Anja Luypaerts

The influence of inulin on the absorption of nitrogen and the production of metabolites of protein fermentation in the colon

In the present study, the production and fate of bacterial metabolites in the colon were investigated in a direct way using two substrates labelled with stable isotopes: lactose [(15)N,(15)N]ureide as a source of labelled ammonia and egg proteins intrinsically labelled with [(2)H4]tyrosine as a precursor of [(2)H4]p-cresol. Both ammonia and phenolic compounds are believed to be carcinogenic. Stimulation of carbohydrate fermentation in order to prevent accumulation of these toxic metabolites was induced by inclusion of inulin in a test meal or by addition of inulin to the daily diet, allowing us to distinguish between changes induced by the actual presence of a fermentable carbohydrate and effects caused by a long-term dietary intervention. When a single dose of inulin was administered together with the labelled substrates, a significant increase in faecal (15)N excretion, accompanied by a proportional decrease in urinary (15)N excretion was observed, probably reflecting an enhanced uptake of ammonia for bacterial biosynthesis, since an increased concentration of labelled N in bacterial pellets was found. A statistically significant reduction of urinary [(2)H4]p-cresol excretion was also noted. Upon supplementation of inulin to the daily diet during 4 weeks, however, only a tendency towards decreased urinary excretion of both labelled and unlabelled p-cresol was noted. Further studies are warranted to confirm these results in a larger cohort.

Inulin is an ideal substrate for a hydrogen breath test to measure the orocaecal transit time.

Background : A better substrate is needed for a hydrogen breath test to measure the orocaecal transit time. The currently used substrate, lactulose, accelerates the orocaecal transit time by increasing the osmolality of the gut contents. The recently developed lactose 13C‐ureide breath test is reliable, but a hydrogen breath test is preferred, as it allows the simultaneous investigation of the digestion and absorption of nutrients by means of 13C‐labelled compounds.

Oxidative breakdown of octanoic acid is maintained in patients with cirrhosis despite advanced disease

Abstract  As an octanoic acid 13CO2 breath test is frequently used to test gastric emptying of solid food, the purpose of the present study was to study whether oxidative breakdown of octanoic acid is affected by severe liver disease. The design of our study was twofold. First, cirrhotic patients (n = 82) of varying severity were compared with healthy controls (n = 17). Values of half‐time, time point of maximal expiration and cumulative recovery of octanoic acid breath tests (OBT) were not significantly different between them. Secondly, cirrhotic patients (n = 10) were studied before placement of transjugular intrahepatic portosystemic shunt, 4–7 days later and 1–2 months later. Values of half‐time, time point of maximal expiration and cumulative recovery of consecutive OBTs did not change significantly. The OBT may therefore be a suitable test in the future to detect delayed gastric emptying of solids in cirrhotic patients with reduced liver function and portal hypertension.

In vivo Influence of Nicotine on Human Basal and NSAID-induced Gut Barrier Function

Background: Smoking reduces the non-steroidal anti-inflammatory drug (NSAID)-induced small intestinal permeability increase in healthy people. It also affects inflammatory bowel disease that is associated with a disturbed gut barrier function. To assess the role of nicotine on barrier function, its influence on basal and NSAID-induced intestinal permeability was studied in healthy volunteers. Methods: Thirty-one healthy non-smoker subjects performed permeability tests with 51Cr-EDTA and sugar markers (sucrose, lactulose, mannitol, sucralose) before and during 2 weeks of nicotine patch application, and with and without indomethacin intake, respectively. Since smoking has been described as affecting motility, transit measurements were also done with the sodium[13C]-octanoate and lactose- [13C]-ureïde breath tests before and during nicotine exposure. Correlations between permeability markers were checked and the influence of gastrointestinal transit was assessed. Results: Nicotine did not affect barrier function in vivo, nor gastric emptying, small-bowel transit time or orocaecal transit. 51Cr-EDTA and lactulose correlated in basal 0–6 h permeability testing (r= 0.529, P < 0.0001), as did 6–24 h excretion of 51Cr-EDTA and sucralose (r= 0.474, P < 0.001); 97% and 90% of the subjects had a permeability increase after indomethacin intake for 0–6 h and 6–24 h excretion of Cr-EDTA, respectively. This population proportion is 63% for lactulose/mannitol and 83% for sucralose. Conclusions: Short-term exposure to nicotine does not alter normal basal or NSAID-induced gut barrier function or transit. 51Cr-EDTA and the respective sugar markers correlate well in in vivo permeability testing in healthy humans. The radioactive test detects more NSAID-induced permeability increase than does the lactulose/mannitol ratio permeability test.

