In situ detection of AP sites and DNA strand breaks bearing 3'-phosphate termini in ischemic mouse brain

The potential effect mechanism of high-fat and high-carbohydrate diet-induced obesity on anxiety and offspring of zebrafish

Anxiety and obesity are two current phenomena. They are among the important public health problems with increasing prevalence worldwide. Although it is claimed that there are strong relations between them, the mechanism of this relationship has not been fully clarified yet. On the other hand, the effect of this relationship on the offspring has been another research subject. In this study, obese zebrafish were obtained by feeding two different diets, one containing high amount of lipid (HF) and the other containing high amount of carbohydrate (HK), and their anxiety levels were evaluated. To establish a relationship between these two phenomena, in addition to histopathological and immunohistochemical analysis in the brain tissues of fish, the transcription levels of some genes related to lipid and carbohydrate metabolisms were determined. In addition, offspring were taken from obese zebrafish and studied to examine the effect of parental obesity on offspring. As a result, it was observed that the HC diet, causing more weight increase than the HF diet, showed an anxiolytic while the HF diet an anxiogenic effect. It was suggested that the probable cause of this situation may be the regulatory effect on the appetite-related genes depending on the upregulation severity of the PPAR gene family based on the diet content. In addition, it was also suggested that it may have contributed to this process in neuron degenerations caused by oxidative stress. Regarding effects on offspring, it can be concluded that HF diet-induced obesity has more negative effects on the next generation than the HC diet.Level of evidenceNo Level of evidence: animal study.

Cooling and Sterile Inflammation in an Oxygen-Glucose-Deprivation/Reperfusion Injury Model in BV-2 Microglia

Objective

Cold-inducible RNA-binding protein (CIRBP) has been shown to be involved not only in cooling-induced cellular protection but also as a mediator of sterile inflammation, a critical mechanism of the innate immune response in ischemia/reperfusion (I/R) injury. The role of microglia and its activation in cerebral I/R injury warrants further investigation as both detrimental and regenerative properties have been described. Therefore, we investigated the effects of cooling, specifically viability, activation, and release of damage associated molecular patterns (DAMPs) on oxygen glucose deprivation/reperfusion- (OGD/R-) induced injury in murine BV-2 microglial cells.

Methods

Murine BV-2 microglial cells were exposed to 2 to 6 h OGD (0.2% O₂ in glucose- and serum-free medium) followed by up to 19 h of reperfusion, simulated by restoration of oxygen (21% O₂) and nutrients. Cells were maintained at either normothermia (37°C) or cooled to 33.5°C, 1 h after experimental start. Cultured supernatants were harvested after exposure to OGD for analysis of DAMP secretions, including high-mobility group box 1 (HMGB1), heat shock protein 70 (HSP70), and CIRBP, and cytotoxicity was assessed by lactate dehydrogenase releases after exposure to OGD and reperfusion. Intracellular cold-shock proteins CIRBP and RNA-binding motif 3 (RBM3) as well as caspases 9, 8, and 3 were also analyzed via Western blot analysis. Furthermore, inducible nitric oxide synthase (iNOS), ionized calcium-binding adaptor molecule 1 (Iba1), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), interleukin-1α (IL-1α), monocyte chemotactic protein 1 (MCP-1), transforming growth factor β (TGFβ), CIRBP, and RBM3 gene expressions were assessed via reverse transcription polymerase chain reaction, and TNF-α, IL-6, and IL-1β releases into the cultured supernatants were assessed via enzyme-linked immunosorbent assays (ELISA).

Results

Prolonged exposure to OGD resulted in increased BV-2 necrotic cell death, which was attenuated by cooling. Cooling also significantly induced cold-shock proteins CIRBP and RBM3 gene expressions, with CIRBP expression more rapidly regulated than RBM3 and translatable to significantly increased protein expression. DAMPs including HMGB-1, HSP70, and CIRBP could be detected in cultured supernatants after 6 h of OGD with CIRBP release being significantly attenuated by cooling. Exposure to OGD suppressed cytokine gene expressions of IL-1β, TNF-α, MCP-1, and TGFβ independently of temperature management, whereas cooling led to a significant increase in IL-1α gene expression after 6 h of OGD. In the reperfusion phase, TNF-α and MCP-1 gene expressions were increased, and cooling was associated with significantly lower TGFβ gene expression. Interestingly, cooled Normoxia groups had significant upregulations of microglial activation marker, Iba1, IL-1β, and TNF-α gene expressions.

Conclusion

BV-2 microglial cells undergo necrotic cell death resulting in DAMP release due to OGD/R-induced injury. Cooling conveyed neuroprotection in OGD/R-injury as observable in increased cell viability as well as induced gene expressions of cold shock proteins. As cooling alone resulted in both upregulation of microglial activation, expression of proinflammatory cytokines, and cold shock protein transcript and protein expression, temperature management might have ambiguous effects in sterile inflammation. However, cooling resulted in a significant decrease of extracellular CIRBP, which has recently been characterized as a novel DAMP and a potent initiator and mediator of inflammation.

Aversive Learning Deficits and Depressive-Like Behaviors Are Accompanied by an Increase in Oxidative Stress in a Rat Model of Fetal Alcohol Spectrum Disorders: The Protective Effect of Rapamycin

Fetal alcohol spectrum disorders (FASDs) are one of the most common consequences of ethanol exposure during pregnancy. In adulthood, these disorders can be manifested by learning and memory deficits and depressive-like behavior. Ethanol-induced oxidative stress may be one of the factors that induces FASD development. The mammalian target of the Rapamycin (mTOR) signaling pathway that acts via two distinct multiprotein complexes, mTORC1 and mTORC2, can affect oxidative stress. We investigated whether mTOR-dependent or mTOR-independent mechanisms are engaged in this phenomenon. Thus, Rapamycin—a selective inhibitor of mTORC1, Torin-2—a non-selective mTORC1/mTORC2 inhibitor, and FK-506—a drug that impacts oxidative stress in an mTOR-independent manner were used. Behavioral tests were performed in adult (PND60-65) rats using a passive avoidance (PA) task (aversive learning and memory) and forced swimming test (FST) (depressive-like behaviors). In addition, the biochemical parameters of oxidative stress, such as lipid peroxidation (LPO), as well as apurinic/apyrimidinic (AP)-sites were determined in the hippocampus and prefrontal cortex in adult (PND65) rats. The rat FASD model was induced by intragastric ethanol (5 g/kg/day) administration at postnatal day (PND)4–9 (an equivalent to the third trimester of human pregnancy). All substances (3 mg/kg) were given 30 min before ethanol. Our results show that neonatal ethanol exposure leads to deficits in context-dependent fear learning and depressive-like behavior in adult rats that were associated with increased oxidative stress parameters in the hippocampus and prefrontal cortex. Because these effects were completely reversed by Rapamycin, an mTORC1 inhibitor, this outcome suggests its usefulness as a preventive therapy in disorders connected with prenatal ethanol exposure.

