Tissue Factor Localization in Non-Human Primate Cerebral Tissue

Tissue factor (TF), the principal procoagulant of human brain, resides in specific regions of the non-human primate central nervous system. Immunohistochemical studies employing murine anti-human TF monoclonal antibodies (MoAbs) detected TF antigen in the cortex, basal ganglia, cerebellum, and cervical spinal cord in three normal baboon subjects. Although significantly less prominent than human cortical gray matter, a distinct partition of TF in gray matter >white matter was noted. The gray matter predilection of TF was confirmed in primate temporal and parietal lobe cortex by both sandwich ELISA and one-stage coagulation assay. Variation in the relative quantity of TF antigen was observed by ELISA among the three subjects studied. Procoagulant activity followed the pattern of TF antigen (cortical gray matter >basal ganglia ≥cerebellum >cortical white matter), and was 96.5–98.5% inhibitable by a function inhibiting anti-human TF MoAb combination. TF antigen was associated with the microvasculature of all cerebral tissues studied, and spared capillaries most selectively in the cerebral cortex, basal ganglia, and cerebellum. These findings suggest a highly specific ordering of TF antigen and related procoagulant activity in the central nervous system of the baboon, confined primarily to gray matter parenchyma, and to the non-capillary microvasculature.

Periprocedural Antithrombotic Treatment During Acute Mechanical Thrombectomy for Ischemic Stroke: A Systematic Review

BACKGROUND

More than one-third of the patients with ischemic stroke caused by an intracranial large vessel occlusion do not recover to functional independence despite fast and successful recanalization by acute mechanical thrombectomy (MT). This may partially be explained by incomplete microvascular reperfusion. Some antithrombotics, e.g., antiplatelet agents and heparin, may be able to restore microvascular reperfusion. However, antithrombotics may also increase the risk of symptomatic intracranial hemorrhage (sICH). The aim of this review was to assess the potential safety and functional outcome of periprocedural antiplatelet or heparin use during acute MT for ischemic stroke.

METHODS

We systematically searched PubMed, Embase, Medline, Web of Science, and Cochrane for studies investigating the safety and functional outcome of periprocedural antiplatelet or heparin treatment during acute MT for ischemic stroke. The primary outcome was the risk for sICH. Secondary outcomes were functional independence after 3-6 months (modified Rankin Scale 0-2) and mortality within 6 months.

RESULTS

837 studies were identified through the search, of which 19 studies were included. The sICH risks of the periprocedural use of antiplatelets ranged from 6 to 17%, and for heparin from 5 to 12%. Two of four studies reporting relative effects of the use of antithrombotics are pointing toward an increased risk of sICH. Among patients treated with antiplatelet agents, functional independence varied from 23 to 60% and mortality from 18 to 33%. For heparin, this was, respectively, 19-54% and 19-33%. The three studies presenting relative effects of antiplatelets on functional independence showed neutral effects. Both studies reporting relative effects of heparin on functional independence found it to increase this chance.

CONCLUSION

Randomized controlled trials investigating the effect of periprocedural antithrombotic treatment in MT are lacking. Some observational studies report a slight increase in sICH risk, which may be acceptable because they also suggest a beneficial effect on functional outcome. Therefore, randomized controlled trials are warranted to address the question whether the potentially higher risk of sICH could be outweighed by improved functional outcome.

Exploring phlebotomy technique as a pre-analytical factor in proteomic analyses by mass spectrometry

Multiple reaction monitoring mass spectrometry (MRM-MS) is an emerging technology for blood biomarker verification and validation; however, the results may be influenced by pre-analytical factors. This exploratory study was designed to determine if differences in phlebotomy techniques would significantly affect the abundance of plasma proteins in an upcoming biomarker development study. Blood was drawn from 10 healthy participants using four techniques: (1) a 20-gauge IV with vacutainer, (2) a 21-gauge direct vacutainer, (3) an 18-gauge butterfly with vacutainer, and (4) an 18-gauge butterfly with syringe draw. The abundances of a panel of 122 proteins (117 proteins, plus 5 matrix metalloproteinase (MMP) proteins) were targeted by LC/MRM-MS. In addition, complete blood count (CBC) data were also compared across the four techniques. Phlebotomy technique significantly affected 2 of the 11 CBC parameters (red blood cell count, p = 0.010; hemoglobin concentration, p = 0.035) and only 12 of the targeted 117 proteins (p < 0.05). Of the five MMP proteins, only MMP7 was detectable and its concentration was not significantly affected by different techniques. Overall, most proteins in this exploratory study were not significantly influenced by phlebotomy technique; however, a larger study with additional patients will be required for confirmation.

