Activation, Androgen receptor

50-06-6

DDBREPKUVSBGFI-UHFFFAOYSA-N

Phenobarbital

2,4,6(1H,3H,5H)-Pyrimidinetrione, 5-ethyl-5-phenyl- 5-Ethyl-5-phenyl-2,4,6(1H,3H,5H)-pyrimidinetrione 5-Ethyl-5-phenylbarbiturate 5-Ethyl-5-phenylbarbituric acid 5-Phenyl-5-ethylbarbituric acid Agrypnal Amylofene Barbenyl Barbiphenyl Barbipil Barbita Barbituric acid, 5-ethyl-5-phenyl- Barbivis Blu-phen Cratecil Dormiral Doscalun Duneryl Eskabarb Etilfen Euneryl Fenemal Fenemal recip fenobarbital Gardenal Gardepanyl Hysteps Lepinal Lepinaletten Liquital Lixophen Lubergal Luminal Neurobarb NSC 128143 NSC 9848 Phenaemal Phenemal Phenobar Phenobarbitone Phenobarbituric acid Phenoluric Phenonyl Phenylethylbarbituric acid Phenylethylmalonylurea Phenyral Sedonal Sedophen Sevenal Solfoton Somonal Stental Extentabs Talpheno Teolaxin Triphenatol Versomnal Aephenal Aphenylbarbit Aphenyletten Austrominal Barbonal Barbophen Bardorm Bialminal Cabronal Calmetten Calminal Cardenal Chinoin Codibarbita Coronaletta Dezibarbitur EINECS 200-007-0 Elixir of phenobarbital Ensobarb Ensodorm Epidorm Episedal Epsylone 5-Ethyl-5-phenyl-2,4,6-(1H,3H,5H)pyrimidinetrione Fenbital Fenosed Fenylettae Glysoletten Haplopan Helional Hennoletten Henotal Hypnaletten Hypnette Hypnogen Hypnolone Hypnoltol Hypno-Tablinetten Lubrokal Lumesettes Lumesyn Lumofridetten Luphenil Luramin Molinal Nirvonal Nova-pheno Parkotal Pharmetten Phen-Bar Phenobarb Phenobarbitalum Phenobarbitonum Phenobarbyl Phenolurio Phenomet Phenoturic Phenylethyl barbituric acid Phenyl-ethyl-barbituric acid Phenyletten Polcominal Promptonal Sedabar Seda-Tablinen Sedicat Sedizorin Sedofen Sedonettes SK-Phenobarbital Solu-Barb Sombutol Somnolens Somnoletten Somnosan Spasepilin Starifen Starilettae Acido 5-fenil-5-etilbarbiturico Fenobarbitale UNII-YQE403BP4D

DTXSID5021122

62229-50-9

Epidermal growth factor

EGF Anthelone U Epidermaler Wachstumsfaktor facteur de croissance epidermique factor de crecimiento epidermico Gastrone, uro- Gastrone, γ-uro- Uroanthelone Uroenterone Urogastron Urogastrone

DTXSID5040469

50892-23-4

SZRPDCCEHVWOJX-UHFFFAOYSA-N

Pirinixic acid

4-Chloro-6-(2,3-xylidino)-2-pyrimidinylthio) acetic acid (WY-14643 Wyeth-14,643

DTXSID4020290

PR:000004191

PR androgen receptor

CL:0000422

CL mitogenic signaling cell

CL:0000182

CL hepatocyte

MP:0003902

MP abnormal cell mass

D000236

MESH Adenoma

D002277

MESH Carcinoma

GO:0004882

GO androgen receptor activity

GO:0008283

GO cell proliferation

GO:0072574

GO hepatocyte proliferation

MP:0002009

MP preneoplasia

D006528

MESH hepatocellular carcinoma

WIKI increased

Androstenedione

2016-11-29T18:42:27

Phenobarbital

2016-11-29T18:42:27

Epidermal growth factor

2018-12-20T15:05:33

pirinixic acid

2016-11-29T18:42:27

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2017-02-09T14:32:32

10116

NCBI rat

10090

NCBI mouse

WCS_9606

common toxicological species human

WikiUser_9

ApacheUser Hamster

WCS_9615

common toxicological species dog

10090

NCBI Mus musculus

10116

NCBI Rattus norvegicus

Activation, Androgen receptor

Molecular

AOPWiki 2016-11-29T18:41:27

2016-12-03T16:37:51

Increase, cell proliferation (hepatocytes)

