[From the laboratory to the clinic in acute ischaemic stroke. In vitro and in vivo experimental models]

INTRODUCTION

Cerebrovascular disease is one of the leading causes of death, disability and dementia around the world. For the most common form of the disease, ischaemic stroke, there is only one drug available, tissue plasminogen activator, and few patients can benefit from this therapy because of the strict inclusion criteria established for its use. This circumstance makes it crucial to search for new forms of treatment to combat the sequelae of the disease, and this requires the development of new biomimetic models that allow for a better understanding of its evolution.

DEVELOPMENT

In this review, we update the platforms and models most widely used in recent years to study the pathophysiology of ischaemic stroke. On the one hand, we review the two- and three-dimensional platforms on which in vitro assays are carried out and, on the other, we describe the most commonly used in vivo experimental models and techniques for assessing ischaemic damage.

CONCLUSIONS

The ultimate aim of developing good experimental models is to find new forms of treatment and thus improve patients' prognosis and quality of life. It is therefore important to generate new in vitro devices and to further refine in vivo models to enable a good clinical translation.

The neurovascular unit and systemic biology in stroke - implications for translation and treatment

Ischaemic stroke is a leading cause of disability and death for which no acute treatments exist beyond recanalization. The development of novel therapies has been repeatedly hindered by translational failures that have changed the way we think about tissue damage after stroke. What was initially a neuron-centric view has been replaced with the concept of the neurovascular unit (NVU), which encompasses neuronal, glial and vascular compartments, and the biphasic nature of neural-glial-vascular signalling. However, it is now clear that the brain is not the private niche it was traditionally thought to be and that the NVU interacts bidirectionally with systemic biology, such as systemic metabolism, the peripheral immune system and the gut microbiota. Furthermore, these interactions are profoundly modified by internal and external factors, such as ageing, temperature and day-night cycles. In this Review, we propose an extension of the concept of the NVU to include its dynamic interactions with systemic biology. We anticipate that this integrated view will lead to the identification of novel mechanisms of stroke pathophysiology, potentially explain previous translational failures, and improve stroke care by identifying new biomarkers of and treatment targets in stroke.

Immune Pathways in Etiology, Acute Phase, and Chronic Sequelae of Ischemic Stroke

Inflammation and immune mechanisms are crucially involved in the pathophysiology of the development, acute damage cascades, and chronic course after ischemic stroke. Atherosclerosis is an inflammatory disease, and, in addition to classical risk factors, maladaptive immune mechanisms lead to an increased risk of stroke. Accordingly, individuals with signs of inflammation or corresponding biomarkers have an increased risk of stroke. Anti-inflammatory drugs, such as IL (interleukin)-1β blockers, methotrexate, or colchicine, represent attractive treatment strategies to prevent vascular events and stroke. Lately, the COVID-19 pandemic shows a clear association between SARS-CoV2 infections and increased risk of cerebrovascular events. Furthermore, mechanisms of both innate and adaptive immune systems influence cerebral damage cascades after ischemic stroke. Neutrophils, monocytes, and microglia, as well as T and B lymphocytes each play complex interdependent roles that synergize to remove dead tissue but also can cause bystander injury to intact brain cells and generate maladaptive chronic inflammation. Chronic systemic inflammation and comorbid infections may unfavorably influence both outcome after stroke and recurrence risk for further stroke. In addition, stroke triggers specific immune depression, which in turn can promote infections. Recent research is now increasingly addressing the question of the extent to which immune mechanisms may influence long-term outcome after stroke and, in particular, cause specific complications such as poststroke dementia or even poststroke depression.

Pathophysiological and pharmacological relevance of TLR4 in peripheral immune cells after stroke

Stroke is a very common disease being the leading cause of death and disability worldwide. The immune response subsequent to an ischemic stroke is a crucial factor in its physiopathology and outcome. This response is not limited to the injury site. In fact, the immune response to the ischemic process mobilizes mainly circulating cells which upon activation will be recruited to the injury site. When a stroke occurs, molecules that are usually retained inside the cell bodies are released into the extracellular space by uncontrolled cell death. These molecules can bind to the Toll-like receptor 4 (TLR4) in circulating immune cells which are then activated, eliciting, although not exclusively, the inflammatory response to the stroke. In this review, we present an up-to-date summary of the role of the different peripheral immune cells in stroke as well as the role of TLR4 in the function of each cell type in ischemia. Also, we summarize the different antagonists developed against TLR4 and their potential as a pharmacological tool for stroke treatment.

Circadian Biology and Stroke

Circadian biology modulates almost all aspects of mammalian physiology, disease, and response to therapies. Emerging data suggest that circadian biology may significantly affect the mechanisms of susceptibility, injury, recovery, and the response to therapy in stroke. In this review/perspective, we survey the accumulating literature and attempt to connect molecular, cellular, and physiological pathways in circadian biology to clinical consequences in stroke. Accounting for the complex and multifactorial effects of circadian rhythm may improve translational opportunities for stroke diagnostics and therapeutics.

Role of TLR4 (Toll-Like Receptor 4) in N1/N2 Neutrophil Programming After Stroke

Background and Purpose- After stroke, the population of infiltrated neutrophils in the brain is heterogeneous, including a population of alternative neutrophils (N2) that express M2 phenotype markers. We explored the role of TLR4 (toll-like receptor 4) on neutrophil infiltration and polarization in this setting. Methods- Focal cerebral ischemia was induced by occlusion of the middle cerebral artery occlusion in TLR4-KO and WT (wild type) mice. Infarct size was measured by Nissl staining and magnetic resonance imaging. Leukocyte infiltration was quantified 48 hours after middle cerebral artery occlusion by immunofluorescence and flow cytometry. To elucidate mechanisms underlying TLR4-mediated N2 phenotype, a cDNA microarray analysis was performed in neutrophils isolated from blood 48 hours after stroke in WT and TLR4-KO mice. Results- As demonstrated previously, TLR4-deficient mice presented lesser infarct volumes than WT mice. TLR4-deficient mice showed higher density of infiltrated neutrophils 48 hours after stroke compared with WT mice, concomitantly to neuroprotection. Furthermore, cytometric and stereological analyses revealed an increased number of N2 neutrophils (YM1⁺ cells) into the ischemic core in TLR4-deficient mice, suggesting a protective effect of this neutrophil subset that was corroborated by depleting peripheral neutrophils or using mice with TLR4 genetically ablated in the myeloid lineage. Finally, cDNA microarray analysis in neutrophils, confirmed by quantitative polymerase chain reaction, showed that TLR4 modulates several pathways associated with ischemia-induced inflammation, migration of neutrophils into the parenchyma, and their functional priming, which might explain the opposite effect on outcome of the different neutrophil subsets. Conclusions- TLR4 deficiency increased the levels of alternative neutrophils (N2)-an effect associated with neuroprotection after stroke-supporting that modulation of neutrophil polarization is a major target of TLR4 and highlighting the crucial role of TLR4 at the peripheral level after stroke. Visual Overview- An online visual overview is available for this article.

Specific Features of SVZ Neurogenesis After Cortical Ischemia: a Longitudinal Study

Stroke is a devastating disease with an increasing prevalence. Part of the current development in stroke therapy is focused in the chronic phase, where neurorepair mechanisms such as neurogenesis, are involved. In the adult brain, one of the regions where neurogenesis takes place is the subventricular zone (SVZ) of the lateral ventricles. Given the possibility to develop pharmacological therapies to stimulate this process, we have performed a longitudinal analysis of neurogenesis in a model of cortical ischemia in mice. Our results show an initial decrease of SVZ proliferation at 24 h, followed by a recovery leading to an increase at 14d and a second decrease 28d after stroke. Coinciding with the 24 h proliferation decrease, an increase in the eutopic neuroblast migration towards the olfactory bulb was observed. The analysis of the neuroblast ectopic migration from the SVZ toward the lesion showed an increase in this process from day 14 after the insult. Finally, our data revealed an increased number of new cortical neurons in the peri-infarct cortex 65d after the insult. In summary, we report here critical check-points about post-stroke neurogenesis after cortical infarcts, important for the pharmacological modulation of this process in stroke patients.

