Pharmacologic targeting of coagulation factors XII and XI by monoclonal antibodies reduces thrombosis in nitinol stents under flow

BACKGROUND

Cardiovascular implantable devices, such as vascular stents, are critical for the treatment of cardiovascular diseases. However, their success is dependent on robust and often long-term antithrombotic therapies. Yet, the current standard-of-care therapies often pose significant bleeding risks to patients. Coagulation factor (F)XI and FXII have emerged as potentially safe and efficacious targets to safely reduce pathologic thrombin generation in medical devices.

OBJECTIVES

To study the efficacy of monoclonal antibody-targeting FXII and FXI of the contact pathway in preventing vascular device-related thrombosis.

METHODS

The effects of inhibition of FXII and FXI using function-blocking monoclonal antibodies were examined in a nonhuman primate model of nitinol stent-related thrombosis under arterial and venous flow conditions.

RESULTS

We found that function-blocking antibodies of FXII and FXI reduced markers of stent-induced thrombosis in vitro and ex vivo. However, FXI inhibition resulted in more effective mitigation of thrombosis markers under varied flow conditions.

CONCLUSION

This work provides further support for the translation of contact pathway of coagulation inhibitors for their adjunctive clinical use with cardiovascular devices.

Factor XII plays a pathogenic role in organ failure and death in baboons challenged with Staphylococcus aureus

Activation of coagulation factor (F) XI promotes multiorgan failure in rodent models of sepsis and in a baboon model of lethal systemic inflammation induced by infusion of heat-inactivated Staphylococcus aureus. Here we used the anticoagulant FXII-neutralizing antibody 5C12 to verify the mechanistic role of FXII in this baboon model. Compared with untreated control animals, repeated 5C12 administration before and at 8 and 24 hours after bacterial challenge prevented the dramatic increase in circulating complexes of contact system enzymes FXIIa, FXIa, and kallikrein with antithrombin or C1 inhibitor, and prevented cleavage and consumption of high-molecular-weight kininogen. Activation of several coagulation factors and fibrinolytic enzymes was also prevented. D-dimer levels exhibited a profound increase in the untreated animals but not in the treated animals. The antibody also blocked the increase in plasma biomarkers of inflammation and cell damage, including tumor necrosis factor, interleukin (IL)-1β, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, nucleosomes, and myeloperoxidase. Based on clinical presentation and circulating biomarkers, inhibition of FXII prevented fever, terminal hypotension, respiratory distress, and multiorgan failure. All animals receiving 5C12 had milder and transient clinical symptoms and were asymptomatic at day 7, whereas untreated control animals suffered irreversible multiorgan failure and had to be euthanized within 2 days after the bacterial challenge. This study confirms and extends our previous finding that at least 2 enzymes of the contact activation complex, FXIa and FXIIa, play critical roles in the development of an acute and terminal inflammatory response in baboons challenged with heat-inactivated S aureus.

Driving towards Precision Medicine for angioedema without wheals

Evidence accumulated over the last two decades indicates that recurrent angioedema without wheals constitutes a diverse family of disorders with a much higher complexity than was previously regarded. Indicatively, during the last two years, novel variants of three genes other than SERPING1 and F12 have been identified in association with hereditary angioedema. Most interestingly, functional studies of at least one of these variants (the variant c.807G > T of ANGPT1 gene) imply the existence of a new disease endotype in which the altered bradykinin metabolism and function does not play a central role. Therefore, using conventional approaches, it seems that the complexity of this disease cannot be sufficiently elucidated and any attempt to interrelate its many diverse aspects seems unrealistic. Similar to other rare and chronic diseases, a Precision Medicine approach, discovering the right target and giving "the right drug, for the right patient, at the right time, every time" seems the optimal future practice. Herein, we review recent data challenging and dictating the need for a switch of angioedema research into high-throughput approaches and we present the expected advantages for better understanding of the disease and patients management.

Antigen levels of coagulation factor XII, coagulation factor XI and prekallikrein, and the risk of myocardial infarction and ischemic stroke in young women

BACKGROUND

High levels of activated protein–inhibitor complexes of the intrinsic coagulation proteins are associated with ischemic stroke (IS) but not with myocardial infarction (MI). This study was aimed at determining whether the antigen levels of coagulation factors(factor XII, FXII, and FXI and prekallikrein (PK)are associated with MI and IS, and whether this association is independent of levels of activated protein–inhibitor complexes.

PATIENTS AND METHODS

The RATIO study included young women (< 50 years) with MI (N = 205)and IS (N = 175), and 638 healthy controls. Antigen levels of FXII, FXI and PK were measured and expressed as percentages of of those in pooled normal plasmas. Odds ratios (ORs) and corresponding 99% confidence intervals (CIs) were calculated for high levels (i.e. ≥ 90th percentile of controls) as measures of rate ratios.

RESULTS

After adjustment for potential confounders, high levels of FXII antigen were not associated with MI risk or IS risk(OR(MI) 1.18, 99% CI 0.51–2.74; ORIS 1.03, 9% CI 0.41–2.55). High levels of FXI antigen were slightly associated with an increase in MI risk (OR(MI) 1.55, 9% CI 0.74–3.21), whereas there was a substantial association with IS risk (ORIS 2.65, 9% CI 1.27–5.56). PK antigen was slightly associated with MI risk but not with IS risk(ORMI 1.54, 9% CI 0.67–3.52; ORIS 0.90, 9% CI 0.35–2.33). All associations remained similar after adjustment for levels of protein–inhibitor complexes.

CONCLUSION

Increased levels of FXI antigen were associated with an increase in IS risk, whereas they showed only a marginal association with MI risk. FXII antigen and PK antigen levels were not substantially associated with MI risk and IS risk.

Factor XII autoantibodies as a novel marker for thrombosis and adverse obstetric history in patients with systemic lupus erythematosus

AIM

To investigate the clinical significance of anti-factor XII (FXII) in a large cohort of patients with systemic lupus erythematosus (SLE).

PATIENTS AND METHODS

This study comprised 127 patients with SLE. IgG and IgM anti-FXII were tested by an in-house ELISA. 123 healthy donors comprised the control group.

