Biomedical subjects

M A Yenari

Publications and source records attributed to M A Yenari.

At least 19 recordsLinked to original sources

PubMed2004

Transplanted human fetal neural stem cells survive, migrate, and differentiate in ischemic rat cerebral cortex.

We characterize the survival, migration, and differentiation of human neurospheres derived from CNS stem cells transplanted into the ischemic cortex of rats 7 days after distal middle cerebral artery occlusion. Transplanted neurospheres survived robustly in naive and ischemic brains 4 wk posttransplant. Survival was influenced by proximity of the graft to the stroke lesion and was negatively correlated with the number of IB4-positive inflammatory cells. Targeted migration of the human cells was seen in ischemic animals, with many human cells migrating long distances ( approximately 1.2 mm) predominantly toward the lesion; in naive rats, cells migrated radially from the injection site in smaller number and over shorter distances (0.2 mm). The majority of migrating cells in ischemic rats had a neuronal phenotype. Migrating cells between the graft and the lesion expressed the neuroblast marker doublecortin, whereas human cells at the lesion border expressed the immature neuronal marker beta-tubulin, although a small percentage of cells at the lesion border also expressed glial fibrillary acid protein (GFAP). Thus, transplanted human CNS (hCNS)-derived neurospheres survived robustly in naive and ischemic brains, and the microenvironment influenced their migration and fate.

Animals↗

PubMed2004

Agmatine reduces infarct area in a mouse model of transient focal cerebral ischemia and protects cultured neurons from ischemia-like injury.

Agmatine is a primary amine formed by the decarboxylation of L-arginine synthesized in mammalian brain. In this study, we investigated the neuroprotective effect of agmatine on ischemic and ischemia-like insults. Primary cortical neuronal cultures were subjected to oxygen-glucose deprivation (OGD), a model of ischemia-like injury, and treated with agmatine before or at the start of OGD, or upon reperfusion. Neuronal death was reduced when agmatine was present during OGD, and this protection was associated with a reduction of nitric oxide (NO) and neuronal nitric oxide synthase (nNOS), but not inducible NOS (iNOS). Protection by agmatine was also studied at the in vivo level using a model of middle cerebral artery occlusion (MCAO) in mice. Mice were subjected to 2 h MCAO. Agmatine was administered either 30 min before ischemia, at the start of MCAO, at the start of reperfusion, or 2 or 5 h into reperfusion. Agmatine markedly reduced infarct area in all treatment groups except when treatment was delayed 5 h. The number of nNOS immunopositive cells was correlated with neuroprotection. Interestingly, immunoreactivity for iNOS was reduced only when agmatine was administered before and at the onset of MCAO. Our study suggests that agmatine may be a novel therapeutic strategy to reduce cerebral ischemic injury, and may act by inhibiting the detrimental effects of nNOS.

Agmatine↗

PubMed2003

Glutathione peroxidase overexpression inhibits cytochrome C release and proapoptotic mediators to protect neurons from experimental stroke.

BACKGROUND AND PURPOSE: Ischemic injury and reperfusion increases superoxide (O2-) production and reduces the ability of neurons to scavenge free radicals, leading to the release of cytochrome c and apoptosis. Here we test whether overexpression with the use of gene therapy of the antioxidant glutathione peroxidase (Gpx), delivered before or after experimental stroke, is protective against ischemic injury. METHODS: Sixty-two rats underwent middle cerebral artery occlusion for 1 hour. Defective herpes simplex viral vectors expressing Gpx/lacZ or lacZ alone (control) were delivered into each striatum 12 hours before or 2 or 5 hours after ischemia onset. RESULTS: Striatal neuron survival at 2 days was improved by 36% when Gpx was delivered 12 hours before ischemia onset, 26% with a 2-hour delay, and 25% when delayed 5 hours. After ischemia, Gpx overexpression significantly reduced cytosolic translocation of cytochrome c and increased the proportion of Bcl-2-positive cells compared with cells transfected with control vector. Bax and activated caspase-3, while present in control-transfected neurons after ischemia, were rarely noted in Gpx-transfected cells. CONCLUSIONS: Expression from these herpes simplex viral vectors begins 4 to 6 hours after injection, which suggests a 9- to 11-hour temporal therapeutic window for Gpx. This is the first study to show that overexpression of Gpx with the use of gene therapy protects against experimental stroke, even with postischemic transfection, and the neuroprotective mechanism involves attenuation of apoptosis-related events.

