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

Implications of Epigenetic Mechanisms and their Targets in Cerebral Ischemia Models

BACKGROUND

Understanding the complexities associated with the ischemic condition and identifying therapeutic targets in ischemia is a continued challenge in stroke biology. Emerging evidence reveals the potential involvement of epigenetic mechanisms in the incident and outcome of stroke, suggesting novel therapeutic options of targeting different molecules related to epigenetic regulation.

OBJECTIVE

This review summarizes our current understanding of ischemic pathophysiology, describes various in vivo and in vitro models of ischemia, and examines epigenetic modifications associated with the ischemic condition.

METHOD

We focus on microRNAs, DNA methylation, and histone modifying enzymes, and present how epigenetic studies are revealing novel drug target candidates in stroke.

CONCLUSION

Finally, we discuss emerging approaches for the prevention and treatment of stroke and post-stroke effects using pharmacological interventions with a wide therapeutic window.

Pandora's Box: mitochondrial defects in ischaemic heart disease and stroke

Ischaemic heart disease and stroke are vascular events with serious health consequences worldwide. Recent genetic and epigenetic techniques have revealed many genetic determinants of these vascular events and simplified the approaches to research focused on ischaemic heart disease and stroke. The pathogenetic mechanisms of ischaemic heart disease and stroke are complex, with mitochondrial involvement (partially or entirely) recently gaining substantial support. Not only can mitochondrial reactive oxygen species give rise to ischaemic heart disease and stroke by production of oxidised low-density lipoprotein and induction of apoptosis, but the impact on pericytes contributes directly to the pathogenesis. Over the past two decades, publications implicate the causative role of nuclear genes in the development of ischaemic heart disease and stroke, in contrast to the potential role of mitochondrial DNA (mtDNA) in the pathophysiology of the disorders, which is much less understood, although recent studies do demonstrate that the involvement of mitochondria and mtDNA in the development of ischaemic heart disease and stroke is likely to be larger than originally thought, with the novel discovery of links among mitochondria, mtDNA and vascular events. Here we explore the molecular events and mtDNA alterations in relation to the role of mitochondria in ischaemic heart disease and stroke.

Delta Opioid Receptor and Peptide: A Dynamic Therapy for Stroke and Other Neurological Disorders

Research of the opioid system and its composite receptors and ligands has revealed its promise as a potential therapy for neurodegenerative diseases such as stroke and Parkinson's Disease. In particular, delta opioid receptors (DORs) have been elucidated as a therapeutically distinguished subset of opioid receptors and a compelling target for novel intervention techniques. Research is progressively shedding light on the underlying mechanism of DORs and has revealed two mechanisms of DOR neuroprotection; DORs function to maintain ionic homeostasis and also to trigger endogenous neuroprotective pathways. Delta opioid agonists such as (D-Ala2, D-Leu5) enkephalin (DADLE) have been shown to promote neuronal survival and decrease apoptosis, resulting in a substantial amount of research for its application as a neurological therapeutic. Most notably, DADLE has demonstrated significant potential to reduce cell death following ischemic events. Current research is working to reveal the complex mechanisms of DADLE's neuroprotective properties. Ultimately, our knowledge of the DOR receptors and agonists has made the opioid system a promising target for therapeutic intervention in many neurological disorders.

Neuroprotection of ischemic preconditioning is mediated by thioredoxin 2 in the hippocampal CA1 region following a subsequent transient cerebral ischemia

Preconditioning by brief ischemic episode induces tolerance to a subsequent lethal ischemic insult, and it has been suggested that reactive oxygen species are involved in this phenomenon. Thioredoxin 2 (Trx2), a small protein with redox-regulating function, shows cytoprotective roles against oxidative stress. Here, we had focused on the role of Trx2 in ischemic preconditioning (IPC)-mediated neuroprotection against oxidative stress followed by a subsequent lethal transient cerebral ischemia. Animals used in this study were randomly assigned to six groups; sham-operated group, ischemia-operated group, IPC plus (+) sham-operated group, IPC + ischemia-operated group, IPC + auranofin (a TrxR2 inhibitor) + sham-operated group and IPC + auranofin + ischemia-operated group. IPC was subjected to a 2 minutes of sublethal transient ischemia 1 day prior to a 5 minutes of lethal transient ischemia. A significant loss of neurons was found in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) in the ischemia-operated-group 5 days after ischemia-reperfusion; in the IPC + ischemia-operated-group, pyramidal neurons in the SP were well protected. In the IPC + ischemia-operated-group, Trx2 and TrxR2 immunoreactivities in the SP and its protein level in the CA1 were not significantly changed compared with those in the sham-operated-group after ischemia-reperfusion. In addition, superoxide dismutase 2 (SOD2) expression, superoxide anion radical ( O2-) production, denatured cytochrome c expression and TUNEL-positive cells in the IPC + ischemia-operated-group were similar to those in the sham-operated-group. Conversely, the treatment of auranofin to the IPC + ischemia-operated-group significantly increased cell damage/death and abolished the IPC-induced effect on Trx2 and TrxR2 expressions. Furthermore, the inhibition of Trx2R nearly cancelled the beneficial effects of IPC on SOD2 expression, O2- production, denatured cytochrome c expression and TUNEL-positive cells. In brief, this study shows that IPC conferred neuroprotection against ischemic injury by maintaining Trx2 and suggests that the maintenance or enhancement of Trx2 expression by IPC may be a legitimate strategy for therapeutic intervention of cerebral ischemia.

Apurinic/apyrimidinic endonuclease 1 upregulation reduces oxidative DNA damage and protects hippocampal neurons from ischemic injury

AIMS

Apurinic/apyrimidinic endonuclease 1 (APE1) is a multifunctional enzyme that participates in base-excision repair of oxidative DNA damage and in the redox activation of transcription factors. We tested the hypothesis that APE1 upregulation protects neuronal structure and function against transient global cerebral ischemia (tGCI).

RESULTS

Upregulation of APE1 by low-dose proton irradiation (PI) or by transgene overexpression protected hippocampal CA1 neurons against tGCI-induced cell loss and reduced apurinic/apyrimidinic sites and DNA fragmentation. Conversely, APE1 knockdown attenuated the protection afforded by PI and ischemic preconditioning. APE1 overexpression inhibited the DNA damage response, as evidenced by lower phospho-histone H2A and p53-upregulated modulator of apoptosis levels. APE1 overexpression also partially rescued dendritic spines and attenuated the decrease in field excitatory postsynaptic potentials in hippocampal CA1. Presynaptic and postsynaptic markers were reduced after tGCI, and this effect was blunted in APE1 transgenics. The Morris water maze test revealed that APE1 protected against learning and memory deficits for at least 27 days post-injury. Animals expressing DNA repair-disabled mutant APE1 (D210A) exhibited more DNA damage than wild-type controls and were not protected against tGCI-induced cell loss.

