Inhibition of Sulfotransferase E1 (SULT1E1)

50-28-2

VOXZDWNPVJITMN-ZBRFXRBCSA-N

17beta-Estradiol

Estradiol Oestradiol Dihydrofolliculin beta-Estradiol Estra-1,3,5(10)-triene-3,17-diol Estra-1,3,5(10)-triene-3,17-diol (17β)- (+)-3,17β-Estradiol 13β-Methyl-1,3,5(10)-gonatriene-3,17β-ol 17β-Estradiol 17β-Oestradiol 3,17-Epidihydroxyestratriene 3,17β-Dihydroxyestra-1,3,5(10)-triene 3,17β-Estradiol Absorlent Matrix Aerodiol Aquadiol Bardiol Benzogynestry Bio-E Gel Climaderm Climara Compudose Compudose 200 Compudose 365 Corpagen Dermestril Dihydrofollicular hormone Dihydromenformon Dihydrotheelin Dihydroxyestrin Dimenformon Diogynets Divigel Epiestriol 50 Estasorb Estra-1,3,5(10)-triene-3,17-diol, (17β)- Estra-1,3,5(10)-triene-3,17β-diol Estrace Estraderm Estraderm MX Estraderm TTS Estraderm TTS 100 Estraderm TTS 50 ESTRADIOL, β- Estradot Estraldine Estrapatch Estredox Estreva Estring Vaginal Ring Estroclim Estroclim 50 Estrogel Estrogel HBF Estropause Estrovite Femanest Femestral Femogen FemSeven Follicyclin Gelestra Ginosedol Gynergon Gynoestryl Lamdiol Macrodiol Menorest Menostar Nordicol NSC 9895 Oesclim Oestergon Oestra-1,3,5(10)-triene-3,17β-diol Oestrogel Oestroglandol Ovahormon Ovasterol Ovastevol Ovocyclin Ovocylin Perlatanol Primofol Profoliol Profoliol B Progynon Progynon DH Syndiol Theelin, dihydro- Vagifem Vivelle Zumenon β-Estradiol 3,17beta-Dihydroxyestra-1,3,5-triene 3,17-beta-Dihydroxyestra-1,3,5(10)-triene 3,17beta-Dihydroxyoestra-1,3,5-triene 3,17-beta-Dihydroxyoestra-1,3,5-triene 3,17-beta-Dihydroxy-1,3,5(10)-oestratriene Dihydroxyoestrin EINECS 200-023-8 3,17-Epidihydroxyoestratriene D-3,17-beta-Estradiol D-3,17beta-Estradiol 3,17-beta-Estradiol Estradiol-3,17beta 1,3,5-Estratriene-3,17-beta-diol Estra-1,3,5(10)-triene-3,17-beta-diol 17-beta-Estra-1,3,5(10)-triene-3,17-diol Estrogens, esterified Gynestrel Microdiol NSC-9895 D-3,17-beta-Oestradiol D-3,17beta-Oestradiol Oestradiol R Oestradiol-17-beta Oestradiol-17beta 3,17-beta-Oestradiol Oestradiolum Oestra-1,3,5(10)-triene-3,17-beta-diol Oestra-1,3,5(10)-triene-3,17beta-diol 17beta-Oestra-1,3,5(10)-triene-3,17-diol 17-beta-Oestra-1,3,5(10)-triene-3,17-diol Oestrogynal 17-beta-OH-estradiol 17-beta-OH-oestradiol Ovociclina Ovocycline Progynon-DH Estrasorb Climara Forte Estrapak 50 Estrifam Estring Fempatch Femtran Ginedisc GynPolar Oestradiol Berco Sandrena Gel Sisare Gel Tradelia Trial SAT Zerella Extrasorb Innofem Evamist Elestrin Gynodiol Estradiolo Estradiolum Estrodiolum UNII-4TI98Z838E Zesteem

DTXSID0020573

NOCAS

Polychlorinated biphenyls; mixture of specific PCBs

Polychlorinated biphenyls (PCBs)

DTXSID0040591

79-94-7

VEORPZCZECFIRK-UHFFFAOYSA-N

3,3',5,5'-Tetrabromobisphenol A

3,3’,5,5’-Tetrabromobisphenol A (Tetrabromobisphenol A) (Phenol, 4,4'-(1-methylethylidene)bis[2,6-dibromo-) (TBBPA) Phenol, 4,4'-(1-methylethylidene)bis[2,6-dibromo- 2, 2-Bis (4'-hydroxy-3',-5'-dibromophenyl) propane 2,2',6,6'-Tetrabrom-4,4'-isopropylidendiphenol 2,2',6,6'-tetrabromo-4,4'-isopropilidendifenol 2,2',6,6'-tetrabromo-4,4'-isopropylidenediphenol 2,2',6,6'-Tetrabromobisphenol A 2,2-Bis(3,5-dibromo-4-hydroxyphenyl)propane 2,2-Bis(4-hydroxy-3,5-dibromophenyl)propane 3,5,3',5'-Tetrabromobisphenol A 4,4'-(1-Methylethylidene)bis[2,6-dibromophenol] 4,4'-Isopropylidenebis[2,6-dibromophenol] BIS(PHENOL, 2,6-DIBROMO), 4,4'-(1-METHYLETHYLIDENE) BISPHENOL A, TETRABROMO- BISPHENOL, 4,4'-(1-METHYLETHYLIDENE)TETRABROMO- Bromdian Fire Guard 2000 Firemaster BP 4A NSC 59775 Phenol, 4,4'-isopropylidenebis[2,6-dibromo- Saytex CP 2000 Saytex RB 100 Saytex RB 100PC Tetrabromobisphenol A TETRABROMOBISPHENOL-A Tetrabromodian Tetrabromodiphenylolpropane

DTXSID1026081

759-73-9

FUSGACRLAFQQRL-UHFFFAOYSA-N

1-Ethyl-1-nitrosourea

ENU Urea, N-ethyl-N-nitroso- N-AETHYL-N-NITROSO-HARNSTOFF N-Ethyl-N-nitrosoharnstoff N-ethyl-N-nitrosourea N-Ethyl-N-nitrosouree N-etil-N-nitrosourea N-Nitroso-N-ethylurea NSC 45403 Urea, 1-ethyl-1-nitroso-

DTXSID8020593

3380-34-5

XEFQLINVKFYRCS-UHFFFAOYSA-N

Triclosan

5-Chloro-2-(2,4-dichlorophenoxy)phenol Phenol, 5-chloro-2-(2,4-dichlorophenoxy)- 2, 4, 4'-Trichloro-2'-hydroxydiphenylether 2,2'-Oxybis(1',5'-dichlorophenyl-5-chlorophenol) 2,4,4'-TRICHLORO-2'-HYDROXY DIPHENYLETHER 2',4',4-Trichloro-2-hydroxydiphenyl ether 2',4,4'-Trichloro-2-hydroxydiphenyl ether 2,4,4'-Trichloro-2'-hydroxydiphenyl ether 2'-Hydroxy-2,4,4'-trichlorodiphenyl ether 2-Hydroxy-2',4,4'-trichlorodiphenyl ether 3-Chloro-6-(2,4-dichlorophenoxy)phenol 4-Chloro-2-hydroxyphenyl 2,4-dichlorophenyl ether 5-Chloro-2-(2', 4'-dichlorophenoxy) phenol Aquasept Bacti-Stat soap Cansan TCH DIPHENYL ETHER, 2,4,4'-TRICHLORO-2'-HYDROXY- Irgacare MP Irgacide LP 10 Irgaguard B 1000 Irgaguard B 1325 Irgasan Irgasan CH 3565 Irgasan DP 30 Irgasan DP 300 Irgasan DP 3000 Irgasan DP 400 Irgasan PE 30 Irgasan PG 60 Microban Additive B Microban B Oletron Phenol, 5-chloro-2-(2,4-dichlorophenoxy) Phenol, 5-chloro-2-(2,4-dichlorophenoxy)-, dihydrogen phosphate Sanitized XTX Sapoderm SterZac Tinosan AM 100 Tinosan AM 110 TRICLOSAM Ultra Fresh NM 100 Ultrafresh NM-V 2 Vinyzene DP 7000 Yujiexin Zilesan UW

DTXSID5032498

82-92-8

UVKZSORBKUEBAZ-UHFFFAOYSA-N

Cyclizine

Piperazine, 1-(diphenylmethyl)-4-methyl- (N-Benzhydryl)(N'-methyl)diethylenediamine 1-Diphenylmethyl-4-methylpiperazine 1-Methyl-4-(α,α'-diphenylmethyl) piperazine ciclizina Cyclizin Marezine Nautazine N-Benzhydryl-N'-methylpiperazine Ne-Devomit Neo-Devomit N-Methyl-N'-benzhydrylpiperazine NSC 26608 Wellcome prepn. 47-83

DTXSID4022864

PR:000032783

PR estrogen sulfotransferase

CHEBI:23965

CHEBI estradiol

FMA:86488

FMA Glandular part of endometrium

PR:000027727

PR estrogen receptor alpha complex

GO:0008146

GO sulfotransferase activity

GO:0035938

GO estradiol secretion

GO:0030520

GO intracellular estrogen receptor signaling pathway

GO:0030284

GO estrogen receptor activity

WIKI decreased

WIKI increased

17beta-Estradiol

2016-11-29T18:42:07

Polychlorinated biphenyls; mixture of specific PCBs

2024-11-19T17:16:08

Tetrabromobisphenol A

2017-03-10T00:10:21

2018-07-20T05:36:51

1-Ethyl-1-nitrosourea

2024-11-19T17:19:35

Triclosan

2020-11-12T18:00:07

Cyclizine

2024-11-19T17:20:51

Redox status

2025-02-21T12:54:46

WikiUser_28

Vertebrates

WikiUser_29

Invertebrates

WikiUser_17

mammals

Inhibition of Sulfotransferase E1 (SULT1E1)

SULT1E1 inhibition

Molecular

Biological state Sulfotransferases (SULTs) are phase-2 enzymes responsible for the sulfation of various endogenous and exogenous substrates using 3’-phosphoadenosine 5’- phosphosulfate (PAP-sulfate, PAPS) as a sulfate donor (Fig. 1). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2023/07/28/29l4u7a2ew_MicrosoftTeams_image.png" /> Figure 1.  SULT-catalyzed reaction with PAPS as the cosubstrate (Wang and James, 2015). SULTs are single globular proteins with a characteristic α/β motif consisting of a five-stranded parallel β -sheet surrounded by α -helices. The b-sheet constitutes the PAPS-binding site and the core of the catalytic site. While sequence conservation is rather low between SULTs, their fold and catalytic features are highly conserved. Two essential components of their actions are the PAPS binding activity (which is common among various SULTs) and the substrate binding activity (which is specific for individual SULTs) (Wang and James, 2006). SULTs are traditionally named after their preferred substrate. Nevertheless, SULTs show a broad substrates specificity, thanks to plasticity at the active site (Mueller et al., 2015). The occupation of one or both of the two essential components of SULT (PAPS and substrate binding regions) may cause inhibition of SULT activity. Various xenobiotics including dietary and environmental chemicals, some therapeutic drugs, PAPS analogues, derivatives of substrate, some library compounds, etc were shown to inhibit one or more SULT. Some inhibitors were isoform selective, while others inhibited all forms of SULT (Wang and James, 2006). At least 9 different forms of human SULT have been cloned and sequenced and according to their amino acid identity they are classified into distinct families (> 45% amino acid sequence identity) and subfamilies (> 60% amino acid sequence identity). The SULT1 family members are divided in four subfamilies e.g., 1A, 1B, 1C and 1E. SULT1E1 is a key enzyme in estrogen homeostasis, the sulfation of estrogens leads to their inactivation i.e., the molecule has no effect at the estrogen receptor (UniProt, available at: <a href="https://www.uniprot.org/">https://www.uniprot.org/</a>; Hempel et al., 2000) (Fig. 2). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/5wncpbtfct_Figure_2_KE2155.png" /> Figure 2. Schematic sulfation pathway of estrogens. STS, steroid sulfatase; PAPS, 3’ -phosphoadenosine 5’ -phosphosulfate; PAP, 3’ -phosphoadenosine 5’ -phosphate (adapted from Yi et al., 2021). The enzyme also sulfates dehydroepiandrosterone (DHEA), pregnenolone, (24S)-hydroxycholesterol and xenobiotic compounds like ethinylestradiol, equalenin, diethyl stilbesterol and 1-naphthol at significantly lower efficiency. In fact, the preferred substrate of SULT1E1 is oestradiol as reflected by the low Km and high Vmax/Km values (Figure 3) (UniProt; Hempel et al., 2000). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/27gzjxkocg_Figure_3_KE2155.png" /> Figure 3. Kinetic Analysis of Wild-Type humSULT1E1 Proteins with Various Sulfotransferase Substrates 9adapted from Hempel et al., 2000). The maximal E2 sulfation was observed at a concentration of approx. 20 nM with substrate inhibition at higher E2 concentrations (Falany et al., 1995). Biological compartment In the mammalian organisms there are membrane and cytosolic SULTs. The membrane bound sulfotransferases sulfonate large endogenous molecules playing a crucial role in the post-translation modification of proteins. Cytosolic sulfotransferases sulfonate endogenous steroids and neurotransmitters, this resulting in alteration of their activity (UniProt: Hempel et al., 2000). SULT1E1 enzyme belongs to the category of cytoplasmic soluble sulfotransferases, with the protein mainly localised in the cytosol (Reinen and Vermeulen 2015). SULT1E1 gene is moderately to highly (intestine, liver, skin, vagina) expressed in various human body tissues (UniProt, Human Protein Atlas - HPA). Regarding the uterus, it was demonstrated by Falany et al., 1998, and then by Utsunomiya and colleagues in 2004, that normal cycling endometrium expresses active SULT1E1 protein in glandular cells during the secretory phase of menstrual cycle. The results of the studies above mentioned indicate that the expression of SULT1E1 in human endometrial tissues is most likely regulated by progesterone secreted from the ovaries. Orthologs to SULT1E1 are described in various mammalian species (including rat and mouse) (bgee.org). In rodents, data demonstrates expression of SULT1E1 in the uterus of mouse, whereas no clear information is available in rats (bgee.org). This is in line with the information reported in another study indicating that the expression of SULT1E1 is species specific; however, despite differences in the tissue distribution pathway it can be concluded that SULT1E1 is mainly expressed in male and female sex organs as well as placenta (Alnouti and Klaassen, 2006). General role in biology SULT1E1 is an enzyme responsible for a major pathway of E2 biotransformation (sulfation) and plays a key role in E2 bioavailability and activity in target tissues. The sulfation of E2 in the liver makes the compound more soluble and favours its renal excretion, but also creates plasmatic stores of sulphated E2 increased stability and longer half-life than unconjugated compounds (e.g., 10– 12 h vs. 20–30 min for and a longer half-life than E2) that serve as a reservoir for the formation of biologically active steroids (Reed et al., 2005, Shevtsov et al., 2003). The sulfation of E2 in estrogen sensitive tissues by locally expressed SULT1E1, contributes to determining the ratio of the active free estrogen to the inactive estrogen sulphate in an interplay with desulphation by the enzyme sulfatase (reviewed by Alnouti and Klaassen, 2006). Local SULT1E1 is suggested to play an important role in protecting estrogen sensitive tissues from extreme estrogenic effects (Secky et al. 2013). Inhibition of SULT1E1 activity by Endocrine Disruptive Chemicals (EDCs) or lower SULT1E1 expression levels may lead to a higher availability of biologically active E2 in the endometrium, which can result in a higher cell proliferation or estrogen stimulated DNA synthesis (Reinen and Vermeulen 2015). The expression of SULT1E1 was significantly downregulated (p = 0.0392) in endometrial cancer tissue from premenopausal women, with significantly lower levels seen in cancer and adjacent control tissue from postmenopausal women as compared to premenopausal women (Sinhrein et al., 2017). While inhibition of SULT1E1 can occur in various tissues, in the context of AOP504 the uterine compartment is considered.

