Attenuation of transient focal cerebral ischemic injury in transgenic mice expressing a mutant ICE inhibitory protein

Interleukin-1β converting enzyme (ICE): A comprehensive review on discovery and development of caspase-1 inhibitors

Caspase-1 is a critical mediator of the inflammatory process by activating various pro-inflammatory cytokines such as pro-IL-1β, IL-18 and IL-33. Uncontrolled activation of caspase-1 leads to various cytokines-mediated diseases. Thus, inhibition of Caspase-1 is considered therapeutically beneficial to halt the progression of such diseases. Currently, rilonacept, canakinumab and anakinra are in use for caspase-1-mediated autoinflammatory diseases. However, the poor pharmacokinetic profile of these peptides limits their use as therapeutic agents. Therefore, several peptidomimetic inhibitors have been developed, but only a few compounds (VX-740, VX-765) have advanced to clinical trials; because of their toxic profile. Several small molecule inhibitors have also been progressing based on the three-dimensional structure of caspase-1. However there is no successful candidate available clinically. In this perspective, we highlight the mechanism of caspase-1 activation, its therapeutic potential as a disease target and potential therapeutic strategies targeting caspase-1 with their limitations.

Pyroptosis in cardiovascular diseases: Pumping gasdermin on the fire

Pyroptosis is a form of programmed cell death associated with activation of inflammasomes and inflammatory caspases, proteolytic cleavage of gasdermin proteins (forming pores in the plasma membrane), and selective release of proinflammatory mediators. Induction of pyroptosis results in amplification of inflammation, contributing to the pathogenesis of chronic cardiovascular diseases such as atherosclerosis and diabetic cardiomyopathy, and acute cardiovascular events, such as thrombosis and myocardial infarction. While engagement of pyroptosis during sepsis-induced cardiomyopathy and septic shock is expected and well documented, we are just beginning to understand pyroptosis involvement in the pathogenesis of cardiovascular diseases with less defined inflammatory components, such as atrial fibrillation. Due to the danger that pyroptosis represents to cells within the cardiovascular system and the whole organism, multiple levels of pyroptosis regulation have evolved. Those include regulation of inflammasome priming, post-translational modifications of gasdermins, and cellular mechanisms for pore removal. While pyroptosis in macrophages is well characterized as a dramatic pro-inflammatory process, pyroptosis in other cell types within the cardiovascular system displays variable pathways and consequences. Furthermore, different cells and organs engage in local and distant crosstalk and exchange of pyroptosis triggers (oxidized mitochondrial DNA), mediators (IL-1β, S100A8/A9) and antagonists (IL-9). Development of genetic tools, such as Gasdermin D knockout animals, and small molecule inhibitors of pyroptosis will not only help us fully understand the role of pyroptosis in cardiovascular diseases but may result in novel therapeutic approaches inhibiting inflammation and progression of chronic cardiovascular diseases to reduce morbidity and mortality from acute cardiovascular events.

Mechanisms of neuronal cell death in ischemic stroke and their therapeutic implications

Ischemic stroke caused by arterial occlusion is the most common type of stroke, which is among the most frequent causes of disability and death worldwide. Current treatment approaches involve achieving rapid reperfusion either pharmacologically or surgically, both of which are time-sensitive; moreover, blood flow recanalization often causes ischemia/reperfusion injury. However, even though neuroprotective intervention is urgently needed in the event of stroke, the exact mechanisms of neuronal death during ischemic stroke are still unclear, and consequently, the capacity for drug development has remained limited. Multiple cell death pathways are implicated in the pathogenesis of ischemic stroke. Here, we have reviewed these potential neuronal death pathways, including intrinsic and extrinsic apoptosis, necroptosis, autophagy, ferroptosis, parthanatos, phagoptosis, and pyroptosis. We have also reviewed the latest results of pharmacological studies on ischemic stroke and summarized emerging drug targets with a focus on clinical trials. These observations may help to further understand the pathological events in ischemic stroke and bridge the gap between basic and translational research to reveal novel neuroprotective interventions.

Protective Effects of Notoginsenoside R1 via Regulation of the PI3K-Akt-mTOR/JNK Pathway in Neonatal Cerebral Hypoxic-Ischemic Brain Injury

Notoginsenoside R1 (NGR1) is a predominant phytoestrogen extracted from Panax notoginseng that has recently been reported to play important roles in the treatment of cardiac dysfunction, diabetic kidney disease, and acute liver failure. Studies have suggested that NGR1 may be a viable treatment of hypoxic-ischemic brain damage (HIBD) in neonates by reducing endoplasmic reticulum stress via estrogen receptors (ERs). However, whether NGR1 has other neuroprotective mechanisms or long-term neuroprotective effects is unclear. In this study, oxygen-glucose deprivation/reoxygenation (OGD/R) in primary cortical neurons and unilateral ligation of the common carotid artery (CCL) in 7-day-old postnatal Sprague Dawley (SD) rats followed by exposure to a hypoxic environment were used to mimic an HIBD episode. We assessed the efficacy of NGR1 by measuring neuronal damage with MTT assay and assessed brain injury by TTC staining and brain water content detection 24–48 h after OGD/HIE. Simultaneously, we measured the long-term neurophysiological effects using the beam walking test (5 weeks after HI) and Morris water maze test 5–6 weeks after HI. Expression of PI3K-Akt-mTOR/JNK (24 h after HI or OGD/R) proteins was detected by Western blotting after stimulation with HI, NGR1, LY294002 (PI3K inhibitor), 740Y-P (PI3K agonist), or ICI 182780(estrogen receptors inhibitor). The results indicated that NGR1 exerted neuroprotective effects by inhibiting neuronal apoptosis and promoting cell survival via the PI3K-Akt-mTOR/JNK signaling pathways by targeting ER in neonatal hypoxic–ischemic injury.

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.

Beyond muscles: The untapped potential of creatine

Creatine is widely used by both elite and recreational athletes as an ergogenic aid to enhance anaerobic exercise performance. Older individuals also use creatine to prevent sarcopenia and, accordingly, may have therapeutic benefits for muscle wasting diseases. Although the effect of creatine on the musculoskeletal system has been extensively studied, less attention has been paid to its potential effects on other physiological systems. Because there is a significant pool of creatine in the brain, the utility of creatine supplementation has been examined in vitro as well as in vivo in both animal models of neurological disorders and in humans. While the data are preliminary, there is evidence to suggest that individuals with certain neurological conditions may benefit from exogenous creatine supplementation if treatment protocols can be optimized. A small number of studies that have examined the impact of creatine on the immune system have shown an alteration in soluble mediator production and the expression of molecules involved in recognizing infections, specifically toll-like receptors. Future investigations evaluating the total impact of creatine supplementation are required to better understand the benefits and risks of creatine use, particularly since there is increasing evidence that creatine may have a regulatory impact on the immune system.

