PhD, Nihon University, Japan, Pharmacology (1999)
MS, West China Univ. Med. Sci., Pharmacognosy (1990)
BS, West China Univ. Med. Sci., Pharmacy (1987)
My lab mainly studies the protective effect of postconditioning against stroke. Reperfusion (the restoration of blood flow) is one of the first choices for ischemic stroke treatment. However, reperfusion can also cause overproduction of reactive oxygen species (ROS) or free radicals that lead to reperfusion injury. Limiting the damage caused by reperfusion is a key issue for stroke treatment. We were the first to demonstrate that interrupting the early hyperemic response after reperfusion reduces infarction after stroke, a novel phenomenon called postconditioning. Since postconditioning is performed after reperfusion, it has great potential for clinical application. In addition, we also study protective effect of preconditioning and mild hypothermia. The rationale for studying three means of neuroprotection is that we may discover mechanisms that these treatments have in common. Conversely, if they have differing mechanisms, we will be able to offer more than one treatment for stroke and increase a patients chance for recovery. Our researches include studying roles of caspase-dependent and independent apoptotic pathway, PKC pathways and Akt pathway, among others, in the ischemic damage development after stroke.
T cells and their subsets modulate ischemic brain injury. We studied the effects of the absence of T cell subsets on brain infarction after in vivo stroke and then used an in vitro coculture system of splenocytes and neurons to further identify the roles of T cell subsets in neuronal death.Stroke was induced by middle cerebral artery suture occlusion in mice and infarct sizes were measured 2 days poststroke. Splenocytes were cocultured with neurons, and neuronal survival was measured 3 days later.A deficiency of both T and B cells (severe combined immunodeficiency) and the paucity of CD4 or CD8 T cells equally resulted in smaller infarct sizes as measured 2 days poststroke. Although a functional deficiency of regulatory T cells had no effect, impaired Th1 immunity reduced infarction and impaired Th2 immunity aggravated brain injury, which may be due to an inhibited and enhanced inflammatory response in mice deficient in Th1 and Th2 immunity, respectively. In the in vitro coculture system, wild-type splenocytes resulted in dose-dependent neuronal death. The neurotoxicity of splenocytes from these immunodeficient mice was consistent with their effects on stroke in vivo, except for the mice with the paucity of CD4 or CD8 T cells, which did not alter the ratio of neuronal death.T cell subsets play critical roles in brain injury induced by stroke. The detrimental versus beneficial effects of Th1 cells and Th2 cells both in vivo and in vitro reveal differential therapeutic target strategies for stroke treatment.
View details for DOI 10.1161/STROKEAHA.112.656611
View details for PubMedID 22678086
We previously reported that ischemic postconditioning with a series of mechanical interruptions of reperfusion reduced infarct volume 2 days after focal ischemia in rats. Here, we extend this data by examining long-term protection and exploring underlying mechanisms involving the Akt, mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) signaling pathways. Post-conditioning reduced infarct and improved behavioral function assessed 30 days after stroke. Additionally, postconditioning increased levels of phosphorylated Akt (Ser473) as measured by western blot and Akt activity as measured by an in vitro kinase assay. Inhibiting Akt activity by a phosphoinositide 3-kinase inhibitor, LY294002, enlarged infarct in postconditioned rats. Postconditioning did not affect protein levels of phosphorylated-phosphatase and tensin homologue deleted on chromosome 10 or -phosphoinositide-dependent protein kinase-1 (molecules upstream of Akt) but did inhibit an increase in phosphorylated-glycogen synthase kinase 3beta, an Akt effector. In addition, postconditioning blocked beta-catenin phosphorylation subsequent to glycogen synthase kinase, but had no effect on total or non-phosphorylated active beta-catenin protein levels. Furthermore, postconditioning inhibited increases in the amount of phosphorylated-c-Jun N-terminal kinase and extracellular signal-regulated kinase 1/2 in the MAPK pathway. Finally, postconditioning blocked death-promoting deltaPKC cleavage and attenuated reduction in phosphorylation of survival-promoting epsilonPKC. In conclusion, our data suggest that postconditioning provides long-term protection against stroke in rats. Additionally, we found that Akt activity contributes to postconditioning's protection; furthermore, increases in epsilonPKC activity, a survival-promoting pathway, and reductions in MAPK and deltaPKC activity; two putative death-promoting pathways correlate with postconditioning's protection.
View details for DOI 10.1111/j.1471-4159.2008.05218.x
View details for PubMedID 18182053
Remote ischemic preconditioning is an emerging concept for stroke treatment, but its protection against focal stroke has not been established. We tested whether remote preconditioning, performed in the ipsilateral hind limb, protects against focal stroke and explored its protective parameters. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery (MCA) combined with a 30 min occlusion of the bilateral common carotid arteries (CCA) in male rats. Limb preconditioning was generated by 5 or 15 min occlusion followed with the same period of reperfusion of the left hind femoral artery, and repeated for two or three cycles. Infarct was measured 2 days later. The results showed that rapid preconditioning with three cycles of 15 min performed immediately before stroke reduced infarct size from 47.7+/-7.6% of control ischemia to 9.8+/-8.6%; at two cycles of 15 min, infarct was reduced to 24.7+/-7.3%; at two cycles of 5 min, infarct was not reduced. Delayed preconditioning with three cycles of 15 min conducted 2 days before stroke also reduced infarct to 23.0+/-10.9%, but with two cycles of 15 min it offered no protection. The protective effects at these two therapeutic time windows of remote preconditioning are consistent with those of conventional preconditioning, in which the preconditioning ischemia is induced in the brain itself. Unexpectedly, intermediate preconditioning with three cycles of 15 min performed 12 h before stroke also reduced infarct to 24.7+/-4.7%, which contradicts the current dogma for therapeutic time windows for the conventional preconditioning that has no protection at this time point. In conclusion, remote preconditioning performed in one limb protected against ischemic damage after focal cerebral ischemia.
View details for DOI 10.1016/j.neuroscience.2007.11.056
View details for PubMedID 18201834
Cerebral ischemic preconditioning protects against stroke, but is clinically feasible only when the occurrence of stroke is predictable. Reperfusion plays a critical role in cerebral injury after stroke; we tested the hypothesis that interrupting reperfusion lessens ischemic injury. We found for the first time that such postconditioning with a series of mechanical interruptions of reperfusion significantly reduces ischemic damage. Focal ischemia was generated by permanent distal middle cerebral artery (MCA) occlusion plus transient bilateral common carotid artery (CCA) occlusion. After 30 secs of CCA reperfusion, ischemic postconditioning was performed by occluding CCAs for 10 secs, and then allowing for another two cycles of 30 secs of reperfusion and 10 secs of CCA occlusion. Infarct size was measured 2 days later. Cerebral blood flow (CBF) was measured in animals subjected to permanent MCA occlusion plus 15 mins of bilateral CCA occlusion, which demonstrates that postconditioning disturbed the early hyperemia immediately after reperfusion. Postconditioning dose dependently reduced infarct size in animals subjected to permanent MCA occlusion combined with 15, 30, and 60 mins of bilateral CCA occlusion, by reducing infarct size approximately 80%, 51%, and 17%, respectively. In addition, postconditioning blocked terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling-positive staining, a marker of apoptosis, in the penumbra 2 days after stroke. Furthermore, in situ superoxide detection using hydroethidine suggested that postconditioning attenuated superoxide products during early reperfusion after stroke. In conclusion, postconditioning reduced infarct size, most plausibly by blocking apoptosis and free radical generation. With further study it may eventually be clinically applicable for stroke treatment.
View details for DOI 10.1038/sj.jcbfm.9600348
View details for PubMedID 16736038
Activation of the Akt/protein kinase B (PKB) kinase pathway can be neuroprotective after stroke. Akt is activated by growth factors via a phosphorylation-dependent pathway involving the kinases phosphoinositide 3 (PI3) kinase and phosphoinositide-dependent protein kinase-1 (PDK1) and is negatively regulated by phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Akt kinase blocks apoptosis by phosphorylating the substrates forkhead transcription factor (FKHR) and glycogen synthase kinase 3beta (GSK3beta). We found that intra-ischemic hypothermia (30 degrees C) reduced infarct size and improved functional outcomes up to 2 months. Changes in phosphorylation levels of Akt, as measured by Western blots and immunostaining, differed from levels of Akt activity measured in an in vitro assay in normothermic animals. Hypothermia blocked most of these changes and maintained Akt activity. Inhibition of PI3/Akt enlarged infarct size in hypothermic animals. Hypothermia improved phosphorylation of PDK1, PTEN, and FKHR. Hypothermia did not improve GSK3beta (Ser9) phosphorylation but blocked the nuclear translocation of phosphorylated beta-catenin (Ser33/37/Thr41) downstream of GSK3beta. Phosphorylation levels of PTEN, Akt, and Akt substrate decreased before apoptotic cytochrome c release and degradation of microtubule-associated protein-2, a marker of neuronal survival. Hypothermia may protect from ischemic damage in part by preserving Akt activity and attenuating the apoptotic effects of PTEN, PDK1, and FKHR.
View details for DOI 10.1523/JNEUROSCI.3163-05.2005
View details for PubMedID 16237183
While pre-conditioning is induced before stroke onset, ischemic post-conditioning (IPostC) is performed after reperfusion, which typically refers to a series of mechanical interruption of blood reperfusion after stroke. IPostC is known to reduce infarction in wild-type animals. We investigated if IPostC protects against brain injury induced by focal ischemia in Tcell-deficient nude rats and to examine its effects on Akt and the mammalian target of rapamycin (mTOR) pathway. Although IPostC reduced infarct size at 2 days post-stroke in wild-type rats, it did not attenuate infarction in nude rats. Despite the unaltered infarct size in nude rats, IPostC increased levels of phosphorylated Akt (p-Akt) and Akt isoforms (Akt1, Akt2, Akt3), and p-mTOR, p-S6K and p-4EBP1 in the mTOR pathway, as well as growth associated Protein 43 (GAP43), both in the peri-infarct area and core, 24 h after stroke. IPostC improved neurological function in nude rats 1-30 days after stroke and reduced the extent of brain damage 30 days after stroke. The mTOR inhibitor rapamycin abolished the long-term protective effects of IPostC. We determined that IPostC did not inhibit acute infarction in nude rats but did provide long-term protection by enhancing Akt and mTOR activity during the acute post-stroke phase.