Characterization of Gcf2/Lrrfip1 in experimental cerebral ischemia and its role as a modulator of Akt, mTOR and β-catenin signaling pathways

Leucine-rich repeat in Flightless-1 interaction protein 1 (Lrrfip1) is an up-regulated protein after cerebral ischemia whose precise role in the brain both in healthy and ischemic conditions is unclear. Different Lrrfip1 isoforms with distinct roles have been reported in human and mouse species. The present study aimed to analyze the Lrrfip1 transcriptional variants expressed in rat cortex, to characterize their expression patterns and subcellular location after ischemia, and to define their putative role in the brain. Five transcripts were identified and three of them (Lrrfip1, CRA_g and CRA_a' (Fli-I leucine-rich repeat associated protein 1 - Flap-1)) were analyzed by quantitative real-time polymerase chain reaction (qPCR). All the transcripts were up-regulated and showed differential expression patterns after in vivo and in vitro ischemia models. The main isoform, Lrrfip1, was found to be up-regulated from the acute to the late phases of ischemia in the cytoplasm of neurons and astrocytes of the peri-infarct area. This study demonstrates that Lrrfip1 activates β-catenin, Akt, and mammalian target of rapamycin (mTOR) proteins in astrocytes and positively regulates the expression of the excitatory amino acid transporter subtype 2 (GLT-1). Our findings point to Lrrfip1 as a key brain protein that regulates pro-survival pathways and proteins and encourages further studies to elucidate its role in cerebral ischemia as a potential target to prevent brain damage and promote functional recovery after stroke.

Pallister-Killian syndrome in a preterm newborn who died soon after precipitous delivery: cytogenetic analysis

The authors report a preterm neonate with dysmorphic traits and cleft palate who was born preterm because of precipitous delivery and died soon after birth notwithstanding neonatal intensive care unit (NICU) support. The cytogenetic analysis on fibroblasts from post-mortem skin biopsy demonstrated a Pallister-Killian syndrome (PKS). PKS is a cytogenetically syndrome characterized by a tissue limited mosaic distribution of one isochromosome 12p (tetrasomy 12p). Clinical manifestations of PKS are variable, and some symptoms may overlap with other malformative syndromes, thus the correct diagnosis mainly depends on the demonstration of the specific cytogenetic abnormality.

Unbalanced 1q whole-arm translocation resulting in der(14)t(1;14)(q11-12;p11) in myelodysplastic syndrome

Unbalanced whole-arm translocations (WATs) of the long arm of chromosome 1, resulting in complete trisomy 1q, are chromosomal abnormalities detectable in both solid tumors and hematologic neoplasms. Among the WATs of 1q to acrocentric chromosomes, a few patients with der(1;15) described as a dicentric chromosome have been reported so far, whereas cases of der(1;14) are much rarer. We report on a case of der(1;14) detected as single anomaly in a patient with myelodysplastic syndrome. The aim of our work was to investigate the breakpoints of the (1;14) translocation leading to the der(1;14). Fluorescence in situ hybridization (FISH) experiments have been performed on chromosome preparations from bone marrow aspirate, using specific centromeric probes of both chromosomes, as well as a probe mapping to 1q11 band. FISH results showed that in our patient the derivative chromosome was monocentric with a unique centromere derived from chromosome 14. The breakpoints of the translocation were located in the short arm of chromosome 14 and in the long arm of chromosome 1, between the alphoid D1Z5 and the satellite II domains. The 1q breakpoint was within the pericentromeric region of chromosome 1, which is notoriously an unstable chromosomal region, involved in different chromosomal rearrangements.

Longitudinal studies of ischemic penumbra by using 18F-FDG PET and MRI techniques in permanent and transient focal cerebral ischemia in rats

At present, the goal of stroke research is the identification of a potential recoverable tissue surrounding the ischemic core, suggested as ischemic penumbra, with the aim of applying a treatment that attenuates the growth of this area. Our purpose was to determine whether a combination of imaging techniques, including (18)F-FDG PET and MRI could identify the penumbra area. Longitudinal studies of (18)F-FDG PET and MRI were performed in rats 3 h, 24 h and 48 h after the onset of ischemia. A transient and a permanent model of focal cerebral ischemia were performed. Regions of interest were located, covering the ischemic core, the border that progresses to infarction (recruited tissue), and the border that recovers (recoverable tissue) with early reperfusion. Analyses show that permanent ischemia produces severe damage, whereas the transient ischemia model does not produce clear damage in ADC maps at the earliest time studied. The only significant differences between values for recoverable tissue, (18)F-FDG (84±2%), ADC (108±5%) and PWI (70±8%), and recruited tissue, (18)F-FDG (77±3%), ADC (109±4%) and PWI (77±4%), are shown in (18)F-FDG ratios. We also show that recoverable tissue values are different from those in non-infarcted tissue. The combination of (18)F-FDG PET, ADC and PWI MRI is useful for identification of ischemic penumbra, with (18)F-FDG PET being the most sensitive approach to its study at early times after stroke, when a clear DWI deficit is not observed.

The natural tissue plasminogen activator inhibitor neuroserpin and acute ischaemic stroke outcome

Neuroserpin is a brain-derived natural inhibitor of tissue plasminogen activator (tPA) that has shown neuroprotective effects in animal models of brain ischaemia. Our aim was to investigate the association of neuroserpin levels in blood with functional outcome in patients with acute ischaemic stroke. Due to the potential effect of tPA treatment interfering on neuroserpin levels, we studied two different cohorts: 129 patients not treated with tPA and 80 patients treated with intravenous tPA within 3 hours (h) from symptoms onset. Neuroserpin levels were measured by ELISA. Good functional outcome at three months was defined as Rankin scale score ≤2. In the two cohorts, serum neuroserpin levels on admission were significantly higher than at 24 h, 72 h and in healthy subjects. In non tPA-treated patients, neuroserpin levels decrease at 24 h, but not levels at baseline, were associated with good outcome (for each quartile decrease, adjusted odds ratio [OR] 15.0; 95% confidence interval [CI], 3.5 to 66). In the tPA-treated cohort, high neuroserpin levels before tPA bolus had the stronger effect on favourable outcome (for each quartile, OR 13.5; 95%CI, 3.9 to 47). Furthermore, for each quartile in neuroserpin levels before tPA bolus there was a 80% (95%CI, 48 to 92) reduction in the probability of subsequent parenchymal haematoma. In summary, high serum neuroserpin levels before intravenous tPA and neuroserpin levels decrease at 24 h after ischaemic stroke, independently of tPA treatment, are associated with good functional outcome. These findings support the concept that neuroserpin might play an important role during cerebral ischaemia.

Lack of adrenomedullin, but not complement factor H, results in larger infarct size and more extensive brain damage in a focal ischemia model

Adrenomedullin (AM) and its binding protein, complement factor H (FH), are expressed throughout the brain. In this study we used a brain-specific conditional knockout for AM and a complete knockout for FH to investigate the effect of these molecules on the pathophysiology of stroke. Following 48 h of middle cerebral artery permanent occlusion, there was a statistically significant infarct size increase in animals lacking AM when compared to their wild type littermates. In contrast, lack of FH did not affect infarct volume. To investigate some of the mechanisms by which lack of AM may augment brain damage, markers of nitrosative stress, apoptosis, and autophagy were studied at the mRNA and protein levels. There was a significant increase of inducible nitric oxide synthase (iNOS), matrix metalloproteinase-9 (MMP9), fractin, and Beclin-1 in the peri-infarct area of AM-deficient mice when compared to their wild type counterparts and to contralateral and sham-operated controls. These data suggest that AM exerts a neuroprotective action in the brain and that this protection may be mediated by regulation of iNOS, matrix metalloproteases, and inflammatory mediators. In the future, substances that increase AM actions in the central nervous system may be used as potential neuroprotective agents in stroke.

