Molecular targets in cerebral ischemia for developing novel therapeutics

Ca2+ and acidosis synergistically lead to the dysfunction of cortical GABAergic neurons during ischemia

Cell death in cerebral ischemia is presumably initiated by neural excitotoxicity resulted from the dysfunction of inhibitory neurons in early stage. Molecular processes underlying the ischemic injury of inhibitory neurons remain to be elusive, which we investigated by biochemical manipulations with cellular imaging and patch clamp at GFP-labeled GABAergic cells in cortical slices. Ischemia induces Ca(2+) elevation, acidosis and dysfunction in GABAergic cells. An elevation of cytoplasmic Ca(2+) or H(+) impairs the encoding of action potentials in these neurons. The effects of Ca(2+) and H(+) are additive in nature and occlude ischemic outcomes. Ischemia impairs spike production through prolonging spike refractory periods and raising threshold potentials. Therefore, calcium toxicity and acidosis during ischemia synergistically impair the dynamics of sodium channels and function of cortical GABAergic neurons, which lead to neural excitotoxicity. Our results also suggest that the cocktail therapeutics is needed to prevent neuronal death from ischemia.

Efficacy of 3,5-dibromo-L-phenylalanine in rat models of stroke, seizures and sensorimotor gating deficit

BACKGROUND AND PURPOSE

Abnormal glutamatergic activity is implicated in neurologic and neuropsychiatric disorders. Selective glutamate receptor antagonists were highly effective in animal models of stroke and seizures but failed in further clinical development because of serious side effects, including an almost complete set of symptoms of schizophrenia. Therefore, the novel polyvalent glutamatergic agent 3,5-dibromo-L-phenylalanine (3,5-DBr-L-Phe) was studied in rat models of stroke, seizures and sensorimotor gating deficit.

EXPERIMENTAL APPROACH

3,5-DBr-L-Phe was administered intraperitoneally as three boluses after intracerebral injection of endothelin-1 (ET-1) adjacent to the middle cerebral artery to cause brain injury (a model of stroke). 3,5-DBr-L-Phe was also given as a single bolus prior to pentylenetetrazole (PTZ) injection to induce seizures or prior to the administration of the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) to cause disruption of prepulse inhibition (PPI) of startle (sensorimotor gating deficit).

KEY RESULTS

Brain damage caused by ET-1 was reduced by 52%, which is comparable with the effects of MK-801 in this model as reported by others. 3,5-DBr-L-Phe significantly reduced seizures induced by PTZ without the significant effects on arterial blood pressure and heart rate normally caused by NMDA antagonists. 3,5-DBr-L-Phe prevented the disruption of PPI measured 3 days after the administration of ET-1. 3,5-DBr-L-Phe also eliminated sensorimotor gating deficit caused by MK-801.

CONCLUSION AND IMPLICATIONS

The pharmacological profile of 3,5-DBr-L-Phe might be beneficial not only for developing a therapy for the neurological and cognitive symptoms of stroke and seizures but also for some neuropsychiatric disorders.

Variants of the Matrix Metalloproteinase-2 but not the Matrix Metalloproteinase-9 genes significantly influence functional outcome after stroke

Background

Multiple lines of evidence suggest that genetic factors contribute to stroke recovery. The matrix metalloproteinases -2 (MMP-2) and -9 (MMP-9) are modulators of extracellular matrix components, with important regulatory functions in the Central Nervous System (CNS). Shortly after stroke, MMP-2 and MMP-9 have mainly damaging effects for brain tissue. However, MMPs also have a beneficial activity in angiogenesis and neurovascular remodelling during the delayed neuroinflammatory response phase, thus possibly contributing to stroke functional recovery.

Methods

In the present study, the role of MMP-2 and MMP-9 genetic variants in stroke recovery was investigated in 546 stroke patients. Functional outcome was assessed three months after a stroke episode using the modified Rankin Scale (mRS), and patients were classified in two groups: good recovery (mRS ≤ 1) or poor recovery (mRS>1). Haplotype tagging single nucleotide polymorphisms (SNPs) in the MMP-2 (N = 21) and MMP-9 (N = 4) genes were genotyped and tested for association with stroke outcome, adjusting for significant non-genetic clinical variables.

Results

Six SNPs in the MMP-2 gene were significantly associated with stroke outcome (0.0018<P < 0.0415), two of which survived the Bonferroni correction for multiple testing. In the subset of ischemic stroke patients, association of five of these SNPs remained positive (0.0042<P < 0.0306). No significant associations were found for the MMP-9 gene.

Conclusions

The results presented strongly indicate that MMP-2 genetic variants are an important mediator of functional outcome after stroke.

Endoplasmic reticulum stress plays critical role in brain damage after cerebral ischemia/reperfusion in rats

The endoplasmic reticulum(ER) stress plays a vital role in mediating ischemic neuronal cell death. However, very little is known about the role of ER stress in mediating pathophysiological reactions to acute brain injuries. An attempt was therefore made to assess the role of cerebral ischemia/reperfusion (I/R) induced ER stress and its modulation on outcome of ischemic insult. Focal cerebral ischemia was induced in rats by middle cerebral artery occlusion (MCAO) for 2 h followed by varying time points of reperfusion. The brain loci specific and time-dependent alterations were seen in the expression pattern of molecular markers, i.e., heat-shock protein 70 (HSP70) for cytoplasmic dysfunction, glucose-regulated protein 78 (GRP78), Caspase-12, C/EBP homologous protein/growth arrest and DNA damage-inducible gene 153 (CHOP/GADD153), activating transcription factor 4 (ATF-4), and Processed X-box protein 1 (xbp1) mRNA for ER dysfunction. Further, histological examinations indicated pronounced brain damage, massive neuronal loss, and DNA fragmentation predominantly in the striatum and cortex. The enhanced expression of GRP78, Caspase-12, CHOP/GADD153, ATF4 and processing of xbp1 mRNA in the affected brain regions clearly indicate the critical involvement of ER-mediated cell death/survival mechanisms and also collectively demonstrated the activation of unfolded protein response (UPR). Moreover, Salubrinal, a selective inhibitor of eIF2alpha dephosphorylation was used to counteract ER stress, which significantly increased the phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha), leading to reduced brain damage after I/R injury. Therefore, inhibition of ER stress following I/R injury may be used as key therapeutic target for neuroprotection.

