Extracellular superoxide dismutase and cardiovascular disease

Up-regulation of Akt and eNOS induces vascular smooth muscle cell differentiation in hypertension in vivo

Recent studies have shown that angiotensin II type 1 (AT1) receptor-mediated Akt activation induces vascular smooth muscle cell (VSMC) dedifferentiation in vitro. However, the critical signal transductions affecting the VSMC phenotype remain unclear in vivo. We examined whether signal transduction through AT1 receptor-mediated reactive oxygen species (ROS) could regulate the VSMC phenotype in stroke-prone spontaneously hypertensive rats (SHRSPs). Male SHRSPs were randomized and treated for 6 weeks with a vehicle, an ACE inhibitor cilazapril, or an AT1 receptor antagonist E4177. The 2 drugs showed equipotent effects on the blood pressure, aortic morphology, and collagen deposition. Both drugs also significantly reduced aortic NAD(P)H oxidase activity and p38MAPK and ERK expression, whereas p-Akt, eNOS, and SM2 were significantly increased in SHRSP aortas. Furthermore, E4177 was more effective than cilazapril at inducing VSMC differentiation by reducing NAD(P)H oxidase activity, and up-regulating p-Akt, eNOS, and SM2. Thus, an ACE inhibitor and an AT1 receptor antagonist inhibited VSMC dedifferentiation through inhibition of NAD(P)H oxidase activity and up-regulation of eNOS and Akt in SHRSP aortas, suggesting that in contrast to the in vitro experiments, AT1 receptor-mediated NAD(P)H oxidase-generated ROS, eNOS, and Akt might be crucial determinants for the VSMC phenotype in hypertension in vivo.

Demonstration of a hyperglycemia-driven pathogenic abnormality of copper homeostasis in diabetes and its reversibility by selective chelation: quantitative comparisons between the biology of copper and eight other nutritionally essential elements in normal and diabetic individuals

We recently showed that treatment with the Cu(II)-selective chelator, trientine, alleviates heart failure in diabetic rats, improves left ventricular hypertrophy in humans with type 2 diabetes, and increases urinary Cu excretion in both diabetic rats and humans compared with nondiabetic control subjects. In this study, we characterized the homeostasis of Cu and eight other nutritionally essential elements in diabetes under fully residential conditions in male subjects with type 2 diabetes and age-matched control subjects. We then probed elemental balance with oral trientine in a parallel-group, placebo-controlled study in these subjects. Before treatment, there were no detectable between-group differences in the balance of any element, although urinary output of several elements was greater in diabetic subjects. Mean extracellular superoxide dismutase (EC-SOD) activity was elevated in diabetic subjects, and its activity correlated strongly with the interaction between [Cu]serum and HbA1c. Trientine caused the Cu balance to become negative in diabetic subjects through elevated urinary Cu losses and suppressed elevated EC-SOD. Basal urinary Cu predicted urinary Cu losses during treatment, which caused extraction of systemic Cu(II). We suggest that cardiovascular complications in diabetes might be better controlled by therapeutic strategies that focus on lowering plasma glucose and loosely bound systemic Cu(II).

Role of Antioxidant-1 in Extracellular Superoxide Dismutase Function and Expression

The extracellular superoxide dismutase (ecSOD or SOD3) is a copper-containing enzyme which is highly expressed in the vasculature. Copper-containing enzymes require copper chaperones for their activity however the chaperone which delivers copper to SOD3 has not previously been defined. Atox1 is a copper chaperone proposed to deliver copper to the trans-Golgi network. Because SOD3 is secreted via the trans-Golgi network, we sought to determine whether Atox1 acts as a copper chaperone for SOD3. Using recombinant human SOD3, we found that the specific activity of SOD3 directly correlates with its copper content (R2=0.99). SOD3 specific activity in the conditioned medium from cultured Atox1-/- fibroblasts was markedly decreased, but could be recovered to that of wild-type cells by copper addition. These results indicated that Atox1 is required for delivering copper to SOD3 for its full activity. Unexpectedly, the protein and mRNA levels of SOD3 were dramatically decreased in cultured Atox1-/- fibroblasts. This was associated with a marked decrease in SOD3 transcription rate but no change in SOD3 mRNA stability. Overexpression of Atox1 markedly increased SOD3 mRNA in both Atox1-/- and Atox1+/+ cells. These findings indicate that Atox1 positively regulates SOD3 transcription. Because SOD3 protein is upregulated in atherosclerotic vessels, we examined expression of Atox1 in vessels from ApoE-/- mice. Western and immunohistochemical analysis in ApoE-/- mice revealed that both Atox1 and SOD3 protein levels are markedly increased in atherosclerotic intimal lesions. In summary, Atox1 functions not only as a copper chaperone for SOD3 but also as a positive regulator for SOD3 transcription and may have an important role in modulating oxidative stress in the cardiovascular system.