Animals↗

PubMed2003

Stroke: molecular mechanisms and potential targets for treatment.

Significant advances have been made over the past few years concerning the cellular and molecular events underlying ischemic cell death. The brain succumbs to ischemic injury as a result of loss of metabolic stores, excessive intracellular calcium accumulation, oxidative stress, and potentiation of the inflammatory response. Neurons can also die via necrotic or apoptotic mechanisms, depending on the nature and severity of the insult. While it has been widely held that ischemia is notable for cessation of protein synthesis, brain regions with marginal reduction in blood supply are especially capable of expressing a variety of genes, the functions of many of which are only beginning to be understood. Gene expression is also upregulated upon reperfusion and reoxygenation. As a result, a number of signaling pathways have been identified and are now known to contribute to ischemic progression or, in some cases, attempts at self preservation. This review will focus on the roles of stress genes, apoptosis-related genes, and inflammation. Knowledge of such molecular events has fueled interest in developing specific molecular targets with the hope of someday affecting outcome in clinical stroke.

Animals↗

PubMed2002

Mild hypothermia reduces ICAM-1 expression, neutrophil infiltration and microglia/monocyte accumulation following experimental stroke.

Mild hypothermia is an established neuroprotectant against cerebral ischemic injury. Studies have shown that inflammation potentiates cerebral ischemic injury, particularly in the setting of reperfusion. To further elucidate the mechanism by which mild hypothermia attenuates the inflammatory response, we assessed endothelial intercellular adhesion molecule-1 (ICAM-1) expression, neutrophil and monocyte infiltration, and microglial activation following 2 h of transient focal cerebral ischemia under normothermic and mildly hypothermic conditions. Ischemia was induced using the intraluminal suture method in Sprague-Dawley rats. Immunohistochemistry was used to detect endothelial ICAM-1, infiltrating neutrophils and monocytes, and microglia at 1, 3, and 7 days post-ischemia. Immunopositive cell and vessel densities were measured in the peri-infarct region. Mild hypothermia was associated with decreased neutrophils at 1 and 3 days post-ischemia, decreased ICAM-1-positive vessels at 1, 3, and 7 days, and decreased monocytes/activated microglia at 3 and 7 days, but not at 1 day. These data demonstrate that mild hypothermia significantly reduces endothelial adhesion molecule expression, acute (neutrophil) and subacute (monocyte) leukocyte infiltration, and microglial activation up to 7 days following insult in a rodent model of transient focal cerebral ischemia.

Animals↗

PubMed2001

Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia.

Mild hypothermia protects the brain against experimental ischemia, but the reasons are not well known. We examined whether the protective effects of mild hypothermia could be correlated with alterations in expression of Bcl-2, an anti-apoptotic protein in a rat model of transient global ischemia. Following 10 min of forebrain ischemia, hippocampal neurons were examined 72 h later for survival, expression of Bcl-2 family proteins and apoptosis. Intraischemic mild hypothermia was applied for 3 h (33 degrees C, isch-33) or normal body temperature was maintained (37 degrees C, isch-37). Survival of CA1 neurons was significantly improved in the isch-33 group compared to the isch-37 group (90 vs. 53% survival; P<0.01). The proportion of Bcl-2-positive cells among surviving CA1 neurons in the isch-33 group was increased compared to that of sham and isch-37 groups (P<0.01). Bax expression in CA1 was no different between sham and isch-33 groups, but was significantly decreased in isch-37 (P<0.05). TUNEL staining was positive in many isch-37 CA1 neurons, but absent in isch-33. Utilizing electron microscopy, more cells meeting criteria for apoptosis were observed in the isch-37 than isch-33. These data suggest that mild hypothermia attenuates apoptotic death, and that this protection may be related to increases in Bcl-2.