INNOVATION

This is the first study that thoroughly characterizes structural and functional protection against ischemia after APE1 upregulation by measuring synaptic markers, electrophysiological function, and long-term neurological deficits in vivo. Furthermore, disabling the DNA repair activity of APE1 was found to abrogate its protective impact.

CONCLUSION

APE1 upregulation, either endogenously or through transgene overexpression, protects DNA, neuronal structures, synaptic function, and behavioral output from ischemic injury.

SOD1 overexpression prevents acute hyperglycemia-induced cerebral myogenic dysfunction: relevance to contralateral hemisphere and stroke outcomes

Admission hyperglycemia (HG) amplifies vascular injury and neurological deficits in acute ischemic stroke, but the mechanisms remain controversial. We recently reported that ischemia-reperfusion (I/R) injury impairs the myogenic response in both hemispheres via increased nitration. However, whether HG amplifies contralateral myogenic dysfunction and whether loss of tone in the contralateral hemisphere contributes to stroke outcomes remain to be determined. Our hypothesis was that contralateral myogenic dysfunction worsens stroke outcomes after acute hyperglycemic stroke in an oxidative stress-dependent manner. Male wild-type or SOD1 transgenic rats were injected with saline or 40% glucose solution 10 min before surgery and then subjected to 30 min of ischemia/45 min or 24 h of reperfusion. In another set of animals (n = 5), SOD1 was overexpressed only in the contralateral hemisphere by stereotaxic adenovirus injection 2-3 wk before I/R. Myogenic tone and neurovascular outcomes were determined. HG exacerbated myogenic dysfunction in contralateral side only, which was associated with infarct size expansion, increased edema, and more pronounced neurological deficit. Global and selective SOD1 overexpression restored myogenic reactivity in ipsilateral and contralateral sides, respectively, and enhanced neurovascular outcomes. In conclusion, our results show that SOD1 overexpression nullified the detrimental effects of HG on myogenic tone and stroke outcomes and that the contralateral hemisphere may be a novel target for the management of acute hyperglycemic stroke.

[Effects of the combination of active component extracts from Astragalus membranaceus and Panax notoginseng on apoptosis, reactive oxygen species and mitochondrial membrane potential of PC12 cells with oxidative injury]

OBJECTIVE

To explore the effects and mechanisms of combining astragaloside IV (the effective component of Astragalus membranaceus) with notoginsenoside R1, ginsenoside Rb1 and ginsenoside Rg1 (the effective components of Panax notoginseng) against oxidative injury in PC12 cells induced by cobalt chloride (CoCl₂).

METHODS

CoCl₂ was used to stimulate PC12 cells to induce injury after transdifferentiation with nerve growth factor. Then the PC12 cells were divided into 10 groups and cultured with corresponding drugs. After culture, apoptotic cells were tested by using Hocchst 33258 fluorescent staining, the level of mitochondrial membrane potential (MMP) was analyzed by rhodamine 123 fluorescent staining and the content of reactive oxygen species (ROS) in PC12 cell was measured by dichlorofluorescin diacetate fluorescent staining.

RESULTS

CoCl₂ induced apoptosis along with the obvious decrease of MMP as well as overproduction of ROS in PC12 cells. Astragaloside IV, ginsenosides Rg1, ginsenosides Rb1 and notoginsenoside R1 had inhibition effects in different degree on PC12 cell apoptosis induced by CoCl₂, reduced the overproduction of ROS and the decrease of MMP. The effects of the combination were better than those of active component alone.

CONCLUSION

Active components extracted from Astragalus and Panax notoginseng can inhibit PC12 cell apoptosis induced by oxidative injury, furthermore, the effects were enhanced by combination of these components, which may be associated with jointly antagonizing the generation of ROS and raising MMP.

17β-estradiol increases expression of the oxidative stress response and DNA repair protein apurinic endonuclease (Ape1) in the cerebral cortex of female mice following hypoxia

While it is well established that 17β-estradiol (E2) protects the rodent brain from ischemia-induced damage, it has been unclear how this neuroprotective effect is mediated. Interestingly, convincing evidence has also demonstrated that maintaining or increasing the expression of the oxidative stress response and DNA repair protein apurinic endonuclease 1 (Ape1) is instrumental in reducing ischemia-induced damage in the brain. Since E2 increases expression of the oxidative stress response proteins Cu/Zn superoxide dismutase and thioredoxin in the brain, we hypothesized that E2 may also increase Ape1 expression and that this E2-induced expression of Ape1 may help to mediate the neuroprotective effects of E2 in the brain. To test this hypothesis, we utilized three model systems including primary cortical neurons, brain slice cultures, and whole animals. Although estrogen receptor α and Ape1 were expressed in primary cortical neurons, E2 did not alter Ape1 expression in these cells. However, immunofluorescent staining and quantitative Western blot analysis demonstrated that estrogen receptor α and Ape1 were expressed in the nuclei of cortical neurons in brain slice cultures and that E2 increased Ape1 expression in the cerebral cortex of these cultures. Furthermore, Ape1 expression was increased and oxidative DNA damage was decreased in the cerebral cortices of ovariectomized female C57Bl/6J mice that had been treated with E2 and exposed to hypoxia. Taken together, our studies demonstrate that the neuronal microenvironment may be required for increased Ape1 expression and that E2 enhances expression of Ape1 and reduces oxidative DNA damage, which may in turn help to reduce ischemia-induced damage in the cerebral cortex and mediate the neuroprotective effects of E2.

Apurinic/apyrimidinic endonuclease 1 is a key modulator of aluminum-induced neuroinflammation

Background

Chronic administration of Aluminum is proposed as an environmental factor that may affect several enzymes and other biomolecules related to neurotoxicity and Alzheimer's disease (AD). APE1 a multifunctional protein, functions in DNA repair and plays a key role in cell survival versus cell death upon stimulation with cytotoxic agent, making it an attractive emerging therapeutic target. The promising protective effect of resveratrol (resv), which is known to exert potent anti-inflammatory effects on neurotoxicity induced by aluminum chloride (AlCl₃), may be derived from its own antioxidant properties. In the present work we investigated the modulation of APE1 expression during AlCl₃-induced neuroinflammation (25 mg/Kg body weight by oral gavages) in experimental rats. We tested the hypothesis that a reactive oxygen species (ROS)-scavenger, resveratrol at 0.5 mg/kg bodyweight, which is known to exert potent anti-inflammatory effects, would attenuate central inflammation and modulate APE1 expression in AlCl₃-fed rats. Neuroinflammation-induced genes including β-secretase (BACE), amyloid-β precursor protein (APP), presenilin 2 (PSEN-2) and sirt-2 were determined by RT-PCR. APE1 is determined at mRNA and protein levels and confirmed by immunohistochemistry. The expression of pro-inflammatory cytokines (TNF-α, IL6) and iNOS by the rat brain extract were measured by RT-PCR.

