Augmented pulmonary responses to acute ozone exposure in obese mice: roles of TNFR2 and IL-13

Impact of obesity in asthma: Possible future therapies

Obesity is one of the factors associated with the severity of asthma. Obesity is associated with aggravation of the pathophysiology of asthma, including exacerbations, airway inflammation, decreased pulmonary function, and airway hyperresponsiveness. The present review addresses the characteristics of asthma with obesity, focusing especially on the heterogeneity caused by the degree of type 2 inflammation, sex differences, the onset of asthma, and race differences. To understand the severity mechanisms in asthma and obesity, such as corticosteroid resistance, fatty acids, gut microbiome, and cytokines, several basic research studies are evaluated. Finally, possible future therapies, including weight reduction, microbiome-targeted therapies, and other molecular targeted therapies are addressed. We believe that the present review will contribute to better understanding of the severity mechanisms and the establishment of novel treatments for severe asthma patients with obesity.

Transcriptomics Underlying Pulmonary Ozone Pathogenesis Regulated by Inflammatory Mediators in Mice

Ozone (O₃) is the predominant oxidant air pollutant associated with airway inflammation, lung dysfunction, and the worsening of preexisting respiratory diseases. We previously demonstrated the injurious roles of pulmonary immune receptors, tumor necrosis factor receptor (TNFR), and toll-like receptor 4, as well as a transcription factor NF-κB, in response to O₃ in mice. In the current study, we profiled time-dependent and TNFR- and NF-κB-regulated lung transcriptome changes by subacute O₃ to illuminate the underlying molecular events and downstream targets. Mice lacking Tnfr1/Tnfr2 (Tnfr^-/-) or Nfkb1 (Nfkb1^-/-) were exposed to air or O₃. Lung RNAs were prepared for cDNA microarray analyses, and downstream and upstream mechanisms were predicted by pathway analyses of the enriched genes. O₃ significantly altered the genes involved in inflammation and redox (24 h), cholesterol biosynthesis and vaso-occlusion (48 h), and cell cycle and DNA repair (48–72 h). Transforming growth factor-β1 was a predicted upstream regulator. Lack of Tnfr suppressed the immune cell proliferation and lipid-related processes and heightened epithelial cell integrity, and Nfkb1 deficiency markedly suppressed lung cell cycle progress during O₃ exposure. Common differentially regulated genes by TNFR and NF-κB1 (e.g., Casp8, Il6, and Edn1) were predicted to protect the lungs from cell death, connective tissue injury, and inflammation. Il6-deficient mice were susceptible to O₃-induced protein hyperpermeability, indicating its defensive role, while Tnf-deficient mice were resistant to overall lung injury caused by O₃. The results elucidated transcriptome dynamics and provided new insights into the molecular mechanisms regulated by TNFR and NF-κB1 in pulmonary subacute O₃ pathogenesis.

IL-33, diet-induced obesity, and pulmonary responses to ozone

Background

Obesity augments pulmonary responses to ozone. We have reported that IL-33 contributes to these effects of obesity in db/db mice. The purpose of this study was to determine whether IL-33 also contributes to obesity-related changes in the response to ozone in mice with diet-induced obesity.

Methods

Male wildtype C57BL/6 mice and mice deficient in ST2, the IL-33 receptor, were placed on chow or high fat diets for 12 weeks from weaning. Because the microbiome has been implicated in obesity-related changes in the pulmonary response to ozone, mice were either housed with other mice of the same genotype (same housed) or with mice of the opposite genotype (cohoused). Cohousing transfers the gut microbiome from one mouse to its cagemates.

Results

Diet-induced increases in body mass were not affected by ST2 deficiency or cohousing. In same housed mice, ST2 deficiency reduced ozone-induced airway hyperresponsiveness and neutrophil recruitment in chow-fed but not HFD-fed mice even though ST2 deficiency reduced bronchoalveolar lavage IL-5 in both diet groups. In chow-fed mice, cohousing abolished ST2-related reductions in ozone-induced airway hyperresponsiveness and neutrophil recruitment, but in HFD-fed mice, no effect of cohousing on these responses to ozone was observed. In chow-fed mice, ST2 deficiency and cohousing caused changes in the gut microbiome. High fat diet-feeding caused marked changes in the gut microbiome and overrode both ST2-related and cohousing-related differences in the gut microbiome observed in chow-fed mice.