Postsynaptic density-93 deficiency protects cultured cortical neurons from N-methyl-D-aspartate receptor-triggered neurotoxicity

It has been reported that N-methyl-D-aspartate receptor (NMDAR)-triggered neurotoxicity is related to excessive Ca(2+) loading and an increase in nitric oxide (NO) concentration. However, the molecular mechanisms that underlie these events are not completely understood. NMDARs and neuronal NO synthase each binds to the scaffolding protein postsynaptic density (PSD)-93 through its PDZ domains. In this study, we determined whether PSD-93 plays a critical role in NMDAR/Ca(2+)/NO-mediated neurotoxicity. We found that the targeted disruption of the PSD-93 gene attenuated the neurotoxicity triggered by NMDAR activation, but not by non-NMDAR activation, in cultured mouse cortical neurons. PSD-93 deficiency reduced the amount of NMDAR subunits NR2A and NR2B in synaptosomal fractions from the cortical neurons and significantly prevented NMDA-stimulated increases in cyclic guanosine 3',5'-monophosphate and Ca(2+) loading in the cortical neurons. These findings indicate that PSD-93 deficiency could block NMDAR-triggered neurotoxicity by disrupting the NMDAR-Ca(2+)-NO signaling pathway and reducing expression of synaptic NR2A and NR2B. Since NMDARs, Ca(2+), and NO play a critical role during the development of brain trauma, seizures, and ischemia, the present work suggests that PSD-93 might contribute to molecular mechanisms of neuronal damage in these brain disorders.

Regulation of Kv2.1 phosphorylation in an animal model of anoxia

Conditions such as hypoxia and anoxia inflict serious damage to the brain and continue to be major medical problems. However, the molecular mechanisms that give rise to such damage are not well understood. To elucidate these mechanisms, we established a clinically relevant rodent model of anoxia/recovery by monitoring blood gas levels after oxygen deprivation. Using this animal model, we examined the regulation of Kv2.1, a voltage-gated potassium channel that plays pivotal roles in the homeostasis and survival of neurons. We found that exposure to anoxia induces rapid dephosphorylation of Kv2.1 in the brain, which can be blocked by pre-administration of a NMDA-type glutamate receptor antagonist, memantine. Furthermore, this change is rapidly reversed as the animal recovers from anoxic stress. These results suggest that Kv2.1 is tightly regulated in a clinically relevant animal model of anoxia and further implicate its role in the homeostasis of neurons during anoxic stress.

Lipid oxidation and peroxidation in CNS health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) are produced at low levels in mammalian cells by various metabolic processes, such as oxidative phosphorylation by the mitochondrial respiratory chain, NAD(P)H oxidases, and arachidonic acid oxidative metabolism. To maintain physiological redox balance, cells have endogenous antioxidant defenses regulated at the transcriptional level by Nrf2/ARE. Oxidative stress results when ROS production exceeds the cell's ability to detoxify ROS. Overproduction of ROS damages cellular components, including lipids, leading to decline in physiological function and cell death. Reaction of ROS with lipids produces oxidized phospholipids, which give rise to 4-hydroxynonenal, 4-oxo-2-nonenal, and acrolein. The brain is susceptible to oxidative damage due to its high lipid content and oxygen consumption. Neurodegenerative diseases (AD, ALS, bipolar disorder, epilepsy, Friedreich's ataxia, HD, MS, NBIA, NPC, PD, peroxisomal disorders, schizophrenia, Wallerian degeneration, Zellweger syndrome) and CNS traumas (stroke, TBI, SCI) are problems of vast clinical importance. Free iron can react with H(2)O(2) via the Fenton reaction, a primary cause of lipid peroxidation, and may be of particular importance for these CNS injuries and disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Atherosclerosis, the major risk factor for ischemic stroke, involves accumulation of oxidized LDL in the arteries, leading to foam cell formation and plaque development. This review will discuss the role of lipid oxidation/peroxidation in various CNS injuries/disorders.

Mineralocorticoid and glucocorticoid receptors in hippocampus: their impact on neurons survival and behavioral impairment after neonatal brain injury

Glucocorticoids (GC) exert multiple effects within the central nervous system via mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) activation. MR expression is associated with a neuroprotective phenotype, whereas GR activation is implicated in the induction of an endangered neural phenotype and the opposite actions are most evident in hippocampus, where these receptors are predominantly present. Hippocampus has an overall inhibitory influence on the activity of the hypothalamic-pituitary-adrenal (HPA) axis and it has been suggested that efficient learning and adequate stress response depend on the appropriate functioning of the axis brought by coordinated activation of MR and GR in this region. There is a growing body of evidence that perinatal asphyxia causes irreversible damage to the brain leading to neurons loss in regions vulnerable to oxygen shortage especially in hippocampus. In the present review, some aspects of recently acquired insight in the role of GC receptors in promoting neuronal death and survival after hippocampal injury are discussed. Since the unbalance of MR and GR in hippocampus creates a condition of disturbed neuroendocrine regulation their potential impact on behavioral impairment will also be reviewed.

Metabolic and transmitter changes in core and penumbra after middle cerebral artery occlusion in mice

Middle cerebral artery occlusion (MCAO) is a popular model in experimental stroke research and causes prominent ischemic damage in the forebrain. To characterize metabolic changes induced by MCAO, we have induced permanent MCAO in mice that were implanted with a microdialysis probe in either striatum or hippocampus. Immediately after the onset of ischemia, glucose levels dropped to <10% of basal values in the striatum while they dropped to 50%, and recovered thereafter, in hippocampus. Extracellular levels of glutamate rose 80-fold in the striatum but only 10-fold, and in a transient fashion, in hippocampus. In striatum, release of acetylcholine briefly increased, then dropped to very low values. Both glycerol and choline levels increased strongly during ischemia in the striatum reflecting membrane breakdown. In hippocampus, glycerol increased transiently while the increase of choline levels was moderate. Taken together, these observations delineate metabolic changes in ischemic mouse brain with the striatum representing the core area of ischemia. In comparison, the dorsal hippocampus was identified as a brain area suitable for monitoring metabolic responses in the penumbra region.

