Nanocomplexes Integrated into a Polymeric Bilayer Film Enhance Buccal Permeation of a GLP-1 Peptide Analogue

Buccal administration of peptide therapeutics offers a noninvasive alternative to injections but remains constrained by limited peptide epithelial permeability and physicochemical instability. Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are important therapeutics with limited noninvasive administration options. Here, we present a buccal peptide delivery platform integrating electrostatic nanocomplexation, design of experiments (DoE)-guided optimization, and solid-state stabilization. Chitosan oligosaccharide (COS) was complexed with a model GLP-1 RA peptide molecule to generate monodisperse nanocomplexes (∼100 nm) with low polydispersity and a positive surface charge (∼+20 mV). Lyophilization preserved nanocomplex integrity during storage at 4 °C for at least one month, enabling dispersibility and retention of colloidal characteristics and GLP-1 RA secondary structure. Nanocomplexes exhibited minimal cytotoxicity in TR-146 cells at 1 mg/mL over 180 min. Mechanistic analyses demonstrated membrane lipid remodelling, dynamin-dependent endocytic involvement, and redistribution of tight junction and desmosomal proteins, supporting a model involving nanocomplex uptake leading to modulation of epithelial barrier properties. The nanocomplexes were then incorporated into a bilayer film composed of a pullulan/sodium carboxymethyl cellulose mucoadhesive layer and an Eudragit RLPO backing layer. GLP-1 RA permeation across porcine buccal mucosae from the nanocomplexes in solution reached ∼13% at 3 h (P_app ∼3.8 × 10^-6 cm/s) while incorporation of complexes in bilayers yielded ∼3.4% permeation (P_app ∼1.2 × 10^-6 cm/s) compared to the absence of flux for the GLP-1 RA in solution. These findings demonstrate that peptide nanocomplexes can be successfully incorporated into mucoadhesive films. This approach offers advantages over films comprising permeation enhancers.