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Relationship: 1599

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, LPO leads to Decrease, Coupling of OXPHOS

Upstream event

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

Increase, LPO

Downstream event

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

Decrease, Coupling of OXPHOS

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 lipid peroxidation and cell death	adjacent	High	Moderate	You Song (send email)	Under development: Not open for comment. Do not cite
Reactive oxygen species leading to growth inhibition via lipid peroxidation and decreased cell proliferation	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 Do not cite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	Moderate	NCBI
mammals	mammals	Moderate	NCBI
fish	fish	Moderate	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 relationship by which increased lipid peroxidation leads to decreased coupling of oxidative phosphorylation. Lipid peroxidation involves oxidative attack on unsaturated lipids, particularly polyunsaturated fatty acids, generating lipid radicals, lipid hydroperoxides, and reactive aldehydes such as malondialdehyde and 4-hydroxy-2-nonenal (Ayala et al., 2014; Yin et al., 2011). When lipid peroxidation occurs in mitochondrial membranes, it can alter membrane fluidity, disrupt membrane protein-lipid interactions, impair the organization of respiratory chain complexes, increase proton leak, and destabilize the protonmotive force needed for ATP synthesis (Chicco and Sparagna, 2007; Paradies et al., 2014).

Cardiolipin is particularly important for this KER because it is a signature phospholipid of the inner mitochondrial membrane and supports the structure and function of respiratory chain complexes, supercomplexes, cytochrome c interactions, and ATP-generating membrane architecture. Oxidative modification of cardiolipin and other inner-membrane lipids can therefore reduce the efficiency with which electron transport is coupled to ATP synthesis. The downstream KE may be measured as decreased mitochondrial membrane potential, increased proton leak, reduced respiratory control ratio, lower OXPHOS coupling efficiency, or reduced ATP-generating respiratory efficiency. The KER does not require lipid peroxidation to be the only cause of decreased OXPHOS coupling, but it captures a mechanistically plausible and empirically supported route by which oxidative membrane damage can impair mitochondrial bioenergetics.

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 as part of the ROS-growth AOP network development process. The evidence search combined AOP-Wiki review, targeted literature searching, and AI-assisted screening followed by manual expert curation. Existing AOP-Wiki KEs and KERs were examined to ensure consistency with the modular AOP framework and to identify reuse of KE 1445, KE 1446, and downstream mitochondrial energy-related KEs. Relationship 1599 was also checked against the current AOP-Wiki relationship entry and the AOPs referencing it.

Search terms included combinations of “lipid peroxidation”, “MDA”, “malondialdehyde”, “TBARS”, “4-HNE”, “lipid hydroperoxide”, “cardiolipin oxidation”, “mitochondrial membrane potential”, “OXPHOS coupling”, “respiratory control ratio”, “proton leak”, “mitochondrial dysfunction”, “oxidative phosphorylation”, “ATP”, “paraquat”, “hypoxia reoxygenation”, “Daphnia”, “Chlamydomonas”, “bivalve”, “fish”, and “mammalian mitochondria”. PubMed, Web of Science, Google Scholar, AOP-Wiki, and the curated ROS-growth concordance table were used. Studies were prioritized when they measured both lipid peroxidation and mitochondrial coupling or a close surrogate such as mitochondrial membrane potential, proton leak, respiratory control ratio, or mitochondrial respiration under the same exposure context.

The screening workflow used AOP-helpFinder and preliminary text-mining to identify studies with co-occurring key-event terms, followed by overlap analysis to remove redundant records. Large language model-assisted screening was used only to extract candidate metadata and prioritize abstracts and full-text records. Final decisions on inclusion, interpretation, and weight-of-evidence category were made manually by expert review. Mechanistic reviews were used to support biological plausibility, whereas primary experimental studies were used to support empirical concordance and uncertainty evaluation.

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

Biological plausibility of this KER is high. Lipid peroxidation can directly affect mitochondrial coupling because the inner mitochondrial membrane is both highly specialized for energy transduction and vulnerable to oxidative lipid damage. The electrochemical proton gradient that drives ATP synthesis depends on low proton conductance, intact membrane architecture, and appropriately organized electron transport chain and ATP synthase complexes. Peroxidation of phospholipids can increase membrane disorder, damage cardiolipin, alter protein-lipid interactions, facilitate proton leak, and impair respiratory chain complex function (Chicco and Sparagna, 2007; Paradies et al., 1998; Paradies et al., 2014).

