Inflammatory mechanisms in ischemic stroke: therapeutic approaches

Variants in the inflammatory IL6 and MPO genes modulate stroke susceptibility through main effects and gene-gene interactions

There is substantial evidence that inflammation within the central nervous system contributes to stroke risk and recovery. Inflammatory conditions increase stroke risk, and the inflammatory response is of major importance in recovery and healing processes after stroke. We investigated the role of inflammatory genes IL1B, IL6, MPO, and TNF in stroke susceptibility and recovery in a population sample of 672 patients and 530 controls, adjusting for demographic, clinical and lifestyle risk factors, and stroke severity parameters. We also considered the likely complexity of inflammatory mechanisms in stroke, by assessing the combined effects of multiple genes. Two interleukin 6 (IL6) and one myeloperoxidase (MPO) single-nucleotide polymorphisms were significantly associated with stroke risk (0.022<(corrected)P<0.042), highlighting gene variants of low to moderate effect in stroke risk. An epistatic interaction between the IL6 and MPO genes was also identified in association with stroke susceptibility (P=0.031 after 1,000 permutations). In a subset of 546 patients, one IL6 haplotype was associated with stroke outcome at 3 months ((corrected)P=0.024), an intriguing finding warranting further validation. Our findings support the association of the IL6 gene and present novel evidence for the involvement of MPO in stroke susceptibility, suggesting a modulation of stroke risk by main gene effects, clinical and lifestyle factors, and gene-gene interactions.

Oxidative toxicity in neurodegenerative diseases: role of mitochondrial dysfunction and therapeutic strategies

Besides fluorine, oxygen is the most electronegative element with the highest reduction potential in biological systems. Metabolic pathways in mammalian cells utilize oxygen as the ultimate oxidizing agent to harvest free energy. They are very efficient, but not without risk of generating various oxygen radicals. These cells have good antioxidative defense mechanisms to neutralize these radicals and prevent oxidative stress. However, increased oxidative stress results in oxidative modifications in lipid, protein, and nucleic acids, leading to mitochondrial dysfunction and cell death. Oxidative stress and mitochondrial dysfunction have been implicated in many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and stroke-related brain damage. Research has indicated mitochondria play a central role in cell suicide. An increase in oxidative stress causes mitochondrial dysfunction, leading to more production of reactive oxygen species and eventually mitochondrial membrane permeabilization. Once the mitochondria are destabilized, cells are destined to commit suicide. Therefore, antioxidative agents alone are not sufficient to protect neuronal loss in many neurodegenerative diseases. Combinatorial treatment with antioxidative agents could stabilize mitochondria and may be the most suitable strategy to prevent neuronal loss. This review discusses recent work related to oxidative toxicity in the central nervous system and strategies to treat neurodegenerative diseases.

Experimental and clinical use of therapeutic hypothermia for ischemic stroke: opportunities and limitations

Stroke remains a disease with a serious impact on quality of life but few effective treatments exist. There is an urgent need to develop and/or improve neuroprotective strategies to combat this. Many drugs proven to be neuroprotective in experimental models fail to improve patient outcome in a clinical setting. An emerging treatment, therapeutic hypothermia (TH), is a promising neuroprotective therapy in stroke management. Several studies with TH in experimental models and small clinical trials have shown beneficial effects. Despite this, implementation into the clinical setting is still lacking due to methodological considerations as well as hypothermia-related complications. This paper discusses the possible opportunities and limitations of the use of TH in animal models and the translation into the clinic.

Cyanine dyes attenuate cerebral ischemia and reperfusion injury in rats

Some photosensitizing cyanine dyes act on the immune system to enhance the phagocytic capacity of macrophages. In this study, we examined whether these dyes have neurotrophin-like activities and neuroprotective effects in vitro and in vivo. By screening more than 250 cyanine dyes, we found that NK-4 and NK-150, which belong to a group of pentamethine trinuclear cyanine dyes, significantly potentiated nerve growth factor (NGF)-primed neurite outgrowth of PC12HS cells in nanomolar to micromolar concentrations. Both NK-4 and NK-150 showed a remarkable hydroxyl radical-scavenging activity using an in vitro electron spin resonance (ESR)-based technique. They also effectively scavenged peroxy radicals, and in addition, NK-4 acted on superoxides to a similar extent as ascorbate. In vivo, NK-4 and NK-150 prevented cerebral ischemic injury induced by 2 h middle cerebral artery occlusion (MCAO) and 24 h reperfusion in rats. Dyes were intravenously administrated twice 1 h after the occlusion and immediately after the start of reperfusion. NK-4 and NK-150 (100 µg/kg) reduced cerebral infarct volumes by 57.0% and 46.0%, respectively. Those dyes also decreased brain swelling in the ischemic semispheres. As a result, administration of NK-4 and NK-150 provided substantial improvements in MCAO-induced neurological deficits in a dose-dependent manner. These results suggest that NK-4 and NK-150 effectively prevented ischemia-induced brain injury through their potent neurotrophin-like activity as well as antioxidative activity.

Lack of enantiomeric influence on the brain cytoprotective effect of ibuprofen and flurbiprofen

R(-) enantiomers of the 2-arylpropionic acid derivatives ibuprofen and flurbiprofen weakly inhibit cyclooxygenase (COX) activity. However, a possible cytoprotective effect has been proposed. The aim of the study is to investigate the possible mechanism of this effect. An in vitro hypoxia-reoxygenation model in rat brain slices was used (n=6 rats per group). After reoxygenation, we measured LDH efflux (neuronal death), brain prostaglandin E(2) (PGE(2)) concentration, interleukins (IL)-1β and 10, oxidative and nitrosative stress (lipid peroxides, glutathione, 3-nitrotyrosine, and nitrites/nitrates). Anti-COX activity was measured in human whole blood. Racemic, R(-), and S(+) enantiomers of ibuprofen and flurbiprofen were tested. All compounds had a cytoprotective effect with IC(50) values in the range of 10(-5) M. R(-) enantiomers did not significantly inhibit brain PGE(2). The concentration of IL-1β was reduced by 53.1% by the racemic form, 30.6% by the S(+) and 43.2% by the R(-) enantiomer of ibuprofen. The IL-10 concentration increased significantly only with S(+)-flurbiprofen (33.1%) and R(-)-flurbiprofen (26.1%). Lipid peroxidation was significantly reduced by all three forms of flurbiprofen. Nitrite + nitrate concentrations were reduced by racemic, S(+), and R(-)-flurbiprofen. Peroxynitrite formation (3-nitrotyrosine) was significantly reduced by racemic and S(+)-ibuprofen. COX inhibition is not the main mechanism of cytoprotection for these compounds. Their influence on inflammatory mediators and oxidative and nitrosative stress could account for the potential cytoprotective effect of R(-) enantiomers.

