Lipid ozonation products activate phospholipases A2, C, and D

The Chemical Reactivity of Membrane Lipids

It is well-known that aqueous dispersions of phospholipids spontaneously assemble into bilayer structures. These structures have numerous applications across chemistry and materials science and form the fundamental structural unit of the biological membrane. The particular environment of the lipid bilayer, with a water-poor low dielectric core surrounded by a more polar and better hydrated interfacial region, gives the membrane particular biophysical and physicochemical properties and presents a unique environment for chemical reactions to occur. Many different types of molecule spanning a range of sizes, from dissolved gases through small organics to proteins, are able to interact with membranes and promote chemical changes to lipids that subsequently affect the physicochemical properties of the bilayer. This Review describes the chemical reactivity exhibited by lipids in their membrane form, with an emphasis on conditions where the lipids are well hydrated in the form of bilayers. Key topics include the following: lytic reactions of glyceryl esters, including hydrolysis, aminolysis, and transesterification; oxidation reactions of alkenes in unsaturated fatty acids and sterols, including autoxidation and oxidation by singlet oxygen; reactivity of headgroups, particularly with reactive carbonyl species; and E/Z isomerization of alkenes. The consequences of reactivity for biological activity and biophysical properties are also discussed.

Cutaneous Redox Senescence

Our current understanding of skin cell senescence involves the role of environmental stressors (UV, O3, cigarette smoke, particulate matter, etc.), lifestyle (diet, exercise, etc.) as well as genetic factors (metabolic changes, hormonal, etc.). The common mechanism of action of these stressors is the disturbance of cellular redox balance characterized by increased free radicals and reactive oxygen species (ROS), and when these overload the intrinsic antioxidant defense system, it can lead to an oxidative stress cellular condition. The main redox mechanisms that activate cellular senescence in the skin involve (1) the oxidative damage of telomeres causing their shortening; (2) the oxidation of proteomes and DNA damage; (3) an a in lysosomal mass through the increased activity of resident enzymes such as senescence-associated β-galactosidase (SA-β-gal) as well as other proteins that are products of lysosomal activity; (4) and the increased expression of SASP, in particular pro-inflammatory cytokines transcriptionally regulated by NF-κB. However, the main targets of ROS on the skin are the proteome (oxi-proteome), followed by telomeres, nucleic acids (DNAs), lipids, proteins, and cytoplasmic organelles. As a result, cell cycle arrest pathways, lipid peroxidation, increased lysosomal content and dysfunctional mitochondria, and SASP synthesis occur. Furthermore, oxidative stress in skin cells increases the activity of p16INK4A and p53 as inhibitors of Rb and CDks, which are important for maintaining the cell cycle. p53 also promotes the inactivation of mTOR-mediated autophagic and apoptotic pathways, leading to senescence. However, these markers alone cannot establish the state of cellular senescence, and multiple analyses are encouraged for confirmation. An updated and more comprehensive approach to investigating skin senescence should include further assays of ox-inflammatory molecular pathways that can consolidate the understanding of cutaneous redox senescence.

Inhaled toxicants and pulmonary lipid metabolism: biological consequences and therapeutic interventions

Inhaled toxicants drive the onset of and exacerbate preexisting chronic pulmonary diseases, however, the biological mechanisms by which this occurs are largely unknown. Exposure to inhaled toxicants, both environmental and occupational, drives pulmonary inflammation and injury. Upon activation of the inflammatory response, polyunsaturated fatty acids (PUFAs) are metabolized into predominately proinflammatory lipid mediators termed eicosanoids which recruit immune cells to the site of injury, perpetuating inflammation to clear the exposed toxicants. Following inflammation, lipid mediator class-switching occurs, a process that leads to increased metabolism of hydroxylated derivates of PUFAs. These mediators, which include mono-hydroxylated PUFA derivatives and specialized proresolving lipid mediators, initiate an active process of inflammation resolution by inhibiting the inflammatory response and activating resolution pathways to return the tissue to homeostasis. Exposure to inhaled toxicants leads to alterations in the synthesis of these proinflammatory and proresolving lipid mediator pathways, resulting in greater pulmonary inflammation and injury, and increasing the risk for the onset of chronic lung diseases. Recent studies have begun utilizing supplementation of PUFAs and their metabolites as potential therapeutics for toxicant-induced pulmonary inflammation and injury. Here we will review the current understanding of the lipid mediators in pulmonary inflammation and resolution as well as the impact of dietary fatty acid supplementation on lipid mediator-driven inflammation following air pollution exposure.

Biological effects of air pollution on the function of human skin equivalents

The World Health Organization reports that 99% of the global population are exposed to pollution levels higher than the recommended air quality guidelines. Pollution-induced changes in the skin have begun to surface; however, the effects require further investigation so that effective protective strategies can be developed. This study aimed to investigate some of the aging-associated effects caused by ozone and particulate matter (PM) on human skin equivalents. Full-thickness skin equivalents were exposed to 0.01 μg/μL PM, 0.05 μg/μL PM, 0.3 ppm ozone, or a combination of 0.01 μg/μL PM and 0.3 ppm ozone, before skin equivalents and culture medium were harvested for histological/immunohistochemical staining, gene and protein expression analysis using qPCR, Western blotting, and ELISA. Markers include MMP-1, MMP-3, COL1A1, collagen-I, 4-HNE, HMGCR, and PGE2. PM was observed to induce a decrease in epidermal thickness and an enhanced matrix building phenotype, with increases in COL1A1 and an increase in collagen-I protein expression. By contrast, ozone induced an increase in epidermal thickness and was found to induce a matrix-degrading phenotype, with decreases in collagen-I gene/protein expression and increases in MMP-1 and MMP-3 gene/protein expression. Ozone was also found to induce changes in lipid homeostasis and inflammation induction. Some synergistic damage was also observed when combining ozone and 0.01 μg/μL PM. The results presented in this study identify distinct pollutant-induced effects and show how pollutants may act synergistically to augment damage; given individuals are rarely only exposed to one pollutant type, exposure to multiple pollutant types should be considered to develop effective protective interventions.

The role of potassium current in the pulmonary response to environmental oxidative stress

Exposure of human lung epithelial cells (A549 cell line) to the oxidant pollutant ozone (O₃) alters cell membrane currents inducing its decrease, when the cell undergoes to a voltage-clamp protocol ranging from -90 to +70mV. The membrane potential of these cells is mainly maintained by the interplay of potassium and chloride currents. Our previous studies indicated the ability of O₃ to activate ORCC (Outward Rectifier Chloride Channel) and consequently increases the chloride current. In this paper our aim was to understand the response of potassium current to oxidative stress challenge and to identify the kind potassium channel involved in O₃ induced current changes. After measuring the total membrane current using an intracellular solution with or without potassium ions, we obtained the contribution of potassium to the overall membrane current in control condition by a mathematical approach. Repeating these experiments after O₃ treatment we observed a significant decrease of I_potassium. Treatment of the cells with Iberiotoxin (IbTx), a specific inhibitor of BK channel, we were able to verify the presence and the functionality of BK channels. In addition, the administration of 4-Aminopyridine (an inhibitor of voltage dependent K channels but not BK channels) and Tetraethylammonium (TEA) before and after O₃ treatment we observed the formation of BK oxidative post-translation modifications. Our data suggest that O₃ is able to inhibit potassium current by targeting BK channel. Further studies are needed to better clarify the role of this BK channel and its interplay with the other membrane channels under oxidative stress conditions. These findings can contribute to identify the biomolecular pathway induced by O₃ allowing a possible pharmacological intervention against oxidative stress damage in lung tissue.

Local and systemic influence of toxic levels of airborne ozone on the inflammatory response in rats

Introduction

Ozone is not harmful itself; however, it directly oxidises biomolecules and produces radical-dependent cytotoxicity. Exposure to ozone is by inhalation and therefore the lungs develop the main anti-inflammatory response, while ozone has an indirect impact on the other organs. This study investigated the local and systemic effects of the ozone-associated inflammatory response.

