Activation of sphingosine 1-phosphate receptor-1 by FTY720 is neuroprotective after ischemic stroke in rats

Acute splenic irradiation reduces brain injury in the rat focal ischemic stroke model

Removing the spleen prior to ischemic stroke abrogates immunologic response to brain injury and reduces cerebral infarction. However, the effectiveness of splenectomy for neuroprotection after stroke has not been established. Moreover, the risks of the surgical splenectomy in stroke patients create a major obstacle to removing the spleen's inflammatory response. We hypothesized that acute splenic irradiation will ablate splenic cells and thereby will diminish stroke progression. Male adult Sprague Dawley rats were subjected to 2-hour middle cerebral artery occlusion (MCAO), then CT scanned for spleen localization and irradiated to the lateral splenic region with 8Gy of Cobalt 60 at 3, 4, 6 or 8 hrs after start of cerebral ischemia. Untreated controls underwent the same procedures except that sham irradiation was applied. At 2 or 7 days after ischemia the rats were euthanized, and brains recovered for the assessment of brain injury and the extent of neuroinflammation. Irradiation at 3 hrs reduced spleen weight and lymphocyte blood levels after stroke. Splenic irradiation at 3 and 4 hrs after start of ischemia significantly reduced cerebral infarction volumes measured at 48 hrs and 7 days, respectively. The histological analysis on day 7 revealed reduced counts of microglia, infiltrating T cells, and apoptotic neurons in the rats irradiated at 4 hrs. The noninvasive single-dose procedure of splenic irradiation performed within a time interval of up to 4 hours offers neuroprotection against ischemic stroke possibly by abrogating deployment of splenic cells to the brain.

Sphingosine-1 phosphate and central nervous system

The development of fingolimod, an unselective functional antagonist of the interactions between sphingosine 1 phosphate (S1P) and sphingosine 1 phosphate receptors (S1PRs), as the first oral therapy for multiple sclerosis (MS) has been a milestone. The parallel intensive research on the role of S1P, sphingosine kinases, and the five known S1PRs, their tissue distribution and expression in physiological and pathological conditions have led to a wide range of interesting findings. The initial focus of this research in the context of developing fingolimod as a treatment of MS has been on its immunological effects. The wide distribution and important roles of sphingosine, its metabolites, and their receptors in the central nervous system (CNS) in general, in myelin, and in all cell types of this organ have spurred interest to examine S1P and its five receptors in the brain as well. The present review will concentrate on the latter area and give a brief overview of what is known about S1P/S1PR interactions in the CNS in physiological and pathological conditions.

Inflammation in intracerebral hemorrhage: from mechanisms to clinical translation

Intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes and is associated with high mortality and morbidity. Currently, no effective medical treatment is available to improve functional outcomes in patients with ICH. Potential therapies targeting secondary brain injury are arousing a great deal of interest in translational studies. Increasing evidence has shown that inflammation is the key contributor of ICH-induced secondary brain injury. Inflammation progresses in response to various stimuli produced after ICH. Hematoma components initiate inflammatory signaling via activation of microglia, subsequently releasing proinflammatory cytokines and chemokines to attract peripheral inflammatory infiltration. Hemoglobin (Hb), heme, and iron released after red blood cell lysis aggravate ICH-induced inflammatory injury. Danger associated molecular patterns such as high mobility group box 1 protein, released from damaged or dead cells, trigger inflammation in the late stage of ICH. Preclinical studies have identified inflammatory signaling pathways that are involved in microglial activation, leukocyte infiltration, toll-like receptor (TLR) activation, and danger associated molecular pattern regulation in ICH. Recent advances in understanding the pathogenesis of ICH-induced inflammatory injury have facilitated the identification of several novel therapeutic targets for the treatment of ICH. This review summarizes recent progress concerning the mechanisms underlying ICH-induced inflammation. We focus on the inflammatory signaling pathways involved in microglial activation and TLR signaling, and explore potential therapeutic interventions by targeting the removal of hematoma components and inhibition of TLR signaling.

FTY720 ameliorates acute ischemic stroke in mice by reducing thrombo-inflammation but not by direct neuroprotection

BACKGROUND AND PURPOSE

Lymphocytes are important players in the pathophysiology of acute ischemic stroke. The interaction of lymphocytes with endothelial cells and platelets, termed thrombo-inflammation, fosters microvascular dysfunction and secondary infarct growth. FTY720, a sphingosine-1-phosphate receptor modulator, blocks the egress of lymphocytes from lymphoid organs and has been shown to reduce ischemic neurodegeneration; however, the underlying mechanisms are unclear. We investigated the mode of FTY720 action in models of cerebral ischemia.

METHODS

Transient middle cerebral artery occlusion (tMCAO) was induced in wild-type and lymphocyte-deficient Rag1(-/-) mice treated with FTY720 (1 mg/kg) or vehicle immediately before reperfusion. Stroke outcome was assessed 24 hours later. Immune cells in the blood and brain were counted by flow cytometry. The integrity of the blood-brain barrier was analyzed using Evans Blue dye. Thrombus formation was determined by immunohistochemistry and Western blot, and was correlated with cerebral perfusion.

RESULTS

FTY720 significantly reduced stroke size and improved functional outcome in wild-type mice on day 1 and day 3 after transient middle cerebral artery occlusion. This protective effect was lost in lymphocyte-deficient Rag1(-/-) mice and in cultured neurons subjected to hypoxia. Less lymphocytes were present in the cerebral vasculature of FTY720-treated wild-type mice, which in turn reduced thrombosis and increased cerebral perfusion. In contrast, FTY720 was unable to prevent blood-brain barrier breakdown and transendothelial immune cell trafficking after transient middle cerebral artery occlusion.

CONCLUSIONS

Induction of lymphocytopenia and concomitant reduction of microvascular thrombosis are key modes of FTY720 action in stroke. In contrast, our findings in Rag1(-/-) mice and cultured neurons argue against direct neuroprotective effects of FTY720.

FTY720 treatment in the convalescence period improves functional recovery and reduces reactive astrogliosis in photothrombotic stroke

BACKGROUND

The Sphingosine-1-phosphate (S1P) signaling pathway is known to influence pathophysiological processes within the brain and the synthetic S1P analog FTY720 has been shown to provide neuroprotection in experimental models of acute stroke. However, the effects of a manipulation of S1P signaling at later time points after experimental stroke have not yet been investigated. We examined whether a relatively late initiation of a FTY720 treatment has a positive effect on long-term neurological outcome with a focus on reactive astrogliosis, synapses and neurotrophic factors.

METHODS

We induced photothrombotic stroke (PT) in adult C57BL/6J mice and allowed them to recover for three days. Starting on post-stroke day 3, mice were treated with FTY720 (1 mg/kg b.i.d.) for 5 days. Behavioral outcome was observed until day 31 after photothrombosis and periinfarct cortical tissue was analyzed using tandem mass-spectrometry, TaqMan®analysis and immunofluorescence.

RESULTS

FTY720 treatment results in a significantly better functional outcome persisting up to day 31 after PT. This is accompanied by a significant decrease in reactive astrogliosis and larger post-synaptic densities as well as changes in the expression of vascular endothelial growth factor α (VEGF α). Within the periinfarct cortex, S1P is significantly increased compared to healthy brain tissue.

CONCLUSION

Besides its known neuroprotective effects in the acute phase of experimental stroke, the initiation of FTY720 treatment in the convalescence period has a positive impact on long-term functional outcome, probably mediated through reduced astrogliosis, a modulation in synaptic morphology and an increased expression of neurotrophic factors.

