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

Cold injury in mice: a model to study mechanisms of brain edema and neuronal apoptosis

Small rodents, mice in particular, have been widely used for genetic manipulation because of the extensive knowledge in development, embryology and other molecular aspects of this species. However, the use of mice for neurobiology research in the area of brain edema and neuronal injury has not been common. Here we summarize the studies of cold injury-induced brain edema and neuronal apoptosis using mice. Blood-brain barrier (BBB) permeability, demonstrated by extravasation of a serum albumin tracer, Evans Blue, was increased immediately after the injury and returned to the control level by 24 hr. Water content was maximized at 24 hr, whereas a secondary lesion gradually progressed up to 72 hr after cold injury. The mechanism of the development of the cold injury-induced edema and the secondary lesion, involving of oxygen radicals in particular, was determined using superoxide dismutase (SOD)-1 transgenic (Tg) mice with overexpressed copper, zinc-SOD. All of the parameters, BBB permeability, water content and secondary lesion, were attenuated in the Tg mice as compared to littermate non-Tg mice. This clearly demonstrates that oxygen radicals, superoxide anion in particular, mediate cold injury. We also studied whether apoptosis contributes to brain injury following cold injury. Staining with terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling showed the apoptotic cells widespread throughout the entire lesion while still remaining in the margin. DNA laddering was exhibited by gel electrophoresis. These studies indicate that oxidative mediates the development of cold injury-induced edema and the secondary injury, and induces apoptotic cell death. We believe that cold injury in mice provides a simple animal model to study the pathogenesis of brain edema and apoptosis in genetically altered animals.

Maternal administration of superoxide dismutase and catalase in phenytoin teratogenicity

Embryonic bioactivation and formation of reactive oxygen species (ROS) are implicated in the mechanism of phenytoin teratogenicity. This in vivo study in pregnant CD-1 mice evaluated whether maternal administration of the antioxidative enzymes superoxide dismutase (SOD) and/or catalase conjugated with polyethylene glycol (PEG) could reduce phenytoin teratogenicity. Initial studies showed that pretreatment with PEG-SOD alone (0.5-20 KU/kg i.p. 4 or 8 h before phenytoin) actually increased the teratogenicity of phenytoin (65 mg/kg i.p. on gestational days [GD] 11 and 12, or 12 and 13) (p < .05), and appeared to increase embryonic protein oxidation. Combined pretreatment with PEG-SOD and PEG-catalase (10 KU/kg 8 or 12 h before phenytoin) was not embryo-protective, nor was PEG-catalase alone, although PEG-catalase alone reduced phenytoin-initiated protein oxidation in maternal liver (p < .05). However, time-response studies with PEG-catalase (10 KU/kg) on GDs 11, or 11 and 12, showed maximal 50-100% increases in embryonic activity sustained for 8-24 h after maternal injection (p < .05), and dose-response studies (10-50 KU/kg) at 8 h showed maximal respective 4-fold and 2-fold increases in maternal and embryonic activities with a 50 KU/kg dose (p < .05). In controls, embryonic catalase activity was about 4% of that in maternal liver, although with catalase treatment, enhanced embryonic activity was about 2% of enhanced maternal activity (p < .05). PEG-catalase pretreatment (10-50 KU/kg 8 h before phenytoin) also produced a dose-dependent inhibition of phenytoin teratogenicity, with maximal decreases in fetal cleft palates, resorptions and postpartum lethality at a 50 KU/kg dose (p < .05). This is the first evidence that maternal administration of PEG-catalase can substantially enhance embryonic activity, and that in vivo phenytoin teratogenicity can be modulated by antioxidative enzymes. Both the SOD-mediated enhancement of phenytoin teratogenicity, and the inhibition of phenytoin teratogenicity by catalase, indicate a critical role for ROS in the teratologic mechanism, and the teratologic importance of antioxidative balance.

Degeneration of NO-synthesizing cerebrocortical neurons in transgenic mice expressing mutated superoxide dismutase is not due to elevated nitric oxide levels

Nitric oxide (NO) synthase (NOS)-containing cerebrocortical neurons degenerate in patients with amyotrophic lateral sclerosis (ALS) and dementia, and in transgenic mice expressing a mutated superoxide dismutase gene (G93A) associated with familial ALS. The cerebral cortex of transgenic mice displayed decreased NOS activity (p<0.001) and cGMP levels (p<0.01), but no changes in NOS content indicating that less NO is produced. Therefore, NOSN degeneration is not caused by elevated NO.

Role of superoxide dismutase in ischemic brain injury: a study using SOD-1 transgenic mice

1. Nitric oxide radicals (NO) play an important role in the pathophysiology of focal cerebral ischemia. 2. Vascular NO can reduce ischemic brain injury by increasing CBF, whereas neuronal NO may mediate neurotoxicity following brain ischemia, mainly by its reaction with superoxide to generate peroxynitrite. 3. These findings could contribute to a strategy for the treatment of cerebral ischemia.

Strain-related brain injury in neonatal mice subjected to hypoxia-ischemia

The development of transgenic mice has led to an increase in the use of mice as models for human disease. We hypothesized that the degree of brain damage sustained by animals in a neonatal mouse model of hypoxia-ischemia depends on the strain used. We compared three strains of mice commonly used to generate transgenic strains (C57Bl/6, 129Sv and CD1), as well as three hybrids of these strains (C57Bl/6x129Sv, CD1xC57Bl/6, and CD1x129Sv). At postnatal day 7 (P7), pups were subjected to a modified Vannucci procedure for hypoxia-ischemia as follows: permanent ligation of right common carotid artery under halothane anesthesia, 2-h recovery period, exposure to 8% oxygen at 37 degreesC for varying durations (30, 60 or 90 min). After 5 days, animals were perfused with 4% paraformaldehyde, brains were removed, postfixed and examined histologically with cresyl violet and Perl's iron stain to assess the degree of damage. Damage was assessed blindly using a score ranging from 0 (none) to 3 (infarct) in eight regions (ant-, mid-, and post- cortex, CA1, CA2, CA3 and dentate gyrus of the hippocampus, and striatum). We found significant differences in susceptibility to brain damage and mortality depending on the strain used. While determining the maximal degree of injury with the least amount of mortality for each strain, it was found that some strains (CD1) are particularly susceptible to brain damage in this model, while others (129Sv) are resistant.

Overexpression of SOD1 in transgenic rats protects vulnerable neurons against ischemic damage after global cerebral ischemia and reperfusion

Transient global cerebral ischemia resulting from cardiac arrest is known to cause selective death in vulnerable neurons, including hippocampal CA1 pyramidal neurons. It is postulated that oxygen radicals, superoxide in particular, are involved in cell death processes. To test this hypothesis, we first used in situ imaging of superoxide radical distribution by hydroethidine oxidation in vulnerable neurons. We then generated SOD1 transgenic (Tg) rats with a five-fold increase in copper zinc superoxide dismutase activity. The Tg rats and their non-Tg wild-type littermates were subjected to 10 min of global ischemia followed by 1 and 3 d of reperfusion. Neuronal damage, as assessed by cresyl violet staining and DNA fragmentation analysis, was significantly reduced in the hippocampal CA1 region, cortex, striatum, and thalamus in SOD1 Tg rats at 3 d, as compared with the non-Tg littermates. There were no changes in the hippocampal CA3 subregion and dentate gyrus, resistant areas in both SOD1 Tg and non-Tg rats. Quantitative analysis of the damaged CA1 subregion showed marked neuroprotection against transient global cerebral ischemia in SOD1 Tg rats. These results suggest that superoxide radicals play a role in the delayed ischemic death of hippocampal CA1 neurons. Our data also indicate that SOD1 Tg rats are useful tools for studying the role of oxygen radicals in the pathogenesis of neuronal death after transient global cerebral ischemia.

