Expression of extracellular superoxide dismutase by human cell lines

Identification and functional characterization of a superoxide dismutase (CuZnSOD) from Pinctada fucata martensii

Copper/zinc superoxide dismutase (Cu/Zn-SOD) can effectively eliminate reactive oxygen species (ROS)，avoid damage from O2 to the body, and maintain O2 balance. In this study, multi-step high-performance liquid chromatography (HPLC), combined with Mass Spectrometry (MS), was used to isolate and identify Cu/Zn-SOD from the serum of Pinctada fucata martensii (P. f. martensii) and was designated as PmECSOD. With a length of 1864 bp and an open reading frame (ORF) of 1422 bp, the cDNA encodes a 473 amino acid protein. The PmECSOD transcript was detected in multiple tissues by quantitative real-time PCR (qRT-PCR), with its highest expression level being in the gills. Additionally, the temporal expression of PmECSOD mRNA in the hemolymph was highest at 48 h after in vivo stimulation with Escherichia coli and Micrococcus luteus. The results from this study provide a valuable base for further exploration of molluscan innate immunity and immune response.

Association among extracellular superoxide dismutase genotype, plasma concentration, and comorbidity in the very old and centenarians

Superoxide dismutase 3 (SOD3), an antioxidant enzyme, is known as extracellular SOD (EC-SOD) because it is the predominant form in extracellular fluids. The diversity of plasma EC-SOD concentration is associated with the SOD3 p.R231G missense variant genotype. To clarify the association among SOD3 genotype, plasma EC-SOD concentration, and comorbidity in Oldest Old, we analyzed genome-wide associations with plasma EC-SOD concentration and associations between EC-SOD concentration and medical history classified by the SOD3 genotype in the Very Old (85–99 years old, n = 505) and Centenarians (over 100 years old, n = 595). The results revealed that SOD3 p.R231G was the most significant variant associated with plasma EC-SOD concentration. Although no significant difference was observed in medical histories between the SOD3 p.R231G variant non-carriers and carriers, higher EC-SOD concentration in plasma of SOD3 p.R231G variant non-carriers was associated with a high odds ratio for chronic kidney disease (OR = 2.70, 95% CI = 1.98–3.72) and low odds ratio for diabetes mellitus (DM) (OR = 0.61, 95% CI = 0.39–0.95). Comparison with 11 plasma biomarkers for age-related disease showed that plasma EC-SOD concentration correlated with adiponectin and estimated glomerular filtration rate with creatinine correction; therefore, we deduced that EC-SOD co-operates with adiponectin and possesses beneficial functions for DM in the Oldest Old.

Pathomechanisms of Blood-Brain Barrier Disruption in ALS

The blood-brain barrier (BBB) and the blood-spinal cord barrier (BSCB) are responsible for controlling the microenvironment within neural tissues in humans. These barriers are fundamental to all neurological processes as they provide the extreme nutritional demands of neural tissue, remove wastes, and maintain immune privileged status. Being a semipermeable membrane, both the BBB and BSCB allow the diffusion of certain molecules, whilst restricting others. In amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases, these barriers become hyperpermeable, allowing a wider variety of molecules to pass through leading to more severe and more rapidly progressing disease. The intention of this review is to discuss evidence that BBB hyperpermeability is potentially a disease driving feature in ALS and other neurodegenerative diseases. The various biochemical, physiological, and genomic factors that can influence BBB permeability in ALS and other neurodegenerative diseases are also discussed, in addition to novel therapeutic strategies centred upon the BBB.

Nanotherapies for Treatment of Cardiovascular Disease: A Case for Antioxidant Targeted Delivery

Purpose of Review

Cardiovascular disease (CVD) involves a broad range of clinical manifestations resulting from a dysfunctional vascular system. Overproduction of reactive oxygen and nitrogen species are causally implicated in the severity of vascular dysfunction and CVD. Antioxidant therapy is an attractive avenue for treatment of CVD associated pathologies. Implementation of targeted nano-antioxidant therapies has the potential to overcome hurdles associated with systemic delivery of antioxidants. This review examines the currently available options for nanotherapeutic targeting CVD, and explores successful studies showcasing targeted nano-antioxidant therapy.

Recent Findings

Active targeting strategies in the context of CVD heavily focus on immunotargeting to inflammatory markers like cell adhesion molecules, or to exposed extracellular matrix components. Targeted antioxidant nanotherapies have found success in pre-clinical studies.

Summary

This review underscores the potential of targeted nanocarriers as means of finding success translating antioxidant therapies to the clinic, all with a focus on CVD.

Role of matrix metalloproteinases and histone deacetylase in oxidative stress-induced degradation of the endothelial glycocalyx

The glycocalyx is crucial for normal endothelial function. It also tethers extracellular superoxide dismutase (SOD3), which protects the endothelium against oxidative damage. Proteolytic enzymes [matrix metalloproteinases (MMPs)] are capable of disrupting endothelial cell surface proteins, such as syndecans, resulting in derangements of the endothelial glycocalyx. We sought to test the role of MMPs in oxidative stress-mediated disruption of the endothelial glycocalyx and examine the effect of pharmacological inhibition of MMPs on mitigating this detrimental effect. We also examined the role of histone deacetylase (HDAC) in the oxidative stress-mediated MMP induction and glycocalyx remodeling. Oxidative stress was experimentally induced in human adipose microvascular endothelial cells using H₂O₂ and buthionine sulfoximine in the presence and absence of potent MMP and HDAC inhibitors. H₂O₂ and buthionine sulfoximine resulted in a notable loss of the endothelial glycocalyx; they also increased the expression and proteolytic activity of MMP-2 and MMP-9 and subsequently increased the shedding of syndecan-1 and SOD3 from the endothelial cell surface. MMP upregulation was accompanied by a decline in mRNA and protein levels of their inhibitors, tissue inhibitors of metalloproteinase (TIMPs; TIMP-1 and TIMP-3). Furthermore, oxidative stress induced HDAC activity. Inhibition of MMPs and HDAC reversed syndecan-1 and SOD3 shedding and maintained endothelial glycocalyx integrity. HDAC inhibition increased TIMP expression and reduced MMP expression and activity in endothelial cells. Our findings shed light on MMPs and HDAC as therapeutically targetable mechanisms in oxidative stress-induced glycocalyx remodeling. NEW & NOTEWORTHY Oxidative stress, a hallmark of many diseases, damages the endothelial glycocalyx, resulting in vascular dysfunction. Studying the mechanistic link between oxidative stress and endothelial glycocalyx derangements might help discover new therapeutic targets to preserve vascular function. In this study, we investigated the involvement of matrix metalloproteinases and histone deacetylase in oxidative stress-induced endothelial glycocalyx degradation.

