This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 956

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

Uncoupling, eNOS leads to Depletion, Nitric Oxide

Upstream event

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

Uncoupling, eNOS

Downstream event

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

Depletion, Nitric Oxide

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
Peptide Oxidation Leading to Hypertension	adjacent	High	High	Frazer Lowe (send email)	Not under active development	Under Development

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
Homo sapiens	Homo sapiens	High	NCBI
Bos taurus	Bos taurus	High	NCBI
Rattus norvegicus	Rattus norvegicus	High	NCBI

Sex Applicability

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

Sex	Evidence
Unspecific	High

Life Stage Applicability

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

Term	Evidence
All life stages	High

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 uncoupling of eNOS occurs through a number of mechanisms like BH4 depletion or S-glutathionylation of eNOS and leads to a reduction in NO bioavailability and an elevation in superoxide production, contributing to endothelial dysfunction (Zweier et al., 2011).

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

Evidence Supporting this KER

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

Biological Plausibility

Addresses the biological rationale for a connection between KEupstream and KEdownstream. This field can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured. More help

It is well-established that uncoupling of eNOS causes eNOS to switch from producing NO to generating superoxides (Förstermann and Münzel, 2006). Many studies that reported BH4 depletion leading to eNOS uncoupling or S-glutathionylation leading to eNOS uncoupling measured levels of NO and superoxide which are indicative of eNOS uncoupling.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Include consideration of temporal concordance here

Multiple experiments demonstrated that eNOS uncoupling results in increased superoxide formation and decreased NO production, which provide strong empirical support for this KER.

Prolonged myocardial ischemia (>30 min) in isolated rat hearts decreased eNOS activity (58% reduction) and increased superoxide generation from <0.01 relative fluorescence unit/mg to 0.3 as measured using a fluorescence detector-based assay (Dumitrescu et al., 2007). Similarly, cardiac reperfusion patients had decreased eNOS activity (40% reduction) and increased superoxide production from 37.83 to 65.02 light unit/s/mg as detected using lucigenin-enhanced chemiluminescence (Jayaram et al., 2015).

In BAECs, treatment with 10 mmol/L DAHP or 25 μM 4-HNE for 24 hours led to a reduction in NO (control: 1678 pmol/mg, DAHP: 1274 pmol/mg, 4-HNE: 1106 pmol/mg) and increased superoxide formation (control: 59 pmol/mg, DAHP: 97 pmol/mg, 4-HNE: 122 pmol/mg) (Whitsett et al., 2007). Similar results were observed in another study using DAHP-treated BAECs; superoxide was increased (control: 100%, DAHP: 257%) and NO was decreased (control: 96%, DAHP: 60%) (Wang et al., 2008).

In BAECs undergoing hypoxia and reoxygenation (H/R), NO decreased from 34.2±1.7% to 63.7±3.0% and superoxide increased from relative intensity of 3.5 to 49.2, demonstrating that these key events are modulated together (De Pascali et al., 2014).

BCNU (25 μM, 80 μM) resulted in increased superoxide (25 μM: 432 fluorescence intensity, 80 μM:759 fluorescence intensity) and decreased NO (25 μM: 61%, 80 μM:36%) in a dose-dependent manner in BAECs (Chen et al., 2010).

Exposure to 50 μmol/L peroxynitrite for 3 hours led to an increase in superoxide from 2 nmol/min/well to 8.6 nmol/min/well and a decrease in NO from 90% to 6.5% in BAECs (Zou et al., 2002).

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

There are no uncertainties or inconsistencies.

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

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

Is it known how much change in the first event is needed to impact the second? Are there known modulators of the response-response relationships? Are there models or extrapolation approaches that help describe those relationships?

The uncoupling of eNOS automatically results in NO depletion and increased superoxide production. The experimental studies above included a number of modulators of the response-response relationship, such as peroxynitrite, BCNU, and DAHP.

Response-response Relationship

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

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

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

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 relationship between NO depletion and eNOS uncoupling was observed in humans, cows, and rats as demonstrated by the above studies.

References

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

Chen, X., Xu, J., Feng, Z., Fan, M., Han, J., and Yang, Z. (2010). Simvastatin combined with nifedipine enhances endothelial cell protection by inhibiting ROS generation and activating Akt phosphorylation. Acta Pharmacol. Sin. 31, 813–820.

De Pascali, F., Hemann, C., Samons, K., Chen, C.-A., and Zweier, J.L. (2014). Hypoxia and reoxygenation induce endothelial nitric oxide synthase uncoupling in endothelial cells through tetrahydrobiopterin depletion and S-glutathionylation. Biochemistry (Mosc.) 53, 3679–3688.

Dumitrescu, C., Biondi, R., Xia, Y., Cardounel, A.J., Druhan, L.J., Ambrosio, G., and Zweier, J.L. (2007). Myocardial ischemia results in tetrahydrobiopterin (BH4) oxidation with impaired endothelial function ameliorated by BH4. Proc. Natl. Acad. Sci. U. S. A. 104, 15081–15086.

Förstermann, U., and Münzel, T. (2006). Endothelial nitric oxide synthase in vascular disease: from marvel to menace. Circulation 113, 1708–1714.

Jayaram, R., Goodfellow, N., Zhang, M.H., Reilly, S., Crabtree, M., De Silva, R., Sayeed, R., and Casadei, B. (2015). Molecular mechanisms of myocardial nitroso-redox imbalance during on-pump cardiac surgery. Lancet Lond. Engl. 385 Suppl 1, S49.

Wang, S., Xu, J., Song, P., Wu, Y., Zhang, J., Chul Choi, H., and Zou, M.-H. (2008). Acute inhibition of guanosine triphosphate cyclohydrolase 1 uncouples endothelial nitric oxide synthase and elevates blood pressure. Hypertension 52, 484–490.

Whitsett, J., Picklo, M.J., and Vasquez-Vivar, J. (2007). 4-Hydroxy-2-nonenal increases superoxide anion radical in endothelial cells via stimulated GTP cyclohydrolase proteasomal degradation. Arterioscler. Thromb. Vasc. Biol. 27, 2340–2347.

Zou, M.-H., Hou, X.-Y., Shi, C.-M., Nagata, D., Walsh, K., and Cohen, R.A. (2002). Modulation by peroxynitrite of Akt- and AMP-activated kinase-dependent Ser1179 phosphorylation of endothelial nitric oxide synthase. J. Biol. Chem. 277, 32552–32557.

Zweier, J.L., Chen, C.-A., and Druhan, L.J. (2011). S-glutathionylation reshapes our understanding of endothelial nitric oxide synthase uncoupling and nitric oxide/reactive oxygen species-mediated signaling. Antioxid. Redox Signal. 14, 1769–1775.