Microvascular responses to cerebral ischemia/inflammation

Brain Maturation as a Fundamental Factor in Immune-Neurovascular Interactions in Stroke

Injuries in the developing brain cause significant long-term neurological deficits. Emerging clinical and preclinical data have demonstrated that the pathophysiology of neonatal and childhood stroke share similar mechanisms that regulate brain damage, but also have distinct molecular signatures and cellular pathways. The focus of this review is on two different diseases-neonatal and childhood stroke-with emphasis on similarities and distinctions identified thus far in rodent models of these diseases. This includes the susceptibility of distinct cell types to brain injury with particular emphasis on the role of resident and peripheral immune populations in modulating stroke outcome. Furthermore, we discuss some of the most recent and relevant findings in relation to the immune-neurovascular crosstalk and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we comment on the current state of treatments geared toward inducing neuroprotection and promoting brain repair after injury and highlight that future prophylactic and therapeutic strategies for stroke should be age-specific and consider gender differences in order to achieve optimal translational success.

Disturbed microcirculation and hyperaemic response in a murine model of systemic inflammation

Systemic inflammation affects cognitive functions and increases the risk of dementia. This phenomenon is thought to be mediated in part by cytokines that promote neuronal survival, but the continuous exposure to which may lead to neurodegeneration. The effects of systemic inflammation on cerebral blood vessels, and their provision of adequate oxygen to support critical brain parenchymal cell functions, remains unclear. Here, we demonstrate that neurovascular coupling is profoundly disturbed in lipopolysaccharide (LPS) induced systemic inflammation in awake mice. In the 24 hours following LPS injection, the hyperaemic response of pial vessels to functional activation was attenuated and delayed. Concurrently, under steady-state conditions, the capillary network displayed a significant increase in the number of capillaries with blocked blood flow, as well as increased duration of 'capillary stalls'-a phenomenon previously reported in animal models of stroke and Alzheimer's disease pathology. We speculate that vascular changes and impaired oxygen availability may affect brain functions following acute systemic inflammation and contribute to the long-term risk of neurodegenerative changes associated with chronic, systemic inflammation.

Pharmacological therapy to cerebral ischemia-reperfusion injury: Focus on saponins

Secondary insult from cerebral ischemia-reperfusion injury (CIRI) is a major risk factor for poor prognosis of cerebral ischemia. Saponins are steroid or triterpenoid glycosides with various pharmacological activities that are effective in treating CIRI. By browsing the literature from 2001 to 2021, 55 references involving 24 kinds of saponins were included. Saponins were shown to relieve CIRI by inhibiting oxidation stress, neuroinflammation, and apoptosis, restoring BBB integrity, and promoting neurogenesis and angiogenesis. This review summarizes and classifies several common saponins and their mechanisms in relieving CIRI. Information provided in this review will benefit researchers to design, research and develop new medicines to treat CIRI-related conditions with saponins.

Absence of endothelial α5β1 integrin triggers early onset of experimental autoimmune encephalomyelitis due to reduced vascular remodeling and compromised vascular integrity

Early in the development of multiple sclerosis (MS) and its mouse model experimental autoimmune encephalomyelitis (EAE), vascular integrity is compromised. This is accompanied by a marked vascular remodeling response, though it is currently unclear whether this is an adaptive vascular repair mechanism or is part of the pathogenic process. In light of the well-described angiogenic role for the α5β1 integrin, the goal of this study was to evaluate how genetic deletion of endothelial α5 integrin (α5-EC-KO mice) impacts vascular remodeling and repair following vascular disruption during EAE pathogenesis, and how this subsequently influences clinical progression and inflammatory demyelination. Immunofluorescence staining revealed that fibronectin and α5 integrin expression were strongly upregulated on spinal cord blood vessels during the pre-symptomatic phase of EAE. Interestingly, α5-EC-KO mice showed much earlier onset and faster progression of EAE, though peak disease severity and chronic disease activity were no different from wild-type mice. At the histological level, earlier disease onset in α5-EC-KO mice correlated with accelerated vascular disruption and increased leukocyte infiltration into the spinal cord. Significantly, spinal cord blood vessels in α5-EC-KO mice showed attenuated endothelial proliferation during the pre-symptomatic phase of EAE which resulted in reduced vascular density at later time-points. Under pro-inflammatory conditions, primary cultures of α5KO brain endothelial cells showed reduced proliferation potential. These findings suggest that α5β1 integrin-mediated angiogenic remodeling represents an important repair mechanism that counteracts vascular disruption during the early stages of EAE development.

Cerebral Ischemic Reperfusion Injury Following Recanalization of Large Vessel Occlusions

Although stroke has recently dropped to become the nation's fifth leading cause of mortality, it remains the top leading cause of morbidity and disability in the US. Recent advances in stroke treatment, including intravenous fibrinolysis and mechanical thromboembolectomy, allow treatment of a greater proportion of stroke patients than ever before. While intra-arterial fibrinolysis with recombinant tissue plasminogen is an effective for treatment of a broad range of acute ischemic strokes, endovascular mechanical thromboembolectomy procedures treat severe strokes due to large artery occlusions, often resistant to intravenous drug. Together, these procedures result in a greater proportion of revascularized stroke patients than ever before, up to 88% in 1 recent trial (EXTEND-IA). Subsequently, there is a growing need for neurointensivists to develop more effective strategies to manage stroke patients following successful reperfusion. Cerebral ischemic reperfusion injury (CIRI) is defined as deterioration of brain tissue suffered from ischemia that concomitantly reverses the benefits of re-establishing cerebral blood flow following mechanical or chemical therapies for acute ischemic stroke. Herein, we examine the pathophysiology of CIRI, imaging modalities, and potential neuroprotective strategies. Additionally, we sought to lay down a potential treatment approach for patients with CIRI following emergent endovascular recanalization for acute ischemic stroke.

Pathogenic mechanisms following ischemic stroke

Stroke is the second most common cause of death and the leading cause of disability worldwide. Brain injury following stroke results from a complex series of pathophysiological events including excitotoxicity, oxidative and nitrative stress, inflammation, and apoptosis. Moreover, there is a mechanistic link between brain ischemia, innate and adaptive immune cells, intracranial atherosclerosis, and also the gut microbiota in modifying the cerebral responses to ischemic insult. There are very few treatments for stroke injuries, partly owing to an incomplete understanding of the diverse cellular and molecular changes that occur following ischemic stroke and that are responsible for neuronal death. Experimental discoveries have begun to define the cellular and molecular mechanisms involved in stroke injury, leading to the development of numerous agents that target various injury pathways. In the present article, we review the underlying pathophysiology of ischemic stroke and reveal the intertwined pathways that are promising therapeutic targets.

Vectorized nanodelivery systems for ischemic stroke: a concept and a need

Neurological diseases of diverse aetiologies have significant effects on the quality of life of patients. The limited self-repairing capacity of the brain is considered to be the origin of the irreversible and progressive nature of many neurological diseases. Therefore, neuroprotection is an important goal shared by many clinical neurologists and neuroscientists. In this review, we discuss the main obstacles that have prevented the implementation of experimental neuroprotective strategies in humans and propose alternative avenues for the use of neuroprotection as a feasible therapeutic approach. Special attention is devoted to nanotechnology, which is a new approach for developing highly specific and localized biomedical solutions for the study of the multiple mechanisms involved in stroke. Nanotechnology is contributing to personalized neuroprotection by allowing us to identify mechanisms, determine optimal therapeutic windows, and protect patients from brain damage. In summary, multiple aspects of these new players in biomedicine should be considered in future in vivo and in vitro studies with the aim of improving their applicability to clinical studies.

