Recommendations and practices to optimize stroke therapy: developing effective translational research programs

Uric Acid Stroke Cerebroprotection Transcended Sex, Age, and Comorbidities in a Multicenter Preclinical Trial

BACKGROUND

Past failures in translating stroke cerebroprotection provoked calls for a more rigorous methodological approach, leading to the stroke preclinical assessment network SPAN (Stroke Preclinical Assessment Network), where uric acid (UA) treatment exceeded a prespecified efficacy boundary for the primary functional outcome. Still, successful translation to humans requires confirmation of the effect of UA across key biological variables relevant to patients with stroke.

METHODS

We measured the effects of intravenous UA treatment (16 mg/kg) versus intravenous saline in groups of animals enrolled in the SPAN network with diverse comorbidities, sex, and age. The masked study drug or placebo was administered during reperfusion in rodents undergoing a transient middle cerebral artery filament occlusion. The primary outcome was the modified corner test index at day 30 poststroke, and numerous secondary outcomes were collected. A modified intention-to-treat population was used in the analysis. We tested for any interactions with sex, age, and comorbidities (obesity-induced hyperglycemia and hypertension).

RESULTS

In total, 710 animals were randomized to receive either intravenous UA or saline. After accounting for procedural dropouts and exclusions from treatment, a total of 687 animals were qualified and analyzed, including 458 assigned to UA and 229 to intravenous saline control. UA-treated animals exhibited a better primary functional outcome at day 30 (probability, 0.56 [95% CI, 0.52-0.60]; P=0.006). UA-treated animals also had a better corner test index at day 7 (probability, 0.55 [95% CI, 0.5-0.59]; P=0.035) and a higher survival rate at day 30 (hazard ratio, 1.41 [95% CI, 1.08-1.83]; P=0.011). Brain morphometry at day 2 and 30 was comparable between the treatment groups. The improved functional outcome and survival in UA-treated animals were preserved across different species, sexes, ages, and comorbidities.

CONCLUSIONS

UA provides ischemic stroke cerebroprotection across key relevant biological variables, making it a promising intervention to be further tested in human clinical trials.

Are researchers moving away from animal models as a result of poor clinical translation in the field of stroke? An analysis of opinion papers

Objectives

Despite decades of research using animals to develop pharmaceutical treatments for patients who have had a stroke, few therapeutic options exist. The vast majority of interventions successful in preclinical animal studies have turned out to have no efficacy in humans or to be harmful to humans. In view of this, we explore whether there is evidence of a move away from animal models in this field.

Methods

We used an innovative methodology, the analysis of opinion papers. Although we took a systematic approach to literature searching and data extraction, this is not a systematic review because the study involves the synthesis of opinions, not research evidence. Data were extracted from retrieved papers in chronological order and analysed qualitatively and descriptively.

Results

Eighty eligible papers, published between 1979 and 2018, were identified. Most authors were from academic departments of neurology, neuroscience or stroke research. Authors agreed that translational stroke research was in crisis. They held diverse views about the causes of this crisis, most of which did not fundamentally challenge the use of animal models. Some, however, attributed the translational crisis to animal–human species differences and one to a lack of human in vitro models. Most of the proposed solutions involved fine-tuning animal models, but authors disagreed about whether such modifications would improve translation. A minority suggested using human in vitro methods alongside animal models. One proposed focusing only on human in vitro methods.

Conclusion

Despite recognising that animal models have been unsuccessful in the field of stroke, most researchers exhibited a strong resistance to relinquishing them. Nevertheless, there is an emerging challenge to the use of animal models, in the form of human-focused in vitro approaches. For the sake of stroke patients there is an urgent need to revitalise translational stroke research and explore the evidence for these new approaches.

