A new approach for the investigation of reperfusion-related brain injury

Immune system disorders in the early post-injury period in patients after severe brain injury from the perspective of the severity of the injury

BACKGROUND

Brain injuries are the most common cause of death in productive age. Besides the extent of the injury, other systemic factors can also affect the outcome. Patients suffering from severe brain injury often experience extracranial inflammatory complications during the early period of treatment. Here, we investigate the changes in immunity in patients with brain injury.

METHODS

121 patients and 92 healthy controls were included in the research. Blood samples were collected on admission and analyzed by flow cytometry and biochemical methods. Multiple clusters of differentiation (CD) and antibody levels were investigated. The results were compared between patients and controls. In addition, results of two classes of severity (Glasgow Coma Scale, GCS, of 3-5 vs. 6-8) were also compared.

RESULTS

Parameters of humoral immunity in patients immediately after admission were significantly lower than those from healthy donors, with the exception of IgE elevated as much as to resemble allergic reaction (p < 0.01). Of cellular parameters, only natural killer (NK) cluster CD56 + was elevated (p < 0.01). Extracranial infectious complications were more common in patients with GCS 3-5.

CONCLUSIONS

Strong immune system disorders were observed in patients after severe brain injury, which may contribute to the worse outcome in such patients.

The involvement of nuclear factor-κB in astroprotection against ischemia-reperfusion injury by ischemia-preconditioned neurons

Ischemic preconditioned (IP) neurons protect astrocytes against ischemia/reperfusion (I/R)-induced injury by inhibiting oxidative stress. However, the relevant mechanisms are unknown. Based on the role of nuclear factor-κB (NF-κB) in cell survival and adaption to oxidative stress, we hypothesized that NF-κB might be associated with astroprotection induced by IP neurons via upregulation of antioxidant enzymes. Here, we investigated the effects of IP neurons on NF-κB activation, cell viability, reactive oxygen species (ROS), expression of antioxidant enzymes, erythropoietin (EPO), and tumor necrosis factor α (TNF-α), in the presence or absence of BAY11-7082 (an NF-κB inhibitor), anti-EPO, and anti-TNF-α antibodies, in astrocytes treated with or without I/R. We found that IP neurons could keep NF-κB activation at a relatively higher but beneficial level, and in turn, upregulated the activity of antioxidant enzymes and hence enhanced cell viability and reduced ROS in I/R treated astrocytes. The results collectively indicated that IP neurons are able to significantly inhibit the I/R-induced NF-κB overactivation, probably via EPO and TNF-α, being essential for IP neuron-induced astroprotection under the conditions of I/R. We concluded that NF-κB-mediated antioxidative stress is one of the mechanisms by which IP neurons protect astrocytes against I/R injury.

Lung injury in brain ischemia/reperfusion is exacerbated by mechanical ventilation with moderate tidal volume in rats

Ischemic stroke is one of the most frequent causes of injury in the central nervous system which may lead to multiorgan dysfunction, including in the lung. The aim of this study was to investigate whether brain ischemia/reperfusion with or without mechanical ventilation leads to lung injury. Male Sprague-Dawley rats were assigned to four groups: Sham, 1-h brain ischemia (MCAO)/24-h reperfusion (I/R), mechanical ventilation with moderate tidal volume (MTV), and I/R+MTV. The pulmonary capillary permeability (K_fc) was measured in the isolated perfused lung. Mean arterial blood pressure (MAP), heart rate (HR), blood-gas variables, histopathological parameters, lung glutathione peroxidase, and TNF-α were measured. K_fc in the I/R, MTV, and I/R+MTV groups were higher than that in the Sham group. In the I/R, MTV, and I/R+MTV groups, arterial partial pressures of oxygen and the arterial partial pressure of oxygen/fraction of inspired oxygen ratios were lower, whereas arterial partial pressures of carbon dioxide were higher than those in the Sham group. The histopathological score in the I/R group was more than that in the Sham group, and in the MTV and I/R+MTV groups were higher than those in the Sham and I/R groups. Furthermore, there were stepwise rises in TNF-α in the I/R, MTV, and I/R+MTV groups, respectively. There was no significant difference in MAP between groups. However, HR in the MTV group was higher than that in the Sham group. Brain ischemia/reperfusion leads to pulmonary capillary endothelial damage and the impairment of gas exchange in the alveolar-capillary barrier, which is exacerbated by mechanical ventilation with moderate tidal volume partially linked to inflammatory reactions.

