C5a causes limited, polymorphonuclear cell-independent, mesenteric ischemia/reperfusion-induced injury

Combined Quantitative (Phospho)proteomics and Mass Spectrometry Imaging Reveal Temporal and Spatial Protein Changes in Human Intestinal Ischemia-Reperfusion

Intestinal ischemia–reperfusion (IR) injury is a severe clinical condition, and unraveling its pathophysiology is crucial to improve therapeutic strategies and reduce the high morbidity and mortality rates. Here, we studied the dynamic proteome and phosphoproteome in the human intestine during ischemia and reperfusion, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to gain quantitative information of thousands of proteins and phosphorylation sites, as well as mass spectrometry imaging (MSI) to obtain spatial information. We identified a significant decrease in abundance of proteins related to intestinal absorption, microvillus, and cell junction, whereas proteins involved in innate immunity, in particular the complement cascade, and extracellular matrix organization increased in abundance after IR. Differentially phosphorylated proteins were involved in RNA splicing events and cytoskeletal and cell junction organization. In addition, our analysis points to mitogen-activated protein kinase (MAPK) and cyclin-dependent kinase (CDK) families to be active kinases during IR. Finally, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MSI presented peptide alterations in abundance and distribution, which resulted, in combination with Fourier-transform ion cyclotron resonance (FTICR) MSI and LC-MS/MS, in the annotation of proteins related to RNA splicing, the complement cascade, and extracellular matrix organization. This study expanded our understanding of the molecular changes that occur during IR in the human intestine and highlights the value of the complementary use of different MS-based methodologies.

Complement Initiation Varies by Sex in Intestinal Ischemia Reperfusion Injury

Intestinal ischemia reperfusion (IR)-induced tissue injury represents an acute inflammatory response with significant morbidity and mortality. The mechanism of IR-induced injury is not fully elucidated, but recent studies suggest a critical role for complement activation and for differences between sexes. To test the hypothesis that complement initiation differs by sex in intestinal IR, we performed intestinal IR on male and female WT C57B6L/, C1q-/-, MBL-/-, or properdin (P)-/- mice. Intestinal injury, C3b and C5a production and ex vivo secretions were analyzed. Initial studies demonstrated a difference in complement mRNA and protein in male and female WT mice. In response to IR, male C1q-, MBL- and P-deficient mice sustained less injury than male WT mice. In contrast, only female MBL-/- mice sustained significantly less injury than female wildtype mice. Importantly, wildtype, C1q-/- and P-/- female mice sustained significant less injury than the corresponding male mice. In addition, both C1q and MBL expression and deposition increased in WT male mice, while only elevated MBL expression and deposition occurred in WT female mice. These data suggested that males use both C1q and MBL pathways, while females tend to depend on lectin pathway during intestinal IR. Females produced significantly less serum C5a in MBL-/- and P-/- mice. Our findings suggested that complement activation plays a critical role in intestinal IR in a sex-dependent manner.

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.

Preclinical Pharmacokinetics of Complement C5a Receptor Antagonists PMX53 and PMX205 in Mice

The cyclic hexapeptides PMX53 and PMX205 are potent noncompetitive inhibitors of complement C5a receptor 1 (C5aR1). They are widely utilized to study the role of C5aR1 in mouse models, including central nervous system (CNS) disease, and are dosed through a variety of routes of administration. However, a comprehensive pharmacokinetics analysis of these drugs has not been reported. In this study, the blood and CNS pharmacokinetics of PMX53 and PMX205 were performed in mice following intravenous, intraperitoneal, subcutaneous, and oral administration at identical doses. The absorption and distribution of both drugs were rapid and followed a two-compartment model with elimination half-lives of ∼20 min for both compounds. Urinary excretion was the major route of elimination following intravenous dosing with ∼50% of the drug excreted unchanged within the first 12 h. Oral bioavailability of PMX205 was higher than that of PMX53 (23% versus 9%), and PMX205 was also more efficient than PMX53 at entering the intact CNS. In comparison to other routes, subcutaneous administration of PMX205 resulted in high bioavailability (above 90%), as well as prolonged plasma and CNS exposure. Finally, repeated daily oral or subcutaneous administration of PMX205 demonstrated no accumulation of drug in blood, the brain, or the spinal cord, promoting its safety for chronic dosing. These results will be helpful in correlating the desired therapeutic effects of these C5aR1 antagonists with their pharmacokinetic profile. It also suggests that subcutaneous dosing of PMX205 may be an appropriate route of administration for future clinical testing in neurological disease.

Opposite Profiles of Complement in Antiphospholipid Syndrome (APS) and Systemic Lupus Erythematosus (SLE) Among Patients With Antiphospholipid Antibodies (aPL)

APS is the association of antiphospholipid antibodies (aPL) with thromboses and/or recurrent pregnancy loss (RPL). Among patients with SLE, one-third have aPL and 10–15% have a manifestation of secondary APS. Animal studies suggested that complement activation plays an important role in the pathogenesis of thrombosis and pregnancy loss in APS. We performed a cross-sectional study on complement proteins and genes in 525 patients with aPL. Among them, 237 experienced thromboses and 293 had SLE; 111 had both SLE and thromboses, and 106 had neither SLE nor thrombosis. Complement protein levels were determined by radial immunodiffusion for C4, C3 and factor H; and by functional ELISA for mannan binding lectin (MBL). Total C4, C4A and C4B gene copy numbers (GCN) were measured by TaqMan-based realtime PCR. Two to six copies of C4 genes are frequently present in a diploid genome, and each copy may code for an acidic C4A or a basic C4B protein. We observed significantly (a) higher protein levels of total C4, C4A, C4B, C3, and anticardiolipin (ACLA) IgG, (b) increased frequencies of lupus anticoagulant and males, and (c) decreased levels of complement factor H, MBL and ACLA-IgM among patients with thrombosis than those without thrombosis (N = 288). We also observed significantly lower GCNs of total C4 and C4A among aPL-positive patients with both SLE and thrombosis than others. By contrast, aPL-positive subjects with SLE had significantly reduced protein levels of C3, total C4, C4A, C4B and ACLA-IgG, and higher frequency of females than those without SLE. Patients with thrombosis but without SLE (N = 126), and patients with SLE but without thrombosis (N = 182) had the greatest differences in mean protein levels of C3 (p = 2.6 × 10⁻⁶), C4 (p = 2.2 × 10⁻⁹) and ACLA-IgG (p = 1.2 × 10⁻⁵). RPL occurred in 23.7% of female patients and thrombotic SLE patients had the highest frequency of RPL (41.0%; p = 3.8 × 10⁻¹⁰). Compared with non-RPL females, RPL had significantly higher frequency of thrombosis and elevated C4 protein levels. Female patients with homozygous C4A deficiency all experienced RPL (p = 0.0001) but the opposite was true for patients with homozygous C4B deficiency (p = 0.017). These results provide new insights and biomarkers for diagnosis and management of APS and SLE.

