Experimental treatments for acute ischaemic stroke

The complexity of neurobiological processes in acute ischemic stroke

There is an urgent need for improved diagnostics and therapeutics for acute ischemic stroke. This is the focus of numerous research projects involving in vitro studies, animal models and clinical trials, all of which are based on current knowledge of disease mechanisms underlying acute focal cerebral ischemia. Insight in the chain of events occurring during acute ischemic injury is essential for understanding current and future diagnostic and therapeutic approaches. In this review, we summarize the actual knowledge on the pathophysiology of acute ischemic stroke. We focus on the ischemic cascade, which is a complex series of neurochemical processes that are unleashed by transient or permanent focal cerebral ischemia and involves cellular bioenergetic failure, excitotoxicity, oxidative stress, blood-brain barrier dysfunction, microvascular injury, hemostatic activation, post-ischemic inflammation and finally cell death of neurons, glial and endothelial cells.

A model of ischemia-induced neuroblast activation in the adult subventricular zone

We have developed a rat brain organotypic culture model, in which tissue slices contain cortex-subventricular zone-striatum regions, to model neuroblast activity in response to in vitro ischemia. Neuroblast activation has been described in terms of two main parameters, proliferation and migration from the subventricular zone into the injured cortex. We observed distinct phases of neuroblast activation as is known to occur after in vivo ischemia. Thus, immediately after oxygen/glucose deprivation (6–24 hours), neuroblasts reduce their proliferative and migratory activity, whereas, at longer time points after the insult (2 to 5 days), they start to proliferate and migrate into the damaged cortex. Antagonism of ionotropic receptors for extracellular ATP during and after the insult unmasks an early activation of neuroblasts in the subventricular zone, which responded with a rapid and intense migration of neuroblasts into the damaged cortex (within 24 hours). The process is further enhanced by elevating the production of the chemoattractant SDf-1α and may also be boosted by blocking the activation of microglia. This organotypic model which we have developed is an excellent in vitro system to study neurogenesis after ischemia and other neurodegenerative diseases. Its application has revealed a SOS response to oxygen/glucose deprivation, which is inhibited by unfavorable conditions due to the ischemic environment. Finally, experimental quantifications have allowed us to elaborate a mathematical model to describe neuroblast activation and to develop a computer simulation which should have promising applications for the screening of drug candidates for novel therapies of ischemia-related pathologies.

Therapeutic hypothermia for neuroprotection

This review briefly discusses induced therapeutic hypothermia (TH), which represents the intentional induction of a lowered core body temperature of 35 degrees C or less. The focus is on resuscitative or postarrest hypothermia, the data that support it, and the practical issues pertaining to TH implementation.

[Therapeutic hypothermia in neurocritical patients]

Induced hypothermia in neurocritical patients is one of the most promising neuroprotective therapies in the last decade. Unfortunately, the promising results obtained in experimental studies have had an unequal reflection in the different diseases that affect the neurocritical patient. The use of therapeutic hypothermia is clearly established in patients with neurological deterioration after cardiac arrest. On the contrary, its use in patients with traumatic brain injury is highly controversial. There is not enough evidence in stroke and hemorrhagic patients to support its use except in clinical trials. Nowadays, the greater understanding of the pathophysiology of secondary brain damage, the go od clinical results obtained in randomized clinical trials in patients with cerebral anoxia after ventricular fibrillation and the new cooling methods that have appeared have improved the interest of hypothermia in neurocritical patients. Induced hypothermia has a role in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hypothermia. This review elaborates on the clinical implications of hypothermia research in traumatic brain injury, anoxic, brain injury, stroke and intracerebral hemorrhage.

Fenofibrate-loaded PLGA microparticles: effects on ischemic stroke

Many drugs are not able to cross the Blood Brain Barrier (BBB) and, thus, cannot reach a target site within the Central Nervous System (CNS). Local controlled drug delivery can help to overcome this restriction. However, this is a highly challenging approach and only one product is yet available on the market: Gliadel, which is used to reduce the risk of local tumor recurrence upon resection of malignant glioma. The aim of this study was to evaluate the potential of local controlled drug delivery to the CNS to reduce the consequences of ischemic stroke. Fenofibrate as well as its active metabolite fenofibric acid were encapsulated within PLGA microparticles. Importantly, fenofibrate-loaded microparticles effectively reduced the consequences of ischemic stroke in Wistar rats: the total, cortical and striatal infarct volumes decreased from 257 to 197, 193 to 139, and 64 to 58 mm(3), respectively. Interestingly, fenofibric acid-loaded microparticles did not show significant in vivo efficacy, which might be attributable to a potentially limited distribution pattern within the brain and/or limited cell uptake. Thus, local controlled drug delivery to the CNS also has a significant potential for the treatment/prevention of other types of diseases than cancer. Furthermore, this approach can help to provide proof of concept in vivo in the early drug discovery phase, if the drug candidate cannot cross the BBB.