The mechanistic connection is especially strong for cardiolipin. Cardiolipin stabilizes respiratory chain complexes and supercomplexes and supports cytochrome c oxidase, ATP synthase, and other components of mitochondrial bioenergetics. Cardiolipin peroxidation has been associated with loss of respiratory chain function, altered cytochrome c interactions, and mitochondrial dysfunction. Thus, increased lipid peroxidation provides a structurally and functionally credible basis for decreased coupling of OXPHOS.

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 for this KER is moderate. Several studies provide concordant evidence linking lipid peroxidation or oxidative membrane damage with impaired mitochondrial membrane potential, proton leak, or OXPHOS coupling. However, fewer studies directly measure lipid peroxidation and a formal coupling metric in the same experiment across multiple time points and doses, and many available studies use related mitochondrial endpoints rather than direct OXPHOS coupling efficiency.

Biological system	Stressor / condition	Evidence for upstream KE 1445	Evidence for downstream KE 1446	Concordance / interpretation	Reference
Chlamydomonas reinhardtii	Paraquat, 48 h	TBARS/MDA increased significantly at >=0.5 uM paraquat.	Mitochondrial membrane potential decreased at >=0.5 uM paraquat, with dose-dependent further reduction.	Dose concordance supports association between lipid peroxidation and impaired mitochondrial polarization/coupling in the same model.	Esperanza et al. (2015).
Daphnia	PUFA-rich diet across lifespan experiment	High-PUFA diet increased lipid peroxidation.	High-PUFA diet lowered mitochondrial membrane potential.	Dietary susceptibility to lipid peroxidation was associated with lower mitochondrial membrane potential, supporting a lipid damage-mitochondrial function linkage.	Moore et al. (2023).
Mya arenaria	Cyclic hypoxia, 3 weeks	Variable oxygen regimes are associated with oxidative stress and lipid oxidative damage risk.	Cyclic hypoxia increased mitochondrial proton leak and lowered OXPHOS coupling efficiency.	Supports environmental relevance of oxygen-fluctuation/oxidative damage conditions leading to reduced coupling efficiency, although lipid peroxidation itself was not the sole measured driver.	Ouillon et al. (2021).
Mammalian mitochondria	Experimental oxidative damage to cardiac mitochondria	Oxidative damage to cardiolipin was observed.	Cytochrome oxidase activity was altered in close association with cardiolipin oxidative damage.	Provides direct mechanistic evidence that peroxidative mitochondrial lipid damage can impair respiratory-chain function.	Paradies et al. (1998).
Mammalian and comparative systems	Cardiolipin alteration / disease contexts	Cardiolipin loss, remodeling, and peroxidation are documented forms of mitochondrial lipid alteration.	Altered cardiolipin status is associated with mitochondrial dysfunction and reduced bioenergetic performance.	Review-level evidence supports broad mechanistic generalization across tissues and disease models.	Chicco and Sparagna (2007); Paradies et al. (2014).

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

A major uncertainty is that lipid peroxidation is often measured by TBARS or MDA assays, which are useful but can lack specificity and may not resolve which lipid class or subcellular membrane compartment is damaged. Because OXPHOS coupling is specifically dependent on mitochondrial inner-membrane integrity, whole-cell or whole-tissue lipid peroxidation measurements may not always provide direct information on mitochondrial lipid peroxidation. More specific measurements of cardiolipin oxidation, 4-HNE adducts, lipid hydroperoxides, or mitochondrial membrane lipidomics would strengthen evidence for this KER (Ayala et al., 2014; Yin et al., 2011).

The relationship may also be modulated by compensatory mechanisms. Mild lipid peroxidation can activate antioxidant and lipid-remodeling responses, and organisms may compensate through increased antioxidant capacity, membrane remodeling, or metabolic reorganization. Therefore, increased lipid peroxidation does not always immediately produce measurable decreases in OXPHOS coupling, especially when damage is below a threshold or when measurements are taken after compensatory recovery. Conversely, decreased OXPHOS coupling can occur through mechanisms independent of lipid peroxidation, including direct uncouplers, respiratory-chain inhibitors, protein oxidation, genetic mitochondrial defects, or ionophore-mediated proton leak.

