Critical role of aldehydes in cigarette smoke-induced acute airway inflammation.

BACKGROUND: Cigarette smoking (CS) is the most important risk factor for COPD, which is associated with neutrophilic airway inflammation. We hypothesize, that highly reactive aldehydes are critical for CS-induced neutrophilic airway inflammation. METHODS: BALB/c mice were exposed to CS, water filtered CS (WF-CS) or air for 5 days. Levels of total particulate matter (TPM) and aldehydes in CS and WF-CS were measured. Six hours after the last exposure, inflammatory cells and cytokine levels were measured in lung tissue and bronchoalveolar lavage fluid (BALF). Furthermore, Beas-2b bronchial epithelial cells were exposed to CS extract (CSE) or WF-CS extract (WF-CSE) in the absence or presence of the aldehyde acrolein and IL-8 production was measured after 24 hrs. RESULTS: Compared to CS, in WF-CS strongly decreased (CS; 271.1 ± 41.5 µM, WF-CS; 58.5 ± 8.2 µM) levels of aldehydes were present whereas levels of TPM were only slightly reduced (CS; 20.78 ± 0.59 mg, WF-CS; 16.38 ± 0.36 mg). The numbers of mononuclear cells in BALF (p<0.01) and lung tissue (p<0.01) were significantly increased in the CS- and WF-CS-exposed mice compared to air control mice. Interestingly, the numbers of neutrophils (p<0.001) in BALF and neutrophils and eosinophils (p<0.05) in lung tissue were significantly increased in the CS-exposed but not in WF-CS-exposed mice as compared to air control mice. Levels of the neutrophil and eosinophil chemoattractants KC, MCP-1, MIP-1α and IL-5 were all significantly increased in lung tissue from CS-exposed mice compared to both WF-CS-exposed and air control mice. Interestingly, depletion of aldehydes in WF-CS extract significantly reduced IL-8 production in Beas-2b as compared to CSE, which could be restored by the aldehyde acrolein. CONCLUSION: Aldehydes present in CS play a critical role in inflammatory cytokine production and neutrophilic- but not mononuclear airway inflammation.

Lipid-soluble components in cigarette smoke induce mitochondrial production of reactive oxygen species in lung epithelial cells.

Reactive oxygen species (ROS) present in cigarette smoke (CS) are thought to contribute to the development of COPD. Although CS-ROS can hardly enter airway epithelial cells, and certainly not the circulation, systemic levels of ROS have been found to be elevated in COPD patients. We hypothesize that lipophilic components present in CS can enter airway epithelial cells and increase intracellular ROS production by disturbing mitochondrial function. Different airway epithelial cells were exposed to CS extract (CSE), hexane-treated CSE (CSE without lipophilic components), gaseous-phase CS, and water-filtered CS (gaseous-phase CS without ROS). Mitochondrial membrane potential (Deltapsi(m)) and ATP levels were assessed using the bronchial epithelial cell line Beas-2b. ROS generation measured directly by DCF fluorescence and indirectly by measuring free thiol groups (-SH) upon exposure to CS was assessed using lung alveolar epithelial cells devoid of functional mitochondria (A549-rho0), with normal A549 cells serving as controls. In Beas-2b cells, CSE (4 h) caused a dose-dependent decrease in Deltapsi(m) and ATP levels, whereas hexane-treated CSE did not. DCF fluorescence in A549 cells increased in response to CSE, whereas this was not the case in A549-rho0 cells. Exposure of A549 cells to CS resulted in a rapid decrease in free -SH, whereas exposure to ROS-depleted CS only resulted in a delayed decrease. This delayed decrease was less pronounced in A549-rho0 cells. Lipophilic components in CS disturb mitochondrial function, which contributes to increased intracellular generation of ROS. Our results are of importance in understanding the systemic effects of smoking observed in patients with COPD.