96-83-3OIRFJRBSRORBCM-UHFFFAOYNA-NOIRFJRBSRORBCM-UHFFFAOYSA-N
Iopanoic acidDTXSID602315960-56-0PMRYVIKBURPHAH-UHFFFAOYSA-NPMRYVIKBURPHAH-UHFFFAOYSA-N
Methimazole2H-Imidazole-2-thione, 1,3-dihydro-1-methyl-
1,3-Dihydro-1-methyl-2H-imidazole-2-thione
1-Methyl-1,3-dihydroimidazole-2-thione
1-Methyl-1H-imidazole-2-thiol
1-Methyl-2-mercapto-1H-imidazole
1-Methyl-2-mercaptoimidazole
1-Methyl-4-imidazoline-2-thione
1-Methylimidazole-2(3H)-thione
1-Methylimidazole-2-thiol
1-Methylimidazole-2-thione
2-Mercapto-1-methyl-1H-imidazole
2-Mercapto-1-methylimidazole
2-Mercapto-N-methylimidazole
4-Imidazoline-2-thione, 1-methyl-
Basolan
Danantizol
Favistan
Frentirox
Imidazole-2-thiol, 1-methyl-
Mercaptazole
Mercazole
Mercazolyl
Metazolo
Methimazol
Methylmercaptoimidazole
Metothyrin
Metothyrine
Metotirin
N-Methyl-2-mercaptoimidazole
N-Methylimidazolethiol
NSC 38608
Strumazol
Tapazole
Thacapzol
Thiamazol
thiamazole
Thycapzol
Thymidazol
Thymidazole
tiamazol
DTXSID402082051-52-5KNAHARQHSZJURB-UHFFFAOYSA-NKNAHARQHSZJURB-UHFFFAOYSA-N
6-Propyl-2-thiouracil6-Propyl-2 thiouracil (PTU)
4(1H)-Pyrimidinone, 2,3-dihydro-6-propyl-2-thioxo-
2,3-Dihydro-6-propyl-2-thioxo-4(1H)-pyrimidinone
2-Mercapto-4-hydroxy-6-n-propylpyrimidine
2-Mercapto-4-hydroxy-6-propylpyrimidine
2-Mercapto-6-propylpyrimidin-4-ol
2-Thio-4-oxo-6-propyl-1,3-pyrimidine
2-Thio-6-propyl-1,3-pyrimidin-4-one
6-n-Propyl-2-thiouracil
6-n-Propylthiouracil
6-Propyl-2-thio-2,4(1H,3H)pyrimidinedione
6-Propylthiouracil
NSC 6498
NSC 70461
Procasil
Propacil
propiltiouracilo
Propycil
Propyl-Thiorist
Propylthiorit
propylthiouracil
Propylthiouracile
Propyl-Thyracil
Prothiucil
Prothiurone
Prothycil
Prothyran
Protiural
Thiuragyl
Thyreostat II
URACIL, 4-PROPYL-2-THIO-
Uracil, 6-propyl-2-thio-
DTXSID5021209149-30-4YXIWHUQXZSMYRE-UHFFFAOYSA-NYXIWHUQXZSMYRE-UHFFFAOYSA-N
2-Mercaptobenzothiazole(2(3H)-Benzothiazolethione)
2(3H)-Benzothiazolethione
1,3-Benzothiazole-2-thiol
1,3-Benzothiazole-2-thione
2,3-Dihydrobenzothiazole-2-thione
2-Benzothiazolethiol
2-Benzothiazolinethione
2-BENZOTHIAZOLTHIOL
2-Benzothiazolyl mercaptan
2-Mercapthobenzothiazole Technical
2-Mercapto-1H-benzothiazole
2-Mercaptobenzthiazole
2-Sulfanylbenzothiazole
Accel M
Accelerator M
Aero Promoter 412
Benz-1,3-thiazolidine-2-thione
Benzo[d]thiazole-2-thiol
Benzothiazol-2-thiol
BENZOTHIAZOLE, 2-MERCAPTO-
Benzothiazole-2-thiol
Benzothiazole-2-thione
Benzothiazolethiol
benzotiazol-2-tiol
Dermacid
Ekagom G
Kaptaks
Mebetizol
Mebetizole
Mebithizol
MERCAPTOBENZOTHIAZOLE
Mercaptobenzthiazole
Nocceler M
Nocceler M-P
Nonflex NB
NSC 2041
Perkacit MBT
Pneumax MBT
Royal MBT
Sanceler M
Sanceler M-G
Soxinol M
Thiotax
Vulkacit M
Vulkacit Mercapto
Vulkacit Mercapto MG/C
Vulkacit Mercapto/C
Vulkacit Mercapto/MG
Vulkafil ZN 94TT01
Wobezit M
DTXSID102080714797-73-0VLTRZXGMWDSKGL-UHFFFAOYSA-MVLTRZXGMWDSKGL-UHFFFAOYSA-M
PerchloratePerchlorate ion
Perchlorate ion (ClO41-)
Perchlorate ion(1-)
Perchlorate(1-)
Perchloric acid, ion(1-)
DTXSID6024252PR:000006481type II iodothyronine deiodinaseCHEBI:182583,3',5-triiodo-L-thyronineCHEBI:81567Thyroid stimulating hormoneGO:0003824catalytic activityGO:0007552metamorphosis2decreased1increased5delayediopanoic acid2016-11-29T18:42:272016-11-29T18:42:27PERFLUOROOCTANOIC ACID2016-11-29T18:42:272016-11-29T18:42:27Methimazole2016-11-29T18:42:192016-11-29T18:42:19Propylthiouracil2016-11-29T18:42:222016-11-29T18:42:22Mercaptobenzothiazole2016-11-29T18:42:172016-11-29T18:42:17Perchlorate2016-11-29T18:42:262016-11-29T18:42:26Stressor:48 Propylthiouracil2020-08-28T17:00:542020-08-28T17:00:5410116ratWCS_9606human9823pigs8128Oreochromis niloticusWCS_7955zebrafishWCS_90988fathead minnowWCS_8355African clawed frog10118Rattus sp.10090mouseInhibition, Deiodinase 2Inhibition, Deiodinase 2Molecular<p>Disruption of the thyroid hormone system is increasingly being recognized as an important toxicity pathway, as it can cause many adverse outcomes. Thyroid hormones do not only play an important role in the adult individual, but they are also critical during embryonic development. Thyroid hormones (THs) play an important role in a wide range of biological processes in vertebrates including growth, development, reproduction, cardiac function, thermoregulation, response to injury, tissue repair and homeostasis. Numerous chemicals are known to disturb thyroid function, for example by inhibiting thyroperoxidase (TPO) or deiodinase (DIO), upregulating excretion pathways or modifying gene expression. The two major thyroid hormones are triiodothyronine (T3) and thyroxine (T4), both iodinated derivatives of tyrosine. Most TH actions depend on the binding of T3 to its nuclear receptors. Active and inactive THs are tightly regulated by enzymes called iodothyronine deiodinases (DIO). The activation occurs via outer ring deiodination (ORD), i.e. removing iodine from the outer, phenolic ring of T4 to form T3, while inactivation occurs via inner ring deiodination (IRD), i.e. removing iodine from the inner tyrosol ring of T4 or T3.</p>
