**3. Antioxidants classification**

Antioxidants are most commonly classified into enzymatic and non-enzymatic systems. Depending on their solubility, non-enzymatic antioxidants are divided into water-soluble and lipid-soluble antioxidants.

The main enzymatic antioxidant systems are:


The main non-enzymatic antioxidant systems are represented by:


**187**

*Antioxidants at Newborns*

the colon;

protein.

its name [23, 27].

**3.1 Antioxidant enzymes**

*DOI: http://dx.doi.org/10.5772/intechopen.85175*

mutase, catalase, and glutathione peroxidase.

convert hydrogen peroxide to water.

cell, causing its destruction.

increase of gestational age [18].

antioxidant enzymes.

Ravin test [16].

animals [16].

period.

Cu2+, known as the Haber-Weiss reaction:

• amino acids such as histidine, taurine, cysteine which ensures protection against toxic aldehydes present in cigarette smoke, methionine which protects

The most important antioxidant enzymes in newborns are: superoxide dis-

Superoxide dismutase has three forms: MnSOD located in mitochondria, copper-zinc superoxide dismutase (Cu/ZnSOD) in the cytoplasm, and extracellular superoxide dismutase (EC-SOD). In newborns, the last one is located intracellularly in the cytoplasm, unlike in adults, where it is located extracellularly, as indicated by

Superoxide dismutase has the role of converting the highly toxic superoxide radical to hydrogen peroxide and water. Catalase and glutathione peroxidase

In the absence of catalase, a cascade reaction is triggered with the formation of hydroxyl radicals, which requires the presence of iron metal ions (Fe2+) and copper

The hydroxyl radical resulting from this reaction will attack the structures of the

In the intrauterine period, there is an interaction between the fetus, placenta, and uterus, which requires a redox signal with a role in maintaining the balance of this interaction and allowing the development of antioxidant systems in the fetal

The decrease in lipid peroxidation in the placenta with the evolution of pregnancy is an indirect marker of the development of antioxidant mechanisms with the

Normal vascular development is conditioned by the activity of nitric oxide controlled by nitric oxide synthase. Nitric oxide plays a role in regulating the activity of

The protective role of SOD was demonstrated in experimental groups of animals—rats—at the Physiology Department of the University of Medicine, Cluj-Napoca, Romania [16]. The authors studied lipid peroxides as oxidative stress parameters by measuring malondialdehyde (MDA) and ceruloplasmin using the

The animals exposed to hypobaric hypoxia had, immediately after SOD administration, significantly increased malondialdehyde (MDA) values, which were close to the values found in unprotected animals exposed to hypobaric hypoxia. At 24 hours after SOD administration, in animals exposed to hypoxia, the values of MDA as a marker of lipid peroxidation were significantly decreased, being lower than those of the control group. In the case of ceruloplasmin, values were significantly lower in protected compared to unprotected

+ OH<sup>−</sup> + Fe3+ (1)

H2O2 + Fe2+ → OH•

• Heme proteins and heme-binding proteins—hemopexin, haptoglobin, porphyrin, carnosine, estrogens, coenzyme Q10, polyamines, saturated fatty acids, flavonoids which stabilize the cell membrane and are used in eye diseases, phenols, and polyphenols. Ceruloplasmin is an extracellular copper-transport


## **3.1 Antioxidant enzymes**

*Antioxidants*

role;

• vitamin C;

• selenium;

• bilirubin;

tive than beta-carotene;

• cysteine-rich metallothioneins;

• uric acid and urates;

ceruloplasmin;

and periventricular leukomalacia [1, 8, 17].

improving the survival rate [13, 26].

**3. Antioxidants classification**

into water-soluble and lipid-soluble antioxidants. The main enzymatic antioxidant systems are:

dase (GSH-Px)—mainly protect the liver;

*peroxide to glutathione disulfide and water*;

released into the blood and extracellular fluid.

• the reduced-oxidized glutathione redox cycle;

• vitamin E—which intercepts the peroxyl radical;

bronchopulmonary dysplasia, retinopathy of prematurity, necrotizing enterocolitis,

In the case of perinatal asphyxia, ROS will exert a considerable harmful effect on the brain because antioxidant levels are low and there is an increased oxygen consumption during transition from fetal life to neonatal life [14, 15, 25]. Randomized studies on relatively large numbers of term newborns with asphyxia have demonstrated the importance of resuscitation with atmospheric air in limiting injury and

Antioxidants are most commonly classified into enzymatic and non-enzymatic systems. Depending on their solubility, non-enzymatic antioxidants are divided

