API

Aop: 163

AOP Title

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PPARgamma activation leading to sarcomas in rats, mice, and hamsters

Short name:

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PPARgamma-related sarcomas

Authors

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Cancer AOP Workgroup. National Health and Environmental Effects Research Laboratory, Office of Research and Development, Integrated Systems Toxicology Division, US Environmental Protection Agency, Research Triangle Park, NC. Corresponding author for wiki entry (wood.charles@epa.gov)

Point of Contact

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Charles Wood

Contributors

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  • Charles Wood

Status

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Author status OECD status OECD project SAAOP status
Under development: Not open for comment. Do not cite Under Development 1.29 Included in OECD Work Plan


This AOP was last modified on December 03, 2016 16:37

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Revision dates for related pages

Page Revision Date/Time
Activation of specific nuclear receptors, PPAR-gamma activation September 16, 2017 10:17
Increased, adipogenesis September 16, 2017 10:17
Increased, secretion of local growth factors September 16, 2017 10:17
Increased, proliferation of mesenchymal cells September 16, 2017 10:17
Increased, IGF-1 (mouse) September 16, 2017 10:17
Increased, Firbrosarcoma September 16, 2017 10:17
Increased, liposarcoma September 16, 2017 10:17
Increased, hemagiosarcoma September 16, 2017 10:17
Activation of specific nuclear receptors, PPAR-gamma activation leads to Increased, adipogenesis December 03, 2016 16:38
Activation of specific nuclear receptors, PPAR-gamma activation leads to Increased, secretion of local growth factors December 03, 2016 16:38
Increased, adipogenesis leads to Increased, secretion of local growth factors December 03, 2016 16:38
Increased, secretion of local growth factors leads to Increased, proliferation of mesenchymal cells December 03, 2016 16:38
Increased, secretion of local growth factors leads to Increased, IGF-1 (mouse) December 03, 2016 16:38
Increased, proliferation of mesenchymal cells leads to Increased, Firbrosarcoma December 03, 2016 16:38
Increased, proliferation of mesenchymal cells leads to Increased, liposarcoma December 03, 2016 16:38
Increased, proliferation of mesenchymal cells leads to Increased, hemagiosarcoma December 03, 2016 16:38
Troglitazone November 29, 2016 18:42

Abstract

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This putative adverse outcome pathway (AOP) outlines potential key events leading to a tumor outcome in standard carcinogenicity models. This information is based largely on modes of action described previously in cited literature sources and is intended as a resource template for AOP development and data organization. Presentation in this Wiki does not indicate EPA acceptance of a particular pathway for a given reference agent, only that the information has been proposed in some manner. In addition, this putative AOP relates to the model species indicated and does not directly address issues of human relevance.



Background (optional)

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This optional section should be used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development. The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below.

Instructions

To add background information, click Edit in the upper right hand menu on the AOP page. Under the “Background (optional)” field, a text editable form provides ability to edit the Background.  Clicking ‘Update AOP’ will update these fields.


Summary of the AOP

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Stressors

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Name Evidence Term
Troglitazone

Molecular Initiating Event

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Title Short name
Activation of specific nuclear receptors, PPAR-gamma activation Activation of specific nuclear receptors, PPAR-gamma activation

Key Events

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Title Short name
Increased, adipogenesis Increased, adipogenesis
Increased, secretion of local growth factors Increased, secretion of local growth factors
Increased, proliferation of mesenchymal cells Increased, proliferation of mesenchymal cells
Increased, IGF-1 (mouse) Increased, IGF-1 (mouse)
Increased, Firbrosarcoma Increased, Firbrosarcoma
Increased, liposarcoma Increased, liposarcoma
Increased, hemagiosarcoma Increased, hemagiosarcoma

Adverse Outcome

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A key criterion of defining the terminal end of an AOP is that it represents an outcome that is considered relevant to regulatory decision-making (i.e., it corresponds to an accepted protection goal or common apical endpoint in an established regulatory guideline study). For example in humans, this may constitute increased risk of disease in a particular organ or organ system in an individual or in either the entire or a specified subset of the population. In wildlife, this will most often be an outcome of demographic significance that has meaning in terms of estimates of population sustainability. Given this consideration, in addition to describing the biological state associated with the AO, how it can be measured, and its taxonomic applicability, it is useful to describe the established regulatory relevance of the AO.