Conclusion

Our data indicate a role for IL-33 in pulmonary responses to ozone in chow-fed but not high fat diet-fed mice and are consistent with the hypothesis that these diet-related differences in the role of IL-33 are the result of changes in the gut microbiome.

The Metabolic Response to Ozone

The respiratory effects of O3 are well established. High ambient O3 concentrations are associated with respiratory symptoms, declines in pulmonary function, asthma exacerbations, and even mortality. The metabolic effects of O3 are less well appreciated. Here we review data indicating that O3 exposure leads to glucose intolerance and hyperlipidemia, characteristics of the metabolic syndrome. We also review the role of stress hormones in these events. We describe how the metabolic effects of O3, including effects within the lungs, are exacerbated in the setting of the metabolic derangements of obesity and we discuss epidemiological data indicating an association between ambient O3 exposure and diabetes. We conclude by describing the role of the gut microbiome in the regulation of metabolism and by discussing data indicating a link between the gut microbiome and pulmonary responses to O3.

Microbiota Contribute to Obesity-related Increases in the Pulmonary Response to Ozone

Obesity is a risk factor for asthma, especially nonatopic asthma, and attenuates the efficacy of standard asthma therapeutics. Obesity also augments pulmonary responses to ozone, a nonatopic asthma trigger. The purpose of this study was to determine whether obesity-related alterations in gut microbiota contribute to these augmented responses to ozone. Ozone-induced increases in airway responsiveness, a canonical feature of asthma, were greater in obese db/db mice than in lean wild-type control mice. Depletion of gut microbiota with a cocktail of antibiotics attenuated obesity-related increases in the response to ozone, indicating a role for microbiota. Moreover, ozone-induced airway hyperresponsiveness was greater in germ-free mice that had been reconstituted with colonic contents of db/db than in wild-type mice. In addition, compared with dietary supplementation with the nonfermentable fiber cellulose, dietary supplementation with the fermentable fiber pectin attenuated obesity-related increases in the pulmonary response to ozone, likely by reducing ozone-induced release of IL-17A. Our data indicate a role for microbiota in obesity-related increases in the response to an asthma trigger and suggest that microbiome-based therapies such as prebiotics may provide an alternative therapeutic strategy for obese patients with asthma.

The influence of maternal and perinatal high-fat diet on ozone-induced pulmonary responses in offspring

There is growing interest in understanding how maternal diet might affect the sensitivity of offspring to environmental exposures. Previous studies demonstrated that adult rat offspring (approximately 6-months-old) from dams given a high-fat diet (HFD) prior to, during, and after pregnancy displayed elevated pulmonary responses to an acute ozone (O3) exposure. The aim of this study was to examine the influence of maternal and perinatal HFD on pulmonary and metabolic responses to O3 in male and female young-adult offspring (approximately 3-month old). One-month-old F0 female Long-Evans rats commenced HFD (60% kcal from fat) or control diet (CD; 10.5% kcal from fat) and were bred on PND 72. Offspring were maintained on respective HFD or CD until PND 29 when all groups were switched to CD. The 3-months-old female and male offspring (n = 10/group) were exposed to air or 0.8 ppm O3 for 5hr/day for 2 consecutive days. Maternal and perinatal HFD significantly increased body weight and body fat % in offspring regardless of gender. Ozone exposure, but not maternal and perinatal diet, induced hyperglycemia and glucose intolerance in the offspring. Ozone-induced alterations in pulmonary function were exacerbated by maternal and perinatal HFD in both offspring genders. Pulmonary injury/inflammation markers in response to O3 exposure such as bronchoalveolar lavage fluid total protein, lactate dehydrogenase, total cells, and neutrophils were further augmented in offspring (males>females) from dams fed the HFD. Data suggest that maternal and perinatal HFD may enhance the susceptibility of offspring to O3-induced pulmonary injury and that these effects may be sex-specific.

