Small Intestine-Targeted Long-Acting Oral Insulin Formulation Based on Engineered Milk Protein Nanoparticles

Insulin therapies remain essential for glycemic control in diabetes mellitus, yet conventional subcutaneous injection is associated with poor patient compliance, risk of hypoglycemia, and other adverse effects. Oral insulin formulations offer a promising alternative by improving patient adherence and mimicking the endogenous insulin pathway. However, their clinical trials, mostly in enteric capsules and tablets, have yielded limited efficacy due to low insulin bioavailability. In this study, we prepared an oral insulin formulation by coencapsulating insulin and the permeation enhancer sodium caprate (C₁₀) into milk protein casein-based nanocarriers (casNP). The casein shell was optimized for stable loading of insulin/C₁₀, guided by ex vivo gut sac studies with different C₁₀ concentrations. Reported casNP/insulin/C₁₀ exhibited excellent stability in simulated gastric fluid and enabled insulin release in simulated jejunal fluid via trypsin-mediated casein degradation. Oral administration in mice resulted in a stomach half-emptying time of <15 min, small intestine delivery efficiency of 10.8 ± 1.7%, and insulin bioavailability of 18.1%, as measured in liver and plasma. Oral casNP/insulin/C₁₀ (50 IU/kg) exhibited a blood sugar-lowering efficacy comparable to subcutaneously injected Insulin Aspart (5 IU/kg), while extending the duration of action by approximately 6 h and preventing hypoglycemia in fasted mice. These findings demonstrate that casNP/insulin/C₁₀ is a promising oral insulin formulation for managing diabetes.