Result

Our results indicate that resveratrol may attenuate AlCl₃-induced direct neuroinflammation in rats, and its mechanisms are, at least partly, due to maintaining high APE1 level. Resveratrol co-administration with aluminum chloride exerted more protective effect than pre-administration or treatment of induced rats. A significant elevation of APE1 at both mRNA and protein levels was observed in addition to a marked reduction in β-secretase and amyloid-β. We found that AlCl₃ stimulated the expression of TNF-α, IL-6, and iNOS in rat brain in which NF-κB was involved. Resveratrol inhibited AlCl₃-induced expression and release of TNF-α, IL-6, and iNOS in rat brain.

Conclusions

These findings establish a role for APE1 as a master regulator of AlCl₃ dependent inflammatory responses in rat brain. In addition, there was an ameliorative change with resveratrol against AlCl₃-induced neurotoxicity. These results suggest that rat brain cells produce pro-inflammatory cytokines in response to AlCl₃ in a similar pattern, and further suggest that resveratrol exerts anti-inflammatory effects in rat brain, at least partly, by inhibiting different pro-inflammatory cytokines and key signaling molecules. It might be a potential agent for treatment of neuroinflammation-related diseases, such as AD.

Estradiol exerts antiapoptotic effects in skeletal myoblasts via mitochondrial PTP and MnSOD

17β-Estradiol (E(2)) protects several non-reproductive tissues from apoptosis, including skeletal muscle. We have shown that E(2) at physiological concentrations prevented apoptosis induced by H(2)O(2) in C2C12 skeletal myoblasts. As we also demonstrated the presence of estrogen receptors in mitochondria, the present work was focused on the effects of E(2) on this organelle. Specifically, we evaluated the actions of E(2) on the mitochondrial permeability transition pore (MPTP) by the calcein-acetoxymethylester/cobalt method using fluorescence microscopy and flow cytometry. Pretreatment with E(2) prevented MPTP opening induced by H(2)O(2), which preceded loss of mitochondrial membrane potential. In addition, it was observed that H(2)O(2) induced translocation of Bax to mitochondria; however, in the presence of the steroid this effect was abrogated suggesting that members of the Bcl-2 family may be regulated by E(2) to exert an antiapoptotic effect. Moreover, E(2) increased mitochondrial manganese superoxide dismutase protein expression and activity, as part of a mechanism activated by E(2) that improved mitochondrial performance. Our results suggest a role of E(2) in the regulation of apoptosis with a clear action at the mitochondrial level in C2C12 skeletal myoblast cells.

17β-Estradiol-mediated increase in Cu/Zn superoxide dismutase expression in the brain: a mechanism to protect neurons from ischemia

A number of studies have demonstrated that 17β-estradiol (E(2)) protects the brain from ischemia and yet the mechanism by which this hormone brings about its protective effect is unclear. Interestingly, like E(2), overexpression of the oxidative stress response protein Cu/Zn superoxide dismutase (SOD1), which plays a critical role in regulating reactive oxygen species, also protects the brain from ischemia. Because we previously showed that E(2) treatment of cultured mammary cells increases SOD1 expression, we hypothesized that E(2) might increase SOD1 expression in the brain and that this E(2)-mediated increase in SOD1 expression might help to protect the brain from ischemia. We now show that SOD1 is expressed in cortical neurons, that SOD1 expression is increased by exposure of brain slice cultures to E(2), and that the E(2)-mediated increase in SOD1 expression is further augmented by exposure of brain slice cultures to increased superoxide levels or oxygen and glucose deprivation. Importantly, when cortical neurons are exposed to increased superoxide levels and markers of protein and DNA damage, nitrotyrosine and 8-oxoguanine, respectively, are measured, both protein and DNA damage are reduced. In fact, E(2) reduces nitrotyrosine and 8-oxoguanine levels in brain slice cultures regardless of whether they have or have not been exposed to increased superoxide levels. Likewise, when brain slice cultures are treated with E(2) and deprived of oxygen and glucose, 8-oxoguanine levels are reduced. Taken together, these studies provide a critical link between E(2) treatment, SOD1 expression, and neuroprotection and help to define a mechanism through which E(2)-mediated neuroprotection may be conferred.

Identification of oxidized serum albumin in the cerebrospinal fluid of ischaemic stroke patients

BACKGROUND AND PURPOSE

  Extensive evidence has shown that oxidative stress mediates neuronal death in animal models of hypoxic-ischaemia. Brain biomarkers of oxidative stress need to be identified in order to better understand and treat brain damage in human stroke patients. The present study was conducted to identify potential target proteins of oxidative stress in the cerebrospinal fluid (CSF) of stroke patients with acute ischaemic brain injury.

METHODS

  We performed two-dimensional polyacrylamide gel electrophoresis to separate protein samples obtained from the CSF of control and stroke patients. To determine protein oxidation levels, oxyblot was then used to detect protein carbonyls that were determined by formation of a stable 2,4-dinitrophenylhydrazine (DNP) product using an anti-DNP antibody.

RESULTS

  We found that oxidation of serum albumin was increased in the CSF from stroke patients as well as rats who underwent permanent middle cerebral artery occlusion (6.5%, 23%, respectively). In stroke patients, oxidized albumin levels correlated to neurologic indications.

CONCLUSIONS

  The present study suggests that oxidized albumin in CSF can be utilized as an oxidative stress marker in human stroke patients.

SOD1 and MitoTEMPO partially prevent mitochondrial permeability transition pore opening, necrosis, and mitochondrial apoptosis after ATP depletion recovery

Generation of excessive reactive oxygen species (ROS) leads to mitochondrial dysfunction, apoptosis, and necrosis in renal ischemia-reperfusion (IR) injury. Previously we showed that lentiviral vector-mediated overexpression of superoxide dismutase-1 (SOD1) in proximal tubular epithelial cells (LLC-PK(1)) reduced cytotoxicity in an in vitro model of IR injury. Here, we examined the effects of SOD1 overexpression on mitochondrial signaling after ATP depletion-recovery (ATP-DR). To examine the role of mitochondrial ROS, a subset of cells was treated with the mitochondrial antioxidant MitoTEMPO. ATP-DR-mediated increase in mitochondrial calcium, loss of mitochondrial membrane potential, and increase in mitochondrial permeability transition pore (MPTP) were attenuated by SOD1 and MitoTEMPO (P<0.01). SOD1 prevented ATP-DR-induced mitochondrial Bax translocation, although the release of proapoptotic proteins from mitochondria was not prevented by SOD1 alone and required the presence of both SOD1 and MitoTEMPO. SOD1 suppressed the increase in c-jun phosphorylation, suggesting that JNK signaling regulates Bax translocation to mitochondria via ROS. ATP-DR-mediated changes in MPTP and mitochondrial signaling increased necrosis and apoptosis, both of which were partially attenuated by SOD1 and MitoTEMPO. These studies show that SOD1 and MitoTEMPO preserve mitochondrial integrity and attenuate ATP-DR-mediated necrosis and apoptosis.