Both SULT1E1 expression and function can be measured in tissues and in recombinant systems, such as e.g., Salmonella typhimurium (Kester et al., 2002), Escherichia coli (Parker et al., 2018), V79-1E1 Chinese hamster cells line (Hamers et al., 2006) and in HepG2 cell (Maiti et al., 2007). Expression (gene expression and proteins level) <ul> <li>qRT-PCRn, Northern blotting: SULT1E1 expression (Konings et al., 2018)</li> <li>Western blotting: SULT1E1 protein levels (Konings et al., 2018)</li> <li>Immunohistochemistry: protein levels (Konings et al., 2018)</li> </ul>   Activity (formation of E2 sulfate) <ul> <li>Sulfotransferase kinetic assay: radiometric assays (Hempel et al., 2000; Falany et al., 1995)</li> </ul> In these assays, different types of inhibition of SULT activity, such as competitive, non-competitive and mixed type can be also determined by Lineweaver-Burk analysis (Kester et al., 2002; Hamers et al., 2006). <ul> <li>Levels of sulphated estrogens and/or ratio of conjugated E2/non conjugated E2 (in tissue or in plasma): <ul> <li>liquid chromatography/mass spectrometry (LC/MS); LC-MS/MS after chemical or enzymatic hydrolysis and extraction (Borghoff et al., 2016, Wudy et al., 2018).</li> <li>Radioimmuno Assay (RIA)</li> </ul> </li> <li>Computational models for SULTE1 activation and such as QSAR model for E2-SULT inhibition are also used to demonstrate the criteria for potent inhibition of estrogen sulfotransferase (Harju et al., 2007; Gosavi et al., 2013). </li> </ul>

SULT1E1 is the high-affinity enzyme responsible for E2 sulfation at nanomolar concentrations and it is expressed in various tissues. SULT1E1 in the liver plays a role in the sulfation of circulating E2, and intestine-liver during hepatic-mediated first-pass metabolism; SULT1E1 in estrogen sensitive tissues has a role in the local modulation of E2 sulfation. Estrogenic signalling is not elicited by sulphated E2 since it does not bind to ERs. Inhibition of SULT1E1 could decrease E2 sulfation, and consequently increase the levels of non-sulphated (active) E2 available to estrogenic activation pathways. Sex: Both sexes. Taxonomic Applicability: in the context of AOP504 the taxonomic applicability is restricted to mammals; however, SULT1E1 is also present in other species invertebrate species and fish/avian/amphibian. SULT1E1 was identified and cloned in human and various mammalian species (Fig. 4). Overall, it has been reported that protein sequence homology between human and some mammalian species is above 71% (UniProt, Yi et al., 2021). Table 1. SULT1E1 expression in other mammalian species (adapted from Yi et al., 2021). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/42caynx599_Table_1_KE2155.png" /> The first SULT1E1 crystal structure to be reported in mammals was the mouse estrogen sulfotransferase (mouSULT1E1); mouSULT1E1 and humSULT1E1 share the 77% amino acid identify and conserve the main active sites (Fig. 5), the Km for E2 is in the nanomolar range for both the species. <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/2y6a2b2hs5_Figure_5_KE2155.png" /> Figure 5. Schematic diagram of the humSULT1E1 substrate binding (Hempel et al., 2000). In rodents, data demonstrates expression of SULT1E1 in uterus of mouse, whereas no clear information is available in rats (bgee.org). Studies in marine and freshwater fish have shown that steroid catabolism pathways are broadly similar to those identified in mammals, including the participation of SULT enzymes; however, it is noted that none of the enzyme studies exhibit Km values at nanomolar levels, as reported for human SULT1E1; further research in this area is needed (James, 2011). Invertebrates are not investigated as part of AOP504. Life Stages: SULT1E1 is expressed in the human embryo and is also highly expressed in a wide range of foetal tissues, such as the liver, lung, kidney, and hormone-dependent tissues—such as the testis or endometrium; its expression in adults is lower than in the foetus and placenta (Yi et al., 2021). However, AOP504 is focused on adulthood. <div> <div> <div> </div> </div> </div>

UBERON:0000062

UBERON organ

UBERON_0004811

UBERON Endometrium epithelium

Not Specified Unspecific

Not Specified

All life stages

Not Specified Not Specified

2025-02-21T13:26:04

Estradiol availability, increased

Increased E2 availability

Tissue

Currently, there is an existing key event in the AOP Wiki (event number 1973) entitled Increased, estrogens which has a role of KE in one AOP (under development) (number 440 - Hypothalamic estrogen receptors inhibition leading to ovarian cancer). Some sections of the KE description were adapted from that event. In the current AOP, “increased E2 availability” is intended as the increased availability of E2 to its intended biological destination, that is the estrogenic signalling pathways in target tissues (estrogen-sensitive tissues). Biological state The three major forms of endogenous estrogens are estrone (E1), oestradiol (E2, or 17β-oestradiol), and estriol (E3).  Estrogen metabolism is complex and multifactorial (Fig.6). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/08/09/7zjvp3k5u5_KE2251_Figure_6.jpg" /> Figure 6. Schematic representation of estrogen metabolism. Dotted circles represent the enzyme system that would influence the bioavailability of oestradiol (Wikoff et al., 2016) Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, E2 is the principal intracellular human estrogen and is substantially more potent than its metabolites, E1 and E3 at the receptor level (NCI Thesaurus (NCIt) in PubChem, available at: <a href="https://ncit.nci.nih.gov/ncitbrowser/">https://ncit.nci.nih.gov/ncitbrowser/</a>, version 22.11d). Oestradiol (E2) is principally produced in the ovaries by follicular thecal and granulosa cells under the regulation of follicle-stimulating hormone (FSH) in the reproductive phase in women (Simpson 2003). Before puberty and after menopause E2 is mainly produced in extragonadal tissues, including kidney, breast, brain, liver and fat (Secky et al., 2013). In males it is mainly produced by the Leydig cells in the testis. Vehiculated via the circulatory system to estrogen-sensitive tissues (female reproductive organs, breasts, hypothalamus and pituitary), E2 becomes available to specific estrogen receptors (subtypes alpha (ERα) and beta (ERβ), triggering the estrogenic signalling pathway: the receptor-ligand complex enters the nucleus of the target and promotes the gene expression necessary for the maintenance of fertility and secondary sexual characteristics in females and other effects, such as mild anabolic and metabolic properties, and increased blood coagulability.  E2 also exerts potent agonism of G Protein-coupled estrogen receptor (GPER), which is recognized an important regulator of E2 rapid effects.   The three major forms of endogenous estrogens are estrone (E1), oestradiol (E2, or 17β-oestradiol), and estriol (E3). Although circulating estrogens exist in a dynamic equilibrium of metabolic interconversions, oestradiol is the principal intracellular human estrogen and is substantially more potent than its metabolites, estrone and estriol at the receptor level (NCI Thesaurus (NCIt) in PubChem). In estrogen-responsive organs (uterus, breast, prostate), E2 availability to the estrogen signalling pathway is fine-tuned at cellular level; E2 activation/deactivation is controlled by a local machinery composed by enzymes analogous to those in gonadal tissue (Secky et al., 2013). This “intracrinological” pathway actively contributes to the modification of intracellular levels of E2, modulating its local effects and playing a major role in physiological and pathological conditions in premenopausal and menopausal women, in men and in animal models (Konings et al., 2018). Huhtinen et al., 2012 showed that E2 concentration in the human uterus (endometrium) is up to 10-fold higher in the proliferative phase compared with the secretory phase of the menstrual cycle, and this is accompanied by cyclic changes in intracrine enzyme levels, indicating that steroid exposure is locally cyclically regulated to support endometrial physiology. An important reaction in the intracrine steroidogenesis is the interconversion of 17-keto and 17b-hydroxysteroids controlled by HSD17Bs. 17b-hydroxysteroids (testosterone and E2) have higher affinity for the receptors than the keto-steroids (A4 and E1). This balance determines the final androgenic/estrogenic activity at target tissue level (Konings et al., 2018). In addition, of relevance is the intracellular balance between unconjugated (free, active) and the sulfo-conjugated (inactive) E2. This is controlled by the “sulfatase pathway”, which is based on the interplay between SULT1E1 and STS and contributes to the modulation of E2 effects and protection versus its excess in target tissues (Cui et al., 2013; Cornel, 2018). Biological compartment Gonadal E2 is produced under the control of the hypothalamus-pituitary-ovary (HPO) axis and mainly released into the bloodstream to reach target tissues. In the female reproductive years E2 levels are physiologically subject to cyclic variations in the blood, reaching the highest level immediately before ovulation. Levels of circulating E2 during the follicular phase, pre-ovulatory phase, and luteal phase are 19–140 pg/ml, 110–410 pg/ml, and 19–160 pg/ml, respectively. During the menopause transition, E2 and E1 levels decrease by 85–90% and 65–75% respectively as compared to mean pre-menopausal levels, and in postmenopausal women they are below 35 pg/ml. The above described “intracrinological” pathway actively contributes to the modification of intracellular levels of E2, modulating its local effects and playing a major role in physiological and pathological conditions in premenopausal and menopausal women, in men and in animal models (Konings et al., 2018). As a consequence, cellular E2 levels do not reflect the blood levels (Cornel et al., 2018); in the endometrium they can be up to five-times higher than in serum during the proliferative phase and 1.5-fold higher in the luteal period (Huhtinen et al., 2012, 2014). Levels of estrogens (E2) in both the circulatory (plasma) and tissue compartments should both be considered and could offer a complementary information. Among enzymes relevant in intracrinology, the sulfatase and sulfotransferase (SULT1E1), combined as the sulfatase pathway, represent a major route of estrogen supply and removal in endometrial cells. In physiological conditions the balance of the pathway is shifted towards the formation of free estrone, as indicated by the STS activity, that is few magnitudes higher than that of SULT1E1. Other enzymes relevant for the intracrine regulation and ultimately tissue level of E2 include aromatase CYP19A1 (converting testosterone to oestradiol), hydroxysteroid-dehydrogenase-17B (HSD17B, interconverting estrone and oestradiol)) (reviewed in see Wikoff et al 2015). In addition, other hormones can also contribute to the regulation of E2 at endometrial level. For example, progesterone diminishes estrogenic action in the endometrium by stimulating the local synthesis of 17-hydroxysteroid dehydrogenase and estrogen sulfotransferase, with the effect peaking in the luteal phase. The up regulation of these enzymes decreases intra-tissue estrogen levels and is one of the mechanisms of the uterine antiestrogenic effects of progesterone (Huntinhen et al., 2012). General role in biology Endogenous estrogens are largely responsible for the development and maintenance of the female reproductive system and secondary sexual characteristics. E2 is the principal intracellular human estrogen and is substantially more potent than its metabolites, estrone and estriol at the receptor level (HSD17B in PubChem). In the reproductive phase E2 together with progesterone controls the menstrual cycle and the reproductive functions; it induces endometrial cell proliferation in premenopausal women. E2 effects are mediated by a complex estrogenic signalling, mainly via two nuclear estrogen receptors (ERα and β) and one membrane receptor (GPER); activating genomic and non-genomic actions upon ligand binding (Cornel et al., 2017) Availability of E2 to its receptors is key to trigger the estrogenic signalling in estrogen-sensitive cells. It is related to the levels of circulating estrogens and it is locally fine-tuned by a set of intracellular enzymes (intracrinology). Disruption of estrogen homeostasis resulting in prolonged increased E2 levels, associated with relative decreased progesterone (P4) would be among the leading risk factors for the development of pathological conditions such as endometrial cancer. An estrogen imbalance is associated with endometrial carcinomas in rats (Hilliard and Norris, 1979; Fox, 1984), spontaneous endometrial adenocarcinomas in the Donryu rat (Nagaoka et al., 1990), and in F344 rats (Tang et al., 1984). Epidemiological studies showed increased endometrial cancer risks among postmenopausal women who have increased blood levels of oestradiol (reviewed in Kaaks et al., 2002) as well as of steroid precursors of E2 (testosterone, androstenedione, DHEA, DHEA-S, estrone and estrone-S) compared with healthy controls (Cornel et al., 2017). This can be interpreted in the light of the “unopposed estrogen” hypothesis, which proposes that endometrial cancer may develop as a result of the mitogenic effects of estrogens, when these are insufficiently counterbalanced by progesterone.  Since the majority of the endometrial cancer patients are postmenopausal women, local formation of E2 from circulating precursors either from circulating androgens via the aromatase pathway or from E1S via the sulfatase pathway becomes important.

