Expression of nitric oxide synthase (NOS)-2 following permanent focal ischemia and the role of nitric oxide in infarct generation in male, female and NOS-2 gene-deficient mice

Depletion of Arg1-Positive Microglia/Macrophages Exacerbates Cerebral Ischemic Damage by Facilitating the Inflammatory Response

Stroke is a serious worldwide disease that causes death and disability, more than 80% of which is ischemic stroke. The expression of arginase 1 (Arg1), a key player in regulating nitrogen homeostasis, is altered in the peripheral circulation after stroke. Growing evidence indicates that ischemic stroke also induces upregulated Arg1 expression in the central nervous system, especially in activated microglia and macrophages. This implies that Arg1 may affect stroke progression by modulating the cerebral immune response. To investigate the effect of Arg1+ microglia/macrophages on ischemic stroke, we selectively eliminated cerebral Arg1+ microglia/macrophages by mannosylated clodronate liposomes (MCLs) and investigated their effects on behavior, neurological deficits, and inflammatory responses in mice after ischemic stroke. More than half of Arg1+ cells, mainly Arg1+ microglia/macrophages, were depleted after MCLs administration, resulting in a significant deterioration of motility in mice. After the elimination of Arg1+ microglia/macrophages, the infarct volume expanded and neuronal degenerative lesions intensified. Meanwhile, the absence of Arg1+ microglia/macrophages significantly increased the production of pro-inflammatory cytokines and suppressed the expression of anti-inflammatory factors, thus profoundly altering the immune microenvironment at the lesion site. Taken together, our data demonstrate that depletion of Arg1+ microglia/macrophages exacerbates neuronal damage by facilitating the inflammatory response, leading to more severe ischemic injury. These results suggest that Arg1+ microglia/macrophages, as a subpopulation regulating inflammation, is beneficial in controlling the development of ischemia and promoting recovery from injury. Regulation of Arg1 expression on microglia/macrophages at the right time may be a potential target for the treatment of ischemic brain injury.

Depletion of iNOS-positive inflammatory cells decelerates neuronal degeneration and alleviates cerebral ischemic damage by suppressing the inflammatory response

Ischemic stroke leads to neuronal damage and severe inflammation that activate iNOS expression in different cell types, especially inflammatory cells in the brain. It is shown that NO released from iNOS contributes to the pathological development of cerebral ischemia. However, the role of these iNOS-expressing inflammatory cells in ischemic stroke has not been fully elucidated. Our purpose is to test if ischemia-induced iNOS⁺ inflammatory cells may exaggerate cerebral inflammation to exacerbate neuronal deficit. We studied the dynamics of iNOS⁺ cells after stroke and found an early and sustained iNOS expression at lesion site. Since iNOS is highly expressed in inflammatory cells after injury, we depleted the iNOS ⁺ inflammatory cells via the selective scavenger GdCl₃, and investigated its effect on stroke outcome, neuronal and vascular deficit, and inflammatory response. After GdCl₃ treatment, half of iNOS⁺ inflammatory cells were depleted, including mainly activated microglia/macrophages and some astrocytes. Selective depletion of iNOS⁺ inflammatory cells resulted in a pronounced reduction in brain damage, resulting in improvement of motor ability. Histologic studies and in vivo two-photon imaging data revealed a slowdown of neuronal degeneration after the depletion of iNOS⁺ inflammatory cells. In contrast to iNOS inhibition alone, depletion of iNOS⁺ inflammatory cells profoundly altered the immune microenvironment profile, in addition to reducing NO production. qRT-PCR analysis showed that depletion of iNOS⁺ inflammatory cells significantly restrained the production of pro-inflammatory cytokines, which moderated the immune microenvironment at the lesion site. Taken together, our data demonstrate that depleting iNOS⁺ inflammatory cells prevents neuronal damage not only by inhibiting NO, but also importantly by suppressing the inflammatory response, which is beneficial to ischemic injury. These results provide evidence that iNOS⁺ inflammatory cells, as a vital source of pro-inflammatory cytokines, contribute to the development of ischemic damage and could be a potential therapeutic target for the treatment of ischemia.

An Overview of Stroke: Mechanism, In vivo Experimental Models Thereof, and Neuroprotective Agents

BACKGROUND

Stroke is one of the causes of death and disability globally. Brain attack is because of the acute presentation of stroke, which highlights the requirement for decisive action to treat it.

OBJECTIVE

The mechanism and in-vivo experimental models of stroke with various neuroprotective agents are highlighted in this review.

METHOD

The damaging mechanisms may proceed by rapid, nonspecific cell lysis (necrosis) or by the active form of cell death (apoptosis or necroptosis), depending upon the duration and severity and of the ischemic insult.

RESULTS

Identification of injury mediators and pathways in a variety of experimental animal models of global cerebral ischemia has directed to explore the target-specific cytoprotective strategies, which are critical to clinical brain injury outcomes.

CONCLUSION

The injury mechanism, available encouraging medicaments thereof, and outcomes of natural and modern medicines for ischemia have been summarized. In spite of available therapeutic agents (thrombolytics, calcium channel blockers, NMDA receptor antagonists and antioxidants), there is a need for an ideal drug for strokes.

Specific depletion of resident microglia in the early stage of stroke reduces cerebral ischemic damage

BACKGROUND

Ischemia can induce rapid activation of microglia in the brain. As key immunocompetent cells, reactive microglia play an important role in pathological development of ischemic stroke. However, the role of activated microglia during the development of ischemia remains controversial. Thus, we aimed to investigate the function of reactive microglia in the early stage of ischemic stroke.

METHODS

A Rose Bengal photothrombosis model was applied to induce targeted ischemic stroke in mice. CX3CR1^CreER:R26^iDTR mice were used to specifically deplete resident microglia through intragastric administration of tamoxifen (Ta) and intraperitoneal injection of diphtheria toxin (DT). At day 3 after ischemic stroke, behavioral tests were performed. After that, mouse brains were collected for further histological analysis and detection of mRNA expression of inflammatory factors.

RESULTS

The results showed that specific depletion of microglia resulted in a significant decrease in ischemic infarct volume and improved performance in motor ability 3 days after stroke. Microglial depletion caused a remarkable reduction in the densities of degenerating neurons and inducible nitric oxide synthase positive (iNOS⁺) cells. Importantly, depleting microglia induced a significant increase in the mRNA expression level of anti-inflammatory factors TGF-β1, Arg1, IL-10, IL-4, and Ym1 as well as a significant decline of pro-inflammatory factors TNF-α, iNOS, and IL-1β 3 days after stroke.

CONCLUSIONS

These results suggest that activated microglia is an important modulator of the brain's inflammatory response in stroke, contributing to neurological deficit and infarct expansion. Modulation of the inflammatory response through the elimination of microglia at a precise time point may be a promising therapeutic approach for the treatment of cerebral ischemia.

