To the extent possible under law, AOP-Wiki has waived all copyright and related or neighboring rights to KER:773

Relationship: 773

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

Increase, cell proliferation (hepatocytes) leads to Increase, Preneoplastic foci (hepatocytes)

Upstream event
The causing Key Event (KE) in a Key Event Relationship (KER). More help
Downstream event
The responding Key Event (KE) in a Key Event Relationship (KER). More help

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
Constitutive androstane receptor activation leading to hepatocellular adenomas and carcinomas in the mouse and the rat adjacent High Moderate Brendan Ferreri-Hanberry (send email) Open for citation & comment EAGMST Under Review
Androgen receptor activation leading to hepatocellular adenomas and carcinomas (in mouse and rat) adjacent Evgeniia Kazymova (send email) Open for adoption 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
rat Rattus norvegicus High NCBI
mouse Mus musculus High NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help
Sex Evidence
Mixed High

Life Stage Applicability

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

Based on altered gene expression under the influence of CAR activation, an increase in cell proliferation of hepatocytes leads to a greater chance of normal, spontaneous errors in DNA replication and thus a higher proportion of altered hepatocytes. The hepatocytes with abnormal DNA can exhibit cell-cell communication differences from normal hepatocytes, and experience greater cell division even in the presence of contact inhibition with other hepatocytes. The islands of more actively dividing hepatocytes can be detected via histology based both on the larger numbers of cells (hyperplasia) and possibly a characteristic staining property of the clonally expanded cells (foci of cellular alteration – either eosinophilic, basophilic or clear cell). Thus, a higher rate of proliferation in the rodent liver leads to greater prevalence of altered hepatocytes, which clonally expand to generate an increase in preneoplastic foci.

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

The increased cell replication rate in the liver due to CAR activation (i.e. via a mitogenic signaling) is similar to other well-understood modes of action where an increase in cell proliferation leads to an eventual increase in preneoplastic foci, such as PPARα activating ligands and AhR activating ligands, which also lead to an increase in preneoplastic foci via clonal expansion of transformed hepatocytes.  In mice lacking the CAR receptor, including initiation-promotion assays, the upstream events (e.g. CAR activation, altered gene expression, and increased cell proliferation) and the downstream events (e.g. preneoplastic foci) are all blocked, providing strong support for the biological plausibility of this Key Event Relationship (Huang et al., 2005; Tamura et al., 2015; Tamura et al., 2013; Yamamoto et al., 2004).

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 incidence of altered foci, and their histological staining properties (e.g. eosinophilic, basophilic, clear cell, mixed) are not always reported in published studies of carcinogenicity with CAR activating compounds. In addition, the timing of interim or final sacrifices and histopathology data may possibly miss a window of time (for certain molecules) where the increase in preneoplastic foci can be quantified. However, the consistent findings with well-known CAR activating compounds and their absence in CAR knockout mouse studies provide a strong basis for their existence in the CAR AOP.

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
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

Studies in various species, or in isolated hepatocytes from various mammalian species including humans, have demonstrated that CAR activators such as phenobarbital or metofluthrin produce a cell proliferation response that is seen in mice or rats, but not in hamsters, guinea pigs or humans (Hasmall and Roberts, 1999; Hirose et al., 2009; James and Roberts, 1996; Yamada et al., 2014; Yamada et al., 2009).   Accordingly, phenobarbital and other CAR activators do not produce liver tumors in long term studies in hamsters (Diwan et al., 1986; Elcombe et al., 2014). Consistent with the lack of effects on proliferation, Diwan et al. (1986) also reported that in Syrian hamsters, phenobarbital treatment at 500 ppm in the drinking water did not produce any increases in preneoplastic foci of cellular alteration compared to groups that received an initiator alone. Therefore, this key event of increased foci in the liver has strong data indicating it is specific to mice and rats, the species which also develop hepatocellular tumors in response to known CAR activators.

References

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

[see reference list at end of this AOP; it includes all cited references]