Greet Vandermeulen

Kinetics of butyrate metabolism in the normal colon and in ulcerative colitis: the effects of substrate concentration and carnitine on the β-oxidation pathway

Aliment Pharmacol Ther 2011; 34: 526–532

Wheat Bran Does Not Affect Postprandial Plasma Short-Chain Fatty Acids from (13)C-inulin Fermentation in Healthy Subjects

Wheat bran (WB) is a constituent of whole grain products with beneficial effects for human health. Within the human colon, such insoluble particles may be colonized by specific microbial teams which can stimulate cross-feeding, leading to a more efficient carbohydrate fermentation and an increased butyrate production. We investigated the extent to which WB fractions with different properties affect the fermentation of other carbohydrates in the colon. Ten healthy subjects performed four test days, during which they consumed a standard breakfast supplemented with 10 g 13C-inulin. A total of 20 g of a WB fraction (unmodified WB, wheat bran with a reduced particle size (WB RPS), or de-starched pericarp-enriched wheat bran (PE WB)) was also added to the breakfast, except for one test day, which served as a control. Blood samples were collected at regular time points for 14 h, in order to measure 13C-labeled short-chain fatty acid (SCFA; acetate, propionate and butyrate) concentrations. Fermentation of 13C-inulin resulted in increased plasma SCFA for about 8 h, suggesting that a sustained increase in plasma SCFA can be achieved by administering a moderate dose of carbohydrates, three times per day. However, the addition of a single dose of a WB fraction did not further increase the 13C-SCFA concentrations in plasma, nor did it stimulate cross-feeding (Wilcoxon signed ranks test).

T2026 A Dietary Intervention With Arabinoxylan Oligosaccharides Reduces Colonic Protein Fermentation in Healthy Subjects: Results From Faecal Metabolite Fingerprint Analysis

Background The addition of prebiotics to the diet may improve host health by modulation of the colonicmetabolism. The effect of a new candidate prebiotic, arabinoxylan oligosaccharides (AXOS), on the colonic metabolism was evaluated by characterization of the metabolite profile in faeces. Methods AXOS was administered for 3 weeks at 10 g/day to 20 healthy volunteers (30% male; age 23(20-45); BMI 21(18-26)). Faecal samples were collected before and after the intervention with AXOS. To determine a broad range of fermentation metabolites, metabolic fingerprinting was applied using a purge-and-trap system coupled on-line to a gas chromatograph time-of-flight mass spectrometer (GC-TOF-MS). Cluster analysis, based on relative indices of all identified volatile organic compounds (VOCs) versus 2ethylbutyric acid as internal standard, was used to compare the metabolite profiles. Results A total of 179 different VOCs were identified in the faecal samples, 24 VOCs were present in more than 70% of the samples. The compounds acetaldehyde, butanoic acid, dimethyl disulfide, dimethyl trisulphide and limonene were present in all samples. Cluster analysis of the VOC fingerprints allowed to discriminate baseline samples from the samples after the intervention with AXOS, suggesting that the impact of the intervention exceeded the interindividual variability (Figure). This discrimination was mainly due to protein fermentation metabolites such as p-cresol, branched-chain fatty acids (4-methyl pentanoic acid, 2-methyl propanoic acid and 3methyl butanoic acid) and sulphur containing compounds (hydrogen sulphide, carbon disulfide, dimethyl tetrasulfide). Faecal short-chain fatty acids did not contribute to discrimination between both groups, although this does not preclude an increased SCFA production in the proximal colon. Conclusion Dietary intervention with AXOS has a considerable impact on the colonic metabolism mainly by decreasing proteolytic activity.

Mo1799 Increased Fecal Water Cytotoxicity in Patients With Ulcerative Colitis Is Associated With Low Levels of Short Chain Fatty Acids

