Ozone-induced airway hyperresponsiveness is reduced in immature mice

Inconsequential role for chemerin-like receptor 1 in the manifestation of ozone-induced lung pathophysiology in male mice

We executed this study to determine if chemerin-like receptor 1 (CMKLR1), a Gi/o protein-coupled receptor expressed by leukocytes and non-leukocytes, contributes to the development of phenotypic features of non-atopic asthma, including airway hyperresponsiveness (AHR) to acetyl-β-methylcholine chloride, lung hyperpermeability, airway epithelial cell desquamation, and lung inflammation. Accordingly, we quantified sequelae of non-atopic asthma in wild-type mice and mice incapable of expressing CMKLR1 (CMKLR1-deficient mice) following cessation of acute inhalation exposure to either filtered room air (air) or ozone (O3), a criteria pollutant and non-atopic asthma stimulus. Following exposure to air, lung elastic recoil and airway responsiveness were greater while the quantity of adiponectin, a multi-functional adipocytokine, in bronchoalveolar lavage (BAL) fluid was lower in CMKLR1-deficient as compared to wild-type mice. Regardless of genotype, exposure to O3 caused AHR, lung hyperpermeability, airway epithelial cell desquamation, and lung inflammation. Nevertheless, except for minimal genotype-related effects on lung hyperpermeability and BAL adiponectin, we observed no other genotype-related differences following O3 exposure. In summary, we demonstrate that CMKLR1 limits the severity of innate airway responsiveness and lung elastic recoil but has a nominal effect on lung pathophysiology induced by acute exposure to O3.

Air pollution and lung function in children

In this narrative review, we summarize the literature and provide updates on recent studies of air pollution exposures and child lung function and lung function growth. We include exposures to outdoor air pollutants that are monitored and regulated through air quality standards, and air pollutants that are not routinely monitored or directly regulated, including wildfires, indoor biomass and coal burning, gas and wood stove use, and volatile organic compounds. Included is a more systematic review of the recent literature on long-term air pollution and child lung function because this is an indicator of future adult respiratory health and exposure assessment tools have improved dramatically in recent years. We present "summary observations" and "knowledge gaps." We end by discussing what is known about what can be done at the individual/household, local/regional, and national levels to overcome structural impediments, reduce air pollution exposures, and improve child lung function. We found a large literature on adverse air pollution effects on children's lung function level and growth; however, many questions remain. Important areas needing further research include whether early-life effects are fixed or reversible; and what are windows of increased susceptibility, long-term effects of repeated wildfire events, and effects of air quality interventions.

Sex Modifies Acute Ozone-Mediated Airway Physiologic Responses

Sex differences clearly exist in incidence, susceptibility, and severity of airway disease and in pulmonary responses to air pollutants such as ozone (O3). Prior rodent O3 exposure studies demonstrate sex-related differences in the expression of lung inflammatory mediators and signaling. However, whether or not sex modifies O3-induced airway physiologic responses remains less explored. To address this, we exposed 8- to 10-week-old male and female C57BL/6 mice to either 1 or 2 ppm O3 or filtered air (FA) for 3 h. At 12, 24, 48, and 72 h following exposure, we assessed airway hyperresponsiveness to methacholine (MCh), bronchoalveolar lavage fluid cellularity, cytokines and total protein/albumin, serum progesterone, and whole lung immune cells by flow cytometry. Male mice generated consistent airway hyperresponsiveness to MCh at all time points following exposure. Alternatively, females had less consistent airway physiologic responses to MCh, which were more variable between individual experiments and did not correlate with serum progesterone levels. Bronchoalveolar lavage fluid total cells peaked at 12 h and were persistently elevated through 72 h. At 48 h, bronchoalveolar lavage cells were greater in females versus males. Bronchoalveolar lavage fluid cytokines and total protein/albumin increased following O3 exposure without sex differences. Flow cytometry of whole lung tissue identified dynamic O3-induced immune cell changes also independent of sex. Our results indicate sex differences in acute O3-induced airway physiology responses and airspace influx without significant difference in other injury and inflammation measures. This study highlights the importance of considering sex as a biological variable in acute O3-induced airway physiology responses.

The interleukin-33 receptor contributes to pulmonary responses to ozone in male mice: role of the microbiome

BACKGROUND

Interleukin-33 is released in the airways following acute ozone exposure and has the ability to cause airway hyperresponsiveness, a defining feature of asthma. Ozone causes greater airway hyperresponsiveness in male than female mice. Moreover, sex differences in the gut microbiome account for sex differences in this response to ozone. The purpose of this study was to determine whether there were sex differences in the role of interleukin-33 in ozone-induced airway hyperresponsiveness and to examine the role of the microbiome in these events.

METHODS

Wildtype mice and mice genetically deficient in ST2, the interleukin-33 receptor, were housed from weaning with either other mice of the same genotype and sex, or with mice of the same sex but opposite genotype. At 15 weeks of age, fecal pellets were harvested for 16S rRNA sequencing and the mice were then exposed to air or ozone. Airway responsiveness was measured and a bronchoalveolar lavage was performed 24 h after exposure.

RESULTS

In same-housed mice, ozone-induced airway hyperresponsiveness was greater in male than female wildtype mice. ST2 deficiency reduced ozone-induced airway hyperresponsiveness in male but not female mice and abolished sex differences in the response to ozone. However, sex differences in the role of interleukin-33 were unrelated to type 2 cytokine release: ozone-induced increases in bronchoalveolar lavage interleukin-5 were greater in females than males and ST2 deficiency virtually abolished interleukin-5 in both sexes. Since gut microbiota contribute to sex differences in ozone-induced airway hyperresponsiveness, we examined the role of the microbiome in these ST2-dependent sex differences. To do so, we cohoused wildtype and ST2 deficient mice, a situation that allows for transfer of microbiota among cage-mates. Cohousing altered the gut microbial community structure, as indicated by 16S rRNA gene sequencing of fecal DNA and reversed the effect of ST2 deficiency on pulmonary responses to ozone in male mice.

