Mechanisms of cefadroxil uptake in the choroid plexus: Studies in wild-type and PEPT2 knockout mice

The choroid plexus uptake of [H-3] cefadroxil was studied in peptide transporter 2 (PEPT2) wild-type and null mice as a function of temperature, transport inhibitors, pH, and saturability. At normal pH (7.4) and temperature (37degreesC), the uptake of 1 muM cefadroxil was reduced by 83% in PEPT2(-/-) mice as compared with PEPT2(+/+) mice (p<0.001). A further reduction was achieved in null animals by reducing the temperature to 4 degrees C, or by adding saturating concentrations of unlabeled cefadroxil or p-aminohippurate (p<0.05). Glycylsarcosine coadministration could inhibit the uptake of cefadroxil in PEPT2(+/+) mice (p<0.01) but not PEPT2(-/-) mice. Although a proton-stimulated uptake of cefadroxil was demonstrated in PEPT2(+/+) mice (pH 6.5 versus pH 7.4; p<0.01), no pH dependence was observed in PEPT2(-/-) mice. Kinetic parameters for cefadroxil (without p-aminohippurate) in wild-type mice were: V-max=5.4 pmol/mg/min, K-m=34 muM, and K-d=0.0069 mul/mg/min; in the presence of p-aminohippurate, the parameters were: V-max=4.1 pmol/mg/min, K-m=27 muM, and K-d=0.0064 mul/mg/min. In null animals, the kinetic parameters of cefadroxil (without p-aminohippurate) were: V-max=2.7 pmol/mg/min, K-m=110 muM, and K-d=0.0084 mul/mg/min; in the presence of p-aminohippurate, only a K-d=0.010 mul/mg/min was observed. Based on kinetic and inhibitor analyses, it was determined that (under linear conditions), 80 to 85% of cefadroxil's uptake in choroid plexus is mediated by PEPT2, 10 to 15% by organic anion transporter(s), and 5% by nonspecific mechanisms. These findings demonstrate that PEPT2 is the primary transporter responsible for cefadroxil uptake in the choroid plexus. Moreover, the data suggest a role for PEPT2 in the clearance of peptidomimetics from cerebrospinal fluid.