Mice lacking extracellular superoxide dismutase are more sensitive to hyperoxia

The high concentration of Arg213-->Gly extracellular superoxide dismutase (EC-SOD) in plasma is caused by a reduction of both heparin and collagen affinities

The C-terminal region of EC-SOD (extracellular superoxide dismutase) mediates the binding to both heparin/heparan sulphate and type I collagen. A mutation (Arg213-->Gly; R213G) within this extracellular matrix-binding region has recently been implicated in the development of heart disease. This relatively common mutation affects the heparin affinity, and the concentration of EC-SOD in the plasma of R213G homozygous individuals is increased 10- to 30-fold. In the present study we confirm, using R213G EC-SOD purified from a homozygous individual, that the heparin affinity is reduced. Significantly, the collagen affinity of the R213G EC-SOD variant was similarly affected and both the heparin and collagen affinities were reduced by 12-fold. Structural analysis of synthetic extracellular matrix-binding regions suggests that the mutation alters the secondary structure. We conclude that the increased concentration of EC-SOD in the plasma of R213G carriers is caused by a reduction in both heparin and collagen affinities.

Overexpression of extracellular superoxide dismutase reduces acute radiation induced lung toxicity

Background

Acute RT-induced damage to the lung is characterized by inflammatory changes, which proceed to the development of fibrotic lesions in the late phase of injury. Ultimately, complete structural ablation will ensue, if the source of inflammatory / fibrogenic mediators and oxidative stress is not removed or attenuated. Therefore, the purpose of this study is to determine whether overexpression of extracellular superoxide dismutase (EC-SOD) in mice ameliorates acute radiation induced injury by inhibiting activation of TGFβ1 and downregulating the Smad 3 arm of its signal transduction pathway.

Methods

Whole thorax radiation (single dose, 15 Gy) was delivered to EC-SOD overexpressing transgenic (XRT-TG) and wild-type (XRT-WT) animals. Mice were sacrificed at 1 day, 1 week, 3, 6, 10 and 14 weeks. Breathing rates, right lung weights, total/differential leukocyte count, activated TGFβ1 and components of its signal transduction pathway (Smad 3 and p-Smad 2/3) were assessed to determine lung injury.

Results

Irradiated wild-type (XRT-WT) animals exhibited time dependent increase in breathing rates and right lung weights, whereas these parameters were significantly less increased (p < 0.05) at 3, 6, 10 and 14 weeks in irradiated transgenic (XRT-TG) mice. An inflammatory response characterized predominantly by macrophage infiltration was pronounced in XRT-WT mice. This acute inflammation was significantly attenuated (p < 0.05) in XRT-TG animals at 1, 3, 6 and 14 weeks. Expression of activated TGFβ1 and components of its signal transduction pathway were significantly reduced (p < 0.05) at later time-points in XRT-TG vs. XRT-WT.

Conclusion

This study shows that overexpression of EC-SOD confers protection against RT-induced acute lung injury. EC-SOD appears to work, in part, via an attenuation of the macrophage response and also decreases TGFβ1 activation with a subsequent downregulation of the profibrotic TGFβ pathway.

IkappaBalpha (inhibitory kappaBalpha) identified as labile repressor of MnSOD (manganese superoxide dismutase) expression

Cytokines, phorbol esters, radiation and chemotherapeutic drugs up-regulate the expression of MnSOD (manganese superoxide dismutase). Using the VA-13 cell line, we studied the regulation of SOD2 upon treatment with PMA. Pre-treatment with CHX (cycloheximide) followed by PMA led to significantly higher levels of MnSOD mRNA compared with those with either agent alone, suggesting de novo synthesis of an inhibitory protein. PMA treatment modulates redox-sensitive transcription factors, therefore we evaluated the effects of this combination treatment upon AP-1 (activator protein 1) and NF-kappaB (nuclear factor kappaB), two trans-acting factors suggested to play a role in SOD2 regulation. Co-administration of CHX and PMA led to a time-dependent increase in the binding activity of NF-kappaB. Therefore we evaluated IkappaBalpha (inhibitory kappaBalpha) and found that co-administration decreased its steady-state level compared with either agent alone, suggesting that enhanced NF-kappaB activation is due to inhibition of IkappaBalpha synthesis. PMA activates PKC (protein kinase C) enzymes which phosphorylate IkappaBalpha, leading to its degradation, therefore we used GF109203X to inhibit PKC activity. Stable transfection utilizing a PMA-responsive element in the human SOD2 gene, showed a concentration-dependent decrease in luciferase and NF-kappaB-binding activity with GF109203X. Western blot analysis indicated the presence of several PKC isoforms in the VA-13 cell line; however, PMA pre-treatment specifically down-regulated alpha and betaI, suggesting a role for one or more of these proteins in SOD2 induction. Taken together, these results indicate that the PKC pathway leading to SOD2 induction proceeds at least in part through NF-kappaB and that inhibition of IkappaBalpha synthesis might serve as a potential pharmacological approach to up-regulate MnSOD.

Expression pattern of cytosolic glutathione peroxidase (cGPx) mRNA during mouse embryogenesis

The selenoprotein cytosolic glutathione peroxidase (cGPx) is ubiquitously distributed in a variety of organs, and its primary function is to protect oxidative damage. To investigate the spatial and temporal expression pattern of cGPx mRNA in embryogenesis, as this has not been studied before, reverse transcription-polymerase chain reaction (RT-PCR) was carried out in a thermal cycler using mouse-specific cGPx primers, and in situ hybridization was performed in whole embryos or embryonic tissues using digoxigenin-labeled mouse cGPx riboprobes. Expression of cGPx mRNA was detected in all the embryos retrieved from embryonic days (EDs) 7.5 to 18.5. On EDs 10.5-12.5, cGPx mRNA was highly expressed in the margin of forelimb and hindlimb buds and dorsally in the cranial neural tube, including the telencephalon, diencephalon, and hindbrain neural tube. On ED 13.5, cGPx mRNA was accumulated especially in vibrissae, forelimb and hindlimb plates, tail, and spinal cord. On EDs 14.5-16.5, cGPx mRNA was found in the developing brain, Rathke's pouch, thymus, lung, and liver. On ED 17.5, the expression of cGPx mRNA was apparent in various tissues such as brain, submandibular gland, vibrissae, heart, lung, liver, stomach, intestine, pancreas, skin, and kidney. In particular, cGPx mRNA was greatly expressed in epithelial linings and metabolically active sites such as whisker follicles, alveolar epithelium of lung, surface epithelium and glandular region of stomach, skin epithelium, and cortex and tubules of kidney. Overall results indicate that cGPx mRNA is expressed in developing embryos, cell-specifically and tissue-specifically, suggesting that cGPx may function to protect the embryo against reactive oxygen species and/or hydroperoxides massively produced by the intracellular or extracellular environment.

Resistance of photoreceptors in the C57BL/6-c2J, C57BL/6J, and BALB/cJ mouse strains to oxygen stress: evidence of an oxygen phenotype

PURPOSE

To assess the vulnerability of retinal photoreceptors in the BALB/cJ, C57BL/6J, and C57BL/6-c2J (c2J) mouse strains to hypoxic and hyperoxic stress.

METHODS

Mice were raised in dim cyclic light. Pups aged postnatal day 7 (P7) were exposed to hypoxia (11-12% oxygen) for periods up to 23 days. Adult mice were exposed to either hypoxia (12% oxygen) or to hyperoxia (75% oxygen) for up to 2 weeks. Using the TUNEL (terminal dUTP-mediated nick end labeling) technique retinas were examined for cell death.

