Food-Based Delivery of Bioactive Peptides for Gut Health

Abstract

This thesis assesses the potential of food proteins as sources of novel self-assembling bioactive peptide (SABP) nanostructures, for oral delivery to the lower gastrointestinal tract. Diseases associated with the gastrointestinal tract, such as stomach, colon, and rectum cancers, are major issues worldwide. The need for new therapeutic approaches to mitigate or cure these diseases is high, with conventional drug delivery often associated with adverse side effects. Functional food ingredients such as bioactive peptides offer a promising alternative. Key characteristics include their capacity to form structures such as hydrogels, with associated inherent simplicity of bioactive delivery. A potentially viable route to manufacturing gels without the need for expensive synthesis is to source peptides from secondary food processing streams. A method for identifying bioactive and self-assembling peptides based on in silico analysis was developed. Among the potential gel-forming peptides, three peptides were selected for further investigation. Proof-of-principle testing with synthetic peptides revealed that one peptide, Ac- FFVAPFPEVFGK-NH2 (capFFV), self-assembled into fibrils and formed a self-supporting gel by water absorption at low pH (+1 charge). The self-assembled network formed was further characterised with spectroscopy, microscopy, oscillatory rheology, and ThT assay. The structural and mechanical studies performed revealed that gels of different strength could be obtained by varying parameters such as the peptide concentration and the incubation time. Enzymatic hydrolysis was chosen to generate peptides from the parent proteins. Chromatography techniques, including size-exclusion and ion-exchange, and solid-phase extraction at preparative scale were used to isolate peptides. The peptides’ (natural and capped) potential for oral delivery was assessed with simulated in vitro digestion according to INFOGEST methodology. Peptide gels were analysed at different digestion times with mass spectrometry and transmission electron microscopy. Peptide gels were found to resist gastric digestion before being fully degraded in the intestinal phase while daughter peptides of capFFV were detected. Further studies are required to determine more precisely the conditions leading to degradation of the gels and assess the release site. Food-derived peptides are promising materials for oral delivery purposes as they are readily available, can be generated using common techniques, and their self-assembly properties can be tuned for specific applications.