Lipid-lysine adducts and modified tyrosines as markers of oxidative stress in the second trimester of pregnancy and their association with infant characteristics

Pregnancy is a physiological state accompanied by excessive levels of oxidative stress (OS), due to the increased demand and utilisation of oxygen. There is increasing evidence that maternally augmented OS exerts an adverse effect on pregnancy outcome. The aim of the present prospective study was to determine the association between the urinary concentration of relatively novel OS markers measured in the second trimester of pregnancy and the infant characteristics at birth. The maternal levels of urinary hexanoyl-lysine (HEL), propanoyl-lysine (PRL), dityrosine (DiY) and 3-nitrotyrosine (NY) were evaluated in generally healthy pregnant subjects to determine their association with birth weight, gestation at delivery and Apgar score. The observed levels of the markers were in agreement with those measured in healthy non-pregnant subjects in a previous study. A positive correlation was detected between HEL and PRL, as well as between HEL and DiY. Although the absence of a correlation between NY and the other markers has been previously noted in a non-pregnant population, a positive correlation in the pair PRL-NY (r=0.367; P<0.001) was observed in the present study. Maternal cigarette smoking was associated with increased urinary PRL levels (P=0.034). The most notable observation in the present study was that high levels of PRL and NY were associated with low Apgar scores at 1 and 5 min after birth (OR, 1.098 and 2.084 for PRL and NY, respectively; P<0.05). However, poor predictive accuracy was shown. For NY, the following results were obtained: Area under the curve (AUC), 0.818; sensitivity, 100%; specificity, 57%; positive predictive value (PPV), 11.54%; and negative predictive value (NPV), 100%. For PLR the values were as follows: AUC, 0.802; sensitivity, 100%; specificity, 62.6%; PPV, 13.05%; and NPV, 100%. DiY was negatively associated with preterm birth risk (OR=0.703; P=0.028). In conclusion, the results of the present study indicated the presence of OS in the second trimester of pregnancy, which was detected with damage to lipids and proteins and associated with an adverse Apgar score; however, the selected urinary markers exhibited poor positive predictive efficacy.