Cellular

Key Event Description: Cell proliferation in the livers of rats and mice occurs through exposure to a mitogen and is characterized by liver enlargement without evidence of necrosis. In contrast, regenerative/compensatory proliferation occurs following loss of liver parenchymal cells from necrosis or hepatectomy. In mammals, the nature of the hepatocyte proliferative response is shaped by the identity of the mitogen, the time course and dose of administration, and the species and strain of the test animal (<a href="#_ENREF_8" title="Columbano, 1996 #152">Columbano and Shinozuka, 1996</a>).

Mitogenic proliferation in vitro and in vivo is measured by the incorporation of labeled nucleosides or nucleoside analogs into newly synthesized DNA (Peffer et al., 2018b), the detection of endogenous markers of proliferation such as antigen Ki-67 or proliferating cell nuclear antigen (PCNA) (Kee et al., 2002;  Muskhelishvili et al., 2003;  Wood et al., 2015), and other immunohistochemical techniques to detect proliferating cells. For each of these methods, a labeling index (fraction of labeled cell population/total number of cells in population) is calculated, and this index can be statistically compared between different groups (Wood et al., 2015). Nucleoside and nucleoside analog labeling. Actively proliferating cells undergo DNA synthesis in a highly regulated process during the S (synthesis) phase of the cell cycle. Once the DNA of a cell is replicated during S phase, the cell undergoes mitosis. This results in two cells, each of which has a complete copy of the genome. The DNA replication that occurs in S phase may be detected by the incorporation radiolabeled (e.g., 3H-thymidine) into the newly synthesized DNA, which can be detected from isolated livers using standard autoradiographic techniques. Nucleoside analogs may also be incorporated into the newly-synthesized DNA, including 5-bromo-2-deoxyuridine (BrdU) or 5-ethyl-2’-deoxy uridine (EdU), which may be detected using standard immunohistochemical and biolabeling techniques, respectively (Cavanagh et al., 2011). Drawbacks of the use of nucleoside analogs include concerns regarding the proper administration (dose, route of administration and length of exposure) to animals that allow for adequate labeling without inducing considerable toxicity (Cavanagh et al., 2011;  Cohen, 2010). In addition, nucleoside/nucleoside analog incorporation techniques are not specific for the detection of proliferation but may also identify cells that are undergoing DNA synthesis during apoptosis or DNA repair. Endogenous markers of proliferation. Ki-67 and PCNA are endogenous proteins expressed by mammalian cells that are in active phases of the cell cycle (G1, S, G2, M) and are not expressed in quiescent (G0) cells (Dietrich, 1993;  Eldrige et al., 1993;  Scholzen and Gerdes, 2000). They are detected in hepatocytes using standard immunohistochemical techniques. The advantage of using endogenous markers is that they do not require administration of exogenous markers for labeling, and they can be used for both prospective and retrospective cell proliferation analysis. A direct comparison of BrdU, Ki67 and PCNA labeling in various proliferating tissues of male Sprague-Dawley rats (Muskhelishvili et al., 2003) has indicated that Ki67 and BrdU immunohistochemistry methods gave similar labelling index results, whereas PCNA immunohistochemistry was not concordant with these methods and gave highly variable results. These authors suggested that PCNA is less accurate as a measure of cell proliferation because it has a long half-life and can be retained in cells that are not dividing, and is more involved in DNA repair mechanisms than Ki67. As a result, Ki67 has emerged as a more preferred endogenous marker for assessing cell proliferation in hepatocytes in recent years compared to PCNA.

