Ischemic Border Research Articles

Vascular endothelial growth factor-B expression in postischemic rat brain

BackgroundVascular endothelial growth factor-B (VEGF-B) protects against experimental stroke, but the effect of stroke on VEGF-B expression is uncertain.MethodsWe examined VEGF-B expression by immunohistochemistry in the ischemic border zone 1–7 days after middle cerebral artery occlusion in rats.ResultsVEGF-B immunoreactivity in the border zone was increased after middle cerebral artery occlusion and was associated with neurons and macrophages/microglia, but not astrocytes or endothelial cells.ConclusionsThese findings provide additional evidence for a role of VEGF-B in the endogenous response to cerebral ischemia.

Neuroprotective effects of focal brain cooling on photochemically-induced cerebral infarction in rats: Analysis from a neurophysiological perspective

Although systemic hypothermia provides favorable outcomes in stroke patients, it has only been adopted in a limited number of patients because of fatal complications. To resolve these issues, focal brain cooling (FBC) has recently drawn attention as a less-invasive treatment for brain injuries. Therefore, we investigated whether FBC has a favorable effect on focal cerebral ischemia (FCI). Male-adult-Wistar rats were used. Under general anesthesia, a small burr hole was made and FCI was induced in the primary sensorimotor area (SI-MI) using photothrombosis. An additional craniotomy was made over the SI-MI and FBC was performed at a temperature of 15°C for 5h. Electrocorticograms (ECoG) were recorded on the border cortex of the ischemic focus. Thereafter, rats were sacrificed and the infarct area was measured. In another experiment, rats were allowed to recover for 5 days after cooling and neurobehavioral function was evaluated. FBC suppressed all ECoG frequency bands during and after cooling (p<0.05), except for the delta frequency band in the precooling versus rewarming periods. The injured areas in the cooling and non-cooling groups were 0.99±0.30 and 1.71±0.54mm2, respectively (p<0.03). The grip strength at 2 days after surgery was preserved in the cooling group (p<0.05). We report the novel finding that epileptiform discharges were suppressed in the ischemic border, the infarct area was reduced and neurobehaviour was preserved by FBC. These results indicate that FBC is neuroprotective in the ischemic brain and has demonstrated therapeutic potential for cerebral infarction.

INTRAMYOCARDIAL INJECTION OF INDUCED PLURIPOTENT STEM CELLS IMPROVES LEFT VENTRICULAR FUNCTION AND PERFUSION: A PRECLINICAL STUDY IN A PORCINE MODEL OF ACUTE MYOCARDIAL INFARCTION

ObjectivesInduced pluripotent stem (iPS) cells, a novel embryonic stem cell-like pluripotent stem cell, have potential to differentiate into different cardiovascular cells and repair the injured heart. The potential therapeutic benefits...

In Vivo Imaging of Neurovascular Remodeling After Stroke

Stroke is one of the leading causes of adult disability throughout the world and, even though neural mechanisms of loss of function have been extensively studied, many aspects of poststroke cerebral responses remain poorly understood. Of particular interest is the mounting evidence of the capacity of the adult brain to reorganize after injury, which is believed to contribute to limitation of the extent of neural dysfunction and to restoration of affected neural functions. Processes such as neuronal plasticity, glial proliferation, and neovascularization may be essential for preservation or recovery of function after stroke and may conceivably go hand-in-hand at nearby and remote sites of active tissue reorganization.1,2 Specifically, the acute initiation of neurovascular remodeling, stimulating the proliferation and growth of existing arteries/arterioles (ie, arteriogenesis) or new capillaries (ie, angiogenesis), may be critical to facilitate the survival and restructuring of neural tissue, which ultimately may contribute to functional recovery at later stages.3 A variety of vascular imaging strategies is available for in vivo detection, characterization, and quantification of these processes, which can significantly aid in elucidation of the role of neurovascular remodeling after stroke, as discussed in this review. Because most of the described imaging modalities are present in experimental and clinical settings, this raises significant opportunities for translational studies. Growth and remodeling of existing and nascent vascular networks in health and disease involve a number of critical steps that have been comprehensively described by Risau4 and Carmeliet.5 Arteriogenesis involves adaptive growth and proliferation of preexisting (collateral) arteries and arterioles in response to increase in intravascular shear forces. The increased shear stress leads to upregulation of cell adhesion molecules, followed by accumulation of monocytes and other leukocytes that release cytokines and growth factors around the proliferating and maturating arteries.6 Although arteriogenic growth of collateral …