Akt2 (Protein Kinase B Beta) Stabilizes ATP7A, a Copper Transporter for Extracellular Superoxide Dismutase, in Vascular Smooth Muscle: Novel Mechanism to Limit Endothelial Dysfunction in Type 2 Diabetes Mellitus

OBJECTIVE

Copper transporter ATP7A (copper-transporting/ATPase) is required for full activation of SOD3 (extracellular superoxide dismutase), which is secreted from vascular smooth muscle cells (VSMCs) and anchors to endothelial cell surface to preserve endothelial function by scavenging extracellular superoxide. We reported that ATP7A protein expression and SOD3 activity are decreased in insulin-deficient type 1 diabetes mellitus vessels, thereby, inducing superoxide-mediated endothelial dysfunction, which are rescued by insulin treatment. However, it is unknown regarding the mechanism by which insulin increases ATP7A expression in VSMCs and whether ATP7A downregulation is observed in T2DM (type2 diabetes mellitus) mice and human in which insulin-Akt (protein kinase B) pathway is selectively impaired.

APPROACH AND RESULTS

Here we show that ATP7A protein is markedly downregulated in vessels isolated from T2DM patients, as well as those from high-fat diet-induced or db/db T2DM mice. Akt2 (protein kinase B beta) activated by insulin promotes ATP7A stabilization via preventing ubiquitination/degradation as well as translocation to plasma membrane in VSMCs, which contributes to activation of SOD3 that protects against T2DM-induced endothelial dysfunction. Downregulation of ATP7A in T2DM vessels is restored by constitutive active Akt or PTP1B^-/- (protein-tyrosine phosphatase 1B-deficient) T2DM mice, which enhance insulin-Akt signaling. Immunoprecipitation, in vitro kinase assay, and mass spectrometry analysis reveal that insulin stimulates Akt2 binding to ATP7A to induce phosphorylation at Ser1424/1463/1466. Furthermore, SOD3 activity is reduced in Akt2^-/- vessels or VSMCs, which is rescued by ATP7A overexpression.

CONCLUSION

Akt2 plays a critical role in ATP7A protein stabilization and translocation to plasma membrane in VSMCs, which contributes to full activation of vascular SOD3 that protects against endothelial dysfunction in T2DM.

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Zinc(II) ion promotes anti-inflammatory effects of rhSOD3 by increasing cellular association

Recently, we demonstrated that superoxide dismutase 3 (SOD3) is a strong candidate for biomedicine. Anti-oxidant function of SOD3 was accomplished without cell penetration, and it inhibited the inflammatory responses via non-enzymatic functions. SOD3 has the heparin binding domain associating cell surface. Interestingly, we found that Zn2＋ promotes transduction effects of recombinant human SOD3 (rhSOD3) by increasing uptake via the heparin binding domain (HBD). We demonstrated an uptake of rhSOD3 from media to cell lysate via HBD, resulting in an accumulation of rhSOD3 in the nucleus, which was promoted by the presence of Zn2＋. This resulted in increased inhibitory effects of rhSOD3 on NF-kB and STAT3 signals in the presence of Zn2＋, which shows elevated association of rhSOD3 into the cells. These results suggest that an optimized procedure can help to enhance the inflammatory efficacy of rhSOD3, as a novel biomedicine. [BMB Reports 2017; 50(2): 85-90].

Tumor necrosis factor-α decreases EC-SOD expression through DNA methylation

Extracellular-superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. EC-SOD expression in cultured cell lines is regulated by various cytokines including tumor necrosis factor-α (TNF-α). TNF-α is a major mediator of pathophysiological conditions and may induce or suppress the generation of various types of mediators. Epigenetics have been defined as mitotically heritable changes in gene expression that do not affect the DNA sequence, and include DNA methylation and histone modifications. The results of the present study demonstrated that TNF-α significantly decreased EC-SOD level in fibroblasts with an accompanying increase in methylated DNA. In DNA methylation and demethylation, cytosine is methylated to 5-methylcytosine (5mC) by DNA methyltransferase (DNMT), and 5mC is then converted to 5-hydroxymethylcytosine (5hmC) and cytosine in a stepwise manner by ten-eleven translocation methylcytosine dioxygenases (TETs). However, DNMT did not participate in TNF-α-induced DNA methylation within the EC-SOD promoter region. On the other hand, TNF-α significantly suppressed TET1 expression and EC-SOD mRNA levels were decreased by the silencing of TET1 in fibroblasts. These results demonstrate that the down-regulation of EC-SOD by TNF-α is regulated by DNA methylation through reductions in TET1.

Short-term regular aerobic exercise reduces oxidative stress produced by acute in the adipose microvasculature

High blood pressure has been shown to elicit impaired dilation in the vasculature. The purpose of this investigation was to elucidate the mechanisms through which high pressure may elicit vascular dysfunction and determine the mechanisms through which regular aerobic exercise protects arteries against high pressure. Male C57BL/6J mice were subjected to 2 wk of voluntary running (~6 km/day) for comparison with sedentary controls. Hindlimb adipose resistance arteries were dissected from mice for measurements of flow-induced dilation (FID; with or without high intraluminal pressure exposure) or protein expression of NADPH oxidase II (NOX II) and superoxide dismutase (SOD). Microvascular endothelial cells were subjected to high physiological laminar shear stress (20 dyn/cm²) or static condition and treated with ANG II + pharmacological inhibitors. Cells were analyzed for the detection of ROS or collected for Western blot determination of NOX II and SOD. Resistance arteries from exercised mice demonstrated preserved FID after high pressure exposure, whereas FID was impaired in control mouse arteries. Inhibition of ANG II or NOX II restored impaired FID in control mouse arteries. High pressure increased superoxide levels in control mouse arteries but not in exercise mouse arteries, which exhibited greater ability to convert superoxide to H₂O₂ Arteries from exercised mice exhibited less NOX II protein expression, more SOD isoform expression, and less sensitivity to ANG II. Endothelial cells subjected to laminar shear stress exhibited less NOX II subunit expression. In conclusion, aerobic exercise prevents high pressure-induced vascular dysfunction through an improved redox environment in the adipose microvasculature.NEW & NOTEWORTHY We describe potential mechanisms contributing to aerobic exercise-conferred protection against high intravascular pressure. Subcutaneous adipose microvessels from exercise mice express less NADPH oxidase (NOX) II and more superoxide dismutase (SOD) and demonstrate less sensitivity to ANG II. In microvascular endothelial cells, shear stress reduced NOX II but did not influence SOD expression.

