This Key Event Relationship is licensed under the Creative Commons BY-SA license. This license allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, so long as attribution is given to the creator. The license allows for commercial use. If you remix, adapt, or build upon the material, you must license the modified material under identical terms.

Relationship: 309

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

Thyroperoxidase, Inhibition leads to TH synthesis, Decreased

Upstream event

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

Thyroperoxidase, Inhibition

Downstream event

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

TH synthesis, Decreased

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
Inhibition of Thyroperoxidase and Subsequent Adverse Neurodevelopmental Outcomes in Mammals	adjacent	High	Low	Kevin Crofton (send email)	Open for citation & comment	WPHA/WNT Endorsed
Thyroperoxidase inhibition leading to increased mortality via reduced anterior swim bladder inflation	adjacent	High	Low	Dries Knapen (send email)	Under Development: Contributions and Comments Welcome	WPHA/WNT Endorsed
Inhibition of thyroid peroxidase leading to impaired fertility in fish	adjacent	High	High	June-Woo Park (send email)	Open for comment. Do not cite	Under Development
Thyroperoxidase inhibition leading to altered amphibian metamorphosis	adjacent	High	Moderate	Jonathan Haselman (send email)	Under Development: Contributions and Comments Welcome
Thyroperoxidase inhibition leading to altered visual function via altered retinal layer structure	adjacent	High	Moderate	Lucia Vergauwen (send email)	Open for citation & comment	Under Review
Thyroperoxidase inhibition leading to altered visual function via decreased eye size	adjacent			Lucia Vergauwen (send email)	Under development: Not open for comment. Do not cite	Under Development
Thyroperoxidase inhibition leading to altered visual function via altered photoreceptor patterning	adjacent			Lucia Vergauwen (send email)	Under development: Not open for comment. Do not cite	Under Development
Inhibition of thyroid peroxidase leading to follicular cell adenomas and carcinomas (in rat and mouse)	adjacent			Charles Wood (send email)	Under Development: Contributions and Comments Welcome

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
human	Homo sapiens	High	NCBI
rat	Rattus norvegicus	High	NCBI
Xenopus laevis	Xenopus laevis	High	NCBI
zebrafish	Danio rerio	High	NCBI
fathead minnow	Pimephales promelas	Low	NCBI

Sex Applicability

An indication of the the relevant sex for this KER. More help

Sex	Evidence
Male	High
Female	High

Life Stage Applicability

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

Term	Evidence
All life stages	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

Thyroperoxidase (TPO) is a heme-containing apical membrane protein within the follicular lumen of thyrocytes that acts as the enzymatic catalyst for thyroid hormone (TH) synthesis (Taurog, 2005) across vertebrates. Two commonly used reference chemicals, propylthiouracil (PTU) and methimazole (MMI), are drugs that inhibit the ability of TPO to: a) activate iodine and transfer it to thyroglobulin (Tg) (Davidson et al., 1978); and, b) couple thyroglobulin (Tg)-bound iodotyrosyls to produce Tg-bound thyroxine (T4) and triiodothyronine (T3) (Taurog, 2005).

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

The weight of evidence supporting a direct linkage between the MIE, TPO inhibition, and the KE of decreased TH synthesis, is strong and supported by more than three decades of research in animals, including humans (Cooper et al., 1982; Cooper et al.,1983; Divi and Doerge, 1994; Fang et al., 2022).

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 biological plausibility for this KER is rated Strong. TPO is the only enzyme capable of de novo synthesis of TH. TPO catalyzes several reactions, including the oxidation of iodide, nonspecific iodination of tyrosyl residues of thyroglobulin (Tg) to form monoiodotyrosyl (MIT) or diiodotyrosyl (DIT) residues, and the coupling of these Tg-bound iodotyrosyls to produce Tg-bound T3 and T4 (Divi and Doerge, 1994; Kessler et al., 2008; Ruf et al., 2006; Taurog et al., 1996, 2005). Therefore, inhibition of TPO activity is widely accepted to directly impact TH synthesis.

