Dual-modified nanoparticles overcome sequential absorption barriers for oral insulin delivery

The efficacy of oral insulin drug delivery is seriously hampered by multiple gastrointestinal barriers, especially transepithelial barriers, including apical endocytosis, lysosomal degradation, cytosolic diffusion and basolateral exocytosis. In this study, a functional nanoparticle (PG-FAPEP) with dual-modification was constructed to sequentially address these important absorption obstacles for improved oral insulin delivery. The dual surface decorations folate and charge-convertible tripeptide endowed PG-FAPEP with the ability to target the apical and basolateral sides of enterocytes, respectively. After fast diffusion across the mucus layer, PG-FAPEP could be efficiently internalized into epithelial cells via a folate receptor-mediated pathway and subsequently became positively charged in acidic lysosomes due to the surface tripeptide, triggering the proton sponge effect to escape lysosomes. When entering the cytosolic medium, PG-FAPEP was converted to neutral charge again, attenuating intracellular adhesion, and gained improved motility toward the basolateral side. Finally, the tripeptide helped PG-FAPEP recognize the proton-coupled oligopeptide transporter (PHT1) in the basolateral membrane, boosting intact exocytosis across intestinal epithelial cells. The in vivo studies further verified that PG-FAPEP could traverse the intestinal epithelium by folate receptor-mediated endocytosis, lysosomal escape, and PHT1-mediated exocytosis, exhibiting a high oral insulin bioavailability of 14.3% and a prolonged hypoglycemic effect. This formulation addresses multiple absorption barriers on demand with a simple dual-modification strategy. Therefore, these features allow PG-FAPEP to unleash the potential of oral macromolecule delivery.