Whole-Body PBPK Modeling of Biliary Sodium Fluorescein Clearance Quantifies Liver Viability Biomarkers of In Vivo Hepatic Ischemia-Reperfusion Injury

Rationale: Physiologically based pharmacokinetic (PBPK) modeling of biliary excretion of fluorescence markers offers a translational strategy to quantitatively assess liver viability in transplantation. In our previous experimental study, we showed that the bile-to-blood fluorescence ratio of sodium fluorescein (SF) inversely correlates with hepatic warm ischemia time in rats and is associated with intracellular internalization of MRP2 during ischemia-reperfusion injury (IRI). To mechanistically interpret these findings, we previously developed a liver-centric PBPK model with blood, hepatocyte, and bile regions that simulated MRP2-mediated excretion of SF into bile; however, this model did not capture the whole-body distribution or elimination of SF. To overcome these limitations and assess systemic impacts of hepatic IRI, we expanded the model to a whole-body PBPK framework. Methods: We developed a whole-body PBPK model with 10 regions: mixed venous blood; rest-of-body high-perfusion and low-perfusion blood and tissue; kidney blood and tissue; liver blood and tissue; and bile. To capture sequestration by albumin and other plasma proteins, binding proteins for SF and its metabolite SF-glucuronate (SFG) were included in all blood regions. This expanded PBPK framework captures systemic SF kinetics and organ-level distribution/elimination processes. Organ volumes, blood flows, and transport processes were based on rat physiology. Previously published fluorescence data for SF in blood and bile under control and hepatic IRI conditions were converted to SF concentration units using calibration curves. Active hepatic transport, including MRP2-mediated canalicular SF excretion, was modeled mechanistically. Unknown parameters were estimated using a randomized multi-start optimization approach, while remaining parameters were fixed to physiologic values. Results: The whole-body PBPK model accurately fit the blood and bile SF concentration data in control animals. Sensitivity analysis identified MRP2-mediated transport as the dominant determinant of SF disposition, followed by intracellular conversion of SF to SFG within hepatocytes. Simulated IRI conditions implemented by reducing MRP2 activity produced decreased biliary SF excretion and elevated blood SF levels, yielding a diminished bile-to-blood SF ratio. These simulations support the hypothesis that reduced MRP2 function is a key driver of impaired biliary SF excretion during hepatic IRI. Conclusions: By extending our prior liver-centric PBPK model to a physiologically detailed whole-body PBPK framework, we demonstrate the systemic impact of hepatic transporter dysfunction during IRI. This whole-body PBPK model links altered hepatic MRP2 activity to changes in systemic SF disposition and provides a quantitative tool for assessing organ-specific and systemic PK for fluorescent markers. This framework supports future translational applications in liver function assessment, therapeutic evaluation, and extrapolation to human physiology via allometric scaling. Funding: NIH R01 HL151587 and NSF DMS 2153387. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.