Pretreated fucoidan confers neuroprotection against transient global cerebral ischemic injury in the gerbil hippocampal CA1 area via reducing of glial cell activation and oxidative stress

Fucoidan is a sulfated polysaccharide derived from brown algae and possesses various beneficial activities, including antioxidant property. Previous studies have shown that fucoidan displays protective effect against ischemia-reperfusion injury in some organs. However, few studies have been reported regarding the protective effect of fucoidan against transient cerebral ischemic insults and its related mechanisms. Therefore, in this study, we examined the neuroprotective effect of fucoidan against transient global cerebral ischemia (tGCI), as well as underlying its mechanism using a gerbil model of tGCI which shows a loss of pyramidal neurons in the hippocampal cornu ammonis 1 (CA1) area after 5 min of tGCI. Fucoidan (25 and 50 mg/kg) was intraperitoneally administered once daily for 5 days before tGCI. Pretreatment with 50 mg/kg of fucoidan, not 25 mg/kg of fucoidan, attenuated tGCI-induced hyperactivity and protected CA1 pyramidal neurons from tGCI. In addition, pretreatment with 50 mg/kg of fucoidan inhibited activations of astrocytes and microglia in the ischemic CA1 area. Furthermore, pretreatment with 50 mg/kg of fucoidan significantly reduced the increased 4-hydroxy-2-noneal and superoxide anion radical production in the ischemic CA1 area and significantly increased expressions of SOD1 and SOD2 in the CA1 pyramidal neurons before and after tGCI. Additionally, treatment with diethyldithiocarbamate (an inhibitor of SODs) to the fucoidan-treated gerbils notably abolished the fucoidan-mediated neuroprotection. In brief, our present results indicate that fucoidan can effectively protect neurons from tGCI through attenuation of activated glial cells and reduction of oxidative stress via increase of SODs. Thus, we strongly suggest that fucoidan can be used as a useful preventive agent in cerebral ischemia.

Oxidative stress and apoptosis after acute respiratory hypoxia and reoxygenation in rat brain

Acute hypoxia increases the formation of reactive oxygen species (ROS) in the brain. However, the effect of reoxygenation, unavoidable to achieve full recovery of the hypoxic organ, has not been clearly established. The aim of the present study was to evaluate the effects of exposition to acute severe respiratory hypoxia followed by reoxygenation on the evolution of oxidative stress and apoptosis in the brain. We investigated the effect of in vivo acute severe normobaric hypoxia (rats exposed to 7% O₂ for 6 h) and reoxygenation in normoxia (21% O₂ for 24 h or 48 h) on oxidative stress markers, the antioxidant system and apoptosis in the brain. After respiratory hypoxia we found increased levels of HIF-1α expression, lipid peroxidation, protein oxidation and nitric oxide in brain extracts. Antioxidant defence systems such as superoxide dismutase (SOD), reduced glutathione (GSH) and glutathione peroxidase (GPx) and the reduced/oxidized glutathione (GSH/GSSG) ratio were significantly decreased in the brain. After 24 h of reoxygenation, oxidative stress parameters and the anti-oxidant system returned to control values. Regarding the apoptosis parameters, acute hypoxia increased cytochrome c, AIF and caspase 3 activity in the brain. The apoptotic effect is greatest after 24 h of reoxygenation. Immunohistochemistry suggests that CA3 and dentate gyrus in the hippocampus seem more susceptible to hypoxia than the cortex. Severe acute hypoxia increases oxidative damage, which in turn could activate apoptotic mechanisms. Our work is the first to demonstrate that after 24 h of reoxygenation oxidative stress is attenuated, while apoptosis is maintained mainly in the hippocampus, which may, in fact, be the cause of impaired brain function.

