Complement mediators in ischemia–reperfusion injury

Immuno-inflammatory pathogenesis in ischemic heart disease: perception and knowledge for neutrophil recruitment

Ischemic heart disease (IHD) can trigger responses from the innate immune system, provoke aseptic inflammatory processes, and result in the recruitment and accumulation of neutrophils. Excessive recruitment of neutrophils is a potential driver of persistent cardiac inflammation. Once recruited, neutrophils are capable of secreting a plethora of inflammatory and chemotactic agents that intensify the inflammatory cascade. Additionally, neutrophils may obstruct microvasculature within the inflamed region, further augmenting myocardial injury in the context of IHD. Immune-related molecules mediate the recruitment process of neutrophils, such as immune receptors and ligands, immune active molecules, and immunocytes. Non-immune-related molecular pathways represented by pro-resolving lipid mediators are also involved in the regulation of NR. Finally, we discuss novel regulating strategies, including targeted intervention, agents, and phytochemical strategies. This review describes in as much detail as possible the upstream molecular mechanism and external intervention strategies for regulating NR, which represents a promising therapeutic avenue for IHD.

Therapeutic Potential of Targeting Complement C5a Receptors in Diabetic Kidney Disease

Diabetic kidney disease (DKD) affects 30-40% of patients with diabetes and is currently the leading cause of end-stage renal disease (ESRD). The activation of the complement cascade, a highly conserved element of the innate immune system, has been implicated in the pathogenesis of diabetes and its complications. The potent anaphylatoxin C5a is a critical effector of complement-mediated inflammation. Excessive activation of the C5a-signalling axis promotes a potent inflammatory environment and is associated with mitochondrial dysfunction, inflammasome activation, and the production of reactive oxygen species. Conventional renoprotective agents used in the treatment of diabetes do not target the complement system. Mounting preclinical evidence indicates that inhibition of the complement system may prove protective in DKD by reducing inflammation and fibrosis. Targeting the C5a-receptor signaling axis is of particular interest, as inhibition at this level attenuates inflammation while preserving the critical immunological defense functions of the complement system. In this review, the important role of the C5a/C5a-receptor axis in the pathogenesis of diabetes and kidney injuries will be discussed, and an overview of the status and mechanisms of action of current complement therapeutics in development will be provided.

Extracellular vesicles: a new communication paradigm of complement in neurological diseases

The complement system is crucial to the innate immune system. It has the function of destroying pathogens by activating the classical, alternative, and lectin pathways. The complement system is important in nervous system diseases such as cerebrovascular and neurodegenerative diseases. Activation of the complement system involves a series of intercellular signaling and cascade reactions. However, research on the source and transport mechanisms of the complement system in neurological diseases is still in its infancy. Studies have increasingly found that extracellular vesicles (EVs), a classic intercellular communication paradigm, may play a role in complement signaling disorders. Here, we systematically review the EV-mediated activation of complement pathways in different neurological diseases. We also discuss the prospect of EVs as future immunotherapy targets.

Identification and Verification of Potential Biomarkers in Renal Ischemia-Reperfusion Injury by Integrated Bioinformatic Analysis

Background

Renal ischemia-reperfusion injury (RIRI) plays an important role in the poor prognosis of patients with renal transplants. However, the potential targets and mechanism of IRI are still unclear.

Method

Differential gene expression (DEG) analysis and weighted correlation network analysis (WGCNA) were performed on the GSE27274 dataset. Pathway enrichment analysis on the DEGs was performed. To identify the hub DEGs, we constructed a protein-protein interaction (PPI) network. Finally, the hub genes were verified, and candidate drugs were screened from the DsigDB database.

Results

A hundred DEGs and four hub genes (Atf3, Psmb6, Psmb8, and Psmb10) were screened out. Pathway enrichment analysis revealed that 100 DEGs were mainly enriched in apoptosis and the TNF signaling pathway. The four hub genes were verified in animal models and another dataset (GSE148420). Thereafter, a PPI network was used to identify the four hub genes (Atf3, Psmb6, Psmb8, and Psmb10). Finally, eight candidate drugs were identified as potential drugs.

Conclusion

Three hub genes (Psmb6, Psmb8, and Psmb10) were associated with RIRI and could be potential novel biomarkers for RIRI.

Predictive value of soluble CD59 for poor 28-day neurological prognosis and all-cause mortality in patients after cardiopulmonary resuscitation: a prospective observatory study

BACKGROUND

sCD59, as a soluble form of CD59, is observed in multiple types of body fluids and correlated with the cell damage after ischemia/reperfusion injury. This study aims to observe the dynamic changes of serum sCD59 in patients after restoration of spontaneous circulation (ROSC) and explore the association of serum sCD59 with neurological prognosis and all-cause mortality in patients after ROSC.

METHODS

A total of 68 patients after ROSC were prospectively recruited and divided into survivors (n = 23) and non-survivors (n = 45) groups on the basis of 28-day survival. Twenty healthy volunteers were enrolled as controls. Serum sCD59 and other serum complement components, including sC5b-9, C5a, C3a, C3b, C1q, MBL, Bb, and pro-inflammatory mediators tumor necrosis factor (TNF)-α, interleukin-6 (IL-6), neurological damage biomarkers neuron-specific enolase (NSE) and soluble protein 100β (S100β) were measured by enzyme linked immunosorbent assay on day 1, 3, and 7 after ROSC. Neurologic outcome was assessed using cerebral performance category scores, with poor neurologic outcome defined as 3-5 points.

RESULTS

In the first week after ROSC, serum levels of sCD59, sC5b-9, C5a, C3a, C3b, C1q, MBL, Bb, TNF-α, IL-6, NSE and S100β were significantly elevated in patients after ROSC compared to healthy volunteers, with a significant elevation in the non-survivors compared to survivors except serum C1q and MBL. Serum sCD59 levels were positively correlated with serum sC5b-9, TNF-α, IL-6, NSE, S100β, SOFA score and APACHE II score. Moreover, serum sCD59 on day 1, 3, and 7 after ROSC could be used for predicting poor 28-day neurological prognosis and all-cause mortality. Serum sCD59 on day 3 had highest AUCs for predicting poor 28-day neurological prognosis [0.862 (95% CI 0.678-0.960)] and 28-day all-cause mortality [0.891 (95% CI 0.769-0.962)]. In multivariate logistic regression analysis, the serum level of sCD59_D1 was independently associated with poor 28-day neurological prognosis and all-cause mortality.

CONCLUSIONS

The elevated serum level of sCD59 was positively correlated with disease severity after ROSC. Moreover, serum sCD59 could have good predictive values for the poor 28-day neurological prognosis and all-cause mortality in patients after ROSC.

Complement-related proteins in crustacean immunity

As an important part of innate immune system, complement system is widely involved in defense response and immune regulation, and plays an important biological role. The complement system has been deeply studied. More than 30 complement-related molecules and three major complement-activation pathways have been identified in vertebrates. Crustacean animals do not have complement system. There are only some complement-related proteins in crustaceans which are important for host defense. In this review, we summarize the current knowledge about complement-related proteins in crustaceans, and their functions in crustacean immunity. We also make a comparation of the crustacean pro-phenoloxidase activating system and the mammalian complement system. This review provides a better understanding of the evolution and function of complement-related proteins in crustaceans.

Free complement and complement containing extracellular vesicles as potential biomarkers for neuroinflammatory and neurodegenerative disorders

The complement system is implicated in a broad range of neuroinflammatory disorders such as Alzheimer's disease (AD) and multiple sclerosis (MS). Consequently, measuring complement levels in biofluids could serve as a potential biomarker for these diseases. Indeed, complement levels are shown to be altered in patients compared to controls, and some studies reported a correlation between the level of free complement in biofluids and disease progression, severity or the response to therapeutics. Overall, they are not (yet) suitable as a diagnostic tool due to heterogeneity of reported results. Moreover, measurement of free complement proteins has the disadvantage that information on their origin is lost, which might be of value in a multi-parameter approach for disease prediction and stratification. In light of this, extracellular vesicles (EVs) could provide a platform to improve the diagnostic power of complement proteins. EVs are nanosized double membrane particles that are secreted by essentially every cell type and resemble the (status of the) cell of origin. Interestingly, EVs can contain complement proteins, while the cellular origin can still be determined by the presence of EV surface markers. In this review, we summarize the current knowledge and future opportunities on the use of free and EV-associated complement proteins as biomarkers for neuroinflammatory and neurodegenerative disorders.

