The intestinal peptide carrier: A potential transport system for small peptide derived drugs

Several laboratories have recently shown that many peptides and peptide-type drugs are absorbed in the small intestine via the peptide transporter for nutrient di-and tripeptides. The peptide carrier has a broad substrate specificity and can provide an efficient route for the absorption of peptide drugs that may not readily penetrate the lipophilic intestinal membrane. The peptide carrier is an active transport system that is H+-coupled, dependent on metabolic energy, saturable and concentration dependent, and that exhibits mutual inhibition of transport among the compounds. Studies of peptide transport are less advanced than for amino acids and there is no general agreement about the absolute number of transporters, the mechanism for basolateral efflux, and the distribution of the carrier(s) along the gastrointestinal tract. The recent successful cloning of the intestinal peptide transport system will contribute to characterize the structural requirements for potential substrates and may aid the development of effective oral drugs in this structural class.