• *superoxide dismutase* (SOD)—an enzyme that detoxifies the superoxide anion;

• *catalase* (CAT)—detoxifies oxygenated water and has a protective antitumor

• *peroxidases*—myeloperoxidase (MPO), lipid peroxidase, glutathione peroxi-

• *glutathione peroxidase (GPx) intracellular selen-protein that reduces hydrogen* 

• *the system of cytochrome oxidases*, which reduce oxygen; they play a role in reducing the amount of oxidant or potentially oxidant substances; they can be

• carotenoids—alpha-carotene, a precursor of vitamin A, is 10 times more effec-

• metal-binding proteins: albumin, transferrin, ferritin, lactoferrin, and

The main non-enzymatic antioxidant systems are represented by:

**186**

The most important antioxidant enzymes in newborns are: superoxide dismutase, catalase, and glutathione peroxidase.

Superoxide dismutase has three forms: MnSOD located in mitochondria, copper-zinc superoxide dismutase (Cu/ZnSOD) in the cytoplasm, and extracellular superoxide dismutase (EC-SOD). In newborns, the last one is located intracellularly in the cytoplasm, unlike in adults, where it is located extracellularly, as indicated by its name [23, 27].

Superoxide dismutase has the role of converting the highly toxic superoxide radical to hydrogen peroxide and water. Catalase and glutathione peroxidase convert hydrogen peroxide to water.

In the absence of catalase, a cascade reaction is triggered with the formation of hydroxyl radicals, which requires the presence of iron metal ions (Fe2+) and copper Cu2+, known as the Haber-Weiss reaction:

$$\text{H}\_2\text{O}\_2 + \text{Fe}^{2+} \rightarrow \text{OH}^\bullet + \text{OH}^- + \text{Fe}^{3+} \tag{1}$$

The hydroxyl radical resulting from this reaction will attack the structures of the cell, causing its destruction.

In the intrauterine period, there is an interaction between the fetus, placenta, and uterus, which requires a redox signal with a role in maintaining the balance of this interaction and allowing the development of antioxidant systems in the fetal period.

The decrease in lipid peroxidation in the placenta with the evolution of pregnancy is an indirect marker of the development of antioxidant mechanisms with the increase of gestational age [18].

Normal vascular development is conditioned by the activity of nitric oxide controlled by nitric oxide synthase. Nitric oxide plays a role in regulating the activity of antioxidant enzymes.

The protective role of SOD was demonstrated in experimental groups of animals—rats—at the Physiology Department of the University of Medicine, Cluj-Napoca, Romania [16]. The authors studied lipid peroxides as oxidative stress parameters by measuring malondialdehyde (MDA) and ceruloplasmin using the Ravin test [16].

The animals exposed to hypobaric hypoxia had, immediately after SOD administration, significantly increased malondialdehyde (MDA) values, which were close to the values found in unprotected animals exposed to hypobaric hypoxia. At 24 hours after SOD administration, in animals exposed to hypoxia, the values of MDA as a marker of lipid peroxidation were significantly decreased, being lower than those of the control group. In the case of ceruloplasmin, values were significantly lower in protected compared to unprotected animals [16].

The preterm neonate is born before the antioxidant systems capable of neutralizing ROS are formed. Birth itself is an oxidative stress-inducing factor, which will cause, in conjunction with other factors mentioned before such as hypoxia, hyperoxia, reperfusion, or inflammation, the rapid exhaustion of impaired defense mechanisms in the premature newborn. Transplacental nutrient supply has an important role in the formation of antioxidant defense mechanisms. However, this supply is limited in the case of preterm neonates. Chorioamnionitis present in a relatively great number of premature births is an induction factor for MnSOD mRNA in fetal membranes. Antenatal corticosteroids, in addition to their role in early lung, brain, and intestinal maturation, influence stimulation of the activity of antioxidant enzymes: SOD, catalase, and glutathione transferase [25, 29].

The endogenous surfactant has SOD and catalase in its composition. Their antioxidant role in the surfactant is to prevent surfactant lipid peroxidation and inactivation following the oxidative attack of ROS. These enzymes with antioxidant effects are not found in similar amounts in the exogenous surfactant used for the treatment of respiratory distress [30].

It is important to identify newborns at risk for oxidative stress in order to initiate early antioxidant therapy with a view to limiting oxidative stress progression. Since oxidative stress can frequently start during the intrauterine period, finding antioxidant therapies for the mother with an impact on the newborn is essential.

