Translational research in stroke: Taking advances in the pathophysiology and treatment of stroke from the experimental setting to clinical trials

Nucleic Acid Therapies for Ischemic Stroke

Stroke remains a leading cause of disability and death worldwide despite significant scientific and therapeutic advances. Therefore, there is a critical need to improve stroke prevention and treatment. In this review, we describe several examples that leverage nucleic acid therapeutics to improve stroke care through prevention, acute treatment, and recovery. Aptamer systems are under development to increase the safety and efficacy of antithrombotic and thrombolytic treatment, which represent the mainstay of medical stroke therapy. Antisense oligonucleotide therapy has shown some promise in treating stroke causes that are genetically determined and resistant to classic prevention approaches such as elevated lipoprotein (a) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Targeting microRNAs may be attractive because they regulate factors involved in neuronal cell death and reperfusion-associated injury, as well as neurorestorative pathways. Lastly, microRNAs may aid reliable etiologic classification of stroke subtypes, which is important for effective secondary stroke prevention.

Effect of L-pGlu-(1-benzyl)-l-His-l-Pro-NH2 against in-vitro and in-vivo models of cerebral ischemia and associated neurological disorders

Central nervous system plays a vital role in regulation of most of biological functions which are abnormally affected in various disorders including cerebral ischemia, Alzheimer's and Parkinson's (AD and PD) worldwide. Cerebral stroke is an extremely fatal and one of the least comprehensible neurological disorders due to limited availability of prospective clinical approaches and therapeutics. Since, some endogenous peptides like thyrotropin-releasing hormone have shown substantial neuroprotective potential, hence present study evaluates the newer thyrotropin-releasing hormone (TRH) analogue L-pGlu-(1-benzyl)-l-His-l-Pro-NH₂ for its neuroprotective effects against oxygen glucose deprivation (OGD), glutamate and H₂O₂ induced injury in pheochromocytoma cell lines (PC-12 cells) and in-vivo ischemic injury in mice. Additionally, the treatment was further analyzed with respect to models of AD and PD in mice. Cerebral ischemia was induced by clamping both bilateral common carotid arteries for ten minutes. Treatment was administered to the mice five minute after restoration of blood supply to brain. Consequential changes in neurobehavioural, biochemical and histological parameters were assessed after a week. L-pGlu-(1-benzyl)-l-His-l-Pro-NH₂ showed significant reduction in glutamate, H₂O₂ and OGD -induced cell death in concentration and time dependent manner. Moreover, L-pGlu-(1-benzyl)-l-His-l-Pro-NH₂ resulted in a substantial reduction in CA1 (Cornus Ammonis 1) hippocampal neuronal cell death, inflammatory cytokines, TNF-α, IL-6 and oxidative stress in hippocampus. In addition, L-pGlu-(1-benzyl)-l-His-l-Pro-NH₂ was found to be protective in two acute models of AD and PD as well these findings demonstrate the neuroprotective potential of L-pGlu-(1-benzyl)-l-His-l-Pro-NH₂ in cerebral ischemia and other diseases, which may be mediated through reduction of excitotoxicity, oxidative stress and inflammation.

A free radical scavenger edaravone suppresses systemic inflammatory responses in a rat transient focal ischemia model

A free radical scavenger edaravone is clinically used in Japan for acute stroke, and several basic researches have carefully examined the mechanisms of edaravone's protective effects. However, its actions on pro-inflammatory responses under stroke are still understudied. In this study, we subjected adult male Sprague-Dawley rats to 90-min middle cerebral artery (MCA) occlusion followed by reperfusion. Edaravone was treated twice via tail vein; after MCA occlusion and after reperfusion. As expected, edaravone-treated group showed less infarct volume and edema formation compared with control group at 24-h after an ischemic onset. Furthermore, edaravone reduced the levels of plasma interleukin (IL)-1β and matrix metalloproteinase-9 at 3-h after ischemic onset. Several molecules besides IL-1β and MMP-9 are involved in inflammatory responses under stroke conditions. Therefore, we also examined whether edaravone treatment could decrease a wide range of pro-inflammatory cytokines/chemokines by testing rat plasma samples with a rat cytokine array. MCAO rats showed elevations in plasma levels of CINC-1, Fractalkine, IL-1α, IL-1ra, IL-6, IL-10, IP-10, MIG, MIP-1α, and MIP-3α, and all these increases were reduced by edaravone treatment. These data suggest that free radical scavengers may reduce systemic inflammatory responses under acute stroke conditions, and therefore, oxidative stress can be still a viable target for acute stroke therapy.

