Delayed treatment with an adenosine kinase inhibitor, GP683, attenuates infarct size in rats with temporary middle cerebral artery occlusion

No-reflow after recanalization in ischemic stroke: From pathomechanisms to therapeutic strategies

Endovascular reperfusion therapy is the primary strategy for acute ischemic stroke. No-reflow is a common phenomenon, which is defined as the failure of microcirculatory reperfusion despite clot removal by thrombolysis or mechanical embolization. It has been reported that up to 25% of ischemic strokes suffer from no-reflow, which strongly contributes to an increased risk of poor clinical outcomes. No-reflow is associated with functional and structural alterations of cerebrovascular microcirculation, and the injury to the microcirculation seriously hinders the neural functional recovery following macrovascular reperfusion. Accumulated evidence indicates that pathology of no-reflow is linked to adhesion, aggregation, and rolling of blood components along the endothelium, capillary stagnation with neutrophils, astrocytes end-feet, and endothelial cell edema, pericyte contraction, and vasoconstriction. Prevention or treatment strategies aim to alleviate or reverse these pathological changes, including targeted therapies such as cilostazol, adhesion molecule blocking antibodies, peroxisome proliferator-activated receptors (PPARs) activator, adenosine, pericyte regulators, as well as adjunctive therapies, such as extracorporeal counterpulsation, ischemic preconditioning, and alternative or complementary therapies. Herein, we provide an overview of pathomechanisms, predictive factors, diagnosis, and intervention strategies for no-reflow, and attempt to convey a new perspective on the clinical management of no-reflow post-ischemic stroke.

The role of the ATP-adenosine axis in ischemic stroke

In ischemic stroke, the primary neuronal injury caused by the disruption of energy supply is further exacerbated by secondary sterile inflammation. The inflammatory cascade is largely initiated by the purine adenosine triphosphate (ATP) which is extensively released to the interstitial space during brain ischemia and functions as an extracellular danger signaling molecule. By engaging P2 receptors, extracellular ATP activates microglia leading to cytokine and chemokine production and subsequent immune cell recruitment from the periphery which further amplifies post-stroke inflammation. The ectonucleotidases CD39 and CD73 shape and balance the inflammatory environment by stepwise degrading extracellular ATP to adenosine which itself has neuroprotective and anti-inflammatory signaling properties. The neuroprotective effects of adenosine are mainly mediated through A₁ receptors and inhibition of glutamatergic excitotoxicity, while the anti-inflammatory capacities of adenosine have been primarily attributed to A_2A receptor activation on infiltrating immune cells in the subacute phase after stroke. In this review, we summarize the current state of knowledge on the ATP-adenosine axis in ischemic stroke, discuss contradictory results, and point out potential pitfalls towards translating therapeutic approaches from rodent stroke models to human patients.

Knockdown of circular RNA tousled-like kinase 1 relieves ischemic stroke in middle cerebral artery occlusion mice and oxygen-glucose deprivation and reoxygenation-induced N2a cell damage

Ischemic stroke (IS) is an essential contributor to the neurological morbidity and mortality throughout the world. The significance of circular RNA tousled-like kinase 1 (circTLK1) in IS has been documented. This study set out to explore the mechanism of circTLK1 in IS. Middle cerebral artery occlusion (MCAO) mouse models in vivo and oxygen-glucose deprivation and reoxygenation (OGD/R) cell models in vitro were first established, followed by evaluation of infarct volume and neurological impairment, and cell viability and apoptosis. The expression patterns of circTLK1, miR-26a-5p, phosphatase and tensin homolog (PTEN), insulin-like growth factor type 1 receptor (IGF-1 R), and glucose transporter type 1 (GLUT1) were detected by RT-qPCR and Western blotting. Co-localization of circTLK1 and miR-26a-5p in N2a cells was tested by fluorescence in situ hybridization assay. The binding relationships among circTLK1, PTEN, and miR-26a-5p were verified by dual-luciferase assay and RNA pull-down. circTLK1 and PTEN were highly expressed while miR-26a-5p was under-expressed in IS models. circTLK1 knockdown decreased infarct volume and neurological impairment in MCAO mouse models and relieved OGD/R-induced neuronal injury in vitro. circTLK1 and miR-26a-5p were co-located in the N2a cell cytoplasm. circTLK1 regulated PTEN as a sponge of miR-26a-5p. PTEN positively regulated IGF-1 R and GLUT1 expressions. miR-26a-5p inhibitor annulled the repressive effects of circTLK1 silencing on OGD/R-induced neuronal injury. sh-PTEN partially annulled the effects of the miR-26a-5p inhibitor on OGD/R-induced neuronal injury. In conclusion, circTLK1 knockdown relieved IS via the miR-26a-5p/PTEN/IGF-1 R/GLUT1 axis. These results may provide a new direction to IS potential therapeutic targets.

Gastrodin Alleviates Cerebral Ischaemia/Reperfusion Injury by Inhibiting Pyroptosis by Regulating the lncRNA NEAT1/miR-22-3p Axis

Cerebral ischaemia/reperfusion (I/R) injury-induced irreversible brain injury is a major cause of mortality and functional impairment in ageing people. Gastrodin (GAS), derived from the traditional Chinese herbal medicine Tianma, has been reported to inhibit the progression of stroke, but the mechanism whereby GAS modulates the progression of cerebral I/R remains unclear. The middle cerebral artery occlusion method was used as a model of I/R in vivo. Rats were pretreated with GAS by intraperitoneal injection 7 days before I/R surgery and were then treated with GAS for 7 days after I/R surgery. Additionally, an oxygen-glucose deprivation/reoxygenation model using neuronal cells was established in vitro to simulate I/R injury. 2,3,5-Triphenyltetrazolium chloride and Nissl staining were used to evaluate infarct size and neuronal damage, respectively. Lactate dehydrogenase release and cell counting kit-8 assays were used to assess neuronal cell viability. Enzyme-linked immunosorbent assay, qPCR, flow cytometry and western blotting were performed to analyse the expression levels of inflammatory factors (IL-1β, IL-18), lncRNA NEAT1, miR-22-3p, NLRP3 and cleaved caspase-1. Luciferase reporter experiments were performed to verify the association between lncRNA NEAT1 and miR-22-3p. The results indicated that GAS could significantly improve the neurological scores of rats and reduce the area of cerebral infarction. Meanwhile, GAS inhibited pyroptosis by downregulating NLRP3, inflammatory factors (IL-1β, IL-18) and cleaved caspase-1. In addition, GAS attenuated I/R-induced inflammation in neuronal cells through the modulation of the lncRNA NEAT1/miR-22-3p axis. GAS significantly attenuated cerebral I/R injury via modulation of the lncRNA NEAT1/miR-22-3p axis. Thus, GAS might serve as a new agent for the treatment of cerebral I/R injury.