#### **3.2 Non-enzymatic antioxidants**

Vitamins have an antioxidant role. Among water-soluble vitamins, vitamin C is the most studied. The most extensively studied lipid-soluble vitamins in neonates are vitamins A and E.

Vitamin A acts on retinol-binding proteins and on retinoic acid receptors. The main actions of retinol consist of maintaining epithelial integrity, regulating growth and proliferation, and modulating the levels of ceruloplasmin, a protein with antioxidant effects [2, 21]. Vitamin A levels are decreased in preterm newborns, proportionally to the degree of prematurity. The benefits of vitamin A in limiting the incidence of bronchopulmonary dysplasia have been described in many studies. Its beneficial effect in reducing the incidence of the disease could not be demonstrated. Also, the fact that it requires intramuscular administration and relatively high doses to exert its antioxidant effects is a major disadvantage [15, 22].

Regarding vitamins E and C, their beneficial effect in preventing the teratogenic effect of maternal diabetes has been studied by a number of authors [19].

In the category of water-soluble vitamins, other vitamins besides vitamin C have an antioxidant role: riboflavin, pyridoxine, and niacin, which maintain GSH activity.

Vitamin E is the antioxidant that is present in the highest amount in the human body. It is a lipophilic vitamin, which accumulates in lipid-rich cell membranes. It is an important lipid peroxyl scavenger [15].

Carotenoids are also lipid-soluble and have a characteristic color. Lutein plays a role in ROS elimination. In umbilical cord blood, studies have evidenced higher lutein levels in preterm compared to term newborns [29].

Ceruloplasmin is an extracellular antioxidant that acts like a ferroxidase enzyme, catalyzing the oxidation reaction of Fe2+ to Fe3+, thus limiting Haber-Weiss and Fenton reaction.

$$\text{LOH} \star \text{Fe}^{2+} \rightarrow \text{L} \blackminus \text{O}^{\bullet} \text{ +OH}^{\bullet} \text{ + Fe}^{3+} \tag{2}$$

**189**

*Antioxidants at Newborns*

frequently measured.

*DOI: http://dx.doi.org/10.5772/intechopen.85175*

**4. Evaluation of antioxidants in neonates**

diseases such as diabetes [15, 30].

cytokine-mediated pro-inflammatory effect, playing a role in the pathogenesis of

Antioxidant defense in neonates can be evaluated by measuring enzymatic and non-enzymatic systems. Among enzymatic systems, glutathione reductase, peroxidase, transferase, the oxidized/reduced glutathione ratio, superoxide dismutase, as well as other antioxidants such as ceruloplasmin, transferring are the most

The non-enzymatic antioxidant systems that can be measured in newborns are vitamins A, E, and C. Vitamin A and E values measured in newborns are presented in many studies. Shah et al. describe a correlation between hepatic vitamin A reserves and gestational age, as well as between nutritional status and maternal vitamin A levels. Vitamin A has an important role in the development of visual acuity, and also in lung development and surfactant synthesis [1]. Vitamin A levels are significantly lower in preterm compared to term neonates. Antenatal corticoid administration has a beneficial effect on vitamin A levels in premature babies. Thus, in preterm newborns benefiting from antenatal corticosteroids, the levels of these vitamins with antioxidant effect are higher than in preterm babies without antenatal treatment. The mechanism of corticosteroids in increasing vitamin synthesis is unknown. It seems that these act by increasing the plasma levels of retinol-binding

Vitamin E, another important non-enzymatic antioxidant, with a role in stabilizing cell membranes, also has lower values in preterm compared to term neonates. Vitamin E has been used in many studies for its antioxidant effect in preventing retinopathy and bronchopulmonary dysplasia. However, in a 2003 Cochrane analysis, Brion et al. demonstrated that vitamin E plays a role in reducing the incidence of ROP and IVH, but increases the incidence of neonatal sepsis [3]. Allopurinol, melatonin, and acetylcysteine have been used in studies for their antioxidant effect, mainly as neuroprotective agents. Melatonin and acetylcysteine were used in the studies of Gitto, and subsequently Barceló, to reduce the incidence of NEC in premature neonates [4, 5]. However, there is no consensus regarding their use for the treatment of NEC in neonates or for the treatment of other conditions associated with hypoxia-ischemia. Nevertheless, it should be taken into consideration that exogenous antioxidant therapy with high doses of vitamin C and beta-carotene in