This KE refers to increased E2 availability in the uterus, where availability is intended as the extent E2 becoming completely available to its intended biological destination ER. Circulating E2 levels are relevant in determining E2 levels available to endometrial cells in the uterus. These are measurable by a variety of standardised routine methods in humans and animals. Circulating levels are intracellularly subject to a complex intracrine control mechanism, activating and deactivating E2 available to receptors. The translation of circulating E2 levels into E2 availability in uterus needs further exploration and it is not fully addressed in this Scientific Opinion. It has been acknowledged that availability of E2 in uterus is strongly associated with estrogenic activity. Therefore, E2 availability in target tissue can be measured with standardised methods evaluating estrogenicity, that are listed below. In vivo <ul> <li>OECD TG 440 Uterotrophic bioassay in rodents</li> </ul> Others Overall, no high resolution and/or standardised methods exist to quantify steroids within target tissues. However, in recent decades it has been recognized that steroid concentration within tissues is modulated independently from circulating levels and therefore investigations in this field are initiated (Cobice et al., 2013). Uterine response to estrogens involves the activation of a large pattern of estrogen-sensitive genes: <ul> <li>Expression of Calbindin-D9k (CaBP-9k) gene and protein. The 9 kilodalton vitamin D-dependent calcium binding protein (CaBP9k), calbindin-D9k, is expressed in the intestine and uterus of mammals (bgee.org; L’ Horset et al., 1990) Different studies demonstrated that in the mammals uterus, the expression of CaBP-9k is regulated by hormones such as E2 and P4.  L’Horset et al., 1993; review by Choi et al., 2005).</li> <li>Complement 3 (C3). It has been demonstrated that C3 could be regarded as an estrogen sensitive marker in rat uterus (Diel et al., 2000; Sundstrom et al., 1989)</li> </ul> In addition to this, it has been reported that blood glutamate levels are inversely related to plasma estrogen and progesterone level in plasma (Zlotnik et al., 2011). In the regulatory area standard methods are available for serum estrogen analysis include radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), and multiplex immunoassay. Liquid chromatography/mass spectrometry (LC/MS)-based methods are also becoming more widely used (as cost and sample size requirements decrease), particularly for measurement of estrogens and estrogen metabolites. For E2, rodent-specific immunoassays are commercially available (Andersson, 2013). In the OECD TG 422 dedicated to repeated dose toxicity and reproduction, sex hormones data are not routine endpoints. In OECD TG 408, measurement of sexual hormones is optional and should be considered on a case-by-case basis. However, it is not recommended to include female reproductive hormonal measurements in first-tier toxicity studies of standard design. Indeed, due to the limited standard number of animals per group the average number of each animal in each stage of the cycle is generally too few to permit conclusions (Stanislaus, 2012). Specifically designed and statistically powered investigative studies (with appropriate animal numbers) are best suited to measure serum hormones in female rodents (Andersson, 2013).

Taxonomic Applicability: mammals. Endocrine systems with respect to hormone structure, receptors, synthesis pathways, hormonal axes and degradation pathways are well conserved across vertebrate taxa especially in the case of estrogen, androgen and thyroid hormones and steroidogenesis (OECD TG 150) Life Stage Applicability: This KE is applicable to adulthood - reproductive and post reproductive (menopausal, aging) phases. Sex Applicability: males, females

UBERON:0000995

UBERON uterus

Not Specified Male Not Specified Female

Not Specified

Adult

Not Specified

Adult, reproductively mature

Not Specified

Old Age

Not Specified

Andersson H, Rehm S, Stanislaus D and Wood CE, 2013. Scientific and Regulatory Policy Committee (SRPC) Paper:Assessment of Circulating Hormones in Nonclinical Toxicity Studies III. Female Reproductive Hormones. Toxicologic Pathology, 41:921-934. doi: 10.1177/0192623312466959 Choi J-Y, Lee K-M, Park SK, Noh D-Y, Ahn S-H, Chung H-W, Han W, Kim JS, Shin SG, Jang I-J, Yoo K-Y, Hirvonen A and Kang D, 2005. Genetic Polymorphisms of SULT1A1 and SULT1E1 and the Risk and Survival of Breast Cancer. Cancer Epidemiology, Biomarkers & Prevention, 14:1090-1095. doi: 10.1158/1055-9965.Epi-04-0688 Cobice DF, Mackay CL, Goodwin RJA, McBride A, Langridge-Smith PR, Webster SP, Walker BR and Andrew R, 2013. Mass Spectrometry Imaging for Dissecting Steroid Intracrinology within Target Tissues. Analytical Chemistry, 85:11576-11584. doi: 10.1021/ac402777k Cornel KM, Krakstad C, Delvoux B, Xanthoulea S, Jori B, Bongers MY, Konings GF, Kooreman LF, Kruitwagen RF, Salvesen HB and Romano A, 2017. High mRNA levels of 17β-hydroxysteroid dehydrogenase type 1 correlate with poor prognosis in endometrial cancer. Mol Cell Endocrinol, 442:51-57. doi: 10.1016/j.mce.2016.11.030 Cornel KMC, Delvoux B, Saya T, Xanthoulea S, Konings GFJ, Kruitwagen RPFM, Bongers MY, Kooreman L and Romano A, 2018. The sulfatase pathway as estrogen supply in endometrial cancer. Steroids, 139:45-52. doi: <a href="https://doi.org/10.1016/j.steroids.2018.09.002">https://doi.org/10.1016/j.steroids.2018.09.002</a> Cui J, Shen Y and Li R, 2013. Estrogen synthesis and signaling pathways during aging: from periphery to brain. Trends Mol Med, 19:197-209. doi: 10.1016/j.molmed.2012.12.007 Diel P, Schulz T, Smolnikar K, Strunck E, Vollmer G and Michna H, 2000. Ability of xeno- and phytoestrogens to modulate expression of estrogen-sensitive genes in rat uterus: estrogenicity profiles and uterotropic activity. The Journal of Steroid Biochemistry and Molecular Biology, 73:1-10. doi: <a href="https://doi.org/10.1016/S0960-0760(00)00051-0">https://doi.org/10.1016/S0960-0760(00)00051-0</a> Hilliard GD and Norris HJ, 1979. Pathologic effects of oral contraceptives. Recent Results Cancer Res, 66:49-71. doi: 10.1007/978-3-642-81267-5_2 Huhtinen K, Desai R, Ståhle M, Salminen A, Handelsman DJ, Perheentupa A and Poutanen M, 2012. Endometrial and endometriotic concentrations of estrone and estradiol are determined by local metabolism rather than circulating levels. J Clin Endocrinol Metab, 97:4228-4235. doi: 10.1210/jc.2012-1154 Kaaks R, Lukanova A and Kurzer MS, 2002. Obesity, endogenous hormones, and endometrial cancer risk: a synthetic review. Cancer Epidemiol Biomarkers Prev, 11:1531-1543 Konings G, Brentjens L, Delvoux B, Linnanen T, Cornel K, Koskimies P, Bongers M, Kruitwagen R, Xanthoulea S and Romano A, 2018. Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery. Frontiers in pharmacology, 9:940. doi: <a href="https://doi.org/10.3389/fphar.2018.00940">10.3389/fphar.2018.00940</a> Available online: <a href="http://europepmc.org/abstract/MED/30283331">http://europepmc.org/abstract/MED/30283331</a> L'Horset F, Blin C, Brehier A, Thomasset M and Perret C, 1993. Estrogen-induced calbindin-D 9k gene expression in the rat uterus during the estrous cycle: late antagonistic effect of progesterone. Endocrinology, 132:489-495. doi: 10.1210/endo.132.2.8425470 Nagaoka T, Onodera H, Matsushima Y, Todate A, Shibutani M, Ogasawara H and Maekawa A, 1990. Spontaneous uterine adenocarcinomas in aged rats and their relation to endocrine imbalance. J Cancer Res Clin Oncol, 116:623-628. doi: 10.1007/bf01637084 OECD, 2007. Test No. 440: Uterotrophic Bioassay in Rodents. OECD, 2016. Test No. 422: Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test. OECD, 2018a. Revised Guidance Document 150 on Standardised Test Guidelines for Evaluating Chemicals for Endocrine Disruption. OECD, 2018b. Test No. 408: Repeated Dose 90-Day Oral Toxicity Study in Rodents. Secky L, Svoboda M, Klameth L, Bajna E, Hamilton G, Zeillinger R, Jäger W and Thalhammer T, 2013. The sulfatase pathway for estrogen formation: targets for the treatment and diagnosis of hormone-associated tumors. J Drug Deliv, 2013:957605. doi: 10.1155/2013/957605 Simpson ER, 2003. Sources of estrogen and their importance. The Journal of Steroid Biochemistry and Molecular Biology, 86:225-230. doi: <a href="https://doi.org/10.1016/S0960-0760(03)00360-1">https://doi.org/10.1016/S0960-0760(03)00360-1</a> Stanislaus D, Andersson H, Chapin R, Creasy D, Ferguson D, Gilbert M, Rosol TJ, Boyce RW and Wood CE, 2012. Society of toxicologic pathology position paper: review series: assessment of circulating hormones in nonclinical toxicity studies: general concepts and considerations. Toxicol Pathol, 40:943-950. doi: 10.1177/0192623312444622 Sundstrom SA, Komm BS, Ponce-de-Leon H, Yi Z, Teuscher C and Lyttle CR, 1989. Estrogen regulation of tissue-specific expression of complement C3. J Biol Chem, 264:16941-16947 Tang FY, Bonfiglio TA and Tang LK, 1984. Effect of estrogen and progesterone on the development of endometrial hyperplasia in the Fischer rat. Biol Reprod, 31:399-413. doi: 10.1095/biolreprod31.2.399 Wikoff DS, Rager JE, Haws LC and Borghoff SJ, 2016. A high dose mode of action for tetrabromobisphenol A-induced uterine adenocarcinomas in Wistar Han rats: A critical evaluation of key events in an adverse outcome pathway framework. Regul Toxicol Pharmacol, 77:143-159. doi: 10.1016/j.yrtph.2016.01.018 Zlotnik A, Gruenbaum BF, Mohar B, Kuts R, Gruenbaum SE, Ohayon S, Boyko M, Klin Y, Sheiner E, Shaked G, Shapira Y and Teichberg VI, 2011. The effects of estrogen and progesterone on blood glutamate levels: evidence from changes of blood glutamate levels during the menstrual cycle in women. Biol Reprod, 84:581-586. doi: 10.1095/biolreprod.110.088120 AOPWiki 2024-08-09T17:32:22

2024-11-21T17:40:26

Activation, estrogen receptor alpha

Activation, ERα

Molecular

Some sections of the KE description were derived and adapted from the External Scientific Report (Viviani et al., 2023). Biological state Estrogen Receptor Alpha (ERα) is a receptor covalently bound by estrogens, which following the dimerization can translocate to the nucleus (Björnström and Sjöberg, 2005), where it can bind to estrogen responsive elements and recruit co-activators or co-repressors, which can attract co-regulatory proteins, like histone acetyltransferase, ubiquitin ligases, and protein remodelers (Thomas and Gustafsson, 2011) (Fig.1). A non-genomic signalling of Erα is described (Fig. 7), not requiring the dimerization for the induction of kinases and calcium flux (Levin, 2002; Vasudevan and Pfaff, 2008). The non-genomic action of ERα is able to regulate more genes (Gu et al., 2014). Both signalling pathways are important for the human organism (Pedram et al., 2014; Pedram et al., 2016). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/08/14/6fttmbh7wt_figure_7_ke1065.png" /> Figure 7. Genomic and non-genomic signalling pathways of ERα The ER structure is composed by different domains (A-F) which are responsible for the binding to the ligands, the dimerization, the binding to the DNA and for the activation of transcription (Nilsson et al., 2001) (Fig. 8). The A/B domain, or activation function 1 (AF1) is responsible for transactivation and protein-protein interaction, and it acts independently of ligand binding. Then, there is the C-domain, which is responsible for DNA binding and receptor dimerization. The D-domain instead is the phosphorylation site or ER and has nuclear localization sequences. The E-domain, or activation function 2 (AF2) is the ligand binding domain and the site for the binding with co-activators and co-repressors (Ellmann et al., 2009). Lastly, the F-domain that prevents improper ligand activation and dimerization (Yang et al., 2008). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/08/14/4whefkoqkg_figure_8_ke1065.png" style="height:264px; width:1430px" /> Therefore, ligand binding, dimerization and DNA binding processes are the first steps to inducing the transcription of target genes. But the ER activity largely depends also on the presence and recruitment of different co-activators and co-repressors. Once ER is bound to estrogen responsive elements, it can recruit different proteins that can favour or obstruct the action of the receptor (Thomas and Gustafsson, 2011). The main co-activators are the steroid receptor co-activators (SRC-1 and SRC-3), which are able to recruit co-regulatory proteins (Heldring et al., 2007). The main transcription factors that can be regulated by ER are activating protein 1 (AP1), specificity protein 1 (SP1), cAMP response element-binding protein (CREB), nuclear factor-κB (NF-κB) and p53 (Biswas et al., 2005; Björnström and Sjöberg, 2005; Fox et al., 2009). Instead in absence of ligands, ER can be activated by the phosphorylation from protein kinases which are stimulated by hyperactive growth factor receptors (Britton et al., 2006). ER is also able to rapidly activate other pathways, namely MAPK, PI3K, EGFR, and SRC (Kousteni et al., 2001; Song et al., 2002; Razandi et al., 2004; Shupnik, 2004). Biological compartment ERα is mainly expressed in uterus, prostate (stroma), ovary (theca cells), testes (Leydig cells), epididymis, bone, breast, various regions of the brain, liver, and white adipose tissue (Dahlaman-Wright et al., 2006). At the subcellular compartments, estrogen receptors (ERs), are localized in cytoplasm where they exist as monomers bound to heat shock proteins (HSPs). Estrogen binding alters receptor conformation and triggers release from the HSPs, thereby allowing receptor dimerization and translocation in the nucleus where these dimers bind to specific DNA sequences and recruit numerous co-factors to regulate gene transcription. Unliganded ER are also characterized as monomers in the nucleus and at the plasma membrane (Gourdy et al., 2018) General role in biology The main function of ERα is to mediate the action of estrogens, known to be involved in physiological pathological conditions (endometrial proliferation in menstrual cycle and endometrial carcinoma in postmenopausal women). This receptor is also involved in apoptotic and proliferative functions involving the MAPK/ERK pathway, mainly in breast cancer cells (Zheng et al., 2007; Lin et al., 2010; Zhang et al., 2012; Li et al., 2013). Another player involved in the increased proliferation induced by ERα is c-myc (Dubik and Shiu, 1992). The increased proliferation induced by ER has been linked to tumours (Thomas and Gustafsson, 2011). The interaction between estrogen and ERα and the increased proliferation has been proved in breast and uterine tissues (Ellmann et al., 2009).

