Abstract
Inter-individual variability in activity of uptake transporters is evident in vivo, yet limited data exist in vitro, confounding the in vitro-in vivo extrapolation. The uptake kinetics of seven OATP substrates was investigated over a concentration range in plated cryopreserved human hepatocytes. Active uptake clearance (CLactive,u), bidirectional passive diffusion (Pdiff), intracellular binding and metabolism were estimated for bosentan, pitavastatin, pravastatin, repaglinide, rosuvastatin, telmisartan and valsartan in HU4122 donor using a mechanistic two-compartment model in Matlab. Full uptake kinetics of rosuvastatin and repaglinide were also characterized in two additional donors, whereas for the remaining drugs CLactive,u was estimated at a single concentration. The Km,u and Pdiff values were consistent across donors, whereas Vmax was on average up to 2.8-fold greater in donor HU4122. Consistency in Km,u allowed extrapolation of single concentration uptake activity data and assessment of inter-individual variability in CLactive,u across donors. The maximal contribution of active transport to total uptake differed between donors, for example 85-96% and 68-87% for rosuvastatin and repaglinide, respectively; however, in all the cases the active process was the major contributor. In vitro-in vivo extrapolation indicated a general under-prediction of hepatic intrinsic clearance; an average empirical scaling factor of 17.1 was estimated based on seven drugs investigated in three hepatocyte donors; donor-specific differences in empirical factors are discussed. Uptake Km,u and CLactive,u were on average 4.3- and 7.1-fold lower in human hepatocytes compared to our previously published rat data. Strategy for the use of rat uptake data to facilitate the experimental design in human hepatocytes is discussed.
- Received April 11, 2012.
- Accepted June 4, 2012.
- The American Society for Pharmacology and Experimental Therapeutics