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AOP: 613

Title

A descriptive phrase which references both the Molecular Initiating Event and Adverse Outcome.It should take the form “MIE leading to AO”. For example, “Aromatase inhibition leading to reproductive dysfunction” where Aromatase inhibition is the MIE and reproductive dysfunction the AO. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

Peroxisome proliferator-activated receptor alpha activation leading to early life stage mortality via increased reactive oxygen species production

Short name

A name that succinctly summarises the information from the title. This name should not exceed 90 characters. More help

PPARα activation leading to ELS mortality via ROS

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Handbook Version v2.7

Graphical Representation

A graphical representation of the AOP.This graphic should list all KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs. More help

Click to download graphical representation template Explore AOP in a Third Party Tool

Authors

The names and affiliations of the individual(s)/organisation(s) that created/developed the AOP. More help

You Song

Norwegian Institute for Water Research (NIVA), Oslo, Norway

Point of Contact

The user responsible for managing the AOP entry in the AOP-KB and controlling write access to the page by defining the contributors as described in the next section. More help

You Song (email point of contact)

Contributors

Users with write access to the AOP page. Entries in this field are controlled by the Point of Contact. More help

You Song

Coaches

This field is used to identify coaches who supported the development of the AOP.Each coach selected must be a registered author. More help

OECD Information Table

Provides users with information concerning how actively the AOP page is being developed and whether it is part of the OECD Workplan and has been reviewed and/or endorsed. OECD Project: Assigned upon acceptance onto OECD workplan. This project ID is managed and updated (if needed) by the OECD. OECD Status: For AOPs included on the OECD workplan, ‘OECD status’ tracks the level of review/endorsement of the AOP . This designation is managed and updated by the OECD. Journal-format Article: The OECD is developing co-operation with Scientific Journals for the review and publication of AOPs, via the signature of a Memorandum of Understanding. When the scientific review of an AOP is conducted by these Journals, the journal review panel will review the content of the Wiki. In addition, the Journal may ask the AOP authors to develop a separate manuscript (i.e. Journal Format Article) using a format determined by the Journal for Journal publication. In that case, the journal review panel will be required to review both the Wiki content and the Journal Format Article. The Journal will publish the AOP reviewed through the Journal Format Article. OECD iLibrary published version: OECD iLibrary is the online library of the OECD. The version of the AOP that is published there has been endorsed by the OECD. The purpose of publication on iLibrary is to provide a stable version over time, i.e. the version which has been reviewed and revised based on the outcome of the review. AOPs are viewed as living documents and may continue to evolve on the AOP-Wiki after their OECD endorsement and publication. More help

OECD Project #	OECD Status	Reviewer's Reports	Journal-format Article	OECD iLibrary Published Version

This AOP was last modified on November 07, 2025 05:16

Revision dates for related pages

Page	Revision Date/Time
Activation, PPARα	December 28, 2020 12:48
Increase, Fatty acid beta-oxidation	December 04, 2020 15:21
Decrease, Coupling of oxidative phosphorylation	November 07, 2025 05:15
Increase, Reactive oxygen species	June 12, 2025 01:27
Decrease, Vascular integrity	November 07, 2025 05:42
Increase, Hemopericardium	October 29, 2025 17:05
Increase, Early Life Stage Mortality	March 22, 2018 10:23
Activation, PPARα leads to Increase, Fatty acid β-oxidation	October 30, 2025 04:18
Increase, Fatty acid β-oxidation leads to Decrease, Coupling of OXPHOS	October 30, 2025 04:18
Decrease, Coupling of OXPHOS leads to Increase, ROS	February 25, 2025 11:13
Increase, ROS leads to Decrease, Vascular integrity	October 30, 2025 04:28
Decrease, Vascular integrity leads to Increase, Hemopericardium	October 30, 2025 04:19
Increase, Hemopericardium leads to Increase, Early Life Stage Mortality	October 30, 2025 04:19

Abstract

A concise and informative summation of the AOP under development that can stand-alone from the AOP page. The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance. More help