Critical role for copper/zinc-superoxide dismutase in preventing spontaneous intracerebral hemorrhage during acute and chronic hypertension in mice

BACKGROUNDS AND PURPOSE

Superoxide is associated with spontaneous intracerebral hemorrhage (ICH) during hypertension. The goal of this study was to test the hypothesis that changes in superoxide, in genetically altered mice with deletion and overexpression of copper/zinc-superoxide dismutase (SOD1), modulate susceptibility to ICH.

METHODS

Chronic hypertension was produced by infusion of angiotensin II and an inhibitor of nitric oxide synthase in drinking water in SOD1 transgenic (SOD1Tg) mice, SOD1-deficient (SOD1(-/-)) mice, and their respective wild-type littermates. Acute hypertension was produced by daily injections of angiotensin II in some mice with chronic hypertension to produce ICH. We evaluated susceptibility to ICH, oxidative stress (superoxide, NAD[P]H oxidase activity, SOD activity), gene expression, and activity of matrix metalloproteinases.

RESULTS

Incidence, size, and number of ICHs were reduced in SOD1Tg mice and were increased in SOD1(-/-) mice compared with their wild-type littermates. Levels of superoxide increased in the brain even before developing ICH in wild-type littermates, whereas levels of superoxide remained low in SOD1Tg mice. Changes in level of matrix metalloproteinase-9 paralleled oxidative stress in SOD1Tg mice and wild-type littermates. Moreover, levels of superoxide and matrix metalloproteinase-9 were greater in SOD1(-/-) mice than wild-type littermates after induction of ICH. Active matrix metalloproteinases colocalized on cerebral vessels that appeared to lead toward regions with ICH.

CONCLUSIONS

These results suggest that superoxide contributes to the pathogenesis of spontaneous ICH, possibly through activation of matrix metalloproteinase-9, and that SOD1 protects against spontaneous ICH during hypertension.

Apurinic/apyrimidinic endonuclease APE1 is required for PACAP-induced neuroprotection against global cerebral ischemia

Inducible DNA repair via the base-excision repair pathway is an important prosurvival mechanism activated in response to oxidative DNA damage. Elevated levels of the essential base-excision repair enzyme apurinic/apyrimidinic endonuclease 1 (APE1)/redox effector factor-1 correlate closely with neuronal survival against ischemic insults, depending on the CNS region, protective treatments, and degree of insult. However, the precise mechanisms by which this multifunctional protein affords protection and is activated by upstream signaling pathways in postischemic neurons are not well delineated. Here we show that intracerebral administration of pituitary adenylate cyclase-activating polypeptide (PACAP), an endogenously occurring small neuropeptide, induces expression of APE1 in hippocampal neurons. Induction of APE1 expression requires PKA- and p38-dependent phosphorylation of cAMP response-element binding and activating transcription factor 2, which leads to transactivation of the APE1 promoter. We further show that PACAP markedly reduces oxidative DNA stress and hippocampal CA1 neuronal death following transient global ischemia. These effects occurred, at least in part, via enhanced APE1 expression. Furthermore, the DNA repair function of APE1 was required for PACAP-mediated neuroprotection. Thus, induction of DNA repair enzymes may be a unique strategy for neuroprotection against hippocampal injury.

Mitochondrial and apoptotic neuronal death signaling pathways in cerebral ischemia

Mitochondria play important roles as the powerhouse of the cell. After cerebral ischemia, mitochondria overproduce reactive oxygen species (ROS), which have been thoroughly studied with the use of superoxide dismutase transgenic or knockout animals. ROS directly damage lipids, proteins, and nucleic acids in the cell. Moreover, ROS activate various molecular signaling pathways. Apoptosis-related signals return to mitochondria, then mitochondria induce cell death through the release of pro-apoptotic proteins such as cytochrome c or apoptosis-inducing factor. Although the mechanisms of cell death after cerebral ischemia remain unclear, mitochondria obviously play a role by activating signaling pathways through ROS production and by regulating mitochondria-dependent apoptosis pathways.

Impact of inorganic nutrients on maintenance of genomic stability

Maintenance of genome stability is of fundamental importance for counteracting carcinogenesis. Many human genome instability syndromes exhibit a predisposition to cancer. An increasing body of epidemiological evidence has suggested a link between nutrient status and risk of cancer. Like other chemicals, nutrients can be toxic when consumed in excess. It has become clear that both nutritional deficiency and toxicity can compromise the integrity of the genome. This article focuses on roles of inorganic trace nutrients, including selenium, copper, zinc, and iron, in the redox regulation of genome stability and how they relate to the pathologies of genomic instability syndromes and cancer.

MnTMPyP, a cell-permeant SOD mimetic, reduces oxidative stress and apoptosis following renal ischemia-reperfusion

Oxidative stress and apoptosis are important factors in the etiology of renal ischemia-reperfusion (I/R) injury. The present study tested the hypothesis that the cell-permeant SOD mimetic manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP) protects the kidney from I/R-mediated oxidative stress and apoptosis in vivo. Male Sprague-Dawley rats (175-220 g) underwent renal I/R by bilateral clamping of the renal arteries for 45 min followed by reperfusion for 24 h. To examine the role of reactive oxygen species (ROS) in renal I/R injury, a subset of animals were treated with either saline vehicle (I/R Veh) or MnTMPyP (I/R Mn) (5 mg/kg ip) 30 min before and 6 h after surgery. MnTMPyP significantly attenuated the I/R-mediated increase in serum creatinine levels and decreased tubular epithelial cell damage following I/R. MnTMPyP also decreased TNF-alpha levels, gp(91phox), and lipid peroxidation after I/R. Furthermore, MnTMPyP inhibited the I/R-mediated increase in apoptosis and caspase-3 activation. Interestingly, although MnTMPyP did not increase expression of the antiapoptotic protein Bcl-2, it decreased the expression of the proapoptotic genes Bax and FasL. These results suggest that MnTMPyP is effective in reducing apoptosis associated with renal I/R injury and that multiple signaling mechanisms are involved in ROS-mediated cell death following renal I/R injury.

