Hemorrhagic transformation after fibrinolytic therapy with tissue plasminogen activator in a rat thromboembolic model of stroke

Inhibition of PI3Kγ by AS605240 plus low-dose tissue plasminogen activator (tPA) combination improves thrombolytic therapy in a rat model of embolic stroke

Our previous study showed that PI3Kγ inhibition with AS605240 plus a standard rat-dose tPA (10 mg/kg) combination attenuates delayed tPA-induced brain hemorrhage and ameliorates acute stroke injury 3 days after ischemic stroke in rats. The purpose of this study was to investigate whether combining AS605240 with tPA can enhance thrombolytic efficacy, so that lower doses of tPA can be applied to improve long-term outcome after ischemic stroke. The results showed that AS605240 plus low-dose tPA (5 mg/kg) combination therapy at 4 h after stroke onset significantly reduced infarct volume and neurological deficits at 24 h after stroke compared with saline, AS605240 or low-dose tPA alone group. Importantly, the combination therapy significantly reduced the delayed tPA-associated brain hemorrhage. Moreover, the combination therapy significantly decreased the size of the residual embolus within the middle cerebral artery, which was associated with a decrease in plasma plasminogen activator inhibitor-1 (PAI-1) activity compared with saline and tPA alone. Finally, AS605240 plus low-dose tPA combination improved long-term outcome for at least 35 days after stroke compared with the saline-treated group. Taken together, these findings suggest that PI3Kγ inhibition with AS605240 might act as an adjunct approach for enhancing tPA thrombolytic efficacy in acute ischemic stroke.

PI3Kγ (Phosphoinositide 3-Kinase-γ) Inhibition Attenuates Tissue-Type Plasminogen Activator-Induced Brain Hemorrhage and Improves Microvascular Patency After Embolic Stroke

Genetic and pharmacological inhibition of the PI3Kγ (phosphoinositide 3-kinase-γ) exerts anti-inflammatory and protective effects in a number of inflammatory and autoimmune diseases. SHRs (spontaneously hypertensive rats) subjected to embolic middle cerebral occlusion were treated with AS605240 (30 mg/kg) at 2 or 4 hours, tPA (tissue-type plasminogen activator; 10 mg/kg) at 2 or 6 hours, or AS605240 at 4 hours plus tPA at 6 hours. Infarct volume, brain hemorrhage, neurological function, microvascular thrombosis, and cerebral microvessel patency were examined. We found that treatment with AS605240 alone at 2 hours or the combination treatment with AS605240 at 4 hours and tPA at 6 hours significantly reduced infarct volume and neurological deficits at 3 days after stroke compared with ischemic rats treated with saline, AS605240 alone at 4 hours, and tPA alone at 6 hours. Moreover, the combination treatment effectively prevented the delayed tPA-induced cerebral hemorrhage. These protective effects are associated with reduced disruption of the blood-brain barrier, reduced downstream microvascular thrombosis, and improved microvascular patency by AS605240. Inhibition of the NF-κB (nuclear transcription factor-κB)-dependent MMP (matrix metalloproteinase)-9 and PAI-1 (plasminogen activator inhibitor-1) in the ischemic brain endothelium may underlie the neurovascular protective effect of AS605240. In addition, the combination treatment significantly reduced circulating platelet P-selectin expression and platelet-leukocyte aggregation compared with ischemic rats treated with saline or tPA alone at 6 hours. In conclusion, inhibition of PI3Kγ with AS605240 reduces delayed tPA-induced intracerebral hemorrhage and improves microvascular patency, which likely contributes to neuroprotective effect of the combination treatment.

Taurine Reduces tPA (Tissue-Type Plasminogen Activator)-Induced Hemorrhage and Microvascular Thrombosis After Embolic Stroke in Rat

BACKGROUND AND PURPOSE

Taurine (2-aminoethansulfolic amino acid) exerts neuroprotective actions in experimental stroke. Here, we investigated the effect of taurine in combination with delayed tPA (tissue-type plasminogen activator) on embolic stroke.

METHODS

Rats subjected to embolic middle cerebral artery occlusion were treated with taurine (50 mg/kg) at 4 hours in combination with tPA (10 mg/kg) at 6 hours. Control groups consisted of ischemic rats treated with either taurine (50 mg/kg) or saline at 4 hours or tPA (10 mg/kg) alone at 2 or 6 hours after middle cerebral artery occlusion.

RESULTS

We found that combination treatment with taurine and tPA robustly reduced infarct volume and neurological deficits 3 days after stroke, whereas treatment with taurine alone had a less-significant protective effect. tPA alone at 6 hours had no effects on infarct volume but instead induced intracerebral hemorrhage. The combination treatment with taurine prevented tPA-associated hemorrhage and reduced intravascular deposition of fibrin/fibrinogen and platelets in downstream microvessels and hence improved microvascular patency. These protective effects are associated with profound inhibition of CD147 (cluster of differentiation 147)-dependent MMP-9 (matrix metalloproteinase-9) pathway in ischemic brain endothelium by taurine. Notably, targeted inhibition of CD147 by intracerebroventricular injection of the rat CD147 siRNA profoundly inhibited ischemia-induced and tPA-enhanced MMP-9 activity in ischemic brain endothelium and blocked tPA-induced cerebral hemorrhage. Finally, the combination treatment with taurine and tPA improved long-term outcome at least 45 days after stroke compared with saline-treated group.

CONCLUSIONS

Our results suggest that taurine in combination with tPA may be a clinically feasible approach toward future attempts at combination stroke therapy.

Permanent flame-blunted monofilament of middle cerebral artery occlusion technique for ischemia stroke induction in animal models

Background: Rat is the most frequently used animal for ischemic stroke studies. Recently, middle cerebral artery occlusion (MCAO) by introducing various types of surgical monofilament intraluminally has been widely used, with their advantages and disadvantages. For permanent occlusion, problems with mortality in rats are higher than transient. In this study, we used permanent occlusion using modified monofilament by flaming on its tip which may reduce mortality rate, so that chronic phase of stroke can be learned extensively.Methods: Three male Sprague-Dawley rats underwent permanent MCAO. The flame-blunted monofilament was introduced through common carotid artery. Hematoxylin eosin histopathology confirmation and functional assessment post-stroke induction were then evaluated.Results: Evaluation was conducted on 3 rats in different time post-stroke induction (48 hours, 72 hours, and 3 weeks). Using histopathological examination, the infarction was proved in all 3 rats showing red neurons, perivascular edema and neutrophil spongiosis, in infarct and peri-infarct area. The changes in histopathology showed spongiosis were more dominant in 3 week-post-MCAO rats. On the other hand, red neurons and perivascular edema were less compared to 48 and 72-hour-post-MCAO rats.Conclusion: Flame–blunted monofilament showed its efficacy in producing infarct area. The advantages of this technique are easy to perform with simple and less expensive modification of the monofilament. Conducting successful permanent occlusion with less mortality rate will give chances to do further research on stroke in chronic phase and its effect on novel treatment.