Empirical Evidence

Provides specific (citable) evidence that supports the idea of a change in the upstream KE (KEupstream) leading to, or being associated with, a subsequent change in the downstream KE (KEdownstream), assuming the perturbation of KEupstream is sufficient. More help

Empirical support for this KER is strong. There are several papers that have measured alterations in TPO and subsequent effects on TH synthesis across vertebrates. Taurog et al. (1996) showed decreased guicaol activity, decreased bound I¹²⁵, and subsequent decreases in newly formed T3 and T4 per molecule of Tg, following exposure to PTU, MMI and some antibiotics. There is important evidence in mammals. Following in vivo exposure to PTU in rats (Cooper et al., 1982; 1983), there are concentration and time-dependent decreases in thyroid protein bound iodine and serum T4 and T3 that recovered one month after cessation of PTU exposure. In addition, measures of thyroidal iodine content were highly correlated with intra-thyroidal PTU concentration. Vickers et al. (2012) demonstrated dose- and time- dependent inhibition of TPO activity in both human and rat thyroid homogenates exposed to MMI. Hassan et al. (2017, 2020) and Handa et al. (2021) predicted the level of THs in serum after treatment with PTU and MMI in rats. They developed a quantitative model by comparing dose- response data.

Tietge et al (2010) showed decreases in thyroidal T4 following MMI exposure in Xenopus. Also in Xenopus, Haselman et al (2020) showed decreases in thyroidal iodotyrosines (MIT/DIT) and iodothyronines (T4/T3) following exposure to MMI. Doerge et al (1998) showed that a tryphenylmethane dye, malachite green, inhibited TPO and lowered thyroxine production. A recent paper used a series of benzothiazoles and showed TPO inhibition (guicaol assay) and inhibition of TSH stimulated thyroxine release from Xenopus thyroid gland explant cultures (Hornung et al., 2015).

Additionally, evidence is available from studies investigating responses to TPO inhibitors in fish. For example, Stinckens et al. (2020) showed reduced whole body T4 concentrations in zebrafish larvae exposed to 50 or 100 mg/L methimazole, a potent TPO inhibitor, from immediately after fertilization until 21 or 32 days of age. Exposure to 37 or 111 mg/L propylthiouracil also reduced T4 levels after exposure up to 14, 21 and 32 days in the same study. Walter et al. (2019) showed that propylthiouracil had no effect on T4 levels in 24h old zebrafish, but decreased T4 levels of 72h old zebrafish. This difference is probably due to the onset of embryonic TH production between the age of 24 and 72 hours (Opitz et al., 2011). Stinckens et al. (2016) showed that exposure to 2-mercaptobenzothiazole (MBT), an environmentally relevant TPO inhibitor, decreased whole body T4 levels in continuously exposed 5 and 32 day old zebrafish larvae. Several other studies have also shown that chemically induced Inhibition of TPO results in reduced TH synthesis in zebrafish (Van der Ven et al., 2006; Raldua and Babin, 2009; Liu et al., 2011; Thienpont et al., 2011; Rehberger et al., 2018). Using a TPO knockout line Fang et al. (2022) showed that TPO inhibition abolished the T4 synthesis in 7 dpf zebrafish mutants. A high concentration of MBT also decreased whole body T4 levels in 6 day old fathead minnows, but recovery was observed at the age of 21 days although the fish were kept in the exposure medium (Nelson et al., 2016). Crane et al. (2006) showed decreased T4 levels in 28 day old fathead minnows continuously exposed to 32 or 100 µg/L methimazole.

Temporal Evidence: In mammals, the temporal nature of this KER is applicable to all life stages, including development (Seed et al., 2005). The impact of decreased TPO activity on TH synthesis is similar across all ages in mammals. Good evidence for the temporal relationship of the KER comes from thyroid system modeling (e.g., Degon et al., 2008; Fisher et al., 2013) using data from studies of iodine deficiency and chemicals that inhibit NIS. In addition, there is ample evidence of the temporal impacts of TPO inhibition on TH synthesis, using ex vivo and in vitro measures that demonstrate the time course of inhibition following chemical exposures, including some data from human thyroid microsomes and ex vivo thyroid slices (Vickers et al., 2012). Future work is needed that measures both TPO inhibition and TH production during development.

