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

• Published in: American journal of physiology: Gastrointestinal and liver physiology 2008-09, Vol.295 (3), p.G570-G580
• Main Authors: Govindarajan, Rajgopal, Endres, Christopher J, Whittington, Dale, LeCluyse, Edward, Pastor-Anglada, Marçal, Tse, Chung-Ming, Unadkat, Jashvant D
• Format: Article
• Language: English
• Subjects: Adult; Aged; Arabinofuranosyluracil - analogs & derivatives; Arabinofuranosyluracil - metabolism; Bile - metabolism; Cell culture; Cell Culture Techniques; Cell Membrane - metabolism; Cells, Cultured; Equilibrative Nucleoside Transporter 1 - genetics; Equilibrative Nucleoside Transporter 1 - metabolism; Equilibrative-Nucleoside Transporter 2 - genetics; Equilibrative-Nucleoside Transporter 2 - metabolism; Female; Formycins - metabolism; Guanosine - metabolism; Hepatocytes - metabolism; Humans; Liver; Liver and Biliary Tract; Liver diseases; Male; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Middle Aged; Nucleosides - metabolism; Ribavirin - metabolism; RNA, Messenger - metabolism; Studies; Thymidine - metabolism
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.00542.2007

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 approximately hENT1>hENT2 approximately 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.