Extracellular superoxide dismutase in pulmonary fibrosis

Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.     

Extracellular superoxide dismutase in macrophages augments bacterial killing by promoting phagocytosis

Extracellular superoxide dismutase (EC-SOD) is abundant in the lung and limits inflammation and injury in response to many pulmonary insults. To test the hypothesis that EC-SOD has an important role in bacterial infections, wild-type and EC-SOD knockout (KO) mice were infected with Escherichia coli to induce pneumonia. Although mice in the EC-SOD KO group demonstrated greater pulmonary inflammation than did wild-type mice, there was less clearance of bacteria from their lungs after infection. Macrophages and neutrophils express EC-SOD; however, its function and subcellular localization in these inflammatory cells is unclear. In the present study, immunogold electron microscopy revealed EC-SOD in membrane-bound vesicles of phagocytes. These findings suggest that inflammatory cell EC-SOD may have a role in antibacterial defense. To test this hypothesis, phagocytes from wild-type and EC-SOD KO mice were evaluated. Although macrophages lacking EC-SOD produced more reactive oxygen species than did cells expressing EC-SOD after stimulation, they demonstrated significantly impaired phagocytosis and killing of bacteria. Overall, this suggests that EC-SOD facilitates clearance of bacteria and limits inflammation in response to infection by promoting bacterial phagocytosis.     

Extracellular superoxide dismutase overexpression protects against aging-induced cognitive impairment in mice

Extracellular superoxide dismutase (EC-SOD) controls the availability of extracellular superoxide and appears to play a role in controlling oxidative stress and intercellular signaling. Whether EC-SOD overexpression would help or hinder neurobehavioral function appears to depend on the age of the individual. In young adult mice, we have found that EC-SOD overexpression can interfere with learning on the radial-arm maze, possibly by reducing control over nitric oxide neurotransmission. In aged mice, we found, in the current study, that EC-SOD overexpression greatly improves learning on the radial-arm maze. Control (N = 17) and EC-SOD overexpressing mice (N = 13) acquired the 8-arm radial maze over 21 sessions of training. The EC-SOD overexpressing mice had significantly better choice accuracy than the control mice (p < 0.005). The EC-SOD overexpressing mice averaged 6.34 ± 0.22 correct arm entries before an error (entries to repeat) during the acquisition phase, while the control mice averaged 5.18 ± 0.22 entries to repeat. EC-SOD genotype did not cause a main effect on response latency. The advantage held by the EC-SOD overexpressing mice persisted during the eight-session post-acquisition phase of testing (p < 0.01). When there was a shift from high to low levels of motivation by reducing the period of food restriction before testing, the EC-SOD overexpression-induced improvement was reduced slightly, but it was still significant compared with the wild-type controls (p < 0.025). Then, after 4 months of no testing, the mice were tested for retention and reacquisition of performance on the radial-arm maze. The EC-SOD overexpressing mice maintained their significantly better choice accuracy (p < 0.05). Enhancement of EC-SOD activity appears to improve learning and memory performance, specifically in aging mice. EC-SOD mimetic treatment during the course of aging may hold promise for aging-induced cognitive impairment.     

Apolipoprotein A-I attenuates ovalbumin-induced neutrophilic airway inflammation via a granulocyte colony-stimulating factor-dependent mechanism

Apolipoprotein A-I (apoA-I) is a key component of high-density lipoproteins that mediates reverse cholesterol transport from cells and reduces vascular inflammation. We investigated whether endogenous apoA-I modulates ovalbumin (OVA)-induced airway inflammation in mice. We found that apoA-I expression was significantly reduced in the lungs of OVA-challenged, compared with saline-challenged, wild-type (WT) mice. Next, to investigate the role of endogenous apoA-I in the pathogenesis of OVA-induced airway inflammation, WT and apoA-I(-/-) mice were sensitized by intraperitoneal injections of OVA and aluminum hydroxide, followed by multiple nasal OVA challenges for 4 weeks. OVA-challenged apoA-I(-/-) mice exhibited a phenotype of increased airway neutrophils compared with WT mice, which could be rescued by an administration of a 5A apoA-I mimetic peptide. Multiple pathways promoted neutrophilic inflammation in OVA-challenged apoA-I(-/-) mice, including the up-regulated expression of (1) proinflammatory cytokines (IL-17A and TNF-α), (2) CXC chemokines (CXCL5), (3) vascular adhesion molecules (i.e., vascular cell adhesion molecule-1), and (4) granulocyte colony-stimulating factors (G-CSF). Because concentrations of G-CSF in bronchoalveolar lavage fluid (BALF) were markedly increased in OVA-challenged apoA-I(-/-) mice, we hypothesized that enhanced G-CSF expression may represent the predominant pathway mediating increased neutrophilic inflammation. This was confirmed by the intranasal administration of a neutralizing anti-G-CSF antibody, which significantly reduced BALF neutrophilia by 72% in OVA-challenged apoA-I(-/-) mice, compared with mice that received a control antibody. We conclude that endogenous apoA-I negatively regulates OVA-induced neutrophilic airway inflammation, primarily via a G-CSF-dependent mechanism. Furthermore, these findings suggest that apoA-I may play an important role in modulating the severity of neutrophilic airway inflammation in asthma.     