Material and Methods

Three groups each of 5 Wistar Han rats aged 6 months were exposed for 2h to airborne ozone at 0.5 ppm and a fourth identical group were unexposed controls. Sacrifice was at 3h after exposure for control rats and one experimental group and at 24 h and 48 h for the others. Lung and liver samples were evaluated for changes in expression of transforming growth factor beta 1, anti-inflammatory interleukin 10, pro-inflammatory tumour necrosis factor alpha and interleukin 1 beta and two nuclear factor kappa-light-chain-enhancer of B cells subunit genes. Total RNA was isolated from the samples in spin columns and cDNA was synthesised in an RT-PCR. Expression levels were compared to those of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and analysed statistically.

Results

All variables changed non-linearly over time comparing experimental groups to the control. Conspicuous expression changes in the subunit genes and cytokines were observed in both evaluated organs.

Conclusion

Locally and systemically, inflammation responses to ozone inhalation include regulation of certain genes’ expression. The mechanisms are unalike in lungs and liver but ozone exerts a similar effect in both organs. A broader range of variables influential on ozone response should be studied in the future.

Oxysterols Modify NLRP2 in Epithelial Cells, Identifying a Mediator of Ozone-induced Inflammation

Ozone (O₃) is a prevalent air pollutant causing lung inflammation. Previous studies demonstrate that O₃ oxidizes lipids, such as cholesterol, in the airway to produce oxysterols, such as secosterol-A (SecoA), which are electrophiles capable of forming covalent linkages preferentially with lysine residues and consequently modify protein function. The breadth of proteins modified by this oxysterol as well as the biological consequences in the lung are unknown. Using an alkynyl-tagged form of SecoA and shotgun proteomics, we identified 135 proteins to be modified bronchial epithelial cells. Among them was NLR Family Pyrin Domain Containing 2 (NLRP2) forming a SecoA-protein adduct at lysine (K1019) in the terminal leucine-rich-repeat, a known regulatory region for NLR proteins. NLRP2 expression in airway epithelial cells was characterized and CRISPR-Cas9 knockout and shRNA knockdown of NLRP2 was used to determine its function in O₃-induced inflammation. No evidence for NLPR2 inflammasome formation or NLRP2-dependent increase in caspase-1 activity in response to O₃ was observed. O₃-induced pro-inflammatory gene expression for CXCL2 and CXCL8/IL8 was further enhanced in NLRP2 knockout cells, suggesting a negative regulatory role. Reconstitution of NLRP2 KO cells with K1019R mutant NLRP2 partially blocked SecoA adduction and enhanced O₃-induced IL-8 release as compared to wild type NLRP2. Together, our findings uncover NLRP2 as a highly abundant, key component of pro-inflammatory signaling pathways in airway epithelial cells and as a novel mediator of O₃-induced inflammation.

Pulmonary surfactant phosphatidylcholines induce immunological adaptation of alveolar macrophages

Pulmonary surfactant plays an important role in lung surface tension, defense against invading pathogens, and immune response. Furthermore, alveolar macrophages (AM) that comprise the front line of immune defense against inhaled microorganisms are covered by a layer of pulmonary fluid. Phosphatidylcholines (PCs), including unsaturated lipids such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), are the most prevalent phospholipids in pulmonary surfactant. POPC reacts with ozone to produce 1-palmitoyl-2-(9-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PONPC), a soluble mediator that initiates an inflammatory reaction in the lungs. However, the modulatory effects of POPC and PONPC on biology and activity of AM remain inconclusive. The exposure of AM (cell line AMJ2-C11) to POPC and PONPC was not directly related to the production of inflammatory mediators. However, AM, pre-incubated with POPC or PONPC, showed enhanced response after lipopolysaccharide (LPS) stimulation, and increased the production of nitric oxide and cytokines. This phenomenon was also observed for classical-polarized macrophages (M1). This increment on the production of inflammatory mediators was not associated with macrophage polarization, but with up-regulation of Tlr4 and Myd88 gene expression, which was in accordance with the adaptation of immune cells. This observation was confirmed by the histone acetylation epigenetic pathway. In contrast to the priming effect of POPC on AM activity, a harmful immune response, induced on incubation with PONPC, improved prostaglandin E2 (PGE2) formation, resulting in diminished bacterial phagocytosis. Additionally, PONPC induced production of CXCL1/KC, which potentially mediates neutrophil recruitment and enhances tissue inflammation. These results disclosed another dynamic mechanism by which pulmonary surfactant lipids (natural or oxidized) primed macrophage activity, thus affecting lung host defense.

Ozone augments interleukin-8 production induced by ambient particulate matter

Background

Experimental and controlled human exposure studies have demonstrated additive effects of ambient particulate matter and ozone on health. A few epidemiological studies have suggested that ambient particulate matter components are important for the combined effects of ambient particulate matter and ozone on health. However, few studies have examined whether ozone changes the effects of ambient particulate matter on pro-inflammatory cytokine production. In this study, the influence of ozone on pro-inflammatory cytokine production in response to ambient particulate matter was evaluated.

Results

Ambient particulate matter smaller than 1 μm was collected and the suspension of this particulate matter was bubbled through 0.12 ppm and 0.24 ppm ozone. THP1 cells were stimulated by the solution containing the particulate matter with and without bubbling through ozone at 1 μg/mL. The interleukin-8 concentrations in the supernatants of THP1 cells stimulated by collected particulate matter dissolved in solution were 108.3 ± 24.7 pg/mL without ozone exposure, 165.0 ± 26.1 pg/mL for 0.12 ppm ozone bubbling for 1 min, 175.1 ± 33.1 pg/mL for 0.12 ppm for 5 min, 183.3 ± 17.8 pg/mL for 0.12 ppm for 15 min, 167.8 ± 35.9 pg/mL for 0.24 ppm for 1 min, 209.2 ± 8.4 pg/mL for 0.24 ppm for 5 min, and 209.3 ± 14.3 pg/mL for 0.24 ppm for 15 min. Ozone significantly increased interleukin-8 concentrations compared to those for particulate matter dissolved in solution without ozone exposure and the solvent only (8.2 ± 0.9 pg/mL) in an ozone concentration-dependent manner. Collected particulate matter in solutions with or without bubbling through ozone had no effect on interleukin-6 production. The antioxidant N-acetyl-_L-cysteine significantly inhibited the increases in interleukin-8 induced by solutions with particulate matter, regardless of ozone exposure. The reactive oxygen species concentration in solutions with collected particulate matter was not associated with ozone bubbling.

Conclusion

Ozone may augment the production of interleukin-8 in response to ambient particulate matter by a mechanism unrelated to reactive oxygen species. These results support the epidemiological evidence for combined effects of ambient particulate matter and ozone on human health.

Ozone Exposure Increases Circulating Stress Hormones and Lipid Metabolites in Humans

RATIONALE

Air pollution has been associated with increased prevalence of type 2 diabetes; however, the mechanisms remain unknown. We have shown that acute ozone exposure in rats induces release of stress hormones, hyperglycemia, leptinemia, and glucose intolerance that are associated with global changes in peripheral glucose, lipid, and amino acid metabolism.

OBJECTIVES

To examine ozone-induced metabolic derangement in humans using serum metabolomic assessment, establish human-to-rodent coherence, and identify novel nonprotein biomarkers.

METHODS

Serum samples were obtained from a crossover clinical study that included two clinic visits (n = 24 each) where each subject was blindly exposed in the morning to either filtered air or 0.3 parts per million ozone for 2 hours during 15-minute on-off exercise. Serum samples collected within 1 hour after exposure were assessed for changes in metabolites using a metabolomic approach.

MEASUREMENTS AND MAIN RESULTS

Metabolomic analysis revealed that ozone exposure markedly increased serum cortisol and corticosterone together with increases in monoacylglycerol, glycerol, and medium- and long-chain free fatty acids, reflective of lipid mobilization and catabolism. Additionally, ozone exposure increased serum lysolipids, potentially originating from membrane lipid breakdown. Ozone exposure also increased circulating mitochondrial β-oxidation-derived metabolites, such as acylcarnitines, together with increases in the ketone body 3-hydroxybutyrate. These changes suggested saturation of β-oxidation by ozone in exercising humans.

CONCLUSIONS

As in rodents, acute ozone exposure increased stress hormones and globally altered peripheral lipid metabolism in humans, likely through activation of a neurohormonally mediated stress response pathway. The metabolomic assessment revealed new biomarkers and allowed for establishment of rodent-to-human coherence. Clinical trial registered with www.clinicaltrials.gov (NCT 01492517).

