THE PREDOMINANT CONTRIBUTION OF OLIGOPEPTIDE TRANSPORTER PEPT1 TO INTESTINAL-ABSORPTION OF BETA-LACTAM ANTIBIOTICS IN THE RAT SMALL-INTESTINE

Although recent evidence suggests that certain beta-lactam antibiotics are absorbed via a specific transport mechanism, its nature is unclea r. To confirm whether peptide transport in the rat can be largely ascr ibed to the intestinal oligopeptide transporter PepT1, the transporter has been functionally characterized and its significance in the intes tinal absorption of beta-lactam antibiotics was evaluated. For evaluat ion of transport activity complementary RNA (cRNA) of rat PepT1 was sy nthesized in-vitro and expressed in Xenopus laevis oocytes. cRNA induc ed uptake of several beta-lactam antibiotics and the dipeptide [C-14]g lycylsarcosine; this was specifically inhibited by various dipeptides and tripeptides but nor by their constituent amino acids or by tetra-o r pentapeptides. The transport activity of PepT1 far beta-lactam antib iotics correlated well with their in-vivo intestinal transport and abs orption. Furthermore, mutual inhibitory effects on uptake were observe d between glycylsarcosine and beta-lactam antibiotics. Hybrid depletio n oi the functional expression of rat PepT1 in oocytes injected with r at intestinal epithelial total mRNA was studied, using an antisense ol igonucleotide corresponding to the 5'-coding region of PepT1. In oocyt es injected with rat mRNA pre-hybridized with the antisense oligonucle otide against rat PepT1, the uptake of [C-14]glycylsarcosine was almos t completely abolished, whereas its uptake was not influenced by a sen se oligonucleotide for the same region of PepT1. Similarly, the uptake of beta-Lactam antibiotics tvas also reduced by the antisense oligonu cleotide against rat PepT1. These results demonstrate that the intesti nal proton-coupled oligopeptide transporter PepT1 plays a predominant role in the carrier-mediated intestinal absorption of beta-lactam anti biotics and native oligopeptides in the rat.