Utility of Rat Liver Slices to Estimate Hepatic Clearance for Application in Physiologically Based Pharmacokinetic Modeling: A Study with Tolbutamide, a Compound with Low Extraction Efficiency

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Abstract
Liver slice experiments were performed to determine the slice intrinsic clearance and to extrapolate this to the in vivo liver intrinsic clearance in a physiologically based pharmacokinetic (PBPK)-like approach. Precision-cut liver slices were incubated with different initial concentrations of tolbutamide, and the time series of parent and metabolite concentrations were measured in slice and incubation medium. A mathematical model was built that modeled the uptake of tolbutamide and its metabolism in the liver slice. In addition, binding of tolbutamide to cellular constituents and partition over the water and lipid phase were accounted for by the model. Model analysis imposed sampling of parent compound in slice and of metabolites pooled from slice and medium. The model was calibrated to the data, fitting the intrinsic clearance, the parent compounds9 free fraction in liver material, and a diffusion parameter describing medium-slice exchange of tolbutamide. In addition, to ensure a meaningful application of the theoretical model, slice viability parameters were monitored before and during the experiment. For the different incubations, the intrinsic clearance per unit of volume of slice ranged from 0.035 to 0.086 min−1 when not correcting for slice viability and from 0.044 to 0.11 min−1 when correcting for slice viability. The results were extrapolated to a PBPK model for tolbutamide in the rat. The value for the intrinsic clearance found by calibrating the PBPK model to previous in vivo data was 0.090 min−1. This result suggests that liver slices are a valuable tool for predicting in vivo intrinsic clearance of low-extraction compounds.

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