Microsphere Embolism Research Articles

Panax notoginseng Saponins Stimulates Neurogenesis and Neurological Restoration After Microsphere-Induced Cerebral Embolism in Rats Partially Via mTOR Signaling.

P. Notoginseng Saponins (PNS), the main active component of herbal medicine Panax notoginseng, has been widely used to treat cerebrovascular diseases. It has been acknowledged that PNS exerted protection on nerve injuries induced by ischemic stroke, however, the long-term impacts of PNS on the restoration of neurological defects and neuroregeneration after stroke have not been thoroughly studied and the underlying molecular mechanism of stimulating neurogenesis is difficult to precisely clarify, much more in-depth researches are badly needed. In the present study, cerebral ischemia injury was induced by microsphere embolism (ME) in rats. After 14 days, PNS administration relieved cerebral ischemia injury as evidenced by alleviating neurological deficits and reducing hippocampal pathological damage. What’s more, PNS stimulated hippocampal neurogenesis by promoting cell proliferation, migration and differentiation activity and modulated synaptic plasticity. Increased number of BrdU/Nestin, BrdU/DCX and NeuroD1-positive cells and upregulated synapse-related GAP43, SYP, and PSD95 expression were observed in the hippocampus. We hypothesized that upregulation of brain-derived neurotrophic factor (BDNF) expression and activation of Akt/mTOR/p70S6K signaling after ME could partially underlie the neuroprotective effects of PNS against cerebral ischemia injury. Our findings offer some new viewpoints into the beneficial roles of PNS against ischemic stroke.

Investigation of the Physical Properties and Clinical Application of Embosphere Microspheres

Background: The aim of this study was to understand physical characteristics of Embosphere microspheres for the clinical use of microsphere chemotherapy embolization of liver cancer. Methods: The morphology of Embosphere microspheres in different states, including static, oscillating, and in a magnetic field was observed with the naked eye. Ninety-five patients diagnosed with primary hepatocellular carcinoma (HCC) were separated into 3 groups based on the types of embolic material as follows: 32 cases of sole microspheres, 34 cases of iodinated oil (17 cases with additional application of gelatin sponge particle), and 29 cases of iodinated oil + Embosphere microspheres. Results: The diameter of the microspheres ranged from 100 to 300 μm, with a sedimentation rate υ = 0.0375 cm/s in physiological saline. The diameter of microspheres ranged from 300 to 500 μm, with a sedimentation rate υ = 0.1875 cm/s. The swelling rate of microspheres was 90%. Microspheres showed nondirectional movement in a 1.5- or 3.0-T magnetic field during magnetic resonance imaging. A volumetric ratio of 1:1.4–1:1.5 between microspheres and contrast agent resulted in optimal suspension properties. Microspheres appeared circular with a smooth surface upon water adsorption. Microsphere embolism was observable in blood vessels of pathological sections. The surface of microspheres can adsorb 5-fluorouracil and arsenic trioxide. There are statistically significant differences in local-regional tumor control conditions among patients treated with sole microspheres, iodinated oil, and iodinated oil + microspheres during transarterial chemoembolization. Conclusions: Embosphere microspheres can be used to embolize patients with rupture and hemorrhage of HCC. Embosphere microsphere embolization is superior to iodinated oil and iodinated oil + microsphere for HCC.

GPR124 facilitates pericyte polarization and migration by regulating the formation of filopodia during ischemic injury.