Pretreatment with rosuvastatin protects against focal cerebral ischemia/reperfusion injury in rats through attenuation of oxidative stress and inflammation

This study aimed to examine the potential protective effect of rosuvastatin against cerebral ischemia/reperfusion injury and its mechanisms. Forty-eight male SD rats underwent 90 min of transient middle cerebral artery occlusion (tMCAO), followed by reperfusion. Rats were orally given (1) rosuvastatin 1mg/kg, (2) rosuvastatin 10mg/kg or (3) water (vehicle) once a day from 7 days before to 1 day after induction of tMCAO. Neurological score, infarct volume, and oxidative stress-related molecules (assessed by immunohistochemistry, dihydroethidium staining, or western blotting) were estimated at 24h after reperfusion. Rosuvastatin prevented the impairment of neurological function and decreased the infarct volume, compared with the vehicle group. The increases in activated microglia, macrophage, and superoxide levels usually caused by ischemia/reperfusion were significantly ameliorated by rosuvastatin. Rosuvastatin also inhibited the upregulation of gp91(phox) and p22phox, phosphorylation of nuclear factor-kappa B, and induction of cyclooxygenase 2 and inducible nitric oxide synthase, compared with vehicle. The results suggest that pretreatment with rosuvastatin may be a promising therapeutic strategy for cerebral ischemia/reperfusion injury, through attenuation of oxidative stress and inflammation.

Involvement of sphingolipids in ethanol neurotoxicity in the developing brain

Ethanol-induced neuronal death during a sensitive period of brain development is considered one of the significant causes of fetal alcohol spectrum disorders (FASD). In rodent models, ethanol triggers robust apoptotic neurodegeneration during a period of active synaptogenesis that occurs around the first two postnatal weeks, equivalent to the third trimester in human fetuses. The ethanol-induced apoptosis is mitochondria-dependent, involving Bax and caspase-3 activation. Such apoptotic pathways are often mediated by sphingolipids, a class of bioactive lipids ubiquitously present in eukaryotic cellular membranes. While the central role of lipids in ethanol liver toxicity is well recognized, the involvement of sphingolipids in ethanol neurotoxicity is less explored despite mounting evidence of their importance in neuronal apoptosis. Nevertheless, recent studies indicate that ethanol-induced neuronal apoptosis in animal models of FASD is mediated or regulated by cellular sphingolipids, including via the pro-apoptotic action of ceramide and through the neuroprotective action of GM1 ganglioside. Such sphingolipid involvement in ethanol neurotoxicity in the developing brain may provide unique targets for therapeutic applications against FASD. Here we summarize findings describing the involvement of sphingolipids in ethanol-induced apoptosis and discuss the possibility that the combined action of various sphingolipids in mitochondria may control neuronal cell fate.

Sphingolipids in cardiovascular and cerebrovascular systems: Pathological implications and potential therapeutic targets

The sphingolipid metabolites ceramide, sphingosine, and sphingosine-1-phosphate (S1P) and its enzyme sphingosine kinase (SphK) play an important role in the regulation of cell proliferation, survival, inflammation, and cell death. Ceramide and sphingosine usually inhibit proliferation and promote apoptosis, while its metabolite S1P phosphorylated by SphK stimulates growth and suppresses apoptosis. Because these metabolites are interconvertible, it has been proposed that it is not the absolute amounts of these metabolites but rather their relative levels that determine cell fate. The relevance of this “sphingolipid rheostat” and its role in regulating cell fate has been borne out by work in many labs using many different cell types and experimental manipulations. A central finding of these studies is that SphK is a critical regulator of the sphingolipid rheostat, as it not only produces the pro-growth, anti-apoptotic messenger S1P, but also decreases levels of pro-apoptotic ceramide and sphingosine. Activation of bioactive sphingolipid S1P signaling has emerged as a critical protective pathway in response to acute ischemic injury in both cardiac and cerebrovascular disease, and these observations have considerable relevance for future potential therapeutic targets.

FTY720 (fingolimod) attenuates beta-amyloid peptide (Aβ42)-induced impairment of spatial learning and memory in rats

Imbalanced lipid metabolism and increase in the ceramide-to-S1P ratio in the brain have been postulated to play a role in amyloidogenesis, neuroinflammatory reactions, and neuronal apoptosis in Alzheimer's disease (AD) pathology. FTY720, the immunomodulatory sphingosine 1-phosphate (S1P) analog, has recently gained interest because of its CNS-directed effects. In addition to its immunomodulatory functions in multiple sclerosis, FTY720 possesses anti-inflammatory and neuroprotective roles in different cerebral ischemia models. In the present study, we examined the effects of FTY720 in a rat model of AD. Memory deficit was induced by bilateral intrahippocampus injection of beta-amyloid peptide (Aβ(42)) and examined through the Morris water maze test. The extent of histological injury in the hippocampus and the activation of caspase-3 were determined respectively by Nissl staining and Western blotting. Chronic daily administration of FTY720 (1 mg/kg, i.p., 14 days) significantly attenuated the Aβ(42)-induced learning and memory impairment and prevented the hippocampus neuronal damage as well as caspase-3 activation. These data show for the first time that FTY720 has a beneficial effect in restoring memory loss in Aβ(42)-induced neurotoxicity and also suggest that S1P receptors and signaling pathways may provide a potential target for the treatment of AD.

Influence of inflammation on poststroke plasticity

Age-related brain injuries including stroke are a leading cause of morbidity and mental disability worldwide. Most patients who survive stroke experience some degree of recovery. The restoration of lost functions can be explained by neuronal plasticity, understood as brain ability to reorganize and remodel itself in response to changed environmental requirements. However, stroke triggers a cascade of events which may prevent the normal development of the plastic changes. One of them may be inflammatory response initiated immediately after stroke, which has been found to contribute to neuronal injury. Some recent evidence though has suggested that inflammatory reaction can be also neuroprotective. This paper attempts to discuss the influence of poststroke inflammatory response on brain plasticity and stroke outcome. We also describe the recent anti-inflammatory strategies that have been effective for recovery in experimental stroke.

Fingolimod reduces hemorrhagic transformation associated with delayed tissue plasminogen activator treatment in a mouse thromboembolic model

BACKGROUND AND PURPOSE

The sphingosine 1-phosphate receptor agonist fingolimod reduces infarct size in rodent models of stroke and enhances blood-brain barrier integrity. Based on these observations, we hypothesized that combination of fingolimod with tissue plasminogen activator (tPA) would reduce the risk of hemorrhagic transformation associated with delayed administration of tPA.

METHODS

We evaluated the effects of fingolimod in a mouse model of thromboembolic stroke, in which both the beneficial effect of reperfusion associated with early tPA treatment and hemorrhagic transformation associated with delayed administration mimic clinical observations in humans.

RESULTS

Our results demonstrate that fingolimod treatment attenuates the neurological deficit and reduces infarct volume after in situ thromboembolic occlusion of the middle cerebral artery. Combination of fingolimod and tPA improves the neurological outcome of the thrombolytic therapy and reduces the risk of hemorrhagic transformation associated with delayed administration of tPA.

CONCLUSIONS

This study confirms the protective efficacy of fingolimod as a treatment against ischemic stroke in another rodent model of stroke (thromboembolic occlusion), and suggests that fingolimod could potentially be used in combination with tPA to reduce the risk of brain hemorrhage.

