Effect of Cigarette Smoke Exposure on Bronchial Hyperresponsiveness in Mice and Response to a Corticosteroid and/or a β2-Adrenergic Agonist and Effect of Cigarette Smoke Extract on Cytokines Release from U937 Cells.
The number of people affected with chronic inflammatory diseases of airways such as asthma and chronic obstructive pulmonary disease (COPD) are growing globally. Asthma is characterized by inflammation driven mainly by eosinophils, reversible airflow obstruction and significant airway hyperesponsiveness to airway stimuli like methacholine (MCh). It is increasingly prevalent in the US (24.6 million in 2009), particularly among children and some minority groups. Three hundred million people worldwide have been reported to have asthma with 250,000 annual deaths attributed to it. COPD is a pulmonary disease with irreversible airway obstruction and inflammation driven by neutrophils and macrophages. In the US in 2005, an estimated 126,000 US deaths were attributed to COPD. |Corticosteroids and/or β2 adrenergic agents are the main line of therapy for both asthma and COPD. However, some people with asthma, and the majority with COPD show diminished response to corticosteroid therapy. Various factors such as an increase in number of glucocorticoid receptors β, increase in activator protein-1 (AP-1), and increase in Th-2 cytokines (IL-4 and IL-13), and diminished histone deacetylase-2 activity are attributed to corticosteroid resistance. Since smoking is the primary risk factor of COPD and most of the patients with COPD show poor response to corticosteroids, oxidative stress should play an important role in causing diminished response to corticosteroids. In addition, various clinical studies have reported that people with asthma who are active smokers show less improvement in lung function with corticosteroids compared to non-smokers.|Based upon these rationales, we wanted to develop a model of smoking and COPD in mice and to study response to inhaled corticosteroid (ICS) and/or long acting beta agonists (LABA) as measured by bronchial hyperresponsiveness (BHR) to MCh and airway inflammation. We designed a 4 weeks smoke exposure study and administered inhaled fluticasone propionate (FP) and/or salmeterol to determine and compare their efficacy in smoke exposed versus non-smoke exposed mice. We also investigated the effect of cigarette smoke extract (CSE) on the contractility of isolated mouse trachea in vitro. Since, alveolar macrophages, and inflammatory proteins released by them, play an important role in causing exacerbations of asthma and worsening COPD, we studied the effect of CSE on cytokines (e.g. IL-6, IL-8 and IL-10) release from macrophage like cells (U937 cell line).|We found that cigarette smoke exposure in mice increased BHR to MCh. Also, the BHR in smoke exposed mice treated with FP and/or salmeterol was significantly higher than BHR in non-smoked mice treated with the same drugs. The drugs did not protect against BHR as demonstrated by Penh and provocative concentration of MCh (PC200). The measured cytokines (IL-1β, TNF-α, IL-13 and GM-CSF) were higher in the bronchial alveolar lavage (BAL) fluid of smoke exposed mice compared to non-smoked mice although the difference was not significant. Further, none of the drugs reduced the level of cytokines in BAL fluid. We found a non-significant increase in MCh induced contraction in CSE pretreated (24 h) isolated mouse tracheas compared to vehicle pretreated tracheas. We also found that there was a significant difference in contractility of the lower portion of trachea compared to the upper portion of trachea. |Treatment of U937 cells with cigarette smoke extract (CSE) showed a differential effect on cytokines release. We found that CSE treatment reduced the release of the inflammatory cytokine, IL-6, from vehicle treated as well as lipopolysaccharide (LPS) stimulated cells. In contrast, CSE treatment induced IL-8 release from these cells in a dose dependent manner. LPS and CSE synergistically stimulated IL-8 release from the cells. Treatment with CSE reduced the release of IL-10, an anti-inflammatory cytokine, from vehicle as well as LPS treated cells. Effect of IL-13 on release of IL-6, 8 and 10 was also evaluated. |In conclusion, cigarette smoke exposure induced BHR to MCh. FP and/or salmeterol did not protect against BHR to MCh in cigarette smoke exposed mice whereas albuterol did protect. Cigarette smoke exposure caused diminished response to a corticosteroids and a long acting β2 adrenergic agnoist compared to non-smoked mice. CSE treatement of U937 cells caused inhibition of IL-6 and IL-10 release whereas it caused induction of IL-8 release.
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