Total sulfur amino acid requirement and metabolism in parenterally fed postsurgical human neonates

Abstract

Background: Except for tyrosine, the amino acid requirements of human neonates receiving parenteral nutrition (PN) have not been experimentally derived. Objectives: The objectives were to determine the total sulfur amino acid (TSAA) requirement (methionine in the absence of cysteine) of postsurgical, PN-fed human neonates by using the indicator amino acid oxidation (IAAO) technique with L-[1-13C]phenylalanine as the indicator. Design: Fifteen postsurgical neonates were randomly assigned to receive 1 of 18 methionine intakes ranging from 10 to 120 mg·kg -1·d-1, delivered in a customized, cysteine-free amino acid solution. Breath and urine samples were collected for the measurement of 13CO2 and amino acid enrichment. Blood samples were collected at baseline and after the test methionine infusion for the measurement of plasma methionine, homocysteine, cystathionine, and cysteine concentrations. Results: Breakpoint analysis determined the mean TSAA requirements to be 47.4 (95% CI: 38.7, 56.1) and 49.0 (95% CI: 39.9, 58.0) mg·kg -1·d-1 with the use of oxidation and F 13CO2, respectively. Conclusions: This is the first study to report the TSAA requirement of postsurgical, PN-fed human neonates. The estimated methionine requirement expressed as a proportion of the methionine content of current commercial pediatric PN solutions was 90% (range: 48-90%) of that found in the lowest methionine-containing PN solution. © 2008 American Society for Nutrition.