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Event: 79

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

Inhibition, Cyclooxygenase activity

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
Inhibition, Cyclooxygenase activity

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
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
prostaglandin-endoperoxide synthase activity prostaglandin G/H synthase 1 decreased
prostaglandin-endoperoxide synthase activity prostaglandin G/H synthase 2 decreased

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
Cyclooxygenase inhibition leading reproductive failure MolecularInitiatingEvent Agnes Aggy (send email) Under Development: Contributions and Comments Welcome
Cyclooxygenase inhibition 2 MolecularInitiatingEvent Cataia Ives (send email) Under Development: Contributions and Comments Welcome
Cyclooxygenase inhibition 3 MolecularInitiatingEvent Brendan Ferreri-Hanberry (send email) Under Development: Contributions and Comments Welcome
Cyclooxygenase inhibition 5 MolecularInitiatingEvent Agnes Aggy (send email) Under Development: Contributions and Comments Welcome
Cyclooxygenase inhibition 1 MolecularInitiatingEvent Agnes Aggy (send email) Under Development: Contributions and Comments Welcome
Cyclooxygenase inhibition 4 MolecularInitiatingEvent Arthur Author (send email) Under Development: Contributions and Comments Welcome


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

Prostaglandin-endoperoxide synthase (PTGS; KEGG ID E.C.; [1]) is an enzyme that has two catalytic sites. Cyclooxygenase site (COX) catalyzes conversion of arachidonic acid into endoperoxide prostaglandin G2 (Simmons et al., 2004). Peroxidase active site converts PGG2 to PGH2 (KEGG reactions 1599, 1590, [2]). PGH2 is a precursor for synthesis of other prostaglandins (e.g., PGEs, PGFs; [3]), prostacyclin and thromboxanes (Simmons et al., 2004; Botting and Botting 2011). Two of the COX isoforms (COX-1 and COX-2) encoded by two different genes (ptgs1 and ptgs2) are well characterized. Ptgs1 is typically expressed constitutively and is involved in maintenance of homeostatic functions. Ptgs2 is largely inducible (e.g., by inflammation, during discrete stages of gamete maturation etc.), but can also be constitutively expressed (e.g., kidney; Green et al, 2012). In mammals, COX-3 (a splice of COX-1) has also been identified (Chandrasekharan et al., 2002), but its function is not well characterized and it is not likely to have prostaglandin producing capacity (Bacchi et al., 2012).

Most COX inhibitors interfere with COX site via competitive inhibition (compete for active site with arachidonic acid), but some are capable of covalent modification of COX (Simmons et al., 2004; Willoughby et al., 2011). The inhibition of COX can lead to reduced efficiency of converting arachidonic acid to PGG2. Therefore inhibition of COX can decrease the rate of prostaglandin production (reviewed Simmons et al, 2004; Bacchi et al., 2012).

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). ?

Multiple methods have been developed to investigate inhibition of COX activity - the cyclooxygenase (COX) reaction can be monitored by measurement of oxygen consumption, peroxidase co-substrate oxidation or prostaglandin (PG) detection (e.g., Jang and Pezzuto, 1997; Cuendet et al., 2006). Commercial kits from many suppliers deploying a variety of methods are available for purchase (e.g., Cayman Chemicals, Ann Arbor, MI). Repeatability and reproducibility of these commercial assays is well documented – the data generated by assays is reproducible and interassay variation is typically below 5%. The preparation of fish ovarian tissue for COX activity assay is described by Lister and Van der Kraak (2008).

  • COX1 activity - US EPA ToxCast assay id: NVS_ENZ_oCOX1
  • COX2 activity - US EPA ToxCast assay id: NVS_ENZ_oCOX2

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

There is a high level of conservation of this molecular target (i.e., COX), as well as its function, especially across vertebrates (Havird et al., 2008, 2015), indicating that many vertebrate taxa may be susceptible to COX inhibition. Typically, teleost fish genomes contain more than one COX-1 and/or COX -2 gene, likely a result of genome duplication after divergence of teleosts from tetrapods (e.g., Ishikawa et al., 2007; Havird et al., 2015). In invertebrates, COX is found in most crustaceans, the majority of molluscs, but only in specific taxa/lineages within Cnidaria and Annelida. COX genes are not found in Hemichordata, Echinodermata, or Platyhelminthes. Insecta COX genes lack in homology, but may function as COX enzymes based on structural analyses (Havird et al., 2015).

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.

Non-steroidal anti-inflammatory drugs have been specifically designed to inhibit cyclooxygenase active site of PTGS; these mechanisms of inhibition are well characterized (Simmons et al, 2004). NSAIDs interfere with COX site via multiple mechanisms including competitive inhibition (most NSAIDs compete for active site with arachidonic acid) and covalent modification (irreversible acetylation) of COX (e.g., aspirin) (Simmons et al., 2004; Willoughby et al., 2011). NSAIDs display different levels of selectivity for the COX-1 vs. COX-2 isoforms (Simmons et al., 2004). Majority of NSAIDs inhibit both isoforms (with variable levels of selectivity for COX-1 vs. COX-2), but several have been designed to preferentially inhibit COX-2 (Bacchi et al., 2012). Recently, COX-1 specific inhibitors have been developed and their therapeutic potential is being explored (Liedtke et al., 2012). Most extensive evidence regarding chemical initiation of this event comes from the mammalian literature and relates to NSAIDs.

