Neuroprotection for ischaemic stroke: Current status and challenges

Central Nervous System Electrical Stimulation for Neuroprotection in Acute Cerebral Ischemia: Meta-Analysis of Preclinical Studies

Background and Purpose- Brain electrical stimulation, widely studied to facilitate recovery from stroke, has also been reported to confer direct neuroprotection in preclinical models of acute cerebral ischemia. Systematic review of controlled preclinical acute cerebral ischemia studies would aid in planning for initial human clinical trials. Methods- A systematic Medline search identified controlled, preclinical studies of central nervous system electrical stimulation in acute cerebral ischemia. Studies were categorized among 6 stimulation strategies. Three strategies applied different stimulation types to tissues within the ischemic zone (cathodal hemispheric stimulation [CHS], anodal hemispheric stimulation, and pulsed hemispheric stimulation), and 3 strategies applied deep brain stimulation to different neuronal targets remote from the ischemic zone (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation). Random-effects meta-analysis assessed electrical stimulation modification of final infarct volume. Study-level risk of bias and intervention-level readiness-for-translation were assessed using formal rating scales. Results- Systematic search identified 28 experiments in 21 studies, including a total of 350 animals, of electrical stimulation in preclinical acute cerebral ischemia. Overall, in animals undergoing electrical stimulation, final infarct volumes were reduced by 37% (95% CI, 34%-40%; P<0.001), compared with control. There was evidence of heterogeneity of efficacy among stimulation strategies (I²=93.1%, P_{heterogeneity}<0.001). Among the within-ischemic zone stimulation strategies, only CHS significantly reduced the infarct volume (27 %; 95% CI, 22%-33%; P<0.001); among the remote-from ischemic zone approaches, all (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation) reduced infarct volumes by approximately half. On formal rating scales, CHS studies had the lowest risk of bias, and CHS had the highest overall quality of intervention-level evidence supporting readiness to proceed to clinical testing. Conclusions- Electrical stimulation reduces final infarct volume across preclinical studies. CHS shows the most robust evidence and is potentially appropriate for progression to early-stage human clinical trial testing as a promising neuroprotective intervention.

Therapeutic Potential of Neurotrophins for Repair After Brain Injury: A Helping Hand From Biomaterials

Stroke remains the leading cause of long-term disability with limited options available to aid in recovery. Significant effort has been made to try and minimize neuronal damage following stroke with use of neuroprotective agents, however, these treatments have yet to show clinical efficacy. Regenerative interventions have since become of huge interest as they provide the potential to restore damaged neural tissue without being limited by a narrow therapeutic window. Neurotrophins, such as brain-derived neurotrophic factor (BDNF), and their high affinity receptors are actively produced throughout the brain and are involved in regulating neuronal activity and normal day-to-day function. Furthermore, neurotrophins are known to play a significant role in both protection and recovery of function following neurodegenerative diseases such as stroke and traumatic brain injury (TBI). Unfortunately, exogenous administration of these neurotrophins is limited by a lack of blood-brain-barrier (BBB) permeability, poor half-life, and rapid degradation. Therefore, we have focused this review on approaches that provide a direct and sustained neurotrophic support using pharmacological therapies and mimetics, physical activity, and potential drug delivery systems, including discussion around advantages and limitations for use of each of these systems. Finally, we discuss future directions of biomaterial drug-delivery systems, including the incorporation of heparan sulfate (HS) in conjunction with neurotrophin-based interventions.

Applications of Liposomal Drug Delivery Systems to Develop Neuroprotective Agents for the Treatment of Ischemic Stroke

Ischemic stroke is one of the leading causes of severe disability and death. In clinical settings, tissue plasminogen activator (t-PA) for thrombolytic therapy is the only globally approved drug for the treatment of ischemic stroke. However, the proportion of patients who receive t-PA therapy is extremely limited due to its narrow therapeutic time window (TTW) and the risk of cerebral hemorrhage. Cerebral ischemia-reperfusion (I/R) injury is also a serious problem for patients' outcomes. Hence, the development of more effective therapies has been desired to prolong the TTW of t-PA and prevent cerebral I/R injury. For delivering drugs into the brain, the blood-brain barrier (BBB) must be overcome since it limits drug penetration into the brain, leading to insufficient therapeutic efficacy. As a distinctive pathology after an ischemic stroke, it was reported that the vascular permeability of the BBB is increased around the ischemic region. We found that nano-sized liposomes can pass through the disrupted BBB and accumulate in the I/R region, and that delivery of neuroprotective agents using a liposomal drug delivery system (DDS) is effective for the treatment of cerebral I/R injury. Moreover, we have recently demonstrated that combination therapy with liposomal drugs and t-PA can suppress the deleterious effects of t-PA and extend its TTW in a rat ischemic stroke model. These findings indicate that applications of nanoparticle DDS technology could be a hopeful approach to drug development for ischemic stroke therapy. In this review, we introduce our findings on ischemic stroke treatment using liposomal DDS and recent advances from other research groups.

Nano-scaled MTCA-KKV: for targeting thrombus, releasing pharmacophores, inhibiting thrombosis and dissolving blood clots in vivo

BACKGROUND

In vitro (1R,3S)-1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxyl-Lys(Pro-Ala-Lys)-Arg-Gly-Asp-Val (MTCA-KKV) adheres activated platelets, targets P-selectin and GPIIb/IIIa. This led to the development of MTCA-KKV as thrombus targeting nano-medicine.

METHODS

MTCA-KKV was characterized by nano-feature, anti-thrombotic activity, thrombolytic activity, thrombus target and targeting release.

RESULTS

In vivo 0.01 μmol/kg of MTCA-KKV formed nano-particles less than 100 nm in diameter, targeted thrombus, released anti-thrombotic and thrombolytic pharmacophores, prevented thrombosis and dissolved blood clots.

CONCLUSION

Based on the profiles of targeting thrombus, targeting release, inhibiting thrombosis and dissolving blood clots MTCA-KKV is a promising nano-medicine.

The Role of Mast Cells in Stroke

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin. Through the release of preformed mediators stored in their granules and newly synthesized molecules, they are able to initiate, modulate, and prolong the immune response upon activation. Their presence in the central nervous system (CNS) has been documented for more than a century. Over the years, MCs have been associated with various neuroinflammatory conditions of CNS, including stroke. They can exacerbate CNS damage in models of ischemic and hemorrhagic stroke by amplifying the inflammatory responses and promoting brain–blood barrier disruption, brain edema, extravasation, and hemorrhage. Here, we review the role of these peculiar cells in the pathophysiology of stroke, in both immature and adult brain. Further, we discuss the role of MCs as potential targets for the treatment of stroke and the compounds potentially active as MCs modulators.

Intra-arterial administration of cell-based biological agents for ischemic stroke therapy

INTRODUCTION

Ischemic stroke is becoming a primary cause of disability and death worldwide. To date, therapeutic options remain limited focusing on mechanical thrombolysis or administration of thrombolytic agents. However, these therapies do not promote neuroprotection and neuro-restoration of the ischemic area of the brain.

AREAS COVERED

This review highlights the option of minimal invasive, intra-arterial, administration of biological agents for stroke therapy. The authors provide an update of all available studies, discuss issues that influence outcomes and describe future perspectives which aim to improve clinical outcomes. New therapeutic options based on cellular and molecular interactions following an ischemic brain event, will be highlighted.

EXPERT OPINION

Intra-arterial administration of biological agents during trans-catheter thrombolysis or thrombectomy could limit neuronal cell death and facilitate regeneration or neurogenesis following ischemic brain injury. Despite the initial progress, further meticulous studies are needed in order to establish the clinical use of stem cell-induced neuroprotection and neuroregeneration.

