Brain tissue responses to ischemia

Morphological heterogeneity of CA1 pyramidal neurons in response to ischemia

We have found, based on the electrophysiological properties, two subtypes of CA1 pyramidal neurons in the CA1 region of the normal hippocampus, late postsynaptic potential (L-PSP) neurons and non-L-PSP neurons. In addition, our previous study has shown that the electrophysiological properties of these two subtypes of pyramidal neurons were differentially modified after ischemia. In the present study, we hypothesized that ischemia might also induce different morphological alterations in these two subtypes of neuron. To test the hypothesis, we compared the changes in the dendritic arborization and soma volume of these two subtypes of neurons in rats subjected to transient global ischemia. We found a significant decrease in the basal dendritic length of L-PSP neurons at 12 hr after reperfusion, resulting mainly from a significant decrease in the dendrite terminal length. The apical dendritic length of L-PSP neurons markedly increased at 24 hr after ischemia, resulting mainly from an increase in the number of branching arbors in the middle part of the apical dendritic trees. The soma size of L-PSP neurons was significantly reduced at 12 hr, but they became slightly larger at 24 hr and 48 hr after reperfusion. In contrast to L-PSP neurons, non-L-PSP neurons showed slight modifications in the dendritic arborization but had persistent swelling of their soma after ischemia. These results indicate that pathological changes in these two subtypes of neurons are different after ischemia.

Neuroprotective effects of edaravone: a novel free radical scavenger in cerebrovascular injury

Recanalization and neuroprotection have been mainly targeted for the specific treatment of acute ischemic stroke. Free radicals play a crucial role in brain ischemic injury by exacerbating membrane damage through peroxidation of unsaturated fatty acids of cell membrane, leading to neuronal death and brain edema. Free radicals have been implicated in stroke pathophysiology as pivotal contributors to cell injury. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a novel potent free radical scavenger that has been clinically used to reduce the neuronal damage following ischemic stroke. Edaravone exerts neuroprotective effects by inhibiting endothelial injury and by ameliorating neuronal damage in brain ischemia. Edaravone provides the desirable features of NOS: it increases eNOS (beneficial NOS for rescuing ischemic stroke) and decreases nNOS and iNOS (detrimental NOS). Post- reperfusion brain edema and hemorrhagic events induced by thrombolytic therapy may be reduced by edaravone pretreatment. Increased productions of superoxide and NO in the brain after reperfusion and a concomitant surge in oxygen free radicals with increased NO during recirculation lead to formation of peroxynitrite, a superpotent radical. Edaravone, which inhibits oxidation and enhances NO production derived from increased eNOS expression, may improve and conserve cerebral blood flow without peroxynitrite generation during reperfusion. Clinical experience with edaravone suggests that this drug has a wide therapeutic time window. The combination therapy (a thrombolytic plus edaravone) is likely to target brain edema, reduce stroke death and improve the recovery from neurological deficits in stoke patients.

The nerve hemoglobin of the bivalve mollusc Spisula solidissima: molecular cloning, ligand binding studies, and phylogenetic analysis

Members of the hemoglobin (Hb) superfamily are present in nerve tissue of several vertebrate and invertebrate species. In vertebrates they display hexacoordinate heme iron atoms and are typically expressed at low levels (microM). Their function is still a matter of debate. In invertebrates they have a hexa- or pentacoordinate heme iron, are mostly expressed at high levels (mM), and have been suggested to have a myoglobin-like function. The native Hb of the surf clam, Spisula solidissima, composed of 162 amino acids, does not show specific deviations from the globin templates. UV-visible and resonance Raman spectroscopy demonstrate a hexacoordinate heme iron. Based on the sequence analogy, the histidine E7 is proposed as a sixth ligand. Kinetic and equilibrium measurements show a moderate oxygen affinity (P(50) approximately 0.6 torr) and no cooperativity. The histidine binding affinity is 100-fold lower than in neuroglobin. Phylogenetic analysis demonstrates a clustering of the S. solidissima nerve Hb with mollusc Hbs and myoglobins, but not with the vertebrate neuroglobins. We conclude that invertebrate nerve Hbs expressed at high levels are, despite the hexacoordinate nature of their heme iron, not essentially different from other intracellular Hbs. They most likely fulfill a myoglobin-like function and enhance oxygen supply to the neurons.

Water soluble prodrug of a COX-2 selective inhibitor suitable for intravenous administration in models of cerebral ischemia

A water soluble choline prodrug (17) of a COX-2 selective inhibitor (16) suitable for intravenous dosing in models of cerebral ischemia has been developed. Constant infusion studies using 17 demonstrate that extrapolated brain levels of 16 may be maintained for over 24h in rats.

Poly(ADP-ribosyl)ation and stroke

Over the past decade, poly(ADP-ribosyl)ation has emerged as a crucial event in the pathogenesis of ischemic stroke. A large body of evidence unambiguously demonstrates that activity of poly(ADP-ribose) polymerase-1 (PARP-1) significantly increases during brain ischemia, and that inhibition of this enzymatic activity affords substantial neuroprotection from ischemic brain injury. This review strictly focuses on literature on poly(ADP-ribosyl)ation and ischemic stroke, highlighting the pathogenetic role of poly(ADP-ribose) in ischemic neuronal death, and the therapeutic relevance of drugs modulating its metabolism to pharmacological treatment of cerebral ischemia.

Modest intracellular acidification suppresses death signaling in ouabain-treated cells

The signaling cascade resulting in the death of several types of cells treated with ouabain or other cardiotonic steroids (CTS) remains poorly understood. Recently, we observed that ouabain kills epithelial and endothelial cells via its interaction with Na(+), K(+) -ATPase, but independently of inhibition of Na(+), K(+) -ATPase-mediated ion fluxes and inversion of the [Na(+)](i)/[K(+)](i) ratio. Here, we report that the death of ouabain-treated epithelial cells from the Madin-Darby canine kidney (C7-MDCK) and endothelial cells from porcine aortae is suppressed by acidification of medium from pH 7.4 to 7.0, i.e. under conditions when pH(i) was decreased from approximately 7.2 to 6.9. The rescue of ouabain-treated C7-MDCK cells was also detected under selective intracellular acidification caused by inhibition of Na(+)/H(+) exchanger. In these cells, neither Na(+), K(+) pump activity nor [(3)H]-ouabain binding was significantly affected by modest acidification. The death of ouabain-treated cells was independent of inhibition of RNA and protein synthesis with actinomycin D and cycloheximide. In contrast, both compounds sharply attenuated the protective action of acidified medium. Thus, our results show that very modest intracellular acidification is sufficient to inhibit the Na(+) (i)/K(+) (i)-independent death signal triggered in epithelial and endothelial cells by CTS. They also suggest that the protective action of acidification is mediated by de novo expression of genes involved in inhibition of the cell death machinery.

Tumor necrosis factor-like weak inducer of apoptosis-induced neurodegeneration

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) family of cytokines. It has proangiogenic and proinflammatory properties in vivo and induces cell death in tumor cell lines. TWEAK effects are mediated by the membrane receptor Fn14. In a systematic search for genes regulated in a murine stroke model with the tag-sequencing technique massively parallel signature sequencing, we have identified TWEAK as an induced gene. After 24 hr of focal cerebral ischemia in vivo or oxygen glucose deprivation in primary cortical neurons, both TWEAK and its receptor Fn14 were significantly upregulated. TWEAK induced cell death in primary neurons. Transfection of a nuclear factor (NF)-kappaB-luciferase fusion gene demonstrated that TWEAK stimulated transcriptional activity of NF-kappaB through Fn14 and the IkappaB kinase. Inhibition of NF-kappaB reduced TWEAK-stimulated neuronal cell death, suggesting that NF-kappaB mediates TWEAK-induced neurodegeneration at least in part. Intraperitoneal injection of a neutralizing anti-TWEAK antibody significantly reduced the infarct size after 48 hr of permanent cerebral ischemia. In summary, our data show that TWEAK induces neuronal cell death and is involved in neurodegeneration in vivo.

