(264b) Silica Nanoparticles Enable Oral Delivery of Insulin

Introduction: Oral delivery of macromolecular drugs is one of the greatest unmet needs in biomedicine, with poor absorption across the intestinal epithelium posing the most significant challenge to clinical translation¹. Several studies have demonstrated an improvement in bioavailability of macromolecules conjugated onto or loaded into orally administered nanoparticles². However, this work presents the previously unreported ability of anionic nanoparticles to improve intestinal absorption of large molecules without chemically linking them to the particle delivery vehicles.

Methods: A collection of nanoparticles comprising four sizes (20, 50, 100, and 200 nm) and six surface chemistries (bare silica, carboxylated silica, aminated silica, silver, gold, or bare polystyrene) was screened for absorption enhancing effects in vivo. Mice received oral gavages of particle suspensions, then either gavages or direct intestinal administration of 4 kDa FITC-labelled dextran (FITC-DX4) or insulin solution. Blood samples were collected and screened for FITC-DX4 or glucose concentration. Mouse intestines were harvested after treatment and processed for histology to assess particle-induced damage. For mechanistic studies, Caco-2 monolayers were used in conjunction with anti-receptor antibodies, enzyme inhibiting peptides, and fluorescent confocal microscopy to investigate tight junction rearrangement.

Results: Nanoparticles with negatively charged surfaces (bare silica, carboxylated silica, silver, and gold) improved oral FITC-DX4 accumulation in the blood, while neutral (polystyrene) and positive (aminated) particles showed little to no effect. Further, silica nanoparticles significantly improved the activity of intestinally administered insulin, matching the total hypoglycemic effect of subcutaneously injected insulin. Intestinal insulin bioactivity exhibited dependence on both nanoparticle dose and insulin dose. Further, orally administered, enterically coated insulin capsules induced pronounced and sustained hypoglycemia at the relatively low oral insulin dose of 40 U/kg, and only when administered alongside silica nanoparticles. Histological analysis of particle-treated mouse intestines showed no evidence of necrosis, inflammation, or changes in tissue architecture. However, in vitro mechanistic studies revealed that the nanoparticle treatment causes a substantial rearrangement of the tight junction protein ZO-1, an integral component to the barrier function of the epithelial lining, via a previously-identified, integrin- and MLCK-dependent mechanism³.

Conclusions and Implications: This is the first study demonstrating the use of co-delivered but unbound nanoparticles for improving adsorption of orally administered protein drugs. These conclusive in vivo results underscore the ability of silica nanoparticles to increase epithelial permeability, enabling the oral delivery of macromolecular drugs without encapsulation or conjugation. Future investigations will include more comprehensive toxicity studies in mice, development of an administration vehicle to better co-localize the particles and insulin, and confirmation of safety and efficacy in higher animal models.

Acknowledgements: N. Lamson would like to acknowledge financial support from the NSF Graduate Research Fellowship Program under Grant No. DGE1252522.

References:

1. Hamman, J.H., Enslin, G.M., Kotzé, A.F. Biodrugs. 2005 19(3) 165-177.
2. Banerjee, A., Qi, J., Gogoi, R., Wong, J., Mitragotri, S. J. Control. Release. 2016 (238) 176-185.
3. Walsh, L., Ryu, J., Bock, S., Koval, M., Mauro, T., Ross, R., Desai, T. NanoLett. 2015 15(4) 2434-2441.