Correlation between epithelial cell permeability of cephalexin and expression of intestinal oligopeptide transporter

The proton-coupled oligopeptide transporter (PEPT1) has been shown to media te mucosal cell transport of di- and tripeptide, and some peptidomimetic dr ugs. In this study, we determined the correlation between PEPT1 protein exp ression and the permeability of cephalexin, a substrate of PEPT1, in human PEPT1 (hPEPT1)-overexpressed Caco-2 cells (Caco-2/hPEPT1 cells) and rat jej unum. Caco-2/hPEPT1 cells with various levels of hPEPT1 expression were est ablished by an adenoviral transfection system. The effective intestinal per meability (P-eff) in rat jejunum was evaluated using a single pass in situ perfusion method. The level of PEPT1 in Caco-2/h1PEPT1 cells and rat intest inal mucosal samples was quantitated by densitometry after immunoblotting a nd enhanced chemiluminescence detection. In Caco-2/hPEPT1 cells, an excelle nt correlation was observed between cephalexin uptake and hPEPT1 expression (R-2 = 0.96, P < 0.005). This demonstrates that cephalexin uptake is direc tly proportional to hPEPT1 expression. In the rat per-fusion study, the mea n P-eff +/- S.D. (n = 15) of cephalexin was 3.89 +/- 1.63 x 10(-5) cm/s. A very significant correlation between PEPT1 expression and cephalexin permea bility with an R-2 = 0.63 (P < 0.001) was observed. This indicates that the variation in PEPT1 expression is one of the major factors accounting for v ariable intestinal cephalexin absorption. To our knowledge, this is the mos t direct evidence that variation of PEPT1 expression is correlated with abs orption permeability variation of peptide-like compounds in vitro and in vi vo.