Future of neuroprotection for acute stroke: in the aftermath of the SAINT trials

Delayed melatonin administration promotes neuronal survival, neurogenesis and motor recovery, and attenuates hyperactivity and anxiety after mild focal cerebral ischemia in mice

Melatonin is a potent antioxidant with neuroprotective activity in animal models of ischemic stroke, which based on its lack of serious toxicity has raised hopes that it might be used for human stroke treatment in the future. This study investigated how subacute delivery of melatonin, starting at 24 hr after stroke onset, and continuing for 29 days (4 mg/kg/day; via drinking water), influences neuronal survival, endogenous neurogenesis, motor recovery and locomotor activity in C57Bl6/j mice submitted to 30-min middle cerebral artery occlusion. Histologic studies showed that melatonin improved neuronal survival and enhanced neurogenesis, even when applied 1 day after stroke. Cell survival was associated with a long-lasting improvement of motor and coordination deficits, evaluated by the grip strength and RotaRod tests, as well as with attenuation of hyperactivity and anxiety of the animals as revealed in open field tests. The robust functional neurologic improvements encourage proof-of-concept studies with melatonin in human stroke patients.

A new penumbra: transitioning from injury into repair after stroke

The penumbra is an area of brain tissue that is damaged but not yet dead after focal ischemia. The existence of a penumbra implies that therapeutic salvage is theoretically possible after stroke. The first decade of penumbral science investigated the ischemic regulation of electrophysiology, cerebral blood flow and metabolism. The second decade advanced our understanding of molecular mechanisms that mediate penumbral cell death. And the third decade saw the rapid development of clinical neuroimaging tools that are now increasingly applied in stroke patients. But how can we look ahead as we move into the fourth decade of penumbra research? This author speculates that a paradigm shift is needed. Most molecular targets for therapy have biphasic roles in stroke pathophysiology. During the acute phase, these targets mediate injury. During the recovery phase, the same mediators contribute to neurovascular remodeling. It is this boundary zone that comprises the new penumbra, and future investigations should dissect where, when and how damaged brain makes the transition from injury into repair.

Pathways to ischemic neuronal cell death: are sex differences relevant?

We have known for some time that the epidemiology of human stroke is sexually dimorphic until late in life, well beyond the years of reproductive senescence and menopause. Now, a new concept is emerging: the mechanisms and outcome of cerebral ischemic injury are influenced strongly by biological sex as well as the availability of sex steroids to the brain. The principal mammalian estrogen (17 β estradiol or E2) is neuroprotective in many types of brain injury and has been the major focus of investigation over the past several decades. However, it is becoming increasingly clear that although hormones are a major contributor to sex-specific outcomes, they do not fully account for sex-specific responses to cerebral ischemia. The purpose of this review is to highlight recent studies in cell culture and animal models that suggest that genetic sex determines experimental stroke outcome and that divergent cell death pathways are activated after an ischemic insult. These sex differences need to be identified if we are to develop efficacious neuroprotective agents for use in stroke patients.

Tissue plasminogen activator (tPA) and matrix metalloproteinases in the pathogenesis of stroke: therapeutic strategies

Today there exists only one FDA-approved treatment for ischemic stroke; i.e., the serine protease tissue-type plasminogen activator (tPA). In the aftermath of the failed stroke clinical trials with the nitrone spin trap/radical scavenger, NXY-059, a number of articles raised the question: are we doing the right thing? Is the animal research truly translational in identifying new agents for stroke treatment? This review summarizes the current state of affairs with plasminogen activators in thrombolytic therapy. In addition to therapeutic value, potential side effects of tPA also exist that aggravate stroke injury and offset the benefits provided by reperfusion of the occluded artery. Thus, combinational options (ultrasound alone or with microspheres/nanobubbles, mechanical dissociation of clot, activated protein C (APC), plasminogen activator inhibitor-1 (PAI-1), neuroserpin and CDP-choline) that could offset tPA toxic side effects and improve efficacy are also discussed here. Desmoteplase, a plasminogen activator derived from the saliva of Desmodus rotundus vampire bat, antagonizes vascular tPA-induced neurotoxicity by competitively binding to low-density lipoprotein related-receptors (LPR) at the blood-brain barrier (BBB) interface, minimizing the tPA uptake into brain parenchyma. tPA can also activate matrix metalloproteinases (MMPs), a family of endopeptidases comprised of 24 mammalian enzymes that primarily catalyze the turnover and degradation of the extracellular matrix (ECM). MMPs have been implicated in BBB breakdown and neuronal injury in the early times after stroke, but also contribute to vascular remodeling, angiogenesis, neurogenesis and axonal regeneration during the later repair phase after stroke. tPA, directly or by activation of MMP-9, could have beneficial effects on recovery after stroke by promoting neurovascular repair through vascular endothelial growth factor (VEGF). However, any treatment regimen directed at MMPs must consider their pleiotropic nature and the likelihood of either beneficial or detrimental effects that might depend on the timing of the treatment in relation to the stage of brain injury.