Arachidonic acid attenuates brain damage in a rat model of ischemia/reperfusion by inhibiting inflammatory response and oxidative stress

The aim of the present study was to study the effects of arachidonic acid (ARA) in a rat brain ischemia/reperfusion model induced by middle cerebral artery occlusion (MCAO). A total of 50 rats were randomly divided into five groups: control group, MCAO group, MCAO + ARA 0.3 g/kg group, MCAO + ARA 1 g/kg group, and MCAO + ARA 3 g/kg group. The MCAO + ARA groups received ARA by intraperitoneal injection daily for 14 consecutive days, while the rats in the control and MCAO groups were given equivalent volume of saline. We detected the Morris water maze test and pathological changes to investigate the ischemia/reperfusion injury. The protein levels of tumor necrosis factor-alpha and interleukin-6 in the hippocampus were detected by enzyme-linked immunosorbent assay kits. In addition, the activities of superoxide dismutase, glutathione peroxidase, and malondialdehyde were assayed in hippocampus homogenates to evaluate the oxidative stress after ischemia/reperfusion. The results indicated that ARA administration decreased biochemical parameters of inflammation and oxidative stress. Morris water maze test and histopathological examination further verified the protective effects of ARA on ischemia/reperfusion injury rats. These findings demonstrated that ARA could protect MCAO-induced brain injury rats by inhibition of inflammation and oxidative stress, suggesting that it may have potential as a therapy for cerebral ischemia/reperfusion injury.

Neuroprotective Effect of Resveratrol on Acute Brain Ischemia Reperfusion Injury by Measuring Annexin V, p53, Bcl-2 Levels in Rats

Background

Cerebral ischemia is as a result of insufficient cerebral blood flow for cerebral metabolic functions. Resveratrol is a natural phytoalexin that can be extracted from grape's skin and had potent role in treating the cerebral ischemia. Apoptosis, a genetically programmed cellular event which occurs after ischemia and leads to biochemical and morphological changes in cells. There are some useful markers for apoptosis like Bcl-2, bax, and p53. The last reports, researchers verify the apoptosis with early markers like Annexin V.

Methods

We preferred in this experimental study a model of global cerebral infarction which was induced by bilateral common carotid artery occlusion method. Rats were randomly divided into 4 groups : sham, ischemia-reperfusion (I/R), I/R plus 20 mg/kg resveratrol and I/R plus 40 mg/kg resveratrol. Statistical analysis was performed using Sigmastat 3.5 ve IBM SPSS Statistics 20. We considered a result significant when p<0.001.

Results

After administration of resveratrol, Bcl-2 and Annexin levels were significantly increased (p<0.001). Depending on the dose of resveratrol, Bcl2 levels increased, p53 levels decreased but Annexin V did not effected. P53 levels were significantly increased in ishemia group, so apoptosis is higher compared to other groups.

Conclusion

In the acute period, Annexin V levels misleading us because the apoptotic cell counts could not reach a certain level. Therefore we should support our results with bcl-2 and p53.

In vitro micro-physiological models for translational immunology

The immune system is a source of regulation of the human body and is key for its stable functioning. Animal models have been successfully used for many years to study human immunity and diseases and provided significant contributions to the development of powerful new therapies. However, such models inevitably display differences from the human metabolism and disease state and therefore may correlate poorly with the human conditions. This explains the interest for the use of in vitro models of human cells, which have better potential to assist in understanding the physiological events that characterize the immune response in humans. Microfluidic technologies offer great capabilities to create miniaturized in vivo-like physiological models that mimic tissue-tissue interactions and simulate the body metabolism in both the healthy and diseased states. The micro-scale features of these microfluidic systems allow positioning heterogeneous cellular cultures in close proximity to each other in a dynamic fluidic environment, thereby allowing efficient cell-cell interactions and effectively narrowing the gap between in vivo and in vitro conditions. Due to the relative simplicity of these systems, compared to animal models, it becomes possible to investigate cell signaling by monitoring the metabolites transported from one tissue to another in real time. This allows studying detailed physiological events and in consequence understanding the influence of metabolites on a specific tissue/organ function as well as on the healthy/diseased state modulation. Numerous in vitro models of human organs have been developed during the last few years, aiming to mimic as closely as possible the in vivo characteristics of such organs. This technology is still in its infancy, but is promised a bright future in industrial and medical applications. Here we review the recent literature, in which functional microphysiological models have been developed to mimic tissues and to explore multi-tissue interactions, focusing in particular on the study of immune reactions, inflammation and the development of diseases. Also, an outlook on the opportunities and issues for further translational development of functional in vitro models in immunology will be presented.

Review of plants and their constituents in the therapy of cerebral ischemia

Cerebral ischemia is a condition in which there is insufficient blood flow to the brain to meet metabolic demand. This leads to cerebral hypoxia and thus to the death of neuronal cells or stroke. The limited number of medicines currently available for patients following ischemic stroke and insufficient data on efficiency of these chemicals in the treatment of stroke led us to the search for novel therapeutic approaches. Recent studies have focused on the possible capacity of natural compounds extracted from vegetables and fruits, to prevent human disabilities caused by cerebral ischemia. In this review, we will discuss some plants and their constituents that may protect brain ischemia or delay the neurological disorders following a stroke. We have reviewed different studies in scientific databases that investigate herbal compounds and their effects on cerebral ischemia.

Curcuminoids limit neutrophil-mediated reperfusion injury in experimental stroke by targeting the endothelium

OBJECTIVE

We sought to test the hypothesis that turmeric-derived curcuminoids limit reperfusion brain injury in an experimental model of stroke via blockade of early microvascular inflammation during reperfusion.

METHODS

Male Sprague Dawley rats subjected to MCAO/R were treated with turmeric-derived curcuminoids (vs. vehicle) 1 hour prior to reperfusion (300 mg/kg ip). Neutrophil adhesion to the cerebral microcirculation and measures of neutrophil and endothelial activation were assayed during early reperfusion (0-4 hours); cerebral infarct size, edema, and neurological function were assessed at 24 hours. Curcuminoid effects on TNFα-stimulated human brain microvascular endothelial cell (HBMVEC) were assessed.

RESULTS

Early during reperfusion following MCAO, curcuminoid treatment decreased neutrophil rolling and adhesion to the cerebrovascular endothelium by 76% and 67% and prevented >50% of the fall in shear rate. The increased number and activation state (CD11b and ROS) of neutrophils were unchanged by curcuminoid treatment, while increased cerebral expression of TNFα and ICAM-1, a marker of endothelial activation, were blocked by >30%. Curcuminoids inhibited NF-κB activation and subsequent ICAM-1 gene expression in HBMVEC.

CONCLUSION

Turmeric-derived curcuminoids limit reperfusion injury in stroke by preventing neutrophil adhesion to the cerebrovascular microcirculation and improving shear rate by targeting the endothelium.

