13C- and 15N-incorporation of doubly stable isotope labelled Lactobacillus johnsonii in humans

Dietary fibre-rich resistant starches promote ammonia detoxification in the human colon as measured by lactose-[¹⁵N₂]ureide

Three resistant starches (RSs), namely fibre of potatoes (FP), wrinkle pea starch (WPS), and high amylose maize starch (HAMS) with different dietary fibre contents, were supplemented in adults to evaluate their effects on urinary nitrogen and ammonia excretion as well as on faecal nitrogen excretion by means of lactose-[(15)N2]ureide ((15)N-LU) degradation. Twenty subjects received a regular diet either without or with the supplementation of FP, WPS, and HAMS in a randomized order. After administration of (15)N-LU, urine and faeces were collected over 48 and 72 h, respectively, whereas blood was collected after 6 h. The (15)N-abundances were measured by isotope ratio mass spectrometry. In comparison to the dry run, supplementation with RS significantly lowered renal (15)N-excretion (dry run: 43.2%, FP: 34.6%, WPS: 37.9%, HAMS: 36.4%) as well as the corresponding (15)NH3-excretion (dry run: 0.08%, FP: 0.06%, HAMS: 0.05%), clearly indicating a reduced colonic nitrogen generation at high dietary fibre intake.

Solution structure of acidocin B, a circular bacteriocin produced by Lactobacillus acidophilus M46

Acidocin B, a bacteriocin produced by Lactobacillus acidophilus M46, was originally reported to be a linear peptide composed of 59 amino acid residues. However, its high sequence similarity to gassericin A, a circular bacteriocin from Lactobacillus gasseri LA39, suggested that acidocin B might be circular as well. Acidocin B was purified from culture supernatant by a series of hydrophobic interaction chromatographic steps. Its circular nature was ascertained by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and tandem mass spectrometry (MS/MS) sequencing. The peptide sequence was found to consist of 58 amino acids with a molecular mass of 5,621.5 Da. The sequence of the acidocin B biosynthetic gene cluster was also determined and showed high nucleotide sequence similarity to that of gassericin A. The nuclear magnetic resonance (NMR) solution structure of acidocin B in sodium dodecyl sulfate micelles was elucidated, revealing that it is composed of four α-helices of similar length that are folded to form a compact, globular bundle with a central pore. This is a three-dimensional structure for a member of subgroup II circular bacteriocins, which are classified based on their isoelectric points of ∼7 or lower. Comparison of acidocin B with carnocyclin A, a subgroup I circular bacteriocin with four α-helices and a pI of 10, revealed differences in the overall folding. The observed variations could be attributed to inherent diversity in their physical properties, which also required the use of different solvent systems for three-dimensional structural elucidation.

The metabolic effect of resistant starch and yoghurt on the renal and faecal nitrogen and ammonia excretion in humans as measured by lactose-[(15)N2]ureide

Resistant starch (RS) and Lactobacillus acidophilus yoghurt (LC1) were supplemented simultaneously in healthy adults to evaluate the effect on the urinary and faecal nitrogen and ammonia excretion by means of lactose-[(15)N2]ureide ((15)N-LU) degradation. Nineteen subjects received a regular daily diet either without or with supplementation of an RS-LC1-mixture composed of fibre of potatoes (RS type 1), wrinkle pea starch (RS type 2), and LC1 over a 20-day period in randomised order. Thereafter, (15)N-LU was administered together with breakfast. Urine and faeces were collected over a period of 48 and 72 h, respectively. The (15)N abundances were measured by isotope ratio mass spectrometry. The intake of the pre- and probiotic mixture composed of RS of type 1, type 2 and of LC1 significantly lowered the colonic generation and the renal excretion of toxic (15)NH3 and functioned as an ammonia shift from urinary to faecal (15)N excretion when using (15)N-LU as a xenobiotic marker.