Intracellular activation of complement C3 in Paneth cells improves repair of intestinal epithelia during acute injury

AIM

To explore whether Paneth cells (PCs) and complement system collaborate in the repair of enteric epithelia during acute gastrointestinal injury (AGI).

METHODS

Wild-type C57BL/6 mice were employed to induce AGI by performing colon ascendens stent surgery, with sham-operated as control. Exogenous C3 treatment was applied at 6-h postsurgery. After 48 h, overall survival, intestinal damage severity, and C3 intracellular activation were assessed in both epithelial cells and PCs.

RESULTS

AGI caused a high mortality, while C3 therapy significantly attenuated epithelial damages and improved survival. Besides, exogenous C3 in vitro enhanced the proliferation and activity of PCs. Importantly, intracellular C3 activation was observed inside of PCs under C3 co-stimulation in vitro.

CONCLUSION

C3 immunotherapy might play a valuable role in turnover of gut epithelia through intracellular activation in PCs.

Biomarkers of necrotizing enterocolitis: a review of literature

Necrotizing enterocolitis (NEC) is among the most serious gastrointestinal emergency in very low birth weight (VLBW), extremely low birth weight (ELBW) and extremely low gestational age neonates (ELGAN), affecting 7-14% of these neonates. Despite extensive research, the underlying aetiology of NEC still remains blurred. Due to high mortality, morbidity and its delayed presentation, early detection of NEC is considered to be lifesaving. A number of biomarkers have been studied for early detection and prediction of severity of NEC but till date, no ideal marker has been discovered. Molecular techniques like proteomic and metabolomic have recently emerged in the field for the development of biomarkers for early detection and understanding the pathophysiology of NEC. We did literature search for identifying all biomarkers that have been used for the detection of NEC and, in this review article, we discuss these biomarkers along with the available current evidence.

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.

Intracellular Activation of Complement 3 Is Responsible for Intestinal Tissue Damage during Mesenteric Ischemia

Intestinal ischemia followed by reperfusion leads to local and remote organ injury attributed to inflammatory response during the reperfusion phase. The extent to which ischemia contributes to ischemia/reperfusion injury has not been thoroughly studied. After careful evaluation of intestinal tissue following 30 min of ischemia, we noticed significant local mucosal injury in wild-type mice. This injury was drastically reduced in C3-deficient mice, suggesting C3 involvement. Depletion of circulating complement with cobra venom factor eliminated, as expected, injury recorded at the end of the reperfusion phase but failed to eliminate injury that occurred during the ischemic phase. Immunohistochemical studies showed that tissue damage during ischemia was associated with increased expression of C3/C3 fragments primarily in the intestinal epithelial cells, suggesting local involvement of complement. In vitro studies using Caco2 intestinal epithelial cells showed that in the presence of LPS or exposure to hypoxic conditions the cells produce higher C3 mRNA as well as C3a fragment. Caco2 cells were also noted to produce cathepsins B and L, and inhibition of cathepsins suppressed the release of C3a. Finally, we found that mice treated with a cathepsin inhibitor and cathepsin B-deficient mice suffer limited intestinal injury during the ischemic phase. To our knowledge, our findings demonstrate for the first time that significant intestinal injury occurs during ischemia prior to reperfusion and that this is due to activation of C3 within the intestinal epithelial cells in a cathepsin-dependent manner. Modulation of cathepsin activity may prevent injury of organs exposed to ischemia.

TLR2 modulates antibodies required for intestinal ischemia/reperfusion-induced damage and inflammation

In multiple clinical conditions, including trauma and hemorrhage, reperfusion magnifies ischemic tissue damage. Ischemia induces expression of multiple neoantigens, including lipid alterations that are recognized by the serum protein, β2-glycoprotein I (β2-GPI). During reperfusion, binding of β2-GPI by naturally occurring Abs results in an excessive inflammatory response that may lead to death. As β2-GPI is critical for intestinal ischemia/reperfusion (IR)-induced tissue damage and TLR2 is one of the proposed receptors for β2-GPI, we hypothesized that IR-induced intestinal damage and inflammation require TLR2. Using TLR2(-/-) mice, we demonstrate that TLR2 is required for IR-induced mucosal damage, as well as complement activation and proinflammatory cytokine production. In response to IR, TLR2(-/-) mice have increased serum β2-GPI compared with wild-type mice, but β2-GPI is not deposited on ischemic intestinal tissue. In addition, TLR2(-/-) mice also did not express other novel Ags, suggesting a sequential response. Unlike other TLRs, TLR2(-/-) mice lacked the appropriate Ab repertoire to induce intestinal IR tissue damage or inflammation. Together, these data suggest that, in addition to the inflammatory response, IR-induced injury requires TLR2 for naturally occurring Ab production.

The receptor for complement component C3a mediates protection from intestinal ischemia-reperfusion injuries by inhibiting neutrophil mobilization

C3a is a key complement activation fragment, yet its neutrophil-expressed receptor (C3aR) still has no clearly defined role. In this study, we used a neutrophil-dependent mouse model of intestinal ischemia-reperfusion (IR) injury to explore the role of C3aR in acute tissue injuries. C3aR deficiency worsened intestinal injury, which corresponded with increased numbers of tissue-infiltrating neutrophils. Circulating neutrophils were significantly increased in C3aR(-/-) mice after intestinal ischemia, and C3aR(-/-) mice also mobilized more circulating neutrophils after granulocyte colony-stimulating factor infusion compared with WT mice, indicating a specific role for C3aR in constraining neutrophil mobilization in response to intestinal injury. In support of this role, C3aR(-/-) mice reconstituted with WT bone marrow reversed IR pathology back to WT levels. Complement C5a receptor (C5aR) antagonism in C3aR(-/-) mice also rectified the worsened pathology after intestinal IR injury but had no effect on circulating neutrophils, highlighting the opposing roles of C3a and C5a in disease pathogenesis. Finally, we found that using a potent C3a agonist to activate C3aR in vivo reduced neutrophil mobilization and ameliorated intestinal IR pathology in WT, but not C3aR(-/-), mice. This study identifies a role for C3aR in regulating neutrophil mobilization after acute intestinal injury and highlights C3aR agonism as a potential treatment option for acute, neutrophil-driven pathologies.