View details for DOI 10.1111/jnc.12342
View details for PubMedID 23777415
Stroke-induced immunodepression (SIID) results when T cell and non-T immune cells, such as B cells, NK cells and monocytes, are reduced in the peripheral blood and spleen after stroke. We investigated the hypothesis that T cells are required for the reductions in non-T cell subsets observed in SIID, and further examined a potential correlation between lymphopenia and High-mobility group protein B1 (HMGB1) release, a protein that regulates inflammation and immunodepression. Our results showed that focal ischemia resulted in similar cortical infarct sizes in both wild type (WT) Sprague Dawley (SD) rats and nude rats with a SD genetic background, which excludes the possibility of different infarct sizes affecting SIID. In addition, the numbers of CD68-positive macrophages in the ischemic brain did not differ between WT and nude rats. Numbers of total peripheral blood mononuclear cells (PBMCs) or splenocytes and lymphocyte subsets, including T cells, CD4(+) or CD8(+) T cells, B cells and monocytes in the blood and spleen, were decreased after stroke in WT rats. In nude rats, however, the total number of PBMCs and absolute numbers of NK cells, B cells and monocytes were increased in the peripheral blood after stroke; nude rats are athymic therefore they have few T cells present. Adoptive transfer of WT splenocytes into nude rats before stroke resulted in lymphopenia after stroke similar to WT rats. Moreover, in vitro T cell proliferation stimulated by Concanavalin A was significantly inhibited in WT rats as well as in nude rats receiving WT splenocyte adoptive transfer, suggesting that T cell function is indeed inhibited after stroke. Lastly, we demonstrated that stroke-induced lymphopenia is associated with a reduction in HMGB1 release in the peripheral blood. In conclusion, T cells are required for stroke-induced reductions in non-T immune cells and they are the most crucial lymphocytes for SIID.
View details for DOI 10.1371/journal.pone.0059602
View details for Web of Science ID 000316409800104
View details for PubMedID 23555048
Ischemic postconditioning has been established for its protective effects against stroke in animal models. It is performed after post-stroke reperfusion and refers to a series of induced ischemia or a single brief one. This review article addresses major hurdles in clinical translation of ischemic postconditioning to stroke patients, including potential hazards, the lack of well-defined protective paradigms, and the paucity of deeply-understood protective mechanisms. A hormetic model, often used in toxicology to describe a dose-dependent response to a toxic agent, is suggested to study both beneficial and detrimental effects of ischemic postconditioning. Experimental strategies are discussed, including how to define the hazards of ischemic (homologous) postconditioning and the possibility of employing non-ischemic (heterologous) postconditioning to facilitate clinical translation. This review concludes that a more detailed assessment of ischemic postconditioning and studies of a broad range of heterologous postconditioning models are warranted for future clinical translation.
View details for DOI 10.1007/s12975-012-0243-0
View details for PubMedID 23524538
Previous studies have reported that T cell deficiency reduced infarct sizes after transient middle cerebral artery (MCA) suture occlusion in mice. However, how reperfusion and different models affect the detrimental effects of T cells have not been studied. We investigated the effects of T cell deficiency in nude rats using two stroke models and compared their infarct sizes with those in WT rats. In the distal MCA occlusion (MCAo) model, the distal MCA was permanently occluded and the bilateral common carotid arteries (CCAs) were transiently occluded for 60 min. In the suture MCAo model, the MCA was transiently occluded for 100 min by the insertion of a monofilament suture. Our results showed that T cell deficiency resulted in about a 50% reduction in infarct size in the suture MCAo model, whereas it had no effect in the distal MCAo model, suggesting the protective effects of T cell deficiency are dependent on the ischemic model used. We further found more total T cells, CD4 T cells and CD8 T cells in the ischemic brains of WT rats in the suture MCAo model than in the distal MCAo model. In addition, we detected more CD68-expressing macrophages in the ischemic brains of WT rats than in nude rats in the suture MCAo but not the distal MCAo model. Lymphocyte reconstitution in nude rats resulted in larger infarct sizes in the suture MCAo, but not in the distal MCAo stroke model. The results of regional CBF measurement indicated a total reperfusion in the MCAo model but only a partial reperfusion in the distal MCAo model. In conclusion, the protective effects of T cell deficiency on brain injury are dependent on the ischemic model used; likely associated with different degrees of reperfusion.
View details for DOI 10.1016/j.neuint.2012.11.016
View details for PubMedID 23228347
Both ischemic preconditioning (IPreC) and ischemic postconditioning (IPostC) trigger endogenous neuroprotective mechanisms in cerebral ischemia. IPreC is defined as a brief ischemia that protects against a subsequent severe ischemia, while IPostC refers to a series of brief cerebral blood vessel occlusions performed at reperfusion following an ischemic event. Hormesis describes a biphasic dose-response relationship in toxicology, where a low dose of toxicant stimulates and a high dose inhibits biological responses. In general, any minor stress will stimulate a biological system to generate an adaptive response; in most cases, if not all, such an adaptive response to a minor stress is beneficial to the biological system. Proponents of hormesis suggest that this effect is independent of any models, either in vivo or in vitro, from animal, plant, fungi, yeast, to bacteria, by any measurement of end points, survival ratio or time, growth, tissue repair, life span, cognition, learning and memory. In this review, we examine whether IPreC and IPostC are actually sub-forms of hormesis and whether quantitative hormetic strategies can be used to study IPreC and IPostC. By integrating the concepts of IPreC and IPostC with hormesis, we aim to broaden the avenues leading to clinical translation of IPreC and IPostC in stroke treatment.
View details for PubMedID 23750305
Lithium is a mood stabilizer shown to have neuroprotective effects against several chronic and acute neuronal injuries, including stroke. However, it is unknown whether lithium treatment protects against brain injury post-stroke in a rat model of permanent distal middle cerebral artery occlusion (MCAo) combined with transient bilateral common carotid artery occlusion (CCAo), a model that mimics human stroke with partial reperfusion. In addition, whether lithium treatment alters Akt activity as measured by the kinase activity assay has not been reported, although it is known to inhibit GSK3β activity. After stroke, Akt activity contributes to neuronal survival while GSK3β activity causes neuronal death. We report that a bolus of lithium injection at stroke onset robustly reduced infarct size measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining at 48 h post-stroke and inhibited cell death in the ischemic penumbra, but not in the ischemic core, as shown by TUNEL staining performed 24 h post-stroke. However, lithium treatment did not alter the reduction in Akt activity as measured by Akt kinase assay. We further showed that lithium did not alter phosphorylated GSK3β protein levels, or the degradation of β-catenin, a substrate of GSK3β, which is consistent with previous findings that long-term treatment is required for lithium to alter GSK3β phosphorylation. In summary, we show innovative data that lithium protects against stroke in a focal ischemia model with partial reperfusion, however, our results dispute the importance of Akt activity in the protective effects of lithium.
View details for Web of Science ID 000208951000001
View details for PubMedCentralID PMC3375079
The extracellular signal-regulated kinase (ERK) 1/2 protein requires a dual phosphorylation at conserved threonine and tyrosine residues to be fully activated under normal physiological conditions. Thus, ERK1/2 kinase activity is often defined by the quantity of phosphorylated kinase. However, this may not accurately represent its true activity under certain pathological conditions. We investigated whether ERK1/2 kinase activity is proportional to its phosphorylation state in a rat focal ischemia model with and without rapid ischemic preconditioning. We showed that phosphorylated-ERK1/2 protein levels were increased 2.6±0.07-fold, and ERK1/2 kinase activity was increased 10.6±1.9-fold in animals receiving ischemic preconditioning alone without test ischemia compared with sham group (P<0.05, n=6/group), suggesting that phosphorylated-ERK1/2 protein levels represent its kinase activity under these conditions. However, preconditioning plus test ischemia robustly blocked ERK1/2 kinase activity, whereas it increased phosphorylated-ERK1/2 protein levels beyond those receiving test ischemia alone, suggesting that phosphorylated-ERK1/2 protein levels were not representative of actual kinase activity in this pathological condition. In conclusion, protein phosphorylation levels of ERK1/2 do not always correspond to kinase activity, thus, measuring the true kinase activity is essential.
View details for DOI 10.1016/j.neuroscience.2012.02.005
View details for PubMedID 22366512
Stroke causes brain dysfunction and neuron death, and the lack of effective therapies heightens the need for new therapeutic targets. Here we identify prokineticin 2 (PK2) as a mediator for cerebral ischemic injury. PK2 is a bioactive peptide initially discovered as a regulator of gastrointestinal motility. Multiple biological roles for PK2 have been discovered, including circadian rhythms, angiogenesis, and neurogenesis. However, the role of PK2 in neuropathology is unknown. Using primary cortical cultures, we found that PK2 mRNA is up-regulated by several pathological stressors, including hypoxia, reactive oxygen species, and excitotoxic glutamate. Glutamate-induced PK2 expression is dependent on NMDA receptor activation and extracellular calcium. Enriched neuronal culture studies revealed that neurons are the principal source of glutamate-induced PK2. Using in vivo models of stroke, we found that PK2 mRNA is induced in the ischemic cortex and striatum. Central delivery of PK2 worsens infarct volume, whereas PK2 receptor antagonist decreases infarct volume and central inflammation while improving functional outcome. Direct central inhibition of PK2 using RNAi also reduces infarct volume. These findings indicate that PK2 can be activated by pathological stimuli such as hypoxia-ischemia and excitotoxic glutamate and identify PK2 as a deleterious mediator for cerebral ischemia.
