Expression of a hybrid Cu/Zn-type superoxide dismutase which has high affinity for heparin-like proteoglycans on vascular endothelial cells

Legal but lethal: functional protein aggregation at the verge of toxicity

Many neurodegenerative disorders are linked to irreversible protein aggregation, a process that usually comes along with toxicity and serious cellular damage. However, it is emerging that protein aggregation can also serve for physiological purposes, as impressively shown for prions. While the aggregation of this protein family was initially considered exclusively toxic in mammalians organisms, it is now almost clear that many other proteins adopt prion-like attributes to rationally polymerize into higher order complexes with organized physiologic roles. This implies that cells can tolerate at least in some measure the accumulation of inherently dangerous protein aggregates for functional profit. This review summarizes currently known strategies that living organisms adopt to preserve beneficial aggregation, and to prevent the catastrophic accumulation of toxic aggregates that frequently accompany neurodegeneration.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

Vascular endothelial function in health and diseases

The vascular endothelium constitutes approximately 1% of body mass (1kg) and has a surface area of approximately 5000m(2). The endothelium is a multifunctional endocrine organ strategically placed between the vessel wall and the circulating blood, and has a key role in vascular homeostasis. The endothelium is both a target for and mediator of cardiovascular disease. The endothelium releases several relaxing and constricting factors, which can affect vascular homeostasis. Endothelial dysfunction, whether caused by physical injury or cellular damage, leads to compensatory responses that alter the normal homeostatic properties of the endothelium. In this review, we summarized some physiological aspects of endothelial function and then we discussed endothelial dysfunction during some pathological conditions.

Synthesis and anti-inflammatory activity of a chimeric recombinant superoxide dismutase: SOD2/3

External surfaces of cells are normally protected by extracellular superoxide dismutase, SOD3, which binds to polyanions such as heparan sulfate. We constructed a fusion gene encoding a chimeric SOD consisting of the mature human mitochondrial SOD2 plus the COOH-terminal 26-amino acid heparin-binding "tail" from SOD3. This tail is responsible for the enzyme's affinity for endothelial surfaces. The fusion gene was expressed in Escherichia coli, and the fully active enzyme SOD2/3 was purified. Although native SOD2 has no affinity for heparin, SOD2/3 binds to a heparin-agarose column. In a rat model of acute lung injury induced by intratracheal instillation of IL-1, SOD2/3, SOD2, and denatured SOD2/3 showed 92%, 13.8%, and 0% reduction of lung leak, respectively. Only SOD2/3 prevented neutrophil accumulation. In the carrageenan-induced foot edema model in the rat, SOD2/3 reduced edema by 62% (P < 0.003) at a dose in which native SOD2 produced no significant effect. Thus SOD2/3 appears to have properties as a therapeutic anti-inflammatory agent that are greatly superior to other available forms of the enzyme.

Gene transfer of extracellular superoxide dismutase reduces arterial pressure in spontaneously hypertensive rats: role of heparin-binding domain

Oxidative stress may contribute to hypertension. The goals of this study were to determine whether extracellular superoxide dismutase (ECSOD) reduces arterial pressure in spontaneously hypertensive rats (SHR) and whether its heparin-binding domain (HBD), which is responsible for cellular binding, is necessary for the function of ECSOD. Three days after intravenous injection of an adenoviral vector expressing human ECSOD (AdECSOD), mean arterial pressure (MAP) decreased from 165+/-4 mm Hg (mean+/-SE, n=7) to 124+/-3 mm Hg (n=7) in adult anesthetized SHR (P<0.01) but was not altered in normotensive Wistar-Kyoto rats. Cardiac output was not changed in SHR 3 days after AdECSOD. Gene transfer of ECSOD with deletion of the HBD (AdECSODDeltaHBD) had no effect on SHR MAP, even though plasma SOD activity was greater after AdECSODDeltaHBD than after AdECSOD. Immunohistochemistry revealed intense staining for ECSOD in blood vessels and kidneys after AdECSOD but not after AdECSODDeltaHBD. Impaired relaxation of the carotid artery to acetylcholine in SHR was significantly improved after AdECSOD. Cumulative sodium balance in SHR was reduced by AdECSOD compared with AdECSODDeltaHBD. Gene transfer of ECSOD also reduced MAP in conscious SHR, although the effect was not as profound as in anesthetized SHR. In summary, gene transfer of ECSOD, with a strict requirement for its HBD, reduces systemic vascular resistance and arterial pressure in a genetic model of hypertension. This reduction in arterial pressure may be mediated by vasomotor and/or renal mechanisms.

