Transgenic mice with increased Cu/Zn-superoxide dismutase activity: animal model of dosage effects in Down syndrome

Methamphetamine-induced alteration in striatal p53 and bcl-2 expressions in mice

Methamphetamine (METH)-induced alterations in the expression of p53 and bcl-2 protein were studied in the striatum of wild type, neuronal nitric oxide synthase knockout (nNOS -/-) and copper zinc superoxide dismutase overexpressed (SOD-Tg) mice. METH treatment up-regulated p53 and down-regulated bcl-2 expression in the striatum of wild type mice. No significant alterations were observed in the expression of these proteins in the nNOS -/- or SOD-Tg mice. These data suggest that METH might cause its neurotoxic effects via the production of free radicals and secondary perturbations in the expression of genes known to be involved in apoptosis and cell death machinery.

Cellular response of antioxidant metalloproteins in Cu/Zn SOD transgenic mice exposed to hyperoxia

Ceruloplasmin, metallothionein, and ferritin are metal-binding proteins with potential antioxidant activity. Despite evidence that they are upregulated in pulmonary tissue after oxidative stress, little is known regarding their influence on trace metal homeostasis. In this study, we have used copper- and zinc-containing superoxide dismutase (Cu/Zn SOD) transgenic-overexpressing and gene knockout mice and hyperoxia to investigate the effects of chronic and acute oxidative stress on the expression of these metalloproteins and to identify their influence on copper, zinc, and iron homeostasis. We found that the oxidative stress-mediated induction of ceruloplasmin and metallothionein in the lung had no effect on tissue levels of copper, iron, or zinc. However, Cu/Zn SOD expression had a marked influence on hepatic copper and iron as well as circulating copper homeostasis. These results suggest that ceruloplasmin and metallothionein may function as antioxidants independent of their role in trace metal homeostasis and that Cu/Zn SOD functions in copper homeostasis via mechanisms distinct from its superoxide scavenging properties.

Neuron-specific expression of mutant superoxide dismutase 1 in transgenic mice does not lead to motor impairment

Mutations were identified in the Cu/Zn superoxide dismutase gene (SOD1) in approximately 15% of patients with familial amyotrophic lateral sclerosis. Transgenic animals expressing mutant SOD1 in all tissues develop an ALS-like phenotype. To determine whether neuron-specific expression of mutant SOD1 is sufficient to produce such a phenotype, we generated transgenic animals carrying the G37R mutation that is associated with the familial form of ALS (FALS), which is driven by the neurofilament light chain promoter. The transgenic animals express high levels of the human SOD1 protein in neuronal tissues, especially in the large motor neurons of the spinal cord, but they show no apparent motor deficit at up to 1.5 years of age. Our animal model suggests that neuron-specific expression of ALS-associated mutant human SOD1 may not be sufficient for the development of the disease in mice.

Chromosome 21: from sequence to applications

Last year we celebrated the sequencing of the entire long arm of human chromosome 21. This achievement now provides unprecedented opportunities to understand the molecular pathophysiology of trisomy 21, elucidate the mechanisms of all monogenic disorders of chromosome 21, and discover genes and functional sequence variations that predispose to common complex disorders. All these steps require the functional analysis of gene products and the determination of the sequence variation of this chromosome.

Oxidative cellular damage and the reduction of APE/Ref-1 expression after experimental traumatic brain injury

The DNA repair enzyme, apurinic/apyrimidinic endonuclease (or redox effector factor-1, APE/Ref-1), is involved in base excision repair of apurinic/apyrimidinic sites after oxidative DNA damage. We investigated the expression of APE/Ref-1 and its relationship to oxidative stress after severe traumatic brain injury produced by controlled cortical impact in normal mice, and in mice over- or underexpressing copper-zinc superoxide dismutase (SOD1TG and SOD1KO, respectively). Oxygen free radical-mediated cellular injury was visualized with 8-hydroxyguanine immunoreactivity as a marker for DNA oxidation, and in situ hydroethidine oxidation as a marker for superoxide production. After trauma there was a reduced expression of APE/Ref-1 in the ipsilateral cortex and hippocampus that correlated with the gene dosage levels of cytosolic superoxide dismutase. The decrease in APE/Ref-1 expression preceded DNA fragmentation. There was also a close correlation between APE/Ref-1 protein levels 4 h after trauma and the volume of the lesion 1 week after injury. Our data have demonstrated that reduction of APE/Ref-1 protein levels correlates closely with the level of oxidative stress after traumatic brain injury. We suggest that APE/Ref-1 immunoreactivity is a sensitive marker for oxidative cellular injury.

Neuron-specific expression of mutant superoxide dismutase 1 in transgenic mice does not lead to motor impairment

Mutations were identified in the Cu/Zn superoxide dismutase gene (SOD1) in approximately 15% of patients with familial amyotrophic lateral sclerosis. Transgenic animals expressing mutant SOD1 in all tissues develop an ALS-like phenotype. To determine whether neuron-specific expression of mutant SOD1 is sufficient to produce such a phenotype, we generated transgenic animals carrying the G37R mutation that is associated with the familial form of ALS (FALS), which is driven by the neurofilament light chain promoter. The transgenic animals express high levels of the human SOD1 protein in neuronal tissues, especially in the large motor neurons of the spinal cord, but they show no apparent motor deficit at up to 1.5 years of age. Our animal model suggests that neuron-specific expression of ALS-associated mutant human SOD1 may not be sufficient for the development of the disease in mice.

Reduction of metallothioneins promotes the disease expression of familial amyotrophic lateral sclerosis mice in a dose-dependent manner

We previously reported that abnormal copper release from mutated Cu, Zn-superoxide dismutase (SOD1) proteins might be a common toxic gain-of-function in the pathogenesis of familial amyotrophic lateral sclerosis (FALS) [Ogawa et al. (1997) Biochem. Biophys. Res. Commun., 241, 251-257.]. In the present study, we first examined metallothioneins (MTs), known to bind copper ions and decrease oxidative toxicity, and found a twofold increase in MTs in the spinal cord of the SOD1 transgenic mice with a FALS-linked mutation (G93A), but not in the spinal cord of wild-type SOD1 transgenic mice. We then investigated whether the clinical course of FALS mice could be modified by the reduced expression of MTs, by crossing the FALS mice with MT-I- and MT-II-deficient mice. FALS mice clearly reached the onset of clinical signs and death significantly earlier in response to the reduction of protein expression. These results indicated that the copper-mediated free radical generation derived from mutant SOD1 might be related to the degeneration of motor neurons in FALS and that MTs might play a protective role against the expression of the disease.

NAD(P)H oxidase-derived superoxide mediates hypercholesterolemia-induced leukocyte-endothelial cell adhesion

Experimental animals placed on a high-cholesterol diet for 2 or more weeks exhibit an inflammatory response in postcapillary venules. The aims of this study were to determine (1) whether superoxide mediates the hypercholesterolemia-induced inflammatory response and (2) whether leukocyte and/or vessel wall NAD(P)H oxidase contributes to this response. Intravital videomicroscopy was used to quantify leukocyte-endothelial cell adhesion in cremasteric postcapillary venules of wild-type (WT) mice, CuZn-superoxide dismutase transgenic (SOD TgN) mice, and mice heterozygous (p47(phox)+/-) or homozygous (p47(phox)-/-) for NAD(P)H oxidase placed on either a normal diet or high-cholesterol diet (HCD) for 2 weeks. The number of adherent and emigrated leukocytes in postcapillary venules of WT HCD mice was significantly higher than that detected in venules of their normal-diet counterparts. However, the HCD-induced recruitment of adherent and emigrated leukocytes was not observed in SOD TgN mice. Whereas hypercholesterolemic p47(phox)+/- and WT mice exhibited similar inflammatory responses, p47(phox)-/- mice did not. Bone marrow chimeras were developed to selectively delete p47(phox) from either the vessel wall or circulating leukocytes. Whereas WT marrow transplanted into WT mice produced a normal inflammatory response of venules to HCD, chimeric mice with p47(phox) deficiency in either the vessel wall or leukocytes exhibited an attenuated inflammatory response to HCD that was comparable with that observed in p47(phox)-/- HCD mice. Our findings indicate that enhanced superoxide production is a critical event that initiates the leukocyte-endothelial cell adhesion in postcapillary venules of HCD mice. NAD(P)H oxidase appears to be an important source of this superoxide.

