Functional and morphological differences of the lung upon acute and chronic ozone exposure in mice

Viral respiratory infections and air pollution: A review focused on research in Poland

The COVID-19 pandemic has reinforced an interest in the relationship between air pollution and respiratory viral infections, indicating that their burden can be increased under poor air quality. This paper reviews the pathways through which air pollutants can enhance susceptibility to such infections and aggravate their clinical course and outcome. It also summarizes the research exploring the links between various viral infections and exposure to solid and gaseous pollution in Poland, a region characterized by poor air quality, especially during a heating season. The majority of studies focused on concentrations of particulate matter (PM; 86.7%); the other pollutants, i.e., BaP, benzene, CO, NOx, O3, and SO2, were studied less often and sometimes only in the context of a particular infection type. Most research concerned COVID-19, showing that elevated levels of PM and NO2 correlated with higher morbidity and mortality, while increased PM2.5 and benzo[a]pyrene levels were related to worse clinical course and outcome in hospitalized, regardless of age and dominant SARS-CoV-2 variant. PM10 and PM2.5 levels were also associated with the incidence of influenza-like illness and, along with NO2 concentrations, with a higher rate of children's hospitalizations due to lower respiratory tract RSV infections. Higher levels of air pollutants also increased hospitalization due to bronchitis (PM, NOx, and O3) and emergency department admission due to viral croup (PM10, PM2.5, NOx, CO, and benzene). Although the conducted studies imply only correlations and have other limitations, as discussed in the present paper, it appears that improving air quality through reducing combustion processes in energy production in Poland should be perceived as a part of multilayered protection measures against respiratory viral infections, decreasing the healthcare costs of COVID-19, lower tract RSV infections, influenza, and other respiratory viral diseases prevalent between autumn and early spring, in addition to other health and climate benefits.

Exposure to Environmental Toxins: Potential Implications for Stroke Risk via the Gut- and Lung-Brain Axis

Recent evidence indicates that exposure to environmental toxins, both short-term and long-term, can increase the risk of developing neurological disorders, including neurodegenerative diseases (i.e., Alzheimer's disease and other dementias) and acute brain injury (i.e., stroke). For stroke, the latest systematic analysis revealed that exposure to ambient particulate matter is the second most frequent stroke risk after high blood pressure. However, preclinical and clinical stroke investigations on the deleterious consequences of environmental pollutants are scarce. This review examines recent evidence of how environmental toxins, absorbed along the digestive tract or inhaled through the lungs, affect the host cellular response. We particularly address the consequences of environmental toxins on the immune response and the microbiome at the gut and lung barrier sites. Additionally, this review highlights findings showing the potential contribution of environmental toxins to an increased risk of stroke. A better understanding of the biological mechanisms underlying exposure to environmental toxins has the potential to mitigate stroke risk and other neurological disorders.

Deflamin Attenuated Lung Tissue Damage in an Ozone-Induced COPD Murine Model by Regulating MMP-9 Catalytic Activity

Chronic obstructive pulmonary disease (COPD) is comprised of histopathological alterations such as pulmonary emphysema and peribronchial fibrosis. Matrix metalloproteinase 9 (MMP-9) is one of the key enzymes involved in both types of tissue remodeling during the development of lung damage. In recent studies, it was demonstrated that deflamin, a protein component extracted from Lupinus albus, markedly inhibits the catalytic activity of MMP-9 in experimental models of colon adenocarcinoma and ulcerative colitis. Therefore, in the present study, we investigated for the first time the biological effect of deflamin in a murine COPD model induced by chronic exposure to ozone. Ozone exposure was carried out in C57BL/6 mice twice a week for six weeks for 3 h each time, and the treated group was orally administered deflamin (20 mg/kg body weight) after each ozone exposure. The histological results showed that deflamin attenuated pulmonary emphysema and peribronchial fibrosis, as evidenced by H&E and Masson's trichrome staining. Furthermore, deflamin administration significantly decreased MMP-9 activity, as assessed by fluorogenic substrate assay and gelatin zymography. Interestingly, bioinformatic analysis reveals a plausible interaction between deflamin and MMP-9. Collectively, our findings demonstrate the therapeutic potential of deflamin in a COPD murine model, and suggest that the attenuation of the development of lung tissue damage occurs by deflamin-regulated MMP-9 catalytic activity.

Repetitive sulfur dioxide exposure in mice models post-deployment respiratory syndrome

Soldiers deployed to Iraq and Afghanistan have a higher prevalence of respiratory symptoms than nondeployed military personnel and some have been shown to have a constellation of findings on lung biopsy termed post-deployment respiratory syndrome (PDRS). Since many of the subjects in this cohort reported exposure to sulfur dioxide (SO2), we developed a model of repetitive exposure to SO2 in mice that phenocopies many aspects of PDRS, including adaptive immune activation, airway wall remodeling, and pulmonary vascular (PV) disease. Although abnormalities in small airways were not sufficient to alter lung mechanics, PV remodeling resulted in the development of pulmonary hypertension and reduced exercise tolerance in SO2-exposed mice. SO2 exposure led to increased formation of isolevuglandins (isoLGs) adducts and superoxide dismutase 2 (SOD2) acetylation in endothelial cells, which were attenuated by treatment with the isoLG scavenger 2-hydroxybenzylamine acetate (2-HOBA). In addition, 2-HOBA treatment or Siruin-3 overexpression in a transgenic mouse model prevented vascular remodeling following SO2 exposure. In summary, our results indicate that repetitive SO2 exposure recapitulates many aspects of PDRS and that oxidative stress appears to mediate PV remodeling in this model. Together, these findings provide new insights regarding the critical mechanisms underlying PDRS.NEW & NOTEWORTHY We developed a mice model of "post-deployment respiratory syndrome" (PDRS), a condition in Veterans with unexplained exertional dyspnea. Our model successfully recapitulates many of the pathological and physiological features of the syndrome, revealing involvement of the ROS-isoLGs-Sirt3-SOD2 pathway in pulmonary vasculature pathology. Our study provides additional knowledge about effects and long-term consequences of sulfur dioxide exposure on the respiratory system, serving as a valuable tool for future PDRS research.

Impact of climate change on immune responses and barrier defense

Climate change is not just jeopardizing the health of our planet but is also increasingly affecting our immune health. There is an expanding body of evidence that climate-related exposures such as air pollution, heat, wildfires, extreme weather events, and biodiversity loss significantly disrupt the functioning of the human immune system. These exposures manifest in a broad range of stimuli, including antigens, allergens, heat stress, pollutants, microbiota changes, and other toxic substances. Such exposures pose a direct and indirect threat to our body's primary line of defense, the epithelial barrier, affecting its physical integrity and functional efficacy. Furthermore, these climate-related environmental stressors can hyperstimulate the innate immune system and influence adaptive immunity-notably, in terms of developing and preserving immune tolerance. The loss or failure of immune tolerance can instigate a wide spectrum of noncommunicable diseases such as autoimmune conditions, allergy, respiratory illnesses, metabolic diseases, obesity, and others. As new evidence unfolds, there is a need for additional research in climate change and immunology that covers diverse environments in different global settings and uses modern biologic and epidemiologic tools.

Transcriptomic-based roadmap to the healthy and ozone-exposed lung

The lung is constantly exposed to a myriad of exogenous stressors. Ground-level ozone represents a ubiquitous and extremely reactive anthropogenic toxicant, impacting the health of millions across the globe. While abundant, epidemiological, in vivo, and in vitro data focuses the ozone toxicity in individual cell types (e.g. epithelial type II, alveolar macrophages) or signaling pathways involved in the injury (e.g., akt, glutathione). When appropriately used, bulk and single cell RNA sequencing techniques have the potential to provide complete, and in certain cases unbiased, information of the molecular events taking place in the steady state and injured lung, and even capture the phenotypic diversity of neighboring cells. To this end, this review compiles information pertaining to the latest understanding of lung cell identity and activation in the steady state and ozone exposed lung. In addition, it discusses the value and benefits of multi-omics approaches and other tools developed to predict cell-cell communication and dissect spatial heterogeneity.