Escape from tolerance of organic nitrate by induction of cytochrome P450

The mechanism of organic nitrate tolerance is poorly defined. We studied the rat P450-catalyzed conversion of organic nitrate to nitric oxide (NO) by purified P450 isoforms relationship between P450 expression and nitrate tolerance following continuous infusion of organic nitrates in rats. The hypotensive effect of an nitroglycerin (NTG) bolus injection was abolished in rats that had been previously provided a continuous 48 h infusion of NTG. This effect was accompanied by a gradual but marked decrease in plasma and urinary nitrate levels following a peak at 18-24 h. Nitrate tolerance was reversible; the decline in the hypotensive effect and P450 levels observed after 2 d of continuous infusion was followed by restoration to control levels 2 d after cessation of the infusion. Similarly, the hypotensive action disappeared in P450-depleted, and -inhibited rats. At 48 h after infusion, NTG-induced NO generation of the vessels increased in acetone (a P450 inducer) -pretreated rats. The appearance and disappearance of P450 paralleled the conversion of organic nitrates to NO. Our observations indicate that nitrate tolerance is in large part the result of decreased P450 expression and activity. Interventions that maintain or increase P450 activity may be a strategy to provide relief from ischemic conditions in humans.

Neonatal Chronic Lung Disease

Chronic lung disease (CLD), formerly known as bronchopulmonary dysplasia, is presently defined as the need for oxygen therapy either at 28 days of age or greater than 36 weeks postmenstrual age. Clinical signs and symptoms include tachypnea, retractions, apnea, and radiographic findings of poorly inflated lungs with reticulogranular opacities. The disease develops as a result of chronic pulmonary inflammation and continuous lung injury induced by oxygen, positive pressure ventilation, and other causes. Fifty to sixty-five percent of neonates with CLD are rehospitalized with respiratory problems, and 21% of very low birth weight neonates are diagnosed with asthma or other respiratory disorders by the age of five. These infants are at risk of adverse neurodevelopmental sequelae as they have a more complicated neonatal course. Many studies have explored various preventive therapies including α1-proteinase inhibitors, superoxide dismutase, antioxidants, and ventilatory management. Although the results from these trials are promising, further studies are needed to define which patients are most likely to benefit from preventive therapy. Two preventive treatment approaches that have shown a decrease in morbidity and an improvement in mortality are antenatal steroids and surfactant therapy. Postnatal corticosteroid therapy continues to be the mainstay of treatment for CLD, however, there are a number of detrimental side effects associated with this treatment. Due to the increased incidence in periventricular leukomalacia, early treatment of steroid therapy cannot be recommended. The optimal time to start steroid therapy appears to be after the first week of life. In addition, the lowest dose and shortest duration of treatment needs to be implemented in order to minimize potential complications. Although bronchodilators and diuretics continue to be used extensively in infants with CLD, there are surprisingly few well-controlled studies that have evaluated the clinical impact of this therapy. Further trials are needed in order to support the routine use of these therapies in CLD. Unfortunately, inhaled steroids have not shown an improvement in long-term outcomes of CLD, however, they have shown a decrease in systemic steroid usage. CLD is a complex disease with many unanswered questions. Further studies are needed to evaluate the effects of various treatment modalities with particular focus on the long-term outcomes such as oxygen and ventilator dependency as well as the incidence of CLD.