Cell adhesion molecules and ischemic stroke

OBJECTIVE

To describe the role of adhesion molecules in ischemic stroke.

METHODS

A PubMed search of literature pertaining to this study was conducted in April 2008 using specific keyword search terms pertaining to stroke and various listed subtopics related to adhesion molecules.

RESULTS

An important contribution of beta2-integrins (CD11/CD18), intercellular adhesion molecule and P-selectin in the recruitment of leukocytes as well as platelets in the post-ischemic cerebral microvasculature has been defined in related studies. Immunoblockade or genetic deletion of these adhesion molecules has been shown to reduce infarct volume, edema, behavioral deficits and/or mortality in different animal models of ischemic stroke. Anti-adhesion agents also appear to widen the therapeutic window for thrombolytic therapy in these experimental models. An emerging role of inflammatory signaling pathways has also been addressed in modulating adhesion properties of post-ischemic cerebral microvasculature. Despite the promising data obtained from animal studies, few clinical trials assessing anti-adhesion therapy in ischemic stroke have failed to show efficacy.

DISCUSSION

Several experiments using cell surface adhesion molecules as targets of stroke therapy are promising yet inadequate. Clinical trials using immune blockade of adhesion molecules by antibodies have failed due to immune reactions of the host. Further clinical trials are needed to test the efficacy of humanized antibodies or non-immunogenic agents that interfere with cell adhesion mechanisms. Adhesion blocking strategies seem to be effective particularly at reperfusion and use of these strategies with thrombolytic therapies justifies a continued effort to define the role of adhesion molecules in the pathophysiology of cerebral ischemia-reperfusion.

Carboxypeptidase U (TAFIa) decreases the efficacy of thrombolytic therapy in ischemic stroke patients

INTRODUCTION

Thrombolytic therapy improves clinical outcome in patients with acute ischemic stroke but is compromised by symptomatic intracranial hemorrhage and an unpredictable therapeutic response. In vitro and in vivo data suggest that activation of procarboxypeptidase U (proCPU) inhibits fibrinolysis.

AIMS

To investigate whether the extent of proCPU activation is related to efficacy and safety of thrombolytic therapy in ischemic stroke patients.

METHODS

In twelve patients with ischemic stroke who were treated with intravenous (n=7) or intra-arterial (n=5) thrombolysis, venous blood samples were taken at different time points before, during and after thrombolytic therapy. ProCPU and carboxypeptidase U (CPU, TAFIa) plasma concentrations were determined by HPLC. The maximal CPU activity (CPU(max)) and the percentage of proCPU consumption during thrombolytic therapy were calculated. The efficacy and safety of the thrombolytic therapy were assessed by evolution of the clinical deficit, recanalisation, final infarct volume, thrombolysis-induced intracranial hemorrhage and mortality.

RESULTS

No correlations between CPU(max) or proCPU consumption and patient or stroke characteristics were found. However, CPU(max) is associated with evolution of the clinical deficit and achieved recanalisation. ProCPU consumption is related to the risk of intracranial hemorrhage, mortality and final infarct volume.

CONCLUSIONS

Irrespective of patient and stroke characteristics, CPU(max) and proCPU consumption during thrombolytic treatment for ischemic stroke are parameters for therapeutic efficacy and safety. Further evaluation of the clinical applicability of these parameters and further investigation of the potential role for CPU inhibitors as adjunctive therapeutics during thrombolytic treatment may be of value.

The Boston Acute Stroke Imaging Scale: ready for use in clinical practice?

