Activation, PPARα

50892-23-4

SZRPDCCEHVWOJX-UHFFFAOYSA-N

Pirinixic acid

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

DTXSID4020290

637-07-0

KNHUKKLJHYUCFP-UHFFFAOYSA-N

Clofibrate

ethyl-p-chlorophenoxyisobutyrate Propanoic acid, 2-(4-chlorophenoxy)-2-methyl-, ethyl ester 2-(p-Chlorophenoxy)-2-methylpropionic acid ethyl ester Abitrate Amotril Anparton Arteriosan Artevil Ateculon Ateriosan Atheropront Atromid S Atromidin Azionyl Bioscleran Cartagyl Claripex Claripex CPIB Clobren SF Clofibrat clofibrato Clofinit Ethyl (p-chlorophenoxy) isobutyrate Ethyl 2-(4-chlorophenoxy)-2-methylpropionate Ethyl 2-(4-chlorophenoxy)isobutyrate Ethyl 2-(p-chlorophenoxy)-2-methylpropionate Ethyl 2-(p-chlorophenoxy)isobutyrate Ethyl clofibrate Ethyl p-chlorophenoxyisobutyrate Ethyl α-(4-chlorophenoxy)isobutyrate Ethyl α-(4-chlorophenoxy)-α-methylpropionate Ethyl α-(p-chlorophenoxy)isobutyrate Ethyl α-(p-chlorophenoxy)-α-methylpropionate Hyclorate Lipavil Lipavlon Lipomid Liprinal Miscleron Misclerone Neo-Atromid Normolipol NSC 79389 p-Chlorophenoxyisobutyric acid ethyl ester Propionic acid, 2-(p-chlorophenoxy)-2-methyl-, ethyl ester Recolip Regelan Serotinex Sklerepmexe Sklerolip Skleromexe Sklero-Tablinene Ticlobran Xyduril

DTXSID3020336

117-81-7

BJQHLKABXJIVAM-UHFFFAOYNA-N

BJQHLKABXJIVAM-UHFFFAOYSA-N

Di(2-ethylhexyl) phthalate

1,2-Benzenedicarboxylic acid, bis(2-ethylhexyl) ester DEHP 1,2-Benzedicarboxylic acid, bis(2-ethyl-hexyl) ester 1,2-Benzenedicarboxylic acid bis(2-ethylhexyl) ester 1,2-Benzenedicarboxylic acid, 1,2-bis(2-ethylhexyl) ester 1,2-Benzenedicarboxylic acid,bis(2-ethylhexylester) Bis(2-ethylhexyl) 1,2-benzenedicarboxylate Bis(2-ethylhexyl) o-phthalate bis(2-ethylhexyl) phthalate Bis(2-ethylhexyl)phthalat Bis(2-ethylhexyl)phthalate Bisoflex 81 Bisoflex DOP Corflex 400 Di(2-ethylhexyl)phthalate Di(isooctyl) phthalate Di-2-ethylhexlphthalate Di-2-ethylhexyl phthalate DI-2-ETHYLHEXYL-PHTHALATE Diacizer DOP Diethylhexyl phthalate Dioctylphthalate DOF Ergoplast FDO Ergoplast FDO-S ETHYLHEXYL PHTHALATE Eviplast 80 Eviplast 81 Fleximel Flexol DOD Flexol DOP ftlalato de bis(2-etilhexilo) Garbeflex DOP-D 40 Good-rite GP 264 Hatco DOP Jayflex DOP Kodaflex DEHP Kodaflex DOP Monocizer DOP NSC 17069 Palatinol AH Palatinol AH-L Phtalate de Bis (Ethyle-2-Hexyle) Phtalate de bis(2-ethylhexyle) PHTHALATE, BIS(2-ETHYLHEXYL) Phthalic acid di(2-ethylhexyl) ester Phthalic acid, bis(2-ethylhexyl) ester PHTHALIC ACID, BIS(2-ETHYLHEXYL)ESTER PHTHALSAEURE-BIS-(2-AETHYLHEXYL)-ESTER Pittsburgh PX 138 Plasthall DOP Reomol D 79P Sansocizer DOP Sansocizer R 8000 Sconamoll DOP Staflex DOP Truflex DOP Vestinol AH Vinycizer 80 Vinycizer 80K Witcizer 312

DTXSID5020607

3771-19-5

XJGBDJOMWKAZJS-UHFFFAOYNA-N

XJGBDJOMWKAZJS-UHFFFAOYSA-N

Nafenopin

DTXSID8020911

52214-84-3

KPSRODZRAIWAKH-UHFFFAOYNA-N

KPSRODZRAIWAKH-UHFFFAOYSA-N

Ciprofibrate

DTXSID8020331

25812-30-0

HEMJJKBWTPKOJG-UHFFFAOYSA-N

Gemfibrozil

Pentanoic acid, 5-(2,5-dimethylphenoxy)-2,2-dimethyl- 2,2-Dimethyl-5-(2,5-xylyloxy)valeric acid 5-(2,5-Dimethylphenoxy)-2,2-dimethylpentanoic acid Decrelip gemfibrozilo Gevilon Lopizid Trialmin 900 Valeric acid, 2,2-dimethyl-5-(2,5-xylyloxy)-

DTXSID0020652

41859-67-0

IIBYAHWJQTYFKB-UHFFFAOYSA-N

Bezafibrate

Propanoic acid, 2-[4-[2-[(4-chlorobenzoyl)amino]ethyl]phenoxy]-2-methyl- Befizal Benzofibrate Bezafibrat bezafibrato Bezalip Bezatol Difaterol

DTXSID3029869

49562-28-9

YMTINGFKWWXKFG-UHFFFAOYSA-N

Fenofibrate

Propanoic acid, 2-[4-(4-chlorobenzoyl)phenoxy]-2-methyl-, 1-methylethyl ester 2-[4-(4-Chlorobenzoyl)phenoxy]-2-methylpropanoic acid 1-methylethyl ester Ankebin Clorofibrate Elasterin Fenobrate Fenofibrat fenofibrato Fenogal Fenotard Isopropyl 2-[p-(p-chlorobenzoyl)phenoxy]-2-methylpropionate Lipanthyl Lipantil Lipicard Lipidil Lipidil Supra Lipirex Lipoclar Lipofene Liposit MeltDose Nolipax NSC 281319 Procetofen Procetofene Procetoken Protolipan Secalip

DTXSID2029874

79902-63-9

RYMZZMVNJRMUDD-HGQWONQESA-N

Simvastatin

Butanoic acid, 2,2-dimethyl-, (1S,3R,7S,8S,8aR)-1,2,3,7,8,8a-hexahydro-3,7-dimethyl-8-[2-[(2R,4R)-tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl]ethyl]-1-naphthalenyl ester (+)-Simvastatin Apo-Simvastatin Bestatin 20 Butanoic acid, 2,2-dimethyl-, 1,2,3,7,8,8a-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthalenyl ester, [1S-[1α,3α,7β,8β(2S*,4S*),8aβ]]- Cholestat Co-Simvastatin Kolestevan L 644128-000U Lipinorm Liponorm Lipovas Lodales Modutrol Nor-Vastina Novo-Simvastatin Pms-simvastatin Simastin 20 Simovil Simvastatin lactone Simvotin Sinvacor Sinvascor Sivastin Starstat 20 Synvinolin Valemia Velostatin

DTXSID0023581

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

PR:000013056

PR peroxisome proliferator-activated receptor alpha

CL:0000422

CL mitogenic signaling cell

CL:0000182

CL hepatocyte

D000236

MESH Adenoma

D002277

MESH Carcinoma

GO:0035357

GO peroxisome proliferator activated receptor signaling pathway

GO:0008283

GO cell proliferation

GO:0072574

GO hepatocyte proliferation

D006528

MESH hepatocellular carcinoma

WIKI increased

pirinixic acid

2016-11-29T18:42:27

Clofibrate

2016-11-29T18:42:27

Bis(2-ethylhexyl) phthalate

2016-11-29T18:42:08

Nafenopin

2016-11-29T18:42:27

ciprofibrate

2016-11-29T18:42:27

Gemfibrozil Fibrate drug

2016-11-29T18:42:27

2020-03-31T10:24:40

PERFLUOROOCTANOIC ACID

2016-11-29T18:42:27

Bezafibrate

2016-11-29T18:42:27

Fenofibrate

2016-11-29T18:42:27

Di(2-ethylhexyl) phthalate

2016-11-29T18:42:26

Mono(2-ethylhexyl) phthalate

2016-11-29T18:42:26

Stressor:205 pirinixic acid (WY-14,643)

2020-12-19T09:06:20

Simvastatin

2020-05-06T09:41:35

Wy-14,6423

2020-12-28T12:52:10

Phthalates

2017-03-09T22:37:12

2017-03-09T22:37:40

Perflourinated chemicals

2017-03-09T22:36:38

Phenobarbital

2016-11-29T18:42:27

Epidermal growth factor

2018-12-20T15:05:33

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

435440

NCBI Rattus sp. ABTC 43906

1090580

NCBI Mus sp. 09ZR5#43

WikiUser_9

ApacheUser Hamster

WCS_9615

common toxicological species dog

Activation, PPARα

Molecular

Gene expression occurs in a coordinated fashion (Judson et al., 2012). The many observations of altered gene expression following binding of ligand to PPARα led to systematic investigations of the genomic signature that corresponds to PPARα activation (Tamura et al., 2006; Kupershmidt et al., 2010; Rosen et al., 2017; Rooney et al., 2018; Corton et al., 2020; Hill et al., 2020; Lewis et al., 2020). Specific gene with increased expression following PPARα activation include Cyp4a1, Cpt1B, and Lpl. More generally, the pathways activated include: <ul> <li>Genes involved in Metabolism of lipids and lipoproteins</li> <li>Fatty acid metabolism</li> <li>Genes involved in Fatty acid, triacylglycerol, and ketone body metabolism</li> <li>PPAR signaling pathway</li> <li>Peroxisome</li> <li>Genes involved in Cell Cycle</li> </ul> Biological state The Peroxisome Proliferator Activated receptor α (PPARα) belongs to the <a href="/wiki/index.php/Peroxisome_Proliferator_Activated_receptors_(PPARs;_NR1C)" title="Peroxisome Proliferator Activated receptors (PPARs; NR1C)">Peroxisome Proliferator Activated receptors (PPARs; NR1C)</a> steroid/thyroid/retinoid receptor superfamily of transcription factors. Biological compartments PPARα is expressed in high levels in tissues that perform significant catabolism of fatty acids (FAs), such as brown adipose tissue, liver, heart, kidney, and intestine (Michalik et al. 2006). The receptor is present also in skeletal muscle, intestine, pancreas, lung, placenta and testes (Mukherjee et al. 1997), (Schultz et al. 1999). General role in biology PPARs are activated by fatty acids and their derivatives; they are sensors of dietary lipids and are involved in lipid and carbohydrate metabolism, immune response and peroxisome proliferation (Wahli and Desvergne 1999), (Evans, Barish, & Wang, 2004). PAPRα is a also a target of hypothalamic hormone signalling and was found to play a role in embryonic development (Yessoufou and Wahli 2010). Fibrates, activators of PPARα, are commonly used to treat hypertriglyceridemia and other dyslipidemic states as they have been shown to decrease circulating lipid levels (Lefebvre et al. 2006).

Binding of ligands to PPARα is measured using binding assays in vitro and in silico, whereas the information about functional activation is derived from transactivation assays (e.g. transactivation assay with reporter gene) that demonstrate functional activation of a nuclear receptor by a specific compound. Binding of agonists within the ligand-binding site of PPARs causes a conformational change of nuclear receptor that promotes binding to transcriptional co-activators. Conversely, binding of antagonists results in a conformation that favours the binding of co-repressors (Yu and Reddy 2007), (Viswakarma et al. 2010). Transactivation assays are performed using transient or stably transfected cells with the PPARα expression plasmid and a reporter plasmid, respectively. There are also other methods that have been used to measure PPARα activity, such as the Electrophoretic Mobility Shift Assay (EMSA) or commercially available PPARα transcription factor assay kits, see Table 1. The transactivation (stable transfection) assay provides the most applicable OECD Level 2 assay (i.e. In vitro assays providing mechanistic data) aimed at identifying the initiating event leading to an adverse outcome (LeBlanc, Norris, and Kloas 2011). A recent study characterized the PPARα ligand binding domain for the purpose of next-generation metabolic disease drugs (Kamata et al. 2020). The most direct measure of this MIE is microarray profiling from large gene expression databases TG-GATEs and DrugMatrix coupled with t statistical analysis of whole genome expression profiles (Svoboda et al., 2019; Igarashi et al., 2015) From these data, A gene expression signature of 131 PPARα-dependent genes was built using microarray profiles from the livers of wild-type and PPARα-null mice. A quantitative measure of this expression signature is a measure of similarity/correlation between the PPARα signature and positive and negative test sets is provided by the Running Fisher test (Corton et al., 2020; Hill et al., 2020; Kupershmidt et al., 2010; Lewis et al., 2020; Rooney et al., 2018). A gene expression signature of 131 PPARα-dependent genes was built using microarray profiles from the livers of wild-type and PPARα-null mice. A quantitative measure of this expression signature would be a measure of similarity/correlation between the PPARα signature and positive and negative test sets is provided by the Running Fisher test (Kupershmidt et al., 2010; Rooney et al., 2018; Corton et al., 2020). For all substances, MIE activation does not rise monotonically over dose or time. These fluctuations are likely due to variations in cofactor availability or access to the site of transcription (Gaillard et al., 2006; Koppen et al., 2009; Kupershmidt et al., 2010; Ong et al., 2010; Chow et al., 2011; De Vos et al., 2011; Simon et al., 2015). . <table align="left" border="1" cellpadding="1" cellspacing="1" style="height:3px; width:100px"> <caption>Measurements of PPARα Activation</caption> <thead> <tr> <th scope="row">Method/Test</th> <th scope="col">Test Principle</th> <th scope="col">Test Environment</th> <th scope="col">Test Outcome</th> <th scope="col">Assay Type/Domain</th> </tr> </thead> <tbody> <tr> <th scope="row"> molecular modelling; docking simulation </th> <td>Computational simulation of  ligand binding </td> <td>In silico</td> <td>Prediction off binding interaction </td> <td>Quantitative virtual screeings</td> </tr> <tr> <th scope="row">Scintillation proximity binding assay</th> <td>Direct binding of ligand</td> <td>In vitro</td> <td>Identifies compouds that bind to PPARα</td> <td>Qualitative in vitro screening</td> </tr> <tr> <th scope="row">PPARα reporter gene assay</th> <td>Quantify changes in in PPARα activation via a sensitive surrogate </td> <td>In vitro, Ex vivo</td> <td>Measures changes in activity of genes linked to a PPARα receptor element</td> <td>Quantitative in vitro screening</td> </tr> <tr> <th scope="row">Electrophoretic Band Shift</th> <td>determines if a protein or protein mixture will bind to a specific DNA or RNA sequence</td> <td>In vitro</td> <td>Measures cofactor binding by changes in gel mobility</td> <td>Quantitative in vitro screening</td> </tr> <tr> <th scope="row">Microarray profiling</th> <td>Develop MIE-specific sets of gene expression biomarkers</td> <td>In vivo</td> <td>Classification of PPARα biomarker genes with statistical methods</td> <td>Quantitative in vivo screening</td> </tr> </tbody> </table>

PPARα has been identified in frog (Xenopus laevis), mouse, human, rat, fish, hamster and chicken (reviewed in (Wahli and Desvergne 1999)).