Cross-talk between NO and oxyradicals, a supersystem that regulates energy metabolism and survival of animals

Mammalian tissues have large amounts of available ATP which are generated by oxidative phosphorylation in mitochondria. For the maintenance of the human body, a large amount of oxygen is required to regenerate these ATP molecules. A small fraction of the inspired oxygen is converted to superoxide radical and related metabolites even under physiological conditions. Most reactive oxygen species react rapidly with a variety of molecules thereby interfering with cellular functions and induce various diseases. Nitric oxide (NO) is an unstable gaseous radical with high affinity for various molecules, such as hemeproteins, thiols, and related radicals. NO easily penetrates through cell membrane/lipid bilayers, forms dissociable complexes with these molecules and modulates cellular metabolism and functions. Because NO has an extremely high affinity for the superoxide radical, the occurrence of the latter might decrease the biological function of NO. Thus, superoxide radicals in and around vascular endothelial cells play critical roles in the pathogenesis of hypertension and vasogenic tissue injury. Because NO also reacts with molecular oxygen, it rapidly loses its biological activity, particularly under ambient atmospheric conditions where the oxygen tension is unphysiologically high. Thus, biological functions of NO are determined by the local concentrations of molecular oxygen and superoxide radicals.

Extracellular superoxide dismutase in tissues from obese (ob/ob) mice

We have examined the protein content and gene expression of three superoxide dismutase (SOD) isoenzymes in eight tissues from obese ob/ob mice, particularly placing the focus on extracellular-SOD (EC-SOD) in the white adipose tissue (WAT). Obesity significantly increased EC-SOD level in liver, kidney, testis, gastrocnemius muscle, WAT, brown adipose tissue (BAT), and plasma, but significantly decreased the isoenzyme level in lung. Tumor necrosis factor-alpha and interleukin-1beta contents in WAT were significantly higher in obese mice than in lean control mice. Immunohistochemically, both WAT and BAT from obese mice could be stained deeply with anti-mouse EC-SOD antibody compared with those from lean mice. Each primary culture per se almost time-dependently enhanced EC-SOD production, and overtly expressed its mRNA. The loss of heparin-binding affinity of EC-SOD type C with high affinity for heparin occurred in kidney of obese mice. These results suggest that the physiological importance of this SOD isoenzyme in WAT may be a compensatory adaptation to oxidative stress.

Synthesis of superoxide dismutase derivative that specifically accumulates in renal proximal tubule cells

Protection of tissues from oxygen toxicity is one of the major prerequisites to aerobic life. Since a wide variety of xenobiotics with prooxidant activity is excreted by the kidney, renal tubule cells should be protected from hazardous oxygen species. Because intravenously injected Cu/Zn-type superoxide dismutase (SOD) is rapidly excreted in the urine in its intact form, effective dismutation of superoxide radicals cannot be achieved in vivo by intravenously administered SOD. To scavenge superoxide radicals and inhibit their toxic effects in and around renal tubule cells, a hexamethylene-diamine (AH)-conjugated SOD (AH-SOD) was synthesized. When injected intravenously into the rat, (125)I-labeled AH-SOD disappeared from the circulation with a half-life of 3 min and accumulated in the kidney. After 30 min of administration, more than 80% of the radioactivity derived from AH-SOD was found to localize in the kidney without being excreted in the urine. Immunohistochemical examination revealed that, 60 min after administration, the major part of AH-SOD localized in renal proximal tubule cells. Kinetic analysis using right-side-out-oriented renal brush border vesicles revealed that AH-SOD bound to their membrane surface by some mechanism which was inhibited by AH but not by heparin and albumin. These results indicated that AH-SOD rapidly underwent renal glomerular filtration, bound to apical plasma membranes of proximal tubule cells, and localized in these cells for a fairly long time without being excreted in the urine. Thus, AH-SOD might permit studies on the role of superoxide radicals in and around renal proximal tubule cells.

