Reperfusion injury of ischemic skeletal muscle is mediated by natural antibody and complement

Complement inhibitors: a resurgent concept in anti-inflammatory therapeutics

In addition to its essential role in immune defense, the complement system contributes to tissue damage in many clinical conditions. Thus, there is a pressing need to develop therapeutically effective complement inhibitors to prevent these adverse effects. This concept, though old, received little scientific attention until recently. Data from animal models of diseases that have been produced using complement-deficient, knockout, and transgenic animals, as well as data demonstrating that complement proteins are produced in many important tissue sites (including the brain) have attracted the interest of many basic research scientists and applied scientists from the biotechnology field and larger pharmaceutical firms. This resurgence of interest has generated a wealth of new information in the field of complement inhibition. In this article, we comprehensively review up-to-date information in the field of complement inhibitors.

Soluble P-selectin moderates complement-dependent reperfusion injury of ischemic skeletal muscle

P-selectin is an adhesion molecule expressed on activated endothelial and platelet surfaces. The function of the short consensus repeats (SCRs) of P-selectin, homologous with the SCRs of complement regulatory proteins is largely unknown. In a model of murine hindlimb ischemia where local reperfusion injury is partly mediated by IgM natural antibody and classical complement pathway activation, we hypothesized that human soluble P-selectin (sP-sel) would moderate the complement component of the inflammatory response. Infusion of sP-sel supernatant or purified (p) sP-sel prepared from activated human platelets, reduced ischemic muscle vascular permeability by 48% and 43%, respectively, following reperfusion. Hindlimb immunohistochemistry demonstrated negligible C3 staining colocalized with IgM in these groups compared with intense staining in the untreated injured mice. In vitro studies of mouse serum complement hemolytic activity showed that psP-sel inhibited the classical but not alternative complement pathway. Flow cytometry demonstrated that psP-sel inhibited C1q adherence to sensitized red blood cells. From these data we conclude that sP-sel moderates skeletal muscle reperfusion injury by inhibition of the classical complement pathway.

Complement activation promotes muscle inflammation during modified muscle use

Modified muscle use can result in muscle inflammation that is triggered by unidentified events. In the present investigation, we tested whether the activation of the complement system is a component of muscle inflammation that results from changes in muscle loading. Modified rat hindlimb muscle loading was achieved by removing weight-bearing from the hindlimbs for 10 days followed by reloading through normal ambulation. Experimental animals were injected with the recombinant, soluble complement receptor sCR1 to inhibit complement activation. Assays for complement C4 or factor B in sera showed that sCR1 produced large reductions in the capacity for activation of the complement system through both the classical and alternative pathways. Analysis of complement C4 concentration in serum in untreated animals showed that the classical pathway was activated during the first 2 hours of reloading. Analysis of factor B concentration in untreated animals showed activation of the alternative pathway at 6 hours of reloading. Administration of sCR1 significantly attenuated the invasion of neutrophils (-49%) and ED1(+) macrophages (-52%) that occurred in nontreated animals after 6 hours of reloading. The presence of sCR1 also reduced significantly the degree of edema by 22% as compared to untreated animals. Together, these data show that increased muscle loading activated the complement system which then briefly contributes to the early recruitment of inflammatory cells during modified muscle loading.

Predominant role for C5b-9 in renal ischemia/reperfusion injury

Previous work has indicated that complement is a mediator of ischemia/reperfusion (I/R) injury. To investigate the components of complement responsible for this effect, we examined a model of renal I/R injury in C3-, C4-, C5-, and C6-deficient mice. We occluded the renal arteries and veins (40-58 minutes) and, after reperfusion (0-72 hours), assessed renal structural and functional injury. C3-, C5-, and C6-deficient mice were protected from renal I/R injury, whereas C4-deficient mice were not protected. C6-deficient mice treated with antibody to block C5a generation showed no additional protection from I/R injury. Reconstitution with C6 alone restored the I/R injury in C6-deficient mice. Tubular epithelial cells were the main structures damaged by complement-mediated attack, and, in contrast, the renal vessels were spared. Neutrophil infiltration and myeloperoxidase activity were reduced in C-deficient mouse kidney, but by a similar extent in C3-deficient and C6-deficient mice. We conclude that the membrane attack complex of complement (in which C5 and C6 participate) may account for the effect of complement on mouse renal I/R injury. Neither C5a-mediated neutrophil infiltration nor the classic pathway, in which C4 participates, appears to contribute to I/R injury in this model. By contrast with other organs, such as the heart, the primary effect of complement in the ischemic area is on the parenchymal cell rather than the vascular endothelial cell. The membrane attack complex of complement is a potential target for prevention of I/R injury in this model.

Complement activation induced by ischemia-reperfusion in humans: a study in patients undergoing partial hepatectomy

BACKGROUND/AIM

Activation of the complement system is induced by ischemia-reperfusion (I/R) in animal models. Whether I/R also induces complement activation in humans is not known. Here, we investigated complement activation in patients undergoing major liver resection.

METHODS

In 11 of 17 patients, the hepatoduodenal ligament was clamped, making the liver transiently ischemic (HEMI+; mean ischemia time, 42 +/- 18 min); 6 patients were operated without clamping (HEMI-). Activation at plasma level (circulating activation products) was studied in blood samples collected prior to surgery and 5, 24 and 48 h thereafter. Parameters analyzed were C4b/c and C3b/c, C4d and C3d, C3a, as well as complexes between complement and C-reactive protein (CRP), which reflect CRP-induced complement activation. Activation at tissue level (C3 and C4 fixation) was studied in liver biopsies obtained before and after resection.

RESULTS

In plasma, post-operative levels of C4b/c and C3b/c were not different from baseline levels in both groups. Mean plasma levels of C4b/c and C3b/c were significantly decreased at 24 h post-surgery in the HEMI+ group (p=0.02 and p=0.07). At the same time, levels of C4d-CRP and C3d-CRP were significantly increased (p<0.01 for both parameters). At tissue level, activated complement fragments were observed intracellularly in some pericentral hepatocytes. In I/R livers, large numbers of hepatocytes were positively stained for all complement activation products.

CONCLUSIONS

Our data show that in situ complement activation via the classical route occurred during liver resection and that ischemia and/or reperfusion may have contributed to activation. Levels of complement activation products in the circulation were low, showing that transient ischemia had no severe influence on systemic complement activation, suggesting a locally contained response.

