Pulmonary Inflammatory and Fibrotic Responses in Fischer 344 Rats After Intratracheal Instillation Exposure to Libby Amphibole

Abstract

Increased incidences of asbestosis have been reported in workers from Libby, MT, associated with exposures to amphibole-contaminated vermiculite. In this study pulmonary and histopathological changes were investigated following Libby amphibole (LA) exposure in a rat model. Rat respirable fractions of LA and amosite (aerodynamic diameter <2.5 μm) were prepared by water elutriation. Male F344 rats were exposed to single doses of either saline (SAL), amosite (0.65 mg/rat), or LA (0.65 or 6.5 mg/rat) by intratracheal instillation. At times from 1 d to 3 mo after exposure, bronchoalveolar lavage (BAL) was performed and right and left lungs were removed for reverse-transcription polymerase chain reaction (RT-PCR) and histopathological analysis, respectively. Data indicated that 0.65 mg amosite resulted in a higher degree of pulmonary injury, inflammation, and fibrotic events than LA at the same mass dose. Exposure to either amosite or high dose LA resulted in higher levels of cellular permeability and injury, inflammatory enzymes, and iron binding proteins in both BAL fluid and lung tissue at most time points when compared to SAL controls. However, mRNA expression for some growth factors (e.g., platelet-derived growth factor [PDGF]-A and transforming growth factor [TGF]-1β), which contribute to fibrosis, were downregulated at several time points. Furthermore, histopathological examination showed notable thickening of interstitial areas surrounding the alveolar ducts and terminal bronchioles. On a mass dose basis, amosite produced a greater acute and persistent lung injury for at least 3 mo after exposure. However, further testing and analysis of LA are needed with regard to the dose metric to fully evaluate its potential fibrogenicity and carcinogenicity.

Acknowledgments

This work was supported by the U.S. EPA/UNC Toxicology Research Program, Training Agreement CR 833237, with the Curriculum in Toxicology, University of North Carolina at Chapel Hill. The authors thank Debora Andrews, Rick Jaskot, and Judy Richards for their technical assistance. We thank Drs. Gary Hatch and Aimen Farraj, and members of the Libby Action Plan working group for their review of the article.

The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and the policies of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.