Polymer integrity related absorption mechanism of superporous hydrogel containing interpenetrating polymer networks for oral delivery of insulin

Superporous hydrogel containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks (SPH-IPN) was evaluated as the oral delivery vehicle for insulin, emphasizing on the effect of polymer integrity on insulin absorption mechanisms. The integral SPH-IPN (I-SPH-IPN) and powdered SPH-IPN (P-SPH-IPN) exhibited potent and equivalent in vitro enzymatic inhibition capacities, which were attributed to both enzyme incorporation and Ca2+ deprivation. Nevertheless, I-SPH-IPN showed marked superiority to P-SPH-IPN in in vivo enzymatic inhibition. Through reversible opening of epithelial tight junctions, I-SPH-IPN notably enhanced paracellular permeability of insulin in Caco-2 cell monolayers and excised rat intestine by 4.9 and 4.2 folds, respectively, wherein I-SPH-IPN outperformed P-SPH-IPN by 2.5 and 2.3 folds, respectively. Besides, orally delivered I-SPH-IPN could retain in rat intestine for more than 8 h while P-SPH-IPN was quickly eliminated, suggesting better retentive properties of I-SPH-IPN. Such results were further confirmed by in vivo assessment in that oral administration of insulin-loaded I-SPH-IPN yielded notable insulin absorption and hypoglycemic effect, while P-SPH-IPN was ineffective. Finally, an oral acute and sub-acute toxicity study in mice confirmed biocompatibility of SPH-IPN. Therefore, the detailed mechanism assessment confirmed that I-SPH-IPN was an effective and safe peroral carrier for protein drugs.