Sphingolipids in neuroinflammation

Sphingolipids, the main component of cellular membranes, are cellular 'jack-of-all-trades', influencing a variety of functions including signal transduction, cell activation, membrane fluidity and cell-cell interactions.In the last few years, sphingolipids have begun to be investigated in the pathophysiology of major diseases of the brain, e.g. multiple sclerosis and dementia. Modulation of neuroinflammatory responses, such as lymphocyte behaviour, is a chance to intervene in the pathways that cause disease. There is much research still to be done in this field, but the prospect of treating previously untreatable medical conditions compels us onwards. Here, we review the current knowledge of the link between sphingolipids and neuroinflammation.

Fingolimod reduces cerebral lymphocyte infiltration in experimental models of rodent intracerebral hemorrhage

T-lymphocytes promote cerebral inflammation, thus aggravating neuronal injury after stroke. Fingolimod, a sphingosine 1-phosphate receptor analog, prevents the egress of lymphocytes from primary and secondary lymphoid organs. Based on these findings, we hypothesized fingolimod treatment would reduce the number of T-lymphocytes migrating into the brain, thereby ameliorating cerebral inflammation following experimental intracerebral hemorrhage (ICH). We investigated the effects of fingolimod in two well-established murine models of ICH, implementing intrastriatal infusions of either bacterial collagenase (cICH) or autologous blood (bICH). Furthermore, we tested the long term neurological improvements by Fingolimod in a collagenase-induced rat model of ICH. Fingolimod, in contrast to vehicle administration alone, improved neurological functions and reduced brain edema at 24 and 72 h following experimental ICH in CD-1 mice (n=103; p<0.05). Significantly fewer lymphocytes were found in blood and brain samples of treated animals when compared to the vehicle group (p<0.05). Moreover, fingolimod treatment significantly reduced the expression of intercellular adhesion molecule-1 (ICAM-1), interferon-γ (INF-γ), and interleukin-17 (IL-17) in the mouse brain at 72 h post-cICH (p<0.05 compared to vehicle). Long-term neurocognitive performance and histopathological analysis were evaluated in Sprague-Dawley rats between 8 and 10 weeks post-cICH (n=28). Treated rats showed reduced spatial and motor learning deficits, along with significantly reduced brain atrophy and neuronal cell loss within the basal ganglia (p<0.05 compared to vehicle). We conclude that fingolimod treatment ameliorated cerebral inflammation, at least to some extent, by reducing the availability and subsequent brain infiltration of T-lymphocytes, which improved the short and long-term sequelae after experimental ICH in rodents.

Systematic review and meta-analysis of the efficacy of sphingosine-1-phosphate (S1P) receptor agonist FTY720 (fingolimod) in animal models of stroke

BACKGROUND AND PURPOSE

FTY720 (fingolimod) is a known sphingosine-1-phosphate (S1P) receptor agonist, which has been used in clinical trials for treating multiple sclerosis, renal transplantation, and decreasing reperfusion injury in heart, liver, and kidney. Most of these clinical trials have showed a positive effect. Especially, the trials of MS showed a reduction of relapse rate in FTY720-treated patients. Now, some animal experiments indicated that FTY720 could be a new compound available treatment for stroke patients by exerting neuroprotection via S1P1 mediated antiapoptotic mechanisms. Whether it could be effective in animals is unclear, so we conducted a systematic review to make it clear.

METHODS

We conducted a systematic review and meta-analysis of the efficacy of FTY720 in animal models of focal cerebral ischemia by electronic and manual searches of the literature. Data on study quality, FTY720 dose, time of administration, and outcome measured as infarct volume or functional deficit were extracted. Data from all studies were analyzed by means of a standardized mean difference meta-analysis.

RESULTS

Of the 19 identified studies, 9 were included. Among all the included studies, 178 animals were calculated for infarct size and 194 animals were assessed of neurological deficits. The methodological quality of the studies ranged from 2 to 10 according to a published 11-item quality scale. Of the nine studies selected, only one reported a negative result of FTY720. The result indicated that FTY720 reduced the infarct volume (SMD = -1.31, 95% CI -1.99 to -0.63) and improve the functional outcome (SMD = -1.61, 95% CI -2.17 to -1.05).

CONCLUSIONS

The data we included supporting FTY720 was a candidate drug for stroke, but it should be considered with caution. More good quality experimental studies should be performed to evaluate the safety of FTY720 in the future. Whether FTY720 is effective in aged animals that mimicked human with comorbidities like diabetes and hypertension should also be deliberated.

Novel therapeutic strategies targeting innate immune responses and early inflammation after stroke

Post-ischemic inflammation is an essential step in the progression of ischemic stroke. This review focuses on the function of infiltrating immune cells, macrophages, and T cells, in ischemic brain injury. The brain is a sterile organ; however, the activation of Toll-like receptor (TLR) 2 and TLR4 is pivotal in the beginning of post-ischemic inflammation. Some endogenous TLR ligands are released from injured brain cells, including high mobility group box 1 and peroxiredoxin family proteins, and activate the infiltrating macrophages and induce the expression of inflammatory cytokines. Following this step, T cells also infiltrate into the ischemic brain and mediate post-ischemic inflammation in the delayed phase. Various cytokines from helper T cells and γδT cells function as neurotoxic (IL-23/IL-17, IFN-γ) or neuroprotective (IL-10, IL-4) mediators. Novel neuroprotective strategies should therefore be developed through more detailed understanding of this process and the regulation of post-ischemic inflammation.

Activation of immune responses to brain antigens after stroke

Infection is common after stroke and is independently associated with a worse outcome. The predisposition to infection following stroke is in part related to a sympathetically mediated suppression of the peripheral immune response. The teleological explanation for this immune dysfunction is that it serves to prevent autoimmune responses to brain antigens. We believe that the systemic immune response in patients who develop infection, however, thwarts this seemingly protective response and predisposes to central nervous system autoimmunity. These autoimmune responses may mediate, at least in part, the worse outcome associated with post-stroke infection.

Fingolimod protects cultured cortical neurons against excitotoxic death

Fingolimod (FTY720), a novel drug approved for the treatment of relapsing-remitting multiple sclerosis, activates different sphingosine-1-phosphate receptor (S1PR) subtypes. Its primary mechanism of action is to reduce the egress of T lymphocytes from secondary lymphoid organs, thus restraining neuroinflammation and autoimmunity. However, recent evidence suggests that the action of FTY720 involves S1PRs expressed by cells resident in the CNS, including neurons. Here, we examined the effect of FTY720, its active metabolite, FTY720-P, and sphingosine-1-phosphate (S1P) on neuronal viability using a classical in vitro model of excitotoxic neuronal death. Mixed cultures of mouse cortical cells were challenged with toxic concentrations of N-methyl-d-aspartate (NMDA) for 10 min, and neuronal death was assessed 20 h later. FTY720, FTY720-P, and S1P were all neuroprotective when applied 18-20 h prior to the NMDA pulse. Neuroprotection was attenuated by pertussis toxin, and inhibited by the selective type-1 S1PR (S1P1R) antagonist, W146, and by inhibitors of the mitogen associated protein kinase (MAPK) and the phosphatidylinositol-3-kinase (PtdIns-3-K) pathways. Both FTY720 and FTY720-P retained their protective activity in pure cultures of mouse or rat cortical neurons. These data offer the first direct demonstration that FTY720 and its active metabolite protect neurons against excitotoxic death.