Neuroinflammatory mechanisms of blood-brain barrier damage in ischemic stroke

As part of the neurovascular unit, the blood-brain barrier (BBB) is a unique, dynamic regulatory boundary that limits and regulates the exchange of molecules, ions, and cells between the blood and the central nervous system. Disruption of the BBB plays an important role in the development of neurological dysfunction in ischemic stroke. Blood-borne substances and cells have restricted access to the brain due to the presence of tight junctions between the endothelial cells of the BBB. Following stroke, there is loss of BBB tight junction integrity, leading to increased paracellular permeability, which results in vasogenic edema, hemorrhagic transformation, and increased mortality. Thus, understanding principal mediators and molecular mechanisms involved in BBB disruption is critical for the development of novel therapeutics to treat ischemic stroke. This review discusses the current knowledge of how neuroinflammation contributes to BBB damage in ischemic stroke. Specifically, we provide an updated overview of the role of cytokines, chemokines, oxidative and nitrosative stress, adhesion molecules, matrix metalloproteinases, and vascular endothelial growth factor as well as the role of different cell types in the regulation of BBB permeability in ischemic stroke.

An alternative surgical approach reduces variability following filament induction of experimental stroke in mice

Animal models are essential for understanding the pathology of stroke and investigating potential treatments. However, in vivo stroke models are associated, particularly in mice, with high variability in lesion volume. We investigated whether a surgical refinement where reperfusion is not reliant on the Circle of Willis reduced outcome variability. Mice underwent 60 min of transient middle cerebral artery occlusion avoiding ligation of the external carotid artery. During reperfusion, the common carotid artery was either ligated (standard approach), or it was repaired to allow re-establishment of blood flow through the common carotid artery. All mice underwent MRI scanning for assessment of infarct volume, apparent diffusion coefficient and fractional anisotropy, along with terminal assessment of infarct volume by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Repairing the common carotid artery following middle cerebral artery occlusion enhanced reperfusion (P<0.01) and reduced the variability seen in both total (histological analysis, P=0.008; T2-weighted MRI, P=0.015) and core (diffusion tensor MRI, P=0.043) lesion volume. Avoiding external carotid artery ligation may improve animal wellbeing, through reduced weight loss, while using an alternative surgical approach that enabled reperfusion through the common carotid artery decreased the variability in lesion volume seen within groups.

Summary: An alternative surgical approach following middle cerebral artery occlusion, which allows reperfusion through the common carotid artery, decreases the variability in lesion volume seen within groups and reduces the number of animals required to detect a treatment effect.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Microglial Polarization and Inflammatory Mediators After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and morbidity. When a diseased artery within the brain bursts, expansion and absorption of the resulting hematoma trigger a series of reactions that cause primary and secondary brain injury. Microglia are extremely important for removing the hematoma and clearing debris, but they are also a source of ongoing inflammation. This article discusses the role of microglial activation/polarization and related inflammatory mediators, such as Toll-like receptor 4, matrix metalloproteinases, high-mobility group protein box-1, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron, in secondary injury after ICH and highlights the potential targets for ICH treatment.

The dichotomy of memantine treatment for ischemic stroke: dose-dependent protective and detrimental effects

Excitotoxicity is a major contributor to cell death during the acute phase of ischemic stroke but aggressive pharmacological targeting of excitotoxicity has failed clinically. Here we investigated whether pretreatment with low doses of memantine, within the range currently used and well tolerated for the treatment of Alzheimer's disease, produce a protective effect in stroke. A coculture preparation exposed to modeled ischemia showed cell death associated with rapid glutamate rises and cytotoxic Ca(2+) influx. Cell death was significantly enhanced in the presence of high memantine concentrations. However, low memantine concentrations significantly protected neurons and glia via excitotoxic cascade interruption. Mice were systemically administered a range of memantine doses (0.02, 0.2, 2, 10, and 20 mg/kg/day) starting 24 hours before 60 minutes reversible focal cerebral ischemia and continuing for a 48-hour recovery period. Low dose (0.2 mg/kg/day) memantine treatment significantly reduced lesion volume (by 30% to 50%) and improved behavioral outcomes in stroke lesions that had been separated into either small/striatal or large/striatocortical infarcts. However, higher doses of memantine (20 mg/kg/day) significantly increased injury. These results show that clinically established low doses of memantine should be considered for patients 'at risk' of stroke, while higher doses are contraindicated.

Inhibition of Rho-kinase protects cerebral barrier from ischaemia-evoked injury through modulations of endothelial cell oxidative stress and tight junctions

Ischaemic strokes evoke blood-brain barrier (BBB) disruption and oedema formation through a series of mechanisms involving Rho-kinase activation. Using an animal model of human focal cerebral ischaemia, this study assessed and confirmed the therapeutic potential of Rho-kinase inhibition during the acute phase of stroke by displaying significantly improved functional outcome and reduced cerebral lesion and oedema volumes in fasudil- versus vehicle-treated animals. Analyses of ipsilateral and contralateral brain samples obtained from mice treated with vehicle or fasudil at the onset of reperfusion plus 4 h post-ischaemia or 4 h post-ischaemia alone revealed these benefits to be independent of changes in the activity and expressions of oxidative stress- and tight junction-related parameters. However, closer scrutiny of the same parameters in brain microvascular endothelial cells subjected to oxygen-glucose deprivation ± reperfusion revealed marked increases in prooxidant NADPH oxidase enzyme activity, superoxide anion release and in expressions of antioxidant enzyme catalase and tight junction protein claudin-5. Cotreatment of cells with Y-27632 prevented all of these changes and protected in vitro barrier integrity and function. These findings suggest that inhibition of Rho-kinase after acute ischaemic attacks improves cerebral integrity and function through regulation of endothelial cell oxidative stress and reorganization of intercellular junctions. Inhibition of Rho-kinase (ROCK) activity in a mouse model of human ischaemic stroke significantly improved functional outcome while reducing cerebral lesion and oedema volumes compared to vehicle-treated counterparts. Studies conducted with brain microvascular endothelial cells exposed to OGD ± R in the presence of Y-27632 revealed restoration of intercellular junctions and suppression of prooxidant NADPH oxidase activity as important factors in ROCK inhibition-mediated BBB protection.

Effect of stroke on arginase expression and localization in the rat brain

Because arginase and nitric oxide (NO) synthases (NOS) compete to degrade l-arginine, arginase plays a crucial role in the modulation of NO production. Moreover, the arginase 1 isoform is a marker of M2 phenotype macrophages that play a key role in tissue remodeling and resolution of inflammation. While NO has been extensively investigated in ischemic stroke, the effect of stroke on the arginase pathway is unknown. The present study focuses on arginase expression/activity and localization before and after (1, 8, 15 and 30 days) the photothrombotic ischemic stroke model. This model results in a cortical lesion that reaches maximal volume at day 1 post-stroke and then decreases as a result of astrocytic scar formation. Before stroke, arginase 1 and 2 expressions were restricted to neurons. Stroke resulted in up-regulation of arginase 1 and increased arginase activity in the region centered on the lesion where inflammatory cells are present. These changes were associated with an early and long-lasting arginase 1 up-regulation in activated macrophages and astrocytes and a delayed arginase 1 down-regulation in neurons at the vicinity of the lesion. A linear positive correlation was observed between expressions of arginase 1 and glial fibrillary acidic protein as a marker of activated astrocytes. Moreover, the pattern of arginase 1 and brain-derived neurotrophic factor (BDNF) expressions in activated astrocytes was similar. Unlike arginase 1, arginase 2 expression was not changed by stroke. In conclusion, increased arginase 1 expression is not restricted to macrophages in inflammation elicited by stroke but also occurs in activated astrocytes where it may contribute to neuroplasticity through the control of BDNF production.