Caffeine and Its Neuroprotective Role in Ischemic Events: A Mechanism Dependent on Adenosine Receptors

Ischemia is characterized by a transient, insufficient, or permanent interruption of blood flow to a tissue, which leads to an inadequate glucose and oxygen supply. The nervous tissue is highly active, and it closely depends on glucose and oxygen to satisfy its metabolic demand. Therefore, ischemic conditions promote cell death and lead to a secondary wave of cell damage that progressively spreads to the neighborhood areas, called penumbra. Brain ischemia is one of the main causes of deaths and summed with retinal ischemia comprises one of the principal reasons of disability. Although several studies have been performed to investigate the mechanisms of damage to find protective/preventive interventions, an effective treatment does not exist yet. Adenosine is a well-described neuromodulator in the central nervous system (CNS), and acts through four subtypes of G-protein-coupled receptors. Adenosine receptors, especially A₁ and A_2A receptors, are the main targets of caffeine in daily consumption doses. Accordingly, caffeine has been greatly studied in the context of CNS pathologies. In fact, adenosine system, as well as caffeine, is involved in neuroprotection effects in different pathological situations. Therefore, the present review focuses on the role of adenosine/caffeine in CNS, brain and retina, ischemic events.

South (S)- and North (N)-Methanocarba-7-Deazaadenosine Analogues as Inhibitors of Human Adenosine Kinase

Adenosine kinase (AdK) inhibitors raise endogenous adenosine levels, particularly in disease states, and have potential for treatment of seizures, neurodegeneration, and inflammation. On the basis of the South (S) ribose conformation and molecular dynamics (MD) analysis of nucleoside inhibitors bound in AdK X-ray crystallographic structures, (S)- and North (N)-methanocarba (bicyclo[3.1.0]hexane) derivatives of known inhibitors were prepared and compared as human (h) AdK inhibitors. 5'-Hydroxy (34, MRS4202 (S); 55, MRS4380 (N)) and 5'-deoxy 38a (MRS4203 (S)) analogues, containing 7- and N(6)-NH phenyl groups in 7-deazaadenine, robustly inhibited AdK activity (IC50 ∼ 100 nM), while the 5'-hydroxy derivative 30 lacking the phenyl substituents was weak. Docking in the hAdK X-ray structure and MD simulation suggested a mode of binding similar to 5'-deoxy-5-iodotubercidin and other known inhibitors. Thus, a structure-based design approach for further potency enhancement is possible. The potent AdK inhibitors in this study are ready to be further tested in animal models of epilepsy.

Purinergic signalling in brain ischemia

Ischemia is a multifactorial pathology characterized by different events evolving in the time. After ischemia a primary damage due to the early massive increase of extracellular glutamate is followed by activation of resident immune cells, i.e microglia, and production or activation of inflammation mediators. Protracted neuroinflammation is now recognized as the predominant mechanism of secondary brain injury progression. Extracellular concentrations of ATP and adenosine in the brain increase dramatically during ischemia in concentrations able to stimulate their respective specific P2 and P1 receptors. Both ATP P2 and adenosine P1 receptor subtypes exert important roles in ischemia. Although adenosine exerts a clear neuroprotective effect through A1 receptors during ischemia, the use of selective A1 agonists is hampered by undesirable peripheral effects. Evidence up to now in literature indicate that A2A receptor antagonists provide protection centrally by reducing excitotoxicity, while agonists at A2A (and possibly also A2B) and A3 receptors provide protection by controlling massive infiltration and neuroinflammation in the hours and days after brain ischemia. Among P2X receptors most evidence indicate that P2X7 receptor contribute to the damage induced by the ischemic insult due to intracellular Ca(2+) loading in central cells and facilitation of glutamate release. Antagonism of P2X7 receptors might represent a new treatment to attenuate brain damage and to promote proliferation and maturation of brain immature resident cells that can promote tissue repair following cerebral ischemia. Among P2Y receptors, antagonists of P2Y12 receptors are of value because of their antiplatelet activity and possibly because of additional anti-inflammatory effects. Moreover strategies that modify adenosine or ATP concentrations at injury sites might be of value to limit damage after ischemia. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

DDR1 may play a key role in destruction of the blood-brain barrier after cerebral ischemia-reperfusion

Discoidin domain receptor 1 (DDR1) has been shown to mediate matrix metalloproteinase-9 (MMP-9) secretions and degrade all extracellular matrix compounds in mammalian tumor cells. We hypothesized that DDR1 expression will be elevated and the blood-brain barrier (BBB) will be damaged after focal cerebral ischemia in rats. Inhibiting DDR1 expression can alleviate BBB disruption and cerebral ischemic damage via down-regulation of MMP-9 expression and activity. To test our hypothesis, we injected specific DDR1 siRNA into ipsilateral ischemic lateral ventricles in a focal ischemic model. Our results showed that phospho-DDR1 expression increased after ischemia/reperfusion (I/R) injury (p < 0.01). Inactivation of DDR1 by specific siRNA caused a decrease in phospho-DDR1 and MMP-9 expression in the ischemic cortex, reduced stroke-induced infarct volume, and alleviated BBB disruption in rat brain following I/R injury (p < 0.01). Our results suggested that DDR1-siRNA attenuates phospho-DDR1 and MMP-9 upregulation, which was followed by a reduction in infarction and BBB disruption in the ischemic brain after I/R injury. DDR1 may represent a molecular target for the prevention of BBB disruption after cerebral I/R injury.

Natural products from marine organisms with neuroprotective activity in the experimental models of Alzheimer's disease, Parkinson's disease and ischemic brain stroke: their molecular targets and action mechanisms

Continuous increases in the incidence of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and brain stroke demand the urgent development of therapeutics. Marine organisms are well-known producers of natural products with diverse structures and pharmacological activities. Therefore, researchers have endeavored to identify marine natural products with neuroprotective effects. In this regard, this review summarizes therapeutic targets for AD, PD, and ischemic brain stroke and marine natural products with pharmacological activities on the targets according to taxonomies of marine organisms. Furthermore, several marine natural products on the clinical trials for the treatment of neurological disorders are discussed.