Glibenclamide in cerebral ischemia and stroke

The sulfonylurea receptor 1 (Sur1)-transient receptor potential 4 (Trpm4) channel is an important molecular element in focal cerebral ischemia. The channel is upregulated in all cells of the neurovascular unit following ischemia, and is linked to microvascular dysfunction that manifests as edema formation and secondary hemorrhage, which cause brain swelling. Activation of the channel is a major molecular mechanism of cytotoxic edema and "accidental necrotic cell death." Blockade of Sur1 using glibenclamide has been studied in different types of rat models of stroke: (i) in conventional non-lethal models (thromboembolic, 1-2 h temporary, or permanent middle cerebral artery occlusion), glibenclamide reduces brain swelling and infarct volume and improves neurological function; (ii) in lethal models of malignant cerebral edema, glibenclamide reduces edema, brain swelling, and mortality; (iii) in models with rtPA, glibenclamide reduces swelling, hemorrhagic transformation, and death. Retrospective studies of diabetic patients who present with stroke have shown that those whose diabetes is managed with a sulfonylurea drug and who are maintained on the sulfonylurea drug during hospitalization for stroke have better outcomes at discharge and are less likely to suffer hemorrhagic transformation. Here, we provide a comprehensive review of the basic science, preclinical experiments, and retrospective clinical studies on glibenclamide in focal cerebral ischemia and stroke. We also compare the preclinical work in stroke models to the updated recommendations of the Stroke Therapy Academic Industry Roundtable (STAIR). The findings reviewed here provide a strong foundation for a translational research program to study glibenclamide in patients with ischemic stroke.

Effect of treatment delay, age, and stroke severity on the effects of intravenous thrombolysis with alteplase for acute ischaemic stroke: a meta-analysis of individual patient data from randomised trials

BACKGROUND

Alteplase is effective for treatment of acute ischaemic stroke but debate continues about its use after longer times since stroke onset, in older patients, and among patients who have had the least or most severe strokes. We assessed the role of these factors in affecting good stroke outcome in patients given alteplase.

METHODS

We did a pre-specified meta-analysis of individual patient data from 6756 patients in nine randomised trials comparing alteplase with placebo or open control. We included all completed randomised phase 3 trials of intravenous alteplase for treatment of acute ischaemic stroke for which data were available. Retrospective checks confirmed that no eligible trials had been omitted. We defined a good stroke outcome as no significant disability at 3-6 months, defined by a modified Rankin Score of 0 or 1. Additional outcomes included symptomatic intracranial haemorrhage (defined by type 2 parenchymal haemorrhage within 7 days and, separately, by the SITS-MOST definition of parenchymal type 2 haemorrhage within 36 h), fatal intracranial haemorrhage within 7 days, and 90-day mortality.

FINDINGS

Alteplase increased the odds of a good stroke outcome, with earlier treatment associated with bigger proportional benefit. Treatment within 3·0 h resulted in a good outcome for 259 (32·9%) of 787 patients who received alteplase versus 176 (23·1%) of 762 who received control (OR 1·75, 95% CI 1·35-2·27); delay of greater than 3·0 h, up to 4·5 h, resulted in good outcome for 485 (35·3%) of 1375 versus 432 (30·1%) of 1437 (OR 1·26, 95% CI 1·05-1·51); and delay of more than 4·5 h resulted in good outcome for 401 (32·6%) of 1229 versus 357 (30·6%) of 1166 (OR 1·15, 95% CI 0·95-1·40). Proportional treatment benefits were similar irrespective of age or stroke severity. Alteplase significantly increased the odds of symptomatic intracranial haemorrhage (type 2 parenchymal haemorrhage definition 231 [6·8%] of 3391 vs 44 [1·3%] of 3365, OR 5·55, 95% CI 4·01-7·70, p<0·0001; SITS-MOST definition 124 [3·7%] vs 19 [0·6%], OR 6·67, 95% CI 4·11-10·84, p<0·0001) and of fatal intracranial haemorrhage within 7 days (91 [2·7%] vs 13 [0·4%]; OR 7·14, 95% CI 3·98-12·79, p<0·0001). The relative increase in fatal intracranial haemorrhage from alteplase was similar irrespective of treatment delay, age, or stroke severity, but the absolute excess risk attributable to alteplase was bigger among patients who had more severe strokes. There was no excess in other early causes of death and no significant effect on later causes of death. Consequently, mortality at 90 days was 608 (17·9%) in the alteplase group versus 556 (16·5%) in the control group (hazard ratio 1·11, 95% CI 0·99-1·25, p=0·07). Taken together, therefore, despite an average absolute increased risk of early death from intracranial haemorrhage of about 2%, by 3-6 months this risk was offset by an average absolute increase in disability-free survival of about 10% for patients treated within 3·0 h and about 5% for patients treated after 3·0 h, up to 4·5 h.

INTERPRETATION

Irrespective of age or stroke severity, and despite an increased risk of fatal intracranial haemorrhage during the first few days after treatment, alteplase significantly improves the overall odds of a good stroke outcome when delivered within 4·5 h of stroke onset, with earlier treatment associated with bigger proportional benefits.

FUNDING

UK Medical Research Council, British Heart Foundation, University of Glasgow, University of Edinburgh.

Thrombolysis for acute ischaemic stroke

BACKGROUND

Most strokes are due to blockage of an artery in the brain by a blood clot. Prompt treatment with thrombolytic drugs can restore blood flow before major brain damage has occurred and improve recovery after stroke in some people. Thrombolytic drugs, however, can also cause serious bleeding in the brain, which can be fatal. One drug, recombinant tissue plasminogen activator (rt-PA), is licensed for use in selected patients within 4.5 hours of stroke in Europe and within three hours in the USA. There is an upper age limit of 80 years in some countries, and a limitation to mainly non-severe stroke in others. Forty per cent more data are available since this review was last updated in 2009.