Ozone-derived Oxysterols Affect Liver X Receptor (LXR) Signaling: A POTENTIAL ROLE FOR LIPID-PROTEIN ADDUCTS

When inhaled, ozone (O₃) interacts with cholesterols of airway epithelial cell membranes or the lung-lining fluid, generating chemically reactive oxysterols. The mechanism by which O₃-derived oxysterols affect molecular function is unknown. Our data show that in vitro exposure of human bronchial epithelial cells to O₃ results in the formation of oxysterols, epoxycholesterol-α and -β and secosterol A and B (Seco A and Seco B), in cell lysates and apical washes. Similarly, bronchoalveolar lavage fluid obtained from human volunteers exposed to O₃ contained elevated levels of these oxysterol species. As expected, O₃-derived oxysterols have a pro-inflammatory effect and increase NF-κB activity. Interestingly, expression of the cholesterol efflux pump ATP-binding cassette transporter 1 (ABCA1), which is regulated by activation of the liver X receptor (LXR), was suppressed in epithelial cells exposed to O₃ Additionally, exposure of LXR knock-out mice to O₃ enhanced pro-inflammatory cytokine production in the lung, suggesting LXR inhibits O₃-induced inflammation. Using alkynyl surrogates of O₃-derived oxysterols, our data demonstrate adduction of LXR with Seco A. Similarly, supplementation of epithelial cells with alkynyl-tagged cholesterol followed by O₃ exposure causes observable lipid-LXR adduct formation. Experiments using Seco A and the LXR agonist T0901317 (T09) showed reduced expression of ABCA1 as compared with stimulation with T0901317 alone, indicating that Seco A-LXR protein adduct formation inhibits LXR activation by traditional agonists. Overall, these data demonstrate that O₃-derived oxysterols have pro-inflammatory functions and form lipid-protein adducts with LXR, thus leading to suppressed cholesterol regulatory gene expression and providing a biochemical mechanism mediating O₃-derived formation of oxidized lipids in the airways and subsequent adverse health effects.

Lung transcriptional profiling: insights into the mechanisms of ozone-induced pulmonary injury in Wistar Kyoto rats

Acute ozone-induced pulmonary injury and inflammation are well characterized in rats; however, mechanistic understanding of the pathways involved is limited. We hypothesized that acute exposure of healthy rats to ozone will cause transcriptional alterations, and comprehensive analysis of these changes will allow us to better understand the mechanism of pulmonary injury and inflammation. Male Wistar Kyoto rats (10-12 week) were exposed to air, or ozone (0.25, 0.5 or 1.0 ppm) for 4 h and pulmonary injury and inflammation were assessed at 0-h or 20-h (n = 8/group). Lung gene expression profiling was assessed at 0-h (air and 1.0 ppm ozone, n = 3-4/group). At 20-h bronchoalveolar lavage, fluid protein and neutrophils increased at 1 ppm ozone. Numerous genes involved in acute inflammatory response were up-regulated along with changes in genes involved in cell adhesion and migration, steroid metabolism, apoptosis, cell cycle control and cell growth. A number of NRF2 target genes were also induced after ozone exposure. Based on expression changes, Rela, SP1 and TP3-mediated signaling were identified to be mediating downstream changes. Remarkable changes in the processes of endocytosis provide the insight that ozone-induced lung injury and inflammation are likely initiated by changes in cell membrane components and receptors likely from oxidatively modified lung lining lipids and proteins. In conclusion, ozone-induced injury and inflammation are preceded by changes in gene targets for cell adhesion/migration, apoptosis, cell cycle control and growth regulated by Rela, SP1 and TP53, likely mediated by the process of endocytosis and altered steroid receptor signaling.

Phospholipid Ozonation Products Activate the 5-Lipoxygenase Pathway in Macrophages

Ozone is a highly reactive environmental toxicant that can react with the double bonds of lipids in pulmonary surfactant. This study was undertaken to investigate the proinflammatory properties of the major lipid-ozone product in pulmonary surfactant, 1-palmitoyl-2-(9'-oxo-nonanoyl)-glycerophosphocholine (16:0/9al-PC), with respect to eicosanoid production. A dose-dependent increase in the formation of 5-lipoxygenase (5-LO) products was observed in murine resident peritoneal macrophages (RPM) and alveolar macrophages (AM) upon treatment with 16:0/9al-PC. In contrast, the production of cyclooxygenase (COX) derived eicosanoids did not change from basal levels in the presence of 16:0/9al-PC. When 16:0/9al-PC and the TLR2 ligand, zymosan, were added to RPM or AM, an enhancement of 5-LO product formation along with a concomitant decrease in COX product formation was observed. Neither intracellular calcium levels nor arachidonic acid release was influenced by the addition of 16:0/9al-PC to RPM. Results from mitogen-activated protein kinase (MAPK) inhibitor studies and direct measurement of phosphorylation of MAPKs revealed that 16:0/9al-PC activates the p38 MAPK pathway in RPM, which results in the activation of 5-LO. Our results indicate that 16:0/9al-PC has a profound effect on the eicosanoid pathway, which may have implications in inflammatory pulmonary disease states where eicosanoids have been shown to play a role.

Mechanisms of the acute effects of inhaled ozone in humans

Ambient air ozone (O3) is generated photochemically from oxides of nitrogen and volatile hydrocarbons. Inhaled O3 causes remarkably reversible acute lung function changes and inflammation. Approximately 80% of inhaled O3 is deposited on the airways. O3 reacts rapidly with CC double bonds in hydrophobic airway and alveolar surfactant-associated phospholipids and cholesterol. Resultant primary ozonides further react to generate bioactive hydrophilic products that also initiate lipid peroxidation leading to eicosanoids and isoprostanes of varying electrophilicity. Airway surface liquid ascorbate and urate also scavenge O3. Thus, inhaled O3 may not interact directly with epithelial cells. Acute O3-induced lung function changes are dominated by involuntary inhibition of inspiration (rather than bronchoconstriction), mediated by stimulation of intraepithelial nociceptive vagal C-fibers via activation of transient receptor potential (TRP) A1 cation channels by electrophile (e.g., 4-oxo-nonenal) adduction of TRPA1 thiolates enhanced by PGE2-stimulated sensitization. Acute O3-induced neutrophilic airways inflammation develops more slowly than the lung function changes. Surface macrophages and epithelial cells are involved in the activation of epithelial NFkB and generation of proinflammatory mediators such as IL-6, IL-8, TNFa, IL-1b, ICAM-1, E-selectin and PGE2. O3-induced partial depolymerization of hyaluronic acid and the release of peroxiredoxin-1 activate macrophage TLR4 while oxidative epithelial cell release of EGFR ligands such as TGFa or EGFR transactivation by activated Src may also be involved. The ability of lipid ozonation to generate potent electrophiles also provides pathways for Nrf2 activation and inhibition of canonical NFkB activation. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Cytotoxicity of organic surface coating agents used for nanoparticles synthesis and stability

Impact on health by nanomaterials has become a public concern with the great advances of nanomaterials for various applications. Surface coating agents are an integral part of nanoparticles, but not enough attention has been paid during toxicity tests of nanoparticles. As a result, there are inconsistent toxicity results for certain nanomaterials. In this study, we explored the cytotoxicity of eleven commonly used surface coating agents in two cell lines, human epidermal keratinocyte (HaCaT) and lung fibroblast (CRL-1490) cells, at surface coating agent concentrations of 3, 10, 30, and 100 μM. Two exposure time points, 2 h and 24 h, were employed for the study. Six of the eleven surface coating agents are cytotoxic, especially those surfactants with long aliphatic chains, both cationic (cetyltrimethylammonium bromide, oleylamine, tetraoctylammonium bromide, and hexadecylamine) and anionic (sodium dodecylsulfate). In addition, exposure time and the use of different cell lines also affect the cytotoxicity results. Therefore, factors such as cell lines used and exposure times must be considered when conducting toxicity tests or comparing cytotoxicity results.