Note: considering the AOPs under development the stressors interacting with the estrogen metabolism should be tested negative in all the in vitro assays reported below.  Additional proof of concept supporting the chain of the events herein described is given by a negative result in the in vitro assays but positive outcome in the Uterotrophic Bioassays. Uterotrophic Bioassay is indeed indicative of a single endocrine mechanism i.e., estrogenicity that could be related to mechanism other than direct binding to ER alpha or ER beta receptor. In the regulatory area methods are available to measure ER receptor activity.  OECD in the “Revised Guidance document 150” give insightful information, including limits on their use, on validated and/or widely accepted assays with estrogenic active substance specific endpoints. OECD in vitro assays <ul> <li>OECD TG 493 (July 2015): Performance-Based Test Guideline for Human Recombinant Estrogen Receptor (HRER) In Vitro Assays to Detect Chemicals with ER Binding Affinity</li> <li>OECD TG 455 (June 2021): Performance-Based Test Guideline (PGBT) For Stably Transfected Transactivation In Vitro Assays to Detect Estrogen Receptor Agonists and Antagonists. It comprises several mechanistically and functionally similar test methods for the identification of estrogen receptor (i.e., ERα, and/or ERβ). The fully validated reference test methods that provide the basis for this PBTG are: 1) The Stably Transfected TA (STTA) assay using the (h) ERα-HeLa-9903 cell line; and 2) The VM7Luc ER TA assay (3) using the VM7Luc4E2 cell line1 which predominately expresses hERα with some contribution from hERβ.</li> <li>OECD TG 457 (October 2012): BG1luc estrogen receptor transactivation test method for identifying estrogen receptor agonists and antagonists.</li> </ul> OECD in vitro screens assays (non-mammalian) <ul> <li>OECD TG 250 (June 2021): EASZY assay - Detection of Endocrine Active Substances, acting through estrogen receptors, using transgenic tg (CYP19A1b:GFP) Zebrafish embryo</li> <li>OECD TG 230 (September 2009): 21-Day Fish Assay a Short-Term Screening for Oestrogenic and Androgenic Activity, and Aromatase Inhibition</li> </ul>  OECD in vivo mammalian screens and test <ul> <li>OECD TG 440 (October 2007): Uterotrophic bioassay in rodents</li> </ul> Others non-OECD tests <ul> <li>US EPA (2009) Estrogen Receptor Binding Assay Using Rat Uterine Cytosol: This assay identifies chemicals that have the potential to interact with the estrogen receptor (ER) in vitro.  Principle of this particular assay is based on the competitive protein-binding methods. A radiolabelled ligand and an unlabelled ligand are presented together to a specific receptor. The radioactivity measurement provides the quantitative estimation of the bound and unbound fraction of the ligand with the receptor. All cytosolic estrogen receptor subtypes that are expressed in the specific tissue, including ERα and ERβ are used for the determination of estrogen receptor binding. This assay is simple and rapid to perform when optimal conditions for binding are determined. Assay determines if a ligand/chemical can interact and displace the endogenous hormone 17β-oestradiol (Freyberger et al., 2010, from KE ID 1046, AOP Wiki)</li> <li>Yeast estrogen screen (YES) (ISO 19040-1 and 19040-2)</li> <li>T47D-Kbluc assay (Wilson et al., 2004);</li> <li>ToxCast Estrogen Receptor Agonist Pathway Model: The ToxCast estrogen receptor (ER) pathway model is a mathematical model that combines the results from 18 high-throughput screening (HTS) assays from the ToxCast and Tox21 research programs. The HTS assays measure ER binding, dimerization, chromatin binding, transcriptional activation and ER-dependent cell proliferation. The model uses activity patterns across the in vitro assays to predict whether a chemical is an ER agonist or antagonist or is otherwise influencing the assays through a manner dependent on the physics and chemistry of the technology platform (“assay interference”). The output of the model provides an area under the curve (AUC) value for the potential of a chemical to cause ER agonism, normalized with respect to the positive control chemical, oestradiol.</li> <li>QSAR models for ER interaction are available at the website of Danish (<a href="https://qsar.food.dtu.dk/">https://qsar.food.dtu.dk/</a>) and US (<a href="https://www.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface">https://www.epa.gov/tsca-screening-tools/epi-suitetm-estimation-program-interface</a>) EPA and OECD (<a href="https://www.oecd.org/chemicalsafety/risk-assessment/oecdquantitativestructure-activityrelationshipsprojectqsars.htm">https://www.oecd.org/chemicalsafety/risk-assessment/oecdquantitativestructure-activityrelationshipsprojectqsars.htm</a>).</li> </ul>

Endocrine systems with respect to hormone structure, receptors, synthesis pathways, hormonal axes and degradation pathways are well conserved across vertebrate taxa especially in the case of estrogen, androgen and thyroid hormones and steroidogenesis (OECD TG 150) Taxonomic applicability: mammals and vertebrates due to evolutionarily conserved hormone pathways. Life stage Applicability: This KE is applicable to juvenile; adulthood; reproductive and post reproductive (menopausal, aging) phases Sex Applicability: This KE is applicable to females and males.

Not Specified Female Not Specified Male

Not Specified

Adult

Not Specified

Adult, reproductively mature

Not Specified

Old Age

Not Specified

Juvenile

Not Specified Not Specified

Björnström L and Sjöberg M, 2005. Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes. Molecular endocrinology, 19 4:833-842 Gu Y, Chen T, López E, Wu W, Wang X, Cao J and Teng L, 2014. The therapeutic target of estrogen receptor-alpha36 in estrogen-dependent tumors. J Transl Med, 12:16. doi: 10.1186/1479-5876-12-16 Levin ER, 2002. Cellular functions of plasma membrane estrogen receptors. Steroids, 67:471-475. doi: 10.1016/s0039-128x(01)00179-9 Lin SL, Yan LY, Zhang XT, Yuan J, Li M, Qiao J, Wang ZY and Sun QY, 2010. ER-alpha36, a variant of ER-alpha, promotes tamoxifen agonist action in endometrial cancer cells via the MAPK/ERK and PI3K/Akt pathways. PLoS One, 5:e9013. doi: 10.1371/journal.pone.0009013 Pedram A, Razandi M, Blumberg B and Levin ER, 2016. Membrane and nuclear estrogen receptor α collaborate to suppress adipogenesis but not triglyceride content. Faseb j, 30:230-240. doi: 10.1096/fj.15-274878 Pedram A, Razandi M, Lewis M, Hammes S and Levin ER, 2014. Membrane-localized estrogen receptor α is required for normal organ development and function. Dev Cell, 29:482-490. doi: 10.1016/j.devcel.2014.04.016 Razandi M, Pedram A, Merchenthaler I, Greene GL and Levin ER, 2004. Plasma membrane estrogen receptors exist and functions as dimers. Mol Endocrinol, 18:2854-2865. doi: 10.1210/me.2004-0115 Thomas C and Gustafsson J-Å, 2011. The different roles of ER subtypes in cancer biology and therapy. Nature Reviews Cancer, 11:597-608. doi: 10.1038/nrc3093 Vasudevan N and Pfaff DW, 2008. Non-genomic actions of estrogens and their interaction with genomic actions in the brain. Front Neuroendocrinol, 29:238-257. doi: 10.1016/j.yfrne.2007.08.003 Viviani B, Bernardini E, Galbiati V, Maddalon A, Melzi A, Midali M, Serafini M, Corsini E, Melcangi RC, Scanziani E, 2023. Development of Adverse Outcome Pathways relevant for the identification of substances having endocrine disruptors properties. EFSA supporting publication 2023:EN-7748 47 pp. doi:10.2903/sp.efsa.2023.EN-7748. NOTE: Italics indicate edits from John Frisch October 2025.  A full list of updates can be found in the Change Log on the View History page. AOPWiki 2016-11-29T18:41:29

2026-01-28T14:32:29

<upstream-id>4c557689-20dc-41ce-9505-f1b01f103a06</upstream-id> <downstream-id>e9243885-c816-4285-8455-035be8bb8aae</downstream-id>

The development of the KER is based on structured literature review of records. Description for KER is based on reviews and books on the topic. The method used are described in <a href="https://efsa.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.2903%2Fj.efsa.2023.7744&file=efs27744-sup-0001-Annex-A.1.docx">Annex A.1</a>.

The biological plausibility of the current KERs is related to the physiological role of SULT1E1 in estrogen metabolism. Estrogen sulfotransferase (EST) is a cytosolic sulfotransferase that transfers a sulfuryl group from the ubiquitous sulphate donor 3´-phosphoadenosine 5´-phosphosulfate (PAPS) to the 3-hydroxyl on 17β-oestradiol (E2). Sulfation of E2 by SULT1E1 represent one of the pathways for the inactivation of this hormone. The sulfonation of E2 makes the compound more soluble for renal excretion as well as for the creation of inactive stores of sulphated E2 that can be de-sulphated by steroid sulfatases. Both the estrogen receptor (ER) and SULT1E1 have affinities for E2 in the nanomolar range (Km approximately 5nM Falany et al 1998), thus suggesting that SULT1E1 may play an important role in the regulation of estrogenic effects by controlling the levels of E2 (Shevtsov et al., 2003). SULT1E1 readily sulphates E2 at concentrations at which it binds to the ER suggesting that it has a significant physiological role in modulating the response of ER-positive tissues to estrogenic stimulation. High levels of SULT1E1 activity in a tissue would render the tissue less responsive to estrogenic stimulation because the sulfated estrogens are not able to bind to the estrogen receptor and/or initiate a cellular response (Falany et al., 1998). The inhibition of SULT1E1 has consequently the potential to increase the bioavailability of E2, thereby causing an estrogenic effect (e.g., changes in metabolism of estrogens resulting in higher oestradiol levels that interact with ER receptors in target tissues (Wang and James, 2006). Only in the last decades increase knowledge of the intracrine (or local) regulation of estrogen and other steroid synthesis and degradation has been expanded. From a physiological point of view, it has been found that estrogen responsive tissues and organs are not passive receivers of the pool of steroids present in the blood, but they can actively modify the intra-tissue steroid concentrations. This allows fine-tuning the exposure of responsive tissues and organs to estrogens and other steroids in order to best respond to the physiological needs of each specific organ (Konings et al., 2018). At first Brooks et al., in 1978 investigated the uterine metabolism of E2 throughout the porcine oestrous cycle underlined a fluctuation of the estrogen sulphate in the different phase of the cycle (Fig. 9). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/2k308g2x7e_figure_9_KER3390.png" style="height:552px; width:952px" /> Figure 9. Pattern of uterine estrogen sulfation and oxidation throughout the days of the porcine estrous cycle. Each incubation lasted 2 h and contained 400 mg gilt uterine minces, [6.73H] - 17β- estradiol {2.5 - 6.6 x 10-9 M} and Na235 SO4 (0.8-1.5 x 10-4 M). (*) Percentage sulfation of total 3H-labeled estrogens in the incubate; (O) percentage estrone sulfate; and (Δ) percentage estrone. An indication of the reproducibility of the results is given by the repeat experiments carried out on d 4, 13, and 14 uteri (adapted from Brooks et al., 1978) Few years later, the ability of SULT1E1 to mediate local estrogen concentration has been also demonstrated in mice by gene disruption studies (Qian et al., 2001; Tong et al., 2005) and also in human proliferative and secretory endometrium obtained from pre-menopausal women (Falany et al., 1998). Deviations in such intracrine control can lead to unbalanced steroid hormone exposure and disturbances. SULT1E1 is suggested to play an important role in protecting peripheral tissues from extreme estrogenic effects. Inhibition of SULT1E1 activity by Endocrine Disruptive Chemicals (EDCs) or lower SULT1E1 expression levels may lead to a higher in situ availability of biologically active estrogens, which can result in a higher cell proliferation or estrogen stimulated DNA synthesis (Reinen and Vermeulen 2015). In fact, the expression of SULT1E1 was significantly downregulated (p = 0.0392) in cancer tissue from premenopausal women, with significantly lower levels seen in cancer and adjacent control tissue from postmenopausal women as compared to premenopausal women (Sinhrein et al., 2017). Utsunomya et al., 2004 and more recently Cornel et al., 2019, investigated the role of intratumorally metabolism and synthesis of estrogen. In line with the results from other experiments (Chetrite et al., 2000, Pasqualini and Chetrite, 1999; Dao et al., 1974; Pasqualini et al., 1986), the studies demonstrated that increased steroid sulfatase and decreased estrogen sulfotransferase expression in human endometrial carcinomas may result in increased availability of biologically active estrogens in situ and may be related to estrogen-dependent biological features of carcinoma.