Exendin-4 induces extracellular-superoxide dismutase through histone H3 acetylation in human retinal endothelial cells

Extracellular-superoxide dismutase (genetic name SOD3) is a secreted anti-oxidative enzyme, and its presence in vascular walls may play an important role in protecting the vascular system against oxidative stress. Oxidative stress has been implicated in the pathogenesis of diabetic retinopathy; therefore, increases in extracellular-superoxide dismutase have been suggested to inhibit the progression of diabetic retinopathy. Incretin-based drugs such as glucagon-like peptide-1 receptor agonists are used in the treatment of type 2 diabetes. Glucagon-like peptide-1 receptor agonists are expected to function as extrapancreatic agents because the glucagon-like peptide-1 receptor is expressed not only in pancreatic tissues, but also in many other tissue types. We herein demonstrated that exendin-4, a glucagon-like peptide-1 receptor agonist, induced the expression of extracellular-superoxide dismutase in human retinal microvascular endothelial cells through epigenetic regulation. The results of the present study demonstrated that exendin-4 induced the expression of extracellular-superoxide dismutase through histone H3 acetylation at the SOD3 proximal promoter region. Moreover, plasma extracellular-superoxide dismutase concentrations in diabetic patients were elevated by incretin-based therapies. Therefore, incretin-based therapies may exert direct extrapancreatic effects in order to protect blood vessels by enhancing anti-oxidative activity.

Regulation of Oxidative Stress in Pulmonary Artery Endothelium. Modulation of Extracellular Superoxide Dismutase and NOX4 Expression Using Histone Deacetylase Class I Inhibitors

An imbalance between oxidants and antioxidants is considered a major factor in the development of pulmonary vascular diseases. Oxidative stress seen in pulmonary vascular cells is regulated by increased expression of prooxidant enzymes (e.g., nicotinamide adenine dinucleotide phosphate reduced oxidases) and/or decreased production of antioxidants and antioxidant enzymes (e.g., superoxide dismutases). We and others have shown that expression of antioxidant genes in pulmonary artery cells is regulated by epigenetic mechanisms. In this study, we investigate the regulation of oxidative stress in pulmonary artery cells using inhibitors of histone deacetylases (HDACs). Human pulmonary artery endothelial cells (HPAECs) and human pulmonary artery smooth muscle cells were exposed to an array of HDAC inhibitors followed by analysis of anti- and prooxidant gene expression using quantitative RT-PCR and quantitative RT-PCR array. We found that exposure of HPAECs to scriptaid, N-[4-[(hydroxyamino)carbonyl]phenyl]-α-(1-methylethyl)-benzeneacetamide, and trichostatin A for 24 hours induced expression of extracellular superoxide dismutase (EC-SOD) up to 10-fold, whereas expression of the prooxidant gene NADPH oxidase 4 was decreased by more than 95%. We also found that this differential regulation of anti- and prooxidant gene expression resulted in significant attenuation in the cellular levels of reactive oxygen species. Induction of EC-SOD expression was attenuated by the Janus kinase 2 protein kinase inhibitor AG490 and by silencing Janus kinase 2 expression. Augmentation of EC-SOD expression using scriptaid was associated with increased histone H3 (Lys27) acetylation and H3 (Lys4) trimethylation at the gene promoter. We have determined that oxidative stress in pulmonary endothelial cells is regulated by epigenetic mechanisms and can be modulated using HDAC inhibitors.

Silica Nanoparticles Induce Oxidative Stress and Autophagy but Not Apoptosis in the MRC-5 Cell Line

This study evaluated the in vitro effects of 62.5 µg/mL silica nanoparticles (SiO₂ NPs) on MRC-5 human lung fibroblast cells for 24, 48 and 72 h. The nanoparticles’ morphology, composition, and structure were investigated using high resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction. Our study showed a decreased cell viability and the induction of cellular oxidative stress as evidenced by an increased level of reactive oxygen species (ROS), carbonyl groups, and advanced oxidation protein products after 24, 48, and 72 h, as well as a decreased concentration of glutathione (GSH) and protein sulfhydryl groups. The protein expression of Hsp27, Hsp60, and Hsp90 decreased at all time intervals, while the level of protein Hsp70 remained unchanged during the exposure. Similarly, the expression of p53, MDM2 and Bcl-2 was significantly decreased for all time intervals, while the expression of Bax, a marker for apoptosis, was insignificantly downregulated. These results correlated with the increase of pro-caspase 3 expression. The role of autophagy in cellular response to SiO₂ NPs was demonstrated by a fluorescence-labeled method and by an increased level of LC3-II/LC3-I ratio. Taken together, our data suggested that SiO₂ NPs induced ROS-mediated autophagy in MRC-5 cells as a possible mechanism of cell survival.

Extracellular superoxide dismutase induced by dopamine in cultured astrocytes

Under some pathological conditions in brain, a large amount of superoxide anion (O(2)(-)) is produced, causing various cellular damages. Among three isozymes of superoxide dismutase (SOD), extracellular (EC)-SOD should play a role to detoxify O(2)(-) in extracellular space; however, a little is known about EC-SOD in brain. Although dopamine (DA) stored in the synaptic vesicle is stable, the excess leaked DA is spontaneously oxidized to yield O(2)(-) and reactive DA quinones, causing damages of dopaminergic neurons. In the present study, we examined the effects of DA on SOD expression in cultured rat cortical astrocytes. By means of RT-PCR, all mRNA of three isozymes of SOD could be detected; however, only EC-SOD was increased by DA exposure for 24 h, dose-dependently. The expression of EC-SOD protein and the cell-surface SOD activity in astrocytes also increased with 100 μM DA exposure. The increase of EC-SOD mRNA by DA was inhibited by a DA transporter inhibitor, GBR12909, whereas it was not changed by DA receptor antagonists, SKF-83566 (D1) and haloperidol (D2). Furthermore, a monoamine oxidase inhibitor, pargyline, and antioxidants, N-acetyl-L-cysteine and glutathione, also did not affect the DA-induced expression of EC-SOD mRNA. On the other hand, an inhibitor of nuclear factor kappaB (NF-κB), ammonium pyrrolidine-1-carbodithioate, suppressed the DA-induced expression of EC-SOD mRNA. These results suggest that DA incorporated into the cells caused the induction of EC-SOD mRNA followed by the enhancements of EC-SOD protein level and the enzyme activity, and that NF-κB activation is involved in the mechanisms of the EC-SOD induction. The regulation of EC-SOD in astrocytes surrounding dopaminergic neurons may contribute to the defensive mechanism against oxidative stress in brain.

IGF-1 induction by acylated steryl β-glucosides found in a pre-germinated brown rice diet reduces oxidative stress in streptozotocin-induced diabetes

Background

The pathology of diabetic neuropathy involves oxidative stress on pancreatic β-cells, and is related to decreased levels of Insulin-like growth factor 1 (IGF-1). Acylated steryl β-glucoside (PR-ASG) found in pre-germiated brown rice is a bioactive substance exhibiting properties that enhance activity of homocysteine-thiolactonase (HTase), reducing oxidative stress in diabetic neuropathy. The biological importance of PR-ASG in pancreatic β-cells remains unknown.

Here we examined the effects of PR-ASG on IGF-1 and glucose metabolism in β-cells exposed to oxidative stress.