Fingolimod (FTY720) inhibits neuroinflammation and attenuates spontaneous convulsions in lithium-pilocarpine induced status epilepticus in rat model

Accumulating evidence has shown that neuroinflammation plays a key role in epileptogenesis. However, the efficacy of anti-inflammatory agents for preventing epilepsy remains controversial. Fingolimod (FTY720), a sphingosine-1-phosphate (S1P) analog, has potent anti-inflammatory effects in multiple sclerosis (MS) patients and animal models. Here, we tested whether FTY720 could exert antiepileptogenic effects in an adult rat model of lithium-pilocarpine induced epilepsy. 24h after onset of status epilepticus (SE), the epileptic rats received saline or 1mg/kg FTY720 i.p. once daily for 14 consecutive days. Thereafter, spontaneous convulsions (SCs), mossy fiber sprouting (MFS), neuronal loss, activation of microglia and astrocytes, expressions of interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNFα) were evaluated in the SE rats. We found that FTY720 treatment reduced neuronal loss and decreased activation of microglia and astrocytes in hippocampus at four days post-SE. Simultaneously, abnormal expressions of IL-1β and TNFα in hippocampus were restrained by FTY720 treatment. In addition, neuroprotective effects of FTY720 were demonstrated by increasing neuronal nuclei (NeuN)-positive cells and decreasing Fluoro-Jade B (FJB)-positive cells in the hippocampus. During 21-34days post-SE, the incidence, duration, frequency and severity of SCs significantly decreased in FTY720 treated rats compared with saline treated rats. Aberrant MFS was also attenuated by FTY720 administration. These results suggest that FTY720 exerts anti-inflammatory and antiepileptogenic effects in lithium-pilocarpine model of epilepsy and it may provide a new therapeutic approach for prevention of epileptogenesis.

Fingolimod, a sphingosine-1 phosphate receptor modulator, increases BDNF levels and improves symptoms of a mouse model of Rett syndrome

The functional relevance of brain-derived neurotrophic factor (BDNF) is beginning to be well appreciated not only in mice, but also in humans. Because reduced levels typically correlate with impaired neuronal function, increasing BDNF levels with well-tolerated drugs diffusing into the central nervous system may help in ameliorating functional deficits. With this objective in mind, we used the sphingosine-1 phosphate receptor agonist fingolimod, a drug that crosses the blood-brain barrier. In addition, fingolimod has recently been introduced as the first oral treatment for multiple sclerosis. In cultured neurons, fingolimod increases BDNF levels and counteracts NMDA-induced neuronal death in a BDNF-dependent manner. Ongoing synaptic activity and MAPK signaling is required for fingolimod-induced BDNF increase, a pathway that can also be activated in vivo by systemic fingolimod administration. Mice lacking Mecp2, a gene frequently mutated in Rett syndrome, show decreased levels of BDNF, and fingolimod administration was found to partially rescue these levels as well as the size of the striatum, a volumetric sensor of BDNF signaling in rodents. These changes correlate with increased locomotor activity of the Mecp2-deficient animals, suggesting that fingolimod may improve the functional output of the nervous system, in addition to its well-documented effects on lymphocyte egress from lymph nodes.

Isoflurane delays the development of early brain injury after subarachnoid hemorrhage through sphingosine-related pathway activation in mice

OBJECTIVE

Isoflurane, a volatile anesthetic agent, has been recognized for its potential neuroprotective properties and has antiapoptotic effects. We examined whether isoflurane posttreatment is protective against early brain injury after subarachnoid hemorrhage and determined whether this effect needs sphingosine-related pathway activation.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred seventy-nine 8-wk-old male CD-1 mice weighing 30-38 g.

INTERVENTIONS

Subarachnoid hemorrhage was induced in mice by endovascular perforation. Animals were randomly assigned to sham-operated, subarachnoid hemorrhage-vehicle, and subarachnoid hemorrhage+2% isoflurane. Neurobehavioral function and brain edema were evaluated at 24 and 72 hrs. The expression of sphingosine kinase, phosphorylated Akt, and cleaved caspase-3 was determined by Western blotting and immunofluorescence. Neuronal cell death was examined by terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling staining. Effects of a sphingosine kinase inhibitor N, N-dimethylsphingosine or a sphingosine 1 phosphate receptor inhibitor VPC23019 on isoflurane's protective action against postsubarachnoid hemorrhage early brain injury were also examined.

MEASUREMENTS AND MAIN RESULTS

Isoflurane significantly improved neurobehavioral function and brain edema at 24 hrs but not 72 hrs after subarachnoid hemorrhage. At 24 hrs, isoflurane attenuated neuronal cell death in the cortex, associated with an increase in sphingosine kinase 1 and phosphorylated Akt, and a decrease in cleaved caspase-3. The beneficial effects of isoflurane were abolished by N, N-dimethylsphingosine and VPC23019.

CONCLUSIONS

Isoflurane posttreatment delays the development of postsubarachnoid hemorrhage early brain injury through antiapoptotic mechanisms including sphingosine-related pathway activation, implying its use for anesthesia during acute aneurysm surgery or intervention.

Sphingosine 1-phosphate receptor 5 mediates the immune quiescence of the human brain endothelial barrier

Background

The sphingosine 1-phosphate (S1P) receptor modulator FTY720P (Gilenya®) potently reduces relapse rate and lesion activity in the neuroinflammatory disorder multiple sclerosis. Although most of its efficacy has been shown to be related to immunosuppression through the induction of lymphopenia, it has been suggested that a number of its beneficial effects are related to altered endothelial and blood–brain barrier (BBB) functionality. However, to date it remains unknown whether brain endothelial S1P receptors are involved in the maintenance of the function of the BBB thereby mediating immune quiescence of the brain. Here we demonstrate that the brain endothelial receptor S1P₅ largely contributes to the maintenance of brain endothelial barrier function.

Methods

We analyzed the expression of S1P₅ in human post-mortem tissues using immunohistochemistry. The function of S1P₅ at the BBB was assessed in cultured human brain endothelial cells (ECs) using agonists and lentivirus-mediated knockdown of S1P₅. Subsequent analyses of different aspects of the brain EC barrier included the formation of a tight barrier, the expression of BBB proteins and markers of inflammation and monocyte transmigration.

Results

We show that activation of S1P₅ on cultured human brain ECs by a selective agonist elicits enhanced barrier integrity and reduced transendothelial migration of monocytes in vitro. These results were corroborated by genetically silencing S1P₅ in brain ECs. Interestingly, functional studies with these cells revealed that S1P₅ strongly contributes to brain EC barrier function and underlies the expression of specific BBB endothelial characteristics such as tight junctions and permeability. In addition, S1P₅ maintains the immunoquiescent state of brain ECs with low expression levels of leukocyte adhesion molecules and inflammatory chemokines and cytokines through lowering the activation of the transcription factor NFκB.

Conclusion

Our findings demonstrate that S1P₅ in brain ECs contributes to optimal barrier formation and maintenance of immune quiescence of the barrier endothelium.

Changes in the cerebrospinal fluid ceramide profile after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The purpose of this study was to investigate changes in the cerebrospinal fluid sphingolipid profile in patients with subarachnoid hemorrhage in relation to the occurrence of symptomatic vasospasm and outcome at hospital discharge.

METHODS

The ceramide profile in the cerebrospinal fluid was determined by mass spectrometry in control subjects and patients with Fisher 3 grade subarachnoid hemorrhage within 48 hours of the bleed. Patients were prospectively followed and subcategorized based on the occurrence of symptomatic vasospasm and modified Rankin Scale at discharge.

RESULTS

Compared to control subjects, patients with subarachnoid hemorrhage had higher cerebrospinal fluid levels of total ceramide (12.4±8.8 versus 54.6±49.3 pmol/mL; P<0.001). In the subgroup analysis, total ceramide levels in individuals with symptomatic vasospasm (104.2±57.0 pmol/mL) were higher than in those with asymptomatic vasospasm (32.4±25.7 pmol/mL; P=0.006) and no vasospasm (30.9±15.7 pmol/mL; P=0.003). In addition, compared to patients with a good outcome (modified Rankin Scale ≤3), individuals with poor outcome (modified Rankin Scale ≥4) had higher cerebrospinal fluid levels of total ceramide (79±25 versus 23±6 pmol/mL; P=0.008). When the relative contributions of the different ceramide species were calculated, a higher relative concentration of C(18:0) ceramide was observed in individuals with symptomatic vasospasm (P=0.018) and poor outcome (P=0.028).