Overexpression of SOD1 in transgenic rats protects vulnerable neurons against ischemic damage after global cerebral ischemia and reperfusion

Transient global cerebral ischemia resulting from cardiac arrest is known to cause selective death in vulnerable neurons, including hippocampal CA1 pyramidal neurons. It is postulated that oxygen radicals, superoxide in particular, are involved in cell death processes. To test this hypothesis, we first used in situ imaging of superoxide radical distribution by hydroethidine oxidation in vulnerable neurons. We then generated SOD1 transgenic (Tg) rats with a five-fold increase in copper zinc superoxide dismutase activity. The Tg rats and their non-Tg wild-type littermates were subjected to 10 min of global ischemia followed by 1 and 3 d of reperfusion. Neuronal damage, as assessed by cresyl violet staining and DNA fragmentation analysis, was significantly reduced in the hippocampal CA1 region, cortex, striatum, and thalamus in SOD1 Tg rats at 3 d, as compared with the non-Tg littermates. There were no changes in the hippocampal CA3 subregion and dentate gyrus, resistant areas in both SOD1 Tg and non-Tg rats. Quantitative analysis of the damaged CA1 subregion showed marked neuroprotection against transient global cerebral ischemia in SOD1 Tg rats. These results suggest that superoxide radicals play a role in the delayed ischemic death of hippocampal CA1 neurons. Our data also indicate that SOD1 Tg rats are useful tools for studying the role of oxygen radicals in the pathogenesis of neuronal death after transient global cerebral ischemia.

Transgenic mice with increased copper/zinc-superoxide dismutase activity are resistant to hepatic leukostasis and capillary no-reflow after gut ischemia/reperfusion

The objectives of this study were to (1) determine whether transgenic (Tg) mice overexpressing copper/zinc-superoxide dismutase (CuZn-SOD) are protected from the deleterious effects of gut ischemia/reperfusion (I/R) and (2) compare the effectiveness of Tg SOD overexpression in attenuating I/R injury to intravascularly administered CuZn-SOD or manganese (Mn)-SOD. The accumulation of fluorescently labeled leukocytes and number of nonperfused sinusoids were monitored by intravital microscopy in livers of wild-type mice (C57BL/6), CuZn-SOD Tg mice, and wild-type mice receiving either CuZn-SOD or Mn-SOD. All parameters were measured for 1 hour after release of the occluded (for 15 minutes) superior mesenteric artery. Gut I/R in wild-type mice led to an increased number of stationary leukocytes, while reducing the number of perfused sinusoids (capillary no-reflow). All of these responses were significantly blunted in CuZn-SOD Tg mice, with a corresponding attenuation of liver enzyme release into plasma. Exogenously administered SOD had little or no effect on gut I/R-induced leukostasis or capillary no-reflow in the liver. These observations suggest a role for superoxide in gut I/R-induced leukostasis and hypoxic stress in the liver. Furthermore, the findings suggest that cellular localization of SOD activity is an important determinant of the protective actions of this enzyme in experimental models of I/R injury.

Methamphetamine-induced increase in striatal NF-kappaB DNA-binding activity is attenuated in superoxide dismutase transgenic mice

Methamphetamine injection (x4 with 2-h interval) caused dose-dependent activation of striatal NF-kappaB activity. Striatal NF-kappaB binding increased significantly at 1-3 h after the last injection of methamphetamine (10 mg/kg, i.p. x4). This induction of striatal NF-kappaB activity was significantly attenuated in Cu, Zn-superoxide dismutase transgenic mice in a gene dosage-dependent fashion. The present results suggest that reactive oxygen species generated by methamphetamine injections can activate striatal NF-kappaB DNA-binding during this drug-induced toxic process.

The nature of antioxidant defense mechanisms: a lesson from transgenic studies

Reactive oxygen species (ROS) have been implicated in the pathogenesis of many clinical disorders such as adult respiratory distress syndrome, ischemia-reperfusion injury, atherosclerosis, neurodegenerative diseases, and cancer. Genetically engineered animal models have been used as a tool for understanding the function of various antioxidant enzymes in cellular defense mechanisms against various types of oxidant tissue injury. Transgenic mice overexpressing three isoforms of superoxide dismutase, catalase, and the cellular glutathione peroxidase (GSHPx-1) in various tissues show an increased tolerance to ischemia-reperfusion heart and brain injury, hyperoxia, cold-induced brain edema, adriamycin, and paraquat toxicity. These results have provided for the first time direct evidence demonstrating the importance of each of these antioxidant enzymes in protecting the animals against the injury resulting from these insults, as well as the effect of an enhanced level of antioxidant in ameliorating the oxidant tissue injury. To evaluate further the nature of these enzymes in antioxidant defense, gene knockout mice deficient in copper-zinc superoxide dismutase (CuZnSOD) and GSHPx-1 have also been generated in our laboratory. These mice developed normally and showed no marked pathologic changes under normal physiologic conditions. In addition, a deficiency in these genes had no effects on animal survival under hyperoxida. However, these knockout mice exhibited a pronounced susceptibility to paraquat toxicity and myocardial ischemia-reperfusion injury. Furthermore, female mice lacking CuZnSOD also displayed a marked increase in postimplantation embryonic lethality. These animals should provide a useful model for uncovering the identity of ROS that participate in the pathogenesis of various clinical disorders and for defining the role of each antioxidant enzyme in cellular defense against oxidant-mediated tissue injury.

Overexpression of copper/zinc superoxide dismutase: a novel cause of murine muscular dystrophy

Oxidative injury underlies the cellular injury and cell death in a variety of disease states. In muscular dystrophies, evidence from in vivo and in vitro studies suggests that muscle degeneration may be secondary to an increased susceptibility to oxidative stress. To address the role of free radical metabolism in the pathogenetic process of muscular dystrophies, we examined the muscle of transgenic mice that overexpress copper/zinc (Cu/Zn) superoxide dismutase. Overexpression of this enzyme can sensitize cells to oxidative injury, and Cu/Zn superoxide dismutase activity was elevated approximately fourfold above control levels in skeletal muscle of the transgenic strain. Examination of serum creatine phosphokinase levels in these mice revealed significant elevations after 2 months of age, indicative of active muscle breakdown. By 8 months of age, there was gross atrophy of the quadriceps muscle, and other hindlimb muscles were variably affected. Histologically, there was evidence of widespread muscle necrosis and regeneration, fiber splitting, and replacement of muscle with adipose and fibrous connective tissue, typical of a muscular dystrophy. Associated with the development of this degeneration was an increase in the levels of lipid peroxidation in the muscle of Cu/Zn superoxide dismutase transgenic mice, highlighting the central role of oxidative injury in this pathogenetic process. These results demonstrate that oxidative damage can be the primary pathogenetic process underlying a muscular dystrophy.

Copper/zinc superoxide dismutase transgenic brain accumulates hydrogen peroxide after perinatal hypoxia ischemia

Unlike the mature animal, immature mice transgenic for copper/zinc superoxide dismutase (SOD1) have greater brain injury after hypoxia-ischemia than their wild-type nontransgenic littermates. To assess the role of oxidative stress in the pathogenesis of this injury, we measured histopathological damage, lipid peroxidation products, enzymatic activities of catalase and glutathione peroxidase, and hydrogen peroxide (H2O2) concentration in these animals before and after hypoxic-ischemic injury. Lipid peroxidation products were significantly increased 2 hours after the insult in both transgenic and nontransgenic brains in hippocampus, the most damaged brain region. Catalase activity did not increase in response to SOD1 overexpression or injury in either group. However, glutathione peroxidase activity, unchanged in response to overexpression, decreased significantly 24 hours after injury in both groups. At 24 hours after injury, greater H2O2 accumulation was observed in transgenic brains. Because SOD1 dismutates superoxide to H2O2, overexpression of SOD1 in the presence of developmentally low activities of the catalytic enzymes glutathione peroxidase and catalase leads to an increased production of H2O2, and may explain the increased brain injury observed after hypoxia-ischemia in neonatal SOD1 mice.

