Neutrophil ß1 adrenoceptor blockade blunts stroke-associated neuroinflammation.

BACKGROUND AND PURPOSE: Reperfusion therapy is the standard of care for ischaemic stroke; however, there is a need to identify new therapeutic targets able to ameliorate cerebral damage. Neutrophil ß1 adrenoceptors (ß1AR) have been linked to neutrophil migration during exacerbated inflammation. Given the central role of neutrophils in cerebral damage during stroke, we hypothesize that ß1AR blockade will improve stroke outcomes. EXPERIMENTAL APPROACH: Rats were subjected to middle cerebral artery occlusion-reperfusion to evaluate the effect on stroke of the selective ß1AR blocker metoprolol (12.5 mg·kg-1 ) when injected i.v. 10 min before reperfusion. KEY RESULTS: Magnetic resonance imaging and histopathology analysis showed that pre-reperfusion i.v. metoprolol reduced infarct size. This effect was accompanied by reduced cytotoxic oedema at 24 h and vasogenic oedema at 7 days. Metoprolol-treated rats showed reduced brain neutrophil infiltration and those which infiltrated displayed a high proportion of anti-inflammatory phenotype (N2, YM1+ ). Additional inflammatory models demonstrated that metoprolol specifically blocked neutrophil migration via ß1AR and excluded a significant effect on the glia compartment. Consistently, metoprolol did not protect the brain in neutrophil-depleted rats upon stroke. In patients suffering an ischaemic stroke, ß1AR blockade by metoprolol reduced circulating neutrophil-platelet co-aggregates. CONCLUSIONS AND IMPLICATIONS: Our findings describe that ß1AR blockade ameliorates cerebral damage by targeting neutrophils, identifying a novel therapeutic target to improve outcomes in patients with stroke. This therapeutic strategy is in the earliest stages of the translational pathway and should be further explored.

Influence of metabolic syndrome on post-stroke outcome, angiogenesis and vascular function in old rats determined by dynamic contrast enhanced MRI.

Stroke affects primarily aged and co-morbid people, aspects not properly considered to date. Since angiogenesis/vasculogenesis are key processes for stroke recovery, we purposed to determine how different co-morbidities affect the outcome and angiogenesis/vasculogenesis, using a rodent model of metabolic syndrome, and by dynamic enhanced-contrast imaging (DCE-MRI) to assess its non-invasive potential to determine these processes. Twenty/twenty-two month-old corpulent (JCR:LA-Cp/Cp), a model of metabolic syndrome and lean rats were used. After inducing the experimental ischemia by transient MCAO, angiogenesis was analyzed by histology, vasculogenesis by determination of endothelial progenitor cells in peripheral blood by flow cytometry and evaluating their pro-angiogenic properties in culture and the vascular function by DCE-MRI at 3, 7 and 28 days after tMCAO. Our results show an increased infarct volume, BBB damage and an impaired outcome in corpulent rats compared with their lean counterparts. Corpulent rats also displayed worse post-stroke angiogenesis/vasculogenesis, outcome that translated in an impaired vascular function determined by DCE-MRI. These data confirm that outcome and angiogenesis/vasculogenesis induced by stroke in old rats are negatively affected by the co-morbidities present in the corpulent genotype and also that DCE-MRI might be a technique useful for the non-invasive evaluation of vascular function and angiogenesis processes.

Pharmacological Modulation of Neutrophil Extracellular Traps Reverses Thrombotic Stroke tPA (Tissue-Type Plasminogen Activator) Resistance.

Background and Purpose- Recanalization of the occluded artery is a primary goal in stroke treatment. Unfortunately, endovascular treatment is not always available, and tPA (tissue-type plasminogen activator) therapy is limited by its narrow therapeutic window; importantly, the rate of early arterial recanalization after tPA administration is low, especially for platelet-rich thrombi. The mechanisms for this tPA resistance are not well known. Since neutrophil extracellular traps (NETs) have been implicated in this setting, our aim was to study whether NET pharmacological modulation can reverse tPA resistance and the role of TLR4 (Toll-like receptor 4), previously related to NET formation, in thrombosis. Methods- To this goal, we have used a mouse photothrombotic stroke model, which produces a fibrin-free thrombus composed primarily of aggregated platelets and thrombi obtained from human stroke patients. Results- Our results demonstrate that (1) administration of DNase-I, which promotes NETs lysis, but not of tPA, recanalizes the occluded vessel improving photothrombotic stroke outcome; (2) a preventive treatment with Cl-amidine, impeding NET formation, completely precludes thrombotic occlusion; (3) platelet TLR4 mediates NET formation after photothrombotic stroke; and (4) ex vivo fresh platelet-rich thrombi from ischemic stroke patients are effectively lysed by DNase-I. Conclusions- Hence, our data open new avenues for recanalization of platelet-rich thrombi after stroke, especially to overcome tPA resistance.