The EPICC Family of Anti-Inflammatory Peptides: Next Generation Peptides, Additional Mechanisms of Action, and In Vivo and Ex Vivo Efficacy

The EPICC peptides are a family of peptides that have been developed from the sequence of the capsid protein of human astrovirus type 1 and previously shown to inhibit the classical and lectin pathways of complement. The EPICC peptides have been further optimized to increase aqueous solubility and identify additional mechanisms of action. Our laboratory has developed the lead EPICC molecule, PA-dPEG24 (also known as RLS-0071), which is composed of a 15 amino acid peptide with a C-terminal monodisperse 24-mer PEGylated moiety. RLS-0071 has been demonstrated to possess other mechanisms of action in addition to complement blockade that include the inhibition of neutrophil-driven myeloperoxidase (MPO) activity, inhibition of neutrophil extracellular trap (NET) formation as well as intrinsic antioxidant activity mediated by vicinal cysteine residues contained within the peptide sequence. RLS-0071 has been tested in various ex vivo and in vivo systems and has shown promise for the treatment of both immune-mediated hematological diseases where alterations in the classical complement pathway plays an important pathogenic role as well as in models of tissue-based diseases such as acute lung injury and hypoxic ischemic encephalopathy driven by both complement and neutrophil-mediated pathways (i.e., MPO activity and NET formation). Next generation EPICC peptides containing a sarcosine residue substitution in various positions within the peptide sequence possess aqueous solubility in the absence of PEGylation and demonstrate enhanced complement and neutrophil inhibitory activity compared to RLS-0071. This review details the development of the EPICC peptides, elucidation of their dual-acting complement and neutrophil inhibitory activities and efficacy in ex vivo systems using human clinical specimens and in vivo efficacy in animal disease models.

Characterization of Novel P-Selectin Targeted Complement Inhibitors in Murine Models of Hindlimb Injury and Transplantation

The complement system has long been recognized as a potential druggable target for a variety of inflammatory conditions. Very few complement inhibitors have been approved for clinical use, but a great number are in clinical development, nearly all of which systemically inhibit complement. There are benefits of targeting complement inhibition to sites of activation/disease in terms of efficacy and safety, and here we describe P-selectin targeted complement inhibitors, with and without a dual function of directly blocking P-selectin-mediated cell-adhesion. The constructs are characterized in vitro and in murine models of hindlimb ischemia/reperfusion injury and hindlimb transplantation. Both constructs specifically targeted to reperfused hindlimb and provided protection in the hindlimb ischemia/reperfusion injury model. The P-selectin blocking construct was the more efficacious, which correlated with less myeloid cell infiltration, but with similarly reduced levels of complement deposition. The blocking construct also improved tissue perfusion and, unlike the nonblocking construct, inhibited coagulation, raising the possibility of differential application of each construct, such as in thrombotic vs. hemorrhagic conditions. Similar outcomes were obtained with the blocking construct following vascularized composite graft transplantation, and treatment also significantly increased graft survival. This is outcome may be particularly pertinent in the context of vascularized composite allograft transplantation, since reduced ischemia reperfusion injury is linked to a less rigorous alloimmune response that may translate to the requirement of a less aggressive immunosuppressive regime for this normally nonlife-threatening procedure. In summary, we describe a new generation of targeted complement inhibitor with multi-functionality that includes targeting to vascular injury, P-selectin blockade, complement inhibition and anti-thrombotic activity. The constructs described also bound to both mouse and human P-selectin which may facilitate potential translation.

C5aR1 Mediates the Progression of Inflammatory Responses in the Brain of Rats in the Early Stage after Ischemia and Reperfusion

C5a receptor 1 (C5aR1) can induce a strong inflammatory response to an injury. Targeting C5aR1 has emerged as a novel anti-inflammatory therapeutic method. However, the role of C5aR1 in cerebral ischemia and reperfusion (I/R) injury and the definitive mechanism have not been elucidated clearly. Here, we determined whether C5aR1 signaling was essential to the post-ischemic inflammation and brain injury and whether it is a valid target for therapeutic blockade by using soluble receptor antagonist PMX53 in the early stage after I/R injury. In an in vitro model (oxygen and glucose deprivation and reperfusion, OGD/R) and in vivo model (middle cerebral artery occlusion and reperfusion, MCAO/R) of I/R, the neuronal cells of rats showed significantly up-regulated gene expression of C5aR1, and a notable inflammatory response was demonstrated with elevated tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6. Inhibition of C5aR1 by PMX53 treatment significantly reduced cell injury and inflammation and promoted brain function recovery. Further mechanism studies showed that inhibiting C5aR1 by PMX53 protected the rats from MCAO/R injury, decreased cell inflammation, and apoptosis via inhibiting the TLR4 and NF-κB signaling pathway and reducing the production of TNF-α, IL-1β, and IL-6 in MCAO/R rats. In addition, manipulation of the C5aR1 gene expression in vitro displayed that the inflammatory cascade signals including TLR4, TNF-α, IL-1β, and IL-6 were coincidently regulated with the regulation of C5aR1 expression levels. Thus, our results demonstrated a pathogenic role for C5aR1 in the progression of brain injury and inflammation response following I/R injury. Our study clearly demonstrated that C5aR1 inhibition might be an effective treatment strategy for ischemic stroke.

Classical complement pathway inhibition reduces brain damage in a hypoxic ischemic encephalopathy animal model

Perinatal hypoxic ischemic encephalopathy (HIE) remains a major contributor of infant death and long-term disability worldwide. The role played by the complement system in this ischemia-reperfusion injury remains poorly understood. In order to better understand the role of complement activation and other modifiable mechanisms of injury in HIE, we tested the dual-targeting anti-inflammatory peptide, RLS-0071 in an animal model of HIE. Using the well-established HIE rat pup model we measured the effects of RLS-0071 during the acute stages of the brain injury and on long-term neurocognitive outcomes. Rat pups subject to hypoxia-ischemia insult received one of 4 interventions including normothermia, hypothermia and RLS-0071 with and without hypothermia. We measured histopathological effects, brain C1q levels and neuroimaging at day 1 and 21 after the injury. A subset of animals was followed into adolescence and evaluated for neurocognitive function. On histological evaluation, RLS-0071 showed neuronal protection in combination with hypothermia (P = 0.048) in addition to reducing C1q levels in the brain at 1hr (P = 0.01) and at 8 hr in combination with hypothermia (P = 0.005). MRI neuroimaging demonstrated that RLS-0071 in combination with hypothermia reduced lesion volume at 24 hours (P<0.05) as well as decreased T2 signal at day 21 in combination with hypothermia (P<0.01). RLS-0071 alone or in combination with hypothermia improved both short-term and long-term memory. These findings suggest that modulation by RLS-0071 can potentially decrease brain damage resulting from HIE.

Emerging recognition of the complement system in hepatic ischemia/reperfusion injury, liver regeneration and recovery (Review)

Hepatic ischemia/reperfusion injury (IRI) is a result of the ischemic cascade and may occur in the settings of liver trauma, resection and transplantation. Components of the complement system have been indicated to be mediators of hepatic IRI and regulators of liver regeneration. As such, their potential to mediate both beneficial and harmful effects render them key targets for therapy. In the present study, the mechanisms of complement mediating hepatic IRI were discussed with a focus on the different functions of complement in hepatic injury and liver recovery, and an explanation for this apparent paradox is provided, i.e. that the complement products C3a and C5a have an important role in liver damage; however, C3a and C5a are also necessary for liver regeneration. Furthermore, situated at the end of the complement activation cascade, the membrane attack complex is crucial in hepatic IRI and inhibiting the complex with a site-targeted murine complement inhibitor, complement receptor 2-CD59, may improve liver regeneration after partial hepatectomy, even when hepatectomy is combined with ischemia and reperfusion.

Therapeutic Hypothermia Inhibits the Classical Complement Pathway in a Rat Model of Neonatal Hypoxic-Ischemic Encephalopathy

OBJECTIVE

Complement activation is instrumental in the pathogenesis of Hypoxic-ischemic encephalopathy (HIE), a significant cause of neonatal mortality and disability worldwide. Therapeutic hypothermia (HT), the only available treatment for HIE, only modestly improves outcomes. Complement modulation as a therapeutic adjunct to HT has been considered, but is challenging due to the wide-ranging role of the complement system in neuroinflammation, homeostasis and neurogenesis in the developing brain. We sought to identify potential therapeutic targets by measuring the impact of treatment with HT on complement effector expression in neurons and glia in neonatal HIE, with particular emphasis on the interactions between microglia and C1q.