This Adverse Outcome Pathway (AOP) describes the mechanistic sequence linking activation of peroxisome proliferator-activated receptor alpha (PPARα) to early life stage mortality in aquatic vertebrates. Activation of PPARα increases fatty acid β-oxidation, which disrupts oxidative phosphorylation (OXPHOS) coupling and elevates reactive oxygen species (ROS) production. The resulting mitochondrial dysfunction and oxidative stress decrease vascular integrity, induce hemopericardium, and culminate in early developmental mortality. The AOP integrates well-established molecular mechanisms of energy metabolism with observable developmental endpoints in fish embryos. It provides a biologically coherent framework to assess developmental toxicity of PPARα agonists, including per- and polyfluoroalkyl substances (PFAS) and fibrates, supporting new approach methodologies (NAMs), read-across, and next-generation risk assessment applications.

AOP Development Strategy

Context

Used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development.The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. More help

The AOP was developed to capture the conserved mitochondrial and oxidative stress mechanisms underlying developmental toxicity following PPARα activation. Chemicals such as PFAS, phthalates, and fibrates activate PPARα, enhancing fatty acid oxidation and increasing ROS generation. Disruption of mitochondrial coupling and energy depletion leads to vascular leakage and cardiac defects that contribute to embryo lethality. This AOP builds on existing AOPs describing PPARα activation (Event 227) and oxidative stress (Event 1115) to form a metabolism-centered AOP network relevant to fish early life stages.

Strategy

Provides a description of the approaches to the identification, screening and quality assessment of the data relevant to identification of the key events and key event relationships included in the AOP or AOP network.This information is important as a basis to support the objective/envisaged application of the AOP by the regulatory community and to facilitate the reuse of its components. Suggested content includes a rationale for and description of the scope and focus of the data search and identification strategy/ies including the nature of preliminary scoping and/or expert input, the overall literature screening strategy and more focused literature surveys to identify additional information (including e.g., key search terms, databases and time period searched, any tools used). More help

A systematic evidence-gathering strategy was applied to identify and evaluate studies linking key events (KEs) and key event relationships (KERs):

Databases searched: PubMed, AOP-Wiki, OECD AOP-KB, Web of Science (2010–2025).
Search terms: PPARα activation, β-oxidation, OXPHOS, ROS, ATP depletion, vascular integrity, hemopericardium, mortality, zebrafish, PFAS, fibrate.
Inclusion criteria: Experimental or mechanistic studies demonstrating sequential or causal linkage between KEs, preferably with dose–response or temporal concordance data.
Approach: Literature screening and expert evaluation to identify essentiality, biological plausibility, and empirical support consistent with OECD AOP development guidelines (2018).

Summary of the AOP

This section is for information that describes the overall AOP.The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help

Events:

Molecular Initiating Events (MIE)

An MIE is a specialised KE that represents the beginning (point of interaction between a prototypical stressor and the biological system) of an AOP. More help

Key Events (KE)

A measurable event within a specific biological level of organisation. More help

Adverse Outcomes (AO)

An AO is a specialized KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help

Type	Event ID	Title	Short name

MIE

227

Activation, PPARα

KE	1312	Increase, Fatty acid beta-oxidation	Increase, Fatty acid β-oxidation
KE	1446	Decrease, Coupling of oxidative phosphorylation	Decrease, Coupling of OXPHOS
KE	1115	Increase, Reactive oxygen species	Increase, ROS
KE	2384	Decrease, Vascular integrity	Decrease, Vascular integrity
KE	2383	Increase, Hemopericardium	Increase, Hemopericardium

947

Increase, Early Life Stage Mortality

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarizes all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP.Each table entry acts as a link to the individual KER description page. More help