Extracellular superoxide dismutase protects against matrix degradation of heparan sulfate in the lung

Asbestosis is a form of interstitial lung disease caused by the inhalation of asbestos fibers, leading to inflammation and pulmonary fibrosis. Inflammation and oxidant/antioxidant imbalances are known to contribute to the disease pathogenesis. Extracellular superoxide dismutase (EC-SOD) is an antioxidant enzyme that has been shown to protect the lung from oxidant-mediated damage, inflammation, and interstitial fibrosis. Extracellular matrix (ECM) components, such as collagen and glycosaminoglycans, are known to be sensitive to oxidative fragmentation. Heparan sulfate, a glycosaminoglycan, is highly abundant in the ECM and tightly binds EC-SOD. We investigated the protective role of EC-SOD by evaluating the interaction of EC-SOD with heparan sulfate in the presence of reactive oxygen species (ROS). We found that ROS-induced heparin and heparan sulfate fragments induced neutrophil chemotaxis across a modified Boyden chamber, which was inhibited by the presence of EC-SOD by scavenging oxygen radicals. Chemotaxis in response to oxidatively fragmented heparin was mediated by Toll-like receptor-4. In vivo, bronchoalveolar lavage fluid from EC-SOD knockout mice at 1, 14, and 28 days after asbestos exposure showed increased heparan sulfate shedding from the lung parenchyma. We demonstrate that one mechanism through which EC-SOD inhibits lung inflammation and fibrosis in asbestosis is by protecting heparin/heparan sulfate from oxidative fragmentation.     

Caffeine attenuates lipopolysaccharide-induced neuroinflammation

Caffeine is an antagonist at A1 and A2A adenosine receptors and epidemiological evidence suggests that caffeine consumption reduces the risk of Alzheimer's and Parkinson's diseases. Neuroinflammation plays a role in the etiology of these diseases and caffeine may provide protection through the modulation of inflammation. Adenosine has a known role in the propagation of inflammation and caffeine may reduce microglia activation directly by blocking adenosine receptors on microglia. Chronic neuroinflammation is associated with an increase in extracellular levels of glutamate and drugs that limit the effects of glutamate at neuronal receptors have been shown to indirectly reduce the neuroinflammatory response of microglia cells. A1 and A2A receptors have been shown to regulate the pre-synaptic release of glutamate, therefore, caffeine may also reduce neuroinflammation via its ability to regulate glutamate release. Caffeine was administered at various doses to young rats with experimentally induced neuroinflammation by chronic infusion of lipopolysaccharide (LPS) over two or four weeks into the 4th ventricle and to aged rats with naturally elevated levels of microglia activation. Caffeine attenuated the number of activated microglia within the hippocampus of animals with LPS-induced and age-related inflammation.     

Suppression by superoxide dismutase of immune-complex--induced pulmonary alveolitis and dermal inflammation.

The possible role of oxygen metabolic products in immune-complex--induced injury of rat lung and of dermal blood vessels has been probed with the use of two inhibitors, superoxide dismutase (SOD) and catalase. With the use of the reversed passive Arthus reaction in the skin, local administration of SOD, but not of catalase, blocked the early phase of the tissue injury, as quantitated by the leakage of homologous albumin. The early phases of immune-complex--induced injury of the lung were completely blocked by the parenteral (intraperitoneal) administration of SOD. Except at very high doses, SOD did not interfere with chemotactic-factor--induced release of lysosomal enzymes from rat neutrophils. These data suggest that oxygen metabolic products such as O(2-) may play an important role in the early phases of damage produced in rat alveolar walls and dermal vasculature by the deposition of immune complexes.     