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	Influence on the KER	Supporting evidence
Membrane lipid composition	Degree of unsaturation, PUFA abundance, cardiolipin content and acyl-chain composition.	Higher PUFA content and susceptible cardiolipin species increase vulnerability to peroxidation and may increase the probability or magnitude of decreased coupling.	Chicco and Sparagna (2007); Paradies et al. (2014); Moore et al. (2023).
Antioxidant capacity	Vitamin E, glutathione systems, glutathione peroxidases, peroxiredoxins, catalase, superoxide dismutase and lipid-soluble antioxidants.	Higher antioxidant capacity can reduce propagation of lipid peroxidation and buffer the effect on mitochondrial coupling; depletion increases sensitivity.	Halliwell and Gutteridge (2015); Sies et al. (2017); Ayala et al. (2014).
Transition metals and redox cycling	Iron, copper and redox-active compounds can promote radical generation and lipid peroxide decomposition.	Can lower the threshold for lipid peroxidation and intensify mitochondrial membrane damage.	Halliwell and Gutteridge (2015); Regoli and Giuliani (2014); Knauert and Knauer (2008).
Oxygen availability and hypoxia/reoxygenation	Fluctuating oxygen regimes alter ROS generation, mitochondrial respiration and oxidative damage.	Cyclic hypoxia or reoxygenation can increase proton leak and reduce OXPHOS coupling efficiency, potentially strengthening the KER.	Ouillon et al. (2021); Sokolov et al. (2019).
Mitochondrial metabolic state	Respiratory substrate, ADP availability, membrane potential and electron pressure on the ETC.	High electron leak and high membrane potential can increase oxidative damage; pre-existing uncoupling can alter both lipid peroxidation and coupling measurements.	Paradies et al. (2014); Sies et al. (2017).
Assay specificity and timing	TBARS, MDA, 4-HNE, lipid hydroperoxides, cardiolipin oxidation and mitochondrial lipidomics differ in specificity and time scale.	Can affect apparent dose-response and temporal concordance between the upstream and downstream KEs.	Ayala et al. (2014); Yin et al. (2011).

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 understanding that lipid peroxidation can impair mitochondrial membrane function and decrease OXPHOS coupling, but a general quantitative function linking the magnitude of lipid peroxidation to the magnitude of coupling loss is not yet established across taxa, tissues, stressors, and assay systems. The relationship is expected to be nonlinear and threshold-dependent because moderate lipid peroxidation may be buffered by antioxidants and lipid repair/remodeling, while more severe damage can abruptly increase proton leak or disrupt respiratory-chain organization.

Response-response Relationship

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

System-specific quantitative evidence exists. In Chlamydomonas reinhardtii, paraquat produced significant lipid peroxidation and decreased mitochondrial membrane potential at similar concentrations, supporting dose concordance over the tested range (Esperanza et al., 2015). In Daphnia, high-PUFA dietary conditions increased lipid peroxidation and lowered mitochondrial membrane potential, indicating a quantitative association between susceptibility to lipid oxidation and mitochondrial bioenergetic status (Moore et al., 2023). In Mya arenaria, cyclic hypoxia increased proton leak by approximately 1.5- to 1.7-fold and reduced OXPHOS coupling efficiency, supporting quantitative characterization of downstream mitochondrial uncoupling under oxidative stress-relevant conditions (Ouillon et al., 2021). However, these studies do not yet provide a single cross-system response-response equation from lipid peroxidation biomarkers to OXPHOS coupling efficiency.

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 the linkage can range from minutes to weeks depending on the stressor and measurement strategy. Chemical peroxidation of mitochondrial lipids can affect membrane function rapidly, but whole-organism or chronic exposure studies often detect stable changes in lipid peroxidation and coupling over days to weeks. Quantitative prediction of decreased coupling from lipid peroxidation is therefore best supported in systems where mitochondrial lipid peroxidation and OXPHOS coupling are measured directly in the same cells or isolated mitochondria across a concentration and time-course series.

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

This KER is applicable to aerobic eukaryotic systems with functional mitochondria and oxidizable membrane lipids. The relationship is especially relevant to biological contexts where mitochondrial membranes are enriched in cardiolipin and other polyunsaturated lipids, where oxidative stress targets membrane compartments, or where environmental conditions promote ROS formation and lipid radical propagation. The KER is likely most useful for stressors that induce oxidative membrane damage, including redox cycling chemicals, metals, radiation, hypoxia/reoxygenation, temperature stress, mitochondrial toxicants, and inflammatory or endogenous ROS-generating conditions.

The KER should be applied with greatest confidence when lipid peroxidation is measured using specific or well-characterized markers and when the downstream mitochondrial event is assessed by direct coupling-related endpoints such as respiratory control ratio, proton leak, OXPHOS coupling efficiency, mitochondrial membrane potential, or state 3/state 4 respiration. Applicability is less certain when lipid peroxidation is measured only at the whole-organism level without compartmental resolution, or when decreased coupling is caused primarily by direct uncouplers or respiratory-chain inhibitors without evidence of lipid oxidative damage.