Bench to cribside: the path for developing a neuroprotectant

The consequences of perinatal brain injury include immeasurable anguish for families and substantial ongoing costs for care and support of effected children. Factors associated with perinatal brain injury in the preterm infant include inflammation and infection, and with increasing gestational age, a higher proportion is related to hypoxic-ischemic events, such as stroke and placental abruption. Over the past decade, we have acquired new insights in the mechanisms underpinning injury and many new tools to monitor outcome in perinatal brain injury in our experimental models. By embracing these new technologies, we can expedite the screening of novel therapies. This is critical as despite enormous efforts of the research community, hypothermia is the only viable neurotherapeutic, and this procedure is limited to term birth and postcardiac arrest hypoxic-ischemic events. Importantly, experimental and preliminary data in humans also indicate a considerable therapeutic potential for melatonin against perinatal brain injury. However, even if this suggested potential is proven, the complexity of the human condition means we are likely to need additional neuroprotective and regenerative strategies. Thus, within this review, we will outline what we consider the key stages of preclinical testing and development for a neuroprotectant or regenerative neurotherapy for perinatal brain injury. We will also highlight examples of novel small animal physiological and behavioral testing that gives small animal preclinical models greater clinical relevance. We hope these new tools and an integrated bench to cribside strategic plan will facilitate the fulfillment of our overarching goal, improving the long-term brain health and quality of life for infants suffering perinatal brain injury.

Progesterone is neuroprotective following cerebral ischaemia in reproductively ageing female mice

Gender differences in both vulnerability to stroke and outcome following cerebral ischaemia have frequently been observed and attributed to the action of steroid hormones. Progesterone is a candidate neuroprotective factor for stroke; however, studies are lacking which: (i) study those groups representing high risk i.e. postmenopausal females; (ii) administer progesterone solely post-ischaemia; and (iii) combine histopathological and functional assessments. Postmenopausal females, along with males, represent the group at highest risk of cerebral stroke and can be modelled using aged or ovariectomized animals. In the current study, we aimed to determine the neuroprotective effects of progesterone administration following cerebral ischaemia in aged and ovariectomized mice. Following transient middle cerebral artery occlusion, progesterone was administered at 1, 6 and 24 h post-ischaemia to aged and ovariectomized female mice. At 48 h post-ischaemia, progesterone significantly reduced the lesion volume (P < 0.05) but had no effect on neurological outcome in aged female mice. Whereas in ovariectomized mice, at 48 h post-ischaemia, progesterone treatment had no effect on the amount of lesion volume present but did significantly improve neurological outcome. In a further study of ovariectomized mice, allowed to survive for 7 days post-ischaemia, progesterone treatment significantly improved motor outcome as assessed using both the rotarod and grid test. In fact, by 7 days post-ischaemia, progesterone-treated ovariectomized mice did not differ significantly in performance compared with shams, whereas vehicle-treated ovariectomized mice displayed a significant functional impairment following ischaemia. The current study has demonstrated that progesterone has different neuroprotective effects whether it is administered to aged or ovariectomized female mice and emphasizes the need to combine histopathological and functional outcomes within the same study. In addition, as progesterone-only treatment may not improve all outcomes in all groups, therapies that combine progesterone with other neuroprotective candidates should be investigated to maximize benefit following stroke.

Methyleugenol reduces cerebral ischemic injury by suppression of oxidative injury and inflammation

The present study tested the cytoprotective effect of methyleugenol in an in vivo ischemia model (i.e. middle cerebral artery occlusion (MCAO) for 1.5 h and subsequent reperfusion for 24 h) and further investigated its mechanism of action in in vitro cerebral ischemic models. When applied shortly after reperfusion, methyleugenol largely reduced cerebral ischemic injury. Methyleugenol decreased the caspase-3 activation and death of cultured cerebral cortical neurons caused by oxygen-glucose deprivation (OGD) for 1 h and subsequent re-oxygenation for 24 h. Methyleugenol markedly reduced superoxide generation in the ischemic brain and decreased the intracellular oxidative stress caused by OGD/re-oxygenation. It was found that methyleugenol elevated the activities of superoxide dismutase and catalase. Further, methyleugenol inhibited the production of nitric oxide and decreased the protein expression of inducible nitric oxide synthase. Methyleugenol down-regulated the production of pro-inflammatory cytokines in the ischemic brain as well as in immunostimulated mixed glial cells. The results indicate that methyleugenol could be useful for the treatment of ischemia/inflammation-related diseases.

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.

Sustained levels of progesterone prior to the onset of cerebral ischemia are not beneficial to female mice

Female gender, which is abolished following ovariectomy and reproductive senescence, is associated with improved outcome following cerebral stroke. Estrogen replacement partially restores this benefit of the female gender but the effect of progesterone in hormone-deficient animals is currently unknown. We evaluated various outcomes following middle cerebral artery occlusion (MCAO) in ovariectomised female mice, with a physiologically relevant restoration of progesterone levels. Ovariectomised female mice had significantly elevated plasma (P=<0.05) and brain progesterone levels (P=<0.01) following implantation of a 21-day release pellet (50mg) compared with mice that received placebo implants 7 days prior to undergoing 60 min MCAO. Assessment of well-being (body weight recovery) and neurological score at 24h and 48h post-MCAO indicated that MCAO significantly worsened outcome compared with sham-operated mice but progesterone had no effect. MCAO resulted in a substantial lesion formation and a significant increase (P<0.05) in ipsilateral brain water content, both of which were not affected by progesterone treatment. Furthermore, there was no significant alteration in ipsilateral Aquaporin-4 (AQP4) expression following MCAO or progesterone treatment. The present study indicates that sustained physiologically relevant levels of progesterone prior to cerebral ischemia neither benefited nor worsened outcomes in previously ovariectomised female mice.