Animals↗

PubMed2001

MRI of subacute hemorrhagic transformation in the rat suture occlusion model.

In this study we investigated the utility of different MRI techniques for the detection and predictability of hemorrhagic transformation (HT) in a rat model of transient focal cerebral ischemia. Hemorrhagic infarction was reliably identified with gradient-echo sequences and developed between 2 and 7 days following the insult. None of the investigated early MRI features of the ischemic lesions (including the apparent diffusion coefficient and post-reperfusion blood-brain barrier damage) was a good predictor of HT severity at 7 days. This indicates that subacute HT at 2-7 days occurs independently of the severity of acute tissue and BBB damage.

Acute Disease↗

PubMed2001

Ischemic vulnerability of primary murine microglial cultures.

Microglia are known to secrete neurotoxic substances and have been implicated in potentiating injury in a variety of neuropathological settings including stroke. However, little is known about the susceptibility of microglia to ischemia. Here we characterize microglial vulnerabilities to ischemia-like insults. Microglia were remarkably resistant to hypoxia, but a majority of cells were killed after 30 h of aglycemia and 24 h continuous exposure to combined oxygen and glucose deprivation. Serum deprivation also resulted in significant cell death after 24 h. Interestingly, microglia activated by lipopolysaccharide were protected against death by serum deprivation, but not aglycemia. We conclude that microglia display susceptibility to ischemia-like insults that most resembles astrocytes, and that activation in some settings renders them capable of generating factors that enhance their own survival.

Animals↗

PubMed2001

Differential neuroprotection from human heat shock protein 70 overexpression in in vitro and in vivo models of ischemia and ischemia-like conditions.

We previously showed that overexpressing the 70-kDa inducible heat shock protein in primary astrocyte cultures and in a rodent stroke model using viral vectors resulted in protection from ischemia and ischemia-like injury. However, viral transfection could potentially provoke a stress response itself; therefore, we examined whether transgenic mice constitutively expressing human heat shock protein 70 were protected from ischemic insults. Astrocyte cultures from brains of heat shock protein 70 transgenic mice were resistant to hydrogen peroxide injury in a dose-dependent fashion, but were less resistant to hypoglycemia and oxygen-glucose deprivation. Because hydrogen peroxide exposure and glucose deprivation are partially dependent on glutathione levels, we determined whether heat shock protein 70 transgenic cultures had altered glutathione levels under normal growth conditions. However, there was no significant difference in glutathione levels between heat shock protein 70 transgenic and wildtype astrocytes. Hippocampal, but not cortical neuron cultures from these same transgenic mice were also protected against oxygen-glucose deprivation and glutamate toxicity. In an in vivo model of permanent focal cerebral ischemia, there was no significant difference in infarct size assessed 24 h postinsult. These results suggest that heat shock protein 70 protects against some but not all kinds of central nervous system injury. The protective effects may be related to the nature and severity of the insults, as well as subpopulations of brain cells and dose-dependent effects of HSP70 overexpression.

Animals↗

PubMed2001

Gene therapy effectiveness differs for neuronal survival and behavioral performance.

If neuronal gene therapy is to be clinically useful, it is necessary to demonstrate neuroprotection when the gene is introduced after insult. We now report equivalent neuronal protection if calbindin D(28K) gene transfer via herpes simplex virus amplicon vector occurs immediately, 30 min, or 1 h after an excitotoxic insult, but not after a 4 h delay. Behavioral performance was evaluated for immediate and 1 h delay groups using a hippocampal-dependent task. Despite equivalent magnitude and pattern of sparing of neurons with the immediate and 1 h delay approaches, the delay animals took a significantly longer time after insult to return to normal performance.

Animals↗

PubMed2001

Overexpression of HSP72 after induction of experimental stroke protects neurons from ischemic damage.