Astrocytes overexpressing Cu,Zn superoxide dismutase have increased resistance to oxidative injury

Overexpression of Cu,Zn SOD (SOD1) can increase survival of neurons under some pathological conditions. Prior studies have shown, however, that SOD1 overexpression can reduce neuronal survival during exposure to superoxide generators by a mechanism involving excess H(2)O(2) accumulation. Since astrocytes exhibit greater H(2)O(2) catabolism capacity than do neurons, the present study examined the effects of SOD1 overexpression on astrocyte survival under these conditions. Cultures were prepared from transgenic mice that overexpress human SOD1 and from nontransgenic littermate controls. Exposure to xanthine oxidase/hypoxanthine (XO/HPX) or menadione caused dose-dependent astrocyte death. In contrast to prior observations with neurons, astrocytes that overexpress SOD1 showed increased resistance to superoxide toxicity. Surprisingly, increased survival in SOD1 overexpressing cultures remained evident even when H(2)O(2) catabolism was inhibited by preincubation with aminotriazole (to block catalase) and buthionine sulfoximine (to deplete glutathione). These findings suggest differences in superoxide metabolism between neurons and astrocytes, and that the greater resistance of astrocytes to oxidative stress is due at least partly to factors other than greater glutathione peroxidase and catalase activity in astrocytes. GLIA 33:343-347, 2001. Published 2001 Wiley-Liss, Inc.

alpha(4)-integrin mediates neutrophil-induced free radical injury to cardiac myocytes

Previous work has demonstrated that circulating neutrophils (polymorphonuclear leukocytes [PMNs]) adhere to cardiac myocytes via beta(2)-integrins and cause cellular injury via the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase enzyme system. Since PMNs induced to leave the vasculature (emigrated PMNs) express the alpha(4)-integrin, we asked whether (a) these PMNs also induce myocyte injury via NADPH oxidase; (b) beta(2)-integrins (CD18) still signal oxidant production, or if this process is now coupled to the alpha(4)-integrin; and (c) dysfunction is superoxide dependent within the myocyte or at the myocyte-PMN interface. Emigrated PMNs exposed to cardiac myocytes quickly induced significant changes in myocyte function. Myocyte shortening was decreased by 30-50% and rates of contraction and relaxation were reduced by 30% within the first 10 min. Both alpha(4)-integrin antibody (Ab)-treated PMNs and NADPH oxidase-deficient PMNs were unable to reduce myocyte shortening. An increased level of oxidative stress was detected in myocytes within 5 min of PMN adhesion. Addition of an anti-alpha(4)-integrin Ab, but not an anti-CD18 Ab, prevented oxidant production, suggesting that in emigrated PMNs the NADPH oxidase system is uncoupled from CD18 and can be activated via the alpha(4)-integrin. Addition of exogenous superoxide dismutase (SOD) inhibited all parameters of dysfunction measured, whereas overexpression of intracellular SOD within the myocytes did not inhibit the oxidative stress or the myocyte dysfunction caused by the emigrated PMNs. These findings demonstrate that profound molecular changes occur within PMNs as they emigrate, such that CD18 and associated intracellular signaling pathways leading to oxidant production are uncoupled and newly expressed alpha(4)-integrin functions as the ligand that signals oxidant production. The results also provide pathological relevance as the emigrated PMNs have the capacity to injure cardiac myocytes through the alpha(4)-integrin-coupled NADPH oxidase pathway that can be inhibited by extracellular, but not intracellular SOD.

Overexpression of copper-zinc superoxide dismutase attenuates acute activation of activator protein-1 after transient focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Reactive oxygen species (ROS) have been implicated in reperfusion injury after focal cerebral ischemia (FCI). ROS are known to regulate the activity of transcription factors such as activator protein-1 (AP-1), which is a dimer consisting of members of the Jun and Fos families. We investigated the role of ROS in AP-1 activity after FCI using transgenic mice that overexpressed copper-zinc superoxide dismutase (SOD1) and that had reduced infarction volume after FCI.

METHODS

The SOD1 transgenic mice and their wild-type littermates were subjected to middle cerebral artery occlusion and reperfusion by intraluminal suture blockade. After 60 minutes of middle cerebral artery occlusion, mice were allowed to recover for 1, 2, and 4 hours before euthanasia. Protein expression of c-Jun and c-Fos was examined by immunohistochemistry and Western blotting. AP-1 DNA-protein binding activity was assessed by electrophoretic mobility shift assays.

RESULTS

In wild-type mice, immunohistochemistry demonstrated acute c-Jun and c-Fos activation in ischemic cortex and its outer boundary. Expression of both was reduced in SOD1 transgenic mice. Western blotting confirmed that SOD1 overexpression was associated with reduced c-Jun and c-Fos protein levels in ischemic brain. Electrophoretic mobility shift assays revealed that the ischemia-enhanced DNA binding activity observed in wild-type mice was reduced in SOD1 transgenic mice. Supershift assays indicated that c-Jun participated in the bound AP-1 complex.

CONCLUSIONS

SOD1 overexpression prevents early activation of AP-1 after transient FCI in mice. This may block the expression of downstream target genes that are injurious, thereby reducing the infarction volume after transient FCI in mice.

Peroxynitrite plays a role in methamphetamine-induced dopaminergic neurotoxicity: evidence from mice lacking neuronal nitric oxide synthase gene or overexpressing copper-zinc superoxide dismutase

The use of methamphetamine (METH) leads to neurotoxic effects in mammals. These neurotoxic effects appear to be related to the production of free radicals. To assess the role of peroxynitrite in METH-induced dopaminergic, we investigated the production of 3-nitrotyrosine (3-NT) in the mouse striatum. The levels of 3-NT increased in the striatum of wild-type mice treated with multiple doses of METH (4 x 10 mg/kg, 2 h interval) as compared with the controls. However, no significant production of 3-NT was observed either in the striata of neuronal nitric oxide synthase knockout mice (nNOS -/-) or copper-zinc superoxide dismutase overexpressed transgenic mice (SOD-Tg) treated with similar doses of METH. The dopaminergic damage induced by METH treatment was also attenuated in nNOS-/- or SOD-Tg mice. These data further confirm that METH causes its neurotoxic effects via the production of peroxynitrite.

Effect of overexpression of wild-type and mutant Cu/Zn-superoxide dismutases on oxidative damage and antioxidant defences: relevance to Down's syndrome and familial amyotrophic lateral sclerosis

Patients with Down's syndrome (DS) show elevated levels of copper, zinc-containing superoxide dismutase (SOD1) and appear to have increased lipid peroxidation and oxidative damage to DNA as well as elevated glutathione peroxidase activity. Increasing SOD1 levels by gene transfection in NT-2 and SK-N-MC cell lines also led to a rise in glutathione peroxidase activity, but this was nevertheless accompanied by decreased proliferation rates, increased lipid peroxidation and protein carbonyls, and a trend to a rise in 8-hydroxyguanine and protein-bound 3-nitrotyrosine. Transfection of these cell lines with DNA encoding two mutant SOD1 enzymes (G37R and G85R) associated with familial amyotrophic lateral sclerosis (FALS), produced similar, but more severe changes, i.e. even lower growth rates, higher lipid peroxidation, 3-nitrotyrosine and protein carbonyl levels, decreased GSH levels, raised GSSG levels and higher glutathione peroxidase activities. Since G85R has little SOD activity, these changes cannot be related to increased O(2)(-) scavenging. In no case was SOD2 (mitochondrial Mn-SOD) level altered. Our cellular systems reproduce many of the biochemical changes observed in patients with DS or ALS, and in transgenic mice overexpressing mutant SOD1. They also show the potentially deleterious effects of SOD1 overexpression on cellular proliferation, which may be relevant to abnormal development in DS.