In oviparous fish such as zebrafish and fathead minnow, the nature of this KER depends on the life stage since the earliest stages of embryonic development rely on maternal THs transferred to the eggs. Embryonic TH synthesis is activated later during embryo-larval development. (See Domain of applicability)

Dose-Response Evidence: Dose-response data is available from a number of studies in mammals that correlate TPO inhibition with decreased TH production measured using a variety of endpoints including iodine organification (e.g., Taurog et al., 1996), inhibition of guicaol oxidation in thyroid microsomes (e.g., Doerge and Chang, 2002), and direct measure of thyroid gland T4 concentrations (e.g., Hornung et al., 2015). However, there is a lack of dose-response data from developmental studies showing direct linkages from TPO inhibition to thyroidal TH synthesis.

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

While it is clear that TPO inhibition will lead to altered TH synthesis, there is a need for data that will inform quantitative modeling of the relationship between TPO inhibition and the magnitude of effects on TH synthesis.

Data from studies on genistein highlight this uncertainty. Doerge and colleagues have demonstrated that for this compound up to 80% TPO inhibition did not result in decreased serum T4 in rats (Doerge and Chang, 2002). This is not consistent with other prototypical TPO inhibitors (e.g., PTU, MMI). Genistein is however a well-known phytoestrogen and the observed inconsistency may be the result of feedback mechanisms resulting from its estrogenic effect.

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

Iodine availability will impact the ability of TPO to iodinate tyrosine residues on thyroglobulin. Iodine availability to TPO can be impacted in a number of ways. First, environmental availability of iodine can vary greatly depending on whether and how much iodine exists in surface waters for aquatic organisms (gill respirators) and in the diets of both terrestrial and aquatic organisms. Second, somewhat regardless of iodine availability through environmental uptake (i.e., barring extremely high iodine exposure), iodine is actively transported into the thyroid follicular cell from the blood via sodium-iodide symporter (NIS), which has been shown to be susceptible to inhibition by, for example, perchlorate. As such, iodine availability to TPO is mediated by functional NIS. Finally, iodine is not fully available to TPO on the apical surface of the thyroid follicular cell until it is transported through the apical membrane by pendrin, an anion exchange protein - mutations or inhibition of pendrin could affect iodine availability to TPO.

Hydrogen peroxide is also needed by TPO to mediate the oxidation of iodide, which is produced locally by dual oxidase (DUOX). A mutation or inhibition of DUOX will impact local production of H₂O₂ leading to lower oxidizing potential of TPO and less organification of iodide.

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

In Xenopus laevis, Haselman et al.(2020) demonstrated temporal profiles of thyroidal iodotyrosines (MIT/DIT) and iodothyronines (T4/T3), the products of TPO activity, following exposure to three different model TPO inhibitors (MMI, PTU, MBT) at multiple concentrations. This study established that, in Xenopus, measurable decreases in the products of TPO activity can occur as early as 2 days of exposure during pro-metamorphosis. However, despite consistent profiles of some iodo-species across chemicals, other iodo-species showed inconsistent profiles across chemicals. This highlights the multiple mechanisms of TPO (iodination and coupling) and differential susceptibility to inhibition of those mechanisms depending on the chemical's type of interaction with TPO. The most consistent concentration-response relationship across chemicals and over time was demonstrated by thyroidal T4, which is the most relevant product to subsequent key events. At the highest concentrations tested for each chemical, thyroidal T4 was below detection by 7 days of exposure across all three TPO inhibitors. Keeping in mind that the thyroid gland has follicular lumen space where thyroglobulin/T4 is stored until proteolysis and release to the blood, full inhibition of TPO would result in a delayed measurable response due to the time it takes to deplete stored hormones. Regardless of the delay, the results from this study imply full inhibition of TPO by each of these three chemicals at the highest test concentrations, but would require chemical residue analysis and/or toxicokinetic modeling to relate cellular/tissue concentrations at the site of TPO catalysis to levels of inhibition via Michaelis-Menten kinetic descriptions.