View details for DOI 10.1073/pnas.1113363109
View details for PubMedID 22431614
We recently demonstrated that limb remote preconditioning (LRP) protects against focal ischemia measured 2 days post-stroke. Here, we studied whether LRP provides long-term protection and improves neurological function. We also investigated whether LRP transmits its protective signaling via the afferent nerve pathways from the preconditioned limb to the ischemic brain and whether inflammatory factors are involved in LRP, including the novel galectin-9/Tim-3 inflammatory cell signaling pathway, which induces cell death in lymphocytes. LRP in the left hind femoral artery was performed immediately before stroke. LRP reduced brain injury size both at 2 days and 60 days post-stroke and improved behavioral outcomes for up to 2 months. The sensory nerve inhibitors capsaicin and hexamethonium, a ganglion blocker, abolished the protective effects of LRP. In addition, LRP inhibited edema formation and blood-brain barrier (BBB) permeability measured 2 days post-stroke. Western blot and immunostaining analysis showed that LRP inhibited protein expression of both galectin-9 and T-cell immunoglobulin domain and mucin domain 3 (Tim-3), which were increased after stroke. In addition, LRP decreased iNOS and nitrotyrosine protein expression after stroke. In conclusion, LRP executes long-term protective effects against stroke and may block brain injury by inhibiting activities of the galectin-9/Tim-3 pathway, iNOS, and nitrotyrosine.
View details for DOI 10.1371/journal.pone.0030892
View details for PubMedID 22347410
Ischemic postconditioning is a concept originally defined to contrast with that of ischemic preconditioning. While both preconditioning and postconditioning confer a neuroprotective effect on brain ischemia, preconditioning is a sublethal insult performed in advance of brain ischemia, and postconditioning, which conventionally refers to a series of brief occlusions and reperfusions of the blood vessels, is conducted after ischemia/reperfusion. In this article, we first briefly review the history of preconditioning, including the experimentation that initially uncovered its neuroprotective effects and later revealed its underlying mechanisms-of-action. We then discuss how preconditioning research evolved into that of postconditioning--a concept that now represents a broad range of stimuli or triggers, including delayed postconditioning, pharmacological postconditioning, remote postconditioning--and its underlying protective mechanisms involving the Akt, MAPK, PKC and K(ATP) channel cell-signaling pathways. Because the concept of postconditioning is so closely associated with that of preconditioning, and both share some common protective mechanisms, we also discuss whether a combination of preconditioning and postconditioning offers greater protection than preconditioning or postconditioning alone.
View details for PubMedID 22204317
Gene therapy has demonstrated the protective potential of a variety of genes against stroke. However, conventional gene therapy vectors are limited due to the inability to temporally control their expression, which can sometimes lead to deleterious side effects. Thus, an inducible vector that can be temporally controlled and activated by the insult itself would be advantageous. Using hypoxia responsive elements (HRE) and antioxidant responsive elements (ARE), we have constructed an insult-inducible vector activated by hypoxia and reactive oxygen species (ROS). In COS7 cells, the inducible ARE-HRE-luciferase vectors are highly activated by oxygen deprivation, hydrogen peroxide treatment, and the ROS-induced transcription factor NF-E2-related factor 2 (Nrf2). Using a defective herpes virus, the neuroprotective potential of this inducible vector was tested by over-expressing the transcription factor Nrf2. In primary cortical cultures, expression of the inducible ARE-HRE-Nrf2 protects against oxygen glucose deprivation, similar to that afforded by the constitutively expressed Nrf2. This ARE+HRE vector system is advantageous in that it allows the expression of a transgene to be activated not only during hypoxia but also maintained after reperfusion, thus prolonging the transgene expression during an ischemic insult. This insult-inducible vector system will be a valuable gene therapy tool for activating therapeutic/protective genes in cerebrovascular diseases.
View details for DOI 10.1007/s12975-010-0060-2
View details for PubMedID 21603078
The author reviews the protective effects of ischemic postconditioning, a recently emerging strategy with broad implications in the search for new treatments in stroke and myocardial ischemic injury. Ischemic postconditioning, which refers to a series of brief ischemia and reperfusion cycles applied immediately at the site of the ischemic organ after reperfusion, results in reduced infarction in both cerebral and myocardial ischemia. Conventional postconditioning induced within a few minutes after reperfusion is arbitrarily defined as rapid postconditioning. In contrast, postconditioning performed hours to days after stroke is defined as delayed postconditioning. In addition, postconditioning can be mimicked using anesthetics or other pharmacological agents as stimuli to protect against ischemia/reperfusion injury or performed in a distant organ, which is known as remote postconditioning. In this article, the author discusses the conceptual origin of classical rapid ischemic postconditioning and its evolution into a term that represents a broad range of stimuli or triggers, including delayed postconditioning, pharmacological postconditioning, and remote postconditioning. Thereafter, various in vivo and in vitro models of postconditioning and its potential protective mechanisms are discussed. Since the concept of postconditioning is so closely associated with that of preconditioning and both share some common protective mechanisms, whether a combination of preconditioning and postconditioning offers greater protection than preconditioning or postconditioning alone is also discussed.
View details for PubMedID 22053169
Although many studies have shown the great potential of induced hypothermia in stroke treatment, we recognize that there are limitations to the protective effects of hypothermia even in the laboratory. Here, we review our experiments on the protective effects of mild-to-moderate hypothermia in rats. Focal ischemia was induced by bilateral common carotid artery (CCA) occlusion for 1 to 2 hours combined with permanent or transient middle cerebral artery (MCA) occlusion. We compared the effects of mild (33°C) and moderate (30°C) hypothermia, evaluated therapeutic time windows, and studied the underlying mechanisms. On review, our findings revealed that the protective effects of induced mild hypothermia (33°C) were limited, and the therapeutic time window of even moderate hypothermia (30°C) was very short in our specific models, although this limitation might be due to the relatively brief periods of hypothermia used. In addition, we found that hypothermia reduced brain injury by preserving Akt activity, PTEN phosphorylation and εPKC activity, while inhibiting ROS production, and δPKC activity.
View details for DOI 10.4061/2011/131834
View details for PubMedID 21876846
Although the protective mechanisms of delayed ischemic preconditioning have received extensive studies, few have addressed the mechanisms associated with rapid ischemic postconditioning. We investigated whether ischemic tolerance induced by rapid preconditioning is regulated by the Akt survival signaling pathway. Stroke was generated by permanent occlusion of the left distal middle cerebral artery (MCA) plus 30 min or 1 h occlusion of the bilateral common carotid artery (CCA) in male rats. Rapid preconditioning performed 1h before stroke onset reduced infarct size by 69% in rats with 30 min CCA occlusion, but by only 19% with 1 h occlusion. After control ischemia with 30 min CCA occlusion, Western Blot showed that P-Akt was transiently increased while Akt kinase assay showed that Akt activity was decreased. Although preconditioning did not change P-Akt levels at 1h and 5h compared with control ischemia, it attenuated reduction in Akt activity at 5h in the penumbra. However, preconditioning did not change the levels of P-PDK1, P-PTEN, and P-GSK3β in the Akt pathway, all of which were decreased after stroke. At last, the PI3K kinase inhibitor, LY294002, completely reversed the protection from ischemic preconditioning. In conclusion, Akt contributes to the protection of rapid preconditionin against stroke.
View details for DOI 10.1007/s12975-010-0017-5
View details for PubMedID 21804899
Remote ischemic postconditioning (RIP) refers to an ischemia conducted in a distant organ that protects against a prior ischemia in another organ. We tested whether RIP protects against focal ischemia in the rat brain. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery combined with a 30-min occlusion of the bilateral common carotid arteries (CCA) in male rats. After CCA release, RIP was generated by three cycles of 15-min occlusion/15-min release of the left-hind femoral artery. The results showed that rapid RIP performed immediately after CCA release reduced infarction by 67% measured at 2 days after stroke. In addition, delayed RIP initiated as late as 3 h, but not 6 h, still robustly reduced infarction by 43% 2 days after stroke. RIP's protective effect was abolished by injecting the protein synthesis inhibitor, cycloheximide, and the afferent nerve blocker, capsaicin, suggesting that RIP blocks ischemic injury by modulating protein synthesis and nerve activity. Nevertheless, rapid RIP did not reduce infarction size 2 months after stroke while it ameliorated the outcome of the behavioral test. In conclusion, RIP attenuates brain injury after focal ischemia.
View details for DOI 10.1016/j.brainres.2009.07.029
View details for PubMedID 19631625
We recently showed that intraischemic moderate hypothermia (30 degrees C) reduces ischemic damage through the Akt pathway after permanent distal middle cerebral artery occlusion in rats. The only Akt pathway component preserved by hypothermia is phosphorylated phosphatase and tensin homolog deleted on chromosome 10 (p-PTEN), which suggests that p-PTEN may have a central role in neuroprotection. Reactive oxygen species (ROS) are critically involved in mediating ischemic damage after stroke by interacting with signaling molecules, including Akt, PTEN, and delta-protein kinase C (PKC). We investigated the protective mechanisms of moderate hypothermia on these signaling proteins after transient focal ischemia in rats. Early moderate hypothermia (3 h) was administered 15 mins before reperfusion, and delayed moderate hypothermia (3 h) was applied 15 mins after reperfusion. Our results indicate that early hypothermia reduced infarction, whereas delayed hypothermia did not. However, both early and delayed hypothermia maintained levels of Mn-SOD (superoxide dismutase) and phosphorylated Akt and blocked delta-PKC cleavage, suggesting that these factors may not be critical to the protection of hypothermia. Nevertheless, early hypothermia preserved p-PTEN levels after reperfusion, whereas delayed hypothermia did not. Furthermore, ROS inhibition maintained levels of p-PTEN after stroke. Together, these findings suggest that phosphorylation levels of PTEN are closely associated with the protective effect of early hypothermia against stroke.
