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Event: 425

Key Event Title

A descriptive phrase which defines a discrete biological change that can be measured. More help

Decrease of Thyroidal iodide

Short name
The KE short name should be a reasonable abbreviation of the KE title and is used in labelling this object throughout the AOP-Wiki. More help
Thyroidal Iodide, Decreased
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Biological Context

Structured terms, selected from a drop-down menu, are used to identify the level of biological organization for each KE. More help
Level of Biological Organization

Cell term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Cell term
thyroid follicular cell

Organ term

The location/biological environment in which the event takes place.The biological context describes the location/biological environment in which the event takes place.  For molecular/cellular events this would include the cellular context (if known), organ context, and species/life stage/sex for which the event is relevant. For tissue/organ events cellular context is not applicable.  For individual/population events, the organ context is not applicable.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Organ term
thyroid gland

Key Event Components

The KE, as defined by a set structured ontology terms consisting of a biological process, object, and action with each term originating from one of 14 biological ontologies (Ives, et al., 2017; Biological process describes dynamics of the underlying biological system (e.g., receptor signalling).Biological process describes dynamics of the underlying biological system (e.g., receptor signaling).  The biological object is the subject of the perturbation (e.g., a specific biological receptor that is activated or inhibited). Action represents the direction of perturbation of this system (generally increased or decreased; e.g., ‘decreased’ in the case of a receptor that is inhibited to indicate a decrease in the signaling by that receptor).  Note that when editing Event Components, clicking an existing Event Component from the Suggestions menu will autopopulate these fields, along with their source ID and description.  To clear any fields before submitting the event component, use the 'Clear process,' 'Clear object,' or 'Clear action' buttons.  If a desired term does not exist, a new term request may be made via Term Requests.  Event components may not be edited; to edit an event component, remove the existing event component and create a new one using the terms that you wish to add.  Further information on Event Components and Biological Context may be viewed on the attached pdf. More help
Process Object Action
iodide transport iodide decreased

Key Event Overview

AOPs Including This Key Event

All of the AOPs that are linked to this KE will automatically be listed in this subsection. This table can be particularly useful for derivation of AOP networks including the KE.Clicking on the name of the AOP will bring you to the individual page for that AOP. More help
AOP Name Role of event in AOP Point of Contact Author Status OECD Status
NIS inhibition and learning and memory impairment KeyEvent Arthur Author (send email) Open for citation & comment WPHA/WNT Endorsed
NIS and Cognitive Dysfunction KeyEvent Evgeniia Kazymova (send email) Under Development: Contributions and Comments Welcome
NIS inhib alters metamorphosis KeyEvent Arthur Author (send email) Under Development: Contributions and Comments Welcome
IYD inhib alters metamorphosis KeyEvent Arthur Author (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 KE.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available in relation to this KE. More help
Term Scientific Term Evidence Link
rat Rattus norvegicus High NCBI
mouse Mus musculus High NCBI
Pig Pig High NCBI
human Homo sapiens High NCBI
zebra fish Danio rerio High NCBI
Xenopus (Silurana) n. sp. tetraploid-1 Xenopus (Silurana) sp. new tetraploid 1 Moderate NCBI
African clawed frog Xenopus laevis NCBI

Life Stages

An indication of the the relevant life stage(s) for this KE. More help
Life stage Evidence
Birth to < 1 month Moderate
Pregnancy Moderate
During brain development Moderate

Sex Applicability

An indication of the the relevant sex for this KE. More help
Term Evidence
Mixed Moderate

Key Event Description

A description of the biological state being observed or measured, the biological compartment in which it is measured, and its general role in the biology should be provided. More help

Biological state: Iodine (I2) is a non-metallic chemical element which is required for the normal cellular metabolism. It is one of the essential components of the TH, comprising 65% and 58% of T4's and T3's weight, respectively and therefore it is crucial for the normal thyroid function. It is a trace element and a healthy human body contains 15-20 mg of iodine, most of which is concentrated in the thyroid gland (Dunn, 1998). Iodide (I-) that enters the thyroid gland remains in the free state only briefly and subsequently it bounds to the tyrosine residues of thyroglobulin to form the precursors of the thyroid hormones mono-iodinated tyrosine (MIT) or di-iodinated tyrosine (DIT) (Berson and Yalow, 1955). The bounding rate of iodide is 50-100% of the intra-thyroidal iodide pool, meaning that only a very small proportion of this element is free in the thyroid and this comes mainly by the deiodination of MIT and DIT.

The body is not able to produce or make iodine, thus the diet is the only source of this element. Iodine is found in nature in various forms, such as inorganic sodium and potassium salts (iodides and iodates), inorganic diatomic iodine and organic monoatomic iodine (Patrick, 2008). Thus, it is widely distributed in the environment but in many regions of the world the soil's iodine has been depleted due to different environmental phenomena. In these regions, the incidence of iodine deficiency is greatly increased (Ahad and Ganie, 2010).

