Contribution of Bacterial Lipopolysaccharide to Carbon Nanotube- and Vanadium Pentoxide-Induced Pulmonary Fibrosis in Rats

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Title: Contribution of Bacterial Lipopolysaccharide to Carbon Nanotube- and Vanadium Pentoxide-Induced Pulmonary Fibrosis in Rats
Author: Cesta, Mark Francis
Advisors: Dr. James C. Bonner, Committee Co-Chair
Dr. David E. Malarkey, Committee Member
Dr. Kenneth B. Adler, Committee Member
Dr. Philip L. Sannes, Committee Chair
Abstract: Pulmonary fibrosis is typically accompanied by inflammation, which is thought to play a role in its pathogenesis, and occurs with occupational exposure to particulates and metals, such as asbestos and vanadium pentoxide (V2O5). Lipopolysaccharide (LPS), a model of acute lung injury and inflammation, chronic bronchitis, and pulmonary fibrosis, upregulates platelet-derived growth factor receptor (PDGF-Rα) in rat lung fibroblasts (RLF). PDGF, a potent mitogen and chemoattractant for mesenchymal cells, is an important mediator in fibrotic lung diseases. This dissertation examines the effects of pre-existing inflammation, induced by LPS, on carbon nanotube (CNT)- and V2O5-induced pulmonary fibrosis in rats and the involvement of PDGF signaling. Rats were pretreated with 2.5 mg/kg LPS by intranasal aspiration, followed 24 hr later by 4 mg /kg CNT, carbon black (CB), or V2O5 administered by intratracheal instillation. Total and differential cell counts, lactate dehydrogenase (LDH), total protein, and PDGF and transforming growth factor-β (TGF-β) protein levels (by ELISA) were examined in bronchoalveolar lavage (BAL) fluid of control and CB- and MWCNT –exposed rats. Lungs from all animals were collected for histopathological analysis, immunohistochemistry, and qPCR of the Pdgf-a, Pdgf-c, Pdgf-rα, and Tgf-β genes. Pdgf-a, Pdgf-c, Pdgf-rα, Tgf-β, and Col1a2 gene expression was also measured in vitro in RLF and NR8383 rat alveolar macrophages in response to CNT or CB with and without LPS. In vivo, CNT and CB caused fibroproliferative, granulomatous lesions, which were located primarily in the alveolar ducts and alveoli. Pretreatment with LPS significantly increased collagen deposition associated with these lesions. In the BAL fluid, LPS pretreatment lead to increases in LDH, total protein, and PDGF-AA protein in rats exposed to MWCNT, and an increase in inflammatory cells in CB-exposed rats compared to controls. In vitro, LPS stimulated Pdgf-rα gene expression in RLF, and LPS and nanoparticles synergistically increased Pdgf-a expression in NR8383 cells. Combined LPS/V2O5 exposure augmented V2O5-induced pulmonary inflammation, airway epithelial necrosis, and fibrosis and amplified in vivo collagen gene expression. The airway lesions were of particular interest because LPS pretreatment increased the incidence of bronchiolitis obliterans-like lesions, including subepithelial fibrosis and intraluminal fibrotic polyps. These data confirm that LPS pretreatment augments the fibrotic effects of CNT and V2O5 in rats, which likely involves enhanced PDGF signaling. This dissertation provides evidence that pre-existing pulmonary inflammation, as occurs with chronic obstructive pulmonary diseases or cigarette smoking, can enhance pulmonary fibrotic responses to environmental agents. Furthermore, exposure to environmental LPS may play a role in the pathogenesis of some fibrotic lung diseases.
Date: 2010-04-20
Degree: PhD
Discipline: Comparative Biomedical Sciences

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