RESULTS

In juvenile mice, hypoxia induced a robust increase in photoreceptor death in the C57BL/6J strain and a weaker increase in the C57BL/6-c2J strains. In the adult, hypoxia was associated with a small reduction in photoreceptor death in the C57BL/6-c2J strains. Hyperoxia caused substantial photoreceptor death in both the C57BL/6-c2J and C57BL/6J strains. The BALB/cJ strain was more resistant to oxygen stress than the C57BL strains.

CONCLUSIONS

The difference in oxygen vulnerability between C57BL/6J and BALB/c strains may provide a useful starting point for the analysis of genetic regulation of this vulnerability. The resistance of the C57BL/6-c2J substrains to hypoxia may reflect their degenerative status.

Skeletal muscle reperfusion injury is enhanced in extracellular superoxide dismutase knockout mouse

This study investigates the role of extracellular SOD (EC-SOD), the major extracellular antioxidant enzyme, in skeletal muscle ischemia and reperfusion (I/R) injury. Pedicled cremaster muscle flaps from homozygous EC-SOD knockout (EC-SOD-/-) and wild-type (WT) mice were subjected to 4.5-h ischemia and 90-min reperfusion followed by functional and molecular analyses. Our results revealed that EC-SOD-/- mice showed significantly profound I/R injury compared with WT littermates. In particular, there was a delayed and incomplete recovery of arterial spasm and blood flow during reperfusion, and more severe acute inflammatory reaction and muscle damage were noted in EC-SOD-/- mice. After 90-min reperfusion, intracellular SOD [copper- and zinc-containing SOD (CuZn-SOD) and manganese-containing (Mn-SOD)] mRNA levels decreased similarly in both groups. EC-SOD mRNA levels increased in WT mice, whereas EC-SOD mRNA was undetectable, as expected, in EC-SOD-/- mice. In both groups of animals, CuZn-SOD protein levels decreased and Mn-SOD protein levels remained unchanged. EC-SOD protein levels decreased in WT mice. Histological analysis showed diffuse edema and inflammation around muscle fibers, which was more pronounced in EC-SOD-/- mice. In conclusion, our data suggest that EC-SOD plays an important role in the protection from skeletal muscle I/R injury caused by excessive generation of reactive oxygen species.

Protective effect of IL-6 on alveolar epithelial cell death induced by hydrogen peroxide

The goal of this study was to examine whether IL-6 could directly protect lung resident cells, especially alveolar epithelial cells, from reactive oxygen species (ROS)-induced cell death. ROS induced IL-6 gene expression in organotypic lung slices of wild-type (WT) mice. ROS also induced IL-6 gene expression in mouse primary lung fibroblasts, dose dependently. The organotypic lung slices of WT were more resistant to ROS-induced DNA fragmentation than those of IL-6-deficient (IL-6−/−) mice. WT resistance against ROS was abrogated by treatment with anti-IL-6 antibody. TdT-mediated dUTP nick end labeling stain and electron microscopy revealed that DNA fragmented cells in the IL-6−/− slice included alveolar epithelial cells and endothelial cells. In vitro studies demonstrated that IL-6 reduced ROS-induced A549 alveolar epithelial cell death. Together, these data suggest that IL-6 played an antioxidant role in the lung by protecting lung resident cells, especially alveolar epithelial cells, from ROS-induced cell death.

Extracellular superoxide dismutase functions as a major repressor of hypoxia-induced erythropoietin gene expression

Hypoxia and biological responses to hypoxia are commonly encountered in both normal and pathologic cellular processes. Here we report that extracellular superoxide dismutase (EC-SOD) plays a major role in regulating the magnitude of hypoxia-induced erythropoietin (Epo) gene expression, thus implicating superoxide as an intermediary signal transduction molecule critical to this process. We found that mice which have the EC-SOD gene inactivated show a marked more than 100-fold elevation in hypoxia-induced Epo gene expression, compared with wild-type controls, which was both dose and time dependent. These mice also showed a significant increase in serum Epo levels after 1 d hypoxia. Interestingly, despite elevated Epo levels, reciprocal changes in hematocrit and reticulocyte counts were not found, suggesting that this newly synthesized Epo lacks functional hematopoietic effects. When EC-SOD was overexpressed in Hep3B cells, we found a significant reduction in Epo gene induction by both CoCl2 (50 microM) and hypoxia (1% O2). Similar findings were noted with another hypoxia-inducible gene, carbonic anhydrase IX. We conclude that EC-SOD functions as a major repressor of hypoxia-induced Epo gene expression, which implicates superoxide as a signaling intermediate whose downstream effects, at least in part, may be mediated by HIF-1alpha.

Mitochondrial dysfunction and oxidative stress: cause and consequence of epileptic seizures

Mitochondrial dysfunction has been implicated as a contributing factor in diverse acute and chronic neurological disorders. However, its role in the epilepsies has only recently emerged. Animal studies show that epileptic seizures result in free radical production and oxidative damage to cellular proteins, lipids, and DNA. Mitochondria contribute to the majority of seizure-induced free radical production. Seizure-induced mitochondrial superoxide production, consequent inactivation of susceptible iron-sulfur enzymes, e.g., aconitase, and resultant iron-mediated toxicity may mediate seizure-induced neuronal death. Epileptic seizures are a common feature of mitochondrial dysfunction associated with mitochondrial encephalopathies. Recent work suggests that chronic mitochondrial oxidative stress and resultant dysfunction can render the brain more susceptible to epileptic seizures. This review focuses on the emerging role of oxidative stress and mitochondrial dysfunction both as a consequence and as a cause of epileptic seizures.

Effects of variation in superoxide dismutases (SOD) on oxidative stress and apoptosis in lens epithelium

Among the critical antioxidant enzymes that protect the cells against oxidative stress are superoxide dismutases: CuZnSOD (Sod1) and MnSOD (Sod2). The latter is also implicated in apoptosis. To determine the importance of these enzymes in protection against reactive oxygen species (ROS) in the lens, we analysed DNA strand breaks in lens epithelium from transgenic and knockout (Sod1) mice following exposure to H2O2 in organ culture. Since Sod2 knockouts do not survive, comparison was made of lenses of partially-deficient (heterozygote) for Sod2 and the wild-type controls which have twice the enzyme level. Antioxidant potential of Sod2 was also studied in human lens epithelial cells (SRA01/04) in which the enzyme was up- and down-regulated by transfection with plasmids containing sense and antisense human cDNA for MnSOD. DNA strand breaks in the epithelium of Sod1 knockouts and Sod2 heterozygotes were much greater than in the corresponding wild-type or in transgenic mice over-expressing the enzymes when the lenses were exposed to H2O2. The functional role of Sod2 in apoptosis was examined in cultured human lens epithelial cells. Cells with higher enzyme levels were more resistant to the cytotoxic effects of H2O2, O2- and UV-B radiation. Furthermore, Sod2-deficient cells showed dramatic mitochondrial damage, cytochrome C leakage, caspase 3 activation and increased apoptotic cell death when they were challenged with O2-. Thus, mitochondrial enzyme (Sod2) deficiency plays an important role in the initiation of apoptosis in the lens epithelium.

Enhancement of collagen-induced arthritis in mice genetically deficient in extracellular superoxide dismutase

OBJECTIVE

To examine the influence of superoxide on the severity of collagen-induced arthritis (CIA) in mice.

METHODS

CIA was induced in DBA/1J mice lacking the extracellular superoxide dismutase (EC-SOD) gene (knockout [KO]) and in normal DBA/1J mice (wild-type [WT]).

