Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis

Our plain-English summary of Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis, by K.E. Driscoll, J.K. Maurer, J. Higgins, et al (Journal of Toxicology and Environmental Health, 1995).

The study

• Authors: K.E. Driscoll, J.K. Maurer, J. Higgins, J. Poynter
• Journal: Journal of Toxicology and Environmental Health
• Published: 1995;46(2):155-69
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The present study was undertaken to further define the role of alveolar macrophages (AM) in the pulmonary response to crocidolite fibers. Briefly, groups of 4 male F344 rats were intratracheally instilled with saline or saline suspensions of crocidolite at 2 or 20 mg/kg body weight. Animals were sacrificed 3, 7, 14, and 28 d after exposure and the lung response was characterized by analysis of bronchoalveolar lavage fluid (BALF) for markers of lung injury and inflammation. AM obtained in BALF were cultured and their production of the pro-inflammatory cytokines, tumor necrosis factor alpha (TNF alpha), and interleukin-1 (IL-1) were characterized along with fibronectin, a protein known to stimulate fibroblast migration and proliferation. Lung hydroxyproline content was determined 28 d after exposure and lung histopathology was characterized on d 28 and 90 after exposure. Crocidolite instillation resulted in transient dose-related pulmonary inflammation as evidenced by increased numbers of BALF neutrophils at the low dose and neutrophils, macrophages, and lymphocytes at the high dose. Cytotoxicity and increased permeability were demonstrated by increased levels of BALF lactate dehydrogenase (LDH) and total protein, respectively. AM TNF alpha and IL-1 production were increased only at the high crocidolite dose. This cytokine response was greatest at d 3 and decreased thereafter. AM TNF alpha and IL-1 release were positively correlated with the increased BALF neutrophils. In contrast to TNF alpha and IL-1, AM fibronectin release was increased at both the low and high doses, with the magnitude of response increasing over time. Consistent with previous acute asbestos inhalation studies, histopathology revealed inflammation localized at the level of the terminal bronchioles and alveolar ducts. Fibrosis was demonstrated at both doses by increased trichrome staining of lung tissue sections. Only the high dose resulted in a detectable increase in lung hydroxyproline. Given the bioactivities of TNF alpha, IL-1, and fibronectin, their increased production after crocidolite exposure indicates they contribute to the pulmonary inflammation and fibrosis occurring with this mineral fiber. In addition, the correlation of increased AM TNF alpha and IL-1 production with increased BALF neutrophils supports a role for these cytokines in crocidolite-induced inflammatory cell recruitment. Lastly, association of a persistent increase in AM fibronectin production with an eventual increase in lung collagen deposition extends the growing database indicating this response is a predictive marker of pulmonary fibrosis.

In plain English

In this animal experiment, male Fischer 344 rats received a single dose of crocidolite asbestos in saline into the windpipe (intratracheal instillation) at 2 or 20 mg/kg body weight; controls received saline. Lungs were washed out 3, 7, 14 and 28 days later (4 rats per group and time) and the recovered scavenger cells (alveolar macrophages) cultured. Crocidolite raised lung injury markers in a dose-related way; both doses increased neutrophils (inflammatory cells). IL-1 and TNF-alpha, inflammatory signals from macrophages, rose only at the high dose; IL-1 was significantly raised on days 3, 7 and 28, whereas TNF-alpha was similar to controls by day 28. Both correlated with neutrophil counts (r = .81 and .69 respectively). Macrophage fibronectin, a protein attracting fibroblasts, rose at both doses and increased over time. Lung hydroxyproline (a collagen measure) rose significantly at 28 days only at the high dose. Under the microscope, added collagen (fibrosis) was minimal at the low dose and slight at the high. The authors concluded that persistent fibronectin release supports its use as a predictive marker of pulmonary fibrosis.

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 of crocidolite in rats, with saline controls
• Who was studied: Specific-pathogen-free male Fischer 344 rats weighing about 200 g. There were 4 rats per treatment per time point, examined at 3, 7, 14 and 28 days, with lung tissue examined at 28 and 90 days.
• Exposure: Crocidolite asbestos in saline suspension, instilled into the trachea at 2 or 20 mg/kg body weight. The fibers were heated to 200°C for 2 h beforehand for sterilization. Control rats received saline.
• Main results:
  • Crocidolite produced dose-related increases in lavage-fluid LDH and total protein (markers of cell damage and leakiness). These decreased with time but were still significantly greater than in controls at 28 days.
  • The 20 mg/kg dose caused a transient increase in lavage-fluid macrophages (day 3) and persistent increases in neutrophils and lymphocytes. The 2 mg/kg dose increased only neutrophils.
  • Only the high dose significantly increased macrophage IL-1 production, on days 3, 7 and 28 after exposure.
  • Only the high dose produced detectable increases in macrophage TNF-alpha production. This declined gradually, and treated and control levels were similar on day 28.
  • Lavage-fluid neutrophil numbers correlated positively with macrophage IL-1 release (r = .81; p less than .001).
  • Lavage-fluid neutrophil numbers correlated positively with macrophage TNF-alpha release (r = .69; p less than .001).
  • Macrophage fibronectin release was significantly increased at all time points at the high dose, and at days 14 and 28 at the low dose.
  • Fibronectin release showed a significant increasing trend over time in both the 2 and 20 mg/kg groups (p less than .05).
  • At 28 days, only the high dose produced a detectable increase in lung hydroxyproline (a measure of collagen).
  • Microscopy showed interstitial inflammation and fibrosis at the terminal bronchioles and alveolar ducts. Increased collagen was minimal in the low-dose group and slight in the high-dose group.
  • Increases in collagen were slightly more prominent at 90 days than at 28 days.
• The authors' conclusion: The authors concluded that the IL-1 and TNF-alpha response, which correlated with neutrophilic inflammation, suggests a role for these cytokines in crocidolite-induced inflammatory cell recruitment. They also concluded that the link between persistent macrophage fibronectin production and later increases in lung collagen supports using this response as a predictive marker of pulmonary fibrosis.

Topics

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

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, Cytokine, Crocidolite, Inflammation, Fibrosis, Bronchoalveolar Lavage (BAL), Necrosis, Fibroblast.

Related studies

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• Bidirectional modulation of TNF-alpha production by alveolar macrophages in asbestos-induced pulmonary fibrosis — S. Ouellet, H. Yang, et al. (1993)
• Refractory ceramic fibers activate alveolar macrophage eicosanoid and cytokine release — G.D. Leikauf, S.P. Fink, et al. (1995)
• Relative release of interleukin-1 beta and interleukin-1 receptor antagonist by alveolar macrophages. A study in asbestos-induced lung disease, sarcoidosis, and idiopathic pulmonary fibrosis — J.N. Kline, D.A. Schwartz, et al. (1993)
• Selective differences in macrophage populations and monokine production in resolving pulmonary granuloma and fibrosis — I. Lemaire (1991)
• Mechanisms of asbestos-induced nitric oxide production by rat alveolar macrophages in inhalation and in vitro models — T.R. Quinlan, K.A. BeruBe, et al. (1998)

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