Successful microbubble sonothrombolysis without tissue-type plasminogen activator in a rabbit model of acute ischemic stroke

BACKGROUND AND PURPOSE

Microbubbles (MB) combined with ultrasound (US) have been shown to lyse clots without tissue-type plasminogen activator (tPA) both in vitro and in vivo. We evaluated sonothrombolysis with 3 types of MB using a rabbit embolic stroke model.

METHODS

New Zealand White rabbits (n=74) received internal carotid angiographic embolization of single 3-day-old cylindrical clots (0.6 × 4.0 mm). Groups included: (1) control (n=11) embolized without treatment; (2) tPA (n=20); (3) tPA+US (n=10); (4) perflutren lipid MB+US (n=16); (5) albumin 3 μm MB+US (n=8); and (6) tagged albumin 3 μm MB+US (n=9). Treatment began 1 hour postembolization. Ultrasound was pulsed-wave (1 MHz; 0.8 W/cm²) for 1 hour; rabbits with tPA received intravenous tPA (0.9 mg/kg) over 1 hour. Lipid MB dose was intravenous (0.16 mg/kg) over 30 minutes. Dosage of 3 μm MB was 5 × 10⁹ MB intravenously alone or tagged with eptifibatide and fibrin antibody over 30 minutes. Rabbits were euthanized at 24 hours. Infarct volume was determined using vital stains on brain sections. Hemorrhage was evaluated on hematoxylin and eosin sections.

RESULTS

Infarct volume percent was lower for rabbits treated with lipid MB+US (1.0%± 0.6%; P=0.013), 3 μm MB+US (0.7% ± 0.9%; P=0.018), and tagged 3 μm MB+US (0.8% ± 0.8%; P=0.019) compared with controls (3.5%± 0.8%). The 3 MB types collectively had lower infarct volumes (P=0.0043) than controls. Infarct volume averaged 2.2% ± 0.6% and 1.7%± 0.8% for rabbits treated with tPA alone and tPA+US, respectively (P=nonsignificant).

CONCLUSIONS

Sonothrombolysis without tPA using these MB is effective in decreasing infarct volumes. Study of human application and further MB technique development are justified.

Role of transcription factors in neurogenesis after cerebral ischemia

Studies have revealed that the adult mammalian brain has the capacity to regenerate some neurons after cerebral ischemia. And this perspective on neurogenesis adds to the conceptual framework for strategies for the repair of ischemia-induced brain injury, that is, if the effect of ischemia-induced neurogenesis is enhanced, then the recovery of brain function after stroke can be promoted. Neurogenesis is a multistep process that requires the proliferation of neural stem/progenitor cells, migration and that new cells differentiate, survive and integrate into existing neural networks. For that to occur, the same concerted action of various factors is needed, especially transcription factors which regulate the expression of many moleculars and interact with them to promote neurogenesis. This review article gives a brief overview of some transcription factors (NF-κB, Hes, STAT3, AP-1, CREB, HIF1, Pax6, Tcf/Lef, Gli, Sox2, Olig2, Dlx2, TLX, Bmi-1) in ischemia-induced neurogenesis.

Niaspan reduces high-mobility group box 1/receptor for advanced glycation endproducts after stroke in type-1 diabetic rats

OBJECTIVE

High-mobility group box 1 (HMGB1), an active receptor for advanced glycation endproducts (RAGE), functions as a potent proinflammatory cytokine-like factor that contributes to the pathogenesis of vasculature. Diabetes mellitus (DM) is associated with accelerated development of both microvascular and macrovascular disease and increases the risk of ischemic stroke. Using a model of streptozotocin-induced type-1 diabetes (T1DM) in rats, we investigated the changes in HMGB and RAGE and tested the effects of Niaspan, a slow release form of niacin, on the expression of pro-inflammatory proteins in rats after stroke.

RESEARCH DESIGN AND METHODS

T1DM rats were subjected to transient middle cerebral artery occlusion (MCAo) and treated without or with Niaspan (40 mg/kg) daily for 14 days after MCAo. Non-streptozotocin rats (WT) were also subjected to MCAo. Immunostaining for inflammatory mediators including HMGB1, RAGE, matrix metalloproteinase-9 (MMP-9) and toll-like receptor 4 (TLR4) immunostaining (n=8/group) and Western blotting (n=4/group) were performed.

RESULTS

Compared to WT-MCAo rats, T1DM-MCAo rats showed an increased expression of HMGB1 (0.82±0.07 vs. 1.81±0.98, P<0.05), RAGE (1.31±0.22 vs. 3.77±0.72, P<0.05), MMP-9 (0.74±0.08 vs. 1.61±0.09, P<0.05) and TLR4 (2.85±0.22 vs. 6.72±0.44, P<0.05) after stroke. Niaspan treatment significantly attenuated the expression of HMGB1 (1.80±0.98 vs. 1.31±0.01, P<0.05), RAGE (3.77±0.71 vs. 1.78±0.45, P<0.05), MMP-9 (1.61±0.09 vs. 0.97±0.07, P<0.05) and TLR4 (6.72±0.44 vs. 2.28±0.43, P<0.05) in the ischemic brain in T1DM-MCAo rats.

CONCLUSIONS

T1DM increases HMGB1/RAGE, TLR4 and MMP-9 expression after stroke. Niaspan treatment of stroke in T1DM rats inhibits HMGB1/RAGE, TLR4 and MMP-9 expression which may contribute to the reduced inflammatory response after stroke in T1DM rats.