Long-term ozone exposure and lung function in middle childhood

BACKGROUND

Ozone (O3) exposure interrupts normal lung development in animal models. Epidemiologic evidence further suggests impairment with higher long-term O3 exposure across early and middle childhood, although study findings to date are mixed and few have investigated vulnerable subgroups.

METHODS

Participants from the CANDLE study, a pregnancy cohort in Shelby County, TN, in the ECHO-PATHWAYS Consortium, were included if children were born at gestational age >32 weeks, completed a spirometry exam at age 8-9, and had a valid residential history from birth to age 8. We estimated lifetime average ambient O3 exposure based on each child's residential history from birth to age 8, using a validated fine-resolution spatiotemporal model. Spirometry was performed at the age 8-9 year study visit to assess Forced Expiratory Volume in the first second (FEV1) and Forced Vital Capacity (FVC) as primary outcomes; z-scores were calculated using sex-and-age-specific reference equations. Linear regression with robust variance estimators was used to examine associations between O3 exposure and continuous lung function z-scores, adjusted for child, sociodemographic, and home environmental factors. Potential susceptible subgroups were explored using a product term in the regression model to assess effect modification by child sex, history of bronchiolitis in infancy, and allergic sensitization.

RESULTS

In our sample (n = 648), O3 exposure averaged from birth to age 8 was modest (mean 26.6 [SD 1.1] ppb). No adverse associations between long-term postnatal O3 exposure were observed with either FEV1 (β = 0.12, 95% CI: -0.04, 0.29) or FVC (β = 0.03, 95% CI: -0.13, 0.19). No effect modification by child sex, history of bronchiolitis in infancy, or allergic sensitization was detected for associations with 8-year average O3.

CONCLUSIONS

In this sample with low O3 concentrations, we did not observe adverse associations between O3 exposures averaged from birth to age 8 and lung function in middle childhood.

Effect of altered human exposome on the skin and mucosal epithelial barrier integrity

Pollution in the world and exposure of humans and nature to toxic substances is continuously worsening at a rapid pace. In the last 60 years, human and domestic animal health has been challenged by continuous exposure to toxic substances and pollutants because of uncontrolled growth, modernization, and industrialization. More than 350,000 new chemicals have been introduced to our lives, mostly without any reasonable control of their health effects and toxicity. A plethora of studies show exposure to these harmful substances during this period with their implications on the skin and mucosal epithelial barrier and increasing prevalence of allergic and autoimmune diseases in the context of the "epithelial barrier hypothesis". Exposure to these substances causes an epithelial injury with peri-epithelial inflammation, microbial dysbiosis and bacterial translocation to sub-epithelial areas, and immune response to dysbiotic bacteria. Here, we provide scientific evidence on the altered human exposome and its impact on epithelial barriers.

Nuclear envelope disruption triggers hallmarks of aging in lung alveolar macrophages

Aging is characterized by gradual immune dysfunction and increased disease risk. Genomic instability is considered central to the aging process, but the underlying mechanisms of DNA damage are insufficiently defined. Cells in confined environments experience forces applied to their nucleus, leading to transient nuclear envelope rupture (NER) and DNA damage. Here, we show that Lamin A/C protects lung alveolar macrophages (AMs) from NER and hallmarks of aging. AMs move within constricted spaces in the lung. Immune-specific ablation of lamin A/C results in selective depletion of AMs and heightened susceptibility to influenza virus-induced pathogenesis and lung cancer growth. Lamin A/C-deficient AMs that persist display constitutive NER marks, DNA damage and p53-dependent senescence. AMs from aged wild-type and from lamin A/C-deficient mice share a lysosomal signature comprising CD63. CD63 is required to limit damaged DNA in macrophages. We propose that NER-induced genomic instability represents a mechanism of aging in AMs.

Airspace Diameter Map-A Quantitative Measurement of All Pulmonary Airspaces to Characterize Structural Lung Diseases

(1) Background: Stereological estimations significantly contributed to our understanding of lung anatomy and physiology. Taking stereology fully 3-dimensional facilitates the estimation of novel parameters. (2) Methods: We developed a protocol for the analysis of all airspaces of an entire lung. It includes (i) high-resolution synchrotron radiation-based X-ray tomographic microscopy, (ii) image segmentation using the free machine-learning tool Ilastik and ImageJ, and (iii) calculation of the airspace diameter distribution using a diameter map function. To evaluate the new pipeline, lungs from adult mice with cystic fibrosis (CF)-like lung disease (βENaC-transgenic mice) or mice with elastase-induced emphysema were compared to healthy controls. (3) Results: We were able to show the distribution of airspace diameters throughout the entire lung, as well as separately for the conducting airways and the gas exchange area. In the pathobiological context, we observed an irregular widening of parenchymal airspaces in mice with CF-like lung disease and elastase-induced emphysema. Comparable results were obtained when analyzing lungs imaged with μCT, sugges-ting that our pipeline is applicable to different kinds of imaging modalities. (4) Conclusions: We conclude that the airspace diameter map is well suited for a detailed analysis of unevenly distri-buted structural alterations in chronic muco-obstructive lung diseases such as cystic fibrosis and COPD.

A time-series analysis of short-term ambient ozone exposure and hospitalizations from acute myocardial infarction in Henan, China

Epidemiological studies in recent years have identified an association between exposure to air pollutants and acute myocardial infarction (AMI); however, the association between short-term ozone (O3) exposure and AMI hospitalization remains unclear, particularly in developing countries. Therefore, this study collected information on 24,489 AMI patients, including daily air pollutant and meteorological data in Henan, China, between 2016 and 2021. A distributed lagged nonlinear model combined with a Poisson regression model was used to estimate the nonlinear lagged effect of O3 on AMI hospitalizations. We also quantified the effects of O3 on the number of AMI hospitalizations, hospitalization days, and hospitalization costs. The results showed that single- and dual-pollution models of O3 at lag0, lag1, and lag (01-07) were risk factors for AMI hospitalizations, with the most significant effect at lag03 (RR = 1.132, 95% CI:1.083-1.182). Further studies showed that males, younger people (15-64 years), warm seasons, and long sunshine duration were more susceptible to O3. Hospitalizations attributable to O3 during the study period accounted for 11.66% of the total hospitalizations, corresponding to 2856 patients, 33,492 hospital days, and 90 million RMB. Maintaining O3 at 10-130 µg/m3 can prevent hundreds of AMI hospitalizations and save millions of RMB per year in Henan, China. In conclusion, we found that short-term exposure to O3 was significantly associated with an increased risk of hospitalization for AMI in Henan, China, and that further reductions in ambient O3 levels may have substantial health and economic benefits for patients and local healthcare facilities.

Role of Air Pollution in the Development of Asthma Among Children with a History of Bronchiolitis in Infancy

BACKGROUND

Infants experiencing bronchiolitis are at increased risk for asthma, but few studies have identified modifiable risk factors. We assessed whether early life air pollution influenced child asthma and wheeze at age 4-6 years among children with a history of bronchiolitis in the first postnatal year.

METHODS

Children with caregiver-reported physician-diagnosed bronchiolitis were drawn from ECHO-PATHWAYS, a pooled longitudinal cohort from six US cities. We estimated their air pollution exposure from age 1 to 3 years from validated spatiotemporal models of fine particulate matter (PM 2.5 ), nitrogen dioxide (NO 2 ), and ozone (O 3 ). Caregivers reported children's current wheeze and asthma at age 4-6 years. We used modified Poisson regression to estimate relative risks (RR) and 95% confidence intervals (CI), adjusting for child, maternal, and home environmental factors. We assessed effect modification by child sex and maternal history of asthma with interaction models.

RESULTS

A total of 224 children had caregiver-reported bronchiolitis. Median (interquartile range) 2-year pollutant concentrations were 9.3 (7.8-9.9) µg/m 3 PM 2.5 , 8.5 (6.4-9.9) ppb NO 2 , and 26.6 (25.6-27.7) ppb O 3 . RRs (CI) for current wheeze per 2-ppb higher O 3 were 1.3 (1.0-1.7) and 1.4 (1.1-1.8) for asthma. NO 2 was inversely associated with wheeze and asthma whereas associations with PM 2.5 were null. We observed interactions between NO 2 and PM 2.5 and maternal history of asthma, with lower risks observed among children with a maternal history of asthma.

