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Created at: 2020-08-14 12:40

AOP ID and Title:

AOP 25: Aromatase inhibition leading to reproductive dysfunction
Short Title: Aromatase inhibition leading to reproductive dysfunction

Graphical Representation

Authors

Dan Villeneuve, US EPA Mid-Continent Ecology Division (villeneuve.dan@epa.gov)


Status

Author status OECD status OECD project SAAOP status
Open for citation & comment TFHA/WNT Endorsed 1.12 Included in OECD Work Plan

Abstract

This adverse outcome pathway details the linkage between inhibition of gonadal aromatase activity in females and reproductive dysfunction, as measured through the adverse effect of reduced cumulative fecundity and spawning. Initial development of this AOP draws heavily on evidence collected using repeat-spawning fish species. Cumulative fecundity is the most apical endpoint considered in the OECD 229 Fish Short Term Reproduction Assay. The OECD 229 assay serves as screening assay for endocrine disruption and associated reproductive impairment (OECD 2012). Cumulative fecundity is one of several variables known to be of demographic significance in forecasting fish population trends. Therefore, this AOP has utility in supporting the application of measures of aromatase, or in silico predictions of the ability to inhibit aromatase, as a means to identify chemicals with known potential to adversely affect fish populations and potentially other oviparous vertebrates.



Summary of the AOP

Events

Molecular Initiating Events (MIE), Key Events (KE), Adverse Outcomes (AO)

Sequence Type Event ID Title Short name
1 MIE 36 Inhibition, Aromatase Inhibition, Aromatase
2 KE 219 Reduction, Plasma 17beta-estradiol concentrations Reduction, Plasma 17beta-estradiol concentrations
3 KE 285 Reduction, Vitellogenin synthesis in liver Reduction, Vitellogenin synthesis in liver
4 KE 309 Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development
5 KE 3 Reduction, 17beta-estradiol synthesis by ovarian granulosa cells Reduction, 17beta-estradiol synthesis by ovarian granulosa cells
6 KE 78 Reduction, Cumulative fecundity and spawning Reduction, Cumulative fecundity and spawning
7 KE 221 Reduction, Plasma vitellogenin concentrations Reduction, Plasma vitellogenin concentrations
8 AO 360 Decrease, Population trajectory Decrease, Population trajectory

Key Event Relationships

Upstream Event Relationship Type Downstream Event Evidence Quantitative Understanding
Inhibition, Aromatase adjacent Reduction, 17beta-estradiol synthesis by ovarian granulosa cells High Moderate
Reduction, 17beta-estradiol synthesis by ovarian granulosa cells adjacent Reduction, Plasma 17beta-estradiol concentrations High Moderate
Reduction, Plasma 17beta-estradiol concentrations adjacent Reduction, Vitellogenin synthesis in liver High Moderate
Reduction, Cumulative fecundity and spawning adjacent Decrease, Population trajectory Moderate Moderate
Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development adjacent Reduction, Cumulative fecundity and spawning Moderate Moderate
Reduction, Plasma vitellogenin concentrations adjacent Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development Moderate Low
Reduction, Vitellogenin synthesis in liver adjacent Reduction, Plasma vitellogenin concentrations High Moderate
Reduction, Plasma 17beta-estradiol concentrations non-adjacent Reduction, Plasma vitellogenin concentrations High Moderate

Overall Assessment of the AOP

Domain of Applicability

Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature
Taxonomic Applicability
Term Scientific Term Evidence Links
medaka Oryzias latipes Moderate NCBI
zebrafish Danio rerio Moderate NCBI
fathead minnow Pimephales promelas High NCBI
Sex Applicability
Sex Evidence
Female High
  • Sex: The AOP applies to females only. Males have relatively low gonadal aromatase expression and activity and the androgen 11-KT, rather than the estrogen E2 is a stronger driver of reproductive functions in males. That said, at least in fish, there is a potential autocrine and paracrine for estrogens synthesized in the brain in regulating reproductive behaviors. However, those potential effects are addressed through an alternative AOP that shares the MIE of aromatase inhibition.
  • Life stages: The relevant life stages for this AOP are reproductively mature adults. This AOP does not apply to adult stages that lack a sexually mature ovary, for example as a result of seasonal or environmentally-induced gonadal senescence (i.e., through control of temperature, photo-period, etc. in a laboratory setting).
  • Taxonomic: At present, the assumed taxonomic applicability domain of this AOP is class Osteichthyes. In all likelihood, the AOP will also prove applicable to all classes of fish (e.g., Agnatha and Chondrithyes as well). Additionally, all the key events described should be conserved among all oviparous vertebrates, suggesting that the AOP may also have relevance for amphibians, reptiles, and birds. However, species-specific differences in reproductive strategies/life histories, ADME (adsorption, distribution, metabolism, and elimination), compensatory reproductive endocrine responses may influence the outcomes, particularly from a quantitative standpoint.

Essentiality of the Key Events

Support for the essentiality of a number of key events in the AOP was provided by several time-course, stop-reversibility, experiments with fathead minnows exposed to aromatase inhibitors.

1. Villeneuve et al. 2009 and 2013 examined a time-course of key event responses to fadrozole as well as the time-course of recovery following cessation of fadrozole delivery. Once fadrozole was removed from the system, ex vivo E2 production increased, followed by increases in plasma E2 concentrations, and then increases in plasma vitellogenin concentrations. Additionally, while exposure to the chemical was on-going, compensatory up-regulation of CYP19a1a gene expression resulted in increases in ex vivo E2 production, followed by increased plasma E2 and plasma VTG. The essentiality of aromatase inhibition relative to impaired E2 production was further supported by the observation of an "overshoot" in E2 production, relative to controls, shortly after cessation of fadrozole delivery.

2. Similar support was provided in a study by Ankley et al. (2009a). Cessation of prochloraz delivery resulted in rapid recovery of ex vivo E2 production and plasma E2 concentrations, with recovery of vitellogenin concentrations lagging slightly behind. Increased expression of cyp19a1a mRNA during the exposure period aligned with increased ex vivo E2 production, and increased plasma E2, compared to the first day of exposure.


Rationale for essentiality calls:

• Aromatase, inhibition: [Strong] There is good evidence from stop/reversibility studies that ceasing delivery of the aromatase inhibitor leads to recovery of the subsequent key events.

• 17beta-estradiol synthesis by ovarian granulosa cells, reduction: [Strong] In both exposure studies and stop/reversibility studies, when ex vivo E2 production (as measure of this KE) recovers either through compensation or due to removal of the stressor, subsequent KEs have been shown to recover after a lag period.

