| The peptide transporters PEPT1 and PEPT2 have become increasingly recognized over the past ten years as being important in drug design, delivery and the disposition of peptides/mimetics. The focus of this research was: (1) to examine the mechanisms of intestinal absorption and renal reabsorption of orally active ACE inhibitors (fosinopril and zofenopril) in cultured cell lines expressing the intestinal PEPT1 (Caco-2 cells) and renal PEPT2 (SKPT cells) peptide transporters, and (2) to study the role of PEPT2 in peptide/mimetic trafficking at the blood-CSF barrier in rat choroid plexus epithelial cells in primary culture.; In the first study, we found that fosinopril and zofenopril inhibited the uptake of GlySar in a competitive manner in both cell lines. Furthermore, intracellular accumulation of fosinpril was higher from apical vs. basolateral surfaces of the membrane, as was the apical-to-basal flux of drug. The apical peptide transporter had a significantly greater affinity for fosinopril than did the basolateral peptide transporter. Our results suggest that distinct peptide transporters exist at the basolateral and apical membranes, and that they play an important role in modulating the intestinal absorption and renal reabsorption of peptides and peptide-like drugs.; In the second study, rat choroid plexus epithelial cells primary culture system was characterized in primary culture. PEPT2, but not PEPT1, was found in choroid plexus cell cultures by immunoblot analysis. GlySar accumulation was higher from the apical vs. basal side and was stimulated by an inwardly-directed proton gradient. The Michaelis constant of GlySar, from apical membranes, was consistent with the high-affinity properties of PEPT2. Indirect immunofluorescent localization with laser scanning confocal microscopy demonstrated that PEPT2, but not PEPT1, was primarily confined to the apical and subapical membrane regions. Combining the results from immunoblot analyses, confocal microscopy and GlySar uptake studies, it appears that PEPT2, but not PEPT1, is expressed at the apical membrane of choroid plexus epithelium. The data suggest that PEPT2 may have a role as an efflux pump for peptides/mimetics from CSF into blood. |