Neural Stem Cells Genetically Modified to Overexpress Cu/Zn-Superoxide Dismutase Enhance Amelioration of Ischemic Stroke in Mice

The harsh host brain microenvironment caused by production of reactive oxygen species after ischemic reperfusion injury offers a significant challenge to survival of transplanted neural stem cells (NSCs) after ischemic stroke. Copper/zinc-superoxide dismutase (SOD1) is a specific antioxidant enzyme that counteracts superoxide anions. We have investigated whether genetic manipulation to overexpress SOD1 enhances survival of grafted stem cells and accelerates amelioration of ischemic stroke. NSCs genetically modified to overexpress or downexpress SOD1 were administered intracerebrally 2 days after transient middle cerebral artery occlusion. Histological and behavioral tests were examined from Days 0 to 28 after stroke. Overexpression of SOD1 suppressed production of superoxide anions after ischemic reperfusion injury and reduced NSC death after transplantation. In contrast, downexpression of SOD1 promoted superoxide generation and increased oxidative stress-mediated NSC death. Transplantation of SOD1-overexpressing NSCs enhanced angiogenesis in the ischemic border zone through upregulation of vascular endothelial growth factor. Moreover, grafted SOD1-overexpressing NSCs reduced infarct size and improved behavioral performance compared with NSCs that were not genetically modified. Our findings reveal a strong involvement of SOD1 expression in NSC survival after ischemic reperfusion injury. We propose that conferring antioxidant properties on NSCs by genetic manipulation of SOD1 is a potential approach for enhancing the effectiveness of cell transplantation therapy in ischemic stroke.

Angiogenesis

It is now appreciated that emerging therapeutic strategies for recovery must include the cerebral vasculature and that induction of angiogenesis will stimulate endogenous recovery mechanisms, including neurogenesis, synaptogenesis, and neuronal and synaptic plasticity. These events are all involved in the long-term repair and restoration process of the brain after an ischemic event. Several recent excellent reviews provided detailed information on the mechanisms and molecular targets for angiogenesis after stroke.1,2 The purpose of this review is to evaluate the evidence that angiogenesis is a target for recovery after an ischemic stroke. ### Angiogenic Response to Ischemic Brain Injury: A Multipurpose Pathway Early reports of increased angiogenesis in the ischemic border zone of human brain autopsy sections,3 which was decreased in patients of advanced age,4 led to interest in the time course and impact of this phenomenon on functional recovery. It is clear that angiogenesis genes are upregulated within minutes of the onset of cerebral ischemia in rodents5 and angiogenic proteins remain increased in the area of ischemia for days to weeks.6 It is unclear, however, whether the angiogenic response leads to the development of functional new blood vessels that improve brain function after stroke. Clinical and experimental studies in other vascular beds have emphasized the potential for adverse consequences related to neovascularization.7,8 In the diabetic retina, for example, pathological angiogenesis results in hemorrhage, edema, and, ultimately, blindness.9 In the brain, pathological angiogenesis is implicated in the development of hereditary hemorrhagic telangiectasia.10 The correlation between angiogenesis and improved functional outcome after ischemic stroke remains and is seen in both animal models and in human patients with stroke.5,11–13 It is likely that the “proangiogenic state,” induced in response to an ischemic insult, has multiple purposes in the hours to weeks after the injury (Figure). First, the …

Spatio-temporal course of macrophage-like cell accumulation after experimental embolic stroke depending on treatment with tissue plasminogen activator and its combination with hyperbaric oxygenation

