Analysis of the urinary glucose-[¹5N, ¹5N]-ureide content in the study of the lactose-[¹5N, ¹5N]-ureide metabolism in healthy humans.

BACKGROUND/OBJECTIVES: Lactose-[(15)N, (15)N]-ureide is used to study the fate of the colonic urea-nitrogen metabolism. During the passage through the gastrointestinal tract, lactose ureide is hydrolysed to glucose ureide, which is absorbed to a limited extent from the small intestine and is excreted urinarily. In the present study, a procedure has been developed to quantify the urinary excretion of glucose-[(15)N, (15)N]-ureide. In addition, urine and faecal samples obtained during a dietary intervention study with the prebiotic lactulose were retrospectively analysed. SUBJECTS/METHODS: The glucose ureide and lactose ureide content was measured by GC-MS in 19 healthy volunteers. After consumption of a standard test meal containing 75 mg lactose-[(15)N, (15)N]-ureide, six healthy volunteers performed a fractionated 24 h urine collection to investigate the urinary excretion of glucose-[(15)N, (15)N]-ureide. In 13 volunteers, the effect of lactulose administration on the urinary excretion of glucose-[(15)N, (15)N]-ureide was analysed. RESULTS: The urinary excretion of glucose-[(15)N, (15)N]-ureide reached its maximum level in the 3-6 h urine collection and decreased in the 6-9 h urine. The label was still detectable in the 9-24 h urine collection. The cumulative excretion of (15)N-labelled glucose ureide after 24 h amounted 12.91%. No significant differences in glucose-[(15)N, (15)N]-ureide excretion were found in either of the urine fractions after administration of lactulose, compared with baseline. In none of the urine samples lactose-[(15)N, (15)N]-ureide was detected. CONCLUSIONS: In conclusion, the results obtained in the present study indicated that the percentage dose glucose-[(15)N, (15)N]-ureide recovered in urine is rather constant and not influenced by the presence of lactulose.

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. METHODS: The usefulness of different types of inulin as a substrate for a hydrogen breath test was studied. Raftilin HP (>99% inulin with a degree of polymerization of between 5 and 60 and <0.5% glucose, fructose and sucrose) was further evaluated and compared with lactulose with regard to its effects on gastric emptying and the digestion of protein and lipids. RESULTS: A good correlation was found between the orocaecal transit times using Raftilin HP (338 min; interquartile range, 300-383 min) and lactose 13C-ureide (353 min; interquartile range, 285-375 min) (r=0.85; P<0.001). The administration of 5 or 10 g Raftilin HP had no influence on the orocaecal transit time, whereas lactulose significantly shortened the orocaecal transit time. Neither inulin nor lactulose had a significant influence on gastric emptying or protein or lipid assimilation. CONCLUSION: Raftilin HP is an ideal substrate for a hydrogen breath test to measure the orocaecal transit time.

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]-ureide 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.

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

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.

Magnesium chloride slows gastric emptying, but does not affect digestive functions.

BACKGROUND: An inverse relationship has been established between serum magnesium and serum lipid levels. By means of breath tests, we tested the hypothesis that magnesium inhibits intraluminal lipid digestion and subsequently causes changes in lipid metabolism. We also investigated the influence of the administration of magnesium chloride on protein digestion and gastric emptying. METHODS: Five healthy volunteers performed simultaneous breath tests for gastric emptying and intraluminal lipid digestion, and six others for gastric emptying and protein digestion. Each test was performed in basal conditions and after the intake of 800 mg of magnesium chloride dissolved in water. Breath samples were taken at regular time intervals and analysed for 13CO2 and 14CO2 enrichment in order to calculate gastric emptying and lipid and protein digestion rates. RESULTS: The oral administration of a single dose of magnesium chloride resulted in a diminished rate of intraluminal lipid and protein digestion. The most pronounced effect of magnesium chloride, however, was a decreased gastric emptying rate of both test meals. After correction for gastric emptying, no differences were noted in intraluminal lipid or protein digestion. Therefore, the lower lipid levels noted after magnesium supplementation are unlikely to be the result of altered lipid assimilation. CONCLUSION: Magnesium chloride slows gastric emptying but does not influence lipid digestion.

13C mixed-triglyceride breath test: isotope selective non-dispersive infrared spectrometry in comparison with 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.

13C-methacetin breath test: isotope-selective nondispersive infrared spectrometry in comparison to isotope ratio mass spectrometry in volunteers and patients with liver cirrhosis.