RESULTS

The clinical disease activity score was significantly higher in EC-SOD-KO mice than in WT mice between days 36 and 53, and the histologic scores for joint damage on day 53 increased 2-fold or more in the EC-SOD-KO mice. There were no significant differences between the 2 groups of mice in proliferation indices of spleen or lymph node cells in vitro after stimulation with type II collagen. Although both IgG1 and IgG2a anticollagen antibody levels increased in both groups of mice between days 21 and 53, there were no significant differences between the 2 groups. Lipopolysaccharide-stimulated spleen cells from EC-SOD-KO mice produced greater levels of tumor necrosis factor alpha (TNFalpha) over 48 hours in culture compared with cells from WT mice. Increased steady-state levels of messenger RNA (mRNA) for interferon-gamma (IFNgamma), TNFalpha, and interleukin-1beta (IL-1beta), and lower levels of IL-1 receptor antagonist (IL-1Ra) mRNA were present in the joints of the EC-SOD-KO mice compared with the WT mice.

CONCLUSION

The absence of EC-SOD leads to more severe CIA, which may be accompanied by enhanced production of the proinflammatory cytokines IFNgamma, TNFalpha, and IL-1beta, and decreased production of the antiinflammatory cytokine IL-1Ra in the joints.

Sp1 and Sp3 transcription factors mediate trichostatin A-induced and basal expression of extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD) is the major extracellular antioxidant enzyme and may play a critical role in the pathogenesis of a variety of pulmonary, neurological, and cardiovascular diseases. We report here that exposure to the deacetylase inhibitor trichostatin A (TSA) induces EC-SOD mRNA levels in mIMCD3 and Hepa 1-6 cells, but reduces EC-SOD mRNA levels in MLg cells. To determine the molecular mechanism of TSA-mediated EC-SOD gene regulation, we analyzed EC-SOD's proximal promoter region, which revealed two previously unknown but putative Sp1 cis elements. Transfection of systematically truncated 5'-flanking sequences revealed that the second Sp1 binding site contributes up to 70% of the constitutive EC-SOD promoter activity. Binding of Sp1 and Sp3 transcription factors to this region was confirmed by DNase I footprinting, electrophoretic mobility shift assay, super-shift assay, and chromatin immunoprecipitation. A dominant-negative Sp1 construct considerably reduced EC-SOD promoter activity in mammalian cells, whereas coexpression of Sp1 and Sp3 greatly enhanced reporter activity in SL2 cells. An EC-SOD promoter-reporter construct showed from 5- to 14-fold induction after exposure to TSA, whereas deletion of the Sp1 binding site significantly reduced reporter activation. These results are consistent with Sp1/Sp3 transcription factors providing essential TSA-dependent and basal transcription of the EC-SOD gene and may represent a novel pharmacological pathway for regulating EC-SOD levels in tissue.

Extracellular superoxide dismutase attenuates lipopolysaccharide-induced neutrophilic inflammation

Extracellular superoxide dismutase (EC-SOD) is an abundant antioxidant in the lung and vascular walls. Previous studies have shown that EC-SOD attenuates lung injury in a diverse variety of lung injury models. In this study, we examined the role of EC-SOD in mediating lipopolysaccharide (LPS)-induced lung inflammation. We found that LPS-induced neutrophilic lung inflammation was exaggerated in EC-SOD-deficient mice and diminished in mice that overexpressed EC-SOD specifically in the lung. Similar patterns were seen for bronchoalveolar lavage cytokines, such as tumor necrosis factor-alpha, keratinocyte-derived chemokines, and macrophage inflammatory protein-2 as well as expression of lung intercellular adhesion molecule-1, vascular cell adhesion molecule-1, endothelial cell selectin, and platelet selectin. In a macrophage cell line, EC-SOD inhibited LPS-induced macrophage cytokine release, but did not alter expression of intercellular adhesion molecules in endothelial cells. These results suggest that EC-SOD plays an important role in attenuating the inflammatory response in the lung most likely by decreasing release of proinflammatory cytokines from phagocytes.

Distribution of antioxidant enzymes in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia

We studied cell-specific protein expression of all the major antioxidant enzymes (AOEs) and related proteins, such as copper-zinc superoxide dismutase (CuZnSOD), manganese SOD (MnSOD), extracellular SOD (ECSOD), catalase, the heavy and light chains of gamma-glutamylcysteine synthetase (gamma-GCS-l and gamma-GCS-h, also called glutamate cysteine ligase), the rate-limiting enzyme in glutathione synthesis, hemeoxygenase-1 (HO-1), and thioredoxin (Trx), in developing human lung, respiratory distress syndrome, and bronchopulmonary dysplasia by immunohistochemistry. Generally, after 17 weeks of gestational age, MnSOD was predominantly expressed in bronchial epithelium, alveolar epithelium, and macrophages, CuZnSOD was expressed in bronchial epithelium, ECSOD was expressed in bronchial epithelium, vascular endothelium, and the extracellular matrix, catalase was expressed in bronchial epithelium and alveolar macrophages, gamma-GCS-h was expressed in bronchial epithelium and endothelium, and gamma-GCS-l was expressed in bronchial epithelium. Trx was restricted to bronchial epithelium and to a lesser extent to alveolar macrophages, and HO-1 found in alveolar macrophages. Basically, the expression of these enzymes was similar in normal and diseased lung. It can be concluded that various AOEs and related proteins differ in their distribution and expression in lung before term, but generally it seems that infants are better adapted to high oxygen tension than might be expected.

Vasomotor responses in MnSOD-deficient mice

MnSOD is the only mammalian isoform of SOD that is necessary for life. MnSOD(-/-) mice die soon after birth, and MnSOD(+/-) mice are more susceptible to oxidative stress than wild-type (WT) mice. In this study, we examined vasomotor function responses in aortas of MnSOD(+/-) mice under normal conditions and during oxidative stress. Under normal conditions, contractions to serotonin (5-HT) and prostaglandin F2alpha (PGF2alpha), relaxation to ACh, and superoxide levels were similar in aortas of WT and MnSOD(+/-) mice. The mitochondrial inhibitor antimycin A reduced contraction to PGF2alpha and impaired relaxation to ACh to a similar extent in aortas of WT and MnSOD(+/-) mice. The Cu/ZnSOD and extracellular SOD inhibitor diethyldithiocarbamate (DDC) paradoxically enhanced contraction to 5-HT and superoxide more in aortas of WT mice than in MnSOD(+/-) mice. DDC impaired relaxation to ACh and reduced total SOD activity similarly in aortas of both genotypes. Tiron, a scavenger of superoxide, normalized contraction to 5-HT, relaxation to ACh, and superoxide levels in DDC-treated aortas of WT and MnSOD(+/-) mice. Hypoxia, which reportedly increases superoxide, reduced contractions to 5-HT and PGF2alpha similarly in aortas of WT and MnSOD(+/-) mice. The vasomotor response to acute hypoxia was similar in both genotypes. In summary, under normal conditions and during acute oxidative stress, vasomotor function is similar in WT and MnSOD(+/-) mice. We speculate that decreased mitochondrial superoxide production may preserve nitric oxide bioavailability during oxidative stress.