View details for DOI 10.1038/jcbfm.2009.81
View details for PubMedID 19553907
Ischemic postconditioning initially referred to a stuttering reperfusion performed immediately after reperfusion, for preventing ischemia/reperfusion injury in both myocardial and cerebral infarction. It has evolved into a concept that can be induced by a broad range of stimuli or triggers, and may even be performed as late as 6 h after focal ischemia and 2 days after transient global ischemia. The concept is thought to be derived from ischemic preconditioning or partial/gradual reperfusion, but in fact the first experiment for postconditioning was carried out much earlier than that of preconditioning or partial/gradual reperfusion, in the research on myocardial ischemia. This review first examines the protective effects and parameters of postconditioning in various cerebral ischemic models. Thereafter, it provides insights into the protective mechanisms of postconditioning associated with reperfusion injury and the Akt, mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and ATP-sensitive K+ (K(ATP)) channel cell signaling pathways. Finally, some open issues and future challenges regarding clinical translation of postconditioning are discussed.
View details for DOI 10.1038/jcbfm.2009.13
View details for PubMedID 19240739
Two pathways that have been shown to mediate cerebral ischemic damage are the MEK/ERK cascade and the pro-apoptotic deltaPKC pathway. We investigated the relationship between these pathways in a rat model of focal ischemia by observing and modifying the activation state of each pathway. The ERK1/2 inhibitor, U0126, injected at ischemia onset, attenuated the increase in phosphorylated ERK1/2 (P-ERK1/2) after reperfusion. The deltaPKC inhibitor, deltaV1-1, delivered at reperfusion, did not significantly change P-ERK1/2 levels. In contrast, the deltaPKC activator, psi deltaRACK, injected at reperfusion, reduced ERK1/2 phosphorylation measured 4 h after reperfusion. Additionally, U0126 pretreatment at ischemia onset reduced infarct size compared with vehicle, but U0126 injected at the onset of reperfusion had no protection. Finally, combination of U0126 injection at ischemia onset plus deltaV1-1 injection at reperfusion further reduced infarct size, while combination of U0126 delivered at ischemia onset with psi deltaRACK injected at reperfusion increased infarct size compared with U0126 alone. In conclusion, we find that inhibiting both the MEK/ERK and the deltaPKC pathways offers greater protection than either alone, indicating they likely act independently.
View details for DOI 10.1016/j.brainres.2008.11.051
View details for PubMedID 19063870
This report describes the synthesis of two cyclic RGD (Arg-Gly-Asp) conjugates, HYNIC-2PEG(4)-dimer (HYNIC = 6-hydrazinonicotinyl; 2PEG(4)-dimer = E[PEG(4)-c(RGDfK)](2); and PEG(4) = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and HYNIC-3PEG(4)-dimer (3PEG(4)-dimer = PEG(4)-E[PEG(4)-c(RGDfK)](2)), and evaluation of their (99m)Tc complexes [(99m)Tc(HYNIC-2PEG(4)-dimer)(tricine)(TPPTS)] ((99m)Tc-2PEG(4)-dimer: TPPTS = trisodium triphenylphosphine-3,3',3''-trisulfonate) and [(99m)Tc(HYNIC-3PEG(4)-dimer)(tricine)(TPPTS)] ((99m)Tc-3PEG(4)-dimer) as novel radiotracers for imaging integrin alpha(v)beta(3) expression in athymic nude mice bearing U87MG glioma and MDA-MB-435 breast cancer xenografts. The integrin alpha(v)beta(3) binding affinities of RGD peptides were determined by competitive displacement of (125)I-c(RGDyK) on U87MG glioma cells. It was found that the two PEG(4) linkers between RGD motifs in HYNIC-2PEG(4)-dimer (IC(50) = 2.8 +/- 0.5 nM) and HYNIC-3PEG(4)-dimer (IC(50) = 2.4 +/- 0.7 nM) are responsible for their higher integrin alpha(v)beta(3) binding affinity than that of HYNIC-PEG(4)-dimer (PEG(4)-dimer = PEG(4)-E[c(RGDfK)](2); IC(50) = 7.5 +/- 2.3 nM). Addition of extra PEG(4) linker in HYNIC-3PEG(4)-dimer has little impact on integrin alpha(v)beta(3) binding affinity. (99m)Tc-2PEG(4)-dimer and (99m)Tc-3PEG(4)-dimer were prepared in high yield with >95% radiochemical purity and the specific activity of >10 Ci/mumol. Biodistribution studies clearly demonstrated that PEG(4) linkers are particularly useful for improving the tumor uptake and clearance kinetics of (99m)Tc-2PEG(4)-dimer and (99m)Tc-3PEG(4)-dimer from noncancerous organs. It was also found that there was a linear relationship between the tumor size and radiotracer tumor uptake expressed as %ID (percentage of the injected dose) in U87MG glioma and MDA-MB-435 breast tumor models. The blocking experiment showed that the tumor uptake of (99m)Tc-2PEG(4)-dimer is integrin alpha(v)beta(3)-mediated. In the metabolism study, (99m)Tc-2PEG(4)-dimer had high metabolic stability during its excretion from renal and hepatobiliary routes. (99m)Tc-3PEG(4)-dimer also remained intact during thee excretion from the renal route, but, had approximately 30% metabolism during the excretion from the hepatobiliary route. Planar imaging studies in U87MG glioma and MDA-MB-435 breast tumor models showed that the tumors of approximately 5 mm in diameter could be readily visualized with excellent contrast. Thus, (99m)Tc-3PEG(4)-dimer is a very promising radiotracer for the early detection of integrin alpha(v)beta(3)-positive tumors, and may have the potential for noninvasive monitoring of tumor growth or treatment efficacy.
View details for DOI 10.1021/mp800150r
View details for Web of Science ID 000263035000024
View details for PubMedID 19067525
Glucocorticoids (GCs) and estrogen can modulate neuron death and dysfunction during neurological insults. Glucocorticoids are adrenal steroids secreted during stress, and hypersecretion of GCs during cerebral ischemia compromises the ability of hippocampal and cortical neurons to survive. In contrast, estrogen can be neuroprotective after cerebral ischemia. Here we evaluate the protective potential of a herpes viral vector expressing a chimeric receptor (ER/GR), which is composed of the ligand-binding domain of the GC receptor (GR) and the DNA-binding domain of the estrogen receptor-alpha (ER). This novel receptor can transduce an endangering GC signal into a protective estrogenic one. Using an in vitro oxygen glucose deprivation model (OGD), GCs exacerbated neuron death in primary cortical cultures, and this worsening effect was completely blocked by ER/GR expression. Moreover, blocking GC actions with a vector expressing a dominant negative GC receptor promoted neuron survival during postischemia, but not preischemia. Thus, gene therapeutic strategies to modulate GC and estrogen signaling can be beneficial during an ischemic insult.
View details for DOI 10.1038/jcbfm.2008.105
View details for PubMedID 18797472
Vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFRs) play important roles during neurovascular repair after stroke. In this study, we imaged VEGFR expression with positron emission tomography (PET) to noninvasively analyze poststroke angiogenesis.Female Sprague-Dawley rats after distal middle cerebral artery occlusion surgery were subjected to weekly MRI, (18)F-FDG PET, and (64)Cu-DOTA-VEGF(121) PET scans. Several control experiments were performed to confirm the VEGFR specificity of (64)Cu-DOTA-VEGF(121) uptake in the stroke border zone. VEGFR, BrdU, lectin staining, and (125)I-VEGF(165) autoradiography on stroke brain tissue slices were performed to validate the in vivo findings.T2-weighed MRI correlated with the "cold spot" on (18)F-FDG PET for rats undergoing distal middle cerebral artery occlusion surgery. The (64)Cu-DOTA-VEGF(121) uptake in the stroke border zone peaked at approximately 10 days after surgery, indicating neovascularization as confirmed by histology (VEGFR-2, BrdU, and lectin staining). VEGFR specificity of (64)Cu-DOTA-VEGF(121) uptake was confirmed by significantly lower uptake of (64)Cu-DOTA-VEGF(mutant) in vivo and intense (125)I-VEGF(165) uptake ex vivo in the stroke border zone. No appreciable uptake of (64)Cu-DOTA-VEGF(121) was observed in the brain of sham-operated rats.For the first time to our knowledge, we successfully evaluated the VEGFR expression kinetics noninvasively in a rat stroke model. In vivo imaging of VEGFR expression could become a significant clinical tool to plan and monitor therapies aimed at improving poststroke angiogenesis.
View details for DOI 10.1161/STROKEAHA.108.517474
View details for PubMedID 18948613
We and others have reported that rapid ischemic postconditioning, interrupting early reperfusion after stroke, reduces infarction in rats. However, its extremely short therapeutic time windows, from a few seconds to minutes after reperfusion, may hinder its clinical translation. Thus, in this study we explored if delayed postconditioning, which is conducted a few hours after reperfusion, offers protection against stroke.Focal ischemia was generated by 30 min occlusion of bilateral common carotid artery (CCA) combined with permanent occlusion of middle cerebral artery (MCA); delayed postconditioning was performed by repetitive, brief occlusion and release of the bilateral CCAs, or of the ipsilateral CCA alone. As a result, delayed postconditioning performed at 3h and 6h after stroke robustly reduced infarct size, with the strongest protection achieved by delayed postconditioning with 6 cycles of 15 min occlusion/15 min release of the ipsilateral CCA executed from 6h. We found that this delayed postconditioning provided long-term protection for up to two months by reducing infarction and improving outcomes of the behavioral tests; it also attenuated reduction in 2-[(18)F]-fluoro-2-deoxy-D-glucose (FDG)-uptake therefore improving metabolism, and reduced edema and blood brain barrier leakage. Reperfusion in ischemic stroke patients is usually achieved by tissue plasminogen activator (tPA) application, however, t-PA's side effect may worsen ischemic injury. Thus, we tested whether delayed postconditioning counteracts the exacerbating effect of t-PA. The results showed that delayed postconditioning mitigated the worsening effect of t-PA on infarction.Delayed postconditioning reduced ischemic injury after focal ischemia, which opens a new research avenue for stroke therapy and its underlying protective mechanisms.
