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

Rajgopal Govindarajan, Christopher J. Endres, Dale Whittington, Edward LeCluyse, Marçal Pastor-Anglada, Chung Ming Tse, Jashvant D. Unadkat

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Pages (from-to)G570-G580
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume295
Issue number3
DOIs
StatePublished - Sep 2008

Keywords

  • Biliary efflux
  • Biliary excretion
  • Hepatic diseases
  • Human concentrative nucleoside transporters
  • Human equilibrative nucleoside transporters
  • Localization
  • Nucleoside drugs
  • Phosphorylation
  • Protein expression
  • mRNA

ASJC Scopus subject areas

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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