Discussion
allergic, death, neutrophilic airway, inflammation, cancer, toxicity, airway neutrophilia, pulmonary adenocarcinoma, asthma, adenocarcinoma, necrosis
INFLAMMATION, DNA DAMAGE, DISEASE, CANCER, PULMONARY ADENOCARCINOMA, ASTHMA, ADENOCARCINOMA, NECROSIS, CYTOTOXICITY
Contrary to our hypothesis, we could not detect any acute airway neutrophilia following exposure to wood smoke. In contrast, there were signs of cytotoxicity in BAL fluid, in terms of increased LDH levels, decreased cellular viability and reduced bacterial phagocytic capacity ex vivo. Furthermore, in vitro cell studies with wood smoke particles collected from the exposure chamber, showed decreased metabolic activity, increased DNA damage and cell cycle disturbances. We did not detect any signs of neutrophilic airway inflammation after wood smoke exposure, neither at 6 h nor at 24 h, which differs to findings from a series of controlled diesel exhaust and ozone studies [A previous wood smoke exposure study in humans has reported an increase in the percentage of neutrophils in BAL and in blood 20 h after exposure to smouldering hardwood [In BAL, a small, but significant increase in LDH was seen, indicative of cytotoxicity, as LDH is considered a marker for cell or tissue damage. LDH is an intracellular protein that is released upon damage of the cell membrane, which can be due to apoptosis, necrosis or other forms of cellular injury [The tendency of a decrease in macrophages in BW is suggestive of an early sign of cytotoxicity at the 6-h time point in the proximal airways. This could have developed to a more established state of cytotoxicity at 24 h, as was present and demonstrated in terms of significantly reduced BW macrophages at the later time point in our preceding study [Alveolar macrophages have a crucial role in the innate immune response. Macrophages are present in the respiratory lining fluid and serve as first line defence, as they phagocytose and kill airway pathogens intracellularly. One of their functions is also to recruit inflammatory cells to the lung and an impaired macrophage response can therefore affect the pulmonary inflammatory cascade negatively [A small, but statistically significant, increase in lavage eosinophils was found after wood smoke exposure. Eosinophils are known to have a key role in asthma and higher levels predict worsening of the disease. In the present study, none of the participants were allergic or had asthma but nevertheless responded with an increase in airway eosinophils. Air pollution has been considered to contribute to the development and worsening of asthma due to oxidative responses and immune dysregulation [In the present study, the mean PMIn this study wood smoke from incomplete combustion conditions was used, resulting in PAH and soot rich PM, compared to more efficient biomass burning applications. The physicochemical properties of the particles are crucial for their toxicological properties and associated health effects [In vitro exposure to WSP at concentrations above 75 µg/mL resulted in a concentration-dependent increase in DNA damage compared to air exposed control cells, but no increase in DNA damage was seen in BW and BAL after wood smoke exposure. DNA damage was expected, due to the high levels of PAH during the exposures, as many PAH compounds cause oxidative DNA damage and are well-known carcinogens [Human lung epithelial cell lines were exposed to WSP collected from the human chamber exposures. The cell lines utilised were chosen to investigate how airway epithelial and alveolar cells may be affected, as well as to investigate toxicological mechanisms. A549 cells are a cancer cell line derived from an adenocarcinoma and are commonly used as a model of type II pulmonary epithelial cells. Overall, the BEAS-2B cells showed a higher sensitivity to WSP than A549 cells, with extensive cell death at concentrations of 150 and 300 µg/mL. This may be due to the different origins of the cell lines, with A549 originating from a pulmonary adenocarcinoma and therefore may be more resistant to the effects of WSP, whereas the BEAS-B2 cells are from an immortalized cell line derived from a normal bronchial epithelium. [The standard exposure procedure in air pollution experiments in vitro has been to resuspend PM in liquid growth media. This may alter the particle composition, since adding e.g. nano particles directly in culture medium increases the possibility of particle agglomeration, which can affect the particle toxicity [We also found an unexpected reduction in cellular ROS activity in BEAS-2B cells, since WSP have previously been reported to cause an increase in intracellular ROS activity [