References

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

Almaida-Pagán PF, Lucas-Sánchez A, Tocher DR. 2014. Changes in mitochondrial membrane composition and oxidative status during rapid growth, maturation and aging in zebrafish, Danio rerio. Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids 1841(7):1003-1011. https://doi.org/10.1016/j.bbalip.2014.04.004.

Ayala A, Munoz MF, Arguelles S. 2014. Lipid peroxidation: production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal. Oxidative Medicine and Cellular Longevity 2014:360438. https://doi.org/10.1155/2014/360438.

Chicco AJ, Sparagna GC. 2007. Role of cardiolipin alterations in mitochondrial dysfunction and disease. American Journal of Physiology-Cell Physiology 292(1):C33-C44. https://doi.org/10.1152/ajpcell.00243.2006.

Cong B, Liu C, Wang L, Chai Y. 2020. The impact on antioxidant enzyme activity and related gene expression following adult zebrafish (Danio rerio) exposure to dimethyl phthalate. Animals 10(4):717. https://doi.org/10.3390/ani10040717.

Esperanza M, Cid A, Herrero C, Rioboo C. 2015. Acute effects of a prooxidant herbicide on the microalga Chlamydomonas reinhardtii: screening cytotoxicity and genotoxicity endpoints. Aquatic Toxicology 165:210-221. https://doi.org/10.1016/j.aquatox.2015.06.004.

Halliwell B, Gutteridge JMC. 2015. Free Radicals in Biology and Medicine. 5th ed. Oxford: Oxford University Press.

Knauert S, Knauer K. 2008. The role of reactive oxygen species in copper toxicity to two freshwater green algae. Journal of Phycology 44(2):311-321. https://doi.org/10.1111/j.1529-8817.2008.00471.x.

Moore TD, Martin-Creuzburg D, Yampolsky LY. 2023. Diet effects on longevity, heat tolerance, lipid peroxidation and mitochondrial membrane potential in Daphnia. Oecologia 202(1):151-163. https://doi.org/10.1007/s00442-023-05382-1.

Ouillon N, Sokolov EP, Otto S, Rehder G, Sokolova IM. 2021. Effects of variable oxygen regimes on mitochondrial bioenergetics and reactive oxygen species production in a marine bivalve Mya arenaria. Journal of Experimental Biology 224(4):jeb237156. https://doi.org/10.1242/jeb.237156.

Pan YX, Luo Z, Zhuo MQ, Wei CC, Chen GH, Song YF. 2018. Oxidative stress and mitochondrial dysfunction mediated Cd-induced hepatic lipid accumulation in zebrafish Danio rerio. Aquatic Toxicology 199:12-20. https://doi.org/10.1016/j.aquatox.2018.03.017.

Paradies G, Ruggiero FM, Petrosillo G, Quagliariello E. 1998. Peroxidative damage to cardiac mitochondria: cytochrome oxidase and cardiolipin alterations. FEBS Letters 424(3):155-158. https://doi.org/10.1016/S0014-5793(98)00161-6.

Paradies G, Petrosillo G, Pistolese M, Ruggiero FM. 2002. Reactive oxygen species affect mitochondrial electron transport complex I activity through oxidative cardiolipin damage. Gene 286(1):135-141. https://doi.org/10.1016/S0378-1119(01)00814-9.

Paradies G, Paradies V, De Benedictis V, Ruggiero FM, Petrosillo G. 2014. Functional role of cardiolipin in mitochondrial bioenergetics. Biochimica et Biophysica Acta - Bioenergetics 1837(4):408-417. https://doi.org/10.1016/j.bbabio.2013.10.006.

Regoli F, Giuliani ME. 2014. Oxidative pathways of chemical toxicity and oxidative stress biomarkers in marine organisms. Marine Environmental Research 93:106-117. https://doi.org/10.1016/j.marenvres.2013.07.006.

Schieber M, Chandel NS. 2014. ROS function in redox signaling and oxidative stress. Current Biology 24(10):R453-R462. https://doi.org/10.1016/j.cub.2014.03.034.

Sies H, Berndt C, Jones DP. 2017. Oxidative stress. Annual Review of Biochemistry 86:715-748. https://doi.org/10.1146/annurev-biochem-061516-045037.

Sokolov EP, Markert S, Hinzke T, Hirschfeld C, Becher D, Ponsuksili S, Sokolova IM. 2019. Effects of hypoxia-reoxygenation stress on mitochondrial proteome and bioenergetics of the hypoxia-tolerant marine bivalve Crassostrea gigas. Journal of Proteomics 194:99-111.

Yin H, Xu L, Porter NA. 2011. Free radical lipid peroxidation: mechanisms and analysis. Chemical Reviews 111(10):5944-5972. https://doi.org/10.1021/cr200084z.