Original ContributionSmoking and COPD increase sputum levels of extracellular superoxide dismutase
Introduction
The pathogenesis of chronic obstructive pulmonary disease (COPD) has been strongly linked with oxidative stress [1], [2], [3], [4], [5], [6]. One of the major antioxidant enzymes of the human lung parenchyma that scavenges superoxide radicals is extracellular superoxide dismutase (ECSOD or SOD3) [7], [8]. Genetic studies have suggested that a functional polymorphism of ECSOD, the Arg213Gly mutation (associated with elevated circulating ECSOD levels) and other ECSOD polymorphisms are protective against COPD in smokers [9], [10], [11], [12]. However, based on current knowledge, the Arg213Gly polymorphism can explain only a small proportion of protection against COPD development given that only 25% of smokers develop COPD [13]. It is unclear whether lung ECSOD tissue levels or airway-secreted ECSOD levels are directly associated with COPD and its severity.
Three SOD enzymes (CuZnSOD, MnSOD, and ECSOD) have been characterized in mammalian cells, and they have a cell-specific distribution in human lung. The regulation and roles of CuZnSOD and MnSOD in nonmalignant and malignant lung diseases have been previously studied and reviewed in detail [14], [15]. However, the significance of ECSOD especially in human lung diseases remains unclear. Experimental studies have shown that mice lacking ECSOD survive but are vulnerable to oxidative stress [16], [17], [18], [19]; transgenic mice overexpressing ECSOD, in contrast, are protected against oxidative stress [17]. ECSOD plays a major role in protecting lung against hyperoxia [17] and asbestos fibers [18], [19]. In experimental studies on asbestos exposure, ECSOD is redistributed and secreted to the bronchoalveolar lavage fluid (BALF) [19]. To our knowledge only two studies have investigated ECSOD in experimental cigarette smoke exposure by using ECSOD (SOD3) transgenic and knockout mice [20.21]. These studies concluded that ECSOD protected against smoke- and elastase-induced emphysema [20] and that macrophages from ECSOD-overexpressing mice had less oxidative stress and lower levels of inflammatory cytokines in response to cigarette smoke [21].
ECSOD is a homotetrameric glycoprotein in which the monomer is secreted in one of two forms: with a polybasic binding tail present or with it proteolytically cleaved [22]. Tetramers consisting solely of monomers lacking the binding tail are postulated to not bind to tissue extracellular proteins, and the lack of tissue binding has in turn been suggested to reduce the local protective effect of the enzyme [23], [24]. ECSOD is expressed in lung tissue, with high levels being found in the vasculature and epithelium [7], [25]. It has an affinity for binding to the negatively charged extracellular macromolecules of collagen, hyaluronan, and heparan sulfate [26]. The Arg213Gly mutation that is associated with protection against COPD in smokers modifies the binding tail, affecting binding to collagen and increasing plasma levels of ECSOD to levels that are 6- to 10-fold higher than normal [27], [28]. It remains unclear how ECSOD modifies the risk of COPD in smokers with and without this mutation and whether there are differences in ECSOD expression in lung tissue or airways.
Only a few studies have been conducted on ECSOD in human lung diseases. Lung ECSOD is low/undetectable in fibroblastic foci lesions of idiopathic pulmonary fibrosis (IPF) [29], and its expression is very low in human lung cancers [30]. A previous study of ECSOD found no changes in lung ECSOD immunoreactivity in mild–moderate COPD [31].
We hypothesized that ECSOD would be secreted into the lung extracellular fluids and that it may differ in extracellular fluids such as sputum and BALF and circulating blood in response to oxidative stress from smoking and/or COPD. Levels of ECSOD in these secretions may provide useful biomarkers to detect early lung injury related to smoking. Plasma and sputum levels of ECSOD were compared in smokers with and without COPD to those in nonsmokers. Sputum and BALF levels of ECSOD were compared to assess their relative utility as biomarkers of disease activity.