Stroke and Drug Delivery--In Vitro Models of the Ischemic Blood-Brain Barrier

Stroke is a major cause of death and disability worldwide. Both cerebral hypoperfusion and focal cerebral infarcts are caused by a reduction of blood flow to the brain, leading to stroke and subsequent brain damage. At present, only few medical treatments of stroke are available, with the Food and Drug Administration-approved tissue plasminogen activator for treatment of acute ischemic stroke being the most prominent example. A large number of potential drug candidates for treatment of ischemic brain tissue have been developed and subsequently failed in clinical trials. A deeper understanding of permeation pathways across the barrier in ischemic and postischemic brain endothelium is important for development of new medical treatments. The blood-brain barrier, that is, the endothelial monolayer lining the brain capillaries, changes properties during an ischemic event. In vitro models of the blood-brain barrier are useful tools to investigate the effects of induced ischemia under controlled conditions. In the present mini review, we aim to give a brief overview of the in vitro models of ischemia. Special focus is given to the expression of uptake and efflux transport pathways in the ischemic and postischemic endothelium. Finally, we will point toward future challenges within the field of in vitro models of brain ischemia.

Neurovascular protection by telmisartan via reducing neuroinflammation in stroke-resistant spontaneously hypertensive rat brain after ischemic stroke

Telmisartan is a highly lipid-soluble angiotensin receptor blocker (ARB), which improves insulin sensitivity and reduces triglyceride levels and, thus, is called metabo-sartan. We examined the effects of telmisartan on neurovascular unit (N-acetylglucosamine oligomer [NAGO], collagen IV, and glial fibrillary acidic protein [GFAP]) and neuroinflammation (matrix metalloproteinase-9 [MMP-9] and inflammasome) in brain of stroke-resistant spontaneously hypertensive rat (SHR-SR). At 12 weeks of age, SHR-SR received transient middle cerebral artery occlusion (tMCAO) for 90 minutes and were divided into the following 3 groups, that is, vehicle group, low-dose telmisartan group (.3 mg/kg/d), and high-dose telmisartan group (3 mg/kg/d, postoral). Immunohistologic analysis at ages 6, 12, and 18 months showed progressive decreases of NAGO-positive endothelium and collagen IV-positive basement membrane and progressive increases of MMP-9-positive neurons, GFAP-positive astrocytes, and NLRP3-positive inflammasome in the cerebral cortex of vehicle group. Low-dose telmisartan reduced such changes without lowering blood pressure (BP), and high-dose telmisartan further improved such changes with lowering BP. The present findings suggest that a persistent hypertension caused a long-lasting inflammation after tMCAO in SHR-SR, which accelerated neurovascular disruption and emergent inflammasome, and that telmisartan greatly reduced such inflammation and protected the neurovascular unit via its pleiotropic effects in living hypertensive rat brain after ischemic stroke.

Oxidative Stress and the Use of Antioxidants in Stroke

Transient or permanent interruption of cerebral blood flow by occlusion of a cerebral artery gives rise to an ischaemic stroke leading to irreversible damage or dysfunction to the cells within the affected tissue along with permanent or reversible neurological deficit. Extensive research has identified excitotoxicity, oxidative stress, inflammation and cell death as key contributory pathways underlying lesion progression. The cornerstone of treatment for acute ischaemic stroke remains reperfusion therapy with recombinant tissue plasminogen activator (rt-PA). The downstream sequelae of events resulting from spontaneous or pharmacological reperfusion lead to an imbalance in the production of harmful reactive oxygen species (ROS) over endogenous anti-oxidant protection strategies. As such, anti-oxidant therapy has long been investigated as a means to reduce the extent of injury resulting from ischaemic stroke with varying degrees of success. Here we discuss the production and source of these ROS and the various strategies employed to modulate levels. These strategies broadly attempt to inhibit ROS production or increase scavenging or degradation of ROS. While early clinical studies have failed to translate success from bench to bedside, the combination of anti-oxidants with existing thrombolytics or novel neuroprotectants may represent an avenue worthy of clinical investigation. Clearly, there is a pressing need to identify new therapeutic alternatives for the vast majority of patients who are not eligible to receive rt-PA for this debilitating and devastating disease.

Reactive oxygen species in inflammation and tissue injury

Abstract Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Therapeutic effects of traditional herbal medicine on cerebral ischemia: a perspective of vascular protection

Although many agents for acute ischemic stroke treatment have been developed from extensive preclinical studies, most have failed in clinical trials. As a result, researchers are seeking other methods or agents based on previous studies. Among the various prospective approaches, vascular protection might be the key for development of therapeutic agents for stroke and for improvements in the efficacy and safety of conventional therapies. Traditional medicines in Asian countries are based on clinical experiences and literature accumulated over thousands of years. To date, many studies have used traditional herbal medicines to prove or develop new agents based on stroke treatments mentioned in traditional medicinal theory or other clinical data. In the current review, we describe the vascular factors related to ischemic brain damage and the herbal medicines that impact these factors, including Salviae Miltiorrhizae Radix, Notoginseng Radix, and Curcumae Rhizoma, based on scientific reports and traditional medical theory. Further, we point out the problems associated with herbal medicines in stroke research and propose better methodologies to address these problems.