The spectrum of translational stroke research

Translational stroke research occurs at the interface between basic science and clinical research, and encompasses contributors with varied backgrounds and areas of expertise. The traditional approach to translational stroke research is to take novel discoveries of basic researchers about the mechanisms and consequences of ischemic brain injury and evaluate the potential of these discoveries to enhance clinical stroke diagnostics and therapeutics. Animal stroke modeling and imaging are key steps in this traditional bench-to-bedside paradigm for translational stroke research. Newer approaches to translational research include reverse and lateral translation. With these paradigms, basic researchers are stimulated to improve our understanding of the pathophysiological mechanisms that underlie a clinically observed phenomenon or treatment effect or improve upon an observed treatment effect by determining if drug modification can enhance a clinically beneficial effect. No matter how translational stroke research is conducted, this type of research is critical for the future and involves multidisciplinary teams that need to have productive and insightful ideas and communications.

Acute but not delayed amphetamine treatment improves behavioral outcome in a rat embolic stroke model

OBJECTIVES

The objective of this study was to examine the effects of d-amphetamine (amph) upon recovery after embolic stroke in rats.

METHODS

Ninety-three rats were embolized in the right middle cerebral artery and assigned to: (1) controls; (2) combination (acute amph and later amph-facilitated retraining); (3) late amph (later amph-facilitated retraining alone); and (4) acute amph (acute amph alone). Animals in the combination and in the acute amph groups received a high dose of amph immediately after embolization, while later amph-facilitated retraining in the combination and late amph groups was done by administering a low dose of amph on post-stroke days 2, 5, 8, and 11 followed by retraining in Montoya's Staircase Test.

RESULTS

Rats receiving acute amph immediately after embolization achieved an 11% increase in median blood pressure (P<0.05). An investigation of performances with the ipsilateral paws during days 14-21 showed that the acute amph group performed better than the control group (P<0.02). Infarct volumes were lower among animals in the acute amph group than in both the combination and the late amph groups (P<0.05), while the controls did not differ from any group.

DISCUSSION

In conclusion, results showed that the acute amph group performed the best, while the late amph and the combination groups performed the worst. Amphetamine treatment in acute stroke may be warranted due to reduced detrimental effects of hypotension and improved brain plasticity.

Magnetic resonance characterization of ischemic tissue metabolism

Magnetic resonance imaging (MRI) and spectroscopy (MRS) are versatile diagnostic techniques capable of characterizing the complex stroke pathophysiology, and hold great promise for guiding stroke treatment. Particularly, tissue viability and salvageability are closely associated with its metabolic status. Upon ischemia, ischemic tissue metabolism is disrupted including altered metabolism of glucose and oxygen, elevated lactate production/accumulation, tissue acidification and eventually, adenosine triphosphate (ATP) depletion and energy failure. Whereas metabolism impairment during ischemic stroke is complex, it may be monitored non-invasively with magnetic resonance (MR)-based techniques. Our current article provides a concise overview of stroke pathology, conventional and emerging imaging and spectroscopy techniques, and data analysis tools for characterizing ischemic tissue damage.

Protective effects of L-pGlu-(2-propyl)-L-His-L-ProNH2, a newer thyrotropin releasing hormone analog in in vitro and in vivo models of cerebral ischemia

In the present study, the newly synthesized TRH analog (L-pGlu-(2-propyl)-L-His-l-ProNH(2); NP-647) was evaluated for its effects in in vitro (oxygen glucose deprivation (OGD)-, glutamate- and H(2)O(2)-induced injury in PC-12 cells) and in vivo (transient global ischemia) models of cerebral ischemic injury. PC-12 cells were subjected to oxygen and glucose deprivation for 6h. Exposure of NP-647 was given before and during OGD. In glutamate and H(2)O(2) induced injury, exposure of NP-647 was given 1, 6 and 24h prior to exposure of glutamate and H(2)O(2) exposure. NP-647, per se found to be non-toxic in 1-100μM concentrations. NP-647 showed protection against OGD at the 1 and 10μM. The concentration-dependent protection was observed in H(2)O(2)- and glutamate-induced cellular injury. In in vivo studies, NP-647 treatment showed protection of hippocampal (CA1) neuronal damage in transient global ischemia in mice and subsequent improvement in memory retention was observed using passive avoidance retention test. Moreover, administration of NP-647 resulted in decrease in inflammatory cytokines TNF-α and IL-6 as well as lipid peroxidation. These results suggest potential of NP-647 in the treatment of cerebral ischemia and its neuroprotective effect may be attributed to reduction of excitotoxicity, oxidative stress and inflammation.

