Why do all drugs work in animals but none in stroke patients? 2. Neuroprotective therapy

Cerebroprotection for Acute Ischemic Stroke: Looking Ahead

We search for ischemic stroke treatment knowing we have failed-intensely and often-to translate mechanistic knowledge into treatments that alleviate our patients' functional impairments. Lessons can be derived from our shared failures that may point to new directions and new strategies. First, the principle criticisms of both preclinical and clinical assessments are summarized. Next, previous efforts to develop single-mechanism treatments are reviewed. Finally, new definitions, novel approaches, and different directions are presented. In previous development efforts, the basic science and preclinical assessment of candidate treatments often lacked rigor and sufficiency; the clinical trials may have lacked power, rigor, or rectitude; or most likely both preclinical and clinical investigations were flawed. Single-target agents directed against specific molecular mechanisms proved unsuccessful. The term neuroprotection should be replaced as it has become ambiguous: protection of the entire neurovascular unit may be called cerebral cytoprotection or cerebroprotection. Success in developing cerebroprotection-either as an adjunct to recanalization or as stand-alone treatment-will require new definitions that recognize the importance of differential vulnerability in the neurovascular unit. Recent focus on pleiotropic multi-target agents that act via multiple mechanisms of action to interrupt ischemia at multiple steps may be more fruitful. Examples of pleiotropic treatments include therapeutic hypothermia and 3K3A-APC (activated protein C). Alternatively, the single-target drug NA-1 triggers multiple downstream signaling events. Renewed commitment to scientific rigor is essential, and funding agencies and journals may enforce quality principles of rigor in preclinical science. Appropriate animal models should be selected that are suited to the purpose of the investigation. Before clinical trials, preclinical assessment could include subjects that are aged, of both sexes, and harbor comorbid conditions such as diabetes or hypertension. With these new definitions, novel approaches, and renewed attention to rigor, the prospect for successful cerebroprotective therapy should improve.

Analysis of the Modified Rankin Scale in Randomised Controlled Trials of Acute Ischaemic Stroke: A Systematic Review

Background. Historically, most acute stroke clinical trials were neutral statistically, with trials typically dichotomising ordinal scales, such as the modified Rankin Scale. Studies published before 2007 have shown that preserving the ordinal nature of these scales increased statistical power. A systematic review of trials published since 2007 was conducted to reevaluate statistical methods used and to assess whether practice has changed. Methods. A search of electronic databases identified RCTs published between January 2007 and July 2014 in acute ischaemic stroke using an ordinal dependency scale as the primary outcome. Findings. Forty-two RCTs were identified. The majority used a dichotomous analysis (25, 59.5%), eight (21.4%) retained the ordinal scale, and nine (19.0%) used another type of analysis. Conclusions. Trials published since 2007 still favoured dichotomous analyses over ordinal. Stroke trials, where appropriate, should consider retaining the ordinal nature of dependency scales.

The Good and Bad Sides of NAAG

Why has such a small peptide been the source of controversy in neuroscience over the last 5 decades? Is N-acetyl-aspartyl-glutamate (NAAG) a neurotransmitter? Is NAAG located in neuronal tissue or in astrocytes? Is NAAG involved in neuropsychiatric and neurodegenerative disorders? Is NAAG therapeutically beneficial in the treatment of stroke or in initiating cascades of events leading to psychosis? After many years of intense research there is no clear consensus within the scientific community on how NAAG behaves in the brain. One of the major controversies about NAAG is its physiological action at N-methyl-d-aspartate (NMDA) receptors. While some researchers strongly argue that NAAG acts as a weak agonist at NMDA receptors, others have suggested that NAAG could behave as a potent antagonist. Published data from our laboratory demonstrate that the effect of NAAG on NMDA receptors could be influenced by a number of factors including the subcellular localization and subunit composition of NMDA receptors, as well as protons. In this chapter, we will summarize the knowledge of the literature on NAAG, however, we will place emphasis on our recently published data. More specifically, we have reported interesting findings on the effects of NAAG on NMDA receptors at synaptic and extrasynaptic sites using a pharmacological paradigm to distinguish the two populations of NMDA receptors. Additionally, we have evaluated the role of NAAG on GluN2A- and GluN2B-containing NMDA receptors using a HEK293 cell recombinant system. Finally, we have studied the effects of NAAG on GluN2A- and GluN2B-containing NMDA receptors in different extracellular pH conditions. We believe that our findings could potentially resolve some aspects of the debate regarding the role of NAAG at NMDA receptors.

Nonsurgical therapy for hydrocephalus: a comprehensive and critical review

Pharmacological interventions have been tested experimentally and clinically to prevent hydrocephalus and avoid the need for shunting beginning in the 1950s. Clinical trials of varied quality have not demonstrated lasting and convincing protective effects through manipulation of cerebrospinal fluid production, diuresis, blood clot fibrinolysis, or manipulation of fibrosis in the subarachnoid compartment, although there remains some promise in the latter areas. Acetazolamide bolus seems to be useful for predicting shunt response in adults with hydrocephalus. Neuroprotection in the situation of established hydrocephalus has been tested experimentally beginning more recently. Therapies designed to modify blood flow or pulsation, reduce inflammation, reduce oxidative damage, or protect neurons are so far of limited success; more experimental work is needed in these areas. As has been recommended for preclinical studies in stroke and brain trauma, stringent conditions should be met for preclinical studies in hydrocephalus.

Multiparametric magnetic resonance imaging of acute experimental brain ischaemia

Ischaemia is a condition in which blood flow either drops to zero or proceeds at severely decreased levels that cannot supply sufficient oxidizable substrates to maintain energy metabolism in vivo. Brain, a highly oxidative organ, is particularly susceptible to ischaemia. Ischaemia leads to loss of consciousness in seconds and, if prolonged, permanent tissue damage is inevitable. Ischaemia primarily results in a collapse of cerebral energy state, followed by a series of subtle changes in anaerobic metabolism, ion and water homeostasis that eventually initiate destructive internal and external processes in brain tissue. (31)P and (1)H NMR spectroscopy were initially used to evaluate anaerobic metabolism in brain. However, since the early 1990s (1)H Magnetic Resonance Imaging (MRI), exploiting the nuclear magnetism of tissue water, has become the key method for assessment of ischaemic brain tissue. This article summarises multi-parametric (1)H MRI work that has exploited diffusion, relaxation and magnetisation transfer as 'contrasts' to image ischaemic brain in preclinical models for the first few hours, with a view to assessing evolution of ischaemia and tissue viability in a non-invasive manner.