Fight to the bitter end: DNA repair and aging

DNA carries the genetic information that directs complex biological processes; thus, maintaining a stable genome is critical for individual growth and development and for human health. DNA repair is a fundamental and conserved mechanism responsible for mending damaged DNA and restoring genomic stability, while its deficiency is closely related to multiple human disorders. In recent years, remarkable progress has been made in the field of DNA repair and aging. Here, we will extensively discuss the relationship among DNA damage, DNA repair, aging and aging-associated diseases based on the latest research. In addition, the possible role of DNA repair in several potential rejuvenation strategies will be discussed. Finally, we will also review the emerging methods that may facilitate future research on DNA repair.

Chronic Variable Stress Is Responsible for Lipid and DNA Oxidative Disorders and Activation of Oxidative Stress Response Genes in the Brain of Rats

Chronic environmental stress is associated with reactive oxygen species (ROS) overproduction and the pathogenesis of depression. The purpose of this study was to evaluate biochemical and molecular changes associated with ROS generation in the brains of rats submitted to chronic variable stress. Male Wistar rats (50–55 days old, weighing 200–250 g) were divided in two groups (n = 10): control and stressed. Rats in the stressed group were exposed to stress conditions for 40 days. The animals were decapitated and the brain samples were collected. In prefrontal cortex, we measured the following biochemical parameters: lipid peroxidation and concentration of glutathione—GSH, GSSG, GSH/GSSG ratio, glutathione peroxidase, and glutathione reductase activities. In the hippocampus marker of DNA, oxidative damage and expression of DNA-repairing genes (Ogg1, MsrA) and gene-encoding antioxidative transcriptional factor (Nrf2) were determined. The results demonstrate indirect evidence of ROS overproduction and presence of oxidative stress. They also reveal disruption of oxidative defense systems (decreased GR activity, diminished GSH/GSSG ratio, and decreased Nrf2 expression) and activation of the oxidative DNA repair system (increased Ogg1 and MsrA expression). Together, the presented data suggest that independent activation of oxidative stress response genes occurs in chronic variable stress conditions.

Inflammatory responses in brain ischemia

Brain infarction causes tissue death by ischemia due to occlusion of the cerebral vessels and recent work has shown that post stroke inflammation contributes significantly to the development of ischemic pathology. Because secondary damage by brain inflammation may have a longer therapeutic time window compared to the rescue of primary damage following arterial occlusion, controlling inflammation would be an obvious therapeutic target. A substantial amount of experimentall progress in this area has been made in recent years. However, it is difficult to elucidate the precise mechanisms of the inflammatory responses following ischemic stroke because inflammation is a complex series of interactions between inflammatory cells and molecules, all of which could be either detrimental or beneficial. We review recent advances in neuroinflammation and the modulation of inflammatory signaling pathways in brain ischemia. Potential targets for treatment of ischemic stroke will also be covered. The roles of the immune system and brain damage versus repair will help to clarify how immune modulation may treat stroke.

Noninvasive tracking of gene transcript and neuroprotection after gene therapy

Gene therapy holds exceptional potential for translational medicine by improving the products of defective genes in diseases and/or providing necessary biologics from endogenous sources during recovery processes. However, validating methods for the delivery, distribution and expression of the exogenous genes from such therapy can generally not be applicable to monitor effects over the long term because they are invasive. We report here that human granulocyte colony-stimulating factor (hG-CSF) cDNA encoded in scAAV-type 2 adeno-associated virus, as delivered through eye drops at multiple time points after cerebral ischemia using bilateral carotid occlusion for 60 min (BCAO-60) led to significant reduction in mortality rates, cerebral atrophy, and neurological deficits in C57black6 mice. Most importantly, we validated hG-CSF cDNA expression using translatable magnetic resonance imaging (MRI) in living brains. This noninvasive approach for monitoring exogenous gene expression in the brains has potential for great impact in the area of experimental gene therapy in animal models of heart attack, stroke, Alzheimer’s dementia, Parkinson’s disorder and amyotrophic lateral sclerosis, and the translation of such techniques to emergency medicine.

Panax notoginseng saponin attenuates hypoxia/reoxygenation-induced oxidative stress in cortical neurons

The present study monitored the effect of 2, 10, and 50 mg/L of Panax notoginseng saponin exposure following hypoxia-reoxygenation injury in fetal rat cortical neurons. Results showed that varying doses of Panax notoginseng saponin significantly enhanced the cell viability of neurons, reduced malondialdehyde content, increased superoxide dismutase activity, inhibited mRNA and protein expression of inducible and neuronal nitric oxide synthase, and decreased the release of nitric oxide in hypoxia/reoxygenation injured cells. In particular, 50 mg/L of Panax notoginseng saponin was the most effective dose. These findings suggest that Panax notoginseng saponin can attenuate neuronal oxidative stress injury caused by hypoxia/reoxygenation in a dose-dependent manner.

Tea polyphenols increase X-ray repair cross-complementing protein 1 and apurinic/apyrimidinic endonuclease/redox factor-1 expression in the hippocampus of rats during cerebral ischemia/reperfusion injury

Recent studies have shown that tea polyphenols can cross the blood-brain barrier, inhibit apoptosis and play a neuroprotective role against cerebral ischemia. Furthermore, tea polyphenols can decrease DNA damage caused by free radicals. We hypothesized that tea polyphenols repair DNA damage and inhibit neuronal apoptosis during global cerebral ischemia/reperfusion. To test this hypothesis, we employed a rat model of global cerebral ischemia/reperfusion. We demonstrated that intraperitoneal injection of tea polyphenols immediately after reperfusion significantly reduced apoptosis in the hippocampal CA1 region; this effect started 6 hours following reperfusion. Immunohistochemical staining showed that tea polyphenols could reverse the ischemia/reperfusion-induced reduction in the expression of DNA repair proteins, X-ray repair cross-complementing protein 1 and apurinic/apyrimidinic endonuclease/redox factor-1 starting at 2 hours. Both effects lasted at least 72 hours. These experimental findings suggest that tea polyphenols promote DNA damage repair and protect against apoptosis in the brain.

Noninvasive detection of neural progenitor cells in living brains by MRI

The presence of pericytes in brain regions undergoing repair is evident of the recruitment of bone marrow-derived multipotent regenerative cells to the neurovascular unit during angiogenesis. At present, post mortem sampling is the only way to identify them. Therefore, such cell typing is inadequate for preserving neural progenitor cells for any meaningful stem cell therapy. We aimed to target cerebral pericytes in vivo using dual gene transcript-targeted MRI (GT-tMRI) in male C57black6 mice after a 60-min bilateral carotid artery occlusion (BCAO). We attached superparamagnetic iron oxide nanoparticles (SPIONs) to phosphorothioate-modified micro-DNA that targets actin or nestin mRNA. Because BCAO compromises the blood-brain barrier (BBB) and induces expression of α-smooth muscle (αSM)-actin and nestin antigens by pericytes in new vessels, we delivered pericyte-specific magnetic resonance contrast agents (SPION-actin or SPION-nestin at 4 mg Fe/kg) by i.p. injection to C57black6 mice that had experienced BCAO. We demonstrated that the surge in cerebral iron content by inductively coupled plasma-mass spectrometry matched the increase in the frequency of relaxivity. We also found that SPION-nestin was colocalized in αSM- actin- and nestin-expressing pericytes in BCAO-treated C57black6 or transgenic mice [B6.Cg-Tg(CAG-mRFP1) 1F1Hadj/J, expressing red fluorescent protein by actin promoter]. We identified pericytes in the repair patch in living brains after BCAO with a voxel size of 0.03 mm(3). The presence of electron-dense nanoparticles in vascular pericytes in the region of BBB injury led us to draw the conclusion that GT-tMRI can noninvasively reveal neural progenitor cells during vascularization.

