Augmented oxygen-mediated transcriptional activation of cytochrome P450 (CYP)1A expression and increased susceptibilities to hyperoxic lung injury in transgenic mice carrying the human CYP1A1 or mouse 1A2 promoter in vivo

Bioluminescence imaging of Cyp1a1-luciferase reporter mice demonstrates prolonged activation of the aryl hydrocarbon receptor in the lung

Aryl hydrocarbon receptor (AHR) signalling integrates biological processes that sense and respond to environmental, dietary, and metabolic challenges to ensure tissue homeostasis. AHR is a transcription factor that is inactive in the cytosol but upon encounter with ligand translocates to the nucleus and drives the expression of AHR targets, including genes of the cytochrome P4501 family of enzymes such as Cyp1a1. To dynamically visualise AHR activity in vivo, we generated reporter mice in which firefly luciferase (Fluc) was non-disruptively targeted into the endogenous Cyp1a1 locus. Exposure of these animals to FICZ, 3-MC or to dietary I3C induced strong bioluminescence signal and Cyp1a1 expression in many organs including liver, lung and intestine. Longitudinal studies revealed that AHR activity was surprisingly long-lived in the lung, with sustained Cyp1a1 expression evident in discrete populations of cells including columnar epithelia around bronchioles. Our data link diet to lung physiology and also reveal the power of bespoke Cyp1a1-Fluc reporters to longitudinally monitor AHR activity in vivo.

Hyperoxia-mediated transcriptional activation of cytochrome P4501A1 (CYP1A1) and decreased susceptibility to oxygen-mediated lung injury in newborn mice

Hyperoxia contributes to the development of bronchopulmonary dysplasia (BPD) in premature infants. In this study, we tested the hypothesis that newborn transgenic mice carrying the human CYP1A1-Luc promoter will display transcriptional activation of the human CYP1A1 promoter in vivo upon exposure to hyperoxia, and that these mice will be less susceptible to hyperoxic lung injury and alveolar simplification than similarly exposed wild type (WT) mice. Newborn WT (CD-1) or transgenic mice carrying a 13.2 kb human CYP1A1 promoter and the luciferase (Luc) reporter gene (CYP1A1-luc) were maintained in room air or exposed to hyperoxia (85% O2) for 7-14 days. Hyperoxia exposure of CYP1A1-Luc mice for 7 and 14 days resulted in 4- and 30-fold increases, respectively, in hepatic Luc (CYP1A1) expression, compared to room air controls. In lung, hyperoxia caused a 2-fold induction of reporter Luc at 7 days, but the induction declined after 14 days. The newborn CYP1A1-Luc mice were less susceptible to lung injury and alveolar simplification than similarly exposed wild type (WT) CD-1 mice. Also, the CYP1A1-Luc mice showed increased levels of hepatic and pulmonary CYP1A1 expression and hepatic CYP1A2 activity after hyperoxia exposure. Hyperoxia also increased NADP(H) quinone reductase (NQO1) pulmonary gene expression in both CD-1 and CYP1A1-Luc mice at both time points, but this was more pronounced in the latter at 14 days. Our results support the hypothesis that hyperoxia activates the human CYP1A1 promoter in newborn mice, and that increased endogenous expression of CYP1A1 and NADP(H) quinone reductase (NQO1) contributes to the decreased susceptibilities to hyperoxic lung injury in the transgenic animals. This is the first report providing evidence of hyperoxia-mediated transcriptional activation of the human CYP1A1 promoter in newborn mice, and this in conjunction with decreased lung injury, suggests that these phenomena have important implications for BPD.

Reactive Oxygen Species, Biomarkers of Microvascular Maturation and Alveolarization, and Antioxidants in Oxidative Lung Injury

The lungs of extremely low gestational age neonates (ELGANs) are deficient in pulmonary surfactant and are incapable of efficient gas exchange necessary for successful transition from a hypoxic intrauterine environment to ambient air. To improve gas exchange and survival, ELGANs often receive supplemental oxygen with mechanical ventilation which disrupts normal lung developmental processes, including microvascular maturation and alveolarization. Factors that regulate these developmental processes include vascular endothelial growth factor and matrix metalloproteinases, both of which are influenced by generation of oxygen byproducts, or reactive oxygen species (ROS). ELGANs are also deficient in antioxidants necessary to scavenge excessive ROS. Thus, the accumulation of ROS in the preterm lungs exposed to prolonged hyperoxia, results in inflammation and development of bronchopulmonary dysplasia (BPD), a form of chronic lung disease (CLD). Despite advances in neonatal care, BPD/CLD remains a major cause of neonatal morbidity and mortality. The underlying mechanisms are not completely understood, and the benefits of current therapeutic interventions are limited. The association between ROS and biomarkers of microvascular maturation and alveolarization, as well as antioxidant therapies in the setting of hyperoxia-induced neonatal lung injury are reviewed in this article.