A rat's whiskers point the way toward a novel stimulus-dependent, protective stroke therapy

Stroke is the fourth leading cause of death in the United States and the leading cause of long-term disability. Ischemic stroke, due to an interruption in blood supply, is particularly prevalent; 87% of all strokes are ischemic. Unfortunately, current options for acute treatment are extremely limited and there is a great need for new treatment strategies. This review will discuss evidence that mild sensory stimulation can completely protect the jeopardized brain from an impending stroke in a rodent model. When delivered within the first 2 hours following ischemic onset, this stimulation results in complete protection, including a full reestablishment of cortical function, sensorimotor capabilities, and blood flow. Identical stimulation, however, initiated 3 hours following ischemic onset, results in an increase in damage compared with untreated animals. The protective effect is not specific to a single sensory modality, anesthesia, or age, and increasing evoked cortical activity by increasing stimulation accelerates recovery. Taken together, these findings demonstrate that cortical activity is a critical factor for protection and suggest a new, exciting potential avenue for the development of acute stroke treatment strategies that may produce a noninvasive, drug-free, equipment-free, and side effect-free means of protecting from ischemic stroke.

Amiloride but not memantine reduces neurodegeneration, seizures and myoclonic jerks in rats with cardiac arrest-induced global cerebral hypoxia and reperfusion

It has been reported that both activation of N-methyl-D-aspartate receptors and acid-sensing ion channels during cerebral ischemic insult contributed to brain injury. But which of these two molecular targets plays a more pivotal role in hypoxia-induced brain injury during ischemia is not known. In this study, the neuroprotective effects of an acid-sensing cation channel blocker and an N-methyl-D-aspartate receptor blocker were evaluated in a rat model of cardiac arrest-induced cerebral hypoxia. We found that intracisternal injection of amiloride, an acid-sensing ion channel blocker, dose-dependently reduced cerebral hypoxia-induced neurodegeneration, seizures, and audiogenic myoclonic jerks. In contrast, intracisternal injection of memantine, a selective uncompetitive N-methyl-D-aspartate receptor blocker, had no significant effect on cerebral hypoxia-induced neurodegeneration, seizure and audiogenic myoclonic jerks. Intracisternal injection of zoniporide, a specific sodium-hydrogen exchanger inhibitor, before cardiac arrest-induced cerebral hypoxia, also did not reduce cerebral hypoxia-induced neurodegeneration, seizures and myoclonic jerks. These results suggest that acid-sensing ion channels play a more pivotal role than N-methyl-D-aspartate receptors in mediating cerebral hypoxia-induced brain injury during ischemic insult.

Modeling disease progression in acute stroke using clinical assessment scales

This article demonstrates techniques for describing and predicting disease progression in acute stroke by modeling scores measured using clinical assessment scales, accommodating dropout as an additional source of information. Scores assessed using the National Institutes of Health Stroke Scale and the Barthel Index in acute stroke patients were used to model the time course of disease progression. Simultaneous continuous and probabilistic models for describing the nature and magnitude of score changes were developed, and used to model the trajectory of disease progression using scale scores. The models described the observed data well, and exhibited good simulation properties. Applications include longitudinal analysis of stroke scale data, clinical trial simulation, and prognostic forecasting. Based upon experience in other areas, it is likely that application of this modeling methodology will enable reductions in the number of patients needed to carry out clinical studies of treatments for acute stroke.

Emulating multicentre clinical stroke trials: a new paradigm for studying novel interventions in experimental models of stroke

The recent meta-analysis of NXY-059 in experimental stroke models using individual animal data found the drug to be an effective neuroprotective agent. However, the failure of translation of both this compound and many others from preclinical studies to the clinic indicates that new approaches must be used in drug discovery so that animal models become more reflective of the clinical situation, and studies using animal models of stroke mimic the design of studies performed in humans, as far as possible. In this review, we suggest that a fundamental paradigm shift is needed away from performing preclinical studies in individual laboratories to performing them in an organised group of independent laboratories. Studies should be run by a steering committee and should be supported by a coordinating centre, external data monitoring committee and outcome adjudication committee. This structure will mimic the practice of multicentre clinical trials. By doing so, future studies will minimise potential sources of bias including randomisation, concealment of allocation, blinding of surgery and outcome assessment and ensure publication of all data. It is likely that individual studies will involve increased heterogeneity and therefore will need to be larger. However, regular independent monitoring of data will allow development of interventions to be ceased immediately if neutral or negative data are obtained. The additional costs involved should be seen as reasonable when compared with the resources that would have been expended in running a clinical trial that subsequently proved negative.

A new model of cortical stroke in the rhesus macaque

Primate models are essential tools for translational research in stroke but are reportedly inconsistent in their ability to produce cortical infarcts of reproducible size. Here, we report a new stroke model using a transorbital, reversible, two-vessel occlusion approach in male rhesus macaques that produces consistent and reproducible cortical infarcts. The right middle cerebral artery (distal to the orbitofrontal branch) and both anterior cerebral arteries were occluded with vascular clips. Bilateral occlusion of the anterior cerebral artery was critical for reducing collateral flow to the ipsilateral cortex. Reversible ischemia was induced for 45, 60, or 90 mins (n=2/timepoint) and infarct volume and neurologic outcome were evaluated. The infarcts were located predominantly in the cortex and increased in size with extended duration of ischemia determined by T(2)-weighted magnetic resonance imaging . Infarct volume measured by 2,3,5-triphenyl tetrazolium chloride and cresyl violet staining corroborated magnetic resonance imaging results. Neurologic deficit scores worsened gradually with longer occlusion times. A subset of animals (n=5) underwent 60 mins of ischemia resulting in consistent infarct volumes primarily located to the cortex that correlated well with neurologic deficit scores. This approach offers promise for evaluating therapeutic interventions in stroke.

REPRINT: Good Laboratory Practice: Preventing Introduction of Bias at the Bench

As a research community, we have failed to demonstrate that drugs that show substantial efficacy in animal models of cerebral ischemia can also improve outcome in human stroke. Accumulating evidence suggests that this may be due, at least in part, to problems in the design, conduct and reporting of animal experiments, which create a systematic bias resulting in the overstatement of neuroprotective efficacy. Here, we set out a series of measures to reduce bias in the design, conduct and reporting of animal experiments modeling human stroke.

