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Colon-targeted delivery offers several benefits for oral protein delivery, such as low proteolytic enzyme activity, a natural pH environment, and extended residence time, which improve the bioavailability of the encapsulated protein. Therefore, we hypothesize that developing a novel colonic nanocarrier system, featuring modified chitosan that is soluble at physiological pH and 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 to evaluate its efficacy both in vitro and in vivo. 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. The in vitro biological cytotoxicity and cellular uptake of the nanoparticles were evaluated against HT-29 cells. The in vivo blood glucose-lowering effect and histological toxicity were assessed in diabetic male Sprague–Dawley rats. 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 % after 24 h of treatment, and exhibited high cellular uptake in the HT-29 cell line with a fluorescence intensity of 37.80 ± 2.40 after 4 h of incubation. Furthermore, the in vivo study demonstrated a sustained reduction in blood glucose levels after oral administration of Ins-P-TMC-NPs, peaking after 8 h with a blood glucose reduction of 87 ± 1.03 %. Histological sections showed no signs of toxicity when compared to those of healthy rats. Overall, the developed colon-targeted oral insulin delivery system exhibits strong potential as a candidate for effective oral insulin administration. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] N-trimethyl chitosan of two quaternization degrees (DQ=20 and 80mol%) were synthesized and characterized. [•] Polyelectrolyte complexes of N-trimethyl chitosan/alginate (TMC/ALG) were prepared at different pHs. [•] Using the N-trimethyl chitosan of DQ 20mol%, it was possible to obtain beads of TMC/ALG, at pH 2. [•] In vitro controlled release of curcumin were evaluated and showed the release being dependent of pH. [Copyright &y& Elsevier]