Regulation of multidrug resistance 2 P-glycoprotein expression by bile salts in rats and in primary cultures of rat hepatocytes

Authors

  • Seema Gupta,

    1. Medicine-Gastroenterology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia
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  • R. Todd Stravitz,

    1. Medicine-Gastroenterology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia
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  • William M. Pandak,

    1. Medicine-Gastroenterology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia
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  • Michael Müller,

    1. Division of Gastroenterology and Hepatology, University of Groningen, Groningen, The Netherlands
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  • Z. Reno Vlahcevic,

    1. Medicine-Gastroenterology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia
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  • Phillip B. Hylemon Ph.D.

    Corresponding author
    1. Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia
    • Department of Microbiology and Immunology, Medical College of VA Campus of VA, Commonwealth University, P.O. Box 980678, Richmond, VA 23298-0678. fax: 804-828-0676.
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Abstract

Biliary phospholipid secretion is tightly coupled to the secretion of free cholesterol and bile salts. The secretion of phospholipids across the canalicular membrane of hepatocytes occurs via the multidrug resistance 2 (mdr2) P-glycoprotein (Pgp). The mechanism underlying the coupling of bile salt and phospholipid secretion has not been elucidated. The aims of this study were to determine the effects of bile acid structure on the expression of mdr2 in vitro and in vivo. Under optimal culture conditions, taurine-conjugated bile acids (50 μmol/L) increased mdr2 messenger RNA (mRNA) levels in the following order: taurocholate (TCA) (288 ± 36%, P < .005) = taurodeoxycholate (TDCA) (276 ± 36%, P < .025) > taurochenodeoxycholate (TCDCA) (216 ± 34%, P < .025) > tauroursodeoxycholate (TUDCA) (175 ± 28%, P < .05) of control levels. The increase in mdr2 mRNA levels by TCA was both time and concentration dependent. Cholate feeding to rats with intact enterohepatic circulation increased mdr2 transcriptional activity by 4-fold and protein mass by 1.9-fold. Chronic biliary diversion (CBD) decreased mdr2 mRNA levels to 66 ± 9% (P < .025) of sham-operated controls. Intraduodenal infusion of TCA for 48 hours in CBD rats caused a significant increase in mdr2 mRNA levels (224%) as compared with CBD controls. A diet high in cholesterol (4%) decreased mdr2 mRNA levels to 57% ± 2 (P < .001) of pair-fed controls. Squalestatin (1 μmol/L), an inhibitor of cholesterol biosynthesis, increased mdr2 mRNA levels by 8.8-fold (P < .005) in hepatocyte cultures after 24 hours. In conclusion, in the rat, bile acids up-regulated mdr2 transcriptional activity whereas cholesterol decreased mdr2 mRNA both in vitro and in vivo.

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