Inhibition of adenosine kinase attenuates inflammation and neurotoxicity in traumatic optic neuropathy

Traumatic optic neuropathy (TON) is associated with apoptosis of retinal ganglion cells. Local productions of reactive oxygen species and inflammatory mediators from activated microglial cells have been hypothesized to underlie apoptotic processes. We previously demonstrated that the anti-inflammatory effect of adenosine, through A2A receptor activation had profound protective influence against retinal injury in traumatic optic neuropathy. This protective effect is limited due to rapid cellular re-uptake of adenosine by equilibrative nucleotside transporter-1 (ENT1) or break down by adenosine kinase (AK), the key enzyme in adenosine clearance pathway. Further, the use of adenosine receptors agonists are limited by systemic side effects. Therefore, we seek to investigate the potential role of amplifying the endogenous ambient level of adenosine by pharmacological inhibition of AK. We tested our hypothesis by comparing TON-induced retinal injury in mice with and without ABT-702 treatment, a selective AK inhibitor (AKI). The retinal-protective effect of ABT-702 was demonstrated by significant reduction of Iba-1, ENT1, TNF-α, IL-6, and iNOS/nNOS protein or mRNA expression in TON as revealed by western blot and real time PCR. TON-induced superoxide anion generation and nitrotyrosine expression were reduced in ABT-702 treated mice retinal sections as determined by immunoflourescence. In addition, ABT-702 attenuated p-ERK1/2 and p-P38 activation in LPS induced activated mouse microglia cells. The results of the present investigation suggested that ABT-702 had a protective role against marked TON-induced retinal inflammation and damage by augmenting the endogenous therapeutic effects of site- and event-specific accumulation of extracellular adenosine.

A microsurgical procedure for middle cerebral artery occlusion by intraluminal monofilament insertion technique in the rat: a special emphasis on the methodology

Introduction

Although there are many experimental studies describing the methodology of the middle cerebral artery occlusion (MCAO) in the literature, only limited data on these distinct anatomical structures and the details of the surgical procedure in a step by step manner. The aim of the present study simply is to examine the surgical anatomy of MCAO model and its modifications in the rat.

Materials and methods

Forty Sprague-Dawley rats were used; 20 during the training phase and 20 for the main study. The monofilament sutures were prepared as described in the literature. All surgical steps of the study were performed under the operating microscope, including insertion of monofilament into middle cerebral artery through the internal carotid artery.

Results

After an extensive training period, we lost two rats in four weeks. The effects of MCAO were confirmed by the evidence of severe motor deficit during the recovery period, and histopathological findings of infarction were proved in all 18 surviving rats.

Conclusion

In this study, a microsurgical guideline of the MCAO model in the rat is provided with the detailed description of all steps of the intraluminal monofilament insertion method with related figures.

Electroacupuncture pretreatment inhibits NADPH oxidase-mediated oxidative stress in diabetic mice with cerebral ischemia

We investigated the protective effect of electroacupuncture (EA) on cerebral ischemic injury in diabetic mice, and explored the role of NADPH oxidase-mediated oxidative stress. Male C57BL/6 mice were injected streptozotocin to induce diabetes. The mice were pretreated with EA at acupoint "Baihui" for 30 min. Two hours after the end of EA pretreatment, focal cerebral ischemia was induced following 24h reperfusion. The neurobehavioral scores and infarction volumes, malondialdehyde (MDA), reactive oxygen species (ROS), and activation of NADPH oxidase were determined in the presence or absence of the NADPH oxidase inhibitor apocynin or activator tetrabromocinnamic acid (TBCA). EA pretreatment reduced infarct size and improved neurological outcomes 24h after reperfusion in the diabetic mice. EA also decreased cerebral MDA and ROS levels compared with the control group, and inhibited the NADPH oxidase activation. The beneficial effects were abolished by TBCA while pretreatment with apocynin mimicked the neuroprotective and anti-oxidative effects of EA. Our results demonstrated that EA attenuated cerebral ischemic injury by inhibiting NAPDH oxidase-mediated oxidative damage in diabetic mice. These results suggest a novel mechanism of EA pretreatment-induced tolerance in diabetic cerebral ischemia.

Improvement of the suture-occluded method in rat models of focal cerebral ischemia-reperfusion

The aim of the present study was to provide a simple method of establishing a rat model for focal cerebral ischemia-reperfusion (FCIR). The suture-occluded method was used to establish FCIR in male Sprague-Dawley rats. An incision was made over the bifurcation of the common carotid artery (CCA), through which a suture was inserted up to the internal carotid artery (ICA). The suture remained in the skin subsequent to model establishment and was withdrawn to the CCA to enable reperfusion. The reliability of the rat model was assessed via analysis of nerve function, tetrazolium (TTC) staining and pathological examination. Following FCIR in rats, the resulting neurological impairments were observed. TTC staining revealed infarcts and pathological examination revealed typical pathological changes. This modified method was simple, reliable and, therefore, may be used to investigate FCIR.

Squalenoyl adenosine nanoparticles provide neuroprotection after stroke and spinal cord injury

There is an urgent need to develop new therapeutic approaches for the treatment of severe neurological trauma, such as stroke and spinal cord injuries. However, many drugs with potential neuropharmacological activity, such as adenosine, are inefficient upon systemic administration because of their fast metabolization and rapid clearance from the bloodstream. Here, we show that conjugation of adenosine to the lipid squalene and the subsequent formation of nanoassemblies allows prolonged circulation of this nucleoside, providing neuroprotection in mouse stroke and rat spinal cord injury models. The animals receiving systemic administration of squalenoyl adenosine nanoassemblies showed a significant improvement of their neurologic deficit score in the case of cerebral ischaemia, and an early motor recovery of the hindlimbs in the case of spinal cord injury. Moreover, in vitro and in vivo studies demonstrated that the nanoassemblies were able to extend adenosine circulation and its interaction with the neurovascular unit. This Article shows, for the first time, that a hydrophilic and rapidly metabolized molecule such as adenosine may become pharmacologically efficient owing to a single conjugation with the lipid squalene.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Regulation of endoplasmic reticulum stress in rat cortex by p62/ZIP through the Keap1-Nrf2-ARE signalling pathway after transient focal cerebral ischaemia

PRIMARY OBJECTIVE

p62/ZIP as the autophagy receptor can transport the misfolded proteins to a macroautophagy-lysosome system for degradation and also create a positive feedback loop between p62/ZIP and Nrf2. However, the role of p62/ZIP on cerebral ischaemia is unclear. The aim of this study was to evaluate the role of p62/ZIP in the regulation of endoplasmic reticulum(ER) stress induced by cerebral ischaemia/reperfusion.