RESULTS

51 (40%) patients with SLE and 9 (7%) healthy controls were positive for anti-FXII. IgG and IgM anti-FXII were frequently found in patients with thrombosis (28% and 13%, respectively). Levels of IgG and IgM anti-FXII were higher in patients with thrombosis than in the control group (p<0.001 and p=0.005, respectively). Anti-FXII was more frequent in patients with arterial thrombosis (31% vs 4% for IgG and 14% vs 3% for IgM, respectively) and venous thrombosis than in controls (37% vs 4% for IgG). IgG anti-FXII were more frequent in patients with miscarriages and fetal death (35% and 40% vs 4% for IgM). The prevalence of IgM anti-FXII was not different between groups.

CONCLUSION

Anti-FXII are frequent in patients with SLE. Their presence is associated with thrombosis and adverse obstetric history, making these antibodies a novel marker for the antiphospholipid syndrome.

Synergistic platelet integrin signaling and factor XII activation in poly--acetyl glucosamine fiber-mediated hemostasis

The polymer poly-N-acetylglucosamine (pGlcNAc) containing fiber material is becoming increasingly important as a topical agent for hemostasis at wound sites. The pGlcNAc polymeric fiber provides hemostasis through redundant mechanisms that include platelet activation for fibrin network formation. The research presented here better defines the mechanism for the effect of pGlcNAc containing fibers on platelet-mediated processes. Adsorption experiments demonstrated that pGlcNAc fibers tightly bind most major plasma proteins and a specific sub-set of platelet surface proteins, including the integrin beta(3) subunit (CD61) and the von Willebrand receptor GP1b (CD42b). The result of this interaction is a platelet-dependent acceleration of fibrin gel formation. Accelerated fibrin polymerization is sensitive to factor XII inhibition by corn trypsin inhibitor and integrin inactivation with integrilin. Confocal microscopy studies show that when platelet integrins contact plasma protein-saturated pGlcNAc fibers, an increase in intracellular free calcium for platelet activation occurs to drive surface expression of phosphatidyl serine (PS). Thus, a catalytic surface for thrombin generation and accelerated fibrin clot formation results from the interaction of platelets with pGlcNAc. These findings, when considered with the observation that pGlcNAc fibers also induce red blood cell agglutination and vasoconstriction, provides an explanation for the ability of the pGlcNAc material to provide hemostasis in a wide variety of clinical applications.

Factor XII auto-antibodies present in a patient with a B-cell lymphoma

A 64-year-old woman was transferred for investigation of a mediastinal mass, biopsy of which showed a diffuse large B-cell lymphoma. She was also found to have an antiphospholipid antibody. The pre-operative coagulation screen showed a prolonged activated partial thromboplastin time, 71.3 s (normal range, 26-36 s), which was not corrected by the addition of normal plasma. The dilute Russell's viper venom time was positive. Anti-cardiolipin assay was strongly positive, immunoglobulin M was 153 AU; immunoglobulin G was normal, 3.1 AU. Assays of factors VIII, IX and XI showed higher concentrations with increasing dilutions in one-stage factor assays from 1: 10 to 1: 80 suggestive of an inhibitor. Factor XII was 9 U/dl and results were unaffected by increasing dilution, suggesting specific antibodies to factor XII. The factor XII antigen was 40 U/dl. The patient had immunoglobulin M auto-antibodies to factor XII.

The antigenic binding site(s) of antibodies to factor XII associated with the antiphospholipid syndrome

Phospholipid binding proteins, including factor XII (FXII), are known to be targeted by antiphospholipid antibodies (aPA). Factor XII antibodies (FXIIab) have been described in some patients with the antiphospholipid syndrome (APS) and have been shown to lead to reduced levels of FXII. The antigenic binding site(s) and the pathophysiological effects of FXIIab are unknown. In an attempt to elucidate the binding site of these antibodies, immobilized plasma kallikrein was used to cleave FXII into its 52-kDa heavy-chain (HCFXII) and 28-kDa light-chain (LCFXII) components. Plasma samples from 12 female patients with definite APS and FXIIab were investigated for the presence of antibodies to FXII, HCFXII and LCFXII. All but one patient's plasma reacted to FXII, HCFXII and LCFXII in a similar manner. One patient gave markedly reduced positivity to HCFXII and LCFXII, suggesting that the FXIIab in this patient had a higher affinity for the intact FXII molecule. To further investigate the antigenic binding site(s) of FXII, 150 biotinylated peptides of the known FXII sequence were synthesized using a Multipin(TM) peptide synthesis procedure. The IgG and IgM fractions of the 12 patients' plasma were purified by affinity chromatography. The synthesized peptides were captured on streptavidin plates and individual patients' purified FXIIab assayed against the peptides in a modified enzyme-linked immunosorbent assay (ELISA). Two regions were identified as possible antigenic binding site(s) for FXIIab: one in the growth factor domain and the other in the catalytic domain.

Antibodies to factor XII: a possible predictive marker for recurrent foetal loss

Antibodies to factor XII (FXIIabs) have been demonstrated in some patients with the anti-phospholipid syndrome (APS). The presence of these antibodies were shown to lead to statistically significantly reduced levels of FXII (p = 0.02). In an extension to this study forty female patients with either primary APS (n = 26) or systemic lupus erythematosus (APS positive) (n = 14) were investigated for levels of factor XII, the presence of lupus anticoagulant and antibodies to cardiolipin, beta 2-glycoprotein I and factor XII. Twenty one of the forty patients had a history of foetal loss (> 2, mean = 2.6). Lupus anticoagulant positivity showed a weak association with foetal loss (odds ratio = 1.1). While there was no association between the presence of antibodies to cardiolipin or beta 2-glycoprotein I with foetal loss, antibodies to factor XII showed a strong and statistically significant association (odds ratio = 5.4, p = 0.025).