Extracellular superoxide dismutase overexpression reduces cuff-induced arterial neointimal formation

The mechanisms of neointimal formation in cuff-injury models are still uncertain. To examine whether extracellular superoxide dismutase (EC-SOD) can reduce neointimal formation in a cuff-injury model, adenoviruses expressing EC-SOD (AxCAEC-SOD) or Escherichia coli beta-galactosidase (AxCALacZ) was injected between the cuff and the adventitia of rat femoral arteries. As a result, EC-SOD protein was effectively produced in the adventitia, as assessed by immunohistochemical staining. In comparison with cuff-treated control arteries and AxCALacZ-transfected arteries, neointimal formation was significantly reduced in AxCAEC-SOD-transfected arteries. Furthermore, proliferating smooth muscle cells in neointima and media were reduced by EC-SOD treatment. Similarly, augmented iNOS expression, apoptosis and collagen content in the vascular wall were also reduced by EC-SOD treatment. Reactive oxygen species (ROS) generation in tissue was reduced by EC-SOD expression, as assessed by dihydroethidium staining and coelenterazine chemiluminescence. These results suggest that ROS, especially superoxide anions at an adventitia, are responsible for neointimal formation in a cuff-injury model.

Antioxidant mechanism of heme oxygenase-1 involves an increase in superoxide dismutase and catalase in experimental diabetes

Increased heme oxygenase (HO)-1 activity attenuates endothelial cell apoptosis and decreases superoxide anion (O2-) formation in experimental diabetes by unknown mechanisms. We examined the effect of HO-1 protein and HO activity on extracellular SOD (EC-SOD), catalase, O2-, inducible nitric oxide synthase (iNOS), and endothelial nitric oxide synthase (eNOS) levels and vascular responses to ACh in control and diabetic rats. Vascular EC-SOD and plasma catalase activities were significantly reduced in diabetic compared with nondiabetic rats (P < 0.05). Upregulation of HO-1 expression by intermittent administration of cobalt protoporphyrin, an inducer of HO-1 protein and activity, resulted in a robust increase in EC-SOD but no significant change in Cu-Zn-SOD. Administration of tin mesoporphyrin, an inhibitor of HO-1 activity, decreased EC-SOD protein. Increased HO-1 activity in diabetic rats was associated with a decrease in iNOS but increases in eNOS and plasma catalase activity. On the other hand, aortic ring segments from diabetic rats exhibited a significant reduction in vascular relaxation to ACh, which was reversed with cobalt protoporphyrin treatment. These data demonstrate that an increase in HO-1 protein and activity, i.e., CO and bilirubin production, in diabetic rats brings about a robust increase in EC-SOD, catalase, and eNOS with a concomitant increase in endothelial relaxation and a decrease in O2-. These observations in experimental diabetes suggest that the vascular cytoprotective mechanism of HO-1 against oxidative stress requires an increase in EC-SOD and catalase.

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.

Voluntary physical exercise-induced vascular effects in spontaneously hypertensive rats

Forced training has been shown to have beneficial vascular effects in various animal exercise models. In the present study, we explored possible physiological and molecular effects of voluntary physical exercise on various vascular beds. SHR (spontaneously hypertensive rats) performed voluntary exercise for 5 weeks in a computerized wheel cage facility. Ex vivo myograph studies revealed an increased sensitivity of the ACh (acetylcholine)-mediated vasodilation in resistance arteries of the exercised animals (ED50=15.0+/-3.5 nmol/l) compared with the controls (ED50=37.0+/-8.8 nmol/l; P=0.05). The exercise/control difference was abolished after scavenging reactive oxygen radicals. In conduit arteries, ACh induced a similar vasodilatory response in both groups. The in vivo aortic wall stiffness, assessed by means of Doppler tissue echography, was significantly lower in the exercising animals than in controls. This was demonstrated by significantly increased peak systolic aortic wall velocity (P=0.03) and the velocity time integral (P=0.01) in exercising animals compared with controls. The relative gene expression of eNOS (endothelial nitric oxide synthase) was similar in both groups of animals, whereas Cu/ZnSOD (copper/zinc superoxide dismutase) gene expression was significantly increased (+111%; P=0.0007) in the exercising animal compared with controls. In conclusion, voluntary physical exercise differentially improves vascular function in various vascular beds. Increased vascular compliance and antioxidative capacity may contribute to the atheroprotective effects associated with physical exercise in conduit vessels.

Hemodynamic and biochemical adaptations to vascular smooth muscle overexpression of p22phox in mice

Protein levels and polymorphisms of p22 phox have been suggested to modulate vascular NAD(P)H oxidase activity and vascular production of reactive oxygen species (ROS). We sought to determine whether increasing p22 phox expression would alter vascular ROS production and hemodynamics by targeting p22 phox expression to smooth muscle in transgenic (Tg) mice. Aortas of Tg p22smc mice had increased p22 phox and Nox1 protein levels and produced more superoxide and H2O2. Surprisingly, endothelium-dependent relaxation and blood pressure in Tg p22smc mice were normal. Aortas of Tg p22smc mice produced twofold more nitric oxide (NO) at baseline and sevenfold more NO in response to calcium ionophore as detected by electron spin resonance. Western blot analysis revealed a twofold increase in endothelial NO synthase (eNOS) protein expression in Tg p22smc mice. Both eNOS expression and NO production were normalized by infusion of the glutathione peroxidase mimetic ebselen or by crossing Tg p22smc mice with mice overexpressing catalase. We have previously found that NO stimulates extracellular superoxide dismutase (ecSOD) expression in vascular smooth muscle. In keeping with this, aortic segments from Tg p22smc mice expressed twofold more ecSOD, and chronic treatment with the NOS inhibitor NG-nitro-l-arginine methyl ester normalized this, suggesting that NO regulates ecSOD protein expression in vivo. These data indicate that chronic oxidative stress caused by excessive H2O2 production evokes a compensatory response involving increased eNOS expression and NO production. NO in turn increases ecSOD protein expression and counterbalances increased ROS production leading to the maintenance of normal vascular function and hemodynamics.