Methodology/Principal Findings

In the present study, a pre-germinated brown rice (PR)-diet was tested in streptozotocin (STZ)-induced diabetic rats. Compared with diabetic rats fed control diets, the PR-diet fed rats showed an improvement of serum metabolic and neurophysiological parameters. In addition, IGF-1 levels were found to be increased in the serum, liver, and pancreas of diabetic rats fed the PR-diet. The increased IGF-1 level in the pancreas led us to hypothesize that PR-ASG is protective for islet β-cells against the extensive injury of advanced or severe diabetes. Thus we examined PR-ASG to determine whether it showed anti-apoptotic, pro-proliferative effects on the insulin-secreting β-cells line, INS-1; and additionally, whether PR-ASG stimulated IGF-1 autocrine secretion/IGF-1-dependent glucose metabolism. We have demonstrated for the first time that PR-ASG increases IGF-1 production and secretion from pancreatic β-cells.

Conclusion/Significance

These findings suggest that PR-ASG may affect pancreatic β-cells through the activation of an IGF-1-dependent mechanism in the diabetic condition. Thus, intake of pre-germinated brown rice may have a beneficial effect in the treatment of diabetes, in particular diabetic neuropathy.

Superoxide dismutases: role in redox signaling, vascular function, and diseases

Excessive reactive oxygen species Revised abstract, especially superoxide anion (O₂•-), play important roles in the pathogenesis of many cardiovascular diseases, including hypertension and atherosclerosis. Superoxide dismutases (SODs) are the major antioxidant defense systems against (O₂•-), which consist of three isoforms of SOD in mammals: the cytoplasmic Cu/ZnSOD (SOD1), the mitochondrial MnSOD (SOD2), and the extracellular Cu/ZnSOD (SOD3), all of which require catalytic metal (Cu or Mn) for their activation. Recent evidence suggests that in each subcellular location, SODs catalyze the conversion of (O₂•-), H2O2, which may participate in cell signaling. In addition, SODs play a critical role in inhibiting oxidative inactivation of nitric oxide, thereby preventing peroxynitrite formation and endothelial and mitochondrial dysfunction. The importance of each SOD isoform is further illustrated by studies from the use of genetically altered mice and viral-mediated gene transfer. Given the essential role of SODs in cardiovascular disease, the concept of antioxidant therapies, that is, reinforcement of endogenous antioxidant defenses to more effectively protect against oxidative stress, is of substantial interest. However, the clinical evidence remains controversial. In this review, we will update the role of each SOD in vascular biologies, physiologies, and pathophysiologies such as atherosclerosis, hypertension, and angiogenesis. Because of the importance of metal cofactors in the activity of SODs, we will also discuss how each SOD obtains catalytic metal in the active sites. Finally, we will discuss the development of future SOD-dependent therapeutic strategies.

Histone acetylation regulates the cell-specific and interferon-γ-inducible expression of extracellular superoxide dismutase in human pulmonary arteries

Extracellular superoxide dismutase (EC-SOD) is the major antioxidant enzyme present in the vascular wall, and is responsible for both the protection of vessels from oxidative stress and for the modulation of vascular tone. Concentrations of EC-SOD in human pulmonary arteries are very high relative to other tissues, and the expression of EC-SOD appears highly restricted to smooth muscle. The molecular basis for this smooth muscle-specific expression of EC-SOD is not known. Here we assessed the role of epigenetic factors in regulating the cell-specific and IFN-γ-inducible expression of EC-SOD in human pulmonary artery cells. The analysis of CpG site methylation within the promoter and coding regions of the EC-SOD gene demonstrated higher levels of DNA methylation within the distal promoter region in endothelial cells compared with smooth muscle cells. Exposure of both cell types to DNA demethylation agents reactivated the transcription of EC-SOD in endothelial cells alone. However, exposure to the histone deacetylase inhibitor trichostatin A (TSA) significantly induced EC-SOD gene expression in both endothelial cells and smooth muscle cells. Concentrations of EC-SOD mRNA were also induced up to 45-fold by IFN-γ in smooth muscle cells, but not in endothelial cells. The IFN-γ-dependent expression of EC-SOD was regulated by the Janus tyrosine kinase/signal transducers and activators of transcription proteins signaling pathway. Simultaneous exposure to TSA and IFN-γ produced a synergistic effect on the induction of EC-SOD gene expression, but only in endothelial cells. These findings provide strong evidence that EC-SOD cell-specific and IFN-γ-inducible expression in pulmonary artery cells is regulated, to a major degree, by epigenetic mechanisms that include histone acetylation and DNA methylation.

Inflammatory cytokine induced regulation of superoxide dismutase 3 expression by human mesenchymal stem cells

Increasing evidence suggests that bone marrow derived-mesenchymal stem cells (MSCs) have neuroprotective properties and a major mechanism of action is through their capacity to secrete a diverse range of potentially neurotrophic or anti-oxidant factors. The recent discovery that MSCs secrete superoxide dismutase 3 (SOD3) may help explain studies in which MSCs have a direct anti-oxidant activity that is conducive to neuroprotection in both in vivo and in vitro. SOD3 attenuates tissue damage and reduces inflammation and may confer neuroprotective effects against nitric oxide-mediated stress to cerebellar neurons; but, its role in relation to central nervous system inflammation and neurodegeneration has not been extensively investigated. Here we have performed a series of experiments showing that SOD3 secretion by human bone marrow-derived MSCs is regulated synergistically by the inflammatory cytokines TNF-alpha and IFN-gamma, rather than through direct exposure to reactive oxygen species. Furthermore, we have shown SOD3 secretion by MSCs is increased by activated microglial cells. We have also shown that MSCs and recombinant SOD are able to increase both neuronal and axonal survival in vitro against nitric oxide or microglial induced damage, with an increased MSC-induced neuroprotective effect evident in the presence of inflammatory cytokines TNF-alpha and IFN-gamma. We have shown MSCs are able to convey these neuroprotective effects through secretion of soluble factors alone and furthermore demonstrated that SOD3 secretion by MSCs is, at least, partially responsible for this phenomenon. SOD3 secretion by MSCs maybe of relevance to treatment strategies for inflammatory disease of the central nervous system.

Extracellular/microenvironmental redox state

Extracellular redox (reduction-oxidation) state is a factor that serves as an important regulator of cell-microenvironmental interactions and is determined by several known variables; including redox-modulating proteins that are located on the plasma membrane or outside of cells, extracellular thiol/disulfide couples, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) that are capable of traveling across plasma membranes into the extracellular space. The extracellular redox state works in concert with the intracellular redox state to control both the influx and efflux of ROS/RNS that may serve to modulate redox signaling or to perturb normal cellular processes or both. Under physiologic conditions, the extracellular space is known to have a relatively more-oxidized redox state than the interior of the cell. During pathologic conditions, such as cancer, the extracellular redox state may be altered, causing specific proteins such as proteases, soluble factors, or the extracellular matrix to have altered functions or activities. Recent studies have strongly supported an important relation between the extracellular redox state and cancer cell aggressiveness. The purpose of this review is to identify redox buffer networks in extracellular spaces and to emphasize the possible roles of the extracellular redox state in cancer, knowledge that may contribute to potential therapeutic interventions.