Instructions

To add an adverse outcome to an AOP page, under Summary of the AOP, click ‘add adverse outcome.’ User will be brought to a new page entitled ‘Add Event to AOP.’ Entering text into the Title field will bring a drop-down list of already existing KE’s. If the user wishes to create a new AO that doesn’t already exist, they should type in the name of the AO without selecting a choice from the drop down menu. User should fill Title, Short name, Biological organization fields and click ‘Create Adverse outcome.’


Relationships Between Two Key Events (Including MIEs and AOs)

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Network View

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Life Stage Applicability

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Is the AOP specific to certain tissues, life stages / age classes? Indicate if there are critical life stages, where exposure must occur, to results in the final adverse effect. Or specify if there are key events along the pathway which are dependent on the life stage although the AOP is known to be initiated regardless of life stage. Indicate also if the AOP is associated also with age- or sex-dependence.

Instructions

To add a life stage term to an AOP page, under “Life Stage Applicability” select ‘add life stage term.’ User will be directed to a page entitled “Add Life Stage to AOP.” This page will list the AOP name, with drop down menu options to select a Life Stage term and Evidence. Evidence can be left blank and added later.

To edit a life stage term on an AOP page, under “Life Stage Applicability” click ‘Edit.’  User will be directed to a page entitled “Editing AOP Life Stage” where they can edit the Evidence field using the drop down menu. Clicking ‘Update Aop life stage’ will update the Evidence field and redirect the user back to the AOP page.


Taxonomic Applicability

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Term Scientific Term Evidence Link
Rattus rattus Rattus rattus Strong NCBI
mouse Mus musculus Moderate NCBI

Sex Applicability

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Graphical Representation

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Click to download graphical representation template

Overall Assessment of the AOP

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This section addresses the relevant domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and weight of evidence for the overall hypothesised AOP (i.e., including the MIE, KEs and AO) as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). It draws upon the evidence assembled for each KER as one of several components which contribute to relative confidence in supporting information for the entire hypothesised pathway. An important component in assessing confidence in supporting information as a basis to consider regulatory application of AOPs beyond that described in Section 6 is the essentiality of each of the key events as a component of the entire pathway. This is normally investigated in specifically-designed stop/reversibility studies or knockout models (i.e., those where a key event can be blocked or prevented). Assessment of the overall AOP also contributes to the identification of KEs for which confidence in the quantitative relationship with the AO is greatest (i.e., to facilitate determining the most sensitive predictor of the AO).

Instructions

To edit the “Overall Assessment of the AOP” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Overall Assessment of the AOP” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Overall Assessment of the AOP” section on the AOP page.

Domain of Applicability

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The relevant domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context are defined in this section. Domain of applicability is informed by the “Description” and “Taxonomic Relevance” section of each KE description and the “Description of the KER” section of each KER description. The relevant domain of applicability of the AOP as a whole will most often be defined based on the most narrowly restricted of its KEs. For example, if most of the KEs apply to either sex, but one is relevant to females only, the domain of applicability of the AOP as a whole would generally be limited to females. While much of the detail defining the domain of applicability may be found in the individual KE descriptions, the rationale for defining the relevant domain of applicability of the overall AOP should be briefly summarised on the AOP page.

Instructions

To edit the “Domain of Applicability” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Domain of Applicability” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Domain of Applicability” section on the AOP page.


