Expression and hepatobiliary transport characteristics of the concentrative and equilibrative nucleoside transporters in sandwich-cultured human hepatocytes.
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.
Govindarajan
Rajgopal
R
Department of Pharmaceutics, University of Washington, Box 357610, Seattle, WA 98195, USA.
Endres
Christopher J
CJ
Whittington
Dale
D
LeCluyse
Edward
E
Pastor-Anglada
Marçal
M
Tse
Chung-Ming
CM
Unadkat
Jashvant D
JD
D000328:Adult; D000368:Aged; D001086:Arabinofuranosyluracil / Q000031:analogs & derivatives / Q000378:metabolism; D001646:Bile / Q000378:metabolism*; D018929:Cell Culture Techniques; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics / Q000378:metabolism*; D033722:Equilibrative-Nucleoside Transporter 2 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005573:Formycins / Q000378:metabolism; D006151:Guanosine / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D009705:Nucleosides / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012254:Ribavirin / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism
D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D005573:Formycins; D026901:Membrane Transport Proteins; D009705:Nucleosides; D012333:RNA, Messenger; C438649:SLC29A1 protein, human; C438654:SLC29A2 protein, human; C065171:cif nucleoside transporter; D006151:Guanosine; C034561:formycin B; D001086:Arabinofuranosyluracil; D012254:Ribavirin; C043457:fialuridine; D013936:Thymidine