Ischemia In Rodents Research Articles

Cognitive Impairment with Vascular Impairment and Degeneration

Ischemic stroke is a leading cause of death and cognitive impairment worldwide. However, the mechanisms of progressive cognitive decline following brain ischemia are not yet certain. Ongoing interest in cerebrovascular diseases research has provided data showing that Alzheimer's proteins and other factors may be involved in the pathogenesis of gradual ischemic brain injury. Thus, both focal and global brain ischemia in rodents produces a stereotyped pattern of selective neuronal degeneration, which is just the same as in Alzheimer's type dementia. Data from animal models and clinical studies of ischemic stroke have demonstrated an increase in expression and processing of amyloid precursor protein (APP) to a neurotoxic form of oligomeric β-amyloid peptide (Aβ) and hyperphosphorylation of tau protein. The authors of this review are using advances in methods and technologies to study cerebrovascular diseases and this review examines the hypothesis that pathological mechanisms common to both brain ischemia and Alzheimer's dementia are contributing to cognitive impairment and brain ischemia-related dementia.

Dibucaine Mitigates Spreading Depolarization in Human Neocortical Slices and Prevents Acute Dendritic Injury in the Ischemic Rodent Neocortex

BackgroundSpreading depolarizations that occur in patients with malignant stroke, subarachnoid/intracranial hemorrhage, and traumatic brain injury are known to facilitate neuronal damage in metabolically compromised brain tissue. The dramatic failure of brain ion homeostasis caused by propagating spreading depolarizations results in neuronal and astroglial swelling. In essence, swelling is the initial response and a sign of the acute neuronal injury that follows if energy deprivation is maintained. Choosing spreading depolarizations as a target for therapeutic intervention, we have used human brain slices and in vivo real-time two-photon laser scanning microscopy in the mouse neocortex to study potentially useful therapeutics against spreading depolarization-induced injury.Methodology/Principal FindingsWe have shown that anoxic or terminal depolarization, a spreading depolarization wave ignited in the ischemic core where neurons cannot repolarize, can be evoked in human slices from pediatric brains during simulated ischemia induced by oxygen/glucose deprivation or by exposure to ouabain. Changes in light transmittance (LT) tracked terminal depolarization in time and space. Though spreading depolarizations are notoriously difficult to block, terminal depolarization onset was delayed by dibucaine, a local amide anesthetic and sodium channel blocker. Remarkably, the occurrence of ouabain-induced terminal depolarization was delayed at a concentration of 1 µM that preserves synaptic function. Moreover, in vivo two-photon imaging in the penumbra revealed that, though spreading depolarizations did still occur, spreading depolarization-induced dendritic injury was inhibited by dibucaine administered intravenously at 2.5 mg/kg in a mouse stroke model.Conclusions/SignificanceDibucaine mitigated the effects of spreading depolarization at a concentration that could be well-tolerated therapeutically. Hence, dibucaine is a promising candidate to protect the brain from ischemic injury with an approach that does not rely on the complete abolishment of spreading depolarizations.

Significance of Outer Blood–Retina Barrier Breakdown in Diabetes and Ischemia

The outer blood-retina barrier (BRB) separates the neural retina from the choroidal vasculature, which is responsible for approximately 80% of blood supplies in the eye. To determine the significance of outer BRB breakdown in diabetic retinopathy, the outer BRB-specific leakage of macromolecules in diabetic and ischemic rodents was investigated. Diabetes and ischemia were induced in rodents by streptozotocin and oxygen-induced retinopathy, respectively. Diabetic and ischemic rodents were injected intravenously with fluorescein isothiocyanate (FITC)-dextran. The outer BRB-specific leakage in diabetic and ischemic rodents was visualized by fluorescent microscopy. A microscopic imaging assay was developed to examine outer BRB breakdown. The outer BRB-specific leakage of fluorescent macromolecules was visualized in diabetic and ischemic rodents. Substantial leakages of macromolecules through the outer BRB in diabetic and ischemic rodents were detected with this assay. The number of severe outer BRB leakage sites is inversely proportional to the size of macromolecules. Significant depletion of occludin in the RPE of ischemic and diabetic rodents was also observed. For the first time, a microscopic imaging assay for directly visualizing macromolecules leaked through the outer BRB in rodents was developed. Using this assay, the authors demonstrated the significance of outer BRB breakdown in diabetes and ischemia, which will have implications to the understanding, diagnosis, and treatment of diabetic macular edema and other ocular diseases with outer BRB defects. The microscopic imaging assay established in this study will likely be very useful to the development of drugs for macular edema.

