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Event: 298

Key Event Title

The KE title should describe a discrete biological change that can be measured. It should generally define the biological object or process being measured and whether it is increased, decreased, or otherwise definably altered relative to a control state. For example “enzyme activity, decreased”, “hormone concentration, increased”, or “growth rate, decreased”, where the specific enzyme or hormone being measured is defined. More help

Insufficiency, Vascular

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. The short name should be less than 80 characters in length. More help
Insufficiency, Vascular

Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. Note, KEs should be defined within a particular level of biological organization. Only KERs should be used to transition from one level of organization to another. Selection of the level of biological organization defines which structured terms will be available to select when defining the Event Components (below). More help
Level of Biological Organization

Cell term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help

Organ term

Further information on Event Components and Biological Context may be viewed on the attached pdf.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable. More help
Organ term

Key Event Components

Further information on Event Components and Biological Context may be viewed on the attached pdf.Because one of the aims of the AOP-KB is to facilitate de facto construction of AOP networks through the use of shared KE and KER elements, authors are also asked to define their KEs using a set of structured ontology terms (Event Components). In the absence of structured terms, the same KE can readily be defined using a number of synonymous titles (read by a computer as character strings). In order to make these synonymous KEs more machine-readable, KEs should also be defined by one or more “event components” consisting of a biological process, object, and action with each term originating from one of 22 biological ontologies (Ives, et al., 2017; See List). Biological process describes dynamics of the underlying biological system (e.g., receptor signalling). The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signalling by that receptor).Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description. To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons. If a desired term does not exist, a new term request may be made via Term Requests. Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add. More help
Process Object Action
blood circulation blood decreased
capillary plexus abnormal

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE. Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
Developmental Vascular Toxicity KeyEvent Tom Knudsen (send email) Open for citation & comment EAGMST Under Review


This is a structured field used to identify specific agents (generally chemicals) that can trigger the KE. Stressors identified in this field will be linked to the KE in a machine-readable manner, such that, for example, a stressor search would identify this as an event the stressor can trigger. NOTE: intermediate or downstream KEs in one AOP may function as MIEs in other AOPs, meaning that stressor information may be added to the KE description, even if it is a downstream KE in the pathway currently under development.Information concerning the stressors that may trigger an MIE can be defined using a combination of structured and unstructured (free-text) fields. For example, structured fields may be used to indicate specific chemicals for which there is evidence of an interaction relevant to this MIE. By linking the KE description to a structured chemical name, it will be increasingly possible to link the MIE to other sources of chemical data and information, enhancing searchability and inter-operability among different data-sources and knowledgebases. The free-text section “Evidence for perturbation of this MIE by stressor” can be used both to identify the supporting evidence for specific stressors triggering the MIE as well as to define broad chemical categories or other properties that classify the stressors able to trigger the MIE for which specific structured terms may not exist. More help

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected from an ontology. 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 in relation to this KE. More help

Life Stages

The structured ontology terms for life-stage are more comprehensive than those for taxa, but may still require further description/development and explanation in the free text section. More help

Sex Applicability

The authors must select from one of the following: Male, female, mixed, asexual, third gender, hermaphrodite, or unspecific. More help

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. For example, the biological state being measured could be the activity of an enzyme, the expression of a gene or abundance of an mRNA transcript, the concentration of a hormone or protein, neuronal activity, heart rate, etc. The biological compartment may be a particular cell type, tissue, organ, fluid (e.g., plasma, cerebrospinal fluid), etc. The role in the biology could describe the reaction that an enzyme catalyses and the role of that reaction within a given metabolic pathway; the protein that a gene or mRNA transcript codes for and the function of that protein; the function of a hormone in a given target tissue, physiological function of an organ, etc. Careful attention should be taken to avoid reference to other KEs, KERs or AOPs. Only describe this KE as a single isolated measurable event/state. This will ensure that the KE is modular and can be used by other AOPs, thereby facilitating construction of AOP networks. More help

Embryonic blood vessels form in a reproducible pattern that interfaces with other embryonic structures and tissues [Hogan et al. 2004]. Many human diseases, including stroke, retinopathy, and cancer, are associated with the vascular biology, including endothelial cells and pericytes that establish the blood-brain barrier and control cerebrovascular exchanges [Bautch and James, 2009; Eichmann and Thomas, 2013; Saili et al. 2017]. Functionally, blood vessel morphogenesis is critical for providing oxygen, nutrients and molecular signals to developing tissues [Maltepe et al. 1997; Vargesson, 2003; Chung and Ferrara, 2011; Eshkar-Oren et al. 2015]. The developing vascular network is shaped into a hierarchical system of arteries and veins, through progressive effects on blood vessel arborization (microvasculature) and pruning (angio-adaptation) [Jin et al. 2017]. The former is morpho-regulatory whereas the reshaping is influenced by regional changes in blood flow and local metabolic demands [Tran et al. 2007]. Evidence supports the ability of physiological parameters such as oxygen and glucose concentrations to affect the expression of genes critical for developmental angiogenesis [Maltepe and Simon, 1998]. Growth in tissue mass during organogenesis is thought to lead to the formation of hypoxic/nutrient-deprived cells. The subsequent activation of sensors such as HIF-1 [Xia et al. 2009; Oladipupo et al. 2011; Li et al. 2018] and ARNT [Maltepe et al. 1997; Abbott and Buckalew, 2000] that rapidly trans-activate the expression of genes such as VEGF that drive angiogenesis.