Mitochondria and reactive oxygen and nitrogen species in neurological disorders and stroke: Therapeutic implications

Mitochondria represent both the main source and target of reactive oxygen and nitrogen species (RONS). In view of the large energy expenditure made by neurons during neurotransmission, an intact mitochondrial function is of paramount importance for the correct function of the brain. Accordingly, the search of therapeutic strategies against situations in which there is an abnormal brain function, such as neurological disorders and stroke, should be focused towards mitochondria. Here, we have reviewed the normal and abnormal mitochondrial bioenergetics and dynamics, highlighting the relevance that, for these processes in the brain RONS exert. Evidence suggests that disruption of mitochondrial bioenergetics and dynamics may have a critical role in the pathogenesis of these brain diseases. Drug therapies directed toward providing safer mitochondria are currently under both pre- and clinical investigations.

Toll-like receptor 4 is involved in subacute stress-induced neuroinflammation and in the worsening of experimental stroke

BACKGROUND AND PURPOSE

Psychological stress causes an inflammatory response in the brain and is able to exacerbate brain damage caused by experimental stroke. We previously reported that subacute immobilization stress in mice worsens stroke outcome through mechanisms that involve inflammatory mechanisms, such as accumulation of oxidative/nitrosative mediators and expression of inducible nitric oxide synthase and cyclooxygenase-2 in the brain. Some of these inflammatory mediators could be regulated by innate immunity, the activation of which takes place in the brain and produces an inflammatory response mediated by toll-like receptors (TLRs). Recently, we described the implications of TLR4 in ischemic injury, but the role of TLR4 in stress has not yet been examined. We therefore investigated whether inflammation produced by immobilization stress differs in mice that lack a functional TLR4 signaling pathway.

METHODS

We used an experimental paradigm consisting of the exposure of mice to repeated immobilization sessions (1 hour daily for 7 days) before permanent middle cerebral artery occlusion.

RESULTS

We found that TLR4-deficient mice subjected to subacute stress had a better behavioral condition compared with normal mice (C3H/HeN) and that this effect was associated with a minor inflammatory response (cyclooxygenase-2 and inducible nitric oxide synthase expression) and lipid peroxidation (malondialdehyde levels) in brain tissue. Furthermore, previous exposure to stress was followed by a smaller infarct volume after permanent middle cerebral artery occlusion in TLR4-deficient mice than in mice that express TLR4 normally.

CONCLUSIONS

Our results indicate that TLR4 is involved in the inflammatory response after subacute stress and its exacerbating effect on stroke. These data implicate the effects of innate immunity on inflammation and damage in the brain after stroke.

Statin treatment withdrawal in ischemic stroke: a controlled randomized study

BACKGROUND

Pretreatment with statins has been shown to reduce brain injury in cerebral ischemia. In this controlled randomized study, we investigated the influence of statin pretreatment and its withdrawal on the outcome of acute ischemic stroke patients.

METHODS

From 215 patients admitted within 24 hours of a hemispheric ischemic stroke, 89 patients on chronic statin treatment were randomly assigned either to statin withdrawal for the first 3 days after admission (n = 46) or to immediately receive atorvastatin 20 mg/day (n = 43). The primary outcome event was death or dependency (modified Rankin Scale [mRS] score > 2) at 3 months. Early neurologic deterioration (END) and infarct volume at days 4 to 7 were secondary outcome variables. In a secondary analysis, outcome variables were compared with the nonrandomized patients without previous statin therapy (n = 126).

RESULTS

Patients with statin withdrawal showed a higher frequency of mRS score > 2 at the end of follow-up (60.0% vs 39.0%; p = 0.043), END (65.2% vs 20.9%; p < 0.0001), and greater infarct volume (74 [45, 126] vs 26 [12, 70] mL; p = 0.002) compared with the non-statin-withdrawal group. Statin withdrawal was associated with a 4.66 (1.46 to 14.91)-fold increase in the risk of death or dependency, a 8.67 (3.05 to 24.63)-fold increase in the risk of END, and an increase in mean infarct volume of 37.63 mL (SE 10.01; p < 0.001) after adjusting for age and baseline stroke severity. Compared with patients without previous treatment with statins, statin withdrawal was associated with a 19.01 (1.96 to 184.09)-fold increase in the risk of END and an increase in mean infarct volume of 43.51 mL (SE 21.91; p = 0.048).

CONCLUSION

Statin withdrawal is associated with increased risk of death or dependency at 90 days. Hence, this treatment should be continued in the acute phase of ischemic stroke.

Delayed post-ischemic administration of CDP-choline increases EAAT2 association to lipid rafts and affords neuroprotection in experimental stroke

Glutamate transport is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels. Among glutamate transporters, EAAT2 is responsible for up to 90% of all glutamate transport and has been reported to be associated to lipid rafts. In this context, we have recently shown that CDP-choline induces EAAT2 translocation to the membrane. Since CDP-choline preserves membrane stability by recovering levels of sphingomyelin, a glycosphingolipid present in lipid rafts, we have decided to investigate whether CDP-choline increases association of EAAT2 transporter to lipid rafts. Flotillin-1 was used as a marker of lipid rafts due to its known association to these microdomains. After gradient centrifugation, we have found that flotillin-1 appears mainly in fractions 2 and 3 and that EAAT2 protein is predominantly found colocalised with flotillin-1 in fraction 2. We have also demonstrated that CDP-choline increased EAAT2 levels in fraction 2 at both times examined (3 and 6 h after 1 g/kg CDP-choline administration). In agreement with this, [(3)H] glutamate uptake was also increased in flotillin-associated vesicles obtained from brain homogenates of animals treated with CDP-choline. Exposure to middle cerebral artery occlusion also increased EAAT2 levels in lipid rafts, an effect which was further enhanced in those animals receiving 2 g/kg CDP-choline 4 h after the occlusion. Infarct volume measured at 48 h after ischemia showed a reduction in the group treated with CDP-choline 4 h after occlusion. In summary, we have demonstrated that CDP-choline redistributes EAAT2 to lipid raft microdomains and improves glutamate uptake. This effect is also found after experimental stroke, when CDP-choline is administered 4 h after the ischemic occlusion. Since we have also shown that this delayed post-ischemic administration of CDP-choline induces a potent neuroprotection, our data provides a novel target for neuroprotection in stroke.

