OLIGOPEPTIDE TRANSPORTER MEDIATED UPTAKE AND TRANSPORT OF D-ASP(OBZL)-ALA, D-GLU(OBZL)-ALA, AND D-SER(BZL)-ALA IN FILTER-GROWN CACO-2 MONOLAYERS

The oligopeptide transporter, which contributes to the absorption of d i-/tri-peptides and various peptidomimetic compounds across intestinal epithelia, is expressed in mature Caco-2 monolayers. It was shown in our previous report that beta-esterified D-Asp(OBzl)-Ala is efficientl y transported across Caco-2 monolayers via the oligopeptide transporte r (Taub et al., Int. J. Pharmaceutics 146, 1997b, 205-212). In this pa per we demonstrate that two additional peptidase resistant side-chain modified dipeptides, D-Glu(OBzl)-Ala and D-Ser(Bzl)-Ala, are also subs trates for the Caco-2 oligopeptide transporter. These three modified d ipeptides, chosen due to their sequential difference in number of CH, groups in the side-chain, demonstrate different affinity (IC50) and ap parent permeability (P-app) values, uptake profiles, and pH-mediated r elease of the benzyl group. Both uptake and transport of D-Asp(OBzI)-A la, D-Glu(OBzl)-Ala, and D-Ser(Bzl)-Ala in Caco-2 monolayers are > 90% inhibitable by the presence of a 20-fold molar excess of Gly-Pro in t he apical chamber. The P-app of D-Asp(OBzl)-Ala is nearly 2-fold great er than that of D-Glu(OBzl)-Ala and 4-fold greater that that of D-Ser( Bzl)-Ala. The half-life (t(1/2)) for the release of benzyl alcohol (BZ -OH) from each dipeptide is also variable; D-Asp(OBzl)-Ala is labile a t pH 6.0 and 7.4 (t(1/2) = 26.1 and 7.8 h, respectively), while D-Glu( OBzl)Ala is extremely stable at pH 6.0 but unstable at pH 7.4 (t(1/2) > 96 and 2.1 h, respectively). D-Ser(Bzl)-Ala, which has a hydrolysis resistant ether linkage rather than a hydrolysis sensitive eater-linke d benzyl group, is highly stable (t(1/2) > 96 h at both pH 6.0 and 7.4 ). These data indicate that it is possible to construct various side-c hain modified, peptidase resistant dipeptides having not only differen t oligopeptide transporter mediated permeability profiles, but also di fferent release characteristics for the attached side-chain moiety. (C ) 1998 Elsevier Science B.V. All rights reserved.