Epidermal growth factor (EGF) is one of several extracellular ligands of the epidermal growth factor receptor (EGFR). The EGFR signaling pathway is conserved in most animals, in which it controls processes such as cell proliferation, differentiation, adhesion, and migration (Barberan and Cebria, 2018). EGFR is a transmembrane protein that is classified as a tyrosine kinase receptor. EGFR has several structural domains: 1) an N-terminal extracellular domain that binds ligands such as EGF, 2) a transmembrane domain, 3) an intracellular domain containing tyrosine kinase activity, and 4) a C-terminal region that contains tyrosine residues that are the sites of autophosphorylation. Ligand binding results in a cascade of events that include EGFR homo-or heterodimerization, activation of the tyrosine kinase domain, tyrosine autophosphorylation, and ultimately the activation of downstream signaling cascades that control various processes in the liver such as proliferation, survival, differentiation, response to injury, and repair (Berasain and Avila, 2014;  Komposch and Sibilia, 2015). EGF has been used as an agent to stimulate proliferation of rat, mouse, and human hepatic cells in culture (Bowen et al., 2014;  Haines et al., 2018c;  Hodges et al., 2000;  Parzefall et al., 1991). Other mitogenic agents produce a cell proliferation response in rats and mice, but not other mammalian species such as humans, hamsters or dogs.  These agents include phenobarbital (a model CAR activator) (Haines et al., 2018c;  Hirose et al., 2009;  Parzefall et al., 1991), WY-14,643 (pirinixic acid) (a model PPARalpha activator) (Corton et al., 2018) and TCDD (a model AhR activator) (Becker et al., 2015;  Budinsky et al., 2014).