• plasma 17beta-estradiol concentrations, reduction: [Strong] In both exposure studies and stop/reversibility studies, when plasma E2 concentrations recover either through compensation or due to removal of the stressor, subsequent KEs have been shown to recover after a lag period.

• vitellogenin production in liver (transcription, translation), reduction: [Moderate] This endpoint was not specifically examined in stop/reversibility studies with aromatase inhibitors, but biological plausibility provides strong support for the essentiality of this event.

• plasma vitellogenin concentrations, reduction: [Strong] Shown to recover in a predictable fashion consistent with the order of events in the AOP in stop/recovery studies.

• vitellogenin accumulation into oocytes and oocyte growth/development, reduction: [Weak] Some contradictory evidence regarding the essentiality of this event. No stop/reversibility studies have explicitly considered this key event.

• cumulative fecundity and spawning, reductions: [Moderate] By definition, some degree of spawning is required to maintain population.

Weight of Evidence Summary

Biological plausibility: Biological plausibility refers to the structural or functional relationship between the key events based on our fundamental understanding of "normal biology". In general, the biological plausibility and coherence linking aromatase inhibition through decreases in circulating concentrations of E2 is very solid. The biochemistry of steroidogenesis and the predominant role of the gonad in synthesis of the sex steroids is well established. Similarly, the role of E2 as the major regulator of hepatic vitellogenin production is widely documented in the literature. The direct link between reduced VTG concentrations in the plasma and reduced uptake into oocytes is highly plausible, as the plasma is the primary source of the VTG. However, the direct connection between reduced VTG uptake and impaired spawning/reduced cumulative fecundity is more tentative. It is not clear, for instance whether impaired VTG uptake limits oocyte growth and failure to reach a critical size in turn impairs physical or inter-cellular signaling processes that promote release of the oocyte from the surrounding follicles. In at least one experiment, oocytes with similar size to vitellogenic oocytes, but lacking histological staining characteristic of vitellogenic oocytes was observed (R. Johnson, personal communication). Regulation of oocyte maturation and spawning involves many factors other than vitellogenin accumulation (Clelland and Peng, 2009). At present, the link between reductions in circulating VTG concentrations and reduced cumulative fecundity are best supported by the correlation between those endpoints across multiple experiments, including those that impact VTG via other molecular initiating events (Miller et al. 2007).

 

Concordance of dose-response relationships: Dose response concordance considers the degree to which upstream events are shown to occur at test concentrations equal to or lower than those that cause significant effects on downstream key events, the underlying assumption being that all KEs can be measured with equal precision. There are a limited number of studies in which multiple key events were considered in the same study. These were considered the most useful for evaluating the concordance of dose-response relationships. In general, effects on downstream key events occurred at concentrations equal to or greater than those at which upstream events occurred (Concordance table: [1]). However, there are exceptions. There are cases where no significant effects on estradiol synthesis by ovarian granulosa cells (ovary explants) were observed, but significant effects on plasma E2 or VTG concentrations were observed. Likewise, there are cases where impacts on plasma VTG were observed at concentrations lower than those reported to reduce plasma E2 concentrations. Based on knowledge of the studies in question, the apparent lack of concordance in some cases is driven by two primary factors. First, differences in the sensitivity and dynamic range of the measurements being made. Second, the effects of compensatory responses along the HPG axis. For instance, although ex vivo E2 production is rapidly affected by exposure to fadrozole, it is also a response that is more rapidly corrected through upregulation of aromatase transcripts (see Villeneuve et al. 2009), meaning that it recovers more quickly than plasma concentrations of E2 or plasma VTG concentrations. Thus, at certain time points, one can get an apparent effect on plasma E2 or T without a measurable impact on E2 production by the gonad tissue, because the upstream insult occurred earlier in time and was subsequently offset by a compensatory response, but the compensation has yet to propagate through the pathway. Sensitivity and dynamic range of the measurement methods is also an issue. Vitellogenin concentrations have a highly dynamic range and can change by orders of magnitude. Other endpoints like plasma steroids are regulated in a narrower range, making differences more difficult to distinguish statistically. Therefore, in our assessment, the deviations from concordance do not call the KERs into question.

 

The concentration-dependence of the key event responses with regard to the concentration of aromatase inhibitor has been established in vitro and/or in vivo for nearly all key events in the AOP.

  1. Concentration-dependent aromatase inhibition: (Villeneuve et al. 2006; Ankley et al. 2005; M et al. 2004; AM et al. 2000; Shilling et al. 1999)
  2. Concentration-dependent decreases in E2 production in vitro, ex vivo: (Ankley et al. 2002; Villeneuve et al. 2007; Villeneuve et al. 2009; Ankley et al. 2005; a Marca Pereira et al. 2011; Lee et al. 2006).
  3. Concentration-dependent decreases in circulating E2 concentrations: (Ankley et al. 2002; Villeneuve et al. 2009; Ankley et al. 2005; Ankley et al. 2009a; GT et al. 2001)
  4. Concentration-dependent decreases in vitellogenin mRNA expression: (Sun et al. 2010; Sun et al. 2011; Zhang et al. 2008)
  5. Concentration-dependent decreases in circulating vitellogenin concentrations: (Ankley et al. 2002; Villeneuve et al. 2009; Ankley et al. 2005; Ankley et al. 2009a; Sun et al. 2007; GT et al. 2001; Ralston-Hooper et al. 2013)
  6. Concentration-dependent reductions in VTG uptake into oocytes or impaired oocyte development: Concentration-dependence of these effects has not been well demonstrated. The effects, when seen, have typically been documented at the greatest exposure concentration tested, but concentration-dependence of the severity or frequency of the impact was not documented (e.g., (Ankley et al. 2002; Ankley et al. 2005; Sun et al. 2007)
  7. Concentration-dependent reductions in cumulative fecundity: (Ankley et al. 2002; Ankley et al. 2005; Sun et al. 2007; Zhang et al. 2008)
  8. Declining population trajectory: Modeled population trajectories show a concentration-dependent reduction in projected population size, however, those results are driven by the concentration-dependence of cumulative fecundity. Population-level effects have not been measured directly.


