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

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.

Gene Expression Profiles Reveal Increased mClca3 (Gob5) Expression and Mucin Production in a Murine Model of Asbestos-Induced Fibrogenesis

“…21,53,54 The up-regulation of IL-1␤ is noteworthy because it is elevated in rodent inhalation models of asbestos exposure and in cell culture systems. 55,56 IL-1␤ is generally considered an early response cytokine that is produced by many different cell types, but is predominantly synthesized and secreted by macrophages during inflammation whereby it acts on lymphocytes to enhance their capacity to respond to antigens. Transient expression of IL-1␤ in vivo has been causally linked to progressive fibrotic changes, including the presence of myofibroblasts, fibroblast foci, and collagen and fibronectin accumulation.…”

Antioxidants as Potential Therapeutics for Lung Fibrosis

“…Both silica and asbestos exposures produce lung fibrosis in animals (64,104) and pneumoconiosis in humans (164). Both silica and asbestos produce injury and oxidative stress in the lungs of animals (1).…”

Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages

“…Asbestos induces a highly inflammatory state in the lung (Fattman et al 2006;Kamp and Weitzman 1999;Tan et al 2004). Moreover, exposure to amphibole asbestos in alveolar macrophages has been previously shown to increase the release of proinflammatory cytokines such as TNF-α and IL-1 (Driscoll et al 1995). In this pro-inflammatory environment an increase in apoptosis may lead to excess presentation of autoantigens thereby exacerbating an autoimmune response.…”