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Event: 209

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

Peptide Oxidation

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
Peptide Oxidation

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
Molecular

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
Cell term
eukaryotic cell

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

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
oxidative stress increased

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
Cholestatic Liver Injury induced by Inhibition of the Bile Salt Export Pump (ABCB11) KeyEvent Mathieu Vinken (send email) Under development: Not open for comment. Do not cite Under Development
PDK inhibition- HCC KeyEvent Charles Wood (send email) Under Development: Contributions and Comments Welcome
Hypertension MolecularInitiatingEvent Frazer Lowe (send email) Not under active development Under Development
JNK, FOXO and WNT alteration leading to reproductive failure: Multi-OMICS approach KeyEvent Jinhee Choi (send email) Under development: Not open for comment. Do not cite

Stressors

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
Term Scientific Term Evidence Link
human Homo sapiens High NCBI
rodents rodents High NCBI
human and other cells in culture human and other cells in culture High NCBI

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
Life stage Evidence
All life stages High

Sex Applicability

No help message More help
Term Evidence
Unspecific High

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

Oxidative stress corresponds to an imbalance between the rate of oxidant production and that of their degradation. The term oxidative stress indicates the outcome of oxidative damage to biologically relevant macromolecules such as nucleic acids, proteins, lipids and carbohydrates. This occurs when oxidative stress-related molecules, generated in the extracellular environment or within the cell, exceed cellular antioxidant defenses. Major reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and superoxide anion, as well as 4-hydroxy- 2,3-nonenal (HNE) and related 4-hydroxy-2,3-alkenals (HAKs), major aldehydic end-products of lipid peroxidation, can act as potential mediators able to affect signal transduction pathways as well as the proliferative and functional response of target cells. H2O2 and superoxide anion may be also generated as molecular messengers within the cell as part of the cellular response to defined growth factors, cytokines and other mediators. The final consequence at tissue, cellular and molecular level is primarily affected by the steady state concentration of oxidative stress-related molecules. The main biological targets of free radicals are proteins, lipids and DNA.

Major consequences of reaction of ROS, HAKs and NO with biologically relevant macromolecules that can mediate pathophysiological effects:

ROS: DNA: oxidation, strand breaks, genotoxicity Proteins: oxidation, fragmentation, formation of carbonyls Lipids: lipid peroxidation and degradation

HAKs: DNA: adducts (low doses), strand breaks, genotoxicity (high doses) Proteins: adducts (Michael type reactions on Lys, Cys and His residues)

NO: DNA: oxidation, strand breaks Proteins: oxidation, nitrosation, nitration (nytrosylation of tyrosine) Lipids: lipid peroxidation and degradation

Continued oxidative stress can lead to chronic inflammation. Oxidative stress can activate a variety of transcription factors including NF-κB, AP-1, p53, HIF-1α, PPAR-γ, β-catenin/Wnt, and Nrf2. Activation of these transcription factors can lead to the expression of over 500 different genes, including those for growth factors, inflammatory cytokines and chemokines, which can activate inflammatory pathways. [1] [2] [3]

Glutathione (GSH) oxidation refers to the conversion of reduced glutathione to its oxidized form glutathione disulfide (GSSG) in the presence of oxidative species. GSH plays an important role as an anti-oxidant in regulating cellular redox homeostasis, and is mainly present in the cell as the reduced form (98%). Deficiency in GSH or a decrease in GSH/GSSG ratio results in decreased anti-oxidant function and increased susceptibility to oxidative stress, thus making it a marker of cellular redox status. An imbalance in GSH/GSSG ratio has been implicated in the onset and progression of human diseases, such as neurodegenerative diseases, cancers, pulmonary diseases and cardiovascular diseases (Ballatori et al., 2009; Kalinina et al., 2014)

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). ?

measuring oxidative stress

Agents for ROS detection are primarily fluorescence based, but recently luminescent based detections have been introduced. The biggest difficulty reported with much of the cellular ROS research has been with the lack of reporter agents specific for discrete molecules. ROS moieties by their nature are reactive with a number of different molecules; as such designing reporter agents has been difficult. With more specific chemistries, particularly for hydrogen peroxide, the specific mechanisms for regulation will be elucidated.

