Coordinated ASBT and EGFR Mechanisms for Optimized Liraglutide Nanoformulation Absorption in the GI Tract.

BACKGROUND: For maintenance therapy in type 2 diabetes, glucagon-like peptide-1 agonist (GLP-1A), which exhibits low cardiovascular risk and high efficacy, is a promising peptide therapeutic. However, developing an oral GLP-1A presents challenges due to the analog's poor cellular permeability and gastrointestinal (GI) stability.

METHODS: To mitigate such limitations, an oral nanoformulation of liraglutide (LG) was designed and achieved by combining LG with bile acid derivatives using the nanoprecipitation method. This strategy allowed the bile acid moieties to localize at the nanoparticle surface, enhancing the binding affinity for apical sodium-dependent bile acid transporter (ASBT) and improving GI stability. The in vitro characteristics, cellular permeability, and absorption mechanisms of the LG nanoformulation (LG/TD-NF) were thoroughly investigated. Furthermore, the in vivo oral absorption in rats and the glucose-lowering effects in a diabetic ( db/db ) mouse model were evaluated.

RESULTS: The LG/TD-NF produced neutral nanoparticles with a diameter of 58.7 ± 4.3 nm and a zeta potential of 4.9 ± 0.4 mV. Notably, when exposed to simulated gastric fluid, 65.7 ± 3.6% of the LG/TD-NF remained stable over 120 min, while free LG was fully degraded. Relative to unformulated LG, the Caco-2 cellular permeability of the nanoformulation improved, measuring 10.9 ± 2.1 (× 10-6 cm/s). The absorption mechanism prominently featured endocytosis simultaneously mediated by both ASBT and epidermal growth factor receptor (EGFR). The oral bioavailability of the LG/TD-NF was determined to be 3.62% at a dosage of 10 mg/kg, which is 45.3 times greater than that of free LG. In a diabetes model, LG/TD-NF at 10 mg/kg/day exhibited commendable glucose sensitivity and reduced HbA1c levels by 4.13% within 28 days, similar to that of subcutaneously administered LG at a dosage of 0.1 mg/kg/day.

CONCLUSION: The oral LG/TD-NF promotes ASBT/EGFR-mediated transcytosis and assures cellular permeability within the GI tract. This method holds promise for the development of oral GLP-1A peptides as an alternative to injections, potentially enhancing patient adherence to maintenance therapy.