The daily iodine intake of adult humans varies greatly due to the different dietary habits between the different regions on earth (Dunn, 1993). In any case, the ingested iodine is absorbed through the intestine and transported into the plasma to reach the thyroid gland. However, thyroid is not the only organ of the body that concentrates iodide. It has been shown that other tissues have also the ability of iodide concentration, such as the salivary glands, the gastric mucosa, the mammary glands and the choroid plexus, all of which express NIS, the iodine transporter protein (Jhiang et al., 1998; Cho et al., 2000).

Biological compartments: A sodium-iodide (Na/I) symporter pumps iodide (IO) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms. This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner. In the colloid, iodide (I−) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase (TPO). IO is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain. In conjugation, adjacent tyrosyl residues are paired together. Thyroglobulin binds the megalin receptor for endocytosis back into the follicular cell. Proteolysis by various proteases liberates thyroxine (T4) and triiodothyronine molecules (T3), which enter the bloodstream where they are bound to thyroid hormone binding proteins, mainly thyroxin binding globulin (TBG) which accounts for about 75% of the bound hormone. The adult thyroid absorbs 60-80 μg of iodide per day to maintain the thyroid homeostasis (Degroot, 1966). Inadequate amount of iodide results to deficient production of thyroid hormones, which consequently leads to an increase of TSH secretion and goiter, as compensating effect (Delange, 2000). On the other hand, excess iodide could also inhibit TH synthesis (Wolff and Chaikoff, 1948). The proposed mechanism for this latter effect is the possible formation of 2-iodohexadecanal that inhibits the generation of H2O2 and the subsequent oxidation of iodide in the thyroid follicular cells. The lack of oxidized free radicals of iodide affects the reaction with the tyrosine residues of Thyroglobulin (Tg) (Panneels et al., 1994). During pregnancy, the organism of the mother is also supporting the needs of the foetus and therefore the iodide requirements are greatly increased (Glinoer, 1997). Additionally, small iodine concentrations have been found to have significant antioxidant effects that resembles to ascorbic acid (Smyth, 2003).

General role in biology: The most important role of iodine is the formation of the thyroid hormones (T4 and T3). The thyroid actively concentrates the circulating iodide through the basolateral membrane of the thyrocytes by the sodium/iodide symporter protein (NIS). The concentrated thyroid-iodine is oxidized in the follicular cells of the gland and consequently binds to tyrosines to form mono- or di-iodotyrosines (MIT and DIT respectively), being incorporated into thyroglobulin. This newly formed iodothyroglobulin forms one of the most important constituents of the colloid material, present in the follicle of the thyroid unit. If two di-iodotyrosine molecules couple together, the result is the formation of thyroxin (T4). If a di-iodotyrosine and a mono-iodotyrosine are coupled together, the result is the formation of tri-iodothyronine (T3). From the perspective of the formation of thyroid hormone, the major coupling reaction is the di-iodotyrosine coupling to produce T4.

How It Is Measured or Detected

A description of the type(s) of measurements that can be employed to evaluate the KE and the relative level of scientific confidence in those measurements.These can range from citation of specific validated test guidelines, citation of specific methods published in the peer reviewed literature, or outlines of a general protocol or approach (e.g., a protein may be measured by ELISA). Do not provide detailed protocols. More help

The radioactive iodine uptake test, or RAIU test, is a type of scan used in the diagnosis of thyroid gland dysfunction (; Kwee, et al., 2007). The patient swallows radioactive iodine in the form of capsule or fluid, and its absorption by the thyroid is studied after 4–6 hours and after 24 hours with the aid of a gamma scintillation counter. The percentage of RAIU 24 hours after the administration of radioiodide is the most useful, since this is the time when the thyroid gland has reached the plateau of isotope accumulation, and because it has been shown that at this time, the best separation between high, normal, and low uptake is obtained. The test does not measure hormone production and release but merely the avidity of the thyroid gland for iodide and its rate of clearance relative to the kidney.