UBERON:0002107

UBERON liver

CL:0000255

CL eukaryotic cell

High High High

Bhattacharya, Nandini, Jannette M Dufour, My-Nuong Vo, Janice Okita, Richard Okita, and Kwan Hee Kim. 2005. “Differential Effects of Phthalates on the Testis and the Liver.” Biology of Reproduction 72 (3) (March): 745–54. doi:10.1095/biolreprod.104.031583. Bility, Moses T, Jerry T Thompson, Richard H McKee, Raymond M David, John H Butala, John P Vanden Heuvel, and Jeffrey M Peters. 2004. “Activation of Mouse and Human Peroxisome Proliferator-Activated Receptors (PPARs) by Phthalate Monoesters.” Toxicological Sciences : An Official Journal of the Society of Toxicology 82 (1) (November): 170–82. doi:10.1093/toxsci/kfh253. Chow, C. C., Ong, K. M., Dougherty, E. J., & Simons, S. S. (2011). Inferring mechanisms from dose-response curves. Methods Enzymol, 487, 465-483. https://doi.org/10.1016/B978-0-12-381270-4.00016-0 Corton, J. C., Hill, T., Sutherland, J. J., Stevens, J. L., & Rooney, J. (2020). A Set of Six Gene Expression Biomarkers Identify Rat Liver Tumorigens in Short-Term Assays. Toxicol Sci. https://doi.org/10.1093/toxsci/kfaa101 De Vos, D., Bruggeman, F. J., Westerhoff, H. V., & Bakker, B. M. (2011). How molecular competition influences fluxes in gene expression networks. PLoS One, 6(12), e28494. https://doi.org/10.1371/journal.pone.0028494 Dufour, Jannette M, My-Nuong Vo, Nandini Bhattacharya, Janice Okita, Richard Okita, and Kwan Hee Kim. 2003. “Peroxisome Proliferators Disrupt Retinoic Acid Receptor Alpha Signaling in the Testis.” Biology of Reproduction 68 (4) (April): 1215–24. doi:10.1095/biolreprod.102.010488. Feige, Jérôme N, Laurent Gelman, Daniel Rossi, Vincent Zoete, Raphaël Métivier, Cicerone Tudor, Silvia I Anghel, et al. 2007. “The Endocrine Disruptor Monoethyl-Hexyl-Phthalate Is a Selective Peroxisome Proliferator-Activated Receptor Gamma Modulator That Promotes Adipogenesis.” The Journal of Biological Chemistry 282 (26) (June 29): 19152–66. doi:10.1074/jbc.M702724200. Gaillard, S., Grasfeder, L. L., Haeffele, C. L., Lobenhofer, E. K., Chu, T.-M., Wolfinger, R., Kazmin, D., Koves, T. R., Muoio, D. M., Chang, C.-y., & McDonnell, D. P. (2006). Receptor-selective coactivators as tools to define the biology of specific receptor-coactivator pairs. Mol Cell, 24(5), 797-803. https://doi.org/10.1016/j.molcel.2006.10.012 Hill, T., Rooney, J., Abedini, J., El-Masri, H., Wood, C. E., & Corton, J. C. (2020). Gene Expression Thresholds Derived From Short-Term Exposures Identify Rat Liver Tumorigens. Toxicol Sci. https://doi.org/10.1093/toxsci/kfaa102 Hurst, Christopher H, and David J Waxman. 2003. “Activation of PPARalpha and PPARgamma by Environmental Phthalate Monoesters.” Toxicological Sciences : An Official Journal of the Society of Toxicology 74 (2) (August): 297–308. doi:10.1093/toxsci/kfg145. Igarashi, Y., Nakatsu, N., Yamashita, T., Ono, A., Ohno, Y., Urushidani, T., & Yamada, H. (2015). Open TG-GATEs: a large-scale toxicogenomics database. Nucleic Acids Res, 43(Database issue), D921-7. https://doi.org/10.1093/nar/gku955 Kamata S, Oyama T, Saito K, Honda A, Yamamoto Y, Suda K, Ishikawa R, Itoh T, Watanabe Y, Shibata T, Uchida K, Suematsu M, Ishii I. PPARα Ligand-Binding Domain Structures with Endogenous Fatty Acids and Fibrates. iScience. 2020;23(11):101727. 10.1016/j.isci.2020.101727 Kaya, Taner, Scott C Mohr, David J Waxman, and Sandor Vajda. 2006. “Computational Screening of Phthalate Monoesters for Binding to PPARgamma.” Chemical Research in Toxicology 19 (8) (August): 999–1009. doi:10.1021/tx050301s. Koppen, A., Houtman, R., Pijnenburg, D., Jeninga, E. H., Ruijtenbeek, R., & Kalkhoven, E. (2009). Nuclear receptor-coregulator interaction profiling identifies TRIP3 as a novel peroxisome proliferator-activated receptor gamma cofactor. Mol Cell Proteomics, 8(10), 2212-2226. https://doi.org/10.1074/mcp.M900209-MCP200 Kupershmidt, I., Su, Q. J., Grewal, A., Sundaresh, S., Halperin, I., Flynn, J., Shekar, M., Wang, H., Park, J., Cui, W., Wall, G. D., Wisotzkey, R., Alag, S., Akhtari, S., & Ronaghi, M. (2010). Ontology-based meta-analysis of global collections of high-throughput public data. PLoS One, 5(9). https://doi.org/10.1371/journal.pone.0013066 Lampen, Alfonso, Susan Zimnik, and Heinz Nau. 2003. “Teratogenic Phthalate Esters and Metabolites Activate the Nuclear Receptors PPARs and Induce Differentiation of F9 Cells.” Toxicology and Applied Pharmacology 188 (1) (April): 14–23. doi:10.1016/S0041-008X(03)00014-0. Lapinskas, Paula J., Sherri Brown, Lisa M. Leesnitzer, Steven Blanchard, Cyndi Swanson, Russell C. Cattley, and J. Christopher Corton. 2005. “Role of PPARα in Mediating the Effects of Phthalates and Metabolites in the Liver.” Toxicology 207 (1): 149–163. Le Maire, Albane, Marina Grimaldi, Dominique Roecklin, Sonia Dagnino, Valérie Vivat-Hannah, Patrick Balaguer, and William Bourguet. 2009. “Activation of RXR-PPAR Heterodimers by Organotin Environmental Endocrine Disruptors.” EMBO Reports 10 (4) (April): 367–73. doi:10.1038/embor.2009.8. LeBlanc, GA, DO Norris, and W Kloas. 2011. “Detailed Review Paper State of the Science on Novel In Vitro and In Vivo Screening and Testing Methods and Endpoints for Evaluating Endocrine Disruptors” (178). Lefebvre, Philippe, Giulia Chinetti, Jean-Charles Fruchart, and Bart Staels. 2006. “Sorting out the Roles of PPAR Alpha in Energy Metabolism and Vascular Homeostasis.” The Journal of Clinical Investigation 116 (3) (March): 571–80. doi:10.1172/JCI27989. Lewis, R. W., Hill, T., & Corton, J. C. (2020). A set of six Gene expression biomarkers and their thresholds identify rat liver tumorigens in short-term assays. Toxicology, 443, 152547. https://doi.org/10.1016/j.tox.2020.152547 Maloney, Erin K., and David J. Waxman. 1999. “Trans-Activation of PPARα and PPARγ by Structurally Diverse Environmental Chemicals.” Toxicology and Applied Pharmacology 161 (2): 209–218. Michalik, Liliane, Johan Auwerx, Joel P Berger, V Krishna Chatterjee, Christopher K Glass, Frank J Gonzalez, Paul A Grimaldi, et al. 2006. “International Union of Pharmacology. LXI. Peroxisome Proliferator-Activated Receptors.” Pharmacological Reviews 58 (4) (December): 726–41. doi:10.1124/pr.58.4.5. Mukherjee, R, L Jow, G E Croston, and J R Paterniti. 1997. “Identification, Characterization, and Tissue Distribution of Human Peroxisome Proliferator-Activated Receptor (PPAR) Isoforms PPARgamma2 versus PPARgamma1 and Activation with Retinoid X Receptor Agonists and Antagonists.” The Journal of Biological Chemistry 272 (12) (March 21): 8071–6. Ong, K. M., Blackford, J. A., Kagan, B. L., Simons, S. S., & Chow, C. C. (2010). A theoretical framework for gene induction and experimental comparisons. Proc Natl Acad Sci U S A, 107(15), 7107-7112. https://doi.org/10.1073/pnas.0911095107 Rooney, J., Hill, T., Qin, C., Sistare, F. D., & Corton, J. C. (2018). Adverse outcome pathway-driven identification of rat liver tumorigens in short-term assays. Toxicol Appl Pharmacol, 356, 99-113. https://doi.org/10.1016/j.taap.2018.07.023 Schultz, R, W Yan, J Toppari, A Völkl, J A Gustafsson, and M Pelto-Huikko. 1999. “Expression of Peroxisome Proliferator-Activated Receptor Alpha Messenger Ribonucleic Acid and Protein in Human and Rat Testis.” Endocrinology 140 (7) (July): 2968–75. doi:10.1210/endo.140.7.6858. Simon, T. W., Budinsky, R. A., & Rowlands, J. C. (2015). A model for aryl hydrocarbon receptor-activated gene expression shows potency and efficacy changes and predicts squelching due to competition for transcription co-activators. PLoS One, 10(6), e0127952. https://doi.org/10.1371/journal.pone.0127952. Staels, B., J. Dallongeville, J. Auwerx, K. Schoonjans, E. Leitersdorf, and J.-C. Fruchart. 1998. “Mechanism of Action of Fibrates on Lipid and Lipoprotein Metabolism.” Circulation 98 (19) (November 10): 2088–2093. doi:10.1161/01.CIR.98.19.2088. Svoboda, D. L., Saddler, T., & Auerbach, S. S. (2019). An Overview of National Toxicology Program’s Toxicogenomic Applications: DrugMatrix and ToxFX.  In Advances in Computational Toxicology (pp. 141-157). Springer. https://link.springer.com/chapter/10.1007/978-3-030-16443-0_8 ToxCastTM Data. “ToxCastTM Data.” US Environmental Protection Agency. <a class="external free" href="http://www.epa.gov/ncct/toxcast/data.html" rel="nofollow" target="_blank">http://www.epa.gov/ncct/toxcast/data.html</a> Vanden Heuvel, John P, Jerry T Thompson, Steven R Frame, and Peter J Gillies. 2006. “Differential Activation of Nuclear Receptors by Perfluorinated Fatty Acid Analogs and Natural Fatty Acids: A Comparison of Human, Mouse, and Rat Peroxisome Proliferator-Activated Receptor-Alpha, -Beta, and -Gamma, Liver X Receptor-Beta, and Retinoid X Rec.” Toxicological Sciences : An Official Journal of the Society of Toxicology 92 (2) (August): 476–89. doi:10.1093/toxsci/kfl014. Venkata, Nagaraj Gopisetty, Jodie a Robinson, Peter J Cabot, Barbara Davis, Greg R Monteith, and Sarah J Roberts-Thomson. 2006. “Mono(2-Ethylhexyl)phthalate and Mono-N-Butyl Phthalate Activation of Peroxisome Proliferator Activated-Receptors Alpha and Gamma in Breast.” Toxicology Letters 163 (3) (June 1): 224–34. doi:10.1016/j.toxlet.2005.11.001. Viswakarma, Navin, Yuzhi Jia, Liang Bai, Aurore Vluggens, Jayme Borensztajn, Jianming Xu, and Janardan K Reddy. 2010. “Coactivators in PPAR-Regulated Gene Expression.” PPAR Research 2010 (January). doi:10.1155/2010/250126. Wahli, Walter, and B Desvergne. 1999. “Peroxisome Proliferator-Activated Receptors: Nuclear Control of Metabolism.” Endocrine Reviews 20 (5) (October): 649–88. Wu, Bin, Jie Gao, and Ming-wei Wang. 2005. “Development of a Complex Scintillation Proximity Assay for High-Throughput Screening of PPARgamma Modulators.” Acta Pharmacologica Sinica 26 (3) (March): 339–44. doi:10.1111/j.1745-7254.2005.00040.x. Xu, Chuan, Ji-An Chen, Zhiqun Qiu, Qing Zhao, Jiaohua Luo, Lan Yang, Hui Zeng, et al. 2010. “Ovotoxicity and PPAR-Mediated Aromatase Downregulation in Female Sprague-Dawley Rats Following Combined Oral Exposure to Benzo[a]pyrene and Di-(2-Ethylhexyl) Phthalate.” Toxicology Letters 199 (3) (December 15): 323–32. doi:10.1016/j.toxlet.2010.09.015. Yessoufou, a, and W Wahli. 2010. “Multifaceted Roles of Peroxisome Proliferator-Activated Receptors (PPARs) at the Cellular and Whole Organism Levels.” Swiss Medical Weekly 140 (September) (January): w13071. doi:10.4414/smw.2010.13071. Yu, Songtao, and Janardan K Reddy. 2007. “Transcription Coactivators for Peroxisome Proliferator-Activated Receptors.” Biochimica et Biophysica Acta 1771 (8) (August): 936–51. doi:10.1016/j.bbalip.2007.01.008. AOPWiki 2016-11-29T18:41:23

