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.

Antagonistic Effects of N-acetylcysteine on Mitogen-activated Protein Kinase Pathway Activation, Oxidative Stress and Inflammatory Responses in Rats with PM2.5 Induced Lung Injuries.

Objective To evaluate the antagonistic effects of N-acetylcysteine (NAC) on mitogen-activated protein kinases (MAPK) pathway activation, oxidative stress and inflammatory responses in rats with lung injury induced by fine particulate matter (PM2.5).Methods Forty eight male Wistar rats were randomly divided into six groups: blank control group (C1), water drip control group (C2), PM2.5 exposed group (P), low-dose NAC treated and PM2.5 exposed group (L), middle-dose NAC treated and PM2.5 exposed group (M), and high-dose NAC treated and PM2.5 exposed group (H). PM2.5 suspension (7.5 mg/kg) was administered tracheally once a week for four times. NAC of 125 mg/kg, 250 mg/kg and 500 mg/kg was delivered intragastrically to L, M and H group respectively by gavage (10 ml/kg) for six days before PM2.5 exposure. The histopathological changes and human mucin 5 subtype AC (MUC5AC) content in lung tissue of rats were evaluated. We investigated IL-6 in serum and bronchoalveolar lavage fluid (BALF) by Enzyme-linked immunosorbent assay (ELISA), MUC5AC in lung tissue homogenate by ELISA, glutathione peroxidase (GSH-PX) in serum and BALF by spectrophotometry, and the expression of p-ERK1/2, p-JNK1/2 and p-p38 proteins by Western blot. All the measurements were analyzed and compared statistically.Results Lung tissue of rats exposed to PM2.5 showed histological destruction and increased mucus secretion of bronchial epithelial cells. Rats receiving NAC treatment showed less histological destruction and mucus secretion. Of P, L, M and H group, MUC5AC in lung tissue, IL-6 in serum and BALF were higher than controls (C1 and C2) (all P<0.05), with the highest levels found in the P group and a decreasing trend with increase of NAC dose. The activity of GSH-PX in serum and BALF of PM2.5 exposed rats (P, L, M and H) was lower than that of controls (all P<0.05), with higher activities found in NAC treated rats (L, M, and H), and an increasing trend with increase of NAC dose. The expressions of p-ERK1/2, p-JNK1/2 and p-p38 proteins in PM2.5 exposed lung tissue (P, L, M and H) was higher than controls (all P<0.05), with decreased levels and dose dependent downregulation found in NAC treated rats.Conclusion NAC can antagonize major MAPK pathway activation, lung oxidative stress and inflammatory injury induced by PM2.5 in rats.

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.

Dexpanthenol therapy reduces lung damage in a hyperoxic lung injury in neonatal rats.

OBJECTIVE: Dexpanthenol (Dxp) plays a major role in cellular defense and in repair systems against oxidative stress and inflammatory response and it has not yet been evaluated in treatment of bronchopulmonary dysplasia (BPD). We tested the hypothesis that proposes whether Dxp decreases the severity of lung injury in an animal model of BPD. METHODS: Forty rat pups were divided into four groups: control, control + Dxp, hyperoxia and hyperoxia + Dxp. All animals were processed for lung histology and tissue analysis. The degree of lung inflammation, oxidative and antioxidant capacity was assessed from lung homogenates. RESULTS: Lung injury score and alveol diameter increased in the hyperoxia group (p < 0.001). Median level of malondialdehyde, total oxidant status and oxidative stress indexes was significantly higher in the hyperoxia group compared to the other groups. The median superoxide dismutase activity in the hyperoxia group was notably less than those of control + Dxp and hyperoxia + Dxp groups (p < 0.01). Similarly, lung catalase, glutathione (GSH) peroxidase and reduced GSH activities in the hyperoxia group were significantly lower than other groups. Furthermore, the hyperoxia + Dxp group had lower tumor necrosis factor-α and interleukin-1ß median levels compared to the hyperoxia group (p = 0.007). CONCLUSION: Dxp treatment results in less emphysematous change as well as decrease in inflammation and oxidative stress markers in an animal model of BPD.

Guanylyl cyclase activation reverses resistive breathing-induced lung injury and inflammation.