Neuroserpin Differentiates Between Forms of Tissue Type Plasminogen Activator via pH Dependent Deacylation

Tissue-type plasminogen activator (t-PA), initially characterized for its critical role in fibrinolysis, also has key functions in both physiologic and pathologic processes in the CNS. Neuroserpin (NSP) is a t-PA specific serine protease inhibitor (serpin) found almost exclusively in the CNS that regulates t-PA's proteolytic activity and protects against t-PA mediated seizure propagation and blood-brain barrier disruption. This report demonstrates that NSP inhibition of t-PA varies profoundly as a function of pH within the biologically relevant pH range for the CNS, and reflects the stability, rather than the formation of NSP: t-PA acyl-enzyme complexes. Moreover, NSP differentiates between the zymogen-like single chain form (single chain t-PA, sct-PA) and the mature protease form (two chain t-PA, tct-PA) of t-PA, demonstrating different pH profiles for protease inhibition, different pH ranges over which catalytic deacylation occurs, and different pH dependent profiles of deacylation rates for each form of t-PA. NSP's pH dependent inhibition of t-PA is not accounted for by differential acylation, and is specific for the NSP-t-PA serpin-protease pair. These results demonstrate a novel mechanism for the differential regulation of the two forms of t-PA in the CNS, and suggest a potential specific regulatory role for CNS pH in controlling t-PA proteolytic activity.

Animal models of ischemic stroke and their application in clinical research

This review outlines the most frequently used rodent stroke models and discusses their strengths and shortcomings. Mimicking all aspects of human stroke in one animal model is not feasible because ischemic stroke in humans is a heterogeneous disorder with a complex pathophysiology. The transient or permanent middle cerebral artery occlusion (MCAo) model is one of the models that most closely simulate human ischemic stroke. Furthermore, this model is characterized by reliable and well-reproducible infarcts. Therefore, the MCAo model has been involved in the majority of studies that address pathophysiological processes or neuroprotective agents. Another model uses thromboembolic clots and thus is more convenient for investigating thrombolytic agents and pathophysiological processes after thrombolysis. However, for many reasons, preclinical stroke research has a low translational success rate. One factor might be the choice of stroke model. Whereas the therapeutic responsiveness of permanent focal stroke in humans declines significantly within 3 hours after stroke onset, the therapeutic window in animal models with prompt reperfusion is up to 12 hours, resulting in a much longer action time of the investigated agent. Another major problem of animal stroke models is that studies are mostly conducted in young animals without any comorbidity. These models differ from human stroke, which particularly affects elderly people who have various cerebrovascular risk factors. Choosing the most appropriate stroke model and optimizing the study design of preclinical trials might increase the translational potential of animal stroke models.

Effects of tissue plasminogen activator timing on blood-brain barrier permeability and hemorrhagic transformation in rats with transient ischemic stroke

The goal of our study was to determine if the timing of the tissue plasminogen activator (tPA) administration influenced its effect on blood-brain barrier (BBB) permeability and the subsequent risk of hemorrhagic transformation. Thirty spontaneously hypertensive male rats were subjected to a 90-minute unilateral middle cerebral artery occlusion. Six rats did not receive tPA treatment (vehicle control: Group 0), intravenous tPA was administered immediately after reperfusion (Group 1) or 4h after reperfusion (Group 2). Dynamic contrast enhancement (DCE) and gradient-echo (GRE) MR sequences were used to assess the dynamic evolution of BBB permeability and hemorrhagic transformation changes at the following time points: during occlusion, and 3h, 6h, and 24h post reperfusion. In all groups, BBB permeability values in the ischemic tissue were low during occlusion. In Group 0, BBB permeability values increased at 3h after reperfusion (p=0.007, compared with the values during occlusion), and further at 6h after reperfusion (p=0.004, compared with those at 3h post reperfusion). At 24h post reperfusion, the values decreased to a level relative to but still higher than those during occlusion (p=0.025, compared with the values during occlusion). At 3h after reperfusion, BBB permeability values in the ischemic tissue increased, but to a greater extent in Group 1 than in Group 0 (p=0.034) and Group 2 (p=0.010). At 6h after reperfusion, BBB permeability values in the ischemic tissue increased further in Group 2 than in Group 0 (p=0.006) and Group 1 (p=0.001), while Group 1 exhibited BBB permeability that were still abnormal but less than those observed at 3h (p=0.001). Group 2 tended to have a higher hemorrhage incidence (36.4%, 4/11) than Group 1 (10.0%, 1/10, p=0.311) and Group 0 (0%), and hemorrhages occurred around 6h after reperfusion when BBB permeability values were the highest. Mortality was higher in Group 2 (63.6%, 7/11) than in Group 0 (0%) and Group 1 (10.0%, 1/10, p=0.024). The findings suggest that the timing of tPA administration is of importance for its impact on BBB permeability and subsequent risk of hemorrhagic transformation.

