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Relationship: 2789

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

Altered, Nitric Oxide Levels leads to Increase, Endothelial Dysfunction

Upstream event

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

Altered, Nitric Oxide Levels

Downstream event

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

Increase, Endothelial Dysfunction

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
Deposition of energy leads to vascular remodeling	adjacent	Moderate	Low	Cataia Ives (send email)	Open for citation & comment

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
human	Homo sapiens	Low	NCBI
rat	Rattus norvegicus	Moderate	NCBI
rabbit	Oryctolagus cuniculus	Low	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Male	Moderate
Female	Low
Unspecific	Low

Life Stage Applicability

An indication of the the relevant life stage(s) for this KER. More help

Term	Evidence
Adult	Low
Not Otherwise Specified	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

Altered nitric oxide (NO) levels can lead to endothelial dysfunction (Soloviev & Kizub, 2019). In a functional endothelium, NO is bioavailable and is involved in preventing inflammation, proliferation and thrombosis (Deanfield, Halcox & Rabelink, 2007; Kruger-Genge et al., 2019). An increase in reactive oxygen species (ROS) along with increased NO can drive cellular senescence in endothelial cells (ECs) and catalyze endothelial dysfunction (Nagane et al., 2021; Wang, Boerma & Zhou, 2016). Another driver of endothelial dysfunction is reduced vasomotion. In a functional state, the endothelium requires a balance of vasoconstrictors and vasodilators (like NO); an interruption of this balance can lead to dysfunction (Deanfield, Halcox & Rabelink, 2007; Marti et al., 2012; Nagane et al., 2021; Schulz, Gori & Münzel, 2011; Soloviev & Kizub, 2019). Decreased NO due to direct reactions with ROS or uncoupling of NOS enzymes will lead to a reduced ability of smooth muscle cells (SMCs) to relax (Soloviev & Kizub, 2019).

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

The strategy for collating the evidence on radiation stressors to support the relationship is described in Kozbenko et al 2022. Briefly, a scoping review methodology was used to prioritize studies based on a population, exposure, outcome, endpoint statement.

Evidence Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

Addresses the scientific evidence supporting KERs in an AOP setting the stage for overall assessment of the AOP. More help

Title	First Author	Biological Plausibility	Dose Concordance	Temporal Concordance	Incidence Concordance

Biological Plausibility

Dose Concordance Evidence

Temporal Concordance Evidence

Incidence Concordance Evidence

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

Directionality of NO changes cannot be compared between studies due to a variety of experimental conditions like stressor type, dose, dose rate, model and time course of the experiment.
Irradiating in vivo rabbit carotid arteries with X-rays showed that endothelial dysfunction was higher after 8 Gy than 16 Gy (Hong et al., 2013). This was inconsistent with the ex vivo model, where endothelial dysfunction was highest after 16 Gy (Hong et al., 2013). Endothelial dysfunction was shown through a relaxation response to ACh.

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	Effects on the KER	References
Drug	AG (selective iNOS inhibitor)	AG treatment prevented radiation-induced increase in peroxynitrite and endothelial dysfunction along with L-NA treatment.	Hong et al., 2013
Drug	L-NA (general NOS inhibitor)	L-NA treatment prevented radiation-induced increase in peroxynitrite and endothelial dysfunction	Hong et al., 2013
Drug	DAHP (Gch1 inhibitor to inhibit BH4 synthesis)	DAHP (100 mg/kg/body weight) further decreased eNOS, nitrite concentration and endothelial relaxation after irradiation.	Yan et al., 2020
Drug	Losartan (AT1 receptor antagonist)	Losartan restored the levels eNOS and iNOS expression and improved endothelial relaxation after HU.	Zhang et al., 2009
Drug	Oxp (XO inhibitor)	Oxp increased NO levels and endothelial relaxation.	Soucy et al., 2010, 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

The following are a few examples of quantitative understanding of the relationship. All data that is represented is statistically significant unless otherwise indicated.