Complement activation after oxidative stress: role of the lectin complement pathway

The complement system plays an important role in mediating tissue injury after oxidative stress. The role of mannose-binding lectin (MBL) and the lectin complement pathway (LCP) in mediating complement activation after endothelial oxidative stress was investigated. iC3b deposition on hypoxic (24 hours; 1% O(2))/reoxygenated (3 hours; 21% O(2)) human endothelial cells was attenuated by N-acetyl-D-glucosamine or D-mannose, but not L-mannose, in a dose-dependent manner. Endothelial iC3b deposition after oxidative stress was also attenuated in MBL-deficient serum. Novel, functionally inhibitory, anti-human MBL monoclonal antibodies attenuated MBL-dependent C3 deposition on mannan-coated plates in a dose-dependent manner. Treatment of human serum with anti-MBL monoclonal antibodies inhibited MBL and C3 deposition after endothelial oxidative stress. Consistent with our in vitro findings, C3 and MBL immunostaining throughout the ischemic area at risk increased during rat myocardial reperfusion in vivo. These data suggest that the LCP mediates complement activation after tissue oxidative stress. Inhibition of MBL may represent a novel therapeutic strategy for ischemia/reperfusion injury and other complement-mediated disease states.

Production and functional analysis of rat CD59 and chimeric CD59-Crry as active soluble proteins in Pichia pastoris

Crry (CR1-related gene/protein) is a rodent complement regulator that inhibits C3 convertases. CD59 is a conserved protein inhibitor active towards C8 and C9. We have previously produced rat Crry as a recombinant soluble (rs) protein in Pichia pastoris. In this study we produced functionally active rat rsCD59 and a chimeric rsCD59-Crry protein in P. pastoris. The GPI anchor addition site of rat CD59 (Asn-79) was replaced either by a stop codon to produce rsCD59, or with the sequence of the first five short consensus repeats of Crry to produce rsCD59-Crry. Proteins were generated by fermentation and purified by affinity chromatography on an anti-CD59 column. In a standard classical pathway haemolysis assay, all three rs proteins had inhibitory activity, with 50% inhibition at 0.5 microM (rsCrry and rsCD59-Crry) and 4.4 microM (rsCD59). In an assay examining inhibition of C5b-9, in which C5b-7 was first formed, followed by purified C8 and C9, rsCD59 and rsCD59-Crry were active with 50% inhibition at 0.8 microM (rsCD59-Crry) and 1.3 microM (rsCD59). The degree of inhibition was independent of whether the C8 and C9 were of rat or human origin. Therefore, we have produced rsCD59 and rsCD59-Crry in P. pastoris. The rsCD59 retains its inhibitory activity towards C5b-9, while rsCD59-Crry appears to have the combined activities of Crry and CD59. In a haemolytic assay, the inclusion of CD59 to Crry is of no additional benefit to Crry, which may illustrate the overall importance of the C3 convertase step. Yet, inclusion of Crry to CD59 increases the potency of CD59 towards C5b-9.

Skeletal muscle reperfusion injury is mediated by neutrophils and the complement membrane attack complex

The relative inflammatory roles of neutrophils, selectins, and terminal complement components are investigated in this study of skeletal muscle reperfusion injury. Mice underwent 2 h of hindlimb ischemia followed by 3 h of reperfusion. The role of neutrophils was defined by immunodepletion, which reduced injury by 38%, as did anti-selectin therapy with recombinant soluble P-selectin glycoprotein ligand-immunoglobulin (Ig) fusion protein. Injury in C5-deficient and soluble complement receptor type 1-treated wild-type mice was 48% less than that of untreated wild-type animals. Injury was restored in C5-deficient mice reconstituted with wild-type serum, indicating the effector role of C5-9. Neutropenic C5-deficient animals showed additive reduction in injuries (71%), which was lower than C5-deficient neutrophil-replete mice, indicating neutrophil activity without C5a. Hindlimb histological injury was worse in ischemic wild-type and C5-deficient animals reconstituted with wild-type serum. In conclusion, the membrane attack complex and neutrophils act additively to mediate skeletal muscle reperfusion injury. Neutrophil activity is independent of C5a but is dependent on selectin-mediated adhesion.

Reduction of myocardial infarct size with sCR1sLe(x), an alternatively glycosylated form of human soluble complement receptor type 1 (sCR1), possessing sialyl Lewis x

1 This study investigated the effects of soluble complement receptor type 1 (sCR1) or sCR1sLex, agents which function as a complement inhibitor or as a combined complement inhibitor and selectin adhesion molecule antagonist, respectively, on the infarct size and cardiac troponin T (cTnT) release caused by regional myocardial ischaemia and reperfusion in the rat. 2 Eighty-two, male Wistar rats were subjected to 30 min occlusion of the left anterior descending coronary artery (LAD) followed by 2 h of reperfusion. Haemodynamic parameters were continuously recorded and at the end of the experiments infarct size (with p-nitro-blue tetrazolium) and cTnT release were determined. 3 Infusion of sCR1 (1, 5 or 15 mg kg-1, each n=7) or sCR1sLe(x) (1, 5 or 15 mg kg-1, n=7, 13 or 13, respectively) 5 min prior to LAD-reperfusion caused a reduction in infarct size from 59+/-2% (PBS - control, n=12) to 46+/-6%, 25+/-9% and 37+/-6% or 42+/-6%, 35+/-6% and 35+/-4%, respectively. 4 Infusion of sCR1 (15 mg kg-1, n=5) or sCR1sLe(x) (15 mg kg-1, n=5) also reduces the myocardial TnT release from 80+/-20 ng ml-1 (control) to 13+/-7 or 4+/-1 ng ml-1, respectively. 5 Thus, sCR1 or sCRsLe(x) significantly reduce infarct size and cardiac TnT release caused by 30 min of regional myocardial ischaemia and 2 h of reperfusion in the rat. The mechanisms of the cardioprotective effects of sCR1 or sCR1sLe(x) are not entirely clear, but may be due complement inhibition and/or prevention of the adhesion and activation of neutrophils.

Complement deposition in early cardiac transplant biopsies is associated with ischemic injury and subsequent rejection episodes

BACKGROUND

Prolonged warm or cold ischemia is associated with poor survival of cardiac transplants, and ischemic changes in early posttransplantation endomyocardial biopsies correlate with the later development of chronic rejection. In animal models, tissue ischemia has been shown to activate complement.

METHODS

To determine whether ischemic changes in endomyocardial biopsies were associated with complement deposition, biopsies obtained 1-3 weeks after transplantation from 33 patients were evaluated immunohistologically for C4d and C3d deposition as well as for IgM, IgG, and IgA. The histological changes associated with ischemic injury were scored independently, using previously reported criteria without knowledge of the immunohistochemical results.