Attenuation of 6-hydroxydopamine-induced dopaminergic nigrostriatal lesions in superoxide dismutase transgenic mice

6-Hydroxydopamine is a neurotoxin that produces degeneration of the nigrostriatal dopaminergic pathway in rodents. Its toxicity is thought to involve the generation of superoxide anion secondary to its autoxidation. To examine the effects of the overexpression of Cu,Zn-superoxide dismutase activity on 6-hydroxydopamine-induced dopaminergic neuronal damage, we have measured the effects of 6-hydroxydopamine on striatal and nigral dopamine transporters and nigral tyrosine hydroxylase-immunoreactive neurons in Cu,Zn-superoxide dismutase transgenic mice. Intracerebroventricular injection of 6-hydroxydopamine (50 microg) in non-transgenic mice produced reductions in the size of striatal area and an enlargement of the cerebral ventricle on both sides of the brains of mice killed two weeks after the injection. In addition, 6-hydroxydopamine caused marked decreases in striatal and nigral [125I]RTI-121-labelled dopamine transporters not only on the injected side but also on the non-injected side of non-transgenic mice; this was associated with decreased cell number and size of tyrosine hydroxylase-immunoreactive dopamine neurons in the substantia nigra pars compacta on both sides in these mice. In contrast, superoxide dismutase transgenic mice were protected against these neurotoxic effects of 6-hydroxydopamine, with the homozygous transgenic mice showing almost complete protection. These results provide further support for a role of superoxide anion in the toxic effects of 6-hydroxydopamine. They also provide further evidence that reactive oxygen species may be the main determining factors in the neurodegenerative effects of catecholamines.

Effect of acute exposure to 3-nitropropionic acid on activities of endogenous antioxidants in the rat brain

The response of endogenous antioxidants to acute exposure of the mitochondrial inhibitor, 3-nitropropionic acid (3-NPA), was investigated in selected rat brain regions. Rats treated with 3-NPA (30 mg/kg, s.c.) were sacrificed at 30, 60, 90 and 120 min after injection to examine the alterations in reduced glutathione levels (GSH), and activities of antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) in the hippocampus (HIP), frontal cortex (FC), and caudate nucleus (CN). CAT activity increased in the HIP 90 min after 3-NPA treatment. While cytosolic copper/zinc SOD (CuZn-SOD) and mitochondrial manganese SOD (Mn-SOD) levels increased in the FC at 120 min, only the Mn-SOD increased in the CN 90 min after treatment. The activity of GPx decreased in the HIP 120 min after 3-NPA injection. When compared with the control, administration of 3-NPA led to GSH depletion in HIP within 120 min. The depletion of GSH and induction of antioxidant enzyme activities after the 3-NPA exposure suggest conditions favorable for oxidative stress.

Superoxide radicals are mediators of the effects of methamphetamine on Zif268 (Egr-1, NGFI-A) in the brain: evidence from using CuZn superoxide dismutase transgenic mice

Administration of methamphetamine (METH) to mammals is known to cause deleterious effects to brain monoaminergic systems. These toxic effects are thought to be due to oxidative stress. Acute administration of METH causes activation of immediate-early genes (IEGs) such as c-fos and Zif268 mRNA in rodent brains. However, the exact mechanisms involved in these changes have not been completely clarified. As a first step towards assessing a possible role for free radicals in METH-induced changes in IEGs, we have used CuZn superoxide dismutase (SOD) transgenic (Tg) mice and have quantified the effects of METH on c-fos and Zif268 mRNAs by in situ hybridization techniques. Mice were injected with 25 mg/kg of METH and sacrificed at various time points afterwards. There were significant METH-induced increases in both c-fos and Zif268 mRNAs in the frontal cortex and striatum of both strains of animals. Interestingly, the increases in Zif268 were markedly attenuated in the CuZn SOD-Tg mice; the increases in c-fos were also attenuated, but to a significantly lesser degree. These results indicate that superoxide radicals might play an important role in the activation of Zif268 after METH administration. Because IEGs are modulators of gene expression, these results also raise the possibility that oxidative mechanisms might be important factors in neuroadaptive changes caused by stimulant drugs.

Effects of overexpression of the cytoplasmic copper-zinc superoxide dismutase on the survival of neurons in vitro

The cytoplasmic copper-zinc superoxide dismutase (Cu, Zn SOD; SOD-1) is an abundant and well-conserved intracellular antioxidant enzyme which has been implicated in a number of oxidative stress mediated phenomena, especially Down Syndrome, in which SOD-1 activity is increased due to triplication of chromosome 21 containing the gene and, in hereditary amyotrophic lateral sclerosis, in which the gene is mutated. Overexpression of SOD-1 could theoretically, therefore, lead to increased vulnerability to oxidative stress in two distinct manners: increasing steady-state hydrogen peroxide levels or increasing toxic side reactions. We used two mouse neuronal culture systems--one in which the murine chromosome containing SOD-1 is triplicated and one in which human SOD-1 is a transgene--to test the effect of overexpression of this enzyme on antioxidant status in general and specifically on glutamate mediated oxidative stress. We found that SOD-1 overexpression increases antioxidant status at the same time it decreases vulnerability to glutamate.

Attenuation of age-dependent oxidative damage to DNA and protein in brainstem of Tg Cu/Zn SOD mice

Age-dependent accumulation of oxidative DNA and protein damage in brainstem and striatum was assessed in normal and transgenic (tg) mice which overexpress human Cu/Zn superoxide dismutase (h-SOD1). A marker of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine (oxo8dG), was measured at 3, 12, and 18 months of age in control and tg mice. Cu/Zn SOD, but not MnSOD, activities in brainstems and striata from tg mice were increased compared to controls at all ages. At 18 months, oxo8dG levels were increased by 58% in brainstem and by 21% in striatum of control mice. In the tg mice, brainstem and striatal oxo8dG levels were increased to a lesser extent than in the corresponding controls. Protein oxidation (carbonyl content), was increased by 59% at 18 months in control brainstem, but not in striatum, and the increase was significantly attenuated in the tg mice. In summary, oxidative damage to DNA and protein increased with age in brainstem (and to a lesser extent in striatum), and augmented Cu/Zn SOD activity modified the extent of DNA and protein damage.

Axonal transport of mutant superoxide dismutase 1 and focal axonal abnormalities in the proximal axons of transgenic mice

Superoxide dismutase 1 (SOD1), a ubiquitously expressed enzyme, detoxifies superoxide radicals and participates in copper homeostasis. Mutations in this enzyme have been linked to a subset of autosomal dominant cases of familial amyotrophic lateral sclerosis (FALS), a disorder characterized by selective degeneration of motor neurons. Transgenic mice expressing FALS mutant human (Hu) SOD1 at high levels develop a motor neuron disease, indicating that mutant Hu SOD1 gains properties that are particularly toxic to motor neurons. In this report, we demonstrate that transgenic mice expressing Hu SOD1 with the G37R FALS mutation, but not mice expressing wild-type enzyme, develop focal increases in immunoreactivity in the proximal axons of spinal motor neurons. This SOD1 immunoreactivity and immunoreactivity to hypophosphorylated neurofilament H epitopes are found adjacent to small vacuoles in axons. Using metabolic radiolabeling methods, we show that mutant G37R HuSOD1 as well as endogenous mouse SOD1 are transported anterograde in slow component b in motor and sensory axons of the sciatic nerve. Together, these findings suggest that anterogradely transported mutant SOD1 may act locally to damage motor axons.