Extracellular SOD-derived H2O2 promotes VEGF signaling in caveolae/lipid rafts and post-ischemic angiogenesis in mice

Reactive oxygen species (ROS), in particular, H(2)O(2), is essential for full activation of VEGF receptor2 (VEGFR2) signaling involved in endothelial cell (EC) proliferation and migration. Extracellular superoxide dismutase (ecSOD) is a major secreted extracellular enzyme that catalyzes the dismutation of superoxide to H(2)O(2), and anchors to EC surface through heparin-binding domain (HBD). Mice lacking ecSOD show impaired postnatal angiogenesis. However, it is unknown whether ecSOD-derived H(2)O(2) regulates VEGF signaling. Here we show that gene transfer of ecSOD, but not ecSOD lacking HBD (ecSOD-DeltaHBD), increases H(2)O(2) levels in adductor muscle of mice, and promotes angiogenesis after hindlimb ischemia. Mice lacking ecSOD show reduction of H(2)O(2) in non-ischemic and ischemic limbs. In vitro, overexpression of ecSOD, but not ecSOD-DeltaHBD, in cultured medium in ECs enhances VEGF-induced tyrosine phosphorylation of VEGFR2 (VEGFR2-pY), which is prevented by short-term pretreatment with catalase that scavenges extracellular H(2)O(2). Either exogenous H(2)O(2) (<500 microM), which is diffusible, or nitric oxide donor has no effect on VEGF-induced VEGFR2-pY. These suggest that ecSOD binding to ECs via HBD is required for localized generation of extracellular H(2)O(2) to regulate VEGFR2-pY. Mechanistically, VEGF-induced VEGFR2-pY in caveolae/lipid rafts, but non-lipid rafts, is enhanced by ecSOD, which localizes at lipid rafts via HBD. One of the targets of ROS is protein tyrosine phosphatases (PTPs). ecSOD induces oxidation and inactivation of both PTP1B and DEP1, which negatively regulates VEGFR2-pY, in caveolae/lipid rafts, but not non-lipid rafts. Disruption of caveolae/lipid rafts, or PTPs inhibitor orthovanadate, or siRNAs for PTP1B and DEP1 enhances VEGF-induced VEGFR2-pY, which prevents ecSOD-induced effect. Functionally, ecSOD promotes VEGF-stimulated EC migration and proliferation. In summary, extracellular H(2)O(2) generated by ecSOD localized at caveolae/lipid rafts via HBD promotes VEGFR2 signaling via oxidative inactivation of PTPs in these microdomains. Thus, ecSOD is a potential therapeutic target for angiogenesis-dependent cardiovascular diseases.

High levels of autoantibodies against catalase and superoxide dismutase in nasopharyngeal carcinoma

INTRODUCTION

Autoantibodies against the antioxidant enzymes have been described in Epstein-Barr virus-associated diseases. Here, we hypothesize that Epstein-Barr virus (EBV), which is associated with nasopharyngeal carcinoma (NPC), induces anticatalase and/or antisuperoxide dismutase autoantibodies that inhibit catalase and/or superoxide dismutase activities and thereby contribute to the oxidative stress status described in this pathology.

METHODS

Using a standard enzyme-linked immunosorbent assay (ELISA), the levels of immunoglobulin G (IgG), and M (IgM) directed against catalase and superoxide dismutase in the sera of 30 NPC patients and 30 healthy control individuals were evaluated. The antioxidative profile was tested among the same patients by measuring serum catalase and superoxide dismutase activities. To investigate the implication of EBV in the establishment of autoantibody production in NPC patients, a correlation study between serological testing for EBV viral capsid antigen immunoglobulin G (VCA IgG) and autoantibodies against both enzymes was undertaken.

FINDINGS

The levels of IgG against superoxide dismutase and catalase were found to be increased in sera patients compared to controls (P<0.001). NPC patients exhibited decreased catalase (P<0.001) and superoxide dismutase activities (P<0.001) in their sera. However, a positive correlation between superoxide dismutase IgM antibody and IgG antibody titers to VCA (P<0.05, r=0.483, n=21) was found. A positive correlation between catalase (IgM) antibodies and IgG antibody titers to VCA (P<0.05, r=0.546, n=30) was also found.

CONCLUSION

High levels of anticatalase and antisuperoxide dismutase antibodies in the sera of NPC patients were found.

Regulation of extracellular-superoxide dismutase in rat retina pericytes

Diabetic retinopathy (DR) is regarded as a disease of the retinal microvascular system and metabolic abnormalities that are characteristic of oxidative stress and endoplasmic reticulum (ER) stress have been identified in the retina. Pericytes are known to be susceptible to oxidative stress and selective dropout of pericytes is one of the earliest pathological changes in DR. Extracellular-superoxide dismutase (EC-SOD) is a major antioxidative enzyme and protects vascular cells from the damaging effects of superoxide. Treatment with own conditioned medium significantly decreased EC-SOD expression in pericytes, while the expression of vascular endothelial growth factor and tumor necrosis factor-α were elevated. The addition of chemical chaperone 4-phenyl butyric acid significantly suppressed the effects of conditioned medium on EC-SOD and GRP78, a prominent ER-resident chaperone. Moreover, the cell viability of pericytes changed in a manner similar to that of EC-SOD expression. These results suggest that the expressions of EC-SOD should be regulated, at least partially, through ER stress. Continuous flow of culture media neutralized the ER-stress triggered decrease of EC-SOD expression. The stagnation of factors related to ER-stress around pericytes might reduce EC-SOD expression under pathophysiological conditions such as retinal edema, and this could induce and/or promote the intraretinal microvascular impairment and development of pathogenesis in DR.

Antimicrobial activity of a C-terminal peptide from human extracellular superoxide dismutase

Background

Antimicrobial peptides (AMP) are important effectors of the innate immune system. Although there is increasing evidence that AMPs influence bacteria in a multitude of ways, bacterial wall rupture plays the pivotal role in the bactericidal action of AMPs. Structurally, AMPs share many similarities with endogenous heparin-binding peptides with respect to secondary structure, cationicity, and amphipathicity.

Findings

In this study, we show that RQA21 (RQAREHSERKKRRRESECKAA), a cationic and hydrophilic heparin-binding peptide corresponding to the C-terminal region of extracellular superoxide dismutase (SOD), exerts antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Candida albicans. The peptide was also found to induce membrane leakage of negatively charged liposomes. However, its antibacterial effects were abrogated in physiological salt conditions as well as in plasma.

Conclusion

The results provide further evidence that heparin-binding peptide regions are multifunctional, but also illustrate that cationicity alone is not sufficient for AMP function at physiological conditions. However, our observation, apart from providing a link between heparin-binding peptides and AMPs, raises the hypothesis that proteolytically generated C-terminal SOD-derived peptides could interact with, and possibly counteract bacteria. Further studies are therefore merited to study a possible role of SOD in host defence.