METHODS

The Vannucci model was used to induce HIE in term-equivalent rat pups. At P10-12, pups were randomly assigned to three different treatment groups: Sham (control), normothermia (NT), and hypothermia (HT) treatment. Local and systemic complement expression and neuronal apoptosis were measured by ELISA, TUNEL and immunofluorescence labeling, and differences compared between groups.

RESULTS

Treatment with HT is associated with decreased systemic and microglial expression of C1q, decreased systemic C5a levels, and decreased microglial and neuronal deposition of C3 and C9. The effect of HT on cytokines was variable with decreased expression of pro and anti-inflammatory effectors. HT treatment was associated with decreased C1q binding on cells undergoing apoptosis.

CONCLUSION

Our data demonstrate the extreme complexity of the immune response in neonatal HIE. We propose modulation of downstream effectors C3a and C5a as a therapeutic adjunct to HT to enhance neuroprotection in the developing brain.

Therapeutic Interventions into Innate Immune Diseases by Means of Aptamers

The immune system plays a crucial role in the body's defense system against various pathogens, such as bacteria, viruses, and parasites, as well as recognizes non-self- and self-molecules. The innate immune system is composed of special receptors known as pattern recognition receptors, which play a crucial role in the identification of pathogen-associated molecular patterns from diverse microorganisms. Any disequilibrium in the activation of a particular pattern recognition receptor leads to various inflammatory, autoimmune, or immunodeficiency diseases. Aptamers are short single-stranded deoxyribonucleic acid or ribonucleic acid molecules, also termed "chemical antibodies," which have tremendous specificity and affinity for their target molecules. Their features, such as stability, low immunogenicity, ease of manufacturing, and facile screening against a target, make them preferable as therapeutics. Immune-system-targeting aptamers have a great potential as a targeted therapeutic strategy against immune diseases. This review summarizes components of the innate immune system, aptamer production, pharmacokinetic characteristics of aptamers, and aptamers related to innate-immune-system diseases.

Absence of the C5a Receptor C5aR2 Worsens Ischemic Tissue Injury by Increasing C5aR1-Mediated Neutrophil Infiltration

Neutrophil infiltration to ischemic tissues following reperfusion worsens injury. A key driver of neutrophil recruitment and activation is the complement factor C5a, which signals through two receptors, C5aR1 and C5aR2. In this study, we used a neutrophil-dependent mouse model of intestinal ischemia-reperfusion (IR) injury to investigate the underexplored role of C5aR2 in neutrophil mobilization, recruitment, and disease outcomes. We show that intestinal IR induces rapid neutrophil mobilization along with a concomitant reduction in plasma C5a levels that is driven by both C5aR1 and C5aR2. Intestinal IR in C5aR2^-/- mice led to worsened intestinal damage and increased neutrophil infiltration. Inhibition of C5aR1 signaling in C5aR2^-/- mice with PMX53 prevented neutrophil accumulation and reduced IR pathology, suggesting a key requirement for enhanced neutrophil C5aR1 activation in the absence of C5aR2 signaling. Interestingly, C5aR2 deficiency also reduced circulating neutrophil numbers after IR, as well as following G-CSF-mediated bone marrow mobilization, which was independent of C5aR1, demonstrating that C5aR2 has unique and distinct functions from C5aR1 in neutrophil egress. Despite enhanced tissue injury in C5aR2^-/- IR mice, there were significant reductions in intestinal proinflammatory cytokines, highlighting complicated dual protective/pathogenic roles for C5aR2 in pathophysiology. Collectively, we show that C5aR2 is protective in intestinal IR by inhibiting C5aR1-mediated neutrophil recruitment to the ischemic tissue. This is despite the potentially local pathogenic effects of C5aR2 in increasing intestinal proinflammatory cytokines and enhancing circulating neutrophil numbers in response to mobilizing signals. Our data therefore suggest that this balance between the dual pro- and anti-inflammatory roles of C5aR2 ultimately dictates disease outcomes.

Neuroprotective mechanism of L-cysteine after subarachnoid hemorrhage

Hydrogen sulfide, which can be generated in the central nervous system from the sulfhydryl-containing amino acid, L-cysteine, by cystathionine-β-synthase, may exert protective effects in experimental subarachnoid hemorrhage; however, the mechanism underlying this effect is unknown. This study explored the mechanism using a subarachnoid hemorrhage rat model induced by an endovascular perforation technique. Rats were treated with an intraperitoneal injection of 100 mM L-cysteine (30 μL) 30 minutes after subarachnoid hemorrhage. At 48 hours after subarachnoid hemorrhage, hematoxylin-eosin staining was used to detect changes in prefrontal cortex cells. L-cysteine significantly reduced cell edema. Neurological function was assessed using a modified Garcia score. Brain water content was measured by the wet-dry method. L-cysteine significantly reduced neurological deficits and cerebral edema after subarachnoid hemorrhage. Immunofluorescence was used to detect the number of activated microglia. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the levels of interleukin 1β and CD86 mRNA in the prefrontal cortex. L-cysteine inhibited microglial activation in the prefrontal cortex and reduced the mRNA levels of interleukin 1β and CD86. RT-PCR and western blot analysis of the complement system showed that L-cysteine reduced expression of the complement factors, C1q, C3α and its receptor C3aR1, and the deposition of C1q in the prefrontal cortex. Dihydroethidium staining was applied to detect changes in reactive oxygen species, and immunohistochemistry was used to detect the number of NRF2- and HO-1-positive cells. L-cysteine reduced the level of reactive oxygen species in the prefrontal cortex and the number of NRF2- and HO-1-positive cells. Western blot assays and immunohistochemistry were used to detect the protein levels of CHOP and GRP78 in the prefrontal cortex and the number of CHOP- and GRP78-positive cells. L-cysteine reduced CHOP and GRP78 levels and the number of CHOP- and GRP78-positive cells. The cystathionine-β-synthase inhibitor, aminooxyacetic acid, significantly reversed the above neuroprotective effects of L-cysteine. Taken together, L-cysteine can play a neuroprotective role by regulating neuroinflammation, complement deposition, oxidative stress and endoplasmic reticulum stress. The study was approved by the Animals Ethics Committee of Shandong University, China on February 22, 2016 (approval No. LL-201602022).

Distinct roles of the anaphylatoxin receptors C3aR, C5aR1 and C5aR2 in experimental meningococcal infections

The complement system is pivotal in the defense against invasive disease caused by Neisseria meningitidis (Nme, meningococcus), particularly via the membrane attack complex. Complement activation liberates the anaphylatoxins C3a and C5a, which activate three distinct G-protein coupled receptors, C3aR, C5aR1 and C5aR2 (anaphylatoxin receptors, ATRs). We recently discovered that C5aR1 exacerbates the course of the disease, revealing a downside of complement in Nme sepsis. Here, we compared the roles of all three ATRs during mouse nasal colonization, intraperitoneal infection and human whole blood infection with Nme. Deficiency of complement or ATRs did not alter nasal colonization, but significantly affected invasive disease: Compared to WT mice, the disease was aggravated in C3ar-/- mice, whereas C5ar1-/- and C5ar2-/- mice showed increased resistance to meningococcal sepsis. Surprisingly, deletion of either of the ATRs resulted in lower cytokine/chemokine responses, irrespective of the different susceptibilities of the mice. This was similar in ex vivo human whole blood infection using ATR inhibitors. Neutrophil responses to Nme were reduced in C5ar1-/- mouse blood. Upon stimulation with C5a plus Nme, mouse macrophages displayed reduced phosphorylation of ERK1/2, when C5aR1 or C5aR2 were ablated or inhibited, suggesting that both C5a-receptors prime an initial macrophage response to Nme. Finally, in vivo blockade of C5aR1 alone (PMX205) or along with C5aR2 (A8Δ71-73) resulted in ameliorated disease, whereas neither antagonizing C3aR (SB290157) nor its activation with a "super-agonist" peptide (WWGKKYRASKLGLAR) demonstrated a benefit. Thus, C5aR1 and C5aR2 augment disease pathology and are interesting targets for treatment, whereas C3aR is protective in experimental meningococcal sepsis.

Hemorrhagic shock induces renal complement activation

PURPOSE

Complement is activated in hemorrhagic shock and protective effects by specific complement inhibition were shown. However, it remains unclear if complement activation contributes to the local tissue damage and organ failure. Zonulin is known to activate complement and affect organ failure. Therefore, local and systemic complement activation during hemorrhagic shock and its consequences on zonulin were examined.