ROS Signaling in the Pathogenesis of Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS)

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Mechanistic role of cytochrome P450 (CYP)1B1 in oxygen-mediated toxicity in pulmonary cells: A novel target for prevention of hyperoxic lung injury

Supplemental oxygen, which is routinely administered to preterm infants with pulmonary insufficiency, contributes to bronchopulmonary dysplasia (BPD) in these infants. Hyperoxia also contributes to the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in adults. The mechanisms of oxygen-mediated pulmonary toxicity are not completely understood. Recent studies have suggested an important role for cytochrome P450 (CYP)1A1/1A2 in the protection against hyperoxic lung injury. The role of CYP1B1 in oxygen-mediated pulmonary toxicity has not been studied. In this investigation, we tested the hypothesis that CYP1B1 plays a mechanistic role in oxygen toxicity in pulmonary cells in vitro. In human bronchial epithelial cell line BEAS-2B, hyperoxic treatment for 1-3 days led to decreased cell viability by about 50-80%. Hyperoxic cytotoxicity was accompanied by an increase in levels of reactive oxygen species (ROS) by up to 110%, and an increase of TUNEL-positive cells by up to 4.8-fold. Western blot analysis showed hyperoxia to significantly down-regulate CYP1B1 protein level. Also, there was a decrease of CYP1B1 mRNA by up to 38% and Cyp1b1 promoter activity by up to 65%. On the other hand, CYP1B1 siRNA appeared to rescue the cell viability under hyperoxia stress, and overexpression of CYP1B1 significantly attenuated hyperoxic cytotoxicity after 48 h of incubation. In immortalized lung endothelial cells derived from Cyp1b1-null and wild-type mice, hyperoxia increased caspase 3/7 activities in a time-dependent manner, but endothelial cells lacking the Cyp1b1 gene showed significantly decreased caspase 3/7 activities after 48 and 72 h of incubation, implying that CYP1B1 might promote apoptosis in wild type lung endothelial cells under hyperoxic stress. In conclusion, our results support the hypothesis that CYP1B1 plays a mechanistic role in pulmonary oxygen toxicity, and CYP1B1-mediated apoptosis could be one of the mechanisms of oxygen toxicity. Thus, CYP1B1 could be a novel target for preventative and/or therapeutic interventions against BPD in infants and ALI/ARDS in adults.

Genetic susceptibility to nosocomial pneumonia, acute respiratory distress syndrome and poor outcome in patients at risk of critical illness

Genetic susceptibility may partially explain the clinical variability observed during the course of similar infections. To establish the contribution of genetic host factors in the susceptibility to critical illness, we genotyped 750 subjects (419 at high risk of critical illness) for 14 single nucleotide polymorphisms (SNPs) in the xenobiotics detoxification/oxidative stress and vascular homeostasis metabolic pathways. In the group of nosocomial pneumonia (NP; 268 patients) the risk of acute respiratory distress syndrome (ARDS) is significantly higher for the carriers of CYP1A1 rs2606345 T/T genotypes and AhR rs2066853 G/A-A/A genotypes. AGTR1 rs5186 allele C is more common among NP non-survivors. The duration of stay in intensive care units (ICU) is higher for NP patients with ABCB1 rs1045642-T allele. The cumulative effect of the risk alleles in the genes comprising two sets of genes partners (xenobiotics detoxification: CYP1A1, AhR and RAS family: ACE, AGT, AGTR1) is associated with the development of both NP and ARDS.

Mice deficient in the gene for cytochrome P450 (CYP)1A1 are more susceptible than wild-type to hyperoxic lung injury: evidence for protective role of CYP1A1 against oxidative stress

Hyperoxia contributes to acute lung injury in diseases such as acute respiratory distress syndrome in adults and bronchopulmonary dysplasia in premature infants. Cytochrome P450 (CYP)1A1 has been shown to modulate hyperoxic lung injury. The mechanistic role(s) of CYP1A1 in hyperoxic lung injury in vivo is not known. In this investigation, we hypothesized that Cyp1a1(-/-) mice would be more susceptible to hyperoxic lung injury than wild-type (WT) mice, and that the protective role of CYP1A1 is in part due to CYP1A1-mediated decrease in the levels of reactive oxygen species-mediated lipid hydroperoxides, e.g., F2-isoprostanes/isofurans, leading to attenuation of oxidative damage. Eight- to ten-week-old male WT (C57BL/6J) or Cyp1a1(-/-) mice were exposed to hyperoxia (>95% O2) or room air for 24-72 h. The Cyp1a1(-/-) mice were more susceptible to oxygen-mediated lung damage and inflammation than WT mice, as evidenced by increased lung weight/body weight ratio, lung injury, neutrophil infiltration, and augmented expression of IL-6. Hyperoxia for 24-48 h induced CYP1A expression at the mRNA, protein, and enzyme levels in liver and lung of WT mice. Pulmonary F2-isoprostane and isofuran levels were elevated in WT mice after hyperoxia for 24 h. On the other hand, Cyp1a1(-/-) mice showed higher levels after 48-72 h of hyperoxia exposure compared to WT mice. Our results support the hypothesis that CYP1A1 protects against hyperoxic lung injury by decreasing oxidative stress. Future research could lead to the development of novel strategies for prevention and/or treatment of acute lung injury.