<p>Three types of iodothyronine deiodinases (DIO1-3) have been described in vertebrates that activate or inactivate THs and are therefore important mediators of TH action. All deiodinases are integral membrane proteins of the thioredoxin superfamily that contain selenocysteine in their catalytic centre. Type I deiodinase is capable to convert T4 into T3, as well as to convert reverse T3 (rT3) to 3,3'-Diiodothyronine (3,3’ T2), through outer ring deiodination. rT3, rather than T4, is the preferred substrate for DIO1. furthermore, DIO1 has a very high Km (µM range, compared to nM range for DIO2) (Darras and Van Herck, 2012). Type II deiodinase (DIO2) is only capable of ORD activity with T4 as a preferred substrate (i.e., activation of T4 to T3). DIO3 can inner ring deiodinate T4 and T3 to the inactive forms of THs, rT3 and 3,3’-T2 respectively. DIO2 is a transmembrane protein anchored to the endoplasmic reticulum and the active site faces the perinuclear cytosol. The relative contribution of the DIOs to thyroid hormone levels varies amongst species, developmental stages and tissues.</p>
<p>At this time, there are no approved OECD or EPA guideline protocols for measurement of DIO inhibition. Deiodination is the major pathway regulating T3 bioavailability in mammalian tissues. In vitro assays can be used to examine inhibition of deiodinase 2 (DIO2) activity upon exposure to thyroid disrupting compounds.</p>
<p>Several methods for deiodinase activity measurements are available. A first in vitro assay measures deiodinase activities by quantifying the radioactive iodine release from iodine-labelled substrates, depending on the preferred substrates of the isoforms of deiodinases (Forhead et al., 2006; Pavelka, 2010; Houbrechts et al., 2016; Stinckens et al., 2018). Each of these assays requires a source of deiodinase which can be obtained for example using unexposed pig liver tissue (available from slaughterhouses) or rat liver tissue. Olker et al. (2019) on the other hand used an adenovirus expression system to produce the DIO2 enzyme and developed an assay for nonradioactive measurement of iodide released using the Sandell-Kolthoff method, a photometric method based on Ce4+ reduction (Renko et al., 2012). This assay was then used to screen the ToxCast Phase 1 chemical library. The specific synthesis of DIO2 through the adenovirus expression system provides an important advantage over other methods where activity of the different deiodinase isoforms needs to be distinguished in other ways, such as based on differences in enzyme kinetics.</p>
<p>Measurements of in vivo deiodinase activity in tissues collected from animal experiments are scarce. Noyes et al. (2011) showed decreased rate of outer ring deiodination (mediated by DIO1 and DIO2) in whole fish microsomes after exposure to BDE-209. After incubation with the substrate, thyroid hormone levels were measured using LC-MS/MS. Houbrechts et al. (2016) confirmed DIO2 deiodination activity in a DIO1-DIO2 knockdown zebrafish at the ages of 3 and 7 days post fertilization. Decreased T3 levels are often used as evidence of DIO inhibition, for example after exposure to iopanoic acid, in fish species such as zebrafish (Stinckens et al., 2020) and fathead minnow (Cavallin et al., 2017). It should be noted that it is difficult to make the distinction between decreased T3 levels caused by outer ring deiodination mediated by DIO2 inhibition or DIO1 inhibition.</p>
<p><strong>Taxonomic: </strong>Deiodination by DIO enzymes is known to exist in a wide range of vertebrates and invertebrates. This KE is plausibly applicable across vertebrates. Reports of inhibition of DIO2 activity are relatively scarce compared to DIO1. Studies reporting DIO2 inhibition have used human recombinant DIO2 enzyme (Olker et al., 2019), primary human astrocytes (Roberts et al., 2015), rat pituitary (Li et al., 2012), pig liver (Stinckens et al., 2018), Nile tilapia (Oreochromis niloticus) liver (Walpita et al., 2007). Evidence for fish (e.g., zebrafish and fathead minnow) is mostly indirect since DIO enzyme activity is usually not measured in chemical exposure experiments. Houbrechts et al. (2016) showed decreased DIO2 activity in a DIO1-DIO2 knockdown zebrafish at the ages of 3 and 7 days post fertilization together with impaired swim bladder inflation, showing that the enzyme is present, the activity is measurable and impairing its activity has negative effects. Noyes confirmed decreased outer ring deiodination activity in fathead minnows exposed to decabromodiphenyl ether (BDE-209). Walpita et al. (2007) showed decreased DIO2 activity in the liver of Nile tilapia injected with dexamethasone. Stinckens et al. (2018) showed that chemicals with DIO inhibitory potential in pig liver impaired swim bladder inflation in zebrafish, a thyroid hormone regulated process. Six out of seven DIO1 inhibitors impaired posterior chamber inflation, but almost all of these compounds also inhibit DIO2. TCBPA, the only compound that inhibits DIO1 and not DIO2, had no effect on the posterior swim bladder. Based on these results, DIO2 seemed to be more important than DIO1. </p>