Complement depletion protects lupus-prone mice from ischemia-reperfusion-initiated organ injury

Ischemia-reperfusion (IR) injury causes a vigorous immune response that is amplified by complement activation, leading to local and remote tissue damage. Using MRL/lpr mice, which are known to experience accelerated tissue damage after mesenteric IR injury, we sought to evaluate whether complement inhibition mitigates organ damage. We found that complement depletion with cobra venom factor protected mice from local and remote lung tissue damage. Protection from injury was associated with less complement (C3) and membrane attack complex deposition, less neutrophil infiltration, and lower levels of local proinflammatory cytokine production. In addition, complement depletion was able to decrease the level of oxidative stress as measured by glutathione peroxidase 1 mRNA levels and superoxide dismutase activity. Furthermore, blockage of C5a receptor protected MRL/lpr mice from local tissue damage, but not from remote lung tissue damage. In conclusion, although treatments with cobra venom factor and C5a receptor antagonist were able to protect mice from local tissue damage, treatment with C5a receptor antagonist was not able to protect mice from remote lung tissue damage, implying that more factors contribute to the development of remote tissue damage after IR injury. These data also suggest that complement inhibition at earlier, rather than late, stages can have clinical benefit in conditions that are complicated with IR injury.

Immunopathogenesis of ischemia/reperfusion-associated tissue damage

Ischemia/reperfusion (IR) instigates a complex array of inflammatory events which result in damage to the local tissue. IR-related organ damage occurs invariably in several clinical conditions including trauma, organ transplantation, autoimmune diseases and revascularization procedures. We critically review available pre-clinical experimental information on the role of immune response in the expression of tissue damage following IR. Distinct elements of the innate and adaptive immune response are involved in the expression of tissue injury. Interventions such as prevention of binding of natural antibody to antigen expressed on the surface of ischemia-conditioned cells, inhibition of the ensuing complement activation, modulation of Toll-like receptors, B or T cell depletion and blockade of inflammatory cytokines and chemokines limit IR injury in preclinical studies. Clinical trials that will determine the therapeutic value of each approach is needed.

Inhibiting the C5-C5a receptor axis

Activation of the complement system is a major pathogenic event that drives various inflammatory responses in numerous diseases. All pathways of complement activation lead to cleavage of the C5 molecule generating the anaphylatoxin C5a and, C5b that subsequently forms the terminal complement complex (C5b-9). C5a exerts a predominant pro-inflammatory activity through interactions with the classical G-protein coupled receptor C5aR (CD88) as well as with the non-G protein coupled receptor C5L2 (GPR77), expressed on various immune and non-immune cells. C5b-9 causes cytolysis through the formation of the membrane attack complex (MAC), and sub-lytic MAC and soluble C5b-9 also possess a multitude of non-cytolytic immune functions. These two complement effectors, C5a and C5b-9, generated from C5 cleavage, are key components of the complement system responsible for propagating and/or initiating pathology in different diseases, including paroxysmal nocturnal hemoglobinuria, rheumatoid arthritis, ischemia-reperfusion injuries and neurodegenerative diseases. Thus, the C5-C5a receptor axis represents an attractive target for drug development. This review provides a comprehensive analysis of different methods of inhibiting the generation of C5a and C5b-9 as well as the signalling cascade of C5a via its receptors. These include the inhibition of C5 cleavage through targeting of C5 convertases or via the C5 molecule itself, as well as blocking the activity of C5a by neutralizing antibodies and pharmacological inhibitors, or by targeting C5a receptors per se. Examples of drugs and naturally occurring compounds used are discussed in relation to disease models and clinical trials. To date, only one such compound has thus far made it to clinical medicine: the anti-C5 antibody eculizumab, for treating paroxysmal nocturnal hemoglobinuria. However, a number of drug candidates are rapidly emerging that are currently in early-phase clinical trials. The C5-C5a axis as a target for drug development is highly promising for the treatment of currently intractable major human diseases.

Complement inhibition alleviates paraquat-induced acute lung injury

The widely used herbicide, paraquat (PQ), is highly toxic and claims thousands of lives from both accidental and voluntary ingestion. The pathological mechanisms of PQ poisoning-induced acute lung injury (ALI) are not well understood, and the role of complement in PQ-induced ALI has not been elucidated. We developed and characterized a mouse model of PQ-induced ALI and studied the role of complement in the pathogenesis of PQ poisoning. Intraperitoneal administration of PQ caused dose- and time-dependent lung damage and mortality, with associated inflammatory response. Within 24 hours of PQ-induced ALI, there was significantly increased expression of the complement proteins, C1q and C3, in the lung. Expression of the anaphylatoxin receptors, C3aR and C5aR, was also increased. Compared with wild-type mice, C3-deficient mice survived significantly longer and displayed significantly reduced lung inflammation and pathology after PQ treatment. Similar reductions in PQ-induced inflammation, pathology, and mortality were recorded in mice treated with the C3 inhibitors, CR2-Crry, and alternative pathway specific CR2-fH. A similar therapeutic effect was also observed by treatment with either C3a receptor antagonist or a blocking C5a receptor monoclonal antibody. Together, these studies indicate that PQ-induced ALI is mediated through receptor signaling by the C3a and C5a complement activation products that are generated via the alternative complement pathway, and that complement inhibition may be an effective clinical intervention for postexposure treatment of PQ-induced ALI.

Targeted complement inhibitors protect against posttransplant cardiac ischemia and reperfusion injury and reveal an important role for the alternative pathway of complement activation

Ischemia reperfusion injury (IRI) is an unavoidable event during solid organ transplantation and is a major contributor to early graft dysfunction and subsequent graft immunogenicity. In a therapeutic paradigm using targeted complement inhibitors, we investigated the role of complement, and specifically the alternative pathway of complement, in IRI to heart isografts. Mouse heterotopic isograft heart transplants were performed in C57BL/6 mice treated with a single injection of either CR2-Crry (inhibits all complement pathways) or CR2-fH (inhibits alternative complement pathway) immediately posttransplantation. Transplanted hearts were harvested at 12 and 48 h for analysis. Both inhibitors resulted in a significant reduction in myocardial IRI, as measured by histology and serum cardiac troponin I levels. Furthermore, compared with untreated controls, both inhibitors reduced graft complement deposition, neutrophil and macrophage infiltration, adhesion molecule expression (P-selectin, E-selectin, and I-CAM-1), and proinflammatory cytokine expression (TNF-α, IL-1β, KC, and MCP-1). The reduction in myocardial damage and cellular infiltration was not significantly different between CR2-Crry- and CR2-fH-treated mice, although adhesion molecule and cytokine levels were significantly lower in CR2-Crry-treated mice compared with CR2-fH-treated mice. In conclusion, the alternative complement pathway plays a major contributing role in myocardial IRI after heart transplantation, and local (targeted) complement inhibition has the potential to provide an effective and safe therapeutic strategy to reduce graft injury. Although total complement blockade may be somewhat more efficacious in terms of reducing inflammation, specific blockade of the alternative pathway is likely to be less immunosuppressive in an already immunocompromised recipient.

