Biomedical subjects

Midori A Yenari

Publications and source records attributed to Midori A Yenari.

At least 19 recordsLinked to original sources

PubMed2007

Therapeutic hypothermia: neuroprotective mechanisms.

Hypothermia has long been known to be a potent putative neuroprotectant. Experimental evidence and clinical experience show that hypothermia protects the brain from cerebral injury. Recent insights into the mechanisms of cerebral ischemia and reperfusion suggest reasons why hypothermia may be an ideal modality for stroke therapy. Hypothermia protects brain tissue in multiple ways. It retards energy depletion, reduces intracellular acidosis, lessens the ischemia related accumulation of excitotoxic neurotransmitters, and attenuates the influx of intracellular calcium. Additionally, hypothermia suppresses the generation of oxygen free radicals involved in secondary damage associated with reperfusion. It also suppresses the mechanisms related to blood-brain barrier degeneration and postischemic remodeling. The clinical application of therapeutic hypothermia and its limitations will be summarized in this paper. Therapeutic hypothermia is likely to undergo phase III clinical trials in various clinical settings. Novel technologies are being developed to optimize the safety and efficacy of this promising approach.

Blood Coagulation↗

PubMed2006

The inflammatory response in stroke.

Recent works in the area of stroke and brain ischemia has demonstrated the significance of the inflammatory response accompanying necrotic brain injury. Acutely, this response appears to contribute to ischemic pathology, and anti-inflammatory strategies have become popular. This chapter will discuss the current knowledge of the contribution of systemic and local inflammation in experimental stroke. It will review the role of specific cell types including leukocytes, endothelium, glia, microglia, the extracellular matrix and neurons. Intracellular inflammatory signaling pathways such as nuclear factor kappa beta and mitogen-activated protein kinases, and mediators produced by inflammatory cells such as cytokines, chemokines, reactive oxygen species and arachidonic acid metabolites will be reviewed as well as the potential for therapy in stroke and hypoxic-ischemic injury.

Animals↗

PubMed2006

Effects of high dose of simvastatin on levels of dopamine and its reuptake in prefrontal cortex and striatum among SD rats.

Statins are increasingly being used for the treatment of a variety of conditions beyond their original indication for cholesterol lowering. We previously reported that simvastatin increased dopamine receptors in the rat prefrontal cortex [Q. Wang, W.L. Ting, H. Yang, P.T. Wong, High doses of simvastatin upregulate dopamine D(1) and D(2) receptor expression in the rat prefrontal cortex: possible involvement of endothelial nitric oxide synthase, Br. J. Pharmacol. 144 (2005) 933-939] and restored its downregulation in a model of Parkinson's disease (PD) [Q. Wang, P.H. Wang, C. McLachlan, P.T. Wong, Simvastatin reverses the downregulation of dopamine D1 and D2 receptor expression in the prefrontal cortex of 6-hydroxydopamine-induced Parkinsonian rats, Brain Res. 1045 (2005) 229-233]. Here we explore the effects of simvastatin treatment on tissue dopamine content and reuptake. Sprague-Dawley rats were given simvastatin (1 and 10 mg kg(-1)day(-1), p.o.) for 4 weeks. Brain tissue from prefrontal cortex and striatum were taken out for dopamine content and its reuptake. Using high-performance liquid chromatographic-mass spectrometer (HPLC-MS), simvastatin (10 mg kg(-1)day(-1)) was found to increase dopamine content by 110% in the striatum but decreased by 76% in the prefrontal cortex compared with the saline treated group. Dopamine (DA) reuptake was unchanged in both brain regions. These results suggest that chronic treatment with high dose of simvastatin may affect DA tissue level in prefrontal cortex and striatum without changing on DA reuptake. This may have important clinical implications in psychiatric and striatal dopaminergic disorders.

Analysis of Variance↗

PubMed2006

Influence of hypothermia on post-ischemic inflammation: role of nuclear factor kappa B (NFkappaB).

Mild hypothermia is one of the most robust neuroprotectant studied in the laboratory to date. The reasons for this protective effect are likely multifactorial, but work from our laboratory and others have shown that this protection is associated with remarkable suppression of the inflammatory response that accompanies brain ischemia. Consistently, laboratories have shown that small decreases in brain temperature to 30-34 degrees C result in reduced inflammatory cell infiltrate, less microglial activation, and reduction of a variety of inflammatory mediators such as nitric oxide, inflammatory cytokines and superoxide. Nuclear factor-kappaB (NFkappaB) is a transcription factor that is activated after cerebral ischemia. NFkappaB activation leads to the expression of many inflammatory genes involved in the pathogenesis of stroke. Our laboratory has shown that hypothermia decreases NFkappaB translocation and binding activity, by affecting NFkappaB regulatory proteins. Mild hypothermia appears to suppress phosphorylation of NFkappaB's inhibitory protein (IkappaB-alpha) by decreasing expression and activity of IkappaB kinase-gamma (IKK). As a consequence, hypothermia suppressed gene expression of two NFkappaB target genes, inducible nitric oxide synthase and TNF-alpha. These data suggest that the protective effect of hypothermia on cerebral injury is, in part, related to NFkappaB inhibition due to decreased activity of IKK.

