The mechanisms of cell death in focal cerebral ischemia highlight neuroprotective perspectives by anti-caspase therapy

Astrocyte-Neuronal Communication and Its Role in Stroke

Astrocytes are the most abundant glial cells in the central nervous system. These cells are an important hub for intercellular communication. They participate in various pathophysiological processes, including synaptogenesis, metabolic transformation, scar production, and blood-brain barrier repair. The mechanisms and functional consequences of astrocyte-neuron signaling are more complex than previously thought. Stroke is a disease associated with neurons in which astrocytes also play an important role. Astrocytes respond to the alterations in the brain microenvironment after stroke, providing required substances to neurons. However, they can also have harmful effects. In this review, we have summarized the function of astrocytes, their association with neurons, and two paradigms of the inflammatory response, which suggest that targeting astrocytes may be an effective strategy for treating stroke.

Apoptosis regulation in the penumbra after ischemic stroke: expression of pro- and antiapoptotic proteins

Ischemic stroke is the leading cause of human disability and mortality in the world. The main problem in stroke therapy is the search of efficient neuroprotector capable to rescue neurons in the potentially salvageable transition zone (penumbra), which is expanding after brain damage. The data on molecular mechanisms of penumbra formation and expression of diverse signaling proteins in the penumbra during first 24 h after ischemic stroke are discussed. Two basic features of cell death regulation in the ischemic penumbra were observed: (1) both apoptotic and anti-apoptotic proteins are simultaneously over-expressed in the penumbra, so that the fate of individual cells is determined by the balance between these opposite tendencies. (2) Similtaneous and concerted up-regulation in the ischemic penumbra of proteins that execute apoptosis (caspases 3, 6, 7; Bcl-10, SMAC/DIABLO, AIF, PSR), signaling proteins that regulate different apoptosis pathways (p38, JNK, DYRK1A, neurotrophin receptor p75); transcription factors that control expression of various apoptosis regulation proteins (E2F1, p53, c-Myc, GADD153); and proteins, which are normally involved in diverse cellular functions, but stimulate apoptosis in specific situations (NMDAR2a, Par4, GAD65/67, caspase 11). Hence, diverse apoptosis initiation and regulation pathways are induced simultaneously in penumbra from very different initial positions. Similarly, various anti-apoptotic proteins (Bcl-x, p21/WAF-1, MDM2, p63, PKBα, ERK1, RAF1, ERK5, MAKAPK2, protein phosphatases 1α and MKP-1, estrogen and EGF receptors, calmodulin, CaMKII, CaMKIV) are upregulated. These data provide an integral view of neurodegeneration and neuroprotection in penumbra. Some discussed proteins may serve as potential targets for anti-stroke therapy.

The Expression and Localization of Histone Acetyltransferases HAT1 and PCAF in Neurons and Astrocytes of the Photothrombotic Stroke-Induced Penumbra in the Rat Brain Cortex

Stroke is one of the leading reasons of human death. Ischemic penumbra that surrounds the stroke-induced infarction core is potentially salvageable, but molecular mechanisms of its formation are poorly known. Histone acetylation induces chromatin decondensation and stimulates gene expression. We studied the changes in the levels and localization of histone acetyltransferases HAT1 and PCAF in penumbra after photothrombotic stroke (PTS, a stroke model). In PTS, laser irradiation induces local occlusion of cerebral vessels after photosensitization by Rose Bengal. HAT1 and PCAF are poorly expressed in normal cortical neurons and astrocytes, but they are overexpressed 4-24 h after PTS. Their predominant localization in neuronal nuclei did not change after PTS, but their levels in the astrocyte nuclei significantly increased. Western blotting showed the increase of HAT1 and PCAF levels in the cytoplasmic fraction of the PTS-induced penumbra. In the nuclear fraction, PCAF level did not change, and HAT1 was overexpressed only at 24 h post-PTS. PTS-induced upregulation of HAT1 and PCAF in the penumbra was mainly associated with overexpression in the cytoplasm of neurons and especially astrocytes. HAT1 and PCAF did not co-localize with TUNEL-positive cells that indicated their nonparticipation in PTS-induced apoptosis.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Up-regulation of Sirt1/miR-149-5p signaling may play a role in resveratrol induced protection against ischemia via p53 in rat brain