CONCLUSION

Our results are consistent with the hypothesis that exposure to modest postnatal O 3 concentrations increases the risk of asthma and wheeze among the vulnerable subpopulation of infants experiencing bronchiolitis.

Repetitive Sulfur Dioxide Exposure in Mice Models Post-Deployment Respiratory Syndrome

Soldiers deployed to Iraq and Afghanistan have a higher prevalence of respiratory symptoms than non-deployed military personnel and some have been shown to have a constellation of findings on lung biopsy termed post-deployment respiratory syndrome (PDRS). Since many of the deployers in this cohort reported exposure to sulfur dioxide (SO 2 ), we developed a model of repetitive exposure to SO 2 in mice that phenocopies many aspects of PDRS, including adaptive immune activation, airway wall remodeling, and pulmonary vascular disease (PVD). Although abnormalities in small airways were not sufficient to alter lung mechanics, PVD was associated with the development of pulmonary hypertension and reduced exercise tolerance in SO 2 exposed mice. Further, we used pharmacologic and genetic approaches to demonstrate a critical role for oxidative stress and isolevuglandins in mediating PVD in this model. In summary, our results indicate that repetitive SO 2 exposure recapitulates many aspects of PDRS and that oxidative stress may mediate PVD in this model, which may be helpful for future mechanistic studies examining the relationship between inhaled irritants, PVD, and PDRS.

Modulation of low-dose ozone and LPS exposed acute mouse lung inflammation by IF1 mediated ATP hydrolysis inhibitor, BTB06584

Ozone and bacterial lipopolysaccharide (LPS) are common air pollutants that are related to high hospital admissions due to airway hyperreactivity and increased susceptibility to infections, especially in children, older population and individuals with underlying conditions. We modeled acute lung inflammation (ALI) by exposing 6-8 week old male mice to 0.005 ppm ozone for 2 h followed by 50 μg of intranasal LPS. We compared the immunomodulatory effects of single dose pre-treatment with CD61 blocking antibody (clone 2C9.G2), ATPase inhibitor BTB06584 against propranolol as the immune-stimulant and dexamethasone as the immune-suppressant in the ALI model. Ozone and LPS exposure induced lung neutrophil and eosinophil recruitment as measured by respective peroxidase (MPO and EPX) assays, systemic leukopenia, increased levels of lung vascular neutrophil regulatory chemokines such as CXCL5, SDF-1, CXCL13 and a decrease in immune-regulatory chemokines such as BAL IL-10 and CCL27. While CD61 blocking antibody and BTB06584 produced maximum increase in BAL leukocyte counts, protein content and BAL chemokines, these treatments induced moderate increase in lung MPO and EPX content. CD61 blocking antibody induced maximal BAL cell death, a markedly punctate distribution of NK1.1, CX3CR1, CD61. BTB06584 preserved BAL cell viability with cytosolic and membrane distribution of Gr1 and CX3CR1. Propranolol attenuated BAL protein, protected against BAL cell death, induced polarized distribution of NK1.1, CX3CR1 and CD61 but presented with high lung EPX. Dexamethasone induced sparse cell membrane distribution of CX3CR1 and CD61 on BAL cells and displayed very low lung MPO and EPX levels despite highest levels of BAL chemokines. Our study unravels ATPase inhibitor IF1 as a novel drug target for lung injury.

The impact of subchronic ozone exposure on serum metabolome and the mechanisms of abnormal bile acid and arachidonic acid metabolisms in the liver

Ambient ozone (O₃) pollution can induce respiratory and cardiovascular toxicity. However, its impact on the metabolome and the underlying mechanisms remain unclear. This study first investigated the serum metabolite changes in rats exposed to 0.5 ppm O₃ for 3 months using untargeted metabolomic approach. Results showed chronic ozone exposure significantly altered the serum levels of 34 metabolites with potential increased risk of digestive, respiratory and cardiovascular disease. Moreover, bile acid synthesis and secretion, and arachidonic acid (AA) metabolism became the most prominent affected metabolic pathways after O₃ exposure. Further studies on the mechanisms found that the elevated serum toxic bile acid was not due to the increased biosynthesis in the liver, but the reduced reuptake from the portal vein to hepatocytes owing to repressed Ntcp and Oatp1a1, and the decreased bile acid efflux in hepatocytes as a results of inhibited Bsep, Ostalpha and Ostbeta. Meanwhile, decreased expressions of detoxification enzyme of SULT2A1 and the important regulators of FXR, PXR and HNF4α also contributed to the abnormal bile acids. In addition, O₃ promoted the conversion of AA into thromboxane A2 (TXA2) and 20-hydroxyarachidonic acid (20-HETE) in the liver by up-regulation of Fads2, Cyp4a and Tbxas1 which resulting in decreased AA and linoleic acid (LA), and increased thromboxane B2 (TXB2) and 20-HETE in the serum. Furthermore, apparent hepatic chronic inflammation, fibrosis and abnormal function were found in ozone-exposed rats. These results indicated chronic ozone exposure could alter serum metabolites by interfering their metabolism in the liver, and inducing liver injury to aggravate metabolic disorders.

Lung Regeneration: Cells, Models, and Mechanisms

Lung epithelium, the lining that covers the inner surface of the respiratory tract, is directly exposed to the environment and thus susceptible to airborne toxins, irritants, and pathogen-induced damages. In adult mammalian lungs, epithelial cells are generally quiescent but can respond rapidly to repair of damaged tissues. Evidence from experimental injury models in rodents and human clinical samples has led to the identification of these regenerative cells, as well as pathological metaplastic states specifically associated with different forms of damages. Here, we provide a compendium of cells and cell states that exist during homeostasis in normal lungs and the lineage relationships between them. Additionally, we discuss various experimental injury models currently being used to probe the cellular sources-both resident and recruited-that contribute to repair, regeneration, and remodeling following acute and chronic injuries. Finally, we discuss certain maladaptive regeneration-associated cell states and their role in disease pathogenesis.

Cigarette smoke-induced gasdermin D activation in bronchoalveolar macrophages and bronchial epithelial cells dependently on NLRP3

Chronic pulmonary inflammation and chronic obstructive pulmonary disease (COPD) are major health issues largely due to air pollution and cigarette smoke (CS) exposure. The role of the innate receptor NLRP3 (nucleotide-binding domain and leucine-rich repeat containing protein 3) orchestrating inflammation through formation of an inflammasome complex in CS-induced inflammation or COPD remains controversial. Using acute and subchronic CS exposure models, we found that Nlrp3-deficient mice or wild-type mice treated with the NLRP3 inhibitor MCC950 presented an important reduction of inflammatory cells recruited into the bronchoalveolar space and of pulmonary inflammation with decreased chemokines and cytokines production, in particular IL-1β demonstrating the key role of NLRP3. Furthermore, mice deficient for Caspase-1/Caspase-11 presented also decreased inflammation parameters, suggesting a role for the NLRP3 inflammasome. Importantly we showed that acute CS-exposure promotes NLRP3-dependent cleavage of gasdermin D in macrophages present in the bronchoalveolar space and in bronchial airway epithelial cells. Finally, Gsdmd-deficiency reduced acute CS-induced lung and bronchoalveolar space inflammation and IL-1β secretion. Thus, we demonstrated in our model that NLRP3 and gasdermin D are key players in CS-induced pulmonary inflammation and IL-1β release potentially through gasdermin D forming-pore and/or pyroptoctic cell death.