Tests neurológicos para la evaluación del pronóstico funcional en modelos de ictus isquémico en roedores

A critical aspect in all models is the assessment of the final outcome of the modelling procedure. In the case of a focal ischaemic brain injury, apart from the determination of the size of the lesion, another valuable tool is the evaluation of the final functional deficit. Indeed, ischaemic damage leads to the appearance of different degrees of sensoriomotor and cognitive impairments, which may yield useful information on location and size of the lesion and on the efficacy of neuroprotective treatments after the acute injury. In addition, the magnitude of these impairments may also be useful to predict final outcome and to evaluate neuro-restorative therapies in a long-term scenario. To this aim, a wide range of tests has been developed which allow the quantification of all these neurological symptoms. This review intends to compile the most useful behavioural tests designed to assess neurological symptoms in studies of focal experimental cerebral ischemia in rodents induced by middle cerebral artery occlusion, the most commonly used model of ischaemic stroke.

Nascent proteomes of ischemic-injured and ischemic-tolerant neuronal cells

In a recent study on ischemic rodent brains, we quantitatively characterised and compared brain proteomes under ischemic-preconditioned or injured or tolerant conditions. We discovered an enriched presence of repressive transcriptional regulator proteins with essential roles as epigenetic regulators in ischemic-tolerant brains (Stapels et al., 2010). We further showed their robust, dynamic and differential changes under different ischemic conditions in brains and in cultured neuronal cells. In the present work, using neuronal cell cultures, we aimed to characterise the nascent proteome, the proteome that presents early when the cells receive an ischemic insult. These would be the proteomic changes of newly synthesised proteins. Identification of effectors of this phase of response to ischemia bears the best promise of identifying therapeutic targets for treating acute stroke when patients present to hospital. We compared these nascent proteomes across different ischemic conditions using bioinformatic tools.

Functional muscle regeneration with combined delivery of angiogenesis and myogenesis factors

Regenerative efforts typically focus on the delivery of single factors, but it is likely that multiple factors regulating distinct aspects of the regenerative process (e.g., vascularization and stem cell activation) can be used in parallel to affect regeneration of functional tissues. This possibility was addressed in the context of ischemic muscle injury, which typically leads to necrosis and loss of tissue and function. The role of sustained delivery, via injectable gel, of a combination of VEGF to promote angiogenesis and insulin-like growth factor-1 (IGF1) to directly promote muscle regeneration and the return of muscle function in ischemic rodent hindlimbs was investigated. Sustained VEGF delivery alone led to neoangiogenesis in ischemic limbs, with complete return of tissue perfusion to normal levels by 3 weeks, as well as protection from hypoxia and tissue necrosis, leading to an improvement in muscle contractility. Sustained IGF1 delivery alone was found to enhance muscle fiber regeneration and protected cells from apoptosis. However, the combined delivery of VEGF and IGF1 led to parallel angiogenesis, reinnervation, and myogenesis; as satellite cell activation and proliferation was stimulated, cells were protected from apoptosis, the inflammatory response was muted, and highly functional muscle tissue was formed. In contrast, bolus delivery of factors did not have any benefit in terms of neoangiogenesis and perfusion and had minimal effect on muscle regeneration. These results support the utility of simultaneously targeting distinct aspects of the regenerative process.

Combination Treatment with Normobaric Hyperoxia and Cilostazol Protects Mice against Focal Cerebral Ischemia-Induced Neuronal Damage Better Than Each Treatment Alone