Prolonged occlusion of multiple microvessels causes microvascular injury. G protein-coupled receptor 124 (GPR124) has been reported to be required for maintaining central nervous system (CNS) angiogenesis and blood-brain barrier integrity. However, the molecular mechanisms by which GPR124 regulates pericytes during ischemia have remained elusive.Methods: A microsphere embolism-induced ischemia model was used to evaluate the expression of GPR124 following microsphere embolism. Immunocytochemistry and stochastic optical reconstruction microscopy imaging were used to assess the expression and distribution of GPR124 in human brain vascular pericytes (HBVPs) and after the treatment with 3-morpholino-sydnonimine (SIN-1) or oxygen-glucose deprivation (OGD). The effect of GPR124 knockdown or overexpression on HBVP migration was analyzed in vitro using wound healing assays and a microfluidic device. GPR124 loss-of-function studies were performed in HBVPs and HEK293 cells using CRISPR-Cas9-mediated gene deletion. Time-lapse imaging was used to assess dynamic changes in the formation of filopodia in an individual cell. Finally, to explore the functional domains required for GPR124 activity, deletion mutants were constructed for each of the N-terminal domains.Results: GPR124 expression was increased in pericytes following microsphere embolism. Morphological analysis showed localization of GPR124 to focal adhesions where GPR124 bound directly to the actin binding protein vinculin and upregulated Cdc42. SIN-1 or OGD treatment redistributed GPR124 to the leading edges of HBVPs where GPR124 signaling was required for pericyte filopodia formation and directional migration. Partial deletion of GPR124 domains decreased SIN-1-induced filopodia formation and cell migration.Conclusion: Taken together, our results provide the first evidence for a role of GPR124 in pericyte migration under ischemic conditions and suggest that GPR124 was essential for Cdc42 activation and filopodia formation.

Therapeutic efficacy of novel microwave-sensitized mPEG-PLGA@ZrO2@(DOX + ILS) drug-loaded microspheres in rabbit VX2 liver tumours.

The use of nanomaterials as drug delivery systems shows good effects in treating tumors. However, the effective dose of drugs targeted to tumor tissues is very low because of the effect of the reticuloendothelial system (RES) in removing such foreign substances. In order to eliminate the RES effect, we developed mPEG-PLGA@ZrO2@(DOX + ILS) (mPEG-PLGA@ZrO2@[DOX + ILS]) drug-loaded microspheres. These microwave (MW)-sensitized microspheres directly embolized the blood-supply vessels of tumors to induce tumor ischemia and hypoxia, as well as to aggregate drugs within tumor tissues in a long-lasting manner. Additionally, combination with MW ablation can triple the effects for the inhibition of tumor growth. The MW sensitive ionic liquid (ILS) in microspheres can rapidly produce a high temperature in a MW field on the basis of MW sensitization, thus accelerating the degradation of microspheres to release DOX-loaded ZrO2 into the lesions to kill tumors. Microspheres can also prolong the pharmacological time and effect of drugs through the enhanced permeability and retention (EPR) effect of nanocarriers, as well as the sustained release of nanomaterials. Studies performed in vivo revealed that mPEG-PLGA@ZrO2@(DOX + ILS) showed good biosafety. We undertook sensitized microsphere embolism therapy using novel mPEG-PLGA@ZrO2@(DOX + ILS) microspheres in a rabbit VX2 liver tumor model. Three, 6 and 9 d after treatment, computed tomography indicated no significant change in tumor size, and diffusion weighted imaging showed a marked decrease of residual tumor tissues. With the multiple functions of inducing embolisms, sensitization, and the sustained release of chemotherapeutics, novel mPEG-PLGA@ZrO2@(DOX + ILS) microspheres can achieve good therapeutic efficacy, in combination with MW ablation and chemotherapy, while embolizing the blood vessels of arterial tumors.

Inflammatory mechanisms contribute to microembolism-induced anxiety-like and depressive-like behaviors

Poor vascular health, atherosclerosis, or cardiac procedures in the elderly result in clinically silent microvascular infarcts that increase susceptibility to larger ischemic episodes and can precipitate changes in mood and cognition. Although the mechanisms that underlie ischemia-induced behavioral changes have not been fully elucidated, chronic inflammation has been implicated in the pathogenesis. Independent of brain injury, elevated levels of inflammatory cytokines can lead to sickness behaviors and symptoms of depression. Furthermore, in the presence of brain injury, inflammatory activation may serve as the linchpin that precipitates dysregulation of biological systems leading to changes to behavior. In the current study, we tested the hypothesis that cerebral inflammation caused by diffuse ischemia is necessary for the expression of post-injury anxiety- and depressive- like behavior. Using a microsphere embolism (ME) rodent model, we demonstrate prolonged elevations in expression of inflammatory genes in the hippocampus ipsilateral to the injury which are reflected in the contralateral hemisphere by two weeks following injury. Prophylactic administration of meloxicam, a preferential inhibitor of COX-2 activity, prevented both central inflammation and deficits in affective-like behaviors. Furthermore, meloxicam was more efficacious than the selective serotonin reuptake inhibitor fluoxetine in prevention of microembolism-induced changes in inflammation and behavior. These data demonstrate that inflammatory activation is necessary for microembolism-induced behavioral changes and suggest that anti-inflammatory treatments may be an effective therapeutic strategy in patients with risk factors for vascular depression or prior to invasive cardiac procedures.