Inflammation resolution in environmental pulmonary health and morbidity

Inflammation and resolution are dynamic processes comprised of inflammatory activation and neutrophil influx, followed by mediator catabolism and efferocytosis. These critical pathways ensure a return to homeostasis and promote repair. Over the past decade research has shown that diverse mediators play a role in the active process of resolution. Specialized pro-resolving mediators (SPMs), biosynthesized from fatty acids, are released during inflammation to facilitate resolution and are deficient in a variety of lung disorders. Failed resolution results in remodeling and cellular deposition through pro-fibrotic myofibroblast expansion that irreversibly narrows the airways and worsens lung function. Recent studies indicate environmental exposures may perturb and deregulate critical resolution pathways. Environmental xenobiotics induce lung inflammation and generate reactive metabolites that promote oxidative stress, injuring the respiratory mucosa and impairing gas-exchange. This warrants recognition of xenobiotic associated molecular patterns (XAMPs) as new signals in the field of inflammation biology, as many environmental chemicals generate free radicals capable of initiating the inflammatory response. Recent studies suggest that unresolved, persistent inflammation impacts both resolution pathways and endogenous regulatory mediators, compromising lung function, which over time can progress to chronic lung disease. Chronic ozone (O3) exposure overwhelms successful resolution, and in susceptible individuals promotes asthma onset. The industrial contaminant cadmium (Cd) bioaccumulates in the lung to impair resolution, and recurrent inflammation can result in chronic obstructive pulmonary disease (COPD). Persistent particulate matter (PM) exposure increases systemic cardiopulmonary inflammation, which reduces lung function and can exacerbate asthma, COPD, and idiopathic pulmonary fibrosis (IPF). While recurrent inflammation underlies environmentally induced pulmonary morbidity and may drive the disease process, our understanding of inflammation resolution in this context is limited. This review aims to explore inflammation resolution biology and its role in chronic environmental lung disease(s).

Parenchymal and Inflammatory Cell Responses to Single and Repeated Ozone Exposure in Healthy and Surfactant Protein-C Mutant Lung

Mutations in the alveolar epithelial-specific gene encoding for surfactant protein C (SP-C) are linked to pulmonary disease. Ozone (O3) is a ubiquitous pollutant known to exacerbate stress through oxidative injury and inflammation. To comprehend the structural, functional, and immunological impact of single and repeated O3 exposure, SP-CWT and SP-CI73T mice were exposed to air or O3 (0.8 ppm, 3 h, up to x4 consecutive days). O3 was associated with mitochondrial and autophagic activation (PINK1, LC3B, and p62), focal remodeling, and inflammation localized at the terminal bronchiole-to-alveolar junctions. Histological damage was exacerbated by repeated exposure. Single O3 challenge resulted in transient elastin fiber loss, while repeated exposure resulted in marked increases in elastance in SP-CI73T mice. Flow cytometric analysis revealed increases in classical monocyte and monocyte-derived macrophages recruitment in conditions of repeated exposure, which peaked earlier (24 h) in SP-CI73T mice. Immunohistochemical analysis also showed clustering of Arg-1+ and CD206+ activated cells within regions of remodeled lung. Lymphoid cell analysis identified CX3CR1-B220+ B cells accumulating after single (24/72 h). Repeated exposure produces a switch in the phenotype of these B cells CX3CR1+ (72 h) only in SP-CWT mice. SP-CI73T mutants also displayed depletion in NK1.1+NKp46+ NK cells in lung, as well as bone marrow, blood, and spleen. These results illustrate the cumulative impact of O3 on lung structure and function in healthy lung, and aberrant myeloid and lymphoid recruitment in SP-C mutants responding to challenge. Together, this work highlights the significance of modeling environmental exposure across the spectrum of genetic susceptibility, consistent with human disease.

The External Exposome and Allergies: From the Perspective of the Epithelial Barrier Hypothesis

Introduction

In the last decades, we have seen a rapid increase in the prevalence of allergic diseases such as asthma, allergic rhinitis, atopic dermatitis, and food allergies. The environmental changes caused by industrialization, urbanization and modernization, including dramatic increases in air pollutants such as particulate matter (PM), diesel exhaust, nitrogen dioxide (NO2), ozone (O3), alarming effects of global warming, change and loss of biodiversity, affect both human health and the entire ecosystem.

Objective

In this review, we aimed to discuss the effects of the external exposome on epithelial barriers and its relationship with the development of allergic diseases by considering the changes in all stakeholders of the outer exposome together, in the light of the recently proposed epithelial barrier hypothesis.

Method

To reach current, prominent, and comprehensive studies on the subject, PubMed databases were searched. We included the more resounding articles with reliable and strong results.

Results

Exposure to altered environmental factors such as increased pollution, microplastics, nanoparticles, tobacco smoke, food emulsifiers, detergents, and household cleaners, and climate change, loss and change in microbial biodiversity, modifications in the consumption of dietary fatty acids, the use of emulsifiers, preservatives and the decrease in the antioxidant content of the widely consumed western diet may disrupt the epithelial barriers of the skin, respiratory and gastrointestinal tracts, making us more vulnerable to exogeneous allergens and microbes. Epithelial cell activation, microbial dysbiosis and bacterial translocation disrupt the immune balance and a chronic Th2 inflammation ensues.

Conclusion

Dramatic increases in air pollution, worrisome effects of global warming, dysbiosis, changing dietary habits and the complex interactions of all these factors affect the epithelial barriers and local and systemic inflammation. We want to draw attention to the emerging health effects of environmental changes and to motivate the public to influence government policies for the well-being of humans and the nature of the earth and the well-being of future generations.

Ozone-Induced Models of Airway Hyperreactivity and Epithelial Injury

Ozone (O₃), a criterion air pollutant produced as a product of internal combustion, generates increased inflammation, lung permeability, and airway hyperreactivity when exposed to rodents in laboratory settings. Airway hyperreactivity is defined as an exaggerated acute obstructive response of the airways to one or more nonspecific stimuli. Lung permeability is a measure of barrier functions that separate internal and external environments to limit access of pathogens and other noxious material. By modeling in vivo O₃ exposure in rodents, this allows investigators to explore pulmonary and nonpulmonary O₃ effects as a means of understanding its impact on human health and lung function. Furthermore, direct effects of O₃ on epithelial permeability can be defined using in vitro exposures to airway epithelial cells. This chapter will focus on methods of generating O₃ and then exposing rodents and cultured epithelial cells in laboratory settings.

[Angiotensin-converting enzyme 2 particapates in ozone-induced lung inflammation and airway remodeling in mice]

OBJECTIVE

To investigate the roles of angiotensin-converting enzyme 2 (ACE2) in ozone-induced pulmonary inflammation and airway remodeling in mice.

METHODS

Sixteen wild-type (WT) C57BL/6J mice and 16 ACE2 knock-out (KO) mice were exposed to either filtered air or ozone (0.8 ppm) for 3 h per day for 5 consecutive days. Masson's staining and HE staining were used to observe lung pathologies. Bronchoalveolar lavage fluid (BALF) was collected and the total cell count was determined. The total proteins and cytokines in BALF were determined by BCA and ELISA method. The transcription levels of airway remodeling-related indicators in the lung tissues were detected using real-time quantitative PCR. The airway resistance of the mice was measured using a small animal ventilator with methacholine stimulation.

RESULTS

Following ozoneexposure ACE2 KO mice had significantly higher lung pathological scores than WT mice (P < 0.05). Masson staining results showed that compared with ozone-exposed WT mice, ozone-exposed ACE2 KO mice presented with significantly larger area of collagen deposition in the bronchi [(19.62±3.16)% vs (6.49±1.34)%, P < 0.05] and alveoli [(21.63±3.78)% vs (4.44±0.99)%, P < 0.05]. The total cell count and total protein contents in the BALF were both higher in ozone-exposed ACE2 KO mice than in WT mice, but these differences were not statistically significant (P > 0.05). The concentrations of IL-6, IL-1β, TNF-α, CXCL1/KC and MCP-1 in the BALF were all higher in ozone-exposed ACE2 KO mice than in ozone-exposed WT mice, but only the difference in IL-1β was statistically significant (P < 0.05). The transcription levels of MMP-9, MMP-13, TIMP 4, COL1A1, and TGF-β in the lung tissues were all significantly higher in ozone-exposed ACE2 KO mice (P < 0.01). No significant difference was found in airway resistance between ozone-exposed ACE KO mice and WT mice after challenge with 0, 10, 25, or 100 mg/mL of methacholine.

CONCLUSION

ACE2 participates in ozone-induced lung inflammation and airway remodeling in mice.