Inflammation following ischaemic stroke attracts high priority in current research, particularly using human-like models and long-term observation periods considering translational aspects. The present study aimed on the spatio-temporal course of macrophage-like cell accumulation after experimental thromboembolic stroke and addressed microglial and astroglial reactions in the ischaemic border zone. Further, effects of tissue plasminogen activator (tPA) as currently best treatment for stroke and the potentially neuroprotective co-administration of hyperbaric oxygen (HBO) were investigated. Rats underwent middle cerebral artery occlusion and were assigned to control, tPA or tPA+HBO. Twenty-four hours, 7, 14 and 28 days were determined as observation time points. The accumulation of macrophage-like cells was semiquantitatively assessed by CD68 staining in the ischaemic area and ischaemic border zone, and linked to the clinical course. CD11b, ionized calcium binding adaptor molecule 1 (Iba), glial fibrillary acidic protein (GFAP) and Neuronal Nuclei (NeuN) were applied to reveal delayed glial and neuronal alterations. In all groups, the accumulation of macrophage-like cells increased distinctly from 24 hours to 7 days post ischaemia. tPA+HBO tended to decrease macrophage-like cell accumulation at day 14 and 28. Overall, a trend towards an association of increased accumulation and pronounced reduction of the neurological deficit was found. Concerning delayed inflammatory reactions, an activation of microglia and astrocytes with co-occurring neuronal loss was observed on day 28. Thereby, astrogliosis was found circularly in contrast to microglial activation directly in the ischaemic area. This study supports previous data on long-lasting inflammatory processes following experimental stroke, and additionally provides region-specific details on glial reactions. The tendency towards a decreasing macrophage-like cell accumulation after tPA+HBO needs to be discussed critically since neuroprotective properties were recently ascribed to long-term inflammatory processes.

Abstract 2622: Human Placental Derived Adherent Cells (PDA001) Treatment Induces Angiogenesis, Synaptogenesis And Improves Functional Outcome After Stroke

Background and purpose: Mesenchymal stem cells (MSCs) show promising therapeutic potential in myocardial, limb, and brain ischemia. Human Placenta-derived Cells (PDA001) is a novel cell population derived from normal, full-term human placental tissue and a rich source of MSC like cells. In this study, we investigated the efficacy of PDA001 cells in a rat stroke model. Methods: Adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion (MCAo) and treated with or without different doses of PDA001 cells (1x10 6 , 4x10 6 and 8x10 6 ) at 24 h after MCAo. A battery of functional outcome tests was performed prior to PDA001 cell therapy and at days 7, 14, 21, 28, 42, and 56 after MCAo. Rats were sacrificed at 56 days after MCAo and lesion volumes were measured. The optimal dose of PDA001 cell treatment of stroke was chosen for bromodeoxyuridine (BrdU),Von Willebrand Factor (vWF), and Synaptophysin immunostaining. Results: PDA001 cell treatment dose-dependently improves functional outcome compared to dermal fibroblast cells (FBC-control) and Dextran vehicle control. PDA001 cell treatment significantly increased the number of BrdU immunoreactive endothelial cells as well as the vascular density and perimeter in the ischemic brain compared with the FBC-control and Dextran control groups (p&lt;0.05). PDA001 cell treatment significantly increased synaptic plasticity as measured by increased Synaptophysin expression in the ischemic border zone (IBZ) compared to FBC-control (p&lt;0.05). Conclusion: PDA001 cell treatment of stroke dose-dependently improves functional outcome in stroke in rats. The neurorestorative effects induced by PDA001 cell treatment may relate to the increase of angiogenesis and synaptic plasticity.