View details for DOI 10.1371/journal.pone.0003851
View details for PubMedID 19066627
We examined the temporal factors of postconditioning, assessed whether gradual reperfusion reduces infarcts, and compared postconditioning's protection with that of both rapid and delayed preconditioning. Focal ischemia was generated by permanent occlusion of the left distal middle cerebral artery (dMCA) combined with 30 min of occlusion of both common carotid arteries (CCA) in rats. Postconditioning was performed by repetitive brief release and occlusion of CCA after 30 min of CCA occlusion. Gradual reperfusion was generated by controlled release of the bilateral CCA. We confirmed that postconditioning disrupted the early reperfusion but improved cerebral blood flow (CBF) thereafter. Postconditioning with three cycles, but not with 10 cycles, of 30 sec CCA release and 10 sec CCA occlusion (30s/10s) reduced infarction measured at 2 days after stroke. In addition, postconditioning with 10 cycles, but not with three cycles, of 10s/10s reduced infarction but it lost protection when initiated at 3 min after reperfusion. In addition, gradual reperfusion also reduced infarction. Moreover, both rapid and delayed preconditioning conducted 60 min and 3 days before stroke reduced infarct sizes. However, no additional protection was detected when postconditioning was combined with either rapid or delayed preconditioning. In conclusion, gradual reperfusion reduced infarction; postconditioning's protection depended on the number of cycles and duration of each cycle of reperfusion and occlusion and the onset time of postconditioning; postconditioning's protection was comparable to that of rapid preconditioning but not as robust as that of delayed preconditioning.
View details for DOI 10.1002/jnr.21703
View details for PubMedID 18438944
Extracellular signal-regulated kinase 1/2 (ERK1/2), one of the best-characterized members of the mitogen-activated protein kinase (MAPK) family, mediates a range of activity from metabolism, motility, and inflammation to cell death and survival. It is phosphorylated and activated through a three-tiered MEK mode via cell surface receptors stimulated by growth factors or cytokines. The phosphorylated ERK1/2 level is usually increased after cerebral ischemia/reperfusion, but whether an increase in ERK1/2 phosphorylation is protective or detrimental is highly debatable. Much of the support for ERK1/2's role as a neuroprotectant against stroke stems from its apparent involvement in the beneficial effects of growth factors, estrogen, preconditioning, and hypothermia on the ischemic brain. Conversely, evidence supporting the detrimental effects of ERK1/2 activity is derived from its activation promoting inflammation and oxidative stress and its inhibition reducing ischemic damage. The dual potential of ERK1/2 actions in the ischemic brain is likely related to its responses to a diverse array of agonists and cell surface receptors. Plausibly, the ERK1/2 activity generated by cytokines and free radicals or other inflammatory factors after stroke may worsen ischemic damage, whereas the ERK1/2 activity produced by exogenous growth factors, estrogen, and preconditioning favors neuroprotection. Future experiments should be conducted to optimize the protective effect of ERK1/2 while blocking its detrimental actions.
View details for DOI 10.1002/jnr.21604
View details for PubMedID 18189318
Beta-catenin can be cleaved by caspase-3 or degraded by activated glycogen synthase kinase-3beta via phosphorylating beta-catenin. We tested the hypothesis that beta-catenin undergoes degradation after stroke, and its degradation is dependent on caspase activity. Stroke was generated by permanent middle cerebral artery occlusion and 1 h of transient bilateral common carotid artery occlusion in rats. Active caspase-3 was expressed in the ischemic cortex from 5 to 48 h after stroke, whereas beta-catenin markedly degraded at 24 and 48 h after stroke. The caspase 3-specific inhibitor, Z-DQMD-FMK, attenuated beta-catenin degradation, but it did not affect phosphorylation of both beta-catenin and glycogen synthase kinase-3beta. In conclusion, beta-catenin degraded after stroke, and its degradation was caspase-3 dependent.
View details for PubMedID 18463494
Identification and pharmacological characterization of two new selective delta-opioid receptor antagonists, derived from the Dmt-Tic pharmacophore, of potential utility in positron emission tomography (PET) imaging are described. On the basis of its high delta selectivity, H-Dmt-Tic--Lys(Z)-OH (reference compound 1) is a useful starting point for the synthesis of (18)F-labeled compounds prepared by the coupling of N-succinimidyl 4-[ (18)F]fluorobenzoate ([(18)F]SFB) with Boc-Dmt-Tic--Lys(Z)-OH under slightly basic conditions at 37 degrees C for 15 min, deprotection with TFA, and HPLC purification. The total synthesis time was 120 min, and the decay-corrected radiochemical yield of [(18)F]- 1 was about 25-30% ( n = 5) starting from [(18)F]SFB ( n = 5) with an effective specific activity about 46 GBq/micromol. In vitro autoradiography studies showed prominent uptake of [ (18)F]- 1 in the striatum and cortex with significant blocking by 1 and UFP-501 (selective delta-opioid receptor antagonist), suggesting high specific binding of [(18)F]- 1 to delta-opioid receptors. Noninvasive microPET imaging studies revealed the absence of [(18)F]- 1 in rat brain, since it fails to cross the blood-brain barrier. This study demonstrates the suitability of [ (18)F]- 1 for imaging peripheral delta-opioid receptors.
View details for DOI 10.1021/jm7014765
View details for PubMedID 18311909
Review of results of clinical studies indicates the number of potential patients who are actually treated for acute ischemic stroke is disappointingly low, and effective treatments are making a minor impact on this major public health problem. Imaging modalities, such as diffusion- and perfusion-weighted images, as well as CT perfusion and CT angiography, to better select patients for treatment are now routinely performed in most academic medical centers. However, there is not a perfect penumbra imaging technique and each one has its own advantages and disadvantages. Recent advances in molecular imaging modalities allow a better understanding of this pathophysiological process that could lead to enhanced therapy for stroke. This article seeks to describe the role of molecular imaging in identifying the pathophysiology of stroke and how it could be incorporated in future decision-making and treatment strategies in stroke.
View details for DOI 10.2741/2779
View details for PubMedID 17981647
Postconditioning, a series of mechanical interruptions of reperfusion after ischemia, prevents ischemia/reperfusion injury in myocardial infarction. The extensive studies of postconditioning in myocardial infarction have led to clinical trials. This article reviews the protective effects of postconditioning against ischemia from the heart to the brain and provides insights on how studies of postconditioning in the field of heart ischemia have shed light on postconditioning of the brain. Because brain ischemia has many mechanisms in common with heart ischemia, it is logical to test whether postconditioning protects against brain ischemia as well. A few groups have reported that postconditioning reduces infarct size in focal cerebral ischemia and improves deficits of short-term memory and motor coordination after global cerebral ischemia. However, many outstanding issues remain elusive regarding the protective effects of postconditioning against cerebral ischemia. Future studies should further identify parameters that generate the strongest protection for postconditioning against cerebral ischemia and should study whether postconditioning provides long-term protection. In addition, clarification of the underlying protective mechanisms should be pursued. This will certainly enhance our understanding of this novel phenomenon and may provide important clues for developing pharmacological analogues for stroke treatment.
View details for DOI 10.1007/s11481-007-9089-8
View details for PubMedID 18040849
Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.
View details for PubMedID 17684517
Apoptosis, a predominant cause of neuronal death after stroke, can be executed in a caspase-dependent or apoptosis inducing factor (AIF)-dependent manner. Herpes simplex virus (HSV) vectors expressing caspase inhibitors p35 and crmA have been shown to be neuroprotective against various excitotoxic insults. Here we further evaluated the possible neuroprotective role of p35 and crmA in a rat stroke model. Overexpression of p35, but not crmA, significantly increased neuronal survival. Results of double immunofluorescence staining indicate that compared with neurons infected with crmA or control vectors, p35-infected neurons had less active caspase-3 expression, cytosolic cytochrome c and nuclear AIF translocation.
View details for DOI 10.1016/j.neuroscience.2007.07.030
View details for PubMedID 17945431
Mild hypothermia is a robust neuroprotective treatment for stroke. Understanding the mechanisms underlying hypothermia's benefits will lead to more effective treatments to prevent stroke damage. Delta protein kinase C (deltaPKC) is a kinase that has been strongly implicated in executing ischemic damage. We investigated the effects of hypothermia on deltaPKC activation, as determined by its subcellular translocation, proteolytic cleavage, and phosphorylation in a focal cerebral ischemia model. The amount of constitutively activated C-terminal catalytic fragment of deltaPKC (CF-deltaPKC) increased after stroke. Both hypothermia (30 degrees C) and the caspase-3-specific inhibitor, Z-DQMD-FMK, blocked the accumulation of activated deltaPKC in the penumbra. Other hallmarks of deltaPKC activation, its translocation to the mitochondria, and nucleus were observed in the penumbra as early as 10 mins after reperfusion. These events were blocked by hypothermia. Hypothermia also blocked CF-deltaPKC increases in the mitochondria and nuclei. Conversely, a specific deltaPKC activator, psideltaRACK, decreased the neuroprotective effect of hypothermia. Finally, deltaPKC activity may lead to mitochondrial injury and cytochrome c release, as the timing of cytochrome c release corresponded to the time course of deltaPKC translocation. Both cytochrome c release and deltaPKC translocation were blocked by hypothermia. In conclusion, hypothermia protects against ischemic damage in part by suppressing deltaPKC activation after stroke.