Pre-emptive gene therapy using recombinant adeno-associated virus delivery of extracellular superoxide dismutase protects heart against ischemic reperfusion injury, improves ventricular function and prolongs survival

In high-risk patients, the ideal cardiovascular gene therapy requires a strategy that provides long-term protection of myocardium against episodes of ischemic/reperfusion injury. We report the development of an efficient, long-lasting pre-emptive gene therapy strategy in a rat model of ischemic-reperfusion (I/R) injury of heart. At 6 weeks prior to myocardial injury, the human extracellular superoxide dismutase (Ec-SOD) gene was delivered by direct intramyocardial injections, using a recombinant adeno-associated virus vector. Significant myocardial protection was documented by the decrease in infarct size at 24 h post I/R, improved left ventricular function at 7 weeks postinjury, and enhanced long-term survival in the SOD treated group. This concept of preinjury delivery and 'pre-emptive' gene therapy via the expression of a secreted protein that renders paracrine therapeutic action can be an effective strategy for organ protection against future injury.

Redistribution of pulmonary EC-SOD after exposure to asbestos

Inhalation of asbestos fibers leads to interstitial lung disease (asbestosis) characterized by inflammation and fibrosis. The pathogenesis of asbestosis is not fully understood, but reactive oxygen species are thought to play a central role. Extracellular superoxide dismutase (EC-SOD) is an antioxidant enzyme that protects the lung in a bleomycin-induced pulmonary fibrosis model, but its role has not been studied in asbestos-mediated disease. EC-SOD is found in high levels in the extracellular matrix of lung alveoli because of its positively charged heparin-binding domain. Proteolytic removal of this domain results in clearance of EC-SOD from the matrix of tissues. We treated wild-type C57BL/6 mice with 0.1 mg of crocidolite asbestos by intratracheal instillation and euthanized them 24 h later. Compared with saline- or titanium dioxide-treated control mice, bronchoalveolar lavage fluid (BALF) from asbestos-treated mice contained significantly higher total protein levels and increased numbers of inflammatory cells, predominantly neutrophils, indicating acute lung injury in response to asbestos. Decreased EC-SOD protein and activity were found in the lungs of asbestos-treated mice, whereas more EC-SOD was found in the BALF of these mice. The EC-SOD in the BALF was predominantly in the proteolyzed form, which lacks the heparin-binding domain. This redistribution of EC-SOD correlated with development of fibrosis 14 days after asbestos exposure. These data suggest that asbestos injury leads to enhanced proteolysis and clearance of EC-SOD from lung parenchyma into the air spaces. The depletion of EC-SOD from the extracellular matrix may increase susceptibility of the lung to oxidative stress during asbestos-mediated lung injury.

Discordant Extracellular Superoxide Dismutase Expression and Activity in Neonatal Hyperoxic Lung

Antioxidant defenses in the neonatal lung are required to adapt to the oxygen (O(2))-rich postnatal environment, and oxidant/antioxidant imbalance is a predisposition to lung injury when high concentrations of inspired O(2) are used in neonatal lung diseases. The lung's main extracellular enzymatic defense against superoxide, extracellular superoxide dismutase (EC-SOD), is closely regulated during development. In testing the hypothesis that developmental change in EC-SOD expression and activity in the immature lung would be disrupted by hyperoxia, we found a doubling of lung EC-SOD protein in newborn rats exposed to 95% O(2) for 1 week. Furthermore, EC-SOD protein secretion increased, but EC-SOD enzyme activity did not change with O(2) exposure. EC-SOD mRNA did not change at multiple points between 6 hours and 8 days. Lung EC-SOD recovered by immunoprecipitation after 1 week of O(2) showed strong increases in protein nitrotyrosine and variable, nonsignificant differences in protein carbonyl content. These data provide the first direct evidence that EC-SOD is itself a target of nitration in hyperoxia, and offer a plausible explanation for low EC-SOD activity despite its increased secretion by O(2)-exposed neonatal lung.

Extracellular superoxide enhances 5-HT-induced murine pulmonary artery vasoconstriction

Accumulating evidence suggests that changes in both 5-hydroxytryptamine (5-HT) receptor activity and in the levels of reactive oxygen species (ROS) play an important role in regulating pulmonary artery (PA) vascular responsiveness, particularly in the setting of pulmonary hypertension. Therefore, we hypothesized that increased levels of superoxide enhance 5-HT-induced PA constriction. With the use of a small-vessel bioassay, 5-HT (0.01–10 μM) induced a concentration-dependent vasoconstriction in isolated wild-type murine intrapulmonary arteries (100–150 μm diameter) that was enhanced by both removal of the endothelium and by treatment with either NG-nitro-l-arginine methyl ester (30 μM) or xanthine (10 μM) + xanthine oxidase (0.005 U/ml). PA isolated from extracellular superoxide dismutase (EC-SOD) knockout mice also showed enhanced constriction. On the other hand, PA constriction to 5-HT was attenuated by either the addition of GR-127935 (0.1 μM, a selective inhibitor of 5-HT1B/1Dreceptor) or copper/zinc-containing superoxide dismutase (Cu/Zn SOD, 150 U/ml) and in PA isolated from transgenic mice overexpressing human EC-SOD. With the use of both oxidative fluorescent confocal microscopy and lucigenin-enhanced chemiluminescence, superoxide levels were increased significantly after 5-HT-induced PA vasoconstriction. This increase in superoxide levels could be blocked by the exogenous addition of Cu/Zn SOD (150 U/ml) or by apocynin (30 μM, an inhibitor of NADPH oxidase) but was not affected by gp91phoxknockout mice. Overall, our results are consistent with 5-HT increasing vascular smooth muscle superoxide production via an NADPH oxidase pathway that is independent of gp91phox, which leads to increases in extracellular superoxide levels, which in turn enhances 5-HT-induced murine pulmonary vasoconstriction.

Superoxide dismutase-3 promotes full expression of the EPO response to hypoxia

Extracellular superoxide dismutase (SOD3) is the primary extracellular enzymatic scavenger of superoxide (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{{\cdot}}\mathrm{O}_{2}^{-}\) \end{document}). SOD3's expression is highest in the kidney, but its distribution and biologic functions there are unknown. To investigate the function of renal SOD3, we colocalized it with erythropoietin (EPO) to proximal tubules using in situ hybridization and immunohistochemistry. We then exposed wild-type (Wt) and SOD3 knock-out (KO) mice to hypoxia and found a late hematocrit response in the KO strain. EPO mRNA expression was attenuated in KO mice during the first 6 hours of hypoxia preceded at 2 hours by less accumulation of nuclear hypoxia-inducible transcription factor 1 α (HIF-1α) protein. Meanwhile KO mice exposed to hypoxia showed increases in renal mRNA for superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX4) and early significant increases in glutathione disulfide (GSSG)/glutathione (GSH), a marker of oxidative stress, compared with Wt mice. Plasma nitrite/nitrate and renal 3-nitrotyrosine (3-NTyr), indicating peroxynitrite formation, increased later in hypoxia, and renal endothelial nitric oxide synthase protein induction was similar in both strains. These data show that hypoxic activation of HIF-1α and its target gene EPO in mouse kidney is regulated closely by the oxidant/antioxidant equilibrium involving SOD3, thus identifying renal SOD3 as a regulatory element in the body's innate adaptation to hypoxia.