Ischemic preconditioning reveals that GLT1/EAAT2 glutamate transporter is a novel PPARgamma target gene involved in neuroprotection

Excessive levels of extracellular glutamate in the nervous system are excitotoxic and lead to neuronal death. Glutamate transport, mainly by glutamate transporter GLT1/EAAT2, is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels in the central nervous system. We recently showed that neuroprotection after experimental ischemic preconditioning (IPC) involves, at least partly, the upregulation of the GLT1/EAAT2 glutamate transporter in astrocytes, but the mechanisms were unknown. Thus, we decided to explore whether activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR) gamma, known for its antidiabetic and antiinflammatory properties, is involved in glutamate transport. First, we found that the PPARgamma antagonist T0070907 inhibits both IPC-induced tolerance and reduction of glutamate release after lethal oxygen-glucose deprivation (OGD) (70.1%+/-3.4% versus 97.7%+/-5.2% of OGD-induced lactate dehydrogenase (LDH) release and 61.8%+/-5.9% versus 85.9%+/-7.9% of OGD-induced glutamate release in IPC and IPC+T0070907 1 mumol/L, respectively, n=6 to 12, P<0.05), as well as IPC-induced astrocytic GLT-1 overexpression. IPC also caused an increase in nuclear PPARgamma transcriptional activity in neurons and astrocytes (122.1%+/-8.1% and 158.6%+/-22.6% of control PPARgamma transcriptional activity, n=6, P<0.05). Second, the PPARgamma agonist rosiglitazone increased both GLT-1/EAAT2 mRNA and protein expression and [(3)H]glutamate uptake, and reduced OGD-induced cell death and glutamate release (76.3%+/-7.9% and 65.5%+/-15.1% of OGD-induced LDH and glutamate release in rosiglitazone 1 mumol/l, respectively, n=6 to 12, P<0.05). Finally, we have identified six putative PPAR response elements (PPREs) in the GLT1/EAAT2 promoter and, consistently, rosiglitazone increased fourfold GLT1/EAAT2 promoter activity. All these data show that the GLT1/EAAT2 glutamate transporter is a target gene of PPARgamma leading to neuroprotection by increasing glutamate uptake.

A chronic treatment with CDP-choline improves functional recovery and increases neuronal plasticity after experimental stroke

Chronic impairment of forelimb and digit movement is a common problem after stroke that is resistant to therapy. Although in the last years some studies have been performed to increase the efficacy of rehabilitative experience and training, the pharmacological approaches in this context remain poorly developed. We decided to study the effect of a chronic treatment with CDP-choline, a safe and well-tolerated drug that is known to stabilize membranes, on functional outcome and neuromorphological changes after stroke. To assess the functional recovery we have performed the staircase reaching test and the elevated body swing test (EBST), for studying sensorimotor integration and asymmetrical motor function respectively. The treatment with CDP-choline, initiated 24 h after the middle cerebral artery occlusion (MCAO) and maintained during 28 days, improved the functional outcome in both the staircase test (MCAO+CDP=87.0+/-6.6% pellets eaten vs. MCAO+SAL=40.0+/-4.5%; p<0.05) and the EBST (MCAO+CDP=70.0+/-6.8% vs. MCAO+SAL=88.0+/-5.4%; contralateral swing p<0.05). In addition, to study potential neuronal substrates of the improved function, we examined the dendritic morphology of layer V pyramidal cells in the undamaged motor cortex using a Golgi-Cox procedure. The animals treated with CDP-choline showed enhanced dendritic complexity and spine density compared with saline group. Our results suggest that a chronic treatment with CDP-choline initiated 24 h after the insult is able to increase the neuronal plasticity within noninjured and functionally connected brain regions as well as to promote functional recovery.

The role of tumor necrosis factor-alpha in stress-induced worsening of cerebral ischemia in rats

Whereas stress is known to be one of the risk factors of stroke, few experimental studies have examined the possible mechanisms by which stress may affect stroke outcome. Most of the knowledge on the effects of stress on cerebrovascular disease in humans is restricted to catecholamines and glucocorticoids effects on blood pressure and/or development of atherosclerosis. By using an experimental paradigm consisting of the exposure of Fischer rats to repeated immobilization sessions (1 h daily during seven consecutive days) prior to permanent middle cerebral artery occlusion (MCAO), we have found that stress worsens behavioral outcome and increases infarct size after MCAO. These changes occur concomitantly to an increase in inducible nitric oxide synthase (iNOS) expression and to the accumulation of lipid peroxidation markers in brain tissue. The possible regulatory role of TNFalpha was studied by looking at the mechanisms of release of this cytokine as well as to the expression of its receptors (TNFR1 and 2). The results of the present study suggest an increase in TNFalpha expression and release after stress, as well as an increase in the expression of TNFR1. Pharmacological blockade of TNFalpha with anti-TNFalpha led to a decrease in the infarct size as well as in the oxidative/nitrosative biochemical parameters seen after ischemia. In summary, our results indicate that TNFalpha accounts, at least partly, for the worsening of MCAO consequences in brain of rats exposed to stress. Furthermore, the data presented here provide evidence that stress can increase brain ischemic damage and support a possible protective effect of treatment of stressful situations before and during the development of the brain ischemia.

Targets of cytoprotection in acute ischemic stroke: present and future

Although the management of stroke has improved remarkably over the last decade due mainly to the advent of thrombolysis, most neuroprotective agents, although successful in animal studies, have failed in humans. Our increasing knowledge concerning the ischemic cascade is leading to a considerable development of pharmacological tools suggesting that each step of this cascade might be a target for cytoprotection. Glutamate has long been recognized to play key roles in the pathophysiology of ischemia. However, although some trials are still ongoing, the results from several completed trials with drugs interfering with the glutamatergic pathway have been disappointing. Regarding the inhibition of glutamate release as a possible target for cytoprotection, it might be afforded either by decreasing glutamate efflux or by increasing glutamate uptake. In this context, it has been shown that glutamate transport is the primary and only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels. This transport is executed by the five high-affinity, sodium-dependent plasma membrane glutamate transporters. Among them, the transporter EAAT2 is responsible for up to 90% of all glutamate transport. We will discuss the effect of different neuroprotective tools (membrane stabilizers or endogenous neuroprotection) affecting glutamate efflux and/or expression of EAAT2. We will also describe the finding of a novel polymorphism in the EAAT2 promoter region which could be responsible for differences in both gene function and regulation under pathological conditions such as cerebral ischemia, and which might well account for the failure of glutamate antagonists in the clinical practice. These results may possess important therapeutic implications in the management of patients at risk of ischemic events, since it has been demonstrated that those patients with progressing stroke have higher plasma concentrations of glutamate which remain elevated up to 24 h when compared to the levels in patients without neurological deterioration.

TNFR1 mediates increased neuronal membrane EAAT3 expression after in vivo cerebral ischemic preconditioning

A short ischemic event (ischemic preconditioning) can result in subsequent resistance to severe ischemic injury (ischemic tolerance). Glutamate is released after ischemia and produces cell death. It has been described that after ischemic preconditioning, the release of glutamate is reduced. We have shown that an in vitro model of ischemic preconditioning produces upregulation of glutamate transporters which mediates brain tolerance. We have now decided to investigate whether ischemic preconditioning-induced glutamate transporter upregulation takes also place in vivo, its cellular localization and the mechanisms by which this upregulation is controlled. A period of 10 min of temporary middle cerebral artery occlusion was used as a model of ischemic preconditioning in rat. EAAT1, EAAT2 and EAAT3 glutamate transporters were found in brain from control animals. Ischemic preconditioning produced an up-regulation of EAAT2 and EAAT3 but not of EAAT1 expression. Ischemic preconditioning-induced increase in EAAT3 expression was reduced by the TNF-alpha converting enzyme inhibitor BB1101. Intracerebral administration of either anti-TNF-alpha antibody or of a TNFR1 antisense oligodeoxynucleotide also inhibited ischemic preconditioning-induced EAAT3 up-regulation. Immunohistochemical studies suggest that, whereas the expression of EAAT3 is located in both neuronal cytoplasm and plasma membrane, ischemic preconditioning-induced up-regulation of EAAT3 is mainly localized at the plasma membrane level. In summary, these results demonstrate that in vivo ischemic preconditioning increases the expression of EAAT2 and EAAT3 glutamate transporters the upregulation of the latter being at least partly mediated by TNF-alpha converting enzyme/TNF-alpha/TNFR1 pathway.

