The administration of cobra venom factor reduces post-ischemic cerebral injury in adult and neonatal rats

The Role of the Complement System in Synaptic Pruning after Stroke

Stroke is a serious disease that can lead to local neurological dysfunction and cause great harm to the patient's health due to blood cerebral circulation disorder. Synaptic pruning is critical for the normal development of the human brain, which makes the synaptic circuit completer and more efficient by removing redundant synapses. The complement system is considered a key player in synaptic loss and cognitive impairment in neurodegenerative disease. After stroke, the complement system is over-activated, and complement proteins can be labeled on synapses. Microglia and astrocytes can recognize and engulf synapses through corresponding complement receptors. Complement-mediated excessive synaptic pruning can cause post-stroke cognitive impairment (PSCI) and secondary brain damage. This review summarizes the latest progress of complement-mediated synaptic pruning after stroke and the potential mechanisms. Targeting complement-mediated synaptic pruning may be essential for exploring therapeutic strategies for secondary brain injury (SBI) and neurological dysfunction after stroke.

Aberrant Complement System Activation in Neurological Disorders

The complement system is an assembly of proteins that collectively participate in the functions of the healthy and diseased brain. The complement system plays an important role in the maintenance of uninjured (healthy) brain homeostasis, contributing to the clearance of invading pathogens and apoptotic cells, and limiting the inflammatory immune response. However, overactivation or underregulation of the entire complement cascade within the brain may lead to neuronal damage and disturbances in brain function. During the last decade, there has been a growing interest in the role that this cascading pathway plays in the neuropathology of a diverse array of brain disorders (e.g., acute neurotraumatic insult, chronic neurodegenerative diseases, and psychiatric disturbances) in which interruption of neuronal homeostasis triggers complement activation. Dysfunction of the complement promotes a disease-specific response that may have either beneficial or detrimental effects. Despite recent advances, the explicit link between complement component regulation and brain disorders remains unclear. Therefore, a comprehensible understanding of such relationships at different stages of diseases could provide new insight into potential therapeutic targets to ameliorate or slow progression of currently intractable disorders in the nervous system. Hence, the aim of this review is to provide a summary of the literature on the emerging role of the complement system in certain brain disorders.

Increased Serum Complement C3 Levels Are Associated With Adverse Clinical Outcomes After Ischemic Stroke

BACKGROUND AND PURPOSE

Complement C3 has been implicated in inflammation and ischemia/reperfusion injury, but its impact on the prognosis of ischemic stroke remains unclear. Aim of this study was to prospectively investigate the association between serum complement C3 and adverse clinical outcomes after ischemic stroke.

METHODS

We measured serum complement C3 levels for 3474 patients with ischemic stroke in 26 participating hospitals and collected data of clinical outcomes at 3 months after ischemic stroke. The primary outcome was composite outcome of death and major disability (modified Rankin Scale score ≥3) at 3 months after stroke onset and secondary outcomes included major disability, death, and vascular events.

RESULTS

During 3 months of follow-up, 866 participants (25.4%) developed primary outcome. After multivariate adjustment, elevated serum complement C3 levels were associated with increased risk of primary outcome (odds ratio, 1.30 [95% CI, 1.02-1.65]; P_trend=0.038) when 2 extreme tertiles were compared. Each SD increase of log-transformed complement C3 was associated with 13% (95% CI, 2%-25%) increased risk of primary outcome. Multivariable-adjusted spline regression model showed a linear relationship between serum complement C3 and the risk of primary outcome (P_linearity=0.022). Addition of serum complement C3 to conventional risk factors significantly improved the risk prediction of primary outcome (net reclassification index: 8.87%, P=0.028; integrated discrimination index: 0.19%, P=0.029).

CONCLUSIONS

High serum complement C3 levels at baseline were associated with increased risks of adverse clinical outcomes at 3 months after ischemic stroke, suggesting that serum complement C3 may be a valuable prognostic biomarker for ischemic stroke.

Endothelial progenitor cell transplantation alleviated ischemic brain injury via inhibiting C3/C3aR pathway in mice

Endothelial progenitor cell transplantation is a potential therapeutic approach in brain ischemia. However, whether the therapeutic effect of endothelial progenitor cells is via affecting complement activation is unknown. We established a mouse focal ischemia model (n = 111) and transplanted endothelial progenitor cells into the peri-infarct region immediately after brain ischemia. Neurological outcomes and brain infarct/atrophy volume were examined after ischemia. Expression of C3, C3aR and pro-inflammatory factors were further examined to explore the role of endothelial progenitor cells in ischemic brain. We found that endothelial progenitor cells improved neurological outcomes and reduced brain infarct/atrophy volume after 1 to 14 days of ischemia compared to the control (p < 0.05). C3 and C3aR expression in the brain was up-regulated at 1 day up to 14 days (p < 0.05). Endothelial progenitor cells reduced astrocyte-derived C3 (p < 0.05) and C3aR expression (p < 0.05) after ischemia. Endothelial progenitor cells also reduced inflammatory response after ischemia (p < 0.05). Endothelial progenitor cell transplantation reduced astrocyte-derived C3 expression in the brain after ischemic stroke, together with decreased C3aR and inflammatory response contributing to neurological function recovery. Our results indicate that modulating complement C3/C3aR pathway is a novel therapeutic target for the ischemic stroke.

