PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “complement C3 inhibitor”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMedDate not supplied

[Determination of proteinase activity of complement system by immunoenzyme methods].

Modern ELISA for determination of functional activity of component C2 and factors B and D, proteinases of a complement system, and component C3, substrate C3-convertases, key complex enzymes of the complement, have been developed. Essential feature of C3-convertases classical (C4bC2a) and alternative (C3bBb) pathways of the complement activation is that their substrate C3 after proteolytic cleavage is converted into C3b, carrying on the surface thioester covalent bond linking C3b with nucleophilic acceptors that results in immobilization of this proteolytic product near the activating enzyme. Cascade character of an activation of complement system allows to create artificial deficit of separate components in the experimental system and to determine (by ELISA) covalently immobilized component C3 during activation, and also to determine functional activity of any of pre-exhausted components. Use of such approach resulted in the development of the ELISA systems suitable for determination of functional activity of component C2 of classical pathway and factors B and D of the alternative pathway by testing quantity of the immobilized C3b at excess C3. The developed methods allow to investigate mechanisms of functioning of complement, inhibition of the cascade activation by endogenic and exogenous inhibitors, and also to find functional deficiency of components in serum and other biological fluids.

Animals↗
PubMed1999

Role of complement regulatory membrane proteins in ischaemia-reperfusion injury of rat gastric mucosa.

BACKGROUND: The role of complement in ischaemia-reperfusion injury has not been well investigated. 5I2 is a monoclonal antibody (mAb) directed against a rat membrane inhibitor of the C3 convertase step, which is the rat counterpart of mouse Crry/p65. 6D1 is a mAb against rat CD59 which inhibits the formation of membrane attack complexes. METHODS: We visualized the tissue distribution of these membrane inhibitors in rat gastrointestinal tract by immunohistochemical staining with the appropriate mAb. Then, we tested the hypothesis that complement regulatory proteins protect rat gastric mucosa against ischaemia-reperfusion stress by using these mAbs. Gastric mucosal integrity was continuously monitored by measuring the blood-to-lumen clearance of [51Cr]-labelled ethylenediaminetetraacetic acid (EDTA) under control conditions, during ischaemia and after reperfusion. RESULTS: Rat 6D1 and 5I2 antigens were both widely distributed and predominantly expressed on smooth muscle and endothelial cells in gastrointestinal tracts. Blockade of complement regulatory proteins with 5I2 and 6D1 mAbs resulted in a significant increase in [51Cr]-EDTA clearance after reperfusion. CONCLUSIONS: These findings support the hypothesis that endogenous complement regulatory proteins may act as important protective factors against ischaemia-reperfusion stress in rat gastric mucosa.

Animals↗
PubMed1989

Accelerated nonproteolytic cleavage of C3 in plasma from patients with primary biliary cirrhosis.

Complement 3 (C3) with decreased net charge and altered immunoreactivity was detected by crossed immunoelectrophoresis when EDTA plasma from patients with primary biliary cirrhosis was incubated in vitro after reconstitution with Ca++ and Mg++. The alpha and beta chains of this C3 were intact. C3 with decreased net charge was not detected in patients' fresh plasma. Similar C3 alterations were obtained after reaction between native C3 in serum from healthy persons or purified C3 nucleophiles that induce cleavage of the single thioester bond in the alpha chain of C3. This C3 alteration was unchanged when the reaction occurred in the presence of protease inhibitors. The electrophoretically slow C3 fraction was labile in serum on further proteolytic cleavage of C3. It is suggested that accelerated nonproteolytic C3 cleavage in patients with primary biliary cirrhosis facilitates subsequent binding of C3 to C3b receptors and targets of complement attack.

Calcium↗
PubMedDate not supplied

Changes in complement and coagulation factors in a patient suffering a severe anaphylactoid reaction to injected contrast material: some considerations of pathogenesis.

A patient, suffering a severe anaphylactoid reaction to contrast material injected for an intravenous pyelogram, developed a consumption coagulopathy and evidence of complement activation. Precontrast complement values suggested that the patient had been processing complement via the classical pathway, perhaps as a consequence of an earlier protracted Klebsiella infection. Following contrast injection, a precipitous fall in hemolytic complement (CH50) and in the concentration of the C1 esterase inhibitor (C1INH) developed, as well as a diminution in C4 and C3 with the evolution of C3 conversion products. The possible role that these changes might play in the pathogenesis of idiosyncratic reactions to contrast media is considered.