RESULTS

Diffuse capillary and pericapillary deposition of C4d or C3d were detected in endomyocardial biopsies of 14 of the 33 patients. The majority of biopsies (79%) with C4d or C3d deposits had histological evidence of ischemic injury, including eight of the nine biopsies containing both C4d and C3d deposition. In contrast, only 8 of 18 (45%) of the biopsies without C4d or C3d deposition had ischemic injury. Only trace amounts of IgM and no IgG or IgA were demonstrable in the biopsies. Only 2 of the 14 biopsies with C4d or C3d deposition had evidence of moderate acute rejection, whereas 5 of the 18 biopsies without C4d or C3d deposition had moderate acute rejection. However, C4d and C3d deposition did correlate with repeated acute rejection episodes on subsequent biopsies.

CONCLUSIONS

Thus, ischemic changes are associated with the activation of complement. Complement activation may in turn promote tissue injury and provide a potential target for future treatment.

Targeting the complement system

Interest has blossomed in the development of complement inhibitors, in parallel with a growth in our understanding of the biology of the complement cascade. The first generation of designed inhibitors was based on naturally occurring complement receptors and regulatory molecules. These agents provided useful tools for exploring the role of complement in experimental models of disease, but may have limited therapeutic application in humans because of their short half-lives, limited bioavailability and possible antigenicity. More recently, humanized antibodies and synthetic molecules that block the activation of complement have been developed, which look as though they may overcome some of these difficulties. The possibility for precision inhibition of a limited part of the complement cascade, or for inhibition confined to a single organ, may offer effective therapeutic results, while avoiding the disadvantages of nonselective complement blockade. This review examines the recent evidence that complement inhibition will reduce tissue damage resulting from organ transplantation, ischaemia-reperfusion injury, cancer, glomerulonephritis and the use of extracorporeal circuits.

The role of complement in transplantation

The complement system contributes critically to the barrier to transplantation of cells and organs. In the case of tissues and organs transplanted between individuals of the same species, that is in allotransplantation, the barrier posed by complement is seemingly eclipsed by the barrier posed by cellular immune responses. In the case of cells and organs transplanted between individuals of disparate species, that is xenotransplantation, the complement system has been thought to pose a nearly insurmountable barrier. With our understanding on how the complement system contributes to rejection, it is now clear that the complement system is more important in allotransplantation and more forgiving in xenotransplantation than was previously thought.

Strategies for targeting complement inhibitors in ischaemia/reperfusion injury

A transplanted organ suffers inherently from an ischaemic insult and subsequent reperfusion injury. The severity of such early events is thought to influence the success of the transplant procedure, not only in the immediate post-transplant period, but also to predispose the graft to both acute and chronic rejection. In this paper, we review the influence of the complement system upon ischaemia,reperfusion injury. The recognition of the involvement of complement has led to novel strategies to try to modulate ischaemia/reperfusion injury, some of which we have summarized. Finally, we note our own strategy to target complement inhibition in ischaemic tissues.

Antibodies against human heat-shock protein (hsp) 60 and mycobacterial hsp65 differ in their antigen specificity and complement-activating ability

Although complement activation appears to have an important role both in the early and late phases of atherosclerosis, the exact mechanism of the initiation of this activation is still unknown. Since injuries of the endothelial cells are known to result in increased stress-protein expression we tested the complement-activating ability of recombinant human 60 kDa heat-shock protein (hsp60). Human hsp60 was found to activate the complement system in normal human serum in a dose-dependent manner. Activation took place through the classical pathway. The lack of complement activation in agammaglobulinemic serum indicates that the classical pathway is triggered by anti-hsp60 antibodies. Hsp60 activated complement in the sera of 74 patients with coronary heart disease as well, and a strong positive correlation (r = 0.459, P < 0.0001) was found between the extent of complement activation and the level of anti-hsp60 IgG antibodies but there was no correlation to the level of anti-hsp65 IgG antibodies. Further distinction between anti-hsp60 and anti-hsp65 antibodies was obtained from competitive ELISA experiments: binding of anti-hsp60 antibodies to hsp60-coated plates was inhibited only by recombinant hsp60 and vice versa. Our present findings indicate that anti-hsp60 and anti-hsp65 antibodies are distinct, showing only partial cross-reactivity. Since complement activation plays an important role in the development of atherosclerosis and the levels of complement-activating anti-hsp60 antibodies are elevated in atherosclerosis-related diseases, our present findings may have important pathological implications.

Complement activation following oxidative stress

It is clear that complement plays an important role in the inflammatory process following oxidative stress in cellular and animal models. Clinical trials underway with novel complement inhibitors will establish the potential therapeutic benefit of complement inhibition in human disease. For as much as we understand about the role of complement in disease states, many questions remain. How is complement activated on endothelial cells following oxidative stress? What is the ligand for MBL on endothelial cells following oxidative stress? Will inhibition of MBL provide tissue protection to the extent observed with other complement inhibitors such as sCR1 or anti-C5 mAbs? These questions and more will undoubtedly be answered in the next millennium.

Selection of a C5a Receptor Antagonist from Phage Libraries Attenuating the Inflammatory Response in Immune Complex Disease and Ischemia/Reperfusion Injury

A C5a-receptor antagonist was selected from human C5a phage display libraries in which the C terminus of des-Arg74-hC5a was mutated. The selected molecule is a competitive C5a receptor antagonist in vitro and in vivo. Signal transduction is interrupted at the level of G-protein activation. In addition, the antagonist does not cause any C5a receptor phosphorylation. Proinflammatory properties such as chemotaxis or lysosomal enzyme release of differentiated U937 cells, as well as C5a-induced changes in intracellular Ca2+ concentration of murine peritoneal macrophages, are inhibited. The in vivo efficacy was evaluated in three different animal models of immune complex diseases in mice, i.e., the reverse passive Arthus reaction in the peritoneum, skin, and lung. The i.v. application of the C5a receptor antagonist abrogated polymorphonuclear neutrophil accumulation in peritoneum and markedly attenuated polymorphonuclear neutrophil migration into the skin and the lung. In a model of intestinal ischemia/reperfusion injury, i.v. administration of the C5a receptor antagonist decreased local and remote tissue injury: bowel wall edema and hemorrhage as well as pulmonary microvascular dysfunction. These data give evidence that C5a is an important mediator triggering the inflammatory sequelae seen in immune complex diseases and ischemia/reperfusion injury. The selected C5a receptor antagonist may prove useful to attenuate the inflammatory response in these disorders.

Hindlimb ischemia-reperfusion increases complement deposition and glycolysis

BACKGROUND

Hindlimb ischemia-reperfusion (HIR) impairs cellular energy metabolism and causes local muscle injury possibly through free radical or complement-mediated mechanisms.

