Why do neuroprotective drugs that are so promising in animals fail in the clinic? An industry perspective

Neuroprotection against supra-lethal 'stroke in a dish' insults by an anti-excitotoxic receptor antagonist cocktail

The goal of this study was to identify cocktails of drugs able to protect cultured rodent cortical neurons against increasing durations of oxygen-glucose deprivation (OGD). As expected, a cocktail composed of an NMDA and AMPA receptor antagonists and a voltage gated Ca²⁺ channel blocker (MK-801, CNQX and nifedipine, respectively) provided complete neuroprotection against mild OGD. Increasingly longer durations of OGD necessitated increasing the doses of MK-801 and CNQX, until these cocktails ultimately failed to provide neuroprotection against supra-lethal OGD, even at maximal drug concentrations. Surprisingly, supplementation of any of these cocktails with blockers of TRPM7 channels for increasing OGD durations was not neuroprotective, unless these blockers possessed the ability to inhibit NMDA receptors. Supplementation of the maximally effective cocktail with other NMDA receptor antagonists augmented neuroprotection, suggesting insufficient NMDAR blockade by MK-801. Substitution of MK-801 in cocktails with high concentrations of a glycine site NMDA receptor antagonist caused the greatest improvements in neuroprotection, with the more potent SM-31900 superior to L689,560. Substitution of CQNX in cocktails with AMPA receptor antagonists at high concentrations also improved neuroprotection, particularly with the combination of SYM 2206 and NBQX. The most neuroprotective cocktail was thus composed of SM-31900, SYM2206, NBQX, nifedipine and the antioxidant trolox. Thus, the cumulative properties of antagonist potency and concentration in a cocktail dictate neuroprotective efficacy. The central target of supra-lethal OGD is excitotoxicity, which must be blocked to the greatest extent possible to minimize ion influx.

Cordycepin confers long-term neuroprotection via inhibiting neutrophil infiltration and neuroinflammation after traumatic brain injury

Background

The secondary injury caused by traumatic brain injury (TBI), especially white matter injury (WMI), is highly sensitive to neuroinflammation, which further leads to unfavored long-term outcomes. Although the cross-talk between the three active events, immune cell infiltration, BBB breakdown, and proinflammatory microglial/macrophage polarization, plays a role in the vicious cycle, its mechanisms are not fully understood. It has been reported that cordycepin, an extract from Cordyceps militaris, can inhibit TBI-induced neuroinflammation although the long-term effects of cordycepin remain unknown. Here, we report our investigation of cordycepin’s long-term neuroprotective function and its underlying immunological mechanism.

Methods

TBI mice model was established with a controlled cortical impact (CCI) method. Cordycepin was intraperitoneally administered twice daily for a week. Neurological outcomes were assessed by behavioral tests, including grid walking test, cylinder test, wire hang test, and rotarod test. Immunofluorescence staining, transmission electron microscopy, and electrophysiology recording were employed to assess histological and functional lesions. Quantitative-PCR and flow cytometry were used to detect neuroinflammation. The tracers of Sulfo-NHS-biotin and Evans blue were assessed for the blood-brain barrier (BBB) leakage. Western blot and gelatin zymography were used to analyze protein activity or expression. Neutrophil depletion in vivo was performed via using Ly6G antibody intraperitoneal injection.

Results

Cordycepin administration ameliorated long-term neurological deficits and reduced neuronal tissue loss in TBI mice. Meanwhile, the long-term integrity of white matter was also preserved, which was revealed in multiple dimensions, such as morphology, histology, ultrastructure, and electrical conductivity. Cordycepin administration inhibited microglia/macrophage pro-inflammatory polarization and promoted anti-inflammatory polarization after TBI. BBB breach was attenuated by cordycepin administration at 3 days after TBI. Cordycepin suppressed the activities of MMP-2 and MMP-9 and the neutrophil infiltration at 3 days after TBI. Moreover, neutrophil depletion provided a cordycepin-like effect, and cordycepin administration united with neutrophil depletion did not show a benefit of superposition.

Conclusions

The long-term neuroprotective function of cordycepin via suppressing neutrophil infiltration after TBI, thereby preserving BBB integrity and changing microglia/macrophage polarization. These findings provide significant clinical potentials to improve the quality of life for TBI patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02188-x.

Biomonitoring and Digital Data Technology as an Opportunity for Enhancing Animal Study Translation

The failure of animal studies to translate to effective clinical therapeutics has driven efforts to identify underlying cause and develop solutions that improve the reproducibility and translatability of preclinical research. Common issues revolve around study design, analysis, and reporting as well as standardization between preclinical and clinical endpoints. To address these needs, recent advancements in digital technology, including biomonitoring of digital biomarkers, development of software systems and database technologies, as well as application of artificial intelligence to preclinical datasets can be used to increase the translational relevance of preclinical animal research. In this review, we will describe how a number of innovative digital technologies are being applied to overcome recurring challenges in study design, execution, and data sharing as well as improving scientific outcome measures. Examples of how these technologies are applied to specific therapeutic areas are provided. Digital technologies can enhance the quality of preclinical research and encourage scientific collaboration, thus accelerating the development of novel therapeutics.

Functional Behavior of the Primary Cortical Neuronal Cells on the Large Surface of TiO₂ and SnO₂ Based Biosensing Device

In this study, we report the fabrication of poly-L-lysine (PLL) coated large surface TiO₂ and SnO₂ based biosensing devices to analyze the influence of the functional behaviour of primary cortical neuronal cells. Through frequency-dependent impedance study, we observed an increase in the impedance values initially most likely due to cell adhesion, proliferation and differentiation processes leading to an increase in both the single-cell mass as well as overall cellular mass; however, it got decreased eventually with the progression of various other cellular functions including neural activity, synapse formation and neuron-neuron communication. Typically, formation and regulation of the neuronal junction i.e., synapses noticeably affected the functional behaviour of the fabricated biosensing device by increasing the neuronal communication and thereby improving the flow of current by altering the thin film resistance and capacitance. Further, the neuro-electrical phenomenon is validated by fitting the experimental impedance data to an equivalent electrical circuit model. A significant shift in the Nyquist plot was also observed visually, which indicates that this alternation is primarily due to change in characteristic behaviour of the fabricated biosensing device. Hence, we anticipate that the fabricated PLL coated large surface TiO₂ and SnO₂ based biosensing device can serve as a promising tool to monitor the influence of the functional behaviour of neuronal cells.