Myeloid cells as therapeutic targets in neuroinflammation after stroke: Specific roles of neutrophils and neutrophil-platelet interactions.

Ischemic brain injury causes a local inflammatory response, involving the activation of resident brain cells such as microglia and the recruitment of infiltrating immune cells. Increasing evidence supports that plasticity of the myeloid cell lineage is determinant for the specific role of these cells on stroke outcome, from initiation and maintenance to resolution of post-ischemic inflammation. The aim of this review is to summarize some of the key characteristics of these cells and the mechanisms for their recruitment into the injured brain through interactions with platelets, endothelial cells and other leukocytes. Also, we discuss the existence of different leukocyte subsets in the ischemic tissue and, specifically, the impact of different myeloid phenotypes on stroke outcome, with special emphasis on neutrophils and their interplay with platelets. Knowledge of these cellular phenotypes and interactions may pave the way to new therapies able to promote protective immune responses and tissue repair after cerebral ischemia.

TLR4-Binding DNA Aptamers Show a Protective Effect against Acute Stroke in Animal Models.

Since Toll-like receptor 4 (TLR4) mediates brain damage after stroke, development of TLR4 antagonists is a promising therapeutic strategy for this disease. Our aim was to generate TLR4-blocking DNA aptamers to be used for stroke treatment. From a random oligonucleotide pool, we identified two aptamers (ApTLR#1R, ApTLR#4F) with high affinity for human TLR4 by systematic evolution of ligands by exponential enrichment (SELEX). Optimized truncated forms (ApTLR#1RT, ApTLR#4FT) were obtained. Our data demonstrate specific binding of both aptamers to human TLR4 as well as a TLR4 antagonistic effect. ApTLR#4F and ApTLR#4FT showed a long-lasting protective effect against brain injury induced by middle cerebral artery occlusion (MCAO), an effect that was absent in TLR4-deficient mice. Similar effects were obtained in other MCAO models, including in rat. Additionally, efficacy of ApTLR#4FT in a model of brain ischemia-reperfusion in rat supports the use of this aptamer in patients undergoing artery recanalization induced by pharmacological or mechanical interventions. The absence of major toxicology aspects and the good safety profile of the aptamers further encourage their future clinical positioning for stroke therapy and possibly other diseases in which TLR4 plays a deleterious role.

Multi-modal imaging of long-term recovery post-stroke by positron emission tomography and matrix-assisted laser desorption/ionisation mass spectrometry.

RATIONALE: Stroke is a leading cause of disability worldwide. Understanding the recovery process post-stroke is essential; however, longer-term recovery studies are lacking. In vivo positron emission tomography (PET) can image biological recovery processes, but is limited by spatial resolution and its targeted nature. Untargeted mass spectrometry imaging offers high spatial resolution, providing an ideal ex vivo tool for brain recovery imaging. METHODS: Magnetic resonance imaging (MRI) was used to image a rat brain 48 h after ischaemic stroke to locate the infarcted regions of the brain. PET was carried out 3 months post-stroke using the tracers [18 F]DPA-714 for TSPO and [18 F]IAM6067 for sigma-1 receptors to image neuroinflammation and neurodegeneration, respectively. The rat brain was flash-frozen immediately after PET scanning, and sectioned for matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) imaging. RESULTS: Three months post-stroke, PET imaging shows minimal detection of neurodegeneration and neuroinflammation, indicating that the brain has stabilised. However, MALDI-MS images reveal distinct differences in lipid distributions (e.g. phosphatidylcholine and sphingomyelin) between the scar and the healthy brain, suggesting that recovery processes are still in play. It is currently not known if the altered lipids in the scar will change on a longer time scale, or if they are stabilised products of the brain post-stroke. CONCLUSIONS: The data demonstrates the ability to combine MALD-MS with in vivo PET to image different aspects of stroke recovery.

Toll-Like Receptor 4 Mediates Hemorrhagic Transformation After Delayed Tissue Plasminogen Activator Administration in In Situ Thromboembolic Stroke.