GW26-e3893 Establishment of an experimental angiographic slow coronary flow model by microsphere embolism in pigs

GW26-e3893 Establishment of an experimental angiographic slow coronary flow model by microsphere embolism in pigs

Microemboli alter the acute stress response and cause prolonged expression of MCP-1 in the hippocampus

Microvascular ischemia is linked to cardiovascular disease pathology, as well as alterations in mood and cognition. Ischemia activates the hypothalamic-pituitary-adrenal (HPA) axis and through chronic activation, alters HPA axis function. Dysregulation of the HPA axis can lead to the chronic release of glucocorticoids, a hyper-inflammatory cerebral response, cell damage, and changes in behavior. Although the interactions between injury and HPA axis activity have been established in global ischemia, HPA-related repercussions of diffuse ischemic damage and subsequent inflammation have not been assessed. The current study used a rat model of microsphere embolism (ME) ischemia to test the hypothesis that microvascular ischemia would lead to long term alterations in HPA axis function and inflammatory activity. Furthermore, given the pro-inflammatory nature of chronic stress, we assessed the implications of chronic stress for gene expression of inflammatory factors and key components of the glucocorticoid receptor response, following microvascular ischemia. Results indicated that ME altered the response to an acute stress fourteen days following ME injury and increased hippocampal expression of monocyte chemoattractant protein 1 (Mcp-1) as long as 4 weeks following ME injury, without concomitant effects on gene expression of the glucocorticoid receptor or its co-chaperones. Furthermore, no exacerbative effects of chronic stress exposure were observed following ME injury beyond the effects of ME injury alone. Together, these results indicate that ME injury is sufficient to alter both HPA axis activity and cerebral inflammation for a prolonged period of time following injury.

27. Neuroinflammation mediates the delayed behavioral effects of microembolism

Microsphere embolism (ME) rodent models recapitulate both the diffuse ischemic infarcts and the behavioral disturbances characteristic to cerebromicrovascular disease (CMVD). Previously, we have shown that ME also leads to increased hippocampal inflammation, weakening of the blood brain barrier, and the infiltration of peripherally circulating inflammatory cells. The current study builds upon these findings to test the hypothesis that anti-inflammatory administration is sufficient to reduce hippocampal cytokine expression and attenuate the behavioral consequences of diffuse ME infarction. Adult male rats received either SHAM or ME surgeries and anti-inflammatory treatments under two dosing strategies: one cohort of rats received meloxicam, a preferential cox-2 inhibitor, prophylactically, beginning five days prior to surgery; a second cohort was administered XPro1595®, an inhibitor of soluble TNF signaling, immediately following surgery or on day seven post-surgery. Both cohorts were behaviorally examined on day fourteen and hippocampal gene expression of inflammatory markers was measured. Both treatments lowered hippocampal inflammation and rescued ME-induced behavioral effects but only when inhibition preceded or coincided with injury. These findings are important because they show that behavioral disruptions precipitated by ME may be mediated by a generalized inflammatory response to the initial injury. Given that peripheral administration of a general or specific anti-inflammatory treatment is sufficient to reduce hippocampal elevation and alter behavior, anti-inflammatory therapeutics may be useful in the slowing of CMVD progression in at-risk patients.