Therapeutic potential of superoxide dismutase (SOD) for resolution of inflammation

Neutrophils play essential roles in several inflammatory reactions. Oxidant/antioxidant imbalance is thought to be partially involved in the pathogenesis of the disorders. Under the conditions of oxidative stress, superoxide dismutase (SOD) acts as an endogenous cellular defense system to degrade superoxide (O₂⁻) into oxygen and hydrogen peroxide. Therefore, SOD is potentially useful as a therapeutic agent for treatment of inflammatory disorders. A further mechanism that may contribute to the efficacy of SOD is the regulation of neutrophil apoptosis. For the resolution of infl ammation, the activated neutrophils must be safely removed by apoptosis. Neutrophil apoptosis has been suggested as a possible target for the control of neutrophil-mediated tissue injury. Exogenously added SOD induces neutrophil apoptosis, and hydrogen peroxide has been suggested to be a possible major mediator of ROS-induced neutrophil apoptosis in a caspase-dependent manner. If the drug can be delivered efficiently to the inflammatory site, SOD may be useful as an inhibitory mediator of neutrophil-mediated inflammation. Received 6 December 2005; returned for revision 15 February 2006; returned for final revision 23 March 2006; accepted by M. Katori 15 April 2006     

Role of superoxide dismutase in vascular inflammation and in coronary artery disease

Abstract Superoxide dismutase (SOD) is reported to be the major enzymatic defence against free radicals and common oxidants. EC-SOD is the only extracellular form of SOD present at a high concentration in vascular intima. The aims of the present study were to elucidate the role of EC-SOD in patients with coronary artery disease (CAD) and evaluate its association with free radicals, inflammation and with the severity of the disease. The study included 36 consecutive subjects with CAD being treated in the Institute of Clinical Physiology (33 males, 3 females) and 19 controls (16 males, 2 females). Each subject, after cardiac catheterisation and coronariography, was evaluated for serum EC-SOD activity, peroxy radicals, high-sensitive interleukin-6 (hs-IL-6), high-sensitive tumour necrosis factor (hs-TNFa) and high-sensitive C-reactive protein (hs-CRP) serum levels. The analysis of EC-SOD serum activity did not show any particular difference between patients and controls, while the serum levels of peroxy radicals, hs-IL-6 and hs-CRP showed a significant difference between the two groups (respectively: P<0.01, P<0.001, P<0.01). Moreover, enhancement of hs-IL-6 serum levels was also observed in severe disease (involvement of 3, 4 coronary arteries; P<0.05), while EC-SOD activity showed a slight increment in association with the number of arteries involved. hs-IL-6 concentrations were statistically significantly associated with peroxy radicals and CRP levels (respectively: P<0.05, r²=0.1; P<0.05, r²=0.14). The present study suggests a low effectiveness of EC-SOD activity in prevention against CAD and further confirms hs-IL-6 as a useful marker in diagnostic prevention and in clinical characterisation of CAD.     

Extracellular superoxide dismutase has a highly specific localization in idiopathic pulmonary fibrosis/usual interstitial pneumonia

Aims : Recent studies suggest the importance of oxidant stress in the progression of pulmonary fibrosis. The aim of this study was to investigate extracellular superoxide dismutase (ECSOD), the major antioxidant enzyme of the extracellular matrix of human lung, in biopsy - proven idiopathic pulmonary fibrosis (IPF) related to usual interstitial pneumonia (UIP).
Methods and results : Fibrotic areas and fibroblastic foci in UIP lungs were notable for absence of ECSOD by immunohistochemistry. Western blotting showed significantly lowered immunoreactivity of ECSOD in fibrotic compared with non-fibrotic areas of the diseased lung. The only cell type that showed intense ECSOD positivity in UIP was the interstitial mast cell. In order to investigate the mechanism for ECSOD depletion in fibrotic areas, alveolar epithelial cells were exposed to tumour necrosis factor-α and transforming growth factor (TGF)-β₁; TGF-β suggested a trend towards decreased synthesis. Patients with UIP were also assessed to determine whether this disease is associated with a naturally occurring mutation in ECSOD (Arg²¹³Gly) which leads to a loss of tissue binding of ECSOD. No significant differences could be found in the allele or genotype frequencies of this polymorphism between 63 UIP patients and 61 control subjects.
Conclusion : Overall, consistent with several other antioxidant enzymes, ECSOD is very low in fibrotic areas of UIP, which may further increase the oxidant burden in this disease.     