Complement C3 participates in the function and mechanism of traumatic brain injury at simulated high altitude

BACKGROUND

Traumatic brain injury (TBI) leads to severe mortality and disability, in which secondary injury induced by complement activation plays an important role. TBI tends to be associated with more severe cerebral edema and worse neurological functional recovery if it occurs in high-altitude areas than in low-altitude areas. However, the underlying mechanism of this difference is unknown. Thus, we used cobra venom factor (CVF) to deplete complement C3 in simulated high-altitude areas to explore whether the differences in outcome at different altitudes are related to secondary injury caused by complement C3.

METHODS

The weight-drop model was adopted to induce TBI in rats. Rats were randomly divided into the following groups: sham + saline (sham), high altitude + TBI + saline (HAT), high altitude + TBI + CVF (H-CVF), low altitude + TBI + saline (LAT), and low altitude + TBI + CVF (L-CVF). Brain contusion and edema volumes, brain water content, myelin basic protein (MBP) expression, tumor necrosis factor alpha (TNF-a) expression, interleukin 1 beta (IL1B) expression, mortality rate, neurological function, and complement component 3 (C3) mRNA expression were measured by techniques such as Evans blue fluorescence, Perls staining, TUNEL staining, ELISA, immunohistochemistry and Western blotting to evaluate correlations between complement activation and secondary injury.

RESULTS

The activation of complement after TBI was significantly higher at high altitude than at low altitude. High-altitude TBI resulted in a leakier blood-brain barrier, more severe cerebral edema and higher mortality than low-altitude TBI did. In addition, high-altitude TBI tended to be associated with more MBP degradation, ferric iron deposition, neuronal apoptosis, and inflammatory factor deposition than low-altitude TBI. All of these effects of TBI were partially reversed by inhibiting complement activation using CVF.

CONCLUSION

Our study provided evidence that TBI at high altitude leads to severe edema and high mortality and disability rates. Complement C3 activation is one of the important factors contributing to secondary brain injury.

Significance of Complement System in Ischemic Stroke: A Comprehensive Review

The complement system is an essential part of innate immunity, typically conferring protection via eliminating pathogens and accumulating debris. However, the defensive function of the complement system can exacerbate immune, inflammatory, and degenerative responses in various pathological conditions. Cumulative evidence indicates that the complement system plays a critical role in the pathogenesis of ischemic brain injury, as the depletion of certain complement components or the inhibition of complement activation could reduce ischemic brain injury. Although multiple candidates modulating or inhibiting complement activation show massive potential for the treatment of ischemic stroke, the clinical availability of complement inhibitors remains limited. The complement system is also involved in neural plasticity and neurogenesis during cerebral ischemia. Thus, unexpected side effects could be induced if the systemic complement system is inhibited. In this review, we highlighted the recent concepts and discoveries of the roles of different kinds of complement components, such as C3a, C5a, and their receptors, in both normal brain physiology and the pathophysiology of brain ischemia. In addition, we comprehensively reviewed the current development of complement-targeted therapy for ischemic stroke and discussed the challenges of bringing these therapies into the clinic. The design of future experiments was also discussed to better characterize the role of complement in both tissue injury and recovery after cerebral ischemia. More studies are needed to elucidate the molecular and cellular mechanisms of how complement components exert their functions in different stages of ischemic stroke to optimize the intervention of targeting the complement system.

Complement depletion with cobra venom factor alleviates acute hepatic injury induced by ischemia‑reperfusion

Increasing evidence has demonstrated that complement activation is required for ischemia‑reperfusion injury (IRI)‑induced hepatic damage, and cobra venom factor (CVF) can deplete the complement components. The aim of the current study was to investigate the effect and intrinsic mechanism of CVF pretreatment on IRI‑induced acute hepatic injury in rats. Acute hepatic injury in rats was induced by bone fracture to simulate trauma, followed by hemorrhage for 90 min, and then the rats were resuscitated for a period of 20 min of reperfusion. The survival times under different CVF treatment doses and schedules for rats with IRI were evaluated. Hepatic tissues and serum samples were analyzed for acute hepatic injury, complement activation, inflammatory mediator release and apoptosis at predetermined times and compared between the IRI group and the CVF pretreatment + IRI groups. Compared to the rats with IRI alone, the survival times were significantly improved among rats with IRI receiving a high‑dose or low‑dose CVF pretreatment (all P<0.01). Upon histological examination, severe hepatic damage was observed in the rats with IRI, accompanied by liver function deterioration, complement and membrane attack complex activation, inflammatory mediator release and hepatic cell apoptosis. CVF pretreatment significantly attenuated the hepatic injury through depletion of anaphylatoxic C5a and membrane attack complex C5b‑9 activation, and subsequent inhibition of inflammatory mediator release and hepatic cell apoptosis (all P<0.05). The results indicated that CVF pretreatment ameliorates IRI‑induced acute hepatic injury. However, further studies are required to determine whether this therapy could be a potential agent for the treatment of IRI injuries in clinical settings.