Domain V peptides inhibit beta2-glycoprotein I-mediated mesenteric ischemia/reperfusion-induced tissue damage and inflammation

Reperfusion of ischemic tissue induces significant tissue damage in multiple conditions, including myocardial infarctions, stroke, and transplantation. Although not as common, the mortality rate of mesenteric ischemia/reperfusion (IR) remains >70%. Although complement and naturally occurring Abs are known to mediate significant damage during IR, the target Ags are intracellular molecules. We investigated the role of the serum protein, β2-glycoprotein I as an initiating Ag for Ab recognition and β2-glycoprotein I (β2-GPI) peptides as a therapeutic for mesenteric IR. The time course of β2-GPI binding to the tissue indicated binding and complement activation within 15 min postreperfusion. Treatment of wild-type mice with peptides corresponding to the lipid binding domain V of β2-GPI blocked intestinal injury and inflammation, including cellular influx and cytokine and eicosanoid production. The optimal therapeutic peptide (peptide 296) contained the lysine-rich region of domain V. In addition, damage and most inflammation were also blocked by peptide 305, which overlaps with peptide 296 but does not contain the lysine-rich, phospholipid-binding region. Importantly, peptide 296 retained efficacy after replacement of cysteine residues with serine. In addition, infusion of wild-type serum containing reduced levels of anti-β2-GPI Abs into Rag-1(-/-) mice prevented IR-induced intestinal damage and inflammation. Taken together, these data suggest that the serum protein β2-GPI initiates the IR-induced intestinal damage and inflammatory response and as such is a critical therapeutic target for IR-induced damage and inflammation.

Complement regulates TLR4-mediated inflammatory responses during intestinal ischemia reperfusion

Innate immune responses including TLR4 and complement activation are required for mesenteric ischemia/reperfusion (IR)-induced tissue damage. We examined the regulation of TLR4 and complement activation in a mouse model of intestinal IR. Intestinal IR-induced C3 deposition in a TLR4 dependent manner. In addition, in wild-type but not TLR4 deficient mice, IR significantly increased C3 and Factor B (FB) mRNA expression within the intestine. To further examine the role of TLR4 and complement, we administered the complement inhibitor, CR2-Crry, to target local complement activation in wild-type C57Bl/10, and TLR4 deficient B10/ScN mice. TLR4 deficient mice sustained less damage and inflammation after IR than wild-type mice, but administration of CR2-Crry did not further reduce tissue damage. In contrast, CR2-Crry treatment of wild-type mice was accompanied by a reduction in complement activation and in C3 and FB transcription in response to IR. CR2-Crry also significantly decreased intestinal IL-6 and IL-12p40 production in both the wild-type and TLR4 deficient mice. These data indicate that TLR4 regulates extrahepatic complement production while complement regulates TLR4-mediated cytokine production during intestinal IR.

Human intestinal ischemia-reperfusion-induced inflammation characterized: experiences from a new translational model

Human intestinal ischemia-reperfusion (IR) is a frequent phenomenon carrying high morbidity and mortality. Although intestinal IR-induced inflammation has been studied extensively in animal models, human intestinal IR induced inflammatory responses remain to be characterized. Using a newly developed human intestinal IR model, we show that human small intestinal ischemia results in massive leakage of intracellular components from ischemically damaged cells, as indicated by increased arteriovenous concentration differences of intestinal fatty acid binding protein and soluble cytokeratin 18. IR-induced intestinal barrier integrity loss resulted in free exposure of the gut basal membrane (collagen IV staining) to intraluminal contents, which was accompanied by increased arteriovenous concentration differences of endotoxin. Western blot for complement activation product C3c and immunohistochemistry for activated C3 revealed complement activation after IR. In addition, intestinal IR resulted in enhanced tissue mRNA expression of IL-6, IL-8, and TNF-alpha, which was accompanied by IL-6 and IL-8 release into the circulation. Expression of intercellular adhesion molecule-1 was markedly increased during reperfusion, facilitating influx of neutrophils into IR-damaged villus tips. In conclusion, this study for the first time shows the sequelae of human intestinal IR-induced inflammation, which is characterized by complement activation, production and release of cytokines into the circulation, endothelial activation, and neutrophil influx into IR-damaged tissue.

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.

Decay-accelerating factor attenuates C-reactive protein-potentiated tissue injury after mesenteric ischemia/reperfusion

BACKGROUND

C-reactive protein (CRP) is an acute pro-inflammatory mediator that has been demonstrated to enhance ischemia/reperfusion (IR) injury by virtue of activating the complement system. CRP is able to interact with complement proteins such as C1q, complement factor H, and C4b-binding protein. Since complement activation is central in the expression of tissue injury following IR, we have investigated the effects of human decay-accelerating factor (DAF), a complement inhibitor, on CRP-potentiated complement activation and tissue injury in mice subjected to mesenteric IR.

MATERIALS AND METHODS

Male C57B1/6 mice were allocated into eight groups: (1) Sham-operated group without IR injury; (2) CRP+Sham group; (3) IR group; (4) CRP+IR group; (5) DAF group; (6) CRP+DAF group; (7) IR+DAF group, and (8) CRP+IR+DAF group. Intestinal and lung injury, neutrophil infiltration, myeloperoxidase (MPO) expression, complement component deposition, and interleukin-6 (IL-6) production were assessed for each treatment group of mice.

RESULTS

We report that administration of DAF significantly attenuates the CRP-enhanced intestinal injury as well as remote lung damages following acute mesenteric IR in mice, while DAF inhibits complement activation, suppresses neutrophil infiltration, and reduces IL-6 production.

CONCLUSIONS

Our study suggests that inhibition complement activation with DAF may prove useful for the treatment of post-ischemic inflammatory injuries associated with an increased production of CRP.

