Relationship: 1913



Increase, Oxidative DNA damage leads to Increase, DNA strand breaks

Upstream event


Increase, Oxidative DNA damage

Downstream event


Increase, DNA strand breaks

Key Event Relationship Overview


AOPs Referencing Relationship


AOP Name Adjacency Weight of Evidence Quantitative Understanding
Oxidative DNA damage leading to chromosomal aberrations and mutations non-adjacent Moderate Low

Taxonomic Applicability


Term Scientific Term Evidence Link
human Homo sapiens NCBI
mice Mus sp. NCBI
rat Rattus norvegicus NCBI

Sex Applicability


Sex Evidence

Life Stage Applicability


Term Evidence
All life stages

Key Event Relationship Description


The repair of oxidative DNA lesions produced by exposure to reactive oxygen species (ROS) involves excision repair, where damaged base is removed by glycosylases, a strand break is generated 5’ to the apurinic/apyrimidinic (AP) site by lyases and endonucleases, and finally, a new strand is synthesized across the break. Although these strand breaks are mostly transient under normal conditions, elevated levels of oxidative DNA lesions can increase the early AP lyase activities generating a higher number of SSBs that can be more persistent (Yang et al., 2004; Yang et al., 2006). These SSBs can exacerbate the DNA damage by interfering with the replication fork causing it to collapse, and ultimately becoming double strand breaks (DSBs).      

Evidence Supporting this KER


Biological Plausibility


The mechanism of repair of oxidative DNA damage in humans is well-established and numerous literature reviews are available on this topic (Berquist and Wilson III, 2012; Cadet and Wagner, 2013). Oxidative DNA damage is mostly repaired via base excision repair (BER) and via nucleotide excision repair (NER) to a lesser extent. With an increase in oxidative DNA lesions, the more glycosylase and lyase activities occur, introducing SSBs at a higher rate than at homeostasis. It is highly plausible that an increase SSBs also increases the risk for DSBs, which are more difficult to repair accurately. Previous studies have reported thresholded dose-response curves in oxidative DNA damage and attributed these observations to failed repair at the inflection point on the curve, thus allowing strand breaks to accumulate (Gagne et al., 2012; Seager et al., 2012).

Empirical Evidence


The studies collected frequently address both dose and temporal concordance within a single study. Thus, we have not split out these types of empirical data by sub-headings. Instead, we indicate what evidence is available both in vitro and in vivo.