Glomerulonephritis and superoxide dismutase]

To study the role of reactive oxygen species (ROS) in chronic renal disease, we studied the localization of Cu, Zn-superoxide dismutase (SOD) in glomeruli of patients with IgA nephropathy by immunohistochemistry on 37 kidney specimens consisting of 32 IgA nephropathy and normal parts of the 5 resected kidneys with renal tumors serving as controls. To evaluate the change in renal function, creatinine clearance (Ccr) was assessed at the time of biopsy and 1 year after the biopsy. In the normal kidney, Cu, Zn-SOD was localized in the tubular cells, and not in the glomeruli. In the kidney with IgA nephropathy, Cu, Zn-SOD was detected on the epithelial side of the glomerular capillary wall in addition to the tubular cells. The extent of localization of this enzyme was compared with the clinical findings at the time of biopsy. When Cu, Zn-SOD was stained strongly in the glomeruli, the histological change of the glomeruli was milder, and the renal function appeared to be more preserved; the decrease in Ccr one year after the renal biopsy was inhibited. These findings suggest that Cu, Zn-SOD has beneficial actions for renal function as anti-oxidative factors.     

Increased superoxide dismutase and Down's syndrome

The enzyme superoxide dismutase (SOD) is a constitutive enzyme coded by a gene located in Chromosome 21 (21q22.1). Thus, the tissues from patients with trisomy 21 contain 50% more SOD activity. It is often suggested that the increased SOD content in the cells of Down's syndrome patients is responsible for many of the neurological symptoms of this disease. This hypothesis is not supported by most of the available data. In this paper we discuss why the increased SOD activity should not influence neuronal function and propose, instead, that the main problem may be an overexpression of other genes also located in chromosome 21 such as the beta amyloid precursor, as well as oncogenes and other Down's syndrome-related genes. We also propose that the increased SOD may be, instead, responsible for the increased incidence of Down's syndrome in children of older women. The augmented antioxidant protection resulting from an extra copy of chromosome 21 may, with time, selectively protect human oocytes from apoptosis, increasing their proportion with age, explaining the higher incidence of this disease.     

Chikusetsusaponin V attenuates lipopolysaccharide-induced liver injury in mice

Chikusetsusaponin V (CsV), a saponin from Panax japonicus, has been reported to inhibit inflammatory responses in lipopolysaccharide (LPS)-induced macrophage cells. However, whether CsV could alleviate LPS-induced liver injury in vivo and the potential mechanisms involved remain unclear. In the present study, we investigated the anti-inflammatory effects of CsV on LPS-induced acute liver injury in mice and further explored the potential mechanisms involved. Our results showed that CsV significantly attenuated elevation of alanine transaminase (ALT) and aspartate aminotransferase (AST) levels and improved liver histopathological changes in LPS-induced mice. In addition, CsV decreased serum tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels and inhibited mRNA expressions of inducible nitric oxide synthase (iNOS), TNF-α and IL-1β in LPS challenged mice. Furthermore, CsV inhibited nuclear factor kappa B (NF-κB) activation by downregulating phosphorylated NF-κB, IκB-α, ERK, c-Jun N-terminal kinase (JNK) and p38 levels in the liver tissue, which ultimately decreased nucleus NF-κB protein level. In conclusion, our data suggested that CsV could be a promising drug for preventing LPS challenged liver injury since it attenuated LPS-induced inflammatory responses, partly via inhibiting NF-κB and MAPK signaling pathways.     

Agmatine attenuates stress- and lipopolysaccharide-induced fever in rats

Physiological stress evokes a number of responses, including a rise in body temperature, which has been suggested to be the result of an elevation in the thermoregulatory set point. This response seems to share similar mechanisms with infectious fever. The aim of the present study was to investigate the effect of agmatine on different models of stressors [(restraint and lipopolysaccharide (LPS)] on body temperature. Rats were either restrained for 4 h or injected with LPS, both of these stressors caused an increase in body temperature. While agmatine itself had no effect on body temperature, treatment with agmatine (20, 40, 80 mg/kg intraperitoneally) dose dependently inhibited stress- and LPS-induced hyperthermia. When agmatine (80 mg/kg) was administered 30 min later than LPS (500 microg/kg) it also inhibited LPS-induced hyperthermia although the effect became significant only at later time points and lower maximal response compared to simultaneous administration. To determine if the decrease in body temperature is associated with an anti-inflammatory effect of agmatine, the nitrite/nitrate levels in plasma was measured. Agmatine treatment inhibited LPS-induced production of nitrates dose dependently. As an endogenous molecule, agmatine has the capacity to inhibit stress- and LPS-induced increases in body temperature.     