Epithelial barrier hypothesis: Effect of the external exposome on the microbiome and epithelial barriers in allergic disease

Environmental exposure plays a major role in the development of allergic diseases. The exposome can be classified into internal (e.g., aging, hormones, and metabolic processes), specific external (e.g., chemical pollutants or lifestyle factors), and general external (e.g., broader socioeconomic and psychological contexts) domains, all of which are interrelated. All the factors we are exposed to, from the moment of conception to death, are part of the external exposome. Several hundreds of thousands of new chemicals have been introduced in modern life without our having a full understanding of their toxic health effects and ways to mitigate these effects. Climate change, air pollution, microplastics, tobacco smoke, changes and loss of biodiversity, alterations in dietary habits, and the microbiome due to modernization, urbanization, and globalization constitute our surrounding environment and external exposome. Some of these factors disrupt the epithelial barriers of the skin and mucosal surfaces, and these disruptions have been linked in the last few decades to the increasing prevalence and severity of allergic and inflammatory diseases such as atopic dermatitis, food allergy, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, and asthma. The epithelial barrier hypothesis provides a mechanistic explanation of how these factors can explain the rapid increase in allergic and autoimmune diseases. In this review, we discuss factors affecting the planet's health in the context of the 'epithelial barrier hypothesis,' including climate change, pollution, changes and loss of biodiversity, and emphasize the changes in the external exposome in the last few decades and their effects on allergic diseases. In addition, the roles of increased dietary fatty acid consumption and environmental substances (detergents, airborne pollen, ozone, microplastics, nanoparticles, and tobacco) affecting epithelial barriers are discussed. Considering the emerging data from recent studies, we suggest stringent governmental regulations, global policy adjustments, patient education, and the establishment of individualized control measures to mitigate environmental threats and decrease allergic disease.

Assessment of toxicological consequences upon acute inhalation exposure to chemically improvised nonlethal riot control combinational formulation (NCF) containing oleoresin capsicum and skatole

Sensory irritation is an acute adverse effect leading to temporary disability posed by riot control agents in various deployable forms are utilized by defense personal in violent mob attacks but their irreversible toxic effects and risk assessment have been a matter of concern. These intimidating risks of available riot control agents have led to exploring the pulmonary toxicity profile of the oil in water emulsion formulation developed for vicious crowd controls containing an irritant oleoresin capsicum, a malodorant (skatole), and a commercial dye, followed by characterization using standard methods. Nonlethal riot control combinational formulation (NCF) has been aimed to be the best possible low-lethal alternative for riot control measures. In this study, 30 min of acute inhalation exposure of NCF was given to Wistar rats and various respiratory parameters like lung dynamics, bronchoalveolar lavage fluid (BALF) cytological assays, pro-inflammatory cytokines estimation, antioxidant activity, collagen accumulation, cytotoxicity, in vivo lung imaging, western blot, histology of lung tissue, etc. were investigated to validate its potentiality and rate of irritation reversibility as nonlethal agents. An exaggerated physiological change like sensory irritation, changes in lung functional variables, increased pro-inflammatory cytokines, etc. were noticed initially without airway obstruction as the expression of nociceptive TRPV1 protein did not alter the physiological regulation of protective proteins like Nrf2 and HO-1 and also no abnormality was found in lung tissue architecture. In conclusion, it can be stated that this formulation can be explored as a nonlethal riot control agent intending to generate discomfort but with early reversibility of sensory irritation and no recurrence of toxicity.

Transcriptomics of single dose and repeated carbon black and ozone inhalation co-exposure highlight progressive pulmonary mitochondrial dysfunction

BACKGROUND

Air pollution is a complex mixture of particles and gases, yet current regulations are based on single toxicant levels failing to consider potential interactive outcomes of co-exposures. We examined transcriptomic changes after inhalation co-exposure to a particulate and a gaseous component of air pollution and hypothesized that co-exposure would induce significantly greater impairments to mitochondrial bioenergetics. A whole-body inhalation exposure to ultrafine carbon black (CB), and ozone (O3) was performed, and the impact of single and multiple exposures was studied at relevant deposition levels. C57BL/6 mice were exposed to CB (10 mg/m3) and/or O3 (2 ppm) for 3 h (either a single exposure or four independent exposures). RNA was isolated from lungs and mRNA sequencing performed using the Illumina HiSeq. Lung pathology was evaluated by histology and immunohistochemistry. Electron transport chain (ETC) activities, electron flow, hydrogen peroxide production, and ATP content were assessed.

RESULTS

Compared to individual exposure groups, co-exposure induced significantly greater neutrophils and protein levels in broncho-alveolar lavage fluid as well as a significant increase in mRNA expression of oxidative stress and inflammation related genes. Similarly, a significant increase in hydrogen peroxide production was observed after co-exposure. After single and four exposures, co-exposure revealed a greater number of differentially expressed genes (2251 and 4072, respectively). Of these genes, 1188 (single exposure) and 2061 (four exposures) were uniquely differentially expressed, with 35 mitochondrial ETC mRNA transcripts significantly impacted after four exposures. Both O3 and co-exposure treatment significantly reduced ETC maximal activity for complexes I (- 39.3% and - 36.2%, respectively) and IV (- 55.1% and - 57.1%, respectively). Only co-exposure reduced ATP Synthase activity (- 35.7%) and total ATP content (30%). Further, the ability for ATP Synthase to function is limited by reduced electron flow (- 25%) and translation of subunits, such as ATP5F1, following co-exposure.

CONCLUSIONS

CB and O3 co-exposure cause unique transcriptomic changes in the lungs that are characterized by functional deficits to mitochondrial bioenergetics. Alterations to ATP Synthase function and mitochondrial electron flow underly a pathological adaptation to lung injury induced by co-exposure.

Environmental Exposures and Lung Aging: Molecular Mechanisms and Implications for Improving Respiratory Health

PURPOSE OF REVIEW

Inhaled environmental exposures cause over 12 million deaths per year worldwide. Despite localized efforts to reduce environmental exposures, tobacco smoking and air pollution remain the urgent public health challenges that are contributing to the growing prevalence of respiratory diseases. The purpose of this review is to describe the mechanisms through which inhaled environmental exposures accelerate lung aging and cause overt lung disease.

RECENT FINDINGS

Environmental exposures related to fossil fuel and tobacco combustion and occupational exposures related to silica and coal mining generate oxidative stress and inflammation in the lungs. Sustained oxidative stress causes DNA damage, epigenetic instability, mitochondrial dysfunction, and cell cycle arrest in key progenitor cells in the lung. As a result, critical repair mechanisms are impaired, leading to premature destruction of the lung parenchyma. Inhaled environmental exposures accelerate lung aging by injuring the lungs and damaging the cells responsible for wound healing. Interventions that minimize exposure to noxious antigens are critical to improve lung health, and novel research is required to expand our knowledge of therapies that may slow or prevent premature lung aging.

Molecular mechanisms of oxidative stress in asthma

The lungs are exposed to reactive oxygen species oxygen (ROS) produced as a result of inhalation of oxygen, as well as smoke and other air pollutants. Cell metabolism and the NADPH oxidases (Nox) generate low levels of intracellular ROS that act as signal transduction mediators by inducing oxidative modifications of histones, enzymes and transcription factors. Redox signalling is also regulated by localised production and sensing of ROS in mitochondria, the endoplasmic reticulum (ER) and inside the nucleus. Intracellular ROS are maintained at low levels through the action of a battery of enzymatic and non-enzymatic antioxidants. Asthma is a heterogeneous airway inflammatory disease with different immune endotypes; these include atopic or non-atopic Th2 type immune response associated with eosinophilia, or a non-Th2 response associated with neutrophilia. Airway remodelling and hyperresponsiveness accompany the inflammatory response in asthma. Over-production of ROS resulting from infiltrating immune cells, particularly eosinophils and neutrophils, and a concomitant impairment of antioxidant responses lead to development of oxidative stress in asthma. Oxidative stress is augmented in severe asthma and during exacerbations, as well as by air pollution and obesity, and causes oxidative damage of tissues promoting airway inflammation and hyperresponsiveness. Furthermore, deregulated Nox activity, mitochondrial dysfunction, ER stress and/or oxidative DNA damage, resulting from exposure to irritants, inflammatory mediators or obesity, may lead to redox-dependent changes in cell signalling. ROS play a central role in airway epithelium-mediated sensing, development of innate and adaptive immune responses, and airway remodelling and hyperresponsiveness. Nonetheless, antioxidant compounds have proven clinically ineffective as therapeutic agents for asthma, partly due to issues with stability and in vivo metabolism of these compounds. The compartmentalised nature of ROS production and sensing, and the role of ROS in homeostatic responses and in the action of corticosteroids and β2-adrenergic receptor agonists, adds another layer of complexity to antioxidant therapy development. Nox inhibitors and mitochondrial-targeted antioxidants are in clinical development for a number of diseases but they have not yet been investigated in asthma. A better understanding of the complex role of ROS in the pathogenesis of asthma will highlight new opportunities for more targeted and effective redox therapies.

