Significance of Basal Membrane Permeability of Epithelial Cells in Predicting Intestinal Drug Absorption

by Selleckchem | Mar 15 2023

Drug absorption from the gastrointestinal tract is often restricted by efflux transport by P-glycoprotein (P-gp) and metabolism by CYP3A4. Both localize in the epithelial cells, and thus, their activities are directly affected by the intracellular drug concentration, which should be regulated by the ratio of permeability between apical (A) and basal (B) membranes. In this study, using Caco-2 cells with forced expression of CYP3A4, we assessed the transcellular permeation of A-to-B and B-to-A directions and the efflux from the preloaded cells to both sides of 12 representative P-gp or CYP3A4 substrate drugs and obtained the parameters for permeabilities, transport, metabolism, and unbound fraction in the enterocytes (fent) using simultaneous and dynamic model analysis. The membrane permeability ratios for B to A (RBA) and fent varied by 8.8-fold and by more than 3000-fold, respectively, among the drugs. The RBA values for digoxin, repaglinide, fexofenadine, and atorvastatin were greater than 1.0 (3.44, 2.39, 2.27, and 1.90, respectively) in the presence of a P-gp inhibitor, thus suggesting the potential involvement of transporters in the B membrane. The Michaelis constant for quinidine for P-gp transport was 0.077 µM for the intracellular unbound concentration. These parameters were used to predict overall intestinal availability (FAFG) by applying an intestinal pharmacokinetic model, advanced translocation model (ATOM), in which permeability of A and B membranes accounted separately. The model predicted changes in the absorption location for P-gp substrates according to its inhibition, and FAFG values of 10 of 12 drugs, including quinidine at varying doses, were explained appropriately. SIGNIFICANCE STATEMENT: Pharmacokinetics has improved predictability by identifying the molecular entities of metabolism and transport and by using mathematical models to appropriately describe drug concentrations at the locations where they act. However, analyses of intestinal absorption so far have not been able to accurately consider the concentrations in the epithelial cells where P-glycoprotein and CYP3A4 exert effects. In this study, the limitation was removed by measuring the apical and basal membrane permeability separately and then analyzing these values using new appropriate models.

Comments：

This study aimed to assess drug absorption from the gastrointestinal tract by investigating the role of P-glycoprotein (P-gp) and CYP3A4 in restricting drug absorption. Both are efflux transporters and localize in the epithelial cells, which are directly affected by the intracellular drug concentration. The study used Caco-2 cells with forced expression of CYP3A4 to assess the transcellular permeation of A-to-B and B-to-A directions and the efflux from the preloaded cells to both sides of 12 representative P-gp or CYP3A4 substrate drugs. The study obtained parameters for permeabilities, transport, metabolism, and unbound fraction in the enterocytes (fent) using simultaneous and dynamic model analysis.

The study found that the membrane permeability ratios for B to A (RBA) and fent varied significantly among the drugs. The RBA values for digoxin, repaglinide, fexofenadine, and atorvastatin were greater than 1.0 in the presence of a P-gp inhibitor, suggesting the potential involvement of transporters in the B membrane. The Michaelis constant for quinidine for P-gp transport was also measured.

The parameters obtained from the study were used to predict overall intestinal availability (FAFG) by applying an intestinal pharmacokinetic model, advanced translocation model (ATOM), which accounted for the permeability of A and B membranes separately. The model predicted changes in the absorption location for P-gp substrates according to its inhibition, and FAFG values of 10 of 12 drugs, including quinidine at varying doses, were explained appropriately.

Overall, the study showed that assessing the permeability of A and B membranes separately can improve the accuracy of predicting drug absorption in the gastrointestinal tract, and that accounting for the intracellular drug concentration can help better understand the role of transporters and enzymes in restricting drug absorption.