Oxidation products of proteins in plasma of newborns reflect damage inflicted by O2 supplementation and correlate with gestational age

Abstract

Treatment of neonates, and especially preterm newborns, with supplementary O₂, can result in oxidative stress and both short- and long-term health complications. Oxidation products formed on proteins, which are the principal targets of reactive species in plasma, can be used to assess damage arising from O₂ therapy. We hypothesized that this may be particularly relevant for preterm neonates. Oxidation products formed on proteins in the plasma of term and preterm newborns were quantified to assess their possible use as biomarkers. Plasma samples from 114 term and preterm neonates with and without O₂ supplementation (fraction of inspired oxygen, FiO₂ > 21 % and 21 %, respectively) were analyzed. Total protein content and protein carbonyls were determined spectrophotometrically, whilst specific oxidation products from Tyr, Trp and Met were quantified using liquid chromatography coupled to mass detection (LC-MS). Kynurenine (Kyn), N-formylkynurenine (NFKyn), dihydroxydiphenylalanine (DOPA), 3-nitrotyrosine (3-NTyr), methionine sulfoxide (MetSO) and di-tyrosine (di-Tyr) were assessed in their protein-bound form. Alcohols, hydroperoxides and dimers of Trp were also investigated. Carbonyl groups, as well as 3-NTyr and MetSO, showed statistical differences between term and preterm neonates. However, only MetSO was sensitive to O₂ supplementation in both term and preterm subjects. The plasma levels of these products showed an inverse association with gestational age. The advantages and limitations of these products as biomarkers of protein oxidation, and the experimental procedures needed to quantify these accurately, should be considered when designing future clinical investigations.