Brain tissue responses to neural implants impact signal sensitivity and intervention strategies

Implantable biosensors are valuable scientific tools for basic neuroscience research and clinical applications. Neurotechnologies provide direct readouts of neurological signal and neurochemical processes. These tools are generally most valuable when performance capacities extend over months and years to facilitate the study of memory, plasticity, and behavior or to monitor patients’ conditions. These needs have generated a variety of device designs from microelectrodes for fast scan cyclic voltammetry (FSCV) and electrophysiology to microdialysis probes for sampling and detecting various neurochemicals. Regardless of the technology used, the breaching of the blood–brain barrier (BBB) to insert devices triggers a cascade of biochemical pathways resulting in complex molecular and cellular responses to implanted devices. Molecular and cellular changes in the microenvironment surrounding an implant include the introduction of mechanical strain, activation of glial cells, loss of perfusion, secondary metabolic injury, and neuronal degeneration. Changes to the tissue microenvironment surrounding the device can dramatically impact electrochemical and electrophysiological signal sensitivity and stability over time. This review summarizes the magnitude, variability, and time course of the dynamic molecular and cellular level neural tissue responses induced by state-of-the-art implantable devices. Studies show that insertion injuries and foreign body response can impact signal quality across all implanted central nervous system (CNS) sensors to varying degrees over both acute (seconds to minutes) and chronic periods (weeks to months). Understanding the underlying biological processes behind the brain tissue response to the devices at the cellular and molecular level leads to a variety of intervention strategies for improving signal sensitivity and longevity.

Cytokines: their role in stroke and potential use as biomarkers and therapeutic targets

Inflammatory mechanisms both in the periphery and in the CNS are important in the pathophysiologic processes occurring after the onset of ischemic stroke (IS). Cytokines are key players in the inflammatory mechanism and contribute to the progression of ischemic damage. This literature review focuses on the effects of inflammation on ischemic stroke, and the role pro-inflammatory and anti-inflammatory cytokines play on deleterious or beneficial stroke outcome. The discovery of biomarkers and novel therapeutics for stroke has been the focus of extensive research recently; thus, understanding the roles of pro-inflammatory and anti-inflammatory cytokines that are up-regulated during stroke will help us further understand how inflammation contributes to the progression of ischemic damage and provide potential targets for novel therapeutics and biomarkers for diagnosis and prognosis of stroke.

Inhibition of inflammatory mediator release from microglia can treat ischemic/hypoxic brain injury

Interleukin-1α and interleukin-1β aggravate neuronal injury by mediating the inflammatory reaction following ischemic/hypoxic brain injury. It remains unclear whether interleukin-1α and interleukin-1β are released by microglia or astrocytes. This study prepared hippocampal slices that were subsequently subjected to oxygen and glucose deprivation. Hematoxylin-eosin staining verified that neurons exhibited hypoxic changes. Results of enzyme-linked immunosorbent assay found that interleukin-1α and interleukin-1β participated in this hypoxic process. Moreover, when hypoxic injury occurred in the hippocampus, the release of interleukin-1α and interleukin-1β was mediated by the P2X4 receptor and P2X7 receptor. Immunofluorescence staining revealed that during ischemia/hypoxia, the P2X4 receptor, P2X7 receptor, interleukin-1α and interleukin-1β expression was detectable in rat hippocampal microglia, but only P2X4 receptor and P2X7 receptor expression was detected in astrocytes. Results suggested that the P2X4 receptor and P2X7 receptor, respectively, mediated interleukin-1α and interleukin-1β released by microglia, resulting in hippocampal ischemic/hypoxic injury. Astrocytes were activated, but did not synthesize or release interleukin-1α and interleukin-1β.

Effects of caspase-1 knockout on chronic neural recording quality and longevity: insight into cellular and molecular mechanisms of the reactive tissue response

Chronic implantation of microelectrodes into the cortex has been shown to lead to inflammatory gliosis and neuronal loss in the microenvironment immediately surrounding the probe, a hypothesized cause of neural recording failure. Caspase-1 (aka Interleukin 1β converting enzyme) is known to play a key role in both inflammation and programmed cell death, particularly in stroke and neurodegenerative diseases. Caspase-1 knockout (KO) mice are resistant to apoptosis and these mice have preserved neurologic function by reducing ischemia-induced brain injury in stroke models. Local ischemic injury can occur following neural probe insertion and thus in this study we investigated the hypothesis that caspase-1 KO mice would have less ischemic injury surrounding the neural probe. In this study, caspase-1 KO mice were implanted with chronic single shank 3 mm Michigan probes into V1m cortex. Electrophysiology recording showed significantly improved single-unit recording performance (yield and signal to noise ratio) of caspase-1 KO mice compared to wild type C57B6 (WT) mice over the course of up to 6 months for the majority of the depth. The higher yield is supported by the improved neuronal survival in the caspase-1 KO mice. Impedance fluctuates over time but appears to be steadier in the caspase-1 KO especially at longer time points, suggesting milder glia scarring. These findings show that caspase-1 is a promising target for pharmacologic interventions.

Glycyrrhizin protects brain against ischemia-reperfusion injury in mice through HMGB1-TLR4-IL-17A signaling pathway

High mobility group box 1 (HMGB1)-Toll-like receptor 4 (TLR4) signaling has been recently found to induce interleukin (IL)-17A secretion in drug-induced hepatitis and myocardial I/R injury. The purpose of this study is to evaluate whether HMGB1-TLR4 signaling could induce IL-17A secretion and lead to brain I/R injury. We also sought to investigate whether glycyrrhizin elucidated its neuroprotective effects through HMGB1-TLR4-IL-17A signaling pathway. Various biochemical estimations, neurological status, and assessment of cerebral infarct size were carried out 72h after middle cerebral artery occlusion (MCAO) stroke. Apoptotic cells were assessed using a terminal deoxynucleotidyl transferase, dUTP nick and labeling (TUNEL) kit. The expression of HMGB1, IL-17A, bcl-2, bax and cleaved caspase-3, were determined by Western blot assay. In the present study we found that glycyrrhizin significantly decreased HMGB1 protein expression. Glycyrrhizin markedly reduced whereas recombinant HMGB1 (rHMGB1) increased IL-17A expression. HMGB1 induced increase of IL-17A was significantly diminished in TLR4-mutant C3H/HeJ mice. Brain injury and neurological deficits were largely abrogated by glycyrrhizin or IL-17A knockout. In contrast, rHMGB1 or recombinant mouse IL-17A markedly increased I/R injury. However, rHMGB1 had no effects on infarct size and neurological deficits in Il17a(-/-) mice following brain I/R injury. In addition, IL-17A knockout mice significantly increased bcl-2 protein expression and had fewer apoptotic cells, whereas recombinant IL-17A-treated mice significantly increased bax and cleaved caspase-3 protein expression and had more apoptotic cells. Together these results indicate that glycyrrhizin has neuroprotective efficacy in the postischemic brain through HMGB1-TLR4-IL-17A signaling pathway.

