The clot thickens--thrombolysis and combination therapies

[Preclinical studies of drugs on animal stroke models]

Preclinical studies are studies using experimental models of stroke in animals as well as on neurons, cell neuronal cultures and surviving brain slices. They directed both towards testing the efficacy and evaluation of the mechanisms of action of drugs, and the study of the mechanisms of ischemic damage to search for new targets for stroke treatment. This article shows the basic principles of the organization and planning of animal models of ischemic stroke. Modeling of cerebral ischemia on the different models and animal species, the modern principles of assessment of brain damage are considered as well.

Tissue Plasminogen Activator Neurotoxicity is Neutralized by Recombinant ADAMTS 13

Tissue plasminogen activator (tPA) is an effective treatment for ischemic stroke, but its neurotoxicity is a significant problem. Here we tested the hypothesis that recombinant ADAMTS 13 (rADAMTS 13) would reduce tPA neurotoxicity in a mouse model of stroke. We show that treatment with rADAMTS 13 in combination with tPA significantly reduced infarct volume compared with mice treated with tPA alone 48 hours after stroke. The combination treatment significantly improved neurological deficits compared with mice treated with tPA or vehicle alone. These neuroprotective effects were associated with significant reductions in fibrin deposits in ischemic vessels and less severe cell death in ischemic brain. The effect of rADAMTS13 on tPA neurotoxicity was mimicked by the N-methyl-D-aspartate (NMDA) receptor antagonist M-801, and was abolished by injection of NMDA. Moreover, rADAMTS 13 prevents the neurotoxicity effect of tPA, by blocking its interaction with the NMDA receptor NR2B and the attendant phosphorylation of NR2B and activation of ERK1/2. Finally, the NR2B-specific NMDA receptor antagonist ifenprodil abolished tPA neurotoxicity and rADAMTS 13 treatment had no further beneficial effect. Our data suggest that the combination of rADAMTS 13 and tPA may provide a novel treatment of ischemic stroke by diminishing the neurotoxic effects of exogenous tPA.

Mild hypothermia reduces tissue plasminogen activator-related hemorrhage and blood brain barrier disruption after experimental stroke

Therapeutic hypothermia has shown neuroprotective promise, but whether it can be used to improve outcome in stroke has yet to be determined in patients. Recombinant tissue plasminogen activator (rt-PA) is only given to a minority of patients with acute ischemic stroke, and is not without risk, namely significant brain hemorrhage.We explored whether mild hypothermia, in combination with rt-PA, influences the safety of rt-PA. Mice were subjected to middle cerebral artery occlusion (MCAO) using a filament model, followed by 24 hours reperfusion.Two paradigms were studied. In the first paradigm, cooling and rt-PA treatment began at the same time upon reperfusion, whereas in the second paradigm, cooling began soon after ischemia onset, and rt-PA began after rewarming and upon reperfusion. Experimental groups included: tPA treatment at normothermia (37°C), rt-PA treatment at hypothermia (33°C), no rt-PA at normothermia, and no rt-PA treatment at hypothermia. Infarct size, neurological deficit scores, blood brain barrier (BBB) permeability, brain hemorrhage, and expression of endogenous tissue plasminogen activator (tPA) and its inhibitor, plasminogen activator inhibitor (PAI-1) were assessed. For both paradigms, hypothermia reduced infarct size and neurological deficits compared to normothermia, regardless of whether rt-PA was given. rt-PA treatment increased brain hemorrhage and BBB disruption compared to normothermia, and this was prevented by cooling. However, mortality was higher when rt-PA and cooling were administered at the same time, beginning 1–2 hours post MCAO. Endogenous tPA expression was reduced in hypothermic mice, whereas PAI-1 levels were unchanged by cooling. In the setting of rt-PA treatment, hypothermia reduces brain hemorrhage, and BBB disruption, suggesting that combination therapy with mild hypothermia and rt-PA appears safe.

