RT Journal Article
SR Electronic
T1 Utility of Drug Depletion - Time Profiles in Isolated Hepatocytes for Accessing Hepatic Uptake Clearance: Identifying Rate Limiting Steps and Role of Passive Processes
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP dmd.112.045732
DO 10.1124/dmd.112.045732
A1 Emilie Jigorel
A1 J Brian Houston
YR 2012
UL http://dmd.aspetjournals.org/content/early/2012/05/16/dmd.112.045732.abstract
AB Drug depletion-time profiles in isolated hepatocytes, as well as microsomes, have become a standard method of assessing hepatic metabolic clearance in vitro. Soars et al. (Drug Metab Dispos. 35: 859-65, 2007) have described an adaptation of the depletion approach to allow determination of hepatic uptake by transporters in addition to metabolism. Dual incubations are carried out where one set of incubations undergo conventional methodology whereas for the second set cells and media are separated for determination of drug loss from the media. The utility of this dual incubation approach has been assessed using eight drugs (atorvastatin, clarithromycin, erythromycin, fexofenadine, pitavastatin, repaglinide, rosuvastatin and saquinavir) with a range of active uptake, passive permeability, cell binding and metabolic characteristics. Four of these compounds (fexofenadine, rosuvastatin, pitavastatin and atorvastatin) show a biphasic time profile when assessing drug loss from media indicative of hepatic uptake prior to elimination within the hepatocyte which is distinct from the time profile in a conventional incubation and show higher clearances. The four other compounds (clarithromycin, saquinavir, erythromycin and repaglinide) show an identical depletion-time profiles (and clearances) in both sets of incubation. Whether or not the biphasic nature (and higher clearance) is evident, indicating transporter activity for a particular drug appears to be dependent upon its passive permeability. Using the parameter Kpu to reflect the relative importance of hepatic transporters versus passive diffusion, a value of 10 was identified as a cut off for whether the biphasic nature was evident or not; those compounds in excess of 10 show this characteristic clearly. There appears to be no relationship between the presence of the biphasic nature and any other parameter, including cellular binding, extent of metabolism or the magnitude of active uptake.