Introduction:
Irritable bowel syndrome (IBS) affects most people, significantly affecting their daily lives without posing severe health risks. While the exact cause remains unclear, mounting evidence links it to the intestinal microbiota. Presently, treatments for IBS mainly focus on managing symptoms due to the absence of a definitive cure.
Fecal microbiota transplantation (FMT), an ancient remedy, has been investigated in randomized controlled trials (RCTs) that showed various levels of improvement in IBS symptoms after FMT. FMT appears to be safe, with mild and temporary side effects such as abdominal discomfort, cramps, and alterations in bowel habits.
However, the mechanisms behind FMT’s effectiveness are not well understood. At the same time, emerging evidence suggests that changes in gut bacteria, along with alterations in fermentation patterns and products like short-chain fatty acids, may play a role in alleviating IBS symptoms post-FMT.
What Is Irritable Bowel Syndrome?
Irritable bowel syndrome (IBS) presents as a chronic gastrointestinal disorder marked by abdominal pain and changes in bowel patterns. It is the most common condition seen by gastroenterologists, diagnosed primarily through the symptom-based Rome criteria. Notably, a significant portion of IBS patients also experience co-existing conditions such as anxiety or depression. Furthermore, patients with IBS tend to exhibit higher levels of somatization compared to those without IBS but with similar GI symptoms.
Despite advancements in unraveling the pathophysiology of IBS through research endeavors, therapeutic strategies primarily target symptom management, involving pharmacological and non-pharmacological approaches. It is imperative to comprehend the origins of gut dysbiosis in IBS. Some research suggests that probiotics and prebiotics may alleviate IBS symptoms, while fecal microbiota transplantation (FMT) emerges as a potential therapeutic avenue for IBS management.
What Is Meant by Fecal Microbiota Transplant (FMT)?
Fecal microbiota transplantation (FMT) involves transferring stool from a healthy donor to a recipient patient. Its roots trace back to ancient Chinese practices and gained modern recognition in 1958, notably for successfully treating pseudomembranous colitis caused by Clostridium difficile infection. Subsequent placebo-controlled studies confirmed its efficacy. FMT is under investigation for various metabolic syndromes, inflammatory bowel diseases, hepatic encephalopathy, and multiple sclerosis, with auspicious results seen in IBD.
FMT donors can be healthy relatives or anonymous individuals. The latter has advantages, including the potential to select donors with diverse microbiota and store pre-screened stools for multiple patients. Administration of FMT varies, including upper or lower endoscopic procedures, gastro-duodenal or rectal tubes, and encapsulation for release in the small intestine, which is notably effective for CDI treatment.
In recurrent CDI, repeated FMT via lower endoscopy yields high cure rates and patient acceptance. In the context of IBS, where the microbiota’s role remains unclear, FMT is hypothesized to correct dysbiosis, potentially alleviating symptoms. Gut dysbiosis in IBS is characterized by reduced bacterial diversity and abnormal proportions compared to healthy individuals’ microbiota.
FMT has increased bacterial diversity and incorporated donor microbiota into the recipient’s gut. However, given the complex composition of donor stool beyond bacteria, the long-term effects on the microbiota remain uncertain.
What Are the Factors Affecting Fecal Microbiota Transplantation?
Factors affecting fecal microbiota transplantation are as follows:
1. Donor Preference: This significantly influences the outcomes of FMT, particularly in conditions like IBD and IBS. In IBD, the concept of a super donor, whose feces elicit a robust response in patients, has been explored. However, efforts to enhance the chances of obtaining super donor feces by pooling donations have often failed due to dilution issues, leading to insufficient dosage for recipients.
Similarly, in IBS, variations in FMT trial results stem from variances in donor selection criteria. Successful trials have established clinical criteria and bacterial profiles for selecting super donors, while less successful ones lack such criteria. Factors affecting the stability and composition of donor intestinal bacteria, such as age, birth method, early diet, antibiotic usage, medication history, and lifestyle factors like exercise and diet, play crucial roles in selecting super donors.
Additionally, the donor should not be related to the recipient. The donor’s fecal microbiota must have high microbial diversity and deviations from the norm in specific bacterial markers, including increased levels of beneficial bacteria like streptococcus and Lactobacillus. Notably, the donor’s fecal bacterial composition should remain stable.
2. Patient Selection: The patient selection of FMT for IBS often involves specific subsets, and caution is necessary when generalizing the findings. The patient should have diarrhea-predominant and mixed diarrhea-and-constipation IBS. Despite adhering to a diet, the patient must have experienced moderate to severe symptoms for at least three months.
3. Route of Administration: The route of administration for fecal transplant varies, including delivery to the small intestine via a gastroscope or a naso-jejunal probe or to the large intestine through a colonoscope. Both routes are efficient, particularly in patients receiving the transplant into the colon, possibly due to the favorable impact of bowel preparation for colposcopy on IBS symptoms. While capsule ingestion has been successful for conditions like CDI, its effectiveness in IBS has been limited, potentially due to donor selection, low transplant dosage, or donor pooling rather than the method of administration.
How Does Fecal Microbiota Transplant Work in Irritable Bowel Syndrome Patients?
Differences in enteroendocrine cells and fecal SCFAs between IBS patients and healthy individuals are believed to be central to IBS pathophysiology. While it is premature to pinpoint the mechanisms behind FMT’s effects. Data suggests that FMT improves IBS symptoms by influencing enteroendocrine cells and SCFAs.
Most serotonin in the body resides in the gastrointestinal tract, primarily in serotonin-containing enterochromaffin (EC) cells. Serotonin regulates gastrointestinal motility and sensation transmission to the central nervous system.
Reduces serotonin reuptake transporter (SERT) levels in IBS patients, leading to impaired serotonin degradation. Certain gut bacteria, like Corynebacterium and Streptococcus spp., promote serotonin biosynthesis, which is potentially affected by FMT-induced changes in the gut microbiota.
Peptide YY (PYY), found in enteroendocrine cells, regulates water and electrolyte absorption. Reduced colonic PYY cells in IBS patients may contribute to symptoms. FMT increases fecal SCFAs, stimulating PYY secretion by up-regulating PYY gene expression.
Butyric acid levels rise post-FMT, providing energy to colonic epithelial cells and modulating the immune response and intestinal motility. Conversely, acetic acid reduction post-FMT may be significant due to its role in inducing visceral hypersensitivity. Increased levels of branched SCFAs suggest a shift towards proteolytic fermentation, akin to changes seen with low-FODMAP diet in IBS patients.
Conclusion:
FMT, a longstanding Chinese treatment utilized for both gastrointestinal and non-gastrointestinal ailments, has emerged as a promising therapy for IBS patients. It significantly improves IBS symptoms, fatigue, and quality of life. However, uncertainty persists regarding the criteria for selecting an influential super donor for FMT, the optimal dose, route of administration, and treatment frequency.