10 years of Genomics, chromosome 21, and Down syndrome

During the first 10 years of Genomics (1987-1997), the molecular structure of human chromosome 21 (HC21) has been intensively investigated. Due to its small size and involvement in Down syndrome, it continues to serve as a model in the development of "genomics technologies." Increasingly more detailed genetic, radiation hybrid, physical, and transcription maps, in addition to NotI restriction and chromosomal breakpoint maps, of HC21 have been developed, and approximately 10% of its genes have been cloned. These maps have been vital in the localization of loci for 15 monogenic disorders to HC21, and 10 of these genes have been identified and characterized. The genetic maps have aided in the detailed elucidation of the origin of the supernumerary HC21 in trisomy 21 from investigations of recombination and nondisjunction events. Mouse models of Down syndrome, with partial trisomy 16, the mouse chromosome principally syntenic to HC21, have been created and initially characterized. A substantial number of the above studies related to the molecular mapping, gene cloning, and infrastructure of HC21 were published in Genomics (e.g., approximately 30% of papers describing HC21 maps were published here). The future goals of genomic analysis of HC21 will be the determination of its complete nucleotide sequence and the identification and functional analysis of all of its genes. These advances will help to provide a molecular explanation of the pathophysiology of Down syndrome and aid in the identification of genes for monogenic and polygenic disorders that map on this chromosome. Novel therapeutic interventions for Down syndrome and the monogenic and polygenic disorders that map to HC21 will be designed and tried based on the knowledge of the disease pathogenesis resulting from the genomic analysis.

Transgenic mice with elevated level of CuZnSOD are highly susceptible to malaria infection

Copper/zinc superoxide dismutase (CuZnSOD) catalyses the conversion of O2.- into H2O2. Constitutive overexpression of CuZnSOD in cells and animals creates an indigenous oxidative stress that predisposes them to added insults. In this study, we used transgenic CuZnSOD (Tg-CuZnSOD) mice with elevated levels of CuZnSOD to determine whether overexpression of CuZnSOD affected the susceptibility of these mice to plasmodium infection. Acute malaria is associated with oxidative stress, mediated by redox-active iron released from the infected RBC. Two independently derived Tg-CuZnSOD lines showed higher sensitivity than control mice to infection by Plasmodium berghei (P. berghei), reflected by an earlier onset and increased rate of mortality. Nevertheless, while Tg-CuZnSOD mice were more vulnerable than control mice, the levels of parasitemia were comparable in both strains. Moreover, treatment of infected red blood cells (RBC) with oxidative stress inducers, such as ascorbate or paraquat, reduced the viability of parasites equally in both transgenic and control RBC. This further confirms that increased CuZnSOD does not support plasmodia development. The data are consistent with the possibility that the combination of increased redox-active iron and elevated H2O2 in the plasmodium-infected Tg-CuZnSOD mice, led to an enhanced Fenton's reaction-mediated HO. production, and the resulting oxidative injury renders the transgenic mice more vulnerable to parasite infection.

Overexpression of human copper, zinc-superoxide dismutase (SOD1) prevents postischemic injury

Superoxide and superoxide-derived oxidants have been hypothesized to be important mediators of postischemic injury. Whereas copper, zinc-superoxide dismutase, SOD1, efficiently dismutates superoxide, there has been controversy regarding whether increasing intracellular SOD1 expression would protect against or potentiate cellular injury. To determine whether increased SOD1 protects the heart from ischemia and reperfusion, studies were performed in a newly developed transgenic mouse model in which direct measurement of superoxide, contractile function, bioenergetics, and cell death could be performed. Transgenic mice with overexpression of human SOD1 were studied along with matched nontransgenic controls. Immunoblotting and immunohistology demonstrated that total SOD1 expression was increased 10-fold in hearts from transgenic mice compared with nontransgenic controls, with increased expression in both myocytes and endothelial cells. In nontransgenic hearts following 30 min of global ischemia a reperfusion-associated burst of superoxide generation was demonstrated by electron paramagnetic resonance spin trapping. However, in the transgenic hearts with overexpression of SOD1 the burst of superoxide generation was almost totally quenched, and this was accompanied by a 2-fold increase in the recovery of contractile function, a 2.2-fold decrease in infarct size, and a greatly improved recovery of high energy phosphates compared with that in nontransgenic controls. These results demonstrate that superoxide is an important mediator of postischemic injury and that increasing intracellular SOD1 dramatically protects the heart from this injury. Thus, increasing intracellular SOD1 expression may be a highly effective approach to decrease the cellular injury that occurs following reperfusion of ischemic tissues.

Effects of over- and under-expression of Cu,Zn-superoxide dismutase on the toxicity of glutamate analogs in transgenic mouse striatum

Considerable evidence suggests that reactive oxygen species mediate the neurotoxic effects of ionotropic glutamate receptor activation. Accordingly, we have examined neuronal degeneration resulting from intrastriatal injection of quinolinic acid, an NMDA receptor agonist, and kainic acid in gene targeted and transgenic mice that under- or over-express copper, zinc superoxide dismutase (Cu,Zn-SOD; SOD-1). Elevated SOD-1 activity significantly protects against quinolinic acid and kainic acid neurotoxicity in the mouse striatum whereas reduced activity appears to potentiate neurotoxicity. Thus a 'gene-dose' effect of SOD-1 has been demonstrated with regard to excitotoxic mechanisms.

Subunit asymmetry in the three-dimensional structure of a human CuZnSOD mutant found in familial amyotrophic lateral sclerosis

The X-ray crystal structure of a human copper/zinc superoxide dismutase mutant (G37R CuZnSOD) found in some patients with the inherited form of Lou Gehrig's disease (FALS) has been determined to 1.9 angstroms resolution. The two SOD subunits have distinct environments in the crystal and are different in structure at their copper binding sites. One subunit (subunit[intact]) shows a four-coordinate ligand geometry of the copper ion, whereas the other subunit (subunit[broken]) shows a three-coordinate geometry of the copper ion. Also, subunit(intact) displays higher atomic displacement parameters for backbone atoms ((B) = 30 +/- 10 angstroms2) than subunit(broken) ((B) = 24 +/- 11 angstroms2). This structure is the first CuZnSOD to show large differences between the two subunits. Factors that may contribute to these differences are discussed and a possible link of a looser structure to FALS is suggested.

Muscle cells from mdx mice have an increased susceptibility to oxidative stress

Several lines of evidence suggest that free radical mediated injury and oxidative stress may lead to muscle necrosis in the muscular dystrophies, including those related to defects in the dystrophin gene. We have examined muscle cell death using an in vitro assay in which the processes that lead to myofiber necrosis in vivo may be amenable to investigation in a simplified cell culture system. Using myotube cultures from normal and dystrophin-deficient (mdx) mice, we have examined the susceptibilities of the cells to different metabolic stresses. Dystrophin-deficient cells were more susceptible to free radical induced injury when compared to normal cells, but the two populations were equally susceptible to other forms of metabolic stress. The differential response appeared to be specifically related to dystrophin expression since undifferentiated myoblasts (which do not express dystrophin) from normal and mdx mice were equally sensitive to oxidative stress. Thus, the absence of dystrophin appears to render muscle specifically more susceptible to free radical induced injury. These results support the hypothesis that oxidative stress may lead to myofiber necrosis in these disorders. Elucidating the mechanisms leading to cell death may help to explain the variabilities in disease expression that are seen as a function of age, among different muscles, and across species in animals with muscular dystrophy due to dystrophin deficiency.

Free radicals and the pathobiology of brain dopamine systems

Oxygen is an essential element for normal life. However, reactive oxygen species (ROS) can also participate in deleterious reactions that can affect lipid, protein, and nucleic acid. Normal physiological function thus depends on a balance between these ROS and the scavenging systems that aerobic organisms have developed over millennia. Tilting of that balance towards a pro-oxidant state might result from both endogenous and exogenous causes. In the present paper, we elaborate on the thesis that the neurodegenerative effects of two drugs, namely methamphetamine (METH, ICE) and methylenedioxymethamphetamine (MDMA, Ecstasy) are due to ROS overproduction in monoaminergic systems in the brain. We also discuss the role of oxygen-based species in 6-hydroxydopamine (6-OHDA)-induced nigrostriatal dopaminergic degeneration and in Parkinson's disease. Studies are underway to identify specific cellular and molecular mechanisms that are regulated by oxygen species. These studies promise to further clarify the role of oxidative stress in neurodegeneration and in plastic changes that occur during the administration of addictive agents that affect the brain.

