Lori Nielsen

Exposure to supplemental oxygen and its effects on oxidative stress and antioxidant enzyme activity in term newborn lambs.

The optimal oxygen concentration for the resuscitation of term infants remains controversial. We studied the effects of 21 versus 100% oxygen immediately after birth, and also exposure for 24 h to 100% oxygen, on oxidant lung injury and lung antioxidant enzyme (AOE) activities in term newborn lambs. Lambs at 139 d gestation were delivered and ventilated with 21% (RAR) or 100% (OXR) for 30 min. A third group of newborn lambs were ventilated with 100% O2 for 24 h (OX24). Oxidized glutathione levels in whole blood were significantly different among the groups with lower values in the RAR group, and these values correlated highly with partial pressure of arterial oxygen (Pao2). The reduced to oxidized glutathione ratio was significantly different among the groups, the ratio decreasing with increasing oxygen exposure. Lipid hydroperoxide (LPO) activity was significantly higher in the OXR and OX24 groups. AOE activity was higher in the whole lung and in red cell lysate in the OX24 group. Increased myeloperoxidase (MPO) activity, percent neutrophils, and proteins in lung lavage suggested inflammation in the OX24 group after maximal oxygen exposure. We conclude that even relatively brief exposure of the lung to 100% oxygen increases systemic oxidative stress and lung oxidant injury in ventilated term newborn lambs.

Role of pulmonary artery reactivity and nitric oxide in injury and inflammation following lung contusion

ABSTRACT The mechanisms contributing to hypoxia in lung contusion (LC) remain unclear and not temporally associated with the peak onset of acute inflammation. We investigated the role of oxidative stress in alteration of pulmonary arterial (PA) reactivity following LC. In addition, the role of antioxidants in reversing this process was examined. PaO2 and PA reactivity were measured in rats subjected to bilateral LC. Rings were pretreated with a nitric oxide synthase (NOS) inhibitor, L-nitro arginine (10−3 M), or PEG–superoxide dismutase (SOD) and PEG-catalase (CAT), or both (L-nitro arginine + SOD/CAT). Rings were constricted with norepinephrine and relaxed with an NOS agonist (A23187) or NO donor (SNAP [S-nitrosyl amino penicillamine]). Immunochemical and mass spectrometric quantification for nitrotyrosine was performed. Rats were hypoxemic at 4 h after contusion compared with controls, but recovered by 24 h (PaO2/FIO2 ratio: baseline, 443 ± 28; 4 h, 288 ± 46; and 24 h, 417 ± 23). Pulmonary arterial constriction to NOS inhibition and relaxation to A23187 were impaired 4 h after LC. Pulmonary arterial relaxation to SNAP was decreased at 4 and 24 h after LC. These alterations in PA reactivity were reversed by SOD/CAT pretreatment. SOD1 and 2 mRNA were upregulated, and soluble guanylyl cyclase mRNA was downregulated 24 h after LC. Immunohistochemistry and mass spectrometry revealed that levels of 3-nitrotyrosine were increased markedly at 4 h following LC consistent with superoxide generation and formation of peroxynitrite. Collectively, these data suggest that consumption of NO due to excess superoxide resulting in peroxynitrite formation leads to diminished vascular reactivity following LC.

Tracheal suctioning improves gas exchange but not hemodynamics in asphyxiated lambs with meconium aspiration

Background:Current neonatal resuscitation guidelines recommend tracheal suctioning of nonvigorous neonates born through meconium-stained amniotic fluid.Methods:We evaluated the effect of tracheal suctioning at birth in 29 lambs with asphyxia induced by cord occlusion and meconium aspiration during gasping.Results:Tracheal suctioning at birth (n = 15) decreased amount of meconium in distal airways (53 ± 29 particles/mm2 lung area) compared to no suction (499 ± 109 particles/mm2; n = 14; P < 0.001). Three lambs in the suction group had cardiac arrest during suctioning, requiring chest compressions and epinephrine. Onset of ventilation was delayed in the suction group (146 ± 11 vs. 47 ± 3 s in no-suction group; P = 0.005). There was no difference in pulmonary blood flow, carotid blood flow, and pulmonary or systemic blood pressure between the two groups. Left atrial pressure was significantly higher in the suction group. Tracheal suctioning resulted in higher Pao2/FiO2 levels (122 ± 21 vs. 78 ± 10 mm Hg) and ventilator efficiency index (0.3 ± 0.05 vs.0.16 ± 0.03). Two lambs in the no-suction group required inhaled nitric oxide. Lung 3-nitrotyrosine levels were higher in the suction group (0.65 ± 0.03 ng/µg protein) compared with the no-suction group (0.47 ± 0.06).Conclusion:Tracheal suctioning improves oxygenation and ventilation. Suctioning does not improve pulmonary/systemic hemodynamics or oxidative stress in an ovine model of acute meconium aspiration with asphyxia.