CNB-001 reduces paraplegia in rabbits following spinal cord ischemia

Spinal cord ischemia associated with trauma and surgical procedures including thoraco-abdominal aortic aneurysm repair and thoracic endovascular aortic repair results in devastating clinical deficits in patients. Because spinal cord ischemia is inadequately treated, we studied the effects of [4-((1E)-2-(5-(4-hydroxy-3-methoxystyryl-)-1-phenyl-1H-pyrazoyl-3-yl) vinyl)-2-methoxy-phenol)] (CNB-001), a novel curcumin-based compound, in a rabbit SCI model. CNB-001 is known to inhibit human 5-lipoxygenase and 15-lipoxygenase and reduce the ischemia-induced inflammatory response. Moreover, CNB-001 can reduce the level of oxidative stress markers and potentiate brain-derived neurotrophic factor and brain-derived neurotrophic factor receptor signaling. The Tarlov scale and quantal analysis technique results revealed that CNB-001 administered as an intravenous dose (bolus) 30 minutes prior to spinal cord ischemia improved the behaviors of female New Zealand White rabbits. The improvements were similar to those produced by the uncompetitive N-methyl-D-aspartate receptor antagonist memantine. At 48 hours after aortic occlusion, there was a 42.7% increase (P < 0.05) in tolerated ischemia duration (n = 14) for rabbits treated with CNB-001 (n = 16), and a 72.3% increase for rabbits treated with the positive control memantine (P < 0.05) (n = 23) compared to vehicle-treated ischemic rabbits (n = 22). CNB-001 is a potential important novel treatment for spinal cord ischemia induced by aortic occlusion. All experiments were approved by the CSMC Institutional Animal Care and Use Committee (IACUC #4311) on November 1, 2012.

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

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

Sustained (S)-roscovitine delivery promotes neuroprotection associated with functional recovery and decrease in brain edema in a randomized blind focal cerebral ischemia study

Stroke is a devastating disorder that significantly contributes to death, disability and healthcare costs. In ischemic stroke, the only current acute therapy is recanalization, but the narrow therapeutic window less than 6 h limits its application. The current challenge is to prevent late cell death, with concomitant therapy targeting the ischemic cascade to widen the therapeutic window. Among potential neuroprotective drugs, cyclin-dependent kinase inhibitors such as (S)-roscovitine are of particular relevance. We previously showed that (S)-roscovitine crossed the blood-brain barrier and was neuroprotective in a dose-dependent manner in two models of middle cerebral artery occlusion (MCAo). According to the Stroke Therapy Academic Industry Roundtable guidelines, the pharmacokinetics of (S)-roscovitine and the optimal mode of delivery and therapeutic dose in rats were investigated. Combination of intravenous (IV) and continuous sub-cutaneous (SC) infusion led to early and sustained delivery of (S)-roscovitine. Furthermore, in a randomized blind study on a transient MCAo rat model, we showed that this mode of delivery reduced both infarct and edema volume and was beneficial to neurological outcome. Within the framework of preclinical studies for stroke therapy development, we here provide data to improve translation of pre-clinical studies into successful clinical human trials.

Vasomodulatory effects of the angiotensin II type 1 receptor antagonist losartan on experimentally induced cerebral vasospasm after subarachnoid haemorrhage

BACKGROUND

Cerebral vasospasm following subarachnoid haemorrhage (SAH) remains one of the major factors contributing to poor overall patient outcome. Prostaglandin F2-alpha (PGF2a) induces vasoconstriction. After SAH, PGF2a leads to cerebral inflammation and enhanced vasoconstriction, resulting in cerebral vasospasm. Losartan is already known to have beneficial effects in stroke models and also on several cerebral inflammatory processes. Therefore, the aim of the study was to analyse the effect of losartan on PGF2a-enhanced vasoconstriction after SAH.

METHODS

To investigate the effect of losartan on PGF2a-enhanced vasoconstriction after SAH, cerebral vasospasm was induced by a double-haemorrhage model. Rats were killed on day 3 and 5 after SAH followed by measurement of the isometric force of basilar artery ring segments in an organ bath.

RESULTS

PGF2a induced a dose-dependent contraction. After pre-incubation with losartan, the maximum contraction (E_max) for sham-operated animals was significantly lowered [E_max 6% in losartan 3 × 10^-4 molar (M) vs. 56% without losartan]. Also, after induced SAH, PGF2a induced no vasoconstriction in pre-incubated vessels with losartan 3 × 10^-4 M on day 3 (d3) as well as on day 5 (d5). For the vasorelaxative investigations, vessel segments were pre-incubated with PFG2a. Cumulative application of losartan completely resolved the pre-contraction in sham-operated animals (non SAH: 95% relaxation). After SAH, losartan not only resolved the pre-contraction (d5: 103%), but also exceeded the pre-contraction (d3: 119%). Therefore, a statistically significantly increased and earlier relaxation was calculated for all losartan concentrations [E_max (d3/d5) and pD₂ (d3/d5)] compared with the solvent control group.