The structure of human extracellular copper-zinc superoxide dismutase at 1.7 A resolution: insights into heparin and collagen binding

Extracellular superoxide dismutase (SOD3) is a homotetrameric copper- and zinc-containing glycoprotein with affinity for heparin. The level of SOD3 is particularly high in blood vessel walls and in the lungs. The enzyme has multiple roles including protection of the lungs against hyperoxia and preservation of nitric oxide. The common mutation R213G, which reduces the heparin affinity of SOD3, is associated with increased risk of myocardial infarctions and stroke. We report the first crystal structure of human SOD3 at 1.7 A resolution. The overall subunit fold and the subunit-subunit interface of the SOD3 dimer are similar to the corresponding structures in Cu-Zn SOD (SOD1). The metal-binding sites are similar to those found in SOD1, but with Asn180 replacing Thr137 at the Cu-binding site and a much shorter loop at the zinc-binding site. The dimers form a functional homotetramer that is fashioned through contacts between two extended loops on each subunit. The N- and C-terminal end regions required for tetramerisation and heparin binding, respectively, are highly flexible. Two grooves fashioned by the tetramer interface are suggestive as the probable sites for heparin and collagen binding.

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.

Essential role of extracellular SOD in reparative neovascularization induced by hindlimb ischemia

Neovascularization is an important physiological repair mechanism in response to ischemic injury, and its process is dependent on reactive oxygen species (ROS). Overproduction of superoxide anion (O2-) rather contributes to various cardiovascular diseases. The extracellular superoxide dismutase (ecSOD) is one of the major antioxidant enzymes against O2- in blood vessels; however, its role in neovascularization induced by tissue ischemia is unknown. Here we show that hindlimb ischemia of mice stimulates a significant increase in ecSOD activity in ischemic tissues where ecSOD protein is highly expressed at arterioles. In mice lacking ecSOD, ischemia-induced increase in blood flow recovery, collateral vessel formation, and capillary density are significantly inhibited. Impaired neovascularization in ecSOD(-/-) mice is associated with enhanced O2- production, TUNEL-positive apoptotic cells and decreased levels of NO2-/NO3- and cGMP in ischemic tissues as compared with wild-type mice, and it is rescued by infusion of the SOD mimetic tempol. Recruitment of inflammatory cells into ischemic tissues as well as numbers of inflammatory cells and endothelial progenitor cells (c-kit+/CD31+ cells) in both peripheral blood and bone marrow (BM) are significantly reduced in these knockout mice. Of note, ecSOD expression is markedly increased in BM after ischemia. NO2-/NO3- and cGMP levels are decreased in ecSOD(-/-) BM. Transplantation of wild-type BM into ecSOD(-/-) mice rescues the defective neovascularization. Thus, ecSOD in BM and ischemic tissues induced by hindlimb ischemia may represent an important compensatory mechanism that blunts the overproduction of O2-, which may contribute to reparative neovascularization in response to ischemic injury.

Endocytosis of extracellular superoxide dismutase into endothelial cells: role of the heparin-binding domain

OBJECTIVE

Extracellular superoxide dismutase (EC-SOD) is a secreted antioxidant enzyme that binds to the outer plasma membrane and extracellular matrix through its heparin-binding domain (HBD). Carriers of a common genetic variant of EC-SOD (EC-SOD(R213G), within the HBD) have higher plasma concentration of EC-SOD and increased risk for vascular disease. In the present study, we used confocal fluorescence microscopy to examine mechanisms of endocytosis of EC-SOD to determine whether EC-SOD translocates to the nucleus of endothelial cells, and to test the hypothesis that EC-SOD, but not EC-SOD(R213G), is endocytosed into endothelial cells.

METHODS AND RESULTS

Mouse endothelial cells (MS-1) were incubated with EC-SOD, EC-SOD(R213G), or HBD-deleted EC-SOD (EC-SODdeltaHBD). Binding to MS-1 was observed only with EC-SOD, but not EC-SOD(R213G) or EC-SODdeltaHBD. Endocytosis of EC-SODs was monitored after coincubation of MS-1 cells with EC-SODs and BSA-Texas Red (BSA-TR), which marks endosomes and lysosomes. Only EC-SOD was endocytosed, colocalizing with BSA-TR. EC-SOD also colocalized with early endosome antigen 1 (EEA-1), a specific marker for endocytosis. Endocytosis of EC-SOD was inhibited by chlorpromazine, but not by methyl-beta-cyclodextrin or nystatin, which suggests that endocytosis of EC-SOD is mediated by clathrin but not by caveolae. Minimal or no localization of EC-SOD in the nucleus of MS-1 cells was detected.

CONCLUSIONS

Our findings indicate that EC-SOD, but not EC-SOD(R213G), is endocytosed into endothelial cells through clathrin-mediated pathway, but does not translocate to the nucleus. We speculate that impairment of endocytosis may contribute to high plasma levels of EC-SOD(R213G) in R213G carriers.

Infliximab Neutralizes the Suppressive Effect of TNF-α on Expression of Extracellular-Superoxide Dismutase in Vitro

Extracellular-superoxide dismutase (EC-SOD) is the major SOD isozyme in blood vessel walls, normal cartilage and synovial fluid and may be important for the antioxidant capability of these tissues. We have reported that EC-SOD gene transferred mice exhibited significant suppression of clinical symptoms of type II collagen induced arthritis [Iyama, et al., Arthritis Rheum., 44, 2160-2167 (2001)] and plasma EC-SOD levels in type 2 diabetic patients were significantly negatively related to indices of insulin resistance [Adachi, et al., J. Endocrinol., 181, 413-417 (2004)]. Tumor necrosis factor-alpha (TNF-alpha) has been implicated in the pathological conditions of the above diseases and is a major therapeutic target, based on clinical studies with anti-TNF-alpha monoclonal antibodies such as infliximab. In this report, we investigated the effect of TNF-alpha on the expression of EC-SOD in cultured cells and the cooperating effect of infliximab. In the in vitro assays examined, expression of EC-SOD, but not other SOD isozymes, in smooth muscle and fibroblast cells were suppressed by the addition of TNF-alpha. Simultaneous addition of infliximab dose-dependently and significantly prevented the suppressive effects of TNF-alpha. p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, prevented significantly the suppressive effect of TNF-alpha suggesting that p38 MAPK is an important signaling molecule downstream of TNF-alpha to inhibit the EC-SOD expression. From the results, it is speculated that the decline in TNF-alpha activity by the administration of infliximab results in the liberation of EC-SOD from the suppressed state of gene expression. This reveals a potential usefulness of infliximab on TNF-alpha related pathological conditions such as arthritis and insulin resistance.