Cerebroprotective effect of resveratrol through antioxidant and anti-inflammatory effects in diabetic rats

Oxidative stress and inflammation have been implicated in cerebral ischemia/reperfusion injury and complication of diabetes. The present study was designed to evaluate whether resveratrol has cerebroprotective action through antioxidant and anti-inflammatory actions in diabetic rats. Bilateral common carotid artery occlusion (30 min) and reperfusion (4 h) was employed to induce cerebral infarction in diabetic Wistar rats. Diabetes was induced by streptozocine (50 mg/kg) intraperitoneally at once. Diabetic animals were divided into groups as: normal, sham, ischemia-reperfusion, and resveratrol-treated (5, 10, 20, and 30 mg/kg). These were used for estimation of cerebral infarction. Furthermore, 20 mg/kg dose was selected for estimation of oxidative stress markers (malondialdehyde, superoxide dismutase, and catalase). Inflammatory markers like TNF-α, IL-6, IL-10, and myeloperoxidase were estimated and histological characters were studied. Resveratrol produced dose-dependent reduction in percent cerebral infarction. With resveratrol of 20 mg/kg dose, levels of oxidative stress markers and inflammatory markers like malondialdehyde, TNF-α, IL-6, and myeloperoxidase were reduced and there was a significant increase in the levels of antioxidant and anti-inflammatory markers like catalase, superoxide dismutase, and IL-10. In the present study, we found that mechanism(s) responsible for the cerebroprotective effect of resveratrol in the diabetic rat brain involves antioxidant and anti-inflammatory actions.

Cerebroprotective potential of resveratrol through anti-oxidant and anti-inflammatory mechanisms in rats

Oxidative stress and inflammation are two important pathological mechanisms involved in cerebral ischemia and reperfusion injury. In pathological conditions such as cerebral infarction, the free radical production is greater than that of elimination by endogenous anti-oxidant system, by this undesirable effect brain is highly injured. Resveratrol is reported to have anti-oxidant and anti-inflammatory, athero-protective activities. Therefore, the aim of the present study is to evaluate the therapeutic potential of resveratrol against cerebral infarction induced by ischemia and reperfusion injury in Wistar rats. Bi-common carotid occlusion followed by 4 h reperfusion model was used to induce cerebral infarction. Percent infarction, oxidative stress markers (malondialdehyde, catalase, superoxide dismutase) and inflammatory markers (myeloperoxidase, TNF-α, IL-6, ICAM-1 and IL-10) were measured. TNF-α, IL-6, IL-10, and intracellular adhesive molecule-I (ICAM-1) levels were quantified by enzyme-linked immunosorbent assay (ELISA). Resveratrol produced significant dose-dependent reduction in percent cerebral infarct volume. At resveratrol 20 mg/kg dose, there was a significant reduction in oxidative stress and inflammatory markers like malondialdehyde, TNF-α, IL-6, myeloperoxidase and ICAM-I and in contrast there was a significant increase in anti-oxidants and anti-inflammatory markers like superoxide dismutase, catalase and IL-10 levels. Resveratrol showed significant cerebroprotective action mediated by anti-oxidant and anti-inflammatory mechanisms.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Age-dependent neurovascular abnormalities and altered microglial morphology in the YAC128 mouse model of Huntington disease

Central nervous system (CNS) inflammatory processes including microglial activation have been implicated in the pathogenesis of neurodegenerative diseases such as Huntington Disease (HD). We report age-dependent changes in striatal microglial morphology and vasculature in the YAC128 mouse model of HD. Decreases in microglial ramification along with a decrease in vessel diameter and increased vessel density and length suggest the presence of microgliosis and proangiogenic activity in YAC128 mice. Our hypothesis for this study was that the changes in microglial morphology and perturbations in vasculature may be involved in the pathogenesis of HD and that peripheral challenge with the bacterial endotoxin, lipopolysaccharide (LPS), will exacerbate these microglial and vascular changes as well as the HD phenotype in YAC128 mice at 12 months. Chronic peripheral LPS (1mg/kg) potentiated microglial activation indicated by an increase in microglial cell body size and retraction of processes. This potentiation in microglial activation with chronic peripheral LPS challenge was paralleled with vascular remodeling including dilatation, increased vessel wall thickness, increased BBB permeability and fibrinogen deposition in YAC128 striatum. Although peripheral LPS caused an increase in microglial activation and degenerative changes in cerebrovasculature, the phenotypic hallmarks of HD in YAC128 mice such as motor coordination deficits and decreased striatal volume were not exacerbated by chronic peripheral LPS exposure. This study identifies age-dependent increases in microglial activation and angiogenesis in YAC128 at 12 months. Peripheral inflammation induced by chronic LPS causes similar changes but does not influence the HD phenotype in YAC128 mice.

The treatment of traumatic brain injury with velcade

Traumatic brain injury (TBI) elicits a strong inflammatory response that contributes to the acute pathological processes seen following TBI, including cerebral edema and disruption of the blood-brain barrier (BBB), in addition to longer-term neurological damage and cognitive impairment. Proteasome inhibitors reduce vascular thrombotic and inflammatory events and consequently protect vascular function. In the present study we evaluated the neuroprotective effect of Velcade (bortezomib), a potent and selective inhibitor of proteasomes, which is in clinical use for the treatment of multiple myeloma. When administered within 2 h after TBI onset, Velcade reduced inflammatory responses, lesion volume, and neurological functional deficits, and enhanced neuronal survival. Western blot and ELISA showed that Velcade decreased the expression of NF-κB. These results suggest that in the experimental setting, Velcade is an effective neuroprotective agent for the treatment of TBI.

Early micro vascular changes after subarachnoid hemorrhage

During the last decade much effort has been invested in understanding the events that occur early after SAH. It is now widely accepted that these early events not only participate in the early ischemic injury but also set the stage for the pathogenesis of delayed vasospasm. That early cerebral ischemia occurs after SAH is documented in both experimental SAH and in human autopsy studies; however, angiographic evidence for vasoconstriction early after SAH is lacking and the source of early ischemic injury is therefore unclear. Recently, the cerebral microvasculature has been identified as an early target of SAH. Changes in the anatomical structure of cerebral microvessels, sufficient to cause functional deficits, are found early after experimental SAH. These changes may explain cerebral ischemia in human in the absence of angiographic evidence of large vessel vasoconstriction. This paper summarizes known alterations in cerebral microvasculature during the first 48 h after SAH.

The paradox of the neutrophil's role in tissue injury

The neutrophil is an essential component of the innate immune system, and its function is vital to human life. Its production increases in response to virtually all forms of inflammation, and subsequently, it can accumulate in blood and tissue to varying degrees. Although its participation in the inflammatory response is often salutary by nature of its normal interaction with vascular endothelium and its capability to enter tissues and respond to chemotactic gradients and to phagocytize and kill microrganisms, it can contribute to processes that impair vascular integrity and blood flow. The mechanisms that the neutrophil uses to kill microorganisms also have the potential to injure normal tissue under special circumstances. Its paradoxical role in the pathophysiology of disease is particularly, but not exclusively, notable in seven circumstances: 1) diabetic retinopathy, 2) sickle cell disease, 3) TRALI, 4) ARDS, 5) renal microvasculopathy, 6) stroke, and 7) acute coronary artery syndrome. The activated neutrophil's capability to become adhesive to endothelium, to generate highly ROS, and to secrete proteases gives it the potential to induce local vascular and tissue injury. In this review, we summarize the evidence for its role as a mediator of tissue injury in these seven conditions, making it or its products potential therapeutic targets.