Reprint: Good laboratory practice: preventing introduction of bias at the bench

As a research community, we have failed to show that drugs, which show substantial efficacy in animal models of cerebral ischemia, can also improve outcome in human stroke. Accumulating evidence suggests this may be due, at least in part, to problems in the design, conduct, and reporting of animal experiments which create a systematic bias resulting in the overstatement of neuroprotective efficacy. Here, we set out a series of measures to reduce bias in the design, conduct and reporting of animal experiments modeling human stroke.

Good laboratory practice: preventing introduction of bias at the bench

BACKGROUND AND PURPOSE

As a research community, we have failed to demonstrate that drugs which show substantial efficacy in animal models of cerebral ischemia can also improve outcome in human stroke. Summary of Review- Accumulating evidence suggests this may be due, at least in part, to problems in the design, conduct and reporting of animal experiments which create a systematic bias resulting in the overstatement of neuroprotective efficacy.

CONCLUSIONS

Here, we set out a series of measures to reduce bias in the design, conduct and reporting of animal experiments modeling human stroke.

Acute ischemic stroke: overview of major experimental rodent models, pathophysiology, and therapy of focal cerebral ischemia

Ischemic stroke is a devastating disease with a complex pathophysiology. Animal modeling of ischemic stroke serves as an indispensable tool first to investigate mechanisms of ischemic cerebral injury, secondly to develop novel antiischemic regimens. Most of the stroke models are carried on rodents. Each model has its particular strengths and weaknesses. Mimicking all aspects of human stroke in one animal model is not possible since ischemic stroke is itself a very heterogeneous disorder. Experimental ischemic stroke models contribute to our understanding of the events occurring in ischemic and reperfused brain. Major approaches developed to treat acute ischemic stroke fall into two categories, thrombolysis and neuroprotection. Trials aimed to evaluate effectiveness of recombinant tissue-type plasminogen activator in longer time windows with finer selection of patients based on magnetic resonance imaging tools and trials of novel recanalization methods are ongoing. Despite the failure of most neuroprotective drugs during the last two decades, there are good chances to soon have effective neuroprotectives with the help of improved preclinical testing and clinical trial design. In this article, we focus on various rodent animal models, pathogenic mechanisms, and promising therapeutic approaches of ischemic stroke.

Can we improve the statistical analysis of stroke trials? Statistical reanalysis of functional outcomes in stroke trials

BACKGROUND AND PURPOSE

Most large acute stroke trials have been neutral. Functional outcome is usually analyzed using a yes or no answer, eg, death or dependency versus independence. We assessed which statistical approaches are most efficient in analyzing outcomes from stroke trials.

METHODS

Individual patient data from acute, rehabilitation and stroke unit trials studying the effects of interventions which alter functional outcome were assessed. Outcomes included modified Rankin Scale, Barthel Index, and "3 questions". Data were analyzed using a variety of approaches which compare 2 treatment groups. The results for each statistical test for each trial were then compared.

RESULTS

Data from 55 datasets were obtained (47 trials, 54,173 patients). The test results differed substantially so that approaches which use the ordered nature of functional outcome data (ordinal logistic regression, t test, robust ranks test, bootstrapping the difference in mean rank) were more efficient statistically than those which collapse the data into 2 groups (chi(2); ANOVA, P<0.001). The findings were consistent across different types and sizes of trial and for the different measures of functional outcome.

CONCLUSIONS

When analyzing functional outcome from stroke trials, statistical tests which use the original ordered data are more efficient and more likely to yield reliable results. Suitable approaches included ordinal logistic regression, t test, and robust ranks test.

Electrical forepaw stimulation during reversible forebrain ischemia decreases infarct volume

BACKGROUND AND PURPOSE

Functional stimulation is accompanied by increases in regional cerebral blood flow which exceed metabolic demands under normal circumstances, but it is unknown whether functional stimulation is beneficial or detrimental in the setting of acute ischemia. The aim of this study was to determine the effect of forepaw stimulation during temporary focal ischemia on neurological and tissue outcome in a rat model of reversible focal forebrain ischemia.

METHODS

Sprague-Dawley rats were prepared for temporary occlusion of the right middle cerebral artery (MCA) using the filament model. Cerebral blood flow in the MCA territory was continuously monitored with a laser-Doppler flowmeter. Subdermal electrodes were inserted into the dorsal forepaw to stimulate either the forepaw ipsilateral or contralateral to the occlusion starting 1 minute into ischemia and continuing throughout the ischemic period. A neurological evaluation was undertaken after 24 hours of reperfusion, and animals were then euthanized and brain slices stained with 2,3,5-triphenyltetrazolium chloride. Cortical and striatal damage was measured separately.

RESULTS

The cortical and striatal infarct volumes were both significantly reduced in the contralateral stimulated group compared with the ipsilateral stimulated group (48% total reduction). There were no statistically significant differences in the neurobehavioral scores between the 2 groups, or in the laser-Doppler flow measurements from the MCA core.

CONCLUSIONS

Functional stimulation of ischemic tissue may decrease tissue damage and improve outcome from stroke. Although the precise mechanism of this effect remains to be determined, functional stimulation could readily be translated to clinical practice.

Methodological quality of animal studies on neuroprotection in focal cerebral ischaemia

BACKGROUND

The recurrent failure of apparently promising neuroprotective drugs to improve outcome in trials of patients with acute ischaemic stroke may partially be explained by over-optimistic conclusions about efficacy as a result of methodological shortcomings in preclinical studies. We assessed the methodological quality of animal studies of five different neuroprotective agents that have been tested in 21 clinical trials including a total of more than 12,000 patients with acute ischaemic stroke.

METHODS

We performed a literature search restricted to full publications on the effects of clomethiazole, gavestinel, lubeluzole, selfotel, or tirilazad mesylate on infarct volume or functional outcome in animal models of acute focal cerebral ischaemia. We used a rating scale to assess the methodological quality of the included studies. One point was attributed to each of 10 items. A score of 4 to 6 points was considered "medium" and a score above 7 "high."

RESULTS

A total of 45 articles were included. The median score on the methodological quality index was 3; 18 studies had a medium score and one a high score. Randomised treatment allocation was mentioned in 19 studies (42 %), blinded administration of study medication in 10 (22 %), and blinded outcome assessment in 18 (40 %). The study drug was administered at a median of 10 min (range, -60 to 360 min) after the onset of ischaemia.

CONCLUSION

The evidence for neuroprotective efficacy that formed the basis for initiating the 21 trials was obtained in animal studies with a methodological quality that would, in retrospect, not justify such a decision. More rigorous preclinical study methodology may lead to more reliable and reproducible results.