The role of the inflammasome in cardiovascular diseases

Inflammasome is a very important signaling platform sensing a variety of triggers of the innate immune system. Inflammasome promotes the production of important pro-inflammatory cytokines such as IL-1β and IL-18. Tight control of inflammasome activity is, therefore, essential and occurs at multiple levels. The activation of inflammasome pathways is linked to the pathogenesis of various prevalent disorders including cardiovascular disease such as atherosclerosis, ischemic injury, cardiomyopathy, and Kawasaki disease. The study of the inflammasome in the cardiovascular system has led to the identification of important triggers and endogenous modulators, and to the exploration of new treatment strategies based on the inhibition of inflammasome activation or its end products, i.e., IL-1β and IL-18. In summary, the discovery of the inflammasome has greatly advanced our understanding of how the innate immune system interferes with cardiovascular disease development and progression, and targeting inflammasome provides new avenues for the treatment and management of cardiovascular diseases.

Pathogenesis of acute stroke and the role of inflammasomes

Inflammation is an innate immune response to infection or tissue damage that is designed to limit harm to the host, but contributes significantly to ischemic brain injury following stroke. The inflammatory response is initiated by the detection of acute damage via extracellular and intracellular pattern recognition receptors, which respond to conserved microbial structures, termed pathogen-associated molecular patterns or host-derived danger signals termed damage-associated molecular patterns. Multi-protein complexes known as inflammasomes (e.g. containing NLRP1, NLRP2, NLRP3, NLRP6, NLRP7, NLRP12, NLRC4, AIM2 and/or Pyrin), then process these signals to trigger an effector response. Briefly, signaling through NLRP1 and NLRP3 inflammasomes produces cleaved caspase-1, which cleaves both pro-IL-1β and pro-IL-18 into their biologically active mature pro-inflammatory cytokines that are released into the extracellular environment. This review will describe the molecular structure, cellular signaling pathways and current evidence for inflammasome activation following cerebral ischemia, and the potential for future treatments for stroke that may involve targeting inflammasome formation or its products in the ischemic brain.

Pharmacological inhibition of TLR4-NOX4 signal protects against neuronal death in transient focal ischemia

Recent data have shown that TLR4 performs a key role in cerebral ischemia-reperfusion injury which serves as the origin of the immunological inflammatory reactions. However, the therapeutic effects of pharmacological inhibitions of TLR4 and its immediate down-stream pathway remain to be uncovered. In the present study, on mice, intracerebroventricular injection of resatorvid (TLR4 signal inhibitor; 0.01 μg) significantly reduced infarct volume and improved neurological score after middle cerebral artery occlusion and reperfusion. The levels of phospho-p38, nuclear factor-kappa B, and matrix metalloproteinase 9 expressions were significantly suppressed in the resatorvid-treated group. In addition, NOX4 associates with TLR4 after cerebral ischemia-reperfusion seen in mice and human. Genetic and pharmacological inhibitions of TLR4 each reduced NOX4 expression, leading to suppression of oxidative/nitrative stress and of neuronal apoptosis. These data suggest that resatorvid has potential as a therapeutic agent for stroke since it inhibits TLR4-NOX4 signaling which may be the predominant causal pathway.

Effect of Sevoflurane postconditioning on gene expression in brain tissue of the middle cerebral artery occlusion rat model

Ischemic postconditioning has been described in both heart and brain. The first aim of this study was to evaluate the effects of Sevoflurane postconditioning (SP) on brain biochemical parameters, Bcl-2, Bax, c-Fos and Caspase-3 protein levels and Bcl-2, Bax, TNF-α and Caspase-3 mRNA expression in the middle cerebral artery occlusion model. Results showed that SP markedly decreased cerebral oxidative injury and improved immunity activity. In addition, SP significantly enhanced cerebral Bcl-2, c-Fos and decreased Bax, Caspase-3 proteins positive expression. Reverse transcription polymerase chain reaction analysis showed that SP markedly enhanced Bcl-2, and decreased Bax, TNF-α and Caspase-3 mRNA expression. Our results confirm that SP can play the protective action against cerebral ischemia reperfusion-induced brain injury by regulating cerebral antioxidant enzymes activities, Bcl-2, Bax, c-Fos and Caspase-3 protein positive expression levels and Bcl-2, Bax, TNF-α and Caspase-3 mRNA expression.

Estrogen and neuroprotection: from clinical observations to molecular mechanisms

We now appreciate that estrogen is a pleiotropic gonadal steroid that exerts profound effects on the plasticity and cell survival of the adult brain. Over the past century, the life span of women has increased, but the age of the menopause remains constant. This means that women may now live over one third of their lives in a hypoestrogenic, postmenopausal state. The impact of prolonged hypoestrogenicity on the brain is now a critical health concern as we realize that these women may suffer an increased risk of cognitive dysfunction and neurodegeneration due to a variety of diseases. Accumulating evidence from both clinical and basic science studies indicates that estrogen exerts critical protective actions against neurodegenerative conditions such as Alzheimer's disease and stroke. Here, we review the discoveries that comprise our current understanding of estrogen action against neurodegeneration. These findings carry far-reaching possibilities for improving the quality of life in our aging population.

Inflammatory cytokines in experimental and human stroke

Inflammation is a hallmark of stroke pathology. The cytokines, tumor necrosis factor (TNF), interleukin (IL)-1, and IL-6, modulate tissue injury in experimental stroke and are therefore potential targets in future stroke therapy. The effect of these cytokines on infarct evolution depends on their availability in the ischemic penumbra in the early phase after stroke onset, corresponding to the therapeutic window (<4.5 hours), which is similar in human and experimental stroke. This review summarizes a large body of literature on the spatiotemporal and cellular production of TNF, IL-1, and IL-6, focusing on the early phase in experimental and human stroke. We also review studies of cytokines in blood and cerebrospinal fluid in stroke. Tumor necrosis factor and IL-1 are upregulated early in peri-infarct microglia. Newer literature suggests that IL-6 is produced by microglia, in addition to neurons. Tumor necrosis factor- and IL-1-producing macrophages infiltrate the infarct and peri-infarct with a delay. This information is discussed in the context of suggestions that neuronal sensitivity to ischemia may be modulated by cytokines. The fact that TNF and IL-1, and suppossedly also IL-6, are produced by microglia within the therapeutic window place these cells centrally in potential future stroke therapy.

Caspase inhibitors: prospective therapies for stroke

In ischemic stroke, apoptosis persists for days to weeks after the onset of an ischemic event. Cysteine-ASPartic proteASEs (caspases) are key mediators of apoptosis and neurodegeneration in stroke. The impact of caspase activity is not restricted to neuronal death, as caspases can exacerbate inflammation and alter glial function. Thus, caspases are logical therapeutic targets for this disease, but they have never been clinically evaluated due to a paucity of ideal drug candidates. Recent developments in caspase inhibition and drug delivery offer novel neuroprotective strategies for stroke, which are deliberated in this review.

