Plasma 8-isoprostane is increased in preterm infants who develop bronchopulmonary dysplasia or periventricular leukomalacia

Cysteine, cystine or N-acetylcysteine supplementation in parenterally fed neonates

BACKGROUND

L-cysteine is thought to be a conditionally essential (i.e., essential under certain conditions) amino acid for neonates. It is a precursor of glutathione, an antioxidant that may reduce oxidation injury. The addition of cysteine to parenteral nutrition (PN) allows for the reduction of the amount of methionine in PN, thereby limiting hepatotoxicity, and acidifies the solution, thereby increasing calcium and phosphate solubility, and potentially improving bone mineralization.

OBJECTIVES

To determine the effects of supplementing parenteral nutrition with cysteine, cystine or its precursor N-acetylcysteine on neonatal growth and short and long-term outcomes.

SEARCH STRATEGY

The standard search method of the Cochrane Neonatal Review Group was used. MEDLINE (1966-December 2005), EMBASE (1974-December 2005), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006) and recent abstracts (until December 2005) from the Society for Pediatric Research/American Pediatric Society, Eastern Society for Pediatric Research, and Society for Parenteral and Enteral Nutrition were searched.

SELECTION CRITERIA

All randomized (RCTs) and quasi-randomized trials that examined the effects of cysteine, cystine or N-acetylcysteine supplementation of neonatal PN were reviewed. Predetermined outcome variables included growth, nitrogen retention, mortality, morbidity secondary to oxidation injury, bone accretion, acidosis, liver disease, and cysteine levels.

DATA COLLECTION AND ANALYSIS

The standard methods of the Cochrane Collaboration and its Neonatal Review Group were used. Statistical analysis included relative risk, risk difference, and weighted mean difference (WMD).

MAIN RESULTS

Six trials fulfilled entry criteria. The majority of patients in these trials were preterm. Five small trials evaluated short-term cysteine supplementation of cysteine-free PN. One large multicenter RCT evaluated short-term N-acetylcysteine supplementation of cysteine-containing PN in extremely low birth weight infants (< or = 1000 grams).

PRIMARY OUTCOMES

Growth was not significantly affected by cysteine supplementation (evaluated in one quasi-randomized trial) or by N-acetylcysteine supplementation (evaluated in one RCT). Nitrogen retention was significantly increased by cysteine supplementation (studied in four trials) (WMD 31.8 mg/kg/day, 95% confidence interval +8.2, +55.4, n = 95, including 73 preterm infants).

SECONDARY OUTCOMES

Plasma levels of cysteine were significantly increased by cysteine supplementation but not by N-acetylcysteine supplementation. N-acetylcysteine supplementation did not significantly affect the risks of death by 36 postmenstrual weeks, bronchopulmonary dysplasia (BPD), death or BPD, retinopathy of prematurity (ROP), severe ROP, necrotizing enterocolitis requiring surgery, periventricular leukomalacia, intraventricular hemorrhage (IVH), or severe IVH. No data were available on other outcomes.

AUTHORS' CONCLUSIONS

Available evidence from RCTs shows that routine short-term cysteine chloride supplementation of cysteine-free PN in preterm infants improves nitrogen balance.However, there is insufficient evidence to assess the risks of cysteine supplementation, especially regarding metabolic acidosis, which has been reported during the first two weeks of cysteine chloride administration. Available evidence from a large RCT trial does not support routine N-acetylcysteine supplementation of cysteine-containing PN in extremely low birth weight infants. A large RCT would be required to assess whether routine prolonged cysteine supplementation of cysteine-free PN affects growth and short and long-term neonatal outcomes in very low birth weight infants.

CXCR2 blockade reduces radical formation in hyperoxia-exposed newborn rat lung

Inflammation contributes greatly to the pathogenesis of bronchopulmonary dysplasia. In previous studies, we showed that blocking neutrophil influx by treatment with SB265610, a selective CXCR2 antagonist, could partly reduce superoxide accumulation and preserve alveolar development in 60% O(2)-exposed newborn rats. The purpose of this study was to further investigate the role of neutrophils in the formation of reactive oxygen and nitrogen species mediating hyperoxia-impaired lung development. We found that hydroxyl radical formation and lipid peroxidation in rat lungs were significantly increased during 60% O(2) exposure. These increases were attenuated by the administration of SB265610. In addition, SB265610 largely inhibited protein nitration induced by hyperoxia. SB265610 partly prevented the hyperoxia-enhanced bronchoalveolar lavage (BAL) protein content in 60% O(2)-exposed animals. Our results demonstrate that neutrophils have a pivotal role in hydroxyl radical formation, lipid peroxidation and protein nitration. Taken together with our previous studies, the present findings show that blocking neutrophil influx protects alveolar development and improves lung function in part by preventing reactive oxygen/nitrogen species accumulation.

Influence of early postnatal nutritional management on oxidative stress and antioxidant defence in extreme prematurity

The increased survival of infants born at mid-gestation in the last decade is associated with significant oxygen free radical-mediated morbidities. Resuscitation with 100% oxygen, oxidant load from parenteral nutrition fluids, and oxidant stress inherent to the systemic inflammatory state subsequent to infection and tissue injury are all contributory.

CONCLUSION

Improving early postnatal protein nutrition and the formulation of parenteral nutrition fluids would potentially reduce the oxidative stress and enhance the antioxidant defence of extremely premature newborns.