Myocardial tissue elastic properties determined by atomic force microscopy after stromal cell–derived factor 1α angiogenic therapy for acute myocardial infarction in a murine model

Ventricular remodeling after myocardial infarction begins with massive extracellular matrix deposition and resultant fibrosis. This loss of functional tissue and stiffening of myocardial elastic and contractile elements starts the vicious cycle of mechanical inefficiency, adverse remodeling, and eventual heart failure. We hypothesized that stromal cell-derived factor 1α (SDF-1α) therapy to microrevascularize ischemic myocardium would rescue salvageable peri-infarct tissue and subsequently improve myocardial elasticity. Immediately after left anterior descending coronary artery ligation, mice were randomly assigned to receive peri-infarct injection of either saline solution or SDF-1α. After 6 weeks, animals were killed and samples were taken from the peri-infarct border zone and the infarct scar, as well as from the left ventricle of noninfarcted control mice. Determination of tissues' elastic moduli was carried out by mechanical testing in an atomic force microscope. SDF-1α-treated peri-infarct tissue most closely approximated the elasticity of normal ventricle and was significantly more elastic than saline-treated peri-infarct myocardium (109 ± 22.9 kPa vs 295 ± 42.3 kPa; P < .0001). Myocardial scar, the strength of which depends on matrix deposition from vasculature at the peri-infarct edge, was stiffer in SDF-1α-treated animals than in controls (804 ± 102.2 kPa vs 144 ± 27.5 kPa; P < .0001). Direct quantification of myocardial elastic properties demonstrates the ability of SDF-1α to re-engineer evolving myocardial infarct and peri-infarct tissues. By increasing elasticity of the ischemic and dysfunctional peri-infarct border zone and bolstering the weak, aneurysm-prone scar, SDF-1α therapy may confer a mechanical advantage to resist adverse remodeling after infarction.

Improved Culture-Based Isolation of Differentiating Endothelial Progenitor Cells from Mouse Bone Marrow Mononuclear Cells

Numerous endothelial progenitor cell (EPC)-related investigations have been performed in mouse experiments. However, defined characteristics of mouse cultured EPC have not been examined. We focused on fast versus slow adherent cell population in bone marrow mononuclear cells (BMMNCs) in culture and examined their characteristics. After 24 h-culture of BMMNCs, attached (AT) cells and floating (FL) cells were further cultured in endothelial differentiation medium separately. Immunological and molecular analyses exhibited more endothelial-like and less monocyte/macrophage-like characteristics in FL cells compared with AT cells. FL cells formed thick/stable tube and hypoxia or shear stress overload further enhanced these endothelial-like features with increased angiogenic cytokine/growth factor mRNA expressions. Finally, FL cells exhibited therapeutic potential in a mouse myocardial infarction model showing the specific local recruitment to ischemic border zone and tissue preservation. These findings suggest that slow adherent (FL) but not fast attached (AT) BMMNCs in culture are EPC-rich population in mouse.

Abstract 17085: MicroRNA-24 Prevents Apoptosis and Preserves Cardiac Function after Myocardial Infarction Through Cell-Autonomous Effects in Cardiomyocytes

Background Apoptosis due to myocardial infarction (MI) leads to an irreversible loss of cardiomyocytes. MicroRNAs may influence this process by post-transcriptionally regulating the expression of proteins involved in apoptotic pathways. We have previously shown that exogenous application of miR-24 after coronary artery ligation in mice preserves cardiac function by repressing the pro-apoptotic protein Bim. Here, we investigate whether miR-24 delivered by local injection exerts its effects primarily within cardiomyocytes or non-cell autonomously through neighboring cells. Methods We genetically targeted miR-24 under control of the cardiac-specific Myh6 promoter, and selected a line of transgenic mice (αMHC-miR-24 mice) with six fold greater expression of miR-24 than control littermates. MI was induced by coronary artery ligation. Apoptosis and infarct size were quantified with TUNEL assays (n=16) and AZAN staining (n=15) 24 hours and 4 weeks post-MI, respectively. Cardiac function was measured by high-resolution echocardiography at baseline and 3 days and 4 weeks post-MI (n=42). QRT-PCR and Western blotting were performed on cardiac tissue 24 hours post-MI (n=6). Results αMHC-miR-24 mice were protected against apoptosis after MI compared to wildtype littermates as indicated by reduced numbers of TUNEL-positive cardiomyocytes in the ischemic zone and border zone compared to wildtype littermates. Cardiac function was preserved (Ejection fraction 55.0 ± 0.9 vs. 56.9 ± 0.9 % at baseline, p=NS, 32.8 ± 1.7 vs. 28.1 ± 1.6% at 3 days, p&lt;0.05, 26.7 ± 1.9 vs. 21.9 ± 1.4% at 4 weeks, p&lt;0.05; Fractional shortening 32.9 ± 1.1 vs. 32.5 ± 1.1% at baseline, 15.1 ± 0.5 vs 12.6 ± 0.08% at 3 days, p&lt;0.05, 15.0 ± 0.9 vs. 12.0 ± 0.7% at 4 weeks, p&lt;0.05). Hearts of αMHC-miR-24 mice exhibited lower levels of Bim protein, lower levels of stress markers such as ANF and BNP and partially restored levels of dysregulated miRNAs 19a, 195 and 208, similar to miR-24 mimic injection in the heart. Conclusion The similarity between the effects of local delivery and cardiomyocyte-specific overexpression of miR-24 provides evidence that miR-24 improves left ventricular function after myocardial infarction by cell autonomously inhibiting cardiomyocyte death.