Antibodies to factor XII are distinct from antibodies to prothrombin in patients with the anti-phospholipid syndrome

Patients with the anti-phospholipid syndrome (APS) have antiphospholipid antibodies (aPA) which are often targeted towards phospholipid binding proteins such as beta2-glycoprotein I and prothrombin. Antibodies to factor XII (FXIIabs) have also been identified in some patients with APS. Factor XII (FXII) is a member of the kringle family of proteins which include plasminogen and prothrombin. Antibodies to prothrombin have been associated with myocardial infarction and have been shown to cross react with plasminogen. Sixteen patients with APS and FXIIabs were investigated for the presence of antibodies to prothrombin, by enzyme linked immunosorbent assay in a calcium (Ca++) independent assay. All sixteen showed different antibody binding patterns than those observed for antibodies to FXII. Eight patients were further investigated using surface plasmon resonance (SPR) for antibody binding to covalently bound FXII and to covalently bound prothrombin in both Ca++ dependent and independent systems. Of three patients demonstrating antibody binding to FXII by SPR, none demonstrated antibody binding to prothrombin in a Ca++ independent system with one demonstrating antibody binding to prothrombin that was Ca++ dependent. Of five patients who did not bind FXII by SPR, one demonstrated antibody binding to prothrombin in a Ca++ independent system while two demonstrated antibody binding to prothrombin in a Ca++ dependent system. Antibodies to FXII in patients with APS appear to be distinct from antibodies to prothrombin.

Autoantibodies to contact proteins in patients with recurrent pregnancy losses

The kallikrein-kinin system or plasma contact system consists of three essential plasma proteins. These are coagulation factor XII, prekallikrein and high molecular weight kininogen. Deficiencies of these proteins are not associated with clinical bleeding despite marked prolongation of in vitro surface-activated coagulation time. Paradoxically, studies suggest that contact proteins have anticoagulant, profibrinolytic functions in a physiologic millieu, on endothelial cells. Recently, evidence has accumulated for the presence of the kallikrein-kinin system or plasma contact system in the fetoplacental unit. Kinins which are released within the placenta may play a role in regulating placental blood flow. This suggests that the plasma contact system may also have an important role in pregnancy. Several studies have reported the presence of autoantibodies to the contact proteins in patients with recurrent early pregnancy losses. Disruption of this system may be a risk factor for early gestational losses.

Activation of complement and contact system in Alzheimer's disease

beta-Amyloid protein (betaA) has been implicated in the pathogenesis of Alzheimer's disease (AD) because of its neurotoxicity and ability to trigger a local inflammatory response. Although assembly of betaA in particular aggregates seems to be crucial event in AD pathogenesis, soluble, non-fibrillar betaA may also be involved. Non-fibrillar betaA1-42, and truncated peptide 1-28, induced dose-dependent activation of C4 sparing C3. The mechanism of C4 activation was not dependent on C1q, because non-fibrillar betaA can still activate C4 in plasma genetically deficient in C1q. A C1q independent mechanism of complement classical pathway activation could be via the activation of contact/kinin system. The possible involvement of contact system in AD is suggested by the finding that this system is massively activated in CSF of AD patients. The mechanism of activation of contact system could be the result of an anionic interaction of residues within the region 1-11 of betaA1-42 with factor XII, and of kallikrein generation. Concomitant incubation of a small cationic peptide (lysine4) with betaA abrogated its ability to trigger the cleavage of high molecular weight kininogen. In vivo, prevention of contact system activation beside the reduction of kallikrein generation, can also decrease the activation of complement system and the release of interleukin-6, both factors being considered to play an important role in the inflammatory reactions in AD brain.

Antibodies to factor XII and recurrent fetal loss in patients with the anti-phospholipid syndrome

Forty female patients with either primary anti-phospholipid syndrome (n = 26) or systemic lupus erythematosus (anti-phospholipid syndrome positive) (n = 14) were investigated for levels of factor XII, the presence of lupus anticoagulant and antibodies to cardiolipin, beta 2-glycoprotein I and factor XII. Twenty-one patients had a history of recurrent fetal loss (> 2, mean = 2.6). Lupus anticoagulant positivity showed a weak association with recurrent fetal loss (odds ratio = 1.1). While there was no association between the presence of antibodies to cardiolipin or beta 2-glycoprotein I with recurrent fetal loss, antibodies to factor XII showed a strong and statistically significant association (odds ratio = 5.4, P = 0.025).

Identification of a putative binding site for negatively charged surfaces in the fibronectin type II domain of human factor XII--an immunochemical and homology modeling approach

Monoclonal antibodies directed against functional sites of proteins provide useful tools for structure-function studies. Here we describe a mAb, KOK5, directed against the heavy chain region of human coagulation factor XII (FXII), which inhibits kaolin-induced clotting activity by preventing the binding of FXII to kaolin. Furthermore, mAb KOK5 enhances FXII susceptibility for cleavage by kallikrein and supports FXII autoactivation. Hence, mAb KOK5 likely is directed against the binding site of FXII for negatively charged surfaces. Screening of two phage-displayed random peptide libraries with mAb KOK5 selected phages that could be grouped on the basis of two amino acid consensus sequences: A) FXFQTPXW and B) HQ/LCTHR/KKC. Sequence A contains two motifs: one shares homology with FXII amino acid residues 30-33 (FPFQ), the second one with residues 57-60 (TPNF); both amino acid stretches belonging to the fibronectin type II domain of FXII. Sequence B also reveals homology with part of the fibronectin type II domain, i.e. the stretch 40-47 (HKCTHKGR). A three-dimensional model of FXII residues 28-65, obtained by homology modeling, indicated that the three amino acid stretches 30-33, 40-47 and 57-60 are close to each other and accessible for the solvent, i.e. in a form available for interaction with the monoclonal antibody, suggesting that mAb KOK5 recognizes a discontinuous epitope on the fibronectin type III domain of FXII. Peptides corresponding to FXII sequences 29-37 (FXII29-37) or 39-47 (FXII39-47), were synthesized and tested for the capability to inhibit FXII binding to negatively charged surfaces. Peptide FXII39-47 inhibited the binding of labeled FXII to kaolin and effectively prevented both dextran sulfate- and kaolin-induced activation of the contact system in plasma. Hence, we suggest that the fibronectin type II domain of FXII, in particular residues 39 to 47, contribute to the binding site of FXII for negatively charged surfaces.

Reduced factor XII levels in patients with the antiphospholipid syndrome are associated with antibodies to factor XII

Antibodies to factor XII (FXII) have previously been identified in some patients who were lupus anti-coagulant-positive. The relationship between these antibodies and FXII levels appeared to be variable. The aim of the present study was to confirm the presence of antibodies to FXII in patients with well characterized antiphospholipid syndrome (APS) and to establish their potential effect on levels of FXII. Forty-two patients with APS were studied; 21 patients were found to have either immunoglobulin (Ig)G or IgM antibodies to FXII by enzyme-linked immunosorbent assay (ELISA) using a highly purified preparation of FXII (> 99% pure). Levels of FXII were statistically significantly lower (P = 0.02) in patients with antibodies to FXII when compared with patients without antibodies to FXII (median = 91 micro/dl, s.d. = 39.1, median = 122 micro/dl, s.d. = 41.1 respectively). Four of the 21 patients with antibodies to FXII were found to have FXII levels below the laboratory normal range. Antibodies to FXII are present in significant numbers of patients with APS and may lead to acquired FXII deficiency.