Preclinical stroke research--advantages and disadvantages of the most common rodent models of focal ischaemia

This review describes the most commonly used rodent models and outcome measures in preclinical stroke research and discusses their strengths and limitations. Most models involve permanent or transient middle cerebral artery occlusion with therapeutic agents tested for their ability to reduce stroke-induced infarcts and improve neurological deficits. Many drugs have demonstrated preclinical efficacy but, other than thrombolytics, which restore blood flow, none have demonstrated efficacy in clinical trials. This failure to translate efficacy from bench to bedside is discussed alongside achievable steps to improve the ability of preclinical research to predict clinical efficacy: (i) Improvements in study quality and reporting. Study design must include randomization, blinding and predefined inclusion/exclusion criteria, and journal editors have the power to ensure statements on these and mortality data are included in preclinical publications. (ii) Negative and neutral studies must be published to enable preclinical meta-analyses and systematic reviews to more accurately predict drug efficacy in man. (iii) Preclinical groups should work within networks and agree on standardized procedures for assessing final infarct and functional outcome. This will improve research quality, timeliness and translational capacity. (iv) Greater uptake and improvements in non-invasive diagnostic imaging to detect and study potentially salvageable penumbral tissue, the target for acute neuroprotection. Drug effects on penumbra lifespan studied serially, followed by assessment of behavioural outcome and infarct within in the same animal group, will increase the power to detect drug efficacy preclinically. Similar progress in detecting drug efficacy clinically will follow from patient recruitment into acute stroke trials based on evidence of remaining penumbra.

Reduction of neutrophil activity decreases early microvascular injury after subarachnoid haemorrhage

Background

Subarachnoid haemorrhage (SAH) elicits rapid pathological changes in the structure and function of parenchymal vessels (≤ 100 μm). The role of neutrophils in these changes has not been determined. This study investigates the role of neutrophils in early microvascular changes after SAH

Method

Rats were either untreated, treated with vinblastine or anti-polymorphonuclear (PMN) serum, which depletes neutrophils, or treated with pyrrolidine dithiocarbamate (PDTC), which limits neutrophil activity. SAH was induced by endovascular perforation. Neutrophil infiltration and the integrity of vascular endothelium and basement membrane were assessed immunohistochemically. Vascular collagenase activity was assessed by in situ zymography.

Results

Vinblastine and anti-PMN serum reduced post-SAH accumulation of neutrophils in cerebral vessels and in brain parenchyma. PDTC increased the neutrophil accumulation in cerebral vessels and decreased accumulation in brain parenchyma. In addition, each of the three agents decreased vascular collagenase activity and post-SAH loss of vascular endothelial and basement membrane immunostaining.

Conclusions

Our results implicate neutrophils in early microvascular injury after SAH and indicate that treatments which reduce neutrophil activity can be beneficial in limiting microvascular injury and increasing survival after SAH.

Are Underlying Assumptions of Current Animal Models of Human Stroke Correct: from STAIRs to High Hurdles?

Animal models of acute ischemic stroke have been criticized for failing to translate to human stroke. Nevertheless, animal models are necessary to improve our understanding of stroke pathophysiology and to guide the development of new stroke therapies. The rabbit embolic clot model is one animal model that has led to an effective therapy in human acute ischemic stroke, namely tissue plasminogen activator (tPA). We propose that potential compounds that demonstrate efficacy in non-rabbit animal models of acute ischemic stroke should also be tested in the rabbit embolic blood clot model and, where appropriate, compared to tPA prior to investigation in humans. Furthermore, the use of anesthesia needs to be considered as a major confounder in animal models of acute ischemic stroke, and death should be included as an outcome measure in animal stroke studies. These steps, along with the current STAIRs recommendations, may improve the successful translation of experimental therapies to clinical stroke treatments.

A mouse model of hemorrhagic transformation by delayed tissue plasminogen activator administration after in situ thromboembolic stroke

BACKGROUND AND PURPOSE

thrombolytic treatment with tissue plasminogen activator (tPA) improves outcome of patients with stroke who can be treated within 3 hours of symptom onset. However, delayed treatment with tPA leads to increased risk of hemorrhagic transformation and can result in enhanced brain injury. The purpose of this study is to validate a reproducible mouse model of hemorrhagic transformation associated with delayed administration of tPA.

METHODS

mice were anesthetized and thrombin was injected into the middle cerebral artery to induce the formation of a clot as described by Orset et al. To induce reperfusion, tPA (10 mg/kg) was intravenously administered 20 minutes or 3 hours after thrombin injection.

RESULTS

thrombin produced a clot in 83.1% of the animals, which caused focal ischemia determined 24 hours after the injection. Different degrees of bleeding were found in the middle cerebral artery occlusion group, including hemorrhagic infarction type 1 (HI-1) in 46.2%, hemorrhagic infarction type 2 (HI-2) in 30.8% and parenchymal hemorrhage type 1 in 23.0%. Administration of tPA 20 minutes after the occlusion produced an effective reperfusion in 62.5% of the animals and reduced both infarct volume and appearance of severe hemorrhage (10% nonhemorrhage, 80% HI-1 and 10% HI-2). However, administration of tPA 3 hours after the occlusion led to effective reperfusion in 47.1% of the animals, did not reduce infarct volume, caused hemorrhagic transformation (25% HI-1, 37.5% HI-2, and 37.5% parenchymal hemorrhage type 1), and increased hemorrhage and brain swelling.

CONCLUSIONS

we have set up a reproducible mouse model of hemorrhagic transformation associated with delayed administration of tPA similar to that observed in humans.

Plasma VAP-1/SSAO activity predicts intracranial hemorrhages and adverse neurological outcome after tissue plasminogen activator treatment in stroke

BACKGROUND AND PURPOSE

Vascular adhesion protein-1 (VAP-1) is a cell surface and circulating enzyme involved in recruitment of lymphocytes and neutrophils through its semicarbazide-sensitive amine oxidase (SSAO) activity. We aimed to study plasma VAP-1/SSAO activity in relation to the risk for intracranial bleeding complications in patients with stroke treated with tissue plasminogen activator (tPA), the greatest safety concern with this treatment.

METHODS

In 141 patients with ischemic stroke, we measured VAP-1/SSAO activity in plasma taken before tPA administration. Hemorrhagic events were classified according to brain CT criteria and functional outcomes evaluated using the National Institutes of Health Stroke Scale. We also assessed the potential therapeutic effect of blocking VAP-1/SSAO activity in a rat embolic stroke model treated with tPA.

RESULTS

We saw significantly higher levels of plasma VAP-1/SSAO activity in patients who subsequently experienced hemorrhagic transformation. Elevated plasma VAP-1/SSAO activity also predicted worse neurological outcome in these patients. In the rat model, we confirmed that use of the inhibitor semicarbazide prevented adverse effects caused by delayed tPA administration, leading to a smaller infarct volume.