Empirical evidence may be extrapolated from different studies investigating the MoA of specific stressors. In the context of the current AOP, evidence have been collected for two stressors known to inhibit the SULT1E1: an environmental contaminant belonging to PHAH (TBBPA) and a consumer product Triclosan. No direct evidence evaluating in the same experiment inhibition of SULT1E1 and increase of estrogen bioavailability in estrogen responsive tissues is currently available. TBBPA (see Table 2) In vitro The potential of TBBPA to interfere with estrogen metabolism by competing with the same enzyme systems involved in the conjugation of estrogens has been investigated by different authors to support the hypothesis that TBBPA exerts estrogenic activity by trough this mechanism. In recombinant human systems, TBBPA inhibits SULT1E1 with an IC50 in the range of 12-33 nM (Kester et al., 2002; Hamers et al., 2006). In both the experiments the IC50 is near the Km of 5 nM for E2, suggesting a high affinity of TBBPA for the SULT1E1. Crystallography studies (Gosavi et al., 2013) showed that hydroxyl moiety, bromine atoms and non-planar structure of TBBPA contribute to stable binding of TBBPA to SULT1E1. Gosavi and colleagues demonstrated that TBBPA is able to mimic oestradiol binding to the active site of the enzyme. In vitro <ul style="margin-left:40px"> <li>Kester et al., 2002. Observed a marked inhibition of SULT1E1 by various PHAH-OHs, in particular by compounds with two adjacent halogen substituents around the hydroxyl group that were effective at (sub)nanomolar concentrations. Depending on the structure, the inhibition is primarily competitive or non-competitive. TBBPA was one of the compounds tested in the study.</li> <li>Hamers et al., 2006. Investigate the In Vitro Profiling of the Endocrine-Disrupting Potency of Brominated Flame Retardants. The author found that TBBPA is a potent inhibitor of SULT1E1 and therefore that the ED potency of such BFR is not directly linked to estrogen receptor (in)activation.</li> </ul> In vivo <ul style="margin-left:40px"> <li>Borghoff et al., 2016, investigated the ratio of TBBPA-S/TBBPA GA in liver, plasma and uterus. The ratio is decrease in uterus indicating, according to the author a potential saturating/limitating effect of SULT on oestradiol sulfation.</li> <li>Sanders et al., 2016. Observed a change in genes indicated to be target of estrogen stimulation. However, is not clear if TBPPA act directly on these genes or whether the effect is mediated by E2 increase bioavailability.</li> </ul>   Others (indicative of a potential link between KE up and KE down) Indirect correlation may be extrapolated from different studies investigating the toxicological profile of TBBPA and/or its mode of action in the induction of uterine adenocarcinoma in rats, that in humans is usually associated to high estrogen concentrations (ECHA, 2006). In its review, Wikoff and co-workers observed that serum glutamate is inversely associated to increase of circulating levels of estrogen; this is also in line with the neuroprotective effect of estrogens against various neurodegenerative conditions.  The EU risk assessment report on TBBPA (ECB, 2006), reported an increase of 17% in serum glutamic pyruvic transaminases at the high – dose (100 mg/kg day) in female Sprague Dawley rats administered dietary TBBPA for 90-day (Table 2). Table 2. Empirical evidence table assembled for KER1, TBBPA <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:630px"> <thead> <tr> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:65px; vertical-align:top; width:66px"> Stressor(s) </td> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Upstream Effect: SULT1E1 inhibition (Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Downstream Effect: increased E2 availability in uterus (Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Effect on SULT1E1 inhibition (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:94px"> Citation </td> </tr> <tr> <td colspan="7" style="background-color:white; height:28px; vertical-align:top; width:630px"> In vitro </td> </tr> <tr> <td style="background-color:white; height:177px; width:94px"> In vitro, enzymatic activity assay: 1) Recombinant human SULT1E1 (expressed in S. typhimurium) 2) Native human SULT1E1 (liver cytosol from human surgical resection of tumours) </td> <td style="background-color:#d9e2f3; height:177px; width:66px"> TBBPA </td> <td style="background-color:white; height:177px; width:94px"> Y </td> <td style="background-color:white; height:177px; width:94px"> Not investigated </td> <td style="background-color:white; height:177px; width:94px"> Inhibition of SULT1E1 by PHAH-OH, in particular by compound with two halogenated substituents around the hydroxyl group. IC 50 0.012 µM – 0.033 µM after 30 minutes of in vitro exposure </td> <td style="background-color:white; height:177px; width:94px"> - </td> <td style="background-color:white; height:177px; width:94px"> Kester et al., 2002 </td> </tr> <tr> <td style="background-color:white; height:65px; width:94px"> Recombinant human SULT (expressed in V79-1E1 Chinese Hamster cell line) enzymatic activity assay </td> <td style="background-color:#d9e2f3; height:65px; width:66px"> TBBPA </td> <td style="background-color:white; height:65px; width:94px"> Y </td> <td style="background-color:white; height:65px; width:94px"> Not investigated </td> <td style="background-color:white; height:65px; width:94px"> TBBPA is the most potent inhibitor of SULT1E1 among the BFRs tested.   IC50 of 0.016 ± 0.007 µM after 30 minutes of in vitro exposure </td> <td style="background-color:white; height:65px; width:94px"> - </td> <td style="background-color:white; height:65px; width:94px"> Hamers et al., 2006 </td> </tr> <tr> <td colspan="7" style="background-color:white; height:18px; vertical-align:top; width:630px"> In vivo </td> </tr> <tr> <td style="background-color:white; height:43px; width:94px"> Wistar Han rats (circa 9 weeks old). </td> <td style="background-color:#d9e2f3; height:43px; width:66px"> TBBPA </td> <td style="background-color:white; height:43px; width:94px"> Y </td> <td style="background-color:white; height:43px; width:94px"> Not investigated </td> <td style="background-color:white; height:43px; width:94px"> Decrease TBBPA-S/TBBPA-GA ratio in uterus. 50 mg/kg per day, 28-days of exposure. Equal to a concentration of free TBBPA of 1478nM </td> <td style="background-color:white; height:43px; width:94px"> - </td> <td style="background-color:white; height:43px; width:94px"> Borghoff et al., 2016 </td> </tr> <tr> <td style="background-color:white; height:168px; width:94px"> Wistar Han rats, circa 9 wks old, female </td> <td style="background-color:#d9e2f3; height:168px; width:66px"> TBBPA </td> <td style="background-color:white; height:168px; width:94px"> N </td> <td style="background-color:white; height:168px; width:94px"> Y (indirect measurement) </td> <td style="background-color:white; height:168px; width:94px"> The study investigates the effect of TBBPA on Sult1e1 mRNA expression in uterus: no effect identified. Sult1e1 gene expression is down-regulated in liver </td> <td style="background-color:white; height:168px; width:94px"> ↑ of estrogen stimulated genes in proximal (near the cervix) and distal section (near the ovaries) of uterus (i.e., Thra, esr1, Ppara, Igf1, Cyp1b1, Ugt1a1), Ccnd2 in distal uterus Changes observed for esr2, ttr in proximal uterus, Thrb in distal uterus, glucocorticoid receptor (GR) in proximal uterus ↓ Cyp11a1 in uterus, HSD17B2 in distal uterus 250 mg/kg bw per day after 5 days of exposure </td> <td style="background-color:white; height:168px; width:94px"> Sanders et al., 2016 </td> </tr> </thead> </table> Triclosan (Table 3) In vitro <ul style="margin-left:40px"> <li> James et al., 2010. Investigated the effect of Triclosan on oestradiol and estrone sulfation in sheep placenta. Triclosan is a substrate of SULT1E1 with Km in the range of 1.14 uM (compared to the 0.27 uM of oestradiol). Triclosan inhibit both oestradiol and estrone sulfation with competitive/uncompetitive type of inhibition </li> </ul> In vivo <ul style="margin-left:40px"> <li> Jung et al., 2012. Investigate the potential estrogenic activity of Triclosan in the uterus of immature rats and rat pituitary GH3 cells. The study author reported an increase uterine weight together with increase expression of Calbidin-d9k and complement C3 that are reversed by steroid antagonists. </li> <li>Louis et al., 2013 investigate the effect of Triclosan on the Uterotrophic response to EE. The evidence of an estrogenic activity was reported only when rats are treated with Triclosan and EE. </li> </ul> Table 3. Empirical evidence table assembled for KER1, Triclosan <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:630px"> <thead> <tr> <td style="background-color:white; height:65px; vertical-align:top; width:75px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:65px; vertical-align:top; width:85px"> Stressor(s) </td> <td style="background-color:white; height:65px; vertical-align:top; width:76px"> Upstream Effect: SULT1E1 inhibition (Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:76px"> Downstream Effect: increased E2 availability in uterus (Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on SULT1E1 inhibition (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:90px"> Citation </td> </tr> <tr> <td colspan="7" style="background-color:white; height:28px; vertical-align:top; width:630px"> In vitro </td> </tr> <tr> <td style="background-color:white; height:65px; width:75px"> Sheep placental cytosol, 126-130 days gestation </td> <td style="background-color:#fff2cc; height:65px; width:85px"> Triclosan (TCS) </td> <td style="background-color:white; height:65px; width:76px"> Y </td> <td style="background-color:white; height:65px; width:76px"> Not investigated </td> <td style="background-color:white; height:65px; width:114px"> TCS induced marked inhibition of oestradiol and estrone sulfonation. TCS is also sulfonated by SULT1E1 in placenta cytosol Kic 0.09 nM, Kiu 5.2nM after 15 minutes exposure in vitro </td> <td style="background-color:white; height:65px; width:114px"> - </td> <td style="background-color:white; height:65px; width:90px"> James et al., 2010 </td> </tr> <tr> <td colspan="7" style="background-color:white; height:18px; vertical-align:top; width:630px"> In vivo </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Sprague-Dawley rats, immature </td> <td style="background-color:#fff2cc; height:43px; width:85px"> Triclosan </td> <td style="background-color:white; height:43px; width:76px"> Not investigated </td> <td style="background-color:white; height:43px; width:76px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> - </td> <td style="background-color:white; height:43px; width:114px"> The antimicrobial agent Triclosan  was found to up-regulate the expression of uterine CaBP-9k. Triclosan  was found to up-regulate the expression of mRNA C3 in uterus. 37.5 mg/kg bw per day after 3 days of exposure Increased uterus weight/bw ratio in TCS rats treated compared to vehicle. 7.5 mg/kg bw per day after 3 days of exposure   </td> <td style="background-color:white; height:43px; width:90px"> Jung et al., 2012 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND19 </td> <td style="background-color:#fff2cc; height:43px; width:85px"> Triclosan </td> <td style="background-color:white; height:43px; width:76px"> Not investigated </td> <td style="background-color:white; height:43px; width:76px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> - </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. The increase uterine weight/bw ratio was observed only in co-treatment with ethylinoestradiol </td> <td style="background-color:white; height:43px; width:90px"> Stoker et al., 2010 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND22 </td> <td style="background-color:#fff2cc; height:43px; width:85px"> Triclosan </td> <td style="background-color:white; height:43px; width:76px"> Not investigated </td> <td style="background-color:white; height:43px; width:76px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> - </td> <td style="background-color:white; height:43px; width:114px"> Female pubertal assay: increase blotted and wet uterine absolute and relative weights at PND 42 at 150 mkd . This picture could be indicative of an estrogenic condition at uterine level, but it is not informative on the MoA. 150 mg/kg bw per day after 21 days of exposure </td> <td style="background-color:white; height:43px; width:90px"> Stoker et al., 2010 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND18 </td> <td style="background-color:#fff2cc; height:43px; width:85px"> Triclosan </td> <td style="background-color:white; height:43px; width:76px"> Not investigated </td> <td style="background-color:white; height:43px; width:76px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> - </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 0.8, 2.4, 8.0 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:90px"> Montagnini et al., 2018 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND21 </td> <td style="background-color:#fff2cc; height:43px; width:85px"> Triclosan </td> <td style="background-color:white; height:43px; width:76px"> Not investigated </td> <td style="background-color:white; height:43px; width:76px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> - </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 1, 10, 50 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:90px"> Rodriguez-Sanchez 2010 </td> </tr> </thead> </table> Dose and temporal concordance In accordance with the OECD handbook for the AOP developers this section should include the extent of the evidence that KE upstream is generally impacted at doses (or stressor severities) equal to or less than those at which KE downstream is impacted. The dose and temporal concordance tables for stressors TBBPA and Triclosan, were included in <a href="https://efsa.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.2903%2Fj.efsa.2023.7744&file=efs27744-sup-0003-Annex-A.3.xlsx">Annex A.3</a> of the Scientific Opinion.   In the case of the current KER the evidence is poor and many inconsistencies were identified. In the following lines general (not applicable to specific stressors) uncertainties and inconsistencies were reported.   Evidence of Perturbation by Stressor  Overview for Molecular Initiating Event The PAPS binding region and substrate binding region are two essential components of SULT enzymes: occupation of one or both of these regions may cause inhibition of SULT activity. Different types of inhibition of SULT activity, competitive, non-competitive and mixed-type inhibition, have been reported for different inhibitors in the different tissues (Wang and James, 2006). <ul> <li>Competitive inhibition</li> </ul> If inhibitors occupy one or both of the binding sites of the cofactor or the substrate of the SULT, the inhibition type will be competitive. <ul> <li>Non-competitive Inhibition</li> </ul> If the inhibitor does not occupy the binding region of the substrate, the inhibition is likely to be non-competitive. <ul> <li>Mixed type Inhibition</li> </ul> There are two types of mixed-type inhibition, competitive- non-competitive inhibition and non-competitive-uncompetitive inhibition. Stressors Various xenobiotics including dietary and environmental chemicals, some therapeutic drugs, PAPS analogues, derivatives of substrate, some library compounds, were shown to inhibit one or more SULTs. Some inhibitors were isoform selective, while others inhibited all forms of SULT. Endogenous chemicals <ul> <li>E2. Substrate inhibition of humSULT1E1 by E2 was observed with inhibition constants of 1.11 ± 0.04 µM (UniProt: Hempel et al., 2000). In other studies, maximal E2 sulfation was observed at concentration of 20 nM and substrate inhibition with higher E2 concentrations (Falany et al.,1995) whereas Kester et al., 2002 reported that IC50 of E2 is in the range between 3.8 – 7.1 nM with relative potency of 1. It has been thought that the binding of E2 to the allosteric site of SULT1E1 is responsible for this phenomenon.  </li> <li>Redox status. SULT1E1 is a cytosolic protein, and it is well-known that the cytoplasm is a highly reducing environment (containing millimolar levels of GSH) in which protein cysteine residues are maintained primarily in their thiol (-SH) state. Redox modification of Cys residues of an enzyme provides a mechanism for regulating enzyme ac DHEA tivity. Maiti and co-workers demonstrated that human liver cytosolic SULT1E1 is sensitive to glutathione (GSSG) treatment in a time and concentration-dependent manner. The inactivation was due to the ability of GSSG to modify the Cys active site of the enzyme (Maiti et al., 2007).</li> </ul> Environmental chemicals <ul> <li>(Hydroxylated) Polychlorinated Biphenyls (PCB and OH-PCBs): PCBs and OH-PCBs have been shown to inhibit human SULT1E1 with IC50 values as low as 0.1 nM (Kester et al., 2000). The crystal structure of human SULT1E1 with the OH-PCB bound gives physical evidence that certain OH-PCBs can mimic binding of estrogenic compounds in biological systems (Shevtsov et al., 2003).</li> <li>Polyhalogenated aromatic hydrocarbons (PHAHs) such as polychlorinated dibenzo-p-dioxins and dibenzofurans, polybrominated diphenylethers, and bisphenol A derivatives are persistent environmental pollutants that induce a broad spectrum of effects in humans. Kester et al., 2002 investigated the possible inhibition of human SULT1E1 by hydroxylated PHAH metabolites. The inhibition of SULT1E1 was found by various PHAH-OHs, in particular by compounds with two adjacent halogen substituents around the hydroxyl group (Kester et al.,2002). Tetrabromobisphenol-A  (TBBPA) is one of the compounds tested by Kester and is a well-known brominated flame retardant used to improve the fire safety of consumer products. TBBPA is metabolised to sulphate and glucuronide conjugates and therefore is able to compete with the same enzyme systems involved in the estrogen metabolism. The IC50 is 12-33 nM and relative potency vs. E2 0.30 (Kester et al., 2002).</li> <li>N-ethyl-N-nitrosourea (ENU) is a carcinogen used in experimental animal models for tumorigenesis/carcinogenesis mainly to induce different types of gynaecological cancer. A recent study demonstrates that ENU induced a reduction of rSULT1E1 in liver tissues of female albino Wistar rats with a consequent increase of serum and liver oestradiol (Nazmeen and Maiti, 2018).</li> </ul> Consumer products   <ul> <li>Triclosan. Triclosan  is a broad-spectrum antibacterial agent used in many household products. Triclosan  has been demonstrated to be a very potent inhibitor of both oestradiol and estrone sulfation suggesting competitive binding of Triclosan  for oestradiol sites on the sulfotransferase enzyme Competitive inhibitory constant Kic 0.09 nM, uncompetitive Kiu 5.2nM (James et al., 2010).</li> </ul> Drugs <ul> <li>Cyclizin eantistaminic) (Konings et al., 2018)</li> </ul>

<ul> <li>There are no studies investigating in the same experiment the KEupstream and KEdownstream.</li> <li>Some empirical evidence is showing changes in KEupstream that did not elicit alterations in KEdownstream.</li> <li>Some experiment test only one dose, so the dose-temporal concordance could not be extrapolated and their use in support to the empirical evidence is limited.</li> <li>It is well-known that there is large variability in the uterotrophic assay (Browne et al., 2015), this can be explained by the differences in the experimental design</li> <li>There are other factors that in target tissue i.e., uterus can contribute to the intra cellular metabolism of E2 e.g., STS, HSD17B (Konings et al.,2018). However, there are gaps in the biological understanding of the contribution of each of these factors.</li> <li>There are two other sulfotransferases in the SULT1 class that catalyse the sulfonation of estrogens: SULT1A1 and SULT1A3 (both EC 2.8.2.1 and phenol sulfotransferase enzymes). These enzymes have much lower affinities for estrogens, with maximal activity at about Km = 25 uM. However, their possible interaction in the current KER has not been investigated in the experiments.</li> <li>The internal quality of the primary research study used to substantiate the empirical evidence has not been evaluated in a systematic way (e.g., using tools to evaluate the risk of bias).</li> <li>Uncertainties and inconsistencies should be further explored.</li> </ul>

It is acknowledged that mutation of one or more amino acid(s) may affect the biological properties of the protein and therefore can affect the KER. It is also noted that the expression of SULT1E1 was significantly downregulated (p = 0.0392) in endometrial cancer tissue from premenopausal women, with significantly lower levels seen in cancer and adjacent control tissue from postmenopausal women as compared to premenopausal women (Sinhrein et al., 2017). However, further investigation on the impact of these modulation factors on quantitative aspects of the response-response function that describe the relationships between KEs should be performed.