Isolation and identification of anti-inflammatory constituents from Ligusticum chuanxiong and their underlying mechanisms of action on microglia

Stroke is the third most common cause of death worldwide. Recent findings showed that the severity of cerebrovascular diseases including ischemic stroke correlates with inflammation mediated responses in the neural cells. During ischemia, inflammatory mediators including tumor necrosis factor-alpha (TNF-α) and nitric oxide are produced by microglia, which play a central role in the pathogenesis of the disease. Ligusticum chuanxiong (LCX) is a commonly used traditional Chinese medicine (TCM) for empiric treatment of cerebrovascular and cardiovascular diseases for many centuries. By applying a bioactivity-guided fractionation scheme, two compounds with inhibition on neuroinflammation were isolated from LCX. Using chromatographic and spectrometric methods, they were identified to be senkyunolide A and Z-ligustilide. They could inhibit the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells and human peripheral blood monocyte derived macrophages. In addition, both compounds protected Neuro-2a cells from neuroinflammatory toxicity induced by the conditioned culture media produced by LPS-stimulated BV-2 cells. The underlying mechanisms of action of senkyunolide A were further delineated. Its inhibitory effects were shown to be independent of the phosphorylation of mitogen-activated protein kinases (MAPK) and translocation of nuclear factor kappa B (NF-κB). However, senkyunolide A could increase the degradation of TNF-α mRNA and reduce its half life by 43%. In conclusion, bioactivity-guided fractionation is an effective way of isolating bioactive compounds from medicinal herbs. In addition, senkyunolide A and Z-ligustilide isolated from LCX may be considered as potential complementary drug candidates for treating inflammatory processes associated with cerebrovascular diseases.

Alzheimer's mechanisms in ischemic brain degeneration

There is increasing evidence for influence of Alzheimer's proteins and neuropathology on ischemic brain injury. This review investigates the relationships between beta-amyloid peptide, apolipoproteins, presenilins, tau protein, alpha-synuclein, inflammation factors, and neuronal survival/death decisions in brain following ischemic episode. The interactions of these molecules and influence on beta-amyloid peptide synthesis and contribution to ischemic brain degeneration and finally to dementia are reviewed. Generation and deposition of beta-amyloid peptide and tau protein pathology are important key players involved in mechanisms in ischemic neurodegeneration as well as in Alzheimer's disease. Current evidence suggests that inflammatory process represents next component, which significantly contribute to degeneration progression. Although inflammation was initially thought to arise secondary to ischemic neurodegeneration, recent studies present that inflammatory mediators may stimulate amyloid precursor protein metabolism by upregulation of beta-secretase and therefore are able to establish a vicious cycle. Functional brain recovery after ischemic lesion was delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and beta-amyloid peptide. Moreover, ischemic neurodegeneration is strongly accelerated with aging, too. New therapeutic alternatives targeting these proteins and repairing related neuronal changes are under development for the treatment of ischemic brain consequences including memory loss prevention.

Oxidative stress alters base excision repair pathway and increases apoptotic response in apurinic/apyrimidinic endonuclease 1/redox factor-1 haploinsufficient mice

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is the redox regulator of multiple stress-inducible transcription factors, such as NF-kappaB, and the major 5'-endonuclease in base excision repair (BER). We utilized mice containing a heterozygous gene-targeted deletion of APE1/Ref-1 (Apex(+/-)) to determine the impact of APE1/Ref-1 haploinsufficiency on the processing of oxidative DNA damage induced by 2-nitropropane (2-NP) in the liver tissue of mice. APE1/Ref-1 haploinsufficiency results in a significant decline in NF-kappaB DNA-binding activity in response to oxidative stress in liver. In addition, loss of APE1/Ref-1 increases the apoptotic response to oxidative stress, in which significant increases in GADD45g expression, p53 protein stability, and caspase activity are observed. Oxidative stress displays a differential impact on monofunctional (UNG) and bifunctional (OGG1) DNA glycosylase-initiated BER in the liver of Apex(+/-) mice. APE1/Ref-1 haploinsufficiency results in a significant decline in the repair of oxidized bases (e.g., 8-OHdG), whereas removal of uracil is increased in liver nuclear extracts of mice using an in vitro BER assay. Apex(+/-) mice exposed to 2-NP displayed a significant decline in 3'-OH-containing single-strand breaks and an increase in aldehydic lesions in their liver DNA, suggesting an accumulation of repair intermediates of failed bifunctional DNA glycosylase-initiated BER.

The adenoviral vector-mediated increase in apurinic/apyrimidinic endonuclease inhibits the induction of neuronal cell death after transient ischemic stroke in mice

Despite the correlation between changes in the levels of apurinic/apyrimidinic endonuclease and ischemic neuronal damage, no studies have addressed the question of whether increased APE/Ref-1 can prevent ischemic neuronal cell death in vivo. Using an adenoviral vector, we investigated whether increased APE/Ref-1 can inhibit the loss of APE/Ref-1 and thereby prevent oxidative DNA damage after transient focal cerebral ischemia. Mice were subjected to intraluminal suture occlusion of the middle cerebral artery for 1 h, followed by reperfusion. Pre-ischemic treatment of the adenoviral vector was introduced intracerebrally. An adenoviral vector harboring the entire APE/Ref-1 gene sequence or a control virus without the APE/Ref-1 sequence was introduced 3 days before ischemia/reperfusion (I/R). The reduction of APE/Ref-1 occurred before DNA fragmentation, which was shown by temporal and spatial analysis. Increased APE/Ref-1 significantly decreased DNA damage and infarct volume after I/R. In conclusion, increased APE/Ref-1 enhanced DNA repair and inhibited the induction of ischemic oxidative DNA damage and cerebral infarction after I/R.