Domain of Applicability

A description of the scientific basis for the indicated domains of applicability and the WoE calls (if provided).  More help

Various species express functional NIS  encoded by the following genes: Human SLC5A5 (6528), Mouse Slc5a5 (114479), Rat Slc5a5 (114613), Zebrafish slc5a5 (561445), chicken SLC5A5 (431544), domestic cat SLC5A5 (101092587), dog SLC5A5 (484830), domestic guinea pig Slc5a5 (100714457), naked mole-rat Slc5a5 (101701995), cow SLC5A5 (505310), sheep SLC5A5 (101112315). The encoded protein is responsible for the uptake of iodine in tissues such as the thyroid and lactating breast tissue. The iodine taken up by the thyroid is incorporated into the metabolic regulators triiodothyronine (T3) and tetraiodothyronine (T4). Mutations in this gene are associated with thyroid dyshormonogenesis that significantly influences phenotypic expressions such as severity of hypothyroidism, goiter rates, and familial clustering demonstrating essentiality of NIS function to maintain TH status (Bakker et al., 2000; Spitzweg and Morris, 2010; Ramesh et al., 2016) . Animal studies have also proven that iodine normalizes elevated adrenal corticosteroid hormone secretion and has the ability to reverse the effects of hypothyroidism in the ovaries, testicles and thymus in thyroidectomized rats (Nolan et al., 2000).


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

Ahad F, Ganie SA. (2010). Iodine, iodine metabolism and iodine deficiency disorders revisited. Indian J Endocrinol Metab. 14: 13-17.

Bakker B, Bikker H, Vulsma T, de Randamie JS, Wiedijk BM, De Vijlder JJ. 2000. Two decades of screening for congenital hypothyroidism in The Netherlands: TPO gene mutations in total iodide organification defects (an update). The Journal of clinical endocrinology and metabolism. Oct;85:3708-3712.

Berson SA, Yalow RS. (1955). The iodide trapping and binding functions of the thyroid. J Clin Invest. 34: 186-204.

Cho JY, Leveille R, Kao R, Rousset B, Parlow AF, Burak WE Jr, Mazzaferri EL, Jhiang SM.(2000). Hormonal regulation of radioiodide uptake activity and Na+/I- symporter expression in mammary glands. J Clin Endocrinol Metab. 85:2936-2943.

Degroot LJ.(1966). Kinetic analysis of iodine metabolism. J Clin Endocrinol Metab. 26: 149-173.

Delange F. (2000). Iodine deficiency. In: Braverman L, Utiger R, editors. Werner and Ingbar's the thyroid: a fundamental and clinical text. Philadelphia: JD Lippincott. pp 295-316.

Dunn JT. (1993). Sources of dietary iodine in industrialized countries. In: Delange F, Dunn JT, Glinoer D, editors. Iodine deficiency in Europe. A continuing concern. New York: Plenum press. pp 17-21.

Dunn JT. (1998). What's happening to our iodine? J Clin Endocrinol Metab. 83: 3398-3400. Glinoer D. (1997). The regulation of thyroid function in pregnancy: pathways of endocrine adaptation from physiology to pathology. Endocr Rev. 18: 404-433. Thyroid Cancer Survivors' Association, Inc.,Radioactive Iodine (RAI)

Jhiang SM, Cho JY, Ryu KY, DeYoung BR, Smanik PA, McGaughy VR, Fischer AH, Mazzaferri EL.(1998). An immunohistochemical study of Na+/I- symporter in human thyroid tissues and salivary gland tissues. Endocrinology. 139:4416-4419.

Kwee, Sandi A.; Coel, Marc N.; Fitz-Patrick, David (2007). Eary, Janet F.; Brenner, Winfried, eds. "Iodine-131 Radiotherapy for Benign Thyroid Disease". Nuclear Medicine Therapy. CRC Press: 172. ISBN 978-0-8247-2876-2.

Nolan LA, Windle RJ, Wood SA, Kershaw YM, Lunness HR, Lightman SL, Ingram CD, Levy A. (2000). Chronic iodine deprivation attenuates stress-induced and diurnal variation in corticosterone secretion in female Wistar rats. J Neuroendocrinol. 12:1149-1159.

Panneels V, Van den Bergen H, Jacoby C, Braekman JC, Van Sande J, Dumont JE, Boeynaems JM. (1994). Inhibition of H2O2 production by iodoaldehydes in cultured dog thyroid cells. Mol Cell Endocrinol. 102:167-176.

Patrick L. (2008).Iodine:Deficiency and therapeutic considerations. Altern MedRev. 13:166-127.

Ramesh BG, Bhargav PR, Rajesh BG, Devi NV, Vijayaraghavan R, Varma BA.(2016). Genotype‑phenotype correlations of dyshormonogenetic goiter in children and adolescents from South India . I J Endocrinol and Metab. 20: 816-824.

Smyth PA. (2003). Role of iodine in antioxidant defense in thyroid and breast disease. Biofactors. 19:121-130.

Spitzweg C, Morris JC. 2010. Genetics and phenomics of hypothyroidism and goiter due to NIS mutations. Molecular and cellular endocrinology. Jun 30;322:56-63.

Wolff J, Chaikoff IL. (1948). Plasma inorganic iodide as a homeostatic regulator of thyroid function. J Biol Chem. 174: 555-564.