Possible Mechanisms Underlying the Effects of Fecal Microbiota Transplantation in Patients With Irritable Bowel Syndrome

Background/Aims: : This study aims to identify the mechanisms underlying the effects of fecal microbiota transplantation (FMT). Methods: : This study investigated 93 patients included in our previous clinical trial: 24 received 30 g of their own feces (placebo group), while 47 and 22 received 30 g and 60 g of donor feces, respectively. The patients underwent sigmoidoscopy with biopsies, provided fecal samples, and completed questionnaires to assess irritable bowel syndrome (IBS) symptoms, fatigue, and quality of life at the baseline and at 1 month following FMT. The biopsy samples were immunostained for Musashi-1, neurogenin-3, and enteroendocrine and immune cells. The cell densities were quantified by computerized image analysis. Fecal short-chain fatty acids (SCFAs) were measured by gas chromatography, and fecal bacteria were measured by 16S ribosomal RNA polymerase chain reaction DNA amplification. Results: : The densities of stem cells, enteroendocrine cell progenitors, serotonin, glucagon-like peptide 1, and peptide YY (PYY) cells increased following FMT in the 30-g and 60-g treated groups but not in the placebo group, and they were inversely correlated with both IBS symptoms and fatigue. The densities of submucosal immune cells and mast cells decreased following FMT in the 30-g and 60-g treated groups but not in the placebo group, and they were correlated with IBS symptoms and fatigue. The fecal level of butyric acid increased in patients treated with donor feces, and this was inversely correlated with IBS symptoms and fatigue. Conclusions: : Stem cells, enteroendocrine progenitors, serotonin, and glucagon-like peptide 1 as well as low-grade inflammation may play roles in IBS symptom manifestations. The effects of FMT are probably due to the amelioration of these abnormalities.