CONCLUSIONS

The data indicate that the interleukin-33 /ST2 pathway contributes to ozone-induced airway hyperresponsiveness in male mice and suggest that the role of interleukin-33 is mediated at the level of the gut microbiome.

TRPC6 modulates adhesion of neutrophils to airway epithelial cells via NF-κB activation and ICAM-1 expression with ozone exposure

Ozone (O₃) is a major component of air pollution, which has been associated with airway inflammation characterized by the influx of neutrophils in asthmatic subjects. Canonical transient receptor potential 6 (TRPC6) channel is recently identified as a target of oxidative stress which is involved in airway inflammation. However, the regulatory role of TRPC6 in airway epithelial cells and neutrophils has not yet been illuminated in detail. In this study, we investigated the role of TRPC6 in neutrophil adhesion to airway epithelial cells exposed to O₃ in vivo and in vitro approaches. Using transgenic mice, the results showed that TRPC6-deficiency attenuated O₃-induced neutrophil recruitment to airway epithelial cells and intercellular adhesion molecule-1 (ICAM-1) expression. In vitro, O₃ induced ICAM-1 expression and neutrophil adhesion to 16HBE cells (human airway epithelial cell line) and which were reduced by both TRPC6 silencing short hairpin RNA (shRNA) and TRPC6 inhibitor Larixyl Acetate (LA). We also confirmed that TRPC6-dependent Ca²⁺ entry and NF-κB activation in 16HBE cells were required for ICAM-1-mediated neutrophil adhesion exposed to O₃. In conclusion, this study demonstrated the contribution of TRPC6 to O₃-induced neutrophil adhesion to airway epithelial cells via NF-κB activation and ICAM-1 expression, which may provide new potential concepts for preventing and treating air pollutant-related inflammatory lung diseases.

The lung response to ozone is determined by age and is partially dependent on toll-Like receptor 4

Background

Ozone pollution has adverse effects on respiratory health in children and adults. This study was carried out in the mouse model to investigate the influence of age and to define the role of toll-like receptor four (TLR4) in the lung response to ozone exposure during postnatal development.

Methods

Female mice (1 to 6 weeks of age) were exposed for 3 h to ozone (1 part per million) or filtered air. Analyses were carried out at six and 24 h after completion of exposure, to assess the effects on lung permeability, airway neutrophilia, expression of antioxidants and chemokines, and mucus production. The role of TLR4 was defined by examining TLR4 expression in the lung during development, and by investigating the response to ozone in tlr4-deficient mice.

Results

Metallothionein-1, calcitonin gene-related product, and chemokine C-X-C ligand (CXCL) five were consistent markers induced by ozone throughout development. Compared with adults, neonates expressed lower levels of pulmonary TLR4 and responded with increased mucus production, and developed an attenuated response to ozone characterized by reduced albumin leakage and neutrophil influx into the airways, and lower expression of CXCL1 and CXCL2 chemokines. Examination of the responses in tlr4-deficient mice indicated that ozone-mediated airway neutrophilia, but not albumin leakage or mucus production were dependent on TLR4.

Conclusions

Collectively, the data demonstrate that the response to ozone is determined by age and is partially dependent on TLR4 signaling. The reduced responsiveness of the neonatal lung to ozone may be due at least in part to insufficient pulmonary TLR4 expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0279-2) contains supplementary material, which is available to authorized users.

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.

Ozone exposure initiates a sequential signaling cascade in airways involving interleukin-1beta release, nerve growth factor secretion, and substance P upregulation

Previous studies demonstrated that interleukin-1β (IL-1β) and nerve growth factor (NGF) increase synthesis of substance P (SP) in airway neurons both after ozone (O3) exposure and by direct application. It was postulated that NGF mediates O3-induced IL-1β effects on SP. The current study specifically focused on the influence of O3 on IL-1β, NGF, and SP levels in mice bronchoalveolar lavage fluid (BALF) and whether these mediators may be linked in an inflammatory-neuronal cascade in vivo. The findings showed that in vivo O3 exposure induced an increase of all three proteins in mouse BALF and that O3-induced elevations in both NGF and SP are mediated by the inflammatory cytokine IL-1β. Further, inhibition of NGF reduced O3 induced increases of SP in both the lung BALF and lung tissue, demonstrating NGF serves as a mediator of IL-1β effects on SP. These data indicate that IL-1β is an early mediator of O3-induced rise in NGF and subsequent SP release in mice in vivo.

Role of the adiponectin binding protein, T-cadherin (cdh13), in pulmonary responses to subacute ozone

Adiponectin, an adipose derived hormone with pleiotropic functions, binds to several proteins, including T-cadherin. We have previously reported that adiponectin deficient (Adipo(-/-)) mice have increased IL-17A-dependent neutrophil accumulation in their lungs after subacute exposure to ozone (0.3 ppm for 72 hrs). The purpose of this study was to determine whether this anti-inflammatory effect of adiponectin required adiponectin binding to T-cadherin. Wildtype, Adipo(-/-) , T-cadherin deficient (T-cad(-/-) ), and bideficient (Adipo(-/-)/T-cad(-/-) ) mice were exposed to subacute ozone or air. Compared to wildtype mice, ozone-induced increases in pulmonary IL-17A mRNA expression were augmented in T-cad(-/-) and Adipo(-/-) mice. Compared to T-cad(-/-) mice, there was no further increase in IL-17A in Adipo(-/-)/T-cad(-/-) mice, indicating that adiponectin binding to T-cadherin is required for suppression of ozone-induced IL-17A expression. Similar results were obtained for pulmonary mRNA expression of saa3, an acute phase protein capable of inducing IL-17A expression. Comparison of lung histological sections across genotypes also indicated that adiponectin attenuation of ozone-induced inflammatory lesions at bronchiolar branch points required T-cadherin. BAL neutrophils and G-CSF were augmented in T-cad(-/-) mice and further augmented in Adipo(-/-)/T-cad(-/-) mice. Taken together with previous observations indicating that augmentation of these moieties in ozone exposed Adipo(-/-) mice is partially IL-17A dependent, the results indicate that effects of T-cadherin deficiency on BAL neutrophils and G-CSF are likely secondary to changes in IL-17A, but that adiponectin also acts via T-cadherin independent pathways. Our results indicate that T-cadherin is required for the ability of adiponectin to suppress some but not all aspects of ozone-induced pulmonary inflammation.

