Metabolic effects of HAY's diet.

The aim of the study was, to evaluate the metabolic effect of HAY's diet on protein turnover, fat oxidation, respiratory quotient, body fat and weight loss. Twelve healthy adults received an individually regular diet and thereafter a corresponding isocaloric and isonitrogenous 10-day HAY-diet. Protein turnover and 13C-fat oxidation were investigated after administration of [15N]glycine and an [U-13C]algae lipid mixture. The 15N and 13C enrichment in urine and breath were measured by isotope ratio mass spectrometry. The respiratory quotient was measured by indirect calorimetry. Body fat, total body water and lean body mass were estimated by bio-electric impedance analysis. HAY's diet led to a significantly higher 13C-fat oxidation (15.4 vs. 22.0% P < 0.01), corresponding to a lower respiratory quotient (0.88 vs. 0.81; P < 0.01), whereas the protein turnover remained constant in both diets (3.06 vs. 3.05 g/kg/day). HAY's diet did not reduce total body water, lean body mass, body fat and body weight (72.2 vs. 71.4 kg).

Clostridium innocuum: a glucoseureide-splitting inhabitant of the human intestinal tract.

Glycosylureides were recently described as non-invasive markers of intestinal transit time. The underlying principle is an enzymatic splitting of (13)C-labelled ureides by intestinal bacteria. The (13)CO(2) released from the urea moiety of the glycosylureides can be measured in breath samples when the ingested tracer substrate reaches the caecum that is colonised with microbes. To date, the microbes that degrade glycosylureides are unknown. In order to identify the glucoseureide (GU)-splitting bacteria, 174 different strains of intestinal microbes obtained from five healthy adults were checked for their ability to degrade GU. The results of the microbial cultures and thin layer chromatography revealed that GU was exclusively degraded by Clostridium innocuum, belonging to the normal human intestinal microflora. C. innocuum probably synthesises a yet unknown enzyme that splits the glucose-urea bond. We suggest that the term glucoseureidehydrolase is the appropriate designation for this enzyme.

Triglyceride oxidation in cystic fibrosis: a comparison between different 13C-labeled tracer substances.

BACKGROUND: For indirect evaluation of pancreatic lipase activity in cystic fibrosis, different 13C-labeled triglycerides may be used. METHODS: Triglyceride oxidation in patients with cystic fibrosis was investigated after administration of different 13C-labeled triglycerides by comparing 13CO2 breath exhalation. In the comparative study, five patients with cystic fibrosis (age, 8-15 years; body weight, 22.5-39.8 kg) were treated with Pangrol (individual dosages: 1-3 capsules per morning meal; Berlin-Chemie, Berlin, Germany). [1,1,1-13C3]Glyceryl tripalmitate and [1,1,1-13C3]glyceryl trioleate were administered as a single oral pulse at 8:00 A.M. (dosage, 4 mg/kg each) with the standard diet Fresubin (dosage, 10 ml/kg; Fresenius, Bad Homburg, Germany). Alternately, the same subjects were given the synthetic mixed triglyceride 1,3-distearyl, 2[13C]octanoyl glycerol (dosage, 12.5 mg/kg) contained in the standard diet Nutri-Mix (dosage, 10 ml/kg; Nutricia, Zoetemeer, The Netherlands). Breath samples were taken in 15- and 30-minute intervals over 8 hours. The 13CO2 enrichment was measured by continuous-flow isotope ratio mass spectrometry. RESULTS: After administration of the 13C-labeled tripalmitin-triolein mixture and the mixed triglyceride, mean maximum 13CO2 enrichments were 4.70 and 7.37 delta over baseline, occurring at 7.0 and 3.5 hours, respectively. The corresponding percentage cumulative 13CO2 exhalations were 12.25% and 29.19%, respectively, and differed significantly in the five paired subjects (p = 0.003). CONCLUSIONS: After using different 13C-labeled triglycerides the resultant 13CO2 exhalation reflected the triglyceride hydrolysis and subsequent oxidation. It is concluded that the different cumulative 13CO2 exhalations were mainly caused by the rate-limiting step of triglyceride hydrolysis to free fatty acids and 2-monoglycerides and by fat deposition. Noninvasive 13C breath tests using different 13C-labeled triglycerides can be used for evaluation of pancreatic lipase activity before and during enzyme supplementation.

The significance of tryptophan in infant nutrition.

