Manuscript DMD-D-25-00346 The impact of glycocalyx on partitioning and distribution of basic drugs.

Concentrations of basic drugs are often overpredicted by physiologically based pharmacokinetic models at very early time points after intravenous dosing. An empirical shallow compartment in our recently published permeability- and perfusion-limited PermQ model improved the prediction of this observed early distribution. This study aimed to determine the impact of glycocalyx, a glycoprotein and glycolipid covering on membranes of red blood cells (RBCs) and endothelium, on the partitioning and distribution of basic drugs. Hyaluronidase (50 μg/mL), heparinase (5 U/mL), and neuraminidase (0.1 U/mL) were used to remove the glycocalyx from rat or human RBCs. Confocal microscopy was used to confirm glycocalyx disruption. RBC partitioning experiments were conducted to obtain partition coefficients (Kp) in RBCs and PBS buffer in the presence or absence of glycocalyx. Experimental Kp for metoprolol and atenolol were scaled with glycocalyx dimensions. The human PermQ model was used to simulate the concentration-time profiles, and results were compared with simulations with empirical Kp values. Confocal microscopy confirmed RBC glycocalyx modification via sialic acid removal. Significant differences were observed for metoprolol and atenolol Kp on human RBC glycocalyx disruption. Modeling suggests that experimental Kp scaled with glycocalyx dimensions, while underestimating empirical Kp estimates, required a similar scalar for both drugs. This underestimation may be due to various reasons, such as incomplete RBC glycocalyx disruption or the RBC glycocalyx being an inadequate surrogate for the endothelial glycocalyx. Our results support the hypothesis that glycocalyx partitioning may partially explain the early distribution of the basic drugs metoprolol and atenolol. SIGNIFICANCE STATEMENT: We explored whether basic drugs can partition into glycocalyx, as this partitioning may explain the observed early time point distribution profile of basic drugs. Erythrocyte glycocalyx was tested as a possible in vitro model for the endothelial cell glycocalyx. Results indicate that glycocalyx partitioning partially explains the observed data for atenolol and metoprolol in humans.