**Oxidative Stress of Newborn**

Eloisa Gitto1, Gabriella D'Angelo1,

 Erika Cusumano1 and Russel J. Reiter2 *1Institute of Medical Pediatrics, Neonatal Intensive Care Unit, University of Messina, 2Department of Cellular and Structural Biology, The University of Texas, 1Italy 2USA* 

#### **1. Introduction**

Free radicals are highly reactive molecules containing one or more unpaired electrons. They donate or abstract electrons from other molecules in an attempt to pair their electrons and generate a more stable species. Oxygen-derived reactants collectively termed reactive oxygen species (ROS) as well as reactive nitrogen species (RNS) are normally produced in living organisms. When produced in excess, they are important mediators of cell and tissue injury [Halliwell, B. (1999), Fridovich, I. (1998), Gitto, E. et al. (2002)]. The resulting damage is referred to as oxidative stress. Free radicals are highly unstable and several enzymes and small-molecular-weight molecules with antioxidant capabilities protect against them [Halliwell, B. (1992)]; these protective molecules are part of the antioxidative defence system. There is a critical balance between free radical generation and antioxidant defences. Free radical reactions lead to the oxidation of lipids, proteins, polysaccharides and to DNA damage (fragmentation, base modifications and strand breaks); as a consequence, radicals have a wide range of biologically toxic effects [Saugstad, OD. (1996), Sarker, AH. et al. (1995)]. The generation of both ROS and RNS are summarised in figure 1.

Newborns and especially pre-term infants are probably more prone to oxidative stress than are children and young adults. There are some special reasons for this. These infants very often 1) are exposed to high oxygen concentrations, 2) have infections or inflammation, 3) have reduced antioxidant defence, and 4) have free iron which enhances the Fenton reaction leading to production of highly toxic hydroxyl radicals [Saugstad, OD. (2003, 2005)]. The Fenton reaction describes the interaction of hydrogen peroxide with a transition metal resulting in the generation of the highly toxic hydroxyl radical. Oxidative stress has been postulated to be implicated in several newborn conditions and, in 1988, SAUGSTAD [Saugstad, OD. (1988)] coined the phrase ''oxygen radical diseases of neonatology''. The idea contends that oxidative stress affects different organs, often simultaneously, giving rise to different signs according to the organ most affected. He included bronchopulmonary dysplasia/chronic lung disease, retinopathy of prematurity and necrotising enterocolitis in this category. Later, it became clear that free radicals are also involved in periventricular

Oxidative Stress of Newborn 75

activity of an important family of antioxidative enzymes, the superoxide dismutases (SOD), are depressed in the blood of pregnant women [Wisdom, SJ. et al. (1991)]. In addition, Walsh and Wang [Walsh, SW. & Wang, Y. (1993)] reported a deficiency in another antioxidative enzyme, glutathione peroxidase (GPx), during pregnancy. GPx is an important antioxidant enzyme present in virtually all tissues. The enzyme limits the accumulation of lipid peroxides and utilizes reduced glutathione (GSH) as its cofactor to convert lipid peroxides into relatively harmless hydroxylated fatty acids, water and glutathione disulfide. Given these actions, it might be expected that a deficiency in this enzyme may lead to elevated oxidative stress during pregnancy. The placenta is a major source of oxidative stress during pregnancy. It is rich in polyunsaturated fatty acids, and the placenta is an abundant source of lipid peroxides which are secreted into the maternal circulation. In normal pregnancy, placental lipid production is believed to be kept under control by placental antioxidant enzymes [Walsh, SW. et al. (1993)]. Major antioxidant enzymes such as SOD, catalase (CAT), GPx, glutathione reductase, glutathione Stransferase and glucose-6-phosphate dehydrogenase are all present in the placenta. In the normal placenta, the activities of SOD and CAT increase as gestation progresses, while the activity of GPx is diminished. On the other hand, placental production of lipid peroxides progressively drop as normal gestation advances, most likely because of the elevated activities of SOD and CAT. Thus, in normal pregnancy, placental antioxidant defenses are considered sufficient to control lipid peroxidation. Pre-eclampsia is a multisystem disorder unique to human pregnancy. It is a complication in 5–10% of pregnancies and remains a leading cause of maternal and neonatal mortality and morbidity. This human disorder is a leading cause of premature delivery and intrauterine fetal growth retardation (IUGR). Pre-eclampsia is usually diagnosed in late pregnancy because of increased blood pressure and proteinuria with the symptoms of pre-eclampsia typically disappearing shortly after delivery of the placenta. A significant rise in lipid peroxidation levels in the placenta of pre-eclampsia has been suggested [Walsh, SW. et al. (2000), Hubel, CA. (1999), Gupta, S. et al. (2005), Vanderlelie, J. et al. (2005), Atamer, Y. et al. (2005)]. Several lines of evidence support this assumption, including increased lipid peroxidation products, elevated nitrotyrosine immunostaining and reduced antioxidant enzyme activities in preeclamptic placentas. In a case control study, Vanderlelie et al. [Vanderlelie, J. et al. (2005)] measured tissue levels of SOD, GPx and lipid peroxidation in placental samples from women with normal pregnancies (18 women) and with preeclampsia (20 women). Placental tissue homogenates from pre-eclamptic patients contained significantly higher levels of lipid peroxides [malondialdehyde (MDA) and 4 hydroxy-2 (E)- nonenal; 20.68 versus 5.33 mm/mg protein], whereas there were significantly lower levels of SOD (2.02 versus 2.48 U/ mg protein) and of GPx (11.50 versus 17.33 mmol/min/mg) than in control placentas. These finding are consistent with a limited enzymatic antioxidant capacity and elevated breakdown of lipids in placental tissue of women suffering from pre-eclampsia. Increased levels of thromboxane and lipid peroxides associated with a loss of GPx activity was also reported in placentas from preeclamptic patients compared with those from normal pregnancies [Walsh, SW. & Wang, Y. (1993)]. In parallel, the in vitro production of lipid peroxides and thromboxane is augmented in both trophoblast cells and villous tissues from women with pre-eclampsia [Walsh, SW. & Wang, Y. (1995)]. Furthermore, production of 8-iso-PGF2a and MDA (a

leukomalacia [Haynes, RL. et al. (2003)] as well as in regulating the ductus arteriosus and pulmonary circulation [Clyman, RI. et al. (1989), Archer, SL. et al. (1989), Sanderud, J. et al. (1993)]. If the concept of ''oxygen radical diseases in neonatology'' is correct, it means that the conditions mentioned are not different diseases but belong to the same frequently have higher plasma levels of non-transferrin-bound iron and higher erythrocyte free iron than adults [Ogihara, T. et al. (1996)].

Fig. 1. Summary of the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS).
