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Relationship: 1516


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

Oxidative Stress leads to Liver Cancer

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
Cyp2E1 Activation Leading to Liver Cancer non-adjacent Moderate Not Specified Francina Webster (send email) Open for citation & comment WPHA/WNT Endorsed

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

Sex Applicability

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

Life Stage Applicability

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

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

There are a variety of ways in which oxidative stress can lead indirectly to cancer. The main routes involve: (a) reactive oxygen species (ROS) that cause cytotoxicity, followed by regenerative proliferation leading to cancer; (b) ROS-induced DNA damage leading to mutations in cancer-driver genes and subsequently cancer; and (c) oncogenic effects of the up-regulation of NRF2. The focus of this iKER is on (b) and (c), as the details of (a) are mapped out elsewhere.  

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 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 types of genotoxic oxidative DNA damage that may occur following exposure to ROS have been extensively reviewed previously (Dizdaroglu 2012, Dizdaroglu 2015). Briefly, ROS can react with nitrogenous bases to produce various adducts that may be converted into a mutation following DNA replication. Further, ROS can damage the sugar phosphate backbone of DNA leading to abasic sites and strand breaks. If DNA damage leads to mutations that increases the expression of oncogenes or decreases the expression of tumour suppressor or DNA damage repair genes, they will transform normal cells into malignant cells. It is generally thought that liver cancer results from an accumulation of mutations in key cancer-driving genes such as TP53 and CTNNB1 (Fujimoto, et al. 2016, Shibata and Aburatani 2014a) ( 

In addition to DNA damage, at the molecular level, chronic activation of the Nrf2 oxidative stress response has been linked to promoting malignant transformation in pre-cancerous cells. Persistent Nrf2 activation results in the long-term up-regulation of antioxidant genes (which protect cancer cells that are known to have elevated ROS) and phase II metabolism genes (which facilitate the rapid metabolism of chemotherapeutics) (Kansanen, et al. 2013) providing a favourable environment for growth of pre-cancerous cells. The connection between chronically activated Nrf2 and cancer has been extensively studied and reviewed, most recently by Furfaro et al. (2016) and Karin and Dhar (2016). Further, Nrf2 control over cellular proliferation and differentiation has also been studied; reviewed most recently by Murakami and Motohashi  (2015).   

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

Not all agents that cause ROS in the liver cause liver cancer. Thus, there are additional modulating factors that must be considered when determining whether a ROS-producing chemical will cause liver cancer.

Overall, ROS-dependent DNA damage causing harmful mutations is known to occur. However, the specific mechanism and the quantitative relationships by which these mutations promote malignant transformation are incompletely understood.

Increase in NRF2 expression is associated with occurrence and recurrence of hepatocellular carcinoma; however, the mechanism is incompletely understood.

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


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

Beddowes, E.J., Faux, S.P., Chipman, J.K., 2003. Chloroform, carbon tetrachloride and glutathione depletion induce secondary genotoxicity in liver cells via oxidative stress. Toxicology 187, 101-115.

Ding, W., Petibone, D.M., Latendresse, J.R., Pearce, M.G., Muskhelishvili, L., White, G.A., Chang, C.-., Mittelstaedt, R.A., Shaddock, J.G., McDaniel, L.P., Doerge, D.R., Morris, S.M., Bishop, M.E., Manjanatha, M.G., Aidoo, A., Heflich, R.H., 2012. In vivo genotoxicity of furan in F344 rats at cancer bioassay doses. Toxicol. Appl. Pharmacol. 261, 164-171.

Dizdaroglu, M., 2015. Oxidatively induced DNA damage and its repair in cancer. Mutat. Res. Rev. Mutat. Res. 763, 212-245.

Dizdaroglu, M., 2012. Oxidatively induced DNA damage: mechanisms, repair and disease. Cancer Lett. 327, 26-47.

Fujimoto, A., Furuta, M., Totoki, Y., Tsunoda, T., Kato, M., Shiraishi, Y., Tanaka, H., Taniguchi, H., Kawakami, Y., Ueno, M., Gotoh, K., Ariizumi, S., Wardell, C.P., Hayami, S., Nakamura, T., Aikata, H., Arihiro, K., Boroevich, K.A., Abe, T., Nakano, K., Maejima, K., Sasaki-Oku, A., Ohsawa, A., Shibuya, T., Nakamura, H., Hama, N., Hosoda, F., Arai, Y., Ohashi, S., Urushidate, T., Nagae, G., Yamamoto, S., Ueda, H., Tatsuno, K., Ojima, H., Hiraoka, N., Okusaka, T., Kubo, M., Marubashi, S., Yamada, T., Hirano, S., Yamamoto, M., Ohdan, H., Shimada, K., Ishikawa, O., Yamaue, H., Chayama, K., Miyano, S., Aburatani, H., Shibata, T., Nakagawa, H., 2016. Whole-genome mutational landscape and characterization of noncoding and structural mutations in liver cancer. Nat. Genet. 48, 500-509.

Furfaro, A.L., Traverso, N., Domenicotti, C., Piras, S., Moretta, L., Marinari, U.M., Pronzato, M.A., Nitti, M., 2016. The Nrf2/HO-1 Axis in Cancer Cell Growth and Chemoresistance. Oxid Med. Cell. Longev 2016, 1958174.

Hickling, K.C., Hitchcock, J.M., Oreffo, V., Mally, A., Hammond, T.G., Evans, J.G., Chipman, J.K., 2010. Evidence of oxidative stress and associated DNA damage, increased proliferative drive, and altered gene expression in rat liver produced by the cholangiocarcinogenic agent Furan. Toxicol. Pathol. 38, 230-243.

