Comparison of Tenecteplase with Alteplase on clinical rating scores following small clot embolic strokes in rabbits

Pharmacological preclinical comparison of tenecteplase and alteplase for the treatment of acute stroke

Alteplase (rtPA) remains the standard thrombolytic drug for acute ischemic stroke. However, new rtPA-derived molecules, such as tenecteplase (TNK), with prolonged half-lives following a single bolus administration, have been developed. Although TNK is currently under clinical evaluation, the limited preclinical data highlight the need for additional studies to elucidate its benefits. The toxicities of rtPA and TNK were evaluated in endothelial cells, astrocytes, and neuronal cells. In addition, their in vivo efficacy was independently assessed at two research centers using an ischemic thromboembolic mouse model. Both therapies were tested via early (20 and 30 min) and late administration (4 and 4.5 h) after stroke. rtPA, but not TNK, caused cell death only in neuronal cultures. Mice were less sensitive to thrombolytic therapies than humans, requiring doses 10-fold higher than the established clinical dose. A single bolus dose of 2.5 mg/kg TNK led to an infarct reduction similar to perfusion with 10 mg/kg of rtPA. Early administration of TNK decreased the hemorrhagic transformations compared to that by the early administration of rtPA; however, this result was not obtained following late administration. These two independent preclinical studies support the use of TNK as a promising reperfusion alternative to rtPA.

Neutralizing RGMa with Elezanumab Promotes Cerebroprotection and Recovery in Rabbit Middle Cerebral Artery Occlusion

Repulsive guidance molecule A (RGMa) is an inhibitor of neuronal growth and survival which is upregulated in the damaged central nervous system following acute spinal cord injury (SCI), traumatic brain injury, acute ischemic stroke (AIS), and other neuropathological conditions. Neutralization of RGMa is neuroprotective and promotes neuroplasticity in several preclinical models of neurodegeneration and injury including multiple sclerosis, AIS, and SCI. Given the limitations of current treatments for AIS due to narrow time windows to intervention (TTI), and restrictive patient selection criteria, there is significant unmet need for therapeutic agents that enable tissue survival and repair following acute ischemic damage for a broader population of stroke patients. In this preclinical study, we evaluated whether elezanumab, a human anti-RGMa monoclonal antibody, could improve neuromotor function and modulate neuroinflammatory cell activation following AIS with delayed intervention times up to 24 h using a rabbit embolic permanent middle cerebral artery occlusion model (pMCAO). In two replicate 28-day pMCAO studies, weekly intravenous infusions of elezanumab, over a range of doses and TTIs of 6 and 24 h after stroke, significantly improved neuromotor function in both pMCAO studies when first administered 6 h after stroke. All elezanumab treatment groups, including the 24 h TTI group, had significantly less neuroinflammation as assessed by microglial and astrocyte activation. The novel mechanism of action and potential for expanding TTI in human AIS make elezanumab distinct from current acute reperfusion therapies, and support evaluation in clinical trials of acute CNS damage to determine optimal dose and TTI in humans.

Tenecteplase or Alteplase: What Is the Thrombolytic Agent of the Future?

Purpose of review

Alteplase has been the thrombolytic of choice for acute ischaemic stroke for more than two decades. A thrombolytic which is easier to administer and with improved or comparable safety and efficacy is desirable. Tenecteplase has emerged as a potential successor, and its off-license use in acute ischaemic stroke has increased in recent years. We aimed to examine the evidence base for each drug and discuss their use in varying patient populations in acute ischaemic stroke.

Recent findings

Several trials comparing tenecteplase and alteplase have reported very recently with the results of the ACT trial strengthening the argument in favour of non-inferiority of tenecteplase to alteplase. Ongoing trials such as ATTEST-2 are of interest, and trials such as TASTE and TEMPO-2 will shed further light on use of tenecteplase in specific populations.

Summary

A single thrombolytic agent for all indications for thrombolysis in acute ischaemic stroke is desirable in streamlining workflows. Based on recent and upcoming trials, guidelines may soon recommend tenecteplase as a suitable alternative to alteplase. The use of tenecteplase in specific subgroups will depend on further recruitment to ongoing clinical trials.

Bacterial staphylokinase as a promising third-generation drug in the treatment for vascular occlusion

Vascular occlusion is one of the major causes of mortality and morbidity. Blood vessel blockage can lead to thrombotic complications such as myocardial infarction, stroke, deep venous thrombosis, peripheral occlusive disease, and pulmonary embolism. Thrombolytic therapy currently aims to rectify this through the administration of recombinant tissue plasminogen activator. Research is underway to design an ideal thrombolytic drug with the lowest risk. Despite the potent clot lysis achievable using approved thrombolytic drugs such as alteplase, reteplase, streptokinase, tenecteplase, and some other fibrinolytic agents, there are some drawbacks, such as high production cost, systemic bleeding, intracranial hemorrhage, vessel re-occlusion by platelet-rich and retracted secondary clots, and non-fibrin specificity. In comparison, bacterial staphylokinase, is a new, small-size plasminogen activator, unlike bacterial streptokinase, it hinders the systemic degradation of fibrinogen and reduces the risk of severe hemorrhage. A fibrin-bound plasmin-staphylokinase complex shows high resistance to a₂-antiplasmin-related inhibition. Staphylokinase has the potential to be considered as a promising thrombolytic agent with properties of cost-effective production and the least side effects.