T-cell immunoglobulin and mucin domain 1 deficiency eliminates airway hyperreactivity triggered by the recognition of airway cell death

BACKGROUND

Studies of asthma have been limited by a poor understanding of how nonallergic environmental exposures, such as air pollution and infection, are translated in the lung into inflammation and wheezing.

OBJECTIVE

Our goal was to understand the mechanism of nonallergic asthma that leads to airway hyperreactivity (AHR), a cardinal feature of asthma independent of adaptive immunity.

METHOD

We examined mouse models of experimental asthma in which AHR was induced by respiratory syncytial virus infection or ozone exposure using mice deficient in T-cell immunoglobulin and mucin domain 1 (TIM1/HAVCR1), an important asthma susceptibility gene.

RESULTS

TIM1(-/-) mice did not have airways disease when infected with RSV or when repeatedly exposed to ozone, a major component of air pollution. On the other hand, the TIM1(-/-) mice had allergen-induced experimental asthma, as previously shown. The RSV- and ozone-induced pathways were blocked by treatment with caspase inhibitors, indicating an absolute requirement for programmed cell death and apoptosis. TIM-1-expressing, but not TIM-1-deficient, natural killer T cells responded to apoptotic airway epithelial cells by secreting cytokines, which mediated the development of AHR.

CONCLUSION

We defined a novel pathway in which TIM-1, a receptor for phosphatidylserine expressed by apoptotic cells, drives the development of asthma by sensing and responding to injured and apoptotic airway epithelial cells.

Impact of aging on pulmonary responses to acute ozone exposure in mice: role of TNFR1

CONTEXT

Chamber studies in adult humans indicate reduced responses to acute ozone with increasing age. Age-related changes in TNFα have been observed. TNFα induced inflammation is predominantly mediated through TNFR1.

OBJECTIVE

To examine the impact of aging on inflammatory responses to acute ozone exposure in mice and determine the role of TNFR1 in age-related differences.

MATERIALS AND METHODS

Wildtype and TNFR1 deficient (TNFR1(-/-)) mice aged 7 or 39 weeks were exposed to ozone (2 ppm for 3 h). Four hours after exposure, bronchoalveolar lavage (BAL) was performed and BAL cells, cytokines, chemokines, and protein were examined.

RESULTS

Ozone-induced increases in BAL neutrophils and in neutrophil chemotactic factors were lower in 39- versus 7-week-old wildtype, but not (TNFR1(-/-)) mice. There was no effect of TNFR1 genotype in 7-week-old mice, but in 39-week-old mice, BAL neutrophils and BAL concentrations of MCP-1, KC, MIP-2, IL-6 and IP-10 were significantly greater following ozone exposure in TNFR1(-/-) versus wildtype mice. BAL concentrations of the soluble form of the TNFR1 receptor (sTNFR1) were substantially increased in 39-week-old versus 7-week-old mice, regardless of exposure.

DISCUSSION AND CONCLUSION

The data suggest that increased levels of sTNFR1 in the lungs of the 39-week-old mice may neutralize TNFα and protect these older mice against ozone-induced inflammation.

Structure-activity relationships in rodent diaphragm muscle fibers vs. neuromuscular junctions

The diaphragm muscle (DIAm) is a highly active muscle of mixed fiber type composition. We hypothesized that consistent with greater activation history and proportion of fatigue-resistant fibers, neuromuscular transmission failure is lower in the mouse compared to the rat DIAm, and that neuromuscular junction (NMJ) morphology will match their different functional demands. Minute ventilation and duty cycle were higher in the mouse than in the rat. The proportion of fatigue-resistant fibers was similar in the rat and mouse; however the contribution of fatigue-resistant fibers to total DIAm mass was higher in the mouse. Neuromuscular transmission failure was less in mice than in rats. Motor end-plate area differed across fibers in rat but not in mouse DIAm, where NMJs displayed greater complexity overall. Thus, differences across species in activation history and susceptibility to neuromuscular transmission failure are reflected in the relative contribution of fatigue resistant muscle fibers to total DIAm mass, but not in type-dependent morphological differences at the NMJ.

Ambient ozone and pulmonary innate immunity

Ambient ozone is a criteria air pollutant that impacts both human morbidity and mortality. The effect of ozone inhalation includes both toxicity to lung tissue and alteration of the host immunologic response. The innate immune system facilitates immediate recognition of both foreign pathogens and tissue damage. Emerging evidence supports that ozone can modify the host innate immune response and that this response to inhaled ozone is dependent on genes of innate immunity. Improved understanding of the complex interaction between environmental ozone and host innate immunity will provide fundamental insight into the pathogenesis of inflammatory airways disease. We review the current evidence supporting that environmental ozone inhalation: (1) modifies cell types required for intact innate immunity, (2) is partially dependent on genes of innate immunity, (3) primes pulmonary innate immune responses to LPS, and (4) contributes to innate-adaptive immune system cross-talk.