Therapeutic targeting of complement to modify disease course and improve outcomes in neurological conditions

The recognition that complement proteins are abundantly present and can have pathological roles in neurological conditions offers broad scope for therapeutic intervention. Accordingly, an increasing number of experimental investigations have explored the potential of harnessing the unique activation pathways, proteases, receptors, complexes, and natural inhibitors of complement, to mitigate pathology in acute neurotrauma and chronic neurodegenerative diseases. Here, we review mechanisms of complement activation in the central nervous system (CNS), and explore the effects of complement inhibition in cerebral ischemic-reperfusion injury, traumatic brain injury, spinal cord injury, Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease and Huntington's disease. We consider the challenges and opportunities arising from these studies. As complement therapies approach clinical translation, we provide perspectives on how promising complement-targeted therapeutics could become part of novel and effective future treatment options to improve outcomes in the initiation and progression stages of these debilitating CNS disorders.

Complement in the Homeostatic and Ischemic Brain

The complement system is a component of the immune system involved in both recognition and response to pathogens, and it is implicated in an increasing number of homeostatic and disease processes. It is well documented that reperfusion of ischemic tissue results in complement activation and an inflammatory response that causes post-reperfusion injury. This occurs following cerebral ischemia and reperfusion and triggers secondary damage that extends beyond the initial infarcted area, an outcome that has rationalized the use of complement inhibitors as candidate therapeutics after stroke. In the central nervous system, however, recent studies have revealed that complement also has essential roles in synaptic pruning, neurogenesis, and neuronal migration. In the context of recovery after stroke, these apparent divergent functions of complement may account for findings that the protective effect of complement inhibition in the acute phase after stroke is not always maintained in the subacute and chronic phases. The development of effective stroke therapies based on modulation of the complement system will require a detailed understanding of complement-dependent processes in both early neurodegenerative events and delayed neuro-reparatory processes. Here, we review the role of complement in normal brain physiology, the events initiating complement activation after cerebral ischemia-reperfusion injury, and the contribution of complement to both injury and recovery. We also discuss how the design of future experiments may better characterize the dual role of complement in recovery after ischemic stroke.

Imaging of activated complement using ultrasmall superparamagnetic iron oxide particles (USPIO)--conjugated vectors: an in vivo in utero non-invasive method to predict placental insufficiency and abnormal fetal brain development

In the current study, we have developed a magnetic resonance imaging-based method for non-invasive detection of complement activation in placenta and foetal brain in vivo in utero. Using this method, we found that anti-complement C3-targeted ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles bind within the inflamed placenta and foetal brain cortical tissue, causing a shortening of the T2* relaxation time. We used two mouse models of pregnancy complications: a mouse model of obstetrics antiphospholipid syndrome (APS) and a mouse model of preterm birth (PTB). We found that detection of C3 deposition in the placenta in the APS model was associated with placental insufficiency characterised by increased oxidative stress, decreased vascular endothelial growth factor and placental growth factor levels and intrauterine growth restriction. We also found that foetal brain C3 deposition was associated with cortical axonal cytoarchitecture disruption and increased neurodegeneration in the mouse model of APS and in the PTB model. In the APS model, foetuses that showed increased C3 in their brains additionally expressed anxiety-related behaviour after birth. Importantly, USPIO did not affect pregnancy outcomes and liver function in the mother and the offspring, suggesting that this method may be useful for detecting complement activation in vivo in utero and predicting placental insufficiency and abnormal foetal neurodevelopment that leads to neuropsychiatric disorders.

Versatility of the complement system in neuroinflammation, neurodegeneration and brain homeostasis

The immune response after brain injury is highly complex and involves both local and systemic events at the cellular and molecular level. It is associated to a dramatic over-activation of enzyme systems, the expression of proinflammatory genes and the activation/recruitment of immune cells. The complement system represents a powerful component of the innate immunity and is highly involved in the inflammatory response. Complement components are synthesized predominantly by the liver and circulate in the bloodstream primed for activation. Moreover, brain cells can produce complement proteins and receptors. After acute brain injury, the rapid and uncontrolled activation of the complement leads to massive release of inflammatory anaphylatoxins, recruitment of cells to the injury site, phagocytosis and induction of blood brain barrier (BBB) damage. Brain endothelial cells are particularly susceptible to complement-mediated effects, since they are exposed to both circulating and locally synthesized complement proteins. Conversely, during neurodegenerative disorders, complement factors play distinct roles depending on the stage and degree of neuropathology. In addition to the deleterious role of the complement, increasing evidence suggest that it may also play a role in normal nervous system development (wiring the brain) and adulthood (either maintaining brain homeostasis or supporting regeneration after brain injury). This article represents a compendium of the current knowledge on the complement role in the brain, prompting a novel view that complement activation can result in either protective or detrimental effects in brain conditions that depend exquisitely on the nature, the timing and the degree of the stimuli that induce its activation. A deeper understanding of the acute, subacute and chronic consequences of complement activation is needed and may lead to new therapeutic strategies, including the ability of targeting selective step in the complement cascade.

