40 research outputs found
Quantification of Hepatic Organic Anion Transport Proteins OAT2 and OAT7 in Human Liver Tissue and Primary Hepatocytes
Organic anion transporter (OAT) 2
and OAT7 were recently shown
to be involved in the hepatic uptake of drugs; however, there is limited
understanding of the population variability in the expression of these
transporters in liver. There is also a need to derive relative expression-based
scaling factors (REFs) that can be used to bridge in vitro functional
data to the in vivo drug disposition. To this end, we quantified OAT2
and OAT7 surrogate peptide abundance in a large number of human liver
tissue samples (<i>n</i> = 52), as well as several single-donor
cryopreserved human hepatocyte lots (<i>n</i> = 30) by a
novel, validated liquid chromatography tandem mass spectrometry (LC–MS/MS)
method. The average surrogate peptide expression of OAT2 and OAT7
in the liver samples was 1.52 ± 0.57 and 4.63 ± 1.58 fmol/μg
membrane protein, respectively. While we noted statistically significant
differences (<i>p</i> < 0.05) in hepatocyte and liver
tissue abundances
for both OAT2 and OAT7, the differences were relatively small (1.8-
and 1.5-fold difference in median values, respectively). Large interindividual
variability was noted in the hepatic expression of OAT2 (16-fold in
liver tissue and 23-fold in hepatocytes). OAT7, on the other hand,
showed less interindividual variability (4-fold) in the
livers, but high variability for the hepatocyte lots (27-fold). A
significant positive correlation in OAT2 and OAT7 expression was observed,
but expression levels were neither associated with age nor sex. In
conclusion, our data suggest marked interindividual variability in
the hepatic expression of OAT2/7, which may contribute to the pharmacokinetic
variability of their substrates. Because both transporters were less
abundant in hepatocytes than livers, a REF-based approach is recommended
when scaling in vitro hepatocyte transport data to predict hepatic
drug clearance and liver exposure of OAT2/7 substrates
Clearance Mechanism Assignment and Total Clearance Prediction in Human Based upon in Silico Models
We
introduce a two-tier model based on an exhaustive data set,
where discriminant models based on principal component analysis (PCA)
and partial least squares (PLS) are used separately and in conjunction,
and we show that PCA is highly discriminant approaching 95% accuracy
in the assignment of the primary clearance mechanism. Furthermore,
the PLS model achieved a quantitative predictive performance comparable
to methods based on scaling of animal data while not requiring the
use of either in vivo or in vitro data,
thus sparing the use of animal. This is likely the highest performance
that can be expected from a computational approach, and further improvements
may be difficult to reach. We further offer the medicinal scientist
a PCA model to guide in vitro and/or in vivo studies to help limit
the use of resources via very rapid computations
Special Section on Prediction of Human Pharmacokinetic Parameters from In Vitro Systems-Perspective A Perspective on the Prediction of Drug Pharmacokinetics and Disposition in Drug Research and Development
ABSTRACT Prediction of human pharmacokinetics of new drugs, as well as other disposition attributes, has become a routine practice in drug research and development. Prior to the 1990s, drug disposition science was used in a mostly descriptive manner in the drug development phase. With the advent of in vitro methods and availability of human-derived reagents for in vitro studies, drugdisposition scientists became engaged in the compound design phase of drug discovery to optimize and predict human disposition properties prior to nomination of candidate compounds into the drug development phase. This has reaped benefits in that the attrition rate of new drug candidates in drug development for reasons of unacceptable pharmacokinetics has greatly decreased. Attributes that are predicted include clearance, volume of distribution, halflife, absorption, and drug-drug interactions. In this article, we offer our experience-based perspectives on the tools and methods of predicting human drug disposition using in vitro and animal data
Hepatic Disposition of Gemfibrozil and Its Major Metabolite Gemfibrozil 1‑<i>O</i>‑β-Glucuronide
Gemfibrozil (GEM), which decreases
serum triglycerides and low
density lipoprotein, perpetrates drug–drug interactions (DDIs)
with several drugs. These DDIs are primarily attributed to the inhibition
of drug transporters and metabolic enzymes, particularly cytochrome
P450 (CYP) 2C8 by the major circulating metabolite gemfibrozil 1-<i>O</i>-β-glucuronide (GG). Here, we characterized the transporter-mediated
hepatic disposition of GEM and GG using sandwich-cultured human hepatocytes
(SCHH) and transporter-transfect systems. Significant active uptake
was noted in SCHH for the metabolite. GG, but not GEM, showed substrate
affinity to organic anion transporting polypeptide (OATP) 1B1, 1B3,
and 2B1. In SCHH, glucuronidation was characterized affinity constants
(<i>K</i><sub>m</sub>) of 7.9 and 61.4 μM, and biliary
excretion of GG was observed. Furthermore, GG showed active basolateral
efflux from preloaded SCHH and ATP-dependent uptake into membrane
vesicles overexpressing multidrug resistance-associated protein (MRP)
2, MRP3, and MRP4. A mathematical model was developed to estimate
hepatic uptake and efflux kinetics of GEM and GG based on SCHH studies.
Collectively, the hepatic transporters play a key role in the disposition
and thus determine the local concentrations of GEM and more so for
GG, which is the predominant inhibitory species against CYP2C8 and
OATP1B1