MATERIALS AND METHODS

To determine the relationship among myocellular energetics, histopathological injury, and mediator activity, male Wistar rats underwent 4 h of Sham (n = 8), Unilateral (n = 8), or Bilateral (n = 8) hindlimb ischemia followed by 4 h of reperfusion. All rats underwent 31P magnetic resonance spectroscopy of their right gastrocnemius muscle to determine various high-energy phosphate ratios including ATP to Pi (ATP/Pi, a measure of energy status) and phosphocreatine to Pi (PCr/Pi, a measure of thermodynamic capacity). Gastrocnemius muscles were then harvested to determine muscle damage and complement membrane attack complex (MAC) deposition by immunohistochemical staining [grade 0 (none) to 3 (very severe)] and to measure glutathione (GSH), DNA, and enzyme activities: beta-hydroxyacyl-CoA dehydrogenase, phosphofructokinase, and citrate synthetase.

RESULTS

HIR was associated with significant declines in ATP/Pi and PCr/Pi (P < 0.001). Progressively more severe HIR (Sham, Unilateral, Bilateral) was associated with greater MAC deposition (0. 0 +/- 0.0, 1.0 +/- 0.3, 1.5 +/- 0.4, P = 0.06, mean +/- SEM) and histological damage (0.0 +/- 0.0, 0.9 +/- 0.3, 1.3 +/- 0.4, P < 0. 05). GSH levels, beta-hydroxyacyl-CoA dehydrogenase, and citrate synthetase activities were not affected by HIR, but phosphofructokinase activity increased (24.09 +/- 2.42, 35.16 +/- 5. 26, 59.29 +/- 9.82 mmol/mg of DNA/min, P < 0.05). Although GSH levels were not significantly altered, complement deposition was closely associated with skeletal muscle injury and compensatory changes in glycolysis. Alterations in myocellular bioenergetics after HIR closely paralleled complement deposition rather than GSH depletion.

CONCLUSIONS

Therapeutic strategies aimed at controlling complement activity and assessment techniques based on bioenergetics may allow more precise determinations of the effects of HIR injury.

Genetic disruption of the murine complement C3 promoter region generates deficient mice with extrahepatic expression of C3 mRNA

Genetic deficiencies of the complement protein C3 occur naturally in humans and animal models and have been induced in mice by targeted deletion of the C3 gene. The study of these deficiencies has provided evidence for C3 functions in immune responses. C3 deficient mice were generated by replacing the 5'-flanking region of the C3 gene with the neomycin-resistance (neo) gene. Serum from these mice had no detectable C3 protein or complement activity. Challenge with Streptococcus pneumoniae revealed approximately 2000-fold increase in bacteremia as compared to littermate controls. C3 mRNA was absent in the liver, but it was detected in the lung, kidney, fat tissue, heart and spleen. Metabolic labeling of the lung tissue and peritoneal macrophages showed synthesis of pro-C3, but no post-synthetic intracellular processing of the protein and no secretion of mature C3. cDNA analysis at the cap site indicated that extrahepatic transcription of the targeted gene was initiated in the neo cassette, close to the C3/neo junction and predicted a primary translation product lacking the leader peptide. The data indicate that these mice provide a good animal model for the study of complete C3 deficiencies and a potential probe for tissue-specific C3 gene regulatory elements.

Recombinant glycoproteins that inhibit complement activation and also bind the selectin adhesion molecules

Soluble human complement receptor type 1 (sCR1, TP10) has been expressed in Chinese hamster ovary (CHO) DUKX-B11 cells and shown to inhibit the classical and alternative complement pathways in vitro and in vivo. A truncated version of sCR1 lacking the long homologous repeat-A domain (LHR-A) containing the C4b binding site has similarly been expressed and designated sCR1[desLHR-A]. sCR1[desLHR-A] was shown to be a selective inhibitor of the alternative complement pathway in vitro and to function in vivo. In this study, sCR1 and sCR1[desLHR-A] were expressed in CHO LEC11 cells with an active alpha(1,3)-fucosyltransferase, which makes possible the biosynthesis of the sialyl-Lewisx (sLex) tetrasaccharide (NeuNAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAc) during post-translational glycosylation. The resulting glycoproteins, designated sCR1sLex and sCR1[desLHR-A]sLex, respectively, retained the complement regulatory activities of their DUKX B11 counterparts, which lack alpha(1-3)-fucose. Carbohydrate analysis of purified sCR1sLex and sCR1[desLHR-A]sLex indicated an average incorporation of 10 and 8 mol of sLex/mol of glycoprotein, respectively. sLex is a carbohydrate ligand for the selectin adhesion molecules. sCR1sLex was shown to specifically bind CHO cells expressing cell surface E-selectin. sCR1[desLHR-A]sLex inhibited the binding of the monocytic cell line U937 to human aortic endothelial cells, which had been activated with tumor necrosis factor-alpha to up-regulate the expression of E-selectin. sCR1sLex inhibited the binding of U937 cells to surface-adsorbed P-selectin-IgG. sCR1sLex and sCR1[desLHR-A]sLex have thus demonstrated both complement regulatory activity and the capacity to bind selectins and to inhibit selectin-mediated cell adhesion in vitro.

A comparison of free radical-induced vascular and skeletal muscle damage in immunocompetent and neutropenic rats

BACKGROUND

Intraarterial infusion of the free radical donor tert. -butyl-hydroperoxide (tert.-BuOOH) into one extremity of the rat induces vascular permeability and considerable skeletal muscle damage. However, it remains unclear what the role of polymorphonuclear neutrophils (PMNs) is in oxidative stress-related processes. Therefore, we investigated possible differences between neutropenic and normal animals in this model.

METHODS

Neutropenia was induced in male rats by intraperitoneal administration of cyclophosphamide. tert.-BuOOH was continuously infused intraarterially into one hindlimb of normal or neutropenic nonanesthetized rats for 24 h. The control neutropenic rats were infused with the same volume of saline. After the infusion, 99mTc-IgG was administered intravenously followed by scintigraphic imaging analysis of the left/right uptake ratio of the hindlimbs and by gamma counting of the tissue samples of the gastrocnemius and gluteus maximus muscles. Samples of these muscles were analyzed by light microscopy.

RESULTS

The uptake ratios were significantly increased in the normal and neutropenic tert.-BuOOH-infused animals as compared with the saline-infused neutropenic rats (P < 0.05). The uptake ratios were significantly higher in normal than in neutropenic tert.-BuOOH-infused rats (P < 0.05). Histological analysis of the saline infused skeletal muscles showed unaffected skeletal muscles with intact arterioles and arteries. In the gastrocnemius and gluteus maximus muscles of the normal tert. -BuOOH-infused and neutropenic rats, similar morphological damage was observed.