The 72-kD inducible heat shock protein (HSP72) can attenuate cerebral ischemic injury when overexpressed before ischemia onset. Whether HSP72 overexpression is protective when applied after ischemia onset is not known, but would have important clinical implications. Fifty-seven rats underwent middle cerebral artery occlusion for 1 hour. Defective herpes simplex viral (HSV) vectors expressing hsp72 with lacZ as a reporter were delivered 0.5, 2, and 5 hours after ischemia onset into each striatum. Control animals received an identical vector containing only lacZ. Striatal neuron survival at 2 days was improved by 23% and 15% when HSP72 vectors were delayed 0.5 and 2 hours after ischemic onset, respectively ( P < 0.05). However, when delayed by 5 hours, HSP72 overexpression was no longer protective. This is the first demonstration that HSP72 gene transfer even after ischemia onset is neuroprotective. Because expression from these HSV vectors begins 4 to 6 hours after injection, this suggests that the temporal therapeutic window for HSP72 is at least 6 hours after ischemia onset. Future strategies aimed at enhancing HSP72 expression after clinical stroke may be worth pursuing. The authors suggest that in the future HSP72 may be an effective treatment for stroke.

Animals↗

PubMed2001

Gene therapy for treatment of cerebral ischemia using defective herpes simplex viral vectors.

Significant advances have been made over the past few years concerning the cellular and molecular events underlying neuron death. Recently, it is becoming increasingly clear that some of genes induced during cerebral ischemia may actually serve to rescue the cell from death. However, the injured cell may not be capable of expressing protein at high enough levels to be protective. One of the most exciting arenas of such interventions is the use of viral vectors to deliver potentially neuroprotective genes at high levels. Neurotropic herpes simplex viral (HSV) strains are an obvious choice for gene therapy to the brain, and we have used bipromoter vectors that are capable of transferring various genes to neurons. Using this system in experimental models of stroke, cardiac arrest, and excitotoxicity, we have found that it is possible to enhance neuron survival against such cerebral insults by overexpressing genes that target various facets of injury. These include energy restoration by the glucose transporter (GLUT-1), buffering calcium excess by calbindin, preventing protein malfolding or aggregation by stress proteins and inhibiting apoptotic death by BCL-2. We show that in some cases, gene therapy is also effective after the onset of injury, and also address whether successful gene therapy necessarily spares function. Although gene therapy is limited to the few hundred cells the vector is capable of transfecting, we consider the possibility of such gene therapy becoming relevant to clinical neurology in the future.

ATP-Binding Cassette Transporters↗

PubMed2001

Calbindin d28k overexpression protects striatal neurons from transient focal cerebral ischemia.

BACKGROUND AND PURPOSE: Increased intracellular calcium accumulation is known to potentiate ischemic injury. Whether endogenous calcium-binding proteins can attenuate this injury has not been clearly established, and existing data are conflicting. Calbindin D28K (CaBP) is one such intracellular calcium buffer. We investigated whether CaBP overexpression is neuroprotective against transient focal cerebral ischemia. METHODS: Bipromoter, replication-incompetent herpes simplex virus vectors that encoded the genes for cabp and, as a reporter gene, lacZ were used. Sprague-Dawley rats received bilateral striatal injections of viral vector 12 to 15 hours before ischemia onset. With the use of an intraluminal occluding suture, animals were subjected to 1 hour of middle cerebral artery occlusion followed by 47 hours of reperfusion. Brains were harvested and stained with X-gal (to visualize beta-galactosidase, the gene product of lacZ). The number of remaining virally transfected, X-gal-stained neurons in both the ischemic and contralateral striata were counted and expressed as the percentage of surviving neurons in the ischemic striatum relative to the contralateral nonischemic striatum. RESULTS: Striatal neuron survivorship among cabp-injected animals was 53.5+/-4.1% (n=10) versus 26.8+/-5.4% among those receiving lacZ (n=9) (mean+/-SEM; P<0.001). CONCLUSIONS: We conclude that viral vector-mediated overexpression of CaBP leads to neuroprotection in this model of central nervous system injury. This is the first demonstration that CaBP overexpression protects neurons in a focal stroke model.