Too much of a good thing: mechanisms of gene action in Down syndrome

The molecular mechanisms underlying the specific traits in individuals with Down syndrome (DS) have been postulated to derive either from nonspecific perturbation of balanced genetic programs, or from the simple, mendelian-like influence of a small subset of genes on chromosome 21. However, these models do not provide a comprehensive explanation for experimental or clinical observations of the effects of trisomy 21. DS is best viewed as a complex genetic disorder, where the specific phenotypic manifestations in a given individual are products of genetic, environmental and stochastic influences. Mouse models that recapitulate both the genetic basis for and the phenotypic consequences of trisomy provide an experimental system to define these contributions.

SOD1 down-regulates NF-kappaB and c-Myc expression in mice after transient focal cerebral ischemia

Reactive oxygen species (ROS) are implicated in reperfusion injury after focal cerebral ischemia (FCI). Reactive oxygen species regulate activity of transcription factors like NF-kappaB. The authors investigated the role of ROS in NF-kappaB activity after FCI using transgenic mice that overexpressed human copper/zinc-superoxide dismutase (SOD1) and that had reduced infarction volume after FCI. Superoxide dismutase transgenic and wild-type mice were subjected to 1 hour of middle cerebral artery occlusion (MCAO) and subsequent reperfusion. Immunohistochemistry showed SOD1 overexpression attenuated ischemia-induced NF-kappaB p65 immunoreactivity. Colocalization of NF-kappaB and the neuronal marker, microtubule-associated proteins (MAPs), showed that NF-kappaB was up-regulated in neurons after FCI. Electrophoretic mobility shift assays showed that SODI overexpression reduced ischemia-induced NF-kappaB DNA binding activity. Supershift assays showed that DNA-protein complexes contained p65 and p50 subunits. Immunoreactivity of c-myc, an NF-kappaB downstream gene, was increased in the ischemic cortex and colocalized with NF-kappaB. Western blotting showed that SOD1 overexpression reduced NF-kappaB and c-Myc protein levels in the ischemic brain. Colocalization of c-Myc and TUNEL staining was observed 24 hours after FCI. The current findings provide the first evidence that SOD1 overexpression attenuates activation of NF-kappaB after transient FCI in mice and that preventing this early activation may block expression of downstream deleterious genes like c-myc, thereby reducing ischemic damage.

Reactive oxygen radicals in signaling and damage in the ischemic brain

Reactive oxygen species have been implicated in brain injury after ischemic stroke. These oxidants can react and damage the cellular macromolecules by virtue of the reactivity that leads to cell injury and necrosis. Oxidants are also mediators in signaling involving mitochondria, DNA repair enzymes, and transcription factors that may lead to apoptosis after cerebral ischemia. Transgenic or knockout mice with cell- or site-specific prooxidant and antioxidant enzymes provide useful tools in dissecting the events involving oxidative stress in signaling and damage in ischemic brain injury.

Endothelial expression of selectins during endotoxin preconditioning

Although bacterial endotoxins [lipopolysaccharide (LPS)] can confer tissue resistance to subsequent inflammatory insults, the mechanisms that underlie this LPS-preconditioning (LPS-PC) response remain poorly defined. The dual-radiolabeled monoclonal antibody technique was used to examine whether LPS-PC alters the upregulation (protein) of E- and P-selectins after subsequent LPS challenge. In the gut of wild-type (C57BL/6J) mice, LPS-PC was associated with a reduction in E- (66%) and P-selectin (33%) expression. A similar reduction in E-selectin expression was observed in mutant mice that were genetically deficient in either the endothelial or inducible isoform of nitric oxide synthase or that overexpressed the human gene for Cu/Zn superoxide dismutase. Severe combined immunodeficient mice, genetically devoid of lymphocytes, did exhibit partial inhibition of the LPS-PC response. We conclude that 1) LPS-PC can be demonstrated for E- and P-selectins in some vascular beds (e.g., gut), 2) the mechanism(s) underlying this blunted selectin response does not include a major role for either nitric oxide and superoxide, and 3) circulating lymphocytes may contribute to the LPS-PC response.

Targeted neuronal gene expression and longevity in Drosophila

Earlier studies from this laboratory have shown that in the insect, Drosophila melanogaster, the motorneuron is an important cellular nexus between the metabolism of reactive oxygen species (ROS) and adult lifespan. This was demonstrated by experiments in which expression of CuZn SOD (SOD1) specifically in motorneurons was shown to extend the mean and maximum adult lifespans to 140% of normal, and to rescue the majority of deliterious phenotypes displayed by SOD1-null mutants. We have interpreted these results to mean either that the lifespan of the organism is normally limited by the functional lifespan of this post-mitotic cell type, or that ROS metabolism in motorneurons affects organismic lifespan via a systemic, perhaps neuroendocrine, signaling mechanism. We have now extended these studies to ask: (i) whether expression of catalase (CAT) or of the mitochondrially-localized Mn SOD (SOD2) in motorneurons, either singly or in combination with SOD1, have similar effects on lifespan; (ii) if expression of SOD2 can rescue SOD1-null mutant phenotypes; and (iii) if ROS metabolism in cell types other than motorneurons has significant impact on aging and lifespan determination.

The involvement of the intracellular superoxide production system in hepatic ischemia-reperfusion injury. In vivo and in vitro experiments using transgenic mice manifesting excessive CuZn-SOD activity

In vivo and in vitro studies were conducted using transgenic mice with 1.8-fold increased SOD activity in the cytoplasmic fraction compared to normal mice in order to evaluate the role of cytoplasmic superoxide dismutase (SOD) in hepatic ischemia-reperfusion injury. In the in vivo study, after inducing 15 min 70% partial hepatic ischemia followed by 45 min reperfusion, we determined the plasma levels of ALT, hyaluronic acid, and phosphatidylcholine hydroperoxide (PCOOH) as the membranous lipoperoxide of the hepatic tissue. In addition, in vitro ischemia-reperfusion studies for cultured hepatocytes were conducted in an anaerobic chamber that could create a hypoxic or oxygen-rich environment in order to clarify the amelioration of reperfusion injuries in the SOD rich hepatocytes. High levels of ALT and PCOOH were found as a result of reperfusion in normal mice, while a suppression of the increase in these levels was noted in the transgenic mice. In both groups, the hyaluronic acid levels were not modified. These results suggest that intracellular superoxide production is involved in the mechanism of hepatic ischemia-reperfusion injury, and that an improvement of the ability to eliminate intracellular superoxide species can contribute to the prevention of reperfusion injury.

Overexpression of CuZnSOD in coronary vascular cells attenuates myocardial ischemia/reperfusion injury

Superoxide dismutase scavenges oxygen radicals, which have been implicated in ischemia/reperfusion (I/R) injury in the heart. Our experiments were designed to study the effect of a moderate increase of copper/zinc superoxide dismutase (CuZnSOD) on myocardial I/R injury in TgN(SOD1)3Cje transgenic mice. A species of 0.8 kb human CuZnSOD mRNA was expressed, and a 273% increase in CuZnSOD activity was detected in the hearts of transgenic mice with no changes in the activities of other antioxidant enzymes. Furthermore, immunoblot analysis revealed no changes in the levels of HSP-70 or HSP-25 levels. Immunocytochemical study indicated that there was increased labeling of CuZnSOD in the cytosolic fractions of both endothelial cells and smooth muscle cells, but not in the myocytes of the hearts from transgenic mice. When these hearts were perfused as Langendorff preparations for 45 min after 35 min of global ischemia, the functional recovery of the hearts, expressed as heart rate x LVDP, was 48 +/- 3% in the transgenic hearts as compared to 30 +/- 5% in the nontransgenic hearts (p <.05). The improved cardiac function was accompanied by a significant reduction in lactate dehydrogenase release from the transgenic hearts. Our results demonstrate that overexpression of CuZnSOD in coronary vascular cells renders the heart more resistant to I/R injury.

