Research Links Gut Microbiome Changes to Brain Structure in Irritable Bowel Syndrome (IBS)

The international gastroenterology conference, Digestive Disease Week, which traditionally takes place annually in mid-to-late May or early June generally brings a wealth of news on state of the science developments in gastroenterology research for a range of conditions, including irritable bowel syndrome (IBS). One of the interesting and groundbreaking articles presented this year,  which has received recent coverage in both scientific and mainstream media, is a collaboration of 14 researchers from UCLA, Texas Children’s Microbiome Center and Baylor College of Medicine,  and the Washington University School of Medicine in St, Louis, Missouri. The authors confirmed the existence of IBS microbiome subgroups as found in various researchers’ past work and made a preliminary identification of some specific microbes and their metabolites that appear to be involved. Also, for the first time, they found that structural differences in the brains of some study volunteers with IBS appear to correlate with gut microbiome composition.

The open access full text of the journal article, “Differences in gut microbial composition correlate with regional brain volumes in irritable bowel syndrome” by J. S. Labus, et al, was published in  Microbiome on May 1, 2017 and is linked above. “Study shows association between gut microbes and brain structure in people with IBS” by Enrique Rivero of the medical news website Medical XPress was published on May 5, 2017 based on information from UCLA. These sources were consulted for the summary below.

International IBS research in past years has previously established that IBS involves disruptions in the brain-gut-microbiome axis in both directions from the brain to the lower GI tract and from the GI tract to the brain. It also has been known that there are structural and functional brain changes in IBS, particularly in the areas controlling sensation and salience (a mechanism of the brain involved in attention to and perception of the relevance of stimuli), and particularly in those with a history of early trauma. Additionally, it has been known that there are changes in microbiome composition in those with IBS compared to healthy controls. However, until now, because of the extremely large number and range of different types of microbes present in the GI tract, it has been challenging to pinpoint specific and consistent microbes or to connect these patterns to the neurological differences. The above study has begun to do so.

The investigators obtained a variety of data from the volunteers including, history, physical exam, numerous standard questionnaires for various aspects of mental health, behavior, diet, and trauma history, if any,  as well as stool samples and brain imaging. The study participants included 29 adults with IBS according to Rome III international diagnostic criteria (in effect at the time, although Rome IV has been in effect since May 2016), about three-quarters of whom were female, representing all of the bowel habit subtypes, diarrhea, constipation, alternating or mixed, and unspecified/unsubtyped. There were 23 control subjects without IBS, all of whom were female. The IBS and control groups were roughly similar in average age. The average length of having IBS for those in the IBS group was 11.3 years, plus or minus 13.2 years.

There were no statistically significant differences in diet. Although a minority of the IBS group showed clinical anxiety and the total trauma history scores were similar between the two groups, those with IBS reported greater anxiety, stress, catastrophizing and trauma history.

The microbiome analyses showed that the participants with IBS fell into two groups. 14 individuals (9 women, 5 men) had a statistically significant altered gut microbiomes while the other 15 (12 women, 3 men) had microbiomes that were essentially indistinguishable from the healthy controls. These differences between groups were not correlated with age, IBS subtype, medication usage, stress, anxiety, depression or catastrophizing. There was some association between history of early life adversity and length of time with IBS and the microbiome alterations in the first group.  Neurological changes in relation to the healthy control group were found in both subgroups of the volunteers with IBS, but were more pronounced and extensive in the group with the microbiome changes.

It should be emphasized that this was a preliminary, exploratory study of a relatively small sample group, and while many details of the findings appeared to the researchers to be consistent with past studies on IBS , some aspects were more surprising, and many unknowns remain, including the causes of these alterations in these individuals with IBS. However, it is hoped that in time, with further research, IBS investigators will be able to identify consistent microbiome patterns in particular subgroups of IBS that will aid in diagnosis and determination of the optimal treatments for  specific individuals.

IBS Impact looks forward to following the progress of research in this aspect of IBS and hopes to report on more advances in the months and years to come.


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