METHODS

Porcine hemorrhagic shock (n = 9) was initiated with mean arterial blood pressure maintained constant for 4 h before retransfusion. Before, 4 h after hemorrhage and 12 and 22 h after resuscitation, central and renal blood samples were drawn. Analysis included HMGB-1, C3a, and zonulin (blood and kidney homogenisates) as well as terminal complement complex (TCC) and CH50 (blood). Organ samples were taken for histological and immunohistochemical analyses (C3c).

RESULTS

HMGB-1 was significantly elevated in plasma 4 h after hemorrhagic shock and in homogenized kidneys. TCC after 12 h was significantly elevated centrally, while renal levels were not altered. In contrast, CH50 showed diminished renal values, while normal central levels were observed. Local complement activation was observed with enhanced C3c deposition in kidneys. Zonulin showed significantly diminished levels at 12 and 22 h after hemorrhagic shock (central and renal) and significantly correlated with levels of CH50 and neutrophil gelatinase-associated lipocalin (NGAL).

CONCLUSION

The more pronounced complement activation centrally might indicate consumption of complement products in kidney tissue, which is underlined by C3c staining. Together with diminished levels of zonulin in both systemic and local samples, results could indicate the involvement of complement as well as zonulin in acute kidney failure.

The complex functioning of the complement system in xenotransplantation

The role of complement in xenotransplantation is well-known and is a topic that has been reviewed previously. However, our understanding of the immense complexity of its interaction with other constituents of the innate immune response and of the coagulation, adaptive immune, and inflammatory responses to a xenograft is steadily increasing. In addition, the complement system plays a function in metabolism and homeostasis. New reviews at intervals are therefore clearly warranted. The pathways of complement activation, the function of the complement system, and the interaction between complement and coagulation, inflammation, and the adaptive immune system in relation to xenotransplantation are reviewed. Through several different mechanisms, complement activation is a major factor in contributing to xenograft failure. In the organ-source pig, the detrimental influence of the complement system is seen during organ harvest and preservation, for example, in ischemia-reperfusion injury. In the recipient, the effect of complement can be seen through its interaction with the immune, coagulation, and inflammatory responses. Genetic-engineering and other therapeutic methods by which the xenograft can be protected from the effects of complement activation are discussed. The review provides an updated source of reference to this increasingly complex subject.

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.

L-Cysteine-Derived H2S Promotes Microglia M2 Polarization via Activation of the AMPK Pathway in Hypoxia-Ischemic Neonatal Mice

We have reported previously that L-cysteine-derived hydrogen sulfide (H₂S) demonstrates a remarkable neuroprotective effect against hypoxia-ischemic (HI) insult in neonatal animals. Here, we assessed some of the mechanisms of this protection as exerted by L-cysteine. Specifically, we examined the capacity for L-cysteine to stimulate microglial polarization of the M2 phenotype and its modulation of complement expression in response to HI in neonatal mice. L-cysteine treatment suppressed the production of inflammatory cytokines, while dramatically up-regulating levels of anti-inflammatory cytokines in the damaged cortex. This L-cysteine administration promoted the conversion of microglia from an inflammatory M1 to an anti-inflammatory M2 phenotype, an effect which was associated with inhibiting the p38 and/or JNK pro-inflammatory pathways, nuclear factor-κB activation and a decrease in HI-derived levels of the C1q, C3a and C3a complement receptor proteins. Notably, blockade of H₂S-production clearly prevented L-cysteine-mediated M2 polarization and complement expression. L-cysteine also inhibited neuronal apoptosis as induced by conditioned media from activated M1 microglia in vitro. We also show that L-cysteine promoted AMP-activated protein kinase (AMPK) activation and the AMPK inhibitor abolished these anti-apoptotic and anti-inflammatory effects of L-cysteine. Taken together, our findings demonstrate that L-cysteine-derived H₂S attenuated neuronal apoptosis after HI and suggest that these effects, in part, result from enhancing microglia M2 polarization and modulating complement expression via AMPK activation.

Bioactive Sphingolipids, Complement Cascade, and Free Hemoglobin Levels in Stable Coronary Artery Disease and Acute Myocardial Infarction

BACKGROUND

Acute myocardial infarction (AMI) and coronary artery bypass graft (CABG) surgery are associated with a pathogen-free inflammatory response (sterile inflammation). Complement cascade (CC) and bioactive sphingolipids (BS) are postulated to be involved in this process.

AIM

The aim of this study was to evaluate plasma levels of CC cleavage fragments (C3a, C5a, and C5b9), sphingosine (SP), sphingosine-1-phosphate (S1P), and free hemoglobin (fHb) in AMI patients treated with primary percutaneous coronary intervention (pPCI) and stable coronary artery disease (SCAD) undergoing CABG.

PATIENTS AND METHODS

The study enrolled 37 subjects (27 male) including 22 AMI patients, 7 CABG patients, and 8 healthy individuals as the control group (CTRL). In the AMI group, blood samples were collected at 5 time points (admission to hospital, 6, 12, 24, and 48 hours post pPCI) and 4 time points in the CABG group (6, 12, 24, and 48 hours post operation). SP and S1P concentrations were measured by high-performance liquid chromatography (HPLC). Analysis of C3a, C5a, and C5b9 levels was carried out using high-sensitivity ELISA and free hemoglobin by spectrophotometry.

RESULTS

The plasma levels of CC cleavage fragments (C3a and C5b9) were significantly higher, while those of SP and S1P were lower in patients undergoing CABG surgery in comparison to the AMI group. In both groups, levels of CC factors showed no significant changes within 48 hours of follow-up. Conversely, SP and S1P levels gradually decreased throughout 48 hours in the AMI group but remained stable after CABG. Moreover, the fHb concentration was significantly higher after 24 and 48 hours post pPCI compared to the corresponding postoperative time points. Additionally, the fHb concentrations increased between 12 and 48 hours after PCI in patients with AMI.

CONCLUSIONS

Inflammatory response after AMI and CABG differed regarding the release of sphingolipids, free hemoglobin, and complement cascade cleavage fragments.

Complement in the Initiation and Evolution of Rheumatoid Arthritis

The complement system is a major component of the immune system and plays a central role in many protective immune processes, including circulating immune complex processing and clearance, recognition of foreign antigens, modulation of humoral and cellular immunity, removal of apoptotic and dead cells, and engagement of injury resolving and tissue regeneration processes. In stark contrast to these beneficial roles, however, inadequately controlled complement activation underlies the pathogenesis of human inflammatory and autoimmune diseases, including rheumatoid arthritis (RA) where the cartilage, bone, and synovium are targeted. Recent studies of this disease have demonstrated that the autoimmune response evolves over time in an asymptomatic preclinical phase that is associated with mucosal inflammation. Notably, experimental models of this disease have demonstrated that each of the three major complement activation pathways plays an important role in recognition of injured joint tissue, although the lectin and amplification pathways exhibit particularly impactful roles in the initiation and amplification of damage. Herein, we review the complement system and focus on its multi-factorial role in human patients with RA and experimental murine models. This understanding will be important to the successful integration of the emerging complement therapeutics pipeline into clinical care for patients with RA.

Differential immunological profiles herald magnetic resonance imaging-defined perioperative cerebral infarction

Background:

The perioperative period is associated with a high risk for human ischaemic stroke. Although inflammatory mechanisms are known to have an important role in cerebral infarction in the nonoperative setting, their role in modulating perioperative risk remains unclear.

Methods:

In this prospective case-control study, we compared 10 patients (cases) who developed magnetic resonance imaging (MRI) evidence of cerebral infarction following transcatheter aortic valve implantation with 10 patients (controls) who underwent the same procedure without neurological complication. Blood sampling was performed preoperatively (baseline) and at 24 h, 48 h and 72 h postoperatively and analysed for specific cytokines, chemokines and complement factors.

Results:

Baseline serum assessments identified significant differences between the two cohorts for levels of complement C3, complement C4b, granulocyte-macrophage colony-stimulating factor, interleukin-15 and macrophage inflammatory protein-1β. Longitudinal regression analysis and best-fit polynomial curves of postoperative analyte profiles identified significantly higher levels of complement C3 and matrix metalloproteinase-9, and lower levels of interferon-γ and macrophage inflammatory protein-1β levels in cases versus controls.

Conclusions:

These results support a potentially important role for inflammatory mechanisms in MRI-defined perioperative stroke and reveal a potentially important role for complement components in this process.