BACKGROUND AND PURPOSE: Hemorrhagic transformation is the main complication of revascularization therapies after stroke. Toll-like receptor 4 (TLR4) is implicated in cerebral damage and inflammation in stroke. This study was designed to determine the role of TLR4 in hemorrhagic transformation development after tissue plasminogen activator (tPA) administration. METHODS: Mice expressing (TLR4+/+) or lacking functional TLR4 (TLR4-/-) were subjected to middle cerebral artery occlusion using an in situ thromboembolic model by thrombin injection into the middle cerebral artery, and tPA (10 mg/kg) was administered 20 minutes or 3 hours after ischemia. Infarct size, hemorrhages, IgG extravasation, matrix metalloproteinase 9 expression, and neutrophil infiltration were assessed 24 hours after ischemia. RESULTS: In TLR4+/+, early reperfusion (tPA at 20 minutes) resulted infarct volume, whereas late recanalization (tPA at 3 hours) did not modify lesion size and increased the rate of the most severe hemorrhages. In TLR4-/- mice, both early and late reperfusion did not modify lesion size. Importantly, late tPA administration did not result in worse hemorrhages and in an increased bleeding area as occurred in TLR4+/+ group. In TLR4-/- animals, late reperfusion produced a lesser increase in matrix metalloproteinase 9 expression when compared with TLR4+/+ animals. CONCLUSIONS: Our results demonstrate TLR4 involvement in hemorrhagic transformation induced by delayed tPA administration, very likely by increasing matrix metalloproteinase 9 expression.

Reparative effects of interleukin-1 receptor antagonist in young and aged/co-morbid rodents after cerebral ischemia.

Neuroprotective strategies for ischemic stroke have failed to translate from bench to bedside, possibly due to the lack of consideration of key clinical co-morbidities. Stroke and co-morbidities are associated with raised levels of the pro-inflammatory cytokine interleukin-1 (IL-1). Inhibition of IL-1 by the administration of interleukin-1 receptor antagonist (IL-1Ra) has shown to be neuroprotective after experimental cerebral ischemia. Stroke can also trigger a robust neuroreparative response following injury, yet many of these new born neurons fail to survive or integrate into pre-existing circuits. Thus, we explore here effects of IL-1Ra on post-stroke neurogenesis in young and aged/co-morbid rats. Aged lean, aged Corpulent (a model of atherosclerosis, obesity and insulin resistance) and young Wistar male rats were exposed to transient cerebral ischemia, received subcutaneous IL-1Ra 3 and 6h during reperfusion, and effects on stroke outcome and neurogenesis were analyzed. Our results show that administration of IL-1Ra improves stroke outcome in both young and aged/co-morbid rats. Furthermore, IL-1Ra not only increases stem cell proliferation, but also significantly enhances neuroblast migration and the number of newly born neurons after cerebral ischemia. Overall, our data demonstrate that systemic administration of IL-1Ra improves outcome and promotes neurogenesis after experimental stroke, further highlighting the therapeutic potential of this clinically approved drug.

Cannabinoid Type-2 Receptor Drives Neurogenesis and Improves Functional Outcome After Stroke.

BACKGROUND AND PURPOSE: Stroke is a leading cause of adult disability characterized by physical, cognitive, and emotional disturbances. Unfortunately, pharmacological options are scarce. The cannabinoid type-2 receptor (CB2R) is neuroprotective in acute experimental stroke by anti-inflammatory mechanisms. However, its role in chronic stroke is still unknown. METHODS: Stroke was induced by permanent middle cerebral artery occlusion in mice; CB2R modulation was assessed by administering the CB2R agonist JWH133 ((6aR,10aR)-3-(1,1-dimethylbutyl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran) or the CB2R antagonist SR144528 (N-[(1S)-endo-1,3,3-trimethylbicyclo-[2.2.1]-heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide) once daily from day 3 to the end of the experiment or by CB2R genetic deletion. Analysis of immunofluorescence-labeled brain sections, 5-bromo-2´-deoxyuridine (BrdU) staining, fluorescence-activated cell sorter analysis of brain cell suspensions, and behavioral tests were performed. RESULTS: SR144528 decreased neuroblast migration toward the boundary of the infarct area when compared with vehicle-treated mice 14 days after middle cerebral artery occlusion. Consistently, mice on this pharmacological treatment, like mice with CB2R genetic deletion, displayed a lower number of new neurons (NeuN+/BrdU+ cells) in peri-infarct cortex 28 days after stroke when compared with vehicle-treated group, an effect accompanied by a worse sensorimotor performance in behavioral tests. The CB2R agonist did not affect neurogenesis or outcome in vivo, but increased the migration of neural progenitor cells in vitro; the CB2R antagonist alone did not affect in vitro migration. CONCLUSIONS: Our data support that CB2R is fundamental for driving neuroblast migration and suggest that an endocannabinoid tone is required for poststroke neurogenesis by promoting neuroblast migration toward the injured brain tissue, increasing the number of new cortical neurons and, conceivably, enhancing motor functional recovery after stroke.

