Preparation and evaluation of oral insulin nanocapsule delivery systems

Insulin therapy is essential for regulating blood sugar levels. Conventional subcutaneous injection is prone to psychological stress, local tissue damage and severe blood glucose fluctuations, and thus the development of oral insulin technology has become an alternative therapy. However, oral insulin faces challenges such as difficult absorption, poor adhesion, low bioavailability, and short duration of action, due to the large molecular weight, low permeability, and easily degradable by enzymes and gastric acids. In this study, oral insulin nanocapsule delivery systems (Orl-Ins-NPs) were developed by using polylactic acid-co-glycolic acid (PLGA) as the encapsulation material for insulin loading. After preparation, optimization and characterization, the mean size of Orl-Ins-NPs was 140.08 nm, the encapsulation efficiency of the system was 54.3 %, and the loading capacity of insulin was 2.2 %. In addition, cationic modification with chitosan/ polyethyleneimine promoted adhesion and permeation of the intestinal mucus layer, and surface coating with pH-responsive methyl methacrylate trimethylamine ethyl chloride copolymer achieved 100 % gastric protection. The results of rat blood glucose test showed that, subcutaneous injection of the control group reduced blood glucose concentrations within 1 h and returned to initial levels within 4 h, while Orl-Ins-NPs slowly reduced blood glucose concentration to 51.3 % of the initial level and maintains stability within 10 h. Orl-Ins-NPs exhibited good physicochemical stabilities, sustained release property, improved in vitro acid resistance, as well as long-term in vivo hypoglycemic effect. This system demonstrates its potential clinical application in oral insulin and other protein drugs delivery.