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This Article Full Text Full Text (PDF) All Versions of this Article: 295/3/G570    most recent 00542.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Govindarajan, R. Articles by Unadkat, J. D. PubMed PubMed Citation Articles by Govindarajan, R. Articles by Unadkat, J. D.

LIVER AND BILIARY TRACT

Expression and hepatobiliary transport characteristics of the concentrative and equilibrative nucleoside transporters in sandwich-cultured human hepatocytes

¹Department of Pharmaceutics, University of Washington, Seattle, Washington; ²CellzDirect, Pittsboro, North Carolina; ³Department of Biochemistry and Molecular Biology, Institute of Biomedicine (IBUB) University of Barcelona and Centro de Investigación Biomédica en Red en el Área temática de Enfermedades Hepáticas y Digestivas (CIBERehd), Barcelona, Spain; and ⁴Department of Medicine, Division of Gastroenterology, The Johns Hopkins University School of Medicine, Baltimore, Maryland

Submitted 19 November 2007 ; accepted in final form 15 July 2008

We previously reported that both the concentrative (hCNT) and equilibrative (hENT) nucleoside transporters are expressed in the human liver (21). Here we report a study that investigated the expression of these transporters (transcripts and proteins) and their role in the hepatobiliary transport of nucleosides/nucleoside drugs using sandwich-cultured human hepatocytes. In the hepatic tissue, the rank order of the mRNA expression of the transporters was hCNT1 hENT1 > hENT2 hCNT2 > hCNT3. In sandwich-cultured hepatocytes, the mRNA expression of hCNT2 and hENT2 was comparable to that in hepatic tissue, whereas the expression of corresponding transporters in the two-dimensional hepatocyte cultures was lower. Colocalization studies demonstrated predominant localization of these transporters at the sinusoidal membrane and of hENT1, hCNT1, and hCNT2 at the canalicular membrane. In the sandwich-cultured hepatocytes, ENTs were the major contributors to the transport of thymidine (hENT1, 63%; hENT2, 23%) or guanosine (hENT1, 53%; hENT2, 24%) into the hepatocytes followed by hCNT1 (10%) for thymidine or hCNT2 (23%) for guanosine. Although ribavirin was predominately transported (89%) into the hepatocytes by hENT1, fialuridine (FIAU) was transported by both hENT1 (30%) and hCNTs (61%). The extensively metabolized natural nucleosides were not effluxed into the bile, whereas significant biliary-efflux was observed of FIAU (19%), ribavirin (30%), and formycin B (35%). We conclude that the hepatic activity of hENT1 and hCNT1/2 transporters will determine the in vivo hepatic distribution and therefore the efficacy and/or toxicity of nucleoside drugs used to treat hepatic diseases.

human equilibrative nucleoside transporters; human concentrative nucleoside transporters; mRNA; protein expression; localization; biliary efflux; biliary excretion; phosphorylation; nucleoside drugs; hepatic diseases