Micro-RNA(miRNA) are well studied small noncoding RNA, which plays a diverse role in the regulation of vital elements in cell survival and apoptosis. However, the functional significance of miRNAs after the pathogenesis of ischemic stroke remains unclear. The present study is designed to investigate the regulatory role of miR-149-5p on Sirtuin-1/p53 axis during ischemic-reperfusion-induced injury. Middle cerebral artery occlusion (MCAO) was performed by nylon monofilament for 60 min. Resveratrol was administered via intraperitoneal (IP) route, 30 min before the MCAO. Our study demonstrated that the miR-149-5p levels were markedly decreased at 24 h after ischemic-reperfusion (I/R) injury. Further, we observed decreased p53 protein expression and increased miR-149-5p activity on sirtuin1 (Sirt1) activation with resveratrol after 24 h following MCAO. Moreover, immunohistochemistry studies found that resveratrol treatment significantly decreased the immunoreactivity of p53 and caspase-3 on activation of Sirt1/miR149-5p axis. In conclusion, our findings suggest that miR-149-5p could play a regulatory role in neuronal cell death via Sirt1/p53 axis, which offers a new target for novel therapeutic interventions during acute ischemic stroke.

Timing of Cord Blood Treatment after Experimental Stroke Determines Therapeutic Efficacy

Embolic stroke is thought to cause irreparable damage in the brain immediately adjacent to the region of reduced blood perfusion. Therefore, much of the current research focuses on treatments such as anti-inflammatory, neuroprotective, and cell replacement strategies to minimize behavioral and physiological consequences. In the present study, intravenous delivery of human umbilical cord blood cells (HUCBC) 48 h after a middle cerebral artery occlusion (MCAo) in a rat resulted in both behavioral and physiological recovery. Nissl and TUNEL staining demonstrated that many of the neurons in the core were rescued, indicating that while both necrotic and apoptotic cell death occur in ischemia, it is clear that apoptosis plays a larger role than first anticipated. Further, immunohistochemical and histochemical analysis showed a diminished and/or lack of granulocyte and monocyte infiltration and astrocytic and microglial activation in the parenchyma in animals treated with HUCBC 48 h poststroke. Successful treatment at this time point should offer encouragement to clinicians that a therapy with a broader window of efficacy may soon be available to treat stroke.

Neuroprotective effect of Panax notoginseng plysaccharides against focal cerebral ischemia reperfusion injury in rats

Our present study was conducted to investigate whether Panax notoginseng plysaccharides (PNPS) exerted a neuroprotective effect against focal cerebral ischemia/reperfusion (I/R) injury in rats. Before mice were subjected to middle cerebral artery occlusion (MCAO) for 2 h and reperfusion for 22 h, PNPS at the doses of 50, 100, and 200 mg/kg was administered once a day intragastrically for continuous 7 days. Oral administration of PNPS could significantly reduce the severity of neurological deficits, infarct volumes, cerebral edema, and neuronal death caused by MCAO in rats. Moreover, in the presence of PNPS, the Bcl-2/Bax ratio increased, but the level of cleaved caspase-3 reduced. Thus, these finding suggested that suppressing apoptosis through increasing Bcl-2/Bax ratio and evoking caspase-3 cascade should be potential mechanism by which PNPS exerts its neuroprotective function against focal cerebral I/R injury.

Neuroprotective effects of quetiapine on neuronal apoptosis following experimental transient focal cerebral ischemia in rats

OBJECTIVE

This study was undertaken in the belief that the atypical antipsychotic drug quetiapine could prevent apoptosis in the penumbra region following ischemia, taking into account findings that show 5-hydroxytryptamine-2 receptor blockers can prevent apoptosis.

METHODS

We created 5 groups, each containing 6 animals. Nothing was done on the K-I group used for comparisons with the other groups to make sure adequate ischemia had been achieved. The K-II group was sacrificed on the 1st day after transient focal cerebral ischemia and the K-III group on the 3rd day. The D-I group was administered quetiapine following ischemia and sacrificed on the 1st day while the D-II group was administered quetiapine every day following the ischemia and sacrificed on the 3rd day. The samples were stained with the immunochemical TUNEL method and the number of apoptotic cells were counted.

RESULTS

There was a significant difference between the first and third day control groups (K-II/K-III : p=0.004) and this indicates that apoptotic cell death increases with time. This increase was not encountered in the drug groups (D-I/D-II : p=1.00). Statistical analysis of immunohistochemical data revealed that quetiapine decreased the apoptotic cell death that normally increased with time.

CONCLUSION

Quetiapine is already in clinical use and is a safe drug, in contrast to many substances that are used to prevent ischemia and are not normally used clinically. Our results and the literature data indicate that quetiapine could help both as a neuronal protector and to resolve neuropsychiatric problems caused by the ischemia in cerebral ischemia cases.