2020-12-28T12:48:16

Increase, Phenotypic enzyme activity

Cellular

UBERON:0002107

UBERON liver

CL:0000182

CL hepatocyte

High Mixed

High

All life stages

High High AOPWiki 2016-11-29T18:41:30

2020-12-28T12:32:39

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, Clonal Expansion of Altered Hepatic Foci

Cellular

<ul> <li> More than 40 years ago, cancer biologists pounced on the Darwinian principles of mutation, selection, and clonal expansion to explain cancer evolution. The occurrence of altered clones of cells in the livers of animals was revealed by enzyme histochemistry with a resulting plethora of different types of clones including those positive for gamma-glutamyltranspeptidase (GGT), placental glutathione transferase and negative for APTase and glucose-6-phosphase (Glauert et al. 1986; Pitot, 1990; Scherer, 1987) Mathematical models of clonal formation were developed soon after suffered from non-identifiability of parameters (Moolgavkar & Lubeck 2003; Connolly & Andersen 1991; Cox & Huber 2007). More recently, an examination of a clonal expansion model of cancer suggested a widely accepted model of clonal expansion appeared biologically implausible when compared to a model based on the concept of dysregulated hyperplasia (Bogen 2014). Notwithstanding the vagaries of understanding and modeling early events in cancer pathogenesis, altered hepatic foci representing clones of presumably premalignant cells have been demonstrably observed as a precursor of rodent liver tumors. Oval cells are similar to fetal hepatoblasts and bipotential in that they can differentiate into either hepatocytes or cholantiocytes (Grompe 2013). primary oval cells from rats treated with PPARa activators differentiated into basophilic cells, similar to those in pre-neoplastic basophilic clones observed in chronic studies of PPARa activators (Kaplanski et al. 2000; Marsman & Popp, 1994).  Continued activation of PPARα is necessary for focal enlargement and the formation of tumors (Grasl-Kraupp et al. 19931a, b, c; Isenberg et al. 1997; Corton et al. 2014). </li> </ul>

Clonal expansion of altered hepatic foci is measure histologically as changes in the number of foci per volume of liver tissue or volume fraction of the liver (Marsman & Popp 1994; Isenberg et al. 1997; Kuwata et al. 2016)

The occurrence and growth of altered hepatic foci have been measured primarily rodents as part of initiation-promotion studies or two-year bioassays (Dragan et al. 1991; Hendrich et al. 1987; Pitot et al. 1989).

UBERON:0002107

UBERON liver

CL:0000182

CL hepatocyte

Conolly, R. B., & Andersen, M. E. (1991). Biologically based pharmacodynamic models: tools for toxicological research and risk assessment. Annu Rev Pharmacol Toxicol, 31, 503-523. https://doi.org/10.1146/annurev.pa.31.040191.002443 Corton, J. C., Cunningham, M. L., Hummer, T. B., Lau, C, Meek, B, Peters, JM, Popp, JA, Rhomberg, L, Seed, J., & Klaunig, J. E. (2014). Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPAR&OElig;±) as a case study. Crit Rev Toxicol, 44(1), 1-49. https://doi.org/10.3109/10408444.2013.835784 Cox, L. A., & Huber, W. A. (2007). Symmetry, identifiability, and prediction uncertainties in multistage clonal expansion (MSCE) models of carcinogenesis. Risk Anal, 27(6), 1441-1453. https://doi.org/10.1111/j.1539-6924.2007.00980.x Dragan, Y. P., Rizvi, T., Xu, Y. H., Hully, J. R., Bawa, N., Campbell, H. A. et al. (1991). An initiation-promotion assay in rat liver as a potential complement to the 2-year carcinogenesis bioassay. Fundam Appl Toxicol, 16(3), 525-547. Glauert, H. P., & Pitot, H. C. (1986). Influence of dietary fat on the promotion of diethylnitrosamine-induced hepatocarcinogenesis in female rats. … of the Society for Experimental Biology …. https://journals.sagepub.com/doi/abs/10.3181/00379727-181-42283. Grasl-Kraupp B, Huber W, Just W, et al. (1993a). Enhancement of peroxisomal enzymes, cytochrome P-452 and DNA synthesis in putative preneoplastic foci of rat liver treated with the peroxisome proliferator nafenopin. Carcinogenesis, 14, 1007–12. Grasl-Kraupp B, Huber W, Timmermann-Trosiener I, Schulte-Hermann R. (1993b). Peroxisomal enzyme induction uncoupled from enhanced DNA synthesis in putative preneoplastic liver foci of rats treated with a single dose of the peroxisome proliferator nafenopin. Carcinogenesis, 14, 2435–7 Grasl-Kraupp B, Waldhor T, Huber W, Schulte-Hermann R. (1993c). Glutathione S-transferase isoenzyme patterns in different subtypes of enzyme-altered rat liver foci treated with the peroxisome proliferator nafenopin or with phenobarbital. Carcinogenesis, 14, 2407–12 Grompe, M. (2009). Adult Liver Stem Cells.  In Essentials of Stem Cell Biology (pp. 285-298). Elsevier. https://www.sciencedirect.com/science/article/pii/B9780123747297000342 Hendrich, S., Campbell, H. A., & Pitot, H. C. (1987). Quantitative stereological evaluation of four histochemical markers of altered foci in multistage hepatocarcinogenesis in the rat. Carcinogenesis, 8(9), 1245-1250. Isenberg JS, Kolaja KL, Ayoubi SA, et al. (1997). Inhibition of WY 14 643-induced hepatic lesion growth in mice by rotenone. Carcinogenesis, 18, 1511–9 Kaplanski, C., Pauley, C. J., Griffiths, T. G., Kawabata, T. T., & Ledwith, B. J. (2000). Differentiation of rat oval cells after activation of peroxisome proliferator-activated receptor alpha43. Cancer Res, 60(3), 580-587. https://pubmed.ncbi.nlm.nih.gov/10676640 Kuwata, K., Inoue, K., Ichimura, R., Takahashi, M., Kodama, Y., & Yoshida, M. (2016). Constitutive active/androstane receptor, peroxisome proliferator-activated receptor α, and cytotoxicity are involved in oxadiazon-induced liver tumor development in mice. Food Chem Toxicol, 88, 75-86. Marsman, D. S., & Popp, J. A. (1994). Biological potential of basophilic hepatocellular foci and hepatic adenoma induced by the peroxisome proliferator, Wy-14,643. Carcinogenesis, 15(1), 111-117. https://doi.org/10.1093/carcin/15.1.111 Moolgavkar, S. H., & Luebeck, E. G. (2003). Multistage carcinogenesis and the incidence of human cancer. Genes Chromosomes Cancer, 38(4), 302-306. https://doi.org/10.1002/gcc.10264 Pitot, H. C., Campbell, H. A., Maronpot, R., Bawa, N., Rizvi, T. A., Xu, Y. H. et al. (1989). Critical parameters in the quantitation of the stages of initiation, promotion, and progression in one model of hepatocarcinogenesis in the rat. Toxicol Pathol, 17(4 Pt 1), 594-611; discussion 611. Pitot, H. C., Dragan, Y., Xu, Y. H., & Pyron…, M. (1990). Role of altered hepatic foci in the stages of carcinogenesis. Progress in clinical …. https://europepmc.org/article/med/2196586. Scherer, E. (1987). Relationship among histochemically distinguishable early lesions in multistep-multistage hepatocarcinogenesis. Mouse Liver Tumors. https://link.springer.com/chapter/10.1007/978-3-642-71617-1_7 AOPWiki 2016-11-29T18:41:30

2021-01-06T16:15:01

Increase, hepatocellular adenomas and carcinomas

Tissue

UBERON:0002107

UBERON liver

AOPWiki 2016-11-29T18:41:26

2020-12-26T10:09:54

<upstream-id>b1772976-0ca8-4ddc-82f6-d438150d1e26</upstream-id> <downstream-id>f16cf0b7-1e6f-4c59-9585-0b4306df76b7</downstream-id> Activation of the PPARα receptor leads to a coordinated gene expression program that produces lipid metabolizing enzymes and proteins associated with control of the cell cycle.

Neither peroxisome proliferation nor increased enzyme activity is observed in PPARα-null mice. (Belury et al. 1998; Peters et al. 1997)

Similar to other nuclear receptors such as the aryl hydrocarbon receptor (AHR) and constitutive androstane receptor (CAR), PPARα induces a coordinated gene expression program (Corton et al. 2014; Elcombe et al. 2014; Budinsky et al. 2014).

Alteration of genes/proteins involved in cell growth by PPARα activators was not observed in PPARα-null mice (Anderson et al. 2004; Belury et al. 1998; Corton et al. 2004, 2014; Cunningham et al. 2010; Fitzgerald et al. 1981; Hartig et al. 1982; NTP, 2007)

Vanishingly few, if any.

Modulating factors include NF-kB activation, cytokines, oxidative stress, and the role of microRNAs.

The activities for acyl coenzyme A oxidase for the three stressors considered on the main page of this AOP (AOP 37) were plotted and fit to a hockey stick dose-response model (Lutz & Lutz, 2009) and shown below. <a href="d06tx821l_dKER1.png"><img alt="" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMzEvZDA2dHg4MjFsX2RLRVIxLnBuZyJdLFsicCIsInRodW1iIiwiMTAweDEwMCJdXQ/dKER1.png?sha=785f6bb300bc39c6" src="d06tx821l_dKER1.png" /></a><img alt="" src="https://aopwiki.org/system/dragonfly/production/2020/12/31/d06tx821l_dKER1.png" />                               The central value for the threshold MIE level was 14.15 MIE units with confidence limits of 3.04 to 19.07.

The enzyme response does not occur until at least 14 MIE units and then rises with a slope of 0.72 per MIE unit.

The time scale of both the MIE and the enzyme response is 1 week.

Increased expression of ACO and associated oxidative stress activated NF-kB

High Mixed

High

All life stages

High High

The domain of applicability is similar to that for the overall MIE.

Anderson, S. P., Dunn, C., Laughter, A., Yoon, L., Swanson, C., Stulnig, T. M., Steffensen, K. R., Chandraratna, R. A., Gustafsson, J. A., & Corton, J. C. (2004). Overlapping transcriptional programs regulated by the nuclear receptors peroxisome proliferator-activated receptor alpha, retinoid X receptor, and liver X receptor in mouse liver. Mol Pharmacol, 66(6), 1440-1452. https://doi.org/10.1124/mol.104.005496 Belury, M. A., Moya-Camarena, S. Y., Sun, H., Snyder, E., Davis, J. W., Cunningham, M. L., & Vanden Heuvel, J. P. (1998). Comparison of dose-response relationships for induction of lipid metabolizing and growth regulatory genes by peroxisome proliferators in rat liver. Toxicol Appl Pharmacol, 151(2), 254-261. https://doi.org/10.1006/taap.1998.8443 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., & 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(1), 83-119. https://doi.org/10.3109/10408444.2013.835787 Corton, J. C., Apte, U., Anderson, S. P., Limaye, P., Yoon, L., Latendresse, J., Dunn, C., Everitt, J. I., Voss, K. A., Swanson, C., Kimbrough, C., Wong, J. S., Gill, S. S., Chandraratna, R. A., Kwak, M. K., Kensler, T. W., Stulnig, T. M., Steffensen, K. R., Gustafsson, J. A., . . . Mehendale, H. M. (2004). Mimetics of caloric restriction include agonists of lipid-activated nuclear receptors. J Biol Chem, 279(44), 46204-46212. https://doi.org/10.1074/jbc.M406739200 Corton, J. C., Cunningham, M. L., Hummer, T. B., Lau, C, Meek, B, Peters, JM, Popp, JA, Rhomberg, L, Seed, J., & Klaunig, J. E. (2014). Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPAR&OElig;±) as a case study. Crit Rev Toxicol, 44(1), 1-49. https://doi.org/10.3109/10408444.2013.835784 Elcombe, C. R., Elcombe, B. M., Foster, J. R., Chang, S. C., Ehresman, D. J., & Butenhoff, J. L. (2012). Hepatocellular hypertrophy and cell proliferation in Sprague-Dawley rats from dietary exposure to potassium perfluorooctanesulfonate results from increased expression of xenosensor nuclear receptors PPARα and CAR/PXR. Toxicology, 293(1-3), 16-29. https://doi.org/10.1016/j.tox.2011.12.014 Cunningham, M. L., Collins, B. J., Hejtmancik, M. R., Herbert, R. A., Travlos, G. S., Vallant, M. K., & Stout, M. D. (2010). Effects of the PPARα Agonist and Widely Used Antihyperlipidemic Drug Gemfibrozil on Hepatic Toxicity and Lipid Metabolism. PPAR Res, 2010. https://doi.org/10.1155/2010/681963 Fitzgerald, J. E., Sanyer, J. L., Schardein, J. L., Lake, R. S., McGuire, E. J., & de la Iglesia, F. A. (1981). Carcinogen bioassay and mutagenicity studies with the hypolipidemic agent gemfibrozil. J Natl Cancer Inst, 67(5), 1105-1116. https://pubmed.ncbi.nlm.nih.gov/7029098 Hartig, F., Stegmeier, K., Hebold, G., Özel, M., & Fahimi, H. D. (1982). Study of liver enzymes: peroxisome proliferation and tumor rates in rats at the end of carcinogenicity studies with bezafibrate and clofibrate. Annals of the New York Academy of Sciences, 386(1), 464-467. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1982.tb21453.x Lutz, W. K., & Lutz, R. W. (2009). Statistical model to estimate a threshold dose and its confidence limits for the analysis of sublinear dose-response relationships, exemplified for mutagenicity data. Mutat Res, 678(2), 118-122. https://doi.org/10.1016/j.mrgentox.2009.05.010 NTP (2007). Toxicity studies of WY-14,643 (CAS No. 50892-23-4) administered in feed to male Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters. Toxic Rep Ser, 62), 1-136. https://pubmed.ncbi.nlm.nih.gov/24743700 Peters, J. M., Cattley, R. C., & Gonzalez, F. J. (1997). Role of PPAR alpha in the mechanism of action of the nongenotoxic carcinogen and peroxisome proliferator Wy-14,643. Carcinogenesis, 18(11), 2029-2033. https://doi.org/10.1093/carcin/18.11.2029 AOPWiki 2016-11-29T18:41:37

2020-12-31T11:42:29

<upstream-id>f16cf0b7-1e6f-4c59-9585-0b4306df76b7</upstream-id> <downstream-id>e06b8258-7b0f-426d-836a-f1c4a91cb42e</downstream-id> Growth factors and other cytokines secreted from Kupffer cells following PPARα activation include tumor necrosis factor α (TNFα), interleukin-1α (IL-1α), and interleukin-1β (IL-1β). Although TNFα levels increase following PPARα activation, proliferation was observed in wild type, TNFα-null, and TNFα receptor-null mice, suggesting that multiple cytokines stimulate cell proliferation (Maeda et al. 2005). PPARα activation reduces the level of miRNA let-7c in liver. In turn, let-7c normally down-regulates c-Myc expression and thus, PPARα activation increases c-Myc expression that increase cell proliferation (Shah et al. 2007). PPARα activation increases levels of other cell cycle proteins including Cdk-1, Cdk-4, Cyclin D1 and Pcna (Currie et al. 2005; Woods et al. 2007).