Adult↗
PubMed2000

Inhibition of heparin/protamine complex-induced complement activation by Compstatin in baboons.

Complement activation products are major components of the inflammatory response induced by cardiac surgery and cardiopulmonary bypass which contribute to postoperative organ dysfunction, fluid accumulation, and morbidity. Activation of the complement system occurs during extracorporeal circulation, during reperfusion of ischemic tissue, and after the formation of heparin-protamine complexes. In this study we examine the efficacy of Compstatin, a recently discovered peptide inhibitor of complement, in preventing heparin/protamine-induced complement activation in baboons. The study was performed in baboons because Compstatin binds to baboon C3 and is resistant to proteolytic cleavage in baboon blood (similar to humans); Compstatin inhibits only the activation of primates' complement system. After testing various doses and administration regimens, Compstatin produced complete inhibition at a total dose of 21 mg/kg when given as a combination of bolus injection and infusion. Compstatin completely inhibited in vivo heparin/protamine-induced complement activation without adverse effects on heart rate or systemic arterial, central venous, and pulmonary arterial pressures. This study indicates that Compstatin is a safe and effective complement inhibitor that has the potential to prevent complement activation during and after clinical cardiac surgery. Furthermore, Compstatin can serve as the prototype for designing an orally administrated drug.

Animals↗
PubMed1998

A novel ELISA for the evaluation of the classical pathway of complement.

Assessment of the overall function of the classical pathway of complement is traditionally performed by the hemolytic titration assay CH50. In the present study, we established a novel method for the quantitation of complement activity by measuring the deposition of C1q, C4, C3 and C9 on solid-phase IgM by an enzyme-linked immunosorbent assay (ELISA). Using the CH50 method as the reference, C9 deposition values displayed a sensitivity of 96.3% and a specificity of 99.4% in sera from patients with a variety of diseases. For C3, the sensitivity was 91.3% and the specificity 100%, for C4, the values were 95% and 100%, and for C1q the corresponding values were 52.9% and 98.9%. A close correlation was found between CH50 values below 30 U/ml and the deposition of C9 (r = 0.92), C3 (r = 0.91) and C4 (r = 0.92). In two patients with postinfectious glomerulonephritis normal C4 and C1q deposition was accompanied by decreased C3 and C9 deposition reflecting complement activation predominantly through the alternative pathway. In contrast, in two patients with complete C2 deficiency the deposition of C3 and C9 was undetectable together with normal C4 deposition values. Furthermore, in two patients with hereditary C1-inhibitor deficiency distinctly increased C1q deposition was accompanied by decreased C4 deposition values. In conclusion, the determination of complement deposition by ELISA represents a novel, quantitative method for the evaluation of complement activity. The measurement of C9 deposition alone or in combination with further complement proteins makes this ELISA a valuable tool for assessing the degree and level of complement consumption as well as localizing the missing protein in the case of complement deficiencies.

Complement C1q↗
PubMedDate not supplied

Activation of the complement pathway: comparison of normal pregnancy, preeclampsia, and systemic lupus erythematosus during pregnancy.

To evaluate a flare of systemic lupus erythematosus (SLE) during pregnancy and to differentiate it from diseases of pregnancy, serological parameters are often utilized. However, there are conflicting reports regarding the merit of conventional measurements of complement and activation products. While in normal pregnancy the levels of serum C3, C4, and CH50 gradually rise, a decline in these levels occurs during the course of pregnancy in selected SLE patients. There is controversy regarding whether such falls represent decreases in the overall synthesis of complement or activation, the former theory being supported by a report of normal levels of the C1s-C1 inhibitor complex. During normal pregnancies, increases of complement split products, such as plasma C3a, may occur, and these correlate positively with elevations of C3. In pregnancies complicated by lupus, increases of C3a are often accompanied by a decline in total C3 and CH50. In a minority of non-SLE patients, preeclampsia has been associated with elevations of a variety of complement split products. Ba, C3a, C4d, SC5b-9, indicating activation of both the classical and alternative pathways. The CH50 levels tend to remain normal in these patients. In contrast, elevations of complement split products frequently accompany disease flares in patients with SLE. A high ratio of CH50/Ba may differentiate patients with preeclampsia from those with active SLE. A decline in conventional measures of C3, C4, or CH50 which is accompanied by elevations of complement split products appears to differentiate a lupus flare from non-SLE diseases of pregnancy.

Complement Activation↗
PubMed1984

Inhibition of immune precipitation by complement.