Establishment of an experimental angiographic slow coronary flow model by microsphere embolism in swines

Establishment of an experimental angiographic slow coronary flow model by microsphere embolism in swines

Abstract 212: Prophylactic Anti-inflammatory Treatment Attenuates The Neuroinflammatory And Behavioral Effects Of Silent Cerebral Infarction

Silent brain infarction is a frequent complication of cardiac surgery and is associated with mood changes and cognitive disruption. Microsphere embolism (ME) rodent models recapitulate both the diffuse ischemic infarcts and the delayed subtle behavioral disturbances characteristic to silent infarction (SI). Previously, we have shown that ME leads to increased hippocampal inflammation, weakening of the blood brain barrier, and the infiltration of peripherally circulating inflammatory cells in rats. Given long-term increases in inflammatory activity following SI, the current study tests the efficacy of anti-inflammatory versus anti-depressant treatment strategies to reduce the inflammatory and behavioral sequelae of injury. Adult rats were administered either chronic meloxicam (preferential COX-2 inhibitor) or fluoxetine (SSRI) beginning five days prior to ME surgeries. After a two week recovery, animals were tested for anxiety-like behaviors in the open field paradigm and the hippocampus was examined for gene expression of inflammatory cytokines. Meloxicam treated animals showed a decrease in hippocampal gene expression of inflammatory markers (SPP1; p = 0.0272) and greater than a 3-fold change improvement in open field central tendency (p = 0.0003). No differences in inflammatory gene expression were observed in fluoxetine treated animals (SPP1; p = 0.3288); however, fluoxetine treatment resulted in a 2-fold change improvement in open field central tendency (p = 0.0138) suggesting that while both treatment strategies attenuate SI induced behavioral disruption, only meloxicam acts via inflammatory mechanisms. Given the long term negative consequences of increased central and peripheral inflammatory activity, the data suggest that anti-inflammatory therapeutic strategies may benefit patients at risk for SI as well as cardiac surgery candidates.

Injection of neural progenitor cells attenuates decrease in level of connexin 43 in brain capillaries after cerebral ischemia

Although functional disruption of the cerebrovasculature, which is called the “neurovascular unit (NVU)”, may lead to amplification of ischemia-induced injury, changes in the gap junctional proteins within the NVU and their pathophysiological roles after brain injury remain controversial. We previously demonstrated that the intravenous injection of neural progenitor cells (NPCs) have therapeutic potential for improving the spatial learning dysfunction and depression-like behaviors observed after cerebral ischemia. In this study, we investigated whether severe cerebral ischemia would alter the expression of gap junctional proteins in isolated brain capillaries and examined the effect of intravenous injection of NPCs on the levels of these proteins. Cerebral ischemia induced a sustained decrease in the level of the gap junctional protein connexin 43 (Cx43) in the isolated brain capillaries, whereas the level of aquaporin 4 (AQP-4) was transiently increased. The injection of NPCs increased the level of Cx43 compared that of vehicle in the microsphere embolism (ME) rats, suggesting this decrease to be a possible mechanism for disruption of the astrocyte-endothelial cell interface within the NVU without causing any changes in the level of AQP-4 and N-cadherin. We also demonstrated that some of the intravenously injected NPCs migrated into the blood vessels in the peri-infarct area. These results suggest that the intravenous injection of the NPCs would remodel the NVU after severe cerebral ischemia, which remodeling might be associated with functional improvement following the NPC injection.

P2X7 signaling promotes microsphere embolism-triggered microglia activation by maintaining elevation of Fas ligand

BackgroundThe cerebral microvascular occlusion elicits microvascular injury which mimics the different degrees of stroke severity observed in patients, but the mechanisms underlying these embolic injuries are far from understood. The Fas ligand (FasL)-Fas system has been implicated in a number of pathogenic states. Here, we examined the contribution of microglia-derived FasL to brain inflammatory injury, with a focus on the potential to suppress the FasL increase by inhibition of the P2X7-FasL signaling with pharmacological or genetic approaches during ischemia.MethodsThe cerebral microvascular occlusion was induced by microsphere injection in experimental animals. Morphological changes in microglial cells were studied immunohistochemically. The biochemical analyses were used to examine the intracellular changes of P2X7/FasL signaling. The BV-2 cells and primary microglia from mice genetically deficient in P2X7 were used to further establish a linkage between microglia activation and FasL overproduction.ResultsThe FasL expression was continuously elevated and was spatiotemporally related to microglia activation following microsphere embolism. Notably, P2X7 expression concomitantly increased in microglia and presented a distribution pattern that was similar to that of FasL in ED1-positive cells at pathological process of microsphere embolism. Interestingly, FasL generation in cultured microglia cells subjected to oxygen-glucose deprivation-treated neuron-conditioned medium was prevented by the silencing of P2X7. Furthermore, FasL induced the migration of BV-2 microglia, whereas the neutralization of FasL with a blocking antibody was highly effective in inhibiting ischemia-induced microglial mobility. Similar results were observed in primary microglia from wild-type mice or mice genetically deficient in P2X7. Finally, the degrees of FasL overproduction and neuronal death were consistently reduced in P2X7−/− mice compared with wild-type littermates following microsphere embolism insult.ConclusionFasL functions as a key component of an immunoreactive response loop by recruiting microglia to the lesion sites through a P2X7-dependent mechanism. The specific modulation of P2X7/FasL signaling and aberrant microglial activation could provide therapeutic benefits in acute and subacute phase of cerebral microembolic injury.

