Folate appended chitosan nanoparticles augment the stability, bioavailability and efficacy of insulin in diabetic rats following oral administration

The present study embarks upon the folic acid (FA) functionalization of chitosan nanoparticles and its implications on stability, oral bioavailability and hypoglycemic activity following oral administration. Folic acid functionalized chitosan nanoparticles (FA-Ch-NPs) were prepared by an ionotropic gelation method by using poly(sodium 4-styrenesulfonate, PSS) as a cross-linking agent. Exhaustive optimization was carried out by using 4-factor, 3-level, 2-replicates "Central Composite Design" by taking the pH of chitosan solution (X1), concentration of PSS (X2), stirring speed (X3) and drug loading (X4) as independent variables while the particle size (Y1), polydispersity index (Y2), zeta potential (Y3) and entrapment efficiency (Y4) as responses. Surface and contour profiles were generated based on maximum desirability. Morphological evaluation revealed the formation of almost spherical particles while lactose 5% w/v resulted in the formation of fluffy, easy to re-disperse cake. Developed nanoparticles exhibited sustained release up to 24 h following the Higuchi model of drug release irrespective of the folic acid functionalization. Entrapped insulin was stable chemically and conformationally throughout the process and the nanoparticles exhibited excellent stability in simulated biological fluids as well as different storage conditions. Uptake studies in Caco-2 cell lines demonstrated 2.98 fold higher uptake of folic acid functionalized nanoparticles (FA-Ch-NPs) in comparison with plain Ch-NPs and remarkably higher uptake in intestinal uptake studies. Oral administration of FA-Ch-NPs demonstrated 2.13 fold higher cumulative hypoglycemia and 21.8 + 2.4% relative bioavailability in comparison with subcutaneously administered insulin solution. Conclusively, the proposed formulation is expected to be a cost effective and easily scalable approach for oral insulin delivery.