Ozone inhalation modifies the rat liver proteome

Ozone (O₃) is a serious public health concern. Recent findings indicate that the damaging health effects of O₃ extend to multiple systemic organ systems. Herein, we hypothesize that O₃ inhalation will cause downstream alterations to the liver. To test this, male Sprague-Dawley rats were exposed to 0.5 ppm O₃ for 8 h/day for 5 days. Plasma liver enzyme measurements showed that 5 day O₃ exposure did not cause liver cell death. Proteomic and mass spectrometry analysis identified 10 proteins in the liver that were significantly altered in abundance following short-term O₃ exposure and these included several stress responsive proteins. Glucose-regulated protein 78 and protein disulfide isomerase increased, whereas glutathione S-transferase M1 was significantly decreased by O₃ inhalation. In contrast, no significant changes were detected for the stress response protein heme oxygenase-1 or cytochrome P450 2E1 and 2B in liver of O₃ exposed rats compared to controls. In summary, these results show that an environmentally-relevant exposure to inhaled O₃ can alter the expression of select proteins in the liver. We propose that O₃ inhalation may represent an important unrecognized factor that can modulate hepatic metabolic functions.

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Rats were exposed to filtered air (FA) or 0.5 ppm ozone (O₃) 8 h/day for 5 days.

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Using this exposure protocol, O₃ caused no detectable lung injury or liver cell death.

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O₃ altered the expression of some drug metabolism and stress proteins in liver.

The effects of pycnogenol on antioxidant enzymes in a mouse model of ozone exposure

BACKGROUND/AIMS

Ozone is an environmentally reactive oxidant, and pycnogenol is a mixture of flavonoid compounds extracted from pine tree bark that have antioxidant activity. We investigated the effects of pycnogenol on reactive nitrogen species, antioxidant responses, and airway responsiveness in BALB/c mice exposed to ozone.

METHODS

Antioxidant levels were determined using high performance liquid chromatography with electrochemical detection. Nitric oxide (NO) metabolites in bronchoalveolar lavage (BAL) fluid from BALB/c mice in filtered air and 2 ppm ozone with pycnogenol pretreatment before ozone exposure (n = 6) were quantified colorimetrically using the Griess reaction.

RESULTS

Uric acid and ascorbic acid concentrations were significantly higher in BAL fluid following pretreatment with pycnogenol, whereas γ-tocopherol concentrations were higher in the ozone exposed group but were similar in the ozone and pycnogenol pretreatment groups. Retinol and γ-tocopherol concentrations tended to increase in the ozone exposure group but were similar in the ozone and pycnogenol pretreatment groups following ozone exposure. Malonylaldehyde concentrations increased in the ozone exposure group but were similar in the ozone and pycnogenol plus ozone groups. The nitrite and total NO metabolite concentrations in BAL fluid, which parallel the in vivo generation of NO in the airways, were significantly greater in the ozone exposed group than the group exposed to filtered air, but decreased with pycnogenol pretreatment.

CONCLUSIONS

Pycnogenol may increase levels of antioxidant enzymes and decrease levels of nitrogen species, suggesting that antioxidants minimize the effects of acute ozone exposure via a protective mechanism.

Combination of LC-MS- and GC-MS-based metabolomics to study the effect of ozonated autohemotherapy on human blood

Ozonated autohemotherapy (O3-AHT) is a medical approach during which blood obtained from the patient is ozonated and injected back into the body. Despite an increasing number of evidence that O3-AHT is safe, this type of therapy remains controversial. To extend knowledge about the changes in blood evoked by O3-AHT, LC-MS- and GC-MS-based metabolic fingerprinting was used to compare plasma samples obtained from blood before and after the treatment with potentially therapeutic concentrations of ozone. The procedure was performed in PVC bags utilized for blood storage to study also possible interactions between ozone and plastic. By use of GC-MS, an increase in lactic acid and pyruvic acid was observed, which indicated an increased rate of glycolysis. With LC-MS, changes in plasma antioxidants were observed. Moreover, concentrations of lipid oxidation products (LOP) and lysophospholipids were increased after ozone treatment. This is the first report of increased LOPs metabolites after ozonation of blood. Seven metabolites detected by LC-QTOF-MS only in ozonated samples could be considered as novel biomarkers of oxidative stress. Several plasticizers have been detected by both techniques in blood stored in PVC bags. PVC is known to be an ozone resistant material, but ozonation of blood in PVC bags stimulates leaching of plasticizers into the blood.

Genes of innate immunity and the biological response to inhaled ozone

Ambient ozone has a significant impact on human health. We have made considerable progress in understanding the fundamental mechanisms that regulate the biological response to ozone. It is increasingly clear that genes of innate immunity play a central role in both infectious and noninfectious lung disease. The biological response to ambient ozone provides a clinically relevant environmental exposure that allows us to better understand the role of innate immunity in noninfectious airways disease. In this brief review, we focus on (1) specific cell types in the lung modified by ozone, (2) ozone and oxidative stress, (3) the relationship between genes of innate immunity and ozone, (4) the role of extracellular matrix in reactive airways disease, and (5) the effect of ozone on the adaptive immune system. We summarize recent advances in understanding the mechanisms that ozone contributes to environmental airways disease.

20-HETE mediates ozone-induced, neutrophil-independent airway hyper-responsiveness in mice

Background

Ozone, a pollutant known to induce airway hyper-responsiveness (AHR), increases morbidity and mortality in patients with obstructive airway diseases and asthma. We postulate oxidized lipids mediate in vivo ozone-induced AHR in murine airways.

Methodology/Principal Findings

Male BALB/c mice were exposed to ozone (3 or 6 ppm) or filtered air (controls) for 2 h. Precision cut lung slices (PCLS; 250 µm thickness) containing an intrapulmonary airway (∼0.01 mm² lumen area) were prepared immediately after exposure or 16 h later. After 24 h, airways were contracted to carbachol (CCh). Log EC₅₀ and E_max values were then calculated by measuring the airway lumen area with respect to baseline. In parallel studies, dexamethasone (2.5 mg/kg), or 1-aminobenzotriazol (ABT) (50 mg/kg) were given intraperitoneal injection to naïve mice 18 h prior to ozone exposure. Indomethacin (10 mg/kg) was administered 2 h prior. Cell counts, cytokine levels and liquid chromatography-mass spectrometry (LC-MS) for lipid analysis were assessed in bronchoalveolar lavage (BAL) fluid from ozone exposed and control mice. Ozone acutely induced AHR to CCh. Dexamethasone or indomethacin had little effect on the ozone-induced AHR; while, ABT, a cytochrome P450 inhibitor, markedly attenuated airway sensitivity. BAL fluid from ozone exposed animals, which did not contain an increase in neutrophils or interleukin (IL)-6 levels, increased airway sensitivity following in vitro incubation with a naïve PCLS. In parallel, significant increases in oxidized lipids were also identified using LC-MS with increases of 20-HETE that were decreased following ABT treatment.

Conclusions/Significance

These data show that ozone acutely induces AHR to CCh independent of inflammation and is insensitive to steroid treatment or cyclooxygenase (COX) inhibition. BAL fluid from ozone exposed mice mimicked the effects of in vivo ozone exposure that were associated with marked increases in oxidized lipids. 20-HETE plays a pivotal role in mediating acute ozone-induced AHR.

Redox control of asthma: molecular mechanisms and therapeutic opportunities

An imbalance in reducing and oxidizing (redox) systems favoring a more oxidative environment is present in asthma and linked to the pathophysiology of the defining symptoms and signs including airflow limitation, hyper-reactivity, and airway remodeling. High levels of hydrogen peroxide, nitric oxide ((*)NO), and 15-F(2t)-isoprostane in exhaled breath, and excessive oxidative protein products in lung epithelial lining fluid, peripheral blood, and urine provide abundant evidence for pathologic oxidizing processes in asthma. Parallel studies document loss of reducing potential by nonenzymatic and enzymatic antioxidants. The essential first line antioxidant enzymes superoxide dismutases (SOD) and catalase are reduced in asthma as compared to healthy individuals, with lowest levels in those patients with the most severe asthma. Loss of SOD and catalase activity is related to oxidative modifications of the enzymes, while other antioxidant gene polymorphisms are linked to susceptibility to develop asthma. Monitoring of exhaled (*)NO has entered clinical practice because it is useful to optimize asthma care, and a wide array of other biochemical oxidative and nitrative biomarkers are currently being evaluated for asthma monitoring and phenotyping. Novel therapeutic strategies that target correction of redox abnormalities show promise for the treatment of asthma.