Profiles of thyroidal iodinated species demonstrated by Haselman et al. (2020) across three different TPO inhibitors suggests that a high level of TPO inhibition must occur in order to elicit responses in subsequent key events. Although the level of TPO inhibition is not directly quantifiable from this study, these data suggest that at least 90-100% inhibition was occurring since circulating T4 was not detectable at 10 days of exposure to the highest concentrations of MMI and MBT. However, additional efforts would be necessary to determine the minimum level of TPO inhibition that leads to a measurable decrease in thyroidal T4 and subsequently circulating T4. Furthermore, Hassan et al. (2017, 2020) and Handa et al. (2021) predicted the level of THs in serum after treatment with PTU and MMI in rats. They developed a quantitative model by comparing dose- response data.

Response-response Relationship

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

There are only a limited number of studies where both TPO inhibition and iodine organification have been measured in vivo, and there is not enough data available to make any definitive quantitative correlations. One in vivo study in rats exposed to the TPO inhibitor genistein found no in vivo impact on serum TH concentrations, even when TPO was inhibited up to 80% (Chang and Doerge, 2000). Genistein is however a well-known phytoestrogen and the observed inconsistency may be the result of feedback mechanisms resulting from its estrogenic effect.

Given that this is an MIE to KE relationship, there is only one response to evaluate in the relationship. Decreased TH synthesis, as measured by responses of iodinated species in the thyroid gland, is the result of TPO inhibition, which cannot be measured directly in vivo.

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

In vivo, evaluations of TPO inhibition are limited to evaluation of the iodinated species, or products of TPO activity, present in the thyroid gland at a particular time. However, as stated previously, any measurable response in these iodinated species is not a discreet assessment of TPO activity given that the gland maintains storage of hormone in the follicular lumen space and any alteration of TPO activity would be detected once the stores begin to be depleted. In Xenopus laevis, Haselman et al. (2020) showed a decrease in thyroidal iodinated species after only 2 days of exposure to potent TPO inhibitor MMI during thyroid-mediated metamorphosis and within 4 days for PTU and MBT, both model TPO inhibitors. In zebrafish, Walter et al. (2019) reported a similar time frame, namely a decrease in T4 levels at 72 hpf after starting the exposure to PTU at 0-2 hpf. It should be noted that the time-scale is probably depending on the developmental stage and whether the embryo is capable of thyroid hormone synthesis, rather than on the exposure duration.

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

Thyroid stimulating hormone (TSH) released from the pituitary positively regulates the synthesis and release of thyroid hormones from the thyroid gland. As such, when TPO is inhibited and thyroid hormone synthesis is decreased, lower systemic levels of hormone cause feedback from the pituitary via TSH to upregulate a number of processes in the thyroid gland as a means of compensation, including (but not limited to) enhanced gene expression of NIS and thyrocyte cell proliferation (Tietge et al., 2010; Haselman et al., 2020).

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

Taxonomic: This KER is plausibly applicable across vertebrates. Inhibition of TPO activity is widely accepted to directly impact TH synthesis. This is true for both rats and humans, as well as some fishes, frogs and birds. Most of the data supporting a causative relationship between TPO inhibition and altered TH synthesis is derived from animal studies, in vitro thyroid microsomes from rats or pigs, and a limited number of human ex vivo (Nagasaka and Hidaka, 1976; Vickers et al., 2012) and clinical studies. There are data to support that gene mutations in TPO result in congenital hypothyroidism, underscoring the essential role of TPO in human TH synthesis.