Quantification of 15N-Nitrate in Urine with Gas Chromatography Combustion Isotope Ratio Mass Spectrometry to Estimate Endogenous NO Production

The use of stable isotope labeled substrates and subsequent analysis of urinary nitrate, forms a noninvasive test for evaluation of the in vivo NO metabolism. The present paper describes a new method for simultaneous quantification of (15)N-nitrate and total nitrate with gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). Nitrate, isolated from urine with a nitrate selective resin, was reduced to nitrite using copperized cadmium. Subsequently, Sudan I was formed by diazotation. Sudan II was added as internal standard, and both molecules were analyzed with GC-C-IRMS as tert-butyldimethylsilyl derivatives. The accuracy was determined during a recovery study of two different known nitrate concentrations and two (15)N-enrichments. A recovery of 101.6% and 103.9% for total nitrate and 107.6% and 91.2% for (15)N-nitrate was obtained, respectively. The validated method was applied on complete 72 h urine collections after intravenous administration of (15)N-nitrate and (15)N-arginine in humans. On average, 51.8% (47.0-71.0%) of administered (15)N-nitrate was excreted, while 0.68% (0.44-1.17%) of (15)N-arginine was metabolized to nitrate. In conclusion, this method can be used for accurate simultaneous determination of (15)N-nitrate and total nitrate concentrations in urine and can be applied in clinical studies for noninvasive evaluation of NO metabolism in vivo.

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).

13C-mixed-triglyceride breath test: Isotope selective non-dispersive infrared spectrometry in comparison to isotope ratio mass spectrometry in volunteers and patients with chronic pancreatitis

BACKGROUND The 13C mixed-triglyceride breath test (MTB) has been proposed for the non-invasive assessment of duodenal pancreatic lipase activity. Until now, stable isotope analysis of CO2 of the MTB has been carried out with isotope ratio mass spectrometry (IRMS). The aim of the present study was to compare MTB results by using the new non-dispersive infrared spectrometry (NDIRS) and the IRMS. METHODS Ten healthy volunteers and 10 patients with chronic pancreatitis and exocrine insufficiency were studied. After an overnight fast each subject received a test meal containing 250 mg 1,3 distearyl, 2[13C] octanoyl glycerol. Breath samples were taken at base line and at 30-min intervals over a period of 6 h postprandially. The 13C/12C ratio was determined in each breath sample by NDIRS and CF-IRMS as delta values. Results were expressed as delta over base line (DOB (per 1000)) and as cumulative percentage dose of 13C recovered (cPDR (%)). Correlations between IRMS and NDIRS were tested by linear regression analysis. For measuring agreement an Altman-Bland plot was performed. RESULTS A linear correlation was found (DOB: y = 0.645 +/- 0.040 x + 1.496 +/- 0.089, r = 0.70, P < 0.0001; cPDR: y = 1.269 +/- 0.031 x + 2.010 +/- 0.353, r = 0.93, P < 0.0001). For DOB the mean difference (d) was 1.0/1000, and the standard deviation (s) of the difference was 1.3/1000. The limits of agreement (d +/- 2 s) were -1.6/1000 and 3.6/1000. CONCLUSION The comparison of DOB and cPDR values by NDIRS and IRMS shows a moderate to good linear correlation. However, the distance of the limits of agreement is rather wide. Consequently, the validity of the MTB is diminished, which makes MTB by NDIRS less suitable for exact evaluation of non-invasive assessment of duodenal pancreatic lipase activity. Further studies are necessary to determine sensitivity and specificity of the MTB with NDIRS in larger study populations.