Imaging the role of toll-like receptor 4 on cell proliferation and inflammation after cerebral ischemia by positron emission tomography.

The influence of toll-like receptor 4 on neurogenesis and inflammation has been scarcely explored so far by using neuroimaging techniques. For this purpose, we performed magnetic resonance imaging and positron emission tomography with 3'-deoxy-3'-[(18)F]fluorothymidine and [(11)C]PK11195 at 2, 7, and 14 days following cerebral ischemia in TLR4(+/+)and TLR4(-/-)mice. MRI showed similar infarction volumes in both groups. Despite this, positron emission tomography with 3'-deoxy-3'-[(18)F]fluorothymidine and [(11)C]PK11195 evidenced an increase of neurogenesis and a decrease of inflammation in TLR4(-/-)mice after ischemia. These results evidence the versatility of neuroimaging techniques to monitor the role of toll-like receptor 4 after cerebral ischemia.

A cross-laboratory preclinical study on the effectiveness of interleukin-1 receptor antagonist in stroke.

Stroke represents a global challenge and is a leading cause of permanent disability worldwide. Despite much effort, translation of research findings to clinical benefit has not yet been successful. Failure of neuroprotection trials is considered, in part, due to the low quality of preclinical studies, low level of reproducibility across different laboratories and that stroke co-morbidities have not been fully considered in experimental models. More rigorous testing of new drug candidates in different experimental models of stroke and initiation of preclinical cross-laboratory studies have been suggested as ways to improve translation. However, to our knowledge, no drugs currently in clinical stroke trials have been investigated in preclinical cross-laboratory studies. The cytokine interleukin 1 is a key mediator of neuronal injury, and the naturally occurring interleukin 1 receptor antagonist has been reported as beneficial in experimental studies of stroke. In the present paper, we report on a preclinical cross-laboratory stroke trial designed to investigate the efficacy of interleukin 1 receptor antagonist in different research laboratories across Europe. Our results strongly support the therapeutic potential of interleukin 1 receptor antagonist in experimental stroke and provide further evidence that interleukin 1 receptor antagonist should be evaluated in more extensive clinical stroke trials.

Aging increases microglial proliferation, delays cell migration, and decreases cortical neurogenesis after focal cerebral ischemia.

BACKGROUND: Aging is not just a risk factor of stroke, but it has also been associated with poor recovery. It is known that stroke-induced neurogenesis is reduced but maintained in the aged brain. However, there is no consensus on how neurogenesis is affected after stroke in aged animals. Our objective is to determine the role of aging on the process of neurogenesis after stroke. METHODS: We have studied neurogenesis by analyzing proliferation, migration, and formation of new neurons, as well as inflammatory parameters, in a model of cerebral ischemia induced by permanent occlusion of the middle cerebral artery in young- (2 to 3 months) and middle-aged mice (13 to 14 months). RESULTS: Aging increased both microglial proliferation, as shown by a higher number of BrdU(+) cells and BrdU/Iba1(+) cells in the ischemic boundary and neutrophil infiltration. Interestingly, aging increased the number of M1 monocytes and N1 neutrophils, consistent with pro-inflammatory phenotypes when compared with the alternative M2 and N2 phenotypes. Aging also inhibited (subventricular zone) SVZ cell proliferation by decreasing both the number of astrocyte-like type-B (prominin-1(+)/epidermal growth factor receptor (EGFR)(+)/nestin(+)/glial fibrillary acidic protein (GFAP)(+) cells) and type-C cells (prominin-1(+)/EGFR(+)/nestin(-)/Mash1(+) cells), and not affecting apoptosis, 1 day after stroke. Aging also inhibited migration of neuroblasts (DCX(+) cells), as indicated by an accumulation of neuroblasts at migratory zones 14 days after injury; consistently, aged mice presented a smaller number of differentiated interneurons (NeuN(+)/BrdU(+) and GAD67(+) cells) in the peri-infarct cortical area 14 days after stroke. CONCLUSIONS: Our data confirm that stroke-induced neurogenesis is maintained but reduced in aged animals. Importantly, we now demonstrate that aging not only inhibits proliferation of specific SVZ cell subtypes but also blocks migration of neuroblasts to the damaged area and decreases the number of new interneurons in the cortical peri-infarct area. Thus, our results highlight the importance of using aged animals for translation to clinical studies.