Oxygen resuscitation and oxidative-stress biomarkers in premature infants

License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited. Information on how to request permission may be found at: http://www.dovepress.com/permissions.php Research and Reports in Neonatology 2014:4 91–99 Research and Reports in Neonatology

Packed red cell transfusions alter mesenteric arterial reactivity and nitric oxide pathway in preterm lambs

Background:Cases of necrotizing enterocolitis occurring within 48 h of packed red blood cell (PRBC) transfusions are increasingly being described in observational studies. Transfusion-associated gut injury is speculated to result from an abnormal mesenteric vascular response to transfusion. However, the mechanism of disruption of the balance between mesenteric vasoconstriction and relaxation following transfusion is not known.Methods:Preterm lambs (n = 16, 134 d gestation; term: 145–147 d) were delivered and ventilated for 24 h. All the lambs received orogastric feeds with colostrum. In addition, 10 of these lambs received PRBC transfusions. Vasoreactivity was evaluated in isolated mesenteric arterial rings using norepinephrine and endothelin-1 as vasoconstrictors. Endothelium-dependent (A23187, a calcium ionophore) and endothelium-independent (SNAP) nitric oxide (NO) donors were used as vasorelaxants. Mesenteric arterial endothelial NO synthase (eNOS), soluble guanylyl cyclase (sGC), and phosphodiesterase 5 (PDE5) mRNA analyses and protein assays were performed.Results:Transfusion with PRBC significantly increased mesenteric vasoconstriction to norepinephrine and endothelin-1 and impaired relaxation to A23187 and SNAP. Mesenteric arterial eNOS protein decreased following PRBC transfusion. No significant changes were noted in sGC and PDE5 mRNA or protein assays.Conclusion:PRBC transfusion in enterally fed preterm lambs promotes mesenteric vasoconstriction and impairs vasorelaxation by reducing mesenteric arterial eNOS.

Ontogeny of atrial natriuretic peptide and its receptor in the lung: effects on perinatal surfactant release.

During the transition at birth to air breathing, regulation of surfactant release from alveolar type II (ATII) cells is critical. Atrial natriuretic peptide (ANP) stimulates natriuretic peptide receptor-A (NPR-A) and increases intracellular cGMP. We examined the changes in ANP and NPR-A in respiratory epithelium during the perinatal period using immunohistochemistry and studied the effect of ANP on surfactant release from ATII cells isolated from fetal and newborn lambs. NPR-A mRNA was detected in the fetal lung by Northern Blot and RT-PCR. At 100 d gestation (term 145 d), ANP staining was absent and NPR-A staining was weak in cuboidal epithelial cells. ANP and NPR-A staining was prominent in ATII cells at 136 d gestation and was undetectable postnatally. ANP stimulated (maximal effect at 10−10M) surfactant release from both late gestation fetal and neonatal ATII cells. Protein kinase G inhibition significantly blocked this release. We conclude that ANP stimulates surfactant release in isolated perinatal ATII cells by a cGMP-dependent mechanism. ANP and NPR-A expression in ATII cells is greatest in late gestation and declines sharply postnatally. We speculate that increased activity of the ANP/NPR-A pathway in late gestation may prime the surfactant system, preparing the lung for air breathing.

Fetal and Postnatal Ovine Mesenteric Vascular Reactivity

Background:Intestinal circulation and mesenteric arterial (MA) reactivity may play a role in preparing the fetus for enteral nutrition. We hypothesized that MA vasoreactivity changes with gestation and vasodilator pathways predominate in the postnatal period.Methods:Small distal MA rings (0.5-mm diameter) were isolated from fetal (116-d, 128-d, 134-d, and 141-d gestation, term ~ 147 d) and postnatal lambs. Vasoreactivity was evaluated using vasoconstrictors (norepinephrine (NE) after pretreatment with propranolol and endothelin-1(ET-1)) and vasodilators (NO donors A23187 and s-nitrosopenicillamine (SNAP)). Protein and mRNA assays for receptors and enzymes (endothelin receptor A, alpha-adrenergic receptor 1A (ADRA1A), endothelial NO synthase (eNOS), soluble guanylyl cyclase (sGC), and phosphodiesterase5 (PDE5)) were performed in mesenteric arteries.Results:MA constriction to NE and ET-1 peaked at 134 d. Relaxation to A23187 and SNAP was maximal after birth. Basal eNOS activity was low at 134 d. ADRA1A mRNA and protein increased significantly at 134 d and decreased postnatally. sGC and PDE5 protein increased from 134 to 141 d.Conclusion:Mesenteric vasoconstriction predominates in late-preterm gestation (134 d; the postconceptional age with the highest incidence of necrotizing enterocolitis (NEC)) followed by a conversion to vasodilatory influences near the time of full-term birth. Perturbations in this ontogenic mechanism, including preterm birth, may be a risk factor for NEC.

