Pathological characterization of lung fibrosis in Sprague-Dawley rats treated with fluoro-edenite fibres by intrapleural injection

Our plain-English summary of Pathological characterization of lung fibrosis in Sprague-Dawley rats treated with fluoro-edenite fibres by intrapleural injection, by E. Tibaldi, F. Gnudi, D. Mandrioli, et al (Journal of Occupational Medicine and Toxicology, 2024).

The study

• Authors: E. Tibaldi, F. Gnudi, D. Mandrioli, C. Bruno, A. Zona, L. Fazzo, P. Comba
• Journal: Journal of Occupational Medicine and Toxicology
• Published: 2024;19(1):45
• Read it: PubMed · Publisher · Free full text

Abstract

Background: An increased incidence of pleural mesotheliomas in Biancavilla (Italy) was attributed to the environmental exposure to fluoro-edenite (FE). Results from the Ramazzini Institute (RI) in vivo long-term study confirmed the evidence that exposure to FE fibres is correlated with an increase of malignant pleural mesotheliomas in Sprague-Dawley rats. Recently asbestosis-like features were substantiated in Biancavilla residents without known occupational exposures. Aim of this work was to establish whether FE induce lung fibrosis with a pathogenetic mechanism similar to other asbestiform fibres.

Methods: Original slides from the RI study were systematically re-examined to characterize the FE-induced lesions. Quantitative analysis of lung fibrosis was assessed following the Ashcroft method. Immunohistochemical analysis of protein involved in fibrotic responses and histochemical staining for FE-fibres identification were performed.

Results: Like asbestos, FE caused fibrotic lesions, pleural plaques or nodules and mesotheliomas. A significant increase of lung fibrosis (p < 0.001) was observed in the FE-treated groups compared to untreated controls. In the fibrotic responses to FE, vimentin was the most expressed protein, followed by collagen-I and alpha-SMA. Finally, ferruginous bodies, characterized by iron deposits and ferritin expression, were observed in FE-induced lesions.

Conclusions: This study confirmed that FE exposure promotes the onset of fibrotic lesions at pleural level, as fibrous plaques or nodules and fibrosis, through a mechanism similar to other form of asbestos. These results combined with epidemiological study reported in Biancavilla residents, corroborate the need to promote health and epidemiological surveillance plans of respiratory diseases in population living in FE contaminated sites.

© 2024. The Author(s).

In plain English

In this animal study, the authors re-examined lung slides from an earlier Ramazzini Institute experiment. In that experiment, 80 Sprague–Dawley rats (40 males, 40 females) each received one intrapleural (chest-cavity) injection of 25 mg of fibrous fluoro-edenite, an amphibole from Biancavilla, Sicily. Another 80 rats received water as controls; all were followed until natural death. Among treated rats, the authors found pleural mesothelioma in 13 of 80 (16.3%), fibrous plaques or nodules in 7.5%, and fibrosis in 60% of females and 67.5% of males. Controls had none of these diagnoses, only minimal, age-compatible fibrosis in a few lung areas. On the Ashcroft fibrosis scale (0 to 8), average scores were 2.28 in treated females and 1.58 in treated males, versus 0.60 and 0.47 in controls, a statistically significant difference. Of three fibrosis-related proteins tested, vimentin was the most expressed. Iron-coated (ferruginous) bodies near fibres appeared in 27 of 39 stained samples. The authors concluded that fluoro-edenite promotes pleural fibrotic lesions through a mechanism similar to other forms of asbestos. They noted inhalation studies could clarify airway effects.

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: re-examination of archived lung slides and tissue from an earlier long-term carcinogenicity study in rats, with blind pathology review, Ashcroft fibrosis scoring, immunohistochemistry and iron (Perls') staining
• Who was studied: Sprague–Dawley rats from the Ramazzini Institute (Bologna, Italy) long-term study: 80 treated rats (40 males, 40 females) and 80 water-injected control rats (40 males, 40 females), observed until natural death
• Exposure: Fibrous fluoro-edenite (an amphibole fibre from the Biancavilla area of Mount Etna, Sicily), given as a single intrapleural injection of 25 mg suspended in 1 cc of water
• Main results:
  • Pleural mesothelioma was diagnosed in 13 of 80 fluoro-edenite-treated rats (16.3%): 6 males and 7 females
  • Fibrous plaques or nodules were seen in 7.5% of treated rats, and fibrosis in 60% of treated females and 67.5% of treated males
  • In the water-injected controls, no mesotheliomas, fibrous plaques or nodules, or diagnosed fibrosis were recorded (Tables 1 and 2). In the fibrosis scoring, fibrosis in controls was limited to a few perivascular, peribronchial or subpleural areas, and the authors judged these minimal lesions compatible with the rats' age.
  • One female control (renal tumour metastasis in the lungs) and one male control (fibro-histiocytic sarcoma of the lungs) were treated as outliers and excluded from fibrosis scoring, leaving 39 controls of each sex
  • Treated females had a group mean Ashcroft score of 2.28 (SD 0.95), compared with 0.60 (SD 0.20) in control females
  • Treated males had a group mean Ashcroft score of 1.58 (SD 0.87), compared with 0.47 (SD 0.24) in control males
  • The increase in fibrosis scores was statistically significant in both treated males and treated females compared with controls (p less than 0.0001)
  • Among the fibrosis markers tested in treated-rat samples, vimentin was the most expressed, including in mild lesions. Alpha-SMA was the least expressed. None of the markers was expressed in untreated controls.
  • Ferruginous bodies near or engulfing fluoro-edenite fibres were seen in 27 of 39 stained lung samples (14 females and 13 males, 69.2%)
• The authors' conclusion: The authors concluded that fluoro-edenite exposure promotes fibrotic lesions at the pleural level (fibrous plaques or nodules and fibrosis) through a mechanism similar to other forms of asbestos. Together with findings in Biancavilla residents, they saw this as supporting health and epidemiological surveillance of respiratory diseases in people living in fluoro-edenite contaminated sites.
• Limitations the authors state:
  • The fibres were given by intrapleural injection rather than by breathing them in. The authors note that further inhalation studies might clarify other fibrosis mechanisms in the airways.

Topics

Medical terms in this study, explained in our Lexicon: Fibrosis, fluoro-edenite, Pleural Mesothelioma, Biancavilla, Environmental Exposure, Occupational Exposure, Asbestiform, Pleural Plaques.

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