Whilst knowledge of the molecular pathways underlying cell proliferation remains incomplete, the consistent observation of increases in both cell proliferation, liver weight and cytokine levels are consistent with biological knowledge.

Alteration of genes/proteins involved in cell growth by PPARα activators was not observed in PPARα-null mice

The precise mechanism for activation of growth control genes is not known.

Cell proliferation measured by BrdU labeling index was plotted against the enzyme response of the three PPARα activators. The enzyme measured was acyl CoA oxidase, a lipid-metabolizing enzyme and was considered a surrogate for the cytokines and other growth-related cytokines stimulated by PPARα activation. These data were well fit by a Michaelis-Menten equation, suggesting that receptor mechanisms are likely involved in the growth response. <a href="https://aopwiki.org/system/dragonfly/production/2020/12/31/4hm69kb8dh_dKER2.png" target="_self"><img alt="" id="dKER2" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMzEvNGhtNjlrYjhkaF9kS0VSMi5wbmciXSxbInAiLCJ0aHVtYiIsIjEwMHgxMDAiXV0/dKER2.png?sha=80756e86e6a62ca7" src="https://aopwiki.org/system/dragonfly/production/2020/12/31/4hm69kb8dh_dKER2.png" style="border-style:solid; border-width:1px; float:left; height:4717px; width:6017px" /></a>               The  The maximal proliferation level was 30.88% and the half-maximal enzyme response was 3.37.

Levels of cytokines and other cellular proteins involved in cell cycle control are increased concomitant with increased enzyme activity and stimulate cell proliferation.

Both responses considered above occured 1 week after commencing PPARα activation.

The domain of applicability is the same as for AOP 37.

AOPWiki 2016-11-29T18:41:37

2020-12-31T13:00:17

<upstream-id>e06b8258-7b0f-426d-836a-f1c4a91cb42e</upstream-id> <downstream-id>e05b0d8e-e31b-44e9-b558-d1fbe1c75e12</downstream-id>

AOPWiki 2016-11-29T18:41:37

2016-12-03T16:38:06

<upstream-id>e05b0d8e-e31b-44e9-b558-d1fbe1c75e12</upstream-id> <downstream-id>8780672d-a119-4a3c-a39e-b81bc9a1232e</downstream-id>

AOPWiki 2016-11-29T18:41:37

2016-12-03T16:38:05

<upstream-id>b1772976-0ca8-4ddc-82f6-d438150d1e26</upstream-id> <downstream-id>e06b8258-7b0f-426d-836a-f1c4a91cb42e</downstream-id>

AOPWiki 2020-12-31T09:43:36

2020-12-31T09:43:36

<upstream-id>b1772976-0ca8-4ddc-82f6-d438150d1e26</upstream-id> <downstream-id>8780672d-a119-4a3c-a39e-b81bc9a1232e</downstream-id>

AOPWiki 2020-12-31T09:46:17

2020-12-31T09:46:17

<upstream-id>e06b8258-7b0f-426d-836a-f1c4a91cb42e</upstream-id> <downstream-id>8780672d-a119-4a3c-a39e-b81bc9a1232e</downstream-id>

AOPWiki 2020-12-31T09:46:47

2020-12-31T09:46:47

PPARα activation leading to hepatocellular adenomas and carcinomas in rodents

PPARalpha-dependent liver tumors in rodents

Chris Corton

J. Christopher Corton, 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 (corton.chris@epa.gov)

BY-SA

Under Development

1.17

1.0

Several therapeutic agents and industrial chemicals induce liver tumors in rats and mice through the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The molecular and cellular events by which PPARα activators induce rodent hepatocarcinogenesis have been extensively studied and elucidated. The weight of evidence relevant to the hypothesized AOP for PPARα activator-induced rodent hepatocarcinogenesis is summarized here. Chemical-specific and mechanistic data support concordance of temporal and dose–response relationships for the key events associated with many PPARα activators including a phthalate ester plasticizer di(2-ethylhexyl)phthalate (DEHP) and the drug gemfibrozil. The key events (KE) identified include the MIE – PPARα activation measured as a characteristic change in gene expression,  KE2 – increased enzyme activation, characteristically those involved in lipid metabolism and cell cycle control, KE3 – increased cell proliferation, KE4 – selective clonal expansion of preneoplastic foci, and the AO –  – increases in hepatocellular adenomas and carcinomas.  Other biological factors modulate the effects of PPARα activators.These modulating events include increases in oxidative stress, activation of NF-kB, and inhibition of gap junction intercellular communication. The occurrence of hepatocellular adenomas and carcinomas is specific to mice and rats. The occurrence of the various KEs in hamsters, guinea pigs, cynomolgous monkeys are generally absent. During the 1970s, an increased incidence of hepatocellular adenomas and carcinomas was observed in rodents treated with a variety of seemingly disparate chemicals. The common effect was an increase in the number and size of peroxisomes and these substances were labeled ‘‘peroxisome proliferators’’ (Rao & Reddy, 1996). Peroxisomes are subcellular organelles involved in long chain fatty acid catabolism through the β-oxidation cycle (de Duve, 1996). Peroxisomes increase in number and/or size following exposure to substances that perturb fatty acid homeostasis. These substances include marketed pharmaceutical agents and drug candidates, phthalate ester plasticizers or their metabolites, herbicides , solvents  and perfluorinated chemicals (Klaunig et al., 2003). Hepatocellular hypertrophy and hyperplasia, changes in apoptosis rates, Kupffer cell activation, and oxidative stress were also observed following chronic exposure of rats and mice to peroxisome proliferators (Corton, 2010). The peroxisome proliferator-activated receptor α (PPARα) was identified after cloning from mouse DNA (Issemann & Green, 1990). PPARα along with the PPARb/d and PPARg subtypes are ligand-activated transcription factors with both DNA-binding and ligand-binding domain with variation in tissue distribution, expression during development, ligand specificity, and biological function. PPARα is expressed in metabolically active tissues, including the liver, kidney, brown fat and heart, which exhibit pleiotropic responses to peroxisome proliferators. The biological functions and role in chemical effects of PPARα has been facilitated by the PPARα-null mouse  the experimental use of which revealed that a functional PPARα was required for the obseved phenotypic effects and led to the identification of the genes involved in lipid catabolism, lipid transport, peroxisome proliferation and hepatocellular adenomas and carcinomas (Corton, 2010; Lee et al., 1995).   Like other nuclear receptors, PPARα forms a heterodimer before translocating to the nucleus.  with another nuclear receptor family member, retinoid X receptor (RXR), the receptor for 9-cis-retinoic acid. The PPARα-RXR heterodimer binds to peroxisome proliferator response elements (PPREs) usually found in the promoter or enhancer regions. The PPRE consensus sequence consists of the sequence 5’-AACT AGGTCA A AGGTCA-3’ with PPARα occupying the 5’ position. After agonist binding to PPARα, co-repressors dissociate from the complex leading to de-acetylation, chromatin remodeling  to enable transcription (Escher & Wahli, 2000; Göttlicher et al., 1992; Moreno et al. 2010).

Fibrates are ligands of PPARα (Staels et al. 1998). Phthalates MHEP (CAS 4376-20-9) directly binds in vitro to PPARα (Lapinskas et al. 2005) and activates this receptor in transactivation assays PPARα (Lapinskas et al. 2005), (Maloney and Waxman 1999), (Hurst and Waxman 2003), (Bility et al. 2004), (Lampen, Zimnik, and Nau 2003), (Venkata et al. 2006) ]. DEHP (CAS 117-81-7) has not been found to bind and activate PPARα (Lapinskas et al. 2005), (Maloney and Waxman 1999). However, the recent studies shown activation of PPARα (ToxCastTM Data). Notably, PPARα are responsive to DEHP in vitro as they are translocated to the nucleus (in primary Sertoli cells) (Dufour et al. 2003), (Bhattacharya et al. 2005). Expression of PPARα [mRNA and protein] has been reported to be also modulated by phthtalates: (to be up-regulated in vivo upon DEHP treatment (Xu et al. 2010) and down-regulated by Diisobutyl phthalate (DiBP) (Boberg et al. 2008)). Perfluorooctanoic Acid (PFOA) is known to activate PPARα (Vanden Heuvel et al. 2006). Organotin Tributyltin (TBT) activates all three heterodimers of PPAR with RXR, primarily through its interaction with RXR (le Maire et al. 2009)

adjacent

High

High adjacent

Moderate

High adjacent

Moderate

High adjacent

Moderate

High non-adjacent

High

High non-adjacent

High

High non-adjacent

High

High Male High Female

High

Adult

High High

<h1>Molecular Initiating Event - PPARα activation</h1> The MIE was characterized using two types of measurements: the earliest is the genomic changes representing the activation of PPARα; (Rooney et al., 2018; Corton et al., 2020; Hill et al., 2020; Lewis et al., 2020) Previously, increases in enzyme activity were used as a measure of PPARα activation . (Liu et al., 1996; David et al., 1999; Isenberg et al., 2000; Klaunig et al., 2003; Kondo et al., 2019) Microarray profiling was used to show that alteration of gene expression following PPARα activation was almost completely abolished in PPARα-null mice s (Anderson et al., 2001, 2004a,b; Corton et al., 2004; Rosen et al.,2008a,b; Woods et al., 2007c; Ren et al., 2009, 2010; Rosen et al., 2008, 2010; Rosen et al., 2017). The genes that were dependent on PPARα were those involved in lipid homeostasis and the cell cycle. The development of large gene expression databases TG-GATEs and DrugMatrix enabled that statistical analysis of whole genome expression profiles that form the basis of the genomic MIEs (Svoboda et al., 2019; Igarashi et al., 2015) From these data, A gene expression signature of 131 PPARα-dependent genes was built using microarray profiles from the livers of wild-type and PPARα-null mice. A quantitative measure of this expression signature is a measure of similarity/correlation between the PPARα signature and positive and negative test sets is provided by the Running Fisher test (Kupershmidt et al., 2010; Rooney et al., 2018; Corton et al., 2020). <h1>Key Event #2 - Increased Phenotypic Enzyme Activity </h1> Increased activity in acyl coenzyme A oxidase, peroxisomal beta-oxidase, carnitine acetyl transferase, catalase and others have been observed uniformly in rats and mice following PPARα activation (Corton et al. 2014; Cunningham et al. 2010; Klaunig et al. 2003; NTP, 2007).  <h1>Key Event #3 - Increased Cell Proliferation</h1> Increased cell proliferation is observed following PPARα and is measured by increases in BrdU labeling index or liver weight.  great deal of work has been conducted to identify the mechanistic events that lead to alterations in cell growth by PPARα activators. Early studies focused mainly on growth factors secreted from Kupffer cells are activated by PPARα activation and may secrete tumor necrosis factor α (TNFα), interleukin-1α (IL-1α), interleukin-1β (IL-1β) and likely other cytokines (Bojes et al., 1997; Rolfe et al.,1997 Holden et al., 2000). Cell proliferation following PPARα did not occur in vivo with pretreatment with antibodies to either TNFα or TNFα receptor 1 (TNFR1) nor in PPARα null mice (West et al., 1999; Bojes et al., 1997; Rolfe et al.,1997 Anderson et al., 2001; Lawrence et al., 2001b). PPARα reduces expression of the miRNA let-7c in the liver that, in turn, reduces the expression of the c-Myc gene. The resulting increased c-Myc expression is likely a causal factor in increased cell proliferation following PPARα activation (Shah et al., 2007; Qu et al., 2014) <h1>Key Event #4 - Clonal Expansion of Altered Hepatic Foci</h1> ATPase-negative foci and basophilic foci were observed following occurrence of the MIE in rats (Marsman & Popp, 1994). PPARα activators promote the growth of chemically- and spontaneously-induced lesions through enhanced cell replication (Cattley & Popp, 1989; Cattley et al., 1991; Isenberg et al., 1997; Marsman et al., 1988). ATPase-negative foci and GGT- weakly basophilic foci were observed following occurrence of the MIE in rats but GGT+ and GST-P+ foci were not observed (Grasl-Kraupp et al. 1993c; Marsman & Popp, 1994). PPARα activators increase cell proliferation in AHF to about half-again that of normal cells measured by labeling index (Grasl-Kraupp et al. 1993b). Continued exposure to PPARα activators causes selective increases in DNA replication within these liver foci in comparison to normal hepatocytes (Isenberg et al., 1997). Although, apoptosis was found to be increased in both normal cells and AHF by PPARα activation, the increase in foci cell proliferation was sufficient to outweigh the increase in focal apoptosis (Isenberg et al., 1997). <h1 style="text-align:start">Adverse Outcome - Hepatocellular tumors in mice and rats</h1> Increases in hepatocellular adenomas and carcinomas has been observed in both rats and mice in a dose-dependent fashion after treatment with PPARα activators. Corton et al. (2014) provide a summary of the dose-response data for di-2-ethylhexyl phthalate (DEHP). Similar increases have been observed after treatement with other PPARα activators. The section on Quantitative Understanding below presents some of these data.      <h1 style="text-align:start">Sex Differences in PPARα activators</h1> For some PPARα activators, differences in the carcinogenic effects can be observed in both rats and mice (Astill et al., 1996; Butala et al., 1997; Kluwe et al., 1985; Gold and Zeiger, 1997; Hollander and Wiegand, 1978; Malley et al., 1995; Shirasu 1987a, 1987b; U.S. EPA, 2000a, 2000b) These differences may reflect variation in the formation of a metabolite that activates PPARα. <h1 style="text-align:start">PPARα Activation in the Fetus, Neonate and Adult</h1> PPARα mRNA and protein has been detected in the fetuses of both rats and mice prior to birth (Balasubramaniyan et al. 2005; Beck et al. 1992). Assembly of peroxisomal proteins into peroxisomes and peroxisomal enzyme activity are detectable in late gestation Stefanini et al. 1989; Wilson et al., 1991). Catalase and palmitoyl CoA oxidase activities were first detected in the GD15 Wistar rat fetus (Cibelli et al., 1988). Stefanini et al. (1995) found no statistically significant differences in numerical density or volume density of peroxisomes in livers of 14-, 21-, or 35-day F344 rat neonates and no differences between neonate groups and adult females. No differences were found between 14- or 21-day neonates or between these groups and adult F344 rats in peroxisomal β-oxidation; the numerical density and volume density of liver peroxisomes were also comparable among groups (Stefanini et al., 1999). No differences were reported for the specific volume density among 7-, 8.5-, 10-, 13-, or 17-day Wistar-derived rat neonates or compared with adults (Wiebel et al., 1969; Staubli et al., 1977). Direct exposure of the neonate to PPARα agonists results in an increase in peroxisomal enzyme activities and an increase in the numerical density or volume of peroxisomes; the increases in these parameters are comparable to those observed in young adult or adult rats (Staubli et al., 1977; Dostal et al., 1987; Yamoto et al., 1996; Yu et al., 2001). <h1 style="text-align:start">Species Differences in PPARα Activation</h1> Whilst mice and rats are responsive to PPARα activator-induced liver cancer and associated responses, hamsters, guinea pigs, and primates, including humans, are less sensitive (Ashby et al., 1994; Bentley et al., 1993; Cattley et al., 1998; Doull et al., 1999). In side-by-side assays human PPARα were less sensitive than rodent PPARα to chemical activation. Hypolipidemic agents and environmental chemicals activated rat or mouse PPARα with greather potency and greater efficacy than human PPARα (Takacs & Abbott, 2007; Maloney & Waxman, 1999; Lapinskas et al., 2005)

