Mucus-penetrating nanoparticles for the oral delivery of insulin

Peptides and proteins have gained increased interest as therapeutics during the recent years due to their potent and specific mode of action. Nevertheless, most of these drugs are administered by the parenteral route which shows some drawbacks regarded to the invasive nature of this route of administration. Consequently, the oral administration remains between the most attractive due to its cost-effectiveness and well-established acceptability. However, the oral delivery of macromolecules presents limitations that end in low bioavailability generated by their degradation in the gastrointestinal tract. To solve these problems, polymeric nanoparticles have been proposed. One of the greatest challenges that limits the success of particles is their ability to penetrate through the mucus layer to reach the epithelium. Mucus protects the underlaying epithelium by efficiently trapping pathogens and foreign particulates limiting their arrival to the absorptive membrane. As a consequence, it also represents a substantial barrier to mucosal drug delivery. In order to overcome this drawback, the use of mucus-penetrating nanoparticles has been suggested. Among the different strategies to produce this type of nanocarriers, slippery nanoparticles have been chosen in this project. This strategy consists in minimizing the hydrophobic interactions between the mucus components and the generally hydrophobic nature of the polymers used for the preparation of nanoparticles. For this purpose, nanoparticles may be coated with hydrophilic compounds (poly(ethylene glycol)s and thiamine) in order to produce an effective shield capable of avoiding the mucoadhesive interactions. Once the nanocarriers were prepared, the evaluation of their permeability through the gastrointestinal mucosa by different in vitro and in vivo techniques was also assessed. Nanoparticles were obtained by different preparative processes leading to three types of nanoparticles. In the first one, poly(anhydride) nanoparticles coated with poly(ethylene glycol)s of different molecular weight were obtained. As second approach, thiamine-decorated poly(anhydride) nanoparticles were prepared from a new polymeric conjugate obtained by the covalent bonding of vitamin B1 to the anhydride residues of Gantrez® AN. In the last one, zein nanoparticles were coated with the Gantrez® AN-thiamine conjugate. Finally, insulin was encapsulated, as model biomacromolecule, in the most promising formulation and its oral bioavailability and pharmacological activity in vivo were assessed. Regarding pegylation of poly(anhydride) nanoparticles, it was evidenced that modified their fate within the gastrointestinal tract of laboratory animals. The coating with poly(ethylene glycol)s within the small intestine, PEGylated nanoparticles displayed mucus-penetrating properties, although this fact was influenced by the molecular weight and surface density of the poly(ethylene glycol). When nanoparticles were decorated with thiamine, the mucoadhesive properties of poly(anhydride) nanoparticles were transformed into mucus-penetrating ones. After the encapsulation of insulin in nanoparticles prepared from Gantrez® AN-thiamine conjugate, a high loading was obtained. However, the resulitng nanoparticles did show neither mucus-penetrating properties nor adequate release profiles for an oral administration. After these negative results, zein nanoparticles coated with Gantrez® AN-thiamine conjugate were successfully prepared as potential carriers for the encapsulation of insulin. These nanoparticles possessed both in vitro and in vivo mucus-penetrating properties. When insulin was encapsulated in these nanocarriers, the intestinal absorption, following oral administration, of insulin was enhanced. At a dose of 50 IU/kg. The pharmacological activity and the relative oral bioavailability of nanoencapsulated insulin were calculated to be 13.5% and 5.2% respectively.