Essentiality of the Key Events

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The essentiality of various of the KEs is influential in considering confidence in an overall hypothesised AOP for potential regulatory application being secondary only to biological plausibility of KERs (Meek et al., 2014; 2014a). The defining question for determining essentiality (included in Annex 1) relates to whether or not downstream KEs and/or the AO is prevented if an upstream event is experimentally blocked. It is assessed, generally, then, on the basis of direct experimental evidence of the absence/reduction of downstream KEs when an upstream KE is blocked or diminished (e.g., in null animal models or reversibility studies). Weight of evidence for essentiality of KEs would be considered high if there is direct evidence from specifically designed experimental studies illustrating essentiality for at least one of the important key events [e.g., stop/reversibility studies, antagonism, knock out models, etc.) moderate if there is indirect 25 evidence that experimentally induced change of an expected modulating factor attenuates or augments a key event (e.g., augmentation of proliferative response (KEupstream) leading to increase in tumour formation (KEdownstream or AO)) and weak if there is no or contradictory experimental evidence of the essentiality of any of the KEs (Annex 1).

Instructions

To edit the “Essentiality of the Key Events” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Essentiality of the Key Events” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Essentiality of the Key Events” section on the AOP page.


Weight of Evidence Summary

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This involves evaluation of the Overall AOP based on Relative Level of Confidence in the KERs, Essentiality of the KEs and Degree of Quantitative Understanding based on Annexes 1 and 2. Annex 1 (“Guidance for assessing relative level of confidence in the Overall AOP”) guides consideration of the weight of evidence or degree of confidence in the predictive relationship between pairs of KEs based on KER descriptions and support for essentiality of KEs. It is designed to facilitate assignment of categories of high, moderate or low against specific considerations for each a series of defined element based on current experience in assessing MOAs/AOPs. In addition to increasing consistency through delineation of defining questions for the elements and the nature of evidence associated with assignment to each of the categories, importantly, the objective of completion of Annex 1 is to transparently delineate the rationales for the assignment based on the specified considerations. While it is not necessary to repeat lengthy text which appears in earlier parts of the document, the entries for the rationales should explicitly express the reasoning for assignment to the categories, based on the considerations for high, moderate or low weight of evidence included in the columns for each of the relevant elements. 24 While the elements can be addressed separately for each of the KERs, the essentiality of the KEs within the AOP is considered collectively since their interdependence is often illustrated through prevention or augmentation of an earlier or later key event. Where it is not possible to experimentally assess the essentiality of the KEs within the AOP (i.e., there is no experimental model to prevent or augment the key events in the pathway), this should be noted. Identified limitations of the database to address the biological plausibility of the KERs, the essentiality of the KEs and empirical support for the KERs are influential in assigning the categories for degree of confidence (i.e., high, moderate or low). Consideration of the confidence in the overall AOP is based, then, on the extent of available experimental data on the essentiality of KEs and the collective consideration of the qualitative weight of evidence for each of the KERs, in the context of their interdependence leading to adverse effect in the overall AOP. Assessment of the overall AOP is summarized in the Network View, which represents the degree of confidence in the weight of evidence both for the rank ordered elements of essentiality of the key events and biological plausibility and empirical support for the interrelationships between KEs. The AOP-Wiki provides such a network graphic based on the information provided in the MIE, KE, AO, and KER tables. The Key Event Essentiality calls are used to determine the size of each key event node with larger sizes representing higher confidence for essentiality. The Weight of Evidence summary in the KER table is used to determine the width of the lines connecting the key events with thicker lines representing higher confidence.

Instructions

To edit the “Weight of Evidence Summary” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Weight of Evidence Summary”  section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Weight of Evidence Summary” section on the AOP page.


Quantitative Considerations

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The extent of quantitative understanding of the various KERs in the overall hypothesised AOP is also critical in consideration of potential regulatory application. For some applications (e.g. doseresponse analysis in in depth risk assessment), quantitative characterisation of downstream KERs may be essential while for others, quantitative understanding of upstream KERs may be important (e.g., QSAR modelling for category formation for testing). Because evidence that contributes to quantitative understanding of the KER is generally not mutually exclusive with the empirical support for the KER, evidence that contributes to quantitative understanding should generally be considered as part of the evaluation of the weight of evidence supporting the KER (see Annex 1, footnote b). General guidance on the degree of quantitative understanding that would be characterised as weak, moderate, or strong is provided in Annex 2.

Instructions

To edit the “Quantitative Considerations” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Quantitative Considerations” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Quantitative Considerations” section on the AOP page.