Multiple deficiencies in antioxidant enzymes in mice result in a compound increase in sensitivity to oxidative stress

To examine the effect of compound deficiencies in antioxidant defense, we have generated mice (Sod2(+/-)/Gpx1(-/-)) that are deficient in Mn superoxide dismutase (MnSOD) and glutathione peroxidase 1 (Gpx1) by breeding Sod2(+/-) and Gpx1(-/-) mice together. Although Sod2(+/-)/Gpx1(-/-) mice showed a 50% reduction in MnSOD and no detectable Gpx1 activity in either mitochondria or cytosol in all tissues, they were viable and appeared normal. Fibroblasts isolated from Sod2(+/-)/Gpx1(-/-) mice were more sensitive (4- to 6-fold) to oxidative stress (t-butyl hydroperoxide or gamma irradiation) than fibroblasts from wild-type mice, and were twice as sensitive as cells from Sod2(+/-) or Gpx1(-/-) mice. Whole-animal studies demonstrated that survival of the Sod2(+/-)/Gpx1(-/-) mice in response to whole body gamma irradiation or paraquat administration was also reduced compared with that of wild-type, Sod2(+/-), or Gpx1(-/-) mice. Similarly, endogenous oxidative stress induced by cardiac ischemia/reperfusion injury led to greater apoptosis in heart tissue from the Sod2(+/-)/Gpx1(-/-) mice than in that from mice deficient in either MnSOD or Gpx1 alone. These data show that Sod2(+/-)/Gpx1(-/-) mice, deficient in two mitochondrial antioxidant enzymes, have significantly enhanced sensitivity to oxidative stress induced by exogenous insults and to endogenous oxidative stress compared with either wild-type mice or mice deficient in either MnSOD or Gpx1 alone.

On the selectivity of superoxide dismutase mimetics and its importance in pharmacological studies

The list of pathophysiological conditions associated with the overproduction of superoxide expands every day. Much of the knowledge compiled on the role of this radical in disease has been gathered using the native superoxide dismutase enzyme and, more recently, by the use of superoxide dismutase knockout models or transgenic models that overexpress the various isoforms of the enzyme. Although the native enzyme has shown promising anti-inflammatory properties in both preclinical and clinical studies, there were drawbacks and issues associated with its use as a therapeutic agent and pharmacological tool. Based on the concept that removal of superoxide modulates the course of inflammation, synthetic, low-molecular-weight mimetics of the superoxide dismutase enzymes that could overcome some of the limitations associated with the use of the native enzyme have been designed. In this review, we will discuss the advances made using various superoxide dismutase mimetics that led to the proposal that superoxide (and/or the product of its interaction with nitric oxide, peroxynitrite) is an important mediator of inflammation, and to the conclusion that superoxide dismutase mimetics can be utilized as therapeutic agents in diseases of various etiologies. The importance of the selectivity of such compounds in pharmacological studies will be discussed.

Falsifying falsifications: the most critical task of theoreticians in biology

Occasionally, experimental biologists obtain results which mystify them so deeply that the paradoxical nature of their finding is acknowledged in the paper reporting it. This constitutes a more-or-less explicit invitation to those who did not perform the experiments - and even those who do not perform experiments at all - to propose explanations that eluded the experimenter. A much more frequent scenario, however, is that the experimenter asserts confidently that his or her data can be explained by a particular model but are at odds with some other model. In such circumstances, it is often overlooked that the stated falsification of the latter model is error-prone: just as the mystified experimenter saw no explanation when in fact there is one, the other experimenter may see only one explanation of the data when there are two. The main reason this phenomenon is neglected is, of course, the fact that here the theoretician (or other experimenter) must take the initiative in critiquing a conclusion that, far from troubling the experimenter, may by the time of its publication be a cornerstone of his or her research program, so whose refutation may be decidedly unwelcome. For precisely this reason, such critiques - especially, perhaps, when they come from those who do not do bench work at all and thus have a complementary approach to the analysis of data - are fundamental to maximising the rate of progress in fields of biology that otherwise risk languishing in ever-better-studied cul-de-sacs for many years. Computational biology, including simulation, plays an especially important role in this, whereas its ability to contribute to biology in other ways is often less than its proponents claim. Here I discuss some representative examples of falsification-falsification, including a previously unpublished analysis of mitochondrial DNA population dynamics in cell culture, in the hope of stimulating more theoreticians - and perhaps also more experimentalists - to engage in it.

Two functional variants of the superoxide dismutase genes in Finnish families with asthma

BACKGROUND

Functional polymorphisms in the genes encoding superoxide dismutases (SOD)-that is, superoxide scavenging antioxidant enzymes-may play an important role in the development of inflammatory airway diseases such as asthma.

METHODS

The allele frequencies of two missense polymorphisms of SOD genes (Ala16Val in MnSOD (SOD2) and Arg213Gly in ECSOD (SOD3)) were investigated in Finnish patients with asthma and compared with family based controls. Both variants have been shown to be functionally interesting in the lung. The polymorphism at the exon-intron 3 boundary of a third SOD, CuZnSOD (SOD1), was also included in the analysis.

RESULTS

None of the SOD genetic variants studied appeared to be major genetic regulators in the development of asthma. We could exclude all models of inheritance that increased the risk of asthma more than 1.2 fold for MnSOD*Val (frequency of allele 0.74 in the population) and more than 6.6 fold for ECSOD*Gly213 (frequency of allele 0.03 in the population) compared with non-carriers. For the intronic polymorphism in CuZnSOD, a relative risk of more than 3.3 (frequency of allele 0.10 in the population) could be excluded.

CONCLUSIONS

It is highly unlikely that the functionally important genetic variants Ala16Val and Arg213Gly of SODs play a major role in the genetic susceptibility of asthma.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

Mitochondrial oxidative stress and increased seizure susceptibility in Sod2(-/+) mice

Epileptic seizures can occur as a result of mitochondrial dysfunction. Mitochondria have vital functions such as energy generation, control of cell death, neurotransmitter synthesis, and free radical production. Which of these critical mitochondrial functions contributes to epileptic seizures is unknown. We demonstrate here that a subset of mice with partial deficiency of the mitochondrial superoxide dismutase (Sod2(-/+)) show increased incidence of spontaneous and handling-induced seizures that correlates with chronic mitochondrial oxidative stress (increased aconitase inactivation and 8-hydroxy-2'-deoxyguanosine formation in mitochondria) and diminished mitochondrial oxygen utilization. Before the age at which spontaneous seizures appear in a subset of the mice, Sod2(-/+) mice demonstrated increased susceptibility to behavioral seizures, mitochondrial aconitase inactivation, and neurodegeneration induced by the administration of kainate. These data suggest that chronic mitochondrial oxidative stress initiated by superoxide (O(2)(.-)) radicals is sufficient to increase seizure susceptibility due to aging, environmental stimulation, or excitotoxin administration. Sod2(-/+) mice showed an age-related decrease in the expression of glial glutamate transporters (GLT-1 and GLAST), suggesting that oxidant-induced inhibition of glutamate transport may play a mechanistic role in rendering some Sod2(-/+) mice susceptible to seizures. In summary, mitochondrial oxidative stress and resultant dysfunction may be an important mechanism underlying certain seizure disorders.

The role of oxidative stress in chronic obstructive pulmonary disease

Tobacco smoke is the number one risk factor for chronic obstructive pulmonary disease (COPD) and contains a high concentration of oxidants. The lung has a high concentration of antioxidants and antioxidant enzymes; however, COPD patients show evidence of increased oxidative stress suggesting that endogenous antioxidants may be insufficient to prevent oxidative damage from cigarette smoke. The consequences of increased oxidative stress in the lung include increased transcription of inflammatory genes, increased protease activity, and increased mucus secretion. Oxidative stress is often associated with impaired skeletal muscle function and may be one of the causes of glucocorticoid resistance. While current pharmacologic approaches to the treatment of chronic obstructive pulmonary disease do not commonly include antioxidants, preclinical studies involving animal models suggest that antioxidant superoxide dismutase mimetics offer a potential new therapeutic approach to the prevention and treatment of chronic obstructive pulmonary disease.