Toll-like receptor 4 modulates cell migration and cortical neurogenesis after focal cerebral ischemia.

Toll-like receptor 4 (TLR4) mediates brain damage after stroke. Now our objective is to determine TLR4 involvement in stroke-induced neurogenesis. Stroke was induced by permanent middle cerebral artery occlusion in wild-type and TLR4-deficient mice. Stereological and densitometric analysis of immunofluorescence-labeled brain sections and FACS analysis of cell suspensions were performed. Our results show that subventricular zone (SVZ) cell proliferation after stroke depends on infarct size. Second, when comparing brains with similar lesions, TLR4 attenuated SVZ proliferation, as shown by a decrease in prominin-1(+)/EGFR(+)/nestin(-) cells (type-C cells) at 1-2 d, and in BrdU(+) cells at 7 d, in TLR4(+/+) vs. TLR4(-/-) mice. Interestingly, 7 d after the infarct, neuroblasts in TLR4(+/+) mice migrated farther distances, reaching areas closer to the lesion than those in TLR4-deficient mice. However, at 14 d, TLR4-deficient mice presented a higher number of neuroblasts in all migratory zones than the TLR4(+/+) counterparts, which suggests that TLR4 deficiency delays neuroblast migration. Consistently, TLR4(+/+) mice showed an increased number of interneurons (NeuN(+)/BrdU(+)/GAD67(+) cells) in peri-infarct cortex 14-28 d after stroke. Our data indicate that, despite a negative effect on SVZ cell proliferation, TLR4 plays an important role in stroke-induced neurogenesis by promoting neuroblasts migration and increasing the number of new cortical neurons after stroke.

Streptococcus pneumoniae worsens cerebral ischemia via interleukin 1 and platelet glycoprotein Ibα.

OBJECTIVE: Bacterial infection contributes to diverse noninfectious diseases and worsens outcome after stroke. Streptococcus pneumoniae, the most common infection in patients at risk of stroke, is a major cause of prolonged hospitalization and death of stroke patients, but how infection impacts clinical outcome is not known. METHODS: We induced sustained pulmonary infection by a human S. pneumoniae isolate in naive and comorbid rodents to investigate the effect of infection on vascular and inflammatory responses prior to and after cerebral ischemia. RESULTS: S. pneumoniae infection triggered atherogenesis, led to systemic induction of interleukin (IL) 1, and profoundly exacerbated (50-90%) ischemic brain injury in rats and mice, a response that was more severe in combination with old age and atherosclerosis. Systemic blockade of IL-1 with IL-1 receptor antagonist (IL-1Ra) fully reversed infection-induced exacerbation of brain injury and functional impairment caused by cerebral ischemia. We show that infection-induced systemic inflammation mediates its effects via increasing platelet activation and microvascular coagulation in the brain after cerebral ischemia, as confirmed by reduced brain injury in response to blockade of platelet glycoprotein (GP) Ibα. IL-1 and platelet-mediated signals converge on microglia, as both IL-1Ra and GPIbα blockade reversed the production of IL-1α by microglia in response to cerebral ischemia in infected animals. INTERPRETATION: S. pneumoniae infection augments atherosclerosis and exacerbates ischemic brain injury via IL-1 and platelet-mediated systemic inflammation. These mechanisms may contribute to diverse cardio- and cerebrovascular pathologies in humans.

Rosiglitazone-induced CD36 up-regulation resolves inflammation by PPARγ and 5-LO-dependent pathways.