CONCLUSIONS

Ceramide profile changes occur in subarachnoid hemorrhage. In this small case-based series elevation of levels of this sphingolipid, particularly C(18:0), was associated with the occurrence of symptomatic vasospasm and poor neurological outcome after subarachnoid hemorrhage.

Junctional protein regulation by sphingosine kinase 2 contributes to blood-brain barrier protection in hypoxic preconditioning-induced cerebral ischemic tolerance

Protection of the blood-brain barrier (BBB) is correlated with improved outcome in stroke. Sphingosine kinase (SphK)-directed production of sphingosine-1-phosphate, which we previously documented as being vital to preconditioning-induced stroke protection, mediates peripheral vascular integrity via junctional protein regulation. We used a hypoxic preconditioning (HPC) model in adult wild-type and SphK2-null mice to examine the isoform-specific role of SphK2 signaling for ischemic tolerance to transient middle cerebral artery occlusion and attendant BBB protection. Reductions in infarct volume and BBB permeability in HPC-treated mice were completely lost in SphK2-null mice. Hypoxic preconditioning-induced attenuation of postischemic BBB disruption in wild types, evidenced by reduced extravascular immunoglobulin G intensity, suggests direct protection of BBB integrity. Measurement of BBB junctional protein status in response to HPC revealed SphK2-dependent increases in triton-insoluble claudin-5 and VE-cadherin, which may serve to strengthen the BBB before stroke. Postischemic loss of VE-cadherin, occludin, and zona occludens-1 in SphK2-null mice with prior HPC suggests that SphK2-dependent protection of these adherens and tight junction proteins is compulsory for HPC to establish a vasculoprotective phenotype. Further elucidation of the mediators of this endogenous, HPC-activated lipid signaling pathway, and their role in protecting the ischemic BBB, may provide new therapeutic targets for cerebrovascular protection in stroke patients.

Post-ischemic inflammation in the brain

Post-ischemic inflammation is an essential step in the progression of brain ischemia-reperfusion injury. In this review, we focus on the post-ischemic inflammation triggered by infiltrating immune cells, macrophages, and T lymphocytes. Brain ischemia is a sterile organ, but injury-induced inflammation is mostly dependent on Toll-like receptor (TLR) 2 and TLR4. Some endogenous TLR ligands, high mobility group box 1 (HMGB1) and peroxiredoxin family proteins, in particular, are implicated in the activation and inflammatory cytokine expression in infiltrating macrophages. Following macrophage activation, T lymphocytes infiltrate the ischemic brain and regulate the delayed phase inflammation. IL-17-producing γδT lymphocytes induced by IL-23 from macrophages promote ischemic brain injury, whereas regulatory T lymphocytes suppress the function of inflammatory mediators. A deeper understanding of the inflammatory mechanisms of infiltrating immune cells may lead to the development of novel neuroprotective therapies.

MALDI-mass spectrometry imaging of desalted rat brain sections reveals ischemia-mediated changes of lipids

Ischemia-mediated lipidomic changes in rat brains were explored by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) profiling and imaging after in situ desalting which drastically simplified the spectral presentation of tissue lipids. Removal of interference from the massively changed cations in response to tissue damage permitted the revelation of subtle yet important lipidomic changes. The identities of the detected lipids were confirmed by MALDI tandem mass spectrometry (MALDI-MS/MS). The MALDI-MS imaging (MALDI-MSI) result of lysophosphatidylcholine 16:0 (LPC 16:0) in the desalted brain section appeared essentially identical to that of sodiated LPC 16:0 in the adjacent undesalted section and verified the suitability of the desalting method for the MALDI-MSI studies of lipids in tissue. Other than the consistently decreased phosphatidylcholine (PC) 16:0/18:1, images of PCs containing all saturated, or combined saturated and monounsaturated fatty acyl (MUFA) residues revealed their parenchymal increase by ischemia. Images of PCs containing polyunsaturated fatty acyl (PUFA) residues in normal cortex showed laminated patterns similar to cortical lamina. Ischemia reduced the abundance of PC 16:0/20:4 and PC 16:0/22:6 and disrupted the laminated distribution of the former. However, ischemia increased the subcortical abundance of PUFA-PCs containing stearoyl residue and confined their cortical increase within limited areas. Image of parenchymal sphingomyelin 18:0 (SM 18:0) showed its consistent decrease by ischemia that paralleled the increase of ceramide 18:0-H(2)O in region of moderate to high SM abundance. The above results presented the lipidomic changes largely different from previous MALDI-MSI results and suggested a window of intervention that may benefit the management of cerebrovascular accident and other brain injuries.

The flavonoid fisetin attenuates postischemic immune cell infiltration, activation and infarct size after transient cerebral middle artery occlusion in mice

The development of the brain tissue damage in ischemic stroke is composed of an immediate component followed by an inflammatory response with secondary tissue damage after reperfusion. Fisetin, a flavonoid, has multiple biological effects, including neuroprotective and antiinflammatory properties. We analyzed the effects of fisetin on infarct size and the inflammatory response in a mouse model of stroke, temporary middle cerebral artery occlusion, and on the activation of immune cells, murine primary and N9 microglial and Raw264.7 macrophage cells and human macrophages, in an in vitro model of inflammatory immune cell activation by lipopolysaccharide (LPS). Fisetin not only protected brain tissue against ischemic reperfusion injury when given before ischemia but also when applied 3 hours after ischemia. Fisetin also prominently inhibited the infiltration of macrophages and dendritic cells into the ischemic hemisphere and suppressed the intracerebral immune cell activation as measured by intracellular tumor necrosis factor α (TNFα) production. Fisetin also inhibited LPS-induced TNFα production and neurotoxicity of macrophages and microglia in vitro by suppressing nuclear factor κB activation and JNK/Jun phosphorylation. Our findings strongly suggest that the fisetin-mediated inhibition of the inflammatory response after stroke is part of the mechanism through which fisetin is neuroprotective in cerebral ischemia.

Ethanol triggers sphingosine 1-phosphate elevation along with neuroapoptosis in the developing mouse brain

Our previous studies have indicated that de novo ceramide synthesis plays a critical role in ethanol-induced apoptotic neurodegeneration in the 7-day-old mouse brain. In this study, we examined whether the formation of sphingosine 1-phosphate (S1P), a ceramide metabolite, is associated with this apoptotic pathway. Analyses of basal levels of S1P-related compounds indicated that S1P, sphingosine, sphingosine kinase 2, and S1P receptor 1 increased significantly during postnatal brain development. In the 7-day-old mouse brain, sphingosine kinase 2 was localized mainly in neurons. Subcellular fractionation studies of the brain homogenates showed that sphingosine kinase 2 was enriched in the plasma membrane and the synaptic membrane/synaptic vesicle fractions, but not in the nuclear and mitochondrial/lysosomal fractions. Ethanol exposure in 7-day-old mice induced sphingosine kinase 2 activation and increased the brain level of S1P transiently 2-4 h after exposure, followed by caspase 3 activation that peaked around 8 h after exposure. Treatment with dimethylsphingosine, an inhibitor of sphingosine kinases, attenuated the ethanol-induced caspase 3 activation and the subsequent neurodegeneration. These results indicate that ethanol activates sphingosine kinase 2, leading to a transient increase in S1P, which may be involved in neuroapoptotic action of ethanol in the developing brain.