Anti-ribonucleoprotein antibodies mediate enhanced lung injury following mesenteric ischemia/reperfusion inRag-1−/−mice

Natural Abs and autoantibodies bind antigens displayed by ischemia-conditioned tissues, followed by complement activation and enhanced tissue injury during reperfusion. Anti-ribonucleoprotein (RNP) Ab is associated with lung disease in patients with autoimmune disease but it is not known whether these abs contribute to lung injury. Mesenteric I/R in mice leads to local and remote lung injury. Accordingly, we used this model to investigate whether anti-RNP Abs would reconstitute I/R damage with prominent lung damage in injury-resistant Rag1(-/-) animals. Rag1(-/-) mice injected with anti-RNP Ab containing serum and subjected to mesenteric I/R suffered greater intestinal injury than control-treated and sham-operated animals. The magnitude of the reconstituted damage was anti-RNP Ab titer-dependent. Anti-RNP Ab-treated animals demonstrated a dose-dependent increase in lung histologic injury scores compared to control and sham animals. Anti-RNP mediated injury was shown to be complement dependent. These experiments reveal a novel mechanism whereby anti-RNP Abs contributes to the development of pulmonary pathology in patients with autoimmune diseases following exposure of remote organs to I/R injury.

Elimination of C5aR prevents intestinal mucosal damage and attenuates neutrophil infiltration in local and remote organs

The complement C5a pathway has been shown to be an important mediator of inflammation and tissue injury. To further understand the role of C5a receptor (C5aR) pathway in ischemia/reperfusion (I/R) injury, and to evaluate the potential of antagonizing C5aR to protect from I/R injury, we tested the effect of eliminating C5aR using C5aR knockout (KO) mice and their wild-type (WT) littermates in a superior mesenteric artery occlusion (SMAO) intestinal I/R injury model. C5aR KO and WT mice were subjected to SMAO or sham for 45 min. After 3 h of reperfusion, the percentage of injured ileal villi was twice as high in WT mice subjected to SMAO as compared with the C5aR KO mice. In addition, the number of neutrophils was 34% higher in WT mice subjected to SMAO as compared with the C5aR KO mice. Moreover, ileum and lung myeloperoxidase activities after SMAO were significantly higher in WT than C5aR KO mice. Apoptotic cell death was induced after reperfusion in WT-SMAO and was reduced by more than 50% in C5aR KO mice. The plasma level of TNF-alpha was increased approximately 3.74-fold in WT subjected to SMAO compared with sham. In contrast, the level was increased only approximately 1.18-fold in the C5aR KO mice subjected to SMAO. In conclusion, this study demonstrates that elimination of the C5aR pathway protects the intestine from I/R injury and diminishes intestine-derived pulmonary neutrophil sequestration. Blocking C5aR may be considered as a potential therapeutic intervention for I/R injury.

A novel inhibitor of the alternative pathway of complement attenuates intestinal ischemia/reperfusion-induced injury

Complement activation has been demonstrated to contribute significantly to the expression of IR-induced tissue damage. Each of the three complement pathways, classic, alternative, and lectin, has been implicated in the instigation of tissue pathology. In this study, we used a selective inhibitor of the alternative pathway, that is, a soluble form of complement receptor of the immunoglobulin superfamily (CRIg-Fc) to determine whether it can prevent IR tissue injury. We demonstrate that treatment of C57B1/6 mice prior to mesenteric IR prevents local (intestinal) and remote (lung) injury by limiting deposition of complement and entry of polymorphonuclear cells to the sites of injury. Our results show that CRIg-Fc represents a candidate to limit IR injury as it occurs in various clinical conditions.

Ischemia-mediated aggregation of the actin cytoskeleton is one of the major initial events resulting in ischemia-reperfusion injury

Ischemia-reperfusion (IR) injury represents a major clinical challenge, which contributes to morbidity and mortality during surgery. The critical role of natural immunoglobulin M (IgM) and complement in tissue injury has been demonstrated. However, cellular mechanisms that result in the deposition of natural IgM and the activation of complement are still unclear. In this report, using a murine intestinal IR injury model, we demonstrated that the beta-actin protein in the small intestine was cleaved and actin filaments in the columnar epithelial cells were aggregated after a transient disruption during 30 min of ischemia. Ischemia also led to deposition of natural IgM and complement 3 (C3). A low dose of cytochalasin D, a depolymerization reagent of the actin cytoskeleton, attenuated this deposition and also attenuated intestinal tissue injury in a dose-dependent manner. In contrast, high doses of cytochalasin D failed to worsen the injury. These data indicate that ischemia-mediated aggregation of the actin cytoskeleton, rather than its disruption, results directly in the deposition of natural IgM and C3. We conclude that ischemia-mediated aggregation of the actin cytoskeleton leads to the deposition of natural IgM and the activation of complement, as well as tissue injury.

A novel targeted inhibitor of the alternative pathway of complement and its therapeutic application in ischemia/reperfusion injury

Bioavailability and therapeutic efficacy of soluble Crry, a mouse inhibitor of all complement activation pathways, is significantly enhanced when linked to a fragment of complement receptor 2 (CR2), a receptor that targets C3 activation products. In this study, we characterize alternative pathway-specific inhibitors consisting of a single or dimeric N-terminal region of mouse factor H (fH; short consensus repeats 1-5) linked to the same CR2 fragment (CR2-fH and CR2-fHfH). Both CR2-fH and CR2-fHfH were highly effective at inhibiting the alternative pathway in vitro and demonstrated a higher specific activity than CR2-Crry. CR2-fH was also more effective than endogenous serum fH in blocking target deposition of C3. Target binding and complement inhibitory activity of CR2-fH/CR2-fHfH was dependent on CR2- and C3-mediated interactions. The alternative pathway of complement plays a role in intestine ischemia/reperfusion injury. However, serum fH fails to provide protection against intestine ischemia/reperfusion injury although it can bind to and provide cell surfaces with protection from complement and is present in plasma at a high concentration. In a mouse model, CR2-fH and CR2-fHfH provided complete protection from local (intestine) and remote (lung) injury. CR2-fH targeted to the site of local injury and greatly reduced levels of tissue C3 deposition. Thus, the targeting mechanism significantly enhances alternative pathway-specific complement inhibitory activity of the N-terminal domain of fH and has the potential to reduce side effects that may be associated with systemic complement blockade. The data further indicate alternative pathway dependence for local and remote injury following intestinal ischemia/reperfusion in a clinically relevant therapeutic paradigm.

Complement component C5a mediates hemorrhage-induced intestinal damage

BACKGROUND

Complement has been implicated in the pathogenesis of intestinal damage and inflammation in multiple animal models. Although the exact mechanism is unknown, inhibition of complement prevents hemodynamic alterations in hemorrhage.

MATERIALS AND METHODS

C57Bl/6, complement 5 deficient (C5-/-) and sufficient (C5+/+) mice were subjected to 25% blood loss. In some cases, C57Bl/6 mice were treated with C5a receptor antagonist (C5aRa) post-hemorrhage. Intestinal injury, leukotriene B4, and myeloperoxidase production were assessed for each treatment group of mice.

