Impact of Exposure to Diesel Exhaust on Inflammation Markers and Proteases in Former Smokers with COPD: A Randomized, Double-Blinded, Crossover Study

Impact of environmental air pollution on respiratory health and function

Environmental air pollution presents a considerable risk to global respiratory health. If critical levels are exceeded, inhaled pollutants can lead to the development of respiratory dysfunction and provoke exacerbation in those with pre-existing chronic respiratory disease. Over 90% of the global population currently reside in areas where environmental air pollution is considered excessive-with adverse effects ranging from acute airway irritation to complex immunomodulatory alterations. This narrative review provides an up-to-date perspective concerning the impact of environmental air pollution on respiratory health and function and describes the underpinning mechanisms that contribute to the development and progression of chronic respiratory disease.

COPD Exposed to Air Pollution: A Path to Understand and Protect a Susceptible Population

TOPIC IMPORTANCE

Air pollution poses a risk to the respiratory health of individuals with COPD. Long- and short-term exposures to higher levels of particulate-rich air pollution are associated with increased COPD exacerbation, hospitalization, and mortality, collectively implicating air pollution as a cause of adverse COPD-related outcomes.

REVIEW FINDINGS

This review summarizes the evidence for COPD as a phenotype that confers susceptibility for adverse health outcomes in the face of common air pollution. We highlight how typical contributors to compromised urban air quality, including that from traffic, wildfire smoke, and indoor biomass combustion, adversely affect the COPD patient population. Evidence underscoring the burden of ongoing air pollution exposure on patients with COPD is discussed. We then detail the detrimental impact of that exposure on COPD pathophysiology, which in turn increases the patient's susceptibility. We specifically propose that indoor air is a particularly rational target for increased monitoring and remediation to protect patients with COPD. Because COPD is a heterogeneous disease with several endotypes, future intervention studies need to better include control populations, to highlight COPD-specific risks and identify subpopulations within patients with COPD who will benefit the most from improved indoor air quality.

SUMMARY

Regulatory efforts must continue to broadly lower emission standards to protect this susceptible population from the negative health impacts of air pollution.

Selected updates on chronic obstructive pulmonary disease

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is preventable disease and yet it remains the third greatest cause of death worldwide. This review focuses on recent updates in COPD research which have had an impact on our understanding of the epidemiology and pathophysiology of COPD.

RECENT FINDINGS

Epidemiological studies of COPD have moved towards trying to understand the global impact of COPD particularly in low- and middle-income countries where disease prevalence continues to increase. In addition, we are beginning to uncover the impact of air pollution on COPD development with recent work showing a relationship between air pollution and COPD exacerbations. Advances in understanding early origins and early development of COPD have the potential to intervene earlier in the disease course to prevent disease progression. Although biomarkers such as peripheral blood eosinophilia have led to trials of biologic agents in COPD suggesting we may be entering an exciting new biologic era in COPD.

SUMMARY

Recent advances suggest there may be a relationship between air pollution and COPD exacerbations. This requires further research to influence environmental policy. New clinical trials of biologics targeting TH2 inflammation in COPD suggest that targeted treatments with biologics may be a possibility COPD.

Short-term air pollution exposure and exacerbation events in mild to moderate COPD: a case-crossover study within the CanCOLD cohort

BACKGROUND

Infections are considered as leading causes of acute exacerbations of chronic obstructive pulmonary disease (COPD). Non-infectious risk factors such as short-term air pollution exposure may play a clinically important role. We sought to estimate the relationship between short-term air pollutant exposure and exacerbations in Canadian adults living with mild to moderate COPD.

METHODS

In this case-crossover study, exacerbations ('symptom based': ≥48 hours of dyspnoea/sputum volume/purulence; 'event based': 'symptom based' plus requiring antibiotics/corticosteroids or healthcare use) were collected prospectively from 449 participants with spirometry-confirmed COPD within the Canadian Cohort Obstructive Lung Disease. Daily nitrogen dioxide (NO2), fine particulate matter (PM2.5), ground-level ozone (O3), composite of NO2 and O3 (Ox), mean temperature and relative humidity estimates were obtained from national databases. Time-stratified sampling of hazard and control periods on day '0' (day-of-event) and Lags ('-1' to '-6') were compared by fitting generalised estimating equation models. All data were dichotomised into 'warm' (May-October) and 'cool' (November-April) seasons. ORs and 95% CIs were estimated per IQR increase in pollutant concentrations.

RESULTS

Increased warm season ambient concentration of NO2 was associated with symptom-based exacerbations on Lag-3 (1.14 (1.01 to 1.29), per IQR), and increased cool season ambient PM2.5 was associated with symptom-based exacerbations on Lag-1 (1.11 (1.03 to 1.20), per IQR). There was a negative association between warm season ambient O3 and symptom-based events on Lag-3 (0.73 (0.52 to 1.00), per IQR).

CONCLUSIONS

Short-term ambient NO2 and PM2.5 exposure were associated with increased odds of exacerbations in Canadians with mild to moderate COPD, further heightening the awareness of non-infectious triggers of COPD exacerbations.

