Distinct Profiles of Fecal Volatile Organic Compounds Discriminate Ulcerative Colitis Patients With an Ileoanal Pouch From Those With an Intact Colon

Abstract

Fecal volatile organic compounds (VOCs) offer insights into gut microbiota function that may drive the pathogenesis of ulcerative colitis (UC). This cross-sectional study aimed to compare dietary intake and VOC patterns in UC patients with an ileoanal pouch compared to those with an intact colon. Seven-day food records and fecal samples were collected from UC patients with an intact colon (n = 28) or an ileoanal pouch (n = 11). Fecal VOC profiles were analyzed using gas chromatography-mass spectrometry. Dietary intake in both groups was largely similar. The mean Jaccard similarity index of VOC was 0.55 (95% CI:0.53, 0.56) in the pouch compared with 0.48 (0.47, 0.49) in the colon group (p < 0.01). A lower proportion of VOC classes was detected in the pouch, including sulfide (9% vs. 57%; p < 0.01), branched-chain fatty acids (BCFAs; 45%-64% vs. 93%-96%; p < 0.01), and ketones (45%-64% vs. 93%-96%; p < 0.01), along with a higher proportion of butyric acid (91% vs. 29%; p < 0.001). Unrelated to diet, VOC profiles show less functional diversity, reduced protein and greater carbohydrate fermentation, and altered production of secondary metabolites in the UC-pouch compared with the intact colon. These differences in the metabolic environment of the gut microbiota provide insights into pathogenesis and suggest that microbial-targeted interventions should be tailored accordingly.

Keywords: diet; ileoanal pouch; metabolomics; ulcerative colitis; volatile organic compounds.

FIGURE 1

(A) Box and whisker plot displaying the median number of VOCs detected in each of the two patient cohorts. (B) Venn diagram showing the number of VOCs detected in ulcerative colitis with an intact colon and those with an ileoanal pouch. (C) Graph showing the Jaccard similarity index as a measure of dissimilarity of volatile organic compounds. Bars and error bars represent mean (95% confidence intervals).

FIGURE 2

Principal component analysis of the presence or absence of volatile organic compounds in the two groups—shaded area shows 95% CI. Absolute values were used for the analysis, such that a present compound was represented by a one and an absent compound was represented by a nought. (A) Principal component analysis of patients with either an intact colon (n = 28) or an ileoanal pouch (n = 11). (B) Principal component analysis of patients with an ileoanal pouch, separated by current pouchitis status defined by total Pouch Disease Activity Index (PDAI) > 7 (n = 5 with current pouchitis, n = 6 without pouchitis).

FIGURE 3

Correlation matrix of dietary intake, fecal calprotectin and individual volatile organic compounds for ulcerative colitis patients with (A) an ileoanal pouch (n = 11) and (B) with an intact colon (n = 28). Positive correlations are shown in blue and negative correlations in red. The size of the circle correlates with the strength of the p value (p ≤ 0.05). Only significant correlations (analyzed using Pearson's correlations) are shown. sulfur AA, sulfur amino acids; CHO, carbohydrates; kJ, kilojoules; Oligos, oligosaccharides; RS, resistant starch; Xs fructose, excess fructose.