Oxidative Stress and Therapeutic Development in Lung Diseases

Oxidative stress has many implications in the pathogenesis of lung diseases. In this review, we provide an overview of Reactive Oxygen Species (ROS) and nitrogen (RNS) species and antioxidants, how they relate to normal physiological function and the pathophysiology of different lung diseases, and therapeutic strategies. The production of ROS/RNS from endogenous and exogenous sources is first discussed, followed by antioxidant systems that restore oxidative balance and cellular homeostasis. The contribution of oxidant/antioxidant imbalance in lung disease pathogenesis is also discussed. An overview of therapeutic strategies is provided, such as augmenting NO bioactivity, blocking the production of ROS/RNS and replacement of deficient antioxidants. The limitations of current strategies and failures of clinical trials are then addressed, followed by discussion of novel experimental approaches for the development of improved antioxidant therapies.

Bone marrow injury induced via oxidative stress in mice by inhalation exposure to formaldehyde

OBJECTIVE

Formaldehyde, a ubiquitous environmental pollutant has been classified as a human leukemogen. However, toxicity of formaldehyde in bone marrow, the target site of leukemia induction, is still poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate bone marrow toxicity (bone marrow pathology, hematotoxicity) and underlying mechanisms (oxidative stress, inflammation, apoptosis) in formaldehyde-exposed mice. Male Balb/c mice were exposed to formaldehyde (0, 0.5, and 3.0 mg/m(3)) by nose-only inhalation for 8 hours/day, over a two week period designed to simulate a factory work schedule, with an exposure-free "weekend" on days 6 and 7, and were sacrificed on the morning of day 13. Counts of white blood cells, red blood cells and lymphocytes were significantly (p<0.05) decreased at 0.5 mg/m(3) (43%, 7%, and 39%, respectively) and 3.0 mg/m(3) (52%, 27%, and 43%, respectively) formaldehyde exposure, while platelet counts were significantly increased by 109% (0.5 mg/m(3)) and 67% (3.0 mg/m(3)). Biomarkers of oxidative stress (reactive oxygen species, glutathione depletion, cytochrome P450 1A1 and glutathione s-transferase theta 1 expression), inflammation (nuclear factor kappa-B, tomour necrosis factor alpha, interleukin-1 beta), and apoptosis (activity of cysteine-aspartic acid protease 3) in bone marrow tissues were induced at one or both formaldehyde doses mentioned above.

CONCLUSIONS/SIGNIFICANCE

Exposure of mice to formaldehyde by inhalation induced bone marrow toxicity, and that oxidative stress, inflammation and the consequential apoptosis jointly constitute potential mechanisms of such induced toxicity.

Coenzyme Q(1) as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type and Nqo1-null mouse lung

Previous studies showed that coenzyme Q(1) (CoQ(1)) reduction on passage through the rat pulmonary circulation was catalyzed by NAD(P)H:quinone oxidoreductase 1 (NQO1) and mitochondrial complex I, but that NQO1 genotype was not a factor in CoQ(1) reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ(1) reduction in the isolated perfused wild-type (NQO1(+/+)) and Nqo1-null (NQO1(-)/(-)) mouse lung. CoQ(1) reduction was measured as the steady-state pulmonary venous CoQ(1) hydroquinone (CoQ(1)H(2)) efflux rate during infusion of CoQ(1) into the pulmonary arterial inflow. CoQ(1)H(2) efflux rates during infusion of 50 μM CoQ(1) were not significantly different for NQO1(+/+) and NQO1(-/-) lungs (0.80 ± 0.03 and 0.68 ± 0.07 μmol·min(-1)·g lung dry wt(-1), respectively, P > 0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ(1)H(2) efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min(-1)·g lung dry wt(-1) for NQO1(+/+) and NQO1(-/-), respectively, P < 0.05). Exposure of mice to 100% O(2) for 48 h also depressed CoQ(1)H(2) efflux rates in NQO1(+/+) and NQO1(-/-) lungs (0.43 ± 0.03 and 0.11 ± 0.04 μmol·min(-1)·g lung dry wt(-1), respectively, P < 0.05 by ANOVA). The impact of rotenone or hyperoxia on CoQ(1) redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ(1) recoveries, the latter measured by spectrophotometry or mass spectrometry. Complex I activity in mitochondria-enriched lung fractions was depressed in hyperoxia-exposed lungs for both genotypes. This study provides new evidence for the potential utility of CoQ(1) as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.