Section snippets
Material and methods
These studies were carried out collaboratively in both Finland and the United States from complementary populations. ELISA measurements were performed in Denver, Colorado, on human samples (plasma, sputum, and BALF) from both Finland and Denver. Lung tissue was studied in two cohorts: the U.S. source was the Lung Tissue Research Consortium (LTRC) and the other was patients from Helsinki. COPD was evaluated by the GOLD criteria [32]. In this classification the various severities include GOLD
Immunohistochemical analysis reveals cell-specific declines in ECSOD in the COPD lung
Immunohistochemistry confirmed previous results in ECSOD distribution in human lung [25], [45], i.e., ECSOD was strongly expressed in the extracellular matrix of the perivascular areas and around the bronchioles, consistent with its known binding to negatively charged extracellular proteins such as collagen and proteoglycans (Fig. 1). It also was seen in the alveolar walls and occasionally as high expression in alveolar type II cells. Within the bronchiolar lumen there was staining along the
Discussion
ECSOD can be detected in lung tissue, in specific cell types within the lung parenchyma, and in airway lining fluid, sputum, and plasma. Under normal conditions levels of ECSOD in each of these tissues or fluids represent a combination of constitutive secretion and response to local regulatory factors. Our results suggest that both cigarette smoking and the disease processes associated with COPD affect ECSOD expression and secretion into specific lung compartments. They further suggest that
Acknowledgments
This study utilized biological specimens and data provided by the Lung Tissue Research Consortium supported by the National Heart, Lung, and Blood Institute. Adjunct Professor Marjukka Myllärniemi is acknowledged for helping with the image analysis, and Mrs. Tiina Marjomaa for her skillful technical assistance. Funding was provided by the Monfort Foundation (E.A.R., E.M., J.D.C., R.P.B.), the Flight Attendant Medical Research Institute (R.P.B.), a government subsidy for health science research
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2022, Archivos de BronconeumologiaCitation Excerpt :On the contrary, immunohistochemistry in lung slices allows for detecting the markers in specific tissue localizations, such as alveolar walls. Indeed, in a previous study the levels of EC-SOD were high in sputum of COPD patients, but not in blood or BALF, whereas EC-SOD tissue immunoreactivity was lower in COPD patients.19 Our results suggest that patients with COPD have a reduced antioxidant activity in their lungs which make them more vulnerable to the disease.
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2020, Redox BiologyCitation Excerpt :Concentrations of glutathione are lower in bronchoalveolar lavage fluid from COPD patients with frequent exacerbations compared to those with stable COPD [25]. Extracellular superoxide dismutase (SOD3) polymorphisms are more frequent in COPD and its expression is increased in sputum of COPD patients, although there is reduced expression around small airways [26,27]. The transcription factors Nrf2 (nuclear factor erythroid 2-related factor 2) and FOXO3a (Forkhead box O3a) regulate multiple antioxidant gens and both are reduced in COPD lungs [28,29].
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2017, Environmental Toxicology and PharmacologyCitation Excerpt :It could owe to that the viability of BEAS–2B cells reduced upon the increasing dose of smoke and influenced the expression of EC-SOD. These findings are consistent with previous reports though they conducted tests mostly in vivo (Kanehira et al., 2006; Regan et al., 2011). It was advantage that the matrix interference in our tests was relatively less.
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2015, Pharmacology and TherapeuticsCitation Excerpt :SOD3 (or extracellular SOD) is located in the extracellular matrix, the junctions of airway epithelial cells, the surface of airway smooth muscle, and the lining of blood vessels of the lung (Kinnula & Crapo, 2003). It should be noted that smokers and COPD patients have increased sputum levels of SOD3 as an adaptive response to the increased oxidative burden (Regan et al., 2011). Additionally, polymorphisms in the SOD3 gene have been associated with emphysema but not COPD susceptibility (Sorheim et al., 2010).
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2012, Molecular and Cellular ProteomicsCitation Excerpt :Specifically, L. acuta secrete large amounts of mucous that contains the antioxidant species catalase, superoxide dismutase, and glutathione peroxidise. These enzymes intercept or degrade environmental peroxyl and hydroxyl radicals originating from organic matter in their aqueous environments (45). Likewise, the antioxidant activity of the mucosa covering respiratory tract epithelial cells in humans has been shown to be crucial for protecting against radical damage from environmental pollutants and bodily microorganisms (46).