Binding of xanthine oxidase to vascular endothelium. Kinetic characterization and oxidative impairment of nitric oxide-dependent signaling

Concentrations of up to 1.5 milliunits/ml xanthine oxidase (XO) (1.1 micrograms/ml) are found circulating in plasma during diverse inflammatory events. The saturable, high affinity binding of extracellular XO to vascular endothelium and the effects of cell binding on both XO catalytic activity and differentiated vascular cell function are reported herein. Xanthine oxidase purified from bovine cream bound specifically and with high affinity (Kd = 6 nM) at 4 degreesC to bovine aortic endothelial cells, increasing cell XO specific activity up to 10-fold. Xanthine oxidase-cell binding was not inhibited by serum or albumin and was partially inhibited by the addition of heparin. Pretreatment of endothelial cells with chondroitinase, but not heparinase or heparitinase, diminished endothelial binding by approximately 50%, suggesting association with chondroitin sulfate proteoglycans. Analysis of rates of superoxide production by soluble and cell-bound XO revealed that endothelial binding did not alter the percentage of univalent reduction of oxygen to superoxide. Comparison of the extent of CuZn-SOD inhibition of native and succinoylated cytochrome c reduction by cell-bound XO indicated that XO-dependent superoxide production was occurring in a cell compartment inaccessible to CuZn-SOD. This was further supported by the observation of a shift of exogenously added XO from extracellular binding sites to intracellular compartments, as indicated by both protease-reversible cell binding and immunocytochemical localization studies. Endothelium-bound XO also inhibited nitric oxide-dependent cGMP production by smooth muscle cell co-cultures in an SOD-resistant manner. This data supports the concept that circulating XO can bind to vascular cells, impairing cell function via oxidative mechanisms, and explains how vascular XO activity diminishes vasodilatory responses to acetylcholine in hypercholesterolemic rabbits and atherosclerotic humans. The ubiquity of cell-XO binding and endocytosis as a fundamental mechanism of oxidative tissue injury is also affirmed by the significant extent of XO binding to human vascular endothelial cells, rat lung type 2 alveolar epthelial cells, and fibroblasts.

Postischemic infusion of Cu/Zn superoxide dismutase or SOD:Tet451 reduces cerebral infarction following focal ischemia/reperfusion in rats

Oxygen-free radicals play a major role in neuronal cell injury following cerebral ischemia/reperfusion. The free-radical scavenging enzyme, Cu/Zn superoxide dismutase (SOD-1), ameliorates various types of brain injury resulting from temporary CNS ischemia. We have compared the cerebroprotective properties of human SOD-1 (hSOD-1) with a novel recombinant SOD-1 hybrid protein, SOD:Tet451, composed of hSOD-1 linked to the neuronal binding fragment of tetanus toxin (TTxC). Following 2 h of temporary middle cerebral artery occlusion, rats infused with equivalent activities of either hSOD-1 or SOD:Tet451 for the initial 3 h of reperfusion showed reductions in cerebral infarct volume of 43 and 57%, respectively, compared to saline-treated controls (P < 0.01). Serum hSOD-1 concentrations in rats receiving SOD:Tet451 were seven-fold higher than those in rats receiving the native enzyme. Animals treated with SOD:Tet451 also demonstrated an extended persistence of hSOD-1 in the bloodstream during drug washout as compared to animals given free enzyme. Immunohistochemical examination of brain sections from an SOD:Tet451-treated ischemic rat showed positive immunoreactivity in the ipsilateral cerebral cortex using either anti-TTxC or anti-human SOD-1 antibodies. Our results document that both hSOD-1 and SOD:Tet451 significantly reduce brain infarct volume in a model of transient focal ischemia/reperfusion in rats. Additionally, our findings suggest that the cerebroprotective effects of SOD-1 may be enhanced by neuronal targeting as seen with the hybrid protein SOD:Tet451.

CuZn superoxide dismutase (SOD-1):tetanus toxin fragment C hybrid protein for targeted delivery of SOD-1 to neuronal cells