Role of nitric oxide after brain ischaemia

Ischaemic stroke is the second or third leading cause of death in developed countries. In the last two decades substantial research and efforts have been made to understand the biochemical mechanisms involved in brain damage and to develop new treatments. The evidence suggests that nitric oxide (NO) can exert both protective and deleterious effects depending on factors such as the NOS isoform and the cell type by which NO is produced or the temporal stage after the onset of the ischaemic brain injury. Immediately after brain ischaemia, NO release from eNOS is protective mainly by promoting vasodilation; however, after ischaemia develops, NO produced by overactivation of nNOS and, later, NO release by de novo expression of iNOS contribute to the brain damage. This review article summarizes experimental and clinical data supporting the dual role of NO in brain ischaemia and the mechanisms by which NO is regulated after brain ischaemia. We also review NO-based therapeutic strategies for stroke treatment, not only those directly linked with the NO pathway such as NO donors and NOS inhibitors but also those partially related like statins, aspirin or lubeluzole.

3,4‐Methylenedioxymethamphetamine increases interleukin‐1β levels and activates microglia in rat brain: studies on the relationship with acute hyperthermia and 5‐HT depletion

3,4-Methylenedioxymethamphetamine (MDMA) administration to rats produces acute hyperthermia and 5-HT release. Interleukin-1beta (IL-1beta) is a pro-inflammatory pyrogen produced by activated microglia in the brain. We examined the effect of a neurotoxic dose of MDMA on IL-1beta concentration and glial activation and their relationship with acute hyperthermia and 5-HT depletion. MDMA, given to rats housed at 22 degrees C, increased IL-1beta levels in hypothalamus and cortex from 1 to 6 h and [(3)H]-(1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)3-isoquinolinecarboxamide) binding between 3 and 48 h. Increased immunoreactivity to OX-42 was also detected. Rats became hyperthermic immediately after MDMA and up to at least 12 h later. The IL-1 receptor antagonist did not modify MDMA-induced hyperthermia indicating that IL-1beta release is a consequence, not the cause, of the rise in body temperature. When MDMA was given to rats housed at 4 degrees C, hyperthermia was abolished and the IL-1beta increase significantly reduced. The MDMA-induced acute 5-HT depletion was prevented by fluoxetine coadministration but the IL-1beta increase and hyperthermia were unaffected. Therefore, the rise in IL-1beta is not related to the acute 5-HT release but is linked to the hyperthermia. Contrary to IL-1beta levels, microglial activation is not significantly modified when hyperthermia is prevented, suggesting that it might be a process not dependent on the hyperthermic response induced by MDMA.

In vitro ischemic tolerance involves upregulation of glutamate transport partly mediated by the TACE/ADAM17-tumor necrosis factor-alpha pathway

A short ischemic event [ischemic preconditioning (IPC)] can result in a subsequent resistance to severe ischemic injury (ischemic tolerance). Although tumor necrosis factor-alpha (TNF-alpha) contributes to the brain damage found after cerebral ischemia, its expression and neuroprotective role in models of IPC have also been described. Regarding the role of TNF-alpha convertase (TACE/ADAM17), we have recently shown its upregulation in rat brain after IPC induced by transient middle cerebral artery occlusion and that subsequent TNF-alpha release accounts for at least part of the neuroprotection found in this model. We have now used an in vitro model of IPC using rat cortical cultures exposed to sublethal oxygen-glucose deprivation (OGD) to investigate TACE expression and activity after IPC and the subsequent mechanisms of ischemic tolerance. OGD-induced cell death was significantly reduced in cells exposed to IPC by sublethal OGD 24 hr before, an effect that was inhibited by the TACE inhibitor BB3103 (1 microm) and anti-TNF-alpha antibody (2 microg/ml) and that was mimicked by TNF-alpha (10 pg/ml) preincubation. Western blot analysis showed that TACE expression is increased after IPC. IPC caused TNF-alpha release, an effect that was blocked by the selective TACE inhibitor BB-3103. In addition, IPC diminished the increase in extracellular glutamate caused by OGD and increased cellular glutamate uptake and expression of EAAT2 and EAAT3 glutamate transporters; however, only EAAT3 upregulation was mediated by increased TNF-alpha. These data demonstrate that neuroprotection induced by IPC involves upregulation of glutamate uptake partly mediated by TACE overexpression.

Effect of subacute and chronic immobilisation stress on the outcome of permanent focal cerebral ischaemia in rats

The aim of this study was to determine the effect of mood disorders, including psychological distress and depression, on stroke outcome. Male Fischer rats were exposed to immobilisation stress, an animal paradigm of psychological stress, major depression and post-traumatic stress disorder. Either a subacute (1 h for 7 days) or a chronic (6 h for 21 days) exposure to stress was applied 24 h before permanent middle cerebral artery occlusion (MCAO). Stroke outcome was assessed by measurement of infarct size and behavioural characterisation. Serum glutamate and brain ATP levels as well as brain glutamate transporter function and expression were studied in the search for the molecular mechanisms involved. Subacute stress exposure increased infarct size and decreased behavioural scores after stroke. On the contrary, chronic stress exposure decreased infarct size. Peak serum glutamate levels correlated with infarct size after MCAO. Expression of glutamate transporters was decreased by subacute stress, whereas the expression of EAAT1, a glial glutamate carrier, was increased after the chronic stress protocol. Our results indicate that distinct patterns of stress determine different stroke outcomes, and that expressional changes of brain glutamate transporters, able to affect glutamate release after stroke, are involved.

Expression and function of tumour necrosis factor-alpha-converting enzyme in the central nervous system

Tumour necrosis factor-alpha (TNF-alpha)-converting enzyme (TACE/ADAM17) is a membrane protein belonging to the ADAM (a disintegrin and a metalloprotease) family able to cleave various membrane proteins, including the transmembrane form of TNF-alpha at its physiological processing site. Being an ADAM, TACE may mediate not only proteolysis but also adhesive interactions; however, the role of the disintegrin domain of TACE has not been studied. In the central nervous system (CNS), little is known about the physiological role of TACE, but some important pathophysiological functions have been reported recently, with both neurotoxic and neuroprotective repercussions. This article discusses and reviews the main contributions to this field of investigation addressing the expression and function of TACE in the CNS.

Cerebrospinal fluid and plasma concentrations of nitric oxide metabolites are increased in dementia with Lewy bodies

We compared cerebrospinal fluid (CSF) and plasma concentrations of nitric oxide metabolites (NO(-)(x)) in 22 patients with dementia with Lewy bodies (DLB) and 13 matched controls. We found a pronounced increase in NO(-)(x) CSF and plasma levels in DLB patients. No changes were found in L-arginine and L-citrulline levels in CSF or plasma. There was no correlation between CSF and plasma levels and age, age of onset, duration of the disease or scores of the MiniMental State Examination. These findings reveal that excessive nitric oxide production may be related to the pathogenesis of DLB.

Inhibition of glutamate release via recovery of ATP levels accounts for a neuroprotective effect of aspirin in rat cortical neurons exposed to oxygen-glucose deprivation

BACKGROUND AND PURPOSE

Aspirin is preventive against stroke not only because of its antithrombotic properties but also by other direct effects. The aim of this study was to elucidate its direct neuroprotective effects.

METHODS

Viability parameters, glutamate release and uptake, and ATP levels were measured in cultured cortical neurons exposed to oxygen-glucose deprivation (OGD). In addition, ATP levels and oxygen consumption were studied in isolated brain mitochondria or submitochondrial particles.

RESULTS

Aspirin inhibited OGD-induced neuronal damage at concentrations lower (0.3 mmol/L) than those reported to act via inhibition of the transcription factor nuclear factor-kappaB (which are >1 mmol/L), an effect that correlated with the inhibition caused by aspirin on glutamate release. This effect was shared by sodium salicylate but not by indomethacin, thus excluding the involvement of cyclooxygenase. A pharmacological dissection of the components involved indicated that aspirin selectively inhibits the increase in extracellular glutamate concentration that results from reversal of the glutamate transporter, a component of release that is due to ATP depletion. Moreover, aspirin-afforded neuroprotection occurred in parallel with a lesser decrease in ATP levels after OGD. Aspirin elevated ATP levels not only in intact cortical neurons but also in isolated brain mitochondria, an effect concomitant with an increase in NADH-dependent respiration by brain submitochondrial particles.

