Pharmacotherapy of cerebral ischemia

Inhibition of Connexin43 hemichannels with Gap19 protects cerebral ischemia/reperfusion injury via the JAK2/STAT3 pathway in mice

Functional disruption of the neurovascular unit may lead to aggravation of ischemic cerebral injury. Connexin43 (Cx43)-dependent gap junctional channels (GJCs) are critical in maintaining brain homeostasis. However, excessive opening of hemichannels (HCs) after cerebral ischemia may cause apoptosis and finally lead to amplification of ischemic injury. Previous studies indicated that Cx43 mimetic peptides Gap26 and Gap27 may protect cerebral ischemic injury, but the latest studies showed they also inhibit the opening of GJCs, which are beneficial for neuroprotection. Recent studies showed that Gap19 is a new specific inhibitor of Cx43 HCs. We investigated the role of Gap19 on cerebral ischemia/reperfusion (I/R) injury in a mouse model of middle cerebral artery occlusion (MCAO). Ventricle-injected Gap19 significantly alleviated infarct volume, neuronal cell damage and neurological deficits after ischemia, the neuroprotective effect of Gap19 was significant stronger than Gap26. Post-treatment with TAT-Gap19 still provided neuroprotection when it was administered intraperitoneally at 4 h after reperfusion. In addition, we found that Gap19 decreased the levels of cleaved caspase-3 and Bax and increased the level of Bcl-2, suggesting the anti-apoptotic activity of specifically blocking the Cx43 HCs. Furthermore, our data indicate that Gap19 treatment increased the levels of phosphorylated JAK2 and STAT3 both in vivo and in vitro. Gap19 inhibited hemichannel activity assessed by dye uptake in astrocytes. And we detected that pSTAT3 co-localized with Cx43 together in astrocytes after oxygen glucose deprivation (OGD) injury. Finally, AG490, a blocker of the JAK2/STAT3 pathway, could reverse the neuroprotective effects of Gap19 both in vivo and in vitro. Our experiment investigated the anti-apoptotic activity of Gap19, the specific inhibitor of Cx43 HCs, and the potential mechanisms. Our results demonstrated that Gap19 plays an anti-apoptotic role via activating the JAK2/STAT3 pathway after cerebral I/R injury, indicating that specific blocking of Cx43 HCs is a potential target for ischemic stroke.

P2 receptor interaction and signalling cascades in neuroprotection

Nucleotides can contribute to the survival of different glial and neuronal models at the nervous system via activation of purinergic P2X and P2Y receptors. Their activation counteracts different proapoptotic events, such as excitotoxicity, mitochondrial impairment, oxidative stress and DNA damage, which concur to elicit cell loss in different processes of neurodegeneration and brain injury. Thus, it is frequent to find that different neuroprotective mediators converge in the activation of the same intracellular survival pathways to protect cells from death. The present review focuses on the role of P2Y₁ and P2Y₁₃ metabotropic receptors, and P2X7 ionotropic receptors to regulate the balance between survival and apoptosis. In particular, we analyze the intracellular pathways involved in the signaling of these nucleotide receptors to elicit survival, including calcium/PLC, PI3K/Akt/GSK3, MAPK cascades, and the expression of antioxidant and antiapoptotic genes. This review emphasizes the novel contribution of nucleotide receptors to maintain cell homeostasis through the regulation of MAP kinases and phosphatases. Unraveling the different roles found for nucleotide receptors in different models and cellular contexts may be crucial to delineate future therapeutic applications based on targeting nucleotide receptors for neuroprotection.

Reframing the Biological Basis of Neuroprotection Using Functional Genomics: Differentially Weighted, Time-Dependent Multifactor Pathogenesis of Human Ischemic Brain Damage

Background: Neuroprotection studies are generally unable to demonstrate efficacy in humans. Our specific hypothesis is that multiple pathophysiologic pathways, of variable importance, contribute to ischemic brain damage. As a corollary to this, we discuss the broad hypothesis that a multifaceted approach will improve the probability of efficacious neuroprotection. But to properly test this hypothesis the nature and importance of the multiple contributing pathways needs elucidation. Our aim is to demonstrate, using functional genomics, in human cardiac surgery procedures associated with cerebral ischemia, that the pathogenesis of perioperative human ischemic brain damage involves the function of multiple variably weighted proteins involving several pathways. We then use these data and literature to develop a proposal for rational design of human neuroprotection protocols.

