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Relationship: 2133

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

Antagonism, Androgen receptor leads to nipple retention, increased

Upstream event

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

Antagonism, Androgen receptor

Downstream event

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

nipple retention, increased

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
Androgen receptor (AR) antagonism leading to nipple retention (NR) in male (mammalian) offspring	non-adjacent	Moderate	Low	Evgeniia Kazymova (send email)	Under development: Not open for comment. Do not cite	Under Development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
Male	High

Life Stage Applicability

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

Term	Evidence
Development	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

Several chemicals can antagonize the androgen receptor (AR) in vitro, resulting in decreased AR activation. Decreased AR activation can lead to incomplete reproductive development in males, which can be expressed in several ways. One endpoint affected is areola/nipple retention (NR), which in vivo studies have shown to be linked to suppressed AR activation. NR in rat and mouse toxicity studies is considered an adverse effect (i.e., an AO).

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

Strategi was described by Pedersen et al (2022): A semi-systematic literature search was conducted during March 2022 in the peer-reviewed databases PubMed and Web of Science, using the search terms “(Nipple) AND (retain* OR retention) AND (androgen)” as well as “(Androgen receptor OR AR) AND (active*) AND (nipple OR areolae) AND (retain* OR retention)”. These searches resulted in 138 papers in total. Upon removal of duplicates, papers were screened according to title, abstract and ultimately full text based on pre-defined inclusion criteria. In vivo studies were included if (i) the study was carried out in mice or rats, (ii) NR in males was investigated as an endpoint, (iii) AR antagonism was the suspected mechanism of action and (iv) anti-androgenic effects of single substance exposures (i.e., not studies on chemical mixtures) were investigated. In vitro studies were included if they contained mechanistic information on AR inhibition by chemical stressors.

Evidence Map 2.0

ID	Experimental Design	Species	Upstream Observation	Downstream Observation	Citation (first author, year)	Notes

Evidence Map

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

Title	First Author	Biological Plausibility	Dose Concordance	Temporal Concordance	Incidence Concordance

Biological Plausibility

Dose Concordance Evidence

Temporal Concordance Evidence

Incidence Concordance Evidence

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

A major challenge with NR as a biomarker is the subjectivity of the measure. In juvenile rat pups, nipples are only present as areolae, i.e., dark shadows with or without a nipple bud. This means that the experience of the personnel assessing the presence and number of areolae/nipples can influence the results. Furthermore, the results are likely prone to larger variation if several assessors are used to record NR within the same study. To minimize these sources of uncertainty, assessors must be trained to recognize areolae and not look for fully developed nipples. Moreover, the number of assessors should be limited to one or two, and they should always be blinded to exposure groups.

Another factor that may affect NR results is the age of the rat pups at the time of assessment. OECD guidelines have standardized the time for measuring occurrence of NR to be optimal at PD 12 or 13, when they are visible in female littermates (OECD, 2013). However, assessment of permanent NR is not included in any international guidelines. Hence, if NR is measured in older offspring, the time of measurement is not consistent between studies and varies between PD 20 and PD 100. Thus, conclusions on whether NR is permanent or not may differ based on study design. This distinction between a transient and a permanent effect is important from a regulatory perspective, since only a permanent effect will be categorized as a malformation according to OECD guidance document 43 (OECD, 2008).

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

The quantitative understanding of the relationship between decreased AR activity and NR is challenged by the fact that the potency of AR antagonism in vitro is not proportional to the magnitude of NR observed in vivo (Gray et al., 2019). Hence, predicting in vivo effects based on in vitro data is not possible. However, in vitro studies can give indications of which chemicals might exhibit anti-androgenic effects in vivo and should be subject to further testing (Hass et al., 2012). Development of more representative in vitro models is necessary if in vivo tests are to be phased out entirely.

Response-response Relationship

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

No response-response relationship has been identified.

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

NR manifest in juvenile male rat pup offspring in response to reduced androgen signaling, e.g. resulting from exposure to an anti-androgenic chemical stressor during fetal development. Developmental sensitivity during fetal development is highest during the so-called male masculinization programming window (MPW) which in rats is between gestational day (GD) 15 and 19 (Welsh et al., 2008).

A study in which pregnant rat dams were exposed to the AR antagonist vinclozolin for two-day periods during gestation showed that GD 16–17 was the most sensitive period for increased NR in male offspring (Wolf et al., 2000). A similar study using di-n-butyl phthalate (reduces testosterone levels) also showed that GD 16–17 was the most sensitive period for increased NR in male rats (Carruthers & Foster, 2005). However, to determine if other chemical stressors also have the highest antagonistic potential towards the AR during GD 16-17, further studies with a similar design would be informative.

NR can only be recorded when pups are old enough to display them, yet before excessive fur has developed. Hence, the most accurate results can be obtained from assessing the number of nipples on PD 12–14 depending on rat strain and the time of female littermates displaying nipples (OECD, 2013).

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

No feedback loops that could influence the KER have been identified.

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