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Relative kinetics of phenylalanine and leucine in low birth weight infants during nutrient administration
L van Toledo-Eppinga1, S C Kalhan, W Kulik
1Department of Paediatrics, Hospital of the Vrije Universiteit, Amsterdam, The Netherlands.
Insights
Nutrient administration route affects amino acid kinetics in low birth weight infants. Premature formula showed higher leucine appearance rates compared to human milk or parenteral nutrition.
Area of Science:
- Neonatal Nutrition
- Amino Acid Metabolism
- Infant Physiology
Background:
- Low birth weight (LBW) infants have unique nutritional needs.
- Understanding amino acid kinetics is crucial for optimizing growth and development in LBW infants.
- The route of nutrient delivery can influence metabolic processes.
Purpose of the Study:
- To investigate the impact of different nutrient administration routes on leucine and phenylalanine kinetics in LBW infants.
- To compare amino acid kinetics among infants receiving premature formula (PF), fortified human milk (HM), and parenteral nutrition (PN).
Main Methods:
- Utilized stable isotope tracers (L-[1-(13)C]leucine, L-[2H5]phenylalanine, L-[2H2]tyrosine) in 30 LBW infants.
- Grouped infants into three feeding regimens: PF (n=10), HM (n=10), and PN (n=10).
- Measured the rate of appearance (Ra) for leucine (RaLeu) and phenylalanine (RaPhe).
Main Results:
- Leucine appearance rate (RaLeu) was significantly higher in the PF group compared to HM and PN groups.
- Phenylalanine appearance rate (RaPhe) was lower in the HM group compared to the PF group.
- The ratio of RaPhe to RaLeu was lower in all groups than expected, suggesting altered amino acid metabolism.
Conclusions:
- Higher RaLeu in the PF group may be due to increased leucine intake or higher turnover of leucine-rich body proteins.
- Calculations of whole-body protein kinetics using a single amino acid tracer may not accurately reflect overall protein metabolism in LBW infants.
- The route of nutrient administration significantly influences amino acid kinetics in LBW infants.
Abstract:
The effect of the route of nutrient administration on the relative rates of leucine and phenylalanine kinetics was examined in 30 low birth weight (LBW) infants using L-[1-(13)C]leucine, L-[2H5]phenylalanine, and L-[2H2]tyrosine tracers. The infants received special premature formula (PF, n = 10, 117 +/- 8 kcal.kg-1.d-1 and 3.2 +/- 0.2 g protein.kg-1.d-1) or fortified human milk (HM, n = 10, 106 +/- 6 kcal.kg-1.d-1 and 3.0 +/- 0.2 g protein.kg-1.d-1), or parenteral nutrition (PN, n = 10, 80 +/- 25 kcal.kg-1.d-1 and 1.8 +/- 0.3 g protein.kg-1.d-1). The rate of appearance (Ra) of leucine (RaLeu), was significantly higher in group PF as compared with groups HM and PN (434 +/- 51 versus 377 +/- 33 and 359 +/- 50 mumol.kg-1.h-1, p < 0.05). The Ra of phenylalanine (RaPhe) was lower in group HM as compared with group PF (94 +/- 18 versus 115 +/- 16, p < 0.05), RaPhe in group PN (108 +/- 24 mumol.kg-1.h-1) was in between group PF and HM. The relative rate of RaPhe and RaLeu expressed as RaPhe/ RaLeu ratio was lower in all groups than that expected from reported whole body protein composition and from that reported in adults. The ratio of phenylalanine hydroxylation to leucine decarboxylation was 0.202 in group PF, 0.212 in group HM, and 0.161 in group PN, suggesting a higher rate of decarboxylation of leucine relative to hydroxylation of phenylalanine. We conclude that: 1) the higher RaLeu compared with the RaPhe may be the result of either a higher turnover of a body protein enriched in leucine or the consequence of higher leucine intake in infant nutrition and 2) whole body protein kinetics calculated from a single amino acid tracer do not adequately represent whole body protein metabolism.