PPARγ-achieved neuroprotection in experimental stroke has been explained by the inhibition of inflammatory genes, an action in which 5-LO, Alox5, is involved. In addition, PPARγ is known to promote the expression of CD36, a scavenger receptor that binds lipoproteins and mediates bacterial recognition and also phagocytosis. As phagocytic clearance of neutrophils is a requisite for resolution of the inflammatory response, PPARγ-induced CD36 expression might help to limit inflammatory tissue injury in stroke, an effect in which 5-LO might also be involved. Homogenates, sections, and cellular suspensions were prepared from brains of WT and Alox5(-/-) mice exposed to distal pMCAO. BMMs were obtained from Lys-M Cre(+) PPARγ(f/f) and Lys-M Cre(-) PPARγ(f/f) mice. Stereological counting of double-immunofluorescence-labeled brain sections and FACS analysis of cell suspensions was performed. In vivo and in vitro phagocytosis of neutrophils by microglia/macrophages was analyzed. PPARγ activation with RSG induced CD36 expression in resident microglia. This process was mediated by the 5-LO gene, which is induced in neurons by PPARγ activation and at least by one of its products--LXA4--which induced CD36 independently of PPARγ. Moreover, CD36 expression helped resolution of inflammation through phagocytosis, concomitantly to neuroprotection. Based on these findings, in addition to a direct modulation by PPARγ, we propose in brain a paracrine model by which products generated by neuronal 5-LO, such as LXA4, increase the microglial expression of CD36 and promote tissue repair in pathologies with an inflammatory component, such as stroke.

Silent information regulator 1 protects the brain against cerebral ischemic damage.

BACKGROUND AND PURPOSE: Sirtuin 1 (SIRT1) is a member of NAD+-dependent protein deacetylases implicated in a wide range of cellular functions and has beneficial properties in pathologies including ischemia/reperfusion processes and neurodegeneration. However, no direct evidence has been reported on the direct implication of SIRT1 in ischemic stroke. The aim of this study was to establish the role of SIRT1 in stroke using an experimental model in mice. METHODS: Wild-type and Sirt1-/- mice were subjected to permanent focal ischemia by permanent ligature. In another set of experiments, wild-type mice were treated intraperitoneally with vehicle, activator 3 (SIRT1 activator, 10 mg/kg), or sirtinol (SIRT1 inhibitor, 10 mg/kg) for 10 minutes, 24 hours, and 40 hours after ischemia. Brains were removed 48 hours after ischemia for determining the infarct volume. Neurological outcome was evaluated using the modified neurological severity score. RESULTS: Exposure to middle cerebral artery occlusion increased SIRT1 expression in neurons of the ipsilesional mouse brain cortex. Treatment of mice with activator 3 reduced infarct volume, whereas sirtinol increased ischemic injury. Sirt1-/- mice displayed larger infarct volumes after ischemia than their wild-type counterparts. In addition, SIRT1 inhibition/deletion was concomitant with increased acetylation of p53 and nuclear factor κB (p65). CONCLUSIONS: These results support the idea that SIRT1 plays an important role in neuroprotection against brain ischemia by deacetylation and subsequent inhibition of p53-induced and nuclear factor κB-induced inflammatory and apoptotic pathways.

The immune system in stroke: clinical challenges and their translation to experimental research.

Stroke represents an unresolved challenge for both developed and developing countries and has a huge socio-economic impact. Although considerable effort has been made to limit stroke incidence and improve outcome, strategies aimed at protecting injured neurons in the brain have all failed. This failure is likely to be due to both the incompleteness of modelling the disease and its causes in experimental research, and also the lack of understanding of how systemic mechanisms lead to an acute cerebrovascular event or contribute to outcome. Inflammation has been implicated in all forms of brain injury and it is now clear that immune mechanisms profoundly influence (and are responsible for the development of) risk and causation of stroke, and the outcome following the onset of cerebral ischemia. Until very recently, systemic inflammatory mechanisms, with respect to common comorbidities in stroke, have largely been ignored in experimental studies. The main aim is therefore to understand interactions between the immune system and brain injury in order to develop novel therapeutic approaches. Recent data from clinical and experimental research clearly show that systemic inflammatory diseases -such as atherosclerosis, obesity, diabetes or infection - similar to stress and advanced age, are associated with dysregulated immune responses which can profoundly contribute to cerebrovascular inflammation and injury in the central nervous system. In this review, we summarize recent advances in the field of inflammation and stroke, focusing on the challenges of translation between pre-clinical and clinical studies, and potential anti-inflammatory/immunomodulatory therapeutic approaches.

Citicoline (CDP-choline) increases Sirtuin1 expression concomitant to neuroprotection in experimental stroke.