Temporal concordance: Temporal concordance refers to the degree to which the data support the hypothesized sequence of the key events; i.e., the effect on KE1 is observed before the effect on KE2, which is observed before the effect on KE3 and so on. Temporal concordance of the AOP from aromatase inhibition to decreased E2 production, decreased circulating E2, and decreased plasma VTG concentrations has been established (e.g., (Villeneuve et al. 2009; Ankley et al. 2009a; Skolness et al. 2011). Temporal concordance has not been established beyond that key event, in large part due to disconnect in the time-scales over which the events can be measured. For example, most small fish used in reproductive toxicity testing will can spawn anywhere from once daily to several days per week. Given the variability in daily spawning rates, it is neither practical nor effective to evaluate cumulative fecundity at a time scale shorter than roughly a week. Since the impacts at lower levels of biological organization can be detected within hours of exposure, lack of impact on cumulative fecundity before the other key events are impacted cannot be effectively measured. Overall, among those key events whose temporal concordance can reasonably be evaluated, the temporal profile observed is consistent with the AOP.

Consistency: We are aware of no cases where the pattern of key events described was observed without also observing a significant impact on cumulative fecundity. The final adverse outcome is not specific to this AOP. Many of the key events included in this AOP overlap with AOPs linking other molecular initiating events to reproductive dysfunction in small fish.

Uncertainties, inconsistencies, and data gaps: The current major uncertainty in this AOP is whether there is a direct biological linkage between impaired VTG uptake into oocytes and impaired spawning/reduced cumulative fecundity. Plausible biological connections have been hypothesized, but have not yet been tested experimentally.

Quantitative Consideration

Assessment of quantitative understanding of the AOP:

At present, quantitative understanding of the AOP is approaching the point where an in vitro measurement of aromatase inhibition could be used as an input parameter into a series of coupled computational models that could generate quantitative predictions across multiple key events (e.g., circulating E2 concentrations, circulating VTG concentrations, predicted impacts on cumulative fecundity, and effects on population trajectories). A sequence of supporting models has been coupled together and predictions have been made for novel aromatase inhibitors (identified through high throughput in vitro screening), but those predictions have not yet been validated experimentally. The present models are also unable to account for pharmacokinetic considerations (e.g., adsorption, distribution, metabolism/biotransformation, and elimination) and have demonstrated only partial success in simulating compensatory/feedback responses to aromatase inhibition (e.g., (Breen et al. 2013).

Considerations for Potential Applications of the AOP (optional)

  • The present AOP can provide potential support for the use of alternatives to the fish short term reproduction assay as a screen for aromatase inhibitors.
  • The present AOP can serve as a foundation for tiered testing strategies and IATA related to risk assessments on chemicals identified as aromatase inhibitors.
  • The present AOP can be used to guide endpoint selection for effects-based monitoring studies at sites where aromatase inhibition has been identified as a relevant biological activity of interest (e.g., through bioeffects prediction or bioeffects surveillance approaches; see Schroeder et al. 2016).

Schroeder, A. L., Ankley, G. T., Houck, K. A. and Villeneuve, D. L. (2016), Environmental surveillance and monitoring—The next frontiers for high-throughput toxicology. Environ Toxicol Chem, 35: 513–525. doi:10.1002/etc.3309

  • A series of computational models aligned with this AOP (i.e., a quantitative AOP construct) can be applied to estimate in vivo bench-mark doses based on in vitro screening results. Case studies evaluating this application are under way.

References

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2. Petkov PI, Temelkov S, Villeneuve DL, Ankley GT, Mekenyan OG. 2009. Mechanism-based categorization of aromatase inhibitors: a potential discovery and screening tool. SAR QSAR Environ Res 20(7-8): 657-678.

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6. Villeneuve DL, Knoebl I, Kahl MD, Jensen KM, Hammermeister DE, Greene KJ, et al. 2006. Relationship between brain and ovary aromatase activity and isoform-specific aromatase mRNA expression in the fathead minnow (Pimephales promelas). Aquat Toxicol 76(3-4): 353-368.

7. Ankley GT, Kahl MD, Jensen KM, Hornung MW, Korte JJ, Makynen EA, et al. 2002. Evaluation of the aromatase inhibitor fadrozole in a short-term reproduction assay with the fathead minnow (Pimephales promelas). Toxicological Sciences 67: 121-130.

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Appendix 1

List of MIEs in this AOP

Event: 36: Inhibition, Aromatase

Short Name: Inhibition, Aromatase

Key Event Component

Process Object Action
aromatase activity aromatase decreased

AOPs Including This Key Event

AOP ID and Name Event Type
Aop:25 - Aromatase inhibition leading to reproductive dysfunction MolecularInitiatingEvent
Aop:346 - Aromatase inhibition leads to male-biased sex ratio via impacts on gonad differentiation MolecularInitiatingEvent

Stressors

Name
Fadrozole
Letrozole
Prochloraz

Biological Context

Level of Biological Organization
Molecular

Cell term

Cell term
granulosa cell

Evidence for Perturbation by Stressor

Overview for Molecular Initiating Event

Characterization of chemical properties: Chemicals are known to inhibit aromatase activity through two primary molecular mechanisms. Steroid-like structures can inhibit the enzyme at its active site, with structures having ∆4 positioned double bonds generally acting as stronger inhibitors than those with ∆5 positioned double bonds (Petkov et al. 2009). Non-steroidal aromatase inhibitors generally act by interfering with electron transfer via the cytochrome P450 heme group of the aromatase enzyme, with greater nucleophilicity of the heteroatom contributing to greater potency as an inhibitor (Petkov et al. 2009). Petkov et al. (Petkov et al. 2009) have provided a detailed analysis of structural categorization of chemicals as potential steroidal or non-steroidal aromatase inhibitors.



Domain of Applicability


Taxonomic applicability: Aromatase (CYP19) orthologs are known to be present among most of the vertebrate lineage, at least down to the cartilaginous fishes. Orthologs have generally not been found in invertebrates, however, CYP19 was detected in the invertebrate chordate, amphioxus and analysis of conservation of gene order and content suggests a possible origin among primitive chordates (Castro et al. 2005). Fishes generally have two aromatase isoforms, cyp19a1a which is predominantly expressed in ovary and cyp19b, predominantly expressed in brain (Callard et al. 2001). Given that cyp19a1a is dominant isoform expressed in ovary and both isoforms appear to show similar sensitivity to aromatase inhibitors (Hinfray et al., 2006), for the purpose of this key event which focuses on gonadal aromatase activty, distinction of effects on one isoform versus the other are considered negligible. Total activity, without regard to isoform can be considered.


Key Event Description

Inhibition of cytochrome P450 aromatase (CYP19; specifically cyp19a1a in fish).

