Pulmonary toxicity following acute coexposures to diesel particulate matter and α-quartz crystalline silica in the Sprague-Dawley rat

Abstract

The effects of acute pulmonary coexposures to silica and diesel particulate matter (DPM), which may occur in various mining operations, were investigated in vivo. Rats were exposed by intratracheal instillation (IT) to silica (50 or 233 µg), DPM (7.89 or 50 µg) or silica and DPM combined in phosphate-buffered saline (PBS) or to PBS alone (control). At one day, one week, one month, two months and three months postexposure bronchoalveolar lavage and histopathology were performed to assess lung injury, inflammation and immune response. While higher doses of silica caused inflammation and injury at all time points, DPM exposure alone did not. DPM (50 µg) combined with silica (233 µg) increased inflammation at one week and one-month postexposure and caused an increase in the incidence of fibrosis at one month compared with exposure to silica alone. To assess susceptibility to lung infection following coexposure, rats were exposed by IT to 233 µg silica, 50 µg DPM, a combination of the two or PBS control one week before intratracheal inoculation with 5 × 10⁵ Listeria monocytogenes. At 1, 3, 5, 7 and 14 days following infection, pulmonary immune response and bacterial clearance from the lung were evaluated. Coexposure to DPM and silica did not alter bacterial clearance from the lung compared to control. Although DPM and silica coexposure did not alter pulmonary susceptibility to infection in this model, the study showed that noninflammatory doses of DPM had the capacity to increase silica-induced lung injury, inflammation and onset/incidence of fibrosis.

Keywords:

• Crystalline silica
• diesel exhaust particulate matter
• immune response
• occupational exposure
• pulmonary fibrosis

Acknowledgements

The authors would like to acknowledge Rosana Schafer of the Department of Microbiology, Immunology, and Cell Biology at West Virginia University School of Medicine for her generous gift of Listeria monocytogenes (strain 10403 S, serotype 1).

Disclosure statement

No potential conflict of interest was reported by the authors.

Disclaimer: The findings and conclusions in this article are those of the author(s) and do not necessarily represent the view of the National Institute for Occupational Safety and Health.

Additional information

Funding

This work was supported by National Institute for Occupational Safety and Health.