Building Robustness into Translational Research

Nonclinical studies form the basis for the decision whether to take a therapeutic candidate into the clinic. These studies need to exhibit translational robustness for both ethical and economic reasons. Key findings confirmed in multiple species have a greater chance to also occur in humans. Given the heterogeneity of patient populations, preclinical studies or at least programs comprising multiple studies need to reflect such heterogeneity, e.g., regarding strains, sex, age, and comorbidities of experimental animals. However, introducing such heterogeneity requires larger studies/programs to maintain statistical power in the face of greater variability. In addition to classic sources of bias, e.g., related to lack of randomization and concealment, translational studies face specific sources of potential bias such as that introduced by a model that may not reflect the full spectrum of underlying pathophysiology in patients, that defined by timing of treatment, or that implied in dosing decisions and interspecies differences in pharmacokinetic profiles. The balance of all these factors needs to be considered carefully for each study and program.

Ischaemic stroke

There are about 25.7 million stroke survivors worldwide. Ischaemic stroke remains the most common type of stroke. Numerous modifiable risk factors have been identified, including behaviors such as cigarette smoking and sedentary lifestyle and treatable medical comorbidities such as hypertension, hyperlipidemia and atrial fibrillation. Once considered irreversible, acute ischaemic stroke is now amenable to acute medical and endovascular therapies to reduce infarct volume. Many advances are expected in the years to come, particularly in the areas of prevention and recovery.

Animal models of hospital-acquired pneumonia: current practices and future perspectives

Lower respiratory tract infections are amongst the leading causes of mortality and morbidity worldwide. Especially in hospital settings and more particularly in critically ill ventilated patients, nosocomial pneumonia is one of the most serious infectious complications frequently caused by opportunistic pathogens. Pseudomonas aeruginosa is one of the most important causes of ventilator-associated pneumonia as well as the major cause of chronic pneumonia in cystic fibrosis patients. Animal models of pneumonia allow us to investigate distinct types of pneumonia at various disease stages, studies that are not possible in patients. Different animal models of pneumonia such as one-hit acute pneumonia models, ventilator-associated pneumonia models and biofilm pneumonia models associated with cystic fibrosis have been extensively studied and have considerably aided our understanding of disease pathogenesis and testing and developing new treatment strategies. The present review aims to guide investigators in choosing appropriate animal pneumonia models by describing and comparing the relevant characteristics of each model using P. aeruginosa as a model etiology for hospital-acquired pneumonia. Key to establishing and studying these animal models of infection are well-defined end-points that allow precise monitoring and characterization of disease development that could ultimately aid in translating these findings to patient populations in order to guide therapy. In this respect, and discussed here, is the development of humanized animal models of bacterial pneumonia that could offer unique advantages to study bacterial virulence factor expression and host cytokine production for translational purposes.

NXY-059: Review of Neuroprotective Potential for Acute Stroke

Objective:

To review available literature on the pharmacology, pharmacokinetics, efficacy, and tolerability of NXY-059, an Investigational agent with a potential role in the treatment of acute stroke.

Data Sources:

Information was obtained from a MEDLINE search (1966–February 2006) of English-language literature utilizing the following search terms: NXY-059, cerovive, nitrones, neuroprotection, free radical trapper, and secondary neurologic injury.

Study Selection and Data Extraction:

Data from animal and human trials were evaluated to summarize the mechanism of action, efficacy, and safety of NXY-059. All published and unpublished trials and abstracts citing NXY-059 were selected.

Data Synthesis:

NXY-059 is an intravenous, nitrone-based, free radical trapping agent in Phase III trials for treatment of acute stroke. In various animal models, NXY-059 has shown reductions in infarct volume and neurologic deficits. Pharmacokinetic studies indicate that NXY-059 displays a predictable pharmacokinetic profile and primarily undergoes renal elimination. Results from 2 Phase II clinical trials showed favorable results for the safety and tolerability of the drug. A recent analysis of one of the Phase III trials showed a statistically significant reduction in the primary outcome of disability after acute stroke in patients who received NXY-059 compared with placebo.

Conclusions:

NXY-059 is a novel agent undergoing worldwide Phase III trials. Initial safety and efficacy data have not revealed any serious adverse events requiring special monitoring and/or precautions, with the exception of drug accumulation in patients with renal insufficiency. The potential benefit of this agent can change the current management algorithm for acute stroke and may represent significant advancement for the care of these patients.

Phytochemicals in Ischemic Stroke

Stroke is the second foremost cause of mortality worldwide and a major cause of long-term disability. Due to changes in lifestyle and an aging population, the incidence of stroke continues to increase and stroke mortality predicted to exceed 12 % by the year 2030. However, the development of pharmacological treatments for stroke has failed to progress much in over 20 years since the introduction of the thrombolytic drug, recombinant tissue plasminogen activator. These alarming circumstances caused many research groups to search for alternative treatments in the form of neuroprotectants. Here, we consider the potential use of phytochemicals in the treatment of stroke. Their historical use in traditional medicine and their excellent safety profile make phytochemicals attractive for the development of therapeutics in human diseases. Emerging findings suggest that some phytochemicals have the ability to target multiple pathophysiological processes involved in stroke including oxidative stress, inflammation and apoptotic cell death. Furthermore, epidemiological studies suggest that the consumption of plant sources rich in phytochemicals may reduce stroke risk, and so reinforce the possibility of developing preventative or neuroprotectant therapies for stroke. In this review, we describe results of preclinical studies that demonstrate beneficial effects of phytochemicals in experimental models relevant to stroke pathogenesis, and we consider their possible mechanisms of action.

