Umbilical Cord and Maternal Plasma Thiol Concentrations in Normal Pregnancy

Abstract

Cysteine is the only sulfhydryl-containing amino acid in proteins and is the thiol residue in glutathione (1). In addition to its importance in the storage and transport of cysteine, glutathione plays a pivotal role in detoxification by the action of glutathione S -transferases and in scavenging free (oxygen) radicals by the action of glutathione peroxidases (1). Thiol metabolism may be altered during pregnancy. In healthy pregnant women, plasma concentrations of cysteine, glutathione, and homocysteine are decreased, whereas increased homocysteine and cysteine concentrations are seen in pathologic conditions, such as preeclampsia, in which oxidative stress may play an important role (2)(3)(4). Thiols may have important physiological functions in fetal metabolism. Although protein and amino acid turnover in the human placenta has been studied extensively (5)(6)(7), few data concerning fetal concentrations of thiols and placental maternal-fetal thiol interactions are currently available (8). During normal pregnancy, fetal growth depends on the supply of nutrients from the mother, and a clear correlation between maternal and fetal amino acid and homocysteine concentrations has been shown (6)(7)(8). Decreased concentrations of amino acids in the umbilical artery, as compared with the umbilical vein, have been interpreted as an uptake of amino acids into fetal tissues where they may be used in protein biosynthesis or as sources of energy (5). We studied fetal and maternal thiol plasma concentrations in normal pregnancies to determine reference concentrations for cysteine, homocysteine, and cysteinylglycine in arterial and venous umbilical cord plasma to gain insight into maternal-fetal thiol interactions. Arterial and venous umbilical cord blood samples from 320 consecutive neonates were drawn in preheparinized tubes …