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.

Clinical pharmacological issues in the development of acute stroke therapies

The demonstration of the ischaemic penumbra in animal models and the effectiveness of reperfusion therapy in humans led to considerable optimism for neuroprotection in acute stroke. Initial experience with failure of phase II and III trials led to the STAIR recommendations for pre-clinical and clinical studies. Review of pre-clinical studies suggests that selection of agents for clinical development may not have been optimal. The neuroprotective agent NXY-059 fulfilled pre-clinical and many clinical STAIR criteria but a second large phase III study failed to demonstrate any benefit. Many of the STAIR criteria have not been fulfilled in the development of recent neuroprotective agents. Other issues not addressed include the use of animal models more reflective of older stroke patients with physiological derangement, demonstration of drug distribution to the proposed site of action in humans, selection of patients with salvageable tissue, achieving very early treatment, refinement of measurement of neurological impairment and disability, and physiological optimization in proof of concept human studies. Increasing the number and quality of clinical centres undertaking acute stroke research, use of surrogate imaging markers and adaptive dose designs in phase II trials could improve the likelihood of identifying an effective neuroprotective. Neuroprotection in acute stroke remains a significant challenge but has not been clearly shown to be ineffective. Given the profound burden of stroke and limited applicability of reperfusion to currently at best 10% patients, further proof of concept studies of neuroprotection remain indicated with careful review of pre-clinical data and more rigorous phase II trial design.

Neuronal plasticity and functional recovery after ischemic stroke

Ischemic stroke affects many new patients each year. The sequelae of brain ischemia can include lasting sensorimotor and cognitive deficits, which negatively impact quality of life. Currently, treatment options for improving poststroke deficits are limited, and the development of new clinical alternatives to improve functional recovery after stroke is actively under investigation. Anti-Nogo-A immunotherapy to reduce the central nervous system inhibitory environment, cell transplantation strategies, pharmacological agents, and movement-based therapies represent emerging treatments of poststroke deficits through enhancement of neuroanatomical plasticity.

Neuroprotection for ischemic stroke: past, present and future

Neuroprotection for ischemic stroke refers to strategies, applied singly or in combination, that antagonize the injurious biochemical and molecular events that eventuate in irreversible ischemic injury. There has been a recent explosion of interest in this field, with over 1000 experimental papers and over 400 clinical articles appearing within the past 6 years. These studies, in turn, are the outgrowth of three decades of investigative work to define the multiple mechanisms and mediators of ischemic brain injury, which constitute potential targets of neuroprotection. Rigorously conducted experimental studies in animal models of brain ischemia provide incontrovertible proof-of-principle that high-grade protection of the ischemic brain is an achievable goal. Nonetheless, many agents have been brought to clinical trial without a sufficiently compelling evidence-based pre-clinical foundation. At this writing, around 160 clinical trials of neuroprotection for ischemic stroke have been initiated. Of the approximately 120 completed trials, two-thirds were smaller early-phase safety-feasibility studies. The remaining one-third were typically larger (>200 subjects) phase II or III trials, but, disappointingly, only fewer than one-half of these administered neuroprotective therapy within the 4-6h therapeutic window within which efficacious neuroprotection is considered to be achievable. This fact alone helps to account for the abundance of "failed" trials. This review presents a close survey of the most extensively evaluated neuroprotective agents and classes and considers both the strengths and weakness of the pre-clinical evidence as well as the results and shortcomings of the clinical trials themselves. Among the agent-classes considered are calcium channel blockers; glutamate antagonists; GABA agonists; antioxidants/radical scavengers; phospholipid precursor; nitric oxide signal-transduction down-regulator; leukocyte inhibitors; hemodilution; and a miscellany of other agents. Among promising ongoing efforts, therapeutic hypothermia, high-dose human albumin therapy, and hyperacute magnesium therapy are considered in detail. The potential of combination therapies is highlighted. Issues of clinical-trial funding, the need for improved translational strategies and clinical-trial design, and "thinking outside the box" are emphasized.