CONCLUSIONS

Taken together, our present findings show a novel mechanism for the neuroprotective effects of aspirin, which takes place at concentrations in the antithrombotic-analgesic range, useful in the management of patients with high risk of ischemic events.

Implication of TNF-alpha convertase (TACE/ADAM17) in inducible nitric oxide synthase expression and inflammation in an experimental model of colitis

Tumour necrosis factor-alpha (TNF-alpha) is a pro-inflammatory cytokine which is shed in its soluble form by a disintegrin and metalloproteinase (ADAM) called TNF-alpha convertase (TACE; ADAM17). TNF-alpha plays a role in inflammatory bowel disease (IBD) and is involved in the expression of inducible nitric oxide synthase (iNOS) which has also been implicated in IBD. The study was designed to investigate whether colitis induced by trinitrobenzene sulphonic acid (TNBS) in rats produces an increase in TACE activity and/or expression and whether its pharmacological inhibition reduces TNF-alpha levels, iNOS expression and colonic damage in this model. TNBS (30 mg in 0.4 ml of 50% ethanol) was instilled into the colon of female Wistar rats. Saline or TACE inhibitor BB1101 (10 mg/kg/day) was administered intraperitoneally 5 days after TNBS instillation. On day 10, colons were removed and assessed for pathological score, myeloperoxidase (MPO), NO synthase (NOS), TACE enzymatic activity and protein levels, colonic TNF-alpha and NOx- levels. Instillation of TNBS caused an increase in TACE activity and expression and the release of TNF-alpha. TNBS also resulted in iNOS expression and colonic damage. BB1101 blocked TNBS-induced increase in TACE activity, TNF-alpha release and iNOS expression. Concomitantly, BB1101 ameliorated TNBS-induced colonic damage and inflammation. TNBS causes TNF-alpha release by an increase in TACE activity and expression and this results in the expression of iNOS and subsequent inflammation, suggesting that TACE inhibition may prove useful as a therapeutic means in IBD.

Neuroprotective effect of aspirin by inhibition of glutamate release after permanent focal cerebral ischaemia in rats

Aspirin reduces the size of infarcts after ischaemic stroke. Although this fact has been attributed to its anti-platelet actions, direct neuroprotective effects have also been reported. We have recently demonstrated that aspirin is neuroprotective by inhibiting glutamate release in 'in vitro' models of brain ischaemia, via an increase in ATP production. The present study was designed to determine whether the inhibition of glutamate release induced by aspirin might be protective in a whole-animal model of permanent focal brain ischaemia. Focal brain ischaemia was produced in male adult Fischer rats by occluding both the common carotid and middle cerebral arteries. Central and serum glutamate levels were determined at fixed intervals after occlusion. The animals were then killed and infarct volume was measured. Aspirin (30 mg/kg i.p. administered 2 h before the occlusion) produced a significant reduction in infarct volume, an effect that correlated with the inhibition caused by aspirin on ischaemia-induced increase in brain and serum glutamate concentrations after the onset of the ischaemia. Aspirin also inhibited ischaemia-induced decrease in brain ATP levels. Our present findings show a novel mechanism for the neuroprotective effects of aspirin, which takes place at concentrations in the anti-aggregant-analgesic range, useful in the management of patients with risk of ischaemic events.

N-(3-(aminomethyl)benzyl)acetamidine, an inducible nitric oxide synthase inhibitor, decreases colonic inflammation induced by trinitrobenzene sulphonic acid in rats

Gastrointestinal inflammation has been associated with an increased generation of nitric oxide (NO) and the expression of the inducible NO synthase (iNOS). Using an experimental model of colitis induced by trinitrobenzene sulphonic acid (TNBS), we sought to determine whether the administration of N-(3-(Aminomethyl)benzyl)acetamidine (1400W), a specific inhibitor of iNOS, has a beneficial action on the colonic injury. 1400W (0.4 and 2 mg/kg/day) was administered intraperitoneally from day 5 to 10 after intrarectal instillation of TNBS. TNBS led to colonic ulceration and inflammation, an increase of colonic myeloperoxidase activity and the expression of the calcium-independent NOS from days 1 to 15. 1400W reduced the macroscopic damage and the histological changes induced by TNBS as well as the calcium-independent NOS activity and myeloperoxidase activity determined over 30 min after sacrifice. These findings indicate that the expression of iNOS accounts for most of the damage caused by TNBS and that the administration of 1400W after the onset of colitis has a beneficial action on the colonic injury.

Up-regulation of TNF-alpha convertase (TACE/ADAM17) after oxygen-glucose deprivation in rat forebrain slices

Tumour necrosis factor-alpha (TNF-alpha) is a major immunomodulatory and proinflammatory cytokine which is shed in its soluble form by a membrane-anchored zinc protease, identified as a disintegrin and metalloproteinase (ADAM) called TNF-alpha convertase (TACE; ADAM17). The role of this protease in the adult nervous system remains poorly understood. During cerebral ischemia and subsequent reperfusion, expression and release of TNF-alpha have been shown. We have investigated the expression and activity of TACE in an in vitro model of brain ischemia consisting of rat forebrain slices exposed to oxygen-glucose deprivation (OGD). OGD caused the release of TNF-alpha, an effect which was inhibited by a hydroxamate-based metalloprotease inhibitor, BB-3103, with an IC(50) of 0.1 microM, suggesting that TNF-alpha release results selectively from TACE activity. Assay of TACE enzymatic activity on a fluorescein-labelled peptide spanning the cleavage site in pro-TNF-alpha, as well as Western blot and RT-PCR analyses showed that TACE is present in control forebrain and, more interestingly, that TACE expression is increased in OGD-exposed tissue. TACE enzymatic activity from OGD-exposed slices was significantly inhibited by cycloheximide, suggesting that de novo synthesis of TACE contributes to TNF-alpha release after ischaemia. Moreover, it was also inhibited by bisindolylmaleimide I, indicating that TACE activity is regulated by PKC. These findings posed the question of what was its function therein. Among other actions, TNF-alpha has been described to be involved in the expression of inducible nitric oxide synthase (iNOS), a high-output NOS isoform associated to cellular damage, but the link between TNF-alpha release after brain ischaemia and iNOS expression in this condition has not been shown. We have now found that iNOS expression in OGD-subjected brain slices is inhibited by BB-3103 at concentrations below 1 microM, indicating that shedding of TNF-alpha by TACE plays a necessary part in the induction of this NOS isoenzyme after OGD. Taken together, these data demonstrate that (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding after OGD in rat forebrain slices, (2) an increase in TACE expression contributes, at least in part, to the rise in TNF-alpha after OGD and (3) iNOS expression in OGD-subjected brain slices results from TACE activity and subsequent increase in TNF-alpha levels.