Study of red wine neuroprotection on astrocytes

Phenolic composition of wine depends not only on the grape variety from which it is made, but on some external factors such as winemaking technology. Red wine possesses the most antioxidant effect because of its high polyphenolic content. The aim of this work is to study for the first time, the neuroprotective activity of four monovarietal Spanish red wines (Merlot (ME), Tempranillo (T), Garnacha (G) and Cabernet-Sauvignon (CS)) through its antioxidant ability, and to relate this neuroprotection to its polyphenolic composition, if possible. The wine effect on neuroprotection was studied through its effect as free radical scavenger against FeSO4, H2O2 and FeSO4 + H2O2. Effect on cell survival was determined by 3(4,5-dimethyltiazol-2-il)-2,5-diphenyltetrazolium reduction assay (MTT) and lactate dehydrogenase (LDH) release assay on astrocytes cultures. Results showed that most of the studied wine varieties induced neuroprotection through their antioxidant ability in astrocytes, Merlot being the most active; this variety is especially rich in phenolic compounds, mainly catechins and oligomeric proanthocyanidins. Our results show that red wine exerts a protection against oxidative stress generated by different toxic agents and that the observed neuroprotective activity is related to their polyphenolic content.

Alternative cell death of Apaf1-deficient neural progenitor cells induced by withdrawal of EGF or insulin

BACKGROUND

Various forms of cell death, such as apoptotic, autophagic and non-lysosomal types, are implicated in normal physiological processes. Apoptotic protease activating factor 1 (Apaf1) is an important component of the intrinsic apoptotic pathway. Deficiency of Apaf1 results in an accumulation of neural progenitor cells (NPCs) in the developing central nervous system and thus, in perinatal lethality. A small percentage of the mutant mice, however, are viable and grow to maturity. The occurrence of such normal mutants implicates alternative cell death pathways during neurogenesis.

METHODS

NPCs prepared from wild-type or Apaf1-deficient embryos were cultured in growth factor-deprived medium and examined for cell death, caspase activation and morphological alterations. Generation of reactive oxygen species (ROS) and the effects of antioxidants were examined.

RESULTS

Wild-type NPCs underwent apoptosis within 24 hours of withdrawal of epidermal growth factor (EGF) or insulin, whereas Apaf1-deficient NPCs underwent cell death but showed no signs of apoptosis. Autophagy was not necessarily accompanied by cell death. Cell death of the Apaf1-deficient NPCs resembled necroptosis-necrosis-like programmed cell death. The necroptosis inhibitor necrostatin-1, however, failed to inhibit the cell death. ROS accumulation was detected in NPCs deprived of growth factors, and an antioxidant partially suppressed the non-apoptotic cell death of Apaf1-deficient NPCs.

CONCLUSIONS

These data indicate that after withdrawal EGF or insulin withdrawal, the Apaf1-deficient cells underwent non-apoptotic cell death. ROS generation may partially participate in the cell death.

GENERAL SIGNIFICANCE

Non-apoptotic cell death in NPCs may be a compensatory mechanism in the developing CNS of Apaf1-deficient embryos.

Tf-lipoplex-mediated c-Jun silencing improves neuronal survival following excitotoxic damage in vivo

Excitotoxicity is one of the main features responsible for neuronal cell death after acute brain injury and in several neurodegenerative disorders, for which only few therapeutic options are currently available. In this work, RNA interference was employed to identify and validate a potential target for successful treatment of excitotoxic brain injury, the transcription factor c-Jun. The nuclear translocation of c-Jun and its upregulation are early events following glutamate-induced excitotoxic damage in primary neuronal cultures. We present evidence for the efficient knockdown of this transcription factor using a non-viral vector consisting of cationic liposomes associated to transferrin (Tf-lipoplexes). Tf-lipoplexes were able to deliver anti-c-Jun siRNAs to neuronal cells in culture, resulting in efficient silencing of c-Jun mRNA and protein and in a significant decrease of cell death following glutamate-induced damage or oxygen-glucose deprivation. This formulation also leads to a significant c-Jun knockdown in the mouse hippocampus in vivo, resulting in the attenuation of both neuronal death and inflammation following kainic acid-mediated lesion of this region. Furthermore, a strong reduction of seizure activity and cytokine production was observed in animals treated with anti-c-Jun siRNAs. These findings demonstrate the efficient delivery of therapeutic siRNAs to the brain by Tf-lipoplexes and validate c-Jun as a promising therapeutic target in neurodegenerative disorders involving excitotoxic lesions.

Targeting eNOS and beyond: emerging heterogeneity of the role of endothelial Rho proteins in stroke protection

Currently available modalities for the treatment of acute ischemic stroke are aimed at preserving or augmenting cerebral blood flow. Experimental evidence suggests that statins, which show 25-30% reduction of stroke incidence in clinical trials, confer stroke protection by upregulation of eNOS and increasing cerebral blood flow. The upregulation of eNOS by statins is mediated by inhibition of small GTP-binding protein RhoA. Our recent study uncovered a unique role for a Rho-family member Rac1 in stroke protection. Rac1 in endothelium does not affect cerebral blood flow. Instead, inhibition of endothelial Rac1 leads to broad upregulation of the genes relevant to neurovascular protection. Intriguingly, inhibition of endothelial Rac1 enhances neuronal cell survival through endothelium-derived neurotrophic factors, including artemin. This review discusses the emerging therapeutic opportunities to target neurovascular signaling beyond the BBB, with special emphasis on the novel role of endothelial Rac1 in stroke protection.

A locus mapping to mouse chromosome 7 determines infarct volume in a mouse model of ischemic stroke

BACKGROUND

In a mouse model of focal cerebral ischemia, infarct volume is highly variable and strain dependent, but the natural genetic determinants responsible for this difference remain unknown. To identify genetic determinants regulating ischemic neuronal damage and to dissect apart the role of individual genes and physiological mechanisms in infarction in mice, we performed quantitative trait locus analysis of surgically induced cerebral infarct volume.