Increased levels of CuZn superoxide dismutase (SOD-1) are cytoprotective in experimental models of neurological disorders associated with free radical toxicity (e.g. stroke, trauma). Targeted delivery of SOD-1 to central nervous system neurons may therefore be therapeutic in such diseases. The nontoxic C-fragment of tetanus toxin (TTC) possesses the nerve cell binding/transport properties of tetanus holotoxin and has been used as a vector to enhance the neuronal uptake of proteins including enzymes. We have now produced a recombinant, hybrid protein in Escherichia coli tandemly joining human SOD-1 to TTC. The expressed hybrid protein (SOD:Tet450) has a subunit molecular mass of 68 kDa and is recognized by both anti-SOD-1 and anti-TTC antibodies. Calculated per mol, SOD:Tet450 has approximately 60% of the expected SOD-1 enzymatic activity. Analysis of the hybrid protein's interaction with the neuron-like cell line, N18-RE-105, and cultured hippocampal neurons by enzyme immunoassay for human SOD-1 revealed that SOD:Tet451 association with cells was neuron-specific and dose-dependent. The hybrid protein was also internalized, but there was substantial loss of internalized hybrid protein over the first 24 h. Hybrid protein associated with cells remained enzymatically active. These results suggest that human SOD-1 and TTC retain their respective functional properties when expressed together as a single peptide. SOD:Tet451 may prove to be a useful agent for the targeted delivery of SOD-1 to neurons.

A site-directed mutant of Cu,Zn-superoxide dismutase modeled after native extracellular superoxide dismutase

The well-studied cytosolic Cu,Zn-superoxide dismutase (SOD) protects against reperfusion injury, although its short (6 min) plasma half-life and negative charge create undesirable pharmacokinetics. We have designed, cloned, and expressed a genetic variant of SOD with altered pharmacological properties. A fusion gene consisting of the entire coding region of human SOD followed by a positively charged carboxy-terminal (C-terminal) "tail" of eight glycine and six arginine residues was constructed. The tail was modeled after the extracellular SOD (EC-SOD) C-terminal 26-amino acid basic peptide. This EC-SOD tail binds to heparin-like proteoglycans on cell surfaces and contributes to the enzyme's very long (30 h) plasma clearance time. After expression in Escherichia coli, the mutant enzyme was purified and characterized. No differences in specific activity or UV absorption spectrum between the mutant and the native enzyme were found. The thermal stability of the fusion protein was greater than that of native SOD. Although native SOD has no affinity for heparin, the modified enzyme bound to a heparin-agarose column. A "designer" SOD able to bind to cell surfaces may aid in the prevention of superoxide-mediated endothelial damage.

Antioxidants and neonatal lung disease

Bronchopulmonary dysplasia (BPD) remains a clinical problem in survivors of neonatal intensive care despite recent advances which include surfactant replacement. Oxygen toxicity may well be a component in the pathogenesis of BPD and disturbance of the oxidant-antioxidant balance constitutes a biochemical problem which should be addressed in the management of preterm babies. Preterm babies appear to have inadequate antioxidant potential and yet when delivered may experience considerable oxidant stress. This imbalance may be ameliorated by antenatal steroid therapy which augments pulmonary antioxidants as well as surfactant production. Augmentation of antioxidants by administration of exogenous enzymes such as superoxide dismutase and catalase is possible in animal models but the clinical use of such therapies awaits further research.

Identification of novel heparin-releasable proteins, as well as the cytokines midkine and pleiotrophin, in human postheparin plasma

The heparin-releasable proteins are a group of proteins that are targeted to the endothelial surface by attachment to glycosaminoglycans and may have functions specific to the endothelium-blood interface. In this study, heparin-affinity chromatography of human postheparin plasma was used as a method to identify and study novel heparin-releasable proteins. Six proteins seen on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels have increased levels in plasma after intravenous heparin. The six proteins are platelet factor 4, midkine, pleiotrophin, and several novel proteins. Midkine and pleiotrophin are related cytokines that are developmentally regulated, neurotrophic, and mitogenic. Additional studies show that levels of midkine and pleiotrophin peak at 10 to 30 minutes after injection of heparin. Heparin-releasable midkine and pleiotrophin do not originate from blood cells or the kidney. Heparin-releasable midkine may originate from endothelial cells. Soft agar culture of an adenocarcinoma cell line (SW-13) demonstrates growth-stimulating activity similar to that described for pleiotrophin in the heparin-agarose eluate of postheparin plasma but not in the heparin-agarose eluate of preheparin plasma. It is concluded there are more heparin-releasable proteins than previously identified, including midkine and pleiotrophin, and that heparin-affinity chromatography of postheparin plasma is a useful technique for identifying novel heparin-releasable proteins.