CONCLUSIONS

Our data demonstrate that baseline VAP-1/SSAO activity predicts parenchymal hemorrhage after tPA, suggesting the safety of thrombolytic agents could be improved by considering VAP-1/SSAO activity. Furthermore, anti-VAP-1/SSAO drugs given with tPA may prevent neurological worsening in patients with ischemic stroke.

Translational stroke research using a rabbit embolic stroke model: a correlative analysis hypothesis for novel therapy development

Alteplase (tissue plasminogen activator, tPA) is currently the only FDA-approved treatment that can be given to acute ischemic stroke (AIS) patients if patients present within 3 h of an ischemic stroke. After 14 years of alteplase clinical research, evidence now suggests that the therapeutic treatment window can be expanded 4.5 h, but this is not formally approved by the FDA. Even though there remains a significant risk of intracerebral hemorrhage associated with alteplase administration, there is an increased chance of favorable outcome with tPA treatment. Over the last 30 years, the use of preclinical models has assisted with the search for new effective treatments for stroke, but there has been difficulty with the translation of efficacy from animals to humans. Current research focuses on the development of new and potentially useful thrombolytics, neuroprotective agents, and devices which are also being tested for efficacy in preclinical and clinical trials. One model in particular, the rabbit small clot embolic stroke model (RSCEM) which was developed to test tPA for efficacy, remains the only preclinical model used to gain FDA approval of a therapeutic for stroke. Correlative analyses from existing preclinical translational studies and clinical trials indicate that there is a therapeutic window ratio (ARR) of 2.43-3 between the RSCEM and AIS patients. In conclusion, the RSCEM can be used as an effective translational tool to gauge the clinical potential of new treatments.

Neutrophils contribute to intracerebral haemorrhages after treatment with recombinant tissue plasminogen activator following cerebral ischaemia

BACKGROUND AND PURPOSE

Polymorphonuclear neutrophils (PMNs) contribute to the vascular damage caused by transient cerebral ischaemia. Here we have evaluated the role of PMNs in intracerebral haemorrhage (ICH) induced in a model of thrombolysis with recombinant tissue plasminogen activator (t-PA) during the acute phase of cerebral ischaemia.

EXPERIMENTAL APPROACH

The middle cerebral artery (MCA) of male spontaneously hypertensive rats was occluded for 1 h followed by reperfusion and, 5 h later, infusion of thrombolytic products (generated in vitro by t-PA on autologous clots). Effects of pretreatment (before the MCA occlusion) with vinblastine (4 days before; 0.5 mg.kg(-1)), monoclonal anti-neutrophil antibody (mAbRP3; 12 h, 0.3 mg.kg(-1)) or saline on ICH, neutrophil infiltration, MCA vascular reactivity and brain infarct volume were assessed, 24 h after the beginning of reperfusion.

KEY RESULTS

Depletion of circulating neutrophils significantly reduced t-PA-induced ICH (vinblastine, 4.6 +/- 1.0; mAbRP3, 5.2 +/- 1.0 vs. saline, 10.8 +/- 2.7 haemorrhages; P < 0.05). This depletion was associated with a decrease in cerebral infiltration by neutrophils and a decrease of endothelium-dependent, vascular dysfunction in isolated MCA, induced by the ischaemia/reperfusion and t-PA treatment. Brain infarct volume was significantly decreased after vinblastine treatment (159 +/- 13 mm(3) vs. 243 +/- 16 mm(3) with saline; P < 0.01) but not after depletion with mAbRP3 (221 +/- 22 mm(3)).

CONCLUSIONS AND IMPLICATIONS

Our results showed that pharmacological depletion of PMNs prevented t-PA-induced ICH, in parallel with a decrease in cerebral infiltration by PMNs and a decreased endothelial dysfunction in cerebral blood vessels.

Efficacy of recombinant annexin 2 for fibrinolytic therapy in a rat embolic stroke model: a magnetic resonance imaging study

Efficacy of recombinant annexin 2 (rAN II) in a rat model of embolic stroke was examined using a magnetic resonance imaging (MRI) and histology. The right middle cerebral artery of male Wistar rats was occluded by autologous clots under anesthesia. Four doses of rAN II (0.125, 0.25, 0.5 and 1.0 mg/kg, n=10 for each group) or saline (1 ml/kg, n=10) were administrated intravenously within 5 min before clot infusion. Serial changes in apparent diffusion coefficient (ADC) and relative blood flow (CBF) were measured with the use of MRI in half of the animals in each group. The remaining half of the animals in each group was evaluated for hemorrhage and final infarct size by histology at 48 h after embolization. At 3 h after embolization, lesion volumes with ADC were abnormality and CBF in the peripheral lesion was improved in groups treated with 0.25, 0.5 and 1.0 mg/kg, but not 0.125 mg/kg, of rAN II in comparison with the saline-treated group (P<0.05). Histological analyses were consistent with MRI findings. More importantly, no hemorrhagic transformation was documented in rats treated with 0.125 and 0.25 mg/kg of rAN II, whereas it was observed at higher doses. We concluded that rAN II at 0.25 mg/kg significantly reduced infarct size and improved CBF without hemorrhagic complications. rAN II is a novel compound that has the potential to be a promising fibrinolytic agent to treat embolic stroke.

Critical role of microvasculature basal lamina in ischemic brain injury

Cerebral vascular system can be divided into two categories: the macrovessels and microvessels. The microvessels consist of arterioles, capillaries and venules. There are three basic components in the microvasculature: endothelial cells, basal lamina and end-feet of astrocytes. The basal lamina is situated between the endothelial cells and the end-feet of astrocytes, and connects these two layers together. Damage to the basal lamina causes the dismantlement of microvascular wall structures, which in turn results in increase of microvascular permeability, hemorrhagic transformation, brain edema and compromise of the microcirculation. The present article reviews microvascular changes during ischemic brain injury, with emphasis on basal lamina damage.

Combination Therapy Using tPA and Edaravone Improves the Neurotoxic Effect of tPA

SUMMARY

In acute ischemic stroke patients, administration of tissue plasminogen activator (tPA) was proven to improve clinical outcome. On the other hand, neurotoxic effects of tPA have been reported in animal experimental studies. Using a rat thromboembolic stroke model, we examined whether or not the free radical scavenger, edaravone, could attenuate such neurotoxic effect of tPA administered for the purpose of fibrinolysis. Even when early recanalization was induced by administering tPA at 30 minutes after the onset of ischemia, significant amount of tPA was extravasated through the cerebral vessels. Edaravone significantly attenuated extravasation of tPA. Combination therapy using tPA and edaravone appears to be a promising strategy for diminishing the negative effects of tPA.

