Microcontainers for oral insulin delivery - In vitro studies of permeation enhancement

Oral delivery of peptides is challenging due to their low uptake through the small intestinal epithelium. Tight junctions, connecting the enterocytes, impede permeability, often necessitating the use of permeation enhancers in the formulation. Loading of peptide and permeation enhancer into micro-scale devices, such as microcontainers, can potentially confine the effective absorptive area through unidirectional release and thereby enhance absorption. This concept is investigated by in vitro permeation studies of insulin across Caco-2 cell and Caco-2/HT29-MTX-E12 co-culture monolayers mimicking the intestinal absorption barrier. The importance of proximity between the microcontainers and the barrier is assessed, by keeping the amounts of insulin and sodium caprate fixed throughout all experiments, while collectively orienting the unidirectional release towards the cell monolayers. Increasing the distance is observed to have a negative effect on insulin permeation matching a one-phase exponential decay function, while no difference in insulin transport is observed between Caco-2 and co-culture monolayers. Although there are no signs of cytotoxicity caused by the microcontainer material, reversible cell deterioration, as a consequence of high local concentrations of sodium caprate, becomes evident upon qualitative assessment of the cell monolayers. These results both suggest a potential of increasing oral bioavailability of peptides by the use of microcontainers, while simultaneously visualising the ability of regaining monolayer integrity upon local permeation enhancer induced toxicity.