Permeation enhancer-induced membrane defects assist the oral absorption of peptide drugs

Abstract The passive membrane permeation of small-molecule drugs and small hydrophobic peptides is relatively well understood. In contrast, how long polar peptides can pass through a membrane has remained a mystery. This process can be achieved with permeation enhancers, contributing significantly to the oral transcellular absorption of important peptide drugs like semaglutide — the active pharmaceutical ingredient in Ozempic, which is used as Rybelsus in a successful oral formulation. Here we now provide a detailed, plausible molecular mechanism of how such a polar peptide can realistically pass through a membrane paired with the permeation enhancer salcaprozate sodium (SNAC). We provide both simulation results, obtained with scalable continuous constant p H molecular dynamics (C p HMD) simulations, and experimental evidence (NMR, DOSY, and DLS) to support this unique permeation mechanism. Our combined evidence points toward the formation of permeation-enhancer-filled, fluid membrane defects, in which the polar peptide can be submerged in a process analogous to quicksand.