Physiologically-based pharmacokinetic (PBPK) modeling of sodium fluorescein (SF) blood clearance for assessing hepatic ischemia-reperfusion injury (IRI)
Authors: Monti Christopher , Womack Justin , Audi Said , Hong Seung , Yang Yongqiang , Kim Joohyun , Dash Ranjan 
Published: May 2023

Rationale: Quantitative analysis of bile formation machinery has potential to assess the viability of a liver for transplantation. Recently, we demonstrated the utility of the fluorescent dye SF by showing that the bile-to-plasma fluorescence ratio inversely correlated with warm ischemia time in rats and associated this finding with IRI-induced intracellular internalization of the MRP2 transporter (PMID: 35700191). However, it is unclear how much SF is cleared by active MRP2 in relation to other contributing factors associated with complex in vivo physiology. We hypothesize that PBPK modeling can account for dominant vascular, tissue, and biochemical processes contributing to SF clearance, including MRP2 activity, and simulate diminished liver function in IRI leading to decreased disposition of SF in the bile. Methods: We considered previously published data of SF fluorescence intensity in blood, plasma, and bile over time in rats under control and IRI conditions. To model these data, we performed SF calibration experiments and converted these data from fluorescence to concentration using standard curves generated from nonlinear regression. We fit an empirical triple-exponential function to the calibrated control blood SF concentration data and used this function as an input for a mechanistic liver-centric PBPK model. The PBPK model accounts for three regions in the liver (blood, hepatocytes, bile) and major physiological processes, including kinetics of basolateral and canalicular transporters governing SF dynamics in different liver regions. We fit this model to the control SF concentration data in the bile using a pseudo-Monte Carlo strategy. Model parameters relating to maximal velocity for the transporters were allowed to vary, while all others were fixed to physiologic values. Results: The PBPK model was able to provide a good fit to control bile SF concentration data. The input model for blood SF concentration was able to predict plasma SF concentration related by a variable partition coefficient, which led to a large difference between plasma and blood SF concentrations at high SF concentrations but diminished at lower concentrations. We simulated the IRI condition by decreasing MRP2 activity, which showed that SF blood clearance through hepatocytes into bile is highly sensitive to changes in the activity of MRP2, consistent with our hypothesis that SF clearance data and PBPK modeling could quantify the effect of IRI on MRP2 activity. These simulations showed a larger decrease in SF concentration in bile relative to the increase in blood resulting in a lower bile-to-blood SF ratio. Conclusions: Based on our experimental data, we developed a liver-centric PBPK model for the blood clearance of SF through hepatocytes and bile and used this model to simulate the contribution of MRP2 to diminished secretion of SF into the bile as measured following IRI. MCW/BME-FP00022381 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.