OBJECTIVES

To determine whether, and in what circumstances, thrombolytic therapy might be an effective and safe treatment for acute ischaemic stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched November 2013), MEDLINE (1966 to November 2013) and EMBASE (1980 to November 2013). We also handsearched conference proceedings and journals, searched reference lists and contacted pharmaceutical companies and trialists.

SELECTION CRITERIA

Randomised trials of any thrombolytic agent compared with control in people with definite ischaemic stroke.

DATA COLLECTION AND ANALYSIS

Two review authors applied the inclusion criteria, extracted data and assessed trial quality. We verified the extracted data with investigators of all major trials, obtaining additional unpublished data if available.

MAIN RESULTS

We included 27 trials, involving 10,187 participants, testing urokinase, streptokinase, rt-PA, recombinant pro-urokinase or desmoteplase. Four trials used intra-arterial administration, while the rest used the intravenous route. Most data come from trials that started treatment up to six hours after stroke. About 44% of the trials (about 70% of the participants) were testing intravenous rt-PA. In earlier studies very few of the participants (0.5%) were aged over 80 years; in this update, 16% of participants are over 80 years of age due to the inclusion of IST-3 (53% of participants in this trial were aged over 80 years). Trials published more recently utilised computerised randomisation, so there are less likely to be baseline imbalances than in previous versions of the review. More than 50% of trials fulfilled criteria for high-grade concealment; there were few losses to follow-up for the main outcomes.Thrombolytic therapy, mostly administered up to six hours after ischaemic stroke, significantly reduced the proportion of participants who were dead or dependent (modified Rankin 3 to 6) at three to six months after stroke (odds ratio (OR) 0.85, 95% confidence interval (CI) 0.78 to 0.93). Thrombolytic therapy increased the risk of symptomatic intracranial haemorrhage (OR 3.75, 95% CI 3.11 to 4.51), early death (OR 1.69, 95% CI 1.44 to 1.98; 13 trials, 7458 participants) and death by three to six months after stroke (OR 1.18, 95% CI 1.06 to 1.30). Early death after thrombolysis was mostly attributable to intracranial haemorrhage. Treatment within three hours of stroke was more effective in reducing death or dependency (OR 0.66, 95% CI 0.56 to 0.79) without any increase in death (OR 0.99, 95% CI 0.82 to 1.21; 11 trials, 2187 participants). There was heterogeneity between the trials. Contemporaneous antithrombotic drugs increased the risk of death. Trials testing rt-PA showed a significant reduction in death or dependency with treatment up to six hours (OR 0.84, 95% CI 0.77 to 0.93, P = 0.0006; 8 trials, 6729 participants) with significant heterogeneity; treatment within three hours was more beneficial (OR 0.65, 95% CI 0.54 to 0.80, P < 0.0001; 6 trials, 1779 participants) without heterogeneity. Participants aged over 80 years benefited equally to those aged under 80 years, particularly if treated within three hours of stroke.

AUTHORS' CONCLUSIONS

Thrombolytic therapy given up to six hours after stroke reduces the proportion of dead or dependent people. Those treated within the first three hours derive substantially more benefit than with later treatment. This overall benefit was apparent despite an increase in symptomatic intracranial haemorrhage, deaths at seven to 10 days, and deaths at final follow-up (except for trials testing rt-PA, which had no effect on death at final follow-up). Further trials are needed to identify the latest time window, whether people with mild stroke benefit from thrombolysis, to find ways of reducing symptomatic intracranial haemorrhage and deaths, and to identify the environment in which thrombolysis may best be given in routine practice.

Evolving role of endovascular treatment of acute ischemic stroke

The perceived advantages of endovascular treatment for acute ischemic stroke in terms of recanalization, the multimodal and targeted approaches, and perhaps the more permissive rules on devices than on medications for their licensing favored the assumption that endovascular treatment is superior to intravenous thrombolysis for acute treatment of ischemic stroke, and its adoption in more advanced stroke centers. However, this assumption has been questioned by recent clinical trial experience showing that endovascular treatment is not superior to intravenous thrombolysis. The new evidence has changed the perception and the importance of conducting randomized trials in this area. This summary examines the background and outcomes of the latest experience with endovascular techniques in acute stroke treatment based on historical data. The new challenge is how to study the latest generation of devices called stent retrievers, which are faster in recanalizing and easier to use, in selected patients with acute ischemic stroke. In the meantime, the available evidence does not provide support for the use of endovascular treatment of acute ischemic stroke in clinical practice.

Hemostasis and alterations of the central nervous system

Modulation of coagulation has been successfully applied to ischemic disorders of the central nervous system (CNS). Some components of the coagulation system have been identified in the CNS, yet with limited exception their functions have not been clearly defined. Little is known about how events within the cerebral tissues affect hemostasis. Nonetheless, the interaction between cerebral cells and vascular hemostasis and the possibility that endogenous coagulation factors can participate in functions within the neurovascular unit provide intriguing possibilities for deeper insight into CNS functions and the potential for treatment of CNS injuries. Here, we consider the expression of coagulation factors in the CNS, the coagulopathy associated with focal cerebral ischemia (and its relationship to hemorrhagic transformation), the use of recombinant tissue plasminogen activator (rt-PA) in ischemic stroke and its study in animal models, the impact of rt-PA on neuron and CNS structure and function, and matrix protease generation and matrix degradation and hemostasis. Interwoven among these topics is evidence for interactions of coagulation factors with and within the CNS. How activation of hemostasis occurs in the cerebral tissues and how the brain responds are difficult questions that offer many research possibilities.