Thrombolytic effects of the snake venom disintegrin saxatilin determined by novel assessment methods: a FeCl3-induced thrombosis model in mice

Saxatilin, a novel disintegrin purified and cloned from the venom of the Korean snake Gloydius saxatilis, strongly inhibits activation and aggregation of platelets. Glycoprotein (GP) IIb/IIIa receptor antagonists can resolve thrombus, so saxatilin might also have thrombolytic effects. We investigated the thrombolytic effects of saxatilin in mice using a ferric chloride-induced carotid arterial thrombosis model. Thrombotic occlusion and thrombus resolution were evaluated quantitatively by measuring blood flow in the carotid artery with an ultrasonic flow meter and calculating the degree of flow restoration on a minute-by-minute basis; results were confirmed by histological examination. Saxatilin dissolved thrombi in a dose-dependent manner. Saxatilin at 5 mg/kg restored blood flow to baseline levels. As saxatilin dose increased, time to recanalization decreased. A bolus injection of 10% of a complete dose with continuous infusion of the remaining dose for 60 minutes resulted in effective recanalization without reocclusion. The thrombolytic effect of saxatilin was also demonstrated in vitro using platelet aggregometry by administering saxatilin in preformed thrombi. Bleeding complications were observed in 2 of 71 mice that received saxatilin. Fibrin/fibrinogen zymography and platelet aggregometry studies indicated that saxatilin does not have fibrinolytic activity, but exerted its action on platelets. Integrin-binding assays showed that saxatilin inhibited multiple integrins, specifically α2bβ3 (GP IIb/IIIa), α5β1, αvβ3, αvβ1, and αvβ5, which act on platelet adhesion/aggregation. Saxatilin inhibited multiple integrins by acting on platelets, and was safe and effective in resolving thrombi in mice.

Atorvastatin extends the therapeutic window for tPA to 6 h after the onset of embolic stroke in rats

We investigated the neuroprotective effect of atorvastatin in combination with delayed thrombolytic therapy in a rat model of embolic stroke. Rats subjected to embolic middle cerebral artery (MCA) occlusion were treated with atorvastatin at 4 h, followed by tissue plasminogen activator (tPA) at 6 or 8 h after stroke. The combination of atorvastatin at 4 h and tPA at 6 h significantly decreased the size of the embolus at the origin of the MCA, improved microvascular patency, and reduced infarct volume, but did not increase the incidence of hemorrhagic transformation compared with vehicle-treated control animals. However, monotherapy with tPA at 6 h increased the incidence of hemorrhagic transformation and failed to reduce infarct volume compared with the control group. In addition, adjuvant treatment with atorvastatin at 4 h and with tPA at 6 h reduced tPA-induced upregulation of protease-activated receptor-1, intercellular adhesion molecule-1, and matrix metalloproteinase-9, and concomitantly reduced cerebral microvascular platelet, neutrophil, and fibrin deposition compared with rats treated with tPA alone at 6 h. In conclusion, a combination of atorvastatin and tPA extended the therapeutic window for stroke to 6 h without increasing the incidence of hemorrhagic transformation. Atorvastatin blocked delayed tPA-potentiated adverse cerebral vascular events, which likely contributes to the neuroprotective effect of the combination therapy.

TTC, fluoro-Jade B and NeuN staining confirm evolving phases of infarction induced by middle cerebral artery occlusion

Considerable debate exists in the literature on how best to measure infarct damage and at what point after middle cerebral artery occlusion (MCAO) infarct is histologically complete. As many researchers are focusing on more chronic endpoints in neuroprotection studies it is important to evaluate histological damage at later time points to ensure that standard methods of tissue injury measurement are accurate. To compare tissue viability at both acute and sub-acute time points, we used 2,3,5-triphenyltetrazolium chloride (TTC), Fluoro-Jade B, and NeuN staining to examine the evolving phases of infarction induced by a 90-min MCAO in mice. Stroke outcomes were examined at 1.5h, 6h, 12h, 24h, 3d, and 7d after MCAO. There was a time-dependent increase in infarct volume from 1.5h to 24h in the cortex, followed by a plateau from 24h to 7d after stroke. Striatal infarcts were complete by 12h. Fluoro-Jade B staining peaked at 24h and was minimal by 7d. Our results indicated that histological damage as measured by TTC and Fluoro-Jade B reaches its peak by 24h after stroke in a reperfusion model of MCAO in mice. TTC staining can be accurately performed as late as 7d after stroke. Neurological deficits do not correlate with the structural lesion but rather transient impairment of function. As the infarct is complete by 24h and even earlier in the striatum, even the most efficacious neuroprotective therapies are unlikely to show any efficacy if given after this point.