There are only a limited number of studies where both SULT1E1 and increase E2 bioavailability in uterus have been measured in vivo, and there is not enough data available to make any definitive quantitative correlations. Overall, given that this is an MIE to KE relationship there is only one response to evaluate in the relationship: increase E2 bioavailability in uterus as a result of the SULT1E1 inhibition.

Measurable response in the KERs is not a discrete assessment of SULT1E1 inhibition. Indeed, a number of factors could contribute to increase the E2 bioavailability in uterus.

Not Specified Unspecific

Not Specified

All life stages

Not Specified Not Specified

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Biochem Pharmacol, 73:1474-1481. doi: 10.1016/j.bcp.2006.12.026 Montagnini BG, Pernoncine KV, Borges LI, Costa NO, Moreira EG, Anselmo-Franci JA, Kiss ACI and Gerardin DCC, 2018. Investigation of the potential effects of Triclosan  as an endocrine disruptor in female rats: Uterotrophic assay and two-generation study. Toxicology, 410:152-165. doi: 10.1016/j.tox.2018.10.005 Nazmeen A and Maiti S, 2018. Oxidant stress induction and signalling in xenografted (human breast cancer-tissues) plus estradiol treated or N-ethyl-N-nitrosourea treated female rats via altered estrogen sulfotransferase (rSULT1E1) expressions and SOD1/catalase regulations. Mol Biol Rep, 45:2571-2584. doi: 10.1007/s11033-018-4425-z Pasqualini JR and Chetrite GS, 1999. Estrone sulfatase versus estrone sulfotransferase in human breast cancer: potential clinical applications. J Steroid Biochem Mol Biol, 69:287-292. doi: 10.1016/s0960-0760(99)00082-5 Pasqualini JR, Gelly C and Lecerf F, 1986. Biological effects and morphological responses to estriol, estriol-3-sulfate, estriol-17-sulfate and tamoxifen in a tamoxifen-resistant cell line (R-27) derived from MCF-7 human breast cancer cells. European Journal of Cancer and Clinical Oncology, 22:1495-1501. doi: 10.1016/0277-5379(86)90086-6 Qian YM, Sun XJ, Tong MH, Li XP, Richa J and Song W-C, 2001. Targeted Disruption of the Mouse Estrogen Sulfotransferase Gene Reveals a Role of Estrogen Metabolism in Intracrine and Paracrine Estrogen Regulation. Endocrinology, 142:5342-5350. doi: 10.1210/endo.142.12.8540 Reinen J and Vermeulen NP, 2015. Biotransformation of endocrine disrupting compounds by selected phase I and phase II enzymes--formation of estrogenic and chemically reactive metabolites by cytochromes P450 and sulfotransferases. Curr Med Chem, 22:500-527. doi: 10.2174/0929867321666140916123022 Rodríguez PE and Sanchez MS, 2010. Maternal exposure to Triclosan  impairs thyroid homeostasis and female pubertal development in Wistar rat offspring. J Toxicol Environ Health A, 73:1678-1688. doi: 10.1080/15287394.2010.516241 Sanders JM, Coulter SJ, Knudsen GA, Dunnick JK, Kissling GE and Birnbaum LS, 2016. Disruption of estrogen homeostasis as a mechanism for uterine toxicity in Wistar Han rats treated with tetrabromobisphenol A. Toxicology and Applied Pharmacology, 298:31-39. doi: <a href="https://doi.org/10.1016/j.taap.2016.03.007">https://doi.org/10.1016/j.taap.2016.03.007</a> Shevtsov S, Petrotchenko EV, Pedersen LC and Negishi M, 2003. Crystallographic analysis of a hydroxylated polychlorinated biphenyl (OH-PCB) bound to the catalytic estrogen binding site of human estrogen sulfotransferase. Environ Health Perspect, 111:884-888. doi: 10.1289/ehp.6056 Stoker TE, Gibson EK and Zorrilla LM, 2010. Triclosan  exposure modulates estrogen-dependent responses in the female wistar rat. Toxicol Sci, 117:45-53. doi: 10.1093/toxsci/kfq180 Tong MH, Jiang H, Liu P, Lawson JA, Brass LF and Song WC, 2005. Spontaneous fetal loss caused by placental thrombosis in estrogen sulfotransferase-deficient mice. Nat Med, 11:153-159. doi: 10.1038/nm1184 Wang LQ and James MO, 2006. Inhibition of sulfotransferases by xenobiotics. Curr Drug Metab, 7:83-104. doi: 10.2174/138920006774832596 AOPWiki 2024-11-15T12:38:18

2025-02-21T12:50:35

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The biological plausibility of this KERs is linked to the physiological role of E2 on estrogen-responsive tissues of all mammals. The uterus in rodents and the human undergoes cyclical changes of growth and degeneration (Fig. 10 and 11). In both species, estrogens produced from the developing follicles stimulate endometrial growth, and progesterone is responsible for converting the estrogen primed endometrium into a receptive state. In rodents, if pregnancy does not occur, dioestrus (secretory phase in humans, cycle days 15–28) terminates with regression of the corpus luteum, and the endometrium is resorbed (menstruation in humans, cycle days 1–5). During proestrus (proliferative phase in humans, cycle days 6–14) follicles develop and start to produce estrogens that stimulate endometrial growth. During oestrous (peri-ovulatory period in humans, cycle days 13–15) ovarian follicles mature. The magnitude of uterine growth stimulation is largely dependent upon the duration of bioavailable E2 and receptor interaction (Groothius et al., 2007). <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/736v98ln59_Figure_10_ker3391.png" /> <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/2f5jo3ae5h_Figure_11_ker3391.png" /> Bergman et al., 1992 studied the role of oestradiol during the mouse oestrus cycle. The study demonstrated that on proestrus, when plasma E2 levels are at the highest, the cell nuclear ER concentration in uterus was greater than metestrus. This increase was attributable to an increase in total cellular ER (cytosolic and nuclear) and secondarily to activation of ER (measured by its distribution from cytosolic to the nuclear fraction) (Tables 4 and 5). Table 4. Uterine weight, DNA, RNA, and plasma concentrations of E2 during the estrous cycle of C57BL/6J mice. from Bergman et al., 1992 <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/33t4jnod7y_table_4_ker3391.png" /> Table 5. Uterine weight, DNA, RNA, and plasma concentrations of E2 in E2-treated OVX mice. from Bergman et al., 1992 <img alt="" src="https://aopwiki.org/system/dragonfly/production/2024/11/15/2vlar3pfiz_table5_KER3391.png" /> Overall, this study demonstrated in mice a strong association between E2 and the biosynthesis and intracellular distribution of the uterine ER and its mRNA. The study indicated that the basis for increased nuclear ER on proestrus involves two estrogen-dependent components: 1. activation of ER to a nucleophilic state and 2. increased concentration of ER available for activation, the latter accounting for most of the increase in nuclear ER. The process probably begins early on the day of proestrus with increased activation of ER in response to the rising levels of E2. Increased activation of ER leads to increased DNA binding of ER, which increases ER mRNA and ER. Increased ER provides the substrate for a further increase in DNA-bound ER, which serves to amplify the effect of the rising E2 in a feed-forward cascade that ultimately leads to the dramatic increases in ER mRNA, ER, and polyadenylated RNA that are observed at midday on proestrus (Bergman et al., 2005).

