Mechanisms of cefadroxil uptake in the choroid plexus: studies in wild-type and PEPT2 knockout mice.
The choroid plexus uptake of [(3)H]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 (37 degrees C), the uptake of 1 microM 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 microM, and K(d) = 0.0069 microl/mg/min; in the presence of p-aminohippurate, the parameters were: V(max) = 4.1 pmol/mg/min, K(m) = 27 microM, and K(d) = 0.0064 microl/mg/min. In null animals, the kinetic parameters of cefadroxil (without p-aminohippurate) were: V(max) = 2.7 pmol/mg/min, K(m) = 110 microM, and K(d) = 0.0084 microl/mg/min; in the presence of p-aminohippurate, only a K(d) = 0.010 microl/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.
Department of Pharmaceutical Sciences, University of Michigan, Ann Arbor, MI 48109-0504, USA.
Scott M
SM
Ocheltree
Hong
H
Shen
Yongjun
Y
Hu
Jianming
J
Xiang
Richard F
RF
Keep
David E
DE
Smith
D000818:Animals; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D001693:Biological Transport, Active; D002434:Cefadroxil / Q000493:pharmacokinetics*; D002831:Choroid Plexus / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D051379:Mice; D018345:Mice, Knockout; D027981:Symporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D000900:Anti-Bacterial Agents; D027981:Symporters; C093694:hydrogen-coupled oligopeptide transporter PepT2; D002434:Cefadroxil