Medical Management of Patients with an Acute Stroke: Treatment and Prevention

Stroke is a common and serious disorder and will probably occur with increasing frequency due to an aging of the population. Acute therapies aimed at reversing the effects of acute ischemic stroke are limited to recombinant tissue plasminogen activator administered intravenously within 3 hours of stroke onset. Neuroprotective agents and acute anticoagulation with agents such as heparinoids and heparin are not effective in most cases. Poststroke medical complications such as infection and venous thromboembolism are common but are largely preventable. A variety of medical therapies such as antiplatelet agents, warfarin, statins, and ACE inhibitors can reduce the risk of a recurrent stroke. A key aspect of management for stroke is selection of the proper treatment regimen for each patient.

A more consistent intraluminal rhesus monkey model of ischemic stroke

Endovascular surgery is advantageous in experimentally induced ischemic stroke because it causes fewer cranial traumatic lesions than invasive surgery and can closely mimic the pathophysiology in stroke patients. However, the outcomes are highly variable, which limits the accuracy of evaluations of ischemic stroke studies. In this study, eight healthy adult rhesus monkeys were randomized into two groups with four monkeys in each group: middle cerebral artery occlusion at origin segment (M1) and middle cerebral artery occlusion at M2 segment. The blood flow in the middle cerebral artery was blocked completely for 2 hours using the endovascular microcoil placement technique (1 mm × 10 cm) (undetachable), to establish a model of cerebral ischemia. The microcoil was withdrawn and the middle cerebral artery blood flow was restored. A reversible middle cerebral artery occlusion model was identified by hematoxylin-eosin staining, digital subtraction angiography, magnetic resonance angiography, magnetic resonance imaging, and neurological evaluation. The results showed that the middle cerebral artery occlusion model was successfully established in eight adult healthy rhesus monkeys, and ischemic lesions were apparent in the brain tissue of rhesus monkeys at 24 hours after occlusion. The rhesus monkeys had symptoms of neurological deficits. Compared with the M1 occlusion group, the M2 occlusion group had lower infarction volume and higher neurological scores. These experimental findings indicate that reversible middle cerebral artery occlusion can be produced with the endovascular microcoil technique in rhesus monkeys. The M2 occluded model had less infarction and less neurological impairment, which offers the potential for application in the field of brain injury research.

De-Risking of Stilbazulenyl Nitrone (STAZN), a Lipophilic Nitrone to Treat Stroke Using a Unique Panel of In Vitro Assays

In the present study, we used a comprehensive panel of in vitro assays to evaluate the efficacy and safety of stilbazulenyl nitrone (STAZN) as a lead compound to treat acute ischemic stroke. First, we measured neuroprotection in vitro using two different HT22 hippocampal nerve cell assays. Secondly, to de-risk drug development, we used CeeTox analysis with the H4IIE rat hepatoma cell line to determine the acute toxicity profile of STAZN. Third, STAZN was tested in microsomes from four species for measures of metabolic stability. Last, we determined the Ames test genotoxicity profile of STAZN using Salmonella typhimurium TA989 and TA100. In vitro, STAZN was neuroprotective against toxicity induced by iodoacetic acid, and oxytosis-induced glutathione depletion was initiated by glutamate, with an EC(50) value of 1-5 μM. Secondly, using CeeTox analysis, the estimated C(Tox) value (i.e., sustained concentration expected to produce toxicity in a rat 14-day repeat dose study) for STAZN was calculated to be 260 μM. Third, the half-life of STAZN in humans, dogs, and rats was 60-78 min. Last, the genotoxicity profile showed that STAZN did not induce bacterial colony growth under any conditions tested, indicating the lack of mutagenicity with this compound. STAZN appears to be a multi-target neuroprotective compound that has an excellent safety profile in both the CeeTox and Ames mutagenicity assays. STAZN may have significant potential as a novel neuroprotective agent to treat stroke and should be pursued in clinically relevant embolic stroke models.

CeeTox™ Analysis of CNB-001 a Novel Curcumin-Based Neurotrophic/Neuroprotective Lead Compound to Treat Stroke: Comparison with NXY-059 and Radicut

In the present study, we used a comprehensive cellular toxicity (CeeTox) analysis panel to determine the toxicity profile for CNB-001 [4-((1E)-2-(5-(4-hydroxy-3-methoxystyryl-)-1-phenyl-1H-pyrazoyl-3-yl)vinyl)-2-methoxy-phenol)], which is a hybrid molecule created by combining cyclohexyl bisphenol A, a molecule with neurotrophic activity and curcumin, a spice with neuro-protective activity. CNB-001 is a lead development compound since we have recently shown that CNB-001 has significant preclinical efficacy both in vitro and in vivo. In this study, we compared the CeeTox profile of CNB-001 with two neuroprotective molecules that have been clinically tested for efficacy: the hydrophilic free radical spin trap agent NXY-059 and the hydrophobic free radical scavenger edaravone (Radicut). CeeTox analyses using a rat hepatoma cell line (H4IIE) resulted in estimated C(Tox) value (i.e., sustained concentration expected to produce toxicity in a rat 14-day repeat dose study) of 42 μM for CNB-001 compared with >300 μM for both NXY-059 and Radicut. The CeeTox panel suggests that CNB-001 produces some adverse effects on cellular adenosine triphosphate content, membrane toxicity, glutathione content, and cell mass (or number), but only with high concentrations of the drug. After a 24-h exposure, the drug concentration that produced a half-maximal response (TC(50)) on the measures noted above ranges from 55 to 193 μM. Moreover, all CNB-001-induced changes in the markers were coincident with loss of cell number, prior to acute cell death as measured by membrane integrity, suggesting a cytostatic effect of CNB-001. NXY-059 and Radicut did not have acute toxic effects on H4IIE cells. We also found that CNB-001 resulted in an inhibition of ethoxyresorufin-o-deethylase activity, indicating that the drug may affect cytochrome P4501A activity and that CNB-001 was metabolically unstable using a rat microsome assay system. For CNB-001, an estimated in vitro efficacy/toxicity ratio is 183-643-fold, suggesting that there is a significant therapeutic safety window for CNB-001 and that it should be further developed as a novel neuroprotective agent to treat stroke.