Base excision repair activities in organotypic hippocampal slice cultures exposed to oxygen and glucose deprivation

The capacity for DNA repair is likely to be one of the factors that determine the vulnerability of neurons to ischemic stress and may influence the pathological outcome of stroke. In this report, initiation of base excision repair (BER) was assessed by analysis of enzyme activity and gene expression level of DNA glycosylases and AP-endonucleases in rat organotypic hippocampal slice cultures exposed to oxygen and glucose deprivation (OGD) - an in vitro model of stroke. Under basal conditions, AP-endonuclease activity and base removal of ethenoadenine and 8-oxoguanine (8-oxoG) were higher (by approximately 20-35 %) in CA3/fascia dentata (FD) than in CA1. Base removal of uracil did not differ between the two hippocampal regions, while removal of 5-hydroxyuracil (5-OHU) was slightly less efficient in CA3/FD than in CA1. Analyses performed immediately after 30 min of OGD revealed a decreased AP-endonuclease activity (by approximately 20%) in CA1 as well as CA3/FD, and an increased ethenoadenine activity (by approximately 25%) in CA1. Activities for 8-oxoG, 5-OHU and uracil showed no significant changes at this time point. At 8h after OGD, none of the enzyme activities differed from control values. Real-time RT-PCR showed that transcription of DNA glycosylases, including Ogg1, Nth1, Ung, Aag, Neil1 and Neil2 were not changed in response to OGD treatment (t=0 h). The hippocampal expression of Neil2 was low compared with the other DNA glycosylases. These data indicate that CA1 has a lower capacity than CA3/FD for removal of base lesions under basal conditions. The relatively low capacity for BER in basal conditions and the apparent failure to upregulate repair of oxidative damage after OGD might contribute to the high vulnerability of CA1 to ischemic injury.

Mitochondrial dysfunction and oxidative stress as determinants of cell death/survival in stroke

Mitochondria are the powerhouse of the cell. Their primary physiological function is to generate ATP through oxidative phosphorylation via the electron transport chain. Reactive oxygen radicals generated from mitochondria have been implicated in acute brain injuries, like stroke and neurodegeneration. Recent studies have shown that mitochondrially formed oxidants are mediators of molecular signaling and have implicated mitochondria-dependent apoptosis involving pro- and antiapoptotic protein binding, the release of cytochrome c and Smac, the activation of downstream caspase-9 and -3, and the fragmentation of DNA. Oxidative stress and the redox state are also implicated in the survival signaling pathway that involves phosphatidylinositol 3-kinase (PI3-K)/Akt and downstream signaling molecular bindings like Bad/Bcl-X(L) and phosphorylated Bad/14-3-3. Genetically modified mice (SOD1, SOD2) or rats that overexpress or are deficient in superoxide dismutase have provided strong evidence in support of the role of mitochondrial dysfunction and oxidative stress as determinants of neuronal death/survival after stroke and neurodegeneration.

The changes in endogenous antioxidant enzyme activity after postconditioning

1. The aim of this work was to study potential mechanisms participating in postischemic protection of selectively vulnerable CA1 neurons in the hippocampus. Experiments were focused on measuring changes in endogenous antioxidant enzyme activity. 2. Forebrain cerebral ischemia was induced in a rat by four-vessel occlusion. Ten minutes of ischemia induces so-called delayed neuronal death in selectively vulnerable CA1 region 3 days later. After 7 days of reperfusion, 71.6% of neurons succumb to neurodegeneration. When 5 min of ischemia was used as postconditioning, 2 days after 10 min of cerebral ischemia, delayed neuronal death in CA1 was almost completely (89.9%) prevented. 3. Searching for mechanisms of protection, we measured the activity of endogenous antioxidant enzymes. Activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) were measured in the hippocampus, striatum and cortex by spectrophotometric methods after 10 min of ischemia used as the preconditioning. Two days after the preconditioning or the sham operation, second ischemia was induced for 5 min. We observed significant increase of total SOD activity in all studied regions of the brain 5 h after postconditioning (5 min of ischemia). SOD activity decreased to control values after 24 h. 4. In some experiments, we used intraperitoneal injections of norepinephrine (3.1 microM/kg) or 3-nitropropionic acid (20 mg/kg) as postconditioning, instead of ischemia. All three treatments resulted in significant increase of SOD activity, but norepinephrine was the most effective. The same effect as was seen for total SOD activity could be observed for CuZn-SOD as well as Mn-SOD activity. Similarly, considerable increase in the activity of catalase was detected 5 h after postconditioning (5 min of ischemia). It is interesting that the greatest changes were established in selectively vulnerable hippocampus and striatum. As in the case of SOD, the highest levels of CAT activity were induced by norepinephrine, while lower but significant increase in CAT activity was induced by 3-nitropropionic acid.5. Our results suggest that endogenous antioxidants SOD and CAT could play considerable neuroprotective role after postconditioning.

Oxidative stress and neuronal death/survival signaling in cerebral ischemia

It has been demonstrated by numerous studies that apoptotic cell death pathways are implicated in ischemic cerebral injury in ischemia models in vivo. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and the numerous reports suggest the involvement of cell survival/death signaling pathways in the pathogenesis of apoptotic cell death in ischemic lesions. In these models, reoxygenation during reperfusion provides oxygen as a substrate for numerous enzymatic oxidation reactions and for mitochondrial oxidative phosphorylation to produce adenosine triphosphate. Oxygen radicals, the products of these biochemical and physiological reactions, are known to damage cellular lipids, proteins, and nucleic acids and to initiate cell signaling pathways after cerebral ischemia. Genetic manipulation of intrinsic antioxidants and factors in the signaling pathways has provided substantial understanding of the mechanisms involved in cell death/survival signaling pathways and the role of oxygen radicals in ischemic cerebral injury. Future studies of these pathways could provide novel therapeutic strategies in clinical stroke.

Neuroprotective effect of an antioxidant in ischemic brain injury: involvement of neuronal apoptosis

The production of reactive oxygen species (ROS) has been implicated in reperfusion injury after cerebral ischemia, and antioxidant enzymes are believed to be among the major mechanisms by which the cells counteract the deleterious effect of ROS after cerebral ischemia. ROS also mediate the mitochondrial signaling pathway that may lead to apoptosis following cerebral ischemia. The recent development and availability of transgenic and knockout mutant rodents that either overexpress or are deficient in antioxidant genes have provided powerful tools for dissecting the molecular and cellular mechanisms of signaling pathways, direct oxidative damage, or both that are involved in ischemic brain injury. This article focuses on the contribution of ROS or an antioxidant system to the molecular pathway of postischemic apoptosis following transient focal cerebral ischemia by using transgenic mice that overexpress the cytosolic antioxidant copper/zinc superoxide dismutase.