CONCLUSIONS

PMNs can increase, to some extent, the vascular permeability of the free radical damaged small arteries and arterioles of a tert.-BuOOH-infused hindlimb. However, in the present animal model, tert.-BuOOH alone can induce oxidative stress-related abnormalities with skeletal muscle tissue damage that is mainly independent of the presence of PMNs.

Intestinal reperfusion injury is mediated by IgM and complement

Intestinal ischemia-reperfusion injury is dependent on complement. This study examines the role of the alternative and classic pathways of complement and IgM in a murine model of intestinal ischemia-reperfusion. Wild-type animals, mice deficient in complement factor 4 (C4), C3, or Ig, or wild-type mice treated with soluble complement receptor 1 were subjected to 40 min of jejunal ischemia and 3 h of reperfusion. Compared with wild types, knockout and treated mice had significantly reduced intestinal injury, indicated by lowered permeability to radiolabeled albumin. When animals deficient in Ig were reconstituted with IgM, the degree of injury was restored to wild-type levels. Immunohistological staining of intestine for C3 and IgM showed colocalization in the mucosa of wild-type controls and minimal staining for both in the intestine of Ig-deficient and C4-deficient mice. We conclude that intestinal ischemia-reperfusion injury is dependent on the classic complement pathway and IgM.

Hypoxia-induced expression of complement receptor type 1 (CR1, CD35) in human vascular endothelial cells

Reoxygenation of hypoxic human umbilical vein endothelial cells (HUVECs) increases protein expression of the complement regulators CD46 and CD55. As the receptor for C3b is known to be present on injured bovine endothelial cells, we investigated whether hypoxia or inflammatory mediators induce complement receptor type 1 (CR1; CD35) expression on HUVECs. CR1 protein expression increased 3.7 +/- 0. 6-fold as measured by ELISA on HUVECs following hypoxia (48 h, 1% O2). Colocalization of CD35 and von Willebrand factor by confocal microscopy confirmed that CD35 was predominantly intracellular. Lipopolysaccharide or tumor necrosis factor-alpha also significantly increased HUVEC CR1 protein expression. Western blot analysis of neutrophil or hypoxic HUVEC lysates revealed a 221-kDa CR1 band under nonreducing conditions. RT-PCR of hypoxic HUVEC mRNA revealed a single band that, after sequencing, was identified as CD35. In situ hybridization of hypoxic HUVECs, but not normoxic HUVECs or fibroblasts, demonstrated increased CD35 mRNA. Hypoxic HUVECs bound immune complexes and acted as a cofactor for factor I-mediated cleavage of C3b. Thus hypoxia induces functional HUVEC CR1 expression.

Lower limb oedema following distal arterial bypass grafting

Lower-limb oedema following arterial bypass surgery for ischemia is a common sequela which can complicate wound healing or delay resumption of mobility. Its exact pathogenesis remains uncertain but many theories have been proposed. Lymphatic disruption during arterial exposure, and endothelial damage from atrophy of the media and oxygen-derived free radical release are currently favoured hypotheses. Infrequently, deep vein thrombosis follows surgery and may exacerbate the condition. Efforts aimed at reducing the oedema, such as the use of lymphatic preserving incisional approaches or the use of antioxidants, have given conflicting results. The use of compression hosiery and leg elevation appear to be the most effective measures in reducing postoperative lower limb oedema.

Complement C6 deficiency protects against diet-induced atherosclerosis in rabbits

Low-density lipoprotein (LDL) can be transformed to an atherogenic moiety by nonoxidative, enzymatic degradation. Enzymatically degraded LDL induces macrophage foam cell formation, provokes release of cytokines, and also activates complement. To determine whether complement activation may contribute to atherogenesis, 6 pairs of homozygous C6-deficient rabbits and their non-C6-deficient heterozygous siblings were fed a cholesterol-rich diet for 14 weeks. Cholesterol levels and plasma lipoprotein profiles of the animals in the C6-competent and C6-deficient groups did not significantly differ, and the high density lipoprotein and LDL cholesterol ratios at the end of the experiment were 0.07+/-0.01 and 0.08+/-0.01 (SEM), respectively. However, differences in atherosclerotic plaque formation were discernible macroscopically, with extensive aortic lesions being visible in all C6-competent animals and absent in all C6-deficient animals. Aortas were sectioned from thorax to abdomen, and 10 sections were stained from each aorta. Quantification of atherosclerotic lesions and lumen stenosis with the use of computer-based morphometry documented a dramatic protective effect of C6 deficiency on the development of diet-induced atherosclerosis. We conclude that the terminal complement sequence is centrally involved in atherosclerotic lesion progression.

The role of complement and complement receptors in induction and regulation of immunity

Covalent attachment of activated complement C3 (C3d) to antigen links innate and adaptive immunity by targeting antigen to follicular dendritic cells (FDC) and B cells via specific receptors CD21 and CD35. Recent characterization of knockout mice deficient in complement components C3, C4, or the receptors CD21 and CD35 as well as biochemical studies of the CD21/CD19/Tapa-1 coreceptor on B cells have helped to elucidate the mechanism of complement regulation of both B-1 and B-2 lymphocytes. Interestingly, natural antibody of the adaptive immune system provides a major recognition role in activation of the complement system, which in turn enhances activation of antigen-specific B cells. Enhancement of the primary and secondary immune response to T-dependent antigens is mediated by coligation of the coreceptor and the B cell antigen receptor, which dramatically increases follicular retention and B cell survival within the germinal center. Most recent evidence suggests that complement also regulates elimination of self-reactive B cells, as breeding of mice that are deficient in C4 or CD21/CD35 with the lupus-prone strain of lpr mice demonstrates an exacerbation of disease due to an increase in autoantibodies.