HMG-CoA Reductase Inhibitors Attenuate Neuronal Damage by Suppressing Oxygen Glucose Deprivation-Induced Activated Microglial Cells

Ischemic stroke is usually followed by inflammatory responses mediated by microglia. However, the effect of statins on directly preventing posthypoxia microglia inflammatory factors to prevent injury to surrounding healthy neurons is unclear. Atorvastatin and rosuvastatin, which have different physical properties regarding their lipid and water solubility, are the most common HMG-CoA reductase inhibitors (statins) and might directly block posthypoxia microglia inflammatory factors to prevent injury to surrounding neurons. Neuronal damage and microglial activation of the peri-infarct areas were investigated by Western blotting and immunofluorescence after 24 hours in a middle cerebral artery occlusion (MCAO) rat model. The decrease in neurons was in accordance with the increase in microglia, which could be reversed by both atorvastatin and rosuvastatin. The effects of statins on blocking secretions from posthypoxia microglia and reducing the secondary damage to surrounding normal neurons were studied in a coculture system in vitro. BV2 microglia were cultured under oxygen glucose deprivation (OGD) for 3 hours and then cocultured following reperfusion for 24 hours in the upper wells of transwell plates with primary neurons being cultured in the bottom wells. Inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and cyclooxygenase-2 (COX2), which are activated by the nuclear factor-kappa B (NF-κB) signaling pathway in OGD-induced BV2 microglia, promoted decreased release of the anti-inflammatory cytokine IL-10 and apoptosis of neurons in the coculture systems according to ELISA and Western blotting. However, pretreatment with atorvastatin or rosuvastatin significantly reduced neuronal death, synaptic injury, and amyloid-beta (Aβ) accumulation, which might lead to increased low-density lipoprotein receptors (LDLRs) in BV2 microglia. We concluded that the proinflammatory mediators released from postischemia damage could cause damage to surrounding normal neurons, while HMG-CoA reductase inhibitors prevented neuronal apoptosis and synaptic injury by inactivating microglia through blocking the NF-κB signaling pathway.

Systems Pharmacology-Based Approach to Comparatively Study the Independent and Synergistic Mechanisms of Danhong Injection and Naoxintong Capsule in Ischemic Stroke Treatment

To provide evidence for the better clinical use of traditional Chinese medicine preparations (TCMPs), comparison of the pharmacological mechanisms between TCMPs with similar therapeutic effect is necessary. However, methodology for dealing with this issue is still scarce. Danhong injection (DHI) and Naoxintong capsule (NXT) are representative TCMPs for ischemic stroke (IS) treatment, which are also frequently used in combination. Here they were employed as research objects to demonstrate the feasibility of systems pharmacology approach in elucidation of the independent and combined effect of TCMPs. By incorporating chemical screening, target prediction, and network construction, a feasible systems pharmacology model has been established to systematically uncover the underlying action mechanisms of DHI, NXT, or their pair in IS treatment. Systematic analysis of the created TCMP-Compound-Target-Disease network revealed that DHI and NXT shared common targets such as PTGS2, F2, ADRB1, IL6, ALDH2, and CCL2, which were involved in the vasomotor system regulation, blood-brain barrier disruption, redox imbalance, neurotrophin activity, and brain inflammation. In comparative mechanism study, the merged DHI/NXT-IS PPI network and pathway enrichment analysis indicated that DHI and NXT exerted the therapeutic effects mainly through immune system and VEGF signaling pathways. Meanwhile, they had their own unique pathways, e.g., calcium signaling pathway for DHI and gap junction for NXT. While for their synergistic mechanism, DHI and NXT participated in chemokine signaling pathway, T cell receptor signaling pathway, VEGF signaling pathway, gap junction, and so on. Our study provided an optimized strategy for dissecting the different and combined effect of TCMPs with similar actions.

Mitochondrial protective effect of neferine through the modulation of nuclear factor erythroid 2-related factor 2 signalling in ischaemic stroke

BACKGROUND AND PURPOSE

Ischaemic stroke is a leading cause of death and long-term disability. Promising neuroprotective compounds are urgently needed to overcome clinical therapeutic limitations. Neuroprotective agents are limited to single-target agents, which further limit their clinical effectiveness. Due to the brain's particular energy requirements, the energy micro-environment, centred in mitochondria, is a new research hotspot in the complex pathology of ischaemic stroke. Here, we studied the effects of neferine (Nef), a bis-benzylisoquinoline alkaloid extracted from the seed embryo of Nelumbo nucifera Gaertn, on ischaemic stroke and its underlying mitochondrial protective mechanisms.

EXPERIMENTAL APPROACH

Rats with permanent middle cerebral artery occlusion (pMCAO)-induced focal cerebral ischaemia and tert-butyl hydroperoxide (t-BHP)-injured PC12 cells were used to investigate the neuroprotective effects of Nef, particularly with regard to energy micro-environment regulation by mitochondria and its mechanism in vivo and in vitro.

KEY RESULTS

Nef protected t-BHP-injured PC12 cells in vitro and ameliorated neurological score, infarct volume, regional cerebral blood flow, cerebral microstructure and oxidant-related enzyme deficits in pMCAO rats in vivo. Nef also prevented mitochondrial dysfunction both in vivo and in vitro. The underlying mechanism of the mitochondrial protective effect of Nef might be attributed to the increased translocation of Nrf2 to the nucleus. Furthermore, the translocation of Nrf2 to nucleus was also decreased by sequestosome 1 (p62) knockdown.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrated that Nef might have therapeutic potential for ischaemic stroke and may exert its protective role through mitochondrial protection. This protection might be attributed to the modulation of Nrf2 signalling.

A11, a novel diaryl acylhydrazone derivative, exerts neuroprotection against ischemic injury in vitro and in vivo

There is an urgent need to develop effective therapies for ischemic stroke, but the complicated pathological processes after ischemia make doing so difficult. In the current study, we identified a novel diaryl acylhydrazone derivative, A11, which has multiple neuroprotective properties in ischemic stroke models. First, A11 was demonstrated to induce neuroprotection against ischemic injury in a dose-dependent manner (from 0.3 to 3 μM) in three in vitro experimental ischemic stroke models: oxygen glucose deprivation (OGD), hydrogen peroxide, and glutamate-stimulated neuronal cell injury models. Moreover, A11 was able to potently alleviate three critical pathological changes, apoptosis, oxidative stress, and mitochondrial dysfunction, following ischemic insult in neuronal cells. Further analysis revealed that A11 upregulated the phosphorylation levels of protein kinase B (AKT) and extracellular signal-regulated kinase (ERK) in OGD-exposed neuronal cells, suggesting joint activation of the phosphoinositide 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MEK)/ERK pathways. In rats with middle cerebral artery occlusion, single-dose administration of A11 (3 mg/kg per day, i.v.) at the onset of reperfusion significantly reduced the infarct volumes and ameliorated neurological deficits. Our study, for the first time, reports the anti-ischemic effect of diaryl acylhydrazone chemical entities, especially A11, which acts on multiple ischemia-associated pathological processes. Our results may provide new clues for the development of an effective therapeutic agent for ischemic stroke.

Ischaemic and hypoxic conditioning: potential for protection of vital organs

NEW FINDINGS

What is the topic of this review? Remote ischaemic preconditioning (RIPC) and hypoxic preconditioning as novel therapeutic approaches for cardiac and neuroprotection. What advances does it highlight? There is improved understanding of mechanisms and signalling pathways associated with ischaemic and hypoxic preconditioning, and potential pitfalls with application of these therapies to clinical trials have been identified. Novel adaptations of preconditioning paradigms have also been developed, including intermittent hypoxia training, RIPC training and RIPC-exercise, extending their utility to chronic settings.