Site of action: The site of action for the molecular initiating event is the ovarian granulosa cells.

While many vertebrates have a single isoform of aromatase, fish are known to have two isoforms. CYP19a1a is predominantly expressed in ovary while cyp19a1b is predominantly expressed in brain (Callard et al. 2001; Cheshenko et al. 2008). For the purposes of this MIE, when applied to fish, the assumed effect is on cyp19a1a. However, given that both isoforms show similar sensitivity to aromatase inhibitors (Hinfray et al. 2006) and catalyze the same reaction, discrimination of specific isoforms is not viewed as critical in relative to determining downstream key events resulting from aromatase inhibition in ovarian granulosa cells.

Responses at the macromolecular level: Aromatase catalyzes three sequential oxidation steps (i.e., KEGG reactions R02501, R04761, R03087 or R01840, R04759, R02351; http://www.genome.jp/kegg/pathway.html) involved in the conversion of C-19 androgens (e.g., testosterone, androstenedione) to C-18 estrogens (e.g., 17β-estradiol, estrone). Aromatase inhibitors interfere with one or more of these reactions, leading to reduced efficiency in converting C-19 androgens into C-18 estrogens. Therefore, inhibition of aromatase activity results in decreased rate of 17β-estradiol (and presumably estrone) production by the ovary.


How it is Measured or Detected

Measurement/detection: Aromatase activity is typically measured by evaluating the production of tritiated water released upon the aromatase catalyzed conversion of radio-labeled androstenedione to estrone (Lephart and Simpson 1991). Aromatase activity can be measured in cell lines exposed in vitro (e.g., human placental JEG-3 cells and JAR choriocarcinoma cells, (Letcher et al. 1999); H295R human adrenocortical carcinoma cells (Sanderson et al. 2000)). Aromatase activity can also be quantified in tissue (i.e., ovary or brain) from vertebrates exposed in vivo (e.g., (Villeneuve et al. 2006; Ankley et al. 2002). In vitro aromatase assays are amenable to high throughput and have been included in nascent high throughput screening programs like the US EPA ToxcastTM program.


References

See Aromatase inhibition leading to reproductive dysfunction (in fish)

  • Petkov PI, Temelkov S, Villeneuve DL, Ankley GT, Mekenyan OG. 2009. Mechanism-based categorization of aromatase inhibitors: a potential discovery and screening tool. SAR QSAR Environ Res 20(7-8): 657-678.
  • Lephart ED, Simpson ER. 1991. Assay of aromatase activity. Methods Enzymol 206: 477-483.
  • Letcher RJ, van Holsteijn I, Drenth H-J, Norstrom RJ, Bergman A, Safe S, et al. 1999. Cytotoxicity and aromatase (CYP19) activity modulation by organochlorines in human placental JEG-3 and JAR choriocarcinoma cells. Toxico App Pharm 160: 10-20.
  • Sanderson J, Seinen W, Giesy J, van den Berg M. 2000. 2-chloro-triazine herbicides induce aromatase (CYP19) activity in H295R human adrenocortical carcinoma cells: a novel mechanism for estrogenicity. Toxicol Sci 54: 121-127.
  • Villeneuve DL, Knoebl I, Kahl MD, Jensen KM, Hammermeister DE, Greene KJ, et al. 2006. Relationship between brain and ovary aromatase activity and isoform-specific aromatase mRNA expression in the fathead minnow (Pimephales promelas). Aquat Toxicol 76(3-4): 353-368.
  • Ankley GT, Kahl MD, Jensen KM, Hornung MW, Korte JJ, Makynen EA, et al. 2002. Evaluation of the aromatase inhibitor fadrozole in a short-term reproduction assay with the fathead minnow (Pimephales promelas). Toxicol Sci 67: 121-130.
  • Castro LF, Santos MM, Reis-Henriques MA. 2005. The genomic environment around the Aromatase gene: evolutionary insights. BMC Evol Biol 5: 43.
  • Callard GV, Tchoudakova AV, Kishida M, Wood E. 2001. Differential tissue distribution, developmental programming, estrogen regulation and promoter characteristics of cyp19 genes in teleost fish. J Ster Biochem Mol Biol 79: 305-314.
  • Cheshenko K, Pakdel F, Segner H, Kah O, Eggen RI. Interference of endocrine disrupting chemicals with aromatase CYP19 expression or activity, and consequences for reproduction of teleost fish. Gen Comp Endocrinol. 2008 Jan 1;155(1):31-62.
  • Hinfray N, Porcher JM, Brion F. Inhibition of rainbow trout (Oncorhynchus mykiss) P450 aromatase activities in brain and ovarian microsomes by various environmental substances. Comp Biochem Physiol C Toxicol Pharmacol. 2006 Nov;144(3):252-62

List of Key Events in the AOP

Event: 219: Reduction, Plasma 17beta-estradiol concentrations

Short Name: Reduction, Plasma 17beta-estradiol concentrations

Key Event Component

Process Object Action
17beta-estradiol decreased

AOPs Including This Key Event

AOP ID and Name Event Type
Aop:7 - Aromatase (Cyp19a1) reduction leading to impaired fertility in adult female KeyEvent
Aop:25 - Aromatase inhibition leading to reproductive dysfunction KeyEvent
Aop:23 - Androgen receptor agonism leading to reproductive dysfunction (in repeat-spawning fish) KeyEvent
Aop:122 - Prolyl hydroxylase inhibition leading to reproductive dysfunction via increased HIF1 heterodimer formation KeyEvent
Aop:123 - Unknown MIE leading to reproductive dysfunction via increased HIF-1alpha transcription KeyEvent
Aop:271 - Inhibition of thyroid peroxidase leading to impaired fertility in fish KeyEvent
Aop:289 - Inhibition of 5α-reductase leading to impaired fecundity in female fish KeyEvent
Aop:310 - Embryonic Activation of the AHR leading to Reproductive failure, via epigenetic down-regulation of GnRHR KeyEvent

Biological Context

Level of Biological Organization
Organ

Organ term

Organ term
blood plasma

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
rat Rattus norvegicus High NCBI
human Homo sapiens High NCBI
fathead minnow Pimephales promelas High NCBI
Fundulus heteroclitus Fundulus heteroclitus High NCBI
Life Stage Applicability
Life Stage Evidence
Adult High
Sex Applicability
Sex Evidence
Unspecific Not Specified

Key enzymes needed to synthesize 17β-estradiol first appear in the common ancestor of amphioxus and vertebrates (Baker 2011). Consequently, this key event is applicable to most vertebrates.