In vitro studies

  • Concentration concordance in the formation of oxidative DNA lesions and strand breaks in  HepG2 cells treated with nodularin (ROS-inducing substance (Bouaicha and Maatouk, 2004)) (Lankoff et al., 2006):
    • A concentration-dependent increase in oxidative lesions and strand breaks was observed after 6, 12, and 24h of treatment using Fpg-modified and regular comet assays, respectively.
      • At 6h, the increase in oxidative lesions was significant at 2.5, 5, and 10 µg/mL, while the increase strand breaks was significant at 5 and 10 µg/mL.
      • At 12 and 24 h, the increase in lesions was significant from 1 µg/mL and above, while significant increase in strand breaks occurred from 2.5 µg/mL and above.  
    • At all time points, significant increase in oxidative DNA lesions occurred at a lower concentration than DNA strand breaks.
    • These results demonstrate the concentration concordance in the formation of oxidative DNA lesions and DNA strand breaks.
  • Concentration and temporal concordance in human glioblastoma LN-229 cells treated with artesunate, a ROS inducing agent (Berdelle et al., 2011).
    • Concentration and time dependent increases in oxidative lesions were observed using the +Fpg comet test and immunofluorescence staining of 8-oxo-dG.
      • Significant increases in oxidative lesions were observed in cells treated with 25 µg/ml after 6 and 24 hours of treatment, but not 2 and 4 hours, using the + Fpg comet. No increases were observed using -Fpg comet.
      • Concentration-dependent increases in oxidative lesions were observed at the 24 hour timepoint using the +Fpg comet (50 and 75 µg/ml).
      • Oxidative lesions were also measured using immunofluorescence staining of 8-OxodG. Significant increases in oxidative lesions were observed at 6 and 8 hours of continuous treatment with 15 ug/ml artesunate, but not 1 and 4 hours.
        • Upon removal of test chemical, 8-OxodG levels decreased, returning to negative control level after 6 hours.
    • Significant increases in strand breaks as measured by ɣH2AX were observed 2 and 10 hours after treatment (15 µg/ml).
  • Deferme et al. (2013) exposed HepG2 cells to 100 µM menadione, 200 µM tert butylhydroperoxide, and 50 µM hydrogen peroxide for increasing durations (30 min, 1, 2, 4, 6, 8, 24 h). The temporal profiles of strand breaks and oxidative lesions were analyzed. The results shown below demonstrate incidence and temporal concordance in oxidative lesion formation and strand breaks (Deferme et al., 2013).
    • Strand breaks were measured by alkaline comet assay.
    • Oxidative DNA lesions were measured by Fpg-modified comet assay
    • Menadione: strand breaks and oxidative lesions increased in a time-dependent manner from 30 min to 4h, when both reached their maximum. The tail moment values of fpg-digested comets were significantly higher than those of no-fpg comets at 1, 2, and 4h, indicating that the induction of oxidative lesions was significant at these time points. After 4h, both strand breaks and oxidative lesions gradually decreased.
    • Tert butylhydroperoxide: From 30 min to 1h, both strand breaks and oxidative lesions increased and gradually decreased from 2 to 24h. Oxidative lesion induction was significant at both 30min and 1h.
    • Hydrogen peroxide: The highest amount of strand breaks and oxidative lesions occurred at 30 min. From 1h onward, the levels of both decreased. Notably, the induction of oxidative lesions was significant at 30min and also at 1h, despite the decrease from 30min.

In vivo studies

  • (Trouiller et al., 2009)Concentration concordance in Wistar rats orally exposed to ochratoxin A (OTA) and fumonisin B1 (FB1), ROS inducing agents (Domijan et al., 2006).
    • Kidney cells of male Wistar rats were examined using the comet assay +/- Fpg after oral exposure to OTA for 15 days (5ng, 0.05 mg, 0.5 mg/kg b.w.) or FB1 for 5 days (200 ng, 0.05 mg, 0.5 mg/kg b.w.).
      • Significant increases in oxidative lesions were observed using +Fpg comet at all concentrations tested of both OTA and FB1
      • Significant increases were observed in strand breaks using the standard comet assay at all concentrations of both OTA and FB1.
  • Concentration concordance in mice exposed to ROS inducing titanium dioxide nanoparticles (Trouiller et al., 2009).
    • Mice were exposed to 50, 100, 250 or 500 mg/kg of 21 nm P25 TiO2 particles via drinking water for 5 days.
      • A significant increase in 8-oxodG in liver was observed at the 500 mg/kg concentration as measured by high performance liquid chromatography (other concentrations were not examined).
      • Significant increases in gamma-H2AX positive bone marrow cells were observed at all concentrations tested.
      • A significant increase in micronuclei in peripheral blood erythrocytes was observed only at the top concentration tested.

Uncertainties and Inconsistencies


As demonstrated by the Domijan et al paper, results can be complicated by mixed MOA’s. The comet results were positive with and without Fpg suggesting oxidative stress is not the only mechanism.

Quantitative Understanding of the Linkage


A limited number of studies explored the quantitative correlation between oxidative DNA lesions and DNA strand breaks. There are computational models availabe that describe this relationship. Spassova et al. (2015) developed a simulated kinetic model of KBrO3-induced oxidative DNA damage based on Michaelis-Menten enzyme kinetics to study the effect of BER on the shape of the dose-response curve of 8-oxo-dG lesions and strand breaks (Spassova et al., 2015).