Mechanisms contributing to cerebral infarct size after stroke: gender, reperfusion, T lymphocytes, and Nox2-derived superoxide

Cerebral infarct volume is typically smaller in premenopausal females than in age-matched males after ischemic stroke, but the underlying mechanisms are poorly understood. In this study we provide evidence in mice that this gender difference only occurs when the ischemic brain is reperfused. The limited tissue salvage achieved by reperfusion in male mice is associated with increased expression of proinflammatory proteins, including cyclooxygenase-2 (Cox-2), Nox2, and vascular cell adhesion molecule-1 (VCAM-1), and infiltration of Nox2-containing T lymphocytes into the infarcted brain, whereas such changes are minimal in female mice after ischemia-reperfusion (I-R). Infarct volume after I-R was no greater at 72 h than at 24 h in either gender. Infarct development was Nox2 dependent in male but not in female mice, and Nox2 within the infarct was predominantly localized in T lymphocytes. Stroke resulted in an approximately 15-fold increase in Nox2-dependent superoxide production by circulating, but not spleen-derived, T lymphocytes in male mice, and this was approximately sevenfold greater than in female mice. These circulating immune cells may thus represent a major and previously unrecognized source of superoxide in the acutely ischemic and reperfused brain of males (and potentially in postmenopausal females). Our findings provide novel insights into mechanisms that could be therapeutically targeted in acute ischemic stroke patients who receive thrombolysis therapy to induce cerebral reperfusion.

G-CSF administration is neuroprotective following transient cerebral ischemia even in the absence of a functional NOS-2 gene

Granulocyte colony-stimulating factor (G-CSF) is a candidate neuroprotective factor following cerebral ischemia. To determine whether G-CSF acts partly through the inhibition of nitric oxide synthase (NOS)-2 expression, we administered G-CSF to male NOS-2-/- mice after cerebral ischemia. Although male NOS-2-/- mice exhibit resistance to the gross effects of cerebral ischemia, they display neuronal loss and skilled motor deficits following cerebral ischemia. Administration of G-CSF during reperfusion reduced motor deficit and neuronal loss. Thus, G-CSF is still effective in NOS-2 gene-deficient mice, suggesting that part of the mechanism of action is independent of NOS-2.

Mechanisms of gender-linked ischemic brain injury

Biological sex is an important determinant of stroke risk and outcome. Women are protected from cerebrovascular disease relative to men, an observation commonly attributed to the protective effect of female sex hormones, estrogen and progesterone. However, sex differences in brain injury persist well beyond the menopause and can be found in the pediatric population, suggesting that the effects of reproductive steroids may not completely explain sexual dimorphism in stroke. We review recent advances in our understanding of sex steroids (estradiol, progesterone and testosterone) in the context of ischemic cell death and neuroprotection. Understanding the molecular and cell-based mechanisms underlying sex differences in ischemic brain injury will lead to a better understanding of basic mechanisms of brain cell death and is an important step toward designing more effective therapeutic interventions in stroke.

Neuroprotective effects of estrogens following ischemic stroke

Our laboratory has investigated whether and how 17beta-estradiol (E(2)) protects the brain against neurodegeneration associated with cerebrovascular stroke. We have discovered that low, physiological concentrations of E(2), which are strikingly similar to low-basal circulating levels found in cycling mice, dramatically protect the brain against stroke injury, and consequently revealed multiple signaling pathways and key genes that mediate protective action of E(2). Here we will review the discoveries comprising our current understanding of neuroprotective actions of estrogens against ischemic stroke. These findings may carry far reaching implications for improving the quality of life in aging populations.

Whole-body periodic acceleration reduces brain damage in a focal ischemia model

Stroke is the second most common cause of death and major cause of disability worldwide. Actual treatment involves surgery and/or thrombolytic drugs, but there is an urgent need for new approaches. Periodic acceleration, a rocking headward to footward movement of the whole body, is a non-invasive method to induce pulsatile shear stress on the vascular endothelium eliciting an enhanced production and secretion of endothelium-derived products such as nitric oxide, prostacyclin, prostaglandin E2, tissue plasminogen activator (tPA), and adrenomedullin. All these products have been shown to protect the brain from ischemic injuries. A rat model of focal brain ischemia was treated with application of periodic acceleration for 3 h immediately after the onset of ischemia. Controls remained static for the same period of time. Brain damage was assessed by magnetic resonance imaging (MRI) and biochemical markers. A significant reduction in brain damage was observed, 7 days post-ischemia, in rocked rats when compared with the static controls, through MRI. Furthermore, rocked animals had significantly lower levels of Beclin 1 and fractin than their static counterparts, and some isoforms of nitric oxide synthase were regulated by periodic acceleration. Our results show that periodic acceleration may provide a novel, affordable, non-invasive therapeutic option for the treatment of stroke.

Inducible nitric oxide synthase does not mediate brain damage after transient focal cerebral ischemia in mice

Nitric oxide produced by the inducible nitric oxide synthase (iNOS) is believed to participate in the pathogenic events after cerebral ischemia. In this study, we examined the expression of iNOS in the brain after transient focal cerebral ischemia in mice. We detected differential expression of exons 2 and 3 of iNOS mRNA (16-fold upregulation at 24 to 72 h after middle cerebral artery occlusion, MCAO) compared with exons 6 to 8, 12 to 14, 21 to 22, and 26 to 27 (2- to 5-fold upregulation after 72 and 96 h), which would be compatible with alternative splicing. Expression levels of iNOS mRNA were too low for detection by the Northern blot analysis. Using specific antibodies, we did not detect any iNOS immunoreactivity in the mouse brain 1 to 5 days after MCAO, although we detected iNOS immunoreactivity in the lungs of mice with stroke-associated pneumonia, and in mouse and rat dura mater after lipopolysaccharide administration. In chimeric iNOS-deficient mice transplanted with wild-type bone marrow (BM) cells expressing the green fluorescent protein (GFP) or in wild-type mice transplanted with GFP(+) iNOS-deficient BM cells, no expression of iNOS was detected in GFP(+) leukocytes invading the ischemic brain or in resident brain cells. Moreover, both experimental groups did not show any differences in infarct size. Analysis of three different strains of iNOS-deficient mice and wild-type controls confirmed that infarct size was independent of iNOS deletion, but strongly confounded by the genetic background of mouse strains. In conclusion, our data suggest that iNOS is not a universal mediator of brain damage after cerebral ischemia.

Nuclear factor-kappaB activation and postischemic inflammation are suppressed in CD36-null mice after middle cerebral artery occlusion

CD36, a class-B scavenger receptor involved in multiple functions, including inflammatory signaling, may also contribute to ischemic brain injury through yet unidentified mechanisms. We investigated whether CD36 participates in the molecular events underlying the inflammatory reaction that accompanies cerebral ischemia and may contribute to the tissue damage. We found that activation of nuclear factor-kappaB, a transcription factor that coordinates postischemic gene expression, is attenuated in CD36-null mice subjected to middle cerebral artery occlusion. The infiltration of neutrophils and the glial reaction induced by cerebral ischemia were suppressed. Treatment with an inhibitor of inducible nitric oxide synthase, an enzyme that contributes to the tissue damage, reduced ischemic brain injury in wild-type mice, but not in CD36 nulls. In contrast to cerebral ischemia, the molecular and cellular inflammatory changes induced by intracerebroventricular injection of interleukin-1beta were not attenuated in CD36-null mice. The findings unveil a novel role of CD36 in early molecular events leading to nuclear factor-kappaB activation and postischemic inflammation. Inhibition of CD36 signaling may be a valuable therapeutic approach to counteract the deleterious effects of postischemic inflammation.