Effects of tissue plasminogen activator on cerebral microvessels of rats during focal cerebral ischemia and reperfusion

The time window in the treatment of ischemic stroke with tissue plasminogen activator (tPA) is narrow, arbitrarily within 3 hours after the onset of symptom. Hemorrhagic transformation resulting from cerebral ischemia may be related to damage of the microvascular basal lamina of the brain, which may in turn cause microvascular fibrin deposition and aggravate cerebral ischemia. Here, we investigated the effect of tPA on the microvascular tissue changes during cerebral ischemia/reperfusion. Sprague-Dawley rats were subjected to focal cerebral ischemia by ligation of the right middle cerebral artery and bilateral common carotid arteries for 90 minutes. Sixty minutes after the onset of ischemia, escalated dosages of tPA from 2.5 to 10 mg/kg or saline were intravenously infused for 60 minutes. Twenty-four hours after reperfusion, the animals were allowed to be killed for examination. Low dosage of tPA (2.5-7.5 mg/kg) reduced post-ischemic brain infarction, suppressed metalloproteinase 2 (MMP-2) activity and restored blood-brain barrier (BBB) integrity. In contrast, high dose of tPA (10 mg/kg) aggravated brain infarction, increased MMP-2 activity and exacerbated BBB disruption. Cerebral ischemia/reperfusion decreased the immunoreactivity of both collagen type IV- and laminin-positive microvessels, whereas the low dosage of tPA (2.5-7.5 mg/kg) attenuated the reduction. When these molecules in whole cortical tissues were analysed, tPA dosage-dependently decreased the total content of collagen type IV, laminin and fibronectin. Although the detailed mechanisms regarding the action of tPA are yet to be investigated, our findings demonstrate that the detrimental effect of tPA was mediated, at least in part, through the destruction of the basal lamina in the cerebral microvessels by activating MMP-2.

Inflammation following stroke

Stroke is one of the leading causes of mortality and morbidity. The stroke process triggers an inflammatory reaction that may last up to several months. Suppression of inflammation using a variety of drugs reduces infarct volume and improves clinical outcomes in animal models of stroke. This benefit occurs even with the initiation of therapy after 3 hours of onset of stroke, beyond the therapeutic window for thrombolysis with tPA. The use of neuroprotectants to suppress inflammation may widen the therapeutic time window for tPA while lessening its side-effects. Suppression of inflammation may also improve outcomes in animal models of haemorrhagic stroke. To date, clinical trials with anti-inflammatory agents in acute ischaemic stroke have failed to improve clinical outcomes. However, because of the potential for broader applicability across all aspects of stroke, a better understanding of anti-inflammatory mechanisms is important.

Attenuation of extravasation of tissue plasminogen activator by the free radical scavenger, edaravone: evaluation in a rat thromboembolic stroke model

OBJECTIVES AND METHODS

Deleterious effects of tissue plasminogen activator (tPA) have been described recently in experimental studies. For example, tPA can aggravate ischemic neuronal damage through its proteolytic activity. The present study was undertaken to examine whether or not the free radical scavenger, edaravone, could prevent the extravasation of tPA administered for the purpose of fibrinolysis in a rat model of thromboembolic stroke.

RESULTS

Significant amounts of tPA were extravasated through the cerebral vessels even when early recanalization was induced by administering tPA at 30 minutes after the onset of schema. Edaravone significantly attenuated such extravasation of tPA.

CONCLUSION

In acute ischemic stroke patients, combination therapy using tPA with edaravone appears to be a reasonable strategy for diminishing the negative effects of tPA.

FK419, a nonpeptide platelet glycoprotein IIb/IIIa antagonist, ameliorates brain infarction associated with thrombotic focal cerebral ischemia in monkeys: comparison with tissue plasminogen activator

The binding of platelet glycoprotein (GP) IIb/IIIa to fibrinogen is the final common pathway in platelet aggregation, a process known to play a key role in the pathogenesis of ischemic brain damage. We compared the effects of FK419, a novel nonpeptide GPIIb/IIIa antagonist, with recombinant tissue plasminogen activator (rt-PA) on middle cerebral artery (MCA) patency and ischemic brain damage in a thrombotic stroke model in squirrel monkeys. FK419 not only inhibited in vitro platelet aggregation (IC50: 88 nmol/L), but also showed disaggregatory activity to aggregated platelet (EC50: 286 nmol/L). FK419 dose-dependently reduced the time to first reperfusion and total occlusion time of MCA blood flow when administered immediately after the termination of photoirradiation. FK419 reduced cerebral infarction and ameliorated neurologic deficits with similar dose-dependency. Although rt-PA reduced the time to first reperfusion, total occlusion time, and cerebral infarction, it did not significantly ameliorate neurologic deficits and induced petechial intracerebral hemorrhages. These results indicate: (1) FK419 restored cerebral blood flow after thrombotic occlusion of MCA, (2) FK419 reduced ischemic brain injury by its thrombolytic actions in a non-human primate stroke model, and (3) FK419 has superior antithrombotic efficacy and is safer than rt-PA.

Spontaneous Intracranial Internal Carotid Artery Dissection Treated by Intra-arterial Thrombolysis and Superficial Temporal Artery-Middle Cerebral Artery Anastomosis in the Acute Stage-Case Report-

A 22-year-old man presented with sudden onset of right retro-orbital headache followed by left hemiparesis. Right carotid angiography demonstrated almost total occlusion of the intracranial internal carotid artery (ICA) and severe stenosis of the middle cerebral artery (MCA), presumably caused by arterial dissection. Local arterial injection of urokinase was performed 2 hours after onset. The ICA became patent, but the M2 portion of the MCA was still occluded, and the left hemiparesis did not improve. Superficial temporal artery-MCA anastomosis was immediately performed. The left hemiparesis disappeared completely 6 days after this procedure. Angiography 2 weeks after the onset revealed occlusion of the ICA, and maintenance of blood flow to the right cerebral hemisphere via the anastomosis. Magnetic resonance imaging showed small infarcts in the right cerebral cortex. Repeat angiography after 5 months showed recanalization of the right ICA and the right MCA. Combination of thrombolytic therapy and bypass surgery may be a useful treatment option for patients with sudden occlusion of the intracranial artery caused by dissection.