Biochemical effects of ozone on asthma during postnatal development

BACKGROUND

Ozone exposure during early life has the potential to contribute to the development of asthma as well as to exacerbate underlying allergic asthma.

SCOPE OF REVIEW

Developmentally regulated aspects of sensitivity to ozone exposure and downstream biochemical and cellular responses.

MAJOR CONCLUSIONS

Developmental differences in antioxidant defense responses, respiratory physiology, and vulnerabilities to cellular injury during particular developmental stages all contribute to disparities in the health effects of ozone exposure between children and adults.

GENERAL SIGNIFICANCE

Ozone exposure has the capacity to affect multiple aspects of the "effector arc" of airway hyperresponsiveness, ranging from initial epithelial damage and neural excitation to neural reprogramming during infancy. This article is part of a Special Issue entitled: Biochemistry of Asthma.

Onset of obesity in carboxypeptidase E-deficient mice and effect on airway responsiveness and pulmonary responses to ozone

When compared with lean, wild-type mice, obese Cpefat mice, 14 wk of age and older, manifest innate airway hyperresponsiveness (AHR) to intravenous methacholine and enhanced pulmonary inflammation following acute exposure to ozone (O3). The purpose of this study was to examine the onset of these augmented pulmonary responses during the onset of obesity. Thus airway responsiveness and O3-induced pulmonary inflammation and injury were examined in 7- and 10-wk-old Cpefat and age-matched, wild-type, C57BL/6 mice. Compared with age-matched controls, 7- and 10-wk-old Cpefat mice were approximately 25 and 61% heavier, respectively. Airway responsiveness to intravenous methacholine was assessed via forced oscillation in unexposed Cpefat and wild-type mice. The 10- but not 7-wk-old Cpefat mice exhibited innate AHR. O3 exposure (2 ppm for 3 h) increased markers of pulmonary inflammation and injury in the bronchoalveolar lavage fluid of all mice. However, most markers were greater in Cpefat vs. wild-type mice, regardless of age. Serum levels of leptin, a satiety hormone and proinflammatory cytokine, were increased in Cpefat vs. wild-type mice of both age groups, but the serum levels of other systemic inflammatory markers were greater only in 10-wk-old Cpefat vs. wild-type mice. These results demonstrate that a 25% increase in body weight is sufficient to augment pulmonary responses to O3, but innate AHR is not manifest until the mice become much heavier. These results suggest that the mechanistic bases for these responses are different and may develop according to the nature and degree of the chronic systemic inflammation that is present.

Maternal exposure to particulate matter increases postnatal ozone-induced airway hyperreactivity in juvenile mice

RATIONALE

Epidemiologic studies implicate air pollutant exposure during pregnancy as a risk factor for wheezing in offspring. Ozone exposure is linked to exacerbations of wheezing in children.

OBJECTIVES

To determine if maternal pulmonary exposure to traffic-related particles during pregnancy augments ozone-induced airway hyperresponsiveness in offspring.

METHODS

C57BL6 time-mated mice were given NIST SRM#1648 (particulate matter [PM]) 0.48 mg, saline vehicle, or no treatment by tracheal insufflation twice weekly for 3 weeks. PM exposure augmented maternal lung inflammation and placental TNF-alpha, Keratinocyte-derived cytokine (KC), and IL-6 (measured at gestation Day 18). After parturition, dams and litters were exposed to air or ozone 1 ppm 3 h/d, every other day, thrice weekly for 4 weeks. Respiratory system resistance in pups was measured at baseline and after administration of nebulized methacholine.

MEASUREMENTS AND MAIN RESULTS

Ozone increased airway hyperresponsiveness, but the increase was greatest in pups born to PM-treated dams. Whole-lung TNF-alpha, IL-1beta, KC, IL-6, and MCP-1 were increased in ozone-treated pups, with the greatest increase in pups born to dams given PM. Airway epithelial mucous metaplasia estimated by periodic acid-Schiff Alcian blue staining was increased in ozone-exposed pups born to PM-treated dams. Alveolar development, determined by morphometry, and airway smooth muscle bulk, estimated using alpha-actin histochemistry, were unaffected by prenatal or postnatal treatment.

CONCLUSIONS

Maternal pulmonary exposure to PM during pregnancy augments placental cytokine expression and postnatal ozone-induced pulmonary inflammatory cytokine responses and ozone-induced airway hyperresponsiveness without altering airway structure.

Ozone modulates IL-6 secretion in human airway epithelial and smooth muscle cells

Although ozone enhances leukocyte function and recruitment in airways, the direct effect of ozone in modulating structural cell-derived inflammatory mediators remains unknown. Using a coculture model comprised of differentiated human airway epithelial cells (NHBE) and smooth muscle cells (ASM), we postulate that ozone regulates IL-6 secretion in basal and cytokine-primed structural cells. Air-liquid interface (ALI) cultures of NHBE cells underwent differentiation as determined by mucin secretion, transepithelial electrical resistance (TEER), and ultrastructure parameters. Whereas TNF enhanced basal secretion of IL-6 (57 +/- 3%), ozone exposure at 0.6 ppm for 6 h augmented IL-6 levels in basal (41 +/- 3%) and TNF- (50 +/- 5%) primed cocultures compared with that derived from NHBE or ASM monolayers alone. Levels of PGE(2), 6-keto-PGF(1alpha), PGF(2alpha), and thromboxane B(2) (TxB(2)) levels in basal and TNF-primed cocultures revealed that ozone selectively enhanced PGE(2) production in TNF- (6 +/- 3-fold) primed cocultures, with little effect (P > 0.05) on diluent-treated cultures. In accordance with ozone-induced increases in PGE(2) levels, cyclooxygenase inhibition with indomethacin partially abolished IL-6 secretion. Surprisingly, indomethacin had little effect on constitutive secretion of IL-6 in cocultures, whereas indomethacin completely restored ozone-mediated TEER reduction in TNF-primed cocultures. Collectively, our data for the first time suggest a dual role of ozone in modulating IL-6 secretion and TEER outcomes in a PGE(2)-dependent (in presence of TNF stimulus) and -independent manner (in absence of cytokine stimulus).