Diffusion-weighted magnetic resonance imaging reversal by gene knockdown of matrix metalloproteinase-9 activities in live animal brains

The involvement of matrix metalloproteinase-9 (MMP-9) activities in the development of abnormal water diffusion in the brain after cardiac arrest is not fully understood. We used magnetic resonance imaging to determine the correlation between MMP-9 activity and the mechanism of abnormal water diffusion after global cerebral ischemia (GCI)-induced brain damage in C57black6 mice. We induced GCI in mice by occluding both carotid arteries for 60 min, then allowing reperfusion. We labeled a short DNA that targets mmp-9 mRNA activity [phosphorothioate-modified oligodeoxynucleotide (sODN)-mmp9] or a control probe without intracellular target (sODN-Ran) with iron-based MR contrast agent [superparamagnetic iron oxide nanoparticle (SPION)-mmp9 or SPION-Ran] or fluorescein isothiocyanate (FITC)-sODN-mmp9 or FITC-sODN-Ran; we then delivered these probes by intracerebroventricular infusion or intraperitoneal injection within 3 h of reperfusion. At low dose (120 pmol/kg) the SPION-mmp9 probe was retained at significant levels in the striatum and cortex of living brains 10 h after GCI. Probe retention was validated by similar elevation of mmp-9 mRNA and antigens in postmortem samples taken from regions that exhibited GCI-induced hyperintensity in diffusion-weighted imaging, and a significant reduction in apparent diffusion coefficient (rADC, p = 0.0006, n = 12). At a higher dose (120 nmol/kg), the FITC-sODN-mmp9 probe revealed significant knockdown of MMP-9 activity, per zymography, and a reversal of striatal rADC (p = 0.004, n = 6). These observations were not duplicated in the control group. We conclude that expression of mmp-9 mRNA is associated with abnormal ADC after GCI.

DNA polymerase beta-catalyzed-PCNA independent long patch base excision repair synthesis: a mechanism for repair of oxidatively damaged DNA ends in post-mitotic brain

Oxidative DNA damage incidental to normal respiratory metabolism poses a particular threat to genomes of highly metabolic-long lived cells. We show that post-mitotic brain has capacity to repair oxidatively damaged DNA ends, which are targets of the long patch (LP) base excision repair (BER) subpathway. LP-BER relies, in part, on proteins associated with DNA replication, including proliferating cell nuclear antigen and is inherent to proliferating cells. Nonetheless, repair products are generated with brain extracts, albeit at slow rates, in the case of 5'-DNA ends modeled with tetrahydrofuran (THF). THF at this position is refractory to DNA polymerase beta 5'-deoxyribose 5-phosphate lyase activity and drives repair into the LP-BER subpathway. Comparison of repair of 5'-THF-blocked termini in the post-mitotic rat brain and proliferative intestinal mucosa, revealed that in mucosa, resolution of damaged 5'-termini is accompanied by formation of larger repair products. In contrast, adducts targeted by the single nucleotide BER are proficiently repaired with both extracts. Our findings reveal mechanistic differences in BER processes selective for the brain versus proliferative tissues. The differences highlight the physiological relevance of the recently proposed 'Hit and Run' mechanism of alternating cleavage/synthesis steps, in the proliferating cell nuclear antigen-independent LP-BER process.

Molecular regulation of DNA damage-induced apoptosis in neurons of cerebral cortex

Cerebral cortical neuron degeneration occurs in brain disorders manifesting throughout life, but the mechanisms are understood poorly. We used cultured embryonic mouse cortical neurons and an in vivo mouse model to study mechanisms of DNA damaged-induced apoptosis in immature and differentiated neurons. p53 drives apoptosis of immature and differentiated cortical neurons through its rapid and prominent activation stimulated by DNA strand breaks induced by topoisomerase-I and -II inhibition. Blocking p53-DNA transactivation with alpha-pifithrin protects immature neurons; blocking p53-mitochondrial functions with mu-pifithrin protects differentiated neurons. Mitochondrial death proteins are upregulated in apoptotic immature and differentiated neurons and have nonredundant proapoptotic functions; Bak is more dominant than Bax in differentiated neurons. p53 phosphorylation is mediated by ataxia telangiectasia mutated (ATM) kinase. ATM inactivation is antiapoptotic, particularly in differentiated neurons, whereas inhibition of c-Abl protects immature neurons but not differentiated neurons. Cell death protein expression patterns in mouse forebrain are mostly similar to cultured neurons. DNA damage induces prominent p53 activation and apoptosis in cerebral cortex in vivo. Thus, DNA strand breaks in cortical neurons induce rapid p53-mediated apoptosis through actions of upstream ATM and c-Abl kinases and downstream mitochondrial death proteins. This molecular network operates through variations depending on neuron maturity.

Noninvasive delivery of gene targeting probes to live brains for transcription MRI

We aimed to test the feasibility of detecting gliosis in living brains when the blood-brain barrier (BBB) is disrupted. We designed a novel magnetic resonance (MR) probe that contains superparamagnetic iron oxide nanoparticles (SPION, a T2 susceptibility contrast agent) linked to a short DNA sequence complementary to the cerebral mRNA of glial fibrillary acidic protein (GFAP) found in glia and astrocytes. As a control, we also used a sequence complementary to the mRNA of beta-actin. Our objectives are to demonstrate that this new probe, SPION-gfap, could be delivered to the brain when administered by eyedrop solution to the conjunctival sac. We induced BBB leakage by puncture wound, global cerebral ischemia, and cortical spreading depression in C57BL6 mice; 1 day after probe delivery we acquired T2* MR images and R2* (R2* = 1/T2*) maps using a transcription MRI technique in live mice. We found that the SPION-gfap probe reported foci with elevated signal in subtraction R2* maps and that these foci matched areas identified as having extensive glial network (gliosis) in postmortem immunohistochemistry. Similarly, animals administered the control probe exhibited foci of R2* elevation that matched beta-actin-expressing endothelia in the vascular wall. We conclude that our modular MR probe, delivered in an eyedrop solution, effectively reports gliosis associated with acute neurological disorders in living animals. As BBB leakage is often observed in acute neurological disorders, this study also served to validate noninvasive delivery of MR probes to the brains of live animals after acute neurological disorders.

MR contrast probes that trace gene transcripts for cerebral ischemia in live animals

The aim of this research was to validate transcription magnetic resonance (MR) imaging (MRI) for gene transcript targeting in acute neurological disorders in live subjects. We delivered three MR probe variants with superparamagnetic iron oxide nanoparticles (SPION, a T2 susceptibility agent) linked to a phosphorothioate-modified oligodeoxynucleotide (sODN) complementary to c-fos mRNA (SPION-cfos) or beta-actin mRNA (SPION-beta-actin) and to sODN with random sequence (SPION-Ran). Each probe (1 microg Fe in 2 microl) was delivered via intracerebroventricular infusion to the left cerebral ventricle of male C57Black6 mice. We demonstrated SPION retention, measured as decreased T2* signal or increased R2* value (R2* = 1/T2*). Animals that received the SPION-beta-actin probe exhibited the highest R2* values, followed (in descending order) by SPION-cfos and SPION-Ran. SPION-cfos retention was localized in brain regions where SPION-cfos was present and where hybrids of SPION-cfos and its target c-fos mRNA were detected by in situ reverse transcription PCR. In animals that experienced cerebral ischemia, SPION-cfos retention was significantly increased in locations where c-fos mRNA increased in response to the ischemic insult; these elevations were not observed for SPION-beta-actin and SPION-Ran. This study should enable MR detection of mRNA alteration in disease models of the central nervous system.