A monoclonal antibody raised against human beta-factor XIIa which also recognizes alpha-factor XIIa but not factor XII or complexes of factor XIIa with C1 esterase inhibitor

A monoclonal antibody (mAb 2/215) against human beta-factor XIIa (beta-FXIIa), was shown by equilibrium binding studies to have a high affinity for alpha-factor XIIa (alpha-FXIIa) (Kd 1.8 nM) and beta-FXIIa (Kd 0.65 nM) but no detectable reaction with FXII zymogen or alpha-FXIIa:C1 esterase inhibitor (C1-INH) complex. Surface plasmon resonance studies showed that the mAb 2/215 bound to immobilized alpha-FXIIa with high affinity (KD 3.93 +/- 1.46 x 10(-11) M). Western blots employing mAb 2/215 indicated that human plasma contained small amounts of alpha-FXIIa but no beta-FXIIa. mAb 2/215 did not inhibit the amidolytic activity of beta-FXIIa and protected beta-FXIIa from inhibition by C1-INH. The recovery by ELISA,employing mAb 2/215 as the capture antibody, of alpha-FXIIa added to plasma was 11.3%, 42% after inhibition of alpha-FXIIa with 3:4dichloroisocoumarin, and 82% when 0.5% Triton-X100 was added to the assay. Gel filtration showed that the majority of plasma alpha-FXIIa existed as a complex (Mr approximately 170,000). This distinctive mAb increases the capacity to study the contact system in health and disease.

Antibodies to factor XII associated with lupus anticoagulant

Falsely low levels of factor XII (FXII) have been documented in patients who are lupus anticoagulant positive (LA+). In addition, we have previously noted a surprisingly high incidence (20.9%) of apparently true FXII deficiency in patients who were LA+. We have hypothesised that this may be partly due to the presence of antibodies to FXII. The aim of the present study was to investigate whether LA+ patient plasmas contain antibodies directed either against FXII or FXII in association with phospholipids. Plasma samples from 60 blood donors, all LA negative, and 51 LA+ patients were tested using ELISA assays employing purified FXII, phosphatidylserine (PS) and phosphatidylethanolamine (PE). We have identified seven patients whose plasma contained either IgG or IgM that reacted with purified FXII in the absence of PS or PE. When PS was included in the assay system four additional patient plasmas were shown to contain either IgG or IgM that reacted with FXII. The plasma of one patient contained IgG that reacted with FXII both in the presence and absence of PS. There was no reactivity to FXII with either IgG or IgM when PE was included in the assay system. Affinity purified IgG from three patients whose plasma reacted with FXII in the ELISA assay in the absence of PS, gave a positive reaction in an immunoblot assay. These results suggest that FXII antibodies are present in a significant proportion of LA+ patients and may lead to an erroneous diagnosis of FXII deficiency.

Elucidation of the core residues of an epitope using membrane-based combinatorial peptide libraries

Combinatorial peptide libraries have proved to be a valuable tool for the study of the interaction of a functional protein with its ligand. Here, the epitope for a monoclonal antibody 201/9, raised against beta-factor XIIa, has been identified with a two-step approach using peptide libraries attached to a polymer (polyvinylidene difluoride) membrane. First, the octapeptide libraries with two amino acids defined at position 2 and 4, represented by the formula X-O2-X-O4-X-X-X-X, were synthesized on a sheet of polymer membrane in which X represents a mixture of all the natural -amino acids except cysteine, while O2 and O4 each represent a single amino acid. The libraries were probed with the antibody 201/9, and the bound antibody was detected with a sensitive chemiluminescent method. In the first cycle, the peptide mixtures X-Phe-X-Gln-X-X-X-X showed the strongest signal development. In the second cycle Phe and Gln were incorporated into new libraries consisting of sequences O1-Phe-X-Gln-X-X-X-X, X-Phe-O3-Gln-X-X-X-X, X-Phe-X-Gln-O5-X-X-X, X-Phe-X-Gln-X-O6-X-X, X-Phe-X-Gln-X-X-O7-X, and X-Phe-X-Gln-X-X-X-O8. After probing these new peptides, the residues representing the core sequence of the epitope for monoclonal antibody 201/9 were elucidated. The sequence Ser-Phe-Leu-Gln-Glu-Asn, identified as the immunodominant epitope, correlates well with the sequence Ser-Phe-Leu-Gln-Glu-Ala previously identified (Gao, B., and Esnouf, M. P. (1996) J. Immunol. 157, 183-188) in a scan of overlapping peptides based on the sequence of human beta-factor XIIa.

An enzyme-linked immunosorbent assay (ELISA) for the measurement of activated factor XII (Hageman factor) in human plasma

A direct enzyme-linked immunosorbent assay (ELISA) employing 2/215 mouse monoclonal hybridoma antibody is described. The assay is capable of detecting activated factor XII in human plasma and can be used to assess early detection of the intrinsic blood coagulation pathway. No cross reactivity with human factor XII zymogen has been found. The assay was used to assess activation of factor XII in patients with renal failure, pregnancy and diabetes compared to a control group.