Animals↗

PubMed2006

Microglia potentiate damage to blood-brain barrier constituents: improvement by minocycline in vivo and in vitro.

BACKGROUND: Blood-brain barrier (BBB) disruption after stroke can worsen ischemic injury by increasing edema and causing hemorrhage. We determined the effect of microglia on the BBB and its primary constituents, endothelial cells (ECs) and astrocytes, after ischemia using in vivo and in vitro models. METHODS AND RESULTS: Primary astrocytes, ECs, or cocultures were prepared with or without added microglia. Primary ECs were more resistant to oxygen-glucose deprivation/reperfusion than astrocytes. ECs plus astrocytes showed intermediate vulnerability. Microglia added to cocultures nearly doubled cell death. This increase was prevented by minocycline and apocynin. In vivo, minocycline reduced infarct volume and neurological deficits and markedly reduced BBB disruption and hemorrhage in mice after experimental stroke. CONCLUSIONS: Inhibition of microglial activation may protect the brain after ischemic stroke by improving BBB viability and integrity. Microglial inhibitors may prove to be an important treatment adjunct to fibrinolysis.

Acetophenones↗

PubMed2006

The application of HSP70 as a target for gene therapy.

The 70-kDa heat shock proteins (HSP70s) are well-studied and characterized heat shock proteins (HSPs). They constitute essential components of a quality control system of protein synthesis, and function as molecular chaperones to prevent proteins from misfolding and aggregating during both de novo synthesis and under conditions of stress. Moreover, it is now well established that HSP70s play important cytoprotective roles in various pathological settings. Recognition of molecular chaperone and cytoprotective functions of HSP70s is fostering active investigations into the potential of HSP70s as therapeutic targets at the laboratory level. Gaining insight into these recent advances may have profound implications in the development of HSP70-based clinical studies.

Adenosine Triphosphatases↗

PubMed2005

Biphasic cytochrome c release after transient global ischemia and its inhibition by hypothermia.

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.

Animals↗

PubMed2005

Antiapoptotic and anti-inflammatory mechanisms of heat-shock protein protection.

We and others have previously shown that heat-shock proteins (HSPs) are involved in protecting the brain from a variety of insults including stroke, epilepsy, and other related insults. While the mechanism of this protection has largely been thought to be due to their chaperone functions (i.e., preventing abnormal protein folding or aggregation), recent work has shown that HSPs may also directly interfere with other cell death pathways such as apoptosis and inflammation. Using models of cerebral ischemic and ischemia-like injury, we overexpressed the 70-kDa heat-shock protein (HSP70) using gene transfer or by studying a transgenic mouse model. HSP70 protected neurons and astrocytes from experimental stroke and stroke-like insults. HSP70 transgenic mice also had better neurological scores following experimental stroke compared to their wild-type littermates. Overexpressing HSP70 was associated with less apoptotic cell death and increased expression of the antiapoptotic protein, Bcl-2. Furthermore, HSP70 suppressed microglial/monocyte activation following experimental stroke. HSP70 overexpression also led to the reduction of matrix metalloproteinases. We suggest that HSPs are capable of protecting brain cells from lethal insults through a variety of mechanisms and should be explored as a potential therapy against stroke and other neurodegenerative diseases.

Animals↗

PubMed2005

Gene therapy in neurological disease.

Advances in the area of stroke and other neurodegenerative disorders have identified a variety of molecular targets for potential therapeutic intervention. The use of modified viral vectors has now made it possible to introduce foreign DNA into central nervous system cells, permitting overexpression of the protein of interest. A particular advantage of the herpes simplex system is that the herpes virus is neurotropic and is therefore suited for gene therapy to the nervous system. The vectors used by our group to date utilize an amplicon-based bipromoter system, which permits expression of both the gene of interest and a reporter gene. Using this strategy, we have been successful in transferring potentially neuroprotective genes to individual central nervous system cells. Using this approach, it is possible to show that gene therapy both before and after insult is feasible. Some limitations of this technique exist, the main one being delivery and extent of transfection. Although application to clinical stroke is probably remote, viral vector-mediated gene therapy provides a unique and powerful tool in the study of molecular mechanisms involved in brain injury.