Title	Adjacency	Evidence	Quantitative Understanding

Activation, PPARα leads to Increase, Fatty acid β-oxidation	adjacent
Increase, Fatty acid β-oxidation leads to Decrease, Coupling of OXPHOS	adjacent
Decrease, Coupling of OXPHOS leads to Increase, ROS	adjacent
Increase, ROS leads to Decrease, Vascular integrity	adjacent
Decrease, Vascular integrity leads to Increase, Hemopericardium	adjacent
Increase, Hemopericardium leads to Increase, Early Life Stage Mortality	adjacent

Network View

This network graphic is automatically generated based on the information provided in the MIE(s), KEs, AO(s), KERs and Weight of Evidence (WoE) summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Prototypical Stressors

A structured data field that can be used to identify one or more “prototypical” stressors that act through this AOP. Prototypical stressors are stressors for which responses at multiple key events have been well documented. More help

Life Stage Applicability

The life stage for which the AOP is known to be applicable. More help

Life stage	Evidence
Embryo
Juvenile

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available. More help

Term	Scientific Term	Evidence	Link
zebrafish	Danio rerio		NCBI

Sex Applicability

The sex for which the AOP is known to be applicable. More help

Sex	Evidence
Unspecific

Overall Assessment of the AOP

Addressess the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and Weight of Evidence (WoE) for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). More help

The AOP demonstrates strong biological plausibility, particularly for the upstream molecular and cellular events. Empirical support is robust for PPARα activation, β-oxidation increase, and ROS formation, which are consistently observed across multiple vertebrate species and chemical stressors. Empirical evidence linking oxidative stress to vascular and cardiac outcomes is moderate but reproducible. Quantitative understanding of the relationships between intermediate and apical events is developing, with growing omics and imaging datasets supporting semi-quantitative modeling. The AOP has moderate to high overall confidence and is suitable for screening-level hazard identification and mechanistic read-across.

Domain of Applicability

Addressess the relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context. More help

Aspect	Applicability
Taxa	Teleost fish (e.g., Danio rerio, Oryzias latipes); mechanistic conservation across vertebrates.
Life stage	Embryonic and early larval development.
Sex	Non-sex-specific (early life stage).
Biological systems	Liver (metabolic activation), mitochondria (energy homeostasis), and cardiovascular system (vascular integrity).

Essentiality of the Key Events

The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently, evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence. The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs. More help

Key Event	Essentiality Evidence	Type of Evidence
Event 227: PPARα activation (MIE)	Knockdown or knockout of ppara in zebrafish blocks β-oxidation induction and oxidative stress after exposure to PPARα agonists.	Direct
Event 1312: Fatty acid β-oxidation (Increase)	Inhibition of β-oxidation (e.g., by etomoxir) reduces ROS formation and prevents cardiac toxicity.	Direct
Event 1446: Coupling of OXPHOS (Decrease)	Reduced mitochondrial membrane potential and respiratory coupling precede ROS accumulation and ATP depletion.	Direct
Event 1115: ROS (Increase)	ROS scavengers (e.g., N-acetylcysteine) or antioxidants mitigate vascular and cardiac damage, supporting causality.	Direct
Event 2384: Vascular integrity (Decrease)	Vascular permeability assays correlate with ROS burden and cardiac edema severity.	Indirect
Event 2383: Hemopericardium (Increase)	Reversible upon antioxidant treatment or metabolic rescue.	Indirect
Event 947: Early life stage mortality (Increase)	Occurs downstream of cumulative mitochondrial and vascular dysfunction.	Outcome

Evidence Assessment

Addressess the biological plausibility, empirical support, and quantitative understanding from each KER in an AOP. More help

Biological Plausibility

High. The mechanistic sequence aligns with established mitochondrial physiology: excessive fatty acid oxidation leads to electron leakage from the respiratory chain, ROS formation, oxidative damage to vascular endothelium, and developmental cardiac failure. The sequence has strong mechanistic coherence across vertebrates.

Empirical Support

Moderate to high. Multiple independent studies in zebrafish embryos and mammalian hepatocytes demonstrate:

PPARα activation induces β-oxidation genes (acox1, cpt1a, echs1).
OXPHOS uncoupling and ROS increase within 24–48 hours of exposure.
ROS elevation precedes vascular collapse and hemopericardium in fish embryos.
Temporal and dose concordance between intermediate and apical events is well supported.