View details for DOI 10.1038/sj.jcbfm.9600450
View details for PubMedID 17293847
Protein kinase C epsilon (epsilonPKC) has been implicated as a neuroprotectant in vitro. We studied epsilonPKC activation (by its localization and proteolysis) in a rodent stroke model and correlated the effects of hypothermia with epsilonPKC activity after cerebral ischemia.Rats were subjected to permanent distal middle cerebral artery occlusion plus 1 hour of bilateral common carotid artery occlusion. Body temperatures were maintained at 37 degrees C or 30 degrees C during common carotid artery occlusion. Brains were harvested at 10 minutes, 4 hours, and 24 hours after common carotid artery release, and the cortex corresponding to the ischemic core and penumbra was dissected. epsilonPKC localization after stroke was assessed by Western blot and immunofluorescence microscopy. A caspase-3 inhibitor was used to test whether epsilonPKC cleavage is caspase dependent.epsilonPKC in the membrane fraction and whole-protein homogenates decreased moderately in the penumbra but decreased markedly in the ischemic core. Hypothermia blocked this decrease in both the ischemic core and penumbra. Confocal microscopy confirmed that neuronal epsilonPKC expression decreased in the ischemic core at 4 hours after reperfusion, and this loss was prevented by hypothermia. Two carboxyl-terminal cleavage products of epsilonPKC with molecular masses of 43 and 35 kDa were detected. Although the protein band of 43 kDa decreased after stroke, the 35-kDa band increased. Such changes were not dependent on caspase-3. However, hypothermia blocked changes in the cleavage form of 35 kDa but not 43 kDa after stroke.Moderate hypothermia preserves epsilonPKC activity after stroke.
View details for DOI 10.1161/01.STR.0000254616.78387.ee
View details for PubMedID 17204679
Reactive oxygen species contribute to neuronal death following cerebral ischemia. Prior studies using transgenic animals have demonstrated the neuroprotective effect of the antioxidant, copper/zinc superoxide dismutase (SOD1). In this study, we investigated whether SOD1 overexpression using gene therapy techniques in non-transgenic animals would increase neuronal survival. A neurotropic, herpes simplex virus-1 (HSV-1) vector containing the SOD1 gene was injected into the striatum either before or after transient focal cerebral ischemia. Striatal neuron survival at 2 days was improved by 52% when vector was delivered 12-15 h prior to ischemia and by 53% when vector delivery was delayed 2 h following ischemia. These data add to the growing literature, which suggests that an antioxidant approach, perhaps by employing gene therapy techniques, may be beneficial in the treatment of stroke.
View details for DOI 10.1016/j.neulet.2006.08.089
View details for PubMedID 17110031
In recent years, the phosphoinositide-3-kinase/Akt cell survival signaling pathway has been increasingly researched in the field of stroke. Akt activity is suggested to be upregulated by phosphorylation through the activation of receptor tyrosine kinases by growth factors. Although the upstream signaling components phosphoinositide-dependent protein kinase (PDK)1 and integrinlinked kinase enhance the activity of Akt, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) decreases it. Upon activation, Akt phosphorylates an array of molecules, including glycogen synthase kinase3beta (GSK3beta), forkhead homolog in rhabdomyosarcoma (FKHR), and Bcl-2-associated death protein, thereby blocking mitochondrial cytochrome c release and caspase activity. Generally, the level of Akt phosphorylation at site Ser 473 (P-Akt) transiently increases after focal ischemia, whereas the levels of phosphorylation of PTEN, PDK1, forkhead transcription factor, and GSK3beta decrease. Numerous compounds (such as growth factors, estrogen, free radical scavengers, and other neuroprotectants) reduce ischemic damage, possibly by upregulating P-Akt. However, preconditioning and hypothermia block ischemic damage by inhibiting an increase of P-Akt. Inhibition of the Akt pathway blocks the protective effect of preconditioning and hypothermia, suggesting the Akt pathway contributes to their protective effects and that the P-Akt level does not represent its true kinase activity. Together, attenuation of the Akt pathway dysfunction contributes to neuronal survival after stroke.
View details for PubMedID 17308356
Dysfunction of the ubiquitin-proteasome system has recently been linked to stroke. Ischemia may cause increased protein misfolding and inhibit the proteasome, shifting the balance from free ubiquitin to conjugated ubiquitin. In this study, we examine the effect of hypothermia on the distribution of total and free ubiquitin, as well as the levels of conjugated ubiquitin after experimental stroke using a focal cerebral ischemia model. We show that hypothermia prevents redistribution of ubiquitin following ischemia, largely through preservation of intracellular cytoplasmic free ubiquitin. We also show that hypothermia blocks the increase in conjugated ubiquitin observed after stroke. Our data indicate that hypothermia's neuroprotection is mediated, in part, through preservation of ubiquitin-proteasome system function.
View details for PubMedID 17047455
Hypothermia is effective in preventing ischemic damage. A caspase-dependent apoptotic pathway is involved in ischemic damage, but how hypothermia inhibits this pathway after global cerebral ischemia has not been well explored. It was determined whether hypothermia protects the brain by altering cytochrome c release and caspase activity. Cerebral ischemia was produced by two-vessel occlusion plus hypotension for 10 mins. Body temperature in hypothermic animals was reduced to 33 degrees C before ischemia onset and maintained for 3 h after reperfusion. Western blots of subcellular fractions revealed biphasic cytosolic cytochrome c release, with an initial peak at about 5 h after ischemia, which decreased at 12 to 24 h, and a second, larger peak at 48 h. Caspase-3 and -9 activity increased at 12 and 24 h. A caspase inhibitor, Z-DEVD-FMK, administered 5 and 24 h after ischemia onset, protected hippocampal CA1 neurons from injury and blocked the second cytochrome c peak, suggesting that caspases mediate this second phase. Hypothermia (33 degrees C), which prevented CA1 injury, did not inhibit cytochrome c release at 5 h, but reduced cytochrome c release at 48 h. Caspase-3 and -9 activity was markedly attenuated by hypothermia at 12 and 24 h. Thus, biphasic cytochrome c release occurs after transient global ischemia and mild hypothermia protects against ischemic damage by blocking the second phase of cytochrome c release, possibly by blocking caspase activity.
View details for DOI 10.1038/sj.jcbfm.9600111
View details for PubMedID 15789032
Chaperones, especially the stress inducible Hsp70, have been studied for their potential to protect the brain from ischemic injury. While they protect from both global and focal ischemia in vivo and cell culture models of ischemia/reperfusion injury in vitro, the mechanism of protection is not well understood. Protein aggregation is part of the etiology of chronic neurodegenerative diseases such as Huntington's and Alzheimer's, and recent data demonstrate protein aggregates in animal models of stroke. We now demonstrate that overexpression of Hsp70 in hippocampal CA1 neurons reduces evidence of protein aggregation under conditions where neuronal survival is increased. We have also demonstrated protection by the cochaperone Hdj-2 in vitro and demonstrated that this is associated with reduced protein aggregation identified by ubiquitin immunostaining. Hdj-2 can prevent protein aggregate formation by itself, but can only facilitate protein folding in conjunction with Hsp70. Pharmacological induction of Hsp70 was found to reduce both apoptotic and necrotic astrocyte death induced by glucose deprivation or oxygen glucose deprivation. Protection from ischemia and ischemia-like injury by chaperones thus involves at least anti-apoptotic, anti-necrotic and anti-protein aggregation mechanisms.
View details for DOI 10.1242/jeb.01034
View details for PubMedID 15299042
The serine/threonine kinase, glycogen synthase kinase 3beta (GSK3beta), is abundant in CNS and is neuron specific. GSK3beta plays a pivotal role in the regulation of numerous cellular functions. GSK3beta phosphorylates and thereby regulates many metabolic, signaling, and structural proteins which can influence cell survival. Increased GSK3beta correlates with increased cell death, whereas reduced GSK3beta expression correlates with increased cell survival. We report that the GSK3beta inhibitor Chir025 is neuroprotective in vitro and in vivo. First, Chir025 reduced cultured hippocampal neuron death following glutamate exposure by 15-20% versus vehicle-treated controls. Second, Chir025 significantly reduced cultured cortical neuron death following oxygen-glucose deprivation (OGD) by approximately 50%. Third, Chir025 reduced infarct size following focal cerebral ischemia by nearly 20%. There were no significant differences in the number of TUNEL-positive neurons or in caspase-3 and -9 activities between Chir025- and vehicle-treated rats, although Chir025 elevated cytosolic Bcl-2 expression. These data show that Chir025-mediated inhibition of GSK3beta is neuroprotective and that the mechanism is probably not anti-apoptotic.
View details for DOI 10.1016/j.expneurol.2004.04.004
View details for PubMedID 15246837
Apoptosis plays a critical role in many neurologic diseases, including stroke. Cytochrome c release and activation of various caspases are known to occur after focal and global ischemia. However, recent reports indicate that caspase-independent pathways may also be involved in ischemic damage. Apoptosis-inducing factor (AIF) is a novel flavoprotein that helps mediate caspase-independent apoptotic cell death. AIF translocates from mitochondria to nuclei where it induces caspase-independent DNA fragmentation. Bcl-2, a mitochondrial membrane protein, protects against apoptotic and necrotic death induced by different insults, including cerebral ischemia. In the present study, Western blots confirmed that AIF was normally confined to mitochondria but translocated to nuclei or cytosol 8, 24, and 48 hours after onset of ischemia. Overall, AIF protein levels also increased after stroke. Confocal microscopy further demonstrated that nuclear AIF translocation occurred in the peri-infarct region but not in the ischemic core where only some cytosolic AIF release was observed. Our data also suggest that AIF translocated into nuclei after cytochrome c was released into the cytosol. Bcl-2 transfection in the peri-infarct region blocked nuclear AIF translocation and improved cortical neuron survival.