<p>In mammals, DIO2 is thought to control the intracellular concentration of T3, while DIO1 is thought to be more important in determining systemic T3 levels. The cells that express DIO2 locally produce T3 that can more rapidly access the thyroid receptors in the nucleus than T3 from plasma (Bianco et al., 2002). For example, DIO2 is highly expressed in the mammalian brain. However, this hypothesis has been challenged. For example, Maia et al. (2005) determined that in a normal physiological situation in humans the contribution of DIO2 to plasma T3 levels is twice that of DIO1. Only in a hyperthyroid state was the contribution of DIO1 higher than that of DIO2. A DIO1 knockout mouse showed normal T3 levels and a normal general phenotype and DIO1 was rather found to play a role in limiting the detrimental effects of conditions that alter normal thyroid function, including hyperthyroidism and iodine deficiency (Schneider et al., 2006). van der Spek et al. concluded that the primary role of DIO1 in vivo is to degrade inactivated TH (van der Spek et al., 2017).</p>
<p>The presence of DIO1 in the liver of teleosts has been a controversial issue and DIO1 function in teleostean and amphibian T3 plasma regulation is unclear (Finnson et al., 1999; Kuiper et al., 2006). In teleosts, DIO2 has a markedly higher activity level compared to other vertebrates and it is expressed in liver (Orozco and Valverde, 2005), suggesting its importance in determining systemic thyroid hormone levels. This could explain why DIO2 inhibition seems to be more important than DIO1 inhibition in determining the adverse outcome in zebrafish (Stinckens et al., 2018). </p>
<p><strong>Life stage</strong>: Deiodinase activity is important for all vertebrate life stages. Already during early embryonic development, deiodinase activity is needed to regulate thyroid hormone concentrations and coordinate developmental processes. DIO2 shows more marked changes in expression around the time of the embryo-larval and larval-to-juvenile transition periods during zebrafish development, highlighting its importance for early life stages (Vergauwen et al., 2018).</p>
<p><strong>Sex</strong>: This KE is plausibly applicable to both sexes. Deiodinases are important for TH homeostasis and identical in both sexes. Therefore inhibition of deiodinases is not expected to be sex-specific.</p>
ModerateUnspecificModerateAll life stagesModerateHighModerateModerateModerateModerateNot Specified<p>Bianco, A.C., Salvatore, D., Gereben, B., Berry, M.J., Larsen, P.R., 2002. Biochemistry, cellular and molecular biology, and physiological roles of the iodothyronine selenodeiodinases. Endocrine Reviews 23, 38-89.</p>
<p>Cavallin JE, Ankley GT, Blackwell BR, Blanksma CA, Fay KA, Jensen KM, Kahl MD, Knapen D, Kosian PA, Poole ST et al. 2017. Impaired swim bladder inflation in early life stage fathead minnows exposed to a deiodinase inhibitor, iopanoic acid. Environmental Toxicology and Chemistry. 36(11):2942-2952.</p>
<p>Darras, V.M., Van Herck, S.L.J., 2012. Iodothyronine deiodinase structure and function: from ascidians to humans. Journal of Endocrinology 215, 189-206.</p>
<p>Forhead, A.J., Curtis, K., Kaptein, E., Visser, T.J., Fowden, A.L., 2006. Developmental control of iodothyronine deiodinases by cortisol in the ovine fetus and placenta near term. Endocrinology 147, 5988-5994.</p>
<p>Houbrechts, A.M., Delarue, J., Gabriels, I.J., Sourbron, J., Darras, V.M., 2016. Permanent Deiodinase Type 2 Deficiency Strongly Perturbs Zebrafish Development, Growth, and Fertility. Endocrinology 157, 3668-3681.</p>
<p>Li, N.N., Jiang, Y.Q., Shan, Z.Y., Teng, W.P., 2012. Prolonged high iodine intake is associated with inhibition of type 2 deiodinase activity in pituitary and elevation of serum thyrotropin levels. British Journal of Nutrition 107, 674-682.</p>
<p>Noyes PD, Hinton DE, Stapleton HM. 2011. Accumulation and debromination of decabromodiphenyl ether (bde-209) in juvenile fathead minnows (pimephales promelas) induces thyroid disruption and liver alterations. Toxicological Sciences. 122(2):265-274.</p>
<p>Olker, J.H., Korte, J.J., Denny, J.S., Hartig, P.C., Cardon, M.C., Knutsen, C.N., Kent, P.M., Christensen, J.P., Degitz, S.J., Hornung, M.W., 2019. Screening the ToxCast Phase 1, Phase 2, and e1k Chemical Libraries for Inhibitors of Iodothyronine Deiodinases. Toxicological Sciences 168, 430-442.</p>