The neurotoxicity of tissue plasminogen activator?

Tissue plasminogen activator (tPA), a fibrin specific activator for the conversion of plasminogen to plasmin, stimulates thrombolysis and rescues ischemic brain by restoring blood flow. However, emerging data suggests that under some conditions, both tPA and plasmin, which are broad spectrum protease enzymes, are potentially neurotoxic if they reach the extracellular space. Animal models suggest that in severe ischemia with injury to the blood brain barrier (BBB) there is injury attributed to the protease effects of this exogenous tPA. Besides clot lysis per se, tPA may have pleiotropic actions in the brain, including direct vasoactivity, cleaveage of the N-methyl-D-aspartate (NMDA) NR1 subunit, amplification of intracellular Ca++ conductance, and activation of other extracellular proteases from the matrix metalloproteinase (MMP) family, e.g. MMP-9. These effects may increase excitotoxicity, further damage the BBB, and worsen edema and cerebral hemorrhage. If tPA is effective and reverses ischemia promptly, the BBB remains intact and exogenous tPA remains within the vascular space. If tPA is ineffective and ischemia is prolonged, there is the risk that exogenous tPA will injure both the neurovascular unit and the brain. Methods of neuroprotection, which prevent tPA toxicity or additional mechanical means to open cerebral vessels, are now needed.

Infiltration of tissue plasminogen activator through cerebral vessels: evaluation using a rat thromboembolic stroke model

In recent years, evidence has been accumulating that tissue plasminogen activator (tPA) possesses neurotoxic effects. However, such deleterious effects have been attributed to endogenously generated tPA. In the present study, focusing on exogenously administered tPA for the purpose of fibrinolysis, we evaluated the extent and the degree of extravasated tPA in a rat model of thromboembolic stroke. Even after early recanalization of occluded cerebral vessels, significant infiltration of tPA occurred through the cerebral vessels. It is assumed that exogenous tPA also exerts neurotoxic effects in the ischemic brain tissue.

Involvement of Thrombolysis in Recombinant Tissue Plasminogen Activator-Induced Cerebral Hemorrhages and Effect on Infarct Volume and Postischemic Endothelial Function

Background and Purpose— In a model of mechanical focal ischemia, we investigated the involvement of thrombolysis products (TLP) in recombinant tissue plasminogen activator (rtPA)-induced intracerebral complications and the effects on infarct volume and postischemic endothelial function.

Methods— Hemorrhage incidence and severity were evaluated by histomorphometric analysis in male spontaneously hypertensive rats (SHR) subjected to 60-minute intraluminal middle cerebral artery (MCA) occlusion and receiving intravenously 5 hours later either saline, rtPA (3, 10, or 30 mg/kg), or rtPA (10 mg/kg) associated with TLP (rtPA+TLP). In addition, MCA reactivity was assessed in rtPA- or rtPA+TLP-treated SHR versus control Wistar-Kyoto rats or SHR.

Results— No hemorrhage was observed visually in SHR receiving saline. In contrast, rtPA administration induced hemorrhagic complications in infarcted areas in a dose-independent manner. Administration of rtPA+TLP solution, containing a high concentration of plasmin, did not affect hemorrhage incidence but significantly increased hemorrhage severity (8.8±2.3 petechiae versus 3.0±1.0 petechiae in rtPA group; P <0.001). This increased severity was associated with a significant increase of both infarct volume (182±10 versus 144±15 mm 3 in rtPA group; P <0.01) and postischemic impairment of MCA endothelium-dependent relaxation (9±0.5% versus 13±1% in rtPA group; P <0.05).

Conclusions— Treatment with rtPA led to intracerebral hemorrhages, in contrast to saline-treated animals, and the presence of TLP increased the severity of these hemorrhages, in parallel with increased infarct volume and worsened endothelial function.

Antiactin-targeted immunoliposomes ameliorate tissue plasminogen activator-induced hemorrhage after focal embolic stroke

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) is limited by serious risks of intracerebral hemorrhage. In this study, the authors show that a novel antiactin-targeted immunoliposome significantly reduced tPA-induced hemorrhage in an established rat model of embolic focal stroke. Spontaneously hypertensive rats were subjected to focal ischemia using homologous blood clot emboli. Delayed administration of tPA (10 mg/kg, 6 hours after ischemia) induced intracerebral hemorrhage at 24 hours. In control rats treated with tPA plus vehicle, hemorrhage volumes were 9.0 +/- 2.4 uL (n = 7). In rats treated with tPA plus antiactin immunoliposomes, hemorrhage volumes were significantly reduced to 4.8 +/- 2.7 uL (n = 8, P < 0.05). No significant effects were seen when rats were treated with tPA plus a nontargeted liposome (7.8 +/- 2.1 uL, n = 9). Fluorescent immunohistochemistry showed that rhodamine-labeled targeted liposomes colocalized with vascular structures in ischemic brain that stained positive for endothelial barrier antigen, a marker of cerebral endothelial cells. These data suggest that immunoliposomes may ameliorate vascular membrane damage and reduce hemorrhagic transformation after thrombolytic therapy in cerebral ischemia.

Reduction of infarction volume by bolus injection of pamiteplase, a modified tissue plasminogen activator with a longer half-life

Using a rat model of thromboembolic stroke we evaluated whether or not fibrinolysis by bolus injection of pamiteplase, a modified tissue plasminogen activator (tPA) with a longer half-life, reduces infarction volume. Infarction volume was significantly reduced by the early administration of pamiteplase at 2 h after the onset of ischemia. Hemorrhagic infarction was observed only in 3 of 10 rats (30%) treated at 6 h. Thus, bolus injection of pamiteplase can reduce infarction volume suppressing the incidence of hemorrhage.