Complement C5a Receptor 1 Exacerbates the Pathophysiology of N. meningitidis Sepsis and Is a Potential Target for Disease Treatment

Sepsis caused by Neisseria meningitidis (meningococcus) is a rapidly progressing, life-threatening disease. Because its initial symptoms are rather unspecific, medical attention is often sought too late, i.e., when the systemic inflammatory response is already unleashed. This in turn limits the success of antibiotic treatment. The complement system is generally accepted as the most important innate immune determinant against invasive meningococcal disease since it protects the host through the bactericidal membrane attack complex. However, complement activation concomitantly liberates the C5a peptide, and it remains unclear whether this potent anaphylatoxin contributes to protection and/or drives the rapidly progressing immunopathogenesis associated with meningococcal disease. Here, we dissected the specific contribution of C5a receptor 1 (C5aR1), the canonical receptor for C5a, using a mouse model of meningococcal sepsis. Mice lacking C3 or C5 displayed susceptibility that was enhanced by >1,000-fold or 100-fold, respectively, consistent with the contribution of these components to protection. In clear contrast, C5ar1^−/− mice resisted invasive meningococcal infection and cleared N. meningitidis more rapidly than wild-type (WT) animals. This favorable outcome stemmed from an ameliorated inflammatory cytokine response to N. meningitidis in C5ar1^−/− mice in both in vivo and ex vivo whole-blood infections. In addition, inhibition of C5aR1 signaling without interference with the complement bactericidal activity reduced the inflammatory response also in human whole blood. Enticingly, pharmacologic C5aR1 blockade enhanced mouse survival and lowered meningococcal burden even when the treatment was administered after sepsis induction. Together, our findings demonstrate that C5aR1 drives the pathophysiology associated with meningococcal sepsis and provides a promising target for adjunctive therapy.

The devastating consequences of N. meningitidis sepsis arise due to the rapidly arising and self-propagating inflammatory response that mobilizes antibacterial defenses but also drives the immunopathology associated with meningococcemia. The complement cascade provides innate broad-spectrum protection against infection by directly damaging the envelope of pathogenic microbes through the membrane attack complex and triggers an inflammatory response via the C5a peptide and its receptor C5aR1 aimed at mobilizing cellular effectors of immunity. Here, we consider the potential of separating the bactericidal activities of the complement cascade from its immune activating function to improve outcome of N. meningitidis sepsis. Our findings demonstrate that the specific genetic or pharmacological disruption of C5aR1 rapidly ameliorates disease by suppressing the pathogenic inflammatory response and, surprisingly, allows faster clearance of the bacterial infection. This outcome provides a clear demonstration of the therapeutic benefit of the use of C5aR1-specific inhibitors to improve the outcome of invasive meningococcal disease.

C5a/C5aR pathway accelerates renal ischemia-reperfusion injury by downregulating PGRN expression

Recent reports indicate that the complement C5a/C5aR pathway and progranulin (PGRN) deficiency both contribute to ischemia-reperfusion (IR)-induced acute kidney injury. However, the underlying relationship between the C5a/C5aR signaling pathway and PGRN expression during acute kidney injury is poorly understood. In this study, we showed that C5aR expression was significantly upregulated after renal IR, and that C5aR deficiency led to a marked increase in PGRN expression and a significant reduction in tubular damage and production of inflammatory cytokines. In accordance with these results, recombinant C5a caused downregulation of PGRN protein and mRNA levels in renal tubular epithelial cells (HK-2 cells), which could be negated by disruption of C5a/C5aR signaling by the C5aR antagonist, as confirmed by immunofluorescence, western blotting, and quantitative real-time PCR. Moreover, C5aR deficiency resulted in attenuated NF-κB expression 24h after IR, and recombinant C5a potentiated TNFα-induced NF-κB activation in HK-2 cells. Inhibition of NF-κB activation reversed C5a-induced downregulation of PGRN expression. Our results show for the first time that the complement C5a/C5aR pathway aggravates IR-induced acute kidney injury by suppressing PGRN expression and confirm that suppression of PGRN expression is associated with increased NF-κB activation induced by C5a.

Prevention of C5aR1 signaling delays microglial inflammatory polarization, favors clearance pathways and suppresses cognitive loss

BACKGROUND

Pharmacologic inhibition of C5aR1, a receptor for the complement activation proinflammatory fragment, C5a, suppressed pathology and cognitive deficits in Alzheimer's disease (AD) mouse models. To validate that the effect of the antagonist was specifically via C5aR1 inhibition, mice lacking C5aR1 were generated and compared in behavior and pathology. In addition, since C5aR1 is primarily expressed on cells of the myeloid lineage, and only to a lesser extent on endothelial cells and neurons in brain, gene expression in microglia isolated from adult brain at multiple ages was compared across all genotypes.

METHODS

C5aR1 knock out mice were crossed to the Arctic AD mouse model, and characterized for pathology and for behavior performance in a hippocampal dependent memory task. CX3CR1GFP and CCR2RFP reporter mice were bred to C5aR1 sufficient and knockout wild type and Arctic mice to enable sorting of microglia (GFP-positive, RFP-negative) isolated from adult brain at 2, 5, 7 and 10 months of age followed by RNA-seq analysis.

RESULTS

A lack of C5aR1 prevented behavior deficits at 10 months, although amyloid plaque load was not altered. Immunohistochemical analysis showed no CCR2+ monocytes/macrophages near the plaques in the Arctic brain with or without C5aR1. Microglia were sorted from infiltrating monocytes (GFP and RFP-positive) for transcriptome analysis. RNA-seq analysis identified inflammation related genes as differentially expressed, with increased expression in the Arctic mice relative to wild type and decreased expression in the Arctic/C5aR1KO relative to Arctic. In addition, phagosomal-lysosomal gene expression was increased in the Arctic mice relative to wild type but further increased in the Arctic/C5aR1KO mice. A decrease in neuronal complexity was seen in hippocampus of 10 month old Arctic mice at the time that correlates with the behavior deficit, both of which were rescued in the Arctic/C5aR1KO.

CONCLUSIONS

These data are consistent with microglial polarization in the absence of C5aR1 signaling reflecting decreased induction of inflammatory genes and enhancement of degradation/clearance pathways, which is accompanied by preservation of CA1 neuronal complexity and hippocampal dependent cognitive function. These results provide links between microglial responses and loss of cognitive performance and, combined with the previous pharmacological approach to inhibit C5aR1 signaling, support the potential of this receptor as a novel therapeutic target for AD in humans.

Leukocyte diversity in resolving and nonresolving mechanisms of cardiac remodeling

In response to myocardial infarction (MI), time-dependent leukocyte infiltration is critical to program the acute inflammatory response. Post-MI leukocyte density, residence time in the infarcted area, and exit from the infarcted injury predict resolving or nonresolving inflammation. Overactive or unresolved inflammation is the primary determinant in heart failure pathology post-MI. Here, our review describes supporting evidence that the acute inflammatory response also guides the generation of healing and regenerative mediators after cardiac damage. Time-dependent leukocyte density and diversity and the magnitude of myocardial injury is responsible for the resolving and nonresolving pathway in myocardial healing. Post MI, the diversity of leukocytes, such as neutrophils, macrophages, and lymphocytes, has been explored that regulate the clearance of deceased cardiomyocytes by using the classic and reparative pathways. Among the innovative factors and intermediates that have been recognized as essential in acute the self-healing and clearance mechanism, we highlight specialized proresolving mediators as the emerging factor for post-MI reparative mechanisms-translational leukocyte modifiers, such as aging, the source of leukocytes, and the milieu around the leukocytes. In the clinical setting, it is possible that leukocyte diversity is more prominent as a result of risk factors, such as obesity, diabetes, and hypertension. Pharmacologic agents are critical modifiers of leukocyte diversity in healing mechanisms that may impair or stimulate the clearance mechanism. Future research is needed, with a focused approach to understand the molecular targets, cellular effectors, and receptors. A clear understanding of resolving and nonresolving inflammation in myocardial healing will help to develop novel targets with major emphasis on the resolution of inflammation in heart failure pathology.-Tourki, B., Halade, G. Leukocyte diversity in resolving and nonresolving mechanisms of cardiac remodeling.