Key Event Description

Estradiol synthesized by the gonads is transported to other tissues via blood circulation. The gonads are generally considered to be the primary source of estrogens in systemic circulation.


How it is Measured or Detected

Total concentrations of 17β-estradiol in plasma can be measured by radioimmunoassay (e.g., (Jensen et al. 2001)), enzyme-linked immunosorbent assay (available through many commercial vendors), or by analytical chemistry (e.g., LC/MS; Owen et al. 2014). Total steroid hormones are typically extracted from plasma or serum via liquid-liquid or solid phase extraction prior to analysis.

Given that there are numerous genes, like those coding for vertebrate vitellogenins, choriongenins, cyp19a1b, etc. which are known to be regulated by estrogen response elements, targeted qPCR or proteomic analysis of appropriate targets could also be used as an indirect measure of reduced circulating estrogen concentrations. However, further support for the specificity of the individual gene targets for estrogen-dependent regulation should be established in order to support their use.

A line of transgenic zebrafish employing green fluorescence protein under control of estrogen response elements could also be used to provide direct evidence of altered estrogen, with decreased GFP signal in estrogen responsive tissues like liver, ovary, pituitary, and brain indicating a reduction in circulating estrogens (Gorelick and Halpern 2011).


References

  • Jensen K, Korte J, Kahl M, Pasha M, Ankley G. 2001. Aspects of basic reproductive biology and endocrinology in the fathead minnow (Pimephales promelas). Comparative Biochemistry and Physiology Part C 128: 127-141.
  • Baker ME. 2011. Origin and diversification of steroids: co-evolution of enzymes and nuclear receptors. Molecular and cellular endocrinology 334(1-2): 14-20.
  • Owen LJ, Wu FC, Keevil BG. 2014. A rapid direct assay for the routine measurement of oestradiol and oestrone by liquid chromatography tandem mass spectrometry. Ann. Clin. Biochem. 51(pt 3):360-367.
  • Gorelick DA, Halpern ME. Visualization of estrogen receptor transcriptional activation in zebrafish. Endocrinology. 2011 Jul;152(7):2690-703. doi: 10.1210/en.2010-1257. Epub 2011 May 3. PubMed PMID: 21540282

Event: 285: Reduction, Vitellogenin synthesis in liver

Short Name: Reduction, Vitellogenin synthesis in liver

Key Event Component

Process Object Action
gene expression vitellogenins decreased

Biological Context

Level of Biological Organization
Tissue

Cell term

Cell term
hepatocyte

Organ term

Organ term
liver

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
Pimephales promelas Pimephales promelas High NCBI
Fundulus heteroclitus Fundulus heteroclitus High NCBI
Oryzias latipes Oryzias latipes High NCBI
Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature High
Sex Applicability
Sex Evidence
Unspecific Not Specified

Oviparous vertebrates. Although vitellogenin is conserved among oviparous vertebrates and many invertebrates, liver is not a relevant tissue for the production of vitellogenin in invertebrates (Wahli 1988)


Key Event Description

Vitellogenin is an egg yolk precursor protein synthesized by hepatocytes of oviparous vertebrates. In vertebrates, transcription of vitellogenin genes is predominantly regulated by estrogens via their action on nuclear estrogen receptors. During vitellogenic periods of the reproductive cycle, when circulating estrogen concentrations are high, vitellogenin transcription and synthesis are typically orders of magnitude greater than during non-reproductive conditions.


How it is Measured or Detected

Relative abundance of vitellogenin transcripts or protein can be readily measured in liver tissue from organisms exposed in vivo (e.g., (Biales et al. 2007)), or in liver slices (e.g., (Schmieder et al. 2000) or hepatocytes (e.g., (Navas and Segner 2006) exposed in vitro, using real-time quantitative polymerase chain reaction (PCR; transcripts) or enzyme linked immunosorbent assay (ELISA; protein).


References

  • Biales AD, Bencic DC, Lazorchak JL, Lattier DL. 2007. A quantitative real-time polymerase chain reaction method for the analysis of vitellogenin transcripts in model and nonmodel fish species. Environ Toxicol Chem 26(12): 2679-2686.
  • Navas JM, Segner H. 2006. Vitellogenin synthesis in primary cultures of fish liver cells as endpoint for in vitro screening of the (anti)estrogenic activity of chemical substances. Aquat Toxicol 80(1): 1-22.
  • Schmieder P, Tapper M, Linnum A, Denny J, Kolanczyk R, Johnson R. 2000. Optimization of a precision-cut trout liver tissue slice assay as a screen for vitellogenin induction: comparison of slice incubation techniques. Aquat Toxicol 49(4): 251-268.
  • Wahli W. 1988. Evolution and expression of vitellogenin genes. Trends in Genetics. 4:227-232.

Event: 309: Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development

Short Name: Reduction, Vitellogenin accumulation into oocytes and oocyte growth/development

Key Event Component

Process Object Action
receptor-mediated endocytosis vitellogenins decreased
oocyte growth decreased
oocyte development decreased

Biological Context

Level of Biological Organization
Cellular

Cell term

Cell term
oocyte

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
fathead minnow Pimephales promelas Moderate NCBI
Oryzias latipes Oryzias latipes Moderate NCBI
Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature High
Sex Applicability
Sex Evidence
Female High

Oviparous vertebrates and invertebrates. Although hormonal regulation of vitellogenin synthesis and mechanisms of vitellogenin transport from the site of synthesis to the ovary vary between vertebrates and invertebrates (Wahli 1988), in both vertebrates and invertebrates, vitellogenin is incorporated into oocytes and cleaved to form yolk proteins.


Key Event Description

Vitellogenin from the blood is selectively taken up by competent oocytes via receptor-mediated endocytosis. Although vitellogenin receptors mediate the uptake, opening of intercellular channels through the follicular layers to the oocyte surface as the oocyte reaches a “critical” size is thought to be a key trigger in allowing vitellogenin uptake (Tyler and Sumpter 1996). Once critical size is achieved, concentrations in the plasma and temperature are thought to impose the primary limits on uptake (Tyler and Sumpter 1996). Uptake of vitellogenin into oocytes causes considerable oocyte growth during vitellogenesis, accounting for up to 95% of the final egg size in many fish (Tyler and Sumpter 1996). Given the central role of vitellogenesis in oocyte maturation, vitellogenin accumulation is a prominent feature used in histological staging of oocytes (e.g., (Leino et al. 2005; Wolf et al. 2004).