Mechanistic Basis for Obesity-related Increases in Ozone-induced Airway Hyperresponsiveness in Mice

Obesity is a risk factor for asthma, especially nonallergic asthma. Ozone, a common air pollutant, is a nonallergic asthma trigger. Importantly, ozone-induced decrements in lung function are greater in obese and overweight human subjects than in lean individuals. Obese mice also exhibit exaggerated pulmonary responses to ozone. Ozone causes greater increases in pulmonary resistance, in bronchoalveolar lavage neutrophils, and in airway hyperresponsiveness in obese than in lean mice. Our data indicate that IL-33 plays a role in mediating these events. Ozone causes greater release of IL-33 into bronchoalveolar lavage fluid in obese than in lean mice. Furthermore, an antibody blocking the IL-33 receptor, ST2, attenuates ozone-induced airway hyperresponsiveness in obese but not in lean mice. Our data also indicate a complex role for tumor necrosis factor (TNF)-α in obesity-related effects on the response to ozone. In obese mice, genetic deficiency in either TNF-α or TNF-α receptor 2 augments ozone-induced airway hyperresponsiveness, whereas TNF-α receptor 2 deficiency virtually abolishes ozone-induced airway hyperresponsiveness in lean mice. Finally, obesity is known to alter the gut microbiome. In female mice, antibiotics attenuate obesity-related increases in the effect of ozone on airway hyperresponsiveness, possibly by altering microbial production of short-chain fatty acids. Asthma control is often difficult to achieve in obese patients with asthma. Our data suggest that therapeutics directed against IL-33 may ultimately prove effective in these patients. The data also suggest that dietary manipulations and other strategies (prebiotics, probiotics) that alter the microbiome and/or its metabolic products may represent a new frontier for treating asthma in obese individuals.

Augmented Responses to Ozone in Obese Mice Require IL-17A and Gastrin-Releasing Peptide

Ozone and obesity both increase IL-17A in the lungs. In mice, obesity augments the airway hyperresponsiveness and neutrophil recruitment induced by acute ozone exposure. Therefore, we examined the role of IL-17A in obesity-related increases in the response to ozone observed in obese mice. Lean wild-type and obese db/db mice were pretreated with IL-17A-blocking or isotype antibodies, exposed to air or ozone (2 ppm for 3 h), and evaluated 24 hours later. Microarray analysis of lung tissue gene expression was used to examine the mechanistic basis for effects of anti-IL-17A. Compared with lean mice, ozone-exposed obese mice had greater concentrations of BAL IL-17A and greater numbers of pulmonary IL-17A⁺ cells. Ozone-induced increases in BAL IL-23 and CCL20, cytokines important for IL-17A⁺ cell recruitment and activation, were also greater in obese mice. Anti-IL-17A treatment reduced ozone-induced airway hyperresponsiveness toward levels observed in lean mice. Anti-IL-17A treatment also reduced BAL neutrophils in both lean and obese mice, possibly because of reductions in CXCL1. Microarray analysis identified gastrin-releasing peptide (GRP) receptor (Grpr) among those genes that were both elevated in the lungs of obese mice after ozone exposure and reduced after anti-IL-17A treatment. Furthermore, ozone exposure increased BAL GRP to a greater extent in obese than in lean mice, and GRP-neutralizing antibody treatment reduced obesity-related increases in ozone-induced airway hyperresponsiveness and neutrophil recruitment. Our data indicate that IL-17A contributes to augmented responses to ozone in db/db mice. Furthermore, IL-17A appears to act at least in part by inducing expression of Grpr.

Late-onset asthma: current perspectives

Because the pathophysiology of asthma has diverse characteristics, to manage the disease effectively, it is important for clinicians to distinguish among the clinical phenotypes. Among them, adult-onset asthma, that is, late-onset asthma (LOA), is increasing because of the aging of the population. The phenotype of LOA is largely divided into two types according to the presence or absence of eosinophilic inflammation, T-helper (Th)2- and non-Th2-associated LOA. Especially in Th2 LOA related to rhinosinusitis, as pulmonary function at onset is poor and asthma exacerbations occur frequently, it is important to detect this phenotype in the early phase by using a biomarker of Th2-type inflammation such as fractional exhaled nitric oxide (FENO). As non-Th2-LOA is often resistant to corticosteroids, this phenotype often requires another treatment strategy such as macrolide, diet, or smoking cessation. We often struggle with the management of LOA patients due to a lack of evidence; therefore, the elucidation of the mechanism of LOA contributes to increased efficiency of diagnosis and treatment of LOA. Age-related immune system and structural changes are thought to be associated with the pathophysiology of LOA. In the former case, changes in inflammatory cell function such as variations in the innate immune response and acquisition of autoimmunity or upregulation of oxidative stress are thought to be involved in the mechanism. Meanwhile, the latter can also become triggers or exacerbating factors of LOA via enhancement of airway hyperresponsiveness, decline in lung function, increased air trapping, and reduction in chest wall compliance. Therefore, appropriate individualized management in LOA may be possible through precisely assessing the pathophysiology based on age-related functional changes, including the immune and structural system.