Plasminogen activators and ischemic stroke: conditions for acute delivery

Appropriate acute treatment with plasminogen activators (PAs) can significantly increase the probability of minimal or no disability in selected ischemic stroke patients. There is a great deal of evidence showing that intravenous recombinant tissue PAs (rt-PA) infusion accomplishes this goal, recanalization with other PAs has also been demonstrated in the development of this treatment. Recanalization of symptomatic, documented carotid or vertebrobasilar arterial territory occlusions have also been achieved by local intra-arterial PA delivery, although only a single prospective double-blinded randomized placebo-controlled study has been reported. The increase in intracerebral hemorrhage with these agents by either delivery approach underscores the need for careful patient selection, dose-appropriate safety and efficacy, proper clinical trial design, and an understanding of the evolution of cerebral tissue injury due to focal ischemia. Principles underlying the evolution of focal ischemia have been expanded by experience with acute PA intervention. Several questions remain open that concern the manner in which PAs can be applied acutely in ischemic stroke and how injury development can be limited.

Toward the Neurovascular Unit A Journey in Clinical Translation

The Nobel laureate Max Delbrück often said that it is the crossover between disciplines where advances are possible in science. This certainly has been true for our understanding of the vascular biology of the central nervous system in the setting of ischemic stroke. The ability to cross the boundaries of hemostasis, neurology, hematology, and neuroscience has facilitated our research direction to define the relation of the microvasculature to neuron function. Work begun with the clinical scientific exploration of the contributions of arterial thrombosis to the acute injury processes initiated by focal cerebral ischemia has led to an increased understanding of the effects of ischemia on microvessel integrity.

Aging and the neurovascular unit

With the demonstration that acute recanalization of obstructed symptomatic cerebral arteries during ischemic stroke can result in substantial improvement in clinical outcome, the variability in clinical responses, and in hemorrhagic transformation, requires attention. This short review addresses the effect of aging and amyloid deposition disease on microvessel integrity, interactions within the neurovascular unit, cerebral tissue susceptibility to ischemic injury, and postischemic inflammation, and ultimately on the outcomes and safety of acute recanalization during ischemic stroke. Microvessels and neighboring neurons respond simultaneously to focal ischemia. The cellular components and matrix barriers of the neurovascular unit all respond to ischemia; however, their coordinate interactions are not understood. Furthermore, there is little known about the cell-cell and cell-matrix interactions within the unit, or about the effect of β-amyloid on microvessel responses during ischemia. These considerations indicate the need for a coordinated research effort to understand the origins of the variability in recanalization outcome.

Microglial cell activation is a source of metalloproteinase generation during hemorrhagic transformation

Hemorrhage and edema accompany evolving brain tissue injury after ischemic stroke. In patients, these events have been associated with metalloproteinase (MMP)-9 in plasma. Both the causes and cellular sources of MMP-9 generation in this setting have not been defined. MMP-2 and MMP-9 in nonhuman primate tissue in regions of plasma leakage, and primary murine microglia and astrocytes, were assayed by immunocytochemistry, zymography, and real-time RT-PCR. Ischemia-related hemorrhage was associated with microglial activation in vivo, and with the leakage of plasma fibronectin and vitronectin into the surrounding tissue. In strict serum-depleted primary cultures, by zymography, pro-MMP-9 was generated by primary murine microglia when exposed to vitronectin and fibronectin. Protease secretion was enhanced by experimental ischemia (oxygen-glucose deprivation, OGD). Primary astrocytes, on each matrix, generated only pro-MMP-2, which decreased during OGD. Microglia-astrocyte contact enhanced pro-MMP-9 generation in a cell density-dependent manner under normoxia and OGD. Compatible with observations in a high quality model of focal cerebral ischemia, microglia, but not astrocytes, respond to vitronectin and fibronectin, found when plasma extravasates into the injured region. Astrocytes alone do not generate pro-MMP-9. These events explain the appearance of MMP-9 antigen in association with ischemia-induced cerebral hemorrhage and edema.

Interendothelial claudin-5 expression depends on cerebral endothelial cell-matrix adhesion by β(1)-integrins

The hypothesis tested by these studies states that in addition to interendothelial cell tight junction proteins, matrix adhesion by β(1)-integrin receptors expressed by endothelial cells have an important role in maintaining the cerebral microvessel permeability barrier. Primary brain endothelial cells from C57 BL/6 mice were incubated with β(1)-integrin function-blocking antibody (Ha2/5) or isotype control and the impacts on claudin-5 expression and microvessel permeability were quantified. Both flow cytometry and immunofluorescence studies demonstrated that the interendothelial claudin-5 expression by confluent endothelial cells was significantly decreased in a time-dependent manner by Ha2/5 exposure relative to isotype. Furthermore, to assess the barrier properties, transendothelial electrical resistance and permeability measurements of the monolayer, and stereotaxic injection into the striatum of mice were performed. Ha2/5 incubation reduced the resistance of endothelial cell monolayers significantly, and significantly increased permeability to 40 and 150  kDa dextrans. Ha2/5 injection into mouse striatum produced significantly greater IgG extravasation than the isotype or the control injections. This study demonstrates that blockade of β(1)-integrin function changes interendothelial claudin-5 expression and increases microvessel permeability. Hence, endothelial cell-matrix interactions via β(1)-integrin directly affect interendothelial cell tight junction claudin-5 expression and brain microvascular permeability.