CNB-001, a pleiotropic drug is efficacious in embolized agyrencephalic New Zealand white rabbits and ischemic gyrencephalic cynomolgus monkeys

Ischemic stroke is an acute neurodegenerative disease that is extremely devastating to patients, their families and society. Stroke is inadequately treated even with endovascular procedures and reperfusion therapy. Using an extensive translational screening process, we have developed a pleiotropic cytoprotective agent with the potential to positively impact a large population of brain ischemia patients and revolutionize the process used for the development of new drugs to treat complex brain disorders. In this unique translational study article, we document that the novel curcumin-based compound, CNB-001, when administered as a single intravenous dose, has significant efficacy to attenuate clinically relevant behavioral deficits following ischemic events in agyrencephalic rabbits when administered 1 h post-embolization and reduces infarct growth in gyrencephalic non-human primates, when administered 5 min after initiation of middle cerebral artery occlusion. CNB-001 is safe and does not increase morbidity or mortality in either research species. Mechanistically, CNB-001 inhibits human 5- and 15-lipoxygenase in vitro, and can attenuate ischemia-induced inflammatory markers, and oxidative stress markers, while potentially promoting synaptic plasticity mediated by enhanced brain-derived neurotrophic factor (BDNF).

The High Cost of Stroke and Stroke Cytoprotection Research

Acute ischemic stroke is inadequately treated in the USA and worldwide due to a lengthy history of neuroprotective drug failures in clinical trials. The majority of victims must endure life-long disabilities that not only affect their livelihood, but also have an enormous societal economic impact. The rapid development of a neuroprotective or cytoprotective compound would allow future stroke victims to receive a treatment to reduce disabilities and further promote recovery of function. This opinion article reviews in detail the enormous costs associated with developing a small molecule to treat stroke, as well as providing a timely overview of the cell-death time-course and relationship to the ischemic cascade. Distinct temporal patterns of cell-death of neurovascular unit components provide opportunities to intervene and optimize new cytoprotective strategies. However, adequate research funding is mandatory to allow stroke researchers to develop and test their novel therapeutic approach to treat stroke victims.

A novel method to promote behavioral improvement and enhance mitochondrial function following an embolic stroke

Tissue plasminogen activator (tPA) is the only FDA-approved treatment for stroke; tPA increases cerebral reperfusion, blood flow and improved behavior. Novel transcranial laser therapy (TLT) also enhances cerebral blood flow and activates mitochondrial function. Using the rabbit small clot embolic stroke model (RSCEM), we studied the effects of continuous wave TLT (7.5mW/cm(2)) alone or in combination with standardized intravenous (IV) tPA (3.3mg/kg) applied 1h post-embolization on 3 endpoints: 1) behavioral function measured 2 days [effective stroke dose (P50 in mg) producing neurological deficits in 50% of embolized rabbits], 2) intracerebral hemorrhage (ICH) rate, and 3) cortical adenosine-5'-triphosphate (ATP) content was measured 6h following embolization. TLT and tPA significantly (p<0.05) increased P50 values by 95% and 56% (p<0.05), respectively over control. TLT-tPA increased P50 by 136% over control (p<0.05). Embolization reduced cortical ATP content by 39%; decreases that were attenuated by either TLT or tPA treatment (p<0.05). TLT-tPA further enhanced cortical ATP levels 22% above that measured in naïve control. TLT and tPA both effectively and safely, without affecting ICH rate, improved behavioral outcome in embolized rabbits; and there was a trend (p>0.05) for the TLT-tPA combination to further increase P50. TLT and tPA both attenuated stroke-induced ATP deficits, and the combination of tPA and TLT produced an additive effect on ATP levels. This study demonstrates that the combination of TLT-tPA enhances ATP production, and suggests that tPA-induced reperfusion in combination with TLT neuroprotection therapy may optimally protect viable cells in the cortex measured using ATP levels as a marker.

How fisetin reduces the impact of age and disease on CNS function

It is becoming increasingly clear that neurological diseases are multi-factorial involving disruptions in multiple cellular systems. Thus, while each disease has its own initiating mechanisms and pathologies, certain common pathways appear to be involved in most, if not all, neurological diseases. Thus, it is unlikely that modulating only a single factor will be effective at either preventing disease development or slowing disease progression. A better approach is to identify small (< 900 daltons) molecules that have multiple biological activities relevant to the maintenance of brain function. We have identified an orally active, novel neuroprotective and cognition-enhancing molecule, the flavonoid fisetin. Fisetin not only has direct antioxidant activity but it can also increase the intracellular levels of glutathione, the major intracellular antioxidant. Fisetin can also activate key neurotrophic factor signaling pathways. In addition, it has anti-inflammatory activity and inhibits the activity of lipoxygenases, thereby reducing the production of pro-inflammatory eicosanoids and their by-products. This wide range of actions suggests that fisetin has the ability to reduce the impact of age-related neurological diseases on brain function.

A blinded, randomized study of L-arginine in small clot embolized rabbits

OBJECTIVE

Tissue plasminogen activator (tPA) is administered to acute ischemic stroke victims in a vehicle formulation containing high concentrations of L-arginine (3.5g/100mg vial), a well-known nitric oxide synthase (NOS) substrate and precursor to nitric oxide (NO), as well as an enhancer of cerebral blood flow.

METHODS

We studied the effects of tPA vehicle compared to tPA (3.3mg/kg) formulated in the same vehicle containing L-arginine, normal saline or normal saline containing L-arginine, on behavioral function following small clot embolic strokes in rabbits using clinical rating scores and quantal analysis curves as the primary end point. Treatments were administered intravenously (1ml/kg; 20% bolus/80% infused over 30min) starting 1h following the injection of small-sized blood clots into the brain vasculature and terminal behavior was measured 2days following embolization. Behavioral rating scores were used to calculate the effective stroke dose (P50 in mg) that produces neurological deficits in 50% of the rabbits.

