Effects of particulate matter from straw burning on lung fibrosis in mice

Objective: To investigate the impacts of particulate matter 2.5 (PM2.5) from straw burning on the acute exacerbation of lung fibrosis in mice and the preventive effects of N-acetylcysteine (NAC). Methods: The composition, particle size, and 30-min concentration change in an exposure system of the PM2.5 from straw-burning were determined. Forty C57BL male mice were equally randomized to two groups: bleomycin (BLM)-induced lung fibrosis with an exposure to air (BLM + air) and BLM + PM2.5 groups. On day 7 after receiving intratracheal injection of BLM, mice were exposed to air or PM2.5 in an exposure system for 30 min twice daily and then sacrificed after one-week or four-week exposure (10 mice/group). Mouse survival, lung histopathology, macrophage accumulation in the lung, and pro-inflammatory cytokine levels in alveolar lavage fluid (ALF) were determined. Results: PM2.5 from straw burning were mainly composed of organic matter (74.1%); 10.92% of the inorganic matter of the PM2.5 were chloride ion; 4.64% were potassium ion; other components were sulfate, nitrate, and nitrite. Particle size was 10nm-2 mu m. Histopathology revealed a greater extent of inflammatory cell infiltration in the lung, widened alveolar septum, and lung fibrosis in the BLM + PM2.5 group than in the BLM + air group and a greater extent of those adverse effects after four-week than after one-week exposure to PM2.5. The BLM + PM2.5 group also showed macrophages containing particular matter and increased pulmonary collagen deposition as the exposure to PM2.5 increased. Interleukin (IL)-6 and TNF-alpha levels in ALF were significantly higher in the BLM + PM2.5 group than in the BLM + air group (P < 0.05) and significantly higher after four-week exposure than after one-week exposure to PM2.5 (P < 0.05). TGF-beta levels in ALF after four-week exposure were significantly higher in the BLM + PM2.5 group than in the BLM + air group (P < 0.05). The levels of IL -6, TNF-alpha, and TGF-beta in peripheral serum were not significantly different in the BLM + PM2.5 and BLM + air groups. Lung hydroxyproline contents increased as the exposure to PM2.5 increased and were significantly higher after four-week than after one-week exposure (P = 0.019). Exposure to PM2.5 did not affect the survival of normal mice (100%) but reduced the survival of mice with BLM-induced IPF (30%), whereas NAC extended the survival (70%, vs. BLM + PM2.5, P = 0,032). Conclusion: Exposure of mice with BLM-induced IPF to PM2.5 from straw burning exacerbated lung inflammation and fibrosis and increased mortality; NAC increased the mouse survival, indicating protective effects.