Forebrain ischemia-reperfusion simulating cardiac arrest in mice induces edema and DNA fragmentation in the brain

Brain injury affects one-third of persons who survive after heart attack, even with restoration of spontaneous circulation by cardiopulmonary resuscitation. We studied brain injury resulting from transient bilateral carotid artery occlusion (BCAO) and reperfusion by simulating heart attack and restoration of circulation, respectively, in live C57Black6 mice. This model is known to induce neuronal death in the hippocampus, striatum, and cortex. We report the appearance of edema after transient BCAO of 60 minutes and 1 day of reperfusion. Hyperintensity in diffusion-weighted magnetic resonance imaging (MRI) was detectable in the striatum, thalamus, and cortex but not in the hippocampus. To determine whether damage to the hippocampus can be detected in live animals, we infused a T(2) susceptibility magnetic resonance contrast agent (superparamagnetic iron oxide nanoparticles [SPIONs]) that was linked to single-stranded deoxyribonucleic acid (DNA) complementary in sequence to c-fos messenger ribonucleic acid (SPION-cfos); we acquired in vivo T(2)*-weighted MRI 3 days later. SPION retention was measured as T(2)* (milliseconds) signal reduction or R(2)* value (s(-1)) elevation. We found that animals treated with 60-minute BCAO and 7-day reperfusion exhibited significantly less SPION retention in the hippocampus and cortex than sham-operated animals. These findings suggest that brain injury induced by cardiac arrest can be detected in live animals.

The inflammatory response in stroke

Recent works in the area of stroke and brain ischemia has demonstrated the significance of the inflammatory response accompanying necrotic brain injury. Acutely, this response appears to contribute to ischemic pathology, and anti-inflammatory strategies have become popular. This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in experimental stroke. It will review the role of specific cell types including leukocytes, endothelium, glia, microglia, the extracellular matrix and neurons. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Ischemic preconditioning in the rat brain enhances the repair of endogenous oxidative DNA damage by activating the base-excision repair pathway

The development of ischemic tolerance in the brain, whereby a brief period of sublethal 'preconditioning' ischemia attenuates injury from subsequent severe ischemia, may involve the activation of multiple intracellular signaling events that promote neuronal survival. In this study, the potential role of inducible DNA base-excision repair (BER), an endogenous adaptive response that prevents the detrimental effect of oxidative DNA damage, has been studied in the rat model of ischemic tolerance produced by three episodes of ischemic preconditioning (IP). This paradigm of IP, when applied 2 and 5 days before 2-h middle cerebral artery occlusion (MCAO), significantly decreased infarct volume in the frontal-parietal cortex 72 h later. Correlated with this protective effect, IP markedly attenuated the nuclear accumulations of several oxidative DNA lesions, including 8-oxodG, AP sites, and DNA strand breaks, after 2-h MCAO. Consequently, harmful DNA damage-responsive events, including NAD depletion and p53 activation, were reduced during postischemic reperfusion in preconditioned brains. The mechanism underlying the decreased DNA damage in preconditioned brain was then investigated by measuring BER activities in nuclear extracts. Beta-polymerase-mediated BER activity was markedly increased after IP, and this activation occurred before (24 h) and during the course of ischemic tolerance (48 to 72 h). In similar patterns, the activities for AP site and 8-oxodG incisions were also upregulated after IP. The upregulation of BER activities after IP was likely because of increased expression of repair enzymes beta-polymerase, AP endonuclease, and OGG1. These results suggest that the activation of the BER pathway may contribute to IP-induced neuroprotection by enhancing the repair of endogenous oxidative DNA damage after ischemic injury.

Simultaneous in situ profiling of DNA lesion endpoints based on image cytometry and a single cell database approach

Analyzing the integrity of DNA is one of the most frequent used endpoints for risk assessment of chemical and physical agents. In the framework of a radiobiological space experiment, this work aimed at having (1) a histochemical tool for the in situ assessment of DNA damage in as long as 20 days old fixed cell cultures, (2) a comprehensive tool for the quantification of different types of DNA lesions, and (3) a methodology of sampling thousands of nuclei based on confocal microscopy, automated stage scanning and digital image processing. For this purpose several fixatives and permeabilization techniques were tested together with the combinatorial use of terminal dUTP transferase-mediated nick end-labeling (TUNEL) and the DNA polymerase I mediated in situ nick translation. These biochemical tools are useful for scoring DNA single and double breaks, and oxidative lesions. Ltk(-) cells were exposed either to hydrogen peroxide or heavy ion beam irradiation. Combination of paraformaldehyde fixation, sodium citrate permeabilization and heat gave the best staining results. A three-channel fluorescence methodology was established including a DNA counter stain for nucleus identification and normalization of DNA content. Communication between confocal imaging software, image analysis software and a relational database proved to be pivotal for a semi-automated high-end single cell analysis and storage of images. In this way, DNA damage data per nucleus can be traced back to the original image. As much as 2500 cells could be analyzed in situ within a day and correlations drawn between different DNA lesion endpoints.

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.

Role of nitric oxide in the regulation of neuronal proliferation, survival and differentiation

Nitric oxide (NO), an important cellular messenger, has been linked to both neurodegenerative and neuroprotective actions. In the present review, we focus on recent data establishing a survival and differentiation role for NO in several neural in vitro and in vivo models. Nitric oxide has been found to be essential for survival of neuronal cell lines and primary neurons in culture under various death challenges. Furthermore, its lack may aggravate some neuropathological conditions in experimental animals. Several cellular pathways and signaling systems subserving this neuroprotective role of NO are considered in the review. Survey of recent data related to the developmental role of NO mainly focus on its action as a negative regulator of neuronal precursor cells proliferation and on its role of promotion of neuronal differentiation. Discussion on discrepancies arising from the literature is focused on the Janus-faced properties of the molecule and it is proposed that most controversial results are related to the intrinsic property of NO to compensate among functionally opposed effects. As an example, the increased proliferation of neural cell precursors under conditions of NO shortage may be, later on in the development, compensated by increased elimination through programmed cell death as a consequence of the lack of the survival-promoting action of the molecule. To elucidate these complex, and possibly contrasting, effects of NO is indicated as an important task for future researches.

DNA single-strand breaks and neurodegeneration

The association of human genetic disorders with defects in the DNA damage response is well established. Most of the major DNA repair pathways are represented by diseases in which that pathway is absent or impaired, including those responsible for repairing DNA double-strand breaks. Conspicuous by their absence, however, have been human disorders associated with defects in the repair or response to DNA single-strand breaks (SSBs). However, three papers have recently associated hereditary spinocerebellar ataxia with mutations in genes connected with SSBR. The emerging links between SSBR and neurodegeneration are discussed.

Oxidative DNA lesions in a rodent model of traumatic brain injury

BACKGROUND

Oxidative DNA lesions have not been well studied in traumatic brain injury (TBI).

