Suppression of oxidative stress after transient focal ischemia in interleukin-1 knock out mice

Neuroinflammatory Mechanisms in Ischemic Stroke: Focus on Cardioembolic Stroke, Background, and Therapeutic Approaches

One of the most important causes of neurological morbidity and mortality in the world is ischemic stroke. It can be a result of multiple events such as embolism with a cardiac origin, occlusion of small vessels in the brain, and atherosclerosis affecting the cerebral circulation. Increasing evidence shows the intricate function played by the immune system in the pathophysiological variations that take place after cerebral ischemic injury. Following the ischemic cerebral harm, we can observe consequent neuroinflammation that causes additional damage provoking the death of the cells; on the other hand, it also plays a beneficial role in stimulating remedial action. Immune mediators are the origin of signals with a proinflammatory position that can boost the cells in the brain and promote the penetration of numerous inflammatory cytotypes (various subtypes of T cells, monocytes/macrophages, neutrophils, and different inflammatory cells) within the area affected by ischemia; this process is responsible for further ischemic damage of the brain. This inflammatory process seems to involve both the cerebral tissue and the whole organism in cardioembolic stroke, the stroke subtype that is associated with more severe brain damage and a consequent worse outcome (more disability, higher mortality). In this review, the authors want to present an overview of the present learning of the mechanisms of inflammation that takes place in the cerebral tissue and the role of the immune system involved in ischemic stroke, focusing on cardioembolic stroke and its potential treatment strategies.

Pathogenic mechanisms following ischemic stroke

Stroke is the second most common cause of death and the leading cause of disability worldwide. Brain injury following stroke results from a complex series of pathophysiological events including excitotoxicity, oxidative and nitrative stress, inflammation, and apoptosis. Moreover, there is a mechanistic link between brain ischemia, innate and adaptive immune cells, intracranial atherosclerosis, and also the gut microbiota in modifying the cerebral responses to ischemic insult. There are very few treatments for stroke injuries, partly owing to an incomplete understanding of the diverse cellular and molecular changes that occur following ischemic stroke and that are responsible for neuronal death. Experimental discoveries have begun to define the cellular and molecular mechanisms involved in stroke injury, leading to the development of numerous agents that target various injury pathways. In the present article, we review the underlying pathophysiology of ischemic stroke and reveal the intertwined pathways that are promising therapeutic targets.

Genome-Wide Transcriptional Analysis Reveals the Protection against Hypoxia-Induced Oxidative Injury in the Intestine of Tibetans via the Inhibition of GRB2/EGFR/PTPN11 Pathways

The molecular mechanisms for hypoxic environment causing the injury of intestinal mucosal barrier (IMB) are widely unknown. To address the issue, Han Chinese from 100 m altitude and Tibetans from high altitude (more than 3650 m) were recruited. Histological and transcriptome analyses were performed. The results showed intestinal villi were reduced and appeared irregular, and glandular epithelium was destroyed in the IMB of Tibetans when compared with Han Chinese. Transcriptome analysis revealed 2573 genes with altered expression. The levels of 1137 genes increased and 1436 genes decreased in Tibetans when compared with Han Chinese. Gene ontology (GO) analysis indicated most immunological responses were reduced in the IMB of Tibetans when compared with Han Chinese. Gene microarray showed that there were 25-, 22-, and 18-fold downregulation for growth factor receptor-bound protein 2 (GRB2), epidermal growth factor receptor (EGFR), and tyrosine-protein phosphatase nonreceptor type 11 (PTPN11) in the IMB of Tibetans when compared with Han Chinese. The downregulation of EGFR, GRB2, and PTPN11 will reduce the production of reactive oxygen species and protect against oxidative stress-induced injury for intestine. Thus, the transcriptome analysis showed the protecting functions of IMB patients against hypoxia-induced oxidative injury in the intestine of Tibetans via affecting GRB2/EGFR/PTPN11 pathways.

Administration of umbilical cord blood cells transiently decreased hypoxic-ischemic brain injury in neonatal rats

