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Decreased cysteine and proline synthesis in parenterally fed, premature infants
R G Miller1, F Jahoor, T Jaksic
1Cora and Webb Mading Department of Surgery, Baylor College of Medicine, Houston, TX, USA.
Insights
Premature infants show limited ability to synthesize nonessential amino acids from glucose. This study investigated glucose conversion to seven amino acids in parenterally fed neonates, finding minimal synthesis.
Area of Science:
- Biochemistry
- Neonatology
- Nutritional Science
Background:
- Amino acid (AA) synthesis in premature infants is poorly understood.
- Parenteral nutrition is common for premature neonates, necessitating knowledge of their metabolic capabilities.
Purpose of the Study:
- To assess the capacity of premature infants to synthesize seven nonessential amino acids from glucose.
- To determine AA requirements in stable, parenterally fed premature neonates.
Main Methods:
- Stable isotope tracer study using D(-)[U13C] glucose infusion in seven premature infants.
- Measurement of isotopic enrichment in plasma amino acids (cysteine, proline, aspartate, serine, glutamate, alanine, glycine) via GC/MS.
- Analysis of plasma glucose enrichment and free plasma amino acid concentrations.
Main Results:
- Conversion of glucose tracer to cysteine and proline was not significantly different from zero.
- Limited evidence of de novo synthesis for other nonessential amino acids from glucose was observed.
- Plasma amino acid concentrations were measured, but synthesis capacity was the focus.
Conclusions:
- Premature infants have a limited capacity to synthesize nonessential amino acids from glucose.
- Findings suggest that exogenous provision of these amino acids may be crucial for premature neonates.
- Further research is needed to fully elucidate AA metabolism and requirements in this population.
Abstract:
Little is known about the amino acid (AA) biosynthetic capacity and requirements of premature infants. This study assessed the synthesis of seven biochemically nonessential AA from a universal precursor, glucose, in stable, parenterally fed, premature neonates. Seven infants (six boys, one girl) were studied at a mean age of 6.3 +/- 0.6 (SEM) days; mean gestational age was 29.7 +/- 1.3 (SEM) weeks, and mean birth weight was 1,222.8 +/- 176.5 (SEM) grams. All infants were parenterally fed a mixture of 7.5% to 12.5% dextrose and 2.2% Trophamine, with or without lipid. Mean caloric intake was 93 +/- 8.4 (SEM) kcal/kg/d, and total AA intake was standardized at 2.86 g/kg/d AA, plus supplemental cysteine (30 mg/g AA/d). Each infant received a 4-hour continuous, unprimed intravenous infusion of a stable isotope tracer of D(-)[U13C] glucose (200 mg/kg). Blood samples were obtained before and at the end of the infusion. Conversion of the glucose tracer into seven biochemically nonessential AA (cysteine [Cys], proline [Pro], aspartate [Asp], serine [Ser], glutamate [Glu], alanine [Ala], and glycine [Gly]) was assessed by measuring their isotopic enrichment in plasma, using gas chromatography/mass spectrometry (GC/MS), and expressed as mole percent excess (MPE) (mean +/- SEM). The isotopic enrichment of plasma glucose was also measured using GC/MS. Free plasma AA concentrations (mean +/- SD) were measured using an automated amino acid analyzer. Mean MPE for M + 1, M + 2 and M + 3 Cys, and for M + 1 and M + 3 Pro were not significantly different from 0; M + 2 Pro barely achieved statistical significance (P = .048).(ABSTRACT TRUNCATED AT 250 WORDS)