<p>Orozco, A., Valverde, R.C., 2005. Thyroid hormone deiodination in fish. Thyroid 15, 799-813.</p>
<p>Pavelka, S., 2010. Radiometric enzyme assays: development of methods for extremely sensitive determination of types 1, 2 and 3 iodothyronine deiodinase enzyme activities. Journal of Radioanalytical and Nuclear Chemistry 286, 861-865.</p>
<p>Renko, K., Hoefig, C.S., Hiller, F., Schomburg, L., Kohrle, J., 2012. Identification of Iopanoic Acid as Substrate of Type 1 Deiodinase by a Novel Nonradioactive Iodide-Release Assay. Endocrinology 153, 2506-2513.</p>
<p>Renko, K., Schache, S., Hoefig, C.S., Welsink, T., Schwiebert, C., Braun, D., Becker, N.P., Kohrle, J., Schomburg, L., 2015. An Improved Nonradioactive Screening Method Identifies Genistein and Xanthohumol as Potent Inhibitors of Iodothyronine Deiodinases. Thyroid 25, 962-968.</p>
<p>Roberts, S.C., Bianco, A.C., Stapleton, H.M., 2015. Disruption of Type 2 Iodothyronine Deiodinase Activity in Cultured Human Glial Cells by Polybrominated Diphenyl Ethers. Chemical Research in Toxicology 28, 1265-1274.</p>
<p>Schneider, M.J., Fiering, S.N., Thai, B., Wu, S.Y., St Germain, E., Parlow, A.F., St Germain, D.L., Galton, V.A., 2006. Targeted disruption of the type 1 selenodeiodinase gene (Dio1) results in marked changes in thyroid hormone economy in mice. Endocrinology 147, 580-589.</p>
<p>Stinckens, E., Vergauwen, L., Ankley, G.T., Blust, R., Darras, V.M., Villeneuve, D.L., Witters, H., Volz, D.C., Knapen, D., 2018. An AOP-based alternative testing strategy to predict the impact of thyroid hormone disruption on swim bladder inflation in zebrafish. Aquatic Toxicology 200, 1-12.</p>
<p>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.</p>
<p>van der Spek, A.H., Fliers, E., Boelen, A., 2017. The classic pathways of thyroid hormone metabolism. Molecular and Cellular Endocrinology 458, 29-38.</p>
<p>Vergauwen, L., Cavallin, J.E., Ankley, G.T., Bars, C., Gabriels, I.J., Michiels, E.D.G., Fitzpatrick, K.R., Periz-Stanacev, J., Randolph, E.C., Robinson, S.L., Saari, T.W., Schroeder, A.L., Stinckens, E., Swintek, J., Van Cruchten, S.J., Verbueken, E., Villeneuve, D.L., Knapen, D., 2018. Gene transcription ontogeny of hypothalamic-pituitary-thyroid axis development in early-life stage fathead minnow and zebrafish. General and Comparative Endocrinology 266, 87-100.</p>
<p>Walpita, C.N., Grommen, S.V., Darras, V.M., Van der Geyten, S., 2007. The influence of stress on thyroid hormone production and peripheral deiodination in the Nile tilapia (Oreochromis niloticus). Gen Comp Endocrinol 150, 18-25.</p>
2016-11-29T18:41:282022-10-07T07:56:32Decreased, Triiodothyronine (T3) in tissuesDecreased, Triiodothyronine (T3) in tissuesTissue<p>In many ways, this key event fundamentally works the same as key event <a href="https://aopwiki.org/events/1093">1093: Thyroxine (T4) in tissues, decreased</a>. However, T3 can only exist in tissues from either direct uptake from the serum or produced locally from outer ring deiodination (ORD) of T4. ORD of T4 can occur in any tissue that expresses either type I or II iodothyronine deiodinases (DIO1, DIO2). Although T3 can be produced in peripheral tissues from T4 via ORD, T4 can only be synthesized in the thyroid gland. The local concentration of T3 in any given cell or tissue will be a function of, (1) local T4 availability, which is a function of plasma T4 concentration and active transport capacity across cell membranes, (2) local DIO1 and/or DIO2 activity, and (3) circulating levels of T3, as a result of remote activation of T4 by either DIO1 or DIO2 and release of T3 to the plasma.</p>
<p>This key event is measured the same as key event <a href="https://aopwiki.org/events/1093">1093: Thyroxine (T4) in tissues, decreased</a>. <a href="https://aopwiki.org/system/dragonfly/production/2020/08/28/4u70cr995r_TH_tissue_measurement_lit_table.pdf">Summary table of measurement methods.</a></p>
<p>The essentiality of this key event applies during thyroid-mediated metamorphosis in amphibians and especially African clawed frog (Xenopus laevis), which provides the basis for this key event leading to altered metamorphosis. However, direct measurements of this key event are not routine or typical. The support for this key event exists primarily as biological plausibility and thyroid endocrinology dogma.</p>
ModerateUnspecificModerateDevelopmentHigh<p><br />
Ackermans, M.T., Kettelarij‐Haas, Y., Boelen, A. and Endert, E., 2012. Determination of thyroid hormones and their metabolites in tissue using SPE UPLC‐tandem MS. Biomedical Chromatography, 26(4), pp.485-490.</p>
<p>Bastian, T.W., Prohaska, J.R., Georgieff, M.K. and Anderson, G.W., 2010. Perinatal iron and copper deficiencies alter neonatal rat circulating and brain thyroid hormone concentrations. Endocrinology, 151(8), pp.4055-4065.</p>