C-Phycocyanin is neuroprotective against global cerebral ischemia/reperfusion injury in gerbils

Although the huge economic and social impact and the predicted incidence increase, neuroprotection for ischemic stroke remains as a therapeutically empty niche. In the present study, we investigated the rationale of the C-Phycocyanin (C-PC) treatment on global cerebral ischemia/reperfusion (I/R) injury in gerbils. We demonstrated that C-PC given either prophylactically or therapeutically was able to significantly reduce the infarct volume as assessed by triphenyltetrazolium chloride (TTC) staining and the neurological deficit score 24h post-stroke. In addition, C-PC exhibited a protective effect against hippocampus neuronal cell death, and significantly improved the functional outcome (locomotor behavior) and gerbil survival after 7 days of reperfusion. Malondialdehyde (MDA), peroxidation potential (PP) and ferric reducing ability of plasma (FRAP) were assayed in serum and brain homogenates to evaluate the redox status 24h post-stroke. The treatment with C-PC prevented the lipid peroxidation and the increase of FRAP in both tissue compartments. These results suggest that the protective effects of C-PC are most likely due to its antioxidant activity, although its anti-inflammatory and immuno-modulatory properties reported elsewhere could also contribute to neuroprotection. To our knowledge, this is the first report of the neuroprotective effect of C-PC in an experimental model of global cerebral I/R damage, and strongly indicates that C-PC may represent a potential preventive and acute disease modifying pharmacological agent for stroke therapy.

Targeting the Nrf2-Keap1 antioxidant defence pathway for neurovascular protection in stroke

Endogenous defence mechanisms by which the brain protects itself against noxious stimuli and recovers from ischaemic damage are a key target of stroke research. The loss of viable brain tissue in the ischaemic core region after stroke is associated with damage to the surrounding area known as the penumbra. Activation of the redox-sensitive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) plays a pivotal role in the cellular defence against oxidative stress via transcriptional upregulation of phase II defence enzymes and antioxidant stress proteins. Although recent evidence implicates Nrf2 in neuroprotection, it is not known whether activation of this pathway within the neurovascular unit protects the brain against blood-brain barrier breakdown and cerebrovascular inflammation. Targeting the neurovascular unit should provide novel insights for effective treatment strategies and facilitate translation of experimental findings into clinical therapy. This review focuses on the cytoprotective role of Nrf2 in stroke and examines the evidence that the Nrf2-Keap1 defence pathway may serve as a therapeutic target for neurovascular protection.

The inflammatory footprints of alcohol-induced oxidative damage in neurovascular components

Microvessels, the main components of the blood-brain barrier (BBB) are vulnerable to oxidative damage during alcohol-induced stress. Alcohol produces oxidative damage within the vessels and in the brain. Using our animal model of catheter implant into the common carotid artery (CCA), we trace the footprints of alcohol-induced oxidative damage and inflammatory process at the BBB and into the brain. The uniqueness of the finding is that ethanol causes oxidative damage in all neurovascular components by activating NADPH oxidase and inducible nitric oxide synthase in the brain. It is not the oxidants but the ethanol that traverses through the BBB because we found that the highly reactive peroxynitrite does not cross the BBB. Thus, oxidative damage is caused at the site of oxidant production in the microvessels and in the brain. Our data indicate that acetaldehyde (the primary metabolite of ethanol) is the inducer/activator of these enzymes that generate oxidants in brain neurovascular cells. Evidence for alcohol-induced BBB damage is indicated by the alterations of the tight junction protein occludin in intact microvessels. Importantly, we demonstrate that the site of BBB oxidative damage is also the site of immune cells aggregation in the microvessels, which paves the path for inflammatory footprints. These findings reveal the underlying mechanisms that ethanol-elicited BBB oxidative damage initiates the brain vascular inflammatory process, which ultimately leads to neuroinflammation.

Cellular and molecular determinants of stroke-induced changes in subventricular zone cell migration

A remarkable aspect of adult neurogenesis is that the tight regulation of subventricular zone (SVZ) neuroblast migration is altered after ischemic stroke and newborn neurons emigrate towards the injury. This phenomenon is an essential component of endogenous repair and also serves to illuminate normal mechanisms and rules that govern SVZ migration. Stroke causes inflammation that leads to cytokine and chemokine release, and SVZ neuroblasts that express their receptors are recruited. Metalloproteinases create pathways and new blood vessels provide a scaffold to facilitate neuroblast migration between the SVZ and the infarct. Most experiments have studied the peri-lesion parenchyma and relatively little is known about SVZ remodeling after stroke. Migration in the SVZ is tightly regulated by cellular interactions and molecular signaling; how are these altered after stroke to allow emigration? Do ependymal cells contribute to this process, given their reported neurogenic potential? How does stroke affect ependymal cell regulation of cerebrospinal fluid flow? Given the heterogeneity of SVZ progenitors, do all types of neuroblasts migrate out, or is this confined to specific subtypes of cells? We discuss these and other questions in our review and propose experiments to address them.

Matrix metalloproteinase inhibitors attenuate neuroinflammation following focal cerebral ischemia in mice

The aim of this study was to investigate whether matrix metalloproteinase (MMP) inhibitors attenuate neuroinflammation in an ischemic brain following photothrombotic cortical ischemia in mice. Male C57BL/6 mice were anesthetized, and Rose Bengal was systemically administered. Permanent focal ischemia was induced in the medial frontal and somatosensory cortices by irradiating the skull with cold white light. MMP inhibitors, such as doxycycline, minocycline, and batimastat, significantly reduced the cerebral infarct size, and the expressions of monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and indoleamine 2,3-dioxygenase (IDO). However, they had no effect on the expressions of heme oxygenase-1 and neuroglobin in the ischemic cortex. These results suggest that MMP inhibitors attenuate ischemic brain injury by decreasing the expression levels of MCP-1, TNF-α, and IDO, thereby providing a therapeutic benefit against cerebral ischemia.