Multitargeted Effects of Statin-Enhanced Thrombolytic Therapy for Stroke With Recombinant Human Tissue-Type Plasminogen Activator in the Rat

Background— Microvascular dysfunction posttreatment of stroke with recombinant human tissue-type plasminogen activator (rht-PA) constrains the therapeutic window to 3 hours. Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) promote vascular thrombolysis and reduce the inflammation response. We therefore investigated the neuroprotective effects of a combination of atorvastatin and delayed rht-PA treatment in a rat model of embolic stroke.

Methods and Results— Rats subjected to embolic middle cerebral artery occlusion were treated with atorvastatin in combination with rht-PA 4 hours after stroke. Magnetic resonance imaging measurements revealed that combination treatment with atorvastatin and rht-PA blocked the expansion of the ischemic lesion, which improved neurological function compared with saline-treated rats. Real-time reverse transcription–polymerase chain reaction analysis of single endothelial cells isolated by laser-capture microdissection from brain tissue and immunostaining showed that combination treatment downregulated expression of tissue factor, von Willebrand factor, protease-activated receptor-1, intercellular adhesion molecule-1, and matrix metalloproteinase-9, which concomitantly reduced cerebral microvascular thrombosis and enhanced microvascular integrity. Combination treatment did not increase cerebrovascular endothelial nitric oxide synthase (eNOS) levels or eNOS activity, and inhibition of NOS activity with N -nitro- l -arginine methyl ester did not block the beneficial effects of combination treatment on stroke. Furthermore, combination treatment compared with thrombolytic monotherapy increased cerebral blood flow and reduced infarct volume in eNOS-null mice.

Conclusions— These data demonstrate that combination treatment with atorvastatin and rht-PA exerts a neuroprotective effect when administered 4 hours after stroke and that the therapeutic benefits are likely attributed to its multitargeted effects on cerebrovascular patency and integrity.

Assessing combination treatments in acute stroke: Preclinical experiences

BACKGROUND

Acute ischemic stroke is a complex disease. Treatment success may require combining different therapeutic approaches. An obvious treatment combination in acute ischemic stroke is a thrombolytic therapy, adjuvant with a neuroprotective agent to have better stroke recovery.

SUMMARY OF REVIEW

Complete factorial designs can assess the synergy of combination treatments and distinguish them from supper-additive, additive or sub-additive effects. A factorial design, a two-way analysis of variance and a novel graphic technique can detect and illustrate interactions of two treatments, which were used to evaluate combination treatments to extend the therapeutic window for thrombolytic therapy in an embolic stroke model on rats. We hypothesized synergy or additive effects on stroke recovery when combining thrombolytic therapy with either an antagonist to the integrin CD11b/CD18 (UK-279,276) or a glycoprotein IIb/IIIa receptor inhibitor.

CONCLUSIONS

Factorial designs offer an efficient approach to study synergistic effects of two treatments. Our graphical technique provides a powerful, intuitive and quantitative explanation of joint treatment effects. Combining thrombolytic therapy with a neuroprotectant yielded a super-additive or additive treatment effect for two preclinical experiments designed to extend the thrombolytic therapeutic window for stroke.