E-Cadherin: An Important Functional Molecule at Respiratory Barrier Between Defence and Dysfunction

While breathing, many microorganisms, harmful environmental particles, allergens, and environmental pollutants enter the human airways. The human respiratory tract is lined with epithelial cells that act as a functional barrier to these harmful factors and provide homeostasis between external and internal environment. Intercellular epithelial junctional proteins play a role in the formation of the barrier. E-cadherin is a calcium-dependent adhesion molecule and one of the most important molecules involved in intercellular epithelial barier formation. E-cadherin is not only physical barrier element but also regulates cell proliferation, differentiation and the immune response to environmental noxious agents through various transcription factors. In this study, we aimed to review the role of E-cadherin in the formation of airway epithelial barier, its status as a result of exposure to various environmental triggers, and respiratory diseases associated with its dysfunction. Moreover, the situations in which its abnormal activation can be noxious would be discussed.

Effects of ozone and particulate matter on airway epithelial barrier structure and function: a review of in vitro and in vivo studies

The airway epithelium represents a crucial line of defense against the spread of inhaled pathogens. As the epithelium is the first part of the body to be exposed to the inhaled environment, it must act as both a barrier to and sentinel against any inhaled agents. Despite its vital role in limiting the spread of inhaled pathogens, the airway epithelium is also regularly exposed to air pollutants which disrupt its normal function. Here we review the current understanding of the structure and composition of the airway epithelial barrier, as well as the impact of inhaled pollutants, including the reactive gas ozone and particulate matter, on epithelial function. We discuss the current in vitro, rodent model, and human exposure findings surrounding the impact of various inhaled pollutants on epithelial barrier function, mucus production, and mucociliary clearance. Detailed information on how inhaled pollutants impact epithelial structure and function will further our understanding of the adverse health effects of air pollution exposure.

Air Pollution and the Airways: Lessons from a Century of Human Urbanization

Since the industrial revolution, air pollution has become a major problem causing several health problems involving the airways as well as the cardiovascular, reproductive, or neurological system. According to the WHO, about 3.6 million deaths every year are related to inhalation of polluted air, specifically due to pulmonary diseases. Polluted air first encounters the airways, which are a major human defense mechanism to reduce the risk of this aggressor. Air pollution consists of a mixture of potentially harmful compounds such as particulate matter, ozone, carbon monoxide, volatile organic compounds, and heavy metals, each having its own effects on the human body. In the last decades, a lot of research investigating the underlying risks and effects of air pollution and/or its specific compounds on the airways, has been performed, involving both in vivo and in vitro experiments. The goal of this review is to give an overview of the recent data on the effects of air pollution on healthy and diseased airways or models of airway disease, such as asthma or chronic obstructive pulmonary disease. Therefore, we focused on studies involving pollution and airway symptoms and/or damage both in mice and humans.

Characterization of low-dose ozone-induced murine acute lung injury

Ozone is a toxic and highly reactive gaseous oxidizing chemical with well‐documented adverse health effects in humans. On the basis of animal and human data, environmental guidelines and air quality standards recommend a threshold for exposure of no more than 0.063 ppm of ozone (daily concentrations). This research describes a standardized sensitive model of sterile murine lung inflammation induced by exposing mice to acute (0, 4 or 24 hr), yet low, levels of ozone (0.005, 0.05 or 0.5 ppm), one that are below the current recommendations for what is considered a safe or “ambient” ozone concentration for humans. Ozone led to concentration and time‐dependent phlogistic cell death in the bronchoalveolar lavage, lung epithelial damage and hemorrhage. Interestingly, we observed distinct large bright CD11b positive cells in the bronchoalveolar lavage, upregulation of lung vascular and alveolar ATP synthase as well as plasminogen and bronchiolar angiostatin expression in ozone‐exposed mice, platelet and neutrophil accumulation in the lung vasculature and an eotaxin‐2, IL‐16, CXCL5, CXCL12, and CXCL13 dominant inflammatory response leading to lung injury. Using a fluorescent intravital microscopy set up, we quantified ozone‐induced extensive alveolar cellular damage. We observed ozone‐induced actin filament disorganization, perturbed respiratory mechanics, acute suppression of the alveolar reactive oxygen species (ROS) production and mitochondrial potential in ventilated lungs. We present evidence of systemic, as well as pulmonary toxicity, at 40‐fold lower ozone concentrations than previously reported in mice. The findings are important in establishing a sensitive means of quantifying structural and functional lung disorganization following exposure to an aerosolized pollutant, even at levels of ozone exposure previously thought to be safe in humans.

Genetic variation in surfactant protein-A2 alters responses to ozone

BACKGROUND

Increased exposure to Ozone (O3) is associated with adverse health effects in individuals afflicted with respiratory diseases. Surfactant protein-A (SP-A), encoded by SP-A1 and SP-A2, is the largest protein component in pulmonary surfactant and is functionally impaired by O3-oxidation.

OBJECTIVE

We used humanized SP-A2 transgenic mice with allelic variation corresponding to a glutamine (Q) to lysine (K) amino acid substitution at position 223 in the lectin domain to determine the impact of this genetic variation in regards to O3 exposure.

METHODS

Mice were exposed to 2ppm O3 or Filtered Air (FA) for 3 hours and 24 hrs post-challenge pulmonary function tests and other parameters associated with inflammation were assessed in the bronchoalveolar lavage (BAL) fluid and lung tissue. Additionally, mouse tracheal epithelial cells were cultured and TEER measurements recorded for each genotype to determine baseline epithelial integrity.

RESULTS

Compared to FA, O3 exposure led to significantly increased sensitivity to methacholine challenge in all groups of mice. SP-A2 223Q variant mice were significantly protected from O3-induced AHR compared to SP-A-/- and SP-A2 223K mice. Neutrophilia was observed in all genotypes of mice post O3-exposure, however, SP-A2 223Q mice had a significantly lower percentage of neutrophils compared to SP-A-/- mice. Albumin levels in BAL were unchanged in O3-exposed SP-A2 223Q mice compared to their FA controls, while levels were significantly increased in all other genotypes of O3-exposed mice. SP-A 223Q MTECS has significant higher TEER values than all other genotypes, and WT MTECS has significantly higher TEER than the SP-A KO and SP-A 223K MTECS.

SIGNIFICANCE

Taken together, our study suggests that expression of a glutamine (Q) as position 223 in SP-A2, as opposed to expression of lysine (K), is more protective in acute exposures to ozone and results in attenuated O3-induced AHR, neutrophilia, and vascular permeability.

Environmental factors in epithelial barrier dysfunction

The main interfaces controlling and attempting to homeostatically balance communications between the host and the environment are the epithelial barriers of the skin, gastrointestinal system, and airways. The epithelial barrier constitutes the first line of physical, chemical, and immunologic defenses and provides a protective wall against environmental factors. Following the industrial revolution in the 19th century, urbanization and socioeconomic development have led to an increase in energy consumption, and waste discharge, leading to increased exposure to air pollution and chemical hazards. Particularly after the 1960s, biological and chemical insults from the surrounding environment-the exposome-have been disrupting the physical integrity of the barrier by degrading the intercellular barrier proteins at tight and adherens junctions, triggering epithelial alarmin cytokine responses such as IL-25, IL-33, and thymic stromal lymphopoietin, and increasing the epithelial barrier permeability. A typical type 2 immune response develops in affected organs in asthma, rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, food allergy, and atopic dermatitis. The aim of this article was to discuss the effects of environmental factors such as protease enzymes of allergens, detergents, tobacco, ozone, particulate matter, diesel exhaust, nanoparticles, and microplastic on the integrity of the epithelial barriers in the context of epithelial barrier hypothesis.

