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Airway Wall Remodeling Induced by Occupational Mineral Dusts and Air Pollutant Particles^*

From the Department of Pathology, University of British Columbia, Vancouver, BC, Canada.

Correspondence to: Andrew Churg, MD, Department of Pathology, University of British Columbia, 2211 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5; e-mail: achurg{at}interchange.ubc.ca

Objectives: COPD has been reported in workers exposed to particulates, and there is increasing evidence that high levels of ambient particulate pollutants may also be associated with COPD. The studies here investigate the hypothesis that particulates, including air pollution particles, can induce airway wall fibrosis, a process that can lead to COPD.

Design: Rat tracheal explants were exposed to various occupationally encountered dusts, air pollution particles, and model air pollution particles. In some experiments, iron was loaded onto the particle surface. Gene expression and nuclear factor (NF)-B activation were measured after 7 days of air culture. Adhesion to and uptake of dusts by the tracheal epithelium were also evaluated.

Results: Known fibrogenic dusts such as amosite asbestos produced increased gene expression of procollagen, transforming growth factor-ß, and platelet-derived growth factor, and increased hydroxyproline in the explants, and the addition of iron increased these effects. The addition of iron also converted nonfibrogenic TiO₂ into a fibrogenic dust. Dusts with surface complexed iron activated NF-B via an oxidant mechanism. However, an ultrafine TiO₂ with very low iron was also fibrogenic. In separate experiments, exogenous tumor necrosis factor- increased dust adhesion to, and exogenous ozone increased dust uptake by, tracheal epithelial cells.

Conclusions: Mineral dusts can directly induce fibrosis in the airway wall. Exogenous inflammatory cells and exogenous agents are not required, but they probably exaggerate the fibrogenic effects. An iron-mediated oxidant mechanism underlies the fibrogenic effects of some, but not all, of these dusts. Particle-induced airway wall fibrosis may lead to COPD.

Key Words: air pollution • COPD • mineral dusts

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