Peptide transporters: Structure, function, regulation and application for drug delivery

Proton-coupled peptide transporters, localized at brush-border membranes of intestinal and renal epithelial cells, play important roles in protein absorption and the conservation of peptide-bound amino nitrogen. These transporters also have significant pharmacological and pharmacokinctic relevance to the transport of various peptide-like drugs such as beta-lactam antibiotics. The identification and molecular characterization of H+/peptide cotransporters (PEPT1 and PEPT2) have facilitated the clarification of many aspects of these transporters such as the structure/function relationship and regulation. Recent findings that intestinal PEPT1 can transport L-valine ester prodrugs such as valacyclovir provided a major step forward toward the development of novel drug delivery systems. It has been demonstrated that peptide transporters, which have a similar substrate specificity to PEPT1 and PEPT2, but possess other distinct functional properties, are localized at basolateral membranes of intestinal and renal epithelial cells. This review highlights the recent advances in our knowledge of the cellular and molecular nature of PEPT1, PEPT2 and the basolateral peptide transporters.