Contribution of CNT1 and ENT1 to ribavirin uptake in human hepatocytes

Abstract

The objective of this study was to investigate thecontributions of a sodium-dependent concentrative nucleosidetransporter (CNT) 1 and an equilibrative nucleosidetransporter (ENT) 1 to ribavirin uptake in human hepatocytes. The initial studies in oocytes expressing CNT1 andENT1 showed increases in ribavirin uptake, indicating thatribavirin was a substrate for both CNT1 and ENT1. TheCNT1- and ENT1-mediated ribavirin uptake showed concentrationdependency with the following kinetics parameters:Km 26.3 lM and Vmax 426.2 fmol/min/oocyte forCNT1; Km 70.5 lM and Vmax 134.3 fmol/min/oocyte forENT1. Ribavirin uptake clearance in six human hepatocytesranged from 21.3 to 300.7 lL/min. Estimation of the contributionsof CNT1 and ENT1 to the hepatic uptake ofribavirin by using a relative activity factor method indicatedthat the relative contribution of ENT1 to the ribavirin uptakewas 82.8 ± 3.9 %. Real-time polymerase chain reactionanalysis of CNT1 and ENT1 expressions in the hepatocytesshowed that ENT1 mRNA expression was closely correlatedwith ribavirin uptake (R = 0.95, P = 0.003) while CNT1was not. The findings indicated that ENT1 was the majortransporter controlling the hepatic uptake of ribavirin.