Free radical pathways in CNS injury

Free radicals are highly reactive molecules implicated in the pathology of traumatic brain injury and cerebral ischemia, through a mechanism known as oxidative stress. After brain injury, reactive oxygen and reactive nitrogen species may be generated through several different cellular pathways, including calcium activation of phospholipases, nitric oxide synthase, xanthine oxidase, the Fenton and Haber-Weiss reactions, by inflammatory cells. If cellular defense systems are weakened, increased production of free radicals will lead to oxidation of lipids, proteins, and nucleic acids, which may alter cellular function in a critical way. The study of each of these pathways may be complex and laborious since free radicals are extremely short-lived. Recently, genetic manipulation of wild-type animals has yielded species that over- or under-express genes such as, copper-zinc superoxide dismutase, manganese superoxide dismutase, nitric oxide synthase, and the Bcl-2 protein. The introduction of the species has improved the understanding of oxidative stress. We conclude here that substantial experimental data links oxidative stress with other pathogenic mechanisms such as excitotoxicity, calcium overload, mitochondrial cytochrome c release, caspase activation, and apoptosis in central nervous system (CNS) trauma and ischemia, and that utilization of genetically manipulated animals offers a unique possibility to elucidate the role of free radicals in CNS injury in a molecular fashion.

Neonatal mouse cardiac myocytes exhibit cardioprotection induced by hypoxic and pharmacologic preconditioning and by transgenic overexpression of human Cu/Zn superoxide dismutase

Although mouse models have been increasingly used for studies of cardiac pathophysiology, there is little information regarding cultured murine cardiac myocytes. Accordingly, we have developed a cell culture model of neonatal mouse cardiac myocytes by modifying a protocol used to prepare neonatal rat myocytes. The principal change is the substitution of cytosine arabinoside for bromodeoxyuridine to prevent fibroblast proliferation. Neonatal murine myocytes exhibited persistent spontaneous contraction and were viable for up to 14 days in culture. By flow cytometry 85% of the cells were cardiac myocytes. In sparse cultures (average cell density 259 cells/mm(2)), both hypoxic preconditioning (n=5) and phenylephrine pretreatment (n=8) produced significant protection of cardiac myocytes from cell death during a prolonged period of severe hypoxia (<0.5% O(2)for 18-20 h, both P<0.05). The phenylephrine effect was inhibited by the alpha(1)-adrenoceptor antagonist prazosin (n=4, P<0.05) and by an xi PKC peptide antagonist (xi V1-2) coupled to a TAT peptide (n=5, P<0. 05). Interestingly, the mixed alpha(1)- and beta -adrenoceptor agonist norepinephrine, which stimulates hypertrophy as measured by(14)[C]phenylalanine incorporation in neonatal rat cardiac myocytes, did not cause hypertrophy in mouse myocytes, suggesting that the signaling pathways for myocardial protection and hypertrophy are likely to be both divergent and species specific. In cardiac myocytes prepared from transgenic mice either homozygous or heterozygous for human Cu/Zn superoxide dismutase, there was protection from cell death (n=3) and restoration of(14)[C]phenyl- alanine uptake (n=4) during prolonged hypoxia (1% O(2)for 3 days, both P<0.05). We conclude that this cellular model, which is relatively simple to prepare, can be used for in-vitro examination of cardiac protection induced by preconditioning agents, various transgenes, and potentially by targeted gene deletions.

Docosahexaenoic acid-deficient phosphatidyl serine and high alpha-tocopherol in a fetal mouse brain over-expressing Cu/Zn-superoxide dismutase

The over-expressed Cu/Zn-superoxide dismutase (Cu/Zn-SOD) gene has been found in some circumstances phenotypically deleterious and associated with oxidative injury-mediated aberrations while in other studies it was considered neuroprotective. In this work we examine a number of biochemical markers in fetal and adult brain from transgenic (tg) mice expressing the human Cu/Zn-SOD gene, which may determine this dual characteristic. These markers include the polyunsaturated fatty acid (PUFA) profile in discrete phospholipid species, the alpha-tocopherol levels, a marker for lipid anti-oxidant status, and thiobarbituric acid reactive substance (TBARS), a marker for the tissue oxidative status. The PUFA profile in choline- and ethanolamine-phosphoglycerides was similar in tg and nontransgenic (ntg) animals of either fetal or adult brain. Serine-phosphoglycerides, however, showed a marked decrease from 20. 07+/-0.53 to 14.92+/-0.87 wt% and 14.52+/-1.15 wt% in docosahexaenoic acid (DHA; 22:6 n3), in the tg 51 and tg 69 fetal brains, respectively, but not in the comparable adult tissues. The alpha-tocopherol levels were significantly higher in the fetal compared to the adult brain. There were no differences in the anti-oxidant levels between the ntg and tg fetal brains, but there were differences in the adult animals; the tg mice were higher by at least two-fold than the control animals. The basal TBARS in the tg 51 fetal brain was 35% lower than that of ntg mouse and in the presence of Fe(2+), brain slices from the former released less TBARS (57% reduction) into the medium than the latter. These results suggest that higher dosages of Cu/Zn-SOD gene are compatible with increased alpha-tocopherol levels, reduced basal TBARS levels and a DHA deficiency in the fetal, but not the adult, tg brain.

Overexpression of Cu,Zn superoxide dismutase attenuates oxidative inhibition of astrocyte glutamate uptake

Glutamate neurotoxicity in brain is normally prevented by rapid uptake of glutamate by astrocytes. Increased expression of Cu,Zn superoxide dismutase (SOD1) can increase resistance to cerebral ischemia and other oxidative insults, but the cellular mechanisms by which this occurs are not well established. Here we examine whether increased SOD1 expression can attenuate inhibition of astrocyte glutamate uptake by reactive oxygen species. Primary cortical astrocyte cultures were prepared from transgenic mice that overexpress human SOD1 and from nontransgenic littermate controls. Glutamate uptake was assessed after exposure of these cultures to xanthine oxidase plus hypoxanthine, an extracellular superoxide generating system, or to menadione, which generates superoxide in the cytosol. These treatments produced dose-dependent reductions in astrocyte glutamate uptake, and the reductions were significantly attenuated in the SOD1 transgenic astrocytes. A specific effect of reactive oxygen species on glutamate transporters was suggested by the much smaller inhibitory effects of xanthine oxidase/hypoxanthine and menadione on GABA uptake than on glutamate uptake. These findings suggest that the cerebroprotective effects of increased SOD1 expression during cerebral ischemia-reperfusion could be mediated in part by astrocyte glutamate transport.

Absence of p53: no effect in a transgenic mouse model of familial amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis (ALS) has been linked in some families to dominantly inherited mutations in the gene encoding copper-zinc superoxide dismutase 1 (Cu-Zn SOD1). Transgenic mice expressing a mutant human Cu-Zn SOD1 (G93A) develop a dominantly inherited adult-onset paralytic disorder that replicates many of the clinical and pathological features of familial ALS. Increased p53 immunoreactivity has been reported in the motor cortex and spinal ventral horns of postmortem tissue from ALS patients. The nuclear phosphoprotein p53 is an important regulator of cellular proliferation, and increasing evidence supports the role of p53 in regulating cellular apoptosis. To assess the role of p53-mediated apoptosis in amyotrophic lateral sclerosis, mice deficient in both p53 alleles (p53-/-) were crossed with transgenic mice expressing the G93A mutant (G93A+), creating novel transgenic knockout mice. The animals (p53 +/+G93A+, p53+/-G93A+, p53-/-G93A+) were examined at regular intervals for cage activity, upper and lower extremity strength, and mortality. At 120 days from birth mice from each genotype were sacrificed, and L2-L3 anterior horn motor neurons were counted. There was no significant difference in time to onset of behavioral decline, mortality, or motor neuron degeneration between the different genotypes. Despite evidence that p53 plays an important role after acute neuronal injury, the current study suggests that p53 is not significantly involved in cell death in the G93A+ transgenic mouse model of familial ALS.