Acute and repeated restraint stress influences cellular damage in rat hippocampal slices exposed to oxygen and glucose deprivation

Several studies have shown that high corticosteroid hormone levels increase neuronal vulnerability. Here we evaluate the consequences of in vivo acute or repeated restraint stress on cellular viability in rat hippocampal slices suffering an in vitro model of ischemia. Cellular injury was quantified by measuring lactate dehydrogenase (LDH) and neuron-specific enolase released into the medium. Acute stress did not affect cellular death when oxygen and glucose deprivation (OGD) was applied both immediately or 24h after restraint. The exposure to OGD, followed by reoxygenation, resulted in increased LDH in the medium. Repeated stress potentiated the effect of OGD both, on LDH and neuron-specific enolase released to the medium. There was no effect of repeated stress on the release of S100B, an astrocytic protein. Additionally, no effect of repeated stress was observed on glutamate uptake by the tissue. These results suggest that repeated stress increases the vulnerability of hippocampal cells to an in vitro model of ischemia, potentiating cellular damage, and that the cells damaged by the exposure to repeated stress+OGD are mostly neurons. The uptake of glutamate was not observed to participate in the mechanisms responsible for rendering the neurons more susceptible to ischemic damage after repeated stress.

Intrinsic mechanisms of poly(ADP-ribose) neurotoxicity: three hypotheses

Poly(ADP-ribose) (PAR) is a branched and negatively charged polymeric macromolecule formed by poly(ADP-ribose) polymerases. Targeting of PAR onto acceptor proteins affects their functioning and regulates cellular homeostasis. A large body of evidence demonstrates that increased neo-formation of PAR has a crucial role in neurodegeneration. Consistently, strategies aimed at reducing PAR synthesis are of therapeutic relevance to treatment of several experimental neurodegenerative diseases. However, how PAR causes neuronal death is still elusive. This review provides an appraisal of the possible molecular mechanisms underlying PAR neurotoxicity, highlighting the pleiotypic effects of the polymer on neural cells exposed to different stressful conditions.

Minocycline delays disease onset and mortality in reovirus encephalitis

Minocycline is neuroprotective in many experimental models of neurodegenerative diseases and central nervous system (CNS) injury but has not previously been tested in a model of viral encephalitis. Experimental infection of neonatal mice with neurotropic reoviruses is a classic model for studying the pathogenesis of viral encephalitis. Intracerebral inoculation of serotype 3 reovirus strain Dearing (T3D) in neonatal mice results in lethal encephalitis caused by neuronal apoptosis throughout the CNS. Minocycline significantly delayed death in mice to 11.6 +/- 0.9 days post-infection vs. 8.6 +/- 0.7 days post-infection in controls (P < 0.01). Virus-induced CNS injury, apoptosis, viral titer and antigen expression were significantly decreased in the brains of minocycline-treated mice on 6 and 8 days post-infection compared to controls. Virus-induced injury and viral titer in minocycline-treated infected mice at 11 days post-infection were similar to those seen in untreated T3D-infected mice at 8 days post-infection. Little microglial or astrocytic invasion of brain regions with viral injury was found at any time-point in untreated or minocycline-treated mice, suggesting that in this model system the neuroprotective effect exerted by minocycline is more likely due to its anti-apoptotic properties rather than its capacity to inhibit microglial activation and limit gliosis. These findings, similar to those reported for neurodegenerative diseases, indicate that minocycline does not prevent development of fatal reovirus encephalitis but delays disease onset and progression, suggesting that minocycline treatment may provide a useful adjunctive therapy in viral CNS infections.

Superiority of early relative to late ischemic preconditioning in spinal cord protection after descending thoracic aortic occlusion

OBJECTIVE

We previously showed that ischemic preconditioning significantly reduced spinal cord injury caused by 35-minute aortic occlusion. In this study we investigated the effect of ischemic preconditioning on spinal cord injury after 45-minute aortic occlusion.

METHODS

Thirty-two pigs were divided as follows: group 1 (n = 6) underwent sham operation, group 2 (n = 6) underwent 20 minutes of aortic occlusion, group 3 (n = 6) underwent 45 minutes of occlusion, group 4 (n = 6) underwent 20 minutes of occlusion and 48 hours later underwent an additional 45 minutes, and group 5 (n = 8) underwent 20 minutes of occlusion and 80 minutes later underwent an additional 45 minutes. Aortic occlusion was accomplished with two balloon occlusion catheters placed fluoroscopically after the origin of the left subclavian artery and at the aortic bifurcation. Neurologic evaluation was by Tarlov score. The lower thoracic and lumbar spinal cords were harvested at 120 hours and examined histologically with hematoxylin-eosin staining. The number of neurons was counted, and the inflammation was scored (0-4). Statistical analysis was by Kruskal-Wallis and 1-way analysis of variance tests.

RESULTS

Group 5 (early ischemic preconditioning) had better Tarlov scores than group 3 ( P < .001) and group 4 (late ischemic preconditioning, P < .001). The histologic changes were proportional to the Tarlov scores, with the least histologic damage in the animals of group 5 relative to group 3 (number of neurons P < .001, inflammation P = .004) and group 4 (number of neurons P < .001, inflammation P = .006).

CONCLUSION

Early ischemic preconditioning is superior to late ischemic preconditioning in reducing spinal cord injury caused by the extreme ischemia of 45 minutes of descending thoracic aortic occlusion.

Neuronal expression of the NADPH oxidase NOX4, and its regulation in mouse experimental brain ischemia

Ischemia-induced neuronal damage has been linked to elevated production of reactive oxygen species (ROS) both in animal models and in humans. NADPH oxidase enzymes (NOX-es) are a major enzymatic source of ROS, but their role in brain ischemia has not yet been investigated. The present study was carried out to examine the expression of NOX4, one of the new NADPH oxidase isoforms in a mouse model of focal permanent brain ischemia. We demonstrate that NOX4 is expressed in neurons using in situ hybridization and immunohistochemistry. Ischemia, induced by middle cerebral artery occlusion resulted in a dramatic increase in cortical NOX4 expression. Elevated NOX4 mRNA levels were detectable as early as 24 h after the onset of ischemia and persisted throughout the 30 days of follow-up period, reaching a maximum between days 7 and 15. The early onset suggests neuronal reaction, while the peak period corresponds to the time of neoangiogenesis occurring mainly in the peri-infarct region. The occurrence of NOX4 in the new capillaries was confirmed by immunohistochemical staining. In summary, our paper reports the presence of the ROS producing NADPH oxidase NOX4 in neurons and demonstrates an upregulation of its expression under ischemic conditions. Moreover, a role for NOX4 in ischemia/hypoxia-induced angiogenesis is suggested by its prominent expression in newly formed capillaries.