Complement activation following reoxygenation of hypoxic human endothelial cells: role of intracellular reactive oxygen species, NF-kappaB and new protein synthesis

Complement plays an important role in ischemia-reperfusion injury. We recently demonstrated that reoxygenation of hypoxic human umbilical vein endothelial cells (HUVECs) activated the classical complement pathway and augmented iC3b deposition. In the present study, we investigated the potential role of oxygen-derived free radicals, NF-kappaB and new protein synthesis in this model. HUVECs subjected to 12 or 24 h hypoxic stress (1% O2) and then reoxygenated (0.5, 1, 2 or 3 h; 21% O2) in 30% human serum activated complement and deposited iC3b. Addition of hydrogen peroxide (H2O2; 1-100 micromol/l) to normoxic HUVECs increased iC3b deposition in a concentration-dependent manner. H2O2 (10 micromol/l), a concentration that did not significantly increase iC3b deposition on normoxic HUVECs, augmented iC3b deposition on hypoxic/reoxygenated HUVECs. We observed a significant increase in intracellular H2O2 and hydroxyl radical (OH.) production in hypoxic/reoxygenated HUVECs using dihydrorhodamine 123. Further, treatment of HUVECs with dimethylthiourea (DMTU, 1-100 micromol/l), deferoxamine (DEF, 1-100 micromol/l), or oxypurinol (10 micromol/l), but not superoxide dismutase (SOD, 500 U/ml), catalase (300 U/ml) or iron-loaded DEF, attenuated iC3b deposition following hypoxia/reoxygenation in a concentration-dependent manner. Western analysis demonstrated hypoxia-induced nuclear NF-kappaB translocation that increased with reoxygenation. Inhibition of new protein synthesis (i.e. cycloheximide) or inhibition of NF-kappaB (ALLN or SN-50) also significantly decreased iC3b deposition on hypoxic/reoxygenated HUVECs. We conclude that (1) hypoxic/reoxygenated HUVECs generate H2O2 and OH.; (2) treatment of HUVECs with cell permeable reactive oxygen species inhibitors/scavengers (i.e. DEF, DMTU, oxypurinol) but not large molecular weight inhibitors (i.e. catalase or SOD) significantly reduces iC3b deposition and (3) inhibition of new protein synthesis or NF-kappaB activation attenuates iC3b deposition. These data suggest that iC3b deposition on the vascular endothelium may be regulated by intracellular oxygen-derived free radical-induced activation of NF-kappaB, new protein synthesis and activation of the classical complement pathway during ischemia/reperfusion.

Linkages of innate and adaptive immunity

The innate immune system is activated by pathogens or environmental antigens following their binding by recognition molecules such as mannan-binding lectin, C-reactive protein and the mannose receptor. Natural antibody, which represents a collection of germline-encoded antigen recognition molecules, is also important in recognition of pathogens and activation of the innate immune system via the classical pathway of complement activation. The major source of natural antibody is CD5+ B-1 cells which differ from conventional B cells (B-2 cells) firstly because they are thought to require contact with antigen for expansion and maintenance and secondly because in general they do not appear to undergo somatic hypermutation. We review results which support an important role for complement in maintenance of B-1 cells, the effect being mediated by B cell expression of complement receptors CD21 and CD35. We propose that complement and natural antibody are interdependent: clonal selection and expansion of CD5+ B-1 cells is dependent on contact with antigen coated by the complement component C3d, while efficient recognition of pathogens and activation of complement is dependent in a large part on natural antibody. This hypothesis is supported by the finding that mice deficient in CD21 and CD35 have a reduced number of CD5+ B-1 cells and are missing specificities for certain antigens commonly found in wild-type mice, such as lipopolysaccharide, Escherichia coli surface antigens and neoepitopes expressed on hypoxic intestinal endothelium.

Acidosis activates complement system in vitro

We investigated the in vitro effect of different forms of acidosis (pH 7.0) on the formation of anaphylatoxins C3a and C5a. Metabolic acidosis due to addition of hydrochloric acid (10 micromol/ml blood) or lactic acid (5.5 micromol/ml) to heparin blood (N=12) caused significant activation of C3a and C5a compared to control (both p=0.002). Respiratory acidosis activated C3a (p=0.007) and C5a (p=0.003) compared to normocapnic controls. Making blood samples with lactic acidosis hypocapnic resulted in a median pH of 7.37. In this respiratory compensated metabolic acidosis, C3a and C5a were not increased. These experiments show that acidosis itself and not lactate trigger for activation of complement components C3 and C5.

Experimental murine acid aspiration injury is mediated by neutrophils and the alternative complement pathway

Acid aspiration may result in the development of the acute respiratory distress syndrome, an event associated with significant morbidity and mortality. Although once attributed to direct distal airway injury, the pulmonary failure after acid aspiration is more complex and involves an inflammatory injury mediated by complement (C) and polymorphonuclear leukocytes. This study examines the injurious inflammatory cascades that are activated after acid aspiration. The role of neutrophils was defined by immunodepletion before aspiration, which reduced injury by 59%. The injury was not modified in either P- or E-selectin-knockout mice, indicating that these adhesion molecules were not operative. C activation after aspiration was documented with immunochemistry by C3 deposition on injured alveolar pneumocytes. Animals in which C activation was inhibited with soluble C receptor type 1 (sCR1) had a 54% reduction in injury, similar to the level of protection seen in C3-knockout mice (58%). However C4-knockout mice were not protected from injury, indicating that C activation is mediated by the alternative pathway. Finally, an additive effect of neutrophils and C was demonstrated whereby neutropenic animals that were treated with sCR1 showed an 85% reduction in injury. Thus acid aspiration injury is mediated by neutrophils and the alternative C pathway.

Soft tissue repair capacity after oxygen-derived free radical-induced damage in one hindlimb of the rat

Oxygen-derived free radicals are suspected to play an important role in the pathogenesis of inflammation and ischemia/reperfusion of an extremity. In this study we investigated the repair capacity of a free radical-damaged hindlimb of the rat and the effect of the anti-oxidant N-acetyl-L-cysteine (NAC). In nonanesthetized rats (n = 39), the left hindlimb was continuously infused intra-arterially (1 ml/hr) for 24 hr with the free radical donor tert-butylhydroperoxide (tert-BuOOH, 25 mM). Subsequently the infusion system was disconnected and the repair of soft tissue damage was observed with special attention to various pain tests, vascular permeability ((99m)Tc-IgG scintigraphy), and histology for a maximum period of 6 weeks. In 12 of these tert-BuOOH-infused rats the antioxidant NAC was injected intraperitoneally. Six of the NAC-treated rats were killed after 24 hr of infusion, while the remaining 6 rats were disconnected, reinjected with NAC, and observed for 1 week. Tert-BuOOH infusion for 24 hr led to significantly increased pain sensations, vascular permeability, and histological damage. Treatment with NAC significantly reduced pain sensations and vascular permeability, though not to control levels. One week after disconnection, tissue damage was almost completely repaired in the NAC-treated rats. In the untreated rats, repair took longer but histology and vascular permeability were completely normalized within the observation period. Soft tissue damage, induced by 24-hr infusion of the free radical donor tert-BuOOH, showed spontaneous repair within 6 weeks. The antioxidant NAC significantly reduced the soft tissue damage and shortened the repair period.