Normobaric hyperoxia (NBO) and cilostazol (6-[4-(1-cyclohexy-1H-tetrazol-5-yl)butoxyl]-3,4-dihydro-2-(1H)-quinolinone) (a selective inhibitor of phosphodiesterase 3) have each been reported to exert neuroprotective effects against acute brain injury after cerebral ischemia in rodents. Here, we evaluated the potential neuroprotective effects of combination treatment with NBO and cilostazol against acute and subacute brain injuries after simulated stroke. Mice subjected to 2-h filamental middle cerebral artery (MCA) occlusion were treated with NBO (95% O(2), during the ischemia) alone, with cilostazol (3 mg/kg i.p. after the ischemia) alone, with both of these treatments (combination), or with vehicle. The histological and neurobehavioral outcomes were assessed at acute (1 day) or subacute (7 days) stages after reperfusion. We measured regional cerebral blood flow (rCBF) during and after ischemia by laser-Doppler flowmetry and recovery (versus vehicle) in the combination therapy group just after reperfusion. Mean acute and subacute lesion volumes were significantly reduced in the combination group but not in the two monotherapy groups. The combination therapy increased endothelial nitric-oxide synthase (eNOS) activity in the lesion area after ischemia versus vehicle. Combination therapy with NBO plus cilostazol protected mice subjected to focal cerebral ischemia by improvement of rCBF after reperfusion, in part in association with eNOS activity.

In Vivo Distribution of Liposome‐Encapsulated Hemoglobin Determined by Positron Emission Tomography

Positron emission tomography (PET) is a noninvasive imaging technology that enables the determination of biodistribution of positron emitter-labeled compounds. Lipidic nanoparticles are useful for drug delivery system (DDS), including the artificial oxygen carriers. However, there has been no appropriate method to label preformulated DDS drugs by positron emitters. We have developed a rapid and efficient labeling method for lipid nanoparticles and applied it to determine the movement of liposome-encapsulated hemoglobin (LEH). Distribution of LEH in the rat brain under ischemia was examined by a small animal PET with an enhanced resolution. While the blood flow was almost absent in the ischemic region observed by [(15)O]H(2)O imaging, distribution of (18)F-labeled LEH in the region was gradually increased during 60-min dynamic PET scanning. The results suggest that LEH deliver oxygen even into the ischemic brain from the periphery toward the core of ischemia. The real-time observation of flow pattern, deposition, and excretion of LEH in the ischemic rodent brain was possible by the new methods of positron emitter labeling and PET system with a high resolution.

Potential Molecular Targets for Translational Stroke Research

The stroke research community is currently at a crossroads, and a shift in focus is necessary to propel basic research forward to develop clinically effective therapeutics. In-depth analysis of the past failures and imposing more stringent standards on future basic research experiments will greatly improve the success of translational research. The purpose of this review is to outline proposed revisions in basic research criteria and offer attractive molecular candidates to mitigate brain damage after cerebral ischemia. A major pitfall encompassing translational stroke research is that a majority of clinical trials conducted have focused on agents involving recanalization of vessels and on excitotoxicity to reduce neuronal death in the penumbra.1 Recanalization using tissue plasminogen activator only modestly improves patient outcome, and inhibiting excitotoxicity has shown no clinical benefit.2 The short duration of excitotoxicity after ischemia does not provide an adequate time window for effective stroke therapy in clinical practice because the exact onset of stroke is often indeterminate and a majority of patients do not seek medical treatment for many hours after the insult. A more reasonable therapeutic window, and hence a greater potential for clinical success, is likely to be attained by placing emphasis on ameliorating the effects of the synergistic processes of programmed cell death (PCD) and inflammation that are active for hours to days after ischemia.3 In addition, it is necessary to identify molecular mediators of ischemic neuroprotection suitable for translation to human clinical trials. Accordingly, more stringent criteria for selection of targets are required. The following criteria will facilitate development of translatable …

Abstract 3593: Wild Type Human Tissue Kallikrein, but Not its Common Polymorphic Variant R53H, Promotes Arteriogenesis in Normoperfused and Ischemic Rodent Models.