Methods: Ninety-four patients undergoing deep hypothermic circulatory arrest (DHCA) and/or aortic valve replacement surgery had brain damage biomarkers, S100β and neurofilament H (NFH), assessed at baseline, 1 and 24 h post-cardiopulmonary bypass (CPB) with analysis for association with 92 single nucleotide polymorphisms (SNPs) (selected by co-author WAK) related to important proteins involved in pathogenesis of cerebral ischemia.

Results: At the nominal significance level of 0.05, changes in S100β and in NFH at 1 and 24 h post-CPB were associated with multiple SNPs involving several prospectively determined pathophysiologic pathways, but were not individually significant after multiple comparison adjustments. Variable weights for the several evaluated SNPs are apparent on regression analysis and, notably, are dissimilar related to the two biomarkers and over time post CPB. Based on our step-wise regression model, at 1 h post-CPB, SOD2, SUMO4, and GP6 are related to relative change of NFH while TNF, CAPN10, NPPB, and SERPINE1 are related to the relative change of S100B. At 24 h post-CPB, ADRA2A, SELE, and BAX are related to the relative change of NFH while SLC4A7, HSPA1B, and FGA are related to S100B.

Conclusions: In support of the proposed hypothesis, association SNP data suggest function of specific disparate proteins, as reflected by genetic variation, may be more important than others with variation at different post-insult times after human brain ischemia. Such information may support rational design of post-insult time-sensitive multifaceted neuroprotective therapies.

Current and future perspectives on the treatment of cerebral ischemia

INTRODUCTION

After heart disease and combined forms of cancer, stroke is the leading cause of death in the United States. Currently, tissue-plasminogen activator (tPA) thrombolysis is the only thrombolytic therapy that has been shown to improve patient outcome. Presently, the only antithrombotic drug treatment that has proven effective at improving acute ischemic stroke patient outcome is aspirin administration. Despite these studies, no clinical trials have yet demonstrated a reliably effective pharmacological treatment. Areas covered: We conducted a search of recent drug studies for ischemic stroke on clinicaltrials.gov in addition to a literature search for acute ischemic stroke therapy using PubMed. This review details our findings of recent advancements in the pharmacological treatment of acute ischemic stroke. Expert commentary: We concluded that recent attempts to establish new pharmacological treatment protocols for acute ischemic stroke have had limited success, but many Phase III and Phase IV clinical trials demonstrate promise. Moreover, several studies have demonstrated the efficacy of dual-antiplatelet therapies at reducing risk of secondary stroke. Studies for novel therapeutic targets for neuroprotection have been largely unsuccessful. Some trials had positive results; however, there is much room for improvement and other studies show promise in their preliminary stages.

General anesthetics as a factor of effective neuroprotection in ischemic stroke models

Stroke is the second leading cause of death in the world. Unfortunately, only a few drugs have been proved in clinical trials. Drug development of the last decade has been focused substantially on a promising and heterogeneous group of neuroprotective drugs. Hundreds of compounds were suggested as new putative neuroprotectors, which effectiveness was confirmed in preclinical trials only. At the present time discrepancy between results of preclinical studies and clinical trials requires careful analysis. One of the least evaluated and probably the most noticeable reasons is general anesthesia - an obligatory component of an overwhelming majority of existing animal stroke models. The aim of the review is to describe known mechanisms of common general anesthetics influence on ionotropic and metabotropic plasma membrane receptors, and key signal pathways involved in neuronal hypoxic-ischemic injury and survival

[Dysfunction of the blood-brain barrier during ischaemia: a therapeutic concern]

Since it was discovered and its brain-protective role characterized, the blood-brain barrier (BBB), through the permeability-restricting action of the brain capillary endothelial cells, has been representing a hurdle for 95% of new medical compounds targeting the central nervous system. Recently, a BBB dysfunction is being found in an increasing number of pathologies such as brain ischaemic stroke, whose only therapy consists in a pharmacological thrombolysis limited to a small percentage of the admitted patients, because of the toxical effects of thrombolytics. And since the clinical failure of promising neuroprotectants, numerous studies of brain ischaemia were carried out, with physiopathological or pharmacological approaches refocused on the BBB, whose structural complexity is now expanded to perivascular cells, all forming a functional unit named the neurovascular unit (NVU). Nevertheless, in spite of the numerous molecular mechanisms identified, the process of BBB dysfunction in the ischaemia/reperfusion cascade remains insufficiently established to explain the pleiotropic action exerted by new pharmacological compounds, possibly protecting the entire NVU and representing potential treatments.