Early and delayed glutamate effects in rat primary cortical neurons

Glutamate-induced changes in the subcellular distribution of protein kinase C isoforms and in the intracellular calcium concentration were investigated in rat primary cortical neurons. Western blot analysis of protein kinase C isoforms (alpha, beta1, beta2, gamma, delta, epsilon, zeta and theta), performed 30 min after a 10 min treatment with 30 microM glutamate, revealed a decrease in the total beta1 (-24%) and beta2 (-40%) isoform levels, without any significant change in any of the other isozymes. All conventional isoforms translocated to the membrane compartment, while delta, epsilon, zeta and theta; maintained their initial subcellular distribution. Twenty-four hours after glutamate treatment, the total protein kinase C labelling had increased, particularly the epsilon isoform, which accounted for 34% of the total densitometric signal. At this time, protein kinase C beta1, delta, epsilon and zeta isoforms were mainly detected in the membrane compartment, while gamma and theta; signals were displayed almost solely in the cytosol. Basal intracellular calcium concentration (FURA 2 assay) was concentration-dependently increased (maximum effect +77%) 30 min, but not 24h after a 10 min glutamate (10-100 microM) treatment, while the net increase induced by electrical stimulation (10 Hz, 10s) was consistently reduced (maximum effect -64%). The N-methyl-d-aspartate receptor antagonist, MK-801, 1 microM, prevented glutamate action both 30 min and 24 h after treatment, while non-selective protein kinase C inhibitors, ineffective at 30 min, potentiated it at 24 h. These findings show that protein kinase C isoforms are differently activated and involved in the early and delayed glutamate actions, and that the prevailing effect of their activation is neuroprotective.

Erythropoietin and the hypoxic brain

Normal tissue function in mammals depends on adequate supply of oxygen through blood vessels. A discrepancy between oxygen supply and consumption (hypoxia) induces a variety of specific adaptation mechanisms at the cellular, local and systemic level. These mechanisms are in part governed by the activation of hypoxia-inducible transcription factors (HIF-1, HIF-2), which in turn modulate expression of hypoxically regulated genes such as those encoding vascular endothelial growth factor (VEGF) and erythropoietin (EPO). EPO is a glycoprotein that is produced mainly by interstitial fibroblasts in the kidneys of the adult and in hepatocytes in the foetus. Released into the circulation, EPO makes its way to the bone marrow, where it regulates red cell production by preventing apoptosis of erythroid progenitor cells. Recently, EPO has emerged as a multifunctional growth factor that plays a significant role in the nervous system. Both EPO and its receptor are expressed throughout the brain in glial cells, neurones and endothelial cells. Hypoxia and ischaemia have been recognised as important driving forces of EPO expression in the brain. EPO has potent neuroprotective properties in vivo and in vitro and appears to act in a dual way by directly protecting neurones from ischaemic damage and by stimulating endothelial cells and thus supporting the angiogenic effect of VEGF in the nervous system. Thus, hypoxia-induced gene products such as VEGF and EPO might be part of a self-regulated physiological protection mechanism to prevent neuronal injury, especially under conditions of chronically reduced blood flow (chronic ischaemia). In this review, I will briefly summarize the recent findings on the molecular mechanisms of hypoxia-regulated EPO expression in general and give an overview of its expression in the central nervous system, its action as a growth factor with non-haematopoietic functions and its potential clinical relevance in various brain pathologies.

Cerebral hemodynamic reserve and early neurologic deterioration in acute ischemic stroke

Early neurological deterioration (END) is associated with increased mortality and morbidity. Although several predictive factors have been reported, there are little data about the hemodynamic factors. Our aim was to determine the capacity of cerebral hemodynamic reserve (CHR) to predict END. We studied 100 hospitalized patients with a first ever ischemic stroke of the middle cerebral artery (MCA) within the first 24 hours of symptoms onset. END was defined as a drop of at least one point in the Canadian Stroke Scale between admission and 72 hours. The mean flow velocity (mV) in the MCA and the CHR were measured by means of transcranial Doppler within the first 24 hours of admission. The CHR was expressed as the percentage increase in the MCA mV divided by the absolute increase in the end-tidal CO2 pressure in mm Hg after carbogen inhalation. END was observed in 23 patients. Reduced values of the mV in the symptomatic MCA (P = 0.043) and of the CHR in the symptomatic hemisphere (P < 0.001) were significantly associated with END. A CHR of less than 2%/1 mm Hg was independently associated with END (OR 8.45, 95% CI 1.82-39.2) after adjusting for potential confounders. CHR impairment within the first 24 hours of acute ischemic stroke is associated with a higher risk of END. This technique may be useful in selecting patients requiring a more intensive management.

Neuregulin-1 is neuroprotective and attenuates inflammatory responses induced by ischemic stroke

Recent work from our laboratory demonstrated that the expression neuregulin-1 in neurons was induced in the ischemic penumbra by focal stroke in the rat. Here, we show that a single intravascular injection of neuregulin-1beta (approximately 2.5 ng/kg) reduced cortical infarct volume by >98% when given immediately before middle cereral artery occlusion. Subcortical infarct volume was reduced by approximately 40%. Analysis of DNA fragmentation in brain tissues indicated that neuregulin-1 blocked apoptosis in cortical neurons in the penumbra. Neuregulin-1 prevented macrophage/microglial infiltration and astrocytic activation following focal ischemia. The neuroprotective effect of neuregulin-1 was also associated with a suppression of interleukin-1beta mRNA levels. These data suggest that neuregulin-1 protects neurons from delayed, ischemia-induced apoptotic cell death in the cortex by inhibiting pro-inflammatory responses. Neuregulins represent a novel, potent neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Nitric oxide signaling: systems integration of oxygen balance in defense of cell integrity

PURPOSE OF REVIEW

Nitric oxide has emerged as a ubiquitous signaling molecule subserving diverse pathophysiologic processes, including cardiovascular homeostasis and its decompensation in atherogenesis. Recent insights into molecular mechanisms regulating nitric oxide generation and the rich diversity of mechanisms by which it propagates signals reveal the role of this simple gas as a principle mediator of systems integration of oxygen balance.

RECENT FINDINGS

The molecular lexicon by which nitric oxide propagates signals encompasses the elements of posttranslational modification of proteins by redox-based nitrosylation of transition metal centers and free thiols. Spatial and temporal precision and specificity of signal initiation, amplification, and propagation are orchestrated by dynamic assembly of supramolecular complexes coupling nitric oxide production to upstream and downstream components in specific subcellular compartments. The concept of local paracrine signaling by nitric oxide over subcellular distances for short durations has expanded to include endocrine-like effects over anatomic spatial and temporal scales. From these insights emerges a role for nitric oxide in integrating system responses controlling oxygen supply and demand to defend cell integrity in the face of ischemic challenge. In this context, nitric oxide coordinates the respiratory cycle to acquire and deliver oxygen to target tissues by regulating hemoglobin function and vascular smooth muscle contractility and matches energy supply and demand by down-regulating energy-requiring functions while shifting metabolism to optimize energy production.

SUMMARY

Insights into mechanisms regulating nitric oxide production and signaling and their integration into responses mediating homeostasis place into specific relief the role of those processes in pathophysiology. Indeed, endothelial dysfunction associated with altered production of nitric oxide regulating tissue integrity contributes to the pathogenesis underlying atherogenesis. Moreover, this central role in pathophysiology identifies nitric oxide signaling as a key target for novel therapeutic interventions to minimize irreversible tissue damage associated with ischemic cardiovascular disease.

Overexpression of genes in the CA1 hippocampus region of adult rat following episodes of global ischemia

Ischemic stress is associated with marked changes in gene expression in the hippocampus--albeit little information exists on the activation of nonabundant genes. We have examined the expression of several known genes and identified novel ones in the adult rat hippocampus after a mild, transient, hypovolemic and hypotensive, global ischemic stress. An initial differential screening using a prototype array to assess gene expression after stress followed by a suppression subtractive hybridization protocol and cDNA microarray revealed 124 nonoverlapped transcripts predominantly expressed in the CA1 rat hippocampus region in response to ischemic stress. About 78% of these genes were not detected with nonsubtracted probes. Reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization on these 124 transcripts confirmed the differential expression of at least 83. Most robustly expressed were gene sequences NFI-B, ATP1B1, RHOGAP, PLA2G4A, BAX, CASP3, P53, MAO-A, FRA1, HSP70.2, and NR4A1 (NUR77), as well as sequence tags of unknown function. New stress-related genes of similar functional motifs were identified, reemphasizing the importance of functional grouping in the analysis of multiple gene expression profiles. These data indicate that ischemia elicits expression of an array of functional gene clusters that may be used as an index for stress severity and a template for target therapy design.