Edema formation exacerbates neurological and histological outcomes after focal cerebral ischemia in CuZn-superoxide dismutase gene knockout mutant mice

In a variety of studies. CuZn-superoxide dismutase (CuZn-SOD) has been shown to protect against ischemic brain injury. A possible role for CuZn-SOD-related modulation of neuronal viability has been suggested by the finding that CuZn-SOD inhibits brain edema formation following various kinds of neurological insults. We have evaluated the role of CuZn-SOD on brain edema formation following focal cerebral ischemia in mice bearing a disruption of the CuZn-SOD gene (Sod1). Homozygous mutants (Sod1-/-) had no detectable CuZn-SOD activity and heterozygous mutants (Sod1+/-) showed a 50% decrease compared to wild-type mice. Sod1-/- mice showed a high level of blood-brain barrier (BBB) disruption shortly after 1 hr of middle cerebral artery occlusion and 100% mortality at 24 hr following ischemia. Sod1+/- mice showed a moderate level of BBB disruption and 30% mortality. The Sod1+/- animals had increased infarct volume and brain swelling, accompanying exacerbated neurological deficits at 24 hr following ischemia. These results indicate the important role of superoxide anions in the development of brain edema after focal cerebral ischemia and suggest the possibility that brain edema formation may contribute to the exacerbation of ischemic brain injury and neurological deficits in knockout mutant mice.

MPTP produces differential oxidative stress and antioxidative responses in the nigrostriatal and mesolimbic dopaminergic pathways

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to produce a differential toxicity in the nigrostriatal and mesolimbic dopaminergic pathways with the nigrostriatal pathway being more vulnerable. We, therefore, investigated whether oxidative stress and the antioxidant system play a role in this phenomenon. Balb/c mice were treated with either saline or MPTP (30 mg/kg/d) for 7 d, and were sacrificed on the next day. Results revealed that MPTP increased lipid peroxidation in the striatum (ST) and decreased glutathione concentration in the substantia nigra (SN) without markedly affecting these measures in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Further, MPTP produced approximately twofold increases in both manganese superoxide dismutase (MnSOD) and copper-zinc superoxide dismutase (CuZnSOD) activities in the VTA while it only increased MnSOD activity in the SN. Both catalase and glutathione peroxidase (GPx) activities were not markedly altered by MPTP in both systems. However, the basal levels of catalase and GPx activities were higher in the VTA and NAc than in the SN and ST. These results together suggest that a lesser degree of oxidative damage and a more inducible CuZnSOD activity observed in the mesolimbic dopaminergic pathway may partially explain the differential toxicity MPTP produced in these two dopaminergic systems.

Modulation of P-selectin expression in the postischemic intestinal microvasculature

The dual radiolabeled monoclonal antibody technique was used to 1) define the magnitude and kinetics of P-selectin expression in murine small intestine exposed to ischemia-reperfusion (I/R), and 2) determine the factor(s) responsible for initiating this response. Within 10 min after release of a 20-min arterial occlusion, intestinal P-selectin expression increased two- to threefold compared with control values. Peak (4-fold) expression of P-selectin was noted at 5 h after reperfusion, returning to the control value at 24 h. The early (10-30 min) I/R-induced upregulation of P-selectin appears to reflect mobilization of a performed pool of the adhesion molecule, whereas the later (5 h) rise appears to be transcription dependent. The early increase in P-selectin expression was not inhibited by pretreatment with either oxypurinol (inhibits xanthine oxidase), diphenhydramine (H1-receptor antagonist), or MK-571 (leukotriene C4/D4 antagonist), nor was it blunted in transgenic mice expressing three times the normal level of copper-zinc superoxide dismutase or in mast cell-deficient mice. However, significant inhibition was noted after treatment with either MK-886 (5-lipoxygenase inhibitor) or a nitric oxide (NO) donor (diethylenetriamine/NO). These findings indicate that the early I/R-induced increase in intestinal P-selectin expression is mediated by a 5-lipoxygenase-dependent NO-inhibitable mechanism.

Overexpression of CuZn-superoxide dismutase reduces hippocampal injury after global ischemia in transgenic mice

BACKGROUND AND PURPOSE

The role of copper, zinc-superoxide dismutase (CuZn-SOD) in hippocampal injury after transient global ischemia was studied using transgenic (Tg) mice and wild-type littermates.

METHODS

Global ischemia was induced by bilateral common carotid artery occlusion. The hemisphere with the hypoplastic posterior communicating artery was determined and then the hippocampus in this hemisphere was evaluated qualitatively using a score of 0 to 4 and quantitatively using an image analyzer.

RESULTS

Hippocampal injury was reduced in Tg mice after both 5 and 10 minutes of ischemia. In the 5-minute ischemia group, the mean score of the injury was significantly lower in Tg than nontransgenic (nTg) mice at 3 days. In the 10-minute group, the hippocampal injury was reduced more in Tg than nTg mice at 1 day. Quantitative evaluation by an image analyzer confirmed the qualitative data. Neurons with fragmented DNA were also studied in the hippocampal injury. In the 5-minute group, despite the reduction of the injury in Tg mice, their neurons with fragmented DNA were relatively increased at 1 day. In the 10-minute group, this ratio was almost the same in both nTg and Tg mice.

CONCLUSIONS

CuZn-SOD plays a protective role in the pathogenesis of selective hippocampal injury after brief ischemia, whether the insult is relatively mild or intense. Furthermore, CuZn-SOD may reduce both necrotic and DNA fragmented neuronal death after global ischemia.

Fatty streak formation in fat-fed mice expressing human copper-zinc superoxide dismutase

Studies in vitro have shown that copper-zinc superoxide dismutase (CuZn-SOD) inhibits a number of events putatively involved in atherogenesis, including cell-mediated oxidation of LDL. To investigate whether increased activity of CuZn-SOD reduces atherogenesis in vivo, we examined diet-induced fatty streak formation in CuZn-SOD transgenic mice (n = 24) as compared with their nontransgenic littermates (n = 28). Transgenic animals were originally created by introduction of an EcoRI-BamHI human genomic DNA fragment containing the CuZn-SOD gene and its regulatory elements into B6SJL zygotes. For the current studies, the transgene was bred for 12 generations into the atherosclerosis-susceptible C57BL/6 background. Animals were fed atherogenic diets (15% fat, 1.25% cholesterol, 0.5% Na cholate) starting at 100 weeks of age and extending for 18 weeks. At the end of the diet period, aortic SOD activity was two-fold higher in transgenics than nontransgenics (mean +/- SE: 46.7 +/- 5.8 versus 20.1 +/- 2.4 units/mg of protein, P < .001). Levels of protein-bound amino acid oxidation products (meta-, ortho-, and dityrosine) were either similar or lower in aorta and heart from transgenics as compared with nontransgenics, suggesting that amplification of CuZn-SOD activity above the normal complement had modest inhibitory effects on basal oxidative stress in these tissues. CuZn-SOD overexpression did not reduce the extent of lesion development as analyzed by quantitative lipid staining of serial sections of the proximal aorta; mean lesion areas (+/- SE) were 997 +/- 478 and 943 +/- 221 mu 2 in transgenics and nontransgenics, respectively. Notably, the range of values for lesion area was 2.2-fold greater in transgenics (0-8403 versus 0-3868 mu 2 in nontransgenics). Moreover, within this group, lesion area showed a significant positive correlation with SOD activity (r = .611, P < .03). These results do not support an antiatherogenic effect of Cu-Zn-SOD over expression and raise the possibility that high tissue SOD activity may potentiate atherogenesis in fat-fed atherosclerosis-susceptible mice [corrected].