RESULTS

In this study, tPA significantly (p=0.001) improved behavior compared to all other treatments including tPA vehicle, saline and saline-L-arginine, increasing the P50 by 141% over tPA vehicle. Saline-L-arginine was not significantly different from either saline or tPA vehicle (p>0.05).

CONCLUSION

This study demonstrates that the L-arginine component of the tPA vehicle does not contribute to the reproducible clinical improvement observed following tPA administration in rabbits. Moreover, the administration of L-arginine was not an effective method to promote behavioral recovery following embolic strokes in the stringent rabbit small clot stroke model, nor did L-arginine exacerbate behavioral deficits or intracerebral hemorrhage in embolized rabbits.

Synergistic Effect of AJW200, a von Willebrand Factor Neutralizing Antibody with Low Dose (0.9 mg/mg) Thrombolytic Therapy Following Embolic Stroke in Rabbits

The von Willebrand factor (vWF) is an acute stroke response protein involved in platelet aggregation, adhesion, inflammation, and thrombus formation, responses that occur following an ischemic stroke. We hypothesize that administration of an anti-vWF antibody (anti-vWF-Ab) may be used as adjunctive therapy with tissue plasminogen activator (tPA) to promote behavioral improvement following an embolic stroke. In this proof-of-concept study, which used a blinded and randomized design, we studied delayed treatment with the anti-vWF-Ab, AJW200 (0.30 mg/kg), alone or in combination with a rabbit low-dose of tPA (0.9 mg/kg) using the rabbit small clot embolic stroke model (RSCEM) with behavioral function as the primary clinically relevant endpoint. To evaluate the quantitative relationship between clot burden in brain and clinical scores, so that an effective stroke dose (P50) could be calculated, logistic sigmoidal quantal analysis curves were constructed. A beneficial treatment significantly increases P50 compared to control. The effect of antibody administration, either alone or with low dose tPA was compared to a "positive control", a standard rabbit optimized dose of tPA (3.3 mg/kg), as a measure of the maximum improvement potential in the RSCEM. The anti-vWF-Ab, AJW200, or control IgG were administered IV 1 hour following embolization, and behavior was measured 48 hours later. AJW200 plus low-dose tPA significantly increased the P50 value by 74% (p<0.05, t=2.612) and 81% (p<0.05, t=2.519) compared to low dose tPA or IgG, respectively, but not the AJW200 group (p>0.05). AJW200 increased the P50 value by 28%, (p>0.05) compared to the control IgG-treated group. Standard dose tPA increased the P50 value by 154% (p<0.05). Statistically, the combination response for AJW200 plus low-dose tPA was not significantly different from standard dose tPA (p=0.26). This study shows that the concomitant administration of the anti-vWF-Ab AJW200 with low dose tPA is synergistic and results in significantly improved behavioral function following embolic stroke. We postulate that neutralization of vWF may suppress or attenuate one or more aspects of the acute phase stroke cascade response including suppression of inflammatory response and reduced leukocyte adhesion.

[Dysfunction of the blood-brain barrier during ischaemia: a therapeutic concern]

Since it was discovered and its brain-protective role characterized, the blood-brain barrier (BBB), through the permeability-restricting action of the brain capillary endothelial cells, has been representing a hurdle for 95% of new medical compounds targeting the central nervous system. Recently, a BBB dysfunction is being found in an increasing number of pathologies such as brain ischaemic stroke, whose only therapy consists in a pharmacological thrombolysis limited to a small percentage of the admitted patients, because of the toxical effects of thrombolytics. And since the clinical failure of promising neuroprotectants, numerous studies of brain ischaemia were carried out, with physiopathological or pharmacological approaches refocused on the BBB, whose structural complexity is now expanded to perivascular cells, all forming a functional unit named the neurovascular unit (NVU). Nevertheless, in spite of the numerous molecular mechanisms identified, the process of BBB dysfunction in the ischaemia/reperfusion cascade remains insufficiently established to explain the pleiotropic action exerted by new pharmacological compounds, possibly protecting the entire NVU and representing potential treatments.

Incremental treatments with laser therapy augments good behavioral outcome in the rabbit small clot embolic stroke model

Transcranial near-infrared laser therapy (TLT) improves behavioral outcome in animal stroke models when applied as single treatment within the 24 h of the stroke onset. It is unknown if the multiple TLT treatments have an added beneficial effect. We aim to determine whether multiple irradiations with TLT would have further improvement in behavioral outcomes in the rabbit small clot embolic stroke model (RSCEM). Using the RSCEM, two and three TLT treatments (7.5-20 mW/cm(2)) were compared against single laser treatment alone (7.5-10.8 mW/cm(2)). Two sham irradiation groups were added for the control curves. The double treatment group received TLT at 3 and 5 h and the triple treatment group at 2, 3, and 4 h after embolization. Behavioral analysis was conducted 24 h after embolization using a dichotomized behavioral score. The determination of the effective clot amount (milligrams) that produces neurological deficits in 50 % of the rabbits (P 50) was used to compare TLT treatments with the sham. The P 50 for double treatment was 5.47 ± 0.90, with n = 39; the corresponding P 50 value for a single treatment was 3.87 ± 0.73, with n = 38; and the corresponding control curve was 3.25 ± 0.4, n = 32. The P 50 for triple treatment was 5.91 ± 0.49, with n = 23; the corresponding P 50 value for a single treatment was 3.09 ± 0.59, with n = 15, and the corresponding control curve was 1.71 ± 0.26, with n = 17. The triple treatment had 91 % improvement when compared with the single treatment and 245 % improvement when compared with the sham. The present study suggests that the additional TLT treatments provide further behavioral improvement when given during the acute ischemic stroke phase.

