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AOP: 614

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 vascular endothelial growth factor

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 VEGF

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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

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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 05:17

Revision dates for related pages

Page	Revision Date/Time
Activation, PPARα	December 28, 2020 12:48
reduced production, VEGF	March 28, 2018 11:48
Reduction, Angiogenesis	July 20, 2022 13:04
Increase, Hemopericardium	October 29, 2025 17:05
Increase, Early Life Stage Mortality	March 22, 2018 10:23
Activation, PPARα leads to reduced production, VEGF	October 30, 2025 04:33
reduced production, VEGF leads to Reduction, Angiogenesis	October 30, 2025 04:34
Reduction, Angiogenesis leads to Increase, Hemopericardium	October 30, 2025 04:34
Increase, Hemopericardium leads to Increase, Early Life Stage Mortality	October 30, 2025 04:19

Abstract

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This Adverse Outcome Pathway (AOP) describes the mechanistic sequence through which activation of peroxisome proliferator-activated receptor alpha (PPARα) disrupts vascular endothelial growth factor (VEGF) signaling and angiogenesis, ultimately resulting in hemopericardium and increased early life stage mortality in fish. The molecular initiating event (MIE) is PPARα activation, which downregulates VEGF expression, reduces angiogenic sprouting, compromises vascular development, and leads to cardiac failure and death. The AOP integrates molecular regulatory pathways controlling lipid metabolism and vascular growth with developmental toxicity endpoints, providing a mechanistically coherent foundation for assessing cardiovascular and embryotoxic effects of peroxisome proliferators, particularly per- and polyfluoroalkyl substances (PFAS). The AOP supports applications in chemical screening, hazard prioritization, and development of non-animal testing strategies under next-generation risk assessment (NGRA) frameworks.

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 elucidate a vascular-specific mechanistic route connecting PPARα activation to developmental toxicity. Activation of PPARα, a key transcription factor in lipid metabolism, modulates numerous downstream targets, including suppression of hypoxia-inducible factor 1-alpha (HIF1α) and VEGF expression, both critical regulators of angiogenesis. Impairment of VEGF signaling and reduced vascular branching are frequently observed in zebrafish embryos exposed to PPARα agonists and PFAS. The resulting loss of vascular integrity contributes to hemopericardium and early developmental mortality. This AOP complements existing PPARα- and mitochondrial-centered AOPs by defining a distinct, angiogenesis-focused mechanistic branch.

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

Objective: Identify and evaluate mechanistic evidence linking PPARα activation to impaired angiogenesis and embryonic lethality.
Data sources: Literature screening in PubMed, AOP-Wiki, OECD AOP-KB, and Web of Science (2010–2025).
Key search terms: PPARα activation, VEGF suppression, angiogenesis, vascular development, hemopericardium, zebrafish embryo, PFAS, fibrates.
Selection criteria: Experimental studies demonstrating sequential causal relationships, dose–response concordance, or temporal consistency between events.
Evaluation: Weight-of-evidence assessment based on OECD (2018) AOP guidance principles—biological plausibility, essentiality, and empirical support.

Summary of the AOP

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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	948	reduced production, VEGF	reduced production, VEGF
KE	28	Reduction, Angiogenesis	Reduction, Angiogenesis
KE	2383	Increase, Hemopericardium	Increase, Hemopericardium

947

Increase, Early Life Stage Mortality

Relationships Between Two Key Events (Including MIEs and AOs)

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Title	Adjacency	Evidence	Quantitative Understanding

Activation, PPARα leads to reduced production, VEGF	adjacent
reduced production, VEGF leads to Reduction, Angiogenesis	adjacent
Reduction, Angiogenesis 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 is supported by strong biological plausibility and moderate empirical evidence. Upstream events (PPARα activation and VEGF suppression) are mechanistically well established. Evidence for downstream outcomes (impaired angiogenesis, hemopericardium, mortality) is consistent across fish species and multiple PPARα agonists. Quantitative understanding of the intermediate key event relationships (KERs) is moderate but growing, with transcriptomic and imaging data supporting causal linkages. The overall confidence level is moderate-to-high, making this AOP suitable for chemical screening, read-across, and mechanistic risk assessment applications.