Emergency Administration of Abciximab for Treatment of Patients With Acute Ischemic Stroke

Background and Purpose— Because of its success in treatment of acute cardiac ischemia, there is interest in the use of abciximab for treating patients with acute ischemic stroke. A previous dose-escalation study determined that abciximab could be given safely in a regimen of 0.25 mg/kg intravenous bolus followed by a 12-hour infusion at 0.125 μg/kg per minute (maximum 10 μg/min). This study was performed to obtain more information about the safety and potential efficacy of abciximab in patients with stroke.

Methods— An international randomized, double-blind, placebo-controlled phase 2 trial enrolled 400 patients within 6 hours of onset of ischemic stroke. The primary safety outcome was the rate of symptomatic hemorrhage that occurred during the first 5 days after stroke. The primary efficacy measure was the distribution of outcomes at 3 months after stroke using the modified Rankin Scale (mRS) based on an ordinal regression model of outcomes, adjusting for baseline severity of stroke, age, and interval from stroke.

Results— Symptomatic intracranial hemorrhage within 5 days was diagnosed in 7 of 195 (3.6%) patients treated with abciximab and 2 of 199 (1%) patients given placebo (odds ratio [OR], 3.7; P =0.09; 95% confidence interval [CI], 0.7 to 25.9). Asymptomatic hemorrhagic transformation was detected by brain imaging in 24 patients administered abciximab and 33 patients receiving placebo (OR, 0.74; P =0.25; 95% CI, 0.4 to 1.3). Treatment with abciximab showed a nonsignificant shift in favorable outcomes as measured by mRS scores at 3 months (OR, 1.20; P =0.33; 95% CI, 0.84 to 1.70).

Conclusions— Intravenously administered abciximab can be given to patients with a reasonable degree of safety. The trial also suggests that abciximab could improve outcomes at 3 months after stroke. A larger randomized, double-blind, placebo-controlled trial is necessary to test the efficacy of abciximab.

Intravenous administration of a GPIIb/IIIa receptor antagonist extends the therapeutic window of intra-arterial tenecteplase-tissue plasminogen activator in a rat stroke model

BACKGROUND AND PURPOSE

Occlusion of the middle cerebral artery triggers platelet accumulation at the site of occlusion and in downstream microvessels. The platelet-induced secondary thrombosis promotes the progressive development of ischemic brain damage and contributes to the resistance to thrombolysis and to the tight 3-hour therapeutic window. We tested the hypothesis that combination of intravenous (IV) administration of a GPIIb/IIIa receptor antagonist, 7E3 F(ab')2, with intra-arterial (IA) administration of tenecteplase-tissue plasminogen activator (TNK-tPA) increases the efficacy of thrombolysis and extends the therapeutic window of stroke.

METHODS

Rats subjected to embolic stroke were treated with IV 7E3 F(ab')2 (6 mg/kg) in combination with IA or IV TNK-tPA (5 mg/kg) at 4 and 6 hours after onset of stroke, respectively; IA TNK-tPA (5 mg/kg) alone at 6 hours after onset of stroke; or saline at 6 hours after onset of stroke.

RESULTS

The combination of IV 7E3 F(ab')2 (4 hours) and IA TNK-tPA (6 hours) significantly (P<0.05) reduced infarct volume and improved neurological functional deficits, which was associated with significant (P<0.05) reductions in the size of embolus at the origin of the occluded middle cerebral artery and in down-stream microvascular platelet and fibrin deposition, and enhanced microvascular patency compared with saline-treated rats. However, combination of IV 7E3 F(ab')2 (4 hours) and IV TNK-tPA (6 hours) or IA TNK-tPA (6 hours) alone failed to reduce infarct volume and improve neurological function compared with the saline-treated rats. No significant differences of the incidence of hemorrhage were detected among groups.

CONCLUSIONS

These data suggest that the combination of IV 7E3 F(ab')2 (4 hours) and IA TNK-tPA (6 hours) extends the therapeutic window of thrombolysis to 6 hours after stroke.

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.

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.

