Total Sulfur Amino Acid Requirements Are Not Altered in Children with Chronic Renal Insufficiency, but Minimum Methionine Needs Are Increased.

Background: The total sulfur amino acid (TSAA) and minimum Met requirements have been previously determined in healthy children. TSAA metabolism is altered in kidney disease. Whether TSAA requirements are altered in children with chronic renal insufficiency (CRI) is unknown.Objective: We sought to determine the TSAA (Met in the absence of Cys) requirements and minimum Met (in the presence of excess Cys) requirements in children with CRI.Methods: Five children (4 boys, 1 girl) aged 10 ± 2.6 y with CRI were randomly assigned to receive graded intakes of Met (0, 5, 10, 15, 25, and 35 mg · kg-1 · d-1) with no Cys in the diet. Four of the children (3 boys, 1 girl) were then randomly assigned to receive graded dietary intakes of Met (0, 2.5, 5, 7.5, 10, and 15 mg · kg-1 · d-1) with 21 mg · kg-1 · d-1 Cys. The mean TSAA and minimum Met requirements were determined by measuring the oxidation of l-[1-13C]Phe to 13CO2 (F13CO2). A 2-phase linear-regression crossover analysis of the F13CO2 data identified a breakpoint at minimal F13CO2 Urine samples collected from all study days and from previous studies of healthy children were measured for sulfur metabolites.Results: The mean and population-safe (upper 95% CI) intakes of TSAA and minimum Met in children with CRI were determined to be 12.6 and 15.9 mg · kg-1 · d-1 and 7.3 and 10.9 mg · kg-1 · d-1, respectively. In healthy school-aged children the mean and upper 95% CI intakes of TSAA and minimum Met were determined to be 12.9 and 17.2 mg · kg-1 · d-1 and 5.8 and 7.3 mg · kg-1 · d-1, respectively. A comparison of the minimum Met requirements between healthy children and children with CRI indicated significant (P < 0.05) differences.Conclusion: These results suggest that children with CRI have a similar mean and population-safe TSAA to that of healthy children, suggesting adequate Cys synthesis via transsulfuration, but higher minimum Met requirement, suggesting reduced remethylation rates.

Minimum methionine requirement and cysteine sparing of methionine in healthy school-age children.

BACKGROUND: Cysteine can provide a portion of the sulfur amino acid requirement in adults. Whether this is true in children-and, if so, to what extent-is not known. OBJECTIVES: The objectives were to determine minimum methionine requirements in healthy, school-age children when excess cysteine is provided and to subsequently determine the cysteine-sparing effect by comparing these methionine requirements with those determined previously in the same children when no cysteine was provided. DESIGN: Six healthy, school-age children randomly received graded intakes of methionine (0, 2.5, 5, 7.5, 10, and 15 mg . kg(-1) . d(-1)) along with 21 mg cysteine . kg(-1) . d(-1) in the diet. The mean methionine requirement was determined by using a biphasic linear regression crossover analysis of measurements of the rate of appearance of (13)CO(2) in the breath (F(13)CO(2)), which identified a breakpoint at the minimal F(13)CO(2) in response to graded levels of methionine intake. RESULTS: The mean and population-safe minimum methionine requirements, in the presence of excess dietary cysteine, were found to be 5.8 and 7.3 mg . kg(-1) . d(-1), respectively. The mean and population-safe (upper 95% CI) methionine requirements, in the absence of dietary cysteine, were previously determined to be 12.9 and 17.2 mg . kg(-1) . d(-1), respectively. These values represent a cysteine-sparing effect of 55% and 58% in comparison with mean and population-safe methionine requirements, respectively. CONCLUSION: Excess intake of dietary cysteine results in the reduction in the requirements for methionine to a minimum obligatory requirement level.

Total sulfur amino acid requirement of healthy school-age children as determined by indicator amino acid oxidation technique.

BACKGROUND: Current total sulfur amino acid (TSAA) requirements of children are based on a factorial estimate that involves several assumptions. OBJECTIVE: The objective was to determine the TSAA requirement (methionine alone) of healthy school-age children by measuring the appearance of 13CO2 (F13CO2) in breath after the oxidation of l-[1-13C]phenylalanine in response to graded methionine intakes. DESIGN: Six healthy school-age children randomly received each of 6 methionine intakes (0, 5, 10, 15, 25, and 35 mg.kg(-1).d(-1)) along with an amino acid mixture to give a final protein intake of 1.5 g.kg(-1).d(-1) and an energy intake of 1.7 x resting energy expenditure. The diet was devoid of cysteine. The mean TSAA requirement was determined by applying a biphase linear regression crossover analysis on F13CO2 data, which identified a breakpoint at minimal F13CO2 in response to graded methionine intakes. RESULTS: The mean and population-safe (upper 95% CI) intakes of TSAA (as methionine) were determined to be 12.9 and 17.2 mg.kg(-1).d(-1), respectively. CONCLUSIONS: The current study suggests that children of this age group have a mean TSAA requirement similar to that of adults (12.6 mg.kg(-1).d(-1)). Therefore, it is valid to use a factorial approach, which assumes that maintenance requirements in childhood are similar to adult requirements, to estimate TSAA requirements in school-age children.