Abstract
Ethinylestradiol (EE) induces cholestasis by affecting bile salt-dependent and -independent fractions of the bile flow. The decrease in bile salt-independent flow is thought to be due, in part, to a reduction in the expression of the canalicular transporter Mrp2. The impact of modulation of Mrp2 function by sodium ursodeoxycholate (UDC) in EE cholestasis is unknown. We evaluated the protective effect of UDC on EE-induced impairment of Mrp2 activity in vivo and in isolated hepatocytes, by using the substrate dinitrophenyl S-glutathione (DNP-SG). EE was administered to male Wistar rats at a dose of 5 mg/kg s.c. for 5 days. UDC was coadministered with EE at a dose of 25 mg/kg b.wt. i.p. for the same period. EE alone reduced DNP-SG biliary excretion by 55% when compared with controls. Coadministration with UDC partially restored the alteration. Secretion rate of DNP-SG was decreased by 30% in isolated hepatocytes from EE-treated rats, but, contrary to in vivo results, UDC coadministration did not restore DNP-SG transport, likely as a consequence of bile salt washout resulting from the isolation procedure. As a confirmation, tauroursodeoxycholate hepatocyte preloading significantly increased Mrp2 activity. Western blotting analysis of Mrp2 indicated that EE administration significantly reduced its level in total and plasma membranes and that UDC coadministration failed to revert this alteration. In conclusion, UDC improvement in Mrp2 transport activity in vivo likely derived from a direct enhancement of Mrp2 function rather than from a restoration of its expression levels. This provides a novel mechanism explaining the beneficial effects of UDC in EE-induced cholestasis.
Footnotes
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Supported by grants from Agencia Nacional de Promoción Científica y Tecnológica, Consejo Nacional de Investigaciones Científicas y Técnicas, Ministerio de Salud de la Nación (Beca Ramón Carrillo–Arturo Oñativia 2004, to F.A.C.), and Fundación Antorchas, Argentina.
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Parts of this study were presented in the Biannual Meeting of the International Association for the Study of the Liver (IASL, San Salvador de Bahia, Brazil), March 16–20, 2004.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.104.003533.
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ABBREVIATIONS: EE, ethinylestradiol; CDNB, 1-chloro-2,4-dinitrobenzene; DNP-SG, dinitrophenyl S-glutathione; MPM, mixed plasma membrane; IM, internal membrane; Mrp2, multidrug resistance-associated protein 2; TLM, total liver membrane; TUDC, sodium tauroursodeoxycholate; UDC, sodium ursodeoxycholate.
- Received December 30, 2004.
- Accepted April 19, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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