Effect of acute ozone exposure on the lung metabolomes of obese and lean mice

Pulmonary responses to the air pollutant, ozone, are increased in obesity. Both obesity and ozone cause changes in systemic metabolism. Consequently, we examined the impact of ozone on the lung metabolomes of obese and lean mice. Lean wildtype and obese db/db mice were exposed to acute ozone (2 ppm for 3 h) or air. 24 hours later, the lungs were excised, flushed with PBS to remove blood and analyzed via liquid-chromatography or gas-chromatography coupled to mass spectrometry for metabolites. Both obesity and ozone caused changes in the lung metabolome. Of 321 compounds identified, 101 were significantly impacted by obesity in air-exposed mice. These included biochemicals related to carbohydrate and lipid metabolism, which were each increased in lungs of obese versus lean mice. These metabolite changes may be of functional importance given the signaling capacity of these moieties. Ozone differentially affected the lung metabolome in obese versus lean mice. For example, almost all phosphocholine-containing lysolipids were significantly reduced in lean mice, but this effect was attenuated in obese mice. Glutathione metabolism was also differentially affected by ozone in obese and lean mice. Finally, the lung metabolome indicated a role for the microbiome in the effects of both obesity and ozone: all measured bacterial/mammalian co-metabolites were significantly affected by obesity and/or ozone. Thus, metabolic derangements in obesity appear to impact the response to ozone.

Ozone Exposure, Cardiopulmonary Health, and Obesity: A Substantive Review

From 1999-2014, obesity prevalence increased among adults and youth. Obese individuals may be uniquely susceptible to the proinflammatory effects of ozone because obese humans and animals have been shown to experience a greater decline in lung function than normal-weight subjects. Obesity is independently associated with limitations in lung mechanics with increased ozone dose. However, few epidemiologic studies have examined the interaction between excess weight and ozone exposure among adults. Using PubMed keyword searches and reference lists, we reviewed epidemiologic evidence to identify potential response-modifying factors and determine if obese or overweight adults are at increased risk of ozone-related health effects. We initially identified 170 studies, of which seven studies met the criteria of examining the interaction of excess weight and ozone exposure on cardiopulmonary outcomes in adults, including four short-term ozone exposure studies in controlled laboratory settings and three community epidemiologic studies. In the studies identified, obesity was associated with decreased lung function and increased inflammatory mediators. Results were inconclusive about the effect modification when data were stratified by sex. Obese and overweight populations should be considered as candidate at-risk groups for epidemiologic studies of cardiopulmonary health related to air pollution exposures. Air pollution is a modifiable risk factor that may decrease lung function among obese individuals with implications for environmental and occupational health policy.

IL-33 Drives Augmented Responses to Ozone in Obese Mice

BACKGROUND

Ozone increases IL-33 in the lungs, and obesity augments the pulmonary effects of acute ozone exposure.

OBJECTIVES

We assessed the role of IL-33 in the augmented effects of ozone observed in obese mice.

METHODS

Lean wildtype and obese db/db mice were pretreated with antibodies blocking the IL-33 receptor, ST2, and then exposed to ozone (2 ppm for 3 hr). Airway responsiveness was assessed, bronchoalveolar lavage (BAL) was performed, and lung cells harvested for flow cytometry 24 hr later. Effects of ozone were also assessed in obese and lean mice deficient in γδ T cells and their wildtype controls.

RESULTS AND DISCUSSION

Ozone caused greater increases in BAL IL-33, neutrophils, and airway responsiveness in obese than lean mice. Anti-ST2 reduced ozone-induced airway hyperresponsiveness and inflammation in obese mice but had no effect in lean mice. Obesity also augmented ozone-induced increases in BAL CXCL1 and IL-6, and in BAL type 2 cytokines, whereas anti-ST2 treatment reduced these cytokines. In obese mice, ozone increased lung IL-13+ innate lymphoid cells type 2 (ILC2) and IL-13+ γδ T cells. Ozone increased ST2+ γδ T cells, indicating that these cells can be targets of IL-33, and γδ T cell deficiency reduced obesity-related increases in the response to ozone, including increases in type 2 cytokines.