Endothelial cells and astrocytes: a concerto en duo in ischemic pathophysiology

The neurovascular/gliovascular unit has recently gained increased attention in cerebral ischemic research, especially regarding the cellular and molecular changes that occur in astrocytes and endothelial cells. In this paper we summarize the recent knowledge of these changes in association with edema formation, interactions with the basal lamina, and blood-brain barrier dysfunctions. We also review the involvement of astrocytes and endothelial cells with recombinant tissue plasminogen activator, which is the only FDA-approved thrombolytic drug after stroke. However, it has a narrow therapeutic time window and serious clinical side effects. Lastly, we provide alternative therapeutic targets for future ischemia drug developments such as peroxisome proliferator- activated receptors and inhibitors of the c-Jun N-terminal kinase pathway. Targeting the neurovascular unit to protect the blood-brain barrier instead of a classical neuron-centric approach in the development of neuroprotective drugs may result in improved clinical outcomes after stroke.

Taking a light approach to treating acute ischemic stroke patients: transcranial near-infrared laser therapy translational science

Transcranial near-infrared laser therapy (NILT) has been investigated as a novel neuroprotective treatment for acute ischemic stroke (AIS), for approximately 10 years. Two clinical trials, NeuroThera Effectiveness and Safety Trial (NEST)-1 and NEST-2, have evaluated the use of NILT to promote clinical recovery in patients with AIS. This review covers preclinical, translational, and clinical studies documented during the period 1997-2010. The primary aim of this article is to detail the development profile of NILT to treat AIS. Secondly, insight into possible mechanisms involved in light therapy will be presented. Lastly, possible new directions that should be considered to improve the efficacy profile of NILT in AIS patients will be discussed. The use of NILT was advanced to clinical trials based upon extensive translational research using multiple species. NILT, which may promote functional and behavioral recovery via a mitochondrial mechanism and by enhancing cerebral blood flow, may eventually be established as an Food and Drug Administration (FDA)-approved treatment for stroke. The NEST-3 trial, which is the pivotal trial for FDA approval, should incorporate hypotheses derived from translational studies to ensure efficacy in patients. Future NILT studies should consider administration of a thrombolytic to enhance cerebral reperfusion alongside NILT neuroprotection.

A critical assessment of edaravone acute ischemic stroke efficacy trials: is edaravone an effective neuroprotective therapy?

IMPORTANCE OF THE FIELD

Edaravone (Radicut) is a free radical scavenger marketed in Japan by Mitsubishi Tanabe Pharma Corp. to treat acute ischemic stroke (AIS) patients presenting within 24 h of the attack. Injectable edaravone ampoules (30 mg b.i.d., i.v., 14 days) were first approved on 23 May 2001. On 19 January 2010, as a new innovation, the Radicut BAG (Intravenous BAG) was approved by the Japanese Ministry of Health and Welfare. Efficacy of edaravone ranges from large significant clinical improvements to only modest improvements in clinical function measured using standard stroke scales when administered 6-72 h following an ischemic stroke. With almost 17 years of edaravone clinical experience, a few adverse events--including acute renal failure--have been noted.

WHAT THE READER WILL GAIN

This is the only article to date to critically review available clinical efficacy and toxicology data published in the literature to ascertain whether edaravone should be further pursued as a candidate for development worldwide.

AREAS COVERED IN THIS REVIEW

This review covers clinical studies carried out over the period 1993-2008.

TAKE HOME MESSAGE

Edaravone may be a useful neuroprotective agent to treat the > 15 million victims worldwide who are devastated by stroke annually. Additional clinical studies are necessary to verify the efficacy of edaravone.

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.

Stroke location and brain function in an embolic rabbit stroke model

PURPOSE

Current rabbit stroke models often depend on symptoms as endpoints for embolization and produce wide variation in location, size, and severity of strokes. In a further refinement of an angiographic embolic stroke model, localized infarctions were correlated to neurologic deficits with the goal to create a rabbit model for long-term studies of therapies after stroke.

MATERIALS AND METHODS

New Zealand White rabbits (4-5 kg; N = 71) had selective internal carotid artery (ICA) angiography and a single clot was injected. At 24 hours, neurologic assessment score (NAS) was measured on an 11-point scale (0, normal; 10, dead). Brains were removed and stained to identify stroke areas. All animals with single strokes (n = 31) were analyzed by specific brain structure involvement, and NAS values were correlated.

RESULTS

Stroke incidence differed by location, with cortex, subcortical, and basal ganglia regions highest. The middle cerebral artery (MCA), at 52%, and anterior cerebral artery (ACA), at 29%, were most commonly involved, with the largest stroke volumes in the ACA distribution. Brainstem and cerebellum strokes had disproportionately severe neurologic deficits, scoring 2.25 +/- 1.0 on the NAS, which represented a significant (P < .02) difference versus cortex (0.5 +/- 0.2), subcortical (1.3 +/- 0.4), and basal ganglia (0.5 +/- 0.3), all in the frontal or parietal regions.

CONCLUSIONS

MCA and ACA distributions included 81% of strokes. These sites were relatively silent (potentially allowing longer-term survival studies) whereas others in the posterior circulation produced disproportionately severe symptoms. Symptoms were not reliable indicators of stroke occurrence, and other endpoints such as imaging may be required. These are important steps toward refinement of the rabbit stroke model.