A review of delayed ischemic neurologic deficit following aneurysmal subarachnoid hemorrhage: historical overview, current treatment, and pathophysiology

Delayed ischemic neurologic deficit (DIND) is a serious and poorly understood complication of aneurysmal subarachnoid hemorrhage. Although advances in treatment have improved prognosis for these patients, long-term clinical outcomes remain disappointing. Historically, angiographic vasospasm was thought to result in a DIND, although an increasing body of evidence suggests that this is an oversimplification, because interventions that have effectively targeted angiographic vasospasm have not improved outcome. Consequently, the relationship between angiographic vasospasm and neurologic outcome may be associative rather than causative. Although our understanding of the underlying molecular processes and pathophysiology is improving, responsible mediators or pathways have yet to be identified. The aim of this review is to summarize the key historical events that have helped shape our understanding of the pathophysiology of this phenomenon (microcirculation, autoregulation, microthrombosis, inflammation, apoptosis, spreading depolarization, oxidative stress) and to present the evidence underlying current treatment strategies (hemodynamic therapy, oral nimodipine, endovascular therapy, statins, cerebrospinal fluid drainage, thrombolysis, magnesium) and the translational and clinical research investigating DIND.

Emerging inflammatory biomarkers with acute stroke

Despite newer neuroimaging techniques, timely and accurate diagnosis of acute stroke remains a significant challenge. The ability to identify stroke patients rapidly using a biologic biomarker would be highly beneficial. Inflammation following stroke is one physiologic mechanism that has been studied extensively in biomarker research. Several emerging inflammatory biomarkers have been identified and may be useful to diagnosis stroke, to predict the evolution of stroke, and to predict hemorrhagic transformation, particularly with the administration of thrombolytic therapy. Many challenges must be overcome before application to clinical practice can be recommended. Nevertheless, emerging inflammatory biomarkers demonstrate considerable promise, particularly as part of a multiple biomarker strategy, and significant improvement in stroke diagnosis, clinical management, and outcomes may be realized.

Neuronal apoptosis is inhibited by cord blood stem cells after spinal cord injury

Spinal cord injury (SCI) induces a series of endogenous biochemical changes that lead to secondary damage involving apoptosis as one of the major events. To understand the molecular basis of apoptosis after spinal cord injury, we subjected male rats to spinal cord injury using a weight drop device (NYU impactor) and evaluated the therapeutic potential of human umbilical cord blood stem cells (hUCB), which were stereotactically transplanted into the injury epicenter 1 week after SCI. We identified genes that render the adult-injured spinal cord nonconducive and the hUCB-treated spinal cord conducive to regeneration and repair at 3 weeks post-injury using an RT-PCR microarray by analyzing 84 apoptotic genes. Genes involved in inflammation and apoptosis were upregulated in injured spinal cords of rats, whereas genes involved in neuroprotection were upregulated in the hUCB-treated rats. Quantitative RT-PCR verified mRNA changes in the apoptotic genes of TNF-alpha, TNFR1, TNFR2, Fas, Lta, and CD40. Based on these results, we evaluated the role of TNF-alpha and its related apoptotic genes in neuronal death after SCI. Changes in the expression of TNF-alpha, TNFR1, and TNFR2 were observed over a period of 3 weeks post-SCI and after treatment with hUCB. Expression of P50 and P65 on neurons after SCI was efficiently downregulated by hUCB. These results were confirmed by the evaluation of apoptotic proteins of co-cultures of spinal neurons with hUCB under in-vitro conditions. The results of this study suggest that hUCB have therapeutic potential in inhibiting neuronal apoptosis during the repair of injured spinal cord.

Inflammatory Reaction in Acute Retinal Artery Occlusion: Cytokine Levels in Aqueous Humor and Serum

PURPOSE

To investigate the role of inflammation in acute retinal artery occlusion (RAO).

METHODS

Levels of interleukin (IL)-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) were measured in serum (n = 14) and aqueous humor (AqH) (n = 8) samples from patients with RAO. Findings were compared with 24 age- and disease-matched patients, 10 healthy subjects (serum), and 16 patients undergoing cataract surgery (AqH).

RESULTS

Patients who arrived early (within 4-6 hours of occlusion) had higher serum IL-8 and IL-6 levels than controls; the IL-6 level in the AqH was lower than that of controls, while the IL-8 level was higher. In seven patients for whom both serum and AqH samples were available, serum IL-6 levels were higher than their corresponding AqH levels in most patients arriving within 10 hours of occlusion, and AqH IL-8 levels were higher than the corresponding serum levels in all but one. TNF-alpha levels were consistently higher in the serum than in the AqH at all time points.

CONCLUSIONS

Serum IL-8 and IL-6 and AqH IL-8 are elevated immediately following acute RAO. The early local suppression of IL-6 may be related to ocular immune mechanisms.

Mechanisms of ischemic brain damage

In the United States stroke is the third leading cause of death and the leading cause of disability. Brain injury following stroke results from the complex interplay of multiple pathways including excitotoxicity, acidotoxicity, ionic imbalance, peri-infarct depolarization, oxidative and nitrative stress, inflammation and apoptosis. There are very few treatments for stroke and the development of new treatments requires a comprehensive understanding of the diverse mechanisms of ischemic brain damage that are responsible for neuronal death. Here, we discuss the underlying pathophysiology of this devastating disease and reveal the intertwined pathways that are the target of therapeutic intervention.

Leukocyte filtration to decrease the number of adherent leukocytes in the cerebral microcirculation after a period of deep hypothermic circulatory arrest

OBJECTIVE

Cardiopulmonary bypass and hypothermic circulatory arrest induce a systemic inflammatory response, including a cascade of leukocyte and endothelial cell activity, during the postischemic reperfusion phase. Accumulation of leukocytes in the brain can lead to neurologic problems after cardiac surgery. The beneficial effects of a leukocyte-depleting filter have been documented, but because of contradictory results the underlying function of the filter remains unclear.

METHODS

Twenty-two juvenile piglets (6 to 8 weeks) were randomly assigned to undergo cardiopulmonary bypass with or without a leukocyte-depleting filter 60 minutes before and 60 minutes after a 75-minute hypothermic circulatory arrest at 18 degrees C. The cerebral vessels were visualized with intravital microscopy through a cranial window placed over the parietal cortex. Rhodamine staining was used to observe adherent and rolling leukocytes in the cerebral postcapillary venules. The animals were electively killed 1 hour after weaning from cardiopulmonary bypass.

RESULTS

There were no significant differences between the study groups regarding hemodynamic data. Numbers of adherent activated leukocytes were lower in the leukocyte filtration group, reaching borderline statistical significance when assessed throughout the experiment (between-groups P = .069) and actual statistical significance when assessed during the rewarming period (between-groups P = .029).

CONCLUSION

The leukocyte-depleting filter succeeded in reducing the number of adherent leukocytes during the reperfusion period in an experimental operation with deep hypothermic circulatory arrest. Such a filter thus could mitigate cerebral reperfusion injury after cardiac surgery.