View details for PubMedID 15181376
Reactive oxygen species (ROS) play key roles in the cascade of brain injury after stroke, and strategies to increase the antioxidant defenses of neurons after stroke hold great promise. In this study we evaluate the neuroprotective potential of using a herpes simplex viral vector to over-express catalase in rats. Vector was microinfused into the striatum either prior to or after middle cerebral artery occlusion (MCAO). Catalase over-expression was protective (relative to control vector) when the vector was delivered 14-16 h prior to ischemia, but not when delivered after ischemia. Thus, the timing of catalase over-expression relative to ischemia is a critical variable determining its potential therapeutic value.
View details for DOI 10.1097/01.wnr.000011132738420.12
View details for PubMedID 15094494
We showed previously that Bcl-2 overexpression with the use of herpes simplex viral (HSV) vectors improved striatal neuron survival when delivered 1.5 hours after stroke but not when delivered 5 hours after stroke onset. Here we determine whether hypothermia prolongs the therapeutic window for gene therapy.Rats were subjected to focal ischemia for 1 hour. Hypothermia (33 degrees C) was induced 2 hours after insult and maintained for 3 hours. Five hours after ischemia onset, HSV vectors expressing Bcl-2 plus beta-gal or beta-gal alone were injected into each striatum. Rats were killed 2 days later.Striatal neuron survival of Bcl-2-treated, hypothermic animals was improved 2- to 3-fold over control-treated, hypothermic animals and Bcl-2-treated, normothermic animals. Neuron survival among normothermic, Bcl-2-treated animals was not different from control normothermics or control hypothermics. Double immunostaining of cytochrome c and beta-gal demonstrated that Bcl-2 plus hypothermia significantly reduced cytochrome c release.Postischemic mild hypothermia extended the time window for gene therapy neuroprotection using Bcl-2 and reduced cytochrome c release.
View details for DOI 10.1161/01.STR.0000110787.42083.58
View details for PubMedID 14726551
Neurons subjected to ischemia undergo necrosis or apoptosis depending on their anatomic distribution and the severity and duration of ischemia. Recent work has shown that apoptosis can occur in some settings, primarily within the ischemic penumbra. It is recognized that both mitochondrial and death-receptor pathways are involved in the transduction of apoptotic signals in the context of cerebral ischemia. Recent data also highlight the pivotal role of caspase 3 in the execution of ischemia-induced apoptosis, although a caspase-independent pathway is gaining increasing attention. In this review, we examine some of these findings and their potential therapeutic implications for ischemic stroke.
View details for PubMedID 14668947
Bcl-2 protects against both apoptotic and necrotic death induced by several cerebral insults. We and others have previously demonstrated that defective herpes simplex virus vectors expressing Bcl-2 protect against various insults in vitro and in vivo, including cerebral ischemia. Because the infarct margin may be a region that is most amenable to treatment, we first determined whether gene transfer to the infarct margin is possible using a focal ischemia model. Since ischemic injury with and without reperfusion may occur by different mechanisms, we also determined whether Bcl-2 protects against focal cerebral ischemic injury either with or without reperfusion in rats. Bax expression, cytochrome c translocation and activated caspase-3 expression were also assessed. Viral vectors overexpressing Bcl-2 were delivered to the infarct margin. Reperfusion resulted in larger infarcts than permanent occlusion. Bcl-2 overexpression significantly improved neuron survival in both ischemia models. Bcl-2 overexpression did not alter overall Bax expression, but inhibited cytosolic accumulation of cytochrome c and caspase-3 activation. Thus, we provide the first evidence that gene transfer to the infarct margin is feasible, that overexpression of Bcl-2 protects against damage to the infarct margin induced by ischemia with and without reperfusion, and that Bcl-2 overexpression using gene therapy attenuates apoptosis-related proteins. This suggests a potential therapeutic strategy for stroke.
View details for DOI 10.1046/j.1471-4159.2003.01756.x
View details for PubMedID 12716434
Recent advances have demonstrated the use of gene therapy in the treatment of stroke in experimental animal models of focal ischemia, global ischemia and subarachnoid hemorrhage. Several different vectors for gene transfer have been studied including herpes simplex virus, adenovirus, adeno-associated virus and liposomes. Genetically modified cell lines (e.g., bone marrow-derived cells) have been studied for ex vivo gene therapy. The effects of gene transfer to several brain regions including the striatum, cortex, hippocampus, subarachnoid space and blood vessels are reviewed. Targets of gene therapy, such as molecular cascades after ischemia onset (Ca2+ influx, ATP loss, increased nitric oxide) and events associated with apoptosis are also reviewed, in addition to how gene transfer may be used to understand pathomechanisms underlying ischemic injury and the temporal therapeutic windows following ischemia within which protective effects of gene therapy have been achieved. The prospects for gene therapy for stroke are discussed in light of these findings and it is concluded that solutions to key technological problems will allow gene therapy to be a viable treatment modality.
View details for DOI 10.1586/14737188.8.131.527
View details for PubMedID 19810903
We have previously reported studies of gene therapy using a neurotropic herpes simplex viral (HSV) vector system containing bipromoter vectors to transfer various protective genes to neurons. Using this system in experimental models of stroke, cardiac arrest, and excitotoxicity, we found that it is possible to enhance neuron survival against such cerebral insults by overexpressing genes that target various facets of injury. Among the genes we studied, the anti-apoptotic protein BCL-2 improved neuron survival following various insults, and was protective even when administered after stroke onset. BCL-2 is thought to protect cells from apoptotic death by preventing cytochrome c release from the mitochondria and subsequent caspase activation. We and others have established that cooling the brain by a few degrees markedly reduces ischemic injury and improves neurologic deficits in models of cerebral ischemia and trauma. This hypothermic neuroprotection is also associated with BCL-2 upregulation in some instances. Furthermore, hypothermia suppresses many aspects of apoptotic death including cytochrome c release, caspase activation, and DNA fragmentation. Here we show that two different kinds of protective therapies, BCL-2 overexpression and hypothermia, both inhibit aspects of apoptotic cell death cascades, and that a combination treatment can prolong the temporal therapeutic window for gene therapy.
View details for PubMedID 12853295
We investigated whether HSV gene transfer of HSP72 in vivo and in vitro: (1) protected cornu ammonis 1 region of the hippocampus neurons from global cerebral ischemia; and (2) affected Bcl-2 expression. HSV vectors expressing HSP72 and beta-galactosidase (reporter) or beta-galactosidase only (control vector) were injected into cornu ammonis 1 region of the hippocampus 15 hours before induction of global cerebral ischemia (n = 10) and sham-operated rats (n = 8). HSP72 vector-treated rats displayed significantly more surviving transfected neurons (X-gal-positive, 31 +/- 8) compared with control vector-treated rats (10 +/- 4) after global cerebral ischemia. Sham-operated rats displayed similar numbers of X-gal-positive neurons (HSP72 vector 18 +/- 8 vs control vector 20 +/- 7). The percentage of beta-galactosidase and Bcl-2 coexpressing neurons in HSP72-treated rats after global cerebral ischemia (84 +/- 4%) was greater than that in control vector-treated rats (58 +/- 9%). The percentage of beta-galactosidase and Bcl-2 coexpressing neurons in sham-operated rats was similar in HSP72 (93 +/- 7%) and in control vector-treated rats (88 +/- 12%). HSP72 vector transfection led to 12 times as much Bcl-2 expression as the control vector in uninjured hippocampal neuronal cultures. In injured (oxygen-glucose deprivation) hippocampal neuron cultures, HSP72 vector transfection led to 2.8 times as much Bcl-2 expression as control vector. We show that HSP72 overexpression protects cornu ammonis 1 region of the hippocampus neurons from global cerebral ischemia, and that this protection may be mediated in part by increased Bcl-2 expression.
View details for DOI 10.1002/ana.10264
View details for PubMedID 12210785
View details for Web of Science ID 000173147700101
Our newly developed method using a dialysis electrode has made it possible to perform real time monitoring of extracellular glutamate concentration ([Glu]e) utilizing the oxygen-independent reaction with glutamate oxidase and ferrocene. In this study, we therefore, investigated [Glu]e changes during brain ischemia using both the conventional microdialysis method and the dialysis electrode method. A comparison between our newly developed dialysis electrode and conventional microdialysis methods provided the following results. When the conventional microdialysis method was employed: (1) the elevation of [Glu]e during complete global ischemia was delayed; and (2) the elevation of concentration and reuptake of glutamate were delayed during 10-min transient ischemia, and the elevation of [Glu]e reached a maximum later using conventional microdialysis than using our dialysis electrode. (3) The biphasic [Glu]e elevation of glutamate concentration detected using the dialysis electrode method was not observed using the conventional microdialysis method. It was additionally investigated why the conventional microdialysis method provides inferior time resolution. In this study, we also demonstrated with the chromatographic SMART procedure coupled to UV detection that biogenic substances, i.e. low molecular weight proteins and peptides, are released during ischemic injury, and they may cause a delay in the time resolution in the microdialysis method.
View details for Web of Science ID 000169308700009
View details for PubMedID 11311451
Numerous reports have suggested that anoxic depolarization is a critical event in the pathogenesis of cerebral ischemia. Extracellular glutamate concentration ([Glu]e) is closely related to the pathogenesis of ischemia. Therefore, these pathogenic mechanisms merit study, especially the relationship between [Glu]e elevation and the ionic basis of early changes in membrane potential after ischemic insult in vivo. It is often presumed from electrophysiological studies that a causal relationship exists between impaired glutamate uptake and/or progressive glutamate increase and anoxic depolarization, but few in vivo reports have found any sign of a progressive increase of [Glu]e elevation preceding anoxic depolarization. Recently, we reported the application of an oxygen-independent real-time technique for monitoring glutamate levels in the extracellular space during in vivo ischemia, and demonstrated that the massive glutamate release during ischemia is biphasic. In the present study, using this real-time monitoring system, we carried out a more detailed analysis of the initial events in the first phase of glutamate release during ischemia-induced anoxic depolarization. The shape of the rising slope that forms the peak of the first phase suggested two components. The second component was approximately 10 times steeper than the first, with two different components of the rise on the way to the peak of the biphasic [Glu]e elevation. This is the first report to demonstrate these components of the initial glutamate peak, and suggests a progressive second component of the [Glu]e increase preceding Ca2+-dependent release from synaptic vesicles with anoxic depolarization, in vivo.