Effects of a selective CD11b/CD18 antagonist and recombinant human tissue plasminogen activator treatment alone and in combination in a rat embolic model of stroke

BACKGROUND AND PURPOSE

We evaluated the neuroprotective effect of UK-279,276 (also referred to as recombinant neutrophil inhibitory factor), a selective CD11b/CD18 antagonist, in combination with thrombolytic therapy on focal cerebral ischemia.

METHODS

Male Wistar rats (n=88) were subjected to embolic middle cerebral artery occlusion. Animals were randomly assigned to the following groups (n=11 in each group): vehicle treatment alone at 2 or 4 hours, UK-279,276 treatment alone at 2 or 4 hours, recombinant human tissue plasminogen activator (rhtPA) treatment alone at 2 or 4 hours, or the combination of UK-279,276 and rhtPA at 2 or 4 hours. Infarct volume, neurological function, hemorrhagic transformation, neutrophil accumulation, and parenchymal fibrin deposition were measured 7 days after middle cerebral artery occlusion.

RESULTS

Treatment with UK-279,276 significantly (P<0.05) improved neurological severity scores, an index of neurological functional deficit, but had no effect on infarct volume compared with vehicle-treated animals. Treatment with rhtPA alone at 2 but not 4 hours significantly (P<0.05) reduced infarct volume and improved neurological function compared with vehicle-treated animals. Combination treatment with UK-279,276 and rhtPA at 2 or 4 hours significantly (P<0.01) reduced infarct volume and enhanced recovery of neurological function compared with control. Neutrophil accumulation and fibrin deposition in the brain parenchyma of combination-treated rats at 2 and 4 hours after stroke were significantly reduced (P<0.05) compared with corresponding vehicle-treated control groups. The neuroprotective effect of the combined treatments was superior to the additive effects from each treatment of rhtPA or UK-279,276 alone.

CONCLUSIONS

These data suggest that the combination treatment with UK-279,276 and rhtPA may extend the window of thrombolytic therapy for the acute treatment of stroke.

Blood-brain barrier disruption and matrix metalloproteinase-9 expression during reperfusion injury: mechanical versus embolic focal ischemia in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Most experimental models of cerebral ischemia use mechanical methods of occlusion and reperfusion. However, differences between mechanical reperfusion versus clot thrombolysis may influence reperfusion injury profiles. In this study we compared blood flow recovery, blood-brain barrier (BBB) permeability, and matrix metalloproteinase-9 (MMP-9) expression in cortex after mechanical versus thrombolytic reperfusion in rat focal ischemia.

METHODS

Male spontaneously hypertensive rats were used. Mechanical ischemia/reperfusion was achieved with the use of an intraluminal filament to occlude the middle cerebral artery for 2 hours. Thrombolytic reperfusion was achieved by administering tissue plasminogen activator at 2 hours after embolic focal ischemia. Regional cortical blood flow was monitored by laser-Doppler flowmetry. BBB permeability in cortex was measured by Evans blue dye leakage. Cortical MMP-9 levels were assessed with zymography and immunohistochemistry.

RESULTS

Blood flow recovery during mechanical reperfusion was complete in both central and peripheral areas of ischemic cortex. However, after thrombolysis, reperfusion was incomplete, with moderate recovery in the periphery only. BBB permeability was mainly increased in the central regions of the ischemic cortex after mechanical reperfusion but was increased in both central and peripheral areas after thrombolysis. Overall, MMP-9 levels were higher after embolic versus mechanical ischemia/reperfusion, even though ischemic injury was similar in both models at 24 hours.

CONCLUSIONS

There are significant differences in the profiles of blood flow recovery, BBB leakage, and MMP-9 upregulation in mechanical versus thrombolytic reperfusion after focal ischemia.

Adjuvant treatment with neuroserpin increases the therapeutic window for tissue-type plasminogen activator administration in a rat model of embolic stroke

BACKGROUND

After stroke, the thrombolytic effect of tissue-type plasminogen activator (tPA) in the intravascular space is beneficial, whereas its extravascular effect on ischemic neurons is deleterious. We tested the hypothesis that neuroserpin, a natural inhibitor of tPA, reduces tPA-induced neuronal toxicity and increases its therapeutic window for treatment of embolic stroke.