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); mechanism likely conserved among vertebrates.
Life stage	Embryonic and early larval stages.
Sex	Non-sex-specific (pre-differentiation).
Biological systems	Hepatic (PPARα activation), vascular endothelium (VEGF signaling), and cardiovascular system (angiogenesis and cardiac 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 of ppara in zebrafish prevents VEGF suppression and vascular abnormalities following PPARα agonist exposure.	Direct
Event 948: VEGF production (Decrease)	VEGF mRNA and protein levels are reduced by PPARα agonists; VEGF mRNA rescue restores angiogenesis.	Direct
Event 28: Angiogenesis (Decrease)	Anti-angiogenic phenotypes (reduced intersegmental vessels, impaired sprouting) observed following VEGF suppression.	Direct
Event 2383: Hemopericardium (Increase)	Occurs secondary to vascular malformation and cardiac congestion; attenuated by VEGF rescue.	Indirect
Event 947: Early life stage mortality (Increase)	Final apical outcome following cumulative vascular collapse.	Outcome

Evidence Assessment

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

Biological Plausibility

High. PPARα activation interferes with the HIF1α–VEGF signaling axis, reducing vascular endothelial proliferation and vessel formation. Reduced VEGF signaling has well-documented consequences for angiogenesis and vascular integrity, which align mechanistically with observed cardiac and mortality endpoints in developing fish embryos.

Empirical Support

Moderate to high.

Zebrafish and medaka exposed to PPARα agonists (e.g., clofibrate, PFOA, HFPO-DA) show consistent suppression of vegfa transcripts.
Inhibition of VEGF signaling recapitulates vascular and cardiac phenotypes identical to those caused by PPARα activation.
Temporal concordance is observed: VEGF downregulation → reduced vessel branching → hemopericardium → mortality.
Dose–response relationships are evident between PPARα activation markers, VEGF suppression, and observed apical outcomes.

Quantitative Understanding

Moderate. Transcriptomic dose–response data demonstrate ≥40% reduction in vegfa expression correlates with reduced intersegmental vessel count and >50% mortality at high exposure levels. Quantitative models for VEGF-to-angiogenesis linkage are emerging but not yet standardized across taxa.

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
Oxygen availability	Hypoxia upregulates HIF1α–VEGF signaling, counteracting PPARα-mediated VEGF suppression.	PPARα activation → VEGF decrease
Nutritional status	Lipid levels influence PPARα activation strength and downstream vascular effects.	PPARα activation → VEGF decrease
Antioxidant capacity	Reduces oxidative stress–mediated modulation of VEGF signaling.	VEGF decrease → angiogenesis decrease
Chemical lipophilicity	Determines bioaccumulation and PPARα binding potency.	MIE and downstream effects
Developmental stage	Early embryos are more sensitive due to rapid angiogenic processes.	VEGF → angiogenesis → hemopericardium

Quantitative Understanding

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

Threshold effects: VEGF mRNA reduction >30–40% predicts loss of angiogenic sprouting.
Temporal sequence: VEGF suppression within 24–36 h post-exposure precedes angiogenic defects and hemopericardium by 12–24 h.
Model potential: Dose–response and time-series data from zebrafish enable semi-quantitative modeling for VEGF–angiogenesis relationships.

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

Regulatory screening: Supports the prioritization of chemicals with PPARα agonist activity for developmental vascular toxicity.
Read-across: Enables grouping of PFAS, fibrates, and related lipid modulators based on shared mechanistic profiles.
NAM integration: Aligns with transcriptomic biomarkers (PPARα target genes, vegfa repression) for use in in vitro assays.
Test guideline refinement: May inform OECD Fish Embryo Test (TG 236) adaptations to include vascular endpoints.
Risk assessment: Provides mechanistic rationale for linking molecular bioactivity data to early life stage lethality outcomes.

References

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