Progesterone and cerebral ischaemia: the relevance of ageing

Cerebral stroke is a leading cause of long-term disability and a major cause of death in the developed world. The total incidence of stroke is projected to rise substantially over the next 20 years as a result of the rising elderly population. Although age is one of the most significant prognostic markers for poor outcome after stroke, very few experimental studies have been conducted in aged animals. Importantly, sex differences in both vulnerability to stroke and outcome after cerebral ischaemia have frequently been reported and attributed to the action of steroid hormones. Progesterone is a candidate neuroprotective factor for stroke, although the majority of pre-clinical studies have focused on using young, healthy adult animals. In terms of cerebral stroke, males and postmenopausal females represent the groups at highest risk of cerebral stroke and these categories can be modelled using either aged or ovariectomised female animals. In this review, we discuss the importance of conducting experimental studies in aged animals compared to young, healthy animals, as well as the impact this has on experimental outcomes. In addition, we focus on reviewing the studies that have been conducted to date examining the neuroprotective potential of progesterone in aged animals. Importantly, the limited studies that have been conducted in aged animals do lend further support to progesterone as a therapeutic option after ischaemic stroke that warrants further investigation.

Pathogenesis of acute stroke and the role of inflammasomes

Inflammation is an innate immune response to infection or tissue damage that is designed to limit harm to the host, but contributes significantly to ischemic brain injury following stroke. The inflammatory response is initiated by the detection of acute damage via extracellular and intracellular pattern recognition receptors, which respond to conserved microbial structures, termed pathogen-associated molecular patterns or host-derived danger signals termed damage-associated molecular patterns. Multi-protein complexes known as inflammasomes (e.g. containing NLRP1, NLRP2, NLRP3, NLRP6, NLRP7, NLRP12, NLRC4, AIM2 and/or Pyrin), then process these signals to trigger an effector response. Briefly, signaling through NLRP1 and NLRP3 inflammasomes produces cleaved caspase-1, which cleaves both pro-IL-1β and pro-IL-18 into their biologically active mature pro-inflammatory cytokines that are released into the extracellular environment. This review will describe the molecular structure, cellular signaling pathways and current evidence for inflammasome activation following cerebral ischemia, and the potential for future treatments for stroke that may involve targeting inflammasome formation or its products in the ischemic brain.

NADPH Oxidase as a Therapeutic Target for Neuroprotection against Ischaemic Stroke: Future Perspectives

Oxidative stress caused by an excess of reactive oxygen species (ROS) is known to contribute to stroke injury, particularly during reperfusion, and antioxidants targeting this process have resulted in improved outcomes experimentally. Unfortunately these improvements have not been successfully translated to the clinical setting. Targeting the source of oxidative stress may provide a superior therapeutic approach. The NADPH oxidases are a family of enzymes dedicated solely to ROS production and pre-clinical animal studies targeting NADPH oxidases have shown promising results. However there are multiple factors that need to be considered for future drug development: There are several homologues of the catalytic subunit of NADPH oxidase. All have differing physiological roles and may contribute differentially to oxidative damage after stroke. Additionally, the role of ROS in brain repair is largely unexplored, which should be taken into consideration when developing drugs that inhibit specific NADPH oxidases after injury. This article focuses on the current knowledge regarding NADPH oxidase after stroke including in vivo genetic and inhibitor studies. The caution required when interpreting reports of positive outcomes after NADPH oxidase inhibition is also discussed, as effects on long term recovery are yet to be investigated and are likely to affect successful clinical translation.

Re-orientation of clinical research in traumatic brain injury: report of an international workshop on comparative effectiveness research

During the National Neurotrauma Symposium 2010, the DG Research of the European Commission and the National Institutes of Health/National Institute of Neurological Disorders and Stroke (NIH/NINDS) organized a workshop on comparative effectiveness research (CER) in traumatic brain injury (TBI). This workshop reviewed existing approaches to improve outcomes of TBI patients. It had two main outcomes: First, it initiated a process of re-orientation of clinical research in TBI. Second, it provided ideas for a potential collaboration between the European Commission and the NIH/NINDS to stimulate research in TBI. Advances in provision of care for TBI patients have resulted from observational studies, guideline development, and meta-analyses of individual patient data. In contrast, randomized controlled trials have not led to any identifiable major advances. Rigorous protocols and tightly selected populations constrain generalizability. The workshop addressed additional research approaches, summarized the greatest unmet needs, and highlighted priorities for future research. The collection of high-quality clinical databases, associated with systems biology and CER, offers substantial opportunities. Systems biology aims to identify multiple factors contributing to a disease and addresses complex interactions. Effectiveness research aims to measure benefits and risks of systems of care and interventions in ordinary settings and broader populations. These approaches have great potential for TBI research. Although not new, they still need to be introduced to and accepted by TBI researchers as instruments for clinical research. As with therapeutic targets in individual patient management, so it is with research tools: one size does not fit all.