Abstract 9070: Secretoneurin is Produced in the Ischemic Border Zone of Animals with Myocardial Infarction and Heart Failure, Attenuates Ischemic Injury, and is Associated with the Progression of Heart Failure in Patients

Background: Secretoneurin (SN) is a peptide belonging to the granin protein family. As two other granin proteins, chromogranin A and B, are increased in cardiac tissue in heart failure (HF), we hypothesized that SN could play a role in cardiovascular pathophysiology. Methods: Production and functional aspects of SN were assessed in experimental models and circulating levels measured in two cohorts of HF patients. Results: Pro-SN mRNA levels were 11.5 fold increased in viable left ventricular (LV) tissue of mice subjected to coronary artery ligation and with echocardiographical confirmed HF. Protein levels were also increased in the LV of HF animals vs. sham-operated animals, including in the ischemic border zone where we observed increased processing from pro-SN to shorter SN fragments (&gt;100% increase, p=0.001). Immunohistochemistry localized myocardial SN production to cardiomyocytes. We did not observe increased SN production in other organs than the LV. Perfusing isolated cardiomyocytes with SN rapidly induced Stat3 and Erk1/2 phosphorylation, protected from hydrogen peroxide-induced cardiomyocyte apoptosis in vitro , and reduced ischemia-reperfusion injury by 30% (p&lt;0.05) in the isolated perfused rat heart. Circulating levels of SN were increased in patients with stable and acute HF compared to control subjects and increased in proportion to HF severity as evaluated by NYHA functional class (p=0.04 for trend). In 68 patients hospitalized for acute HF, admission SN levels provided excellent discrimination for all-cause mortality (n=17) during a median follow-up of 373 days: Hazard ratio [per 0.05 nmol/L increase of SN] 2.34 (95% CI 1.63-3.38), p&lt;0.001. Adjustment for established clinical risk factors including comorbidities, renal function, and LV ejection fraction in multivariate analysis did not attenuate the association between SN levels and mortality: HR 2.43 (95% CI 1.63-3.61), p&lt;0.001. Conclusion: SN production is increased in viable cardiomyocytes adjacent to the infarcted area in animals with myocardial infarction and HF, which could be beneficial as SN protects from myocardial ischemia. Based on our results, SN could represent a protective feedback response that is activated in proportion to the severity of HF.

Upregulation of fibronectin and the α5β1 and αvβ3 integrins on blood vessels within the cerebral ischemic penumbra