METHODS AND RESULTS

After permanent occlusion of the distal middle cerebral artery, infarct volume was determined for 16 inbred strains of mice, chromosome substitution strains, and for 2 intercross cohorts, F2 (B6xBALB/c) and F2 (B6xSWR/J). Genome-wide linkage analysis was performed for infarct volume as a quantitative trait. Infarct volume varied up to 30-fold between strains, with heritability estimated at 0.88. Overall, 3 quantitative trait locus were identified that modulate infarct volume, with a major locus (Civq1) on chromosome 7 accounting for >50% of the variation, with a combined LOD score of 21.7. Interval-specific single nucleotide polymorphism haplotype analysis for Civq1 results in 12 candidate genes.

CONCLUSIONS

The extent of ischemic tissue damage after distal middle cerebral artery occlusion in inbred strains of mice is modulated by genetic variation mapping to at least 3 different loci. A single locus on chromosome 7 determines the majority of the observed variation in the trait. This locus seems to be identical to LSq1, a locus conferring limb salvage and reperfusion in a mouse model of hindlimb ischemia. The identification of the genes underlying these loci may uncover novel genetic and physiological pathways that modulate cerebral infarction and provide new targets for therapeutic intervention in ischemic stroke, and possibly other ischemic diseases.

Control of NMDA receptor function by the NR2 subunit amino-terminal domain

NMDA receptors comprised of different NR2 subunits exhibit strikingly unique biophysical and pharmacological properties. Here, we report that the extracellular amino-terminal domain (ATD) of the NR2 subunit controls pharmacological and kinetic properties of recombinant NMDA receptors, such as agonist potency, deactivation time course, open probability (P(OPEN)), and mean open/shut duration. Using ATD deletion mutants of NR2A, NR2B, NR2C, NR2D, and chimeras of NR2A and NR2D with interchanged ATD [NR2A-(2D-ATD) and NR2D-(2A-ATD)], we show that the ATD contributes to the low glutamate potency of NR2A-containing NMDA receptors and the high glutamate potency of NR2D-containing receptors. The ATD influences the deactivation time courses of NMDA receptors, as removal of the ATD from NR2A slows the deactivation rate, while removal of the ATD from NR2B, NR2C and NR2D accelerates the deactivation rate. Open probability also is influenced by the ATD. Removal of the ATD from NR2A or replacement of the NR2A-ATD with that of NR2D decreases P(OPEN) in single-channel recordings from outside-out patches of HEK 293 cells. In contrast, deletion of the ATD from NR2D or replacement of the NR2D ATD with that of NR2A increases P(OPEN) and mean open duration. These data demonstrate the modular nature of NMDA receptors, and show that the ATD of the different NR2 subunits plays an important role in fine-tuning the functional properties of the individual NMDA receptor subtypes.

The mechanisms of brain ischemic insult and potential protective interventions

The mechanisms of brain ischemic insult include glutamate excitoxicity, calcium toxicity, free radicals, nitric oxide, inflammatory reactions, as well as dysfunctions of endoplasmic reticulum and mitochondrion. These injury cascades are interconnected in complex ways, thus it is hard to compare their pathogenic importances in ischemia models. And the research in cellular and molecular pathways has spurred the studies in potential neuroprotections mainly in pharmacological fields, such as anti-excitotoxic treatment, calcium-channel antagonism, approaches for inhibition of oxidation, inflammation and apoptosis, etc. Besides, other protective interventions including thrombolysis, arteriogenesis, regeneration therapy, and ischemia preconditioning or postconditioning, are also under investigations. Despite the present difficulties, we are quite optimistic towards future clinical applications of neuroprotective agents, by optimizing experimental approaches and clinical trials.

Astrocyte-neuron interactions in neurological disorders

Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.

Neuronal caspase-3 and PARP-1 correlate differentially with apoptosis and necrosis in ischemic human stroke

Apoptotic cell death contributes to neuronal loss in the penumbral region of brain infarction. Activated caspase-3 (ACA-3) cleaves proteins including poly(ADP-ribose) polymerase-1 (PARP-1) important in DNA repair, thus promoting apoptosis. Overactivation of PARP-1 depletes NAD(+) and ATP, resulting in necrosis. These cell death phenomena have been investigated mostly in experimental animals. We studied an autopsy cohort of 13 fatal ischemic stroke cases (symptoms 15 h to 18 days) and 2 controls by immunohistochemical techniques. The number of PARP-1 immunoreactive neurons was highest in the periinfarct area. Nuclear PARP-1 correlated with increasing neuronal necrosis (P = 0.013). Cytoplasmic PARP-1 correlated with TUNEL in periinfarct and core areas (P = 0.01). Cytoplasmic cleaved PARP-1 was inversely correlated with increasing necrotic damage (P = 0.001). PAR-polymers were detected in neurons confirming enzymatic activity of PARP-1. Cytoplasmic ACA-3 correlated with death receptor Fas (r (s) = 0.48; P = 0.005). In conclusion, the confirmation of the same pathways of cell death than previously described in experimental animal models encourages neuroprotective treatments acting on these mediators also in human stroke.

NOX enzymes in the central nervous system: from signaling to disease

Oxidative stress has been implicated in the pathogenesis of neurologic and psychiatric diseases. The brain is particularly vulnerable to oxidative damage due to high oxygen consumption, low antioxidant defense, and an abundance of oxidation-sensitive lipids. Production of reactive oxygen species (ROS) by mitochondria is generally thought to be the main cause of oxidative stress. However, a role for ROS-generating NADPH oxidase NOX enzymes has recently emerged. Activation of the phagocyte NADPH oxidase NOX2 has been studied mainly in microglia, where it plays a role in inflammation, but may also contribute to neuronal death in pathologic conditions. However, NOX-dependent ROS production can be due to the expression of other NOX isoforms, which are detected not only in microglia, but also in astrocytes and neurons. The physiologic and pathophysiologic roles of such NOX enzymes are only partially understood. In this review, we summarize the present knowledge about NOX enzymes in the central nervous system and their involvement in neurologic and psychiatric diseases.

