Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole

Our plain-English summary of Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole, by D.J. Padilla-Carlin, M.C. Schladweiler, J.H. Shannahan, et al (Journal of Toxicology and Environmental Health. Part a, 2011).

The study

• Authors: D.J. Padilla-Carlin, M.C. Schladweiler, J.H. Shannahan, U.P. Kodavanti, A. Nyska, L.D. Burgoon, S.H. Gavett
• Journal: Journal of Toxicology and Environmental Health. Part a
• Published: 2011;74(17):1111-32
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

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.

In plain English

This was an animal experiment. Male Fischer 344 rats received one dose, placed directly into the windpipe, of saline, amosite (0.65 mg per rat) or Libby amphibole (0.65 or 6.5 mg per rat). There were eight rats per group at each of five time points from 1 day to 3 months. Both materials had been processed to keep only the fraction small enough to reach deep into a rat's lung. One day after dosing, cells in lung washings rose significantly, fourfold with amosite and twofold with the high Libby amphibole dose; the low dose gave only a numerical 1.5-fold rise. At 3 months, all 8 amosite rats showed interstitial fibrosis (scarring). Staining showed minimal fibrosis in the high-dose Libby amphibole group and no such increase in the low-dose group. Lung-tissue mRNA for some fibrosis-linked growth factors was lower, not higher, at 3 months in some exposed groups. The authors concluded that, at equal mass, amosite caused greater changes than Libby amphibole, consistent with its longer fibers. They called for further testing of Libby amphibole. They noted that putting material into the windpipe spreads it differently from breathing it in.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: single intratracheal instillation in rats, with examinations at several times afterwards (1, 3 and 7 days, 2 weeks, 3 months)
• Who was studied: Healthy male Fischer 344 rats, 6 to 8 weeks old, from Charles River Laboratories (Raleigh, NC). There were 4 groups of 8 rats at each of 5 necropsy time points. The rats were housed in an EPA (NHEERL) facility.
• Exposure: Respirable fractions (aerodynamic diameter 2.5 µm or less, prepared by water elutriation) of Libby amphibole and of amosite, used as the positive control. Libby amphibole was described as mainly winchite, richterite and tremolite. Doses were saline (0.0 mg per rat), amosite 0.65 mg per rat, low-dose Libby amphibole 0.65 mg per rat and high-dose Libby amphibole 6.5 mg per rat.
• Main results:
  • One day after dosing, total cells in lung washing fluid were significantly raised fourfold in the amosite group and twofold in the high-dose Libby amphibole group compared with saline.
  • The low-dose Libby amphibole group (same mass as the amosite dose) showed only a numerical 1.5-fold rise in total cells compared with controls. This was significantly lower than in the amosite group.
  • A very small but significant rise in neutrophils was present at all time points in the high-dose (6.5 mg per rat) Libby amphibole group compared with saline.
  • At 3 months, protein in lung washing fluid was significantly higher (by 40 to 80%) in all Libby amphibole and amosite groups than in saline controls.
  • At 1 day, IL-6 mRNA in lung tissue was raised about 15-fold in the high-dose Libby amphibole group and about 25-fold in the amosite group.
  • At 3 months, lung-tissue mRNA for the growth factors PDGF-A and TGF-1β and for Pro-Coll IA was lower (downregulated) in some of the Libby amphibole and amosite groups.
  • In the amosite group at 3 months, Masson's trichrome staining confirmed fibrosis within interstitial granulomas, up to grade 2 to 3. The incidence table lists interstitial fibrosis in 8 of 8 amosite rats at 3 months.
  • The high-dose Libby amphibole group showed a minimal time-related increase in collagen staining, which the authors described as minimal interstitial fibrosis. The low-dose group did not show this increase. The incidence table lists interstitial fibrosis in 1 of 8 high-dose rats and 0 of 8 low-dose rats at 3 months.
  • The fibrosis score at 3 months correlated best with the number of fibers 20 µm or longer (R-squared .9945). Protein in lung washing fluid at 1 day correlated better with fibers 5 µm or longer (.8266) and 10 µm or longer (.8661). The authors said this suggested long fibers may better predict fibrosis.
• The authors' conclusion: The authors concluded that, after a single dose, biochemical, inflammatory and tissue changes were greater with amosite than with Libby amphibole at the same mass dose for up to 3 months. They linked this to amosite's longer fibers. They said Libby amphibole needs further testing, particularly on how dose is measured, to fully evaluate its potential to cause fibrosis and cancer.
• Limitations the authors state:
  • Measuring growth-factor mRNA in whole lung tissue may have diluted the signal and been less sensitive than other techniques.
  • Material placed into the windpipe is distributed in the lung differently from material that is inhaled.
  • Rats were dosed by mass, whereas comparing fibers by number or surface area has been recommended.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Libby amphiboles, Amphibole Group, vermiculite, Respirable Fraction, Amosite, Bronchoalveolar Lavage (BAL), Inflammation, BAL Fluid.

Related studies

• Comparative long-term toxicity of Libby amphibole and amosite asbestos in rats after single or multiple intratracheal exposures — J.M. Cyphert, D.J. Carlin, et al. (2015)
• Long-term response of rats to single intratracheal exposure of Libby amphibole or amosite — J.M. Cyphert, D.J. Padilla-Carlin, et al. (2012)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)
• Vascular and thrombogenic effects of pulmonary exposure to Libby amphibole — J.H. Shannahan, M.C. Schladweiler, et al. (2012)
• Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats — S.H. Gavett, C.U. Parkinson, et al. (2016)
• Transcriptional activation of inflammasome components by Libby amphibole and the role of iron — J.H. Shannahan, A.J. Ghio, et al. (2012)

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