Endothelial cells and astrocytes: a concerto en duo in ischemic pathophysiology

The neurovascular/gliovascular unit has recently gained increased attention in cerebral ischemic research, especially regarding the cellular and molecular changes that occur in astrocytes and endothelial cells. In this paper we summarize the recent knowledge of these changes in association with edema formation, interactions with the basal lamina, and blood-brain barrier dysfunctions. We also review the involvement of astrocytes and endothelial cells with recombinant tissue plasminogen activator, which is the only FDA-approved thrombolytic drug after stroke. However, it has a narrow therapeutic time window and serious clinical side effects. Lastly, we provide alternative therapeutic targets for future ischemia drug developments such as peroxisome proliferator- activated receptors and inhibitors of the c-Jun N-terminal kinase pathway. Targeting the neurovascular unit to protect the blood-brain barrier instead of a classical neuron-centric approach in the development of neuroprotective drugs may result in improved clinical outcomes after stroke.

Preclinical evaluation of postischemic dehydroascorbic Acid administration in a large-animal stroke model

Dehydroascorbic acid (DHA), a blood-brain barrier transportable form of ascorbic acid, confers robust neuroprotection following murine stroke. In an effort to translate this promising neuroprotective strategy into human clinical trial, we evaluated postischemic DHA administration in a large-animal stroke model. Thirty-six adult male baboons were initially randomized to undergo transorbital craniectomy to induce transient cerebral artery occlusion and to receive postischemic dosing of either 500 mg/kg of DHA or vehicle. Primary outcomes included infarct volume, determined by magnetic resonance imaging, as well as neurological function evaluated on the day of sacrifice. The midpoint interim analysis (n = 9 per cohort) revealed that DHA administration did not significantly improve either infarct volume or neurological function. The study was terminated after a determination of statistical futility. We were unable to confirm a neuroprotective effect for postischemic DHA administration in our large-animal model using a dosing scheme that was previously successful in rodents. Further analysis of the efficacy of DHA administration must thus be undertaken prior to clinical translation.

Therapeutic targets for neuroprotection in acute ischemic stroke: lost in translation?

The development of a suitable neuroprotective agent to treat ischemic stroke has failed when transitioned to the clinical setting. An understanding of the molecular mechanisms involved in neuronal injury during ischemic stroke is important, but must be placed in the clinical context. Current therapeutic targets have focused on the preservation of the ischemic penumbra in the hope of improving clinical outcomes. Unfortunately, most patients in the ultra-early time windows harbor penumbra but have tremendous variability in the size of the core infarct, the ultimate predictor of prognosis. Understanding this variability may allow for proper patient selection that may better correlate to bench models. Reperfusion therapies are rapidly evolving and have been shown to improve clinical outcomes. The use of neuroprotective agents to prolong time windows prior to reperfusion or to prevent reperfusion injury may present future therapeutic targets for the treatment of ischemic stroke. We review the molecular pathways and the clinical context from which future targets may be identified.

The immunomodulatory sphingosine 1-phosphate analog FTY720 reduces lesion size and improves neurological outcome in a mouse model of cerebral ischemia

Cerebral ischemia is accompanied by fulminant cellular and humoral inflammatory changes in the brain which contribute to lesion development after stroke. A tight interplay between the brain and the peripheral immune system leads to a biphasic immune response to stroke consisting of an early activation of peripheral immune cells with massive production of proinflammatory cytokines followed by a systemic immunosuppression within days of cerebral ischemia that is characterized by massive immune cell loss in spleen and thymus. Recent work has documented the importance of T lymphocytes in the early exacerbation of ischemic injury. The lipid signaling mediator sphingosine 1-phosphate-derived stable analog FTY720 (fingolimod) acts as an immunosuppressant and induces lymphopenia by preventing the egress of lymphocytes, especially T cells, from lymph nodes. We found that treatment with FTY720 (1mg/kg) reduced lesion size and improved neurological function after experimental stroke in mice, decreased the numbers of infiltrating neutrophils, activated microglia/macrophages in the ischemic lesion and reduced immunohistochemical features of apoptotic cell death in the lesion.