PURPOSE: This study was aimed at examining the extent and mechanism of uptake of cobalamin (Cbl)-conjugated peptides in vitro and in vivo. METHODS: To enable acquisition of quantitative absorption data of Cbl-peptides, metabolically stable octapeptides (DP3), with (Cbl-Hex-DP3) or without a hexyl spacer (Cbl-DP3), were coupled to Cbl and radiolabeled. For comparison, LHRH coupled to Cbl was used as metabolically susceptible peptide. Biological recognition of Cbl-peptides was studied in the physiological order: binding by Intrinsic Factor (IF), recognition and transport of the IF-complexes by IF-Cbl receptors (IFCR) on Caco-2 monolayers and oral absorption of the Cbl-conjugates in the rat. RESULTS: All Cbl-peptides bound to IF and the IF-complexes were recognized by IFCR receptors on Caco-2 monolayers. Binding was saturable and could be inhibited by a 20-fold excess of IF-Cbl, but not of Non-intrinsic Factor (NIF)-Cbl. Oral administration of these ligands to rats resulted in absorption of 53%, 45%, 42%, and 23% of the applied radioactivity for Cbl, Cbl-LHRH, Cbl-Hex-DP3, and Cbl-DP3, respectively. Simultaneous administration of a >10(5)-fold excess of unlabeled Cbl reduced uptake of all compounds to <4%. Tissue distribution and elimination of the metabolically stable Cbl-conjugates were comparable to Cbl. CONCLUSIONS: The endogenous Cbl uptake pathway can be exploited for oral peptide delivery as indicated by the specific and high (40-45%) uptake of metabolically stable Cbl-coupled octapeptides.
PURPOSE: This study was aimed at examining the extent and mechanism of uptake of cobalamin (Cbl)-conjugated peptides in vitro and in vivo. METHODS: To enable acquisition of quantitative absorption data of Cbl-peptides, metabolically stable octapeptides (DP3), with (Cbl-Hex-DP3) or without a hexyl spacer (Cbl-DP3), were coupled to Cbl and radiolabeled. For comparison, LHRH coupled to Cbl was used as metabolically susceptible peptide. Biological recognition of Cbl-peptides was studied in the physiological order: binding by Intrinsic Factor (IF), recognition and transport of the IF-complexes by IF-Cbl receptors (IFCR) on Caco-2 monolayers and oral absorption of the Cbl-conjugates in the rat. RESULTS: All Cbl-peptides bound to IF and the IF-complexes were recognized by IFCR receptors on Caco-2 monolayers. Binding was saturable and could be inhibited by a 20-fold excess of IF-Cbl, but not of Non-intrinsic Factor (NIF)-Cbl. Oral administration of these ligands to rats resulted in absorption of 53%, 45%, 42%, and 23% of the applied radioactivity for Cbl, Cbl-LHRH, Cbl-Hex-DP3, and Cbl-DP3, respectively. Simultaneous administration of a >10(5)-fold excess of unlabeled Cbl reduced uptake of all compounds to <4%. Tissue distribution and elimination of the metabolically stable Cbl-conjugates were comparable to Cbl. CONCLUSIONS: The endogenous Cbl uptake pathway can be exploited for oral peptide delivery as indicated by the specific and high (40-45%) uptake of metabolically stable Cbl-coupled octapeptides.
Authors: W Kramer; G Wess; G Neckermann; G Schubert; J Fink; F Girbig; U Gutjahr; S Kowalewski; K H Baringhaus; G Böger Journal: J Biol Chem Date: 1994-04-08 Impact factor: 5.157
Authors: Hesham H Salman; Carlos Gamazo; P Chris de Smidt; Gregory Russell-Jones; Juan M Irache Journal: Pharm Res Date: 2008-08-05 Impact factor: 4.200