Therapeutic angiogenesis via administration of recombinant growth factors or vector-mediated overexpression has been largely unsuccessful in part due to the inadequacy of a single growth factor to induce all aspects of vascular growth. We have previously shown that human tissue kallikrein (hK1) promotes angiogenesis by kinin-mediated activation of the Akt-eNOS pathway, independently of VEGF. To further characterise the cellular mechanisms of hK1 induced neovascularisation, we delivered adenovirus encoding the wild type kallikrein gene ( Ad.KLK1 , 5x10 6 or 5x10 5 pfu) or a polymorphic variant ( Ad.R53H-KLK1 ), which is 50% less potent as a kinin generating enzyme, or control virus ( Ad.eGFP ) in the rat mesenteric assay, a non-ischemic model of angiogenesis. In separate experiments, Ad.KLK1 was injected into the mesentery of rats given the bradykinin-2-receptor (B2R) antagonist, Icatibant (Subc 300nmol/kg/day). Intravital and confocal imaging was used to examine vessel morphology and histology. Ad.KLK1 increased the functional vessel area (445±76 vs 32±4% in Ad.eGFP, p<0.01), conduit vessel density (193±12 vs 63±7mm −2 , p<0.001) and average vessel diameter (15±1 vs 12.6±1μm, p<0.001). Ad.KLK1 -induced neovasculature showed an increased pericyte (58±5% vs 31±5, p<0.05) and smooth muscle cell coverage (4±1 vs 0%, p<0.001). In addition, we found that B2R co-localises with pericytes in the mesentery. Following Icatibant, Ad.KLK1 stimulated the formation of a network of small-size vessels, without pericyte or smooth muscle cell coverage and surrounded by spots of micro-hemorrhaging. Ad.R53H-KLK1 was less efficient than Ad.KLK1 in promoting angiogenesis and recruiting vascular smooth muscle cells. In a model of limb ischemia, disruption of the kallikrein gene resulted in dysfunctional reparative arteriogenesis and delayed hemodynamic recovery, which were both corrected by local Ad.KLK1 but not by Ad.R53H-KLK1. These data provide a mechanistic explanation for the robust arteriogenic effect of Ad.KLK1 , indicating a key role for the kinin B2R. We also demonstrate for the first time that a single nucleotide polymorphism in the KLK1 gene, present in 5–7% of the Caucasian population, leads to a reduced neovascularisation in-vivo . All data mean±SEM, n=6

Role of PACAP in Ischemic Neural Death

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that was first isolated from an ovine hypothalamus in 1989. Since its discovery, more than 2,000 papers have reported on the tissue and cellular distribution and functional significance of PACAP. A number of papers have reported that PACAP but not the vasoactive intestinal peptide suppressed neuronal cell death or decreased infarct volume after global and focal ischemia in rodents, even if PACAP was administered several hours after ischemia induction. In addition, recent studies using PACAP gene-deficient mice demonstrated that endogenous PACAP also contributes greatly to neuroprotection similarly to exogenously administered PACAP. The studies suggest that neuroprotection by PACAP might extend the therapeutic time window for treatment of ischemia-related conditions, such as stroke. This review summarizes the effects of PACAP on ischemic neuronal cell death, and the mechanism clarified in vivo ischemic studies. In addition, the prospective mechanism of PACAP on ischemic neuroprotection from in vitro neuronal and neuronal-like cell cultures with injured stress model is reviewed. Finally, the development of PACAP and/or receptor agonists for human therapy is discussed.

Biomarker evidence for mild central nervous system injury after surgically-induced circulation arrest

Previously, we identified 14-3-3 β and ζ isoforms and proteolytic fragments of α-spectrin as proteins released from degenerating neurons that also rise markedly in cerebrospinal fluid (CSF) following experimental brain injury or ischemia in rodents, but these proteins have not been studied before as potential biomarkers for ischemic central nervous system injury in humans. Here we describe longitudinal analysis of these proteins along with the neuron-enriched hypophosphorylated neurofilament H (pNFH) and the deubiquitinating enzyme UCH-L1 in lumbar CSF samples from 19 surgical cases of aortic aneurysm repair, 7 involving cardiopulmonary bypass with deep hypothermic circulatory arrest (DHCA). CSF levels of the proteins were near the lower limit of detection by Western blot or enzyme-linked fluorescence immunoassay at the onset of surgical procedures, but increased substantially in a subset of cases, typically within 12–24 h. All cases involving DHCA were characterized by > 3-fold elevations in CSF levels of the two 14-3-3 isoforms, UCH-L1, and pNFH. Six of 7 also exhibited marked increases in α-spectrin fragments generated by calpain, a protease known to trigger necrotic neurodegeneration. Among cases involving aortic cross-clamping but not DHCA, the proteins rose in CSF preferentially in the subset experiencing acute neurological complications. Our results suggest the neuron-enriched 14-3-3β, 14-3-3ζ, pNFH, UCH-L1, and calpain-cleaved α-spectrin may serve as a panel of biomarkers with clinical potential for the detection and management of ischemic central nervous system injury, including for mild damage associated with surgically-induced circulation arrest.

