Threonine requirement of parenterally fed postsurgical human neonates

Background: The threonine requirement of human neonates who receive parenteral nutrition (PN) has not been determined experimentally. Objective: The objective was to determine the parenteral threonine requirement for human neonates by using the minimally invasive indicator amino acid oxidation technique with L-[1-C-13]phenylalanine as the indicator amino acid. Design: Nine postsurgical neonates were randomly assigned to 16 threonine intakes ranging from 10 to 100 mg.kg(-1).d(-1). Breath and urine samples were collected at baseline and at plateau for (CO2)-C-13 and amino acid enrichment, respectively. The mean threonine requirement was determined by applying a 2-phase linear regression crossover analysis to the measured rates of (CO2)-C-13 release ((FCO2)-C-13) and L-[1-C-13] phenylalanine oxidation. Results: The mean threonine parenteral requirement determined by using phenylalanine oxidation was 37.6 mg.kg(-1).d(-1) (upper and lower confidence limits, respectively: 29.9 and 45.2 mg.kg(-1).d(-1)) and by using (FCO2)-C-13 oxidation was 32.8 mg.kg(-1).d(-1) (upper and lower confidence limits, respectively: 29.7 and 35.9 mg.kg(-1).d(-1)). Graded intakes of threonine had no effect on phenylalanine flux. Conclusion: This is the first study to report on the threonine requirement for human neonates receiving PN. We found that the threonine requirement for postsurgical PN-fed neonates is 22-32% of the content of threonine that is presently found in commercial PN solutions (111-165 mg.kg(-1).d(-1)). Am J Clin Nutr 2009; 89: 134-41.