The role of cytochrome P450 (CYP) enzymes in hyperoxic lung injury.

INTRODUCTION: Hyperoxic lung injury is a condition that can occur in patients in need of supplemental oxygen, such as premature infants with bronchopulmonary dysplasia or adults with acute respiratory distress syndrome. Cytochrome P450 (CYP) enzymes play critical roles in the metabolism of endogenous and exogenous compounds. AREAS COVERED: Through their complex pathways, some subfamilies of these enzymes may contribute to or protect against hyperoxic lung injury. Oxidative stress from reactive oxygen species (ROS) production is most likely a major contributor of hyperoxic lung injury. CYP1A enzymes have been shown to protect against hyperoxic lung injury while CYP1B enzymes seem to contribute to it. CYP2J2 enzymes help protect against hyperoxic lung injury by triggering EET production, thereby, increasing antioxidant enzymes. The metabolism of arachidonic acid to ω-terminal hydroxyeicosatetraenoic acid (20-HETEs) by CYP4A and CYP4F enzymes could impact hyperoxic lung injury via the vasodilating effects of 20-HETE. CYP2E1 and CYP2A enzymes may contribute to the oxidative stress in the lungs caused by ethanol- and nicotine-metabolism, respectively. EXPERT OPINION: Overall, the CYP enzymes, depending upon the isoform, play a contributory or protective role in hyperoxic lung injury, and are, therefore, ideal candidates for developing drugs that can treat oxygen-mediated lung injury.

Does lack of glutathione peroxidase 1 gene expression exacerbate lung injury induced by neonatal hyperoxia in mice?

Supplemental oxygen (O2) increases the risk of lung injury in preterm infants, owing to an immature antioxidant system. Our objective was to determine whether impairing antioxidant defense by decreasing glutathione peroxidase 1 (GPx1) gene expression increases the injurious effects of hyperoxia (Hyp). GPx1+/+ and GPx1-/- C57Bl/6J mice were exposed to 21% O2 (Air) or 40% O2 (Hyp) from birth to postnatal day 7 (P7d); they were euthanized on P7d or maintained in air until adulthood [postnatal day 56 (P56d)] to assess short-term and long-term effects, respectively. We assessed lung architecture, three markers of pulmonary oxidative stress (P7d, P56d), macrophages in lung tissue (P7d), immune cells in bronchoalveolar lavage fluid (BALF; P56d), and GPx1-4 and catalase gene expression in lung tissue (P7d, P56d). On P7d, macrophages were decreased by lack of GPx1 expression and further decreased by hyperoxia. GPx1 expression was increased in GPx1+/+Hyp mice and decreased in both GPx1-/- groups. On P56d, heme oxygenase-1 was increased by hyperoxia when GPx1 was absent. There were significantly more immune cells from Hyp groups than from the GPx1+/+Air group and a greater proportion of lymphocytes in GPx1-/-Hyp mice. GPx1 expression was significantly decreased in GPx1-/- mice; GPx2-4 and catalase expression was increased in GPx1-/-Hyp mice compared with other groups. Tissue fraction was decreased in GPx1-/-Air mice; bronchiolar smooth muscle was decreased in GPx1-/- mice. GPx1 does not clearly exacerbate hyperoxia-induced increases in oxidative stress or lung injury but may alter pulmonary immune function. Increased expression of GPx2-4 and catalase in GPx1-/-Hyp mice suggests gene redundancy within the model.

Soluble guanylate cyclase modulators blunt hyperoxia effects on calcium responses of developing human airway smooth muscle.

Exposure to moderate hyperoxia in prematurity contributes to subsequent airway dysfunction and increases the risk of developing recurrent wheeze and asthma. The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic GMP (cGMP) axis modulates airway tone by regulating airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)]i) and contractility. However, the effects of hyperoxia on this axis in the context of Ca(2+)/contractility are not known. In developing human ASM, we explored the effects of novel drugs that activate sGC independent of NO on alleviating hyperoxia (50% oxygen)-induced enhancement of Ca(2+) responses to bronchoconstrictor agonists. Treatment with BAY 41-2272 (sGC stimulator) and BAY 60-2770 (sGC activator) increased cGMP levels during exposure to 50% O2. Although 50% O2 did not alter sGCα1 or sGCß1 expression, BAY 60-2770 did increase sGCß1 expression. BAY 41-2272 and BAY 60-2770 blunted Ca(2+) responses to histamine in cells exposed to 50% O2. The effects of BAY 41-2272 and BAY 60-2770 were reversed by protein kinase G inhibition. These novel data demonstrate that BAY 41-2272 and BAY 60-2770 stimulate production of cGMP and blunt hyperoxia-induced increases in Ca(2+) responses in developing ASM. Accordingly, sGC stimulators/activators may be a useful therapeutic strategy in improving bronchodilation in preterm infants.