Mitochondria, oxidative metabolism and cell death in stroke

Stroke most commonly results from occlusion of a major artery in the brain and typically leads to the death of all cells within the affected tissue. Mitochondria are centrally involved in the development of this tissue injury due to modifications of their major role in supplying ATP and to changes in their properties that can contribute to the development of apoptotic and necrotic cell death. In animal models of stroke, the limited availability of glucose and oxygen directly impairs oxidative metabolism in severely ischemic regions of the affected tissue and leads to rapid changes in ATP and other energy-related metabolites. In the less-severely ischemic "penumbral" tissue, more moderate alterations develop in these metabolites, associated with near normal glucose use but impaired oxidative metabolism. This tissue remains potentially salvageable for at least the first few hours following stroke onset. Early restoration of blood flow can result in substantial recovery of energy-related metabolites throughout the affected tissue. However, glucose oxidation is markedly decreased due both to lower energy requirements in the post-ischemic tissue and limitations on the mitochondrial oxidation of pyruvate. A secondary deterioration of mitochondrial function subsequently develops that may contribute to progression to cell loss. Mitochondrial release of multiple apoptogenic proteins has been identified in ischemic and post-ischemic brain, mostly in neurons. Pharmacological interventions and genetic modifications in rodent models strongly implicate caspase-dependent and caspase-independent apoptosis and the mitochondrial permeability transition as important contributors to tissue damage, particularly when induced by short periods of temporary focal ischemia.

Cerebral protection of purified Herba Leonuri extract on middle cerebral artery occluded rats

AIM OF STUDY

Oxidative stress is involved in stroke. In particular, Chinese Herbal Medicine with antioxidant properties is believed to have potential therapeutic effect. In this study, neuroprotective effects of purified Herba Leonuri (pHL) were evaluated in Wistar rats undergone middle cerebral artery occlusion (MCAO).

MATERIALS AND METHODS

The rats were treated with their respective treatments for 2 weeks prior to the MCAO, continually treated for another 7 days after MCAO. During the post-surgery treatment period, neurological deficit score was measured. At the end of treatment, animals were sacrificed and samples were collected for analysis of infarct volume, apoptosis and antioxidant analysis.

RESULTS

Under the treatment of pHL, the infarct volume was reduced significantly from 20.75+/-0.03% to 15.19+/-0.02% (p<0.05). The neurological impairment was alleviated to 1.82 as compared to vehicle (2.43). Plasma antioxidant concentration was increased from 0.31+/-0.03 mM to 0.42+/-0.05 mM (p<0.05). DNA oxidative damage was reduced to 1.19+/-0.03 in stroke pHL treated group (p<0.05 as compared to vehicle group, 1.78+/-0.03). pHL could reduce the level of apoptosis and also the pro-apoptotic proteins, but increase the level of anti-apoptotic proteins.

CONCLUSION

pHL is believed to have promising therapeutic effect for stroke treatment through antioxidant mechanisms.

Mitochondrial targets for stroke: focusing basic science research toward development of clinically translatable therapeutics

BACKGROUND AND PURPOSE

Stroke is a major cause of death and disability, and it is imperative to develop therapeutics to mitigate stroke-related injury. Despite many promising prospects, attempts at translating neuroprotective agents that show success in animal models of stroke have resulted in very limited clinical success.

SUMMARY OF REVIEW

This review discusses reasons for the lack of translational success based on the therapeutic targets tested and the pathophysiology of stroke. New recanalization therapies and alternative therapeutic strategies are discussed concerning mitochondria-mediated cell death. Mitochondrial death-regulation pathways are divided into 3 categories: Upstream signaling pathways, agents that target mitochondria directly, and downstream death-execution effectors. The apoptosis signal-related kinase/c-Jun-terminal kinase pathway is used as an example to provide rationale as to why inhibiting signaling pathway upstream of mitochondrial dysfunction is a promising therapeutic approach. Finally, the mechanisms of autophagy and mitochondrial biogenesis are discussed in relation to stroke.

CONCLUSIONS

Increasing evidence suggests that reperfusion is necessary for improved neurological outcomes after stroke. Development of improved recanalization methods with increased therapeutic windows will aid in improving clinical outcome. Adjunct neuroprotective interventions must also be developed to ensure maximal brain tissue salvage. Targeting prodeath signaling pathways upstream of mitochondrial damage is promising for potential clinically effective treatment. Further understanding of the roles of equilibrium of autophagy and mitochondrial biogenesis in the pathogenesis of stroke could also lead to novel therapeutics.

The molecular mechanisms of cell death in the course of transient ischemia are differentiated in evolutionary distinguished brain structures

There is large body of evidence suggesting distinct susceptibility to ischemia in various brain regions. However, the reason for this remains unexplained. Comparative studies of programmed cell death (PCD) pathways indicate their differentiated evolutional origin. The caspase-independent pathway is regarded as an older, whereas the caspase-dependent--as more advanced. In our study we address the question of whether there are any characteristic differences in the activation and course of PCD in phylogenetically and morphologically distinguished brain structures after transient focal ischemia. Using Western blot, we studied changes in expression of caspases: 3, 8, 9, and AIF in the frontoparietal neocortex, archicortex (CA1 and CA2 sectors of the hippocampus) and striatum, during reperfusion after 1 h occlusion of the middle cerebral artery. The caspase and AIF expression were differentiated between the studied structures. The activation of only the caspase-dependent pathway was observed in the neocortex. In the archicortex and striatum both caspase-dependent and caspase-independent pathways were activated, although in the latter the extrinsic apoptotic pathway was not activated. In summary, it is conceivable that structures of different evolutionary origin undergo cell-death processes with the participation of phylogenetically distinguished mechanisms. The previously reported unequal susceptibility to ischemia may co-exist with activation of different cell death pathways.