Inducible nitric oxide synthase and estradiol exhibit complementary neuroprotective roles after ischemic brain injury

Estradiol-17beta exerts profound neuroprotective actions following cerebral ischemia through multiple molecular mechanisms. To examine the putative anti-inflammatory mechanisms employed by estradiol during stroke, we explored the interactions between estradiol and inducible nitric oxide synthase (iNOS) in both wildtype and iNOS knockout (iNOSKO) female mice following permanent middle cerebral artery occlusion (MCAO). Female mice were ovariectomized and treated with estradiol. One week later, they were subjected to MCAO, and then killed 24 h later. Analysis of total, cortical and striatal infarct volumes confirmed that estradiol is neuroprotective in wildtype mice. Infarct volumes were also significantly smaller in female iNOSKO female mice, but estradiol did not further decrease injury. We found that one mechanism by which estradiol may act is by decreasing nitric oxide synthase 2 gene expression in the cortex and in the striatum of wildtype mice. These results show that the pro-inflammatory actions of iNOS exacerbate stroke-induced injury within the cortex and striatum, and that iNOS deletion is neuroprotective in ovariectomized and estrogen-replaced female mice.

Neurological implications of urea cycle disorders

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular (1)H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate-nitric oxide-cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia-lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.

Nitric oxide, ischaemia and brain inflammation

Cerebral ischaemia results in the activation of three isoforms of NOS (nitric oxide synthase) that contribute to the development of and recovery from stroke pathology. This review discusses, in particular, the role of the transcriptionally activated NOS-2 (inducible NOS) isoform and summarizes the outcomes of experimental stroke studies with regard to the therapeutic utility of nitric oxide donors and NOS inhibitors.

Apoptotic neuronal death in Parkinson's disease: Involvement of nitric oxide

Apoptosis of nigral dopaminergic neurons by various mechanisms is an emerging phenomenon involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Both extrinsic and intrinsic pathways seems to be involved in death of nigral neurons, intrinsic pathway however, seems to be more important due to the energy crisis. Apoptosis by intrinsic pathway is executed by several initiators and effector caspases, which have been found activated in PD patients, experimental models as well as in neuronal cultures. Nitric oxide (NO) seems to be a central molecule due to its ability to modulate both pro and antiapoptotic phenomenon. The review focuses on the diverse extrinsic and intrinsic factors, signaling pathways and their modulation by NO leading to the death of dopaminergic neurons.

Decreased focal inflammatory response by G-CSF may improve stroke outcome after transient middle cerebral artery occlusion in rats

Recent studies have shown that administration of granulocyte colony-stimulating factor (G-CSF) is neuroprotective. However, the precise mechanisms of the neuroprotective effect of G-CSF are not entirely known. We carried out 90-min transient middle cerebral occlusion (tMCAO) of rats. The rats were injected with vehicle or G-CSF (50 mug/kg) immediately after reperfusion and sacrificed 8, 24, or 72 hr later. 2,3,5-Triphenyltetrazolium chloride (TTC) staining was carried out using brain sections of 72 hr, and immunohistochemistry was carried out with those of 8, 24, and 72 hr. TTC-staining showed a significant reduction of infarct volume in the G-CSF-treated group (**P < 0.01). Immunohistochemistry showed a significant decrease of the number of cells expressing tumor necrosis factor-alpha (TNF-alpha) at 8-72 hr, transforming growth factor-beta (TGF-beta) and inducible nitric oxide synthase (iNOS) at 24 and 72 hr after tMCAO in the peri-ischemic area (*P < 0.05 each). Our data suggest that the suppression of inflammatory cytokines and iNOS expression may be one mechanism of neuroprotection by G-CSF.

Microglia in cerebral ischemia: molecular actions and interactions

The precise role of microglia in stroke and cerebral ischemia has been the subject of debate for a number of years. Microglia are capable of synthesizing numerous soluble and membrane-bound biomolecules, some known to be neuroprotective, some neurotoxic, whereas others have less definitive bioactivities. The molecular mechanisms through which microglia activate these molecules have thus become an important area of ischemia research. Here we provide a survey review that summarizes the key actions of microglial factors in cerebral ischemia including complement proteins, chemokines, pro-inflammatory cytokines, neurotrophic factors, hormones, and proteinases, as well several important messenger molecules that play a part in how these factors respond to extracellular signals during ischemic injuries. We also provide some new perspectives on how microglial intracellular signaling may contribute to the seemingly contradictory roles of several microglial effector molecules.

Inducible nitric oxide synthase contributes to gender differences in ischemic brain injury

Estrogens have antiinflammatory actions and protect the brain from ischemic injury. Cerebral ischemia is accompanied by an inflammatory reaction that contributes to the tissue damage, an effect mediated in part by toxic amounts of nitric oxide (NO) produced by the inducible isoform of NO synthase (iNOS). Therefore, estrogens may protect the female brain by modulating postischemic iNOS expression. To test this hypothesis, we studied whether iNOS plays a role in the mechanisms of the reduced susceptibility to ischemic injury observed in female mice. The middle cerebral artery was occluded for 20 mins using an intraluminal filament in C57Bl/6 mice, and infarct volume was assessed 3 days later in cresyl violet-stained sections. Infarcts were 53% smaller in female mice than in males (P < 0.05), a reduction abolished by ovariectomy (OVX) and reinstated by estrogen replacement. In normal female mice, postischemic iNOS mRNA was lower than in males (P < 0.05). Ovariectomy increased iNOS mRNA after ischemia and estrogen replacement blocked this effect. Furthermore, the iNOS inhibitor aminoguanidine reduced infarct volume in male, but not in female, mice. Similarly, male iNOS-null mice had smaller infarcts than wild-type mice, but female iNOS nulls were not protected. Ovariectomy and OVX with estrogen replacement did not affect infarct volume in iNOS-null female mice. The findings suggest that the neuroprotection conferred by estrogens is, in part, related to attenuation of iNOS expression. Such attenuation could result from the potent antiinflammatory effects of estrogens that downregulate iNOS expression via transcriptional or posttranscriptional mechanisms.