N-terminally cleaved Bcl-xL mediates ischemia-induced neuronal death

Transient global ischemia in rats induces delayed death of hippocampal CA1 neurons. Early events include caspase activation, cleavage of anti-death Bcl-2 family proteins and large mitochondrial channel activity. However, whether these events have a causal role in ischemia-induced neuronal death is unclear. We found that the Bcl-2 and Bcl-x(L) inhibitor ABT-737, which enhances death of tumor cells, protected rats against neuronal death in a clinically relevant model of brain ischemia. Bcl-x(L) is prominently expressed in adult neurons and can be cleaved by caspases to generate a pro-death fragment, ΔN-Bcl-x(L). We found that ABT-737 administered before or after ischemia inhibited ΔN-Bcl-x(L)-induced mitochondrial channel activity and neuronal death. To establish a causal role for ΔN-Bcl-x(L), we generated knock-in mice expressing a caspase-resistant form of Bcl-x(L). The knock-in mice exhibited markedly reduced mitochondrial channel activity and reduced vulnerability to ischemia-induced neuronal death. These findings suggest that truncated Bcl-x(L) could be a potentially important therapeutic target in ischemic brain injury.

Neuroprotective properties of Loranthus parasiticus aqueous fraction against oxidative stress-induced damage in NG108-15 cells

Loranthus parasiticus, a Chinese folk medicine, has been widely used for the treatment of brain diseases, particularly in southwest China. Hence, the present neuroprotection model was designed to investigate its neuroprotective properties against H(2)O(2)-induced oxidative stress in NG108-15 cells. L. parasiticus aqueous fraction (LPAF), which was selected in the present study, had proved to be the most active fraction among the other tested extracts and fractions in our previous screening. The restoration of depleted intracellular glutathione (GSH), a major endogenous antioxidant, by LPAF was observed after H(2)O(2) insult. Pretreatment with LPAF substantially reduced the production of intracellular reactive oxygen species generated from H(2)O(2). Apoptotic features such as externalization of phosphatidylserine and disruption of mitochondrial membrane potential were significantly attenuated by LPAF. In addition, cell cycle analysis revealed a prominent decrease in the H(2)O(2)-induced sub-G(1) population by LPAF. Moreover, apoptotic morphological analysis by DAPI nuclear staining demonstrated that NG108-15 cells treated with H(2)O(2) exhibited apoptotic features, while such changes were greatly reduced in cells pretreated with LPAF. Taken together, these findings confirmed that LPAF exerts marked neuroprotective activity, which raises the possibility of potential therapeutic application of LPAF for managing oxidative stress-related neurological disorders and supports the traditional use of L. parasiticus in treating brain-related diseases.

Oxygen resuscitation after hypoxia ischemia stimulates prostaglandin pathway in rat cortex

Exposure to hypoxia and hyperoxia in a rodent model of perinatal ischemia results in delayed cell death and inflammation. Hyperoxia increases oxidative stress that can trigger inflammatory cascades, neutrophil activation, and brain microvascular injury. Here we show that 100% oxygen resuscitation in our rodent model of perinatal ischemia increases cortical COX-2 protein levels, S-nitrosylated COX-2cys526, PGE2, iNOS and 5-LOX, all components of the prostaglandin and leukotriene inflammatory pathway.

Induction of ER stress in response to oxygen-glucose deprivation of cortical cultures involves the activation of the PERK and IRE-1 pathways and of caspase-12

Disturbance of calcium homeostasis and accumulation of misfolded proteins in the endoplasmic reticulum (ER) are considered contributory components of cell death after ischemia. However, the signal-transducing events that are activated by ER stress after cerebral ischemia are incompletely understood. In this study, we show that caspase-12 and the PERK and IRE pathways are activated following oxygen-glucose deprivation (OGD) of mixed cortical cultures or neonatal hypoxia–ischemia (HI). Activation of PERK led to a transient phosphorylation of eIF2α, an increase in ATF4 levels and the induction of gadd34 (a subunit of an eIF2α-directed phosphatase). Interestingly, the upregulation of ATF4 did not lead to an increase in the levels of CHOP. Additionally, IRE1 activation was mediated by the increase in the processed form of xbp1, which would be responsible for the observed expression of edem2 and the increased levels of the chaperones GRP78 and GRP94. We were also able to detect caspase-12 proteolysis after HI or OGD. Processing of procaspase-12 was mediated by NMDA receptor and calpain activation. Moreover, our data suggest that caspase-12 activation is independent of the unfolded protein response activated by ER stress.

Toll-like receptor 4 (TLR4), but not TLR3 or TLR9, knock-out mice have neuroprotective effects against focal cerebral ischemia

Toll-like receptors (TLRs) are signaling receptors in the innate immune system that is a specific immunologic response to systemic bacterial infection. We investigated whether cerebral ischemia induced by the middle cerebral artery occlusion (MCAO) for 2 h differed in mice that lack a functional TLR3, TLR4, or TLR9 signaling pathway. TLR4, but not TLR3 or TLR9, knock-out (KO) mice had significantly smaller infarct area and volume at 24 h after ischemia-reperfusion (I/R) compared with wild-type mice. In addition, TLR4 KO mice improved in neurological deficits after I/R compared with wild-type mice. Moreover, we investigated the expression of TLR4 in the ischemic brain with immunohistochemistry. The number of TLR4-positive cells gradually increased from 1 h after MCAO to 22 h after I/R. We also examined the localization of TLR4 in the ischemic area. TLR4 was localized with CD11b-positive microglial cells in the ischemic striatum and the number of CD11b-positive microglial cells was smaller in TLR4 KO mice than in wild-type mice. In addition, we investigated the translocation of NF-κB among TLR3, 4, and 9 KO mice after I/R injury using western blotting. NF-κB's p65 subunit was decreased in TLR4 KO mice compared to wild-type mice, but not TLR3 or 9 KO mice. These data suggest that TLR4 knockout, but not TLR3 or TLR9 knockout, may play a neuroprotective role in ischemic brain injury induced by MCAO in mice.

Ginsenoside Rb1 regulates the expressions of brain-derived neurotrophic factor and caspase-3 and induces neurogenesis in rats with experimental cerebral ischemia

AIM OF THE STUDY

Recent studies have revealed that ginsenoside Rb1 (GRb1) is neuroprotective for cerebral ischemia. However, the mechanism underlying of this function is unclear. We assessed whether this neuroprotective effect of GRb1 was mediated by the levels of brain-derived neurotrophic factor (BDNF), by the levels of caspase-3 proteins and by induced neurogenesis in rats following transient cerebral ischemia or not.

MATERIALS AND METHODS

Cerebral ischemia was prepared by a 2 h occlusion of the middle cerebral artery and reperfusion, followed by infusion of GRb1 (40 mg/kg) and saline (GRb1 and ischemia groups, respectively). All rats were sacrificed at 3 and 12 h, 1, 2, 3, 5, and 10 days after reperfusion. Normal and sham-operated rats were used in control group. Modified Neurological Severity Scores (mNSS) test and hematoxylin and eosin staining were respectively performed to evaluate neurological function and histological feature. Immunohistochemistry was used to identify intrinsic neurogenesis by nestin antibody. Western blotting was used to detect BDNF and caspase-3 protein content.