Life stage: Applicability to certain life stages may depend on the species and their dependence on maternally transferred THs during the earliest phases of development. The earliest life stages of teleost fish rely on maternally transferred THs to regulate certain developmental processes until embryonic TH synthesis is active (Power et al., 2001). As a result, TPO inhibition is not expected to decrease TH synthesis during these earliest stages of development. Evidence supporting this hypothesis is obtained from a zebrafish TPO knockout line. In homozygous individuals TPO is inhibited from the embryonic developmental stage onwards, resulting in an abolished T4 production in thyroid follicles with phenotypical abnormalities such as reduced swim bladder inflation and growth retardation appearing at 20 dpf but not before 10 dpf (Fang et al., 2022). In zebrafish, Opitz et al. (2011) showed the formation of a first thyroid follicle at 55 hours post fertilization (hpf), Chang et al. (2012) showed a first significant TH increase at 120 hpf and Walter et al. (2019) showed clear TH production already at 72 hpf but did not analyse time points between 24 and 72 hpf. In fathead minnow, a significant increase of whole body TH levels was already observed between 1 and 2 dpf, which corresponds to the appearance of the thyroid anlage at 35 hpf prior to the first observation of thyroid follicles at 58 hpf (Wabuke-Bunoti and Firling, 1983). It is still uncertain when exactly embryonic TH synthesis is activated and how this determines sensitivity to TH system disruptors.

Sex: The KE is plausibly applicable to both sexes. Thyroid hormones are essential in both sexes and the components of the HPT-axis are identical in both sexes. There can however be sex-dependent differences in the sensitivity to the disruption of thyroid hormone levels and the magnitude of the response. In humans, females appear more susceptible to hypothyroidism compared to males when exposed to certain halogenated chemicals (Hernandez‐Mariano et al., 2017; Webster et al., 2014). In adult zebrafish, Liu et al. (2019) showed sex-dependent changes in thyroid hormone levels and mRNA expression of regulatory genes including corticotropin releasing hormone (crh), thyroid stimulating hormone (tsh) and deiodinase 2 after exposure to organophosphate flame retardants. The underlying mechanism of any sex-related differences remains unclear.

References

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

Chang HC, Doerge DR. Dietary genistein inactivates rat thyroid peroxidase in vivo without an apparent hypothyroid effect. Toxicol Appl Pharmacol 168:244–252 (2000).

Chang, J., Wang, M., Gui, W., Zhao, Y., Yu, L., Zhu, G., 2012. Changes in Thyroid Hormone Levels during Zebrafish Development. Zoological Science 29, 181-184.

Cooper DS, Kieffer JD, Halpern R, Saxe V, Mover H, Maloof F, Ridgway EC (1983) Propylthiouracil (PTU) pharmacology in the rat. II. Effects of PTU on thyroid function. Endocrinology 113:921-928.

Cooper DS, Saxe VC, Meskell M, Maloof F, Ridgway EC. Acute effects of propylthiouracil (PTU) on thyroidal iodide organification and peripheral iodothyronine deiodination: correlation with serum PTU levels measured by radioimmunoassay. J Clin Endocrinol Metab. 1982 54(1):101-7.

Crane HM, Pickford DB, Hutchinson TH, Brown JA. 2006. The effects of methimazole on development of the fathead minnow, pimephales promelas, from embryo to adult. Toxicological Sciences. 93(2):278-285.

Davidson, B., Soodak, M., Neary, J.T., Strout, H.V., and Kieffer, J.D. (1978). The irreversible inactivation of thyroid peroxidase by methylmercaptoimidazole, thiouracil, and propylthiouracil in vitro and its relationship to in vivo findings. Endocrinology 103:871–882.

Divi, R. L., and Doerge, D. R. (1994). Mechanism-based inactivation of lactoperoxidase and thyroid peroxidase by resorcinol derivatives. Biochemistry 33(32), 9668-74.

Doerge DR, Chang HC, Divi RL, Churchwell Mechanism for inhibition of thyroid peroxidase by leucomalachite green. Chem Res Toxicol. 1998 11(9):1098-104.

Doerge DR, Chang HC. Inactivation of thyroid peroxidase by soy isoflavones, in vitro and in vivo. J Chromatogr B Analyt Technol Biomed Life Sci. 2002 Sep 25;777(1-2):269-79

Fang, Y., Wan, J. P., Zhang, R. J., Sun, F., Yang, L., Zhao, S. X., Dong, M., & Song, H. D. (2022). Tpo knockout in zebrafish partially recapitulates clinical manifestations of congenital hypothyroidism and reveals the involvement of TH in proper development of glucose homeostasis. General and Comparative Endocrinology, 323–324. https://doi.org/10.1016/j.ygcen.2022.114033

Handa S, Hassan I, Gilbert M, El-Masri H. 2021. Mechanistic Computational Model for Extrapolating In Vitro Thyroid Peroxidase (TPO) Inhibition Data to Predict Serum Thyroid Hormone Levels in Rats. Toxicological Sciences 183(1):36-48.