Challenges of Neuroprotection and Neurorestoration in Ischemic Stroke Treatment

Currently, the most important therapeutic approaches in the acute phase of ischemic stroke are focused on the restoration of regional cerebral blood flow, early admission to a stroke unit and the attempt to block, using neuroprotective drugs, the biochemical and metabolic changes involved in the 'ischemic cascade'. Treatment with rt-PA in the acute phase, although very effective, is still limited to a small number of patients and positive preclinical results of neuroprotective treatment have not, as yet, been endorsed in clinical trials. The remarkable lack of concordance between the positive results in experimental models and the negative results obtained in clinical trials has led to a change in attitude in the conduct of preclinical studies as well as to a modification of the design of clinical trials, with special attention being paid to patient selection criteria and clinical evaluation. Some neuroprotective drugs, such as citicoline, have shown some efficacy in subgroups of patients with cerebral infarction, even with a therapeutic window of up to 24 h, which would suggest a possible neurorestorative effect. Different degrees of functional recovery, weeks or months after the ischemic event, are currently observed in clinical practice and have been related to endogenous self-repair mechanisms. The growing understanding of the mechanisms involved in the phenomena of brain plasticity and their modulation, together with the possibility of restoring functional deficits by encouraging endogenous neurogenesis or by cell therapy, open up new directions in the treatment of stroke patients.

Sample Size Calculations in Acute Stroke Trials: A Systematic Review of Their Reporting, Characteristics, and Relationship With Outcome

BACKGROUND AND PURPOSE

Only a few randomized controlled trials in acute stroke have shown a treatment-related benefit. Inadequate trial design, especially low sample size, may partly explain this failure. We investigated sample size calculations (SSCs) in a systematic review of acute stroke trials.

METHODS

Full reports of nonconfounded randomized controlled trials that recruited patients within 1 week of stroke onset and were published before the end of 2001 were identified from the Cochrane Library and other bibliographic databases. Information on the SSC and outcome event rates was collected for each trial.

RESULTS

Of 189 identified trial reports, 57 (30%) reported > or =1 components of the SSC, phase II 14/129 (11%) versus phase III 43/60 (72%) (P<0.001), with 32 (56%) giving all the required parameters. Significance (alpha) was mentioned in 54 (96%) reports; 53 used a significance level of alpha=0.05. And 55 (98%) reports gave the power (1-beta) of the study (median [25th and 75th percentile] 0.80 [0.80, 0.90]). The anticipated percentage of control subjects having a primary outcome event was given in 24 (42%) articles: case fatality 21.8% (11.8%, 23.5%, n=4) and combined death or disability/dependency 55.5% (44.5%, 66.3%, n=20); 25 studies used other outcomes and 8 studies gave insufficient information. Four of the 22 trials achieved a control rate within 5% of their prediction. 49 (86%) reports gave the anticipated treatment effect; case fatality: anticipated 9.5% (1.1%, 12.5%, n=6), achieved -0.3% (-4.1%, +2.4%); combined death or disability/dependency: anticipated 13.0% (10.0%, 16.0%, n=25), achieved 1.8% (-0.5%, +5.4%). The median calculated sample size was 600 (198, 995, n=54).

CONCLUSIONS

Too few trial publications report the assumptions underlying their SSC. Most trials were underpowered, ie, power <0.90, used inappropriate assumptions for event rates, and were grossly overoptimistic in their expectation of treatment effect. These deficiencies will together have resulted in trials being far too small and reduced their chance of being able to detect real treatment effects.

Potential role of neuroprotective agents in the treatment of patients with acute ischemic stroke

Currently, intravenous recombinant tissue plasminogen activator is the only US Food and Drug Administration-approved therapy for acute ischemic stroke. Although efficacious, its usefulness is limited, mainly because of the very limited time window for its administration. Neuroprotective treatments are therapies that block the cellular, biochemical, and metabolic elaboration of injury during or after exposure to ischemia, and have a potential role in ameliorating brain injury in patients with acute ischemic stroke. More than 50 neuroprotective agents have reached randomized human clinical trials in focal ischemic stroke, but none have been unequivocally proven efficacious, despite successful preceding animal studies. The failed neuroprotective trials of the past have greatly increased understanding of the fundamental biology of ischemic brain injury and have laid a strong foundation for future advance. Moreover, the recent favorable results of human clinical trials of hypothermia in human cardiac arrest and global brain ischemia have validated the general concept of neuroprotection for ischemic brain injury. Recent innovations in strategies of preclinical drug development and clinical trial design that rectify past defects hold great promise for neuroprotective investigation, including novel approaches to accelerating time to initiation of experimental treatment, use of outcome measures sensitive to treatment effects, and trial testing of combination therapies rather than single agents alone. Although no neuroprotective agent is of proven benefit for focal ischemic stroke, several currently available interventions have shown promising results in preliminary trials and may be considered for cautious, off-label use in acute stroke, including hypothermia, magnesium sulfate, citicoline, albumin, and erythropoietin. Overall, the prospects for safe and effective neuroprotective therapies to improve stroke outcome remain promising.

Potential Role of Neuroprotective Agents in the Treatment of Patients with Acute Ischemic Stroke

Currently, intravenous recombinant tissue plasminogen activator is the only US Food and Drug Administration-approved therapy for acute ischemic stroke. Although efficacious, its usefulness is limited, mainly because of the very limited time window for its administration. Neuroprotective treatments are therapies that block the cellular, biochemical, and metabolic elaboration of injury during or after exposure to ischemia, and have a potential role in ameliorating brain injury in patients with acute ischemic stroke. More than 50 neuroprotective agents have reached randomized human clinical trials in focal ischemic stroke, but none has been unequivocally proven efficacious, despite successful preceding animal studies. The failed neuroprotective trials of the past have greatly increased understanding of the fundamental biology of ischemic brain injury and have laid a strong foundation for future advance. Moreover, the recent favorable results of human clinical trials of hypothermia in human cardiac arrest and global brain ischemia have validated the general concept of neuroprotection for ischemic brain injury. Recent innovations in strategies of preclinical drug development and clinical trial design that rectify past defects hold great promise for neuroprotective investigation, including novel approaches to accelerating time to initiation of experimental treatment, use of outcome measures sensitive to treatment effects, and trial testing of combination therapies rather than single agents alone. Although no neuroprotective agent is of proven benefit for focal ischemic stroke, several currently available interventions have shown promising results in preliminary trials and may be considered for cautious, off-label use in acute stroke, including hypothermia, magnesium sulfate, citicoline, albumin, and erythropoietin. Overall, the prospects for safe and effective neuroprotective therapies to improve stroke outcome remain promising.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Neuroprotective agents for the treatment of acute ischemic stroke

Neuroprotective treatments are therapies designed to interrupt the cellular, biochemical, and metabolic elaboration of injury during or following exposure to ischemia; they encompass a rapidly expanding array of pharmacologic interventions. Various classes of neuroprotective agents have reached phase III efficacy trials in focal ischemic stroke, but none has proven effective, despite successful preceding animal studies. This notwithstanding, recent favorable results of hypothermia in human cardiac arrest trials have validated the general concept of neuroprotection. In addition, the promise of neuroprotective therapy for focal acute ischemic stroke has been renewed by innovations in strategies of preclinical drug development and clinical trial design that rectify past defects, including trial testing of combination therapies rather than single agents and novel approaches to accelerating time to initiation of experimental treatment.