Attenuation of acute lung injury caused by hind-limb ischemia-reperfusion injury by butyrolactone anti-inflammatory agent FL1003

OBJECTIVE

Activation of systemic inflammation after reperfusion of ischemic tissue results in severe acute lung injury. Neutrophil activation and oxygen radical generation have been implicated in the pathogenesis. This study tested the hypothesis that treatment with FL1003, a butyrolactone with in vitro antioxidant properties, will down-regulate this response and abrogate acute lung injury.

METHODS

Male Sprague-Dawley rats (n = 16) were divided into a surgical sham group (n = 4), a group that received 2 hours of ischemia by infrarenal aortic clip followed by 1 hour of reperfusion (n = 7), and an ischemia-reperfusion (I/R) group that received FL1003 100 mg/kg intravenously before ischemia (n = 5). After reperfusion, the heart and lungs were excised en bloc in an isolated lung perfusion apparatus for 1.5 hours of perfusion, while pulmonary artery pressures were held between 5 and 12 mm Hg and venous effluent was collected. Bronchoalveolar lavage fluid and both lungs were harvested at death for determination of tissue water content, pulmonary microvascular permeability, and indicators of neutrophil activation and tissue oxidation.

RESULTS

After I/R, there were significant (p < 0.05) increases in intravenous fluid (IVF) requirements (18 +/- 1.2 mL) to maintain hemodynamic stability, wet weight/dry weight ratio of lung tissue, and isolated-lung lavage Ficoll concentrations (0.58 +/- 0.02 microg/mL) compared with sham animals (IVF, 0 mL; Ficoll concentration, 0.08 +/- 0.03 microg/mL). In addition, lung myeloperoxidase activity (0.60 +/- 0.03 vs. 0.12 +/- 0.02 units/g of tissue) and levels of lipid-conjugated dienes (0.042 +/- 0.012 vs. 0.018 +/- 0.006 optical density of 233 nm (OD233)/mL) were significantly higher (p < 0.05) compared with the sham group. In I/R animals treated with FL1003, the IVF requirement (8.5 +/- 1.0 mL), wet weight/dry weight ratio, lung tissue Ficoll concentration (0.21 +/- 0.02 microg/mL), myeloperoxidase concentration (0.217 +/- 0.02 units/g), and lipid-conjugated diene levels (0.012 +/- 0.005 OD233/ mL) were all significantly lower (p < 0.05) than after untreated I/R.

CONCLUSION

A pulmonary microvascular permeability defect with pulmonary edema, neutrophil aggregation, and cell membrane damage resulted from ischemia and reperfusion. Treatment of animals with FL1003 significantly attenuated the inflammatory response associated with acute lung injury.

Reoxygenation of hypoxic human umbilical vein endothelial cells activates the classic complement pathway

BACKGROUND

Ischemia-reperfusion injury leads to the activation and endothelial deposition of complement. We investigated whether exposure of human umbilical vein endothelial cells (HUVECs) to hypoxia and/or reoxygenation activates complement and decreases HUVEC-surface expression of the C3 regulatory proteins CD46 and CD55.

METHODS AND RESULTS

HUVECs were subjected to 0, 12, or 24 hours of hypoxia (O2 = 1%) and then reoxygenated for 3 hours (O2 = 21%) in the presence of 30% human serum. C3 deposition and HUVEC-surface expression of CD46 and CD55 were evaluated by ELISA and flow cytometry. C3 deposition on HUVECs subjected to 12 or 24 hours of hypoxia followed by 3 hours of reoxygenation was significantly greater than normoxic HUVECs. Inhibition of the classic but not the alternative complement pathway during reoxygenation attenuated C3 deposition. Western blot analysis of HUVEC lysates under reducing conditions demonstrated significantly increased iC3b deposition in hypoxic/reoxygenated HUVECs compared with normoxic HUVECs. FACS analysis confirmed iC3b deposition. HUVEC-surface expression of CD46 and CD55 increases after hypoxia and/or reoxygenation.

CONCLUSIONS

We conclude that (1) hypoxia and reoxygenation of HUVECs significantly increases iC3b deposition on HUVECs, (2) C3 deposition after hypoxia and reoxygenation is largely mediated by the classic complement pathway, and (3) HUVEC-surface expression of CD46 and CD55 increases after hypoxia and reoxygenation. These data demonstrate that hypoxia and reoxygenation of human endothelial cells activates the classic complement pathway despite an increase in complement C3 regulatory proteins.

Effect of graft preservation and IgM depletion on guinea pig to rat cardiac xenograft survival

BACKGROUND

Heterotopic guinea pig (GP) cardiac xenografts (XG) are hyperacutely rejected within minutes when transplanted into rats.

METHODS

In this GP to rat cardiac XG model, we studied the effect on graft survival of a short cold preservation time (1 hr at 4 degrees C) in the presence or absence of rat anti-GP IgM preformed antibodies. The complete depletion of circulating IgM was obtained by two intraperitoneal injections of anti-rat IgM monoclonal antibody (MARM-4) on preoperative days -3 and -1.

RESULTS

When the GP cardiac XG was cold preserved for 1 hr before transplantation, the mean graft survival time (MST) was 13.5+/-2.8 min, whereas without previous cold preservation, the MST was significantly prolonged to 51.5+/-12.3 min (P<0.001). Interestingly, the complete depletion of preformed circulating IgM before grafting significantly prolonged the MST of a cold-preserved XG to 37.1+/-11.3 min in comparison with a nondepleted recipient of a cold-preserved XG (P<0.02), but did not prolong the graft survival of a XG that was not cold preserved (42.5+/-14.1 min). To assess the effect of cold preservation and/or ischemia reperfusion, we intravenously injected a superoxide-dismutase mimetic (EUK-134) just before transplantation of a cold-preserved XG. This antioxidant regimen improved the MST from 13.5+/-2.8 min to 35.3+/-7.3 min (P<0.001). These results clearly suggested that either preservation lesions or preformed IgM are capable of accelerating the loss of the cardiac graft function, but also that the presence of preformed IgM seems to be especially deleterious when the cardiac XG has previously been ischemically injured. Analyzing the histological data, we also observed that the prompt cessation of cardiac function seen in cold-preserved grafts was uniformly associated with massive interstitial hemorrhage, thereby suggesting a particular susceptibility of the GP cardiac XG to cold preservation. To assess the effect of preservation on the GP cardiac function in a nonimmunological model, we performed syngeneic GP cardiac grafts and found that 1 hr of cold preservation provoked massive interstitial hemorrhage capable of promptly inducing the cessation of the heartbeat.

CONCLUSIONS

Overall, this study demonstrated that both ischemic lesions and immunological processes might induce the cessation of cardiac graft function in the GP to rat model and this cessation of graft function is probably often misinterpreted as a XG rejection only.