ABSTRACT

Myocardial infarction and stroke remain leading causes of death worldwide, despite extensive resources directed towards developing effective treatments. In this Symposium Report we highlight the potential applications of intermittent ischaemic and hypoxic conditioning protocols to combat the deleterious consequences of heart and brain ischaemia. Insights into mechanisms underlying the protective effects of intermittent hypoxia training are discussed, including the activation of hypoxia-inducible factor-1 and Nrf2 transcription factors, synthesis of antioxidant and ATP-generating enzymes, and a shift in microglia from pro- to anti-inflammatory phenotypes. Although there is little argument regarding the efficacy of remote ischaemic preconditioning (RIPC) in pre-clinical models, this strategy has not consistently translated into the clinical arena. This lack of translation may be related to the patient populations targeted thus far, and the anaesthetic regimen used in two of the major RIPC clinical trials. Additionally, we do not fully understand the mechanism through which RIPC protects the vital organs, and co-morbidities (e.g. hypercholesterolemia, diabetes) may interfere with its efficacy. Finally, novel adaptations have been made to extend RIPC to more chronic settings. One adaptation is RIPC-exercise (RIPC-X), an innovative paradigm that applies cyclical RIPC to blood flow restriction exercise (BFRE). Recent findings suggest that this novel exercise modality attenuates the exaggerated haemodynamic responses that may limit the use of conventional BFRE in some clinical settings. Collectively, intermittent ischaemic and hypoxic conditioning paradigms remain an exciting frontier for the protection against ischaemic injuries.

Ginaton improves neurological function in ischemic stroke rats via inducing autophagy and maintaining mitochondrial homeostasis

PURPOSE

The present study was carried out to confirm the protective effect of extract of Ginkgo biloba (Ginaton) against ischemic neuronal damage post-treatment at 24 h after reperfusion in rats with middle cerebral artery occlusion (MCAO) and further reveal its possible mechanisms.

METHODS

Adult male Sprague-Dawley rats were modeled by MCAO for 2 h. The rats were divided into three groups: sham, model, and Ginaton (50 mg/kg). All animals received treatment once a day for 14 days from 24 h after reperfusion. Modified neurological severity score test was performed in 1, 7 and 14 days after MCAO, and beam walking test was performed only 14 days after MCAO. Hematoxylin-eosin straining was implemented to measure infarct volume and immunohistochemical analysis was performed to calculate the number of neurons in ischemic cortex penumbra. Western blot was used to evaluate the expression of autophagy (Beclin1, LC3, AMPK, mTOR, ULK), mitochondrial dynamic protein (Parkin, DRP1, OPA1) and apoptosis (Bcl-2, Bax).

RESULTS

Post-treatment with Ginaton for 14 days decreased neurological deficit score, promoted the recovery of motor function, and noticeably reduced infarct size. Besides, Ginaton also alleviated the loss of NeuN-positive cells in ischemic cortex penumbra. In ischemic cortex, Ginaton increased the expression of Beclin1 and LC3-Ⅱ, elevated the AMPK, mTOR and ULK1, and induced autophagy. Moreover, Ginaton treatment upregulated Parkin, DRP1, and OPA1, and elevated the ratio of Bcl-2/Bax in 14 days after MCAO reperfusion injury.

CONCLUSION

Ginaton exhibited obvious neuroprotective effects in MCAO rats with initial administered 24 h after MCAO. The mechanism of Ginaton included induction of autophagy via activation of the AMPK pathway, maintenance of mitochondrial homeostasis and inhibition of apoptosis.

Cornel Iridoid Glycoside Protects Against White Matter Lesions Induced by Cerebral Ischemia in Rats via Activation of the Brain-Derived Neurotrophic Factor/Neuregulin-1 Pathway

BACKGROUND

Ischemic stroke often induces profound white matter lesions, resulting in poor neurological outcomes and impaired post-stroke recovery. The present study aimed to investigate the effects of cornel iridoid glycoside (CIG), a major active component extracted from Cornus officinalis, on the white matter injury induced by ischemic stroke and further investigate its neuroprotective mechanisms.

METHODS

Adult male Sprague-Dawley rats underwent middle cerebral artery occlusion (MCAO) surgery for 2 h, followed by reperfusion. Rats were intragastrically administered CIG (60 mg/kg and 120 mg/kg) beginning 6 h afters reperfusion, once daily for seven days. A series of behavioral tests (modified neurological severity scores test, object recognition test, adhesive removal test, and beam walking test) were performed to evaluate the neurological functioning in MCAO rats. Histology of the white matter was studied using luxol fast blue staining and transmission electron microscopy. Immunohistochemical staining was performed to assess myelin loss, oligodendrocyte maturation, and glial activation. Activation of the brain-derived neurotrophic factor (BDNF)/neuregulin-1 (NRG1) pathway was evaluated by Western blotting.

RESULTS

CIG treatment remarkably decreased the neurological deficit score, accelerated the recovery of somatosensory and motor functions, and ameliorated the memory deficit in MCAO rats. Furthermore, CIG alleviated white matter lesions and demyelination, increased myelin basic protein expression and the number of mature oligodendrocytes, and decreased the number of activated microglia and astrocytes in the corpus callosum of MCAO rats. In addition, Western blot analysis indicated that CIG increased the expression of BDNF/p-TrkB, NRG1/ErbB4 proteins, which further elevated PI3K p110α/p-Akt/p-mTOR signaling in the corpus callosum of MCAO rats.

CONCLUSION

We demonstrated that CIG protects against white matter lesions induced by cerebral ischemia partially by decreasing the number of activated microglia and astrocytes, increasing BDNF level, and activating NRG1/ErbB4 and its downstream PI3K/Akt/mTOR pathways in the white matter. CIG might be used as a potential neuroprotective agent for the treatment of ischemic stroke.

Role of immune responses for extracellular matrix remodeling in the ischemic brain

Neuroinflammation is one of the key components contributing to the devastating outcome of ischemic stroke. Starting with stroke onset, inflammatory processes contribute both to cell damage and tissue remodeling. The early release of alarmins triggers the upregulation of multiple proinflammatory cytokines, resulting in the compromised integrity of the blood–brain barrier. From this moment on, the infiltration of peripheral immune cells, reactive gliosis and extracellular matrix (ECM) alterations become intricately intertwined and act as one unit during the tissue remodeling. While the mechanisms of leukocyte and glia activation are amply reviewed, the field of ECM modification remains as yet under explored. In this review, we focus on the interplay between neuroinflammatory cascades and ECM in the ischemic brain. By summarizing the currently available evidence obtained by in vitro research, animal experimentation and human studies, we aim to propose a new direction for the future investigation of stroke recovery.

A new era for stroke therapy: Integrating neurovascular protection with optimal reperfusion

Recent advances in stroke reperfusion therapies have led to remarkable improvement in clinical outcomes, but many patients remain severely disabled, due in part to the lack of effective neuroprotective strategies. In this review, we show that 95% of published preclinical studies on "neuroprotectants" (1990-2018) reported positive outcomes in animal models of ischemic stroke, while none translated to successful Phase III trials. There are many complex reasons for this failure in translational research, including that the majority of clinical trials did not test early delivery of neuroprotectants in combination with successful reperfusion. In contrast to the clinical trials, >80% of recent preclinical studies examined the neuroprotectant in animal models of transient ischemia with complete reperfusion. Furthermore, only a small fraction of preclinical studies included long-term functional assessments, aged animals of both genders, and models with stroke comorbidities. Recent clinical trials demonstrate that 70%-80% of patients treated with endovascular thrombectomy achieve successful reperfusion. These successes revive the opportunity to retest previously failed approaches, including cocktail drugs that target multiple injury phases and different cell types. It is our hope that neurovascular protectants can be retested in future stroke research studies with specific criteria outlined in this review to increase translational successes.

