Transsulfuration pathway components in premature infants duing the first month of life. 1445

Background: In the transsulfuration pathway, methionine is converted to cysteine: methionine ⇒ S-Adenosyl methionine ⇒ homocysteine⇒ cystathionine ⇒ cysteine; the last reaction is controlled by cystathionase. Higher concentrations of cystathionine and lower levels of cysteine have been reported in the first 24 hours of life in preterm compared to term neonates, and may reflect a limitation at the cystathionase level (Am J Clin Nutr 1995;61:1067-9). Objective: To measure the components of the transsulfuration pathway longitudinally in premature infants. Design: Plasma samples were obtained on days 3, 7, 14 and 21 from 53 premature infants (mean ± SD: gestation: 27 ± 1.6 weeks; birth weight: 957 ± 176 g). Cystine, methionine and cystathionine were measured on a LKB 4151 Alpha Plus amino acid analyzer. The remaining sample was reduced and total (T) cyst(e)ine and total homocysteine were determined by HPLC. Results: see table (mean ± se). Cystathionine was detectable (≥lμmol/L) in only 6,9,6 and 4 infants on days 3,7,14 and 21 respectively. Cystine and total cyst(e)ine were significantly higher in the group where cystathionine could be detected. In infants with measurable cystathionine, levels of the latter correlated with cystine (r = 0.53, p= 0.007) and total cyst(e)ine (r = 0.54, p= 0.03). Conclusion: Cystine levels remain below the normal reference range in premature infants through the first month of life. We did not find evidence of limitation of cystathionase activity.