This Practice Point commentary discusses a report by Torres-Mozqueda et al. on a newly developed classification instrument for predicting outcome after stroke, the Boston Acute Stroke Imaging Scale (BASIS). This tool incorporates imaging data on the patency of the vasculature and the parenchyma and classifies ischemic strokes as major (if large vessels are occluded or parenchymal changes are present) or minor (all others). When testing the scale, the authors looked at short-term outcome at the time of hospital discharge; patients classified with major stroke by BASIS had a higher mortality and longer hospital stay and were more likely to be discharged to a rehabilitation facility than patients with minor stroke. The authors concluded that BASIS can predict outcome after stroke. We point to several shortcomings in the study methodology and argue that, although BASIS has potential as a prognostic tool, further studies are needed before it can be widely used.

Stroke-induced immunodepression: consequences, mechanisms and therapeutic implications

The clinical picture of stroke is not only characterized by neurological deficits but also by the high incidence of infectious complications, in particular pneumonia. The occurrence of pneumonia in stroke patients is associated with higher mortality, larger neurological deficits, longer hospitalization and increased costs for medical care. Immobilization and impaired protective reflexes are known to increase the risk of aspiration pneumonia. However, recent experimental and clinical evidence indicates that stroke-induced immunodepression is an independent risk factor that increases susceptibility to infections. This review provides an update on the mechanisms and consequences of stroke-induced immunodepression. The growing insight into these mechanisms may allow new immunomodulatory treatment approaches in stroke patients in the future. In the meantime, several trials on preventive antibacterial treatment to reduce the incidence of post-stroke infections have been conducted, which will be summarized in this review.

Tissue-type plasminogen activator as a therapeutic target in stroke

BACKGROUND

Ischemic stroke is a leading cause of morbidity and mortality worldwide and recombinant human tissue-type plasminogen activator (tPA) is the prominent therapeutic among very few therapeutics used in its treatment. Due to complications attributed to the drug, most notably transformation of ischemia to hemorrhage, tPA is only used in a small number of ischemic stroke cases, albeit significantly more often in specialized stroke centers.

OBJECTIVE

What are the mechanisms of tPA action and side effects in ischemic stroke, and can the knowledge about these mechanisms aid in making tPA a more efficacious and safe therapeutic or in developing alternative therapeutics?

METHODS

tPA use and alternative/combination therapies in acute ischemic stroke treatment are summarized. The review focuses on literature concerning tPA neurotoxicity and its implications for further development of tPA as a stroke therapeutic.

RESULTS/CONCLUSION

Exogenously administered recombinant tPA and endogenous tPA have both turned into promising therapeutic targets for the stroke patient.

Recently published papers: Tracheostomy: why rather than when? Obesity: does it matter? And stroke: diagnosis, thrombosis and prognosis

Three studies explore the case for tracheostomies in the intensive care unit (ICU). Tracheostomies appear to have no effect on ICU survival, according to a prospective observational cohort study that used a propensity score. In obese patients, surgical tracheostomies were associated with an increased risk of complications, although these patients appeared to have a lower mortality in the ICU. A third study failed to show that tracheostomies reduced sedation requirements. MRI appears to be the investigation of choice for the diagnosis of acute stroke and thrombolysis is a safe and effective treatment for acute ischaemic strokes. Virtually all patients with a stroke may benefit from ongoing care in a stroke unit.

Hypothermia effects on neurovascular coupling and cerebral metabolic rate of oxygen

Neuronal activation is accompanied by a local increase in cerebral blood flow (CBF) and in cerebral metabolic rate of oxygen (CMRO(2)), caused by neurovascular and neurometabolic coupling. Hypothermia is used as a neuroprotective approach in surgical patients and therapeutically after cardiac arrest or stroke. The effect of hypothermia on neurovascular coupling is of interest for evaluating brain function in these patients, but has not been determined so far. It is not clear whether functional hyperaemia actually operates at subnormal temperatures. In addition, decreasing brain temperature reduces spontaneous CMRO(2) following a known quantitative relationship (Q(10)). Q(10) determination may serve to validate a recently introduced CMRO(2) measurement approach relying on optical measurements of CBF and hemoglobin concentration. We applied this method to investigate hypothermia in a functional study of the somatosensory cortex. Anesthetized Wistar rats underwent surgical implantation of a closed cranial window. Using laser Doppler flowmetry and optical spectroscopy, relative changes in CBF and hemoglobin concentration were measured continuously. At the same time, an electroencephalogram (EEG) was recorded from the measurement site. By the application of ice packs, whole-body hypothermia was induced, followed by rewarming. Spontaneous EEG, CBF and CMRO(2) were measured, interleaved by blocks of electrical forepaw stimulation. The Q(10) obtained from spontaneous CMRO(2) changes of 4.4 (95% confidence interval 3.7-5.1) was close to published values, indicating the reliability of the CMRO(2) measurement. Lowering brain temperature decreased functional changes of CBF and CMRO(2) as well as amplitudes of somatosensory evoked potentials (SEP) to the same degree. In conclusion, neurovascular and neurometabolic coupling is preserved during hypothermia.

