Background -Epidemiological evidence has implicated fine particulate air pollution, particularly particles less than 10 tm in diameter (PMO), in the development of exacerbations of asthma and chronic obstructive pulmonary disease (COPD) although the mechanism is unknown. The hypothesis that PM10 particles induce oxidant stress, causing inflammation and injury to airway epithelium, was tested. Methods -The effects of intratracheal instillation of PM,0 was assessed in rat lungs (three per group). Inflammatory cell influx was measured by bronchoalveolar lavage (BAL) and air space epithelial permeability was assessed as the total protein in BAL fluid in vivo. The oxidant properties of PM10 particles were determined by their ability to cause damage to plasmid DNA and by changes in reduced (GSH) and oxidised (GSSG) glutathione. The effects of PM10 particles were compared in some experiments with those of fine (CB) and ultrafine (ufCB) carbon black particles. Results -Six hours after intratracheal instillation of PM10 there was an influx of neutrophils (up to 15% oftotal cells in BAL fluid) into the alveolar space, increased epithelial permeability, the mean (SE) total protein in the BAL fluid increasing from 0.39 (0.01) to 0.62 (0.01) mg/ml, and increased lactate dehydrogenase (LDH) concentrations in the BAL fluid. An even greater inflammatory response was seen following intratracheal instillation ofufCB but not following CB instillation. PM10 particles had free radical activity in vivo, as shown by a decrease in GSH levels in the BAL fluid from 0.36 (0.05) to 0.25 (0.01) nmollml following instillation. The free radical activity ofPM1o was confirmed in vitro by its ability to deplete supercoiled plasmid DNA, an effect which could be reversed by mannitol, a specific hydroxyl radical scavenger. BAL fluid leucocytes from rats treated with PM10 produced greater amounts of nitric oxide (NO), measured as nitrite (control 3.07 (0.33), contaminated with small amounts of filter fibres due to the extraction process, the effects of instillation of filter fibres alone was assessed. These studies showed that filter fibres did not account for the proinflammatory and injurious effects of the PM10 suspension.Conclusions -These findings provide evidence that PM10 has free radical activity and causes lung inflammation and epithelial injury. These data support the proposed hypothesis for the mechanism by which particulate air pollution causes adverse effects in patients with airways diseases.

We studied the acute effects of cigarette smoke condensate (CSC), H2O2, and tumor necrosis factor (TNF)-alpha on the glutathione (GSH) redox system in a human type II epithelial cell line (A549) in vitro. CSC, in vitro and in vivo after intratracheal instillation of CSC in the rat, produced a depletion of intracellular soluble GSH, concomitant with GSH-conjugate formation, without significant elevation of oxidized GSH (GSSG), protein-GSH mixed disulfides (PrSSG), nor any GSH efflux from the cells. By contrast, H2O2 (500 microM) after 5-min exposure to A549 cells caused significant depletion of intracellular GSH associated with an efflux of GSSG and a significant increase in the formation of PrSSG. TNF-alpha, in concentrations of 100 U/ml and 1,000 U/ml, produced a significant depletion of GSH in A549 cells after 4- and 24-h exposure, with an associated elevation of GSSG. The activities of glutathione peroxidase, gamma-glutamylcysteine synthetase, and glucose-6-phosphate dehydrogenase were significantly decreased in epithelial cells and in rat lungs after CSC exposure, without change in glutathione S-transferase and glutathione reductase activities. By contrast, H2O2 and TNF-alpha did not alter these enzyme activities in epithelial cells. Thus GSH depletion and alteration in enzyme activities in alveolar epithelial cells by CSC, H2O2, and TNF-alpha occur by different mechanisms.

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