In the newborn, tryptophan (Trp) and its metabolites are essential to brain maturation and to the development of neurobehavioral regulations of food intake, satiation and sleep-wake-rhythm. Due to the high Trp concentration in human milk in relation to the total of neutral amino acids, the blood-brain transfer of tryptophan as a precursor of its metabolites serotonin and melatonin is optimal. In contrast, commercial infant formulas are lower in Trp and higher in neutral amino acid levels resulting in comparatively lower Trp serum concentrations. alpha-lactalbumin enriched, protein-reduced formulas adapted to 2.2% Trp were shown to be capable of producing Trp serum values that did not differ from those in breast-fed infants.

Metabolism of glycosyl ureides by human intestinal brush border enzymes.

13C-labeled glycosyl ureides were recently proposed as a new marker of the orocecal transit time: after passing the small bowel the sugar-urea bond is split by bacterial allantoicase. Further degradation results in 13CO2 which can be measured in the exhaled breath. The aim of this study was to detect an eventual allantoicase-like activity in the human gut and to elucidate the metabolism of glycosyl ureides by human intestinal brush border enzymes. Biopsies of 15 duodenal specimen and 6 colon specimen were homogenised and incubated with several disaccharides and their corresponding disaccharide ureides under various experimental conditions. Hydrolysis of the sugar-urea bond could not be observed neither in the small bowel nor in the colon. However, the conjugation between the two sugars was split. In a modified Dahlqvist assay lactase showed the same kinetics with lactose and lactose ureide as substrates whereas maltose showed a significantly 2.6-fold higher affinity to maltase than maltose ureide (P < 0.001). No major difference between these two substrates could be detected when total maltase activity was inhibited by acarbose. In summary, the human gut tissue possesses no allantoicase-like activity. Therefore, glycosyl ureides seem to be appropriate substances to test the orocecal transit time.

Evaluation of oro-coecal transit time: a comparison of the lactose-[13C, 15N]ureide 13CO2- and the lactulose H2-breath test in humans.

OBJECTIVE: The lactulose H2-breath test is the most widely used non-invasive approach for evaluation of orocoecal transit time (OCTT). In the present study, doubly-labelled lactose-[13C, 15N]ureide (DLLU) was synthesized to investigate the OCTT in comparison to the conventional lactulose H2-breath test. Additionally the bacterial breakdown rate (BBR) and rate of elimination and the metabolic pathways of the cleavage products of DLLU (13CO2, [15N]urea, and 15NH3) were investigated. DESIGN AND SUBJECTS: In a first study, DLLU was administered as a single oral-pulse-labelling (dosage: one gram) either without and after pretreatment of five grams of unlabelled lactoseureide (LU) on the day prior to the study to twelve healthy adult volunteers after breakfast. Breath and urine were collected in one and two hour-intervals, respectively, over a one-day period. 13C-enrichment in breath as well as 15N-enrichment in urine fractions were measured by continuous flow-isotope ratio mass spectrometry (CF-IRMS). In a second study, lactulose was administered to the same subjects (dosage: ten grams). Breath was collected in quarter, half and one hour-intervals over a ten hour-period. Hydrogen concentration in breath was analysed using an electrochemical detector. RESULTS: The comparison of the lactose-[13C]ureide 13CO2-breath test and the lactulose H2-breath test showed that the mean increase of the 13C-enrichment in CO2 occurred 1.18 h later than the mean increase of H2 in breath. The resulting OCTTs derived from the two methods were 3.02 +/- 1.4 and 1.84 +/- 0.5 h (P < 0.05) and the corresponding BRs were 9.63 +/- 3.4 and 6.07 +/- 1.7 h (P < 0.01), respectively. The 15N-enrichment of urinary urea and ammonia without and after pretreatment with LU started between two and three hours after DLLU-administration. The cumulative percentage urinary excretion of the 15N- and 13C-tracer was 29.9% and 13.6% respectively, and was slightly increased after LU-pretreatment to 32.1% and 14.6% of the dose administered. A total of 35.2% of the 13C was found to be exhaled and remained approximately constant after LU-pretreatment (36.2%). CONCLUSIONS: The use of the lactulose H2-breath test for evaluation of the OCTT showed a statistically significant shortening of 1.18 h in comparison to the lactose-[13C]ureide 13CO2-breath test in healthy adults. The most important limitations of the lactulose H2-breath test are its low specificity and sensitivity due to dose-dependent accelerations of OCTT, interfering H2-rise from malabsorbed dietary fibre and H2-non-producers. In contrast, our lactose-[13C]ureide 13CO2-breath test was confirmed to avoid these disadvantages and to yield reliable results. This test is recommended especially if higher sensitivity and specificity is required, if IRMS-technique is available and if lactulose H2-tests lead to insufficient results.

