15N tracer kinetic studies on the validity of various 15N tracer substances for determining whole-body protein parameters in very small preterm infants
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1Children's Hospital, Faculty of Medicine, Wilhelm-Pieck University, Rostock, G.D.R.
Insights
Reliable protein turnover measurement in preterm infants is crucial. [15N]-labeled yeast protein hydrolysate offers a valid and cost-effective alternative to [15N]glycine for determining whole-body protein parameters.
Area of Science:
- Neonatal Nutrition
- Biochemical Tracers
- Metabolic Research
Background:
- Accurate assessment of whole-body protein parameters in preterm infants is essential for optimizing nutritional support.
- Doubts exist regarding the validity of [15N]glycine as a tracer for protein kinetic studies in this population.
- Novel tracer substances are needed to reliably determine protein metabolism in very small preterm infants.
Purpose of the Study:
- To compare the efficacy of different 15N tracer substances for determining whole-body protein parameters in very small preterm infants.
- To evaluate the validity of a [15N]amino acid mixture and [15N]-labeled yeast protein hydrolysate against [15N]glycine.
- To identify a reliable and cost-effective tracer for protein turnover studies in neonates.
Main Methods:
- Paired comparison study involving very small preterm infants (post-conceptual age ~32 weeks).
- Administration of two different 15N tracer substances: a [15N]amino acid mixture (Ia) and [15N]glycine (Ib).
- Use of 15N-labeled yeast protein hydrolysate (II) in a separate group of infants.
- Application of a three-pool model accounting for renal and fecal 15N losses for data analysis.
Main Results:
- [15N]glycine (Ib) led to an overestimation of protein turnover compared to the [15N]amino acid mixture (Ia) and yeast protein hydrolysate (II).
- Protein turnover rates were: 11.9 ± 3.1 g/kg/d (Ia), 16.2 ± 2.5 g/kg/d (Ib), and 10.8 ± 3.0 g/kg/d (II).
- Results obtained using the [15N]amino acid mixture (Ia) and yeast protein hydrolysate (II) showed expected correspondence.
Conclusions:
- [15N]glycine is not a reliable tracer for determining whole-body protein parameters in very small preterm infants due to overestimation.
- [15N]-labeled yeast protein hydrolysate provides a reliable and cost-effective alternative for assessing protein metabolism in this vulnerable population.
- The [15N]amino acid mixture also appears suitable for accurate protein kinetic determination in preterm neonates.
Abstract:
Reliable 15N tracer substances for tracer kinetic determination of whole-body protein parameters in very small preterm infants are still a matter of intensive research, especially after some doubts have been raised about the validity of [15N]glycine, a commonly used 15N tracer. Protein turnover, synthesis, breakdown, and further protein metabolism data were determined by a paired comparison in four preterm infants. Their post-conceptual age was 32.2 +/- 0.8 weeks, and their body weight was 1670 +/- 181 g. Tracer substances applied in this study were a [15N]amino acid mixture (Ia) and [15N]glycine (Ib). In a second group of three infants with a post conceptual age of 15N-labeled 32.0 +/- 1.0 weeks and a body weight of 1,907 +/- 137 g, yeast protein hydrolysate (II) was used as a tracer substance. A three-pool model was employed for the analysis of the data. This model takes into account renal and fecal 15N losses after a single 15N pulse. Protein turnovers were as follows: 11.9 +/- 3.1 g kg-1 d-1 (Ia), 16.2 +/- 2.5 g kg-1 d-1 (Ib), and 10.8 +/- 3.0 g kg-1 d-1 (II). We were able to demonstrate an overestimation of the protein turnover when Ib was used. There was an expected correspondence in the results obtained from Ia and II. The 15N-labeled yeast protein hydrolysate is a relatively cheap tracer that allows reliable determination of whole-body protein parameters in very small preterm infants.