Cytoglobin expression is upregulated in all tissues upon hypoxia: an in vitro and in vivo study by quantitative real-time PCR

The vertebrate globin family has been extended with two members: neuroglobin and cytoglobin. We here investigate the changes of expression levels upon hypoxia of cytoglobin in parallel with neuroglobin, in vivo and in vitro, by using real-time quantitative PCR. Our data prove that cytoglobin is upregulated upon hypoxia in all tissues. The mechanism of induction of cytoglobin is regulated by the hypoxia-inducible factor 1, a posttranscriptionally regulated transcription factor controlling several hypoxia-inducible genes. The latter is argumented by: (1) cytoglobin is significantly upregulated upon hypoxia and this is dependent on the tissue and severity of hypoxia; (2) the regulation of cytoglobin expression in HIF-1 (+/-) knockout mice is affected; (3) the variations of the expression regulation are in the same manner as seen in the expression of our control gene VEGF, that is proven to be regulated by the HIF-1-pathway; and (4) cytoglobin promoter region contains HRE sites.

Novel method for quantification of brain cell swelling in rat hippocampal slices

We have developed a novel device for the quantification of edematous morphology changes in acute brain slices. We can also carry out real-time monitoring of detailed hippocampal cells. The device we developed is based on infrared differential interference contrast microscopy (IR-DIC) and a custom-made real-time computerized image-analysis system for quantification of the morphological dynamics of cells in slice preparations. We applied the coefficient of variation (CV) of light intensity in IR-DIC images to evaluate the change in morphological dynamics. We examined three kinds of edema in the CA1 region of rat hippocampal acute slices under conditions of hypotonic, strong excitation, and experimental ischemia, together with field excitatory postsynaptic potential (fEPSP) recording from radiatum in CA1 the region. There were notable close relationships among the edema formations, the light transmittance, the extent of changes in CV, and features of fEPSP during the three different insults. The present results indicate that CV is a reliable quantification index for edema formation in brain tissue and confirm that applying CV for the analysis in addition to the light transmittance analysis presents additional important information on brain tissue swelling.

Prostanoids, not reactive oxygen species, mediate COX-2-dependent neurotoxicity

The prostaglandin synthesizing enzyme cyclooxygenase-2 (COX-2) has emerged as a critical pathogenic factor in brain diseases associated with activation of N-methyl-D-aspartate (NMDA) receptors, including stroke and neurodegenerative diseases. However, the COX-2 reaction products responsible for these deleterious effects have not been identified. In particular, the relative contribution to the neurotoxicity of COX-2-derived prostanoids and reactive oxygen species has not been defined. We found that the brain damage produced by direct injection of NMDA into the somatosensory cortex is attenuated by the COX-2 inhibitor NS-398 or in COX-2-null mice, but that the associated production of free radicals is not. Furthermore, COX-2 inhibition reduces the lesions even if the deleterious effects of free radicals are eliminated by the scavenger superoxide dismutase. The protection exerted by NS-398 is counteracted by a stable analog of prostaglandin E2. The findings directly implicate COX-2-derived prostanoids, rather then radicals, in the COX-2-dependent component of the damage mediated by NMDA receptors and strengthen the rationale for using COX-2 inhibitors in the treatment of neurological diseases associated with glutamate neurotoxicity.

Nitric oxide produced during ischemia is toxic but crucial to preconditioning-induced ischemic tolerance of neurons in culture

The present study investigated the roles of nitric oxide (NO) in preconditioning (PC)-induced neuronal ischemic tolerance in cortical cultures. Ischemia in vitro was simulated by subjecting cultures to both oxygen and glucose deprivation (OGD). A sublethal OGD (PC) significantly increased the survival rate of neurons when cultures were exposed to a lethal OGD 24 h later. Both the inhibition of nitric oxide synthase (NOS) and scavenging of NO during PC significantly attenuated the PC-induced neuronal tolerance. In addition, exposure to an NO donor emulated the PC. In contrast, the inhibition of NOS and the scavenging of NO during lethal OGD tended to increase the survival rate of neurons. This study suggested that NO produced during ischemia was fundamentally toxic, but critical to the development of PC-induced neuronal tolerance.

Potentiation of NMDA receptor-mediated excitotoxicity linked with intrinsic apoptotic pathway in YAC transgenic mouse model of Huntington's disease

Evidence suggests N-methyl-D-aspartate receptor (NMDAR) activation is involved in the degeneration of striatal medium-sized spiny neurons (MSNs) in Huntington's disease (HD). We tested the hypothesis that enhanced NMDAR-mediated excitotoxicity is mediated by the mitochondrial-associated apoptotic pathway in cultured MSNs from YAC transgenic mice expressing full-length huntingtin (htt) with a polyglutamine (polyQ) expansion of 46 or 72 (YAC46 or YAC72). NMDAR-mediated Ca(2+) transients and mitochondrial membrane depolarization were significantly increased in YAC compared to wild-type mice MSNs. Inhibitors of the mitochondrial permeability transition (mPT), cyclosporin A and bongkrekic acid, and coenzyme Q10 (an anti-oxidant involved in bioenergetic metabolism) dramatically diminished NMDA-induced cell death and eliminated genotypic differences. In YAC46 MSNs, NMDA stimulated significantly higher activation of caspase-3 and caspase-9 but not caspase-8, and NMDA-induced caspase-3 and -9 activation was markedly attenuated by cyclosporin A. Agents that improve mitochondrial function or inhibit the permeability transition may eliminate increased caspase activation and cell death associated with enhanced NMDAR activity in HD.

Tactile stimulation and maternal separation prevent hippocampal damage in rats submitted to neonatal hypoxia–ischemia

Unilateral neonatal hypoxia-ischemia causes important damage to the hippocampus of the hemisphere ipsilateral to carotid artery occlusion; two forms of neonatal handling, tactile stimulation and maternal separation for a short period, have been shown to produce functional/behavioral protection in distinct models of CNS challenge. In this paper we investigated whether neonatal handling could alter the hippocampal damage caused by neonatal hypoxia-ischemia (HI) in the Wistar rat. Pups at postnatal day 7, P7, received HI (8% O(2)-92% N(2)) for 90 min and were submitted to neonatal handling, tactile stimulation of maternal separation daily, from P8 to P21, for 10 min. On adulthood, hippocampal volume was analyzed by stereological techniques, along with measures of cortical thickness and hemispheric area at the level -3.30 mm from bregma. HI caused a reduction of volume of whole hippocampus, of Amon's horn and of dentate gyrus, with no effect on cortical and hemispheric measures; neonatal handling prevented such effect. This is the first report showing that both tactile stimulation and neonatal handling exert a morphological neuroprotective action for HI-induced damage to the hippocampus.