CONCLUSION

In a physiological and pathophysiological setup, losartan reduces a PGF2-induced vasoconstriction and reverses a PGF2a-precontraction completely. This fact can be integrated in pushing forward further concepts trying to antagonise/prevent cerebral vasospasm after SAH.

Cytoprotective Drug-Tissue Plasminogen Activator Protease Interaction Assays: Screening of Two Novel Cytoprotective Chromones

Tissue plasminogen activator (tPA) is currently used in combination with endovascular procedures to enhance recanalization and cerebral reperfusion and is also currently administered as standard-of-care thrombolytic therapy to patients within 3-4.5 h of an ischemic stroke. Since tPA is not neuroprotective or cytoprotective, adjuvant therapy with a neuroprotective or an optimized cytoprotective compound is required to provide the best care to stroke victims to maximally promote clinical recovery. In this article, we describe the use of a sensitive standardized protease assay with CH3SO2-D-hexahydrotyrosine-Gly-Arg-p-nitroanilide•AcOH, a chromogenic protease substrate that is cleaved to 4-nitroaniline (p-nitroaniline) and measured spectrophotometrically at 405 nm (OD405 nm), and how the assay can be used as an effective screening assay to study drug-tPA interactions. While we focus on two compounds of interest in our drug development pipeline, the assay is broadly applicable to all small molecule neuroprotective or cytoprotective compounds currently being discovered and developed worldwide. In this present study, we found that the specific tPA inhibitor, plasminogen activator inhibitor-1 (PAI-1; 0.25 μM), significantly (p < 0.0001) inhibited 4-nitroaniline release, by 97.74% during the 10-min duration of the assay, which is indicative of tPA protease inhibition. In addition, two lead chromone cytoprotective candidates, 2-(3',4',5'-trihydroxyphenyl)chromen-4-one (3',4',5'-trihydroxyflavone) (CSMC-19) and 3-hydroxy-2-[3-hydroxy-4-(pyrrolidin-1-yl)phenyl]benzo[h]chromen-4-one (CSMC-140), also significantly (p < 0.05) reduced 4-nitroaniline accumulation, but to a lesser extent. The reduction was 68 and 45%, respectively, at 10 μM, and extrapolated IC50 values were 4.37 and >10 μM for CSMC-19 and CSMC-140, respectively. Using bonafide 4-nitroaniline, we then demonstrated that the reduction of 4-nitroaniline detection was not due to drug-4-nitroaniline quenching of signal detection at OD405 nm. In conclusion, the results suggest that high concentrations of both cytoprotectives reduced 4-nitroaniline production in vitro, but the inhibition only occurs with concentrations 104-1025-fold that of EC50 values in an efficacy assay. Thus, CSMC-19 and CSMC-140 should be further developed and evaluated in embolic stroke models in the absence or presence of a thrombolytic. If necessary, they could be administered once effective tPA thrombolysis has been confirmed to avoid the possibility that the chromone will reduce the efficacy of tPA in patients. Stroke investigator developing new cytoprotective small molecules should consider adding this sensitive assay to their development and screening repertoire to assess possible drug-tPA interactions in vitro as a de-risking step.

Data Standardization and Quality Management

Important questions regarding the conduct of scientific research and data transparency have been raised in various scientific forums over the last 10 years. It is becoming clear, that in spite of published RIGOR guidelines, that improvement in the transparency of scientific research is required to focus on the discovery and drug development process so that a treatment can be provided to stroke patients. We have the unique privilege of conducting research using animal models of a disease so that we can address the development of a new therapy, and we should do this with great care and vigilance. This document identifies valuable resources for researchers to become Good Laboratory Practices compliant and increase and improve data transparency and provides guidelines for accurate data management to continue to propel the translational stroke research field forward while recognizing that there is a shortage of research funds worldwide. While data audits are being considered worldwide by funding agencies and they are used extensively by industry, they are still quite controversial for basic researchers. Due to the special exploratory nature of basic and translational science research, the current challenging funding environment, and independent and individualized laboratory activities, it is debatable if current individualized non-standardized data management and monitoring represents the best approach. Thus, herein, we propose steps to prepare research study data in an acceptable form for archival purposes so that standards for translational research data can be comparable to those that are accepted and adhered to by the clinical community. If all translational research laboratories follow and institute the guidelines while conducting translational research, data from all sources may be more comparable and reliable.