<p>Bastian, T.W., Anderson, J.A., Fretham, S.J., Prohaska, J.R., Georgieff, M.K. and Anderson, G.W., 2012. Fetal and neonatal iron deficiency reduces thyroid hormone-responsive gene mRNA levels in the neonatal rat hippocampus and cerebral cortex. Endocrinology, 153(11), pp.5668-5680.</p>
<p>Bastian, T.W., Prohaska, J.R., Georgieff, M.K. and Anderson, G.W., 2013. Fetal and neonatal iron deficiency exacerbates mild thyroid hormone insufficiency effects on male thyroid hormone levels and brain thyroid hormone-responsive gene expression. Endocrinology, 155(3), pp.1157-1167.</p>
<p>Crane, H.M., Pickford, D.B., Hutchinson, T.H. and Brown, J.A., 2004. Developmental changes of thyroid hormones in the fathead minnow, Pimephales promelas. General and comparative endocrinology, 139(1), pp.55-60.</p>
<p>Donzelli, R., Colligiani, D., Kusmic, C., Sabatini, M., Lorenzini, L., Accorroni, A., Nannipieri, M., Saba, A., Iervasi, G. and Zucchi, R., 2016. Effect of Hypothyroidism and Hyperthyroidism on Tissue Thyroid Hormone Concentrations in Rat. European thyroid journal, 5(1), pp.27-34.</p>
<p>ESCOBAR, G.M.D., Pastor, R., Obregón, M.J. and REY, F.E.D., 1985. Effects of Maternal Hypothyroidism on the Weight and Thyroid Hormone Content of Rat Embryonic Tissues, before and after Onset of Fetal Thyroid Function*. Endocrinology, 117(5), pp.1890-1900.</p>
<p>Gilbert, M.E., Hedge, J.M., Valentín-Blasini, L., Blount, B.C., Kannan, K., Tietge, J., Zoeller, R.T., Crofton, K.M., Jarrett, J.M. and Fisher, J.W., 2013. An animal model of marginal iodine deficiency during development: the thyroid axis and neurodevelopmental outcome. toxicological sciences, p.kfs335.</p>
<p>Hornung, M.W., Kosian, P.A., Haselman, J.T., Korte, J.J., Challis, K., Macherla, C., Nevalainen, E. and Degitz, S.J., 2015. In vitro, ex vivo, and in vivo determination of thyroid hormone modulating activity of benzothiazoles. Toxicological Sciences, 146(2), pp.254-264.</p>
<p>Kunisue, T., Fisher, J.W., Fatuyi, B. and Kannan, K., 2010. A method for the analysis of six thyroid hormones in thyroid gland by liquid chromatography–tandem mass spectrometry. Journal of Chromatography B, 878(21), pp.1725-1730.</p>
<p>Kunisue, T., Fisher, J.W. and Kannan, K., 2011. Determination of six thyroid hormones in the brain and thyroid gland using isotope-dilution liquid chromatography/tandem mass spectrometry. Analytical chemistry, 83(1), pp.417-424.</p>
<p>Lavado-Autric, R., Calvo, R.M., de Mena, R.M., de Escobar, G.M. and Obregon, M.J., 2012. Deiodinase activities in thyroids and tissues of iodine-deficient female rats. Endocrinology, 154(1), pp.529-536.</p>
<p>Pinna, G., Hiedra, L., Prengel, H., Broedel, O., Eravci, M., Meinhold, H. and Baumgartner, A., 1999. Extraction and quantification of thyroid hormones in selected regions and subcellular fractions of the rat brain. Brain Research Protocols, 4(1), pp.19-28.</p>
<p>Simon, R., Tietge, J., Michalke, B., Degitz, S. and Schramm, K.W., 2002. Iodine species and the endocrine system: thyroid hormone levels in adult Danio rerio and developing Xenopus laevis. Analytical and bioanalytical chemistry, 372(3), pp.481-485.</p>
<p>Saba, A., Donzelli, R., Colligiani, D., Raffaelli, A., Nannipieri, M., Kusmic, C., Dos Remedios, C.G., Simonides, W.S., Iervasi, G. and Zucchi, R., 2014. Quantification of thyroxine and 3, 5, 3′-triiodo-thyronine in human and animal hearts by a novel liquid chromatography-tandem mass spectrometry method. Hormone and Metabolic Research, 46(09), pp.628-634.</p>
<p>Tietge, J.E., Butterworth, B.C., Haselman, J.T., Holcombe, G.W., Hornung, M.W., Korte, J.J., Kosian, P.A., Wolfe, M. and Degitz, S.J., 2010. Early temporal effects of three thyroid hormone synthesis inhibitors in Xenopus laevis. Aquatic Toxicology, 98(1), pp.44-50.</p>
<p>Tietge, J.E., Degitz, S.J., Haselman, J.T., Butterworth, B.C., Korte, J.J., Kosian, P.A., Lindberg-Livingston, A.J., Burgess, E.M., Blackshear, P.E. and Hornung, M.W., 2013. Inhibition of the thyroid hormone pathway in Xenopus laevis by 2-mercaptobenzothiazole. Aquatic toxicology, 126, pp.128-136.</p>
2016-11-29T18:41:292020-09-01T16:29:27Altered, Amphibian metamorphosisAltered, Amphibian metamorphosisOrgan<p>Vertebrate metamorphosis is a biological transformation process that transitions an organism from one life stage to another; it is defined by growth of new tissues, programmed death of other tissues and physiological transformation of yet other tissues (Laudet, 2011; Brown and Cai, 2007). In the case of most amphibians, metamorphosis mediates the transition from aquatic to terrestrial life, while in bony and jawless fish, metamorphosis mediates transitions between life stages that offer various advantages for survival and reproduction. In vertebrates, metamorphosis is orchestrated by the hypothalamus-pituitary-thyroid (HPT) axis involving complex timing of gene expression/repression within various tissues, whereas in some cases across taxonomic classes, metamorphosis has been shown to be controlled very differently by the HPT axis.</p>
