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Phenylalanine and tyrosine kinetics in critically ill children with sepsis
L Castillo1, Y M Yu, J S Marchini
1Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge 02139.
Insights
Critically ill children require more tyrosine than typically provided. Current nutritional support may be insufficient for maintaining amino acid balance in these vulnerable patients.
Area of Science:
- Biochemistry
- Pediatric critical care
- Nutritional science
Background:
- Severe illness significantly impacts nutrient metabolism in pediatric patients.
- Understanding amino acid economy is crucial for optimizing nutritional support in critically ill infants and children.
Purpose of the Study:
- To investigate plasma phenylalanine and tyrosine kinetics in critically ill pediatric patients.
- To assess the adequacy of current nutritional support for maintaining aromatic amino acid balance.
Main Methods:
- Studied eleven critically ill pediatric patients (newborns and young infants).
- Administered stable isotope-labeled L-phenylalanine and L-tyrosine via intravenous infusion.
- Monitored plasma amino acid kinetics and phenylalanine hydroxylation rates.
Main Results:
- Phenylalanine and tyrosine fluxes and phenylalanine hydroxylation rates were determined.
- Routine nutritional support was found to be inadequate for achieving phenylalanine balance.
- The rate of phenylalanine hydroxylation appeared high compared to published data.
Conclusions:
- Tyrosine may be a conditionally indispensable amino acid in critically ill pediatric patients.
- Further research is needed to establish optimal intake levels and phenylalanine-to-tyrosine ratios.
- Optimizing nutritional strategies is essential for improving outcomes in pediatric critical care.
Abstract:
To better understand the impact of severe illness on the amino acid economy and nutritional needs of pediatric patients, we studied plasma phenylalanine and tyrosine kinetics in eleven critically ill patients (six full-term newborns and five young infants). Within 48 h of the diagnosis of sepsis they were given primed constant i.v. infusions of L-[1-13C]phenylalanine and L-[3,3,2H2]tyrosine for 4 h. Routine nutritional support continued during this period by parenteral administration of dextrose, lipid emulsion, and an amino acid mixture low in tyrosine. Phenylalanine and tyrosine fluxes and rate of phenylalanine hydroxylation did not differ significantly between the two age groups, and so the data were combined for evaluation. For the entire group, values (mumol.kg-1.h-1; mean +/- SD) for phenylalanine and tyrosine fluxes and rate of phenylalanine hydroxylation were 132 +/- 24, 66 +/- 16, and 29 +/- 12, respectively. Plasma phenylalanine to tyrosine concentration ratio was 1.67 +/- 0.6. From a comparison of the rate of phenylalanine hydroxylation with measured phenylalanine intakes, it was concluded that their routine, clinical nutritional support was inadequate to achieve body phenylalanine balance. In comparison with published data, the relative rate of phenylalanine hydroxylation appears to be high. We speculate that tyrosine is a conditionally indispensable amino acid under these conditions; it would be desirable to establish the intake levels and ratio of phenylalanine to tyrosine that effectively support aromatic amino acid balance in these critically ill patients.