CDP-choline has shown neuroprotective effects in cerebral ischemia. In humans, although a recent trial International Citicoline Trial on Acute Stroke (ICTUS) has shown that global recovery is similar in CDP-choline and placebo groups, CDP-choline was shown to be more beneficial in some patients, such as those with moderate stroke severity and not treated with t-PA. Several mechanisms have been proposed to explain the beneficial actions of CDP-choline. We have now studied the participation of Sirtuin1 (SIRT1) in the neuroprotective actions of CDP-choline. Fischer rats and Sirt1⁻/⁻ mice were subjected to permanent focal ischemia. CDP-choline (0.2 or 2 g/kg), sirtinol (a SIRT1 inhibitor; 10 mg/kg), and resveratrol (a SIRT1 activator; 2.5 mg/kg) were administered intraperitoneally. Brains were removed 24 and 48 h after ischemia for western blot analysis and infarct volume determination. Treatment with CDP-choline increased SIRT1 protein levels in brain concomitantly to neuroprotection. Treatment with sirtinol blocked the reduction in infarct volume caused by CDP-choline, whereas resveratrol elicited a strong synergistic neuroprotective effect with CDP-choline. CDP-choline failed to reduce infarct volume in Sirt1⁻/⁻ mice. Our present results demonstrate a robust effect of CDP-choline like SIRT1 activator by up-regulating its expression. Our findings suggest that therapeutic strategies to activate SIRT1 may be useful in the treatment of stroke. Sirtuin 1 (SIRT1) is implicated in a wide range of cellular functions. Regarding stroke, there is no direct evidence. We have demonstrated that citicoline increases SIRT1 protein levels in brain concomitantly to neuroprotection. Citicoline fails to reduce infarct volume in Sirt1⁻/⁻ mice. Our findings suggest that therapeutic strategies acting on SIRT1 may be useful in the treatment of stroke.

Surgical manipulation compromises leukocyte mobilization responses and inflammation after experimental cerebral ischemia in mice.

Acute brain injury results in peripheral inflammatory changes, although the impact of these processes on neuronal death and neuroinflammation is currently unclear. To facilitate the translation of experimental studies to clinical benefit, it is vital to characterize the mechanisms by which acute brain injury induces peripheral inflammatory changes, and how these are affected by surgical manipulation in experimental models. Here we show that in mice, even mild surgical manipulation of extracranial tissues induced marked granulocyte mobilization (300%) and systemic induction of cytokines. However, intracranial changes induced by craniotomy, or subsequent induction of focal cerebral ischemia were required to induce egress of CXCR2-positive granulocytes from the bone marrow. CXCR2 blockade resulted in reduced mobilization of granulocytes from the bone marrow, caused an unexpected increase in circulating granulocytes, but failed to affect brain injury induced by cerebral ischemia. We also demonstrate that isoflurane anaesthesia interferes with circulating leukocyte responses, which could contribute to the reported vascular and neuroprotective effects of isoflurane. In addition, no immunosuppression develops in the bone marrow after experimental stroke. Thus, experimental models of cerebral ischemia are compromised by surgery and anaesthesia in proportion to the severity of surgical intervention and overall tissue injury. Understanding the inherent confounding effects of surgical manipulation and development of new models of cerebral ischemia with minimal surgical intervention could facilitate better understanding of interactions between inflammation and brain injury.

Iron overload, measured as serum ferritin, increases brain damage induced by focal ischemia and early reperfusion.

High levels of iron, measured as serum ferritin, are associated to a worse outcome after stroke. However, it is not known whether ischemic damage might increase ferritin levels as an acute phase protein or whether iron overload affects stroke outcome. The objectives are to study the effect of stroke on serum ferritin and the contribution of iron overload to ischemic damage. Swiss mice were fed with a standard diet or with a diet supplemented with 2.5% carbonyl iron to produce iron overload. Mice were submitted to permanent (by ligature and by in situ thromboembolic models) or transient focal ischemia (by ligature for 1 or 3h). Treatment with iron diet produced an increase in the basal levels of ferritin in all the groups. However, serum ferritin did not change after ischemia. Animals submitted to permanent ischemia had the same infarct volume in the groups studied. However, in mice submitted to transient ischemia followed by early (1h) but not late reperfusion (3h), iron overload increased ischemic damage and haemorrhagic transformation. Iron worsens ischemic damage induced by transient ischemia and early reperfusion. In addition, ferritin is a good indicator of body iron levels but not an acute phase protein after ischemia.