Toward wisdom from failure: lessons from neuroprotective stroke trials and new therapeutic directions

BACKGROUND

Neuroprotective drugs for acute stroke have appeared to work in animals, only to fail when tested in humans. With the failure of so many clinical trials, the future of neuroprotective drug development is in jeopardy. Current hypotheses and methodologies must continue to be reevaluated, and new strategies need to be explored. Summary of Review- In part 1, we review key challenges and complexities in translational stroke research by focusing on the "disconnect" in the way that neuroprotective agents have traditionally been assessed in clinical trials compared with animal models. In preclinical studies, determination of neuroprotection has relied heavily on assessment of infarct volume measurements (instead of functional outcomes), short-term (instead of long-term) end points, transient (instead of permanent) ischemia models, short (instead of extended) time windows for drug administration, and protection of cerebral gray matter (instead of both gray and white matter). Clinical trials have often been limited by inappropriately long time windows, insufficient statistical power, insensitive outcome measures, inclusion of protocol violators, failure to target specific stroke subtypes, and failure to target the ischemic penumbra. In part 2, we explore new concepts in ischemic pathophysiology that should encourage us also to think beyond the hyperacute phase of ischemia and consider the design of trials that use multiagent therapy and exploit the capacity of the brain for neuroplasticity and repair.

CONCLUSIONS

By recognizing the strengths and limitations of animal models of stroke and the shortcomings of previous clinical trials, we hope to move translational research forward for the development of new therapies for the acute and subacute stages after stroke.

Nimodipine in animal model experiments of focal cerebral ischemia: a systematic review

BACKGROUND AND PURPOSE

Based on the results of animal experiments, clinical trials were performed with nimodipine, which did not demonstrate a beneficial effect on outcome after stroke. The aim of this study was to determine whether the evidence from animal experiments with nimodipine supported the use of nimodipine in clinical trials.

METHODS

- We performed a systematic review of animal experiments with nimodipine in focal cerebral ischemia. Studies were identified by searching Medline and Embase. We assessed whether these studies showed a beneficial effect of active treatment. In-depth analyses were performed on infarct size and amount of edema, and subgroup analyses were performed on the length of the time window to the initiation of treatment and the methodological quality of the studies.

RESULTS

- Of 225 identified articles, 20 studies were included. The methodological quality of the studies was poor. Of the included studies, 50% were in favor of nimodipine. In-depth analyses showed statistically significant effects in favor of treatment (10 studies). No influence of the length of time to the initiation of treatment or of the methodological quality on the results was found.

CONCLUSIONS

- We conclude that the results of this review did not show convincing evidence to substantiate the decision to perform trials with nimodipine in large numbers of patients. There were no differences between the results of the animal experiments and clinical studies. Surprisingly, we found that animal experiments and clinical studies ran simultaneously.

The role of proteolytic enzymes in focal ischaemic brain damage

Although various neuroprotective and fibrinolytic drugs are currently under evaluation in the acute stages of ischaemic stroke, their therapeutic potential is likely to be limited by unwanted side effects and a narrow time window of opportunity for intervention. Proteolytic enzymes are involved in the catabolism of peptide neurotransmitters and structural cellular proteins in normal brain and have been implicated in the pathogenesis of neurodegenerative disorders. We hypothesised that activation of these enzymes might also play a crucial role in effecting ischaemic neuronal injury, thereby providing a potential site for therapeutic intervention in human stroke. Focal cerebral ischaemia was induced by thermocoagulation of the left middle cerebral artery in aged (30 month) male Wistar rats who were pre-treated with saline or the competitive N-methyl-D-Aspartate antagonist D-CPP-ene, which has been shown to be neuroprotective in young animal models of stroke. Major protease activities were analysed in the left (ischaemic) and right (non-ischaemic) hemispheres, following tissue homogenisation. Data have been analysed using Mann-Whitney tests and are presented as means +/- standard errors. Enzyme activity decreased in ischaemic brain; for example, the mean activity of dipeptidyl aminopeptidase I was 23 +/- 3 and 43 +/- 6 nmol substrate/hour/ml brain extract in the left and right hemispheres respectively (n = 10, p < 0.05). Ischaemic neuronal injury is not effected by the early activation of proteolytic enzymes and protease inhibitors are therefore unlikely to be of benefit in human stroke.

Entry criteria and baseline characteristics predict outcome in acute stroke trials

Background and Purpose-We sought to study the range of entry criteria and baseline characteristics in acute stroke trials and to understand their effects on patient outcomes.

METHODS

-Randomized, placebo-controlled therapeutic trials in patients with acute ischemic stroke were identified. Entry criteria, baseline clinical characteristics, and outcome were extracted for the placebo group of each trial. The relationship between key variables was then determined.

RESULTS

-Across 90 placebo groups identified, there was great variation in entry criteria and outcome measures. This was associated with divergent outcomes; for example, in some studies most placebo group patients died, while in other studies nearly all had no disability. Entry criteria were significantly correlated with outcome; for example, higher age cutoff for study entry correlated with 3-month mortality. Entry criteria also predicted baseline clinical characteristics; for example, wider time window for study entry correlated directly with time to treatment and inversely with stroke severity (initial National Institutes of Health Stroke Scale score). Baseline characteristics predicted outcome. Greater stroke severity predicted higher 3-month mortality rate; despite this, successful thrombolytic trials have enrolled more severe strokes than most trials. The mean age of enrollees also predicted 3-month mortality and was inversely related to percentage of patients with 3-month Barthel Index score >/=95. The strongest predictors of 3-month mortality were obtained with multivariate models.

