Role of Inducible Nitric Oxide Synthase-Derived Nitric Oxide in Silica-Induced Pulmonary Inflammation and Fibrosis

Abstract

Inhalation of crystalline silica can produce lung inflammation and fibrosis. Inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) is believed to be involved in silica-induced lung disease. To investigate the role of iNOS-derived NO in this disease, the responses of iNOS knockout (KO) versus C57Bl/6J wild-type (WT) mice to silica were compared. Male mice (8-10 wk old, mean body weight 24.0 g) were anesthetized and exposed, by aspiration, to silica (40 mg/kg) or saline. At 24 h and 42 d postexposure, lungs were lavaged with saline. The first bronchoalveolar lavage (BAL) fluid supernatant was analyzed for lactate dehydrogenase (LDH) activity, levels of albumin, tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 (MIP-2), as well as total antioxidant capacity (TAC). The cellular fraction of the total BAL was used to determine alveolar macrophage (AM) and polymorphonuclear leukocyte (PMN) counts, and zymosanstimulated AM chemiluminescence (AM-CL). In separate mice, lung histopathological changes were evaluated 42 d postexposure. Acute (24-h) silica exposure decreased AMs, increased PMNs, increased LDH activity and levels of albumin, TNF-alpha, and MIP-2 in BAL fluid, and enhanced AM-CL in both iNOS KO and WT mice. However, iNOS KO mice exhibited less AM activation (defined as increased AM-CL and decreased AM yield) than WT. Furthermore, TAC following acute silica decreased in WT but was maintained in iNOS KO mice. Pulmonary reactions to subchronic (42 d) silica exposure were similar to acute. However, histopathological and BAL fluid indices of lung damage and inflammation, AM activation, and lung hydroxyproline levels were significantly less in iNOS KO compared to WT mice. These results suggest that iNOS-derived NO contributes to the pathogenesis of silica-induced lung disease in this mouse model.

Role of nitric oxide synthases in elastase-induced emphysema

“…Increases in lung iNOS expression and protein nitration were previously described in the lungs of patients with COPD 7 as well as in experimental emphysema induced by inhibition of the VEGF receptor or surfactant protein D deficiency 18,19 ; whether these phenomena contributed to airspace enlargement in these models was not reported, but could be suspected as iNOS contributes to inflammation and tissue remodeling in other models of lung injury such as endotoxin-induced pneumonitis, 17 ventilator-induced lung injury, 16 and silica-induced pulmonary fibrosis. 20 In contrast with these observations, we observed that, whereas iNOS was strongly induced in the lung following elastase instillation, iNOS inhibition had no evident impact on pulmonary inflammation or emphysema development in this model. eNOS was not implicated neither in lung protein nitration nor in the development of emphysema following a tracheal instillation of elastase; deletion of eNOS was not deleterious either, although eNOS promotes compensatory alveologenesis after pneumonectomy.…”

The Phagocytosis of Crystalline Silica Particles by Macrophages

“…Surprisingly, this pretreatment was not protective. Both Fc receptor activation and silica have been shown to cause an increase in reactive oxygen species (ROS) production by macrophages (11,18,35,36). If ROS were damaging to the cell, then it would seem likely that both particle types would be toxic, and that antibodycoated silica might be even more toxic.…”

“…Although the interaction of silica with cells has been intensively studied, the molecular mechanisms underlying this toxicity are not well understood (8). There is evidence that silica causes the production of free radicals and reactive oxygen species (9)(10)(11) and that some cells die due to activation of the apoptotic cascade (12)(13)(14). However, the actual mechanism of silica-induced cell death is still unclear.…”

Systemic Oxidative Stress Promoted by Emissions of Particulate Matter is Attenuated by Antioxidant Supplementation

“…In particular, chronic inhalation of coal dust in miners leads to several diseases such as pneumoconiosis, fibrosis, bronchitis, emphysema, cancer and other pathologic-related events [16]. In any case, a chronic inflammatory process takes place, leading to the generation of proinflammatory factors, synthesis of extra cellular matrix, fibroblast proliferation, and altering the prooxidant/antioxidant balance, therefore producing OS resulting in lung damage, even after cessation of exposure to the contaminants [17][18][19]. Around 30% of the local medical procedures from Lauro Müller was caused by respiratory diseases and 4% related to different kinds of cancer in this region [20].…”