UBERON:0002107

UBERON liver

CL:0000182

CL hepatocyte

High Unspecific

High

All life stages

Not Specified Not Specified Not Specified Not Specified Not Specified

<a name="_ENREF_1">Barberan, S. and Cebria, F. (2018), The role of the EGFR signaling pathway in stem cell differentiation during planarian regeneration and homeostasis. Semin Cell Dev Biol, 10.1016/j.semcdb.2018.05.011. </a> <a name="_ENREF_2">Becker, R. A., Patlewicz, G., Simon, T. W., Rowlands, J. C. and Budinsky, R. A. (2015), The adverse outcome pathway for rodent liver tumor promotion by sustained activation of the aryl hydrocarbon receptor. Regul Toxicol Pharmacol 73, 172-90, 10.1016/j.yrtph.2015.06.015. </a> <a name="_ENREF_3">Berasain, C. and Avila, M. A. (2014), The EGFR signalling system in the liver: from hepatoprotection to hepatocarcinogenesis. J Gastroenterol 49, 9-23, 10.1007/s00535-013-0907-x. </a>   <a name="_ENREF_4">Bowen, W. C., Michalopoulos, A. W., Orr, A., Ding, M. Q., Stolz, D. B. and Michalopoulos, G. K. (2014), Development of a chemically defined medium and discovery of new mitogenic growth factors for mouse hepatocytes: mitogenic effects of FGF1/2 and PDGF. PLoS One 9, e95487, 10.1371/journal.pone.0095487. </a>   <a name="_ENREF_5">Budinsky, R. A., Schrenk, D., Simon, T., Van den Berg, M., Reichard, J. F., Silkworth, J. B., Aylward, L. L., Brix, A., Gasiewicz, T., Kaminski, N., Perdew, G., Starr, T. B., Walker, N. J. and Rowlands, J. C. (2014), Mode of action and dose-response framework analysis for receptor-mediated toxicity: The aryl hydrocarbon receptor as a case study. Crit Rev Toxicol 44, 83-119, 10.3109/10408444.2013.835787. </a> <a name="_ENREF_6">Cavanagh, B. L., Walker, T., Norazit, A. and Meedeniya, A. C. (2011), Thymidine analogues for tracking DNA synthesis. Molecules 16, 7980-93, 10.3390/molecules16097980. </a> <a name="_ENREF_7">Cohen, S. M. (2010), Evaluation of possible carcinogenic risk to humans based on liver tumors in rodent assays: the two-year bioassay is no longer necessary. Toxicol Pathol 38, 487-501, 10.1177/0192623310363813. </a> <a name="_ENREF_8">Columbano, A. and Shinozuka, H. (1996), Liver regeneration versus direct hyperplasia. FASEB J 10, 1118-28. </a> <a name="_ENREF_9">Corton, J. C., Peters, J. M. and Klaunig, J. E. (2018), The PPARalpha-dependent rodent liver tumor response is not relevant to humans: addressing misconceptions. Arch Toxicol 92, 83-119, 10.1007/s00204-017-2094-7. </a> <a name="_ENREF_10">Dietrich, D. R. (1993), Toxicological and pathological applications of proliferating cell nuclear antigen (PCNA), a novel endogenous marker for cell proliferation. Crit Rev Toxicol 23, 77-109, 10.3109/10408449309104075. </a> <a name="_ENREF_11">Eldrige, S. R., Butterworth, B. E. and Goldsworthy, T. L. (1993), Proliferating cell nuclear antigen: a marker for hepatocellular proliferation in rodents. Environ Health Perspect 101 Suppl 5, 211-8, 10.1289/ehp.93101s5211. </a> <a name="_ENREF_12">Haines, C., Elcombe, B. M., Chatham, L. R., Vardy, A., Higgins, L. G., Elcombe, C. R. and Lake, B. G. (2018c), Comparison of the effects of sodium phenobarbital in wild type and humanized constitutive androstane receptor (CAR)/pregnane X receptor (PXR) mice and in cultured mouse, rat and human hepatocytes. Toxicology 396-397, 23-32, 10.1016/j.tox.2018.02.001. </a> <a name="_ENREF_13">Hirose, Y., Nagahori, H., Yamada, T., Deguchi, Y., Tomigahara, Y., Nishioka, K., Uwagawa, S., Kawamura, S., Isobe, N., Lake, B. G. and Okuno, Y. (2009), Comparison of the effects of the synthetic pyrethroid Metofluthrin and phenobarbital on CYP2B form induction and replicative DNA synthesis in cultured rat and human hepatocytes. Toxicology 258, 64-9. </a> <a name="_ENREF_14">Hodges, N. J., Orton, T. C., Strain, A. J. and Chipman, J. K. (2000), Potentiation of epidermal growth factor-induced DNA synthesis in rat hepatocytes by phenobarbitone: possible involvement of oxidative stress and kinase activation. Carcinogenesis 21, 2041-7. </a> <a name="_ENREF_15">Jones, H. B., Orton, T. C. and Lake, B. G. (2009), Effect of chronic phenobarbitone administration on liver tumour formation in the C57BL/10J mouse. Food Chem Toxicol 47, 1333-40, 10.1016/j.fct.2009.03.014. </a> <a name="_ENREF_16">Kee, N., Sivalingam, S., Boonstra, R. and Wojtowicz, J. M. (2002), The utility of Ki-67 and BrdU as proliferative markers of adult neurogenesis. J Neurosci Methods 115, 97-105. </a> <a name="_ENREF_17">Kolaja, K. L., Stevenson, D. E., Johnson, J. T., Walborg, E. F., Jr. and Klaunig, J. E. (1996a), Subchronic effects of dieldrin and phenobarbital on hepatic DNA synthesis in mice and rats. Fundam Appl Toxicol 29, 219-28. </a> <a name="_ENREF_18">Komposch, K. and Sibilia, M. (2015), EGFR Signaling in Liver Diseases. Int J Mol Sci 17, 10.3390/ijms17010030. </a> <a name="_ENREF_19">Muskhelishvili, L., Latendresse, J. R., Kodell, R. L. and Henderson, E. B. (2003), Evaluation of cell proliferation in rat tissues with BrdU, PCNA, Ki-67(MIB-5) immunohistochemistry and in situ hybridization for histone mRNA. J Histochem Cytochem 51, 1681-8. </a> <a name="_ENREF_20">Parzefall, W., Erber, E., Sedivy, R. and Schulte-Hermann, R. (1991), Testing for induction of DNA synthesis in human hepatocyte primary cultures by rat liver tumor promoters. Cancer Res 51, 1143-7. </a> <a name="_ENREF_21">Peffer, R. C., LeBaron, M. J., Battalora, M., Bomann, W. H., Werner, C., Aggarwal, M., Rowe, R. R. and Tinwell, H. (2018b), Minimum datasets to establish a CAR-mediated mode of action for rodent liver tumors. Regul Toxicol Pharmacol 96, 106-120, 10.1016/j.yrtph.2018.04.001. </a> <a name="_ENREF_22">Scholzen, T. and Gerdes, J. (2000), The Ki-67 protein: from the known and the unknown. J Cell Physiol 182, 311-22, 10.1002/(sici)1097-4652(200003)182:3<311::aid-jcp1>3.0.co;2-9. </a> <a name="_ENREF_23">Wood, C. E., Hukkanen, R. R., Sura, R., Jacobson-Kram, D., Nolte, T., Odin, M. and Cohen, S. M. (2015), Scientific and Regulatory Policy Committee (SRPC) Review: Interpretation and Use of Cell Proliferation Data in Cancer Risk Assessment. Toxicol Pathol 43, 760-75, 10.1177/0192623315576005. </a> <a name="_ENREF_24">Yamada, T., Okuda, Y., Kushida, M., Sumida, K., Takeuchi, H., Nagahori, H., Fukuda, T., Lake, B. G., Cohen, S. M. and Kawamura, S. (2014), Human hepatocytes support the hypertrophic but not the hyperplastic response to the murine nongenotoxic hepatocarcinogen sodium phenobarbital in an in vivo study using a chimeric mouse with humanized liver. Toxicol Sci 142, 137-57, 10.1093/toxsci/kfu173. </a> AOPWiki 2016-11-29T18:41:26