Response-response Relationship

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

Dose/Incidence Concordance

Reference	Experiment Description	Result
Soucy et al., 2011	In vivo. 3-4 months-old rats were irradiated with 1 Gy ⁵⁶Fe ions. Endothelial NO levels from male rat aorta were measured with a DAF-FM DA fluorescent probe in response to ACh-induced relaxation. Vascular tension response to ACh was measured in male rat aorta after 0, 0.5 and 1 Gy ⁵⁶Fe ion irradiation. Doses were given at 0.5 Gy/min.	Iron ion irradiation at 1 Gy produced a decrease of 0.8-fold in NO levels compared to aorta without irradiation. At 10-5 M ACh, aorta without irradiation relaxed by 88%, while aorta with 1 Gy irradiation had significantly lower relaxation of 75%. No significant changes were observed at 0.5 Gy.
Hong et al., 2013	In vivo, in vitro and ex vivo. HUVECs were irradiated with 4 Gy X-rays (2.7 Gy/min) and amounts of eNOS, iNOS and nitrotyrosine (a biomarker for peroxynitrite) were determined by western blot. Rabbit carotid arteries were irradiated with 8 or 16 Gy X-rays. In vivo arteries were irradiated at 4.1 Gy/min, and ex vivo arteries were irradiated at 3.9 Gy/min. Arteries were contracted with phenylephrine then relaxed with ACh to determine vascular responsiveness, which was measured with a computerized automated isometric transducer system.	In 4 Gy irradiated HUVECs, iNOS was increased 6.6-fold and nitrotyrosine was increased 6.4-fold. eNOS expression did not change. The responsiveness of the ex vivo carotid artery to ACh-induced relaxation was 77.4% without irradiation, 65.7% with 8 Gy and 60.1% with 16 Gy. The in vivo irradiated carotid artery also showed decreased ACh-induced relaxation, but relaxation was lowest after 8 Gy.
Zhang et al., 2009	In vivo. HU rats were exposed to altered gravity conditions as a stressor. Western blot was used to measure eNOS and iNOS protein in arteries. Endothelial dysfunction was determined by vasodilation.	Following HU, there was a 2-fold increase of eNOS in carotid arteries compared to control. A 4.3- and 3.3-fold increase in iNOS in carotid and cerebral arteries, respectively, was found in HU rats. Vasodilation was reduced by ~30% in the ACh induced relaxation of basilar arteries in HU rats. Vasoconstriction was increased in HU rats by 1.6 and 1.8-fold in the basilar artery in response to KCl (100 mmol/L) and 5-hydroxytryptamine (5-HT), respectively, and 1.2 and 1.3-fold in the carotid artery in response to KCl and phenylephrine (PE) respectively
Soucy et al., 2010	In vivo. In 4-month-old rats were irradiated with 0 or 5 Gy ¹³⁷Cs gamma radiation. Altered NO levels and endothelial function were investigated through fluorescent measurements of NO and vascular tension dose responses.	After 5 Gy NO production decreased 0.7-fold. There was a 0.7-fold decrease of relaxation response to ACh after 5 Gy compared to control.
Yan et al., 2020	In vivo. Rats were irradiated with 4 Gy abdominal X-ray radiation. Nitrite and eNOS levels were measured by NO assay kit and western blot, respectively. Endothelial dysfunction was determined by changes in vasodilation.	After radiation nitrite (NO metabolite and marker) levels and the eNOS ratio decreased 0.6-fold. With increasing ACh concentration the control group dropped to ~7% constriction while the irradiated group remained at ~75% constricted.

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

Time Concordance

Reference	Experiment Description	Result
Hong et al., 2013	In vivo and ex vivo. HUVECs were irradiated with 4 Gy X-rays (2.7 Gy/min) and amounts of iNOS and nitrotyrosine (a biomarker for peroxynitrite) were determined by western blot at various times over 6 hours. Rabbit carotid arteries were irradiated with 0, 8 or 16 Gy X-rays and the contraction was measured every 2 minutes for 10 minutes. In vivo arteries were irradiated at 4.1 Gy/min, and ex vivo arteries were irradiated at 3.9 Gy/min. Arteries were contracted with phenylephrine then relaxed with ACh to determine vascular responsiveness, which was measured with a computerized automated isometric transducer system.	After 4 Gy X-ray irradiation, iNOS levels in HUVECs increased consistently over 6 hours, while nitrotyrosine did not change at the 1.5- or 3-hour timepoint, but then increased at 6 hours. 20 hours after irradiation, relaxation with ACh was increased in the irradiated arteries compared to the non-irradiated arteries. This occurred in both the in vivo and ex vivo models.

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

Not identified

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

The majority of the evidence is derived from in vivo rat models. A limited number of studies were in human and rabbit models. The relationship has been more commonly shown in vivo in male animals, specifically in adult male rodents.