Increased superoxide production causes coronary endothelial dysfunction and depressed oxygen consumption in the failing heart

This study examined whether increased superoxide (O2−·) production contributes to coronary endothelial dysfunction and decreased coronary blood flow (CBF) in congestive heart failure (CHF). To test this hypothesis, the effects of the low-molecular-weight SOD mimetic M40401 on CBF and myocardial oxygen consumption (MV̇o2) were examined in dogs during normal conditions and after CHF was produced by 4 wk of rapid ventricular pacing. The development of CHF was associated with decreases of left ventricular (LV) systolic pressure, maximum first derivative of LV pressure, MV̇o2, and CBF at rest and during treadmill exercise as well as endothelial dysfunction with impaired vasodilation in response to intracoronary acetylcholine. M40401 increased CBF (18 ± 5%, P < 0.01) and MV̇o2 (14 ± 6%, P < 0.01) in CHF dogs and almost totally reversed the impaired CBF response to acetylcholine. M40401 had no effect on acetylcholine-induced coronary vasodilation, CBF, or MV̇o2 in normal dogs. Western blot analysis demonstrated that extracellular SOD (EC-SOD) was significantly decreased in CHF hearts, whereas mitochondrial Mn-containing SOD was increased. Cytosolic Cu/Zn-containing SOD was unchanged. Both increased O2−· production and decreased vascular O2−· scavenging ability by EC-SOD could have contributed to endothelial dysfunction in the failing hearts.

Polymorphism of host response genes: Implications in the pathogenesis and treatment of acute renal failure

Acute inflammatory disorders are the result of an interaction between genetic and environmental factors, and are often characterized by an imbalance between pro- and anti-inflammatory host immune responses. Over the past decade, polymorphisms of host response genes have been explored as genetic risk and prognostic markers in the course and severity of acute inflammatory disorders. Increasing evidence supports an important role for inflammatory mechanisms in the pathogenesis of acute renal failure (ARF) following both ischemic and nephrotoxic injury. The use of genetic epidemiology may become a useful tool to identify patients with an altered susceptibility to developing hospital-acquired ARF, and stratify those who may benefit from preventive therapies that modulate host immune responses in a favorable way. This review summarizes the existing experimental and clinical studies supporting the role of inflammation in ARF and critically appraises studies that have examined polymorphism of immune response genes as potential determinants of susceptibility to and severity of acute inflammatory disorders. Conclusions are drawn on the application of genetic epidemiology to the field of ARF and the rationale for further research on the role of genetic markers in ARF.

Inhibition of iNOS attenuates skeletal muscle reperfusion injury in extracellular superoxide dismutase knockout mice

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are closely involved in the mechanism of skeletal muscle ischemia/reperfusion (I/R) injury. This study was designed to determine the effects of inducible nitric oxide synthase (iNOS) inhibitor 1400 W on the reperfused cremaster muscle in extracellular super-oxide dismutase knockout (EC-SOD(-/-)) mice. The muscle was exposed to 4.5 h of ischemia, followed by 90 min of reperfusion. Mice received either 3 mg/kg of 1400 W or the same amount of phosphate-buffered saline (PBS, as a control) subcutaneously at 10 min before the start of reperfusion. 1400 W treatment markedly improved the recovery speed of vessel diameter and blood flow in the reperfused cremaster muscle of EC-SOD(-/-) mice compared to controls. Histological examination showed reduced edema in the interstitial space and muscle fiber, and reduced density of nitrotyrosine (a marker of total peroxi-nitrate (ONOO(-)) level) in 1400 W-treated muscles compared to controls. Our results suggest that iNOS and ONOO(-) products are involved in skeletal muscle I/R injury. Reduced I/R injury by using selective inhibition of iNOS perhaps works by limiting cytotoxic ONOO(-) generation, a reaction product of nitric oxide (NO) and super-oxide anion (O(2) (-)). Thus, inhibition of iNOS appears to be a treatment strategy for reducing clinical I/R injury.

Fibulin-5 is a novel binding protein for extracellular superoxide dismutase

The extracellular superoxide dismutase (ecSOD) plays an important role in atherosclerosis and endothelial function by modulating levels of the superoxide anion (O2*-) in the extracellular space. Although heparan sulfate proteoglycan is an important ligand for ecSOD, little is known about other biological binding partners of ecSOD. The goal of this study was to identify novel proteins that interact with ecSOD. A yeast two-hybrid screening of a human aorta cDNA library using ecSOD as bait identified fibulin-5 as a predominant binding protein for ecSOD. Further analysis showed that the binding domain of ecSOD within fibulin-5 mapped to its C-terminal domain. In vitro pulldown assays and coimmunoprecipitation analysis further confirmed that ecSOD interacts with fibulin-5 in vitro and in vivo. Studies using fibulin-5-/- mice indicated that fibulin-5 is required for binding of ecSOD to vascular tissue. Importantly, the decrease in tissue-bound ecSOD levels in aortas from fibulin-5-/- mice was associated with an increase in vascular O2*- levels. Furthermore, immunohistochemical analysis using ApoE-/- mice suggested a codistribution of ecSOD and fibulin-5 in atherosclerotic vessels. In summary, we provide in this study the first evidence that the ecSOD-fibulin-5 interaction is required for ecSOD binding to vascular tissues, thereby regulating vascular O2*- levels. This interaction may represent a novel mechanism for controlling vascular redox state in the extracellular space in various cardiovascular diseases such as atherosclerosis and hypertension in which oxidative stress is increased.