Inflammation in stroke and focal cerebral ischemia

BACKGROUND

A growing number of recent investigations have established a critical role for leukocytes in propagating tissue damage after ischemia and reperfusion in stroke. Experimental data obtained from animal models of middle cerebral artery occlusion implicate inflammatory cell adhesion molecules, chemokines, and cytokines in the pathogenesis of this ischemic damage.

METHODS

Data from recent animal and human studies were reviewed to demonstrate that inflammatory events occurring at the blood-endothelium interface of the cerebral capillaries underlie the resultant ischemic tissue damage.

RESULTS

After arterial occlusion, the up-regulated expression of cytokines including IL-1, and IL-6 act upon the vascular endothelium to increase the expression of intercellular adhesion molecule-1, P-selectin, and E-selectin, which promote leukocyte adherence and accumulation. Integrins then serve to structurally modify the basal lamina and extracellular matrix. These inflammatory signals then promote leukocyte transmigration across the endothelium and mediate inflammatory cascades leading to further cerebral infarction.

CONCLUSIONS

Inflammatory interactions that occur at the blood-endothelium interface, involving cytokines, adhesion molecules, chemokines and leukocytes, are critical to the pathogenesis of tissue damage in cerebral infarction. Exploring these pathophysiological mechanisms underlying ischemic tissue damage may direct rational drug design in the therapeutic treatment of stroke.

Endothelin-1 receptor antagonist (LU-135252) improves the microcirculation and course of TNBS colitis in rats

The role of microcirculation in the pathogenesis and course of chronic inflammatory bowel disease is still unclear. The aim of this study was the evaluation of the role of microcirculation in colitis activity in the rat TNBS (trinitrobenzenesulfonic acid) colitis model using endothelin-1 and a selective endothelin-1 receptor antagonist (LU-135252). Target parameters were capillary blood flow, functional capillary density, vascular permeability, and leukocyte sticking as well as recording of hematocrit, weight course, diuresis, stool quality, and degree of inflammation using a histological colitis score. The acute phase of TNBS colitis is characterized by an extensive disturbance of microcirculation (a significant decrease in capillary blood flow and capillary density and a significant increase in capillary permeability and leukocyte sticking in the mucosa). There is also a significant increase in hematocrit and a significant decrease in diuresis and weight. An exogenous supply of endothelin-1 does not lead to an aggravation of these disorders because of a possible blockage of the endothelin-1 receptors by endogenous endothelin-1 in this florid inflammatory phase. Applying the selective endothelin-1 receptor A antagonist LU-135252 leads to a significant improvement of all microcirculatory parameters and clinical findings compared to the untreated colitis group. Direct improvement of capillary blood flow in the early phase of colitis leads to reduced colitis activity, which underscores the pathogenetic role of the microcirculation in the progression of colitis.

Analysis of inflammation

In the past, inflammation has been associated with infections and with the immune system. But more recent evidence suggests that a much broader range of diseases have telltale markers for inflammation. Inflammation is the basic mechanism available for repair of tissue after an injury and consists of a cascade of cellular and microvascular reactions that serve to remove damaged and generate new tissue. The cascade includes elevated permeability in microvessels, attachment of circulating cells to the vessels in the vicinity of the injury site, migration of several cell types, cell apoptosis, and growth of new tissue and blood vessels. This review provides a summary of the major microvascular, cellular, and molecular mechanisms that regulate elements of the inflammatory cascade. The analysis is largely focused on the identification of the major participants, notably signaling and adhesion molecules, and their mode of action in the inflammatory cascade. We present a new hypothesis for the generation of inflammatory mediators in plasma that are derived from the digestive pancreatic enzymes responsible for digestion. The inflammatory cascade offers a large number of opportunities for development of quantitative models that describe various aspects of human diseases.

Influence of the duration of ischemia and reperfusion on infarct volume and microvascular damage in mice

OBJECTIVES

Focal cerebral ischemia is responsible for alterations of vascular permeability, and the loss of microvascular integrity is a primary source of subsequent hemorrhages. We evaluated the influence of different durations of ischemia and reperfusion on infarction size and microvascular damage after focal cerebral ischemia in the mouse.

METHODS

C57BL/6 mice (n=39) were subjected to focal cerebral ischemia (I) and reperfusion (R). Consecutive brain sections were analysed for infarction volumes (Nissl-staining) and for collagen type IV (immunohistochemistry and western blot).

RESULTS

Infarction size (percentage of the infarction volume versus ipsilateral hemisphere) increased with total time of ischemia and reperfusion: 19+/-2% (I3R0), 30+/-2% (I3R3), 36+/-4% (I3R12), 41+/-4% (I1R24), 45+/-6% (I2R24) and 58+/-2% (I3R24). The ischemic hemispheres showed a significant progressive reduction of collagen type IV positive vessels (ischemic versus non-ischemic contralateral area): 90+/-3% (I3R0), 88+/-1% (I3R3), 82+/-3% (I3R12), 85+/-3% (I1R24), 79+/-3% (I2R24), 72+/-2% (I3R24).

CONCLUSIONS

Both prolonged ischemia and reperfusion lead to an increased infarction volume, as well as progressive microvascular damage.

Selective COX-2 inhibition reduces leukocyte sticking and improves the microcirculation in TNBS colitis

The role of cyclooxygenase-2 inhibitors in the course of experimental colitis is controversially discussed. The aim of this study was to evaluate leukocyte-endothelium interaction and colitis activity after applying the selective cyclooxygenase-2 inhibitor NS-398 in a rat trinitrobenzene sulfonic acid (TNBS) colitis model. The acute phase of TNBS colitis is characterized by a significant reduction of capillary blood flow, capillary density, diuresis, and weight and a significant increase in capillary permeability, leukocyte sticking, and hematocrit. Applying the selective cyclooxygenase-2 inhibitor NS-398 leads to a significant improvement of all microcirculatory parameters and clinical findings compared to the (untreated) colitis group. There are no histopathological differences between the individual colitis groups. Acute colitis is characterized by an extensive disturbance of microcirculation together with signs of systemic inflammatory response syndrome. These alterations are significantly improved by inhibiting cyclooxygenase-2. The results support the described correlation between cyclooxygenase activation and leukocyte-endothelium interaction. Moreover, they underscore the postulated relation between leukocyte-endothelium interaction and capillary blood flow.

Inhibitory effects of edaravone on the production of tumor necrosis factor-α in the isolated heart undergoing ischemia and reperfusion

We evaluated the effects of edaravone, a hydroxyl radical scavenging agent, on the production of tumor necrosis factor-alpha (TNF-alpha) in myocardium, and the release of TNF-alpha and P-selectin from myocardium after ischemia-reperfusion injury in isolated Langendorff-perfused rat hearts. Cardiodynamic function at stable points during perfusion and 5, 15, 30, and 60 min after the initiation of reperfusion was evaluated by left ventricular developed pressure, rate of increase in left ventricular pressure and rate of decrease in ventricular pressure, coronary flow, and heart rate. At 60 min after the initiation of reperfusion, myocardial infarct size was estimated microscopically using triphenyltetrazolium chloride staining, and expression of TNF-alpha in myocardium was detected by Western blot and immunohistochemistry. At the same time points as the measurement of cardiodynamic function, TNF-alpha and the soluble form of P-selectin in coronary effluent were measured by enzyme immunoassay. At all time points during reperfusion, edaravone markedly improved cardiodynamic function and reduced myocardial infarct size in comparison to the control. In myocardium in the control, TNF-alpha was detected in the endothelial cells and other cells bearing some resemblance to interstitial cells and monocyte cells. Edaravone suppressed this cytokine expression in the corresponding sites. P-selectin as well as TNF-alpha was found in the coronary effluent of the control, and edaravone significantly decreased soluble P-selectin levels in comparison to the control (P < 0.01). Edaravone might have protective effects on cardiac function through reduction of infarct size via decrease of production of TNF-alpha in myocardium induced by ischemia-reperfusion injury and through reduction of the release of adhesion molecules such as P-selectin from vascular endothelial cells.