Animals↗

PubMed2005

Mild hypothermia decreases GSK3beta expression following global cerebral ischemia.

INTRODUCTION: The serine/threonine kinase glycogen synthase kinase 3beta (GSK3beta) is abundant in the central nervous system and is neuron-specific. GSK3beta plays a pivotal role in the regulation of numerous cellular functions (including phosphorylation) and, thereby, regulation of many metabolic, signaling, and structural proteins as well as transcription factors that can influence cell survival. This article reports that GSK3beta expression following global cerebral ischemia (GCI) is altered by the neuroprotectant, mild hypothermia (33 degrees C). METHODS: Male Sprague-Dawley rats were anesthetized and subjected to GCI; arterial blood pressure was reduced to 30 mmHg by blood withdrawal via the jugular vein, and both common carotid arteries were occluded with aneurysm clips for 8 minutes. Hypothermia (33 degrees C) was induced in half the rats 10 minutes prior to GCI and was maintained for 3 hours. Rats were killed 24 or 72 hours later to assess cell death and GSK3beta expression. RESULTS: At 72 hours post-GCI, levels of GSK3beta expression were significantly lower in hypothermic rats than in normothermic rats. This reduction in GSK3beta correlated with marked neuroprotection and reduced terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling staining in hippocampal CA1 neurons. No significant changes in phosphorylated GSK3beta expression were observed. CONCLUSION: These data suggest that GSK3beta plays a role in GCI pathology that can be altered by mild hypothermia.

Animals↗

PubMed2005

Reduction in levels of matrix metalloproteinases and increased expression of tissue inhibitor of metalloproteinase-2 in response to mild hypothermia therapy in experimental stroke.

OBJECT: Mild hypothermia is a robust neuroprotectant, and the results of prospective clinical trials have indicated that it may improve neurological outcome in certain instances. One aspect of this protection has been associated with the prevention of blood-brain barrier (BBB) disruption. Matrix metalloproteinases (MMPs) have been implicated in BBB disruption because they can degrade the extracellular matrix. In this study the authors explored the relationship between hypothermia and MMPs and whether BBB preservation resulting from mild hypothermia therapy is due to alterations in MMP expression. METHODS: Rats were subjected to middle cerebral artery occlusion for 2 hours; the animals were maintained in a state of normothermia or mild hypothermia (33 degrees C) immediately after the onset of ischemia. The animals' brains were collected 2, 6, and 24 hours after ischemia began. Contrast-enhanced T1-weighted magnetic resonance imaging was performed at 24 hours to assess the extent of BBB disruption. Consistent with prior reports, areas of BBB disruption detected on T1-weighted images were smaller in the brains of rats maintained in a state of hypothermia (normothermia group 8.6 +/- 3% of the brain; hypothermia group 0.2 +/-0.1% of the brain; p < 0.01). Expression of both MMP-2 and MMP-9 at the transcriptional and translational levels was reduced in hypothermic brains at 6 hours and 24 hours after ischemic injury. Matrix metalloproteinase-9 was primarily localized to cells of monocytic origin but was also observed in neurons and astrocytes. Matrix metalloproteinase-2 was found in some neurons and astrocytes but not in inflammatory cells. In addition, hypothermia increased the levels of the endogenous MMP inhibitor, tissue inhibitor of metalloproteinases-2. CONCLUSIONS: The authors conclude that mild hypothermia attenuates BBB disruption, decreases MMP expression, and suppresses MMP activity.

Animals↗

PubMed2004

Protein kinase C delta mediates cerebral reperfusion injury in vivo.

Protein kinase C (PKC) has been implicated in mediating ischemic and reperfusion damage in multiple organs. However, conflicting reports exist on the role of individual PKC isozymes in cerebral ischemic injury. Using a peptide inhibitor selective for deltaPKC, deltaV1-1, we found that deltaPKC inhibition reduced cellular injury in a rat hippocampal slice model of cerebral ischemia [oxygen-glucose deprivation (OGD)] when present both during OGD and for the first 3 hr of reperfusion. We next demonstrated peptide delivery to the brain parenchyma after in vivo delivery by detecting biotin-conjugateddeltaV1-1 and by measuring inhibition of intracellular deltaPKC translocation, an indicator of deltaPKC activity. Delivery of deltaV1-1 decreased infarct size in an in vivo rat stroke model of transient middle cerebral artery occlusion. Importantly, deltaV1-1 had no effect when delivered immediately before ischemia. However, delivery at the onset, at 1 hr, or at 6 hr of reperfusion reduced injury by 68, 47, and 58%, respectively. Previous work has implicated deltaPKC in mediating apoptotic processes. We therefore determined whether deltaPKC inhibition altered apoptotic cell death or cell survival pathways in our models. We found that deltaV1-1 reduced numbers of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells, indicating decreased apoptosis, increased levels of phospho-Akt, a kinase involved in cell survival pathways, and inhibited BAD (Bcl-2-associated death protein) protein translocation from the cell cytosol to the membrane, indicating inhibition of proapoptotic signaling. These data support a deleterious role for deltaPKC during reperfusion and suggest that deltaV1-1 delivery, even hours after commencement of reperfusion, may provide a therapeutic advantage after cerebral ischemia.