Ischemia/reperfusion injury: effect of simultaneous inhibition of plasma cascade systems versus specific complement inhibition

Ischemia/reperfusion injury (IRI) may occur from ischemia due to thrombotic occlusion, trauma or surgical interventions, including transplantation, with subsequent reestablishment of circulation. Time-dependent molecular and structural changes result from the deprivation of blood and oxygen in the affected tissue during ischemia. Upon restoration of blood flow a multifaceted network of plasma cascades is activated, including the complement-, coagulation-, kinin-, and fibrinolytic system, which plays a major role in the reperfusion-triggered inflammatory process. The plasma cascade systems are therefore promising therapeutic targets for attenuation of IRI. Earlier studies showed beneficial effects through inhibition of the complement system using specific complement inhibitors. However, pivotal roles in IRI are also attributed to other cascades. This raises the question, whether drugs, such as C1 esterase inhibitor, which regulate more than one cascade at a time, have a higher therapeutic potential. The present review discusses different therapeutic approaches ranging from specific complement inhibition to simultaneous inhibition of plasma cascade systems for reduction of IRI, gives an overview of the plasma cascade systems in IRI as well as highlights recent findings in this field.

Neuroprotective effects of the SCR1-3 functional domain of CR1 on acute cerebral ischemia and reperfusion injury in rats

OBJECTIVE

Complement receptor type 1 (CR1), one of the most potent inhibitors in complement activation, shows a protective effect on cerebral ischemia/reperfusion (CI/R) injury due to its ability to bind C3b and C4b and to inactivate C3/C5 convertases. So far, no study assessed the effect of the first three short consensus repeats (SCR1-3) with low molecular weight, one of the most active functional domains of CR1, binding C4b with a powerful decay-acceleration effect on classical and alternative C3/C5 convertases pathways. Therefore, we aim to assess this effect on CI/R injury in the present study.

METHODS

Seventy-five adult male Sprague-Dawley rats were randomly divided into three groups: sham operation group (n = 15), CI/R group (n = 30), and CI/R group treated with CR1-SCR1-3 protein (n = 30). After middle cerebral artery occlusion (MCAO) for 1 hour and reperfusion for 24 hours, neurological motor deficits, cerebral infarct size, and biochemical parameters including myeloperoxidase (MPO), malondialdehyde (MDA), and superoxide dismutase (SOD) were assessed. Meanwhile, tissues in cerebral cortex were collected and processed for western blotting, immunohistochemistry, and HE staining.

RESULTS

CR1-SCR1-3 could improve neurological functions in brain with a 26.8% decrease in neurological motor deficit score and could lead to a 63.8% reduction in cerebral infarct size. Besides, pretreatment using CR1-SCR1-3 could prevent neutrophil infiltration and alleviate inflammation severity and subsequent tissue damage. Decreased C4b expression and action, as well as improved morphological changes, were also observed in cerebral tissues of CI/R+CR1-SCR1-3 rats.

CONCLUSION

CR1-SCR1-3 protein could possess a neuroprotective effect on acute CI/R injury.

Influence of inflammation on poststroke plasticity

Age-related brain injuries including stroke are a leading cause of morbidity and mental disability worldwide. Most patients who survive stroke experience some degree of recovery. The restoration of lost functions can be explained by neuronal plasticity, understood as brain ability to reorganize and remodel itself in response to changed environmental requirements. However, stroke triggers a cascade of events which may prevent the normal development of the plastic changes. One of them may be inflammatory response initiated immediately after stroke, which has been found to contribute to neuronal injury. Some recent evidence though has suggested that inflammatory reaction can be also neuroprotective. This paper attempts to discuss the influence of poststroke inflammatory response on brain plasticity and stroke outcome. We also describe the recent anti-inflammatory strategies that have been effective for recovery in experimental stroke.

Biochemistry of envenomation

Venoms and toxins are of significant interest due to their ability to cause a wide range of pathophysiological conditions that can potentially result in death. Despite their wide distribution among plants and animals, the biochemical pathways associated with these pathogenic agents remain largely unexplored. Impoverished and underdeveloped regions appear especially susceptible to increased incidence and severity due to poor socioeconomic conditions and lack of appropriate medical treatment infrastructure. To facilitate better management and treatment of envenomation victims, it is essential that the biochemical mechanisms of their action be elucidated. This review aims to characterize downstream envenomation mechanisms by addressing the major neuro-, cardio-, and hemotoxins as well as ion-channel toxins. Because of their use in folk and traditional medicine, the biochemistry behind venom therapy and possible implications on conventional medicine will also be addressed.

