Role of microbial fermentation products in irritable bowel syndrome

Dear Editors, We read the recent comment of Valeur et al. to our original article by Tana et al. We appreciate their interest in our works. However, we disagree their notion of difference in the proportion of fecal butyrate between our study and previous reports. In that study, we described that there were no significant difference in butyrate between patients with irritable bowel syndrome (IBS) and controls. To describe more precisely, butyrate in IBS patients (11.1 ± 1.5 lmol g, mean ± SE) showed trend higher value than that in controls (7.8 ± 1.3 lmol g, P = 0.088). The newest study of ours confirmed that butyrate is significantly increased in IBS patients compared with controls (T. Handa, C. Tana, Y. Umesaki, A. Imaoka, M. Kanazawa, S. Fukudo, unpublished data). Therefore, our studies on butyrate are in the same direction with the previous reports. The same condition of sampling in IBS patients as that in controls supports our report reflecting biological difference in fecal microbiota and their products. In the technical analysis in our laboratory, total organic acids in the stool sample under the temperature with 4 C showed 106.8 mmol L at 6 h, 102.6 mmol L at 24 h, and 109.8 mmol L at 48 h after the defecation, suggesting relatively stable levels of organic acids. Of course, we should not ignore possibility of some continued fermentation by microbiota during storage of fecal samples in the refrigerator although we analyzed them within 36 h. However, as was seen in the positive comments by Lee and Tack to our article, we should be aware of highly possible sequence of properties of microbiota, their products, acid-sensing receptors in the gut mucosa, and major symptoms in IBS patients. Further study on this issue is warranted.