RESEARCH DESIGN

Different ischemic periods were designed by transient middle cerebral artery occlusion (tMCAO) using the suture method.

METHODS AND PROCEDURES

At 24 hours after reperfusion, the ischaemic brain tissue was studied histologically and biochemically for autophagic, ER stress and Keap1-Nrf2-ARE signalling pathway markers.

MAIN OUTCOMES AND RESULTS

Prolongation of ischaemia significantly increased the cortical injury observed in rats and was associated with a gradual increase in the protein expression of ubiquitin-aggregates, Grp78, GADD153/CHOP and p62/ZIP. Autophagy marker Atg12-Atg5 and LC3-PE increased and then decreased. Moreover, p62/ZIP mRNA expression increased and then decreased and was consistent with Nrf2 activation.

CONCLUSIONS

p62/ZIP not only plays a key role in scavenging protein aggregates during autophagy, but it may also be involved in preventing oxidative injury and alleviating ER stress through the Keap1-Nrf2-ARE signalling pathway during cerebral ischaemia/reperfusion injury.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Adenosine kinase: exploitation for therapeutic gain

Adenosine kinase (ADK; EC 2.7.1.20) is an evolutionarily conserved phosphotransferase that converts the purine ribonucleoside adenosine into 5'-adenosine-monophosphate. This enzymatic reaction plays a fundamental role in determining the tone of adenosine, which fulfills essential functions as a homeostatic and metabolic regulator in all living systems. Adenosine not only activates specific signaling pathways by activation of four types of adenosine receptors but it is also a primordial metabolite and regulator of biochemical enzyme reactions that couple to bioenergetic and epigenetic functions. By regulating adenosine, ADK can thus be identified as an upstream regulator of complex homeostatic and metabolic networks. Not surprisingly, ADK dysfunction is involved in several pathologies, including diabetes, epilepsy, and cancer. Consequently, ADK emerges as a rational therapeutic target, and adenosine-regulating drugs have been tested extensively. In recent attempts to improve specificity of treatment, localized therapies have been developed to augment adenosine signaling at sites of injury or pathology; those approaches include transplantation of stem cells with deletions of ADK or the use of gene therapy vectors to downregulate ADK expression. More recently, the first human mutations in ADK have been described, and novel findings suggest an unexpected role of ADK in a wider range of pathologies. ADK-regulating strategies thus represent innovative therapeutic opportunities to reconstruct network homeostasis in a multitude of conditions. This review will provide a comprehensive overview of the genetics, biochemistry, and pharmacology of ADK and will then focus on pathologies and therapeutic interventions. Challenges to translate ADK-based therapies into clinical use will be discussed critically.

M9, a novel region of amino-Nogo-A, attenuates cerebral ischemic injury by inhibiting NADPH oxidase-derived superoxide production in mice

AIMS

In acute stroke, neurological damage is due to oxidative stress and neuronal apoptotic death. This study investigated whether Nogo-A 290-562 residues region (M9), fused to the transduction domain of the HIV trans-activator (TAT) protein, is neuroprotective against cerebral ischemia and the mechanisms.

METHODS

Transient focal cerebral ischemia was induced by middle cerebral artery occlusion in male C57BL/6J mice. TAT-M9, its mutation or vehicle was applied via intraperitoneal injection at the onset of reperfusion. The neurobehavioral scores, infarction volumes, neuronal apoptosis, and the ratio of Bax/Bcl-2 were evaluated. Malondialdehyde (MDA), reactive oxygen species (ROS) levels, and NADPH oxidase activation were measured in the presence or absence of the NADPH oxidase inhibitor apocynin or activator tetrabromocinnamic acid (TBCA).

RESULTS

Immunofluorescence results confirmed that TAT-M9 was transduced into brain parenchyma, and it significantly improved neurological behavior, reduced infarct volumes, protected neuronal cells from apoptosis, inhibited activation of NADPH oxidase, and decreased MDA and ROS contents. Furthermore, apocynin imitated the beneficial effects of TAT-M9, while TBCA abolished them.

CONCLUSIONS

Our results demonstrate that TAT-M9 administration attenuates cerebral ischemia by inhibiting NADPH oxidase-mediated oxidative damage and neuronal apoptosis in mice. TAT-M9 may be a potential treatment for cerebrovascular disease.

Hormesis pervasiveness and its potential implications for pharmaceutical research and development

This mini-review illustrates that hormesis is not only confined to the areas of biochemistry, radiation biology and toxicology, where it is traditionally known, but illustrates, by citing published scientific literature, that it is found across a wide range of biomedical science and clinical medicine such as neuroscience, cardiology and oncology. The use of techniques and technology, including high through-put screening, micro-dosing or phase 0 studies, pharmacometrics and adaptive trial design in the clinic, are proposed to illustrate how acknowledging the potential impact of hormesis throughout different stages of drug discovery and development, including hurdles related to efficacy and safety, could help the pharmaceutical industry address some of its major and frequently mentioned challenges.

Adenosine and stroke: maximizing the therapeutic potential of adenosine as a prophylactic and acute neuroprotectant

Stroke is a leading cause of morbidity and mortality in the United States. Despite intensive research into the development of treatments that lessen the severity of cerebrovascular injury, no major therapies exist. Though the potential use of adenosine as a neuroprotective agent in the context of stroke has long been realized, there are currently no adenosine-based therapies for the treatment of cerebral ischemia and reperfusion. One of the major obstacles to developing adenosine-based therapies for the treatment of stroke is the prevalence of functional adenosine receptors outside the central nervous system. The activities of peripheral immune and vascular endothelial cells are particularly vulnerable to modulation via adenosine receptors. Many of the pathophysiological processes in stroke are a direct result of peripheral immune infiltration into the brain. Ischemic preconditioning, which can be induced by a number of stimuli, has emerged as a promising area of focus in the development of stroke therapeutics. Reprogramming of the brain and immune responses to adenosine signaling may be an underlying principle of tolerance to cerebral ischemia. Insight into the role of adenosine in various preconditioning paradigms may lead to new uses for adenosine as both an acute and prophylactic neuroprotectant.