Early prediction of revascularisation by angiomotin-targeting positron emission tomography

This study aimed to develop a PET imaging agent of angiomotin (AMOT) expression, a potential biomarker of functional tissue regeneration in post-ischaemic conditions.

Methods: Hindlimb ischaemia was induced by ligature and resection of the right femoral artery in mice, and clinical score and limb perfusion were evaluated up to 30 days after surgery. AMOT expression was evaluated by histology and Western blot analysis. NODAGA-conjugates of AMOT ligand, sCD146, were designed, synthesised and radiolabelled with gallium-68. ⁶⁸Ga-sCD146 microPET/CT imaging was performed from day 1 to day 30 after ischaemia. ⁶⁸Ga-sCD146 specificity for AMOT was evaluated by autoradiography.

Results: Immunohistochemistry showed a significant endothelial overexpression of AMOT from day 5 up to day 10 in the ischaemic hindlimb. ⁶⁸Ga-sCD146 PET signal intensity correlated significantly with AMOT immunohistochemistry evaluation. ⁶⁸Ga-sCD146 PET imaging showed a significant uptake in the ischaemic hindlimb from day 2 to day 15, peaking on day 5 (ipsi/contralateral ratio = 2.4 ± 1.3, P = 0.0005) and significantly decreased after pharmacological blocking (62.57 ± 11% decrease in PET signal P = 0.032). Finally, we observed a significant correlation between day 5 ⁶⁸Ga-sCD146 PET signal intensity and clinical recovery (day 28) or hindlimb perfusion recovery (day 30).

Conclusions: This work reports for the first time an early and sustained increase in AMOT expression after hindlimb ischaemia in mice. We therefore developed an AMOT-targeting imaging agent, ⁶⁸Ga-sCD146, and showed its specific uptake up to 21 days after ischaemic hindlimb using microPET imaging. Correlation of early post-ischaemic PET signal with both delayed perfusion recovery and clinical outcome allows us to postulate that ⁶⁸Ga-sCD146 represents a promising radiotracer for tissue angiogenesis assessment.

Brain-selective mild hypothermia promotes long-term white matter integrity after ischemic stroke in mice

INTRODUCTION

The neuroprotective effects of hypothermia in acute ischemic stroke are well documented. However, the mechanisms involved in the effects remain to be clearly elucidated and the role of hypothermia on long-term white matter integrity after acute ischemic stroke has yet to be investigated.

AIMS

To investigate the role of mild focal hypothermia on long-term white matter (WM) integrity after transient cerebral ischemia.

RESULTS

Mild focal hypothermia treatment immediately after ischemic stroke significantly promotes WM integrity 28 days after the occlusion of the middle cerebral artery (MCAO) in mice. Higher integrity of white matter, lower activation of total microglia, less infarct volume, and better neurobehavioral function were detected in hypothermia-treated mice compared to normothermia-treated mice. Furthermore, we found that hypothermia could decrease detrimental M1 phenotype microglia and promote healthy M2 phenotype microglia. In vitro, results also indicated that hypothermia promoted oligodendrocytes differentiation and maturation after oxygen glucose deprivation.

CONCLUSION

Hypothermia promotes long-term WM integrity and inhibits neuroinflammation in a mouse model of ischemic brain injury.

Tetramethylpyrazine‑2'O‑sodium ferulate provides neuroprotection against neuroinflammation and brain injury in MCAO/R rats by suppressing TLR-4/NF-κB signaling pathway

BACKGROUND

Neuroinflammation following cerebral ischemia is a serious risk factor in stroke patients. The purpose of this study was to investigate the neuroprotective effects of tetramethylpyrazine‑2'O‑sodium ferulate (TSF), a structurally modified compound from tetramethylpyrazine and ferulate, on cerebral ischemic injury and the underlying mechanisms.

METHODS

Focal transient cerebral ischemia was induced in rat for 2 h by middle cerebral artery occlusion (MCAO) and the protective effect of TSF was studied using different doses of the drug (10.8, 18, 30 mg/kg, intravenously); Ozagrel (18 mg/kg) was used as the positive control. The drugs were given immediately after MCAO and the efficacy and mechanisms were evaluated at 72 h of reperfusion. The level of pro-inflammatory cytokines such as TNF-α, IL-1β and anti-inflammatory molecules such as IL-10 was measured; other factors such as neurological deficit, brain water content and infarct size and the level of MCP-1, ICAM-1, iNOS, CD11b, TLR-4/NF-κBp65 were also measured.

RESULTS

TSF at the doses of 18, 30 mg/kg significantly improved neurological deficit, reduced brain water content and infarct size, accompanied by a decrease in the concentration of TNF-α, IL-1β, MCP-1, ICAM-1, iNOS and an increase in the concentration of IL-10. The amount of CD11b and ICAM-1 was found largely decreased and the expression of TLR-4 and the nuclear NF-κBp65 was weakened in TSF-treatment group.

CONCLUSIONS

Our study suggests that TSF possesses a neuroprotective effect against ischemic stroke which might be mediated through suppression of the inflammatory pathways in the brain following ischemic stroke.

Retinal Neuroprotection: Overcoming the Translational Roadblocks

PURPOSE

To elucidate the issues that have prevented successful translation of neuroprotective therapeutic modalities for retinal disease from the preclinical to the clinical realm and to suggest strategies to circumvent these barriers in order to develop novel treatments to prevent vision loss.

DESIGN

Interpretive essay.

METHODS

Review and synthesis of selected reports of neuroprotective approaches for retinal disease, with interpretation and perspective.

RESULTS

Retinal neuroprotection is defined as any measure that reduces the death of retinal cells or axonal extensions into the optic nerve, and there is a great unmet need for such therapeutic modalities. Despite encouraging preclinical data, the translation of neuroprotective therapies to the clinic has been fraught with failure. Fundamental issues that have plagued this transition include the animal models used in preclinical studies, the reproducibility of the preclinical data, and the choice of meaningful clinical trial endpoints. Developing animal models that more aptly mimic human disease, defining a set of guidelines for preclinical evaluation of neuroprotective therapies in retinal disease, and identifying and validating biomarkers as surrogate clinical endpoints that shorten and optimize drug development timelines may circumvent some of these barriers to translation.

CONCLUSIONS

Neuroprotective therapeutic approaches have the potential to prevent vision loss in millions of people affected with eye diseases worldwide. However, a stigma currently accompanies the concept of neuroprotection because of the many past failures to bridge the gap between the preclinical and clinical realms. Understanding and addressing the fundamental reasons for the failure of translatable research provides hope for the future development of neuroprotective therapies.

Diterpene ginkgolides protect against cerebral ischemia/reperfusion damage in rats by activating Nrf2 and CREB through PI3K/Akt signaling

Diterpene ginkgolides meglumine injection (DGMI) is a therapeutic extract of Ginkgo biloba L, which has been used for the treatment of cerebral ischemic stroke in China. Ginkgolides A, B and C are the main components of DGMI. This study was designed to investigate the neuroprotective effects of DGMI components against ischemic stroke in vivo and in vitro. Acute cerebral ischemic injury was induced in rats by occlusion of the middle cerebral artery (MCA) for 1.5 h followed by 24 h reperfusion. The rats were treated with DGMI (1, 3 and 10 mg/kg, iv) at the onset of reperfusion and 12 h after reperfusion. Administration of DGMI significantly decreased rat neurological deficit scores, reduced brain infarct volume, and induced protein kinase B (Akt) phosphorylation, which prompted the nuclear translocation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and phosphorylation of the survival regulatory protein cyclic AMP-responsive element binding protein (CREB). Nrf2 activation led to expression of the downstream protein heme oxygenase-1 (HO-1). In addition, PC12 cells were subjected to oxygen-glucose deprivation/reperfusion (OGD/R) in vitro, treatment with DGMI (1, 10 and 20 μg/mL) or ginkgolides A, B or C (10 μmol/L for each) significantly reduced PC12 cell death and increased phosphorylation of Akt, nuclear translocation of Nrf2 and activation of CREB. Activation of Nrf2 and CREB could be reversed by co-treatment with a phosphoinositide-3-kinase (PI3K) inhibitor LY294002. These observations suggest that ginkgolides act as novel extrinsic regulators activating both Akt/Nrf2 and Akt/CREB signaling pathways, protecting against cerebral ischemia/reperfusion (I/R) damage in vivo and in vitro.