RESULTS

GRb1 infusion after cerebral ischemia significantly promoted recoveries of neurological functions at 3 and 5 days after reperfusion compared to ischemic rats. The number of nestin-positive cells was apparently increased after GRb1 infusion compared to ischemia rats at given time. Moreover, BDNF was significantly increased in GRb1-treated rats compared to ischemia rats at different time points. In contrast, GRb1 infusion after the onset of reperfusion, caspase-3 at a given time was significantly reduced compared to ischemia rats, but still significantly increased compared to control rats.

CONCLUSIONS

Promotion of the neurogenesis and regulation of the expressions of BDNF and caspase-3 may be involved in GRb1-induced neuroprotection against cerebral ischemia.

Activation of caspase-8 by tumour necrosis factor receptor 1 is necessary for caspase-3 activation and apoptosis in oxygen-glucose deprived cultured cortical cells

TNF-alpha has been reported to be relevant in stroke-induced neuronal death. However the precise function of TNF-alpha in brain ischemia remains controversial since there are data supporting either a detrimental or a protective effect. Here we show that TNF-alpha is released after oxygen-glucose deprivation (OGD) of cortical cultures and is a major contributor to the apoptotic death observed without affecting the OGD-mediated necrotic cell death. In this paradigm, apoptosis depends on TNF-alpha-induced activation of caspase-8 and -3 without affecting the activation of caspase-9. By using knock-out mice for TNF-alpha receptor 1, we show that the activation of both caspase-3 and -8 by TNF-alpha is mediated by TNF-alpha receptor 1. The pro-apoptotic role of TNF-alpha in OGD is restricted to neurons and microglia, since astrocytes do not express either TNF-alpha or TNF-alpha receptor 1. Altogether, these results show that apoptosis of cortical neurons after OGD is mediated by TNF-alpha/TNF-alpha receptor 1.

Neuroprotective strategies targeting apoptotic and necrotic cell death for stroke

It has been a major challenge to develop effective therapeutics for stroke, a leading cause of death and serious debilitation. Intensive research in the past 15 years have implicated many regulators and the related mechanisms by which neuronal cell death is regulated. It is now clear that even a brief ischemic stroke may trigger complex cellular events that lead to both apoptotic and necrotic neuronal cell death in a progressive manner. Although efforts at developing specific chemical inhibitors for validated targets have been successful for in vitro enzymatic assays, the development of some of such inhibitors into human therapy has been often hindered by their in vivo bioavailability profile. Considerations for the ability to chemically target a cellular mechanism in manner compatible with disease targets in vivo might be emphasized early in the development process by putting a priority on identifying key targets that can be effectively targeted chemically. Thorough interrogation of cellular pathways by saturation chemical genetics may provide a novel strategy to identify multiple key molecular entities that can be targeted chemically in order to select a target suitable for the treatment of intended human diseases such as stroke.

Interleukin-1beta: a bridge between inflammation and excitotoxicity?

Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1beta to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1beta as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity.

Inhibitory effect of PACAP on caspase activity in neuronal apoptosis: a better understanding towards therapeutic applications in neurodegenerative diseases

Programmed cell death, which is part of the normal development of the central nervous system, is also implicated in various neurodegenerative disorders. Cysteine-dependent aspartate-specific proteases (caspases) play a pivotal role in the cascade of events leading to apoptosis. Many factors that inhibit cell death have now been identified, but the underlying mechanisms are not fully understood. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to exert neurotrophic activities during development and to prevent neuronal apoptosis induced by various insults such as ischemia. Most of the neuroprotective effects of PACAP are mediated through the PAC1 receptor. This receptor activates a transduction cascade of second messengers to stimulate Bcl-2 expression, which inhibits cytochrome c release and blocks the activation of caspases. The inhibitory effect of PACAP on the apoptotic cascade suggests that selective, stable, and potent PACAP derivatives could potentially be of therapeutic value for the treatment of post-traumatic and/or chronic neurodegenerative processes.

Acute neurodegeneration and the inflammasome: central processor for danger signals and the inflammatory response?

Activation of the inflammatory response is a crucial event in the adverse outcome of cerebral ischemia, which is promoted by proinflammatory cytokines such as interleukin (IL)-1beta. Although caspase-1 is necessary for IL-1beta processing, the 'upstream' signaling pathways were, until recently, essentially unknown. Fortunately, the inflammasome, a multiprotein complex responsible for activating caspase-1 and caspase-5, has recently been characterized. The activation of the inflammasome can result in one of several consequences such as cytokine secretion, cell death, or the development of a stress-resistant state. The significance of the inflammasome for the initiation of the inflammatory response during systemic diseases has already been shown and members of the inflammasome complex were recently found to be induced in acute brain injury. However, the specific pathophysiologic role of the inflammasome in neurodegenerative disorders still remains to be clarified. The underlying theories (e.g., danger signal theory) along with the signaling pathways that link the inflammasome to acute neurodegeneration will be discussed here. Furthermore, the stimuli that potentially activate the inflammasome in cerebral ischemia will be specified, as well as their relation to well-known pathways activating the innate immune response (e.g., Toll-like receptor signaling) and the consequences that result from their activation (beneficial versus deleterious).

Long-term monitoring of post-stroke plasticity after transient cerebral ischemia in mice using in vivo and ex vivo diffusion tensor MRI

WE USED A MURINE MODEL OF TRANSIENT FOCAL CEREBRAL ISCHEMIA TO STUDY: 1) in vivo DTI long-term temporal evolution of the apparent diffusion coefficient (ADC) and diffusion fractional anisotropy (FA) at days 4, 10, 15 and 21 after stroke 2) ex vivo distribution of a plasticity-related protein (GAP-43) and its relationship with the ex vivo DTI characteristics of the striato-thalamic pathway (21 days). All animals recovered motor function. In vivo ADC within the infarct was significantly increased after stroke. In the stroke group, GAP-43 expression and FA values were significantly higher in the ipsilateral (IL) striatum and contralateral (CL) hippocampus compared to the shams. DTI tractography showed fiber trajectories connecting the CL striatum to the stroke region, where increased GAP43 and FA were observed and fiber tracts from the CL striatum terminating in the IL hippocampus.Our data demonstrate that DTI changes parallel histological remodeling and recovery of function.

Interleukin-1 and inflammatory neurodegeneration

Inflammation occurs rapidly in response to acute brain insults such as stroke, haemorrhage or trauma, and can be sustained for long periods of time, for example in Alzheimer's or Parkinson's diseases and multiple sclerosis. Experimental evidence indicates that inflammation plays a major role in neurodegeneration under these conditions, and that the cytokine IL-1 (interleukin-1) is a pivotal mediator. IL-1 is expressed rapidly in response to neuronal injury, predominantly by microglia, and elevated levels of endogenous or exogenous IL-1 markedly exacerbate injury. The naturally occurring IL-1RA (IL-1 receptor antagonist) markedly inhibits ischaemic, excitotoxic and traumatic brain injury in rodents, and has shown promise in a Phase II clinical trial in stroke patients. The mechanisms of IL-1 expression, release and action in neurodegeneration are not fully elucidated and appear multiple. Systemic IL-1 markedly enhances ischaemic brain injury via release of neutrophils into circulation, neutrophil adhesion to injured cerebrovasculature and CNS (central nervous system) invasion, and cell death via activation of matrix metalloproteinase-9. IL-1 also influences the release of toxins from glial and endothelial cells. Neuronal responses to excitotoxins and physiological factors may have an impact on neuronal survival. IL-1RA, delivered peripherally, can enter the CNS in animals and humans and has no adverse effects in stroke or subarachnoid haemorrhage patients, but shows potential benefit in acute stroke patients.