Post-ischemic blood-brain barrier leakage in rats: one-week follow-up by MRI

Blood-brain barrier (BBB) disruption following ischemia-reperfusion is associated with such devastating consequences as edema and hemorrhagic transformation. Although several earlier reports on BBB disruption after experimental focal cerebral ischemia-reperfusion pointed out a biphasic opening, discrepancies occurred among the results of these studies as to the second opening. Furthermore, rarely was any evaluation longitudinal. We therefore performed repeated dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to monitor BBB permeability to gadopentetate dimeglumine (Gd-DTPA) following 90 min of transient focal cerebral ischemia in a single group of rats (n=10). At five time-points after reperfusion (at 2, 24, 48, 72 h, and 1 week), we estimated the blood-to-brain transfer rate constant (K(i)) of gadolinium with the Patlak plot graphical approach, and calculated contrast enhancement magnitude based on signal intensities of pre- and postcontrast T1-weighted images. Both methods revealed a persistent permeability to gadolinium during the whole experiment. The magnitude of contrast enhancement appeared higher at 1 week than at any of the other time-points (p<0.001), whereas no difference appeared in K(i) estimations when we analyzed the enhancement areas as an entirety. Sub-region K(i) values in a limited cortical area showed a difference at 1 week (p=0.014). The present study confirms that following transient focal cerebral ischemia, BBB leakage to Gd-DTPA is continuous, and during 1 week postreperfusion no BBB closure occurs.

Ischemic stroke in mice and rats

Ischemic stroke occurs most often in the territory of the middle cerebral artery (MCA) in humans. Since its description in rats more than two decades ago, the minimally invasive intraluminal suture occlusion of MCA is an increasingly used model of stroke in both rats and mice due to its ease of inducing ischemia and achieving reperfusion under well-controlled conditions. This method can be used under the guidance of laser-Doppler flowmetry to ascertain the magnitude of occlusion or reperfusion and to decrease the rate of subarachnoid hemorrhage. Ninety minutes of transient ischemia in the territory of MCA results in substantial and reproducible ischemic lesions in both the striatum and the cortex, with characteristics of lesion core and penumbra. Thus, this model is applicable to neuroprotective drug studies, including ischemic brain lesion evaluation (either in vivo with magnetic resonance imaging or post-mortem with brain tissue staining) and neurological status (motor deficits simply assessed by a six-point neurological score scale) as outcome parameters.

Drug therapies for stroke and traumatic brain injury often display U-shaped dose responses: occurrence, mechanisms, and clinical implications

This article explores the occurrence of U-shaped dose responses induced by neuroprotective agents in animal stroke and traumatic brain injury (TBI) screening/preclinical studies. The assessment was stimulated by suggestions that U-shaped dose responses may be common for neuroprotective agents in stroke and TBI models, and its lack of both recognition and understanding may be a factor contributing to the failure of many promising drugs to be protective in clinical trials. Over 30 agents with neuroprotective properties in animal stroke/TBI models were identified that act via U-shaped dose responses in a broad range of experimental protocols. These findings suggest that U-shaped dose responses in animal stroke/TBI models may be a general occurrence and have significant implications for drug discovery, drug development, and clinical practice.

The blood-brain barrier is continuously open for several weeks following transient focal cerebral ischemia

The blood-brain barrier (BBB) is the principal regulator of blood-borne substance entry into the brain parenchyma. Therefore, BBB leakage, which leads to cerebral edema and influx of toxic substances, is common in pathological conditions such as cerebral ischemia, inflammation, trauma, and tumors. The leakage of BBB after ischemia-reperfusion injury has long been considered to be biphasic, although a considerable amount of discrepancies as for the timing of the second opening does exist among the studies. This led us to evaluate systematically and quantitatively the dynamics of BBB leakage in a rat model of 90-min ischemia-reperfusion, using gadolinium-enhanced (small molecule) magnetic resonance imaging and fluorescent dye Evans Blue (large molecule). BBB leakage was assessed at the following time points after reperfusion: 25 min, 2, 4, 6, 12, 18, 24, 36, 48, and 72 h, and 1, 2, 3, 4, and 5 weeks. We observed BBB leakage for both gadolinium and Evans Blue as early as 25 min after reperfusion. Thereafter, BBB remained open for up to 3 weeks for Evans Blue and up to 5 weeks for gadolinium. Our results show that BBB leakage after ischemia-reperfusion injury in the rat is continuous and long-lasting, without any closure up to several weeks. This is the first systematic and extensive study fully demonstrating BBB leakage dynamics following transient brain ischemia and the findings are of major clinical and experimental interest.

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.

Mast cell blocking reduces brain edema and hematoma volume and improves outcome after experimental intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is associated with high mortality and disability, and there is no widely approved clinical therapy. Poor outcome after ICH results mostly from a mass effect owing to enlargement of the hematoma and brain swelling, leading to displacement and disruption of brain structures. Cerebral mast cells (MC) are resident inflammatory cells that are located perivascularly and contain potent vasoactive, proteolytic, and fibrinolytic substances. We previously found pharmacological MC stabilization and genetic MC deficiency to be associated with up to 50% reduction of postischemic brain swelling in rats. Here, we studied the role of MC and MC stabilization in ICH using in vivo magnetic resonance imaging and ex vivo digital imaging for calculating brain edema and hematoma volume. In a rat ICH model of autologous blood injection into the basal ganglia, four groups of Wistar rats received either saline or sodium cromoglycate (MC stabilizer, two groups) or compound 48/80 (MC degranulator). Evaluated 24 h later, MC stabilization had resulted in highly significantly better neurologic scores (P<0.001), decrease mortality (P=0.002), less brain swelling (P<0.001), and smaller hematoma volume growth (P<0.001) compared with saline and compound 48/80. Moreover, to support our hypothesis, we induced ICH in MC-deficient rats and their wild-type littermates (WT). MC-deficient rats responded with significantly better neurologic scores (P<0.001), decrease mortality (0% versus 25%), less brain swelling (P<0.05), and smaller hematoma growth (P<0.05) than WT. The role of MC deserves a close evaluation as a potential target in the development of novel forms of ICH therapy.

