A Study of Polarized Peptide Transporters in Caco-2 Cells : Characterization of AcPhe2 (NMePhe) NH2 and AcPhe (NMePhe)2 NH2
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Improved drug delivery through rational drug design has been a major focus of pharmaceutical research in recent years. A major approach to this outcome has been the critical analysis of membrane transport and the processes and mechanisms guiding it. preliminary experiments focused on the mechanisms of peptide transport across Caco-2 cells, an in vitro model of the human intestinal mucosa, showed that both passive and polarized active transport processes contributed to the transport of AcPhe(NMePhe)2NH2. The active component was found to be inhibited by verapamil. Further preliminary studies with a related peptide, AcPhe2(NMePhe)NH2, suggested the involvement of another non-verapamil inhibited system in addition to the verapamil sensitive one. Accordingly, the purpose of the present study was to determine whether or not AcPhe2(NMePhe)NH2 is transported by a non-verapamil inhibited transporter, and to characterize the transport of both AcPhe2(NMePhe)NH2 and AcPhe(NMePhe)2NH2. The experimental methods used were the bidirectional transflux and the apical efflux of compounds across Caco-2 cell monolayers. The transflux experiments demonstrated that the transport of ACPhe2(NMePhe)NH2 is not mediated by a non-verapamil inhibited transporter. The efflux studies showed that the passive permeability of ACPhe2(NMePhe)NH2 is lower than that of AcPhe(NMePhe)2NH2. Furthermore, preliminary estimates of the KM and Vmax values indicate that this peptide has a lower affinity for the transporter than does AcPhe(NMePhe)2NH2. A greater concentration of AcPhe(NMePhe)2NH2 is required to reach the transporter's maximal velocity. The results of this study should help elucidate the mechanisms behind peptide transport which will, in turn, lead to more efficient drug delivery.