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AOP: 612

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 reduced adenosine triphosphate

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 reduced ATP

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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

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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

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You Song

Coaches

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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 05:15

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
Decrease, Adenosine triphosphate pool	June 14, 2021 13:40
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 Decrease, ATP pool	July 06, 2022 07:39
Decrease, ATP pool leads to Decrease, Vascular integrity	October 30, 2025 04:19
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 linkage between activation of peroxisome proliferator-activated receptor alpha (PPARα) and increased mortality during early developmental stages in fish. The molecular initiating event (MIE) involves chemical activation of PPARα, leading to enhanced fatty acid β-oxidation, disrupted oxidative phosphorylation (OXPHOS) coupling, ATP depletion, loss of vascular integrity, hemopericardium, and ultimately early life stage mortality. This AOP integrates molecular, biochemical, and apical endpoints relevant to energy metabolism and cardiovascular development. It provides a mechanistically coherent framework for understanding developmental toxicity of peroxisome proliferators, including certain per- and polyfluoroalkyl substances (PFAS), and supports application of new approach methodologies (NAMs) and read-across strategies in ecological risk assessment.

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

This AOP was developed to capture the conserved mitochondrial and metabolic perturbations following PPARα activation observed in multiple species. Peroxisome proliferators, including PFAS and phthalates, activate PPARα and induce transcriptional programs that increase β-oxidation of fatty acids. Excessive β-oxidation perturbs mitochondrial homeostasis, resulting in oxidative stress, ATP depletion, and vascular defects. These mechanisms are consistent with observed early life stage lethality in zebrafish and other fish models exposed to PPARα agonists. The AOP contributes to the expanding network of metabolism-centered AOPs and provides biological context for developmental toxicity mechanisms without relying on animal testing.

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

Data were identified through systematic searches of PubMed, AOP-Wiki, and OECD databases (2010–2025) using combinations of the following keywords: PPARα, fatty acid oxidation, oxidative phosphorylation, ATP depletion, vascular integrity, hemopericardium, developmental toxicity, zebrafish, PFAS, phthalate, peroxisome proliferator. Inclusion criteria required mechanistic or quantitative evidence linking key events (KEs) in vertebrate embryos or early juvenile stages. Empirical data from in vitro bioassays, zebrafish embryos, and rodent models were considered. The weight of evidence was evaluated using the OECD principles of AOP development—biological plausibility, essentiality, and empirical support.

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	1771	Decrease, Adenosine triphosphate pool	Decrease, ATP pool
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 Decrease, ATP pool	adjacent
Decrease, ATP pool 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

This AOP is biologically coherent and supported by moderate-to-strong empirical data across molecular and organismal levels. The essentiality of upstream events (PPARα activation and increased β-oxidation) is well supported by experimental data using PPARα knockouts and pharmacological antagonists. Downstream events, such as decreased ATP levels, compromised vascular integrity, and hemopericardium, have been observed across diverse PPARα activators in fish embryos, indicating reproducibility. However, quantitative relationships between intermediate KEs and mortality remain incompletely defined. The AOP has moderate confidence overall and is applicable for screening-level hazard identification, read-across, and developmental toxicity prioritization.

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

Taxa: Primarily teleost fish (e.g., Danio rerio, Oryzias latipes); mechanistic plausibility extends to other vertebrates.
Life stage: Embryonic and early larval development.
Sex: Not sex-specific at early life stages.
Biological systems: Liver, muscle, and cardiovascular systems.

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
PPARα activation (MIE)	Knockdown or knockout of ppara in zebrafish prevents β-oxidation induction and metabolic effects following exposure to PPARα agonists.	Direct
Increased fatty acid β-oxidation	Chemical inhibitors (e.g., etomoxir) of β-oxidation prevent ATP depletion and vascular effects.	Direct
Decreased coupling of OXPHOS	Reduced mitochondrial efficiency and ROS generation precede ATP loss and morphological abnormalities.	Indirect
Decreased ATP pool	ATP supplementation or metabolic rescue mitigates vascular and cardiac defects.	Direct
Decreased vascular integrity	Vascular permeability assays correlate strongly with cardiac edema and mortality outcomes.	Indirect
Increased hemopericardium	Observed consistently in PPARα agonist-exposed embryos; severity predicts mortality.	Indirect
Increased early life stage mortality (AO)	Apical endpoint following 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 pathway aligns with well-characterized PPARα-mediated transcriptional regulation of energy metabolism. Excessive β-oxidation generates ROS and perturbs mitochondrial homeostasis, leading to ATP depletion and vascular collapse, consistent with observed early life stage mortality.

Empirical Support

Moderate. Numerous studies report coherent concentration–response relationships between upstream and downstream KEs. Zebrafish embryos exposed to PFAS (e.g., HFPO-DA, PFOA) or fibrates (e.g., clofibrate) exhibit transcriptional activation of ppara target genes, mitochondrial dysfunction, hemopericardium, and mortality.

Quantitative Understanding

Low to moderate. While dose–response data exist for individual KEs, quantitative linkage functions (KERs) are not yet formalized. The AOP can be qualitatively modeled but lacks a complete mathematical framework.

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
Energy/nutrient availability	Limited glucose or lipid substrates reduce β-oxidation flux and lower ATP depletion severity; conversely, high lipid load enhances PPARα activation and downstream metabolic disruption.	PPARα activation (increase) → Fatty acid β-oxidation (increase); β-oxidation (increase) → Coupling of OXPHOS (decrease)
Antioxidant capacity	Elevated antioxidant defenses (e.g., glutathione, SOD, catalase) buffer ROS generated by excessive β-oxidation and OXPHOS uncoupling, mitigating ATP loss and vascular effects.	Coupling of OXPHOS (decrease) → ATP pool (decrease); ATP pool (decrease) → Vascular integrity (decrease)
Oxygen availability	Hypoxia limits oxidative metabolism, reducing ROS formation and ATP depletion; hyperoxia or increased oxygen tension enhances oxidative damage and mitochondrial uncoupling.	Coupling of OXPHOS (decrease) → ATP pool (decrease)
Temperature	Elevated temperature accelerates mitochondrial respiration and energy turnover, intensifying ATP depletion and vascular damage.	β-oxidation (increase) → OXPHOS coupling (decrease); ATP pool (decrease) → Vascular integrity (decrease)
Developmental stage	Early embryos are more vulnerable due to higher energy demand and immature mitochondrial and antioxidant systems.	ATP pool (decrease) → Vascular integrity (decrease); Vascular integrity (decrease) → Hemopericardium (increase)
Mitochondrial density and efficiency	Tissues with high mitochondrial density (heart, liver, muscle) show more pronounced energy depletion and structural defects.	OXPHOS coupling (decrease) → ATP pool (decrease); ATP pool (decrease) → Vascular integrity (decrease)
Chemical lipophilicity	Lipophilic compounds bioaccumulate in lipid-rich embryonic ti

Quantitative Understanding

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

Limited quantitative KERs available. Correlative evidence suggests that ≥40–50% reduction in ATP levels is associated with severe vascular leakage and increased mortality probability.

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 read-across of PPARα-activating chemicals (e.g., PFAS, fibrates, phthalates).
Enables in vitro-to-in vivo extrapolation through metabolic biomarkers (e.g., β-oxidation gene expression, ATP depletion).
Applicable to screening-level developmental toxicity assessments in non-animal frameworks (e.g., NGRA, IATA).
May inform adverse outcome network linkages with hepatic steatosis and mitochondrial dysfunction AOPs.

References

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