Anionic nanoparticles enable the oral delivery of proteins by enhancing intestinal permeability

The oral delivery of bioactive peptides and proteins is prevented by the intestinal epithelial barrier, in which intercellular tight junction complexes block the uptake of macromolecules. Here we show that anionic nanoparticles induce tight junction relaxation, increasing intestinal permeability and enabling the oral delivery of proteins. This permeation-enhancing effect is a function of nanoparticle size and charge, with smaller (≤ 200 nm) and more negative particles (such as silica) conferring enhanced permeability. In healthy mice, silica nanoparticles enabled the oral delivery of insulin and exenatide, with 10 U kg^-1 orally delivered insulin sustaining hypoglycaemia for a few hours longer than a 1 U kg^-1 dose of subcutaneously injected insulin. In healthy, hyperglycaemic and diabetic mice, the oral delivery of 10 U kg^-1 insulin led to a dose-adjusted bioactivity of, respectively, 35%, 29% and 23% that of the subcutaneous injection of 1 U kg^-1 insulin. The permeation-enhancing effect of the nanoparticles was reversible, non-toxic, and attributable to the binding to integrins on the surface of epithelial cells.