Transcranial near infrared laser treatment (NILT) increases cortical adenosine-5'-triphosphate (ATP) content following embolic strokes in rabbits

Transcranial near infrared laser therapy (NILT) improves behavioral outcome following embolic strokes in embolized rabbits and clinical rating scores in acute ischemic stroke (AIS) patients; however, the cellular mechanism(s) involved in NILT neuroprotection have not been elucidated. It has been proposed that mitochondrial energy production may underlie a response to NILT, but this has not been demonstrated using an in vivo embolic stroke model. Thus, we evaluated the effect of NILT on cortical ATP content using the rabbit small clot embolic stroke model (RSCEM), the model originally used to demonstrate NILT efficacy and initiate the NEST-1 clinical trial. Five minutes following embolization, rabbits were exposed to 2 min of NILT using an 808 nm laser source, which was driven to output either continuous wave (CW), or pulsed wave modes (PW). Three hours after embolization, the cerebral cortex was excised and processed for the measurement of ATP content using a standard luciferin-luciferase assay. NILT-treated rabbits were directly compared to sham-treated embolized rabbits and naïve control rabbits. Embolization decreased cortical ATP content in ischemic cortex by 45% compared to naive rabbits, a decrease that was attenuated by CW NILT which resulted in a 41% increase in cortical ATP content compared to the sham embolized group (p>0.05). The absolute increase in ATP content was 22.5% compared to naive rabbits. Following PW NILT, which delivered 5 (PW1) and 35 (PW2) times more energy than CW, we measured a 157% (PW1 p=0.0032) and 221% (PW2 p=0.0001) increase in cortical ATP content, respectively, compared to the sham embolized group. That represented a 41% and 77% increase in ATP content compared to naive control rabbits. This is the first demonstration that embolization can decrease ATP content in rabbit cortex and that NILT significantly increases cortical ATP content in embolized rabbits, an effect that is correlated with cortical fluence and the mode of NILT delivery. The data provide new insight into the molecular mechanisms associated with clinical improvement following NILT.

Effect of internal carotid artery reperfusion in combination with Tenecteplase on clinical scores and hemorrhage in a rabbit embolic stroke model

In the present study, we used a modification of the rabbit small clot embolic stroke model (RSCEM), a multiple infarct ischemia model to achieve reperfusion (REP) through the internal carotid artery (ICA) following small clot embolization. We determined if increasing regional cortical blood flow (RCBF) following an embolic stroke is beneficial to neurological outcome. We compared this to cerebral reperfusion induced by the administration of the thrombolytic Tenecteplase (TNK, 1.5 mg/kg, IV bolus) in the presence or absence of REP. In this study, we also measured the incidence of ICH following REP and thrombolytic treatment. Following embolization, RCBF was reduced to 48-55% of baseline. When REP was induced by removal of a CCA ligature, RCBF initially increased to 185% of baseline. REP (P(50)=1.18+/-0.43 mg) had no effect on embolization-induced behavior measured 24 h following embolization compared to control (P(50)=1.01+/-0.48 mg). However, TNK treatment (2-hours post-embolization) in the absence or presence of REP (initiated 2 h following embolization) significantly (p<0.05) increased the group P(50) to 2.92+/-0.55 mg and 2.42+/-0.40 mg, respectively. In addition, ICH was increased in the REP (42%, p<0.05) and REP-TNK (35%, p>0.05) group compared to either the control group (5.5%) or TNK group (10%). This study show that reperfusion of ICA can increase RCBF following embolization, but this is not associated with improved neurological outcome measured using quantal analysis. However, TNK administration significantly increased behavioral outcome when given 2 h following embolization; an increase that is not affected by combining TNK with REP.

Novel thrombolytic drugs: will they make a difference in the treatment of ischaemic stroke?

Treatment of acute ischaemic stroke aims to recanalize the occluded artery, salvage the at-risk brain tissue and thus minimize neurological sequelae. Efforts a decade ago have led to the only currently approved medical treatment for acute ischaemic stroke, i.e. intravenous alteplase given within 3 hours of stroke onset. Recanalization occurs in only one-half of the patients receiving alteplase, and only approximately 5% of all ischaemic stroke patients in industrialized countries receive this treatment. Studies are currently being carried out to determine whether intravenous alteplase would be safe and effective for up to 4.5 hours after ischaemic stroke onset, and whether it should be followed by an intra-arterial approach. Two novel thrombolytic drugs being studied for acute ischaemic stroke are desmoteplase and tenecteplase. Although the first trials were promising, the most recent evidence suggests that desmoteplase is not superior to placebo, even in carefully selected patients, in the 3- to 9-hour time window after stroke onset. Tenecteplase has only been studied for acute ischaemic stroke in a single noncontrolled, dose-finding trial in the 3-hour time window after stroke onset, which suggested a similar efficacy to that demonstrated in the historical data from the alteplase trials. A trial to compare the safety and efficacy of tenecteplase versus alteplase is ongoing. Safer and more effective thrombolytic drugs for the treatment of ischaemic stroke are thus being sought. Such agents will be welcome, but they are not here yet. While waiting we are likely to see the emergence of additive therapies, including ultrasound insonation, neuroprotective/regenerative agents and invasive intra-arterial techniques. Novel thrombolytic drugs, or other novel therapies, possess great potential to make a difference in the future, but the most urgent priority now is in the organization of stroke treatment in such a way that more patients receive the currently available optimal treatments.