Pulmonary ozone exposure induces vascular dysfunction, mitochondrial damage, and atherogenesis

More than 100 million people in the United States live in areas that exceed current ozone air quality standards. In addition to its known pulmonary effects, environmental ozone exposures have been associated with increased hospital admissions related to cardiovascular events, but to date, no studies have elucidated the potential molecular mechanisms that may account for exposure-related vascular impacts. Because of the known pulmonary redox and immune biology stemming from ozone exposure, we hypothesized that ozone inhalation would initiate oxidant stress, mitochondrial damage, and dysfunction within the vasculature. Accordingly, these factors were quantified in mice consequent to a cyclic, intermittent pattern of ozone or filtered air control exposure. Ozone significantly modulated vascular tone regulation and increased oxidant stress and mitochondrial DNA damage (mtDNA), which was accompanied by significantly decreased vascular endothelial nitric oxide synthase protein and indices of nitric oxide production. To examine influences on atherosclerotic lesion formation, apoE-/- mice were exposed as above, and aortic plaques were quantified. Exposure resulted in significantly increased atherogenesis compared with filtered air controls. Vascular mitochondrial damage was additionally quantified in ozone- and filtered air-exposed infant macaque monkeys. These studies revealed that ozone increased vascular mtDNA damage in nonhuman primates in a fashion consistent with known atherosclerotic lesion susceptibility in humans. Consequently, inhaled ozone, in the absence of other environmental toxicants, promotes increased vascular dysfunction, oxidative stress, mitochondrial damage, and atherogenesis.

NAD(P)H quinone oxidoreductase 1 is essential for ozone-induced oxidative stress in mice and humans

One host susceptibility factor for ozone identified in epidemiologic studies is NAD(P)H quinone oxidoreductase 1 (NQO1). We hypothesized that after ozone exposure, NQO1 is required to increase 8-isoprostane (also known as F(2)-isoprostane) production, a recognized marker of ozone-induced oxidative stress, and to enhance airway inflammation and hyperresponsiveness. In this report, we demonstrate that in contrast to wild-type mice, NQO1-null mice are resistant to ozone and have blunted responses, including decreased production of F(2)-isoprostane and keratinocyte chemokine, decreased airway inflammation, and diminished airway hyperresponsiveness. Importantly, these results in mice correlate with in vitro findings in humans. In primary human airway epithelial cells, inhibition of NQO1 by dicumarol blocks ozone-induced F(2)-isoprostane production and IL-8 gene expression. Together, these results demonstrate that NQO1 modulates cellular redox status and influences the biologic and physiologic effects of ozone.

Vgamma1+ T cells and tumor necrosis factor-alpha in ozone-induced airway hyperresponsiveness

gammadelta T cells regulate airway reactivity, but their role in ozone (O3)-induced airway hyperresponsiveness (AHR) is not known. Our objective was to determine the role of gammadelta T cells in O3-induced AHR. Different strains of mice, including those that were genetically manipulated or antibody-depleted to render them deficient in total gammadelta T cells or specific subsets of gammadelta T cells, were exposed to 2.0 ppm of O3 for 3 hours. Airway reactivity to inhaled methacholine, airway inflammation, and epithelial cell damage were monitored. Exposure of C57BL/6 mice to O3 resulted in a transient increase in airway reactivity, neutrophilia, and increased numbers of epithelial cells in the lavage fluid. TCR-delta(-/-) mice did not develop AHR, although they exhibited an increase in neutrophils and epithelial cells in the lavage fluid. Similarly, depletion of gammadelta T cells in wild-type mice suppressed O3-induced AHR without influencing airway inflammation or epithelial damage. Depletion of Vgamma1+, but not of Vgamma4+ T cells, reduced O3-induced AHR, and transfer of total gammadelta T cells or Vgamma1+ T cells to TCR-delta(-/-) mice restored AHR. After transfer of Vgamma1+ cells to TCR-delta(-/-) mice, restoration of AHR after O3 exposure was blocked by anti-TNF-alpha. However, AHR could be restored in TCR-delta(-/-)mice by transfer of gammadelta T cells from TNF-alpha-deficient mice, indicating that another cell type was the source of TNF-alpha. These results demonstrate that TNF-alpha and activation of Vgamma1+ gammadelta T cells are required for the development of AHR after O3 exposure.

Oxidants and the pathogenesis of lung diseases

The increasing number of population-based and epidemiologic associations between oxidant pollutant exposures and cardiopulmonary disease exacerbation, decrements in pulmonary function, and mortality underscores the important detrimental effects of oxidants on public health. Because inhaled oxidants initiate a number of pathologic processes, including inflammation of the airways, which may contribute to the pathogenesis and/or exacerbation of airways disease, it is critical to understand the mechanisms through which exogenous and endogenous oxidants interact with molecules in the cells, tissues, and epithelial lining fluid of the lung. Furthermore, it is clear that interindividual variation in response to a given exposure also exists across an individual lifetime. Because of the potential impact that oxidant exposures may have on reproductive outcomes and infant, child, and adult health, identification of the intrinsic and extrinsic factors that may influence susceptibility to oxidants remains an important issue. In this review, we discuss mechanisms of oxidant stress in the lung, the role of oxidants in lung disease pathogenesis and exacerbation (eg, asthma, chronic obstructive pulmonary disease, and acute respiratory distress syndrome), and the potential risk factors (eg, age, genetics) for enhanced susceptibility to oxidant-induced disease.

Suppressed signal transduction in the bronchial epithelium of patients with systemic sclerosis

INTRODUCTION

Systemic sclerosis (SSc) is an autoimmune disorder, which frequently affects the lungs, with manifestations of interstitial lung disease (ILD) with lung fibrosis and of pulmonary hypertension. The pathogenesis remains largely unrecognised.

OBJECTIVE

The aim of this study was to elucidate the inflammation in the bronchial mucosa in patients with SSc.

SUBJECTS AND METHODS

Twenty-three subjects diagnosed with SSc participated. Twelve of the SSc patients showed signs of ILD, four were smokers and seven were treated with oral corticosteroids. Seventeen non-smoking, age- and sex-matched healthy subjects served as controls. Bronchoscopy was performed to sample endobronchial mucosal biopsies, which were immunohistochemically stained using a panel of antibodies against inflammatory markers.

RESULTS

The number of neutrophils was significantly elevated in the submucosa of SSc patients, regardless of ILD, or whether the subject was smoking or using oral corticosteroids. No up-regulation of neutrophil chemoattractants or cytokines was seen in the bronchial epithelium. The signal transduction pathways and adhesion molecule expression tended to be suppressed or unchanged in SSc patients compared with controls.

CONCLUSION

It is concluded that SSc is associated with a chronic neutrophilic inflammation in the bronchial mucosal, with signs of suppressed signal transduction, regardless of the presence of interstitial lung disease.

Ozone enhances diesel exhaust particles (DEP)-induced interleukin-8 (IL-8) gene expression in human airway epithelial cells through activation of nuclear factors- kappaB (NF-kappaB) and IL-6 (NF-IL6)

Ozone, a highly reactive oxidant gas is a major component of photochemical smog. As an inhaled toxicant, ozone induces its adverse effects mainly on the lung. Inhalation of particulate matter has been reported to cause airway inflammation in humans and animals. Furthermore, epidemiological evidence has indicated that exposure to particulate matter (PM[2.5-10]), including diesel exhaust particles (DEP) has been correlated with increased acute and chronic respiratory morbidity and exacerbation of asthma. Previously, exposure to ozone or particulate matter and their effect on the lung have been addressed as separate environmental problems. Ozone and particulate matter may be chemically coupled in the ambient air. In the present study we determined whether ozone exposure enhances DEP effect on interleukin-8 (IL-8) gene expression in human airway epithelial cells. We report that ozone exposure (0.5 ppm x 1 hr) significantly increased DEP-induced IL-8 gene expression in A549 cells (117 +/- 19 pg/ml, n = 6, p < 0.05) as compared to cultures treated with DEP (100 microg/ml x 4 hr) alone (31 +/- 3 pg/ml, n = 6), or cultures exposed to purified air (24 +/- 6 pg/ml, n = 6). The increased DEP-induced IL-8 gene expression following ozone exposure was attributed to ozone-induced increase in the activity of the transcription factors NF-kappaB and NF-IL6. The results of the present study indicate that ozone exposure enhances the toxicity of DEP in human airway epithelial cells by augmenting IL-8 gene expression, a potent chemoattractant of neutrophils in the lung.