CXCL17 Attenuates Diesel Exhaust Emissions Exposure-Induced Lung Damage by Regulating Macrophage Function

Exposure to diesel exhaust emissions (DEE) is strongly linked to innate immune injury and lung injury, but the role of macrophage chemoattractant CXCL17 in the lung damage caused by DEE exposure remains unclear. In this study, whole-body plethysmography (WBP), inflammatory cell differential count, and histopathological analysis were performed to assess respiratory parameters, airway inflammation, and airway injury in C57BL/6 male mice exposed to DEE for 3 months. qRT-PCR, IHC (immunohistochemistry), and ELISA were performed to measure the CXCL17 expression in airway epithelium or BALF (bronchoalveolar lavage fluid) following DEE/Diesel exhaust particle (DEP) exposure. Respiratory parameters, airway inflammation, and airway injury were assessed in CXCL17-overexpressing mice through adeno-associated virus vector Type 5 (AAV5) infection. Additionally, an in vitro THP-1 and HBE co-culture system was constructed. Transwell assay was carried out to evaluate the effect of rh-CXCL17 (recombinant human protein-CXCL17) on THP-1 cell migration. Flow cytometry and qRT-PCR were conducted to assess the impacts of rh-CXCL17 on apoptosis and inflammation/remodeling of HBE cells. We found that the mice exposed to DEE showed abnormal respiratory parameters, accompanied by airway injury and remodeling (ciliary injury in airway epithelium, airway smooth muscle hyperplasia, and increased collagen deposition). Carbon content in airway macrophages (CCAM), but not the number of macrophages in BALF, increased significantly. CXCL17 expression significantly decreased in mice airways and HBE after DEE/DEP exposure. AAV5-CXCL17 enhanced macrophage recruitment and clearance of DEE in the lungs of mice, and it improved respiratory parameters, airway injury, and airway remodeling. In the THP-1/HBE co-culture system, rh-CXCL17 increased THP-1 cell migration while attenuating HBE cell apoptosis and inflammation/remodeling. Therefore, CXCL17 might attenuate DEE-induced lung damage by recruiting and activating pulmonary macrophages, which is expected to be a novel therapeutic target for DEE-associated lung diseases.

Comparable Response Following Exposure to Biodiesel and Diesel Exhaust Particles in Advanced Multicellular Human Lung Models

Biodiesel is considered to be a sustainable alternative for fossil fuels such as petroleum-based diesel. However, we still lack knowledge about the impact of biodiesel emissions on humans, as airways and lungs are the primary target organs of inhaled toxicants. This study investigated the effect of exhaust particles from well-characterized rapeseed methyl ester (RME) biodiesel exhaust particles (BDEP) and petro-diesel exhaust particles (DEP) on primary bronchial epithelial cells (PBEC) and macrophages (MQ). The advanced multicellular physiologically relevant bronchial mucosa models were developed using human primary bronchial epithelial cells (PBEC) cultured at air-liquid interface (ALI) in the presence or absence of THP-1 cell-derived macrophages (MQ). The experimental set-up used for BDEP and DEP exposures (18 µg/cm² and 36 µg/cm²) as well as the corresponding control exposures were PBEC-ALI, MQ-ALI, and PBEC co-cultured with MQ (PBEC-ALI/MQ). Following exposure to both BDEP and DEP, reactive oxygen species as well as the stress protein heat shock protein 60 were upregulated in PBEC-ALI and MQ-ALI. Expression of both pro-inflammatory (M1: CD86) and repair (M2: CD206) macrophage polarization markers was increased in MQ-ALI after both BDEP and DEP exposures. Phagocytosis activity of MQ and the phagocytosis receptors CD35 and CD64 were downregulated, whereas CD36 was upregulated in MQ-ALI. Increased transcript and secreted protein levels of CXCL8, as well as IL-6 and TNF-α, were detected following both BDEP and DEP exposure at both doses in PBEC-ALI. Furthermore, the cyclooxygenase-2 (COX-2) pathway, COX-2-mediated histone phosphorylation and DNA damage were all increased in PBEC-ALI following exposure to both doses of BDEP and DEP. Valdecoxib, a COX-2 inhibitor, reduced the level of prostaglandin E2, histone phosphorylation, and DNA damage in PBEC-ALI following exposure to both concentrations of BDEP and DEP. Using physiologically relevant multicellular human lung mucosa models with human primary bronchial epithelial cells and macrophages, we found BDEP and DEP to induce comparable levels of oxidative stress, inflammatory response, and impairment of phagocytosis. The use of a renewable carbon-neutral biodiesel fuel does not appear to be more favorable than conventional petroleum-based alternative, as regards of its potential for adverse health effects.