Therapeutic window for nonerythropoietic carbamylated-erythropoietin to improve motor function following multiple infarct ischemic strokes in New Zealand white rabbits

Carbamylated erythropoietin (CEPO) is a novel neuroprotective agent that does not bind to the classical erythropoietin receptor or affect hematocrit. Since CEPO has not been systematically studied in a fully blinded and randomized manner in an embolic stroke model, we determined if CEPO would be useful to attenuate clinical deficits associated with multiple infarct ischemia using the rabbit small clot embolic stroke model (RSCEM). Rabbits were embolized and treated with vehicle or CEPO within 6 h of embolization and behavioral analysis was conducted 48 h after embolization. Using quantal analysis, we determined the quantity of blood clot (mg) in brain that produce neurologic dysfunction in 50% of the rabbits (P(50)), with intervention considered beneficial if it increased the P(50) compared to controls. CEPO administered between 5 min and 3 h after embolization significantly (p<0.05) improved behavioral function and increased the P(50) value by 55-216%. However, CEPO administration did not improve behavior when administered 6 h following embolization. In conclusion, in the RSCEM, CEPO had a therapeutic window of at least 3 h, where it effectively improved clinical rating scores and motor function. Our results suggest that CEPO may be useful to treat acute ischemic stroke and supports the study of CEPO in stroke patients.

Safety profile of transcranial near-infrared laser therapy administered in combination with thrombolytic therapy to embolized rabbits

BACKGROUND AND PURPOSE

Transcranial near-infrared laser therapy (TLT) is currently under investigation in a pivotal clinical trial that excludes thrombolytic therapy. To determine if combining tissue plasminogen activator (tPA; Alteplase) and TLT is safe, this study assessed the safety profile of TLT administered alone and in combination with Alteplase. The purpose for this study is to determine if the combination of TLT and thrombolysis should be investigated further in a human clinical trial.

METHODS

We determined whether postembolization treatment with TLT in the absence or presence of tPA would affect measures of hemorrhage or survival after large clot embolism-induced strokes in New Zealand white rabbits.

RESULTS

TLT did not significantly alter hemorrhage incidence after embolization, but there was a trend for a modest reduction of hemorrhage volume (by 65%) in the TLT-treated group compared with controls. Intravenous administration of tPA, using an optimized dosing regimen, significantly increased hemorrhage incidence by 160%. The tPA-induced increase in hemorrhage incidence was not significantly affected by TLT, although there was a 30% decrease in hemorrhage incidence in combination-treated rabbits. There was no effect of TLT on hemorrhage volume measured in tPA-treated rabbits and no effect of any treatment on 24-hour survival rate.

CONCLUSIONS

In the embolism model, TLT administration did not affect the tPA-induced increase in hemorrhage incidence. TLT may be administered safely either alone or in combination with tPA because neither treatment affected hemorrhage incidence or volume. Our results support the study of TLT in combination with Alteplase in patients with stroke.

Laser Therapy in Acute Stroke Treatment

Recent development of near infrared light therapy (NILT) as an acute stroke treatment is promising. In various preclinical animal stroke models, NILT has been shown to be effective in improving long-term stroke outcome. More importantly, NILT has a long postischemic therapeutic window that has not been previously observed in other treatment modalities. The preliminary efficacy and safety of NILT in acute stroke patients were demonstrated in the recently published phase II ***NeuroThera Effectiveness and Safety Trial (NEST-1). If confirmed by the NEST-II trial, ***NILT will revolutionize acute stroke management as ***ut has a long time window (possible 24 hr) for therapy. Moreover, understanding the mechanisms of action of NILT will provide a new therapeutic target for future drug or device development.

Baicalein, an antioxidant 12/15-lipoxygenase inhibitor improves clinical rating scores following multiple infarct embolic strokes

The present study assessed whether baicalein (5,6,7-trihydroxyflavone), a polyphenolic antioxidant 12/15-lipoxygenase inhibitor would attenuate oxidative cell death in vitro using a mouse hippocampal HT22 cell assay. Moreover, we determined if baicalein would be useful to attenuate behavioral deficits associated with multiple infarct ischemic events in vivo using a rabbit small clot embolic stroke model (RSCEM). Using HT22 cell in vitro, baicalein was shown to significantly promote cell survival with an estimated dose for 50% cell survival of 2 muM following incubation in the presence of iodoacetic acid (20 muM), an irreversible inhibitor of the glycolytic pathway that results in the free radical production, lipid peroxidation and cell death. Since baicalein was neuroprotective and attenuated iodoacetic acid (IAA) toxicity in vitro, we studied its effects in vivo in an embolic stroke model using behavioral measures as the endpoint. Quantal analysis for each treatment in the embolism model identifies the quantity of microclots (mg) that produce neurologic dysfunction in 50% of a group of animals (P(50)), with intervention considered neuroprotective if it increases the P(50) compared with controls. Baicalein (100 mg/kg, s.c.) injected 5 and 60 min post-embolization significantly (P<0.05) improved behavioral function. The calculated P(50) values were 2.85+/-0.64 mg (n=21) and 2.15+/-0.12 mg (n=14), respectively compared with 1.37+/-0.20 mg (n=23) for the control group. In conclusion, we have shown that baicalein effectively attenuated cell death in vitro using HT22 cells and also significantly reduced behavioral deficits in rabbits when given up to 1 h following an embolic stroke. The results suggest that baicalein, or derivatives of baicalein with multiple pharmacological activities may be useful to develop as novel treatments for acute ischemic stroke.