Substance P protects against hyperoxic-induced lung injury in neonatal rats.

The aim of the study was to investigate the effects of substance P (SP) in hyperoxia-induced lung injury in newborn rats. Thirty-two rat pups were randomly divided into four groups: normoxia/saline, normoxia/SP, hyperoxia/saline and hyperoxia/SP. In a separate set of experiments, the neonatal rat pups were exposed to 21% or >95% O2 for 14 days with or without intraperitoneal administration of SP. On day 14, the animals were sacrificed and the lungs were processed for histology and biochemical analysis. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was used for the detection of apoptosis. Antioxidant capacity was assessed by glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), oxidative stress was assessed by determining the extent of formation of malondialdehyde (MDA), activities of NADPH oxidase activity, and formation of reactive oxygen species (ROS). The activity of phospho-p38 (p-p38) and -ERK1/2 (p-ERK1/2) proteins and expression of NF-E2-related factor 2 (NRF2) were detected by Western blot, and the expression of p-p38 was detected by immunofluorescence analysis. Compared with the hyperoxia treatment, the lung damage was significantly ameliorated following the SP treatment. Furthermore, the lungs from the pups exposed to hyperoxia TUNEL-positive nuclei increased markedly and decreased significantly after SP treatment. The levels of MDA decreased and that of GSH-Px and SOD increased following the SP treatment. The SP treatment significantly suppressed the activity of NADPH oxidase and reduced ROS production. SP stimulation may result in blocking p38 MAPK and ERK signaling pathways, and the activities of p-p38 and p-ERK, and expression of NRF2 decreased following the SP treatment. These findings indicate that SP can ameliorate hyperoxic lung injury through decreasing cell apoptosis, elevating antioxidant activities, and attenuating oxidative stress.

Targeting glycogen synthase kinase-3ß to prevent hyperoxia-induced lung injury in neonatal rats.

The pathological hallmarks of bronchopulmonary dysplasia (BPD), a chronic lung disease of premature infants, include inflammation, arrested alveolarization, and dysregulated angiogenesis. Severe BPD is often complicated by pulmonary hypertension (PH) that significantly increases morbidity and mortality. Glycogen synthase kinase (GSK)-3ß plays a pivotal role in embryonic development, cell proliferation and survival, and inflammation by modulating multiple signaling pathways, particularly the nuclear transcription factor, NF-κB, and Wnt/ß-catenin pathways. Aberrant GSK-3ß signaling is linked to BPD. We tested the hypothesis that inhibition of GSK-3ß is beneficial in preventing hyperoxia-induced neonatal lung injury, an experimental model of BPD. Newborn rats were exposed to normoxia or hyperoxia (90% oxygen), and received daily intraperitoneal injections of placebo (DMSO) or SB216763, a specific pharmacological inhibitor of GSK-3ß, for 14 days. Hyperoxia exposure in the presence of the placebo increased GSK-3ß phosphorylation, which was correlated with increased inflammation, decreased alveolarization and angiogenesis, and increased pulmonary vascular remodeling and PH. However, treatment with SB216763 decreased phosphorylation of NF-κB p65, expression of monocyte chemotactic protein-1, and lung inflammation during hyperoxia. Furthermore, treatment with the GSK-3ß inhibitor also improved alveolarization and angiogenesis, and decreased pulmonary vascular remodeling and PH. These data indicate that GSK-3ß signaling plays an important role in the pathogenesis of hyperoxia-induced neonatal lung injury, and that inhibition of GSK-3ß is beneficial in preventing inflammation and protecting alveolar and vascular structures during hyperoxia. Thus, targeting GSK-3ß signaling may offer a novel strategy to prevent and treat preterm infants with BPD.

Sex-dependent changes in the pulmonary vasoconstriction potential of newborn rats following short-term oxygen exposure.