<p>Thyroid hormone-mediated amphibian metamorphosis can be characterized by three phases during larval development: (1) pre-metamorphosis, (2) pro-metamorphosis and (3) metamorphic climax. All three of these phases coincide with activity states of the HPT axis. Pre-metamorphosis is characterized by a fully aquatic organism with low-level function of the thyroid gland and very low circulating levels of thyroid hormone. Pro-metamorphosis is characterized by the onset of full thyroid axis function and the initiation of rising levels of thyroid hormone in the plasma, with consequential changes in anatomy and physiology defining the transition from aquatic to terrestrial life. Metamorphic climax occurs when circulating thyroid hormone levels peak, which subsequently decrease to levels maintained homeostatically as adults. This climax period also represents the time at which all anatomical and physiological changes induced by thyroid hormone have either been initiated or are already completed. Detailed descriptions of these processes are reviewed by Brown and Cai (2007).</p>
<p>Altered metamorphosis occurs when these thyroid hormone-mediated processes are perturbed, primarily during pro-metamorphosis and metamorphic climax. These perturbations can lead to either, delayed/arrested development, accelerated development or asynchronous development depending on the xenobiotic mode of action or MIE. Genetic defects or xenobiotic exposure that reduce thyroid hormone synthesis can delay metamorphosis, and in extreme cases, can completely arrest development. The most profound impacts on TH-mediated metamorphosis have be demonstrated through inhibition of key proteins in the TH synthesis pathway including the sodium-iodide symporter (Tietge et al., 2005, 2010; Hornung et al., 2010) and thyroperoxidase (Degitz et al., 2005; Tietge et al., 2010, 2013; Hornung et al., 2010, 2015). Alternatively, agonism of the thyroid axis through inhibition of negative feedback at the level of the hypothalamus-pituitary, or premature activation of thyroid receptor-mediated transcription can accelerate metamorphosis (Degitz et al., 2005), which can lead to asynchronous development due to errors in gene expression timing across the various metamorphic tissues. Asynchronous development can also occur due to inhibition of deiodinase (DIO) enzymes in peripheral tissues. DIO enzymes are responsible for activation and catabolism of TH; when <em>dio</em> gene expression profiles are altered, or the enzymes themselves undergo chemical inhibition, the imbalance of prohormone (T4), active hormone (T3) and inactive hormone (rT3, T2) can cause aberrant tissue development.</p>
<p>Rates of metamorphosis in model amphibian species, <em>Xenopus laevis</em>, are measured multiple ways, both of which rely on a developmental staging atlas developed by Nieuwkoop and Faber (NF)(1994). The method utilized within the 21 d Amphibian Metamorphosis Assay regulatory test guideline (OECD, 2009; US EPA 2009) relate the distribution of developmental stage of control larvae to the distributions of developmental stages of treated/exposed larvae. These data are typically analyzed for differences from control using non-parametric statistical approaches such as the Kruskal-Wallis test followed by Dunn's test for pairwise comparisons. The method utilized within the Larval Amphibian Growth and Development Assay regulatory test guideline (OECD, 2015; US EPA 2015) relate the number of days to reach metamorphic climax (NF stage 62) in control larvae to the number of days to NF stage 62 in treated/exposed larvae. These data are typically analyzed for differences from control using a Cox mixed-effects proportional hazard model.</p>
<p>Asynchronous development is identified as disruption of the relative timing of morphogenic milestones and/or somatic development within a single larvae undergoing metamorphosis. The inability to identify an organism's developmental stage based on accepted criteria, such as outlined in Nieuwkoop and Faber (1994) for <em>Xenopus sp.</em> or Gosner (1960) for anurans, constitutes evidence of asynchronous development and would be counted as an incidence. Evaluations of severity are possible but the accuracy and resolution of the results would depend on the experience of the observer. One possible statistical approach for analyzing these data collected from a regulatory test guideline (OECD, 2009, 2015) would be a Rao-Scott-Cochran-Armitage by slices test (Green et al., 2014), as is often used for analysis of histopathology incidence and severity data. </p>