Molecular Mechanisms in the Pathogenesis and Treatment of Acute Ischemic Stroke

The management of acute ischemic stroke has not made significant strides since the introduction of recombinant tissue plasminogen activator (r-TPA) two decades ago. The use of other therapies, such as heparin, aspirin, dipyridamole, and/or clopidogrel, have only moderately aided in the treatment of this ischemic disease. Therefore, major medical innovative approaches are critically needed. Because of the side effects associated with r-TPA (specifically bleeding) and its limited 3-h therapeutic window, new studies using current developments encountered in the molecular biology of ischemia are being incorporated into the potential therapy of ischemic stroke. A review of the major advances in the field, including glutamate receptor blockade, magnesium infusion, inflammation blockade, apoptosis inhibition, and other therapies, is introduced with special emphasis on the molecular findings recognized as targets for a better and more effective treatment. As new therapies are being considered, the time of administration is becoming a central point of study for the application of novel therapeutic initiatives.

Controlled delivery of heat shock protein using an injectable microsphere/hydrogel combination system for the treatment of myocardial infarction

Myocardial infarction causes a high rate of morbidity and mortality worldwide, and heat shock proteins as molecular chaperones have been attractive targets for protecting cardiomyoblasts under environmental stimuli. In this study, in order to enhance the penetration of heat shock protein 27 (HSP27) across cell membranes, we fused HSP27 with transcriptional activator (TAT) derived from human immunodeficiency virus (HIV) as a protein transduction domain (PTD). We loaded the fusion protein (TAT-HSP27) into microsphere/hydrogel combination delivery systems to control the release behavior for prolonged time periods. We found that the release behavior of TAT-HSP27 was able to be controlled by varying the ratio of PLGA microspheres and alginate hydrogels. Indeed, the released fusion protein maintained its bioactivity and could recover the proliferation of cardiomyoblasts cultured under hypoxic conditions. This approach to controlling the release behavior of TAT-HSP27 using microsphere/hydrogel combination delivery systems may be useful for treating myocardial infarction in a minimally invasive manner.

Protection from brain damage and bacterial infection in murine stroke by the novel caspase-inhibitor Q-VD-OPH

Infarction size and infections are important determinants of stroke outcome in humans. Bacterial infections are promoted by stroke-induced immunodeficiency which in experimental stroke is mainly characterized by extensive lymphocyte apoptosis and dysfunction. Pharmacological inhibition of caspases may improve stroke outcome not only by reducing apoptotic brain damage but also by attenuating stroke-induced immunodeficiency. We investigated the effects of systemic administration of the novel, non-toxic caspase-inhibitor quinolyl-valyl-O-methylaspartyl-[-2,6-difluorophenoxy]-methyl ketone (Q-VD-OPH) on stroke-induced neuronal and lymphocyte apoptosis, susceptibility to infections, and mortality in a murine model of stroke induced by middle cerebral artery occlusion (MCAO). Q-VD-OPH reduced ischemic brain damage and stroke-induced programmed cell death in thymus and spleen, decreased susceptibility to post-stroke bacteremia, and improved survival. Therefore, Q-VD-OPH may be a promising therapeutic agent in stroke.

Apoptotic cell death progression after photothrombotic focal cerebral ischaemia: effects of the lipophilic iron chelator 2,2'-dipyridyl

Two different forms of cell death have been distinguished morphologically following cerebral ischaemia: necrotic and apoptotic cell death. The aim of this study was to investigate the contribution of apoptosis to ischaemic damage by carefully depicting the temporal and spatial neuronal death following focal ischaemia. For this purpose, rats were subjected to chemical photothrombosis, and histological and biochemical analyses were performed over a period of 24 h after the onset of ischaemia. In addition, the effects of the lipophilic antioxidant iron chelator 2,2'-dipyridyl (DP) were evaluated 24 h after photothrombosis when the lesion volume was maximal. Our results showed two separate waves of neuronal death. In the first wave, shrunken dark neurons were massively present as early as 2 h after photothrombosis in the infarct core. From this initial neuronal abnormal population, progressive and time-dependent changes of both necrotic and apoptotic cell death were observed, leading to ghost neurons and apoptotic bodies after 24 h. The extension of the lesion coincided with a second wave of cell death. Massive and rapid neuronal loss occurred at the infarct border, which appeared as a sharply demarcated pale region. Procaspase and poly(ADP-ribose) polymerase-1 (PARP-1) cleavages were also detected in the infarct core and surrounding damaged tissue. DP treatment markedly blocked the enlargement of the lesion, the infarct border being rescued from infarction. Furthermore, a large decrease of apoptotic bodies was associated with a significant drop of caspase and PARP-1 cleavages, suggesting that the protective effect of DP closely correlates with limitation of apoptosis expansion.

