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Development of an in vitro cellular model to predict the immunological impact of dietary proteins

Periodic Reporting for period 1 - IVSysImmunoProt (Development of an in vitro cellular model to predict the immunological impact of dietary proteins)

Reporting period: 2016-09-01 to 2018-08-31

The global incidence of chronic diseases is increasing at an alarming rate. While it is recognized that diet plays a crucial role in the incidence of chronic diseases, much remains to be discovered regarding the mechanisms by which food components affect the body’s metabolic functions. Proteins are essential dietary factors recognized to be instrumental in a wide range of nutritional and biological processes. In addition to providing amino acids for protein synthesis, food proteins and their products of digestion can influence a number of regulatory systems, including the immune system. By interacting with the immune system, proteins can help balance and stabilize immune responses, but may also cause adverse effects such as inflammation and gut disorders. Despite the knowledge that proteins and protein-derived peptides can exert regulatory activities, few studies have investigated the absorption of these bioactive molecules through the gastrointestinal wall. Little is also known on the actual mechanisms by which proteins and peptides exert these functions nor how food processing, such as heat treatment or hydrolysis, may impact proteins’ absorption and their regulatory effects. The overall objective of this project is to study the intestinal transport of dietary proteins and investigate the effect of the absorbed proteins/peptides on the immune system in vitro.
In the first step of the project, an in vitro model systems closely mimicking the intestinal epithelium was developed by co-culturing different human cell lines. The model was then validated for the presence of key features found in human enterocytes, including M-cells, using scanning electron microscopy. Following validation, the model system was used on its own to investigate the intestinal transport of a number of commonly consumed and emerging protein sources such as those from milk, quinoa, hemp and lesser mealworm. Additionally, it was used in combination with immunes cells such as macrophages to investigate the immunomodulating properties of the transported proteins/peptides as well as their impact on enzymes, particularly dipeptidyl-peptidase IV (DPP-IV), found in the gastrointestinal tract and expressed on the membrane of various type of lymphocytes.

While un-treated proteins showed low intestinal permeability and displayed no or weak immunological effect, peptides generated from their in vitro gastrointestinal digestion were able to generate immune responses, such as influencing cell proliferation and cytokine secretion, and this ability was retained following their intestinal transport. Some active peptides were transported intact across the intestinal epithelium, while other where hydrolyzed by intestinal brush border enzymes into fragments of various potency levels. Protein digests and hydrolysates, particularly those from milk and mealworm proteins, were shown to have inhibitory activity against the DPP-IV enzyme, suggesting that they may play a dual role in preventing the degradation of chemokines as well as the incretin hormones which are involved in blood glucose regulation.

The work performed, and results obtained, during this project were shared at training and networking events organized at the University of British Columbia (Vancouver, Canada) and the European Molecular Biology Laboratory (Heidelberg, Germany) as well as at scientific meetings such as the American Diary Science Association (ADSA) annual meeting (Knoxville, United States) and the XI ISIN conference on immunonutrition (London, England).
Nutrition being a crucial factor in the incidence of chronic diseases, it is essential to develop tools that will help gain a better understanding of the impact of dietary components on health. The in vitro model system developed during this project can help shed light on the intestinal uptake of food components and their potential immunological effects as well as provide information on how food processing can impact these properties. As the world population continues to grow, there is an urgent need to find alternative, more sustainable sources of nutrients, particularly proteins. While these new food sources must be safe for human consumption, it is also essential to be able to evaluate their nutritional and biological effects. The findings generated during this project could be of interest to the European food industry/companies as a screening tool to assess the nutritional impact of novel, alternative proteins and help identify those with beneficial health properties.
Experimental set-up for the induction of M-cells in a Caco-2 culture