2021-01-06T16:21:39

Increase, Preneoplastic foci (hepatocytes)

Cellular

CL:0000182

CL hepatocyte

AOPWiki 2016-11-29T18:41:26

2017-09-16T10:16:04

Increase, hepatocellular adenomas and carcinomas

Tissue

UBERON:0002107

UBERON liver

AOPWiki 2016-11-29T18:41:26

2020-12-26T10:09:54

<upstream-id>d194287a-dd44-495f-89ad-ea9e59006313</upstream-id> <downstream-id>fefcf480-9e88-4df3-84cf-b2027195d59d</downstream-id>

#<Reference::ActiveRecord_Associations_CollectionProxy:0x00005eb8a287d3e0> AOPWiki 2016-11-29T18:41:35

2016-12-03T16:38:00

<upstream-id>fefcf480-9e88-4df3-84cf-b2027195d59d</upstream-id> <downstream-id>f4ab147d-75d4-47f2-92aa-a36c0b4ee6c6</downstream-id> Based on altered gene expression under the influence of CAR activation, an increase in cell proliferation of hepatocytes leads to a greater chance of normal, spontaneous errors in DNA replication and thus a higher proportion of altered hepatocytes. The hepatocytes with abnormal DNA can exhibit cell-cell communication differences from normal hepatocytes, and experience greater cell division even in the presence of contact inhibition with other hepatocytes. The islands of more actively dividing hepatocytes can be detected via histology based both on the larger numbers of cells (hyperplasia) and possibly a characteristic staining property of the clonally expanded cells (foci of cellular alteration – either eosinophilic, basophilic or clear cell). Thus, a higher rate of proliferation in the rodent liver leads to greater prevalence of altered hepatocytes, which clonally expand to generate an increase in preneoplastic foci.

