PEPT2 immunolocalization and its role in cefadroxil renal tubular reabsorption and brain penetration.

Abstract

Given the nutritional, clinical, and pharmacological relevance of mammalian proton-coupled oligopeptide transporters (POTs), it is clear that membrane transporters offer a unique opportunity in drug design, delivery and targeting to select tissues. PEPT2, a member of the POT family, is expressed primarily in the kidney and brain. There, PEPT2 is believed to function in the reabsorption of peptides/mimetics from glomerular filtrate in kidney and in the maintenance of neuropeptide homeostasis in brain. However, there are multiple POTs in the kidney and brain and, as a result, it is uncertain how significant a role PEPT2 plays in these tissues. Using immunocytochemistry in rats, PEPT2 protein was expressed on the apical membrane of choroid plexus epithelia (adult and neonate), in neurons (adult and neonate) as well as in astrocytes (neonate but not adult). Using primary-cultured epithelial cells of rat choroid plexus, we demonstrated that cefadroxil, a clinically used peptide-like drug, had a preferential apical uptake and apical-to-basal transepithelial transport across choroid plexus epithelia. Moreover, we successively generated PEPT2-deficient mice by targeted gene disruption, and demonstrated that PEPT2 is the only member of the POT family responsible for peptide/mimetic uptake in choroid plexus. Finally, using wild type and PEPT2 null mice, the relative importance of PEPT2 in affecting the <italic>in vivo</italic> pharmacokinetics, tissue distribution and systemic exposure of cefadroxil was evaluated in the body. We demonstrated that PEPT2 is the predominant peptide transporter in kidney, that it acts as an efflux transporter at the blood-CSF barrier and that it has a dramatic effect on cefadroxil tissue distribution. In addition, the disposition kinetics of cefadroxil was clearly nonlinear, which is attributed to saturable renal tubular reabsorption and secretion of this aminocephalosporin antibiotic. The results of this research have advanced our understanding of the significance of PEPT2-mediated transport in the body (as opposed to other POT transporters) and provided rare insight into the variability of peptide/mimetic kinetics that might occur in human subjects with genetic polymorphisms. These results could have important implications in the design, delivery and tissue targeting of peptide-based pharmaceuticals.