Prediction of the enhanced insulin absorption across a triple co-cultured intestinal model using mucus penetrating PLGA nanoparticles

Insulin is a protein macromolecule used to treat diabetes mellitus. Currently, insulin requires multiple daily subcutaneous (SC) injections to control blood sugar in diabetics. Thus, reducing the patients' compliance and adherence to medication as SC route is invasive. Insulin is poorly absorbed through intestinal epithelium because it is a large and hydrophilic molecule, degraded by proteases, and due to the presence of mucosal biophysical barrier. Herein, insulin was encapsulated into different poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) formulations prepared by microfluidic technique, which were further appended with heparin sulfate for oral insulin delivery. The average particle size was ca. 200 nm, PDI at ca. 0.3 and the zeta potential at ca. -20 mV. The maximal achieved association efficiency of insulin was similar to 55% at 3% theoretical loading. PLGA exhibited a protective effect against insulin release in harsh acidic conditions (pH = 2.2) with only a small burst release (similar to 15%) and sustained release at pH 6.8. Although the encapsulation process altered insulin secondary structure whilst encapsulated into PLGA NPs, insulin restored its tertiary structure once released from the NPs. Mucopenetrating heparin sulfate conjugated PLGA NPs significantly improved insulin permeability in triple cocultured intestinal model compared to unmodified and free insulin with two and three-fold increase. Thus, they could be utilised as carriers for oral insulin delivery.