View details for Web of Science ID 000089360300023
View details for PubMedID 11006971
Changes in brain temperature are known to modulate the marked neuronal damage caused by an approximately 10-min intra-ischemic period. Numerous studies have suggested that the extracellular glutamate concentration ([Glu](e)) in the intra-ischemic period and the initial postischemia period is strongly implicated in such damage. In this study, the effects of intra-ischemic brain temperature (32, 37, 39 degrees C) on [Glu](e) were investigated utilizing a dialysis electrode combined with ferrocene bovine serum albumin (BSA), which allows oxygen-independent real-time measurement of [Glu](e). This system allowed separate quantitative evaluation of intra-ischemic biphasic glutamate release from the neurotransmitter and metabolic pools, and of postischemic glutamate re-uptake in ischemia-reperfusion models. The biphasic [Glu](e) elevation in the intra-ischemic period did not differ markedly among intra-ischemic brain temperatures ranging from 32 to 39 degrees C. Intra-ischemic normothermia (37 degrees C) and mild hyperthermia (39 degrees C) markedly inhibited [Glu](e) re-uptake during the postischemic period, although the intra-ischemic [Glu](e) elevation did not differ from that during intra-ischemic hypothermia (32 degrees C). It was assumed that normothermia or mild hyperthermia in the intra-ischemic period influences intracellular functional abnormalities other than the intra-ischemic [Glu](e) elevation, thereby inhibiting glutamate re-uptake after reperfusion rather than directly modulating intra-ischemic [Glu](e) dynamics.
View details for Web of Science ID 000087002900007
View details for PubMedID 10793187
Whereas a 2-3 degrees C decrease in intraischemic brain temperature can be neuroprotective, mild brain hyperthermia significantly worsens outcome. Our previous study suggested that an ischemic injury mechanism which is sensitive to temperature may not actually increase the extracellular glutamate concentration ([Glu](e)) during the intraischemic period, but rather impairs the Glu re-uptake system, which has been suggested to be involved in the reversed uptake of Glu. We speculated that enhancing Glu re-uptake, pharmacologically or hypothermically, may shorten exposure to high [Glu](e) in the postischemic period and thereby decrease its deleterious excitotoxic effect on neuronal cells. In the present study, rats treated with nicergoline (32 mg/kg, i.p.), an ergot alkaloid derivative, showed minimal inhibition of the [Glu](e) elevation which characteristically occurs during the 10-min intraischemic period, while Glu re-uptake was dramatically improved in the postischemic period, when severe transient global ischemia was caused by mild hyperthermia. Moreover, the nicergoline (32 mg/kg, i.p.) treated rats showed reduced cell death morphologically and clearly had a far lower mortality. The present study suggests that the development of therapeutic strategies aimed at inhibition or prevention of the reversed uptake of glutamate release during ischemia, i.e., activation of the glutamate uptake mechanism, is a promising approach to reduce neural damage occurring in response to brain ischemia.
View details for Web of Science ID 000083941400006
View details for PubMedID 10594318
Accumulating evidence on the molecular and cellular basis of ischemia/reperfusion-induced neurodegeneration suggests that oxidative stress is involved. Heme oxygenase (HO) and cyclooxygenase (COX) play physiologically important roles in the CNS. Conversely, HO and COX also can increase oxidative stress. Recent studies suggest that c-Jun phosphorylation is an important step in some forms of stress-induced neuronal apoptosis. In this study, the authors tried to clarify the association of HO and COX with c-Jun phosphorylation. Inducible forms of HO and COX (HO-1 and COX-2, respectively) were transiently induced in CA1 pyramidal neurons after ischemia. c-Jun also was induced in pyramidal neurons throughout the hippocampal formation, but its phosphorylation was limited to CA1. In contrast, these molecules were constitutively expressed at low levels. Most (84%) of the CA1 pyramidal neurons examined expressed HO-1, COX-2, or both, and such expression showed good co-localization with c-Jun phosphorylation. These results suggest the following: (1) c-Jun phosphorylation was associated with ischemia/reperfusion-induced neuronal apoptosis; (2) HO-1 and COX-2 were induced in CA1 pyramidal neurons, which undergo cell death; and (3) most CA1 pyramidal neurons expressed HO-1, COX-2, or both, which strongly suggests that these are candidates for neuron killers.
View details for Web of Science ID 000084884000009
View details for PubMedID 10566971
Increased extracellular glutamate ([GLU]e), under the condition of cerebral ischemia, anoxia or hypoxia, has been recognized as being associated with neuronal cell damage and death. We performed real-time monitoring of [GLU]e dynamics in vivo in the rat striatum during systemic acute anoxia or hypoxia, as well as monitoring the direct current potential (DC) and cerebral blood flow (CBF). Adult Wistar rats were orotracheally intubated and artificially ventilated with room air. A microdialysis electrode, temperature sensor probe, DC microelectrode and laser Doppler probe were then implanted. The inspired gas was changed to 100% N(2) (anoxia), or to 3, 5 or 8% O(2) (remainder N(2)) (hypoxia). With 100% N(2), distinct biphasic [GLU]e elevations were observed. With 3% O(2), a transient [GLU]e increase was seen before anoxic depolarization (AD). With 5% O(2), however, the start of the transient [GLU]e increase was significantly delayed. Anoxia-induced depolarization started at about 100 s. The 3% O(2)-induced transient depolarization and AD began at nearly the same time as the transient and AD-induced increase in [GLU]e. Similarly, the responses to 5% O(2) showed significant delays in the transient depolarization and AD-induced increase in [GLU]e. CBF during 3 or 5% O(2) hypoxic insult was consistently maintained above the control level, i.e., prior to cardiac arrest. Our new dialysis electrode method employing both GOX and ferrocene-conjugated bovine serum albumin allowed evaluation of transient [GLU]e dynamics in the early phase of severe hypoxia in vivo.
View details for Web of Science ID 000080939700029
View details for PubMedID 10412006
Both the rise in extracellular glutamate concentration and anoxic depolarization in the rat striatum during 15 min of global ischemia and reperfusion were monitored using glutamate biosensor and direct current potential electrodes, respectively. Cerebral blood flow (CBF) was simultaneously monitored with a glutamate biosensor or a direct current potential electrode. Before the onset of ischemia, treatment with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) decreased CBF, while L-arginine increased CBF. However, neither L-NAME nor L-arginine significantly changed CBF during ischemia and reperfusion compared with vehicle-treated animals. The time-course and extracellular glutamate concentration increase during ischemia and reperfusion among L-NAME-, L-arginine- and vehicle-treated animals were very similar. These results were strengthened by the time-course and amplitude of anoxic depolarization. The study suggests that NO is not an important mediator of glutamate release during ischemia and reperfusion.
View details for Web of Science ID 000079393000021
View details for PubMedID 10203328
Using a dialysis electrode, we recently developed an oxygen-independent system for real-time measurement of the glutamate concentration in the extracellular space ([Glu]e) during ischemia. This system allows separate evaluation of intra-ischemic biphase [Glu]e elevation, i.e. release from synaptic vesicles (1st phase), reversed uptake of glutamate from metabolic pools in neuronal cells (2nd phase), and post-ischemic glutamate re-uptake in ischemia-reperfusion models. Using the system, we attempted to clarify the relationship between biphase glutamate release and brain temperature in a model of acute global ischemia produced by transecting both carotid arteries. Our results showed that, in contrast to mild hyperthermia, hypothermia did not inhibit the 1st phase of [Glu]e release, and changes in intra-ischemic brain temperature had a minimal effect on the 2nd phase of [Glu]e elevation during severe acute ischemia. These findings, together with our previous data, indicate that brain temperature change in the intra-ischemic period plays an important role in disturbance of the glutamate re-uptake system during ischemia.
View details for Web of Science ID 000077790300018
View details for PubMedID 9875719
We simultaneously measured extracellular glutamate ([Glu]e) elevation and local CBF using a real-time monitoring method and laser-Doppler flowmetry, respectively, in the rat striatum in a modified graded global ischemia model. Ischemic brain temperatures were kept at 32 degrees C, 37 degrees C and 39 degrees C. Three distinct types of intraischemic [Glu]e elevation, reflecting mild, moderate and massive glutamate release, were observed. Brain temperature plays an important role in determining CBF thresholds for each of the three types of [Glu]e elevation. CBF thresholds for [Glu]e elevations shifted to a lower level range as brain temperature was reduced. In mild or moderate ischemia, there is no exposure to sustained [Glu]e elevation, which is seen only in relatively severe ischemia characterized by biphasic [Glu]e elevation.
View details for Web of Science ID 000076974600013
View details for PubMedID 9831448
Brain hypothermia during ischemia may have a neuroprotective effect on pathological and functional outcomes in vivo. Although a microdialysis study demonstrated that hypothermia decreases glutamate release into the extracellular space, the issue of whether this suppression of the glutamate elevation normally accompanying ischemia is attributable to inhibition of intra-ischemic release or acceleration of post-ischemic re-uptake was not addressed. Recently, we established a real-time method for monitoring glutamate levels in extracellular space, utilizing a dialysis electrode. This method allows detailed analysis of the in vivo dynamics of biphasic glutamate elevation in the extracellular space during the intra-ischemic period and post-ischemic re-uptake. The present results show that post-ischemic hypothermia has little effect on the initial glutamate release, but remarkably enhances post-ischemic glutamate re-uptake.
View details for Web of Science ID A1997XL18000058
View details for PubMedID 9243646