[The physiologic significance of Bifidobacteria and fecal lysozyme in the breast fed infant. A contribution on the the microecology of the intestine]. / Zur physiologischen Bedeutung der Bifidusflora und des faekalen Lysozyms beim Brustkind. Ein Beitrag zur Mikroökologie des Intestinums.

The fecal microflora of the breast-fed infant consists of nearly 100% Bifidobacteria. The importance of this long-known and unique phenomenon is still not clearly understood. Likewise, the presence of lysozyme in the feces of breast-fed infants, which is administered in significant amounts with the human milk is not adequately known. New hints and hypotheses concerning digestion in ruminants are cited. In ruminants Lysozyme c functions as digestive enzyme in the rumen. Lysozyme causes lysis of the bacterial cell membrane leading to the release of bacterial contents i.e. proteins. The proteins synthesised in bacteria are the main source of nitrogen for ruminants. The hypothesis is established, that the enormous amounts of Bifidobacteria in the colon of the human newborn can be made of use in a similar way. The lysozyme in the colon of breast-fed infants leads to lysis of Bifidobacteria in connection with tryptic digestive enzymes, in turn leading to release of proteins and protein substances. It has recently been demonstrated that catabolic products of these proteins can be absorbed in the colon. The same group has shown that lysis of Bifidobacteria can take place in the presence of lysozyme in connection with trypsin.

A novel stable isotope breath test: 13C-labeled glycosyl ureides used as noninvasive markers of intestinal transit time.

OBJECTIVES: Breath tests are widely used for diagnosis and control of treatment efficacy. There is a need for breath test substrates that reflect intestinal transit times under various conditions. METHODS: We synthesized a new class of breath test substrates, 13C-labeled glycosyl ureides, which are specific markers for the action of colonic microbial flora. We then investigated their usefulness as markers of intestinal transit time. RESULTS: Bolus ingestion of 1 g lactose or cellobiose 13C-ureide resulted in bacterial cleavage of the N-glycosyl bond and subsequent urea hydrolysis. 13CO2 appeared in breath and was determined by gas-isotope-ratio-mass spectrometry. Label first appeared after 5-6 h, peak excretion occurred between 8-14 h, and the signal returned to baseline after 18-24 h. Metoclopramide (10 mg) administered 1 h before the substrate advanced the onset of the signal by 2.4 +/- 1.95 h (mean +/- SD; n = 7; p < 0.05) and the time of peak response by 0.8 +/- 1.44 h. Loperamide (16 mg) broadened the peak and delayed the time of breath signal onset by 1.0 +/- 2.78 h and peak excretion by 4.0 +/- 3.7 h (p < 0.05). CONCLUSIONS: The glycosyl ureide breath test reflected intestinal transit time and rapid changes in gastrointestinal motility. This test should be useful in the diagnosis of a variety of gastrointestinal motility disorders and in the development of drugs that affect gastrointestinal motility.

The importance of alpha-lactalbumin in infant nutrition.

The ideal "humanization" of milk substitutes should include the creation of an amino acid pattern closely resembling that of human milk. Because the mixture of proteins in human milk is particularly rich in tryptophan and cysteine and low in methionine, this pattern is difficult to achieve with commercially available proteins. Even whey-predominant formulas only approximate human milk. Human milk has a high concentration of whey protein (70% of total protein). Of this, alpha-lactalbumin, a component of the lactase synthetase complex, accounts for 41% of the whey and 28% of the total protein. Only 3% of the protein in bovine milk is alpha-lactalbumin. Human and bovine alpha-lactalbumin share a 72% amino acid sequence homology. Both proteins contain (wt/wt) 6% tryptophan and 5% cysteine but only 0.9% methionine. Thus the differences in the amino acid compositions of bovine and human milks are largely attributable to differences in their alpha-lactalbumin contents. Commercial availability of bovine alpha-lactalbumin would allow the construction of infant formulas with amino acid compositions that are very close to that of human milk. alpha-Lactalbumin would also be a valuable constituent of diets for patients whose protein intake must be restricted.