Heterogeneity in the penumbra

Original experimental studies in nonhuman primate models of focal ischemia showed flow-related changes in evoked potentials that suggested a circumferential zone of low regional cerebral blood flow with normal K(+) homeostasis, around a core of permanent injury in the striatum or the cortex. This became the basis for the definition of the ischemic penumbra. Imaging techniques of the time suggested a homogeneous core of injury, while positing a surrounding 'penumbral' region that could be salvaged. However, both molecular studies and observations of vascular integrity indicate a more complex and dynamic situation in the ischemic core that also changes with time. The microvascular, cellular, and molecular events in the acute setting are compatible with heterogeneity of the injury within the injury center, which at early time points can be described as multiple 'mini-cores' associated with multiple 'mini-penumbras'. These observations suggest the progression of injury from many small foci to a homogeneous defect over time after the onset of ischemia. Recent observations with updated imaging techniques and data processing support these dynamic changes within the core and the penumbra in humans following focal ischemia.

The neurovascular unit, matrix proteases, and innate inflammation

In the central nervous system, microvessel-neuron interactions appear highly coordinated. The rapid simultaneous responses of the microvasculature, neurons, and glia to focal ischemia in experimental ischemic stroke suggest that these responses could be viewed in a unitary fashion, rather than as individual components. The "neurovascular unit" consists of microvessels (endothelial cells-basal lamina matrix-astrocyte end-feet [and pericytes]), astrocytes, neurons and their axons, and other supporting cells that are likely to modulate the function of the "unit." Each cell component generates an inflammatory response to ischemia. Matrix metalloproteinase (MMP)-9 was first associated with hemorrhagic transformation following focal ischemia in an experimental model. A series of studies of ischemic stroke patients also suggests a relationship between MMP-9 levels and several consequences of ischemic injury, including hemorrhagic transformation. Recent experimental work suggests specific cell sources for MMP-9 generation and for matrix proteases from four distinct families that could impact neurovascular unit integrity.

Acute anti-inflammatory approaches to ischemic stroke

In preparation for designing and undertaking trials of strategies that can modulate "innate inflammation" to improve outcomes of ischemic injury, consideration of approaches that have managed cellular inflammation in ischemic stroke are instructive. Robust experimental work has demonstrated the efficacy (and apparent safety) of targeting PMN leukocyte-endothelial cell interactions in the early moments following focal ischemia onset in model systems. Four clinical trial programs were undertaken to assess the safety and efficacy of inhibitors to PMN leukocyte interactions with the endothelial cell during ischemic stroke. Experiences in those clinical trial programs indicate specific limitations that halted progress in this line of investigation before an adequate hypothesis test could be achieved. Although innate inflammation is a central part of injury evolution following focal ischemia, great care in the translation from experimental studies to Phase I/II clinical safety assessments and to the design and conduct of Phase III trials is needed.

In the hypoxic central nervous system, endothelial cell proliferation is followed by astrocyte activation, proliferation, and increased expression of the alpha 6 beta 4 integrin and dystroglycan

Cerebral hypoxia induces a profound angiogenic response in the central nervous system (CNS). Using a mouse model of chronic cerebral hypoxia, we previously demonstrated that angiogenic vessels in the hypoxic CNS show marked upregulation of the extracellular matrix (ECM) protein fibronectin, along with increased expression of its major receptor, alpha 5 beta 1 integrin on brain endothelial cells (BEC). As cerebral hypoxia also leads to glial activation, the aim of the current study was to define the temporal relationship between BEC responses and glial cell activation in this model of cerebral hypoxia. This revealed that BEC fibronectin/alpha 5 beta 1 integrin expression and proliferation both reached maximal level after 4-day hypoxia. Interestingly, up to 4-day hypoxia, all dividing cells were BEC, but at later time-points proliferating astrocytes were also observed. GFAP staining revealed that hypoxia induced marked astrocyte activation that reached maximal level between 7- and 14-day hypoxia. As newly formed cerebral capillaries require ensheathment by astrocyte end-feet to acquire mature brain endothelium characteristics, we next examined how expression of astrocyte end-feet adhesion molecules is regulated by hypoxia. This showed that the astrocyte adhesion receptors alpha 6 beta 4 integrin and dystroglycan were both markedly upregulated, with a time-course that closely resembled astrocyte activation. Taken together, this evidence shows that cerebral hypoxia promotes first an endothelial response, in which fibronectin promotes BEC proliferation. This is then followed by an astrocyte response, involving astrocyte activation, proliferation, and reorganization of astrocyte end-feet, which correlates with increased expression of astrocyte end-feet adhesion molecules.