The High Cost of Stroke and Stroke Cytoprotection Research

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

Shining light on the head: Photobiomodulation for brain disorders

Photobiomodulation (PBM) describes the use of red or near-infrared light to stimulate, heal, regenerate, and protect tissue that has either been injured, is degenerating, or else is at risk of dying. One of the organ systems of the human body that is most necessary to life, and whose optimum functioning is most worried about by humankind in general, is the brain. The brain suffers from many different disorders that can be classified into three broad groupings: traumatic events (stroke, traumatic brain injury, and global ischemia), degenerative diseases (dementia, Alzheimer's and Parkinson's), and psychiatric disorders (depression, anxiety, post traumatic stress disorder). There is some evidence that all these seemingly diverse conditions can be beneficially affected by applying light to the head. There is even the possibility that PBM could be used for cognitive enhancement in normal healthy people. In this transcranial PBM (tPBM) application, near-infrared (NIR) light is often applied to the forehead because of the better penetration (no hair, longer wavelength). Some workers have used lasers, but recently the introduction of inexpensive light emitting diode (LED) arrays has allowed the development of light emitting helmets or "brain caps". This review will cover the mechanisms of action of photobiomodulation to the brain, and summarize some of the key pre-clinical studies and clinical trials that have been undertaken for diverse brain disorders.

Nicotinamide mononucleotide inhibits post-ischemic NAD(+) degradation and dramatically ameliorates brain damage following global cerebral ischemia

Nicotinamide adenine dinucleotide (NAD(+)) is an essential cofactor for multiple cellular metabolic reactions and has a central role in energy production. Brain ischemia depletes NAD(+) pools leading to bioenergetics failure and cell death. Nicotinamide mononucleotide (NMN) is utilized by the NAD(+) salvage pathway enzyme, nicotinamide adenylyltransferase (Nmnat) to generate NAD(+). Therefore, we examined whether NMN could protect against ischemic brain damage. Mice were subjected to transient forebrain ischemia and treated with NMN or vehicle at the start of reperfusion or 30min after the ischemic insult. At 2, 4, and 24h of recovery, the proteins poly-ADP-ribosylation (PAR), hippocampal NAD(+) levels, and expression levels of NAD(+) salvage pathway enzymes were determined. Furthermore, animal's neurologic outcome and hippocampal CA1 neuronal death was assessed after six days of reperfusion. NMN (62.5mg/kg) dramatically ameliorated the hippocampal CA1 injury and significantly improved the neurological outcome. Additionally, the post-ischemic NMN treatment prevented the increase in PAR formation and NAD(+) catabolism. Since the NMN administration did not affect animal's temperature, blood gases or regional cerebral blood flow during recovery, the protective effect was not a result of altered reperfusion conditions. These data suggest that administration of NMN at a proper dosage has a strong protective effect against ischemic brain injury.

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

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

Critical early thrombolytic and endovascular reperfusion therapy for acute ischemic stroke victims: a call for adjunct neuroprotection

