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Oral delivery of therapeutic peptides is limited by degradation by digestive proteases and poor gastrointestinal permeability. We have investigated how physicochemical properties, including degree of lipidation and degree of amino acid sequence modification, along with formulation with a permeation enhancer (PE), influence the enzymatic stability and intestinal absorption of glucagon-like peptide-1(GLP-1) receptor agonists. We compared four peptides: J211 (non-lipidated; modified), J229 (mono-lipidated; modified), MEDI7219 (bis-lipidated; modified), and semaglutide (mono-lipidated control; least modified). J211, J229 and MEDI7219 have similar amino acid modifications in the peptide sequence to reduce the number of labile proteolytic sites. An in vitro head-to-head comparison between MEDI7219 and semaglutide showed that MEDI7219 was more proteolytically stable (% remaining after 90 min) than semaglutide, which was degraded completely within 10 min. Notably, co-formulation with sodium caprate (C10) improved semaglutide stability, and at least doubled its half-life. Results from in vivo studies in rats following intraduodenal bolus administration, showed that in the absence of C10, the absorption of all the peptides was minimal, with cumulative fractions absorbed below 1 % for all four compounds. Co-formulation with C10 increased the bioavailability of the modified peptides by 35-40-fold, with J211, J229, and MEDI7219 reaching 7.5 %, 4 %, and 17.3 % respectively. Semaglutide's bioavailability improved by similar to 200-fold, however bioavailability did not exceed 2 %. These results demonstrate that C10 enhances peptide absorption primarily by increasing intestinal permeability but also likely by improving enzymatic stability of a labile peptide like semaglutide. Furthermore, when comparing the three modified peptides, the degree of lipidation positively correlated with increased intestinal absorption in both the presence and absence of C10.