Role of p38 mitogen-activated protein kinase in ozone-induced airway hyperresponsiveness and inflammation

Ozone is a potent oxidant and causes airway hyperresponsiveness and neutrophilia. To determine the role of p38 mitogen-activated protein kinase (MAPK) activation, we studied the effect of a p38alpha inhibitor SD-282 (Scios Inc, Fremont, CA USA) on ozone-induced airway hyperresponsiveness and neutrophilia. Balb/c mice received SD-282 (30 or 90 mg/kg i.p) or vehicle 1 h before exposure to either ozone (3 ppm, 3 h) or air. Three hours after exposure, lungs were analysed for cytokine levels and bronchoalveolar lavage was performed. Another set of mice were dosed 6 h after exposure and 1 h before assessing airway hyperresponsiveness. SD-282 (90 mg/kg) significantly inhibited ozone-induced airway hyperresponsiveness (-LogPC(150): SD-282: -1.73+/-0.14 vs. vehicle: -0.99+/-0.15, P<0.05). Bronchoalveolar lavage neutrophil numbers were time-dependently increased in vehicle-dosed, ozone-exposed mice, greatest at 20-24 h after exposure. SD-282 (30 and 90 mg/kg) significantly inhibited ozone induced neutrophil numbers at 3 h and 20-24 h after ozone SD-282 significantly inhibited ozone-induced increases in phosphorylated p38 MAPK expression, and in cyclooxygenase-2 (COX-2), interleukin-6 (IL-6) and IL-1beta but not MIP-1alpha gene expression. We conclude that p38 MAPK is involved in ozone-induced airway hyperresponsiveness and lung neutrophilia. Inhibition of p38 MAPK with small molecule kinase inhibitors may be a means of reducing ozone-induced inflammation and airway hyperresponsiveness.

No effect of metformin on the innate airway hyperresponsiveness and increased responses to ozone observed in obese mice

We have previously reported that obese db/db mice exhibit innate airway hyperresponsiveness. These mice also have enhanced inflammatory responses to ozone, a common air pollutant that exacerbates asthma. Since db/db mice are diabetic as well as obese, the purpose of the present study was to determine whether metformin, an antihyperglycemic agent, alters the pulmonary phenotype of db/db mice. Lean wild-type (C57BL/6J) and obese db/db mice were treated by gavage with water or metformin (300 microg/g) once a day for 2 wk. Twenty-four hours after the last treatment, in mice of both genotypes, we either measured airway responsiveness to methacholine by forced oscillation, or we exposed the mice to ozone (2 parts per million for 3 h) and examined the ensuing inflammatory response. Compared with water, treatment with metformin caused a significant decrease in fasting blood glucose in obese mice. Airway responsiveness was increased in db/db versus wild-type mice, but metformin did not affect responsiveness in either group. Four hours after exposure to ozone, there was a significant increase in bronchoalveolar lavage fluid neutrophils and chemokines in mice of both genotypes, but the magnitude of these changes was greater in db/db than wild-type mice. Metformin did not affect ozone-induced inflammation in mice of either genotype. The results indicate that hyperglycemia is unlikely to account for the pulmonary phenotype of obese mice.

Ozone exposure in a mouse model induces airway hyperreactivity that requires the presence of natural killer T cells and IL-17

Exposure to ozone, which is a major component of air pollution, induces a form of asthma that occurs in the absence of adaptive immunity. Although ozone-induced asthma is characterized by airway neutrophilia, and not eosinophilia, it is nevertheless associated with airway hyperreactivity (AHR), which is a cardinal feature of asthma. Because AHR induced by allergens requires the presence of natural killer T (NKT) cells, we asked whether ozone-induced AHR had similar requirements. We found that repeated exposure of wild-type (WT) mice to ozone induced severe AHR associated with an increase in airway NKT cells, neutrophils, and macrophages. Surprisingly, NKT cell-deficient (CD1d(-/-) and Jalpha18(-/-)) mice failed to develop ozone-induced AHR. Further, treatment of WT mice with an anti-CD1d mAb blocked NKT cell activation and prevented ozone-induced AHR. Moreover, ozone-induced, but not allergen-induced, AHR was associated with NKT cells producing interleukin (IL)-17, and failed to occur in IL-17(-/-) mice nor in WT mice treated with anti-IL-17 mAb. Thus, ozone exposure induces AHR that requires the presence of NKT cells and IL-17 production. Because NKT cells are required for the development of two very disparate forms of AHR (ozone- and allergen-induced), our results strongly suggest that NKT cells mediate a unifying pathogenic mechanism for several distinct forms of asthma, and represent a unique target for effective asthma therapy.