This study aimed to investigate whether the administration of mononuclear cells derived from human umbilical cord blood cells (UCBCs) could ameliorate hypoxic-ischemic brain injury in a neonatal rat model. The left carotid arteries of 7-day-old rats were ligated, and the rats were then exposed to 8% oxygen for 60 min. Mononuclear cells derived from UCBCs using the Ficoll-Hypaque technique were injected intraperitoneally 6 h after the insult (1.0 × 10(7) cells). Twenty-four hours after the insult, the number of cells positive for the oxidative stress markers 4-hydroxy-2-nonenal and nitrotyrosine, in the dentate gyrus of the hippocampus in the UCBC-treated group, decreased by 36 and 42%, respectively, compared with those in the control group. In addition, the number of cells positive for the apoptosis markers active caspase-3 and apoptosis-inducing factor decreased by 53 and 58%, respectively. The number of activated microglia (ED1-positive cells) was 51% lower in the UCBC group compared with the control group. In a gait analysis performed 2 weeks after the insult, there were no significant differences among the sham-operated, control and UCBC groups. An active avoidance test using a shuttle box the following week also revealed no significant differences among the groups. Neither the volumes of the hippocampi, corpus callosum and cortices nor the numbers of neurons in the hippocampus were different between the UCBC and control groups. In summary, a single intraperitoneal injection of UCBC-derived mononuclear cells 6 h after an ischemic insult was associated with a transient reduction in numbers of apoptosis and oxidative stress marker-positive cells, but it did not induce long-term morphological or functional protection. Repeated administration or a combination treatment may be required to achieve sustained protection.

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.

Therapeutic time window for edaravone treatment of traumatic brain injury in mice

Traumatic brain injury (TBI) is a major cause of death and disability in young people. No effective therapy is available to ameliorate its damaging effects. Our aim was to investigate the optimal therapeutic time window of edaravone, a free radical scavenger which is currently used in Japan. We also determined the temporal profile of reactive oxygen species (ROS) production, oxidative stress, and neuronal death. Male C57Bl/6 mice were subjected to a controlled cortical impact (CCI). Edaravone (3.0 mg/kg), or vehicle, was administered intravenously at 0, 3, or 6 hours following CCI. The production of superoxide radicals (O₂^∙−) as a marker of ROS, of nitrotyrosine (NT) as an indicator of oxidative stress, and neuronal death were measured for 24 hours following CCI. Superoxide radical production was clearly evident 3 hours after CCI, with oxidative stress and neuronal cell death becoming apparent after 6 hours. Edaravone administration after CCI resulted in a significant reduction in the injury volume and oxidative stress, particularly at the 3-hour time point. Moreover, the greatest decrease in O₂^∙− levels was observed when edaravone was administered 3 hours following CCI. These findings suggest that edaravone could prove clinically useful to ameliorate the devastating effects of TBI.

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.

Depletion of Nrf2 enhances inflammation induced by oxyhemoglobin in cultured mice astrocytes

Nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element pathway has been proved to be the key regulator in reducing inflammatory damage, which is involved in subarachnoid hemorrhage (SAH). Here, in a traditional in vitro SAH model, we investigated the effect of Nrf2 depletion on pro-inflammatory cytokines production. Primary cultured astrocytes from Nrf2 wild type (WT) or knockout (KO) mouse were exposed or not exposed to oxyhemoglobin (OxyHb). Then the DNA-binding activity of transcription factor nuclear factor-κB (NF-κB) was detected by EMSA. The expression of TNF-α, IL-1β, IL-6 and MMP9 were evaluated. The activity of MMP9 was measured by Gelatin zymography. After exposure to OxyHb, NF-κB was activated and the expression of downstream pro-inflammatory cytokines was up-regulated in astrocytes. And such up-regulation was much higher in KO astrocytes than in WT astrocytes, which means more aggravated inflammation in Nrf2 deficient astrocytes. These results suggest that astrocytes participate in inflammatory process after SAH and the absence of Nrf2 may induce more aggressive inflammation through activation of NF-κB pathway.

Targeting astrocytes for stroke therapy

Stroke remains a major health problem and is a leading cause of death and disability. Past research and neurotherapeutic clinical trials have targeted the molecular mechanisms of neuronal cell death during stroke, but this approach has uniformly failed to reduce stroke-induced damage or to improve functional recovery. Beyond the intrinsic molecular mechanisms inducing neuronal death during ischemia, survival and function of astrocytes is absolutely required for neuronal survival and for functional recovery after stroke. Many functions of astrocytes likely improve neuronal viability during stroke. For example, uptake of glutamate and release of neurotrophins enhances neuronal viability during ischemia. Under certain conditions, however, astrocyte function may compromise neuronal viability. For example, astrocytes may produce inflammatory cytokines or toxic mediators, or may release glutamate. The only clinical neurotherapeutic trial for stroke that specifically targeted astrocyte function focused on reducing release of S-100β from astrocytes, which becomes a neurotoxin when present at high levels. Recent work also suggests that astrocytes, beyond their influence on cell survival, also contribute to angiogenesis, neuronal plasticity, and functional recovery in the several days to weeks after stroke. If these delayed functions of astrocytes could be targeted for enhancing stroke recovery, it could contribute importantly to improving stroke recovery. This review focuses on both the positive and the negative influences of astrocytes during stroke, especially as they may be targeted for translation to human trials.