Haselman, J.T., Olker, J.H., Kosian, P.A., Korte, J.J., Swintek, J.A., Denny, J.S., Nichols, J.W., Tietge, J.E., Hornung, M.W. and Degitz, S.J., 2020. Targeted pathway-based in vivo testing using thyroperoxidase inhibition to evaluate plasma thyroxine as a surrogate metric of metamorphic success in model amphibian Xenopus laevis. Toxicological Sciences, 175(2), pp.236-250.

Hassan I, El-Masri H, Ford J, Brennan A, Handa S, Friedman KP, Gilbert ME. 2020. Extrapolating In Vitro Screening Assay Data for Thyroperoxidase Inhibition to Predict Serum Thyroid Hormones in the Rat. Toxicological Sciences 173(2):280-292.

Hassan I, El-Masri H, Kosian PA, Ford J, Degitz SJ, Gilbert ME. 2017. Neurodevelopment and Thyroid Hormone Synthesis Inhibition in the Rat: Quantitative Understanding Within the Adverse Outcome Pathway Framework. Toxicological Sciences 160(1):57-73.

Hernandez-Mariano JA, Torres-Sanchez L, Bassol-Mayagoitia S, Escamilla-Nunez M, Cebrian ME, Villeda-Gutierrez EA, Lopez-Rodriguez G, Felix-Arellano EE, Blanco-Munoz J. 2017. Effect of exposure to p,p '-dde during the first half of pregnancy in the maternal thyroid profile of female residents in a mexican floriculture area. Environmental Research. 156:597-604.

Hornung MW, Kosian PA, Haselman JT, Korte JJ, Challis K, Macherla C, Nevalainen E, Degitz SJ. In Vitro, Ex Vivo, and In Vivo Determination of Thyroid Hormone Modulating Activity of Benzothiazoles.Toxicol Sci. 2015 146(2):254-64.

Kessler, J., Obinger, C., and Eales, G. (2008). Factors influencing the study of peroxidase-generated iodine species and implications for thyroglobulin synthesis. Thyroid 18(7), 769-74, 10.1089/thy.2007.0310.

Liu CS, Zhang XW, Deng J, Hecker M, Al-Khedhairy A, Giesy JP, Zhou BS. 2011. Effects of prochloraz or propylthiouracil on the cross-talk between the hpg, hpa, and hpt axes in zebrafish. Environmental Science & Technology. 45(2):769-775.

Liu XS, Cai Y, Wang Y, Xu SH, Ji K, Choi K. 2019. Effects of tris(1,3-dichloro-2-propyl) phosphate (tdcpp) and triphenyl phosphate (tpp) on sex-dependent alterations of thyroid hormones in adult zebrafish. Ecotoxicology and Environmental Safety. 170:25-32.

Nagasaka, A., and Hidaka, H. (1976). Effect of antithyroid agents 6-propyl-2-thiouracil and 1-mehtyl-2-mercaptoimidazole on human thyroid iodine peroxidase. J. Clin. Endocrinol. Metab. 43:152–158.

Nelson K, Schroeder A, Ankley G, Blackwell B, Blanksma C, Degitz S, Flynn K, Jensen K, Johnson R, Kahl M et al. 2016. Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part i: Fathead minnow. Aquatic Toxicology. 173:192-203.

Opitz, R., Maquet, E., Zoenen, M., Dadhich, R., Costagliola, S., 2011. TSH Receptor Function Is Required for Normal Thyroid Differentiation in Zebrafish. Molecular Endocrinology 25, 1579-1599.

Power, D.M., Llewellyn, L., Faustino, M., Nowell, M.A., Bjornsson, B.T., Einarsdottir, I.E., Canario, A.V., Sweeney, G.E., 2001. Thyroid hormones in growth and development of fish. Comp Biochem Physiol C Toxicol Pharmacol 130, 447-459.