Novel Na+-independent and adenine-specific transport system for adenine in primary cultured rat cortical neurons

Endogenous adenine is an important modulator of cell survival and activity in the central nervous system. In the present study, we examined the transport mechanisms for adenine in primary cultured rat cortical neurons and astrocytes. [3H]Adenine was time-dependently taken up into neurons, but not into astrocytes. In kinetic analysis, the [3H]adenine uptake by neurons was observed to be saturable, and an Eadie-Hofstee plot showed that a single component was involved in the uptake, with kinetic parameters of Km=6.09 microM and Vmax=0.340 nmol/mg protein per min. In inhibition assaying by nucleobases and nucleosides, and inhibitors for equilibrative nucleoside transporters, organic ion transporters and peptide transporters, which were reported to transport nucleobases and their analogues, the [3H]adenine uptake by neurons was found to be significantly inhibited by excess concentrations of adenine, hypoxanthine and adenosine, and was greatly reduced only by the addition of adenine. Therefore, it was indicated that adenine in the extracellular fluid in the central nervous system is taken up into neurons, but not into astrocytes, and that neurons may present a novel Na+ -independent and adenine-specific transport system.

Isoflurane tolerance against focal cerebral ischemia is attenuated by adenosine A1 receptor antagonists

PURPOSE

To investigate the role of the adenosine A1 receptor in the rapid tolerance to cerebral ischemia induced by isoflurane preconditioning.

METHODS

Seventy-five rats were randomly assigned into five groups (n = 15 each): Control, 8-cyclopentyl-1,3-dipropulxanthine (DPCPX), Isoflurane, DPCPX+Isoflurane and Vehicle+Isoflurane groups. All animals underwent right middle cerebral artery occlusion (MCAO) for two hours. Isoflurane preconditioning was conducted one hour before MCAO in Isoflurane, DPCPX+Isoflurane and Vehicle+Isoflurane groups by exposing the animals to 1.5% isoflurane in 98% oxygen for one hour. In the Control and DPCPX groups, animals were exposed to 98% oxygen one hour before MCAO for one hour. A selective adenosine A1 receptor antagonist, DPCPX, was administered (0.1 mg x kg(-1)) 15 min before isoflurane/oxygen exposure in the DPCPX and DPCPX+Isoflurane groups to evaluate the effect of adenosine A1 receptor antagonist on isoflurane preconditioning. Dimethyl sulfoxide, the solvent of DPCPX, was administered (1 mL x kg(-1)) 15 min before isoflurane exposure in the Vehicle+Isoflurane group. Neurological deficit scores and brain infarct volumes were evaluated 24 hr after reperfusion.

RESULTS

Animals in the Isoflurane and Vehicle+Isoflurane groups developed lower neurological deficit scores and smaller brain infarct volumes than the Control group (P < 0.01). Animals in the DPCPX+Isoflurane group developed higher neurological deficit scores and larger brain infarct volumes than the Isoflurane and Vehicle+Isoflurane groups (P < 0.01).

CONCLUSION

The present study demonstrates that preconditioning with isoflurane reduces focal cerebral ischemic injury in rats, and the adenosine A1 receptor antagonist (DPCPX) attenuates the neuroprotection induced by isoflurane preconditioning.

The pre-ischaemic neuroprotective effects of the polyamine analogues BU43b and BU36b in permanent and transient focal cerebral ischaemia models in mice

The present study investigated the neuroprotective potential of two novel polyamine analogues, BU43b and BU36b, when administered 30 min prior to cerebral ischaemia. Neuroprotection in a permanent and a transient focal cerebral ischaemia mouse model (induced by intraluminal middle cerebral artery occlusion (MCAO)) was investigated using a range of histological and behavioural assessments. In the permanent ischaemia model, BU43b reduced oedema and showed a trend towards reduction in %HLV (percentage hemisphere lesion volume) when administered at a dose of 30 mg/kg i.p. Following transient ischaemia, treatment with BU43b decreased the %HLV and reduced oedema when administered at 30 mg/kg. BU43b also improved the locomotor activity (LMA) in MCAO mice at both 20 mg/kg and 30 mg/kg doses. BU36b was less effective than BU43b in both the permanent and the transient models, with its most pronounced effect being a trend towards reduction in oedema in both models. These results demonstrate that BU43b administered 30 min before ischaemia provided a good level of neuroprotection in the two models of cerebral ischaemia used and may have potential as a neuroprotective treatment for stroke.

Effect of allopurinol on brain adenosine levels during hypoxia in newborn piglets

Adenosine, a purine nucleoside, is a potent inhibitory neuromodulator in the brain which may provide an important endogenous neuroprotective role during hypoxia-ischemia. Allopurinol, a xanthine oxidase inhibitor, blocks purine degradation and may result in the accumulation of purine metabolites, including adenosine, during hypoxia. The present study determines the effect of allopurinol administration prior to hypoxia on brain levels of adenosine and purine metabolites in the newborn piglet. Twenty-two newborn piglets (age 3-7 days) were studied: 5 untreated normoxic and 6 allopurinol-treated normoxic controls were compared to 5 untreated hypoxic and 6 allopurinol-treated hypoxic animals. Brain tissue energy metabolism was continuously monitored during hypoxia by (31)P NMR spectroscopy. Brain tissue levels of purines increased in both hypoxic groups during hypoxia, however, there were significantly higher increases in brain tissue levels of adenosine (66.5 +/- 30.5 vs. 19.4 +/- 10.7 nmol/gm), P < 0.01 and inosine (265 +/- 97.6 vs. 162.8 +/- 38.3 nmol/gm), P = 0.05 in the allopurinol-treated hypoxic group. Allopurinol inhibits purine degradation under severe hypoxic conditions and results in a significant increase in brain tissue levels of adenosine and inosine. The increased accumulation of CNS adenosine during hypoxia which is seen in the allopurinol-treated animals may potentiate adenosine's intrinsic neuroprotective mechanisms.

