Prediction of the Pharmacokinetics of Atorvastatin, Cerivastatin, and Indomethacin Using Kinetic Models Applied to Isolated Rat Hepatocytes

Abstract

ABSTRACT:The disposition of atorvastatin, cerivastatin, and indomethacin, established substrates of rat hepatic basolateral uptake transporters, has been evaluated in suspended rat hepatocytes. Cell and media concentration-time data were simultaneously fitted to a model incorporating active uptake, permeation, binding, and metabolism. Use of the model to estimate the ratio of intracellular to extracellular steadystate free drug concentrations demonstrated the strong influence of active uptake on the kinetics of atorvastatin (18:1) and cerivastatin Isolated hepatocytes are an important in vitro system for studying the disposition of drugs, reflecting both the key role of the liver in the elimination of foreign compounds and also the ability of isolation and maintenance procedures to retain the integrity of many functional hepatic components (Li et al., 1999;Soars et al., 2007). Pharmacokinetic models can be applied to study the movement of molecules in and out of cells and to quantify their intracellular binding and metabolism. This approach has been used extensively to study the kinetics of compounds within the whole organ (Goresky and Schwab, 1988;Sirianni and Pang, 1997;Liu and Pang, 2005) but can also be applied to derive a greater understanding of the behavior of drugs in isolated hepatocytes, thereby exploiting this model system.Hepatocyte intrinsic metabolic clearance (CL int,met ) can be obtained from in vitro metabolism experiments by sampling a homogeneous hepatocyte suspension over time and either dividing the rate of metabolite formation by the initial substrate concentration (Houston et al., 2003) or by estimating the depletion rate of parent compound; for both methods, a correction is made to the clearance from the incubation (CL inc ) for the fraction unbound in the incubation (fu inc ). This latter approach has been used widely in the industry for the last 5 to 10 years Houston, 2004, 2005;McGinnity et al., 2004;Riley et al., 2005;Soars et al., 2007) and is referred to as the "standard method" in the manuscript. For many highly permeable drugs, where the intracellular concentration of free drug can be assumed to be equal to that in the plasma, relatively simple liver models can be used to estimate intrinsic metabolic clearance in the liver (CL int,L ) from in vitro data (Houston and Carlile, 1997;Lau et al., 2002;McGinnity et al., 2004). CL int,L can also be estimated from in vivo data by correcting plasma concentration-time data for plasma protein binding (Houston, 1994).However, where the intracellular concentration of free drug is likely to be significantly different to that in the media (for example, diffusion-limited or uptake transporter protein mediated kinetics), more Article, publication date, and citation information can be found at http://dmd.aspetjournals.org. doi:10.1124/dmd.107.019455.□ S The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.ABBREVIATIONS: CL int,met , unbound metabolic intrinsic clearance; CL inc , clearance f...

Comparative Use of Isolated Hepatocytes and Hepatic Microsomes for Cytochrome P450 Inhibition Studies: Transporter-Enzyme Interplay

“…The activity of members of the solute carrier and ATP-binding cassette families of transporter proteins may provide a mechanistic explanation for the limited success achieved for some drugs using standard (hepatic microsomal) in vitro experiments to predict pharmacokinetic aspects of clearance and drug-drug interaction (DDI) potential (Lam et al, 2006;Soars et al, 2007;Parker and Houston, 2008). Although various theoretical scenarios involving hepatic transporters can be proposed, specific examples with experimental confirmation of an unequivocal nature have been largely restricted to the statins (Lau et al, 2006;Shitara et al, 2006;Paine et al, 2008). It seems that the consequences of hepatic transporters may not always be intuitive because of transporter-enzyme interplay and "transporter-like" interactions involving other cellular processes.…”

Physiologically based pharmacokinetic (PBPK) modelling tools: how to fit with our needs?

“…The group of Pang have also been instrumental in contributing new insights into physiological modelling of transporter-mediated processes and metabolite kinetic, again using open modelling software to write and solve their models of intestinal and zonal hepatic transport and metabolism, which when incorporated into WB-PBPK models are able to account for phenomena such as routedependent metabolism which were not explainable when using simpler, more standard PBPK models [44]. Within the pharmaceutical industry, several publications by the R & D DMPK group of AstraZeneca have also reported the use of software such as WinNonlin and Berkley Madonna in the construction of their hepatocyte PBPK models [29,45,46].…”

“…Several recent publications have highlighted the importance of active transporter-driven uptake on the hepatic disposition of certain types of drugs, such as statins, and some have proposed mechanistic models separating active uptake from intrinsic metabolism in hepatocyte incubations [27,28]. Since the aim of such models is to extrapolate the experimentally determined uptake and clearance parameters to their in vivo equivalents, the next logical step is to incorporate them into a PBPK model, as has been done by Paine et al [29], and others. This differs from the approach of Pang and Durk [30], since the latter PBPK model further incorporates transporter processes, which are estimated from fitting to in vivo concentration data.…”

Functional Consequences of Active Hepatic Uptake on Cytochrome P450 Inhibition in Rat and Human Hepatocytes

“…The model includes terms for membrane and intracellular binding and for passive and active uptake into isolated rat hepatocytes. All the parameters were the same as those defined previously, including intracellular atorvastatin binding of 99% (Paine et al, 2008), except that the model was refined to incorporate saturation of the uptake process. A K m of 20 M was used for Fig.…”

“…As described previously, a physiologically based model was used to simulate the in vitro kinetics of atorvastatin (Paine et al, 2008). The model includes terms for membrane and intracellular binding and for passive and active uptake into isolated rat hepatocytes.…”