CONCLUSIONS

Our data indicate that IL-33 contributes to augmented responses to ozone in obese mice. Obesity and ozone also interacted to promote type 2 cytokine production in γδ T cells and ILC2 in the lungs, which may contribute to the observed effects of IL-33. Citation: Mathews JA, Krishnamoorthy N, Kasahara DI, Cho Y, Wurmbrand AP, Ribeiro L, Smith D, Umetsu D, Levy BD, Shore SA. 2017. IL-33 drives augmented responses to ozone in obese mice. Environ Health Perspect 125:246-253; http://dx.doi.org/10.1289/EHP272.

The administration of a high refined carbohydrate diet promoted an increase in pulmonary inflammation and oxidative stress in mice exposed to cigarette smoke

This study aimed to evaluate the effects of a high refined carbohydrate diet and pulmonary inflammatory response in C57BL/6 mice exposed to cigarette smoke (CS). Twenty-four male mice were divided into four groups: control group (CG), which received a standard diet; cigarette smoke group (CSG), which was exposed to CS; a high refined carbohydrate diet group (RG), which received a high refined carbohydrate diet; and a high refined carbohydrates diet and cigarette smoke group (RCSG), which received a high refined carbohydrate diet and was exposed to CS. The animals were monitored for food intake and body weight gain for 12 weeks. After this period, the CSG and RCSG were exposed to CS for five consecutive days. At the end of the experimental protocol, all animals were euthanized for subsequent analyses. There was an increase of inflammatory cells in the bronchoalveolar lavage fluid (BALF) of CSG compared to CG and RCSG compared to CG, CSG, and RG. In addition, in the BALF, there was an increase of tumor necrosis factor alpha in RCSG compared to CG, CSG, and RG; interferon gamma increase in RCSG compared to the CSG; and increase in interleukin-10 in RCSG compared to CG and RG. Lipid peroxidation increased in RCSG compared to CG, CSG, and RG. Furthermore, the oxidation of proteins increased in CSG compared to CG. The analysis of oxidative stress showed an increase in superoxide dismutase in RCSG compared to CG, CSG, and RG and an increase in the catalase activity in RCSG compared with CG. In addition, there was a decrease in the glutathione reduced/glutathione total ratio of CSG, RG, and RCSG compared to CG. Therefore, the administration of a high refined carbohydrate diet promoted an increase in pulmonary inflammation and oxidative stress in mice exposed to CS.

Obesity, Asthma, and the Microbiome

Obesity is a risk factor for asthma, but standard asthma drugs have reduced efficacy in the obese. Obesity alters the gastrointestinal microbial community structure. This change in structure contributes to some obesity-related conditions and also could be contributing to obesity-related asthma. Although currently unexplored, obesity may also be altering lung microbiota. Understanding the role of microbiota in obesity-related asthma could lead to novel treatments for these patients.

ROCK insufficiency attenuates ozone-induced airway hyperresponsiveness in mice

Ozone causes airway hyperresponsiveness (AHR) and pulmonary inflammation. Rho kinase (ROCK) is a key regulator of smooth muscle cell contraction and inflammatory cell migration. To determine the contribution of the two ROCK isoforms ROCK1 and ROCK2 to ozone-induced AHR, we exposed wild-type, ROCK1(+/-), and ROCK2(+/-) mice to air or ozone (2 ppm for 3 h) and evaluated mice 24 h later. ROCK1 or ROCK2 haploinsufficiency did not affect airway responsiveness in air-exposed mice but significantly reduced ozone-induced AHR, with a greater reduction in ROCK2(+/-) mice despite increased bronchoalveolar lavage (BAL) inflammatory cells in ROCK2(+/-) mice. Compared with wild-type mice, ozone-induced increases in BAL hyaluronan, a matrix protein implicated in ozone-induced AHR, were lower in ROCK1(+/-) but not ROCK2(+/-) mice. Ozone-induced increases in other inflammatory moieties reported to contribute to ozone-induced AHR (IL-17A, osteopontin, TNFα) were not different in wild-type vs. ROCK1(+/-) or ROCK2(+/-) mice. We also observed a dose-dependent reduction in ozone-induced AHR after treatment with the ROCK1/ROCK2 inhibitor fasudil, even though fasudil was administered after induction of inflammation. Ozone increased pulmonary expression of ROCK2 but not ROCK1 or RhoA. A ROCK2 inhibitor, SR3677, reduced contractile forces in primary human airway smooth muscle cells, confirming a role for ROCK2 in airway smooth muscle contraction. Our results demonstrate that ozone-induced AHR requires ROCK. Whereas ROCK1-dependent changes in hyaluronan may contribute to ROCK1's role in O3-induced AHR, the role of ROCK2 is downstream of inflammation, likely at the level of airway smooth muscle contraction.