Hemorrhagic transformation is related to the duration of occlusion and treatment with tissue plasminogen activator in a nonembolic stroke model

The availability of reperfusion therapy for acute ischemic stroke patients has made the causes and significance of hemorrhagic transformation an area of intense interest and controversy. Ninety-two male Wistar rats underwent transient middle cerebral artery occlusion (MCAO) of between 1 and 6 h. Forty animals received 10 mg kg-1 of recombinant tissue plasminogen activator (rtPA), infused over 20 min, starting 5 min before reperfusion. At 18-24 h, the animals were sacrificed. The presence of hemorrhagic transformation (HT) on stained sections was recorded and total ischemic lesion area was quantified using image analysis software. Seventeen animals (11 with HT) were subjected to immunohistochemical analysis for detection of endothelial barrier antigen (EBA), quantified in three sections, in eight different fields per section. Chi-squared analysis and logistic regression were used to assess the contribution of rtPA and duration of occlusion to HT development. Nested, repeated measures analyses of variance were performed to assess the changes in EBA caused by ischemia and associated with HT. Fifty-nine animals developed HT that was significantly associated with occlusion duration (p < 0.0001) and ischemic lesion size (p = 0.0007). The presence of rtPA accelerated HT development. Statistically significant side-to-side differences in the presence of EBA were found in the striatum (core of the infarct) of animals with HT (p < 0.001) and without HT (p < 0.001), but only in animals with durations of occlusion of 2 h or more. Duration of occlusion is an important predictor of HT in transient MCAO in the rat and is closely associated with EBA expression.

Matrix metalloproteinase-9 pretreatment level predicts intracranial hemorrhagic complications after thrombolysis in human stroke

BACKGROUND

Matrix metalloproteinase (MMP) expression is related to blood brain barrier disruption after cerebral ischemia. Moreover, MMP inhibitors reduce hemorrhagic transformation (HT) after embolic ischemia in tissue plasminogen activator (t-PA)-treated animals. We aimed to correlate plasmatic MMP levels with the appearance of intracranial bleeding complications in stroke patients treated with t-PA.

METHODS AND RESULTS

Serial MMP-2 and MMP-9 determinations were performed (ELISA, ng/mL) in 41 strokes involving the middle cerebral artery territory in patients who received t-PA within 3 hours of stroke onset. Blood samples were obtained at baseline (pretreatment) and at 12 and 24 hours after symptom onset. Hemorrhagic events were classified according to CT criteria (petechial hemorrhagic infarctions [HI, 1 to 2] and large parenchymal hemorrhages [PH, 1 to 2]). Brain CT scan was obtained at 48 hours or when a neurological worsening occurred. HT was present in 36.5% of the patients (24.4% HI and 12.1% PH). MMP-2 values were unrelated to any subtype of HT. The highest baseline MMP-9 level (normal range <97 ng/mL) corresponded to patients who later developed a PH (PH: 270.2+/-87.8, non-HT: 126.3+/-127.5, HI: 94.6+/-88.7; P=0.047). A graded response was found between mean baseline MMP-9 levels and the degree of bleeding (HI-1=37.4; HI-2=111.0; PH-1=202.5; PH-2=337.8). Baseline MMP-9 was the most powerful predictor of PH appearance in the multiple logistic regression model (OR= 9.62; CI 1.31 to 70.26; P=0.025).

CONCLUSIONS

Baseline MMP-9 level predicts PH appearance after t-PA treatment. Therefore, we suggest that MMP determination may increase the safety profile for thrombolysis and, in the future, anti-MMP drugs might be combined with t-PA to prevent hemorrhagic complications.

Neuroprotective effects of YM872 coadministered with t-PA in a rat embolic stroke model

YM872, an AMPA receptor antagonist, was administered together with t-PA to investigate the effects of coadministration on neuroprotection in a rat embolic stroke model, when administered 2 h after embolism. T-PA or YM872 alone decreased infarct volume and improved the neurological deficit score. Coadministration of YM872 and t-PA resulted in a further decrease in infarct volume and improvement of the neurological score as compared with single administration of t-PA. These data demonstrate that coadministration of YM872 and t-PA produces more potent neuroprotective effects than when t-PA is administered alone.

Monteplase reduces infarct volume and hemorrhagic transformation in rat model of embolic stroke

Monteplase, a modified recombinant tissue plasminogen activator (rt-PA), has a long half-life and reduces binding to plasminogen activator inhibitor. In this study we investigated whether its systemic administration reduces infarct volume without increasing the risk of intra-cerebral hemorrhage. The effect of the drug was tested on an embolic stroke rat model that uses white clots. Thirty minutes after clot embolization, rats were infused with 2.2 mg kg(-1) of monteplase or the same amount of saline, over 60 min. Relative regional cerebral blood flow had recovered 60 min after monteplase administration and infarct volume was significantly smaller 24 h after clot embolization in the monteplase-treated rats (47.0 mm3) than in the saline-treated rats (130.4 mm3). Also, the hemorrhagic transformation area was significantly smaller in monteplase-treated rats (0.8 mm2 vs. 18.0 mm2, respectively). These results indicate monteplase can be a promising thrombolytic agent for treatment of the acute stage of cerebral ischemia.

Involvement of matrix metalloproteinase in thrombolysis-associated hemorrhagic transformation after embolic focal ischemia in rats

BACKGROUND AND PURPOSE

Thrombolytic therapy with tissue plasminogen activator (tPA) for acute ischemic stroke remains complicated by risks of hemorrhagic transformation. In this study we used a previously established quantitative rat model of tPA-associated hemorrhage to test the hypothesis that matrix metalloproteinases (MMPs) are involved.

METHODS

Spontaneously hypertensive rats were subjected to embolic focal ischemia by placing homologous blood clots into the middle cerebral artery. Three groups of rats were studied: (1) untreated controls that received saline at 6 hours after ischemia; (2) rats that received tPA alone (10 mg/kg at 6 hours after ischemia); and (3) rats that received tPA plus the broad-spectrum MMP inhibitor BB-94 (50 mg/kg of BB-94 before ischemia and at 3 and 6 hours after ischemia plus tPA at 6 hours). Gelatin zymography was used to quantify MMP levels. A hemoglobin spectrophotometry method was used to quantify cerebral hemorrhage. Ischemic lesions were measured at 24 hours with tetrazolium staining.