<p>Anurans</p>
<p><em>Xenopus laevis</em></p>
HighUnspecificHighDevelopmentHigh<p><br />
Brown, D.D. and Cai, L., 2007. Amphibian metamorphosis. Developmental biology, 306(1), pp.20-33.</p>
<p>Degitz, S.J., Holcombe, G.W., Flynn, K.M., Kosian, P.A., Korte, J.J. and Tietge, J.E., 2005. Progress towards development of an amphibian-based thyroid screening assay using Xenopus laevis. Organismal and thyroidal responses to the model compounds 6-propylthiouracil, methimazole, and thyroxine. Toxicological sciences, 87(2), pp.353-364.</p>
<p>Gosner, K.L., 1960. A simplified table for staging anuran embryos and larvae with notes on identification. <em>Herpetologica</em>, <em>16</em>(3), pp.183-190.</p>
<p>Green, J.W., Springer, T.A., Saulnier, A.N. and Swintek, J., 2014. Statistical analysis of histopathological endpoints. <em>Environmental toxicology and chemistry</em>, <em>33</em>(5), pp.1108-1116.</p>
<p>Hornung, M.W., Degitz, S.J., Korte, L.M., Olson, J.M., Kosian, P.A., Linnum, A.L. and Tietge, J.E., 2010. Inhibition of thyroid hormone release from cultured amphibian thyroid glands by methimazole, 6-propylthiouracil, and perchlorate. Toxicological Sciences, 118(1), pp.42-51.</p>
<p>Laudet, V., 2011. The origins and evolution of vertebrate metamorphosis. Current Biology, 21(18), pp.R726-R737.</p>
<p>Nieuwkoop, P.D. and Faber, J., 1994. Normal Table of Xenopus laevis (Daudin) Garland Publishing. <em>New York</em>, <em>252</em>.</p>
<p>OECD. (2009). Test No. 231: Amphibian Metamorphosis Assay, OECD Guidelines for the Testing of Chemicals, Section 2. OECD Publishing, Paris.</p>
<p>OECD. (2015). Test No. 241: The Larval Amphibian Growth and Development Assay (LAGDA), OECD Guidelines for the Testing of Chemicals, Section 2. OECD Publishing, Paris.</p>
<p>Tietge, J.E., Butterworth, B.C., Haselman, J.T., Holcombe, G.W., Hornung, M.W., Korte, J.J., Kosian, P.A., Wolfe, M. and Degitz, S.J., 2010. Early temporal effects of three thyroid hormone synthesis inhibitors in Xenopus laevis. Aquatic Toxicology, 98(1), pp.44-50.</p>
<p>Tietge, J.E., Holcombe, G.W., Flynn, K.M., Kosian, P.A., Korte, J.J., Anderson, L.E., Wolf, D.C. and Degitz, S.J., 2005. Metamorphic inhibition of Xenopus laevis by sodium perchlorate: effects on development and thyroid histology. Environmental Toxicology and Chemistry, 24(4), pp.926-933.</p>
<p>Tietge, J.E., Degitz, S.J., Haselman, J.T., Butterworth, B.C., Korte, J.J., Kosian, P.A., Lindberg-Livingston, A.J., Burgess, E.M., Blackshear, P.E. and Hornung, M.W., 2013. Inhibition of the thyroid hormone pathway in Xenopus laevis by 2-mercaptobenzothiazole. Aquatic toxicology, 126, pp.128-136.</p>
<p>U.S. EPA. (2009). OCSPP 890.1100: Amphibian Metamorphosis Assay (AMA), Endocrine Disruptor Screening Program Test Guidelines, 890 Series. Available at: www.regulations.gov, ID: EPA-HQ-OPPT-2009-0576-0002. Accessed March 20, 2020.</p>
<p>U.S. EPA. (2015). OCSPP 890.2300: Larval Amphibian Growth and Development Assay (LAGDA), Endocrine Disruptor Screening Program Test Guidelines, 890 Series. Available at: www.regulations.gov, ID: EPA-HQ-OPPT-2014-0766-0020. Accessed March 20, 2020.</p>
2016-11-29T18:41:292020-09-02T11:19:05Increased, Thyroid-stimulating hormone (TSH)Increased, Thyroid-stimulating hormone (TSH)TissueUBERON:0001977serumNot SpecifiedNot SpecifiedNot Specified2016-11-29T18:41:282017-09-16T10:17:01Increased, Thyroxine (T4) in serumIncreased, Thyroxine (T4) in serumOrganNot Specified2020-12-09T14:21:072020-12-09T14:21:07Altered, Thyroid hormone-dependent gene expressionAltered, TH-dependent gene expressionMolecularNot Specified2020-12-09T14:22:382020-12-09T14:22:3811217f52-a494-4e0b-ba60-434a068d2b5d4f12ad63-7948-4b5b-896d-782e1d7a21f3Not Specified2016-11-29T18:41:372016-12-03T16:38:05ba131f50-f063-44c3-9ac1-6cd45d830426fe522415-13b1-4062-b24c-074c9c057477Not Specified2020-12-09T14:26:432020-12-09T14:26:434f12ad63-7948-4b5b-896d-782e1d7a21f3a481e758-73c8-4417-815f-49043bd168d8Not Specified2020-12-09T14:24:182020-12-09T14:24:18ba131f50-f063-44c3-9ac1-6cd45d83042624a118a6-fe32-49e7-8a52-3a41347a4a43Not Specified2020-12-09T14:27:262020-12-09T14:27:264f12ad63-7948-4b5b-896d-782e1d7a21f324a118a6-fe32-49e7-8a52-3a41347a4a43Not Specified2020-12-09T14:25:042020-12-09T14:25:04a481e758-73c8-4417-815f-49043bd168d8ba131f50-f063-44c3-9ac1-6cd45d830426Not Specified2020-12-09T14:25:492020-12-09T14:25:49Type II iodothyronine deiodinase (DIO2) inhibition leading to altered amphibian metamorphosisDIO2 inhib alters metamorphosis<p>Jonathan T. Haselman, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <haselman.jon@epa.gov></p>
<p>Sigmund J. Degitz, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <degitz.sigmund@epa.gov></p>
<p>Michael W. Hornung, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <hornung.michael@epa.gov></p>