Protection of porcine oocytes against cell damage caused by oxidative stress during in vitro maturation: role of superoxide dismutase activity in porcine follicular fluid

To elucidate the beneficial effects of porcine follicular fluid (pFF) added to maturation medium on the sustenance of cytoplasmic maturation responsible for the subsequent developmental competence after in vitro fertilization (IVF) of porcine oocytes, we focused on the antioxidative role of pFF in its function of protecting oocytes from reactive oxygen species (ROS)-induced cell damage. Porcine follicular fluid collected from small (2-6 mm) follicles had about 7.2-fold higher levels of superoxide dismutase (SOD) activity than that of fetal bovine serum (FBS), and this activity was markedly blocked by the CuZn-SOD inhibitor, diethyldithiocarbamate (DETC). The interruption of meiotic progression and the increasing intracellular glutathione (GSH) content throughout the maturation period, as well as an outbreak of DNA damage in oocytes and cumulus cells were difficult to detect in oocytes cultured in a medium supplemented with 10% pFF, even in the presence of ROS generated by the hypoxanthine-xanthine oxidase system, whereas cell damage encompassed by ROS was prominent in oocytes cultured with 10% FBS and 10% pFF plus 100 microM DETC. Similarly, significant enhancement to the degree of transformation of the sperm nucleus into the male pronucleus (MPN) after in vitro fertilization was shown by the addition of pFF to the maturation medium. The presence of DETC during in vitro maturation reduced the ability of oocytes to promote MPN formation to the same extent as oocytes matured with FBS. The proportion developing to the blastocyst stage was increased in oocytes that matured with pFF, but this developmental competence was significantly lowered by treatment with DETC (P < 0.05). These findings suggest that pFF plays a critical role in protecting oocytes from oxidative stress through a higher level of radical scavenging activity elicited from SOD isoenzymes, resulting in the enhancement of cytoplasmic maturation responsible for developmental competence postfertilization.

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.

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.

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.

Vascular oxidative stress and endothelial dysfunction in patients with chronic heart failure: role of xanthine-oxidase and extracellular superoxide dismutase

BACKGROUND

Impaired flow-dependent, endothelium-mediated vasodilation (FDD) in patients with chronic heart failure (CHF) results, at least in part, from accelerated degradation of nitric oxide by oxygen radicals. The mechanisms leading to increased vascular radical formation, however, remain unclear. Therefore, we determined endothelium-bound activities of extracellular superoxide dismutase (ecSOD), a major vascular antioxidant enzyme, and xanthine-oxidase, a potent radical producing enzyme, and their relation to FDD in patients with CHF.

METHODS AND RESULTS

ecSOD and xanthine-oxidase activities, released from endothelium into plasma by heparin bolus injection, were determined in 14 patients with CHF and 10 control subjects. FDD of the radial artery was measured using high-resolution ultrasound and was assessed before and after administration of the antioxidant vitamin C (25 mg/min; IA). In patients with CHF, endothelium-bound ecSOD activity was substantially reduced (5.0+/-0.7 versus 14.4+/-2.6 U x mL(-1) x min(-1); P<0.01) and closely related to FDD (r=0.61). Endothelium-bound xanthine-oxidase activity was increased by >200% (38+/-10 versus 12+/-4 nmol O2*- x microL(-1); P<0.05) and inversely related to FDD (r=-0.35) in patients with CHF. In patients with low ecSOD and high xanthine-oxidase activity, a greater benefit of vitamin C on FDD was observed, ie, the portion of FDD inhibited by radicals correlated negatively with ecSOD (r=-0.71) but positively with xanthine-oxidase (r=0.75).

CONCLUSIONS

These results demonstrate that both increased xanthine-oxidase and reduced ecSOD activity are closely associated with increased vascular oxidative stress in patients with CHF. This loss of vascular oxidative balance likely represents a novel mechanism contributing to endothelial dysfunction in CHF.

Preservation of extracellular glutathione by an astrocyte derived factor with properties comparable to extracellular superoxide dismutase

Cultured rat and human astrocytes and rat neurones were shown to release reduced glutathione (GSH). In addition, GSH oxidation was retarded by the concomitant release of a factor from the cells. One possibility is that this factor is extracellular superoxide dismutase (SOD). In support of this, the factor was found to bind heparin, have a molecular mass estimated to be between 50 and 100 kDa, and CuZn-type SOD protein and cyanide sensitive enzyme activity were demonstrated in the cell-conditioned medium. In addition, supplementation of native medium with exogenous CuZn-type SOD suppressed GSH oxidation. We propose that preservation of released GSH is essential to allow for maximal up-regulation of GSH metabolism in neurones. Furthermore, cytokine stimulation of astrocytes increased release of the extracellular SOD, and enhanced stability of GSH. This may be a protective strategy occurring in vivo under conditions of oxidative stress, and suggests that SOD mimetics may be of therapeutic use.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.

The expression of extracellular-superoxide dismutase is increased by lysophosphatidylcholine in human monocytic U937 cells

Extracellular-superoxide dismutase (EC-SOD) [EC 1.15.1.1] is a secretory glycoprotein with an affinity for heparin-like proteoglycans. This enzyme locates in blood vessel walls at high levels and may be important for the antioxidant capability of vascular walls. Oxidative process plays an important role in atherogenesis. Lysophosphatidylcholine (lysoPC) is generated during oxidation of low-density lipoprotein (LDL) and is located within atherosclerotic plaques. Recently, lysoPC has been reported to induce transcription of a variety of cellular genes. In this study, we observed that lysoPC significantly increased the expression of EC-SOD mRNA and protein in human monocytic U937 cells, but not those of CuZn-SOD or Mn-SOD. Induced EC-SOD by lysoPC had a high affinity for heparin, and may bind to the endothelial cell surface. Very recently, it has been reported that exogenous addition of EC-SOD or overexpression of EC-SOD prevented endothelial cell-mediated oxidative modification of LDL. Therefore, it is speculated that EC-SOD is induced by lysoPC-stimulated monocytes as a feedback mechanism in vascular homeostasis.

Superoxide dismutase multigene family: a comparison of the CuZn-SOD (SOD1), Mn-SOD (SOD2), and EC-SOD (SOD3) gene structures, evolution, and expression

Superoxide dismutases are an ubiquitous family of enzymes that function to efficiently catalyze the dismutation of superoxide anions. Three unique and highly compartmentalized mammalian superoxide dismutases have been biochemically and molecularly characterized to date. SOD1, or CuZn-SOD (EC 1.15.1.1), was the first enzyme to be characterized and is a copper and zinc-containing homodimer that is found almost exclusively in intracellular cytoplasmic spaces. SOD2, or Mn-SOD (EC 1.15.1.1), exists as a tetramer and is initially synthesized containing a leader peptide, which targets this manganese-containing enzyme exclusively to the mitochondrial spaces. SOD3, or EC-SOD (EC 1.15.1.1), is the most recently characterized SOD, exists as a copper and zinc-containing tetramer, and is synthesized containing a signal peptide that directs this enzyme exclusively to extracellular spaces. What role(s) these SODs play in both normal and disease states is only slowly beginning to be understood. A molecular understanding of each of these genes has proven useful toward the deciphering of their biological roles. For example, a variety of single amino acid mutations in SOD1 have been linked to familial amyotrophic lateral sclerosis. Knocking out the SOD2 gene in mice results in a lethal cardiomyopathy. A single amino acid mutation in human SOD3 is associated with 10 to 30-fold increases in serum SOD3 levels. As more information is obtained, further insights will be gained.