Adenosine kinase inhibitors. 5. Synthesis, enzyme inhibition, and analgesic activity of diaryl-erythro-furanosyltubercidin analogues

Adenosine is an endogenous neuromodulator that when produced in the central and the peripheral nervous systems has anticonvulsant, anti-inflammatory, and analgesic properties. However, efforts to use adenosine receptor agonists are plagued by dose-limiting cardiovascular side effects. As an alternative, we explored the use of adenosine kinase inhibitors (AKIs) as potential antiseizure agents and demonstrated an adenosine receptor mediated therapeutic effect in the absence of overt cardiovascular side effects. These activities were associated with elevation of extracellular adenosine concentrations due to inhibition of AK in a site and event specific manner. Several tubercidin based AKIs, including the ribo- and lyxo-furanosyltubercidin analogues as well as the newly discovered erythro-furanosyltubercidin analogues, designed to prevent 5'-O-phosphorylation and associated toxicities, were tested for their analgesic activity in the rat formalin paw model. Described herein are the synthesis, enzyme inhibition structure-activity relationships (SARs) of erythro-furanosyltubercidin analogues, and SARs of analgesic activity of various classes of AKIs. Also reported is the characterization of a lead AKI, 19d (GP3966), an orally bioavailable compound (F% = 60% in dog) which exhibits broad-spectrum analgesic activities (ED50 < or = 4 mg/kg, per os) that are reversible with an adenosine receptor antagonist (theophylline).

Transport mechanisms for adenosine and uridine in primary-cultured rat cortical neurons and astrocytes

Endogenous adenosine and uridine are important modulators of neural survival and activity. In the present study, we examined transport mechanisms of adenosine and uridine in primary-cultured rat cortical neurons, and compared the results for neurons with those for astrocytes. Reverse transcription-polymerase chain reaction identified the mRNAs for ENT1, ENT2, and CNT2, but not CNT1 and CNT3, in neurons and astrocytes. [3H]Adenosine and [3H]uridine were time-, temperature-, and concentration-dependently taken up into neurons and astrocytes. In kinetic analyses, the uptake of both substrates by neurons and astrocytes consisted of two and one, respectively, saturable transport components. The uptake clearance for both substrates by neurons was greater than that by astrocytes. The relative contribution of the high-affinity major component of both substrates to total uptake was estimated to be approximately 80% in neurons. The uptake of [3H]adenosine and [3H]uridine by both neurons and astrocytes was almost entirely Na+-independent, and sensitive to micro, but not nano, molar concentrations of nitrobenzylmercaptopurine riboside, which are transport characteristics of ENT2. Therefore, it was indicated that adenosine and uridine are more efficiently taken up into neurons than into astrocytes, and ENT2 may predominantly contribute to the transport of the nucleosides as a high-affinity transport system in neurons, as in the case of astrocytes.

Indirect activation of adenosine A1 receptors in cultured rat hippocampal neurons by volatile anaesthetics

BACKGROUND AND OBJECTIVE

Volatile anaesthetics depress excitatory signal transmission by potentiating the inhibitory action of GABAA receptors and there is strong evidence that this is related with anaesthesia. Using primary hippocampal cultures we analyzed the possibility that the volatile anaesthetics enflurane and sevoflurane depress excitatory signal transmission by activation of adenosine A1 receptors.

METHODS

Primary rat hippocampal cultures on 4 cm poly-L-lysine coated glass coverslips were loaded with the Ca2+-indicator fluo-3 and incorporated in a gastight, temperature-controlled perfusion chamber. The intracellular Ca2+-concentration was monitored with a confocal laser-scanning microscope (BioRad) using the 488 nm laser line of a krypton-argon laser for excitation and the Lasersharp Acquisition software for analysis.

RESULTS

Continuous perfusion in Mg2+-free medium generated spontaneous synchronized calcium oscillations, which were dose dependently depressed by the volatile anaesthetics enflurane and sevoflurane (0.25-1 minimum alveolar concentration). Addition of 100 nmol of 2-chloro-N6-cyclopentyladenosine, a specific adenosine A1 receptor antagonist, partly reversed the anaesthetic-induced inhibition of the oscillation amplitude of the oscillating cells. The effect of the anaesthetics was mimicked by the addition of S-(p-nitrobenzyl)-6-thioguanosine, an adenosine transport inhibitor and by the addition of 5-amino-5-deoxyadenosine, an inhibitor of adenosine kinase.

CONCLUSIONS

The volatile anaesthetics sevoflurane and enflurane activate adenosine A1 receptors in primary rat hippocampal cultures. This effect is mediated by liberation of adenosine most likely by an interaction of the volatile anaesthetics with adenosine transport or key enzymes in adenosine metabolism.

Neuroprotection by adenosine in the brain: From A(1) receptor activation to A (2A) receptor blockade

Adenosine is a neuromodulator that operates via the most abundant inhibitory adenosine A(1) receptors (A(1)Rs) and the less abundant, but widespread, facilitatory A(2A)Rs. It is commonly assumed that A(1)Rs play a key role in neuroprotection since they decrease glutamate release and hyperpolarize neurons. In fact, A(1)R activation at the onset of neuronal injury attenuates brain damage, whereas its blockade exacerbates damage in adult animals. However, there is a down-regulation of central A(1)Rs in chronic noxious situations. In contrast, A(2A)Rs are up-regulated in noxious brain conditions and their blockade confers robust brain neuroprotection in adult animals. The brain neuroprotective effect of A(2A)R antagonists is maintained in chronic noxious brain conditions without observable peripheral effects, thus justifying the interest of A(2A)R antagonists as novel protective agents in neurodegenerative diseases such as Parkinson's and Alzheimer's disease, ischemic brain damage and epilepsy. The greater interest of A(2A)R blockade compared to A(1)R activation does not mean that A(1)R activation is irrelevant for a neuroprotective strategy. In fact, it is proposed that coupling A(2A)R antagonists with strategies aimed at bursting the levels of extracellular adenosine (by inhibiting adenosine kinase) to activate A(1)Rs might constitute the more robust brain neuroprotective strategy based on the adenosine neuromodulatory system. This strategy should be useful in adult animals and especially in the elderly (where brain pathologies are prevalent) but is not valid for fetus or newborns where the impact of adenosine receptors on brain damage is different.

Adenosine kinase inhibitor attenuates the expression of inducible nitric oxide synthase in glial cells

The present study demonstrates the anti-inflammatory effect of adenosine kinase inhibitor (ADKI) in glial cells. Treatment of glial cells with IC51, an ADKI, stimulated the extracellular adenosine release and reduced the LPS/IFNgamma-mediated production of NO, and induction of iNOS and TNF-alpha gene expression. The recovery of IC51-mediated inhibition of iNOS expression by adenosine transport inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI), and the inhibition of LPS/IFNgamma-induced iNOS gene expression by exogenous adenosine indicate a role for adenosine release in IC51-mediated iNOS expression. The rescue of IC51-mediated inhibition of iNOS expression by adenosine receptor antagonist for A2A, 8-(3-chlorostyryl)caffeine (CSC) and alloxazine for A2B, further supports a role for interaction of adenosine and its receptors in anti-inflammatory activity. The IC51-mediated induction of cAMP levels, downstream target of A2A and A2B, and inhibition of LPS/IFNgamma-induced expression of iNOS by forskolin, a cAMP activator, document a role for cAMP mediated pathway in anti-inflammatory activity of IC51. Taken together, these studies document that IC51-mediated inhibition of iNOS expression is through activation of adenosine receptors, which activates A2A and A2B resulting in increased cAMP levels following LPS/IFNgamma stimulation. Moreover, the lack of effect of IC51 or adenosine on NFkappaB DNA binding activity and its transactivity indicates that the inhibition of iNOS expression mediated by IC51 may be through an NFkappaB independent pathway.