Senescence in Pulmonary Fibrosis: Between Aging and Exposure

To date, chronic pulmonary pathologies represent the third leading cause of death in the elderly population. Evidence-based projections suggest that >65 (years old) individuals will account for approximately a quarter of the world population before the turn of the century. Genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication, are described as the nine “hallmarks” that govern cellular fitness. Any deviation from the normal pattern initiates a complex cascade of events culminating to a disease state. This blueprint, originally employed to describe aberrant changes in cancer cells, can be also used to describe aging and fibrosis. Pulmonary fibrosis (PF) is the result of a progressive decline in injury resolution processes stemming from endogenous (physiological decline or somatic mutations) or exogenous stress. Environmental, dietary or occupational exposure accelerates the pathogenesis of a senescent phenotype based on (1) window of exposure; (2) dose, duration, recurrence; and (3) cells type being targeted. As the lung ages, the threshold to generate an irreversibly senescent phenotype is lowered. However, we do not have sufficient knowledge to make accurate predictions. In this review, we provide an assessment of the literature that interrogates lung epithelial, mesenchymal, and immune senescence at the intersection of aging, environmental exposure and pulmonary fibrosis.

Repetitive Ozone Exposures and Evaluation of Pulmonary Inflammation and Remodeling in Diabetic Mouse Strains

BACKGROUND

Epidemiological studies support the hypothesis that diabetes alters pulmonary responses to air pollutants like ozone (O 3 ). The mechanism(s) underlying these associations and potential links among diabetes, O 3 , and lung inflammation and remodeling are currently unknown.

OBJECTIVES

The goal was to determine whether pulmonary responses to repetitive ozone exposures are exacerbated in murine strains that are hyperglycemic and insulin resistant.

METHODS

Normoglycemic and insulin-sensitive C57BL/6J mice; hyperglycemic, but mildly insulin-resistant, KK mice; and hyperglycemic and markedly insulin-resistant KKAy mice were used for ozone exposure studies. All animals were exposed to filtered air (FA) or repetitive ozone (0.5  ppm O 3 , 4 h/d, for 13 consecutive weekdays). Tissue analysis was performed 24 h following the final exposure. This analysis included bronchoalveolar lavage (BAL) for cell and fluid analysis, and tissue for pathology, immunohistology, mRNA, and hydroxyproline.

RESULTS

Following repetitive O 3 exposure, higher bronchoalveolar lavage fluid inflammatory cells were observed in all mice (KKAy > KK > C 57 BL / 6 ), with a notable influx of neutrophils and eosinophils in KK and KKAy mice. Although the lungs of O 3 -exposed C57BL/6J and KK mice had minimal centriacinar histological changes without fibrosis, the lungs of O 3 -exposed KKAy mice contained marked epithelial hyperplasia in proximal alveolar ducts and adjacent alveoli with associated centriacinar fibrosis. Fibrosis in O 3 -exposed KKAy lungs was confirmed with immunohistochemistry, tissue hydroxyproline content, and tissue mRNA expression of fibrosis-associated genes (Ccl11, Il13, and Mmp12). Immunofluorescence staining and confocal microscopy revealed alterations in the structure and composition of the airway and alveolar epithelium in regions of fibrosis.

DISCUSSION

Our results demonstrate that in diabetic animal strains repetitive ambient ozone exposure led to early and exaggerated pulmonary inflammation and remodeling. Changes in distal and interstitial airspaces and the activation of Th2 inflammatory and profibrotic pathways in experimental animals provide a preliminary, mechanistic framework to support the emerging epidemiological associations among air pollution, diabetes, and lung disease. https://doi.org/10.1289/EHP7255.

Oxidative Stress in Ozone-Induced Chronic Lung Inflammation and Emphysema: A Facet of Chronic Obstructive Pulmonary Disease

Oxidative stress plays an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD) caused by cigarette smoke and characterized by chronic inflammation, alveolar destruction (emphysema) and bronchiolar obstruction. Ozone is a gaseous constituent of urban air pollution resulting from photochemical interaction of air pollutants such as nitrogen oxide and organic compounds. While acute exposure to ozone induces airway hyperreactivity and neutrophilic inflammation, chronic ozone exposure in mice causes activation of oxidative pathways resulting in cell death and a chronic bronchial inflammation with emphysema, mimicking cigarette smoke-induced COPD. Therefore, the chronic exposure to ozone has become a model for studying COPD. We review recent data on mechanisms of ozone induced lung disease focusing on pathways causing chronic respiratory epithelial cell injury, cell death, alveolar destruction, and tissue remodeling associated with the development of chronic inflammation and AHR. The initial oxidant insult may result from direct effects on the integrity of membranes and organelles of exposed epithelial cells in the airways causing a stress response with the release of mitochondrial reactive oxygen species (ROS), DNA, and proteases. Mitochondrial ROS and mitochondrial DNA activate NLRP3 inflammasome and the DNA sensors cGAS and STING accelerating cell death pathways including caspases with inflammation enhancing alveolar septa destruction, remodeling, and fibrosis. Inhibitors of mitochondrial ROS, NLRP3 inflammasome, DNA sensor, cell death pathways, and IL-1 represent novel therapeutic targets for chronic airways diseases underlined by oxidative stress.

Distal lung epithelial progenitor cell function declines with age

Tissue stem cell exhaustion is a key hallmark of aging, and in this study, we characterised its manifestation in the distal lung. We compared the lungs of 3- and 22-month old mice. We examined the gross morphological changes in these lungs, the density and function of epithelial progenitor populations and the epithelial gene expression profile. Bronchioles became smaller in their cross-sectional area and diameter. Using long-term EdU incorporation analysis and immunohistochemistry, we found that bronchiolar cell density remained stable with aging, but inferred rates of bronchiolar club progenitor cell self-renewal and differentiation were reduced, indicative of an overall slowdown in cellular turnover. Alveolar Type II progenitor cell density and self-renewal were maintained per unit tissue area with aging, but rates of inferred differentiation into Type I cells, and indeed overall density of Type I cells was reduced. Microarray analysis revealed age-related changes in multiple genes, including some with roles in proliferation and differentiation, and in IGF and TGFβ signalling pathways. By characterising how lung stem cell dynamics change with aging, this study will elucidate how they contribute to age-related loss of pulmonary function, and pathogenesis of common age-related pulmonary diseases.

miRNAs in Lung Development and Diseases

The development of the lung involves a diverse group of molecules that regulate cellular processes, organ formation, and maturation. The various stages of lung development are marked by accumulation of small RNAs that promote or repress underlying mechanisms, depending on the physiological environment in utero and postnatally. To some extent, the pathogenesis of various lung diseases is regulated by small RNAs. In this review, we discussed miRNAs regulation of lung development and diseases, that is, COPD, asthma, pulmonary fibrosis, and pulmonary arterial hypertension, and also highlighted possible connotations for human lung health.

Ozone-Induced Aryl Hydrocarbon Receptor Activation Controls Lung Inflammation via Interleukin-22 Modulation

Airborne ozone exposure causes severe lung injury and inflammation. The aryl hydrocarbon Receptor (AhR) (1), activated in pollutant-induced inflammation, is critical for cytokine production, especially IL-22 and IL-17A. The role of AhR in ozone-induced lung inflammation is unknown. We report here that chronic ozone exposure activates AhR with increased tryptophan and lipoxin A4 production in mice. AhR-/- mice show increased lung inflammation, airway hyperresponsiveness, and tissue remodeling with an increased recruitment of IL-17A and IL-22-expressing cells in comparison to control mice. IL-17A- and IL-22-neutralizing antibodies attenuate lung inflammation in AhR-/- and control mice. Enhanced lung inflammation and recruitment of ILC3, ILC2, and T cells were observed after T cell-specific AhR depletion using the AhRCD4cre-deficient mice. Together, the data demonstrate that ozone exposure activates AhR, which controls lung inflammation, airway hyperresponsiveness, and tissue remodeling via the reduction of IL-22 expression.