Neuroprotective effect of selective kappa opioid receptor agonist is gender specific and linked to reduced neuronal nitric oxide

We have previously shown that treatment with selective kappa-opioid receptor agonist BRL 52537 hydrochloride [(+/-)-1-(3,4-dichlorophenyl) acetyl-2-(1-pyrrolidinyl) methylpiperidine] (1) has a long therapeutic window for providing ischemic neuroprotection and (2) attenuates ischemia-evoked nitric oxide (NO) production in vivo in rats. Neuronally derived NO has been shown to be deleterious in the male, but not in the female, rodent model of focal ischemic stroke. We sought to determine if the agent fails to protect ischemic brain when neuronal NO synthase (nNOS) is genetically deleted in male, but not female, mice. Halothane-anesthetized adult male and female nNOS null mutants (nNOS(-/-)) and the genetically matched wildtype (WT) strain were subjected to transient (2 h) middle cerebral artery occlusion by the intraluminal filament technique. Vehicle or BRL 52537 treatment with continuous intravenous infusion was instituted at the onset of reperfusion and continued for 22 h. In WT male mice, infarct volumes measured at 72 h of reperfusion were robustly decreased with BRL 52537 treatment. In contrast, BRL 52537 did not decrease infarct volume in male nNOS(-/-) mice. BRL 52537 had no effect in the WT or nNOS(-/-) female mice. These data support that BRL 52537's mechanism of neuroprotection in vivo is through attenuation of nNOS activity and ischemia-evoked NO production. Neuroprotective effects of BRL 52537 are lost in the male when nNOS is not present; therefore, BRL 52537 likely acts upstream from NO generation and its subsequent neurotoxicity.

Mechanisms of Brain Injury after Global Cerebral Ischemia

Cerebral ischemia results in a rapid depletion of energy stores that triggers a complex cascade of cellular events such as cellular depolarization and Ca2+ influx, resulting in excitotoxic cell death. The critical determinant of severity of brain injury is the duration and severity of the ischemic insult and early restoration of CBF. Induced therapeutic hypothermia following CA is the only strategy that has demonstrated improvement in outcomes in prospective, randomized clinical trials. Although pharmacologic neuro-protection has been disappointing thus far in a variety of experimental animal models, further research efforts are directed at using some agents that demonstrate marginal or moderate efficacy in combination with hypothermia. Although the signal transduction pathways and intracellular molecular events during cerebral ischemia and reperfusion are complex, potential therapeutic neuroprotective strategies hold promise for the future.

Different apoptotic mechanisms are activated in male and female brains after neonatal hypoxia-ischaemia

Sex-related brain injury was evaluated after unilateral hypoxia-ischaemia (HI) in C57/BL6 mice on postnatal day (P) 5, 9, 21 or 60, corresponding developmentally to premature, term, juvenile and adult human brains. There was no sex difference in brain injury when the insult was severe, as evaluated by pathological scoring or tissue loss, but when the insult was moderate, adult (P60) females displayed less injury. In the immature (P9) male brains, neurones displayed a more pronounced translocation of apoptosis-inducing factor (AIF) (loss of AIF from the mitochondrial fraction and increase in nuclear AIF) after HI, whereas the female brain neurones displayed a stronger activation of caspase 3 (more pronounced loss of pro-caspase 3, increase in cleaved caspase 3 and increase in caspase 3 enzymatic activity). Two other mechanisms of injury, peroxynitrite-induced formation of nitrotyrosine and autophagy, were no different between males and females at P9. These data show that the CNS is more resistant to HI in adult females compared with males, whereas no sex differences were found in the extent of injury in neonatal mice. However, critical sex-dependent differences were demonstrated in vivo with regard to cellular, apoptosis-related mechanisms.

Neuroinflammation and both cytotoxic and vasogenic edema are reduced in interleukin-1 type 1 receptor-deficient mice conferring neuroprotection

BACKGROUND AND PURPOSE

Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple neurodegenerative diseases, including stroke. However, to date, there is no consensus regarding which receptor(s) mediates the detrimental effects of IL-1. We hypothesized that abrogating IL-1 type 1 receptor (IL-1R1) signaling would reduce edema, chemokine expression, and leukocyte infiltration; lower levels of iNOS; and, consequently, decrease free radical damage after mild hypoxia/ischemia (H/I), thus preserving brain cells.

METHODS

IL-1R1 null mice and wild-type mice were subjected to a mild H/I insult. MRI was used to measure the area affected at 30 minutes and 48 hours after H/I. An RNAse protection assay was used to evaluate changes in chemokine mRNA expression. RT-PCR was used to assess inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase mRNA levels. Immunohistochemistry was used to assess leukocyte infiltration. Western blots were used to assess iNOS and glutamate aspartate transporter protein levels.

RESULTS

IL-1R1 null mice had reduced cytotoxic and vasogenic edema. The volume of hyperintense signal on T2-weighted images was reduced on average by 90% at 48 hours after H/I. The induction of multiple chemokine mRNAs was significantly reduced in IL-1R1 null mice compared with wild-type mice at 18 and 72 hours after H/I, which correlated with fewer infiltrating CD3+ leukocytes. Levels of iNOS protein and mRNA (but not glutamate aspartate transporter) were significantly reduced in the IL-1R1 mouse brain.

CONCLUSIONS

These findings indicate that abrogating IL-1R1 signaling could protect brain cells subsequent to a mild stroke by reducing edema and immune cell recruitment, as well as by limiting iNOS-mediated free radical damage.

G-CSF Suppresses Edema Formation and Reduces Interleukin-1β Expression After Cerebral Ischemia in Mice

Granulocyte-colony stimulating factor (G-CSF) is reported to be neuroprotective after transient cerebral ischemia with respect to decreasing lesion volume and enhancing functional recovery. We investigated whether G-CSF is neuroprotective after permanent ischemia and the possible mechanisms underlying this neuroprotection. Mice underwent permanent or 60-minute middle cerebral artery occlusion (MCAO) and received G-CSF (50 microg/kg) or vehicle at the onset or 1 hour post-MCAO. Forty-eight hours after transient MCAO, structural magnetic resonance imaging revealed a significant reduction (50%) in the amount of edematous tissue present in G-CSF-treated mice (p < 0.05). G-CSF treatment also prevented a significant increase in ipsilateral brain water content that was present in vehicle-treated mice after transient (p < 0.05) and permanent (p < 0.001) MCAO. Forty-eight hours after permanent MCAO, G-CSF decreased (50%) the cortical lesion volume (p < 0.05). Using real-time polymerase chain reaction, we found that G-CSF treatment significantly suppressed (p < 0.05) the injury-induced upregulation of IL-1beta mRNA while having no effect on TNFalpha and NOS-2 mRNA expression. This suggests that part of the neuroprotection may be attributed to the ability of G-CSF to reduce the inflammatory response.

Nitric oxide synthase inhibitors in experimental ischemic stroke and their effects on infarct size and cerebral blood flow: a systematic review

Nitric oxide produced by the neuronal or inducible isoform of nitric oxide synthase (nNOS, iNOS) is detrimental in acute ischemic stroke (IS), whereas that derived from the endothelial isoform is beneficial. However, experimental studies with nitric oxide synthase inhibitors have given conflicting results. Relevant studies were found from searches of EMBASE, PubMed, and reference lists; of 456 references found, 73 studies involving 2321 animals were included. Data on the effects of NOS inhibition on lesion volume (mm3, %) and cerebral blood flow (CBF; %, ml * min(-1) * g(-1)) were analyzed using the Cochrane Review Manager software. NOS inhibitors reduced total infarct volume in models of permanent (standardized mean difference (SMD) -0.56, 95% confidence interval (95% CI) -0.86, -0.26) and transient (SMD -0.99, 95% CI -1.25, -0.72) ischemia. Cortical CBF was reduced in models of permanent but not transient ischemia. When assessed by type of inhibitor, total lesion volume was reduced in permanent models by nNOS and iNOS inhibitors, but not by nonselective inhibitors. All types of NOS inhibitors reduced infarct volume in transient models. NOS inhibition may have negative effects on CBF but further studies are required. Selective nNOS and iNOS inhibitors are candidate treatments for acute IS.