On the importance of long-term functional assessment after stroke to improve translation from bench to bedside

Despite extensive research efforts in the field of cerebral ischemia, numerous disappointments came from the translational step. Even if experimental studies showed a large number of promising drugs, most of them failed to be efficient in clinical trials. Based on these reports, factors that play a significant role in causing outcome differences between animal experiments and clinical trials have been identified; and latest works in the field have tried to discard them in order to improve the scope of the results. Nevertheless, efforts must be maintained, especially for long-term functional evaluations. As observed in clinical practice, animals display a large degree of spontaneous recovery after stroke. The neurological impairment, assessed by basic items, typically disappears during the firsts week following stroke in rodents. On the contrary, more demanding sensorimotor and cognitive tasks underline other deficits, which are usually long-lasting. Unfortunately, studies addressing such behavioral impairments are less abundant. Because the characterization of long-term functional recovery is critical for evaluating the efficacy of potential therapeutic agents in experimental strokes, behavioral tests that proved sensitive enough to detect long-term deficits are reported here. And since the ultimate goal of any stroke therapy is the restoration of normal function, an objective appraisal of the behavioral deficits should be done.

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.

Exploring new routes for neuroprotective drug development in traumatic brain injury

Worldwide, traumatic brain injury (TBI) is a major cause of mortality and morbidity with a substantial predicted increase in incidence. Despite an obvious need, there are no pharmacological treatment options for TBI because translation of neuroprotection from preclinical studies to clinical practice has so far failed. Here, we identify potential causes for this failure. We suggest that the monitoring and investigation tools that are commonly used in patients with TBI may provide an experimental medicine route to facilitate a more rational approach to translational research. This suggestion is underpinned by existing research data on disease biology, drug delivery, and treatment response obtained with these methods.

The site of embolization related to infarct size, oedema and clinical outcome in a rat stroke model - further translational stroke research

Background and purpose

Reliable models are essential for translational stroke research to study the pathophysiology of ischaemic stroke in an effort to find therapies that may ultimately reduce oedema, infarction and mortality in the clinic. The purpose of this study was to investigate the relation between the site of arterial embolization and the subsequent oedema, infarction and clinical outcome in a rat embolic stroke model.

Methods

Thirty-six male Sprague-Dawley rats were thromboembolized into the internal carotid artery. The site of occlusion was demonstrated by arteriography. Following histological preparation and evaluation, the size of the hemispheres and the infarcts were measured by quantitative histology and planimetry. Another parallel stroke model study was subsequently examined to investigate if the conclusions from the first study could be applied to the second study.

Results

The median size of the infarct was 40% of the ipsilateral hemisphere in both the 19 animals with occlusion localised to the intracranial part of the internal carotid artery and in the 11 animals where the main trunk of the middle cerebral artery was occluded. In 5 animals, occlusion of the extracranial part of the internal carotid artery resulted in significantly smaller infarcts compared to other groups (p < 0.01). Another independent study re-confirmed these results. Furthermore, significant correlations (R > 0.76, p < 0.0001) were found between 1) cortical, subcortical, and total infarct volumes, 2) oedema in percent of the left hemisphere, 3) clinical score before termination and 4) postoperative weight loss.

Conclusions

Distal occlusions of the intracranial part of the internal carotid or middle cerebral arteries resulted in comparable large sized infarctions and oedema. This indicates that investigators do not need a similar number of such occlusions in each experimental group. Contrary to observations in the clinic, distal internal carotid artery occlusions did not result in worse outcome than middle cerebral stem occlusions, but this finding may be explained by the controlled emboli size in this experimental stroke model.

Glutamate receptor ion channels: structure, regulation, and function

The mammalian ionotropic glutamate receptor family encodes 18 gene products that coassemble to form ligand-gated ion channels containing an agonist recognition site, a transmembrane ion permeation pathway, and gating elements that couple agonist-induced conformational changes to the opening or closing of the permeation pore. Glutamate receptors mediate fast excitatory synaptic transmission in the central nervous system and are localized on neuronal and non-neuronal cells. These receptors regulate a broad spectrum of processes in the brain, spinal cord, retina, and peripheral nervous system. Glutamate receptors are postulated to play important roles in numerous neurological diseases and have attracted intense scrutiny. The description of glutamate receptor structure, including its transmembrane elements, reveals a complex assembly of multiple semiautonomous extracellular domains linked to a pore-forming element with striking resemblance to an inverted potassium channel. In this review we discuss International Union of Basic and Clinical Pharmacology glutamate receptor nomenclature, structure, assembly, accessory subunits, interacting proteins, gene expression and translation, post-translational modifications, agonist and antagonist pharmacology, allosteric modulation, mechanisms of gating and permeation, roles in normal physiological function, as well as the potential therapeutic use of pharmacological agents acting at glutamate receptors.

The adhesive removal test: a sensitive method to assess sensorimotor deficits in mice

Long-term functional deficits after a brain injury are difficult to assess in the mouse. If no deficit is observed, researchers could conclude either that the animal has fully recovered or that the tests they used were not appropriate or sensitive enough to the modality of the deficits. We present here a detailed protocol describing how to conduct an adhesive removal test for this species. It consists of applying adhesive tape on each forepaw of the animal and measuring the time-to-contact and the time-to-remove them. This behavior implies correct paw and mouth sensitivity (time-to-contact) and correct dexterity (time-to-remove). To decrease interindividual differences, we recommend a training session (1 week, 1 trial per day) before surgical procedures so that mice to reach optimal performances.