A selective, non-peptide caspase-1 inhibitor, VRT-018858, markedly reduces brain damage induced by transient ischemia in the rat

Numerous preclinical studies have reported neuroprotective effects of new agents in animal studies. None of these agents has yet translated into a successful clinical trial and therefore to a new therapy. There are many possible reasons for this failure, including poor design of clinical trials, mismatch between preclinical and clinical protocols, and insufficient preclinical data. The enzyme caspase-1 has been implicated in neuronal death. Deletion of the caspase-1 gene, or administration of partially selective inhibitors, reduces neuronal injury induced by cerebral ischemia in rodents. We report here, for the first time, that VRT-018858, the non-peptide, active metabolite of the selective caspase-1 inhibitor pro-drug, pralnacasan, markedly reduced ischemic injury in rats. VRT-018858 was neuroprotective when delivered at 1 and 3 h (42% and 58% neuroprotection, respectively) but not 6 h after injury, and protection was sustained 7 days after the induction of ischemia (66% neuroprotection). These data confirm caspase-1 as an important target for intervention in acute CNS injury, and propose a new class of caspase-1 inhibitors as highly effective neuroprotective agents.

An extended window of opportunity for G-CSF treatment in cerebral ischemia.

BackgroundGranulocyte-colony stimulating factor (G-CSF) is known as a powerful regulator of white blood cell proliferation and differentiation in mammals. We, and others, have shown that G-CSF is effective in treating cerebral ischemia in rodents, both relating to infarct size as well as functional recovery. G-CSF and its receptor are expressed by neurons, and G-CSF regulates apoptosis and neurogenesis, providing a rational basis for its beneficial short- and long-term actions in ischemia. In addition, G-CSF may contribute to re-endothelialisation and arteriogenesis in the vasculature of the ischemic penumbra. In addition to these trophic effects, G-CSF is a potent neuroprotective factor reliably reducing infarct size in different stroke models.ResultsHere, we have further delayed treatment and studied effects of G-CSF on infarct volume in the middle cerebral artery occlusion (MCAO) model and functional outcome in the cortical photothrombotic model. In the MCAO model, we applied a single dose of 60 μg/kg bodyweight G-CSF in rats 4 h after onset of ischemia. Infarct volume was determined 24 h after onset of ischemia. In the rat photothrombotic model, we applied 10 μg/kg bodyweight G-CSF daily for a period of 10 days starting either 24 or 72 h after induction of ischemia. G-CSF both decreased acute infarct volume in the MCAO model, and improved recovery in the photothrombotic model at delayed timepoints.ConclusionThese data further strengthen G-CSF's profile as a unique candidate stroke drug, and provide an experimental basis for application of G-CSF in the post-stroke recovery phase.

Extended therapeutic time window after focal cerebral ischemia by non-competitive inhibition of AMPA receptors

In acute stroke, the therapeutic time window is a critical factor which may have contributed to the failure of several phase III clinical trials with so-called neuroprotective agents. Since cerebral glutamate levels are elevated for many hours in progressing stroke, we investigated the novel AMPA glutamate receptor antagonist ZK 187638 in rodent models of stroke using up to 12 h delays in the start of therapy after permanent occlusion of the middle cerebral artery (MCA). In rats, ZK 187638 reduced total infarct volume by 43% and 33% when therapy was started immediately or with a delay of 6 h, respectively, but no effect was observed after a 12 h delay. Dose-dependent decreases of total infarct volume (up to 42%) were measured in mice given the first injection of ZK 187638 6 h after permanent MCA occlusion. In conclusion, the AMPA receptor antagonist ZK 187638 has a therapeutic time window of at least 6 h after permanent focal cerebral ischemia in rodents.