Relationship of neurovascular elements to neuron injury during ischemia

Occlusion of flow to the brain regions identifies regions of vulnerability within the vascular territory at risk, which coalesce to become the mature ischemic lesion. A large number of unsuccessful clinical trials have focused on neuron and extravascular targets in humans that have shown apparent salvage in preclinical models. However, the observation that microvessel and neuron responses to ischemia occur simultaneously in these regions suggest that the responses could be coordinated. This presentation examines evidence in support of the conceptual 'neurovascular unit' and its application to the setting of acute intervention trials in ischemic stroke. There are no uniform reasons for which nonvascular interventions, as a class, have not been successful in clinical trials, but both the clinical observations and the hypothesis imply the need to understand interactions with the neurovascular unit as a prelude to further neuron protectant trials.

Ultrastructural and temporal changes of the microvascular basement membrane and astrocyte interface following focal cerebral ischemia

Microvascular integrity is lost during cerebral ischemia. Detachment of the microvascular basement membrane (BM) from the astrocyte, as well as degradation of the BM, is responsible for the loss of microvascular integrity. However, their ultrastructural and temporal changes during cerebral ischemia are not well known. Male Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO) for 1, 4, 8, 12, 16, 20, and 48 hr. By using transmission electron microscopy, the proportion of intact BM-astrocyte contacts and electron densities of the BM were measured from five randomly selected microvessels in the ischemic basal ganglia. Their temporal changes and associations with activities of the matrix metalloproteinases (MMPs) were investigated. The intact portion of the BM-astrocyte contacts was decreased significantly within 4 hr and was rarely observed at 48 hr after MCAO. Decreases in the electron density and degradation of the BM were significant 12 hr after MCAO. The intact BM-astrocyte contacts and the mean BM density showed a significant positive correlation (r = 0.784, P < 0.001). MMP-9 activity was correlated negatively with the intact BM-astrocyte contacts (r = -0.711, P < 0.001) and with the BM density (r = -0.538, P = 0.0016). The increase in MMP-9 coincided temporally with the loss of the BM-astrocyte contacts and a decrease in the BM density. Ultrastructural alterations occurring in the microvascular BM and its contacts with astrocyte endfeet were temporally associated in cerebral ischemia. Time courses of their alterations should be considered in the treatment targeted to the microvascular BM and its contact with astrocytes.

Hyperfibrinogenemia and functional outcome from acute ischemic stroke

BACKGROUND AND PURPOSE

Epidemiological studies have found strong correlations between elevated plasma fibrinogen levels and both ischemic stroke incidence and stroke mortality. Little is known about the influence of fibrinogen levels on functional stroke outcome.

METHODS

Placebo data from the Stroke Treatment with Ancrod Trial (STAT) and European Stroke Treatment with Ancrod Trial (ESTAT) were analyzed. Fibrinogen levels were determined within 3 hours (STAT) or 6 hours (ESTAT) of stroke onset and at preset intervals throughout 5 days of intravenous infusions. Barthel Index scores at 90 days quantified functional outcomes. The association between initial fibrinogen levels and functional outcomes was evaluated using a multiple logistic regression analysis.

RESULTS

Fibrinogen levels increased gradually over the first 24 hours from a pretreatment median value of 340 mg/dL to a 24-hour median value of 376 mg/dL. In a univariate analysis, the proportion of patients with good functional outcome decreased with increasing quartiles of initial fibrinogen levels in both STAT (36.0% to 26.2%) and ESTAT (53.8% to 24.8%). In a multifactorial analysis, the same trend was observed. Patients with initial fibrinogen levels <450 mg/dL had better outcomes in both studies; the difference (42.0% versus 21.6%) was significant in ESTAT (P=0.0006), even when corrected for age and initial stroke severity.

CONCLUSIONS

The independent association of higher initial fibrinogen levels with poor outcome needs to be verified using a larger acute stroke dataset. Even in the present small populations, the apparent association of these 2 variables suggests that treatments designed to reduce fibrinogen levels could potentially be important in treating acute ischemic stroke.

Can gender differences be evaluated in a rhesus macaque (Macaca mulatta) model of focal cerebral ischemia?

Gender differences, sex steroid effects, and sex-specific candidate therapeutics in ischemic stroke have been studied in rodents but not in nonhuman primates. In this feasibility study (n = 3 per group), we developed a model of transient focal cerebral ischemia in adult male and female rhesus macaques that consistently includes white matter injury. The animals also were used to determine whether gender-linked differences in histopathologic outcomes could be evaluated in this model in future, larger preclinical trials. Histologic brain pathology was evaluated at 4 d after 90 min of reversible occlusion of the middle cerebral artery (MCA). MCA occlusion was accomplished by using a transorbital approach and temporary placement of an aneurysm clip. Male and female rhesus macaques 7 to 11 y of age were studied. Baseline and intraischemic blood glucose, systolic blood pressure, heart rate, oxygen saturation, end-tidal CO2, and rectal temperatures were not different among groups. The variability in injury volume was comparable to that observed in human focal cerebrovascular ischemia and in other nonhuman primate models using proximal MCA occlusion. In this small sample, the volume of injury was not different between male and female subjects, but observed variability was higher in female caudate nucleus, putamen, and hemisphere. This report is the first to compare cerebral ischemic outcomes in female and male rhesus macaques. The female rhesus macaque ischemic stroke model could be used after rodent studies to provide preclinical data for clinical trials in women.