Mice that overexpress Cu/Zn superoxide dismutase are resistant to allergen-induced changes in airway control

Within the respiratory epithelium of asthmatic patients, copper/zinc-containing superoxide dismutase (Cu/Zn SOD) is decreased. To address the hypothesis that lung Cu/Zn SOD protects against allergen-induced injury, wild-type and transgenic mice that overexpress human Cu/Zn SOD were either passively sensitized to ovalbumin (OVA) or actively sensitized by repeated airway exposure to OVA. Controls included nonsensitized wild-type and transgenic mice given intravenous saline or airway exposure to saline. After aerosol challenge to saline or OVA, segments of tracheal smooth muscle were obtained for in vitro analysis of neural control. In response to electrical field stimulation, wild-type sensitized mice challenged with OVA had significant increases in cholinergic reactivity. Conversely, sensitized transgenic mice challenged with OVA were resistant to changes in neural control. Stimulation of tracheal smooth muscle to elicit acetylcholine release showed that passively sensitized wild-type but not transgenic mice released more acetylcholine after OVA challenge. Function of the M(2) muscarinic autoreceptor was preserved in transgenic mice. These results demonstrate that murine airways with elevated Cu/Zn SOD were resistant to allergen-induced changes in neural control.

Spreading depression-induced expression of c-fos and cyclooxygenase-2 in transgenic mice that overexpress human copper/zinc-superoxide dismutase

Spreading depression (SD) is a wave of sustained depolarization challenging the energy metabolism of cells without causing irreversible damage. SD is a major mechanism of gene induction that takes place in cortical injury, including ischemia. We studied the role of oxygen radicals in SD-induced c-fos and cyclooxygenase-2 (COX-2) induction using transgenic (Tg) mice that overexpress copper/zinc-superoxide dismutase (SOD1). The frequency, amplitude and duration of SD waves were similar in the Tg mice and wild-type littermates. c-fos and COX-2 mRNAs were strongly induced 1 and 4 h after SD. The induction of both genes was slightly but significantly less at 4 h in the Tg mice. The results indicate that even a mild, noninjurious metabolic stimulation increases the concentration of oxygen radicals to the level that contributes to gene expression.

Role of superoxide in hemorrhagic shock-induced P-selectin expression

Superoxide has been implicated in the regulation of endothelial cell adhesion molecule expression and the subsequent initiation of leukocyte-endothelial cell adhesion in different experimental models of inflammation. The objective of this study was to assess the contribution of oxygen radicals to P-selectin expression in a murine model of whole body ischemia-reperfusion, i.e., hemorrhage-resuscitation (H/R), with the use of different strategies that interfere with either the production (allopurinol, CD11/CD18-deficient or p47(phox)-/- mice) or accumulation [intravenous superoxide dismutase (SOD), mutant mice that overexpress SOD] of oxygen radicals. P-selectin expression was quantified in different regional vascular beds by use of the dual-radiolabeled monoclonal antibody technique. H/R elicited a significant increase in P-selectin expression in all vascular beds. This response was blunted in SOD transgenic mice and in wild-type mice receiving either intravenous SOD or the xanthine oxidase inhibitor allopurinol. Mice genetically deficient in either a subunit of NADPH oxidase or the leukocyte adhesion molecule CD11/CD18 also exhibited a reduced P-selectin expression. These results implicate superoxide, derived from both xanthine oxidase and NADPH oxidase, as mediators of the increased P-selectin expression observed in different regional vascular beds exposed to hemorrhage and retransfusion.

Role of CuZn superoxide dismutase in regulating lymphocyte apoptosis during sepsis

OBJECTIVE

The lymphocyte is a principal mediator of the inflammatory response, and lymphocyte depletion via apoptosis may be an important mechanism of modulating inflammation. Increased oxygen consumption occurs during sepsis and results in the generation of reactive oxygen species. Although reactive oxygen species initiate apoptosis in many biological systems, their role in controlling lymphocyte apoptosis during sepsis is unclear. The objective of this study was to better characterize the role of oxidative stress in precipitating lymphocyte apoptosis during sepsis and to specifically define the role of the CuZn superoxide dismutase (SOD) enzyme complex, a major antioxidant defense, in modulating this process.

DESIGN

Prospective, randomized, controlled study.

SETTING

Research laboratory at an academic medical center.

SUBJECTS

Mice that were either genetically normal or that were deficient in or overexpressed the enzyme CuZn SOD.

INTERVENTIONS

Mice from each genetic group were randomized to no manipulation (control), sham surgery, or cecal ligation and puncture. Mice were killed 18-24 hrs after study entry, and the thymi and spleen were removed for analysis of apoptosis.

MEASUREMENTS AND MAIN RESULTS

Lymphocyte apoptosis was assessed by three independent methods: light microscopy, fluorescent terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling, and DNA gel electrophoresis. Comparisons were performed using standard parametric statistical tests. Lymphocyte apoptosis was present in mice after CLP but not in control mice or in mice after sham surgery (p < .05). Mice completely lacking CuZn SOD developed significantly more lymphocyte apoptosis than did either partially CuZn SOD-deficient or genetically normal mice (p < .05). This apoptosis was more pronounced in the thymus than the spleen and, within the thymus, more prominent in the cortex than medulla (p < .05 for all). In contrast, mice that overexpressed CuZn SOD did not differ in the amount of apoptosis after CLP compared with genetically normal mice (p = NS for all).

CONCLUSIONS

Oxidative stress occurs in sepsis and appears to be one stimulus for the development of lymphocyte apoptosis, a process that is partly regulated by CuZn SOD. However, we were unable to demonstrate that overexpression of this enzyme suppressed lymphocyte apoptosis, suggesting that either other antioxidant defenses or other pathways independent of oxidative stress may mediate lymphocyte elimination in this syndrome.

Regulation of E-selectin expression in postischemic intestinal microvasculature

Monolayers of cultured endothelial cells exposed to hypoxia-reoxygenation exhibit a transcription-dependent increase in E-selectin expression and E-selectin-dependent neutrophil-endothelial cell adhesion. The overall objectives of this study were 1) to determine whether ischemia-reperfusion (I/R) promotes upregulation of E-selectin in vivo; 2) if so, to define the mediators of this response; and 3) to assess the contribution of E-selectin to I/R-induced neutrophil recruitment. The dual-radiolabeled monoclonal antibody (MAb) technique was used to measure E-selectin expression in the intestinal vasculature. Ischemia was induced by complete occlusion (30-60 min) of the superior mesenteric artery followed by 3-24 h of reperfusion. Increasing durations of ischemia elicited progressively increasing (2- to 5-fold) levels of E-selectin expression, with the peak response noted after 45 min of ischemia and 5 h of reperfusion. Subsequent experiments revealed that I/R-induced increase in E-selectin expression (at 5 h) is significantly blunted in transgenic mice that overexpress Cu,Zn-superoxide dismutase or by treatment of wild-type mice with either a blocking antibody against tumor necrosis factor (TNF)-alpha or an inhibitor of nuclear factor-kappaB (NF-kappaB) activation (PS341). Administration of an E-selectin-specific MAb dramatically reduced I/R-induced recruitment of neutrophils in the intestine. These findings suggest that superoxide and TNF-alpha mediate gut I/R-induced E-selectin expression via an NF-kappaB-dependent mechanism; this upregulation of E-selectin contributes significantly to I/R-induced neutrophil recruitment.

The cytosolic antioxidant copper/zinc-superoxide dismutase prevents the early release of mitochondrial cytochrome c in ischemic brain after transient focal cerebral ischemia in mice

Release of mitochondrial cytochrome c into the cytosol is a critical step in apoptosis. We have reported that early release of cytochrome c in vivo occurs after permanent focal cerebral ischemia (FCI) and is mediated by the mitochondrial antioxidant manganese superoxide dismutase (SOD). However, the role of reactive oxygen species produced after ischemia-reperfusion in the mitochondrial apoptosis process is still unknown, although overexpression of copper/zinc-SOD (SOD1), a cytosolic isoenzyme, protects against ischemia-reperfusion. We now hypothesize that the overexpression of SOD1 also prevents apoptosis after FCI. To address this issue, we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and in SOD1 transgenic (Tg) mice after transient FCI. Cytosolic cytochrome c was detected as early as 2 hr after reperfusion, and correspondingly, mitochondrial cytochrome c was significantly reduced after FCI. Cytosolic cytochrome c was significantly lower in the SOD1 Tg mice compared with wild types 2 (p < 0.0001) and 4 (p < 0.05) hr after FCI. Apaf-1, which interacts with cytochrome c and activates caspases, was constitutively expressed in both groups of animals, with no alteration after FCI. Double staining with cytochrome c immunohistochemistry and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling showed a spatial relationship between cytosolic cytochrome c expression and DNA fragmentation. A significant amount of DNA laddering was detected 24 hr after ischemia and was reduced in SOD1 Tg mice. These data suggest that SOD1 blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after transient FCI.