The contribution of mannose binding lectin to reperfusion injury after ischemic stroke

After complement system (CS) activation, the sequential production of complement products increases cell injury and death through opsonophagocytosis, cytolysis, adaptive, and inflammatory cell responses. These responses potentiate cerebral ischemia-reperfusion (IR) injury after ischemic stroke and reperfusion. Activation of the CS via mannose binding lectin (MBL)-initiated lectin pathway is known to increase tissue damage in response to IR in muscle, myocardium and intestine tissue. In contrast, the contribution of this pathway to cerebral IR injury, a neutrophil-mediated event, is less clear. Therefore, we investigated the potential protective role of MBL deficiency in neutrophil-mediated cerebral injury after IR. Using an intraluminal filament method, neutrophil activation and cerebral injury were compared between MBL-deficient and wild type C57Bl/6 mice subjected to 60 minutes of MCA ischemia and reperfusion. Systemic neutrophil activation was not decreased in MBL-deficient animals after IR. In MBL-deficient animals, cerebral injury was significantly decreased only in the striatum (p < 0.05). Despite MBL deficiency, C3 depositions were evident in the injured hemisphere during reperfusion. These results indicate that while MBL deficiency results in a modest protection of a sub-cortical brain region during IR, redundant complement pathway activation may overwhelm further beneficial effects of MBL deficiency during reperfusion.

Low ficolin-3 levels in early follow-up serum samples are associated with the severity and unfavorable outcome of acute ischemic stroke

Background

A number of data indicate that the lectin pathway of complement activation contributes to the pathophysiology of ischemic stroke. The lectin pathway may be triggered by the binding of mannose-binding lectin (MBL), ficolin-2 or ficolin-3 to different ligands. Although several papers demonstrated the significance of MBL in ischemic stroke, the role of ficolins has not been examined.

Methods

Sera were obtained within 12 hours after the onset of ischemic stroke (admission samples) and 3-4 days later (follow-up samples) from 65 patients. The control group comprised 100 healthy individuals and 135 patients with significant carotid stenosis (patient controls). The concentrations of ficolin-2 and ficolin-3, initiator molecules of the lectin complement pathway, were measured by ELISA methods. Concentration of C-reactive protein (CRP) was also determined by a particle-enhanced immunturbidimetric assay.

Results

Concentrations of both ficolin-2 and ficolin-3 were significantly (p < 0.001) decreased in both the admission and in the follow-up samples of patients with definite ischemic stroke as compared to healthy subjects. Concentrations of ficolin-2 and ficolin-3 were even higher in patient controls than in healthy subjects, indicating that the decreased levels in sera during the acute phase of stroke are related to the acute ischemic event. Ficolin-3 levels in the follow-up samples inversely correlated with the severity of stroke indicated by NIH scale on admission. In follow-up samples an inverse correlation was observed between ficolin-3 levels and concentration of S100β, an indicator of the size of cerebral infarct. Patients with low ficolin-3 levels and high CRP levels in the follow up samples had a significantly worse outcome (adjusted ORs 5.6 and 3.9, respectively) as measured by the modified Rankin scale compared to patients with higher ficolin-3 and lower CRP concentrations. High CRP concentrations were similarly predictive for worse outcome, and the effects of low ficolin-3 and high CRP were independent.

Conclusions

Our findings indicate that ficolin-mediated lectin pathways of complement activation contribute to the pathogenesis of ischemic stroke and may be additive to complement-independent inflammatory processes.

Protective effects of hypothalamic proline-rich peptide and cobra venom Naja Naja Oxiana on dynamics of vestibular compensation following unilateral labyrinthectomy

We tested the action of proline-rich peptide (PRP-1) and cobra venom Naja Naja Oxiana (NOX) on Deiters' nucleus neurons at 3rd, 15th and 35th days after unilateral labyrinthectomy (UL). Early and late tetanic, post-tetanic potentiation and depression of Deiters'neurons to bilateral high frequency stimulation of hypothalamic supraoptic and paraventricualar nuclei was studied. The analysis of spike activity was carried out by mean of on-line selection and special program. The complex averaged peri-event time and frequency histograms shows the increase of inhibitory and excitatory reactions of Deiters' neurons at early stage of vestibular compensation following PRP-1 and NOX injection, reaching the norm at the end of tests. In histochemical study the changes in Ca(2+)-dependent acidic phosphatase (AP) activity in neurons was discovered. It was shown that in UL animals the total disappearance or delay of decolorizing of Deiters' neurons lead to neurodegenerative pattern as cellular "shade". AP activity after UL and PRP-1 injection exerts more effective recovery of neurons in comparison with events, observed after the administration of NOX. The data of this study indicate that PRP-1 and NOX are protectors, which may successfully recover the disturbed vestibular functions.