Animals↗

PubMed2001

Reversal of early diffusion-weighted magnetic resonance imaging abnormalities does not necessarily reflect tissue salvage in experimental cerebral ischemia.

BACKGROUND AND PURPOSE: Diffusion-weighted MRI (DWI) can detect early ischemic changes and is sometimes used as a surrogate neurological end point in clinical trials. Recent experimental stroke studies have shown that with brief periods of ischemia, some DWI lesions transiently reverse, only to recur later. This study examined the histological condition of the tissue during the period of DWI reversal. METHODS: Rats underwent 30 minutes of middle cerebral artery occlusion followed by reperfusion. DWI images were obtained during ischemia and 3 to 5 hours, 1 day, and 7 days later. MRI scans were compared with histology (5 hours, n=5; 7 days, n=5) with the use of neuronal (microtubule-associated protein 2 [MAP2]) and astrocytic (glial fibrillary acidic protein [GFAP]) markers and heat-shock protein 72 (HSP72). RESULTS: DWI abnormalities reversed 3 to 5 hours after ischemia onset but recurred at 1 day. Four animals showed complete reversal of the initial DWI hyperintensity, and 6 showed partial reversal. When the 5-hour DWI was completely normal, there was significant loss of MAP2 immunoreactivity, comprising approximately 30% of the initial DWI lesion. However, GFAP staining revealed morphologically normal astrocytes. HSP72 immunoreactivity at 5 hours was extensive and corresponded to the initial DWI lesion. CONCLUSIONS: After brief ischemic periods, normalization of the DWI does not necessarily imply that the tissue is normal. Neurons already exhibit evidence of structural damage and stress. Normal GFAP staining suggests that other nonneuronal cell populations may partially compensate for altered fluid balances at the time of DWI reversal despite the presence of neuronal injury. These observations suggest that caution is warranted when relying solely on DWI for assessment of ischemic damage.

Animals↗

PubMed2001

L-selectin inhibition does not reduce injury in a rabbit model of transient focal cerebral ischemia.

Neutrophils are known to mediate injury in acute ischemic stroke especially during reperfusion. Migration of neutrophils into regions of ischemic injury involves binding to the endothelial cells via interactions with various adhesion molecules. One adhesion molecule, L-selectin, is found on the surface of leukocytes, and is shed prior to leukocyte infiltration. We studied whether a humanized antibody to L-selectin (HuDREG200) might limit ischemic injury in an experimental stroke model. New Zealand White rabbits underwent transorbital occlusion of the left middle cerebral, anterior cerebral and internal carotid arteries using aneurysm clips for 2 h followed by 6 h of reperfusion. Treatment with a saturating dose (4 mg kg-1) of HuDREG200 (n = 8) or vehicle (n = 8) was administered 20 min after occlusion and given as a single i.v. bolus. Hemispheric ischemic neuronal damage (IND) as seen on hematoxylin and eosin stained sections was no different between groups (HuDREG200, 23.3% +/- 6%; vehicle, 19.6% +/- 6%; mean +/- SEM, n.s., t-test). Immunohistochemical staining with neutrophil elastase confirmed the presence of neutrophils within regions of IND in control brains, but treatment did not alter their numbers within ischemic tissue. We conclude that antagonism of neutrophil adhesion at the level of L-selectin does not alter ischemic injury in experimental stroke.

Animals↗

PubMed2001

Gene therapy for treatment of cerebral ischemia using defective herpes simplex viral vectors.