Reduced glutathione (GSH) is regenerated from its oxidized form (GSSH) by the action of an NADPH dependent reductase GSSH + NADPH + H+ à 2 GSH + NADP+ Due to the rapid nature of the reduction of GSSH relative to its synthesis or secretion, the ratio of GSH to GSSH is a good indicator of oxidative stress within cells. GSH and GSSH levels can be determined by HPLC, capillary electrophoresis, or biochemically in microplates. Several different assays have been designed to measure glutathione in samples. By using a luciferin derivative in conjunction with glutathione S-transferase enzyme the amount of GSH would be proportional to the luminescent signal generated when luciferase is added in a subsequent step. Total glutathione can be determined colorimetrically by reacting GSH with DTNB (Ellman’s reagent) in the presence of glutathione reductase. Glutathione reductase reduces GSSH to GSH, which then reacts with DTNB to produce a yellow colored 5-thio-2-nitrobenzoic acid (TNB), which absorbs at 412 nm.

Lipid peroxidation is one of the most widely used indicators of free radical formation, a key indicator of oxidative stress. Measurement of lipid peroxidation has historically relied on the detection of thiobarbituric acid (TBA) reactive compounds such as malondialdehyde generated from the decomposition of lipid peroxidation products. While this method is controversial in that it is quite sensitive, but not necessarily specific to MDA, it remains the most widely used means to determine lipid peroxidation. This reaction, which takes place under acidic conditions at 90-100ºC, results in an adduct that can be measured colorimetrically at 532 nm or by fluorescence using a 530 nm excitation wavelength and a 550 nm emission wavelength. A number of commercial assay kits are available for this assay using absorbance or fluorescence detection technologies. The formation of F2-like prostanoid derivatives of arachidonic acid, termed F2-isoprostanes (IsoP) has been shown to be specific for lipid peroxidation. Unlike the TBA assay, measurement of IsoP appears to be specific to lipid peroxides, they are stable and are not produced by any enzymatic pathway making interpretation easier. There have been a number of commercial ELISA kits developed for IsoPs, but interfering agents in samples requires partial purification of samples prior to running the assay. The only reliable means for detection is through the use of GC/MS, which makes it expensive and limits throughput.

Superoxide detection is based on the interaction of superoxide with some other compound to create a measurable result. The reduction of ferricytochrome c to ferrocytochrome c has been used in a number of situations to assess the rate of superoxide formation. While not completely specific for superoxide this reaction can be monitored colorimetrically at 550 nm. Chemiluminescent reactions have been used for their potential increase in sensitivity over absorbance-based detection methods. The most widely used chemiluminescent substrate is Lucigenin, but this compound has a propensity for redox cycling, which has raised doubts about its use in determining quantitative rates of superoxide production. Coelenterazine has also been used as a chemiluminescent substrate. Hydrocyanine dyes are fluorogenic sensors for superoxide and hydroxyl radical. These dyes are synthesized by reducing the iminium cation of the cyanine (Cy) dyes with sodium borohydride. While weakly fluorescent, upon oxidation their fluorescence intensity increases 100 fold. In addition to being fluorescent, oxidation also converts the molecule from being membrane permeable to an ionic impermeable moiety. The most characterized of these probes are Hydro-Cy3 and Hydro-Cy5.

Hydrogen peroxide (H2O2) is the most important ROS in regards to mitogenic stimulation or cell cycle regulation. There are a number of fluorogenic substrates, which serve as hydrogen donors that have been used in conjunction with horseradish peroxidase (HRP) enzyme to produce intensely fluorescent products. The more commonly used substrates include diacetyldichloro-fluorescein, homovanillic acid, and Amplex® Red. In these examples, increasing amounts of H2O2 form increasing amounts of fluorescent product.