Lung adenocarcinoma promotion by air pollutants

A complete understanding of how exposure to environmental substances promotes cancer formation is lacking. More than 70 years ago, tumorigenesis was proposed to occur in a two-step process: an initiating step that induces mutations in healthy cells, followed by a promoter step that triggers cancer development1. Here we propose that environmental particulate matter measuring ≤2.5 μm (PM2.5), known to be associated with lung cancer risk, promotes lung cancer by acting on cells that harbour pre-existing oncogenic mutations in healthy lung tissue. Focusing on EGFR-driven lung cancer, which is more common in never-smokers or light smokers, we found a significant association between PM2.5 levels and the incidence of lung cancer for 32,957 EGFR-driven lung cancer cases in four within-country cohorts. Functional mouse models revealed that air pollutants cause an influx of macrophages into the lung and release of interleukin-1β. This process results in a progenitor-like cell state within EGFR mutant lung alveolar type II epithelial cells that fuels tumorigenesis. Ultradeep mutational profiling of histologically normal lung tissue from 295 individuals across 3 clinical cohorts revealed oncogenic EGFR and KRAS driver mutations in 18% and 53% of healthy tissue samples, respectively. These findings collectively support a tumour-promoting role for  PM2.5 air pollutants  and provide impetus for public health policy initiatives to address air pollution to reduce disease burden.

Contemporary Concise Review 2022: Chronic obstructive pulmonary disease

International respiratory organizations now recommend using lower limit of normal and standardized residuals to diagnose airflow obstruction and COPD though using a fixed ratio <0.7 is simpler and robustly predicts important clinical outcomes. The most common COPD comorbidities are coronary artery calcification, emphysema and bronchiectasis. COPD patients with psychological (high anxiety and depression) and cachectic (underweight and osteoporotic) comorbidity have higher mortality and exacerbate more. Serum eosinophil count remains an important COPD biomarker and we have greater clarity about normal eosinophil levels in COPD and the wider population. Criteria for entry into COPD clinical trials continue to exclude many patients, in particular those at greater risk of exacerbation and death. The effect of hyperinflation on cardiac function impacts COPD mortality and is an important target for successful lung volume reduction procedures.

Exposure to diesel exhaust alters the functional metagenomic composition of the airway microbiome in former smokers

The lung microbiome plays a crucial role in airway homeostasis, yet we know little about the effects of exposures such as air pollution therein. We conducted a controlled human exposure study to assess the impact of diesel exhaust (DE) on the human airway microbiome. Twenty-four participants (former smokers with mild to moderate COPD (N = 9), healthy former smokers (N = 7), and control healthy never smokers (N = 8)) were exposed to DE (300 μg/m³ PM_2.5) and filtered air (FA) for 2 h in a randomized order, separated by a 4-week washout. Endobronchial brushing samples were collected 24 h post-exposure and sequenced for the 16S microbiome, which was analyzed using QIIME2 and PICRUSt2 to examine diversity and metabolic functions, respectively. DE exposure altered airway microbiome metabolic functions in spite of statistically stable microbiome diversity. Affected functions included increases in: superpathway of purine deoxyribonucleosides degradation (pathway differential abundance 743.9, CI 95% 201.2 to 1286.6), thiazole biosynthesis I (668.5, CI 95% 139.9 to 1197.06), and L-lysine biosynthesis II (666.5, CI 95% 73.3 to 1257.7). There was an exposure-by-age effect, such that menaquinone biosynthesis superpathways were the most enriched function in the microbiome of participants aged >60, irrespective of smoking or health status. Moreover, exposure-by-phenotype analysis showed metabolic alterations in former smokers after DE exposure. These observations suggest that DE exposure induced substantial changes in the metabolic functions of the airway microbiome despite the absence of diversity changes.

Effect of traffic-related air pollution on cough in adults with polymorphisms in several cough-related genes

With prevalent global air pollution, individuals with certain genetic predispositions and sensitivities are at of higher risk of developing respiratory symptoms including chronic cough. Studies to date have relied on patient-filled questionnaires in epidemiological studies to evaluate the gene-by-environment interactions. In a controlled human exposure study, we evaluated whether genetic risk score (GRS) based on cough-related single-nucleotide polymorphisms (SNPs) are associated with a cough count over 24 h post-exposure to diesel exhaust (DE), a model for traffic-related air pollution. DE is a mixture of several known air pollutants including PM_2.5, CO, NO, NO₂, and volatile organic compounds. Under closely observed circumstances, we determined that GRS constructed from 7 SNPs related to TRPA1, TRPV1, and NK-2R were correlated with cough count. Selection of channels were based on prior knowledge that SNPs in these channels lead to acute airway inflammation as a result of their increased sensitivity to particulate matter. We performed a linear regression analysis and found a significant, positive correlation between GRS and cough count following DE exposure (p = 0.002, R² = 0.61) and filtered air (FA) exposure (p = 0.028, R² = 0.37). Although that correlation was stronger for DE than for FA, we found no significant exposure-by-GRS interaction. In summary, cough-relevant GRS was associated with a higher 24 h cough count in a controlled setting, suggesting that individuals with a high GRS may be more susceptible to developing cough regardless of their exposure. The trend towards this susceptibility being more prominent in the context of traffic-related air pollution remains to be confirmed.

Trial registration: ClinicalTrial.gov NCT02236039; NCT0223603. Registered on August 11, 2014, https://clinicaltrials.gov/ct2/show/NCT02236039.