Spontaneous hypomorphic mutations in antioxidant enzymes of mice

An antioxidant enzymatic system is pivotal for aerobic animals to minimize the damage induced by reactive oxygen species. Spontaneous mutant animals with altered antioxidant enzyme activity should be useful for the study of the function of these enzymes in vivo. We examined the nucleotide sequences of the genes for the major antioxidant enzymes, including catalase (Cat), superoxide dismutase (Sod1, Sod2, Sod3), glutathione peroxidase (Gpx1, Gpx2, Gpx3, Gpx4, Gpx5), and glutathione reductase (Gsr) in 10 inbred mouse strains. Nonsynonymous nucleotide polymorphisms were identified in all genes, except for Gpx1, Gpx3, and Gpx4. Notably, the SJL/J mouse strain possessed unique nucleotide substitutions in the Gsr and Sod2 genes, which led to Asp39Ala and Val138Met amino acid substitutions in GSR and SOD2, respectively. The specific activity of GSR of SJL/J mice was reduced to 65% of that of NZB/N mice. In vivo activity, however, was higher in SJL/J, due to upregulated expression of the enzyme. The SOD2 activity in SJL/J mice was reduced to half that of other mouse strains. Consistent with this reduction, oxidative damage in the mitochondria was increased as demonstrated by a decrease of total glutathione and an increase in the levels of protein oxidation. These spontaneous hypomorphic alleles would be valuable in the study of free radical biology.

Minute quantities of misfolded mutant superoxide dismutase-1 cause amyotrophic lateral sclerosis

Mutant forms of superoxide dismutase-1 (SOD1) cause amyotrophic lateral sclerosis (ALS) by an unknown noxious mechanism. Using an antibody against a novel epitope in the G127insTGGG mutation, mutant SOD1 was studied for the first time in spinal cord and brain of an ALS patient. The level was below 0.5% of the SOD1 level in controls. In corresponding transgenic mice the content of mutant SOD1 was also low, although it was enriched in spinal cord and brain compared with other tissues. In the mice the misfolded mutant SOD1 aggregated rapidly and 20% occurred in steady state as detergent-soluble protoaggregates. The misfolded SOD1 and the protoaggregates form, from birth until death, a potentially noxious burden that may induce the motor neuron injury. Detergent-resistant aggregates, as well as inclusions of mutant SOD1 in motor neurons and astrocytes, accumulated in spinal cord ventral horns of the patient and mice with terminal disease. The inclusions and aggregates may serve as terminal markers of long-term assault by misfolded SOD1 and protoaggregates.

Extracellular superoxide dismutase is a major determinant of nitric oxide bioavailability: in vivo and ex vivo evidence from ecSOD-deficient mice

The bioavailability of nitric oxide (NO) within the vascular wall is limited by superoxide anions (O2.-). The relevance of extracellular superoxide dismutase (ecSOD) for the detoxification of vascular O2.- is unknown. We determined the involvement of ecSOD in the control of blood pressure and endothelium-dependent responses in angiotensin II-induced hypertension and renovascular hypertension induced by the two-kidney, one-clip model in wild-type mice and mice lacking the ecSOD gene. Blood pressure was identical in sham-operated ecSOD+/+ and ecSOD-/- mice. After 6 days of angiotensin II-treatment and 2 and 4 weeks after renal artery clipping, blood pressure was significantly higher in ecSOD-/- than ecSOD+/+ mice. Recombinant ecSOD selectively decreased blood pressure in hypertensive ecSOD-/- mice, whereas ecSOD had no effect in normotensive and hypertensive ecSOD+/+ mice. Compared with sham-operated ecSOD+/+ mice, sham-operated ecSOD-/- mice exhibited attenuated acetylcholine-induced relaxations. These responses were further depressed in vessels from clipped animals. Vascular O2.-, as measured by lucigenin chemiluminescence, was higher in ecSOD-/- compared with ecSOD+/+ mice and was increased by clipping. The antioxidant tiron normalized relaxations in vessels from sham-operated and clipped ecSOD-/-, as well as from clipped ecSOD+/+ mice. In contrast, in vivo application of ecSOD selectively enhanced endothelium-dependent relaxation in vessels from ecSOD-/- mice. These data reveal that endogenous ecSOD is a major antagonistic principle to vascular O2.-, controlling blood pressure and vascular function in angiotensin II-dependent models of hypertension. ecSOD is expressed in such an abundance that even in situations of high oxidative stress no relative lack of enzyme activity occurs.

Mitochondrial oxidative stress causes chromosomal instability of mouse embryonic fibroblasts

Reactive oxygen species are an inevitable by-product of mitochondrial respiration. It has been estimated that between 0.4 and 4% of molecular oxygen is converted to the radical superoxide (O2*-) and this level is significantly influenced by the functional status of the mitochondria. It is well established that exogenous oxidative stress and high doses of mitochondrial poisons such as paraquat and carbonyl cyanide 4 (trifluoromethoxy) phenylhydrazone (FCCP) can lead to genomic instability. In this report we show for the first time that endogenous mitochondrial oxidative stress in standard cell culture conditions results in nuclear genomic instability in primary mouse embryonic fibroblasts (MEFs). We show that lack of mitochondrial superoxide dismutase in MEFs leads to a severe increase of double strand breaks, end-to-end fusions, chromosomal translocations, and loss of cell viability and proliferative capacity. Our results predict that endogenous mitochondrial oxidative stress can induce genomic instability, and therefore may have a profound effect in cancer and aging.

Enhanced bleomycin-induced pulmonary damage in mice lacking extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD) is highly expressed in the extracellular matrix of lung and vascular tissue. Localization of EC-SOD to the matrix of the lung may protect against oxidative tissue damage that leads to pulmonary fibrosis. This study directly examines the protective role of EC-SOD in a bleomycin model of pulmonary fibrosis and the effect of this enzyme on oxidative protein fragmentation. Mice null for ec-sod display a marked increase in lung inflammation at 14 d post-bleomycin treatment as compared to their wild-type counterparts. Hydroxyproline analysis determined that both wild-type and ec-sod null mice display a marked increase in interstitial fibrosis at 14 d post-treatment, and the severity of fibrosis is significantly increased in ec-sod null mice compared to wild-type mice. To determine if the lack of EC-SOD promotes bleomycin-induced oxidative protein modification, 2-pyrrolidone content (as a measure of oxidative protein fragmentation at proline residues) was assessed in lung tissue from treated mice. 2-Pyrrolidone levels in the lung hydrolysates from ec-sod null mice were increased at both 7 and 14 d post-bleomycin treatment as compared to wild-type mice, indicating EC-SOD can inhibit oxidative fragmentation of proteins in this specific model of oxidative stress.

A function for novel uncoupling proteins: antioxidant defense of mitochondrial matrix by translocating fatty acid peroxides from the inner to the outer membrane leaflet

It is hypothesized that mitochondrial uncoupling proteins operate as carriers of fatty acid peroxide anions. This is assumed to result in electrophoretic extrusion of such anions from the inner to the outer leaflet of the inner mitochondrial membrane, being driven by membrane potential (mitochondrial interior negative). In this way, the inner leaflet is ridded of fatty acid peroxides that otherwise can form very aggressive oxidants damaging mitochondrial DNA, aconitase, and other mitochondrial matrix-localized components of vital importance. The steady-state concentration the fatty acid peroxides is known to be low. This explains why UCP2, 3, 4, and 5 are present in small amounts usually insufficient to make a large contribution to the H+ conductance of the mitochondrial membrane.