The rapid decrease in astrocyte-associated dystroglycan expression by focal cerebral ischemia is protease-dependent

During focal cerebral ischemia, the detachment of astrocytes from the microvascular basal lamina is not completely explained by known integrin receptor expression changes. Here, the impact of experimental ischemia (oxygen-glucose deprivation (OGD)) on dystroglycan expression by murine endothelial cells and astrocytes grown on vascular matrix laminin, perlecan, or collagen and the impact of middle cerebral artery occlusion on alphabeta-dystroglycan within cerebral microvessels of the nonhuman primate were examined. Dystroglycan was expressed on all cerebral microvessels in cortical gray and white matter, and the striatum. Astrocyte adhesion to basal lamina proteins was managed in part by alpha-dystroglycan, while ischemia significantly reduced expression of dystroglycan both in vivo and in vitro. Furthermore, dystroglycan and integrin alpha6beta4 expressions on astrocyte end-feet decreased in parallel both in vivo and in vitro. The rapid loss of astrocyte dystroglycan during OGD appears protease-dependent, involving an matrix metalloproteinase-like activity. This may explain the rapid detachment of astrocytes from the microvascular basal lamina during ischemic injury, which could contribute to significant changes in microvascular integrity.

Virchow's triad: the vascular basis of cerebral injury

Both the large arteries and microvascular beds of the central nervous system respond to injury by initiating processes compatible with Virchow's triad: alterations in the microvascular permeability barrier, reduction in flow with the target bed, and/or thrombosis of brain-supplying arteries and of the microvasculature. This is particularly true during focal cerebral ischemia. The temporal and topographical coincidence of neuron injury and microvessel response during focal ischemia has suggested that neuron-microvessel interactions could be bidirectional. The neurovascular unit offers a conceptual and structural framework with which to examine events within the microvasculature and their impact on neuron integrity, with the participation of the intervening astrocytes, matrix, and other supportive cells (eg, pericytes and oligodendroglia). Activation of the endothelium and of coagulation, capture of leukocytes, and increased microvessel permeability lead to the focal "no-reflow" phenomenon. Decreased shear stress is a component of the evolving ischemia. Strategies that inhibit the interactions within the microvasculature have been shown to prevent no-reflow and improve neurological outcome. It is, therefore, possible that addressing the processes of Virchow's triad in the setting of focal ischemia could promote neurovascular function.

Responses of endothelial cell and astrocyte matrix-integrin receptors to ischemia mimic those observed in the neurovascular unit

BACKGROUND AND PURPOSE

Apposition of endothelial cells and astrocyte foot processes to the basal lamina matrix is postulated to underlie the cerebral microvessel permeability barrier. Focal cerebral ischemia induces rapid loss of select matrix-binding integrins from both cell compartments in the nonhuman primate. This study is the first to examine the conditions underlying integrin loss from these cell-types during ischemia in vitro and their relation to the changes in vivo.

METHODS

The impact of normoxia or standardized oxygen-glucose deprivation on integrin expression by murine primary cerebral endothelial cells and astrocytes grown on matrix substrates (collagen IV, laminin, and perlecan) of the basal lamina were quantitatively assessed by flow cytometry.

RESULTS

Endothelial cell expression of the beta1 and alpha 5 subunits significantly increased on all matrix ligands, whereas astrocytes displayed modest significant decreases in alpha 5 and alpha 6 subunits. Oxygen-glucose deprivation produced a further significant increase in subunit beta1 expression by both cell types, but a clear decrease in both alpha1 and alpha 6 subunits by murine astrocytes.

CONCLUSIONS

Ischemia in vitro significantly increased endothelial cell beta1 expression, which is consistent with the increase in beta1 transcription by microvessels peripheral to the ischemic core. The loss of alpha1 and alpha 6 integrins from murine astrocytes is identical to that seen in the nonhuman primate in vivo. These findings establish both isolated murine cerebral endothelial cells and astrocytes as potential integrin response cognates of microvascular cells of the neurovascular unit in primates, and allow determination of the mechanisms of their changes to ischemia.

Sulfonylureas improve outcome in patients with type 2 diabetes and acute ischemic stroke

BACKGROUND AND PURPOSE

The sulfonylurea receptor 1-regulated NC(Ca-ATP) channel is upregulated in rodent models of stroke with block of the channel by the sulfonylurea, glibenclamide (glyburide), significantly reducing mortality, cerebral edema, and infarct volume. We hypothesized that patients with type 2 diabetes mellitus taking sulfonylurea agents both at the time of stroke and during hospitalization would have superior outcomes.

METHODS

We reviewed medical records of patients with diabetes mellitus hospitalized within 24 hours of onset of acute ischemic stroke in the Neurology Clinic, Charité Hospital, Berlin, Germany, during 1994 to 2000. After exclusions, the cohort comprised 33 patients taking a sulfonylurea at admission through discharge (treatment group) and 28 patients not on a sulfonylurea (control group). The primary outcome was a decrease in National Institutes of Health Stroke Scale of 4 points or more from admission to discharge or a discharge National Institutes of Health Stroke Scale score of 0. The secondary outcome was a discharge modified Rankin Scale score < or =2.

