Modification of macrophage adhesion by ozone: role of cytokines and cell adhesion molecules

Beta-2 Adrenergic and Glucocorticoid Receptor Agonists Modulate Ozone-Induced Pulmonary Protein Leakage and Inflammation in Healthy and Adrenalectomized Rats

We have shown that acute ozone inhalation activates sympathetic-adrenal-medullary and hypothalamus-pituitary-adrenal stress axes, and adrenalectomy (AD) inhibits ozone-induced lung injury and inflammation. Therefore, we hypothesized that stress hormone receptor agonists (β2 adrenergic-β2AR and glucocorticoid-GR) will restore the ozone injury phenotype in AD, while exacerbating effects in sham-surgery (SH) rats. Male Wistar Kyoto rats that underwent SH or AD were treated with vehicles (saline + corn oil) or β2AR agonist clenbuterol (CLEN, 0.2 mg/kg, i.p.) + GR agonist dexamethasone (DEX, 2 mg/kg, s.c.) for 1 day and immediately prior to each day of exposure to filtered air or ozone (0.8 ppm, 4 h/day for 1 or 2 days). Ozone-induced increases in PenH and peak-expiratory flow were exacerbated in CLEN+DEX-treated SH and AD rats. CLEN+DEX affected breath waveform in all rats. Ozone exposure in vehicle-treated SH rats increased bronchoalveolar lavage fluid (BALF) protein, N-acetyl glucosaminidase activity (macrophage activation), neutrophils, and lung cytokine expression while reducing circulating lymphocyte subpopulations. AD reduced these ozone effects in vehicle-treated rats. At the doses used herein, CLEN+DEX treatment reversed the protection offered by AD and exacerbated most ozone-induced lung effects while diminishing circulating lymphocytes. CLEN+DEX in air-exposed SH rats also induced marked protein leakage and reduced circulating lymphocytes but did not increase BALF neutrophils. In conclusion, circulating stress hormones and their receptors mediate ozone-induced vascular leakage and inflammatory cell trafficking to the lung. Those receiving β2AR and GR agonists for chronic pulmonary diseases, or with increased circulating stress hormones due to psychosocial stresses, might have altered sensitivity to air pollution.

Stress axis variability is associated with differential ozone-induced lung inflammatory signaling and injury biomarker response

Ozone (O₃), a ubiquitous urban air pollutant, causes adverse pulmonary and extrapulmonary effects. A large variability in acute O₃-induced effects has been observed; however, the basis for interindividual differences in susceptibility is unclear. We previously demonstrated a role for the hypothalamic-pituitary-adrenal (HPA) stress axis and glucocorticoid response in acute O₃ toxicity. Glucocorticoids have important anti-inflammatory actions, and have been shown to regulate lung inflammatory responses. We hypothesised that a hyporesponsive HPA axis would be associated with greater O₃-dependent lung inflammatory signaling. Two genetically-related rat strains with known differences in stress axis reactivity, highly-stress responsive Fischer (F344) and less responsive Lewis (LEW), were exposed for 4 h by nose-only inhalation to clean air or 0.8 ppm O₃, and euthanized immediately after exposure. As expected, baseline (air-exposed) plasma corticosterone was significantly lower in the hypo-stress responsive LEW. Although O₃ exposure increased plasma corticosterone in both strains, corticosterone remained significantly lower in LEW when compared to F334. LEW exhibited greater O₃-induced inflammatory cytokine/chemokine signaling compared to F344, consistent with the lower corticosterone levels. Since we observed strain-specific differences in inflammatory signaling, we further investigated injury biomarkers (total protein, albumin and lactate dehydrogenase). Although the hyper-responsive F344 exhibited lower inflammatory signaling in response to O₃ compared with LEW, they had greater levels of lung injury biomarkers. Our results indicate that stress axis variability is associated with differential O₃-induced lung toxicity. Given the large variability in stress axis reactivity among humans, stress axis regulation could potentially be a determining factor underlying O₃ sensitivity.

The impact of surfactant protein-A on ozone-induced changes in the mouse bronchoalveolar lavage proteome

Background

Ozone is a major component of air pollution. Exposure to this powerful oxidizing agent can cause or exacerbate many lung conditions, especially those involving innate immunity. Surfactant protein-A (SP-A) plays many roles in innate immunity by participating directly in host defense as it exerts opsonin function, or indirectly via its ability to regulate alveolar macrophages and other innate immune cells. The mechanism(s) responsible for ozone-induced pathophysiology, while likely related to oxidative stress, are not well understood.

Methods

We employed 2-dimensional difference gel electrophoresis (2D-DIGE), a discovery proteomics approach, coupled with MALDI-ToF/ToF to compare the bronchoalveolar lavage (BAL) proteomes in wild type (WT) and SP-A knockout (KO) mice and to assess the impact of ozone or filtered air on the expression of BAL proteins. Using the PANTHER database and the published literature most identified proteins were placed into three functional groups.