CONCLUSIONS

-Acute stroke studies vary widely in entry criteria and outcome measures. Across multiple studies, differences in entry criteria, and the baseline clinical characteristics they predict, influence patient outcomes along a continuum. In some studies, enrolling a specific subset of patients may have improved the chances of identifying a treatment-related effect, while in others, such chances may have been reduced. These findings may be useful in the design of future stroke therapeutic trials.

Understanding and managing ischemic stroke

Transient or permanent focal brain injury following acute thromboembolic occlusion develops from a complex cascade of pathophysiological events. The processes of excitotoxicity, peri-infarct depolarisation, inflammation, and apoptosis within the ischemic penumbra are proposed. While the translation of therapeutic agents from the animal models to human clinical trials have been disappointing, there remains an atmosphere of optimism as a result of the development of new diagnostic and therapeutic approaches, which include physiological, as opposed to pharmacological, intervention. This article provides an insight into the understanding of cerebral ischemia, together with current and future treatment strategies.Key words: cerebral ischemia, stroke, pathophysiology.

Tirilazad for acute ischaemic stroke

BACKGROUND

Tirilazad mesylate is neuroprotective in experimental models of ischaemic stroke suggesting it might be of benefit clinically.

OBJECTIVES

To assess whether tirilazad mesylate is safe and effective at improving outcome in patients with acute ischaemic stroke.

SEARCH STRATEGY

Trials of tirilazad were identified from searches of the Cochrane Stroke Group Specialised Trials Register (last searched: May 2001) and the Cochrane Controlled Trials Register (CENTRAL/CCTR). In addition, we contacted the Pharmacia & Upjohn company, the manufacturer of tirilazad, to identify unpublished studies and further information.

SELECTION CRITERIA

Truly and quasi-randomised unconfounded placebo or open controlled trials of tirilazad administered within 24 hours onset of suspected or proven acute ischaemic stroke.

DATA COLLECTION AND ANALYSIS

Data relating to early and end-of-trial case fatality, disability (Barthel Index and Glasgow Outcome Scale), phlebitis, and QTc were extracted by treatment group from published data and company reports.

MAIN RESULTS

Six trials (four published, two unpublished) assessing tirilazad in 1757 patients with presumed acute ischaemic stroke were identified; all were double-blind and placebo-controlled in design. Tirilazad did not alter early case fatality (odds ratio, OR 1.11, 95% confidence intervals, 95% CI 0.79 to 1.56) or end-of-trial case fatality (OR 1.12, 95% CI 0.88 to 1.44). Tirilazad increased the odds of being dead or disabled by about one fifth, though the result was only just statistically significant; the odds ratios were similar whether the expanded Barthel Index or Glasgow Outcome Scale were used to assess outcome (OR 1.23, 95% CI 1.01 to 1.51; OR 1.23, 95% CI 1.01 to 1.50 respectively). Tirilazad significantly increased the rate of infusion site phlebitis (OR 2.81, 95% CI 2.14 to 3.69). Functional outcome (EBI) was significantly worse in prespecified subgroups of patients: females (OR 1.46, 95% CI 1.08 to 1.98) and subjects receiving low dose tirilazad (OR 1.31, 95% CI 1.03 to 1.67); a non-significant worse outcome was also seen in patients with mild-moderate stroke (OR 1.40, 95% CI 0.99 to 1.98).

REVIEWER'S CONCLUSIONS

Tirilazad mesylate increased the combined end-point of 'death or disability' by about one-fifth, but did not alter case fatality, when given to patients with acute ischaemic stroke. Although further trials of tirilazad are now not warranted, analysis of individual patient data from the trials may help elucidate why tirilazad appears to worsen outcome in acute ischaemic stroke.

Tirilazad mesylate in acute ischemic stroke: A systematic review. Tirilazad International Steering Committee

BACKGROUND AND PURPOSE

Tirilazad is a nonglucocorticoid, 21-aminosteroid that inhibits lipid peroxidation. Studies in experimental models of ischemic stroke had suggested that tirilazad had neuroprotective properties. As a result, clinical studies were undertaken to assess the safety and efficacy of tirilazad in the treatment of acute ischemic stroke. We performed a systematic review of randomized, controlled trials that assessed the safety and efficacy of tirilazad in patients with acute ischemic stroke.

METHODS

Trials of tirilazad were identified from searches of the Cochrane Library and communication with the Pharmacia & Upjohn company, the manufacturer of tirilazad. Data relating to early and end-of-trial case fatality, disability (Barthel Index and Glasgow Outcome Scale), phlebitis, and corrected QT interval were extracted by treatment group from published data and company reports and analyzed by using the Cochrane Collaboration meta-analysis software REVMAN.

RESULTS

Six trials (4 published, 2 unpublished) assessing tirilazad in 1757 patients with presumed acute ischemic stroke were identified; all were double-blind and placebo controlled in design. Tirilazad did not alter early case fatality (odds ratio [OR] 1.11, 95% confidence interval [CI] 0.79 to 1.56) or end-of-trial case fatality (OR 1.12, 95% CI 0.88 to 1.44). A just-significant increase in death and disability, assessed as either the expanded Barthel Index (OR 1.23, 95% CI 1.01 to 1.51) or Glasgow Outcome Scale (OR 1. 23, 95% CI 1.01 to 1.50) was observed. Tirilazad significantly increased the rate of infusion site phlebitis (OR 2.81, 95% CI 2.14 to 3.69). Functional outcome (expanded Barthel Index) was significantly worse in prespecified subgroups of patients: females (OR 1.46, 95% CI 1.08 to 1.98) and subjects receiving low-dose tirilazad (OR 1.31, 95% CI 1.03 to 1.67); a nonsignificant worse outcome was also seen in patients with mild to moderate stroke (OR 1. 40, 95% CI 0.99 to 1.98).

CONCLUSIONS

Tirilazad mesylate increases death and disability by about one fifth when given to patients with acute ischemic stroke. Although further trials of tirilazad are now unwarranted, analysis of individual patient data from the trials may help elucidate why tirilazad appears to worsen outcome in acute ischemic stroke.

