The addition of cysteine to the total sulphur amino acid requirement as methionine does not increase erythrocytes glutathione synthesis in the TPN fed human neonate

Abstract

Controversy exists as to whether the total parenteral nutrition (TPN) fed human neonate is capable of synthesizing adequate cysteine from methionine when the total sulphur amino acid (TSAA) is provided as methionine only. Our recent study, in which we determined the TSAA requirement as methionine only, provided evidence that the TPN fed human neonate is capable of synthesizing adequate cysteine from methionine; at least for protein synthesis. However, there is evidence that protein synthesis takes precedence over glutathione (GSH) synthesis when sulphur amino acid supply is low. The goal of this study was to determine whether GSH synthesis is maximized at a methionine intake adequate for protein synthesis in the TPN fed human neonate. We measured GSH concentration, fractional and absolute synthesis rate in 5 TPN fed post‐surgical human neonates in a repeated measures design. Each neonate received a cysteine free methionine adequate TPN for 3 d followed by a methionine adequate cysteine supplemented TPN for another 3 d and GSH kinetics measured on the 3rd d of each study period. The isotope used was [U‐13C2 ‐15N]glycine. Cysteine supplementation did not increase glutathione synthesis. Further studies in neonates on TPN for prolonged periods with evidence of TPN associated liver disease are required to determine if cysteine supplementation positively affects GSH synthesis under such conditions.