The effect of diesel emission exposure on primary human bronchial epithelial cells from a COPD cohort: N-acetylcysteine as a potential protective intervention
Introduction
The World Health Organization (WHO) has estimated that 3 million people die of chronic obstructive pulmonary disease (COPD) each year and that COPD will be the third leading cause of death in 2020 (GOLD, 2018). COPD results from a prolonged interaction between the airways and noxious inhalants such as cigarette smoke and air pollution. A major contributor to ambient outdoor air pollution is particulate matter (PM), and diesel emissions are a major source particulate matter pollution. Prolonged exposure to PM is associated with COPD progression and mortality (Ni et al., 2015, Shaw et al., 2014).
Diesel emissions have a high level of fine particulate matter (PM2.5), and upon inhalation, these particles can reach the lower airways (Ristovski et al., 2012). Exposure to diesel emissions can cause secretion of proinflammatory cytokines and recruitment of immune cells to the airways (Sydbom et al., 2001), which can trigger acute exacerbations of COPD (Brusselle et al., 2011). Diesel emissions exposure, if prolonged, can have a severe impact on airway epithelium, causing inflammation, oxidative stress and tissue injury (Durga et al., 2014, Li et al., 2008). Damage to the airway epithelium is a key driver of the pathogenesis and progression of COPD. Effective therapeutic intervention to protect the airway epithelium from diesel emission exposure may prevent inflammation and oxidative stress in the airways, and potentially, progression of COPD. Unfortunately, there are currently no effective interventions to protect airways from diesel emission exposure.
Current therapeutic interventions for COPD include bronchodilators, antibiotics and corticosteroids to reduce inflammation (GOLD, 2018), reduce airflow obstruction, suppress inflammation and prevent exacerbation. Attempts have been made to reduce air pollution generated by traffic, including changes to the engine (refinement of current EGR systems and fuel injection systems), exhaust control technologies (catalytic reduction, diesel particulate filters (DPFs), cleaner diesel fuel and fuel saving technologies. As the benefits of implementing such strategies may take years to be realized, other means of protecting vulnerable airways from the adverse effects of air pollution are needed. Therefore, the aim of this study was to test the ability of the antioxidant, N-acetylcysteine (NAC), to protect primary human bronchial epithelial cells from COPD patients against diesel emissions.
Section snippets
Establishing primary cell lines
Primary human bronchial epithelial cells (pHBEC) lines were established at the University of Queensland Thoracic Research Centre (UQTRC) from clinical samples donated, with written informed consent, by patients undergoing surgery to resect lung cancer at The Prince Charles Hospital. pHBECs were established from the bronchi of resected lung tissue as previously described (Vaughan et al., 2015). Briefly, bronchial tissue isolated from a lung resection specimen was incubated in a dissociation mix
Diesel emission characterization
The physical and chemical characteristics of the diesel emissions were assessed through the measurement of particle size distribution (Fig. 1), gas concentrations, particle number and particle mass (Table 3). The particle size distribution was comparable to previous research with the same engine parameters (Vaughan et al., 2015). The average concentration of CO2, CO and NOx were 0.24 ppm, 7.8 ppm and 20.4 ppm, respectively. The particle number was 1.93 × 106 with an average particle mass of
Discussion
The aim of this study was to test the efficiency of an antioxidant therapy, N-acetylcysteine (NAC), as a protective intervention against diesel emission exposure on primary human bronchial epithelial cells from a COPD cohort. There are four main findings from this study. First, SOD1 was suppressed after diesel emission exposure in COPD bronchial epithelial cells. Second, COPD bronchial epithelial cells had a stronger metabolic response to diesel emissions with increased CYP1A1 mRNA expression
Limitations
A limitation of this study is that the pHBECs from the non-COPD cohort used as controls were not from disease-free lungs. In both non-COPD and COPD cohorts HBECs were obtained from bronchi within resected lung donated by patients undergoing surgery for lung cancer. Both pHBECs lines were matched for a diagnosis of lung adenocarcinoma. Hence, observed differences in epithelial cell responses between the two groups are likely due to presence or absence of COPD than to lung cancer.
Two normal pHBEC
Conclusion
This study has shown evidence that bronchial epithelial cells from COPD patients may be vulnerable to diesel emission exposure due to reduced antioxidant capacity and heightened CYP1a1 mRNA expression. NAC was not an effective intervention against the adverse effects of diesel emission exposure in COPD. These findings provide new insight into the epithelial responses of the COPD lung to diesel emission exposure. Future research will focus on characterizing the epithelial immune phenotype in the
Funding
This research was funded by the Australian Research Council Discovery Grant (DP120100126), The Prince Charles Hospital Foundation Ph.D. Scholarship (PhD2014-10), The Prince Charles Hospital Foundation New Investigator Grant (NR2013-232) and National Health and Medical Research Council Career Development Fellowship (APP1026215).
Research ethics
This study was approved by the Human Research Ethics Committee for the Metro North Hospital and Health Service and the University of Queensland (HREC/11/QPCH/196: Interventions to reduce pulmonary toxicity of ultrafine particles: SSA/11/QPCH/233).
References (39)
New insights into the immunology of chronic obstructive pulmonary disease
Lancet
(2011)Effects of ultrafine petrol exhaust particles on cytotoxicity, oxidative stress generation, DNA damage and inflammation in human A549 lung cells and murine RAW 264.7 macrophages
Environ. Toxicol. Pharmacol.
(2014)Function and regulation of MHC class II molecules in T-lymphocytes: of mice and men
Hum. Immunol.
(2004)Effect of N-acetylcysteine administration on the expression and activities of antioxidant enzymes and the malondialdehyde level in the blood of lead-exposed workers
Environ. Toxicol. Pharmacol.
(2014)Induction of IL-8(CXCL8) and MCP-1(CCL2) with oxidative stress and its inhibition with N-acetyl cysteine (NAC) in cell culture model using HK-2 cell
Transplant. Immunol.
(2016)The role of oxidative stress in ambient particulate matter-induced lung diseases and its implications in the toxicity of engineered nanoparticles
Free Radic. Biol. Med.
(2008)Present yourself! By MHC class I and MHC class II molecules
Trends Immunol.
(2016)Radical differences in CYP1A1 genotype and function
Toxicol. Lett.
(1995)Decreased expression of antioxidant enzymes and increased expression of chemokines in COPD lung
Pulm. Pharmacol. Ther.
(2007)CYP1A1, CYP1A2 and CYBA gene polymorphisms associated with oxidative stress in COPD
Clin. Chim. Acta
(2010)