Today, there is an enormous amount of excitement in the field of stroke victim care due to the recent success of MR. CLEAN, SWIFT PRIME, ESCAPE, EXTEND-IA, and REVASCAT endovascular trials. Successful intravenous (IV) recombinant tissue plasminogen activator (rt-PA) clinical trials [i.e., National Institute of Neurological Disorders and Stroke (NINDS) rt-PA trial, Third European Cooperative Acute Stroke Study (ECASSIII), and Third International Stroke study (IST-3)] also need to be emphasized. In the recent endovascular and thrombolytic trials, there is statistically significant improvement using both the National Institutes of Health Stroke Scale (NIHSS) and the modified Rankin Score (mRS) scale, but neither approach promotes complete recovery in patients enrolled within any particular NIHSS or mRS score tier. Absolute improvement (mRS 0-2 at 90 days) with endovascular therapy is 13.5-31 %, whereas thrombolytics alone also significantly improve patient functional independence, but to a lesser degree (NINDS rt-PA trial 13 %). This article has 3 main goals: (1) first to emphasize the utility and cost-effectiveness of rt-PA to treat stroke; (2) second to review the recent endovascular trials with respect to efficacy, safety, and cost-effectiveness as a stroke treatment; and (3) to further consider and evaluate strategies to develop novel neuroprotective drugs. A thesis will be put forth so that future stroke trials and therapy development can optimally promote recovery so that stroke victims can return to "normal" life.

Pre-differentiation of human neural stem cells into GABAergic neurons prior to transplant results in greater repopulation of the damaged brain and accelerates functional recovery after transient ischemic stroke

INTRODUCTION

Despite attempts to prevent brain injury during the hyperacute phase of stroke, most sufferers end up with significant neuronal loss and functional deficits. The use of cell-based therapies to recover the injured brain offers new hope. In the current study, we employed human neural stem cells (hNSCs) isolated from subventricular zone (SVZ), and directed their differentiation into GABAergic neurons followed by transplantation to ischemic brain.

METHODS

Pre-differentiated GABAergic neurons, undifferentiated SVZ-hNSCs or media alone were stereotaxically transplanted into the rat brain (n=7/group) 7 days after endothelin-1 induced stroke. Neurological outcome was assessed by neurological deficit scores and the cylinder test. Transplanted cell survival, cellular phenotype and maturation were assessed using immunohistochemistry and confocal microscopy.

RESULTS

Behavioral assessments revealed accelerated improvements in motor function 7 days post-transplant in rats treated with pre-differentiated GABAergic cells in comparison to media alone and undifferentiated hNSC treated groups. Histopathology 28 days-post transplant indicated that pre-differentiated cells maintained their GABAergic neuronal phenotype, showed evidence of synaptogenesis and up-regulated expression of both GABA and calcium signaling proteins associated with neurotransmission. Rats treated with pre-differentiated cells also showed increased neurogenic activity within the SVZ at 28 days, suggesting an additional trophic role of these GABAergic cells. In contrast, undifferentiated SVZ-hNSCs predominantly differentiated into GFAP-positive astrocytes and appeared to be incorporated into the glial scar.

CONCLUSION

Our study is the first to show enhanced exogenous repopulation of a neuronal phenotype after stroke using techniques aimed at GABAergic cell induction prior to delivery that resulted in accelerated and improved functional recovery.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Clinical trials in acute ischemic stroke

Acute ischemic stroke (AIS) is a major cause of mortality and disability and remains a serious and significant global health problem. The development of neurovascular protectants to treat AIS successfully has been beset by disappointments and setbacks. Many promising candidates have lacked significant pleiotropic protective activity for brain tissue and cerebral blood vessels in clinical trials, while those with protective activity have had poor bioavailability or high toxicity. Moreover, the majority of agents did not confer significant neurovascular protection or clinical efficacy, as measured by standard behavioral endpoints in clinical trials of heterogeneous populations of patients with AIS. The recombinant tissue plasminogen activator alteplase is approved in many countries for the treatment of AIS in the first 3 h after symptom onset. Many drug candidates have been subject to clinical trials, including those with anti-excitotoxic, anti-inflammatory, antioxidant, antiapoptotic/regenerative, calcium/adrenergic-modulating/antihypertensive, thrombolytic, nootropic/stimulant, fluid regulatory, or oxygen-delivering mechanisms of action. Some agents, such as tenecteplase, edaravone and minocycline, may be approved for global use in the future. This review evaluates almost all neurovascular protectants subject to clinical trial evaluation for the treatment of AIS, and includes 241 studies conducted between 1978 and 2014. The development of agents that reduce brain injury after AIS will require new and different approaches based on a deeper understanding of the pathophysiology of AIS. Moreover, the future treatment for AIS is likely to lie in combination therapy rather than monotherapy. Additional approaches to the testing and use of neurovascular protectants should be considered.