Microbiota research opens up promising paths for improving the diagnosis — online press conference at 2nd World Summit “Gut Microbiota For Health” held on 26 February
(24 February 2013) An estimated 50 per cent of patients consulting a gastroenterologist suffer from functional bowel disorders (FBD), such as dyspepsia or irritable bowel syndrome (IBS). It is characteristic for these conditions that underlying physiological mechanisms are hard to be found. “However, recent research shows that the gut microbiota is a likely candidate for filling some of the gaps in the causal chain leading to FBD,” says Professor Fernando Azpiroz, Chairman of the Gut Microbiota & Health Section of the European Society of Neurogastroenterology & Motility (ESNM). This is one of the topics to be presented at the 2nd World Summit “Gut Microbiota For Health” in Madrid, Spain. From today until 26 February 2013, internationally leading experts will be discussing the latest advances in gut microbiota research and its impact on health.
Every second patient consulting a gastroenterologist complains of symptoms, such as nausea, bloating, constipation, diarrhoea or abdominal pain, without the doctor being able to detect a physiological cause by conventional diagnostic methods. These conditions are labelled as FBD. Among them, different subgroups, such as functional dyspepsia and IBS, have been defined, based on the symptom pattern and the presumable region of the gut where it originates. “A major problem we are facing with FBD is that the same symptom pattern can be produced by various pathophysiological mechanisms, as the expression capability and the symptom repertoire of the gut are very limited,” says Prof. Azpiroz. “This does not only impede efficient treatment, but also makes research difficult: although there are specific clinical diagnostic criteria to select patients for studies, these subgroups are heterogeneous.”
What causes functional bowel disorders?
In normal conditions, gut homeostasis is controlled by a complex net of feedback reflex mechanisms, and the digestive process evolves without being perceived by the individual. However, under certain circumstances, afferent pathways — which carry neuronal impulses from organs towards the brain — can be activated, causing the individual to consciously perceive abdominal symptoms that make up large parts of what is subsumed under the notion of FBD. These symptoms can be produced by abnormal gut contents, for instance, complaints of excessive gas production that may even interfere with the patients’ daily activities. FBD may also originate from impaired motor responses of the gut. Although conventional tests, such as intestinal manometry, may fail to identify these disorders, methods with higher sensitivity reveal motor abnormalities due to altered gut reflexes in a substantial proportion of patients with FBD. Another condition underlying FBD is visceral hypersensitivity. These patients perceive symptoms in response to stimuli that are well tolerated by healthy subjects. Over the past 20 years, a vast series of studies have characterised the mechanism of abnormal sensitivity in these patients.
The role of the gut microbiota
There are several indications that the gut microbiota is involved in the onset of FBD, such as dyspepsia and IBS. The gut microbiota participates in gut homeostasis and plays an important role in a number of digestive processes, one of them being gas production: meal substrates that are not absorbed in the small bowel enter the colon, where they may be fermented by colonic bacteria releasing gas. The volume of gas produced depends on the fermentative pathway, and hence the composition of the colonic microbiota. Some data also indicate that the colonic microbiota may modulate motor reflexes and influence gut motility, as the administration of probiotics in patients with constipation accelerates gut transit. Animal trials demonstrate that the sensory pathways between gut and brain are also affected by the microbial composition, as germ-free rats (i.e. rats without gut microbes) exhibit visceral hypersensitivity. In healthy individuals, there seems to be a regulating cross-talk between the colonic microbiota and nerve endings in the gut. Not only the absence of the gut microbiota, but also its abnormal composition may induce disorders. According to current opinion among researchers, this may cause the host to react and thus cause gastrointestinal disorders, among them FBD.
“However, while recent findings within the field of microbiota research have been encouraging, it often is still far from clear what they imply for clinical practice,” says Prof. Azpiroz. “Although there is evidence that the gut microbiota in IBS patients exhibits differences as compared to healthy subjects, these differences become blurred by the heterogeneity of IBS and FBD in general. Facing these difficulties, thorough physiological tests should be applied to select specific subgroups of FBD patients that share a clear pathophysiological mechanism, in order to then analyse the composition of their colonic microbiota. In these homogeneous subgroups, the likelihood of detecting significant differences in the gut microbiota composition may be higher.” Small intestinal bacterial overgrowth (SIBO) — excessive bacterial growth in the small intestine — has frequently been held responsible for the onset of IBS. “Whether SIBO really is crucial for the pathogenesis of IBS, is unclear,” Prof. Azpiroz says, “as the breath tests that have been used to establish its causal role have not been validated due to various methodological problems and large differences between studies.” Nevertheless, he points out that, apart from the many open questions, there is also some clinical advice that can already be drawn from current microbiota research findings: some data show that probiotics, prebiotics and synbiotics (combinations of pro- and prebiotics) may have some effect on IBS.
About the Gut Microbiota For Health Experts Exchange website
The www.gutmicrobiotaforhealth.com Experts Exchange, provided by the Gut Microbiota & Health Section of ESNM, is an online platform for health-care professionals, scientists, and other people interested in the field. Thanks to being an open, independent and participatory medium, this digital service enables a scientific debate in the field of gut microbiota.
Connected to www.gutmicrobiotaforhealth.com, the Twitter account @GMFHx, animated by experts, for experts from the medical and scientific community, actively contributes to the online exchanges about the gut microbiota. Follow @GMFHx on Twitter. Join the event on #GMFH2013
About the Gut Microbiota & Health Section of ESNM
ESNM stands for the European Society of Neurogastroenterology and Motility, a member of United European Gastroenterology (UEG). The mission of the ESNM is to defend the interests of all professionals in Europe involved in the study of neurobiology and pathophysiology of gastrointestinal function. The Gut Microbiota & Health Section was set up to increase recognition of the links between the gut microbiota and human health, to spread knowledge and to raise interest in the subject. The Gut Microbiota & Health Section is open to professionals, researchers, and practitioners from all fields related to gut microbiota and health. www.esnm.eu/gut_health/gut_micro_health.php?navId=68
About the AGA
The American Gastroenterological Association is the trusted voice of the GI community. Founded in 1897, the AGA has grown to include more than 16,000 members from around the globe who are involved in all aspects of the science, practice and advancement of gastroenterology. The AGA Institute administers the practice, research and educational programmes of the organisation. www.gastro.org
About Danone Dairy and Gut Microbiota For Health
Danone’s conviction is that food plays an essential role in human health namely through the impact that gut microbiota may have on health. That is why Danone Dairy supports the Gut Microbiota For Health World Summit and Experts Exchange web platform with the aim to encourage research and increase knowledge in this promising area, in line with its mission to “bring health through food to as many people as possible”.
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For further information on this topic, the article “Intestinal microbiota in functional bowel disorders: a Rome foundation report” by Magnus Simrén, Giovanni Barbara and others, published in Gut (Volume 62, Issue 1, pages 159–176, January 2013), can be downloaded at gut.bmj.com/content/62/1/159.full