Molecular changes in normal appearing white matter in multiple sclerosis are characteristic of neuroprotective mechanisms against hypoxic insult

Multiple sclerosis is a chronic inflammatory disease of the CNS leading to focal destruction of myelin, still the earliest changes that lead to lesion formation are not known. We have studied the gene-expression pattern of 12 samples of normal appearing white matter from 10 post-mortem MS brains. Microarray analysis revealed upregulation of genes involved in maintenance of cellular homeostasis, and in neural protective mechanisms known to be induced upon ischemic preconditioning. This is best illustrated by the upregulation of the transcription factors such as HIF-1alpha and associated PI3K/Akt signalling pathways, as well as the upregulation of their target genes such as VEGF receptor 1. In addition, a general neuroprotective reaction against oxidative stress is suggested. These molecular changes might reflect an adaptation of cells to the chronic progressive pathophysiology of MS. Alternatively, they might also indicate the activation of neural protective mechanisms allowing preservation of cellular and functional properties of the CNS. Our data introduce novel concepts of the molecular pathogenesis of MS with ischemic preconditioning as a major mechanism for neuroprotection. An increased understanding of the underlying mechanisms may lead to the development of new more specific treatment to protect resident cells and thus minimize progressive oligondendrocyte and axonal loss.

Effect of excess extracellular glutamate on dendrite growth from cerebral cortical neurons at 3 days in vitro: Involvement of NMDA receptors

Glutamate is an important regulator of dendrite development; however, during cerebral ischemia, massive glutamate release can lead to neurodegeneration and death. An early consequence of glutamate excitotoxicity is dendrite injury, which often precedes cell death. We examined the effect of glutamate on dendrite growth from embryonic day 18 (E18) mouse cortical neurons grown for 3 days in vitro (DIV) and immunolabeled with anti-microtubule-associated protein (MAP)2 and anti-neurofilament (NF)-H, to identify dendrites and axons, respectively. Cortical neurons exposed to excess extracellular glutamate (100 microM) displayed reduced dendrite growth, which occurred in the absence of cell death. This effect was mimicked by the ionotropic glutamate receptor agonist N-methyl-D-aspartate (NMDA) and blocked by the ionotropic glutamate receptor antagonist kynurenic acid and the NMDA receptor-specific antagonist MK-801. The non-NMDA receptor agonist AMPA, however, did not affect process growth. Neither NMDA nor AMPA influenced neuron survival. Immunolabeling and Western blot analysis of NMDA receptors using antibodies against the NR1 subunit, demonstrated that immature cortical neurons used in this study, express NMDA receptors. These results suggest that excess glutamate decreases dendrite growth through a mechanism resulting from NMDA receptor subclass activation. Furthermore, these data support the possibility that excess glutamate activation of NMDA receptors mediate both cell death in mature neurons and the inhibitory effect of excess glutamate on dendrite growth in immature neurons or in the absence of cell death.

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism

Defending cellular integrity against disturbances in intracellular concentrations of ATP ([ATP](i)) is predicated on coordinating the selection of substrates and their flux through metabolic pathways (metabolic signaling), ATP transfer from sites of production to utilization (energetic signaling), and the regulation of processes consuming energy (cell signaling). Whereas NO and its receptor, soluble guanylyl cyclase (sGC), are emerging as key mediators coordinating ATP supply and demand, mechanisms coupling this pathway with metabolic and energetic signaling remain undefined. Here, we demonstrate that sGC is a nucleotide sensor whose responsiveness to NO is regulated by [ATP](i). Indeed, ATP inhibits purified sGC with a K(i) predicting >60% inhibition of NO signaling in cells maintaining physiological [nucleotide](i). ATP inhibits sGC by interacting with a regulatory site that prefers ATP > GTP. Moreover, alterations in [ATP](i), by permeabilization and nucleotide clamping or inhibition of mitochondrial ATP synthase, regulate NO signaling by sGC. Thus, [ATP](i) serves as a "gain control" for NO signaling by sGC. At homeostatic [ATP](i), NO activation of sGC is repressed, whereas insults that reduce [ATP](i,) derepress sGC and amplify responses to NO. Hence, sGC forms a key synapse integrating metabolic, energetic, and cell signaling, wherein ATP is the transmitter, allosteric inhibition the coupling mechanism, and regulated accumulation of cGMP the response.

Does nitric oxide contribute to iron-dependent brain injury after experimental cerebral ischaemia?

Experimental and clinical data suggest that iron has a key role in cerebral ischaemia. We measure infarct volume and analyse the nitric oxide responses to brain injury in rat stroke model after increased oral iron intake. Permanent middle cerebral artery occlusion (MCAO) was performed in a group of 20 male Wistar rats, 10 of which were fed with a control diet and 10 of which were fed with iron-enriched diet containing 2.5% carbonyl iron for 9 weeks. L-arginine and nitric oxide metabolites were determined in blood samples before and at 2, 6, 8 and 48 h after MCAO. Infarct volume, thiobarbituric acid reaction substances (TBARS) and tissue iron were measured at 48 h. Infarct volume was 66% greater in the iron-fed rats than in the control group. Iron-fed animals showed significantly higher levels of TBARS. Liver iron stores (3500 +/- 199 vs 352 +/- 28 microg Fe/g, p<0.0001) but not brain iron stores (131 +/- 11 vs 139 +/- 8 microg Fe/g, p=0.617), were significantly higher in the iron-fed group. L-arginine levels were slightly lower in iron-fed rats and decreased significantly in both groups at 6 and 8 hours after MCAO. The levels of the stable end products of NOS (NOx = nitrite + nitrate) were significantly higher in iron-fed rats before MCAO (16.2 +/- 2.2 vs. 9.6 +/- 0.8 micromol x L(-1), p<0.05), with a further increase during the six first hours after MCAO in both groups. These results suggest that the iron overload that increases both superoxide and nitric oxide production leads to peroxynitrite formation, thus enhancing brain damage.

Differential effects of natural polyphenols on neuronal survival in primary cultured central neurons against glutamate- and glucose deprivation-induced neuronal death

Neuronal injury in the central nervous system following ischemic insult is believed to result from glutamate toxicity and glucose deprivation. In this study, polyphenols isolated from Scutellaria baicalensis Georgi, including baicalin, baicalein, and wogonin, were investigated for their neuroprotective effects against glutamate/NMDA (Glu/NMDA) stimulation and glucose deprivation in primary cultured rat brain neurons. Cell death was accessed by lactate dehydrogenase (LDH) release assay for necrosis, and mitochondrial activity was accessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction activity assay. It was found that both baicalin and baicalein decreased LDH release of the cultured neurons after 24 h treatment, whereas wogonin profoundly increased LDH release after 2 h treatment and resulted in neuronal death after 24 h. Glu/NMDA treatment profoundly increased LDH release and moderately decreased MTT reduction activity in an NMDA receptor-dependent manner. Both baicalin and baicalein significantly reduced Glu/NMDA-increased LDH release, in which baicalein is much more potent than baicalin. Glu/NMDA-increased intracellular calcium was also significantly attenuated by baicalin and baicalein. Baicalin and baicalein did not affect glutamate receptor binding activity, but baicalein did moderately decrease Glu/NMDA-induced nitric oxide (NO) production. In the glucose deprivation (GD) study, baicalein but not baicalin showed significant protective effects on the GD-increased LDH release, without affecting the GD-induced NO production, in cultured rat brain neurons. These results suggest that baicalein is the most effective compound among three polyphenols tested in preventing neurotoxicity induced by both glutamate and GD, whereas baicalin was only effective in preventing glutamate toxicity. Wogonin might have a neurotoxic effect on the brain.