METHODS

TBI was induced with a controlled cortical impact injury in rats. Brain tissue was examined for 8-hydroxy-2'-deoxyguanosine (oh8dG) using mono-clonal antibodies at different time frames; 15 minutes (n = 4), 30 minutes (n = 7), 60 minutes (n = 6), and 240 minutes (n = 5). The control group consisted of sham-operated animals undergoing the same surgery without the controlled cortical impact injury (n = 5).

RESULTS

An elevation of oh8dG was detected in the nuclear and perinuclear (mitochondrial) regions of the ipsilateral cortex, but seldom in those of the contralateral cortex. The amount of oh8dG in those animals with TBI was significant in all time frames when compared with sham-operated controls (p < 0.001). The oh8dG levels were more prominent at 15 minutes (p < 0.0001) when compared with controls.

CONCLUSION

Oxidative DNA lesions occurred in this model of TBI maximally early after TBI. This suggests that oh8dGs may affect genetic material of the brain and that oh8dGs may adversely affect gene expression that occurs early after head injury.

Comparison of iNOS Inhibition by Antisense and Pharmacological Inhibitors after Spinal Cord Injury

Inducible nitric oxide synthase (iNOS) is a key mediator of inflammation during pathological conditions. We examined, through the use of selective iNOS inhibitors, the role of iNOS in specific pathophysiological processes after spinal cord injury (SCI), including astrogliosis, blood-spinal cord barrier (BSCB) permeability, polymorphonuclear leukocyte infiltration, and neuronal cell death. Administration of iNOS antisense oligonucleotides (ASOs) (intraspinally at 3 h) or the pharmacological inhibitors, N-[3(Aminomethyl) benzyl] acetamidine (1400 W) (i.v./i.p. 3 and 9 h) or aminoguanidine (i.p. at 3 and 9 h) after moderate contusive injury decreased the number of iNOS immunoreactive cells at the injury site by 65.6% (iNOS ASOs), 62.1% (1400 W), or 59% (aminoguanidine) 24 h postinjury. iNOS activity was reduced 81.8% (iNOS ASOs), 56.7% (1400 W), or 67.9% (aminoguanidine) at this time. All iNOS inhibitors reduced the degree of BSCB disruption (plasma leakage of rat immunoglobulins), with iNOS ASO inhibition being more effective (reduced by 58%). Neutrophil accumulation within the injury site was significantly reduced by iNOS ASOs and 1400 W by 78.8% and 20.9%, respectively. Increased astrogliosis was diminished with iNOS ASOs but enhanced following aminoguanidine. Detection of necrotic and apoptotic neuronal cell death by propidium iodide and an FITC-conjugated Annexin V antibody showed that iNOS inhibition could significantly retard neuronal cell death rostral and caudal to the injury site. These novel findings indicate that acute inhibition of iNOS is beneficial in reducing several pathophysiological processes after SCI. Furthermore, we demonstrate that the antisense inhibition of iNOS is more efficacious than currently available pharmacological agents.

Inducible repair of oxidative DNA lesions in the rat brain after transient focal ischemia and reperfusion

To determine the role of oxidative DNA damage and repair in brain injury after focal ischemia and reperfusion, the authors investigated DNA base damage and DNA base excision repair (BER) capacity, the predominant repair mechanism for oxidative DNA lesions, in the rat model of temporary middle cerebral artery occlusion. Contents of 8-hydroxyl-2'-deoxyguanosine (8-oxodG) and apurinic/apyrimidinic abasic site (AP site), hallmarks of oxidative DNA damage, were quantitatively measured in nuclear DNA extracts from brains 0.25 to 72 hours after 1 hour of middle cerebral artery occlusion. In parallel to the detection of DNA lesions, the capacity for 8-oxodG- or AP site-dependent DNA repair synthesis was measured in nuclear protein extracts using specific in vitro DNA repair assays. After postischemic reperfusion, the levels of 8-oxodG and AP sites were markedly increased in ischemic tissues. In frontal/parietal cortex, regions that survived ischemia, 8-oxodG and AP sites were efficiently repaired during reperfusion. However, in the caudate, a region that was destined to infarct, the DNA lesions were poorly repaired. In consistent with the patterns of endogenous lesion repair, a markedly induced and long-lasting (at least 72 hours) BER activity was detected in the cortex but not in the caudate after ischemia. The induced BER activity in ischemic cortex was attributed to the upregulation of gene expression and activation of selective BER enzymes, particularly DNA polymerase-beta and OGG1. These results strongly suggest that inducible DNA BER constitutes an important endogenous mechanism that protects brain against ischemia-induced oxidative neuronal injury.

Molecular mechanisms of cerebral ischemia-induced neuronal death

The mode of neuronal death caused by cerebral ischemia and reperfusion appears on the continuum between the poles of catastrophic necrosis and apoptosis: ischemic neurons exhibit many biochemical hallmarks of apoptosis but remain cytologically necrotic. The position on this continuum may be modulated by the severity of the ischemic insult. The ischemia-induced neuronal death is an active process (energy dependent) and is the result of activation of cascades of detrimental biochemical events that include perturbion of calcium homeostasis leading to increased excitotoxicity, malfunction of endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, alteration in proapoptotic gene expression, and activation of the effector cysteine proteases (caspases) and endonucleases leading to the final degradation of the genome. In spite of strong evidence showing that brain infarction can be reduced by inhibiting any one of the above biochemical events, such as targeting excitotoxicity, up-regulation of an antiapoptotic gene, or inhibition of a down-stream effector caspase, it is becoming clear that targeting a single gene or factor is not sufficient for stroke therapeutics. An effective neuroprotective therapy is likely to be a cocktail aimed at all of the above detrimental events evoked by cerebral ischemia and the success of such therapeutic intervention relies upon the complete elucidation of pathways and mechanisms of the cerebral ischemia-induced active neuronal death.

Accumulation of 8-oxoguanine in the cellular DNA and the alteration of the OGG1 expression during ischemia-reperfusion injury in the rat kidney

During ischemia-reperfusion (I/R) injury in the rat kidney, apoptosis was observed in the distal tubules of the cortico-medullary region and outer medulla (OM) while severe necrosis was seen in the proximal straight tubules of the OM. The majority of these changes disappeared within 2 weeks. We examined the contents of 8-oxo-2'-deoxyguanosine (8-oxo-dG), which is a major type of oxidative damage in DNA, in the rat kidney during I/R injury, and also investigated the expression level of the OGG1 gene encoding the 8-oxoguanine DNA glycosylase. High-performance liquid chromatography with an MS/MS analysis of the nuclear DNA revealed an immediate accumulation of 8-oxo-dG in the nuclear DNA prepared from the cortex and OM of the kidney 1h after I/R, and an immunohistochemical analysis demonstrated the immediate accumulation of 8-oxo-dG in the nuclei of renal tubular cells both in the cortex and OM. A delayed increase of cytoplasmic staining with anti-8-oxo-dG was observed only in the cortico-medulla and OM, where the cytoplasmic staining in the proximal tubular cells is higher than in the distal tubular cells. The level of cytoplasmic staining representing 8-oxo-dG in mitochondrial DNA, peaked at 6h after I/R and preceded the necrosis of proximal tubular cells in the OM. An RNase protection assay showed a high level of OGG1 mRNA in the normal kidney, and the level decreased within 3h only in the OM, and increased thereafter 1-7 days of I/R both in the cortex and OM. In situ hybridization showed higher levels of OGG1 mRNA expression in the renal tubules in the OM than in the cortex of the normal kidney, which decreased rapidly within 3h of I/R. Thus, the accumulation of 8-oxo-dG in the mitochondrial DNA rather than in nuclear DNA is likely to be involved in the pathogenic responses such as necrosis of renal tubular cells during I/R injury of the kidney, together with an altered level of OGG1 expression.