Inhibition of factor XII in septic baboons attenuates the activation of complement and fibrinolytic systems and reduces the release of interleukin-6 and neutrophil elastase

In previous studies, we have shown that administration of monoclonal antibody (MoAb) C6B7 against human factor XII to baboons challenged with a lethal dose of Escherichia coli abrogates activation of the contact system and modulates secondary hypotension. To evaluate the contribution of activated contact proteases to the appearance of other inflammatory mediators in this experimental model of sepsis, we studied the effect of administration of MoAb C6B7 on activation of complement and fibrinolytic cascades, stimulation of neutrophil degranulation, and release of the proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). Activation of the complement system, as reflected by circulating C3b/c and C4b/c levels, was significantly reduced in five animals that had received MoAb C6B7 before a lethal dose of E coli as compared with five control animals that had been given a lethal challenge only. Inhibition of contact activation also modulated the fibrinolytic response, since the release of tissue-type plasminogen activator (t-PA) and the appearance of plasmin-alpha2-antiplasmin (PAP) complexes into the circulation was significantly attenuated upon pretreatment with anti-factor XII MoAb. In contrast, plasma levels of plasminogen activator inhibitor (PAI) were modestly enhanced in the treatment group. Degranulation of neutrophils, as assessed by circulating elastase-alpha1-protease inhibitor complexes, and release of IL-6 but not of TNF-alpha was decreased in anti-factor XII-treated animals. Observed differences in the inflammatory response between treatment and control groups were not likely due to different challenges, since the number of E coli that had been infused, as well as circulating levels of endotoxin after the challenge, were similar for both groups. These data suggest that activation of the contact system modulates directly or indirectly various mediator systems involved in the inflammatory response during severe sepsis in nonhuman primates.

Activation of the intrinsic pathway of coagulation in children with meningococcal septic shock

Meningococcal septic shock (MSS) is complicated by activation of coagulation, fibrinolytic, and complement systems. We studied the contact system of the intrinsic pathway of coagulation in thirteen children with MSS. Activation was assessed upon admittance to the intensive care unit and 48 h thereafter, based on the measurement of factor XII- (FXII), prekallikrein- and factor XI (FXI) antigen levels, as well as on the detection of FXIa-FXIa inhibitor, FXIIa-C1-inhibitor, and kallikrein-C1-inhibitor complexes, respectively. Levels of FXII, prekallikrein and FXI were reduced to about 50% in all patients on admission, and were significantly higher 48 h later. FXIIa-C1-inhibitor complexes were elevated in 7 patients, and kallikrein-C1-inhibitor complexes in 2 patients. FXIa-alpha 1-antitrypsin complexes were elevated in all patients, FXIa-C1-inhibitor complexes in nine, and FXIa-antithrombin III complexes in one patient. We conclude that patients with MSS have activation of the contact system, which may contribute to activation of coagulation, and thus to morbidity and mortality.

Monoclonal antibody F1 binds to the kringle domain of factor XII and induces enhanced susceptibility for cleavage by kallikrein

In a previous study we have shown that monoclonal antibody F1 (MoAb F1), directed against an epitope on the heavy chain of factor XII distinct from the binding site for anionic surfaces, is able to activate factor XII in plasma (Nuijens JH, et al: J Biol Chem 264; 12941, 1989). Here, we studied in detail the mechanism underlying the activation of factor XII by MoAb F1 using purified proteins. Formation of factor XIIa was assessed by measuring its amidolytic activity towards the chromogenic substrate H-D-Pro-Phe-Arg-pNA (S-2302) in the presence of soybean trypsin inhibitor and by assessing cleavage on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Upon incubation with MoAb F1 alone, factor XII was auto-activated in a time-dependent fashion, activation being maximal after 30 hours. Factor XII incubated in the absence of MoAb F1 was hardly activated by kallikrein, whereas in the presence of MoAb F1, but not in that of a control MoAb, the rate of factor XII activation by kallikrein was promoted at least 60-fold. Maximal activation of factor XII with kallikrein in the presence of MoAb F1 was reached within 1 hour. This effect of kallikrein on the cleavage of factor XII bound to MoAb F1 was specific because the fibrinolytic enzymes plasmin, urokinase, and tissue-type plasminogen activator could not substitute for kallikrein. Also, trypsin could easily activate factor XII, but in contrast to kallikrein, this activation was independent of MoAb F1. SDS-PAGE analysis showed that the appearance of amidolytic activity correlated well with cleavage of factor XII. MoAb F1-induced activation of factor XII in this purified system was not dependent on the presence of high-molecular-weight kininogen (HK), in contrast to the activation of the contact system in plasma by MoAb F1. Experiments with deletion mutants revealed that the epitopic region for MoAb F1 on factor XII is located on the kringle domain. Thus, this study shows that binding of ligands to the kringle domain, which does not contribute to the proposed binding site for negatively charged surfaces, may induce activation of factor XII. Therefore, these findings point to the existence of multiple mechanisms of activation of factor XII.

Contact, coagulation and platelet interaction with heparin treated equipment during heart surgery

Heparin coating of an extracorporeal device may reduce blood activation. To evaluate protein and platelet interaction with Duraflo II surface treatment of the cardiopulmonary bypass (CPB) circuit, thirty coronary artery bypass grafting patients were randomly divided into two groups (Duraflo II, n = 15 or Control, n = 15). Binding of antibodies against factor XII, antithrombin III (ATIII) and platelet receptor GpIb were significantly higher (p < 0.01) on the Duraflo II treated surface. Hageman Factor fragment (HFf or factor XIIf) activity observed in the fluid phase tended to be lower in the treated circuits, although complexes of factor XIIf-C1 inhibitor (C1INH) increased by the same extent in both groups. Thrombin was effectively bound on the Duraflo II surface while thrombin-antithrombin III formation was reduced during the first phase of CPB. As expected, this thrombin inhibiting capacity remained higher on the Duraflo II, although in the arterial line a reduction of 10% per hour was observed. This indicated loss of functional bound heparin of the Duraflo II surface. During the second phase of CPB, after release of the aortic crossclamp, factor XII and thrombin were strongly activated in both groups indicated by a sharp increase in concentrations of T/AT complex as well as FPA. Platelet numbers tended to increase more in the control group during CPB than in the Duraflo II group, likely by interaction of platelet GpIb receptors on the Duraflo II treated surface (p < 0.01). However, platelet activation assessed by beta-TG was similar in both groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

The contact system contributes to hypotension but not disseminated intravascular coagulation in lethal bacteremia. In vivo use of a monoclonal anti-factor XII antibody to block contact activation in baboons

The hypotension and disseminated intravascular coagulation (DIC) in bacteremia is thought to be mediated by the combined actions of cytokines, prostaglandins, and complement. The contact system, via the release of bradykinin and the activation of Factor XI, has been postulated to be contributing to the observed hypotension and DIC. Using a mAb to Factor XII (C6B7), we blocked the activation of the contact system in an established experimental baboon model in which Escherichia coli was infused to produce lethal bacteremia with hypotension. The untreated group (n = 5) displayed contact activation, manifested by a significant decrease in high molecular weight kininogen (HK) and a significant increase in alpha 2 macroglobulin-kallikrein complexes (alpha 2M-Kal). The C6B7-treated group (n = 5) showed an inactivation of Factor XII and the changes in HK and alpha 2M-Kal complexes were prevented. Both groups developed DIC manifested by a decrease in platelet, fibrinogen, and Factor V levels. The untreated group developed irreversible hypotension. The treated group experienced an initial hypotension that was reversed and extended the life of the animals. This study suggests that irreversible hypotension correlates with prolonged activation of the contact system, and specific antibody therapy can modulate both the pathophysiological and biochemical changes.