Role of TLR2, TLR4, and MyD88 in murine ozone-induced airway hyperresponsiveness and neutrophilia

Exposure to air pollutants such as ozone (O(3)) induces airway hyperresponsiveness (AHR) and airway inflammation. Toll-like receptors (TLR) are first-line effector molecules in innate immunity to infections and signal via adapter proteins, including myeloid differentiation factor-88 (MyD88). We investigated the sensing of ozone by TLR2, TLR4, and MyD88. Ozone induced AHR in wild-type (WT) C57BL/6 mice, but AHR was absent in TLR2(-/-), TLR4(-/-), and MyD88(-/-) mice. Bronchoalveolar lavage neutrophilia induced by ozone was inhibited at 3 h but not at 24 h in TLR2(-/-) and TLR4(-/-) mice, while in MyD88(-/-) mice, this was inhibited at 24 h. We investigated the expression of inflammatory cytokines and TLR2, TLR4, and MyD88 in these mice. Ozone induced time-dependent increases in inflammatory gene expression of keratinocyte chemoattractant (KC) and IL-6 and of TLR2, TLR4, and MyD88 in WT mice. IL-6 and KC expression induced by ozone was inhibited in TLR2(-/-), TLR4(-/-), and MyD88(-/-) mice. Expression of MyD88 was increased in TLR2(-/-) and TLR4(-/-) mice, while induction of TLR2 or TLR4 was reduced in TLR2(-/-) and TLR4(-/-) mice, respectively. TLR2 and TLR4 mediate AHR induced by oxidative stress such as ozone, while the adapter protein MyD88, but not TLR2 or TLR4, is important in mediating ozone-induced neutrophilia. TLR2 and TLR4 may also be important in regulating the speed of neutrophilic response. Therefore, ozone may induce murine AHR and neutrophilic inflammation through the activation of the Toll-like receptor pathway that may sense noninfectious stimuli such as oxidative stress.

Type I interleukin-1 receptor is required for pulmonary responses to subacute ozone exposure in mice

Interleukin (IL)-1, a proinflammatory cytokine, is expressed in the lung after ozone (O(3)) exposure. IL-1 mediates its effects through the type I IL-1 receptor (IL-1RI), the only signaling receptor for both IL-1alpha and IL-1beta. The purpose of this study was to determine the role of IL-1RI in pulmonary responses to O(3.) To that end, wild-type, C57BL/6 (IL-1RI(+/+)) mice and IL-1RI-deficient (IL-1RI(-/-)) mice were exposed to O(3) either subacutely (0.3 ppm for 72 h) or acutely (2 ppm for 3 h). Subacute O(3) exposure increased bronchoalveolar lavage fluid (BALF) protein, interferon-gamma-inducible protein (IP)-10, soluble tumor necrosis factor receptor 1 (sTNFR1), and neutrophils in IL-1RI(+/+) and IL-1RI(-/-) mice. With the exception of IP-10, all outcome indicators were reduced in IL-1RI(-/-) mice. Furthermore, subacute O(3) exposure increased IL-6 mRNA expression in IL-1RI(+/+), but not IL-1RI(-/-) mice. Acute (2 ppm) O(3) exposure increased BALF protein, IL-6, eotaxin, KC, macrophage inflammatory protein (MIP)-2, IP-10, monocyte chemotactic protein-1, sTNFR1, neutrophils, and epithelial cells in IL-1RI(+/+) and IL-1RI(-/-) mice. For IL-6, eotaxin, MIP-2, and sTNFR1, there were small but significant reductions of these outcome indicators in IL-1RI(-/-) versus IL-1RI(+/+) mice at 6 hours after exposure, but not at other time points, whereas other outcome indicators were unaffected by IL-1RI deficiency. These results suggest that IL-1RI is required for O(3)-induced pulmonary inflammation during subacute O(3) exposure, but plays a more minor role during acute O(3) exposure. In addition, these results suggest that the induction of IL-6 via IL-1RI may be important in mediating the effects of O(3) during subacute exposure.

Attenuation of ozone-induced airway inflammation and hyper-responsiveness by c-Jun NH2 terminal kinase inhibitor SP600125

Ozone has potent oxidizing properties, and exposure to ozone causes airway hyper-responsiveness (AHR) and lung inflammation. We determined the importance of c-Jun NH(2) terminal kinase (JNK), a member of the mitogen-activated protein kinase pathway, in ozone-induced AHR and inflammation. SP600125 [anthra[1,9-cd] pyrazol-6 (2H)-one], a specific JNK inhibitor (30 mg/kg) or vehicle, was administered by intraperitoneal injection before and after ozone exposure (3 ppm for 3 h). SP600125 significantly reduced total cells, and neutrophils in bronchoalveolar fluid recovered at 20 to 24 h after exposure and inhibited ozone-induced AHR. Ozone exposure induced activation of JNK in the lung as measured by the expression of phosphorylated-c-Jun, an effect abolished by SP600125. Gene-microarray analysis revealed that ozone increased the expression of over 400 genes by more than 2-fold, including interleukin-6 (IL-6), CXCL1 (keratinocyte cytokine), and CCL2 (monocyte chemoattractant protein-1). SP600125 modulated the expression of a subset of 29 ozone-induced genes; IL-6 and CCL2 expression were further increased, whereas the expression of metallothionein 1, hemopexin, and mitogen-activated 3 kinase 6 was decreased in SP600125-treated ozone-exposed mice. Changes in mRNA for IL-6, CXCL1, and CCL2 were confirmed by real-time polymerase chain reaction. Ozone also decreased the expression of over 500 genes, with the most potent effect on angiopoietin-1. SP600125 modulated the expression of 15 of these genes, and in particular, SP600125 reversed ozone-induced decrease in expression of the redox-sensitive transcription factor, hypoxia-induced factor-1alpha. This study highlights an important role for JNK in response to oxidative stress through modulation of specific inflammatory and redox mediators. Inhibition of JNK with small molecule kinase inhibitors may be a means of reducing ozone-induced inflammation and AHR.