Microsurgical intraluminal middle cerebral artery occlusion model in rodents

OBJECTIVES

Focal brain ischemia induced in rodents by occlusion of the middle cerebral artery (MCA) is a widely used paradigm of human brain infarct. The objective of this study is to compare the effectiveness and reproducibility of MCA filament occlusion model in rats and mice.

MATERIALS AND METHODS

A total of 140 rodents (69 rats and 71 mice) were operated. Ninety-five animals were subjected to MCA occlusion; the surgical procedure consisted of introducing an uncoated surgical nylon monofilament into the cervical common carotid artery (CCA) and advancing it intracranially to permanently block blood flow into the right MCA. Forty-five sham-occluded rodents underwent CCA ligation. Surgical success, autopsy confirmed success and mortality rate were evaluated. Effective MCA occlusion was confirmed by the evidence of motor neurological deficit, by histopathology, immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR). IHC was performed in a randomly selected number of animals to detect the protein product of monocyte chemoattractant protein-1. The brain tissue in mice was examined by RT-PCR for the expression of macrophage inflammatory protein-1 alpha mRNA.

RESULTS

Surgical success rate was 89% in the rats, significantly lower than that in the mice (100%, P < 0.05). Autopsy confirmed success rate in the rats, 60%, was also significantly different from that in the mice (92.5%, P < 0.001). The operative mortality rate was 4.3% in the rats and 15% in the mice.

CONCLUSION

The present study demonstrates that the microsurgical filament occlusion of the MCA can be more successfully performed in mice. The lower rate of success in rats seems to be as a result of the architecture of the carotid canal in this animal. No previous reports, using a considerable number of animals, have compared the feasibility of intraluminal model in the rat with that in the mouse.

Delayed treatment with MLN519 reduces infarction and associated neurologic deficit caused by focal ischemic brain injury in rats via antiinflammatory mechanisms involving nuclear factor-kappaB activation, gliosis, and leukocyte infiltration

Secondary brain injury due to ischemia includes the infiltration of leukocytes into the brain parenchyma mediated by activation of nuclear factor-kappaB (NF-kappaB), which is activated by proteasome degradation. Neuroprotection with the proteasome inhibitor MLN519 has previously been reported to decrease ischemic brain injury in rats. The authors used higher doses of MLN519 to evaluate the neuroprotection therapeutic window after 24 hours of brain injury in rats as correlated to proteasome levels, activated NF-kappaB immunoreactivity, and leukocyte infiltration. Male Sprague-Dawley rats were subjected to 2-hour middle cerebral artery occlusion (MCAO) and recovery. MLN519 or vehicle was administered after injury with a single injection given in delayed increments of 2 hours (i.e., 4, 6, or 8 hours after MCAO). Treatment with MLN519 up to 6 hours after MCAO (4 hours after reperfusion) effectively reduced neuronal and astrocytic degeneration, decreased cortical infarct volume, and increased neurologic recovery. These effects were related to >80% reductions in blood proteasome levels, reduced neutrophil infiltration, and a decrease in activated NF-kappaB immunoreactivity. This improved neuroprotection profile and antiinflammatory effect of MLN519 provides an exciting avenue for potential treatment of focal ischemic brain injury in humans.

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

1. No neuroprotective drug has yet been shown to be effective in treating acute ischaemic stroke in the clinic, despite evidence of efficacy in animal models. 2. An academic/industry round-table group recently published guidelines to be met if a drug was to be progressed to clinical trial. 3. Major points included obtaining full dose-response evaluation and measurement of the therapeutic time window for efficacy, functional behavioural testing in addition to measurement of infarct volume, measurement of physiological parameters, use of appropriate models (transient and permanent focal ischaemia) and reproducibility of data by external laboratories. 4. The present paper examines both failed compounds and disodium 4-[(tert-butylimino) methyl] benzene-1, 3-disulphonate N-oxide (NXY-059), a nitrone radical-trapping agent currently in clinical development. It aims to determine whether these guidelines were met by compounds that have failed and, thus, determine whether following the guidelines, as is being done with NXY-059, will increase the chances of developing efficacious drugs for treating acute ischaemic stroke. 5. It is concluded that we will only achieve the goal of producing a clinically effective neuroprotective agent if the guidelines have been met by the novel compound under investigation.

Intracerebral adenosine infusion improves neurological outcome after transient focal ischemia in rats

Second Institute of New Drug Research, Otsuka Pharmaceutical Co., Ltd., Tokushima, Japan In order to elucidate the role of adenosine in brain ischemia, the possible protective effects of adenosine on ischemic brain injury were investigated in a rat model of brain ischemia both in vitro and in vivo. Exogenous adenosine dose-dependently rescued cortical neuronal cells from injury after glucose deprivation in vitro. Adenosine (1 mM) also significantly reduced hypoglycemia/hypoxia-induced glutamate release from the hippocampal slice. In a rat model of transient middle cerebral artery occlusion (MCAO), extracellular adenosine concentration was increased immediately after occlusion, and then returned to the baseline by 30 min after reperfusion. Adenosine infusion through a microdialysis probe into the ipsilateral striatum (1 mM adenosine, 2 microl min(-1), total 4.5 h from the occlusion to 3 h after reperfusion) showed a significant improvement in the neurological outcome, and about 25% reduction of infarct volume, although the effect did not reach statistical significance, compared with the vehicle-treated group at 20 h after 90 min of MCAO. These results demonstrated the neuroprotective effect of adenosine against ischemic brain injury both in vitro and in vivo, suggesting the possible therapeutic application of adenosine regulating agents, which inhibit adenosine uptake or metabolism to enhance or maintain extracellular endogenous adenosine levels, for stroke treatment.