γδ T Cells Are Required for M2 Macrophage Polarization and Resolution of Ozone-Induced Pulmonary Inflammation in Mice

We examined the role of γδ T cells in the induction of alternatively activated M2 macrophages and the resolution of inflammation after ozone exposure. Wildtype (WT) mice and mice deficient in γδ T cells (TCRδ^-/- mice) were exposed to air or to ozone (0.3 ppm for up to 72h) and euthanized immediately or 1, 3, or 5 days after cessation of exposure. In WT mice, M2 macrophages accumulated in the lungs over the course of ozone exposure. Pulmonary mRNA abundance of the M2 genes, Arg1, Retnla, and Clec10a, also increased after ozone. In contrast, no evidence of M2 polarization was observed in TCRδ^-/- mice. WT but not TCRδ^-/- mice expressed the M2c polarizing cytokine, IL-17A, after ozone exposure and WT mice treated with an IL-17A neutralizing antibody exhibited attenuated ozone-induced M2 gene expression. In WT mice, ozone-induced increases in bronchoalveolar lavage neutrophils and macrophages resolved quickly after cessation of ozone exposure returning to air exposed levels within 3 days. However, lack of M2 macrophages in TCRδ^-/- mice was associated with delayed clearance of inflammatory cells after cessation of ozone and increased accumulation of apoptotic macrophages in the lungs. Delayed restoration of normal lung architecture was also observed in TCRδ^-/- mice. In summary, our data indicate that γδ T cells are required for the resolution of ozone-induced inflammation, likely because γδ T cells, through their secretion of IL-17A, contribute to changes in macrophage polarization that promote clearance of apoptotic cells.

Innate and ozone-induced airway hyperresponsiveness in obese mice: role of TNF-α

Innate airway hyperresponsiveness (AHR) and augmented responses to ozone, an asthma trigger, are characteristics of obese mice. Systemic inflammation, a condition of increased circulating concentrations of inflammatory moieties, occurs in obesity. We hypothesized that TNF-α, via its effects as a master effector of this systemic inflammation, regulates innate AHR and augmented responses to ozone in obese mice. Therefore, we examined pulmonary inflammation and airway responsiveness in unexposed or ozone-exposed (2 ppm for 3 h) lean wild-type and obese Cpe(fat) mice that were TNF-α sufficient or deficient. Cpe(fat) mice lack carboxypeptidase E, which regulates satiety. Compared with wild type, Cpe(fat) mice had elevated serum IL-17A, G-CSF, KC, MCP-1, IL-9, MIG, and leptin, indicating systemic inflammation. Despite reductions in most of these moieties in TNF-α-deficient vs. -sufficient Cpe(fat) mice, we observed no substantial difference in airway responsiveness in these two groups of mice. Ozone-induced increases in bronchoalveolar lavage (BAL) neutrophils and macrophages were lower, but ozone-induced AHR and increases in BAL hyaluronan, osteopontin, IL-13, and protein carbonyls, a marker of oxidative stress, were augmented in TNF-α-deficient vs. -sufficient Cpe(fat) mice. Our data indicate that TNF-α has an important role in promoting the systemic inflammation but not the innate AHR of obesity, suggesting that the systemic inflammation of obesity is not the major driver of this AHR. TNF-α is required for the augmented effects of acute ozone exposure on pulmonary inflammatory cell recruitment in obese mice, whereas TNF-α protects against ozone-induced AHR in obese mice, possibly by suppressing ozone-induced oxidative stress.

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 many faces of asthma in obesity

Obesity is a major risk factor for the development of asthma, and causes severe, uncontrolled disease that responds poorly to therapy. The obese state alters early onset allergic asthma, and leads to the development of a novel form of late onset asthma secondary to obesity. The presentation of early onset allergic asthma is altered through effects on immune function. Factors such as mechanical loading, effects of adipokines on airways, altered diet, insulin resistance and altered metabolism of nitric oxide likely all contribute to increased airway reactivity in obesity, causing late onset asthma in obesity. Obesity also alters responses to environmental factors such as ozone and particulate matter. Focused studies to understand the importance of these factors in the pathogenesis of airway disease in obesity will be essential to develop therapies to intervene in this new epidemic of airway disease.