Reduction of lipoxidative load by secretory phospholipase A2 inhibition protects against neurovascular injury following experimental stroke in rat

BACKGROUND

In animal models, ischemia reperfusion (IR) injury triggers membrane lipid degradation and accumulation of lipoxidative exacerbations in neurovascular unit, leading to blood brain barrier (BBB) damage and neurologic deficits. In this study, we investigated whether impeding membrane lipid breakdown by inhibiting secretory phospholipase A2 (sPLA2) activity reduces BBB leakage, leading to neuroprotection and functional recovery.

METHODS

Focal cerebral IR injury was induced by middle cerebral artery occlusion (MCAO) in adult male rats. A sPLA2 inhibitor, 7,7-dimethyleicosadienoic acid (DEDA), was administered following IR injury. DEDA-treated animals were compared with vehicle-treated in terms of BBB leakage, edema, infarct volume, and neurological deficit. Membrane lipid degradation and the expression/activity of sPLA2 were also assessed. The role of one of the sPLA2 products, arachidonic acid (AA), on the morphology of the differentiated neuronal cell PC12 was examined by light microscopy.

RESULTS

Treatment with DEDA after IR injury not only reduced BBB leakage but also decreased infarct volume and improved neurologic function. The treatment attenuated both the activity of sPLA2 and the levels of sPLA2-derived oxidized products. The metabolites of lipid oxidation/peroxidation, including the protein carbonyl, were reduced as well. The treatment also restored the levels of glutathione, indicating attenuation of oxidative stress. In vitro treatment of PC12 cells with DEDA did not restore the AA-mediated inhibition of neurite formation and the levels of glutathione, indicating that effect of DEDA is up stream to AA release.

CONCLUSION

sPLA2-derived oxidative products contribute to significant neurovascular damage, and treatment with sPLA2 inhibitor DEDA ameliorates secondary injury by reducing exacerbations from lipoxidative stress.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Oxygen free radicals regulate energy metabolism via AMPK pathway following cerebral ischemia

OBJECTIVE

One basic consequence of cerebral ischemia is energy depletion, manifested by falling levels of adenosine triphosphate (ATP) and a concomitant rise of adenosine monophosphate (AMP). Energy sensor AMP activated protein kinase (AMPK) can be activated in situations of energy stress to maintain ATP reserves. Here, we investigated the mechanism underlying AMPK pathway following cerebral ischemia in rat hippocampus.

METHODS

Male Sprague-Dawley rats (250 g or so) were subjected to 10 minute four-vessel occlusion, and ketamine or alpha-tocopherol was administered to the rats before ischemia, respectively. The plasma membrane and post-plasma membrane fractions were separated by centrifugation, and protein activity was assessed using immunoblot analysis.

RESULTS

AMPK was activated and reached its highest level at 1 hour reperfusion post-ischemia. Glucose transporter 4 (GLUT4), a downstream protein of AMPK, was increased in the plasma membrane while decreased in post-plasma membrane during reperfusion. Both N-methyl-D-aspartic acid (NMDA) receptor antagonist (ketamine) and oxygen free radical scavenger (alpha-tocopherol) decreased AMPK activity as well as the content of GLUT4 in the plasma membrane following cerebral ischemia.

DISCUSSION

Up-regulation of NMDA receptor activity or oxygen free radical production elicited by cerebral ischemia contributes to AMPK activation and increment of glucose uptake through facilitating the transportation of GLUT4 to the plasma membrane, involving in regulation of energy metabolism.

Necrostatin-1 reverts shikonin-induced necroptosis to apoptosis

Degterev et al. previously demonstrated that death receptor mediated apoptosis could be diverted to necroptosis when apoptosis signaling was blocked, suggesting that necroptosis may function as a backup mechanism to insure the elimination of damaged cells under certain conditions when apoptosis was inhibited. Here, we show that shikonin-induced necroptosis can be reverted to apoptosis in the presence of necrostatin-1 (Nec-1), a specific necroptosis inhibitor and that the death mode switch is at least partially due to the conversion from mitochondrial inner membrane permeability to mitochondrial outer membrane permeability, which is associated with Bax translocation. The data combined with the previous reports support a notion that apoptosis and necroptosis may function as reciprocal backup mechanisms of cellular demise. To the best of our knowledge, this is the first study to document a conversion from necroptosis to apoptosis.

Protection by tetrahydroxystilbene glucoside against cerebral ischemia: involvement of JNK, SIRT1, and NF-kappaB pathways and inhibition of intracellular ROS/RNS generation

Many natural polyphenolic compounds have been shown to attenuate reactive oxygen/nitrogen species (ROS/RNS) formation and protect against ischemia/reperfusion injury both in vitro and in vivo. 2,3,5,4'-tetrahydroxystilbene-2-O-beta-D-glucoside (TSG), an active component of the rhizome extract from Polygonum multiflorum, exhibits antioxidative and anti-inflammatory effects. Here, we used an in vitro ischemic model of oxygen-glucose deprivation followed by reperfusion (OGD-R) and an in vivo ischemic model of middle cerebral artery occlusion (MCAO) to investigate the neuroprotective effects of TSG on ischemia/reperfusion brain injury and the related mechanisms. We demonstrated that OGD-R-induced neuronal injury, intracellular ROS generation, and mitochondrial membrane potential dissipation were reversed by TSG. The elevation of H2O2-induced [Ca2+]i was also attenuated by TSG. Inhibition of the c-Jun N-terminal kinase (JNK) and Bcl-2 family-related apoptotic signaling pathway was involved in the neuroprotection afforded by TSG. Meanwhile, TSG inhibited iNOS mRNA expression induced by OGD-R, which may be mediated by the activation of SIRT1 and inhibition of NF-kappaB activation. In vivo studies further demonstrated that TSG significantly reduced the brain infarct volume and the number of positive cells by TUNEL staining in the cerebral cortex compared to the MCAO group. Our study indicates that TSG protects against cerebral ischemia/reperfusion injury through multifunctional cytoprotective pathways.