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.

Nitric oxide is significantly reduced in ex vivo porcine arteries during reverse flow because of increased superoxide production

Oscillatory and negative flows occur normally in the cardiovascular system, which predispose those regions to atherosclerosis. Nitric oxide (NO) production increases in proportion to the magnitude of flow and is known to be athero-protective. What is not known, however, is the effect of flow reversal on NO concentration ([NO]). The hypothesis of the present study is that [NO] is reduced in reverse flow. An additional hypothesis is that the reduction in [NO] is mediated through an increase in superoxide production during flow reversal. These hypotheses were tested in an ex vivo preparation of porcine elastic and muscular arteries. The flow of a physiological solution through the vessels was regulated in the forward and reverse direction and the effluent was assayed for nitrite levels using a combination of a diazo coupling method and high performance liquid chromatography. Our results show that [NO] is significantly reduced during reverse flow. Furthermore, addition of tempol (superoxide dismutase-mimetic) which is a superoxide scavenger returns the [NO] during reverse flow to mirror those of forward flow. These results have important implications since the action of superoxide is implicated in many cardiovascular diseases, and the present finding suggests that flow reversal should be added to the list.

Gene transfer of extracellular superoxide dismutase improves relaxation of aorta after treatment with endotoxin

Lipopolysaccharide (LPS) impairs vascular function, in part by generation of reactive oxygen species. One goal of this study was to determine whether gene transfer of extracellular SOD (ECSOD) improves vascular responsiveness in LPS-treated rats. A second goal was to determine whether effects of ECSOD are dependent on the heparin-binding domain of the enzyme, which facilitates binding of ECSOD to the outside of cells. Adenoviruses containing ECSOD (AdECSOD), ECSOD with deletion of its heparin-binding domain (AdECSOD-HBD), or a control virus (AdLacZ) were injected intravenously into rats. Three days later, vehicle or LPS (10 mg/kg ip) was injected. After 24 h, vascular reactivity was examined in aortic rings in vitro. Maximum relaxation to acetylcholine was 95 +/- 1% (means +/- SE) after AdlacZ plus vehicle and 77 +/- 3% after AdlacZ plus LPS (P < 0.05). Responses to calcium ionophore A-23187 and submaximal concentrations of nitroprusside also were impaired by LPS. Gene transfer of ECSOD, but not AdECSOD-HBD, improved (P < 0.05) relaxation to acetylcholine and A-23187 after LPS. Maximum relaxation to acetylcholine was 88 +/- 3% after LPS plus AdECSOD. Superoxide was increased in aorta after LPS, and the levels were reduced after AdECSOD but not AdECSOD-HBD. LPS-induced adhesion of leukocytes to aortic endothelium was reduced by AdECSOD but not by AdECSOD-HBD. We conclude that after gene transfer in vivo, binding of ECSOD to arteries effectively decreases the numbers of adherent leukocytes and levels of superoxide and improves impaired endothelium-dependent relaxation produced by LPS.

Novel isoforms of NADPH oxidase in vascular physiology and pathophysiology

1. Vascular cells have evolved to use reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, as signalling molecules. Under physiological conditions, ROS are important regulators of cell cycle, protein kinase activity and gene expression. However, in vascular disease states, such as hypertension and hypercholesterolaemia, excessive production of ROS may overwhelm the anti-oxidant defence mechanisms of cells, resulting in 'oxidative stress', damage to the artery wall and, ultimately, development of atherosclerotic plaques. 2. The primary source of ROS in the vasculature is NADPH oxidase. There appear to be at least three isoforms of NADPH oxidase expressed in the vascular wall, each differing with respect to the flavin-containing catalytic subunit it uses to transfer electrons from NADPH to molecular oxygen. Thus, although endothelial cells and adventitial fibroblasts express a gp91phox-containing NADPH oxidase similar to that originally identified in phagocytes, vascular smooth muscle cells may rely on novel homologues of gp91phox, namely Nox1 and Nox4, to produce superoxide. 3. Controversy remains over which isoform(s) of NADPH oxidase is responsible for the oxidative stress associated with vascular diseases. We and others have shown that although gp91phox mRNA expression is upregulated during atherogenesis in human and animal models, expression of the Nox4 subunit remains unchanged. Nox1 expression is also likely to be increased in diseased arteries; however, its relative level of expression, at least at the mRNA level, appears to be markedly lower than that of the other gp91phox homologues, even after upregulation. 4. Whether these findings suggest that a gp91phox-containing NADPH oxidase is more important than either Nox4 or Nox1 in vascular disease awaits studies examining relative protein expression and enzyme kinetics of each subunit, as well as the effects of targeted gene deletion of each of these gp91phox homologues on atherogenesis.