Detrimental effects of tropisetron on permanent ischemic stroke in the rat

Background

Recent in vitro evidence indicates that blockade of 5-hydroxytryptamine (5-HT) receptor 3 (5-HT₃) is able to confer protection in different models of neuronal injury. The purpose of the present study was to investigate the effect of tropisetron, a 5-HT₃ receptor antagonist, on infarct size and neurological score in a model of ischemic stroke induced by permanent middle cerebral artery occlusion (pMCAO) in the rat.

Methods

Two different doses of tropisetron (5 and 10 mg/kg) or vehicle were administered intraperitoneally 30 min before pMCAO. Neurological deficit scores, mortality rate and infarct volume were determined 24 h after permanent focal cerebral ischemia.

Results

Tropisetron failed to reduce cerebral infarction. Animals receiving tropisetron showed a significant increase (p < 0.05) in neurological deficits and mortality rate.

Conclusion

Data from this study indicate that blockade of 5-HT₃ receptors with tropisetron worsens ischemic brain injury induced by pMCAO. These findings could have important clinical implications. Patients taking tropisetron, and possibly other 5-HT₃ antagonists, could potentially have a worse outcome following a brain infarct.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.

Cerebral ischemia, cell cycle elements and Cdk5

Stroke is a devastating disorder that significantly contributes to death, disability, and healthcare costs. New therapeutic strategies have been recently focusing on the development of neuroprotective agents that could halt the underlying mechanisms of neuronal death leading to brain damage. Accumulating evidence implicates proteins that are normally involved in the regulation of the cell cycle to neuronal death following ischemic insult, suggesting that these proteins could be suitable targets for stroke therapy. In this brief review, we present in vitro and in vivo arguments linking cell cycle molecules, i.e., cyclins, mitotic cyclin-dependent kinases (Cdks), as well as non-mitotic Cdk5, to ischemic neuronal death. We also report the evaluation of the potential of Cdk inhibitors as neuroprotective strategy for ischemic injury.

Neuroprotection and stroke: time for a compromise

In April 2007, there existed a repertory of 286 trials concerned with acute ischemic stroke on the Stroke Trials Registry (http://www.strokecenter.org/trials/), of which 209 trials were considered as complete (with no evidence of patient benefit unless one considers the much hard fought for and modest results of the tPA studies). Among other questions arising from such failures, one can wonder whether the plethora of pharmacological agents that exhibited neuroprotective properties in pre-clinical studies were selected for clinical trials entirely based upon their experimental efficacy. This mini-review will try to point out some of the weaknesses that could underline the failure of both researchers and clinicians involved in the field of stroke to obtain their ultimate goal--brain protection.

Possible involvement of different connexin43 domains in plasma membrane permeabilization induced by ischemia-reperfusion

In vitro and in vivo studies support the involvement of connexin 43-based cell-cell channels and hemichannels in cell death propagation induced by ischemia-reperfusion. In this context, open connexin hemichannels in the plasma membrane have been proposed to act as accelerators of cell death. Progress on the mechanisms underlying the cell permeabilization induced by ischemia-reperfusion reveals the involvement of several factors leading to an augmented open probability and increased number of hemichannels on the cell surface. While open probability can be increased by a reduction in extracellular concentration of divalent cations and changes in covalent modifications of connexin 43 (oxidation and phosphorylation), increase in number of hemichannels requires an elevation of the intracellular free Ca(2+) concentration. Reversal of connexin 43 redox changes and membrane permeabilization can be induced by intracellular, but not extracellular, reducing agents, suggesting a cytoplasmic localization of the redox sensor(s). In agreement, hemichannels formed by connexin 45, which lacks cytoplasmic cysteines, or by connexin 43 with its C-terminal domain truncated to remove its cysteines are insensitive to reducing agents. Although further studies are required for a precise localization of the redox sensor of connexin 43 hemichannels, modulation of the redox potential is proposed as a target for the design of pharmacological tools to reduce cell death induced by ischemia-reperfusion in connexin 43-expressing cells.

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.