Nimodipine improves the disruption of spatial cognition induced by cerebral ischemia

The direct neuroprotective effect of nimodipine, a central Ca antagonist, was investigated in in vitro experiments. Also, in in vivo experiments, the effects of nimodipine and amlodipine, a noncentral Ca antagonist, on rat cerebral ischemia models developing by different mechanisms were compared. In an in vitro ischemic model using acidotic and hypoglycemic rat cerebellar granule cells, nimodipine directly protects against brain neuronal cell damage. In in vivo models of single (one 10-min, four-vessel occlusion) and repeated rat cerebral ischemia (two 10-min, four-vessel occlusions; a 50-min interval), the impairment observed 24 h after the single ischemic procedure was likely to be prevented by nimodipine (0. 1-5mg/kg, i.p.). At 7 days after the repeated cerebral ischemia, the disruption of spatial cognition was significantly prevented by nimodipine (5 mg/kg, i.p.) but not amlodipine (5 mg/kg, i.p.), which was given after each ischemia. These results indicated that nimodipine may protect neuronal cells by a more persistent mode of action, that is, nimodipine may enter into the cell and control the intracellular Ca ion cascade by inhibiting excessive Ca(2)+ influx into the mitochondria.

Selfotel in acute ischemic stroke : possible neurotoxic effects of an NMDA antagonist

BACKGROUND AND PURPOSE

Based on neuroprotective efficacy in animal models, we evaluated the N-methyl D-aspartate antagonist Selfotel in patients with ischemic stroke, after doses up to 1.5 mg/kg were shown to be safe in phase 1 and phase 2a studies.

METHODS

Two pivotal phase 3 ischemic stroke trials tested the hypothesis, by double-blind, randomized, placebo-controlled parallel design, that a single intravenous 1.5 mg/kg dose of Selfotel, administered within 6 hours of stroke onset, would improve functional outcome at 90 days, defined as the proportion of patients achieving a Barthel Index score of >/=60. The trials were performed in patients aged 40 to 85 years with acute ischemic hemispheric stroke and a motor deficit.

RESULTS

The 2 trials were suspended on advice of the independent Data Safety Monitoring Board because of an imbalance in mortality after a total enrollment of 567 patients. The groups were well matched for initial stroke severity and time from stroke onset to therapy. There was no difference in the 90-day mortality rate, with 62 deaths (22%) in the Selfotel group and 49 (17%) in the placebo-treated group (RR=1.3; 95% CI 0.92 to 1.83; P=0.15). However, early mortality was higher in the Selfotel-treated patients (day 30: 54 of 280 versus 37 of 286; P=0.05). In patients with severe stroke, mortality imbalance was significant throughout the trial (P=0.05).

CONCLUSIONS

Selfotel was not an effective treatment for acute ischemic stroke. Furthermore, a trend toward increased mortality, particularly within the first 30 days and in patients with severe stroke, suggests that the drug might have a neurotoxic effect in brain ischemia.

A predictive risk model for outcomes of ischemic stroke

BACKGROUND AND PURPOSE

The great variability of outcome seen in stroke patients has led to an interest in identifying predictors of outcome. The combination of clinical and imaging variables as predictors of stroke outcome in a multivariable risk adjustment model may be more powerful than either alone. The purpose of this study was to determine the multivariable relationship between infarct volume, 6 clinical variables, and 3-month outcomes in ischemic stroke patients.

METHODS

Included in the study were 256 eligible patients from the Randomized Trial of Tirilazad Mesylate in Acute Stroke (RANTTAS). Six clinical variables and 1-week infarct volume were the prespecified predictor variables. The National Institutes of Health Stroke Scale, Barthel Index, and Glasgow Outcome Scale were the outcomes. Multivariable logistic regression techniques were used to develop the model equations, and bootstrap techniques were used for internal validation. Predictive performance of the models was assessed for discrimination with receiver operator characteristic (ROC) curves and for calibration with calibration curves.

RESULTS

The predictive models had areas under the ROC curve of 0.79 to 0.88 and demonstrated nearly ideal calibration curves. The areas under the ROC curves were statistically greater (P<0.001) with both clinical and imaging information combined than with either alone for predicting excellent recovery and death or severe disability.

CONCLUSIONS

Combined clinical and imaging variables are predictive of 3-month outcome in ischemic stroke patients. Demonstration of this relationship with acute clinical variables and 1-week infarct information supports future attempts to predict 3-month outcome with all acute variables.

Neuroprotection in acute ischaemic stroke. II: Clinical potential

In the 4 years since our first article, there has been considerable progress in our understanding of the pathophysiology of acute ischaemic stroke, and the results of well-conducted trials have at last begun to change everyday clinical practice. The timing of the various processes of the ischaemic cascade and the potential time windows for different interventions are better understood. Furthermore, the importance of maintaining cerebral perfusion and optimizing systemic physiological and biochemical factors in order to prevent neurological deterioration ('progressing stroke') is increasingly being realized. Numerous antithrombotic and neuroprotective drugs have been evaluated in clinical trials, and while none has shown unequivocal benefits on its own, prospects for successful intervention are still good. This will probably involve different combinations of treatments targeted on different pathophysiological stroke types, so that the management of acute stroke will offer a considerable challenge to the stroke physicians of the future.

Inhibition of iron-dependent and ischemia-induced brain damage by the alpha-tocopherol analogue MDL 74,722

Free radical-induced lipid peroxidation is an important factor in the pathogenesis of ischemic brain damage. We studied the effects of the alpha-tocopherol analogue MDL 74,722 on iron-dependent lipid peroxidation and infarct volume after transient focal cerebral ischemia. The effects of MDL 74,722 on iron-induced lipid peroxidation were tested in cerebellar granule cell cultures by means of a thiobarbituric acid reactive substances (TBARS) assay. The absorbance resulting from mitochondrial reduction of 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) was taken as a measure of cell viability. Besides, in male Wistar rats the left middle cerebral artery (MCA) was occluded for 3 h by means of an intraluminal filament. Rats were treated with vehicle (n = 19) or MDL 74,722 (n = 17), administered intravenously for 3 h in a dose of 2 mg/(kg.h), starting 105 min after MCA occlusion. Infarct volume was measured in coronal brain sections stained with hematoxylin and eosin. In cerebellar granule cell cultures, MDL 74,722 resulted in a dose-dependent inhibition of TBARS formation and prevention of cell toxicity. The compound reduced infarct volume after transient occlusion of the MCA in rats by 49%. It is concluded that MDL 74,722 is a potent inhibitor of lipid peroxidation and reduces infarct volume by about one half, even when treatment is delayed. This contributes to its potential clinical usefulness.

Design and retrospective analysis of the Los Angeles Prehospital Stroke Screen (LAPSS)

OBJECTIVES

The therapeutic window for intervention in acute cerebral ischemia is brief. Prehospital identification of acute stroke patients and paramedic administration of neuroprotective agents may soon become critical components of successful acute stroke treatment. This preliminary study sought to demonstrate that a new prehospital screening instrument, the Los Angeles Prehospital Stroke Screen (LAPSS), sensitively identifies acute stroke patients. Further, the study evaluated the potential time savings that could be achieved by paramedic administration of neuroprotective agents in the field.

