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Relationship: 2774

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

Oxidative Stress leads to Altered, Nitric Oxide Levels

Upstream event

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

Oxidative Stress

Downstream event

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

Altered, Nitric Oxide Levels

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	High	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	Moderate
Juvenile	Low

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

The increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during oxidative stress can lead to altered nitric oxide (NO) levels, specifically a reduction in its bioavailability.

Although RNS can also interfere with NO levels, most studies focus on ROS and not RNS (Nagane et al., 2021). Oxidative stress influences the production and activity of endothelial nitric oxide synthase (eNOS), thereby altering and reducing NO levels and its bioavailability. eNOS, otherwise known as NOS3, is an enzyme that catalyzes NO production from the amino acid L-arginine in vascular endothelial cells. NO mediates vascular tone and blood flow via the activation of soluble guanylate cyclase (sGC) within the vascular smooth muscle (Chen, Pittman and & Popel, 2008). A form of ROS known as superoxide anion (O₂^-) causes increased NO degradation (Incalza et al., 2018), converting NO into the RNS peroxynitrite. In addition, ROS can uncouple eNOS by oxidation of the enzyme’s cofactor, BH4 (Matsubara et al., 2015; Forstermann, 2010). Uncoupled eNOS produces ROS instead of NO, which can further convert existing NO into peroxynitrite (Forstermann, 2010).

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

The directionality of changes to NO is inconsistent between studies, as some studies show increased NO levels and other studies show decreased NO levels. Improved methods are needed to assess NO levels directly, which may facilitate an understanding of the relationship (Cervelli et al., 2017, Hasan, Radwan & Galal, 2019). This, along with variation in experimental conditions, can account for the inconsistencies in NO changes between studies.

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	BPF (ACE inhibitor)	BPF treatment led to decreased iNOS, angiotensin II and aldosterone following irradiation. Oxidative stress indices returned closer to control levels.	Hasan, Radwan & Galal, 2019
Drug	OXP (XO inhibitor)	OXP can increase NO levels and decrease ROS after irradiation.	Soucy et al., 2010; Soucy et al., 2011
Drug	RiduROS (A combination of antioxidants resveratrol, extramel, seleno-L-methionine, Curcuma longa, reduced L-glutathione, vitamin C)	RiduROS led to decreased ROS and NO production after irradiation.	Cervelli et al., 2017
Drug	DAHP (Gch1 inhibitor which is involved in BH4 synthesis)	DAHP can decrease ROS production and increase NO production after irradiation.	Yan et al., 2020
Drug	Losartan (AT1 receptor antagonist)	Treatment with Losartan after microgravity decreased superoxide production and returned eNOS and iNOS to control levels.	Zhang et al., 2009
Drug	ZnO-NPs (Zinc oxide nanoparticles that act as antioxidants)	Treatment with ZnO-NPs returned serum and cardiac NO levels and ROS indicators closer to control levels after irradiation.	Abdel-Magied & Shedid, 2020
Drug	Biotin	Biotin (6mg) increased GSH content, SOD activity, and CAT activity closer to control levels following irradiation in hippocampus. NOx levels also returned to near control values.	Abdel-Magied & Shedid, 2020