Transgenic or knockout animals can often provide a powerful counterfactual demonstration supporting the identification of a KE (Phillips and Goodman 2006; Simon et al. 2014) Such work demonstrates the necessity of a given KE studies show that preventing a given KE also prevents the occurrence of downstream KEs. Hence, the PPARα-null mouse has provided critical evidence identifying the MIE as well as subsequent downstream KEs. Global gene expression profiling revealed that alteration of gene expression following PPARα-activation was almost completely abolished in PPARα-null mice at multiple time points (Anderson et al., 2004a,b; Corton et al., 2004; Li et al. 2018; Woods et al., 2007; Rosen et al., 2008. 2010, 2017; Sanderson et al. 2008; Ren et al., 2010; Wang et al. 2020). Following PPARα activation, wild-type mice exhibited increased hepatocyte proliferation compared to untreated controls and no increase was observed in PPARα-null mice (Peters et al., 1997, 1998; Valles et al., 2003; Laughter et al., 2004; Wolf et al., 2008). Apoptosis was suppressed in hepatocytes from wild-type mice but not in those from the knockouts (Hasmall et al., 2000). Finally, chronic treatment with PPARα activators resulted in 100% incidence of hepatocellular tumor in wild-type mice but the knockouts remained unaffected (Peters et al., 1997; Hays et al., 2005). KE#2, increased enzyme activity, KE#3, increased cell proliferation and KE#4, clonal expansion of preneoplastic lesions have been recognized as KEs in many carcinogenic modes of action and are not specific to PPARα activation. Finally, in an initiation-promotion study, 25% of wild-type mice receiving only diethylnitrosamine (DEN) developed tumors (25%) whereas 63% of wild-type mice receiving both DEN and a PPARα activator developed tumors. (Glauert et al., 2006).

<h1 style="text-align:start">Evidence supporting PPARα activation as the MIE</h1> <ul> <li>All PPARα activators exhibit a characteristic genomic signature that was used to characterize the MIE (Corton et al. 2020; Hill et al. 2020; Rooney et al. (2018).</li> <li>The potency of PPARα activation is roughly proportional to the potency of the chemical as an inducer of the liver tumor response (Klaunig et al., 2003).</li> <li>Characteristic gene expression changes do not occur in PPARα-null mice (Anderson et al., 2004a,b; Corton et al., 2004; Rosen et al.,2008, 2017; Ren et al. 2009, 2010;  Woods et al., 2007c). </li> </ul> <h2>Evidence supporing KE2 - Increased enzyme activity</h2> <ul> <li>Increased activity of lipid metabolizing enzymes following PPARα has been repeated demonstrated (Amacher et al 1997; Klaunig et al. 2003; Belury et al. 1998; Corton et al. 2000).</li> </ul> Weaknesses in the evidence <ul> <li>Hepatocytes from PPARα-null mice can respond PPARα activators if adjacent to wild-type hepatocytes (Weglarz & Sandgren, 2004).</li> </ul> <h2>Evidence supporting KE3 - Increased Cell Proliferation</h2>   <ul> <li>PPARα activators increase cell proliferation.</li> <li>Increases in cell proliferation after exposure to a number of PPARα activators were abolished in PPARα-null mice.</li> </ul> <h2>Evidence supporting KE4 - Clonal Expansion of altered foci</h2> <ul> <li>Clonal expansion is consistently induced in mice and rats by diverse PPARα activators (Marsman & Popp 1994).</li> <li>Clonal expansion and the appearance of foci and tumors by PPARα activators were not observed in PPARα-null mice after exposure to PPARα activators (Hays et al. 2005; Peters et al. 1997).</li> </ul> <h2>Evidence supporting the AO - Hepatocellular Adenomas and Carcinomas</h2> <ul> <li>Chronic treatment with PPARα activators produced hepatocellular neoplasia in 100% of wild-type mice and not in PPARα-null mice (Hays et al., 2005; Peters et al., 1997).</li> </ul> <h2>Strength and Specificity of the Evidence</h2> The activation of PPARα is specific this AOP, (AOP 37) whereas the downstream key events are common to the neoplastic process in the rodent liver, e.g AOP 107 and AOP 41. Data supporting each key event were determined to be strong in that several studies support that key event as part of the AOP using multiple PPARα activators from multiple laboratories with no or limited evidence of contradiction.