Breath condensate levels of 8-isoprostane and leukotriene B4 after ozone inhalation are greater in sensitive versus nonsensitive subjects

Ozone (O3) inhalation induces pulmonary function decrements and inflammation. The present study was designed to determine if a relationship exists between O3 induced pulmonary function changes and the presence of inflammatory markers as measured in exhaled breath condensates (EBCs) obtained from O3-sensitive and nonsensitive human subjects. Eight healthy adult volunteers (4 males/4 females, age 18 to 30 years) were studied, characterized as to their ozone sensitivity and placed into 2 groups (sensitive and nonsensitive) with each group having 2 males and 2 females. Subjects completed a 20-minute EBC collection and pulmonary function test (PFT) prior to a single 60-minute bout of cycle ergometer exercise (V(E) = 50-55 L/min) while breathing filtered air (FA) or 0.35 ppm O3. Subjective symptom scores (SSSs) were collected at 6, 20, 40, and 60 minutes during exposure. An immediate postexposure PFT was performed followed by an EBC collection. Subjective symptom scores, EBCs, and PFTs were collected at 1, 4 and 8 hours post exposure. EBCs were analyzed for prostaglandin E2 (PGE2), leukotriene B4 (LTB4), 8-isoprostane, and total nitric oxide (NO) metabolites (nitrate + nitrite content). Sensitive subjects, breathing O3, had significantly greater functional decrements in PFTs, increased SSSs, and increased rapid shallow breathing as well as elevated levels of 8-isoprostane and LTB4 in EBCs compared to those breathing FA. In addition, there were significant increases in nitrate + nitrite content in both sensitive and nonsensitive subjects breathing O3 compared to FA. These results indicate that sensitive subjects have elevated arachidonic acid metabolites in EBCs compared to nonsensitive subjects after O3 inhalation.

Protection against inhaled oxidants through scavenging of oxidized lipids by macrophage receptors MARCO and SR-AI/II

Alveolar macrophages (AMs) express the class A scavenger receptors (SRAs) macrophage receptor with collagenous structure (MARCO) and scavenger receptor AI/II (SRA-I/II), which recognize oxidized lipids and provide innate defense against inhaled pathogens and particles. Increased MARCO expression in lungs of ozone-resistant mice suggested an additional role protecting against inhaled oxidants. After ozone exposure, MARCO-/- mice showed greater lung injury than did MARCO+/+ mice. Ozone is known to generate oxidized, proinflammatory lipids in lung lining fluid, such as 5beta,6beta-epoxycholesterol (beta-epoxide) and 1-palmitoyl-2-(9'-oxo-nonanoyl)-glycerophosphocholine (PON-GPC). Intratracheal instillation of either lipid caused substantial neutrophil influx in MARCO-/- mice, but had no effect in MARCO+/+ mice. Normal AMs showed greater uptake in vitro of beta-epoxide compared with MARCO-/- AMs, consistent with SRA function in binding oxidized lipids. SR-AI/II-/- mice showed similar enhanced acute lung inflammation after beta-epoxide or another inhaled oxidant (aerosolized leachate of residual oil fly ash). In contrast, subacute ozone exposure did not enhance inflammation in SR-AI/II-/- versus SR-AI/II+/+ mice, reflecting increased AM expression of MARCO. These data identify what we believe to be a novel function for AM SRAs in decreasing pulmonary inflammation after oxidant inhalation by scavenging proinflammatory oxidized lipids from lung lining fluids.

Activation of transcription factor IL-6 (NF-IL-6) and nuclear factor-kappaB (NF-kappaB) by lipid ozonation products is crucial to interleukin-8 gene expression in human airway epithelial cells

Ozone (O(3)) is a major component of smog and an inhaled toxicant to the lung. O(3) rapidly reacts with the airway epithelial cell membrane phospholipids to generate lipid ozonation products (LOP). 1-Hydroxy-1-hydroperoxynonane (HHP-C9) is an important LOP, produced from the ozonation of 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphatidylcholine. This LOP, at a biologically relevant concentration (100 microM), increases the activity of phospholipase C, nuclear factors-kappaB (NF-kappaB), and interleukin-6 (NF-IL-6) and the expression of the inflammatory gene, interleukin-8 (IL-8) in a cultured human bronchial epithelial cell line (BEAS-2B). The signaling pathways of ozone and its biologically-active products are as yet undefined. In the present study, we report that the HHP LOP, HHP-C9 (100 microM x 4 h), activated the expression of IL-8 (218 +/- 26% increase over control, n = 4, P < 0.01) through an apparent interaction between the two transcription factors, NF-kappaB and NF-IL-6. Transfection studies using luciferase reporter assays demonstrated that HHP-C9 induced a significant increase in NF-kappaB-DNA binding activity (37 +/- 7% increase over control, n = 6, P < 0.05). Inhibition of NF-kappaB showed a statistically significant but modest decrease in IL-8 release, which suggested a role for another transcription factor, NF-IL-6. Exposure of BEAS-2B cells to HHP-C9 induced a significant increase in the DNA binding activity of NF-IL-6 (45 +/- 11% increase over control, n = 6, P < 0.05). The results of the present study indicate that NF-IL-6 interacts with NF-kappaB in regulating the expression of IL-8 in cultured human airway epithelial cells exposed to LOP, the biological products of ozone in the lung.

Time course of ozone-induced changes in breathing pattern in healthy exercising humans

We examined the time course of O3-induced changes in breathing pattern in 97 healthy human subjects (70 men and 27 women). One- to five-minute averages of breathing frequency (fB) and minute ventilation (V̇e) were used to generate plots of cumulative breaths and cumulative exposure volume vs. time and cumulative exposure volume vs. cumulative breaths. Analysis revealed a three-phase response; delay, no response detected; onset, fB began to increase; response, fB stabilized. Regression analysis was used to identify four parameters: time to onset, number of breaths at onset, cumulative inhaled dose of ozone at onset of O3-induced tachypnea, and the percent change in fB. The effect of altering O3 concentration, V̇e, atropine treatment, and indomethacin treatment were examined. We found that the lower the O3 concentration, the greater the number of breaths at onset of tachypnea at a fixed ventilation, whereas number of breaths at onset of tachypnea remains unchanged when V̇e is altered and O3 concentration is fixed. The cumulative inhaled dose of O3 at onset of tachypnea remained constant and showed no relationship with the magnitude of percent change in fB. Atropine did not affect any of the derived parameters, whereas indomethacin did not affect time to onset, number of breaths at onset, or cumulative inhaled dose of O3 at onset of tachypnea but did attenuate percent change in fB. The results are discussed in the context of dose response and intrinsic mechanisms of action.

Free radical biology and medicine: it's a gas, man!

We review gases that can affect oxidative stress and that themselves may be radicals. We discuss O(2) toxicity, invoking superoxide, hydrogen peroxide, and the hydroxyl radical. We also discuss superoxide dismutase (SOD) and both ground-state, triplet oxygen ((3)O(2)), and the more energetic, reactive singlet oxygen ((1)O(2)). Nitric oxide ((*)NO) is a free radical with cell signaling functions. Besides its role as a vasorelaxant, (*)NO and related species have other functions. Other endogenously produced gases include carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen sulfide (H(2)S). Like (*)NO, these species impact free radical biochemistry. The coordinated regulation of these species suggests that they all are used in cell signaling. Nitric oxide, nitrogen dioxide, and the carbonate radical (CO(3)(*-)) react selectively at moderate rates with nonradicals, but react fast with a second radical. These reactions establish "cross talk" between reactive oxygen (ROS) and reactive nitrogen species (RNS). Some of these species can react to produce nitrated proteins and nitrolipids. It has been suggested that ozone is formed in vivo. However, the biomarkers that were used to probe for ozone reactions may be formed by non-ozone-dependent reactions. We discuss this fascinating problem in the section on ozone. Very low levels of ROS or RNS may be mitogenic, but very high levels cause an oxidative stress that can result in growth arrest (transient or permanent), apoptosis, or necrosis. Between these extremes, many of the gasses discussed in this review will induce transient adaptive responses in gene expression that enable cells and tissues to survive. Such adaptive mechanisms are thought to be of evolutionary importance.