Different expression patterns of Ngb and EPOR in the cerebral cortex and hippocampus revealed distinctive therapeutic effects of intranasal delivery of Neuro-EPO for ischemic insults to the gerbil brain

The purpose of this study was to evaluate the neuroprotective effects of intranasally delivered recombinant human neuronal erythropoietin (Neuro-EPO) on brain injury induced by unilateral permanent ischemia in the Mongolian gerbil. Expression of EPO receptor (EPOR) and neuroglobin (Ngb) over 5 weeks after intranasal treatment with Neuro-EPO was determined using immunohistochemistry. Mortality of Neuro-EPO-treated gerbils decreased after surgery, and the sensory and motor function was significantly improved. Histopathological mapping showed that Neuro-EPO significantly reduced delayed neuronal death in the brain. Expression of Ngb was upregulated in the cerebral cortex at most time points (expect for 10 min and 48 hr) and in the hippocampus at 10 min and from 48 hr to 5 weeks, whereas EPOR was almost downregulated or unchanged in the brain (expect for 48 hr). The 10 min and 48 hr seemed to be two time points for the brain to switch the expression of both Ngb and EPOR to early and late recovery phase, respectively. In addition, there were two phases, 10 min to 1 hr and 24 hr to 72 hr, respectively, closing to the "golden hour" of about 60 min and the "silver day" of 1 to 3 days, for the brain to recover from stroke onset with intranasal Neuro-EPO treatment. Therefore, the results suggest that the intranasal administration of Neuro-EPO is effective in the treatment of acute brain ischemia. The different expression patterns of Ngb and EPOR is probably due to ischemic tolerance in the cerebral cortex and ischemic sensitivity in the hippocampus.

Treating inflammation in childhood neurodegenerative disorders

Inflammation of the central nervous system is a prominent feature in many childhood neurodegenerative conditions, with various studies demonstrating the upregulation of the innate and adaptive immune system. Recent evidence also suggests that this inflammatory process can contribute to further neurodegeneration. Furthermore, immunosuppression in mouse models of a few lysosomal storage disorders has demonstrated that attenuation of this immune response can influence the clinical and neuropathological progression. However, there are significant challenges before this finding translates to patient care. Treating inflammation in neurodegenerative conditions requires the identification of the time point when inflammation becomes pathogenic, after which the safest therapeutic strategies are required to target the various components and confounders of inflammation. Nevertheless, as the progress made towards effective gene-, cellular-, and enzyme-based therapy in most of these disorders has been disappointing, treating pathogenic inflammation may offer the clinician another therapeutic strategy in managing these devastating disorders.

Mildronate treatment improves functional recovery following middle cerebral artery occlusion in rats

Mildronate (3-(2,2,2-trimethylhydrazinium) propionate) is an inhibitor of l-carnitine biosynthesis and an anti-ischemic drug. In the present study, we investigated the effects of mildronate in rats following focal cerebral ischemia. Male Wistar rats were subjected to transient occlusion of the middle cerebral artery (MCAO) for 90min, followed by the intraperitoneal administration of mildronate at doses of 100 and 200mg/kg 2h after reperfusion and then daily for an additional 14days. The beam-walking, rota-rod and cylinder tests were used to assess sensorimotor function, and vibrissae-evoked forelimb-placing and limb-placing tests examined responses to tactile and proprioceptive stimulation. Following behavioural testing, the infarct volume was measured. The cerebellar concentrations of l-carnitine, γ-butyrobetaine (GBB) and mildronate were also measured. The results showed that saline-treated MCAO rats had minor or no spontaneous recovery in sensorimotor and proprioceptive function up to 14days post-stroke. Treatment with mildronate at a dose of 200mg/kg was found to accelerate recovery of motor and proprioceptive deficits in limb-placing, cylinder and beam-walking tests. Analysis of rat cerebellar tissue extracts revealed that l-carnitine and GBB concentrations changed with mildronate treatment; the concentration of l-carnitine was significantly decreased by mildronate treatment, whereas the concentration of GBB was significantly increased. Cerebellar concentrations of mildronate also increased in a dose-dependent manner following systemic administration. Infarct size did not differ among the experimental groups on post-stroke day 14. The present study suggests that mildronate treatment improves the functional outcome in MCAO rats without influencing infarct size.

A global transcriptomic view of the multifaceted role of glutathione peroxidase-1 in cerebral ischemic-reperfusion injury

Transient cerebral ischemia often results in secondary ischemic/reperfusion injury, the pathogenesis of which remains unclear. This study provides a comprehensive, temporal description of the molecular events contributing to neuronal injury after transient cerebral ischemia. Intraluminal middle cerebral artery occlusion (MCAO) was performed to induce a 2-h ischemia with reperfusion. Microarray analysis was then performed on the infarct cortex of wild-type (WT) and glutathione peroxidase-1 (a major antioxidant enzyme) knockout (Gpx1(-/-)) mice at 8 and 24h postreperfusion to identify differential gene expression profile patterns and potential alternative injury cascades in the absence of Gpx1, a crucial antioxidant enzyme, in cerebral ischemia. Genes with at least ±1.5-fold change in expression at either time point were considered significant. Global transcriptomic analyses demonstrated that 70% of the WT-MCAO profile overlapped with that of Gpx1(-/-)-MCAO, and 28% vice versa. Critical analysis of the 1034 gene probes specific to the Gpx1(-/-)-MCAO profile revealed regulation of additional novel pathways, including the p53-mediated proapoptotic pathway and Fas ligand (CD95/Apo1)-mediated pathways; downplay of the Nrf2 antioxidative cascade; and ubiquitin-proteasome system dysfunction. Therefore, this comparative study forms the foundation for the establishment of screening platforms for target definition in acute cerebral ischemia intervention.

Glibenclamide ameliorates ischemia-reperfusion injury via modulating oxidative stress and inflammatory mediators in the rat hippocampus

Stroke remains a debilitating disease with high incidence of morbidity and mortality, where many reports provide promising venues for prevention/treatment of such ailment. Glibenclamide, a selective blocker of KATP channels, was reported to protect against ischemia and ischemia-reperfusion (IR) injury in several experimental models. Hence, the present study aimed to investigate the possible involvement of free radicals as well as inflammatory and anti-inflammatory mediators in the hippocampus of rats exposed to IR. To this end, male Wistar rats were divided into 3 groups: group I served as sham operated controls; group II was subjected to 15 min ischemia by occlusion of both common carotid arteries, followed by 60 min reperfusion; group III was injected with glibenclamide (1mg/kg, i.p.) 10 min before ischemic-reperfusion injury. IR increased lipid peroxides, myeloperoxidase activity, TNF-α and PGE(2), while decreasing glutathione, total antioxidant capacity, nitric oxide and IL-10 levels in the hippocampus. Glibenclamide reversed all the former alterations, thus highlighting a potential therapeutic utility for this sulphonyl urea in IR brain injury via modulating oxidative stress and inflammatory mediators.