Stroke neuroprotection: targeting mitochondria

Stroke is the fourth leading cause of death and the leading cause of long-term disability in the United States. Blood flow deficit results in an expanding infarct core with a time-sensitive peri-infarct penumbra that is considered salvageable and is the primary target for treatment strategies. The only current FDA-approved drug for treating ischemic stroke is recombinant tissue plasminogen activator (rt-PA). However, this treatment is limited to within 4.5 h of stroke onset in a small subset of patients. The goal of this review is to focus on mitochondrial-dependent therapeutic agents that could provide neuroprotection following stroke. Dysfunctional mitochondria are linked to neurodegeneration in many disease processes including stroke. The mechanisms reviewed include: (1) increasing ATP production by purinergic receptor stimulation, (2) decreasing the production of ROS by superoxide dismutase, or (3) increasing antioxidant defenses by methylene blue, and their benefits in providing neuroprotection following a stroke.

Occludin protein family: oxidative stress and reducing conditions

The occludin-like proteins belong to a family of tetraspan transmembrane proteins carrying a marvel domain. The intrinsic function of the occludin family is not yet clear. Occludin is a unique marker of any tight junction and is found in polarized endothelial and epithelial tissue barriers, at least in the adult vertebrate organism. Occludin is able to oligomerize and to form tight junction strands by homologous and heterologous interactions, but has no direct tightening function. Its oligomerization is affected by pro- and antioxidative agents or processes. Phosphorylation of occludin has been described at multiple sites and is proposed to play a regulatory role in tight junction assembly and maintenance and, hence, to influence tissue barrier characteristics. Redox-dependent signal transduction mechanisms are among the pathways modulating occludin phosphorylation and function. This review discusses the novel concept that occludin plays a key role in the redox regulation of tight junctions, which has a major impact in pathologies related to oxidative stress and corresponding pharmacologic interventions.

Protection against ischemic stroke damage by synergistic treatment with amlodipine plus atorvastatin in Zucker metabolic rat

Ischemic stroke is a major neurologic disorder and a leading cause of disability and death in the world. We compared neuroprotective effects of single or combination therapy of amlodipine (AM) and atorvastatin (AT) in such a metabolic syndrome model Zucker rat. The animals were pretreated with vehicle, AM, AT, or the combination of AM plus AT for 28days, and physical and serum parameters were analyzed, then 90min of transient middle cerebral artery occlusion (tMCAO), was performed followed by immunohistochemical analyses at 24h. Without affecting serum levels of lipids, adiponectin, and leptin, the combination therapy of AM plus AT ameliorated the post-ischemic brain weight increase. The single treatment with AM or AT itself exerted neuroprotective effects with reducing inductions of MMP-9 and AT2R, as well as with preserving collagen IV, and the combination therapy of AM plus AT showed a further synergistic benefit against acute ischemic neural damages. Single AT was more protective on these 3 molecules than single AM at this time point of 24h after tMCAO. Thus, the combination therapy with AM plus AT extended the neuroprotectives effect of single treatment with AM or AT on a part of neurovascular unit and a hypertension-related receptor.

Extension of the neuroprotective time window for thiazolidinediones in ischemic stroke is dependent on time of reperfusion

