Marissa Holden, MD, on the Altered Autonomic Nervous System in IBS
The autonomic nervous system (ANS) is known to be altered in irritable bowel syndrome (IBS). However, the impact of the alteration on bowel function, gut microbiota, and cortisol response in IBS has remained unknown.
Results of a study presented at Digestive Disease Week 2019 showed that ANS activity both at rest and under stress influenced bowel function and microbial composition, which suggests that the ANS has a role in IBS symptom generation.
Gastroenterology Consultant caught up with Marissa Holden, an MD candidate at the David Geffen School of Medicine at UCLA, about the research.
Gastroenterology Consultant: What prompted you to conduct the study?
Marissa Holden: The pathogenesis of IBS is not completely understood, but evidence supports that it is a stress-sensitive disorder. The ANS, along with the hypothalamic-pituitary-adrenal (HPA) axis, are the two main central response systems to stress. IBS is considered a disorder of altered brain-gut interactions, which can affect the ANS. In turn, this can cause disturbances in gastrointestinal function, resulting in symptoms such as abdominal pain and diarrhea and/or constipation. There is also increasing evidence that the gut microbiome is altered in IBS. We thought it would be important to determine how this dysregulated ANS affects the microbial composition of the gut, its role in IBS, and whether it could be a potential therapeutic target. Our guts have a whole community of microbes that may have a role in the development of numerous diseases, which I find fascinating.
GASTRO CON: Why do you think the relationship between the ANS and IBS is important for gastroenterologists to understand?
MH: While our bodies are equipped to handle acute stress with responses from our sympathetic nervous system and the HPA axis (cortisol), chronic stress—as seen among patients with IBS—leads to overactivation and dysregulation of these systems. In the study, we found that basal cortisol was associated with a greater autonomic response to a visceral stressor, which indicated that both arms of our stress response are correlated. We also demonstrated that this stress response may be altering the composition of the gut microbiota, with greater sympathetic tone being associated with Prevotella species and greater parasympathetic tone being associated with Lachnospiraceae.
GASTRO CON: What surprised you most about the findings?
MH: Our study confirmed our previous findings that greater sympathetic/vagal response is seen in men compared with women. However, we were surprised that there were not more significant findings between IBS patients and healthy controls. We were also surprised to see that the ANS response was similar at rest and in response to a visceral stressor. The associations between the ANS and the gut microbiome composition was also pleasantly surprising, because it suggests that the ANS can modulate the gut microbiome.
GASTRO CON: How can a gastroenterologist apply the findings to clinical practice?
MH: These results can be used by gastroenterologists to educate and better counsel their IBS patients about the pathophysiology of this common condition. It is important to identify any triggers, eg stress, related to the onset of IBS, as well as symptom flares. Relaxation breathing has been shown to be efficacious in IBS, and this would help increase vagal tone and hopefully provide greater autonomic balance and improve symptoms. In regard to differences in microbiome composition, more research needs to be done to understand if microbial composition or the metabolites are altered in IBS, as well as their impact on disease phenotype.
GASTRO CON: What are the next steps of your research?
MH: We would like to explore how the ANS can alter the fecal and mucosal adherent microbial composition in response to stress based on sex, bowel habit, symptom severity, and trauma.
Reference:
Holden MG, Naliboff BD, Shih W, et al. Autonomic nervous system response in irritable bowel syndrome is associated with sex, bowel habit and gut microbiota [Su1606]. Presented at: Digestive Disease Week; May 18-21; San Diego, CA. https://www.gastrojournal.org/article/S0016-5085(19)38345-3/pdf. Accessed June 5, 2019.