The effect of pre- and probiotics on the colonic ammonia metabolism in humans as measured by lactose-[¹⁵N₂]ureide

BACKGROUND

The evaluation of ammonia detoxification by pre- and probiotics by means of colonic lactose-[(15)N(2)]ureide ((15)N-LU) degradation is of great interest both scientifically and in terms of nutrition physiology.

OBJECTIVE

Pre- and probiotics were supplemented in healthy adults to evaluate the effect of the ammonia metabolism in the human colon by means of (15)N-LU.

METHODS

A total of 14 participants aged 20-28 years daily received a regular diet either without (no treatment) or with supplementation of 30 g fibre of potatoes (FPs), 30 g wrinkle pea starch (WPS, resistant starch content: 12 and 70%, respectively) and 375 g Lactobacillus acidophilus (LC1) yoghurt, over a 10-day period in a randomised order. After 1 week, 5.7 mg/kg body weight (15)N-LU was administered together with breakfast. A venous blood sample was taken after 6 h. Urine and faeces were collected over a period of 48 and 72 h, respectively. The (15)N abundances were measured by isotope ratio mass spectrometry.

RESULTS

The mean renal (15)N-excretion differed significantly between the supplementation of FP and no treatment (32.5 versus 46.3%, P=0.034), FP and LC1 (32.5 versus 51.6%, P=0.001), and WPS and LC1 (38.5 versus 51.6%, P=0.048). The mean faecal (15)N-excretion amounted to 42.7% (no treatment), 59.7% (FP), 41.8% (WPS) and 44.0% (LC1). In comparison with no treatment, the urinary (15)NH(3)-enrichment was significantly decreased at 16 h after FP supplementation.

CONCLUSION

The prebiotic intake of FP and WPS lowered the colonic generation and the renal excretion of toxic (15)NH(3), respectively, when using (15)N-LU as a xenobiotic marker.

The metabolic fate of doubly stable isotope labelled heat-killed Lactobacillus johnsonii in humans

OBJECTIVE

In this study, heat-killed Lactobacillus johnsonii (La1), doubly labelled with (13)C and (15)N (hk-dlLa1), was used to follow the metabolic fate after oral administration in humans.

DESIGN

Experimental study.

SETTING

University of Rostock, Children's Hospital, Research Laboratory.

SUBJECTS

Ten healthy adults aged 23-26 years.

INTERVENTION

The subjects received 74.6 mg/kg body weight hk-dlLa1 and 10 g alpha-D-raffinose together with breakfast. A sample of venous blood was taken after 2 h. Expired air samples were taken over 14 h, whereas urine and faeces were collected over a period of 48 h. (13)C- and (15)N-enrichments were measured by isotope ratio mass spectrometry. Hydrogen concentrations were measured by electrochemical detection.

RESULTS

The orocaecal transit time (OCTT) was reached after 3.4 h. After 2 h, (13)C- and (15)N-enrichment of fibrinogen amounted to 2 and 25 p.p.m. excess, respectively. The (13)CO(2)-exhalation amounted to 9.2% of the ingested dose. The urinary excretion of (13)C and (15)N was 2.1 and 10.4% of the ingested dose, respectively, whereas the faecal excretion was 47.9 and 43.7% of the ingested dose, respectively.

CONCLUSIONS

In comparison to OCTT of 3.4 h, both stable isotopes appear after 30 min in breath and urine, indicating that hk-dlLa1 is rapidly digested in the small bowel before reaching the caecum. This is confirmed by (13)C-and (15)N-enrichments of blood plasma fractions. The ingestion of hk-dlLa1 led to a (13)C- and (15)N-excretion of 59.2 and 54.1% of the ingested dose, respectively, of both stable isotopes.

The duration of enzyme induction in orocaecal transit time measurements

OBJECTIVE

In this study, the duration of enzyme induction provoked by unlabelled lactose ureide (LU) in orocaecal transit time (OCTT) measurements with lactose-[(13)C]ureide ((13)C-LU) was evaluated.

