Modeling of P-glycoprotein-involved epithelial drug transport in MDCK cells

Abstract

P-glycoprotein (P-gp) on the apical membranes of epithelial cells is known as a drug efflux pump. However, unclear is its integral quantitative role in the overall epithelial drug transfer, which also involves distinct diffusion processes in parallel and sequence. We used a simple three-compartment model to obtain kinetic parameters of each drug transfer mechanism, which can quantitatively describe the transport time courses of P-gp substrates, digoxin and vinblastine, across P-gp-expressing MDCK cell monolayers grown on permeable filters. Our results show that the model, which assumes a functionally single drug efflux pump in the apical membrane with diffusion across two membranes and intercellular junctions, is the least complex model with which to quantitatively reproduce the characteristics of the data. Interestingly, the model predicts that the MDCK apical membranes are less diffusion permeable than the basolateral membrane for both drugs and that the distribution volume of vinblastine is 10-fold higher than that of digoxin. Additional experiments verified these model predictions. The modeling approach is feasible to quantitatively describe overall kinetic picture of epithelial drug transport. Further model refinement is necessary to incorporate other modes of drug transport such as transcytosis. Also, whether P-gp solely accounts for the pump function in this model awaits more studies.

Permeability, Transport, and Metabolism of Solutes in Caco-2 Cell Monolayers: A Theoretical Study

“…Additional data on metabolite transport or metabolic data are absolutely necessary and would greatly add to the accuracy of the fit. The model was able to describe saturable efflux (Ito et al, 1999), saturable apical absorption, and basolateral influx (Irie et al, 2004), and recently, saturable metabolism and substrate inhibition (H. Sun, L. Zhang, E. C. Chow, G. Lin, K. S. Pang, and Z. Zuo, unpublished data). Proper data interpretation with the catenary model would definitely remove the bias in parameter estimates, avoid viewing the Caco-2 cell monolayer as a single barrier, and provide accurate estimates.…”

“…A catenary model similar to those used by others (Ito et al, 1999;Tam et al, 2003;Irie et al, 2004;González-Alvarez et al, 2005) was employed to appraise various aspects of the effective permeability, efflux ratio, and data interpretation on transporters and enzymes in Caco-2 monolayers. The model comprised the absorptive and ABC transporters of the apical membrane and influx and efflux barriers at the basolateral membrane as two sets of potential barriers.…”

“…We are of the view that the single-barrier model for the Caco-2 cell monolayer is inadequate and that a catenary model comprising basolateral (B), apical (A), and cellular compartments (Ito et al, 1999;Tam et al, 2003;Irie et al, 2004;González-Alvarez et al, 2005) is more appropriate than what routine analyses subscribe, especially under nonlinear conditions. Given the importance of the Caco-2 system in drug discovery and development, we explored properties of the catenary model to gain a mechanistically based understanding of the asymmetric observations arising from transporters, enzymes, and effective permeability under both linear and nonlinear conditions.…”

Property-based design of a glucosylceramide synthase inhibitor that reduces glucosylceramide in the brain

“…However, because of the importance of MDR1 in determining brain penetration of many therapeutics ( 9 ), a second assay was used to assess MDR1 interactions by determining whether GCS inhibitors increased [ 3 H]vinblastine uptake into MDR-MDCKII cells. Vinblastine is an MDR substrate and evidence indicates that MDR is the sole/predominant effl ux mechanism present for vinblastine in MDR-MDCKII cells ( 27,28 ]vinblastine assay measures whole cell uptake, whereas the effective concentration for inhibition of GCS is the drug level at the outer Golgi membrane. However, these compounds are also cationic amphiphilic drugs that are protonated under the acidic conditions and trapped in the lysosome where they may exert other effects.…”

Decrease in Intracellular Concentration Causes the Shift in Km Value of Efflux Pump Substrates

“…1) was constructed with Stella 8.1.4 software (isee systems, Lebanon, NH) to simulate mass flow in a permeability experiment. Three-compartment models have been used to simulate in vitro permeability experiments (Ito et al, 1999;González-Alvarez et al, 2005). We introduce an apparent cellular distribution coefficient (K ϭ M bound /M free ) to the model.…”