Heptapeptide-based modification leading to enhancing the action of MTCA on activated platelets, P-selectin, GPIIb/IIIa

AIM

The modification of platelet inhibitor to enhance its targeting capacity toward platelets is of clinical importance. Thus, (1R, 3S)-1-methyl-1, 2, 3, 4-tetrahydro-β-carboline-3-carboxylic acid (MTCA), a platelet inhibitor, was modified with Lys(Pro-Ala-Lys)-Arg-Gly-Asp-Val (KKV), platelet targeting peptide, to form MTCA-KKV.

MATERIALS & METHODS

MTCA and MTCA-KKV were synthesized to identify the effect of KKV modification on MTCA and platelets.

RESULTS

Atomic force microscopy imaged MTCA-KKV effectively accumulated on activated platelets. UV spectra showed that MTCA-KKV concentration dependently changed P-selectin and GPIIb/IIIa conformations. For platelet aggregation, the IC₅₀ of MTCA-KKV was approximately 1/10 folds of MTCA.

CONCLUSION

KKV modification led to forming MTCA-KKV that is superior to MTCA in terms of accumulating on activated platelets, targeting P-selectin and GPIIb/IIIa and inhibiting platelet aggregation. MTCA-KKV could be a promising lead for further investigation.

Glutamate metabolism in cerebral mitochondria after ischemia and post-ischemic recovery during aging: relationships with brain energy metabolism

Glutamate is involved in cerebral ischemic injury, but its role has not been completely clarified and studies are required to understand how to minimize its detrimental effects, contemporarily boosting the positive ones. In fact, glutamate is not only a neurotransmitter, but primarily a key metabolite for brain bioenergetics. Thus, we investigated the relationships between glutamate and brain energy metabolism in an in vivo model of complete cerebral ischemia of 15 min and during post-ischemic recovery after 1, 24, 48, 72, and 96 h in 1-year-old adult and 2-year-old aged rats. The maximum rates (V_max ) of glutamate dehydrogenase (GlDH), glutamate-oxaloacetate transaminase, and glutamate-pyruvate transaminase were assayed in somatic mitochondria (FM) and in intra-synaptic 'Light' mitochondria and intra-synaptic 'Heavy' mitochondria ones purified from cerebral cortex, distinguishing post- and pre-synaptic compartments. During ischemia, none of the enzymes were modified in adult animals. In aged ones, glutamate-oxaloacetate transaminase was increased in FM and GlDH in intra-synaptic 'Heavy' mitochondria, stimulating glutamate catabolism. During post-ischemic recovery, FM did not show modifications at both ages while, in intra-synaptic mitochondria of adult animals, glutamate catabolism was increased after 1 h of recirculation and decreased after 48 and 72 h, whereas it remained decreased up to 96 h in aged rats. These results, with those previously published about Krebs' cycle and Electron Transport Chain (Villa et al., [2013] Neurochem. Int. 63, 765-781), demonstrate that: (i) V_max of energy-linked enzymes are different in the various cerebral mitochondria, which (ii) respond differently to ischemia and post-ischemic recovery, also (iii) with respect to aging.

2-Methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine, an edaravone analog, exerts neuroprotective effects against acute ischemic injury via inhibiting oxidative stress

Oxidative stress plays an indispensable role in the pathogenesis of cerebral ischemia. Inhibiting oxidative stress has been considered as an effective approach for stroke treatment. Edaravone, a free radical scavenger, has been shown to prevent cerebral ischemic injury. However, the clinical efficacy of edaravone is limited because it has a low scavenging activity for superoxide anions (O₂^·-). Here, we report that 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine, a novel small-molecule compound structurally related to edaravone, showed a stronger inhibitory effect on oxidative stress in vitro. In vivo, 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine reversed transient middle cerebral artery occlusion-induced dysfunctions of superoxide dismutases and malondialdehyde, two proteins crucial for oxidative stress, suggesting a strengthened antioxidant system. Moreover, 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine decreased blood brain barrier permeability. Then, we found that 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine had a stronger neuroprotective effect than edaravone. More importantly, 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine decreased not only infarct size and neurological deficits in the acute phase but also modified neurological severity score and escape latency in Morris water maze task in the delayed period, indicating enhanced neuroprotection, sensorimotor function and spatial memory. Together, these findings suggest that 2-methyl-5H-benzo[d]pyrazolo[5,1-b][1,3]oxazin-5-imine could be a preferable option for stroke treatment.

cPKCγ alleviates ischemic injury through modulating synapsin Ia/b phosphorylation in neurons of mice

Conventional protein kinase C (cPKC)γ and synapsin Ia/b have been implicated in the development of ischemic stroke, but their relationships and functions are unclear. In the present study, the oxygen-glucose deprivation (OGD)-induced ischemic insult in primary cultured cortical neurons in vitro and middle cerebral artery occlusion (MCAO)-induced ischemic stroke model in vivo were used to elucidate the function of cPKCγ and its modulation on synapsin Ia/b phosphorylation in ischemic stroke. We found that cPKCγ knockout significantly increased the infarct volume of mice after 1 h MCAO/72 h reperfusion by using triphenyltetrazolium chloride (TTC) staining. In the primarily cultured cortical neurons, cPKCγ knockout also aggravated the OGD-induced cell death and morphological damage of neurites, while cPKCγ restoration could alleviate the ischemic injury. Among the five phosphorylation sites of synapsin Ia/b, only the phosphorylation levels of Ser549 and 553 could be modulated by cPKCγ in neurons following 0.5 h OGD/24 h reoxygenation. In addition, we found that cPKCγ and synapsin Ia/b could be reciprocally co-immunoprecipitated in the cerebral cortex of MCAO mice. Taken together, we proposed that cPKCγ alleviates ischemic injury through modulating Ser549/553- synapsin Ia/b phosphorylation in neurons of mice.

Neuroprotective effect of the group III mGlu receptor agonist ACPT-I after ischemic stroke in rats with essential hypertension

Our previous studies have shown that ACPT-I [(1S, 3R,4S)-1-aminocyclopentane-1,2,4-tricarboxylic acid], a blood-brain barrier permeable agonist of group III metabotropic glutamate (mGlu) receptors, was neuroprotective against middle cerebral artery occlusion/reperfusion (MCAO/R) in normotensive rats. Preclinical studies are typically performed on healthy animals, whereas stroke patients predominately exhibit comorbidities, such as hypertension; therefore, in the present study, we investigated the effect of ACPT-I in spontaneously hypertensive rats (SHR) after MCAO/R. We examined the potential neuroprotective action of ACPT-I (30 mg/kg) when administered during occlusion or reperfusion via the assessment of not only the brain infarction volume but also motor (CatWalk gait analysis and open field test) and sensorimotor (vibrissae-evoked forelimb-placing test) functions following MCAO/R. We determined that ACPT-I not only reduced the cortico-striatal infarction but also improved several gait parameters (run speed, run and stand durations, swing speed and stride length) and mobility when administered 30 min after the start of the occlusion or 30 min after the start of reperfusion. Moreover, the sensorimotor function was improved in hypertensive rats treated with ACPT-I during occlusion. In conclusion, the current findings provide further evidence for the neuroprotective effects of ACPT-I against ischemic damage. These findings may have clinical implications because hypertension is an important risk factor for ischemic stroke.