Improving outcome after stroke: overcoming the translational roadblock

Stroke poses a massive burden of disease, yet we have few effective therapies. The paucity of therapeutic options stands contrary to intensive research efforts. The failure of these past investments demands a thorough re-examination of the pathophysiology of ischaemic brain injury. Several critical areas hold the key to overcoming the translational roadblock: (1) vascular occlusion: current recanalization strategies have limited effectiveness and may have serious side effects; (2) complexity of stroke pathobiology: therapy must acknowledge the 'Janus-faced' nature of many stroke targets and must identify endogenous neuroprotective and repair mechanisms; (3) inflammation and brain-immune-system interaction: inflammation contributes to lesion expansion, but is also instrumental in lesion containment and repair; stroke outcome is modulated by the interaction of the injured brain with the immune system; (4) regeneration: the potential of the brain for reorganization, plasticity and repair after injury is much greater than previously thought; (5) confounding factors, long-term outcome and predictive modelling. These 5 areas are linked on all levels and therefore need to be tackled by an integrative approach and innovative therapeutic strategies.

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.

Neuroprotection in mice by NGP1-01 after transient focal brain ischemia

The effect of the polycyclic cage amine NGP1-01, a dual action antagonist at both L-type calcium channels and NMDA receptors, was measured after transient (1 h) focal cerebral ischemia in the mouse middle cerebral artery occlusion (MCAO) model. Mice were left untreated, or received NGP1-01 (20 mg/kg per dose intraperitoneally), memantine (20 mg/kg per dose intraperitoneally), or vehicle (DMSO) at 15 min, 24 h and 48 h after reperfusion. Sensorimotor function was tested daily for two weeks using the "corner test", a proven paradigm for the assessment of functional integrity in rodents. NGP1-01 significantly reduced sensorimotor deficits over the 2-week period (p<0.001, ANOVA). Although memantine was less effective than NGP1-01 (p<0.05), it still significantly attenuated sensorimotor deficits in the animals. In a separate study, brain damage 3 days after stroke was determined histologically in mice receiving no treatment, DMSO, or NGP1-01 (dosages and dosage schedule same as above). Serial brain sections were stained for nonviable neurons with Fluoro-Jade B and the volume of damaged tissue was estimated. NGP1-01 treated mice had a significantly lower volume of brain damage (13+/-7 mm(3), p<0.01) than both control groups (no treatment: 47+/-4 mm(3), DMSO: 50+/-10 mm(3)). In conclusion, at weight-equivalent doses, NGP1-01 was at least as neuroprotective as the established NMDA receptor antagonist memantine. It may be a promising lead structure for the development of novel multiple-action drugs in treating ischemic stroke and other neurodegenerative diseases with an excitotoxic component.

Harnessing hypoxic adaptation to prevent, treat, and repair stroke

The brain demands oxygen and glucose to fulfill its roles as the master regulator of body functions as diverse as bladder control and creative thinking. Chemical and electrical transmission in the nervous system is rapidly disrupted in stroke as a result of hypoxia and hypoglycemia. Despite being highly evolved in its architecture, the human brain appears to utilize phylogenetically conserved homeostatic strategies to combat hypoxia and ischemia. Specifically, several converging lines of inquiry have demonstrated that the transcription factor hypoxia-inducible factor-1 (HIF1-1) mediates the activation of a large cassette of genes involved in adaptation to hypoxia in surviving neurons after stroke. Accordingly, pharmacological or molecular approaches that engage hypoxic adaptation at the point of one of its sensors (e.g., inhibition of HIF prolyl 4 hydroxylases) leads to profound sparing of brain tissue and enhanced recovery of function. In this review, we discuss the potential mechanisms that could subserve protective and restorative effects of augmenting hypoxic adaptation in the brain. The strategy appears to involve HIF-dependent and HIF-independent pathways and more than 70 genes and proteins activated transcriptionally and post-transcriptionally that can act at cellular, local, and system levels to compensate for oxygen insufficiency. The breadth and depth of this homeostatic program offers a hopeful alternative to the current pessimism towards stroke therapeutics.

