Abstract

Therapeutic peptides have gained significant attention due to their high specificity, potency, and safety profiles in treating various diseases. However, their clinical application via the oral route remains challenging. Peptides are inherently unstable in the gastrointestinal environment, where they are rapidly degraded by proteolytic enzymes and acidic pH, leading to poor bioavailability. Additionally, their large molecular size and hydrophilicity restrict passive diffusion across the epithelial barriers of the gastrointestinal tract. These limitations have traditionally necessitated parenteral administration, which reduces patient compliance and convenience. The oral cavity, comprising the buccal and sublingual mucosa, offers a promising alternative for peptide delivery. Its rich vascularization allows for rapid systemic absorption while bypassing hepatic first-pass metabolism. Furthermore, the mucosal surface provides a relatively permeable and accessible site for drug administration. However, the oral cavities also present significant barriers: the mucosal epithelium limits permeability, the presence of saliva causes rapid clearance, and enzymes in saliva contribute to peptide degradation. Therefore, innovative strategies are essential to enhance peptide stability, retention, and permeation in this environment. Nanoparticle-based delivery systems, including lipid-based carriers such as liposomes and niosomes, as well as polymeric nanoparticles like chitosan and PLGA, offer promising solutions. These nanocarriers protect peptides from enzymatic degradation, enhance mucoadhesion to prolong residence time, and facilitate controlled release. Their size and surface properties can be engineered to improve mucosal penetration, including through receptor-mediated endocytosis or by transiently opening tight junctions. Among these, niosomes have shown high encapsulation efficiency and sustained release potential, making them particularly suitable for oral peptide delivery. Despite advances, challenges remain in translating these technologies clinically, including ensuring biocompatibility, scalable manufacturing, and patient acceptance. Nevertheless, the oral cavity’s accessibility, combined with nanotechnological innovations, offers a compelling platform for personalized, non-invasive peptide therapies that could significantly improve treatment outcomes and patient quality of life.