Aop: 271

AOP Title


Inhibition of thyroid peroxidase leading to impaired fertility in fish

Short name:


TPO inhibition and impaired fertility

Graphical Representation


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  • June-Woo Park, Korea Institute of Toxicology JRC-APT (Joint Research Center for Alternative and Predictive Toxicology)
  • Carlie LaLone, US EPA
  • Young Jun Kim, Environmental Safety Group, KIST Europe, JRC-APT 

Point of Contact


June-Woo Park   (email point of contact)



  • June-Woo Park
  • Carlie LaLone
  • Young Jun Kim



Author status OECD status OECD project SAAOP status
Open for comment. Do not cite Under Development 1.59 Included in OECD Work Plan

This AOP was last modified on October 15, 2020 21:12


Revision dates for related pages

Page Revision Date/Time
Thyroperoxidase, Inhibition August 07, 2018 15:09
Thyroid hormone synthesis, Decreased August 11, 2018 13:21
Reduction, Plasma 17beta-estradiol concentrations September 26, 2017 11:30
Reduction, Plasma vitellogenin concentrations September 16, 2017 10:14
Reduction, Cumulative fecundity and spawning March 20, 2017 17:52
Thyroperoxidase, Inhibition leads to TH synthesis, Decreased September 02, 2020 16:32
TH synthesis, Decreased leads to Reduction, Plasma 17beta-estradiol concentrations September 18, 2018 20:54
Reduction, Plasma 17beta-estradiol concentrations leads to Reduction, Plasma vitellogenin concentrations October 18, 2018 11:02
Reduction, Plasma vitellogenin concentrations leads to Reduction, Cumulative fecundity and spawning September 18, 2018 20:55
Propylthiouracil November 29, 2016 18:42
Methimazole November 29, 2016 18:42
Ethylene thiourea November 29, 2016 18:42



This AOP links inhibition of thyroid peroxidase to reproductive toxicity in fish. This AOP describes one adverse outcome that may result from the inhibition of thyroid peroxidase (TPO). Thyroid peroxidase (TPO) is an enzyme for thyroid hormone (TH) synthesis. Chemical inhibition of TPO, the molecular-initiating event (MIE), results in decreased thyroid hormone (TH) synthesis. Reduction of TH induces the decline of E2 and VTG, which leads to decreased cumulative fecundity and spawning. Cumulative fertility is major endpoint for evaluation of reproductive toxicity caused by endocrine disruption. It is used as an endpoint for endocrine disruptor screening in OECD 229. Therefore, this AOP would be useful as a means to identify chemicals with known potential to adversely affect fish populations.

Background (optional)


Summary of the AOP


Events: Molecular Initiating Events (MIE)


Key Events (KE)


Adverse Outcomes (AO)


Sequence Type Event ID Title Short name
1 MIE 279 Thyroperoxidase, Inhibition Thyroperoxidase, Inhibition
2 KE 277 Thyroid hormone synthesis, Decreased TH synthesis, Decreased
3 KE 219 Reduction, Plasma 17beta-estradiol concentrations Reduction, Plasma 17beta-estradiol concentrations
4 KE 221 Reduction, Plasma vitellogenin concentrations Reduction, Plasma vitellogenin concentrations
5 AO 78 Reduction, Cumulative fecundity and spawning Reduction, Cumulative fecundity and spawning

Relationships Between Two Key Events
(Including MIEs and AOs)


Title Adjacency Evidence Quantitative Understanding
Thyroperoxidase, Inhibition leads to TH synthesis, Decreased adjacent High High
TH synthesis, Decreased leads to Reduction, Plasma 17beta-estradiol concentrations adjacent
Reduction, Plasma 17beta-estradiol concentrations leads to Reduction, Plasma vitellogenin concentrations adjacent High High
Reduction, Plasma vitellogenin concentrations leads to Reduction, Cumulative fecundity and spawning adjacent High High

Network View





Name Evidence Term
Propylthiouracil High
Methimazole High
Ethylene thiourea High

Life Stage Applicability


Life stage Evidence
Adult, reproductively mature High

Taxonomic Applicability


Term Scientific Term Evidence Link
fish fish High NCBI

Sex Applicability


Sex Evidence
Female High

Overall Assessment of the AOP


Domain of Applicability


Essentiality of the Key Events


  •  MIE: Thyroperoxidase, Inhibition: The present MIE, an inhibition peroxidase (TPO) function led to a perturbation in the expression of key genes in thyroid hormone synthesis and release pathways. Specifically as the TPO inhibited by MMI and PTU was reflected in the several thyroid hormone synthesis and release pathway genes (Alison et al., 2012).
  • KE 1: Thyroid hormone synthesis, Decrease: A lot of studies have a correlation between TPO activition leading to decrease of thyroid hormone. Many studies was exposed that TPO inhibition lead to a decreased or inactivate of thyroid hormones levels (Shaoying et al., 2011; Antonio et al., 2006; Tonacchera et al., 2004; De Groef et al., 2006; Waltz wt al., 2010).

Evidence Assessment


Quantitative Understanding


Considerations for Potential Applications of the AOP (optional)




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