Reduced cerebral injury in CRH-R1 deficient mice after focal ischemia: a potential link to microglia and atrocytes that express CRH-R1

Corticotropin releasing hormone (CRH) and its family of related peptides are involved in regulating physiologic responses to multiple stressors, including stroke. Although CRH has been implicated in the exacerbation of injury after stroke, the mechanism remains unclear. After ischemia, both excitotoxic damage and inflammation contribute to the pathology of stroke. CRH is known to potentiate excitotoxic damage in the brain and has been shown to modulate inflammatory responses in the periphery. Here the present authors examine the relative contribution of the two known CRH receptors, CRH-R1 and CRH-R2, to ischemic injury using CRH receptor knockout mice. These results implicate CRH-R1 as the primary mediator of ischemic injury in this mouse model of stroke. In addition, the authors examine a potential role for CRH in inflammatory injury after stroke by identifying functional CRH receptors on astrocytes and microglia, which are cells that are known to be involved in brain inflammation. By single cell PCR, the authors show that microglia and astrocytes express mRNA for both CRH-R1 and CRH-R2. However, CRH-R1 is the primary mediator of cAMP accumulation in response to CRH peptides in these cells. The authors suggest that astrocytes and microglia are cellular targets of CRH, which could serve as a link between CRH and inflammatory responses in ischemic injury via CRH-R1.

The role of Zn2+ in Shal voltage-gated potassium channel formation

Voltage-gated potassium channels are formed by the tetramerization of their alpha subunits, in a process that is controlled by their conserved N-terminal T1 domains. The crystal structures of Shaker and Shaw T1 domains reveal interesting differences in structures that are contained within a highly conserved BTB/POZ domain fold. The most surprising difference is that the Shaw T1 domain contains an intersubunit Zn2+ ion that is lacking in the Shaker T1 domain. The Zn2+ coordination motif is conserved in other non-Shaker channels making this the most distinctive difference between these channels and Shaker. In this study we show that Zn2+ is an important co-factor for the tetramerization of isolated Shaw and Shal T1 domains. Addition of Zn2+ increases the amount of tetramer formed, whereas chelation of Zn2+ with phenanthroline blocks tetramerization and causes assembled tetramers to disassemble. Within an intact cell, full-length Shal subunits containing Zn2+ site mutations also fail to form functional channels, with the majority of the protein found to remain monomeric by size exclusion chromatography. Therefore, zinc-mediated tetramerization also is a physiologically important event for full-length functional channel formation.

Peroxisome proliferator-activated receptor-alpha activation as a mechanism of preventive neuroprotection induced by chronic fenofibrate treatment

The treatment of ischemic strokes is limited to the prevention of cerebrovascular risk factors and to the modulation of the coagulation cascade during the acute phase. A new therapeutic strategy could be to preventively protect the brain against noxious biological reactions induced by cerebral ischemia such as oxidative stress and inflammation to minimize their neurological consequences. Here, we show that a peroxisome proliferator-activated receptor (PPAR-alpha) activator, fenofibrate, protects against cerebral injury by anti-oxidant and anti-inflammatory mechanisms. A 14 d preventive treatment with fenofibrate reduces susceptibility to stroke in apolipoprotein E-deficient mice as well as decreases cerebral infarct volume in C57BL/6 wild-type mice. The neuroprotective effect of fenofibrate is completely absent in PPAR-alpha-deficient mice, suggesting that PPAR-alpha activation is involved as a mechanism of the protection against cerebral injury. Furthermore, this neuroprotective effect appears independently of any improvement in plasma lipids or glycemia and is associated with (1) an improvement in middle cerebral artery sensitivity to endothelium-dependent relaxation unrelated to an increase in nitric oxide synthase (NOS) type III expression, (2) a decrease in cerebral oxidative stress depending on the increase in numerous antioxidant enzyme activities, and (3) the prevention of ischemia-induced expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in cerebral vessels without any change in NOS II expression. These data demonstrate that PPAR-alpha could be a new pharmacological target to preventively reduce the deleterious neurological consequences of stroke in mice and suggest that PPAR-alpha activators could preventively decrease the severity of stroke in humans.

Neuronal overexpression of cyclooxygenase-2 increases cerebral infarction

Increases in COX-2 enzymatic activity and prostaglandin production have been associated with neuronal injury in both acute and age-related degenerative neurological diseases. In this study, we tested the effects of increased COX-2 activity in a model of transient focal ischemia using a transgenic mouse model in which human COX-2 is constitutively expressed selectively in neurons of the striatum, cerebral cortex, and hippocampus. These COX-2 transgenic mice harbor elevated levels of PGE(2) that are 10-fold higher than nontransgenic levels. A significant increase in infarct volume was observed after middle cerebral artery occlusion with 4 days of reperfusion in COX-2 transgenic mice as compared with nontransgenic littermates. Pretreatment of nontransgenic mice with the selective COX-2 inhibitor SC58236 resulted in a significant reduction of infarct volume in nontransgenic mice, consistent with previous pharmacological studies. However, transgenic COX-2 mice treated with SC58236 did not show a significant reduction. This suggests that chronic increases in COX-2 expression and enzymatic activity, which can occur in aging and in pathological states characterized by oxidative stress and chronic inflammatory processes, can lead to downstream cellular changes that have a negative impact on neuronal survival in cerebrovascular disease.

Neuroprotective effects of Buyang Huanwu Decoction on neuronal injury in hippocampus after transient forebrain ischemia in rats

Buyang Huanwu Decoction (BYHWD), a traditional Chinese medicine, has been developed as a drug to be used for treatment of stroke for hundreds of years. However, the underlying mechanisms remain unknown. In the present study, the effects of BYHWD on delayed neuronal death of hippocampus after transient forebrain ischemia were examined in rats. Transient forebrain ischemia in a duration of 15 min was induced with the four-vessel occlusion method. BYHWD (per 6.65 g/kg) was given orally to rats twice each day for 7 days before ischemia. In BYHWD-pretreated rats, the neuronal injury in the hippocampal CA1 region was significantly less than that of controls. Oral administration of BYHWD also markedly attenuated the number of TUNEL-positive neurons and suppressed the expression of caspase-3p20, a product of catalytically active caspase-3, in the CA1 region. Our results suggest that an inhibition of caspase-3 and apoptosis by BYHWD may partially account for its neuroprotection against ischemic injury in the hippocampal CA1 region.

Peroxisome proliferator-activated receptor-alpha activation as a mechanism of preventive neuroprotection induced by chronic fenofibrate treatment

The treatment of ischemic strokes is limited to the prevention of cerebrovascular risk factors and to the modulation of the coagulation cascade during the acute phase. A new therapeutic strategy could be to preventively protect the brain against noxious biological reactions induced by cerebral ischemia such as oxidative stress and inflammation to minimize their neurological consequences. Here, we show that a peroxisome proliferator-activated receptor (PPAR-alpha) activator, fenofibrate, protects against cerebral injury by anti-oxidant and anti-inflammatory mechanisms. A 14 d preventive treatment with fenofibrate reduces susceptibility to stroke in apolipoprotein E-deficient mice as well as decreases cerebral infarct volume in C57BL/6 wild-type mice. The neuroprotective effect of fenofibrate is completely absent in PPAR-alpha-deficient mice, suggesting that PPAR-alpha activation is involved as a mechanism of the protection against cerebral injury. Furthermore, this neuroprotective effect appears independently of any improvement in plasma lipids or glycemia and is associated with (1) an improvement in middle cerebral artery sensitivity to endothelium-dependent relaxation unrelated to an increase in nitric oxide synthase (NOS) type III expression, (2) a decrease in cerebral oxidative stress depending on the increase in numerous antioxidant enzyme activities, and (3) the prevention of ischemia-induced expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in cerebral vessels without any change in NOS II expression. These data demonstrate that PPAR-alpha could be a new pharmacological target to preventively reduce the deleterious neurological consequences of stroke in mice and suggest that PPAR-alpha activators could preventively decrease the severity of stroke in humans.