Granzymes A and B levels in serum of patients with amyotrophic lateral sclerosis

OBJECTIVES

There are evidences that immuno-inflammatory mechanisms and apoptosis may play a role in the pathophysiology of amyotrophic lateral sclerosis (ALS). It is known that Granzyme A (GzmA) and granzyme B (GzmB) are implicated in these mechanisms. The aim of the study was to investigate serum GzmA and GzmB levels in patients with ALS.

DESIGN AND METHODS

The study included 30 patients with ALS and 30 patients from the control group. Serum GzmA and GzmB levels were measured using the enzyme-linked immunosorbent method.

RESULTS

The study showed that GzmA and GzmB levels are significantly increased in serum of patients with ALS when compared to the control group (p<0.05). There was a significant correlation of serum GzmB levels with severity of clinical state of ALS patients (p<0.05).

CONCLUSION

The results indicate that GzmA and GzmB are implicated in mechanisms of neurodegeneration in ALS.

Alcohol-induced exacerbation of ischemic brain injury: role of NAD(P)H oxidase

BACKGROUND

 Chronic alcohol consumption increases ischemic stroke and exacerbates ischemic brain injury. We determined the role of NAD(P)H oxidase in exacerbated ischemic brain injury during chronic alcohol consumption.

METHODS

 Sprague Dawley rats were fed a liquid diet with or without alcohol (6.4% v/v) for 8 weeks. We measured the effect of apocynin on 2-hour middle cerebral artery occlusion (MCAO)/24-hour reperfusion-induced brain injury. In addition, superoxide production and expression of NAD(P)H oxidase subunit, gp91phox, in the peri-infarct area were assessed.

RESULTS

Chronic alcohol consumption produced a larger infarct volume, worse neurological score, and higher superoxide production. Acute (5 mg/kg, ip, 30 minutes before MCAO) and chronic treatment with apocynin (7.5 mg/kg/d in the diet, 4 weeks prior to MCAO) reduced infarct volume, improved neurological outcome, and attenuated superoxide production in alcohol-fed rats. Expression of gp91phox at basal conditions and following ischemia/reperfusion was greater in alcohol-fed rats compared to non-alcohol-fed rats. In addition, neurons are partially responsible for upregulated gp91phox during alcohol consumption.

CONCLUSIONS

Our findings suggest that NAD(P)H oxidase may play an important role in exacerbated ischemic brain injury during chronic alcohol consumption.

The scavenger receptor CD36 contributes to the neurotoxicity of bone marrow-derived monocytes through peroxynitrite production

CD36, a class B scavenger receptor present in microglia, endothelium and leukocytes, plays a key role in ischemic brain injury by promoting the expression of inflammatory genes and production of reactive oxygen species (ROS). However, it is not known whether ischemic brain damage is mediated by CD36 activation in resident brain cells, i.e., microglia, or by blood-borne cells that infiltrate the brain. To address this question, we studied oxygen-glucose deprivation (OGD) in hippocampal slice cultures, a model of ischemic injury that does not involve cells extrinsic to the brain. We found that CD36 gene knockout does not afford protection of hippocampal slices to OGD-induced cytotoxicity. In contrast, immunoactivated bone marrow-derived monocytes-macrophages (BMM) from wild type (WT) mice trigger hippocampal damage when incubated with brain slices via a mechanism that is prevented in CD36-/- BMM. The neurotoxic activity of CD36+/+ BMM was attributed to reactive oxygen species (ROS) since it was concomitant with increased ROS production and could be prevented by treatment with a selective ROS scavenger, MnTBAP, or a peroxynitrite decomposition catalyst, FeTPPS. Importantly, ROS production and accumulation 3-nitrotyrosine in hippocampal proteins (a hallmark of peroxynitrite production) was significantly dampened in immunoactivated CD36-/- BMM, whereas production of NO-derived metabolites (nitrite and nitrate) was unaltered. We conclude that CD36 signaling may not contribute to injury induced by OGD in the brain itself but is involved in the neurotoxicity mediated by activated BMM. These findings are consistent with the hypothesis that CD36 in infiltrating inflammatory cells drives peroxynitrite-mediated ischemic brain damage. Accordingly, targeting CD36 in the vascular compartment may protect against neurotoxicity in the ischemic brain.

Cocaine-and amphetamine-regulated transcript modulates peripheral immunity and protects against brain injury in experimental stroke

Ischemic stroke can induce immediate activation and later inhibition of the peripheral immune system which may contribute to a worse outcome. Cocaine-and amphetamine-regulated transcript (CART) peptides have been reported to have neuroprotective and immunomodulatory effects in various cell and animal experimental models, respectively. In this study, CART's role in experimental stroke and the relevant immune-regulating mechanisms was investigated. In male C57BL/6 mice subjected to 120 min of middle cerebral artery occlusion (MCAO), with or without CART treatment or sham operation, peripheral immune parameters and serum catecholamins (CAs) were analyzed. CART reduced blood CD4(+)/CD8(+) ratio and pro-inflammatory cytokine expression in MCAO mice at 24 h, while upregulated spleen CD4(+)/CD8(+) ratio and enhanced anti-inflammatory cytokines expressions in MCAO mice at 96 h. In addition, in comparison to control mice, CART-treated mice demonstrated elevated serum CAs at 6 and 24 h, whereas reduced serum levels of CAs and blood regulatory T (Treg) cells at 96 h. The cytokine expression, infarct volume and neurological deficits in mouse brain were also measured. CART reduced post-stroke infarct volume and improved neurological functions, with reduced expression of inflammatory factors in the injured brain. Findings indicate that CART plays an important role in modulating post-stroke immune response and exerts a neuroprotective effect in experimental stroke. Findings also suggest that the possible mechanism of CART's protective action in stroke is the regulation of the sympathetic nervous system (SNS) pathway since CAs, Treg cells and interleukin (IL)-10 are the major modulators of SNS.

