Tracer kinetic studies on a methionine-supplemented soy-based infant formula using 1-13C- and 15N-methionine as tracers

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C]methacetin- and [methyl-13C]methionine-breath tests

The aim of this study was to investigate the hepatic microsomal and mitochondrial functions by using the 13CO2-breath test in healthy subjects either before or after the consumption of red wine. Fourteen adults received [13C]methacetin and [methyl-13C]methionine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol/kg/day together with dinner over a 10-day period. Thereafter, 13C-tracer administration was repeated under identical conditions. The 13CO2-enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage 13C-dose recovery (CPDR) after administration of [13C]methacetin and [methyl-13C]methionine either without or with red wine consumption amounted to 38.2+/-6.3 vs. 36.3+/-6.7% (p=0.363) and 9.5+/-3.3 vs. 8.8+/-2.5% (p=0.47), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the mitochondrial functions of the human liver in healthy subjects.

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.

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

OBJECTIVE

In the present study, Lactobacillus johnsonii (La1) doubly labelled with 15N and 13C (dlLa1) was used to follow the metabolic fate of orally administered dlLa1 in humans.

DESIGN

Experimental study.

SETTING

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

SUBJECTS

A total of 10 healthy adults aged 23-36 y.

INTERVENTION

The subjects received 87 mg/kg body weight viable dlLa1 and 10 g raffinose 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) and H2-concentrations were measured by electrochemical detection (Stimotron, Germany).

RESULTS

The orocaecal transit time (OCTT) was reached after 3.7 h. The 13CO2-exhalation amounted to 8.6% of ingested dose. The urinary excretion of 13C and 15N was 1.3 and 12.4% of ingested dose, respectively, whereas the faecal excretion was 39.9 and 37.6% of ingested dose, respectively. After 2 h, 13C- and 15N-enrichment of fibrinogen amounted to 70 and 90 ppm excess, respectively.

CONCLUSIONS

In comparison to OCTT of 3.7 h, both stable isotopes appear after 30 min in breath and urine, indicating that dlLa1 is rapidly digested in the small bowel before reaching the caecum. This is confirmed by 13C-and 15N-enrichments of blood plasma fractions. The ingestion of dlLa1 led to an excretion of 50% of ingested dose of both stable isotopes.

The effect of l-carnitine on fat oxidation, protein turnover, and body composition in slightly overweight subjects

We used a combined tracer technique with the stable isotopes 13C and 15N to gain further insight into the metabolic changes that accompany supplementation of L-carnitine. The aim of the present study was to investigate whether L-carnitine supplementation can influence fat oxidation, protein turnover, body composition, and weight development in slightly overweight subjects. Twelve volunteers received an individual regular diet either without or with L-carnitine supplementation of 3 g/d for 10 days. Protein turnover and 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. Body fat mass (BFM), total body water (TBW), and lean body mass (LBM) were calculated by using bioelectric impedance analysis. L-carnitine supplementation led to a significant increase in 13C-fat oxidation (15.8% v 19.3%; P = .021) whereas protein synthesis and breakdown rates (3.7 and 3.4 g/kg/d, respectively) remained unchanged, indicating that the increased dietary fat oxidation in slightly overweight subjects was not accompanied by protein catabolism.

The use of 13C-labelled glycosyl ureides for evaluation of orocaecal transit time

OBJECTIVE

In the present study, cellobiose-[13C]ureide and glucose-[13C]ureide were synthesized and tested as alternative substrates for noninvasive evaluation of the orocaecal transit time (OCTT).

DESIGN

Experimental study.

INTERVENTION

In total, 1 g cellobiose-[13C]ureide was administered together with a continental breakfast either without or after predosing of 5 x 1 g unlabelled cellobiose ureide on the day prior to study commencement. After 2 weeks, the same subjects ingested glucose-[13C]ureide (dosage: 0.57 g) either without or after predosing of the respective unlabelled ureide under identical conditions. Expired air samples were taken over 10 h. 13CO2-enrichment was measured by isotope ratio mass spectrometry (PDZ Europa, Sandbach, UK). The OCTT was calculated from the interval between 13C-ureide administration and the detection of a significant and sustained 13C-rise of 2 delta over baseline in breath.

SETTING

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

SUBJECTS

Eight healthy adults aged 22-55 y.

RESULTS

After application of cellobiose-[13C]ureide and glucose-[13C]ureide OCTTs of 401 and 415 min, respectively, were measured. The predosing resulted in higher and steeper 13C-enrichments and caused a significant shortening of OCTTs of 265 and 287 min, respectively (P=0.012 and 0.017).

CONCLUSIONS

The onset of 13CO2-enrichment reflected the degradation of glycosyl-[13C]ureides by glucose ureide hydrolase. The predosing with unlabelled ureides prior to pulse labelling with cellobiose-[13C]ureide and glucose-[13C]ureide (the latter is the key substance of the enzymatic sugar-ureide degradation) led to an induction of enzyme activity and resulted in a more precise and similar estimation of the OCTT when using both 13C-labelled ureides.

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).

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.