Hypertension caused by angiotensin II infusion involves increased superoxide production in the central nervous system

Hypertension caused by angiotensin II (Ang II) infusion is associated with oxidative stress in the peripheral vasculature and kidney. The role of redox mechanisms in the central nervous system (CNS), a tissue known to be pivotal in Ang II-dependent hypertension, has not been investigated. We recently identified superoxide (O2*-) in the brain as a key signaling intermediate in the transient pressor response elicited by acute injection of Ang II directly into the CNS. Here we tested the hypothesis that hypertension caused by chronic systemic infusion of Ang II is mediated by a central neurogenic mechanism involving O2*-. Infusion of Ang II (600 ng x kg(-1) x min(-1)) over a 2-week period in mice caused a gradually developing hypertension that was correlated with marked elevations in O2*- production specifically in the subfornical organ (SFO), a brain region lying outside the blood-brain barrier and known to be a primary sensor for blood-borne Ang II. Adenoviral-mediated delivery of cytoplasmically targeted superoxide dismutase (SOD) selectively to this site prevented the hypertension and the increased O2*- production, whereas gene transfer of SOD targeted to the extracellular matrix had no effect. These data suggest that increased intracellular O2*- production in the SFO is critical in the development of Ang II-induced hypertension.

Comparison of acute and chronic antioxidant interventions in experimental renovascular disease

Reactive oxygen species (ROS) can modulate renal hemodynamics and function both directly, by leading to vasoconstriction, and indirectly, by inducing renal inflammation and tissue growth. The involvement of oxidative stress in the pathogenesis of renovascular disease (RVD) is increasingly recognized, but the relative contribution of long-term tissue injury to renal dysfunction remains unclear. We hypothesized that functional and structural alterations elicited by oxidative stress in RVD would be more effectively modulated by chronic than by acute antioxidant intervention. Renal hemodynamics and function were quantified in vivo in pigs using electron-beam computed tomography at baseline and after vasoactive challenge (ACh and sodium nitroprusside); after 12 wk of RVD (simulated by concurrent hypercholesterolemia and renal artery stenosis, n = 7); RVD acutely infused with the SOD-mimetic tempol (RVD+tempol, n = 7); RVD chronically supplemented with antioxidant vitamins C (1 g) and E (100 IU/kg; RVD+vitamins, n = 7); or control (normal, n = 7). Renal tissue was studied ex vivo using immunoblotting and immunohistochemistry. Basal renal blood flow (RBF) and glomerular filtration rate were similarly decreased in all RVD groups. ACh-stimulated RBF remained unchanged in RVD, increased in RVD+tempol, but further increased (similarly to normal) in RVD+vitamins ( P < 0.05 vs. RVD). Furthermore, RVD+vitamins also showed a decreased presence of superoxide anion, decreased NAD(P)H-oxidase and nitrotyrosine expression, increased endothelial nitric oxide synthase expression, and attenuated renal fibrosis. Chronic antioxidant intervention in early RVD improved renal hemodynamic responses more effectively than acute intervention, likely due to increased nitric oxide bioavailability and decreased structural injury. These suggest that chronic tissue changes play an important role in renal compromise mediated by oxidative stress in RVD.

Vascular protection: superoxide dismutase isoforms in the vessel wall

Blood vessels express 3 isoforms of superoxide dismutase (SOD): cytosolic or copper-zinc SOD (CuZn-SOD), manganese SOD (Mn-SOD) localized in mitochondria, and an extracellular form of CuZn-SOD (EC-SOD). Because there are no selective pharmacological inhibitors of individual SOD isoforms, the functional importance of the different SODs has been difficult to define. Recent molecular approaches, primarily the use of genetically-altered mice and viral-mediated gene transfer, have allowed investigators to begin to define the role of specific SOD isoforms in vascular biology. This review will focus mainly on the role of individual SODs in relation to endothelium under normal conditions and in disease states. This area is important because reactive oxygen species and superoxide anion are thought to play major roles in changes in vascular structure and function in pathophysiology.

Evidence for superoxide anion generation in aortas of cholesterol-fed rabbits treated with l -arginine

The inducible form of nitric oxide synthase (iNOS) is present in advanced atherosclerotic lesions. The aim of the present paper was to compare the functionality of iNOS in rabbits fed a 0.3% cholesterol-diet for 24 weeks (Baseline), and 36 weeks, with l-arginine (l-Arg) or vehicle supplementation (Saline) for the last 12 weeks. N-iminoethyl-l-lysine (l-NIL; 10 microM), a selective inhibitor of iNOS, potentiated the contractions to phenylephrine in aortas from Baseline, Saline and l-Arg rabbits confirming the presence of a functional iNOS. In l-Arg rabbits, the contractions induced by l-NIL were less pronounced than those noted in Baseline and Saline rabbits; superoxide dismutase (150 U/ml) significantly increased the phenylephrine-induced contractions only in the l-Arg rabbits. In the presence of NADPH, aortas from l-Arg rabbits produced more superoxide anions than aortas from saline rabbits as evidenced by the lucigenin-enhanced chemiluminescence technique. In conclusion, our results show functional and biochemical evidence for an increased superoxide anion production in atherosclerotic aortas from hypercholesterolemic rabbits treated with l-Arg for 12 weeks. These data may thus help to explain the lack of beneficial effects of l-Arg on atherosclerosis progression in long-term experimental hypercholesterolemia as well as in severely atherosclerotic humans.