Inhaled nitric oxide attenuates hyperoxic lung injury in lambs

Cytochrome P450 (CYP) inhibition with cimetidine reduces hyperoxic lung injury in young lambs. Nitric oxide (NO), also a CYP inhibitor, has been shown to either aggravate or protect against oxidant stress depending on experimental context. The objective of this study was to determine whether NO, like cimetidine, would protect young lambs against hyperoxic lung injury, and whether its effect was associated with CYP inhibition. Three groups of lambs were studied: 1) room air exposure, 2) >95% O2, and 3) >95% O2 plus inhaled NO. After 72 h, hyperoxia alone resulted in a significant increase in arterial P(CO2) and number of polymorphonuclear leukocytes in bronchoalveolar lavage (BAL), and a significant decrease in arterial/alveolar O2 tension (a/A). The addition of inhaled NO significantly decreased the hypercarbia and BAL polymorphonuclear cellular response associated with hyperoxia but had no beneficial effect on a/A ratio. There were no significant differences in F2-isoprostanes or isofurans (markers of lipid peroxidation) measured in BAL or lung tissue among study groups. No intergroup differences were detected in BAL epoxyeicosatrienoic acid levels (index of CYP activity). The results of this study indicate that hypercarbia and inflammation accompanying hyperoxic lung injury in young lambs can be attenuated by inhaled NO. However, this study provides no direct evidence that NO is inhibiting CYP-mediated oxidant lung injury.

Selective vulnerability of preterm white matter to oxidative damage defined by F2-isoprostanes

Periventricular white matter injury (PWMI) is the leading cause of cerebral palsy and chronic neurological disability in survivors of prematurity. Despite the large number of affected children, the pathogenetic mechanisms related to PWMI remain controversial. Through studies of 33 human autopsy brains, we determined that early PWMI was related to oxidative damage that particularly targeted the oligodendrocyte lineage, whereas other neuronal and glial cell types were markedly more resistant. F(2)-isoprostanes, an arachidinate metabolite/lipid peroxidation marker of oxidative damage, were significantly increased in early PWMI lesions but not in cerebral cortex. That deleterious lipid peroxidation accompanied early PWMI was supported by similar increases in F(2)-isoprostanes levels in the cerebral cortex from term infants with hypoxic-ischemic cortical injury. Detection of F(4)-neuroprostanes, a neuronal-specific oxidative damage marker, confirmed that neuroaxonal elements were resistant to injury in cerebral cortex and white matter. Significant protein nitration was not detected in PWMI lesions by 3-nitrotyrosine staining. Significant cellular degeneration was confirmed in early PWMI lesions by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling and a marked depletion of oligodendrocyte progenitors of 71 +/- 8%. Hence, the predilection of preterm infants for PWMI is related to selective lipid peroxidation-mediated injury of cerebral white matter and targeted death of oligodendrocyte progenitors.

Age-related differences in vasoconstrictor responses to isoprostanes in piglet pulmonary and mesenteric vascular smooth muscle

Isoprostanes are prostaglandin (PG)-like compounds produced nonenzymatically by free radical-catalyzed peroxidation of arachidonic acid. Isoprostanes evoke potent vascular effects but their actions in the neonatal vasculature are poorly known. We aimed to study the effects of 8-iso-PGE(1), 8-iso-PGE(2), 8-iso-PGF(1alpha), 8-iso-PGF(1beta), 8-iso-PGF(2alpha), and 8-iso-PGF(2beta) in pulmonary arteries (PA), pulmonary veins (PV), and mesenteric arteries (MA) from newborn and 2-wk-old piglets. Isoprostanes produced concentration-dependent contractions of PA, PV, and MA (magnitudes up to 1.5- to 2-fold greater than the responses to 62.5 mM KCl) but they were markedly less potent vasoconstrictors than the thromboxane A(2) (TXA(2)) mimetic U46619. Neonatal PA were more sensitive to 8-iso-PGF(1alpha), 8-iso-PGF(1beta), and 8-iso-PGF(2beta) than 2-wk-old PA. Neonatal PV were more sensitive to 8-iso-PGE(2) and 8-iso-PGF(1alpha), and neonatal MA were more sensitive to 8-iso-PGE(2), 8-iso-PGF(1alpha), 8-iso-PGF(1beta), 8-iso-PGF(2alpha), and 8-iso-PGF(2beta) than the corresponding 2-wk-old vessels. The sensitivity to U46619 decreased with postnatal age in MA but did not change in PA and PV. The contractile responses to all the isoprostanes and to U46619 were reverted by the TXA(2) receptor (TP) antagonist SQ 29,548. Moreover, isoprostane-evoked contractions in 2-wk-old PA were reduced by inhibitors of tyrosine kinase (genistein) and Rho kinase (Y 27632 and hydroxyfasudil) but not by inhibitors of protein kinase C (chelerythrine), mitogen-activated protein kinase kinase (PD 98059) or p38-kinase (SB 203580). In conclusion, isoprostanes produced compound-, tissue-, and age-dependent constriction of neonatal porcine pulmonary and mesenteric vascular smooth muscle. Isoprostane-evoked PA vasoconstriction involved TP receptors and activation of tyrosine kinases and Rho kinases.