How it is Measured or Detected

Relative vitellogenin accumulation can be evaluated qualitatively using routine histological approaches (Leino et al. 2005; Wolf et al. 2004). Oocyte size can be evaluated qualitatively or quantitatively using routine histological and light microscopy and/or imaging approaches.


References

  • Leino R, Jensen K, Ankley G. 2005. Gonadal histology and characteristic histopathology associated with endocrine disruption in the adult fathead minnow. Environmental Toxicology and Pharmacology 19: 85-98.
  • Tyler C, Sumpter J. 1996. Oocyte growth and development in teleosts. Reviews in Fish Biology and Fisheries 6: 287-318.
  • Wolf JC, Dietrich DR, Friederich U, Caunter J, Brown AR. 2004. Qualitative and quantitative histomorphologic assessment of fathead minnow Pimephales promelas gonads as an endpoint for evaluating endocrine-active compounds: a pilot methodology study. Toxicol Pathol 32(5): 600-612.

Event: 3: Reduction, 17beta-estradiol synthesis by ovarian granulosa cells

Short Name: Reduction, 17beta-estradiol synthesis by ovarian granulosa cells

Key Event Component

Process Object Action
estrogen biosynthetic process 17beta-estradiol decreased

Biological Context

Level of Biological Organization
Cellular

Cell term

Cell term
granulosa cell

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
fathead minnow Pimephales promelas High NCBI
Fundulus heteroclitus Fundulus heteroclitus High NCBI
Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature High
Sex Applicability
Sex Evidence
Female High

Key enzymes needed to synthesize 17β-estradiol first appear in the common ancestor of amphioxus and vertebrates (Markov et al. 2009; Baker 2011). Consequently, it is plausible that this key event is applicable to most vertebrates. This key event is not applicable to invertebrates, which lack the enzymes required to synthesize 17ß-estradiol.

 


Key Event Description

Like all steroids, estradiol is a cholesterol derivative. Estradiol synthesis in ovary is mediated by a number of enzyme catalyzed reactions involving cyp11 (cholesterol side chain cleavage enzyme), cyp 17 (17alpha-hydroxylase/17,20-lyase), 3beta hydroxysteroid dehyrogenase, 17beta hydroxysteroid dehydrogenase, and cyp19 (aromatase). Among those enzyme catalyzed reactions, conversion of testosterone to estradiol, catalyzed by aromatase, is considered to be rate limiting for estradiol synthesis. Within the ovary, aromatase expression and activity is primarily localized in the granulosa cells (reviewed in (Norris 2007; Yaron 1995; Havelock et al. 2004) and others). Reactions involved in synthesis of C-19 androgens are primarily localized in the theca cells and C-19 androgens diffuse from the theca into granulosa cells where aromatase can catalyze their conversion to C-18 estrogens.


How it is Measured or Detected

Due to the importance of both theca and granulosa cells in ovarian steroidogenesis, it is generally impractical to measure E2 production by isolated granulosa cells (Havelock et al. 2004). However, this key event can be evaluated by examining E2 production by intact ovarian tissue explants either exposed to chemicals in vitro (e.g., (Villeneuve et al. 2007; McMaster ME 1995) or in vivo (i.e., via ex vivo steroidogenesis assay; e.g., (Ankley et al. 2007)). Estradiol released by ovarian tissue explants into media can be quantified by radioimmunoassay (e.g., Jensen et al. 2001), ELISA, or analytical methods such as LC-MS (e.g., Owen et al. 2014).

OECD TG 456 (OECD 2011) is the validated test guideline for an in vitro screen for chemical effects on steroidogenesis, specifically the production of 17ß-estradiol (E2) and testosterone (T).

The synthesis of E2 can be measured in vitro cultured ovarian cells. The methods for culturing mammalian ovarian cells can be found in the Database Service on Alternative Methods to animal experimentation (DB-ALM): Culture of Human Cumulus Granulosa Cells (EURL ECVAM Protocol No. 92), Granulosa and Theca Cell Culture Systems (EURL ECVAM Method Summary No. 92).


References

  • Ankley GT, Jensen KM, Kahl MD, Makynen EA, Blake LS, Greene KJ, et al. 2007. Ketoconazole in the fathead minnow (Pimephales promelas): reproductive toxicity and biological compensation. Environ Toxicol Chem 26(6): 1214-1223.
  • Baker ME. 2011. Origin and diversification of steroids: co-evolution of enzymes and nuclear receptors. Molecular and cellular endocrinology 334(1-2): 14-20.
  • EURL ECVAM Method Summary no 92. Granulosa and Theca Cell Culture Systems - Summary
  • EURL ECVAM Protocol no 92 Culture of Human Cumulus Granulosa Cells. Primary cell culture method. Contact Person: Dr. Mahadevan Maha M.
  • Havelock JC, Rainey WE, Carr BR. 2004. Ovarian granulosa cell lines. Molecular and cellular endocrinology 228(1-2): 67-78.
  • Jensen K, Korte J, Kahl M, Pasha M, Ankley G. 2001. Aspects of basic reproductive biology and endocrinology in the fathead minnow (Pimephales promelas). Comparative Biochemistry and Physiology Part C 128: 127-141.
  • McMaster ME MK, Jardine JJ, Robinson RD, Van Der Kraak GJ. 1995. Protocol for measuring in vitro steroid production by fish gonadal tissue. Canadian Technical Report of Fisheries and Aquatic Sciences 1961 1961: 1-78.
  • Norris DO. 2007. Vertebrate Endocrinology. Fourth ed. New York: Academic Press.
  • OECD (2011), Test No. 456: H295R Steroidogenesis Assay, OECD Guidelines for the Testing of Chemicals, Section 4, OECD Publishing, Paris.DOI: http://dx.doi.org/10.1787/9789264122642-en
  • Owen LJ, Wu FC, Keevil BG. 2014. A rapid direct assay for the routine measurement of oestradiol and oestrone by liquid chromatography tandem mass spectrometry. Ann. Clin. Biochem. 51(pt 3):360-367.
  • Villeneuve DL, Ankley GT, Makynen EA, Blake LS, Greene KJ, Higley EB, et al. 2007. Comparison of fathead minnow ovary explant and H295R cell-based steroidogenesis assays for identifying endocrine-active chemicals. Ecotoxicol Environ Saf 68(1): 20-32.
  • Villeneuve DL, Mueller ND, Martinovic D, Makynen EA, Kahl MD, Jensen KM, et al. 2009. Direct effects, compensation, and recovery in female fathead minnows exposed to a model aromatase inhibitor. Environ Health Perspect 117(4): 624-631.
  • Yaron Z. 1995. Endocrine control of gametogenesis and spawning induction in the carp. Aquaculture 129: 49-73.