Results

We identified 66 proteins and focused our analysis on these proteins. Many of them fell into three categories: defense and immunity; redox regulation; and protein metabolism, modification and chaperones. In response to the oxidative stress of acute ozone exposure (2 ppm; 3 hours) there were many significant changes in levels of expression of proteins in these groups. Most of the proteins in the redox group were decreased, the proteins involved in protein metabolism increased, and roughly equal numbers of increases and decreases were seen in the defense and immunity group. Responses between WT and KO mice were similar in many respects. However, the percent change was consistently greater in the KO mice and there were more changes that achieved statistical significance in the KO mice, with levels of expression in filtered air-exposed KO mice being closer to ozone-exposed WT mice than to filtered air-exposed WT mice.

Conclusion

We postulate that SP-A plays a role in reactive oxidant scavenging in WT mice and that its absence in the KO mice in the presence or absence of ozone exposure results in more pronounced, and presumably chronic, oxidative stress.

Ozone effects on airway responsiveness, lung injury, and inflammation. Comparative rat strain and in vivo/in vitro investigations

Asthmatic individuals appear to be particularly sensitive to the effects of certain air pollutants-including ozone (O(3)), an oxidant ambient air pollutant-for reasons that are poorly understood. The general purpose of these studies, therefore, was to expand and improve upon toxicologic methods for assessing ozone-induced effects on the airways of the rat by (1) developing an in vivo testing procedure that allows detection of airway responsiveness changes in rats exposed to ozone; (2) identifying a strain of rat that may be inherently more sensitive to the effects of ozone; and (3) validation of an in vitro epithelial culture system to more directly assess airway cellular/subcellular effects of ozone. Using methacholine inhalation challenges, we detected increased airway responsiveness in senescent F344 rats acutely after ozone exposure (2 ppm x 2 h). We also determined that acutely after ozone exposure (0.5 ppm x 8 h), Wistar rats developed significantly greater lung injury, neutrophilic inflammation, and bronchoalveolar lavage (BAL) fluid concentrations of IL-6 than either Sprague-Dawley (SD) or F344 rats. SD rats had greater BAL fluid concentrations of prostaglandin E(2) (PGE(2)), while F344 rats consistently exhibited the least effect. Wistar rat-derived tracheal epithelial (RTE) cultures were exposed in vitro to air or ozone (0.1-1.0 ppm x 1 h), and examined for analogous effects. In a concentration-dependent manner, ozone exposure resulted in acute but minor cytotoxicity. RT polymerase chain reaction (PCR) analysis of RNA isolated from ozone-exposed cells demonstrated variable increases in steady-state gene expression of IL-6 at 4 h postexposure, while at 24 h cellular fibronectin expression (EIIIA domain) was decreased. Exposure was without effect on macrophage inflammatory protein 2 (MIP-2) or gamma-glutamyl cysteine synthetase expression. At 6 h postexposure, IL-6 synthesis and apical release appeared increased in ozone-exposed cells (1 ppm x 1 h). MIP-2 release was not significantly increased in ozone-exposed cells. At 2 h postexposure, ozone exposure resulted in minor increases in apical fibronectin, but exposure was without effect on basolateral accumulation of fibronectin. Exposure to 1.0, but not 0.1 ppm (x 1 h), increased production of cyclooxygenase (i.e., PGE(2)) and noncyclooxygenase products of arachidonic acid. Results demonstrate that multiple inflammatory mediator pathways are affected by ozone exposure. Such effects could exacerbate morbidity in individuals with preexisting airway inflammation such as asthmatics.

The failure of STAT6-deficient mice to develop airway eosinophilia and airway hyperresponsiveness is overcome by interleukin-5

While signal transducer and activator of transcription protein 6 (STAT6) is important in interleukin-4 (IL-4)-induced commitment of CD4(+) T cells to the T helper cell, type 2 (Th2) phenotype and IgE isotype switching in B cells, its role in other IL-4-mediated events and their impact upon the allergic response is less evident. In the present study we demonstrate the critical role of STAT6 in the development of allergic airway eosinophilia and airway hyperresponsiveness (AHR) after allergen sensitization and challenge. STAT6-deficient (STAT6-/-) mice did not develop a Th2 cytokine response or an allergen-specific IgE response. Further, STAT6-/- mice had a reduced constitutive and allergen-induced expression of CD23 as well as lower mucus production in the airway epithelium. Critically, we show that IL-5 alone can reconstitute airway eosinophilia and AHR in sensitized and challenged STAT6-/- mice. This emphasizes the essential nature of the IL-4-dependent signaling of T cells to the Th2 phenotype and secretion of IL-5, resulting in the airway eosinophilia and AHR. These observations underscore the importance of targeting this pathway in new antiallergic asthma drug development.