Normal human complement serum (NHS) inhibited precipitin reactions between tetanus toxoid and human or rabbit anti-tetanus toxoid IgG antibody, between bovine serum albumin (BSA) and rabbit anti-BSA IgG antibody, and between hen egg albumin and rabbit anti-egg albumin IgG antibody. Ethylene-diaminetetraacetic acid (EDTA) prevented this inhibition. Mg-ethyleneglycol-bis(aminoethyl)-tetra-acetic acid-(EGTA) also prevented the inhibition except with lower concentrations of antibody and antigen. Therefore, the inhibition of immune precipitation seemed to occur mainly through the classical pathway of complement activation. The alternative pathway was usually dispensable, but it augmented the inhibition. Guinea pig complement serum (NGS) was less effective than NHS in inhibiting immune precipitation. Guinea pig serum deficient in C4 (C4DGS) did not inhibit the immune precipitation. Mouse complement serum was effective for inhibiting precipitation, and C5-deficient serum was as effective as normal serum. Therefore, the inhibition of immune precipitation is considered to occur by activation of complement up to the step of C3. The size of the soluble immune complexes formed in the presence of NHS varied depending on the concentrations of antibody and antigen, even when the ratio of antigen to antibody was constant. On incubation at 37 degrees C immune precipitation was inhibited by 1/2 dilution of NHS for 2 to 3 hr and then gradually increased to the level in the absence of complement. When the immune complexes were formed in the presence of serum containing complement, fragments of C4 and C3 were incorporated into the soluble immune complexes. The C3 fragments incorporated into the soluble complexes were C3b, iC3b, C3c, and C3d, some of which were bound covalently with heavy chains of IgG antibody molecules. Some of the covalent linkages between C3 fragments and IgG seemed to be destroyed by alkali treatment, but not by hydroxylamine treatment. The formation of covalent bonds between IgG and C3 and probably C4 was essential for inhibition of immune precipitation, because inhibitors of their formation, such as putrescine, cadaverine, and salicylhydroxamic acid, effectively prevented the inhibition of precipitation. When antigen and antibody reacted in the presence of mixtures of various combinations of isolated complement components, C1, C4, C2, and C3 showed maximal inhibition of immune precipitation, whereas factors I and H had little effect.

Animals↗
PubMed1989

Complement biosynthesis in human synovial tissue.

Molecular biological and immunochemical techniques have been used to study the synthesis of complement components by synovial tissue from patients with rheumatoid arthritis or osteoarthritis and by normal synovial tissue from a patient undergoing patellectomy. Using Northern and dot-blot analyses, mRNAs coding for C1-inhibitor, C2, C3, C4 and factor B have been detected, but not for C5. Quantitative analyses of the data have not shown any significant differences in the steady state levels of any of the mRNAs in synovium from rheumatoid arthritis and osteoarthritis patients. When synovial membrane fragments from rheumatoid arthritis, osteoarthritis patients or normal synovium were cultured in vitro, synthesis of C1-inhibitor, C2, C3, C4 and factor B detected by ELISA and C2, C3 and factor B were shown to be functionally active. This study thus provides conclusive evidence that synthesis of complement components occurs locally within normal and inflamed synovial tissue. The local synthesis of complement within normal synovial joints may be of importance in their defence against infection, whereas in inflamed joints it may contribute to the inflammatory response.

Arthritis, Rheumatoid↗
PubMed1987

A reason for the cytolytic inefficiency of murine serum.

Murine serum exhibits very poor haemolytic and bactericidal activity. We report that this is due, at least in part, to the presence of a potent, naturally occurring plasma inhibitor of the terminal complement sequence. The inhibitor is a heat-stable euglobulin. It is highly effective in suppressing haemolysis following complement activation on target erythrocytes with heterologous serum. It also inhibits C3-independent reactive haemolysis of guinea-pig erythrocytes with human C5b-9. Current evidence indicates that the inhibitory factor acts at the C5b-7 stage by preventing binding of the terminal complement complex to cells undergoing complement attack. In this respect, the inhibitor differs from the previously recognized regulators of the terminal complement sequence including plasma S-protein. The inhibitor does not protect C5b-7-laden cells from the action of C8 and C9, and also does not suppress formation of haemolytically inactive SC5b-9 in the fluid phase. The action of murine inhibitory factor is not confined to the red cell, and its presence can totally abolish the bactericidal activity of human serum on a sensitive, rough E. coli K12 strain.

Animals↗
PubMed1983

Effect of a protein-bound polysaccharide PS-K on the complement system.