Nitric Oxide The free radical nitric oxide (•NO) is produced by a number of different cell types with a variety of biological functions. Regardless of the source or role, the free radical •NO has a very short half life (t½= 4 seconds), reacting with several different molecules normally present to form either nitrate (NO3-) or nitrite (NO2-) A commonly used method for the indirect determination of •NO is the determination of its composition products nitrate and nitrite colorimetrically. This reaction requires that nitrate (NO3) first be reduced to nitrite (NO2), typically by the action of nitrate reductase. Subsequent determination of nitrite by a two step process provides information on the “total” of nitrate and nitrite. In the presence of hydrogen ions nitrite forms nitrous acid, which reacts with sulfanilamide to produce a diazonium ion. This then coupled to N-(1-napthyl) ethylenediamine to form the chromophore which absorbs at 543 nm. Nitrite only determinations can then be made in a parallel assay where the samples were not reduced prior to the colorimetric assay. Actual nitrate levels are then calculated by the subtraction of nitrite levels from the total. [4]

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

The concentrations of GSH and GSSG have been shown in tissues of human and laboratory animals, including rats, mice and cows (Chen et al., 2010; Giustarini et al., 2013).

Evidence for Perturbation by Stressor

Overview for Molecular Initiating Event

When a specific MIE can be defined (i.e., the molecular target and nature of interaction is known), in addition to describing the biological state associated with the MIE, how it can be measured, and its taxonomic, life stage, and sex applicability, it is useful to list stressors known to trigger the MIE and provide evidence supporting that initiation. This will often be a list of prototypical compounds demonstrated to interact with the target molecule in the manner detailed in the MIE description to initiate a given pathway (e.g., 2,3,7,8-TCDD as a prototypical AhR agonist; 17α-ethynyl estradiol as a prototypical ER agonist). Depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). Known stressors should be included in the MIE description, but it is not expected to include a comprehensive list. Rather initially, stressors identified will be exemplary and the stressor list will be expanded over time. For more information on MIE, please see pages 32-33 in the User Handbook.

References

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 (https://www.oecd.org/about/publishing/OECD-Style-Guide-Third-Edition.pdf) (OECD, 2015). More help

Ballatori, N., Krance, S.M., Notenboom, S., Shi, S., Tieu, K., and Hammond, C.L. (2009). Glutathione dysregulation and the etiology and progression of human diseases. Biol. Chem. 390, 191–214.

Chen, C.-A., Wang, T.-Y., Varadharaj, S., Reyes, L.A., Hemann, C., Talukder, M.A.H., Chen, Y.-R., Druhan, L.J., and Zweier, J.L. (2010). S-glutathionylation uncouples eNOS and regulates its cellular and vascular function. Nature 468, 1115–1118.

Giustarini, D., Dalle-Donne, I., Milzani, A., Fanti, P., and Rossi, R. (2013). Analysis of GSH and GSSG after derivatization with N-ethylmaleimide. Nat. Protoc. 8, 1660–1669.

Held P., 2010 Biotek, Measurement of ROS in Cells, http://www.biotek.com/assets/tech_resources/ROS%20Application%20Guide.pdf

Kalinina, E.V., Chernov, N.N., and Novichkova, M.D. (2014). Role of glutathione, glutathione transferase, and glutaredoxin in regulation of redox-dependent processes. Biochem. Biokhimii︠a︡ 79, 1562–1583.

Kamencic, H., Lyon, A., Paterson, P.G., and Juurlink, B.H. (2000). Monochlorobimane fluorometric method to measure tissue glutathione. Anal. Biochem. 286, 35–37.

Parola, M. and Robino, G. (2001). Oxidative stress-related molecules and liver fibrosis. J Hepatol. 35, 297-306

Reuter S. et al., (2010) Oxidative stress, inflammation, and cancer: how are they linked? Free Radic Biol Med.49, 1603-1616

Sánchez-Valle V. et al., (2012) Role of oxidative stress and molecular changes in liver fibrosis: a review. Curr Med Chem. 19, 4850-4860

Tipple, T.E., and Rogers, L.K. (2012). Methods for the Determination of Plasma or Tissue Glutathione Levels. Methods Mol. Biol. Clifton NJ 889, 315–324