Caco-2 versus Caco-2/HT29-MTX co-cultured cell lines: Permeabilities via diffusion, inside- and outside-directed carrier-mediated transport

Purpose. The objective of this study was a systematic characterization and evaluation of cell culture models based on mixtures of Caco-2/HT29-MTX co-c ultures for their use in screening for drug absorption and intestinal perme ability in comparison to the properties of the respective mono-cultures. Methods. Go-cultures of Caco-2 cells (absorptive-type) and HT29-MTX cells ( goblet-type) were set up. Three different cocultures (initial seeding ratio s Caco-2/HT29-MTX: 90/10, 70/30, and 50/50) were grown on permeable filter supports, and monolayers were used for permeability studies with model comp ounds for paracellular absorption (atenolol, furosemide, H334/75, mannitol, terbutaline), transcellular absorption (antipyrine, ketoprofen, metoprolol , piroxicam), carrier-mediated absorption (D-glucose, Gly-Pro, and L-phenyl alanine) as well as substrates for carrier-mediated secretion via P-glycopr otein (cimetidine and talinolol). Electrophysiological and microscopic cont rols were performed to characterize the cell cultures. Results. For compounds undergoing passive intestinal absorption permeabilit ies were generally higher in co-cultures than in Caco-2 monolayers, yieldin g highest values in pure HT29-MTX monolayers. This difference was most obvi ous for compounds transported via the paracellular pathway, where HT29-MTX cells may be up to 30 times more permeable than Caco-2 cells, whereas for l ipophilic and highly permeable compounds, the difference in permeability va lues was less obvious. For drugs undergoing intestinal secretion mediated b y P-glycoprotein, co-cultivation of Caco-2 cells with HT29-MTX cells led to increased apical to basolateral permeability which was decreased in the op posite direction, consistent with the fact that HT29-MTX cells do not expre ss P-glycoprotein. When a carrier-mediated absorption mechanism is involved , the permeabilities observed were lower than the values reported for human small intestine and co-cultivation of HT29-MTX cells with Caco-2 cells res ulted in even lower values as compared to the plain Caco-2 cultures. Conclusions. Go-cultures of HT29-MTX and Caco-2 cells offer the opportunity of modifying the permeability barrier of the cell monolayers both with res pect to paracellular resistance and secretory transport via P-gp. Thus, in special cases, they allow more flexibility in adapting the in vitro system to the in vivo situation as compared to the monocultures. Another advantage is the obvious robustness of the method with respect to the reproducibilit y of the results. A problem remaining, however, is the quantitative express ion of carriers involved in intestinal uptake of many nutrients and drugs. (C) 2000 Wiley-Liss, Inc. and the American Pharmaceutical Association.