Regulation of the ischemia-induced autophagy-lysosome processes by nitrosative stress in endothelial cells

The cellular mechanisms that underlie the diverse nitrosative stress-mediated cellular events associated with ischemic complications in endothelial cells are not yet clear. To characterize whether autophagic elements are associated with the nitrosative stress that causes endothelial damage after ischemia injury, an in vitro sustained oxygen-glucose deprivation (OGD) and an in vivo microsphere embolism model were used in the present study. Consistent with OGD-induced peroxynitrite formation, a rapid induction of microtubule-associated protein 1 light chain 3 (LC3)-I/II conversion and green fluorescent protein-LC3 puncta accumulation were observed in endothelial cells. The Western blot analyses indicated that OGD induced elevations in lysosome-associated membrane protein 2 and cathepsin B protein levels. Similar results were observed in the microvessel insult model, following occlusion of the microvessels using microsphere injections in rats. Furthermore, cultured endothelial cells treated with peroxynitrite (1-50 μm) exhibited a concentration-dependent change in the pattern of autophagy-lysosome signaling. Intriguingly, OGD-induced autophagy-lysosome processes were attenuated by PEP-19 overexpression and by a small-interfering RNA (siRNA)-mediated knockdown of eNOS. The importance of nitrosative stress in ischemia-induced autophagy-lysosome cascades is further supported by our finding that pharmacological inhibition of nitrosative stress by melatonin partially inhibits the ischemia-induced autophagy-lysosome cascade and the degradation of the tight junction proteins. Taken together, the present results demonstrate that peroxynitrite-mediated nitrosative stress at least partially potentiates autophagy-lysosome signaling during sustained ischemic insult-induced endothelial cell damage.

Melatonin ameliorates ischemic-like injury-evoked nitrosative stress: Involvement of HtrA2/PED pathways in endothelial cells

Peroxynitrite contributes to diverse cellular stresses in the pathogenesis of ischemic complications. Here, we investigate the downstream effector signaling elements of nitrosative stress which regulate ischemia-like cell death in endothelial cells and protective effect of melatonin. When the mitochondrial membrane potential (ΔΨm) of oxygen-glucose deprivation (OGD)-treated cells was assessed using the fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol -carbocyanine iodide, we observed spontaneous changes in peroxynitrite formation. Concomitantly, western blot and confocal microscopy analyses indicated that prolonged OGD exposure initiates the release of mitochondrial HtrA2 and dramatically decreases phosphoprotein enriched in astrocytes (PED or PEA-15) protein levels. Consistently, cultured endothelial cells treated with peroxynitrite (1-50 μm) exhibited a concentration-dependent release of mitochondrial HtrA2 and concomitant PED degradation in vitro. Notably, HtrA2 activation coincided with increased nitrotyrosine immunoreactivity in microvessels of rats following microsphere embolism. Additionally, the protective effect of PED overexpression in OGD-induced apoptosis was abolished by transfection with the PED(S104A/S116A) mutant. Furthermore, the effect of melatonin, an potential antioxidant, on endothelial apoptotic cascade was examined in OGD-evoked nitrosative stress. Our data showed that the application of melatonin provided significant protection against OGD-induced peroxynitrite formation and mitochondrial HtrA2 release, accompanied with a decrease in degradation PED and x-linked inhibitor of apoptosis protein, which is associated with activation of the caspase cascade. Taken together, the protective effect of melatonin is likely mediated, in part, by inhibition of peroxynitrate-mediated nitrosative stress, which in turn relieves imbalance of mitochondrial HtrA2-PED signaling and endothelial cell death.