The Janus-faced effects of hypoxia on astrocyte function

Astrocytes are increasingly recognized for their impact on neuronal function and viability in health and disease. Hypoxia has Janus-faced influences on astrocytes and their ability to support neuronal viability. For example, hypoxia induces astrocyte-dependent protection of neurons following hypoxia preconditioning. Yet, hypoxia induces processes in astrocytes that augment neuronal death in other situations, such as the coincidence of hypoxia with inflammatory signaling. A complex array of gene expression is induced by hypoxia within astrocytes and neurons through multiple transcription factors and intracellular molecular pathways. The hypoxia inducible factors (HIFs) are transcription factors that are likely instrumental in orchestrating adaptive and pathological functions of astrocytes. As such, the HIFs are postulated to mediate both adaptive and pathological functions during hypoxia/ ischemia. Identifying the conditions under which hypoxia induces signaling in astrocytes that alters autonomous or neuronal survival will undoubtedly have important implications regarding the development of new strategies for stroke treatment.

Deleterious effects of dihydrotestosterone on cerebral ischemic injury

Outcome from cerebral ischemia is sexually dimorphic in many experimental models. Male animals display greater sensitivity to ischemic injury than do their female counterparts; however, the underlying mechanism is unclear. The present study determined if the potent and nonaromatizable androgen, dihydrotestosterone (DHT), exacerbates ischemic damage in the male rat and alters postischemic gene expression after middle cerebral artery occlusion. At 22 h reperfusion, removal of androgens by castration provided protection from ischemic injury in both cortex and striatum (2,3,5-triphenyltetrazolium chloride (TTC) histology), whereas DHT replacement (50 mg subcutaneous implant) restored infarction volume to that of the intact male; testosterone (50 mg) had similar but less potent effects. We utilized microarray and real-time quantitative polymerase chain reaction (PCR) to identify genes differentially expressed at 6 h reperfusion in periinfarct cortex from castrated rats with or without DHT replacement. We identify, for the first time, a number of gene candidates that are induced by DHT with or without ischemia, many of which could account for cell death through enhanced inflammation, dysregulation of blood-brain barrier and the extracellular matrix, apoptosis, and ionic imbalance. Our data suggest that androgens are important mediators of ischemic damage in male brain and that transcriptional mechanisms should be considered as we seek to understand innate male sensitivity to cerebral ischemia.

Increased mitochondrial DNA oxidative damage after transient middle cerebral artery occlusion in mice

Oxidative stress and DNA oxidation play important roles in the induction of ischemic neuronal cell death. However, the subcellular source of oxidized DNA detected by 8-hydroxy-2'-deoxyguanosine (8-OHdG) after ischemia has not been clarified although it is known to increase in the brain after ischemia. One-hour transient ischemia of the middle cerebral artery was induced in mice utilizing an intraluminal filament. The occurrence of superoxide anion as an ethidium (Et) signal, 8-OHdG, cytochrome c release and neuronal cell death were examined using immunohistological and biochemical techniques in sham-operated control (0h) and 1, 3, 6, 24, or 96h after reperfusion. Et signals were prominent in the cortical neurons of ipsilateral hemisphere 3h after reperfusion. Strong 8-OHdG immunoreactivity was observed 3-6h after reperfusion. Immunoassays after cell fractionation revealed a significant increase of 8-OHdG in mitochondria 6h after reperfusion. Immunohistochemistry revealed that the 8-OHdG immunoreactivity colocalized with a neuronal marker, microfilament 200 and a mitochondrial marker, cytochrome oxidase subunit I. Cytochrome c rose in cytoplasm at 6h and TUNEL-positive neurons noted 6-24h after ischemia. The present results suggest the possibility that the mitochondrial damage including mitochondrial DNA oxidation might be responsible for the induction of ischemic neuronal cell death.

Orexin-1 receptor expression after global ischemia in mice

Orexins are neuropeptides that have a range of physiological effects including the regulation of feeding behavior and the sleep-wakefulness cycle. Recently, we reported that level of orexin A in spinal fluid was decreased in the patients of some neurodegenerative diseases and it is considered that orexin A and the receptors might be related to central nervous system disorders. However, the expression and localization of orexin receptors is not elicited well. Therefore, the purpose of this study is to investigate the time-dependent changes and the cellular localization of orexin receptor focusing on orexin-1 receptor (OX1R) in the mouse brain after transient common carotid artery occlusion (tCCAO) model by using immunohistochemical techniques. OX1R immunoreactivity dramatically increased and peaked in the hippocampus and cortex 2 days after tCCAO, but remained unchanged in the hypothalamus. Using double-immunohistochemistry, the OX1R immunopositive cells at 2 days after tCCAO were co-localized not only with neuronal marker, NeuN-immunoreactivity but also with astroglial and oligodendroglial markers, GFAP- and CNPase-immunoreactivities, respectively. These results suggested that OX1R is induced other cells in addition to the neurons during stress such as ischemia and orexins and its receptor might play an important role for ischemic insult.