Application of quantitative structure activity relationship (QSAR) models to predict ozone toxicity in the lung

The sequence of events leading to ozone-induced airway inflammation is not well known. To elucidate the molecular and cellular events underlying ozone toxicity in the lung, we hypothesized that lipid ozonation products (LOPs) generated by the reaction of ozone with unsaturated fatty acids in the epithelial lining fluid and cell membranes play a key role in mediating ozone-induced airway inflammation. To test our hypothesis, we ozonized 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) and generated LOPs. Confluent human bronchial epithelial cells were exposed to the derivatives of ozonized POPC-9-oxononanoyl, 9-hydroxy-9-hydroperoxynonanoyl, and 8-(5-octyl-1,2,4-trioxolan-3-yl-)octanoyl-at a concentration of 10 muM, and the activity of phospholipases A2 (PLA2), C (PLC), and D (PLD) was measured (1, 0.5, and 1 h, respectively). Quantitative structure-activity relationship (QSAR) models were utilized to predict the biological activity of LOPs in airway epithelial cells. The QSAR results showed a strong correlation between experimental and computed activity (r = 0.97, 0.98, 0.99, for PLA2, PLC, and PLD, respectively). The results indicate that QSAR models can be utilized to predict the biological activity of the various ozone-derived LOP species in the lung.

Modulatory effects of ozone on THP-1 cells in response to SP-A stimulation

Ozone (O(3)), a major component of air pollution and a strong oxidizing agent, can lead to lung injury associated with edema, inflammation, and epithelial cell damage. The effects of O(3) on pulmonary immune cells have been studied in various in vivo and in vitro systems. We have shown previously that O(3) exposure of surfactant protein (SP)-A decreases its ability to modulate proinflammatory cytokine production by cells of monocyte/macrophage lineage (THP-1 cells). In this report, we exposed THP-1 cells and/or native SP-A obtained from bronchoalveolar lavage of patients with alveolar proteinosis to O(3) and studied cytokine production and NF-kappaB signaling. The results showed 1) exposure of THP-1 cells to O(3) significantly decreased their ability to express TNF-alpha in response to SP-A; TNF-alpha production, under these conditions, was still significantly higher than basal (unstimulated) levels in filtered air-exposed THP-1 cells; 2) exposure of both THP-1 cells and SP-A to O(3) did not result in any significant differences in TNF-alpha expression compared with basal levels; 3) O(3) exposure of SP-A resulted in a decreased ability of SP-A to activate the NF-kappaB pathway, as assessed by the lack of significant increase and decrease of the nuclear p65 subunit of NF-kappaB and cytoplasmic IkappaBalpha, respectively; and 4) O(3) exposure of THP-1 cells resulted in a decrease in SP-A-mediated THP-1 cell responsiveness, which did not seem to be mediated via the classic NF-kappaB pathway. These findings indicate that O(3) exposure may mediate its effect on macrophage function both directly and indirectly (via SP-A oxidation) and by involving different mechanisms.

Ozone exposure in vivo and formation of biologically active oxysterols in the lung

Ozone toxicity in the lung is thought to be mediated by products derived from the reaction of ozone with components of the lung epithelial lining fluid. Cholesterol is an abundant component of this epithelial lining fluid, and it is susceptible to ozonolysis, yielding several stable products including 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al and 5beta,6beta-epoxycholesterol. Both 5beta,6beta-epoxycholesterol and its metabolite, cholestan-6-oxo-3,5-diol, have been shown to cause cytotoxicity in vitro, suggesting that they may be potential mediators of ozone toxicity in vivo. An ozone-sensitive mouse strain, C57BL/6J, was exposed to varying concentrations of ozone (0.5-3.0 ppm), and subsequently the levels of these cholesterol ozonolysis products were quantitated by electrospray ionization mass spectrometry in bronchoalveolar lavage fluid, lavaged cells, and lung homogenate. An ozone dose-dependent formation of these biologically active oxysterols was observed in vivo, supporting a role for these compounds in ozone toxicity. Since the 5beta,6beta-epoxycholesterol metabolite, cholestan-6-oxo-3,5-diol, was isobaric with other cholesterol ozonolysis products, 3beta-hydroxy-5-oxo-5,6-secocholestan-6-al and its aldol condensation product, 3beta-hydroxy-5beta-hydroxy-B-norcholestan-6beta-carboxaldehyde, detailed mass spectral analysis using electron impact ionization was utilized to differentiate these isobaric cholesterol ozonolysis products. The specific detection of cholestan-6-oxo-3,5-diol in lung homogenate after ozone exposure established formation of 5beta,6beta-epoxycholesterol within the lung after exposure to 0.5 ppm ozone.

Superoxide dismutase-overexpressing mice are resistant to ozone-induced tissue injury and increases in nitric oxide and tumor necrosis factor-alpha

Reactive oxygen intermediates have been implicated in lung injury induced by inhaled irritants. The present studies used mice overexpressing Cu/Zn-superoxide dismutase (SOD+/+) to analyze their role in ozone-induced lung inflammation and cytotoxicity. Treatment of wild-type mice with ozone (0.8 ppm, 3 h) resulted in increased bronchoalveolar lavage fluid protein, which was maximal after 24-48 h. Significant increases in lung macrophages and 4-hydroxyalkenals were also observed. In contrast, bronchoalveolar lavage fluid protein and macrophage content and 4-hydroxyalkenals were at control levels in ozone-treated SOD+/+ mice. There was also no evidence of peroxynitrite-mediated lung damage, demonstrating that SOD+/+ mice are resistant to ozone toxicity. Whereas alveolar macrophages from wild-type mice produced increased amounts of nitric oxide and expressed more inducible nitric oxide synthase, phospholipase A(2), and tumor necrosis factor-alpha after ozone inhalation, this was not evident in cells from SOD+/+ mice. Ozone-induced decreases in interleukin-10 were also not observed. In wild-type mice, ozone inhalation resulted in activation of nuclear factor-kappaB, which regulates proinflammatory gene activity. This response was significantly reduced in SOD+/+ mice. These data demonstrate that antioxidant enzymes play a critical role in ozone-induced tissue injury and in inflammatory mediator production.

Increased gene expression of novel cytosolic and secretory phospholipase A(2) types in human airway epithelial cells induced by tumor necrosis factor-alpha and IFN-gamma

Phospholipase A(2) (PLA(2)) is a growing family of enzymes that may play a major role in inflammation. We investigated the effect of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) on the gene expression of 19 different PLA(2) types (IB, IIA, IID, IIE, IIF, III, IVA, IVB, IVC, V, VIA, VIB, VIIA, VIIB, VIIIA, VIIIB, X, XII, and XIII) in human bronchoepithelial (BEAS-2B) and nasal epithelial (RPMI 2650) cells. The cells were stimulated with TNF-alpha or IFN-gamma for different lengths of time (1, 4, 18, and 48 h), and the mRNA levels of the different PLA(2) types were determined by reverse transcriptase-PCR (RT-PCR) and normalized to those of the housekeeping gene, GAPDH. In both cell lines, TNF-alpha increased the expression of PLA(2) IVA and IVC, and IFN-gamma increased the expression of PLA(2) IIA and IID. No influence on the gene expression of PLA(2)-activating protein (PLAP) was noted on cytokine stimulation. These findings indicate that TNF-alpha and IFN-gamma induce gene expression of two novel cytosolic and secretory PLA(2) types (IVC and IID, respectively) in human airway epithelial cells. The possibility that these PLA(2) types are involved in cytokine-mediated inflammation in the respiratory tract is inferred.