Stroke is a leading cause of death and disability but has limited therapeutic options. Thiazolidinediones (TZDs), agonists for the nuclear receptor, peroxisome proliferator-activated receptor (PPAR)γ, reduce infarct volume and improve neurologic function following transient middle cerebral artery occlusion (MCAO) in rats. Translation of these findings into clinical therapy will require careful assessment of dosing paradigms and effective time windows for treatment. Understanding the mechanisms by which TZDs protect the brain provides insight into how time windows for neuroprotection might be extended. We find that two TZDs, pioglitazone and rosiglitazone, significantly reduce infarct volume at doses similar to those used clinically (1 mg/kg for pioglitazone and 0.1 mg/kg for rosiglitazone). We also find that pioglitazone reduces infarction volume in a transient, but not a permanent MCAO model suggesting that reperfusion plays an important role in TZD mediated neuroprotection. Since PPARγ agonists reduce inflammation and oxidative stress, both of which are exacerbated by reperfusion, we hypothesized that TZDs would be most effective if administered prior to reperfusion. We administered TZDs 3 h after MCAO and found that infarction volume and neurologic function are significantly improved in animals reperfused at 3 h and 15 min (after TZD treatment), but not in animals reperfused at 2 h (before TZD treatment) when assessed either 24 h or 3 weeks after MCAO. While TZDs reduce intercellular adhesion molecule (ICAM) expression to a similar extent regardless of the time of reperfusion, leukocyte entry into brain parenchyma is more dramatically reduced when reperfusion is delayed until after drug treatment. The finding that delaying reperfusion until after TZD treatment is beneficial despite a longer period of ischemia, is dramatic given the widely held view that duration of ischemia is the most important determinate of injury.

Redox-sensitivity of the dimerization of occludin

Occludin is a self-associating transmembrane tight junction protein affected in oxidative stress. However, its function is unknown. The cytosolic C-terminal tail contains a coiled coil-domain forming dimers contributing to the self-association. Studying the hypothesis that the self-association is redox-sensitive, we found that the dimerization of the domain depended on the sulfhydryl concentration of the environment in low-millimolar range. Under physiological conditions, monomers and dimers were detected. Masking the sulfhydryl residues in the domain prevented the dimerization but affected neither its helical structure nor cylindric shape. Incubation of cell extracts containing full-length occludin with sulfhydryl reagents prevented the dimerization; a cysteine/alanine exchange mutant also did not show dimer formation. This demonstrates, for the first time, that disulfide bridge formation of the domain is involved in the occludin dimerization. It is concluded that the redox-dependent dimerization of occludin may play a regulatory role in the tight junction assembly under physiological and pathological conditions.

The oligomerization of the coiled coil-domain of occludin is redox sensitive

The transmembrane tight junction protein occludin is sensitive to oxidative stress. Occludin oligomerizes; however, its function in the tight junction is unknown. The cytosolic C-terminal tail contains a coiled coil-domain and forms dimers contributing to the oligomerization. The regulation of the oligomerization remains unclear. As the domain area contains sulfhydryl residues, we tested the hypothesis that the dimerization of the coiled coil-domain depends on these residues. We showed that the dimerization is modulated by the thiol concentration in the low-millimolar range, which is relevant both for physiological and pathophysiological conditions. Masking the sulfhydryl residues in the fragment by covalent binding of 4-vinyl pyridine prevented the dimerization but did not affect its helical structure and cylindric shape. The data demonstrate, for the first time, that disulfide bridge formation of murine cystein 408 is involved in the dimerization. This process is redox-sensitive but the secondary structure of the domain is not. It is concluded that the dimerization of occludin may play a regulatory role in the tight junction assembly under physiological and pathological conditions.

Minocycline treatment following hypoxic/ischaemic injury attenuates white matter injury in a rodent model of periventricular leucomalacia

AIMS

Periventricular white matter injury in premature infants occurs following hypoxia/ischaemia and systemic infection, and results in hypomyelination, as well as neuromotor and cognitive deficits later in life. Inflammatory infiltrates are seen within human cerebral white matter from periventricular leucomalacia (PVL) cases.

METHODS

In this study, we examine the time course of CD-68+ microglial cell responses relative to cell death within white matter following hypoxia/ischaemia in a rat model of PVL. We also tested the efficacy of the minocycline, an agent that suppresses microglial activation, in this model when administered as a post-insult treatment.

RESULTS

We show that preoligodendrocyte injury in the post-natal day 6 begins within 24 h and continues for 48-96 h after hypoxia/ischaemia, and that microglial responses occur primarily over the first 96 h following hypoxia/ischaemia. Minocycline treatment over this 96 h time window following the insult resulted in significant protection against white matter injury, and this effect was concomitant with a reduction in CD-68+ microglial cell numbers.

CONCLUSIONS

These results suggest that anti-inflammatory treatments may represent a useful strategy in the treatment of PVL, where clinical conditions would favour a post-insult treatment strategy.