RESULTS

No significant differences, other than stroke subtype, were observed among baseline variables between control and treatment groups. The primary outcome was reached by 36.4% of patients in the treatment group and 7.1% in the control group (P=0.007). The secondary outcome was reached by 81.8% versus 57.1% (P=0.035). Subgroup analyses showed that improvements occurred only in patients with nonlacunar strokes and were independent of gender, previous transient ischemic attack, and blood glucose levels.

CONCLUSIONS

Sulfonylureas may be beneficial for patients with diabetes mellitus with acute ischemic stroke. Further investigation of similar cohorts and a prospective randomized trial are recommended to confirm the present observations.

Fibronectin- and vitronectin-induced microglial activation and matrix metalloproteinase-9 expression is mediated by integrins alpha5beta1 and alphavbeta5

Early in the pathogenesis of multiple sclerosis, the blood-brain barrier is compromised, which leads to deposition of the plasma proteins fibronectin and vitronectin in cerebral parenchyma. In light of our previous finding that microglial activation in vitro is strongly promoted by fibronectin and vitronectin, we set out to examine the possibility that modulation of microglial activation by fibronectin or vitronectin is an important regulatory mechanism in vivo. In an experimental autoimmune encephalomyelitis mouse model of demyelination, total brain levels of fibronectin and vitronectin were strongly increased and there was a close relationship between fibronectin and vitronectin deposition, microglial activation, and microglial expression of matrix metalloproteinase-9. In murine cell culture, flow cytometry for MHC class I and gelatin zymography revealed that microglial activation and expression of pro-matrix metalloproteinase-9 were significantly increased by fibronectin and vitronectin. Function-blocking studies showed that the influence of fibronectin and vitronectin was mediated by the alpha(5)beta(1) and alpha(v)beta(5) integrins, respectively. Taken together, this work suggests that fibronectin and vitronectin deposition during demyelinating disease is an important influence on microglial activation state. Furthermore, it provides the first evidence that the alpha(5)beta(1) and alpha(v)beta(5) integrins are important mediators of microglial activation.

Microglial activation and matrix protease generation during focal cerebral ischemia

Local environmental conditions contribute to the activation state of cells. Extracellular matrix glycoproteins participate in cell-cell boundaries within the microvascular and extravascular tissues of the central nervous system and provide a scaffold for the local environment. These conditions are altered during focal cerebral ischemia (and other central nervous system disorders) when extracellular matrix boundaries are degraded or when matrix proteins in the vascular circulation enter the neuropil as the microvascular permeability barrier is degraded. Microglia in the resting state become activated after the onset of ischemia. During activation these cells can express a number of factors and proteases, including latent matrix metalloproteinase-9 (pro-MMP-9). Whereas MMP-9 and MMP-2 are generated early during focal ischemia in select models, their cellular sources in vivo are still under study. In vitro microglia cells activate and respond to exposure to specific matrix proteins (eg, vitronectin, fibronectin) that circulate. Certain MMP inhibitors, specifically tetracycline derivatives, can modulate microglial activation and reduce injury volume in limited studies. But, the injury reduction relies on preinjury exposure to the tetracycline. Other studies underway suggest the hypothesis that microglial cell activation and pro-MMP-9 generation during focal cerebral ischemia is promoted in part by matrix proteins in the circulation that extravasate into the neuropil when the blood-brain barrier is compromised. These matrix proteins are known to activate microglia through their specific cell surface matrix receptors.

Integrin-matrix interactions in the cerebral microvasculature

The integrity of all organ systems requires faithful interaction between its component cells and the extracellular matrix (ECM). In the central nervous system (CNS), matrix adhesion receptors are uniquely expressed by the cells comprising the microvascular compartment, and by neurons and their supporting glial cells. Cells within the cerebral microvasculature express both the integrin and dystroglycan families of matrix adhesion receptors. However, the functional significance of these receptors is only now being explored. Capillaries of the cerebral microvasculature consist of the luminal endothelium, which is separated from circumferential astrocyte end-feet by the intervening ECM of the basal lamina. Endothelial cells and astrocytes cooperate to generate and maintain the basal lamina and the unique barrier functions of the endothelium. Integrins and the dystroglycan complex are found on the matrix-proximate faces of both endothelial cells and astrocyte end-feet. Pericytes rest against the basal lamina. In the extravascular compartment, select integrins are expressed on neurons, microglial cells, and oligodendroglia. Significant alterations in both cellular adhesion receptors and their ligands occur under the conditions of focal cerebral ischemia, multiple sclerosis (MS) and the modeled condition experimental autoimmune encephalomyelitis (EAE), certain tumors of the CNS, and arteriovenous malformations (AVMs). The changes in matrix adhesion receptor expression in these conditions support their functional significance in the normal state. We propose that matrix adhesion receptors are essential for the maintenance of the integrity of the blood-brain permeability barrier, and that modulation of these receptors contribute to alterations in the barrier during brain injury. This review examines current information about cell adhesion receptor expression within the cerebral microvasculature and surrounding tissue, and their potential roles during the vascular responses to local injury.