While mammalian embryos become sensitive to hypoxia during early organogenesis, the small size of zebrafish embryos renders this species less vulnerable to hypoxia than vertebrate counterparts; however, the genetic control of microvascular development is conserved among vertebrate species as evidenced by hypoxia-responsive signaling (HIF-1) via local oxygen-sensing gradients in the zebrafish, chick and mouse embryo [Hogan et al. 2004; Liu et al. 2017; Gerri et al. 2017]. The neural tube, for example, provides vascular patterning signals that direct formation of the perineural vascular plexus (PNVP) that encompasses the neural tube at mid-gestation [Hogan et al. 2004]. This process is temporally and spatially associated with Vegfa expression as the neural tube signal through VEGFR-2. Mesodermal VEGFR-2 expression is localized to the lateral portion of the somite and later to sclerotomal cells surrounding the neural tube under the positive control of BMP4 signaling and negative control by Noggin, a BMP4 antagonist [Nimmagadda et al. 2005]. Reciprocal signaling between VEGF-induced endothelial cells and neuroprogenitor cells enhanced formation of the brain neurovascular unit [Vissapragada et al. 2014]. In transgenic zebrafish embryos, the VEGFR-2 antagonist, Vatalanib produced a direct concentration-dependent progression of impaired intersegmental vessel (ISV) outgrowth in early embryos, increased rates of malformed hatched larva, and reduced survival in juvenile cohorts [Tal et al. 2014]. These data show that disruption in the early embryo has a lasting impact on advanced life stages.

Another key cell sensing activity is the recruitment of macrophage (microglia?) cells that secrete pro-angiogenic cytokines and proteases, remodeling the extracellular matrix (ECM) and providing survival and guidance cues to endothelial cells [Gerri et al. 2017]. Macrophages play crucial roles at each step of the angiogenic cycle, from sprouting to maturation and remodelling of the vascular plexus through angiopoietin-TIE2 signaling [Du Cheyne et al. 2020], which is known to synergize with the VEGF-pathway during developmental angiogenesis [Li et al. 2014]. A seminal study showed that loss of immature blood vessels is the primary cause of Thalidomide-induced teratogenesis in the chick embryo, where anti-angiogenic but not anti-inflammatory analogues of Thalidomide induced limb reduction defects. Outgrowth and remodeling of more mature blood vessels delayed, whereas newly formed angiogenic vessels were lost prior to limb dysmorphogenesis and altered patterns of gene expression [Therapontos et al. 2009; Vargesson, 2015]. Vascular insufficiency is likely important in human embryos where the window of vulnerability to Thalidomide-induced phocomelia precedes full establishment of the adult arterial pattern by the 8th week of gestation [Hootnick et al. 2016; Hootnick et al. 2017; Vargesson and Hootnick, 2017].

As such, a chemical’s potential to disrupt vascular patterning and/or remodeling during organogenesis can have profound effects on many systems, including: early limb development [Beedie et al. 2016a, 2016b, 2017 and 2020]; neurovascular development [Hogan et al. 2004; Hallene et al. 2006; Bautch and James, 2009; Eichman and Thomas, 2013; Vissapragada et al. 2014;  Fiorentino et al. 2016; Uwamori et al. 2017; Huang, 2020]; and utero-placental development [Abbott and Buckalew, 2000; Douglas et al. 2009; Rutland et al. 2009; Chen, 2014; Araujo et al. 2021].

How It Is Measured or Detected

One of the primary considerations in evaluating AOPs is the relevance and reliability of the methods with which the KEs can be measured. The aim of this section of the KE description is not to provide detailed protocols, but rather to capture, in a sentence or two, per method, the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements. Methods that can be used to detect or measure the biological state represented in the KE should be briefly described and/or cited. These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA).Key considerations regarding scientific confidence in the measurement approach include whether the assay is fit for purpose, whether it provides a direct or indirect measure of the biological state in question, whether it is repeatable and reproducible, and the extent to which it is accepted in the scientific and/or regulatory community. Information can be obtained from the OECD Test Guidelines website and the EURL ECVAM Database Service on Alternative Methods to Animal Experimentation (DB-ALM). ?