Overexpression of copper/zinc superoxide dismutase does not prevent neonatal lethality in mutant mice that lack manganese superoxide dismutase

There are two types of intracellular superoxide dismutases: the mitochondrial manganese SOD (MnSOD) and the cytoplasmic copper/zinc SOD (CuZnSOD). Mutant mice that lack MnSOD die shortly after birth because of cardiomyopathy and mitochondrial injury. In order to verify if CuZnSOD could compensate for MnSOD deficiency, a new mutant mouse that overexpresses CuZnSOD but is deficient in MnSOD was generated by crossing MnSOD knockout mice with CuZnSOD transgenic mice. CuZnSOD activity was significantly increased in the blood, brain, liver, and heart of MnSOD knockout, CuZnSOD transgenic mice when compared with nontransgenic mice. However, overexpression of CuZnSOD did not prevent neonatal lethality in mice that lack MnSOD, nor did it prevent oxidative aconitase inactivation, nor did it rescue MnSOD-deficient astrocytes in culture. Based on our findings, which emphasize the strong enzymatic compartmentalization of CuZnSOD and MnSOD, therapeutic antioxidant strategies should consider the final intracellular localization of the antioxidant used, especially when those strategies are directed against mitochondrial diseases.

The cytosolic antioxidant copper/zinc-superoxide dismutase prevents the early release of mitochondrial cytochrome c in ischemic brain after transient focal cerebral ischemia in mice

Release of mitochondrial cytochrome c into the cytosol is a critical step in apoptosis. We have reported that early release of cytochrome c in vivo occurs after permanent focal cerebral ischemia (FCI) and is mediated by the mitochondrial antioxidant manganese superoxide dismutase (SOD). However, the role of reactive oxygen species produced after ischemia-reperfusion in the mitochondrial apoptosis process is still unknown, although overexpression of copper/zinc-SOD (SOD1), a cytosolic isoenzyme, protects against ischemia-reperfusion. We now hypothesize that the overexpression of SOD1 also prevents apoptosis after FCI. To address this issue, we examined the subcellular distribution of the cytochrome c protein in both wild-type mice and in SOD1 transgenic (Tg) mice after transient FCI. Cytosolic cytochrome c was detected as early as 2 hr after reperfusion, and correspondingly, mitochondrial cytochrome c was significantly reduced after FCI. Cytosolic cytochrome c was significantly lower in the SOD1 Tg mice compared with wild types 2 (p < 0.0001) and 4 (p < 0.05) hr after FCI. Apaf-1, which interacts with cytochrome c and activates caspases, was constitutively expressed in both groups of animals, with no alteration after FCI. Double staining with cytochrome c immunohistochemistry and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling showed a spatial relationship between cytosolic cytochrome c expression and DNA fragmentation. A significant amount of DNA laddering was detected 24 hr after ischemia and was reduced in SOD1 Tg mice. These data suggest that SOD1 blocks cytosolic release of cytochrome c and could thereby reduce apoptosis after transient FCI.

The neuroprotective effect of deferoxamine in the hypoxic-ischemic immature mouse brain

The iron chelator deferoxamine is efficacious in ameliorating hypoxic-ischemic brain injury in some models, perhaps by decreasing oxidative stress. Transgenic copper/zinc superoxide dismutase-1 (SOD1) overexpression in neonatal mice increases brain injury after hypoxia-ischemia compared to non-transgenic wildtype littermates because of increased oxidative stress. A neonatal mouse model of hypoxia-ischemia was used to examine histopathological damage, iron histochemistry and free iron concentration in the brains of SOD1 transgenic and non-transgenic littermates. Deferoxamine significantly decreased injury in non-transgenics compared to controls with a trend toward neuroprotection in the transgenics. There was no difference in free iron concentrations in the brains of SOD1 overexpressors or non-transgenics. Deferoxamine may protect the neonatal brain by a number of anti-oxidant mechanisms including iron chelation, enhancement of stress gene expression, or induction of other factors responsible for neuroprotection.

The use of transgenic and mutant mice to study oxygen free radical metabolism

To distinguish the role of Mn superoxide dismutase (MnSOD) from that of cytoplasmic CuZn superoxide dismutase (CuZnSOD), the mouse MnSOD gene (Sod2) was inactivated by homologous recombination. Sod2 -/- mice on a CD1 (outbred) genetic background die within the first 10 days of life (mean, 5.4 days) with a complex phenotype that includes dilated cardiomyopathy, accumulation of lipid in liver and skeletal muscle, metabolic acidosis and ketosis, and a severe reduction in succinate dehydrogenase (complex II) and aconitase (a TCA cycle enzyme) activities in the heart and, to a lesser extent, in other organs. These findings indicate that MnSOD is required to maintain the integrity of mitochondrial enzymes susceptible to direct inactivation by superoxide. On the other hand, Lebovitz et al. reported an independently derived MnSod null mouse (Sod2tmlLeb) on a mixed C57BL/6 and 129Sv background with a different phenotype. Because a difference in genetic background is the most likely explanation for the phenotypic differences, the two mutant lines were crossed into different genetic backgrounds for further analyses. To study the phenotype of Sod2tmlLeb mice CD1 background, the Sod2tmlLeb mice were crossed to CD1 for two generations before the -/+ mice were intercrossed to generate -/- mice. The life span distribution of CD1 < Sod2-/- > Leb was shifted to the left, indicating a shortened life span on the CD1 background. Furthermore, the CD1 < Sod2-/- > Leb mice develop metabolic acidosis at an early stage as was observed with CD1 < Sod2-/- > Cje. When Sod2tmlCje was placed on C57BL/6J (B6) background, the -/- mice were found to die either during midgestation or within the first 4 days after birth. However, when the B6 < Sod2 -/+ > Cje were crossed with DBA/2J (D2) for the generation of B6D2F2 < Sod2-/- > Cje mice, an entirely different phenotype, similar to that described by Lebovitz et al., was observed. The F2 Sod -/- mice were able to survive up to 18 days, and the animals that lived for more than 15 days displayed neurological abnormalities including ataxia and seizures. Their hearts were not as severely affected as were those of the CD1 mice, and neurological degeneration rather than heart defect appears to be the cause of death.

Differing effects of copper,zinc superoxide dismutase overexpression on neurotoxicity elicited by nitric oxide, reactive oxygen species, and excitotoxins

Overexpression of Cu,Zn superoxide dismutase (SOD1) reduces ischemic injury in some stroke models but exacerbates injury in a neonatal stroke model and in other settings. The current study used a SOD1 transgenic (SOD1-Tg) murine cortical culture system, derived from the same mouse strain previously used for the stroke models, to identify conditions that determine whether SOD1 overexpression in neurons is protective or detrimental. The nitric oxide (NO) donors S-nitroso-N-acetylpenicillamine, spermine-NONOate, and diethylamine-NONOate produced less death in SOD1-Tg neurons than in wild-type neurons (p < 0.01). Also, NO produced markedly less 3-nitrotyosine in SOD1-Tg cells. In contrast, the superoxide generator menadione produced significantly greater death and nearly twice as much 2'7'-dichlorofluorescein fluorescence in SOD1-Tg neurons than in wild-type neurons, suggesting increased peroxide formation in the SOD1-Tg cells. No significant difference was observed in the vulnerability of the two cell types to H2O2, the product of the SOD reaction. Overexpression of SOD1 also had no effect on neuronal vulnerability to glutamate, N-methyl-D-aspartate, or kainate. These observations suggest that SOD1 overexpression can reduce neuronal death under conditions where peroxynitrite formation is a significant factor, but may exacerbate neuronal death under conditions of rapid intracellular superoxide formation or impaired H2O2 disposal.