The effect of preconditioning on the Cu, Zn superoxide dismutase expression and enzyme activity in rat brain at the early period after severe hypobaric hypoxia

Severe hypoxia results in functional and structural injury of the brain. A preconditioning with repetitive episodes of mild hypoxia considerably ameliorates neuronal resistance to subsequent severe hypoxia. Activation of endogenous antioxidants including Cu, Zn-depending superoxide dismutase (Cu, Zn-SOD) (EC.1.15.1.1) is one of the main cell defense mechanisms against oxidative stress induced by hypoxia. Alterations of expression and enzyme activity of Cu, Zn-SOD 3 and 24h after severe hypobaric hypoxia in forebrain structures of preconditioned and non-preconditioned rats were investigated. We found that hypoxia without preconditioning suppressed the Cu, Zn-SOD enzyme activity at 3h time-point but preconditioning essentially modified the reaction to severe hypoxia by increasing the expression and activity of Cu, Zn-SOD during early stages of reoxygenation crucial for apoptosis initiation.

Role of matrix metalloproteinases in apoptosis after transient focal cerebral ischemia in rats and mice

The involvement of matrix metalloproteinases (MMPs) in cerebral ischemia-induced apoptosis was investigated in a model of transient focal cerebral ischemia in rats treated intracerebroventricularly (i.c.v.) with 4-((3-(4-phenoxylphenoxy)propylsulfonyl)methyl)-tetrahydropyran-4-carboxylic acid N-hydroxy amide, a broad spectrum non-peptidic hydroxamic acid MMP inhibitor, and in MMP-9-deficient mice. Our results showed that MMP inhibition reduced DNA fragmentation by 51% (P < 0.001) and cerebral infarct by 60% (P < 0.05) after ischemia. This protection was concomitant with a 29% reduction of cytochrome c release into the cytosol (P < 0.005) and a 54% reduction of calpain-related alpha-spectrin degradation (P < 0.05), as well as with an 84% increase in the immunoreactive signal of the native form of poly(ADP) ribose polymerase (P < 0.01). By contrast, specific targeting of the mmp9 gene in mice did reduce cerebral damage by 34% (P < 0.05) but did not modify the apoptotic response after cerebral ischemia. However, i.c.v. injection of MMP-9-deficient mice with the same broad-spectrum inhibitor used in rats significantly reduced DNA degradation by 32% (P < 0.05) and contributed even further to the protection of the ischemic brain. Together, our pharmacological and genetic results indicate that MMPs other than MMP-9 are actively involved in cerebral ischemia-induced apoptosis.

Overexpression of human copper/zinc-superoxide dismutase in transgenic animals attenuates the reduction of apurinic/apyrimidinic endonuclease expression in neurons afterin vitroischemia and after transient global cerebral ischemia

Oxidative stress after ischemia/reperfusion has been shown to induce DNA damage and subsequent DNA repair activity. Apurinic/apyrimidinic endonuclease (APE) is a multifunctional protein in the DNA base excision repair pathway which repairs apurinic/apyrimidinic sites in DNA. We investigated the involvement of oxidative stress and expression of APE in neurons after oxygen-glucose deprivation and after global cerebral ischemia. Our results suggest that overexpression of human copper/zinc-superoxide dismutase reduced oxidative stress with a subsequent decrease in APE expression. Production of oxygen free radicals and inhibition of the base excision repair pathway may play pivotal roles in the cell death pathway after ischemia.

Modulation of p53 degradation via MDM2-mediated ubiquitylation and the ubiquitin-proteasome system during reperfusion after stroke: role of oxidative stress

The tumor suppressor gene p53 plays an important role in the regulation of apoptosis through transcriptional activation of cell cycle control. Degradation of p53 hinders its role in apoptosis regulation. Recent studies have shown that MDM2-mediated ubiquitylation and the ubiquitin-proteasome system are critical regulating systems of p53 ubiquitylation. However, the mechanism regulating p53-mediated neuronal apoptosis after cerebral ischemia remains unknown. We examined the MDM2 pathway and the ubiquitin-proteasome system using a transient focal cerebral ischemia (tFCI) model and analyzed the interaction between p53 regulation and superoxide using copper/zinc superoxide dismutase (SOD1) transgenic mice after tFCI. p53 degradation and ubiquitylation were detected after tFCI. The accumulation of ubiquitylated p53 was inhibited and p53 degradation was facilitated by SOD1. Nuclear translocation and MDM2/Akt interaction were detected after tFCI and were inhibited by phosphatidylinositol 3-kinase inhibition and promoted by SOD1. Cytosolic translocation of the p53/MDM2 complex was detected after tFCI and was promoted by SOD1. Moreover, accumulation of multiubiquitin chains and direct oxidative injury to a proteasome were detected and inhibited by SOD1 after tFCI. These results suggest that SOD1 promotes the MDM2 pathway and the ubiquitin-proteasome system after tFCI and that production of reactive oxygen species after tFCI prevents p53 degradation by inhibiting both systems.

Oxidants, antioxidants and the ischemic brain

Despite numerous defenses, the brain is vulnerable to oxidative stress resulting from ischemia/reperfusion. Excitotoxic stimulation of superoxide and nitric oxide production leads to formation of highly reactive products, including peroxynitrite and hydroxyl radical, which are capable of damaging lipids, proteins and DNA. Use of transgenic mutants and selective pharmacological antioxidants has greatly increased understanding of the complex interplay between substrate deprivation and ischemic outcome. Recent evidence that reactive oxygen/nitrogen species play a critical role in initiation of apoptosis, mitochondrial permeability transition and poly(ADP-ribose) polymerase activation provides additional mechanisms for oxidative damage and new targets for post-ischemic therapeutic intervention. Because oxidative stress involves multiple post-ischemic cascades leading to cell death, effective prevention/treatment of ischemic brain injury is likely to require intervention at multiple effect sites.