Glial nitric oxide and ischemia

One of the responses to cerebral ischemia is an increase in the production of nitric oxide, catalyzed by enzymes expressed in both resident and infiltrating cells. The nitric oxide that is generated does contribute to the ensuing pathology, but it can also be beneficial. The effects of nitric oxide depend on the cell site of production, the amount generated, and the chemical nature of the products of further oxidation. Understanding how nitric oxide production from microglia and astrocytes contributes to ischemic pathology is important for the development and application of future therapeutics based on inhibiting or amplifying its production in the injured brain.

Progesterone suppresses the inflammatory response and nitric oxide synthase-2 expression following cerebral ischemia

Gender differences in outcome following cerebral ischemia have frequently been observed and attributed to the actions of steroid hormones. Progesterone has been shown to possess neuroprotective properties following transient ischemia, with respect to decreasing lesion volume and improving functional recovery. The present study was designed to determine the mechanisms of progesterone neuroprotection, and whether these relate to the inflammatory response. Male mice underwent either 60 min or permanent middle cerebral artery occlusion (MCAO) and received progesterone (8 mg/kg ip) or vehicle 1 h, 6 h and 24 h post-MCAO. Forty-eight hours following transient MCAO, structural magnetic resonance imaging revealed a significant decrease in the amount of edematous tissue present in progesterone-treated mice as compared with vehicle. Using real-time PCR we found that progesterone treatment significantly suppressed the injury-induced upregulation of interleukin (IL)-1beta, transforming growth factor (TGF)beta2, and nitric oxide synthase (NOS)-2 mRNAs in the ipsilateral hemisphere while having no effect on tumor necrosis factor (TNF)-alpha mRNA expression. Progesterone treatment following permanent MCAO also resulted in a significant decrease in lesion volume. This was not apparent in mice lacking a functional NOS-2 gene. Thus, progesterone is neuroprotective in both permanent and transient ischemia, and this effect is related to the suppression of specific aspects of the inflammatory response.

Astroglial nitration after postnatal excitotoxic damage: correlation with nitric oxide sources, cytoskeletal, apoptotic and antioxidant proteins

Oxygen free radicals and nitric oxide (NO) participate in the pathogenesis of acute central nervous system (CNS) injury by forming peroxynitrite, which promotes oxidative damage and tyrosine nitration. Neuronal nitration is associated with cell death, but little is known of the characteristics and cell fate of nitrated astrocytes. In this study, we have used a postnatal excitotoxic lesion model (intracortical NMDA injection) and our aims were (i) to evaluate the temporal and spatial pattern of astroglial nitration in correlation with the neuropathological process and the sources of NO; and (ii) to establish, if any, the correlation among astrocyte nitration and other events such as expression of cytoskeletal proteins, antioxidant enzymes, and cell death markers to cope with nitration and/or undergo cell death. Our results show that after postnatal excitotoxic damage two distinct waves of nitration were observed in relation to astrocytes. At 24 h post-lesion, early-nitrated astrocytes were found within the neurodegenerating area, coinciding with the time of maximal cell death. These early-nitrated astrocytes are highly ramified protoplasmic cells, showing diffuse glial fibrillary acidic protein (GFAP) content and expressing inducible NOS. At later time-points, when astrogliosis is morphologically evident, nitrated hypertrophied reactive astrocytes are observed in the penumbra and the neurodegenerated area, displaying increased expression of GFAP and vimentin cytoskeletal proteins and of metallothionein I-II and Cu/Zn superoxide dismutase antioxidant proteins. Moreover, despite revealing activated caspase-3, they do not show TUNEL labeling. In summary, we show that nitrated astrocytes in vivo constitute a subpopulation of highly reactive astrocytes which display high resistance towards oxidative stress induced cell death.

Modulatory effects of progesterone on inducible nitric oxide synthase expression in vivo and in vitro

Nitric oxide (NO) is produced in the CNS following injury-induced expression of inducible nitric oxide synthase (iNOS), yet its role as protective or damaging is unclear. Previous studies investigating the therapeutic potential of female sex steroids in stroke and trauma suggest that NO from this source is harmful, since oestradiol and progesterone decreased the level of iNOS expression in vitro and improved neurological outcome. We investigated the effects of progesterone on stroke-induced expression of iNOS in mice, as well as cytokine-induced expression of iNOS and its transcriptional activators in cells relevant to injury. We observed a significant reduction in stroke-induced iNOS transcript in progesterone-treated mice and in cultured macrophages. In contrast, progesterone significantly amplifed cytokine-induced iNOS mRNA in cultured primary astrocytes, although the expression of protein was decreased. We sequenced upstream of the 1.5 kb reported iNOS promoter region and identified a potential progesterone response element (PRE). Astrocytes transiently transfected with iNOS promoter/CAT reporter gene constructs containing the PRE displayed a significant increase in induction of CAT expression after progesterone treatment, and this was diminished in cells transfected with a construct containing a disrupted PRE. These observations suggest the involvement of iNOS in the neuroprotective effects of progesterone.

G-CSF reduces infarct volume and improves functional outcome after transient focal cerebral ischemia in mice

Growth factors possess neuroprotective and neurotrophic properties in vitro, but few have been extensively studied in vivo after stroke. In the present study, we investigated the potential functional benefits of granulocyte colony-stimulating factor (G-CSF) administration after focal cerebral ischemia. Male mice underwent 60-minute middle cerebral artery occlusion (MCAO) and received G-CSF (50 microg/kg, subcutaneously) or vehicle (saline) at the onset of reperfusion. Granulocyte colony-stimulating factor-treated mice killed at 48 hours after MCAO revealed a >45% reduction (P<0.05) in lesion volume. In terms of body weight recovery, and in tests of motor (grid test and rotarod) and cognitive ability (water maze), MCAO significantly worsened the outcome in vehicle-treated mice as compared with shams (P<0.05). However, G-CSF treatment was beneficial as, compared with vehicle, this significantly improved weight recovery and motor ability. This effect was most apparent on the water maze where G-CSF-treated mice were indistinguishable from shams in terms of acquiring the task. These results indicate long-term beneficial effects of a single dose of G-CSF administered on reperfusion, and illustrate the need to further investigate the mechanisms of G-CSF action.