Effect of C1-INH on ischemia/reperfusion injury in a porcine limb ex vivo perfusion model

Revascularization of an amputated limb within 4-6h is essential to avoid extensive ischemia/reperfusion (I/R) injury leading to vascular leakage, edema and tissue necrosis. I/R injury is a pathological inflammatory condition that occurs during reperfusion of an organ or tissue after prolonged ischemia. It is characterized by a complex crosstalk between endothelial cell activation and the activation of plasma cascades. Vasculoprotective pharmacological intervention to prevent I/R injury might be an option to prolong the time window between limb amputation and successful replantation. We used C1-easterase inhibitor (C1-INH) in this study because of its known inhibitory effects on the activation of the complement, coagulation and kinin cascades. Forelimbs of 8 large white pigs were amputated, subjected to ischemia, and then reperfused with autologous whole blood. All limbs were exposed to 9h of cold ischemia at 4°C. After 2h of cold ischemia the limbs were either perfused with of C1-INH (1U/ml in hydroxyethyl starch, n=8) or hydroxyethyl starch alone (n=7). After completion of the 9-h ischemia period, all limbs were ex vivo perfused with heparinized autologous whole blood for 12h using a pediatric heart lung machine to simulate in vivo revascularization. Our results show that I/R injury in the control group led to a significant elevation of tissue deposition of IgG and IgM, complement C3b/c, C5b-9 and MBL. Also, activation of the kinin system was significantly increased, namely bradykinin in plasma, and expression of bradykinin receptors 1 and 2 in tissue. In addition, markers for endothelial integrity like expression of CD31, VE-cadherin and heparan sulfate proteoglycans were decreased in reperfused tissue. Limb I/R injury also led to activation of the coagulation cascade with a significant elevation of fibrin and thrombin deposition and increased fibrinogen-like protein-2 expression. C1-INH treated limbs showed much less activation of plasma cascades and better protection of endothelial integrity compared to the reperfused control limbs. In conclusion, the use of the cytoprotective drug C1-INH significantly reduced I/R injury by protecting the vascular endothelium as well as the muscle tissue from deposition of immunoglobulins, complement and fibrin.

Polysaccharides from Arnebia euchroma Ameliorated Endotoxic Fever and Acute Lung Injury in Rats Through Inhibiting Complement System

Arnebiaeuchroma (Royle) Johnst (Ruanzicao) is a traditional Chinese herbal medicine (TCM). It is extensively used in China and other countries for treatment of inflammatory diseases. It is known that hyper-activated complement system involves in the fever and acute lung injury (ALI) in rats. In our preliminary studies, anti-complementary activity of crude Arnebiaeuchroma polysaccharides (CAEP) had been demonstrated in vitro. This study aimed to investigate the role and mechanism of crude Arnebiaeuchroma polysaccharides (CAEP) using two animal models, which relate with inappropriate activation of complement system. In lipopolysaccharide (LPS)-induced fever model, the body temperature and leukocytes of peripheral blood in rats were significantly increased, while the complement levels of serum were remarkably decreased. CAEP administration alleviated the LPS-induced fever, reduced the number of leukocytes, and improved the levels of complement. Histological assay showed that there were severe damages and complement depositions in lung of the ALI rats. Further detection displayed that the oxidant stress was enhanced, and total hemolytic activity and C3/C4 levels in serum were decreased significantly in the ALI model group. Remarkably, CAEP not only attenuated the morphological injury, edema, and permeability in the lung but also significantly weakened the oxidant stress in bronchoalveolar lavage fluid (BALF) in the ALI rats. The levels of complement and complement depositions were improved by the CAEP treatment. In conclusion, the CAEP treatment ameliorated febrile response induced by LPS and acute lung injury induced by LPS plus ischemia-reperfusion. CAEP exerted beneficial effects on inflammatory disease potentially via inhibiting the inappropriate activation of complement system.

Role of the plasma cascade systems in ischemia/reperfusion injury of bone

Ischemia/reperfusion (I/R) injury has been extensively studied in organs such as heart, brain, liver, kidney, and lung. As a vascularized organ, bone is known to be susceptible to I/R injury too, but the respective mechanisms are not well understood to date. We therefore hypothesized that, similar to other organs, plasma cascade-induced inflammation also plays a role in bone I/R injury. Reperfusion injury in rat tibia was induced by unilateral clamping of the femoral artery and additional use of a tourniquet, while keeping the femoral vein patent to prevent venous congestion. Rats were subjected to 4h ischemia and 24h reperfusion. Deposition of complement fragment C3b/c and fibrin as well as expression of tissue factor (TF), tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1), and E-selectin was detected by immunohistochemistry. In plasma, the levels of high mobility group box1 (HMGB1) were measured by ELISA. The total level of complement in serum was assessed by the CH50 test. Our results show that deposition of C3b/c was significantly increased with respect to healthy controls in cortical bone as well as in marrow of reperfused limbs. C3b/c deposition was also increased in cortical bone, but not in bone marrow, of contralateral limbs. Deposition of fibrin, as well as expression of PAI-1, was significantly increased in bone after ischemia and reperfusion, whereas expression of tPA was reduced. These differences were most prominent in vessels of bone, both in marrow and cortical bone, and both in reperfused and contralateral limbs. However, PAI-1, was only increased in vessels of reperfused cortical bone and there were no significant changes in expression of E-selectin. With respect to solid bone tissue, a significant increase of C3b/c and fibrin deposition was shown in osteocytes, and for fibrin also in the bone matrix, in both contralateral and reperfused cortical bone compared with normal healthy controls. A slight expression of TF was visible in osteocytes of the normal healthy control group, while TF was not present in the experimental groups. Moreover, CH50 values in serum decreased over time and HMGB1 was significantly increased in plasma of animals at the end of reperfusion. We conclude that ischemia and reperfusion of bone leads to activation of the complement and coagulation systems and a downregulation of the fibrinolytic cascade. In the acute phase, a vascular inflammation induced by activation of the plasma cascade systems also occurs in the bone. This is similar to I/R injury of other vascularized organs and tissues.

Therapeutic hypothermia modulates complement factor C3a and C5a levels in a rat model of hypoxic ischemic encephalopathy

BACKGROUND

Therapeutic hypothermia (HT) is the only intervention that improves outcomes in neonatal hypoxic-ischemic encephalopathy (HIE). However, the multifactorial mechanisms by which HT impacts HIE are incompletely understood. The complement system plays a major role in the pathogenesis of ischemia-reperfusion injuries such as HIE. We have previously demonstrated that HT modulates complement activity in vitro.

METHODS

Term equivalent rat pups were subjected to unilateral carotid ligation followed by hypoxia (8% O2) for 45 min to simulate HIE. A subset of animals was subjected to HT (31-32°C for 6 h). Plasma and brain levels of C3a and C5a were measured. Receptors for C3a (C3aR) and C5a (C5aR) along with C1q, C3, and C9 were characterized in neurons, astrocytes, and microglia.

RESULTS

We found that HT increased systemic expression of C3a and decreased expression of C5a after HIE. In the brain, C3aR and C5aR are predominantly expressed on microglia after HIE. HT increased local expression of C3aR and decreased expression on C5aR after HIE. Furthermore, HT decreased local expression of C1q, C3-products, and C9 in the brain.

CONCLUSION

HT is associated with significant alteration of complement effectors and their cognate receptors. Complement modulation may improve outcomes in neonatal HIE.

Functional Role of Milk Fat Globule-Epidermal Growth Factor VIII in Macrophage-Mediated Inflammatory Responses and Inflammatory/Autoimmune Diseases

Inflammation involves a series of complex biological processes mediated by innate immunity for host defense against pathogen infection. Chronic inflammation is considered to be one of the major causes of serious diseases, including a number of autoimmune/inflammatory diseases, cancers, cardiovascular diseases, and neurological diseases. Milk fat globule-epidermal growth factor 8 (MFG-E8) is a secreted protein found in vertebrates and was initially discovered as a critical component of the milk fat globule. Previously, a number of studies have reported that MFG-E8 contributes to various biological functions including the phagocytic removal of damaged and apoptotic cells from tissues, the induction of VEGF-mediated neovascularization, the maintenance of intestinal epithelial homeostasis, and the promotion of mucosal healing. Recently, emerging studies have reported that MFG-E8 plays a role in inflammatory responses and inflammatory/autoimmune diseases. This review describes the characteristics of MFG-E8-mediated signaling pathways, summarizes recent findings supporting the roles of MFG-E8 in inflammatory responses and inflammatory/autoimmune diseases, and discusses MFG-E8 targeting as a potential therapeutic strategy for the development of anti-inflammatory/autoimmune disease drugs.