Upregulation of GABA neurotransmission suppresses hippocampal excitability and prevents long-term potentiation in transgenic superoxide dismutase-overexpressing mice

Cu/Zn superoxide dismutase (SOD-1) is a key enzyme in oxygen metabolism in the brain. Overexpression of SOD-1 in transgenic (Tg) mice has been used to study the functional roles of this enzyme in oxidative stress, lipid peroxidation, and neurotoxicity. We found that Tg-SOD-1 mice are strikingly less sensitive to kainic acid-induced behavioral seizures than control mice. Furthermore, the hippocampus of Tg-SOD-1 mice was far less sensitive to local application of bicuculline, a GABA-A antagonist, than the hippocampus of control mice. GABAergic functions, expressed in extracellular paired-pulse depression, and in IPSCs recorded in dentate granular cells were enhanced in Tg-SOD-1 mice. Finally, long-term potentiation (LTP), not found in the dentate gyrus of Tg-SOD-1 mice, could be restored by local blockade of inhibition and could be blocked in control mice by injection of diazepam, which amplifies inhibition. These results indicate that constitutive elevation of SOD-1 activity exerts a major effect on neuronal excitability in the hippocampus, which, in turn, controls hippocampal ability to express LTP.

Overexpression of copper and zinc superoxide dismutase in transgenic mice prevents the induction and activation of matrix metalloproteinases after cold injury-induced brain trauma

Matrix metalloproteinases (MMPs), a family of proteolytic enzymes which degrade the extracellular matrix, are implicated in blood-brain barrier disruption, which is a critical event leading to vasogenic edema. To investigate the role of reactive oxygen species (ROS) in the expression of MMPs in vasogenic edema, the authors measured gelatinase activities before and after cold injury (CI) using transgenic mice that overexpress superoxide dismutase-l. A marked induction of pro-gelatinase B (pro-MMP-9) was seen 2 hours after CI and was maximized at 12 hours in wild-type mice. The pro-MMP-9 level was significantly lower in transgenic mice 4 hours (P < 0.001) and 12 hours (P < 0.05) after CI compared to wild-type mice. The activated MMP-9 was detected from 6 to 24 hours after injury. A mild induction of pro-gelatinase A (pro-MMP-2) was seen at 6 hours and was sustained until 7 days. In contrast. the activated form of MMP-2 appeared at 24 hours, was maximized at 7 days, and was absent in transgenic mice. Western blot analysis showed that the tissue inhibitors of metalloproteinases were not modified after CI. The results suggest that ROS production after CI may contribute to the induction and/or activation of MMPs and could thereby exacerbate endothelial cell injury and the development of vasogenic edema after injury. Key Words: Metalloproteinases-Brain-Vasogenic edema-Reactive oxygen species-Superoxide dismutase.

Upregulation of GABA neurotransmission suppresses hippocampal excitability and prevents long-term potentiation in transgenic superoxide dismutase-overexpressing mice

Cu/Zn superoxide dismutase (SOD-1) is a key enzyme in oxygen metabolism in the brain. Overexpression of SOD-1 in transgenic (Tg) mice has been used to study the functional roles of this enzyme in oxidative stress, lipid peroxidation, and neurotoxicity. We found that Tg-SOD-1 mice are strikingly less sensitive to kainic acid-induced behavioral seizures than control mice. Furthermore, the hippocampus of Tg-SOD-1 mice was far less sensitive to local application of bicuculline, a GABA-A antagonist, than the hippocampus of control mice. GABAergic functions, expressed in extracellular paired-pulse depression, and in IPSCs recorded in dentate granular cells were enhanced in Tg-SOD-1 mice. Finally, long-term potentiation (LTP), not found in the dentate gyrus of Tg-SOD-1 mice, could be restored by local blockade of inhibition and could be blocked in control mice by injection of diazepam, which amplifies inhibition. These results indicate that constitutive elevation of SOD-1 activity exerts a major effect on neuronal excitability in the hippocampus, which, in turn, controls hippocampal ability to express LTP.

Evidence against the generation of free hydroxyl radicals from the interaction of copper,zinc-superoxide dismutase and hydrogen peroxide

Prior spin trapping studies reported that H(2)O(2) is metabolized by copper,zinc-superoxide dismutase (SOD) to form (.)OH that is released from the enzyme, serving as a source of oxidative injury. Although this mechanism has been invoked in a number of diseases, controversy remains regarding whether the hydroxylation of spin traps by SOD is truly derived from free (.)OH or (.)OH scavenged off the Cu(2+) catalytic site. To distinguish whether (.)OH is released from the enzyme, a comprehensive EPR investigation of radical production and the kinetics of spin trapping was performed in the presence of a series of structurally different (.)OH scavengers including ethanol, formate, and azide. Although each of these have similar potency in scavenging (.)OH as the spin trap 5, 5-dimethyl-1-pyrroline-N-oxide and form secondary radical adducts, each exhibited very different potency in scavenging (.)OH from SOD. Ethanol was 1400-fold less potent than would be expected for reaction with free (.)OH. The anionic scavenger formate, which readily accesses the active site, was still 10-fold less effective than would be predicted for free (.)OH, whereas azide was almost 2-fold more potent than would be predicted. Analysis of initial rates of adduct formation indicated that these reactions did not involve free (.)OH. EPR studies of the copper center demonstrated that while high H(2)O(2) concentrations induce release of Cu(2+), the magnitude of spin adducts produced by free Cu(2+) was negligible compared with that from intact SOD. Further studies with a series of peroxidase substrates demonstrated that characteristic radicals formed by peroxidases were also efficiently generated by H(2)O(2) and SOD. Thus, SOD and H(2)O(2) oxidize and hydroxylate substrates and spin traps through a peroxidase reaction with bound (.)OH not release of (.)OH from the enzyme.

Transcriptional induction of metallothionein-I and -II genes in the livers of Cu,Zn-superoxide dismutase knockout mice

The levels of metallothionein-I and -II (MT-I and MT-II) mRNAs were elevated (10- to 12-fold), specifically in the livers of mice with homozygous deletion of the gene for Cu,Zn-SOD (Sod1-/-), the enzyme that catalyzes the removal of O(-)(2). The induction of MT mRNA occurred primarily at the level of transcription. In vivo genomic footprinting of the MT-I promoter region revealed distinctive footprinting at MRE-d, MRE-c, and MLTF/ARE sites in the livers of knockout mice. MTF-1, the key factor responsible for the heavy-metal and oxidative stress-induced expression of the MT-I gene, was activated 3-fold in the nuclear extract from the livers of Cu,Zn-SOD null mice. Because metallothioneins are potent scavengers of reactive oxygen species and protect cells from oxidative stress, the apparent normal characteristics of the mice with the disrupted Cu, Zn-SOD gene are probably due to overexpression of MT-I and MT-II in the livers of these animals.

Copper-zinc superoxide dismutase prevents the early decrease of apurinic/apyrimidinic endonuclease and subsequent DNA fragmentation after transient focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

DNA damage and its repair mechanism are thought to be involved in ischemia/reperfusion injury in the brain. We have previously shown that apurinic/apyrimidinic endonuclease (APE/Ref-1), a multifunctional protein in the DNA base excision repair pathway, rapidly decreased after transient focal cerebral ischemia (FCI) before the peak of DNA fragmentation. To further investigate the role of reactive oxygen species in APE/Ref-1 expression in vivo, we examined the expression of APE/Ref-1 and DNA damage after FCI in wild-type and transgenic mice overexpressing copper-zinc superoxide dismutase.

METHODS

Transgenic mice overexpressing copper-zinc superoxide dismutase and wild-type littermates were subjected to 60 minutes of transient FCI by intraluminal blockade of the middle cerebral artery. APE/Ref-1 protein expression was analyzed by immunohistochemistry and Western blot analysis. DNA damage was evaluated by gel electrophoresis and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling (TUNEL).

RESULTS

A similar level of APE/Ref-1 was detected in the control brains from both groups. APE/Ref-1 was significantly reduced 1 hour after transient FCI in both groups, whereas the transgenic mice had less reduction than that seen in wild-type mice 1 and 4 hours after FCI. DNA laddering was detected 24 hours after FCI and was decreased in transgenic mice. Double staining with APE/Ref-1 and TUNEL showed that the neurons that lost APE/Ref-1 immunoreactivity became TUNEL positive.