System x(c)- activity and astrocytes are necessary for interleukin-1 beta-mediated hypoxic neuronal injury

The purpose of this study was to elucidate the cellular/biochemical pathway(s) by which interleukin-1beta (IL-1beta) contributes to the pathogenesis of hypoxic-ischemic brain damage. In vivo, IL-1 receptor type I (IL-1RI)-deficient mice showed smaller infarcts and less neurological deficits than wild-type animals after a 90 min reversible middle cerebral artery occlusion. In vitro, IL-1beta mediated an enhancement of hypoxic neuronal injury in murine cortical cultures that was lacking in cultures derived from IL-1RI null mutant animals and was blocked by the IL-1 receptor antagonist or an IL-1RI blocking antibody. This IL-1beta-mediated potentiation of hypoxic neuronal injury was associated with an increase in both cellular cystine uptake ([cystine]i) and extracellular glutamate levels ([glutamate]e) and was prevented by either ionotropic glutamate receptor antagonism or removal of L-cystine, suggesting a role for the cystine/glutamate antiporter (System x(c)-). Indeed, dual System x(c)-/metabotropic glutamate receptor subunit 1 (mGluR1) antagonism but not selective mGluR1 antagonism prevented neuronal injury. Additionally, cultures derived from mGluR1-deficient mice exhibited the same potentiation in injury after treatment with IL-1beta as wild-type cultures, an effect prevented by System x(c)-/mGluR1 antagonism. Finally, assessment of System x(c)- function and kinetics in IL-1beta-treated cultures revealed an increase in velocity of cystine transport (Vmax), in the absence of a change in affinity (Km). Neither the enhancement in [cystine]i, [glutamate]e, or neuronal injury were observed in chimeric cultures consisting of IL-1RI(+/+) neurons plated on top of IL-1RI(-/-) astrocytes, highlighting the importance of astrocyte-mediated alterations in System x(c)- as a novel contributor to the development and progression of hypoxic neuronal injury.

A decoy oligonucleotide inhibiting nuclear factor-kappaB binding to the IgGkappaB consensus site reduces cerebral injury and apoptosis in neonatal hypoxic-ischemic encephalopathy

We examined the effect of treatment with intraventricular injection of a decoy oligonucleotide that binds and inhibits nuclear factor-kappaB on cytokine expression, ICAM-1 expression, neutrophil recruitment, apoptosis, and tissue injury in a model of neonatal hypoxic-ischemic cerebral injury with varying degrees of hypoxia. We found a reduction of interleukin-1beta, tumor necrosis factor-alpha, soluble ICAM-1, neutrophil counts, and activity after 2 hr of hypoxia, but not with 90 min of hypoxia. By contrast, a significant reduction of apoptosis was seen in animals treated after 90 min of hypoxia but not in those treated after 2 hr of hypoxia. Overall evidence of an inflammatory response was sparse, with low levels of ICAM-1 expression and neutrophil recruitment even in the more severe hypoxic ischemic injury. It is likely that the decoy oligonucleotide affects cerebral injury and apoptosis not through suppression of downstream elements of the inflammatory response but through other mechanisms, one of which is the reduction of transcription and synthesis of cytokines, which are known to affect other responses to cellular injury.

Characterization of the early neuroinflammation after spinal cord injury in mice

The occurrence of neuroinflammation after spinal cord injury (SCI) is well established, but its function is debated, with both beneficial and detrimental consequences ascribed. A discriminate of the role of neuroinflammation may be the time period after SCI, and there is evidence to favor early neuroinflammation being undesirable, whereas the later evolving phase may have useful roles. Here, we have focused on the inflammatory response in the first 24 hours of SCI in mice. We found elevation of interleukin (IL)-1beta and other cytokines and chemokines within 15 minutes to 3 hours of injury. The early neuroinflammation in SCI is likely to be CNS-derived and involves microglia, as demonstrated by in situ hybridization for IL-1beta in microglia, by an in vitro model of SCI in which elevation of inflammatory cytokines occurs in the absence of a dynamic source of infiltrating leukocytes, and by the correlation of decreased levels of inflammatory molecules and microglia activity in IL-1beta-null mice. Nonetheless, as there are no specific immunohistochemical markers that clearly differentiate microglia from their peripheral counterparts, macrophages, the latter cannot be definitively excluded as participants in early neuroinflammation in mouse SCI. These results of an instantaneous inflammatory response validate approaches to modulate microglia/macrophage activity to improve recovery from SCI.

Early Upregulation of Matrix Metalloproteinases Following Reperfusion Triggers Neuroinflammatory Mediators in Brain Ischemia in Rat

Abnormal expression of matrix metalloproteinases (MMPs) has been implicated in the pathophysiology of neuroinflammatory processes that accompany most central nervous system disease. In particular, early upregulation of the gelatinases MMP-2 and MMP-9 has been shown to contribute to disruption of the blood-brain barrier and to death of neurons in ischemic stroke. In situ zymography reveals a significant increase in gelatinolytic MMPs activity in the ischemic brain hemisphere after 2-h middle cerebral artery occlusion (MCAo) followed by 2-h reperfusion in rat. Accordingly, gel zymography demonstrates that expression and activity of MMP-2 and MMP-9 are enhanced in cortex and striatum ipsilateral to the ischemic insult. The latter effect appears to be instrumental for development of delayed brain damage since administration of a broad spectrum, highly specific MMPs inhibitor, GM6001, but not by its negative control, results in a significant (50%) reduction in ischemic brain volume. Increased gelatinase activity in the ischemic cortex coincides with elevation (166% vs sham) of mature interleukin-1beta (IL-1beta) after 2-h reperfusion and this does not appear to implicate a caspase-1-dependent processing of pro(31kDa)-IL-1beta to yield mature (17kDa) IL-1beta. More importantly, when administered at a neuroprotective dose GM6001 abolishes the early IL-1beta increase in the ischemic cortex and reduces the cleavage of the cytokine proform supporting the deduction that MMPs may initiate IL-1beta processing. In conclusion, development of tissue damage that follows transient ischemia implicates a crucial interplay between MMPs and mediators of neuroinflammation (e.g., IL-1beta), and this further underscores the therapeutic potential of MMPs inhibitors in the treatment of stroke.