Looking Beyond the Terrestrial: The Potential of Seaweed Derived Bioactives to Treat Non-Communicable Diseases

Seaweeds are a large and diverse group of marine organisms that are commonly found in the maritime regions of the world. They are an excellent source of biologically active secondary metabolites and have been shown to exhibit a wide range of therapeutic properties, including anti-cancer, anti-oxidant, anti-inflammatory and anti-diabetic activities. Several Asian cultures have a strong tradition of using different varieties of seaweed extensively in cooking as well as in herbal medicines preparations. As such, seaweeds have been used to treat a wide variety of health conditions such as cancer, digestive problems, and renal disorders. Today, increasing numbers of people are adopting a "westernised lifestyle" characterised by low levels of physical exercise and excessive calorific and saturated fat intake. This has led to an increase in numbers of chronic Non-communicable diseases (NCDs) such as cancer, cardiovascular disease, and diabetes mellitus, being reported. Recently, NCDs have replaced communicable infectious diseases as the number one cause of human mortality. Current medical treatments for NCDs rely mainly on drugs that have been obtained from the terrestrial regions of the world, with the oceans and seas remaining largely an untapped reservoir for exploration. This review focuses on the potential of using seaweed derived bioactives including polysaccharides, antioxidants and fatty acids, amongst others, to treat chronic NCDs such as cancer, cardiovascular disease and diabetes mellitus.

Cardiac Sirt1 mediates the cardioprotective effect of caloric restriction by suppressing local complement system activation after ischemia-reperfusion

Caloric restriction (CR) confers cardioprotection against ischemia-reperfusion (I/R) injury. We previously found the essential roles of endothelial nitric oxide synthase in the development of CR-induced cardioprotection and Sirt1 activation during CR (Shinmura K, Tamaki K, Ito K, Yan X, Yamamoto T, Katsumata Y, Matsuhashi T, Sano M, Fukuda K, Suematsu M, Ishii I. Indispensable role of endothelial nitric oxide synthase in caloric restriction-induced cardioprotection against ischemia-reperfusion injury.Am J Physiol Heart Circ Physiol 308: H894-H903, 2015). However, the exact mechanism by which Sirt1 in cardiomyocytes mediates the cardioprotective effect of CR remains undetermined. We subjected cardiomyocyte-specific Sirt1 knockout (CM-Sirt1(-/-)) mice and the corresponding control mice to either 3-mo ad libitum feeding or CR (-40%). Isolated perfused hearts were subjected to 25-min global ischemia, followed by 60-min reperfusion. The recovery of left ventricle function after I/R was improved, and total lactate dehydrogenase release into the perfusate during reperfusion was attenuated in the control mice treated with CR, but a similar cardioprotective effect of CR was not observed in the CM-Sirt1(-/-)mice. The expression levels of cardiac complement component 3 (C3) at baseline and the accumulation of C3 and its fragments in the ischemia-reperfused myocardium were attenuated by CR in the control mice, but not in the CM-Sirt1(-/-)mice. Resveratrol treatment also attenuated the expression levels of C3 protein in cultured neonatal rat ventricular cardiomyocytes. Moreover, the degree of myocardial I/R injury in conventional C3 knockout (C3(-/-)) mice treated with CR was similar to that in the ad libitum-fed C3(-/-)mice, although the expression levels of Sirt1 were enhanced by CR. These results demonstrate that cardiac Sirt1 plays an essential role in CR-induced cardioprotection against I/R injury by suppressing cardiac C3 expression. This is the first report suggesting that cardiac Sirt1 regulates the local complement system during CR.

Ischemic, traumatic and neurodegenerative brain inflammatory changes

This review serves to link the role of the immune system in the neuropathology of acute ischemic stroke, traumatic brain injury and neurodegenerative disease. The blood–brain barrier delineates the CNS from the peripheral immune system. However, the blood–cerebrospinal fluid barrier acts as a gate between the periphery and the brain, permitting immune activity crosstalk and modulation. In acute ischemic stroke, traumatic brain injury and other neurodegenerative diseases, the blood–brain barrier is compromised and an influx of inflammatory cells and plasma proteins occurs, resulting in edema, demyelination, cell dysfunction and death, and neurobehavioral changes. The role of the complement system, key cytokines, microglia and other neuroglia in brain degenerative pathology will be discussed.

Using next-generation RNA sequencing to examine ischemic changes induced by cold blood cardioplegia on the human left ventricular myocardium transcriptome

BACKGROUND

The exact mechanisms that underlie the pathological processes of myocardial ischemia in humans are unclear. Cardiopulmonary bypass with cardioplegic arrest allows the authors to examine the whole transcriptional profile of human left ventricular myocardium at baseline and after exposure to cold cardioplegia-induced ischemia as a human ischemia model.

METHODS

The authors obtained biopsies from 45 patients undergoing aortic valve replacement surgery at baseline and after an average of 79 min of cold cardioplegic arrest. Samples were RNA sequenced and analyzed with the Partek Genomics Suite (Partek Inc., St. Louis, MO) for differential expression. Ingenuity Pathway Analysis (Ingenuity Systems, Redwood City, CA) and Biobase ExPlain (Biobase GmbH, Wolfenbuettel, Germany) systems were used for functional and pathway analyses.

RESULTS

Of the 4,098 genes with a mean expression value greater than 5, 90% were down-regulated and 9.1% were up-regulated. Of those, 1,241 were significantly differentially expressed. Gene ontology analysis revealed significant down-regulation in immune inflammatory response and complement activation categories and highly consistent was the down-regulation of intelectin 1, proteoglycan, and secretory leukocyte peptidase inhibitor. Up-regulated genes of interest were FBJ murine osteosarcoma viral oncogene homolog and the hemoglobin genes hemoglobin α1 (HBA1) and hemoglobin β. In addition, analysis of transcription factor-binding sites revealed interesting targets in factors regulating reactive oxygen species production, apoptosis, immunity, cytokine production, and inflammatory response.

CONCLUSIONS

The authors have shown that the human left ventricle exhibits significant changes in gene expression in response to cold cardioplegia-induced ischemia during cardiopulmonary bypass, which provides great insight into the pathophysiology of ventricular ischemia, and thus, may help guide efforts to reduce myocardial damage during surgery.

Complement component 3 is necessary to preserve myocardium and myocardial function in chronic myocardial infarction

Activation of the complement cascade (CC) with myocardial infarction (MI) acutely initiates immune cell infiltration, membrane attack complex formation on injured myocytes, and exacerbates myocardial injury. Recent studies implicate the CC in mobilization of stem/progenitor cells and tissue regeneration. Its role in chronic MI is unknown. Here, we consider complement component C3, in the chronic response to MI. C3 knockout (KO) mice were studied after permanent coronary artery ligation. C3 deficiency exacerbated myocardial dysfunction 28 days after MI compared to WT with further impaired systolic function and LV dilation despite similar infarct size 24 hours post-MI. Morphometric analysis 28 days post-MI showed C3 KO mice had more scar tissue with less viable myocardium within the infarct zone which correlated with decreased c-kit(pos) cardiac stem/progenitor cells (CPSC), decreased proliferating Ki67(pos) CSPCs and decreased formation of new BrdU(pos) /α-sarcomeric actin(pos) myocytes, and increased apoptosis compared to WT. Decreased CSPCs and increased apoptosis were evident 7 days post-MI in C3 KO hearts. The inflammatory response with MI was attenuated in the C3 KO and was accompanied by attenuated hematopoietic, pluripotent, and cardiac stem/progenitor cell mobilization into the peripheral blood 72 hours post-MI. These results are the first to demonstrate that CC, through C3, contributes to myocardial preservation and regeneration in response to chronic MI. Responses in the C3 KO infer that C3 activation in response to MI expands the resident CSPC population, increases new myocyte formation, increases and preserves myocardium, inflammatory response, and bone marrow stem/progenitor cell mobilization to preserve myocardial function.