The increased cell replication rate in the liver due to CAR activation (i.e. via a mitogenic signaling) is similar to other well-understood modes of action where an increase in cell proliferation leads to an eventual increase in preneoplastic foci, such as PPARα activating ligands and AhR activating ligands, which also lead to an increase in preneoplastic foci via clonal expansion of transformed hepatocytes.  In mice lacking the CAR receptor, including initiation-promotion assays, the upstream events (e.g. CAR activation, altered gene expression, and increased cell proliferation) and the downstream events (e.g. preneoplastic foci) are all blocked, providing strong support for the biological plausibility of this Key Event Relationship (Huang et al., 2005; Tamura et al., 2015; Tamura et al., 2013; Yamamoto et al., 2004).

The observed increase in numbers of preneoplastic foci, usually with eosinophilic staining properties, is observed with great regularity in mode of action work of CAR activating xenobiotics where histopathology at later times has been examined. This increase in foci (mixed or eosinophilic) after 2 years was observed at tumorigenic dose levels with metofluthrin in male rats (Deguchi et al., 2009), and at tumorigenic dose levels in mice treated with phenobarbital (Jones et al., 2009). With TCPOBOP in mice, multiple eosinophilic foci were reported to co-occur along with an increased incidence of eosinophilic adenomas and carcinomas after 60 weeks of treatment (Diwan et al., 1992). With well-studied CAR activators such as phenobarbital and TCPOBOP, increased cell proliferation has been detected at similar dose levels where increased altered foci are seen (Geter et al., 2014; Huang et al., 2005; Kolaja et al., 1996a; Kolaja et al., 1996b) (Tables 2 and 3); therefore, there is strong support for the linkage of these earlier key events with CAR activators leading to an increase in pre-neoplastic foci.

The incidence of altered foci, and their histological staining properties (e.g. eosinophilic, basophilic, clear cell, mixed) are not always reported in published studies of carcinogenicity with CAR activating compounds. In addition, the timing of interim or final sacrifices and histopathology data may possibly miss a window of time (for certain molecules) where the increase in preneoplastic foci can be quantified. However, the consistent findings with well-known CAR activating compounds and their absence in CAR knockout mouse studies provide a strong basis for their existence in the CAR AOP.

Increases in altered foci (primarily eosinophilic, or mixed) have typically occurred at the same dose levels where the preceding key event was observed (increased cell proliferation), and where the subsequent adverse outcome occurred (increased hepatocellular adenomas and carcinomas). With phenobarbital in C57BL/10J mice, 1000 ppm (113 mg/kg/day) produced increases in BrdU labelling index, eosinophilic foci and liver tumors, whereas 200 ppm (22 mg/kg/day) had no effects on any of these findings (Table 3) (Jones et al., 2009). With metofluthrin in male Wistar rats, 900 ppm and 1800 ppm produced increases in BrdU labelling index, altered foci (mixed or eosinophilic) and liver tumors, and these dose levels also produced the earlier key events in the proposed AOP with metofluthrin (Table 5) (Deguchi et al., 2009; Yamada et al., 2009). In these rat studies, 200 ppm metofluthrin represented a No Effect Level for both altered foci and hepatocellular tumors, and it also failed to produce any of the earlier key events in the proposed MOA for metofluthrin including cell proliferation. Thus, for these well-studied CAR activators that have ample dose-response data, a strong quantitative understanding of this linkage is available in mice and in rats.