Following focal cerebral ischemia, blood vessels in the ischemic border, or penumbra, launch an angiogenic response. In light of the critical role for fibronectin in angiogenesis, and the observation that fibronectin and its integrin receptors are strongly upregulated on angiogenic vessels in the hypoxic CNS, the aim of this study was to establish whether angiogenic vessels in the ischemic CNS also show this response. Focal cerebral ischemia was established in C57/Bl6 mice by middle cerebral artery occlusion (MCA:O), and brain tissue analyzed 7days following re-perfusion, a time at which angiogenesis is ongoing. Within the ischemic core, immunofluorescent (IF) studies demonstrated vascular expression of MECA-32, a marker of leaky cerebral vessels, and vascular breakdown, defined by loss of staining for the endothelial marker, CD31, and the vascular adhesion molecules, laminin, dystroglycan and α6 integrin. Within the ischemic penumbra, dual-IF with CD31 and Ki67 revealed the presence of proliferating endothelial cells, indicating ongoing angiogenesis. Significantly, vessels in the ischemic penumbra showed strong upregulation of fibronectin and the fibronectin receptors, α5β1 and αvβ3 integrins. Taken together with our recent finding that the α5β1 integrin plays an important role in promoting cerebral angiogenesis in response to hypoxia, these results suggest that stimulation of the fibronectin-α5β1 integrin signaling pathway may provide a novel approach to amplifying the intrinsic angiogenic response to cerebral ischemia.

P53-TIGAR axis attenuates mitophagy to exacerbate cardiac damage after ischemia

Inhibition of tumor suppressor p53 is cardioprotective against ischemic injury and provides resistance to subsequent cardiac remodeling. We investigated p53-mediated expansion of ischemic damage with a focus on mitochondrial integrity in association with autophagy and apoptosis. p53−/− heart showed that autophagic flux was promoted under ischemia without a change in cardiac tissue ATP content. Electron micrographs revealed that ischemic border zone in p53−/− mice had 5-fold greater numbers of autophagic vacuoles containing mitochondria, indicating the occurrence of mitophagy, with an apparent reduction of abnormal mitochondria compared with those in WT mice. Analysis of autophagic mediators acting downstream of p53 revealed that TIGAR (TP53-induced glycolysis and apoptosis regulator) was exclusively up-regulated in ischemic myocardium. TIGAR−/− mice exhibited the promotion of mitophagy followed by decrease of abnormal mitochondria and resistance to ischemic injury, consistent with the phenotype of p53−/− mice. In p53−/− and TIGAR−/− ischemic myocardium, ROS production was elevated and followed by Bnip3 activation which is an initiator of mitophagy. Furthermore, the activation of Bnip3 and mitophagy due to p53/TIGAR inhibition were reversed with antioxidant N-acetyl-cysteine, indicating that this adaptive response requires ROS signal. Inhibition of mitophagy using chloroquine in p53−/− or TIGAR−/− mice exacerbated accumulation of damaged mitochondria to the level of wild-type mice and attenuated cardioprotective action. These findings indicate that p53/TIGAR-mediated inhibition of myocyte mitophagy is responsible for impairment of mitochondrial integrity and subsequent apoptosis, the process of which is closely involved in p53-mediated ventricular remodeling after myocardial infarction.

Transforming Growth Factor-α Enhances Stem Cell-Mediated Postischemic Myocardial Protection

Transforming growth factor-α (TGF-α) has been shown to augment mesenchymal stem cell-mediated cardioprotection during acute ischemia and reperfusion in isolated heart models. To determine whether this pretreatment strategy would be effective in vivo, we hypothesized that the intramyocardial injection of mesenchymal stem cells pretreated with TGF-α after coronary artery ligation would confer greater preservation of cardiac function, reduction in infarct size, and reduction myocardial inflammation. Sprague-Dawley rats underwent left anterior descending coronary artery ligation. Ischemic border zones were injected 30 minutes later with vehicle (n = 11), 1 million mesenchymal stem cells (n = 9), or mesenchymal stem cells pretreated with TGF-α (250 ng/mL for 24 hours; n = 10). Cardiac function was assessed by echocardiography at 7 and 28 days after ligation. Infarct size was measured using triphenyltetrazolium chloride. Ischemic border zone cytokine expression was measured 30 days after infarction. Myocardial function after ligation was greatest in hearts injected with cells pretreated with TGF-α in association with reduced ventricular remodeling and infarct size compared with vehicle-injected hearts. Myocardial interleukin 1β, interleukin 6, and TNF-α concentrations were lower, and Bcl-2 expression was higher, in hearts injected with either cell type. Vascular endothelial growth factor and matrix metalloproteinase-2 expression were highest in hearts that received pretreated cells. Intramyocardial injection of mesenchymal stem cells pretreated with TGF-α further protects cardiac function and reduces infarct size compared with injection of untreated cells. Pretreating donor cells with TGF-α may be useful for enhancing cell-based therapies for myocardial ischemia.