Dynamic Evaluation of Notch Signaling-Mediated Angiogenesis in Ischemic Rats Using Magnetic Resonance Imaging

Objective

The Notch signaling pathway is involved in angiogenesis induced by brain ischemia and can be efficiently inhibited by the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butyl ester (DAPT). The aim of the present study was to noninvasively investigate the effect of DAPT treatment on angiogenesis in brain repair after stroke using magnetic resonance imaging (MRI).

Methods

Sprague-Dawley rats (n = 40) were subjected to 90 minutes of transient middle cerebral artery (MCA) occlusion and treated with PBS (n = 20) or DAPT (n = 20) at 72 hours after the onset of ischemia. MRI measurements including T2-weighted imaging (T2WI), susceptibility-weighted imaging (SWI), and cerebral blood flow (CBF) were performed at 24 hours after reperfusion and weekly up to 4 weeks using a 3-Tesla system. Histological measurements were obtained at each time point after MRI scans.

Results

SWI showed that DAPT treatment significantly enhanced angiogenesis in the ischemic boundary zone (IBZ) with respect to the control group, with local CBF in the angiogenic area elevated, along with increases in vascular density confirmed by histology.

Conclusion

Treatment of ischemic stroke with DAPT significantly augments angiogenesis, which promotes poststroke brain remodeling by elevating CBF level, and these processes can be dynamically monitored and evaluated by MRI.

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

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

Intra-arterial human urinary kallidinogenase alleviates brain injury in rats with permanent middle cerebral artery occlusion through PI3K/AKT/FoxO1 signaling pathway

An urgent need exists to develop intra-arterial treatment for acute ischemic stroke in animal study. This study aimed to explore the beneficial effects of intra-arterial administration of human urinary kallidinogenase (HUK) on brain injury after permanent middle cerebral artery occlusion (pMCAO) in a rat model, and the potential underlying molecular mechanisms. Brain injury induced by pMCAO was evaluated through measuring neurological deficit scores, neuropathological changes, and inflammatory factors. Neurological deficits were observed 24 h after pMCAO and were alleviated by intra-arterial HUK treatment obviously. Inhibition of PI3K by LY294002 blocked the beneficial effect of HUK on neurological functions. In contrast to the pMCAO group, the intra-arterial HUK treatment group showed relatively more regularly arranged neurons and fewer pyknosis. Neurodegeneration, necrosis, infarct area and markers for brain injury were all ameliorated by intra-arterial HUK treatment. Moreover, a lower expression of inflammatory factors including interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, and a higher expression of IL-10 were observed in the intra-arterial HUK treatment group than that in the pMCAO group. Additionally, when comparing with pMCAO group, a lower level of caspase-3, bax, and apoptotic rate, and a higher level of bcl-2, p-PI3K, p-AKT and p-FoxO1were observed in the pMCAO + HUK group. These results suggest that intra-arterial administration of HUK is a promising therapeutic strategy against pMCAO induced brain injury, and PI3K/AKT/FoxO1 signaling pathway may be involved in this process.

Mild focal hypothermia regulates the dynamic polarization of microglia after ischemic stroke in mice

Objectives The protective effects of hypothermia on acute stroke have been demonstrated in many studies. However, its underlying mechanisms have not been thoroughly elucidated. Following an ischemic stroke event, microglia undertakes an early 'healthy' M2 phenotype and gradually transform into a 'sick' M1 phenotype over time. This transformation of polarity of microglia has influence on the degree of damage following a stroke. This study investigated the effects of mild focal hypothermia on microglia polarization following ischemic stroke. Methods Transient cerebral ischemic models were created by intraluminal filament occlusion of right middle cerebral artery (MCAO) in mice for one hour. By placing an ice box under their skull, hypothermia of mice brain was initiated immediately following MCAO for 2 h. Temporal muscle temperature was recorded and maintained between 32 and 34 °C. Brain tissue loss was assessed by hematoxylin and eosin (H&E) staining 28 days after MCAO. Quantitative real-time polymerase chain reaction (qPCR) and immunostaining were used to assess phenotype of microglia in different ischemic perfusion time. Results Hypothermia reduced brain tissue loss 28 days after ischemic stroke. Hypothermia also reduced the number of CD16-positive M1 microglia and increased the numbers of CD206-positive M2 microglia following ischemic stroke. Moreover, hypothermia also led to the reduction of the M1 markers at the level of transcription, while it increased the expression of mRNA for M2 markers. Conclusions Hypothermia is protective following ischemic stroke and can reduce brain tissue loss. Moreover, hypothermia shifts the polarization of microglia from the M1 to the M2 phenotype in the ischemic mice brain. This observed biological phenomenon may partially explain the protective effects seen due to hypothermia in acute ischemic stroke.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Effect of fluoxetine on three-year recurrence in acute ischemic stroke: A randomized controlled clinical study

OBJECTIVE

To evaluate the effect of fluoxetine on three-year recurrence rate of acute ischemic stroke.

PATIENTS AND METHODS

404 enrolled patients with acute ischemic stroke were randomly divided into control and treatment groups, and underwent conventional secondary preventive therapy for ischemic stroke. In addition, the treatment group was administered fluoxetine (20 mg daily for 90 days). A three-year follow-up was performed, and indicators related to risk factors of stroke were assessed at day 90 of follow-up. The effect of fluoxetine on the three-year recurrence rate of acute ischemic stroke was evaluated by survival analysis, as well as multifactor Cox regression analysis.

RESULTS

The values of systolic blood pressure, blood total cholesterol, blood low density lipoprotein and glycosylated hemoglobin at day 90 of follow-up were significantly lower in treatment group than control group (P = 0.002, P = 0.002, P = 0.018, P = 0.011, respectively). The occurrence rates of epilepsy, gastrointestinal bleeding, syncope, allergic reactions, hemorrhagic infarction, and death were not significantly different between the two groups during the follow-up (P > 0.05). The recurrence-free survival rate of ischemic stroke was significantly lower in the treatment group than control group as assessed by the Kaplan-Meier test (85.1% Vs 75.7%, P = 0.016), as well as the recurrence-free survival rate after day 90 in the three-year follow-up (87.0% Vs 79.3%, P = 0.043). Multifactor Cox regression analysis demonstrated treatment with fluoxetine was an independent factor reducing three-year recurrence in acute ischemic stroke (HR = 0.594, 95% CI: 0.376-0.938).

CONCLUSION

Treatment with fluoxetine for 90 days after acute ischemic stroke significantly reduces the three-year recurrence rate of ischemic stroke.

Quantitative high-throughput screening identifies cytoprotective molecules that enhance SUMO conjugation via the inhibition of SUMO-specific protease (SENP)2

The development of novel neuroprotective treatments for acute stroke has been fraught with failures, which supports the view of ischemic brain damage as a highly complex multifactorial process. Post-translational modifications such as small ubiquitin-like modifier (SUMO)ylation have emerged as critical molecular regulatory mechanisms in states of both homeostasis and ischemic stress, as evidenced by our previous work. Accordingly, the clinical significance of the selective control of the global SUMOylation process has become apparent in studies of ischemic pathobiology and pathophysiology. Herein, we describe a process capable of identifying and characterizing small molecules with the potential of targeting the SUMO system through inhibition of SUMO deconjugation in an effort to develop novel stroke therapies.-Bernstock, J. D., Ye, D., Smith, J. A., Lee, Y.-J., Gessler, F. A., Yasgar, A., Kouznetsova, J., Jadhav, A., Wang, Z., Pluchino, S., Zheng, W., Simeonov, A., Hallenbeck, J. M., Yang, W. Quantitative high-throughput screening identifies cytoprotective molecules that enhance SUMO-conjugation via the inhibition of SUMO-specific protease (SENP)2.

