Clarification of transcellular transport mechanism of drugs utilizing tissue cultured cell systems

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Tissue cultured cells, which retain energy-dependent transport and metabolic functions in vivo, are useful as in vitro model to investigate drug transport at the cellular level. The purpose of the present research is to prove, by utilizing proper cultured cell systems, our new hypotheses, which are different from the passive diffusion mechanism for drug transports through the intestinal epithelial cells and brain capillary endothelial cells. The following results including several new findings were obtained :1)Utilizing cultured human intestinal cell line Caco-2, we have successfully proved that characteristics of the apical to basolateral transepithelial transport of [^<14>C]benzoic acid and[^<14>] salicylic acid in Caco-2 are very similar to those obtained for intestinal brush-border membrane vesicle and that the pH dependent intestinal-absorption of weak-acidic drugs is attributed not to the previously believed "pH-partition theory" but to "protoncoupled and carrier-mediated transpo … More rt" for monocarboxylic acids.2)A heterologous gene expression system, Xenopus laevis oocytes injected with mRNA from the intestinal mucosa, were used to prove the carrier-mediated transport of beta-lactam amtibiotics in small intestine. As the results, the intestinal transport of zwitterionic and dicarboxylic-acid beta-lactam antibiotics was confirmed to be mediated by a specialized transport system which is common to dipeptides. beta-lactam antibiotics were also to be transported by carrier-mediated mechanisms in rabbits and humans as well as rats.3)The uptake of [^3H]vincristine (VCR) and [^3H]cyclosporin A(CsA) by cultured monolayrs of bovine brain capillary endothelial cells (BCECs), which express P-glycoprotein (P-gp) at the luminal membrane sruface, was significantly enhanced by treatment of MDR reversing agents, an anti-P-gp monoclonal antibody and metabolic inhibitors. These results indicate that low permeability of VCR and CsA into the brain is caused by the active efflux from BCEC by P-gp and suggest that P-gp functions as blood-brain barrier for lipophilic and cytotoxic comounds. Less