Complement component c1q mediates mitochondria-driven oxidative stress in neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury in infants is a leading cause of lifelong disability. We report a novel pathway mediating oxidative brain injury after hypoxia-ischemia in which C1q plays a central role. Neonatal mice incapable of classical or terminal complement activation because of C1q or C6 deficiency or pharmacologically inhibited assembly of membrane attack complex were subjected to hypoxia-ischemia. Only C1q(-/-) mice exhibited neuroprotection coupled with attenuated oxidative brain injury. This was associated with reduced production of reactive oxygen species (ROS) in C1q(-/-) brain mitochondria and preserved activity of the respiratory chain. Compared with C1q(+/+) neurons, cortical C1q(-/-) neurons exhibited resistance to oxygen-glucose deprivation. However, postischemic exposure to exogenous C1q increased both mitochondrial ROS production and mortality of C1q(-/-) neurons. This C1q toxicity was abolished by coexposure to antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). Thus, the C1q component of complement, accelerating mitochondrial ROS emission, exacerbates oxidative injury in the developing HI brain. The terminal complement complex is activated in the HI neonatal brain but appeared to be nonpathogenic. These findings have important implications for design of the proper therapeutic interventions against HI neonatal brain injury by highlighting a pathogenic priority of C1q-mediated mitochondrial oxidative stress over the C1q deposition-triggered terminal complement activation.

Membrane attack complex inhibitor CD59a protects against focal cerebral ischemia in mice

Background

The complement system is a crucial mediator of inflammation and cell lysis after cerebral ischemia. However, there is little information about the exact contribution of the membrane attack complex (MAC) and its inhibitor-protein CD59.

Methods

Transient focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in young male and female CD59a knockout and wild-type mice. Two models of MCAO were applied: 60 min MCAO and 48 h reperfusion, as well as 30 min MCAO and 72 h reperfusion. CD59a knockout animals were compared to wild-type animals in terms of infarct size, edema, neurological deficit, and cell death.

Results and Discussion

CD59a-deficiency in male mice caused significantly increased infarct volumes and brain swelling when compared to wild-type mice at 72 h after 30 min-occlusion time, whereas no significant difference was observed after 1 h-MCAO. Moreover, CD59a-deficient mice had impaired neurological function when compared to wild-type mice after 30 min MCAO.

Conclusion

We conclude that CD59a protects against ischemic brain damage, but depending on the gender and the stroke model used.

Complement inhibition as a proposed neuroprotective strategy following cardiac arrest

Out-of-hospital cardiac arrest (OHCA) is a devastating disease process with neurological injury accounting for a disproportionate amount of the morbidity and mortality following return of spontaneous circulation. A dearth of effective treatment strategies exists for global cerebral ischemia-reperfusion (GCI/R) injury following successful resuscitation from OHCA. Emerging preclinical as well as recent human clinical evidence suggests that activation of the complement cascade plays a critical role in the pathogenesis of GCI/R injury following OHCA. In addition, it is well established that complement inhibition improves outcome in both global and focal models of brain ischemia. Due to the profound impact of GCI/R injury following OHCA, and the relative lack of effective neuroprotective strategies for this pathologic process, complement inhibition provides an exciting opportunity to augment existing treatments to improve patient outcomes. To this end, this paper will explore the pathophysiology of complement-mediated GCI/R injury following OHCA.

Synergistic neuroprotective effects of C3a and C5a receptor blockade following intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is associated with neurological injury that may be ameliorated by a neuroprotective strategy targeting the complement cascade. We investigated the role of C5a-receptor antagonist (C5aRA) solely and in combination with C3a-receptor antagonist (C3aRA) following ICH in mice.

METHODS

Adult male C57BL/6J mice were randomized to receive vehicle, C5aRA alone or C3aRA and C5aRA 6 and 12 h after ICH, and every 12 h thereafter. A double injection technique was used to infuse 30 microL of autologous whole blood into the right striatum. A final group of mice received a sham procedure consisting only of needle insertion followed by vehicle injections. Brain water content and flow cytometry analysis for leukocyte and microglia infiltration and activation in both hemispheres were measured on day 3 post ICH. Neurological dysfunction was assessed using a Morris water-maze (MWM), a 28-point scale, and a corner test at 6, 12, 24, 48 and 72 h after ICH induction.

RESULTS

Neurological deficits were present and comparable in all three cohorts 6 h after ICH. Animals treated with C5aRA and animals treated with combined C3aRA/C5aRA demonstrated significant improvements in neurological function assessed by both the corner turn test and a 28-point neurological scale at 24, 48 and 72 h relative to vehicle-treated animals. Similarly, C5aRA and C3aRA/C5aRA-treated mice demonstrated better spatial memory retention in the Morris water-maze test compared with vehicle-treated animals (C3aRA/C5aRA: 23.4+/-2.0 s p< or =0.0001 versus vehicle: 10.0+/-1.7 s). Relative to vehicle-treated mice, the brain water content in C3aRA/C5aRA-treated mice was significantly decreased in the ipsilateral cortex and ipsilateral striatum (ipsilateral cortex: C3aRA/C5aRA: 0.755403+/-0.008 versus 0.773327+/-0.003 p=0.01 striatum: 0.752273+/-0.007 versus 0.771163+/-0.0036 p=0.02). C5aRA-treated mice and C3aRA/C5aRA-treated mice had a decreased ratio of granulocytes (CD45(+)/CD11b(+)/Ly-6G(+)) in the hemorrhagic versus non-hemorrhagic hemispheres relative to vehicle-treated animals (C5aRA: 1.78+/-0.36 p=0.02 C3aRA/C5aRA: 1.59+/-0.22 p=0.005 versus vehicle: 3.01).