Induction of chromosomal instability by chronic oxidative stress

Earlier studies using GM10115 cells analyzed the capability of different DNA-damaging agents to induce genomic instability and found that acute oxidative stress was relatively inefficient at eliciting a persistent destabilization of chromosomes. To determine whether this situation would change under chronic exposure conditions, the human-hamster hybrid line GM10115 was cultured under conditions of oxidative stress. Chronic treatments consisted of 1-hour incubations using a range of hydrogen peroxide (25-200 microM) or glucose oxidase (GO; 5-50 mU/ml) concentrations that were administered once daily over 10 to 30 consecutive days. The toxicity of chronic treatments was modest (- one log kill) and consistent with the low yield of first division aberrations (<5%). However, analysis of over 180 clones and 36,000 metaphases indicated that chronic oxidative stress led to a high incidence of chromosomal instability. Treatment of cells with 100 and 200 microM hydrogen peroxide or 50 mU/ml GO was found to elicit chromosomal instability in 11%, 22%, and 19% of the clones analyzed, respectively. In contrast, control clones isolated after mock treatment did not show signs of chromosomal destabilization. These data suggest that chronic oxidative stress constitutes a biochemical mechanism capable of disrupting the genomic integrity of cells.

Upregulation of Vascular Extracellular Superoxide Dismutase in Patients With Acute Coronary Syndromes

OBJECTIVE

We examined the vascular expression levels of extracellular superoxide dismutase (EC-SOD), a major antioxidant enzyme in the cardiovascular system, in patients with acute coronary syndromes.

METHODS AND RESULTS

Twenty-one consecutive patients with acute myocardial infarction (AMI), 14 patients with unstable angina, 11 patients with stable angina, and 20 control subjects were studied. The levels of vascular EC-SOD expression were assessed by the difference in plasma EC-SOD concentrations before and after intravenous heparan injection. In the patients with AMI, vascular EC-SOD expression (ng/mL) was significantly higher on day 1 after the onset of AMI (148+/-10) as compared with the control subjects (116+/-6, P<0.05). The vascular EC-SOD expression returned to the normal range on day 7 (104+/-8), and that level persisted thereafter. The vascular EC-SOD expression was also significantly higher in the patients with unstable angina (160+/-13) than in those with stable angina (122+/-10) or in the controls (116+/-6) (P<0.05 each). Moreover, in the patients with AMI, higher levels of vascular EC-SOD expression on day 1 were significantly associated with smaller myocardial infarct size (P<0.05).

CONCLUSIONS

This is the first clinical demonstration showing that vascular EC-SOD may be upregulated in acute coronary syndromes in humans in vivo. EC-SOD may play an important protective role against increased oxidative stress during acute ischemic coronary events.

Calcium Antagonist Reduces Oxidative Stress by Upregulating Cu/Zn Superoxide Dismutase in Stroke-Prone Spontaneously Hypertensive Rats

Recent studies have suggested that the calcium antagonists have an antiatherogenic antioxidant property. The effects of the calcium antagonists on reactive oxygen species (ROS)-related enzymes, however, remain unknown. We hypothesized that the calcium antagonists inhibit oxidative stress in the hearts of stroke-prone spontaneously hypertensive rats (SHRSP) through the ROS-scavenging enzymes known as superoxide dismutases (SODs). Male 12-week-old Wister-Kyoto rats (WKY) and SHRSP were used for the study. SHRSP were randomized and treated for 6 weeks with a vehicle, amlodipine (5 mg/kg/day), or enalapril (10 mg/kg/day). NAD(P)H oxidase activity was measured by a luminescence assay, and SOD activity was measured spectrophotometrically. Protein expressions were analyzed by immunoblots. Both drugs showed equipotent effects on systolic blood pressure, left ventricular hypertrophy and fibrosis, the wall-to-lumen ratio, the manganese SOD activity, ROS, and the endothelial NO synthase expression in the SHRSP hearts. Furthermore, amlodipine significantly restored copper/zinc-containing SOD (Cu/ZnSOD) expression and its activity in SHRSP hearts to a level equal to that of WKY more effectively than did enalapril (p <0.05), whereas enalapril downregulated NAD(P)H oxidase activity more than did amlodipine (p <0.05) in the SHRSP hearts. Furthermore, amlodipine restored Cu/ZnSOD expression and its activity in SHRSP hearts to a level equal to that in WKY hearts, and this restoration was significantly more effective than that by enalapril (p <0.05); on the other hand, enalapril induced a greater downregulation of NAD(P)H oxidase activity in SHRSP hearts than did amlodipine (p <0.05). Thus, amlodipine may inhibit vascular remodeling and oxidative stress in the SHRSP heart by efficiently upregulating Cu/ZnSOD, suggesting that the calcium antagonist may exhibit an antiatherogenic antioxidative action beyond blood-pressure lowering through the restoration of Cu/ZnSOD activity in the heart in cases of hypertension.