A protein-bound polysaccharide from mycelia of Coriolus versicolor PS-K, clinically used as an immunomodulator, has been shown to restore the decreased cellular immune response and to exhibit host-mediated antitumor activity. In this experiment, PS-K was found to increase serum complement level in guinea pig and in human without malignancy, when hemolytic assay of complement was performed using sensitized sheep erythrocytes for the classical pathway activity and unsensitized rabbit erythrocytes for the alternative pathway activity. Assay of complement components revealed increase in C3 level in guinea pig, but no significant changes in C1q, C4, C3, properdin, C3 activator, and C1-inhibitor in human, while C5 and C9 were depressed. Conversion of beta 1C to beta 1A was observed in the 7th day's plasma of these patients by crossed immunoelectrophoresis. Biosynthesis of guinea pig C3 was accelerated by administration of PS-K, but that of C4 was not affected. These evidences suggested that PS-K might potentiate immune response of the host by elevating serum complement level, in addition to the activation of the complement system.

Animals↗
PubMedDate not supplied

A trypsin method for coating human red blood cells with plasma C3 and/or C4.

Simple procedures are described for the production of human red blood cells coated with C3 and/or C4 by brief trypsin treatment of cell-plasma mixtures at room temperature. These cells ('EC3/4'-try) were unusual in that their agglutinability by anticomplement sera, as compared to sucrose-water RBC, was similar when tested by AutoAnalyzer but was markedly reduced in manual testing, especially against anti-C4. In spite of this, both 'EC34'-try and 'EC3'-try were found to be suitable indicator cells for determining the adequacy of anti-C3c and/or anti-C3d activities in reagents used for manual antiglobulin tests.

Antibodies, Anti-Idiotypic↗
PubMed1972

Inactivator of the third component of complement as an inhibitor in the properdin pathway.

Evidence has been obtained that a single protein, known to modulate classical complement activation, also acts as an inhibitor in the properdin or alternate complement pathway. A highly purified inactivator of the third component of complement (C3) from human serum inhibited the proteolysis of Factor B in the properdin system (glycine-rich beta-glycoprotein) by glycine-rich beta-glycoproteinase. The inhibition was by the enzymatic destruction of glycine-rich beta-glycoproteinase activity. The major fragment of C3, C3b, which is the only known substrate of the C3 inactivator, blocked the destruction of glycine-rich beta-glycoproteinase by the C3 inactivator. Thus, in its inhibition of the porperdin pathway, the C3 inactivator destroys both the active form of glycine-rich beta-glycoproteinase and a protein involved in the conversion of the zymogen form of this enzyme (proglycine-rich beta-glycoproteinase) to its active form. The increased susceptibility to infections in a patient homozygous for deficiency of the C3 inactivator demonstrates the biologic significance of this protein.

Adult↗
PubMed1977

Human complement C3b inactivator: isolation, characterization, and demonstration of an absolute requirement for the serum protein beta1H for cleavage of C3b and C4b in solution.

The complement regulatory enzyme, C3b inactivator (C3bINA), has been purified from human serum by affinity chromatography on an anti-C3bINA Sepharose column. Subsequent chromatography on DEAE-cellulose and removal of IgG with anti-IgG Sepharose resulted in a product which was found to be homogeneous by polyacrylamide gel electrophoresis at pH 8.9 and by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The molecule is composed of two disulfide bonded polypeptide chains with mol wt of 50,000 and 38,000 daltons. Human CobINA was found to be a glycoprotein containing at least 10.7% carbohydrate and to have a normal serum concentration of 34 +/- 7 mug/ml (mean +/- 1 SD). Highly purified C3bINA cleaved neither free C3b nor free C4b if trace amounts of contaminating beta1H were removed from these proteins with anti-beta1H Sepharose. However, in the presence of highly purified beta1H and C3bINA, both C3bIna, both C3b and C4b were cleaved. Incubation of native C3 or C4 with C3bINA and beta1H had no effect on their cleaved. Incubation of native C3 or C4 with C3bINA and beta1H had no effect on their structure. The action of C3bINA and beta1H on C3b produced two fragments of the alpha1-chain which did not dissociate without reduction of the molecule. These fragments have mol wt of 67,000 and 40,000 daltons. The action of C3bINA and beta1H on C4b resulted in cleavage of the alpha'-chain giving rise to the 150,000-dalton C4c and the 49,000-dalton C4d fragments which dissociated without reduction. To produce from C3b the immunochemically defined C3c and C3d, fragments, the action of an additional serum enzyme appears to be required, the effect of which can be mimicked by trypsin.