Evolution of Spiral and Scroll Waves of Excitation in a Mathematical Model of Ischaemic Border Zone

Abnormal electrical activity from the boundaries of ischemic cardiac tissue is recognized as one of the major causes in generation of ischemia-reperfusion arrhythmias. Here we present theoretical analysis of the waves of electrical activity that can rise on the boundary of cardiac cell network upon its recovery from ischaemia-like conditions. The main factors included in our analysis are macroscopic gradients of the cell-to-cell coupling and cell excitability and microscopic heterogeneity of individual cells. The interplay between these factors allows one to explain how spirals form, drift together with the moving boundary, get transiently pinned to local inhomogeneities, and finally penetrate into the bulk of the well-coupled tissue where they reach macroscopic scale. The asymptotic theory of the drift of spiral and scroll waves based on response functions provides explanation of the drifts involved in this mechanism, with the exception of effects due to the discreteness of cardiac tissue. In particular, this asymptotic theory allows an extrapolation of 2D events into 3D, which has shown that cells within the border zone can give rise to 3D analogues of spirals, the scroll waves. When and if such scroll waves escape into a better coupled tissue, they are likely to collapse due to the positive filament tension. However, our simulations have shown that such collapse of newly generated scrolls is not inevitable and that under certain conditions filament tension becomes negative, leading to scroll filaments to expand and multiply leading to a fibrillation-like state within small areas of cardiac tissue.

Long-lasting neuronal loss following experimental focal cerebral ischemia is not affected by combined administration of tissue plasminogen activator and hyperbaric oxygen

Acute focal cerebral ischemia and consecutive energy failure are accompanied by neuronal death in regions with impaired cerebral blood flow. Several translational attempts of potential neuroprotective agents have failed, hence extended perspectives are required regarding the regional differences of neuronal impairment and glial involvement by using clinically relevant stroke models. This study aimed on neuronal loss following experimental focal cerebral ischemia, considering tissue plasminogen activator (tPA) as established treatment in stroke and hyperbaric oxygenation (HBO) as potential neuroprotective co-treatment. Wistar rats were subjected to embolic middle cerebral artery occlusion and underwent either treatment with tPA only, combined tPA + HBO, or no treatment. Neuronal impairment was assessed by Neuronal Nuclei (NeuN) staining in 4 ischemia-related areas and at 4 different time points after stroke induction (24 hours, 7, 14 and 28 days). Additionally, spatial relationships between neuronal loss and gliosis were revealed by triple fluorescence staining of neurons, astrocytes and microglia, comparing the ipsi- and contra-lesional hemisphere. Analyzing the ischemic injury in general, a shell-like distribution of neuronal damage was observed, starting in the ischemic core and diminishing over the general ischemic area to the ischemic border zone and the primary non-affected area. This pattern remained detectable up to 4 weeks after ischemia induction. Surprisingly, tPA and tPA + HBO did not markedly affect the post-ischemic course of neuronal impairment. Further studies are needed to investigate the effects of treatment with tPA or potential neuroprotective agents on neuronal integrity, with emphasis on the separation of intact neurons from those undergoing apoptosis or necrosis.