Anticancer therapy by overexpression of superoxide dismutase

Cancer cells are in general low in the enzymatic activities of both manganese-containing (MnSOD) and copper- and zinc-containing superoxide dismutase. We have hypothesized that part of the tumor cell phenotype is due to this loss of enzymatic activity. To test this hypothesis, we have overexpressed MnSOD via plasmid and adenovirus transfection in various cancer cell types and have shown tumor suppression. This tumor suppression is via a noncytotoxic mechanism and probably occurs due to cell-cycle perturbations. We have also shown that MnSOD overexpression causes the anticancer drug 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to have increased cytotoxicity. Our hypothesis for the mechanism of action of this combination is that overexpression of MnSOD leads to increased peroxide levels and that BCNU inhibits peroxide removal. We currently are investigating the use of adenovirus MnSOD plus BCNU in the treatment of cancer. Results thus far are consistent with the idea that we can use the alterations in antioxidant enzymes observed in cancer cells to therapeutic advantage.     

Effect of aging on pulmonary superoxide dismutase

Pulmonary Cu,Zn superoxide dismutase was examined in young (1-month-old), adult (4-5-month-old) and aged (24-months-old) rats to determine if partially inactive forms of the enzyme accumulate in the lung with age. Measurement of Cu,Zn superoxide dismutase activity in lung homogenates showed that total Cu,Zn superoxide dismutase activity/mg DNA was essentially the same in adult and aged rats. The average value of Cu,Zn superoxide dismutase/mg DNA for young rats was less than half that of adult and aged rats. Cu,Zn superoxide dismutase was purified from the lung homogenates and fractionated into isoelectric variants by either isoelectric focusing or chromatofocusing. Three main isoelectric variants of Cu,Zn superoxide dismutase were recovered with pI values of 5.15, 4.88 and 4.75. In all age groups studied, the pI 4.88 variant had a markedly higher specific activity than the other two variants, as well as the highest metal content and greatest resistance to inactivation of all three variants. The pI 4.88 variant declined from 88% of the total Cu,Zn superoxide dismutase activity in the young animals to only 70% in the aged animals. The results of this study indicate that the proportion of the relatively inactive forms of pulmonary Cu,Zn superoxide dismutase increased with age.     

Extracellular matrix and lung inflammation

Lung injury triggers an acute inflammatory response characterized by increased expression and deposition of extracellular matrix (ECM) components such as fibronectin and collagen. Although the function of newly deposited matrices in injured lungs is unknown, their ability to affect the migration, proliferation, differentiation, and activation state of cells in vitro suggests an important role in the initiation and maintenance of the inflammatory response in vivo. Interactions between immune and nonimmune cells with the lung ECM are mediated via cell surface receptors of the integrin family which link the ECM with intracellular molecules involved in signal transduction. Activation of integrin-mediated intracellular signals may promote inflammation by facilitating leukocyte recruitment and cytokine expression. *** DIRECT SUPPORT *** A02GS030 00009     

Role of Mycobacterium tuberculosis copper-zinc superoxide dismutase

Superoxide dismutases (SODs) play an important role in protection against oxidative stress and have been shown to contribute to the pathogenicity of many bacterial species. To determine the function of the mycobacterial copper and zinc-cofactored SOD (CuZnSOD), we constructed and characterized Mycobacterium tuberculosis and Mycobacterium bovis BCG CuZnSOD null mutants. Both strains were more sensitive to superoxides and hydrogen peroxide than were their respective parental strains. The survival of M. bovis BCG in unstimulated as well as activated mouse bone marrow-derived macrophages was not affected by the loss of CuZnSOD. The survival of CuZnSOD deficient-M. tuberculosis in guinea pig tissues was comparable to that of its parental strain. These results indicate that the mycobacterial CuZnSOD is not essential for intracellular growth within macrophages and does not detectably contribute to the pathogenicity of M. tuberculosis.