Amino Acids↗
PubMed1990

Soluble human complement receptor type 1: in vivo inhibitor of complement suppressing post-ischemic myocardial inflammation and necrosis.

The complement system is an important mediator of the acute inflammatory response, and an effective inhibitor would suppress tissue damage in many autoimmune and inflammatory diseases. Such an inhibitor might be found among the endogenous regulatory proteins of complement that block the enzymes that activate C3 and C5. Of these proteins, complement receptor type 1 (CR1; CD35) has the most inhibitory potential, but its restriction to a few cell types limits its function in vivo. This limitation was overcome by the recombinant, soluble human CR1, sCR1, which lacks the transmembrane and cytoplasmic domains. The sCR1 bivalently bound dimeric forms of its ligands, C3b and methylamine-treated C4 (C4-ma), and promoted their inactivation by factor I. In nanomolar concentrations, sCR1 blocked complement activation in human serum by the two pathways. The sCR1 had complement inhibitory and anti-inflammatory activities in a rat model of reperfusion injury of ischemic myocardium, reducing myocardial infarction size by 44 percent. These findings identify sCR1 as a potential agent for the suppression of complement-dependent tissue injury in autoimmune and inflammatory diseases.

Animals↗
PubMed1990

Lysis of complement-sensitive Entamoeba histolytica by activated terminal complement components. Initiation of complement activation by an extracellular neutral cysteine proteinase.

Activation of complement by Entamoeba histolytica may be initiated by the extracellular 56-kD neutral cysteine proteinase which cleaves the alpha chain of C3. To determine the relationship between the fluid-phase activation of complement and our observation that only strains isolated from patients with invasive disease are resistant to complement-mediated lysis, we investigated the fate of C3 with recent amebic isolates. When 125I-C3 was incubated with trophozoites in serum, C3 in the fluid phase was cleaved to C3b or C3bi, but the alpha chain of the C3 molecules on the cell surface appeared intact. Since the lysis of nonpathogenic strains takes place in the absence of bound C3b, we demonstrated that this reaction occurs by reactive lysis initiated in the fluid phase: (a) the killing of nonpathogenic strains was enhanced when alternative pathway activation was accelerated by the addition of cobra venom factor; (b) non-pathogenic strains were lysed by purified terminal components; and (c) sera incubated with pathogenic E. histolytica produced passive lysis of chicken erythrocytes. These results demonstrate for the first time that complement-sensitive E. histolytica are lysed by activation of the terminal complement components in the fluid phase where the 56-kD neutral cysteine proteinase cleaves C3, and not by the surface deposition of activated C3.

Animals↗
PubMed2001

Expression of a soluble complement inhibitor protects transgenic mice from antibody-induced acute renal failure.

Crry is a potent complement regulator in rodents that inhibits C3 convertases. In rats, intrarenal arterial injection of anti-glomerular endothelial cell (GEN) antibodies leads to complement-dependent microvascular injury and acute renal failure. In this study, a mouse variant of this model and the effects of complement inhibition were examined. Transgenic mice that overexpressed soluble Crry systemically and in their kidneys were studied. Anti-GEN IgG was injected intravenously into eight Crry transgenic mice and seven transgene-negative littermates (which were used as control animals). Thirty h after injection, blood urea nitrogen (BUN) levels were 30.3 +/- 4.4 and 114.8 +/- 23.5 mg/dl for transgene-positive and -negative animals, respectively (P = 0.012). Four of five transgene-negative animals with BUN levels of > 100 mg/dl were anuric; the remaining animal exhibited minimal albuminuria and no detectable urinary C3. In animals with renal failure, glomerular capillary collapse and tubular necrosis were observed. There was significant tubular staining for C3 in transgene-negative animals, with cellular and basal distributions, both of which were statistically greater than those in transgene-positive animals. Tubular cell C3 staining was strongly correlated with BUN values (r = 0.83, P < 0.001), as was C9 staining (r = 0.56, P = 0.037), suggesting that complement activation to the C5b-9 membrane attack complex had a casual role in renal failure. Thus, systemic injection of anti-GEN antibodies into mice leads to acute renal failure, with glomerular and tubular injury. Animals that overexpress soluble Crry in renal tubules and elsewhere are protected from the acute renal failure that occurs in this model, which ultimately seems to develop because of complement activation focused on tubules.

Acute Kidney Injury↗