Inhibition of vascular endothelial growth factor receptor 2 activity in experimental brain contusions aggravates injury outcome and leads to early increased neuronal and glial degeneration

Angiogenesis following traumatic brain injuries (TBIs) may be of importance for post-traumatic reparative processes and the development of secondary injuries. We have previously shown expression of vascular endothelial growth factor (VEGF), a major regulator of endothelial cell proliferation, angiogenesis and vascular permeability, and VEGF receptors (VEGFR1 and 2) after TBI in rat. In the present work we tried to further elucidate the role of VEGF after TBI by performing specific VEGFR2 activity inhibition. In rats subjected to VEGFR2 blockage we report an increased haemorrhagic area (P < 0.05), early increase in serum levels of neural injury marker neuron-specific enolase (P < 0.05) and glial injury marker S100beta (P < 0.05), and increased numbers of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labelling- (TUNEL-) and FluoroJade B- (P < 0.05) positive cells, all increases preceding the known VEGF/VEGFR vascular response in brain trauma. An increase in lesion area, as measured by decreased microtubuli-associated protein 2 expression (P < 0.05) and increased glial fibrillary acidic protein reactivity (P < 0.05), could also be demonstrated. In addition, vascular density, as measured by von Willebrandt factor-positive cells, was decreased (P < 0.05). No differences in post-traumatic inflammatory response, as measured by stainings for macrophages, granulocytes and intracellular adhesion molecules, were shown between the groups. Taken together, our findings point towards VEGF/VEGFR2 up-regulation after TBI as being an important endogenous cytoprotective mechanism in TBI. The possible importance of VEGF on the vascular, neuronal and glial compartments of the neurovascular unit after TBI is discussed.

Acute microvascular platelet aggregation after subarachnoid hemorrhage

OBJECT

The mechanisms underlying acute cerebral ischemia after subarachnoid hemorrhage (SAH) are not well established. Platelets aggregate within major cerebral vessels hours after SAH, but this has not been studied in the microvasculature. Platelet aggregates within the microvasculature could mechanically obstruct the lumen and initiate events that injure vessel structure. In the present study the authors examined the hypothesis that platelets aggregate within the cerebral microvasculature acutely after SAH.

METHODS

Subarachnoid hemorrhage was induced in the rat by using the endovascular perforation model. The animals were killed between 10 minutes and 48 hours after SAH. Immunostaining for the platelet surface receptor glycoprotein (GP)IIb/IIIa, which mediates platelet aggregation, was used to detect platelet aggregation. Sham-operated animals were used as controls. The GPIIb/IIIa immunoreactive platelet aggregates were abundant in the microvasculature of the basal and frontal cortex, striatum, and hippocampus 10 minutes after SAH. These aggregates decreased in number from 1 to 6 hours post-SAH and then increased to a peak at 24 hours. No immunoreactive aggregates were observed 48 hours after SAH.

CONCLUSIONS

The data indicate that widespread platelet aggregation occurs very rapidly in response to SAH followed by a decrease within 6 hours and a subsequent increase 24 hours after SAH. Microvascular platelet aggregates may contribute to decreased cerebral blood flow and ischemic injury after SAH via a number of mechanisms.

VEGF and VEGF receptor expression after experimental brain contusion in rat

Angiogenesis following traumatic brain injury (TBI) may be of importance not only for post-traumatic reparative processes but also for the development of secondary injuries. Vascular endothelial growth factor (VEGF) is a major regulator of endothelial cell proliferation, angiogenesis, and vascular permeability, though its possible involvement in secondary injuries after TBI is largely unknown. This study was undertaken to analyze the expression of VEGF and the VEGF receptors in experimental brain contusion in rat. Twenty-three adult female Sprague-Dawley rats were subjected to a focal cerebral contusion injury by use of a weight-drop model. Four additional rats underwent craniotomy only. The animals were sacrificed 6 h, or 1, 2, 4, 6, 8, or 16 days post-injury. Expression of VEGF and the VEGF receptors VEGFR1 (Flt-1) and VEGFR2 (Flk-1) were studied by in situ hybridization and immunohistochemistry. VEGF messenger (m)RNA and protein expression were detected in astrocytes, neutrophils, and macrophages in or adjacent to the injury from 1 day after injury, with a peak expression after 4-6 days. Flt-1 and Flk-1 mRNA and protein were detected in vessels adjacent to the lesion from 1 day after injury throughout day 6 after injury. It was also noted that Flt-1/Flk-1 and VEGF-positive vessels often were negative for SMI-71, a marker for vessels in areas with blood-brain barrier (BBB). In conclusion, we have demonstrated that TBI leads to an upregulation of VEGF, Flt-1, and Flk-1 mRNA and protein in and around the lesion. The data provide a foundation for future pharmacological intervention studies focusing on posttraumatic angiogenesis and possible injury repair effects of the VEGF system in TBI.

Effect of cerebral ischemia on brain mast cells in rats

The purpose of this study was to investigate the effect of transient cerebral ischemia on brain mast cells in rats. The mast cells decreased significantly at 1 h, 2 h, 4 h and 7 days after ischemia. At 1 day following ischemia, the increase of the number of mast cells in the middle aspect of the thalamus (bregma -2.80 to -3.16 mm) was twice as that of other regions in the thalamus. In addition, histamine contents increased significantly in the thalamus and striatum after ischemia. These results indicate that brain mast cells participate in the pathological process after ischemia.

Aging is associated with increased collagen type IV accumulation in the basal lamina of human cerebral microvessels

Background

Microvascular alterations contribute to the development of stroke and vascular dementia. The goal of this study was to evaluate age and hypertension related changes of the basal lamina in cerebral microvessels of individuals, who died from non-cerebral causes.

Results

We examined 27 human brains: 11 young and 16 old patients. Old patients were divided into two subgroups, those with hypertension (n = 8) and those without hypertension (n = 8). Basal lamina changes of the cerebral microvessels were determined in the putamen using antibodies against collagen type IV and by quantitative analysis of vessel number, total stained area of collagen, thickness of the vessel wall and lumen, and relative staining intensity using immunofluorescence. The total number of collagen positive vessels per microscopic field was reduced in old compared to young subjects (12.0+/-0.6 vs. 15.1+/-1.2, p = 0.02). The relative collagen content per vessel (1.01+/-0.06 vs. 0.76+/-0.05, p = 0.01) and the relative collagen intensity (233.1+/-4.5 vs. 167.8+/-10.6, p < 0.0001) shown by immunofluorescence were higher in the older compared to the younger patients with a consecutive reduction of the lumen / wall ratio (1.29+/-0.05 vs. 3.29+/-0.15, p < 0.0001). No differences were observed for these parameters between old hypertensive and non-hypertensive patients.