Long-term behavioral assessment of function in an experimental model for ischemic stroke

Middle cerebral artery occlusion (MCAO) in rats is a well-studied experimental model for ischemic stroke leading to brain infarction and functional deficits. Many preclinical studies have focused on a small time window after the ischemic episode to evaluate functional outcome for screening therapeutic candidates. Short evaluation periods following injury have led to significant setbacks due to lack of information on the delayed effects of treatments, as well as short-lived and reversible neuroprotection, so called false-positive results. In this report, we evaluated long-term functional deficit for 90 days after MCAO in two rat strains with two durations of ischemic insult, in order to identify the best experimental paradigm to assess injury and subsequent recovery. Behavioral outcomes were measured pre-MCAO followed by weekly assessment post-stroke. Behavioral tests included the 18-point composite neurological score, 28-point neuroscore, rearing test, vibrissae-evoked forelimb placing test, foot fault test and the CatWalk. Brain lesions were assessed to correlate injury to behavior outcomes at the end of study. Our results indicate that infarction volume in Sprague-Dawley rats was dependent on occlusion duration. In contrast, the infarction volume in Wistar rats did not correlate with the duration of ischemic episode. Functional outcomes were not dependent on occlusion time in either strain; however, measurable deficits were detectable long-term in limb asymmetry, 18- and 28-point neuroscores, forelimb placing, paw swing speed, and gait coordination. In conclusion, these behavioral assays, in combination with an extended long-term assessment period, can be used for evaluating therapeutic candidates in preclinical models of ischemic stroke.

Translati onal challenges of neuroprotection strategy in ischemic stroke

Neuroprotection is a therapeutic strategy that attempts to save neurons from irreversible injury by modifying the effects of the ischemic cascade or facilitating reperfusion. Although numerous agents have shown neuroprotective effect in preclinical trials, their translation to clinical trials failed to show any meaningful effect. The Stroke Therapy Academic Industry Roundtable (STAIR) guidelines were made for performing research on neuroprotective agents in pre-clinical and clinical trials. Although the STAIR guidelines have been available for more than ten years, we still do not have any adequate neuroprotective agents. Reasons for unsuccessful translation from preclinical to clinical research can be considered along stages of drug development: 1) preclinical, 2) transitional and 3) clinical. By extending the therapeutic window for application of intravenous thrombolysis in acute stroke patients to 4.5 hours, as well as increasing the use intra-arterial thrombolysis and development of mechanical devices for thrombectomy in 6 hour period we may be able to achieve some degree of neuroprotection in acute stroke. Future therapy is likely to add to the current thrombolytic therapy with potential neuroprotective drugs or procedures.

Vascular Protection Following Cerebral Ischemia and Reperfusion

Despite considerable research that has contributed to a better understanding of the pathophysiology of stroke, translation of this knowledge into effective therapies has largely failed. The only effective treatment for ischemic stroke is rapid recanalization of an occluded vessel by dissolving the clot with tissue plasminogen activator (tPA). However, stroke adversely affects vascular function as well that can cause secondary brain injury and limit treatment that depends on a patent vasculature. In middle cerebral arteries (MCA), ischemia/reperfusion (I/R) cause loss of myogenic tone, vascular paralysis, and endothelial dysfunction that can lead to loss of autoregulation. In contrast, brain parenchymal arterioles retain considerable tone during I/R that likely contributes to expansion of the infarct into the penumbra. Microvascular dysregulation also occurs during ischemic stroke that causes edema and hemorrhage, exacerbating the primary insult. Ischemic injury of vasculature is progressive with longer duration of I/R. Early postischemic reperfusion has beneficial effects on stroke outcome but can impair vascular function and exacerbate ischemic injury after longer durations of I/R. This review focuses on current knowledge on the effects of I/R on the structure and function of different vascular segments in the brain and highlight some of the more promising targets for vascular protection.

Targeting the melanocortin receptor system for anti-stroke therapy

The melanocortin receptors are a subfamily of G-protein-coupled, rhodopsin-like receptors that are rapidly being acknowledged as an extremely promising target for pharmacological intervention in a variety of different inflammatory pathologies, including stroke. Stroke continues to be a leading cause of death worldwide, with risk factors including smoking, diabetes, hypertension and obesity. The pathophysiology of stroke is highly complex: reintroduction of blood flow to the infarcted brain region is paramount in limiting ischaemic damage caused by stroke, yet a concomitant inflammatory response can compound tissue damage. The possibilities of pro-resolving treatments that target this inflammatory response have only recently begun to be explored. This review discusses the endogenous roles of the melanocortin system in reducing characterized aspects of inflammation, and how these, together with potent neuroprotective actions, suggest its potential as a therapeutic target in stroke.

Modulation of NADPH oxidase activation in cerebral ischemia/reperfusion injury in rats

NADPH oxidase is a major complex that produces reactive oxygen species (ROSs) during the ischemic period and aggravates brain damage and cell death after ischemic injury. Although many approaches have been tested for preventing production of ROSs by NADPH oxidase in ischemic brain injury, the regulatory mechanisms of NADPH oxidase activity after cerebral ischemia are still unclear. The aim of this study is identifying apocynin as a critical modulator of NADPH oxidase and elucidating its role as a neuroprotectant in an experimental model of brain ischemia in rat. Treatment of apocynin 5min before of reperfusion attenuated cerebral ischemia in rats. Administration of apocynin showed marked reduction in infarct size compared with that of control rats. Medial carotid artery occlusion (MCAo)-induced cerebral ischemia was also associated with an increase in, nitrotyrosine formation, as well as IL-1β expression, IκB degradation and ICAM expression in ischemic regions. These expressions were markedly inhibited by the treatment of apocynin. We also demonstrated that apocynin reduces levels of apoptosis (TUNEL, Bax and Bcl-2 expression) resulting in a reduction in the infarct volume in ischemia-reperfusion brain injury. This new understanding of apocynin induced adaptation to ischemic stress and inflammation could suggest novel avenues for clinical intervention during ischemic and inflammatory diseases.

Lesional expression of EMAPII in macrophages/microglia following cerebral ischemia in rats

OBJECTIVE

Cerebral ischemia triggers acute inflammation, which exacerbates primary brain damage. Characterization of cytokine expression to the early damaged tissue might aid in further understanding of lesion development and contribute to definition of molecular targets for selective immunotherapy. Endothelial monocyte-activating polypeptide II (EMAPII) is a proinflammatory, antiangiogenic cytokine whose expression following cerebral ischemia remained unknown. Therefore, we studied the spatiotemporal expression of EMAPII in early brain lesions after cerebral ischemia-reperfusion injury.

METHODS

Unilateral transient focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 1 hr followed by different reperfusion periods using male Sprague-Dawley rats. Subsequently, rats were sacrificed on Day 1, 3, 5, or 7 following surgery. EMAPII expression was investigated by immunohistochemistry.