METHODS AND RESULTS

Rats were subjected to embolic middle cerebral artery occlusion (MCAO). Ischemic brains were treated with neuroserpin in combination with recombinant human tPA (n=7), tPA alone (n=7), or saline (n=9). Neuroserpin (20 micro L of 16 micro mol/L active neuroserpin) was intracisternally injected 3 hours and tPA (10 mg/kg) was intravenously administered 4 hours after ischemia. MRI measurements were performed to study blood brain barrier (BBB) leakage and ischemic lesion volume. Administration of tPA alone 4 hours after ischemia significantly (P<0.05) increased BBB leakage in the ischemic core measured by Gd-DTPA-enhanced MRI compared with rats treated with saline. However, treatment with neuroserpin in combination with tPA significantly (P<0.05) reduced BBB leakage, brain edema, and ischemic lesion volume compared with rats treated with tPA alone, although ischemic lesion volumes were the same in both groups before the treatment. Immunostaining revealed that MCAO resulted in reduction of neuroserpin immunoreactivity in the ipsilateral hemisphere after 2 to 6 hours of ischemia. Zymographic assay showed increased plasminogen activity in areas with BBB leakage in rats treated with tPA.

CONCLUSIONS

Administration of neuroserpin after stroke is neuroprotective, seemingly because it blocks the extravascular effect of tPA, leading to subsequent decrease in stroke volume and widening of the therapeutic window for the thrombolytic effect of tPA.

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.

Management of acute ischaemic stroke in the elderly: tolerability of thrombolytics

Stroke and its consequences are of global concern. Although stroke can affect individuals of any age, it primarily affects the elderly. It is among the leading causes of severe disability and mortality. In recent years, acute stroke has become a medical emergency requiring urgent evaluation and treatment. Effective management of patients with acute stroke starts with organisation of the entire stroke care chain, from the community and prehospital scene, through the emergency department, to a dedicated stroke unit and then to comprehensive rehabilitation. Intravenous thrombolysis with alteplase (recombinant tissue plasminogen activator; rt-PA) 0.9 mg/kg (maximum dose 90 mg) was shown to significantly improve outcome of acute ischaemic stroke, despite an increased rate of symptomatic intracerebral haemorrhage, if treatment is initiated within 3 hours after the onset of symptoms to patients who meet strict eligibility criteria. Post-marketing studies have demonstrated that intravenous alteplase can be administered appropriately in a wide variety of hospital settings. However, strict adherence to the published protocol is mandatory, as failure to comply may be associated with an increased risk of symptomatic intracerebral haemorrhage. Intra-arterial revascularisation may provide more complete restitution of flow than intravenous thrombolytic therapy and improve the clinical outcome if it can be undertaken in patients with occlusion of the middle cerebral artery, and possibly the basilar artery, within the first hours from stroke onset. However, further data are needed. Although intravenous alteplase is recommended for any age beyond 18 years, elderly patients, in particular patients aged > or = 80 years, were often excluded or under-represented in randomised clinical trials of thrombolysis, so that available data on risk/benefit ratio for the very elderly are limited. Small post-marketing series suggest that despite elderly patients over 80 years having greater pre-stroke disability, the use of intravenous alteplase in this patient group does not significantly differ in effectiveness and complications compared with the same treatment in patients aged under age 80 years. Further studies are necessary and elderly patients with acute stroke should be included in future trials of the merits of thrombolytic therapy.

The nonpeptide glycoprotein IIb/IIIa platelet receptor antagonist SM-20302 reduces tissue plasminogen activator-induced intracerebral hemorrhage after thromboembolic stroke

BACKGROUND AND PURPOSE

Platelet activation and deposition in brain microvessels appear to be key events in the pathogenesis of ischemia-induced neuronal degeneration and behavioral deficits. It has been hypothesized that activated platelets in combination with polymorphonuclear leukocytes and fibrin may play a role in vessel reocclusion leading to the "no-reflow" phenomenon after administration of the thrombolytic tissue plasminogen activator (tPA). We studied the effects of the novel glycoprotein IIb/IIIa platelet receptor antagonist SM-20302 when administered in combination with tPA on infarct and hemorrhage rate and volume to determine whether activated platelets are involved in either infarct or hemorrhage generation after a thromboembolic stroke.

