Science of the Total Environment 619-620: 1-8.

Paul-Pont, I., Lacroix, C., Gonzalez Fernandez, D., Hegaret, H., Lambert, C., Le Goic, N., Frere, L., Cassone, A.L., Sussarellu, R. Fabioux, C., Guyomarch, J., Albentosa, M., Huvet, A., and Soudant, P.  2016.  Exposure of marine mussels Mytillus spp. to polystyrene microplastics: Toxicity and influence on fluoranthene bioaccumulation.  Environmental Pollution 216: 724-737.

Ray, P.D., Huang, B.-W., and Tsuji, Y.  2012.  Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signalling.  Cellular Signalling 24:981-990.

Schrinzi, G.F., Perez-Pomeda, I., Sanchis, J., Rossini, C., Farre, M., and Barcelo, D.  2017.  Cytotoxic effects of commonly used nanomaterials and microplastics on cerebral and epithelial human cells. Environmental Research 159: 579-587.

Shields, H.J., Traa, A., and Van Raamsdonk, J.M.  2021.  Beneficial and Detrimental Effects of Reactive Oxygen Species on Lifespan: A Comprehensive Review of Comparative and Experimental Studies.

Veneman, W.J., Spaink, H.P., Brun, N.R., Bosker, T., and Vijver, M.G.  2017.  Pathway analysis of systemic transcriptome responses to injected polystyrene particles in zebrafish larvae.  Aquatic Toxicology 190: 112-120.

Yu, P., Liu, Z., Wu, D., Chen, M., Lv, W., and Zhao, Y.  2018.  Accumulation of polystyrene microplastics in juvenile Eriocheir sinensis and oxidative stress effects in the liver.  Aquatic Toxicology 200: 28-36.