RESULTS

EMAPII-positive cell accumulation was observed as early as Day 1 postreperfusion and increased steadily. Significant accumulation of EMAPII-positive cells was seen in lesion and penumbra areas but not in the translateral hemisphere. Both amoeboid and ramified EMAPII-positive cells were observed and mainly localized to lesion and penumbra areas, respectively.

CONCLUSION

The known pathological functions together with abundant cellular accumulation in cerebral ischemia lesions suggest that EMAPII might contribute to pathophysiological consequences of cerebral ischemia.

The dual role of the neuroinflammatory response after ischemic stroke: modulatory effects of hypothermia

Neuroinflammation is a key element in the ischemic cascade after cerebral ischemia that results in cell damage and death in the subacute phase. However, anti-inflammatory drugs do not improve outcome in clinical settings suggesting that the neuroinflammatory response after an ischemic stroke is not entirely detrimental. This review describes the different key players in neuroinflammation and their possible detrimental and protective effects in stroke. Because of its inhibitory influence on several pathways of the ischemic cascade, hypothermia has been introduced as a promising neuroprotective strategy. This review also discusses the influence of hypothermia on the neuroinflammatory response. We conclude that hypothermia exerts both stimulating and inhibiting effects on different aspects of neuroinflammation and hypothesize that these effects are key to neuroprotection.

Deletion of mitochondrial uncoupling protein-2 increases ischemic brain damage after transient focal ischemia by altering gene expression patterns and enhancing inflammatory cytokines

Mitochondrial hyperpolarization inhibits the electron transport chain and increases incomplete reduction of oxygen, enabling production of reactive oxygen species (ROS). The consequence is mitochondrial damage that eventually causes cell death. Uncoupling proteins (UCPs) are inner mitochondrial membrane proteins that dissipate the mitochondrial proton gradient by transporting H(+) across the inner membrane, thereby stabilizing the inner mitochondrial membrane potential and reducing the formation of ROS. The role of UCP2 in neuroprotection is still in debate. This study seeks to clarify the role of UCP2 in transient focal ischemia (tFI) and to further understand the mechanisms of ischemic brain damage. Both wild-type and UCP2-knockout mice were subjected to tFI. Knocking out UCP2 significantly increased the infarct volume to 61% per hemisphere as compared with 18% in wild-type animals. Knocking out UCP2 suppressed antioxidant, cell-cycle, and DNA repair genes, including Sod1 and Sod2, Gstm1, and cyclins. Furthermore, knocking out UCP2 significantly upregulated the protein levels of the inflammatory cytokines, including CTACK, CXCL16, Eotaxin-2, fractalkine, and BLC. It is concluded that knocking out the UCP2 gene exacerbates neuronal death after cerebral ischemia with reperfusion and this detrimental effect is mediated by alteration of antioxidant genes and upregulation of inflammatory mediators.

Targeting astrocytes for stroke therapy

Stroke remains a major health problem and is a leading cause of death and disability. Past research and neurotherapeutic clinical trials have targeted the molecular mechanisms of neuronal cell death during stroke, but this approach has uniformly failed to reduce stroke-induced damage or to improve functional recovery. Beyond the intrinsic molecular mechanisms inducing neuronal death during ischemia, survival and function of astrocytes is absolutely required for neuronal survival and for functional recovery after stroke. Many functions of astrocytes likely improve neuronal viability during stroke. For example, uptake of glutamate and release of neurotrophins enhances neuronal viability during ischemia. Under certain conditions, however, astrocyte function may compromise neuronal viability. For example, astrocytes may produce inflammatory cytokines or toxic mediators, or may release glutamate. The only clinical neurotherapeutic trial for stroke that specifically targeted astrocyte function focused on reducing release of S-100β from astrocytes, which becomes a neurotoxin when present at high levels. Recent work also suggests that astrocytes, beyond their influence on cell survival, also contribute to angiogenesis, neuronal plasticity, and functional recovery in the several days to weeks after stroke. If these delayed functions of astrocytes could be targeted for enhancing stroke recovery, it could contribute importantly to improving stroke recovery. This review focuses on both the positive and the negative influences of astrocytes during stroke, especially as they may be targeted for translation to human trials.

Neuroprotective effect of astaxanthin on H(2)O(2)-induced neurotoxicity in vitro and on focal cerebral ischemia in vivo

Astaxanthin (AST) is a powerful antioxidant that occurs naturally in a wide variety of living organisms. Much experimental evidence has proved that AST has the function of eliminating oxygen free radicals and can protect organisms from oxidative damage. The present study was carried out to further investigate the neuroprotective effect of AST on oxidative stress induced toxicity in primary culture of cortical neurons and on focal cerebral ischemia-reperfusion induced brain damage in rats. AST, over a concentration range of 250-1000nM, attenuated 50μM H(2)O(2)-induced cell viability loss. 500nM AST pretreatment significantly inhibited H(2)O(2)-induced apoptosis measured by Hoechst 33342 staining and restored the mitochondrial membrane potential (MMP) measured by a fluorescent dye, Rhodamine 123. In vivo, AST prevented cerebral ischemic injury induced by 2h middle cerebral artery occlusion (MCAO) and 24h reperfusion in rats. Pretreatment of AST intragastrically twice at 5h and 1h prior to ischemia dramatically diminished infarct volume and improved neurological deficit in a dose-dependent manner. Nissl staining showed that the neuronal injury was significantly improved by pretreatment of AST at 80mg/kg. Taken together, these results suggest that pretreatment with AST exhibits noticeable neuroprotection against brain damage induced by ischemia-reperfusion and the antioxidant activity of AST maybe partly responsible for it.

Oxygen toxicity: chemistry and biology of reactive oxygen species

Oxygen has a central role in the evolution of complex life on Earth mainly because of the biochemical symmetry of oxygenic photosynthesis and aerobic respiration that can maintain homeostasis within our planet biosphere. Oxygen can also produce toxic molecules, reactive oxygen species (ROS). ROS is a collective term that includes both oxygen radicals and certain oxidizing agents that are easily converted into radicals. They can be produced from both endogenous and exogenous substances. ROS play a dual role in biological systems, since they can be either harmful or beneficial to living systems. They can be considered a double-edged sword because on the one hand oxygen-dependent reactions and aerobic respiration have significant advantages but, on the other, overproduction of ROS has the potential to cause damage.