Evidence for neuroprotection by the fenamate NSAID, mefenamic acid

Fenamate NSAIDs are inhibitors of cyclooxygenases, antagonists of non-selective cation channels, subtype-selective modulators of GABA(A) receptors, weak inhibitors of glutamate receptors and activators of some potassium channels. These pharmacological actions are all implicated in the pathogenesis of ischemic stroke. The aim of this study was to investigate the hypothesis that the fenamate, mefenamic acid, is neuroprotective in an in vitro and in vivo model of stroke. Embryonic rat hippocampal neurons were cultured and maintained for up to 14 days in vitro. At 9 or 14 days, cells were exposed to glutamate (5microM) or glutamate (5microM) plus mefenamic acid (10-100microM) or the control agent, MK-801 (10microM) for 10min. 24h later, cell death was determined by measuring lactate dehydrogenase (LDH) levels in the culture media. In vivo, male Wistar rats (300-350g) were subjected to 2h middle cerebral artery occlusion (MCAO) followed by 24h reperfusion. Animals received either a single i.v. dose of MFA (10mg/kg or 30mg/kg), or MK-801 (2mg/kg) or saline prior to MCAO or, four equal doses of MFA (20mg/kg) at 1h intervals beginning 1h prior to MCAO. Ischemic damage was then assessed 24h after MCAO. In vitro, mefenamic acid (10-100microM) and MK-801 (10microM) significantly reduced glutamate-evoked cell death compared with control cultures. In vivo, MFA (20mg/kgx4) significantly reduced infarct volume, total ischemic brain damage and edema by 53% (p< or =0.02), 41% (p< or =0.002) and 45% (p< or =0.002) respectively. Furthermore, mefenamic acid reduced cerebral edema when measured as a function of brain water content. MK-801 was also neuroprotective against MCAO brain injury. This study demonstrates a significant neuroprotective effect by a fenamate NSAID against glutamate-induced cell toxicity, in vitro and against ischemic stroke in vivo. Further experiments are currently addressing the mechanism(s) of this neuroprotection.

Permanent middle cerebral artery occlusion in sheep: a novel large animal model of focal cerebral ischemia

As effective stroke treatment by thrombolysis is bound to a narrow time window excluding most patients, numerous experimental treatment strategies have been developed to gain new options for stroke treatment. However, all approaches using neuroprotective agents that have been successfully evaluated in rodents have subsequently failed in clinical trials. Existing large animal models are of significant scientific value, but sometimes limited by ethical drawbacks and mostly do not allow for long-term observation. In this study, we are introducing a simple, but reliable stroke model using permanent middle cerebral artery occlusion in sheep. This model allows for control of ischemic lesion size and subsequent neurofunctional impact, and it is monitored by behavioral phenotyping, magnetic resonance imaging, and positron emission tomography. Neuropathologic and (immuno)histologic investigations showed typical ischemic lesion patterns whereas commercially available antibodies against vascular, neuronal, astroglial, and microglial antigens were feasible for ovine brain specimens. Based on absent mortality in this study and uncomplicated species-appropriate housing, long-term studies can be realized with comparatively low expenditures. This model could be used as an alternative to existing large animal models, especially for longitudinal analyses of the safety and therapeutic impact of novel therapies in the field of translational stroke research.

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 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.

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.

Anesthetic-mediated protection/preconditioning during cerebral ischemia

Cerebral ischemia is a multi-faceted neurodegenerative pathology that causes cellular injury to neurons within the central nervous system. In light of the underlying mechanisms being elucidated, clinical trials to find possible neuroprotectants to date have failed, thus highlighting the need for new putative targets to offer protection. Recent evidence has clearly shown that anesthetics can confer significant protection and or induce a preconditioning effect against cerebral ischemia-induced injury. This review will focus on the putative protection/preconditioning that is afforded by anesthetics, their possible interaction with GABA(A) and glutamate receptors and two-pore potassium channels. In addition, the interaction with inflammatory, apoptotic and underlying molecular (particularly immediately early genes and inducible nitric oxide synthase etc) pathways, the activation of K(ATP) channels and the ability to provide lasting protection will also be addressed.

Bench to bedside: the quest for quality in experimental stroke research

Over the past decades, great progress has been made in clinical as well as experimental stroke research. Disappointingly, however, hundreds of clinical trials testing neuroprotective agents have failed despite efficacy in experimental models. Recently, several systematic reviews have exposed a number of important deficits in the quality of preclinical stroke research. Many of the issues raised in these reviews are not specific to experimental stroke research, but apply to studies of animal models of disease in general. It is the aim of this article to review some quality-related sources of bias with a particular focus on experimental stroke research. Weaknesses discussed include, among others, low statistical power and hence reproducibility, defects in statistical analysis, lack of blinding and randomization, lack of quality-control mechanisms, deficiencies in reporting, and negative publication bias. Although quantitative evidence for quality problems at present is restricted to preclinical stroke research, to spur discussion and in the hope that they will be exposed to meta-analysis in the near future, I have also included some quality-related sources of bias, which have not been systematically studied. Importantly, these may be also relevant to mechanism-driven basic stroke research. I propose that by a number of rather simple measures reproducibility of experimental results, as well as the step from bench to bedside in stroke research may be made more successful. However, the ultimate proof for this has to await successful phase III stroke trials, which were built on basic research conforming to the criteria as put forward in this article.

Mechanisms of action of green tea catechins, with a focus on ischemia-induced neurodegeneration

Catechins are dietary polyphenolic compounds associated with a wide variety of beneficial health effects in vitro, in vivo and clinically. These therapeutic properties have long been attributed to the catechins' antioxidant and free radical scavenging effects. Emerging evidence has shown that catechins and their metabolites have many additional mechanisms of action by affecting numerous sites, potentiating endogenous antioxidants and eliciting dual actions during oxidative stress, ischemia and inflammation. Catechins have proven to modulate apoptosis at various points in the sequence, including altering expression of anti- and proapoptotic genes. Their anti-inflammatory effects are activated through a variety of different mechanisms, including modulation of nitric oxide synthase isoforms. Catechins' actions of attenuating oxidative stress and the inflammatory response may, in part, account for their confirmed neuroprotective capabilities following cerebral ischemia. The versatility of the mechanisms of action of catechins increases their therapeutic potential as interventions for numerous clinical disorders. However, more epidemiological and clinical studies need to be undertaken for their efficacy to be fully elucidated.