Importance of T lymphocytes in brain injury, immunodeficiency, and recovery after cerebral ischemia

Following an ischemic stroke, T lymphocytes become activated, infiltrate the brain, and appear to release cytokines and reactive oxygen species to contribute to early inflammation and brain injury. However, some subsets of T lymphocytes may be beneficial even in the early stages after a stroke, and recent evidence suggests that T lymphocytes can also contribute to the repair and regeneration of the brain at later stages. In the hours to days after stroke, T-lymphocyte numbers are then reduced in the blood and in secondary lymphoid organs as part of a 'stroke-induced immunodeficiency syndrome,' which is mediated by hyperactivity of the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis, resulting in increased risk of infectious complications. Whether or not poststroke T-lymphocyte activation occurs via an antigen-independent process, as opposed to a classical antigen-dependent process, is still controversial. Although considerable recent progress has been made, a better understanding of the roles of the different T-lymphocyte subpopulations and their temporal profile of damage versus repair will help to clarify whether T-lymphocyte targeting may be a viable poststroke therapy for clinical use.

FTY720 improves functional recovery after spinal cord injury by primarily nonimmunomodulatory mechanisms

Spinal cord injury (SCI) is an incapacitating injury that can result in limited functional recovery. We have previously shown increases in the lysophospholipid mediator, sphingosine-1-phosphate (S1P), in the spinal cord after contusion injury. To apply S1P receptor modulation to the treatment of SCI, we examined the therapeutic effects of FTY720, an S1P receptor agonist, on locomotor recovery after SCI in mice. Oral administration of FTY720 shortly after contusion SCI significantly improved motor function recovery, as assessed by both Basso Mouse Scale scores and Rotarod Performance test results. FTY720 induced lymphopenia and reduced T-cell infiltration in the spinal cord after SCI but did not affect the early infiltration of neutrophils and the activation of microglia. In addition, plasma levels and mRNA expression of inflammatory cytokines in the spinal cord after SCI were not attenuated by FTY720. Vascular permeability and astrocyte accumulation were both decreased by FTY720 in the injured spinal cord. The therapeutic effects of FTY720 were not solely dependent on immune modulation, as confirmed by the demonstration that FTY720 also ameliorated motor function after SCI in mice with severe combined immunodeficiency. Finally, the S1P(1) receptor agonist, SEW2871, partly mimicked the therapeutic effect of FTY720. Our data highlight the importance of immune-independent functions of FTY720 in decreasing vascular permeability and astrogliosis in the injured spinal cord and promoting locomotor function recovery after SCI.

Sphingosine-1-phosphate signaling and its role in disease

The bioactive sphingolipid metabolite sphingosine-1-phosphate (S1P) is now recognized as a critical regulator of many physiological and pathophysiological processes, including cancer, atherosclerosis, diabetes and osteoporosis. S1P is produced in cells by two sphingosine kinase isoenzymes, SphK1 and SphK2. Many cells secrete S1P, which can then act in an autocrine or paracrine manner. Most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. More recently, it was shown that S1P also has important intracellular targets involved in inflammation, cancer and Alzheimer's disease. This suggests that S1P actions are much more complex than previously thought, with important ramifications for development of therapeutics. This review highlights recent advances in our understanding of the mechanisms of action of S1P and its roles in disease.

Sphingosine kinase 2 mediates cerebral preconditioning and protects the mouse brain against ischemic injury

BACKGROUND AND PURPOSE

Cerebral preconditioning provides insights into endogenous mechanisms that protect the brain from ischemic injury. Hypoxia and the anesthetic isoflurane are powerful preconditioning agents. Recent data show that sphingosine 1-phosphate receptor stimulation improves outcome in rodent models of stroke. Endogenous sphingosine 1-phosphate levels are controlled by the expression and activity of sphingosine kinases (SPK). We hypothesize that SPK upregulation mediates preconditioning induced by isoflurane and hypoxia and reduces ischemic injury.

METHODS

Male wild-type C57BL/J, SPK1(-/-) and SPK2(-/-) mice were exposed to isoflurane or hypoxia preconditioning before transient middle cerebral artery occlusion. Infarct volume and neurological outcome were measured 24 hours later. SPK inhibitors (SKI-II and ABC294640) were used to test the involvement of SPK2. Expressions of SPK1, SPK2, and hypoxia-inducible factor 1α were determined. Primary cultures of mouse cortical neurons were exposed to isoflurane before glutamate- or hydrogen peroxide-induced cell death.

RESULTS

Isoflurane preconditioning and hypoxia preconditioning significantly reduced infarct volume and improved neurological outcome in wild-type and SPK1(-/-) mice but not in SPK2(-/-) mice. Pretreatment with SKI-II or ABC294640 abolished the isoflurane preconditioning-induced tolerance. Western blot showed a rapid and sustained increase in SPK2 level, whereas SPK1 level was similar between preconditioned mice and controls. Hypoxia-inducible factor 1α was upregulated in wild-type isoflurane-preconditioned mice but not in SPK2(-/-). Isoflurane preconditioning protected primary neurons against cell death, which was abolished in ABC294640-treated cells.

CONCLUSIONS

Applying genetic and pharmacological approaches, we demonstrate that neuronal SPK2 isoform plays an important role in cerebral preconditioning.

Activation of sphingosine kinase 2 is an endogenous protective mechanism in cerebral ischemia

The two ubiquitously expressed sphingosine kinases (SphK) 1 and 2 are key regulators of the sphingolipid signaling pathway. Despite the formation of an identical messenger, i.e. sphingosine 1-phosphate (S1P), they exert strikingly different functions. Particularly, SphK2 is necessary for the phosphorylation of the sphingosine analog fingolimod (FTY720), which is protective in rodent stroke models. Using gene deficient mice lacking either SphK1 or SphK2, we investigated the role of the two lipid kinases in experimental stroke. We performed 2h transient middle cerebral artery occlusion (tMCAO) and analyzed lesion size and neurological function after 24h. Treatment groups received 1mg/kg FTY720. Neutrophil infiltration, microglia activation, mRNA and protein expression of SphK1, SphK2 and the S1P(1) receptor after tMCAO were studied. Genetic deletion of SphK2 but not SphK1 increased ischemic lesion size and worsened neurological function after tMCAO. The protective effect of FTY720 was conserved in SphK1(-/-) mice but not in SphK2(-/-) mice. This suggests that SphK2 activity is an important endogenous protective mechanism in cerebral ischemia and corroborates that the protective effect of FTY720 is mediated via phospho-FTY720.

FTY720 reduces post-ischemic brain lymphocyte influx but does not improve outcome in permanent murine cerebral ischemia

BACKGROUND

The contribution of neuroinflammation and specifically brain lymphocyte invasion is increasingly recognised as a substantial pathophysiological mechanism after stroke. FTY720 is a potent treatment for primary neuroinflammatory diseases by inhibiting lymphocyte circulation and brain immigration. Previous studies using transient focal ischemia models showed a protective effect of FTY720 but did only partially characterize the involved pathways. We tested the neuroprotective properties of FTY720 in permanent and transient cortical ischemia and analyzed the underlying neuroimmunological mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

FTY720 treatment resulted in substantial reduction of circulating lymphocytes while blood monocyte counts were significantly increased. The number of histologically and flow cytometrically analyzed brain invading T- and B lymphocytes was significantly reduced in FTY720 treated mice. However, despite testing a variety of treatment protocols, infarct volume and behavioural dysfunction were not reduced 7d after permanent occlusion of the distal middle cerebral artery (MCAO). Additionally, we did not measure a significant reduction in infarct volume at 24 h after 60 min filament-induced MCAO, and did not see differences in brain edema between PBS and FTY720 treatment. Analysis of brain cytokine expression revealed complex effects of FTY720 on postischemic neuroinflammation comprising a substantial reduction of delayed proinflammatory cytokine expression at 3d but an early increase of IL-1β and IFN-γ at 24 h after MCAO. Also, serum cytokine levels of IL-6 and TNF-α were increased in FTY720 treated animals compared to controls.