Long-Term Effects of Neonatal Hyperoxia in Adult Mice: NEONATAL HYPEROXIA & LONG-TERM EFFECTS IN MICE

The outcomes of premature infants have improved greatly; however, the health risks in adulthood are still relatively unclear. Bronchopulmonary dysplasia (BPD) in premature infants is a major risk factor for alteration in lung function and predisposition to respiratory morbidity, and is associated with hyperoxia. The study explores the effect of neonatal hyperoxia on organ systems in adult mice. Newborn mouse litters were randomized to 85%O2 or room air (RA) on P3 for 12 days; mice were sacrificed at P3, P7, P15, 3 months and 9 months. Lungs were assessed by histopathology, radial alveolar count, mean linear intercept, and α‐Smooth muscle actin immunohistochemistry. Aortic assessment included histology, wall thickness, elastin, and collagen content. Glomerular histology and nephron number were assessed in the kidneys. Hyperoxia‐exposed mice had progressive alveolar simplification and poor weight gain over time. Greater thickness of pulmonary arterioles by 3 months and a higher Fulton index by 9 months suggest worsening pulmonary hypertension. Aortic wall thickness to lumen ratio was greater with a lower aortic elastin‐to‐collagen ratio suggesting long‐term effects of neonatal hyperoxia. Hyperoxia‐exposed mice at 9 months had smaller glomeruli as indicated by glomerular diameter and volume. Prolonged neonatal hyperoxia during the critical period of development induces irreversible lung damage, pulmonary hypertension and structural changes in the kidneys and aorta in adult mice. This could have implications for chronic adult diseases following exposure to high levels of oxygen in the newborn period. Anat Rec, 301:717–726, 2018.

Adaptive immune responses are altered in adult mice following neonatal hyperoxia

Premature infants with bronchopulmonary dysplasia (BPD), are at risk for frequent respiratory infections and reduced pulmonary function. We studied whether neonatal hyperoxia disrupts adaptive immune responses in adult mice, contributing to higher respiratory‐related morbidities seen in these infants. Newborn mice litters were randomized at 3 days to 85% O2 or room air (RA) for 12 days. Whole lung mRNA was isolated in both the groups at 2 weeks and 3 months. Gene expression for T‐cell and B‐cell adaptive immune response was performed by real‐time PCR and qRT‐PCR; protein expression (p21, IL4, IL10, IL27, cd4) was performed by enzyme immunoassay along with p21 immunohistochemistry. Hyperoxia increased expression of p21 and decreased expression of 19 genes representing T/B‐cell activation by ≥ fourfold; three of them significantly (Rag1, Cd1d1, Cd28) compared to the RA group at 2 weeks. Despite RA recovery, the expression of IFNγ, IL27, and CD40 was significantly reduced at 3 months in the hyperoxia group. Expression of p21 was significantly higher and IL27 protein lower at 2 weeks following hyperoxia. Adult mice exposed to neonatal hyperoxia had lower IL4 and IL10 in the lung at 3 months. Adaptive immune responses are developmentally regulated and neonatal hyperoxia suppresses expression of genes involved in T‐/B‐cell activation with continued alterations in gene expression at 3 months. Dysfunction of adaptive immune responses increases the risk for susceptibility to infection in premature infants.

Nfib hemizygous mice are protected from hyperoxic lung injury and death

Nuclear Factor I (Nfi) genes encode transcription factors essential for the development of organ systems including the lung. Nfib null mice die at birth with immature lungs. Nfib hemizygous mice have reduced lung maturation with decreased survival. We therefore hypothesized that these mice would be more sensitive to lung injury and would have lower survival to hyperoxia. Adult Nfib hemizygous mice and their wild‐type (Wt) littermates were exposed to 100% O2 for 89, 80, 72 and 66 h for survival studies with lung outcome measurements at 66 h. Nfib hemizygous and Wt controls were also studied in RA at 66 h. Cell counts and cytokines were measured in bronchoalveolar lavage (BAL); lung sections examined by histopathology; lung angiogenic and oxidative stress gene expression assessed by real‐time PCR. Unexpectedly, Nfib hemizygous mice (0/14–0%) had significantly lower mortality compared to Wt mice (10/22–45%) at 80 h of hyperoxia (P < 0.003). LD50 was 80 h in the Wt group versus 89 h in the hemizygous group. There were no differences in BAL cell counts between the groups. Among the cytokines studied, MIP‐2 was significantly lower in hemizygous mice exposed to hyperoxia. New vessel formation, edema, congestion, and alveolar hemorrhage were noted on histopathology at 72 and 80 h in wild‐type mice. Nfib hemizygous lungs had significant downregulation of genes involved in redox signaling and inflammatory pathways. Adult Nfib hemizygous mice are relatively resistant to hyperoxia compared to wild‐type littermates. Mechanisms contributing to this resistance are not clear; however, transcription factors such as Nfib may regulate cell survival and play a role in modulating postnatal lung development.