Glutathione depletion, lipid peroxidation and mitochondrial dysfunction are induced by chronic stress in rat brain

Damage to the mitochondrial electron transport chain has been suggested to be an important factor in the pathogenesis of a range of neurodegenerative disorders. We have previously demonstrated that chronic stress induced an increase in nitric oxide (NO) production via an expression of inducible NO synthase (iNOS) in brain. Since it has been demonstrated that NO regulates mitochondrial function, we sought to study the susceptibility of the mitochondrial respiratory chain complexes to chronic restrain stress exposure in brain cortex. In adult male rats, stress (immobilization for six hours during 21 days) inhibits the activities of the first complexes of the mitochondrial respiratory chain (inhibition of 69% in complex I-III and of 67% in complex II-III), without affecting complex IV activity, ATP production and oxygen consumption. The mitochondrial marker citrate synthase is not significantly affected by stress after 21 days, indicating that at this time the mitochondrial structure is still intact. Moreover, the administration of the preferred inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine (400 mg/kg i.p. daily from days 7 to 21 of stress) protects against the inhibition of the activity of complexes of the mitochondrial respiratory chain as well as prevents NO(x)(-) accumulation, lipid peroxidation and glutathione depletion induced by stress. These results suggest that a sustained overproduction of NO via iNOS is responsible, at least in part, of the inhibition of mitochondrial respiratory chain caused by stress and that this pathway also accounts for the oxidative stress found in this situation.

Two different NO-dependent mechanisms account for the low virulence of a non-mycelial morphological mutant of Candida albicans

We have previously described the low virulence of a Candida albicans morphological mutant: 92'. We have now used this strain to examine the role of phagocytes in its pathogenesis. Our results show that C. albicans 92' cannot evade innate host macrophage defence mechanisms as efficiently as the parental strain. In addition to the high susceptibility to phagocytosis by peritoneal macrophages, the NO produced by macrophages is a very important element in the low virulence of this agerminative mutant, a thesis supported by in vivo and in vitro experiments. Whereas the parental strain was able to inhibit macrophage NO production, the mutant was quite inefficient at reducing NO production by macrophages. In addition, the mutant showed high sensitivity to a NO generator. Treatment of mice with aminoguanidine (a preferred inducible NO synthase inhibitor) caused 90% mortality in 92' systemic infection, thus supporting a role for NO in the low virulence of this strain. Our data show that both the low inhibitory effect of 92' on macrophage NO production and the higher sensitivity to NO underlie the low virulence of this strain.

Inducible nitric oxide synthase expression in brain cortex after acute restraint stress is regulated by nuclear factor kappaB-mediated mechanisms

The underlying mechanisms by which physical or psychological stress causes neurodegeneration are still unknown. We have demonstrated that the high-output and long-lasting synthesizing source of nitric oxide (NO), inducible NO synthase (iNOS), is expressed in brain cortex during stress and that its overexpression accounts for the neurodegenerative changes seen after 3 weeks of repeated stress. Now we have found that acute stress (restraint for 6 h) increases the activity of a calcium-independent NOS and induces the expression of iNOS in brain cortex in adult male rats. In order to elucidate the possible mechanisms involved in this induction, we studied the role of transcription nuclear factor kappaB (NF-kappaB), which is required for iNOS synthesis. We have observed that an acute restraint stress session stimulates the translocation of the NF-kappaB to the nucleus after 4 h and that the administration of the NF-kappaB inhibitor pyrrolidine dithiocarbamate [PDTC, 75 and 150 mg/kg intraperitoneally (i.p.)] at the onset of stress inhibits the stress-induced increase in iNOS expression. Since glutamate release and subsequent NMDA (N-methyl-D-aspartate) receptor activation has been recognized as an early change after exposure to stressful stimuli, and glutamate has been shown to induce iNOS in brain via a NF-kappaB-dependent mechanism, we studied the possible role of excitatory amino acids in the induction of iNOS in our model. Pretreatment with the NMDA receptor antagonist dizocilpine (MK-801, 0.1 and 0.3 mg/kg i.p.) inhibits the stress-induced NF-kappaB activation as well as the stress-induced increase in iNOS expression. Taken together, these findings indicate that excitatory amino acids and subsequent activation of NF-kappaB account for stress-induced iNOS expression in cerebral cortex, and support a possible neuroprotective role for specific inhibitors in this situation.

Fructose-1,6-bisphosphate inhibits the expression of inducible nitric oxide synthase caused by oxygen-glucose deprivation through the inhibition of glutamate release in rat forebrain slices

Fructose-1,6-bisphosphate (FBP) is a glycolytic pathway intermediate with a neuroprotective action in animal models of brain ischaemia. We addressed the question of whether FBP acts through inhibiting inducible nitric oxide synthase (iNOS) expression via reduction of glutamate release, since we have recently demonstrated that glutamate is involved in the expression of iNOS. FBP (5 mM) added to the incubation solution of rat forebrain slices subjected to oxygen-glucose deprivation (OGD) inhibited glutamate release significantly (around 40%). FBP also inhibited the induction of the calcium-independent NOS activity and reduced the levels of iNOS protein in rat forebrain slices subjected to OGD. We conclude that the action of FBP by reducing glutamate release and iNOS expression, both of which have been implicated in cell damage, is a reason for further evaluation of FBP as a neuroprotectant.

Implication of glutamate in the expression of inducible nitric oxide synthase after oxygen and glucose deprivation in rat forebrain slices

Nitric oxide synthesis by inducible nitric oxide synthase (iNOS) has been postulated to contribute to ischemia-reperfusion neurotoxicity. The expression of this enzyme has been demonstrated in cells present in the postischemic brain. The mechanisms of iNOS expression after cerebral ischemia are a subject of current research. We therefore decided to investigate whether glutamate, which is released in ischemia and is implicated in neurotoxicity, might be involved in the mechanisms by which oxygen and glucose deprivation (OGD) leads to the expression of iNOS in rat forebrain slices. In this model, we have shown previously that 20 min of OGD causes the expression of iNOS. We have now found that the NMDA receptor antagonist MK-801 blocks the expression of iNOS, suggesting that the activation of the NMDA subtype of glutamate receptor is implicated in the mechanisms that lead to the expression of this isoform. Moreover, we have found that glutamate alone could trigger the induction process, as shown by the appearance of a Ca(2+)-independent NOS activity and by the detection of iNOS mRNA and protein in slices exposed to glutamate. Glutamate-dependent iNOS expression was concentration-dependent and was blocked by EGTA and by the inhibitors of nuclear factor kappaB (NF-kappaB) activation pyrrolidine dithiocarbamate and MG132. In addition, glutamate induced NF-kappaB translocation to the nucleus, an effect that was inhibited by MG132. Taken together, our data suggest that activation of NMDA receptors by glutamate released in ischemia is involved in the expression of iNOS in rat forebrain slices via a Ca(2+)-dependent activation of the transcription factor NF-kappaB. To our knowledge, this is the first report showing an implication of excitatory amino acids in the expression of iNOS caused by ischemia.

Mechanisms of the neuroprotective effect of aspirin after oxygen and glucose deprivation in rat forebrain slices

Acetylsalicylic acid (ASA, Aspirin) is an anti-inflammatory drug with a wide spectrum of pharmacological activities and multiple sites of action. Apart from its preventive actions against stroke due to its antithrombotic properties, recent data in the literature suggest that high concentrations of ASA also exert direct neuroprotective effects. We have used an in vitro model of brain ischaemia using rat forebrain slices deprived of oxygen and glucose to test ASA neuroprotective properties. We have found that ASA inhibits neuronal damage at concentrations lower than those previously reported (0.1-0.5 mM), and that these effects correlate with the inhibition of excitatory amino acid release, of NF-kappaB translocation to the nucleus and iNOS expression caused by ASA. All of these three mechanisms may mediate the neuroprotective effects of this drug. Our results also show that the effects of ASA are independent of COX inhibition. Taken together, our present findings show that ASA is neuroprotective in an in vitro model of brain ischaemia at doses close to those recommended for its antithrombotic effects.