High Mixed

High

Adult

High High

Studies in various species, or in isolated hepatocytes from various mammalian species including humans, have demonstrated that CAR activators such as phenobarbital or metofluthrin produce a cell proliferation response that is seen in mice or rats, but not in hamsters, guinea pigs or humans (Hasmall and Roberts, 1999; Hirose et al., 2009; James and Roberts, 1996; Yamada et al., 2014; Yamada et al., 2009).   Accordingly, phenobarbital and other CAR activators do not produce liver tumors in long term studies in hamsters (Diwan et al., 1986; Elcombe et al., 2014). Consistent with the lack of effects on proliferation, Diwan et al. (1986) also reported that in Syrian hamsters, phenobarbital treatment at 500 ppm in the drinking water did not produce any increases in preneoplastic foci of cellular alteration compared to groups that received an initiator alone. Therefore, this key event of increased foci in the liver has strong data indicating it is specific to mice and rats, the species which also develop hepatocellular tumors in response to known CAR activators.

#<Reference::ActiveRecord_Associations_CollectionProxy:0x00005eb8a25526e8> AOPWiki 2016-11-29T18:41:35

2017-02-14T17:05:29

<upstream-id>f4ab147d-75d4-47f2-92aa-a36c0b4ee6c6</upstream-id> <downstream-id>128d5ff5-a0b6-4b9b-aa14-b474ffba59f1</downstream-id> Clonally expanded cells (foci of cellular alteration – either eosinophilic, basophilic or clear cell) have been shown to be increased at tumorigenic dose levels of CAR activators such as phenobarbital, TCPOBOP and metofluthrin. As discussed for earlier key events, the CAR-mediated events that lead to an increase in altered foci lead to a greater abundance of cells with mutations in their DNA that are less responsive to normal cell-cell signaling and control mechanisms. As a result, these foci are considered preneoplastic lesions, and can progress with time into adenomas and carcinomas. The continued CAR-mediated stimulus for increased cell proliferation within these foci (e.g. as demonstrated in studies by Kolaja et al., 1996b) will also provide an environment where the mutant cells can survive and develop into tumors.

The development of liver tumors in rodents, whether spontaneously or induced by a non-genotoxic carcinogen, has consistently included the development of altered foci as a precursor step to hepatocellular adenomas and carcinomas (Goldsworthy and Fransson-Steen, 2002; Tamura et al., 2015). These foci are considered preneoplastic lesions, and their ability to progress to form adenomas and/or carcinomas in rodents has been previously recognized. In the case of CAR activators, an increased incidence of preneoplastic foci has been consistently shown to precede tumor development, and there is a high biological plausibility for this Key Event Relationship (Elcombe et al., 2014; Goldsworthy and Fransson-Steen, 2002; Jones et al., 2009; Lake, 2009).

The observed increase in numbers of preneoplastic foci, usually with eosinophilic staining properties, is observed with great regularity in mode of action work of CAR activating xenobiotics where histopathology at later times has been examined. This increase in foci (mixed or eosinophilic) after 2 years was observed at tumorigenic dose levels with metofluthrin in male rats (Deguchi et al., 2009), and at tumorigenic dose levels in mice treated with phenobarbital (Jones et al., 2009). With TCPOBOP in mice, multiple eosinophilic foci were reported to co-occur along with an increased incidence of eosinophilic adenomas and carcinomas after 60 weeks of treatment (Diwan et al., 1992). In addition, experiments where the MIE (CAR activation) is blocked have been performed with these model CAR activators. For phenobarbital and TCPOBOP in mice, the early key events and the progression to increased altered foci and hepatocellular tumors were all blocked in CAR knockout mice (Huang et al., 2005; Yamamoto et al., 2004). Foci of cellular alteration in CAR knockout mice were also prevented in an initiation-promotion model using the CAR activators cyproconazole and fluconazole (Tamura et al., 2015), and the incidence of adenomas and carcinomas was similarly decreased (Tamura et al., 2015). Thus, there is strong support for the involvement of CAR activation in these mechanisms, and that the stated sequence of key events following CAR activation leads to an increase in pre-neoplastic foci and then liver tumors in mice and rats.