In addition to NSAIDs, common environmental contaminants of diverse chemical structures and uses (e.g., parabens, phthalates, benzophenones) have been postulated to inhibit prostaglandin synthesis via COX inhibition (Kristensen et al., 2011). U.S. EPA’s high throughput screening program (ACToR, indicated COX as a frequent contaminant target - 61% of 143 tested chemicals inhibited COX-1 and 59% of 106 inhibited COX-2 activity. Several chemicals were either similar in potency (e.g., monobutylphthalate) or more potent than NSAIDs (e.g., insecticide emamectin benzoate and industrial intermediary 1-Chloro-4-nitrobenzene were more potent inhibitors of COX2 than NSAID celecoxib, which was specifically designed to inhibit COX-2). Mechanisms of inhibition for these chemicals are not well elucidated.


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

Bacchi, S., Palumbo, P., Sponta, A., & Coppolino, M. F. (2012). Clinical pharmacology of non-steroidal anti-inflammatory drugs: a review. Anti-Inflammatory & Anti-Allergy Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry-Anti-Inflammatory and Anti-Allergy Agents), 11(1), 52-64.

Botting, R. M., & Botting, J. H. (2011). C14 Non-steroidal anti-inflammatory drugs. In Principles of Immunopharmacology (pp. 573-584). Birkhäuser Basel.

Cao, H., Yu, R., Tao, Y., Nikolic, D., & van Breemen, R. B. (2011). Measurement of cyclooxygenase inhibition using liquid chromatography–tandem mass spectrometry. Journal of pharmaceutical and biomedical analysis, 54(1), 230-235.

Chandrasekharan, N. V., Dai, H., Roos, K. L. T., Evanson, N. K., Tomsik, J., Elton, T. S., & Simmons, D. L. (2002). COX-3, a cyclooxygenase-1 variant inhibited by acetaminophen and other analgesic/antipyretic drugs: cloning, structure, and expression. Proceedings of the National Academy of Sciences,99(21), 13926-13931.

Cuendet, M., Mesecar, A. D., DeWitt, D. L., & Pezzuto, J. M. (2006). An ELISA method to measure inhibition of the COX enzymes. Nature protocols,1(4), 1915-1921. Green, T., Gonzalez, A. A., Mitchell, K. D., & Navar, L. G. (2012). The Complex Interplay between COX-2 and Angiotensin II in Regulating Kidney Function. Current opinion in nephrology and hypertension, 21(1), 7.

Havird, J. C., Kocot, K. M., Brannock, P. M., Cannon, J. T., Waits, D. S., Weese, D. A., ... & Halanych, K. M. (2015). Reconstruction of Cyclooxygenase Evolution in Animals Suggests Variable, Lineage-Specific Duplications, and Homologs with Low Sequence Identity. Journal of molecular evolution, 1-16.

Havird, J. C., Miyamoto, M. M., Choe, K. P., & Evans, D. H. (2008). Gene duplications and losses within the cyclooxygenase family of teleosts and other chordates. Molecular biology and evolution, 25(11), 2349-2359.

Ishikawa, T. O., Griffin, K. J., Banerjee, U., & Herschman, H. R. (2007). The zebrafish genome contains two inducible, functional cyclooxygenase-2 genes.Biochemical and biophysical research communications, 352(1), 181-187.

Jang, M. S., & Pezzuto, J. M. (1997). Assessment of cyclooxygenase inhibitors using in vitro assay systems. Methods in cell science, 19(1), 25-31.

Kristensen, D. M., Skalkam, M. L., Audouze, K., Lesné, L., Desdoits-Lethimonier, C., Frederiksen, H., ... & Leffers, H. (2011). Many putative endocrine disruptors inhibit prostaglandin synthesis. Environmental health perspectives, 119(4), 534-41.

Liedtke, A. J., Crews, B. C., Daniel, C. M., Blobaum, A. L., Kingsley, P. J., Ghebreselasie, K., & Marnett, L. J. (2012). Cyclooxygenase-1-selective inhibitors based on the (E)-2′-des-methyl-sulindac sulfide scaffold. Journal of medicinal chemistry, 55(5), 2287-2300.

Lister, A. L., & Van Der Kraak, G. (2008). An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation. General and comparative endocrinology, 159(1), 46-57.

Simmons, D. L., Botting, R. M., & Hla, T. (2004). Cyclooxygenase isozymes: the biology of prostaglandin synthesis and inhibition. Pharmacological reviews,56(3), 387-437.

Willoughby, D. A., Moore, A. R., & Colville-Nash, P. R. (2000). COX-1, COX-2, and COX-3 and the future treatment of chronic inflammatory disease. The Lancet, 355(9204), 646-648.