Aprotinin decreases the incidence of cognitive deficit following CABG and cardiopulmonary bypass: a pilot randomized controlled study

PURPOSE

Cognitive deficit after coronary artery bypass surgery (CABG) has a high prevalence and is persistent. Meta-analysis of clinical trials demonstrates a decreased incidence of stroke after CABG when aprotinin is administrated perioperatively. We hypothesized that aprotinin administration would decrease the incidence of cognitive deficit after CABG.

METHODS

Thirty-six ASA III-IV patients undergoing elective CABG were included in a prospective, randomized, single-blinded pilot study. Eighteen patients received aprotinin 2 x 10(6) KIU (loading dose), 2 x 10(6) KIU (added to circuit prime) and a continuous infusion of 5 x 10(5) KIU.hr(-1). A battery of cognitive tests was administered to patients and spouses (n = 18) the day before surgery, four days and six weeks postoperatively.

RESULTS

Four days postoperatively new cognitive deficit (defined by a change in one or more cognitive domains using the Reliable Change Index method) was present in ten (58%) patients in the aprotinin group compared to 17 (94%) in the placebo group [95% confidence interval (CI) 0.10-0.62, P = 0.005); (P = 0.01)]. Six weeks postoperatively, four (23%) patients in the aprotinin group had cognitive deficit compared to ten (55%) in the placebo group (95% CI 0.80-0.16, P = 0.005); (P = 0.05).

CONCLUSION

In this prospective pilot study, the incidence of cognitive deficit after CABG and cardiopulmonary bypass is decreased by the administration of high-dose aprotinin.

NXY-059: a neuroprotective agent in acute stroke

Free radicals play an important role in secondary processes in ischaemic brain injury. Disodium 4-[(tert-butylimino) methyl] benzene-1,3-disulphonate N-oxide (NXY-059) is a nitrone-based free radical trapping agent. Findings from animal stroke models showed that NXY-059 is a potent neuroprotective agent that has a large window of therapeutic opportunity and long-lasting effects. Therefore, NXY-059 may be used as a monotherapy agent for treatment of acute stroke. NXY-059 may also be used as an adjunct agent to thrombolytic therapy, as it can reduce tissue plasminogen activator-induced haemorrhage in ischaemic stroke.

Coadministration of NXY-059 and tenecteplase six hours following embolic strokes in rabbits improves clinical rating scores

Currently, the only FDA-approved treatment for acute ischemic stroke (AIS) is the thrombolytic, tissue plasminogen activator (tPA; alteplase; activase). It has been proposed that both the spin trap agent NXY-059 (cerovive) and tenecteplase (TNK-tPA), which are currently in phase II clinical trials, may also be useful for the treatment of ischemic stroke. However, there is little information available concerning the dose-response profiles or therapeutic window for NXY-059 in a validated embolic stroke model, nor is there information available pertaining to the effects of combining NXY-059 with tenecteplase. Thus, we determined the pharmacological profile of NXY-059 on behavioral outcome following small clot embolic strokes in rabbits when administered alone or in combination with tenecteplase. Male New Zealand white rabbits were embolized by injecting a suspension of small blood clots into cerebral circulation via a carotid catheter. NXY-059 (0.1-100 mg/kg) was infused intravenously (IV), 1 h following embolization, whereas control rabbits received infusions of saline. We also determined the therapeutic window for NXY-059 by administering the drug 1, 3, or 6 h following embolic strokes. Lastly, in combination studies, NXY-059 was given concomitantly with tenecteplase 1 or 6 h following embolization. In the vehicle control group, the P(50) value (milligrams of clots that produce behavioral deficits in 50% of the rabbits) measured 24 h following embolism was 1.20 +/- 0.15 mg, and this was increased by 100-134% if NXY-059 (1-100 mg/kg) was administered following embolization. If NXY-059 was administered beginning 3 or 6 h following embolization, there was no significant behavioral improvement. If NXY-059 (100 mg/kg) and tenecteplase (0.9 mg/kg) were administered concomitantly 1 h postembolization, we did not measure any additional behavioral improvement compared to either drug alone. However, if the drugs were administered 6 h following embolization, we measured a statistically significant reduction of behavioral deficits. This study shows that NXY-059 is neuroprotective over a wide range if administered early following an embolic stroke. In addition, the study shows that NXY-059 can be administered in combination with tenecteplase to provide additional behavioral improvement at extended delays following embolization.

Development of the nitrone-based spin trap agent NXY-059 to treat acute ischemic stroke

The only current FDA-approved treatment for acute ischemic stroke is thrombolysis with tissue plasminogen activator (tPA). However, there are numerous shortcomings to tPA treatment including an increased incidence of intracerebral hemorrhage (ICH) and a short therapeutic window (3-6 h). In recent years, studies have attempted to identify new therapeutics that might be neuroprotective following ischemic strokes. Free radical scavenging spin trap agents have been proposed as potential candidates for stroke therapy because of the hypothesized role of free radicals in the progression of stroke and ischemia-induced neurodegeneration. Novel spin trap agents like (disodium-[(tert-butylimino) methyl] benzene-1,3-disulfonate N-oxide (NXY-059) are of particular interest, not only because they are broad-spectrum nitrone-based free radical scavengers, but also because of their safety profile in humans. Moreover, the rationale for developing NXY-059 for the treatment of acute ischemic stroke is further supported by the drug's reported neuroprotective effects. In addition, NXY-059 may represent a useful adjunct stroke therapy to tPA, since preclinical studies have demonstrated that NXY-059 increases the therapeutic window for tPA and lowers the occurrence of tPA-induced ICH.