Kainate-induced hippocampal DNA damage is attenuated in superoxide dismutase transgenic mice

Peripheral administration of kainic acid (KA) can cause cell death in the hippocampus of rodents. This is thought to involve oxidative stress. In the present study, we tested the possibility that KA-induced neuronal cell death might be attenuated in CuZn superoxide dismutase transgenic (SOD-Tg) mice. Acute administration of KA causes animal death in a dose-dependent fashion; this was attenuated in SOD-Tg mice. Similarly, KA caused dose-dependent neuronal cell death in the hippocampus of wild-type mice; this cell death was attenuated in the SOD-Tg mice, in a gene-dosage-dependent fashion, with homozygous mice showing complete protection even at the highest dose (45 mg/kg) of KA used in this study. These results provide further support for the involvement of oxygen-based radicals in the toxic effects of KA.

New directions for studying the role of free radicals in aging

Oxidative damage caused by free radicals in vivo is believed to play an important role in the etiology of aging and age-associated degenerative diseases. The most direct evidence supporting this theory is the recent finding that the transgenic Drosophila that overexpress the antioxidant enzymes catalase and superoxide dismutase exhibit an increase in life span. Although the increase in life span in Drosophila by these enzymes is certainly important, the next logical direction is to demonstrate whether increased antioxidant protection occurs similarly in mammals. Several transgenic mouse models that overexpress antioxidant enzymes are currently available. However, one major shortcoming in using these transgenic mice is the difficulty of producing antioxidant overexpression in more than a few tissues. Despite the potential shortcomings of using transgenic mice, these animals provide a unique system in which individual components of a complex system, such as the antioxidant defense system, can be modulated and examined independently. Transgenic mice are therefore potentially powerful tools to study the role of various components of the antioxidant system in the aging process. A parallel direction in the study of free radical roles in aging is to investigate the modulation of transcription factors by oxidative stress. Among these, the transcription factors, NF-κB and AP-1 are implicated in oxidative stress. The activities of these oxidative stress-response transcription factors are regulated by upstream signaling molecules, which involve a cascade of phosphorylation and dephosphorylation events leading to their activation. In this article, we review recent studies that use molecular approaches to investigate the biological role of oxidant stress. Each of these studies potentially provide new insights into the roles of free radicals and free radical damage in the aging process.

Reduction of CuZn-superoxide dismutase activity exacerbates neuronal cell injury and edema formation after transient focal cerebral ischemia

Apoptotic neuronal cell death has recently been associated with the development of infarction after cerebral ischemia. In a variety of studies, CuZn-superoxide dismutase (CuZn-SOD) has been shown to protect the brain from ischemic injury. A possible role for CuZn-SOD-related modulation of neuronal viability is suggested by the finding that CuZn-SOD inhibits apoptotic neuronal cell death in response to some forms of cellular damage. We evaluated this possibility in the model of transient focal cerebral ischemia in mice bearing a disruption of the CuZn-SOD gene (Sod1). Homozygous mutant (Sod1 -/-) mice had no detectable CuZn-SOD activity, and heterozygous mutants (Sod1 +/-) showed a 50% decrease compared with wild-type mice. Sod1 -/- mice showed a high level of blood-brain barrier disruption soon after 1 hr of middle cerebral artery occlusion and 100% mortality at 24 hr after ischemia. Sod1 +/- mice showed 30% mortality at 24 hr after ischemia, and neurological deficits were exacerbated compared with wild-type controls. The Sod1 +/- animals also had increased infarct volume and brain swelling, accompanied by increased apoptotic neuronal cell death as indicated by the in situ nick-end labeling technique to detect DNA fragmentation and morphological criteria. These results suggest that oxygen-free radicals, especially superoxide anions, are an important factor for the development of infarction by brain edema formation and apoptotic neuronal cell death after focal cerebral ischemia and reperfusion.

Premature thymic involution, observed at the ultrastructural level, in two lineages of human-SOD-1 transgenic mice

The human Cu/Zn superoxide dismutase (hSOD-1) gene, catalyses the dismutation of O2 to H2O2 and O2. It is located on chromosome 21 in q22.1 and is overexpressed in Down's syndrome (DS) patients. These patients present various abnormalities including mental retardation, congenital heart disease, immunological deficits and premature aging. In order to explore the potential role of SOD-1 overexpression in DS, we have generated two lineages of transgenic mice for the hSOD-1 gene and studied, at the ultrastructural level, the effect of hSOD-1 overexpression on the thymic microenvironment. Modification of the cellular architecture and morphology associated with a lipidic invasion, signs of a premature involution of the thymus, were observed in both lineages. A rupture of the filamentous network in the extracellular and probably also in the intracellular matrix was first observed. These results correlate the thymic alterations visualized in light microscopy, on the thymus from DS patients, and raise the question of the relationship between the SOD-1 overexpression and the different morphological alterations associated with the premature thymic involution observed in SOD-1 transgenic mice. They suggest that thymic and immunological impairments present in DS patients may be related to the SOD-1 gene dosage effect.

Reduction of CuZn-superoxide dismutase activity exacerbates neuronal cell injury and edema formation after transient focal cerebral ischemia

Apoptotic neuronal cell death has recently been associated with the development of infarction after cerebral ischemia. In a variety of studies, CuZn-superoxide dismutase (CuZn-SOD) has been shown to protect the brain from ischemic injury. A possible role for CuZn-SOD-related modulation of neuronal viability is suggested by the finding that CuZn-SOD inhibits apoptotic neuronal cell death in response to some forms of cellular damage. We evaluated this possibility in the model of transient focal cerebral ischemia in mice bearing a disruption of the CuZn-SOD gene (Sod1). Homozygous mutant (Sod1 -/-) mice had no detectable CuZn-SOD activity, and heterozygous mutants (Sod1 +/-) showed a 50% decrease compared with wild-type mice. Sod1 -/- mice showed a high level of blood-brain barrier disruption soon after 1 hr of middle cerebral artery occlusion and 100% mortality at 24 hr after ischemia. Sod1 +/- mice showed 30% mortality at 24 hr after ischemia, and neurological deficits were exacerbated compared with wild-type controls. The Sod1 +/- animals also had increased infarct volume and brain swelling, accompanied by increased apoptotic neuronal cell death as indicated by the in situ nick-end labeling technique to detect DNA fragmentation and morphological criteria. These results suggest that oxygen-free radicals, especially superoxide anions, are an important factor for the development of infarction by brain edema formation and apoptotic neuronal cell death after focal cerebral ischemia and reperfusion.

Transgenic animal models of familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) occurs in both sporadic and familial forms, which have very similar clinical presentation and course. Approximately 20% of the familial cases of ALS are caused by mutation of the SODI gene encoding Cu, Zn superoxide dismutase (SOD). Over 30 different SODI gene mutations have been found in patients. Most are missense mutations that cause the substitution of one amino acid for another. The failure to find deletions in familial ALS suggests that the mutant protein is required for pathogenesis. Studies in transgenic mice indicate that familial ALS is caused by gain-of-function mutations in the SODI gene. These enhance formation of free radicals by the mutant enzyme. When expressed at high levels in transgenic mice, mutant human Cu,Zn SOD causes a clinical disease that resembles human ALS. Selective degeneration of motor neurones in the spinal cord and brainstem is accompanied by progressive motor impairment. Pathogenesis in the transgenic model of familial ALS is a sequential, two-step process in which damage mediated by free radicals accumulates to a threshold that triggers catastrophic motor neurone loss through glutamate-mediated, excitotoxic mechanisms. Evidence in support of this hypothesis comes from therapeutic studies with antioxidants and inhibitors of glutamatergic neurotransmission.