Metalloporphyrins improve the survival of Sod2-deficient neurons

The objective of this study was to determine whether metalloporphyrin catalytic antioxidants influence the survival of neuronal cultures in an in vitro model of age-related mitochondrial oxidative stress. Neuronal cultures were prepared from cerebral cortices of manganese superoxide dismutase (MnSOD or Sod2) knockout (homozygous -/-, heterozygous -/+ or wild-type +/+) mice. The ability of catalytic antioxidants, manganese tetrakis-(4-benzoic acid) porphyrin (MnTBAP) and manganese tetrakis-(N-ethyl-2-pyridyl) porphyrin (MnTE-2-PyP) to influence the survival of cultured cerebrocortical neurones from Sod2-replete (+/+) and Sod2-deficient (+/- or -/-) mice was assessed. Sod2-/- cultures showed accelerated cell death in serum-free conditions when grown in ambient oxygen. MnTBAP and MnTE-2-PyP delayed the death of Sod2-/- cultures and improved the survival of Sod2+/+ and Sod2+/- cultures in serum-free conditions. The results suggest that metalloporphyrin antioxidants can delay neuronal death resulting specifically from increased mitochondrial oxidative stress. Furthermore, Sod2-deficient neuronal cultures provide a simple model system to screen the biological efficacy of mitochondrial antioxidants.

Extracellular superoxide dismutase in biology and medicine

Accumulated evidence has shown that reactive oxygen species (ROS) are important mediators of cell signaling events such as inflammatory reactions (superoxide) and the maintenance of vascular tone (nitric oxide). However, overproduction of ROS such as superoxide has been associated with the pathogenesis of a variety of diseases including cardiovascular diseases, neurological disorders, and pulmonary diseases. Antioxidant enzymes are, in part, responsible for maintaining low levels of these oxygen metabolites in tissues and may play key roles in controlling or preventing these conditions. One key antioxidant enzyme implicated in the regulation of ROS-mediated tissue damage is extracellular superoxide dismutase (EC-SOD). EC-SOD is found in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. In addition, EC-SOD is likely to play an important role in mediating nitric oxide-induced signaling events, since the reaction of superoxide and nitric oxide can interfere with nitric oxide signaling. This review will discuss the regulation of EC-SOD and its role in a variety of oxidant-mediated diseases.

Superoxide dismutases in the lung and human lung diseases

The lungs are directly exposed to higher oxygen concentrations than most other tissues. Increased oxidative stress is a significant part of the pathogenesis of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease, parenchymal lung diseases (e.g., idiopathic pulmonary fibrosis and lung granulomatous diseases), and lung malignancies. Lung tissue is protected against these oxidants by a variety of antioxidant mechanisms among which the superoxide dismutases (SODs) are the only ones converting superoxide radicals to hydrogen peroxide. There are three SODs: cytosolic copper-zinc, mitochondrial manganese, and extracellular SODs. These enzymes have specific distributions and functions. Their importance in protecting lung tissue has been confirmed in transgenic and knockout animal studies. Relatively few studies have been conducted on these enzymes in the normal human lung or in human lung diseases. Most human studies suggest that there is induction of manganese SOD and, possibly, extracellular SOD during inflammatory, but not fibrotic, phases of parenchymal lung diseases and that both copper-zinc SOD and manganese SOD may be downregulated in asthmatic airways. Many previous antioxidant therapies have been disappointing, but newly characterized SOD mimetics are being shown to protect against oxidant-related lung disorders in animal models.

Early embryonic lethality caused by targeted disruption of the mouse PHGPx gene

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is the only known intracellular antioxidant enzyme that can directly reduce lipid hydroperoxide in membrane. Mitochondrial and non-mitochondrial PHGPx and sperm nuclei GPx are transcribed from one gene by alternative transcription using different first exons Ia and Ib, respectively. To examine the role of PHGPx in development, we generated mice deficient in PHGPx by a targeted disruption of all exons of the PHGPx gene. Heterozygotes are viable, fertile, and appear normal, despite having decreased levels of three types of PHGPx mRNA and protein. Embryos homozygous for PHGPx-null die between 7.5 and 8.5 days post coitum (dpc), probably developing distal apoptosis. We examined the expression of PHGPx in mouse embryos using immunohistochemical analysis with anti-PHGPx mAb. The expression of PHGPx was detected in the embryonic ectoderm and the yolk sac membrane at 7.5dpc. The results demonstrated that PHGPx is expressed in early gastrulation stage at 7.5dpc and that the expression of PHGPx was essential for normal mouse development.

Analysis of doppel protein toxicity

The recently described doppel protein (Dpl) is a homologue of the prion protein (PrP(c)). This protein, expressed in the brains of mice that lack the expression of PrP(c), causes neuronal death as the mice age. Previous studies have suggested this neuronal damage is caused by oxidative assault and changes in the activity of NOS proteins. We investigated the toxicity of Dpl in cell culture models and showed that Dpl was toxic to neurons. This toxicity was inhibited by the expression of PrP(c) and possibly involved direct interaction between the two proteins. The mechanism of toxicity involved stimulation of nitric oxide production via activation of the nitric oxide synthases, nNOS and iNOS. This mechanism of toxicity is quite different from that of PrP(Sc) and does not require the protein to change conformation. These results provide the first evidence for the mechanism of Dpl toxicity.

Evidence for extracellular superoxide dismutase as a mediator of hemorrhage-induced lung injury

Hemorrhage results in excessive production of superoxide that is associated with severe lung injury. We examined whether the superoxide dismutase (SOD) mimetic manganese(III) mesotetrakis (di-N-ethylimidazole) porphyrin (AEOL 10150) could attenuate this lung injury and whether extracellular (EC)-SOD-deficient mice would have increased hemorrhage-induced lung injury. Compared with wild-type mice, EC-SOD-deficient mice had increased lung neutrophil accumulation, a 3.9-fold increase in myeloperoxidase activity, a 1.5-fold increase in nuclear factor (NF)-kappaB activation, and a 1.5-fold increase in lipid peroxidation 1 h after hemorrhage. Pretreatment with AEOL 10150 did not attenuate neutrophil accumulation but significantly reduced NF-kappaB activation and lipid peroxidation in both wild-type and EC-SOD-deficient mice. The increase in hemorrhage-induced neutrophil accumulation in the lungs of EC-SOD-deficient mice suggests that EC-SOD might play a role in mediating neutrophil recruitment to the lung.

In vitro cell free synthesis of human manganese superoxide dismutase with the RTS 500 system

Reduced activity of manganese superoxide dismutase (MnSOD) is the basis of several pathologic features and complications occurring in the course of infectious mononucleosis. In order to supply future research with easily accessible enzyme, an in vitro protocol was developed based on the RTS 500 system and an overexpression vector. Translation of MnSOD monomers could be detected by SDS-PAGE, and assembly of the active homotetramer by native PAGE. Enzyme activity was successfully shown by in gel activity tests and enzyme assays. With 15 micro g of DNA, 2.45 micro kat were generated. The purification of MnSOD was performed by chromatography applying the His-tag technology. In SDS-PAGE of the eluate, a band showed up at M(r) 25000.