DESIGN

Experimental study.

SETTING

University of Rostock, Children's Hospital, Research Laboratory.

SUBJECTS

Fifteen healthy adults aged 19-54 years.

INTERVENTION

One-half gram of (13)C-LU was administered together with a continental breakfast. After 1 week, the test was repeated after pre-dosing of 5 x 100 mg LU on the day before the study began. The (13)C-LU ingestion was repeated under identical conditions but without pre-dosing 1 and 3 weeks after pre-dosing. Expired air samples were taken over 14 h. (13)CO(2)-enrichment was measured by isotope ratio mass spectrometry (SerCon, Crewe, UK). The OCTT was calculated from the interval between (13)C-LU administration and the detection of a significant and sustained (13)C-rise of 2 delta over baseline in breath.

RESULTS

Without pre-dosing, an OCTT of 419+/-82 min was measured. The pre-dosing resulted in higher (13)C-enrichments and caused a significant OCTT shortening of 311+/-99 min (P=0.028). One and 3 weeks after pre-dosing, the measured OCTT again increased to 404+/-124 and 379+/-103 min, respectively.

CONCLUSIONS

Pre-dosing with LU before pulse labelling with (13)C-LU led to an induction of enzyme activity and resulted in a definitive estimation of the OCTT when using a threshold of 2 delta over baseline. After 1 and 3 weeks, respectively, the OCTT was no longer significantly different to those without pre-dosing, indicating the disappearance of enzyme induction. Therefore, a pre-dosing with LU on the day before (13)C-LU ingestion is essential for OCTT measurements.

Nutridynamics--studying the dynamics of food components in products and in the consumer

The concentrations and biological effects of nutrients, antinutrients and bioactive compounds, including microbes and their constituents, are affected by production and processing steps, the food matrix in which they reside, the way they are digested and metabolized in the human body, and whether or not and in what form they subsequently reach their target site. A new scientific concept, denoted here as 'nutridynamics', aims to unravel the dynamics of these processes by using a systematic approach to study how a food component is affected by the food matrix itself and what it does in the body. This holistic concept has potential synergy with the areas of food technology and nutrigenomics, and provides a link between food production and the mechanistic effects of bioactive ingredients.

15N-excretion of heat-killed Lactobacillus casei in humans

OBJECTIVE

In the present study, Lactobacillus casei (L. casei) labelled with 15N was used to follow the metabolic fate of orally administered heat-killed 15N-labelled L. casei (15N-L.casei) in humans.

DESIGN

Experimental study.

SETTING

University of Rostock, Children's Hospital, Research Laboratory.

SUBJECTS

Twelve healthy adults aged 23-32 years.

INTERVENTION

The subjects received 36 mg/kg body weight heat-killed 15N-L.casei and 500 mg Lactose-[13C]ureide together with breakfast. Expired air samples were taken over 14 h, whereas urine and faeces were collected over 2 days. A blood sample was taken after 2 h. 13C- and 15N-enrichments were measured by isotope ratio mass spectrometry (SerCon, UK).

RESULTS

The orocaecal transit time (OCTT) was reached after 4.1 h. The urinary 15N-excretion was 9.3% of the ingested dose, whereas the faecal excretion was 65.1% of the ingested dose. After 2 h, 15N-enrichment of supernatant, fibrinogen, and plasma protein precipitate amounted to 254, 11, and 2 p.p.m. excess, respectively.

CONCLUSIONS

In comparison to the OCTT of 4.1 h, 15N-enrichment in urinary ammonia and urinary total nitrogen already began to rise 30 min after 15N-L.casei ingestion, indicating that 15N-L.casei is rapidly digested in the small bowel. This is confirmed by 15N-enrichments of blood plasma fractions. The ingestion of heat-killed 15N-L.casei led to a total excretion of 74.4% of the ingested 15N-dose.