Ischemia-reperfusion-related repair deficit after oxidative stress: implications of faulty transcripts in neuronal sensitivity after brain injury

Diseases of the heart are the No. 1 killer in industrialized countries. Brain injury can develop as a result of cerebral ischemia-reperfusion due to stroke (brain attack) and other cardiovascular diseases. Learning about the disease is the best way to reduce disability and death. We present here whether gene repair activities are associated with neuronal death in an ischemia-reperfusion model that simulates stroke in male Long-Evans rats. This experimental stroke model is known to induce necrosis in the ischemic cortex. Cerebral ischemia causes overactivation of membrane receptors and accumulation of extracellur glutamate and intracellular calcium, which activates neuronal nitric oxide synthase, causing damage to lipids, proteins, and nucleic acids, and reduces energy sources with consequent functional deterioration, leading to cell death. Restoration processes normally repair genes with few errors. However, ischemia elevates oxidative DNA lesions despite these repair mechanisms. These episodes concurrently occur with the induction of immediate-early genes that critically activate other late genes in the signal transduction pathway. Damage, repair, and transcription of the c-FOS gene are presented here as examples, because Fos peptide, one of the components of activator protein 1, activates nerve growth factor and repair mechanisms. The results of our studies show that treatments with 7-nitroindazole, a specific inhibitor of nitric oxide synthase known to attenuate nitric oxide, oxidative DNA lesions, and necrosis, increase intact c-fos mRNA levels after stroke. This suggests that the accuracy of gene expression could be accounted for the recovery of cellular function after cerebral injury.

Ischemia-reperfusion-related repair deficit after oxidative stress: implications of faulty transcripts in neuronal sensitivity after brain injury

Diseases of the heart are the No. 1 killer in industrialized countries. Brain injury can develop as a result of cerebral ischemia-reperfusion due to stroke (brain attack) and other cardiovascular diseases. Learning about the disease is the best way to reduce disability and death. We present here whether gene repair activities are associated with neuronal death in an ischemia-reperfusion model that simulates stroke in male Long-Evans rats. This experimental stroke model is known to induce necrosis in the ischemic cortex. Cerebral ischemia causes overactivation of membrane receptors and accumulation of extracellur glutamate and intracellular calcium, which activates neuronal nitric oxide synthase, causing damage to lipids, proteins, and nucleic acids, and reduces energy sources with consequent functional deterioration, leading to cell death. Restoration processes normally repair genes with few errors. However, ischemia elevates oxidative DNA lesions despite these repair mechanisms. These episodes concurrently occur with the induction of immediate-early genes that critically activate other late genes in the signal transduction pathway. Damage, repair, and transcription of the c-FOS gene are presented here as examples, because Fos peptide, one of the components of activator protein 1, activates nerve growth factor and repair mechanisms. The results of our studies show that treatments with 7-nitroindazole, a specific inhibitor of nitric oxide synthase known to attenuate nitric oxide, oxidative DNA lesions, and necrosis, increase intact c-fos mRNA levels after stroke. This suggests that the accuracy of gene expression could be accounted for the recovery of cellular function after cerebral injury.

Transcripts of damaged genes in the brain during cerebral oxidative stress

Recent studies using ischemia/reperfusion models of brain injury suggest that there is a period of time during which the formation of oxidative DNA lesions (ODLs) exceeds removal. This interval is a window of opportunity in which to study the effect of gene damage on gene expression in the brain, because the presence of excessive ODLs mimics a deficiency in gene repair, which has been shown to be associated with neurological disorders. Evidence from studies using similar models indicates that expression of faulty transcripts from ODL-infested genes and non-sense mutation in repaired genes occur before the process of cell death. Preventing the formation of ODLs and enhancing ODL repair are shown to increase the expression of intact transcripts and attenuate cell death. Understanding this mechanism could lead to the development of therapeutic techniques (physiologic, pharmacological, and/or genomic) that can enhance recovery.

Aged endothelial nitric oxide synthase knockout mice exhibit higher mortality concomitant with impaired open-field habituation and alterations in forebrain neurotransmitter levels

Endothelial nitric oxide synthase (eNOS) has been implicated in various brain and peripheral pathologies such as renal failure, heart failure or stroke. Consequently, the mortality rate of aged eNOS knockout mice (eNOS-/-) was higher than that of age-matched (18-22 months old) controls. Only seven of the original 14 eNOS-/- animals that participated in the study reached the age of 18 months or older, whereas no control mice died during this life span. In order to assess the behavioral and neurochemical consequences of chronic eNOS deficiency we examined whether the surviving aged eNOS-/- mice showed changes in terms of motor, emotional, exploratory and neurochemical parameters. Aged eNOS-/- mice showed reduced exploratory activity in the open-field with no habituation observable neither within sessions nor after repeated exposures. Pole test performance of eNOS-/- mice was comparable to controls. In the elevated plus-maze eNOS-/- mice did not differ from controls in terms of time spent in and entries into arms, but showed less locomotion on the open arms. The most prominent neurochemical alterations in the forebrains of aged eNOS-/- mice were: (a) increased acetylcholine levels in the neostriatum; (b) decreased noradrenaline concentrations in the ventral striatum; and (c) lower serotonin levels in the frontal cortex and ventral striatum. The present findings suggest that mice which survived chronic eNOS-deficiency into old age, show some behavioral and neurochemical phenotypes distinct from adult eNOS-/- mice.

S-nitrosylation of matrix metalloproteinases: signaling pathway to neuronal cell death

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of neurodegenerative diseases and stroke. However, the mechanism of MMP activation remains unclear. We report that MMP activation involves S-nitrosylation. During cerebral ischemia in vivo, MMP-9 colocalized with neuronal nitric oxide synthase. S-Nitrosylation activated MMP-9 in vitro and induced neuronal apoptosis. Mass spectrometry identified the active derivative of MMP-9, both in vitro and in vivo, as a stable sulfinic or sulfonic acid, whose formation was triggered by S-nitrosylation. These findings suggest a potential extracellular proteolysis pathway to neuronal cell death in which S-nitrosylation activates MMPs, and further oxidation results in a stable posttranslational modification with pathological activity.