The neuroprotective mechanism of brain ischemic preconditioning

Brain ischemia is one of the most common causes of death and the leading cause of adult disability in the world. Brain ischemic preconditioning (BIP) refers to a transient, sublethal ischemia which results in tolerance to later, otherwise lethal, cerebral ischemia. Many attempts have been made to understand the molecular and cellular mechanisms underlying the neuroprotection offered by ischemic preconditioning. Many studies have shown that neuroprotective mechanisms may involve a series of molecular regulatory pathways including activation of the N-methyl-D-aspartate (NMDA) and adenosine receptors; activation of intracellular signaling pathways such as mitogen activated protein kinases (MAPK) and other protein kinases; upregulation of Bcl-2 and heat shock proteins (HSPs); and activation of the ubiquitin-proteasome pathway and the autophagic-lysosomal pathway. A better understanding of the processes that lead to cell death after stroke as well as of the endogenous neuroprotective mechanisms by which BIP protects against brain ischemic insults could help to develop new therapeutic strategies for this devastating neurological disease. The purpose of the present review is to summarize the neuroprotective mechanisms of BIP and to discuss the possibility of mimicking ischemic preconditioning as a new strategy for preventive treatment of ischemia.

Src kinase up-regulates the ERK cascade through inactivation of protein phosphatase 2A following cerebral ischemia

BACKGROUND

The regulation of protein phosphorylation requires a balance in the activity of protein kinases and protein phosphatases. Our previous data indicates that Src can increase ERK activity through Raf kinase in response to ischemic stimuli. This study examined the molecular mechanisms by which Src activates ERK cascade through protein phosphatases following cerebral ischemia.

RESULTS

Ischemia-induced Src activation is followed by phosphorylation of PP2A at Tyr307 leading to its inhibition in the rat hippocampus. SU6656, a Src inhibitor, up-regulates PP2A activity, resulting in a significant decreased activity in ERK and its targets, CREB and ERalpha. In addition, the PP2A inhibitor, cantharidin, led to an up-regulation of ERK activity and was able to counteract Src inhibition during ischemia.

CONCLUSION

Src induces up-regulation of ERK activity and its target transcription factors, CREB and ERalpha, through attenuation of PP2A activity. Therefore, activation of ERK is the result of a crosstalk between two pathways, Raf-dependent positive regulators and PP2A-dependent negative regulators.

Cholinergic deficiency involved in vascular dementia: possible mechanism and strategy of treatment

Vascular dementia (VaD) is a progressive neurodegenerative disease with a high prevalence. Several studies have recently reported that VaD patients present cholinergic deficits in the brain and cerebrospinal fluid (CSF) that may be closely related to the pathophysiology of cognitive impairment. Moreover, cholinergic therapies have shown promising effects on cognitive improvement in VaD patients. The precise mechanisms of these cholinergic agents are currently not fully understood; however, accumulating evidence indicates that these drugs may act through the cholinergic anti-inflammatory pathway, in which the efferent vagus nerve signals suppress pro-inflammatory cytokine release and inhibit inflammation, although regulation of oxidative stress and energy metabolism, alleviation of apoptosis may also be involved. In this paper, we provide a brief overview of the cholinergic treatment strategy for VaD and its relevant mechanisms of anti-inflammation.Acta Pharmacologica Sinica (2009) 30: 879-888; doi: 10.1038/aps.2009.82.

Clovamide and rosmarinic acid induce neuroprotective effects in in vitro models of neuronal death

BACKGROUND AND PURPOSE

Phenolic compounds exert cytoprotective effects; our purpose was to investigate whether the isosteric polyphenolic compounds clovamide and rosmarinic acid are neuroprotective.

EXPERIMENTAL APPROACH

Three in vitro models of neuronal death were selected: (i) differentiated SH-SY5Y human neuroblastoma cells exposed to tert-butylhydroperoxide (t-BOOH), for oxidative stress; (ii) differentiated SK-N-BE(2) human neuroblastoma cells treated with L-glutamate, for excitotoxicity; and (iii) differentiated SH-SY5Y human neuroblastoma cells exposed to oxygen-glucose deprivation/reoxygenation, for ischaemia-reperfusion. Cell death was evaluated by lactate dehydrogenase measurements in the cell media, while the mechanisms underlying the effects by measuring: (i) t-BOOH-induced glutathione depletion and increase in lipoperoxidation; and (ii) L-glutamate-induced intracellular Ca(2+) overload (fura-2 method) and inducible gene expression (c-fos, c-jun), by reverse transcriptase-PCR. The ability of compounds to modulate nuclear factor-kappaB and peroxisome proliferator-activated receptor-gamma activation was evaluated by Western blot in SH-SY5Y cells not exposed to harmful stimuli.

KEY RESULTS

Both clovamide and rosmarinic acid (10-100 micromol x L(-1)) significantly protected neurons against insults with similar potencies and efficacies. The EC(50) values were in the low micromolar range (0.9-3.7 micromol x L(-1)), while the maximal effects ranged from 40% to -60% protection from cell death over untreated control at 100 micromol x L(-1). These effects are mediated by the prevention of oxidative stress, intracellular Ca(2+) overload and c-fos expression. In addition, rosmarinic acids inhibited nuclear factor-kappaB translocation and increased peroxisome proliferator-activated receptor-gamma expression in SH-SY5Y cells not exposed to harmful stimuli.

CONCLUSION AND IMPLICATIONS

Clovamide and rosmarinic acid are neuroprotective compounds of potential use at the nutritional/pharmaceutical interface.

Neuroprotective role of mitochondrial uncoupling protein 2 in cerebral stroke

The uncoupling proteins (UCPs) are mitochondrial transporter proteins involved in proton conductance across inner mitochondrial membrane (IMM). UCP2, which is one of the members of this class of proteins, has a wide but restricted tissue distribution including brain. Its physiologic role according to emerging evidences, although still not clear, indicate that distribution of UCP2 may be related to regulation of mitochondria membrane potential (DeltaPsim), production of reactive oxygen species (ROS), preservation of calcium homeostasis, modulation of neuronal activity, and eventually inhibition of cellular damage. These factors are very important in determining the fate of neurons and damage progression in the brain during various neurodegenerative diseases including cerebral stroke. Recent evidence indicates that an increased expression and activity of UCP2 are well correlated with neuronal survival after stroke and trauma. This review briefly covers the present understanding of UCP2, which eventually may be beneficial to understand the precise role of UCP2 to develop strategy to identify its potential therapeutic application.