  • Both time and concentration dependence of the responses were explored.
  • The time course simulation of a sustained exposure at various concentrations produced a sharp increase in 8-oxo-dG immediately following exposure.
    • The authors attributed this accumulation to lagged, inefficient repair.
  • This increase was later followed by a steep decrease in 8-oxo-dG lesions, accompanied by a linear increase in SSBs.
    • The repair of adducts by BER, both successful and failed, are responsible for the decrease of 8-oxo-dG; the SSBs are generated as a result of repair failure. 
  • Moreover, the concentration-response model of 8-oxo-dG showed a thresholded curve, where no DNA damage was observed at low concentrations due to effective repair up to a certain concentration of KBrO3 indicating insufficient repair at the inflection point.

Response-response Relationship




Known modulating factors


Known Feedforward/Feedback loops influencing this KER


Domain of Applicability


DNA in any cell type is susceptible to oxidative damage due to endogenous (e.g., aerobic respiration) and exogenous (i.e., exposure to oxidants) oxidative insults.




Berdelle, N., Nikolova, T., Quiros, S., Efferth, T., Kaina, B. (2011), Artesunate Induces Oxidative DNA Damage, Sustained DNA Double-Strand Breaks, and the ATM/ATR Damage Response in Cancer Cells, Mol Cancer Ther, 10:2224-2233.

Berquist, B., Wilson III, D. (2012), Pathways for Repairing and Tolerating the Spectrum of Oxidative DNA Lesions, Cancer Lett, 327:61-72.

Bouaicha, N., Maatouk, I. (2004), Microcystin-LR and nodularin induce intracellular glutathione alteration, reactive oxygene species production and lipid peroxidation in primary cultured rat hepatocytes, Toxicol Lett, 148:53-63.

Cadet, J., Wagner, J.R. (2013), DNA Base Damage by Reactive Oxygen Species, Oxidizing Agents, and UV Radiation, Cold Spring Harb Perspect Biol, 5:a012559.

Deferme, L., Briede, J.J., Claessen, S.M., Jennen, D.G., Cavill, R., Kleinjans, J.C. (2013), Time series analysis of oxidative stress response patterns in HepG2: A toxicogenomics approach  , Toxicol, 306:24-34.

Domijan, A., Zeljezic, D., Kopjar, D., Peraica, M. (2006), Standard and Fpg-modified comet assay in kidney cells of ochratoxin A- and fumonisin B(1)-treated rats, Toxciol, 222:53-59.

Gagne, J., Rouleau, M., Poirier, G. (2012), PARP-1 Activation— Bringing the Pieces Together, Science, 336:678-279.

Lankoff, A., Wojcik, A., Fessard, V., Meriluoto, J. (2006), Nodularin-induced genotoxicity following oxidative DNA damage and aneuploidy in HepG2 cells, Toxicol Lett, 164:239-248.

Seager, A., Shah, U., Mikhail, J., Nelson, B., Marquis, B., Doak, S., Johnson, G., Griffiths, S., Carmichael, P., Scott, S., Scott, A., Jenkins, G. (2012), Pro-oxidant Induced DNA Damage in Human Lymphoblastoid Cells: Homeostatic Mechanisms of Genotoxic Tolerance, Toxicol Sci, 128:387-397.

Spassova, M., Miller, D., Nikolov, A. (2015), Kinetic Modeling Reveals the Roles of Reactive Oxygen Species Scavenging and DNA Repair Processes in Shaping the Dose-Response Curve of KBrO3-Induced DNA Damage, Oxid Med Cell Longev, 2015:764375.

Trouiller, B., Reliene, R., Westbrook, A., Solaimani, P., Schiestl, R. (2009), Titanium dioxide nanoparticles induce DNA damage and genetic instability in vivo in mice, Cancer Res, 69:8784-8789.

Yang, N., Chaudry, A., Wallace, S. (2006), Base excision repair by hNTH1 and hOGG1: A two edged sword in the processing of DNA damage in gamma-irradiated human cells, DNA Repair, 5:43-51.

Yang, N., Galick, H., Wallace, S. (2004), Attempted base excision repair of ionizing radiation damage in human lymphoblastoid cells produces lethal and mutagenic double strand breaks, DNA Repair, 3:1323-1334.