The complement system in human cardiometabolic disease

The complement system has been implicated in obesity, fatty liver, diabetes and cardiovascular disease (CVD). Complement factors are produced in adipose tissue and appear to be involved in adipose tissue metabolism and local inflammation. Thereby complement links adipose tissue inflammation to systemic metabolic derangements, such as low-grade inflammation, insulin resistance and dyslipidaemia. Furthermore, complement has been implicated in pathophysiological mechanisms of diet- and alcohol induced liver damage, hyperglycaemia, endothelial dysfunction, atherosclerosis and fibrinolysis. In this review, we summarize current evidence on the role of the complement system in several processes of human cardiometabolic disease. C3 is the central component in complement activation, and has most widely been studied in humans. C3 concentrations are associated with insulin resistance, liver dysfunction, risk of the metabolic syndrome, type 2 diabetes and CVD. C3 can be activated by the classical, the lectin and the alternative pathway of complement activation; and downstream activation of C3 activates the terminal pathway. Complement may also be activated via extrinsic proteases of the coagulation, fibrinolysis and the kinin systems. Studies on the different complement activation pathways in human cardiometabolic disease are limited, but available evidence suggests that they may have distinct roles in processes underlying cardiometabolic disease. The lectin pathway appeared beneficial in some studies on type 2 diabetes and CVD, while factors of the classical and the alternative pathway were related to unfavourable cardiometabolic traits. The terminal complement pathway was also implicated in insulin resistance and liver disease, and appears to have a prominent role in acute and advanced CVD. The available human data suggest a complex and potentially causal role for the complement system in human cardiometabolic disease. Further, preferably longitudinal studies are needed to disentangle which aspects of the complement system and complement activation affect the different processes in human cardiometabolic disease.

Effect of complement C1q expression on hepatic ischemia-reperfusion injury in rats

The effect of the complement C1q expression on total hepatic ischemia-reperfusion (I/R) injury in rats was investigated. Sixty healthy male Sprague Dawley (SD) rats weighing 180-200 g were randomly divided into 5 groups: sham-operation group (S group, n=12); group of I/R for 1 h (I/R 1 h group, n=12); group of I/R for 3 h (I/R 3 h group, n=12); group of I/R for 6 h (I/R 6 h group, n=12); group of I/R for 24 h (I/R 24 h group, n=12). The hepatic I/R model of rats was established, and liver tissues were obtained 1 h, 3 h, 6 h and 24 h after hepatic I/R, respectively. Furthermore, the tissues were stained using hematoxylin-eosin, and the liver injuries of rats were observed using a microscope. The malondialdehyde (MDA) level and superoxide dismutase (SOD) activity in liver tissue were determined. Real-time polymerase chain reaction (PCR) and Western blotting were used to detect the expression levels of C1q mRNA and protein, respectively. As compared with the S group, the histopathological changes in I/R 1 h-24 h groups were gradually aggravated with the extension of I/R time. As compared with the S group, SOD activity and MDA content in the I/R groups were reduced and increased respectively with the extension of I/R time (P<0.01). Furthermore, the C1q expression at mRNA and protein levels in the I/R groups (especially in the I/R 3 h group) was significantly higher than that in the S group (P<0.05). It is suggested that C1q expression may play a principal role in hepatic I/R injury, particularly at the early stage of perfusion.

Leucocyte expression of complement C5a receptors exacerbates infarct size after myocardial reperfusion injury

AIMS

Early reperfusion is mandatory for the treatment of acute myocardial infarction. This process, however, also induces additional loss of viable myocardium, called ischaemia-reperfusion (IR) injury. Complement activation plays an important role in IR injury, partly through binding of C5a to its major receptor (C5aR). We investigated the role of C5aR on infarct size and cardiac function in a model for myocardial IR injury.

METHODS AND RESULTS

BALB/c (WT) mice and C5aR(-/-) mice underwent coronary occlusion for 30 min, followed by reperfusion. Infarct size, determined 24 h after IR, was reduced in C5aR(-/-) mice compared with WT mice (28.5 ± 2.1 vs. 35.7 ± 2.5%, P = 0.017). Bone marrow (BM) chimaera experiments showed that this effect was due to the absence of C5aR on circulating leucocytes, since a similar reduction in infarct size was observed in WT mice with C5aR-deficient BM cells (25.3 ± 2.2 vs. 34.6 ± 2.8%, P < 0.05), but not in C5aR(-/-) mice with WT BM cells. Reduced infarct size was associated with fewer neutrophils, T cells, and macrophages in the infarcted area 24 h after IR in C5aR(-/-) mice, and also with lower levels of Caspase-3/7 indicating less inflammation and apoptosis. Echocardiography 4 weeks after IR showed an improved ejection fraction in C5aR(-/-) mice (25.8 ± 5.5 vs. 19.2 ± 5.4%, P < 0.001).

CONCLUSION

The absence of C5aR on circulating leucocytes reduces infarct size, is associated with reduced leucocyte infiltration and with less apoptosis in the infarcted myocardium, and improves cardiac function in a mouse model of myocardial IR injury. Selective blocking of C5aR might be a promising strategy to prevent myocardial IR injury.

Membrane lipid interactions in intestinal ischemia/reperfusion-induced Injury

Ischemia, lack of blood flow, and reperfusion, return of blood flow, are a common phenomenon affecting millions of Americans each year. Roughly 30,000 Americans per year experience intestinal ischemia-reperfusion (IR), which is associated with a high mortality rate. Previous studies of the intestine established a role for neutrophils, eicosanoids, the complement system and naturally occurring antibodies in IR-induced pathology. Furthermore, data indicate involvement of a lipid or lipid-like moiety in mediating IR-induced damage. It has been proposed that antibodies recognize exposure of neo-antigens, triggering action of the complement cascade. While it is evident that the pathophysiology of IR-induced injury is complex and multi-factorial, we focus this review on the involvement of eicosanoids, phospholipids and neo-antigens in the early pathogenesis. Lipid changes occurring in response to IR, neo-antigens exposed and the role of a phospholipid transporter, phospholipid scramblase 1 will be discussed.

Endothelial-to-mesenchymal transition and renal fibrosis in ischaemia/reperfusion injury are mediated by complement anaphylatoxins and Akt pathway

BACKGROUND

Increasing evidence demonstrates a phenotypic plasticity of endothelial cells (ECs). Endothelial-to-mesenchymal transition (EndMT) contributes to the development of tissue fibrosis. However, the pathogenic factors and signalling pathways regulating this process in ischaemia/reperfusion (I/R) injury are still poorly understood.

METHODS

We investigated the possible role of complement in the induction of this endothelial dysfunction in a swine model of renal I/R injury by using recombinant C1 inhibitor in vivo.

RESULTS

Here, we showed that I/R injury reduced the density of renal peritubular capillaries and induced tissue fibrosis with generation of CD31(+)/α-SMA(+) and CD31(+)/FPS-1(+) cells indicating EndMT. When we inhibited complement, the process of EndMT became rare, with preserved density of peritubular capillaries and significant reduction in renal fibrosis. When we activated ECs by anaphylatoxins in vitro, C3a and C5a led to altered endothelial phenotype with increased expression of fibroblast markers and decrease expression of specific endothelial markers. The activation of Akt pathway was pivotal for the C3a and C5a-induced EndMT in vitro. In accordance, inhibition of complement in vivo led to the abrogation of Akt signalling, with hampered EndMT and tissue fibrosis.

CONCLUSIONS

Our data demonstrate a critical role for complement in the acute induction of EndMT via the Akt pathway. Therapeutic inhibition of these systems may be essential to prevent vascular damage and tissue fibrosis in transplanted kidney.

Anti-C5a complementary peptide ameliorates acute peritoneal injury induced by neutralization of Crry and CD59

In peritoneal dialysis (PD) therapy, physical stresses such as exposure to peritoneal dialysate, catheter trauma, and peritonitis may induce peritoneal injury that can prevent continued long-term PD therapy. Therefore, protection of the peritoneum is an important target to enable long-term PD therapy in patients with end-stage renal disease. We previously showed that neutralization of the membrane complement regulators (CRegs) Crry and CD59 in rat peritoneum provokes development of acute peritoneal injury due to uncontrolled complement activation. C5a is a key effecter molecule of the complement system released during acute inflammation. Control of C5a has been proposed as a strategy to suppress inflammatory reactions and, because peritoneal injury is accompanied by inflammation, we hypothesized that C5a targeted therapy might be an effective way to suppress peritoneal injury. In the present study we used an established acute peritonitis model induced by neutralization of CRegs to investigate the effects on acute peritoneal injury of inhibiting C5a. Intravenous administration of an anti-C5a complementary peptide (AcPepA) up to 4 h after induction of injury significantly and dose-dependently prevented accumulation of inflammatory cells and reduced tissue damage in the model, accompanied by decreased C3b deposition. We show that C5a contributed to the development of peritoneal injury. Our results suggest that C5a is a target for preventing or treating peritoneal injury in patients undergoing prolonged PD therapy or with infectious complications.