<p>Sally A. Mayasich, Center for Computational Toxicology and Exposure, US EPA, Duluth, MN, USA <mayasich.sally@epa.gov></p>
Under Development: Contributions and Comments WelcomeUnder Development1.29<p>This putative AOP describes the potential for an adverse outcome resulting from the inhibition of Type 2 iodothyronine deiodinase (DIO2) during amphibian metamorphosis. Initial development of this AOP is based largely on literature in which amphibian deiodinases are genetically disrupted or blocked by the deiodinase inhibitor iopanoic acid, and prediction from tissue expression patterns. Thyroid hormones (THs) are essential for normal sequential development of amphibian tissues and organs, and activities of the three deiodinases found in amphibians, as in mammals, function in a highly regulated balance. Chemical inhibition of DIO2, the molecular-initiating event (MIE), results in decreased transformation of thyroxine (T4) to the active form, 3,5,3’-triiodothyronine (T3) in peripheral tissues. Chemicals that interfere with the DIO2 catalyzing reaction of T4 to T3 have the potential to cause insufficiency of the active form that may result in altered metamorphosis. Adverse consequences of T3 insufficiency may vary based on timing of exposure and produce different effects at different developmental stages. For example, T3 insufficiency due to DIO2 inhibition in the African clawed frog, <em>Xenopus laevis</em>, within several days post-fertilization (pre-metamorphosis) could affect brain development, and could alter T4/T3 feedback. It has been found that DIO2 does not regulate T3 levels in serum. However, D2 inhibition in peripheral tissues through the larval phase and post-metamorphic climax may cause alterations in limb development, intestinal remodeling, gill resorption and/or tail resorption.</p>
<p>Olker et al. (2019) identified 20 DIO2-specific inhibitors using a human recombinant DIO2 enzyme (e.g., tetramethrin, elzasonan). Another typical inhibitor of DIO2 (and DIO1 and 3) is iopanoic acid (IOP), which acts as a substrate of all three DIO isoforms (Renko et al., 2015). In fact, many compounds inhibit all three DIO isoforms. Olker et al. (2019) identified 93 compounds that inhibit DIOs 1, 2 and 3.</p>
<p>Altered metamorphosis is a critical apical endpoint evaluated as part of regulatory test guideline studies (OECD, 2009, 2015; US EPA 2009, 2015). Measurable effects on metamorphic rates can be an indication of endocrine disruption, and more specifically thyroid disruption, due to the requirement of thyroid hormone for amphibians to undergo metamorphosis. Although this outcome is evaluated at the level of the individual organism, delayed or arrested metamorphosis can have implications toward population-level effects; however, significant effects on metamorphic rates are typically considered in a weight-of-evidence evaluation to determine a chemical's potential to cause thyroid disruption. </p>
adjacentLowModerateadjacentLowModerateadjacentLowModerateadjacentLowModeratenon-adjacentLowModeratenon-adjacentLowModerateHighUnspecificHighDevelopmentModerate<p><br />
Becker, K.B., Stephens, K.C., Davey, J.C., Schneider, M.J., Galton, V.A. (1997). “The Type 2 and Type 3 iodothyronine deiodinases play important roles in coordinating development in Rana catesbeiana tadpoles.” Endocrinology 138(7): 2989-2997.</p>
<p>Cai, L. Q., Brown, D.D. (2004). "Expression of type II iodothyronine deiodinase marks the time that a tissue responds to thyroid hormone-induced metamorphosis in Xenopus laevis." Developmental Biology 266(1): 87-95.</p>
<p>Galton, V.A., Schneider, M.J., Clark, A.S., St. Germain, D.L. (2009). “Life without thyroxine to 3,5,3’-triiodothyronine conversion: studies in mice devoid of the 5’-deiodinases.” Endocrinology 150(6): 2957–2963.</p>
<p>Huang, H., Cai, L., Remo, B. F., Brown, D. D.. (2001). "Timing of metamorphosis and the onset of the negative feedback loop between the thyroid gland and the pituitary is controlled by type II iodothyronine deiodinase in Xenopus laevis." Proc Natl Acad Sci U S A 98(13): 7348-7353.</p>
<p>Morvan-Dubois, G., Demeneix, B.A., Sachs, L.M. (2008). “Xenopus laevis as a model for studying thyroid hormone signaling: From development to metamorphosis.” Mol Cell Endocrinol. 293: 71-79.</p>
<p>Morvan-Dubois, G., Sebillot, A., Kuiper, G.G.J.M., Verhoelst, C.H.J., Darras, V.M., Visser, T.J., Demeneix, B.A. (2006). “Deiodinase activity is present in Xenopus laevis during early embryogenesis.” Endocrinolgy 147(10): 4941-4949.</p>
<p>Schneider MJ, Fiering SN, Pallud SE, Parlow AF, St Germain DL, GaltonVA (2001) Targeted disruption of the type 2 selenodeiodinase gene (DIO2) results in a phenotype of pituitary resistance to T4. Mol Endocrinol 15:2137–2148.</p>
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