tert-Butyl hydroperoxide-induced lipid signaling in hepatocytes: involvement of glutathione and free radicals

tert-Butyl hydroperoxide (TBHP) mobilizes arachidonic acid (AA) from membrane phospholipids in rat hepatocytes under cytotoxic conditions, thus leading to an increase in intracellular AA, which precedes cell death. In the present work, the involvement of lipid peroxidation, thiol status, and reactive oxygen species (ROS) in the intracellular AA accumulation induced by 0.5 mM TBHP was studied in rat hepatocytes. Cells treated with TBHP maintained viability and energy status at 10 min. However, TBHP depleted GSH, as well as inducing lipid peroxidation and ROS formation, detected by dichlorofluorescein (DCF) fluorescence. TBHP also significantly increased (32.5%) the intracellular [14C]-AA from [14C]-AA-labelled hepatocytes. The phospholipase A(2) (PLA(2)) inhibitor, mepacrine, completely inhibited the [14C]-AA response. The addition of antioxidants to the cell suspensions affected the TBHP-induced lipid response differently. The [14C]-AA accumulation correlated directly with ROS and negatively with endogenous GSH. No correlation between [14C]-AA and lipid peroxidation was found. Promethazine prevented lipid peroxidation and did not affect the [14C]-AA increase. We conclude that TBHP stimulates the release of [14C]-AA from membrane phospholipids through a PLA(2)-mediated mechanism. Endogenous GSH and ROS play a major role in this effect, while lipid peroxidation-related events are unlikely to be involved. Results suggest that specific ROS generated in iron-dependent reactions, different from lipid peroxyl radicals, are involved in PLA(2) activation, this process being important in TBHP-induced hepatocyte injury.

Toll-like receptor 4 mediates ozone-induced murine lung hyperpermeability via inducible nitric oxide synthase

We tested the hypotheses that 1) inducible nitric oxide synthase (iNOS) mediates ozone (O3)-induced lung hyperpermeability and 2) mRNA levels of the gene for iNOS (Nos2) are modulated by Toll-like receptor 4 (Tlr4) during O3 exposure. Pretreatment of O3-susceptible C57BL/6J mice with a specific inhibitor of total NOS (N(G)-monomethyl-L-arginine) significantly decreased the mean lavageable protein concentration (a marker of lung permeability) induced by O3 (0.3 parts/million for 72 h) compared with vehicle control mice. Furthermore, lavageable protein in C57BL/B6 mice with targeted disruption of Nos2 [Nos2(-/-)] was 50% less than the protein in wild-type [Nos2(+/+)] mice after O3. To determine whether Tlr4 modulates Nos2 mRNA levels, we studied C3H/HeJ (HeJ) and C3H/HeOuJ mice that differ only at a missense mutation in Tlr4 that confers resistance to O3-induced lung hyperpermeability in the HeJ strain. Nos2 and Tlr4 mRNA levels were significantly reduced and correlated in resistant HeJ mice after O3 relative to those in susceptible C3H/HeOuJ mice. Together, the results are consistent with an important role for iNOS in O3-induced lung hyperpermeability and suggest that Nos2 mRNA levels are mediated through Tlr4.

Genetic susceptibility to ozone-induced lung hyperpermeability: role of toll-like receptor 4

The pollutant ozone (O(3)) induces lung hyperpermeability and inflammation in humans and animal models. Among inbred strains of mice, there is a 3-fold difference in total protein (a marker of permeability) recovered in bronchoalveolar lavage (BAL) fluid after a 72-h exposure to 0.3 ppm O(3). To determine the chromosomal locations of susceptibility genes, we performed a genome screen using recombinant inbred (RI) strains of mice derived from O(3)-susceptible C57BL/6J (B6) and O(3)-resistant C3H/HeJ (HeJ) progenitors. Each RI strain was phenotyped for O(3)-induced hyperpermeability, and linkage was assessed for 558 markers using Map Manager QTb27. A significant quantitative trait locus (QTL) was identified on chromosome 4. The likelihood ratio chi(2) statistic (16.6) for the peak of the QTL was greater than the significance threshold (16.3) determined empirically by permutation test. This QTL contains a candidate gene, Toll-like receptor 4 (Tlr4 ), that recently has been implicated in innate immunity and endotoxin susceptibility. The amount of the total trait variance explained by the QTL at Tlr4, the gene with the highest likelihood ratio statistic in the QTL, was approximately 70%. To test the role of Tlr4 in O(3)-induced hyperpermeability, BAL protein responses to O(3) were compared in C3H/HeOuJ (OuJ) and HeJ mice that differ only at a polymorphism in the coding region of Tlr4. Significantly greater protein concentrations (430 +/- 35 microg/ml) were found in OuJ mice compared with HeJ mice (258 +/- 18 microg/ml) after exposure to O(3). Furthermore, reverse transcriptase/polymerase chain reaction analysis demonstrated differential expression of Tlr4 message levels between HeJ and OuJ mice after O(3) exposure. Together, results indicate that a QTL on mouse chromosome 4 explains a significant portion of the genetic variance in O(3)-induced hyperpermeability, and support a role for Tlr4 as a strong candidate susceptibility gene.

Induction of inflammatory mediators in human airway epithelial cells by lipid ozonation products

We have proposed that exposure of epithelial cell membrane lipids in the lung (mainly phospholipids) to ozone will generate lipid ozonation products (LOP), which could be responsible for the proinflammatory effects of ozone. The ozonation of phosphocholine, the principal membrane phospholipid, produces a limited number of LOP, including hydroxyhydroperoxides and aldehydes. We now report that exposure of cultured human bronchial epithelial cells to the ozonized 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) product, 1-palmitoyl-2-(9-oxononanoyl)-sn-glycero-3-phosphocholine (PC-ALD), a phospholipase A(2) (PLA(2))-stimulatory LOP, resulted in a 113 +/- 11% increase in the amounts of tritiated platelet-activating factor ((3)H-PAF) released apically. (3)H-PAF release was also induced by 1-hydroxy-1-hydroperoxynonane of ozonized POPC (HHP-C9), a phospholipase C (PLC)- stimulatory LOP (134 +/- 40% increase in (3)H-PAF). PC-ALD at 10 microM, but not HHP-C9, induced a 127 +/- 24% increase in prostaglandin E(2) (PGE(2)) release (n = 6, p < 0.05). In contrast, HHP-C9, but not PC-ALD, induced interleukin (IL)-6 release (178 +/- 23% increase, n = 6, p < 0.05) and IL-8 release (101 +/- 23% increase, n = 8, p < 0. 05). These results suggest that LOP-dependent release of proinflammatory mediators may play an important role in the early inflammatory response seen during exposure to ozone.

Oxidative stress and pulmonary inflammation: pharmacological intervention with antioxidants

Reactive oxygen and nitrogen species are generated by several inflammatory and structural cells of the airways. These oxidant species may have important effects on different lung cells as regulators of signal transduction, activators of key transcription factors, and modulators of gene expression and apoptosis. Thus, an increased oxidative stress accompanied by reduced endogenous antioxidant defences may have a role in the pathogenesis of a number of inflammatory pulmonary diseases including asthma. Although antioxidant drugs could play a useful role in the therapy of inflammatory lung diseases, their clinical impact is relatively modest at present. Rigorous clinical investigation with the existing antioxidants and development of new drugs with improved lung bioavailability are necessary in the future.pc 1999 Academic Press@p$hr

Acute airway effects of formaldehyde and ozone in BALB/c mice

1. Concentration and time-effect relationships of formaldehyde and ozone on the airways were investigated in BALB/c mice. The effects were obtained by continuous monitoring of the respiratory rate, tidal volume, expiratory flow rate, time of inspiration, time of expiration, and respiratory patterns. 2. With concentrations up to 4 p.p.m., formaldehyde showed mainly sensory irritation effects of the upper airways that decrease the respiratory rate from a trigeminal reflex. The no-effect level (NOEL) was about 0.3 p.p.m. This value is close to the human NOEL, which is about 0.08 p.p.m. 3. Ozone caused rapid, shallow breathing in BALB/c mice. Later on, the respiratory rate decreased due to another vagal response that indicated an incipient lung oedema. The NOEL in mice was about 1 p.p.m. during 30 min of ozone exposure. No major effect occurs in resting humans at about 0.4 p.p.m. 4. Thus, the upper airway irritant, formaldehyde, and the deep lung irritant, ozone, showed the same types of respiratory effects in humans and in BALB/c mice. Also, the sensitivity was nearly identical. Continuous monitoring of respiratory effects in BALB/c mice, therefore, may be a valuable method for the study of effects of other environmental pollutants, which, however, should be confirmed in further studies.