A novel model of acute murine hind limb ischemia

I. Introduction: The McGivney Hemorrhoidal Ligator band (MHL) is an established model of tourniquet induced hind-limb ischemia-reperfusion (IR) injury in rodents. The MHL model has been criticized for its inability to control for confounding factors such as crush injury and neurological damage to the area directly below the rubber band. This problem may be avoided, if complete hind-limb ischemia could be induced with minimal tension. These experiments were designed to (1) define and compare the ex-vivo force generated by the MHL as compared to Orthodontic Rubber Bands (ORB) of different diameters over a 3 hour period; (2) determine whether MHL and ORB create similar grades of in-vivo limb ischemia as measured by Laser Doppler Imaging (3); correlate the tension produced by the MHL and ORB with neurological assessment of murine hind limbs. The overall goal of these experiments is to determine whether orthodontic rubber bands (ORBs) provide an alternate, specific model of complete hind-limb ischemia by generating significantly less force and non-specific neurologic injury than previously established models. II. Methods: Ex- vivo force measurements were performed on 1/8” internal diameter 4.0 oz. ORB and MHL by mounting the bands on circular rods of varying sizes (0.86 and 1.04 cm), secured onto a magnetic-based micromanipulator. Force was then measured using a tensiometer which stretched each mounted band exactly 1 mm. Measurements were done in duplicate and the bands remained on the rods for 90 minutes to evaluate force decay. The in-vivo consequences of limb ischemia documented by applying ORBs and MHL to the hind limbs of anesthetized C57BL6 mice (25-30g, which were then scanned with Laser Doppler Imaging to confirm ischemia for at least 90 minutes. Once complete ischemia was confirmed for 90 minutes, the limbs were reperfused for 24 hours and subjected to neurologic scoring (paralysis, gait) by two blinded observers. III. Results: The force generated by the 4 oz. ORBs and MHL bands were significantly different (MHL: 0.28 + 0.009 vs. ORB: 0.08 + 0.002 kg, p= 0.0079) at 90 minutes. Variations in rod diameter (0.86 vs. 1.04 cm), did not affect the amount of force applied by the 4 oz ORB (p = .5141); In contrast, the force applied by the MHL varied significantly between these two measured diameters (p=0.0248). There was no significant decay in the force applied by the 4.0 oz. ORB up to 90 minutes (p = 0.1862); whereas the MHL showed significant force decay (p=0.0085). Absolute flux measurements compared to baseline perfusion, using LDI showed significant reduction in flow for both the 4 oz. (n = 10, p < 0.0001) ORB and MHL (n = 10, p < 0.0001). Furthermore, the degree of ischemia was equivalent in both ORB and MHL mice-(MHL: 50.1 + 5.6 vs. ORB: 36 + 6.3 flux units, p = 0.1431). At 24 hours reperfusion, the neurological score in MHL mice was significantly worse than ORB mice (MHL: 2.9 + 0.1, ORB: 1.8 + 0.3, p = 0.0137). IV. Conclusion: MHL bands deliver erratic and excessive force to create limb ischemia in rodents. The excessive force may promote non-ischemic neurologic injury, which may be related primarily to crush injury. The ORB provides and attractive alternative to the MHL, and thus may decrease experimental artifacts in studies of rodent hind limb ischemia reperfusion.

Effects of Estrogen on Platelet Reactivity After Transient Forebrain Ischemia in Rats

Estrogen's prothrombotic effects are of increasing concern, particularly in stroke risk and recovery. Using an ischemic rodent model, the authors sought to determine (a) if estrogen replacement increases postischemic platelet reactivity, (b) if changes in estrogen status alter intraplatelet endothelial nitric oxide synthase (eNOS) synthesis, and (c) if estrogen-mediated effects on platelets alter cerebral blood flow during reperfusion. Intact (I), ovariectomized (OVX), and OVX + 17 beta-estradiol (E50) rats were subjected to 30 min of forebrain ischemia and 60 min of reperfusion. Using the platelet activation marker P-selectin, postischemic platelet reactivity was quantified by flow cytometry. In a separate cohort (I, OVX, E50), the authors quantified platelet eNOS by Western blot. Another cohort (OVX, E50) was subjected to ischemia/reperfusion, and cerebral blood flow was determined using the iodoantipyrine technique. Collagen-stimulated platelet P-selectin expression was increased in the OVX rats at 60 min of reperfusion, and this effect was reversed by estrogen treatment. No differences in platelet eNOS expression were detected among groups. Cerebral blood flow at 60 min reperfusion was comparable between the OVX and the E50 rats. The authors conclude that during reper-fusion, estrogen deficiency increases postischemic platelet sensitivity to stimuli in estrogen-deficient rats. Estrogen treatment mitigates effects of estrogen loss on platelets, but this early effect is apparently not caused by intraplatelet eNOS depression. Neither estrogen deficiency nor estrogen treatment changes early postischemic regional brain blood flow. In this rodent global cerebral ischemic model, physiologic doses of estrogen are not deleterious to platelet reactivity and may initially reduce postischemic platelet reactivity.