Jackson, A.F., Williams, A., Recio, L., Waters, M.D., Lambert, I.B., Yauk, C.L., 2014. Case study on the utility of hepatic global gene expression profiling in the risk assessment of the carcinogen furan. Toxicol. Appl. Pharmacol. 274, 63-77.

Jaramillo, M.C., Zhang, D.D., 2013. The emerging role of the Nrf2-Keap1 signaling pathway in cancer. Genes Dev. 27, 2179-2191.

Kansanen, E., Kuosmanen, S.M., Leinonen, H., Levonen, A.L., 2013. The Keap1-Nrf2 pathway: Mechanisms of activation and dysregulation in cancer. Redox Biol. 1, 45-49.

Karin, M., Dhar, D., 2016. Liver carcinogenesis: from naughty chemicals to soothing fat and the surprising role of NRF2. Carcinogenesis 37, 541-546.

Linhart, K., Bartsch, H., Seitz, H.K., 2014. The role of reactive oxygen species (ROS) and cytochrome P-450 2E1 in the generation of carcinogenic etheno-DNA adducts. Redox Biol. 3, 56-62.

Moser, G.J., Foley, J., Burnett, M., Goldsworthy, T.L., Maronpot, R., 2009. Furan-induced dose–response relationships for liver cytotoxicity, cell proliferation, and tumorigenicity (furan-induced liver tumorigenicity). Experimental and Toxicologic Pathology 61, 101-111.

Murakami, S., Motohashi, H., 2015. Roles of Nrf2 in cell proliferation and differentiation. Free Radic. Biol. Med. 88, 168-178.

Poungpairoj, P., Whongsiri, P., Suwannasin, S., Khlaiphuengsin, A., Tangkijvanich, P., Boonla, C., 2015. Increased Oxidative Stress and RUNX3 Hypermethylation in Patients with Hepatitis B Virus-Associated Hepatocellular Carcinoma (HCC) and Induction of RUNX3 Hypermethylation by Reactive Oxygen Species in HCC Cells. Asian Pac. J. Cancer. Prev. 16, 5343-5348.

Schulze, K., Imbeaud, S., Letouze, E., Alexandrov, L.B., Calderaro, J., Rebouissou, S., Couchy, G., Meiller, C., Shinde, J., Soysouvanh, F., Calatayud, A.L., Pinyol, R., Pelletier, L., Balabaud, C., Laurent, A., Blanc, J.F., Mazzaferro, V., Calvo, F., Villanueva, A., Nault, J.C., Bioulac-Sage, P., Stratton, M.R., Llovet, J.M., Zucman-Rossi, J., 2015. Exome sequencing of hepatocellular carcinomas identifies new mutational signatures and potential therapeutic targets. Nat. Genet. 47, 505-511.

Takahashi, S., Hirose, M., Tamano, S., Ozaki, M., Orita, S., Ito, T., Takeuchi, M., Ochi, H., Fukada, S., Kasai, H., Shirai, T., 1998. Immunohistochemical detection of 8-hydroxy-2'-deoxyguanosine in paraffin-embedded sections of rat liver after carbon tetrachloride treatment. Toxicol. Pathol. 26, 247-252.

Totoki, Y., Tatsuno, K., Covington, K.R., Ueda, H., Creighton, C.J., Kato, M., Tsuji, S., Donehower, L.A., Slagle, B.L., Nakamura, H., Yamamoto, S., Shinbrot, E., Hama, N., Lehmkuhl, M., Hosoda, F., Arai, Y., Walker, K., Dahdouli, M., Gotoh, K., Nagae, G., Gingras, M.C., Muzny, D.M., Ojima, H., Shimada, K., Midorikawa, Y., Goss, J.A., Cotton, R., Hayashi, A., Shibahara, J., Ishikawa, S., Guiteau, J., Tanaka, M., Urushidate, T., Ohashi, S., Okada, N., Doddapaneni, H., Wang, M., Zhu, Y., Dinh, H., Okusaka, T., Kokudo, N., Kosuge, T., Takayama, T., Fukayama, M., Gibbs, R.A., Wheeler, D.A., Aburatani, H., Shibata, T., 2014. Trans-ancestry mutational landscape of hepatocellular carcinoma genomes. Nat. Genet. 46, 1267-1273.

Wacker, M., Wanek, P., Eder, E., 2001. Detection of 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal after gavage of trans-4-hydroxy-2-nonenal or induction of lipid peroxidation with carbon tetrachloride in F344 rats. Chem. Biol. Interact. 137, 269-283.

Wang, E., Chen, F., Hu, X., Yuan, Y., 2014. Protective effects of apigenin against furan-induced toxicity in mice. Food Funct. 5, 1804-1812.

Wang, Y., Millonig, G., Nair, J., Patsenker, E., Stickel, F., Mueller, S., Bartsch, H., Seitz, H.K., 2009. Ethanol-induced cytochrome P4502E1 causes carcinogenic etheno-DNA lesions in alcoholic liver disease. Hepatology 50, 453-461.

Winczura, A., Zdzalik, D., Tudek, B., 2012. Damage of DNA and proteins by major lipid peroxidation products in genome stability. Free Radic. Res. 46, 442-459.

Xiang, M., Namani, A., Wu, S., Wang, X., 2014. Nrf2: Bane or blessing in cancer? J. Cancer Res. Clin. Oncol. 140, 1251-1259.

Zhang, T.T., Zhao, G., Li, X., Xie, F.W., Liu, H.M., Xie, J.P., 2015. Genotoxic and oxidative stress effects of 2-amino-9H-pyrido[2,3-b]indole in human hepatoma G2 (HepG2) and human lung alveolar epithelial (A549) cells. Toxicol. Mech. Methods 25, 212-222.