BACKGROUND: Chronic exposure to supplemental oxygen (O(2)) induces lung damage and mortality in a sex-dependent manner. The effect of short-term hyperoxia on the newborn pulmonary vasculature is unknown but is, however, of clinical significance in the neonatal resuscitation context. We hypothesize that short-term hyperoxia has a sex-dependent effect on the pulmonary vasculature. METHODS: Following 1-h 100% O(2) exposure, the pulmonary arteries and lung tissues of newborn rats were evaluated. RESULTS: Superoxide dismutase 3 (SOD3) expression in female pups' lungs was increased as compared with that in the lungs of male pups. As compared with air-treated pups, the response of male pups to thromboxane was increased by O(2), whereas the opposite effect was documented in the vessels of female pups. The enhanced force of hyperoxia-exposed arteries of the male pups was suppressed with superoxide or peroxynitrite scavengers, and increased lung SOD activity and hydrogen peroxide content were seen in female, but not in male, rats. Hyperoxia induced an increase in lung tissue oxidative products and Rho-kinase (ROCK) activity in male, but not in female, pups. CONCLUSION: A lower lung SOD content and failure to upregulate SOD activity facilitates peroxynitrite generation and ROCK activation in hyperoxia-exposed males, predisposing them to pulmonary vasoconstriction. These observations, if relevant to humans, may explain the increased mortality and higher incidence of pulmonary hypertension in male neonates.

Superoxide dismutase responds to hyperoxia in rat hippocampus.

The brain's anti-oxidant response to highly elevated oxygen (O2) partial pressures is poorly understood. In this study we hypothesized that hyperbaric O2 (HBO2) would stimulate superoxide dismutase (SOD) transcription in the oxidative stress-sensitive rat hippocampus and measured the time course and extent of the changes in hippocampal mRNA for all three SOD isoforms and total SOD enzyme activity. Comparisons were made between exposures to 2 hours of 1 atmosphere pressure normobaric oxygen (NBO); 2 hours of 3 atmospheres HBO2; and room air. Hyperoxia (HBO2 > NBO) was associated with statistically significant increases in transcript levels of the antioxidant enzymes SOD2 (MnSOD) and SOD3 (EC-SOD) at 6 and 18 hours but not SOD1 (Cu, Zn SOD) respectively. Hyperoxia, however, did not affect total hippocampal SOD activity measured at 6 and 24 hours, indicating that the mRNA responses were necessary to maintain the anti-oxidant enzyme activity after oxidative stress.

Hyperoxia induces Egr-1 expression through activation of extracellular signal-regulated kinase 1/2 pathway.

Early growth response gene (Egr-1) is a stress response gene activated by various forms of stress and growth factor signaling. We report that supraphysiologic concentrations of O(2) (hyperoxia) induced Egr-1 mRNA and protein expression in cultured alveolar epithelial cells, as well as in mouse lung in vivo. The contribution of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK), p38 MAPK and PI3-kinase pathways to the activation of Egr-1 in response to hyperoxia was examined. Exposure to hyperoxia resulted in a rapid phosphorylation of ERK 1/2 kinases in mouse alveolar epithelial cells LA4. MEK inhibitor PD98059, but not inhibitors of p38 MAPK or PI3-kinase pathway, prevented Egr-1 induction by hyperoxia. The signaling cascade preceding Egr-1 activation was traced to epidermal growth factor receptor (EGFR) signaling. Hyperoxia is used as supplemental therapy in some diseases and typically results in elevated levels of reactive oxygen intermediates (ROI) in many lung cell types, the organ that receives highest O(2) exposure. Our results support a pathway for the hyperoxia response that involves EGF receptor, MEK/ERK pathway, and other unknown signaling components leading to Egr-1 induction. This forms a foundation for analysis of detailed mechanisms underlying Egr-1 activation during hyperoxia and understanding its consequences for regulating cell response to oxygen toxicity.

Influence of inhaled nitric oxide and hyperoxia on Na,K-ATPase expression and lung edema in newborn piglets.

This study was undertaken to examine the combined effect of nitric oxide (NO) and hyperoxia on lung edema and Na,K-ATPase expression. Newborn piglets were exposed to room air (FiO2 = 0.21), room air plus 50 ppm NO, hyperoxia (FiO2 >/= 0.96) or to hyperoxia plus 50 ppm NO for 4-5 days. Animals exposed to NO in room air experienced only a slight decrease in Na,K-ATPase alpha subunit protein level. Hyperoxia, in the absence of NO, induced both the mRNA and the protein level of Na,K-ATP-ase alpha subunit and significantly increased wet lung weight, extravascular lung water, and alveolar permeability. NO in hyperoxia decreased the hyperoxic-mediated induction of Na,K-ATPase alpha subunit mRNA and protein while wet lung weight, extravascular lung water, and alveolar permeability remained elevated. These results suggest that 50 ppm of inhaled NO may not improve hyperoxic-induced lung injury and may interfere with the expression of Na,K-ATPase which constitutes a part of the cellular defense mechanism against oxygen toxicity.