Sustained decrease in superoxide dismutase activity underlies constrictive remodeling after balloon injury in rabbits

OBJECTIVE

The redox pathophysiology of vascular repair is incompletely understood. We assessed the role of vascular superoxide dismutase (SOD) activity in oxidative/nitrative stress and caliber loss postinjury (PI).

METHODS AND RESULTS

Rabbits submitted to iliac artery balloon overdistension were followed for 14 days PI. Significant decrease in vascular SOD activity occurred at 7 and 14 days PI (by 45% and 34%, respectively, versus control, 96+/-1 U/mg, P<0.05). Separation in concanavalin-A column showed that both extracellular SOD (ecSOD) and CuZn SOD activities were reduced, whereas Western analysis showed normal or augmented protein expression. Immunoreactivity to nitrotyrosine, neuronal NO synthase (NOS), and inducible NOS (iNOS) increased in media and neointima PI; iNOS mRNA also augmented. Administration of ecSOD from days 7 to 14 PI corrected the SOD activity decrease and minimized caliber loss by 59% (P=0.007) despite unaltered neointima. Nitrate levels markedly increased with ecSOD in injured artery homogenates (26+/-5 versus 4+/-0.3 micromol/L per mg, P=0.001). Such increase was 70% inhibited by specific iNOS antagonist 1400w. Nitrotyrosine and neuronal NOS expression decreased after ecSOD.

CONCLUSIONS

Sustained low vascular SOD activity has a key role in constrictive remodeling after injury, promoting oxidative/nitrative stress and impairment of iNOS-derived NO bioavailability. SOD function may critically determine whether iNOS induction is beneficial or deleterious in vivo.

Glutathione peroxidase 1 activity and cardiovascular events in patients with coronary artery disease

BACKGROUND

Cellular antioxidant enzymes such as glutathione peroxidase 1 and superoxide dismutase have a central role in the control of reactive oxygen species. In vitro data and studies in animal models suggest that these enzymes may protect against atherosclerosis, but little is known about their relevance to human disease.

METHODS

We conducted a prospective study among 636 patients with suspected coronary artery disease, with a median follow-up period of 4.7 years (maximum, 5.4) to assess the risk of cardiovascular events associated with base-line erythrocyte glutathione peroxidase 1 and superoxide dismutase activity.

RESULTS

Glutathione peroxidase 1 activity was among the strongest univariate predictors of the risk of cardiovascular events, whereas superoxide dismutase activity had no association with risk. The risk of cardiovascular events was inversely associated with increasing quartiles of glutathione peroxidase 1 activity (P for trend <0.001); patients in the highest quartile of glutathione peroxidase 1 activity had a hazard ratio of 0.29 (95 percent confidence interval, 0.15 to 0.58; P<0.001), as compared with those in the lowest quartile. Glutathione peroxidase 1 activity was affected by sex and smoking status but retained its predictive power in these subgroups. After adjustment for these and other cardiovascular risk factors, the inverse association between glutathione peroxidase 1 activity and cardiovascular events remained nearly unchanged.

CONCLUSIONS

In patients with coronary artery disease, a low level of activity of red-cell glutathione peroxidase 1 is independently associated with an increased risk of cardiovascular events. Glutathione peroxidase 1 activity may have prognostic value in addition to that of traditional risk factors. Furthermore, increasing glutathione peroxidase 1 activity might lower the risk of cardiovascular events.

Enalapril prevents impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in diabetic rats

BACKGROUND AND PURPOSE

Our goal was to identify the effects of chronic treatment with enalapril on cerebrovascular dysfunction and endothelial nitric oxide synthase (eNOS) protein in diabetic rats.

METHODS

Rats were assigned to 1 of 4 groups: nondiabetic, diabetic, nondiabetic/enalapril-treated, and diabetic/enalapril-treated groups. Rats assigned to the nondiabetic groups were injected with vehicle (sodium citrate buffer), and rats assigned to the diabetic groups were injected with streptozotocin (50 mg/kg IP). Enalapril (10 mg/kg per day) was administered in the drinking water and coincided with the injection of vehicle or streptozotocin. Two to 3 months later, we examined responses of pial arterioles to nitric oxide synthase (NOS)-dependent agonists (acetylcholine and ADP) and a NOS-independent agonist (nitroglycerin). After these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein.

RESULTS

We found that acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared with nondiabetic rats. In addition, while enalapril did not alter responses in nondiabetic rats, enalapril prevented diabetes-induced impairment of NOS-dependent vasodilatation. Furthermore, eNOS protein was higher in diabetic than in nondiabetic rats, and enalapril did not produce a further increase in eNOS protein in enalapril-treated diabetic rats compared with untreated diabetic rats.

CONCLUSIONS

These results suggest that enalapril prevents cerebrovascular dysfunction in diabetic rats. We speculate that the protective role of enalapril may be independent of an alteration in eNOS protein in cerebral microvessels.

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.

Extracellular superoxide dismutase polymorphism in mice

OBJECTIVE

In this study, we describe a previously unrecognized murine extracellular superoxide dismutase (ecSOD) allele and examine its distribution among various strains and its effect on the ecSOD phenotype.