Conclusions

The present data show age-related changes of the cerebral microvessels in sections of human putamen for the first time. Due to the accumulation of collagen, microvessels thicken and show a reduction in their lumen. Besides this, the number of vessels decreases. These findings might represent a precondition for the development of vascular cognitive impairment. However, hypertension was not proven to modulate these changes.

Tumor necrosis factor alpha expression and protein levels after fluid percussion injury in rats: the effect of injury severity and brain temperature

OBJECTIVE

Tumor necrosis factor alpha (TNFalpha) is elevated in some models of traumatic brain injury (TBI). However, it is unclear how TNFalpha messenger ribonucleic acid (mRNA) expression and protein levels are affected by injury severity and posttraumatic temperature modification. This study determined the regional and temporal profile of TNFalpha levels after moderate and severe TBI and assessed the effects of posttraumatic hypothermia or hyperthermia on this proinflammatory cytokine.

METHODS

Adult male Sprague-Dawley rats were subjected to sham procedures (no injury), moderate fluid-percussion TBI (1.8-2.2 atm), or severe fluid-percussion TBI (2.4-2.6 atm). After 1 to 72 hours of survival, animals were killed, and brain samples, cerebrospinal fluid, and serum were harvested for enzyme-linked immunosorbent assay quantification of TNFalpha levels. In a subsequent study, a 3-hour period of posttraumatic hypothermia (33 degrees C) or hyperthermia (39.5 degrees C) was applied, followed by immediate killing and cytokine assay. Another group was subjected to moderate TBI (1.8-2.2 atm), followed by killing at 15 minutes or at 1, 3, or 24 hours for TNFalpha reverse transcriptase-polymerase chain reaction analysis.

RESULTS

A significant increase in TNFalpha mRNA and protein levels in cellular lysates of injured cortex and ipsilateral hippocampus was noted by 1 hour after TBI; it was sustained to 3 hours, followed by a rapid decline. Increased injury severity was associated with increased protein levels at remote injury sites and in the injured cerebral cortex at 72 hours. Posttraumatic hypothermia significantly reduced TNFalpha mRNA expression in the hippocampus compared with that in normothermic rats. In contrast, no temperature effects on TNFalpha protein levels were documented.

CONCLUSION

Rapid and marked increase in TNFalpha mRNA expression and protein levels follows moderate and severe TBI. Injury severity and posttraumatic temperature play a modest but significant role on TNFalpha expression and protein levels. These findings suggest that the effects of posttraumatic temperature on histopathological and behavioral outcome primarily may involve secondary mediators that do not operate directly through their effect on TNFalpha.

Higher bypass temperature correlates with increased white cell activation in the cerebral microcirculation

OBJECTIVE

Cardiopulmonary bypass induces a systemic inflammatory response, which in turn promotes a cascade of leukocyte and endothelial cell activity. We investigated whether differences in bypass temperature and flow rate affect endothelial cell and leukocyte adhesion in the cerebral microcirculation.

METHODS

Thirty-six piglets (13.0 +/- 1.1 kg) had a cranial window placed over the parietal cortex to evaluate the microcirculation by means of intravital microscopy. Animals were cooled to a temperature of 15 degrees C, 25 degrees C, or 34 degrees C on cardiopulmonary bypass with hematocrit levels of 20% or 30% by using pH-stat management, followed by 60 minutes of reduced flow (10, 25, or 50 mL.kg(-1).min(-1)). Rhodamine staining was used to observe adherent and rolling leukocytes in postcapillary venules.

RESULTS

Higher bypass temperature correlated with significantly more adherent and rolling leukocytes during the full 60 minutes of low-flow bypass (P <.05). Poisson regression revealed more adherent leukocytes at 34 degrees C than at 15 degrees C and at a flow rate of 10 mL.kg(-1).min(-1) compared with a flow rate of 50 mL.kg(-1).min(-1). There was an inverse correlation between flow rate and the number of adherent and rolling leukocytes at 30, 45, and 60 minutes of low-flow bypass (P <.05). Temperature was a multivariable predictor of histologic score, with greater neurologic damage found after bypass at 34 degrees C (P <.01).

CONCLUSIONS

Leukocyte activation in cerebral microcirculation is increased with higher temperature and lower flow rate, suggesting that these variables influence the inflammatory response during cardiopulmonary bypass.

Pathophysiology of cerebral ischemia and brain trauma: similarities and differences

Current knowledge regarding the pathophysiology of cerebral ischemia and brain trauma indicates that similar mechanisms contribute to loss of cellular integrity and tissue destruction. Mechanisms of cell damage include excitotoxicity, oxidative stress, free radical production, apoptosis and inflammation. Genetic and gender factors have also been shown to be important mediators of pathomechanisms present in both injury settings. However, the fact that these injuries arise from different types of primary insults leads to diverse cellular vulnerability patterns as well as a spectrum of injury processes. Blunt head trauma produces shear forces that result in primary membrane damage to neuronal cell bodies, white matter structures and vascular beds as well as secondary injury mechanisms. Severe cerebral ischemic insults lead to metabolic stress, ionic perturbations, and a complex cascade of biochemical and molecular events ultimately causing neuronal death. Similarities in the pathogenesis of these cerebral injuries may indicate that therapeutic strategies protective following ischemia may also be beneficial after trauma. This review summarizes and contrasts injury mechanisms after ischemia and trauma and discusses neuroprotective strategies that target both types of injuries.

Hypothermia for Acute Ischemic Stroke: Not Just Another Neuroprotectant

BACKGROUND

Based on empirical experience, hypothermia has long been known to be a potent putative neuroprotectant. Recent insights into the mechanisms of central ischemia and reperfusion suggest reasons why hypothermia may be an ideal modality for extending the time window for thrombolytic stroke therapy.

REVIEW SUMMARY

Hypothermia protects brain tissue from the effects of ischemia in multiple ways. It retards energy depletion, reduces intracellular acidosis, and lessens the ischemic overdose of excitatory neurotransmitters. This attenuates the influx of intracellular calcium, the herald of subsequent neuronal death. Additionally, hypothermia suppresses synthesis of oxygen free radicals involved in secondary damage associated with reperfusion. It also suppresses the mechanisms related to blood-brain barrier degeneration and post-ischemic remodeling. Animal and human data show that deep hypothermia is primarily protective and is used in several cardiothoracic and neurosurgical applications, and that mild hypothermia enhances recovery after focal and global ischemic brain injuries. Preliminary data on hypothermia in human stroke also show promising potential. Current methods of instituting hypothermia, including patient selection, temperature and timing, cooling methods, and complications are reviewed in detail.

CONCLUSIONS

Neuroprotection conferred by mild to moderate hypothermia is likely to undergo phase III clinical trials in various clinical settings. Novel technology promises a broad application even outside intensive care settings. Preliminary studies suggest that mild to moderate hypothermia is a useful adjunct to thrombolytic therapy for stroke. Timing, degree, and duration rules are being developed and methods of cooling further perfected to optimize the safety and efficacy of this promising approach.