In vivo protein transduction: biologically active intact pep-1-superoxide dismutase fusion protein efficiently protects against ischemic insult

Reactive oxygen species (ROS) are implicated in reperfusion injury after transient focal cerebral ischemia. The antioxidant enzyme Cu,Zn-superoxide dismutase (SOD) is one of the major means by which cells counteract the deleterious effects of ROS after ischemia. Recently, we reported that denatured Tat-SOD fusion protein is transduced into cells and skin tissue. Moreover, PEP-1 peptide, which has 21 amino acid residues, is a known carrier peptide that delivers full-length native proteins in vitro and in vivo. In the present study, we investigated the protective effects of PEP-1-SOD fusion protein after ischemic insult. A human SOD gene was fused with PEP-1 peptide in a bacterial expression vector to produce a genetic in-frame PEP-1-SOD fusion protein. The expressed and purified fusion proteins were efficiently transduced both in vitro and in vivo with a native protein structure. Immunohistochemical analysis revealed that PEP-1-SOD injected intraperitoneally (i.p.) into mice can have access into brain neurons. When i.p.-injected into gerbils, PEP-1-SOD fusion proteins prevented neuronal cell death in the hippocampus caused by transient forebrain ischemia. These results suggest that the biologically active intact forms of PEP-1-SOD provide a more efficient strategy for therapeutic delivery in various human diseases related to this antioxidant enzyme or to ROS, including stroke.

Neuronal death/survival signaling pathways in cerebral ischemia

Cumulative evidence suggests that apoptosis plays a pivotal role in cell death in vitro after hypoxia. Apoptotic cell death pathways have also been implicated in ischemic cerebral injury in in vivo ischemia models. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and the numerous reports suggest the involvement of cell survival/death signaling pathways in the pathogenesis of apoptotic cell death in ischemic lesions. In these models, reoxygenation during reperfusion provides a substrate for numerous enzymatic oxidation reactions. Oxygen radicals damage cellular lipids, proteins and nucleic acids, and initiate cell signaling pathways after cerebral ischemia. Genetic manipulation of intrinsic antioxidants and factors in the signaling pathways has provided substantial understanding of the mechanisms involved in cell death/survival signaling pathways and the role of oxygen radicals in ischemic cerebral injury. Future studies of these pathways may provide novel therapeutic strategies in clinical stroke.

Reactive oxygen radicals and pathogenesis of neuronal death after cerebral ischemia

Reactive oxygen species have been implicated in brain injury after cerebral ischemia. These oxidants can damage proteins, lipids, and DNA, and lead to cell injury and necrosis. Oxidants are also initiators in intracellular cell death signaling pathways that may lead to apoptosis. The possible targets of this redox signaling include mitochondria, death membrane receptors, and DNA repair enzymes. Genetic manipulation of intrinsic antioxidants and the factors in the signaling pathways has provided substantial progress in understanding the mechanisms in cell death signaling pathways and involvement of oxygen radicals in ischemic brain injury. Future studies of these pathways may provide novel therapeutic strategies in clinical stroke.

Evaluation of MCAO stroke models in normotensive rats: standardized neocortical infarction by the 3VO technique

The temporary three-vessel occlusion (3VO) technique with a surgical approach for middle cerebral artery (MCA) produces consistent cerebral infarction in the neocortex in normotensive rats. The intraluminal thread-occlusion technique with an endovascular approach targeting the MCA occlusion (MCAO) is more widely used since it does not require complicated intracranial procedures. The aim of this study was to review the methods/models for MCAO stroke in normotensive rats and to evaluate a 3VO stroke model that provides consistent degrees and variance of cortical stroke injury for additional discussion. First, we analyzed a model with modified temporary 3VO technique requiring less complicated procedures than the temporary 3VO model, i.e., temporary occlusion of the bilateral common carotid arteries (CCAs) superimposed on a permanent occlusion of the MCA, in Sprague-Dawley rats or C57BL/6J mice. In the microvascular tissue (cerebral) perfusion study, significant reductions in regional cerebral perfusion during the 3VO accompanied a rapid return to baseline after release of the CCAs, showing that the technique induces temporary focal ischemia. The average sizes and variances of the neocortical infarction in this model, together with those in the other normotensive rat models caused by the 3VO technique in the literature, indicated a standard size and variance of infarcted lesion in the control groups relative to the specific ischemic period. However, stroke injuries in the neocortex induced by the thread occlusion technique showed greater variability with less consistent lesion sizes. Inclusion/exclusion criteria to avoid inappropriate cases with too mild (no/faint infarction) or too great (huge/fatal infarction) severity in the ischemic injury may differ between laboratories in the thread occlusion model.

Treatment with dihydroethidium reduces infarct size after transient focal cerebral ischemia in mice

A transient focal ischemia model with C57Bl/6 mice was used to investigate whether dihydroethidium is neuroprotective. Different doses (25, 50, 100 mg/kg body weight) were used for pretreatment and the lowest effective dose was used for delayed treatment 1 and 2 h after reperfusion. Our results demonstrate that all the doses used for treatment reduced infarct volume. We conclude that dihydroethidium is neuroprotective by reducing superoxide in mice after stroke.

The protective effect of M40401, a superoxide dismutase mimetic, on post-ischemic brain damage in Mongolian gerbils

BACKGROUND

Overproduction of free radical species has been shown to occur in brain tissues after ischemia-reperfusion injury. However, most of free radical scavengers known to antagonize oxidative damage (e.g. superoxide dismutase, catalase), are unable to protect against ischemia-reperfusion brain injury when given in vivo, an effect mainly due to their difficulty to gain access to brain tissues. Here we studied the effect of a low molecular weight superoxide dismutase mimetic (M40401) in brain damage subsequent to ischemia-reperfusion injury in Mongolian gerbils.

RESULTS

In animals undergoing ischemia-reperfusion injury, neuropathological and ultrastructural changes were monitored for 1-7 days either in the presence or in the absence of M40401 after bilateral common carotid artery occlusion (BCCO). Administration of M40401 (1-40 mg/kg, given i.p. 1 h after BCCO) protected against post-ischemic, ultrastructural and neuropathological changes occurring within the hippocampal CA1 area. The protective effect of M40401 was associated with a significant reduction of the levels of malondialdehyde (MDA; a marker of lipid peroxidation) in ischemic brain tissues after ischemia-reperfusion.

CONCLUSION

Taken together, these results demonstrate that M40401 provides protective effects when given early after the induction of ischemia-reperfusion of brain tissues and suggest the possible use of such compounds in the treatment of neurological dysfunction subsequent to cerebral flow disturbances.

Role of superoxide in poly(ADP-ribose) polymerase upregulation after transient cerebral ischemia

Oxidative stress plays a pivotal role in ischemic-reperfusion cell injury. Oxygen-derived free radicals trigger DNA strand damage, which is responsible for the activation of poly(ADP-ribose) polymerase (PARP). Recent studies have shown that peroxynitrite is the primary mediator of DNA damage and, hence, PARP activation after ischemia. PARP activation depletes NAD and ATP pools, ultimately resulting in necrotic cell death by loss of energy stores. Our study shows that PARP is upregulated as early as 15 min after 1 h of transient focal cerebral ischemia and remains for 8 h. We also examined the role of superoxide in PARP induction using copper/zinc-superoxide dismutase transgenic mice. Immunohistochemical and Western blotting data showed that there was no increased induction in PARP expression in these mice, suggesting that one of the mechanisms by which ischemic injury is attenuated in these mice might be by the inhibition of PARP induction. Furthermore, double staining of ischemic tissue with a PARP antibody and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling (TUNEL) indicated that most cells that are positive for TUNEL do not stain for the PARP antibody, confirming recent reports that PARP activation is involved in necrotic cell death rather than apoptosis during ischemic-reperfusion injury.

