Impact of Gastrointestinal Proteolytic Stability on Macrocyclic Peptide Absorption with Sodium Decanoate as a Membrane Permeation Enhancer in the Rat

Abstract The two major barriers to effective oral peptide delivery are proteolytic degradation in the gastrointestinal environment and low membrane permeability. In this work, we aimed to evaluate the minimum level of intrinsic proteolytic stability in the upper small intestinal environment required to achieve maximal peptide absorption when dosed with permeation enhancers (PEs). We used sodium decanoate (C10) as a representative PE and studied its effect on two chemically distinct series of macrocyclic peptides (MCPs) in vitro and in vivo. The MCPs (within each series) were selected based on their closely related amino acid sequences and physicochemical properties but differing levels of intrinsic proteolytic stability towards pancreatic enzymes. The MCPs were formulated with and without C10 and dosed intrajejunally to rats to determine absolute bioavailability, and the effect of different concentrations of C10 on MCP proteolytic stability was evaluated in the in vitro pancreatin stability assay. C10 protected all MCPs from proteolytic degradation by pancreatic enzymes in a concentration-dependent manner in vitro and increased the absolute bioavailability of all MCPs in vivo. The findings described herein demonstrate that an MCP half-life of approximately 60 min in the in vitro pancreatin stability assay (without C10) is sufficient to enable maximal in vivo absorption in rats when C10 is used as a PE.