Event: 78: Reduction, Cumulative fecundity and spawning

Short Name: Reduction, Cumulative fecundity and spawning

Key Event Component

Process Object Action
egg quantity decreased

AOPs Including This Key Event

AOP ID and Name Event Type
Aop:29 - Estrogen receptor agonism leading to reproductive dysfunction KeyEvent
Aop:25 - Aromatase inhibition leading to reproductive dysfunction KeyEvent
Aop:23 - Androgen receptor agonism leading to reproductive dysfunction (in repeat-spawning fish) KeyEvent
Aop:30 - Estrogen receptor antagonism leading to reproductive dysfunction KeyEvent
Aop:122 - Prolyl hydroxylase inhibition leading to reproductive dysfunction via increased HIF1 heterodimer formation AdverseOutcome
Aop:123 - Unknown MIE leading to reproductive dysfunction via increased HIF-1alpha transcription AdverseOutcome
Aop:271 - Inhibition of thyroid peroxidase leading to impaired fertility in fish AdverseOutcome
Aop:310 - Embryonic Activation of the AHR leading to Reproductive failure, via epigenetic down-regulation of GnRHR AdverseOutcome
Aop:289 - Inhibition of 5α-reductase leading to impaired fecundity in female fish KeyEvent

Stressors

Name
Tris(1,3-dichloropropyl)phosphate - TDCPP

Biological Context

Level of Biological Organization
Individual

Evidence for Perturbation by Stressor


Tris(1,3-dichloropropyl)phosphate - TDCPP

Reduction of cumulative fecundity and spawning following exposure to low levels of TDCIPP (15, 46 and 90 nM) has been reported in 3 different zebrafish studies (Liu et al., 2013; Wang et al., 2015a; Zhu et al., 2015).


Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
fathead minnow Pimephales promelas High NCBI
Fundulus heteroclitus Fundulus heteroclitus High NCBI
Oryzias latipes Oryzias latipes High NCBI
Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature High
Sex Applicability
Sex Evidence
Female High

Cumulative fecundity and spawning can, in theory, be evaluated for any egg laying animal.


Key Event Description

Spawning refers to the release of eggs. Cumulative fecundity refers to the total number of eggs deposited by a female, or group of females over a specified period of time.


How it is Measured or Detected

In laboratory-based reproduction assays (e.g., OECD Test No. 229; OECD Test No. 240), spawning and cumulative fecundity can be directly measured through daily observation of egg deposition and egg counts.

In some cases, fecundity may be estimated based on gonado-somatic index (OECD 2008).


Regulatory Significance of the AO

Cumulative fecundity is the most apical endpoint considered in the OECD 229 Fish Short Term Reproduction Assay. The OECD 229 assay serves as screening assay for endocrine disruption and associated reproductive impairment (OECD 2012). Fecundity is also an important apical endpoint in the Medaka Extended One Generation Reproduction Test (MEOGRT; OECD Test Guideline 240; OECD 2015).

A variety of fish life cycle tests also include cumulative fecundity as an endpoint (OECD 2008).

 


References

  • OECD 2008. Series on testing and assessment, Number 95. Detailed Review Paper on Fish Life-cycle Tests. OECD Publishing, Paris. ENV/JM/MONO(2008)22.
  • OECD (2015), Test No. 240: Medaka Extended One Generation Reproduction Test (MEOGRT), OECD Publishing, Paris.
    DOI: http://dx.doi.org/10.1787/9789264242258-en
  • OECD. 2012a. Test no. 229: Fish short term reproduction assay. Paris, France:Organization for Economic Cooperation and Development.

Event: 221: Reduction, Plasma vitellogenin concentrations

Short Name: Reduction, Plasma vitellogenin concentrations

Key Event Component

Process Object Action
vitellogenins decreased

AOPs Including This Key Event

AOP ID and Name Event Type
Aop:25 - Aromatase inhibition leading to reproductive dysfunction KeyEvent
Aop:23 - Androgen receptor agonism leading to reproductive dysfunction (in repeat-spawning fish) KeyEvent
Aop:30 - Estrogen receptor antagonism leading to reproductive dysfunction KeyEvent
Aop:122 - Prolyl hydroxylase inhibition leading to reproductive dysfunction via increased HIF1 heterodimer formation KeyEvent
Aop:123 - Unknown MIE leading to reproductive dysfunction via increased HIF-1alpha transcription KeyEvent
Aop:271 - Inhibition of thyroid peroxidase leading to impaired fertility in fish KeyEvent
Aop:289 - Inhibition of 5α-reductase leading to impaired fecundity in female fish KeyEvent
Aop:310 - Embryonic Activation of the AHR leading to Reproductive failure, via epigenetic down-regulation of GnRHR KeyEvent

Biological Context

Level of Biological Organization
Organ

Organ term

Organ term
blood plasma

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
fathead minnow Pimephales promelas High NCBI
Oryzias latipes Oryzias latipes High NCBI
Danio rerio Danio rerio High NCBI
Life Stage Applicability
Life Stage Evidence
Adult, reproductively mature High

Oviparous vertebrates synthesize yolk precursor proteins that are transported in the circulation for uptake by developing oocytes. Many invertebrates also synthesize vitellogenins that are taken up into developing oocytes via active transport mechanisms. However, invertebrate vitellogenins are transported in hemolymph or via other transport mechanisms rather than plasma.


Key Event Description

Vitellogenin synthesized in the liver is secreted into the blood and circulates to the ovaries for uptake.


How it is Measured or Detected

Vitellogenin concentrations in plasma are typically detected using enzyme linked Immunosorbent assay (ELISA; e.g., (Korte et al. 2000; Tyler et al. 1996; Holbech et al. 2001; Fenske et al. 2001). Although less specific and/or sensitive, determination of alkaline-labile phosphate or Western blotting has also been employed.