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
Cervelli et al., 2017	In vitro. HUVECs were irradiated with 0.25 Gy X-rays. Levels of ROS as well as nitrite and nitrate (NO markers) were determined using a fluorescent probe and Griess assay, respectively.	The irradiated samples had a 2.8-fold increase in ROS (not significant) and a 1.6-fold increase in nitrite/nitrate compared to controls.
Yan et al., 2020	In vitro and in vivo. Rat arteries were irradiated with 4 Gy abdominal X-ray radiation. HUVEC were irradiated by 10 Gy X-rays. Oxidative stress was indicated by superoxide anions. Nitrite and eNOS levels were measured by NO assay kit and SDS-PAGE.	Following 4 Gy irradiation of rats, O2- levels increased by 2.1-fold. Nitrite (NO metabolite and marker) and eNOS ratio decreased by 0.6-fold. Following 10 Gy irradiation of HUVEC, O2- levels increased by 3.6-fold and nitrite along with eNOS decreased 0.5 and 0.6-fold respectively.
Soucy et al., 2011	In vivo. Male rats irradiated with 1 Gy ⁵⁶Fe ions. ROS and NO levels in rat aorta were measured using fluorescence rates of dihydroethidium and diaminofluorescein, respectively.	Iron ion irradiation at 1 Gy produced a 1.8-fold increase in ROS levels and 0.8-fold decrease in NO levels compared to controls.
Soucy et al., 2010	In vivo. 4-month-old rats were irradiated with 5 Gy ¹³⁷Cs gamma radiation. ROS and NO levels in rat aorta were measured using fluorescence rates of dihydroethidium and diaminofluorescein, respectively.	After 5 Gy, ROS increased 1.7-fold. NO production decreased 0.7-fold compared to controls.
Hasan, Radwan & Galal, 2019	In vivo. Rats were irradiated by 6 Gy ¹³⁷Cs gamma rays and serum was collected. Oxidative damage biomarker MDA ROS-clearing enzyme reduced GSH and FRAP were measured using various assays.	Irradiation with 6 Gy led to a 1.4-fold increase in MDA, a 0.5-fold decrease in GSH and a 0.4-fold decrease in FRAP. A 3.3-fold increase in iNOS levels was observed.
Zhang et al., 2009	In vivo. Hindlimb unweighted (HU) rats had superoxide and NOS levels measured in carotid arteries. Western blot was used to measure eNOS and iNOS levels, while dihydroethidium fluorescence was used to measure superoxide.	In HU rats, eNOS levels increased 2-fold in carotid arteries. A 4.2- and 3.3-fold increase in iNOS in carotid and cerebral arteries, respectively, was found in HU rats. Superoxide levels were not quantitatively shown but increased greatly after altered gravity.
Abdel-Magied & Shedid, 2020	In vivo. Male rats were irradiated with 8 Gy ¹³⁷Cs gamma irradiation at 0.4092 Gy/min. Oxidative damage biomarker MDA and ROS-clearing enzymes SOD, CAT and glutathione peroxidase (GPx) activities and GSH were measured using respective assay kits. Total nitrite/nitrate content was measured with nitrite/nitrite assay kit. The oxidative damage biomarker and ROS-clearing enzymes were measured in heart tissue and nitrite/nitrate was measured in heart tissue and blood serum.	Irradiated cardiac tissue showed a 1.8-fold increase in MDA levels, 0.4-fold decrease in GSH levels, 0.4-fold decrease in CAT activity, 0.5-fold decrease in SOD activity and a 0.5-fold decrease in GPx activity compared to control. XO levels increased 2-fold. Irradiated heart tissue showed a 2-fold increase in nitrite/nitrate content, while irradiated blood serum showed a 1.8-fold increase in nitrite/nitrate content compared to the control.
Sakata et al., 2015	In vitro. HUVECs were irradiated with various doses of X-rays. eNOS, p-eNOS (Ser1177 & Thr495), iNOS, citrulline (produced by NOS with NO) and NOx levels were measured with western blots for proteins and various assay kits for molecules. ROS intensity was measured using fluorescence microscopy.	At maximum after 10 Gy, ROS increased 15.5-fold, eNOS expression did not significantly change, p-eNOS (Ser1177) increased 1.8-fold, p-eNOS (Thr495) decreased 0.3-fold, iNOS showed a non-significant 1.4-fold increase and citrulline increased 1.3-fold. NOx increased consistently from 1-20 Gy with significant fold changes at 10 and 20 Gy and a maximum 10-fold increase after 10 Gy.

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
Cervelli et al., 2017	In vitro. HUVECs were irradiated with 0.25 Gy X-rays. Levels of ROS as well as nitrite and nitrate (NO markers) were determined using a fluorescent probe and Griess assay, respectively.	The irradiated samples had a 2.8-fold increase in ROS (not significant) measured after 45 minutes and a 1.6-fold increase in nitrite/nitrate measured after 24 hours.
Hasan, Radwan & Galal, 2019	In vivo. Rats were exposed to irradiation by 6 Gy ¹³⁷Cs gamma rays and serum was collected. Oxidative damage biomarker MDA, ROS-clearing enzyme reduced GSH and FRAP were measured using various assays.	Irradiation with 6 Gy led to a 1.4-fold increase in MDA, a 0.5-fold decrease in GSH and a 0.4-fold decrease in FRAP all measured after 4 weeks. A 3.3-fold increase in iNOS levels was observed after 4 weeks as well.

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 evidence for the taxonomic applicability to humans is low as evidence comes from in vitro human cell-derived models. Many studies use in vivo rat models, predominately males. Occasionally, animal age is not specified in studies; most studies indicate the animals are adult or adolescent. In addition, the relationship is also plausible in preadolescent animals.