Pulmonary responses to acute ozone exposure in fasted mice: effect of leptin administration

Leptin is a satiety hormone that also has proinflammatory effects, including augmentation of ozone-induced pulmonary inflammation. The purpose of this study was to determine whether reductions in endogenous levels of leptin can attenuate pulmonary responses to ozone. To reduce serum leptin, we fasted mice overnight before ozone exposure. Fasting caused a marked reduction in serum leptin to approximately one-sixth the levels observed in fed mice, and continuous infusion of leptin via Alzet micro-osmotic pumps restored serum leptin to, but not above, fed levels. Ozone exposure (2 ppm for 3 h) caused a significant, ∼40% increase in pulmonary resistance ( P < 0.01) and increased airway responsiveness in fasted but not in fed mice. The increased effect of ozone on pulmonary mechanics and airway responsiveness in fasted mice was not observed when leptin was restored via continuous infusion. Ozone exposure caused pulmonary inflammation, as evident by increases in bronchoalveolar lavage cells, protein, and soluble tumor necrosis factor receptors. There was no effect of fasting status on ozone-induced changes in the bronchoalveolar lavage inflammatory profile, and leptin treatment did not alter these responses. Our results indicate that fasting augments ozone-induced changes in pulmonary mechanics and airway responsiveness in mice. These effects of fasting are the result of declines in serum leptin. The mechanistic basis for this protective effect of leptin in fasted mice remains to be determined but is not related to effects on ozone-induced inflammation.

Restrained whole body plethysmography for measure of strain-specific and allergen-induced airway responsiveness in conscious mice

The mouse is the most extensively studied animal species in respiratory research, yet the technologies available to assess airway function in conscious mice are not universally accepted. We hypothesized that whole body plethysmography employing noninvasive restraint (RWBP) could be used to quantify specific airway resistance (sRaw-RWBP) and airway responsiveness in conscious mice. Methacholine responses were compared using sRaw-RWBP vs. airway resistance by the forced oscillation technique (Raw-FOT) in groups of C57, A/J, and BALB/c mice. sRaw-RWBP was also compared with sRaw derived from double chamber plethysmography (sRaw-DCP) in BALB/c. Finally, airway responsiveness following allergen challenge in BALB/c was measured using RWBP. sRaw-RWBP in C57, A/J, and BALB/c mice was 0.51 +/- 0.03, 0.68 +/- 0.03, and 0.63 +/- 0.05 cm/s, respectively. sRaw derived from Raw-FOT and functional residual capacity (Raw*functional residual capacity) was 0.095 cm/s, approximately one-fifth of sRaw-RWBP in C57 mice. The intra- and interanimal coefficients of variations were similar between sRaw-RWBP (6.8 and 20.1%) and Raw-FOT (3.4 and 20.1%, respectively). The order of airway responsiveness employing sRaw-RWBP was AJ > BALBc > C57 and for Raw-FOT was AJ > BALB/c = C57. There was no difference between the airway responsiveness assessed by RWBP vs. DCP; however, baseline sRaw-RWBP was significantly lower than sRaw-DCP. Allergen challenge caused a progressive decrease in the provocative concentration of methacholine that increased sRaw to 175% postsaline values based on sRaw-RWBP. In conclusion, the technique of RWBP was rapid, reproducible, and easy to perform. Airway responsiveness measured using RWBP, DCP, and FOT was equivalent. Allergen responses could be followed longitudinally, which may provide greater insight into the pathogenesis of chronic airway disease.

Augmented responses to ozone in obese carboxypeptidase E-deficient mice

We reported previously that mice obese as a result of leptin deficiency (ob/ob) have enhanced ozone (O3)-induced airway hyperresponsiveness (AHR) and inflammation compared with wild-type (C57BL/6) controls. To determine whether this increased response to O3 was independent of the modality of obesity, we examined O3-induced AHR and inflammation in Cpe(fat) mice. These mice are obese as a consequence of a mutation in the gene encoding carboxypeptidase E (Cpe), an enzyme important in processing prohormones and proneuropeptides involved in satiety and energy expenditure. Airway responsiveness to intravenous methacholine, measured by forced oscillation, was increased in Cpe(fat) vs. wild-type mice after air exposure. In addition, compared with air exposure, airway responsiveness was increased 24 h after O3 exposure (2 ppm for 3 h) in Cpe(fat) but not in wild-type mice. Compared with air-exposed controls, O3 exposure increased bronchoalveolar lavage fluid (BALF) protein, IL-6, KC, MIP-2, MCP-1, and soluble TNF receptors (sTNFR1 and sTNFR2) as well as BALF neutrophils. With the exception of sTNFR1 and sTNFR2, all of these outcome indicators were greater in Cpe(fat) vs. wild-type mice. Serum sTNFR1, sTNFR2, MCP-1, leptin, and blood leukocytes were elevated in Cpe(fat) compared with wild-type mice even in the absence of O3 exposure, similar to the chronic systemic inflammation observed in human obesity. These results indicate that increased O3-induced AHR and inflammation are consistent features of obese mice, regardless of the modality of obesity. These results also suggest that chronic systemic inflammation may enhance airway responses to O3 in obese mice.

Role of interleukin-6 in murine airway responses to ozone

This study sought to examine the role of interleukin-6 (IL-6) in ozone (O(3))-induced airway injury, inflammation, and hyperresponsiveness (AHR). Subacute (72 h) exposure to 0.3 ppm O(3) significantly elevated bronchoalveolar lavage fluid (BALF) protein, neutrophils, and soluble TNF receptors (sTNFR1 and sTNFR2) in wild-type C57BL/6 (IL-6(+/+)) mice; however, all four outcome indicators were significantly reduced in IL-6-deficient (IL-6(-/-)) compared with IL-6(+/+) mice. Acute O(3) exposure (2 ppm for 3 h) increased BALF protein, KC, macrophage inflammatory protein(MIP)-2, eotaxin, sTNFR1, and sTNFR2 in IL-6(+/+) mice. However, MIP-2 and sTNFR2 were not significantly increased following O(3) exposure in IL-6(-/-) mice. Increases in BALF neutrophils induced by O(3) (2 ppm for 3 h) were also significantly reduced in IL-6(-/-) vs. IL-6(+/+) mice. Airway responsiveness to methacholine was measured by whole body plethysmography before and following acute (3 h) or subacute (72 h) exposure to 0.3 ppm O(3). Acute O(3) exposure caused AHR in both groups of mice, but there was no genotype-related difference in the magnitude of O(3)-induced AHR. AHR was absent in mice of either genotype exposed for 72 h. Our results indicate that IL-6 deficiency reduces airway neutrophilia, as well as the levels of BALF sTNFR1 and sTNFR2 following acute high dose and/or subacute low-dose O(3) exposure, but has no effect on O(3)-induced AHR.