Chronic stress induces the expression of inducible nitric oxide synthase in rat brain cortex

Long-term exposure to stress has detrimental effects on several brain functions in many species, including humans, and leads to neurodegenerative changes. However, the underlying neural mechanisms by which stress causes neurodegeneration are still unknown. We have investigated the role of endogenously released nitric oxide (NO) in this phenomenon and the possible induction of the inducible NO synthase (iNOS) isoform. In adult male rats, stress (immobilization for 6 h during 21 days) increases the activity of a calcium-independent NO synthase and induces the expression of iNOS in cortical neurons as seen by immunohistochemical and western blot analysis. Three weeks of repeated immobilization increases immunoreactivity for nitrotyrosine, a nitration product of peroxynitrite. Repeated stress causes accumulation of the NO metabolites NO2+ NO3- (NOx-) accumulation in cortex, and these changes occur in parallel with lactate dehydrogenase (LDH) release and impairment of glutamate uptake in synaptosomes. Administration of the selective iNOS inhibitor aminoguanidine (400 mg/kg i.p. daily from days 7 to 21 of stress) prevents NOx- accumulation in cortex, LDH release, and impairment of glutamate uptake in synaptosomes. Taken together, these findings indicate that a sustained overproduction of NO via iNOS expression may be responsible, at least in part, for some of the neurodegenerative changes caused by stress and support a possible neuroprotective role for specific iNOS inhibitors in this situation.

Up-regulation of neuronal NO synthase immunoreactivity in opiate dependence and withdrawal

RATIONALE

Nitric oxide (NO) has been postulated to contribute significantly to analgesic effects of opiates as well as to the development of tolerance and physical dependence to morphine.

OBJECTIVE

The present study was undertaken to determine the effect of chronic morphine treatment and abstinence on the expression of neuronal NO synthase (neuronal NOS, nNOS) in several brain regions of mice.

METHODS

Seven days after the implantation of a 75 mg morphine pellet, adult male CD1 mice received a SC dose of 1 mg/kg naloxone. Fifteen minutes after the naloxone injection, brains were removed and nNOS expression was studied by using immunohistochemical methods.

RESULTS

Morphine-dependence produced an increase in the number of nNOS-positive cells in the main and accessory olfactory bulb, olfactory nuclei, cerebellum, locus coeruleus, medulla oblongata (nucleus of the solitary tract and prepositus hypoglossal nucleus), and a decrease in nNOS immunoreactivity in hypothalamus. The administration of naloxone to morphine-dependent mice to induce abstinence increased nNOS immunoreactivity in the hypothalamus and locus coeruleus.

CONCLUSIONS

These results indicate that the chronic treatment with morphine leads to alterations in nNOS expression in important regions implicated in the physical tolerance and dependence to opiates and suggest the use of specific inhibitors of this isoform in these conditions.

Neuroprotective effects of DETA-NONOate, a nitric oxide donor, on hydrogen peroxide-induced neurotoxicity in cortical neurones

Nitric oxide (NO) has been proposed to exert neuroprotective actions against oxidative damage acting directly as an antioxidant; in addition, it has also been suggested that NO might be cytoprotective by increasing cyclic GMP concentrations via activation of soluble guanylate cyclase. In this context, we have previously shown that cyclic GMP elevations confer cytoprotection against the neurotoxicity induced by SIN-1 in the presence of superoxide dismutase, conditions in which cell death seems to be a consequence of hydrogen peroxide (H2O2) formation. We have now found that H2O2 (20-100 microM) causes neurotoxicity in 1-week-old rat cortical neurones and that this effect is inhibited by the NO donor DETA-NONOate (1-10 microM). We have also found that 1H-[1,2,4]oxadiazolo[4,3,-alpha]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylate cyclase, reverses the effect induced by DETA-NONOate, and that this action of ODQ is mimicked by 8-(4-chlorophenylthio)guanosine-3',5'-monophosphorothioate (Rp-8-pCPT-cGMPS), an inhibitor of cyclic GMP-dependent protein kinase, suggesting that the pathway affording protection involves activation of this kinase by cyclic GMP elevations. Simultaneously, ODQ inhibits the elevation of cyclic GMP concentrations induced by DETA-NONOate (1-3 microM) in cortical cells. Finally, we have also shown that the cyclic GMP mimetic, 8-bromoguanosine 3':5'-cyclic monophosphate (8-Br-cyclic GMP) inhibits the neurotoxicity induced by H2O2 (30-40 microM). Taken together, these data demonstrate that NO-induced cyclic GMP elevations confer cytoprotection against H2O2-induced neuronal cell death.

Use of brain slices in the study of pathogenic role of inducible nitric oxide synthase in cerebral ischemia-reperfusion

We have recently demonstrated that inducible nitric oxide synthase (iNOS) is expressed in rat forebrain slices exposed to oxygen and glucose deprivation (OGD). Now, we have found that the expression of iNOS after OGD is time-dependent since 20 min of OGD produces the appearance of iNOS at earlier times than 10 min of OGD. OGD also causes neurotoxicity in this model, as revealed by the increase in excitatory amino acid, neuron specific enolase and lactate dehydrogenase (LDH) efflux to the incubation solution. Finally, the administration of the NMDA receptor antagonist MK-801 (100 nM) inhibits both the expression of iNOS and the release of LDH. Our findings demonstrate that this method may be considered an useful in vitro model of ischemia-reperfusion to determine the therapeutic role of neuroprotective tools.

Nitric oxide synthase activity in human squamous cell carcinoma of the head and neck

OBJECTIVES

To test whether nitric oxide synthase (NOS) is expressed in primary otolaryngologic tumors and whether this expression is associated with the degree of malignancy.

STUDY DESIGN

Twenty-six samples from the primary localization of human pharyngolaryngeal squamous cell carcinoma.

MATERIALS AND METHODS

the activity of calcium-dependent and calcium-independent NOS was analyzed by the conversion of L-[14C]-arginine into L-[14C]-citrulline.

RESULTS

NOS activity is below detectable levels in pharyngolaryngeal mucosa from noncancer patients. In the primary localization of the tumor, calcium-independent NOS activity is maximal at early stages of tumor growth, whereas calcium-dependent activity increases from early to advanced stages.

CONCLUSIONS

These data suggest that tumor growth and malignancy is associated with a change in the enzymatic source of NO from calcium-independent NOS to calcium-dependent NOS isoform in primary localization. These data suggest that the inhibition of calcium-independent NOS activity in early stages and/or inhibition of calcium-dependent NOS activity in later stages could delay growth of solid tumors.

Down-regulation of neuronal nitric oxide synthase by nitric oxide after oxygen-glucose deprivation in rat forebrain slices

The precise role that nitric oxide (NO) plays in the mechanisms of ischemic brain damage remains to be established. The expression of the inducible isoform (iNOS) of NO synthase (NOS) has been demonstrated not only in blood and glial cells using in vivo models of brain ischemia-reperfusion but also in neurons in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). We have used this experimental model to study the effect of OGD on the neuronal isoform of NOS (nNOS) and iNOS. In OGD-exposed rat forebrain slices, a decrease in the calcium-dependent NOS activity was found 180 min after the OGD period, which was parallel to the increase during this period in calcium-independent NOS activity. Both dexamethasone and cycloheximide, which completely inhibited the induction of the calcium-independent NOS activity, caused a 40-70% recovery in calcium-dependent NOS activity when compared with slices collected immediately after OGD. The NO scavenger oxyhemoglobin produced complete recovery of calcium-dependent NOS activity, suggesting that NO formed after OGD is responsible for this down-regulation. Consistently, exposure to the NO donor (Z)-1-[(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-iu m-1,2-diolate (DETA-NONOate) for 180 min caused a decrease in the calcium-dependent NOS activity present in control rat forebrain slices. Furthermore, OGD and DETA-NONOate caused a decrease in level of both nNOS mRNA and protein. In summary, our results indicate that iNOS expression down-regulates nNOS activity in rat brain slices exposed to OGD. These studies suggest important and complex interactions between NOS isoforms, the elucidation of which may provide further insights into the physiological and pathophysiological events that occur during and after cerebral ischemia.