Microvascular Basal lamina damage after embolic stroke in the rat: relationship to cerebral blood flow

Microvascular basal lamina damage has been demonstrated after balloon occlusion of the middle cerebral artery in the nonhuman primate and after intravascular filament occlusion in the rat. The aim of the present study was to investigate in the rat whether microvascular damage can be found in the stroke model of intracarotid clot injection as early as 3 hours after clot injection and whether microvascular damage relates to the level of regional cerebral blood flow (rCBF). Microvascular densities and total stained microvascular areas were determined by immunohistochemistry of collagen type IV in cortex and basal ganglia and automatic video-imaging analysis. rCBF was measured by autoradiography in the same brain areas. Compared with the corresponding areas in the nonischemic hemisphere, a significant loss of microvascular density (-16%) and total stained microvascular areas (-10%) was observed in these areas. The reduction of microvascular basal lamina staining was comparable in all animals and was not related to the value of rCBF when measured 3 hours after onset of embolic stroke. In conclusion, microvascular damage occurs as soon as 3 hours after intracarotid clot injection, even in brain areas in which rCBF has returned to normal values.

Vascular endothelial growth factor regulates focal adhesion assembly in human brain microvascular endothelial cells through activation of the focal adhesion kinase and related adhesion focal tyrosine kinase

Vascular endothelial growth factor (VEGF) plays a significant role in blood-brain barrier breakdown and angiogenesis after brain injury. VEGF-induced endothelial cell migration is a key step in the angiogenic response and is mediated by an accelerated rate of focal adhesion complex assembly and disassembly. In this study, we identified the signaling mechanisms by which VEGF regulates human brain microvascular endothelial cell (HBMEC) integrity and assembly of focal adhesions, complexes comprised of scaffolding and signaling proteins organized by adhesion to the extracellular matrix. We found that VEGF treatment of HBMECs plated on laminin or fibronectin stimulated cytoskeletal organization and increased focal adhesion sites. Pretreating cells with VEGF antibodies or with the specific inhibitor SU-1498, which inhibits Flk-1/KDR receptor phosphorylation, blocked the ability of VEGF to stimulate focal adhesion assembly. VEGF induced the coupling of focal adhesion kinase (FAK) to integrin alphavbeta5 and tyrosine phosphorylation of the cytoskeletal components paxillin and p130cas. Additionally, FAK and related adhesion focal tyrosine kinase (RAFTK)/Pyk2 kinases were tyrosine-phosphorylated by VEGF and found to be important for focal adhesion sites. Overexpression of wild type RAFTK/Pyk2 increased cell spreading and the migration of HBMECs, whereas overexpression of catalytically inactive mutant RAFTK/Pyk2 markedly suppressed HBMEC spreading ( approximately 70%), adhesion ( approximately 82%), and migration ( approximately 65%). Furthermore, blocking of FAK by the dominant-interfering mutant FRNK (FAK-related non-kinase) significantly inhibited HBMEC spreading and migration and also disrupted focal adhesions. Thus, these studies define a mechanism for the regulatory role of VEGF in focal adhesion complex assembly in HBMECs via activation of FAK and RAFTK/Pyk2.

Neuroprotection during cardiac surgery: a randomised trial of a platelet activating factor antagonist

OBJECTIVE

To assess platelet activating factor (PAF) antagonists, potent neuroprotective agents in experimental cerebral dysfunction, in clinical practice.

DESIGN

Double blind, minimised, placebo controlled trial of low and high dose PAF antagonist (lexipafant).

SETTING

Cardiac surgery unit.

PATIENTS

150 patients undergoing coronary artery bypass graft (CABG) surgery using cardiopulmonary bypass.

INTERVENTIONS

Randomisation to placebo, low dose (10 mg) or high dose (100 mg) lexipafant.

MAIN OUTCOME MEASURES

Incidence of impairment on four established cognitive tests, undertaken before, five days, and three months after CABG, examined by three methods for defining impairment.

RESULTS

The three groups were similar with respect to preoperative and intraoperative factors. Observed levels of cognitive impairment were less than had been predicted from previous studies. There was no difference in the groups in cognitive change scores at five days or three months. Group mean analysis showed significant time factors for all four tests but not for interactions or for the lexipafant group. A composite cognitive index, based on the aggregate of four normally distributed tests, showed a significant effect for timing of the test but not for the lexipafant group or interaction. Age, but not duration of bypass, was the most important determinant of postoperative cognitive impairment.

CONCLUSIONS

The neuroprotective PAF antagonist lexipafant did not differentially reduce the level of cognitive impairment after CABG as determined by power estimates derived from published studies. The strongest predictors of cognitive impairment were age and timing of the test after operation.

Anti-epileptic drugs as possible neuroprotectants in cerebral ischemia

Many similarities exist between cerebral ischemia and epilepsy regarding brain-damaging and auto-protective mechanisms that are activated following the injurious insult. Therefore, drugs that are effective in minimizing seizure-induced brain damage may also be useful in minimizing ischemic injury. Use of such drugs in stroke victims may have important clinical and financial advantages. Therefore, the authors conducted a Medline search of studies involving the use of anti-epileptic drugs (AEDs) as possible neuroprotectants and summarize the data. Most AEDs have been tested in animal models of focal or global ischemia and some were already tested in humans, for a possible neuroprotective effect. The existing data is rather scant and insufficient but it appears that only drugs that have multiple mechanisms of action seem to have some potential in conferring a degree of neuroprotection that could be clinically applicable to stroke patients. In conclusion, some of the newer AEDs show promise as possible neuroprotectants in the setup of acute ischemic stroke but more studies are needed before clinical trials in humans could be undertaken.

Protein S confers neuronal protection during ischemic/hypoxic injury in mice

BACKGROUND

Protein S is an antithrombotic factor that also exhibits mitogenic activity. Thus, we hypothesized that protein S may control cerebrovascular thrombosis in stroke and protect brain tissue from ischemic injury.

METHODS AND RESULTS

We studied protein S in a murine in vivo model of stroke and an in vitro model of neuronal hypoxia/reoxygenation injury. Animals received purified human plasma-derived protein S or vehicle intravenously 10 minutes after initiation of middle cerebral artery occlusion followed by reperfusion. Protein S at 0.2 to 2 mg/kg significantly improved the motor neurological deficit by 3.8- to 3.2-fold and reduced infarction and edema volumes by 45% to 54% and 45% to 62%, respectively. Protein S at 2 mg/kg improved postischemic cerebral blood flow by 21% to 26% and reduced brain fibrin deposition and infiltration with neutrophils by 40% and 53%, respectively. Intracerebral bleeding was not observed with protein S. Protein S protected ischemic neurons in vivo and cultured neurons from hypoxia/reoxygenation-induced apoptosis in a time- and dose-dependent manner. Recombinant human protein S exerted protective effects from hypoxia-induced damage similar to the plasma-derived protein S both in vivo and in vitro.

CONCLUSIONS

Protein S is a significant neuroprotectant during ischemic brain injury with direct effects on neurons and antithrombotic effects. Thus, protein S could be a prototype of a new class of agents for clinical stroke with combined direct neuronal protective effects and systemic antithrombotic and antiinflammatory activities.