The mechanism of action for E2 in uterus is well-known as well as its interaction with ER and consequent activation of the signalling cascade. One study has been included in support of the empirical evidence of the current KERs in the context of the postulated AOP. OESTRADIOL (see Table 6) Table 6. Empirical evidence table assembled for KER2, Oestradiol <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:630px"> <thead> <tr> <td style="background-color:white; height:65px; vertical-align:top; width:75px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:65px; vertical-align:top; width:74px"> Stressor(s) </td> <td style="background-color:white; height:65px; vertical-align:top; width:77px"> Upstream Effect: increased E2 availability in uterus(Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:85px"> Downstream Effect: ER activation in uterus(Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on ER activation in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:90px"> Citation </td> </tr> <tr> <td style="background-color:white; height:65px; vertical-align:top; width:75px"> C57BL/6J mice female 3-6 months old. 2 OVX </td> <td style="background-color:white; height:65px; width:74px"> E2 </td> <td style="background-color:white; height:65px; width:77px"> Y (indirect measurment) </td> <td style="background-color:white; height:65px; width:85px"> Y </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> E2 administered in OVX mice simulated this KE. Implanted. </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Increase of nuclear ER and ER mRNA </td> <td style="background-color:white; height:65px; vertical-align:top; width:90px"> Bergman et al., 1992 </td> </tr> </thead> </table> OTHER Stressors Empirical evidence may be extrapolated from different studies investigating the MoA of specific stressors; however, the KE upstream and KE downstream have never been investigated directly and together in the same experiment. The current empirical support is based on indirect evidence. TBBPA (see Table 7) <ul style="margin-left:40px"> <li>Sanders et al., 2016 investigated the mechanism responsible for the increased incidence of uterine lesions in TBBPA-treated rats as observed in a chronic toxicity study conducted by the National Toxicology Program (NTP). Data involving a direct evaluation of a potential increase in circulating or tissue-specific levels of oestradiol following exposure to TBBPA are not available. The authors determined that the most sensitive and efficient method to test the hypothesis that uterine lesions correlate with TBBPA-mediated disruption of estrogen homeostasis at the site-of-action was to search for TBBPA-mediated effects on genes associated with specific pathways of estrogen biosynthesis and metabolism. These changes may correlate with increased E2 or estrogen-derived reactive metabolites in the tissue; as a matter of facts, at the phenotypic level, increases in estrogen and its related signalling can cause uterine tissues to rapidly grow in size, as demonstrated by the common use of the rat uterus as a target organ for the in vivo screening of estrogen agonists and antagonists. As reported in the review by Wikoff et al.,2016 it is important to note that in the study by Sanders et al., 2016 not all gene expression changes related to estrogen signalling were increased. For example, TBBPA resulted in decreased expression of ESR2 in the proximal uterus. However, there are some lines of evidence showing that, in some instances, ESR2 may act as a repressor of ESR1 in which lower expression of ESR2 may lead to enhanced oestradiol action via increased ESR1 levels in endometrial cancer.</li> <li>Kitamura et al., 2005 investigated the effect of administered TBBPA in a uterotrophic assay.  Uterine weight is a very useful index of estrogenicity (ER activation) in the immature or adult ovariectomized female rats. As a matter of facts, uterine weight (indicative of ER activation) increases many folds during proestrus under the influence of estrogen.</li> </ul> Table 7. Empirical evidence table assembled for KER2, TBBPA <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:669px"> <thead> <tr> <td style="background-color:white; height:.45in; vertical-align:top; width:80px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:.45in; vertical-align:top; width:70px"> Stressor(s) </td> <td colspan="2" style="background-color:white; height:.45in; vertical-align:top; width:100px"> Upstream Effect: increased E2 availability in uterus(Y/N) </td> <td style="background-color:white; height:.45in; vertical-align:top; width:80px"> Downstream Effect: ER activation in uterus(Y/N) </td> <td style="background-color:white; height:.45in; vertical-align:top; width:121px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:.45in; vertical-align:top; width:121px"> Effect on ER activation in uterus (descriptive) </td> <td style="background-color:white; height:.45in; vertical-align:top; width:96px"> Citation </td> </tr> <tr> <td colspan="8" style="background-color:white; height:12px; vertical-align:top; width:669px"> In vivo </td> </tr> <tr> <td style="background-color:white; height:112px; width:80px"> Wistar Han rats, circa 9 wks old, female </td> <td style="background-color:#d9e2f3; height:112px; width:70px"> TBBPA </td> <td style="background-color:white; height:112px; width:90px"> Y (indirect measurement) </td> <td colspan="2" style="background-color:white; height:112px; width:90px"> Y (indirect measurement) </td> <td style="background-color:white; height:112px; width:121px"> ↑ of estrogen stimulated genes in proximal (near the cervix) and distal section (near the ovaries) of uterus (e.g., Thra, esr1, Ppara, Igf1, Cyp1b1, Ugt1a1), Ccnd2 in distal uterus Changes observed for ESR2, ttr in proximal uterus, Thrb in distal uterus, glucocorticoid receptor (GR) in proximal uterus ↓ Cyp11a1 in uterus, Hsd17B2 in distal uterus 250 mg/kg bw per day after 5 days of exposure </td> <td style="background-color:white; height:112px; width:121px"> ↑ of estrogen stimulated genes in proximal (near the cervix) and distal section (near the ovaries) of uterus (e.g., Thra, esr1, Ppara, Igf1, Cyp1b1, Ugt1a1), Ccnd2 in distal uterus Changes observed for ESR2, ttr in proximal uterus, Thrb in distal uterus, glucocorticoid receptor (GR) in proximal uterus ↓ Cyp11a1 in uterus, Hsd17B2 in distal uterus 250 mg/kg bw per day after 5 days of exposure </td> <td style="background-color:white; height:112px; width:96px"> Sanders et al., 2016 </td> </tr> <tr> <td style="background-color:white; height:112px; width:80px"> B6C3F1 mice (ovariectomized), 8 wks old, female </td> <td style="background-color:#d9e2f3; height:112px; width:70px"> TBBPA </td> <td style="background-color:white; height:112px; width:90px"> Y (indirect measurement) </td> <td colspan="2" style="background-color:white; height:112px; width:90px"> Y (indirect measurement) </td> <td style="background-color:white; height:112px; width:121px"> ↑ uterus/body weight in vivo with weak activity on ERE luciferase assay indicative that the substance does not bind directly to the ER 20 mg/kg bw per day after 3 days of exposure </td> <td style="background-color:white; height:112px; width:121px"> ↑ uterus/body weight in vivo with weak activity on ERE luciferase assay indicative that the substance does not bind directly to the ER 20 mg/kg bw per day after 3 days of exposure </td> <td style="background-color:white; height:112px; width:96px"> Kitamura et al., 2005 </td> </tr> </thead> </table> Triclosan (see Table 8) <ul style="margin-left:40px"> <li>Jung et al., 2012; modulation of complement 3 (C3) mRNA in uterus is demonstrated to be an estrogen sensitive marker. Triclosan was found to up-regulate the expression of such gene. The mRNA expression is blocked by the steroid antagonists ICI and RU</li> <li>Jung et al., 2012; Uterotrophic assay. Triclosan was found to induce uterine weight. The increase uterine is reversed by the treatment with steroid antagonists ICI and RU</li> <li>Jung et al., 2012; Calbindin-D9k (CaBP-9k) has been shown to be a novel biomarker for detecting endocrine disrupting chemicals (EDCs). The CaBP-9k is an intracellular calcium binding protein and may increase calcium ion (Ca2+) absorption by buffering Ca2+ in the intestine. CaBP-9k has two calcium-binding domains that interact with Ca2+ with high affinity in the cytoplasm. The CaBP-9k gene is expressed in various tissues, including intestine, kidney, uterus, placenta, pituitary gland, and bone. The expression of the CaBP-9k gene in uterus is up-regulated by estrogen and down-regulated by progesterone (P4) during the oestrous cycle and during early pregnancy in the rat uterus. In the study by Jung et al., 2012 TCS effects on the induction of CaBP-9k mRNA and protein expression were examined by real-time PCR and Western blot analysis in the uteri of immature rats and in GH3 cells. In addition, the steroid antagonists, ICI 182,780 (ICI) and RU 486 (RU), were used to examine the involvement of E2 receptor and/or P4 receptor to verify endocrine effects of TCS. The antimicrobial agent Triclosan was found to up-regulate the expression of uterine CaBP-9k.</li> <li>Stoker et al., 2010; the present study demonstrates that Triclosan alters female postnatal reproductive development and uterine response to exogenous estrogen in the developing female rat. These responses suggest that Triclosan augments estrogen action and that there is the potential for Triclosan to alter estrogen-dependent function.</li> </ul> Table 8. Empirical evidence table assembled for KER2, Triclosan <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:630px"> <thead> <tr> <td style="background-color:white; height:84px; vertical-align:top; width:75px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:84px; vertical-align:top; width:66px"> Stressor(s) </td> <td style="background-color:white; height:84px; vertical-align:top; width:85px"> Upstream Effect: increased E2 availability in uterus(Y/N) </td> <td style="background-color:white; height:84px; vertical-align:top; width:85px"> Downstream Effect: ER activation in uterus(Y/N) </td> <td style="background-color:white; height:84px; vertical-align:top; width:114px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:84px; vertical-align:top; width:114px"> Effect on ER activation in uterus (descriptive) </td> <td style="background-color:white; height:84px; vertical-align:top; width:90px"> Citation </td> </tr> <tr> <td colspan="7" style="background-color:white; height:18px; vertical-align:top; width:630px"> In vivo </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Sprague-Dawley rats, immature </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> The antimicrobial agent Triclosan  was found to up-regulate the expression of uterine CaBP-9k. Triclosan  was found to up-regulate the expression of mRNA C3 in uterus. 37.5 mg/kg bw per day after 3 days of exposure Increased uterus weight/bw ratio in TCS rats treated compared to vehicle. 7.5 mg/kg bw per day after 3 days of exposure   </td> <td style="background-color:white; height:43px; width:114px"> The antimicrobial agent Triclosan  was found to up-regulate the expression of uterine CaBP-9k. Triclosan  was found to up-regulate the expression of mRNA C3 in uterus. 37.5 mg/kg bw per day after 3 days of exposure Increased uterus weight/bw ratio in TCS rats treated compared to vehicle. 7.5 mg/kg bw per day after 3 days of exposure   </td> <td style="background-color:white; height:43px; width:90px"> Jung et al., 2012 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND19 </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. The increase uterine weight/bw ratio was observed only in co-treatment with ethylinoestradiol </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. The increase uterine weight/bw ratio was observed only in co-treatment with ethylinoestradiol </td> <td style="background-color:white; height:43px; width:90px"> Stoker et al., 2010 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND22 </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> Y (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> Female pubertal assay: increase blotted and wet uterine absolute and relative weights at PND 42 at 150 mkd . This picture could be indicative of an estrogenic condition at uterine level but it is not informative on the MoA. 150 mg/kg bw per day after 21 days of exposure </td> <td style="background-color:white; height:43px; width:114px"> Female pubertal assay: increase blotted and wet uterine absolute and relative weights at PND 42 at 150 mkd . This picture could be indicative of an estrogenic condition at uterine level but it is not informative on the MoA. 150 mg/kg bw per day after 21 days of exposure </td> <td style="background-color:white; height:43px; width:90px"> Stoker et al., 2010 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND18 </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 0.8, 2.4, 8.0 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 0.8, 2.4, 8.0 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:90px"> Montagnini et al., 2018 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Female, Wistar rats, PND21 </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 1, 10, 50 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. Doses 0, 1, 10, 50 mg/kg bw per day </td> <td style="background-color:white; height:43px; width:90px"> Rodriguez-Sanchez 2010 </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Wistar rats (Charles River) PND 13 </td> <td style="background-color:#fff2cc; height:43px; width:66px"> Triclosan </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:85px"> N (indirect measurement) </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. </td> <td style="background-color:white; height:43px; width:114px"> No effect in a uterotrophic assay. </td> <td style="background-color:white; height:43px; width:90px"> Louis et al., 2013 </td> </tr> </thead> </table> Parabens (i.e., Methylparabens/Ethylparabens) (see Table 9) Sun et al., 2016: In this study, the uterotrophic activities of methylparaben (MP) and ethylparaben (EP) at doses close to the acceptable daily intake as allocated by JECFA were demonstrated in immature Sprague-Dawley rats by intragastric administration, and up-regulations of estrogen-responsive biomarker genes were found in uteri of the rats by quantitative real-time RT–PCR (Q-RT-PCR). Table 9. Empirical evidence table assembled for KER2, Parabens <table align="center" cellspacing="0" class="Table" style="background:white; border-collapse:collapse; width:630px"> <thead> <tr> <td style="background-color:white; height:65px; vertical-align:top; width:75px"> Species, life-stage, sex tested </td> <td style="background-color:white; height:65px; vertical-align:top; width:70px"> Stressor(s) </td> <td style="background-color:white; height:65px; vertical-align:top; width:81px"> Upstream Effect: increased E2 availability in uterus(Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:85px"> Downstream Effect: ER activation in uterus(Y/N) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on increased E2 availability in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:114px"> Effect on ER activation in uterus (descriptive) </td> <td style="background-color:white; height:65px; vertical-align:top; width:90px"> Citation </td> </tr> <tr> <td colspan="7" style="background-color:white; height:18px; vertical-align:top; width:630px"> In vivo </td> </tr> <tr> <td style="background-color:white; height:43px; width:75px"> Sprague-Dawley rats, female, PND20 </td> <td style="background-color:#fbe4d5; height:43px; width:70px"> Parabens * </td> <td style="background-color:white; height:43px; width:81px"> Y </td> <td style="background-color:white; height:43px; width:85px"> Y </td> <td style="background-color:white; height:43px; width:114px"> ↑ expression of estrogen-responsive genes (i.e., icabp, CaBP-9k, itmap1, pgr) Starting from 4 mg/kg bw per day after 3 days of exposure ↑ Uterus weight Starting from 20 mg/kg bw per day after 3 days of exposure </td> <td style="background-color:white; height:43px; width:114px"> ↑ expression of estrogen-responsive genes (i.e., icabp, CaBP-9k, itmap1, pgr) Starting from 4 mg/kg bw per day after 3 days of exposure ↑ Uterus weight Starting from 20 mg/kg bw per day after 3 days of exposure </td> <td style="background-color:white; height:43px; width:90px"> Sun et al., 2016 </td> </tr> </thead> </table> * Methylparaben, Ethylparaben. Dose and temporal concordance In accordance with the OECD handbook for the AOP developers this section should include the extent of the evidence that KE upstream is generally impacted at doses (or stressor severities) equal to or less than those at which KE downstream is impacted. In the case of the current KER the evidence is poor, and many inconsistencies were identified. The dose and temporal concordance tables for stressors TBBPA, Triclosan and Parabens were included in <a href="https://efsa.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.2903%2Fj.efsa.2023.7744&file=efs27744-sup-0003-Annex-A.3.xlsx">Annex A.3</a> of the Scientific Opinion.

<ul> <li style="text-align:justify">E2 availability in uterus is rarely measured as stand-alone endpoint. The evidence collected on different stressors indicates the induction of specific estrogen-responsive genes; however, there is still little knowledge in this field</li> <li>There are few studies indicating which genes can be used as biomarkers indicative of an increase of E2 availability in uterus / ER activation in uterus.</li> <li>It is well-known that there is large variability in the uterotrophic assay (Brown et al., 2015), this can be explained by the differences in the experimental design</li> <li>The presence of phytoestrogen in the diet could influence the outcome of the experiments</li> </ul>

It is acknowledged that the increase of oestradiol (E2) content in malignant endometrium compared to macroscopically normal looking endometrium supports the idea of an important role of excessive estrogenic stimulation in the development and further progression of endometrial cancer in endometrial cancer. However, further investigation on the impact of these modulation factors on quantitative aspects of the response-response function that describe the relationships between KEs should be performed

In AOP504, there is only one study where the increase of E2 bioavailability in uterus and ER activation has been measured in the same experiment in vivo (Bergman et al., 1992). Therefore, there are not enough data available to make any definitive quantitative correlations.

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Bergman MD, Schachter BS, Karelus K, Combatsiaris EP, Garcia T and Nelson JF, 1992. Up-regulation of the uterine estrogen receptor and its messenger ribonucleic acid during the mouse estrous cycle: the role of estradiol. Endocrinology, 130:1923-1930. doi: 10.1210/endo.130.4.1547720 Jung EM, An BS, Choi KC and Jeung EB, 2012. Potential estrogenic activity of Triclosan  in the uterus of immature rats and rat pituitary GH3 cells. Toxicol Lett, 208:142-148. doi: 10.1016/j.toxlet.2011.10.017 Kitamura S, Suzuki T, Sanoh S, Kohta R, Jinno N, Sugihara K, Yoshihara Si, Fujimoto N, Watanabe H and Ohta S, 2005. Comparative Study of the Endocrine-Disrupting Activity of Bisphenol A and 19 Related Compounds. Toxicological Sciences, 84:249-259. doi: 10.1093/toxsci/kfi074 Louis GW, Hallinger DR and Stoker TE, 2013. The effect of Triclosan  on the uterotrophic response to extended doses of ethinyl estradiol in the weanling rat. Reprod Toxicol, 36:71-77. doi: 10.1016/j.reprotox.2012.12.001 Montagnini BG, Pernoncine KV, Borges LI, Costa NO, Moreira EG, Anselmo-Franci JA, Kiss ACI and Gerardin DCC, 2018. Investigation of the potential effects of Triclosan  as an endocrine disruptor in female rats: Uterotrophic assay and two-generation study. Toxicology, 410:152-165. doi: 10.1016/j.tox.2018.10.005 Rodríguez PE and Sanchez MS, 2010. Maternal exposure to Triclosan  impairs thyroid homeostasis and female pubertal development in Wistar rat offspring. J Toxicol Environ Health A, 73:1678-1688. doi: 10.1080/15287394.2010.516241 Sanders JM, Coulter SJ, Knudsen GA, Dunnick JK, Kissling GE and Birnbaum LS, 2016. Disruption of estrogen homeostasis as a mechanism for uterine toxicity in Wistar Han rats treated with tetrabromobisphenol A. Toxicology and Applied Pharmacology, 298:31-39. doi: <a href="https://doi.org/10.1016/j.taap.2016.03.007">https://doi.org/10.1016/j.taap.2016.03.007</a> Stoker TE, Gibson EK and Zorrilla LM, 2010. Triclosan  exposure modulates estrogen-dependent responses in the female wistar rat. Toxicol Sci, 117:45-53. doi: 10.1093/toxsci/kfq180 Sun L, Yu T, Guo J, Zhang Z, Hu Y, Xiao X, Sun Y, Xiao H, Li J, Zhu D, Sai L and Li J, 2016. The estrogenicity of methylparaben and ethylparaben at doses close to the acceptable daily intake in immature Sprague-Dawley rats. Sci Rep, 6:25173. doi: 10.1038/srep25173 Wikoff DS, Rager JE, Haws LC and Borghoff SJ, 2016. A high dose mode of action for tetrabromobisphenol A-induced uterine adenocarcinomas in Wistar Han rats: A critical evaluation of key events in an adverse outcome pathway framework. Regul Toxicol Pharmacol, 77:143-159. doi: 10.1016/j.yrtph.2016.01.018 AOPWiki 2024-11-15T14:01:45

2024-11-21T17:53:22

SULT1E1 inhibition leading to uterine adenocarcinoma via increased estrogen availability at target organ level

SULT1E1 inhibition and increased oestradiol availability

Martina Panzarea

Anna Lanzoni Martina Panzarea

BY-SA

2.6

As for other steroids, the circulatory transport and action of estrogens in target tissues are regulated by a complex interplay between sulfation and desulfation pathways. Non-sulfated estrogens may exert their biological effect by binding to the cognate nuclear receptor or may be downstream converted to more active steroids. Sulfated steroids are highly soluble, and this facilitates not only their renal excretion, but also their circulatory transit fuelling peripheral steroid metabolism. Sulfated steroids, as such, are inert and unable to bind and activate their nuclear receptor; active transportation into the cell and intracellular desulfation are required (Foster and Mueller, <a href="https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2023.7744#efs27744-bib-0042" id="#efs27744-bib-0042_R_d38536291e1471">2018</a>). The expression and activities of enzymes involved in these pathways is regulated by hormonal factors, and it shows a cyclic pattern in the human endometrium. Sulfation and desulfation pathways dramatically alter the levels of available active steroids and in disease, such as steroid dependent cancer, where the SULT pathway is down-regulated (decreased enzyme expression and activity), while steroid sulfatase (STS) activity is elevated (reviewed in Mueller et al., <a href="https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2023.7744#efs27744-bib-0095" id="#efs27744-bib-0095_R_d38536291e1474">2015</a>). Potent inhibitors of estrogen sulfotransferases have the potential to increase the bioavailability of E2 in target tissues (e.g. uterus), thereby causing an estrogenic effect.

Please refer to the <a href="https://efsa.onlinelibrary.wiley.com/doi/full/10.2903/j.efsa.2023.7744">EFSA Scientific Opinion</a> for an overview of the Context and Strategy of the AOP development.