RESULTS

Mice subjected to significant blood loss without major trauma develop intestinal inflammation and tissue damage within 2 hours. We report here that complement 5 (C5) deficient mice are protected from intestinal tissue damage when subjected to hemorrhage (injury score = 0.36 compared with wildtype hemorrhaged animal injury score = 2.89; P < 0.05). We present evidence that C5a represents the effector molecule because C57Bl/6 mice treated with a C5a receptor antagonist displayed limited intestinal injury (injury score = 0.88), leukotriene B4 (13.16 pg/mg tissue), and myeloperoxidase (115.6 pg/mg tissue) production compared with hemorrhaged C57Bl/6 mice (P < 0.05).

CONCLUSIONS

Complement activation is important in the development of hemorrhage-induced tissue injury and C5a generation is critical for tissue inflammation and damage. Thus, therapeutics targeting C5a may be useful therapeutics for hemorrhage-associated injury.

Early plasma complement C3a levels correlate with functional outcome after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Studies have documented an inflammatory response in the circulating plasma and cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage (aSAH). In particular, early upregulation of several complement proteins, including C3a, C4a, and C5b-9, has been demonstrated after the initial hemorrhagic insult. The inflammatory actions of the complement cascade are largely mediated through the anaphylatoxins, C3a and C5a. Recent investigations have established a critical role for C3a in the pathogenesis of cerebral ischemia. We attempt to confirm that plasma C3a and C5a values are elevated in patients with aSAH and to determine whether or not these levels are reliable independent predictors of functional outcome irrespective of clinical presentation.

METHODS

Fifty-two patients with aSAH were prospectively enrolled and stratified according to admission Hunt and Hess grade, demographic variables, and functional status at the time of discharge (modified Rankin Scale score). Plasma C3a and C5a levels were determined at early and late time points after aSAH through enzyme-linked immunosorbent assay.

RESULTS

After aSAH, early C3a and C5a values were increased compared with levels in non-SAH control patients (P < 0.001). Univariate analysis demonstrated that elevations in early C3a (P = 0.010) and C5a (P = 0.041) levels and poor admission Hunt and Hess grade (P = 0.015) correlated significantly with unfavorable outcome. In our multivariate model, only early C3a levels retained a strong correlation with outcome when modeled with Hunt and Hess grade (P = 0.009).

CONCLUSION

These results demonstrate an association between early complement C3a levels and outcome after aSAH that seems to be independent of the initial hemorrhage. The findings suggest that inflammatory processes involving C3a may contribute to delayed morbidity and mortality after aneurysmal rupture.

Intestinal inflammation caused by magnesium deficiency alters basal and oxidative stress-induced intestinal function

The aim of this study was to determine the effect of magnesium deficiency on small intestinal morphology and function. Rats were assigned to 4 groups and placed on magnesium sufficient or deficient diet for 1 or 3 weeks. Infiltration of neutrophils and mucosal injury were assessed in stained sections of small intestine. Magnesium deficiency alone induced a significant increase in neutrophil infiltration and increased vascular ICAM-1 expression, in the absence of changes in mucosal injury or expression of proinflammatory mediators. Magnesium deficiency was associated with hyposecretory epithelial cell responses and vascular macromolecular leak in the small intestine and lung, which was attributed partly to reduced expression of NOS-3. To determine the effect of hypomagnesmia on the intestinal responses to a known oxidative stress, groups of rats were randomized to either sham operation or superior mesenteric artery occlusion for 10 (non-injurious) or 30 (injurious) minutes followed by a 1- or 4-hour reperfusion period. In response to mesenteric ischemia/reperfusion, deficient rats showed exaggerated PMN influx, but similar mucosal injury. Intestinal ischemia in sufficient animals induced vascular macromolecular leak in the small intestine and lung at 4 hours of reperfusion, with levels similar to those observed in untreated deficient rats. Acute magnesium repletion of deficient rats 24 h before surgery attenuated the exaggerated inflammation in deficient rats. These data show that magnesium deficiency induced a subclinical inflammation in the small intestine in the absence of mucosal injury, but with significant functional changes in local and remote organs and increased sensitivity to oxidative stress.

Decay-accelerating factor attenuates remote ischemia-reperfusion-initiated organ damage

Complement activation contributes to the expression of local and remote organ injury in animal models of ischemia-reperfusion (IR). We demonstrate here that a soluble form of decay-accelerating factor (DAF) protects normal C57Bl/6 and autoimmunity-prone B6.MRL/lpr mice subjected to hindlimb IR from remote intestinal and lung injury without affecting the degree of local skeletal muscle injury. In addition, DAF treatment attenuates remote organ injury in mice subjected to mesenteric IR. Soluble DAF allowed the deposition of complement 3 in local and remote injury sites while it limited the presence of terminal membrane attack complex and did not increase animal susceptibility to sepsis. These data provide evidence that soluble DAF might offer clinical benefit to patients suffering remote intestinal or lung damage in response to muscle or other organ injury.

Function, structure and therapeutic potential of complement C5a receptors

Complement fragment (C)5a is a 74 residue pro-inflammatory polypeptide produced during activation of the complement cascade of serum proteins in response to foreign surfaces such as microorganisms and tissue damaged by physical or chemical injury. C5a binds to at least two seven-transmembrane domain receptors, C5aR (C5R1, CD88) and C5L2 (gpr77), expressed ubiquitously on a wide variety of cells but particularly on the surface of immune cells like macrophages, neutrophils and T cells. C5aR is a classical G protein-coupled receptor that signals through G alpha i and G alpha 16, whereas C5L2 does not appear to couple to G proteins and has no known signalling activity. Although C5a was first described as an anaphylatoxin and later as a leukocyte chemoattractant, the widespread expression of C5aR suggested more general functionality. Our understanding of the physiology of C5a has improved significantly in recent years through exploitation of receptor knockout and knocking mice, C5 and C5a antibodies, soluble recombinant C5a and C5a analogues and newly developed receptor antagonists. C5a is now also implicated in non-immunological functions associated with developmental biology, CNS development and neurodegeneration, tissue regeneration, and haematopoiesis. Combined receptor mutagenesis, molecular modelling, structure-activity relationship studies and species dependence for ligand potency on C5aR have been helpful for identifying ligand binding sites on the receptor and for defining mechanisms of receptor activation and inactivation. This review will highlight major developments in C5a receptor research that support C5aR as an important therapeutic target. The intriguing possibilities raised by the existence of a non-signalling C5a receptor are also discussed.

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.

