The role of biorelevant media components on the diffusion and enzymatic stability of oral cyclic peptide analogs.

Despite significant advances in the design and development of peptide molecules, oral delivery remains a major challenge. Biorelevant colloids, composed of bile salts and phospholipids (PL), forming bile acid-phospholipid mixed micelles (BAPMM), are a critical factor that may influence the behavior of orally administered peptides. The role of biorelevant media composition in the absorption of peptide drugs remains underexplored. In this work, we investigated how BAPMM composition affects peptide-micelle interactions, focusing on the impact of bile salt hydroxylation state and phospholipid concentration. Amino acid-substituted analogs of octreotide (water-soluble cyclic octapeptide) were used as model molecules. In vitro experiments included measuring flux rates through a porous cellulose dialysis membrane and assessing pancreatic enzymatic stability. Additionally, a generalized linear regression model was used to identify the main factors and cofactors that may influence the observed membrane flux. Based on the data, the most important factor affecting flux rate is attributed to the interaction between logD and charge at residue 5 (charge5). Analogs with a positive charge5 and higher logD are more sensitive to PL levels in BAPMM and generally show increased interaction with mixed micelles. This interaction tends to reduce membrane flux and protect against enzymatic degradation. Conversely, analogs with a negative charge5 are less influenced by changes in PL concentration. All peptides exhibit stronger interactions with dihydroxy-versus trihydroxy-containing BAPMM, with the lowest flux observed for analogs with positive charge5 and higher logD. Understanding the complex interactions between oral peptides, bile salts, and phospholipids would be valuable in optimizing oral peptide delivery.