Periodic Reporting for period 1 - OraPickering (Effective co-delivery of therapeutic peptides and intestinal permeation enhancers using a double Pickering emulsion oral delivery system)
Reporting period: 2023-06-01 to 2025-05-31
Therapeutic peptides (TPs) are one of the fastest growing classes of pharmaceuticals with clinical applications in cancer therapy, hormonal or immune disorders, and infectious or metabolic diseases. The number of approved TPs is rapidly increasing, however, to date the vast majority of TPs (> 90%) rely on administration via injections, e.g. insulin, whereof half even need to be administered intravenously and are therefore limited to the clinical environment. This considerably affects patient wellbeing and compliance, as well as treatment costs and ease of distribution. Oral delivery of TPs provides an alternative administration route that is straightforward, cheap, and highly accepted by patients and clinicians. However, the oral administration of TPs is limited by I) the proteolytic gastric and intestinal environments which are detrimental for TPs and II) limited permeation of TPs across the intestinal epithelium. Double water-in-oil-in-water emulsions are of interest as potential oral delivery systems as they allow the encapsulation and co-delivery of hydrophilic and hydrophobic compounds such as TPs and permeation enhancers, respectively. Particularly emulsions stabilized by solid particles, known as Pickering emulsions, have proven promising for the formation of gastric stable emulsions. The goal of OraPickering was to establish Pickering double emulsions as novel oral delivery systems for co-delivery of hydrophilic TPs and hydrophobic permeation enhancers, towards more safe, cheap, and compliant administration of TPs like insulin. The main objectives of OraPickering were 1) to find stable formulations for Pickering double emulsions, 2) test the stability of emulsions and encapsulated TPs under gastric conditions, and 3) confirm their efficacy for intestinal delivery in in vitro cell models.
Cellulose nanocrystals (CNCs) that were previously shown to form gastric stable single emulsions were successfully modified via a surface acylation to stabilize Pickering double emulsions in a two step emulsification at lower shear rates. Double emulsions were produced and characterized in detail regarding their droplet size and particularly their stability over time. The formed Pickering double emulsions were found to remain stable for several months and were able to permanently encapsulate the model hydrophilic macromolecule 4 kDa FITC-dextran (FD4) under storage as well as in vitro digestive conditions. FD4 delivered by Pickering double emulsions permeated to a similar extent across an in vitro Caco-2 cell monolayer as non-formulated FD4, confirming the suitability of the formulation to deliver large hydrophilic macromolecules. The use of medium chain triglyceride oil as double emulsion oil phase facilitated the reduction of Caco-2 monolayer transepithelial electrical resistance due to its hydrolysis into medium chain fatty acids that act as inherent permeation enhancers, making the further addition of permeation enhancers obsolete. In a second step, this established formulation was tested for the encapsulation of the three model TPs insulin, octreotide, and semaglutide. The encapsulation efficiency of TPs varied depending on their size and chemical properties, but stable longterm encapsulation could be achieved for insulin. Unlike FD4, insulin was released under in vitro gastric conditions, which could be oppressed by incorporation of a lipase inhibitor in the emulsion oil phase. Ultimately, the permeation of insulin delivered by Pickering double emulsion across model Caco-2 monolayers could be confirmed and was at a similar level as non-formulated insulin in presence of a permeation enhancer.
The project presented a new method for the formation of Pickering double emulsions using CNCs, which have shown promise for gastric stable emulsion stabilization but were too hydrophilic to stabilize double emulsions for encapsulation applications. This novel Pickering double emulsions were characterized in detail and a proof of concept was provided for their application as oral delivery systems for hydrophilic macromolecules, specifically three model TPs, in an in vitro model. This provides a useful framework for the further investigation of Pickering double emulsions for encapsulation and delivery applications of TPs and other macromolecules such as monoclonal antibodies or nucleic acids.