The gamut of blood flow responses coupled to spreading depolarization in rat and human brain: from hyperemia to prolonged ischemia

Cortical spreading depolarizations (SD) have been shown to occur frequently in patients with aneurysmal subarachnoid hemorrhage (SAH) and are associated with delayed ischemic brain damage. In animal models the link between SD and cell damage is the microvascular spasm coupled to the passage of SDs, resulting in spreading ischemia. Here we compared the hemodynamic changes induced by SD between human and rat cerebral cortex. Specifically, we addressed the question, whether the full spectrum of regional cerebral blood flow (rCBF) responses to SD is found in the human brain in a similar fashion to animal models. SDs were identified by slow potential changes in electrocorticographic recordings and the rCBF response profiles and magnitudes were analyzed. We found a large variability of rCBF changes concomitant to SDs in rat and in human recordings. The spectrum ranged from normal hyperemic responses to prolonged cortical spreading ischemia with intermediate forms characterized by biphasic (hypoemic-hyperemic) responses. The bandwidths of rCBF responses were comparable and the relative response magnitudes of hypo- and hyperperfusion phases did not differ significantly between rats and humans. The correspondence of the rCBF response spectrum to SD between human and animal brain underscores the importance of animal models to learn more about the mechanisms underlying the early and delayed pathological sequelae of SAH.

Oxygen glucose deprivation model of cerebral stroke in PC-12 cells: glucose as a limiting factor

Optimum time points for oxygen-glucose deprivation (OGD) and re-oxygenation have been identified to suggest the suitability of PC-12 cells as rapid and sensitive in vitro model of cerebral stroke. Further, the precise role of glucose as one of the limiting factors was ascertained. PC-12 cells were subjected to receive OGD of 1-8 h followed by re-oxygenation for 6 to 96 h in medium having glucose 0-10 mg/ml. Loss of cell viability was assessed using trypan blue dye exclusion and MTT assays. The significant (p < 0.05) reduction in percent viable cell count was started at 2 h of OGD (80.7 +/- 2.0) and continued in further OGD periods (3, 4, 5, 6, 7, and 8 h), i.e. 65.7 +/- 3.5, 59.7 +/- 4.6, 54.3 +/- 3.2, 44.7 +/- 2.9, 20.3 +/- 4.3, 5.7 +/- 2.0 of counted cells, respectively. Cells growing in glucose-free medium have shown a gradual (p < 0.001) decrease in cell viability throughout the re-oxygenation. Re-oxygenation of 24 h was found to be first statistically significant time point for all the glucose concentrations. Glucose concentration during re-oxygenation was found to be one of the key factors involved in the growth and proliferation in PC-12 cells. The OGD of 6 h followed by a re-oxygenation period of 24 h with 4-6 mg/ml glucose concentration could be recorded as optimum conditions under our experimental conditions.

Edaravone, a free radical scavenger, protects components of the neurovascular unit against oxidative stress in vitro

The concept of the neurovascular unit suggests that to be successful, stroke therapies must protect all neuronal, glial and endothelial components in brain. In this study, we tested the efficacy of the free radical scavenger edaravone in three cellular models of oxidative stress. HT22 neuronal cells were subjected to oxidative stress using the standard glutamate-induced glutathione depletion model. Primary rat astrocytes were exposed to H(2)O(2). Oxidative stress was induced in human brain endothelial cells with sodium nitroprusside (SNP). Edaravone significantly reduced oxidative cell death in both HT22 neuronal cells and primary rat astrocytes in a dose-dependent manner. SNP did not kill brain endothelial cells but instead reduced their production of brain-derived neurotrophic factor (BDNF). Edaravone significantly ameliorated this response. These data suggest that free radical scavengers are effective in all cell types of the neurovascular unit, and should still be considered as a potential therapeutic approach for stroke.

The Continued Promise of Neuroprotection for Acute Stroke Treatment

Stroke is the second leading cause of death. However, effective pharmocologic treatment options are still extremely limited and applicable to only a small fraction of patents. The translational failure in finding an effective neuroprotectant for ischemic strokes has generated an active discussion in this field. One focus has been on validating systems for testing neuroprotectants. This review discusses some fundamental issues in experimental stroke that are worthy of further exploration. We begin with a general review of the current status of experimental stroke research and then move on to a discussion of the determining factors and processes that control and differentiate the fate of ischemic ischemic cells and tissue. We propose several strategies of neuroprotection for ischemic strokes with an emphasis on manipulating cellular energy state.

Proteomic identification of an upregulated isoform of annexin A3 in the rat brain following reversible cerebral ischemia

We used proteomics to identify regulated proteins following cerebral ischemia in a rat model. Young rats were subjected to reversible middle cerebral artery (MCA) occlusion and proteins were extracted from the peri-infarcted and the corresponding contralateral area at days 3 and 14 postischemia. Proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis followed by mass spectrometry. We report for the first time that an isoform of annexin A3 (ANXA3) was among the upregulated proteins in the postischemic rat brain. The results were confirmed by real-time PCR and by western blotting. Double- and triple-immunostaining with neuronal and microglia/macrophagic markers demonstrated that ANXA3 is produced by resting microglia in control tissue and by activated microglial/macrophage cells in the infarcted area. 3D-images of the infarcted area suggest that ANXA3 is associated with a phagocytic phenotype. Our study identifies ANXA3 as a novel marker of brain microglia, which should be of substantial value in future studies of microglial cells and its role in the postischemic brain.