Surface charge triggered intestinal epithelial tight junction opening based on chitosan nanoparticles for insulin oral delivery

The aim of this research work was to explore the possibility of providing multifunctional oral insulin delivery system by conjugating several types of dipeptides on chitosan and trimethyl chitosan to be used as drug carriers.Conjugates of Glycyl-glycine and alanyl-alanine of chitosan and trimethyl chitosan (on primary alcohol group of polymer located on carbon 6) were synthesized and nanoparticles containing insulin were prepared for oral delivery. Preparation conditions of nanoparticles were optimized and their performance to enhance the permeability of insulin as well as cytotoxicity of nanoparticles in Caco-2 cell line was evaluated. To evaluate the efficacy of orally administered nanoparticles, nanoparticles with the most permeability enhancing ability were studied in male Wistar rats as animal model by measuring insulin and glucose Serum levels.Structural study of all the conjugates by infrared spectroscopy and nuclear magnetic resonance confirmed the successful formation of the conjugates with the desirable substitution degree. By optimizing preparation conditions, nanoparticles with expected size (157.3–197.7 nm), Zeta potential (24.35–34.37 mV), polydispersity index (0.365–0.512), entrapment efficiency (70.60–86.52%) and loading capacity (30.92–56.81%), proper morphology and desirable release pattern were obtained. Glycyl-glycine and alanyl-alanine conjugate nanoparticles of trimethyl chitosan showed 2.5–3.3 folds more effective insulin permeability in Caco-2 cell line than their chitosan counterparts. In animal model, oral administration of glycyl-glycine and alanyl-alanine conjugate nanoparticles of trimethyl chitosan demonstrated reasonable increase in Serum insulin level with relative bioavailability of 17.19% and 15.46% for glycyl-glycine and alanyl-alanine conjugate nanoparticles, respectively, and reduction in Serum glucose level compared with trimethyl chitosan nanoparticles (p < 0.05).It seems that glycyl-glycine and alanyl-alanine conjugate nanoparticles of trimethyl chitosan have met the aim of this research work and have been able to orally deliver insulin with more than one mechanism in animal model. Hence, they are promising candidates for further research studies.