The 13C-methacetin breath test (MBT) has been proposed for the noninvasive evaluation of the hepatic mixed function oxidase activity. Up to now, stable isotope analysis of carbon dioxide of the MBT has been carried out with isotope ratio mass spectrometry (IRMS). The aim of the present study was to test a recently developed isotope-selective nondispersive infrared spectrometer (NDIRS) in comparison to IRMS in healthy volunteers and patients with liver cirrhosis. Ten healthy volunteers (range 22 to 76 years) and ten patients with histologically proven liver cirrhosis (range 47 to 71 years; Child Pugh score A = 5, B = 3, C = 2) were studied. After an overnight fast each subject received 2 mg/kg BW of 13C-methacetin dissolved in 100 ml of tea. Breath samples were obtained before substrate administration and after 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, 120, 150, 180 min. The 13C/12C-ratio was analyzed in each breath sample both by NDIRS (IRIS, Wagner Analysen Technik, Worpswede, Germany) and CF-IRMS (ABCA, Europa Scientific, Crewe, UK). Results were expressed as delta over baseline (DOB [/1000]) and as cumulative percentage doses of 13C recovered (cPDR [%]) at each time interval. Correlations between IRMS and NDIRS were tested by linear regression correlation. For measuring agreement an Altman-Bland-plot was performed. Applying correlation analysis a linear correlation was found (DOB: y = 1.068 +/- 0.0012.x + 2.088 +/- 0.2126, r = 0.98, p < 0.0001; cPDR: y = 1.148 +/- 0.0109.x + 0.569 +/- 0.172; r = 0.99, p < 0.0001). For DOB the mean difference (d) was 2.9/1000 and the standard deviation (SD) of the difference was 2.7/1000. The limits of agreement (d +/- SD) were -2.5/1000 and 8.3/1000. The comparison of DOB- and cPDR-values by NDIRS and IRMS shows a high linear correlation. However, the distance of the limits of agreement is wide. Consequently, the validity of the MBT could be influenced which could make MBT by NDIRS unprecise for exact evaluation of hepatocellular dysfunction. Further studies are necessary to determine sensitivity and specifity of the MBT with NDIRS in larger study populations.

Digestibility of cooked and raw egg protein in humans as assessed by stable isotope techniques.

Egg proteins contribute substantially to the daily nitrogen allowances in Western countries and are generally considered to be highly digestible. However, information is lacking on the true ileal digestibility of either raw or cooked egg protein. The recent availability of stable isotope-labeled egg protein allowed determination of the true ileal digestibility of egg protein by means of noninvasive tracer techniques. Five ileostomy patients were studied, once after ingestion of a test meal consisting of 25 g of cooked 13C- and 15N-labeled egg protein, and once after ingestion of the same test meal in raw form. Ileal effluents and breath samples were collected at regular intervals after consumption of the test meal and analyzed for 15N- and 13C-content, respectively. The true ileal digestibility of cooked and raw egg protein amounted to 90.9 +/- 0.8 and 51.3 +/- 9.8%, respectively. A significant negative correlation (r = -0.92, P < 0.001) was found between the 13C-recovery in breath and the recovery of exogenous N in the ileal effluents. In summary, using the 15N-dilution technique we demonstrated that the assimilation of cooked egg protein is efficient, albeit incomplete, and that the true ileal digestibility of egg protein is significantly enhanced by heat-pretreatment. A simple 13C-breath test technique furthermore proved to be a suitable alternative for the evaluation of the true ileal digestibility of egg protein.

Production of egg proteins, enriched with L-leucine-13C1, for the study of protein assimilation in humans using the breath test technique.

Protein assimilation and metabolism studies are hindered by the lack of an adequate oral tracer, i.e., labeled proteins. We present a new and easily reproducible methodology for producing large amounts of egg proteins labeled with L-leucine-13C1. Laying hens were fed a 0.2% leucine-deficient food supplemented with 0.2% L-leucine-13C1 (99 atom %). At plateau, eggs containing highly enriched proteins were obtained. The 13C content of egg white relative to the total C content was 1.3371 atom %, corresponding to delta = 206%. The overall tracer recovery in egg proteins was high (40.2%), making this method financially attractive as well. Accurately measurable levels of 13CO2 in breath were obtained after ingestion of a physiological load of labeled egg white proteins. Thus, egg proteins with sufficient 13C enrichment and applicable for human protein assimilation and metabolism kinetic studies were produced in an easily reproducible and highly efficient manner.