Considerations for Potential Applications of the AOP (optional)

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At their discretion, the developer may include in this section discussion of the potential applications of an AOP to support regulatory decision-making. This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. While it is challenging to foresee all potential regulatory application of AOPs and any application will ultimately lie within the purview of regulatory agencies, potential applications may be apparent as the AOP is being developed, particularly if it was initiated with a particular application in mind. This optional section is intended to provide the developer with an opportunity to suggest potential regulatory applications and describe his or her rationale. Detailing such considerations can aid the process of transforming narrative descriptions of AOPs into practical tools. In this context, it is necessarily beneficial to involve members of the regulatory risk assessment community on the development and assessment team. The Network view which is generated based on assessment of weight of evidence/degree of confidence in the hypothesized AOP taking into account the elements described in Section 7 provides a useful summary of relevant information as a basis to consider appropriate application in a regulatory context. Consideration of application needs then, to take into consideration the following rank ordered qualitative elements: Confidence in biological plausibility for each of the KERs Confidence in essentiality of the KEs Empirical support for each of the KERs and overall AOP The extent of weight of evidence/confidence in both these qualitative elements and that of the quantitative understanding for each of the KERs (e.g., is the MIE known, is quantitative understanding restricted to early or late key events) is also critical in determining appropriate application. For example, if the confidence and quantitative understanding of each KER in a hypothesised AOP are low and or low/moderate and the evidence for essentiality of KEs weak (Section 7), it might be considered as appropriate only for applications with less potential for impact (e.g., prioritisation, category formation for testing) versus those that have immediate implications potentially for risk management (e.g., in depth assessment). If confidence in quantitative understanding of late key events is high, this might be sufficient for an in depth assessment. The analysis supporting the Network view is also essential in identifying critical data gaps based on envisaged regulatory application.

Instructions

To edit the “Considerations for Potential Applications of the AOP” section, on an AOP page, in the upper right hand menu, click ‘Edit.’ This brings you to a page entitled, “Editing AOP.” Scroll down to the “Considerations for Potential Applications of the AOP” section, where a text entry box allows you to submit text. In the upper right hand menu, click ‘Update AOP’ to save your changes and return to the AOP page.  The new text should appear under the “Considerations for Potential Applications of the AOP” section on the AOP page.


References

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1. Cohen, S. M. (2005). Effects of PPARgamma and combined agonists on the urinary tract of rats and other species. Toxicological sciences : an official journal of the Society of Toxicology 87(2), 322-7, 10.1093/toxsci/kfi266.

2. Hardisty, J. F., Elwell, M. R., Ernst, H., Greaves, P., Kolenda-Roberts, H., Malarkey, D. E., Mann, P. C., and Tellier, P. A. (2007). Histopathology of hemangiosarcomas in mice and hamsters and liposarcomas/fibrosarcomas in rats associated with PPAR agonists. Toxicologic pathology 35(7), 928-41, 10.1080/01926230701748156.

3. Kakiuchi-Kiyota, S., Arnold, L. L., Yokohira, M., Koza-Taylor, P., Suzuki, S., Varney, M., Pennington, K. L., and Cohen, S. M. (2011a). Evaluation of direct and indirect effects of the PPARgamma agonist troglitazone on mouse endothelial cell proliferation. Toxicologic pathology 39(7), 1032-45, 10.1177/0192623311422080.

4. Kakiuchi-Kiyota, S., Arnold, L. L., Yokohira, M., Suzuki, S., Pennington, K. L., and Cohen, S. M. (2011b). Evaluation of PPARgamma agonists on rodent endothelial cell proliferation. Toxicology 287(1-3), 91-8, 10.1016/j.tox.2011.05.019.

5. Long, G. G., Reynolds, V. L., Dochterman, L. W., and Ryan, T. E. (2009). Neoplastic and non-neoplastic changes in F-344 rats treated with Naveglitazar, a gamma-dominant PPAR alpha/gamma agonist. Toxicologic pathology 37(6), 741-53, 10.1177/0192623309343775.