Animals↗

PubMed2004

Therapeutic hypothermia for acute ischemic stroke: what do laboratory studies teach us?

BACKGROUND AND PURPOSE: The significance of brain temperature to outcome in cerebral ischemia is recognized. Numerous variations of depth, duration, and delay of cooling have been studied in animal models. It is important to become familiar with these studies to design appropriate clinical trials. With that in mind, a critical review of the pertinent literature is presented, taking into consideration potential limitations in translating such laboratory work to the clinical level. METHODS: Hypothermia is an especially robust neuroprotectant in the laboratory and has been shown to alter many of the damaging effects of cerebral ischemia. Most laboratory research on therapeutic cooling in cerebral ischemia has been conducted in rodent models of temporary and permanent middle cerebral artery occlusion and report the effects of mild or moderate hypothermia arranged during or after ischemia. RESULTS: Intraischemic cooling vastly reduces infarct size in most occlusion models. Tissue salvage with delayed onset of cooling is less dramatic but is commonly observed when cooling is begun within 60 minutes of stroke onset in permanent and 180 minutes of stroke onset in temporary occlusion models. Prolonged postischemic cooling further enhances efficacy. CONCLUSIONS: Laboratory studies have shown that intraischemic hypothermia is more protective than postischemic hypothermia and more benefit is conferred with temporary occlusion than permanent occlusion models. The efficacy of postischemic hypothermia is critically dependent on the duration and depth of hypothermia and its timing relative to ischemia.

Acute Disease↗

PubMed2004

Catalase over-expression protects striatal neurons from transient focal cerebral ischemia.

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.

Animals↗

PubMed2004

The 70 kDa heat shock protein suppresses matrix metalloproteinases in astrocytes.

The 70 kDa heat shock protein (Hsp70) is synthesized in response to a variety of stresses, including ischemia, and is thought to act as a molecular chaperone to prevent protein denaturation and facilitate protein folding. Matrix metalloproteinases (MMPs), a family of serine proteases, are also upregulated by ischemia and are thought to promote cell death and tissue injury. We examined the influence of Hsp70 on expression and activity of MMPs. Astrocyte cultures were prepared from neonatal mice and transfected with retroviral vectors containing hsp70 or lacZ or mock infected, then exposed to oxygen-glucose deprivation followed by reperfusion. Zymograms and Western blots showed that Hsp70 over-expression suppressed MMP-2 and MMP-9. These findings suggest that Hsp70 may protect by regulating MMPs.

Animals↗

PubMed2004

Mild postischemic hypothermia prolongs the time window for gene therapy by inhibiting cytochrome C release.

BACKGROUND AND PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Postischemic mild hypothermia extended the time window for gene therapy neuroprotection using Bcl-2 and reduced cytochrome c release.

Animals↗

PubMed2004

Glycogen synthase kinase 3beta inhibitor Chir025 reduces neuronal death resulting from oxygen-glucose deprivation, glutamate excitotoxicity, and cerebral ischemia.

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.

Animals↗

PubMed2004

Many mechanisms for hsp70 protection from cerebral ischemia.

Overexpression of inducible Hsp70 has been shown to provide protection from cerebral ischemia both in animal models of stroke and in cell culture models. New work suggests that there are multiple routes of cell death, including apoptotic and necrotic cell death. Hsp70 is known to protect from both necrotic and apoptotic cell death. In addition to the well-studied role of Hsp70 as a molecular chaperone assisting in correct protein folding, several new mechanisms by which Hsp70 can prevent cell death have been described. Hsp70 is now known to regulate apoptotic cell death both directly by interfering with the function of several proteins that induce apoptotic cell death as well as indirectly by increasing levels of the anti-death protein bcl-2. Despite these new insights into the ways in which Hsp70 functions as an anti-death protein, further surprises are likely as we continue to gain insight into the functioning of this multifaceted protein.

Animals↗