Colonic targeting insulin-loaded trimethyl chitosan nanoparticles coated pectin for oral delivery: In vitro and In vivo studies

Colon-targeted delivery offers several benefits for oral protein delivery, such as low proteolytic enzyme activity, natural pH, and extended residence time, which improve the bioavailability of the encapsulated protein. Therefore, we hypothesize that developing a novel colonic nanocarrier system based on modified chitosan, which enhances solubility at natural pH and is coated with a colon-degradable polymer, will provide an effective delivery system for oral insulin. This study aims to synthesize insulin-loaded pectin-trimethyl chitosan nanoparticles (Ins-P-TMC-NPs) as an oral insulin delivery system and evaluate their efficacy both in vitro and in streptozotocin-induced diabetic male rats. N-trimethyl chitosan (TMC), synthesized via a methylation method, was used to prepare insulin-TMC nanoparticles coated with pectin via the ionic gelation method. The nanoparticles were characterized for their physicochemical properties, cumulative release profile, and surface morphology. In vitro biological cytotoxicity and cellular uptake of the nanoparticles were evaluated against HT-29 cells using an MTT assay and fluorescent microscopy, respectively. The in vivo blood glucose-lowering effect was assessed in diabetic male Sprague-Dawley rats, with in vivo toxicity evaluated in the liver, spleen, duodenum, pancreas, and kidney through histological studies (H&E staining). The results showed that Ins-P-TMC-NPs were spherical, with an average size of 379.40 ± 40.26 nm, a polydispersity index of 24.10 ± 1.03 %, a zeta potential of +17.20 ± 0.52 mV, and a loading efficiency of 83.21 ± 1.23 %. Compared to uncoated TMC nanoparticles, Ins-P-TMC-NPs reduced insulin loss in simulated gastrointestinal fluid by approximately 67.23 ± 0.97 % and provided controlled insulin release in simulated colonic fluid. In vitro bioactivity studies revealed that Ins-P-TMC-NPs were non-toxic, with cell viability of 91.12 ± 0.91 %, and exhibited high cellular uptake in the HT-29 cell line with a fluorescence intensity of 37.80 ± 2.40. Furthermore, in vivo studies demonstrated a sustained reduction in blood glucose levels after oral administration, peaking after 8 h with a glucose reduction of 87 ± 1.03 %. Histological sections showed no signs of toxicity. Overall, the developed colon-targeted oral insulin delivery system shows great potential as a candidate for oral insulin administration.