RESULTS

At 6, 12, and 24 hours, pro-MMP-9 and cleaved MMP-9 were upregulated in ischemic brain. At 12 hours, tPA-treated rats showed significantly higher levels of pro-MMP-9 and cleaved MMP-9 than untreated controls. By 24 hours, all rats showed evidence of hemorrhagic transformation in the ischemic territory. Rats treated with BB-94 and tPA showed significantly reduced hemorrhage volumes compared with those that received tPA alone. There was no effect on infarct size.

CONCLUSIONS

These results indicate that (1) tPA treatment increases levels of MMP-9 after embolic focal cerebral ischemia, (2) MMPs are involved in the mechanism of tPA-associated hemorrhage, and (3) combination therapies with MMP inhibitors may be useful for decreasing the risk and severity of this dreaded complication of thrombolytic therapy.

Delayed rt-PA treatment in a rat embolic stroke model: diagnosis and prognosis of ischemic injury and hemorrhagic transformation with magnetic resonance imaging

The authors characterized effects of late recombinant tissue plasminogen activator (rt-PA) administration in a rat embolic stroke model with magnetic resonance imaging (MRI), to assess potential MRI correlates, or predictors, or both, of rt-PA-induced hemorrhage. Diffusion-, perfusion-, and postcontrast T1-weighted MRI were performed between 4 and 9 hours and at 24 hours after embolic stroke in spontaneously hypertensive rats. Treatment with either rt-PA or saline was started 6 hours after stroke. A spectrophotometric hemoglobin assay quantified hemorrhage severity. Before treatment, relative cerebral blood flow index (rCBFi) and apparent diffusion coefficient (ADC) in the ischemic territory were 30% +/- 23% and 60% +/- 5% (of contralateral), respectively, which increased to 45% +/- 39% and 68% +/- 4% 2 hours after rt-PA. After 24 hours, rCBFi and ADC were 27% +/- 27% and 59 +/- 5%. Hemorrhage volume after 24 hours was significantly greater in rt-PA-treated animals than in controls (8.7 +/- 3.7 microL vs. 5.1 +/- 2.4 microL, P < 0.05). Before rt-PA administration, clear postcontrast T1-weighted signal intensity enhancement was evident in areas of subsequent bleeding. These areas had lower rCBFi levels than regions without hemorrhage (23% +/- 22% vs. 36% +/- 29%, P < 0.05). In conclusion, late thrombolytic therapy does not necessarily lead to successful reperfusion. Hemorrhage emerged in areas with relatively low perfusion levels and early blood-brain barrier damage. Magnetic resonance imaging may be useful for quantifying effects of thrombolytic therapy and predicting risks of hemorrhagic transformation.

Elements of cerebral microvascular ischaemia

Although neuronal cells have long been thought to be the prime target of ischaemic insults, events which occur at the blood-vascular-parenchymal interface are necessary for the initiation of ischaemic tissue injury. This cascade of microvascular events includes fibrin accumulation, endothelium expression of leukocyte adhesion receptors, breakdown of the basal laminae with loss of astrocyte and endothelial cell contacts leading to blood-brain barrier disruption and consequently oedema formation and haemorrhagic transformation. Potential stroke treatments have been studied in the clinic and many have not been particularly successful, probably due to the delicate balance between improved outcome and adverse reactions as well as the window of opportunity for drug treatment after symptom onset. The only acute intervention trial demonstrating any benefit in patients was that of intravenous tissue plasminogen activator (tPA), administered within 3 h of the onset of symptoms of ischaemic stroke. Such treatment improved clinical outcome at 3 months, although there was an increased incidence of symptomatic haemorrhage [New Engl. J. Med. 333 (1995) 1581]. The recent progress made in defining the mechanisms involved in the initiation of ischaemic events, as described in this review, may lead to the identification of new strategies for intervention in the ischaemic cascade.

Targeting the central nervous system inflammatory response in ischemic stroke

In experimental models of stroke, inflammation appears to contribute to cerebral ischemic injury. Clinical trials that are aimed at limiting the postischemic inflammatory response, however, have thus far had disappointing results. These clinical failures probably reflect the fact that there has been insufficient preclinical data and inadequate trial design, rather than provide evidence against a role for inflammation in ischemic brain injury.

Hemorrhagic transformation after fibrinolysis with tissue plasminogen activator: evaluation of role of hypertension with rat thromboembolic stroke model

BACKGROUND AND PURPOSE

We used a rat model of thromboembolic stroke to evaluate whether hypertension increases the incidence of hemorrhage after fibrinolysis with tissue plasminogen activator (tPA).

METHODS

In this model, a microclot suspension was injected into the middle cerebral artery territory to induce focal ischemia. Reperfusion was induced in spontaneously hypertensive rats (SHR) by administering tPA (10 mg/kg) intravenously at 2 hours or 6 hours after the onset of thromboembolic focal ischemia. In untreated control rats, saline was administered at 2 hours after ischemia.

RESULTS

Hemorrhagic transformation was observed only in rats that received tPA at 6 hours (6 of 8 rats [75%]). Reduction of mean arterial blood pressure from 122+/-3 to 99+/-2 mm Hg with hydralazine, given to SHR for 1 week before ischemia, significantly decreased the incidence of hemorrhage in 2 of 11 rats (18%). tPA reduced infarct volumes, but cotreatment with hydralazine did not result in further protection.

CONCLUSIONS

This study demonstrates that in this rat thromboembolic model of stroke, tPA-induced hemorrhage is dependent on blood pressure and that pharmacological reduction of hypertension during fibrinolysis can reduce the risk of hemorrhagic transformation.

Protective effects of pamiteplase, a modified t-PA, in a rat model of embolic stroke

The effects of alteplase (tissue plasminogen activator, t-PA) and pamiteplase (a modified t-PA with longer half-life and increased potency) were compared in a clinically relevant model of embolic stroke. Rats were treated with pamiteplase (0.5 mg/kg or 1 mg/kg bolus), alteplase (10 mg/kg infusion) or normal saline. Pamiteplase (1 mg/kg) was as effective as alteplase in reducing 24 h brain infarct volumes, neurological deficit scores and residual clot grades. Cerebral blood flow recovery at 30 min after thrombolytic treatment was partial and did not correlate with 24 h infarct volumes or neurological deficits. However, there was good correlation between 24 h residual clot grades and infarct volumes, suggesting a delayed timeframe for pamiteplase- and alteplase-induced reperfusion.