Natural antibodies, autoantibodies and complement activation in tissue injury

Ischemia/reperfusion-induced tissue damage is a significant problem occurring in multiple clinical conditions. Antibodies and complement activation contribute significantly to this pathology. Mice deficient in complement receptors 1 and 2 fail to produce a component of the natural antibody repertoire that binds to ischemia-conditioned tissues and activate complement. In contrast, mice prone to autoimmunity display accelerated tissue injury that results from the binding of autoantibodies to injured tissues. The specificity and production of natural antibodies, their role in autoimmunity and the mode of complement activation are reviewed from the perspective of the processes involved in ischemia/reperfusion-induced tissue damage.

Complement inhibitors selectively attenuate injury following administration of cobra venom factor to rats

Systemic activation of complement is a pathophysiological response common to severe disturbances such as hemorrhagic shock, major burn injury and sepsis. Intravenous infusion of cobra venom factor (CVF) has been used as an animal model of acute respiratory distress syndrome (ARDS), and reliably and selectively induces rapid intravascular activation of the complement system, leading to acute organ damage. In the present study, we have used different complement inhibitors to investigate the roles of complement products in CVF-induced responses in the rat. Rats were treated with either a C5a receptor antagonist (C5aRA, AcF-[OP(d-Cha)WR], 1 mg/kg i.v. or 10 mg/kg p.o.), a C3a receptor antagonist (C3aRA, N(2)-[(2,2-diphenylethoxy)acetyl]-l-arginine, 0.1 mg/kg i.v.) or a convertase inhibitor, rosmarinic acid (RMA, 10 mg/kg i.v.), prior to CVF-induced complement challenge. Intravenous CVF resulted in hallmark events evident in the development of ARDS, including systemic neutropenia followed by neutrophil migration to the lung and bronchoalveolar vascular leakage, blood pressure alterations, and an increase in TNFalpha levels in both serum and bronchoalveolar lavage fluid. These hemodynamic changes were differentially inhibited by antagonism of C5a receptors, C3a receptors or by inhibition of the entire complement cascade using RMA. This evidence strongly implicates complement factors in the development of lung injury associated with systemic complement activation and identifies complement inhibition as a potential therapeutic target for acute syndromes such as ARDS and other severe systemic shock states mediated by activation of complement.

Complement, natural antibodies, autoantibodies and tissue injury

Activation of the classical complement pathway represents an effector mechanism of intestinal ischemia/reperfusion injury. Mice deficient in complement receptors 1 and 2 fail to produce a component of the natural antibody repertoire that binds to ischemia-conditioned tissues and activate complement. In contrast, mice prone to autoimmunity display accelerated and enhanced tissue injury that results from the binding of autoantibodies to injured tissues. Our experiments demonstrate that naturally occurring antibodies and autoantibodies mediate tissue injury only after an organ has been subjected to a stressor such as ischemia.

Identification of the target self-antigens in reperfusion injury

Reperfusion injury (RI), a potential life-threatening disorder, represents an acute inflammatory response after periods of ischemia resulting from myocardial infarction, stroke, surgery, or trauma. The recent identification of a monoclonal natural IgM that initiates RI led to the identification of nonmuscle myosin heavy chain type II A and C as the self-targets in two different tissues. These results identify a novel pathway in which the innate response to a highly conserved self-antigen expressed as a result of hypoxic stress results in tissue destruction.

Targeted complement inhibition by C3d recognition ameliorates tissue injury without apparent increase in susceptibility to infection

Previous studies indicate a pivotal role for complement in mediating both local and remote injury following ischemia and reperfusion of the intestine. Here, we report on the use of a mouse model of intestinal ischemia/reperfusion injury to investigate the strategy of targeting complement inhibition to sites of complement activation by linking an iC3b/C3dg-binding fragment of mouse complement receptor 2 (CR2) to a mouse complement-inhibitory protein, Crry. We show that the novel CR2-Crry fusion protein targets sites of local and remote (lung) complement activation following intestinal ischemia and reperfusion injury and that CR2-Crry requires a 10-fold lower dose than its systemic counterpart, Crry-Ig, to provide equivalent protection from both local and remote injury. CR2-Crry has a significantly shorter serum half-life than Crry-Ig and, unlike Crry-Ig, had no significant effect on serum complement activity at minimum effective therapeutic doses. Furthermore, the minimum effective dose of Crry-Ig significantly enhanced susceptibility to infection in a mouse model of acute septic peritonitis, whereas the effect of CR2-Crry on susceptibility to infection was indistinguishable from that of PBS control. Thus, compared with systemic inhibition, CR2-mediated targeting of a complement inhibitor of activation improved bioavailability, significantly enhanced efficacy, and maintained host resistance to infection.

Pathophysiology of mesenteric ischemia/reperfusion: a review

During ischemia, the cell structures are progressively damaged, but restoration of the blood flow, paradoxically, intensifies the lesions caused by the ischemia. The mechanisms of ischemia injury and reperfusion (I/R) have not been completely defined and many studies have been realized in an attempt to find an ideal therapy for mesenteric I/R. The occlusion and reperfusion of the splanchnic arteries provokes local and systemic alterations principally derived from the release of cytotoxic substances and the interaction between neutrophils and endothelial cells. Substances involved in the process are discussed in the present review, like oxygen-derived free radicals, nitric oxide, transcription factors, complement system, serotonin and pancreatic proteases. The mechanisms of apoptosis, alterations in other organs, therapeutic and evaluation methods are also discussed.

Impact of vitamin E or selenium deficiency on nematode-induced alterations in murine intestinal function

The effects of deficiencies in the antioxidant nutrients, vitamin E and selenium, on the host response to gastrointestinal nematode infection are unknown. The aim of the study was to determine the effect of antioxidant deficiencies on nematode-induced alterations in intestinal function in mice. BALB/c mice were fed control diets or diets deficient in selenium or vitamin E and the response to a secondary challenge inoculation with Heligmosomoides polygyrus was determined. Egg and worm counts were assessed to determine host resistance. Sections of jejunum were mounted in Ussing chambers to measure changes in permeability, absorption, and secretion, or suspended in organ baths to determine smooth muscle contraction. Both selenium and vitamin E deficient diets reduced resistance to helminth infection. Vitamin E, but not selenium, deficiency prevented nematode-induced decreases in glucose absorption and hyper-contractility of smooth muscle. Thus, vitamin E status is an important factor in the physiological response to intestinal nematode infection and may contribute to antioxidant-dependent protective mechanisms in the small intestine.