Functional characterization of a variant factor XII (F XII Locarno) in a cross reacting material positive F XII deficient plasma

The plasma of a healthy woman was found to contain half normal factor XII (FXII) antigen level (0.46 U/ml) without any FXII clotting activity (less than 0.01 U/ml). The variant FXII in this plasma, denoted as FXII Locarno, was partially characterized by immunological and functional studies on the proposita's plasma. FXII Locarno is a single chain molecule with the same size (Mr = 80 kDa) as normal FXII. Isoelectric focusing suggested an excess of negative charge in the variant FXII as compared to normal FXII. In contrast to FXII in normal plasma, FXII Locarno was not proteolytically cleaved upon prolonged incubation of proposita's plasma with dextran sulfate. Adsorption to kaolin was similar for both, abnormal and normal FXII. Incubation of the proposita's plasma with dextran sulfate and exogenous plasma kallikrein showed normal cleavage of FXII Locarno outside of the tentative disulfide loop Cys340-Cys467, but only partial cleavage within this disulfide loop. Furthermore, plasma kallikrein-cleaved abnormal FXII showed neither amidolytic activity nor proteolytic activity against factor XI and plasma prekallikrein. These results suggest a structural alteration of FXII Locarno, affecting the plasma kallikrein cleavage site Arg353-Val354 and thus formation of activated FXII (alpha-FXIIa).

Mitogenic effects of coagulation factor XII and factor XIIa on HepG2 cells

The structure of coagulation factor XII (Hageman factor), inferred from its DNA sequence, includes two epidermal growth factor (EGF)-homologous domains in its amino-terminal region. This suggests that factor XII may exhibit EGF-like activities. Reciprocal antigenic cross-reactivity between factor XII and EGF was shown by exposing purified human factor XII or mouse EGF to anti-mouse EGF or anti-human factor XII. Western blot analysis showed that anti-mouse EGF recognized intact factor XII at 80 kDa. Together, these results suggest that the EGF-homologous domains are accessible for anti-EGF binding in native factor XII. To determine whether factor XII has mitogenic activity, HepG2 or L cells (10(4) cells per well) were grown in serum-free medium in the presence or absence of factor XII or kaolin-activated factor XII (factor XIIa). Both factors XII and XIIa (6.0 micrograms/ml) enhanced cell proliferation by approximately 2-fold (P less than 0.001 and P less than 0.005, respectively). In contrast, L cells, which are not EGF target cells, were not affected by either factor XII or factor XIIa. Various doses of factor XII enhanced cell proliferation, [3H]thymidine incorporation, and [3H]leucine incorporation in HepG2 cells cultured under the same conditions. These data indicate that factor XII, like EGF, is a mitogen for HepG2 cells and suggest a possible autocrine role in the liver.

Activation of the contact system of coagulation by a monoclonal antibody directed against a neodeterminant in the heavy chain region of human coagulation factor XII (Hageman factor)

We studied the characteristics of two monoclonal antibodies (mAbs), F1 and F3, against human coagulation factor XII (Hageman factor). Experiments with trypsin-digested 125I-factor XII revealed that the epitope for mAb F1 is located in the NH2-terminal Mr 40,100 portion of factor XII, whereas that for mAb F3 resides in the COOH-terminal Mr 30,000 portion of this protein. Factor XII in fresh plasma (single-chain factor XII) bound approximately 190 times less to mAb F1 than factor XII in dextran sulfate-activated plasma (cleaved factor XII). However, no difference in accessibility of the epitope for mAb F1 was observed between cleaved and single-chain factor XII when bound to glass. mAb F3 appeared to bind to both single-chain and cleaved factor XII in plasma as well as when bound to glass. Neither mAb F1, nor F3 affected the amidolytic activity of factor XIIa, whereas both mAb F1 and F3 inhibited factor XII-coagulant activity to about 15 and 70%, respectively, at a molar ratio of mAb to factor XII of 20 to 1. mAb F1, as well as F(ab')2 and F(ab') fragments of this antibody induced activation of the contact system in plasma, as reflected by the generation of factor XIIa. C1 inhibitor and kallikrein. C1 inhibitor complexes. Activation was induced neither upon incubation with mAb F3, nor with that of control mAbs. mAb F1-induced contact activation required the presence of factor XII, prekallikrein, and high molecular weight kininogen and, in contrast to activation by negatively charged surfaces, was not inhibited by the presence of Polybrene. Based on these results we propose that a conformational change in factor XII is a key event in the activation process of this molecule. This conformational change can be induced by binding of factor XII to a surface as well as by proteolytic cleavage. As mAb F1 can also induce this conformational change, this antibody may provide a unique tool in studies of the activation of factor XII.

Mapping of a putative surface-binding site of human coagulation factor XII

We have localized the binding epitope(s) of two murine monoclonal antibodies (B7C9 and P5-2-1) that were shown previously to inhibit the activation of human coagulation factor XII by negatively charged surfaces. A factor XII cDNA expression library in lambda gt11 was screened with antibody B7C9, and 16 immunoreactive bacteriophage were isolated. Fusion proteins from each of the recombinant phage were reactive with both monoclonal antibodies. Two of the phage cDNA inserts were found to code for amino acid residues -6-+31 and +1-+47 of factor XII, respectively, thereby defining the limits of the antigenic peptide to amino acids +1-+31. Each of the remaining 14 recombinant phage contained longer factor XII cDNA inserts that included sequences coding for the amino-terminal 31 amino acid residues. These results were confirmed by direct binding of antibody B7C9 to synthetic peptides containing amino acids 1-14 and 1-28 of factor XII. Further experiments with a set of nested peptides also indicated that amino acid residues 1-4 were essential but not sufficient for binding of B7C9 to the peptides. Hydrophobicity analysis of the amino-terminal region of plasma factor XII revealed a highly hydrophilic region between amino acid residues 5 and 15 that contained positively charged lysine residues at positions 8, 11, and 13. We conclude that a major epitope(s) recognized by monoclonal antibodies B7C9 and P5-2-1 is present in the amino-terminal 28 amino acids of factor XII. It is proposed that binding of these antibodies to factor XII blocks interaction of the positively charged region between residues 5 and 15 with negatively charged surfaces, thereby inhibiting activation.