γδ T cells are required for pulmonary IL-17A expression after ozone exposure in mice: role of TNFα

Ozone is an air pollutant that causes pulmonary symptoms. In mice, ozone exposure causes pulmonary injury and increases bronchoalveolar lavage macrophages and neutrophils. We have shown that IL-17A is important in the recruitment of neutrophils after subacute ozone exposure (0.3 ppm for 24–72 h). We hypothesized that γδ T cells are the main producers of IL-17A after subacute ozone. To explore this hypothesis we exposed wildtype mice and mice deficient in γδ T cells (TCRδ^−/−) to ozone or room air. Ozone-induced increases in BAL macrophages and neutrophils were attenuated in TCRδ^−/− mice. Ozone increased the number of γδ T cells in the lungs and increased pulmonary Il17a mRNA expression and the number of IL-17A⁺ CD45⁺ cells in the lungs and these effects were abolished in TCRδ^−/− mice. Ozone-induced increases in factors downstream of IL-17A signaling, including G-CSF, IL-6, IP-10 and KC were also decreased in TCRδ^−/− versus wildtype mice. Neutralization of IL-17A during ozone exposure in wildtype mice mimicked the effects of γδ T cell deficiency. TNFR2 deficiency and etanercept, a TNFα antagonist, also reduced ozone-induced increases in Il17a mRNA, IL-17A⁺ CD45⁺ cells and BAL G-CSF as well as BAL neutrophils. TNFR2 deficient mice also had decreased ozone-induced increases in Ccl20, a chemoattractant for IL-17A⁺ γδ T cells. Il17a mRNA and IL-17A⁺ γδ T cells were also lower in obese Cpe^fat versus lean WT mice exposed to subacute ozone, consistent with the reduced neutrophil recruitment observed in the obese mice. Taken together, our data indicate that pulmonary inflammation induced by subacute ozone requires γδ T cells and TNFα-dependent recruitment of IL-17A⁺ γδ T cells to the lung.

Pivotal role of IL-6 in the hyperinflammatory responses to subacute ozone in adiponectin-deficient mice

Adiponectin is an adipose-derived hormone with anti-inflammatory activity. Following subacute ozone exposure (0.3 ppm for 24-72 h), neutrophilic inflammation and IL-6 are augmented in adiponectin-deficient (Adipo(-/-)) mice. The IL-17/granulocyte colony-stimulating factor (G-CSF) axis is required for this increased neutrophilia. We hypothesized that elevated IL-6 in Adipo(-/-) mice contributes to their augmented responses to ozone via effects on IL-17A expression. Therefore, we generated mice deficient in both adiponectin and IL-6 (Adipo(-/-)/IL-6(-/-)) and exposed them to ozone or air. In ozone-exposed mice, bronchoalveolar lavage (BAL) neutrophils, IL-6, and G-CSF, and pulmonary Il17a mRNA expression were greater in Adipo(-/-) vs. wild-type mice, but reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice. IL-17A(+) F4/80(+) cells and IL-17A(+) γδ T cells were also reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice exposed to ozone. Only BAL neutrophils were reduced in IL-6(-/-) vs. wild-type mice. In wild-type mice, IL-6 was expressed in Gr-1(+)F4/80(-)CD11c(-) cells, whereas in Adipo(-/-) mice F4/80(+)CD11c(+) cells also expressed IL-6, suggesting that IL-6 is regulated by adiponectin in these alveolar macrophages. Transcriptomic analysis identified serum amyloid A3 (Saa3), which promotes IL-17A expression, as the gene most differentially augmented by ozone in Adipo(-/-) vs. wild-type mice. After ozone, Saa3 mRNA expression was markedly greater in Adipo(-/-) vs. wild-type mice but reduced in Adipo(-/-)/IL-6(-/-) vs. Adipo(-/-) mice. In conclusion, our data support a pivotal role of IL-6 in the hyperinflammatory condition observed in Adipo(-/-) mice after ozone exposure and suggest that this role of IL-6 involves its ability to induce Saa3, IL-17A, and G-CSF.