Oxidative stress mediates impairment of muscle function in transgenic mice with elevated level of wild-type Cu/Zn superoxide dismutase

Cases of familial amyotrophic lateral sclerosis (fALS; a neurodegenerative disorder) have been reported in which the gene for Cu/Zn superoxide dismutase (CuZnSOD) was mutated. Several studies with the fALS mutant CuZnSOD in transgenic mice and cells showed that the fALS mutations act through an as yet undefined dominant gain-of-function mechanism. Wild-type CuZnSOD catalyzes the dismutation of superoxide (O(2)(-).) but also produces hydroxyl radicals (.OH) with H(2)O(2) as substrate. Two laboratories have recently demonstrated that the .OH production ability was preferentially enhanced by the fALS mutant CuZnSOD, suggesting that this might be the function gained in fALS. In this study, we used transgenic CuZnSOD (Tg-CuZnSOD) mice with elevated levels of CuZnSOD to determine whether overexpression of wild-type CuZnSOD was also associated with increased .OH production and impaired muscle function. Enhanced formation of .OH was detected, by spin trapping, in brain and muscle extracts of the Tg-CuZnSOD mice. Three independently derived Tg-CuZnSOD lines showed muscle abnormalities, reflected by altered electromyography (EMG) and diminished performance in the rope grip test. After treatment with paraquat (PQ), a widely used herbicide and O(2)(-).-generating compound, muscle disability significantly deteriorated in Tg-CuZnSOD mice but not in control mice. The results indicate that elevated levels of CuZnSOD cause indigenous long-term oxidative stress leading to impairment of muscle function. These findings may provide valuable clues about the concurred role of indigenous oxidative stress and exogenous agents in the etiology of sporadic ALS and several other neurodegenerative diseases in which a specific subset of neurons is affected.

Transgenic copper/zinc-superoxide dismutase ameliorates caerulein-induced pancreatitis in mice

The role of oxidative stress in acute pancreatitis was investigated by comparing the pathological features of caerulein pancreatitis between transgenic mice that overexpress human Cu/Zn-superoxide dismutase (SOD) and nontransgenic littermates. Both the elevation of serum amylase and the formation of pancreatic edema during the pancreatitis were significantly reduced in the transgenic mice compared with the nontransgenic littermates. In the transgenic mice, the pancreatitis-associated reduction of Cu/Zn-SOD activity in the pancreatic tissues was significantly smaller than that in the nontransgenic mice. These results provide direct evidence that the elevation of intracellular oxygen radicals is an important factor for the progress of acute edematous pancreatitis.

Midbrain dopaminergic neuronal degeneration in a transgenic mouse model of familial amyotrophic lateral sclerosis

Familial amyotrophic lateral sclerosis has been linked in 15% of families to mutations in the gene encoding for copper-zinc superoxide dismutase (Cu/Zn-SOD), a key enzyme in the cellular defense mechanisms against free radical attack. We used a transgenic mouse model of familial amyotrophic lateral sclerosis (transgenic G1H mice) based on expression of mutant human Cu/Zn-SOD to examine the influence of the transgene expression on midbrain dopaminergic neurons, cells that contain conspicuous amounts of this enzyme. At the time that 50% of motor neurons of the spinal cord were lost, we observed concurrent reductions in dopamine levels in the caudate-putamen and the nucleus accumbens of transgenic G1H mice. In addition, numbers of tyrosine hydroxylase-immunostained neurons were significantly reduced in both the substantia nigra (26%) and the ventral tegmental area (16%) compared to those in their nontransgenic littermates. Similar abnormalities were not observed in the brains of transgenic mice overexpressing wild-type Cu/Zn-SOD. These findings indicate that overexpression of the mutated Cu/Zn-SOD protein caused a significant loss of midbrain dopaminergic neurons in addition to the loss of spinal motor neurons. The potential of the mutated enzyme to induce cell death extending beyond the motor neurons is consistent with the description of substantia nigra degeneration in some patients with familial amyotrophic lateral sclerosis. Furthermore, if mutated Cu/Zn-SOD is conclusively shown to kill cells by oxidative stress, such an observation would be in keeping with the known sensitivity of dopaminergic neurons to free radical attack.

DNA fragmentation and Prolonged expression of c-fos, c-jun, and hsp70 in kainic acid-induced neuronal cell death in transgenic mice overexpressing human CuZn-superoxide dismutase

Kainic acid (KA) neurotoxicity was examined in transgenic (Tg) mice overexpressing human CuZn-superoxide dismutase (SOD-1). The doses of KA required to produce seizures, the severity of the seizures, and the regions damaged were similar in SOD-1 Tg and non-transgenic wild-type mice. Intraperitoneal KA injection induced seizure-related neuronal damage in the CA3 and CA1 regions of the hippocampus and in other regions of the brain in both SOD-1 Tg and wild-type mice. These damaged neurons were labeled with the terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) technique up to 72 h, although no significant difference in the number of TUNEL-positive neurons was observed between SOD-1 Tg and wild-type mice. In situ hybridization showed that c-fos, c-jun, and hsp70 genes were expressed in the hippocampus, cortex, and other regions of the brain after KA treatment. The expression of these genes was maximal 1 to 4 h following KA treatment but persisted longer in the hippocampus and other regions in SOD-1 Tg compared with wild-type mice; however, cell death in the hippocampus, assessed using cresyl violet staining, was similar in SOD-1 Tg and wild-type mice. The data show that superoxide radicals modulate both immediate early gene and heat shock gene expression after KA-induced seizures. The prolonged expression of c-fos, c-jun, and hsp70 in SOD-1 Tg compared with wild-type mice may indicate that hippocampal neurons survive longer in SOD-1 Tg than in wild-type animals; however, cell death as well as the seizure threshold, seizure severity and the pattern of regional vulnerability were not affected substantially by increased levels of SOD in the brain.

Novel mutations in an otherwise strictly conserved domain of CuZn superoxide dismutase

All mutations in the human gene for CuZn superoxide dismutase (CuZnSOD) reported to date are associated with the disease amyotrophic lateral sclerosis (ALS). These mutations, mostly of a familial nature (ALS 1, MIM 105400), span all of the coding region of this enzyme except for a highly conserved centrally located domain that includes all of exon III. We describe the identification and characterization of two mutations in this region, both found in mice. One mutation, a glutamate to lysine amino acid substitution was found in position 77 (E77K) of the strain SOD1/Ei distributed by the Jackson Laboratory. The other mutation, a lysine to glutamate substitution at position 70 (K70E) of a human transgene, was discovered in mouse line TgHS/SF-155. Enzyme activity measurements and heterodimer analysis of the CuZn SOD variant in SOD1/Ei suggest a mild loss of activity, which differs from the enzyme activity losses detected in patients with autosomal dominant ALS 1. Similarly, the presence of the mutant transgene in TgHS/SF 155 does not produce any phenotypic manifestations.

ALS-linked SOD1 mutant G85R mediates damage to astrocytes and promotes rapidly progressive disease with SOD1-containing inclusions

High levels of familial Amyotrophic Lateral Sclerosis (ALS)-linked SOD1 mutants G93A and G37R were previously shown to mediate disease in mice through an acquired toxic property. We report here that even low levels of another mutant, G85R, cause motor neuron disease characterized by an extremely rapid clinical progression, without changes in SOD1 activity. Initial indicators of disease are astrocytic inclusions that stain intensely with SOD1 antibodies and ubiquitin and SOD1-containing aggregates in motor neurons, features common with some cases of SOD1 mutant-mediated ALS. Astrocytic inclusions escalate markedly as disease progresses, concomitant with a decrease in the glial glutamate transporter (GLT-1). Thus, the G85R SOD1 mutant mediates direct damage to astrocytes, which may promote the nearly synchronous degeneration of motor neurons.

