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Cysteine: a conditionally essential amino acid in low-birth-weight preterm infants?

Maaike A Riedijk1, Ron H T van Beek, Gardi Voortman

  • 1Department of Pediatrics, Division of Neonatology, Erasmus MC-Sophia Children's Hospital, University Medical Center, Rotterdam, the Netherlands.

The American Journal of Clinical Nutrition
|October 9, 2007
PubMed

Insights

Cystine is not essential for preterm infants born at 32-34 weeks gestation, as their bodies can synthesize enough. This finding suggests cystine is likely not conditionally essential for these infants when fed adequate methionine.

Area of Science:

  • Nutritional biochemistry
  • Neonatal physiology
  • Amino acid metabolism

Background:

  • Cystine, typically nonessential, may be conditionally essential in preterm infants due to immature synthesis pathways.
  • Limited data exists on cystine requirements for low-birth-weight (LBW) preterm infants.

Purpose of the Study:

  • To determine the cystine requirements in LBW infants (gestational age 32-34 weeks) one month after birth.
  • To assess if cystine is conditionally essential in this population.

Main Methods:

  • Utilized the indicator amino acid oxidation technique with [1-(13)C]phenylalanine.
  • LBW infants received formulas with varying cystine concentrations (11-65 mg/100 mL) and ample methionine.
  • Measured 13CO2 in breath to determine cystine requirement.

Main Results:

  • Twenty-five LBW infants (gestational age 33±1 weeks) participated.
  • No significant difference in phenylalanine oxidation was observed across different cystine intake groups.
  • Determined cystine requirement to be less than 18 mg/kg/day.

Conclusions:

  • Endogenous cystine synthesis appears sufficient in 4-week-old LBW preterm infants (32-34 weeks gestation).
  • Cystine is likely not conditionally essential for enterally fed LBW preterm infants born at 32-34 weeks gestation, given adequate methionine supply.
  • Established a cystine requirement threshold below 18 mg/kg/day for this infant population.
Abstract

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