Supplemental Analysis of the Prediction of Hepatic Clearance of Binary Mixtures of Bisphenol A and Naproxen Determined in an Isolated Perfused Rat Liver Model to Promote the Understanding of Potential Albumin-Facilitated Hepatic Uptake Mechanism

The hepatic clearance (CL) of bisphenol A (BPA) in the isolated perfused rat liver (IPRL) model has been studied for the impact of albumin (ALB) binding and coadministration with naproxen (NAP) in a companion manuscript (Bounakta et al. Xenobiotica. 2017;3:1-13.). We reported that the extrapolations of hepatic CL of BPA, NAP, and the binary mixtures between 2 ALB concentrations did not follow the free drug hypothesis; however, potential ALB-facilitated hepatic uptake mechanism(s) were highly suspected. Therefore, the objective of the present study was to reanalyze the IPRL data to provide a deeper quantitative extrapolation of CL; however, the focus was made on the impact of ALB binding on the intrinsic clearance (CLint) versus unbound CLint instead of only the global hepatic CL to verify whether the concept of ALB-facilitated hepatic uptake still holds for these 2 additional parameters for binary mixtures. Firstly, the variations in CLint that were observed between the IPRL model using no ALB and ALB in the perfusates were compared to the corresponding variations in the unbound fraction measured in the perfusates (fup) according to the free drug hypothesis, or to the variations in the fup values adjusted for potential ALB-facilitated uptake mechanism (i.e., fup-adjusted). The parameter fup-adjusted showed a greater predictability compared to fup (average fold error ∼ 1 vs. 5.2), suggesting that both the free and bound drug moieties should be available for hepatic uptake. Secondly, the supplemental data analysis showed a greater decrease in unbound Km than in Vmax resulting in increased uptake CLint of the unbound drug (Vmax/unbound Km) with increased ALB concentration at a given substrate concentration, which is compatible with an ALB-facilitated hepatic uptake mechanism. Interestingly, the unbound CLint increased by a factor that corresponds to the bound drug moiety also assumed available for hepatic uptake. These additional findings corroborate the recent literature. Overall, this study showed the importance of quantifying any differential of ALB concentration (in vitro vs. in vivo or hypoalbuminemia in vivo vs. hyperalbuminemia in vivo) in the IPRL-based, in vitro-to-in vivo or in vivo-to-in vivo extrapolation-based or physiologically based pharmacokinetics-based CL prediction of chemical-drug interactions between xenobiotics significantly bound to ALB.