Neuroprotective activity of 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (PAN-811), a cancer therapeutic agent

3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) is a highly-hydrophobic small molecule that was originally developed for cancer therapy (Triapine, Vion Pharmaceuticals) due to its ability to inhibit ribonucleotide reductase, a key enzyme required for DNA synthesis. 3-AP has a high affinity for divalent cations, chelating the Fe(2+) at the R2 subunit of the enzyme and inhibiting formation of a tyrosyl radical essential for ribonucleotide reduction. We have demonstrated that 3-AP is also a potent neuroprotectant (as such, it is referred to as "PAN-811"). In vitro it completely blocks ischemic neurotoxicity at a concentration of 0.5 microM (EC(50) approximate, equals 0.35 microM) and hypoxic toxicity at 1.2 microM (EC(50) approximate, equals 0.75 microM). Full protection of primary cortical and striatal neurons can be achieved with 3-AP when it is added to the medium at up to six hours after an ischemic insult. 3-AP also suppresses cell death induced by neurotoxic agents, including staurosporine, veratridine and glutamate, indicating activity against a central target(s) in the neurodegenerative process. 3-AP acts via neutralization of two important intracellular effectors of excitatory neurotoxicity; calcium and free radicals. Its reported ability to elevate anti-apoptotic proteins is likely to be a consequence of the suppression of excessive intracellular free calcium. In a rat model of transient ischemia, a single bolus delivery of 3-AP 1 h after the initiation of ischemic attack reduced infarct volume by 59% when administered i.c.v. (50 mug per rat) and by 35% when administered i.v. (1 mg/kg). In Phase I clinical trials in cancer therapy 3-AP had no cardiovascular, CNS or other major adverse effects. Thus, 3-AP has a high potential for development as a novel, potent neuroprotectant for the treatment of neurodegenerative diseases.

Development of cerebral infarction, apoptotic cell death and expression of X-chromosome-linked inhibitor of apoptosis protein following focal cerebral ischemia in rats

The aim of this study was to investigate the role of apoptosis or necrosis in the development of delayed infarct, and the relationship between the level of XIAP gene, caspase-3 activation and ischemic cell death following transient focal cerebral ischemia. Adult male Sprague-Dawley rats underwent right middle cerebral artery occlusion (MCAo) for 50 min and reperfusion for 0.5, 4, 8, 24 h, 3, 7, 14 days. On TTC-stained coronal sections, delayed infarct was observed to develop in the whole MCA territory, especially in frontoparietal cortex after ischemia. Near total infarct was shown in striatum 24 h after MCAo, while delayed infarct was evident in the cortex. By day 3, the infarct had progressively expanded to the nearly whole area of the frontoparietal cortex. Flow cytometric analysis of Annexin-V (marks apoptosis) and PI (propidium iodide, marks necrosis) labeling cells showed that MCAo dominantly induced necrosis in ischemic core, striatum. Apoptosis contributed to delayed infarct and cell death in the border zone, dorsolateral cortex and hippocampus. The time-course of caspase-3 activation was consistent with the changes of apoptosis and infarct following MCAo. Further RT-PCR experiments indicated that there was a biphasic regulation of XIAP in time- and region-dependent manner after ischemia. In the infarct core (striatum), following a transient and slight increase during 0.5 h to 4 h post-MCAo, expression of XIAP mRNA markedly decreased. On the other hand, a longer and larger upregulation of XIAP was observed at early time points in border zone (0.5 to 8 h, in dorsolateral cortex; 0.5 to 24 h in hippocampus), then the level of XIAP reduced. A negative correlation was observed between apoptosis and regulation of XIAP gene in these regions. Our findings suggest a possible association between expression of XIAP gene, apoptosis and delayed infarct following ischemia.

Apoptosis dominant in the periinfarct area of human ischaemic stroke--a possible target of antiapoptotic treatments