Attenuation of acute and chronic damage following traumatic brain injury in copper, zinc-superoxide dismutase transgenic mice

To elucidate the role of oxygen-derived free radicals and superoxide dismutase in traumatic brain injury (TBI), blood-brain barrier (BBB) permeability, brain edema, behavioral function, and necrotic cavity volume (CV) were evaluated after TBI using nontransgenic (nTg) mice and heterozygous and homozygous transgenic (Tg) mice with a 1.5- (Tg 1.5x), 3.1-(Tg3.1x) and five- (Tg5x) fold increase in human copper, zinc-superoxide dismutase (CuZn-SOD) activity. Traumatic brain injury was produced by the weight-drop method. Evans blue dye leakage 4 hours after injury was attenuated in a CuZn-SOD dose-dependent manner with decreases of 18.6%, 40.9%, and 48.8%, in the Tg1.5x, Tg3.1x, and Tg5x groups, respectively. The water content 6 hours after injury in the Tg3.1x (79.64%) and Tg5x (79.45%) groups was significantly lower than in nTg mice (81.37%). There was an initial decrease in body weight and in motor performance, as measured by beam walk and beam balance tasks undertaken 1 day after TBI. However, the average reduction in beam balance and beam walk performance deficits and changes in body weight postinjury were significantly ameliorated in Tg mice. The CV was significantly smaller in Tg mice than in nTg mice (p < 0.01). These results indicate that superoxide radicals play a deleterious role following TBI. Furthermore, Tg mice provide a useful model for demonstrating the beneficial role of an antioxidant enzyme in TBI without the confounding effect of pharmacokinetics, toxicity, and BBB permeability associated with exogenous agents.

Effects of nitric oxide synthase inhibition on brain infarction in SOD-1-transgenic mice following transient focal cerebral ischemia

To investigate the role of superoxide in the toxicity of nitric oxide (NO), we examined the effect of nitric oxide synthase (NOS) inhibition on brain infarction in transgenic mice overexpressing CuZn-superoxide dismutase (SOD-1). Male SOD-transgenic mice and non-transgenic littermates (30-35 g) were subjected to 60 min of middle cerebral artery occlusion followed by 24 h of reperfusion. Either NG-nitro-L-arginine methyl ester (L-NAME; 3 mg/kg), a mixed neuronal and endothelial NOS inhibitor, or 7-nitroindazole (7-NI; 25 mg/kg), a selective neuronal NOS inhibitor, was administered intraperitoneally 5 min after the onset of ischemia. At 24 h of reperfusion, the mice were decapitated and the infarct volume was evaluated in each group. In the nontransgenic mice, L-NAME significantly increased the infarct volume as compared with the vehicle, while 7-NI significantly decreased it. In the SOD-transgenic mice, L-NAME-treated animals showed a significantly larger infarct volume than vehicle-treated ones, whereas there were no significant differences between 7-NI- and vehicle-treated mice. Our findings suggest that selective inhibition of neuronal NOS ameliorates ischemic brain injury and that both neuronal and endothelial NOS inhibition may result in the deterioration of ischemic injury due to vasoconstriction of the brain. Since L-NAME increased infarct volume even in SOD-transgenic mice, the protective effect of SOD could result from the vasodilation by increased endothelial NO as well as the reduction of neuronal injury due to less production of peroxynitrite compared to wild-type mice. Moreover, the neurotoxic role of NO might not be dependent on NO itself, but the reaction with superoxide to form peroxynitrite, because of no additive effects of SOD and a neuronal NOS inhibitor.

Rapid fluorescence in situ hybridization on interphasic nuclei to discriminate between homozygous and heterozygous transgenic mice

Homozygous and heterozygous transgenic mice of the Tg152 line overexpressing the human copper/zinc superoxide dismutase (hSOD-1) were rapidly differentiated by fluorescence in situ hybridization (FISH) using interphase lymphocyte nuclei. We have devised a simple and fast method for preparing interphase nuclei with very small quantities of whole mouse blood, avoiding several steps of the classical FISH technique. Lymphocyte separation and cell culture were not required. This technique provides an excellent tool for the unambiguous detection of homozygous and heterozygous transgenic mice in a litter. It can be used to check young animals since 2 microliters of whole blood is sufficient. We also show that in this transgenic line numerous copies of the hSOD-1 transgene are integrated at a single autosomal locus, in tandem head-to-tail organization.

Nitric oxide is a mediator of methamphetamine (METH)-induced neurotoxicity. In vitro evidence from primary cultures of mesencephalic cells

METH is a monoaminergic toxic that destroys dopamine terminals in vivo. Oxidative mechanisms associated with DA metabolism are thought to play an important role in its toxic effects. These ideas were supported by the demonstration that CuZn-superoxide dismutase (CuZnSOD) transgenic mice were protected against the toxic effects of the drug. In the present study, we sought to determine if nitric oxide (NO) production was also involved in METH-induced neurotoxicity using primary cultures obtained from fetal rat mesencephalon. METH caused dose- and time-dependent cell death in vitro. Blockade of nitric oxide (NO) formation with several nitric oxide (NO) synthase blockers attenuated METH-mediated toxicity. Moreover, inhibition of ADP-ribosylation with nicotinamide and benzamide also provided protection against the toxicity of the drug. These results, together with our previous results in transgenic mice, support a role for free radicals in METH-induced toxic effects.

Expression of hsp70 mRNA is induced in the brain of transgenic mice overexpressing human CuZn-superoxide dismutase following transient global cerebral ischemia

We examined hsp70 mRNA expression in the brains of transgenic (Tg) mice overexpressing CuZn-superoxide dismutase and in wild-type (Wt) littermates after 3 min of bilateral common carotid artery occlusion. Significant induction of hsp70 mRNA occurred in the hippocampus, the cortex, and other brain regions of the Tg mice 4 h after ischemia compared to the Wt mice. However, there was no histological damage in the brains of Tg and Wt mice as assessed by both Cresyl violet staining and by TUNEL staining for DNA fragmentation. These data suggest that high levels of CuZn-superoxide dismutase activity increase hsp70 mRNA expression and that intense hsp70 mRNA expression does not predict neuronal damage, even in vulnerable hippocampal CA1 neurons.

DNA and RNA strand scission by copper, zinc and manganese superoxide dismutases

Copper/zinc (Cu/ZnSOD) and manganese (MnSOD) superoxide dismutases which catalyze the dismutation of toxic superoxide anion, O(2-)-, to O2 and H2O2, play a major role in protecting cells from toxicity of oxidative stress. However, cells overexpressing either form of the enzyme show signs of toxicity, suggesting that too much SOD may be injurious to the cell. To elucidate the possible mechanism of this cytotoxicity, the effect of SOD on DNA and RNA strand scission was studied. High purity preparations of Cu/ZnSOD and MnSOD were tested in an in vitro assay in which DNA cleavage was measured by conversion of phage phi X174 supercoiled double-stranded DNA to open circular and linear forms. Both types of SOD were able to induce DNA strand scission generating single- and double-strand breaks in a process that required oxygen and the presence of fully active enzyme. The DNA strand scission could be prevented by specific anti-SOD antibodies added directly or used for immunodepletion of SOD. Requirement for oxygen and the effect of Fe(II) and Fe(III) ions suggest that cleavage of DNA may be in part mediated by hydroxyl radicals formed in Fenton-type reactions where enzyme-bound transition metals serve as a catalyst by first being reduced by superoxide and then oxidized by H2O2. Another mechanism was probably operative in this system, since in the presence of magnesium DNA cleavage by SOD was oxygen independent and not affected by sodium cyanide. It is postulated that SOD, by having a similar structure to the active center of zinc-containing nucleases, is capable of exhibiting non-specific nuclease activity causing hydrolysis of the phosphodiester bonds of DNA and RNA. Both types of SOD were shown to effectively cleave RNA. These findings may help explain the origin of pathology of certain hereditary diseases genetically linked to Cu/ZnSOD gene.