To understand the dose-response of the PPARα genomic MIE over time, the level of MIE activation of seven most active substances from the TG-GATEs database were fit to a gain-loss model used a dose range normalized over the range of zero to one at each of the time-points, i.e., 3, 6 and 9 hours and 1, 3, 7, 14 and 28 days. The gain-loss model is shown below as Eq. 1 (Watt and Judson, 2018).  <img alt="Gain-loss function used to model the Genomic MIE" src="https://aopwiki.org/system/dragonfly/production/2020/12/20/1q2guk2lde_gainloss.png" style="height:76px; width:599px" /> <div style="background:#eeeeee; border:1px solid #cccccc; padding:5px 10px">Gain-loss function. mu[i] = response at the ith dose; x[i] = the ith dose; tp = maximal response as -log(p-value); gw = Hill parameter for gain; ga = dose at the half-maximal gain; lw = Hill parameter for loss; la = dose at the half maximal loss. The model was applied without constraints.</div>   The gain-loss model was chosen because the response variable -log(p-value) from the Running Fisher test did not increase monotonically with dose. This model provided a flexible means of fitting all dose responses for the PPARα agonists in the TG-GATES database at all times. The fits were compared to the data and both visual comparisons and calculated AICs revealed very good fits. The fitted curves were plotted against both dose and time in both 2D and 3D surface plots. <img alt="2D and 3D surface plots of the Genomic MIE for 3 PPARα activators" src="https://aopwiki.org/system/dragonfly/production/2020/12/20/1gpjgoin4p_surf.png" style="border-style:solid; border-width:1px; float:left; height:2117px; width:2050px" /> As noted, for all substances, MIE activation does not rise monotonically over dose or time. These fluctuations are likely due to variations in cofactor availability or access to the site of transcription (Gaillard et al., 2006; Koppen et al., 2009; Kupershmidt et al., 2010; Ong et al., 2010; Chow et al., 2011; De Vos et al., 2011; Simon et al., 2015). A more extensive analysis was conducted for the three PPARalpha agonists shown above to understand the KERs between the genomic MIE and downstream KEs. For all these analyses, the MIE response at 7 days was chosen as the most representative due to the generally steeper response. The 7 day response was also steepest for the PPARalpha activators fenofibrate, benzbromarone, benzodiarone and simvastatin (not shown). <h1>Relationship between the Genomic MIE and Tumor Frequency</h1> To assess this relationship, the dose-response of all three PPARalpha activation at all times measured in the TG-GATES database were plotted along with the corresponding tumor frequency. <a href="https://aopwiki.org/system/dragonfly/production/2020/12/27/913k45q0n1_3plot2.png" target="_self"><img alt="" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMjcvOTEzazQ1cTBuMV8zcGxvdDIucG5nIl0sWyJwIiwidGh1bWIiLCIxMDB4MTAwIl1d/3plot2.png?sha=03430fe7782f694e" src="https://aopwiki.org/system/dragonfly/production/2020/12/27/913k45q0n1_3plot2.png" style="border-style:solid; border-width:1px; height:2167px; width:8417px" /></a> <div style="background:#eeeeee; border:1px solid #cccccc; padding:5px 10px">Figure. Comparison of the Genomic MIE at all time points from TG-GATES compared to tumor frequency. The 7-day Genomic MIE used in the analyses below is shown with a thick violet line. The tumor frequencies are shown with dashed lines. For clofibrate, the tumor plots show hepatocellular tumors in males and female. For gemfibrozil, the tumor plot shows hepatocellular carcinomas. For WY-14,643, the tumor plot shows the tumor frequency from combined studies in the carcdb at <a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__carcdb.lhasalimited.org_carcdb-2Dfrontend_&d=DwMGaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=nyReptakh2iRXI_pak71911gPtnb2CTR3JIugwBVVyc&m=b9TkZ3hVEOlIsCepVJfhEOLt0nYL-w8RsKDEINweCW8&s=9zPzvmerDWah5uxXh6KrMpnQ8zPh4kyMFylDDan2sbU&e=" title="https://urldefense.proofpoint.com/v2/url?u=https-3A__carcdb.lhasalimited.org_carcdb-2Dfrontend_&d=DwMGaQ&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=nyReptakh2iRXI_pak71911gPtnb2CTR3JIugwBVVyc&m=b9TkZ3hVEOlIsCepVJfhEOLt0nYL-w8RsKDEINweCW8&s=9zPzvmerDWah5uxXh6KrMpnQ8zPh4kyMFylDDan2sbU&e=">https://carcdb.lhasalimited.org/carcdb-frontend/</a></div>    The apparent potency of Gemfibrozil (middle plot) increased with time. This trend was weaker for Clofibrate. For gemfibrozil, the potency was higher than the other two PPARalpha activators at all time points. For all chemicals, the  efficacy of the MIE response at the 7-day time point is generally proportional to the tumor frequency at the highest dose and is apparent in the table below. The value for efficacy was tp in the gain-loss equation <table border="1" cellpadding="1" cellspacing="1" style="width:20px"> <caption>Comparison of Efficacy Values for three PPARalpha activators at a range of time points</caption> <thead> <tr> <th scope="row">Time point</th> <th scope="col">Clofibrate</th> <th scope="col">Gemfibrozil</th> <th scope="col">WY-14,643</th> </tr> </thead> <tbody> <tr> <th scope="row">3h</th> <td>6.36</td> <td>3.73</td> <td>37.7</td> </tr> <tr> <th scope="row">6h</th> <td>11.4</td> <td>4.49</td> <td>42.8</td> </tr> <tr> <th scope="row">9h</th> <td>18.9</td> <td>24.6</td> <td>48.6</td> </tr> <tr> <th scope="row">24h</th> <td>20.8</td> <td>29.7</td> <td>51.4</td> </tr> <tr> <th scope="row">3d</th> <td>20.7</td> <td>19.4</td> <td>50.2</td> </tr> <tr> <th scope="row">7d</th> <td>23.6</td> <td>20.3</td> <td>62.0</td> </tr> <tr> <th scope="row">14d</th> <td>23.2</td> <td>35.0</td> <td>54.7</td> </tr> <tr> <th scope="row">28d</th> <td>40.4</td> <td>18.4</td> <td>53.5</td> </tr> <tr> <th scope="row">Max. Tumor Freq.</th> <td>0.26</td> <td>0.36</td> <td>1.0</td> </tr> </tbody> </table> <h2>KERs for PPARalpha Activation by Clofibrate</h2> The figure below displays the analysis. <a href="https://aopwiki.org/system/dragonfly/production/2020/12/26/9pigyltj63_Clo26.png" target="_self"><img alt="" id="clo5" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMjYvOXBpZ3lsdGo2M19DbG8yNi5wbmciXSxbInAiLCJ0aHVtYiIsIjEwMHgxMDAiXV0/Clo26.png?sha=a57c963b4b135fef" src="https://aopwiki.org/system/dragonfly/production/2020/12/26/9pigyltj63_Clo26.png" style="border-style:solid; border-width:1px; height:8700px; width:7217px" /></a> <div style="background:#eeeeee; border:1px solid #cccccc; padding:5px 10px">KER Figure for Clofibrate. A. Detailed surface plot of the genomic MIE in dose and time. B. Dose-response plots of the genomic MIE (solid line and open circles) and the tumor response in males and female rats from Hartig et al. (1982) (dotted line and gender symbols). C. Equation and parameters for the genomic MIE response at 7 d. D. KERs between the MIE and measures of subsequent KEs. Top: KE#1: Peroxisome volume % of the liver vs. MIE; Upper and lower middle: KE#2: liver weight and labeling index v. MIE. Both are measures of cell proliferation. Bottom: tumor respose in males and female rats v. the MIE response. The dotted lines in this plot and in B are the second order multistage model fits to the tumor response data.</div>   The KER between the MIE and the AO is revealed by plots B and the bottom panel in D: tumors don't occur until the MIE is sustained at an MIE level of between 10 and 15. Fatty acid CoA oxidase is a lipid metabolizing enzyme and thus a measure of KE#1 and rises more steeply in female rats. The two responses measuring KE#2 also show male-female differences. Labeling index is a measure of cell proliferation and rises more steeply than in females with increasing MIE levels. Liver weight, another measure of KE#2 changes little in females and more in males, consistent with labeling index, which is a more direct measure of cell proliferation. The tumor response in both males and females trends upward somewhere between and MIE level of 10 to 15. Specifying a response level related to tumors would require a bioassay with more doses. <h1>KERs for PPARalpha Activation by Gemfibrozil</h1> The figure below displays the analysis. <a href="https://aopwiki.org/system/dragonfly/production/2020/12/26/7coo0krvwx_Gem26.png" target="_self"><img alt="" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMjYvN2NvbzBrcnZ3eF9HZW0yNi5wbmciXSxbInAiLCJ0aHVtYiIsIjEwMHgxMDAiXV0/Gem26.png?sha=10f111e89b9c9fbc" src="https://aopwiki.org/system/dragonfly/production/2020/12/26/7coo0krvwx_Gem26.png" style="border-style:solid; border-width:1px; float:left; height:9134px; width:7217px" /></a>                                                             <div style="background:#eeeeee; border:1px solid #cccccc; padding:5px 10px">KER Figure for Gemfibrozil. A. Detailed surface plot of the genomic MIE in dose and time. B. Dose-response plots of the genomic MIE (solid line and open circles) and the tumor response in males and female rats from pooled data  (dotted line and gender symbols). C. Equation and parameters for the genomic MIE response at 7 d. D. KERs between the MIE and measures of subsequent KEs. Top: KE#1: Peroxisome volume % of the liver vs. MIE; Upper and lower middle: KE#2: liver weight and labeling index v. MIE. Both are measures of cell proliferation. Bottom: tumor respose in males and female rats v. the MIE response. The dotted lines in this plot and in B are the second order multistage model fits to the tumor response data.</div>   The KER between the MIE and the AO is revealed by plots B and the bottom panel in D: the MIE reaches a plateau at an MIE level of 20 corresponding to a dose of 30 mg/kg/d; an increase in the frequency of neoplastic nodules to 4% occurs at this dose and MIE level; an increase in the frequency of carcinomas to 8% also occurs at this dose level. At a dose of 100 mg/kg/d corresponding to the plateau value of the MIE at 20, the frequency of neoplastic nodules rises to 36% and for carcinomas to 10%. The steepness in the rise of the MIE between doses of 0 and 30 mg/kg/d occurs along with any level of increase in downstream KEs. In the four graphs in D, Acyl CoA oxidase is a lipid metabolizing enzyme and thus a measure of KE#1 and continues to rise at the plateau level of the MIE. Labeling index as a measure of KE#2 continued to rise from 4% in controls to 26% at a dose of 510 mg/kg/d. At the highest dose of 1300 mg/kg/d, the MIE was at the plateau level of 20 and Labeling Index was 7%. Relative Liver weight, a less direct measure of KE#2, rose to between 55 and 60 mg liver / g BW and remained at the level at the three highest doses with the same MIE level of 20 (Cunningham et al. 2010) The tumor response was evident only in male rats. (Fitzgerald et al. 1981). Specifying a range of the MIE corresponding to an increase in tumors because of the apparently steep dose-response curve of the MIE [B], and the lack of any doses between 0 and 30 in either the TG-GATES database or the bioassay (Corton et al. 2020; Fitzgerald et al. 1981; Hill et al. 2020; Rooney et al. 2018). <h1>KERs for PPARalpha Activation by WY-14,643</h1> The figure below displays the analysis. <a href="https://aopwiki.org/system/dragonfly/production/2020/12/26/79im15bg3c_WY27.png" target="_self"><img alt="" longdesc="https://aopwiki.org/media/W1siZiIsIjIwMjAvMTIvMjYvNzlpbTE1YmczY19XWTI3LnBuZyJdLFsicCIsInRodW1iIiwiMTAweDEwMCJdXQ/WY27.png?sha=5d7d2d3afa59d82a" src="https://aopwiki.org/system/dragonfly/production/2020/12/26/79im15bg3c_WY27.png" style="border-style:solid; border-width:1px; height:9217px; width:7217px" /></a> <div style="background:#eeeeee; border:1px solid #cccccc; padding:5px 10px">KER Figure for WY-14,643. A. Detailed surface plot of the genomic MIE in dose and time. B. Dose-response plots of the genomic MIE (solid line and open circles) and the tumor response in males and female rats from pooled data  (dotted line and gender symbols). C. Equation and parameters for the genomic MIE response at 7 d. D. KERs between the MIE and measures of subsequent KEs. Top: KE#1: Peroxisome volume % of the liver vs. MIE; Upper and lower middle: KE#2: liver weight and labeling index v. MIE. Both are measures of cell proliferation. Bottom: tumor respose in males and female rats v. the MIE response. The dotted lines in this plot and in B are the second order multistage model fits to the tumor response data.</div>   The combined tumor response was obtained from the carcdb at <a href="https://carcdb.lhasalimited.org/carcdb-frontend/" style="color:blue; text-decoration:underline">https://carcdb.lhasalimited.org/carcdb-frontend/</a>. Because the studies used no more than three dose levels (and a single dose in some), the results from four of the studies were combined. The table below shows the dose response and primary sources. <table cellspacing="0" class="MsoTableGrid" style="border-collapse:collapse; border:none"> <tbody> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:82px"> Dose (mg/kg/d) </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:39px"> N </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:77px"> Incidence </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:48px"> ftumor </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:54px"> LCL </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:54px"> UCL </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:1px solid black; vertical-align:top; width:222px"> Sources </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:bottom; width:82px"> 0 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:39px"> 156 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:77px"> 0 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:48px"> 0.00 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.00 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.02 </td> <td rowspan="5" style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:top; width:222px"> Hayashi et al. 1994; Lalwani et al. 1981; Marsman & Popp 1984; Reddy et al. 1979 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:bottom; width:82px"> 14.2 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:39px"> 20 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:77px"> 3 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:48px"> 0.15 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.03 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.38 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:bottom; width:82px"> 20 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:39px"> 20 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:77px"> 11 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:48px"> 0.55 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.32 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.77 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:bottom; width:82px"> 40 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:39px"> 37 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:77px"> 35 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:48px"> 0.95 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.82 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.99 </td> </tr> <tr> <td style="border-bottom:1px solid black; border-left:1px solid black; border-right:1px solid black; border-top:none; vertical-align:bottom; width:82px"> 80 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:39px"> 14 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:77px"> 14 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:48px"> 1.00 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 0.77 </td> <td style="border-bottom:1px solid black; border-left:none; border-right:1px solid black; border-top:none; vertical-align:bottom; width:54px"> 1.00 </td> </tr> </tbody> </table> The MIE rises steeply and falls less steeply with increasing dose (A). The KER between the MIE and the AO is revealed by plots B and the bottom panel in D: the MIE reaches a plateau at an MIE level of over 30 corresponding to a dose of 10 mg/kg/d; an increase in the frequency of combined liver tumors to 15% occurs a dose of 14 mg/kg/d. Tumor frequency increases monotonically with dose and the MIE falls slightly to about 26 over the dose range of 10 to 100.  The KER between the MIE and the AO is revealed by plots B and the bottom panel in D: the MIE reaches a plateau at an MIE level of over 30 corresponding to a dose of 10 mg/kg/d; an increase in the frequency of combined liver tumors to 15% occurs a dose of 14 mg/kg/d. Tumor frequency increases monotonically with dose and the MIE falls slightly to about 26 over the dose range of 10 to 100.  At a dose of 100 mg/kg/d corresponding to the plateau value of the MIE at 20, the frequency of neoplastic nodules rises to 36% and for carcinomas to 10%. Similar to the KERs for Gemfibrozil, increases in KE#1 were not observed until the peak of the MIE response and continued as dose continued to rise (D, upper plot).

This AOP has no potential application for human risk assessment save to provide a case example of the mode of action of a type of non-genotoxic carcinogen (Wolf et al. 2019; Doe et al. 2019; Cohen et al. 2019). The application to ecological risk assessment is also unlikely. Although some PPARα activators occur in the enviroment, e.g. perfluorinated chemicals, the levels may not be sufficient to produce effects in wild rodent populations. Several large retrospective epidemiological studies observed no elevated risk of death from liver cancer associated with chronic treatment with PPARα activatorsr (Peters et al., 2005). Over a decade of chronic use of these pharmaceuticals was not associated with liver tumors in large human cohorts  (Frick et al., 1987; Huttunen et al., 1994).  PPARα activators do not induce cell proliferation or suppress apoptosis in human hepatocytes cultured in vitro (Goll et al., 1999; Hasmall et al., 1999, 2000b; Perrone et al., 1998; Williams & Perrone, 1995). In non-human primates, PPARα activators did not induce cell proliferation in vitro or in vivo (Doull et al., 1999). In summary, humans are not responsive to the effects of PPARα activators as are mice and rats.