Intravenous immunoglobulin attenuates mesenteric ischemia-reperfusion injury

Intravenous immunoglobulin (IVIG) has been found useful in the treatment of various clinical entities and its effect has been associated with inhibition of complement-mediated tissue damage. The aim of this study was to determine the ability of IVIG to protect against mesenteric ischemia-reperfusion (IR)-induced local and remote injury. Rats received vehicle or IVIG (150-600 mg/kg) 5 min prior to sham operation or 30 min of superior mesenteric artery occlusion, followed by 5, 120, or 240 min of reperfusion. IVIG reduced IR-induced mucosal injury without altering IR-induced increases in PMN infiltration or LTB(4) generation. At 5 min post IR, the deposition of IgG and C3 in the lamina propria and surface epithelial cells was attenuated by IVIG. The increased capillary leak, evident at 240 min, was inhibited by IVIG and coincided with a reduction in C3 deposition in lung tissue. The beneficial effects of IVIG may be related to the ability to scavenge deleterious products.

Anti-phospholipid antibodies restore mesenteric ischemia/reperfusion-induced injury in complement receptor 2/complement receptor 1-deficient mice

Complement receptor 2-deficient (Cr2(-/-)) mice are resistant to mesenteric ischemia/reperfusion (I/R) injury because they lack a component of the natural Ab repertoire. Neither the nature of the Abs that are involved in I/R injury nor the composition of the target Ag, to which recognition is lacking in Cr2(-/-) mice, is known. Because anti-phospholipid Abs have been shown to mediate fetal growth retardation and loss when injected into pregnant mice, we performed experiments to determine whether anti-phospholipid Abs can also reconstitute I/R injury and, therefore, represent members of the injury-inducing repertoire that is missing in Cr2(-/-) mice. We demonstrate that both murine and human monoclonal and polyclonal Abs against negatively charged phospholipids can reconstitute mesenteric I/R-induced intestinal and lung tissue damage in Cr2(-/-) mice. In addition, Abs against beta2 glycoprotein I restore local and remote tissue damage in the Cr2(-/-) mice. Unlike Cr2(-/-) mice, reconstitution of I/R tissue damage in the injury-resistant Rag-1(-/-) mouse required the infusion of both anti-beta2-glycoprotein I and anti-phospholipid Ab. We conclude that anti-phospholipid Abs can bind to tissues subjected to I/R insult and mediate tissue damage.

The role of the complement system in ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a common clinical event with the potential to seriously affect, and sometimes kill, the patient. Interruption of blood supply causes ischemia, which rapidly damages metabolically active tissues. Paradoxically, restoration of blood flow to the ischemic tissues initiates a cascade of pathology that leads to additional cell or tissue injury. I/R is a potent inducer of complement activation that results in the production of a number of inflammatory mediators. The use of specific inhibitors to block complement activation has been shown to prevent local tissue injury after I/R. Clinical and experimental studies in gut, kidney, limb, and liver have shown that I/R results in local activation of the complement system and leads to the production of the complement factors C3a, C5a, and the membrane attack complex. The novel inhibitors of complement products may find wide clinical application because there are no effective drug therapies currently available to treat I/R injuries.

Accelerated ischemia/reperfusion-induced injury in autoimmunity-prone mice

Natural Abs have been implicated in initiating mesenteric ischemia/reperfusion (I/R)-induced tissue injury. Autoantibodies have affinity and self-Ag recognition patterns similar to natural Abs. We considered that autoimmunity-prone mice that express high titers of autoantibodies should have enhanced I/R-induced injury. Five-month-old B6.MRL/lpr mice displayed accelerated and enhanced intestinal I/R-induced damage compared with 2-mo-old B6.MRL/lpr and age-matched C57BL/6 mice. Similarly, older autoimmune mice had accelerated remote organ (lung) damage. Infusion of serum IgG derived from 5-mo-old but not 2-mo-old B6.MRL/lpr into I/R resistant Rag-1-/- mice rendered them susceptible to local and remote organ injury. Injection of monoclonal IgG anti-DNA and anti-histone Abs into Rag-1-/- mice effectively reconstituted tissue injury. These data show that like natural Abs, autoantibodies, such as anti-dsDNA and anti-histone Abs, can instigate I/R injury and suggest that they are involved in the development of tissue damage in patients with systemic lupus erythematosus.

Complement C5a receptor is essential for the optimal generation of antiviral CD8+ T cell responses

The complement system has been long regarded as an important effector of the innate immune response. Furthermore, complement contributes to various aspects of B and T cell immunity. Nevertheless, the role of complement in CD8(+) T cell antiviral responses has yet to be fully delineated. We examined the CD8(+) T cell response in influenza type A virus-infected mice treated with a peptide antagonist to C5aR to test the potential role of complement components in CD8(+) T cell responses. We show that both the frequency and absolute numbers of flu-specific CD8(+) T cells are greatly reduced in C5aR antagonist-treated mice compared with untreated mice. This reduction in flu-specific CD8(+) T cells is accompanied by attenuated antiviral cytolytic activity in the lungs. These results demonstrate that the binding of the C5a component of complement to the C5a receptor plays an important role in CD8(+) T cell responses.

Systemic complement activation following human acute ischaemic stroke

The brain tissue damage after stroke is mediated partly by inflammation induced by ischaemia-reperfusion injury where the complement system plays a pivotal role. In the present study we investigated systemic complement activation and its relation to C-reactive protein (CRP), a known complement activator, and other inflammatory mediators after acute ischaemic stroke. Sequential plasma samples from 11 acute stroke patients were obtained from the time of admittance to hospital and for a follow-up period of 12 months. Nine healthy gender- and age-matched subjects served as controls. The terminal SC5b-9 complement complex (TCC), CRP, soluble adhesion molecules (L-, E- and P- selectin, ICAM, VCAM) and cytokines [tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-8] were analysed. All parameters were within normal values and similar to the controls the first hours after stroke. Terminal complement complex (TCC) increased significantly from 0.54 to 0.74 AU/ml at 72 h (P = 0.032), reached maximum at 7 days (0.90 AU/ml, P < 0.001), was still significantly increased at 12 days (0.70 AU/ml, P = 0.009) and thereafter normalized. CRP increased significantly from 1.02 to 2.11 mg/l at 24 h (P = 0.023), remained significantly increased for 1 week (2.53-2.94 mg/l, P = 0.012-0.017) and thereafter normalized. TCC and C-reactive protein (CRP) correlated significantly (r = 0.36, P < 0.001). The increase in TCC and CRP correlated to the size of infarction (r = 0.80 and P = 0.017 for TCC; r = 0.72 and P = 0.043 for CRP). No significant changes were seen for adhesion molecules and cytokines. In conclusion, transitory systemic complement activation takes place after stroke. The early rise in CRP and the following TCC increase suggest a possible role for CRP in complement activation, which may contribute to inflammation after stroke.