Extracellular superoxide dismutase and glomerular mesangial cells: its production and regulation

Extracellular superoxide dismutase (EC-SOD) is synthesized in mesenchymally derived cells and prevents the oxygen radical-induced injury. We studied whether kidney mesangial cells (MCs) produce EC-SOD and how its production is associated with chemokine secretion. Under unstimulated condition, MCs produced EC-SOD, and its production was correlated positively with cyclic adenosine monophosphate (cAMP), but negatively with interleukin (IL)-6 or IL-8 production. By prednisolone or phorbol myristate acetate treatment, EC-SOD levels were correlated negatively with levels of IL-6 and IL-8. The presence of adenylate cyclase inhibitor 2',3'-dideoxyadenosine lost the prednisolone effect. The stimulation of EC-SOD production might be one of the important effects of prednisolone via cAMP pathway in MCs.

Molecular evolution and structure--function relationships of the superoxide dismutase gene families in angiosperms and their relationship to other eukaryotic and prokaryotic superoxide dismutases

This study assesses whether the phylogenetic relationships between SODs from different organisms could assist in elucidating the functional relationships among these enzymes from evolutionarily distinct species. Phylogenetic trees and intron positions were compared to determine the relationships among these enzymes. Alignment of Cu/ZnSOD amino acid sequences indicates high homology among plant sequences, with some features that distinguish chloroplastic from cytosolic Cu/ZnSODs. Among eukaryotes, the plant SODs group together. Alignment of the Mn and FeSOD amino acid sequences indicates a higher degree of homology within the group of MnSODs (>70%) than within FeSODs (approximately 60%). Tree topologies are similar and reflect the taxonomic classification of the corresponding species. Intron number and position in the Cu/Zn Sod genes are highly conserved in plants. Genes encoding cytosolic SODs have seven introns and genes encoding chloroplastic SODs have eight introns, except the chloroplastic maize Sod1, which has seven. In Mn Sod genes the number and position of introns are highly conserved among plant species, but not among nonplant species. The link between the phylogenetic relationships and SOD functions remains unclear. Our findings suggest that the 5' region of these genes played a pivotal role in the evolution of function of these enzymes. Nevertheless, the system of SODs is highly structured and it is critical to understand the physiological differences between the SODs in response to different stresses in order to compare their functions and evolutionary history.

High-level expression of human extracellular superoxide dismutase in Escherichia coli and insect cells

Much is known about the physical properties of the Cu,Zn- and Mn-superoxide dismutases (SODs). However, the biochemical characteristics and pharmacological properties of extracellular (EC)-SOD have been severely limited due to difficulties in obtaining and purifying the enzyme. The EC-SOD cDNA was inserted into the Escherichia coli expression plasmid pET-28a(+) which contains the T7 promoter and transformed into the E. coli BL21(DE3). After induction with 1 mmol/L isopropyl beta-D-thiogalactoside, the recombinant human EC-SOD was highly expressed as inclusion bodies. SDS-PAGE analysis revealed that recombinant EC-SOD accumulated up to 26% of the total soluble protein of E. coli cells. The expression product was purified by a Ni(2+)-IDA-Sepharose 6B column. After the denaturing and refolding processes, the recombinant human EC-SOD retains the specific enzymatic activity of 920 U/mg of the purified product. The gene encoding human EC-SOD mature peptide was also inserted into the donor plasmid pFastBacHTb. After transposition, transfection, and amplification were performed, the recombinant baculoviruses infected the Tn-5B1-4 cells and EC-SOD was highly expressed in Tn-5B1-4 cells. SDS-PAGE and Western blot analysis revealed that the subunit molecular weight of the expression product is 28 kDa. Furthermore, recombinant human EC-SOD retains the enzymatic specific activity of 200 U/mg of the Tn-5B1-4 cell lysates.

Heparin-stimulated expression of extracellular-superoxide dismutase in human fibroblasts

Extracellular-superoxide dismutase (EC-SOD) is the major SOD isozyme in the arterial wall and may be important for antioxidation capability of the vascular wall and normal vascular function. EC-SOD is expressed in various cell types in the vascular wall such as fibroblasts, smooth muscle cells and macrophages, and the synthesis of EC-SOD by human fibroblasts is known to be highly responsive to various inflammatory cytokines, although there is no response to oxidative stress. Heparin is a highly sulfated glycosaminoglycan with many functions such as antithrombotic, antilipemic and antiatherosclerotic effects. Another less well-known function of heparin is regulation of protein synthesis. In this study, we measured the induction of EC-SOD after treatment with heparin to understand the role of heparin in the antiatherosclerotic response of fibroblasts. Heparin induced EC-SOD expression at both the mRNA and protein levels. Heparin showed the greatest stimulatory effect and heparan sulfate showed moderate effects. The effect of chondroitin sulfate A was not clear. In contrast, desulfated heparin and chondroitin sulfate C did not increase EC-SOD expression. The stimulatory effect seemed to increase roughly with the degree of glycosaminoglycan sulfation. The enhanced expression of EC-SOD by heparin must contribute to the antiatherosclerotic effect of heparin.

Extracellular superoxide dismutase overexpression improves behavioral outcome from closed head injury in the mouse

Oxidative stress is known to play an important role in the response of brain to traumatic insults. We tested the hypothesis that increased extracellular superoxide dismutase (EC-SOD) expression can reduce injury in a mouse model of closed head injury. Neurologic, cognitive, and histologic outcomes were compared between transgenic mice exhibiting a fivefold increase in EC-SOD activity and wild-type littermate controls. Severe or moderate transcranial impact was induced in anesthetized and physiologically controlled animals. After severe impact, transgenic mice had better neurological outcome at 24 hr postinjury (p = 0.038). Brain water content was increased, but there was no difference between groups. Moderate impact resulted in predominantly mild neurologic deficits in both groups at both 24 hr and 14 days postinjury. Morris water maze performance, testing cognitive function at 14-17 days after trauma, was better in EC-SOD overexpressors (p = 0.018). No differences were observed between groups for histologic damage in hippocampal CA1 and CA3. We conclude that EC-SOD has a beneficial effect on behavioral outcome after both severe and moderate closed head injury in mice. Because EC-SOD is believed to be predominantly located in the extracellular space, these data implicate an adverse effect of extracellular superoxide anion on outcome from closed head injury.