CONCLUSIONS

These results suggest that reactive oxygen species contribute to the early decrease of APE/Ref-1 and thereby exacerbate DNA fragmentation after transient FCI in mice.

Exacerbation of delayed cell injury after transient global ischemia in mutant mice with CuZn superoxide dismutase deficiency

BACKGROUND AND PURPOSE

We have demonstrated that copper-zinc superoxide dismutase (CuZn-SOD), a cytosolic isoenzyme of SODs, has a protective role in the pathogenesis of superoxide radical-mediated brain injury. Using mice bearing a disruption of the CuZn-SOD gene (Sod1), the present study was designed to clarify the role of superoxide anion in the pathogenesis of selective vulnerability after transient global ischemia.

METHODS

Sod1 knockout homozygous mutant mice (Sod1 -/-) with a complete absence of endogenous CuZn-SOD activity, heterozygous mutant mice (Sod1 +/-) with a 50% decrease in the activity, and littermate wild-type mice (male, 35 to 45 g) were subjected to global ischemia. Since the plasticity of the posterior communicating artery (PcomA) has been reported to influence the outcome of hippocampal injury, we assessed the relation between the plasticity of PcomAs and the decrease of regional cerebral blood flow in global ischemia.

RESULTS

The fluorescence intensity of hydroethidine oxidation, a measurement of ethidium fluorescence for superoxide radicals, was increased in mutant mice 1 day after both 5 and 10 minutes of global ischemia, compared with wild-type mice. Hippocampal injury in the PcomA hypoplastic brains showed significant exacerbation in mutant mice compared with wild-type littermates 3 days after 5 minutes of global ischemia, although a marked difference was not observed at 1 day.

CONCLUSIONS

These data suggest that superoxide radicals play an important role in the pathogenesis of delayed injury in the vulnerable hippocampal CA1 subregion after transient global ischemia.

Overexpression of human copper/zinc superoxide dismutase in transgenic mice attenuates oxidative stress caused by methylenedioxymethamphetamine (Ecstasy)

Administration of 3,4-methylenedioxymethamphetamine (4 x 20 mg/kg) to non-transgenic CD-1 mice caused marked depletion in dopamine, 3,4-dihydroxyphenylacetic acid and 5-hydroxytryptamine in the caudate-putamen. There were no significant changes in serotonergic markers in the hippocampus and frontal cortex. Homozygous and heterozygous copper/zinc superoxide dismutase transgenic mice show partial protection against the toxic effects of 3,4-methylenedioxymethamphetamine on striatal dopaminergic markers. In addition, 3,4-methylenedioxymethamphetamine injections caused marked decreases in copper/zinc superoxide dismutase activity in the frontal cortex, caudate-putamen and hippocampus of wild-type mice. Moreover, there were concomitant 3,4-methylenedioxymethamphetamine-induced decreases in catalase activity in the caudate-putamen and hippocampus, decreases in glutathione peroxidase activity in the frontal cortex as well as increases in lipid peroxidation in the frontal cortex, caudate-putamen, and hippocampus of wild-type mice. In contrast, administration of 3,4-methylenedioxymethamphetamine to homozygous superoxide dismutase transgenic mice caused no significant changes in antioxidant enzyme activities nor in lipid peroxidation. These results provide further substantiation of a role for oxygen-based radicals in 3,4-methylenedioxymethamphetamine-induced neurotoxicity. The present data also suggest that free radicals generated during 3,4-methylenedioxymethamphetamine administration may perturb antioxidant enzymes. Consequently, there might be further overproduction of free radicals with associated peroxidative damage to cell membranes and associated terminal degeneration.

Targeted expression of human CuZn superoxide dismutase gene in mouse central nervous system

Copper zinc superoxide dismutase (CuZnSOD) is an important enzyme for the detoxification of reactive oxygen species. Particularly in the central nervous system (CNS), reactive oxygen species are often associated with acute brain injuries and chronic neurodegeneration. It has been demonstrated in vivo that there is an inverse correlation between CuZnSOD activity and neuronal death after acute brain injury. To further understand the protective role of CuZnSOD upon neurons, we have generated transgenic mouse lines with targeted expression of the human CuZnSOD gene (SOD1) that is driven by a rat neuron-specific enolase gene promoter in neurons of the CNS. The transgenic SOD1 expression was restricted to the CNS identified by reverse transcriptase polymerase chain reaction and SOD gel electrophoresis assays. The CuZnSOD activity was significantly increased in the brain stem of the transgenic mice. Immunostaining of human CuZnSOD activity showed that Purkinje cells in the cerebellar cortex were the most intensely stained neurons in the CNS of the transgenic mice.

Ionizing radiation accelerates aortic lesion formation in fat-fed mice via SOD-inhibitable processes

Ionizing radiation promotes formation of reactive oxygen species, including the superoxide anion (O2-). To evaluate whether O2- or O2--mediated perturbations may contribute to the known atherogenic effects of radiation, we examined aortic lesion formation in irradiated C57BL/6 mice and evaluated the effects of CuZn-superoxide dismutase (CuZn-SOD) overexpression. Ten-week-old mice were exposed to a 2-, 4-, or 8-Gy dose of 250-keV x-rays to the upper thorax and then placed on a high-fat diet for 18 weeks. Based on quantitative lipid staining of serial sections of the proximal aorta, mean lesion area was increased with increasing radiation dose and was 3-fold greater in 8-Gy-irradiated than sham-irradiated mice (7800+/-2140 versus 2635+/-709 micrometer(2), P<0.05). These effects were absolutely dependent on a high-fat diet, which had to be introduced within 1 to 2 weeks of the radiation exposure, suggesting the early involvement of atherogenic lipoproteins that were elevated in response to the diet. The importance of radiation-induced oxidative stress was supported by the observation of a 2-fold lower mean lesion area in irradiated CuZn-SOD transgenic mice than in their irradiated, nontransgenic littermates (3026+/-1590 versus 6102+/-1834 micrometer(2), P<0.05). Lucigenin-enhanced chemiluminescence, used as an index of aortic O2- concentrations, was significantly elevated in the postradiation period, and this response was reduced in CuZn-SOD transgenics. On the basis of these results, we propose that radiation may be a useful tool for initiating oxidative or redox-regulated events that promote atherogenesis and for testing the antiatherogenic properties of antioxidants.

N-tert-butyl-alpha-phenylnitrone protects against 3,4-methylenedioxymethamphetamine-induced depletion of serotonin in rats

The present study examined the effect of N-tert-butyl-alpha-phenylnitrone (PBN) on 3,4-methylenedioxmathamphetamine (MDMA)-induced depletion of serotonin in the CNS. Rats were treated with two concurrent injections of MDMA (20 mg/kg, s.c.), PBN (50-400 mg/kg dissolved in ethanol, 50 mg/ml of 25% ethanol, i.p.), saline or 25% ethanol, alone or in combination, 6 h apart, and sacrificed 5 days later. Rectal temperature was measured prior to and hourly following the drug injection for 5 h. Monoamine levels in the tissue were measured by HPLC. Density of the 5-HT transporters was assayed by [3H]paroxetine binding. Rectal temperature of rats increased after MDMA, decreased after PBN, ethanol, PBN plus ethanol, and MDMA plus ethanol, and was not significantly altered after MDMA plus PBN. Levels of 5-HT and 5-HIAA in the frontal cortex, hippocampus, striatum, and brain stem of rats decreased significantly after MDMA or MDMA plus ethanol, but not after MDMA plus PBN, PBN plus ethanol (PBN dissolved in ethanol), or ethanol as compared to the saline controls. Levels of 5-HT and 5-HIAA in the brain tissues of rats treated with MDMA plus PBN were elevated as compared to those treated with MDMA plus saline. Similar results were observed in the density of 5-HT transporters in the frontal cortex and hippocampus. These results indicate that scavenging of free radicals of MDMA metabolites or reactive oxygen species by PBN and with lowering of body temperature protected against MDMA-induced depletion of serotonin transmitter.