Functional investigations of enteroendocrine cell signalling in the intestine.

This research will investigate the chemical sensing capability of the digestive tract. We know that the gut digests fats, proteins and carbohydrates in our diet and absorbs their breakdown constituents. It also protects us from toxins in the gut lining. In order to achieve these two important functions the intestine has to sense its environment and contents continually. How it does this is not well understood, but exciting recent research indicates that specialised cells embedded in the inner lining of the gut sense nutrients within the gut lumen and also in circulating blood. These specialised cells, called enteroendocrine cells make and release hormones that can then alter gut function en route to the bloodstream, finally acting on the brain to stop feeding. We believe that animals put on weight when these hormones do not work efficiently. This is evident during the re-plumbing the intestine, which occurs during bariatric surgery (e.g. Roux-en-Y gastric bypass). Following this type of surgery the levels of 'good hormones' released from enteroendocrine cells are increased, and this is thought to result in long-term weight loss and to the unexpected rapid cure of type 2 diabetes (in 80% of bypass patients).

Our published research shows that certain sensing mechanisms in human and mouse gut are identical and therefore we use mice as our preferred model for investigation. Combinations of selective drugs may better mimic the combinations of hormone effects observed following the detection of mixed nutrient. However, we need to first understand the detail in order to anticipate the potential improvements of particular nutrient combinations that might optimally slow gut activities, reduce hunger and maintain a healthier weight for longer. This area of nonclinical research is consequently exciting and now that we have access to new, selective drugs (from our collaborators in Copenhagen and Nashville), that mimic or block specific pathways, we have the following aims.

We have 3 objectives:
1. To determine the cellular signalling pathways that occur when enteroendocrine cells come in to contact with individual chemicals that mimic nutrients in isolated preparations from normal mouse and human intestinal lining.
2. To determine whether the same mechanisms slow the passage of gut contents down the colon and slow stomach emptying in live mice.
3. Finally we will establish how mixed stimuli alter enteroendocrine cell signalling, and whether this results in amplified hormone responses that reduce gut transit further.
These studies are expected to shed light on the ability of the gut to signal via hormones in response to individual and combined stimuli that mimic dietary nutrients. The work will also contribute to a better understanding of the complexity of gut nutrient-sensing and identify how hormones released from the gut then alter its activity, and ultimately result in satiety, and reduced body weight.
Through this research we will provide a firm basis for the functional roles of several gut hormones as targets of therapeutic potential, possibly providing a basis for non-surgical weight loss in future. By understanding better what individual nutrients do within the gut wall, this work may also lead to improved functional foods in the future.

The groups of people who will benefit from this research include our collaborators and their teams in academia (in Copenhagen, Nashville and Sydney) collaborators in industry (Takeda Cambridge, Novo Nordisk, Astra Zeneca, GSK USA) our clinical colleagues and their patients (at KCL) plus BSc and MSc students studying at KCL who are interested in this research area and elect annually to perform research projects in our laboratory.

Nutrient sensing by enteroendocrine cells (EECs) in the gut is fundamental to hormone secretion, glucose homeostasis and food intake. How the gut responds to and modulates the nutrient delivery to different gut areas can have profound effects on the hormones released e.g. following bariatric surgery. However, our understanding of the cellular mechanisms underpinning nutrient sensing in healthy native tissues remains poor.
Our pilot data demonstrate how key peptides (e.g PYY, GLP-1, GIP) and 5HT present in EECs, signal to alter mucosal function. We also show that selective stimulation of different GPCRs found only on specific EECs can be recruited to cause PYY secretion, inhibit epithelial ion transport and gut transit. Notably, some of these mechanisms are identical in mouse and human mucosa.

Hypothesis: Nutrient metabolites trigger mucosal responses that depend on endogenous hormones released from EECs. These sensing mechanisms are modifiable by co-stimulation of specific nutrient GPCRs.
We will use Ussing chamber electrophysiology to measure vectorial ion transport across gut mucosae from mouse and human intestinal specimens. This technique maintains the polarised epithelium and is tailor-made to identify the sidedness of nutrient responses and will enable the signalling pathways to be characterised using selective synthetic ligands. The identification of endogenous mediators will be achieved using proven pharmacological strategies and gold standard tools. We will establish the extent of gut hormone release by assessing the same EEC stimuli on faecal pellet transit (in vitro) and on transit in vivo, measuring upper GI (a charcoal meal) and colonic (bead excretion) in mice.
This work will determine the mechanisms by which gut hormone mixtures recruited by specific receptor-signalling pathways alter intestinal functions. A better understanding of these neuroendocrine mechanisms may facilitate their exploitation as targets for improvements in functional foods.

The proposed work will provide much needed information critical for establishing the functional significance of gut-specific sensing mechanisms that have potential to contribute to satiety, leading to a reduced risk of obesity and its comorbidities.

Who will benefit from this research?
It is anticipated that the application of the data from this proposed work will have potential for improving health and thus the quality of life in an increasingly obesity-prone society. The data will first benefit those studying the treatment of obesity and diabetes in academia and the pharmaceutical industry, and possibly also those in the food industry working on nutraceuticals to aid the management of body weight.

This project aims primarily to provide a foundation for future work investigating the complexity of gut-specific mechanisms involved in obesity and diabetes, as well as the mechanisms involved in the acute and longer-term therapeutic benefits of bariatric surgery. It may thus benefit stake holders such as obese and diabetic patients, and the National Health Service.

How will they benefit from this research?
Determining the signalling pathways by which the gut senses the multiplicity of nutrient stimuli it receives and then co-ordinates the appropriate healthy hormonal response to this intake will provide vital information to those investigating the systems that regulate food intake and energy homeostasis in animals models and man.

If supported by further studies showing that specific nutrient ligand combinations can amplify the release of satiety-inducing hormones such as PYY and GLP-1 over the longer term, then targeting these mechanisms to optimally mimic these nutrient combinations may provide new therapeutic strategies for treating obesity and have a significant impact on obesity treatment. Current obesity therapies are few and relatively ineffective. Roux-en-Y bariatric surgery in contrast is very effective at causing long-term weight loss and resolving diabetes in a high proportion (~80%) of patients, but it is expensive and not available to the growing numbers of obese patients. A chemical alterative to, or an an adjunct with bypass surgery could potentially have economic benefits by reducing the costs of obesity to the NHS and reducing the costs of associated losses in economic productivity. There could thus be significant quality-of-life benefits and health benefits to the obese and over-weight. Such benefits would however require further preclinical and clinical human studies well beyond the time line of this project, and these may be expected to yield therapeutic benefit within 10 years.