Abstract

The proton-coupled oligopeptide transporter (PEPT1) has been shown to mediate mucosal cell transport of di- and tripeptide, and some peptidomimetic drugs. In this study, we determined the correlation between PEPT1 protein expression and the permeability of cephalexin, a substrate of PEPT1, in human PEPT1 (hPEPT1)-overexpressed Caco-2 cells (Caco-2/hPEPT1 cells) and rat jejunum. Caco-2/hPEPT1 cells with various levels of hPEPT1 expression were established by an adenoviral transfection system. The effective intestinal permeability (P_eff) in rat jejunum was evaluated using a single pass in situ perfusion method. The level of PEPT1 in Caco-2/hPEPT1 cells and rat intestinal mucosal samples was quantitated by densitometry after immunoblotting and enhanced chemiluminescence detection. In Caco-2/hPEPT1 cells, an excellent correlation was observed between cephalexin uptake and hPEPT1 expression (R² = 0.96, P < 0.005). This demonstrates that cephalexin uptake is directly proportional to hPEPT1 expression. In the rat perfusion study, the mean P_eff ± S.D. (n = 15) of cephalexin was 3.89 ± 1.63 × 10⁻⁵ cm/s. A very significant correlation between PEPT1 expression and cephalexin permeability with an R² = 0.63 (P < 0.001) was observed. This indicates that the variation in PEPT1 expression is one of the major factors accounting for variable intestinal cephalexin absorption. To our knowledge, this is the most direct evidence that variation of PEPT1 expression is correlated with absorption permeability variation of peptide-like compounds in vitro and in vivo.