Background: Many studies have focused on the fecal microbiota however it is now widely accepted that the gastrointestinal (GI) mucosa associated microbiota, rather than luminal content, is critically important in host-microbe interactions linked to health and disease. Mucosal biopsy is the most common sampling technique used to assess the mucosa associated microbiota. However, normal biopsy devices are designed to take samples for histologic assessment. Thus when biopsies are taken via working channels that are also used to aspirate luminal content it is highly likely that cross contamination occurs, that ultimately questions the validity of these samples. In view of this difficulty we have developed a novel device that allows targeted biopsies to be taken in any segment of the GI tract without cross contamination in an aseptic manner. Methods: Six patients undergoing upper GI endoscopy for iron deficiency were recruited with consent and ethical approval. In pilot experiments various prototypes of a sampling device were tested in vivo. Two final configurations of a sheath that covered miniature biopsy forceps were tested and compared with the normal single-use biopsy forceps (18 samples). Matched duodenal biopsy samples were collected from each patient, transferred individually into RNA later, and subject to gDNA extraction. Amplicon libraries spanning the V6-V8 region of the 16S rRNA gene were constructed, sequenced using the Illumina MiSeq platform, and analysed via the QIIME pipeline. Results: Microbial DNA, representing a diverse community, was observed in all duodenal samples obtained using the aseptic device, indicating this device is effective in sampling mucosa associated organisms present in the duodenum (Chao 1 estimated richness = 386, Goods coverage 99.8%). Assessment of the duodenal microbiota revealed a community dominated by the genera Streptococcus, Prevotella, Veillonella, Neisseria and Porphyromonas. There were substantial differences in the microbiota of samples obtained using the aseptic device and samples obtained with standard biopsy forceps. Only a low level of correlation (Pearsons r<0.6) between the matched biopsy pairs was seen across all bacterial phyla observed. Phylogenetic based (UniFrac) evaluation of beta-diversity revealed the aseptic samples clustered together and showed reduced inter-individual variability compared to those obtained with standard forceps. Conclusions: Sampling of duodenal biopsies with routine biopsy forceps resulted in greater microbial diversity as compared to samples acquired under aseptic conditions. This suggests cross contamination from other sites of the upper GI tract when utilising standard forceps. Based upon our data, aseptic techniques with a specific sampling device should be used to collect samples for studies that aim to define the mucosa associated microbiota.

Mo1800 Colonic Luminal Compounds Do Not Affect Butyrate Metabolism in Ulcerative Colitis

Background: Many studies have focused on the fecal microbiota however it is now widely accepted that the gastrointestinal (GI) mucosa associated microbiota, rather than luminal content, is critically important in host-microbe interactions linked to health and disease. Mucosal biopsy is the most common sampling technique used to assess the mucosa associated microbiota. However, normal biopsy devices are designed to take samples for histologic assessment. Thus when biopsies are taken via working channels that are also used to aspirate luminal content it is highly likely that cross contamination occurs, that ultimately questions the validity of these samples. In view of this difficulty we have developed a novel device that allows targeted biopsies to be taken in any segment of the GI tract without cross contamination in an aseptic manner. Methods: Six patients undergoing upper GI endoscopy for iron deficiency were recruited with consent and ethical approval. In pilot experiments various prototypes of a sampling device were tested in vivo. Two final configurations of a sheath that covered miniature biopsy forceps were tested and compared with the normal single-use biopsy forceps (18 samples). Matched duodenal biopsy samples were collected from each patient, transferred individually into RNA later, and subject to gDNA extraction. Amplicon libraries spanning the V6-V8 region of the 16S rRNA gene were constructed, sequenced using the Illumina MiSeq platform, and analysed via the QIIME pipeline. Results: Microbial DNA, representing a diverse community, was observed in all duodenal samples obtained using the aseptic device, indicating this device is effective in sampling mucosa associated organisms present in the duodenum (Chao 1 estimated richness = 386, Goods coverage 99.8%). Assessment of the duodenal microbiota revealed a community dominated by the genera Streptococcus, Prevotella, Veillonella, Neisseria and Porphyromonas. There were substantial differences in the microbiota of samples obtained using the aseptic device and samples obtained with standard biopsy forceps. Only a low level of correlation (Pearsons r<0.6) between the matched biopsy pairs was seen across all bacterial phyla observed. Phylogenetic based (UniFrac) evaluation of beta-diversity revealed the aseptic samples clustered together and showed reduced inter-individual variability compared to those obtained with standard forceps. Conclusions: Sampling of duodenal biopsies with routine biopsy forceps resulted in greater microbial diversity as compared to samples acquired under aseptic conditions. This suggests cross contamination from other sites of the upper GI tract when utilising standard forceps. Based upon our data, aseptic techniques with a specific sampling device should be used to collect samples for studies that aim to define the mucosa associated microbiota.