Activation of innate immunity in the CNS triggers neurodegeneration through a Toll-like receptor 4-dependent pathway

Innate immunity is an evolutionarily ancient system that provides organisms with immediately available defense mechanisms through recognition of pathogen-associated molecular patterns. We show that in the CNS, specific activation of innate immunity through a Toll-like receptor 4 (TLR4)-dependent pathway leads to neurodegeneration. We identify microglia as the major lipopolysaccharide (LPS)-responsive cell in the CNS. TLR4 activation leads to extensive neuronal death in vitro that depends on the presence of microglia. LPS leads to dramatic neuronal loss in cultures prepared from wild-type mice but does not induce neuronal injury in CNS cultures derived from tlr4 mutant mice. In an in vivo model of neurodegeneration, stimulating the innate immune response with LPS converts a subthreshold hypoxic-ischemic insult from no discernable neuronal injury to severe axonal and neuronal loss. In contrast, animals bearing a loss-of-function mutation in the tlr4 gene are resistant to neuronal injury in the same model. The present study demonstrates a mechanistic link among innate immunity, TLRs, and neurodegeneration.

Differential neuronal fates in the CA1 hippocampus after hypoxia in newborn and 7-day-old rats: Effects of pre-treatment with MK-801

The brain displays an age-dependent sensitivity to ischemic insults. However, the consequences of oxygen deprivation per se in the developing brain remain unclear, and the role of glutamate excitotoxicity via N-methyl-D-aspartate (NMDA) receptors is controversial. To gain a better understanding of the mechanisms involved in the cerebral response to severe hypoxia, cell damage was temporally monitored in the CA1 hippocampus of rat pups transiently exposed to in vivo hypoxia (100% N2) at either 24 h or 7 days of age. Also, the influence of a pre-treatment with the NMDA receptor antagonist MK-801 (5 mg/kg, i.p.) was examined. At both ages, morphometric analyses and cell counts showed hypoxia-induced significant neuronal loss (30-35%) in the pyramidal layer, with injury appearing more rapidly in rats exposed at 7 days. Morphological alterations of 4,6-diamidino-2-phenylindole (DAPI)-labeled nuclei, DNA fragmentation patterns on agarose gels, as well as expression profiles of the apoptosis-related regulatory proteins Bax and Bcl-2 showed that apoptosis was prevalent in younger animals, whereas only necrosis was detected in hippocampi of rats treated at 7 days. Moreover, pre-treatment with MK-801 was ineffective in protecting hippocampal neurons from hypoxic injury in newborn rats, but significantly reduced necrosis in older subjects. These data confirm that hypoxia alone may trigger neuronal death in vivo, and the type of cell death is strongly influenced by the degree of brain maturity. Finally, NMDA receptors are not involved in the apoptotic consequences of hypoxia in the newborn rat brain, but they were found to mediate necrosis at 7 days of age.

Brain edema induced by in vitro ischemia: causal factors and neuroprotection

Decreased cerebral blood flow, hence decreased oxygen and glucose, leads to ischemic brain injury via complex pathophysiological events, including excitotoxicity, mitochondrial dysfunction, increased intracellular Ca2+, and reactive oxygen species (ROS) generation. Each of these could also contribute to cerebral edema, which is the primary cause of patient mortality after stroke. In vitro brain slices are widely used to study ischemia. Here we introduce a slice model to investigate ischemia-induced edema. Significant water gain was induced in coronal slices of rat brain by 5 min of oxygen and glucose deprivation (OGD) at 35 degrees C, with progressive edema formation after return to normoxic, normoglycemic medium. Edema increased with increasing injury severity, determined by OGD duration (5-30 min). Underlying factors were assessed using glutamate-receptor antagonists (AP5/CNQX), blockade of mitochondrial permeability transition [cyclosporin A (CsA) versus FK506], inhibition of Na+/Ca2+ exchange (KB-R7943), and ROS scavengers (ascorbate, Trolox, dimethylthiourea, Tempol). All agents except KB-R7943 and FK506 significantly attenuated edema when applied after OGD; KB-R7943 was effective when applied before OGD. Significantly, complete prevention of ischemia-induced edema was achieved with a cocktail of AP5/CNQX, CsA and Tempo applied after OGD, which demonstrates the involvement of multiple, additive mechanisms. The efficacy of this cocktail further shows the potential value of combination therapies for the treatment of cerebral ischemia.

Postinsult treatment with lithium reduces brain damage and facilitates neurological recovery in a rat ischemia/reperfusion model

Lithium has long been a primary drug used to treat bipolar mood disorder, even though the drug's therapeutic mechanisms remain obscure. Recent studies demonstrate that lithium has neuroprotective effects against glutamate-induced excitotoxicity in cultured neurons and in vivo. The present study was undertaken to examine whether postinsult treatment with lithium reduces brain damage induced by cerebral ischemia. We found that s.c. injection of lithium dose dependently (0.5-3 mEq/kg) reduced infarct volume in the rat model of middle cerebral artery occlusionreperfusion. Infarct volume was reduced at a therapeutic dose of 1 mEq/kg even when administered up to 3 h after the onset of ischemia. Neurological deficits induced by ischemia were also reduced by daily administration of lithium over 1 week. Moreover, lithium treatment decreased the number of neurons showing DNA damage in the ischemic brain. These neuroprotective effects were associated with an up-regulation of cytoprotective heat shock protein 70 (HSP70) in the ischemic brain hemisphere as determined by immunohistochemistry and Western blotting analysis. Lithium-induced HSP70 up-regulation in the ischemic hemisphere was preceded by an increase in the DNA binding activity of heat shock factor 1, which regulates the transcription of HSP70. Physical variables and cerebral blood flow were unchanged by lithium treatment. Our results suggest that postinsult lithium treatment reduces both ischemia-induced brain damage and associated neurological deficits. Moreover, the heat shock response is likely to be involved in lithium's neuroprotective actions. Additionally, our studies indicate that lithium may have clinical utility for the treatment of patients with acute stroke.

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.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Prolonged drug-induced hypothermia in experimental stroke

In experimental and human stroke, hypothermia is strongly related to a favorable outcome. Previous attempts to manipulate the core temperature in focal cerebral ischemia have been based on mechanical cooling. The purpose of the study is to establish a model for long-term drug-induced hypothermia in focal ischemia by pharmacological alteration of the central thermoregulatory set-point. We tested the hypothesis that the dopaminergic agonist Talipexole, which induces hypothermia, reduces infarct size. Body temperature was monitored by a radio-pill-implant. Rats had reversible occlusion of the middle cerebral artery (MCAO) for 30 minutes. Thirty minutes after reflow, the experimental group of rats (n = 10) received an intravenous bolus injection of Talipexole followed by a continuous infusion of Talipexole during the following 24 hours. The control group of rats (n = 10) received a similar treatment regimen with saline only. All rats were killed 7 days after MCAO. Infarct volume was quantified stereologically. The mean body temperature (35.6 + 1.0 degrees C) during 24 hours after bolus injection of Talipexole was significantly lower than in control rats (37.3 +/- 0.5 degrees C), P < .05. Infarct volumes were significantly lower in the Talipexole group (4.7 +/- 1.9 mm3) than in the control group (8.8 +/- 4.7 mm3), P < .04. In the Talipexole treated rats we also observed a significant hypokalemia (P = .001) and a significantly lower index of relative degree of movement (P < .02). Our study shows that the core body temperature was reduced by 1.7 degrees C for 24 hours after MCAO in rats treated with Talipexole. This treatment induced a significant reduction of infarct volume at 7 days after focal ischemia by 47%. We suggest that the reduction in infarct volume is related to drug-induced hypothermia. The hypokalemia in the hypothermic rats is possibly explained by the observed lower degree of movement.

