Abstract
Estrogens cause intrahepatic cholestasis in susceptible women during pregnancy, after administration of oral contraceptives, or during postmenopausal hormone replacement therapy. 17α-Ethinylestradiol (EE) is a synthetic estrogen widely used to cause experimental cholestasis in rodents with the aim of examining molecular mechanisms involved in this disease. EE actions on the liver are thought to be mediated by estrogen receptor α (ERα) and pituitary hormones. We tested this hypothesis by analyzing metabolic changes induced by EE in livers from hypophysectomized (HYPOX) and hypothyroid rats. Microarray studies revealed that the number of genes regulated by EE was increased almost 4-fold in HYPOX rat livers compared with intact males. Little overlap was apparent between the effects of EE in intact and HYPOX rats, demonstrating that pituitary hormones play a critical role in the hepatic effects of EE. Consistently, hypophysectomy protects the liver against induction by EE of serum bilirubin and alkaline phosphatase, two markers of cholestasis and hepatotoxicity and modulates the effects of EE on several genes involved in bile acid homeostasis (e.g., FXR, SHP, BSEP, and Cyp8b1). Finally, we demonstrate a novel mechanism of action of EE through binding and negative regulation of glucocorticoid receptor-mediated transcription. In summary, pituitary- and ERα-independent mechanisms contribute to development of EE-induced changes in liver transcriptome. Such mechanisms may be relevant when this model of EE-induced cholestasis is evaluated. The observation that the pharmacological effects of estrogen in liver differ in the absence or presence of the pituitary could be clinically relevant, because different drugs that block actions of pituitary hormones are now available.
Footnotes
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This research was supported by grants to L.F.-P. from the Ministerio de Sanidad y Consumo (FIS 1/1000), the Ministerio de Ciencia y Tecnología (PETRI1995-0711 and SAF2003-02117), and Universidad de Las Palmas de Gran Canaria-Pfizer Spain (CN-78/02-05045). A.F.-M. was supported by Vetenskapsrådet and Wallenberg Consortium North (Sweden). L.H.-H. and R.S.-F. are recipients of predoctoral fellowships from the Ministerio de Educación, Cultura y Deporte (AP2001-3499) and Ministerio de Ciencia y Tecnología (SAF2003-02117), respectively.
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L.A.H.-H. and A.F.-M. contributed equally to this work. Therefore, they should be considered interchangeably as the first author.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.113209.
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ABBREVIATIONS: EE, 17α-ethinylestradiol; BSIF, bile-salt-independent fraction of the bile flow; BSDF, bile-salt-dependent fraction of the bile flow; Ntcp, Na+ taurocholate cotransporter protein; Bsep, bile salt export pump; FXR, farnesoid X receptor; SHP, small heterodimer partner; SREBP-1c, sterol regulatory element-binding protein-1c; CA, cholic acid; ER, estrogen receptor; GH, growth hormone; Cy, cyanine; rh, recombinant human; TX, hypothyroid; T3, triiodothyronine; HYPOX, hypophysectomized; SAM, significance analysis for microarrays; FDR, false discovery rate; GO, Gene Ontology; qRT, quantitative real-time; PCR, polymerase chain reaction; ALP, alkaline phosphatase; CYP7A1, cholesterol 7α-hydroxylase; C4, 7α-hydroxy-4-cholesten-3-one; GR, glucocorticoid receptor; DEX, dexamethasone; DCC, dextran T70-coated charcoal; MMTV, mouse mammary tumor virus; Luc, luciferase; LDLR, low-density lipoprotein receptor; Mrp2, multidrug resistance protein 2; CYP8B1, cholesterol 12α-hydroxylase; CYP27A1, sterol 27-hydroxylase; LXR, liver X receptor; PPAR, peroxisome proliferator-activated receptor; TAT, tyrosine aminotransferase.
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↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
- Received August 30, 2006.
- Accepted November 13, 2006.
- The American Society for Pharmacology and Experimental Therapeutics