Complex functional assays such as the rat aortic explant assay, rat whole embryo culture, and the zebrafish embryotoxicity along with transcriptomic signatures provide a tiered approach to evaluate HTS signatures and their taxonomic implications for conserved pathways to prioritize further in vivo testing studies [Ellis-Hutchings et al. 2017].

Zebrafish reporter assays: Blood flow begins in the zebrafish embryo at 24 h postfertilization. Shortly after this, the angiogenic vessels that perfuse the trunk of the embryo (intersegmental vessels) sprout from the vasculogenic vessels [Tran et al. 2007]. These effects can be visualized in automated, quantitative screening assays using transgenic zebrafish expressing green fluorescent protein (GFP) under the control of the vascular endothelial growth factor receptor (VEGFR) Vegfr2 promoter that restricts reporter gene expression to developing blood vessels. Phenotypic readouts have been used to screen and validate anti-angiogenic compounds [Tran et al. 2007; Yano et al. 2012; Yozzo et al. 2013; Tal et al. 2014; McCollum et al. 2017]. Live-cell imaging has been used to quantitatively detect the trajectory dynamics of vascular patterning [Clendenon et al. 2013; Shirinfard et al. 2013] and confocal cell imaging has been used to develop a quantitative assay capable of detecting relatively subtle changes (~8%) in relative to controls during chemical exposure [Tal et al. 2017].

ToxCast: A study evaluated two anti-angiogenic agents, 5HPP-33, a synthetic Thalidomide analog [Noguchi et al. 2005] and TNP-470, a synthetic Fumagillan analog [Ingber et al. 1990] across the ToxCast HTS assay platform and anchored the results to complex in vitro functional assays: the rat aortic explant assay, rat whole embryo culture, and zebrafish embryotoxicity [Saili et al. 2019]. Both compounds disrupted angiogenesis and embryogenesis in the functional assays, with differences in potency and adverse effects. 5HPP-33 was embryolethal, whereas TNP-470 produced caudal defects at low concentrations [Ellis-Hutchings et al. 2017]. Anti-angiogenic modes of action are known for 5HPP-33, which blocks tubulin polymerization inhibition [Yeh et al. 2000; Inatsuki et al. 2005; Kizaki et al. 2008; Rashid et al. 2015); and TNP-470, a methionine aminopeptidase II (MetAP2) inhibition, through non-canonical Wnt inhibition of endothelial proliferation [Ingber et al. 1990]. Transcriptomic profiles of exposed embryos pathways unique to each and in common to both, strongest being the TP53 pathway [Saili et al. 2019]. In mouse, TNP-470 reduced fetal intraocular microvasculature and induced microphthalmia, either directly or via effects on placental morphology [Rutland et al. 2009].

Computational models: Critical pathways for developmental angiogenesis and potential disruptions have critical signal-response systems embedded in three types of receptors that play key roles in a number of morphoregulatory processes: receptor tyrosine kinases (e.g., growth factor-signaling), G-protein coupled receptors (e.g., chemokine signaling), and GPI-anchored receptors (e.g., uPAR system). Computational approaches have been used to predict vascular insufficiency for potential vascular disrupting chemicals (pVDCs) that are developmental toxicants or non-toxicants [Kleinstreuer et al. 2011; Knudsen and Kleinstreuer, 2011]. This has been applied to the ToxCast inventory to rank order over a thousand chemicals for validation testing [McCollum et al. 2017; Tal et al. 2017; Saili et al. 2019; Zurlinden et al. 2020].

Domain of Applicability

This free text section should be used to elaborate on the scientific basis for the indicated domains of applicability and the WoE calls (if provided). While structured terms may be selected to define the taxonomic, life stage and sex applicability (see structured applicability terms, above) of the KE, the structured terms may not adequately reflect or capture the overall biological applicability domain (particularly with regard to taxa). Likewise, the structured terms do not provide an explanation or rationale for the selection. The free-text section on evidence for taxonomic, life stage, and sex applicability can be used to elaborate on why the specific structured terms were selected, and provide supporting references and background information.  More help

Complex functional assays such as the rat aortic explant assay (AEA), rat whole embryo culture (WEC), and the zebrafish embryotoxicity (ZET) along with transcriptomic signatures provide a tiered approach to evaluate HTS signatures and their taxonomic implications for conserved pathways to prioritize further in vivo testing studies [Ellis-Hutchings et al. 2017].


List of the literature that was cited for this KE description. Ideally, the list of references, should conform, to the extent possible, with the OECD Style Guide ( (OECD, 2015). More help

Chung AS, Ferrara N. Developmental and pathological angiogenesis. Annual review of cell and developmental biology. 2011;27:563-84. PubMed PMID: 21756109.