Significant advances have been made over the past few years concerning the cellular and molecular events underlying neuron death. Recently, it is becoming increasingly clear that some of the genes induced during cerebral ischemia may actually serve to rescue the cell from death. However, the injured cell may not be capable of expressing protein at levels high enough to be protective. One of the most exciting arenas of such interventions is the use of viral vectors to deliver potentially neuroprotective genes at high levels. Neurotrophic herpes simplex viral strains are an obvious choice for gene therapy to the brain, and we have utilized bipromoter vectors that are capable of transferring various genes to neurons. Using this system in experimental models of stroke, cardiac arrest and excitotoxicity, we have found that it is possible to enhance neuron survival against such cerebral insults by over-expressing genes that target various facets of injury. These include energy restoration by the glucose transporter (GLUT-1), buffering calcium excess by calbindin, preventing protein malfolding or aggregation by stress proteins and inhibiting apoptotic death by BCL-2. We show that in some cases, gene therapy is also effective after the onset of injury, and also address whether successful gene therapy necessarily spares function. Although gene therapy is limited to the few hundred cells the vector is capable of transfecting, we consider the possibility of such gene therapy becoming relevant to clinical neurology in the future.

Animals↗

PubMed2001

Delayed induction and long-term effects of mild hypothermia in a focal model of transient cerebral ischemia: neurological outcome and infarct size.

OBJECT: The goals of this study were to determine the effects of delaying induction of mild hypothermia (33 degrees C) after transient focal cerebral ischemia and to ascertain whether the neuroprotective effects of mild hypothermia induced during the ischemic period are sustained over time. METHODS: In the first study, rats underwent 2 hours of middle cerebral artery (MCA) occlusion. Animals in one group were maintained under normothermic conditions (N group, 23 rats) throughout the period of ischemia and reperfusion. Rats in four additional groups were exposed to 2 hours of hypothermia, which commenced at ischemia onset (H0 group, 11 rats) or with delays of 90 (H90 group, 10 rats), 120 (H120 group, 10 rats), or 180 (H180 group, five rats) minutes, and allowed to survive for 3 days. In the second study, animals underwent 1.5 hours of MCA occlusion and were maintained under normothermic (48 rats) or hypothermic (44 rats) conditions during the ischemia period, after which they survived for 3 days, 1 week, or 2 months. All animals were evaluated for neurological findings at 24 hours and 48 hours postischemia and before they were killed. Regions of infarct were determined by examining hematoxylin and eosinstained brain slices obtained at six coronal levels. CONCLUSIONS: Mild hypothermia conferred significant degrees of neuroprotection in terms of survival, behavioral deficits, and histopathological changes, even when its induction was delayed by 120 minutes after onset of MCA occlusion (p < 0.05) compared with normothermic conditions. Furthermore, the neuroprotective effect of mild hypothermia (2-hour duration) that was induced during the ischemia period was sustained over 2 months. These studies lend further support to the use of mild hypothermia in the treatment of stroke.

Animals↗

PubMed2000

Diffusion- and perfusion-weighted magnetic resonance imaging of focal cerebral ischemia and cortical spreading depression under conditions of mild hypothermia.

In a model of experimental stroke, we characterize the effects of mild hypothermia, an effective neuroprotectant, on fluid shifts, cerebral perfusion and spreading depression (SD) using diffusion- (DWI) and perfusion-weighted MRI (PWI). Twenty-two rats underwent 2 h of middle cerebral artery (MCA) occlusion and were either kept normothermic or rendered mildly hypothermic shortly after MCA occlusion for 2 h. DWI images were obtained 0.5, 2 and 24 h after MCA occlusion, and maps of the apparent diffusion coefficient (ADC) were generated. SD-like transient ADC decreases were also detected using DWI in animals subjected to topical KCl application (n=4) and ischemia (n=6). Mild hypothermia significantly inhibited DWI lesion growth early after the onset of ischemia as well as 24 h later, and improved recovery of striatal ADC by 24 h. Mild hypothermia prolonged SD-like ADC transients and further decreased the ADC following KCl application and immediately after MCA occlusion. Cerebral perfusion, however, was not affected by temperature changes. We conclude that mild hypothermia is neuroprotective and suppresses infarct growth early after the onset of ischemia, with better ADC recovery. The ADC decrease during SD was greater during mild hypothermia, and suggests that the source of the ADC is more complex than previously believed.

Animals↗