METHODS

One hundred thirty-two male New Zealand White rabbits were included in the present study. Rabbits were embolized by injecting a blood clot into the middle cerebral artery via a catheter. Five or 65 minutes after embolization, SM-20302 (5 mg/kg) was infused intravenously. In drug combination studies, tPA was infused intravenously for 30 minutes starting 60 minutes after embolization, and SM-20302 was administered 5 or 65 minutes after embolization. Postmortem analysis included assessment of hemorrhage, infarct size and location, and clot lysis.

RESULTS

In the vehicle control group, the hemorrhage rate after a thromboembolic stroke was 33%. There was a significant increase (109%) in the hemorrhage rate in the group of rabbits treated with the thrombolytic tPA. SM-20302 by itself did not significantly alter the embolism-induced hemorrhage rate when administered either 5 or 65 minutes after embolism. The SM-20302 groups had a 42% and 33% incidence of hemorrhage in the 5- and 65-minute groups, respectively. In groups treated with a combination of drugs, the SM-20302/tPA group had a 31% and 71% incidence of hemorrhage when SM-20302 was administered 5 and 65 minutes after embolization, respectively. SM-20302 in combination with tPA also significantly increased infarct rate, but not hemorrhage or infarct volume.

CONCLUSIONS

This study suggests that treatment of thromboembolic stroke with the combination of a platelet inhibitor and tPA may have a beneficial outcome on the basis of the following: First, acute administration of SM-20302 did not significantly increase hemorrhage rate. Second, SM-20302 in combination with tPA significantly reduced tPA-induced intracerebral hemorrhage. Third, there appears to be a specific window of opportunity when a platelet inhibitor must be administered to produce a beneficial effect. Overall, on the basis of our results, we hypothesize that the increased rate of intracerebral hemorrhage observed after tPA administration may be partly due to increased reocclusion of cerebral vessels following lysis of the emboli and that reocclusion can be controlled by administration of a platelet inhibitor.

Hemorrhagic transformation following ischemic stroke: significance, causes, and relationship to therapy and treatment

Hemorrhagic transformation (HT) is a frequent consequence of ischemic stroke that becomes more prevalent after thrombolytic therapy. Despite concerns about safety parameters, thrombolytic drugs remain the first course of action available to clinicians for stroke management. However, recent efforts in preclinical studies have attempted to discover other drugs that can lessen the risk of hemorrhage associated with thrombolytic administration. This review focuses on three classes of pharmacologic agents that have shown some promise in animal models of stroke, and can thus be considered as possible candidates for coadministration with thrombolytics in the treatment of stroke. These include the following: 1) spin trap agents, such as alpha-phenyl-N-t-butylnitrone (PBN) that scavenge free radicals; 2) matrix metalloproteinase (MMP) inhibitors, such as BB-94, that prevent membrane and vessel remodeling following ischemia; and 3) the novel glycoprotein (GP) IIb/IIIa platelet receptor antagonist SM-20302. Although these drugs affect different mechanisms, the common denominator seemed to be their effectiveness in reducing the incidence of hemorrhage in response to thrombolytic infusion following an embolic stroke.

Postischemic (6-Hour) treatment with recombinant human tissue plasminogen activator and proteasome inhibitor PS-519 reduces infarction in a rat model of embolic focal cerebral ischemia

BACKGROUND AND PURPOSE

The proteasome inhibitor PS-519 blocks activation of nuclear factor-kappaB, a major mediator of inflammation. We tested the hypothesis that combination treatment of recombinant human tissue plasminogen activator (rhtPA) and PS-519 extends the therapeutic window for treatment of stroke with rhtPA without increasing incidence of hemorrhagic transformation.