Investigational anti-inflammatory agents for the treatment of ischaemic brain injury

Stroke is the third leading cause of death and the leading cause of disability in Western countries. To date, only approximately 2% of stroke patients are eligible for thrombolysis treatment with recombinant tissue plasminogen activator. The very limited options available for stroke treatment and recent disappointing clinical trials in stroke call for novel therapeutic approaches. Inflammation represents one of the key pathophysiological mechanisms for the progression of ischaemic stroke. Recent advances in preclinical models of stroke using investigational small molecular antagonists, neutralising antibodies/proteins or genetically altered gene functions against various inflammatory mediators suggest a great therapeutic potential of anti-inflammation for ischaemic stroke. The scope of the present review is to update the evidence for a role of inflammatory pathways in stroke and to summarise the investigational drugs currently available both in preclinical and clinical development for potential treatment of ischaemic stroke.

Decreased retinal neuronal cell death in caspase-1 knockout mice

PURPOSE

To determine whether apoptosis of retinal neurons induced by excessive light exposure and ischemia-reperfusion injury is altered in caspase-1 knockout mice.

METHODS

Eight- to 10-week-old caspase-1 knockout mice (Casp1-/-) and wild-type (WT) mice (C57BL/6) were exposed to diffuse, cool, white fluorescent light of 25,000 lux for 2 h. Other mice were subjected to retinal ischemia by increasing the intraocular pressure to 110 mmHg for 45 min. Electroretinograms (ERGs) were recorded before and after the light exposure. TdT-dUTP terminal nick-end labeling (TUNEL) was performed to identify the apoptotic cells after the insults. The inner retinal thickness was measured to evaluate the retinal injury after the ischemia-reperfusion. Expression of caspase-1 protein was studied by immunohistochemical analysis and Western blotting. Caspase-1-like protease activity was determined by a colorimetric tetrapeptide substrate.

RESULTS

The morphology of the retina and the amplitudes of the a and b waves of the ERGs of Casp1-/- mice did not differ from those of WT mice. After the light exposure, TUNEL-positive cells were observed in the outer nuclear layer of the WT mice retina. The number of TUNEL-positive photoreceptor nuclei after the light exposure, and the number of nuclei in the inner nuclear layer after the ischemia-reperfusion injury, were significantly less in Casp1-/- mice than in WT mice. There were more caspase-1-positive photoreceptor cells in WT mice after the light injury. The inner retinal layer of Casp1-/- mice was significantly thicker in Casp1-/- mice than in WT mice 2 weeks after the ischemic insult.

CONCLUSIONS

Retinal neuronal apoptosis was less prominent in Casp1-/- mice after excessive light exposure and ischemia-reperfusion injury. These data indicate that caspase-1 plays a role in retinal neuronal apoptosis.

Hypocapnia induces caspase-3 activation and increases Abeta production

BACKGROUND

At least half of all cases of early onset (<60) familial Alzheimer's disease (FAD) are caused by any of over 150 mutations in three genes: the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2). Mutant forms of PS1 have been shown to sensitize cells to apoptotic cell death.

OBJECTIVE

We investigated the effects of hypocapnia, a risk factor for both cognitive and neurodevelopment deficits, on caspase-3 activation, apoptosis, and amyloid beta-protein (Abeta) production, and assessed the influence of the PS1Delta9 FAD mutation on these effects.

METHOD

For this purpose, we exposed stably transfected H4 human neuroglioma cells to conditions consistent with hypocapnia (PCO2<40 mm Hg) and hypocapnia plus hypoxia (PO2<21%).

RESULTS

Hypocapnia (20 mm Hg CO2 for 6 h) induced caspase-3 activation and apoptosis; the PS1Delta9 FAD mutation significantly potentiated these effects. Moreover, the combination of hypocapnia (20 mm Hg CO2) and hypoxia (5%O2) induced caspase-3 activation and apoptosis in a synergistic manner. Hypocapnia (5 and 20 mm Hg CO2 for 6 h) also led to an increased Abeta production.

CONCLUSION

The findings suggest that hypocapnia (e.g. during general anesthesia) could exacerbate AD neuropathogenesis.

Ca2+ signals and death programmes in neurons

Cell death programmes are generally defined by biochemical/genetic routines that are linked to their execution and by the appearance of more or less typical morphological features. However, in pathological settings death signals may engage complex and interacting lethal pathways, some of which are common to different cells, whereas others are linked to a specific tissue and differentiation pattern. In neurons, death programmes can be spatially and temporally segregated. Most importantly physiological Ca2+ signals are essential for cell function and survival. On the other hand, Ca2+ overload or perturbations of intracellular Ca2+ compartmentalization can activate or enhance mechanisms leading to cell death. An imbalance between Ca2+ influx and efflux from cells is the initial signal leading to Ca2+ overload and death of ischaemic neurons or cardiomyocytes. Alterations of intracellular Ca2+ storage can integrate with death signals that do not initially require Ca2+, to promote processing of cellular components and death by apoptosis or necrosis. Finally, Ca2+ can directly activate catabolic enzymes such as proteases, phospholipases and nucleases that directly cause cell demise and tissue damage.

The combination of isoflurane and caspase 8 inhibition results in sustained neuroprotection in rats subject to focal cerebral ischemia

Although isoflurane can reduce ischemic neuronal injury after short postischemic recovery intervals, data from our laboratory have demonstrated that this neuroprotection is not sustained and that delayed apoptotic neuronal death, mediated in part by activation of caspases, contributes to the gradual increase in the size of the infarction. We tested the hypothesis that the neuroprotective efficacy of isoflurane can be prolonged with the administration of z-IETD-fmk, a specific inhibitor of caspase 8. Fasted Wister rats were anesthetized with isoflurane and randomly allocated to awake-vehicle, isoflurane-vehicle, awake-IETD, or isoflurane-IETD groups (n = 25 per group). Animals were subjected to 60 min focal ischemia by filament occlusion of the middle cerebral artery (MCAO). Daily intracerebroventricular injections of z-IETD-fmk or vehicle were administered via an implanted cannula starting before ischemia and continuing until 14 days post-MCAO. Neurological assessment was performed 14 days after ischemia after which the volume of cerebral infarction and number of intact neurons in the peri-infarct cortex were determined. Total infarction volume was less in the isoflurane-IETD group than in awake-vehicle, isoflurane-vehicle, and awake-IETD groups. Infarction volume was also less in the awake-IETD group versus the awake-vehicle group. The number of intact neurons within the peri-infarct cortex was significantly less in the awake-vehicle group in comparison with the other three experimental groups. The isoflurane-IETD group had better neurologic outcomes than both vehicle-treated groups at 14 days post-MCAO. These results suggest that a combination of isoflurane and a caspase 8 inhibitor can produce neuroprotection that is evident even after a recovery period of 14 days. This combination demonstrated greater efficacy than the administration of either isoflurane or z-IETD-fmk alone. These results are consistent with the premise that continuing apoptosis contributes to the enlargement of cerebral infarction during the recovery period and that its inhibition can provide sustained neuroprotection.