Oxidative Stress Mechanisms in the Pathogenesis of Environmental Lung Diseases

Globally, respiratory diseases are major cause of disability and mortality, and more alarmingly, it disproportionately affects developing countries, which is largely attributed to poor quality of air. Tobacco smoke and emissions from combustion of fossil fuel and biomass fuel are the major airborne pollutants affecting human lung health. Oxidative stress is the dominant driving force by which the airborne pollutants exert their toxicity in lungs and cause respiratory diseases. Most airborne pollutants are associated with intrinsic oxidative potential and, additionally, stimulate endogenous production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Elevated ROS and RNS in lungs modulate redox signals and cause irreversible damage to critical biomolecules (lipids, proteins and DNA) and initiate various pathogenic cellular process. This chapter provides an insight into oxidative stress-linked pathogenic cellular process such as lipid peroxidation, inflammation, cell death, mitochondrial dysfunction, endoplasmic reticulum stress, epigenetic changes, profibrotic signals and mucus hypersecretion, which drive the development and progression of lung diseases. Lungs are associated with robust enzymatic and non-enzymatic (GSH, ascorbic acid, uric acid, vitamin E) antioxidant defences. However, sustained production of free radicals due to continuous exposures to airborne pollutants overwhelms lung antioxidant defences and causes oxidative injury. Preclinical studies have demonstrated the critical roles and therapeutic potential of upregulating lung antioxidants for intervention of respiratory diseases; however, so far clinical benefits in antioxidant supplementation trials have been minimal and conflicting. Antioxidants alone may not be effective in treatment of respiratory diseases; however it could be a promising adjunctive therapy.

Long-Term Exposure to Ozone and Cause-Specific Mortality Risk in the United States

Rationale: Many studies have linked short-term exposure to ozone (O3) with morbidity and mortality, but epidemiologic evidence of associations between long-term O3 exposure and mortality is more limited.Objectives: To investigate associations of long-term (annual or warm season average of daily 8-h maximum concentrations) O3 exposure with all-cause and cause-specific mortality in the NIH-AARP Diet and Health Study, a large prospective cohort of U.S. adults with 17 years of follow-up from 1995 to 2011.Methods: The cohort (n = 548,780) was linked to census tract-level estimates for O3. Associations between long-term O3 exposure (averaged values from 2002 to 2010) and multiple causes of death were evaluated using multivariate Cox proportional hazards models, adjusted for individual- and census tract-level covariates, and potentially confounding copollutants and temperature.Measurements and Main Results: Long-term annual average exposure to O3 was significantly associated with deaths caused by cardiovascular disease (per 10 ppb; hazard ratio [HR], 1.03; 95% confidence interval [CI], 1.01-1.06), ischemic heart disease (HR, 1.06; 95% CI, 1.02-1.09), respiratory disease (HR, 1.04; 95% CI, 1.00-1.09), and chronic obstructive pulmonary disease (HR, 1.09; 95% CI, 1.03-1.15) in single-pollutant models. The results were robust to alternative models and adjustment for copollutants (fine particulate matter and nitrogen dioxide), although some evidence of confounding by temperature was observed. Significantly elevated respiratory disease mortality risk associated with long-term O3 exposure was found among those living in locations with high temperature (Pinteraction < 0.05).Conclusions: This study found that long-term exposure to O3 is associated with increased risk for multiple causes of mortality, suggesting that establishment of annual and/or seasonal federal O3 standards is needed to more adequately protect public health from ambient O3 exposures.

Transcriptional Effects of Ozone and Impact on Airway Inflammation

Epidemiological and challenge studies in healthy subjects and in individuals with asthma highlight the health impact of environmental ozone even at levels considered safe. Acute ozone exposure in man results in sputum neutrophilia in 30% of subjects particularly young children, females, and those with ongoing cardiopulmonary disease. This may be associated with systemic inflammation although not in all cases. Chronic exposure amplifies these effects and can result in the formation of asthma-like symptoms and immunopathology. Asthmatic patients who respond to ozone (responders) induce a greater number of genes in bronchoalveolar (BAL) macrophages than healthy responders with up-regulation of inflammatory and immune pathways under the control of cytokines and chemokines and the enhanced expression of remodeling and repair programmes including those associated with protease imbalances and cell-cell adhesion. These pathways are under the control of several key transcription regulatory factors including nuclear factor (NF)-κB, anti-oxidant factors such as nuclear factor (erythroid-derived 2)-like 2 NRF2, the p38 mitogen activated protein kinase (MAPK), and priming of the immune system by up-regulating toll-like receptor (TLR) expression. Murine and cellular models of acute and chronic ozone exposure recapitulate the inflammatory effects seen in humans and enable the elucidation of key transcriptional pathways. These studies emphasize the importance of distinct transcriptional networks in driving the detrimental effects of ozone. Studies indicate the critical role of mediators including IL-1, IL-17, and IL-33 in driving ozone effects on airway inflammation, remodeling and hyperresponsiveness. Transcription analysis and proof of mechanisms studies will enable the development of drugs to ameliorate the effects of ozone exposure in susceptible individuals.

Role of transient receptor potential cation channel subfamily V member 1 (TRPV1) on ozone-exacerbated allergic asthma in mice

Around the globe, worsening air pollution is spawning major public health and environmental concerns, especially in the poorest and most populous cities. As a major secondary air pollutant, ozone is a potential risk factor for exacerbated asthma, although the underlying mechanisms remain uncertain. In this study, we aim to investigate the role of ozone on asthma exacerbation using a classic asthmatic model with allergic airway inflammation by treating Balb/c mice with ovalbumin (OVA). Our study shows ozone exposure significantly exacerbated OVA-induced asthmatic phenotypes, including serum immunoglobulin, Th cytokines, inflammatory cell counts, mucus production, airway remodeling, and airway hyper-responsiveness (AHR). Interestingly, expression of transient receptor potential cation channel subfamily V member1 (TRPV1) was also significantly elevated in ozone-exacerbated asthmatic mice and that treatment with TRPV1 antagonist effectively suppressed AHR, airway inflammation and remodeling. The underlying mechanisms of these effects may be associated with suppression of neuropeptide calcitonin gene-related peptide (CGRP) and thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine. Base on the role of TRPV1 in allergic asthma, this study further revealed that inhibition of TRPV1 by TRPV1 antagonist has significant anti-inflammatory effects on ozone-induced asthma exacerbation in this study. Induction of TRPV1 expression may be an important mechanism underlying the increased risks for asthma after exposure to environmental pollutants.

Development of a large-scale computer-controlled ozone inhalation exposure system for rodents

Objective: Complete systems for laboratory-based inhalation toxicology studies are typically not commercially available; therefore, inhalation toxicologists utilize custom-made exposure systems. Here we report on the design, construction, testing, operation and maintenance of a newly developed in vivo rodent ozone inhalation exposure system. Materials and methods: Key design requirements for the system included large-capacity exposure chambers to facilitate studies with large sample sizes, automatic and precise control of chamber ozone concentrations, as well as automated data collection on airflow and environmental conditions. The exposure system contains two Hazelton H-1000 stainless steel and glass exposure chambers, each providing capacity for up to 180 mice or 96 rats. We developed an empirically tuned proportional-integral-derivative control loop that provides stable ozone concentrations throughout the exposure period (typically 3h), after a short ramp time (∼8 min), and across a tested concentration range of 0.2-2 ppm. Specific details on the combination of analog and digital input/output system for environmental data acquisition, control and safety systems are provided, and we outline the steps involved in maintenance and calibration of the system. Results: We show that the exposure system produces consistent ozone exposures both within and across experiments, as evidenced by low coefficients of variation in chamber ozone concentration and consistent biological responses (airway inflammation) in mice, respectively. Conclusion: Thus, we have created a large and robust ozone exposure system, facilitating future studies on the health effects of ozone in rodents.