Ischemic nitric oxide and poly (ADP-ribose) polymerase-1 in cerebral ischemia: male toxicity, female protection

It is well established that tissue damage and functional outcome after experimental or clinical stroke are shaped by biologic sex. We investigated the novel hypothesis that ischemic cell death from neuronally derived nitric oxide (NO) or poly-ADP ribose polymerase (PARP-1) activation is sexually dimorphic and that interruption of these molecular death pathways benefits only the male brain. Female neuronal nitric oxide synthase (nNOS) knockout (nNOS-/-) mice exhibited exacerbated histological injury after middle cerebral artery occlusion (MCAO) relative to wild-type (WT) females, unlike the protection observed in male nNOS-/- littermates. Similarly, treatment with the nNOS inhibitor (7-nitroindozole, 25 mg/kg) increased infarction in female C57Bl6 WT mice, but protected male mice. The mechanism for this sexually specific response is not mediated through changes in protein expression of endothelial NOS or inducible NOS, or differences in intraischemic cerebral blood flow. Unlike male PARP-1 knockouts (PARP1-/-), female PARP1-/- littermates sustained grossly increased ischemic damage relative to sex-matched WT mice. Treatment with a PARP inhibitor (PJ-34, 10 mg/kg) resulted in identical results. Loss of PARP-1 resulted in reversal of the neuroprotective activity by the female sex steroid, 17beta estradiol. These data suggest that the previously described cell death pathways involving NO and PARP ischemic neurotoxicity may be operant solely in male brain and that the integrity of nNO/PARP-1 signaling is paradoxically protective in the female.

Neuropeptide Y and its receptor analogs differentially modulate the immunoreactivity for neuronal or endothelial nitric oxide synthase in the rat brain following focal ischemia with reperfusion

An intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) or [Leu31, Pro34]-NPY (non-Y2 receptor agonist) given during middle cerebral artery occlusion (MCAO) increases the infarct volume and nitric oxide (NO) overproduction in the rat brain. An i.c.v. injection of NPY3-36 (non-Y1 receptor agonist) has no effects, while BIBP3226 (selective Y1 receptor antagonist) reduces the infarct volume and NO overproduction. This study examined the effects of NPY or its receptor analog on the immunoreactivity (ir) for three isoforms of NO synthase (NOS) following 1 h of MCAO and 3 h of reperfusion. Focal ischemia/reperfusion led to increased ir for neuronal NOS (nNOS) within the ipsilateral caudate putamen and insular cortex. NPY or [Leu31, Pro34]-NPY enhanced but BIBP3226 suppressed such increase in the nNOS-ir. Focal ischemia/reperfusion also led to an ipsilateral increase in extent and/or intensity of the ir for endothelial NOS (eNOS) in the caudate putamen and/or parietal cortex. NPY or [Leu31, Pro34]-NPY suppressed but BIBP3226 enhanced such change in the eNOS-ir. NPY3-36 did not consistently influence the nNOS-ir or eNOS-ir following MCAO. Specific ir for inducible NOS was undetectable. These opposing effects of NPY-Y1 receptor activation or inhibition on nNOS and eNOS may lead to harmful or beneficial consequences following ischemia/reperfusion.

Relationship between S100β and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion.

A detrimental role for nitric oxide synthase-2 in the pathology resulting from acute cerebral injury

Nitric oxide (NO) synthesized from the inducible isoform of nitric oxide synthase (NOS-2) has been suggested to play both beneficial and deleterious roles in various neuropathologies. To define the role of nitric oxide in traumatic brain injury, we subjected male mice lacking a functional NOS-2 gene (NOS-2-/-) and their wild-type littermates (NOS-2+/+) to mild or severe aseptic cryogenic cerebral injury. Expression of NOS-2 mRNA and protein was observed in NOS-2+/+ animals following injury. Lesion volume (as measured by histology and brain imaging) and neurological outcome (using motor and cognitive behavioral paradigms) were assessed at various times after injury. While magnetic resonance imaging revealed the extent of edema of the 2 genotypes to be similar, histology showed a reduced (32%) lesion volume in severely injured NOS-2-/- compared with NOS-2+/+ mice. In addition, NOS-2-/- mice showed significant improvements in both contralateral sensorimotor deficits (grid test: p = 0.011) and cognitive function (Morris water maze: p = 0.009) after severe injury compared to their wild-type littermates. This indicates that lesion volume is reduced and neurological recovery is improved after acute traumatic injury in mice lacking a functional NOS-2 gene, and strongly suggests that the post-trauma production of NO from this source contributes to neuropathology.

Progesterone enhances functional recovery after middle cerebral artery occlusion in male mice

Sex differences have been observed in the outcome after ischemia that are believed to be attributable to sex steroid hormones. The present study investigated the possible benefits of progesterone administration after focal cerebral ischemia. Male mice underwent 60-minute middle cerebral artery occlusion (MCAO) and received progesterone (8 mg/kg, intraperitoneally) or vehicle (dimethyl sulfoxide) 1, 6, and 24 hours after MCAO. The lesion volume at 48 hours after MCAO was significantly reduced (P < 0.05) in progesterone-treated mice compared with vehicle-treated mice. All other mice underwent tests of well being (survival rate and body weight recovery), motor ability (grid test and rotarod), and cognitive ability (water maze) for up to 21 days. MCAO significantly worsened outcome in all of these tests compared with shams. Progesterone treatment was beneficial in that compared with vehicle, it significantly improved survival rate, weight recovery, and motor ability. This improvement was most apparent during water maze testing, where progesterone-treated mice were indistinguishable from shams in terms of acquiring the task. These results indicate beneficial effects of progesterone administration after cerebral ischemia and illustrate the need to further investigate the mechanisms of progesterone action.

Defined inflammatory states in astrocyte cultures: correlation with susceptibility towards CD95-driven apoptosis

A complete cytokine mix (CCM) or its individual components tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) were used to switch resting murine astrocytes to reactive states. The transformation process was characterized by differential up-regulation of interleukin-6 (IL-6), cyclooxygenase-2 (COX-2) and inducible nitric oxide synthetase (iNOS) mRNA and protein and a subsequent release of prostaglandin E2, nitric oxide (NO) and IL-6. Both CD95L and anti-CD95 antibodies triggered caspase activation followed by apoptotic death in fully pro-inflammatory astrocytes, whereas resting cells were totally resistant. Two other death-inducing ligands, TNF and TNF-related apoptosis-inducing ligand (TRAIL) did not induce apoptosis in reactive astrocytes. The switch in astrocyte sensitivity was accompanied by up-regulation of caspase-8 and CD95 as well as the capacity to recruit Fas-associated death domain (FADD) to the activated death receptor complex. Neither CD95-mediated death, nor other inflammatory parameters were affected by inhibition of iNOS or COX, respectively. Accordingly, IFN-gamma was absolutely essential for up-regulation of iNOS, but not for the switch in apoptosis sensitivity. In contrast, p38 kinase activity was identified as an important controller of both the inflammatory reaction and apoptosis both in astrocytes stimulated with CCM and in glia exposed to TNF and IL-1 only.