The association between neuronal nitric oxide synthase and neuronal sensitivity in the brain after brain injury

Injury to the central nervous system is the leading cause of disability in the United States. Neuronal death is one of the causes of disability. Among patients who survive this type of injury, various degrees of recovery in brain function are observed. The molecular basis of functional recovery is poorly understood. Clinical observations and research using experimental injury models have implicated several metabolites in the cascade of events that lead to neuronal degeneration. The levels of intracellular ATP (energy source) and pH are decreased, whereas levels of extracellular glutamate, intracellular calcium ions, and oxidative damage to RNA/DNA, protein, and lipid are increased. These initiating events can be associated with energy failure and mitochondrial dysfunction, resulting in functional or structural brain damage. The injured brain is known to express immediate early genes. Recent studies show that reactive oxygen species (ROS) cause lesions in genes from which mRNA is transcribed as part of the endogenous neuroprotective response. Although degenerating proteins and lipids may contribute to necrosis significantly after severe injury, abnormalities in genetic material, if not repaired, disturb cellular function at every level by affecting replication, transcription, and translation. These lesions include abnormal nucleic acids, known as oxidative lesions of DNA (ODLs) or of RNA (ORLs). In this review, we focus on our current understanding of the various effects of neuronal nitric oxide synthase on the formation of modified bases in DNA and RNA that are induced in the brain after injury, and how ODLs and ORLs affect cell function.

Ischemic injury and faulty gene transcripts in the brain

The brain has the highest metabolic rate of all organs and depends predominantly on oxidative metabolism as a source of energy. Oxidative metabolism generates reactive oxygen species, which can damage all cellular components, including protein, lipids and nucleic acids. The processes of DNA repair normally remove spontaneous gene damage with few errors. However, cerebral ischemia followed by reperfusion leads to elevated oxidative stress and damage to genes in brain tissue despite a functional mechanism of DNA repair. These critical events occur at the same time as the expression of immediate early genes, the products of which trans-activate late effector genes that are important for sustaining neuronal viability. These findings open the possibility of applying genetic tools to identify molecular mechanisms of gene repair and to derive new therapies for stroke and brain injury.

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.

Increased cytochrome c-mediated DNA fragmentation and cell death in manganese-superoxide dismutase-deficient mice after exposure to subarachnoid hemolysate

BACKGROUND AND PURPOSE

We sought to investigate the mechanisms for oxidative injury caused by subarachnoid hemolysate, a pro-oxidant.

METHODS

Injection of 50 microL of subarachnoid hemolysate or saline was performed in CD1 mice (n=75), mutant mice deficient in Mn-superoxide dismutase (Sod2+/-; n=23), and their wild-type littermates (n=23). Subcellular location of cytochrome c was studied by immunocytochemistry, immunofluorescence, and immunoblotting of cellular fractions. DNA fragmentation was assessed though DNA laddering and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL). Cell death was examined through basic histology.

RESULTS

Cytochrome c immunoreactivity was present in the cytosol of neurons at 2 hours after hemolysate injection and increased by 4 hours compared with saline-injected animals (P:<0.02). Cytosolic cytochrome c was more abundant in Sod2+/- mutants. DNA fragmentation was evident at 24 hours, but not 4 hours, after hemolysate injection as determined by DNA laddering and TUNEL staining (P:<0.02). DNA fragmentation colocalized to cells with cytosolic cytochrome c and iron. In Sod2+/- mutants, the extent of fragmentation was increased as determined by TUNEL staining (52% increase; P:<0.02) and DNA laddering (optical density=0.819 versus 0.391; P:<0.01). Cell death was evident on basic histology as early as 4 hours after hemolysate injection. No cell death was evident in controls. In Sod2+/- mutants, cell death was increased by 51% compared with wild-type littermates (P:<0.05).

CONCLUSIONS

These results demonstrate that subarachnoid blood products are associated with the presence of cytochrome c in the cytosol and subsequent cell death in neurons. It appears that Mn-superoxide dismutase plays a role in preventing cell death after exposure to subarachnoid blood products.

Neuronal NOS inhibitor that reduces oxidative DNA lesions and neuronal sensitivity increases the expression of intact c-fos transcripts after brain injury

In response to oxidative stress, the ischemic brain induces immediate early genes when its nuclear genes contain gene damage. Antioxidant that reduces gene damage also reduces cell death. To study the mechanism of neuronal sensitivity, we investigated the transcription of the c-fos gene after brain injury of the ischemia-reperfusion type using focal cerebral ischemia-reperfusion in Long-Evans hooded rats. We observed a significant (p < 0.01) increase in c-fos mRNA in the ischemic cortex immediately after brain injury. However, the c-fos transcript was sensitive to RNase A protection assay (RPA) upon reperfusion. The transcript became significantly resistant to RPA (42%, p < 0.03) when 3-bromo-7-nitroindazole (25 mg/kg, i.p.), known to abolish nitric oxide, gene damage and neuronal sensitivity, was injected. Our data suggest that neuronal nitric oxide synthase and aberrant mRNA from genes with oxidative damage could be associated with neuronal sensitivity.

Oxidative DNA damage precedes DNA fragmentation after experimental stroke in rat brain

Experimental stroke using a focal cerebral ischemia and reperfusion (FCIR) model was induced in male Long-Evans rats by a bilateral occlusion of both common carotid arteries and the right middle cerebral artery for 30-90 min, followed by various periods of reperfusion. Oxidative DNA lesions in the ipsilateral cortex were demonstrated using Escherichia coli formamidopyrimidine DNA N-glycosylase (Fpg protein)-sensitive sites (FPGSS), as labeled in situ using digoxigenin-dUTP and detected using antibodies against digoxigenin. Because Fpg protein removes 8-hydroxy-2'-deoxyguanine (oh8dG) and other lesions in DNA, FPGSS measure oxidative DNA damage. The number of FPGSS-positive cells in the cortex from the sham-operated control group was 3 +/- 3 (mean +/- SD per mm(2)). In animals that received 90 min occlusion and 15 min of reperfusion (FCIR 90/15), FPGSS-positive cells were significantly increased by 200-fold. Oxidative DNA damage was confirmed by using monoclonal antibodies against 8-hydroxy-guanosine (oh8G) and oh8dG. A pretreatment of RNase A (100 microg/ml) to the tissue reduced, but did not abolish, the oh8dG signal. The number of animals with positive FPGSS or oh8dG was significantly (P<0.01) higher in the FCIR group than in the sham-operated control group. We detected few FPGSS of oh8dG-positive cells in the animals treated with FCIR of 90/60. No terminal UTP nicked-end labeling (TUNEL)-positive cells, as a detection of cell death, were detected at this early reperfusion time. Our data suggest that early oxidative DNA lesions elicited by experimental stroke could be repaired. Therefore, the oxidative DNA lesions observed in the nuclear and mitochondrial DNA of the brain are different from the DNA fragmentation detected using TUNEL.