Toluene inhalation induced 8-hydroxy-2'-deoxyguanosine formation as the peroxidative degeneration in rat organs

The effect of toluene inhalation on oxidative damage in rat organs was examined. Male Wistar rats was inhaled toluene (1500 ppm for 4 h a day) for 7 days. Quantitatively and immunohistochemically, oxidative DNA damage, lipid peroxide (LPO) and superoxide dismutase (SOD) were examined. As a marker of the oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (8-OH-dG) immunoreactivity increased in the lung, liver and kidney. The amount of 8-OH-dG also increased in liver and kidney significantly. In the testis, the amount of 8-H-dG did not increase, however 8-OH-dG immunoreactivity enhanced in the spermatogonia. SOD immunoreactivity increased in the lung, liver and kidney. However, 4-hydroxy-nonenal immunoreactivity and the amount of LPO did not change in each organ. Thus, oxidative damage by toluene is mainly DNA damage, especially, the oxidative DNA damage observed in the lung, liver and kidney for the increase of the immunoreactivity and amount of 8-OH-dG.

Pulmonary outcome at 1 year corrected age in premature infants treated at birth with recombinant human CuZn superoxide dismutase

OBJECTIVE

To examine whether treatment of premature infants with intratracheal recombinant human CuZn superoxide dismutase (r-h CuZnSOD) reduces bronchopulmonary dysplasia and improves pulmonary outcome at 1 year corrected age.

DESIGN

Three hundred two premature infants (600-1200 g birth weight) treated with exogenous surfactant at birth for respiratory distress syndrome were randomized to receive either intratracheal r-h CuZnSOD (5 mg/kg in 2 mL/kg saline) or placebo every 48 hours (as long as intubation was required) for up to 1 month of age. Short-term, as well as longer-term pulmonary outcome was assessed.

RESULTS

There were no differences between groups in the incidence of death or the development of bronchopulmonary dysplasia (oxygen requirement with an Edwards chest radiograph score of >or=3) at 28 days of life or 36 weeks' postmenstrual age. r-h CuZnSOD was well-tolerated and not associated with significant increases in any adverse event. At a median of 1 year corrected age, health assessments and physical examinations were performed on 209 (80%) surviving infants, with complete data available on 189 infants. Thirty-seven percent of placebo-treated infants had repeated episodes of wheezing or other respiratory illness severe enough to require treatment with asthma medications such as bronchodilators and/or corticosteroids compared with 24% of r-h CuZnSOD-treated infants, a 36% reduction. In infants <27 weeks' gestation, 42% treated with placebo received asthma medications compared with 19% of r-h CuZnSOD-treated infants, a 55% decrease. Infants <27 weeks' gestation who received r-h CuZnSOD also had a 55% decrease in emergency department visits and a 44% decrease in subsequent hospitalizations. Growth measurements and the results of physical examinations were comparable between groups.

CONCLUSIONS

These data indicate that treatment at birth with r-h CuZnSOD may reduce early pulmonary injury, resulting in improved clinical status when measured at 1 year corrected age. r-h CuZnSOD appears to be a safe and effective therapy that improves pulmonary outcome in high-risk premature infants.

Extracellular superoxide dismutase is a major antioxidant in human fibroblasts and slows telomere shortening

There is good evidence that telomere shortening acts as a biological clock in human fibroblasts, limiting the number of population doublings a culture can achieve. Oxidative stress also limits the growth potential of human cells, and recent data show that the effect of mild oxidative stress is mediated by a stress-related increased rate of telomere shortening. Thus, fibroblast strains have donor-specific antioxidant defense, telomere shortening rate, and growth potential. We used low-density gene expression array analysis of fibroblast strains with different antioxidant potentials and telomere shortening rates to identify gene products responsible for these differences. Extracellular superoxide dismutase was identified as the strongest candidate, a correlation that was confirmed by Northern blotting. Over-expression of this gene in human fibroblasts with low antioxidant capacity increased total cellular superoxide dismutase activity, decreased the intracellular peroxide content, slowed the telomere shortening rate, and elongated the life span of these cells under normoxia and hyperoxia. These results identify extracellular superoxide dismutase as an important antioxidant gene product in human fibroblasts, confirm the causal role of oxidative stress for telomere shortening, and strongly suggest that the senescence-like arrest under mild oxidative stress is telomere-driven.

Superoxide dismutase mimetics

In this review we describe the potential role(s) of superoxide in inflammatory disorders.

Extracellular superoxide dismutase protects lung development in hyperoxia-exposed newborn mice

We tested the hypothesis that targeted transgenic overexpression of human extracellular superoxide dismutase (EC-SOD) would preserve alveolar development in hyperoxia-exposed newborn mice. We exposed newborn transgenic and wild-type mice to 95% oxygen (O2) or air x 7 days and measured bronchoalveolar lavage cell counts, and lung homogenate EC-SOD, oxidized and reduced glutathione, and myeloperoxidase. We found that total EC-SOD activity in transgenic newborn mice was approximately 2.5x the wild-type activity. Hyperoxia-exposed transgenic mice had less pulmonary neutrophil influx and oxidized glutathione than wild-type littermates at 7 days. We measured alveolar surface and volume density in animals exposed to 14 days more of air or 60% O2. Hyperoxia-exposed transgenic EC-SOD mice had significant preservation of alveolar surface and volume density compared with wild-type littermates. After 7 days 95% O2 + 14 days 60% O2, lung inflammation measured as myeloperoxidase activity was reduced to control levels in all treatment groups.

Role of oxidant injury in the pathogenesis of neonatal lung disease

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that develops in newborn infants treated with oxygen and mechanical ventilation for a primary lung disorder. With significant improvements in survival of many critically ill infants, BPD has become an extremely important complication of newborn intensive care. The pathogenesis of BPD is complex and involves a variety of causative factors. However, increasing evidence has suggested that an oxidative insult could be an extremely important component of the injury process. Premature infants are especially sensitive to oxidant injury since they are exposed to supraphysiological concentrations of oxygen at birth while endogenous antioxidant enzyme activity may be relatively deficient.

CONCLUSION

Superoxide dismutase is an antioxidant enzyme that has been shown in numerous basic and clinical studies to protect cells against oxidant injury.

Myeloid zinc finger (MZF)-like, Kruppel-like and Ets families of transcription factors determine the cell-specific expression of mouse extracellular superoxide dismutase

Extracellular superoxide dismutase (EC-SOD or SOD3) is an important protective enzyme against the toxicity of superoxide radicals that are produced under both physiological and pathophysiological conditions. We have isolated and characterized over 11 kb of the mouse EC-SOD gene and its 5'- and 3'-flanking regions. The gene consists of two exons, with the entire coding region located within exon 2. In order to study the mechanism of cell-specific gene regulation for mouse EC-SOD, we characterized 2500 bp of its 5'-flanking region using cultured cells derived from mouse lung fibroblasts (MLg), kidney medulla (mIMCD3) and hepatocytes (Hepa 1-6). Real-time PCR showed that basal expression of EC-SOD was considerably higher in MLg cells compared with the other cell types. Reporter-gene assays revealed that the proximal promoter region was sufficient to support this high expression in MLg cells. Although no obvious TATA box was identified, our results show that a highly purine-rich region from -208 to +104 contains active binding sites for both the Kruppel-like and Ets families of transcription factors. Using electrophoretic mobility shift, DNase footprinting and reporter gene assays, we identified myeloid zinc finger 1 and gut-enriched Kruppel-like-factor-like nuclear transcription factors as repressors of EC-SOD expression, whereas nuclear transcription factors from the Ets family, such as Elf-1 and GA-binding protein alpha and beta, were potent activators of EC-SOD transcription. We propose a model that highlights competition between Ets activators and Kruppel-like repressors within the proximal promoter region that determines the level of EC-SOD expression in a particular cell type.