Neuroprotective and regenerative roles of intranasal Wnt-3a administration after focal ischemic stroke in mice

Wnt signaling is a conserved pathway involved in expansion of neural progenitors and lineage specification during development. However, the role of Wnt signaling in the post-stroke brain has not been well-elucidated. We hypothesized that Wnt-3a would play an important role for neurogenesis and brain repair. Adult male mice were subjected to a focal ischemic stroke targeting the sensorimotor cortex. Mice that received Wnt-3a (2 µg/kg/day, 1 h after stroke and once a day for the next 2 days, intranasal delivery) had reduced infarct volume compared to stroke controls. Wnt-3a intranasal treatment of seven days upregulated the expression of brain-derived growth factor (BDNF), increased the proliferation and migration of neuroblasts from the subventricular zone (SVZ), resulting in increased numbers of newly formed neurons and endothelial cells in the peri-infarct zone. Both the molecular and cellular effects of Wnt-3a were blocked by the Wnt specific inhibitors XAV-939 or Dkk-1. In functional assays, Wnt-3a treatment enhanced the local cerebral blood flow (LCBF) in the peri-infarct, as well as improved sensorimotor functions in a battery of behavioral tests. Together, our data demonstrates that the Wnt-3a signaling can act as a dual neuroprotective and regenerative factor for the treatment of ischemic stroke.

Neuroprotective Effects of neuroEPO Using an In Vitro Model of Stroke

Erythropoietin (EPO) is a glycoprotein initially identified as a hormone synthesized and secreted by the kidney that regulates erythropoiesis. EPO, and a group of its derivatives, are being evaluated as possible neuroprotective agents in cerebral ischemia. The objective of this study, using an in vitro model, was to determine how neuroEPO—which is a variant of EPO with a low sialic acid content—protects neurons from the toxic action of glutamate. Primary neuronal cultures were obtained from the forebrains of Wistar rat embryos after 17 days of gestation. Excitotoxicity was induced after nine days of in vitro culture by treatment with a medium containing 100 µM glutamate for 15 min. After this time, a new medium containing 100 ng of neuroEPO/mL was added. Morphological cell change was assessed by phase-contrast microscopy. Oxidative stress was analysed by measuring antioxidant and oxidant activity. After 24 h, the treatment with 100 ng of neuroEPO/mL showed a significant (p < 0.01) decrease in mortality, compared to cells treated with glutamate alone. neuroEPO treatment decreased mortality and tended to reproduce the morphological characteristics of the control. The oxidative stress induced by glutamate is reduced after neuroEPO treatment. These results confirm that neuroEPO has a protective effect against neuronal damage induced by excitotoxicity, improving antioxidant activity in the neuron, and protecting it from oxidative stress.

Neuronal-like differentiated SH-SY5Y cells adaptation to a mild and transient H2 O2 -induced oxidative stress

Preconditioning (PC) is a cell adaptive response to oxidative stress and, with regard to neurons, can be considered as a neuroprotective strategy. The aim of the present study was to verify how neuronal-like differentiated SH-SY5Y cells adapt to a mild and transient H₂ O₂ -induced oxidative stress and, hence, whether may be considered as more sensitive cell model to study PC pathways. A first screening allowed to define H₂ O₂ concentrations for PC (10μM-50μM), applied before damage(100μM H₂ O₂ ). Cell viability measured 24 hours after 100μM H₂ O₂ -induced damage was ameliorated by 24-hour pre-exposure to low-concentration H₂ O₂ (10μM-30μM) with cell size as well restored. Markers for apoptosis (Bcl-2 and Bad), inflammation (iNOS), and redox system (MnSOD) were also determined, showing that, in cells pre-exposed to 10μM H₂ O₂ and then submitted to 100μM H₂ O₂ , Bcl-2 levels were higher, Bad and iNOS levels were lower than those observed in damaged cells, and MnSOD levels were unchanged. Such findings show that (1) neuronal-like differentiated SH-SY5Y cells are a suitable model to investigate PC response and more sensitive to the effect of a mild and transient H₂ O₂ -induced oxidative stress with respect to other neuronal cells; (2) 10μM H₂ O₂ -induced PC is mediated by apoptotic and inflammatory pathways, unlike antioxidant system; (3) such neuroprotective strategy and underlying signals proven in neuronal-like differentiated SH-SY5Y cells may contribute to understand in vivo PC mechanisms and to define a window for pharmacological intervention, namely, related to ischemic brain damage.

SIGNIFICANCE OF THE STUDY

Neuronal-like differentiated SH-SY5Y cells are a suitable model to investigate PC, an endogenous neuroprotective response to a mild and transient H₂ O₂ -induced oxidative stress, elicited by 24-hour exposure to very low H₂ O₂ concentrations and mediated by both apoptotic and inflammatory pathways. This model reflects in vivo PC mechanisms occurring after brain trauma and provides novel information about pathways and time of protection useful for an appropriate pharmacological intervention.

Sustained anti-inflammatory effects of TGF-β1 on microglia/macrophages

Ischemic brain injuries caused release of damage-associated molecular patterns (DAMPs) that activate microglia/macrophages (MG/MPs) by binding to Toll-like receptors. Using middle cerebral artery transiently occluded rats, we confirmed that MG/MPs expressed inducible nitric oxide synthase (iNOS) on 3days after reperfusion (dpr) in ischemic rat brain. iNOS expression almost disappeared on 7dpr when transforming growth factor-β1 (TGF-β1) expression was robustly increased. After transient incubation with TGF-β1 for 24h, rat primary microglial cells were incubated with lipopolysaccharide (LPS) and released NO level was measured. The NO release was persistently suppressed even 72h after removal of TGF-β1. The sustained TGF-β1 effects were not attributable to microglia-derived endogenous TGF-β1, as revealed by TGF-β1 knockdown and in vitro quantification studies. Then, boiled supernatants prepared from ischemic brain tissues showed the similar sustained inhibitory effects on LPS-treated microglial cells that were prevented by the TGF-β1 receptor-selective blocker SB525334. After incubation with TGF-β1 for 24h and its subsequent removal, LPS-induced phosphorylation of IκB kinases (IKKs), IκB degradation, and NFκB nuclear translocation were inhibited in a sustained manner. SB525334 abolished all these effects of TGF-β1. In consistent with the in vitro results, phosphorylated IKK-immunoreactivity was abundant in MG/MPs in ischemic brain lesion on 3dpr, whereas it was almost disappeared on 7dpr. The findings suggest that abundantly produced TGF-β1 in ischemic brain displays sustained anti-inflammatory effects on microglial cells by persistently inhibiting endogenous Toll-like receptor ligand-induced IκB degradation.

