Enhancement of oral insulin bioavailability: in vitro and in vivo assessment of nanoporous stimuli-responsive hydrogel microparticles

Objective: Oral insulin administration suffers gastrointestinal tract (GIT) degradation and inadequate absorption from the intestinal epithelium resulting in poor bioavailability. This study entails in vitro and in vivo assessment of stimuli-responsive hydrogel microparticles (MPs) in an attempt to circumvent GI barrier and enhance oral insulin bioavailability.

Methods: Bacterial cellulose-g-poly(acrylic acid) (BC-g-P(AA)) hydrogel MPs were evaluated for morphology, swelling, entrapment efficiency (EE), in vitro insulin release and enzyme inhibition. The ex vivo mucoadhesion, insulin degradation and transport were investigated in excised intestinal tissues. The effect of MPs on paracellular transport was studied in Caco-2/HT29-MTX monolayers. The in vivo hypoglycemic effect and pharmacokinetics of insulin-loaded MPs were investigated in diabetic rats.

Results: Hydrogel MPs efficiently entrapped insulin (EE up to 84%) and exhibited pH-responsive in vitro release. The MPs decreased the proteolytic activity of trypsin (up to 60%). Insulin transport across monolayers was increased up to 5.9-times by MPs. Histological assessment of GI tissues confirmed the non-toxicity of MPs. Orally administered insulin-loaded MPs showed higher hypoglycemic effect as compared to insulin solution and enhanced relative oral bioavailability of insulin up to 7.45-times.

Conclusion: These findings suggest that BC-g-P(AA) MPs are promising biomaterials to overcome the barriers of oral insulin delivery and enhancing its bioavailability.