Inspiratory resistive breathing (RB), encountered in obstructive lung diseases, induces lung injury. The soluble guanylyl cyclase (sGC)/cyclic guanosine monophosphate (cGMP) pathway is down-regulated in chronic and acute animal models of RB, such as asthma, chronic obstructive pulmonary disease, and in endotoxin-induced acute lung injury. Our objectives were to: (1) characterize the effects of increased concurrent inspiratory and expiratory resistance in mice via tracheal banding; and (2) investigate the contribution of the sGC/cGMP pathway in RB-induced lung injury. Anesthetized C57BL/6 mice underwent RB achieved by restricting tracheal surface area to 50% (tracheal banding). RB for 24 hours resulted in increased bronchoalveolar lavage fluid cellularity and protein content, marked leukocyte infiltration in the lungs, and perturbed respiratory mechanics (increased tissue resistance and elasticity, shifted static pressure-volume curve right and downwards, decreased static compliance), consistent with the presence of acute lung injury. RB down-regulated sGC expression in the lung. All manifestations of lung injury caused by RB were exacerbated by the administration of the sGC inhibitor, 1H-[1,2,4]oxodiazolo[4,3-]quinoxalin-l-one, or when RB was performed using sGCα1 knockout mice. Conversely, restoration of sGC signaling by prior administration of the sGC activator BAY 58-2667 (Bayer, Leverkusen, Germany) prevented RB-induced lung injury. Strikingly, direct pharmacological activation of sGC with BAY 58-2667 24 hours after RB reversed, within 6 hours, the established lung injury. These findings raise the possibility that pharmacological targeting of the sGC-cGMP axis could be used to ameliorate lung dysfunction in obstructive lung diseases.

P38 activation is more important than ERK activation in lung injury induced by prolonged hyperbaric oxygen.

Prolonged exposure to hyperbaric oxygen can cause pulmonary and nerve system toxicity. Although hyperbaric oxygen treatment has been used for a broad spectrum of ailments, the mechanisms of prolonged hyperbaric oxygen-induced lung injury are not fully understood. The purpose of the present work was to investigate the roles of ERK, p38, and caspase-3 in rat lung tissue exposed to hyperbaric oxygen at 2.3 atmospheres absolute (atm abs) for two, six and 10 hours. The results showed that the ERK and p38 were phosphorylated at two hours and reached a peak at six hours into exposure to hyperbaric oxygen. While the phosphorylation level of ERK decreased, p38 remained at a high level of activation at 10 hours. The activation of ERK and p38 was down-regulated when rats were exposed to normoxic hyperbaric nitrogen for 10 hours. However, caspase-3 was activated at six hours and 10 hours into exposure to hyperbaric oxygen. These results demonstrated different changes of activation of ERK and p38 during lung injury induced by prolonged exposure to hyperbaric oxygen. The time course changes of activated caspase-3 were similar to the process of p38 activation upon exposure to hyperbaric oxygen. In this way, activation of p38, not ERK, seems to be a mechanism associated with prolonged hyperbaric oxygen-induced lung injury.

Protective effects of asiaticoside on septic lung injury in mice.

Asiaticoside (AS), a major triterpenoid saponin component isolated from Centella asiatica, has been described to exhibit antioxidant and anti-inflammatory activities. The present study aimed to determine the protective effects and the underlying mechanisms of AS on septic lung injury induced by cecal ligation and puncture (CLP). Mice were pretreated with the AS (45 mg/kg) or AS as well as GW9662 at 1h before CLP, the survival, lung injury, inflammatory mediators and signaling molecules, and Peroxisome proliferator-activated receptor-γ (PPAR-γ) were determined 24 h after CLP. The results showed that AS significantly decreased CLP-induced the mortality, lung pathological damage, the infiltration of mononuclear, polymorphonuclear (PMN) leucocytes and total proteins. Moreover, AS inhibited CLP-induced the activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB), the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) protein in lung tissues, and the production of serum tumor necrosis factor (TNF-α) and interleukin-6 (IL-6). Interestingly, the expression of PPAR-γ protein in lung tissue was up-regulated by AS. Furthermore, GW9662 (the inhibitor of PPAR-γ) significantly reversed these beneficial effects of AS in septic mice. These findings suggest that AS could effectively protect from septic lung injury induced by CLP and the underlying mechanisms might be related to up-regulation of PPAR-γ expression to some extent, which inhibits MAPKs and NF-κB pathway.