METHODS

The authors designed a simple stroke screening tool for use by prehospital personnel, emphasizing motor deficits. They then tested instrument performance and time savings retrospectively, employing data from patients enrolled within six hours of symptom onset in randomized stroke trials at three university-associated paramedic receiving hospitals.

RESULTS

Fifty of 83 patients enrolled in hyperacute stroke trials arrived by ambulance, including 41 with ischemic infarcts and seven with hemorrhages. Of the 41 with acute ischemic stroke, 38 (93%) would have been accurately identified by the LAPSS. For these 38 patients, 1 hour and 50 minutes would have been saved had neuroprotective drug been administered by paramedics at the time of transport vs the actual time of study agent administration in the emergency department.

CONCLUSIONS

The LAPSS sensitively identifies ambulance-arriving acute stroke patients, and a substantial time savings will potentially occur if neuroprotective agents are administered by paramedics in the field. The LAPSS is a promising tool that may enable paramedic recognition of stroke with a high degree of sensitivity and simplicity in a short period of time.

Degeneration of spared axons following partial white matter lesion: implications for optic nerve neuropathies

Neuroprotective therapy is a relatively new development in the approach to the treatment of acute and chronic brain damage. Though initially viewed in the framework of acute CNS injuries, the concept was recently extended to include chronic injuries, in which at any given time there are some neurons in an acute phase of degeneration coexisting with others that are healthy, marginally damaged, or dead. The healthy neurons and those that are only marginally damaged are the potential targets for neuroprotection. For the development of neuroprotective therapies, it is essential to employ an animal model in which the damage resulting from secondary degeneration can be quantitatively distinguished from primary degeneration. This is of particular relevance when the site of the damage is in the white matter (nerve fibers) rather than in the gray matter (cell bodies). In the present work we reexamine the concepts of secondary degeneration and neuroprotection in white matter lesions. Using a partial crush injury of the adult rat optic nerve as a model, we were able to assess both primary and secondary nerve damage. We show that neurons whose axons were not damaged or only marginally damaged after an acute insult will eventually degenerate as a consequence of their existence in the degenerative environment produced by the injury. This secondary degeneration does not occur in all of the neurons at once, but affects them in a stepwise fashion related to the severity of the damage inflicted. These findings, which may be applicable to the progression of acute or chronic neuropathy, imply that neuroprotective therapy may have a beneficial effect even if there is a time lag between injury and treatment.

A new clinical scoring system fails to differentiate hemorrhagic from ischemic stroke when used in the acute care setting

Recently, a new diagnostic scoring system has been proposed to help differentiate intracranial hemorrhage (ICH) from ischemic infarct. The system, derived using data from hospitalized stroke patients, is based on eight variables readily available to all clinicians. A diagnostic score <1.0 is reportedly 100% predictive of ischemic infarct. The clinical scoring system is asserted to be a useful adjunct in the initial evaluation of patients with acute stroke syndrome. The purpose of this study was to prospectively evaluate this clinical scoring system in our emergency department (ED). Sixty-one ED patients with focal neurologic deficit undergoing cranial computed tomography (CT) scan to rule out ICH were entered in the study. Thirteen [21% (95% CI, 12-34%)] were found to have an ICH. Twenty-two [36% (95% CI, 24-49%)] had a diagnostic score < 1.0. The CT scans on 4 of these 22 patients showed ICH. The positive predictive value for ischemic infarct for these 22 patients using the diagnostic scoring system was 82% (95% CI, 60-95%). Our results suggest that this new clinical scoring system is of no value in helping to differentiate ICH from ischemic stroke in the acute care setting.

Inhibition of nonselective cation channels reduces focal ischemic injury of rat brain

The effect of the novel inhibitor of receptor-activated and calcium store-operated nonselective cation channels, (RS)-(3,4-dihydro-6,7-dimethoxyisoquinoline-1-gamma 1)-2-phenyl-N, N-di-[2(2,3,4-trimethoxyphenyl) ethyl]acetamide (LOE 908 MS), on focal cerebral ischemia was studied in halothane-anesthetized rats submitted to permanent suture occlusion of the right middle cerebral artery (MCA). The treated group (n = 7) received subcutaneous injections of 30 mg/kg LOE 908 MS (in 1 ml saline) 10 min after vascular occlusion and again after 3 h. The untreated group (n = 11) was injected subcutaneously with 1 ml saline at the same times. Evolution of infarct was monitored by electrophysiological recording of EEG and cortical steady potential and by diffusion-weighted magnetic resonance imaging during the initial 6 h of vascular occlusion. The hemodynamic, biochemical, and morphological changes were studied after 6 h by combining autoradiographic measurement of blood flow with histological stainings and pictorial measurements of ATP, glucose, and tissue pH. In the untreated animals, the ischemic lesion volume [defined as the region in which the apparent diffusion coefficient (ADC) of water declined to below 80% of control] steadily increased by approximately 50% during the initial 6 h of vascular occlusion relative to the first set of data 10 min postocclusion. In the treated animals, in contrast, the ADC lesion volume declined by approximately 20% during the same interval. Treatment also led to a significant reduction in the number of periinfarct depolarizations. After 6 h of vascular occlusion, blood flow was significantly higher in the treated animals, and the volume of ATP-depleted and morphologically injured tissue representing the infarct core was 60-70% smaller. The volume of severely acidic tissue, in contrast, did not differ, indicating that LOE 908 MS does not reduce the size of ischemic penumbra. These findings demonstrate that postocclusion treatment of permanent focal ischemia with LOE 908 MS delays the expansion of the infarct core into the penumbra for a duration of at least 6 h and therefore substantially prolongs the window of opportunity for the reversal of the ischemic impact in the peripheral parts of the evolving infarct.

Radiologic intervention in the acute stroke patient

Overall, stroke is a common disease that can have devastating results. Treatment of stoke has been, for the most part, supportive in nature. Recently, more aggressive intervention has been used, particularly thrombolysis. Although such intervention can have devastating consequences, it has shown some promise, particularly in the arena of intraarterial administration. Although much work is needed to find the ideal agents and methods of administration, screening of patients may hold the key to success and the limitations of complications. Determination of exactly which patients will benefit and which will not and which will have complications and which will not, remains for the most part an enigma. Only through further investigation in a controlled, collaborative manner can such information be obtained.