The incidence of altered foci, and their staining properties (e.g. eosinophilic, basophilic, clear cell, mixed) are not always reported in published studies of carcinogenicity with CAR activation compounds. However, the consistent findings with well-known CAR activating compounds and their absence in CAR knockout mouse studies provide a strong basis for their existence in the CAR AOP.

In studies where their incidences are reported, increases in altered foci (primarily eosinophilic, or mixed) have typically occurred at the same dose levels where increases in hepatocellular adenomas and carcinomas occurred. With phenobarbital in male C57BL/10J mice, 1000 ppm (113 mg/kg/day) produced an increase in eosinophilic and clear cell foci and an increase in liver tumors, whereas 200 ppm (22 mg/kg/day) had no effects on either finding (Table 3) (Jones et al., 2009). With metofluthrin in male Wistar rats, 900 ppm and 1800 ppm produced increases in mixed foci and eosinophilic foci, respectively, and an increased incidence of liver tumors was observed at 900 ppm and above (Table 5) (Deguchi et al., 2009; Yamada et al., 2014). For metofluthrin in rats, 200 ppm represented a No Effect Level for both altered foci and hepatocellular tumors, and it also failed to produce any of the earlier key events in the proposed AOP for metofluthrin. Thus, for these well-studied CAR activators that have ample dose-response data, a strong quantitative understanding of this linkage is available in mice and in rats.

High Mixed

High

Adults

High High

Phenobarbital and other CAR activators do not produce liver tumors in long term studies in hamsters (Diwan et al., 1986; Elcombe et al., 2014). Consistent with the lack of effects on proliferation and on tumor development, Diwan et al. (1986) also reported that phenobarbital treatment at 500 ppm in the drinking water did not produce any increases in preneoplastic foci of cellular alteration compared to groups that received an initiator alone. Further, treatment of CAR knockout mice lacking the CAR nuclear receptor with phenobarbital or TCPOBOP produced none of the early key events (e.g. altered expression of CAR-responsive cell cycle genes, increased cell proliferation) and no increases in altered foci or tumors (Huang et al., 2005; Yamamoto et al., 2004). Therefore, the development of increased foci in the liver in response to treatment with CAR activators has strong data indicating it is specific to mice and rats, the species which also develop hepatocellular tumors in response to known CAR activators.

#<Reference::ActiveRecord_Associations_CollectionProxy:0x00005eb8a2719648> AOPWiki 2016-11-29T18:41:35

2017-02-15T10:20:59

Androgen receptor activation leading to hepatocellular adenomas and carcinomas (in mouse and rat)

AR- HCC

Evgeniia Kazymova

Cancer AOP Workgroup. National Health and Environmental Effects Research Laboratory, Office of Research and Development, Integrated Systems Toxicology Division, US Environmental Protection Agency, Research Triangle Park, NC. Corresponding author for wiki entry (wood.charles@epa.gov)

Open for adoption

Under Development

1.26

1.0

This putative adverse outcome pathway (AOP) outlines potential key events leading to a tumor outcome in standard carcinogenicity models. This information is based largely on modes of action described previously in cited literature sources and is intended as a resource template for AOP development and data organization. Presentation in this Wiki does not indicate EPA acceptance of a particular pathway for a given reference agent, only that the information has been proposed in some manner. In addition, this putative AOP relates to the model species indicated and does not directly address issues of human relevance.

adjacent

Not Specified

Not Specified adjacent

Not Specified

Not Specified adjacent

Not Specified

Not Specified Male Not Specified Female Not Specified Not Specified

NTP (National Toxicology Program). (September 2010). Toxicology and Carcinogenesis Studies of Androstenedione in F344/N Rats and B6C3F1 Mice (Vol. NTP TR 560). AOPWiki 2016-11-29T18:41:16

2023-09-25T16:26:50