Pathophysiology of ischaemic stroke: insights from imaging, and implications for therapy and drug discovery

Preventing death and limiting handicap from ischaemic stroke are major goals that can be achieved only if the pathophysiology of infarct expansion is properly understood. Primate studies showed that following occlusion of the middle cerebral artery (MCA)--the most frequent and prototypical stroke, local tissue fate depends on the severity of hypoperfusion and duration of occlusion, with a fraction of the MCA territory being initially in a 'penumbral' state. Physiological quantitative PET imaging has translated this knowledge in man and revealed the presence of considerable pathophysiological heterogeneity from patient to patient, largely unpredictable from elapsed time since onset or clinical deficit. While these observations underpinned key trials of thrombolysis, they also indicate that only patients who are likely to benefit should be exposed to its risks. Accordingly, imaging-based diagnosis is rapidly becoming an essential component of stroke assessment, replacing the clock by individually customized management. Diffusion- and perfusion-weighted MR (DWI-PWI) and CT-based perfusion imaging are increasingly being used to implement this, and are undergoing formal validation against PET. Beyond thrombolysis per se, knowledge of the individual pathophysiology also guides management of variables like blood pressure, blood glucose and oxygen saturation, which can otherwise precipitate the penumbra into the core, and the oligaemic tissue into the penumbra. We propose that future therapeutic trials use physiological imaging to select the patient category that best matches the drug's presumed mode of action, rather than lumping together patients with entirely different pathophysiological patterns in so-called 'large trials', which have all failed so far.

Neuroprotection in cerebral infarction: the opportunity of new studies

Therapeutic options in the acute phase of a stroke are limited despite a great number of neuroprotectant drugs that have been developed in the last few decades. Although neuroprotection has been proved in animal models, translation of experimental efficacy into clinical benefit in humans is a difficult task. With the aim of bringing closer laboratory and clinical results, a change and unification of the methodology used is needed. Evaluating neuroprotectant capacity to salvage the penumbra using MRI both in animals and humans as a surrogate outcome can help to select drugs more likely to demonstrate clinical benefit. In addition, neuroprotection should enlarge the window of opportunity for reperfusion therapies and protect vascular structures to reduce reperfusion injury and the clinical complications related to thrombolytic treatment. A better understanding of ischemic and restorative brain mechanisms beyond the acute phase of stroke may open new therapeutic options to improve stroke recovery.

Poxvirus-derived cytokine response modifier A (CrmA) does not protect against focal cerebral ischemia in mice

In ischemic stroke, cytosolic death pathways are activated in injured neurons destined to die. Neuronal injury is modulated by cell surface receptors, among which the tumor necrosis factor receptor family obtained particular interest. Cytokine response modifier A (CrmA) is a cowpox virus-derived caspase inhibitor, which interferes with the so-called death-inducing signaling complex, thereby blocking receptor-mediated apoptosis. To elucidate CrmA's therapeutic potential in ischemic stroke, we characterized a transgenic mouse line expressing CrmA under a Thy1 promoter, which we subjected to intraluminal middle cerebral artery (MCA) occlusion. Using in situ hybridization histochemistry and Western blots, we show that the crmA gene integrated into chromosome 8 of the mouse genome, CrmA being expressed in the cerebral cortex and striatum. Although robustly expressed, transgenic CrmA did not influence ischemic injury, both when relatively long-lasting (90 min) and mild (30 min) MCA occlusions were imposed. As such, neither infarct volume, brain swelling or neurological deficits following 90-min ischemia, nor disseminated neuronal injury or caspase-3 activation following 30-min ischemia were influenced by CrmA. Our data argue against a therapeutic effect of CrmA in ischemic stroke.

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.

Role of Lipids in Brain Injury and Diseases

Lipid metabolism is of particular interest due to its high concentration in CNS. The importance of lipids in cell signaling and tissue physiology is demonstrated by many CNS disorders and injuries that involve deregulated metabolism. The long suffering lipid field is gaining reputation and respect as evidenced through the Center of Biomedical Research Excellence in Lipidomics and Pathobiology (COBRE), Lipid MAPS (Metabolites And Pathways Strategy) Consortium sponsored by NIH, European initiatives for decoding the lipids through genomic approaches, and Genomics of Lipid-associated Disorder (GOLD) project initiated by Austrian government. This review attempts to provide an overview of the lipid imbalances associated with neurological disorders (Alzheimer's, Parkinson's; Niemann-Pick; Multiple sclerosis, Huntington, amyotrophic lateral sclerosis, schizophrenia, bipolar disorders and epilepsy) and CNS injury (Stroke, traumatic brain injury; and spinal cord injury) and a few provocative thoughts. Lipidomic analyses along with RNA silencing will provide new insights into the role of lipid intermediates in cell signaling and hopefully open new avenues for prevention or treatment options.