Neuroprotective effects of neuregulin-1 in rat models of focal cerebral ischemia

The purpose of this study was to investigate the therapeutic efficacy and mechanism of recombinant human NRG-1 to attenuate ischemia/reperfusion brain injury. NRG-1(3.0 ng/kg) was applied intravascularly 10 min before middle cerebral artery occlusion (MCAO) and then focal cerebral ischemia for 90 min and reperfusion for 24 h. The rats were scored post-reperfusion for neurological deficits and infarct volume in the brain was assessed by 2,3,5-triphenyltetrazolium chloride(TTC). Apoptosis was evaluated by TUNEL staining. Reverse transcription polymerase chain reaction (RT-PCR) was used to measure changes of caspase-3 mRNA. The level of TNF-alpha was determined using enzyme-linked immunosorbent assay (ELISA). Our results demonstrated that recombinant human NRG-1 could reduce cerebral infarct volume by about 71% (P < 0.05) and TUNEL positive cells when given immediately before MCAO, and improved behavior of animals. Furthermore, we also showed that NRG-1 could also decrease the expression of caspase-3 mRNA and production of TNF-alpha protein. These data suggest that pre-administration of NRG-1 attenuates cerebral ischemia and reperfusion injury. This protective effect may be involved in the inhibition of caspase-3 and TNF-alpha.

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.

Neuroinflammation and both cytotoxic and vasogenic edema are reduced in interleukin-1 type 1 receptor-deficient mice conferring neuroprotection

BACKGROUND AND PURPOSE

Interleukin-1 (IL-1) is a proinflammatory cytokine implicated in multiple neurodegenerative diseases, including stroke. However, to date, there is no consensus regarding which receptor(s) mediates the detrimental effects of IL-1. We hypothesized that abrogating IL-1 type 1 receptor (IL-1R1) signaling would reduce edema, chemokine expression, and leukocyte infiltration; lower levels of iNOS; and, consequently, decrease free radical damage after mild hypoxia/ischemia (H/I), thus preserving brain cells.

METHODS

IL-1R1 null mice and wild-type mice were subjected to a mild H/I insult. MRI was used to measure the area affected at 30 minutes and 48 hours after H/I. An RNAse protection assay was used to evaluate changes in chemokine mRNA expression. RT-PCR was used to assess inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase mRNA levels. Immunohistochemistry was used to assess leukocyte infiltration. Western blots were used to assess iNOS and glutamate aspartate transporter protein levels.

RESULTS

IL-1R1 null mice had reduced cytotoxic and vasogenic edema. The volume of hyperintense signal on T2-weighted images was reduced on average by 90% at 48 hours after H/I. The induction of multiple chemokine mRNAs was significantly reduced in IL-1R1 null mice compared with wild-type mice at 18 and 72 hours after H/I, which correlated with fewer infiltrating CD3+ leukocytes. Levels of iNOS protein and mRNA (but not glutamate aspartate transporter) were significantly reduced in the IL-1R1 mouse brain.

CONCLUSIONS

These findings indicate that abrogating IL-1R1 signaling could protect brain cells subsequent to a mild stroke by reducing edema and immune cell recruitment, as well as by limiting iNOS-mediated free radical damage.

Activation of nuclear factor-kappaB signaling pathway by interleukin-1 after hypoxia/ischemia in neonatal rat hippocampus and cortex

Perinatal hypoxia/ischemia (HI) is a common cause of neurological deficits in children. Interleukin-1 (IL-1) activity has been implicated in HI-induced brain damage. However, the mechanisms underlying its action in HI have not been characterized. We used a 7-day-old rat model to elucidate the role of nuclear factor-kappaB (NF-kappaB) activation in HI stimulation of IL-1 signaling. HI was induced by permanent ligation of the left carotid artery followed by 90 min of hypoxia (7.8% O(2)). Using ELISA assays, we observed increased cell death and caspase 3 activity in hippocampus and cortex 3, 6, 12, 24 and 48 h post-HI. IL-1beta protein expression increased, beginning at 3 h after HI and lasting until 24 h post-HI in hippocampus and 12 h post-HI in cortex. Intracerebroventricular injection of 2 microg IL-1 receptor antagonist (IL-1Ra) 2 h after HI significantly reduced cell death and caspase 3 activity. Electrophoretic mobility shift assay analyses of hippocampus and cortex after HI for NF-kappaB activity showed increased p65/p50 DNA-binding activity at 24 h post-HI. Western blot analyses showed significant nuclear translocation of p65. Protein expression levels of two known inflammatory agents, inducible nitric oxide synthase and cycloxygenase 2, known to be transcriptionally regulated by NF-kappaB, also increased at 24 h after HI. All these HI-induced changes were reversed by IL-1Ra blockade of IL-1 signaling, consistent with IL-1 triggering of inflammatory apoptotic outcomes via NF-kappaB transcriptional activation. The observed increase in cytoplasmic phosphorylated inhibitor kappaBalpha (IkappaBalpha) and nuclear translocation of Bcl-3 24 h after HI was also significantly attenuated by IL-1Ra blockade, suggesting that HI-induced IL-1 activation of NF-kappaB is via both the degradation of IkappaBalpha and the nuclear translocation of Bcl-3.

Potential new strategies to prevent the development of diabetic retinopathy

Recent studies have demonstrated that diabetic retinopathy has several characteristics of a chronic inflammatory disease, such as increased nitric oxide production, intracellular adhesion molecule-1 upregulation, leukostasis and increased vascular permeability. In addition, diabetes leads to the activation of caspase-1, the enzyme responsible for the production of the pro-inflammatory cytokines IL-1beta and IL-18 in the retinae of diabetic animals and diabetic patients. Minocycline, a second-generation tetracycline derivative, was able to prevent the activation of capase-1 in the retinae of diabetic mice. Therefore, this review is focused on discussing the role of caspase-1 as a mediator of chronic inflammation and/or apoptosis inducer in the development of diabetic retinopathy and the suitability of caspase-1 as a new potential therapeutic target.

Prophylactic creatine administration mediates neuroprotection in cerebral ischemia in mice

Creatine mediates remarkable neuroprotection in experimental models of amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease, and traumatic brain injury. Because caspase-mediated pathways are shared functional mechanistic components in these diseases, as well as in ischemia, we evaluated the effect of creatine supplementation on an experimental stroke model. Oral creatine administration resulted in a remarkable reduction in ischemic brain infarction and neuroprotection after cerebral ischemia in mice. Postischemic caspase-3 activation and cytochrome c release were significantly reduced in creatine-treated mice. Creatine administration buffered ischemia-mediated cerebral ATP depletion. These data provide the first direct correlation between the preservation of bioenergetic cellular status and the inhibition of activation of caspase cell-death pathways in vivo. An alternative explanation to our findings is that creatine is neuroprotective through other mechanisms that are independent of mitochondrial cell-death pathways, and therefore postischemic ATP preservation is the result of tissue sparing. Given its safety record, creatine might be considered as a novel therapeutic agent for inhibition of ischemic brain injury in humans. Prophylactic creatine supplementation, similar to what is recommended for an agent such as aspirin, may be considered for patients in high stroke-risk categories.