Tumor necrosis factor-α is involved in thrombolytic-induced hemorrhage following embolic strokes in rabbits

The present study assessed whether tumor necrosis factor-alpha (TNFalpha) is involved in hemorrhage following large clot embolism-induced ischemia in New Zealand white rabbits by intracisternally administering either TNFalpha or a goat-anti-rabbit-TNFalpha antibody following a stroke. The first aim of the study showed that TNFalpha administration increased stroke-induced hemorrhage incidence to 53.3% from 18.5% (an increase of 188%) in the control group and also increased hemorrhage volume by 87% (p<0.05). The second aim showed that administration of tissue plasminogen activator (tPA) using a standard dose of 3.3 mg/kg increased hemorrhage incidence in rabbits to 76.5% from 18.5% (an increase of 314%) and this effect was reversed by administration of an anti-TNFalpha antibody. In the tPA-anti-TNFalpha antibody group, the absolute hemorrhage rate was 38.8% and the hemorrhage volume was 98% of control. In conclusion, following an embolic stroke, TNFalpha administration increased the incidence and volume of hemorrhage and an anti-TNFalpha antibody counteracted tPA-induced hemorrhage. The results suggest that TNFalpha may either be directly or indirectly involved in vascular damage following an embolic stroke. Moreover, TNFalpha may mediate some of the detrimental effects of tPA on the vascular compartment. Based upon our studies, TNFalpha receptor antagonists or TNFalpha processing inhibitors should be further pursued as targets for the treatment of hemorrhagic stroke as adjuvant treatment for stroke patients receiving thrombolytic treatment.

A novel approach to screening for new neuroprotective compounds for the treatment of stroke

Despite the significant advances that have been made in understanding the pathophysiology of cerebral ischemia on the cellular and molecular level, only one drug, the thrombolytic tissue plasminogen activator (rt-PA), is approved by the FDA for use in patients with acute ischemic stroke. Therefore, there is a critical need for additional safe and effective treatments for stroke. In order to identify novel compounds that might be effective, we have developed a cell culture-based assay with death being an endpoint as a screening tool. We have performed an initial screening for potential neuroprotective drugs among a group of flavonoids by using the mouse hippocampal cell line, HT22, in combination with chemical ischemia. Further screens were provided by biochemical assays for ATP and glutathione, the major intracellular antioxidant, as well as for long-term induction of antioxidant proteins. Based upon the results of these screens, we tested the best flavonoid, fisetin, in the small clot embolism model of cerebral ischemia in rabbits. Fisetin significantly reduced the behavioral deficits following a stroke, providing proof of principle for this novel approach to identifying new compounds for the treatment of stroke.

Transcranial near-infrared light therapy improves motor function following embolic strokes in rabbits: an extended therapeutic window study using continuous and pulse frequency delivery modes

Photon or near-infrared light therapy (NILT) may be an effective neuroprotective method to reduce behavioral dysfunction following an acute ischemic stroke. We evaluated the effects of continuous wave (CW) or pulse wave (P) NILT administered transcranially either 6 or 12 h following embolization, on behavioral outcome. For the studies, we used the rabbit small clot embolic stroke model (RSCEM) using three different treatment regimens: 1) CW power density of 7.5 mW/cm(2); 2) P1 using a frequency of 300 mus pulse at 1 kHz or 3) P2 using a frequency of 2 ms pulse at 100 Hz. Behavioral analysis was conducted 48 h after embolization, allowing for the determination of the effective stroke dose (P(50)) or clot amount (mg) that produces neurological deficits in 50% of the rabbits. Using the RSCEM, a treatment is considered beneficial if it significantly increases the P(50) compared with the control group. Quantal dose-response analysis showed that the control group P(50) value was 1.01+/-0.25 mg (n=31). NILT initiated 6 h following embolization resulted in the following P(50) values: (CW) 2.06+/-0.59 mg (n=29, P=0.099); (P1) 1.89+/-0.29 mg (n=25, P=0.0248) and (P2) 1.92+/-0.15 mg (n=33, P=0.0024). NILT started 12 h following embolization resulted in the following P(50) values: (CW) 2.89+/-1.76 mg (n=29, P=0.279); (P1) 2.40+/-0.99 mg (n=24, P=0.134). At the 6-h post-embolization treatment time, there was a statistically significant increase in P(50) values compared with control for both pulse P1 and P2 modes, but not the CW mode. At the 12-h post-embolization treatment time, neither the CW nor the P1 regimens resulted in statistically significant effect, although there was a trend for an improvement. The results show that P mode NILT can result in significant clinical improvement when administered 6 h following embolic strokes in rabbits and should be considered for clinical development.

The phenylpropanoid micronutrient chlorogenic acid improves clinical rating scores in rabbits following multiple infarct ischemic strokes: Synergism with tissue plasminogen activator

The present study assessed whether chlorogenic acid (CGA), a phenylpropanoid molecule that has multiple mechanisms of action would be useful to attenuate behavioral deficits associated with embolic strokes using the rabbit small clot embolic stroke model (RSCEM). Quantal analysis for each treatment determines the quantity of microclots (mg) that produce neurologic dysfunction in 50% of a group of animals (P(50)), with intervention considered beneficial if it increases the P(50) compared to controls. CGA (50 mg/kg) injected 5 min post-embolization significantly increased behavioral function and the P(50) to 3.61+/-0.52 mg (n=19) compared to 1.58+/-0.15 mg (n=26) in controls. In addition, CGA also increased the P(50) to 2.57+/-0.28 mg (n=18) when administered 1 h post-embolization, but was ineffective when given 3 h following embolization (P(50)=1.22+/-0.24 mg, n=18). For combination studies with the thrombolytic tissue plasminogen activator (tPA), we used tPA at a standard dose of 3.3 mg/kg, which significantly increased the P(50) to 2.89+/-0.29 mg (n=17) when administered 1 h after embolization, but not 3 h after embolization (P(50)=1.54+/-0.27 mg, n=18). However, when tPA (3.3 mg/kg) was combined with CGA (50 mg/kg) and administered 3 h following embolization, there was a significant increase in behavioral function as evidenced by an increase in the P(50) value to 3.40+/-0.76 mg (n=23). In conclusion, as a mono-therapy CGA effectively reduced behavioral deficits when given up to 1 h following embolic strokes in rabbits. Moreover, there was a synergistic effect of the combination of tPA with CGA when administered 3 h following embolization. The results show that the therapeutic window for a standard effective dose of tPA could be increased by administration of CGA, suggesting that it may be most useful as a co-therapy with a standard thrombolytic treatment regimen.