Hageman factor dependent kinin generation system in guinea pig skin: extravascular localization of the components, and prolonged vascular reaction in inhibitor-depleted animal of this system

1. Monospecific antibodies against components of the guinea pig Hageman factor-dependent system, such as Hageman factor, prekallikrein and high-molecular-weight (HMW) kininogen were prepared. These antibodies demonstrated the presence of all of these components in the normal guinea pig skin extract with the properties identical to them in plasma on western immunoblotting analysis. 2. Guinea pig macroalbumin which is a major circulating inhibitor of activated Hageman factor was immunologically depleted from three animals. Duration of a vascular permeability reaction caused by an intradermal injection of activated Hageman factor was prolonged in all of these guinea pigs approximately twice as long as the control, indicating a presence of negative feedback regulation of the Hageman factor-dependent kinin generation cascade in dermal tissue via the circulating protease inhibitor.

A monoclonal antibody recognizing an iscosapeptide sequence in the heavy chain of human factor XII inhibits surface-catalyzed activation

A monoclonal antibody (mAb B7C9) to human factor XII was produced which blocked the surface mediated coagulant activity of factor XII but not the amidolysis of H-D-ProPheArg-pNA. The mAb epitope was localized to a 20 amino acid sequence of 2.5 kDa in the heavy chain of factor XII.

Identification of a defective factor XI cross-reacting material in a factor XI-deficient patient

A homozygous factor XI-deficient girl, who appeared to be positive for cross-reacting material (CRM+) was studied for clarification. Factor XI antigen (F XI:Ag) was measured by radial immunodiffusion using monospecific, heterologous anti-factor XI antibodies. Factor XI coagulant activity (F XI:C) was determined in a modified activated partial thromboplastin time (APTT) test. The ratio of F XI:C to F XI:Ag was 0.04 for the proposita, as compared with 0.7 to 0.74 in the other family members. In contrast, 12 normal individuals had ratios of F XI:C to F XI:Ag of 1.04 +/- 0.15. F XI esterolytic activity was clearly higher than F XI:C in the proband, but not in her relatives. Immunoblotting studies demonstrated F XI CRM in the patient's plasma. Chromatography on diethylaminoethanol (DEAE)-Sephadex at pH 8.4 led to an almost complete removal of F XI from the plasma. The defective F XI was not bound to a negatively charged kaolin surface due to an abnormal interaction with high-mol-wt kininogen (HMWK).

Immunoblotting studies of coagulation factor XII, plasma prekallikrein, and high molecular weight kininogen

Immunoblotting techniques for the qualitative and quantitative analysis of FXII, PK, and HMWK in whole plasma are presented. Sensitive, specific, and quantitative immunodetection of FXII and PK can be achieved by developing the blots with polyclonal antiserum followed by radiolabeled FXII or PK, respectively. This approach is based on the assumption that bivalent antibodies bind monovalently to the NC-bound antigen and have available binding sites to bind radiolabeled antigen derived from the fluid phase. This radiolabeled antigen overlay principle may be generally useful for immunodetection of any trace protein in complex mixtures, provided that the radiolabeled purified antigen is available. Immunoblotting may also be helpful for the partial characterization of the structural or functional abnormalities of CRM-positive variant molecules. For example, earlier studies of a FXII-variant molecule that had been purified and characterized were supported by immunoblotting studies of the CRM-positive deficient plasma. Quantitative measurement of HMWK is possible using a monoclonal antibody directed against the light chain of HMWK followed by radiolabeled secondary antibody. Quantitation of cleaved and single-chain HMWK is possible using dilutions of dextran sulfate-activated NHP on unreduced SDS-PAGE and dilutions of unactivated NHP with reduced SDS-PAGE as standards. These assays allow assessment of the degree of in vivo activation of the contact system in various disease states.

Production and characterization of a murine monoclonal antibody against a heavy chain of Hageman factor (factor XII)

A murine hybridoma cell line that produces a monoclonal antibody to human Hageman factor (HF, factor XII) is described. The antibody (P 5-2-1) consists of mouse IgG2b heavy chains and lambda light chains, selectively neutralizes HF procoagulant activity, and prevents the proteolytic cleavage of HF during contact activation in plasma. When HF is exposed to P 5-2-1 before the absorption of HF to kaolin, HF procoagulant activity is markedly inhibited. In contrast, P 5-2-1 does not interfere with HF activity after the adsorption of HF to kaolin. P 5-2-1 does not inactivate the prekallikrein-activating activity of 28,000-mol wt HF fragments (HFf). P 5-2-1 binds exclusively to the 40,000-mol wt portion of a heavy chain of HF and inhibits the adsorption of HF to negatively charged surfaces. P 5-2-1 immobilized on Sepharose can be used to deplete HF from normal human plasma. This immunoaffinity-depleted plasma is indistinguishable from congenital HF-deficient plasma and can be used as the substrate for HF procoagulant activity assay.