High

Amacher, D. E., Beck, R., Schomaker, S. J., & Kenny, C. V. (1997). Hepatic microsomal enzyme induction, beta-oxidation, and cell proliferation following administration of clofibrate, gemfibrozil, or bezafibrate in the CD rat. Toxicol Appl Pharmacol, 142(1), 143-150. https://doi.org/10.1006/taap.1996.8007 Anderson, S. P., Dunn, C., Laughter, A., Yoon, L., Swanson, C., Stulnig, T. M., Steffensen, K. R., Chandraratna, R. A., Gustafsson, J. A., & Corton, J. C. (2004a). Overlapping transcriptional programs regulated by the nuclear receptors peroxisome proliferator-activated receptor alpha, retinoid X receptor, and liver X receptor in mouse liver. Mol Pharmacol, 66(6), 1440-1452. https://doi.org/10.1124/mol.104.005496 Anderson, S. P., Dunn, C. S., Cattley, R. C., & Corton, J. C. (2001a). Hepatocellular proliferation in response to a peroxisome proliferator does not require TNFalpha signaling. Carcinogenesis, 22(11), 1843-1851. https://doi.org/10.1093/carcin/22.11.1843 Anderson, S. P., Dunn, C. S., Cattley, R. C., & Corton, J. C. (2001b). Hepatocellular proliferation in response to a peroxisome proliferator does not require TNFalpha signaling. Carcinogenesis, 22(11), 1843-1851. https://doi.org/10.1093/carcin/22.11.1843 Anderson, S. P., Howroyd, P., Liu, J., Qian, X., Bahnemann, R., Swanson, C., Kwak, M. K., Kensler, T. W., & Corton, J. C. (2004b). The transcriptional response to a peroxisome proliferator-activated receptor alpha agonist includes increased expression of proteome maintenance genes. J Biol Chem, 279(50), 52390-52398. https://doi.org/10.1074/jbc.M409347200 Ashby, J., Brady, A., Elcombe, C. R., Elliott, B. M., Ishmael, J., Odum, J., Tugwood, J. D., Kettle, S., & Purchase, I. F. (1994). Mechanistically-based human hazard assessment of peroxisome proliferator-induced hepatocarcinogenesis. Hum Exp Toxicol, 13 Suppl 2, S1-117. https://doi.org/10.1177/096032719401300201 Balasubramaniyan, N., Shahid, M., Suchy, F. J., & Ananthanarayanan, M. (2005). Multiple mechanisms of ontogenic regulation of nuclear receptors during rat liver development. Am J Physiol Gastrointest Liver Physiol, 288(2), G251-60. https://doi.org/10.1152/ajpgi.00351.2004 Beck, F., Plummer, S., Senior, P. V., Byrne, S., Green, S., & Brammar, W. J. (1992). The ontogeny of peroxisome-proliferator-activated receptor gene expression in the mouse and rat. Proc Biol Sci, 247(1319), 83-87. https://doi.org/10.1098/rspb.1992.0012 Belury, M. A., Moya-Camarena, S. Y., Sun, H., Snyder, E., Davis, J. W., Cunningham, M. L., & Vanden Heuvel, J. P. (1998). Comparison of dose-response relationships for induction of lipid metabolizing and growth regulatory genes by peroxisome proliferators in rat liver. Toxicol Appl Pharmacol, 151(2), 254-261. https://doi.org/10.1006/taap.1998.8443 Bentley, P., Calder, I., Elcombe, C., Grasso, P., Stringer, D., & Wiegand, H. J. (1993). Hepatic peroxisome proliferation in rodents and its significance for humans. Food Chem Toxicol, 31(11), 857-907. https://doi.org/10.1016/0278-6915(93)90225-n Bojes, H. K., Germolec, D. R., Simeonova, P., Bruccoleri, A., Schoonhoven, R., Luster, M. I., & Thurman, R. G. (1997). Antibodies to tumor necrosis factor alpha prevent increases in cell replication in liver due to the potent peroxisome proliferator, WY-14,643. Carcinogenesis, 18(4), 669-674. https://doi.org/10.1093/carcin/18.4.669 Cattley, R. C., DeLuca, J., Elcombe, C., Fenner-Crisp, P., Lake, B. G., Marsman, D. S., Pastoor, T. A., Popp, J. A., Robinson, D. E., Schwetz, B., Tugwood, J., & Wahli, W. (1998). Do peroxisome proliferating compounds pose a hepatocarcinogenic hazard to humans. Regul Toxicol Pharmacol, 27(1 Pt 1), 47-60. https://www.ncbi.nlm.nih.gov/pubmed/9629596 Cattley, R. C., Marsman, D. S., & Popp, J. A. (1991). Age-related susceptibility to the carcinogenic effect of the peroxisome proliferator WY-14,643 in rat liver. Carcinogenesis, 12(3), 469-473. https://doi.org/10.1093/carcin/12.3.469 Cattley, R. C., & Popp, J. A. (1989). Differences between the promoting activities of the peroxisome proliferator WY-14,643 and phenobarbital in rat liver. Cancer Res, 49(12), 3246-3251. https://pubmed.ncbi.nlm.nih.gov/2566380 Chow, C. C., Ong, K. M., Dougherty, E. J., & Simons, S. S. (2011). Inferring mechanisms from dose-response curves. Methods Enzymol, 487, 465-483. https://doi.org/10.1016/B978-0-12-381270-4.00016-0 Corton, J. C., Apte, U., Anderson, S. P., Limaye, P., Yoon, L., Latendresse, J., Dunn, C., Everitt, J. I., Voss, K. A., Swanson, C., Kimbrough, C., Wong, J. S., Gill, S. S., Chandraratna, R. A., Kwak, M. K., Kensler, T. W., Stulnig, T. M., Steffensen, K. R., Gustafsson, J. A., . . . Mehendale, H. M. (2004). Mimetics of caloric restriction include agonists of lipid-activated nuclear receptors. J Biol Chem, 279(44), 46204-46212. https://doi.org/10.1074/jbc.M406739200 Corton, J. C., Cunningham, M. L., Hummer, T. B., Lau, C, Meek, B, Peters, JM, Popp, JA, Rhomberg, L, Seed, J., & Klaunig, J. E. (2014). Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPAR&OElig;±) as a case study. Crit Rev Toxicol, 44(1), 1-49. https://doi.org/10.3109/10408444.2013.835784 Corton, J. C., Hill, T., Sutherland, J. J., Stevens, J. L., & Rooney, J. (2020). A Set of Six Gene Expression Biomarkers Identify Rat Liver Tumorigens in Short-Term Assays. Toxicol Sci. https://doi.org/10.1093/toxsci/kfaa101 Corton, J. C., Lapinskas, P. J., & Gonzalez, F. J. (2000). Central role of PPARalpha in the mechanism of action of hepatocarcinogenic peroxisome proliferators. Mutat Res, 448(2), 139-151. https://doi.org/10.1016/s0027-5107(99)00232-8 Corton JC. (2010). Mode of action analysis and human relevance of liver tumors induced by PPARα activation. In: Hsu C-H, Stedeford T, eds. Cancer risk assessment: chemical carcinogenesis, hazard evaluation, and risk quantification. Hoboken (NJ): John Wiley & Sons, Inc, 438—81 Cunningham, M. L., Collins, B. J., Hejtmancik, M. R., Herbert, R. A., Travlos, G. S., Vallant, M. K., & Stout, M. D. (2010). Effects of the PPARα Agonist and Widely Used Antihyperlipidemic Drug Gemfibrozil on Hepatic Toxicity and Lipid Metabolism. PPAR Res, 2010. https://doi.org/10.1155/2010/681963 David, R. M., Moore, M. R., Cifone, M. A., Finney, D. C., & Guest, D. (1999). Chronic peroxisome proliferation and hepatomegaly associated with the hepatocellular tumorigenesis of di(2-ethylhexyl)phthalate and the effects of recovery. Toxicol Sci, 50(2), 195-205.https://doi.org/10.1093/toxsci/50.2.195 de Duve, C. (1996). The peroxisome in retrospect. Ann N Y Acad Sci, 804, 1-10. https://doi.org/10.1111/j.1749-6632.1996.tb18603.x De Vos, D., Bruggeman, F. J., Westerhoff, H. V., & Bakker, B. M. (2011). How molecular competition influences fluxes in gene expression networks. PLoS One, 6(12), e28494. https://doi.org/10.1371/journal.pone.0028494 Dostal, L. A., Jenkins, W. L., & Schwetz, B. A. (1987). Hepatic peroxisome proliferation and hypolipidemic effects of di(2-ethylhexyl)phthalate in neonatal and adult rats. Toxicol Appl Pharmacol, 87(1), 81-90. https://doi.org/10.1016/0041-008x(87)90086-x Doull, J., Cattley, R., Elcombe, C., Lake, B. G., Swenberg, J., Wilkinson, C., Williams, G., & van Gemert, M. (1999). A cancer risk assessment of di(2-ethylhexyl)phthalate: application of the new U.S. EPA Risk Assessment Guidelines. Regul Toxicol Pharmacol, 29(3), 327-357. https://doi.org/10.1006/rtph.1999.1296 Escher, P., & Wahli, W. (2000). Peroxisome proliferator-activated receptors: insight into multiple cellular functions. Mutat Res, 448(2), 121-138. https://doi.org/10.1016/s0027-5107(99)00231-6 Fitzgerald, J. E., Sanyer, J. L., Schardein, J. L., Lake, R. S., McGuire, E. J., & de la Iglesia, F. A. (1981). Carcinogen bioassay and mutagenicity studies with the hypolipidemic agent gemfibrozil. J Natl Cancer Inst, 67(5), 1105-1116. https://pubmed.ncbi.nlm.nih.gov/7029098 Gaillard, S., Grasfeder, L. L., Haeffele, C. L., Lobenhofer, E. K., Chu, T. M., Wolfinger, R., Kazmin, D., Koves, T. R., Muoio, D. M., Chang, C. Y., & McDonnell, D. P. (2006). Receptor-selective coactivators as tools to define the biology of specific receptor-coactivator pairs. Mol Cell, 24(5), 797-803. https://doi.org/10.1016/j.molcel.2006.10.012 Glauert, H. P., Eyigor, A., Tharappel, J. C., Cooper, S., Lee, E. Y., & Spear, B. T. (2006). Inhibition of hepatocarcinogenesis by the deletion of the p50 subunit of NF-kappaB in mice administered the peroxisome proliferator Wy-14,643. Toxicol Sci, 90(2), 331-336. https://doi.org/10.1093/toxsci/kfj116 Göttlicher, M., Widmark, E., Li, Q., & Gustafsson, J. A. (1992). Fatty acids activate a chimera of the clofibric acid-activated receptor and the glucocorticoid receptor. Proc Natl Acad Sci U S A, 89(10), 4653-4657. https://doi.org/10.1073/pnas.89.10.4653 Grasl-Kraupp, B., Huber, W., Timmermann-Trosiener, I., & Schulte-Hermann, R. (1993a). Peroxisomal enzyme induction uncoupled from enhanced DNA synthesis in putative preneoplastic liver foci of rats treated with a single dose of the peroxisome proliferator nafenopin. Carcinogenesis, 14(11), 2435-2437. https://doi.org/10.1093/carcin/14.11.2435 Grasl-Kraupp, B., Waldhör, T., Huber, W., & Schulte-Hermann, R. (1993b). Glutathione S-transferase isoenzyme patterns in different subtypes of enzyme-altered rat liver foci treated with the peroxisome proliferator nafenopin or with phenobarbital. Carcinogenesis, 14(11), 2407-2412. https://doi.org/10.1093/carcin/14.11.2407 Hartig, F., Stegmeier, K., Hebold, G., Özel, M., & Fahimi, H. D. (1982). Study of liver enzymes: peroxisome proliferation and tumor rates in rats at the end of carcinogenicity studies with bezafibrate and clofibrate. Annals of the New York Academy of Sciences, 386(1), 464-467. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1982.tb21453.x Hasmall, S. C., James, N. H., Macdonald, N., Gonzalez, F. J., Peters, J. M., & Roberts, R. A. (2000). Suppression of mouse hepatocyte apoptosis by peroxisome proliferators: role of PPARalpha and TNFalpha. Mutat Res, 448(2), 193-200. https://doi.org/10.1016/s0027-5107(99)00236-5 Hayashi, F., Tamura, H., Yamada, J., Kasai, H., & Suga, T. (1994). Characteristics of the hepatocarcinogenesis caused by dehydroepiandrosterone, a peroxisome proliferator, in male F-344 rats. Carcinogenesis, 15(10), 2215-2219. https://doi.org/10.1093/carcin/15.10.2215 Hays, T., Rusyn, I., Burns, A. M., Kennett, M. J., Ward, J. M., Gonzalez, F. J., & Peters, J. M. (2005). Role of peroxisome proliferator-activated receptor-alpha (PPARalpha) in bezafibrate-induced hepatocarcinogenesis and cholestasis. Carcinogenesis, 26(1), 219-227. https://doi.org/10.1093/carcin/bgh285 Hill, T., Rooney, J., Abedini, J., El-Masri, H., Wood, C. E., & Corton, J. C. (2020). Gene Expression Thresholds Derived From Short-Term Exposures Identify Rat Liver Tumorigens. Toxicol Sci. https://doi.org/10.1093/toxsci/kfaa102 Holden, P. R., Hasmall, S. C., James, N. H., West, D. R., Brindle, R. D., Gonzalez, F. J., Peters, J. M., & Roberts, R. A. (2000). Tumour necrosis factor alpha (TNFalpha): role in suppression of apoptosis by the peroxisome proliferator nafenopin. Cell Mol Biol (Noisy-le-grand), 46(1), 29-39. https://pubmed.ncbi.nlm.nih.gov/10726969 Igarashi, Y., Nakatsu, N., Yamashita, T., Ono, A., Ohno, Y., Urushidani, T., & Yamada, H. (2015). Open TG-GATEs: a large-scale toxicogenomics database. Nucleic Acids Res, 43(Database issue), D921-7. https://doi.org/10.1093/nar/gku955 Isenberg, J. S., Kamendulis, L. M., Smith, J. H., Ackley, D. C., Pugh, G., Lington, A. W., & Klaunig, J. E. (2000). Effects of Di-2-ethylhexyl phthalate (DEHP) on gap-junctional intercellular communication (GJIC), DNA synthesis, and peroxisomal beta oxidation (PBOX) in rat, mouse, and hamster liver. Toxicol Sci, 56(1), 73-85. https://doi.org/10.1093/toxsci/56.1.73 Isenberg, J. S., Kolaja, K. L., Ayoubi, S. A., Watkins, J. B., & Klaunig, J. E. (1997). Inhibition of WY-14,643 induced hepatic lesion growth in mice by rotenone. Carcinogenesis, 18(8), 1511-1519. https://doi.org/10.1093/carcin/18.8.1511 Issemann, I., & Green, S. (1990). Activation of a member of the steroid hormone receptor superfamily by peroxisome proliferators. Nature, 347(6294), 645-650. https://doi.org/10.1038/347645a0 Klaunig, J. E., Babich, M. A., Baetcke, K. P., Cook, J. C., Corton, J. C., David, R. M., DeLuca, J. G., Lai, D. Y., McKee, R. H., Peters, J. M., Roberts, R. A., & Fenner-Crisp, P. A. (2003). PPARalpha agonist-induced rodent tumors: modes of action and human relevance. Crit Rev Toxicol, 33(6), 655-780. https://doi.org/10.1080/713608372 Kondo, M., Miyata, K., Nagahori, H., Sumida, K., Osimitz, T. G., Cohen, S. M., Lake, B. G., & Yamada, T. (2019). Involvement of Peroxisome Proliferator-Activated Receptor-Alpha in Liver Tumor Production by Permethrin in the Female Mouse. Toxicol Sci, 168(2), 572-596. https://doi.org/10.1093/toxsci/kfz012 Koppen, A., Houtman, R., Pijnenburg, D., Jeninga, E. H., Ruijtenbeek, R., & Kalkhoven, E. (2009). Nuclear receptor-coregulator interaction profiling identifies TRIP3 as a novel peroxisome proliferator-activated receptor gamma cofactor. Mol Cell Proteomics, 8(10), 2212-2226. https://doi.org/10.1074/mcp.M900209-MCP200 Kupershmidt, I., Su, Q. J., Grewal, A., Sundaresh, S., Halperin, I., Flynn, J., Shekar, M., Wang, H., Park, J., Cui, W., Wall, G. D., Wisotzkey, R., Alag, S., Akhtari, S., & Ronaghi, M. (2010). Ontology-based meta-analysis of global collections of high-throughput public data. PLoS One, 5(9). https://doi.org/10.1371/journal.pone.0013066 