Advances in ischemic stroke treatment: neuroprotective and combination therapies

Thrombolysis with intravenous alteplase (recombinant tissue-type plasminogen activator) continues to be the sole recourse for acute ischemic stroke therapy, provided that patients seek treatment preferably within 3 h of stroke onset. The narrow window of efficacy, coupled with the significant risk of hemorrhage and the high mortality rate, preclude the use of alteplase beyond this time frame. Moreover, in part because of safety concerns, only a small percentage (6-15%) of eligible patients is treated with alteplase. Clearly, safer and more effective treatments that focus on improving the shortcomings of the present thrombolysis for stroke need to be identified. Therefore, newer thrombolytics are being developed with the goal of minimizing side effects, while also shortening the time of cerebral reperfusion and extending the therapeutic window of efficacy. Besides thrombolytics, new and potentially useful drugs and devices are also being studied either as monotherapeutic agents or for use in conjunction with alteplase. In animal models of stroke, neuroprotective agents that affect various components of the ischemic injury cascade that results in neurodegeneration have shown promise for the latter. Examples of such agents include spin traps that block oxidative stress, metalloprotease inhibitors that prevent vascular damage, anti-inflammatory drugs that suppress inflammation and transcranial infrared laser irradiation, which promotes recovery of function. Ideally, a successful combination of neuroprotectant (drug or device) and thrombolytic therapy for stroke would minimize the side effects of thrombolysis followed by supplementary neuroprotection thereafter.

Endovascular management of acute ischemic stroke: advances in patient and treatment selection

Selection of patients for acute-stroke therapy has traditionally been based on rigid time criteria in clinical trials. Recent advances in radiographic imaging have allowed clinicians to estimate brain physiology and thus utilize radiographic parameters to select patients for acute-stroke therapies. Both a better understanding and the quantification methods of salvageable tissue versus irreversibly injured tissue can help guide clinicians to which treatment modality to utilize. The evolution of endovascular techniques to treat acute stroke has resulted in treatment modalities that include mechanical and chemical methods to revascularize occluded cerebral arteries. Prior technical limitations to accessing distal-cerebral arteries have been partially overcome by modifications in technology. Patient and treatment-modality selection can help reduce hemorrhagic complication rates and also potentially increase revascularization rates, which may translate into improved clinical outcomes. We review the recent advances in radiographic imaging that have advanced patient selection in treating acute ischemic stroke and also consider current endovascular treatment options that are available to interventionalists performing these procedures.

Investigation of the safety of tenecteplase to the outer retina

PURPOSE

To investigate the safety of the thrombolytic agent, tenecteplase to the outer retina in pig eyes.

METHODS

Tenecteplase (50 microg) was injected into the subretinal space in one eye while the fellow eye received balanced salt solution. At 24 h, 1 week and 9 weeks the eyes were examined by indirect ophthalmoscopy and photographed. Animals were killed at 9 weeks, eyes enucleated and processed for light and transmission electron microscopy. Three locations within the area of the injection bleb were analysed.

RESULTS

Retinal pigment epithelial defects, which appeared to be iatrogenic and confined to the injection site, were seen in most of the treated and control eyes. There was no significant difference in the degree of retinal damage between the two groups of eyes at the three sites examined (P > 0.05).

CONCLUSION

Fifty micrograms of tenecteplase appears to be a safe dose with no evidence of toxicity to the outer retina and may have a potential role in the treatment of submacular haemorrhage.

Memantine, an uncompetitive low affinity NMDA open-channel antagonist improves clinical rating scores in a multiple infarct embolic stroke model in rabbits

The blockade of NMDA receptors has been pursued as a strategy to reduce the consequences of acute ischemic stroke (AIS) and NMDA receptors remain a valid therapeutic target to treat AIS. Because the pharmacological and toxicity profile of memantine in Alzheimer's disease patients appears to be good, we determined whether memantine would be effective at improving behavioral performance following embolic strokes in rabbits. For these studies, we used a rabbit multiple infarct ischemia model with a well-defined behavioral endpoint. In this study, memantine dissolved in PBS was given intravenously either as a bolus injection (over 1 min) or infused over 60 min. The P(50) of the control groups measured 24 h after embolization were 1.12 +/- 0.18 mg and 1.08 +/- 0.23 mg for the bolus injected and infused groups, respectively. Bolus injections of memantine at 1 mg/kg and 10 mg/kg were not effective at altering the P(50) value and memantine at a dose of 25 mg/kg was lethal. However, slowly infused memantine (25 mg/kg) significantly increased the P(50) value to 2.31 +/- 0.48 mg and 3.13 +/- 1.13 mg when given 5 and 60 min following embolization, respectively. Memantine administered 180 min following embolization also increased the P(50) value to 2.69 +/- 2.21 mg, but the response was variable. These results suggest that uncompetitive NMDA antagonists, more specifically open channel blockers, which may be alternatives to high affinity NMDA antagonists, may have substantial therapeutic benefit for the treatment of AIS and memantine or new dual activity analogs of memantine should be further pursued as a useful therapy to treat the behavioral deficits associated with multiple-infarct ischemia.