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Life stage applicability: the relevant life stage for this AOP is adulthood. Taxonomic Applicability: Based on the majority of the available evidence the taxonomic applicability domains of this AOP is mammals. Most evidence for this AOP has been gathered primarily from laboratory rodents and humans. Sex Applicability: This AOP applies to females. Inhibition of SULT1E1 in pre- and post-menopausal period can have impacts on the E2 bioavailability and consequently on the ER activation in uterus.

Essentiality MIE1. SULT1E1 inhibition Direct evidence None Indirect evidence (because this evidence is not related to the blockage of KEupstream, but is related to evidence that modulating the KE upstream the KE downstream is changed): <ul style="margin-left:40px"> <li>The antimicrobial agent Triclosan  was found to up-regulate the expression of uterine CaBP-9k and complement C3; the mRNA expression is blocked by the steroid antagonists ICI and RU (Jung et al., 2012)</li> <li>Barbosa et al., 2020 (review). Several classes of drugs may indirectly modulate SULT1E1 activity. For instance, glucocorticoids, such as dexamethasone (Dex), have been shown to reduce estrogenic activity in vivo and in vitro by increasing the expression of SULT1E1. The induction of SULT1E1 and the resultant inhibition of estrogen activity by Dex were consistent with previous reports that glucocorticoids can inhibit estrogen responses.</li> <li>Qian et al., 2001. Evidence from mutation and knockout models demonstrated that targeted disruption, in male mice, of estrogen sulfotransferase (EST), causes structural and functional lesions in the male reproductive system. Although knockout males were fertile and phenotypically normal initially, they developed age dependent Leydig cell hypertrophy/hyperplasia and seminiferous tubule damage. Development of these lesions in the testis could be recapitulated by exogenous E2 administration in younger knockout mice, suggesting that they arose in older knockout mice from chronic estrogen stimulation. These finding suggested a role of estrogen metabolism in intracrine and paracrine estrogen regulation.</li> <li>Tong et al., 2005. Another study is showing that ablation of the mouse Sult1e1 gene caused placental thrombosis and spontaneous fetal loss. The fetal death is caused by estrogen excess related to the lack of SULT1E1 in placenta. Similar placental defects were induced in wild-type (WT) animals exposed to high doses of estrogen.</li> <li>Hirata et al., 2008. increase single nucleotide polymorphism for SULT1A1 and SULT1E1 genes may be risk factor for endometrial cancer in Caucasian.</li> </ul> Essentiality KE1: Estradiol availability, increased Direct evidence <ul style="margin-left:40px"> <li>Ovariectomized (OVX) rodents are commonly used for studying the influence of estrogen deprivation in intact organisms; proliferation of the vagina and uterus in rodents is stimulated by ovarian estrogen, and ovariectomy induces regression of these tracts. OVX rodents are also quite used to study the effect of menopause and of estrogen-based treatments in reversing menopausal changes in women.</li> <li>Evidence that the Uterotrophic action of E2 depends on its binding to receptors was first provided by experiments with specific binding inhibitors. Certain substances, such as ethamoxytriphetol (MER-25, Richardson-Merrell), clomiphene, nafoxidine (Upjohn-11,100), and CI-628 (Parke-Davis) (Fig. I), which had been known to inhibit the uterotrophic action of oestradiol, were shown to prevent the characteristic uptake of estrogens by target tissues in vivo (reviewed by Jensen and DeSombre, 1973).</li> </ul> <ul style="margin-left:40px"> <li>Evidence that a decrease of oestradiol availability in estrogen responsive tissues such as uterus is leading to the implication related to a lack of estrogen receptor activation is observed in menopausal women that develop symptoms such as, loss of bone density, hot flushes and cardiovascular problems (Paterni et al., 2014).</li> <li>E2-induced uterine epithelial cell proliferation is mediated by stromal ERα. ERα knockout mice showed no expression of estrogen responsive genes in the uterus, and the basic levels of PR mRNA in the aERKO uterus were equal to those in wild type mice (Yu et al., 2022).</li> <li>In Sprague Dawley rats Triclosan was found to increase uterine weight of immature rats and up-regulate the expression of calbidin-D9k (CaBP-9k) and complement C3 (C3) indicating that TCS can induce their expression mediated by estrogenic activity. Co-treatment with steroid antagonists ICI 182,780 (ICI) and RU 486 in conjunction with TCS (37.5 mg/kg) reversed TCS-induced uterine weight and CaBP-9k mRNA and protein expression increases in immature rats (Jung et al., 2012).</li> <li>In Sprague Dawley rats MP and EP were found to increase uterine weight. The uterotrophic effects were antagonized in rats treated with 25 μ g/kg bw/day E2, 20 mg/kg bw/day MP, or 20 mg/kg bw/day EP in combination with 10 mg/kg bw/day fulvestrant (FULV) (Sun et al.,2016) </li> </ul>

<table cellspacing="0" class="MsoTableGridLight" style="border-collapse:collapse; border:none; width:863px"> <tbody> <tr> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:1px solid #bfbfbf; border-right:1px solid #bfbfbf; border-top:1px solid #bfbfbf; height:40px; width:151px"> KER title </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:1px solid #bfbfbf; height:40px; width:89px"> Biological Plausibility </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:1px solid #bfbfbf; height:40px; width:84px"> Empirical Support </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:1px solid #bfbfbf; height:40px; width:87px"> Essentiality </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:1px solid #bfbfbf; height:40px; width:452px"> Brief Explanation (summary) </td> </tr> <tr> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:1px solid #bfbfbf; border-right:1px solid #bfbfbf; border-top:none; height:94px; width:151px"> KER 1: SULT1E1 inhibition leads to Increased E2 availability </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:94px; width:89px"> H </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:94px; width:84px"> L </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:94px; width:87px"> L->M </td> <td style="border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:94px; vertical-align:top; width:452px"> Biological Plausibility. The role of SULT1E1 in estrogen sulfatation with consequent inactivation of E2 is a consolidated scientific concept (dogma). As consequence, the inhibition of SULT1E1 leading to higher free E2 level in target tissue is considered a high biological plausible KER.   Empirical Support. There are no studies reporting a dependent change in both events following the exposure to a specific stressor. In fact, the endpoints described by the two KEs have never been measured in the same study. The empirical support was therefore considered low.   Essentiality. Indirect evidence where the estrogenic effects of SULT1E1 inhibitor is reversed by steroid antagonists is reported for specific stressor (Jung et al., 2012). Moreover, several classes of drugs may indirectly modulate SULT1E1 activity: mouse uterine estrogen responses were inhibited by Dexamethasone, a glucocorticoid drug, in a SULT1E1 dependent manner. In fact, glucocorticoids are known to interact with the glucocorticoid receptor (GR) which acts as a transcriptional factor promoting the upregulation of one of its transcriptional target, SULT1E1. Consequently, SULT1E1 induction is responsible for reducing the level of active estrogen resulting in inhibition of estrogen activity (reviewed by Barbosa et al., 2020). The available evidence on KO models is mainly in support of the KER and highlighted that modulation of MIE is associated to effects indicative of an increase of E2 availability; this evidence is mainly available in males. Evidence on mutation and knockout models demonstrated that targeted disruption, in male mice, of estrogen sulfotransferase (EST), causes structural and functional lesions in the male reproductive system. Although knockout males were fertile and phenotypically normal initially, they developed age dependent Leydig cell hypertrophy/hyperplasia and seminiferous tubule damage. Development of these lesions in the testis could be recapitulated by exogenous E2 administration in younger knockout mice, suggesting that they arose in older knockout mice from chronic estrogen stimulation. These finding suggested a role of estrogen metabolism in intracrine and paracrine estrogen regulation (Qian et al., 2001). Ablation of the mouse Sult1e1 gene caused placental thrombosis and spontaneous foetal loss. The foetal death is caused by estrogen excess related to the lack of SULT1E1 in placenta. Similar placental defects were induced in wild-type (WT) animals exposed to high doses of estrogen (Tong et al., 2005). Moreover, increase single nucleotide polymorphisms in SULT1E1 is associated to increase risk of endometrial cancer (an estrogen-dependent cancer) in Caucasians (Hirata et al., 2007). The total available evidence is limited and mainly based on indirect data; the essentiality was therefore graded low to moderate.  </td> </tr> <tr> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:1px solid #bfbfbf; border-right:1px solid #bfbfbf; border-top:none; height:37px; width:151px"> KER 2: Increased E2 availability leads to Activation, estrogen receptor alpha </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:37px; width:89px"> H </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:37px; width:84px"> H -> M </td> <td style="background-color:#e7e6e6; border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:37px; width:87px"> M -> H </td> <td style="border-bottom:1px solid #bfbfbf; border-left:none; border-right:1px solid #bfbfbf; border-top:none; height:37px; vertical-align:top; width:452px"> Biological Plausibility. The biological plausibility of this KERs is linked to the physiological role of E2 on estrogen-responsive tissues of all mammals and is a consolidated scientific concept (dogma). The biological plausibility is therefore high. Empirical support. Empirical evidence for this KE is extrapolated from a study investigating the interaction between E2 and estrogen receptor in uterus of mice: the E2 administration in OVX mice increase the expression of E2 and ER mRNA in the cells (Bergman et al., 1992). In addition, empirical evidence may be extrapolated from different studies investigating the MoA of specific stressors (i.e., TBBPA, Parabens and Triclosan ); however, in these cases the evidence is indirect since the two events are not measured in the same experiment.   Essentiality.  Ovariectomized (OVX) rodents are commonly used for studying the influence of estrogen deprivation in intact organisms; proliferation of the vagina and uterus in rodents is stimulated by ovarian estrogen, and ovariectomy induces regression of these tracts. OVX rodents are also quite used to study the effect of menopause and of estrogen-based treatments in reversing menopausal changes in women. In addition to this, one of the first study investigating the role of E2 in in vivo organisms, underlined that the uptake of E2 by target tissues in vivo is prevented by treatment with inhibitors of uterotrophic action of oestradiol providing evidence that the reactivity of oestradiol depends on its binding to estrogen receptor (Jensen and Sombre, 1973). The essentiality of this KER is also supported by direct evidence with specific stressors: in Sprague Dawley rats Triclosan  was found to increase uterine weight of immature rats and up-regulate the expression of calbidin-D9k (CaBP-9k) and complement C3 (C3) indicating that TCS can induce their expression mediated by estrogenic activity. Co-treatment with steroid antagonists ICI 182,780 (ICI) and RU 486 in conjunction with TCS reversed TCS-induced uterine weight and CaBP-9k mRNA and protein expression increases in immature rats (Jung et al.,2012); in Sprague Dawley rats MP and EP were found to increase uterine weight. The uterotrophic effects of methyl and ethylparaben were antagonized in rats treated with E2, MP, or EP in combination with fulvestrant (FULV) (Sun et al., 2016). The essentiality has been graded moderate to high. The evidence is strong; however, there are further data that can be used in support of this that were not evaluated/assessed as part of this AOP. </td> </tr> </tbody> </table>

<div> <table class="table table-bordered table-fullwidth"> <thead> <tr> <th>Modulating Factor (MF)</th> <th>Influence or Outcome</th> <th>KER(s) involved</th> </tr> </thead> <tbody> <tr> <td> </td> <td> </td> <td> </td> </tr> </tbody> </table> </div>

At present, the overall quantitative understanding of the AOP is insufficient to directly link a measure of chemical potency as a SULT1E1 inhibitor to a quantitative prediction of effect on uterine adenocarcinoma trough an increase of oestradiol bioavailability in uterus.

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Barbosa ACS, Feng Y, Yu C, Huang M and Xie W, 2019. Estrogen sulfotransferase in the metabolism of estrogenic drugs and in the pathogenesis of diseases. Expert Opin Drug Metab Toxicol, 15:329-339. doi: 10.1080/17425255.2019.1588884 Bergman MD, Schachter BS, Karelus K, Combatsiaris EP, Garcia T and Nelson JF, 1992. Up-regulation of the uterine estrogen receptor and its messenger ribonucleic acid during the mouse estrous cycle: the role of estradiol. Endocrinology, 130:1923-1930. doi: 10.1210/endo.130.4.1547720 Foster PA and Mueller JW, 2018. Sulfation pathways: insights into steroid sulfation and desulfation pathways. Journal of Molecular Endocrinology, 61, T271–t283 Hirata H, Hinoda Y, Okayama N, Suehiro Y, Kawamoto K, Kikuno N, Rabban JT, Chen LM and Dahiya R, 2008. CYP1A1, SULT1A1, and SULT1E1 polymorphisms are risk factors for endometrial cancer susceptibility. Cancer, 112:1964-1973. doi: <a href="https://doi.org/10.1002/cncr.23392">https://doi.org/10.1002/cncr.23392</a> Jensen EV and DeSombre ER, 1973. Estrogen-receptor interaction. Science, 182:126-134. doi: 10.1126/science.182.4108.126 Jung EM, An BS, Choi KC and Jeung EB, 2012. Potential estrogenic activity of Triclosan  in the uterus of immature rats and rat pituitary GH3 cells. Toxicol Lett, 208:142-148. doi: 10.1016/j.toxlet.2011.10.017 Mueller JW, Gilligan LC, Idkowiak J, Arlt W and Foster PA, 2015. The Regulation of Steroid Action by Sulfation and Desulfation. Endocrine Reviews, 36, 526–563. Paterni I, Granchi C, Katzenellenbogen JA and Minutolo F, 2014. Estrogen receptors alpha (ERα) and beta (ERβ): subtype-selective ligands and clinical potential. Steroids, 90:13-29. doi: 10.1016/j.steroids.2014.06.012 Qian YM, Sun XJ, Tong MH, Li XP, Richa J and Song W-C, 2001. Targeted Disruption of the Mouse Estrogen Sulfotransferase Gene Reveals a Role of Estrogen Metabolism in Intracrine and Paracrine Estrogen Regulation. Endocrinology, 142:5342-5350. doi: 10.1210/endo.142.12.8540 Sun L, Yu T, Guo J, Zhang Z, Hu Y, Xiao X, Sun Y, Xiao H, Li J, Zhu D, Sai L and Li J, 2016. The estrogenicity of methylparaben and ethylparaben at doses close to the acceptable daily intake in immature Sprague-Dawley rats. Sci Rep, 6:25173. doi: 10.1038/srep25173 Tong MH, Jiang H, Liu P, Lawson JA, Brass LF and Song WC, 2005. Spontaneous fetal loss caused by placental thrombosis in estrogen sulfotransferase-deficient mice. Nat Med, 11:153-159. doi: 10.1038/nm1184 Yu, K., Huang, Z. Y., Xu, X. L., Li, J., Fu, X. W., & Deng, S. L. (2022). Estrogen receptor function: impact on the human endometrium. Frontiers in endocrinology, 13, 827724.  AOPWiki 2023-07-28T06:28:31

2025-04-03T15:56:08