CONCLUSIONS/SIGNIFICANCE

In the present study we were able to detect a reduction of lymphocyte brain invasion by FTY720 but could not achieve a significant reduction of infarct volumes and behavioural dysfunction. This lack of neuroprotection despite effective lymphopenia might be attributed to a divergent impact of FTY720 on cytokine expression and possible activation of innate immune cells after brain ischemia.

Translational aspects of sphingosine 1-phosphate biology

Sphingosine 1-phosphate (S1P) is a bioactive lipid that has both physiological and pathophysiological roles. It regulates cellular processes such as proliferation, migration, survival and differentiation and affects all organ systems. S1P not only activates S1P-specific receptors to initiate cellular signalling pathways but also directly regulates specific intracellular target proteins. The therapeutic opportunities surrounding S1P signalling are numerous and exemplified by the recent approval of FTY720 (a sphingosine analogue, Gilenya™) for the treatment of relapsing multiple sclerosis. A major focus of research is to develop small-molecule antagonists/agonists/inhibitors that are specific to the different S1P receptor subtypes and the enzymes that regulate S1P levels. This review describes fundamental aspects of S1P biology with an emphasis on the translational potential of intervention therapeutics.

Treatment with the immunomodulator FTY720 does not promote spontaneous bacterial infections after experimental stroke in mice

Background

FTY720, an immunomodulator derived from a fungal metabolite which reduces circulating lymphocyte counts by increasing the homing of lymphocytes to the lymph nodes has recently gained interest in stroke research. The aim of this study was to evaluate the protective efficacy of FTY720 in cerebral ischemia in two different application paradigms and to gather first data on the effect of FTY720 on the rate of spontaneous bacterial infections in experimental stroke.

Methods

Middle cerebral artery occlusion (MCAO) in C57BL/6 mice (strain J, groups of 10 animals) was performed with two different durations of ischemia (90 min and 3 h) and FTY720 was applied 2 h after vessel occlusion to study the impact of reperfusion on the protective potency of FTY720. Lesion size was determined by TTC staining. Mice treated with FTY720 or vehicle were sacrificed 48 h after 90 min MCAO to determine the bacterial burden in lung and blood.

Results

FTY720 1 mg/kg significantly reduced ischemic lesion size when administered 2 h after the onset of MCAO for 3 h (45.4 ± 22.7 mm³ vs. 84.7 ± 23.6 mm³ in control mice, p = 0.001) and also when administered after reperfusion, 2 h after the onset of MCAO for 90 min (31.1 ± 28.49 mm³ vs. 69.6 ± 27.2 mm³ in control mice, p = 0.013). Bacterial burden of lung homogenates 48 h after stroke did not increase in the group treated with the immunomodulator FTY720 while there was no spontaneous bacteremia 48 h after MCAO in treated and untreated animals.

Conclusions

Our results corroborate the experimental evidence of the protective effect of FTY720 seen in different rodent stroke models. Interestingly, we found no increase in bacterial lung infections even though FTY720 strongly reduces the number of circulating leukocytes.

Adoptive transfer of FTY720-treated immature BMDCs significantly prolonged cardiac allograft survival

A sphingosine 1 phosphate receptor modulator, FTY720, has been used to alleviate symptoms in allotransplantation and autoimmune disease models with impressive efficacy, while it only achieved moderate success in clinical trials. Infusion of immature bone marrow-derived dendritic cell (BMDC) progenitors before transplantation could induce donor specific tolerance. In this study, we investigated the possibility of using FTY720-DCs (FTY720-treated immature BMDCs) to prevent severe alloimmune response. Our results indicate that FTY720-DCs could markedly prolong graft survival compared with Ctrl-DCs (nonconditioned immature BMDCs) as manifested by reduced inflammatory infiltration into the graft. IFN-γ production by CD4(+) and CD8(+) T cells were significantly reduced, while FoxP3(+) regulatory T cells among CD4(+) T cells were upregulated. Although FTY720 seldom altered the phenotype or the phagocytosis of BMDCs in vitro, it severely hampered their capability to trigger antigen-specific and allogeneic T-cell response. When splenic T cells were co-cultured with FTY720-DCs, the proportion of regulatory T cells increased, accompanied by elevated IL-10 production. Consistently, infusion of FTY720-DCs could preferentially promote Treg proliferation and upregulate PD-1 expression on conventional T cells in allogeneic mature BMDC priming experiment. These results suggest that infusion of FTY720-DCs before cardiac transplantation could significantly prolong functional graft survival by acting as a balancer of alloimmune response.

FTY720 is neuroprotective and improves functional outcomes after intracerebral hemorrhage in mice

Intracerebral hemorrhage (ICH) accounts for 20% of all strokes and is the most devastating form across all stroke types. Lymphocytes have been shown to potentiate cerebral inflammation and brain injury after stroke. FTY720 (Fingolimod) is an immune-modulating drug that prevents the egress of peripheral lymphocytes from peripheral stores. We hypothesized that FTY720 would reduce peripheral circulating lymphocytes, resulting in reduced brain injury and improved functional outcomes. CD-1 mice were anesthetized and then injected with collagenase into the right basal ganglia. Animals were divided into three groups: sham, ICH+Vehicle, and ICH+FTY720, by the intra-peritoneal route at 1 h after ICH induction. Brain water content was measured at 24 and 72 h. Neurobehavioral tests included corner test, forelimb use asymmetry, paw placement, wire-hang test, beam balance test, and a Neuroscore. FTY720 significantly reduced brain edema and improved neurological function at all time points tested. Lymphocyte modulation with FTY720 is an effective neuroprotective strategy to reduce brain injury and promote functional recovery after ICH.

Fingolimod provides long-term protection in rodent models of cerebral ischemia

OBJECTIVE

The sphingosine-1-phosphate (S1P) receptor agonist fingolimod (FTY720), that has shown efficacy in advanced multiple sclerosis clinical trials, decreases reperfusion injury in heart, liver, and kidney. We therefore tested the therapeutic effects of fingolimod in several rodent models of focal cerebral ischemia. To assess the translational significance of these findings, we asked whether fingolimod improved long-term behavioral outcomes, whether delayed treatment was still effective, and whether neuroprotection can be obtained in a second species.

METHODS

We used rodent models of middle cerebral artery occlusion and cell-culture models of neurotoxicity and inflammation to examine the therapeutic potential and mechanisms of neuroprotection by fingolimod.

RESULTS

In a transient mouse model, fingolimod reduced infarct size, neurological deficit, edema, and the number of dying cells in the core and periinfarct area. Neuroprotection was accompanied by decreased inflammation, as fingolimod-treated mice had fewer activated neutrophils, microglia/macrophages, and intercellular adhesion molecule-1 (ICAM-1)-positive blood vessels. Fingolimod-treated mice showed a smaller infarct and performed better in behavioral tests up to 15 days after ischemia. Reduced infarct was observed in a permanent model even when mice were treated 4 hours after ischemic onset. Fingolimod also decreased infarct size in a rat model of focal ischemia. Fingolimod did not protect primary neurons against glutamate excitotoxicity or hydrogen peroxide, but decreased ICAM-1 expression in brain endothelial cells stimulated by tumor necrosis factor alpha.