Dying for a cause: invertebrate genetics takes on human neurodegeneration

If invertebrate neurons are injured by hostile environments or aberrant proteins they die much like human neurons, indicating that the powerful advantages of invertebrate molecular genetics might be successfully used for testing specific hypotheses about human neurological diseases, for drug discovery and for non-biased screens for suppressors and enhancers of neurodegeneration. Recent molecular dissection of the genetic requirements for hypoxia, excitotoxicity and death in models of Alzheimer disease, polyglutamine-expansion disorders, Parkinson disease and more, is providing mechanistic insights into neurotoxicity and suggesting new therapeutic interventions. An emerging theme is that neuronal crises of distinct origins might converge to disrupt common cellular functions, such as protein folding and turnover.

Reperfusion differentially induces caspase-3 activation in ischemic core and penumbra after stroke in immature brain

BACKGROUND AND PURPOSE

Different strategies for neuroprotection of neonatal stroke may be required because the developing brain responds differently to hypoxia-ischemia than the mature brain. This study was designed to determine the role of caspase-dependent injury in the pathophysiology of pure focal cerebral ischemia in the immature brain.

METHODS

Postnatal day 7 rats were subjected to permanent or transient middle cerebral artery (MCA) occlusion. Diffusion-weighted MRI was used during occlusion to noninvasively map the evolving ischemic core. The time course of caspase-3 activation in ischemic brain tissue was determined with the use of an Asp-Glu-Val-Asp-aminomethylcoumarin cleavage assay. The anatomy of caspase-3 activation in the ischemic core and penumbra was mapped immunohistochemically with an anti-activated caspase-3 antibody in coronal sections that matched the imaging planes on diffusion-weighted MRI.

RESULTS

A marked increase in caspase-3 activity occurred within 24 hours of reperfusion after transient MCA occlusion. In contrast, caspase-3 activity remained significantly lower within 24 hours of permanent MCA occlusion. Cells with activated caspase-3 were prominent in the penumbra beginning at 3 hours after reperfusion, while a more delayed but marked caspase-3 activation was observed in the ischemic core by 24 hours after reperfusion.

CONCLUSIONS

In the neonate, caspase-3 activation is likely to contribute substantially to cell death not only in the penumbra but also in the core after ischemia with reperfusion. Furthermore, persistent perfusion deficits result in less caspase-3 activation and appear to favor caspase-independent injury.

Protein kinase C activity, translocation, and selective isoform subcellular redistribution in the rat cerebral cortex after in vitro ischemia

Protein kinase C (PKC) involvement in ischemia-induced neuronal damage has been investigated in superfused rat cerebral cortex slices submitted to 15 min of oxygen-glucose deprivation (OGD) and in primary cultures of rat cortical neurons exposed to 100 microM glutamate (GLU) for 10 min. OGD significantly increased the total PKC activity in the slices, mostly translocated in the particulate fraction. After 1 hr of reperfusion, the total PKC activity was reduced and the translocated fraction dropped by 84% with respect to the control. Western blot analysis of OGD samples showed an increase in total beta(2) and epsilon PKC isoform levels. After reperfusion, the total levels of alpha, beta(1), beta(2) and gamma isoforms were significantly reduced, whereas the epsilon isoform remained at an increased level. Endogenous GLU release from OGD slices increased to about 15 times the basal values after 15 min of oxygen-glucose deprivation, and to 25 and 35 times the basal level in the presence of the PKC inhibitors staurosporine (0.1 microM) and bisindolylmaleimide (1 microM), respectively. Western blot analysis of GLU-treated cortical neurons showed a significant decrease only in the total level of beta(2) isoforms. Cell survival was reduced to 31% in GLU-treated neuronal cultures; PKC inhibitors were not able to modify this effect. These findings demonstrate that the cell response to OGD and GLU involves PKC in a complex way. The net role played by PKC during OGD may be to reduce GLU release and, consequently, neurotoxicity. The isoforms beta(2) and epsilon are affected the most and may play a significant role in the mechanisms underlying neurotoxicity/neuroprotection.

New perspectives on developing acute stroke therapy

The development of additional acute stroke therapies to complement and supplement intravenous recombinant tissue-type plasminogen activator within the first 3 hours after stroke onset remains an important and pressing need. Much has been learned about the presumed target of acute stroke therapy, the ischemic penumbra, and clinically available imaging modalities such as magnetic resonance imaging and computed tomography hold great promise for at least partially identifying this region of potentially salvageable ischemic tissue. Understanding the biology of ischemia-related cell injury has also evolved rapidly. New treatment approaches to improve outcome after focal brain ischemia will likely be derived by looking at naturally occurring adaptive mechanisms such as those related to ischemic preconditioning and hibernation. Many clinical trials previously performed with a variety of neuroprotective and thrombolytic drugs provide many lessons that will help to guide future acute stroke therapy trials and enhance the likelihood of success in future trials. Combining knowledge from these three areas provides optimism that additional acute stroke therapies can be developed to maximize beneficial functional outcome in the greatest proportion of acute stroke patients possible.

Changes in oxidative stress, iNOS activity and neutrophil infiltration in severe transient focal cerebral ischemia in rats

Oxidative stress, inducible nitric oxide synthase (iNOS) and neutrophils all contribute to post-ischemic brain damage. This study has determined the time courses of these three phenomena after ischemia in parallel with histological and functional outcomes. Ischemia was produced in rats by occluding the left middle cerebral artery and both common carotid arteries for 20 min. Regional cerebral blood flow (rCBF) rapidly decreased to 20% of its preischemic value during occlusion and stabilized at 60% following reperfusion. The striatal infarction was maximal 15 h after reperfusion (50+/-3 mm(3)), whereas the cortical infarction reached its maximum at 48 h (183+/-10 mm(3)). This drastic decrease in rCBF followed by incomplete reperfusion and massive infarction is, thus, extremely severe. The cortical infarction was strongly correlated with the neurologic deficit and loss of body weight. Oxidative stress, evaluated by the decrease in glutathione concentrations, appeared in the striatum at 6 h after reperfusion and in the cortex at 15 h. Calcium-independent NOS activity, considered as inducible NOS activity, was significantly enhanced at 24 h in the striatum and at 48 h in the cortex. Myeloperoxidase activity, a marker of neutrophil infiltration, was significantly increased at 48 h in both the striatum and cortex. These time courses show that the delayed iNOS activity and neutrophil infiltration that occur after the maturation of infarction in severe ischemia may not contribute to ischemic brain damage. By contrast, early oxidative stress may well be implicated in cerebral injury.

DAPK catalytic activity in the hippocampus increases during the recovery phase in an animal model of brain hypoxic-ischemic injury

Death-associated protein kinase (DAPK) is a pro-apoptotic, calmodulin (CaM)-regulated protein kinase whose mRNA levels increase following cerebral ischemia. However, the relationship between DAPK catalytic activity and cerebral ischemia is not known. This knowledge is critical as DAPK function is dependent on the catalytic activity of its kinase domain. Consequently, we examined DAPK catalytic activity in a rat model of neonatal cerebral hypoxia-ischemia (HI). An increase in DAPK specific activity was found in homogenates of the hippocampus from the injured right hemisphere, compared to the uninjured left hemisphere, 7 days after injury. The results raised the possibility that an upregulation of DAPK activity might be associated with the recovery phase of HI, during which neuronal repair and differentiation are initiated. Therefore, we examined the change of DAPK in an experimentally tractable cell culture model of neuronal differentiation. We found that DAPK catalytic activity and protein levels increase after nerve growth factor (NGF)-induced differentiation of rat PC12 cells. These results suggest that DAPK may have a previously unappreciated role in neuronal development or recovery from injury, and that potential future therapies targeting DAPK should consider a restricted time window.