CONCLUSIONS

While administration of C5aRA alone provided neuroprotection, combined C3aRA/C5aRA therapy led to synergistic improvements in neurofunctional outcome while reducing inflammatory cell infiltration and brain edema. The results of this study indicate that simultaneous blockade of the C3a and C5a receptors represents a promising neuroprotective strategy in hemorrhagic stroke.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Neuroprotection in stroke by complement inhibition and immunoglobulin therapy

Activation of the complement system occurs in a variety of neuroinflammatory diseases and neurodegenerative processes of the CNS. Studies in the last decade have demonstrated that essentially all of the activation components and receptors of the complement system are produced by astrocytes, microglia, and neurons. There is also rapidly growing evidence to indicate an active role of the complement system in cerebral ischemic injury. In addition to direct cell damage, regional cerebral ischemia and reperfusion (I/R) induces an inflammatory response involving complement activation and generation of active fragments, such as C3a and C5a anaphylatoxins, C3b, C4b, and iC3b. The use of specific inhibitors to block complement activation or their mediators such as C5a, can reduce local tissue injury after I/R. Consistent with therapeutic approaches that have been successful in models of autoimmune disorders, many of the same complement inhibition strategies are proving effective in animal models of cerebral I/R injury. One new form of therapy, which is less specific in its targeting of complement than monodrug administration, is the use of immunoglobulins. Intravenous immunoglobulin (IVIG) has the potential to inhibit multiple components of inflammation, including complement fragments, pro-inflammatory cytokine production and leukocyte cell adhesion. Thus, IVIG may directly protect neurons, reduce activation of intrinsic inflammatory cells (microglia) and inhibit transendothelial infiltration of leukocytes into the brain parenchyma following an ischemic stroke. The striking neuroprotective actions of IVIG in animal models of ischemic stroke suggest a potential therapeutic potential that merits consideration for clinical trials in stroke patients.

Platelet C4d Is Associated With Acute Ischemic Stroke and Stroke Severity

Background and Purpose— Platelets bearing complement C4d were recently reported to be 99% specific for a diagnosis of systemic lupus erythematosus (SLE) and associated with neuropsychiatric lupus. We compared the prevalence of platelet C4d and investigated the clinical associations of platelet C4d in patients with acute ischemic stroke.

Methods— We recruited 80 patients hospitalized for acute ischemic stroke. Stroke severity was measured by the National Institutes of Health Stroke Scale (NIH-SS). Infarct volume was determined by MRI. Platelet C4d was measured by flow cytometry.

Results— Mean age was 57.9 years (range: 24.6 to 86.8 years), 58% were male, and 91% were white. Eight patients (10%) with acute ischemic stroke were platelet C4d-positive, which was significantly higher in prevalence compared to healthy controls (0%, P <0.0001) and non-SLE patients with immune/inflammatory disease (2%, P =0.004). The median NIH-SS score and infarct volume for acute stroke patients were 6 (interquartile range [IQR]: 2 to 13) and 3.4 cc (IQR: 1.1 to 16.6), respectively. Platelet C4d-positive patients were more likely to have a severe stroke compared to those with negative platelet C4d (NIH-SS median: 17.5 versus 5, P =0.003). Positive platelet C4d was independently associated with stroke severity ( P =0.03) after controlling for age, anticardiolipin antibody (aCL) status, and total anterior circulation of stroke involvement, and also with infarct volume ( P =0.005) after controlling for age, aCL status, and old stroke by MRI.

Conclusions— Platelet C4d is associated with severe acute ischemic stroke. Platelet C4d may be a biomarker as well as pathogenic clue that links cerebrovascular inflammation and thrombosis.

Strong complement activation after acute ischemic stroke is associated with unfavorable outcomes

OBJECTIVE

According to data from animal models, complement activation plays a major role in the brain injury after acute ischemic stroke. Scarce findings are, however, available on the detection of complement activation products in stroke patients.

METHODS

We have measured plasma levels of the five complement activation products (C1rC1sC1inh, C4d, C3a, C5a and SC5b-9) in samples of 26 patients with ischemic stroke upon admission. Twenty-six patients with severe carotid atherosclerosis served as patient controls.

RESULTS

Levels of two activation products (SC5b-9 and C4d)) were significantly elevated in the plasma of stroke patients, SC5b-9 levels, exhibited significant positive correlation with the clinical severity of stroke, the severity of neurological deficit, as well as with the level of functional disability.

CONCLUSION

These findings suggest that complement activation plays an active role in the development of brain infarct. The measurement of complement activation products might help to determine the clinical prognosis after acute ischemic stroke. Furthermore, there is potential usefulness of complement modulating therapy in ischemic stroke.