INTERPRETATION

These findings suggest that anti-inflammatory mechanisms, and possibly vasculoprotection, rather than direct effects on neurons, underlie the beneficial effects of fingolimod after stroke. S1P receptors are a highly promising target in stroke treatment.

Immunological consequences of ischemic stroke: immunosuppression and autoimmunity

Stroke may be accompanied by immunological consequences including local autoimmunity and peripheral immune suppression. Since the blood brain barrier is disturbed cells of the immune system gain direct access to the brain parenchyma. Here local autoimmunity contributes to lesion formation and, in experimental stroke, inhibition of this immune response has been shown to be beneficial. More recently, however, stroke has been shown to also induce severe peripheral immune suppression which predisposes for subsequent bacterial infections that impair the clinical outcome. Here we summarize current knowledge on the immunological consequences of ischemic stroke and will discuss implications of these findings for our understanding of the immunopathogenesis of Multiple Sclerosis.

Therapeutic effect of IL-12/23 and their signaling pathway blockade on brain ischemia model

Recently, T cell cytokines such as IL-17 and IFN-γ have been shown to play important roles in the progression of brain injury induced by ischemia. We have shown that IL-23 from infiltrated macrophages activates γδT cells, thereby inducing IL-17 from these cells. However, deletion of the IL-23 gene in mice showed a more dramatic protective effect against brain ischemia reperfusion (I/R) model than γδT cell depletion did, suggesting that IL-23 plays some other pivotal role in brain injury in addition to its role in IL-17 induction. To develop therapeutic methods based on these findings, we examined the effect of the JAK kinase inhibitor CP-690550 and an anti-IL12/23 monoclonal antibody on an I/R model. CP-690550 efficiently inhibited IL-17 production from memory T cells in vitro and partly suppressed infarct volume increase after I/R. Anti-p40 antibody, which blocks both IL-12 and IL-23, efficiently suppressed I/R injury and improved recovery of neurological deficits. The number of IL-17-producing cells was decreased by anti-p40 antibody treatment. Thus the JAK inhibitor and anti-p40 antibody, both of which have already been under trial for the treatment of several human inflammatory diseases, appear to be promising therapeutic agents for the amelioration of stroke.

An update on sphingosine-1-phosphate and other sphingolipid mediators

Sphingolipids comprise a complex family of naturally occurring molecules that are enriched in lipid rafts and contribute to their unique biochemical properties. Membrane sphingolipids also serve as a reservoir for bioactive metabolites including sphingosine, ceramide, sphingosine-1-phosphate and ceramide-1-phosphate. Among these, sphingosine-1-phosphate has emerged as a central regulator of mammalian biology. Sphingosine-1-phosphate is essential for mammalian brain and cardiac development and for maturation of the systemic circulatory system and lymphatics. In addition, sphingosine-1-phosphate contributes to trafficking and effector functions of lymphocytes and other hematopoietic cells and protects against various forms of tissue injury. However, sphingosine-1-phosphate is also an oncogenic lipid that promotes tumor growth and progression. Recent preclinical and clinical investigations using pharmacological agents that target sphingosine-1-phosphate, its receptors and the enzymes required for its biosynthesis and degradation demonstrate the promise and potential risks of modulating sphingosine-1-phosphate signaling in treatment strategies for autoimmunity, cancer, cardiovascular disease and other pathological conditions.

Mechanisms of osteopontin-induced stabilization of blood-brain barrier disruption after subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

Osteopontin (OPN) is an inducible, multifunctional, extracellular matrix protein that may be protective against blood-brain barrier (BBB) disruption after subarachnoid hemorrhage (SAH). However, the protective mechanisms remain unclear.

METHODS

We produced the endovascular perforation model of SAH in rats and studied the time course of OPN induction in brains by Western blotting and immunofluorescence (n=50). Then, 34 rats were randomly assigned to sham (n=3), sham+OPN small interfering RNA (siRNA, n=3), SAH+negative control siRNA (n=14), and SAH+OPN siRNA (n=14) groups, and 109 rats were allocated to sham+vehicle (n=17), sham+recombinant OPN (n=17), SAH+vehicle (n=33), SAH+recombinant OPN (n=31), and SAH+recombinant OPN+L-arginyl-glycyl-L-aspartate motif-containing hexapeptide (n=11) groups. The effects of OPN siRNA or recombinant OPN on BBB disruption and related proteins were studied.

RESULTS

OPN was significantly induced in reactive astrocytes and capillary endothelial cells, peaking at 72 hours after SAH, during the recovery phase of BBB disruption. Blockage of endogenous OPN induction exacerbated BBB disruption and was associated with a reduction of angiopoietin-1 and mitogen-activated protein kinase (MAPK) phosphatase-1 (an endogenous MAPK inhibitor), activation of MAPKs, and induction of vascular endothelial growth factor-A at 72 hours after SAH, whereas recombinant OPN treatment improved it and was associated with MAPK phosphatase-1 induction, MAPK inactivation, and vascular endothelial growth factor-A reduction, which was blocked by L-arginyl-glycyl-L-aspartate motif-containing hexapeptide at 24 hours after SAH. Vascular endothelial growth factor-B and angiopoietin-2 levels were unchanged.

CONCLUSIONS

OPN may increase MAPK phosphatase-1 that inactivates MAPKs, upstream and downstream of vascular endothelial growth factor-A, by binding to L-arginyl-glycyl-L-aspartate-dependent integrin receptors, suggesting a novel mechanism of OPN-induced post-SAH BBB protection.

Isoflurane posttreatment reduces neonatal hypoxic-ischemic brain injury in rats by the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway

BACKGROUND AND PURPOSE

Isoflurane, administered before or during cerebral ischemia, has been shown to exhibit neuroprotection in animal models of ischemic stroke. However, the underlying mechanism remains to be elucidated. In the present study, we determined whether isoflurane posttreatment provides neuroprotection after neonatal hypoxia-ischemia (HI) in rats and evaluated the role of the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway in this volatile anesthetic-mediated neuroprotection.

METHODS

HI was induced in postnatal day 10 (P10) rat pups by unilateral carotid ligation and 2 hours of hypoxia. For treatment, 2% isoflurane was administered immediately after HI for 1 hour. As pharmacological interventions, the sphingosine-1-phosphate antagonist VPC23019, phosphatidylinositol-3-kinase inhibitor wortmannin, or opioid antagonist naloxone was administered before HI. Isoflurane posttreatment was evaluated for effects on infarct volume at 48 hours after HI and brain atrophy and neurological outcomes at 4 weeks after HI. The expression of phosphorylated Akt and cleaved caspase-3 was determined by Western blotting and immunofluorescence analysis.

RESULTS

Isoflurane posttreatment significantly reduced infarct volume at 48 hours after HI. VPC23019 or wortmannin abrogated the neuroprotective effect of isoflurane, whereas naloxone did not inhibit the isoflurane-induced neuroprotection. Isoflurane posttreatment significantly preserved phosphorylated Akt expression and decreased cleaved caspase-3 levels. These effects were reversed by VPC23019 and wortmannin, respectively. Isoflurane also confers long-term neuroprotective effects against brain atrophy and neurological deficits at 4 weeks after HI.

CONCLUSIONS

Isoflurane posttreatment provides lasting neuroprotection against hypoxic-ischemic brain injury in neonatal rats. Activation of the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway may play a key role in isoflurane posttreatment-induced neuroprotection.