Clendenon SG, Sankaran DG, Shirinifard A, McColluma CW, Bondesson MB, Gustafssona JA and Glazier JA. Arsenic exposure inhibits angiogenesis in zebrafish via downregulation of both VEGFA and VEGFR2. Microscopy and Microanalysis. 2013 19(S2): 778-779.

Ellis-Hutchings RG, Settivari RS, McCoy AT, Kleinstreuer N, Franzosa J, Knudsen TB and Carney EW. Embryonic vascular disruption adverse outcomes: Linking high throughput signaling signatures with functional consequences. Reprod Toxicol. 2017; 70: 82-96. PMID:28527947.

Eshkar-Oren I, Krief S, Ferrara N, Elliott AM, Zelzer E. Vascular patterning regulates interdigital cell death by a ROS-mediated mechanism. Development (Cambridge, England). 2015 Feb 15;142(4):672-80. PubMed PMID: 25617432.

Jin SW, Beis D, Mitchell T, Chen JN,Stainier DY. Cellular and molecular analyses of vascular tube and lumen formation in zebrafish. Development. 2005 132: 5199-209.

Kleinstreuer NC, Judson RS, Reif DM, Sipes NS, Singh AV, Chandler KJ, et al. Environmental impact on vascular development predicted by high-throughput screening. Environmental health perspectives. 2011 Nov;119(11):1596-603. PubMed PMID: 21788198. Pubmed Central PMCID: PMC3226499.

Knudsen TB, Kleinstreuer NC. Disruption of embryonic vascular development in predictive toxicology. Birth defects research Part C, Embryo today : reviews. 2011 Dec;93(4):312-23. PubMed PMID: 22271680.

Maltepe E, Schmidt JV, Baunoch D, Bradfield CA, Simon MC. Abnormal angiogenesis and responses to glucose and oxygen deprivation in mice lacking the protein ARNT. Nature. 1997 Mar 27;386(6623):403-7. PubMed PMID: 9121557.

McCollum CW, Conde-Vancells J, Hans C, Vazquez-Chantada M, Kleinstreuer N, Tal T, Knudsen T, Shah SS, Merchant FA, Finnell RH, Gustafsson JA, Cabrera R and Bondesson M. Identification of vascular disruptor compounds by analysis in zebrafish embryos and mouse embryonic endothelial cells. Reprod Toxicol. 2017; 70: 60-69. PMID:27838387.

Saili KS, Franzosa JA, Baker NC, Ellis-Hutchings RG, Settivari RS, Carney EW, Spencer R, Zurlinden TJ, Kleinstreuer NC, Li S, Xia M and Knudsen TB. Systems Modeling of Developmental Vascular Toxicity. Curr Opin Toxicol. 2019; 15(1): 55-63. PMID:32030360.

Shirinifard A, McCollum CW, Bondesson MB, Gustafsson JA, Glazier JA and Clendenon SG. 3D Quantitative analyses of angiogenic sprout growth dynamics Devel Dynam. 2013 242(5): 518-526.

Tal T, Kilty C, Smith A, LaLone C, Kennedy B, Tennant A, McCollum CW, Bondesson M, Knudsen T, Padilla S and Kleinstreuer N. Screening for angiogenic inhibitors in zebrafish to evaluate a predictive model for developmental vascular toxicity. Reprod Toxicol. 2017; 70: 70-81. PMID:28007540.

Tal TL, McCollum CW, Harris PS, Olin J, Kleinstreuer N, Wood CE, Hans C, Shah S, Merchant FA, Bondesson M, Knudsen TB, Padilla S and Hemmer MJ. Immediate and long-term consequences of vascular toxicity during zebrafish development. Reproductive Toxicology. 2014;48:51-61.

Therapontos C, Erskine L, Gardner ER, Figg WD, Vargesson N. Thalidomide induces limb defects by preventing angiogenic outgrowth during early limb formation. Proceedings of the National Academy of Sciences of the United States of America. 2009 May 26;106(21):8573-8. PubMed PMID: 19433787. Pubmed Central PMCID: 2688998.

Tran TC, Sneed B, Haider J, Blavo D, White A, Aiyejorun T, et al. Automated, quantitative screening assay for antiangiogenic compounds using transgenic zebrafish. Cancer research. 2007;67: 11386-92.

van Gelder MM, van Rooij IA, Miller RK, Zielhuis GA, de Jong-van den Berg LT, Roeleveld N. Teratogenic mechanisms of medical drugs. Human reproduction update. 2010 Jul-Aug;16(4):378-94. PubMed PMID: 20061329.

Vargesson N. Thalidomide-induced teratogenesis: history and mechanisms. Birth defects Research Part C, Embryo today: reviews. 2015 Jun;105(2):140-56. PubMed PMID: 26043938.

Yozzo KL, Isales GM, Raftery TD,Volz DC. High-content screening assay for identification of chemicals impacting cardiovascular function in zebrafish embryos. Environmental science & technology. 2013;47: 11302-10.