Lalwani, N. D., Reddy, M. K., Qureshi, S. A., & Reddy, J. K. (1981). Development of hepatocellular carcinomas and increased peroxisomal fatty acid beta-oxidation in rats fed [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (Wy-14,643) in the semipurified diet. Carcinogenesis, 2(7), 645-650. https://doi.org/10.1093/carcin/2.7.645 Lapinskas, P. J., Brown, S., Leesnitzer, L. M., Blanchard, S., Swanson, C., Cattley, R. C., & Corton, J. C. (2005). Role of PPARalpha in mediating the effects of phthalates and metabolites in the liver. Toxicology, 207(1), 149-163. https://doi.org/10.1016/j.tox.2004.09.008 Laughter, A. R., Dunn, C. S., Swanson, C. L., Howroyd, P., Cattley, R. C., & Corton, J. C. (2004). Role of the peroxisome proliferator-activated receptor alpha (PPARalpha) in responses to trichloroethylene and metabolites, trichloroacetate and dichloroacetate in mouse liver. Toxicology, 203(1-3), 83-98. https://doi.org/10.1016/j.tox.2004.06.014 Lawrence, J. W., Wollenberg, G. K., & DeLuca, J. G. (2001). Tumor necrosis factor alpha is not required for WY14,643-induced cell proliferation. Carcinogenesis, 22(3), 381-386. https://doi.org/10.1093/carcin/22.3.381 Lee, S. S., Pineau, T., Drago, J., Lee, E. J., Owens, J. W., Kroetz, D. L., Fernandez-Salguero, P. M., Westphal, H., & Gonzalez, F. J. (1995). Targeted disruption of the alpha isoform of the peroxisome proliferator-activated receptor gene in mice results in abolishment of the pleiotropic effects of peroxisome proliferators. Mol Cell Biol, 15(6), 3012-3022. https://doi.org/10.1128/mcb.15.6.3012 Lewis, R. W., Hill, T., & Corton, J. C. (2020). A set of six Gene expression biomarkers and their thresholds identify rat liver tumorigens in short-term assays. Toxicology, 443, 152547. https://doi.org/10.1016/j.tox.2020.152547 Li, G., Brocker, C. N., Xie, C., Yan, T., Noguchi, A., Krausz, K. W., Xiang, R., & Gonzalez, F. J. (2018). Hepatic peroxisome proliferator-activated receptor alpha mediates the major metabolic effects of Wy-14643. J Gastroenterol Hepatol, 33(5), 1138-1145. https://doi.org/10.1111/jgh.14046 Liu, M. H., Li, J., Shen, P., Husna, B., Tai, E. S., & Yong, E. L. (2008). A natural polymorphism in peroxisome proliferator-activated receptor-alpha hinge region attenuates transcription due to defective release of nuclear receptor corepressor from chromatin. Mol Endocrinol, 22(5), 1078-1092. https://doi.org/10.1210/me.2007-0547 Maloney, E. K., & Waxman, D. J. (1999). trans-Activation of PPARalpha and PPARgamma by structurally diverse environmental chemicals. Toxicol Appl Pharmacol, 161(2), 209-218. https://doi.org/10.1006/taap.1999.8809 Marsman, D. S., Cattley, R. C., Conway, J. G., & Popp, J. A. (1988). Relationship of hepatic peroxisome proliferation and replicative DNA synthesis to the hepatocarcinogenicity of the peroxisome proliferators di(2-ethylhexyl)phthalate and [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (Wy-14,643) in rats. Cancer Res, 48(23), 6739-6744. https://pubmed.ncbi.nlm.nih.gov/3180084 Marsman, D. S., & Popp, J. A. (1994). Biological potential of basophilic hepatocellular foci and hepatic adenoma induced by the peroxisome proliferator, Wy-14,643. Carcinogenesis, 15(1), 111-117. https://doi.org/10.1093/carcin/15.1.111 Moreno, M., Lombardi, A., Silvestri, E., Senese, R., Cioffi, F., Goglia, F., Lanni, A., & de Lange, P. (2010). PPARs: Nuclear Receptors Controlled by, and Controlling, Nutrient Handling through Nuclear and Cytosolic Signaling. PPAR Res, 2010. https://doi.org/10.1155/2010/435689 Program, N. T. (2007). Toxicity studies of WY-14,643 (CAS No. 50892-23-4) administered in feed to male Sprague-Dawley rats, B6C3F1 mice, and Syrian hamsters. Toxic Rep Ser, 62), 1-136. https://pubmed.ncbi.nlm.nih.gov/24743700 Ong, K. M., Blackford, J. A., Kagan, B. L., Simons, S. S., & Chow, C. C. (2010). A theoretical framework for gene induction and experimental comparisons. Proc Natl Acad Sci U S A, 107(15), 7107-7112. https://doi.org/10.1073/pnas.0911095107 Peters, J. M., Cattley, R. C., & Gonzalez, F. J. (1997). Role of PPAR alpha in the mechanism of action of the nongenotoxic carcinogen and peroxisome proliferator Wy-14,643. Carcinogenesis, 18(11), 2029-2033. https://doi.org/10.1093/carcin/18.11.2029 Phillips, C. V., & Goodman, K. J. (2006). Causal criteria and counterfactuals; nothing more (or less) than scientific common sense. Emerg Themes Epidemiol, 3, 5. https://doi.org/10.1186/1742-7622-3-5 Qu, A., Jiang, C., Cai, Y., Kim, J. H., Tanaka, N., Ward, J. M., Shah, Y. M., & Gonzalez, F. J. (2014). Role of Myc in hepatocellular proliferation and hepatocarcinogenesis. J Hepatol, 60(2), 331-338. https://doi.org/10.1016/j.jhep.2013.09.024 Rao, M. S., & Reddy, J. K. (1996). Hepatocarcinogenesis of peroxisome proliferators. Ann N Y Acad Sci, 804, 573-587. https://doi.org/10.1111/j.1749-6632.1996.tb18646.x Reddy, J. K., Rao, M. S., Azarnoff, D. L., & Sell, S. (1979). Mitogenic and carcinogenic effects of a hypolipidemic peroxisome proliferator, [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (Wy-14, 643), in rat and mouse liver. Cancer Res, 39(1), 152-161. https://pubmed.ncbi.nlm.nih.gov/83907 Ren, H., Aleksunes, L. M., Wood, C., Vallanat, B., George, M. H., Klaassen, C. D., & Corton, J. C. (2010). Characterization of peroxisome proliferator-activated receptor alpha--independent effects of PPARalpha activators in the rodent liver: di-(2-ethylhexyl) phthalate also activates the constitutive-activated receptor. Toxicol Sci, 113(1), 45-59. https://doi.org/10.1093/toxsci/kfp251 Ren, H., Vallanat, B., Nelson, D. M., Yeung, L. W. Y., Guruge, K. S., Lam, P. K. S., Lehman-McKeeman, L. D., & Corton, J. C. (2009). Evidence for the involvement of xenobiotic-responsive nuclear receptors in transcriptional effects upon perfluoroalkyl acid exposure in diverse species. Reprod Toxicol, 27(3-4), 266-277. https://doi.org/10.1016/j.reprotox.2008.12.011 Rolfe, M., James, N. H., & Roberts, R. A. (1997). Tumour necrosis factor alpha (TNF alpha) suppresses apoptosis and induces DNA synthesis in rodent hepatocytes: a mediator of the hepatocarcinogenicity of peroxisome proliferators. Carcinogenesis, 18(11), 2277-2280. https://doi.org/10.1093/carcin/18.11.2277 Rooney, J., Hill, T., Qin, C., Sistare, F. D., & Corton, J. C. (2018). Adverse outcome pathway-driven identification of rat liver tumorigens in short-term assays. Toxicol Appl Pharmacol, 356, 99-113. https://doi.org/10.1016/j.taap.2018.07.023 Rosen, M. B., Das, K. P., Rooney, J., Abbott, B., Lau, C., & Corton, J. C. (2017). PPARα-independent transcriptional targets of perfluoroalkyl acids revealed by transcript profiling. Toxicology, 387, 95-107. https://doi.org/10.1016/j.tox.2017.05.013 Rosen, M. B., Lee, J. S., Ren, H., Vallanat, B., Liu, J., Waalkes, M. P., Abbott, B. D., Lau, C., & Corton, J. C. (2008). Toxicogenomic dissection of the perfluorooctanoic acid transcript profile in mouse liver: evidence for the involvement of nuclear receptors PPAR alpha and CAR. Toxicol Sci, 103(1), 46-56. https://doi.org/10.1093/toxsci/kfn025 Rosen, M. B., Schmid, J. R., Corton, J. C., Zehr, R. D., Das, K. P., Abbott, B. D., & Lau, C. (2010). Gene Expression Profiling in Wild-Type and PPARα-Null Mice Exposed to Perfluorooctane Sulfonate Reveals PPARα-Independent Effects. PPAR Res, 2010. https://doi.org/10.1155/2010/794739 Sanderson, L. M., de Groot, P. J., Hooiveld, G. J., Koppen, A., Kalkhoven, E., Müller, M., & Kersten, S. (2008). Effect of synthetic dietary triglycerides: a novel research paradigm for nutrigenomics. PLoS One, 3(2), e1681. https://doi.org/10.1371/journal.pone.0001681 Shah, Y. M., Morimura, K., Yang, Q., Tanabe, T., Takagi, M., & Gonzalez, F. J. (2007). Peroxisome proliferator-activated receptor alpha regulates a microRNA-mediated signaling cascade responsible for hepatocellular proliferation. Mol Cell Biol, 27(12), 4238-4247. https://doi.org/10.1128/MCB.00317-07 Simon, T. W., Budinsky, R. A., & Rowlands, J. C. (2015). A model for aryl hydrocarbon receptor-activated gene expression shows potency and efficacy changes and predicts squelching due to competition for transcription co-activators. PLoS One, 10(6), e0127952. https://doi.org/10.1371/journal.pone.0127952 Simon, T. W., Simons, S. S., Preston, R. J., Boobis, A. R., Cohen, S. M., Doerrer, N. G., Fenner-Crisp, P. A., McMullin, T. S., McQueen, C. A., Rowlands, J. C., & RISK21 Dose-Response Subteam. (2014). The use of mode of action information in risk assessment: Quantitative key events/dose-response framework for modeling the dose-response for key events. Crit Rev Toxicol, 44 Suppl 3, 17-43. https://doi.org/10.3109/10408444.2014.931925 Stäubli, W., Schweizer, W., Suter, J., & Weibel, E. R. (1977). The proliferative response of hepatic peroxidomes of neonatal rats to treatment with SU-13 437 (nafenopin). J Cell Biol, 74(3), 665-689. https://doi.org/10.1083/jcb.74.3.665 Stefanini, S., Nardacci, R., Farioli-Vecchioli, S., Pajalunga, D., & Sartori, C. (1999a). Liver and kidney peroxisomes in lactating rats and their pups after treatment with ciprofibrate. Biochemical and morphometric analysis. Cell Mol Biol (Noisy-le-grand), 45(6), 815-829. https://pubmed.ncbi.nlm.nih.gov/10541478 Stefanini, S., Nardacci, R., Farioli-Vecchioli, S., Pajalunga, D., & Sartori, C. (1999b). Liver and kidney peroxisomes in lactating rats and their pups after treatment with ciprofibrate. Biochemical and morphometric analysis. Cell Mol Biol (Noisy-le-grand), 45(6), 815-829. https://pubmed.ncbi.nlm.nih.gov/10541478 Svoboda, D. L., Saddler, T., & Auerbach, S. S. (2019). An Overview of National Toxicology Program’s Toxicogenomic Applications: DrugMatrix and ToxFX.  In Advances in Computational Toxicology (pp. 141-157). Springer. https://link.springer.com/chapter/10.1007/978-3-030-16443-0_8 Takacs, M. L., & Abbott, B. D. (2007). Activation of mouse and human peroxisome proliferator-activated receptors (alpha, beta/delta, gamma) by perfluorooctanoic acid and perfluorooctane sulfonate. Toxicol Sci, 95(1), 108-117. https://doi.org/10.1093/toxsci/kfl135 Tanaka, K., Smith, P. F., Stromberg, P. C., Eydelloth, R. S., Herold, E. G., Grossman, S. J., Frank, J. D., Hertzog, P. R., Soper, K. A., & Keenan, K. P. (1992). Studies of early hepatocellular proliferation and peroxisomal proliferation in Sprague-Dawley rats treated with tumorigenic doses of clofibrate. Toxicol Appl Pharmacol, 116(1), 71-77. https://doi.org/10.1016/0041-008x(92)90146-j Valles, E. G., Laughter, A. R., Dunn, C. S., Cannelle, S., Swanson, C. L., Cattley, R. C., & Corton, J. C. (2003). Role of the peroxisome proliferator-activated receptor alpha in responses to diisononyl phthalate. Toxicology, 191(2-3), 211-225. https://doi.org/10.1016/s0300-483x(03)00260-9 Wang, Y., Nakajima, T., Gonzalez, F. J., & Tanaka, N. (2020). PPARs as Metabolic Regulators in the Liver: Lessons from Liver-Specific PPAR-Null Mice. Int J Mol Sci, 21(6). https://doi.org/10.3390/ijms21062061 Watt, E. D., & Judson, R. S. (2018). Uncertainty quantification in ToxCast high throughput screening. PLoS One, 13(7), e0196963. https://doi.org/10.1371/journal.pone.0196963 Weglarz, T. C., & Sandgren, E. P. (2004). Cell cross-talk mediates PPARalpha null hepatocyte proliferation after peroxisome proliferator exposure. Carcinogenesis, 25(1), 107-112. https://doi.org/10.1093/carcin/bgg180 Weibel, E. R., Stäubli, W., Gnägi, H. R., & Hess, F. A. (1969). Correlated morphometric and biochemical studies on the liver cell. I. Morphometric model, stereologic methods, and normal morphometric data for rat liver. J Cell Biol, 42(1), 68-91. https://doi.org/10.1083/jcb.42.1.68 West, D. A., James, N. H., Cosulich, S. C., Holden, P. R., Brindle, R., Rolfe, M., & Roberts, R. A. (1999). Role for tumor necrosis factor alpha receptor 1 and interleukin-1 receptor in the suppression of mouse hepatocyte apoptosis by the peroxisome proliferator nafenopin. Hepatology, 30(6), 1417-1424. https://doi.org/10.1002/hep.510300612 Williams GM, Perrone C. (1995). Mechanism based risk assessment of peroxisome proliferating rodent hepatocarcinogens. In: Peroxisomes: Biology and Role in Toxicology and Disease, eds. J.K. Reddy, T. Wolf, D. C., Moore, T., Abbott, B. D., Rosen, M. B., Das, K. P., Zehr, R. D., Lindstrom, A. B., Strynar, M. J., & Lau, C. (2008). Comparative hepatic effects of perfluorooctanoic acid and WY 14,643 in PPAR-alpha knockout and wild-type mice. Toxicol Pathol, 36(4), 632-639. https://doi.org/10.1177/0192623308318216 Woods, C. G., Kosyk, O., Bradford, B. U., Ross, P. K., Burns, A. M., Cunningham, M. L., Qu, P., Ibrahim, J. G., & Rusyn, I. (2007). Time course investigation of PPARalpha- and Kupffer cell-dependent effects of WY-14,643 in mouse liver using microarray gene expression. Toxicol Appl Pharmacol, 225(3), 267-277. https://doi.org/10.1016/j.taap.2007.08.028 Yamoto, T., Ohashi, Y., Furukawa, T., Teranishi, M., Manabe, S., & Makita, T. (1996). Change of the sex-dependent response to clofibrate in F344 rat liver during postnatal development. Toxicol Lett, 85(2), 77-83. https://doi.org/10.1016/0378-4274(96)03643-0 Yu, S., Cao, W. Q., Kashireddy, P., Meyer, K., Jia, Y., Hughes, D. E., Tan, Y., Feng, J., Yeldandi, A. V., Rao, M. S., Costa, R. H., Gonzalez, F. J., & Reddy, J. K. (2001). Human peroxisome proliferator-activated receptor alpha (PPARalpha) supports the induction of peroxisome proliferation in PPARalpha-deficient mouse liver. J Biol Chem, 276(45), 42485-42491. https://doi.org/10.1074/jbc.M106480200 AOPWiki 2016-11-29T18:41:16

2023-04-29T16:02:55