References

  • Fenske M, van Aerle R, Brack S, Tyler CR, Segner H. Development and validation of a homologous zebrafish (Danio rerio Hamilton-Buchanan) vitellogenin enzyme-linked immunosorbent assay (ELISA) and its application for studies on estrogenic chemicals. Comp Biochem Physiol C Toxicol Pharmacol. 2001. Jul;129(3):217-32.
  • Holbech H, Andersen L, Petersen GI, Korsgaard B, Pedersen KL, Bjerregaard P. Development of an ELISA for vitellogenin in whole body homogenate of zebrafish (Danio rerio). Comp Biochem Physiol C Toxicol Pharmacol. 2001 Sep;130(1):119-31.
  • Korte JJ, Kahl MD, Jensen KM, Mumtaz SP, Parks LG, LeBlanc GA, et al. 2000. Fathead minnow vitellogenin: complementary DNA sequence and messenger RNA and protein expression after 17B-estradiol treatment. Environmental Toxicology and Chemistry 19(4): 972-981.
  • Tyler C, van der Eerden B, Jobling S, Panter G, Sumpter J. 1996. Measurement of vitellogenin, a biomarker for exposure to oestrogenic chemicals, in a wide variety of cyprinid fish. Journal of Comparative Physiology and Biology 166: 418-426.
  • Wahli W. 1988. Evolution and expression of vitellogenin genes. Trends in Genetics. 4:227-232.

List of Adverse Outcomes in this AOP

Event: 360: Decrease, Population trajectory

Short Name: Decrease, Population trajectory

Key Event Component

Process Object Action
population growth rate decreased
population growth rate population of organisms decreased

AOPs Including This Key Event

AOP ID and Name Event Type
Aop:23 - Androgen receptor agonism leading to reproductive dysfunction (in repeat-spawning fish) AdverseOutcome
Aop:25 - Aromatase inhibition leading to reproductive dysfunction AdverseOutcome
Aop:29 - Estrogen receptor agonism leading to reproductive dysfunction AdverseOutcome
Aop:30 - Estrogen receptor antagonism leading to reproductive dysfunction AdverseOutcome
Aop:100 - Cyclooxygenase inhibition leading to reproductive dysfunction via inhibition of female spawning behavior AdverseOutcome
Aop:122 - Prolyl hydroxylase inhibition leading to reproductive dysfunction via increased HIF1 heterodimer formation AdverseOutcome
Aop:123 - Unknown MIE leading to reproductive dysfunction via increased HIF-1alpha transcription AdverseOutcome
Aop:155 - Deiodinase 2 inhibition leading to reduced young of year survival via posterior swim bladder inflation AdverseOutcome
Aop:156 - Deiodinase 2 inhibition leading to reduced young of year survival via anterior swim bladder inflation AdverseOutcome
Aop:157 - Deiodinase 1 inhibition leading to reduced young of year survival via posterior swim bladder inflation AdverseOutcome
Aop:158 - Deiodinase 1 inhibition leading to reduced young of year survival via anterior swim bladder inflation AdverseOutcome
Aop:159 - Thyroperoxidase inhibition leading to reduced young of year survival via anterior swim bladder inflation AdverseOutcome
Aop:101 - Cyclooxygenase inhibition leading to reproductive dysfunction via inhibition of pheromone release AdverseOutcome
Aop:102 - Cyclooxygenase inhibition leading to reproductive dysfunction via interference with meiotic prophase I /metaphase I transition AdverseOutcome
Aop:63 - Cyclooxygenase inhibition leading to reproductive dysfunction AdverseOutcome
Aop:103 - Cyclooxygenase inhibition leading to reproductive dysfunction via interference with spindle assembly checkpoint AdverseOutcome
Aop:290 - DNA methyltransferase inhibition leading to reduced fecundity associated population decline AdverseOutcome
Aop:291 - DNA methyltransferase inhibition leading to transgenerational DNA methylation associated population decline AdverseOutcome
Aop:292 - Inhibition of tyrosinase leads to decreased population in fish AdverseOutcome
Aop:310 - Embryonic Activation of the AHR leading to Reproductive failure, via epigenetic down-regulation of GnRHR AdverseOutcome
Aop:16 - Acetylcholinesterase inhibition leading to acute mortality AdverseOutcome
Aop:312 - Acetylcholinesterase Inhibition leading to Acute Mortality via Impaired Coordination & Movement​ AdverseOutcome
Aop:334 - Glucocorticoid Receptor Agonism Leading to Impaired Fin Regeneration AdverseOutcome
Aop:336 - DNA methyltransferase inhibition leading to population decline (#1) AdverseOutcome
Aop:337 - DNA methyltransferase inhibition leading to population decline (#2) AdverseOutcome
Aop:338 - DNA methyltransferase inhibition leading to population decline (#3) AdverseOutcome
Aop:339 - DNA methyltransferase inhibition leading to population decline (#4) AdverseOutcome
Aop:340 - DNA methyltransferase inhibition leading to transgenerational effects (#1) AdverseOutcome
Aop:341 - DNA methyltransferase inhibition leading to transgenerational effects (#2) AdverseOutcome
Aop:289 - Inhibition of 5α-reductase leading to impaired fecundity in female fish AdverseOutcome
Aop:297 - Inhibition of retinaldehyde dehydrogenase leads to population decline AdverseOutcome
Aop:346 - Aromatase inhibition leads to male-biased sex ratio via impacts on gonad differentiation AdverseOutcome

Biological Context

Level of Biological Organization
Population

Domain of Applicability


Taxonomic Applicability
Term Scientific Term Evidence Links
all species all species NCBI
Life Stage Applicability
Life Stage Evidence
All life stages Not Specified
Sex Applicability
Sex Evidence
Unspecific Not Specified

Consideration of population size and changes in population size over time is potentially relevant to all living organisms.


Key Event Description

Maintenance of sustainable fish and wildlife populations (i.e., adequate to ensure long-term delivery of valued ecosystem services) is an accepted regulatory goal upon which risk assessments and risk management decisions are based.


How it is Measured or Detected

Population trajectories, either hypothetical or site specific, can be estimated via population modeling based on measurements of vital rates or reasonable surrogates measured in laboratory studies. As an example, Miller and Ankley 2004 used measures of cumulative fecundity from laboratory studies with repeat spawning fish species to predict population-level consequences of continuous exposure.


Regulatory Significance of the AO

Maintenance of sustainable fish and wildlife populations (i.e., adequate to ensure long-term delivery of valued ecosystem services) is a widely accepted regulatory goal upon which risk assessments and risk management decisions are based.


References

  • Miller DH, Ankley GT. 2004. Modeling impacts on populations: fathead minnow (Pimephales promelas) exposure to the endocrine disruptor 17ß-trenbolone as a case study. Ecotoxicology and Environmental Safety 59: 1-9.

Appendix 2

List of Key Event Relationships in the AOP