Neuroprotective effects of MK-801 in different rat stroke models for permanent middle cerebral artery occlusion: adverse effects of hypothalamic damage and strategies for its avoidance

BACKGROUND AND PURPOSE

Permanent middle cerebral artery occlusion (MCAO) with the use of the suture technique causes hypothalamic damage with subsequent hyperthermia, which can confound neuroprotective drug studies. In the present study the neuroprotective effects of dizocilpine (MK-801) were compared in different permanent MCAO models with and without hypothalamic damage and hyperthermia.

METHODS

Sixty Sprague-Dawley rats were treated with MK-801 or placebo, beginning 15 minutes before MCAO, and assigned to the following groups: suture MCAO (group I), macrosphere MCAO without hypothalamic damage (group II), or macrosphere MCAO with intentionally induced hypothalamic infarction (group III). Body temperature was measured at 3, 6, and 24 hours. Lesion size was determined after 24 hours (2,3,5-triphenyltetrazolium chloride staining).

RESULTS

Hypothalamic damage was present in animals in group I and was intentionally induced in group III with the use of a modified macrosphere MCAO technique. Body temperature was significantly increased 3, 6, and 24 hours after MCAO in these 2 groups of animals. Hypothalamic damage and subsequent hyperthermia could be avoided effectively by limiting the number of macrospheres (group II). MK-801 provided a highly significant neuroprotective effect in group II but not in groups I and III.

CONCLUSIONS

Hypothalamic damage with subsequent hyperthermia masked the neuroprotective effect of MK-801. This side effect can be avoided by using the macrosphere MCAO technique with a limited number of spheres. This model therefore may be more appropriate to study the effects of neuroprotective drugs in permanent focal cerebral ischemia than the suture method.

Functional and histological evidence for the protective effect of NXY-059 in a primate model of stroke when given 4 hours after occlusion

BACKGROUND AND PURPOSE

NXY-059 has substantial protective effects when administered immediately after the onset of ischemia in a primate model of stroke. This study examined the efficacy of this drug when administered 4 hours after onset, a more clinically relevant time point.

METHODS

Before surgery, marmosets were trained and tested on a number of neurological tests, which assessed general neurological function, motor ability, and spatial awareness. Four hours after permanent middle cerebral artery occlusion (pMCAO), marmosets received a bolus of saline (n=13) or NXY-059 (n=13), and osmotic minipumps were implanted, providing 48-hour saline or drug (85 micromol/kg per hour) infusion. The monkeys were retested 3 and 10 weeks after surgery. Finally, infarct size was evaluated with histological analysis.

RESULTS

The unbound plasma NXY-059 concentration was 200+/-9 micromol/L after 24-hour infusion, a concentration well tolerated in stroke patients. Drug treatment ameliorated the long-term motor impairment produced by pMCAO; the marmosets were better at using their contralesional, stroke-affected arm than controls at both 3 and 10 weeks. Saline-treated animals had a debilitating spatial neglect at 3 weeks with residual signs evident at 10 weeks. NXY-059 treatment substantially attenuated neglect at 3 weeks, with no deficit being seen at 10 weeks. NXY-059 reduced the overall infarct size by 28% (saline, 324+/-46 mm3; NXY-059, 234+/-30 mm3) with protection to the cortex, white matter, and subcortical structures.

CONCLUSIONS

NXY-059 is an effective neuroprotective agent when administered 4 hours after pMCAO in a primate species, attenuating both motor and spatial neglect. The compound also substantially lessened the volume of cerebral damage.

Animal models of stroke: do they have value for discovering neuroprotective agents?

There has been a series of high-profile failures of drugs in clinical trials of acute ischaemic stroke that were designed to meet criteria necessary for drug regulatory approval. This has, again, called into question the value of animal models for identifying effective neuroprotective agents. Here, we review evidence that physiological changes (reperfusion, hyperglycaemia, hypothermia and blood pressure) produce comparable changes in outcome in both animal models and human stroke patients, which indicates that the models should identify clinically effective neuroprotective agents. We suggest that most clinical failures have occurred because compounds were administered differently in animal and clinical studies. We review earlier guidelines on the information that is necessary from preclinical studies before a compound enters clinical trials, and propose modifications to these guidelines.

Assessment of cognitive and motor deficits in a marmoset model of stroke

The Stroke Therapy Academic Industry Roundtable noted the need for standardized, well-accepted primate models of stroke to help develop both neuroprotective and restorative therapies. One primate model has been developed using the marmoset, a small New World species of monkey, in which long-term functional deficits can be assessed. The surgery and postoperative care of the animals is described, as well as the behavioral tests used to quantify the postoperative disability. The types of deficits seen are illustrated by reference to some of the findings with neuroprotective treatments. Nevertheless, the long-term nature and consistency of the motor deficits make this model ideal for assessing the worth of restorative therapies.

Oxidative stress in neurodegenerative diseases: therapeutic implications for superoxide dismutase mimetics

Evidence of oxidative stress is apparent in both acute and chronic neurodegenerative diseases, such as stroke, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Increased generation of reactive oxygen species simply overwhelm endogenous antioxidant defences, leading to subsequent oxidative damage and cell death. Tissue culture and animal models have been developed to mimic some of the biochemical changes and neuropathology found in these diseases. In doing so, it has been experimentally demonstrated that oxidative stress plays a critical role in neuronal cell death. Antioxidant enzymes, such as superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) have demonstrated therapeutic efficacy in models of neurodegeneration. However, delivery and stability issues have reduced the enthusiasm to clinically develop these proteins. Most recently, SOD mimetics, small molecules which mimic the activity of endogenous superoxide dismutase, have come to the forefront of antioxidant therapeutics. This review will examine the experimental evidence supporting the use of scavengers of superoxide anions in treating some neurodegenerative diseases, such as stroke, PD and ALS, but also the pitfalls that have met antioxidant molecules in clinical trials.