Urinary excretion of free cysteine in critically ill neonates

Abstract

In preliminary observations, significant amounts of free cysteine, a neurotoxic amino acid, were noted in the urine of asphyxiated or septic‐shocked neonates. The present study was conducted to determine whether free urinary cysteine was elevated in these critically ill neonates compared with a control group, and to assess the clinical significance of this generation. Free cysteine was measured in the urine of newborn infants with perinatal asphyxia (n= 16) or neonatal sepsis (n= 14) and the urine of a control group (n= 10) by ion‐exchange chromatography. Relationships between cysteine levels and the clinical severity, sulfite supply and neurological outcome of the patients were then studied. Urinary cysteine was 27.6 (15‐49) mmol mol−1 creatinine for the patients but was not detectable in the control group. Cysteine levels were correlated with the severity of neonatal septic shock but not with the grade of perinatal asphyxia and did not have a specific influence on the neurological outcome of these patients. The correlation between cysteine level and the severity of neonatal septic shock was indirect and probably linked to higher sulfite administration in this population. Conclusion: The mean daily supply of sulfites is high in critically ill neonates, mainly originating from dopamine and generating significant amounts of cysteine. Although a worsening effect attributable to cysteine on the neurological outcome of the patients could not be demonstrated, the appropriateness of cryptic administration of sulfites by way of drug excipients is called into question.

Pyridoxal 5'‐phosphate in cerebrospinal fluid; factors affecting concentration

“…The safe upper level for sulfite plasma concentration is not known, but many adverse effects have been reported after exposure to exogenous sulfites (Smolinske 1992), including the development of seizures following administration of morphine containing sodium bisulfite (Meisel and Welford 1992). Cambonie et al (2001) described elevated urinary cysteine excretion in neonates with septic shock compared with well neonates and showed that cysteine excretion was indirectly related (the proposed mechanism being nonenzymatic sulphitolysis) to the amount of sulfite administered by drug infusions. Some of these children also had positive urine sulfite test strips and mildly elevated sulfocysteine excretion.…”

Efficacy of screening immune system function in at-risk newborns

“…Cysteine is a crucial limiting factor in glutathione synthesis 62 and excessive urinary excretion of cysteine is observed in critically ill neonates. 63 The amino acid cysteine is found in whey protein, which constitutes 60 per cent of human breast milk. 64 …”