Quantitative analysis of extracellular-superoxide dismutase in serum and urine by ELISA with monoclonal antibody

The superoxide anion has been implicated in a wide range of diseases. The major protector against superoxide anion in the extracellular space is extracellular-superoxide dismutase (EC-SOD). EC-SOD is the major SOD isozyme in plasma and forms an equilibrium between the plasma phase and heparan sulfate proteoglycan on the surface of the endothelium. An ELISA method for the measurement of human EC-SOD with monoclonal antibody was established. The proposed method had a high sensitivity (assay range, 0.05-50 ng/ml), good recovery (recovery percentage, 96.9 +/- 5.6%) and reproducibility (within-day assay, C.V. = 8.6-10.2%; between-day assay, C.V. = 6.5-11.7%). EC-SOD levels in sera from healthy persons are clearly divided into two groups: a lower group (Group I, below 120 ng/ml, n = 146) and higher group (Group II, above 400 ng/ml, n = 10). The EC-SOD in Group I were almost normally distributed and the mean level was 55.8 +/- 18.8 ng/ml. The serum EC-SOD level assayed by ELISA correlated well with serum SOD activity. The serum EC-SOD in Group I is heterogeneous with regard to affinity for heparin-Sepharose and could be separated into three approximately equal fractions, whereas the EC-SOD in Group II is mainly one fraction with a high affinity for the column. The apparent molecular weight and carbohydrate structure of serum EC-SOD in Group II are identical to those in Group I. The high EC-SOD level in sera from some individuals may reflect the excessive stimulation of EC-SOD synthesis in vivo or the growth of selected cells in vivo, because EC-SOD is known to be expressed by a few cell types in vivo as a high-heparin-affinity subtype.

Reduction of the anticoagulant activity of glycosaminoglycans on the surface of the vascular endothelium by endotoxin and neutrophils: evaluation by an amidolytic assay

The processes that underlie the coagulopathy observed in severe infection are not fully understood, but seem to be due to an imbalance in the antithrombotic, and prothrombotic properties of the vascular endothelium. Sulphated glycosaminoglycans (GAGs) present on the vessel wall represent an important component of the non-thrombogenic nature of the endothelium. We have modified an amidolytic assay to study the functional ability of GAGs on human umbilical vein endothelial cells (HUVECS), and investigate the effect of E. coli endotoxin and neutrophils on HUVEC surface anticoagulant activity (SAA). Neither endotoxin alone, nor separated neutrophils at lower concentrations (less than 10(6) neutrophils per ml), had major effects on endothelial SAA. When activated neutrophils were incubated with HUVECS pre-stimulated with endotoxin, a significant decrease in SAA was seen using either plasma (mean percentage of control 67.8% +/- sem 7.8; p < 0.02) or purified ATIII (mean percentage of control 69% +/- sem 4.6; p < 0.001). We suggest that alterations in endothelial surface GAGs may occur during sepsis and inflammation, and that this may have important consequences for vascular function. This system will allow the further study of the role of GAGs in the intravascular thrombosis of severe sepsis, and other inflammatory diseases.

The site of nonenzymic glycation of human extracellular-superoxide dismutase in vitro

The secretory enzyme extracellular-superoxide dismutase (EC-SOD) has affinity for heparin and some other sulfated glycosaminoglycans and is in vivo bound to heparan sulfate proteoglycan. Nonenzymic glycation of EC-SOD, both in vivo and in vitro, is associated with a reduction in heparin affinity, whereas the enzymic activity is not affected. The glycation sites in EC-SOD are further studied in the present article. It is shown that modification of a few of the five lysyl residues of the subunits of the enzyme with trinitrobenzene sulfonic acid nearly abolishes the in vitro glycation susceptibility. From a chymotryptic digest of in vitro glycated EC-SOD, two peptides with affinity for boronate could be isolated. Amino acid sequence analysis showed that both encompassed the carboxyterminal end. epsilon-Glucitol lysine was identified in both peptides at positions 211 and 212. The primary glycation sites in EC-SOD are thus lysine-211 and lysine-212 in the putative heparin-binding domain in the carboxyterminal end.