Induction of heat shock proteins for protection against oxidative stress

Heat shock proteins (Hsps) have been studied for many years and there is now a large body of evidence that demonstrates the role of Hsp upregulation in tissue and cell protection in a wide variety of stress conditions. Oxidative stress is known to be involved in a number of pathological conditions, including neurodegeneration, cardiovascular disease and stroke, and even plays a role in natural aging. In this review we summarize the current understanding of the role of Hsps and the heat shock response (HSR) in these pathological conditions and discuss the therapeutic potential of an Hsp therapy for these disorders. However, although an Hsp based therapy appears to be a promising approach for the treatment of diseases that involve oxidative damage, there are some significant hurdles that must be overcome before this approach can be successful. For example, to be effective an Hsp based therapy will need to ensure that the upregulation of Hsps occurs in the right place (i.e. be cell specific), at the right time and to a level and specificity that ensures that all the important binding partners, namely the co-chaperones, are also present at the appropriate levels. It is therefore unlikely that strategies that involve genetic modifications that result in overexpression of specific Hsps will achieve such sophisticated and coordinated effects. Similarly, it is likely that some pharmaceutical inducers of Hsps may be too generic to achieve the desired specific effects on Hsp expression, or may simply fail to reach their target cells due to delivery problems. However, if these difficulties can be overcome, it is clear that an effective Hsp based therapy would be of great benefit to the wide range of depilating conditions in which oxidative stress plays a critical role.

A white matter stroke model in the mouse: axonal damage, progenitor responses and MRI correlates

Subcortical white matter stroke is a common stroke subtype but has had limited pre-clinical modeling. Recapitulating this disease process in mice has been impeded by the relative inaccessibility of the subcortical white matter arterial supply to induce white matter ischemia in isolation. In this report, we detail a subcortical white matter stroke model developed in the mouse and its characterization with a comprehensive set of MRI, immunohistochemical, neuronal tract tracing and electron microscopic studies. Focal injection of the vasoconstrictor endothelin-1 into the subcortical white matter produces an infarct core that develops a maximal MRI signal by day 2, which is comparable in relative size and location to human subcortical stroke. Immunohistochemical studies indicate that oligodendrocyte apoptosis is maximal at day 1 and apoptotic cells extend away from the stroke core into the peri-infarct white matter. The amount of myelin loss exceeds axonal fiber loss in this peri-infarct region. Activation of microglia/macrophages takes place at 1 day after injection near injured axons. Neuronal tract tracing demonstrates that subcortical white matter stroke disconnects a large region of bilateral sensorimotor cortex. There is a robust glial response after stroke by BrdU pulse-labeling, and oligodendrocyte precursor cells are initiated to proliferate and differentiate within the first week of injury. These results demonstrate the utility of the endothelin-1 mediated subcortical stroke in the mouse to study post-stroke repair mechanisms, as the infarct core extends through the partially damaged peri-infarct white matter and induces an early glial progenitor response.

Modulation of stress proteins and apoptotic regulators in the anoxia tolerant turtle brain

Freshwater turtles survive prolonged anoxia and reoxygenation without overt brain damage by well-described physiological processes, but little work has been done to investigate the molecular changes associated with anoxic survival. We examined stress proteins and apoptotic regulators in the turtle during early (1 h) and long-term anoxia (4, 24 h) and reoxygenation. Western blot analyses showed changes within the first hour of anoxia; multiple stress proteins (Hsp72, Grp94, Hsp60, Hsp27, and HO-1) increased while apoptotic regulators (Bcl-2 and Bax) decreased. Levels of the ER stress protein Grp78 were unchanged. Stress proteins remained elevated in long-term anoxia while the Bcl-2/Bax ratio was unaltered. No changes in cleaved caspase 3 levels were observed during anoxia while apoptosis inducing factor increased significantly. Furthermore, we found no evidence for the anoxic translocation of Bax from the cytosol to mitochondria, nor movement of apoptosis inducing factor between the mitochondria and nucleus. Reoxygenation did not lead to further increases in stress proteins or apoptotic regulators except for HO-1. The apparent protection against cell damage was corroborated with immunohistochemistry, which indicated no overt damage in the turtle brain subjected to anoxia and reoxygenation. The results suggest that molecular adaptations enhance pro-survival mechanisms and suppress apoptotic pathways to confer anoxia tolerance in freshwater turtles.

Pharmacological inhibition of mitochondrial membrane permeabilization for neuroprotection

Recent data have provided important clues about the molecular mechanisms underlying certain neurodegenerative diseases. Most cell death in vertebrates proceeds via the mitochondrial pathway of apoptosis. Mitochondria contain proapoptotic factors such as cytochrome c and AIF in their intermembrane space. Furthermore, mitochondrial membrane permeabilization (MMP) is a critical event during apoptosis, representing the "point of no return" of the lethal process. Modern medicine is developing an increasing number of drugs for neurodegenerative disease, but no neuroprotective treatment has yet been established. While current treatments temporarily alleviate symptoms, they do not halt disease progression. This paper briefly reviews the pharmacological inhibition of mitochondrial membrane permeabilization for neuroprotection.

Riluzole protects against glutamate-induced slowing of neurofilament axonal transport

Riluzole is the only drug approved for the treatment of amyotrophic lateral sclerosis (ALS) but its precise mode of action is not properly understood. Damage to axonal transport of neurofilaments is believed to be part of the pathogenic mechanism in ALS and this has been linked to defective glutamate handling and increased phosphorylation of neurofilament side-arm domains. Here, we show that riluzole protects against glutamate-induced slowing of neurofilament transport. Protection is associated with decreased neurofilament side-arm phosphorylation and inhibition of the activities of two neurofilament kinases, ERK and p38 that are activated in ALS. Thus, the anti-glutamatergic properties of riluzole include protection against glutamate-induced changes to neurofilament phosphorylation and transport.