Sulfur amino acid metabolism in children with severe childhood undernutrition: cysteine kinetics

Sulfur amino acid metabolism in children with severe childhood undernutrition: cysteine kinetics 1,2,3 Farook Jahoor, Asha Badaloo, Marvin Reid and Terrence Forrester 1 From the US Department of Agriculture, Agricultural Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX (FJ), and the Tropical Metabolism Research Unit, Tropical Medicine Research Institute, University of the West Indies, Mona, Kingston, Jamaica (AB, MR, and TF) Background: Children with edematous but not nonedematous severe childhood undernutrition (SCU) have lower plasma and erythrocyte-free concentrations of cysteine, the rate-limiting precursor of glutathione synthesis. We propose that these lower cysteine concentrations are due to reduced production secondary to slower de novo synthesis plus decreased release from protein breakdown. Objective: We aimed to measure cysteine production, de novo synthesis, and the rate of cysteine release from protein breakdown in children with SCU. Design: Cysteine flux, de novo synthesis, and release from protein breakdown were measured in 2 groups of children with edematous (n =3D 11) and nonedematous (n =3D 11) SCU when they were infected and malnourished (clinical phase 1), when they were still severely malnourished but no longer infected (clinical phase 2), and when they had recovered (clinical phase 3). Results: In clinical phase 1, cysteine production and its release from protein breakdown were slower in both groups of children than were the values in the recovered state. These kinetic variables were significantly slower, however, in the children with edematous SCU than in those with nonedematous SCU. De novo cysteine synthesis in clinical phase 1 was faster than the rate at recovery in the edematous SCU group, and there were no significant differences between the groups at any clinical phase. Conclusion: These findings suggest that cysteine production is reduced in all children with SCU because of a decreased contribution from protein breakdown and not from decreased de novo synthesis. The magnitude of this reduction, however, is much greater in children with edematous SCU than in those with nonedematous SCU. Key Words: Cysteine kinetics \u95 edematous severe childhood undernutrition \u95 nonedematous severe childhood undernutritio