Oral administration of insulin is still a big challenge due to the harsh gastrointestinal environment. In this study, starch and chitosan were utilized to prepare insulin-loaded microcapsules with controllable releasing properties. Herein, the complexation between chitosan and insulin upon pH adjustment tended to form positively charged insulin nanoparticles (iNPs). At a chitosan/insulin ratio of 1:2, the diameter of iNPs and corresponding insulin loading capacity reached 196.2 nm and 0.70 mg/mg iNPs, respectively. Amylolytic hydrolysis of rice starch granules for 120 min could produce porous rice starch (PRs), enabling the encapsulation of iNPs to form iNPs-loaded PRs (PRs@iNPs). The iNPs were much easier encapsulated by PRs than the free insulin at an equivalent insulin concentration of 0.60 mg/mL. When PRs@iNPs mixed with different concentrations of sodium alginate, the calcium chloride initiated the cross-linking of calcium alginate, and the formation of calcium alginate layer not only protected the starch from the amylase hydrolysis, but also maintained the sustained release of insulin in the simulated gastrointestinal fluid. Moreover, both starch digestion and insulin releasing can be controlled by the concentration of sodium alginate used. This study may provide an efficient benign technology to produce microcapsules loaded with insulin nanoparticles for controllable releasing properties.
Purpose Peptide drugs have been used in therapy various diseases. However, the poor bioavailability of peptide drugs for oral administration has limited their clinical applications, on account of the acidic environment and digestive enzymes inside the human gastrointestinal tract. To enhance stability in the human gastrointestinal tract, bioavailability, and targeted drug delivery of peptide drugs through oral administration, a vitamin B12-modified amphiphilic sodium alginate derivative (CSAD-VB12) was synthesized.Materials and methods A vitamin B12-modified amphiphilic sodium alginate derivative (CSAD-VB12) was synthesized via the N,N’-dicyclohexylcarbodiimide active method at room temperature, and then characterized using FTIR and 1H NMR spectroscopy. Insulin was used as a model peptide drug and the insulin-loaded CSAD-VB12 (CSAD-VB12/insulin) nanoparticles with negative zeta potentials were prepared in PBS (pH=7.4). Scanning electron microscopy was used to observe CSAD-VB12/insulin as spherical nanoparticles. The CSAD-VB12 derivatives and CSAD-VB12/insulin nanoparticles displayed nontoxicity towards the human colon adenocarcinoma (Caco-2) cells by CCK-8 test. Caco-2 cell model was used to measure the apparent permeability (Papp) of insulin, CSAD/insulin and CSAD-VB12/insulin. Furthermore, confocal was used to confirm the endocytosis of intestinal enterocytes. Type 1 diabetes mice were used to evaluate the intestinal absorption and retention effect of test nanoparticles.Results They were observed as spherical nanoparticles in the size of 30–50 nm. The CSAD-VB12 derivatives and CSAD-VB12/insulin nanoparticles displayed nontoxicity towards the human colon adenocarcinoma (Caco-2) cells. Comparing with insulin and the CSAD/insulin nanoparticles, the CSAD-VB12/insulin nanoparticles exhibited higher permeation ability through intestinal enterocytes in the Caco-2 cell model. Oral administration of the CSAD-VB12/insulin nanoparticles to Type 1 diabetic mice yields higher intestinal retention effect, targeted absorption, and outstanding efficacy.Conclusion CSAD-VB12 derivatives enhance the small intestinal absorption efficacy and retention of peptide by oral administration, which indicated that it could be a promising candidate for oral peptide delivery in the prospective clinical application.
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