Characteristics of fecal metabolic profiles in patients with irritable bowel syndrome with predominant diarrhea investigated using ¹H‐NMR coupled with multivariate statistical analysis

Abstract

Background: Gut microbiota are known to be closely related to irritable bowel syndrome (IBS). However, not much is known about characteristic fecal metabolic profiles of IBS. We aimed to characterize fecal metabolites in patients with IBS with predominant diarrhea (IBS-D) using 1 H-nuclear magnetic resonance ( 1 H-NMR) spectroscopy. Methods:In this study, we enrolled 29 patients diagnosed with IBS-D according to the Rome IV criteria, 22 healthy controls (HC) and 11 HC administered laxatives (HC-L) in the age group of 20-69 year. The usual diet of the patients and HC was maintained, their fecal samples were collected and investigated by NMR-based global metabolic profiling coupled with multivariate statistical analysis. Results:We detected 55 metabolites in 1 H-NMR spectra of fecal samples: four amines, 16 amino acids, six fatty acids, eight organic acids, three sugars, and 18 other compounds. Orthogonal partial least square-discriminant analysis derived score plots showed clear separation between the IBS-D group and the HC and HC-L groups.Among the 55 metabolites identified, we found five disease-relevant potential biomarkers distinguishing the IBS-D from the HC, namely, cadaverine, putrescine, threonine, tryptophan, and phenylalanine. Conclusions:The patients with IBS-D were clearly differentiated from the HC and HC-L by fecal metabolite analysis using 1 H-NMR spectroscopy, and five fecal metabolites characteristic of IBS-D were found. The findings of this study could be used to develop alternative and complementary diagnostic methods and as a source of fundamental information for developing novel therapies for IBS-D.

Application of metabolomics to the study of irritable bowel syndrome

“…1 H‐NMR 6,29‐35 and mass spectroscopy (MS) 5,19,27,33,36‐46 are the main detection techniques available that determine the types of metabolites detected. 1 H‐NMR detects all organic classes, is quantitative, and can be used to identify the molecular structure but is more expensive, has relatively lower sensitivity, requires greater sample volumes and cannot detect inorganic ions or salts.…”

“…Understanding the nature and rigor of bioinformatics applied to the data generated in each study is critical to understanding the validity and implications of the findings, but these details are often not fully reported. Table 1 shows that the predominant method is multivariate analysis (see Worley et al 49 for details), but other bioinformatics approaches have also been used 6,19,27,29‐35,38,40,43‐46,50‐52 …”

“…In this issue of the journal, Lee et al show that by using proton ( 1 H) nuclear magnetic resonance (NMR) to examine fecal metabolites, they could separate IBS‐D patients and healthy controls based on their metabolite profiles. Interestingly, they could also differentiate IBS‐D patients from healthy controls given a stimulant laxative and therefore concluded that the changes in metabolite profiles were likely due to the disease rather than fast intestinal transit per se 6 . Based on these findings they suggest that the metabolites could provide biomarkers of IBS and some may play a pathophysiological role.…”

“…Therefore, new approaches are needed that might enable non‐invasive studies with sufficient sensitivity and specificity to advance the field. In this issue of the journal, Lee et al focused on IBS‐D patients and aimed to characterize fecal metabolite profiles of patients compared with healthy controls as well as to determine if diarrhea in and of itself can impact fecal metabolite composition 6 . This review will focus on the use of metabolomics to study IBS patients highlighting key methodological issues underlying the interpretation of these studies, whether identified molecules provide novel insights into pathophysiology and/or serve as biomarkers, 6 and how the study by Lee et al have contributed to these concepts.…”

“…Metabolomics can be performed on any biological sample, such as stool, urine, blood, and tissue but there are a number of considerations, such as ease of collection, the properties of the metabolite, for example, half‐life, its source, lipid solubility, and interaction with other compounds such as bile 25 . Degradation of metabolites in stool and urine is of particular concern and investigators typically have patients freeze the samples at home following collection, or if possible, as in the study by Lee et al, have the patients provide the samples for processing within minutes after sample collection 6 …”