Protamine nanocapsules as carriers for oral peptide delivery

Abstract

The number of peptide drugs in the industry pipelines has significantly increased in the last decades due to their high therapeutic efficacy and excellent selectivity. However, their utility has been limited due to their difficulties for crossing mucosal barriers, making it virtually impossible to deliver them by the oral route. The aim of this work was to design and develop protamine-based nanocapsules (NCs), capable of encapsulating insulin, protecting it from the harsh intestinal environment and promoting its absorption across the epithelial wall. The NCs consisted of an oily core, containing Miglyol® and sodium glycocholate (SGC), surrounded by a polymer layer made of protamine and PEG-stearate. The NCs were also provided with a double protamine/polysialic acid (PSA) layer. These polymer layers were intended to enhance the stability against intestinal degrading enzymes and to facilitate the interaction of the NCs with the epithelial mucosa. Protamine and PSA/protamine NCs exhibited a size between 300-400 nm, with a spherical shape and the capacity to load insulin. The provision of the NCs with a PSA layer reinforced their colloidal stability in different simulated intestinal media and preserved the loaded insulin from enzymatic degradation when incubated in fed-state simulated intestinal fluid. In addition, both formulations released insulin in a controlled manner. These NCs could also be lyophilized and stored as a thermostable powder formulation up to 6 months at 25 °C, while preserving insulin stability. The interaction of the protamine and PSA-protamine NCs with the Caco-2 cells was found to occur at the transcellular and paracellular level. The NCs were able to cross the monolayer and, simultaneously open the tight junctions between cells. Moreover, both systems interacted with the epithelium of human intestinal tissue without any cytotoxic effects. Finally, in vivo efficacy studies showed a moderate decrease (20% reduction) of blood glucose levels in non-diabetic rats. Overall, these results highlight the potential for protamine-based NCs to interact with intestinal mucosa and promote the absorption of the peptide across the intestinal epithelium.