Baicalein is neuroprotective in rat MCAO model: role of 12/15-lipoxygenase, mitogen-activated protein kinase and cytosolic phospholipase A2

Inflammatory damage and oxidative stress play an important role in cerebral ischemic pathogenesis and may represent a target for treatment. Baicalein, isolated from the traditional Chinese herbal medicine Huangqin, is an antioxidant and anti-inflammatory agent on one hand and a lipoxygenase inhibitor on the other hand. However, little is known regarding the mechanism of baicalein's neuroprotection in ischemic stroke. We therefore investigated the potential neuroprotective effects of baicalein and explored the underlying mechanisms. Male, Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO) and baicalein was administered intravenously immediately after cerebral ischemia. At 24h after MCAO neurological deficit, brain water content and infarct sizes were measured. Immunohistochemistry, western blot and reverse transcription-polymerase chain reaction (RT-PCR) were used to analyse the expression of 12/15-lipoxygenase (12/15-LOX), p38 mitogen-activated protein kinase (p38 MAPK) and cytosolic phospholipase A2 (cPLA2) at gene and protein levels in ischemic brain cortex. The results showed that baicalein improved neurological deficit, reduced brain water content and infarct sizes, and downregulated the overexpression of 12/15-LOX, p38 MAPK and cPLA2 typically seen with MCAO. The results indicated that baicalein protected the brain from damage caused by MCAO, and this effect may be through downregulation of 12/15-LOX, p38 MAPK and cPLA2 expression.

Neuroprotection and underlying mechanisms of oxymatrine in cerebral ischemia of rats

OBJECTIVES

Oxymatrine, extracted from a traditional Chinese herb, Sophora flavescens Ait, has shown a variety of pharmacological actions. Recently, we have proved that oxymatrine protected brain from ischemic damage. However, little is known about the exact mechanisms of this effect. This study is to investigate the potential neuroprotection of oxymatrine and explore the underlying mechanisms.

METHODS

Male Sprague-Dawley rats were subjected to acute permanent middle cerebral artery occlusion (MCAO). Oxymatrine was administered immediately after cerebral ischemia. At 24 hours after MCAO, brain water content and infarct volume were measured. The expression of 12/15-lipoxygenase (12/15-LOX), p38 mitogen-activated protein kinase (p38 MAPK), phosphorylated p38 MAPK (phospho-p38 MAPK), and cytosolic phospholipase A2 (cPLA2) was measured by immunohistochemistry, western blot and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Compared with MCAO group, oxymatrine dramatically reduced brain water content (P<0.05) and infarct volume (P<0.05). Consistent with these indices, the overexpressions of 12/15-LOX, phospho-p38 MAPK, and cPLA2 were significantly decreased in oxymatrine group. But the expression of p38 MAPK was not affected at the mRNA level.

CONCLUSIONS

Oxymatrine protected the brain from damage caused by MCAO; this effect may be through down-regulation of 12/15-LOX, phospho-p38 MAPK, and cPLA2, but not through down-regulation of p38 MAPK.

Therapeutic Potential of Non-Psychotropic Cannabidiol in Ischemic Stroke

Cannabis contains the psychoactive component delta⁹-tetrahydrocannabinol (delta⁹-THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta⁹-THC and other cannabinoid CB₁ receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta⁹-THC also mediates psychological effects through the activation of the CB₁ receptor in the central nervous system. In addition to the CB₁ receptor agonists, cannabis also contains therapeutically active components which are CB₁ receptor independent. Of the CB₁ receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB₁ receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.

Z-ligustilide attenuates lipopolysaccharide-induced proinflammatory response via inhibiting NF-kappaB pathway in primary rat microglia

AIM

To investigate the anti-inflammatory effect of Z-ligustilide (LIG) on lipopolysaccharide (LPS)-activated primary rat microglia.

METHODS

Microglia were pretreated with LIG 1 h prior to stimulation with LPS (1 microg/mL). After 24 h, cell viability was tested with MTT, nitric oxide (NO) production was assayed with Griess reagent, and the content of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and monocyte chemoattractant protein (MCP-1) was measured with ELISA. Protein expression of the nuclear factor-kappaB (NF-kappaB) p65 subunit, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) was detected with immunocytochemistry 1 h or 24 h after LPS treatment.

RESULTS

LIG showed a concentration-dependent anti-inflammatory effect in LPS-activated microglia, without causing cytotoxicity. Pretreatment with LIG at 2.5, 5, 10, and 20 micromol/L decreased LPS-induced NO production to 75.9%, 54.4%, 43.1%, and 47.6% (P<0.05 or P< 0.01), TNF-alpha content to 86.2%, 68.3%, 40.1%, and 39.9% (P<0.01, with the exception of 86.2% for 2.5 micromol/L LIG), IL-1beta content to 31.5%, 27.7%, 0.6%, and 0% (P<0.01), and MCP-1 content to 84.4%, 50.3%, 45.1%, and 42.2% (P<0.05 or P<0.01), respectively, compared with LPS treatment alone. LIG (10 micromol/L) significantly inhibited LPS-stimulated immunoreactivity of activated NF-kappaB, COX-2, and iNOS (P<0.01 vs LPS group).

CONCLUSION

LIG exerted a potent anti-inflammatory effect on microglia through inhibition of NF-kappaB pathway. The data provide direct evidence of the neuroprotective effects of LIG and the potential application of LIG for the treatment of the neuroinflammatory diseases characterized by excessive microglial activation.

Towards a dynamical network view of brain ischemia and reperfusion. Part IV: additional considerations

The general failure of neuroprotectants in clinical trials of ischemic stroke points to the possibility of a fundamental blind spot in the current conception of ischemic brain injury, the "ischemic cascade". This is the fourth in a series of four papers whose purpose is to work towards a revision of the concept of brain ischemia by applying network concepts to develop a bistable model of brain ischemia. Here we consider additional issues to round out and close out this initial presentation of the bistable network view of brain ischemia. Initial considerations of the network architecture underlying the post-ischemic state space are discussed. Network and differential equation models of brain ischemia are compared. We offer a first look at applying the bistable model to focal cerebral ischemia. The limitations of the present formulation of the bistable model are discussed. This work concludes with a series of questions by which to direct future efforts.