METHODS AND RESULTS

Polymerase chain reaction analysis of genomic and cDNA from apolipoprotein E/LDLR-/- mice indicates the presence of 2 distinct transcripts for this enzyme independent of the extent of atherosclerosis or age. Sequencing and genotyping analyses reveal the presence of 2 alleles for ecSOD. One is a short variant with a 10-base pair deletion in the 3'UTR, accompanied by a single nucleotide substitution (position 61) found in the 129P3/J strain of mice. By contrast, all other strains examined carry the long form. Both free and heparin-releasable ecSOD activities in the 129P3/J strain are more than 3-fold higher than those in the C57Bl/6 mice. Corresponding differences in plasma enzyme mass are observed by immunoblotting. A clear allele dose effect can be observed in F2 hybrids of these 2 strains; free and total ecSOD activities in mice homozygous for the short allele are twice those of mice homozygous for the long allele, with the heterozygote values in between.

CONCLUSIONS

These data clearly demonstrate the allele-specific effects on the ecSOD phenotype independent of other strain-specific factors and underline the need for backcrossing of genetically modified mice.

Nitric oxide stimulates Nrf2 nuclear translocation in vascular endothelium

Vascular endothelial cells respond to nitric oxide by activating MAPK pathways and upregulating stress-activated proteins such as gamma-glutamylcysteine synthetase (gamma-GCS) and heme oxygenase-1 (HO-1). Since consensus sequences for the antioxidant response element (ARE) are found in the promoters of the gamma-GCS and HO-1 genes, we examined nuclear translocation of Nrf2, a CNC-bZIP protein which binds to and activates the ARE. We found a dramatic increase in Nrf2 nuclear translocation 1-8h following the nitric oxide donor spermine NONOate. Translocation was inhibited by pretreatment of cells with N-acetylcysteine suggesting involvement of an oxidative mechanism in this response. Translocation was also blocked by PD 98059 and SB 203580, inhibitors of ERK and p38 pathways, respectively. In addition to effects on Nrf2 subcellular localization, spermine NONOate increased Nrf2 protein levels by a mechanism which was inhibited by PD 98059. Pretreatment with N-acetylcysteine, PD 98059, and SB 203580 decreased HO-1 upregulation in spermine NONOate-treated cells. These results suggest that ERK and p38 pathways may regulate nitric oxide-mediated adaptive responses in vascular endothelium via translocation of Nrf2 and activation of the ARE.

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.

Effect of steady versus oscillating flow on porcine coronary arterioles: involvement of NO and superoxide anion

Coronary blood vessels are compressed by the contracting myocardium. This leads to oscillations in flow in especially the subendocardium. We examined the effects of steady and oscillating flow on isolated, cannulated subendocardial and subepicardial porcine arterioles. Steady flow-induced dilation in both vessel types, up to 12.9+/-0.8% of the passive diameter in subendocardials and 9.6+/-1.4% in subepicardials at 40 dyne/cm2. Dilation was completely abolished after treatment with 10 micromol/L L-NNA. Sinusoidal modulation of steady flow at 1.5 Hz and 50% to 200% amplitude did not affect dilation. Oscillating flow without a net forward component with peak-peak shear values up to 100 dyne/cm2 caused no dilation at all in these vessels. However, in the presence of 100 U/mL superoxide dismutase (SOD), oscillating flow induced dilation up to 19.5+/-2.3% in subendocardial vessels and 11.5+/-4.3% in subepicardials. LNNA (10 micromol/L) blocked this dilation by approximately 50%. SOD did not affect the magnitude of steady flow-induced dilation, but the response time after onset of steady flow shortened from 23.4+/-1.5 to 14.3+/-2.1 seconds. Diphenyleneiodinium, an inhibitor of NAD(P)H oxidase, uncovered dilation to oscillating flow in subendocardial vessels up to 9.5+/-1.6%. Flow causes production of both NO and O2-. During steady flow, the bioavailability of NO is sufficient to cause vasodilation. During oscillating flow, NO is quenched by the O2-, suppressing vasodilation. Considering the pulsatile nature of subendocardial flow and the vulnerability of this layer, pharmacological manipulation of the balance between NO and O2- may improve subendocardial perfusion.

[Structural and antigenic differences of pancreatic RNAse preparations modified by dextran ethers in an azo-combination reaction]

Background

Diabetes is characterized by chronic hyperglycemia, which can increase reactive oxygen species (ROS) production by the mitochondrial electron transport chain. The formation of ROS induces oxidative stress and activates oxidative damage-inducing genes in cells. No research has been published on oxidative damage-related extracellular superoxide dismutase (EC-SOD) protein levels in human diabetic skin. We investigated the expression of EC-SOD in diabetic skin compared with normal skin tissue in vivo.

Methods

The expression of EC-SOD protein was evaluated by western blotting in 6 diabetic skin tissue samples and 6 normal skin samples. Immunohistochemical staining was also carried out to confirm the EC-SOD expression level in the 6 diabetic skin tissue samples.

Results

The western blotting showed significantly lower EC-SOD protein expression in the diabetic skin tissue than in the normal tissue. Immunohistochemical examination of EC-SOD protein expression supported the western blotting analysis.

Conclusions

Diabetic skin tissues express a relatively small amount of EC-SOD protein and may not be protected against oxidative stress. We believe that EC-SOD is related to the altered metabolic state in diabetic skin, which elevates ROS production.