Copper/zinc superoxide dismutase attenuates neuronal cell death by preventing extracellular signal-regulated kinase activation after transient focal cerebral ischemia in mice

Recent studies have revealed that activation of extracellular signal-regulated kinase (ERK) may contribute to apoptosis, a cell death process involved in oxidative stress. We examined phosphorylation of ERK1/2 and oxidative stress after transient focal cerebral ischemia (FCI) using transgenic (Tg) mice that overexpress copper/zinc superoxide dismutase (SOD1). The mice were subjected to 60 min of middle cerebral artery (MCA) occlusion by intraluminal suture blockade followed by 1, 4, and 24 hr of reperfusion. Immunohistochemistry and Western blot analysis showed that phospho-ERK1 was markedly increased in the cortex within the MCA territory at 1 hr of reperfusion (p < 0.01), followed by a decrease at 24 hr in wild-type mice. Double staining with phospho-ERK1/2 and neuron-specific nuclear protein showed that phospho-ERK1/2 was primarily expressed in neurons. In SOD1 Tg mice, phospho-ERK1/2 was prominently reduced compared with nonischemic controls, shown by immunohistochemistry. Western blot analysis confirmed a significant decrease in phospho-ERK1/2 1 hr after FCI in the ischemic cortex (p < 0.005). Apoptotic-related DNA fragmentation was reduced in the ischemic cortex of SOD1 Tg mice compared with wild-type mice using a cell death assay. These results suggest that phosphorylation of ERK1/2 may be involved in apoptosis or cell death after transient FCI and that SOD1 may attenuate apoptotic cell death mediated by the mitogen-activated protein kinase/ERK pathway.

Distinct gene expression signatures in the striata of wild-type and heterozygous c-fos knockout mice following methamphetamine administration: evidence from cDNA array analyses

Methamphetamine (METH) is a drug of abuse which can cause apoptosis and degeneration of monoaminergic terminals in the mammalian brain. c-fos appears to play a protective role against METH-induced damage because METH toxicity is exacerbated in c-fos heterozygous knockout mice. In the present study, we used the comprehensive technique of cDNA array to test the idea that heterozygous c-fos knockout mice might show differential METH-induced molecular responses in comparison to wild-type (WT) animals. Of 1,176 genes examined, the expression of 195 genes in either of the two groups of mice was affected by at least 2-fold at 2 or 12 h after METH treatment. More genes were either up- or downregulated in the WT mice. Moreover, there were substantial differences in the pattern of responses between the two genotypes, with more genes involved in DNA repair and protective processes being upregulated in WT mice after METH administration. These results support the idea that the c-fos knockout genotype may render the animals unable to trigger multicomponent responses in order to protect against the multifaceted toxic effects of this illicit neurotoxin.

Molecular Mechanisms of Neurologic Injury Following Cardiopulmonary Bypass

Neurologic injury is a potentially devastating consequence of heart surgery. Between 1% and 5% of patients undergoing cardiopulmonary bypass have postoperative strokes and 30% to 80% of patients demonstrate some neurologic dysfunction postoperatively. This review focuses on anatomic, molecular and clinical markers of neurologic injury following cardiopulmonary bypass. Attention is directed to the molecular mechanisms underlying neurologic injury and clinical biochemical markers of injury during heart surgery. Novel strategies to modulate injury are also discussed.

The cytosolic antioxidant, copper/zinc superoxide dismutase, attenuates blood-brain barrier disruption and oxidative cellular injury after photothrombotic cortical ischemia in mice

Oxidative stress has been associated with the development of blood-brain barrier disruption and cellular injury after ischemia. The cytosolic antioxidant, copper/zinc superoxide dismutase, has been shown to protect against blood-brain barrier disruption and infarction after cerebral ischemia-reperfusion. However, it is not clear whether copper/zinc superoxide dismutase can protect against evolving ischemic lesions after thromboembolic cortical ischemia. In this study, the photothrombotic ischemia model, which is physiologically similar to thromboembolic stroke, was used to develop cortical ischemia. Blood-brain barrier disruption and oxidative cellular damage were investigated in transgenic mice that overexpress copper/zinc superoxide dismutase and in littermate wild-type mice after photothrombotic ischemia, which was induced by both injection of erythrosin B (30 mg/kg) and irradiation using a helium neon laser for 3 min. Free radical production, particularly superoxide, was increased in the lesioned cortex as early as 4 h after ischemia using hydroethidine in situ detection. The transgenic mice showed a prominent decrease in oxidative stress compared with the wild-type mice. Blood-brain barrier disruption, evidenced by quantitation of Evans Blue leakage, occurred 1 h after ischemia and gradually increased up to 24 h. Compared with the wild-type mice, the transgenic mice showed less blood-brain barrier disruption, a decrease in oxidative DNA damage using 8-hydroxyguanosine immunohistochemistry, a subsequent decrease in DNA fragmentation using the in situ nick-end labeling technique, and decreased infarct volume after ischemia. From these results we suggest that superoxide anion radical is an important factor in blood-brain barrier disruption and oxidative cellular injury, and that copper/zinc superoxide dismutase could protect against the evolving infarction after thromboembolic cortical ischemia.

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.

Oxidative stress and neuronal DNA fragmentation mediate age-dependent vulnerability to the mitochondrial toxin, 3-nitropropionic acid, in the mouse striatum

Oxidative stress is involved in the neuropathology of several neurodegenerative diseases and stroke, all of which are related to excitotoxicity. Age-dependent vulnerability is characteristic of these conditions. It is not clear whether apoptosis-related neuronal death is involved in age-dependent vulnerability to excitotoxicity. We evaluated whether apoptosis-related neuronal death after treatment with 3-nitropropionic acid (3-NP) is age-dependent in the mouse striatum. We have demonstrated that oxidative stress occurs early after 3-NP treatment and even more so in aged mice. DNA fragmentation with terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling staining and gel electrophoresis occurred in an age-dependent fashion. Expression of the DNA repair enzyme, apurinic/apyrimidinic endonuclease, was more attenuated in old mice. Therefore, these results suggest that oxidative stress induces age-dependent neuronal apoptosis in the mouse striatum after 3-NP treatment, which in turn produces an age-dependent vulnerability to 3-NP.