METHODS

The middle cerebral artery (MCA) of male Wistar rats (n=56) was occluded by an embolus. After embolization, animals were randomly divided into the following groups: PS-519 treatment groups: PS-519 was given at 2, 4, or 6 hours after MCA occlusion; rhtPA treatment groups: rhtPA was given at 2 or 4 hours after MCA occlusion; combination treatment groups: PS-519 and rhtPA were given at 2, 4, or 6 hours after MCA occlusion; control group: the same volume of saline was given at 2 hours after MCA occlusion.

RESULTS

Administration of PS-519 alone at 2 or 4 hours, but not 6 hours, significantly (P<0.05) reduced infarct volume and improved neurological recovery compared with the control group. Administration of rhtPA alone at 2 hours, but not 4 hours, significantly (P<0.05) reduced infarct volume and improved neurological recovery compared with the control group. Furthermore, combination treatment with rhtPA and PS-519 even at 6 hours significantly (P<0.05) reduced infarct volume, improved neurological recovery, and did not increase the incidence of hemorrhagic transformation compared with the control group or the group treated with PS-519 alone.

CONCLUSIONS

Our data suggest that combination treatment with PS-519 and rhtPA extends the neuroprotective effect to at least 6 hours after embolization.

Application of magnetic resonance to animal models of cerebral ischemia

The present review has been compiled to highlight the role of magnetic resonance imaging (MRI) and MR spectroscopy (MRS) for the investigation of cerebral ischemia in the animal experimental field of basic research. We have focused on stroke investigations analyzing the pathomechanisms of the disease evolution and on new advances in both nuclear MR (NMR) methodology or genetic engineering of transgenic animals for the study of complex molecular relationships and causes of the disease. Furthermore, we have tried to include metabolic and genetic aspects, as well as the application of functional imaging, for the investigation of the disturbance or restitution of functional brain activation under pathological conditions as relates to controlled animal experiments.

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.

Reduction of tissue plasminogen activator-induced hemorrhage and brain injury by free radical spin trapping after embolic focal cerebral ischemia in rats

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) remains complicated by serious risks of cerebral hemorrhage and brain injury. In this study, a novel model of tPA-induced hemorrhage was used in spontaneously hypertensive rats to examine the correlates of hemorrhage, and test methods of reducing hemorrhage and brain injury. Homologous blood clot emboli were used to occlude the middle cerebral artery in spontaneously hypertensive rats, and delayed administration of tPA (6 hours postischemia) resulted in high rates of cerebral hemorrhage 24 hours later. Compared with untreated rats, tPA significantly increased hemorrhage volumes by almost 85%. Concomitantly, infarction and neurological deficits were worsened by tPA. A parallel experiment in normotensive Wistar-Kyoto rats showed markedly reduced rates of hemorrhage, and tPA did not significantly increase hemorrhage volumes. To examine whether tPA-induced hemorrhage was caused by the delayed onset of reperfusion per se, another group of spontaneously hypertensive rats was subjected to focal ischemia using a mechanical method of arterial occlusion. Delayed (6 hours) reperfusion via mechanical means did not induce hemorrhage. However, administration of tPA plus delayed mechanical reperfusion significantly increased hemorrhage volumes. Since reperfusion injury was implicated, a final experiment compared outcomes in spontaneously hypertensive rats treated with tPA plus the free radical spin trap alpha-phenyl tert butyl nitrone (alpha-PBN) versus tPA alone. tPA-induced hemorrhage volumes were reduced by 40% with alpha-PBN, and infarction and neurological deficits were also decreased. These results indicate that (1) blood pressure is an important correlate of tPA-induced hemorrhage, (2) tPA interacts negatively with reperfusion injury to promote hemorrhage, and (3) combination therapies with anti-free radical treatments may reduce the severity of tPA-induced hemorrhage and brain injury after cerebral ischemia.