Oxygen therapy improves energy metabolism in focal cerebral ischemia

Oxygen therapy (OT) with hyperbaric oxygen (HBO) or normobaric hyperoxia (NBO) improves the oxygenation of penumbral tissue in experimental ischemic stroke. However, whether this results in the improvement of energy metabolism is unclear. We investigated the effect of both OTs on tissue acidosis and on ATP production. Beginning 25min after filament middle cerebral artery occlusion (MCAO), mice breathed either air, 100% O2 (NBO), or 100% O2 at 3 ata (HBO) for 60min. Regional tissue pH was measured using the umbelliferone fluorescence. Regional ATP concentration was depicted by substrate-specific bioluminescence. Severity of ischemia did not differ among groups in laser-Doppler flowmetry. Both NBO (70.1±14.0mm3) and, more effectively, HBO (57.2±11.9mm3) significantly reduced volume of tissue acidosis compared to air (89.4±4.0mm3, p<0.05). Topographically, acidosis was less pronounced in the medial striatum and in the cortical ischemic border areas. This resulted in significantly smaller volumes of ATP depletion (77.8±7.7mm3 in air, 61.4±15.2mm3 in NBO and 51.2±14.4mm3 in HBO; p<0.05). In conclusion, OT significantly improves energy metabolism in the border zones of focal cerebral ischemia which are the areas protected by OT in this model.

Cardioprotection of Insulin-Like Growth Factor-1 During Reperfusion Therapy

In the setting of acute myocardial infarction, reperfusion of ischemic myocardium carried out early after coronary occlusion can salvage reversibly injured, viable myocardium. Although still controversial, however, reperfusion itself may cause a population of reversibly injured cells to die, a phenomenon termed lethal reperfusion injury .1 A variety of pharmacological agents have been studied to limit ischemia/reperfusion injury as an adjunct to current reperfusion, and some beneficial effects have been demonstrated in experimental animal research, but their clinical applications have not been achieved.2–4 Article see p 327 Among the various agents claimed to have cardioprotective effects is insulin-like growth factor-1 (IGF-1), which is a hormone produced primarily by the liver. Its molecular structure is similar to that of insulin. IGF-1 plays an important role in cellular survival and growth by binding to its specific receptor (IGF1R), which is present on many cell types, including cardiac cells. Activation of IGF1R, a receptor tyrosine kinase, has been demonstrated to attenuate both apoptotic and necrotic cell death induced by ischemia/reperfusion injury through stimulating both the intracellular phosphoinositide 3-kinase/protein kinase B signaling pathway and extracellular signal-regulated kinase 1/2 signaling cascades.5 Buerke at al6 administered IGF-I 1 hour before ischemia in a murine model of 20 minutes of myocardial ischemia followed by 24 hours of reperfusion. IGF-I preserved ischemic/reperfused myocardium through inhibition of polymorphonuclear leukocyte-induced cardiac necrosis and inhibition of reperfusion-induced apoptosis of cardiac myocytes. Davani et al7 subjected isolated murine hearts to 20 minutes of global ischemia followed by 2 hours of reperfusion with either modified Kreb's solution alone or …

Porcine coronary collateral formation in the absence of a pressure gradient remote of the ischemic border zone

In the current paradigm on coronary collateral development, it is assumed that these vessels develop consequentially from increased fluid shear stress (FSS) through preexisting collateral arteries. The increased FSS follows from an increase in pressure gradient between the region at risk and well-perfused surroundings. The objective of this study was to test the hypothesis that, in the heart, collateral connections can form in the absence of an increased FFS and consequentially at any depth and region within the ventricular wall. In Yorkshire pigs, gradual left circumflex coronary artery occlusion was obtained over 6 wk by an ameroid constrictor, whereas the control group underwent a sham operation. Hearts were harvested and subsequently processed in an imaging cryomicrotome, resulting in 40-μm voxel resolution three-dimensional reconstructions of the intramural vascular vessels. Dedicated software segmented the intramural vessels and all continuous vascular pathways containing a collateral connection. In the ameroid group, 192 collaterals, 22-1,049 μm in diameter, were detected with 62% within the subendocardium. Sixty percent of collaterals bridged from the left anterior descending artery to left circumflex coronary artery. A novel result is that 25% (n = 48) of smaller-radius collaterals (P = 0.047) connected with both origin and terminus in the nontarget area where perfusion was assumed uncompromised. In the porcine heart, collateral vessels develop not only in ischemic border zones with increased FSS but also away from such border zones where increased FSS is unlikely. The majority of collaterals were located at the subendocardium, corresponding to the region with highest prevalence for ischemia.