cefdinir and glycylsarcosine

Cefdinir (Omnicef; Abbott Laboratories) is a cephalosporin antibiotic primarily eliminated by the kidney. Nonlinear renal elimination of cefdinir has been previously reported. Cefdinir renal transport mechanisms were studied in the erythrocyte-free isolated perfused rat kidney. Studies were performed with drug-free perfusate and perfusate containing cefdinir alone to establish the baseline physiology and investigate cefdinir renal elimination characteristics. To investigate cefdinir renal transport mechanisms, inhibition studies were conducted by coperfusing cefdinir with inhibitors of the renal organic anion (probenecid), organic cation (tetraethylammonium), or dipeptide (glycylsarcosine) transport system. Cefdinir concentrations in biological samples were determined using reversed-phase high-performance liquid chromatography. Differences between treatments and controls were evaluated using analysis of variance and Dunnett's test. The excretion ratio (ER; the renal clearance corrected for the fraction unbound and glomerular filtration rate) for cefdinir was 5.94, a value indicating net renal tubular secretion. Anionic, cationic, and dipeptide transport inhibitors all significantly affected the cefdinir ER. With probenecid, the ER was reduced to 0.59, clearly demonstrating a significant reabsorptive component to cefdinir renal disposition. This finding was confirmed by glycylsarcosine studies, in which the ER was elevated to 7.95, indicating that reabsorption was mediated, at least in part, by the dipeptide transporter system. The effects of the organic cation tetraethylammonium, in which the ER was elevated to 7.53, were likely secondary in nature. The anionic secretory pathway was found to be the predominant mechanism for cefdinir renal excretion.

Topics: Animals; Biological Transport; Cefdinir; Cephalosporins; Chromatography, High Pressure Liquid; Dipeptides; Kidney; Male; Metabolic Clearance Rate; Probenecid; Protein Binding; Rats; Rats, Sprague-Dawley; Tetraethylammonium

The present study was undertaken to investigate the interaction of anionic cephalosporins (cefixime, ceftibuten, and cefdinir) with the renal peptide transporter (PEPT 2) and the intestinal peptide transporter (PEPT 1) using four different experimental model systems. In the first approach, the human colon carcinoma cell line Caco-2 which expresses PEPT 1 and the SHR rat kidney cell line SKPT which expresses PEPT 2 were used. The uptake of the dipeptide Gly-Sar mediated by PEPT 1 or PEPT 2 in these cells was inhibited significantly by the anionic cephalosporins, with the following order of potency: ceftibuten > cefixime > cefdinir. The inhibition was competitive in nature. Even though the order of potency was the same for PEPT 1 and PEPT 2, PEPT 1 exhibited much lesser sensitivity to inhibition than PEPT 2. In the second approach, the cloned human PEPT 1 and PEPT 2 were functionally expressed in HeLa cells following which the cells were used to study the interaction of anionic cephalosporins with PEPT 1 and PEPT 2. Again, Gly-Sar uptake mediated by the human PEPT 1 and PEPT 2 in HeLa cells was found to be inhibited by the anionic cephalosporins with the same order potency as in Caco-2 and SKPT cells. In the third approach, brush border membrane vesicles isolated from rat kidneys were employed. In this approach also it was found that PEPT 2-mediated Gly-Sar uptake was inhibited by cefixime and ceftibuten. In the fourth approach, the human PEPT 1 was expressed in Xenopus laevis oocytes and PEPT 1-mediated transport of ceftibuten was investigated directly by electrophysiological methods. Ceftibuten evoked inward currents in PEPT 1-expressing oocytes but not in water-injected oocytes, showing that the transport of the anionic cephalosporin via PEPT 1 is associated with transfer of positive charge. The ceftibuten-evoked currents were saturable with respect to ceftibuten concentration and were markedly dependent on membrane potential. It is concluded that anionic cephalosporins interact with the peptide transporters expressed in the intestine (PEPT 1) as well as in the kidney (PEPT 2).

Topics: Animals; Biological Transport; Caco-2 Cells; Carrier Proteins; Cell Line; Cephalosporins; Colon; Dipeptides; Evoked Potentials; HeLa Cells; Humans; Kidney; Microvilli; Oocytes; Peptide Transporter 1; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley; Symporters; Transfection; Xenopus laevis

PEPT1 and PEPT2 are H(+)-coupled peptide transporters expressed preferentially in the intestine and kidney, respectively, which mediate uphill transport of oligopeptides and peptide-like drugs such as beta-lactam antibiotics. In the present study, we have compared the recognition of beta-lactam antibiotics by LLC-PK1 cells stably transfected with PEPT1 or PEPT2 cDNA. Cyclacillin (aminopenicillin) and ceftibuten (anionic cephalosporin without an alpha-amino group) showed potent inhibitory effects on the glycylsarcosine uptake in the PEPT1-expressing cells. Other beta-lactams, such as cephalexin, cefadroxil, and cephradine (aminocephalosporins), inhibited modestly the PEPT1-mediated glycylsarcosine uptake. Except for ceftibuten, these beta-lactams showed much more potent inhibitions on the glycylsarcosine uptake via PEPT2 than via PEPT1. Comparison of the inhibition constant (Ki) values between cefadroxil and cephalexin suggested that the hydroxyl group at the NH2-terminal phenyl ring increased affinity for both PEPT1 and PEPT2. It is concluded that PEPT2 has a much higher affinity for beta-lactam antibiotics having an alpha-amino group than PEPT1 and that substituents at the NH2-terminal side chain of these drugs are involved in the recognition by both peptide transporters.

Topics: Animals; Anti-Bacterial Agents; Biological Transport; Carrier Proteins; Ceftibuten; Cephalosporins; Cyclacillin; Dipeptides; Hydrogen-Ion Concentration; Kidney; Kinetics; LLC-PK1 Cells; Peptide Transporter 1; Rats; Recombinant Proteins; Structure-Activity Relationship; Symporters; Transfection