A monoclonal antibody that inhibits activation of human Hageman factor (factor XII)

A monoclonal antibody to human Hageman factor (HF, factor XII) was derived from BALB/c mouse spleen cells fused with NS-1 mouse myeloma cells. This antibody, purified from ascites fluid, reacted with HF to inhibit the activation of HF, purified or in normal pooled plasma, as measured by a coagulation assay. The antibody did not inhibit the coagulant activity of activated HF. The antibody also inhibited the generation of amidolytic activity in HF-ellagic acid mixtures, but failed to inhibit the amidolytic properties of the carboxy-terminal fragment of HF (HFf). Amidolytic activity, absent in an HF-monoclonal antibody mixture, was generated upon treatment with insoluble trypsin. Monoclonal antibody, bound to CNBr Sepharose 4B gel (Pharmacia Fine Chemicals, Piscataway, NJ), reversibly bound HF in plasma or in buffer, without activating it. HF was then eluted with 4 mol/L guanidine HCI. The passage of 125I-labeled HF enzymatically cleaved by trypsin through a column of monoclonal antibody-CNBr Sepharose 4B gel resulted in flow-through of HFf with a molecular weight (mol wt) of 30,000 and HF fragments of mol wt 12,000. Elution with 4 mol/L guanidine HCI yielded several HF fragments (mol wt 80,000, 52,000, and 40,000) but not HFf. These data suggest that the single determinant recognized by the murine monoclonal antibody is not on HFf, but rather on the amino-terminal fragment thought to be involved in the binding activity of HF. The monoclonal anti-HF bound to CNBr-activated Sepharose 4B gel could be used to artificially deplete plasma samples of HF.

Activation of purified human plasma prekallikrein triggered by cell wall fractions of Escherichia coli and Staphylococcus aureus

Whether Escherichia coli and Staphylococcus aureus cell wall fractions can trigger the activation of prekallikrein was investigated in a mixture of purified human factor XII, prekallikrein, and high-relative-molecular-weight (Mr) kininogen. After exposure for 30 min to bacterial preparations (0.02-5 mg/ml) at 0 C, lallikrein amidolytic activity was expressed as a percentage of the optimal activation of prekallikrein induced by dextran sulfate. Lipopolysaccharide (LPS) fractions of five E coli strains and lipid A of E coli O111B4 induced 50%-90% optimal activity. However, the polysaccharide fraction induced less than 5% activity. Peptidoglycan and teichoic acid of S aureus induced 70%-100% optimal activity at 5 mg/ml, but protein A did not generate activity. No activation of prekallikrein occurred in the absence of factor XII. Thus, LPS and lipid A of E coli and peptidoglycan and teichoic acid of S aureus can generate kallikrein amidolytic activity in a mixture of purified factor XII, prekallikrein, and high-Mr kininogen.

Synthesis and release of Hageman factor (Factor XII) by the isolated perfused rat liver

The site of synthesis of Hageman factor (HF, Factor XII) has not been previously demonstrated with certainty. We have studied the production and release of HF in the isolated perfused rat liver and have compared rates of synthesis in this system with absolute rates of degradation measured in vivo. Rat livers, perfused for 5 h with a recycling fluid consisting of a perfluorochemical emulsion (Fluosol 43), were used to demonstrate a cumulative increase of HF in the perfusate as measured by a specific and sensitive radioimmunoassay. The rate of increase in the perfusate pool of HF during the final 4 h of perfusion yielded a mean synthetic rate of 3.5 micrograms/h per 100 g body wt, which was approximately 0.2% of the synthetic rate of albumin in the same system. The cumulative appearance of albumin and transferrin was linear after 1 h and calculated rates of synthesis were 2,012 micrograms/h per 100 g and 263 micrograms/h per 100 g body wt, respectively. De novo synthesis of HF was confirmed by demonstrating incorporation of [14C]lysine into specific immunoprecipitates of HF, and by the observations that both specific incorporation of labeled amino acid and net release of immunoassayable HF were inhibited by the administration of cycloheximide. Finally, it was evident that the rates of synthesis observed in the isolated perfused liver agreed closely with absolute rates of degradation of HF measured in vivo with 125I-rat HF (4.0 micrograms/h per 100 g). From these data we conclude that the liver is the principal site of synthesis of HF.

Anaphylactic release of a prekallikrein activator from human lung in vitro

We have demonstrated the in vitro IgE-mediated release of a prekallikrein activator from human lung. The lung prekallikrein activator was partially purified by sequential chromatography on sulfopropyl-Sephadex, DEAE-Sephacel, and Sepharose 6B. Purified human prekallikrein was converted to its active form (kallikrein) by the lung protease. The generated kallikrein was shown to be biologically active; that is, it generates bradykinin from purified human high-molecular weight kininogen and also cleaves benzoyl-propyl-phenyl-arginyl-p-nitroanilide, a known synthetic substrate of kallikrein. The lung prekallikrein activator differs from the known physiologic activators of prekallikrein (the activated forms of Hageman factor) with respect to: (a) size (it has a mol wt of approximately 175,000); (b) synthetic substrate specificity (D-propyl/phenyl/arginyl-p-nitroanilide is a substrate for the activated forms of Hageman factor, but not the lung protease); (c) antigenic specificity (an anti-Hageman factor immunoadsorbent column did not remove significant amounts of the lung protease, while it removed most of the activity of activated Hageman factor fragments); and (d) inhibition profile (the lung proteases was not inhibited by corn trypsin inhibitor). This prekallikrein activator provides a physiologic mechanism by which prekallikrein can be directly activated during IgE-mediated reactions of the lung. While the role of this lung prekallikrein activator in immediate hypersensitivity reactions and in other inflammatory processes is not clear, it does represent a first and important interface between IgE-mediated reactions and the Hageman factor-dependent pathways of the inflammatory response.

Factor XII and other hemostatic protein abnormalities in nephrotic syndrome patients

Factor XII clotting activities and antigen levels were assayed in 14 plasma samples from 10 patients with nephrotic syndrome; the group was heterogeneous clinically and histologically. Factor XII was low at initial sampling in 7 of the 10 patients; in 7 of the 14 samples, factor XII antigen was in excess over clotting activity. Inhibition of factor XII could not be demonstrated; excess plasma antigen and urinary antigen (when present) had normal patterns on crossed-immunoelectrophoresis, indicating no major changes in charge or size. In 3 patients tested more than once, plasma levels of factor XII were increased up to 6fold in steroid-induced remission. Of other hemostatic factors assessed for comparison, factor VIII was elevated in 11 of the 14 samples; eight of these had elevated factor VII levels as well. Eight samples from six patients showed low antithrombin III levels; one of these patients had recurrent thromboses. Antithrombin III levels correlated with the serum albumin concentration. Only two of the eight urines tested had detectable factor XII antigen; a third had factor IX and prothrombin and no factor XII. Plasminogen and antithrombin III were readily demonstrated in all urine samples with higher concentrations in those patients with less selective proteinuria. Urinary and plasma levels were not correlated, suggesting that increased consumption or turnover was not simply related to increased filtration.