Oxidative Stress and Neuronal Death/Survival Signaling in Cerebral Ischemia

It has been demonstrated by numerous studies that apoptotic cell death pathways are implicated in ischemic cerebral injury in ischemia models in vivo. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and the numerous reports suggest the involvement of cell survival/death signaling pathways in the pathogenesis of apoptotic cell death in ischemic lesions. In these models, reoxygenation during reperfusion provides oxygen as a substrate for numerous enzymatic oxidation reactions and for mitochondrial oxidative phosphorylation to produce adenosine triphosphate. Oxygen radicals, the products of these biochemical and physiological reactions, are known to damage cellular lipids, proteins, and nucleic acids and to initiate cell signaling pathways after cerebral ischemia. Genetic manipulation of intrinsic antioxidants and factors in the signaling pathways has provided substantial understanding of the mechanisms involved in cell death/survival signaling pathways and the role of oxygen radicals in ischemic cerebral injury. Future studies of these pathways could provide novel therapeutic strategies in clinical stroke.

Mitochondria and Neuronal Death/Survival Signaling Pathways in Cerebral Ischemia

Apoptotic cell death pathways have been implicated in acute brain injuries, including cerebral ischemia, brain trauma, and spinal cord injury, and in chronic neurodegenerative diseases. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and suggest the involvement of mitochondria and the cell survival/death signaling pathways in cell death/survival cascades. Recent studies have implicated mitochondria-dependent apoptosis involving pro- and antiapoptotic protein binding, the release of cytochrome c and second mitochondria-derived activator of caspase, the activation of downstream caspases-9 and -3, and DNA fragmentation. Reactive oxygen species are known to be significantly generated in the mitochondrial electron transport chain in the dysfunctional mitochondria during reperfusion after ischemia, and are also implicated in the survival signaling pathway that involves phosphatidylinositol-3-kinase (PI3-K), Akt, and downstream signaling molecules, like Bad, 14-3-3, and the proline-rich Akt substrate (PRAS), and their bindings. Further studies of these survival pathways may provide novel therapeutic strategies for clinical stroke.

Differential expression of chemokines and chemokine receptors during microglial activation and inhibition

Intrauterine infection produces an inflammatory response in the fetus characterized by increased inflammatory cytokines in the fetal brain and activation of brain microglial cells. Intrauterine infection can release bacterial cell wall products into the fetal circulation. Lipopolysaccharides (LPS) are derived from the cell walls of gram negative organisms. The degree of microglial cell activation may influence the extent of brain injury following an inflammatory stimulus. Chemokines, which are released by activated microglia, regulate the influx of inflammatory cells to the brain. Accordingly, therapeutic strategies that reduce the extent of chemokine expression in microglial cells may prove neuroprotective. Minocycline (MN), a semisynthetic tetracycline derivative, protects brain against global and focal ischemia in rodents and inhibits microglial cell activation. To determine if minocycline can reduce the production of chemokines and chemokine receptors in response to LPS, microglial-like BV-2 and HAPI cells were cultured in the presence or absence of 100 ng/ml of LPS. Enzyme-linked immunosorbent assay (ELISA) and semi-quantitative RT-PCR were used to examine changes in inflammatory chemokines (macrophage inflammatory protein-1 (MIP-1α), regulated upon activation, normal T cell expressed and secreted (RANTES), and inducible protein-10 (IP-10)) and chemokine receptor (C-C chemokine receptor 5 (CCR5) and C-X-C chemokine receptor 3 (CXCR3)) production, respectively. We found that in both cell lines chemokine release after 4-, 8-, and 16-h exposure to LPS was significantly higher compared to non-exposed cells for all the chemokines measured, P<0.001. Minocycline inhibited chemokine release of LPS-stimulated BV-2 cells. There was even greater inhibition (up to 50%) of mRNA expression after exposure to LPS ( P<0.001). We conclude that endotoxin enhanced the expression of chemokines and chemokine receptors in microglial-like cell lines. Modulation of this expression was achieved with minocycline. Recognition of the mechanisms whereby minocycline exerts its anti-inflammatory effect on microglia may uncover specific targets for pharmacologic intervention.