β-Amyloid Accumulation in Neurovascular Units Following Brain Embolism

Nitric oxide (NO) toxicity is in part mediated by generation of peroxynitrite with concomitant production of superoxide under pathological brain conditions such as ischemia and Alzheimer’s disease. The pathophysiological relevance of endothelial nitric oxide synthase (eNOS) to brain embolism-induced neurovascular injury has not been documented. We found that microsphere embolism (ME)–induced aberrant eNOS expression in vascular endothelial cells likely mediates blood-brain barrier (BBB) disruption via peroxynitrite formation and in turn causes brain edema. We also demonstrated that a mild ME model was useful for investigating the sequential events of neurovascular injury followed by β-amyloid accumulation and tau hyperphosphorylation. Indeed, immunoblotting of purified brain microvessels revealed that β-amyloid accumulation significantly increased one week after ME induction and remained elevated for twelve weeks in those animals. Moreover, we also confirmed that peroxynitrite formation and eNOS uncoupling–mediated superoxide generation in microvessels are inhibited by a novel calmodulin inhibitor. Thus, peroxynitrite formation via elevated eNOS is associated with endothelial cell injury with concomitant β-amyloid accumulation in microvessels of aged rats. In this review, we focus on the detrimental effects of eNOS expression following brain embolism and introduce an attractive model representing progressive Alzheimer’s disease pathology in brain.

Hepatocyte growth factor suppresses ischemic cerebral edema in rats with microsphere embolism

The present study was aimed at determining whether human recombinant hepatocyte growth factor (HGF) ameliorates cerebral edema induced by microsphere embolism (ME). Rats were injected with 700 microspheres (48μm in diameter). Continuous administration of HGF at 13μg/3 days/animal into the right ventricle was started from 10min after embolism to the end of the experiment by using an osmotic pump. On day 3 after the ME, the rats were anesthetized, and their brains were perfused with an isotonic mannitol solution to eliminate constituents in the vascular and extracellular spaces. Thereafter, tissue water and cation contents were determined. A significant increase in tissue water content of the right hemisphere by ME was seen. This ME-induced increase in water content was associated with increases in tissue sodium and calcium ion contents and decreases in tissue potassium and magnesium ion contents of the right hemisphere. The treatment of the animal with HGF suppressed the increases in water and sodium and calcium ion contents, but not the decreases in potassium and magnesium ion contents. These results suggest that HGF suppresses the formation of ischemic cerebral edema provoked intracellularly in rats with ME.

Accumulation of beta-amyloid in the brain microvessels accompanies increased hyperphosphorylated tau proteins following microsphere embolism in aged rats

To define mechanisms underlying neurovascular injury following brain embolism-induced neurodegeneration, we investigated temporal and spatial pathological changes in brain microvessels up to 12 weeks after microsphere embolism (ME) induction in aged male rats. Mild ME upregulated endothelial nitric oxide synthase (eNOS) and protein tyrosine nitration in brain microvessels. Strong β-amyloid immunoreactivity coincident with increased eNOS immunoreactivity was observed in microvessels. Immunoblotting of purified brain microvessels revealed that β-amyloid accumulation significantly increased 1 week after ME induction and remained elevated for 12 weeks. Importantly, β-amyloid accumulation in brain parenchyma was also observed in areas surrounding injured microvessels at 12 weeks. Levels of Alzheimer's-related hyperphosphorylated tau proteins also concomitantly increased in neurons surrounding regions of β-amyloid accumulation 12 weeks after ME induction, as did glycogen synthase kinase (GSK3β) (Tyr-216) phosphorylation. Taken together, ME-induced aberrant eNOS expression and subsequent protein tyrosine nitration in microvessels preceded β-amyloid accumulation both in microvessels and brain parenchyma, leading to hyperphosphorylation of neuronal tau proteins through GSK3β activation.

