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Human Nutrition and Metabolism

Supplementation with Aromatic Amino Acids Improves Leucine Kinetics but Not Aromatic Amino Acid Kinetics in Infants with Infection, Severe Malnutrition, and Edema^1,2

Marvin Reid^*,, Terrence Forrester^*, Asha Badaloo^*, William C. Heird and Farook Jahoor^,3

^* Tropical Metabolism Research Unit, University of the West Indies, Mona, Kingston 7, Jamaica and U.S. Department of Agriculture/Agricultural Research Service, Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030

³To whom correspondence should be addressed. E-mail: fjahoor{at}bcm.tmc.edu.

We investigated whether supplementation with an aromatic amino acid (AAA) cocktail consisting of 0.5 mmol each of phenylalanine, tryptophan, and tyrosine compared with isonitrogenous amounts of alanine (Ala) would improve measures of protein kinetics in 14 (8 with AAA, 6 Ala) children with edematous malnutrition (aged 6–24 mo) during the infected acute malnourished state. Supplementation started immediately after the baseline experiment, 2 d postadmission and continued to the end of the acute phase of treatment. The second (postsupplementation) experiment was done 12 d postadmission. We measured leucine kinetics, phenylalanine and tyrosine fluxes, using an i.g. 8-h prime continuous infusion of ²H₃-leucine, and an i.v. 6-h prime continuous infusion of ¹³C-leucine, ²H₂-tyrosine, and ²H₅-phenylalanine in the fed state. Leucine flux tended to be faster (P = 0.06) in the AAA group compared with Ala group after supplementation (mean difference ± SEM): 22.6 ± 10.9 µmol/(kg · h). The rate of leucine appearance from protein breakdown [28.1 ± 9.4 µmol/(kg · h)] and the nonoxidative disposal of leucine [i.e., leucine to protein synthesis; 35.4 ± 12.9 µmol/(kg · h)] were faster (P < 0.02) in the AAA group than in the Ala group. There was no significant effect of supplementation on leucine splanchnic metabolism, phenylalanine, and tyrosine fluxes. These findings are consistent with the hypothesis that the blunting of the protein catabolic response to infection in children with edematous malnutrition syndrome is due to limited availability of aromatic amino acids.

KEY WORDS: • leucine kinetics • aromatic amino acids • protein metabolism • edematous protein-energy malnutrition • stable isotope