For the evaluation of antioxidant defense in newborns, the levels of ceruloplasmin were measured in our service. This non-enzymatic antioxidant defense marker proved to be deficient in preterm compared to term neonates. Ceruloplasmin is a peroxyl radical scavenger. Free oxygen radical excess caused by certain oxidative stress-inducing situations will put a strain on the impaired defense mechanisms of the premature newborn. Antioxidant values will be lower compared to those of fullterm newborns. Ceruloplasmin determined by spectrophotometry had lower values in preterm neonates with respiratory distress. Also, ceruloplasmin levels decreased with the decrease in gestational age. Determinations evidenced lower ceruloplasmin

Exposure to asphyxia at birth results in decreased ceruloplasmin levels. Under these oxidative stress-inducing conditions, the measurements performed evidenced lower ceruloplasmin values in preterm newborns with asphyxia compared to term newborns with asphyxia. Asphyxia is followed by a diminution of antioxidant levels and an increase in transferrin saturation. Current data confirm the fact that in

proteins, stimulating the hepatic synthesis of these proteins [2].

values on the first day compared to the third day of life (**Table 1**).

particular will have a pro-oxidant effect.

Uric acid is a non-enzymatic antioxidant resulting from purine metabolism. It is a scavenger of many ROS, but in certain situations, in excessive amounts, it has a *Antioxidants*

The preterm neonate is born before the antioxidant systems capable of neutralizing ROS are formed. Birth itself is an oxidative stress-inducing factor, which will cause, in conjunction with other factors mentioned before such as hypoxia, hyperoxia, reperfusion, or inflammation, the rapid exhaustion of impaired defense mechanisms in the premature newborn. Transplacental nutrient supply has an important role in the formation of antioxidant defense mechanisms. However, this supply is limited in the case of preterm neonates. Chorioamnionitis present in a relatively great number of premature births is an induction factor for MnSOD mRNA in fetal membranes. Antenatal corticosteroids, in addition to their role in early lung, brain, and intestinal maturation, influence stimulation of the activity of

antioxidant enzymes: SOD, catalase, and glutathione transferase [25, 29].

dant therapies for the mother with an impact on the newborn is essential.

treatment of respiratory distress [30].

**3.2 Non-enzymatic antioxidants**

an important lipid peroxyl scavenger [15].

lutein levels in preterm compared to term newborns [29].

are vitamins A and E.

The endogenous surfactant has SOD and catalase in its composition. Their antioxidant role in the surfactant is to prevent surfactant lipid peroxidation and inactivation following the oxidative attack of ROS. These enzymes with antioxidant effects are not found in similar amounts in the exogenous surfactant used for the

It is important to identify newborns at risk for oxidative stress in order to initiate early antioxidant therapy with a view to limiting oxidative stress progression. Since oxidative stress can frequently start during the intrauterine period, finding antioxi-

Vitamins have an antioxidant role. Among water-soluble vitamins, vitamin C is the most studied. The most extensively studied lipid-soluble vitamins in neonates

Vitamin A acts on retinol-binding proteins and on retinoic acid receptors. The main actions of retinol consist of maintaining epithelial integrity, regulating growth and proliferation, and modulating the levels of ceruloplasmin, a protein with antioxidant effects [2, 21]. Vitamin A levels are decreased in preterm newborns, proportionally to the degree of prematurity. The benefits of vitamin A in limiting the incidence of bronchopulmonary dysplasia have been described in many studies. Its beneficial effect in reducing the incidence of the disease could not be demonstrated. Also, the fact that it requires intramuscular administration and relatively high doses to exert its antioxidant effects is a major disadvantage [15, 22]. Regarding vitamins E and C, their beneficial effect in preventing the teratogenic

effect of maternal diabetes has been studied by a number of authors [19].

In the category of water-soluble vitamins, other vitamins besides vitamin C have an antioxidant role: riboflavin, pyridoxine, and niacin, which maintain GSH activity. Vitamin E is the antioxidant that is present in the highest amount in the human body. It is a lipophilic vitamin, which accumulates in lipid-rich cell membranes. It is

Carotenoids are also lipid-soluble and have a characteristic color. Lutein plays a role in ROS elimination. In umbilical cord blood, studies have evidenced higher

catalyzing the oxidation reaction of Fe2+ to Fe3+, thus limiting Haber-Weiss and

LOH + Fe2+ → L▬O**•**

Ceruloplasmin is an extracellular antioxidant that acts like a ferroxidase enzyme,

Uric acid is a non-enzymatic antioxidant resulting from purine metabolism. It is a scavenger of many ROS, but in certain situations, in excessive amounts, it has a

+OH**•**

+ Fe3+ (2)

**188**

Fenton reaction.

cytokine-mediated pro-inflammatory effect, playing a role in the pathogenesis of diseases such as diabetes [15, 30].