Animal experiments have suggested that apoptotic programmed cell death is responsible for an important portion of the delayed ischaemic brain damage. Antiapoptotic signalling through erythropoietin (EPO) binding to its receptor (EPOR) is triggered by systemic or local hypoxia and may exist in the post-ischaemic brain, and a neuroprotective effect by EPO was described recently and proposed for clinical stroke treatment. The objective of the study was to determine whether apoptosis occurs in human ischaemic stroke and to describe its topographical distribution. An autopsy cohort consisting of 13 cases of fatal ischaemic stroke (symptom duration from 15 h to 18 days) treated at the Department of Neurology, Helsinki University Central Hospital and 3 controls were studied. DNA damage was investigated by immunofluorescent TUNEL-labelling in combination with apoptotic cell morphology and by visualization of a major signalling system of apoptosis, Fas-FasL (Fas-ligand), by the immunoperoxidase technique. The relationship of EPO and EPOR in the face of TUNEL-labelled and necrotic cell death was co-registered in human cerebral neurons undergoing different stages of ischaemic change. TUNEL-labelled cells with apoptotic morphology were disproportionately more frequent, 148% (30) [mean (SE)] in the periinfarct versus 97% (22) in the core, as percentage of the cells in the contralateral hemisphere (P = 0.027). The apoptotic cell percentage reached up to 26% (2) of all cells in periinfarct area. A linear correlation was found for Fas and its counterpart FasL expression (r(S) = 0.774, P < 0.001). Ischaemia induced widespread neuronal expression of EPOR, which was inversely related to the severity of ischaemic neuronal necrosis (P < 0.05). To conclude, these data verify the predominance of apoptosis in the periphery of human ischaemic infarctions. Fas and FasL were linearly overexpressed supporting that this 'death-receptor' complex may promote the completion of cell death. Increased EPO signalling may be a cellular response for survival in less severely damaged areas. These results support antiapoptotic therapies against delayed neuronal cell death in human ischaemic stroke.

Ischemia and ischemic tolerance in the brain: an overview

Stroke is the third leading cause of death and the leading cause of adult disability in the United States. This review outlines the pathways that lead to cell death following stroke, and also summarizes the current literature on the phenomenon of ischemic tolerance. Ischemic tolerance is an endogenous neuroprotective mechanism by which neurons are protected from the deleterious effects of brain ischemia that occur during and after stroke. A better understanding of the processes that lead to cell death after stroke and endogenous neuroprotective mechanisms like ischemic tolerance could help in the development of new treatment strategies for this devastating neurological disease.

Tenoxicam Exerts a Neuroprotective Action after Cerebral Ischemia in Rats

In this study we investigated the effects of Tenoxicam, a type 2 cyclooxygenase (COX-2) inhibitor, on brain damage induced by ischemia-reperfusion. Male Wistar rats (18-month old average) were anesthetized and submitted to ischemia occlusion of both common carotid arteries (BCAO) for 45 min. After 24 h of reperfusion, rats were decapitated and hippocampi removed for further assays. Animals were divided into sham-operated, ischemia, ischemia + Tenoxicam 2.5 mg/kg, and ischemia + Tenoxicam 10 mg/kg groups. Tenoxicam was administered intraperitoneally immediately after BCAO. Histological analyses show that ischemia produced significant striatal as well as hippocampal lesions which were reversed by the Tenoxicam treatment. Tenoxicam also significantly reduced, to control levels, the increased myeloperoxidase activity in hippocampus homogenates observed after ischemia. However, nitrite concentrations showed only a tendency to decrease in the ischemia + Tenoxicam groups, as compared to that of ischemia alone. On the other hand, hippocampal glutamate and aspartate levels were not altered by Tenoxicam. In conclusion, we showed that ischemia is certainly related to inflammation and to increased free radical production, and selective COX-2 inhibitors might be neuroprotective agents of potential benefit in the treatment of cerebral brain ischemia.

Wide therapeutic time window for nimesulide neuroprotection in a model of transient focal cerebral ischemia in the rat

Results from several studies indicate that cyclooxygenase-2 (COX-2) is involved in ischemic brain injury. The purpose of this study was to evaluate the neuroprotective effects of the selective COX-2 inhibitor nimesulide on cerebral infarction and neurological deficits in a standardized model of transient focal cerebral ischemia in rats. Three doses of nimesulide (3, 6 and 12 mg/kg; i.p.) or vehicle were administered immediately after stroke and additional doses were given at 6, 12, 24, 36 and 48 h after ischemia. In other set of experiments, the effect of nimesulide was studied in a situation in which its first administration was delayed for 3-24 h after ischemia. Total, cortical and subcortical infarct volumes and functional outcome (assessed by neurological deficit score and rotarod performance) were determined 3 days after ischemia. The effect of nimesulide on prostaglandin E(2) (PGE(2)) levels in the injured brain was also investigated. Nimesulide dose-dependently reduced infarct volume and improved functional recovery when compared to vehicle. Of interest is the finding that neuroprotection conferred by nimesulide (reduction of infarct size and neurological deficits and improvement of rotarod performance) was also observed when treatment was delayed until 24 h after ischemia. Further, administration of nimesulide in a delayed treatment paradigm completely abolished PGE(2) accumulation in the postischemic brain, suggesting that COX-2 inhibition is a promising therapeutic strategy for cerebral ischemia to target the late-occurring inflammatory events which amplify initial damage.