PT  - JOURNAL ARTICLE
AU  - Huadong Sun
AU  - K. Sandy Pang
TI  - Permeability, Transport, and Metabolism of Solutes in Caco-2 Cell Monolayers: A Theoretical Study
AID  - 10.1124/dmd.107.015321
DP  - 2008 Jan 01
TA  - Drug Metabolism and Disposition
PG  - 102--123
VI  - 36
IP  - 1
4099  - http://dmd.aspetjournals.org/content/36/1/102.short
4100  - http://dmd.aspetjournals.org/content/36/1/102.full
SO  - Drug Metab Dispos2008 Jan 01; 36
AB  - We explored the properties of a catenary model that includes the basolateral (B), apical (A), and cellular compartments via simulations under linear and nonlinear conditions to understand the asymmetric observations arising from transporters, enzymes, and permeability in Caco-2 cells. The efflux ratio (EfR; Papp,B→A/Papp,A→B), obtained from the effective permeability from the A→B and B→A direction under linear conditions, was unity for passively permeable drugs whose transport does not involve transporters; the value was unaffected by cellular binding or metabolism, but increased with apical efflux. Metabolism was asymmetric, showing lesser metabolite accrual for the B→A than A→B direction because of inherent differences in the volumes for A and B. Moreover, the net flux (total - passive permeation) due to saturable apical efflux, absorption, or metabolism showed nonconformity to simple Michaelis-Menten kinetics against CD,0, the loading donor concentration. EfR values differed with saturable apical efflux and metabolism (>1), as well as apical absorption (EfRs <1), but approached unity with high passive diffusive clearance (CLd) and increasing CD,0 at a higher degree of saturation of the process. The Jmax (apparent Vmax estimated for the carrier system) and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{m}}^{{^\prime}}\) \end{document} [or the \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{m}}^{{^{\prime\prime}}}\) \end{document} based on a modified equation with the Hill coefficient (β)] estimates from the Eadie-Hofstee plot revealed spurious correlations with the assigned Vmax and Km. The sampling time, CLd, and parameter space of Km and Vmax strongly influenced both the correlation and accuracy of estimates. Improved correlation was found for compounds with high CLd. These observations showed that the catenary model is appropriate in the description of transport and metabolic data in Caco-2 cells. The American Society for Pharmacology and Experimental Therapeutics