Quantitative Understanding

Moderate. Dose–response data exist for several KEs, including ROS induction and mortality. Transcriptomic and metabolomic data enable modeling of upstream relationships, but quantitative linkage between oxidative stress and vascular integrity remains semi-quantitative.

Known Modulating Factors

Modulating factors (MFs) may alter the shape of the response-response function that describes the quantitative relationship between two KES, thus having an impact on the progression of the pathway or the severity of the AO.The evidence supporting the influence of various modulating factors is assembled within the individual KERs. More help

Modulating Factor (MF)	Influence or Outcome	KER(s) Involved
Antioxidant capacity	High antioxidant levels (e.g., glutathione, superoxide dismutase, catalase) can buffer ROS accumulation, mitigating oxidative stress and reducing vascular and cardiac toxicity.	ROS (increase) → Vascular integrity (decrease); ROS (increase) → Hemopericardium (increase)
Oxygen availability	Hypoxic or low-oxygen conditions decrease mitochondrial ROS generation, attenuating downstream vascular effects, while hyperoxia enhances ROS formation and vascular damage.	OXPHOS coupling (decrease) → ROS (increase)
Nutritional and metabolic status	Lipid-rich diets or high energy reserves enhance fatty acid β-oxidation and PPARα activation, increasing ROS and developmental toxicity risk.	PPARα activation (increase) → Fatty acid β-oxidation (increase); β-oxidation (increase) → OXPHOS coupling (decrease)
Temperature	Elevated temperature increases metabolic rate and mitochondrial respiration, enhancing ROS production and sensitivity to mitochondrial uncoupling.	OXPHOS coupling (decrease) → ROS (increase)
Chemical lipophilicity	Highly lipophilic compounds bioaccumulate in lipid-rich tissues, leading to stronger PPARα activation and more pronounced metabolic and oxidative effects.	PPARα activation (increase) → β-oxidation (increase)
Developmental stage	Early embryonic stages are more susceptible due to immature antioxidant defenses and higher mitochondrial activity.	ROS (increase) → Vascular integrity (decrease); Vascular integrity (decrease) → Hemopericardium (increase)
Mitochondrial density and activity	Tissues with high mitochondrial content (e.g., heart, liver) are more vulnerable to OXPHOS disruption and oxidative injury.	OXPHOS coupling (decrease) → ROS (increase); ROS (increase) → Vascular integrity (decrease)
Exposure duration and timing	Prolonged or early developmental exposures amplify cumulative ROS burden and downstream damage, while short, late exposures may be reversible.	Across all KERs—temporal accumulation enhances downstream outcomes
Chemical co-exposure (e.g., PPARγ or CAR agonists)	May synergistically amplify or modulate PPARα-driven metabolic changes and oxidative stress.	PPARα activation (increase) → downstream metabolic and ROS pathways

Quantitative Understanding

Optional field to provide quantitative weight of evidence descriptors. More help

While no fully parameterized quantitative AOP model exists, several dose–response relationships are established:

ROS levels above ~2× baseline associate with mitochondrial uncoupling and decreased ATP.
A ≥40% reduction in ATP or mitochondrial potential predicts vascular leakage onset.
Hemopericardium incidence correlates with ROS intensity and exposure concentration (e.g., EC50 ~50–100 µM PFOA-equivalents).

Considerations for Potential Applications of the AOP (optional)

Addressess potential applications of an AOP to support regulatory decision-making.This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. More help

Supports chemical read-across and prioritization of PPARα agonists for developmental toxicity screening.
Provides mechanistic context for non-animal test methods assessing mitochondrial and oxidative stress pathways.
Applicable for Adverse Outcome Network integration with hepatic steatosis and mitochondrial dysfunction AOPs.
Facilitates NGRA and IATA development focused on energy metabolism perturbation and oxidative stress biomarkers.

References

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