CXCR2 is essential for maximal neutrophil recruitment and methacholine responsiveness after ozone exposure

Ozone (O(3)), a common air pollutant, induces airway inflammation and airway hyperresponsiveness. In mice, the neutrophil chemokines KC and macrophage inflammatory protein-2 (MIP-2) are expressed in the lungs following O(3) exposure. The purpose of this study was to determine whether CXCR2, the receptor for these chemokines, is essential to O(3)-induced neutrophil recruitment, injury to lungs, and increases in respiratory system responsiveness to methacholine (MCh). O(3) exposure (1 ppm for 3 h) increased the number of neutrophils in the bronchoalveolar lavage fluid (BALF) of wild-type (BALB/c) and CXCR2-deficient mice. However, CXCR2-deficient mice had significantly fewer emigrated neutrophils than did wild-type mice. The numbers of neutrophils in the blood and concentrations of BALF KC and MIP-2 did not differ between genotypes. Together, these data suggest CXCR2 is essential for maximal chemokine-directed migration of neutrophils to the air spaces. In wild-type mice, O(3) exposure increased BALF epithelial cell numbers and total protein levels, two indirect measures of lung injury. In contrast, in CXCR2-deficient mice, the number of BALF epithelial cells was not increased by O(3) exposure. Responses to inhaled MCh were measured by whole body plethysmography using enhanced pause as the outcome indicator. O(3) exposure increased responses to inhaled MCh in both wild-type and CXCR2-deficient mice 3 h after O(3) exposure. However, at 24 h after exposure, responses to inhaled MCh were elevated in wild-type but not CXCR2-deficient mice. These results indicate CXCR2 is essential for maximal neutrophil recruitment, epithelial cell sloughing, and persistent increases in MCh responsiveness after an acute O(3) exposure.

Airway mucosal thickening and bronchial hyperresponsiveness induced by inhaled beta 2-agonist in mice

BACKGROUND

Patients with chronic persistent asthma require frequent use of inhaled beta(2)-agonist, which may result in aggravation of asthma symptoms. Our recent in vitro study has shown that beta(2)-agonist stimulates the growth of human airway epithelial cell lines.

STUDY OBJECTIVE

To determine whether beta(2)-agonist likewise affects airway epithelial cell proliferation in vivo and, if so, what the mechanism of action is, we examined the effect of salbutamol on the morphology of murine airways.

METHODS

Seventy-two BALB/c mice were administered aerosolized salbutamol using "flow-through" nose-only inhalation chambers at daily doses of 0.2 to 20 microg for up to 6 weeks. Morphology of tracheal mucosa, labeling of epithelial cells with 5-bromo-2'-deoxyuridine (BrdU), and bronchial responsiveness were assessed.

RESULTS

Exposure to salbutamol increased the thickness of tracheal epithelial layer and the number of BrdU-positive epithelial cells in a dose- and time-dependent manner: the values in mice receiving 20 microg salbutamol for 6 weeks were 247% and 642%, respectively, of those in control animals receiving saline solution alone. These effects were inhibited by the mitogen-activated protein (MAP) kinase kinase inhibitors PD98059 and U0126. Salbutamol also caused a decrease in the provocative concentration of methacholine to achieve 400% of baseline enhanced pause. Combined treatment with inhaled budesonide attenuated salbutamol-induced airway morphologic changes and bronchial hyperresponsiveness.

CONCLUSION

beta(2)-agonist stimulates proliferation of airway epithelial cells and produces airway wall thickening in vivo via MAP kinase-dependent pathway, and these effects are prevented by inhaled corticosteroid.

Responses to ozone are increased in obese mice

Epidemiological data indicate an increased incidence of asthma in overweight adults and children. Ozone (O3) is a common trigger for asthma. Accordingly, the purpose of this study was to compare O3-induced airway hyperresponsiveness and airway inflammation in lean, wild-type (C57BL/6J) mice and mice that are obese as a consequence of a genetic defect in the gene encoding the satiety hormone leptin (ob/ob mice). The ob/ob mice eat excessively and weighed more than twice as much as age- and gender-matched wild-type mice. Airway responsiveness to intravenous methacholine was measured by forced oscillation. In air-exposed controls, baseline pulmonary resistance was greater, and the dose of methacholine required to double pulmonary resistance was lower in ob/ob than wild-type mice. Exposure to O3 (2 parts/million for 3 h) caused AHR and airway inflammation in both groups of mice, but responses to O3 were enhanced in ob/ob compared with wild-type mice. Administration of exogenous leptin did not reverse the enhanced inflammatory response observed in ob/ob mice, but augmented airway inflammation in wild-type mice. The inhaled dose of O3 per gram of lung tissue was greater in ob/ob than wild-type mice. Our results indicate that O3-induced airway responses are enhanced in ob/ob mice and suggest that inhaled O3 dose may be one factor contributing to this difference, but other aspects of the obese phenotype may also contribute. Our results also indicate that the hormone leptin, which is increased in the obese, has the capacity to increase airway inflammation.