Intravenous immunoglobulin (IVIG) protects the brain against experimental stroke by preventing complement-mediated neuronal cell death

Stroke is among the three leading causes of death worldwide and the most frequent cause of permanent disability. Brain ischemia induces an inflammatory response involving activated complement fragments. Here we show that i.v. Ig (IVIG) treatment, which scavenges complement fragments, protects brain cells against the deleterious effects of experimental ischemia and reperfusion (I/R) and prevents I/R-induced mortality in mice. Animals administered IVIG either 30 min before ischemia or after 3 h of reperfusion exhibited a 50-60% reduction of brain infarct size and a 2- to 3-fold improvement of the functional outcome. Even a single low dose of IVIG given after stroke was effective. IVIG was protective in the nonreperfusion model of murine stroke as well and did not exert any peripheral effects. Human IgG as well as intrinsic murine C3 levels were significantly higher in the infarcted brain region compared with the noninjured side, and their physical association was demonstrated by immuno-coprecipitation. C5-deficient mice were significantly protected from I/R injury compared with their wild-type littermates. Exposure of cultured neurons to oxygen/glucose deprivation resulted in increased levels of C3 associated with activation of caspase 3, a marker of apoptosis; both signals were attenuated with IVIG treatment. Our data suggest a major role for complement-mediated cell death in ischemic brain injury and the prospect of using IVIG in relatively low doses as an interventional therapy for stroke.

Complement mediators in ischemia–reperfusion injury

BACKGROUND

Ischemia-reperfusion (I/R) injury occurs when a tissue is temporarily deprived of blood supply and the return of the blood supply triggers an intense inflammatory response. Pathologically, increased complement activity can cause substantial damage to blood vessels, tissues and also facilitate leukocyte activation and recruitment following I/R injury. Herein, previously published studies are reported and critically reviewed.

METHODS

Medline and the World Wide Web were searched and the relevant literature was classified under the following categories: (1) Complement pathways; (2) The complement system and the inflammatory response; (3) Complement in ischemia-reperfusion injuries; and (4) Therapeutic approaches against complement in I/R injuries.

RESULTS AND CONCLUSIONS

I/R injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient and is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. Complement activation leads to the release of biologically active potent inflammatory complement substances including the anaphylatoxins (C3a and C5a) and the cytolytic terminal membrane attack complement complex C5b-9 (MAC). The use of specific complement inhibitors to block complement activation at various levels of the cascade has been shown to prevent or reduce local tissue injury after I/R. Several agents that inhibit all or part of the complement system, such as soluble complement receptor type 1 (sCR1), C1 inhibitor (C1-INH), C5a monoclonal antibodies, a C5a receptor antagonist and soluble CD59 (sCD59) have been shown to reduce I/R injury of various organs. The novel inhibitors of complement products may eventually find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Role of complement component C5 in cerebral ischemia/reperfusion injury

We evaluated the role of complement component C5 during the course of cerebral ischemic reperfusion injury in a rat model of middle cerebral artery occlusion (MCAO). Systemic C5 inhibition was achieved with an anti-C5 monoclonal antibody, which significantly prevented the deterioration of the motor functions by reducing cerebral lesion and edema. Our results show that activated C5 complement components played an important role in cerebral tissue inflammation resulting from ischemia/reperfusion injury.

Effects of endotoxin administration and cerebral hypoxia-ischemia on complement activity and local transcriptional regulation in neonatal rats

It is not known whether up-regulation of complement components, either circulating or locally synthesized, contributes to an increased susceptibility to neonatal hypoxic-ischemic (HI) cerebral injury. Therefore, we tested the hypothesis that in neonatal rats subjected to a unilateral HI cerebral insult, prior administration of E. coli lipopolysaccharide (LPS) augments (1) complement-mediated serum hemolytic activity, and (2) C3 mRNA and C9 mRNA levels in hepatic and cerebral tissue. Pregnant rats were injected subcutaneously with sterile normal saline (NS) or 500 microg/kg of LPS on gestational days 18 and 19. Following birth, the pups received intraperitoneal injections of NS or 250 microg/kg of LPS on postnatal days 3 and 5. On postnatal day 7, each animal was subjected to ligation of the right common carotid artery followed by 2.5h of hypoxia (8% O(2)). At 3, 6,18, 24 and 48 h after hypoxia, the complement-mediated hemolytic activity of pooled serum was measured. Hepatic and cerebral C3 mRNA and C9 mRNA were quantified by qRT-PCR at 3, 6, and 18 h after HI. Serum hemolytic activity, hepatic C3 mRNA, and hepatic C9 mRNA were up-regulated after cerebral HI. LPS administration potentiated the effect of HI on serum hemolytic activity and increased cerebral C3 mRNA levels. Cerebral C9 mRNA was not detected and was not affected by HI, with or without the prior LPS administration. These observations support the theory that previously reported C9-mediated neurotoxicity following cerebral HI is induced by circulating, rather than locally synthesized C9.