Biophysical defence in the mammalian gut: Unlocking the molecular mechanisms of dietary fibre interaction with mucin glycoproteins.

Public Health England dietary recommendation for fibre is 30 g/day - twice above the average adult consumption in the UK. The recommendation is based on epidemiological evidence in which beneficial health outcomes, such as decreased risks of developing diabetes, heart disease and arthritis, are found to be associated with the diet rich in naturally integrated dietary fibre associated with the consumption of whole cereals, vegetables and fruit [SACN Carbohydrates and Health Report (2015)]. The definition of dietary fibre - "a type of carbohydrate that cannot be digested by our bodies' enzymes" - is based on chemical analysis and does not provide a fair prediction of its physiological effects. To date, there are no reliable measures of fibre "goodness" in term of its impact on the overall digestive health. This is partly due to a lack of understanding of fundamental mechanisms of how fibre "works" in human body.
In this project, we aim to advance our understanding about the role of dietary fibre in the protection of the gut and its mucus lining. Mucus secretions play a vital role in maintaining gut health by forming a physical barrier and supporting healthy gut microbiota. In the healthy gut, microbes reside in the upper layers of the mucus film, and thus are kept separate from the intestinal tissues. This physical separation minimises the possibility of microbes' incursion into the epithelium, which can cause inflammatory response and possibility of developing a chronic condition or gut dysfunction.
The mucus role in digestion and drug delivery is often overlooked due to mucus chemical complexity and heterogeneity. We take a different approach and put our focus on mucus biophysical properties such as flow properties (viscosity), "sliminess" (viscoelasticity) and lubrication. The project will consider and explore the role of these biophysical factors in order to identify the mechanisms by which dietary fibre affects barrier and protective functionality of mucus to ensure our digestive organs remain in good working order, especially in aging population.
Taking full advantage of novel characterisation and imaging facilities, the proposed study will consider a systematic approach whereby research will progress from model dietary fibre systems to food fibre particles isolated form white wheat flour. We will seek to vary systematically the dietary fibre composition, particles size and its mechanical property. The latter is of particular importance for advancing the area of minimally processed foods, which must strive to retain the natural structure of dietary fibre where the "soft" components (soluble fibre) are integrated within the solid-like particles (insoluble fibre). Further, through enzymatic modification and physical processing, we seek to develop dietary fibre assemblies that specifically designed to interact with mucus. In particular, we will focus on processing of wheat endosperm cell walls, a key fibre component of white wheat flour, to target the delivery of fibre functionality through one of the key cereal crops.
The outcomes of this study will advance the knowledge base of how functional dietary fibre can benefit mucus integrity and its barrier function. In practice, the results of this study will provide scientific underpinning and a set of new measurement techniques and tools for the food industry to enable rational development of healthier foods in an effort to increase the fibre intake across the UK. The insights generated will also guide the development of improved crops with enhanced dietary fibre functionality. The broader impact of this study has the potential to guide emerging research that targets major problems and challenges of digestive health such as gluten intolerance, inflammatory bowel dysfunctions and cystic fibrosis.

Mucus plays pivotal role in gut health, including its role in maintaining healthy microbiota. Despite the importance of mucus biofluids to human health and well-being, there is a limited knowledge about how dietary fibre interact with mucus. The emerging evidence suggests that fibre-rich diet can support mucus integrity and boost its barrier function.
This project considers the effect of dietary fibre on biophysical properties of mucus, such as rheology (flow, viscoelasticity), hydration, lubrication and permeability. The key scientific question is to uncover the interaction mechanisms between dietary fibre polymers / fibre assemblies (e.g., plant cell walls) and mucus. Common dietary fibre with proven health benefits (e.g., oat b-glucan) display no mucoadhesive properties when tested using instrumental techniques commonly employed in drug delivery research. The emerging hypothesis is that interactions are mediated by the bound water and are physical in nature amplified by polymer entanglement.
By bringing key capabilities in analytical centrifugation, rheology, micromechanical testing and advanced microscopy, the project aims to tackle this fundamental problem by addressing three specific research questions: (a) uncover the role of DF molecular architecture on hydration, viscoelasticity, and responsiveness of mucus/dietary fibre complexes; (b) by controlling the molecular architecture of fibre polymers, unlock the potential of fibre to control mucus rheological properties; and (c) design dietary fibre composites to tune and modulate mucus barrier functionality.
Methodologically, the project focuses on three groups of fibre materials: (a) soluble fibre polymers, (b) model dietary fibre assemblies (soluble/insoluble fibre composite), as well as (c) natural dietary fibre from wheat endosperm cell walls. The research platform enables delivering impact in the areas of food structure design, dietary recommendation policy, and biomedical areas.

The key challenge facing the effectiveness of dietary fibre (DF)-rich foods is establishing the link between DF structure/composition and the DF role in the gut. This limits our ability to define functional DF beyond rudimentary 'soluble'/'insoluble' categories and constrains development of technological solutions for selecting and modulating fibre structure in order to achieve positive health outcomes. The capability to measure the relevant biophysical and chemical properties of DF is one of the key outcomes of the proposed project. This advance will enable rational design of functional DF by targeting the development of specific DF structures through food manufacture and processing, as well as by optimising growth conditions of the crops.
Our focused project will stimulate wider consideration and discussion across a broader research community, raising awareness of policymakers and industry about the need for revisiting DF categorisation. The link between DF structure and physiological function will provide a set of hypotheses to drive future clinical and epidemiological research, outcomes of which will guide DF recommendation policy to effect improved DF intake globally. The need for improved DF functionality is of great concern to the developed and developing countries alike. In the former, there is a need to increase DF intake, whilst across the latter regions high intake of coarse or non-functional DF may inhibit absorption of proteins and lipids, leading to malnutrition.
By addressing a specific problem of DF interaction with mucins, this project will uncover how DF structure/composition affects mucus rheological and barrier properties, which is one of the least explored functions of DF. In addition, the project will develop biophysical characterisation techniques that deliver, for the first time, the toolbox of methods to characterise DF from the molecular level to nano-mechanics and macroscopic properties such as rheology. These techniques will be utilised by others in the field to probe the relationship between DF structure/composition and other functions of DF in the gut, such as influence on gut microbiota, competitive binding to digestive enzymes and influence on bile salt transport. Further, the outcomes of the project will be instrumental for tackling key digestive health challenges such as gluten intolerance and mucus dysfunction conditions such as inflammatory bowel conditions and cystic fibrosis.
In addition to providing a unique contribution to BBSRC's strategic priority area "Food, nutrition and health", the project will have direct impact on three areas within the food/animal nutrition industry. PI Yakubov's industrial background and CI Harding's track record of working with industry will ensure new insights will be leveraged and expedited with industry.
1. The food industry will receive a map of DF properties that influence mucus barrier function, thus providing a new technology platform for modifying DF from well-established sources (e.g., psyllium husk, oat b-glucan, wheat bran/endosperm cell walls) to produce highly efficiency food thickeners and gluten-replacing ingredients.
2. Improved understanding of functionality of DF from wheat can guide the development of wheat cultivars with specific composition and architectures of arabinoxylan fibre that positively influence mucus barrier function. DF in a form of wheat endosperm cell walls has high industrial potential due to ubiquity of wheat flour-based foods.
3. In addition to human nutrition, the outcomes will have impact in the area of animal nutrition, where fibre-modifying enzymes (e.g., xylanases) are already in use. We envisage that advances of this project associated with the use of arabinofuranosidases will benefit the introduction of solids to weaned pigs as well as in poultry. In addition, we expect that similar technologies can be applied in the area of pet nutrition to target the gut health.