Inhibitory effect of zinc on PEPT1-mediated transport of glycylsarcosine and beta-lactam antibiotics in human intestinal cell line Caco-2.

The aim of this study was to examine the effects of zinc on the intestinal peptide transporters (PEPT1 and basolateral peptide transporter) and to elucidate the mechanism of the interactions. Caco-2 cells were pretreated with zinc, and the uptake studies were carried out. Zinc treatment resulted in the inhibition of [14C]glycylsarcosine (Gly-Sar) uptake via PEPT1 in a concentration-dependent manner, whereas it showed moderate inhibitory effect on the basolateral peptide transporter. Zinc also inhibited the uptake of oral beta-lactam antibiotics such as ceftibuten and cephradine by PEPT1. Kinetic analysis showed that zinc treatment increased Km values without affecting Vmax values of the [14C]Gly-Sar uptake. The inhibition of [14C]Gly-Sar uptake induced by zinc was observed in the presence of an H+ gradient but not in the absence of an H+ gradient. These results indicate that zinc is a competitive inhibitor of PEPT1. Zinc inhibited the PEPT1 function, possibly by interacting with histidine residues of PEPT1 that are part of an H+-binding site. These findings would provide important information for clinical, physiologic, and biochemical aspects of peptide transporters.