Downregulation of glutamate transporters is associated with elevation in extracellular glutamate concentration following rat microsphere embolism

Sodium-dependent glutamate transporters expressed in astroglial cells and neurons are essential for clearance of extracellular glutamate. In the present study, we found elevation of extracellular glutamate concentration associated with concomitant downregulation of glutamate transporters following rat microsphere embolism (ME). A marked increase in extracellular glutamate in the rat striatum was observed by microdialysis immediately after ME induction, and glutamate remained elevated at least 12 h after ischemia. Concomitantly, impairment of high KCl (146 mM)-induced glutamate release was observed in the striatum 12 h after ME. Consistent with the persistent increase in extracellular glutamate, expression of the glutamate transporters EAAC1 and GLT-1 significantly decreased 6 h after insult without a change in GLAST levels. GLT-1 expression was restored to basal levels within 48 h, whereas EAAC1 expression remained decreased up to at least 72 h after ME. Restoration of GLT-1 was associated with increased expression of the astroglial marker GFAP, whereas markedly reduced EACC1 levels were correlated with reduced levels of the neuronal marker MAP2, likely due to loss of vulnerable neurons. Taken together, downregulation of glutamate transporters after ME is associated with dysregulation of basal glutamate concentrations and KCl-induced glutamate release in the brain.

Ischemic Brain Injury and Hepatocyte Growth Factor

Cerebral ischemia causes an irreversible and neurodegenerative disorder that may lead to progressive dementia and global cognitive deterioration. Since the overall process of ischemic brain injuries is extremely complex, treatment with endogenous multifunctional factors would be better choices for preventing complicated ischemic brain injuries. Hepatocyte growth factor, HGF, is a multifunctional cytokine originally identified and purified as a potent mitogen for hepatocyte. The activation of the c-Met/HGF receptor evokes diverse cellular responses, including mitogenic, morphogenic, angiogenic and anti-apoptotic activities in various types of cell. Previous studies showed that HGF and c-Met were expressed in various brain regions under normal conditions and that HGF enhanced the survival of hippocampal and cortical neurons during the aging of cells in culture. The protective effects of HGF on in vivo ischemic brain injuries and their mechanisms have not fully understood. To elucidate therapeutic potencies of HGF for ischemic brain injuries, we examined effects of HGF on ischemia-induced learning and memory dysfunction, neuronal cell death and endothelial cell damage by using the 4-vessel occlusion model and the microsphere embolism model in rats. Our findings suggested that treatment with HGF was capable of protecting hippocampal neurons against ischemia-induced cell death through the prevention of apoptosis-inducing factor translocation to the nucleus. Furthermore, we demonstrated that HGF had the ability to prevent tissue degeneration and improved learning and memory function after cerebral embolism, possibly through prevention of cerebral vessel injuries. As HGF has a potent cerebroprotective effect, it could be a prospective agent for the therapy against complicated ischemic brain diseases.

Brain Embolism-induced Injury of Vascular Endothelial Cells and a Novel Vasoprotective Drug

Microsphere embolism-induced up-regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells of brain microvessels was found after brain ischemia. The eNOS induction preceded disruption of the blood-brain barrier following ischemia. In vascular endothelial cells, microsphere embolism-induced eNOS expression was associated with protein tyrosine nitration, which is a marker of generation of peroxynitrite. To determine whether eNOS expression and protein tyrosine nitration in vascular endothelial cells mediates the blood-brain barrier disruption in the microsphere embolism brain, we tested the effect of a novel calmodulin-dependent NOS inhibitor, DY-9760e, which inhibits eNOS activity and in turn protein tyrosine nitration. Concomitant with inhibition of protein tyrosine nitration in vascular endothelial cells, DY-9760e significantly inhibited BBB disruption as assessed by Evans blue excretion. DY-9760e also inhibited cleavage of poly(ADP-ribose) polymerase as a marker of the apoptotic pathway in vascular endothelial cells. Taken together with previous evidence in which DY-9760e inhibited brain edema, microsphere embolism-induced eNOS expression in vascular endothelial cells likely mediates BBB disruption and in turn brain edema.