The cytokine-adhesion molecule cascade in ischemia/reperfusion injury of the rat kidney. Inhibition by a soluble P-selectin ligand

Ischemia/reperfusion (I/R) injury associated with renal transplantation may influence both early graft function and late changes. The initial (</= 7 d) events of warm and in situ perfused cold ischemia of native kidneys in uninephrectomized rats were examined. mRNA expression of the early adhesion molecule, E-selectin, peaked within 6 h; PMNs infiltrated in parallel. T cells and macrophages entered the injured kidney by 2-5 d; the associated upregulation of MHC class II antigen expression suggested increased immunogenicity of the organ. Th1 products (IL-2, TNFalpha, IFNgamma) and macrophage-associated products (IL-1, IL-6, TGFbeta) remained highly expressed after 2 d. To examine directly the effects of selectins in I/R injury, a soluble P-selectin glycoprotein ligand (sPSGL) was used. Ischemic kidneys were perfused in situ with 5 microg of sPSGL in UW solution; 50 microg was administered intravenously 3 h after reperfusion. E-selectin mRNA remained at baseline, leukocytes did not infiltrate the injured organs throughout the 7-d period, and their associated products were markedly inhibited. Class II expression did not increase. No renal dysfunction secondary to I/R occurred. The early changes of I/R injury may be prevented by treatment with soluble P- and E-selectin ligand. This may reduce subsequent host inflammatory responses after transplantation.

Dexamethasone treatment does not ameliorate subglottic ischemic injury in rabbits

BACKGROUND

Following tracheal intubation, a small proportion of patients develop laryngeal inflammation or tissue necrosis severe enough to result in clinical symptoms. Although corticosteroids are frequently advocated to prevent such injury, human studies have been inconclusive because of the low incidence of the problem. This study developed a rabbit model of endotracheal tube-induced laryngeal injury to test the hypothesis that a corticosteroid, dexamethasone, could ameliorate the inflammation and necrosis.

METHODS

Subglottic injury was induced in 21 anesthetized rabbits by inflating the cuff of an endotracheal tube to 100 mm Hg with the cuff just below the vocal cords. Every 30 min for 2 h, the cuff was deflated, the tube turned 90 degrees, and the cuff then reinflated. After 2 h, the rabbits' tracheas were extubated. Rabbits were divided into two groups: the treatment group received dexamethasone (1 mg/kg) i.v. 1 h prior to extubation with the dose repeated 6 h following extubation; the untreated group received a saline solution placebo. Four additional rabbits were anesthetized for the same period but did not have a tracheal tube inserted. All rabbits were killed 24 h later and the larynxes were harvested. Sections through the larynx at the level of the cricoid cartilage were randomized and submitted blindly to a veterinary pathologist. Larynxes were scored and ranked according to the severity of mucosal inflammation and necrosis, and submucosal hemorrhage, edema, inflammation, and necrosis. Specimens were also evaluated for focal vs diffuse disease.

RESULTS

Injured rabbits demonstrated focal to diffuse mucosal and submucosal inflammation and necrosis. Inflammatory exudates were present in sections from most of the injured rabbits and large sections of the larynxes were denuded of epithelium. There were no differences in injury scores between the treated and untreated rabbits. The four uninjured control rabbits had normal larynxes.

CONCLUSIONS

Two hours of endotracheal tube cuff inflation to 100 mm Hg causes an inflammatory laryngeal injury. The histologic features of the injury are unaltered by treatment with 2 mg/kg dexamethasone.

A novel animal model to evaluate oxygen derived free radical damage in soft tissue

We present a novel animal model which allows the continuous intra-arterial infusion in one hindlimb of non-anaesthetized rats, without inducing ischemia. Using this model the effect of continuous infusion (1 ml/h) for 24 h with tert-butylhydroperoxide (tert-BuOOH) at a concentration of 25 mM on soft tissue of the left hind limb was studied and compared to the effect of saline infusion (control group). The tert-BuOOH-infused foot showed increased skin temperature, increased circumference, redness of the plantar skin, impaired function and increased pain sensation, while in the contralateral foot and in rats only perfused with saline these signs of inflammation were absent (p < 0.01). Histological analysis of the left gastrocnemius muscle showed edema, muscle cell degeneration with a patchy distribution pattern and vascular damage. All these features increased in severity from 4 to 24 h tert-BuOOH infusion. After 24 h of tert-BuOOH infusion infiltration of neutrophils in the interstitium was observed. Vascular permeability, expressed as left to right gastrocnemius muscle 99mTc-IgG uptake ratio, was similarly increased after 4 h (2.09 +/- 0.26) and 12 h (2.04 +/- 0.08) of tert-BuOOH infusion compared to saline (1.05 +/- 0.08) (p < 0.001), and further increased after 24 h (3.84 +/- 0.13): (p < 0.001). In this animal model free radical-related soft tissue damage was induced, by continuous infusion of tert-BuOOH, followed by increasing necrosis and vascular permeability in skeletal muscle coinciding with neutrophilic infiltration.

Intracoronary application of C1 esterase inhibitor improves cardiac function and reduces myocardial necrosis in an experimental model of ischemia and reperfusion

BACKGROUND

Myocardial injury from ischemia can be aggravated by reperfusion of the jeopardized area. The precise underlying mechanisms have not been clearly defined, but proinflammatory events, including complement activation, leukocyte adhesion, and infiltration and release of diverse mediators, probably play important roles. The present study addresses the possibility of reducing reperfusion damage by the application of C1 esterase inhibitor (C1-INH).

METHODS AND RESULTS

Cardioprotection by C1-INH 20 IU/kg IC was examined in a pig model with 60 minutes of coronary occlusion, followed by 120 minutes of reperfusion. C1-INH was administered during the first 5 minutes of coronary reperfusion Compared with the NaCl controls, C1-INH reduced myocardial injury (48.8 +/- 7.8% versus 73.4 +/- 4.0% necrosis of area at risk, P < or = .018). C1-INH treatment significantly reduced circulating C3a and slightly attenuated C5a plasma concentrations. Myocardial protection was accompanied by reduced plasma concentration of creatine kinase and troponin-T. C1-INH had no effect on global hemodynamic parameters, but local myocardial contractility was markedly improved in the ischemic zone. In the short-axis view, 137 degrees of the anteroseptal region showed significantly improved wall motion at early and 29 degrees at late reperfusion with C1-INH treatment.

CONCLUSIONS

C1-INH significantly protects ischemic tissue from reperfusion damage, reduces myocardial necrosis, and improves local cardiac function.