Engineered acetylated inulin nanoparticles for enhanced oral insulin delivery: sustained release, structural stability, and <i>in vivo</i> efficacy

Oral insulin administration is limited by enzymatic degradation and poor gastrointestinal absorption. This study aimed to develop a biopolymer-based nanocarrier using acetylated inulin (InAc) to improve the structural stability and oral bioavailability of insulin. Inulin was produced from <i>Salinivibrio</i> sp. GM01 and chemically modified <i>via</i> acetylation. Insulin-loaded InAc (InAc-Ins) nanoparticles were prepared and characterized for morphology, size, zeta potential, and encapsulation efficiency. <i>In vitro</i> insulin release was evaluated under simulated gastric (SGF) and small intestinal (SSIF) conditions. <i>In vivo</i> efficacy was determined through oral glucose tolerance tests (OGTT) in mice. The InAc-Ins nanoparticles were spherical with mean diameter of 349 ± 38 nm and high encapsulation efficiency (92.14%). Insulin release half-life were observed in 37.1 hours in SGF and 24.3 hours in SSIF conditions. Biophysical analysis revealed enhanced structural stability of encapsulated insulin, with increased half-life and activation energy for the secondary and tertiary structure denaturation. The secondary structure denaturation half-life increased to 195 min (SGF) and 231 min (SSIF), with denaturation enthalpy of 4.03 kcal mol^-1 and 1.83 kcal mol^-1, respectively. Tertiary structure denaturation half-life were 765 min (SGF) and 919 min (SSIF), and denaturation enthalpy of 18.67 kcal mol^-1 and 4.58 kcal mol^-1, respectively. OGTT results showed that orally administered InAc-Ins nanoparticles reduced blood glucose levels more effectively than free insulin, achieving 42.8% of subcutaneous insulin efficacy. InAc nanoparticles offer effective protection and sustained release of insulin under gastrointestinal conditions, enhancing its structural integrity and hypoglycemic efficacy. This platform presents a promising strategy for non-invasive oral insulin delivery.