The relationship between dietary iron and the gut microbiota. Can dietary iron regime be exploited to improve health?

The adult human gut is home to ~100 trillion microbes collectively known as the 'microbiota'. The gut microbiota is largely composed of bacteria and plays a key role in maintaining our wellbeing. The microbiota assists in processing food into favourable energy sources that sustain our health, and it also generates essential vitamins (e.g. vitamin K, folate, biotin), protects against gut infections and contributes to the development of our immune system. Over 1000 different types of bacteria reside within the gut, but composition varies between individuals and is subject to change. Importantly, it is now clear that alterations in our microbiota are linked to various diseases, e.g. allergy, anorexia, autism, Coeliac's disease, Crohn's disease/Ulcerative Colitis (IBD), obesity and diabetes. However, the manner in which disease state is influenced by our microbiota is poorly understood, as is the way in which diet affects the composition of our gut microbiota to influence disease.

Iron is a minor yet crucial dietary component required by virtually all lifeforms. Iron deficiency in humans is the most common form of malnutrition causing iron-deficiency anaemia (IDA) affecting ~2.4 million adults and ~2.3 million children in the UK alone. IDA causes fatigue, poor concentration, weakened immunity and poor performance at school and work - representing a major economic and societal burden. IDA is treated by oral iron supplements and incidence may be reduced by iron fortification (e.g. white flour). However, iron supplements often cause undesirable gastrointestinal side-effects (nausea, abdominal pain, constipation, diarrhoea). In addition, there is mounting evidence demonstrating that dietary iron influences composition of the microbiota, with iron supplementation causing deleterious reductions in levels of beneficial commensals. Such changes are negative indicators of gut health. Indeed, extra iron provision in the diet can promote growth of pathogenic enterobacteria which may in turn provoke debilitating infectious diarrhoea. Currently, it is not clear how iron enhances these populations and diminishes the protective resident microbiota, nor is it understood how dietary iron influences the gut microbiota in general. However, it is likely that a major component of such iron-induced alterations in the microbiota is due to differences in the way in which the distinct types of bacteria within our gut respond to iron. Unfortunately, the relationship between dietary iron, gut microbiota and health/disease remains little explored, and so the potential for positive manipulation of the gut microbiota through dietary-iron regime cannot yet be exploited to promote our health and combat disease.

This project will employ controlled in vitro models of our large intestine (where most gut microbiota reside) and human trials to investigate how the composition and metabolic activity of the microbiota are influenced by iron, and the impact that this has on health-related outcomes. We will explore different iron sources as well as dietary components that enhance or decrease iron availability. The ability of prebiotics to reverse unfavourable iron-induced alterations in the gut microbiota will also be investigated. In addition, the impact of iron on the gut microbiota during weaning will be examined, as this crucial period involves a dramatic increase in dietary iron content and availability, along with major changes in the gut microbiome. Increases in dietary-iron provision may be key in the development of an 'adult'-like microbiota upon weaning, a possibility that remains unexplored. We will thus shed new light on the relationship between our microbiota, and diet & health, allowing us to inform key interest groups such as nutritional scientists, the food & drink industry, government and the general public so that the effects of dietary iron on the status of our microbiota can be incorporated into current thinking to improve health.

Previous work indicates a major role for iron in dictating the makeup of the gut microbiome, showing that colonisation by specific bacterial species is governed by their iron-acquisition capacity. However, no systematic analysis has been performed that allows sound understanding of the manner in which forms and amounts of dietary iron affect the profile and metabolic output of the entire gut microbial community, and the consequence of such effects upon health. Our aim is to close this information gap by using in vitro gut systems that allow us to reveal the impact of a wide range of iron regimes on the gut microbiota in a controlled fashion.

Gut cultures will employ faecal inocula from healthy adults with a re-formulated 'low iron' gut-model medium (see preliminary data). This will be supplemented with a range of relevant iron compounds that may alter the microbiota composition during growth. We will test other relevant factors including iron chelators and reductants affecting iron speciation, as well as prebiotics that may ameliorate negative impacts caused by iron supplements. Various analyses of culture samples will be performed to test Fe-regime impact: NGS-community profiling, SCFA, NH3, Fe redistribution, metabonomics, total bacteria (FISH-Flow) and cytotoxicity. We will also compare faecal inocula from pre-/post-weaned infants to determine how the pre-weaned microbiota community is modulated by iron regime. Data collected will be used to design regimens for continuous-culture gut-model systems to explore the effect of switching from low to high iron availability (and vice-versa), which will reveal whether the microbiota can recover from iron perturbation. Double-blind human intervention studies will be used to test the effect of iron-supplementation and chelators on the gut microbiota, gut-health and iron-status. In both cases, the additional impact of prebiotics will determined.

The proposed project matches the needs of the food & drink industry since it will provide new knowledge assisting the selection of guidelines for healthier products. Also, the proposed metabolomics work could identify novel biomarkers for those subject to low or high iron diets. The proposed work will promote our understanding of how iron nutrition (including fortification and supplementations) can best support life-long health and wellbeing, and will further establish in vitro cultures as applicable models for studies on the influence of micronutrients on the microbiota. It could also contribute to developing strategically-important dietary intervention strategies for public-health conditions (e.g. type-2 diabetes, obesity, IBD). By determining how different dietary-iron components influence the gut microbiome (and the potential impact that this has on health), our proposed research will provide a unique perspective on how dietary iron can be manipulated to support and maintain a healthy digestive tract.

The outputs from the project would include publications in peer-reviewed open-access scientific journals and presentations at national/international conferences (e.g. the Gut Microbiota For Health Summit, Wellcome Trust Annual Microbiome Conference, International Scientific Association for Probiotics and Prebiotics, UK Nutrition Society meetings, European Iron Club, European Nutrition Conference). We will engage with the Food & Drink Industry (e.g. through DRINC Club workshops and our own contacts) to promote our work and findings - making use of the experienced Communications and Media Office facilities at our institutions, and good links with the London Science Media Centre for targeted press releases of significant findings to audiences including policy makers such as BNF, DoH, EU, FSA, ILSI, NHS, NS. The applicants are frequently approached by the media for comments on latest research and have a wide range of contacts in this area (e.g. BBC, Channels 4 and 5, CNN, ITV, Sky TV; national, local and international radio outlets; influential health writers in the UK). These provide multiple routes for engagement with the public. Moreover, we are active in public dissemination programmes such as University public lecture series, Royal Society of Chemistry's public event series Uo3rd Age, Women's Institute, Café Scientifique, Universities week at the Natural History Museum, Royal Berkshire Show, University Public Lectures and the STEM Network. We also have a collaborative demonstration with the London Science Museum throughout 2015, the theme of which is entirely relevant to this project - this will be viewed by >4m visitors. This will transfer to the Manchester Museum of Science and Industry in 2016.

The main routes for implementing these benefits will be initially through dissemination and further research. Dissemination activities in the form of publications in high impact journals and international conferences will increase the opportunities for further funding and collaboration. We recognise the importance of dissemination to industry, other users and consumers, so publications will be made through partners' newsletters and websites, and published findings highlighted via press releases. We will host a dissemination workshop at the end of the project for relevant stakeholders (e.g. nutritionists, food & drink industry, DRINC Club members). The project will be promoted by establishing a web page summarising the relevance of the research, and its objectives, findings and conclusions. To ensure that maximum impact arises from our work, any potentially useful intellectual property will be referred to the University Intellectual Property Management and the Research & Enterprise Development teams. Both patentability and commercial value will be considered, and where relevant possible commercial partners will be sought using our current connections with the Food & Drink Industry.