title: Cefaclor uptake by the proton-dependent dipeptide transport carrier of human intestinal Caco-2 cells and comparison to cephalexin uptake.
abstract: The human Caco-2 cell line spontaneously differentiates in culture to epithelial cells possessing intestinal enterocytic-like properties. These cells possess a proton-dependent dipeptide transport carrier that mediates the uptake of the cephalosporin antibiotic cephalexin (Dantzig, A.H. and Bergin, L. (1990) Biochim. Biophys. Acta 1027, 211-217). In the present study, the uptake of cefaclor was examined and found to be sodium-independent, proton-dependent, and energy-dependent. The initial rate of D-[3-phenyl-3H]cefaclor uptake was measured over a wide concentration range; uptake was mediated by a single saturable transport carrier with a Km of 7.6 mM and a Vmax of 7.6 nmol/min per mg protein and by a non-saturable component. Uptake was inhibited by dipeptides but not amino acids. The carrier showed a preference for the L-isomer. The effect of the presence of a 5-fold excess of other beta-lactam antibiotics was examined on the initial rates of 1 mM cefaclor and 1 mM cephalexin uptake. Uptake rates were inhibited by the orally absorbed antibiotics, cefadroxil, cefaclor, loracarbef, and cephradine and less so by the parenteral agents tested. The initial uptake rates of both D-[9-14C]cephalexin and D-[3-phenyl-3H]cefaclor were competitively inhibited by cephalexin, cefaclor, and loracarbef with Ki values of 9.2-13.2, 10.7-6.2, and 7.7-6.4 mM, respectively. Taken together, these data suggest that a single proton-dependent dipeptide transport carrier mediates the uptake of these orally absorbed antibiotics into Caco-2 cells, and provide further support for the use of Caco-2 cells as a cellular model for the study of the intestinal proton-dependent dipeptide transporter.
authors.affiliation: Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN 46285-0424.
authors.forename: A H
authors.initials: AH
authors.lastname: Dantzig
authors.forename: L B
authors.initials: LB
authors.lastname: Tabas
authors.forename: L
authors.initials: L
authors.lastname: Bergin
mesh_terms: D019297:2,4-Dinitrophenol; D000230:Adenocarcinoma; D000596:Amino Acids / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D001667:Binding, Competitive; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002433:Cefaclor / Q000378:metabolism*; D002506:Cephalexin / Q000378:metabolism*; D002511:Cephalosporins / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology; D004151:Dipeptides / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007414:Intestinal Neoplasms; D007422:Intestines / Q000187:drug effects; D007700:Kinetics; D009550:Nigericin / Q000494:pharmacology; D009840:Oligomycins / Q000494:pharmacology; D019810:Sodium Azide; D014407:Tumor Cells, Cultured
chemical_list: D000596:Amino Acids; D001386:Azides; D002352:Carrier Proteins; D002511:Cephalosporins; D004140:Dinitrophenols; D004151:Dipeptides; D009840:Oligomycins; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002433:Cefaclor; D019810:Sodium Azide; D002506:Cephalexin; D019297:2,4-Dinitrophenol; D009550:Nigericin