Co-administration of liposomal fasudil and tissue plasminogen activator ameliorated ischemic brain damage in occlusion model rats prepared by photochemically induced thrombosis

Delivery of neuroprotectants with liposomes has been shown to be effective for the treatment of ischemic stroke. We have recently revealed that intravenous administration of liposomal fasudil (Fasudil-Lip), a Rho-kinase inhibitor, prior to thrombolysis with tissue plasminogen activator (t-PA) can extend the narrow therapeutic time window (TTW) of t-PA. In the present study, we examined the influence of t-PA treatment on liposomal accumulation into the ischemic region and cerebroprotective effect of combined treatment with Fasudil-Lip and t-PA performed at the same timing after the onset of ischemia in middle cerebral artery occlusion (MCAO) prepared by photochemically induced thrombosis. The t-PA administration into MCAO rats 3 h after occlusion brought about significantly higher accumulation of intravenously injected PEGylated liposomes in wide area of ischemic region. Confocal images showed that extravasation of the liposomes from cerebral vessels into brain parenchyma was markedly facilitated by the t-PA treatment which increased blood flow in cerebral vessels. Importantly, co-administration of Fasudil-Lip and t-PA after 3 h occlusion, beyond the TTW of t-PA in MCAO rats, significantly suppressed brain cell damage compared with t-PA treatment alone. These findings suggest that co-administration of Fasudil-Lip and t-PA should lead to prolong t-PA's TTW and become a useful therapeutic option for ischemic stroke.

An open-label, one-arm, dose-escalation study to evaluate safety and tolerability of extremely low frequency magnetic fields in acute ischemic stroke

Extremely low frequency magnetic fields (ELF-MF) could be an alternative neuroprotective approach for ischemic stroke because preclinical studies have demonstrated their effects on the mechanisms underlying ischemic damage. The purpose of this open-label, one arm, dose-escalation, exploratory study is to evaluate the safety and tolerability of ELF-MF in patients with acute ischemic stroke. Within 48 hours from the stroke onset, patients started ELF-MF treatment, daily for 5 consecutive days. Clinical follow-up lasted 12 months. Brain MRI was performed before and 1 month after the treatment. The distribution of ELF-MF in the ischemic lesion was estimated by dosimetry. Six patients were stimulated, three for 45 min/day and three for 120 min/day. None of them reported adverse events. Clinical conditions improved in all the patients. Lesion size was reduced in one patient stimulated for 45 minutes and in all the patients stimulated for 120 minutes. Magnetic field intensity within the ischemic lesion was above 1 mT, the minimum value able to trigger a biological effect in preclinical studies. Our pilot study demonstrates that ELF-MF are safe and tolerable in acute stroke patients. A prospective, randomized, placebo-controlled, double-blind study will clarify whether ELF-MFs could represent a potential therapeutic approach.

Neuroprotection of Catalpol for Experimental Acute Focal Ischemic Stroke: Preclinical Evidence and Possible Mechanisms of Antioxidation, Anti-Inflammation, and Antiapoptosis

Neuroprotection is defined as using a therapy that affects the brain tissue in the still-viable ischemic penumbra to salvage or delay the infarction. Catalpol, the main active principle of the root of Radix Rehmanniae, was reported to have pleiotropic neuroprotective effects in neurodegenerative diseases including ischemic stroke. Here, we evaluated the neuroprotective effects of catalpol in experimental acute ischemic stroke. Studies on catalpol in animal models of acute ischemic stroke were identified from 6 databases. Twenty-five studies involving 805 animals were included. Twelve comparisons showed significant effects of catalpol on decreasing infarct size according to 2,3,5-triphenyltetrazolium chloride staining compared with the control (P < 0.05). One study reported significant effect of catalpol on reducing infarct size according to magnetic resonance imaging scan compared with the control (P < 0.05). Meta-analysis of these studies indicated that catalpol significantly improved the neurological function score according to Zea Longa score, Bederson score, balance beam-walking test, adhesive removal test, bar-grasping score, and corner test compared with the control (P < 0.05). In conclusion, catalpol exerted neuroprotective effects for experimental acute focal ischemic stroke, largely through reducing oxidative reactions, inhibiting apoptosis, and repressing inflammatory reactions and autophagy. However, these apparently positive findings should be interpreted with caution because of the methodological flaws.

Opening a New Time Window for Treatment of Stroke by Targeting HDAC2

Narrow therapeutic window limits treatments with thrombolysis and neuroprotection for most stroke patients. Widening therapeutic window remains a critical challenge. Understanding the key mechanisms underlying the pathophysiological events in the peri-infarct area where secondary injury coexists with neuroplasticity over days to weeks may offer an opportunity for expanding the therapeutic window. Here we show that ischemia-induced histone deacetylase 2 (HDAC2) upregulation from 5 to 7 d after stroke plays a crucial role. In this window phase, suppressing HDAC2 in the peri-infarct cortex of rodents by HDAC inhibitors, knockdown or knock-out of Hdac2 promoted recovery of motor function from stroke via epigenetically enhancing cells survival and neuroplasticity of surviving neurons as well as reducing neuroinflammation, whereas overexpressing HDAC2 worsened stroke-induced functional impairment of both WT and Hdac2 conditional knock-out mice. More importantly, inhibiting other isoforms of HDACs had no effect. Thus, the intervention by precisely targeting HDAC2 in this window phase is a novel strategy for the functional recovery of stroke survivors.SIGNIFICANCE STATEMENT Narrow time window phase impedes current therapies for stroke patients. Understanding the key mechanisms underlying secondary injury may open a new window for pharmacological interventions to promote recovery from stroke. Our study indicates that ischemia-induced histone deacetylase 2 upregulation from 5 to 7 d after stroke mediates the secondary functional loss by reducing survival and neuroplasticity of peri-infarct neurons as well as augmenting neuroinflammation. Thus, precisely targeting histone deacetylase 2 in the window phase provides a novel therapeutic strategy for stroke recovery.

Opportunities for the repurposing of PARP inhibitors for the therapy of non-oncological diseases

The recent clinical availability of the PARP inhibitor olaparib (Lynparza) opens the door for potential therapeutic repurposing for non-oncological indications. Considering (a) the preclinical efficacy data with PARP inhibitors in non-oncological diseases and (b) the risk-benefit ratio of treating patients with a compound that inhibits an enzyme that has physiological roles in the regulation of DNA repair, we have selected indications, where (a) the severity of the disease is high, (b) the available therapeutic options are limited, and (c) the duration of PARP inhibitor administration could be short, to provide first-line options for therapeutic repurposing. These indications are as follows: acute ischaemic stroke; traumatic brain injury; septic shock; acute pancreatitis; and severe asthma and severe acute lung injury. In addition, chronic, devastating diseases, where alternative therapeutic options cannot halt disease development (e.g. Parkinson's disease, progressive multiple sclerosis or severe fibrotic diseases), should also be considered. We present a preclinical and clinical action plan for the repurposing of PARP inhibitors.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Activation of the ATF6 branch of the unfolded protein response in neurons improves stroke outcome

Impaired function of the endoplasmic reticulum (ER stress) is a hallmark of many human diseases including stroke. To restore ER function in stressed cells, the unfolded protein response (UPR) is induced, which activates 3 ER stress sensor proteins including activating transcription factor 6 (ATF6). ATF6 is then cleaved by proteases to form the short-form ATF6 (sATF6), a transcription factor. To determine the extent to which activation of the ATF6 UPR branch defines the fate and function of neurons after stroke, we generated a conditional and tamoxifen-inducible sATF6 knock-in mouse. To express sATF6 in forebrain neurons, we crossed our sATF6 knock-in mouse line with Emx1-Cre mice to generate ATF6-KI mice. After the ATF6 branch was activated in ATF6-KI mice with tamoxifen, mice were subjected to transient middle cerebral artery occlusion. Forced activation of the ATF6 UPR branch reduced infarct volume and improved functional outcome at 24 h after stroke. Increased autophagic activity at early reperfusion time after stroke may contribute to the ATF6-mediated neuroprotection. We concluded that the ATF6 UPR branch is crucial to ischemic stroke outcome. Therefore, boosting UPR pro-survival pathways may be a promising therapeutic strategy for stroke.