Raldua, D., Babin, P.J., 2009. Simple, Rapid Zebrafish Larva Bioassay for Assessing the Potential of Chemical Pollutants and Drugs to Disrupt Thyroid Gland Function. Environmental Science & Technology 43, 6844-6850.

Rehberger, K., Baumann, L., Hecker, M., Braunbeck, T., 2018. Intrafollicular thyroid hormone staining in whole-mount zebrafish (Danio rerio) embryos for the detection of thyroid hormone synthesis disruption. Fish Physiology and Biochemistry 44, 997-1010.

Ruf, J., and Carayon, P. (2006). Structural and functional aspects of thyroid peroxidase. Archives of biochemistry and biophysics 445(2), 269-77, 10.1016/j.abb.2005.06.023.

Stinckens E, Vergauwen L, Blackwell BR, Anldey GT, Villeneuve DL, Knapen D. 2020. Effect of thyroperoxidase and deiodinase inhibition on anterior swim bladder inflation in the zebrafish. Environmental Science & Technology. 54(10):6213-6223.

Stinckens E, Vergauwen L, Schroeder A, Maho W, Blackwell B, Witters H, Blust R, Ankley G, Covaci A, Villeneuve D et al. 2016. Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part ii: Zebrafish. Aquatic Toxicology. 173:204-217.

Taurog A. 2005. Hormone synthesis. In: Werner and Ingbar’s The Thyroid: A Fundamental and Clinical Text (Braverman LE, Utiger RD, eds). Philadelphia:Lippincott, Williams and Wilkins, 47–81.

Taurog, A., Dorris, M. L., and Doerge, D. R. (1996). Mechanism of simultaneous iodination and coupling catalyzed by thyroid peroxidase. Archives of biochemistry and biophysics 330(1), 24-32,

Thienpont, B., Tingaud-Sequeira, A., Prats, E., Barata, C., Babin, P.J., Raldua, D., 2011. Zebrafish Eleutheroembryos Provide a Suitable Vertebrate Model for Screening Chemicals that Impair Thyroid Hormone Synthesis. Environmental Science & Technology 45, 7525-7532.

Tietge JE, Butterworth BC, Haselman JT, Holcombe GW, Hornung MW, Korte JJ, Kosian PA, Wolfe M, Degitz SJ. Early temporal effects of three thyroid hormone synthesis inhibitors in Xenopus laevis. Aquat Toxicol. 2010 98(1):44-50

van der Ven LTM, van den Brandhof EJ, Vos JH, Power DM, Wester PW. 2006. Effects of the antithyroid agent propylthiouracil in a partial life cycle assay with zebrafish. Environmental Science & Technology. 40(1):74-81.

Vickers AE, Heale J, Sinclair JR, Morris S, Rowe JM, Fisher RL. Thyroid organotypic rat and human cultures used to investigate drug effects on thyroid function, hormone synthesis and release pathways. Toxicol Appl Pharmacol. 2012 260(1):81-8.

Wabukebunoti MAN, Firling CE. 1983. The prehatching development of the thyroid-gland of the fathead minnow, pimephales-promelas (rafinesque). General and Comparative Endocrinology. 49(2):320-331.

Walter KM, Miller GW, Chen XP, Yaghoobi B, Puschner B, Lein PJ. 2019. Effects of thyroid hormone disruption on the ontogenetic expression of thyroid hormone signaling genes in developing zebrafish (danio rerio). General and Comparative Endocrinology. 272:20-32.

Walter, K.M., Miller, G.W., Chen, X.P., Yaghoobi, B., Puschner, B., Lein, P.J., 2019. Effects of thyroid hormone disruption on the ontogenetic expression of thyroid hormone signaling genes in developing zebrafish (Danio rerio). General and Comparative Endocrinology 272, 20-32.

Webster GM, Venners SA, Mattman A, Martin JW. 2014. Associations between perfluoroalkyl acids (pfass) and maternal thyroid hormones in early pregnancy: A population-based cohort study. Environmental Research. 133:338-347.